Skeletal muscle contraction evokes numerous biochemical alterations that underpin exercise benefits. This present study aimed to elucidate the mechanism for electrical pulse stimulation (EPS)-induced antioxidant adaptation in C2C12 myotubes. We found that EPS significantly upregulated Nrf2 and a broad array of downstream antioxidant enzymes involved in multiple antioxidant systems. These effects were completely abolished by pretreatment with a ROS scavenger, N-acetylcysteine. MitoSOX-Red, CM-H2DCFDA, and EPR spectroscopy revealed a significantly higher ROS level in mitochondria and cytosol in EPS cells compared to non-stimulated cells. Seahorse and Oroboros revealed that EPS significantly increased the maximal mitochondrial oxygen consumption rate, along with an upregulated protein expression of mitochondrial complexes I/V, mitofusin-1, and mitochondrial fission factor. A post-stimulation time-course experiment demonstrated that upregulated NQO1 and GSTA2 last at least 24 h following the cessation of EPS, whereas elevated ROS declines immediately. These findings suggest an antioxidant preconditioning effect in the EPS cells. A cell viability study suggested that the EPS cells displayed 11- and 36-fold higher survival rates compared to the control cells in response to 2 and 4 mM H₂O₂ treatment, respectively. In summary, we found that EPS upregulated a large group of antioxidant enzymes in C2C12 myotubes via a contraction-mitochondrial-ROS-Nrf2 pathway. This antioxidant adaptation protects cells against oxidative stress-associated cytotoxicity.

Gabapentin (GBP), a GABA analogue, is primarily used as an anticonvulsant for the treatment of partial seizures and neuropathic pain. Whereas a majority of the side effects are associated with the nervous system, emerging evidence suggests there is a high risk of heart diseases in patients taking GBP. In the present study, we first used a preclinical model of rats to investigate, firstly, the acute cardiovascular responses to GBP (bolus i.v. injection, 50 mg/kg) and secondly the effects of chronic GBP treatment (i.p. 100 mg/kg/day × 7 days) on cardiovascular function and the myocardial proteome. Under isoflurane anesthesia, rat blood pressure (BP), heart rate (HR), and left ventricular (LV) hemodynamics were measured using Millar pressure transducers. The LV myocardium and brain cortex were analyzed by proteomics, bioinformatics, and western blot to explore the molecular mechanisms underlying GBP-induced cardiac dysfunction. In the first experiment, we found that i.v. GBP significantly decreased BP, HR, maximal LV pressure, and maximal and minimal dP/dt, whereas it increased IRP-AdP/dt, Tau, systolic, diastolic, and cycle durations (* p < 0.05 and ** p < 0.01 vs. baseline; n = 4). In the second experiment, we found that chronic GBP treatment resulted in hypotension, bradycardia, and LV systolic dysfunction, with no change in plasma norepinephrine. In the myocardium, we identified 109 differentially expressed proteins involved in calcium pathways, cholesterol metabolism, and galactose metabolism. Notably, we found that calmodulin, a key protein of intracellular calcium signaling, was significantly upregulated by GBP in the heart but not in the brain. In summary, we found that acute and chronic GBP treatments suppressed cardiovascular function in rats, which is attributed to abnormal calcium signaling in cardiomyocytes. These data reveal a novel side effect of GBP independent of the nervous system, providing important translational evidence to suggest that GBP can evoke adverse cardiovascular events by depression of myocardial function.

Skeletal muscle contraction evokes numerous genetic and biochemical alterations that underpin the beneficial effects of exercise. The present study aimed to elucidate the mechanism and significance for contraction-evoked antioxidant adaptation in C2C12 myotubes using electrical pulse stimulation (EPS). As NQO1 and GSTA2 are the top antioxidants upregulated by Nrf2, dose-response and time-course experiments of EPS were performed to optimize the parameter at 10 volts for 4 days by evaluating their protein expression. Western blot analysis demonstrated that EPS-cells expressed significantly higher Nrf2 and a broad array of downstream antioxidant enzymes involved in multiple antioxidant systems. These effects were completely abolished by pretreatment with a ROS scavenger, N-acetylcysteine. MitoSOX-Red, CM-H2DCFDA, and EPR spectroscopy revealed a significantly higher ROS level in mitochondria and cytosol in EPS-cells compared to non-stimulated cells. Seahorse and Oroboros revealed that EPS significantly increased maximal mitochondrial oxygen consumption rate, along with upregulated protein expression of mitochondrial complexes I/V, mitofusin-1, and mitochondrial fission factor. A post-stimulation time-course experiment demonstrated that upregulated NQO1 and GSTA2 last at least 24 hours following the cessation of EPS, whereas elevated ROS declines immediately. These finding suggest an antioxidant preconditioning effect in the EPS-cells. A cell viability study using the CCK-8 assay suggested that EPS-cells displayed 11- and 36-fold higher survival rate compared to control-cells in response to 2 and 4 mM H₂O₂ treatment, respectively. In summary, we found that EPS upregulated a large group of antioxidant enzymes in C2C12 myotubes via a contraction-mitochondrial-ROS-Nrf2 pathway. This antioxidant adaptation protects cells against oxidative stress-associated cytotoxicity.

Gabapentin (GBP), at high plasma concentrations, negatively impacts cardiovascular function, causing bradycardia, hypotension, and impaired left ventricular (LV) function in rats. This study examines the combined effects of GBP with Verapamil (Ver) or Metoprolol (Met) on cardiovascular function in anesthetized male rats and its impact on Ca²⁺ current and calmodulin (CaM) protein expression in cultured H9c2 cells. Twenty-two male Sprague Dawley rats were assigned to four groups: Saline + Ver, GBP + Ver, Saline + Met, and GBP + Met. Under isoflurane anesthesia, rats underwent ECG monitoring and LV hemodynamic and blood pressure (BP) assessment. GBP (50 mg/kg) was administered intravenously, followed by Ver (0.05-0.4 mg/kg) or Met (0.5 mg/kg). In the first experiment, Ver induced a dose-dependent reduction in BP, heart rate (HR), and maximal dP/dt, while increasing minimal dP/dt, in both saline control and GBP-treated groups with the latter group showing greater effects. In the second experiment, GBP significantly reduced BP, HR, and maximal dP/dt while increasing minimal dP/dt compared to baseline. These effects were further exacerbated by Met, leading to greater reductions in BP, HR, and maximal dP/dt, and increases in minimal dP/dt compared to Met alone. In addition, in vitro experiments demonstrated that GBP reduced Ca²⁺ current and downregulated CaM protein. These findings suggest that, at high plasma concentrations, GBP enhances the negative chronotropic, negative inotropic, and hypotensive effects of both Ver and Met, further highlighting the need for additional preclinical and clinical studies to characterize the potential drug interactions between GBP and calcium channel blockers or beta-1 blockers, particularly in patients with cardiovascular disease.

Gabapentin (GBP), a GABA analogue, is primarily used as an anticonvulsant to treat partial seizures and neuropathic pain. While a majority of the side effects are associated with the nervous system, emerging evidence suggests a high risk for heart diseases in the patients taking GBP. In the present study, we used a preclinical model of rats to investigate (1) the acute cardiovascular responses to GBP (bolus i.v. injection, 50 mg/kg) and (2) the effects of chronic GBP treatment (i.p. 100 mg/kg/day x 7 days) on cardiovascular function and the myocardial proteome. Under isoflurane-anesthesia, rat blood pressure (BP), heart rate (HR), and left ventricular (LV) hemodynamics were measured using Millar pressure transducers. The LV myocardium and brain cortex were analyzed by proteomics, bioinformatics, and western blot to explore the molecular mechanisms underlying GBP-induced cardiac dysfunction. In experiment (1), we found that i.v. GBP significantly decreased BP, HR, maximal LV pressure, and maximal and minimal dP/dt, whereas it increased IRP-AdP/dt, Tau, systolic, diastolic, and cycle durations (*p < 0.05 and **p < 0.01 vs baseline; n = 4/group). In experiment (2), we found that chronic GBP treatment resulted in hypotension, bradycardia, and LV systolic dysfunction, with no change in plasma norepinephrine. In the myocardium, we identified 109 differentially expressed proteins involved in calcium pathways, cholesterol metabolism, and galactose metabolism. Particularly, we found that calmodulin, a key protein of intracellular calcium signaling, was significantly upregulated by GBP in the heart but not in the brain. In summary, we found that acute and chronic GBP treatments suppressed cardiovascular function in rats, which is attributed to abnormal calcium signaling in cardiomyocytes. These data reveal a novel side effect of GBP independent of the nervous system, providing important translational evidence to suggest that GBP can evoke adverse cardiovascular events by depression of myocardial function.

Background: Aging elevates reactive oxygen species (ROS) and weakens antioxidant defenses, contributing to cardiac dysfunction. The objective of this study was to determine whether sustained activation of skeletal muscle (SkM) Nrf2 preserves cardiac function during aging and to explore the underlying mechanisms, focusing on myocardial antioxidant pathways. Methods: Tamoxifen-induced SkM-specific Keap1 knockout male mice (iMS-Keap1^flox/flox; SkM-Nrf2 overexpression) were divided into young wild-type (Y-WT), aged wild-type (A-WT), and aged knockout (A-KO) groups. Cardiac performance was evaluated by echocardiography and invasive hemodynamics. Myocardial proteomics identified differentially expressed proteins (DEPs) and enriched biological pathways. Results: Compared with Y-WT, A-WT mice showed impaired left ventricular function, including reduced ejection fraction, prolonged isovolumic relaxation time, blunted inotropic response to dobutamine, and elevated Tau index. These age-related deficits were partially reversed in A-KO mice. Proteomic analysis revealed 561 DEPs between A-WT and Y-WT, and 741 DEPs between A-KO and A-WT, enriched in calcium signaling, Nrf2-mediated oxidative stress response, oxidative phosphorylation, ROS detoxification, and cardiac-specific processes, such as hypertrophy, conduction, and dilated cardiomyopathy. Conclusions: Lifelong SkM-Nrf2 activation strengthens myocardial antioxidant capacity and alleviates age-related cardiac dysfunction. These data support an antioxidant crosstalk between skeletal muscle and the heart, highlighting a potential therapeutic target for aging-associated heart failure.