Effects of glycine supplementation on myocardial damage and cardiac function after severe burn

1H-nuclear magnetic resonance analysis reveals dynamic changes in the metabolic profile of patients with severe burns

Background

Severe burn injury causes a hypermetabolic response, resulting in muscle protein catabolism and multiple organ damage syndrome. However, this response has not yet been continuously characterized by metabolomics in patients. This study aims to quantify temporal changes in the metabolic processes of patients with severe burns.

Methods

We employed 1H-nuclear magnetic resonance (NMR) spectroscopy to scrutinize metabolic alterations during the initial 35 days following burn injury in a cohort of 17 adult patients with severe burns, with 10 healthy individuals included as controls. Plasma specimens were collected from patients on postburn days 1, 3, 7, 14, 21, 28 and 35. After performing multivariate statistical analysis, repeated-measures analysis of variance and time-series analysis, we quantified changes in metabolite concentrations.

Results

Among the 36 metabolites quantified across 119 samples from burn patients, branched-chain amino acids, glutamate, glycine, glucose, pyruvate, lactate, trimethylamine N-oxide and others exhibited obvious temporal variations in concentration. Notably, these metabolites could be categorized into three clusters based on their temporal characteristics. The initial response to injury was characterized by changes in lactate and amino acids, while later changes were driven by an increase in fatty acid catabolism and microbial metabolism, leading to the accumulation of ketone bodies and microbial metabolites.

Conclusions

Metabolomics techniques utilizing NMR have the potential to monitor the intricate processes of metabolism in patients with severe burns. This study confirmed that the third day after burn injury serves as the boundary between the ebb phase and the flow phase. Furthermore, identification of three distinct temporal patterns of metabolites revealed the intrinsic temporal relationships between these metabolites, providing clinical data for optimizing therapeutic strategies.

Mitochondrial Glutathione in Cellular Redox Homeostasis and Disease Manifestation

Mitochondria are critical for providing energy to maintain cell viability. Oxidative phosphorylation involves the transfer of electrons from energy substrates to oxygen to produce adenosine triphosphate. Mitochondria also regulate cell proliferation, metastasis, and deterioration. The flow of electrons in the mitochondrial respiratory chain generates reactive oxygen species (ROS), which are harmful to cells at high levels. Oxidative stress caused by ROS accumulation has been associated with an increased risk of cancer, and cardiovascular and liver diseases. Glutathione (GSH) is an abundant cellular antioxidant that is primarily synthesized in the cytoplasm and delivered to the mitochondria. Mitochondrial glutathione (mGSH) metabolizes hydrogen peroxide within the mitochondria. A long-term imbalance in the ratio of mitochondrial ROS to mGSH can cause cell dysfunction, apoptosis, necroptosis, and ferroptosis, which may lead to disease. This study aimed to review the physiological functions, anabolism, variations in organ tissue accumulation, and delivery of GSH to the mitochondria and the relationships between mGSH levels, the GSH/GSH disulfide (GSSG) ratio, programmed cell death, and ferroptosis. We also discuss diseases caused by mGSH deficiency and related therapeutics.

Glycine: The Smallest Anti-Inflammatory Micronutrient

Glycine is a non-essential amino acid with many functions and effects. Glycine can bind to specific receptors and transporters that are expressed in many types of cells throughout an organism to exert its effects. There have been many studies focused on the anti-inflammatory effects of glycine, including its abilities to decrease pro-inflammatory cytokines and the concentration of free fatty acids, to improve the insulin response, and to mediate other changes. However, the mechanism through which glycine acts is not clear. In this review, we emphasize that glycine exerts its anti-inflammatory effects throughout the modulation of the expression of nuclear factor kappa B (NF-κB) in many cells. Although glycine is a non-essential amino acid, we highlight how dietary glycine supplementation is important in avoiding the development of chronic inflammation.

Glutathione system enhancement for cardiac protection: pharmacological options against oxidative stress and ferroptosis

The glutathione (GSH) system is considered to be one of the most powerful endogenous antioxidant systems in the cardiovascular system due to its key contribution to detoxifying xenobiotics and scavenging overreactive oxygen species (ROS). Numerous investigations have suggested that disruption of the GSH system is a critical element in the pathogenesis of myocardial injury. Meanwhile, a newly proposed type of cell death, ferroptosis, has been demonstrated to be closely related to the GSH system, which affects the process and outcome of myocardial injury. Moreover, in facing various pathological challenges, the mammalian heart, which possesses high levels of mitochondria and weak antioxidant capacity, is susceptible to oxidant production and oxidative damage. Therefore, targeted enhancement of the GSH system along with prevention of ferroptosis in the myocardium is a promising therapeutic strategy. In this review, we first systematically describe the physiological functions and anabolism of the GSH system, as well as its effects on cardiac injury. Then, we discuss the relationship between the GSH system and ferroptosis in myocardial injury. Moreover, a comprehensive summary of the activation strategies of the GSH system is presented, where we mainly identify several promising herbal monomers, which may provide valuable guidelines for the exploration of new therapeutic approaches.

Myocardial Adipose Triglyceride Lipase Overexpression Protects against Burn-Induced Cardiac Lipid Accumulation and Injury

Maladaptive cardiac metabolism is a common trigger of cardiac lipid accumulation and cardiac injury under serious burn challenge. Adipose triglyceride lipase (ATGL) is the key enzyme that catalyzes triglyceride hydrolysis; however, its alteration and impact on cardiac function following serious burn injury are still unknown. Here, we found that the cardiac fatty acid (FA) metabolism increased, accompanied by augmented FA accumulation and ATGL expression, after serious burn injury. We generated heterozygous ATGL knockout and heterozygous cardiac-specific ATGL overexpression thermal burn mice. The results demonstrated that partial loss of ATGL could not relieve burn-induced cardiac lipid accumulation and cardiac injury, possibly due to the suppression of cardiac FA metabolism plus insufficient compensatory glucose utilization. In contrast, cardiac-specific overexpression of ATGL alleviated cardiac lipid accumulation and cardiac injury following burn challenge by switching the substrate preference from FA towards increased glucose utilization. The underlying mechanism was possibly related to increased glucose transporter-1 expression and reduced cardiac lipid accumulation induced by ATGL overexpression. Our data first demonstrated that elevated cardiac ATGL expression after serious burn injury is an adaptive, albeit insufficient, response to compensate for the increase in energy consumption and that further overexpression of ATGL is beneficial for ameliorating cardiac injury, indicating its therapeutic potential.

Dietary Glycine Is Rate-Limiting for Glutathione Synthesis and May Have Broad Potential for Health Protection

BACKGROUND

Glutathione is a key scavenging antioxidant that opposes the proinflammatory signaling of hydrogen peroxide. Boosting cellular glutathione levels may have broad utility in the prevention and treatment of disorders driven by oxidative stress. Supplemental N-acetylcysteine has been employed for this purpose. Could supplemental glycine likewise promote glutathione synthesis?

METHODS

We conducted a review of the pertinent literature using PubMed.

RESULTS

Tissue glycine levels are lower than the glutathione synthase Michaelis constant (K_m) for glycine. When glycine availability is too low to sustain a normal rate of glutathione synthesis, the consequent rise in tissue levels of gamma-glutamylcysteine leads to an increase in urinary excretion of its alternative metabolite 5-L-oxoproline. The fact that urinary excretion of this metabolite is elevated in vegetarians and others consuming relatively low-protein diets strongly suggests that dietary glycine can be rate-limiting for glutathione synthesis in normally fed humans. Moreover, supplemental glycine has been reported to increase tissue glutathione levels in several animal studies. Glycine is a biosynthetic precursor for porphyrins, purines, creatine, sarcosine, and bile salts; is an agonist for glycine-gated chloride channels and a coagonist for N-methyl-D-aspartate receptors; inhibits protein glycation; and increases hepatic production of pyruvate, an effective scavenger of hydrogen peroxide. Supplemental glycine may have the potential for improving endothelial function, preventing cardiac hypertrophy, aiding control of metabolic syndrome, preventing the complications of diabetes, dampening inflammation, protecting the liver, and promoting effective sleep.

CONCLUSION

Clinical research is warranted to evaluate the impact of supplemental glycine on glutathione levels and on various health disorders.

The role of glycine in regulated cell death

The cytoprotective effects of glycine against cell death have been recognized for over 28 years. They are expressed in multiple cell types and injury settings that lead to necrosis, but are still not widely appreciated or considered in the conceptualization of cell death pathways. In this paper, we review the available data on the expression of this phenomenon, its relationship to major pathophysiologic pathways that lead to cell death and immunomodulatory effects, the hypothesis that it involves suppression by glycine of the development of a hydrophilic death channel of molecular dimensions in the plasma membrane, and evidence for its impact on disease processes in vivo.

Notch1 Pathway Protects against Burn-Induced Myocardial Injury by Repressing Reactive Oxygen Species Production through JAK2/STAT3 Signaling

Oxidative stress plays an important role in burn-induced myocardial injury, but the cellular mechanisms that control reactive oxygen species (ROS) production and scavenging are not fully understood. This study demonstrated that blockade of Notch signaling via knockout of the transcription factor RBP-J or a pharmacological inhibitor aggravated postburn myocardial injury, which manifested as deteriorated serum CK, CK-MB, and LDH levels and increased apoptosis in vitro and in vivo. Interruption of Notch signaling increased intracellular ROS production, and a ROS scavenger reversed the exacerbated myocardial injury after Notch signaling blockade. These results suggest that Notch signaling deficiency aggravated postburn myocardial injury through increased ROS levels. Notch signaling blockade also decreased MnSOD expression in vitro and in vivo. Notably, Notch signaling blockade downregulated p-JAK2 and p-STAT3 expression. Inhibition of JAK2/STAT3 signaling with AG490 markedly decreased MnSOD expression, increased ROS production, and aggravated myocardial injury. AG490 plus GSI exerted no additional effects. These results demonstrate that Notch signaling protects against burn-induced myocardial injury through JAK2/STAT3 signaling, which activates the expression of MnSOD and leads to decreased ROS levels.

Evaluation of toxicological effects induced by tributyltin in clam Ruditapes decussatus using high-resolution magic angle spinning nuclear magnetic resonance spectroscopy: Study of metabolic responses in heart tissue and detection of a novel metabolite

Tributyltin (TBT) is a highly toxic pollutant present in many aquatic ecosystems. Its toxicity in mollusks strongly affects their performance and survival. The main purpose of this study was to elucidate the mechanisms of TBT toxicity in clam Ruditapes decussatus by evaluating the metabolic responses of heart tissues, using high-resolution magic angle-spinning nuclear magnetic resonance (HRMAS NMR), after exposure to TBT (10^-9, 10^-6 and 10^-4 M) during 24 h and 72 h. Results show that responses of clam heart tissue to TBT exposure are not dose dependent. Metabolic profile analyses indicated that TBT 10^-6 M, contrary to the two other doses tested, led to a significant depletion of taurine and betaine. Glycine levels decreased in all clam groups treated with the organotin. It is suggested that TBT abolished the cytoprotective effect of taurine, betaine and glycine thereby inducing cardiomyopathie. Moreover, results also showed that TBT induced increase in the level of alanine and succinate suggesting the occurrence of anaerobiosis particularly in clam group exposed to the highest dose of TBT. Taken together, these results demonstrate that TBT is a potential toxin with a variety of deleterious effects on clam and this organotin may affect different pathways depending to the used dose. The main finding of this study was the appearance of an original metabolite after TBT treatment likely N-glycine-N'-alanine. It is the first time that this molecule has been identified as a natural compound. Its exact role is unknown and remains to be elucidated. We suppose that its formation could play an important role in clam defense response by attenuating Ca²⁺ dependent cell death induced by TBT. Therefore this compound could be a promising biomarker for TBT exposure.