Insulin Control of Blood Glucose and GLUT4 Expression in the Skeletal Muscle of Septic Rats

Lipid oxidation dysregulation: an emerging player in the pathophysiology of sepsis

Sepsis is a life-threatening organ dysfunction caused by abnormal host response to infection. Millions of people are affected annually worldwide. Derangement of the inflammatory response is crucial in sepsis pathogenesis. However, metabolic, coagulation, and thermoregulatory alterations also occur in patients with sepsis. Fatty acid mobilization and oxidation changes may assume the role of a protagonist in sepsis pathogenesis. Lipid oxidation and free fatty acids (FFAs) are potentially valuable markers for sepsis diagnosis and prognosis. Herein, we discuss inflammatory and metabolic dysfunction during sepsis, focusing on fatty acid oxidation (FAO) alterations in the liver and muscle (skeletal and cardiac) and their implications in sepsis development.

The role of the microcirculation and integrative cardiovascular physiology in the pathogenesis of ICU-acquired weakness

Skeletal muscle dysfunction after critical illness, defined as ICU-acquired weakness (ICU-AW), is a complex and multifactorial syndrome that contributes significantly to long-term morbidity and reduced quality of life for ICU survivors and caregivers. Historically, research in this field has focused on pathological changes within the muscle itself, without much consideration for their in vivo physiological environment. Skeletal muscle has the widest range of oxygen metabolism of any organ, and regulation of oxygen supply with tissue demand is a fundamental requirement for locomotion and muscle function. During exercise, this process is exquisitely controlled and coordinated by the cardiovascular, respiratory, and autonomic systems, and also within the skeletal muscle microcirculation and mitochondria as the terminal site of oxygen exchange and utilization. This review highlights the potential contribution of the microcirculation and integrative cardiovascular physiology to the pathogenesis of ICU-AW. An overview of skeletal muscle microvascular structure and function is provided, as well as our understanding of microvascular dysfunction during the acute phase of critical illness; whether microvascular dysfunction persists after ICU discharge is currently not known. Molecular mechanisms that regulate crosstalk between endothelial cells and myocytes are discussed, including the role of the microcirculation in skeletal muscle atrophy, oxidative stress, and satellite cell biology. The concept of integrated control of oxygen delivery and utilization during exercise is introduced, with evidence of physiological dysfunction throughout the oxygen delivery pathway - from mouth to mitochondria - causing reduced exercise capacity in patients with chronic disease (e.g., heart failure, COPD). We suggest that objective and perceived weakness after critical illness represents a physiological failure of oxygen supply-demand matching - both globally throughout the body and locally within skeletal muscle. Lastly, we highlight the value of standardized cardiopulmonary exercise testing protocols for evaluating fitness in ICU survivors, and the application of near-infrared spectroscopy for directly measuring skeletal muscle oxygenation, representing potential advancements in ICU-AW research and rehabilitation.

Magnesium supplementation enhances insulin sensitivity and decreases insulin resistance in diabetic rats

Objective(s):

Diabetes mellitus has been suggested to be the most common metabolic disorder associated with magnesium deficiency. This study aimed to investigate the effects and mechanisms of magnesium supplementation on insulin receptor activity in elderly type 2 diabetes using a rat model and to provide experimental evidence for insulin resistance improvement by magnesium supplementation.

Materials and Methods:

Rat model of type 2 diabetes was developed using a high-fat diet along with low dose streptozotocin (STZ) treatment. Magnesium supplement was given orally by mixing with the high-fat diet. Serum insulin level, insulin sensitivity, and insulin receptor affinity were assessed using radioimmunoassay (RIA). Insulin receptor, insulin receptor substrate (IRS-2), and β-Arrestin-2 gene and protein expression levels were measured using immunohistochemistry and RT-PCR. Xanthine oxidase assay, thiobarbituric acid reactive substance assay (TCA method), colorimetric assay, and ELISA were used to determine the serum SOD, MDA, T-AOC, and ox-LDL levels, respectively.

Results:

Magnesium supplementation enhanced insulin sensitivity and decreased insulin resistance in diabetic rats mainly through increasing insulin receptor expression, affinity, and augmenting insulin receptor signaling. Magnesium supplementation also inhibited lipid peroxidation in diabetic rats and protected against pancreatic cell injury in diabetic rats. In addition, we found that β-arrestin-2 gene expression was suppressed in diabetes, which was possibly attributed to gene methylation modification, as β-arrestin 2 promotor was rich in methylation-regulating sites. Magnesium supplementation could affect β-arrestin-2 gene expression and methylation.

Conclusion:

Magnesium supplementation has a positive effect on insulin receptor activity and insulin sensitivity in type 2 diabetes.

Systemic bioinformatics analysis of skeletal muscle gene expression profiles of sepsis

Sepsis is a type of systemic inflammatory response syndrome with high morbidity and mortality. Skeletal muscle dysfunction is one of the major complications of sepsis that may also influence the outcome of sepsis. The aim of the present study was to explore and identify potential mechanisms and therapeutic targets of sepsis. Systemic bioinformatics analysis of skeletal muscle gene expression profiles from the Gene Expression Omnibus was performed. Differentially expressed genes (DEGs) in samples from patients with sepsis and control samples were screened out using the limma package. Differential co-expression and coregulation (DCE and DCR, respectively) analysis was performed based on the Differential Co-expression Analysis package to identify differences in gene co-expression and coregulation patterns between the control and sepsis groups. Gene Ontology terms and Kyoto Encyclopedia of Genes and Genomes pathways of DEGs were identified using the Database for Annotation, Visualization and Integrated Discovery, and inflammatory, cancer and skeletal muscle development-associated biological processes and pathways were identified. DCE and DCR analysis revealed several potential therapeutic targets for sepsis, including genes and transcription factors. The results of the present study may provide a basis for the development of novel therapeutic targets and treatment methods for sepsis.