The nonessential amino acid cysteine is required to prevent ferroptosis in acute myeloid leukemia.

ABSTRACT: Cysteine is a nonessential amino acid required for protein synthesis, the generation of the antioxidant glutathione, and for synthesizing the nonproteinogenic amino acid taurine. Here, we highlight the broad sensitivity of leukemic stem and progenitor cells to cysteine depletion. By CRISPR/CRISPR-associated protein 9-mediated knockout of cystathionine-γ-lyase, the cystathionine-to-cysteine converting enzyme, and by metabolite supplementation studies upstream of cysteine, we functionally prove that cysteine is not synthesized from methionine in acute myeloid leukemia (AML) cells. Therefore, although perhaps nutritionally nonessential, cysteine must be imported for survival of these specific cell types. Depletion of cyst(e)ine increased reactive oxygen species (ROS) levels, and cell death was induced predominantly as a consequence of glutathione deprivation. nicotinamide adenine dinucleotide phosphate hydrogen oxidase inhibition strongly rescued viability after cysteine depletion, highlighting this as an important source of ROS in AML. ROS-induced cell death was mediated via ferroptosis, and inhibition of glutathione peroxidase 4 (GPX4), which functions in reducing lipid peroxides, was also highly toxic. We therefore propose that GPX4 is likely key in mediating the antioxidant activity of glutathione. In line, inhibition of the ROS scavenger thioredoxin reductase with auranofin also impaired cell viability, whereby we find that oxidative phosphorylation-driven AML subtypes, in particular, are highly dependent on thioredoxin-mediated protection against ferroptosis. Although inhibition of the cystine-glutamine antiporter by sulfasalazine was ineffective as a monotherapy, its combination with L-buthionine-sulfoximine (BSO) further improved AML ferroptosis induction. We propose the combination of either sulfasalazine or antioxidant machinery inhibitors along with ROS inducers such as BSO or chemotherapy for further preclinical testing.

Multiomic screening of invasive GBM cells reveals targetable transsulfuration pathway alterations.

While the poor prognosis of glioblastoma arises from the invasion of a subset of tumor cells, little is known of the metabolic alterations within these cells that fuel invasion. We integrated spatially addressable hydrogel biomaterial platforms, patient site-directed biopsies, and multiomics analyses to define metabolic drivers of invasive glioblastoma cells. Metabolomics and lipidomics revealed elevations in the redox buffers cystathionine, hexosylceramides, and glucosyl ceramides in the invasive front of both hydrogel-cultured tumors and patient site-directed biopsies, with immunofluorescence indicating elevated reactive oxygen species (ROS) markers in invasive cells. Transcriptomics confirmed upregulation of ROS-producing and response genes at the invasive front in both hydrogel models and patient tumors. Among oncologic ROS, H2O2 specifically promoted glioblastoma invasion in 3D hydrogel spheroid cultures. A CRISPR metabolic gene screen revealed cystathionine γ-lyase (CTH), which converts cystathionine to the nonessential amino acid cysteine in the transsulfuration pathway, to be essential for glioblastoma invasion. Correspondingly, supplementing CTH knockdown cells with exogenous cysteine rescued invasion. Pharmacologic CTH inhibition suppressed glioblastoma invasion, while CTH knockdown slowed glioblastoma invasion in vivo. Our studies highlight the importance of ROS metabolism in invasive glioblastoma cells and support further exploration of the transsulfuration pathway as a mechanistic and therapeutic target.

A Methionine-Portioning-Based Medical Nutrition Therapy with Relaxed Fruit and Vegetable Consumption in Patients with Pyridoxine-Nonresponsive Cystathionine-ß-Synthase Deficiency.

The main treatment for pyridoxine-nonresponsive cystathionine-ß-synthase deficiency is a strict diet. Most centers prescribe low-protein diets based on gram-protein exchanges, and all protein sources are weighed. The purpose of this study is to investigate the effects of a more liberal methionine (Met)-based diet with relaxed consumption of fruits and vegetables on metabolic outcomes and dietary adherence. Ten patients previously on a low-protein diet based on a gram-protein exchange list were enrolled. The natural protein exchange lists were switched to a "Met portion exchange list". Foods containing less than 0.005 g methionine per 100 g of the food were accepted as exchange-free foods. The switch to Met portioning had no adverse effects on the control of plasma homocysteine levels in terms of metabolic outcomes. It resulted in a significant reduction in patients' daily betaine dose. All patients preferred to continue with this modality. In conclusion, methionine-portion-based medical nutrition therapy with relaxed consumption of fruits and vegetables seems to be a good and safe option to achieve good metabolic outcomes and high treatment adherence.

Beneficial Effect of H2S-Releasing Molecules in an In Vitro Model of Sarcopenia: Relevance of Glucoraphanin.

Sarcopenia is a gradual and generalized skeletal muscle (SKM) syndrome, characterized by the impairment of muscle components and functionality. Hydrogen sulfide (H2S), endogenously formed within the body from the activity of cystathionine-γ-lyase (CSE), cystathionine- ß-synthase (CBS), and mercaptopyruvate sulfurtransferase, is involved in SKM function. Here, in an in vitro model of sarcopenia based on damage induced by dexamethasone (DEX, 1 µM, 48 h treatment) in C2C12-derived myotubes, we investigated the protective potential of exogenous and endogenous sources of H2S, i.e., glucoraphanin (30 µM), L-cysteine (150 µM), and 3-mercaptopyruvate (150 µM). DEX impaired the H2S signalling in terms of a reduction in CBS and CSE expression and H2S biosynthesis. Glucoraphanin and 3-mercaptopyruvate but not L-cysteine prevented the apoptotic process induced by DEX. In parallel, the H2S-releasing molecules reduced the oxidative unbalance evoked by DEX, reducing catalase activity, O2- levels, and protein carbonylation. Glucoraphanin, 3-mercaptopyruvate, and L-cysteine avoided the changes in myotubes morphology and morphometrics after DEX treatment. In conclusion, in an in vitro model of sarcopenia, an impairment in CBS/CSE/H2S signalling occurs, whereas glucoraphanin, a natural H2S-releasing molecule, appears more effective for preventing the SKM damage. Therefore, glucoraphanin supplementation could be an innovative therapeutic approach in the management of sarcopenia.

Exogenous hydrogen sulfide restores CSE and CBS but no 3-MST protein expression in the hypothalamus and brainstem after severe traumatic brain injury.

Hydrogen sulfide (H2S) is a gasotransmitter endogenously synthesized by cystathionine-γ-lyase (CSE), cystathionine-ß-synthase (CBS), and 3-mercaptopiruvate sulfurtransferase (3-MST) enzymes. H2S exogenous administration prevents the development of hemodynamic impairments after traumatic brain injury (TBI). Since the hypothalamus and the brainstem highly regulate the cardiovascular system, this study aimed to evaluate the effect of NaHS subchronic treatment on the changes of H2S-sythesizing enzymes in those brain areas after TBI and in physiological conditions. For that purpose, animals were submitted to a lateral fluid percussion injury, and the changes in CBS, CSE, and 3-MST protein expression were measured by western blot at days 1, 2, 3, 7, and 28 in the vehicle group, and 7 and 28 days after NaHS treatment. After severe TBI induction, we found a decrease in CBS and CSE protein expression in the hypothalamus and brainstem; meanwhile, 3-MST protein expression diminished only in the hypothalamus compared to the Sham group. Remarkably, i.p. daily injections of NaHS, an H2S donor, (3.1 mg/kg) during seven days: (1) restored CBS and CSE but no 3-MST protein expression in the hypothalamus at day 28 post-TBI; (2) reestablished only CSE in brainstem 7 and 28 days after TBI; and (3) did not modify H2S-sythesizing enzymes protein expression in uninjured animals. Mainly, our results show that the NaHS effect on CBS and CSE protein expression is observed in a time- and tissue-dependent manner with no effect on 3-MST expression, which may suggest a potential role of H2S synthesis in hypothalamus and brainstem impairments observed after TBI.

[Serum metabolomics of chronic obstructive pulmonary disease with lung-Qi deficiency syndrome].

The present study analyzed the potential biomarkers of chronic obstructive pulmonary disease(COPD) with lung-Qi deficiency syndrome by non-targeted metabolomics and explored the biological basis of this syndrome. Blood samples of 96 COPD patients with lung-Qi deficiency syndrome(COPD with lung-Qi deficiency syndrome group) and 106 healthy people(healthy control group) were collected, and the metabolic profiles of both groups were analyzed by ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry(UPLC-Q-TOF-MS). Multivariate statistical analysis and differential metabolite screening were carried out by using Progenesis QI and Simca-P. Metabolic pathways were constructed through the MetaboAnalyst. Seven potential biomarkers, such as L-cystathionine, protoporphyrinogen Ⅸ, and citalopram aldehyde, were identified. Compared with the results in the healthy control group, the content of citalopram aldehyde, N1-methyl-2-pyridone-5-carboxamide, and 11ß,17ß-dihydroxy-4-androsten-3-one was significantly up-regulated, while that of the other four compounds such as L-cystathionine, dihydrotestosterone, protoporphyrinogen Ⅸ, and D-urobilinogen was down-regulated. These potential biomarkers involved six metabolic pathways, including cysteine and methionine metabolism, porphyrin and chlorophyll metabolism, drug metabolism of cytochrome P450, steroid hormone biosynthesis, glycine, serine, and threonine metabolism, and nicotinate and nicotinamide meta-bolism. This study is expected to provide a certain scientific basis for the research on traditional Chinese medicine syndrome of COPD with lung-Qi deficiency syndrome from the molecular biology level.

Serum metabolomics of chronic obstructive pulmonary disease with lung-Qi deficiency syndrome / 中国中药杂志

The present study analyzed the potential biomarkers of chronic obstructive pulmonary disease(COPD) with lung-Qi deficiency syndrome by non-targeted metabolomics and explored the biological basis of this syndrome. Blood samples of 96 COPD patients with lung-Qi deficiency syndrome(COPD with lung-Qi deficiency syndrome group) and 106 healthy people(healthy control group) were collected, and the metabolic profiles of both groups were analyzed by ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry(UPLC-Q-TOF-MS). Multivariate statistical analysis and differential metabolite screening were carried out by using Progenesis QI and Simca-P. Metabolic pathways were constructed through the MetaboAnalyst. Seven potential biomarkers, such as L-cystathionine, protoporphyrinogen Ⅸ, and citalopram aldehyde, were identified. Compared with the results in the healthy control group, the content of citalopram aldehyde, N1-methyl-2-pyridone-5-carboxamide, and 11β,17β-dihydroxy-4-androsten-3-one was significantly up-regulated, while that of the other four compounds such as L-cystathionine, dihydrotestosterone, protoporphyrinogen Ⅸ, and D-urobilinogen was down-regulated. These potential biomarkers involved six metabolic pathways, including cysteine and methionine metabolism, porphyrin and chlorophyll metabolism, drug metabolism of cytochrome P450, steroid hormone biosynthesis, glycine, serine, and threonine metabolism, and nicotinate and nicotinamide meta-bolism. This study is expected to provide a certain scientific basis for the research on traditional Chinese medicine syndrome of COPD with lung-Qi deficiency syndrome from the molecular biology level.

Water soluble selenometabolome of Cardamine violifolia.

Low molecular weight selenium containing metabolites in the leaves of the selenium hyperaccumulator Cardamine violifolia (261 mg total Se per kg d.w.) were targeted in this study. One dimensional cation exchange chromatography coupled to ICP-MS was used for purification and fractionation purposes prior to LC-Unispray-QTOF-MS analysis. The search for selenium species in full scan spectra was assisted with an automated mass defect based filtering approach. Besides selenocystathionine, selenohomocystine and its polyselenide derivative, a total number of 35 water soluble selenium metabolites other than selenolanthionine were encountered, including 30 previously unreported compounds. High occurrence of selenium containing hexoses was observed, together with the first assignment of N-glycoside derivatives of selenolanthionine. Quantification of the most abundant selenium species, selenolanthionine, was carried out with an ion pairing LC - post column isotope dilution ICP-MS setup, which revealed that this selenoamino acid accounted for 30% of the total selenium content of the leaf (78 mg (as Se) per kg d.w.).

Cystathionine ß-synthase is involved in cysteine biosynthesis and H2S generation in Toxoplasma gondii.

Cystathionine ß-synthase (CBS) catalyzes the condensation of serine and homocysteine to water and cystathionine, which is then hydrolyzed to cysteine, α-ketobutyrate and ammonia by cystathionine γ-lyase (CGL) in the reverse transsulfuration pathway. The protozoan parasite Toxoplasma gondii, the causative agent of toxoplasmosis, includes both CBS and CGL enzymes. We have recently reported that the putative T. gondii CGL gene encodes a functional enzyme. Herein, we cloned and biochemically characterized cDNA encoding CBS from T. gondii (TgCBS), which represents a first example of protozoan CBS that does not bind heme but possesses two C-terminal CBS domains. We demonstrated that TgCBS can use both serine and O-acetylserine to produce cystathionine, converting these substrates to an aminoacrylate intermediate as part of a PLP-catalyzed ß-replacement reaction. Besides a role in cysteine biosynthesis, TgCBS can also efficiently produce hydrogen sulfide, preferentially via condensation of cysteine and homocysteine. Unlike the human counterpart and similar to CBS enzymes from lower organisms, the TgCBS activity is not stimulated by S-adenosylmethionine. This study establishes the presence of an intact functional reverse transsulfuration pathway in T. gondii and demonstrates the crucial role of TgCBS in biogenesis of H2S.

A possible mechanism of inhibition of U87MG and SH-SY5Y cancer cell proliferation by diallyl trisulfide and other aspects of its activity.

The study was conducted to elucidate the mechanism of antiproliferative and antioxidative action of diallyl trisulfide (DATS), a garlic-derived organosulfur compound. Changes in the L-cysteine desulfuration, and the levels of cystathionine and non-protein thiols in DATS-treated human glioblastoma (U87MG) and neuroblastoma (SH-SY5Y) cells were investigated. The inhibition of proliferation of the investigated cells by DATS was correlated with an increase in the inactivated form of Bcl-2. In U87MG cells, an increased level of sulfane sulfur and an increased activity of 3-mercaptopyruvate sulfurtransferase (MPST) and rhodanese, the enzymes involved in sulfane sulfur generation and transfer, suggest that DATS can function as a donor of sulfane sulfur atom, transferred by sulfurtransferases, to sulfhydryl groups of cysteine residues of Bcl-2 and in this way lower the level of active form of Bcl-2 by S-sulfuration. Diallyl trisulfide antioxidative effects result from an increased level of cystathionine, a precursor of cysteine, and an increased glutathione level. MPST and rhodanese, the level of which is increased in the presence of DATS, can serve as antioxidant proteins.

Methionine and Choline Supply during the Periparturient Period Alter Plasma Amino Acid and One-Carbon Metabolism Profiles to Various Extents: Potential Role in Hepatic Metabolism and Antioxidant Status.

The objective of this study was to profile plasma amino acids (AA) and derivatives of their metabolism during the periparturient period in response to supplemental rumen-protected methionine (MET) or rumen-protected choline (CHOL). Forty cows were fed from -21 through 30 days around parturition in a 2 × 2 factorial design a diet containing MET or CHOL. MET supply led to greater circulating methionine and proportion of methionine in the essential AA pool, total AA, and total sulfur-containing compounds. Lysine in total AA also was greater in these cows, indicating a better overall AA profile. Sulfur-containing compounds (cystathionine, cystine, homocystine, and taurine) were greater in MET-fed cows, indicating an enriched sulfur-containing compound pool due to enhanced transsulfuration activity. Circulating essential AA and total AA concentrations were greater in cows supplied MET due to greater lysine, arginine, tryptophan, threonine, proline, asparagine, alanine, and citrulline. In contrast, CHOL supply had no effect on essential AA or total AA, and only tryptophan and cystine were greater. Plasma 3-methylhistidine concentration was lower in response to CHOL supply, suggesting less tissue protein mobilization in these cows. Overall, the data revealed that enhanced periparturient supply of MET has positive effects on plasma AA profiles and overall antioxidant status.

Reduced folate and serum vitamin metabolites in patients with rectal carcinoma: an open-label feasibility study of pemetrexed with folic acid and vitamin B12 supplementation.

The objectives of this single-center, open-label, phase II study were to evaluate (a) the feasibility and safety of neoadjuvant administration of pemetrexed with oral folic acid and vitamin B12 (FA/B12) in newly diagnosed patients with resectable rectal cancer and (b) intracellular and systemic vitamin metabolism. Patients were treated with three cycles of pemetrexed (500 mg/m, every 3 weeks) and FA/B12 before surgery. The reduced folates tetrahydrofolate, 5-methyltetrahydrofolate, and 5,10-methylenetetrahydrofolate were evaluated from biopsies in tumor tissue and in adjacent mucosa. Serum levels of homocysteine, cystathionine, and methylmalonic acid were also measured. All 37 patients received three cycles of pemetrexed; 89.2% completed their planned dosage within a 9-week feasibility time frame. Neither dose reductions nor study drug-related serious adverse events were reported. Reduced folate levels were significantly higher in tumor tissue compared with adjacent mucosa at baseline. After FA/B12 administration, tissue levels of reduced folates increased significantly and remained high during treatment in both tumor and mucosa until surgery. Serum levels of cystathionine increased significantly compared with baseline after FA/B12 administration, but then decreased, fluctuating cyclically during pemetrexed therapy. Homocysteine and methylmalonic acid levels decreased significantly after FA/B12 administration, and remained below baseline levels during the study. These results indicate that administration of three neoadjuvant cycles of single-agent pemetrexed, every 3 weeks, with FA/B12 in patients with resectable rectal cancer is feasible and tolerable. Tissue and serum vitamin metabolism results demonstrate the influence of pemetrexed and FA/B12 on vitamin metabolism and warrant further study.

Long-term dietary supplementation with cystathionine improves tissue glutathione in ageing rats.

BACKGROUND: Ageing is associated with decrease in tissue glutathione that can be reduced by food fortification with the amino acid cysteine. However, cysteine is not stable in solution and generates bad taste. Cystathionine, the direct precursor of cysteine, could be a valuable alternative. AIMS: This study aimed to determine whether long-term dietary supplementation with cystathionine induces an increase in glutathione pools. METHODS: Aged rats (20.5-month-old) were fed ad libitum during 29 weeks with either a cystathionine-supplemented diet (7.3 g/kg, n = 90 rats) or a control iso-nitrogenous alanine-supplemented diet (2.9 g/kg, n = 90 rats). RESULTS: Cystathionine was detected in the plasma of the cystathionine-supplemented rats but not in the control alanine-supplemented rats. Cystathionine increased glutathione concentrations in liver, small intestine and gastrocnemius muscle (P < 0.03). No adverse effect was observed. CONCLUSION: Cystathionine supplementation being able to increase moderately glutathione in healthy old rats could be considered as a candidate for nutritional supports aiming to revert the stronger glutathione depletions occurring in unhealthy elderly.

Folic acid causes higher prevalence of detectable unmetabolized folic acid in serum than B-complex: a randomized trial.

PURPOSE: Unmetabolized folic acid (UMFA) is common in serum of elderly individuals receiving folic acid (FA)-fortified foods or supplements. We studied the effect of supplementing FA or B-complex on serum concentrations of (6S)-5-methyltetrahydropteroylglutamate [(6S)-5-CH3-H4Pte] and UMFA in elderly people and explored factors associated with detectable UMFA post-supplementation. METHODS: This is a randomized single-blind non-controlled trial on 58 elderly people using daily 400 µg FA (n = 31) or 400 µg FA, 10 µg cyanocob(III)alamin and 8 mg pyridoxine (n = 27) for a median of 23 days. Main outcome includes changes in concentrations of serum (6S)-5-CH3-H4Pte and UMFA. RESULTS: Total homocysteine declined by a median of 1.6 (p = 0.074) in the FA and 1.3 µmol/L (p = 0.009) in the B-complex arms (p = 0.66 between the arms). Serum (6S)-5-CH3-H4Pte significantly (p < 0.001 vs. baseline) increased by a median of 9.2 and 6.5 nmol/L in the FA and B-complex groups, respectively (p = 0.152 between the groups). Compared to FA, B-complex reduced cystathionine and caused lower post-intervention serum UMFA, percentage of UMFA to (6S)-5-CH3-H4Pte and prevalence of UMFA ≥ 0.21 nmol/L. Higher serum cystathionine and whole-blood folate predicted higher post-intervention serum UMFA. CONCLUSIONS: FA caused higher UMFA as compared to B-complex. Pyridoxine appears to improve folate recycling. Data on serum UMFA should be interpreted in relation to other vitamins involved in folate metabolism. Serum UMFA is suggested to play a sensory role through which the cell recognizes FA available for metabolism via dihydrofolate reductase.

Pyridoxine supplementation does not alter in vivo kinetics of one-carbon metabolism but modifies patterns of one-carbon and tryptophan metabolites in vitamin B-6-insufficient oral contraceptive users.

BACKGROUND: Low chronic vitamin B-6 status can occur in a subset of women who use oral contraceptives (OCs) with uncertain metabolic consequences. An insufficiency of cellular pyridoxal 5'-phosphate (PLP), which is the coenzyme form of vitamin B-6, may impair many metabolic processes including one-carbon and tryptophan metabolism. OBJECTIVE: We investigated the effects of vitamin B-6 supplementation on the in vivo kinetics of one-carbon metabolism and the concentration of one-carbon and tryptophan metabolites in vitamin B-6-deficient OC users. DESIGN: A primed, constant infusion of [(13)C5]methionine, [3-(13)C]serine, and [(2)H3]leucine was performed on 10 OC users (20-40 y old; plasma PLP concentrations <30 nmol/L) before and after 28 d of supplementation with 10 mg pyridoxine hydrochloric acid/d. In vivo fluxes of total homocysteine remethylation, the remethylation of homocysteine from serine, and rates of homocysteine and cystathionine production were assessed. Targeted metabolite profiling was performed, and data were analyzed by using orthogonal partial least-squares-discriminant analysis and paired t tests adjusted for multiple testing. RESULTS: Pyridoxine supplementation increased the mean ± SD plasma PLP concentration from 25.8 ± 3.6 to 143 ± 58 nmol/L (P < 0.001) and decreased the leucine concentration from 103 ± 17 to 90 ± 20 nmol/L (P = 0.007) and glycine concentration from 317 ± 63 to 267 ± 58 nmol/L (P = 0.03). Supplementation did not affect in vivo rates of homocysteine remethylation or the appearance of homocysteine and cystathionine. A multivariate analysis showed a clear overall effect on metabolite profiles resulting from supplementation. Leucine, glycine, choline, cysteine, glutathione, trimethylamine N-oxide, and the ratios glycine:serine, 3-hydroxykynurenine:kynurenine, 3-hydroxykynurenine:3-hydroxyanthranilic acid, and 3-hydroxykynurenine:anthranilic acid were significant discriminating variables. CONCLUSIONS: Consistent with previous vitamin B-6-restriction studies, fluxes of one-carbon metabolic processes exhibited little or no change after supplementation in low-vitamin B-6 subjects. In contrast, changes in the metabolic profiles after supplementation indicated perturbations in metabolism, suggesting functional vitamin B-6 deficiency. This study was registered at clinicaltrials.gov as NCT01128244.

Homocysteine, iron and cardiovascular disease: a hypothesis.

Elevated circulating total homocysteine (tHcy) concentrations (hyperhomocysteinemia) have been regarded as an independent risk factor for cardiovascular disease (CVD). However, several large clinical trials to correct hyperhomocysteinemia using B-vitamin supplements (particularly folic acid) have largely failed to reduce the risk of CVD. There is no doubt that a large segment of patients with CVD have hyperhomocysteinemia; therefore, it is reasonable to postulate that circulating tHcy concentrations are in part a surrogate marker for another, yet-to-be-identified risk factor(s) for CVD. We found that iron catalyzes the formation of Hcy from methionine, S-adenosylhomocysteine and cystathionine. Based on these findings, we propose that an elevated amount of non-protein-bound iron (free Fe) increases circulating tHcy. Free Fe catalyzes the formation of oxygen free radicals, and oxidized low-density lipoprotein is a well-established risk factor for vascular damage. In this review, we discuss our findings on iron-catalyzed formation of Hcy from thioethers as well as recent findings by other investigators on this issue. Collectively, these support our hypothesis that circulating tHcy is in part a surrogate marker for free Fe, which is one of the independent risk factors for CVD.

Plasma sulfur amino acids and stearoyl-CoA desaturase activity in two Caucasian populations.

In rats, dietary restriction of the cysteine precursor methionine suppresses hepatic stearoyl-CoA desaturase (SCD)-1 expression and activity, whereas cysteine supplementation reverses these effects. In 2 independent cohorts: Hordaland Health Study (HUSK; N=2021, aged 71-74y), Norway, and Hoorn study (N=686, aged 50-87y), Netherlands, we examined the cross-sectional associations of plasma sulfur-containing compounds (SCC; methionine, S-adenosylmethionine, S-adenosylhomocysteine, homocysteine, cystathionine, total cysteine (tCys), glutathione and cysteinylglycine) with SCD-16 index (16:1n-7/16:0), estimated from fatty acid profiles of total plasma or serum lipids. Only tCys was consistently associated with SCD-16 index after adjustments for sex and age (HUSK: partial r=0.14; Hoorn: partial r=0.11, P<0.001 for both), and after further adjustments for other SCC, body fat, diet, exercise and plasma lipids (HUSK: partial r=0.07, P=0.004; Hoorn: partial r=0.12, P=0.013). Together with animal data showing an effect of dietary cysteine on SCD1, our results suggest a role for cysteine in SCD1 regulation in humans.

The cysteine dioxgenase knockout mouse: altered cysteine metabolism in nonhepatic tissues leads to excess H2S/HS(-) production and evidence of pancreatic and lung toxicity.

AIMS: To define the consequences of loss of cysteine dioxygenase (CDO) on cysteine metabolism at the tissue level, we determined levels of relevant metabolites and enzymes and evidence of H2S/HS(-) (gaseous hydrogen sulfide and its conjugate base) toxicity in liver, pancreas, kidney, and lung of CDO(-/-) mice that were fed either a taurine-free or taurine-supplemented diet. RESULTS: CDO(-/-) mice had low tissue and serum taurine and hypotaurine levels and high tissue levels of cysteine, consistent with the loss of CDO. CDO(-/-) mice had elevated urinary excretion of thiosulfate, high tissue and serum cystathionine and lanthionine levels, and evidence of inhibition and destabilization of cytochrome c oxidase, which is consistent with excess production of H2S/HS(-). Accumulation of cystathionine and lanthionine appeared to result from cystathionine ß-synthase (CBS)-mediated cysteine desulfhydration. Very high levels of hypotaurine in pancreas of wild-type mice and very high levels of cystathionine and lanthionine in pancreas of CDO(-/-) mice were observed, suggesting a unique cysteine metabolism in the pancreas. INNOVATION: The CDO(-/-) mouse model provides new insights into tissue-specific cysteine metabolism, particularly the role of pancreas in metabolism of excess cysteine by CBS-catalyzed reactions, and will be a useful model for studying the effects of excess endogenous production of H2S/HS(-). CONCLUSION: The CDO(-/-) mouse clearly demonstrates that H2S/HS(-) production in tissues can exceed the capacity of the animal to oxidize sulfide to sulfate and demonstrates that pancreas and lung are more susceptible to toxicity from endogenous H2S/HS(-)production than are liver and kidney.

Methionine metabolic pathway in alcoholic liver injury.

PURPOSE OF REVIEW: To outline recent advances in the understanding of the consequences of the alterations in the methionine metabolic pathway and to present new treatment options for alcoholic liver disease (ALD). RECENT FINDINGS: ALD is a major healthcare problem worldwide. Findings in many laboratories, including ours, have demonstrated that ethanol consumption impairs several of the multiple steps in methionine metabolism that ultimately impairs the activity of many methyltransferases critical for normal functioning of the liver. Recent studies buttress the important role genetics may play in the development and progression of alcoholic liver injury. Treatment modalities using two important metabolites of the pathway, S-adenosylmethionine and betaine, have been shown to attenuate ethanol-induced liver injury in a variety of experimental models of liver disease. S-adenosylmethionine has been used in several clinical studies; however, the outcomes have been unclear and its efficacy in liver diseases continues to be debated. To date, no clinical trials have been conducted for treatment of ALD with betaine. SUMMARY: Future treatment modalities for ALD should consider loss-of-function polymorphisms in the enzymes of the methionine metabolic and related pathways. Further new treatment modalities for ALD should consider supplementation with betaine that may prove to be a promising therapeutic agent.

Cysteine and obesity: consistency of the evidence across epidemiologic, animal and cellular studies.

PURPOSE OF REVIEW: The concentrations of several plasma amino acids increase in obesity. Notably, plasma total concentrations of the sulphur amino acid cysteine (tCys) are linearly associated with fat mass in large population studies. Animal and cellular experiments support the concept that cysteine may be obesogenic. Here we review experimental and epidemiologic findings linking cysteine and related compounds with fat regulation and obesity. RECENT FINDINGS: tCys, and to a lesser extent cystathionine, are the only plasma sulphur amino acids consistently associated with human obesity, whereas glutathione is inversely associated with BMI. Supplementing cyste(i)ne in rodents decreases energy expenditure and promotes adiposity, whereas defects of cysteine-synthesizing enzymes decrease body weight. In adipocytes, cysteine inhibits lipolysis and promotes lipogenesis via H2O2 production. Unlike most plasma amino acids, tCys levels do not decrease with gastric bypass-induced weight loss, further supporting the concept that elevated cysteine may be a cause, not a consequence of obesity. Although cysteine products (glutathione, taurine and H2S) are altered in obesity, they do not appear to explain cysteine's effects on body weight. SUMMARY: Cellular, animal and epidemiologic data are consistent with the view that cysteine is obesogenic. Targeted research linking in-vitro and in-vivo findings is needed to elucidate mechanisms involved.