Possible Involvement of Hydrosulfide in B12-Dependent Methyl Group Transfer

The role of the transsulfuration pathway in spermatogenesis of vitamin D deficient mice

Vitamin D deficiency is a global health problem and has been linked to defective spermatogenesis and male infertility. In this study, we aimed to investigate the main enzymes involved in the transsulfuration pathway of 1-carbon metabolism, and spermatogenesis function. Therefore, sixteen male C57 mice were addressed to a control (standard diet) or vitamin D deficient (VDD) diet for 14 weeks. The results show that compared to the standard diet, VDD increased final body weight and reduced sperm quality, caused damage to the testicular structure, and decreased the serum levels of testosterone. In addition, serum concentrations of homocysteine, vitamin B12, and sperm oxidative stress markers increased. In testicular tissues, the CBS and CSE protein levels were down-regulated whereas HO-1 was up-regulated at both mRNA and protein expression levels. Within a mice deprivation model, VDD deeply suppressed testosterone and impaired spermatogenesis with oxidative stress-mediated mechanisms. The effects of the deprivation appeared to be at least in part independent of genomic and receptor-mediated vitamin D actions and suggest a specific impairment of the alternative transsulfuration pathway.

Follicular homocysteine as a marker of oocyte quality in PCOS and the role of micronutrients

PURPOSE

Does follicular homocysteine predict the reproductive potential of oocytes following FSH stimulation in PCOS women? Can it be modulated by dietary interventions?

METHODS

This was a prospective, randomized, interventional clinical study. Forty-eight PCOS women undergoing in vitro fertilization at a private fertility clinic were randomized for a dietary supplementation providing micronutrients involved in homocysteine clearance or no treatment. The supplement was assumed 2 months before stimulation until pick-up day. Monofollicular fluids were collected and frozen. After embryo transfer, the fluids from the follicles generating the transferred embryos were thawed and analyzed.

RESULTS

Follicular homocysteine showed a negative correlation with clinical pregnancy both in the whole population (r =  - 0.298; p = 0.041) and in controls (r =  - 0.447, p = 0.053). The support achieved a non-significantly lower concentration of follicular homocysteine (median [IQR]-7.6 [13.2] vs 24.3 [22.9]). Supplemented patients required far less FSH for stimulation (1650 [325] vs 2250 [337], p = 0.00002) with no differences in the number of oocytes collected, MII rate, and fertilization rate. Supplemented patients enjoyed higher blastocyst rate (55% [20.5] vs 32% [16.5]; p = 0.0009) and a trend for improved implantation rate (64% vs 32%; p = 0.0606). Clinical pregnancy rates were 58% vs 33% in controls (p = ns).

CONCLUSION

Follicular homocysteine is a suitable reporter that might be investigated as a tool for oocyte-embryo selection. A diet enriched with methyl donors may be useful in PCOS and supplements may also help. These findings may be also true for non-PCOS women, which warrants investigation. The study was approved by the Acibadem University Research Ethics Committee (2017-3-42). Clinical trial retrospective registration number ISRCTN55983518.

Interactions of reactive sulfur species with metalloproteins

Reactive sulfur species (RSS) entail a diverse family of sulfur derivatives that have emerged as important effector molecules in H₂S-mediated biological events. RSS (including H₂S) can exert their biological roles via widespread interactions with metalloproteins. Metalloproteins are essential components along the metabolic route of oxygen in the body, from the transport and storage of O₂, through cellular respiration, to the maintenance of redox homeostasis by elimination of reactive oxygen species (ROS). Moreover, heme peroxidases contribute to immune defense by killing pathogens using oxygen-derived H₂O₂ as a precursor for stronger oxidants. Coordination and redox reactions with metal centers are primary means of RSS to alter fundamental cellular functions. In addition to RSS-mediated metalloprotein functions, the reduction of high-valent metal centers by RSS results in radical formation and opens the way for subsequent per- and polysulfide formation, which may have implications in cellular protection against oxidative stress and in redox signaling. Furthermore, recent findings pointed out the potential role of RSS as substrates for mitochondrial energy production and their cytoprotective capacity, with the involvement of metalloproteins. The current review summarizes the interactions of RSS with protein metal centers and their biological implications with special emphasis on mechanistic aspects, sulfide-mediated signaling, and pathophysiological consequences. A deeper understanding of the biological actions of reactive sulfur species on a molecular level is primordial in H₂S-related drug development and the advancement of redox medicine.

Versatile Enzymology and Heterogeneous Phenotypes in Cobalamin Complementation Type C Disease

Nutritional deficiency and genetic errors that impair the transport, absorption, and utilization of vitamin B₁₂ (B₁₂) lead to hematological and neurological manifestations. The cblC disease (cobalamin complementation type C) is an autosomal recessive disorder caused by mutations and epi-mutations in the MMACHC gene and the most common inborn error of B₁₂ metabolism. Pathogenic mutations in MMACHC disrupt enzymatic processing of B₁₂, an indispensable step before micronutrient utilization by the two B₁₂-dependent enzymes methionine synthase (MS) and methylmalonyl-CoA mutase (MUT). As a result, patients with cblC disease exhibit plasma elevation of homocysteine (Hcy, substrate of MS) and methylmalonic acid (MMA, degradation product of methylmalonyl-CoA, substrate of MUT). The cblC disorder manifests early in childhood or in late adulthood with heterogeneous multi-organ involvement. This review covers current knowledge on the cblC disease, structure–function relationships of the MMACHC protein, the genotypic and phenotypic spectra in humans, experimental disease models, and promising therapies.

Down-Regulated Expression of Cystathionine β-Synthase and Cystathionine γ-Lyase in Varicocele, and Infertile Men: A Case-Control Study

Objective

Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are two important enzymes involved in One-Carbon metabolism. These enzymes play important roles in modulating oxidative stress and inflammation in male factor infertility through participating in the synthesis of glutathione (GSH) antioxidants in the trans-sulfuration pathway. Besides, the direct release of hydrogen sulfide (H2S) has anti-inflammatory and antioxidant effects. Therefore, the expression of CBS and CSE genes at mRNA levels in infertile and varicocele men was evaluated and compared to the healthy counterparts to clarify their possible role in the pathology of male infertility.

Materials and Methods

In this case-control study, semen parameter assessment (concentration, morphology, and motility of sperms) was performed on 28 men with varicocele, 43 infertile men with abnormal sperm parameters, and 19 fertile men. RNA was extracted from sperm samples followed by cDNA synthesis and real-time polymerase chain reaction (PCR) using CBS, CSE, and GAPDH primers.

Results

Sperm concentration and motility in infertile and varicocele groups were significantly lower (P=0.001), while spermatoza normal morphology was higher than fertile group (P=0.05). The expression levels of both CBS and CSE genes in infertile (P=0.04 and P=0.037 respectively) and varicocele (P=0.01 and P=0.046 respectively) groups were significantly lower than fertile group. Additionally, CBS gene expression indicated a positive correlation with expression of CBS gene (r=0.296, P=0.025) and sperm parameters.

Conclusion

In light of our findings, there is a valid rationale to consider the primary role of CBS and CSE enzymes impairment in male factor infertility which specifically may point to a deficit in the release of essential antioxidants including the H2S as a molecular basis of infertility and warrants further investigation.

Vitamin B12 and chronic kidney disease

Chronic Kidney Disease (CKD) is an emerging public health issue with a fast-growing global prevalence. Impairment in vitamin B12 metabolism is considered a nontraditional risk factor of poor outcomes associated with CKD, and there is greater interest from the scientific community than ever before to explore the role and influence of vitamin B12 in CKD. Homocysteine metabolism forms an important component of the vitamin B12 metabolic pathway. Hyperhomocysteinemia is frequently observed in CKD and End-Stage Kidney Disease (ESKD), but its representation as a prognostic marker for CKD outcomes is still not fully clear. This chapter reviews the vitamin B12 and homocysteine metabolic pathways and their dysfunction in CKD states. Biochemical factors and the MTHFR genetic polymorphisms which disrupt vitamin B12 and homocysteine metabolism are explored. The mechanisms of homocysteine-mediated and vitamin B12-mediated tissue damage in CKD are discussed. This chapter reviews current perspective on definition and measurement of plasma vitamin B12 levels in the CKD population. Updated evidence investigating the prognostic role of vitamin B12 for CKD outcomes is presented. Findings from major clinical trials conducted relating to outcomes from multivitamin (including folic acid and vitamin B12) supplementation in nondialysis and dialysis-dependent CKD are highlighted. The prognostic value of vitamin B12 and effects of vitamin B12 supplementation in the context of kidney transplantation and acute kidney injury is also reviewed. Future research considerations are summarized based on evidence gaps in our knowledge base of this topic. Greater abundance of high-level evidence to guide an approach toward vitamin B12 measurement, monitoring and supplementation in CKD may contribute to improved clinical outcomes.

Modulation of Human Hydrogen Sulfide Metabolism by Micronutrients, Preliminary Data

Background:

Hydrogen sulfide (H₂S) is a pivotal gasotransmitter networking with nitric oxide (NO) and carbon monoxide (CO) to regulate basic homeostatic functions. It is released by the alternative pathways of transulfuration by the enzymes Cystathionine Beta Synthase (CBS) and Cystathionine Gamma Lyase (CSE), and by Cysteine AminoTransferase (CAT)/ 3-Mercaptopyruvate Sulfur Transferase (3MPST). A non-enzymatic, intravascular release is also in place. We retrospectively investigated the possibility to modulate the endogenous H₂S release and signaling in humans by a dietary manipulation with supplemented micronutrients (L-cystine, Taurine and pyridoxal 5-phopsphate/P5P).

Methods:

Patients referring for antiaging purposes underwent a 10-day supplementation. Blood was collected at baseline and after treatment and the metabolome was investigated by mass spectrometry to monitor the changes in the metabolites reporting on H₂S metabolism and related pathways.

Results:

Data were available from 6 middle aged subjects (2 women). Micronutrients increased 3-mercaptopyruvate (P = .03), reporting on the activity of CAT that provides the substrate for H₂S release within mitochondria by 3MPST, decreased lanthionine (P = .024), reporting the release of H₂S from CBS, and had no significant effect of H₂S release from CSE. This is compatible with a homeostatic balancing. We also recorded a strong increase of reporters of H₂S-induced pathways including 5-MethylTHF (P = .001) and SAME (P = .022), reporting on methylation capacity, and of BH4 (P = .021) and BH2 (P = .028) reporting on nitric oxide metabolism. These activations may be explained by the concomitant induction of non-enzymatic release of H₂S.

Conclusions:

Although the current evidences are weak and will need to be confirmed, the effect of micronutrients was compatible with an increase of the H₂S endogenous release and signaling within the control of homeostatic mechanisms, further endorsing the role of feeding in health and disease. These effects might result in a H₂S boosting effect in case of defective activity of pathologic origin, which should be checked in duly designed clinical trials.

Gasping for Sulfide: A Critical Appraisal of Hydrogen Sulfide in Lung Disease and Accelerated Aging

Hydrogen sulfide (H₂S) is a gaseous signaling molecule involved in a plethora of physiological and pathological processes. It is primarily synthesized by cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase as a metabolite of the transsulfuration pathway. H₂S has been shown to exert beneficial roles in lung disease acting as an anti-inflammatory and antiviral and to ameliorate cell metabolism and protect from oxidative stress. H₂S interacts with transcription factors, ion channels, and a multitude of proteins via post-translational modifications through S-persulfidation ("sulfhydration"). Perturbation of endogenous H₂S synthesis and/or levels have been implicated in the development of accelerated lung aging and diseases, including asthma, chronic obstructive pulmonary disease, and fibrosis. Furthermore, evidence indicates that persulfidation is decreased with aging. Here, we review the use of H₂S as a biomarker of lung pathologies and discuss the potential of using H₂S-generating molecules and synthesis inhibitors to treat respiratory diseases. Furthermore, we provide a critical appraisal of methods of detection used to quantify H₂S concentration in biological samples and discuss the challenges of characterizing physiological and pathological levels. Considerations and caveats of using H₂S delivery molecules, the choice of generating molecules, and concentrations are also reviewed. Antioxid. Redox Signal. 35, 551-579.

Evidence to Support the Use of S-Adenosylmethionine for Treatment of Post-Concussive Sequelae in the Military

INTRODUCTION

Since the year 2000, over 413,000 service members have sustained traumatic brain injury (TBI) and may present with post-concussive sequelae including headaches, fatigue, irritability, cognitive problems, depression, insomnia, and chronic pain. Although the focus of the article is on military TBI, the usefulness of S-adenosylmethionine (SAMe) would extend to both civilian and military populations. This narrative review examines the preclinical and clinical literature of SAMe's metabolism and alterations seen in disease states such as depressive disorders, pain disorders, fatigue, cognition, dementia, use in pregnancy and peripartum, children, adolescents, and adults, to the elderly with and without dementia, stroke, and neurodegeneration, in order to highlight its potential benefit in post-concussive sequelae after TBI.

MATERIALS AND METHODS

A MEDLINE/PubMed and Cochrane Database search was conducted between May 3, 2018 and July 30, 2019 by combining search terms for SAMe with terms for relevant disease states including depression, brain injury, dementia, Alzheimer's disease, Parkinson's disease, cognition, fatigue, and pain. This search retrieved a total of 676 references. 439 were excluded for being over a 10-year publication date, except where clinically relevant. After additional removal of repeated articles, the number of articles were totaled 197. An additional 59 articles were excluded: 10 not in English, 4 duplicates, 4 not original investigations, and 41 outside the scope of this article. The remaining 138 articles were used in this review and included 25 clinical studies, 46 preclinical studies, 63 reviews, and 4 case reports.

RESULTS

This narrative review examined the preclinical and clinical literature of SAMe's metabolism and alterations seen in MDD, pain disorders, fatigue, cognition and memory, dementia, and other disorders to highlight the potential benefit of SAMe in post-concussive sequelae in mTBI. The literature showed potential for improvement, safety, and tolerability in these symptom clusters commonly seen in military mild TBI (mTBI).

CONCLUSION

There is evidence of a potential benefit of SAMe as an intervention to help with symptoms across the range of post-concussive sequelae and syndromes commonly seen in military mTBI. Since the discovery of SAMe in 1952, this pleiotropic molecule has shown the significance of its involvement in several metabolic cascades in such disparate systems as epigenetics, bioenergetics, DNA methylation, neurotransmitter systems, and potential usefulness in military TBI. Significant limitations include disparate presentations seen in patients with mild TBI, those with post-concussive syndrome, as well as those with comorbid depression and posttraumatic stress disorder. Also, over-the-counter medications are not regulated and SAMe products may vary widely in price and quality. Given the potential for mania in patients with bipolar disorder, evaluation and recommendations should be made by a physician able to evaluate the underlying bipolar diathesis. Furthermore, this narrative review serves as the rationale for future open-label and double-blind placebo-controlled trials in military mTBI and SAMe.

Correlation between total homocysteine and cerebral small vessel disease: A Mendelian randomization study

BACKGROUND AND PURPOSE

Cerebral small vessel disease (CSVD) is a clinical imaging syndrome with diverse etiology. Total homocysteine (HCY) level might increase the risk of myocardial and cerebral infarction by damaging the vascular endothelium. We aimed to explore the correlation between total HCY and CSVD imaging burden, based on Mendelian randomization methods.

METHODS

A total of 1,023 participants of the Shunyi study, a population-based cohort study, were included. Vascular risk factors, total HCY levels and methylenetetrahydrofolate reductase (MTHFR) gene mutations (C677T and A1298C) were examined. CSVD imaging markers, including lacunes, cerebral microbleeds, white matter hyperintensity, enlarged perivascular space and brain parenchymal fraction (BPF) were also assessed.

RESULTS

Mutations of C677T were significantly correlated with increased total HCY levels (CC→TT: β = 0.28, p < 0.0001), while mutations of A1298C were correlated with decreased total HCY levels (AA→AC: β = -0.13, p < 0.0001; AA→CC: β = -0.25, p = 0.004). In the Mendelian randomization study, the C677T genotype was significantly associated with lacunes (CC→CT: odds ratio [OR] 2.76, p = 0.008; CC→TT: OR 2.50, p = 0.018), and the A1298C genotype was significantly correlated with BPF (AA→CC: β = 1.32, p = 0.015). Similarly, in multivariate regression analysis, total HCY levels were significantly correlated with lacunes (OR 2.14, p < 0.0001) and negatively correlated with BPF (β = -0.55, p = 0.004). Age, sex and vascular risk factors were adjusted for.

CONCLUSIONS

Total HCY level was correlated with imaging burden of CSVD, especially with lacunes and brain volume loss. For individuals with risk genetic predisposition, enhanced homocysteine-lowering strategies might be necessary to reduce the risk and progress of CSVD.

Is Hydrogen Sulfide a Concern During Treatment of Lung Adenocarcinoma With Ammonium Tetrathiomolybdate?

Ammonium tetrathiomolybdate (ATTM) has been used in breast cancer therapy for copper chelation, as elevated copper promotes tumor growth. ATTM is also an identified H₂S donor and endogenous H₂S facilitates VitB₁₂-induced S-adenosylmethionine (SAM) generation, which have been confirmed in m⁶A methylation and lung cancer development. The m⁶A modification was recently shown to participate in lung adenocarcinoma (LUAD) progression. These conflicting analyses of ATTM's anticancer vs. H₂S's carcinogenesis suggest that H₂S should not be ignored during LUAD's treatment with ATTM. This study was aimed to explore ATTM's effects on LUAD cells and mechanisms associated with H₂S and m⁶A. It was found that treatment with ATTM inhibited cell growth at high concentrations, while enhanced cell growth at low concentrations in three LUAD cell lines (A549, HCC827, and PC9). However, another copper chelator triethylenetetramine, without H₂S releasing activity, was not found to induce cell growth. Low ATTM concentrations also elevated m⁶A content in A549 cells. Analysis of differentially expressed genes in TCGA cohort indicated that m⁶A writer METTL3 and reader YTHDF1 were upregulated while eraser FTO was downregulated in LUAD tissues, consistent with the findings of protein expression in patient tissues. ATTM treatment of A549 cells significantly increased METTL3/14 and YTHDF1 while decreased FTO expression. Furthermore, inhibition of m⁶A with shMETTL3 RNA significantly attenuated eukaryotic translation initiation factor (eIF) expressions in A549 cells. Correlation analysis indicated that small nuclear ribonucleic protein PRPF6 was positively expressed with YTHDF1 in LUAD tissues. Knockdown of YTHDF1 partially blocked both basal and ATTM-induced PRPF6 expression, as well as A549 cell growth. Lastly, ATTM treatment not only raised intracellular H₂S content but also upregulated H₂S-producing enzymes. Exogenous H₂S application mimicked ATTM's aforementioned effects, but the effects could be weakened by zinc-induced H₂S scavenging. Collectively, H₂S impedes ATTM-induced anticancer effects through YTHDF1-dependent PRPF6 m⁶A methylation in lung adenocarcinoma cells.

Micronutrients in Support to The Carbon Cycle Activate Antioxidant Defences and Reduce Sperm DNA Damage in Infertile Men Attending Assisted Reproductive Technology Programs: Clinical Trial Study

Background

Micronutrients in support to the carbon cycle were shown to reduce sperm DNA damage both in animal models and infertile men. Besides supporting DNA methylation, their positive effect may be mediated by an improved performance of the endogenous antioxidant system but this has not yet been proven in clinical settings. The present study aimed at evaluating the effects of micronutrient supplementation in infertile male partners of assisted reproductive technology (ART) resistant couples.

Materials and Methods

In this experimental clinical trial study, infertile male partners of couples resistant to at least one ART cycle, with a sperm fragmentation rate >20% (TUNEL), underwent a 4-month oral supplementation with micronutrients in support to the carbon cycle including folates, B vitamins, zinc and cysteines. Semen, sperm DNA fragmentation (TUNEL), nuclear maturation (CMA3 and blue aniline staining) and lipid peroxidation (BODIPY) were assessed before and after treatment. The couples were followed-up to record clinical outcomes.

Results

Forty-three patients completed the program but full data of pre- and post-treatment were available only for 25 patients. The treatment did not modify sperm concentration or motility but improved morphology. Nuclear maturation, DNA fragmentation and lipid peroxidation significantly improved after the treatment. Overall, 10 clinical pregnancies (23.3%) and 4 live births (9.3%) were recorded during the follow-up following expectant management (25 couples) or a new intracytoplasmic sperm injection (ICSI) cycle (18 couples).

Conclusion

The micronutrients appeared to induce both DNA methylation, resulting in improved sperm nuclear matu- ration, and antioxidant defences, resulting in less DNA fragmentation and lipid peroxidation. The clinical outcomes were aligned with a possible positive effect on reproductive function. Micronutrients could be regarded as an alternative to antioxidants in correcting oxidative damage in infertile men; however, to confirm such findings, further clinical investigations are warranted (Registration number: IRCT201510207223N6).

Assessment of folate and cobalamin concentrations in relation to their dependent intracellular metabolites in serum of pigs between 6 and 26 weeks of age

Folate (vitamin B₉) and cobalamin (vitamin B₁₂) play an important role in amino acid metabolism, nucleic acid synthesis, and methyl group transfer. Two intracellular enzymes, methionine synthase and methylmalonyl-CoA mutase, are folate and/or cobalamin-dependent, respectively. At the cellular level, a lack of folate and cobalamin leads to accumulation of serum homocysteine (HCY) and a lack of cobalamin leads to increased methylmalonic acid (MMA) concentrations. Altered serum HCY and MMA concentrations can influence amino acid metabolism and nucleic acid synthesis in pigs. Therefore, we aimed to evaluate serum folate, cobalamin, HCY, and MMA concentrations in postweaning pigs between 6 and 26 weeks of age. Serum samples from 12 pigs collected at week 6, 7, 8, 9, 10, 14, 18, 22, and 26 as part of an unrelated study were analyzed. Serum folate (p < .0001), cobalamin (p = .0001), HCY (p < .0001), and MMA (p < .0001) concentrations differed significantly during the postweaning period between 6 and 26 weeks of age; with significantly higher serum HCY (at weeks 6 and 7 compared to weeks 9, 14, 18, 22, and 26) and MMA concentrations (at weeks 6, 7, and 8 compared to weeks 14, 18, 22, and 26) and an overall decrease of serum MMA concentrations from week 6 to week 14 in the pigs studied. This study suggests age-dependent changes in intracellular folate- and cobalamin-dependent metabolites (i.e., HCY and MMA) in pigs between 6 and 26 weeks of age, possibly reflecting decreased availability of intracellular folate and/or cobalamin for amino acid metabolism, nucleic acid synthesis, and methyl group transfer.

Effects of altered maternal folate and vitamin B12 on neurobehavioral outcomes in F1 male mice

Maternal folate and vitamin B₁₂ status during pregnancy may influence development of central nervous system (CNS) in the offspring. Very little attention has been paid to understand the combined effects of both the vitamins during pregnancy. The present study was designed to evaluate the biochemical and behavioral outcomes following alterations in folate and vitamin B₁₂ levels in C57BL/6 mice. The female mice were fed with different combinations of folate and vitamin B₁₂ whereas; males were fed with normal diet for 4 weeks. The mice were mated and the pregnant mice received the same diets as before pregnancy. The F1 male mice were further continued on maternal diet for 6 weeks following neurobehavioral and biochemical assessment. The body weight of the F1 male mice was significantly decreased in the mice that received folate and vitamin B₁₂ deficient diet. Altered cognitive functions were observed in the folate and B₁₂ deficient F1 male mice as assessed by Morris water maze and novel object recognition tests. Spontaneous locomotor activity was decreased in F1 male mice fed with folate and B₁₂ deficient diets. Elevated homocysteine levels and decreased hydrogen sulfide levels were also observed in the brain of F1 male mice on folate and B₁₂ deficient diets. However, GSH and GSSG levels were increased in the brain of the animals supplemented with folate deficient diet with different combinations of B₁₂. The study suggests that exposure of female mice to folate and vitamin B₁₂ deficiency during pregnancy effects in-utero development of fetus, which further leads to behavioral anomalies in adult life and is sufficient to cause impaired cognitive behavior in the subsequent generation. Thus, elucidating the role and importance of maternal dietary folate and B₁₂ ratio during pregnancy.

Reactivity of Small Oxoacids of Sulfur

Oxidation of sulfide to sulfate is known to consist of several steps. Key intermediates in this process are the so-called small oxoacids of sulfur (SOS)—sulfenic HSOH (hydrogen thioperoxide, oxadisulfane, or sulfur hydride hydroxide) and sulfoxylic S(OH)₂ acids. Sulfur monoxide can be considered as a dehydrated form of sulfoxylic acid. Although all of these species play an important role in atmospheric chemistry and in organic synthesis, and are also invoked in biochemical processes, they are quite unstable compounds so much so that their physical and chemical properties are still subject to intense studies. It is well-established that sulfoxylic acid has very strong reducing properties, while sulfenic acid is capable of both oxidizing and reducing various substrates. Here, in this review, the mechanisms of sulfide oxidation as well as data on the structure and reactivity of small sulfur-containing oxoacids, sulfur monoxide, and its precursors are discussed.

The Contribution of Homocysteine Metabolism Disruption to Endothelial Dysfunction: State-of-the-Art

Homocysteine (Hcy) is a sulfur-containing non-proteinogenic amino acid formed during the metabolism of the essential amino acid methionine. Hcy is considered a risk factor for atherosclerosis and cardiovascular disease (CVD), but the molecular basis of these associations remains elusive. The impairment of endothelial function, a key initial event in the setting of atherosclerosis and CVD, is recurrently observed in hyperhomocysteinemia (HHcy). Various observations may explain the vascular toxicity associated with HHcy. For instance, Hcy interferes with the production of nitric oxide (NO), a gaseous master regulator of endothelial homeostasis. Moreover, Hcy deregulates the signaling pathways associated with another essential endothelial gasotransmitter: hydrogen sulfide. Hcy also mediates the loss of critical endothelial antioxidant systems and increases the intracellular concentration of reactive oxygen species (ROS) yielding oxidative stress. ROS disturb lipoprotein metabolism, contributing to the growth of atherosclerotic vascular lesions. Moreover, excess Hcy maybe be indirectly incorporated into proteins, a process referred to as protein N-homocysteinylation, inducing vascular damage. Lastly, cellular hypomethylation caused by build-up of S-adenosylhomocysteine (AdoHcy) also contributes to the molecular basis of Hcy-induced vascular toxicity, a mechanism that has merited our attention in particular. AdoHcy is the metabolic precursor of Hcy, which accumulates in the setting of HHcy and is a negative regulator of most cell methyltransferases. In this review, we examine the biosynthesis and catabolism of Hcy and critically revise recent findings linking disruption of this metabolism and endothelial dysfunction, emphasizing the impact of HHcy on endothelial cell methylation status.

Folic Acid and Vitamin B12 Administration in CKD, Why Not?

Patients affected by chronic kidney disease (CKD) or end-stage renal disease (ESRD) experience a huge cardiovascular risk and cardiovascular events represent the leading causes of death. Since traditional risk factors cannot fully explain such increased cardiovascular risk, interest in non-traditional risk factors, such as hyperhomocysteinemia and folic acid and vitamin B12 metabolism impairment, is growing. Although elevated homocysteine blood levels are often seen in patients with CKD and ESRD, whether hyperhomocysteinemia represents a reliable cardiovascular and mortality risk marker or a therapeutic target in this population is still unclear. In addition, folic acid and vitamin B12 could not only be mere cofactors in the homocysteine metabolism; they may have a direct action in determining tissue damage and cardiovascular risk. The purpose of this review was to highlight homocysteine, folic acid and vitamin B12 metabolism impairment in CKD and ESRD and to summarize available evidences on hyperhomocysteinemia, folic acid and vitamin B12 as cardiovascular risk markers, therapeutic target and risk factors for CKD progression.