Sulfur Amino Acid Catabolism Research Articles

H2S serves as the immunoregulatory essence of apoptotic cell death

Apoptosis supports tissue homeostasis and prevents immune disorders by removing damaged and functionally aberrant cells. Here, Ou etal. utilized genetic, pharmacological, and proteomic approaches focused on sulfur amino acid catabolism to discover that hydrogen sulfide (H2S) release during apoptosis suppresses Th17 cell differentiation, thus providing therapeutic targets for autoimmune diseases.

Molybdenum - a scoping review for Nordic Nutrition Recommendations 2023.

Molybdenum is an essential element in the form of the molybdenum cofactor (Moco). In humans, Moco is required for four enzymes: xanthine oxidase (XO), aldehyde oxidase, sulfite oxidase (SO), and mitochondrial amidoxime-reducing component (mARC). The enzymes are involved in the oxidation of purines to uric acid, metabolism of aromatic aldehydes and heterocyclic compounds, and in the catabolism of sulfur amino acids. Molybdenum cofactor deficiency is a rare autosomal recessive syndrome due to a defective synthesis of Moco, resulting in a deficiency of all the molybdoenzymes. There are no reports on clinical signs of dietary molybdenum deficiency in otherwise healthy humans. Water-soluble molybdate is efficiently absorbed from the digestive tract. The body retention is regulated by urinary excretion. Plasma molybdenum reflects long-term intake and 24-h urinary excretion is related to recent intake. There are no biochemical markers of molybdenum status. Cereal products are the main contributors to molybdenum dietary intake, estimated to 100-170 μg/day in Nordic studies. Little data are available on molybdenum toxicity in humans. A tolerable upper intake level of molybdenum has been based on reproductive toxicity in rats, but the effects have not been reproduced in more recent studies. The U.S. Institute of Medicine (IOM, present National Academy of Sciences, Engineering, and Medicine; NASEM) established a Recommended Dietary Allowance of 45 μg/day in adult men and women in 2001, based on a small study reporting urinary excretion in balance with intake at 22 μg/day. The European Food Safety Authority (EFSA) considered in 2013 the evidence to be insufficient to derive an Average Requirement and a Population Reference Intake, but proposed an Adequate Intake of 65 μg/day for adults.

Combining Genome-Wide Gene Expression Analysis (RNA-seq) and a Gene Editing Platform (CRISPR-Cas9) to Uncover the Selectively Pro-oxidant Activity of Aurone Compounds Against Candida albicans.

Candida albicans is the major fungal cause of healthcare-associated bloodstream infections worldwide with a 40% mortality rate. The scarcity of antifungal treatments due to the eukaryotic origin of fungal cells has challenged the development of selectively antifungal drugs. In an attempt to identify novel antifungal agents, aurones SH1009 and SH9051, as synthetically bioactive compounds, have been recently documented as anti-Candida agents. Since the molecular mechanisms behind the inhibitory activities of these aurones in C. albicans are unclear, this study aimed to determine the comprehensive cellular processes affected by these aurones and their molecular targets. Genome-wide transcriptional analysis of SH1009- and SH9051-treated C. albicans revealed uniquely repressed expression in different metabolic pathways, particularly trehalose and sulfur amino acid metabolic processes for SH1009 and SH9051, respectively. In contrast, the most commonly enriched process for both aurones was the up-regulation of RNA processing and ribosomal cleavages as an indicator of high oxidative stress, suggesting that a common aspect in the chemical structure of both aurones led to pro-oxidative properties. Additionally, uniquely induced responses (iron ion homeostasis for SH1009 and arginine biosynthesis for SH9051) garnered attention on key roles for the aurone functional groups. Deletion of the transcription factor for the trehalose biosynthesis pathway, Tye7p, resulted in an SH1009-resistant mutant, which also exhibited low trehalose content, validating the primary molecular target of SH1009. Aurone SH9051 uniquely simulated an exogenous supply of methionine or cysteine, leading to sulfur amino acid catabolism as evidenced by quantifying an overproduction of sulfite. Phenyl aurone, the common structure of aurones, contributed proportionally in the pro-oxidative activity through ferric ion reduction effects leading to high ROS levels. Our results determined selective and novel molecular mechanisms for aurone SH1009 and also elucidated the diverse cellular effects of different aurones based on functional groups.

ETMM-01. CANCER STEM CELL ENRICHMENT AND METABOLIC SUBSTRATE ADAPTABILITY ARE DRIVEN BY HYDROGEN SULFIDE SUPPRESSION IN GLIOBLASTOMA

Glioblastoma (GBM) remains among the deadliest of human malignancies. The emergence of the cancer stem cell (CSC) phenotype represents a major challenge to disease management and durable treatment response. The extrinsic, environmental, and lifestyle factors that result in CSC enrichment are not well understood. The CSC state endows cells with a fluid metabolic profile, enabling the utilization of multiple nutrient sources. Therefore, to test the impact of diet on CSC enrichment, we evaluated disease progression in tumor-bearing mice fed an obesity-inducing high-fat diet (HFD) versus an energy-balanced, low-fat control diet. HFD consumption resulted in hyper-aggressive disease that was accompanied by CSC enrichment and shortened survival. HFD consumption also drove intracerebral accumulation of saturated fats, which in turn inhibited the production and signaling of the gasotransmitter hydrogen sulfide (H2S). H2S is an endogenously produced bio-active metabolite derived from sulfur amino acid catabolism. It functions principally through protein S-sulfhydration and regulates a variety of programs including mitochondrial bioenergetics and cellular metabolism. Inhibition of H2S synthesis resulted in increased proliferation and chemotherapy resistance, whereas treatment with H2S donors led to cytotoxicity and death of cultured GBM cells. Compared to non-cancerous controls, patient GBM specimens were reduced in overall protein S-sulfhydration, which was primarily lost from proteins regulating cellular metabolism. These findings support the hypothesis that diet-regulated H2S signaling serves to suppress GBM by restricting metabolic adaptability, while its loss triggers CSC enrichment and disease acceleration. Interventions augmenting H2S bioavailability concurrent with GBM standard of care may improve outcomes for GBM patients.

TAMI-12. CANCER STEM CELL ENRICHMENT AND METABOLIC SUBSTRATE ADAPTABILITY ARE DRIVEN BY HYDROGEN SULFIDE SUPPRESSION IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) remains among the deadliest of human malignancies. The emergence of the cancer stem cell (CSC) phenotype represents a major challenge to disease management and durable treatment response. The extrinsic, environmental, and lifestyle factors that result in CSC enrichment are not well understood. The CSC state endows cells with a fluid metabolic profile, enabling the utilization of multiple nutrient sources. Therefore, to test the impact of diet on CSC enrichment, we evaluated disease progression in tumor-bearing mice fed an obesity-inducing high-fat diet (HFD) versus an energy-balanced, low-fat control diet. HFD consumption resulted in hyper-aggressive disease that was accompanied by CSC enrichment and shortened survival. HFD consumption also drove intracerebral accumulation of saturated fats, which in turn inhibited the production and signaling of the gasotransmitter hydrogen sulfide (H2S). H2S is an endogenously produced bio-active metabolite derived from sulfur amino acid catabolism. It functions principally through protein S-sulfhydration and regulates a variety of programs including mitochondrial bioenergetics and cellular metabolism. Inhibition of H2S synthesis resulted in increased proliferation and chemotherapy resistance, whereas treatment with H2S donors led to cytotoxicity and death of cultured GBM cells. Compared to non-cancerous controls, patient GBM specimens were reduced in overall protein S-sulfhydration, which was primarily lost from proteins regulating cellular metabolism. These findings support the hypothesis that diet-regulated H2S signaling serves to suppress GBM by restricting metabolic adaptability, while its loss triggers CSC enrichment and disease acceleration. Interventions augmenting H2S bioavailability concurrent with GBM standard of care may improve outcomes for GBM patients.

Assessment of Dietary Intake of Molybdenum in Relation to Tolerable Upper Intake Level

The Norwegian Scientific Committee for Food and Environment (Vitenskapskomiteen for mat og miljø, VKM) has, at the request of the Norwegian Food Safety Authority (Mattilsynet; NFSA), evaluated the intake of molybdenum. VKM has also conducted scenario calculations to illustrate the consequences of amending maximum limits for molybdenum to 100, 250, 500 or 1000 µg/day in food supplements. The previous maximum limit was 250 µg/day.
 Molybdenum is as a cofactor for some important enzymes in humans. These enzymes are involved in the catabolism of sulfur amino acids and heterocyclic compounds, including purines and pyridines. A distinct molybdenum deficiency has not been described in animals when subjected to molybdenum restriction, despite considerable reduction in the activity of molybdoenzymes. Molybdenum deficiency is not observed in healthy humans. The estimated Adequate Intake (AI) proposed by the European Food Safety Authority (EFSA) is 65 µg per day for men and women. Legumes, grains, and nuts are major contributors of molybdenum in the diet. 
 Molybdenum is a potential antagonist to copper absorption, but symptoms of copper deficiencies due to excess molybdenum intake have only been observed in ruminants. Based on the effect on reproduction and growth in animals, tolerable upper intake levels (ULs) have been estimated to be 2 mg/day by the U.S. Institute of Medicine (IOM) in 2001 and 0.6 mg/day by the Scientific Committee on Food (SCF) in 2000. These ULs were based on the same scientific evidence, but IOM used an uncertainty factor (UF) of 30 and SCF used a UF of 100 because the evidence base was considered to be weak.
 Because of the limited safety data on molybdenum, VKM support the use of the default uncertainty factors at 100 for extrapolation of data from animal studies to humans. Additionally, molybdenum deficiency is very rare and no studies have indicated a nutritional need for additional molybdenum from dietary supplements. The ULs for children were derived by adjusting the adult UL according to default body weights. 
 According to the scenario estimations, only the highest suggested maximum limit of 1000 µg molybdenum from food supplements will lead to exceedance of the UL for adults. For 1-3 year old children, all the suggested maximum limits for molybdenum will lead to exceedance of the UL. In children 4-10 years, supplements with 250, 500 or 1000 µg molybdenum will lead to exceedance of the ULs, whereas for adolescents 11-17 years, the UL will be exceeded with supplemental doses at 500 or 1000 µg per day.
 VKM emphasises that the current assessment of maximum limits for molybdenum in food supplements is merely based on published reports concerning upper levels from the SCF (2000, EU), IOM (2001, USA), EVM (2003, UK) and NNR (2012, Nordic countries). VKM has not conducted any systematic review of the literature for the current opinion, as this was outside the scope of the terms of reference from NFSA.

MPTAC Determines APP Fragmentation via Sensing Sulfur Amino Acid Catabolism

Metabolic disorder has been suggested to underlie Alzheimer's disease (AD). However, the decisive molecular linkages remain unclear. We discovered that human Molybdopterin Synthase Associating Complex, MPTAC, promotes sulfur amino acid catabolism to prevent oxidative damage from excess sulfur amino acids, which, in turn, advances fatty acid oxidation and acetyl coenzyme A (acetyl-CoA) synthesis. The association of MPTAC with Protein arginine (R) Methyltransferase 5 (PRMT5) complex and small nuclear ribonucleoprotein (SNRP) splicing factors enables SNRPs to sense metabolic states through their methylation. This promotes the splicing fidelity of amyloid precursor protein (APP) pre-mRNA and proper APP fragmentation, abnormalities of which have been observed in the platelets of AD patients. The functions of MPTAC are crucial to maintain expression of drebrin 1, which is required for synaptic plasticity, through prevention from oxidative damage. Thus, adjustment of sulfur amino acid catabolism by MPTAC prevents events that occur early in the onset of AD.

The Mitochondrial Sulfur Dioxygenase ETHYLMALONIC ENCEPHALOPATHY PROTEIN1 Is Required for Amino Acid Catabolism during Carbohydrate Starvation and Embryo Development in Arabidopsis

The sulfur dioxygenase ETHYLMALONIC ENCEPHALOPATHY PROTEIN1 (ETHE1) catalyzes the oxidation of persulfides in the mitochondrial matrix and is essential for early embryo development in Arabidopsis (Arabidopsis thaliana). We investigated the biochemical and physiological functions of ETHE1 in plant metabolism using recombinant Arabidopsis ETHE1 and three transfer DNA insertion lines with 50% to 99% decreased sulfur dioxygenase activity. Our results identified a new mitochondrial pathway catalyzing the detoxification of reduced sulfur species derived from cysteine catabolism by oxidation to thiosulfate. Knockdown of the sulfur dioxygenase impaired embryo development and produced phenotypes of starvation-induced chlorosis during short-day growth conditions and extended darkness, indicating that ETHE1 has a key function in situations of high protein turnover, such as seed production and the use of amino acids as alternative respiratory substrates during carbohydrate starvation. The amino acid profile of mutant plants was similar to that caused by defects in the electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase complex and associated dehydrogenases. Thus, in addition to sulfur amino acid catabolism, ETHE1 also affects the oxidation of branched-chain amino acids and lysine.

Identification of a Powerful Aroma Compound in Munster and Camembert Cheeses: Ethyl 3-Mercaptopropionate

With the view to investigate the presence of thiols in cheese, the use of different methods of preparation and extraction with an organomercuric compound ( p-hydroxymercuribenzoate) enabled the isolation of a new compound. The analysis of cheese extracts by gas chromatography coupled with pulse flame photometry, mass spectrometry, and olfactometry detections led to the identification of ethyl 3-mercaptopropionate in Munster and Camembert cheeses. This compound, described at low concentrations as having pleasant, fruity, grapy, rhubarb, and empyreumatic characters, has previously been reported in wine and Concord grape but was never mentioned before in cheese. A possible route for the formation of this compound in relation with the catabolism of sulfur amino acids is proposed.

Low-carbohydrate, high-protein diets that restrict potassium-rich fruits and vegetables promote calciuria

In a recent issue of Osteoporosis International, Carter et al. reported that subjects adhering to a ketogenic, lowcarbohydrate/high-protein (LCHP) diet for weight loss did not display increased bone turnover markers after 3 months compared to control subjects consuming a typical, unrestricted diet [1]. In this trial, weight loss averaged 6.4 kg versus 1.1 kg in the dieters and controls respectively (p=0.0008), whereas the mean urinary N-telopeptide increased by 1.6 versus 1.9 nmol BCE/mmol creatinine in the dieters and controls, respectively (p=0.86). Although this trial supports the view that high-protein diets do not adversely affect bone [2, 3], the dietary level of alkalizing minerals was not considered. High-protein diets generate excessive amounts of acid due to the obligatory catabolism of sulfur amino acids, and bone may respond by releasing basic salts into the circulation [4]. Hence, if high-protein intakes are not accompanied by an adequate intake of alkalizing minerals, which have a neutralizing effect in vivo, bone health may be adversely affected [4–6]. Here we discuss unpublished data regarding acid/base metabolism from our recent trial comparing ketogenic and nonketogenic LCHP diets [7]. In this trial, 19 adults (body mass index: 34.4T1.0 kg/m) were randomly assigned to a ketogenic LCHP diet (k-LCHP; 60% of energy as fat; 5% energy as carbohydrate) or to a nonketogenic LCHP diet (n-LCHP; 30% of energy as fat; 40% of energy as carbohydrate). The n-LCHP diet was composed mainly of low-fat dairy products, fruits and vegetables, and low-fat meats, whereas the k-LCHP diet consisted primarily of high-fat meats and some vegetables. The diets were similar in protein content (~20 g/mJ), but daily intakes of potassium (1,935 versus 3,535 mg) and calcium (715 versus 1,110 mg) were markedly different for the k-LCHP versus n-LCHP diets. Blood and urine samples were collected at baseline and at week 2. Weight loss, blood ketone concentrations and anion gap values, and urinary calcium concentrations at baseline and week 2 are shown in Table 1. The blood anion gap, the interval between the sum of blood cations and blood anions, is a direct indication of the acidity of blood. For comparison, Table 1 also displays values for urine calcium calculated from predictive equations based on the dietary protein:potassium ratio [8, 9]. These data indicate that n-LCHP diets are associated with lower acid loads and lower rates of calcium excretion as compared to k-LCHP diets. Moreover, anion gap values and urinary calcium were highly correlated (r=0.542, p=0.016). Since the predicted calciuria was similar to actual values, it would appear that potassium-rich foods favorably influence acid/base metabolism and reduce calciuria. Alexy et al. [10] have presented longitudinal evidence that inadequate intakes of alkalizing minerals from fruits and vegetables may adversely impact bone health. Also, based on data from Lewis et al. [11], the calcium-rich Osteoporos Int (2006) 17:1820–1821 DOI 10.1007/s00198-006-0214-y

Effect of potassium salts in rats adapted to an acidogenic high-sulfur amino acid diet

Low-grade metabolic acidosis, consecutive to excessive catabolism of sulfur amino acids and a high dietary Na:K ratio, is a common feature of Western food habits. This metabolic alteration may exert various adverse physiological effects, especially on bone, muscle and kidneys. To assess the actual effects of various K salts, a model of the Westernised diet has been developed in rats: slight protein excess (20 % casein); cations provided as non-alkalinising salts; high Na:K ratio. This diet resulted in acidic urine (pH 5.5) together with a high rate of divalent cation excretion in urine, especially Mg. Compared with controls, K supplementation as KCl accentuated Ca excretion, whereas potassium bicarbonate or malate reduced Mg and Ca excretion and alkalinised urine pH (up to 8). In parallel, citraturia was strongly increased, together with 2-ketoglutarate excretion, by potassium bicarbonate or malate in the diet. Basal sulfate excretion, in the range of 1 mmol/d, was slightly enhanced in rats fed the potassium malate diet. The present model of low-grade metabolic acidosis indicates that potassium malate may be as effective as KHCO3 to counteract urine acidification, to limit divalent cation excretion and to ensure high citrate concentration in urine.

Urinary Sulfur Excretion and the Nitrogen/Sulfur Balance Ratio Reveal Nonprotein Sulfur Amino Acid Retention in Piglets

We evaluated the use of urinary sulfur (S) excretion as a measure of sulfur amino acid (SAA) catabolism and the nitrogen/sulfur (N/S) molar balance ratio as an indicator of nonprotein SAA storage in growing piglets. After confirming that an intravenous dose of sulfate is fully recovered in urinary sulfate, we measured urinary S recovery after an intravenous dose of methionine in 6 piglets fed an adequate protein (AP) diet and 6 piglets fed a low protein (LP) diet with normal energy provision. As measured over 48 h, recoveries of the methionine load as urinary total S was 106% in the AP group but only 69% in the LP group (P < 0.05). On the baseline diets the N/S balance ratio in the AP group was 36, whereas that in the LP group was 30 (P < 0.05); immediately after the methionine load, this ratio remained constant in the AP group but decreased further, to 26 (P < 0.05) in the LP group. These results indicate that protein-deficient piglets accumulate relatively more S than N from their diet, and under these conditions a significant portion of the S derived from a methionine load is retained in nonprotein compounds. Urinary S excretion, a simple nontracer measurement, can provide an accurate measure of SAA catabolism, and the N/S balance ratio is a potentially useful indicator of changes in nonprotein SAA stores of growing piglets.

Effect of protein restriction on sulfur amino acid catabolism in insulin-dependent diabetes mellitus.

Persons with conventionally treated insulin-dependent diabetes mellitus (IDDM) appear to be impaired in their ability to reduce fed-state urea production appropriately in response to dietary protein restriction (Hoffer LJ, Taveroff A, and Schiffrin A. Am J Physiol 272: E59-E67, 1997). To determine whether these conclusions apply to whole body sulfur amino acid (SAA) catabolism, we used samples from this protocol to measure daily urinary sulfate excretion and fed-state sulfate production after a high-protein test meal before and after dietary protein restriction. Eight normal subjects and six IDDM subjects treated with twice-daily intermediate- and short-acting insulin consumed a mixed test meal containing 0.50 g protein/kg after adaptation to 4 days of high protein intake (1.28 g protein/kg body wt) and again after 5 days of dietary protein restriction (0.044 g/kg). Adaptation to protein restriction decreased daily urinary sulfate and urea-N excretion by approximately 80%. Over the first 24 h of protein restriction, urinary sulfate excretion decreased more than urea-N excretion for both the normal and IDDM subjects. Under conditions of a high prior protein intake, fed-state sulfate production was normal for the IDDM subjects; protein restriction reduced fed-state sulfate production by 51% (normal subjects) and 59% (IDDM subjects; not significant). We conclude that whole body SAA metabolism is normal in conventionally treated IDDM before and after dietary protein restriction. SAA catabolism, as measured by fed-state sulfate production, may be a convenient and useful method to determine the extent of whole body protein dysregulation in IDDM.

Sulfate production depicts fed-state adaptation to protein restriction in humans

One feature of the adaptation to dietary protein restriction is reduced urea production over the hours after consumption of a test meal of fixed composition. This adaptation is impaired in conventionally treated insulin-dependent diabetes mellitus (Hoffer LJ, Taveroff A, and Schiffrin A. Am J Physiol Endocrinol Metab 272: E59--E67, 1997). We have now tested the response to a test meal containing less protein and included as a main outcome variable the production of sulfate, a specific indicator of sulfur amino acid catabolism. Six normal men consumed a mixed test meal containing 0.25 g protein/kg and 10 kcal/kg while adapted to high (1.5 g x kg(-1) x day(-1)) and low (0.3 g. kg(-1) x day(-1)) protein intakes. They followed the identical protocol twice. Six subjects with insulin-dependent diabetes consumed the test meal while adapted to their customary high-protein diet. Adaptation to protein restriction reproducibly reduced 9-h cumulative postmeal urea N and S production by 22--29% and 49--52%, respectively (both P < 0.05). Similar results were obtained for a postmeal collection period of 6 h. The response of the diabetic subjects was normal. We conclude that reductions in postmeal urea and sulfate production after protein restriction are reproducible and are evident using a postmeal collection period as short as 6 h. Sulfate production effectively depicts fed-state adaptation to protein restriction.

The oxidation of hypotaurine to taurine: bis-aminoethyl-alpha-disulfone, a metabolic intermediate in mammalian tissue.

The primary mammalian metabolic pathway leading to taurine is generally recognized as beginning with the oxidation of cysteine to cysteine sulfinate via cysteine dioxygenase (19). This rate limiting enzyme is, carefully regulated thus setting the rate for the catabolism of sulfur amino acids (4). A major portion of cysteine sulfinate is subject to unidirectional transamination leading to pyruvate and sulfite; a smaller fraction of cysteine sulfinate is decarboxylated by cysteine sulfinate decarboxylase to hypotaurine (8). The ratio of the two pathways appears to be relatively constant; what controls the pathway bifurcation remains unknown. Although a small fraction (10%) of the hypotaurine is subject to unidirectional transamination to acetaldehyde and sulfate (4,6), the bulk of hypotaurine is oxidized to taurine. A possible alternate metabolic route involves initial oxidation of cysteine sulfinate to cysteic acid by an unspecified mechanism followed by decarboxylation of cysteic acid to taurine. The latter is an established capacity of the enzyme cysteine sulfinate decarboxylase (10).