Differential-display polymerase chain reaction identifies nicotinamide adenine dinucleotide-ubiquinone oxidoreductase as an ischemia/reperfusion-regulated gene in cardiomyocytes

Metformin Protects H9C2 Cardiomyocytes from High-Glucose and Hypoxia/Reoxygenation Injury via Inhibition of Reactive Oxygen Species Generation and Inflammatory Responses: Role of AMPK and JNK

Metformin is a first-line drug for the management of type 2 diabetes. Recent studies suggested cardioprotective effects of metformin against ischemia/reperfusion injury. However, it remains elusive whether metformin provides direct protection against hypoxia/reoxygenation (H/R) injury in cardiomyocytes under normal or hyperglycemic conditions. This study in H9C2 rat cardiomyoblasts was designed to determine cell viability under H/R and high-glucose (HG, 33 mM) conditions and the effects of cotreatment with various concentrations of metformin (0, 1, 5, and 10 mM). We further elucidated molecular mechanisms underlying metformin-induced cytoprotection, especially the possible involvement of AMP-activated protein kinase (AMPK) and Jun NH(2)-terminal kinase (JNK). Results indicated that 5 mM metformin improved cell viability, mitochondrial integrity, and respiratory chain activity under HG and/or H/R (P < 0.05). The beneficial effects were associated with reduced levels of reactive oxygen species generation and proinflammatory cytokines (TNF-α, IL-1α, and IL-6) (P < 0.05). Metformin enhanced phosphorylation level of AMPK and suppressed HG + H/R induced JNK activation. Inhibitor of AMPK (compound C) or activator of JNK (anisomycin) abolished the cytoprotective effects of metformin. In conclusion, our study demonstrated for the first time that metformin possessed direct cytoprotective effects against HG and H/R injury in cardiac cells via signaling mechanisms involving activation of AMPK and concomitant inhibition of JNK.

AMP-activated protein kinase activation during cardioplegia-induced hypoxia/reoxygenation injury attenuates cardiomyocytic apoptosis via reduction of endoplasmic reticulum stress

Cardioplegic-induced H/R injury results in cardiomyocytic apoptosis. AMPK has been shown to reduce ER stress and the unfolded protein response (UPR). Whether AMPK activation can attenuate cardiomyocytic apoptosis after cardioplegia-induced H/R injury is unknown. Cardiomyocytes were exposed to simulated ischemia by incubation in a hypoxic chamber with intermittent cold cardioplegia solution infusion at 20-minute intervals and subsequently reoxygenated in a normoxic environment. Various doses of AMPK activators (AICAR or metformin) were given 2 days before H/R injury. The cardiomyocytes were harvested after reoxygenation for subsequent examination. With both AMPK activators, the antiapoptotic genes of ER stress and UPR, the subsequent production of proapoptotic proteins was attenuated, and the antiapoptotic proteins were elevated. The activity of the apoptotic effectors of ER stress was also reduced with AMPK activation. Moreover, TUNEL staining showed that AMPK activation significantly reduced the percentage of apoptotic cardiomyocytes after cardioplegia-induced H/R injury. Our results revealed that AMPK activation during cardioplegia-induced H/R injury attenuates cardiomyocytic apoptosis, via enhancement of antiapoptotic and reduction of proapoptotic responses, resulting from lessening ER stress and the UPR. AMPK activation may serve as a future pharmacological target to reduce H/R injury in the clinical setting.

eIF4A inhibition allows translational regulation of mRNAs encoding proteins involved in Alzheimer's disease

Alzheimer's disease (AD) is the main cause of dementia in our increasingly aging population. The debilitating cognitive and behavioral symptoms characteristic of AD make it an extremely distressing illness for patients and carers. Although drugs have been developed to treat AD symptoms and to slow disease progression, there is currently no cure. The incidence of AD is predicted to increase to over one hundred million by 2050, placing a heavy burden on communities and economies, and making the development of effective therapies an urgent priority. Two proteins are thought to have major contributory roles in AD: the microtubule associated protein tau, also known as MAPT; and the amyloid-beta peptide (A-beta), a cleavage product of amyloid precursor protein (APP). Oxidative stress is also implicated in AD pathology from an early stage. By targeting eIF4A, an RNA helicase involved in translation initiation, the synthesis of APP and tau, but not neuroprotective proteins, can be simultaneously and specifically reduced, representing a novel avenue for AD intervention. We also show that protection from oxidative stress is increased upon eIF4A inhibition. We demonstrate that the reduction of these proteins is not due to changes in mRNA levels or increased protein degradation, but is a consequence of translational repression conferred by inhibition of the helicase activity of eIF4A. Inhibition of eIF4A selectively and simultaneously modulates the synthesis of proteins involved in Alzheimer's disease: reducing A-beta and tau synthesis, while increasing proteins predicted to be neuroprotective.

cDNA representational difference analysis used in the identification of genes related to the aging process in rat kidney

Aging is a complex physiological process by which the functions of many organ systems deteriorate. Growing evidence shows that age-related changes and damage are causally related to oxidative stress and inflammatory responses from reactive species. The aim of this study was to identify differentially expressed genes in old and young kidneys of Fisher 344 male rats during the aging process using complementary DNA representational difference analysis (cDNA RDA). cDNA RDA is a subtractive technique for identifying a focused set of differentially expressed genes. The distinctive advantage of this technique is its capability of detecting differences in gene expressions at less than one copy per cell and identifying genes not previously described in the database. Reverse transcription-polymerase chain reaction with specific primers was applied to confirm the differences found by RDA. Twenty-one putative differentially expressed genes were identified. Sixteen genes were up-regulated during aging and were associated with stress-response and inflammatory reactions, while five genes were down-regulated. These data suggested that the inflammatory process is a plausible cause of the aging process.

Inhibition of NF-kappa B activation can attenuate ischemia/reperfusion-induced contractility impairment via decreasing cardiomyocytic proinflammatory gene up-regulation and matrix metalloproteinase expression

Following cardiopulmonary bypass (CPB) and cardiac global ischemia and reperfusion, proinflammatory genes are up-regulated, and nuclear factor (NF)-kappaB is involved in this regulation. We studied whether inactivation of NF-kappaB could decrease myocardial ischemia/reperfusion injury with cardioplegia during CPB, attenuate matrix metalloproteinase (MMP) activation, and prevent cardiac mechanical dysfunction. Rabbits received normal saline (group 1) or curcumin (70 and 7 micromol/kg in groups 2 and 3) injection 2 hours before CPB. Total CPB was initiated, and myocardial protection was delivered every 20 minutes for 60 minutes of cardiac arrest. Rabbits were weaned from CPB and reperfused for 4 hours before the hearts were harvested. Blood was sampled at various time points. Postoperative expression of myocardial mRNA levels of interleukin 6, monocyte chemoattractant protein-1, and tumor necrosis factor-alpha, postreperfusion plasma level of troponin I, and cardiac mechanical dysfunction were significantly decreased in the curcumin groups. The myocardial levels of activated MMP-2 and -9 were also significantly reduced compared with the control group. In conclusion, by inhibiting NF-kappaB activation, the up-regulation of cardiac proinflammatory genes can be ameliorated, and the activation of MMPs can be decreased during CPB, thereby lessening severity of cardiac mechanical dysfunction after global cardiac ischemia/reperfusion injury.

Nitric oxide attenuates cardiomyocytic apoptosis via diminished mitochondrial complex I up-regulation from cardiac ischemia-reperfusion injury under cardiopulmonary bypass

OBJECTIVE

This study tested the hypothesis that cardioplegic solution supplemented with a nitric oxide donor agent attenuates postischemic cardiomyocytic apoptosis by reduction of mitochondrial complex I up-regulation during global cardiac arrest under cardiopulmonary bypass.

METHODS

Twenty-four anesthetized dogs supported by total vented bypass were divided evenly into 4 groups (n = 6) and subjected to 60 minutes of hypothermic ischemia followed by 4 degrees C multidose crystalloid cardioplegic solution infusion. Hearts received either standard crystalloid cardioplegic solution (control), crystalloid cardioplegic solution supplemented with 2 mmol/L L-arginine (L-Arg group), crystalloid cardioplegic solution supplemented with 400 micromol/L N(G)-monomethyl-L-arginine (L-NMMA group), or crystalloid cardioplegic solution supplemented with 100 micromol/L of NO donor compound (3-morpholinosydnonimine; SIN-1 group). After 60 minutes of cardioplegic arrest, the heart was reperfused for a total of 240 minutes after discontinuation of bypass. The occurrence of cardiomyocytic apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling and Western blot analysis of caspase-3.

RESULTS

The occurrence of cardiomyocytic apoptosis was significantly reduced in SIN-1 and L-Arg groups compared with the control group. Mitochondrial complex I mRNA was up-regulated in the control group, and its expression was significantly higher in the L-NMMA group but significantly reduced in the SIN-1 and L-Arg groups. Western blot analysis of Bcl-2 and cytochrome c, an index of mitochondrial damage in postischemic myocardium, revealed a similar pattern.

CONCLUSION

Nitric oxide-supplemented crystalloid cardioplegic solution diminished postischemic cardiomyocytic apoptosis after global cardiac arrest under cardiopulmonary bypass, possibly via prevention of mitochondrial complex I up-regulation.