Physical inactivity decreases whole body glutamine turnover independently from changes in proteolysis

Imbalanced Brain Neurochemicals in Long COVID and ME/CFS: A Preliminary Study Using MRI

PURPOSE

Long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) patients experience multiple complex symptoms, potentially linked to imbalances in brain neurochemicals. This study aims to measure brain neurochemical levels in long COVID and ME/CFS patients as well as healthy controls to investigate associations with severity measures.

METHODS

Magnetic resonance spectroscopy data were acquired with a 3T Prisma magnetic resonance imaging scanner (Siemens Healthcare, Erlangen, Germany). We measured absolute levels of brain neurochemicals in the posterior cingulate cortex in long COVID (n = 17), ME/CFS (n = 17), and healthy controls (n = 10) using Osprey software. The statistical analyses were performed using SPSS version 29 (IBM, Armonk, NY). Age and sex were included as nuisance covariates.

RESULTS

Glutamate levels were significantly higher in patients with long COVID (P = .02) and ME/CFS (P = .017) than in healthy controls. No significant difference was found between the 2 patient cohorts. Additionally, N-acetyl-aspartate levels were significantly higher in long COVID patients (P = .012). Importantly, brain neurochemical levels were associated with self-reported severity measures in long COVID and ME/CFS.

CONCLUSION

Our study identified significantly elevated glutamate and N-acetyl-aspartate levels in long COVID and ME/CFS patients compared with healthy controls. No significant differences in brain neurochemicals were observed between the 2 patient cohorts, suggesting a potential overlap in their underlying pathology. These findings suggest that imbalanced neurochemicals contribute to the complex symptoms experienced by long COVID and ME/CFS patients.

Early lean mass sparing effect of high-protein diet with excess leucine during long-term bed rest in women

Muscle inactivity leads to muscle atrophy. Leucine is known to inhibit protein degradation and to promote protein synthesis in skeletal muscle. We tested the ability of a high-protein diet enriched with branched-chain amino acids (BCAAs) to prevent muscle atrophy during long-term bed rest (BR). We determined body composition (using dual energy x-ray absorptiometry) at baseline and every 2-weeks during 60 days of BR in 16 healthy young women. Nitrogen (N) balance was assessed daily as the difference between N intake and N urinary excretion. The subjects were randomized into two groups: one received a conventional diet (1.1 ± 0.03 g protein/kg, 4.9 ± 0.3 g leucine per day) and the other a high protein, BCAA-enriched regimen (1.6 ± 0.03 g protein-amino acid/kg, 11.4 ± 0.6 g leucine per day). There were significant BR and BR × diet interaction effects on changes in lean body mass (LBM) and N balance throughout the experimental period (repeated measures ANCOVA). During the first 15 days of BR, lean mass decreased by 4.1 ± 0.9 and 2.4 ± 2.1% (p < 0.05) in the conventional and high protein-BCAA diet groups, respectively, while at the end of the 60-day BR, LBM decreased similarly in the two groups by 7.4 ± 0.7 and 6.8 ± 2.4%. During the first 15 days of BR, mean N balance was 2.5 times greater (p < 0.05) in subjects on the high protein-BCAA diet than in those on the conventional diet, while we did not find significant differences during the following time intervals. In conclusion, during 60 days of BR in females, a high protein-BCAA diet was associated with an early protein-LBM sparing effect, which ceased in the medium and long term.

Longitudinal Changes in Circulating Metabolites and Lipoproteins After Breast Cancer Treatment

The multimodal treatment of breast cancer may induce long term effects on the metabolic profile and increase the risk of future cardiovascular disease. In this study, we characterized longitudinal changes in serum lipoprotein subfractions and metabolites after breast cancer treatment, aiming to determine the long-term effect of different treatment modalities. Further, we investigated the prognostic value of treatment-induced changes in breast cancer-specific and overall 10-year survival. In this study, serum samples from breast cancer patients (n = 250) were collected repeatedly before and after radiotherapy, and serum metabolites and lipoprotein subfractions were quantified by NMR spectroscopy. Longitudinal changes were assessed by univariate and multivariate data analysis methods applicable for repeated measures. Distinct changes were detectable in levels of lipoprotein subfractions and circulating metabolites during the first year, with similar changes despite large differences in treatment regimens. We detect increased free cholesterol and decreased esterified cholesterol levels of HDL subfractions, a switch towards larger LDL particles and higher total LDL-cholesterol, in addition to a switch in the glutamine-glutamate ratio. Non-survivors had different lipid profiles from survivors already at baseline. To conclude, our results show development towards an atherogenic lipid profile in breast cancer patients with different treatment regimens.

Amino acid metabolism, transport and signalling in the liver revisited

The liver controls the systemic exposure of amino acids entering via the gastro-intestinal tract. For most amino acids except branched chain amino acids, hepatic uptake is very efficient. This implies that the liver orchestrates amino acid metabolism and also controls systemic amino acid exposure. Although many amino acid transporters have been identified, cloned and investigated with respect to substrate specificity, transport mechanism, and zonal distribution, which of these players are involved in hepatocellular amino acid transport remains unclear. Here, we aim to provide a review of current insight into the molecular machinery of hepatic amino acid transport. Furthermore, we place this information in a comprehensive overview of amino acid transport, signalling and metabolism.

Regulatory principles in metabolism–then and now

The importance of metabolic pathways for life and the nature of participating reactions have challenged physiologists and biochemists for over a hundred years. Eric Arthur Newsholme contributed many original hypotheses and concepts to the field of metabolic regulation, demonstrating that metabolic pathways have a fundamental thermodynamic structure and that near identical regulatory mechanisms exist in multiple species across the animal kingdom. His work at Oxford University from the 1970s to 1990s was groundbreaking and led to better understanding of development and demise across the lifespan as well as the basis of metabolic disruption responsible for the development of obesity, diabetes and many other conditions. In the present review we describe some of the original work of Eric Newsholme, its relevance to metabolic homoeostasis and disease and application to present state-of-the-art studies, which generate substantial amounts of data that are extremely difficult to interpret without a fundamental understanding of regulatory principles. Eric's work is a classical example of how one can unravel very complex problems by considering regulation from a cell, tissue and whole body perspective, thus bringing together metabolic biochemistry, physiology and pathophysiology, opening new avenues that now drive discovery decades thereafter.

The time course of the adaptations of human muscle proteome to bed rest and the underlying mechanisms

In order to get a comprehensive picture of the complex adaptations of human skeletal muscle to disuse and further the understanding of the underlying mechanisms, we participated in two bed rest campaigns, one lasting 35 days and one 24 days. In the first bed rest (BR) campaign, myofibrillar proteins, metabolic enzymes and antioxidant defence systems were found to be down-regulated both post-8 days and post-35 days BR by proteomic analysis of vastus lateralis muscle samples from nine subjects. Such profound alterations occurred early (post-8 days BR), before disuse atrophy developed, and persisted through BR (post-35 days BR). To understand the mechanisms underlying the protein adaptations observed, muscle biopsies from the second bed rest campaign (nine subjects) were used to evaluate the adaptations of master controllers of the balance between muscle protein breakdown and muscle protein synthesis (MuRF-1 and atrogin-1; Akt and p70S6K), of autophagy (Beclin-1, p62, LC3, bnip3, cathepsin-L), of expression of antioxidant defence systems (NRF2) and of energy metabolism (PGC-1α, SREBP-1, AMPK). The results indicate that: (i) redox imbalance and remodelling of muscle proteome occur early and persist through BR; (ii) impaired energy metabolism is an early and persistent phenomenon comprising both the oxidative and glycolytic one; (iii) although both major catabolic systems, ubiquitin proteasome and autophagy, could contribute to the progression of atrophy late into BR, a decreased protein synthesis cannot be ruled out; (iv) a decreased PGC-1α, with the concurrence of SREBP-1 up-regulation, is a likely trigger of metabolic impairment, whereas the AMPK pathway is unaltered.

Prolonged inactivity up-regulates cholesteryl ester transfer protein independently of body fat changes in humans

CONTEXT

Physical inactivity is associated with insulin resistance and decreased high-density lipoprotein (HDL) cholesterol. Cholesteryl ester transfer protein (CETP) is involved in cholesterol metabolism, being responsible for the transfer of cholesteryl esters from HDL to very low- and low-density lipoproteins.

OBJECTIVE

We hypothesized that physical inactivity could decrease HDL cholesterol through changes in CETP availability.

DESIGN AND PARTICIPANTS

Twenty-four healthy, male volunteers (aged 23.1 +/- 0.5 yr) were investigated in eucaloric conditions before and at the end of 35 d of experimental bed rest.

MEASURES

Changes in body composition were monitored by bioimpedance throughout the study. Before and at the end of the experimental period, plasma insulin and glucose and plasma lipid pattern as well as CETP concentrations were determined.

RESULTS

Our results demonstrated that during bed rest, fat mass did not change significantly, whereas fat-free mass decreased by 3.9 +/- 0.4% (P < 0.01). The homeostatic model assessment index of insulin resistance significantly (P < 0.001) increased by 47 +/- 11% after bed rest. Bed rest decreased HDL cholesterol by 12 +/- 3% (P < 0.05), increased triglycerides by 51 +/- 10% (P < 0.05), whereas it did not change significantly low-density lipoprotein cholesterol. Plasma CETP concentration increased after bed rest by 27 +/- 9% (P < 0.01). Bed rest-induced changes in CETP concentrations inversely correlated with changes in the ratio between HDL and non-HDL cholesterol (n = 24; R = -0.43; P < 0.05).

CONCLUSIONS

Physical inactivity decreases HDL cholesterol, at least in part, through CETP up-regulation.

Effect of physical activity on glutamine metabolism

PURPOSE OF REVIEW

Glutamine is largely synthesized in skeletal muscles and provides fuel to rapidly dividing cells of the immune system and precursors to gluconeogenesis in the liver. Physical exercise is known to affect glutamine synthesis and to modulate glutamine uptake. Overtraining is frequently associated with reduced availability of glutamine and decreased immunocompetence. Inactivity affects glutamine metabolism, but this subject was poorly investigated.

RECENT FINDINGS

Strenuous physical exercise as well as exhaustive training programs lead to glutamine depletion due to lowered synthesis and enhanced uptake by liver and immune cells. Evidence suggests that postexercise glutamine depletion is associated with immunodepression. Counterwise, moderate training leads to improved glutamine availability due to a positive balance between muscle synthesis and peripheral clearance. Physical inactivity, as investigated by experimental bed rest in healthy volunteers, reduced glutamine synthesis and availability.

SUMMARY

After exercise, a reduced glutamine availability may be considered as a marker of overtraining. An increased glutamine availability may contribute to decreased inflammation and health benefits associated with optimal training. Thus, glutamine supplementation may enhance immunocompetence after strenuous exercise. The potential of glutamine supplementation during physical inactivity needs to be explored.