By Vince Giuliano – updated Feb 8 and Feb 9, 2012
This is the second of three blog entries relating to the Nrf2 pathway. The previous blog entry The pivotal role of Nrf2. Part 1 – a new view on the control of oxidative damage and generation of hormetic effects dealt with the general mechanisms of operation of Nrf2, and with positive effects of Nrf2 in preventing or treating a number of pathological conditions via its ability to turn on genes for the body’s own antioxidant system and genes for combating stress – hundreds of such genes. This second blog entry deals with how a number of substances that are incidentally antioxidants, plant-derived phyto-substances in particular, actually exercise their benefits through promoting the expression of Nrf2 which in turn activates the body’s own antioxidant and hormetic defense systems. A third blog entry The pivotal role of Nrf2. Part 3– Is promotion of Nrf2 expression a viable strategy for human human healthspan and lifespan extension? will explore whether supplementation with substances that promote Nrf2 might be life-extending. Taken together the three blog entries answer a question that has frequently been addressed to me: “How can you simultaneously warn against indiscriminant antioxidant supplementation and at the same time so enthusiastically endorse consuming foods which have strong antioxidant capabilities, ones like broccoli, coffee, olive oil, chocolate, garlic, green tea and blueberries? And, if antioxidants are bad for you, how can you continue to advocate taking so many antioxidant supplements like curcumin, alpha-lipoic acid, ashwagandha, boswellia, ginger and resveratrol?”
I have written before rather extensively about phytochemicals and how they activate the Nrf2 pathway. In my blog entry Nrf2 and cancer chemoprevention by phytochemicals I indicated “A cluster of research reports has appeared during the last few years looking at mechanisms through which substances rich in phytochemicals (e.g. coffee, chocolate, turmeric, olive oil, broccoli, red hot peppers, green tea, garlic, blueberries, rosemary, oregano, sage) are cancer-preventative. While these foods have been studied for many years a new focal point has been moving to center stage – study of what these substances are doing in terms of gene expression as a key to understanding their therapeutic value. — Recent studies have provided strong evidence that many daily-consumed dietary compounds possess cancer-protective properties that might interrupt the carcinogenesis process. These properties include the induction of cellular defense detoxifying and antioxidant enzymes, which can protect against cellular damage caused by environmental carcinogens or endogenously generated reactive oxygen species. These compounds can also affect cell-death signaling pathways, which could prevent the proliferation of tumor cells.” — One master activator of antioxidant and anticancer genes appears to be Nuclear factor-erythroid-2-related factor 2 (Nrf2). The sequence of events involved in phytochemical chemoprevention mediated by Nrf2 is complex and is summarized in the 2008 publication Nrf2 as a master redox switch in turning on the cellular signaling involved in the induction of cytoprotective genes by some chemopreventive phytochemicals. “A wide array of dietary phytochemicals have been reported to induce the expression of enzymes involved in both cellular antioxidant defenses and elimination/inactivation of electrophilic carcinogens. Induction of such cytoprotective enzymes by edible phytochemicals largely accounts for their cancer chemopreventive and chemoprotective activities.” I also repeated much of the same information related to Nrf2 in the May 2011 blog entry Focus on ginger
Foods and supplements can simultaneously affect multiple biological pathways related to health and longevity such as Keap1-Nrf2, NF-kappaB, GH-IGF, the heat shock response pathway (HSR), AMPK, FOXO and the unfolded protein response pathway (UPR). Further, these pathways can interact so as to reinforce or inhibit each other.
A case in point with respect to Nrf2 is the effects of unsaturated acids. The December 2011 publication Activation of stress signaling pathways by electrophilic oxidized and nitrated lipids reports: “Unsaturated fatty acids are prone to radical reactions that occur in biological situations where extensive formation of reactive oxygen and nitrogen species (ROS and RNS) takes place. These reactions are frequent in inflammatory conditions such as atherosclerosis, and yield a variety of biologically active species, many of which are electrophilic in nature. Electrophilic lipid oxidation and nitration products can influence redox cell signaling via S-alkylation of protein thiols, and moderate exposure to these species evokes protective cell signaling responses through this mechanism. Herein, we review the stress signaling pathways elicited by electrophiles derived from unsaturated fatty acids, focusing on the Keap1-Nrf2 pathway, the heat shock response pathway (HSR), and the unfolded protein response pathway (UPR).”
I comment that. in practical terms in the particular case of a substantial dose of unsaturated fatty acids, the pro-inflammatory actions of the NF-kappaB is likely to be stronger than the anti-inflammatory actions of the Keap1-Nrf2 pathway. However augmenting the action of the Keap1-Nrf2 pathway, say, by supplementation with curcumin and essential fatty acids (EFAs) might serve to quell the inflammation.
The way dietary flavonoids work to confer their multiple health effects, is probably mainly via the keap1-Nrf2 pathway. That is substances which are both themselves antioxidants and activators of the keap1-Nrf2 pathway produce their main results through keap1-Nrf2 and activating the body’s own antioxidant and defensive systems.
“Flavonoids are a large family of polyphenolic compounds synthesized by plants.
Table 1: Common Dietary Flavonoids
|Some Common Food Sources
|Cyanidin, Delphinidin, Malvidin, Pelargonidin, Peonidin, Petunidin
|Red, blue, and purple berries; red and purple grapes; red wine
Catechin, Epicatechin, Epigallocatechin Epicatechin gallate, Epigallocatechin gallate
Dimers and Polymers:
Theaflavins, Thearubigins, Proanthocyanidins
|Catechins: Teas (particularly green and white), chocolate, grapes, berries, apples
Theaflavins, Thearubigins: Teas (particularly black and oolong)
Proanthocyanidins: Chocolate, apples, berries, red grapes, red wine
|Hesperetin, Naringenin, Eriodictyol
|Citrus fruits and juices, e.g., oranges, grapefruits, lemons
|Quercetin, Kaempferol, Myricetin, Isorhamnetin
|Widely distributed: yellow onions, scallions, kale, broccoli, apples, berries, teas
|Parsley, thyme, celery, hot peppers,
|Daidzein, Genistein, Glycitein
|Soybeans, soy foods, legumes
The September 2011 publication Dietary flavonoids are neuroprotective through Nrf2-coordinated induction of endogenous cytoprotective proteins reports: “Epidemiological studies have demonstrated that the consumption of fruits and vegetables is associated with reduced risk for cardiovascular disease and stroke. Detailed investigations into the specific dietary components of these foods have revealed that many polyphenolic constituents exert anti-oxidant effects on key substrates involved in the pathogenesis and progression of ischemic injury. These data have perpetuated the belief that the protective effects of flavonoids result from direct anti-oxidant actions at the levels of the cerebral vasculature and brain parenchyma. While many in vitro studies using purified extracts support this contention, first-pass metabolism alters the bioavailability of flavonoids such that the achievable concentrations after oral consumption are not consistent with this mechanism. — Importantly, oral consumption of flavonoids may promote neural protection by facilitating the expression of gene products responsible for detoxifying the ischemic microenvironment through both anti-oxidative and anti-inflammatory actions. In particular, the transcriptional factor nuclear factor erythroid 2-related factor 2 has emerged as a critical regulator of flavonoid-mediated protection through the induction of various cytoprotective genes. The pleiotropic effects associated with potent transcriptional regulation likely represent the primary mechanisms of neural protection, as the flavonoid concentrations reaching ischemic tissues in vivo are sufficient to alter intracellular signal transduction but likely preclude the one-to-one stoichiometry necessary to confer protection by direct anti-oxidation. These data reflect an exciting new direction in the study of complementary and alternative medicine that may lead to the development of novel therapies for ischemic/hemorrhagic stroke, traumatic brain injury, and other neurological disorders.”
In addition to flavonoids many other plant based substances that have been discussed in this blog appear to produce health benefits through hormetic effects mediated by Nrf2.
The November 2010 publication Nutraceutical antioxidants as novel neuroprotective agent expands on the classes of “antioxidant” compounds that are neuroprotective and operate either via direct antioxidant action or via the keap1-Nrf2 pathway. “A variety of antioxidant compounds derived from natural products (nutraceuticals) have demonstrated neuroprotective activity in either in vitro or in vivo models of neuronal cell death or neurodegeneration, respectively. These natural antioxidants fall into several distinct groups based on their chemical structures: (1) flavonoid polyphenols like epigallocatechin 3-gallate (EGCG) from green tea and quercetin from apples; (2) non-flavonoid polyphenols such as curcumin from tumeric and resveratrol from grapes; (3) phenolic acids or phenolic diterpenes such as rosmarinic acid or carnosic acid, respectively, both from rosemary; and (4) organosulfur compounds including the isothiocyanate, L-sulforaphane, from broccoli and the thiosulfonate allicin, from garlic. All of these compounds are generally considered to be antioxidants. They may be classified this way either because they directly scavenge free radicals or they indirectly increase endogenous cellular antioxidant defenses, for example, via activation of the nuclear factor erythroid-derived 2-related factor 2 (Nrf2) transcription factor pathway. Alternative mechanisms of action have also been suggested for the neuroprotective effects of these compounds such as modulation of signal transduction cascades or effects on gene expression. Here, we review the literature pertaining to these various classes of nutraceutical antioxidants and discuss their potential therapeutic value in neurodegenerative diseases.”
The December 2011 publication Nutritional antioxidants and adaptive cell responses: an update reports: “Many plant antioxidants, intaken through the daily diet or plant-derived dietary supplements, have been shown able to prevent free radical-related diseases by counteracting cell oxidative stress. However, it is now considered that the in vivo beneficial effects of these phytochemicals are unlikely to be explained just by their antioxidant capability. Several plant antioxidants exhibit hormetic properties, by acting as ‘low-dose stressors’ that may prepare cells to resist more severe stress. In fact, low doses of these phytochemicals activate cell signaling pathways (being the most prominent examples the modulation of the Nrf2/Keap1 pathway, the NF-κB pathway and the Sirtuin-FOXO pathway) but high doses are cytotoxic. Herein we review the adaptive responses induced by the most known plant hormetic antioxidants, which are sulforaphane, resveratrol, curcumin, flavonoids, green tea catechins and diallylsulphides, as well as the molecular mechanisms involved in such responses. Furthermore, this review outlines that the hormetic properties of these bioactive plant antioxidants might be successfully employed for realizing health-promoting dietary interventions especially in the field of neurodegenerative diseases and cancer.”
Numerous substances – perhaps a hundred – are known to promote the expression of Nrf2. I start by discussing drugs and then turn to food and then to selected supplementary phytosubstances.
Drugs that promote the expression of Nrf2
I start with three important classes of drugs known to promote expression of Nrf2: metformin, lansoprazole and possibly other proton pump inhibitors and statins.
Metformin appears to extend lifespan and healthspan through activating AMPK and its influence on Nrf2, at least in nematodes.
The 2010 publication Metformin Induces a Dietary Restriction–Like State and the Oxidative Stress Response to Extend C. elegans Healthspan via AMPK, LKB1, and SKN-1 reports: “Metformin, a biguanide drug commonly used to treat type-2 diabetes, has been noted to extend healthspan of nondiabetic mice, but this outcome, and the molecular mechanisms that underlie it, have received relatively little experimental attention. To develop a genetic model for study of biguanide effects on healthspan, we investigated metformin impact on aging Caenorhabditis elegans. We found that metformin increases nematode healthspan, slowing lipofuscin accumulation, extending median lifespan, and prolonging youthful locomotory ability in a dose-dependent manner. Genetic data suggest that metformin acts through a mechanism similar to that operative in eating-impaired dietary restriction (DR) mutants, but independent of the insulin signaling pathway. Energy sensor AMPK and AMPK-activating kinase LKB1, which are activated in mammals by metformin treatment, are essential for health benefits in C. elegans, suggesting that metformin engages a metabolic loop conserved across phyla. We also show that the conserved oxidative stress-responsive transcription factor SKN-1/Nrf2 is essential for metformin healthspan benefits in C. elegans, a mechanistic requirement not previously described in mammals. skn-1, which functions in nematode sensory neurons to promote DR longevity benefits and in intestines for oxidative stress resistance lifespan benefits, must be expressed in both neurons and intestines for metformin-promoted healthspan extension, supporting that metformin improves healthy middle-life aging by activating both DR and antioxidant defense longevity pathways. In addition to defining molecular players operative in metformin healthspan benefits, our data suggest that metformin may be a plausible pharmacological intervention to promote healthy human aging.”
Lansoprazole – much more than an antiacid.
The 2009 publication The expression of heme oxygenase-1 induced by lansoprazole reported: “Our previous studies have demonstrated that lansoprazole inhibits acute inflammatory reactions as well as intestinal mucosal injuries induced by ischemia-reperfusion or indomethacin administration in rats. Thus, proton pump inhibitors such as lansoprazole have been demonstrated to prevent gastrointestinal mucosal injury by mechanisms independent of acid inhibition. In our in vitro study, lansoprazole induced the expression of heme oxygenase-1 (HO-1) on rat gastric epithelial cells (RGM-1 cells), and exerted anti-inflammatory effect on the dependent of HO-1 expression. Furthermore, NF-E2-related factor-2 (Nrf2) played an important role in HO-1 expression induced by lansoprazole. In this review, we focused on lansoprazole-induced HO-1 expression, its anti-inflammatory action, and the role of Nrf2 in its expression.”
Other publications relating the actions of lansoprazole in promoting Nrf2 include the 2009 report Lansoprazole, a proton pump inhibitor, mediates anti-inflammatory effect in gastric mucosal cells through the induction of heme oxygenase-1 via activation of NF-E2-related factor 2 and oxidation of kelch-like ECH-associating protein 1. “Induction of heme oxygenase-1 (HO-1) expression has been associated with cytoprotective and anti-inflammatory actions of lansoprazole, a proton pump inhibitor, but the underlying molecular mechanisms remain largely unresolved. In this study, we investigate the role of transcriptional NF-E2-related factor 2 (Nrf2), its phosphorylation/activation, and oxidation of Kelch-like ECH-associating protein 1 (Keap1) in lansoprazole-induced HO-1 up-regulation using cultured gastric epithelial cells (rat gastric mucosal cell line, RGM-1). HO-1 expression of RGM-1 cells was markedly enhanced in a time- and dose-dependent manner by the treatment with lansoprazole, and this up-regulation of HO-1 contributed to the inhibition of chemokine production from stimulated RGM-1 cells. — Finally, an oxidative form of the Keap1 protein was detected in lansoprazole-treated RGM-1 cells by analyzing S-oxidized proteins using biotinylated cysteine as a molecular probe. These results indicate that lansoprazole up-regulates HO-1 expression in rat gastric epithelial cells, and the up-regulated HO-1 contributes to the anti-inflammatory effects of the drug. Phosphorylation of ERK and Nrf2, activation and nuclear translocation of Nrf2, and oxidation of Keap1 are all involved in the lansoprazole-induced HO-1 up-regulation.”
Statins too appear to activate Nrf2. The 2008 publication Simvastatin activates Keap1/Nrf2 signaling in rat liver reports: “Some of the statins’ pleiotropic actions have been attributed to their antioxidant activity. The Nrf2 transcription factor controls the expression of a number of protective genes in response to oxidative stress. In the present study, wistar rats, primary hepatocytes as well as ST2 cells, were employed to explore the potential role of Nrf2 in mediating the reported antioxidant effects of statins. Simvastatin triggered nuclear translocation of Nrf2 in rat liver and in primary rat hepatocytes in a mevalonate-dependent and cholesterol-independent way. In liver, nuclear extracts from simvastatin-treated rats, the DNA-binding activity of Nrf2, was significantly increased and the mRNA of two known targets of Nrf2 (HO-1 and GPX2) was induced. In ST2 cells stably transfected with constructs bearing Nrf2-binding site (antioxidant responsive element), simvastatin enhanced Nrf2-mediated transcriptional activity in a mevalonate-dependent and cholesterol-independent fashion. In conclusion, activation of Keap1/Nrf2 signaling pathway by simvastatin might provide effective protection of the cell from the deleterious effects of oxidative stress.”
The January 2008 publication Simvastatin-induced heme oxygenase-1 increases apoptosis of Neuro 2A cells in response to glucose deprivation looked at neuronal cells. “Heme oxygenase-1 (HO-1) has been suggested as an important mediator of the cholesterol-independent cytoprotection actions of statins, which may be of benefit for the treatment of degenerative neurological diseases and for reduction of infarct volume after cerebral ischemia. Overexpression of HO-1, however, has dual effects under oxidative stress, and the release of ferric iron from heme under these conditions may result in detrimental rather than cytoprotective effects. This study was designed to investigate the effect of simvastatin-induced HO-1 on Neuro 2A cells in response to glucose deprivation. We demonstrated that simvastatin induced a dose- and time-dependent upregulation of HO-1 protein expression in Neuro 2A cells. The induction of HO-1 after simvastatin treatment was mediated by nuclear factor erythroid 2-related factor 2 (Nrf2), which was expressed by Western blots of nuclear fractions and retarded complex formation in the electrophoretic mobility shift assay reaction. In addition, simvastatin activated the extracellular signal-regulated kinase and p38, but not the phosphorylation of c-Jun N-terminal kinase and Akt. Glucose deprivation in the cells pretreated with simvastatin induced more HO-1 expression, and the transcript could be decreased by small interfering RNA for Nrf2. This upregulation of HO-1 was significantly associated with increased apoptosis, manifested as expression at the protein level of 17-kDa cleaved caspase-3 and increased percentage of apoptotic cells shown by flow cytometry. The increased cleaved caspase-3 expression and percentage of apoptotic cells was significantly reduced by the HO inhibitor zinc protoporphyrin. Addition of the iron chelator desferrioxamine also resulted in blockade of the aggravated apoptosis, which implies that iron production from HO-1 activity may play an important role in the increased apoptosis in response to glucose deprivation in neuronal cells pretreated with simvastatin.”
Histone deacetylase inhibitors can reverse toxicity-induced loss of Nrf2 expression.
Specifically, valproic acid and lithium can reverse depression in Nrf2 activity in astrocytes induced by the toxin lipopolysaccharide (LPS). The October 2010 publication Activated microglia decrease histone acetylation and Nrf2-inducible anti-oxidant defence in astrocytes: restoring effects of inhibitors of HDACs, p38 MAPK and GSK3β reports: “Histone deacetylase (HDAC) inhibitors have promising neuroprotective and anti-inflammatory properties although the exact mechanisms are unclear. We have earlier showed that factors from (LPS)-activated microglia can down-regulate the astroglial nuclear factor-erythroid 2-related factor 2 (Nrf2)-inducible anti-oxidant defence. Here we have evaluated whether histone modification and activation of GSK3β are involved in these negative effects of microglia. Microglia were cultured for 24 h in serum-free culture medium to achieve microglia-conditioned medium from non-activated cells (MCM(0)) or activated with 10 ng/mL of LPS to produce MCM(10). Astrocyte-rich cultures treated with MCM(10) showed a time-dependent (0-72 h) increase in astroglial HDAC activity that correlated with lower levels of acetylation of histones H3 and H4 and decreased levels of the transcription factor Nrf2 and γ-glutamyl cysteine ligase modulatory subunit (γGCL-M) protein levels. The HDAC inhibitors valproic acid (VPA) and trichostatin-A (TSA) elevated the histone acetylation levels, restored the Nrf2-inducible anti-oxidant defence and conferred protection from oxidative stress-induced (H(2)O(2)) death in astrocyte-rich cultures exposed to MCM(10). Inhibitors of GSK3β (lithium) and p38 MAPK (SB203580) signaling pathways restored the depressed histone acetylation and Nrf2-related transcription whereas an inhibitor of Akt (Ly294002) caused a further decrease in Nrf2-related transcription. In conclusion, the study shows that well tolerated drugs such as VPA and lithium can restore an inflammatory induced depression in the Nrf2-inducible antioxidant defence, possibly via normalised histone acetylation levels.” See the blog entry Valproic acid – The phoenix drug arises again.
Nrf2 activity is an important mechanism of hormesis. Dozens of dietary substances exercise hormetic effects via Nrf2.
The general concept of hormesis is that a controlled amount of exposure to a body stressor may produce an overall positive effect. Hormesis involves, challenging cells and body systems by mild stress resulting in them becoming stronger and resistant to aging(ref). See the blog entry Hormesis and age retardation . A stress challenge that causes keap1 to release Nrf2 where the resulting positive effects due to Nrf2 action on genes outweigh the negative effects of the challenge stress is a good example of hormesis in action. A number of research publications speak to this hormetic effect such as the November 2011 publication Hormetics: dietary triggers of an adaptive stress response. “A series of dietary ingredients and metabolites are able to induce an adaptive stress response either by generation of reactive oxygen species (ROS) and/or via activation of the Nrf2/Keap1 stress response network. Most of the molecules belong to activated Michael acceptors, electrophiles capable to S-alkylate redox sensitive cysteine thiols. This review summarizes recent advances in the (re)search of these compounds and classifies them into distinct groups. More than 60 molecules are described that induce the Nrf2 network, most of them found in our daily diet. Although known as typical antioxidants, a closer look reveals that these molecules induce an initial mitochondrial or cytosolic ROS formation and thereby trigger an adaptive stress response and hormesis, respectively. This, however, leads to higher levels of intracellular glutathione and increased expression levels of antioxidant enzymes such as glutathione peroxidase, thioredoxin reductase, and superoxide dismutase. According to this principle, the author suggests the term hormetics to describe these indirect antioxidants.”
The July 2011 publication Xenohormesis mechanisms underlying chemopreventive effects of some dietary phytochemicals calls Nrf2-mediated protection induced by low-levels of phytochemical stress “xenohormesis.” “A wide variety of phytochemicals present in our diet, including fruits, vegetables, and spices, have been shown to possess a broad range of health-beneficial properties. The cytoprotective and restorative effects of dietary phytochemicals are likely to result from the modulation of several distinct cellular signal transduction pathways. Many dietary phytochemicals that are synthesized as secondary metabolites function as toxins, that is, “phytoalexins,” and hence protect plants against insects and other damaging organisms and stresses. However, at the relatively low doses consumed by humans and other mammals, these same toxic plant-derived chemicals, as mild stressors, activate adaptive cellular response signaling, conferring stress resistance and other health benefits. This phenomenon has been referred to as xenohormesis. This review highlights the xenohormesis mechanisms underlying chemopreventive effects of some dietary chemopreventive phytochemicals, with special focus on the nuclear transcription factor erythroid 2p45 (NF-E2)-related factor 2 (Nrf2) as a key player.”
A protective hormetic response to body injury or insult may involve simultaneous activation of HSP70 and Nrf2.
The July 2010 blog entry HSP70 to the rescue describes how heat shock protein 70 (HSP70) works to promote survival of cells under stress and provides examples of the positive hormetic effects of this chaperone protein. For example HSP70 is neuroprotection in case of cerebral ischemia. The 2010 publication The Nrf2–Keap1 cellular defense pathway and heat shock protein 70 (Hsp70) response. Role in protection against oxidative stress in early neonatal unilateral ureteral obstruction (UUO) reports: “Perturbation of renal tubular antioxidants and overproduction of reactive oxygen species may amplify the proinflammatory state of renal obstruction, culminating in oxidative stress and tubular loss. Here, we analyzed the heat shock protein 70 (Hsp70) response and the function and signal transduction of NF-E2-related protein 2 (Nrf2) transcription factor on oxidative stress modulation in obstruction. Rats were subjected to unilateral ureteral obstruction or sham operation and kidneys harvested at 5, 7, 10, and 14 days after obstruction. Hsp70 expression and Nrf2 activity and its downstream target gene products were assessed. After 10 and 14 days of obstruction, enhanced lipid peroxidation through higher thiobarbituric acid reactive substances levels and increased oxidative stress resulted in reduced total antioxidant activity and enhanced nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase activity were demonstrated. This was accompanied by decreased inducible Hsp70 expression and a progressive reduction of nuclear Nrf2 and its target gene products glutathione S-transferase A2 (GSTA2) and NADPH/quinone oxidoreductase 1 (NQO1), whereas the Nrf2 repressor Kelch-like ECH-associated protein-1 (Keap1) was upregulated. By contrast, on early obstruction for 7 days, lack of increased oxidative markers associated with higher inducible Hsp70 protein levels and a rapid nuclear accumulation of Nrf2, Keap1 downregulation, and mRNA induction of the identified Nrf2-dependent genes, NQO1 and GSTA2, were shown. For these results, we suggest that the magnitude of cytoprotection in early obstruction depends on the combined contribution of induced activation of Nrf2 upregulating its downstream gene products and Hsp70 response. Impaired ability to mount the biological response to the prevailing oxidative stress leading to renal injury was shown in prolonged obstruction.”
A large number of foods promote the expression of Nrf2
The March 2011 Epub Biochemical Basis for Functional Ingredient Design from Fruits reports: “Functional food ingredients (nutraceuticals) in fruits range from small molecular components, such as the secondary plant products, to macromolecular entities, e.g., pectin and cellulose, that provide several health benefits. In fruits, the most visible functional ingredients are the color components anthocyanins and carotenoids. In addition, several other secondary plant products, including terpenes, show health beneficial activities. A common feature of several functional ingredients is their antioxidant function. For example, reactive oxygen species (ROS) can be oxidized and stabilized by flavonoid components, and the flavonoid radical can undergo electron rearrangement stabilizing the flavonoid radical. Compounds that possess an orthodihydroxy or quinone structure can interact with cellular proteins in the Keap1/Nrf2/ARE pathway to activate the transcription of antioxidant enzymes. Carotenoids and flavonoids can also exert their action by modulating the signal transduction and gene expression within the cell. Recent results suggest that these activities are primarily responsible for the health benefits associated with the consumption of fruits and vegetables.”
A substantial number of supplements in the anti-aging firewall list which are known to be antioxidants exercise at least some of their benefits through Nrf2.
I cite publications for some of these.
Our old friend curcumin seems to exert many of its beneficial effects via Nrf2.
I have written extensively about the health-producing properties of curcumin (ref)(ref)(ref), The 2010 publication Curcumin, the golden spice from Indian saffron, is a chemosensitizer and radiosensitizer for tumors and chemoprotector and radioprotector for normal organs relates: “The protective effects of curcumin appear to be mediated through its ability to induce the activation of NRF2 and induce the expression of antioxidant enzymes (e.g., hemeoxygenase-1, glutathione peroxidase, modulatory subunit of gamma-glutamyl-cysteine ligase, and NAD(P)H:quinone oxidoreductase 1, increase glutathione (a product of the modulatory subunit of gamma-glutamyl-cysteine ligase), directly quench free radicals, and inhibit p300 HAT activity.”
Among the many other relevant articles on curcumin is the April 2011 publication New mechanisms and the anti-inflammatory role of curcumin in obesity and obesity-related metabolic diseases reports: “Purpose: A metabolic abnormality such as obesity is a major obstacle in the maintenance of the human health system and causes various chronic diseases including type 2 diabetes, hypertension, cardiovascular diseases, as well as various cancers. This study was designed to summarize the recent scientific knowledge regarding the anti-obesity role of curcumin (diferuloylmethane), which is isolated from the herb curcuma longa, known to possess anti-inflammatory activities. However, little is known about its exact underlying molecular mechanisms in the treatment of obesity and metabolic diseases. Furthermore, cell cultures, animal models of obesity, and few human clinical and epidemiological studies have added the promise for future therapeutic interventions of this dietary compound. Methods: An electronic search was performed using Science finder, Medline, Scopus, Google scholar and collected English language articles from 2000 to 2010, relating to the role of curcumin in obesity and metabolic diseases. Results: Obesity has been classified as a growing epidemic and its associated metabolic disorders are considered a major risk to the health system. Curcumin interacts with specific proteins in adipocytes, pancreatic cells, hepatic stellate cells, macrophages, and muscle cells, where it suppresses several cellular proteins such as transcription factor NF-kB, STAT-3, Wnt/β-catenin and activates PPAR-γ, Nrf2 cell signaling pathway. In addition, curcumin downregulates the inflammatory cytokines, resistin and leptin, and upregulates adiponectin as well as other associated proteins. The interactions of curcumin with several signal transduction pathways reverse insulin resistance, hyperglycemia, hyperlipidemia, and other inflammatory symptoms associated with obesity and metabolic diseases. Conclusion: The modulation of several cellular transduction pathways by curcumin has recently been extended to elucidate the molecular basis for obesity and obesity-related metabolic diseases. These findings might enable novel phytochemical treatment strategies as well as curcumin translation to the clinical practice for the treatment and prevention of obesity-related chronic diseases. Furthermore, the relatively low cost of curcumin, safety and proven efficacy make it advisable to include curcumin as part of healthy diet.”
Those of you who regularly follow this blog know I heartily endorse this conclusion.
In the May 2011 blog entry Focus on ginger,I stated “Ginger as will see is an antioxidant, a COX-2 inhibitor of inflammation, an inhibitor of inflammatory cytokines, an inhibitor of NF-kappaB, an activator of Nrf2, a modulator of macrophage functions, a cancer chemo preventative, a possible treatment for diarrhea, Alzheimer’s disease pathology and anxiety, can reverse forms of asthma and can help overcome bacterial resistance to an antibiotic.”
The June 2011 pubication -Gingerol attenuates β-amyloid-induced oxidative cell death via fortifying cellular antioxidant defense systemreports: “β-Amyloid (Aβ) is involved in the formation of senile plaques, the typical neuropathological marker for Alzheimer’s disease (AD) and has been reported to cause apoptosis in neurons via oxidative and/or nitrosative stress. In this study, we have investigated the neuroprotective effect and molecular mechanism of -gingerol, a pungent ingredient of ginger against Αβ(25-35)-induced oxidative and/or nitrosative cell death in SH-SY5Y cells. -Gingerol pretreatment protected against Aβ(25-35)-induced cytotoxicity and apoptotic cell death such as DNA fragmentation, disruption of mitochondrial membrane potential, elevated Bax/Bcl-2 ratio, and activation of caspase-3. To elucidate the neuroprotective mechanism of -gingerol, we have examined Aβ(25-35)-induced oxidative and/or nitrosative stress and cellular antioxidant defense system against them. -Gingerol effectively suppressed Aβ(25-35)-induced intracellular accumulation of reactive oxygen and/or nitrogen species and restored Aβ(25-35)-depleted endogenous antioxidant glutathione levels. Furthermore, -gingerol treatment up-regulated the mRNA and protein expression of antioxidant enzymes such as γ-glutamylcysteine ligase (GCL) and heme oxygenase-1 (HO-1), the rate limiting enzymes in the glutathione biosynthesis and the degradation of heme, respectively. The expression of aforementioned antioxidant enzymes seemed to be mediated by activation of NF-E2-related factor 2 (Nrf2). These results suggest that -gingerol exhibits preventive and/or therapeutic potential for the management of AD via augmentation of antioxidant capacity.”
The June 2011 publication Zerumbone induces heme oxygenase-1 expression in mouse skin and cultured murine epidermal cells through activation of Nrf2reports: “Zerumbone, a sesquiterpene derived from tropical ginger, contains an electrophilic α,β-unsaturated carbonyl moiety and was found to suppress chemically induced papilloma formation in mouse skin. Here, we report that topical application of zerumbone onto dorsal skin of hairless mice induces activation of NF-E2-related factor 2 (Nrf2) and expression of heme oxygenase-1 (HO-1). We compared the levels of HO-1 protein in the skin of zerumbone-treated Nrf2 wild-type and Nrf2 knockout mice, and nrf2-deficient mice expressed HO-1 protein to a much lesser extent than the wild-type animals following topical application of zerumbone. Treatment of mouse epidermal JB6 cells with zerumbone caused a marked increase of Nrf2 nuclear translocation followed by the promoter activity of HO-1, and also enhanced direct binding of Nrf2 to the antioxidant response element. Moreover, knockdown of Nrf2 in JB6 cells diminished the zerumbone-induced upregulation of HO-1. Notably, α-humulene and 8-hydroxy-α-humulene, the structural analogues of zerumbone that lack the α,β-unsaturated carbonyl group, failed to activate Nrf2 and were unable to increase HO-1 expression. Unlike zerumbone, these nonelectrophilic analogues could not suppress the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced JB6 cell transformation and the intracellular accumulation of reactive oxygen species (ROS). Interestingly, when JB6 cells were treated with carbon monoxide-releasing molecule that mimics the HO-1 activity, the TPA-induced ROS production was markedly reduced. Taken together, these findings suggest that upregulation of HO-1 expression by zerumbone is mediated through activation of Nrf2 signaling, which provides a mechanistic basis for the chemopreventive effects of this sesquiterpene on mouse skin carcinogenesis.”
Sulforaphane is an isothiocyanate substance found in broccoli and alfalfa sprouts and other cruciferous vegetables. From the July 2011 publication: Regulation of the Keap1/Nrf2 system by chemopreventive sulforaphane: implications of posttranslational modifications: “The chemopreventive agent sulforaphane is an isothiocyanate derived from cruciferous vegetables. Transcriptional activation of antioxidant response element (ARE)-regulated phase II detoxification and antioxidant genes through the induction of transcription factor NF-E2-related factor-2 (Nrf2) is considered as the prime mechanism of its chemopreventive action. Cellular level of Nrf2 is tightly regulated by proteolysis through Cullin3 (Cul3)/Kelch-like ECH-associated protein 1 (Keap1)-dependent polyubiquitination. Sulforaphane is an electrophile that can react with protein thiols to form thionoacyl adducts and is believed to affect the Cys residues in Keap1 protein. In addition, sulforaphane might affect the activity of a variety of intracellular kinases to phosphorylate Nrf2 proteins, which dictates the nucleocytoplasmic trafficking of Nrf2 or modulates the Nrf2 protein stability.”
Another of the articles relevant to sulforphane and Nrf2 is the March 2011 publication Nuclear factor-erythroid 2-related factor 2 as a chemopreventive target in colorectal cancer. “Introduction: Numerous epidemiological studies have linked consumption of cruciferous vegetables to a reduced risk of colorectal cancer (CRC) in individuals. It is currently well accepted that chronic inflammation is a contributing factor in 15 – 20% malignancies including CRC. Many chemopreventive compounds are effective in preclinical systems and many ongoing clinical trials are showing promising findings. Many of these compounds could activate the antioxidant responsive element (ARE), a critical regulatory element for Phase II protective/detoxification and antioxidative stress enzymes mediated by nuclear factor-erythroid 2-related factor 2 (Nrf2). Recently, Nrf2 has emerged as a novel target for the prevention of CRC. Areas covered: A full literature search was performed using PubMed with the key words ‘ARE, Nrf2, colon, colorectal cancer, chemoprevention, cancer prevention’, and all relevant publications are included. Expert opinion: The use of Nrf2 knockout mice has provided key insights into the toxicological and chemopreventive importance of this pathway. Mounting evidence has revealed that Nrf2 is a critical regulator of inflammation as well, a major driving force for CRC progression and formation. Targeting the Nrf2/ARE pathway may present a novel therapeutic approach for the treatment of not only colorectal inflammatory diseases but the frequent subsequent development of CRC as well.”
According to the April 2011 publication Modification of keap1 cysteine residues by sulforaphane: “Activation of the transcription factor NF-E2-related factor-2 (Nrf2) through modification of Kelch-like ECH-associated protein 1 (Keap1) cysteines, leading to up-regulation of the antioxidant response element (ARE), is an important mechanism of cellular defense against reactive oxygen species and xenobiotic electrophiles. Sulforaphane, occurring in cruciferous vegetables such as broccoli, is a potent natural ARE activator that functions by modifying Keap1 cysteine residues, but there are conflicting in vitro and in vivo data regarding which of these cysteine residues react. Although most biological data indicate that modification of C151 is essential for sulforaphane action, some recent studies using mass spectrometry have failed to identify C151 as a site of Keap1 sulforaphane reaction. We have reconciled these conflicting data using mass spectrometry with a revised sample preparation protocol and confirmed that C151 is indeed among the most readily modified cysteines of Keap1 by sulforaphane. Previous mass spectrometry-based studies used iodoacetamide during sample preparation to derivatize free cysteine sulfhydryl groups causing the loss of sulforaphane from highly reactive and reversible cysteine residues on Keap1 including C151. By omitting iodoacetamide from the protocol and reducing sample preparation time, our mass spectrometry-based studies now confirm previous cell-based studies which showed that sulforaphane reacts with at least four cysteine residues of Keap1 including C151.”
At least four clinical trials are underway or planned of sulforaphane:
Active, not recruiting
|Effect of Sulforaphane in Broccoli Sprouts on Nrf2 Activation
|Broccoli Sprout Extracts Trial
|Dietary Interventions in Asthma Treatment: Sprouts Study
|Effects of Sulforaphane (SFN) on Immune Response to Live Attenuated Influenza Virus in Smokers and Nonsmokers
The Broccoli effect is an interesting online source offering a selection of relevant short online videos. From the article there The Nrf2 system and cell protection: “Smoking, inflammations, grilled meat, sunlight and oxygen all have one thing in common. They induce radicals and other highly reactive substances into our bodies, substances that damage our cells. This is likely one of the main reasons as to why we age! — Cell damage also contributes to diseases like arteriosclerosis, stroke, asthma (Rangasamy, T. et al.), cardiac infarctions, Alzheimer’s disease, Parkinson’s disease and cancer. — Our cells protect themselves against radicals and other reactive substances by a whole battery of enzymes and radical scavengers, called the Nrf2 system. Unfortunately, this system isn’t working optimally, but has to be stimulated in order to provide satisfactory protection. Several vegetables, if they are harvested at the correct point in time, contain substances (phytonutrition) that stimulate the cells radical protection. Lately, several phytonutrients from plants such as broccoli (sulforaphane), turmeric (curcumin) and garlic (allicin) have been identified. They are all strong stimulants of the Nrf2 system and thus they can help protect against cancer and other diseases. It is likely this Nrf2 stimulating phytonutrition, and not antioxidants such as vitamin C or Beta-carotene that provide the beneficial effect of eating a lot of fruit and vegetables. — The switch that regulates our radical protection is the transcription factor Nrf2 (Itoh, K. et al., Chan, J.Y. et al., Thimmulappa, RK. et al., Chanas, S.A. et al.). Mice, genetically modified to lack Nrf2, contract diseases even from minor exposure to cigarette smoke (Ishii, Y. et al.), sunlight (Hirota, A. et al.) and other radical inducers, since they are unable to activate their radical protection system (Copple, Ian M. et al.). — The connection to Nrf2 has been proved in several studies, since phytonutrition from broccoli and similar vegetables have no beneficial effect when it comes to radical protection in mice lacking Nrf2. However, mice that have been genetically modified with maximum Nrf2 activation in their livers are highly resistant to several different poisons (Okawa, H. et al.). This goes to show that the so called “broccoli effect”, i.e. the protection against several diseases connected to a high intake of broccoli and similar vegetables, are mediated via Nrf2 activation. This means that a high intake of vegetables leads to stimulation of the Nrf2 system via the phytonutrients that they contain and therefore an increase in radical protection. Several animal studies now shows that Nrf2 stimulation via vegetables or phytonutrition may protect against COPD, stroke, cancer (Fagerholm, R. et al.) and several other diseases (Copple, Ian M. et al., Issaa, Ala Y. et al.). — The brief Nrf2 stimulation that you get from eating broccoli (Ye, Lingxiang a et al.) or similar vegetables, leads to an extended stimulation of cell radical protection for approximately 24 hours. In addition, repeated brief stimulation of Nrf2 leads to an overall increased radical protection (Andersson, H. et al.). By a regular intake of Nrf2 stimulating phytonutrition it is therefore possible to boost radical protection (Andersson, H. et al.). Animal studies also show that the activity of the Nrf2 system decreases with age, but that it is still possible to increase activity by stimulation with phytonutrition (Suh, Jung H. et al.). Therefore it is possible to rejuvenate your radical protection by eating broccoli sprouts. — More and more studies are pointing to the fact that the protection against diseases provided by a high intake of fruit and vegetables (the broccoli effect) is caused by the ability of phytonutrition to induce a protracted radical protection in our cells via the transcription factor Nrf2. This is vastly different from an intake of antioxidants like vitamin C, which disappears from our bodies after approximately two hours (Wikipedia) and then leaves our cells unprotected.”
Red Ginsing can mitigate toxicity induced by polychlorinated biphenyls via Nrf2 and induction of HO-1.
The November 2010 publication A formulated red ginseng extract rescues PC12 cells from PCB-induced oxidative cell death through Nrf2-mediated upregulation of heme oxygenase-1 and glutamate cysteine ligase reports: “Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that display a broad spectrum of biological and toxicological properties. There has been compelling evidence supporting that PCB-induced cytotoxicity is mediated through generation of reactive oxygen species (ROS). Considerable attention has been focused on identifying naturally occurring phytochemicals that are able to scavenge excess ROS, thereby protecting against oxidative cell death. Red ginseng, which has a variety of biological and pharmacological activities including antioxidant, anti-inflammatory, antimutagenic and anticarcinogenic effects, has been used for thousands of years as a general tonic in traditional oriental medicine. In this study, we have investigated the effect of red ginseng extract (RGE) on PCB126-induced oxidative cell death in cultured rat pheochromocytoma (PC12) cells. PC12 cells treated with PCB126 exhibited increased accumulation of intracellular ROS and underwent apoptosis as determined by positive in situ terminal end-labeling (TUNEL staining) and the perturbation of the mitochondrial membrane potential (ΔΨ(m)). RGE treatment attenuated PCB126-induced cytotoxicity, apoptotic features and intracellular ROS accumulation. — RGE treatment upregulated heme oxygenase-1 (HO-1) and glutamate cysteine ligase (GCLC) that are key antioxidant enzymes essential for cellular defense against oxidative stress. To elucidate the molecular mechanisms underlying RGE-mediated HO-1 and GCLC induction, we have examined the possible involvement of NF-E2-related factor 2 (Nrf2), a redox-sensitive transcription factor, that plays an important role in the transcriptional regulation of diverse antioxidative genes via interaction with the antioxidant response element (ARE). — Treatment of PC12 cells with RGE increased the nuclear translocation, ARE-binding and transcriptional activity of Nrf2. Moreover, U0126 and LY294002, pharmacological inhibitors of MEK1/2 and phosphatidylinositol 3-kinase which are upstream of ERK1/2 and Akt/protein kinase B, respectively attenuated HO-1 and GCLC expression as well as the ARE-driven transcriptional activation of Nrf2. These findings, taken together, suggest that HO-1 and GCLC induction via Nrf2 activation may contribute to cytoprotection exerted by RGE against PCB126-induced oxidative stress.”
“Tocotrienols are members of the vitamin E family. An essential nutrient for the body, vitamin E is made up of four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). The slight difference between tocotrienols and tocopherols lie in the unsaturated side chain having three double bonds in its farnesyl isoprenoid tail. Tocotrienols are natural compounds found in select vegetable oils, wheat germ, barley, saw palmetto, and certain types of nuts and grains. This variant of vitamin E typically only occurs at very low levels in nature (ref).”
The January 2012 publicationTocotrienols fight cancer by targeting multiple cell signaling pathways makes a key point which I emphasize in italics: “Cancer cells are distinguished by several distinct characteristics, such as self-sufficiency in growth signal, resistance to growth inhibition, limitless replicative potential, evasion of apoptosis, sustained angiogenesis, and tissue invasion and metastasis. Tumor cells acquire these properties due to the dysregulation of multiple genes and associated cell signaling pathways, most of which are linked to inflammation. For that reason, rationally designed drugs that target a single gene product are unlikely to be of use in preventing or treating cancer. Moreover, targeted drugs can cause serious and even life-threatening side effects. Therefore, there is an urgent need for safe and effective promiscuous (multitargeted) drugs. “Mother Nature” produces numerous such compounds that regulate multiple cell signaling pathways, are cost effective, exhibit low toxicity, and are readily available. One among these is tocotrienol, a member of the vitamin E family, which has exhibited anticancer properties. This review summarizes data from in vitro and in vivo studies of the effects of tocotrienol on nuclear factor-κB, signal transducer and activator of transcription (STAT) 3, death receptors, apoptosis, nuclear factor (erythroid-derived 2)-like 2 (Nrf2), hypoxia-inducible factor (HIF) 1, growth factor receptor kinases, and angiogenic pathways.”
Another of my favorite supplement substances in resveratrol. There is no surprise finding it on the list of substances that do good things by upregulating Nrf2. For example, going back to 2005, the publication Resveratrol upregulates heme oxygenase-1 expression via activation of NF-E2-related factor 2 in PC12 cells reported: “Resveratrol (3,4′,5-trihydroxy stilbene), a phytoalexin found in the skin and seeds of grapes, has been reported to possess anti-inflammatory, anticarcinogenic, and antioxidant activities. In this work, we assessed the ability of resveratrol to upregulate heme oxygenase-1 (HO-1) gene expression via activation of NF-E2-related factor 2 (Nrf2) in cultured PC12 cells. Nrf2 is a transcription factor involved in the cellular protection against oxidative stress through antioxidant response element (ARE)-directed induction of several phase 2 detoxifying and antioxidant enzymes, such as HO-1. Here, we report that resveratrol induces HO-1 expression via the ARE-mediated transcriptional activation of Nrf2. Moreover, PC12 cells treated with resveratrol exhibited transient activation of Akt/protein kinase B and extracellular signal-regulated protein kinase 1/2 (ERK1/2). LY294002 and U0126, pharmacological inhibitors of phosphatidylinositol 3-kinase and MEK1/2 which are upstream of Akt and ERK1/2, respectively, attenuated resveratrol-induced HO-1 expression and exhibited antioxidant effects. Taken together, the above findings suggest that resveratrol augments cellular antioxidant defense capacity through induction of HO-1 via Nrf2-ARE signaling, thereby protecting PC12 cells from oxidative stress.”
Several other publications have picked up on this theme including a December 2011 publication which implies resveratrol’s ability to induce HO-1 via Nrf2 in a rat model makes the substance a candidate for treatment of Alzheimer’s disease: Resveratrol Protects Rats from Aβ-induced Neurotoxicity by the Reduction of iNOS Expression and Lipid Peroxidation. “Alzheimer disease (AD) is an age-dependent neurodegenerative disease characterized by the formation of β-amyloid (Aβ)-containing senile plaque. The disease could be induced by the administration of Aβ peptide, which was also known to upregulate inducible nitric oxide synthase (iNOS) and stimulate neuronal apoptosis. The present study is aimed to elucidate the cellular effect of resveratrol, a natural phytoestrogen with neuroprotective activities, on Aβ-induced hippocampal neuron loss and memory impairment. On adult Sprague-Dawley rats, we found the injection of Aβ could result in a significant impairment in spatial memory, a marked increase in the cellular level of iNOS and lipid peroxidation, and an apparent decrease in the expression of heme oxygenase-1 (HO-1). By combining the treatment with Aβ, resveratrol was able to confer a significant improvement in spatial memory, and protect animals from Aβ-induced neurotoxicity. These neurological protection effects of resveratrol were associated with a reduction in the cellular levels of iNOS and lipid peroxidation and an increase in the production of HO-1. Moreover, the similar neurological and cellular response were also observed when Aβ treatment was combined with the administration of a NOS inhibitor, N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME). These findings strongly implicate that iNOS is involved in the Aβ-induced lipid peroxidation and HO-1 downregulation, and resveratrol protects animals from Aβ-induced neurotoxicity by suppressing iNOS production.”
Green tea and its active ingredient epigallocatechin-3-gallate (EGCG) are among the “usual suspects” of health producing foods and sure enough, along with most of the others works at least in part via the Nrf2 pathway. The August 2011 publicationEpigallocatechin-3-gallate prevents lupus nephritis development in mice via enhancing the Nrf2 antioxidant pathway and inhibiting NLRP3 inflammasome activationreports: “Patients with lupus nephritis show an impaired oxidative status and increased levels of interleukin (IL)-1β and IL-18, which are closely linked to inflammation and correlated with disease activity. Although epigallocatechin-3-gallate (EGCG), the major bioactive polyphenol present in greentea with antioxidant and free radical scavenging activities, has been reported to have anti-inflammatory effects by inhibiting nuclear factor-kappa B (NF-κB)-mediated inflammatory responses in vivo, its effectiveness for the treatment of lupus nephritis is still unknown. In the present study, 12-week-old New Zealand black/white (NZB/W) F1 lupus-prone mice were treated daily with EGCG by gavage until sacrificed at 34 weeks old for clinical, pathological, and mechanistic evaluation. We found that the administration (1) prevented proteinuria, renal function impairment, and severe renal lesions; (2) increased renal nuclear factor E2-related factor 2 (Nrf2) and glutathione peroxidase activity; (3) reduced renal oxidative stress, NF-κB activation, and NLRP3 mRNA/protein expression and protein levels of mature caspase-1, IL-1β, and IL-18; and (4) enhanced splenic regulatory T (Treg) cell activity. Our data clearly demonstrate that EGCG has prophylactic effects on lupus nephritis in these mice that are highly associated with its effects of enhancing the Nrf2 antioxidant signaling pathway, decreasing renal NLRP3 inflammasome activation, and increasing systemic Treg cell activity.”
At this point I am pretty well convinced that with diligent enough research I could find publications documenting the ability of most of the foods and supplements in my anti-aging lifestyle and supplement firewall regimens in my treatise to regimen to act via Nrf2. I will be content to document only a few more, starting with coffee which I am sipping as I write this.
The April 2011 publication Coffee and its consumption: benefits and risks strives to present a balanced view on coffee: “Coffee is the leading worldwide beverage after water and its trade exceeds US $10 billion worldwide. Controversies regarding its benefits and risks still exist as reliable evidence is becoming available supporting its health promoting potential; however, some researchers have argued about the association of coffee consumption with cardiovascular complications and cancer insurgence. The health-promoting properties of coffee are often attributed to its rich phytochemistry, including caffeine, chlorogenic acid, caffeic acid, hydroxyhydroquinone (HHQ), etc. Many research investigations, epidemiological studies, and meta-analyses regarding coffee consumption revealed its inverse correlation with that of diabetes mellitus, various cancer lines, Parkinsonism, and Alzheimer’s disease. Moreover, it ameliorates oxidative stress because of its ability to induce mRNA and protein expression, and mediates Nrf2-ARE pathway stimulation. Furthermore, caffeine and its metabolites help in proper cognitive functionality. Coffee lipid fraction containing cafestol and kahweol act as a safeguard against some malignant cells by modulating the detoxifying enzymes. On the other hand, their higher levels raise serum cholesterol, posing a possible threat to coronary health, for example, myocardial and cerebral infarction, insomnia, and cardiovascular complications. Caffeine also affects adenosine receptors and its withdrawal is accompanied with muscle fatigue and allied problems in those addicted to coffee. An array of evidence showed that pregnant women or those with postmenopausal problems should avoid excessive consumption of coffee because of its interference with oral contraceptives or postmenopausal hormones. This review article is an attempt to disseminate general information, health claims, and obviously the risk factors associated with coffee consumption to scientists, allied stakeholders, and certainly readers.”
A number of other less-familiar phytosubstances also work through Nrf2 to promote production of HO-1 and are health-protective.
An example is Eckol. The 2010 publication Up-regulation of Nrf2-mediated heme oxygenase-1 expression by eckol, a phlorotannin compound, through activation of Erk and PI3K/Akt reports: The aim of the present study was to examine the cytoprotective effect of eckol, a phlorotannin found in Ecklonia cava and to elucidate underlying mechanisms. Heme oxygenase-1 (HO-1) is an important antioxidant enzyme that plays a role in cytoprotection against oxidative stress. Eckol-induced HO-1 expression both at the level of mRNA and protein in Chinese hamster lung fibroblast (V79-4) cells, resulting in increased HO-1 activity. The transcription factor NF-E2-related factor 2 (Nrf2) is a critical regulator of HO-1, achieved by binding to the antioxidant response element (ARE). Eckol treatment resulted in the enhanced level of phosphorylated form, nuclear translocation, ARE-binding, and transcriptional activity of Nrf2. Extracellular regulated kinase (Erk) and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB, Akt) contributed to ARE-driven HO-1 expression. Eckol activated both Erk and Akt, and treatments with U0126 (an Erk kinase inhibitor), LY294002 (a PI3K inhibitor), specific Erk1 siRNA, and Akt siRNA suppressed the eckol-induced activation of Nrf2, resulting in a decrease in HO-1 expression. ZnPP (a HO-1 inhibitor), HO-1 siRNA, and Nrf2 siRNA markedly abolished the cytoprotective effect of eckol against hydrogen peroxide-induced cell damage. Likewise, U0126 and LY294002 inhibited the eckol-induced cytoprotective effect against oxidative cell damage. These studies demonstrate that eckol attenuates oxidative stress by activating Nrf2-mediated HO-1 induction via Erk and PI3K/Akt signaling.”
In the December 2011 blog entry Focus on phytosubstances – Danshen root – amazing properties of salvia miltiorrhiza Bunge, I reported on the December 2011 publication Extract of Salvia miltiorrhiza (Danshen) induces Nrf2-mediated heme oxygenase-1 expression as a cytoprotective action in RAW 264.7 macrophages. “Conclusion: Danshen induced HO-1 expression through PI3K/Akt-MEK1-Nrf2 pathway and reduced intracellular production of reactive oxygen species via induction of HO-1 expression. The results support a role of HO-1 in the cytoprotective effect of Danshen.”
Lycopene and Fish oils
The September 2011 publication Gee expression and biological pathways in tissue of men with prostate cancer in a randomized clinical trial of lycopene and fish oil supplementation offers some additional important comments which I have italicized. “Background: Studies suggest that micronutrients may modify the risk or delay progression of prostate cancer; however, the molecular mechanisms involved are poorly understood. We examined the effects of lycopene and fish oil on prostate gene expression in a double-blind placebo-controlled randomized clinical trial. Methods: Eighty-four men with low risk prostate cancer were stratified based on self-reported dietary consumption of fish and tomatoes and then randomly assigned to a 3-month intervention of lycopene (n = 29) or fish oil (n = 27) supplementation or placebo (n = 28). Gene expression in morphologically normal prostate tissue was studied at baseline and at 3 months via cDNA microarray analysis. Differential gene expression and pathway analyses were performed to identify genes and pathways modulated by these micronutrients. Results: Global gene expression analysis revealed no significant individual genes that were associated with high intake of fish or tomato at baseline or after 3 months of supplementation with lycopene or fish oil. However, exploratory pathway analyses of rank-ordered genes (based on p-values not corrected for multiple comparisons) revealed the modulation of androgen and estrogen metabolism in men who routinely consumed more fish (p = 0.029) and tomato (p = 0.008) compared to men who ate less. In addition, modulation of arachidonic acid metabolism (p = 0.01) was observed after 3 months of fish oil supplementation compared with the placebo group; and modulation of nuclear factor (erythroid derived-2) factor 2 or Nrf2-mediated oxidative stress response for either supplement versus placebo (fish oil: p = 0.01, lycopene: p = 0.001). Conclusions: We did not detect significant individual genes associated with dietary intake and supplementation of lycopene and fish oil. However, exploratory analyses revealed candidate in vivo pathways that may be modulated by these micronutrients.”
A January 2012 publication is A Diet Rich in Olive Oil Phenolics Reduces Oxidative Stress in the Heart of SAMP8 Mice by Induction of Nrf2-Dependent Gene Expression. “A Mediterranean diet rich in olive oil has been associated with health benefits in humans. It is unclear if and to what extent olive oil phenolics may mediate these health benefits. In this study, we fed senescence-accelerated mouse-prone 8 (SAMP8, n=11 per group) semisynthetic diets with 10% olive oil containing either high (HP) or low amounts of olive oil phenolics (LP) for 4.5 months. Mice consuming the HP diet had significantly lower concentrations of the oxidative damage markers thiobarbituric acid-reactive substances and protein carbonyls in the heart, whereas proteasomal activity was similar in both groups. Nrf2-dependent gene expression may be impaired during the aging process. Therefore, we measured Nrf2 and its target genes glutathione-S-transferase (GST), γ-glutamyl cysteine synthetase (γ-GCS), nicotinamide adenine dinucleotide phosphate [NAD(P)H]:quinone oxidoreductase (NQO1), and paraoxonase-2 (PON2) in the hearts of these mice. Nrf2 as well as GST, γ-GCS, NQO1, and PON2 mRNA levels were significantly higher in heart tissue of the HP as compared to the LP group. The HP-fed mice had significantly higher PON1 activity in serum compared to those receiving the LP diet. Furthermore, HP feeding increased relative SIRT1 mRNA levels. Additional mechanistic cell culture experiments were performed, and they suggest that the olive oil phenolic hydroxytyrosol present in the HP oil may be responsible for the induction of Nrf2-dependent gene expression and the increase in PON activity. In conclusion, a diet rich in olive oil phenolics may prevent oxidative stress in the heart of SAMP8 mice by modulating Nrf2-dependent gene expression.”
A few general observations:
- Activation of pathways involved with metabolism and longevity such as Keap1-Nrf2, AMPK, PI3-kinase, AKT, mTOR, MAPK, PPAR-gamma, FoxO/DAF-16, the GH-IGF axis, P16(Ink4a), SIRT1, telomerase, Klotho and NF-kappaB seems to be more important in assessing the impacts of phytosubstances and their health-producing effects than activation of single genes.
- Dozens or hundreds of genes in pathways may be involved when something biologically important is going on, be that development of a cancer or Alzheimer’s disease or diabetes or be that a protective program that protects against such diseases.
- Complicated natural substances, phytochemicals, have evolved to address such pathways while traditional pharmaceuticals, simpler substances that address a single protein or gene or inhibit a single kinase, do not. That is one reason why pharmaceutical approaches to the age related diseases such as cancers, diabetes and Alzheimer’s disease have achieved only limited successes.
- Keap-1 – Nrf2 appears to be such a critical pathway. In the future I plan to look further into the interaction of this pathways with other important ones involved with metabolism and longevity.
- It appears that once the keap1-Nrf2 pathway is activated it remains so for up to 24 hours, suggesting daily consumption of phytosubstances could be beneficial.
- For the moment I am struck hard by one particular observation. A large number of phytosubstances seem to limit inflammation by downregulating the expression of NF-kappaB. In my treatise I point out that control of expression of NF-kappaB is a major strategy for longevity. See there the proposed firewalls for the Programmed Epigenomic Changes theory of aging. Some 39 supplements in my suggested anti-aging firewall supplement regimen limit expression of NF-kappaB, mainly by preventing its translocation into a cell’s nucleus where it activates inflammatory genes. Looking at that list, it appears to me that pretty much the very same supplements promote the translocation of Nrf2 to a cell’s nucleus where it activates antioxidant and other protective genes. This happy circumstance seems to be a no-accident product of evolution and I intend to investigate it further.
The final blog entry in this triad The pivotal role of Nrf2. Part 3– Is promotion of Nrf2 expression a viable strategy for human human healthspan and lifespan extension? explores whether consuming foods and supplements that promote Nrf2 might be life-extending.