Late cardioprotection of exercise preconditioning against exhaustive exercise-induced myocardial injury by up-regulatation of connexin 43 expression in rat hearts

Optimization of exercise preconditioning duration in protecting from exhausted exercise-induced cardiac injury in rats

The effect of different duration of exercise preconditioning (EP) on protecting from exhaustive exercise-induced cardiac injury (EECI) has been optimized in rats. Male Sprague-Dawley rats were divided into six groups: the control group, exhaustive exercise (EE) group, EP 20-min + EE group, EP 40-min + EE group, EP 60-min + EE group and EP 80-min + EE group. The EP groups were subjected to treadmill running at the intensity of 74.0% V̇O_{2 max}. Changes of exercise capacity, cardiac pathology, myocardial enzymology, electrocardiogram (ECG), cardiac function, and mitochondrial respiratory function were compared. Compared to the C group, the EE group has shown significant decrease of exercise capacity, elevation of serum N-terminal pro B-type natriuretic peptide (NT-proBNP) and cardiac troponin-I (cTn-I) levels, cardiac morphology change, ECG disturbance, cardiac dysfunction and reduction of myocardial mitochondrial respiration function. Compared to the EE group, the EP groups have shown significant elevation of exercise capacity, decrease of serum NT-proBNP and cTn-I, improvement of cardiac function and myocardial mitochondrial electron transfer pathway complex I, II and IV activity. The correlation analyses showed protection of EP was proportional to EP duration from 20-min to 60-min. EE caused cardiac injury. EP could protect from EECI by alleviating myocardial damage, improving cardiac function and mitochondrial ETP complex I, II and IV activity. EP protection was positively correlated to EP duration from 20-min to 60-min with EP intensity fixed at 74.0% V̇O_{2 max}.

Arrhythmogenic Cardiomyopathy: Exercise Pitfalls, Role of Connexin-43, and Moving beyond Antiarrhythmics

Arrhythmogenic Cardiomyopathy (ACM), a Mendelian disorder that can affect both left and right ventricles, is most often associated with pathogenic desmosomal variants that can lead to fibrofatty replacement of the myocardium, a pathological hallmark of this disease. Current therapies are aimed to prevent the worsening of disease phenotypes and sudden cardiac death (SCD). Despite the use of implantable cardioverter defibrillators (ICDs) there is no present therapy that would mitigate the loss in electrical signal and propagation by these fibrofatty barriers. Recent studies have shown the influence of forced vs. voluntary exercise in a variety of healthy and diseased mice; more specifically, that exercised mice show increased Connexin-43 (Cx43) expression levels. Fascinatingly, increased Cx43 expression ameliorated the abnormal electrical signal conduction in the myocardium of diseased mice. These findings point to a major translational pitfall in current therapeutics for ACM patients, who are advised to completely cease exercising and already demonstrate reduced Cx43 levels at the myocyte intercalated disc. Considering cardiac dysfunction in ACM arises from the loss of cardiomyocytes and electrical signal conduction abnormalities, an increase in Cx43 expression-promoted by low to moderate intensity exercise and/or gene therapy-could very well improve cardiac function in ACM patients.

Paraoxonase and oxidative stress changes in left and right ventricles of exhaustively exercised rats

Exhaustive exercise can cause subclinical inflammation to the heart, as it is an oxidative tissue that works continuously. The effect of exhaustive exercise on left and right ventricles (LVs, RVs) may be different. It is claimed that paraoxonase-1 (PON1), an antioxidant enzyme, has a cardioprotective effect on oxidative stress. Rats were separated as non-exercised controls (Con), those euthanized immediately after (E-0) and 24 h after exhaustive exercise (E-24). Cardiac troponin-I (cTnI), total antioxidant status (TAS), total oxidant status (TOS), PON1 activities, and histological findings in LV and RV of the exhausted rats were evaluated. TAS and PON1 levels were lower in LVs compared with RVs of all groups. TOS levels were high in LVs compared with RVs of all groups. In LVs, TAS levels decreased significantly in the E-0 group while PON1 activity decreased in E-0 and E-24 groups compared with controls. In LVs, TOS levels decreased significantly in E-0 and E-24 groups, but in RVs a decrease was seen only in the E-0 group. cTnI levels increased significantly in the E-0 group and decreased to control levels in the E-24 group. Considering the histological and biochemical findings, exhaustive exercise affected the heart to the maximum during and just after exhaustion, and LV was influenced more than RV.

Whole body hypoxic preconditioning-mediated multiorgan protection in db/db mice via nitric oxide-BDNF-GSK-3β-Nrf2 signaling pathway

The beneficial effects of hypoxic preconditioning are abolished in the diabetes. The present study was designed to investigate the protective effects and mechanisms of repeated episodes of whole body hypoxic preconditioning (WBHP) in db/db mice. The protective effects of preconditioning were explored on diabetesinduced vascular dysfunction, cognitive impairment and ischemia-reperfusion (IR)-induced increase in myocardial injury. Sixteen-week old db/db (diabetic) and C57BL/6 (non-diabetic) mice were employed. There was a significant impairment in cognitive function (Morris Water Maze test), endothelial function (acetylcholineinduced relaxation in aortic rings) and a significant increase in IR-induced heart injury (Langendorff apparatus) in db/db mice. WBHP stimulus was given by exposing mice to four alternate cycles of low (8%) and normal air O₂ for 10 min each. A single episode of WBHP failed to produce protection; however, two and three episodes of WBHP significantly produced beneficial effects on the heart, brain and blood vessels. There was a significant increase in the levels of brain-derived neurotrophic factor (BDNF) and nitric oxide (NO) in response to 3 episodes of WBHP. Moreover, pretreatment with the BDNF receptor, TrkB antagonist (ANA-12) and NO synthase inhibitor (LNAME) attenuated the protective effects imparted by three episodes of WBHP. These pharmacological agents abolished WBHP-induced restoration of p-GSK-3β/GSK-3β ratio and Nrf2 levels in IR-subjected hearts. It is concluded that repeated episodes of WHBP attenuate cognitive impairment, vascular dysfunction and enhancement in IRinduced myocardial injury in diabetic mice be due to increase in NO and BDNF levels that may eventually activate GSK-3β and Nrf2 signaling pathway to confer protection.

β-Amyrin supplementation ameliorates the toxic effect of glycerol in the kidney of rat model

Acute kidney injury (AKI) is a common life-threatening complication. In this study, β-amyrin is hypothesized to exert a potential nephroprotective effect against glycerol-induced nephrotoxicity in rats. Thirty-two female Sprague-Dawley rats were divided into four groups: normal control, β-amyrin treated (50 mg kg^-1 body weight) for 14 days, glycerol 25% (10 ml kg^-1 BW volume/volume in sterile saline, intramuscular), and β-amyrin + glycerol-treated rats. Assessing kidney function was done through the measurement of serum urea and creatinine (SCr). Real-time quantitative polymerase chain reaction analysis was done to measure the changes in the gap junction protein and intermediate filament proteins (IFPs) messenger RNA (mRNA) levels. Renal tissue histopathology was also observed. Glycerol exhibited significant elevation in the SCr and urea with significant upregulation of connexin43, vimentin, and nestin. The levels of all disrupted parameters were improved by the pre-administration of β-amyrin. The β-amyrin exerts significant improvement of the biochemical parameters with a restoration of the renal tissue histopathological picture. Significant downregulation of the expression levels of the gap junction protein and IFPs mRNA was also seen. Collectively, the administration of β-amyrin showed a promising effect for a protection against glycerol-induced AKI in rats.

Trimetazidine Attenuates Exhaustive Exercise-Induced Myocardial Injury in Rats via Regulation of the Nrf2/NF-κB Signaling Pathway

Exhausted exercise has been reported to cause the damage of myocardial structure and function in terms of cardiomyocyte apoptosis, oxidative stress, and energy metabolism disturbance. Trimetazidine (TMZ), as an anti-ischemic agent, has been approved to be effective in promoting myocardial energy metabolism, anti-inflammatory, and anti-oxidation. However, few studies examined the effects of TMZ on myocardial injury induced by exhausted exercise. To investigate whether TMZ could ameliorate the exhaustive exercise-induced myocardial injury and explore the underlying mechanisms, here the rat model of exhaustive exercise was induced by prolonged swimming exercise and TMZ was administrated to rats before exhaustive exercise. According to the results, we demonstrated that exhaustive exercise led to cardiomyocyte damage in rats as evidenced by elevations in cTnI and NT-proBNP levels, and decrease in CX43 expression, which was attenuated by TMZ treatment. Moreover, the administration of TMZ was found to restrain exhaustive exercise-induced oxidative stress damage by increasing GSH level, SOD and GSH-Px activities, and decreasing MDA level. Additionally, TMZ ameliorated myocardial injury by inhibiting apoptosis via reducing Bax/Bcl-2 ratio and down-regulating cleaved caspase-3, cleaved PARP, and cytochrome c levels in the myocardium of rats. Furthermore, we found that TMZ suppressed oxidative stress and cardiomyocyte apoptosis via activation of Nrf2/HO-1 and inactivation of NF-κB signaling pathways. Therefore, our study suggested that TMZ provided cardioprotection in rats after exhaustive exercise, indicating TMZ might served as a potential therapeutic drug for exhaustive exercise-induced myocardial injury.

Differential susceptibility of kidneys and livers to proliferative processes and transcriptional level of the genes encoding desmin, vimentin, connexin 43, and nestin in rats exposed to furan

In this study, we aimed to assess the differential toxic impact, induced by furan exposure, on the liver and kidney tissues by estimating reactive oxygen species (ROS) level, total antioxidant capacity (TAC), oxidative damage, and the tissue injury markers in a male rat model. To explain such impacts, 20 rats were assigned into two groups: a control group, where rats were administered corn oil as a vehicle, and a furan-administered group, where furan was orally administered to rats at a dose of 16 mg/kg b wt/day (five days per week over eight weeks). The transcriptional levels of intermediate filament proteins (desmin, vimentin, nestin, and connexin 43) were assessed by using quantitative real-time polymerase chain reaction (PCR), and the cell proliferation markers (proliferating cell nuclear antigen [PCNA] and proliferation-associated nuclear antigen [Ki-67]) were recognized by immunohistochemical analysis. Furthermore, the ultrastructural changes of liver and kidney were monitored using electron microscopy. Our findings showed that furan exposure could induce hepatic and renal damage to different extents. Furan can increase the ROS content, oxidative damage indices, and liver tissue injury indices but not kidney injury indices. Furthermore, it decreases the TAC in the serum of exposed rats. In addition, furan exposure was associated with changes in the mRNA expression pattern of intermediate filament proteins in both kidney and liver tissues. Moreover, furan enhances the expression of PCNA and Ki-67 in the liver tissues but not in the kidney tissues. The ultrastructure evaluation revealed the incidence of glomerular podocyte degeneration and hepatocyte injury. These results conclusively demonstrate that the deleterious effects of furan are caused by promoting fibrosis and hepatocyte proliferation in liver tissues and triggering podocyte injury in the kidney tissues.

Effects of aluminum oxide (Al2O3) nanoparticles on ECG, myocardial inflammatory cytokines, redox state, and connexin 43 and lipid profile in rats: possible cardioprotective effect of gallic acid

The objectives of present study were to examine the effects of aluminum oxide (Al2O3) nanoparticles on myocardial functions, electrical activities, morphology, inflammation, redox state, and myocardial expression of connexin 43 (Cx43) and the effect of gallic acid (GA) on these effects in a rat animal model. Forty male albino rats were divided into 4 equal groups: the control (normal) group; the Al2O3 group, rats received Al2O3 (30 mg·kg(-1), i.p.) daily for 14 days; the nano-alumina group, rats received nano-alumina (30 mg·kg(-1), i.p.) daily for 14 days; and the nano-alumina + GA group, rats received GA (100 mg·kg(-1) orally once daily) for 14 days before nano-alumina administration. The results showed disturbed ECG variables and significant increases in serum levels of LDH, creatine phosphokinase (CPK), CK-MB, triglycerides (TGs), cholesterol and LDL, nitric oxide (NO), and TNF-α and myocardial concentrations of NO, TNF-α, and malondialdehyde (MDA), with significant decreases in serum HDL and myocardial GSH, SOD, catalase (CAT), and Cx43 expression in the nano-alumina group. Pretreatment with GA improved significantly all parameters except serum and myocardial NO. We concluded that chronic administration of Al2O3 NPs caused myocardial dysfunctions, and pretreatment with GA ameliorates myocardial injury induced by nano-alumina, probably through its hypolipidaemic, anti-inflammatory, and antioxidant effects and upregulation of Cx43 in heart.