Putative role of ischemic postconditioning in a rat model of limb ischemia and reperfusion: involvement of hypoxia-inducible factor-1α expression

Effects of ischaemic post-conditioning on eccentric exercise-induced muscle damage

Exercise-induced muscle damage (EIMD) is a common phenomenon resulting from high-intensity exercise that impairs subsequent performance. Ischaemic post-conditioning (IPOC) is a simple intervention that has been shown to reduce muscle damage after prolonged ischaemia, a condition mechanistically similar to EIMD. The purpose of this study was to determine whether IPOC could alleviate muscle damage after eccentric exercise. Thirty-two young male participants were randomized into either a sham (n = 16) or an IPOC (n = 16) intervention group. Biceps brachii muscle damage was induced by eccentric exercise, with IPOC or sham intervention applied on the dominant arm following exercise (3 cycles of 30 s ischaemia). Visual analogue scale (VAS) pain, arm circumference, muscle thickness, echo-intensity, and microvascular function (using near-infrared spectroscopy) were measured bilaterally at baseline, 24, 48, and 72 hours after eccentric exercise. Biceps curl one repetition maximum (1RM) was also measured. 1RM was higher for the IPOC group at 48 and 72 hours (both p < 0.05). On the dominant arm, VAS pain was lower at 72 hours for the IPOC group (p = 0.039). Muscle thickness was lower at all post-exercise time points for the IPOC group (all p < 0.05). VAS pain, echo-intensity, and arm circumference were elevated on the non-dominant arm in the sham group at 72 hours (all p < 0.05). These parameters all returned to the baseline level for the IPOC group at 72 hours (all p > 0.05IPOC could attenuate the decrease in strength, and alleviate EIMD with both local and remote effects after high-intensity exercise.

Carbon Monoxide Alleviates Post-ischemia-reperfusion Skeletal Muscle Injury and Systemic Inflammation

Restoration of blood flow in skeletal muscle after a prolonged period of ischemia induces muscular ischemia-reperfusion injury, leading to local injury/dysfunction in muscles followed by systemic inflammatory responses. However, preventive/curative agents for skeletal muscle ischemia injury are unavailable in clinics to date. Increasing evidence has validated that carbon monoxide (CO) prevents the progression of ischemia-reperfusion injury in various organs owing to its versatile bioactivity. Previously, we developed a bioinspired CO donor, CO-bound red blood cells (CO-RBC), which mimics the dynamics of RBC-associated CO in the body. In the present study, we have tested the therapeutic potential of CO-RBC in muscular injury/dysfunction and secondary systemic inflammation induced by skeletal muscle ischemia-reperfusion. The results indicate that CO-RBC rather than RBC alone suppressed elevation of plasma creatine phosphokinase, a marker of muscular injury, in rats subjected to both hind limbs ischemia-reperfusion. In addition, the results of the treadmill walking test revealed a significantly decreased muscular motor function in RBC-treated rats subjected to both hind limbs ischemia-reperfusion than that in healthy rats, however, CO-RBC treatment facilitated sustained muscular motor functions after hind limbs ischemia-reperfusion. Furthermore, CO-RBC rather than RBC suppressed the production of tumour necrosis factor (TNF)-α and interleukin (IL)-6, which were upregulated by muscular ischemia-reperfusion. Interestingly, CO-RBC treatment induced higher levels of IL-10 compared to saline or RBC treatments. Based on these findings, we suggest that CO-RBC exhibits a suppressive effect against skeletal muscle injury/dysfunction and systemic inflammatory responses after skeletal muscle ischemia-reperfusion.

Low-intensity pulsed ultrasound mitigates cognitive impairment by inhibiting muscle atrophy in hindlimb unloaded mice

Microgravity leads to muscle loss, usually accompanied by cognitive impairment. Muscle reduction was associated with the decline of cognitive ability. Our previous studies showed that low-intensity pulsed ultrasound (LIPUS) promoted muscle hypertrophy and prevented muscle atrophy. This study aims to verify whether LIPUS can improve cognitive impairment by preventing muscle atrophy in hindlimb unloaded mice. In this study, mice were randomly divided into normal control (NC), hindlimb unloading (HU), hindlimb unloading + LIPUS (HU+LIPUS) groups. The mice in the HU+LIPUS group received a 30 mW/cm2 LIPUS irradiation on gastrocnemius for 20 min/d. After 21 days, LIPUS significantly prevented the decrease in muscle mass and strength caused by tail suspension. The HU+LIPUS mice showed an enhanced desire to explore unfamiliar environments and their spatial learning and memory abilities, enabling them to quickly identify differences between different objects, as well as their social discrimination abilities. MSTN is a negative regulator of muscle growth and also plays a role in regulating cognition. LIPUS significantly inhibited MSTN expression in skeletal muscle and serum and its receptor ActRIIB expression in brain, upregulated AKT and BDNF expression in brain. Taken together, LIPUS may improve the cognitive dysfunction in hindlimb unloaded rats by inhibiting muscle atrophy through MSTN/AKT/BDNF pathway.

Obstructive sleep apnea and liver injury in severely obese patients with nonalcoholic fatty liver disease

OBJECTIVES

Obstructive sleep apnea (OSA) and nonalcoholic fatty liver disease (NAFLD) are common in subjects with severe obesity. It has been suggested that insulin resistance and systemic inflammation may play a role in the development of nonalcoholic steatohepatitis (NASH), but the mechanisms remain controversial. The aim of this study was to explore the influence of OSA on liver injury and its potential mechanisms in severely obese patients with NAFLD.

METHODS

Severely obese patients requiring bariatric surgery were consecutively recruited between November 2017 and June 2018. Demographic, biochemical, liver ultrasound, and ambulatory polygraph data were collected.

RESULTS

One hundred fifty-three subjects with liver ultrasound-verified NAFLD were classified into three groups according to the apnea-hypopnea index (AHI). The level of serum alanine aminotransferase (ALT) and gamma-glutamyl transpeptidase (GGT) tended to increase with more severe OSA (P = 0.024 and P = 0.004, respectively). In the unadjusted analysis, both ALT and GGT were positively correlated with AHI, oxygen desaturation index, percentage of total sleep time spent with oxyhemoglobin saturation below 90%, male sex, homeostasis model assessment of insulin resistance (HOMA-IR), and total cholesterol, while liver enzymes were negatively related to lowest oxygen saturation. In multiple regression analysis, AHI (odds ratio (OR) = 1.052, P = 0.044) and HOMA-IR (OR = 1.135, P = 0.001) were independent risk factors for an elevated ALT level. High-sensitivity C-reactive protein (hs-CRP) was positively associated with BMI and GGT (r = 0.349 and r = 0.164 (P < 0.05), respectively), and no correlation was found between hs-CRP and AHI or other parameters of hypoxia. hs-CRP and GGT remained significantly correlated after adjusting for confounding parameters (OR = 2.509, P = 0.013).

CONCLUSIONS

OSA may play a role in liver injury among severely obese individuals with NAFLD. Insulin resistance and systemic inflammation were possible contributing factors in this process.

MicroRNA regulatory pattern in spinal cord ischemia-reperfusion injury

After spinal cord injury, dysregulated miRNAs appear and can participate in inflammatory responses, as well as the inhibition of apoptosis and axon regeneration through multiple pathways. However, the functions of miRNAs in spinal cord ischemia-reperfusion injury progression remain unclear. miRCURY LNATM Arrays were used to analyze miRNA expression profiles of rats after 90 minutes of ischemia followed by reperfusion for 24 and 48 hours. Furthermore, subsequent construction of aberrantly expressed miRNA regulatory patterns involved cell survival, proliferation, and apoptosis. Remarkably, the mitogen-activated protein kinase (MAPK) signaling pathway was the most significantly enriched pathway among 24- and 48-hour groups. Bioinformatics analysis and quantitative reverse transcription polymerase chain reaction confirmed the persistent overexpression of miR-22-3p in both groups. These results suggest that the aberrant miRNA regulatory network is possibly regulated MAPK signaling and continuously affects the physiological and biochemical status of cells, thus participating in the regulation of spinal cord ischemia-reperfusion injury. As such, miR-22-3p may play sustained regulatory roles in spinal cord ischemia-reperfusion injury. All experimental procedures were approved by the Animal Ethics Committee of Jilin University, China [approval No. 2020 (Research) 01].

Batroxobin accelerated tissue repair via neutrophil extracellular trap regulation and defibrinogenation in a murine ischemic hindlimb model

Batroxobin, isolated from Bothrops moojeni, is a defibrinogenating agent used as a thrombin-like serine protease against fibrinogen for improving microcirculation. Here, we investigated whether, and if so, how batroxobin restores ischemic tissue injury in terms of anti-inflammatory effects. In an in vitro flow cytometry assay for human neutrophil extracellular traps (NETs), batroxobin (DF-521; Defibrase) inhibited human NETs induced by tumor necrosis factor-α (TNF-α) in the presence of human fibrinogen. Next, the effect of batroxobin was investigated by immunohistochemistry of the anterior tibial muscle (ATM) in an ischemic hindlimb model using C57BL/6J mice intraperitoneally injected with DF-521 versus the saline control. NETs and fibrinogen deposition in the ischemic ATM decreased in DF-521-treated mice on day 2 after ischemia. Meanwhile, reverse transcription-quantitative PCR assay of the ischemic ATM unveiled continuous downregulation in the expression of the genes; Tnf-α and nitric oxide synthase2 (Nos2) with hypoxia-inducible factor-1α (Hif-1α) and vascular endothelial growth factor-a (Vegf-a) from day 3 to day 7, but the upregulation of arginase-1 (Arg-1) and placental growth factor (Plgf) with myogenin (Myog) on day 7. Daily intraperitoneal DF-521 injection for the initial 7 days into mice with ischemic hindlimbs promoted angiogenesis and arteriogenesis on day 14. Moreover, DF-521 injection accelerated myofiber maturation after day 14. Laser doppler imaging analysis revealed that blood perfusion in DF-521-injected mice significantly improved on day 14 versus the saline control. Thus, DF-521 improves microcirculation by protecting NETs with tissue defibrinogenation, thereby protecting against severe ischemic tissue injury and accelerating vascular and skeletal muscular regeneration. To our knowledge, batroxobin might be the first clinically applicable NET inhibitor against ischemic diseases.

Garlic antagonizes skeletal muscle ischemia reperfusion injury through regulating inflammation, apoptosis and desmin expression in adult male rats

BACKGROUND

Skeletal muscle injuries with subsequent bleeding is common cause of death on both sports and battle grounds. Application and removal of tourniquet is fast intervention to control hemorrhage resulting ischemia reperfusion (IR) injury. The effect of IR in skeletal muscle is far more severe compared to other body tissues because of the devastating systemic complication. Garlic has beneficial effects in IR of various organs. However, using garlic in IR of skeletal muscle is deficient Goals: To investigate the possible protective effect of garlic in rat model of hind limb IR and its possible mechanisms of action.

METHODS

Fifty adult male rats divided into five groups; C: control, IR: ischemia/reperfusion group subjected to 2 hours ischemia followed by 2 hours reperfusion (2/2 hr IR) and three garlic treated groups; G1+IR: 24 hr before I/R, G2+IR: 30 min before IR and G3+IR: immediately before reperfusion. We measured wet to dry weight ratio (W/D) of gastrocnemius muscle, serum creatine kinase (CK), Interleukin 1β (IL-1β), Interleukin-10 (IL-10), gastrocnemius caspase-3 and desmin expression and histopathological damage score.

RESULTS

Garlic treatment caused significant decrease in W/D, serum CK, IL-1β, caspase-3 expression and significant increase in IL-10 as well as desmin expression when compared to IR group. Garlic ameliorated IR-induced histopathological damage and significantly reduced the apoptosis score. Better results obtained with earlier administration before IR.

CONCLUSION

Garlic protected against IR-induced skeletal muscle damage through reducing inflammation, apoptosis score and elevating desmin expression. We recommend the earlier use of garlic as prophylactic natural medicine in skeletal muscle IR.

High-intensity interval training in hypoxia does not affect muscle HIF responses to acute hypoxia in humans

PURPOSE

The myocellular response to hypoxia is primarily regulated by hypoxia-inducible factors (HIFs). HIFs thus conceivably are implicated in muscular adaptation to altitude training. Therefore, we investigated the effect of hypoxic versus normoxic training during a period of prolonged hypoxia ('living high') on muscle HIF activation during acute ischaemia.

METHODS

Ten young male volunteers lived in normobaric hypoxia for 5 weeks (5 days per week, ~ 15.5 h per day, F_iO₂: 16.4-14.0%). One leg was trained in hypoxia (TR_HYP, 12.3% F_iO₂) whilst the other leg was trained in normoxia (TR_NOR, 20.9% F_iO₂). Training sessions (3 per week) consisted of intermittent unilateral knee extensions at 20-25% of the 1-repetition maximum. Before and after the intervention, a 10-min arterial occlusion and reperfusion of the leg was performed. Muscle oxygenation status was continuously measured by near-infrared spectroscopy. Biopsies were taken from m. vastus lateralis before and at the end of the occlusion.

RESULTS

Irrespective of training, occlusion elevated the fraction of HIF-1α expressing myonuclei from ~ 54 to ~ 64% (P < 0.05). However, neither muscle HIF-1α or HIF-2α protein abundance, nor the expression of HIF-1α or downstream targets selected increased in any experimental condition. Training in both TR_NOR and TR_HYP raised muscular oxygen extraction rate upon occlusion by ~ 30%, whilst muscle hyperperfusion immediately following the occlusion increased by ~ 25% in either group (P < 0.05).

CONCLUSION

Ten minutes of arterial occlusion increased HIF-1α-expressing myonuclei. However, neither normoxic nor hypoxic training during 'living high' altered muscle HIF translocation, stabilisation, or transcription in response to acute hypoxia induced by arterial occlusion.

Isometric Exercise Training for Managing Vascular Risk Factors in Mild Cognitive Impairment and Alzheimer's Disease

Alzheimer’s disease (AD) is the most common form of dementia diagnosed amongst the elderly. Mild cognitive impairment (MCI) is a condition often indicative of the earliest symptomatology of AD with 10%–15% of MCI patients reportedly progressing to a diagnosis of AD. Individuals with a history of vascular risk factors (VRF’s) are considered high risk candidates for developing cognitive impairment in later life. Evidence suggests that vascular injury resulting from untreated VRF’s promotes progression from MCI to AD and exacerbates the severity of dementia in AD, and neuroimaging studies have found that the neurodegenerative processes associated with AD are heavily driven by VRF’s that promote cerebral hypoperfusion. Subsequently, common links between vascular disorders such as hypertension and neurodegenerative disorders such as AD include compromised vasculature, cerebral hypoperfusion and chronic low grade inflammation (a hallmark of both hypertension and AD). Exercise has been demonstrated to be an effective intervention for blood pressure management, chronic low grade inflammation and improvements in cognition. Data from recent analyses suggests that isometric exercise training (IET) may improve vascular integrity and elicit blood pressure reductions in hypertensives greater than those seen with dynamic aerobic and resistance exercise. IET may also play an effective role in the management of VRF’s at the MCI stage of AD and may prove to be a significant strategy in the prevention, attenuation or delay of progression to AD. A plausible hypothesis is that the reactive hyperemia stimulated by IET initiates a cascade of vascular, neurotrophic and neuro-endocrine events that lead to improvements in cognitive function.

Improving the therapeutic efficacy of mesenchymal stromal cells to restore perfusion in critical limb ischemia through pulsed focused ultrasound

Mesenchymal stem cells (MSC) are promising therapeutics for critical limb ischemia (CLI). Mechanotransduction from pulsed focused ultrasound (pFUS) upregulates local chemoattractants to enhance homing of intravenously (IV)-infused MSC and improve outcomes. This study investigated whether pFUS exposures to skeletal muscle would improve local homing of iv-infused MSCs and their therapeutic efficacy compared to iv-infused MSCs alone. CLI was induced by external iliac arterial cauterization in 10–12-month-old mice. pFUS/MSC treatments were delayed 14 days, when surgical inflammation subsided. Mice were treated with iv-saline, pFUS alone, IV-MSC, or pFUS and IV-MSC. Proteomic analyses revealed pFUS upregulated local chemoattractants and increased MSC tropism to CLI muscle. By 7 weeks post-treatment, pFUS + MSC significantly increased perfusion and CD31 expression, while reducing fibrosis compared to saline. pFUS or MSC alone reduced fibrosis, but did not increase perfusion or CD31. Furthermore, MSCs homing to pFUS-treated CLI muscle expressed more vascular endothelial growth factor (VEGF) and interleukin-10 (IL-10) than MSCs homing to non-pFUS-treated muscle. pFUS + MSC improved perfusion and vascular density in this clinically-relevant CLI model. The molecular effects of pFUS increased both MSC homing and MSC production of VEGF and IL-10, suggesting microenvironmental changes from pFUS also increased potency of MSCs in situ to further enhance their efficacy.

Postischemic conditioning does not reduce muscle injury after tourniquet-induced ischemia-reperfusion injury in rats

BACKGROUND

The widespread application of tourniquets has reduced battlefield mortality related to extremity exsanguinations. Tourniquet-induced ischemia-reperfusion injury (I/R) can contribute to muscle loss. Postischemic conditioning (PostC) confers protection against I/R in cardiac muscle and skeletal muscle flaps. The objective of this study was to determine the effect of PostC on extremity muscle viability in an established rat hindlimb tourniquet model.

METHODS

Rats were randomly assigned to PostC-1, PostC-2, or no conditioning ischemic groups (n = 10 per group). Postischemic conditioning, performed immediately after tourniquet release, consisted of four 15-second cycles (PostC-1) or eight 15-second cycles (PostC-2) of alternating occlusion and perfusion of hindlimbs. Twenty-four hours later, muscles were excised. The primary end points were muscle edema and viability; secondary end points were histologic and markers of oxidative stress.

RESULTS

Ischemia-reperfusion injury decreased viability in all tourniquet limbs, but viability was not improved in either PostC group. Likewise, I/R resulted in substantial muscle edema that was not reduced by PostC. The predominant histologic feature was necrosis, but no significant differences were found among groups. Markers of oxidative stress were increased similarly among groups after I/R, although myeloperoxidase activity was significantly increased only in the no conditioning ischemic group. A protective effect from PostC was not observed in our model suggesting that PostC was not effective in reducing I/R skeletal muscle injury or any benefits of PostC were not sustained for 24 hours when tissues were assessed.

CONCLUSION

These negative findings are pertinent as the military investigates different strategies to extend the safe time for tourniquet application.

Circulating Endocannabinoids and Insulin Resistance in Patients with Obstructive Sleep Apnea

Objectives. The purpose of this study is to investigate the relationship between plasma endocannabinoids and insulin resistance (IR) in patients with obstructive sleep apnea (OSA). Methods. A population of 64 with OSA and 24 control subjects was recruited. Body mass index (BMI), waist circumference, lipids, blood glucose and insulin, homeostasis model of assessment for insulin resistance index (HOMA-IR), anandamide (AEA), 1/2-arachidonoylglycerol (1/2-AG), and apnea-hypopnea index (AHI) were analyzed. Results. Fasting blood insulin (22.9 ± 7.8 mIU/L versus 18.5 ± 7.2 mIU/L, P < 0.05), HOMA-IR (2.9 ± 1.0 versus 2.4 ± 0.9, P < 0.01), AEA (3.2 ± 0.7 nmol/L versus 2.5 ± 0.6 nmol/L, P < 0.01), and 1/2-AG (40.8 ± 5.7 nmol/L versus 34.3 ± 7.7 nmol/L, P < 0.01) were higher in OSA group than those in control group. In OSA group, AEA, 1/2-AG, and HOMA-IR increase with the OSA severity. The correlation analysis showed significant positive correlation between HOMA-IR and AHI (r = 0.44, P < 0.01), AEA and AHI (r = 0.52, P < 0.01), AEA and HOMA-IR (r = 0.62, P < 0.01), and 1/2-AG and HOMA-IR (r = 0.33, P < 0.01). Further analysis showed that only AEA was significantly correlated with AHI and HOMA-IR after adjusting for confounding factors. Conclusions. The present study indicated that plasma endocannabinoids levels, especially AEA, were associated with IR and AHI in patients with OSA.

Effect of Intermittent Hypoxia and Rimonabant on Glucose Metabolism in Rats: Involvement of Expression of GLUT4 in Skeletal Muscle

Background

Obstructive sleep apnea (OSA) and its main feature, chronic intermittent hypoxia (IH) during sleep, is closely associated with insulin resistance (IR) and diabetes. Rimonabant can regulate glucose metabolism and improve IR. The present study aimed to assess the effect of IH and rimonabant on glucose metabolism and insulin sensitivity, and to explore the possible mechanisms.

Material/Methods

Thirty-two rats were randomly assigned into 4 groups: Control group, subjected to intermittent air only; IH group, subjected to IH only; IH+NS group, subjected to IH and treated with normal saline; and IH+Rim group, subjected to IH and treated with 10 mg/kg/day of rimonabant. All rats were killed after 28 days of exposure. Then, the blood and skeletal muscle were collected. We measured fasting blood glucose levels, fasting blood insulin levels, and the expression of glucose transporter 4 (GLUT4) in both mRNA and protein levels in skeletal muscle.

Results

IH can slow weight gain, increase serum insulin level, and reduce insulin sensitivity in rats. The expressions of GLUT4 mRNA, total GLUT4, and plasma membrane protein of GLUT4 (PM GLUT4) in skeletal muscle were decreased. Rimonabant treatment was demonstrated to improve weight gain and insulin sensitivity of the rats induced by IH. Rimonabant significantly upregulated the expression of GLUT4 mRNA, PM GLUT4, and total GLUT4 in skeletal muscle.

Conclusions

The present study demonstrates that IH can cause IR and reduced expression of GLUT4 in both mRNA and protein levels in skeletal muscle of rats. Rimonabant treatment can improve IH – induced IR, and the upregulation of GLUT4 expression may be involved in this process.

Postconditioning in major vascular surgery: prevention of renal failure

Background

Postconditioning is a novel reperfusion technique to reduce ischemia-reperfusion injuries. The aim of the study was to investigate this method in an animal model of lower limb revascularization for purpose of preventing postoperative renal failure.

Methods

Bilateral lower limb ischemia was induced in male Wistar rats for 3 hours by infrarenal aorta clamping under narcosis. Revascularization was allowed by declamping the aorta. Postconditioning (additional 10 sec reocclusion, 10 sec reperfusion in 6 cycles) was induced at the onset of revascularization. Myocyte injury and renal function changes were assessed 4, 24 and 72 hours postoperatively. Hemodynamic monitoring was performed by invasive arterial blood pressure registering and a kidney surface laser Doppler flowmeter.

Results

Muscle viability studies showed no significant improvement with the use of postconditioning in terms of ischemic rhabdomyolysis (4 h: ischemia-reperfusion (IR) group: 42.93 ± 19.20% vs. postconditioned (PostC) group: 43.27 ± 27.13%). At the same time, renal functional laboratory tests and kidney myoglobin immunohistochemistry demonstrated significantly less expressed kidney injury in postconditioned animals (renal failure index: 4 h: IR: 2.37 ± 1.43 mM vs. PostC: 0.92 ± 0.32 mM; 24 h: IR: 1.53 ± 0.45 mM vs. PostC: 0.77 ± 0.34 mM; 72 h: IR: 1.51 ± 0.36 mM vs. PostC: 0.43 ± 0.28 mM), while systemic hemodynamics and kidney microcirculation significantly improved (calculated reperfusion area: IR: 82.31 ± 12.23% vs. PostC: 99.01 ± 2.76%), and arterial blood gas analysis showed a lesser extent systemic acidic load after revascularization (a defined relative base excess parameter: 1^st s: IR: 2.25 ± 1.14 vs. PostC: 1.80 ± 0.66; 2^nd s: IR: 2.14 ± 1.44 vs. PostC: 2.44 ± 1.14, 3^rd s: IR: 3.99 ± 3.09 vs. PostC: 2.07 ± 0.82; 4^th s: IR: 3.28 ± 0.32 vs. PostC: 2.05 ± 0.56).

Conclusions

The results suggest a protective role for postconditioning in major vascular surgeries against renal complications through a possible alternative release of nephrotoxic agents and exerting a positive effect on hemodynamic stability.