Protective vs. Therapeutic Effects of Mitochondria-Targeted Antioxidant MitoTEMPO on Rat Sciatic Nerve Crush Injury: A Comprehensive Electrophysiological Analysis.

Protective vs. Therapeutic Effects of Mitochondria-Targeted Antioxidant MitoTEMPO on Rat Sciatic Nerve Crush Injury: A Comprehensive Electrophysiological Analysis. Peripheral nerve injuries often result in long-lasting functional deficits, prompting the need for effective interventions. MitoTEMPO (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl) triphenylphosphonium chloride) is a mitochondria-targeted antioxidant that has shown protective and therapeutic effects against pathologies associated with reactive oxygen species. This study explores the utilization of MitoTEMPO as a therapeutic and protective agent for sciatic nerve crush injuries. By employing advanced mathematical approaches, the study seeks to comprehensively analyze nerve conduction parameters, nerve excitability, and the distribution of nerve conduction velocities to gauge the potential. Forty Wistar-Albino rats were randomly divided into following groups: (I) SHAM-animals subjected to sham operation and treated intraperitoneally (i.p.) with vehicle (bidistilled water) for 14 days; (II) CI (crush injury)-animals subjected to CI and treated with vehicle 14 days; (III) MiP-animals subjected to 7 days i.p. MitoTEMPO treatment before CI (0.7 mg/kg/day dissolved in vehicle) and, only vehicle for 7 days after CI, protective MitoTEMPO; and (IV) MiT-animals i.p. treated with only vehicle for 7 days before CI and 7 days with MitoTEMPO (0.7 mg/kg/day dissolved in vehicle) after CI, therapeutic MitoTEMPO. Nerve excitability parameters were measured, including rheobase and chronaxie, along with compound action potential (CAP) recordings. Advanced mathematical analyses were applied to CAP recordings to determine nerve conduction velocities and distribution patterns. The study revealed significant differences in nerve excitability parameters between groups. Nerve conduction velocity was notably reduced in the MiP and CI groups, whereas CAP area values were diminished in the MiP and CI groups compared to the MiT group. Furthermore, CAP velocity was lower in the MiP and CI groups, and maximum depolarization values were markedly lower in the MiP and CI groups compared to the SHAM group. The distribution of nerve conduction velocities indicated alterations in the composition of nerve fiber groups following crush injuries. In conclusion, postoperative MitoTEMPO administration demonstrated promising results in mitigating the detrimental effects of nerve crush injuries.

Abdominal Ischemia-Reperfusion Induced Cardiac Dysfunction Can Be Prevented by MitoTEMPO.

BACKGROUND: Cardiac dysfunction is secondary to acute mesenteric ischemia (AMI) and abdominal aortic aneurysms (AAA). The underlying cause of distant organ damage in the heart is the formation of oxidative stress caused by ischemia-reperfusion. In this study, we investigated the possible protective effects of a novel mitochondria-targeted antioxidant MitoTEMPO on contractile dysfunction and structural defects of the rat papillary muscle caused by abdominal ischemia-reperfusion (AIR). METHODS AND RESULTS: In the experiments, adult Wistar-Albino rats were used and animals were divided randomly into 3 groups; sham-operated group (SHAM), an IR group that had aortic cross-clamping for 1 h followed by 2 h reperfusion, and a third group that received protective 0.7 mg/kg/day MitoTEMPO injection for 28-day before IR. As a result, it was observed that MitoTEMPO injection had a protective effect on the mechanical activities and structural properties of the papillary muscle impaired by AIR. Our study also showed that AIR disrupted the contractile function of the papillary muscle for each stimulation frequency and post-potentiation responses tested. This is common for each measured and calculated mechanical parameter and MitoTEMPO injection showed its protective effects. CONCLUSION: Consequently, calcium homeostasis seems to be impaired by AIR, and MitoTEMPO may exert its protective effect through energy metabolism by directly targeting the mitochondria.

Can MitoTEMPO protect rat sciatic nerve against ischemia-reperfusion injury?

Abdominal ischemia-reperfusion (I/R) is known to cause both structural and functional damage to sciatic nerve which is related to the oxidative stress. We investigated the protective effects of mitochondria-targeted antioxidant (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl) triphenylphosphonium chloride (MitoTEMPO) on ischemia-reperfusion-induced nerve damage by using the conduction velocity distribution (CVD) calculations from in vitro compound nerve action potential (CNAP) recordings from rat sciatic nerve. Adult male Wistar albino rats were divided into three groups. The IR and IR + MT groups had aortic cross-clamping for 1 h followed by 2 h reperfusion, while SHAM group had the same procedure without cross-clamping. IR + MT group received 0.7 mg/kg/day MitoTEMPO injection for 28 days before I/R, while other groups received vehicle alone. Ischemia-reperfusion resulted in a significant decrease (p < .05) in maximum depolarizations (mV), areas (mV.ms), and maximum and minimum upstroke velocities (mV/ms) of CNAPs, while injection of MitoTEMPO showed a complete protective effect on these impairments. The histograms for CVD showed that I/R blocked the contribution of fast-conducting fibers (> 60 m/s). MitoTEMPO prevented that blockage and caused a shift in the CVD. Functional nerve damage caused by I/R can be prevented by MitoTEMPO, which can enter mitochondria, the main source of reactive oxygen species (ROS).

Effects of prasugrel on membrane potential and contractile activity of rat ventricular myocytes.

BACKGROUND: Though prasugrel is one of the important P2Y12 inhibitors currently in use for antiplatelet therapy, its potential effects on contractility and electrical activity of ventricular myocytes have not yet been investigated. Hence this study was designed to study the impact of prasugrel on contractile function and membrane potential of isolated ventricular myocytes. METHODS: Freshly isolated rat ventricular myocytes were used in this study. Myocyte contraction was measured during electrical stimulation of cardiomyocytes and the action potential (AP) recordings were obtained with current clamp mode of the patch-clamp amplifier. RESULTS: AP duration and fractional shortening of ventricular myocytes did not show any change with the administration of 1µM of prasugrel. However, remarkable depolarization of resting membrane potential followed by apparent fibrillation episodes was detected in the cardiomyocytes. Similar events were observed in the contractile activity of myocytes during field stimulation. Also, a higher concentration of prasugrel (10µM) elicited repeated fibrillations, which disappeared after washout or nitric oxide synthase (NOS) inhibition with L-NAME. In contrast, the same concentration of ticagrelor, another P2Y12 inhibitor did not induce fibrillation events though it decreased the contractility of ventricular myocytes significantly. The perfusion of ventricular myocytes with L-NAME did not alter the negative inotropic effect of ticagrelor. CONCLUSIONS: Prasugrel, a widely used antithrombotic agent, may induce depolarization in the membrane potential of myocytes as well as fibrillation via NO mediated pathway.

Rho-kinase inhibition reverses impaired Ca2+ handling and associated left ventricular dysfunction in pressure overload-induced cardiac hypertrophy.

Recent studies have implicated a relationship between RhoA/ROCK activity and defective Ca2+ homeostasis in hypertrophic hearts. This study investigated molecular mechanism underlying ROCK inhibition-mediated cardioprotection against pressure overload-induced cardiac hypertrophy, with a focus on Ca2+ homeostasis. Cardiac hypertrophy model was established by performing transverse aortic constriction (TAC) in 8-week-old male rats. Groups were assigned as SHAM, TAC and TAC+Fas (rats undergoing TAC and treated with fasudil). Rats in the TAC+Fas group were administered fasudil (5mg/kg/day), and rats in the SHAM and TAC groups were treated with vehicle for 10 weeks. Electrophysiological recordings were obtained from isolated left ventricular myocytes and expression levels of proteins were determined using western blotting. Rats in the TAC group showed remarkable cardiac hypertrophy, and fasudil treatment significantly reversed this alteration. TAC+Fas myocytes showed significant improvement in reduced contractility and Ca2+ transients. Moreover, these myocytes showed restoration of slow relaxation rate and Ca2+ reuptake. Although L-type Ca2+ currents did not change in TAC group, there was a significant reduction in the triggered Ca2+ transients which was reversed either by long-term fasudil treatment or incubation of TAC myocytes with fasudil. The hearts of rats in the TAC group showed a significant decrease in ROCK1, ROCK2, RyR2 protein levels and p-PLBS16/T17/SERCA2 ratio and increase in RhoA expression and MLC phosphorylation. However, fasudil treatment largely reversed TAC-induced alterations in protein expression. Thus, our findings indicate that upregulation of the RhoA/ROCK pathway is significantly associated with cardiac hypertrophy-related Ca2+ dysregulation and suggest that ROCK inhibition prevents hypertrophic heart failure.

2.1 GHz electromagnetic field does not change contractility and intracellular Ca2+ transients but decreases ß-adrenergic responsiveness through nitric oxide signaling in rat ventricular myocytes.

PURPOSE: Due to the increasing use of wireless technology in developing countries, particularly mobile phones, the influence of electromagnetic fields (EMF) on biologic systems has become the subject of an intense debate. Therefore, in this study we investigated the effect of 2.1 GHz EMF on contractility and beta-adrenergic (ß-AR) responsiveness of ventricular myocytes. MATERIALS AND METHODS: Rats were randomized to the following groups: Sham rats (SHAM) and rats exposed to 2.1 GHz EMF for 2 h/day for 10 weeks (EM-10). Sarcomere shortening and Ca(2+) transients were recorded in isolated myocytes loaded with Fura2-AM and electrically stimulated at 1 Hz, while L-type Ca(2+) currents (I(CaL)) were measured using whole-cell patch clamping at 36 ± 1°C. Cardiac nitric oxide (NO) levels were measured in tissue samples using a colorimetric assay kit. RESULTS: Fractional shortening and amplitude of the matched Ca(2+) transients were not changed in EM-10 rats. Although the isoproterenol-induced (10(-6) M) I(CaL) response was reduced in rats exposed to EMF, basal I(CaL) density in myocytes was similar between the two groups (p < 0.01). Moreover, EMF exposure led to a significant increase in nitric oxide levels in rat heart (p < 0.02). CONCLUSIONS: Long-term exposure to 2.1 GHz EMF decreases ß-AR responsiveness of ventricular myocytes through NO signaling.