Effects of streptozotocin-induced diabetes and of insulin treatment on homocysteine metabolism in the rat

The functions of hydrogen sulfide on the urogenital system of both males and females: from inception to the present

Hydrogen sulfide (H2S) is known as a chemical gas in nature with both enzymatic and non-enzymatic biosynthesis in different human organs. A couple of studies have demonstrated the function of H2S in regulating the homeostasis of the human body. Additionally, they have shown its synthesis, measurement, chemistry, protective effects, and interaction in various aspects of scientific evidence. Furthermore, many researches have demonstrated the beneficial impacts of H2S on genital organs and systems. According to various studies, it is recognized that H2S-producing enzymes and the endogenous production of H2S are expressed in male and female reproductive systems in different mammalian species. The main goal of this comprehensive review is to assess the potential therapeutic impacts of this gasotransmitter in the male and female urogenital system and find underlying mechanisms of this agent. This narrative review investigated the articles that were published from the 1970s to 2022. The review's primary focus is the impacts of H2S on the male and female urogenital system. Medline, CINAHL, PubMed, and Google scholar databases were searched. Keywords used in this review were "Hydrogen sulfide," "H2S," "urogenital system," and "urogenital tract". Numerous studies have demonstrated the therapeutic and protective effects of sodium hydrosulfide (Na-HS) as an H2S donor on male and female infertility disorders. Furthermore, it has been observed that H2S plays a significant role in improving different diseases such as ameliorating sperm parameters. The specific localization of H2S enzymes in the urogenital system provides an excellent opportunity to comprehend its function and role in various disorders related to this system. It is noteworthy that H2S has been demonstrated to be produced in endocrine organs and exhibit diverse activities. Moreover, it is important to recognize that alterations in H2S biosynthesis are closely linked to endocrine disorders. Therefore, hormones can be pivotal in regulating H2S production, and H2S synthesis pathways may aid in establishing novel therapeutic strategies. H2S possesses pharmacological effects on essential disorders, such as anti-inflammation, anti-apoptosis, and anti-oxidant activities, which render it a valuable therapeutic agent for human urogenital disease. Furthermore, this agent shows promise in ameliorating the detrimental effects of various male and female diseases. Despite the limited clinical research, studies have demonstrated that applying H2S as an anti-oxidant source could ameliorate adverse effects of different conditions in the urogenital system. More clinical studies are required to confirm the role of this component in clinical settings.

Gut Microbial Genes and Metabolism for Methionine and Branched-Chain Amino Acids in Diabetic Nephropathy

Diabetic mellitus nephropathy (DMN) is a serious complication of diabetes and a major health concern. Although the pathophysiology of diabetes mellitus (DM) leading to DMN is uncertain, recent evidence suggests the involvement of the gut microbiome. This study aimed to determine the relationships among gut microbial species, genes, and metabolites in DMN through an integrated clinical, taxonomic, genomic, and metabolomic analysis. Whole-metagenome shotgun sequencing and nuclear magnetic resonance metabolomic analyses were performed on stool samples from 15 patients with DMN and 22 healthy controls. Six bacterial species were identified to be significantly elevated in the DMN patients after adjusting for age, sex, body mass index, and estimated glomerular filtration rate (eGFR). Multivariate analysis found 216 microbial genes and 6 metabolites (higher valine, isoleucine, methionine, valerate, and phenylacetate levels in the DMN group and higher acetate levels in the control group) that were differentially present between the DMN and control groups. Integrated analysis of all of these parameters and clinical data using the random-forest model showed that methionine and branched-chain amino acids (BCAAs) were among the most significant features, next to the eGFR and proteinuria, in differentiating the DMN group from the control group. Metabolic pathway gene analysis of BCAAs and methionine also revealed that many genes involved in the biosynthesis of these metabolites were elevated in the six species that were more abundant in the DMN group. The suggested correlation among taxonomic, genetic, and metabolic features of the gut microbiome would expand our understanding of gut microbial involvement in the pathogenesis of DMN and may provide potential therapeutic targets for DMN. IMPORTANCE Whole metagenomic sequencing uncovered specific members of the gut microbiota associated with DMN. The gene families derived from the discovered species are involved in the metabolic pathways of methionine and branched-chain amino acids. Metabolomic analysis using stool samples showed increased methionine and branched-chain amino acids in DMN. These integrative omics results provide evidence of the gut microbiota-associated pathophysiology of DMN, which can be further studied for disease-modulating effects via prebiotics or probiotics.

Melatonin as a Reducer of Neuro- and Vasculotoxic Oxidative Stress Induced by Homocysteine

The antioxidant properties of melatonin can be successfully used to reduce the effects of oxidative stress caused by homocysteine. The beneficial actions of melatonin are mainly due to its ability to inhibit the generation of the hydroxyl radical during the oxidation of homocysteine. Melatonin protects endothelial cells, neurons, and glia against the action of oxygen radicals generated by homocysteine and prevents the structural changes in cells that lead to impaired contractility of blood vessels and neuronal degeneration. It can be, therefore, assumed that the results obtained in experiments performed mainly in the in vitro models and occasionally in animal models may clear the way to clinical applications of melatonin in patients with hyperhomocysteinemia, who exhibit a higher risk of developing neurodegenerative diseases (e.g., Parkinson’s disease or Alzheimer’s disease) and cardiovascular diseases of atherothrombotic etiology. However, the results that have been obtained so far are scarce and have seldom been performed on advanced in vivo models. All findings predominately originate from the use of in vitro models and the scarcity of clinical evidence is huge. Thus, this mini-review should be considered as a summary of the outcomes of the initial research in the field concerning the use of melatonin as a possibly efficient attenuator of oxidative stress induced by homocysteine.

The Mechanisms of Type 2 Diabetes-Related White Matter Intensities: A Review

The continually increasing number of patients with type 2 diabetes is a worldwide health problem, and the incidence of microvascular complications is closely related to type 2 diabetes. Structural brain abnormalities are considered an important pathway through which type 2 diabetes causes brain diseases. In fact, there is considerable evidence that type 2 diabetes is associated with an increased risk of structural brain abnormalities such as lacunar infarcts (LIs), white matter hyperintensities (WMHs), and brain atrophy. WMHs are a common cerebral small-vessel disease in elderly adults, and it is characterized histologically by demyelination, loss of oligodendrocytes, and vacuolization as a result of small-vessel ischemia in the white matter. An increasing number of studies have found that diabetes is closely related to WMHs. However, the exact mechanism by which type 2 diabetes causes WMHs is not fully understood. This article reviews the mechanisms of type 2 diabetes-related WMHs to better understand the disease and provide help for better clinical treatment.

Co-administration of prazosin and propranolol with glibenclamide improves anti-oxidant defense system in endothelial tissue of streptozotocin-induced diabetic Wistar rats

Background Due to increasing prevalence of diabetes and associated endothelial dysfunction, this study was carried out to investigate the effects of co-administration of adrenoceptor blockers (prazosin and propranolol) and glibenclamide on plasma biomarkers of endothelial functions in diabetic rats. Methods Experiments were carried out on 35 male Wistar rats (170-200 g). They were divided into seven groups (n=5) as follows: normal control, diabetic control, diabetic + glibenclamide (GLB-5mg/kg/day), diabetic+ prazosin (PRZ-0.5 mg/kg/day), diabetic + PRZ + GLB, diabetic + propranolol (PRP-10 mg/kg/day), diabetes + PRP + GLB. Experimental diabetes was induced with streptozotocin (60 mg/kg) and drugs were administered orally for 3 weeks. Blood pressure was measured and animals were sacrificed afterwards. Blood samples were collected by cardiac puncture, and major marker of endothelial functions, nitric oxide derivatives (NOx), as well as superoxide dismutase (SOD) and malondialdehyde (MDA) were measured on the plasma. The aorta was harvested for histological examination. Data were subjected to descriptive statistics and analysed using ANOVA at α 0.05. Results There was a significant increase in levels of NOx and SOD, and a decrease in MDA level in diabetic treated groups compared to diabetic control. Mean blood pressure increased in diabetic control and diabetic + GLB group when compared with normal control, while it was mildly reduced in diabetic group treated with PRZ and PRP, and co-administered GLB. More so, Aorta histology was altered in diabetic control groups when compared with normal control and all diabetic treated groups. Conclusions Results from this study suggest that PRZ, PRP, and GLB (singly and in combined therapy) could have a restorative effect on endothelial functions in diabetes.

Regulation of carbohydrate metabolism by nitric oxide and hydrogen sulfide: Implications in diabetes

Nitric oxide (NO) and hydrogen sulfide (H₂S) are two gasotransmitters that are produced in the human body and have a key role in many of the physiological activities of the various organ systems. Decreased NO bioavailability and deficiency of H₂S are involved in the pathophysiology of type 2 diabetes and its complications. Restoration of NO levels have favorable metabolic effects in diabetes. The role of H₂S in pathophysiology of diabetes is however controversial; H₂S production is decreased during development of obesity, diabetes, and its complications, suggesting the potential therapeutic effects of H₂S. On the other hand, increased H₂S levels disturb the pancreatic β-cell function and decrease insulin secretion. In addition, there appear to be important interactions between NO and H₂S at the levels of both biosynthesis and signaling pathways, yet clear an insight into this relationship is lacking. H₂S potentiates the effects of NO in the cardiovascular system as well as NO release from its storage pools. Likewise, NO increases the activity and the expression of H₂S-generating enzymes. Inhibition of NO production leads to elimination/attenuation of the cardioprotective effects of H₂S. Regarding the increasing interest in the therapeutic applications of NO or H₂S-releasing molecules in a variety of diseases, particularly in the cardiovascular disorders, much is to be learned about their function in glucose/insulin metabolism, especially in diabetes. The aim of this review is to provide a better understanding of the individual and the interactive roles of NO and H₂S in carbohydrate metabolism.

Hydrogen sulfide-mediated regulation of cell death signaling ameliorates adverse cardiac remodeling and diabetic cardiomyopathy

The death of cardiomyocytes is a precursor for the cascade of hypertrophic and fibrotic remodeling that leads to cardiomyopathy. In diabetes mellitus (DM), the metabolic environment of hyperglycemia, hyperlipidemia, and oxidative stress causes cardiomyocyte cell death, leading to diabetic cardiomyopathy (DMCM), an independent cause of heart failure. Understanding the roles of the cell death signaling pathways involved in the development of cardiomyopathies is crucial to the discovery of novel targeted therapeutics and biomarkers for DMCM. Recent evidence suggests that hydrogen sulfide (H2S), an endogenous gaseous molecule, has cardioprotective effects against cell death. However, very little is known about signaling by which H2S and its downstream targets regulate myocardial cell death in the DM heart. This review focuses on H2S in the signaling of apoptotic, autophagic, necroptotic, and pyroptotic cell death in DMCM and other cardiomyopathies, abnormalities in H2S synthesis in DM, and potential H2S-based therapeutic strategies to mitigate myocardial cell death to ameliorate DMCM.

Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review

This report on vitamin B-12 (B12) is part of the Biomarkers of Nutrition for Development (BOND) Project, which provides state-of-the art information and advice on the selection, use, and interpretation of biomarkers of nutrient exposure, status, and function. As with the other 5 reports in this series, which focused on iodine, folate, zinc, iron, and vitamin A, this B12 report was developed with the assistance of an expert panel (BOND B12 EP) and other experts who provided information during a consultation. The experts reviewed the existing literature in depth in order to consolidate existing relevant information on the biology of B12, including known and possible effects of insufficiency, and available and potential biomarkers of status. Unlike the situation for the other 5 nutrients reviewed during the BOND project, there has been relatively little previous attention paid to B12 status and its biomarkers, so this report is a landmark in terms of the consolidation and interpretation of the available information on B12 nutrition. Historically, most focus has been on diagnosis and treatment of clinical symptoms of B12 deficiency, which result primarily from pernicious anemia or strict vegetarianism. More recently, we have become aware of the high prevalence of B12 insufficiency in populations consuming low amounts of animal-source foods, which can be detected with ≥1 serum biomarker but presents the new challenge of identifying functional consequences that may require public health interventions.

A Possible Mechanism: Vildagliptin Prevents Aortic Dysfunction through Paraoxonase and Angiopoietin-Like 3

The collected data have revealed the beneficial effects of dipeptidyl peptidase-4 (DPP-4) inhibitors on the vascular endothelium, including vildagliptin. However, the involved mechanisms are not yet clear. In this study, Sprague-Dawley rats were randomly divided into the following four groups: control, diabetic, diabetic + low-dose vildagliptin (10 mg/kg/d), and diabetic + high-dose vildagliptin (20 mg/kg/d). The diabetic model was created by feeding a high-fat diet for four weeks and injection of streptozotocin. Then, vildagliptin groups were given oral vildagliptin for twelve weeks, and the control and diabetic groups were given the same volume of saline. The metabolic parameters, endothelial function, and whole genome expression in the aorta were examined. After 12 weeks of treatment, vildagliptin groups showed significantly reduced blood glucose, blood total cholesterol, and attenuated endothelial dysfunction. Notably, vildagliptin may inhibit angiopoietin-like 3 (Angptl3) and betaine-homocysteine S-methyltransferase (Bhmt) expression and activated paraoxonase-1 (Pon1) in the aorta of diabetic rats. These findings may demonstrate the vasoprotective pathway of vildagliptin in vivo.

Hydrogen Sulfide and Glucose Homeostasis: A Tale of Sweet and the Stink

SIGNIFICANCE

Among many endogenous mediators, the gasotransmitter hydrogen sulfide (H₂S) plays an important role in the regulation of glucose homeostasis. In this article we discuss different functional roles of H₂S in several metabolic organs/tissues required in the maintenance of glucose homeostasis. Recent Advances: New evidence has emerged revealing the insulin sensitizing role of H₂S in adipose tissue and skeletal muscle biology. In addition, H₂S was demonstrated to be a potent stimulator of gluconeogenesis via the induction and stimulation of various glucose-producing pathways in the liver.

CRITICAL ISSUES

Similar to its other physiological effects, H₂S exhibits paradoxical characteristics in the regulation of glucose homeostasis: (1) H₂S stimulates glucose production via activation of gluconeogenesis and glycogenolysis in hepatocytes, yet inhibits lipolysis in adipocytes; (2) H₂S stimulates glucose uptake into adipocytes and skeletal muscle but inhibits glucose uptake into hepatocytes; (3) H₂S inhibits insulin secretion from pancreatic β cells, yet sensitizes insulin signaling and insulin-triggered response in adipose tissues and skeletal muscle. It is also unclear the impact H₂S may have on glucose metabolism and utilization by other vital organs, such as the brain.

FUTURE DIRECTIONS

Recent reports and ongoing studies lay the foundation for a general, although highly incomplete, understanding of the effect of H₂S on regulating glucose homeostasis. In this review, we describe the molecular mechanisms and physiological outcomes of the gasotransmitter H₂S on organs and tissues required for homeostatic maintenance of blood glucose. Future directions highlighting the H₂S-mediated homeostatic control of glucose metabolism under physiological and insulin-resistant conditions are also discussed. Antioxid. Redox Signal. 28, 1463-1482.

Inverse association between plasma homocysteine concentrations and type 2 diabetes mellitus among a middle-aged and elderly Chinese population

BACKGROUND AND AIMS

Plasma homocysteine concentrations have been reported to be associated with type 2 diabetes mellitus (T2DM) with controversial findings. The aim of the present study was to investigate the association between plasma homocysteine concentrations and T2DM.

METHODS AND RESULTS

A cross-sectional study including 19,085 eligible participants derived from the Dongfeng-Tongji cohort was conducted. Plasma homocysteine concentrations were measured by Abbott Architect i2000 Automatic analyzer and T2DM was defined according to American Diabetes Association criteria. Logistic regression model was used to explore the association between plasma homocysteine concentrations and T2DM. The prevalence of T2DM was 19.0% in the whole population (mean age 62.9 years), 21.8% in males, and 17.1% in females. In the multivariable logistic regression analyses, compared with those in the lowest quintile, the OR (95% CI) of T2DM was 1.05 (0.92-1.21), 0.99 (0.86-1.14), 0.90 (0.78-1.05), and 0.77 (0.66-0.90) for quintile 2 to quintile 5 of homocysteine concentrations after adjustment for potential confounders (P for trend < 0.0001). Homocysteine concentrations were associated with decreased T2DM prevalence risk (OR = 0.88 per SD increase of homocysteine concentration; 95% CI: 0.84-0.93). A significant interaction between homocysteine concentrations and drinking status on T2DM prevalence risk was observed (P for interaction = 0.03). The inverse association of plasma homocysteine concentrations with T2DM prevalence risk was observed in non-drinkers but not in current drinkers.

CONCLUSION

Plasma homocysteine concentrations were inversely correlated with T2DM among a middle-aged and elderly Chinese population.

Age-Related Changes in Sulfur Amino Acid Metabolism in Male C57BL/6 Mice

Alterations in sulfur amino acid metabolism are associated with an increased risk of a number of common late-life diseases, which raises the possibility that metabolism of sulfur amino acids may change with age. The present study was conducted to understand the age-related changes in hepatic metabolism of sulfur amino acids in 2-, 6-, 18- and 30-month-old male C57BL/6 mice. For this purpose, metabolite profiling of sulfur amino acids from methionine to taurine or glutathione (GSH) was performed. The levels of sulfur amino acids and their metabolites were not significantly different among 2-, 6- and 18-month-old mice, except for plasma GSH and hepatic homocysteine. Plasma total GSH and hepatic total homocysteine levels were significantly higher in 2-month-old mice than those in the other age groups. In contrast, 30-month-old mice exhibited increased hepatic methionine and cysteine, compared with all other groups, but decreased hepatic S-adenosylmethionine (SAM), S-adenosylhomocysteine and homocysteine, relative to 2-month-old mice. No differences in hepatic reduced GSH, GSH disulfide, or taurine were observed. The hepatic changes in homocysteine and cysteine may be attributed to upregulation of cystathionine β-synthase and down-regulation of γ-glutamylcysteine ligase in the aged mice. The elevation of hepatic cysteine levels may be involved in the maintenance of hepatic GSH levels. The opposite changes of methionine and SAM suggest that the regulatory role of SAM in hepatic sulfur amino acid metabolism may be impaired in 30-month-old mice.

Heat stress prevents the decrease in succinate dehydrogenase activity in the extensor digitorum longus of streptozotocin-induced diabetic rats

This study aimed to investigate whether heat stress (HS) prevents a decrease in succinate dehydrogenase (SDH) activity and heat shock protein 60 (HSP60) and superoxide dismutase 2 (SOD2) contents in the extensor digitorum longus of streptozotocin (STZ)-induced diabetic rats. Twelve-week-old male Wistar rats were assigned to one of the four groups (n=6/group): control (Con), HS, diabetes mellitus (DM), and diabetes mellitus and heat stress (DM+HS). Diabetes was induced by the administration of STZ (50 mg/kg). HS was initiated 7 days after STZ treatment and performed at 42 °C for 30 min 5 times a week for 3 weeks. SDH activity was decreased in the DM and DM+HS groups. However, SDH activity was greater in the DM+HS group than in the DM group. Although HSP60 content was lower in the DM group than in the Con group, it was maintained in the DM+HS groups and was higher than that in the DM group. SOD2 content was decreased only in the DM group. These findings suggest that HS prevents the decrease in SDH activity in the skeletal muscle induced by DM. According to this mechanism, the maintenance of SOD2 and HSP60 by HS may suppress the increase in oxidative stress.

Folic Acid Reduces Tau Phosphorylation by Regulating PP2A Methylation in Streptozotocin-Induced Diabetic Mice

High incidence rate of Alzheimer’s disease (AD) is observed in patients with type 2 diabetes. Aggregated β-amyloid (Aβ) and hyperphosphorylated tau are the hallmarks of AD. Hyperphosphorylated tau has been detected in diabetic animals as well as in diabetic patients. Folates mediate the transfer of one carbon unit, required in various biochemical reactions. The effect of folate on tau phosphorylation in diabetic models still remains unknown. In this study, we investigated the effect and mechanism of folic acid on hyperphosphorylation of tau in streptozotocin (STZ)-induced diabetic mice. Diabetic mice induced by STZ, at the age of 10 weeks, were administered with three levels of folic acid: folic acid-deficient diet, diet with normal folic acid content, and 120 μg/kg folic acid diet for 8 weeks. Levels of serum folate and blood glucose were monitored. Tau phosphorylation, protein phosphatase 2A (PP2A) methylation, and Glycogen synthase kinase 3β (GSK-3β) phosphorylation were detected using Western blot. The S-adenosyl methionine:S-adenosyl homocysteine ratio (SAM:SAH) in brain tissues was also determined. DNA methyltransferase (DNMT) mRNA expression levels were detected using real-time PCR. Folic acid reduced tau hyperphosphorylation at Ser396 in the brain of diabetes mellitus (DM) mice. In addition, PP2A methylation and DNMT1 mRNA expression were significantly increased in DM mice post folic acid treatment. GSK-3β phosphorylation was not regulated by folic acid administration. Folic acid can reduce tau phosphorylation by regulating PP2A methylation in diabetic mice. These results support that folic acid can serve as a multitarget neuronal therapeutic agent for treating diabetes-associated cognitive dysfunction.

Epigenetics in type 1 diabetes: TNFa gene promoter methylation status in Chilean patients with type 1 diabetes mellitus

TNF-α is a pro-inflammatory cytokine that is involved in type 1 diabetes (T1D) pathogenesis. The TNFa gene is subject of epigenetic regulation in which folate and homocysteine are important molecules because they participate in the methionine cycle where the most important methyl group donor (S-adenosylmethionine) is formed. We investigated whether TNFa gene promoter methylation status in T1D patients was related to blood folate, homocysteine and TNF-α in a transversal case-control study. We studied T1D patients (n 25, mean=13·7 years) and healthy control subjects (n 25, mean=31·1 years), without T1D and/or other autoimmune diseases or direct family history of these diseases. A blood sample was obtained for determination of serum folate, plasma homocysteine and TNF-α concentrations. Whole blood was used for the extraction of DNA to determine the percentage of methylation by real-time PCR and melting-curve analysis. Results are expressed as means and standard deviations for parametric variables and as median (interquartile range) for non-parametric variables. T1D patients showed a higher TNFa gene promoter methylation (39·2 (sd 19·5) %) when compared with control subjects (25·4 (sd 13·7) %) (P=0·008). TNFa gene promoter methylation was positively associated only with homocysteine levels in T1D patients (r 0·55, P=0·007), but not in control subjects (r -0·122, P=0·872). To our knowledge, this is the first work that reports the methylation status of the TNFa gene promoter and its relationship with homocysteine metabolism in Chilean T1D patients without disease complications.

Heme-dependent Metabolite Switching Regulates H2S Synthesis in Response to Endoplasmic Reticulum (ER) Stress

Substrate ambiguity and relaxed reaction specificity underlie the diversity of reactions catalyzed by the transsulfuration pathway enzymes, cystathionine β-synthase (CBS) and γ-cystathionase (CSE). These enzymes either commit sulfur metabolism to cysteine synthesis from homocysteine or utilize cysteine and/or homocysteine for synthesis of H2S, a signaling molecule. We demonstrate that a kinetically controlled heme-dependent metabolite switch in CBS regulates these competing reactions where by cystathionine, the product of CBS, inhibits H2S synthesis by the second enzyme, CSE. Under endoplasmic reticulum stress conditions, induction of CSE and up-regulation of the CBS inhibitor, CO, a product of heme oxygenase-1, flip the operating preference of CSE from cystathionine to cysteine, transiently stimulating H2S production. In contrast, genetic deficiency of CBS leads to chronic stimulation of H2S production. This metabolite switch from cystathionine to cysteine and/or homocysteine renders H2S synthesis by CSE responsive to the known modulators of CBS: S-adenosylmethionine, NO, and CO. Used acutely, it regulates H2S synthesis; used chronically, it might contribute to disease pathology.

Central role of betaine-homocysteine S-methyltransferase 3 in chondral ossification and evidence for sub-functionalization in neoteleost fish

BACKGROUND

To better understand the complex mechanisms of bone formation it is fundamental that genes central to signaling/regulatory pathways and matrix formation are identified. Cell systems were used to analyze genes differentially expressed during extracellular matrix mineralization and bhmt3, coding for a betaine-homocysteine S-methyltransferase, was shown to be down-regulated in mineralizing gilthead seabream cells.

METHODS

Levels and sites of bhmt3 expression were determined by qPCR and in situ hybridization throughout seabream development and in adult tissues. Transcriptional regulation of bhmt3 was assessed from the activity of promoter constructs controlling luciferase gene expression. Molecular phylogeny of vertebrate BHMT was determined from maximum likelihood analysis of available sequences.

RESULTS

bhmt3 transcript is abundant in calcified tissues and localized in cartilaginous structures undergoing endo/perichondral ossification. Promoter activity is regulated by transcription factors involved in bone and cartilage development, further demonstrating the central role of Bhmt3 in chondrogenesis and/or osteogenesis. Molecular phylogeny revealed the explosive diversity of bhmt genes in neoteleost fish, while tissue distribution of bhmt genes in seabream suggested that neoteleostean Bhmt may have undergone several steps of sub-functionalization.

CONCLUSIONS

Data on bhmt3 gene expression and promoter activity evidences a novel function for betaine-homocysteine S-methyltransferase in bone and cartilage development, while phylogenetic analysis provides new insights into the evolution of vertebrate BHMTs and suggests that multiple gene duplication events occurred in neoteleost fish lineage.

GENERAL SIGNIFICANCE

High and specific expression of Bhmt3 in gilthead seabream calcified tissues suggests that bone-specific betaine-homocysteine S-methyltransferases could represent a suitable marker of chondral ossification.

The CBS/CSE system: a potential therapeutic target in NAFLD?

Non-alcoholic fatty liver disease (NAFLD) is a broad spectrum liver disorder diagnosed in patients without a history of alcohol abuse. NAFLD is growing at alarming rates worldwide. Its pathogenesis is complex and incompletely understood. The cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) system regulates homocysteine and cysteine metabolism and contributes to endogenous hydrogen sulfide (H2S) biosynthesis. This review summarizes our current understanding of the hepatic CBS/CSE system, and for the first time, positions this system as a potential therapeutic target in NAFLD. As will be discussed, the CBS/CSE system is highly expressed and active in the liver. Its dysregulation, presenting as alterations in circulating homocysteine and (or) H2S levels, has been reported in NAFLD patients and in NAFLD-associated co-morbidities such as obesity and type 2 diabetes. Intricate links between the CBS/CSE system and a number of metabolic and stress related molecular mediators have also emerged. Various dysfunctions in the hepatic CBS/CSE system have been reported in animal models representative of each NAFLD spectrum. It is anticipated that a newfound appreciation for the hepatic CBS/CSE system will emerge that will improve our understanding of NAFLD pathogenesis, and give rise to new prospective targets for management of this disorder.

Sulfur as a signaling nutrient through hydrogen sulfide

Hydrogen sulfide (H₂S) has emerged as an important signaling molecule with beneficial effects on various cellular processes affecting, for example, cardiovascular and neurological functions. The physiological importance of H₂S is motivating efforts to develop strategies for modulating its levels. However, advancement in the field of H₂S-based therapeutics is hampered by fundamental gaps in our knowledge of how H₂S is regulated, its mechanism of action, and its molecular targets. This review provides an overview of sulfur metabolism; describes recent progress that has shed light on the mechanism of H₂S as a signaling molecule; and examines nutritional regulation of sulfur metabolism, which pertains to health and disease.

Associations of common variants in methionine metabolism pathway genes with plasma homocysteine and the risk of type 2 diabetes in Han Chinese

BACKGROUND/AIMS

An association of genetic variants of homocysteine (Hcy) metabolic genes with type 2 diabetes mellitus (T2DM) has been reported. The objective of the present study was to investigate the relationship between the genetic variants in Hcy metabolism-related genes and plasma Hcy levels and T2DM susceptibility in Han Chinese.

METHODS

A total of 774 patients with T2DM and 500 healthy individuals were recruited. Single-nucleotide polymorphism was determined by standard methods.

RESULTS

The Hcy-increasing allele score was positively associated with plasma Hcy levels in both T2DM patients and healthy subjects (r = 0.171 and 0.247, respectively). Subjects with the genotype CC of MTHFR (rs1801131) had a significantly higher likelihood of T2DM compared with subjects with the AA or AA+AC genotypes (OR = 1.93 for CC vs. AA, p = 0.041; OR = 3.13 for CC vs. AA+AC, p = 0.017, respectively). Subjects with the genotype AA of the MTHFD variant (rs2236225) had a significantly lower likelihood of T2DM compared with subjects with the GG or GG+GA genotypes (OR = 0.36 for AA vs. GG, p = 0.027; OR = 0.36 for AA vs. GG+GA, p = 0.017, respectively). In addition, the genotype CT+TT of the PEMT (rs4646356) variants displayed a significant association with an increased risk of T2DM (OR = 1.52 for CT+TT vs. CC, p = 0.042).

CONCLUSIONS

MTHFR rs1801131 C allele and PEMT rs4646356 T allele were associated with a high risk of T2DM in these Han Chinese.

Estrogens increase cystathionine-γ-lyase expression and decrease inflammation and oxidative stress in the myocardium of ovariectomized rats

OBJECTIVE

Hydrogen sulfide (H2S), generated in the myocardium predominantly via cystathionine-γ-lyase (CSE), is cardioprotective. The objectives of the present study were to investigate the effects of estrogens on CSE expression and H2S generation in the myocardium and to examine whether serum 17β-estradiol (E2) level is associated with CSE activity and H2S generation and whether H2S or E2 level is associated with proinflammatory cytokines and oxidative stress status.

METHODS

Ovariectomized Sprague-Dawley rats received subcutaneous E2 (30 μg/kg/d) or vehicle for 12 weeks. At the end of the 12-week treatment, CSE expression, H2S generation, reduced glutathione/oxidized glutathione (GSH/GSSG) ratio, total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity, catalase (CAT) activity, interleukin (IL)-6 concentration, and tumor necrosis factor-α (TNF-α) concentration in the left ventricle were determined.

RESULTS

E2 increased CSE expression and H2S generation in the myocardium of ovariectomized rats. H2S production rate and serum E2 were positively correlated. E2 increased GSH/GSSG ratio, T-AOC, CAT, and SOD activity but decreased IL-6 and TNF-α levels. Serum E2 level was positively correlated with GSH/GSSG ratio, T-AOC, CAT, and SOD activity, and inversely correlated with IL-6 and TNF-α levels. H2S generation rate was positively correlated with T-AOC and GSH/GSSG ratio, and inversely correlated with IL-6 and TNF-α levels.

CONCLUSIONS

E2 increases CSE expression and endogenous H2S generation in the myocardium. The effects of E2 are associated with decreased oxidative stress and inflammatory status. Our data suggest that estrogens might exert cardioprotective effects through up-regulation of CSE expression and H2S generation.

Decreased cystathionine-γ-lyase (CSE) activity in livers of type 1 diabetic rats and peripheral blood mononuclear cells (PBMC) of type 1 diabetic patients

The liver plays a major role in the formation of H2S, a novel signaling molecule. Diabetes is associated with lower blood levels of H2S. This study investigated the activities of cystathionine-γ-lyase (CSE, the enzyme that catalyzes H2S formation) in livers of type 1 diabetic (T1D) animals and in peripheral blood mononuclear cells (PBMC) isolated from T1D patients. T1D is associated with both hyperketonemia (acetoacetate and β-hydroxybutyrate) and hyperglycemia. This study also examined the role of hyperglycemia and hyperketonemia per se in decreased CSE activity using U937 monocytes and PBMC isolated from healthy subjects. Livers from streptozotocin-treated T1D rats demonstrated a significantly higher reactive oxygen species production, lower CSE protein expression and activity, and lower H2S formation compared with those of controls. Studies with T1D patients showed a decrease in CSE protein expression and activity in PBMC compared with those of age-matched normal subjects. Cell culture studies demonstrated that high glucose (25 mm) and/or acetoacetate (4 mm) increased reactive oxygen species, decreased CSE mRNA expression, protein expression, and enzymatic activity, and reduced H2S levels; however, β-hydroxybutyrate treatment had no effect. A similar effect, which was also observed in PBMC treated with high glucose alone or along with acetoacetate, was prevented by vitamin D supplementation. Studies with CSE siRNA provide evidence for a relationship between impaired CSE expression and reduced H2S levels. This study demonstrates for the first time that both hyperglycemia and hyperketonemia mediate a reduction in CSE expression and activity, which can contribute to the impaired H2S signaling associated with diabetes.

Enzymology of H2S biogenesis, decay and signaling

SIGNIFICANCE

Hydrogen sulfide (H2S), produced by the desulfuration of cysteine or homocysteine, functions as a signaling molecule in an array of physiological processes including regulation of vascular tone, the cellular stress response, apoptosis, and inflammation.

RECENT ADVANCES

The low steady-state levels of H2S in mammalian cells have been recently shown to reflect a balance between its synthesis and its clearance. The subversion of enzymes in the cytoplasmic trans-sulfuration pathway for producing H2S from cysteine and/or homocysteine versus producing cysteine from homocysteine, presents an interesting regulatory problem.

CRITICAL ISSUES

It is not known under what conditions the enzymes operate in the canonical trans-sulfuration pathway and how their specificity is switched to catalyze the alternative H2S-producing reactions. Similarly, it is not known if and whether the mitochondrial enzymes, which oxidize sulfide and persulfide (or sulfane sulfur), are regulated to increase or decrease H2S or sulfane-sulfur pools.

FUTURE DIRECTIONS

In this review, we focus on the enzymology of H2S homeostasis and discuss H2S-based signaling via persulfidation and thionitrous acid.

Plasma homocysteine and coronary artery calcification in Korean men

BACKGROUND

Homocysteine is an independent risk factor for atherosclerosis, plausibly through induction of endothelial dysfunction and smooth muscle cell proliferation. Under oxidative stress and inflammatory stimuli, vascular smooth muscle cells may undergo osteogenic differentiation, which leads to coronary artery calcification. This study evaluated the association between plasma homocysteine and coronary artery calcification.

DESIGN AND METHODS

Coronary artery calcium scores (CACSs) and plasma homocysteine concentrations were measured in 21,235 men (42 ± 6.5 years) who participated in the Kangbuk Samsung Health Study between 2010 and 2011. Subjects were grouped by quartile of plasma homocysteine.

RESULTS

The prevalence of coronary artery calcification (CAC) among the 21,235 men was 13.5%. In the first to fourth homocysteine quartiles, CAC(+) prevalence rates were 12.1%, 12.6%, 13.9%, and 15.3%, respectively. The CAC(+) group had unfavorable cardiometabolic and lipid profiles. In multivariate regression analysis after adjusting for variables with a univariate relationship (p < 0.20), the odds ratio (OR) for the presence of CAC was higher for the highest homocysteine quartile than for the lowest quartile group (OR (95% confidence interval (CI)), 1.275 (1.027, 1.583)), and presence of CAC was positively associated with quartile of homocysteine (p for trend = 0.009). Moreover, absolute plasma homocysteine concentration was positively and significantly related to presence of CAC and to CACS, respectively (OR (95% CI) 1.399 (1.089, 1.796): standardized β = 0.040, p < 0.001).

CONCLUSIONS

This study shows that plasma homocysteine is independently related to coronary artery calcification in Korean men, suggesting that plasma homocysteine concentration may serve as a marker for CAC.

Inhibition of cystathionine β-synthase is associated with glucocorticoids over-secretion in psychological stress-induced hyperhomocystinemia rat liver

Hyperhomocysteinemia (HHcy), a pathological condition characterized by an increase in plasma concentration of total homocysteine (Hcy), is recognized as a risk factor for several diseases. The transsulfuration pathway is the main metabolic fate of Hcy utilization, which requires the activity of cystathionine β-synthase (CBS). Our results showed the development of HHcy induced by psychological stress was mainly derived from a reduction of CBS activity in the liver, which was accompanied by a significant decrease in its mRNA level. It suggested that the hepatic CBS enzyme regulated by stress at the level of transcription would have a profound effect on circulating Hcy levels. The expression of Sp3, a negative factor for cbs transcription, obviously increased in hepatocytes nuclei of stressed rats, but Sp1 was not altered. It indicated that Sp3 was the key point of variations in cbs transcription caused by stress. Meanwhile, we detected that augmented plasma Hcy concentrations correlated with glucocordicoids (GCs) over-secretion in response to stress, and CBS mRNA levels were markedly lowered in GCs-treated rat hepatocytes. Further results found that glucocorticoids receptor (GR) expression in hepatocyte nuclei of stress rats and GR nuclear translocation ratio was increased, and the same results were proved by experiments in vitro, i.e., GR nuclear translocation and Sp3 expression was remarkably increased in GCs-treated hepatocytes. Moreover, results from ChIP suggested GCs enhanced the binding of GR to the regulatory region of the Sp3 promoter. These results indicated that GCs inhibit CBS transcription by up-regulating Sp3 in psychological stress-induced HHcy.

Exercise prevents hyperhomocysteinemia in a dietary folate-restricted mouse model

Hyperhomocysteinemia is a condition that results from altered methyl group metabolism and is associated with numerous pathological conditions. A number of nutritional and hormonal factors have been shown to influence circulating homocysteine concentrations; however, the impact of exercise on homocysteine and methyl group balance is not well understood. Our hypothesis was that exercise represents an effective means to prevent hyperhomocysteinemia in a folate-independent manner. The purpose of this study was to determine the influence of exercise on homocysteine metabolism in a dietary folate-restricted mouse model characterized by moderate hyperhomocysteinemia. Female outbred mice (12 weeks old) were assigned to either a sedentary or free-access wheel exercise group. Following a 4-week acclimation period, half of the mice in each group were provided a folate-restricted diet for 7-weeks prior to euthanasia and tissue collection. As expected, folate-restricted sedentary mice exhibited a 2-fold increase in plasma total homocysteine concentrations; however, exercise completely prevented the increase in circulating homocysteine concentrations. Moreover, exercise reduced plasma homocysteine concentrations 36% within the group fed only the control diet. The prevention of hyperhomocysteinemia by exercise appears, at least in part, to be the result of increased folate-independent homocysteine remethylation owing to a 2-fold increase in renal betaine homocysteine S-methyltransferase. To our knowledge, this is the first report demonstrating the prevention of hyperhomocysteinemia by exercise in a dietary folate-restriction model. Future research will be directed at determining if exercise can have a positive impact on other nutritional, hormonal, and genetic models of hyperhomocysteinemia relevant to humans.

Hepatic methionine homeostasis is conserved in C57BL/6N mice on high-fat diet despite major changes in hepatic one-carbon metabolism

Obesity is an underlying risk factor in the development of cardiovascular disease, dyslipidemia and non-alcoholic fatty liver disease (NAFLD). Increased hepatic lipid accumulation is a hallmark in the progression of NAFLD and impairments in liver phosphatidylcholine (PC) metabolism may be central to the pathogenesis. Hepatic PC biosynthesis, which is linked to the one-carbon (C1) metabolism by phosphatidylethanolamine N-methyltransferase, is known to be important for hepatic lipid export by VLDL particles. Here, we assessed the influence of a high-fat (HF) diet and NAFLD status in mice on hepatic methyl-group expenditure and C1-metabolism by analyzing changes in gene expression, protein levels, metabolite concentrations, and nuclear epigenetic processes. In livers from HF diet induced obese mice a significant downregulation of cystathionine β-synthase (CBS) and an increased betaine-homocysteine methyltransferase (BHMT) expression were observed. Experiments in vitro, using hepatoma cells stimulated with peroxisome proliferator activated receptor alpha (PPARα) agonist WY14,643, revealed a significantly reduced Cbs mRNA expression. Moreover, metabolite measurements identified decreased hepatic cystathionine and L-α-amino-n-butyrate concentrations as part of the transsulfuration pathway and reduced hepatic betaine concentrations, but no metabolite changes in the methionine cycle in HF diet fed mice compared to controls. Furthermore, we detected diminished hepatic gene expression of de novo DNA methyltransferase 3b but no effects on hepatic global genomic DNA methylation or hepatic DNA methylation in the Cbs promoter region upon HF diet. Our data suggest that HF diet induces a PPARα-mediated downregulation of key enzymes in the hepatic transsulfuration pathway and upregulates BHMT expression in mice to accommodate to enhanced dietary fat processing while preserving the essential amino acid methionine.

Hepatic metabolism of sulfur amino acids in db/db mice

To determine the effect of type-2 diabetes and obesity on the hepatic metabolism of sulfur amino acids, hepatic sulfur amino acid metabolism was determined in db/db mice. Hepatic methionine was markedly decreased in db/db mice, although the hepatic activity of betaine homocysteine methyltransferase was increased. The decrease in hepatic methionine was reflected by decreased sulfur-containing methionine metabolites, including S-adenosylmethionine, homocysteine, cysteine, and hypotaurine in liver and plasma. In contrast, S-adenosylhomocysteine, putrescine, and spermidine were increased in db/db mice. The hepatic level and activity of methionine adenosyltransferase I/III, an S-adenosylmethionine synthesizing enzyme, were significantly increased. These results suggest that increased polyamine synthesis, in conjunction with decreased hepatic methionine levels, is partly responsible for the reduction in hepatic S-adenosylmethionine. Decreased homocysteine in liver and plasma may be attributable to the decrease in hepatic methionine and upregulation of hepatic betaine homocysteine methyltransferase. Glutathione in liver and plasma did not change despite decreased γ-glutamylcysteine ligase activity. The decreased hepatic hypotaurine may be attributable to the downregulation of cysteine dioxygenase. The major finding of this study is that db/db mice exhibited decreases in hepatic methionine and its sulfurcontaining metabolites.

Homocysteine imbalance: a pathological metabolic marker

Perturbations in methyl group metabolism and homocysteine balance have emerged over the past few decades as having defining roles in a number of pathological conditions. Numerous nutritional, hormonal, and genetic factors that are characterized by elevations in circulating homocysteine concentrations are also associated with specific pathological conditions, including cancer development, autoimmune diseases, vascular dysfunction, and neurodegenerative disease. Although much remains to be explored, our understanding of the relationship between disease, methyl balance, and epigenetic control of gene expression has steadily progressed. However, homocysteine balance and its role in health and disease are not as clearly understood. This review presents our current understanding of homocysteine metabolism and its link to specific pathologies.

Hydrogen sulfide in the pathogenesis of atherosclerosis and its therapeutic potential

Hydrogen sulfide (H(2)S) was the third gaseous transmitter to be discovered, along with nitric oxide and carbon monoxide, and has been proposed to be involved in numerous physiological processes and pathology of various diseases. Hyperhomocysteinemia is an independent risk factor for cardiovascular disease, including atherosclerosis. Atherosclerosis is characterized by multiple key events including endothelial dysfunction, monocyte infiltration and their differentiation into macrophages, conversion of lesion-resident macrophages into foam cells, and smooth muscle cell proliferation. Increasing evidence has indicated that H(2)S plays a potentially significant role in all of these biological processes and that malfunction of H(2)S homeostasis may contribute to the pathogenesis of atherosclerosis. Experiments have demonstrated that H(2)S supplementation ameliorated many of these atherogenic processes and hence, such supplementation potentially may prove to be of therapeutic benefit in the prevention or treatment of atherosclerosis. H(2)S levels may be induced by the administration of H(2)S or H(2)S donors, or alternatively be reduced by the administration of specific cystathionine β-synthase or cystathionine γ-lyase inhibitors. However, issues remain with the potential use of currently available H(2)S-modulating agents in a clinical setting. This review will provide a description of the current literature on the involvement of H(2)S in these key aspects of vascular biology that contribute to the development of atherosclerosis, as well as the therapeutic potential of currently available H(2)S-modulating agents.

Use of serum homocysteine to predict cardiovascular disease in Korean men with or without metabolic syndrome

The aim of this study was to examine whether serum homocysteine (Hcy) levels correlated with cardiovascular disease (CVD) depending on the presence or absence of metabolic syndrome (MetS) in Korean men. We conducted a case-control study, including 138 CVD and 290 non-CVD age-matched control subjects. The subjects were divided into four subgroups: 34 CVD/MetS, 104 CVD, 77 MetS, and 213 normal subgroups. The mean Hcy was significantly higher, whereas HDL and intake of vitamin B(1) and B(2) were lower in the CVD group (P < 0.05) than non-CVD group. When compared to the control group, subjects with CVD/MetS, CVD and MetS exhibited high Hcy levels, with the highest observed in the CVD/MetS subgroup (P < 0.001). Multivariate stepwise linear regression between CVD and markers of CVD showed Hcy significantly correlated with CVD (P < 0.05). To predict CVD based on Hcy, Hcy threshold of 11.72 µM in non-MetS subjects had an area under the curve (AUC) of 0.664 (95% CI 0.598-0.731). In MetS subjects, the AUC was 0.618 and Hcy threshold was 13.32 µM (95% CI 0.509-0.726). The results of our study show that the presence of MetS needs to be considered when using Hcy levels for predicting CVD.

Protein phosphorylation involved in the gene expression of the hydrogen sulphide producing enzyme cystathionine γ-lyase in the pancreatic β-cell

Cystathionine γ-lyase (CSE) is one of the major enzymes for the production of hydrogen sulphide (H(2)S), a multifunctional gasotransmitter in the pancreatic β-cell. We examined the mechanisms by which glucose induces CSE expression in mouse pancreatic islets and the insulin-secreting cell line MIN6. CSE expression was increased by anti-diabetic sulphonylureas, and decreased by the ATP-sensitive K(+)-channel opener diazoxide and the voltage-dependent Ca(2+) channel blocker nitrendipine. Application of the synthetic inhibitors of protein kinases revealed the involvement of Ca(2+)/calmodulin-dependent protein kinase (CaMK) II and extracellular signal-regulated protein kinase (ERK) in glucose- and thapsigargin-induced CSE expression. The CaMK IIδ knockdown also suppressed CSE expression. Knockdown of the transcription factors Sp1 and Elk1, both of which can be phosphorylated by ERK, blunted CSE expression. By a reporter assay, we found Sp1 may directly and Elk1 may indirectly regulate CSE expression. These findings suggest Ca(2+)-dependent CSE expression may be mediated via protein phosphorylation of Sp1 and Elk1 in pancreatic β-cells.

Tissue-specific alterations of methyl group metabolism with DNA hypermethylation in the Zucker (type 2) diabetic fatty rat

BACKGROUND

Altered methyl group and homocysteine metabolism were tissue-specific, persistent, and preceded hepatic DNA hypomethylation in type 1 diabetic rats. Similar metabolic perturbations have been shown in the Zucker (type 2) diabetic fatty (ZDF) rat in the pre-diabetic and early diabetic stages, but tissue specificity and potential impact on epigenetic marks are unknown, particularly during pathogenesis.

METHODS

ZDF (fa/fa) and lean (+/?) control rats were killed at 12 and 21 weeks of age, representing early and advanced diabetic conditions. Blood and tissues were analysed with respect to methyl group and homocysteine metabolism, including DNA methylation.

RESULTS

At 12 weeks, hepatic glycine N-methyltransferase (GNMT), methionine synthase, and cystathionine β-synthase (CBS) activity and/or abundance were increased in ZDF rats. At 21 weeks, GNMT activity was increased in liver and kidney; however, only hepatic CBS protein abundance (12 weeks) and betaine-homocysteine S-methyltransferase mRNA expression (21 weeks) were significantly elevated (78 and 100%, respectively). Hepatic phosphatidylethanolamine N-methyltransferase expression was also elevated in the ZDF rat. Homocysteine concentrations were decreased in plasma and kidney, but not in liver, at 12 and 21 weeks. In contrast to hepatic DNA hypomethylation in the type 1 diabetic rat, genomic DNA was hypermethylated at 12 and 21 weeks in the liver of ZDF rats, concomitant with an increase in DNA methyltransferase 1 expression at 21 weeks.

CONCLUSIONS

The pathogenesis of type 2 diabetes in the ZDF rat was associated with tissue and disease stage-specific aberrations of methyl group and homocysteine metabolism, with persistent hepatic global DNA hypermethylation.

Insulin resistance, metabolic stress, and atherosclerosis

Atherosclerosis, a pathological process that underlies the development of cardiovascular disease, is the primary cause of morbidity and mortality in patients with type 2 diabetes mellitus (T2DM). T2DM is characterized by hyperglycemia and insulin resistance (IR), in which target tissues fail to respond to insulin. Systemic IR is associated with impaired insulin signaling in the metabolic tissues and vasculature. Insulin receptor is highly expressed in the liver, muscle, pancreas, and adipose tissue. It is also expressed in vascular cells. It has been suggested that insulin signaling in vascular cells regulates cell proliferation and vascular function. In this review, we discuss the association between IR, metabolic stress, and atherosclerosis with focus on 1) tissue and cell distribution of insulin receptor and its differential signaling transduction and 2) potential mechanism of insulin signaling impairment and its role in the development of atherosclerosis and vascular function in metabolic disorders including hyperglycemia, hypertension, dyslipidemia, and hyperhomocysteinemia. We propose that insulin signaling impairment is the foremost biochemical mechanism underlying increased cardiovascular morbidity and mortality in atherosclerosis, T2DM, and metabolic syndrome.

Increased renal methylglyoxal formation with down-regulation of PGC-1α-FBPase pathway in cystathionine γ-lyase knockout mice

We have previously reported that hydrogen sulfide (H(2)S), a gasotransmitter and vasodilator has cytoprotective properties against methylglyoxal (MG), a reactive glucose metabolite associated with diabetes and hypertension. Recently, H(2)S was shown to up-regulate peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α, a key gluconeogenic regulator that enhances the gene expression of the rate-limiting gluconeogenic enzyme, fructose-1,6-bisphosphatase (FBPase). Thus, we sought to determine whether MG levels and gluconeogenic enzymes are altered in kidneys of 6-22 week-old cystathionine γ-lyase knockout (CSE(-/-); H(2)S-producing enzyme) male mice. MG levels were determined by HPLC. Plasma glucose levels were measured by an assay kit. Q-PCR was used to measure mRNA levels of PGC-1α and FBPase-1 and -2. Coupled-enzymatic assays were used to determine FBPase activity, or triosephosphate levels. Experimental controls were either age-matched wild type mice or untreated rat A-10 cells. Interestingly, we observed a significant decrease in plasma glucose levels along with a significant increase in plasma MG levels in all three age groups (6-8, 14-16, and 20-22 week-old) of the CSE(-/-) mice. Indeed, renal MG and triosephosphates were increased, whereas renal FBPase activity, along with its mRNA levels, were decreased in the CSE(-/-) mice. The decreased FBPase activity was accompanied by lower levels of its product, fructose-6-phosphate, and higher levels of its substrate, fructose-1,6-bisphosphate in renal extracts from the CSE(-/-) mice. In agreement, PGC-1α mRNA levels were also significantly down-regulated in 6-22 week-old CSE(-/-) mice. Furthermore, FBPase-1 and -2 mRNA levels were reduced in aorta tissues from CSE(-/-) mice. Administration of NaHS, a H(2)S donor, increased the gene expression of PGC-1α and FBPase-1 and -2 in cultured rat A-10 cells. In conclusion, overproduction of MG in CSE(-/-) mice is due to a H(2)S-mediated down-regulation of the PGC-1α-FBPase pathway, further suggesting the important role of H(2)S in the regulation of glucose metabolism and MG generation.

Emerging role of hydrogen sulfide in health and disease: critical appraisal of biomarkers and pharmacological tools

H2S (hydrogen sulfide) is a well known and pungent gas recently discovered to be synthesized enzymatically in mammalian and human tissues. In a relatively short period of time, H2S has attracted substantial interest as an endogenous gaseous mediator and potential target for pharmacological manipulation. Studies in animals and humans have shown H2S to be involved in diverse physiological and pathophysiological processes, such as learning and memory, neurodegeneration, regulation of inflammation and blood pressure, and metabolism. However, research is limited by the lack of specific analytical and pharmacological tools which has led to considerable controversy in the literature. Commonly used inhibitors of endogenous H2S synthesis have been well known for decades to interact with other metabolic pathways or even generate NO (nitric oxide). Similarly, commonly used H2S donors release H2S far too quickly to be physiologically relevant, but may have therapeutic applications. In the present review, we discuss the enzymatic synthesis of H2S and its emerging importance as a mediator in physiology and pathology. We also critically discuss the suitability of proposed 'biomarkers' of H2S synthesis and metabolism, and highlight the complexities of the currently used pharmacological H2S 'donor' molecules and 'specific' H2S synthesis inhibitors in their application to studying the role of H2S in human disease.

Insulin administration abrogates perturbation of methyl group and homocysteine metabolism in streptozotocin-treated type 1 diabetic rats

Modifications in methyl group and homocysteine metabolism are associated with a number of pathologies, including vascular disease, cancer, and neural tube defects. A diabetic state is known to alter both methyl group and homocysteine metabolism, and glycine N-methyltransferase (GNMT) is a major regulatory protein that controls the supply and utilization of methyl groups. We have shown previously that diabetes induces GNMT expression and reduces plasma homocysteine pools by stimulating both its catabolism and folate-independent remethylation. This study was conducted to determine whether insulin plays a role in the control of homocysteine concentrations and GNMT as well as other key regulatory proteins. Male Sprague-Dawley rats were randomly assigned to one of three groups: control, streptozotocin (STZ)-induced diabetic (60 mg/kg body wt), and insulin-treated diabetic (1.0 U bid). After 5 days, rats were anesthetized (ketamine-xylazine) for procurement of blood and tissues. A 1.5-fold elevation in hepatic GNMT activity and hypohomocysteinemia in diabetic rats was completely prevented by insulin treatment. Additionally, diabetes-mediated alterations in methionine synthase, phosphatidylethanolamine N-methyltransferase, and DNA methylation were also prevented by insulin. We hypothesize that the concentration of blood glucose may represent a regulatory signal to modify GNMT and homocysteine. In support of this, blood glucose concentrations were negatively correlated with total plasma homocysteine (r = -0.75, P < 0.001) and positively correlated with GNMT activity (r = 0.77, P < 0.001). Future research will focus on further elucidating the role of glucose or insulin as a signal for regulating homocysteine and methyl group metabolism.

Methionine and protein metabolism in non-alcoholic steatohepatitis: evidence for lower rate of transmethylation of methionine

Hepatic metabolism of methionine is the source of cysteine, the precursor of glutathione, the major intracellular antioxidant in the body. Methionine also is the immediate precursor of SAM (S-adenosylmethionine) the key methyl donor for phosphatidylcholine synthesis required for the export of VLDL (very-low-density lipoprotein) triacylglycerols (triglycerides) from the liver. We have examined the kinetics of methionine, its transmethylation and trans-sulfuration with estimates of whole body rate of protein turnover and urea synthesis in clinically stable biopsy-confirmed subjects with NASH (non-alcoholic steatohepatitis). Subjects with NASH were more insulin-resistant and had significantly higher plasma concentrations of usCRP (ultrasensitive C-reactive protein), TNFα (tumour necrosis factor α) and other inflammatory cytokines. There was no significant effect of insulin resistance and NASH on whole body rate of protein turnover [phenylalanine Ra (rate of appearance)] and on the rate of urea synthesis. The rates of methylation of homocysteine and transmethylation of methionine were significantly lower in NASH compared with controls. There was no difference in the rate of trans-sulfuration of methionine between the two groups. Enteric mixed nutrient load resulted in a significant increase in all the measured parameters of methionine kinetics. Heterozygosity for MTHFR (5,10-methylene-tetrahydrofolate reductase) (677C→T) did not have an impact on methionine metabolism. We speculate that, as a result of oxidant stress possibly due to high fatty acid oxidation, the activity of methionine adenosyltransferase is attenuated resulting in a lower rate of transmethylation of methionine and of SAM synthesis. These results are the first evidence for perturbed metabolism of methionine in NASH in humans and provide a rationale for the development of targeted intervention strategies.

Homocysteine levels are associated with hippocampus volume in type 2 diabetic patients

BACKGROUND

Elevated total plasma homocysteine (tHcy) levels are associated with cognitive dysfunction, in which changes in the hippocampus plausibly play a pivotal role. We tested the hypothesis that elevated tHcy levels are correlated with hippocampus volume and insulin resistance in nondementia patients with type 2 diabetes.

MATERIALS AND METHODS

The study included 43 nondementia patients with type 2 diabetes, who were divided into two groups: a high tHcy group (age: 65 ± 8 years, mean ± standard deviation, n = 16) and a normal tHcy group (64 ± 9 years, n = 27). Hippocampus volume was quantified with a computer-assisted analysis using a magnetic resonance imaging (MRI) voxel-based specific regional analysis system developed for the study of Alzheimer's disease (VSRAD), which yields a Z-score as the end point for the assessment of hippocampal volume. Results  The Z-score was higher in the high tHcy group compared to the normal tHcy group (P < 0·0001). The fasting plasma glucose (P < 0·01) and insulin (P < 0·0001) concentrations and the homoeostasis model assessment (HOMA) index (P < 0·0001) were higher in the high tHcy group than in the normal tHcy group. Multiple regression analysis showed that the main factors that influenced tHcy levels may be the Z-score and the HOMA index.

CONCLUSIONS

Our results indicate that the elevated levels of tHcy in Japanese nondementia patients with type 2 diabetes are characterised by hippocampal atrophy and insulin resistance and that the Z-score and HOMA index may be the primary factors that influence tHcy levels.