Ischemia/reperfusion-induced changes in intracellular free Ca2+ levels in rat skeletal muscle fibers--an in vivo study

Methods of ex vivo analysis of tissue status in vascularized composite allografts

Vascularized composite allotransplantation can improve quality of life and restore functionality. However, the complex tissue composition of vascularized composite allografts (VCAs) presents unique clinical challenges that increase the likelihood of transplant rejection. Under prolonged static cold storage, highly damage-susceptible tissues such as muscle and nerve undergo irreversible degradation that may render allografts non-functional. Skin-containing VCA elicits an immunogenic response that increases the risk of recipient allograft rejection. The development of quantitative metrics to evaluate VCAs prior to and following transplantation are key to mitigating allograft rejection. Correspondingly, a broad range of bioanalytical methods have emerged to assess the progression of VCA rejection and characterize transplantation outcomes. To consolidate the current range of relevant technologies and expand on potential for development, methods to evaluate ex vivo VCA status are herein reviewed and comparatively assessed. The use of implantable physiological status monitoring biochips, non-invasive bioimpedance monitoring to assess edema, and deep learning algorithms to fuse disparate inputs to stratify VCAs are identified.

Ischemia-Reperfusion Injury in Peripheral Artery Disease and Traditional Chinese Medicine Treatment

Peripheral artery disease (PAD) is a serious public health issue, characterized by circulation disorder of the lower extreme that reduces the physical activity of the lower extremity muscle. The artery narrowed by atherosclerotic lesions initiates limb ischemia. In the progression of treatment, reperfusion injury is still inevitable. Ischemia-reperfusion injury induced by PAD is responsible for hypoxia and nutrient deficiency. PAD triggers hindlimb ischemia and reperfusion (I/R) cycles through various mechanisms, mainly including mitochondrial dysfunction and inflammation. Alternatively, mitochondrial dysfunction plays a central role. The I/R injury may cause cells' injury and even death. However, the mechanism of I/R injury and the way of cell damage or death are still unclear. We review the pathophysiology of I/R injury, which is majorly about mitochondrial dysfunction. Then, we focus on the cell damage and death during I/R injury. Further comprehension of the progress of I/R will help identify biomarkers for diagnosis and therapeutic targets to PAD. In addition, traditional Chinese medicine has played an important role in the treatment of I/R injury, and we will make a brief introduction.

Preservation solutions for attenuation of ischemia-reperfusion injury in vascularized composite allotransplantation

Vascularized composite allotransplantation represents the final level of the reconstructive ladder, offering treatment options for severe tissue loss and functional deficiencies. Vascularized composite allotransplantation is particularly susceptible to ischemia–reperfusion injury and requires preservation techniques when subjected to extended storage times prior to transplantation. While static cold storage functions to reduce ischemic damage and is widely employed in clinical settings, there exists no consensus on the ideal preservation solution for vascularized composite allotransplantation. This review aims to highlight current clinical and experimental advances in preservation solution development and their critical role in attenuating ischemia–reperfusion injury in the context of vascularized composite allotransplantation.

Effects of muscle relaxants on ischaemia damage in skeletal muscle

Muscle ischaemia is frequently induced intraoperatively by i.e. a surgical tourniquet or during the re-grafting phase of a free muscle transplant. The resulting muscle cell damage may impact on postoperative recovery. Neuromuscular paralysis may mitigate the effects of ischaemia. After ethics approval, 25 male Sprague-Dawley rats were anaesthetized and randomly assigned to 1 of 4 groups: Sham operation, treatment with normal saline, treatment with rocuronium (muscle relaxant) 0.6 or 1 mg kg⁻¹, respectively. In the non-sham groups, ischaemia of one hind leg was achieved by ligation of the femoral vessels. Muscle biopsies were taken at 30 and 90 min, respectively. Cell damage was assessed in the biopsies via the expression of dystrophin, free calcium, as well as the assessment of cell viability. Pre-ischaemia muscle relaxation led to a reduction in ischaemia-induced muscle cell damage when measured by the expression of dystrophin, cell viability and the expression of free calcium even after 90 min of ischaemia (i.e. ratio control/ischaemic site for dystrophin expression after saline 0.58 ± 0.12 vs. after 1 mg/kg rocuronium 1.08 ± 0.29; P < 0.05). Muscle relaxation decreased the degree of ischaemia-induced muscle cell damage. The results may have significant clinical implications.

Chronology of mitochondrial and cellular events during skeletal muscle ischemia-reperfusion

Peripheral artery disease (PAD) is a common circulatory disorder of the lower limb arteries that reduces functional capacity and quality of life of patients. Despite relatively effective available treatments, PAD is a serious public health issue associated with significant morbidity and mortality. Ischemia-reperfusion (I/R) cycles during PAD are responsible for insufficient oxygen supply, mitochondriopathy, free radical production, and inflammation and lead to events that contribute to myocyte death and remote organ failure. However, the chronology of mitochondrial and cellular events during the ischemic period and at the moment of reperfusion in skeletal muscle fibers has been poorly reviewed. Thus, after a review of the basal myocyte state and normal mitochondrial biology, we discuss the physiopathology of ischemia and reperfusion at the mitochondrial and cellular levels. First we describe the chronology of the deleterious biochemical and mitochondrial mechanisms activated by I/R. Then we discuss skeletal muscle I/R injury in the muscle environment, mitochondrial dynamics, and inflammation. A better understanding of the chronology of the events underlying I/R will allow us to identify key factors in the development of this pathology and point to suitable new therapies. Emerging data on mitochondrial dynamics should help identify new molecular and therapeutic targets and develop protective strategies against PAD.

Intracellular calcium accumulation following eccentric contractions in rat skeletal muscle in vivo: role of stretch-activated channels

Although the accumulation of intracellular calcium ions ([Ca2+]i) is associated with muscle damage, little is known regarding the temporal profile of muscle [Ca2+]iunder in vivo conditions, and, specifically, the effects of different contraction types [e.g., isometric (ISO); eccentric (ECC)] on [Ca2+]iremain to be determined. The following hypotheses were tested. 1) For 90 min at rest, an in vivo vs. in vitro preparation would better maintain initial [Ca2+]i. 2) Compared with ISO, ECC contractions (50 contractions, 10 sets, 5-min interval) would lead to a greater increase of [Ca2+]i. 3) Elevated [Ca2+]iduring ECC would be reduced or prevented by the stretch-activated ion channel blockers streptomycin and gadolinium (Gd3+). Spinotrapezius muscles of Wistar rats were exteriorized (in vivo) or excised (in vitro). [Ca2+]iwas evaluated by loading the muscle with fura 2-AM using fluorescence imaging. [Ca2+]irose progressively beyond 40 min at rest under in vitro but not in vivo conditions during the 90-min protocol. In vivo [Ca2+]iincreased more rapidly during ECC (first set) than ISO (fifth set) ( P < 0.05 vs. precontraction values). The peak level of [Ca2+]iwas increased by 21.5% (ISO) and 42.8% (ECC) after 10 sets (both P < 0.01). Streptomycin and Gd3+abolished the majority of [Ca2+]iincrease during ECC (69 and 86% reduction, respectively; P < 0.01 from peak [Ca2+]iof ECC). In conclusion, in vivo quantitative analyses demonstrated that ECC contractions elevate [Ca2+]isignificantly more than ISO contractions and that stretch-activated channels may play a permissive role in this response.

Impaired calcium release during fatigue

Impaired calcium release from the sarcoplasmic reticulum (SR) has been identified as a contributor to fatigue in isolated skeletal muscle fibers. The functional importance of this phenomenon can be quantified by the use of agents, such as caffeine, which can increase SR Ca2+release during fatigue. A number of possible mechanisms for impaired calcium release have been proposed. These include reduction in the amplitude of the action potential, potentially caused by extracellular K+accumulation, which may reduce voltage sensor activation but is counteracted by a number of mechanisms in intact animals. Reduced effectiveness of SR Ca2+channel opening is caused by the fall in intracellular ATP and the rise in Mg2+concentrations that occur during fatigue. Reduced Ca2+available for release within the SR can occur if inorganic phosphate enters the SR and precipitates with Ca2+. Further progress requires the development of methods that can identify impaired SR Ca2+release in intact, blood-perfused muscles and that can distinguish between the various mechanisms proposed.

Sarcolemmal damage in dystrophin deficiency is modulated by synergistic interactions between mechanical and oxidative/nitrosative stresses

Dystrophin deficiency is the cause of Duchenne muscular dystrophy, but the precise physiological basis for muscle necrosis remains unclear. To determine whether dystrophin-deficient muscles are abnormally susceptible to oxidative and nitric oxide (NO)-driven tissue stress, a hindlimb ischemia/reperfusion (I/R) model was used. Dystrophic mdx mice exhibited abnormally high levels of lipid peroxidation and protein nitration, which were preceded by exaggerated NO production during ischemia. Visualization of NO with the fluorescent probe 4,5-diaminofluorescein diacetate suggested that excess NO production during ischemia occurred within a subset of mdx fibers. In mdx muscles only, prior exposure to I/R dramatically increased the level of sarcolemmal damage resulting from stretch-mediated mechanical stress, indicating greatly exacerbated hyperfragility of the dystrophic fiber membrane. Treatment with NO synthase inhibitors (l-N(G)-nitroarginine methyl ester hydrochloride or 7-nitroindazol) effectively blocked the synergistic interaction between I/R and mechanical stress-mediated sarcolemmal damage under these conditions. Taken together, our findings provide direct ex-perimental evidence that several prevailing hy-potheses regarding the cause of muscle fiber damage in dystrophin-deficient muscle can be integrated into a common pathophysiological framework involving interactions between oxidative stress, ab-normal NO regulation, and hyperfragility of the sarcolemma.

The effects of carbenoxolone, a semisynthetic derivative of glycyrrhizinic acid, on peripheral and central ischemia-reperfusion injuries in the skeletal muscle and hippocampus of rats

As carbenoxolone, a semisynthetic derivative of glycyrrhizinic acid, has a free radical scavenging property, thus the effects of carbenoxolone during ischemia-reperfusion was evaluated on an animal model of ischemia-reperfusion injury in the rat hind limb and hippocampus. Peripheral and central ischemia were induced by free-flap surgery in skeletal muscle and four-vessel-occulation (4VO) of rat, respectively. Carbenoxolone (50-200 mg/kg) and normal saline (10 ml/ kg) were administered intraperitoneally. In peripherlal ischemia, during preischemia, ischemia and reperfusion conditions the electromyographic (EMG) potentials in the muscles were recorded. The malondialdehyde (MDA) was measured by the thiobarbituric acid (TBA) test after reperfusion in peripheral and central ischemia. In peripheral ischemia, the average peak-to-peak amplitude during ischemic-reperfusion was found to be significantly larger in carbenoxolone group (100-200mg/kg) in comparison to control group. The MDA levels were recovered significantly upon carbenoxolone (100-200 mg/kg) therapy in the skeletal muscle and hippocampus of ischemic rats. These results suggest that carbenoxolone can salvage the skeletal muscle and hippocampus from acute ischemia-reperfusion injury.