Background: The post-COVID-19 condition, defined as COVID-19-related signs and symptoms lasting at least 2 months and persisting more than 3 months after infection, appears now as a public health issue in terms of frequency and quality of life alterations. Nevertheless, few data are available concerning long term evolution of malnutrition and sarcopenia, which deserve further attention. Method: Sarcopenia was investigated prospectively, together with weight evolution, at admission and at 3 and 6 months after hospital discharge in 139 COVID-19 patients, using the European Working Group on Sarcopenia in Older People (EWGSOP2) criteria, associating both decreased muscle strength and muscle mass, assessed, respectively, with hand dynamometer and dual-energy X-ray absorptiometry. Results: Of the 139 patients, 22 presented with sarcopenia at 3 months; intensive care units (ICU) length of stay was the sole factor associated with sarcopenia after multivariate analysis. Although the entire group did not demonstrate significant weight change, weight decreased significantly in the sarcopenia group (Five and eight patients, showing, respectively, >5 or >10% weight decrease). Interestingly, at 6 months, 16 of the 22 patients recovered from sarcopenia and their weight returned toward baseline values. Conclusions: Sarcopenia and malnutrition are frequently observed in patients hospitalized for COVID-19, even 3 months after infection occurrence, but can largely be reversed at 6 months after discharge. Enhanced patient care is needed in sarcopenic patients, particularly during long stays in an ICU.

Skeletal muscle ischemia reperfusion is very frequent in humans and results not only in muscle destruction but also in multi-organ failure and death via systemic effects related to inflammation and oxidative stress. In addition to overabundance of pro-inflammatory stimuli, excessive and uncontrolled inflammation can also result from defects in resolution signaling. Importantly, the resolution of inflammation is an active process also based on specific lipid mediators including lipoxins, resolvins and maresins that orchestrate the potential return to tissue homeostasis. Thus, lipid mediators have received growing attention since they dampen deleterious effects related to ischemia–reperfusion. For instance, the treatment of skeletal muscles with resolvins prior to ischemia decreases polymorphonuclear leukocyte (PMN) infiltration. Additionally, remote alterations in lungs or kidneys are reduced when enhancing lipid mediators’ functions. Accordingly, lipoxins prevented oxidative-stress-mediated tissue injuries, macrophage polarization was modified and in mice lacking DRV2 receptors, ischemia/reperfusion resulted in excessive leukocyte accumulation. In this review, we first aimed to describe the inflammatory response during ischemia and reperfusion in skeletal muscle and then discuss recent discoveries in resolution pathways. We focused on the role of specialized pro-resolving mediators (SPMs) derived from polyunsaturated fatty acids (PUFAs) and their potential therapeutic applications.

Peripheral blood mononuclear cells’ (PBMCs) mitochondrial respiration is impaired and likely involved in myocardial injury and heart failure pathophysiology, but its response to acute and severe hypoxia, often associated with such diseases, is largely unknown in humans. We therefore determined the effects of acute hypoxia on PBMC mitochondrial respiration and ROS production in healthy volunteers exposed to controlled oxygen reduction, achieving an inspired oxygen fraction of 10.5%. We also investigated potential relationships with gene expression of key biomarkers of hypoxia, succinate and inflammation, as hypoxia and inflammation share common mechanisms involved in cardiovascular disease. Unlike global mitochondrial respiration, hypoxemia with a spO₂ ≤ 80% significantly reduced PBMC complex II respiration (from 6.5 ± 1.2 to 3.1 ± 0.5 pmol/s/10⁶ cell, p = 0.04). Complex II activity correlated positively with spO₂ (r = 0.63, p = 0.02) and inversely correlated with the succinate receptor SUCNR1 (r = −0.68), the alpha-subunit of the hypoxia-inducible factor (HIF-1α, r = −0.61), the chemokine ligand-9 (r = −0.68) and interferon-stimulated gene 15 (r = −0.75). In conclusion, severe hypoxia specifically impairs complex II respiration in association with succinate, inflammation and HIF-1α pathway interactions in human PBMCs. These results support further studies investigating whether modulation of complex II activity might modify the inflammatory and metabolic alterations observed in heart failure.

COVID-19 is a public health issue with a significant mortality rate and potential long-lasting disabling symptoms responsible for the long-COVID syndrome. Mitochondrial dysfunction is a key mechanism but whether peripheral blood mononuclear cell (PBMC) mitochondrial respiration changes might be associated with mortality and/or occurrence and severity of long-COVID syndrome remains to be investigated. We determined mitochondrial respiratory chain oxygen consumption in twenty COVID-19 patients hospitalized in the intensive care unit and analyzed their remaining symptoms at the third year after hospital release. PBMC mitochondrial respiration was decreased in COVID-19 patients compared to the control group (14.13 ± 2.35 vs. 6.21 ± 0.88 pmol/s/10⁶ cell, p = 0.0006 for the OXPHOS state by CII). Considering COVID severity, such a decrease was greater in long-COVID patients and in patients who deceased (4.91 ± 0.75, p = 0.008 and 4.94 ± 1.11 pmol/s/10⁶ cell, p = 0.04, respectively). PBMC markers of inflammation also increased with the severity of COVID (1.0 ± 0.08 vs. 14.45 ± 2.07, p = 0.02 for ISG15 in patients who died) and ISG15 negatively correlated with PBMC mitochondrial respiration (r = −0.67, p = 0.02 for CII). In conclusion, this study shows that the greater the impairment in PBMC mitochondrial respiration in patients hospitalized in the intensive care unit for COVID-19, the greater the mortality rate and the more severe the long-COVID symptoms—three years after hospital discharge. Further, PBMC markers of inflammation also increased with the severity of COVID and ISG15 negatively correlated with PBMC mitochondrial respiration. These results support that PBMC mitochondrial respiration might be a biomarker of COVID severity and further studies investigating whether modulation of PBMC mitochondrial respiration might improve COVID-19 patients’ prognosis.

Peripheral arterial disease (PAD) strikes more than 200 million people worldwide and has a severe prognosis by potentially leading to limb amputation and/or death, particularly in older patients. Skeletal muscle mitochondrial dysfunctions and oxidative stress play major roles in this disease in relation with ischemia-reperfusion (IR) cycles. Mitochondrial dynamics through impairment of fission–fusion balance may contribute to skeletal muscle pathophysiology, but no data were reported in the setting of lower-limb IR despite the need for new therapeutic options. We, therefore, investigated the potential protective effect of mitochondrial division inhibitor-1 (mDivi-1; 50 mg/kg) in young (23 weeks) and old (83 weeks) mice submitted to two-hour ischemia followed by two-hour reperfusion on systemic lactate, muscle mitochondrial respiration and calcium retention capacity, and on transcripts specific for oxidative stress and mitochondrial dynamics. At the systemic levels, an IR-related increase in circulating lactate was still major despite mDivi-1 use (+305.9% p < 0.0001, and +269.4% p < 0.0001 in young and old mice, respectively). Further, IR-induced skeletal muscle mitochondrial dysfunctions (more severely impaired mitochondrial respiration in old mice (OXPHOS CI state, –68.2% p < 0.0001 and −84.9% p < 0.0001 in 23- and 83-week mice) and reduced calcium retention capacity (–46.1% p < 0.001 and −48.2% p = 0.09, respectively) were not corrected by mDivi-1 preconditioning, whatever the age. Further, mDivi-1 treatment did not oppose superoxide anion production (+71.4% p < 0.0001 and +37.5% p < 0.05, respectively). At the transcript level, markers of antioxidant enzymes (SOD 1, SOD 2, catalase, and GPx) and fission markers (Drp1, Fis) remained unchanged or tended to be decreased in the ischemic leg. Fusion markers such as mitofusin 1 or 2 decreased significantly after IR in both groups. In conclusion, aging enhanced the deleterious effects or IR on muscle mitochondrial respiration, and in this setting of lower-limb IR, mDivi-1 failed to protect the skeletal muscle both in young and old mice.

The anti-inflammatory and analgesic properties of cannabis might be useful to treat muscle diseases, including those linked or not to alcohol. Nevertheless, delta 9 tetrahydrocannabinol (THC) and ethanol (EtOH), often used concomitantly, can have deleterious effects on cardiac mitochondria. We therefore determined whether EtOH, alone and associated with THC, impairs skeletal muscle mitochondrial respiration. Further, we investigated potential modulation by metabolic phenotype and age by analyzing predominantly glycolytic gastrocnemius and oxidative soleus muscles in young and middle-aged rats (12 and 49 weeks). Considering the gastrocnemius, EtOH impaired mitochondrial respiration in a similar manner in young- and middle-aged muscles (−34.97 ± 2.97% vs. −37.50 ± 6.03% at 2.1 × 10⁻⁵ M; p < 0.05). Interestingly, concomitant THC aggravated EtOH-related mitochondrial impairment in young gastrocnemius (−49.92 ± 1.69%, vs. −34.97 ± 2.97 p < 0.05). Concerning the soleus, EtOH alone mainly decreased young muscle mitochondrial respiration (−42.39 ± 2.42% vs. −17.09 ± 7.61% at 2.1 × 10⁻⁵ M, p < 0.001, at 12 and 49 weeks). The soleus was less impaired at 12 weeks by THC and EtOH association than the gastrocnemius (−49.92 ±1.69 vs. −27.22 ± 8.96% in gastrocnemius and soleus, respectively, p < 0.05). In conclusion, EtOH, alone and associated with THC, significantly impairs skeletal muscle mitochondrial respiration and THC aggravates EtOH-induced effects on young glycolytic muscle. Age and metabolic phenotypes modulate these deleterious effects, with the glycolytic muscles of young rats being more prone to impairments than oxidative muscles.