Influence of Nutritional Status and Physical Exercise on Immune Response in Metabolic Syndrome

Abstract

Metabolic Syndrome (MetS) is a cluster of metabolic alterations mostly related to visceral adiposity, which in turn promotes glucose intolerance and a chronic systemic inflammatory state, characterized by immune cell infiltration. Such immune system activation increases the risk of severe disease subsequent to viral infections. Strong correlations between elevated body mass index (BMI), type-2-diabetes and increased risk of hospitalization after pandemic influenza H1N1 infection have been described. Similarly, a correlation between elevated blood glucose level and SARS-CoV-2 infection severity and mortality has been described, indicating MetS as an important predictor of clinical outcomes in patients with COVID-19. Adipose secretome, including two of the most abundant and well-studied adipokines, leptin and interleukin-6, is involved in the regulation of energy metabolism and obesity-related low-grade inflammation. Similarly, skeletal muscle hormones-called myokines-released in response to physical exercise affect both metabolic homeostasis and immune system function. Of note, several circulating hormones originate from both adipose tissue and skeletal muscle and display different functions, depending on the metabolic context. This review aims to summarize recent data in the field of exercise immunology, investigating the acute and chronic effects of exercise on myokines release and immune system function.

Keywords: COVID-19; adipokines; adipose tissue; aging; immune function; myokines; nutrition; obesity; physical activity; skeletal muscle.

Figure 1

Skeletal muscle as an endocrine organ: metabolic effects of muscle-contraction-induced myokines. Physical exercise stimulates myokine release showing endocrine function at target tissues level, including adipose organ, liver and endothelium. Indeed, the skeletal muscle secretome plays an essential role in the maintenance of whole-body metabolic homeostasis, regulating lipolysis, fat oxidation, inflammation and insulin sensitivity. In particular, myokines release induced by physical exercise contributes to the immune system stimulation, producing an anti-inflammatory cellular response with potential protective effects against infections. Abbreviations: TNF-α (Tumor necrosis factor-alpha), IL-1ra (Interleukin-1 Receptor Antagonist), IL-10 (Interleukin-10), PAI-1 (Plasminogen activator inhibitor-1), eNOS (Endothelial nitric oxide synthase), SOD1 (Superoxide Dismutase 1), SOD2 (Superoxide Dismutase 2), FGF21 (Fibroblast growth factor 21), BDNF (Brain-derived neurotrophic factor), MCP-1 (Monocyte chemoattractant protein-1), IL-6 (Interleukin-6), IL-15 (Interleukin-15), METRNL (Meteorin-like protein), BAIBA (Beta-Aminoisobutyric acid), MSTN (Myostatin), LIF (Leukemia inhibitory factor), (↓) decrease, (↑) increase.