Early energy metabolism-related molecular events in skeletal muscle of diabetic rats: The effects of l-arginine and SOD mimic

Aging-Related Sarcopenia: Metabolic Characteristics and Therapeutic Strategies

The proportion of the elderly population is gradually increasing as a result of medical care advances, leading to a subsequent surge in geriatric diseases that significantly impact quality of life and pose a substantial healthcare burden. Sarcopenia, characterized by age-related decline in skeletal muscle mass and quality, affects a considerable portion of older adults, particularly the elderly, and can result in adverse outcomes such as frailty, fractures, bedridden, hospitalization, and even mortality. Skeletal muscle aging is accompanied by underlying metabolic changes. Therefore, elucidating these metabolic profiles and specific mechanisms holds promise for informing prevention and treatment strategies for sarcopenia. This review provides a comprehensive overview of the key metabolites identified in current clinical studies on sarcopenia and their potential pathophysiological alterations in metabolic activity. Besides, we examine potential therapeutic strategies for sarcopenia from a perspective focused on metabolic regulation.

The glucotoxicity protecting effect of honokiol in human hepatocytes via directly activating AMPK

Introduction

Sustained hyperglycemia causes glucotoxicity, which has been regarded as a contributor to hepatocyte damage in type 2 diabetes (T2D) and its metabolic comorbidities. Honokiol is a natural biphenolic component derived from the dietary supplement Magnolia officinalis extract. This study aimed to investigate the effects of honokiol on glucose metabolism disorders and oxidative stress in hepatocytes and the underlying mechanisms.

Methods

HepG2 cells were treated with glucosamines (18 mM) to induce glucotoxicity as a diabetic complication model in vitro.

Results and discussion

Honokiol significantly increased glucose consumption, elevated 2-NBDG uptake, and promoted GLUT2 translocation to the plasma membrane in glucosamine-treated HepG2 cells, indicating that honokiol ameliorates glucose metabolism disorders. Furthermore, glucosamine-induced ROS accumulation and loss of mitochondrial membrane potential were markedly reduced by honokiol, suggesting that honokiol alleviated glucotoxicity-induced oxidative stress. These effects were largely abolished by compound C, an AMPK inhibitor, suggesting an AMPK activation-dependent manner of honokiol function in promoting glucose metabolism and mitigating oxidative stress. Molecular docking results revealed that honokiol could interact with the amino acid residues (His151, Arg152, Lys243, Arg70, Lys170, and His298) in the active site of AMPK. These findings provide new insights into the antidiabetic effect of honokiol, which may be a promising agent for the prevention and treatment of T2D and associated metabolic comorbidities.

l-Arginine Induces White Adipose Tissue Browning-A New Pharmaceutical Alternative to Cold

The beneficial effects of l-arginine supplementation in obesity and type II diabetes involve white adipose tissue (WAT) reduction and increased substrate oxidation. We aimed to test the potential of l-arginine to induce WAT browning. Therefore, the molecular basis of browning was investigated in retroperitoneal WAT (rpWAT) of rats exposed to cold or treated with 2.25% l-arginine for 1, 3, and 7 days. Compared to untreated control, levels of inducible nitric oxide (NO) synthase protein expression and NO signaling increased in both cold-exposed and l-arginine-treated groups. These increases coincided with the appearance of multilocular adipocytes and increased expression levels of uncoupling protein 1 (UCP1), thermogenic and beige adipocyte-specific genes (Cidea, Cd137, and Tmem26), mitochondriogenesis markers (peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α, mitochondrial DNA copy number), nuclear respiratory factor 1, PPARα and their respective downstream lipid oxidation enzymes after l-arginine treatment. Such browning phenotype in the l-arginine-treated group was concordant with end-course decreases in leptinaemia, rpWAT mass, and body weight. In conclusion, l-arginine mimics cold-mediated increases in NO signaling in rpWAT and induces molecular and structural fingerprints of rpWAT browning. The results endorse l-arginine as a pharmaceutical alternative to cold exposure, which could be of great interest in obesity and associated metabolic diseases.

L-Arginine Reduces Nitro-Oxidative Stress in Cultured Cells with Mitochondrial Deficiency

L-Arginine (L-ARG) supplementation has been suggested as a therapeutic option in several diseases, including Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like syndrome (MELAS), arguably the most common mitochondrial disease. It is suggested that L-ARG, a nitric oxide (NO) precursor, can restore NO levels in blood vessels, improving cerebral blood flow. However, NO also participates in mitochondrial processes, such as mitochondrial biogenesis, the regulation of the respiratory chain, and oxidative stress. This study investigated the effects of L-ARG on mitochondrial function, nitric oxide synthesis, and nitro-oxidative stress in cell lines harboring the MELAS mitochondrial DNA (mtDNA) mutation (m.3243A>G). We evaluated mitochondrial enzyme activity, mitochondrial mass, NO concentration, and nitro-oxidative stress. Our results showed that m.3243A>G cells had increased NO levels and protein nitration at basal conditions. Treatment with L-ARG did not affect the mitochondrial function and mass but reduced the intracellular NO concentration and nitrated proteins in m.3243A>G cells. The same treatment led to opposite effects in control cells. In conclusion, we showed that the main effect of L-ARG was on protein nitration. Lowering protein nitration is probably involved in the mechanism related to L-ARG supplementation benefits in MELAS patients.

Oxidative Stress and Advanced Lipoxidation and Glycation End Products (ALEs and AGEs) in Aging and Age-Related Diseases

Oxidative stress is a consequence of the use of oxygen in aerobic respiration by living organisms and is denoted as a persistent condition of an imbalance between the generation of reactive oxygen species (ROS) and the ability of the endogenous antioxidant system (AOS) to detoxify them. The oxidative stress theory has been confirmed in many animal studies, which demonstrated that the maintenance of cellular homeostasis and biomolecular stability and integrity is crucial for cellular longevity and successful aging. Mitochondrial dysfunction, impaired protein homeostasis (proteostasis) network, alteration in the activities of transcription factors such as Nrf2 and NF-κB, and disturbances in the protein quality control machinery that includes molecular chaperones, ubiquitin-proteasome system (UPS), and autophagy/lysosome pathway have been observed during aging and age-related chronic diseases. The accumulation of ROS under oxidative stress conditions results in the induction of lipid peroxidation and glycoxidation reactions, which leads to the elevated endogenous production of reactive aldehydes and their derivatives such as glyoxal, methylglyoxal (MG), malonic dialdehyde (MDA), and 4-hydroxy-2-nonenal (HNE) giving rise to advanced lipoxidation and glycation end products (ALEs and AGEs, respectively). Both ALEs and AGEs play key roles in cellular response to oxidative stress stimuli through the regulation of a variety of cell signaling pathways. However, elevated ALE and AGE production leads to protein cross-linking and aggregation resulting in an alteration in cell signaling and functioning which causes cell damage and death. This is implicated in aging and various age-related chronic pathologies such as inflammation, neurodegenerative diseases, atherosclerosis, and vascular complications of diabetes mellitus. In the present review, we discuss experimental data evidencing the impairment in cellular functions caused by AGE/ALE accumulation under oxidative stress conditions. We focused on the implications of ALEs/AGEs in aging and age-related diseases to demonstrate that the identification of cellular dysfunctions involved in disease initiation and progression can serve as a basis for the discovery of relevant therapeutic agents.