Mabel Buelna-Chontal

Redox activation of Nrf2 & NF-κB: A double end sword?

Moderate concentrations of reactive oxygen species (ROS) are produced by diverse sources under physiological conditions. At such low levels, these molecules may act as upstream mediators of relevant signaling pathways; however an increase in their concentration with respect to the antioxidant system activity, changes their redox signaling function into a deleterious role. Thus, cell health depends, at least in part, on redox balance. This review includes global aspects of oxygen chemistry, ROS generation, antioxidant system, and redox signaling. It is also focused on the description of two relevant redox-sensitive transcription factors: nuclear factor erythroid 2-related factor 2 (Nrf2), which may be a potential target to confer cell protection, and nuclear factor κB (NF-κB), which is involved in deleterious effects in the cell. Finally, recent findings on the interplay between both factors for the development of different pathologies are discussed.

Curcumin maintains cardiac and mitochondrial function in chronic kidney disease

Curcumin, a natural pigment with antioxidant activity obtained from turmeric and largely used in traditional medicine, is currently being studied in the chemoprevention of several diseases for its pleiotropic effects and nontoxicity. In chronic renal failure, the pathogenic mechanisms leading to cardiovascular disorders have been associated with increased oxidative stress, a process inevitably linked with mitochondrial dysfunction. Thus, in this study we aimed at investigating if curcumin pretreatment exerts cardioprotective effects in a rat model of subtotal nephrectomy (5/6Nx) and its impact on mitochondrial homeostasis. Curcumin was orally administered (120mg/kg) to Wistar rats 7 days before nephrectomy and after surgery for 60 days (5/6Nx+curc). Renal dysfunction was detected a few days after nephrectomy, whereas changes in cardiac function were observed until the end of the protocol. Our results indicate that curcumin treatment protects against pathological remodeling, diminishes ischemic events, and preserves cardiac function in uremic rats. Cardioprotection was related to diminished reactive oxygen species production, decreased oxidative stress markers, increased antioxidant response, and diminution of active metalloproteinase-2. We also observed that curcumins cardioprotective effects were related to maintaining mitochondrial function. Aconitase activity was significantly higher in the 5/6Nx + curc (408.5±68.7nmol/min/mg protein) than in the 5/6Nx group (104.4±52.3nmol/min/mg protein, P<0.05), and mitochondria from curcumin-treated rats showed enhanced oxidative phosphorylation capacities with both NADH-linked substrates and succinate plus rotenone (3.6±1 vs 1.1±0.9 and 3.1±0.7 vs 1.2±0.8, respectively, P<0.05). The mechanisms involved in cardioprotection included both direct antioxidant effects and indirect strategies that could be related to protein kinase C-activated downstream signaling.

Protective effect of α-mangostin on cardiac reperfusion damage by attenuation of oxidative stress.

This study was designed to investigate if α-mangostin (α-M), a xanthone present in the pericarp of Garcinia mangostana L., was able to protect against reperfusion injury in Langendorff-reperfused hearts. It was observed that α-M maintains the cardiac mechanical work, diminishes the area of infarct, and prevents the decrease in cardiac ATP and phosphocreatine levels in the reperfused myocardium. The protective effect of this xanthone was associated with reduction of oxidative stress. α-M treatment prevented reperfusion injury-induced protein oxidation (protein carbonyl content), lipid peroxidation (malondialdehyde and 4-hydroxynonenal content), and diminution of glutathione content. In fact, after α-M treatment, the values in these parameters were comparable to those obtained in nonreperfused hearts. In summary, α-M induces a protective effect in postischemic heart associated to the prevention of oxidative stress secondary to reperfusion injury.

Cardioprotective kinase signaling to subsarcolemmal and interfibrillar mitochondria is mediated by caveolar structures

The demonstration that caveolin-3 overexpression reduces myocardial ischemia/reperfusion injury and our own finding that multiprotein signaling complexes increase in mitochondria in association with caveolin-3 levels, led us to investigate the contribution of caveolae-driven extracellular signal-regulated kinases 1/2 (ERK1/2) on maintaining the function of cardiac mitochondrial subpopulations from reperfused hearts subjected to postconditioning (PostC). Rat hearts were isolated and subjected to ischemia/reperfusion and to PostC. Enhanced cardiac function, reduced infarct size and preserved ultrastructure of cardiomyocytes were associated with increased formation of caveolar structures, augmented levels of caveolin-3 and mitochondrial ERK1/2 activation in PostC hearts in both subsarcolemmal (SSM) and interfibrillar (IFM) subpopulations. Disruption of caveolae with methyl-β-cyclodextrin abolished cardioprotection in PostC hearts and diminished pho-ERK1/2 gold-labeling in both mitochondrial subpopulations in correlation with suppression of resistance to permeability transition pore opening. Also, differences between the mitochondrial subpopulations in the setting of PostC were evaluated. Caveolae disruption with methyl-β-cyclodextrin abolished the cardioprotective effect of postconditioning by inhibiting the interaction of ERK1/2 with mitochondria and promoted decline in mitochondrial function. SSM, which are particularly sensitive to reperfusion damage, take advantage of their location in cardiomyocyte boundary and benefit from the cardioprotective signaling driven by caveolae, avoiding injury propagation.

Nrf2-regulated antioxidant response is activated by protein kinase C in postconditioned rat hearts.

Postconditioning (PostC) activates endogenous protective mechanisms that contend against reperfusion injury. Nevertheless, although PostC efficiency in both experimental studies and clinical trials has been demonstrated, a complete picture of the interacting mechanisms, particularly the relationship between kinase signaling and redox maintenance, is still lacking. To unravel such association, in this work we focus on the participation of protein kinase C (PKC) and the transcription factor nuclear factor E2-related factor 2 (Nrf2) in the cardioprotective response elicited by PostC. PostC was performed in an in vivo rat model by applying three repetitive cycles of ischemia and reperfusion (10 s each), followed by evaluation of heart function and infarct size measurements. PKC activation and Nrf2 phosphorylation were evaluated after 10 min of reperfusion, whereas Nrf2 activity and the content and activities of Nrf2-regulated antioxidant proteins were evaluated after 60 min of reperfusion in PostC hearts. Maintenance of heart function and diminution in infarct size concurred with PKC activation and Nrf2 phosphorylation. PKC inhibition diminished Nrf2 phosphorylation and transcriptional activity in association with diminished levels and activities of Nrf2-regulated antioxidant proteins. In conclusion, this study proposes that the novel pathway PKC/Nrf2 participates in the long-term protective mechanisms induced by PostC application by maintaining the antioxidant defense system.

Targeting Mitochondria for Cardiac Protection

The critical role of mitochondria in cardiomyocyte survival and death has become an exciting field of research in cardiac biology. Indeed, it is accepted that mitochondrial dysfunction plays a crucial role in the pathogenesis of multiple cardiac diseases. Besides the obvious relevance of mitochondria in energy production, calcium homeostasis, and reactive oxygen species (ROS) production, new processes like mitochondrial fusion/fission, phosphorylation and nitrosylation modifications in mitochondrial proteins have been suggested to form part of a cast of key players in cardiac disease. This review describes currently studied drugs and compounds that target mitochondria in the scenario of cardiovascular diseases.

Attenuation of oxidant damage in the postconditioned heart involves non‐enzymatic response and partial catalytic protection

Oxidant stress, among other effectors, is implicated in the sequel of myocardial reperfusion injury. It is generally accepted that maintaining the balance between oxidant and antioxidant signalling within the cell provides protection against reperfusion damage. The cardioprotective strategy of postconditioning (PC) reduces reperfusion injury through complex mechanisms; however, the contribution of the antioxidant system has not been fully investigated. In this study, isolated rat hearts were subjected to PC after 30 min global ischaemia, and then to 5 min (IR5) or 60 min of reperfusion (IR60). Postconditioning significantly increased the left ventricular developed pressure and the double product (heart rate × left ventricular developed pressure) for both early (PC5) and prolonged reperfusion (PC60, PC before 60 min of reperfusion). Necrotic tissue diminished to 10.8% in PC60 hearts, compared with 49% of infarct size measured in IR60 hearts (P < 0.05 versus IR60). Also, protein carbonylation and malondialdehyde levels decreased and were correlated with a significant augmentation in CuZn superoxide dismutase activity (P < 0.05, PC60 versus IR60) and increased glutathione redox state (GSH:GSSG ratio; P < 0.05, PC60 versus IR60). Diethylthiocarbamate, a non‐selective superoxide dismutase inhibitor, significantly diminished the protection afforded by PC when administered throughout the protocol. However, administration of this inhibitor only during reperfusion had no effect on PC‐induced cardioprotection. These results indicate that non‐enzymatic antioxidants account for the protective effect of PC, modifying the oxidant stress caused by ischaemic reperfusion in rats. The contribution of CuZn superoxide dismutase activity in the observed cardioprotective effect is less clear, and could be relevant if acting in concert with other PC‐activated mechanisms.

Cardioprotective properties of citicoline against hyperthyroidism-induced reperfusion damage in rat hearts.

Hyperthyroidism represents an increased risk factor for cardiovascular morbidity, especially when the heart is subjected to an ischemia/reperfusion process. The aim of this study was to explore the possible protective effect of the nucleotide citicoline on the susceptibility of hyperthyroid rat hearts to undergo reperfusion-induced damage, which is associated with mitochondrial dysfunction. Hence, we analyzed the protective effect of citicoline on the electrical behavior and on the mitochondrial function in rat hearts. Hyperthyroidism was established after a daily i.p. injection of triiodothyronine (at 2 mg/kg of body weight) during 5 days. Thereafter, citicoline was administered i.p. (at 125 mg/kg of body weight) for 5 days. In hyperthyroid rat hearts, citicoline protected against reperfusion-induced ventricular arrhythmias. Moreover, citicoline maintained the accumulation of mitochondrial Ca(2+), allowing mitochondria to reach a high transmembrane electric gradient that protected against the release of cytochrome c. It also preserved the activity of the enzyme aconitase that inhibited the release of cytokines. The protection also included the inhibition of oxidative stress-induced mDNA disruption. We conclude that citicoline protects against the reperfusion damage that is found in the hyperthyroid myocardium. This effect might be due to its inhibitory action on the permeability transition in mitochondria.

Citicoline (CDP-choline) protects myocardium from ischemia/ reperfusion injury via inhibiting mitochondrial permeability transition

AIMS Oxidative stress emerges after reperfusion of an organ following an ischemic period and results in tissue damage. In the heart, an amplified generation of reactive oxygen species and a significant Ca(2+) accumulation cause ventricular arrhythmias and mitochondrial dysfunction. This occurs in consequence of increased non-specific permeability. A number of works have shown that permeability transition is a common substrate that underlies the reperfusion-induced heart injury. The aim of this work was to explore the possibility that CDP-choline may circumvent heart damage and mitochondrial permeability transition. MAIN METHODS Rats were injected i.p. with CDP-choline at 20 mg/kg body weight. Heart electric behavior was followed during a closure/opening cycle of the left coronary descendent artery. Heart mitochondria were isolated from rats treated with CDP-choline, and their function was evaluated by analyzing Ca(2+) movements, achievement of a high level of the transmembrane potential, and respiratory control. Oxidative stress was estimated following the activity of the enzymes cis-aconitase and superoxide dismutase, as well as the disruption of mitochondrial DNA. KEY FINDINGS This study shows that CDP-choline avoided ventricular arrhythmias and drop of blood pressure. Results also show that mitochondria, isolated from CDP-choline-treated rats, maintained selective permeability, retained accumulated Ca(2+), an elevated value of transmembrane potential, and a high ratio of respiratory control. Furthermore, activity of cis-aconitase enzyme and mDNA structure were preserved. SIGNIFICANCE This work introduces CDP-choline as a useful tool to preserve heart function from reperfusion damage by inhibiting mitochondrial permeability transition.

Inhibition of the nitric oxide/cyclic guanosine monophosphate pathway limited the cardioprotective effect of post-conditioning in hearts with apical myocardial infarction

Reperfusion damage involves opening of the mitochondrial permeability transition pore (mPTP) and loss of ATP synthesis. Several cardioprotective pathways are activated by ischemic or pharmacological post-conditioning (PC). The mechanisms that are activated by PC in no co-morbidity murine models include: activation of rescue kinases, oxidative stress reduction, glycolytic flux regulation and preservation of ATP synthesis. However, relatively scarce efforts have been made to define whether the efficacy of PC signaling is blunted by risk factors or systemic diseases associated with ischemic heart pathology. Experimental evidence has shown that the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling is a main mechanism activated by PC in hearts without pathological history. In this work we evaluated the participation of the NO pathway, through downstream kinase activation and inhibition of mPTP in hearts with previous infarct. Myocardial infarction was induced with a single dose of isoproterenol (85 mg/kg i.p.) to male Wistar rats. After 24 h, the hearts were mounted into the Langendorff system and subjected to 30 min of ischemia and 60 min of reperfusion. PC consisted of 5 cycles of 30 s of reperfusion/30 s of ischemia, then the hearts were reperfused with or without inhibitors of the NO/cGMP pathway. PC activates the NO/cGMP pathway, as increased cGMP and NO levels were detected in isoproterenol-treated hearts. The cardioprotective effect of PC was abolished with both L-NAME (inhibitor of constitutive NO synthase) and ODQ (inhibitor of soluble guanylate cyclase), whereas the NO donor (DETA-NO) restored cardioprotection even in the presence of L-NAME or ODQ. We also found that mitochondrial structure and function was preserved in PC hearts. We conclude that PC exerts cardioprotection in hearts with previous infarct by maintaining mitochondrial structure and function through NO-dependent pathway.