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Diabetic hearts are susceptible to damage from inappropriate activation of the renin angiotensin system (RAS) and hyperglycemic events both of which contribute to increased oxidant production. Prolonged elevation of oxidants impairs mitochondrial enzyme function, further contributing to metabolic derangement. Nuclear factor erythriod-2-related factor 2 (Nrf2) induces antioxidant genes including those for glutathione (GSH) synthesis following translocation to the nucleus. We hypothesized that an acute elevation in glucose impairs Nrf2-related gene expression in diabetic hearts, while AT1 antagonism would aid in Nrf2-mediated antioxidant production and energy replenishment. We used four groups (n = 6-8/group) of 25-week-old rats: 1) LETO (lean strain-control), 2) type II diabetic OLETF, 3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d × 8 wks), and 4) ARBM (4 weeks on ARB, 4 weeks off) to study the effects of acutely elevated glucose on cardiac mitochondrial function and Nrf2 signaling in the diabetic heart. Animals were gavaged with a glucose bolus (2 g/kg) and groups were dissected at T0, T180, and T360 minutes. Nrf2 mRNA was 32% lower in OLETF rats compared to LETO and remained suppressed in response to glucose. LETO Nrf2 mRNA increased 25% at T360 in response to glucose while no changes were observed in diabetic hearts. GCLC and GCLM mRNA decreased in diabetic hearts 33% and 44% respectively and remained suppressed in response to glucose while ARB treatment increased GCLM transcripts 90% at T180. These data illustrate that during T2DM and in response to glucose, cardiac Nrf2's adaptive response to environmental stressors such as glucose is impaired in diabetic hearts and that ARB treatment may aid Nrf2's impaired dynamic response.

A paradox is a seemingly absurd or impossible concept, proposition, or theory that is often difficult to understand or explain, sometimes apparently self-contradictory, and yet ultimately correct or true. How is it possible, for example, that oxygen "a toxic environmental poison" could be also indispensable for life (Beckman and Ames Physiol Rev 78(2):547-81, 1998; Stadtman and Berlett Chem Res Toxicol 10(5):485-94, 1997)?: the so-called Oxygen Paradox (Davies and Ursini 1995; Davies Biochem Soc Symp 61:1-31, 1995). How can French people apparently disregard the rule that high dietary intakes of cholesterol and saturated fats (e.g., cheese and paté) will result in an early death from cardiovascular diseases (Renaud and de Lorgeril Lancet 339(8808):1523-6, 1992; Catalgol et al. Front Pharmacol 3:141, 2012; Eisenberg et al. Nat Med 22(12):1428-1438, 2016)?: the so-called, French Paradox. Doubtless, the truth is not a duality and epistemological bias probably generates apparently self-contradictory conclusions. Perhaps nowhere in biology are there so many apparently contradictory views, and even experimental results, affecting human physiology and pathology as in the fields of free radicals and oxidative stress, antioxidants, foods and drinks, and dietary recommendations; this is particularly true when issues such as disease-susceptibility or avoidance, "healthspan," "lifespan," and ageing are involved. Consider, for example, the apparently paradoxical observation that treatment with low doses of a substance that is toxic at high concentrations may actually induce transient adaptations that protect against a subsequent exposure to the same (or similar) toxin. This particular paradox is now mechanistically explained as "Adaptive Homeostasis" (Davies Mol Asp Med 49:1-7, 2016; Pomatto et al. 2017a; Lomeli et al. Clin Sci (Lond) 131(21):2573-2599, 2017; Pomatto and Davies 2017); the non-damaging process by which an apparent toxicant can activate biological signal transduction pathways to increase expression of protective genes, by mechanisms that are completely different from those by which the same agent induces toxicity at high concentrations. In this review, we explore the influences and effects of paradoxes such as the Oxygen Paradox and the French Paradox on the etiology, progression, and outcomes of many of the major human age-related diseases, as well as the basic biological phenomenon of ageing itself.

GPx8 is a mammalian Cys-glutathione peroxidase of the endoplasmic reticulum membrane, involved in protein folding. Its regulation is mostly unknown. We addressed both the functionality of two hypoxia-response elements (HREs) within the promoter, GPx8 HRE1 and GPx8 HRE2, and the GPx8 physiological role. In HeLa cells, treatment with HIFα stabilizers, such as diethyl succinate (DES) or 2-2'-bipyridyl (BP), induces GPx8 expression at both mRNA and protein level. Luciferase activity of pGL3(GPx8wt), containing a fragment of the GPx8 promoter including the two HREs, is also induced by DES/BP or by overexpressing either individual HIFα subunit. Mutating GPx8 HRE1 within pGL3(GPx8wt) resulted in a significantly higher inhibition of luciferase activity than mutating GPx8 HRE2. Electrophoretic mobility-shift assay showed that both HREs exhibit enhanced binding to a nuclear extract from DES/BP-treated cells, with stronger binding by GPx8 HRE1. In DES-treated cells transfected with pGL3(GPx8wt) or mutants thereof, silencing of HIF2α, but not HIF1α, abolishes luciferase activity. Thus GPx8 is a novel HIF target preferentially responding to HIF2α binding at its two novel functional GPx8 HREs, with GPx8 HRE1 playing the major role. Fibroblast growth factor (FGF) treatment increases GPx8 mRNA expression, and reporter gene experiments indicate that induction occurs via HIF. Comparing the effects of depleting GPx8 on the downstream effectors of FGF or insulin signaling revealed that absence of GPx8 results in a 16- or 12-fold increase in phosphorylated ERK1/2 by FGF or insulin treatment, respectively. Furthermore, in GPx8-depleted cells, phosphorylation of AKT by insulin treatment increases 2.5-fold. We suggest that induction of GPx8 expression by HIF slows down proliferative signaling during hypoxia and/or growth stimulation through receptor tyrosine kinases.

We present arguments for an evolution in our understanding of how antioxidants in fruits and vegetables exert their health-protective effects. There is much epidemiological evidence for disease prevention by dietary antioxidants and chemical evidence that such compounds react in one-electron reactions with free radicals in vitro. Nonetheless, kinetic constraints indicate that in vivo scavenging of radicals is ineffective in antioxidant defense. Instead, enzymatic removal of nonradical electrophiles, such as hydroperoxides, in two-electron redox reactions is the major antioxidant mechanism. Furthermore, we propose that a major mechanism of action for nutritional antioxidants is the paradoxical oxidative activation of the Nrf2 (NF-E2-related factor 2) signaling pathway, which maintains protective oxidoreductases and their nucleophilic substrates. This maintenance of "nucleophilic tone," by a mechanism that can be called "para-hormesis," provides a means for regulating physiological nontoxic concentrations of the nonradical oxidant electrophiles that boost antioxidant enzymes, and damage removal and repair systems (for proteins, lipids, and DNA), at the optimal levels consistent with good health.