Nicorandil improves post-fatigue tension in slow skeletal muscle fibers by modulating glutathione redox state

Mitochondrial Cation Signalling in the Control of Inflammatory Processes

Mitochondria are the bioenergetic organelles responsible for the maintenance of cellular homeostasis and have also been found to be associated with inflammation. They are necessary to induce and maintain innate and adaptive immune cell responses, acting as signalling platforms and mediators in effector responses. These organelles are also known to play a pivotal role in cation homeostasis as well, which regulates the inflammatory responses through the modulation of these cation channels. In particular, this review focuses on mitochondrial Ca2+ and K+ fluxes in the regulation of inflammatory response. Nevertheless, this review aims to understand the interplay of these inflammation inducers and pathophysiological conditions. In detail, we discuss some examples of chronic inflammation such as lung, bowel, and metabolic inflammatory diseases caused by a persistent activation of the innate immune response due to a dysregulation of mitochondrial cation homeostasis.

Diazoxide improves muscle function in association with improved dyslipidemia and decreased muscle oxidative stress in streptozotocin-induced diabetic rats

AIM/INTRODUCTION

Diabetes Mellitus is a chronic degenerative disease, and its main biochemical characteristic is hyperglycemia due to impaired insulin secretion, resistance to peripheral actions of insulin, or both. Hyperglycemia causes dyslipidemia and stimulates oxidative damage, leading to the main symptoms, such as fatigue and culminates in diabetic complications. Previous studies have shown that ATP-sensitive potassium channels counteract muscle fatigue and metabolic stress in healthy mouse models. To determine the effect of diazoxide on muscle strength development during diabetes, we tested the effect of diazoxide in streptozotocin-diabetic rats in muscle function, lipid profile and oxidative stress biomarkers.

MATERIALS AND METHODS

Wistar rats were divided into 4 groups of six animals each: (1) Control group, (2) diabetes group, (3) Control group + diazoxide, and (4) Diabetic + diazoxide (DB + DZX). 4 weeks after rats were sacrificed, soleus and extensor digitorum longus muscles (EDL) were extracted to prepare homogenates and serum was obtained for biochemical measurements. Oxidative damage was evaluated by the thiobarbituric acid method and the fluorescent for reactive oxygen species (ROS) probe 2,4-H₂DCFDA, respectively.

RESULTS

Diabetic rats with diazoxide administration showed an increase in the development of muscle strength in both muscles; in turn, the onset of fatigue was longer compared to the group of diabetic rats without treatment. Regarding the lipid profile, diazoxide decreased total cholesterol levels in the group of diabetic rats treated with diazoxide (x̅46.2 mg/dL) compared to the untreated diabetic group (x̅=104.4 mg/dL); secondly, diazoxide decreased triglyceride concentrations (x̅=105.3 mg/dL) compared to the untreated diabetic rats (x̅=412.2 mg/dL) as well as the levels of very low-density lipoproteins (x̅=20.4 mg/dL vs. x̅=82.44 mg/dL). Regarding the various markers of oxidative stress, the diabetic group treated with diazoxide was able to reduce the concentrations of TBARS and total reactive oxygen species as well as preserve the concentrations of reduced glutathione.

CONCLUSION

Diazoxide administration in diabetic rats increases muscle strength development in EDL and soleus muscle, decreases fatigue, reduces cholesterol and triglyceride concentrations and improves oxidative stress parameters such as TBARS, ROS, and glutathione status.

Combined Systemic Intake of K-ATP Opener (Nicorandil) and Mesenchymal Stem Cells Preconditioned With Nicorandil Alleviates Pancreatic Insufficiency in a Model of Bilateral Renal Ischemia/Reperfusion Injury

We used nicorandil, a K-ATP channel opener, to study the role of these channels in the amelioration of renal ischemia/reperfusion (I/R)-induced pancreatic injury, and the possible involvement of PI3K/Akt/mTOR signaling pathway. Forty-two male Wistar rats were included in this study, six were sacrificed for extraction of bone marrow mesenchymal stem cells (BM-MSCs) and conducting the in-vitro work, the others were included in vivo study and equally divided into six groups. Group 1 (sham control), but groups 2–6 were subjected to bilateral renal I/R: Group 2 (I/R); Group 3 (I/R-NC), treated with nicorandil; Group 4 (I/R-MSCs), treated with BM-MSCs; Group 5 (I/R-MSCC), treated with nicorandil-preconditioned BM-MSCs; Group 6 (I/R-NC-MSCC), treated with both systemic nicorandil and preconditioned BM-MSCC. Renal injury and subsequent pancreatic damage were detected in the I/R group by a significant increase in serum urea, creatinine, fasting glucose, and pancreatic enzymes. The pancreatic tissues showed a reduction in cellularity and a significant decrease in the expression of the cell survival pathway, PI3K/Akt/mTOR, in the I/R group compared to the control. Preconditioning MSCs with nicorandil significantly enhanced the proliferation assay and decreased their apoptotic markers. Indeed, combined systemic nicorandil and nicorandil-preconditioning maintained survival of MSC in the pancreatic tissue and amelioration of apoptotic markers and pancreatic TNF-α production. Histologically, all treated groups revealed better pancreatic architecture, and increased area % of anti-insulin antibody and CD31, which were all best observed in the NC-MSCC group. Thus, using K-ATP channel opener was efficient to enhance PI3K/Akt/mTOR expression levels (in vivo and in vitro).

Alternative Targets for Modulators of Mitochondrial Potassium Channels

Mitochondrial potassium channels control potassium influx into the mitochondrial matrix and thus regulate mitochondrial membrane potential, volume, respiration, and synthesis of reactive oxygen species (ROS). It has been found that pharmacological activation of mitochondrial potassium channels during ischemia/reperfusion (I/R) injury activates cytoprotective mechanisms resulting in increased cell survival. In cancer cells, the inhibition of these channels leads to increased cell death. Therefore, mitochondrial potassium channels are intriguing targets for the development of new pharmacological strategies. In most cases, however, the substances that modulate the mitochondrial potassium channels have a few alternative targets in the cell. This may result in unexpected or unwanted effects induced by these compounds. In our review, we briefly present the various classes of mitochondrial potassium (mitoK) channels and describe the chemical compounds that modulate their activity. We also describe examples of the multidirectional activity of the activators and inhibitors of mitochondrial potassium channels.

Protective Effect of Nicorandil on Cardiac Microvascular Injury: Role of Mitochondrial Integrity

A major shortcoming of postischemic therapy for myocardial infarction is the no-reflow phenomenon due to impaired cardiac microvascular function including microcirculatory barrier function, loss of endothelial activity, local inflammatory cell accumulation, and increased oxidative stress. Consequently, inadequate reperfusion of the microcirculation causes secondary ischemia, aggravating the myocardial reperfusion injury. ATP-sensitive potassium ion (KATP) channels regulate the coronary blood flow and protect cardiomyocytes from ischemia-reperfusion injury. Studies in animal models of myocardial ischemia-reperfusion have illustrated that the opening of mitochondrial KATP (mito-KATP) channels alleviates endothelial dysfunction and reduces myocardial necrosis. By contrast, blocking mito-KATP channels aggravates microvascular necrosis and no-reflow phenomenon following ischemia-reperfusion injury. Nicorandil, as an antianginal drug, has been used for ischemic preconditioning (IPC) due to its mito-KATP channel-opening effect, thereby limiting infarct size and subsequent severe ischemic insult. In this review, we analyze the protective actions of nicorandil against microcirculation reperfusion injury with a focus on improving mitochondrial integrity. In addition, we discuss the function of mitochondria in the pathogenesis of myocardial ischemia.

Nicorandil decreases oxidative stress in slow- and fast-twitch muscle fibers of diabetic rats by improving the glutathione system functioning

AIMS/INTRODUCTION

Myopathy is a common complication of any diabetes type, consisting in failure to preserve mass and muscular function. Oxidative stress has been considered one of the main causes for this condition. This study aimed to search if Nicorandil, a KATP channel opener, could protect slow- and fast-twitch diabetic rat muscles from oxidative stress, and to unveil its possible mechanisms.

MATERIALS AND METHODS

Diabetes was induced in male Wistar rats by applying intraperitoneally streptozotocin (STZ) at 100 mg/kg doses. Nicorandil (3 mg/kg/day) was administered along 4 weeks. An insulin tolerance test and assessment of fasting blood glucose (FBG), TBARS, reduced (GSH), and disulfide (GSSG) glutathione levels, GSH/GSSG ratio, and mRNA expression of glutathione metabolism-related genes were performed at end of treatment in soleus and gastrocnemius muscles.

RESULTS

Nicorandil significantly reduced FBG levels and enhanced insulin tolerance in diabetic rats. In gastrocnemius and soleus muscles, Nicorandil attenuated the oxidative stress by decreasing lipid peroxidation (TBARS), increasing total glutathione and modulating GPX1-mRNA expression in both muscle's types. Nicorandil also increased GSH and GSH/GSSG ratio and downregulated the GCLC- and GSR-mRNA in gastrocnemius, without significative effect on those enzymes' mRNA expression in diabetic soleus muscle.

CONCLUSIONS

In diabetic rats, Nicorandil attenuates oxidative stress in slow- and fast-twitch skeletal muscles by improving the glutathione system functioning. The underlying mechanisms for the modulation of glutathione redox state and the transcriptional expression of glutathione metabolism-related genes seem to be fiber type-dependent.

Diazoxide and Exercise Enhance Muscle Contraction during Obesity by Decreasing ROS Levels, Lipid Peroxidation, and Improving Glutathione Redox Status

Obesity causes insulin resistance and hyperinsulinemia which causes skeletal muscle dysfunction resulting in a decrease in contraction force and a reduced capacity to avoid fatigue, which overall, causes an increase in oxidative stress. K_ATP channel openers such as diazoxide and the implementation of exercise protocols have been reported to be actively involved in protecting skeletal muscle against metabolic stress; however, the effects of diazoxide and exercise on muscle contraction and oxidative stress during obesity have not been explored. This study aimed to determine the effect of diazoxide in the contraction of skeletal muscle of obese male Wistar rats (35 mg/kg), and with an exercise protocol (five weeks) and the combination from both. Results showed that the treatment with diazoxide and exercise improved muscular contraction, showing an increase in maximum tension and total tension due to decreased ROS and lipid peroxidation levels and improved glutathione redox state. Therefore, these results suggest that diazoxide and exercise improve muscle function during obesity, possibly through its effects as K_ATP channel openers.

N-(2-mercaptopropionyl)-glycine enhances in vitro pig embryo production and reduces oxidative stress

This study evaluated the effects of different concentrations (1, 10, 25, 50, and 100 µM) of the antioxidant N-(2-mercaptopropionyl)-glycine (NMPG), during the culture of in vitro-fertilized porcine oocytes. While the highest concentrations of NMPG (50 and 100 µM) were toxic to the developing embryos during the first two days of culture, 25 µM NMPG achieved cleavage rates that were similar to those achieved by the control but did not sustain blastocyst production by Day 7 of culture. Compared to the control culture medium, the culture medium supplemented with 10 µM NMPG increased (P < 0.05) the rates of blastocyst formation, decreased (P < 0.05) the intracellular levels of reactive oxygen substances, and downregulated (P < 0.05) the expression of the oxidative stress related gene GPX1. In conclusion, these results demonstrated that supplementation of porcine embryo culture medium with 10 µM NMPG can attenuate oxidative stress and increase the yield of in vitro production of blastocysts.

Nicorandil Affects Mitochondrial Respiratory Chain Function by Increasing Complex III Activity and ROS Production in Skeletal Muscle Mitochondria

Adenosine triphosphate (ATP)-dependent potassium channels openers (K_ATP) protect skeletal muscle against function impairment through the activation of the mitochondrial K_ATP channels (mitoK_ATP). Previous reports suggest that modulators of the mitochondrial K_ATP channels have additional effects on isolated mitochondria. To determine whether the K_ATP channel opener nicorandil has non-specific effects that explain its protective effect through the mitochondrial function, chicken muscle mitochondria were isolated, and respiration rate was determined pollarographically. The activity of the electron transport chain (ETC) complexes (I-IV) was measured using a spectrophotometric method. Reactive oxygen species (ROS) levels and lipid peroxidation were assessed using flow cytometry and thiobarbituric acid assay, respectively. Both K_ATP channel opener nicorandil and K_ATP channel blocker 5-hydroxydecanoate (5-HD) decreased mitochondrial respiration; nicorandil increased complex III activity and decreased complex IV activity. The effects of nicorandil on complex III were antagonized by 5-HD. Nicorandil increased ROS levels, effect reverted by either 5-HD or the antioxidant N-2-mercaptopropionyl glycine (MPG). None of these drugs affected lipid peroxidation levels. These findings suggest that K_ATP channel opener nicorandil increases mitochondrial ROS production from complex III. This results by partially blocking electron flow in the complex IV, setting electron carriers in a more reduced state, which is favored by the increase in complex III activity by nicorandil. Overall, our study showed that nicorandil like other mitochondrial K_ATP channel openers might not act through mitoK_ATP channel activation.

Signaling pathways targeting mitochondrial potassium channels

In this review, we describe key signaling pathways regulating potassium channels present in the inner mitochondrial membrane. The signaling cascades covered here include phosphorylation, redox reactions, modulation by calcium ions and nucleotides. The following types of potassium channels have been identified in the inner mitochondrial membrane of various tissues: ATP-sensitive, Ca²⁺-activated, voltage-gated and two-pore domain potassium channels. The direct roles of these channels involve regulation of mitochondrial respiration, membrane potential and synthesis of reactive oxygen species (ROS). Changes in channel activity lead to diverse pro-life and pro-death responses in different cell types. Hence, characterizing the signaling pathways regulating mitochondrial potassium channels will facilitate understanding the physiological role of these proteins. Additionally, we describe in this paper certain regulatory mechanisms, which are unique to mitochondrial potassium channels.

Nicorandil reversed homocysteine-induced coronary microvascular dysfunction via regulating PI3K/Akt/eNOS pathway

OBJECTIVE

Nicorandil exerts a protective effect against coronary microvascular dysfunction in acute myocardial infarction (AMI) patients. However, the mechanism and effect of nicorandil in hyperhomocysteinemia (HHcy) AMI patients remain unclear.

METHODS

C57/BL6 mice with mild to moderate HHcy and human coronary artery endothelial cells (HCAECs) cotreated with HHcy (1 mmol/L) for 24 h and hypoxia for 6 h were selected as models. Small animal ultrasound detection was used to compare cardiac function. CD31 immunofluorescence staining and tomato lectin staining were used to assess the number of microcirculation changes in vivo. MTT, tube formation and western blotting assays were used to evaluate the effect of nicorandil on HCAECs and the PI3K/Akt/eNOS pathway.

RESULTS

The results showed that nicorandil improved cell viability and p-PI3K/PI3K, p-Akt/Akt, and p-eNOS/eNOS expression in the vitro HHcy and hypoxia models. The beneficial effects of nicorandil on HCAECs could be inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and the nitric oxide synthase (NOS) inhibitor L-NAME. In vivo, nicorandil improved the left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS) in the post-HHcy + MI model, and the levels of CD31 and tomato lectin expression were higher in the nicorandil treatment group. The effectiveness of nicorandil was inhibited in the PI3K and L-NAME groups.

CONCLUSION

The results suggest that nicorandil improves Hcy-induced coronary microvascular dysfunction through the PI3K/Akt/eNOS signalling pathway.

Discrepant effects of copper (II) stress on different types of skeletal muscles in chicken: Elements and amino acids

Different distributions of 28 elements and 17 amino acids in pectoralis, wing biceps brachii and leg gastrocnemius of chicken upon CuSO₄ (300 mg/kg) exposure for 90 days were investigated. Accompanied by copper accumulation, pathological injuries were observed in those three kinds of skeletal muscles using histological and ultrastructural methods. Based on data obtained, we analyzed leg gastrocnemius displayed the most increases (P < 0.000) in all three kinds of elements detected, including macroelements (131%), essential microelements (129%) and toxic microelements (179%) than the other two skeletal muscles. Furthermore, decreased total amino acids (P = 0.006), a susceptibility of lipid peroxidation/oxidative stress and a disequilibrium of nutrition and taste were analyzed in the leg gastrocnemius, indicating an unsuitability for human consumption. Intriguingly, these anomalies were scarce in pectoralis and wing biceps brachii. Combined with multivariate analysis we may conclude that leg gastrocnemius are more vulnerable to copper stress than pectoralis and wing biceps brachii in chicken.