Sulfur amino acid metabolism: pathways for production and removal of homocysteine and cysteine

A FRET-based ratiometric fluorescent probe to detect cysteine metabolism in mitochondria

As an important biothiol in living cells, cysteine is closely related to oxidative damage in living organisms. Sulfite from cysteine metabolism in living cells plays a crucial role in maintaining homeostasis in an organism, and the unbalance of sulfite in vivo would lead to multiple diseases. Thus the development of a new fluorescent probe for cysteine metabolism is needed urgently in mitochondria which are the main place of cysteine metabolism. Herein we construct a novel targeting mitochondria fluorescent probe CP-K based on the FRET mechanism to visualize sulfite in living MCF-7 cells. Probe CP-K displays a large Stokes shift of 150 nm, a low detection limit (26.3 nM) and "naked eye" detection after the addition of HSO3-. Importantly, it is appropriate for imaging the endogenous sulfite from cysteine metabolism in living cells.

A New Endoplasmic Reticulum (ER)-Targeting Fluorescent Probe for the Imaging of Cysteine in Living Cells

Cysteine (Cys) is an important endogenous amino acid and plays critical physiological roles in living systems. Herein, an endoplasmic reticulum (ER)-targeting fluorescent probe (FER-Cys) was designed and prepared for imaging of Cys in living cells. The probe FER-Cys consists of a fluorescein framework as the fluorescent platform, acrylate group as the response site for the selective recognition of Cys, and ER-specific p-toluenesulfonamide fragment. After the response of probe FER-Cys to Cys, a turn-on fluorescence signal at 546 nm could be detected obviously. The probe FER-Cys further shows desirable selectivity to Cys. Finally, the probe FER-Cys was proven to selectively detect Cys in live cells and successfully image the changes of Cys level in the cell models of H₂O₂-induced redox imbalance.

The effect of total sulfur amino acid levels on growth performance and bone metabolism in pullets under heat stress

A study was conducted to investigate the effects of total sulfur amino acid (TSAA) levels on performance and bone metabolism in pullets under heat stress (HS). Hy-Line W36 day-old pullets (n = 216) were randomly distributed in 3 dietary treatments (70, 85, and 100% of TSAA), with 6 replicates of 12 birds. The treatments were defined as percentages of the TSAA level recommendation (100, 85, and 70%), and 85 and 100% of TSAA were obtained by adding L-Methionine to the basal deficient diet (70% of TSAA). The birds were raised under HS (35°C/7 h/D) from 1 to 18 wk. At 6, 12, and 18 wk, growth performance was measured. At 12 and 18 wk, bone weight, ash, collagenous (ColP), and noncollagenous proteins (NColP), tissue volume (TV), bone mineral content (BMC), and mineral density from total, cortical, and trabecular bones were evaluated. The means were subjected to ANOVA and, when significant (P ≤ 0.05), were compared by Dunnett's test. Regression analyses were performed to evaluate trends of TSAA dose response. Overall, birds fed 70% of TSAA showed poor growth and feed efficiency compared with other groups. Additionally, in at least 1 phase, birds fed 70% of TSAA showed lower bone ash, NColP, total BMC, and TV and higher ColP than the other treatments, whereas the cortical and trabecular TV and BMC were lower than 100% of TSAA (P < 0.04). Quadratic effects of TSAA levels on body weight gain (BWG) were found, and the level for maximum BWG was 95% of the TSAA recommendation (P < 0.03, R² > 0.83). In conclusion, the use of a TSAA-deficient diet resulted in poor performance and delayed bone development. Additionally, the use of 100% of TSAA led to better initial structural bone development than 85% of TSAA. Therefore, the TSAA level recommended by the primary breeder guideline was enough to support growth and bone quality under HS, suggesting that HS does not alter TSAA requirement in pullets.

Interactive Effects of Glycine Equivalent, Cysteine, and Choline on Growth Performance, Nitrogen Excretion Characteristics, and Plasma Metabolites of Broiler Chickens Using Neural Networks Optimized with Genetic Algorithms

Simple Summary

The negative effects of nitrogen emissions caused by animal husbandry on the environment can be reduced by lowering the crude protein content in the diets of broiler chickens. The nonessential amino acids glycine and serine, investigated together as glycine equivalent, can limit the growth of broiler chickens fed diets that are low in crude protein. The response of broiler chickens to dietary glycine equivalent is not constant and is affected by endogenous precursors of glycine equivalent and metabolic processes that dissipate glycine equivalent. Choline can be converted to glycine, and glycine equivalent is required to form cysteine from methionine. The present study investigated interactive effects among dietary glycine equivalent, cysteine, and choline in broiler chickens. The results showed that the gain:feed ratio increased with dietary glycine equivalent supplementation. The extent of interactive effects among glycine equivalent, cysteine, and choline on the gain:feed ratio was hardly pronounced. Very high nitrogen-utilization efficiency with low variation among treatments was found. The findings indicate that small differences in nitrogen-utilization efficiency caused low glycine equivalent dissipation for nitrogen excretion, likely resulting in small interactive effects among dietary glycine equivalent, cysteine, and choline. These results contribute to further dietary crude protein reduction in feed for broiler chickens.

Abstract

Responses of broiler chickens to dietary glycine equivalent (Gly_equi) are affected by dietary cysteine and choline. Hence, this study investigated interactive effects among dietary Gly_equi, cysteine, and choline on the growth of broiler chickens. Male Ross 308 broiler chickens were maintained in 105 metabolism units (10 birds/unit) from days 7 to 22. Excreta were collected in 12-h intervals from days 18 to 21. Blood was sampled on day 22 (1 bird/unit). Five levels each of Gly_equi (9–21 g/kg), cysteine (2–5 g/kg), and choline (0.5–1.7 g/kg) were tested under 15 diets in 7 replicates each following a fractional central composite design. Another diet was provided to five metabolism units (15 birds/unit) to measure prececal amino acid digestibility. Data were evaluated using neural networks. The gain:feed ratio (G:F) increased with digestible Gly_equi intake. Differences between low and high digestible cysteine intake were low. Effects of choline intake on G:F were low. Nitrogen-utilization efficiency (NUE) was high (≥77%), with low variation among treatments. Plasma metabolites varied among treatments and indicated that metabolism of Gly_equi, cysteine, and choline was influenced. These findings showed that interactive effects of dietary Gly_equi, cysteine, and choline on growth were small, possibly because NUE was barely influenced.

Multi-Omics Reveals Impact of Cysteine Feed Concentration and Resulting Redox Imbalance on Cellular Energy Metabolism and Specific Productivity in CHO Cell Bioprocessing

Chinese hamster ovary (CHO) cells are currently the primary host cell lines used in biotherapeutic manufacturing of monoclonal antibodies (mAbs) and other biopharmaceuticals. Cellular energy metabolism and endoplasmic reticulum (ER) stress are known to greatly impact cell growth, viability, and specific productivity of a biotherapeutic; but the molecular mechanisms are not fully understood. The authors previously employed multi-omics profiling to investigate the impact of a reduction in cysteine (Cys) feed concentration in a fed-batch process and found that disruption of the redox balance led to a substantial decline in cell viability and titer. Here, the multi-omics findings are expanded, and the impact redox imbalance has on ER stress, mitochondrial homeostasis, and lipid metabolism is explored. The reduced Cys feed activates the amino acid response (AAR), increases mitochondrial stress, and initiates gluconeogenesis. Multi-omics analysis reveals that together, ER stress and AAR signaling shift the cellular energy metabolism to rely primarily on anaplerotic reactions, consuming amino acids and producing lactate, to maintain energy generation. Furthermore, the pathways are demonstrated in which this shift in metabolism leads to a substantial decline in specific productivity and altered mAb glycosylation. Through this work, meaningful bioprocess markers and targets for genetic engineering are identified.

Ambient air pollution and homocysteine: Current epidemiological evidence and a call for further research

Elevated blood homocysteine (Hcy) is an independent risk factor for cardiovascular disease. A growing number of studies have evaluated the link between air pollution and blood Hcy levels, but the results are inconsistent. To date, no systematic review of the published studies has been conducted yet. We aimed to provide a comprehensive overview of these studies. We systematically searched three international databases (PubMed, Web of Science, and Embase) and four Chinese databases (Wanfang, CNKI, CBM, and VIP) for peer-reviewed epidemiological studies investigating associations between ambient air pollutants and Hcy levels published before December 2019. We screened literature, extracted data, assessed methodological quality, and evaluated the risk of bias of the included studies. Of 1157 identified articles, 10 were finally included in this systematic review. Most were cross-sectional studies and were performed in developed countries. Particulate matter with aerodynamic diameters less than 2.5 μm (PM2.5) and/or 10 μm (PM10) were investigated in all of the included studies. Overall, the evidence generally supports a positive association between higher PM concentrations and elevated Hcy levels. However, high heterogeneity in terms of study participants, study design, exposure duration, and particle components and sources, low methodological quality and probable high risk of bias in some studies, and limited literature number precluded us from drawing a robust conclusion. Associations between Hcy and gaseous pollutants were explored in only one or two studies, and the results were inconclusive. Additional, well-designed studies remain required to validate the association between air pollution and Hcy.

High-concentration homocysteine inhibits mitochondrial respiration function and production of reactive oxygen species in neuron cells

OBJECTIVE

Homocysteine plays critical roles in cellular redox homeostasis, and hyperhomocysteinemia has been associated with multiple diseases, including neurological disorders involving reactive oxygen species-inducing and pro-inflammatory effects of homocysteine that are related to mitochondria. This study investigated the role of homocysteine in regulating mitochondria of neuron cell lines.

METHODS

Neuron cells were pre-treated with homocysteine, and then flow cytometry was used to detect reactive oxygen species production and mitochondrial membrane potential, while Seahorse XFp Mito stress assay was used to comprehensively analyze mitochondrial function.

RESULTS

The experimental results showed that high-concentration homocysteine diminished carbonyl cyanide-4 (trifluoromethoxy) phenylhydrazone-stimulated oxygen consumption rate and mitochondrial spare respiration capacity in a time- and concentration-dependent manner, and homocysteine also reduced reactive oxygen species in cultured neuron cell lines while no changes in mitochondrial membrane potential were observed.

CONCLUSION

These results indicate that homocysteine diminished mitochondrial respiration function in neuron cell lines mediated by its reactive oxygen species-reducing effects, which may underlie the association between hyperhomocysteinemia and human diseases.

Developmental changes in physiological amino acids and hepatic methionine remethylation enzyme activities in E10-21 chick embryos and D1-49 broilers

The remethylation of homocysteine to methionine is important for chick embryos to sustain the S-adenosylmethionine transmethylation reactions, which are essential for the rapid proliferation of cells. Developmental changes in hepatic 5-methyltetrahydrofolate-homocysteine methyltransferase (MFMT), betaine-homocysteine methyltransferase (BHMT) and hepatic serine hydroxymethyltransferase (SHMT) were determined in E10-21 Cobb 500 broiler chick embryos and hatched chicks from D1-49. Hepatic levels of free serine, glycine, putrescine, spermidine and spermine levels were also determined. Analyses showed hepatic MFMT-specific activity doubled from E10 to E12, with remaining embryo development experiencing small fluctuations in activity through E21. Hepatic MFMT doubled immediately after hatch, with peak activity occurring at D3. Afterwards, hepatic MFMT-specific activity steadily declined from D7-49. Hepatic BHMT activity was higher from E10 to E16 of embryogenesis, decreased rapidly at E17 and remained lower through E21 (p < .05). Hepatic BHMT-specific activity was also lower in chicks, with the exception of a peak in specific activity on D7. BHMT activity returned to lower levels by D21. Throughout embryogenesis, hepatic SHMT activity in chick embryos remained relatively constant except for a decrease at 13E, followed by an increase at 14E. Maximal activity of SHMT was found the first day post-hatch. Additionally, SHMT activity was significantly lower in growing chicks than that in embryos. Hepatic-free serine and glycine levels were negatively correlated with SHMT in hatched chicks. Hepatic polyamine, putrescine and spermidine shared a similar development pattern: peak level in the middle of incubation, low at late embryogenesis and lowest during the post-hatch period except an increase within one week after hatch. The sharp increase in hepatic concentrations of glycine, serine and putrescine, along with increased specific activities of MHMT, BHMT and SHMT from D1-7, suggests that methionine conservation (remethylation from homocysteine) and glycine/serine is critical for young chicks for organ growth, maturation, and development.

Serum Metabolome Changes in Relation to Prothrombotic State Induced by Combined Oral Contraceptives with Drospirenone and Ethinylestradiol

The association between hypercoagulability and use of drospirenone (DRSP) and ethinylestradiol (EE) containing combined oral contraceptives (COCs) is an important clinical concern. We have previously reported that the two formulations of DRSP combined with EE (namely, DRSP/20EE and DRSP/30EE) bring about a prothrombotic state in hemostatic traits of female users. We report here the serum metabolomic changes in the same study cohort in relation to the attendant prothrombotic state induced by COC use, thus offering new insights on the underlying biochemical mechanisms contributing to the altered coagulatory profile with COC use. A total of 78 healthy women participated in this study and were grouped as follows: control group not using oral contraceptives (n = 25), DRSP/20EE group (n = 27), and DRSP/30EE group (n = 26). Untargeted metabolomics revealed changes in amino acid concentrations, particularly a decrease in glycine and an increase in both cysteine and lanthionine in the serum, accompanied by variations in oxidative stress markers in the COC users compared with the controls. Of importance, this study is the first to link specific amino acid variations, serum metabolites, and the oxidative metabolic profile with DRSP/EE use. These molecular changes could be linked to specific biophysical coagulatory alterations observed in the same individuals. These new findings lend evidence on the metabolomic substrates of the prothrombotic state associated with COC use in women and informs future personalized/precision medicine research. Moreover, we underscore the importance of an interdisciplinary approach to evaluate venous thrombotic risk associated with COC use.

Nutritional Deficiencies, Bariatric Surgery, and Serum Homocysteine Level: Review of Current Literature

Obesity is currently one of the biggest global health problems. In the case of severe obesity, bariatric surgeries are considered to be the most important method of treatment. The 2 most commonly performed bariatric surgery procedures include Roux-en-Y gastric bypass and sleeve gastrectomy. However, these methods are not free from complications, and the most common ones (moderately long or long term) are micronutrient deficiencies. The deficiency of vitamins B6, B12, and folic acid as cofactors of the folate cycle contributes to the development of hyperhomocysteinemia. It seems that apart from nutritional factors, there are other aspects that have a significant influence on the concentration of homocysteine in blood, such as the type of conducted bariatric surgery, the post-surgical concentration of betaine and creatinine, and the clearance of methionine (i.e., the mutations of the gene that encodes the MTHFR reductase as well as other genes associated with the process of methylation, e.g., methionine synthase). Their presence might be one of the causes of the increased concentration of homocysteine after surgery despite the fact that patients take vitamin-mineral supplementation.

Multiple Sclerosis: Lipids, Lymphocytes, and Vitamin D

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. We review the two core MS features, myelin instability, fragmentation, and remyelination failure, and dominance of pathogenic CD4+ Th17 cells over protective CD4+ Treg cells. To better understand myelin pathology, we describe myelin biosynthesis, structure, and function, then highlight stearoyl-CoA desaturase (SCD) in nervonic acid biosynthesis and nervonic acid's contribution to myelin stability. Noting that vitamin D deficiency decreases SCD in the periphery, we propose it also decreases SCD in oligodendrocytes, disrupting the nervonic acid supply and causing myelin instability and fragmentation. To better understand the distorted Th17/Treg cell balance, we summarize Th17 cell contributions to MS pathogenesis, then highlight how 1,25-dihydroxyvitamin D3 signaling from microglia to CD4+ T cells restores Treg cell dominance. This signaling rapidly increases flux through the methionine cycle, removing homocysteine, replenishing S-adenosyl-methionine, and improving epigenetic marking. Noting that DNA hypomethylation and inappropriate DRB1*1501 expression were observed in MS patient CD4+ T cells, we propose that vitamin D deficiency thwarts epigenetic downregulation of DRB1*1501 and Th17 cell signature genes, and upregulation of Treg cell signature genes, causing dysregulation within the CD4+ T cell compartment. We explain how obesity reduces vitamin D status, and how estrogen and vitamin D collaborate to promote Treg cell dominance in females. Finally, we discuss the implications of this new knowledge concerning myelin and the Th17/Treg cell balance, and advocate for efforts to address the global epidemics of obesity and vitamin D deficiency in the expectation of reducing the impact of MS.

Methylation deficiency disrupts biological rhythms from bacteria to humans

The methyl cycle is a universal metabolic pathway providing methyl groups for the methylation of nuclei acids and proteins, regulating all aspects of cellular physiology. We have previously shown that methyl cycle inhibition in mammals strongly affects circadian rhythms. Since the methyl cycle and circadian clocks have evolved early during evolution and operate in organisms across the tree of life, we sought to determine whether the link between the two is also conserved. Here, we show that methyl cycle inhibition affects biological rhythms in species ranging from unicellular algae to humans, separated by more than 1 billion years of evolution. In contrast, the cyanobacterial clock is resistant to methyl cycle inhibition, although we demonstrate that methylations themselves regulate circadian rhythms in this organism. Mammalian cells with a rewired bacteria-like methyl cycle are protected, like cyanobacteria, from methyl cycle inhibition, providing interesting new possibilities for the treatment of methylation deficiencies.

Fustin et al. reveal the evolutionarily conserved link between methyl metabolism and biological clocks. This study suggests the possibility of translating fundamental understanding of methylation deficiencies to clinical applications.

An imidazo[1,5-α]pyridine-derivated fluorescence sensor for rapid and selective detection of sulfite

Sulfur-containing species are essential in the composition and the metabolism of the organisms, thus developing a full set of implements to cover all of them is still a favorable choice. Herein, we chose imidazo [1,5-α]pyridine moiety as the basic fluorophore for the detection of sulfite, and preliminarily completed the toolset since biothiols (GSH, Cys, Hcy), H₂S, and PhSH could be detected by sensors based on the same backbone. The designed sensor, IPD-SFT, with structural novelty and large Stokes shift (130 nm), indicated the most attractive advantages of remarkably rapid response period (within 1 min) and high selectivity for sulfite from all the sulfur-containing species. Other practical properties included high sensitivity (LOD = 50 nM) and wide pH adaptability (5.0-11.0). Furthermore, IPD-SFT could monitor both exogenous and endogenous sulfite. It not only raised a potential tool for sulfite detection, but also preliminarily completed the toolset for all the sulfur-containing species. The development of such toolsets might reveal the sulfur-containing metabolism and corresponding physiology and pathological procedures.

Immune system stimulation increases the irreversible loss of cysteine to taurine, but not sulfate, in starter pigs

An isotope tracer study was conducted to evaluate the effects of immune system stimulation (ISS) on the irreversible loss of cysteine (Cys) to taurine (Tau) and sulfate (SO4), as well as glutathione (GSH) synthesis, during the fed state in pigs. We previously have reported that ISS increases plasma Cys flux and the GSH synthesis rate at the tissue and whole-body levels in growing pigs. Thus, the current article presents the data on the irreversible loss of Cys during ISS in pigs. Ten gilts (BW: 7.0 ± 0.12 kg) were feed restricted a sulfur amino acids (SAA) limiting diet and injected twice with either saline (n = 4) or increasing amounts of E. coli lipopolysaccharide (n = 6). The day after the second injection, a 5-h primed continuous intravenous infusion of 35S-Cys was conducted. ISS reduced plasma Cys and total SAA concentrations (16% and 21%, respectively; P < 0.05). However, ISS had no effect on the plasma concentrations of Tau and SO4, nor did it affect the appearance of 35S in plasma Tau, plasma SO4, urinary Tau, or urinary SO4 (P > 0.19). On a whole-body basis and including urinary excretion, ISS increased the appearance of 35S in Tau by 67% (P < 0.05), but tended to decrease the appearance of 35S in SO4 by 22% (P < 0.09). Overall, the current findings indicate that during ISS, decreased plasma SAA concentrations and increased plasma Cys flux are attributed in part to increased rates of Cys conversion to Tau, but not Cys catabolism to SO4. Thus, increased utilization of Cys for the synthesis of immune system metabolites, such as GSH and Tau, is likely the main contributor to increased Cys flux during ISS in pigs. In addition, the irreversible loss of Cys during ISS is small and has a minimal impact on the daily SAA requirements of starter pigs.

Multidirectional Changes in Parameters related to Sulfur Metabolism in Frog Tissues exposed to Heavy Metal-related Stress

The investigations showed changes of the cystathionine γ-lyase (CTH), 3-mercaptopyruvate sulfurtransferase (MPST) and rhodanese (TST) activity and gene expression in the brain, heart, liver, kidney, skeletal muscles and testes in frogs Pelophylax ridibundus, Xenopus laevis and Xenopus tropicalis in response to Pb²⁺, Hg²⁺ and Cd²⁺ stress. The results were analyzed jointly with changes in the expression of selected antioxidant enzymes (cytoplasmic and mitochondrial superoxide dismutase, glutathione peroxidase, catalase and thioredoxin reducatase) and with the level of malondialdehyde (a product of lipid peroxidation). The obtained results allowed for confirming the role of sulfurtransferases in the antioxidant protection of tissues exposed to heavy metal ions. Our results revealed different transcriptional responses of the investigated tissues to each of the examined heavy metals. The CTH, MPST and TST genes might be regarded as heavy metal stress-responsive. The CTH gene expression up-regulation was confirmed in the liver (Pb²⁺, Hg²⁺, Cd²⁺) and skeletal muscle (Hg²⁺), MPST in the brain (Pb²⁺, Hg²⁺), kidney (Pb²⁺, Cd²⁺), skeletal muscle (Pb²⁺, Hg²⁺,Cd²⁺) and TST in the brain (Pb²⁺) and kidney (Pb²⁺, Hg²⁺, Cd²⁺). Lead, mercury and cadmium toxicity was demonstrated to affect the glutathione (GSH) and cysteine levels, the concentration ratio of reduced to oxidized glutathione ([GSH]/[GSSG]) and the level of sulfane sulfur-containing compounds, which in case of enhanced reactive oxygen species generation can reveal their antioxidative properties. The present report is the first to widely describe the role of the sulfane sulfur/H₂S generating enzymes and the cysteine/glutathione system in Pb²⁺, Hg²⁺ and Cd²⁺ stress in various frog tissues, and to explore the mechanisms mediating heavy metal-related stress.

Methionine Dependence of Cancer

Tumorigenesis is accompanied by the reprogramming of cellular metabolism. The shift from oxidative phosphorylation to predominantly glycolytic pathways to support rapid growth is well known and is often referred to as the Warburg effect. However, other metabolic changes and acquired needs that distinguish cancer cells from normal cells have also been discovered. The dependence of cancer cells on exogenous methionine is one of them and is known as methionine dependence or the Hoffman effect. This phenomenon describes the inability of cancer cells to proliferate when methionine is replaced with its metabolic precursor, homocysteine, while proliferation of non-tumor cells is unaffected by these conditions. Surprisingly, cancer cells can readily synthesize methionine from homocysteine, so their dependency on exogenous methionine reflects a general need for altered metabolic flux through pathways linked to methionine. In this review, an overview of the field will be provided and recent discoveries will be discussed.

Cystine transporter regulation of pentose phosphate pathway dependency and disulfide stress exposes a targetable metabolic vulnerability in cancer

SLC7A11-mediated cystine uptake is critical for maintaining redox balance and cell survival. Here we show that this comes at a significant cost for cancer cells with high levels of SLC7A11. Actively importing cystine is potentially toxic due to its low solubility, forcing cancer cells with high levels of SLC7A11 (SLC7A11high) to constitutively reduce cystine to the more soluble cysteine. This presents a significant drain on the cellular NADPH pool and renders such cells dependent on the pentose phosphate pathway. Limiting glucose supply to SLC7A11high cancer cells results in marked accumulation of intracellular cystine, redox system collapse and rapid cell death, which can be rescued by treatments that prevent disulfide accumulation. We further show that inhibitors of glucose transporters selectively kill SLC7A11high cancer cells and suppress SLC7A11high tumour growth. Our results identify a coupling between SLC7A11-associated cystine metabolism and the pentose phosphate pathway, and uncover an accompanying metabolic vulnerability for therapeutic targeting in SLC7A11high cancers.

Structure-activity relationships study of isothiocyanates for H2S releasing properties: 3-Pyridyl-isothiocyanate as a new promising cardioprotective agent

Introduction

The gasotransmitter hydrogen sulphide (H₂S), an endogenous ubiquitous signalling molecule, is known for its beneficial effects on different mammalian systems. H₂S exhibits cardioprotective activity against ischemia/reperfusion (I/R) or hypoxic injury.

Methods

A library of forty-five isothiocyanates, selected for their different chemical properties, has been evaluated for its hydrogen sulfide (H₂S) releasing capacity. The obtained results allowed to correlate several factors such as steric hindrance, electronic effects and position of the substituents to the observed H₂S production. Moreover, the chemical-physical profiles of the selected compounds have been studied by an in silico approach and from a combination of the obtained results, 3-pyridyl-isothiocyanate (25) has been selected as the most promising one. A detailed pharmacological characterization of its cardioprotective action has been performed.

Results

The results herein obtained strongly indicate 3-pyridyl-isothiocyanate (25) as a suitable pharmacological option in anti-ischemic therapy. The cardioprotective effects of compound 25 were tested in vivo and found to exhibit a positive effect.

Conclusion

Results strongly suggest that isothiocyanate-based H₂S-releasing drugs, such as compound 25, can trigger a ‘‘pharmacological pre-conditioning” and could represent a suitable pharmacological option in antiischemic therapy.

Methionine dietary supplementation potentiates ionizing radiation-induced gastrointestinal syndrome

Methionine is an essential amino acid needed for a variety of processes in living organisms. Ionizing radiation depletes tissue methionine concentrations and leads to the loss of DNA methylation and decreased synthesis of glutathione. In this study, we aimed to investigate the effects of methionine dietary supplementation in CBA/CaJ mice after exposure to doses ranging from 3 to 8.5 Gy of ¹³⁷Cs of total body irradiation. We report that mice fed a methionine-supplemented diet (MSD; 19.5 vs. 6.5 mg/kg in a methionine-adequate diet, MAD) developed acute radiation toxicity at doses as low as 3 Gy. Partial body irradiation performed with hindlimb shielding resulted in a 50% mortality rate in MSD-fed mice exposed to 8.5 Gy, suggesting prevalence of radiation-induced gastrointestinal syndrome in the development of acute radiation toxicity. Analysis of the intestinal microbiome demonstrated shifts in the gut ecology, observed along with the development of leaky gut syndrome and bacterial translocation into the liver. Normal gut physiology impairment was facilitated by alterations in the one-carbon metabolism pathway and was exhibited as decreases in circulating citrulline levels mirrored by decreased intestinal mucosal surface area and the number of surviving crypts. In conclusion, we demonstrate that a relevant excess of methionine dietary intake exacerbates the detrimental effects of exposure to ionizing radiation in the small intestine.NEW & NOTEWORTHY Methionine supplementation, instead of an anticipated health-promoting effect, sensitizes mice to gastrointestinal radiation syndrome. Mechanistically, excess of methionine negatively affects intestinal ecology, leading to a cascade of physiological, biochemical, and molecular alterations that impair normal gut response to a clinically relevant genotoxic stressor. These findings speak toward increasing the role of registered dietitians during cancer therapy and the necessity of a solid scientific background behind the sales of dietary supplements and claims regarding their benefits.

Short-term determination and long-term evaluation of the dietary methionine requirement in adult dogs

Methionine, an essential sulphur-containing amino acid (SAA), plays an integral role in many metabolic processes. Evidence for the methionine requirements of adult dogs is limited, and we employed the indicator amino acid oxidation (IAAO) method to estimate dietary methionine requirements in Labrador retrievers (n 21). Using semi-purified diets, the mean requirement was 0·55 (95 % CI 0·41, 0·71) g/4184 kJ. In a subsequent parallel design study, three groups of adult Labrador retrievers (n 52) were fed semi-purified diets with 0·55 g/4184 kJ (test diet 1), 0·71 g/4184 kJ (test diet 2) or 1·37 g/4184 kJ (control diet) of methionine for 32 weeks to assess the long-term consequences of feeding. The total SAA content (2·68 g/4184 kJ) was maintained through dietary supplementation of cystine. Plasma methionine did not decrease in test group and increased significantly on test diet 1 in weeks 8 and 16 compared with control. Reducing dietary methionine did not have a significant effect on whole blood, plasma or urinary taurine or plasma N-terminal pro B-type natriuretic peptide. Significant effects in both test diets were observed for cholesterol, betaine and dimethylglycine. In conclusion, feeding methionine at the IAAO-estimated mean was sufficient to maintain plasma methionine over 32 weeks when total SAA was maintained. However, choline oxidation may have increased to support plasma methionine and have additional consequences for lipid metabolism. While the IAAO can be employed to assess essential amino acid requirements, such as methionine in the dog using semi-purified diets, further work is required to establish safe levels for commercial diet formats.

Cysteine Toxicity Drives Age-Related Mitochondrial Decline by Altering Iron Homeostasis

Mitochondria and lysosomes are functionally linked, and their interdependent decline is a hallmark of aging and disease. Despite the long-standing connection between these organelles, the function(s) of lysosomes required to sustain mitochondrial health remains unclear. Here, working in yeast, we show that the lysosome-like vacuole maintains mitochondrial respiration by spatially compartmentalizing amino acids. Defects in vacuole function result in a breakdown in intracellular amino acid homeostasis, which drives age-related mitochondrial decline. Among amino acids, we find that cysteine is most toxic for mitochondria and show that elevated non-vacuolar cysteine impairs mitochondrial respiration by limiting intracellular iron availability through an oxidant-based mechanism. Cysteine depletion or iron supplementation restores mitochondrial health in vacuole-impaired cells and prevents mitochondrial decline during aging. These results demonstrate that cysteine toxicity is a major driver of age-related mitochondrial deterioration and identify vacuolar amino acid compartmentation as a cellular strategy to minimize amino acid toxicity.

Dietary methionine level alters growth, digestibility, and gene expression of amino acid transporters in meat-type chickens

Imbalance in nutrients can affect digestibility of amino acids by altering gene expression of amino acid transporters. We investigated digestibility and molecular transporters of essential amino acids in chickens fed a methionine-deficient diet. A total of 40 chicks (23 D old) were randomly assigned to either a control (0.49% methionine) or a deficient (0.28%) diet until 41 D when they were sampled for Pectoralis (P.) major, kidney, ileum, and hypothalamus for mRNA expression analysis. The ileal content was collected for apparent ileal digestibility (AID) analysis. Birds fed the deficient diet had reduced growth and worse feed efficiency compared to control. The AID of methionine was similar between both groups. The AID of other essential amino acids was higher in the deficient group than control. mRNA expression of b0,+ AT and LAT4 were upregulated in the ileum and kidney but LAT1 was downregulated only in kidney of the deficient group compared to control. In the P. major, SNAT1, SNAT2, and CAT1 were upregulated in the deficient group compared to control. A diet deficiency in methionine affects digestibility of essential amino acids and cysteine, but not the digestibility of methionine. The change in digestibility is reflected in the mRNA expression of amino acid transporters across different tissues.

Outer-Sphere Tyrosine 159 within the 3-Mercaptopropionic Acid Dioxygenase S-H-Y Motif Gates Substrate-Coordination Denticity at the Non-Heme Iron Active Site

Thiol dioxygenases are non-heme mononuclear iron enzymes that catalyze the O₂-dependent oxidation of free thiols (-SH) to produce the corresponding sulfinic acid (-SO₂^-). Regardless of the phylogenic domain, the active site for this enzyme class is typically comprised of two major features: (1) a mononuclear ferrous iron coordinated by three protein-derived histidines and (2) a conserved sequence of outer Fe-coordination-sphere amino acids (Ser-His-Tyr) spatially adjacent to the iron site (∼3 Å). Here, we utilize a promiscuous 3-mercaptopropionic acid dioxygenase cloned from Azotobacter vinelandii (Av MDO) to explore the function of the conserved S-H-Y motif. This enzyme exhibits activity with 3-mercaptopropionic acid (3mpa), l-cysteine (cys), as well as several other thiol-bearing substrates, thus making it an ideal system to study the influence of residues within the highly conserved S-H-Y motif (H157 and Y159) on substrate specificity and reactivity. The pK_a values for these residues were determined by pH-dependent steady-state kinetics, and their assignments verified by comparison to H157N and Y159F variants. Complementary electron paramagnetic resonance and Mössbauer studies demonstrate a network of hydrogen bonds connecting H157-Y159 and Fe-bound ligands within the enzymatic Fe site. Crucially, these experiments suggest that the hydroxyl group of Y159 hydrogen bonds to Fe-bound NO and, by extension, Fe-bound oxygen during native catalysis. This interaction alters both the NO binding affinity and rhombicity of the 3mpa-bound iron-nitrosyl site. In addition, Fe coordination of cys is switched from thiolate only to bidentate (thiolate/amine) for the Y159F variant, indicating that perturbations within the S-H-Y proton relay network also influence cys Fe binding denticity.

Adenosine inhibits human astrocyte proliferation independently of adenosine receptor activation

Brain adenosine concentrations can reach micromolar concentrations in stressful situations such as stroke, neurodegenerative diseases or hypoxic regions of brain tumours. Adenosine can act by receptor-independent mechanism by reversing the reaction catalysed by S-adenosylhomocysteine (SAH) hydrolase, leading to SAH accumulation and inhibition of S-adenosylmethionine (SAM)-dependent methyltransferases. Astrocytes are essential in maintaining brain homeostasis but their pathological activation and uncontrolled proliferation plays a role in neurodegeneration and glioma. Adenosine can affect cell proliferation, but the effect of increased adenosine concentration on proliferation of astrocytes is not clarified and was addressed in present work. Human astrocytes (HA) were treated for 3 days with test drugs. Cell proliferation/viability was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium assay and by cell counting. Cell death was evaluated by assessing lactate dehydrogenase release and by western blot analysis of αII-Spectrin cleavage. 30 µM-Adenosine caused a 40% ± 3% (p < .05, n = 5) reduction in cell proliferation/viability, an effect reversed by 2U/ml-adenosine deaminase, but unchanged in the presence of antagonists of any of the adenosine receptors. Adenosine alone did not induce cell death. 100 µM-Homocysteine alone caused 16% ± 3% (p < .05) decrease in HA proliferation. Combined action of adenosine and homocysteine decreased HA proliferation by 76% ± 4%, an effect higher (p < .05) than the sum of the effects of adenosine and homocysteine alone (56% ± 5%). The inhibitory effect of adenosine on HA proliferation/viability was mimicked by two adenosine kinase inhibitors and attenuated in the presence of folate (100 µM) or SAM (50-100 µM). The results suggest that adenosine reduces HA proliferation by a receptor-independent mechanism probably involving reversal of SAH hydrolase-catalysed reaction.

The effect of total sulfur amino acid levels on growth performance, egg quality, and bone metabolism in laying hens subjected to high environmental temperature

This study evaluated the effects of total sulfur amino acid (TSAA) levels on performance, egg quality, and bone metabolism in laying hens subjected or not to high environmental temperature (HT). HyLine W36 layers (n = 144) were randomly distributed in a 2 × 3 factorial arrangement. Room temperature (control, CR: 21°C/24 h; and high temperature, HR: 32°C/8 h) and diets (70, 85, or 100% of TSAA) were the main factors, with 4 replicates of 6 birds (19 to 45 wk). The TSAA levels were obtained by adding L-Methionine (L-Met) to the basal diet (70% of TSAA) until 85 and 100% of TSAA were reached. At weeks 21, 34, and 45, growth performance, egg production, and egg quality traits were evaluated. At 45 wk, bones were evaluated for collagenous and non-collagenous proteins, bone volume, mineral content, and mineral density from total, cortical, trabecular, and medullary portions. When interactions were found, the increase of TSAA levels (85 and 100%) was able to counteract the negative effects of HT. In general, HT reduced egg production (P < 0.05) and did not significantly affect bone quality. The birds fed 70% of TSAA showed higher feed conversion, lower body weight, egg weight, and egg mass than birds fed 85 and 100% of TSAA in at least one phase. The birds fed 100% of TSAA showed higher egg production and egg mass than the other treatments at 21 wk of age. The cortical and trabecular bone mineral densities were higher for birds fed 100 than 70% of TSAA, whereas the medullary bone mineral content and density were higher for birds fed 70 than 100% of TSAA. In conclusion, HT had negative impact on performance, egg quality and no effect on bone development. The supplementation of L-Met until either 85 or 100% of TSAA levels were reached was enough to assure good performance, egg quality, and bone development in laying hens subjected or not to HT.

Spectroscopic and Computational Comparisons of Thiolate-Ligated Ferric Nonheme Complexes to Cysteine Dioxygenase: Second-Sphere Effects on Substrate (Analogue) Positioning

Parallel spectroscopic and computational studies of iron(III) cysteine dioxygenase (CDO) and synthetic models are presented. The synthetic complexes utilize the ligand tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (^Ph2TIP), which mimics the facial three-histidine triad of CDO and other thiol dioxygenases. In addition to the previously reported [Fe^II(CysOEt)(^Ph2TIP)]BPh₄ (1; CysOEt is the ethyl ester of anionic l-cysteine), the formation and crystallographic characterization of [Fe^II(2-MTS)(^Ph2TIP)]BPh₄ (2) is reported, where the methyl 2-thiosalicylate anion (2-MTS) resembles the substrate of 3-mercaptopropionate dioxygenase (MDO). One-electron chemical oxidation of 1 and 2 yields ferric species that bind cyanide and azide anions, which have been used as spectroscopic probes of O₂ binding in prior studies of Fe^III-CDO. The six-coordinate Fe^III-CN and Fe^III-N₃ adducts are examined with UV-vis absorption, electron paramagnetic resonance (EPR), and resonance Raman (rRaman) spectroscopies. In addition, UV-vis and rRaman studies of cysteine- and cyanide-bound Fe^III-CDO are reported for both the wild-type (WT) enzyme and C93G variant, which lacks the Cys-Tyr cross-link that is present in the second coordination sphere of the WT active site. Density functional theory (DFT) and ab initio calculations are employed to provide geometric and electronic structure descriptions of the synthetic and enzymatic Fe^III adducts. In particular, it is shown that the complete active space self-consistent field (CASSCF) method, in tandem with n-electron valence state second-order perturbation theory (NEVPT2), is capable of elucidating the structural basis of subtle shifts in EPR g values for low-spin Fe^III species.

Selective Hydrogen Atom Abstraction from Dihydroflavonol by a Nonheme Iron Center Is the Key Step in the Enzymatic Flavonol Synthesis and Avoids Byproducts

The plant non-heme iron dioxygenase flavonol synthase performs a regioselective desaturation reaction as part of the biosynthesis of the signaling molecule flavonol that triggers the growing of leaves and flowers. These compounds also have health benefits for humans. Desaturation of aliphatic compounds generally proceeds through two consecutive hydrogen atom abstraction steps from two adjacent carbon atoms and in nature often is performed by a high-valent iron(IV)-oxo species. We show that the order of the hydrogen atom abstraction steps, however, is opposite of those expected from the C-H bond strengths in the substrate and determines the product distributions. As such, flavonol synthase follows a negative catalysis mechanism. Using density functional theory methods on large active-site model complexes, we investigated pathways for desaturation and hydroxylation by an iron(IV)-oxo active-site model. Contrary to thermochemical predictions, we find that the oxidant abstracts the hydrogen atom from the strong C²-H bond rather than the weaker C³-H bond of the substrate first. We analyze the origin of this unexpected selective hydrogen atom abstraction pathway and find that the alternative C³-H hydrogen atom abstraction would be followed by a low-energy and competitive substrate hydroxylation mechanism hence, should give considerable amount of byproducts. Our computational modeling studies show that substrate positioning in flavonol synthase is essential, as it guides the reactivity to a chemo- and regioselective substrate desaturation from the C²-H group, leading to desaturation products efficiently.

Serum Betaine and Dimethylglycine Are Higher in South Asian Compared with European Pregnant Women in Canada, with Betaine and Total Homocysteine Inversely Associated in Early and Midpregnancy, Independent of Ethnicity

BACKGROUND

As a methyl donor required in the folate-vitamin B-12 independent remethylation of total homocysteine (tHcy) to methionine, betaine is critical for fetal development. Pregnant South Asian women living in Canada had a higher reported prevalence of low vitamin B-12 status compared with Europeans; betaine concentrations in this population are unknown.

OBJECTIVES

We aimed to compare serum betaine concentrations between South Asian and European pregnant women, and to determine the relation between betaine and tHcy concentrations in early pregnancy.

METHODS

A retrospective cohort study was conducted using biobanked serum samples of 723 apparently healthy pregnant women of South Asian (50%) and European ethnicity residing in British Columbia, Canada. Betaine, dimethylglycine (DMG), tHcy, and related metabolites were quantified in samples collected in the first (8-13 weeks of gestation) and second (14-20 weeks of gestation) trimesters. The relation between betaine and tHcy concentrations was assessed using a generalized regression model adjusted for weeks of gestation, ethnicity, prepregnancy BMI, maternal age, neonatal sex, parity, total vitamin B-12, folate, pyridoxal 5'-phosphate, and methionine concentrations.

RESULTS

Median serum concentrations of betaine and its metabolite DMG were higher in South Asian women in the first (19.8 [IQR: 16.3-25.0] and 1.55 [IQR: 1.30-1.96] $\mu {\rm mol/L} $, respectively) and second trimesters (16.1 [IQR: 12.9-19.8] and 1.42 [IQR: 1.14-1.81] $\mu {\rm mol/L} $, respectively) compared with European women (17.6 [IQR: 13.7-22.6] and 1.38 [IQR: 1.12-1.77] $\mu {\rm mol/L} $, respectively) and (12.9 [IQR: 10.6-16.7] and 1.19 [IQR: 0.97-1.52] $\mu {\rm mol/L} $, respectively; all P values < 0.0001). Betaine was inversely associated with tHcy concentration (β = -0.0208; 95% CI: -0.0341, -0.00742; P = 0.002). Additionally, total vitamin B-12 was associated with tHcy concentration (β = -0.0312; 95% CI: -0.0401, -0.0224), after adjusting for confounding factors.

CONCLUSIONS

Pregnant South Asian women residing in Canada had higher betaine and DMG concentrations, compared with women of European ethnicity, while betaine and total vitamin B-12 predicted tHcy independent of ethnicity. Our results emphasize the role of betaine, as methyl donor, in the remethylation of tHcy in a folate-replete population.

Recent progress in the small-molecule fluorescent probes for the detection of sulfur dioxide derivatives (HSO3-/SO32-)

Sulfur dioxide (SO₂) had been recognized as an environmental pollutant produced from industrial processes. SO₂ is water soluble and forms hydrated SO₂ (SO₂·H₂O), bisulfite ion (HSO₃^-), and sulfite ion (SO₃^2-) upon dissolution in water. SO₂ could be also produced endogenously from sulfur-containing amino acids l-cysteine in mammals. Endogenous SO₂ can maintain the balance of biological sulfur and redox equilibrium in vivo, regulate blood insulin levels and reduce blood pressure. Excess intake of exogenous SO₂ can result in respiratory diseases, cardiovascular diseases and neurological disorders. As a result, fluorescent probes to detect HSO₃^-/SO₃^2- have attracted great attention in recent years. Herein, a general overview was provided with the aim to highlight the typical examples of the HSO₃^-/SO₃^2- fluorescent probes reported since 2010, especially those in the past five years. We have classified HSO₃^-/SO₃^2- fluorescent probes through different chemical reaction mechanisms and wish this review will give some help to the researchers in this field.

Glutathione Deficiency and Alterations in the Sulfur Amino Acid Homeostasis during Early Postnatal Development as Potential Triggering Factors for Schizophrenia-Like Behavior in Adult Rats

Impaired glutathione (GSH) synthesis and dopaminergic transmission are important factors in the pathophysiology of schizophrenia. Our research aimed to assess the effects of l-buthionine-(S,R)-sulfoximine (BSO), a GSH synthesis inhibitor, and GBR 12909, a dopamine reuptake inhibitor, administered alone or in combination, to Sprague–Dawley rats during early postnatal development (p5–p16), on the levels of GSH, sulfur amino acids, global DNA methylation, and schizophrenia-like behavior. GSH, methionine (Met), homocysteine (Hcy), and cysteine (Cys) contents were determined in the liver, kidney, and in the prefrontal cortex (PFC) and hippocampus (HIP) of 16-day-old rats. DNA methylation in the PFC and HIP and schizophrenia-like behavior were assessed in adulthood (p90–p93). BSO caused the tissue-dependent decreases in GSH content and alterations in Met, Hcy, and Cys levels in the peripheral tissues and in the PFC and HIP. The changes in these parameters were accompanied by alterations in the global DNA methylation in the studied brain structures. Parallel to changes in the global DNA methylation, deficits in the social behaviors and cognitive functions were observed in adulthood. Only BSO + GBR 12909-treated rats exhibited behavioral alterations resembling positive symptoms in schizophrenia patients. Our results suggest the usefulness of this neurodevelopmental model for research on the pathomechanism of schizophrenia.

Effects of the Methionine Hydroxyl Analogue Chelate Zinc on Antioxidant Capacity and Liver Metabolism Using 1H-NMR-Based Metabolomics in Aged Laying Hens

Simple Summary

Zinc, an essential trace element for laying hens, plays an important role in biological processes, such as growth, tissue growth and repairment, skeletal development, and immune competence, which also has better effects on growth performance, biochemical indexes, and antioxidant capacity. Our previous work has shown that methionine hydroxyl analogue chelated zinc (MHA-Zn) has better effects on eggshell quality, the apparent retention of minerals and nutrients, trace element deposit, and metallothionein (MT) mRNA expression. The objective of the current study was to investigate the effects of different levels of MHA-Zn on antioxidant capacity and liver metabolism of aged laying hens. The results suggest that dietary supplementation of MHA-Zn levels at 80 mg/kg has better effects on antioxidant capacity and liver metabolism, as well as homeostasis of the body.

Abstract

This study aimed to investigate the effects of different levels of methionine hydroxyl analogue chelated zinc (MHA-Zn) on antioxidant capacity and liver metabolism of aged laying hens. A total of 960 57-week-old layers were fed a basal diet (Zn: 35.08 mg/kg) without extra zinc for two weeks, and then allocated to four treatments consisting of eight replicates of 30 birds each for 14 weeks. Four levels of Zn (zinc sulfate (ZnSO₄): 80 mg/kg; MHA-Zn: 20, 40, 80 mg/kg) were added to the diet. The results indicated that compared with inorganic zinc, organic zinc of 80 mg/kg has a significant advantage in improving the antioxidant capacity of aged hens, which increased the level of Cu/Zn-superoxide dismutase (SOD) and the total antioxidant capacity (T-AOC) in the serum and liver, and reduced the concentration of malondialdehyde (MDA) of laying hens. The serum albumen composition was significantly modified, meanwhile, the level of total protein, globulin, and urea increased remarkably, whereas serum glutamic-oxaloacetic transaminase decreased notably in 80 mg/kg MHA-Zn groups. Compared with the 20 mg/kg MHA-Zn group, the metabolic profile of 40 and 80 mg/kg MHA-Zn groups was higher than that of the inorganic zinc group. Furthermore, integrated key metabolic pathway analysis showed that 40 and 80 mg/kg MHA-Zn groups participated in the regulation of glutathione metabolism, glycine, serine, and threonine metabolism. Therefore, this study suggests that 40 and 80 mg/kg supplementation of MHA-Zn can increase the activity of Cu/Zn-SOD and T-AOC and decrease MDA; additionally the 80 mg/kg MHA-Zn group has better antioxidant capacity. Meanwhile, the enhanced MHA-Zn promoted methionine (Met) synthesis and protein metabolism.

Plant sulphur metabolism is stimulated by photorespiration

Intense efforts have been devoted to describe the biochemical pathway of plant sulphur (S) assimilation from sulphate. However, essential information on metabolic regulation of S assimilation is still lacking, such as possible interactions between S assimilation, photosynthesis and photorespiration. In particular, does S assimilation scale with photosynthesis thus ensuring sufficient S provision for amino acids synthesis? This lack of knowledge is problematic because optimization of photosynthesis is a common target of crop breeding and furthermore, photosynthesis is stimulated by the inexorable increase in atmospheric CO2. Here, we used high-resolution 33S and 13C tracing technology with NMR and LC-MS to access direct measurement of metabolic fluxes in S assimilation, when photosynthesis and photorespiration are varied via the gaseous composition of the atmosphere (CO2, O2). We show that S assimilation is stimulated by photorespiratory metabolism and therefore, large photosynthetic fluxes appear to be detrimental to plant cell sulphur nutrition.

Chemoselective Methionine Bioconjugation on a Polypeptide, Protein, and Proteome

Methionine is one of the most hydrophobic, redox-sensitive, and one of the only two sulfur-containing amino acids on protein. Because of these biochemical properties, the methionine residue plays a central role in a variety of biological processes, such as metal coordination, antioxidant stress, and aging. However, studies on the molecular functions of methionine are much less common than the other primary sulfur-containing amino acid, cysteine. The limited number of publications on methionine-related studies is partially due to the lack of tools for methionine modification. Methionine bioconjugation offers a new strategy to decipher the biological function of methionine and expands the toolbox for protein functionalization in the context of the application, such as synthesizing proteins with novel properties and producing new biomaterials. The purpose of this Perspective is to highlight the biochemical properties and functions of methionine, list recent progress in the development of methionine bioconjugation reagents, and briefly demonstrate the application of these reagents on polypeptides, proteins, and proteomes.

Elimination of human folypolyglutamate synthetase alters programming and plasticity of somatic cells

Folates are vital cofactors for the regeneration of S-adenosyl methionine, which is the methyl source for DNA methylation, protein methylation, and other aspects of one-carbon (C1) metabolism. Thus, folates are critical for establishing and preserving epigenetic programming. Folypolyglutamate synthetase (FPGS) is known to play a crucial role in the maintenance of intracellular folate levels. Therefore, any modulation in FPGS is expected to alter DNA methylation and numerous other metabolic pathways. To explore the role of polyglutamylation of folate, we eliminated both isoforms of FPGS in human cells (293T), producing FPGS knockout (FPGS^ko) cells. The elimination of FPGS significantly decreased cell proliferation, with a major effect on oxidative phosphorylation and a lesser effect on glycolysis. We found a substantial reduction in global DNA methylation and noteworthy changes in gene expression related to C1 metabolism, cell division, DNA methylation, pluripotency, Glu metabolism, neurogenesis, and cardiogenesis. The expression levels of NANOG, octamer-binding transcription factor 4, and sex-determining region Y-box 2 levels were increased in the mutant, consistent with the transition to a stem cell-like state. Gene expression and metabolite data also indicate a major change in Glu and GABA metabolism. In the appropriate medium, FPGS^ko cells can differentiate to produce mainly cells with characteristics of either neural stem cells or cardiomyocytes.-Srivastava, A. C., Thompson, Y. G., Singhal, J., Stellern, J., Srivastava, A., Du, J., O'Connor, T. R., Riggs, A. D. Elimination of human folypolyglutamate synthetase alters programming and plasticity of somatic cells.

Immune system stimulation increases the plasma cysteine flux and whole-body glutathione synthesis rate in starter pigs1

Glutathione (GSH) is the major intracellular thiol that plays a role in numerous detoxification, bio-reduction, and conjugation reactions. The availability of Cys is thought to be the rate-limiting factor for the synthesis of GSH. The effects of immune system stimulation (ISS) on GSH levels and the GSH synthesis rate in various tissues, as well as the plasma flux of Cys, were measured in starter pigs fed a sulfur AA (SAA; Met + Cys) limiting diet. Ten feed-restricted gilts with initial body weight (BW) of 7.0 ± 0.12 kg were injected i.m. twice at 48-h intervals with either sterile saline (n = 4; ISS-) or increasing amounts of Escherichia coli lipopolysaccharide (n = 6; ISS+). The day after the second injection, pigs received a primed constant infusion of 35S-Cys (9,300 kBq/pig/h) for 5 h via a jugular catheter. Blood and tissue free Cys and reduced GSH were isolated and quantified as the monobromobimane derivatives by HPLC. The rate of GSH synthesis was determined by measurement of the specific radioactivity of GSH and tissue free Cys at the end of the infusion period. Plasma Cys and total SAA levels were reduced (16% and 21%, respectively), but plasma Cys flux was increased (26%) by ISS (P < 0.05). Immune system stimulation increased GSH levels in the plasma (48%; P < 0.05), but had no effect on GSH levels in the liver, small and large intestines, heart, muscle, spleen, kidney, lung, and erythrocytes. The fractional synthesis rate (FSR) of GSH was higher (P < 0.05) in the liver (34%), small intestine (78%), large intestine (72%), heart (129%), muscle (37%), and erythrocytes (47%) of ISS+ pigs compared to ISS- pigs. The FSR of GSH tended (P = 0.08) to be higher in the lungs (45%) of ISS+ pigs than in ISS- pigs. The absolute rate of GSH synthesis was increased by ISS (mmol/kg wet tissue/d ± SE, ISS- vs. ISS+; P < 0.05) in the liver (5.22 ± 0.22 vs. 7.20 ± 0.59), small intestine (2.54 ± 0.25 vs. 4.52 ± 0.56), large intestine (0.61 ± 0.06 vs. 1.06 ± 0.16), heart (0.21 ± 0.03 vs. 0.48 ± 0.08), lungs (1.50 ± 0.10 vs. 2.90 ± 0.21), and muscle (0.21 ± 0.03 vs. 0.34 ± 0.04), but it remained unchanged in erythrocytes, the kidney, and the spleen (P > 0.80). The current findings suggest that GSH synthesis is increased during ISS, contributing to enhanced maintenance sulfur amino acid requirements in starter pigs during ISS.

Association of retinol binding protein-4, cystatin C, homocysteine and high-sensitivity C-reactive protein levels in patients with newly diagnosed type 2 diabetes mellitus

INTRODUCTION

To investigate the serum retinol binding protein (RBP)-4, cystatin C (Cys C), homocysteine (HCY) and high-sensitivity C-reactive protein (hs-CRP) levels in newly diagnosed type 2 diabetes mellitus (NT2DM) patients, prediabetes mellitus (PDM) subjects and normal controls, as well as their correlation with clinical and laboratory indexes, such as blood pressure and lipoprotein.

MATERIAL AND METHODS

A total of 242 subjects, including 141 NT2DM patients, 48 PDM subjects and 53 healthy controls, were recruited in the present study. Serum RBP-4, Cys C and hs-CRP concentrations were measured by enzyme-linked immunosorbent assay (ELISA). HCY concentration was determined by the chemical luminescence method.

RESULTS

There were significant differences in Cys C and hs-CRP among NT2DM patients, PDM subjects and normal controls. In comparison to controls, there were significantly elevated Cys C and hs-CRP levels in PDM (both p < 0.001), and a significantly increased Cys C level in NT2DM (p < 0.001); however, there were no significant differences in Cys C and hs-CRP levels between NT2DM and PDM, and no significant differences of hs-CRP levels between NT2DM and normal controls. No significant differences of RBP-4 and HCY levels among NT2DM, PDM and normal control groups were observed.

CONCLUSIONS

Aberrant Cys C expression and its clinical associations in NT2DM suggest their important role in this disease.

Hepatic 1-carbon metabolism enzyme activity, intermediate metabolites, and growth in neonatal Holstein dairy calves are altered by maternal supply of methionine during late pregnancy

Maternal supply of methyl donors such as methionine (Met) during late pregnancy can affect offspring growth and development. The objective was to investigate the effect of postruminal Met supply during late pregnancy on 1-carbon, Met cycle, and transsulfuration pathways in the calf liver. During the last 28 d of pregnancy, cows were individually fed a control diet or the control diet plus rumen-protected dl-Met (MET; 0.09% dry matter intake). Liver samples obtained from calves (n = 14/group) at 4, 14, 28, and 50 d of age were used for metabolomics, real-time PCR, and enzyme activity analyses. Genes associated with 1-carbon metabolism, DNA methylation, and the cytidine 5'-diphosphocholine-choline pathway were analyzed via real-time PCR. Activity of betaine homocysteine methyltransferase, cystathionine β-synthase, and 5-methyltetrahydrofolate homocysteine methyltransferase (MTR) was analyzed using ¹⁴C isotopes. Data were analyzed using a mixed model that included the fixed effects of maternal treatment, day, and their interaction, and the random effect was calf within maternal diet. Calves born to dams offered MET tended to have greater birth body weight and had overall greater body weight during the first 9 wk of life. However, no differences were detected for daily feed intake and average daily gain between groups. Concentrations of betaine and choline, reflecting Met cycle activity, at d 14 through 28 were greater in MET calves. Transsulfuration pathway intermediates also were altered in MET calves, with concentrations of cysteine sulfinic acid and hypotaurine (d 4 and 14) and taurine being greater (d 4, 14, 28, and 50). Despite the lack of differences in daily feed intake, the greater concentrations of the tricarboxylic acid cycle intermediates fumarate and glutamate along with NAD/NADH in MET calves indicated enhanced rates of energy metabolism. Although activity of betaine homocysteine methyltransferase was greater in MET calves at d 14, cystathionine β-synthase was lower and increased at d 14 and 28, where it was greater compared with the control diet. Activity of MTR was lower at d 4 and 50 in MET calves. Among gene targets measured, MET calves had greater overall expression of MTR, phosphatidylethanolamine N-methyltransferase, and choline kinase α and β. An interaction of maternal diet by time was detected for mRNA abundance of DNA methyltransferase 3α (involved in de novo methylation) due to greater values at d 4 and 14 in MET calves. Overall, the data indicate that enhanced postruminal supply of Met to cows during late pregnancy may program hepatic metabolism of the calf in the context of maintaining Met homeostasis, phosphatidylcholine and taurine synthesis, DNA methylation, and energy metabolism. These alterations potentially result in better efficiency of nutrient use, hence conferring the calf a physiologic advantage during a period of rapid growth and development. The precise biologic mechanisms remain to be established.

Different dietary methionine to lysine ratios in the lactation diet: effects on the performance of sows and their offspring and methionine metabolism in lactating sows

Background

Over the last decade, the nutritional requirements of lactating modern genotype sows have increased. The current nutritional recommendations might be unable to meet the needs of increased litter size and milk production, and thus the nutritional requirements need to be re-evaluated. The current study was conducted to investigate the effects of dietary methionine to lysine (Met:Lys) ratios on the performance of and methionine metabolism in lactating sows.

Results

During the 1^st week of lactation, piglets reared on sows in the 0.37 to 0.57 Met:Lys ratio groups grew faster than those reared on sows in the control group (0.27) (P < 0.01). The 0.37-ratio group showed increased levels of GSH-Px in plasma during lactation (P < 0.01) and decreased concentrations of urea nitrogen in the plasma of sows (P < 0.05). Compared with the 0.27-ratio group, the levels of T-AOC and GSH-Px in the plasma and homocysteine in the milk of lactating sows were significantly increased in sows in the 0.47-ratio group (P < 0.01). In sows fed a 0.57-ratio diet, the levels of glutathione and taurine in the plasma and milk were improved significantly during lactation. However, the content of TBARS in the blood (P < 0.05 at day 7 and P = 0.06 at weaning day) was increased (P < 0.01). Moreover, there were linear increases in the levels of homocysteine in the blood and milk of sows during the lactation period (P < 0.01) with increased dietary Met:Lys ratios in the lactation diet.

Conclusions

The current study indicated that increasing the dietary Met:Lys ratio (0.37~0.57) in the lactation diet had no significant effect on the overall performance of sows or the colostrum and milk composition, but it increased piglet mean BW and piglet ADG during the first week of lactation. Increasing dietary methionine levels had no significant effect on antioxidant function in lactation sows, even though it increased levels of GSH and GSH-Px in the plasma of sows during lactation. However, the content of homocysteine in the plasma and milk increased during lactation due to a high level of dietary methionine.

Tacrine-Hydrogen Sulfide Donor Hybrid Ameliorates Cognitive Impairment in the Aluminum Chloride Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by progressive loss of memory and cognitive function, and is associated with the deficiency of synaptic acetylcholine, as well as chronic neuroinflmmation. Tacrine, a potent acetylcholinesterase (AChE) inhibitor, was previously a prescribed clinical therapeutic agent for AD, but it was recently withdrawn because it caused widespread hepatotoxicity. Hydrogen sulfide (H₂S) has neuroprotective, hepatoprotective, and anti-inflammatory effects. In this study, we synthesized a new compound, a tacrine-H₂S donor hybrid (THS) by introducing H₂S-releasing moieties (ACS81) to tacrine. Subsequently, pharmacological and biological evaluations of THS were conducted in the aluminum trichloride (AlCl₃)-induced AD mice model. We found that THS (15 mmol/kg) improved cognitive and locomotor activity in AD mice in the step-through test and open field test, respectively. THS showed strong AChE inhibitory activity in the serum and hippocampus of AD mice and induced increased hippocampal H₂S levels. Furthermore, THS reduced mRNA expression of the proinflammatory cytokines, TNF-α, IL-6, and IL-1β and increased synapse-associated proteins (synaptophysin and postsynaptic density protein 95) in the hippocampus of AD mice. Importantly, THS, unlike tacrine, did not increase liver transaminases (alanine transaminase and aspartate transaminase) or proinflammatory cytokines, indicating THS is much safer than tacrine. Therefore, the multifunctional effects of this new hybrid compound of tacrine and H₂S indicate it is a promising compound for further research into the treatment of AD.

Secondary sulfur metabolism in cellular signalling and oxidative stress responses

The sulfur metabolism pathway in plants produces a variety of compounds that are central to the acclimation response to oxidative stresses such as drought and high light. Primary sulfur assimilation provides the amino acid cysteine, which is utilized in protein synthesis and as a precursor for the cellular redox buffer glutathione. In contrast, the secondary sulfur metabolism pathway produces sulfated compounds such as glucosinolates and sulfated peptides, as well as a corresponding by-product 3'-phosphoadenosine 5'-phosphate (PAP). Emerging evidence over the past decade has shown that secondary sulfur metabolism also has a crucial engagement during oxidative stress. This occurs across various cellular, tissue, and organismal levels including chloroplast-to-nucleus retrograde signalling events mediated by PAP, modulation of hormonal signalling by sulfated compounds and PAP, control of physiological responses such as stomatal closure, and potential regulation of plant growth. In this review, we examine the contribution of the different components of plant secondary metabolism to oxidative stress homeostasis, and how this pathway is metabolically regulated. We further outline the key outstanding questions in the field that are necessary to understand how and why this 'specialized' metabolic pathway plays significant roles in plant oxidative stress tolerance.