Dysfunctional mitochondrial metabolism has been linked to skeletal muscle loss in several physio-pathological states. Although it has been reported that vitamin D (VD) supports cellular redox homeostasis by maintaining normal mitochondrial functions, and VD deficiency often occurs in conditions associated with skeletal muscle loss, the efficacy of VD supplementation to overcome muscle wasting is debated. Investigations on the direct effects of VD metabolites on skeletal muscle using C2C12 myotubes have revealed an unexpected pro-atrophic activity of calcitriol (1,25VD), while its upstream metabolites cholecalciferol (VD3) and calcidiol (25VD) have anti-atrophic effects. Here, we investigated if the atrophic effects of 1,25VD on myotubes depend on its activity on mitochondrial metabolism. The impact of 1,25VD and its upstream metabolites VD3 and 25VD on mitochondria dynamics and the activity of C2C12 myotubes was evaluated by measuring mitochondrial content, architecture, metabolism, and reactive oxygen species (ROS) production. We found that 1,25VD induces atrophy through protein kinase C (PKC)-mediated ROS production, mainly of extramitochondrial origin. Consistent with this, cotreatment with the antioxidant N-acetylcysteine (NAC), but not with the mitochondria-specific antioxidant mitoTEMPO, was sufficient to blunt the atrophic activity of 1,25VD. In contrast, VD3 and 25VD have antioxidant properties, suggesting that the efficacy of VD supplementation might result from the balance between atrophic pro-oxidant (1,25VD) and protective antioxidant (VD3 and 25VD) metabolites.

Dietary advanced glycation end-products (dAGEs) contained in high-sugar/fat and ultra-processed foods of the “Western diet” (WD) pattern predispose to several diseases by altering protein function or increasing oxidative stress and inflammation via RAGE (receptor for advanced glycation end-products). Although elevated endogenous AGEs are associated with loss of muscle mass and functionality (i.e., muscle wasting; MW), the impact of dAGEs on MW has not been elucidated. Here, we show that the most common dAGEs or their precursor, methylglyoxal (MGO), induce C2C12 myotube atrophy as endogenous AGE-derived BSA. ROS production, mitochondrial dysfunction, mitophagy, ubiquitin–proteasome activation, and inhibition of myogenic potential are common atrophying mechanisms used by MGO and AGE-BSA. Although of different origins, ROS are mainly responsible for AGE-induced myotube atrophy. However, while AGE-BSA activates the RAGE-myogenin axis, reduces anabolic mTOR, and causes mitochondrial damage, MGO induces glycolytic stress and STAT3 activation without affecting RAGE expression. Among thirty selected natural compounds, Vaccinium macrocarpon (VM), Camellia sinensis, and chlorophyll showed a surprising ability in counteracting in vitro AGE formation. However, only the standardized VM, containing anti-glycative metabolites as revealed by UHPLC-HRMS analysis, abrogates AGE-induced myotube atrophy. Collectively, our data suggest that WD-linked dAGE consumption predisposes to MW, which might be restricted by VM food supplements.

Background: Oxidative stress and chronic inflammation contribute to the pathogenesis of obesity and type 2 diabetes (T2D), yet the effects of dietary interventions on endogenous antioxidant defences remain poorly defined. This is a non-randomized study evaluates the effects of very-low-energy ketogenic therapy (VLEKT), compared with a Mediterranean diet (MedD) and a control group, on antioxidants, metabolic, and inflammatory markers. Materials and Methods: Thirty adults with obesity and T2D were assigned to VLEKT (n = 10), MedD (n = 10), or control (n = 10) for 90 days. Metabolic parameters, inflammatory cytokines, superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were assessed. Longitudinal changes were analyzed using linear mixed models. Results: VLEKT exhibited significant reductions in body weight, fat mass, HbA1c, and HOMA-IR. SOD activity increased in the VLEKT group, whereas no significant changes were observed in MedD. Changes in SOD were inversely associated with changes in HOMA-IR. GPx showed a less consistent response pattern, while inflammatory markers did not differ between groups. Conclusions: VLEKT was associated with substantial metabolic improvement accompanied by a selective modulation of antioxidant enzyme activity. The increase in SOD activity and its association with HOMA-IR suggest a link between metabolic and redox adaptations in subjects with obesity and T2D.