Effect of endurance training and PGC-1α overexpression on calculated lactate production volume during exercise based on blood lactate concentration

Exercise influence on monocarboxylate transporter 1 (MCT1) and 4 (MCT4) in the skeletal muscle: A systematic review

This review aims to systematically analyze the effect of exercise on muscle MCT protein levels and mRNA expression of their respective genes, considering exercise intensity, and duration (single-exercise session and training program) in humans and rodents, to observe whether both models offer aligned results. The review also aims to report methodological aspects that need to be improved in future studies. A systematic search was conducted in the PubMed and Web of Science databases, and the Preferred Reporting Items for Systematic review and Meta-Analyses (PRISMA) checklist was followed. After applying inclusion and exclusion criteria, 41 studies were included and evaluated using the Cochrane collaboration tool for risk of bias assessment. The main findings indicate that exercise is a powerful stimulus to increase MCT1 protein content in human muscle. MCT4 protein level increases can also be observed after a training program, although its responsiveness is lower compared to MCT1. Both transporters seem to change independently of exercise intensity, but the responses that occur with each intensity and each duration need to be better defined. The effect of exercise on muscle mRNA results is less defined, and more research is needed especially in humans. Moreover, results in rodents only agree with human results on the effect of a training program on MCT1 protein levels, indicating increases in both. Finally, we addressed important and feasible methodological aspects to improve the design of future studies.

Cmah deficiency blunts cellular senescence in adipose tissues and improves whole-body glucose metabolism in aged mice

AIM

Cytidine monophosphate-N-acetylneuraminic acid (Neu5Ac) hydroxylase (Cmah) is an enzyme, which converts Neu5Ac to the sialic acid Neu5Gc. Neu5Gc is thought to increase inflammatory cytokines, which are, in part, produced in senescent cells of adipose tissues. Cellular senescence in adipose tissues induces whole-body aging and impaired glucose metabolism. Therefore, we hypothesized that Cmah deficiency would prevent cellular senescence in adipose tissues and impaired glucose metabolism.

METHODS

Wild-type (WT) and Cmah knockout (KO) mice aged 24-25 months were used. Whole-body metabolism was assessed using a metabolic gas analysis system. We measured blood glucose and insulin concentrations after oral glucose administration. The size of the lipid droplets in the liver was quantified. Markers of cellular senescence and senescence-associated secretory phenotypes were measured in adipose tissues.

RESULTS

Cmah KO had significantly increased VO2 and energy expenditure (P < 0.01). Unlike glucose, the insulin concentration after oral glucose administration was significantly lower in the Cmah KO group than in the WT group (P < 0.001). Lipid droplets in the liver were significantly lower in the Cmah KO group than in the WT group (P < 0.05). The markers of cellular senescence and senescence-associated secretory phenotypes in the adipose tissues were significantly lower in the Cmah KO group than in the WT group (P < 0.05).

CONCLUSIONS

Cmah deficiency blunted cellular senescence in adipose tissues and improved whole-body glucose metabolism. These characteristics in aged Cmah KO mice might be associated with higher energy expenditure. Geriatr Gerontol Int 2023; 23: 958-964.

Physiological significance of elevated levels of lactate by exercise training in the brain and body

For the past 200 years, lactate has been regarded as a metabolic waste end product that causes fatigue during exercise. However, lactate production is closely correlated with energy metabolism. The lactate dehydrogenase-catalyzed reaction uses protons to produce lactate, which delays ongoing metabolic acidosis. Of note, lactate production differs depending on exercise intensity and is not limited to muscles. Importantly, controlling physiological effect of lactate may be a solution to alleviating some chronic diseases. Released through exercise, lactate is an important biomarker for fat oxidation in skeletal muscles. During recovery after sustained strenuous exercise, most of the lactate accumulated during exercise is removed by direct oxidation. However, as the muscle respiration rate decreases, lactate becomes a desirable substrate for hepatic glucose synthesis. Furthermore, improvement in brain function by lactate, particularly, through the expression of vascular endothelial growth factor and brain-derived neurotrophic factor, is being increasingly studied. In addition, it is possible to improve stress-related symptoms, such as depression, by regulating the function of hippocampal mitochondria, and with an increasingly aging society, lactate is being investigated as a preventive agent for brain diseases such as Alzheimer's disease. Therefore, the perception that lactate is equivalent to fatigue should no longer exist. This review focuses on the new perception of lactate and how lactate acts extensively in the skeletal muscles, heart, brain, kidney, and liver. Additionally, lactate is now used to confirm exercise performance and should be further studied to assess its impact on exercise training.

Beyond Mechanical Tension: A Review of Resistance Exercise-Induced Lactate Responses & Muscle Hypertrophy

The present review aims to explore and discuss recent research relating to the lactate response to resistance training and the potential mechanisms by which lactate may contribute to skeletal muscle hypertrophy or help to prevent muscle atrophy. First, we will discuss foundational information pertaining to lactate including metabolism, measurement, shuttling, and potential (although seemingly elusive) mechanisms for hypertrophy. We will then provide a brief analysis of resistance training protocols and the associated lactate response. Lastly, we will discuss potential shortcomings, resistance training considerations, and future research directions regarding lactate's role as a potential anabolic agent for skeletal muscle hypertrophy.