Glycine treatment decreases proinflammatory cytokines and increases interferon-gamma in patients with type 2 diabetes

Metabolomics in cardiometabolic diseases: Key biomarkers and therapeutic implications for insulin resistance and diabetes

Cardiometabolic diseases-including Type 2 diabetes and obesity-remain leading causes of global mortality. Recent advancements in metabolomics have facilitated the identification of metabolites that are integral to the development of insulin resistance, a characteristic feature of cardiometabolic disease. Key metabolites, such as branched-chain amino acids (BCAAs), ceramides, glycine, and glutamine, have emerged as valuable biomarkers for early diagnosis, risk stratification, and potential therapeutic targets. Elevated BCAAs and ceramides are strongly associated with insulin resistance and Type 2 diabetes, whereas glycine exhibits an inverse relationship with insulin resistance, making it a promising therapeutic target. Metabolites involved in energy stress, including ketone bodies, lactate, and nicotinamide adenine dinucleotide (NAD⁺), regulate insulin sensitivity and metabolic health, with ketogenic diets and NAD⁺ precursor supplementation showing potential benefits. Additionally, the novel biomarker N-lactoyl-phenylalanine further underscores the complexity of metabolic regulation and its therapeutic potential. This review underscores the potential of metabolite-based diagnostics and precision medicine, which could enhance efforts in the prevention, diagnosis, and treatment of cardiometabolic diseases, ultimately improving patient outcomes and quality of life.

Accelerated biological aging, mediating amino acids, and risk of incident type 2 diabetes: a prospective cohort study

PURPOSE

Aging plays an important role in type 2 diabetes mellitus (T2DM). But the association between accelerated biological age and T2DM, and the mechanisms underlying this association remains unclear. Thus, this study aimed to examine the associations of biological aging with T2DM, and explore the potential mediation effect of amino acids.

METHODS

This prospective cohort study included 95,773 participants in the UK Biobank who were free of diabetes at baseline. Biological age was measured from clinical traits using PhenoAgeAccel. Cox proportional hazard models were used to estimate the hazard ritios (HRs) and 95% confidence intervals (CIs), and mediation analysis was used to explore the mediation effect of amino acids.

RESULTS

During a median follow-up of 14.02 years, 6,347 incident T2DM cases were recorded. After multivariable adjustment for sociodemographic characteristics, lifestyle factors, and other risk factors of T2DM, participants with older biological age were at increased risk of incident T2DM (30% increase per standard deviation of PhenoAgeAccel, 95% CI: 28.0-33.0%). Additionally, higher branched chain amino acids (BCAAs) including isoleucine and leucine, aromatic amino acids (AAAs) including phenylalanine and tyrosine, were associated with increased PhenoAgeAccel and risk of incident T2DM; while glutamine and glycine were inversely associated. Alanine, glutamine, glycine, phenylalanine, tyrosine, isoleucine, leucine, and total concentration of branched-chain amnio acids could partially explain the associations between PhenoAgeAccel and T2DM.

CONCLUSION

Accelerated biological aging was associated with increased risk of incident T2DM independent of chronological age and may be a risk factor of T2DM, partially mediated by several amino acids.

A gut pathobiont regulates circulating glycine and host metabolism in a twin study comparing vegan and omnivorous diets

Metabolic diseases including type 2 diabetes and obesity pose a significant global health burden. Plant-based diets, including vegan diets, are linked to favorable metabolic outcomes, yet the underlying mechanisms remain unclear. In a randomized trial involving 21 pairs of identical twins, we investigated the effects of vegan and omnivorous diets on the host metabolome, immune system, and gut microbiome. Vegan diets induced significant shifts in serum and stool metabolomes, cytokine profiles, and gut microbial composition. Despite lower dietary glycine intake, vegan diet subjects exhibited elevated serum glycine levels linked to reduced abundance of the gut pathobiont Bilophila wadsworthia. Functional studies demonstrated that B. wadsworthia metabolizes glycine via the glycine reductase pathway and modulates host glycine availability. Removing B. wadsworthia from a complex microbiota in mice elevated glycine levels and improved metabolic markers. These findings reveal a previously underappreciated mechanism by which diet regulates host metabolic status via the gut microbiota.

Functional Foods and Nutraceuticals for the Management of Cardiovascular Disease Risk in Postmenopausal Women

Cardiovascular disease (CVD) is a leading cause of death in women and risk of development is greatly increased following menopause. Menopause occurs over several years and is associated with hormonal changes, including a reduction in estradiol and an increase in follicle-stimulating hormone. This hormonal shift may result in an increased risk of developing abdominal adiposity, insulin resistance, dyslipidemia, vascular dysfunction, hypertension, type 2 diabetes mellitus (T2DM), metabolic dysfunction-associated fatty liver disease (MAFLD), and metabolic syndrome (MetS). Furthermore, with the onset of menopause, there is an increase in oxidative stress that is associated with impaired vascular function, inflammation, and thrombosis, further increasing the risk of CVD development. Despite the harmful consequences of the menopause transition being well known, women in premenopausal, perimenopausal, and postmenopausal stages are unlikely to be enrolled in research studies. Therefore, investigations on the prevention and treatment of cardiovascular and metabolic disease in middle-aged women are still relatively limited. Whilst lifestyle interventions are associated with reduced CVD risk in this population sample, the evidence still remains inconclusive. Therefore, it is important to explore the effectiveness of early intervention and potential therapeutic approaches to maintain cellular redox balance, preserve endothelium, and reduce inflammation. Glycine, N-acetylcysteine, and L-theanine are amino acids with potential antioxidant and anti-inflammatory activity and are identified as therapeutic interventions in the management of age-related and metabolic diseases. The benefits of the intake of these amino acids for improving factors associated with cardiovascular health are discussed in this review. Future studies using these amino acids are warranted to investigate their effect on maintaining the vascular health and cardiovascular outcomes of postmenopausal women.

Dysregulation of amino acids balance as potential serum-metabolite biomarkers for diagnosis and prognosis of diabetic retinopathy: a metabolomics study

Objectives

Diabetic retinopathy (DR), an earnest complication of diabetes, is one of the most common causes of blindness worldwide. This study aimed to investigate the altered metabolites in the serum of non-DR (NDR) and DR including non-proliferative diabetic retinopathy (NPDR), and proliferative diabetic retinopathy (PDR) subjects.

Methods

In this study, the 1HNMR platform was applied to reveal the discriminating serum metabolites in three diabetic groups based on the status of their complications: T2D or NDR (n = 15), NPDR, (n = 15), and PDR (n = 15) groups. Multivariate analyses include principal component analysis (PCA) and Partial Least Structures-Discriminant Analysis (PLS-DA) analysis that were performed using R software. The main metabolic pathways were also revealed by KEGG pathway enrichment analysis.

Results

The results revealed the significantly different metabolites include 10 metabolites of the NPDR versus PDR group, 24 metabolites of the PDR versus NDR group, and 25 metabolites of the NPDR versus NDR group. The results showed that the significantly altered metabolites in DR compared with NDR serum samples mainly belonged to amino acids. The most important pathways between NPDR/PDR, and NDR/DR groups include ascorbate and aldarate metabolism, galactose metabolism, glutathione metabolism, and tryptophan metabolism, respectively. In addition, some metabolites were detected for the first time.

Conclusions

We created a metabolomics profile for NDR, PDR and NPDR groups. The impairment in the ascorbate/aldarate, galactose, and especially amino acids metabolism was identified as metabolic dysregulation associated with DR, which may provide new insights into potential pathogenesis pathways for DR.

Graphical Abstract

Glycine by enteral route does not improve major clinical outcomes in severe COVID-19: a randomized clinical pilot trial

There is a worrying scarcity of drug options for patients with severe COVID-19. Glycine possesses anti-inflammatory, cytoprotective, endothelium-protective, and platelet-antiaggregant properties, so its use in these patients seems promising. In this open label, controlled clinical trial, inpatients with severe COVID-19 requiring mechanical ventilation randomly received usual care (control group) or usual care plus 0.5 g/kg/day glycine by the enteral route (experimental group). Major outcomes included mortality, time to weaning from mechanical ventilation, total time on mechanical ventilation, and time from study recruitment to death. Secondary outcomes included laboratory tests and serum cytokines. Patients from experimental (n = 33) and control groups (n = 23) did not differ in basal characteristics. There were no differences in mortality (glycine group, 63.6% vs control group, 52.2%, p = 0.60) nor in any other major outcome. Glycine intake was associated with lower fibrinogen levels, either evaluated per week of follow-up (p < 0.05 at weeks 1, 2, and 4) or as weighted mean during the whole hospitalization (608.7 ± 17.7 mg/dl vs control 712.2 ± 25.0 mg/dl, p = 0.001), but did not modify any other laboratory test or cytokine concentration. In summary, in severe COVID-19 glycine was unable to modify major clinical outcomes, serum cytokines or most laboratory tests, but was associated with lower serum fibrinogen concentration.Registration: ClinicalTrials.gov NCT04443673, 23/06/2020.

Amino Acid Metabolism and Atherosclerotic Cardiovascular Disease

Despite significant advances in medical treatments and drug development, atherosclerotic cardiovascular disease (ASCVD) remains a leading cause of death worldwide. Dysregulated lipid metabolism is a well-established driver of ASCVD. Unfortunately, even with potent lipid-lowering therapies, ASCVD-related deaths have continued to increase over the past decade, highlighting an incomplete understanding of the underlying risk factors and mechanisms of ASCVD. Accumulating evidence over the past decades indicates a correlation between amino acids and disease state. This review explores the emerging role of amino acid metabolism in ASCVD, uncovering novel potential biomarkers, causative factors, and therapeutic targets. Specifically, the significance of arginine and its related metabolites, homoarginine and polyamines, branched-chain amino acids, glycine, and aromatic amino acids, in ASCVD are discussed. These amino acids and their metabolites have been implicated in various processes characteristic of ASCVD, including impaired lipid metabolism, endothelial dysfunction, increased inflammatory response, and necrotic core development. Understanding the complex interplay between dysregulated amino acid metabolism and ASCVD provides new insights that may lead to the development of novel diagnostic and therapeutic approaches. Although further research is needed to uncover the precise mechanisms involved, it is evident that amino acid metabolism plays a role in ASCVD.

The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review

Functional decline of physiological systems during ageing leads to age-related diseases. Dietary glycine increases healthy lifespan in model organisms and might decrease inflammation in humans, suggesting its geroprotective potential. This review summarises the evidence of glycine administration on the characteristics of eleven physiological systems in adult humans. Databases were searched using key search terms: 'glycine', 'adult', 'supplementation'/ 'administration'/ 'ingestion'/ 'treatment'. Glycine was administered to healthy and diseased populations (18 and 34 studies) for up to 14 days and 4 months, respectively. The nervous system demonstrated the most positive effects, including improved psychiatric symptoms from longer-term glycine administration in psychiatric populations. While longer-term glycine administration improved sleep in healthy populations, these studies had small sample sizes with a high risk of bias. Larger and long-term studies with more robust study designs in healthy populations to examine the effects of glycine administration on preventing, delaying or reversing the ageing process are warranted.

Serine synthesis via reversed SHMT2 activity drives glycine depletion and acetaminophen hepatotoxicity in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects one-third of the global population. Understanding the metabolic pathways involved can provide insights into disease progression and treatment. Untargeted metabolomics of livers from mice with early-stage steatosis uncovered decreased methylated metabolites, suggesting altered one-carbon metabolism. The levels of glycine, a central component of one-carbon metabolism, were lower in mice with hepatic steatosis, consistent with clinical evidence. Stable-isotope tracing demonstrated that increased serine synthesis from glycine via reverse serine hydroxymethyltransferase (SHMT) is the underlying cause for decreased glycine in steatotic livers. Consequently, limited glycine availability in steatotic livers impaired glutathione synthesis under acetaminophen-induced oxidative stress, enhancing acute hepatotoxicity. Glycine supplementation or hepatocyte-specific ablation of the mitochondrial SHMT2 isoform in mice with hepatic steatosis mitigated acetaminophen-induced hepatotoxicity by supporting de novo glutathione synthesis. Thus, early metabolic changes in MASLD that limit glycine availability sensitize mice to xenobiotics even at the reversible stage of this disease.

Effects of soda water on blood lipid and metabolic profiling of urine in hyperlipidemia rats using UPLC/Triple-TOF MS

The effects of a natural soda water (Shi Han Quan, SHQ) on hyperlipidemia and the changes of urine metabolic profiling by metabolomics techniques were investigate. Thirty six Wistar rats weighing 160-200 g were divided into control group, hyperlipidemia (HL) group, and hyperlipidemia + SHQ water (SHQ) group. The metabolites in urine were determined using ultra high performance liquid chromatography-triple-time of flight-mass spectrometry (UPLC/Triple-TOF MS). At the end of 1 month and 3 months, the total glyceride (TG) level was significantly lower in SHQ group compared to HL group. There was no significantly difference in total cholesterol (TC) levels in HL group compared with SHQ group. The results showed that dinking SHQ water can improve the TG, but with no effects on TC. After drinking SHQ water for 3 months, the rats in different groups could be classified into different clusters according to the metabolites in urine. Total 15 important metabolites were found and correlated with disturbance of amino acid, phospholipid, fatty acid and vitamin metabolism, which suggested the changes of metabolism in the body and possible mechanism by which SHQ improved the TG. These findings provide a new insight for the prevention and control of hyperlipidemia.

Effect of L-serine on oxidative stress markers in the kidney of streptozotocin-induced diabetic mice

Oxidative stress is critical in the occurrence and development of diabetes and its related complications. L-serine has recently been shown to reduce oxidative stress, the incidence of autoimmune diabetes and improve glucose homeostasis. The aim of this study was to investigate the effects of daily L-serine administration on blood glucose, renal function and oxidative stress markers in the kidney of streptozotocin-induced diabetic mice. Eighteen C57BL/6 male mice were randomly divided into three groups (n = 6 per group). Streptozotocin was used to induce diabetes and a group of diabetic mice was treated with 280 mg/day of L-serine dissolved in drinking water for 4 weeks. The level of blood glucose, biochemical markers of renal function (total protein, urea, creatinine and albumin) and oxidative stress markers (protein carbonyls, malondialdehyde, glutathione peroxidase, superoxide dismutase and catalase) were measured using spectrophotometry. The results indicated that L-serine significantly decreased the glucose level in diabetic mice (188.6 ± 22.69 mg/dL, P = 0.02). Moreover, treatment of diabetic mice with L-serine reduced protein carbonyls (3.249 ± 0.9165 nmol/mg protein, P < 0.05) and malondialdehyde levels (1.891 ± 0.7696 μM/mg protein, P = 0.051). However, L-serine showed no significant effects on renal function, and a slight reduction in histopathological changes was observed in mice receiving L-serine. This study revealed that L-serine effectively ameliorates oxidative stress in kidney tissue and reduces the blood glucose concentration in diabetic mice.

Glycine and aging: Evidence and mechanisms

The restriction of calories, branched-chain amino acids, and methionine have all been shown to extend lifespan in model organisms. Recently, glycine was shown to significantly boost longevity in genetically heterogenous mice. This simple amino acid similarly extends lifespan in rats and improves health in mammalian models of age-related disease. While compelling data indicate that glycine is a pro-longevity molecule, divergent mechanisms may underlie its effects on aging. Glycine is abundant in collagen, a building block for glutathione, a precursor to creatine, and an acceptor for the enzyme Glycine N-methyltransferase (GNMT). A review of the literature strongly implicates GNMT, which clears methionine from the body by taking a methyl group from S-adenosyl-L-methionine and methylating glycine to form sarcosine. In flies, Gnmt is required for reduced insulin/insulin-like growth factor 1 signaling and caloric restriction to fully extend lifespan. The geroprotector spermidine requires Gnmt to upregulate autophagy genes and boost longevity. Moreover, the overexpression of Gnmt is sufficient to extend lifespan and reduce methionine levels. Sarcosine, or methylglycine, declines with age in multiple species and is capable of inducing autophagy both in vitro and in vivo. Taken all together, existing evidence suggests that glycine prolongs life by mimicking methionine restriction and activating autophagy.

Fatty liver-mediated glycine restriction impairs glutathione synthesis and causes hypersensitization to acetaminophen

Non-alcoholic fatty liver disease (NAFLD) affects nearly one third of the population worldwide. Understanding metabolic pathways involved can provide insights into disease progression. Untargeted metabolomics of livers from mice with early-stage steatosis indicated a decrease in methylated metabolites suggesting altered one carbon metabolism. The levels of glycine, a central component of one carbon metabolism, were lower in steatotic mice, in line with clinical evidence. Isotope tracing studies demonstrated that increased synthesis of serine from glycine is the underlying cause for glycine limitation in fatty livers. Consequently, the low glycine availability in steatotic livers impaired glutathione (GSH) synthesis under oxidative stress induced by acetaminophen (APAP), enhancing hepatic toxicity. Glycine supplementation mitigated acute liver damage and overall toxicity caused by APAP in fatty livers by supporting de novo GSH synthesis. Thus, early metabolic changes in NAFLD that lead to glycine depletion sensitize mice to xenobiotic toxicity even at a reversible stage of NAFLD.

Characterization of zearalenone-induced hepatotoxicity and its mechanisms by transcriptomics in zebrafish model

Zearalenone is a mycotoxin produced by several species of Fusarium fungi, which contaminates crop and cereal products worldwide. It is widely distributed and can be transported from agricultural fields to the aquatic environment via soil run-off. Zearalenone exposure can cause serious health problems to humans and animals, including estrogenic, immunotoxic, and xenogenic effects. Though its hepatotoxicity has been reported by few studies, the underlying mechanisms are yet to be investigated. This study aimed to comprehensively evaluate the hepatotoxic effects of zearalenone and its molecular mechanism in the zebrafish model system. First, we found zearalenone exposure can cause liver injury, as evidenced by reduced liver size, decreased liver-specific fluorescence, increased aspartate aminotransferase (AST) activity, delayed yolk sac absorption and lipid accumulation. Then, RNA sequencing (RNA-seq) was performed using dissected zebrafish fry liver, which found genes involved in oxidation and reduction were significantly enriched. Quantitative real-time PCR further confirmed the dysregulated expression of several antioxidant enzymes. Additionally, lipid peroxidation was proved by increased malondialdehyde (MDA) production and gene expression at the mRNA level. In contrast to the previous study, apoptosis was likely decreased in response to zearalenone exposure. Last, glucuronidation and amino acid metabolism were also disrupted by zearalenone. Our results revealed the complex mechanism of zearalenone-induced hepatotoxicity, which is a valuable contribution to a more comprehensive understanding of the toxicity of zearalenone.

NMR-Based Metabolomic Analysis of Cardiac Tissues Clarifies Molecular Mechanisms of CVB3-Induced Viral Myocarditis and Dilated Cardiomyopathy

Viral myocarditis (VMC), which is defined as inflammation of the myocardium with consequent myocardial injury, may develop chronic disease eventually leading to dilated cardiomyopathy (DCM). Molecular mechanisms underlying the progression from acute VMC (aVMC), to chronic VMC (cVMC) and finally to DCM, are still unclear. Here, we established mouse models of VMC and DCM with Coxsackievirus B3 infection and conducted NMR-based metabolomic analysis of aqueous metabolites extracted from cardiac tissues of three histologically classified groups including aVMC, cVMC and DCM. We showed that these three pathological groups were metabolically distinct from their normal counterparts and identified three impaired metabolic pathways shared by these pathological groups relative to normal controls, including nicotinate and nicotinamide metabolism; alanine, aspartate and glutamate metabolism; and D-glutamine and D-glutamate metabolism. We also identified two extra impaired metabolic pathways in the aVMC group, including glycine, serine and threonine metabolism; and taurine and hypotaurine metabolism Furthermore, we identified potential cardiac biomarkers for metabolically distinguishing these three pathological stages from normal controls. Our results indicate that the metabolomic analysis of cardiac tissues can provide valuable insights into the molecular mechanisms underlying the progression from acute VMC to DCM.

A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage

Glycine and cysteine are non-essential amino acids that are required to generate glutathione, an intracellular tripeptide that neutralizes reactive oxygen species and prevents tissue damage. During aging glutathione demand is thought to increase, but whether additional dietary intake of glycine and cysteine contributes towards the generation of glutathione in healthy older adults is not well understood. We investigated supplementation with glycine and n-acetylcysteine (GlyNAC) at three different daily doses for 2 weeks (low dose: 2.4 g, medium dose: 4.8 g, or high dose: 7.2 g/day, 1:1 ratio) in a randomized, controlled clinical trial in 114 healthy volunteers. Despite representing a cohort of healthy older adults (age mean = 65 years), we found significantly higher baseline levels of markers of oxidative stress, including that of malondialdehyde (MDA, 0.158 vs. 0.136 µmol/L, p < 0.0001), total cysteine (Cysteine-T, 314.8 vs. 276 µM, p < 0.0001), oxidized glutathione (GSSG, 174.5 vs. 132.3 µmol/L, p < 0.0001), and a lower ratio of reduced to oxidized glutathione (GSH-F:GSSG) (11.78 vs. 15.26, p = 0.0018) compared to a young reference group (age mean = 31.7 years, n = 20). GlyNAC supplementation was safe and well tolerated by the subjects, but did not increase levels of GSH-F:GSSG (end of study, placebo = 12.49 vs. 7.2 g = 12.65, p-value = 0.739) or that of total glutathione (GSH-T) (end of study, placebo = 903.5 vs. 7.2 g = 959.6 mg/L, p-value = 0.278), the primary endpoint of the study. Post-hoc analyses revealed that a subset of subjects characterized by high oxidative stress (above the median for MDA) and low baseline GSH-T status (below the median), who received the medium and high doses of GlyNAC, presented increased glutathione generation (end of study, placebo = 819.7 vs. 4.8g/7.2 g = 905.4 mg/L, p-value = 0.016). In summary GlyNAC supplementation is safe, well tolerated, and may increase glutathione levels in older adults with high glutathione demand.

Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT05041179, NCT05041179.

The Effects of Fenugreek Extract on Growth Performance, Serum Biochemical Indexes, Immunity and NF-κB Signaling Pathway in Broiler

In order to study the regulation of Fenugreek seed extract (FSE) on the immunity of broilers, and explore the appropriate amount of FSE in broilers' production, 1-day-old yellow feather broilers with a total of 420 birds were randomly allocated into seven treatments. Each treatment had six replicates, with 10 birds per replicate. The two control groups were the basic fodder group fed with basal diet and the bacitracin zinc group added 30 mg/kg bacitracin zinc to the basal diet. Experimental groups included five levels of FSE (50, 100, 200, 400, and 800 mg/kg FSE to the basal diet, respectively). The pre-test period was 7 days and the formal test lasted for 56 days. The results showed that the average daily gain (ADG) of 50 and 800 mg/kg FSE groups was significantly increased (P < 0.01), and the feed to gain ratio (F/G) of FSE groups was significantly decreased (P < 0.01) compared with the basic fodder and the bacitracin zinc groups. Compared with the basic fodder group, the serum total cholesterol (TC) content in the FSE groups was significantly decreased (P < 0.05), the serum low density lipoprotein cholesterol (LDL-C) content of 50, 100, and 800 mg/kg FSE groups was significantly lower than that of the basic fodder group (P < 0.05). Compared with the basic fodder and bacitracin zinc groups, the serum immunoglobulins (IgG, IgM, IgA) content of 100 and 200 mg/kg FSE groups were significantly increased (P < 0.05). Compared with the bacitracin zinc group, the serum interleukins (IL-1, IL-10) content of 400 mg/kg FSE group were significantly increased (P ≤ 0.05), and the serum interferon-γ (IFN-γ) content of 100 and 200 mg/kg FSE groups was significantly increased (P < 0.05). Compared with the basic fodder group, the lower doses (0–400 mg/kg) of FSE had no significant effect on the mRNA expression of toll-like receptors 4/ myeloid differentiation factor 88/ nuclear factor-κB (TLR4/MyD88/NF-κB) signaling pathways (P > 0.05). The 800 mg/kg FSE treatment group significantly increased the expression levels of nuclear factor-κB (NF-κB) mRNA in the spleen of broilers (P < 0.05). The zinc bacitracin group significantly increased the expression levels of myeloid differentiation factor 88 (MyD88) and nuclear factor-κB (NF-κB) mRNA (P ≤ 0.05). The results showed that FSE could promote the secretion of immunoglobulins, regulate the body's cytokines, and have a positive effect on immunity in broilers. Furthermore, the recommended supplement of FSE is 100 mg/kg in the broiler diet.

Effects of glycine on metabolic syndrome components: a review

PURPOSE

Glycine is the simplest and major amino acid in humans. It is mainly generated in the liver and kidney and is used to produce collagen, creatine, glucose and purine. It is also involved in immune function, anti-inflammatory processes and anti-oxidation reactions. Here, we reviewed the current evidence supporting the role of glycine in the development and treatment of metabolic syndrome components.

METHODS

We searched Scopus, PubMed and EMBASE databases for papers concerning glycine and metabolic syndrome.

RESULTS

Available evidence shows that the amount of glycine synthesized in vivo is insufficient to meet metabolic demands in these species. Plasma glycine levels are lower in subjects with metabolic syndrome than in healthy individuals. Interventions such as lifestyle modification, exercise, weight loss, or drugs that improve manifestations of metabolic syndrome remarkably increase circulating glycine concentrations.

CONCLUSION

Glycine supplementation improves various components of metabolic syndrome including diabetes, obesity, hyperlipidemia and hypertension. In the future, the use of glycine may have a significant clinical impact on the treatment of patients with metabolic syndrome.

Induction of glutathione biosynthesis by glycine-based treatment mitigates atherosclerosis

Lower circulating levels of glycine are consistently reported in association with cardiovascular disease (CVD), but the causative role and therapeutic potential of glycine in atherosclerosis, the underlying cause of most CVDs, remain to be established. Here, following the identification of reduced circulating glycine in patients with significant coronary artery disease (sCAD), we investigated a causative role of glycine in atherosclerosis by modulating glycine availability in atheroprone mice. We further evaluated the atheroprotective potential of DT-109, a recently identified glycine-based compound with dual lipid/glucose-lowering properties. Glycine deficiency enhanced, while glycine supplementation attenuated, atherosclerosis development in apolipoprotein E-deficient (Apoe^−/−) mice. DT-109 treatment showed the most significant atheroprotective effects and lowered atherosclerosis in the whole aortic tree and aortic sinus concomitant with reduced superoxide. In Apoe^−/− mice with established atherosclerosis, DT-109 treatment significantly reduced atherosclerosis and aortic superoxide independent of lipid-lowering effects. Targeted metabolomics and kinetics studies revealed that DT-109 induces glutathione formation in mononuclear cells. In bone marrow-derived macrophages (BMDMs), glycine and DT-109 attenuated superoxide formation induced by glycine deficiency. This was abolished in BMDMs from glutamate-cysteine ligase modifier subunit-deficient (Gclm^−/-) mice in which glutathione biosynthesis is impaired. Metabolic flux and carbon tracing experiments revealed that glycine deficiency inhibits glutathione formation in BMDMs while glycine-based treatment induces de novo glutathione biosynthesis. Through a combination of studies in patients with CAD, in vivo studies using atherosclerotic mice and in vitro studies using macrophages, we demonstrated a causative role of glycine in atherosclerosis and identified glycine-based treatment as an approach to mitigate atherosclerosis through antioxidant effects mediated by induction of glutathione biosynthesis.

Gut barrier and microbiota changes with glycine and branched-chain amino acid supplementation in chronic haemodialysis patients

BACKGROUND

We have previously shown that glycine increases fat-free mass in chronic haemodialysis patients with features of malnutrition as compared with branched-chain amino acids (BCAAs). This multicentre randomized double-blind crossover study evaluates the impact of these amino acids on the gut barrier and microbiota.

METHODS

Haemodialysis patients were included if they had plasma albumin <38 g/L or weight loss >5% of dry body weight, and daily dietary intakes <30 kcal/kg and <1 g protein/kg. They consumed glycine or BCAA (7 g twice daily) for 4 months and underwent a 1 month washout period, before crossover of supplementations. Faecal microbiota (16S rRNA gene sequencing) and immunoglobulin A (IgA), serum levels of cytokines, surrogate markers of intestinal permeability, appetite mediators, and endocannabinoids were obtained at the start and end of each supplementation. Supplementations were compared by multiple mixed linear regression models, adjusted for age, sex, month of supplementation (0 and 4 in each period), and period (Period 1: first 4 months; Period 2: last 4 months). Microbiota comparisons were performed using principal coordinate analysis and permutational multivariate analysis of variance, Shannon diversity index estimate and analysis of composition of microbiomes analysis, and Wilcoxon tests.

RESULTS

We analysed 27 patients compliant to the supplementations. Multiple mixed linear regression models were significant only for interleukin-6 (P = 0.002), glucagon-like peptide 1 (P = 0.028), cholecystokinin (P = 0.021), and peptide YY (P = 0.002), but not for the other outcomes. The significant models did not show any impact of the type of supplementation (P < 0.05 in all models). Principal coordinate analysis and permutational multivariate analysis of variance (P = 0.0001) showed strong microbiota clustering by subject, but no effect of the amino acids. Bacterial alpha diversity and zero-radius operational taxonomic unit richness remained stable, whatever the supplementation. Lacticaseibacillus paracasei (0.030; Q1-Q3 0.008-0.078 vs. 0.004; Q1-Q3 0.001-0.070) and Bifidobacterium dentium (0.0247; Q1-Q3 0.002-0.191 vs. 0.003; Q1-Q3 0.001-0.086) significantly decreased with the BCAA supplementation.

CONCLUSIONS

The BCAA and glycine supplementations had no impact on the serum levels of cytokines, appetite mediators, intestinal permeability, endocannabinoids, or faecal IgA. Overall faecal microbiota composition and microbial diversity did not change with the glycine or BCAA supplementation but decreased the abundance of L. paracasei and B. dentium.

Circulating amino acids as fingerprints of visceral adipose tissue independent of insulin resistance: a targeted metabolomic research in women

Introduction: Although obesity and its biomarkers have been intensively studied, little is known about the metabolomic signature of visceral adiposity independent of insulin resistance that frequently accompanies increased levels of visceral fat. Our study aimed to investigate specific changes in amino acid (AA) levels as biomarkers of increased visceral adiposity independent of insulin resistance, in healthy subjects.

Methods: Forty-two adult women were included in this cross-sectional study. Serum samples were analyzed by AAs targeted metabolomics according to their visceral fat area (<100 cm2 and ≥100 cm2).

Results: By corrected t-test and supervised partial least-squares discriminant analysis (PLS-DA) we identified 4 AAs that were significantly higher in the group with higher visceral fat: proline (variable importance in the projection [VIP] predicted value: 1.97), tyrosine (VIP: 2.21), cysteine (VIP: 1.19), isoleucine (VIP: 1.04; p-values <0.05). Also, glycine was significantly lower in the group with higher visceral fat (VIP: 1.65; p-value <0.05). All AAs identified were associated with visceral fat independent of homeo-static model assessment for insulin resistance (p-value for regression coefficients <0.05).

Conclusion: Metabolic pathways that might be disrupted in persons with increased visceral fat are phenylalanine, tyrosine, and tryptophan biosynthesis; tyrosine metabolism; glycine, serine, and threonine metabolism; glyoxylate and dicarboxylate metabolism, and cysteine and methionine metabolism.

Dietary Supplementation with Glycine Enhances Intestinal Mucosal Integrity and Ameliorates Inflammation in C57BL/6J Mice with High-Fat Diet-Induced Obesity

BACKGROUND

Obesity, a major public health problem worldwide, is associated with dysfunction of the intestinal barrier. Glycine (Gly) has been reported to enhance the expression of tight-junction proteins in porcine enterocytes. It is unknown whether Gly can improve intestinal barrier integrity in obese mice.

OBJECTIVES

This study tested the hypothesis that Gly enhances the intestinal epithelial barrier by regulating endoplasmic reticulum (ER) stress-related signaling and mitigating inflammation in high-fat diet (HFD)-induced obese mice.

METHODS

Five-week-old male C57BL/6J mice were fed a normal-fat diet (ND; fat = 10% energy) or an HFD (fat = 60% energy) and received drinking water supplemented with 2% Gly or 2.37% l-alanine (Ala; isonitrogenous control) daily for 12 wk. Body weight gain and tissue weights, glucose tolerance and the activation of immune cells, as well as the abundances of tight-junction proteins, ER stress proteins, and apoptosis-related proteins in the jejunum and colon were determined. In addition, the body weights of naïve ND and HFD groups (nND and nHFD, respectively) were also recorded for comparison. Differences were analyzed statistically by ANOVA followed by the Duncan multiple-comparison test using SAS software.

RESULTS

Compared with ND-Ala, HFD-feeding resulted in enhanced macrophage (CD11b+ and F4/80+) infiltration and immune cell activation by 1.9- to 5.4-fold (P < 0.05), as well as the upregulation of ER stress sensor proteins (including phospho-inositol-requiring enzyme 1α and binding immunoglobulin protein) by 2.5- to 4.5-fold, the induction of apoptotic proteins by 1.5- to 3.2-fold, and decreased abundances of tight-junction proteins by 35%-65% (P < 0.05) in the intestine. These HFD-induced abnormalities were significantly ameliorated by Gly supplementation in the HFD-Gly group (P < 0.05). Importantly, Gly supplementation also significantly enhanced glucose tolerance (P < 0.05) by 1.5-fold without affecting the fat accumulation of HFD-induced obese mice.

CONCLUSIONS

Gly supplementation enhanced the intestinal barrier and ameliorated inflammation and insulin resistance in HFD-fed mice. These effects of Gly were associated with reduced ER stress-related apoptosis in the intestine of obese mice.

Extending lifespan by modulating the growth hormone/insulin-like growth factor-1 axis: coming of age

Progress made in the years of aging research have allowed the opportunity to explore potential interventions to slow aging and extend healthy lifespan. Studies performed in yeast, worms, flies and mice subjected to genetic and pharmacological interventions have given insight into the cellular and molecular mechanisms associated with longevity. Furthermore, it is now possible to effectively modulate pathways that slow aging at different stages of life (early life or at an adult age). Interestingly, interventions that extend longevity in adult mice have had sex-specific success, suggesting a potential link between particular pathways that modulate aging and sex. For example, reduction of the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis at an adult age extends lifespan preferentially in females. Moreover, several postnatal dietary interventions tested by the 'Intervention Testing Program (ITP)' from the National Institute of Aging (NIA) have shown that while pharmacological interventions like rapamycin affect the IGF-1/insulin pathway and preferentially extend lifespan in females; dietary compounds that target other cellular pathways are effective only in male mice-indicating mutually exclusive sex-specific pathways. Therefore, a combination of interventions that target non-overlapping aging-related pathways appears to be an effective approach to further extend healthy lifespan in both sexes. Here, we review the germline and postnatal mouse lines that target the GH/IGF-1 axis as a mechanism to extend longevity as well as the dietary compounds that tested positive in the NIA program to increase lifespan. We believe that the interventions reviewed in this paper could constitute feasible combinations for an extended healthy lifespan in both male and female mice.

The regulation of healthspan and lifespan by dietary amino acids

As a key macronutrient and source of essential macromolecules, dietary protein plays a significant role in health. For many years, protein-rich diets have been recommended as healthy due to the satiety-inducing and muscle-building effects of protein, as well as the ability of protein calories to displace allegedly unhealthy calories from fats and carbohydrates. However, clinical studies find that consumption of dietary protein is associated with an increased risk of multiple diseases, especially diabetes, while studies in rodents have demonstrated that protein restriction can promote metabolic health and even lifespan. Emerging evidence suggests that the effects of dietary protein on health and longevity are not mediated simply by protein quantity but are instead mediated by protein quality - the specific amino acid composition of the diet. Here, we discuss how dietary protein and specific amino acids including methionine, the branched chain amino acids (leucine, isoleucine, and valine), tryptophan and glycine regulate metabolic health, healthspan, and aging, with attention to the specific molecular mechanisms that may participate in these effects. Finally, we discuss the potential applicability of these findings to promoting healthy aging in humans.

Nutraceutical, Dietary, and Lifestyle Options for Prevention and Treatment of Ventricular Hypertrophy and Heart Failure

Although well documented drug therapies are available for the management of ventricular hypertrophy (VH) and heart failure (HF), most patients nonetheless experience a downhill course, and further therapeutic measures are needed. Nutraceutical, dietary, and lifestyle measures may have particular merit in this regard, as they are currently available, relatively safe and inexpensive, and can lend themselves to primary prevention as well. A consideration of the pathogenic mechanisms underlying the VH/HF syndrome suggests that measures which control oxidative and endoplasmic reticulum (ER) stress, that support effective nitric oxide and hydrogen sulfide bioactivity, that prevent a reduction in cardiomyocyte pH, and that boost the production of protective hormones, such as fibroblast growth factor 21 (FGF21), while suppressing fibroblast growth factor 23 (FGF23) and marinobufagenin, may have utility for preventing and controlling this syndrome. Agents considered in this essay include phycocyanobilin, N-acetylcysteine, lipoic acid, ferulic acid, zinc, selenium, ubiquinol, astaxanthin, melatonin, tauroursodeoxycholic acid, berberine, citrulline, high-dose folate, cocoa flavanols, hawthorn extract, dietary nitrate, high-dose biotin, soy isoflavones, taurine, carnitine, magnesium orotate, EPA-rich fish oil, glycine, and copper. The potential advantages of whole-food plant-based diets, moderation in salt intake, avoidance of phosphate additives, and regular exercise training and sauna sessions are also discussed. There should be considerable scope for the development of functional foods and supplements which make it more convenient and affordable for patients to consume complementary combinations of the agents discussed here. Research Strategy: Key word searching of PubMed was employed to locate the research papers whose findings are cited in this essay.

Glycine-based treatment ameliorates NAFLD by modulating fatty acid oxidation, glutathione synthesis, and the gut microbiome

Nonalcoholic fatty liver disease (NAFLD) including nonalcoholic steatohepatitis (NASH) has reached epidemic proportions with no pharmacological therapy approved. Lower circulating glycine is consistently reported in patients with NAFLD, but the causes for reduced glycine, its role as a causative factor, and its therapeutic potential remain unclear. We performed transcriptomics in livers from humans and mice with NAFLD and found suppression of glycine biosynthetic genes, primarily alanine-glyoxylate aminotransferase 1 (AGXT1). Genetic (Agxt1 -/- mice) and dietary approaches to limit glycine availability resulted in exacerbated diet-induced hyperlipidemia and steatohepatitis, with suppressed mitochondrial/peroxisomal fatty acid β-oxidation (FAO) and enhanced inflammation as the underlying pathways. We explored glycine-based compounds with dual lipid/glucose-lowering properties as potential therapies for NAFLD and identified a tripeptide (Gly-Gly-L-Leu, DT-109) that improved body composition and lowered circulating glucose, lipids, transaminases, proinflammatory cytokines, and steatohepatitis in mice with established NASH induced by a high-fat, cholesterol, and fructose diet. We applied metagenomics, transcriptomics, and metabolomics to explore the underlying mechanisms. The bacterial genus Clostridium sensu stricto was markedly increased in mice with NASH and decreased after DT-109 treatment. DT-109 induced hepatic FAO pathways, lowered lipotoxicity, and stimulated de novo glutathione synthesis. In turn, inflammatory infiltration and hepatic fibrosis were attenuated via suppression of NF-κB target genes and TGFβ/SMAD signaling. Unlike its effects on the gut microbiome, DT-109 stimulated FAO and glutathione synthesis independent of NASH. In conclusion, impaired glycine metabolism may play a causative role in NAFLD. Glycine-based treatment attenuates experimental NAFLD by stimulating hepatic FAO and glutathione synthesis, thus warranting clinical evaluation.

Identifying metabolomic profiles of inflammatory diets in postmenopausal women

BACKGROUND

We previously showed that a food-based empirical dietary inflammatory pattern (EDIP) score is associated with circulating inflammatory biomarkers. Metabolomic profiling of inflammatory diets may therefore provide insights on mechanisms contributing to disease etiology and prognosis. We aimed to elucidate metabolites associated with inflammatory diets among postmenopausal women, utilizing a robust study design that incorporates independent discovery and validation datasets.

METHODS

This baseline cross-sectional investigation evaluated associations between continuous EDIP scores calculated from food frequency questionnaires and 448 log-transformed plasma metabolites as outcomes in multivariable-adjusted linear regression analyses. Metabolites were measured with liquid chromatography tandem mass spectroscopy. Metabolite discovery was conducted among 1109 Women's Health Initiative (WHI) Hormone Therapy trial participants and results were replicated in an independent dataset of 810 WHI Observational Study participants. Secondary analyses were stratified by standard body mass index (BMI, kg/m2) categories. In discovery and replication datasets statistical significance was based on false-discovery rate adjusted P < 0.05.

RESULTS

After adjusting for energy intake, BMI, physical activity, and other confounding variables, 23 metabolites were significantly associated with EDIP score in the discovery dataset. Of these, the following ten were replicated: trigonelline, caffeine, acethylamino-6-amino-3-methyluracil, 7-methylxanthine, 1,7-dimethyluric acid, 3-methylxanthine, C18:3CE, glycine, associated with lower dietary inflammatory potential; whereas C52:3 triacylglycerol and linoleate associated with higher dietary inflammatory potential. Four of the ten were associated [glycine (inversely), caffeine, 1,7-dimethyluric acid, C52:3 triacylglycerol, (positively)], with C-reactive protein levels. In secondary analyses, associations showed differences by BMI category. Four metabolites, related to coffee/caffeine metabolism were inversely associated among normal weight women, and 83 metabolites associated with EDIP among overweight/obese women, including 40 (48%) that were also associated with C-reactive protein.

CONCLUSION

Metabolites associated with coffee/caffeine and lipid metabolism may reflect the inflammatory potential of diet. Potential differences by BMI and the linkage to disease outcomes, require further study.

Dissociation of Adaptive Thermogenesis from Glucose Homeostasis in Microbiome-Deficient Mice

Recent studies suggest that a key mechanism whereby the gut microbiome influences energy balance and glucose homeostasis is through the recruitment of brown and beige adipocytes, primary mediators of the adaptive thermogenic response. To test this, we assessed energy expenditure and glucose metabolism in two complementary mouse models of gut microbial deficiency, which were exposed to a broad range of thermal and dietary stresses. Neither ablation of the gut microbiome, nor the substantial microbial perturbations induced by cold ambient temperatures, influenced energy expenditure during cold exposure or high-fat feeding. Nevertheless, we demonstrated a critical role for gut microbial metabolism in maintaining euglycemia through the production of amino acid metabolites that optimized hepatic TCA (tricarboxylic acid) cycle fluxes in support of gluconeogenesis. These results distinguish the dispensability of the gut microbiome for the regulation of energy expenditure from its critical contribution to the maintenance of glucose homeostasis.

Triterpenoid Saponins from Anemone flaccida Suppress Tumor Cell Proliferation by Regulating MAPK, PD1/PDL1, and STAT3 Signaling Pathways and Altering Cancer Metabolism

Purpose

Natural triterpenoid saponins isolated from Anemone flaccida Fr. Schmidt have exhibited anti-cancer properties and exerted remarkable inhibitory effects on tumor growth. Herein, we investigated the potential mechanism involved in the suppression of hepatocellular carcinoma (HCC) development by triterpenoid saponins in a mouse model.

Methods

An HCC model was established in H22 tumor-bearing mice and triterpenoid saponins were administered at various doses. Immunofluorescence, flow cytometry, and western blot were performed to analyze the effect of triterpenoid saponins on immune response in tumor tissues. Metabolomic analysis was carried out to assess the metabolites involved in mediating the effect of triterpenoid saponins on tumor tissues.

Results

Triterpenoid saponins induced anti-tumor immune response by decreasing the number of Treg cells, increasing that of B cells, natural killer cells, and CD3⁺/CD28⁺ T cells, and reducing the secretion of inflammatory factors including nuclear factor-κB, cyclooxygenase-2, and microsomal prostaglandin E synthase-1. In addition, triterpenoid saponins inhibited tumor growth and induced the apoptosis of HCC cells by blocking the activation of PD1/PD-L1, ERK1/2, p38 MAPK, JNK, and STAT3 signaling pathways. Furthermore, triterpenoid saponins regulated tumor immune response by upregulating a number of metabolites (including 1,3-diaminopropane, lauric acid, 2,4-diaminobutyric acid 2, and ribitol) and modulating the metabolism of histidine, arginine, proline, beta-alanine, glycine, serine, and threonine.

Conclusion

The findings suggested that triterpenoid saponins interfered with multiple signaling cascades involved in tumorigenesis and tumor metabolism and have potential applications in HCC therapy.

Metabolomics profiles associated with HbA1c levels in patients with type 2 diabetes

Glycated hemoglobin (HbA1c) is an indicator of the average blood glucose concentration. Failing to control HbA1c levels can accelerate the development of complications in patients with diabetes. Although metabolite profiles associated with HbA1c level in diabetes patients have been characterized using different platforms, more studies using high-throughput technology will be helpful to identify additional metabolites related to diabetes. Type 2 diabetes (T2D) patients were divided into two groups based on the HbA1c level: normal (HbA1c ≤6%) and high (HbA1c ≥9%) in both discovery and replication sets. A targeted metabolomics approach was used to quantify serum metabolites and multivariate logistic regression was used to identify significant differences between groups. The concentrations of 22 metabolites differed significantly between the two groups in the discovery set. In the replication set, the levels of 21 metabolites, including 16 metabolites identified in the discovery set, differed between groups. Among these, concentrations of eleven amino acids and one phosphatidylcholine (PC), lysoPC a C16:1, were higher and four metabolites, including three PCs (PC ae C36:1, PC aa C26:0, PC aa C34:2) and hexose, were lower in the group with normal HbA1c group than in the group with high HbA1c. Metabolites with high concentrations in the normal HbA1c group, such as glycine, valine, and PCs, may contribute to reducing HbA1c levels in patients with T2D. The metabolite signatures identified in this study provide insight into the mechanisms underlying changes in HbA1c levels in T2D.

Glycine Supplementation Ameliorates Retinal Neuronal Damage in an Experimental Model of Diabetes in Rats: A Light and Electron Microscopic Study

Purpose

To investigate the potential neuroprotective effect of glycine supplementation on the retinal ultrastructure of streptozocin (STZ)-induced diabetic rats.

Methods

Adult male Wistar rats weighing 200–250 g (n = 40) were randomly divided into four groups of 10 each: normal group (C), glycine + normal group (G), STZ group (D), and glycine + STZ group (DG). The G and DG groups received glycine (130 mM and 1% w/v) freely in their drinking water seven days after the induction of diabetes for up to 16 weeks. Retinal samples for histopathology were examined using light and electron microscopy.

Results

Diabetes-induced histological changes were attenuated in the retinas of rats in the DG group. The ultrastructural alterations produced by experimental diabetes in the inner nuclear layer, outer nuclear layer, and ganglion cell layer were significantly ameliorated by glycine supplementation.

Conclusion

Our findings suggest that glycine supplementation effectively attenuates retinal neuronal damage in experimental diabetic rats, and thus may be a potential candidate to protect retinal ultrastructure against diabetes.

Glycine supplementation extends lifespan of male and female mice

Diets low in methionine extend lifespan of rodents, though through unknown mechanisms. Glycine can mitigate methionine toxicity, and a small prior study has suggested that supplemental glycine could extend lifespan of Fischer 344 rats. We therefore evaluated the effects of an 8% glycine diet on lifespan and pathology of genetically heterogeneous mice in the context of the Interventions Testing Program. Elevated glycine led to a small (4%-6%) but statistically significant lifespan increase, as well as an increase in maximum lifespan, in both males (p = 0.002) and females (p < 0.001). Pooling across sex, glycine increased lifespan at each of the three independent sites, with significance at p = 0.01, 0.053, and 0.03, respectively. Glycine-supplemented females were lighter than controls, but there was no effect on weight in males. End-of-life necropsies suggested that glycine-treated mice were less likely than controls to die of pulmonary adenocarcinoma (p = 0.03). Of the 40 varieties of incidental pathology evaluated in these mice, none were increased to a significant degree by the glycine-supplemented diet. In parallel analyses of the same cohort, we found no benefits from TM5441 (an inhibitor of PAI-1, the primary inhibitor of tissue and urokinase plasminogen activators), inulin (a source of soluble fiber), or aspirin at either of two doses. Our glycine results strengthen the idea that modulation of dietary amino acid levels can increase healthy lifespan in mice, and provide a foundation for further investigation of dietary effects on aging and late-life diseases.

Glycine promotes longevity in Caenorhabditis elegans in a methionine cycle-dependent fashion

The deregulation of metabolism is a hallmark of aging. As such, changes in the expression of metabolic genes and the profiles of amino acid levels are features associated with aging animals. We previously reported that the levels of most amino acids decline with age in Caenorhabditis elegans (C. elegans). Glycine, in contrast, substantially accumulates in aging C. elegans. In this study we show that this is coupled to a decrease in gene expression of enzymes important for glycine catabolism. We further show that supplementation of glycine significantly prolongs C. elegans lifespan, and early adulthood is important for its salutary effects. Moreover, supplementation of glycine ameliorates specific transcriptional changes that are associated with aging. Glycine feeds into the methionine cycle. We find that mutations in components of this cycle, methionine synthase (metr-1) and S-adenosylmethionine synthetase (sams-1), completely abrogate glycine-induced lifespan extension. Strikingly, the beneficial effects of glycine supplementation are conserved when we supplement with serine, which also feeds into the methionine cycle. RNA-sequencing reveals a similar transcriptional landscape in serine- and glycine-supplemented worms both demarked by widespread gene repression. Taken together, these data uncover a novel role of glycine in the deceleration of aging through its function in the methionine cycle.

Interorgan Metabolic Crosstalk in Human Insulin Resistance

Excessive energy intake and reduced energy expenditure drive the development of insulin resistance and metabolic diseases such as obesity and type 2 diabetes mellitus. Metabolic signals derived from dietary intake or secreted from adipose tissue, gut, and liver contribute to energy homeostasis. Recent metabolomic studies identified novel metabolites and enlarged our knowledge on classic metabolites. This review summarizes the evidence of their roles as mediators of interorgan crosstalk and regulators of insulin sensitivity and energy metabolism. Circulating lipids such as free fatty acids, acetate, and palmitoleate from adipose tissue and short-chain fatty acids from the gut effectively act on liver and skeletal muscle. Intracellular lipids such as diacylglycerols and sphingolipids can serve as lipotoxins by directly inhibiting insulin action in muscle and liver. In contrast, fatty acid esters of hydroxy fatty acids have been recently shown to exert a series of beneficial effects. Also, ketoacids are gaining interest as potent modulators of insulin action and mitochondrial function. Finally, branched-chain amino acids not only predict metabolic diseases, but also inhibit insulin signaling. Here, we focus on the metabolic crosstalk in humans, which regulates insulin sensitivity and energy homeostasis in the main insulin-sensitive tissues, skeletal muscle, liver, and adipose tissue.

Autocatalytic cycle in the pathogenesis of diabetes mellitus: biochemical and pathophysiological aspects of metabolic therapy with natural amino acids on the example of glycine

In this work systematization (classification) of biochemical and physiological processes that cause disorders in the human body during the development of diabetes mellitus is carried out. The development of the disease is considered as the interaction and mutual reinforcement of two groups of parallel processes. The first group has a molecular nature and it is associated with impairment of ROS-regulation system which includes NADPH oxidases, RAGE receptors, mitochondria, cellular peroxireductase system and the immune system. The second group has a pathophysiological nature and it is associated with impairment of microcirculation and liver metabolism. The analysis of diabetes biochemistry based on different published references yields a creation of a block diagram evaluating the disease development over time. Two types of autocatalytic processes were identified: autocatalysis in the cascade of biochemical reactions and "cross-section" catalysis, in which biochemical and pathophysiological processes reinforce each other. The developed model has shown the possibility of using pharmacologically active natural metabolite glycine as a medicine inhibiting the development of diabetes. Despite the fact that glycine is a substitute amino acid the drop in the glycine blood concentration occurs even in the early stages of diabetes development and can aggravate the disease. It is shown that glycine is a potential blocker of key autocatalytic cycles, including biochemical and pathophysiological processes. The analysis of the glycine action based on the developed model is in complete agreement with the results of clinical trials in which glycine has improved blood biochemistry of diabetic patients and thereby it prevents the development of diabetic complications.

The study of the serum level of IL-4, TGF-β, IFN-γ, and IL-6 in overweight patients with and without diabetes mellitus and hypertension

BACKGROUND

Obesity increases the risk of diabetes mellitus (DM) and hypertension. We aimed to analyze the serum levels of cytokines that have relevance to the pathologies including, interleukin-4 (IL-4), transforming growth factor-β (TGF-β), interferon-γ (IFN-γ), and IL-6 cytokines of overweight men with DM and/or hypertension.

METHODS

The study collected serum from 164 men. The sample population contained, 54 overweight men without DM or hypertension (control [CTL] group), 36 men with both DM and hypertension (DH group), 20 men with DM but no hypertension (D group), and 54 had hypertension without DM (H).

RESULTS

The main results showed that the concentration of IFN-γ in the DH group was significantly higher than the D, H, and CTL groups, IL-6 in DH and D groups was significantly lower than the CTL group. The serum level of TGF-β and IL-4 cytokines did not show any significant differences across the four groups. Serum levels of IL-6 were also significantly lower in untreated patients in D group than controls and in DH when compared with H groups.

CONCLUSION

In conclusion, it appears that the proinflammatory and anti-inflammatory cytokines either play a significant role in the pathogenesis of hypertension and DM or serve as markers for these pathologies. Accordingly, increased serum levels of IFN-γ may participate in the pathogenesis of hypertension in the diabetic patients and decreased IL-6 is associated with type 2 DM.

Toll-Like Receptor 2 (TLR-2) Gene Polymorphisms in Type 2 Diabetes Mellitus

Objective

Innate immunity factors are associated with type 2 diabetes (T2DM) and its complications. Therefore, T2DM has been suggested to be an immune-dependent disease. Elevated fasting glucose level and higher concentrations of innate immunity soluble molecules are not only related with insulin resistance, but inflammation is also an important factor in beta cell dysfunction in T2DM. Toll-like receptor 2 (TLR-2), which has an important role in inducing innate immune cells, is thought to have suppressive roles on immune responses in T2DM. We therefore aimed to investigate the possible role of TLR-2 del -196-174 and Arg753Gln variants in T2DM pathogenesis.

Materials and Methods

This study was designed as a case-control study. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used to genotype the two variants in 100 T2DM patients and 98 age- matched controls.

Results

We found significantly higher frequencies of TLR-2 del -196-174 DD genotype (P=0.003), ID genotype (P=0.009) and D allele (P=0.001) in patients compared with controls. In addition, the II genotype (P=0.001) and the I allele (P=0.003) frequencies were elevated in healthy controls. We did not find any significant differences in frequency distribution for the Arg753Gln variant in study groups.

Conclusion

We suggest that carrying the D allele of the TLR-2 del -196-174 variant may be related as a risk factor for T2DM.

Effect of oral glycine on the clinical, spirometric and inflammatory status in subjects with cystic fibrosis: a pilot randomized trial

Background

Patients with cystic fibrosis (CF) have airway inflammation that contributes to symptoms and to pulmonary function derangement. Current drugs used to diminish airway inflammation improve the clinical and spirometric status of patients with CF, but their use is limited due to their undesired side effects, for example, glucose intolerance, growth retardation, and cataracts with corticosteroids, gastrointestinal toxicity with ibuprofen, and macrolide resistance with azythromycin. Glycine is known to decrease activation of inflammatory cells, including alveolar macrophages and neutrophils, and is relatively inexpensive, palatable, and virtually devoid of untoward effects. These features make glycine a good candidate for antiinflammatory treatment of CF. Thus, we aimed to explore whether glycine can exert a beneficial effect in a population of patients with CF.

Methods

This was a randomized, double blinded, cross-over pilot clinical trial. Subjects with CF received, in random order, oral glycine (0.5 g/kg/day, dissolved in any liquid) and placebo (glass sugar), each during 8 weeks with an intermediate 2-week wash-out period.

Results

Thirteen subjects aged 6–23 years, 8 females, completed the two arms of the study. As compared with placebo, after glycine intake patients had better symptom questionnaire scores (p = 0.02), mainly regarding sputum features and dyspnea. While spirometric variables tended to decline during placebo intake, they remained stable or even increased during glycine treatment (p = 0.04 to p = 0.003). In this context, FEV₁ declined 8.6% after placebo and increased 9.7% at the end of the glycine period. Pulse oximetry improved after glycine intake (p = 0.04 vs. placebo). TNF-α in serum and IL-6 and G-CSF in sputum tended to decline at the end of the glycine period (p = 0.061, p = 0.068 and p = 0.04, respectively, vs placebo). Glycine was remarkably well tolerated.

Conclusions

The clinical, spirometric and inflammatory status of subjects with CF improved after just 8 weeks of glycine intake, suggesting that this amino acid might constitute a novel therapeutic tool for these patients. Thus, further studies are warranted.

Trial registration

www.clinicaltrials.gov, registration number: NCT01417481, date of registration: March 12, 2012.

Electronic supplementary material

The online version of this article (10.1186/s12890-017-0528-x) contains supplementary material, which is available to authorized users.

Dysregulated metabolic enzymes and metabolic reprogramming in cancer cells

Tumor cells carry various genetic and metabolic alterations, which directly contribute to their growth and malignancy. Links between metabolism and cancer are multifaceted. Metabolic reprogramming, such as enhanced aerobic glycolysis, mutations in the tricarboxylic acid (TCA) cycle metabolic enzymes, and dependence on lipid and glutamine metabolism are key characteristics of cancer cells. Understanding these metabolic alterations is crucial for development of novel anti-cancer therapeutic strategies. In the present review, the broad importance of metabolism in tumor biology is discussed, and the current knowledge on dysregulated metabolic enzymes involved in the vital regulatory steps of glycolysis, the TCA cycle, the pentose phosphate pathway, and lipid, amino acid, and mitochondrial metabolism pathways are reviewed.

Nutrient sensing in pancreatic islets: lessons from congenital hyperinsulinism and monogenic diabetes

Pancreatic beta cells sense changes in nutrients during the cycles of fasting and feeding and release insulin accordingly to maintain glucose homeostasis. Abnormal beta cell nutrient sensing resulting from gene mutations leads to hypoglycemia or diabetes. Glucokinase (GCK) plays a key role in beta cell glucose sensing. As one form of congenital hyperinsulinism (CHI), activating mutations of GCK result in a decreased threshold for glucose-stimulated insulin secretion and hypoglycemia. In contrast, inactivating mutations of GCK result in diabetes, including a mild form (MODY2) and a severe form (permanent neonatal diabetes mellitus (PNDM)). Mutations of beta cell ion channels involved in insulin secretion regulation also alter glucose sensing. Activating or inactivating mutations of ATP-dependent potassium (K_ATP ) channel genes result in severe but completely opposite clinical phenotypes, including PNDM and CHI. Mutations of the other ion channels, including voltage-gated potassium channels (K_v 7.1) and voltage-gated calcium channels, also lead to abnormal glucose sensing and CHI. Furthermore, amino acids can stimulate insulin secretion in a glucose-independent manner in some forms of CHI, including activating mutations of the glutamate dehydrogenase gene, HDAH deficiency, and inactivating mutations of K_ATP channel genes. These genetic defects have provided insight into a better understanding of the complicated nature of beta cell fuel-sensing mechanisms.

Impaired "Glycine"-mia in Type 2 Diabetes and Potential Mechanisms Contributing to Glucose Homeostasis

The onset and/or progression of type 2 diabetes (T2D) can be prevented if intervention is early enough. As such, much effort has been placed on the search for indicators predictive of prediabetes and disease onset or progression. An increasing body of evidence suggests that changes in plasma glycine may be one such biomarker. Circulating glycine levels are consistently low in patients with T2D. Levels of this nonessential amino acid correlate negatively with obesity and insulin resistance. Plasma glycine correlates positively with glucose disposal, and rises with interventions such as exercise and bariatric surgery that improve glucose homeostasis. A role for glycine in the regulation of glucose, beyond being a potential biomarker, is less clear, however. Dietary glycine supplementation increases insulin, reduces systemic inflammation, and improves glucose tolerance. Emerging evidence suggests that glycine, a neurotransmitter, also acts directly on target tissues that include the endocrine pancreas and the brain via glycine receptors and as a coligand for N-methyl-d-aspartate glutamate receptors to control insulin secretion and liver glucose output, respectively. Here, we review the current evidence supporting a role for glycine in glucose homeostasis via its central and peripheral actions and changes that occur in T2D.

Study of IL4-590C/T and IL6-174G/C Gene Polymorphisms in Type 2 Diabetic Patients With Chronic Kidney Disease in North Indian Population

To explore the associations between potential functional promoter polymorphisms in pro-inflammatory and anti-inflammatory (IL-4(-590C/T) and IL-6(-174G/C) cytokine genes, and kidney dysfunction in North Indian type 2 diabetic subjects with chronic kidney disease. A total of 150 subjects aged 25-75 year were included in this study. The glomerular filtration rate (GFR) and serum creatinine were estimated. PCR was performed to analyse genotype distribution in IL-4 (-590T/C) and IL-6 (-174G/C) among healthy, type 2 diabetic patients with or without CKD. The genotype distributions were determined by Hardy-Weinberg equilibrium. CKD patients showed lower GFR (59.36 ± 1.33 ml/min/1.73 m² ) and higher serum creatinine (1.93 ± 0.99% mg) level in comparison to diabetic patients without CKD and healthy subjects. Genotypic distribution of the different genotypes among the study groups in IL-4 gene was genotype CC = 30, TC = 12, and TT = 8 in CKD patients. In type 2 diabetic patients without CKD, genotype distribution was CC = 38, TC = 10, and TT = 2. In healthy subjects, distribution of genotype was CC = 35, TC = 14, and TT = 1. The distribution of different genotype among the study groups for IL-6 gene was GG = 27, GC = 20, and CC = 3 in healthy subjects; GG = 28, GC = 19, and CC = 3 in diabetic patients without CKD and GG = 38, GC = 11, and CC = 1 in diabetic patients with CKD. There was no significant difference in the distribution of genotype frequencies between healthy subjects and diabetic patients without CKD but a significant difference was found in diabetic patients with CKD. The functional promoter polymorphisms IL4-590C/T and IL6-174G/C, which affect the IL-4 and IL-6 levels in north Indian subjects, were associated with kidney dysfunction and CKD. J. Cell. Biochem. 118: 1803-1809, 2017. © 2016 Wiley Periodicals, Inc.

Influence of Amino Acids in Dairy Products on Glucose Homeostasis: The Clinical Evidence

Dairy products have been hypothesized to protect against type 2 diabetes because of their high content of whey proteins, rich in branched-chain amino acids (BCAAs) - leucine, isoleucine and valine - and lysine, which may decrease postprandial glucose responses and stimulate insulin secretion. Paradoxically, epidemiologic studies also show that higher levels of plasma BCAAs have been linked to insulin resistance and type 2 diabetes. Therefore, the objective was to review the recent clinical evidence concerning the intake of amino acids found in dairy proteins so as to determine their impact on glucose homeostasis in healthy persons and in those with prediabetes and type 2 diabetes. Clinical studies have reported that the major dairy amino acids, namely, leucine, isoleucine, glutamine, phenylalanine, proline and lysine, have beneficial effects on glucose homeostasis. Yet the reported doses of amino acids investigated are too elevated to be reached through adequate dairy product intake. The minor dairy amino acids, arginine and glycine, may improve glucose homeostasis by improving other risk factors for type 2 diabetes. Further, the combination of amino acids may also improve glucose-related outcomes, suggesting additive or synergistic effects. Nevertheless, additional long-term studies in individuals with prediabetes and type 2 diabetes are needed to ascertain the benefits for glucose homeostasis of amino acids found in dairy foods.

Inflammation, vitamin B6 and related pathways

The active form of vitamin B6, pyridoxal 5'-phosphate (PLP), serves as a co-factor in more than 150 enzymatic reactions. Plasma PLP has consistently been shown to be low in inflammatory conditions; there is a parallel reduction in liver PLP, but minor changes in erythrocyte and muscle PLP and in functional vitamin B6 biomarkers. Plasma PLP also predicts the risk of chronic diseases like cardiovascular disease and some cancers, and is inversely associated with numerous inflammatory markers in clinical and population-based studies. Vitamin B6 intake and supplementation improve some immune functions in vitamin B6-deficient humans and experimental animals. A possible mechanism involved is mobilization of vitamin B6 to the sites of inflammation where it may serve as a co-factor in pathways producing metabolites with immunomodulating effects. Relevant vitamin B6-dependent inflammatory pathways include vitamin B6 catabolism, the kynurenine pathway, sphingosine 1-phosphate metabolism, the transsulfuration pathway, and serine and glycine metabolism.

Toll-like receptor 2 and type 2 diabetes

Innate immunity plays a crucial role in the pathogenesis of type 2 diabetes and related complications. Since the toll-like receptors (TLRs) are central to innate immunity, it appears that they are important participants in the development and pathogenesis of the disease. Previous investigations demonstrated that TLR2 homodimers and TLR2 heterodimers with TLR1 or TLR6 activate innate immunity upon recognition of damage-associated molecular patterns (DAMPs). Several DAMPs are released during type 2 diabetes, so it may be hypothesized that TLR2 is significantly involved in its progression. Here, we review recent data on the important roles and status of TLR2 in type 2 diabetes and related complications.

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.