Dealing with methionine/homocysteine sulfur: cysteine metabolism to taurine and inorganic sulfur

Sulfur Metabolism Under Stress

Significance: In humans, imbalances in the reduction-oxidation (redox) status of cells are associated with many pathological states. In addition, many therapeutics and prophylactics used as interventions for diverse pathologies either directly modulate oxidant levels or otherwise influence endogenous cellular redox systems. Recent Advances: The cellular machineries that maintain redox homeostasis or that function within antioxidant defense systems rely heavily on the regulated reactivities of sulfur atoms either within or derived from the amino acids cysteine and methionine. Recent advances have substantially advanced our understanding of the complex and essential chemistry of biological sulfur-containing molecules. Critical Issues: The redox machineries that maintain cellular homeostasis under diverse stresses can consume large amounts of energy to generate reducing power and/or large amounts of sulfur-containing nutrients to replenish or sustain intracellular stores. By understanding the metabolic pathways underlying these responses, one can better predict how to protect cells from specific stresses. Future Directions: Here, we summarize the current state of knowledge about the impacts of different stresses on cellular metabolism of sulfur-containing molecules. This analysis suggests that there remains more to be learned about how cells use sulfur chemistry to respond to stresses, which could in turn lead to advances in therapeutic interventions for some exposures or conditions.

Maternal Methyl-Donor Micronutrient Supplementation During Pregnancy Promotes Skeletal Muscle Differentiation and Maturity in Newborn and Weaning Pigs

Adequate maternal methyl-donor micronutrient (MET) intake is an important determinant of the organ development and metabolic renovation of offspring. The mechanism involved in skeletal myogenesis and the effect of MET supplementation during pregnancy on the maternal body remain unclear. Thus, this study aimed to investigate the potential effect of methyl donor micronutrients (MET) on skeletal muscle development and metabolism in offspring using pig models. Forty-three Duroc × Erhualian gilts were assigned to two dietary groups during gestation: control diet (CON) and CON diet supplemented with MET (folic acid, methionine, choline, vitamin B6, and vitamin B12). The results showed that maternal MET exposure during pregnancy significantly increased the concentrations of protein, triiodothyronine (T3), and thyroxine (T4) in colostrum and methyl metabolites, including S-adenosylmethionine (SAM), S-adenosyl-L-homocysteine (SAH), 5-methyl-tetrahydrofolate (5-MTHF), and betaine, in the maternal and offspring umbilical vein serum. A similar pattern was demonstrated in the body weight gain and myofiber diameters in offspring. In addition, maternal MET supplementation significantly increased the concentration of offspring serum insulin-like growth factor 1 (IGF-1), T3, and T4; upregulated the mRNA expression of IGF-1 and IGF-1 receptor (IGF-1r) and the phosphorylation level of protein kinases in offspring longissimus dorsi muscle; and upregulated the expression of myogenic genes and fast myosin heavy chain (fast MyHC) in offspring skeletal muscle. Supplementing sows with higher levels of MET during gestation may promote skeletal muscle differentiation and maturity and improve the skeletal muscle mass of the piglets.

The role of glutamate oxaloacetate transaminases in sulfite biosynthesis and H2S metabolism

Molybdenum cofactor deficiency and isolated sulfite oxidase deficiency are two rare genetic disorders that are caused by impairment of the mitochondrial enzyme sulfite oxidase. Sulfite oxidase is catalyzing the terminal reaction of cellular cysteine catabolism, the oxidation of sulfite to sulfate. Absence of sulfite oxidase leads to the accumulation of sulfite, which has been identified as a cellular toxin. However, the molecular pathways leading to the production of sulfite are still not completely understood. In order to identify novel treatment options for both disorders, the understanding of cellular cysteine catabolism – and its alterations upon loss of sulfite oxidase – is of utmost importance. Here we applied a new detection method of sulfite in cellular extracts to dissect the contribution of cytosolic and mitochondrial glutamate oxaloacetate transaminase (GOT) in the transformation of cysteine sulfinic acid to sulfite and pyruvate. We found that the cytosolic isoform GOT1 is primarily responsible for the production of sulfite. Moreover, loss of sulfite oxidase activity results in the accumulation of sulfite, H₂S and persulfidated cysteine and glutathione, which is consistent with an increase of SQR protein levels. Surprisingly, none of the known H₂S-producing pathways were found to be upregulated under conditions of sulfite toxicity suggesting an alternative route of sulfite-induced shift from oxidative to H₂S dependent cysteine catabolism.

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Cellular sulfite detection enables investigation of cysteine catabolism in cell extracts.

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Cytosolic glutamate oxaloacetate transaminase 1 is the primary source for cellular sulfite.

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Deficiency of sulfite oxidase leads to accumulation of H₂S and persulfidated small molecules.

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Sulfite oxidase deficiency results in a downregulation of H₂S synthesis and increased SQR expression.

Roles of Hydrogen Sulfide Donors in Common Kidney Diseases

Hydrogen sulfide (H2S) plays a key role in the regulation of physiological processes in mammals. The decline in H2S level has been reported in numerous renal disorders. In animal models of renal disorders, treatment with H2S donors could restore H2S levels and improve renal functions. H2S donors suppress renal dysfunction by regulating autophagy, apoptosis, oxidative stress, and inflammation through multiple signaling pathways, such as TRL4/NLRP3, AMP-activated protein kinase/mammalian target of rapamycin, transforming growth factor-β1/Smad3, extracellular signal-regulated protein kinases 1/2, mitogen-activated protein kinase, and nuclear factor kappa B. In this review, we summarize recent developments in the effects of H2S donors on the treatment of common renal diseases, including acute/chronic kidney disease, renal fibrosis, unilateral ureteral obstruction, glomerulosclerosis, diabetic nephropathy, hyperhomocysteinemia, drug-induced nephrotoxicity, metal-induced nephrotoxicity, and urolithiasis. Novel H2S donors can be designed and applied in the treatment of common renal diseases.

A novel fluorescent probe with dual-sites for simultaneously monitoring metabolisms of cysteine in living cells and zebrafishes

Understanding cellular metabolism holds immense potential for developing new drugs that regulate metabolic pathways. Two gas signal molecules, SO₂ and H₂S, are the main metabolites from cysteine (Cys) via oxidation and desulfurization pathways, respectively. However, a few fluorescent probes for real-time monitor of the metabolic pathways of cysteine have been reported. To understand metabolic alterations of cysteine, we have rationally designed and prepared a dual-signal fluorescent probe HN, which could differentiate SO₂ and H₂S through two different fluorescence channels simultaneously, along with similar reaction kinetics and both "off-on" fluorescence responses. Probe HN exhibits the potential to monitor the metabolism pathways of cysteine, and the distinguishment of cancer cells from normal cells could be realized. This methodology will promote further understanding of the physiological and pathological roles of cysteine.

Current perspective and scope of fetal therapy: part 2

Fetal therapy has been defined as any therapeutic intervention either invasive or noninvasive for correcting or treating any fetal malformation or condition. Invasive fetal therapy have its own set of maternal and fetal complications and invasive approach is not feasible in many of fetal conditions that are candidate for fetal therapy. Many such fetal conditions have been treated successfully by medical or noninvasive management. In medical fetal therapy, mothers are treated with medications which are transferred to fetus through placenta and exert positive effect on the fetus, thus avoiding complications that are seen secondary to invasive fetal therapy. The fetal conditions that have been managed with medical therapy includes fetal and neonatal alloimmune thrombocytopenia, neural tube defect, congenital adrenal hyperplasia, perinatal infections, respiratory distress syndrome, inborn error of metabolism, and congenital cystic adenomatoid malformation. This review will cover the medical or noninvasive aspect of fetal therapy and will highlight the progress made in the management of these fetal conditions.

Taurine Enhances Iron-Related Proteins and Reduces Lipid Peroxidation in Differentiated C2C12 Myotubes

Taurine is a nonproteinogenic amino sulfonic acid in mammals. Interestingly, skeletal muscle is unable to synthesize taurine endogenously, and the processing of muscular taurine changes throughout ageing and under specific pathophysiological conditions, such as muscular dystrophy. Ageing and disease are also associated with altered iron metabolism, especially when there is an excess of labile iron. The present study addresses the question of whether taurine connects cytoprotective effects and redox homeostasis in a previously unknown iron-dependent manner. Using cultured differentiated C2C12 myotubes, the impact of taurine on markers of lipid peroxidation, redox-sensitive enzymes and iron-related proteins was studied. Significant increases in the heme protein myoglobin and the iron storage protein ferritin were observed in response to taurine treatment. Taurine supplementation reduced lipid peroxidation and BODIPY oxidation by ~60 and 25%, respectively. Furthermore, the mRNA levels of redox-sensitive heme oxygenase (Hmox1), catalase (Cat) and glutamate-cysteine ligase (Gclc) and the total cellular glutathione content were lower in taurine-supplemented cells than they were in the control cells. We suggest that taurine may inhibit the initiation and propagation of lipid peroxidation by lowering basal levels of cellular stress, perhaps through reduction of the cellular labile iron pool.

The Microbial Composition in Circumneutral Thermal Springs from Chignahuapan, Puebla, Mexico Reveals the Presence of Particular Sulfur-Oxidizing Bacterial and Viral Communities

Terrestrial thermal springs are widely distributed globally, and these springs harbor a broad diversity of organisms of biotechnological interest. In Mexico, few studies exploring this kind of environment have been described. In this work, we explore the microbial community in Chignahuapan hot springs, which provides clues to understand these ecosystems' diversity. We assessed the diversity of the microorganism communities in a hot spring environment with a metagenomic shotgun approach. Besides identifying similarities and differences with other ecosystems, we achieved a systematic comparison against 11 metagenomic samples from diverse localities. The Chignahuapan hot springs show a particular prevalence of sulfur-oxidizing bacteria from the genera Rhodococcus, Thermomonas, Thiomonas, Acinetobacter, Sulfurovum, and Bacillus, highlighting those that are different from other recovered bacterial populations in circumneutral hot springs environments around the world. The co-occurrence analysis of the bacteria and viruses in these environments revealed that within the Rhodococcus, Thiomonas, Thermonas, and Bacillus genera, the Chignahuapan samples have specific species of bacteria with a particular abundance, such as Rhodococcus erytropholis. The viruses in the circumneutral hot springs present bacteriophages within the order Caudovirales (Siphoviridae, Myoviridae, and Podoviridae), but the family of Herelleviridae was the most abundant in Chignahuapan samples. Furthermore, viral auxiliary metabolic genes were identified, many of which contribute mainly to the metabolism of cofactors and vitamins as well as carbohydrate metabolism. Nevertheless, the viruses and bacteria present in the circumneutral environments contribute to the sulfur cycle. This work represents an exhaustive characterization of a community structure in samples collected from hot springs in Mexico and opens opportunities to identify organisms of biotechnological interest.

Unexplored nutritive potential of tomato to combat global malnutrition

Tomato, a widely consumed vegetable crop, offers a real potential to combat human nutritional deficiencies. Tomatoes are rich in micronutrients and other bioactive compounds (including vitamins, carotenoids, and minerals) that are known to be essential or beneficial for human health. This review highlights the current state of the art in the molecular understanding of the nutritional aspects, conventional and molecular breeding efforts, and biofortification studies undertaken to improve the nutritional content and quality of tomato. Transcriptomics and metabolomics studies, which offer a deeper understanding of the molecular regulation of the tomato's nutrients, are discussed. The potential uses of the wastes from the tomato processing industry (i.e., the peels and seed extracts) that are particularly rich in oils and proteins are also discussed. Recent advancements with CRISPR/Cas mediated gene-editing technology provide enormous opportunities to enhance the nutritional content of agricultural produces, including tomatoes. In this regard, genome editing efforts with respect to biofortification in the tomato plant are also discussed. The recent technological advancements and knowledge gaps described herein aim to help explore the unexplored nutritional potential of the tomato.

Mechanistic Insights into Dissolved Organic Sulfur Photomineralization through the Study of Cysteine Sulfinic Acid

Photochemical reactions convert dissolved organic matter (DOM) into inorganic and low-molecular-weight organic products, contributing to its cycling across environmental compartments. However, knowledge on the formation mechanisms of these products is still scarce. In this work, we investigate the triplet-sensitized photodegradation of cysteine sulfinic acid, a (photo)degradation product of cysteine, to sulfate (SO₄^2-). We use kinetic analysis, targeted experiments, and previous literature from several fields of chemistry to explain the elementary steps that lead to the release of sulfate. Our analysis indicates that triplet sensitizers act as one-electron oxidants on the sulfinate S lone pair. The resulting radical undergoes C-S fragmentation to form SO₂, which becomes hydrated to sulfite/bisulfite (S(IV)). S(IV) is further oxidized to SO₄^2- in the presence of triplet sensitizers and oxygen. We point out that the reaction sequence SO₂ ⇌ S(IV) → SO₄^2- is valid independently of the chemical structure of the model compound and might represent a sulfate photoproduction mechanism with general validity for DOS. Our mechanistic investigation revealed that amino acids in general might also be photochemical precursors of CO₂, ammonia, acetaldehyde, and H₂O₂ and that reaction byproducts can influence the rate and mechanism of S(IV) (photo)oxidation.

Role of Hypotaurine in Protection against UVA-Induced Damage in Keratinocytes

Photoageing and skin cancer are major causes of morbidity and are a high cost to society. Interest in the development of photoprotective agents for inclusion in topical cosmetic and sunscreen products is profound. Recently, amino acids with a sulfinic group, notably hypotaurine, have been included as ingredients in cosmetic preparations. However, the mechanism of action of hypotaurine as a possible anti-aging agent is unknown, despite its use as a free radical scavenger. To address this issue, we investigated hypotaurine uptake in a human keratinocyte model and examined its effect on UVR-induced cytotoxicity. Hypotaurine was taken up by keratinocytes in a time- and concentration-dependent manner, with levels remaining significantly above baseline 48 h after washout. A cytoprotective effect of pre-incubation with 2.5-5 mMhypotaurine was shown as indicated by increased cell viability when keratinocytes were irradiated with UVA at 5 or 10 Jcm^-2 , with the level of hypotaurine also significantly reduced. These findings indicate a potential cytoprotective effect of hypotaurine against the deleterious effects of UVA irradiation. This provides support for further studies to evaluate the potential photoprotective benefits of hypotaurine supplementation of topical cosmetic and sunscreen products.

Metabolism of Sulfur-Containing Amino Acids: How the Body Copes with Excess Methionine, Cysteine, and Sulfide

Metabolism of excess methionine (Met) to homocysteine (Hcy) by transmethylation is facilitated by the expression of methionine adenosyltransferase (MAT) I/III and glycine N-methyltransferase (GNMT) in liver, and a lack of either enzyme results in hypermethioninemia despite normal concentrations of MATII and methyltransferases other than GNMT. The further metabolism of Hcy by the transsulfuration pathway is facilitated by activation of cystathionine β-synthase (CBS) by S-adenosylmethionine (SAM) as well as the relatively high KM of CBS for Hcy. Transmethylation plus transsulfuration effects catabolism of the Met molecule along with transfer of the sulfur atom of Met to serine to synthesize cysteine (Cys). Oxidation and excretion of Met sulfur depend upon Cys catabolism and sulfur oxidation pathways. Excess Cys is oxidized by cysteine dioxygenase 1 (CDO1) and further metabolized to taurine or sulfate. Some Cys is normally metabolized by desulfhydration pathways, and the hydrogen sulfide (H2S) produced is further oxidized to sulfate. If Cys or Hcy concentrations are elevated, Cys or Hcy desulfhydration can result in excess H2S and thiosulfate production. Excess Cys or Met may also promote their limited metabolism by transamination pathways.

Metabolic Consequences of Supplemented Methionine in a Clinical Context

The central position of methionine (Met) in protein metabolism indicates the importance of this essential amino acid for growth and maintenance of lean body mass. Therefore, Met might be a tempting candidate for supplementation. However, because Met is also the precursor of homocysteine (Hcy), a deficient intake of B vitamins or excessive intake of Met may result in hyperhomocysteinemia (HHcy), which is a risk factor for cardiovascular disease. This review discusses the evidence generated in preclinical and clinical studies on the importance and potentially harmful effects of Met supplementation and elaborates on potential clinical applications of supplemental Met with reference to clinical studies performed over the past 20 y. Recently acquired knowledge about the NOAEL (no observed adverse effect level) of 46.3 mg · kg-1 · d-1 and the LOAEL (lowest observed adverse effect level) of 91 mg · kg-1 · d-1 of supplemented Met will guide the design of future studies to further establish the role of Met as a potential (safe) candidate for nutritional supplementation in clinical applications.

Chemistry and Biochemistry of Sulfur Natural Compounds: Key Intermediates of Metabolism and Redox Biology

Sulfur contributes significantly to nature chemical diversity and thanks to its particular features allows fundamental biological reactions that no other element allows. Sulfur natural compounds are utilized by all living beings and depending on the function are distributed in the different kingdoms. It is no coincidence that marine organisms are one of the most important sources of sulfur natural products since most of the inorganic sulfur is metabolized in ocean environments where this element is abundant. Terrestrial organisms such as plants and microorganisms are also able to incorporate sulfur in organic molecules to produce primary metabolites (e.g., methionine, cysteine) and more complex unique chemical structures with diverse biological roles. Animals are not able to fix inorganic sulfur into biomolecules and are completely dependent on preformed organic sulfurous compounds to satisfy their sulfur needs. However, some higher species such as humans are able to build new sulfur-containing chemical entities starting especially from plants' organosulfur precursors. Sulfur metabolism in humans is very complicated and plays a central role in redox biochemistry. The chemical properties, the large number of oxidation states, and the versatile reactivity of the oxygen family chalcogens make sulfur ideal for redox biological reactions and electron transfer processes. This review will explore sulfur metabolism related to redox biochemistry and will describe the various classes of sulfur-containing compounds spread all over the natural kingdoms. We will describe the chemistry and the biochemistry of well-known metabolites and also of the unknown and poorly studied sulfur natural products which are still in search for a biological role.

Effect of post-ruminal guanidinoacetic acid supplementation on creatine synthesis and plasma homocysteine concentrations in cattle

Creatine stores high-energy phosphate bonds in muscle, which is critical for muscle activity. In animals, creatine is synthesized in the liver from guanidinoacetic acid (GAA) with methylation by S-adenosylmethionine. Because methyl groups are used for the conversion of GAA to creatine, methyl group deficiency may occur as a result of GAA supplementation. With this study, the metabolic responses of cattle to post-ruminal supplementation of GAA were evaluated with and without methionine (Met) supplementation as a source of methyl groups. Six ruminally cannulated Holstein heifers (520 kg) were used in a split-plot design with treatments arranged as a 2 × 5 factorial. The main plot treatments were 0 or 12 g/d of l-Met arranged in a completely randomized design; three heifers received each main plot treatment throughout the entire experiment. Subplot treatments were 0, 10, 20, 30, and 40 g/d of GAA, with GAA treatments provided in sequence from lowest to highest over five 6-d periods. Treatments were infused continuously to the abomasum. Heifers were limit-fed twice daily a diet consisting of (dry matter basis) 5.3 kg/d rolled corn, 3.6 kg/d alfalfa hay, and 50 g/d trace-mineralized salt. Plasma Met increased (P < 0.01) when Met was supplemented, but it was not affected by supplemental GAA. Supplementing GAA linearly increased plasma arginine (% of total amino acids) and plasma concentrations of GAA and creatinine (P < 0.001). Plasma creatine was increased at all levels of GAA except when 40 g/d of GAA was supplemented with no Met (GAA-quadratic × Met, P = 0.07). Plasma homocysteine was not affected by GAA supplementation when heifers received 12 g/d Met, but it was increased when 30 or 40 g/d of GAA was supplemented without Met (GAA-linear × Met, P = 0.003); increases were modest and did not suggest a dangerous hyperhomocysteinemia. Urinary concentrations of GAA and creatine were increased by all levels of GAA when 12 g/d Met was supplemented; increasing GAA supplementation up to 30 g/d without Met increased urinary GAA and creatine concentrations, but 40 g/d GAA did not affect urine concentrations of GAA and creatine when no Met was supplemented. Overall, post-ruminal GAA supplementation increased creatine supply to cattle. A methyl group deficiency, demonstrated by modest increases in plasma homocysteine, became apparent when 30 or 40 g/d of GAA was supplemented, but it was ameliorated by 12 g/d Met.

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.

Metabolomic characterization of semen from asthenozoospermic patients using ultra-high-performance liquid chromatography-tandem quadrupole time-of-flight mass spectrometry

Asthenozoospermia (AS) is a common factor of male infertility, and its pathogenesis remains unclear. The purpose of this study was to investigate the differential seminal plasma metabolic pattern in asthenozoospermic men and to identify potential biomarkers in relation to spermatogenic dysfunction using sensitive ultra-high-performance liquid chromatography-tandem quadruple time-of-flight MS (UHPLC-Q-TOF/MS). The samples of seminal plasma from patients with AS (n = 20) and healthy controls (n = 20) were checked and differentiated by UHPLC-Q-TOF/MS. Compared with the control group, the AS group showed a total of nine significantly different metabolites, including increases in creatinine, uric acid, N6 -methyladenosine (m6 A), uridine, and taurine and decreases in carnitine, nicotinamide, N-acetylputrescine and l-palmitoylcarnitine. By analyzing the correlation among these metabolites and clinical computer-assisted semen analysis reports, we found that m6 A is significantly correlated with not only the four decreased metabolites but also with sperm count, motility, and curvilinear velocity. Furthermore, nicotinamide was shown to correlate with other identified metabolites, indicating its important role in the metabolic pathway of AS. Current results implied that sensitive untargeted seminal plasma metabolomics could identify distinct metabolic patterns of AS and would help clinicians by offering novel cues for discovering the pathogenesis of male infertility.

Enzymatic Regulation and Biological Functions of Reactive Cysteine Persulfides and Polysulfides

Cysteine persulfide (CysSSH) and cysteine polysulfides (CysSS_nH, n > 1) are cysteine derivatives that have sulfane sulfur atoms bound to cysteine thiol. Advances in analytical methods that detect and quantify persulfides and polysulfides have shown that CysSSH and related species such as glutathione persulfide occur physiologically and are prevalent in prokaryotes, eukaryotes, and mammals in vivo. The chemical properties and abundance of these compounds suggest a central role for reactive persulfides in cell-regulatory processes. CysSSH and related species have been suggested to act as powerful antioxidants and cellular protectants and may serve as redox signaling intermediates. It was recently shown that cysteinyl-tRNA synthetase (CARS) is a new cysteine persulfide synthase. In addition, we discovered that CARS is involved in protein polysulfidation that is coupled with translation. Mitochondrial activity in biogenesis and bioenergetics is supported and upregulated by CysSSH derived from mitochondrial CARS. In this review article, we discuss the mechanisms of the biosynthesis of CysSSH and related persulfide species, with a particular focus on the roles of CARS. We also review the antioxidative and anti-inflammatory actions of persulfides.

The biothiol-triggered organotrisulfide-based self-immolative fluorogenic donors of hydrogen sulfide enable lysosomal trafficking

Biothiol-reactive organotrisulfide-based self-immolative fluorogenic donors of H2S are rationally designed for the efficient monitoring of intracellular and lysosomal trafficking of H2S with a concomitant turn-on fluorescence. The non-toxic nature of the donors with a sustained release of H2S will certainly be helpful for their biomedical applications in the future.

Effects of Partially Defatted Hermetia illucens Meal in Rainbow Trout Diet on Hepatic Methionine Metabolism

Simple Summary

For sustainable aquaculture development, fish meal from the sea in aquafeed should be replaced with other sustainable materials such as insect larvae. The authors fed black soldier fly maggot meal to rainbow trout and examined the expression of three genes and two metabolites involved in turn-over of methionine that is an essential amino acid in fish. According to the increase in the maggot content in the aquafeed, gene expression was modulated to maintain an optimal level of methionine metabolites. Dietary replacement of up to 50% of fish meal with the maggot meal was acceptable, implying future development of a new aquafeed for sustainable aquaculture.

Abstract

This study investigated, for the first time, the effects of replacement of fishmeal (FM) with insect meal from Hermetia illucens (HI) on the transcript levels of three genes involved in methionine (Met) metabolism in rainbow trout (Oncorhynchus mykiss) liver. Two target genes—betaine-homocysteine S-methyltransferase (BHMT) and S-adenosylhomocysteine hydrolase (SAHH)—are involved in Met resynthesis and the third one—cystathionine β synthase (CBS)—is involved in net Met loss (taurine synthesis). We also investigated the levels of two Met metabolites involved in the maintenance of methyl groups and homocysteine homeostasis in the hepatic tissue: S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). Three diets were formulated, an FM-based diet (HI0) and two diets in which 25% (HI25) and 50% (HI50) of FM was replaced with HI larvae meal. A 78-day feeding trial involved 360 rainbow trout with 178.9 ± 9.81 g initial average weight. Dietary replacement of up to 50% of FM with HI larvae meal, without any Met supplementation, did not negatively affect rainbow trout growth parameters and hepatic Met metabolism. In particular, Met availability from the insect-based diets directly modulated the transcript levels of two out of three target genes (CBS, SAHH) to maintain an optimal level of one-carbon metabolic substrates, i.e., the SAM:SAH ratio in the hepatic tissue.

The design and synthesis of two imidazole fluorescent probes for the special recognition of HClO/NaHSO3 and their applications

Two fluorescent probes (L1 and L2) based on an imidazole unit were synthesized for the specific detection of ClO- and HSO3-. Density functional theory (DFT) calculations were used to assist in designing the probes. As predicted, L1 could be used to detect ClO- in real water samples and in living cells. It was shown to be a quenching probe. L2 could be used to monitor HSO3- in living cells and is an enhanced fluorescence probe. Further details of the fluorescence recognition mechanism were obtained via HRMS analysis. Moreover, both fluorescent probes showed relatively low detection limits (0.96 and 0.59 μM, respectively), and fast and highly selective fluorescence responses.

Lipid peroxidation and ferroptosis: The role of GSH and GPx4

Ferroptosis (FPT) is a form of cell death due to missed control of membrane lipid peroxidation (LPO). According to the axiomatic definition of non-accidental cell death, LPO takes place in a scenario of altered homeostasis. FPT, differently from apoptosis, occurs in the absence of any known specific genetically encoded death pathway or specific agonist, and thus must be rated as a regulated, although not "programmed", death pathway. It follows that LPO is under a homeostatic metabolic control and is only permitted when indispensable constraints are satisfied and the antiperoxidant machinery collapses. The activity of the selenoperoxidase Glutathione Peroxidase 4 (GPx4) is the cornerstone of the antiperoxidant defence. Converging evidence on both mechanism of LPO and GPx4 enzymology indicates that LPO is initiated by alkoxyl radicals produced by ferrous iron from the hydroperoxide derivatives of lipids (LOOH), traces of which are the unavoidable drawback of aerobic metabolism. FPT takes place when a threshold has been exceeded. This occurs when the major conditions are satisfied: i) oxygen metabolism leading to the continuous formation of traces of LOOH from phospholipid-containing polyunsaturated fatty acids; ii) missed enzymatic reduction of LOOH; iii) availability of ferrous iron from the labile iron pool. Although the effectors impacting on homeostasis and leading to FPT in physiological conditions are not known, from the available knowledge on LPO and GPx4 enzymology we propose that it is aerobic life itself that, while supporting bioenergetics, is also a critical requisite of FPT. Yet, when the homeostatic control of the steady state between LOOH formation and reduction is lost, LPO is activated and FPT is executed.

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.

Red-Emission Probe for Ratiometric Fluorescent Detection of Bisulfite and Its Application in Live Animals and Food Samples

Key roles of bisulfite (HSO3 -) in food quality assurance and human health necessitate a reliable analytical method for rapid, sensitive, and selective detection of HSO3 -. Herein, a new red-emitting ratiometric fluorescence probe, BIQ, is reported for sensitive and selective detection of HSO3 - in food samples and live animals. Probe BIQ recognizes HSO3 - via a 1,4-nucleophilic addition reaction. As a result of this specific reaction, emission intensities at 625 and 475 nm are dramatically changed, allowing the detection of HSO3 - in a ratiometric fluorescence model in an aqueous solution. The obvious changes of solution color from pink to transparent and fluorescence color from rose-red to cyan allow the detection of HSO3 - by naked eyes. Furthermore, probe BIQ has fast response in color and fluorescence (<2 min), excellent selectivity, and a low detection limit (0.29 μM), which enables its application in HSO3 - detection in food samples and live organisms. The practical applications of probe BIQ are then demonstrated by the visualization of HSO3 - in live animals (zebrafish and nude mouse) as well as the determination of HSO3 - in white wine and sugar.

Identification and characterization of a bacterial core methionine synthase

Methionine synthases are essential enzymes for amino acid and methyl group metabolism in all domains of life. Here, we describe a putatively anciently derived type of methionine synthase yet unknown in bacteria, here referred to as core-MetE. The enzyme appears to represent a minimal MetE form and transfers methyl groups from methylcobalamin instead of methyl-tetrahydrofolate to homocysteine. Accordingly, it does not possess the tetrahydrofolate binding domain described for canonical bacterial MetE proteins. In Dehalococcoides mccartyi strain CBDB1, an obligate anaerobic, mesophilic, slowly growing organohalide-respiring bacterium, it is encoded by the locus cbdbA481. In line with the observation to not accept methyl groups from methyl-tetrahydrofolate, all known genomes of bacteria of the class Dehalococcoidia lack metF encoding for methylene-tetrahydrofolate reductase synthesizing methyl-tetrahydrofolate, but all contain a core-metE gene. We heterologously expressed core-MetECBDB in E. coli and purified the 38 kDa protein. Core-MetECBDB exhibited Michaelis-Menten kinetics with respect to methylcob(III)alamin (KM ≈ 240 µM) and L-homocysteine (KM ≈ 50 µM). Only methylcob(III)alamin was found to be active as methyl donor with a kcat ≈ 60 s-1. Core-MetECBDB did not functionally complement metE-deficient E. coli strain DH5α (ΔmetE::kan) suggesting that core-MetECBDB and the canonical MetE enzyme from E. coli have different enzymatic specificities also in vivo. Core-MetE appears to be similar to a MetE-ancestor evolved before LUCA (last universal common ancestor) using methylated cobalamins as methyl donor whereas the canonical MetE consists of a tandem repeat and might have evolved by duplication of the core-MetE and diversification of the N-terminal part to a tetrahydrofolate-binding domain.

A mitochondria-targeting ratiometric fluorescent probe for the detection of sulfur dioxide in living cells

A mitochondria-targeting ratiometric fluorescent probe was developed for the detection of sulfur dioxide in living cells.

Detecting and imaging of SO2 derivatives in living cells with zero cross-talk colorimetric mitochondria-targeted fluorescent probe

It is well known that excessive levels of sulfur dioxide and its derivatives are connected to diverse diseases. Therefore, developing highly sensitive probes to detect and monitor sulfite in living cells is important for the diagnosis of disease and the study of biochemical processes in vivo. In this report, two zero cross-talk ratiometric fluorescent probes were synthesized (CA-ID-MC and CA-BI-MC), which were derived from carbazole-indolenine π-conjugated system for effective detection of sulfite in living cells. Observably, CA-BI-MC exhibited the largest emission shift of 157 nm from 617 to 460 nm with the addition of various concentrations of sulfite, which is beneficial for high-resolution imaging of the sulfite. CA-BI-MC also exhibits high sensitivity and low cytotoxicity. More importantly, this probe successfully located mitochondria and sensed the sulfite in HeLa cells caused by exogenous stimulation.

A near-infrared fluorescent probe for ratiometric sensing of SO2 in cells and zebrafish

SO₂ sensing and imaging: the first near-infrared fluorescent probe Mito-HN with AIEE characteristics for ratiometric sensing of SO₂ derivatives in vitro, in cells, and in zebrafish was rationally designed and synthesized.

Sex-specific hippocampal metabolic signatures at the onset of systemic inflammation with lipopolysaccharide in the APPswe/PS1dE9 mouse model of Alzheimer's disease

Systemic inflammation enhances the risk and progression of Alzheimer's disease (AD). Lipopolysaccharide (LPS), a potent pro-inflammatory endotoxin produced by the gut, is found in excess levels in AD where it associates with neurological hallmarks of pathology. Sex differences in susceptibility to inflammation and AD progression have been reported, but how this impacts on LPS responses remains under investigated. We previously reported in an APP/PS1 model of AD that systemic LPS administration rapidly altered hippocampal metabolism in males. Here, we used untargeted metabolomics to comprehensively identify hippocampal metabolic processes occurring at onset of systemic inflammation with LPS (100 µg/kg, i.v.) in APP/PS1 mice, at an early pathological stage, and investigated the sexual dimorphism in this response. Four hours after LPS administration, pathways regulating energy metabolism, immune and oxidative stress responses were simultaneously recruited in the hippocampi of 4.5-month-old mice with a more protective response in females despite their pro-inflammatory and pro-oxidant metabolic signature in the absence of immune stimulation. LPS induced comparable behavioural sickness responses in male and female wild-type and APP/PS1 mice and comparable activation of both the serotonin and nicotinamide pathways of tryptophan metabolism in their hippocampi. Elevations in N-methyl-2-pyridone-5-carboxamide, a major toxic metabolite of nicotinamide, correlated with behavioural sickness regardless of sex, as well as with the LPS-induced hypothermia seen in males. Males also exhibited a pro-inflammatory-like downregulation of pyruvate metabolism, exacerbated in APP/PS1 males, and methionine metabolism whereas females showed a greater cytokine response and anti-inflammatory-like downregulation of hippocampal methylglyoxal and methionine metabolism. Metabolic changes were not associated with morphological markers of immune cell activation suggesting that they constitute an early event in the development of LPS-induced neuroinflammation and AD exacerbation. These data suggest that the female hippocampus is more tolerant to acute systemic inflammation.

A ratiometric fluorescent probe for reversible monitoring of endogenous SO2/formaldehyde in cytoplasm and nucleoli regions and its applications in living mice

A ratiometric fluorescent probe was engineered for the reversible imaging of endogenous sulfur dioxide in the cytoplasm and nucleoli regions of living cells and in living mice.

A near-infrared ratiometric fluorescent probe based on the CN double bond for monitoring SO2 and its application in biological imaging

A near-infrared ratiometric fluorescent probe based on CN double bond was developed for monitoring SO₂ and its application in biological imaging.

Role of Hydrogen Sulfide in Chronic Diseases

In the past, hydrogen sulfide (H₂S) was considered as a poisonous gas or waste of the body. Later, researchers found that H₂S-producing enzymes exist in mammals. Moreover, their findings indicated that endogenous H₂S was associated with the occurrence of many diseases. Therefore, endogenous H₂S is able to participate in the regulation of physiological and pathological functions of the body as a gas signaling molecule. In this review, we summarize the regulation mechanism of endogenous H₂S on the body, such as proliferation, apoptosis, migration, angiogenesis, as well as vasodilation/vasoconstriction. Furthermore, we also analyze the relationship between H₂S and some chronic diseases, including hypoxic pulmonary hypertension, myocardial infarction, ischemic perfusion kidney injury, diabetes, and chronic intestinal diseases. Finally, we discuss dietary restriction and drugs that target for H₂S. Hence, H₂S is expected to become a potential target for treatment of these chronic diseases.

A new ratiometric fluorescence assay based on resonance energy transfer between biomass quantum dots and organic dye for the detection of sulfur dioxide derivatives

Sulfur dioxide (SO2) is considered as the fourth gas signal molecule after nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S). It plays important roles in several physiological processes. Therefore, the design and synthesis of nanoprobes for the detection of SO2 derivatives in cells is of great significance. Herein, we report a new ratiometric fluorescence nanoprobe based on resonance energy transfer (RET) between biomass quantum dots (BQDs) and organic dye (DMI) for the detection of SO2 derivatives. The proposed ratiometric fluorescence assay allows the determination of HSO3 - in the range of 1.0 to 225 μM with a detection limit of 0.5 μM. Importantly, the proposed ratiometric fluorescence nanoprobe exhibits a high photostability and good selectivity for HSO3 - over other chemical species including H2S and biological mercaptans. Quantitation of HSO3 - in cell lysates by using the nanoprobe is demonstrated.

Metabolomics facilitates the discovery of metabolic biomarkers and pathways for ischemic stroke: a systematic review

INTRODUCTION

Ischemic stroke (IS) is a major contributor to the global disease burden, and effective biomarkers for IS management in clinical practice are urgently needed. Metabolomics can detect metabolites that are small enough to cross the blood-brain barrier in a high-throughput manner, and thus represents a powerful tool for discovering biomarkers of IS.

OBJECTIVES

In this study, we conducted a systematic review to identify potential metabolic biomarkers and pathways that might facilitate risk predictions, clinical diagnoses, the recognition of complications, predictions of recurrence and an understanding of the pathogenesis of IS.

METHODS

The PubMed and Web of Science databases were searched for relevant studies published between January 2000 and July 2019. The study objectives, study designs and reported metabolic biomarkers were systematically examined and compared. Pathway analysis was performed using the MetaboAnalyst online software.

RESULTS

Twenty-eight studies were included in this systematic review. Many consistent metabolites, including isoleucine, leucine, valine, glycine, lysine, glutamate, LysoPC(16:0), LysoPC(18:2), serine, uric acid, citrate and palmitic acid, possess potential as biomarkers of IS. Metabolic pathways and dysregulations that are implicated in excitotoxicity, inflammation, apoptosis, oxidative stress, neuroprotection, energy failure, and elevation of intracellular Ca²⁺ levels, were indicated as playing important roles in the development and progression of IS.

CONCLUSIONS

This systematic review summarizes potential metabolic biomarkers and pathways related to IS, which may provide opportunities for the construction of diagnostic or predictive models for IS and the discovery of novel therapeutic targets.

A Ratiometric and Colorimetric Hemicyanine Fluorescent Probe for Detection of SO2 Derivatives and Its Applications in Bioimaging

Based upon the intramolecular charge transfer (ICT) mechanism, a novel ratiometric fluorescent probe EB was developed to detect SO₃²⁻/HSO₃⁻. The probe displayed both colorimetric and ratiometric responses toward SO₃²⁻/HSO₃⁻. It displayed a quick response (within 60 s), good selectivity and high sensitivity (a detection limit of 28 nM) towards SO₃²⁻/HSO₃⁻. The SO₃²⁻/HSO₃⁻ sensing mechanism was confirmed as the Michael addition reaction by ESI-MS. Moreover, the probe could be applied to measure the level of sulfite in real samples, like sugar and chrysanthemum, and it could also be used to detect SO₃²⁻/HSO₃⁻ in HepG2 cells through confocal fluorescence microscopy, which proved its practical application in clinical diagnosis.

Association of Methionine to Homocysteine Status With Brain Magnetic Resonance Imaging Measures and Risk of Dementia

IMPORTANCE

Impairment of methylation status (ie, methionine to homocysteine ratio) may be a modifiable risk factor for structural brain changes and incident dementia.

OBJECTIVE

To investigate the association of serum markers of methylation status and sulfur amino acids with risk of incident dementia, Alzheimer disease (AD), and the rate of total brain tissue volume loss during 6 years.

DESIGN, SETTING, AND PARTICIPANTS

This population-based longitudinal study was performed from March 21, 2001, to October 10, 2010, in a sample of 2570 individuals aged 60 to 102 years from the Swedish Study on Aging and Care in Kungsholmen who were dementia free at baseline and underwent comprehensive examinations and structural brain magnetic resonance imaging (MRI) on 2 to 3 occasions during 6 years. Data analysis was performed from March 1, 2018, to October 1, 2018.

MAIN OUTCOMES AND MEASURES

Incident dementia, AD, and the rate of total brain volume loss.

RESULTS

This study included 2570 individuals (mean [SD] age, 73.1 [10.4] years; 1331 [56.5%] female). The methionine to homocysteine ratio was higher in individuals who consumed vitamin supplements (median, 1.9; interquartile range [IQR], 1.5-2.6) compared with those who did not (median, 1.8; IQR, 1.3-2.3; P < .001) and increased per each quartile increase of vitamin B12 or folate. In the multiadjusted model, an elevated baseline serum total homocysteine level was associated with an increased risk of dementia and AD during 6 years: for the highest homocysteine quartile compared with the lowest, the hazard ratios (HRs) were 1.60 (95% CI, 1.01-2.55) for dementia and 2.33 (95% CI, 1.26-4.30) for AD. In contrast, elevated concentrations of methionine were associated with a decreased risk of dementia (HR, 0.54; 95% CI, 0.36-0.81) for the highest quartile compared with the lowest. Higher values of the methionine to homocysteine ratio were significantly associated with lower risk of dementia and AD: for the fourth methionine-homocysteine quartile compared with the first quartile, the HR was 0.44 (95% CI, 0.27-0.71) for incident dementia and 0.43 (95% CI, 0.23-0.80) for AD. In the multiadjusted linear mixed models, a higher methionine to homocysteine ratio was associated with a decreased rate of total brain tissue volume loss during the study period (β [SE] per 1-SD increase, 0.038 [0.014]; P = .007).

CONCLUSIONS AND RELEVANCE

The methionine to homocysteine status was associated with dementia development and structural brain changes during the 6-year study period, suggesting that a higher methionine to homocysteine ratio may be important in reducing the rate of brain atrophy and decreasing the risk of dementia in older adults.

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.

AND-Logic Based Fluorescent Probe for Selective Detection of Lysosomal Bisulfite in Living Cells

Sulfur dioxide (SO₂) plays significant roles in regulating cell apotosis and inflammation. However, there are complex interactions between small biomolecules in cells, and the identification of these coexisting biomarkers remains a challenge. Herein, we report an AND logic gate based fluorescent probe (NY-Lyso), operating by responding to pH differences between organelles in cell and selectively reacting with bisulfite (HSO₃^-). This approach allows the fluorescence of the probe to remain silent under neutral or alkaline conditions, notably, is activated by costimulation of lower pH and bisulfite. Furthermore, it was confirmed to be biocompatible and could be employed to monitor HSO₃^- in lysosomes of living cells. The proposed method demonstrated more practical and outstanding capabilities in targeted and real-time monitoring, providing an effective optical tool for biomarker sensing.

Hydrogen sulfide, reactive sulfur species and coping with reactive oxygen species

Life began in a ferruginous (anoxic and Fe²⁺ dominated) world around 3.8 billion years ago (bya). Hydrogen sulfide (H₂S) and other sulfur molecules from hydrothermal vents and other fissures provided many key necessities for life's origin including catalytic platforms (primordial enzymes) that also served as primitive boundaries (cell walls), substrates for organic synthesis and a continuous source of energy in the form of reducing equivalents. Anoxigenic photosynthesis oxidizing H₂S followed within a few hundred million years and laid the metabolic groundwork for oxidative photosynthesis some half-billion years later that slightly and episodically increased atmospheric oxygen around 2.3 bya. This oxidized terrestrial sulfur to sulfate which was washed to the sea where it was reduced creating vast euxinic (anoxic and sulfidic) areas. It was in this environment that eukaryotic cells appeared around 1.5 bya and where they evolved for nearly 1 billion additional years. Oxidative photosynthesis finally oxidized the oceans and around 0.6 bya oxygen levels in the atmosphere and oceans began to rise toward present day levels. This is purported to have been a life-threatening event due to the prevalence of reactive oxygen species (ROS) and thus necessitated the elaboration of chemical and enzymatic antioxidant mechanisms. However, these antioxidants initially appeared around the time of anoxigenic photosynthesis suggesting a commitment to metabolism of reactive sulfur species (RSS). This review examines these events and suggests that many of the biological attributes assigned to ROS may, in fact, be due to RSS. This is underscored by observations that ROS and RSS are chemically similar, often indistinguishable by analytical methods and the fact that the bulk of biochemical and physiological experiments are performed in unphysiologically oxic environments where ROS are artifactually favored over RSS.

Metabolic adaptation of short-living growth hormone transgenic mice to methionine restriction and supplementation

Extension of mammalian health and life span has been achieved using various dietary interventions. We previously reported that restricting dietary methionine (MET) content extends life span only when growth hormone signaling is intact (no life span increase in GH deficiency or GH resistance). To understand the metabolic responses of altered dietary MET in the context of accelerated aging (high GH), the current study evaluated MET and related pathways in short-living GH transgenic (GH Tg) and wild-type mice following 8 weeks of restricted (0.16%), low (0.43%), or enriched (1.3%) MET consumption. Liver MET metabolic enzymes were suppressed in GH Tg compared to diet-matched wild-type mice. MET metabolite levels were differentially affected by GH status and diet. SAM:SAH ratios were markedly higher in GH Tg mice. Glutathione levels were lower in both genotypes consuming 0.16% MET but reduced in GH Tg mice when compared to wild type. Tissue thioredoxin and glutaredoxin were impacted by diet and GH status. The responsiveness to the different MET diets is reflected across many metabolic pathways indicating the importance of GH signaling in the ability to discriminate dietary amino acid levels and alter metabolism and life span.

A Benzopyronin-Based Two-Photon Fluorescent Probe for Ratiometric Imaging of Lysosomal Bisulfite with Complete Spectral Separation

Bisulfite (HSO₃^-), which equilibrates with sulfite (SO₃^2-) and sulfur dioxide (SO₂) in aqueous media, can be produced endogenously during oxidation of hydrogen sulfide or sulfur-containing amino acids. Lysosomes, known as the scavengers of living cells, play a crucial role in the metabolic process, and bisulfite is often produced inside the lysosomes. Therefore, detection of bisulfite in lysosomes is a subject of significant interest. Herein, we disclose a lysosome-targeting, two-photon excitable, and ratiometric signaling (near-infrared/green) fluorescent probe that detects bisulfite through a fast 1,6-conjugate addition reaction. The probe shows excellent selectivity toward bisulfite over other biologically relevant species. Notably, the probe allows ratiometric fluorescence imaging of lysosomal bisulfite with complete spectral separation under one-photon as well as two-photon excitation conditions.

Genes and genetics in hyperhomocysteinemia and the "1-carbon metabolism": implications for retinal structure and eye functions

Homocysteine (Hcy), a sulfur-containing nonproteinogenic amino acid, is generated as a metabolic intermediate. Hcy constitutes an important part of the "1-carbon metabolism" during methionine turnover. Elevated levels of Hcy known as hyperhomocysteinemia (HHcy) results from vitamin B deficiency, lack of exercise, smoking, excessive alcohol intake, high-fat and methionine-rich diet, and the underlying genetic defects. These factors directly affect the "1-carbon metabolism (methionine-Hcy-folate)" of a given cell. In fact, the Hcy levels are determined primarily by dietary intake, vitamin status, and the genetic blueprint of the susceptible individual. Although Hcy performs an important role in cellular functions, genetic alterations in any of the key enzymes responsible for the "1-carbon metabolism" could potentially upset the metabolic cycle, thus causing HHcy environment in susceptible people. As such, HHcy relates to several clinical conditions like atherosclerosis, myocardial infarction, stroke, cognitive impairment, dementia, Parkinson's disease, multiple sclerosis, epilepsy, and ocular disorders, among others. This article summarizes the findings from our laboratory and public database regarding genetics of HHcy and its effects on ocular disorders, their respective management during dysregulation of the 1-carbon metabolism.

Metabolic consequences of cystinuria

Background

Cystinuria is an inherited disorder of renal amino acid transport that causes recurrent nephrolithiasis and significant morbidity in humans. It has an incidence of 1 in 7000 worldwide making it one of the most common genetic disorders in man. We phenotypically characterized a mouse model of cystinuria type A resultant from knockout of Slc3a1.

Methods

Knockout of Slc3a1 at RNA and protein levels was evaluated using real-time quantitative PCR and immunofluorescence. Slc3a1 knockout mice were placed on normal or breeder chow diets and evaluated for cystine stone formation over time suing x-ray analysis, and the development of kidney injury by measuring injury biomarkers. Kidney injury was also evaluated via histologic analysis. Amino acid levels were measured in the blood of mice using high performance liquid chromatography. Liver glutathione levels were measured using a luminescent-based assay.

Results

We confirmed knockout of Slc3a1 at the RNA level, while Slc7a9 RNA representing the co-transporter was preserved. As expected, we observed bladder stone formation in Slc3a1^−/− mice. Male Slc3a1^−/− mice exhibited lower weights compared to Slc3a1^+/+. Slc3a1^−/− mice on a regular diet demonstrated elevated blood urea nitrogen (BUN) without elevation of serum creatinine. However, placing the knockout animals on a breeder chow diet, containing a higher cystine concentration, resulted in the development of elevation of both BUN and creatinine indicative of more severe chronic kidney disease. Histological examination revealed that these dietary effects resulted in worsened kidney tubular obstruction and interstitial inflammation as well as worsened bladder inflammation. Cystine is a precursor for the antioxidant molecule glutathione, so we evaluated glutathione levels in the livers of Slc3a1^−/− mice. We found significantly lowered levels of both reduced and total glutathione in the knockout animals.

Conclusions

Our results suggest that that diet can affect the development and progression of chronic kidney disease in an animal model of cystinuria, which may have important implications for patients with this disease. Additionally, reduced glutathione may predispose those with cystinuria to injury caused by oxidative stress.

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Electronic supplementary material

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