S-adenosylmethionine is associated with fat mass and truncal adiposity in older adults

Hepatic levels of S-adenosylmethionine regulate the adaptive response to fasting

There has been an intense focus to uncover the molecular mechanisms by which fasting triggers the adaptive cellular responses in the major organs of the body. Here, we show that in mice, hepatic S-adenosylmethionine (SAMe)-the principal methyl donor-acts as a metabolic sensor of nutrition to fine-tune the catabolic-fasting response by modulating phosphatidylethanolamine N-methyltransferase (PEMT) activity, endoplasmic reticulum-mitochondria contacts, β-oxidation, and ATP production in the liver, together with FGF21-mediated lipolysis and thermogenesis in adipose tissues. Notably, we show that glucagon induces the expression of the hepatic SAMe-synthesizing enzyme methionine adenosyltransferase α1 (MAT1A), which translocates to mitochondria-associated membranes. This leads to the production of this metabolite at these sites, which acts as a brake to prevent excessive β-oxidation and mitochondrial ATP synthesis and thereby endoplasmic reticulum stress and liver injury. This work provides important insights into the previously undescribed function of SAMe as a new arm of the metabolic adaptation to fasting.

The Associations of Habitual Intake of Sulfur Amino Acids, Proteins and Diet Quality with Plasma Sulfur Amino Acid Concentrations: The Maastricht Study

BACKGROUND

Plasma sulfur amino acids (SAAs), i.e., methionine, total cysteine (tCys), total homocysteine (tHcy), cystathionine, total glutathione (tGSH), and taurine, are potential risk factors for obesity and cardiometabolic disorders. However, except for plasma tHcy, little is known about how dietary intake modifies plasma SAA concentrations.

OBJECTIVE

To investigate whether the intake of SAAs and proteins or diet quality is associated with plasma SAAs.

METHODS

Data from a cross-sectional subset of The Maastricht Study (n = 1145, 50.5% men, 61 interquartile range: [55, 66] y, 22.5% with prediabetes and 34.3% with type 2 diabetes) were investigated. Dietary intake was assessed using a validated food frequency questionnaire. The intake of SAAs (total, methionine, and cysteine) and proteins (total, animal, and plant) was estimated from the Dutch and Danish food composition tables. Diet quality was assessed using the Dutch Healthy Diet Index, the Mediterranean Diet Score, and the Dietary Approaches to Stop Hypertension score. Fasting plasma SAAs were measured by liquid chromatography (LC) tandem mass spectrometry (MS) (LC/MS-MS). Associations were investigated with multiple linear regressions with tertiles of dietary intake measures (main exposures) and z-standardized plasma SAAs (outcomes).

RESULTS

Intake of total SAAs and total proteins was positively associated with plasma tCys and cystathionine. Associations were stronger in women and in those with normal body weight. Higher intake of cysteine and plant proteins was associated with lower plasma tHcy and higher cystathionine. Higher methionine intake was associated with lower plasma tGSH, whereas cysteine intake was positively associated with tGSH. Higher intake of methionine and animal proteins was associated with higher plasma taurine. Better diet quality was consistently related to lower plasma tHcy concentrations, but it was not associated with the other SAAs.

CONCLUSION

Targeted dietary modifications might be effective in modifying plasma concentrations of tCys, tHcy, and cystathionine, which have been associated with obesity and cardiometabolic disorders.

The association of fasting plasma thiol fractions with body fat compartments, biomarker profile, and adipose tissue gene expression

People with high plasma total cysteine (tCys) have higher fat mass and higher concentrations of the atherogenic apolipoprotein B (apoB). The disulfide form, cystine, enhanced human adipogenesis and correlated with total fat mass in a Middle-Eastern cohort. In 35 European adults with overweight (88.6% women) and with dual-X-ray absorptiometry measurements of regional fat, we investigated how cystine compared to other free disulfides in their association with total regional adiposity, plasma lipid and glucose biomarkers, and adipose tissue lipid enzyme mRNA (n = 19). Most total plasma homocysteine (tHcy) (78%) was protein-bound; 63% of total glutathione (tGSH) was reduced. tCys was 49% protein-bound, 30% mixed-disulfide, 15% cystine, and 6% reduced. Controlling for age and lean mass, cystine and total free cysteine were the fractions most strongly associated with android and total fat: 1% higher cystine predicted 1.97% higher android fat mass (95% CI 0.64, 3.31) and 1.25% (0.65, 2.98) higher total fat mass (both p = 0.005). A positive association between tCys and apoB (β: 0.64%; 95% CI 0.17, 1.12%, p = 0.009) was apparently driven by free cysteine and cystine; cystine was also inversely associated with the HDL-associated apolipoprotein A1 (β: -0.57%; 95% CI -0.96, -0.17%, p = 0.007). No independent positive associations with adiposity were noted for tGSH or tHcy fractions. Plasma cystine correlated with CPT1a mRNA (Spearman's r = 0.68, p = 0.001). In conclusion, plasma cystine-but not homocysteine or glutathione disulfides-is associated with android adiposity and an atherogenic plasma apolipoprotein profile. The role of cystine in human adiposity and cardiometabolic risk deserves investigation. ClinicalTrials.gov identifiers: NCT02647970 and NCT03629392.

Time-restricted feeding promotes muscle function through purine cycle and AMPK signaling in Drosophila obesity models

Obesity caused by genetic and environmental factors can lead to compromised skeletal muscle function. Time-restricted feeding (TRF) has been shown to prevent muscle function decline from obesogenic challenges; however, its mechanism remains unclear. Here we demonstrate that TRF upregulates genes involved in glycine production (Sardh and CG5955) and utilization (Gnmt), while Dgat2, involved in triglyceride synthesis is downregulated in Drosophila models of diet- and genetic-induced obesity. Muscle-specific knockdown of Gnmt, Sardh, and CG5955 lead to muscle dysfunction, ectopic lipid accumulation, and loss of TRF-mediated benefits, while knockdown of Dgat2 retains muscle function during aging and reduces ectopic lipid accumulation. Further analyses demonstrate that TRF upregulates the purine cycle in a diet-induced obesity model and AMPK signaling-associated pathways in a genetic-induced obesity model. Overall, our data suggest that TRF improves muscle function through modulations of common and distinct pathways under different obesogenic challenges and provides potential targets for obesity treatments.

Associations between plasma sulfur amino acids and specific fat depots in two independent cohorts: CODAM and The Maastricht Study

PURPOSE

Sulfur amino acids (SAAs) have been associated with obesity and obesity-related metabolic diseases. We investigated whether plasma SAAs (methionine, total cysteine (tCys), total homocysteine, cystathionine and total glutathione) are related to specific fat depots.

METHODS

We examined cross-sectional subsets from the CODAM cohort (n = 470, 61.3% men, median [IQR]: 67 [61, 71] years) and The Maastricht Study (DMS; n = 371, 53.4% men, 63 [55, 68] years), enriched with (pre)diabetic individuals. SAAs were measured in fasting EDTA plasma with LC-MS/MS. Outcomes comprised BMI, skinfolds, waist circumference (WC), dual-energy X-ray absorptiometry (DXA, DMS), body composition, abdominal subcutaneous and visceral adipose tissues (CODAM: ultrasound, DMS: MRI) and liver fat (estimated, in CODAM, or MRI-derived, in DMS, liver fat percentage and fatty liver disease). Associations were examined with linear or logistic regressions adjusted for relevant confounders with z-standardized primary exposures and outcomes.

RESULTS

Methionine was associated with all measures of liver fat, e.g., fatty liver disease [CODAM: OR = 1.49 (95% CI 1.19, 1.88); DMS: OR = 1.51 (1.09, 2.14)], but not with other fat depots. tCys was associated with overall obesity, e.g., BMI [CODAM: β = 0.19 (0.09, 0.28); DMS: β = 0.24 (0.14, 0.34)]; peripheral adiposity, e.g., biceps and triceps skinfolds [CODAM: β = 0.15 (0.08, 0.23); DMS: β = 0.20 (0.12, 0.29)]; and central adiposity, e.g., WC [CODAM: β = 0.16 (0.08, 0.25); DMS: β = 0.17 (0.08, 0.27)]. Associations of tCys with VAT and liver fat were inconsistent. Other SAAs were not associated with body fat.

CONCLUSION

Plasma concentrations of methionine and tCys showed distinct associations with different fat depots, with similar strengths in the two cohorts.

Methionine adenosyltransferase 1a antisense oligonucleotides activate the liver-brown adipose tissue axis preventing obesity and associated hepatosteatosis

Altered methionine metabolism is associated with weight gain in obesity. The methionine adenosyltransferase (MAT), catalyzing the first reaction of the methionine cycle, plays an important role regulating lipid metabolism. However, its role in obesity, when a plethora of metabolic diseases occurs, is still unknown. By using antisense oligonucleotides (ASO) and genetic depletion of Mat1a, here, we demonstrate that Mat1a deficiency in diet-induce obese or genetically obese mice prevented and reversed obesity and obesity-associated insulin resistance and hepatosteatosis by increasing energy expenditure in a hepatocyte FGF21 dependent fashion. The increased NRF2-mediated FGF21 secretion induced by targeting Mat1a, mobilized plasma lipids towards the BAT to be catabolized, induced thermogenesis and reduced body weight, inhibiting hepatic de novo lipogenesis. The beneficial effects of Mat1a ASO were abolished following FGF21 depletion in hepatocytes. Thus, targeting Mat1a activates the liver-BAT axis by increasing NRF2-mediated FGF21 secretion, which prevents obesity, insulin resistance and hepatosteatosis.

Potential Mechanisms for How Long-Term Physical Activity May Reduce Insulin Resistance

Insulin became available for the treatment of patients with diabetes 100 years ago, and soon thereafter it became evident that the biological response to its actions differed markedly between individuals. This prompted extensive research into insulin action and resistance (IR), resulting in the universally agreed fact that IR is a core finding in patients with type 2 diabetes mellitus (T2DM). T2DM is the most prevalent form of diabetes, reaching epidemic proportions worldwide. Physical activity (PA) has the potential of improving IR and is, therefore, a cornerstone in the prevention and treatment of T2DM. Whereas most research has focused on the acute effects of PA, less is known about the effects of long-term PA on IR. Here, we describe a model of potential mechanisms behind reduced IR after long-term PA to guide further mechanistic investigations and to tailor PA interventions in the therapy of T2DM. The development of such interventions requires knowledge of normal glucose metabolism, and we briefly summarize an integrated physiological perspective on IR. We then describe the effects of long-term PA on signaling molecules involved in cellular responses to insulin, tissue-specific functions, and whole-body IR.

Dietary protein and amino acid restriction: Roles in metabolic health and aging-related diseases

The prevalence of obesity is a worldwide phenomenon in all age groups and is associated with aging-related diseases such as type 2 diabetes, as well metabolic and cardiovascular diseases. The use of dietary restriction (DR) while avoiding malnutrition has many profound beneficial effects on aging and metabolic health, and dietary protein or specific amino acid (AA) restrictions, rather than overall calorie intake, are considered to play key roles in the effects of DR on host health. Whereas comprehensive reviews of the underlying mechanisms are limited, protein restriction and methionine (Met) restriction improve metabolic health and aging-related neurodegenerative diseases, and may be associated with FGF21, mTOR and autophagy, improved mitochondrial function and oxidative stress. Circulating branched-chain amino acids (BCAAs) are inversely correlated with metabolic health, and BCAAs and leucine (Leu) restriction promote metabolic homeostasis in rodents. Although tryptophan (Trp) restriction extends the lifespan of rodents, the Trp-restricted diet is reported to increase inflammation in aged mice, while severe Trp restriction has side effects such as anorexia. Furthermore, inadequate protein intake in the elderly increases the risk of muscle-centric health. Therefore, the restriction of specific AAs may be an effective and executable dietary manipulation for metabolic and aging-related health in humans, which warrants further investigation to elucidate the underlying mechanisms.

Extracellular cystine influences human preadipocyte differentiation and correlates with fat mass in healthy adults

Plasma cysteine is associated with human obesity, but it is unknown whether this is mediated by reduced, disulfide (cystine and mixed-disulfides) or protein-bound (bCys) fractions. We investigated which cysteine fractions are associated with adiposity in vivo and if a relevant fraction influences human adipogenesis in vitro. In the current study, plasma cysteine fractions were correlated with body fat mass in 35 adults. Strong positive correlations with fat mass were observed for cystine and mixed disulfides (r ≥ 0.61, P < 0.001), but not the quantitatively major form, bCys. Primary human preadipocytes were differentiated in media containing cystine concentrations varying from 10-50 μM, a range similar to that in plasma. Increasing extracellular cystine (10-50 μM) enhanced mRNA expression of PPARG2 (to sixfold), PPARG1, PLIN1, SCD1 and CDO1 (P = 0.042- < 0.001). Adipocyte lipid accumulation and lipid-droplet size showed dose-dependent increases from lowest to highest cystine concentrations (P < 0.001), and the malonedialdehyde/total antioxidant capacity increased, suggesting increased oxidative stress. In conclusion, increased cystine concentrations, within the physiological range, are positively associated with both fat mass in healthy adults and human adipogenic differentiation in vitro. The potential role of cystine as a modifiable factor regulating human adipocyte turnover and metabolism deserves further study.

Dietary Selenium Requirement for the Prevention of Glucose Intolerance and Insulin Resistance in Middle-Aged Mice

BACKGROUND

Although dietary selenium (Se) deficiency or excess induces type 2 diabetes-like symptoms in mice, suboptimal body Se status usually causes no symptoms but may promote age-related decline in overall health.

OBJECTIVES

We sought to determine the dietary Se requirement for protection against type 2 diabetes-like symptoms in mice.

METHODS

Thirty mature (aged 4 mo) male C57BL/6J mice were fed a Se-deficient torula yeast AIN-93M diet supplemented with Na2SeO4 in graded concentrations totaling 0.01 (basal), 0.04, 0.07, 0.10, and 0.13 (control) mg Se/kg for 4 mo (n = 6) until they were middle-aged (8 mo). Droplets of whole blood were used to determine glucose tolerance and insulin sensitivity in the mice from ages 5 to 8 mo. Postmortem serum, liver, and skeletal muscle were collected to assay for selenoprotein expression and markers of glucose metabolism. Data were analyzed by 1-way ANCOVA with or without random effects for time-repeated measurements using live mice or postmortem samples, respectively.

RESULTS

Compared with control, the consumption of basal diet increased (P < 0.05) fasting serum insulin (95% CI: 52%, 182%) and leptin (95% CI: 103%, 118%) concentrations in middle-aged mice. Dietary Se insufficiency decreased (P < 0.05) 1) glucose tolerance (13-79%) and insulin sensitivity (15-65%) at ≤0.10 mg Se/kg; 2) baseline thymoma viral proto-oncogene phosphorylation on S473 (27-54%) and T308 (22-46%) at ≤0.10 and ≤0.07 mg Se/kg, respectively, in the muscle but not the liver; and 3) serum glutathione peroxidase 3 (51-83%), liver and muscle glutathione peroxidase 1 (32-84%), serum and liver selenoprotein P (28-42%), and liver and muscle selenoprotein H (39-48%) and selenoprotein W (16-73%) protein concentrations at ≤0.04, ≤0.10, ≤0.07, and ≤0.10 mg Se/kg, respectively.

CONCLUSIONS

Mice fed diets containing ≤0.10 mg Se/kg display impaired glucose tolerance and insulin sensitivity, suggesting increased susceptibility to type 2 diabetes by suboptimal Se status at levels ≤23% of nutritional needs.

Effects of short-term methionine and cysteine restriction and enrichment with polyunsaturated fatty acids on oral glucose tolerance, plasma amino acids, fatty acids, lactate and pyruvate: results from a pilot study

Objective

In this 7-day pilot study we randomized healthy, normal-weight men and women to either a dietary intervention with methionine and cysteine restriction enriched in PUFA (Met/Cys_low + PUFA, n = 7) or with high contents of methionine, cysteine and SFA (Met/Cys_high + SFA, n = 7). The objective was to describe the short-term responses in oral glucose tolerance, amino acid profile, total fatty acid profile, pyruvate and lactate following a Met/Cys_low + PUFA diet vs. Met/Cys_high + SFA.

Results

The diet groups consisted of five women and two men, aged 20–38 years. After the 7-d intervention median pre- and post-oral glucose tolerance test (OGTT) glucose concentrations were 5 mmol/L and 4 mmol/L respectively in the Met/Cys_low + PUFA group. In the Met/Cys_high + SFA group, median pre- and post-OGTT glucose concentrations were 4.8 mmol/L and 4.65 mmol/L after the 7-d intervention. The responses in the amino acid profiles were similar in both groups during the intervention with the exception of serine. Fatty acids decreased from baseline to day 7 in both groups. Plasma lactate and pyruvate were similar for both groups with an increase to day 3 before approaching baseline values at day 7.

Trial registration

ClinicalTrials.gov: NCT02647970, registration date: January 6^th 2016.

Effect of Methionine Restriction on Aging: Its Relationship to Oxidative Stress

Enhanced oxidative stress is closely related to aging and impaired metabolic health and is influenced by diet-derived nutrients and energy. Recent studies have shown that methionine restriction (MetR) is related to longevity and metabolic health in organisms from yeast to rodents. The effect of MetR on lifespan extension and metabolic health is mediated partially through a reduction in oxidative stress. Methionine metabolism is involved in the supply of methyl donors such as S-adenosyl-methionine (SAM), glutathione synthesis and polyamine metabolism. SAM, a methionine metabolite, activates mechanistic target of rapamycin complex 1 and suppresses autophagy; therefore, MetR can induce autophagy. In the process of glutathione synthesis in methionine metabolism, hydrogen sulfide (H₂S) is produced through cystathionine-β-synthase and cystathionine-γ-lyase; however, MetR can induce increased H₂S production through this pathway. Similarly, MetR can increase the production of polyamines such as spermidine, which are involved in autophagy. In addition, MetR decreases oxidative stress by inhibiting reactive oxygen species production in mitochondria. Thus, MetR can attenuate oxidative stress through multiple mechanisms, consequently associating with lifespan extension and metabolic health. In this review, we summarize the current understanding of the effects of MetR on lifespan extension and metabolic health, focusing on the reduction in oxidative stress.

Revealing Alteration in the Hepatic Glucose Metabolism of Genetically Improved Carp, Jayanti Rohu Labeo rohita Fed a High Carbohydrate Diet Using Transcriptome Sequencing

Although feed cost is the greatest concern in aquaculture, the inclusion of carbohydrates in the fish diet, and their assimilation, are still not well understood in aquaculture species. We identified molecular events that occur due to the inclusion of high carbohydrate levels in the diets of genetically improved 'Jayanti rohu' Labeo rohita. To reveal transcriptional changes in the liver of rohu, a feeding experiment was conducted with three doses of gelatinized starch (20% (control), 40%, and 60%). Transcriptome sequencing revealed totals of 15,232 (4464 up- and 4343 down-regulated) and 15,360 (4478 up- and 4171 down-regulated) differentially expressed genes. Up-regulated transcripts associated with glucose metabolisms, such as hexokinase, PHK, glycogen synthase and PGK, were found in fish fed diets with high starch levels. Interestingly, a de novo lipogenesis mechanism was found to be enriched in the livers of treated fish due to up-regulated transcripts such as FAS, ACCα, and PPARγ. The insulin signaling pathways with enriched PPAR and mTOR were identified by Kyoto Encyclopedia of Genes and Genome (KEGG) as a result of high carbohydrates. This work revealed for the first time the atypical regulation transcripts associated with glucose metabolism and lipogenesis in the livers of Jayanti rohu due to the inclusion of high carbohydrate levels in the diet. This study also encourages the exploration of early nutritional programming for enhancing glucose efficiency in carp species, for sustainable and cost-effective aquaculture production.

Association of Maternal Plasma Total Cysteine and Growth among Infants in Nepal: A Cohort Study

Cysteine is a semi-essential amino acid that has been positively associated with growth in children. However, transgenerational effects remain unclear. The aim of this analysis was to assess whether maternal plasma total cysteine (tCys) concentration is associated with various growth indicators in infants living in peri-urban settings in Bhaktapur, Nepal. We used data from the 561 mothers enrolled in an ongoing randomized controlled trial. We built linear regression models to evaluate the associations between maternal tCys and birth weight, length-for-age Z-scores (LAZ) and weight-for-length Z-scores (WLZ) at birth and six months of age. Maternal tCys was inversely associated with birth weight among boys after adjusting for confounders (p < 0.05). In addition, there was a negative association between maternal tCys and LAZ at birth (p < 0.01). No associations between maternal tCys and the other anthropometric indicators were found significant, although there was a tendency for maternal tCys to be associated positively with WLZ at birth among girls (p < 0.10). This is a first study evaluating transgenerational relation of tCys on growth in infants. Further, larger and more comprehensive studies are needed to determine if and how maternal tCys alters child growth.

Dietary Regulation of Immunity

Integrated immunometabolic responses link dietary intake, energy utilization, and storage to immune regulation of tissue function and is therefore essential for the maintenance and restoration of homeostasis. Adipose-resident leukocytes have non-traditional immunological functions that regulate organismal metabolism by controlling insulin action, lipolysis, and mitochondrial respiration to control the usage of substrates for production of heat versus ATP. Energetically expensive vital functions such as immunological responses might have thus evolved to respond accordingly to dietary surplus and deficit of macronutrient intake. Here, we review the interaction of dietary intake of macronutrients and their metabolism with the immune system. We discuss immunometabolic checkpoints that promote healthspan and highlight how dietary fate and regulation of glucose, fat, and protein metabolism might affect immunity.

Mechanism of Activation of Mechanistic Target of Rapamycin Complex 1 by Methionine

Nutrients are closely involved in the regulation of lifespan and metabolic health. Cellular activities, such as the regulation of metabolism, growth, and aging, are mediated by a network of nutrients and nutrient-sensing pathways. Among the nutrient-sensing pathways, the mechanistic target of rapamycin complex 1 (mTORC1) acts as the central regulator of cellular functions, which include autophagy. Autophagy plays a significant role in the removal of protein aggregates and damaged or excess organelles, including mitochondria, to maintain intracellular homeostasis, which is involved in lifespan extension and cardiometabolic health. Moreover, dietary methionine restriction may have a beneficial effect on lifespan extension and metabolic health. In contrast, methionine may activate mTORC1 and suppress autophagy. As the mechanism of methionine sensing on mTORC1, SAMTOR was identified as a sensor of S-adenosyl methionine (SAM), a metabolite of methionine, in the cytoplasm. Conversely, methionine may activate the mTORC1 signaling pathway through the activation of phosphatase 2A (PP2A) because of increased methylation in response to intracellular SAM levels. In this review, we summarized the recent findings regarding the mechanism via which methionine activates mTORC1.

Postprandial effects of a meal low in sulfur amino acids and high in polyunsaturated fatty acids compared to a meal high in sulfur amino acids and saturated fatty acids on stearoyl CoA-desaturase indices and plasma sulfur amino acids: a pilot study

Objective

The sulfur amino acid (SAA) cysteine is positively related, whereas polyunsaturated fatty acids (PUFAs) are inversely related to activity of the lipogenic enzyme stearoyl-CoA desaturase (SCD). High SCD activity promotes obesity in animals, and plasma activity indices positively associates with fat mass in humans. SCD may thus be a target for dietary intervention with SAA restriction and PUFA enrichment with unknown potential benefits for body composition. We randomized ten healthy individuals to a meal restricted in SAAs and enriched with PUFAs (Cys/Met_low + PUFA) (n = 5) or a meal enriched in SAA and saturated fatty acids (Cys/Met_high + SFA) (n = 5). We measured plasma SCD activity indices (SCD16 and SCD18) and SAAs response hourly from baseline and up to 4 h postprandial.

Results

SCD16 was unchanged whereas SCD18 tended to increase in the Cys/Met_low + PUFA compared to the Cys/Met_high + SFA group (p_{time*group interaction} = 0.08). Plasma concentrations of total cysteine fractions including free and reduced cysteine decreased in the Cys/Met_low + PUFA compared to the Cys/Met_high + SFA group (both p_{time*group interaction} < 0.001). In conclusion, a meal low in SAA but high in PUFAs reduced plasma cysteine fractions but not SCD activity indices. This pilot study can be useful for the design and diet composition of future dietary interventions that targets SCD and SAA.

Trial registration ClinicalTrials.gov: NCT02647970, registration date: 6 January 2016

Long-term exposure to TET increases body weight of juvenile zebrafish as indicated in host metabolism and gut microbiome

The application of tetracycline (TET) is very common in medical treatment, fisheries, and animal husbandry, resulting in its frequent detection with abundant concentrations in the aquatic environment. Though the effects of TET on zebrafish (Danio rerio) at embryonic and larval stages have been reported, there is very limited information on the possible long-term effect on aquatic fishes at the juvenile stage, especially at environmentally relevant levels. In this study, we have exposed juvenile zebrafish to two levels of TET at 1 and 100 µg/L for one month until their adulthood. The result showed that both levels of TET can significantly increase the body weight of the zebrafish, while there is no change in the body length. TET exposure also affected the liver microstructure by lipid vacuoles generation and global lipidomics analysis revealed a significant upregulation in hepatic triglyceride (TAG) levels. The metabolomics analysis showed great dysregulations in hepatic metabolic pathways including linoleic acid metabolism, tyrosine metabolism, and methionine metabolism, which are known to be linked with increased body weight gain through hepatic lipid accumulation. The hepatic gene expression involved in lipid transport (e.g., apoa4 and fabp11) and lipogenic factors (e.g., ppar) have been significantly upregulated in the livers of TET exposed zebrafish. Interestingly, the 16 rRNA gene sequence-based zebrafish gut microbial community analysis revealed an enhanced community diversity and altered microbial community composition upon TET exposure. To our knowledge, this is the first study showing that TET exposure can increase the body weight in juvenile zebrafish and the study on the ecotoxicity of antibiotic occurrences in the aquatic system can be further warranted.

Methionine abrogates the renoprotective effect of a low-protein diet against diabetic kidney disease in obese rats with type 2 diabetes

Dietary interventions, including a low-protein diet (LPD) and methionine (Met) restriction, have shown longevity, anti-aging and metabolic health effects. We previously reported that the LPD has a renoprotective effect against diabetic kidney disease (DKD) in rats with type 2 diabetes and obesity. However, it is unclear whether the beneficial effect of the LPD is mediated by low-Met intake or how Met is related to the pathogenesis for DKD. We herein show that the addition of Met with the LPD abrogates the beneficial effects induced by the LPD such as anti-oxidative stress, anti-inflammation and anti-fibrosis, in diabetic kidney. Additionally, the increased levels of S-adenosylmethionine (SAM) in renal tubular cells, which are associated with the reduced expression of glycine N-methyltransferase (Gnmt) and non-restricted Met intake, contributes to the activation of mechanistic target of rapamycin complex 1 (mTORC1) and impaired autophagy, in diabetic kidney. Moreover, starvation-induced autophagy was suppressed in renal cortex of Gnmt null mice and amino acid free-induced autophagy was also suppressed by administration of SAM in cultured HK-2 cells. A LPD could exert a renoprotective effect through the suppression of mTORC1 and restoration of autophagy, which is associated with reduced levels of SAM due to low-Met intake, in diabetic kidney.

The impact of dietary protein intake on longevity and metabolic health

Lifespan and metabolic health are influenced by dietary nutrients. Recent studies show that a reduced protein intake or low-protein/high-carbohydrate diet plays a critical role in longevity/metabolic health. Additionally, specific amino acids (AAs), including methionine or branched-chain AAs (BCAAs), are associated with the regulation of lifespan/ageing and metabolism through multiple mechanisms. Therefore, methionine or BCAAs restriction may lead to the benefits on longevity/metabolic health. Moreover, epidemiological studies show that a high intake of animal protein, particularly red meat, which contains high levels of methionine and BCAAs, may be related to the promotion of age-related diseases. Therefore, a low animal protein diet, particularly a diet low in red meat, may provide health benefits. However, malnutrition, including sarcopenia/frailty due to inadequate protein intake, is harmful to longevity/metabolic health. Therefore, further study is necessary to elucidate the specific restriction levels of individual AAs that are most effective for longevity/metabolic health in humans.

Whole-genome RNAi screen identifies methylation-related genes influencing lipid metabolism in Caenorhabditis elegans

Lipid droplets (LDs) are highly conserved multifunctional cellular organelles and aberrant lipid storage in LDs can lead to many metabolic diseases. However, the molecular mechanisms governing lipid dynamic changes remain elusive, and the high-throughput screen of genes influencing LD morphology was limited by lacking specific LD marker proteins in the powerful genetic tool Caenorhabditis elegans. In this study, we established a new method to conduct whole-genome RNAi screen using LD resident protein DHS-3 as a LD marker, and identified 78 genes involved in significant LD morphologic changes. Among them, mthf-1, as well as a series of methylation-related genes, was found dramatically influencing lipid metabolism. SREBP-1 and SCD1 homologs in C. elegans were involved in the lipid metabolic change of mthf-1(RNAi) worms, and the regulation of ATGL-1 also contributed to it by decreasing triacylglycerol (TAG) hydrolysis. Overall, this study not only identified important genes involved in LD dynamics, but also provided a new tool for LD study using C. elegans, with implications for the study of lipid metabolic diseases.

One-carbon metabolism markers are associated with cardiometabolic risk factors

BACKGROUND AND AIMS

Alterations to one-carbon metabolism, especially elevated plasma homocysteine (Hcy), have been suggested to be both a cause and a consequence of the metabolic syndrome (MS). A deeper understanding of the role of other one-carbon metabolites in MS, including s-adenosylmethionine (SAM), s-adenosylhomocysteine (SAH), and the methylation capacity index (SAM:SAH ratio) is required.

METHODS AND RESULTS

118 men and women with MS-risk factors were included in this cross-sectional study and cardiometabolic outcomes along with markers of one-carbon metabolism, including fasting plasma SAM, SAH, Hcy and vitamin B₁₂ concentrations, were analysed. Multiple linear regression models were also used to examine the association between plasma one-carbon metabolites and cardiometabolic health features. We found that fasting plasma concentrations of Hcy, SAM and SAH were all positively correlated with markers of adiposity, including BMI (increase in BMI per 1-SD increase in one-carbon metabolite: 0.92 kg/m² 95% CI (0.28; 1.56), p = 0.005; 0.81 (0.15; 1.47), p = 0.02; 0.67 (-0.01; 1.36), p = 0.05, respectively). Hcy, but not SAM, SAH or SAM:SAH ratio was associated with BMI and body fat percentage after mutual adjustments. SAM concentrations were associated with higher fasting insulin (9.5% 95% CI (0.3; 19.5) per SD increase in SAM, p = 0.04), HOMA-IR (10.8% (0.8; 21.9), p = 0.03) and TNF-α (11.8% (5.0; 19.0), p < 0.001).

CONCLUSION

We found little evidence for associations between SAM:SAH ratio and cardiometabolic variables, but higher plasma concentrations of SAM, SAH and Hcy are related to an overall higher risk of metabolic dysfunctions. The studies were registered at www.clinicaltrials.gov (NCT01719913 &NCT01731366).

Disease prevention and delayed aging by dietary sulfur amino acid restriction: translational implications

Sulfur amino acids (SAAs) play numerous critical roles in metabolism and overall health maintenance. Preclinical studies have demonstrated that SAA-restricted diets have many beneficial effects, including extending life span and preventing the development of a variety of diseases. Dietary sulfur amino acid restriction (SAAR) is characterized by chronic restrictions of methionine and cysteine but not calories and is associated with reductions in body weight, adiposity and oxidative stress, and metabolic changes in adipose tissue and liver resulting in enhanced insulin sensitivity and energy expenditure. SAAR-induced changes in blood biomarkers include reductions in insulin, insulin-like growth factor-1, glucose, and leptin and increases in adiponectin and fibroblast growth factor 21. On the basis of these preclinical data, SAAR may also have similar benefits in humans. While little is known of the translational significance of SAAR, its potential feasibility in humans is supported by findings of its effectiveness in rodents, even when initiated in adult animals. To date, there have been no controlled feeding studies of SAAR in humans; however, there have been numerous relevant epidemiologic and disease-based clinical investigations reported. Here, we summarize observations from these clinical investigations to provide insight into the potential effectiveness of SAAR for humans.

Higher Mediterranean Diet Quality Scores and Lower Body Mass Index Are Associated with a Less-Oxidized Plasma Glutathione and Cysteine Redox Status in Adults

Background

Both systemic redox status and diet quality are associated with risk outcomes in chronic disease. It is not known, however, the extent to which diet quality influences plasma thiol/disulfide redox status.

Objective

The purpose of this study was to investigate the influence of diet, as measured by diet quality scores and other dietary factors, on systemic thiol/disulfide redox status.

Methods

We performed a cross-sectional study of 685 working men and women (ages ≥18 y) in Atlanta, GA. Diet was assessed by 3 diet quality scores: the Alternative Healthy Eating Index (AHEI), Dietary Approaches to Stop Hypertension (DASH), and the Mediterranean Diet Score (MDS). We measured concentrations of plasma glutathione (GSH), cysteine, their associated oxidized forms [glutathione disulfide (GSSG) and cystine (CySS), respectively], and their redox potentials (EhGSSG and EhCySS) to determine thiol/disulfide redox status. Linear regression modeling was performed to assess relations between diet and plasma redox after adjustment for age, body mass index (BMI), sex, race, and history of chronic disease.

Results

MDS was positively associated with plasma GSH (β = 0.02; 95% CI: 0.003, 0.03) and total GSH (GSH + GSSG) (β = 0.02; 95% CI: 0.003, 0.03), and inversely associated with the CySS:GSH ratio (β = -0.02; 95% CI: -0.04, -0.004). There were significant independent associations between individual MDS components (dairy, vegetables, fish, and monounsaturated fat intake) and varying plasma redox indexes (P < 0.05). AHEI and DASH diet quality indexes and other diet factors of interest were not significantly correlated with plasma thiol and disulfide redox measures.

Conclusion

Adherence to the Mediterranean diet was significantly associated with a favorable plasma thiol/disulfide redox profile, independent of BMI, in a generally healthy working adult population. Although longitudinal studies are warranted, these findings contribute to the feasibility of targeting a Mediterranean diet to improve plasma redox status.

Higher intake of fish and fat is associated with lower plasma s-adenosylhomocysteine: a cross-sectional study

Several B-vitamins act as co-factors in one-carbon metabolism, a pathway that plays a central role in several chronic diseases. However, there is a lack of knowledge of how diet affects markers in one-carbon metabolism. The aim of this study was to explore dietary patterns and components associated with one-carbon metabolites. We hypothesized that intake of whole-grains and fish would be associated with lower Hcy, and higher SAM:SAH ratio due to their nutrient content. We assessed dietary information using a four-day dietary record in 118 men and women with features of the metabolic syndrome. In addition we assessed whole-blood fatty acid composition and plasma alkylresorcinols. Plasma s-adenosylmethionine (SAM), s-adenosylhomocysteine (SAH), homocysteine (Hcy) and vitamin B₁₂ was included as one-carbon metabolism markers. We used principal component analysis (PCA) to explore dietary patterns and multiple linear regression models to examine associations between dietary factors and one-carbon metabolites. PCA separated subjects based on prudent and unhealthy dietary patterns, but the dietary pattern score was not related to the one-carbon metabolites. Whole grain intake was found to be inversely associated to plasma Hcy (-4.7% (-9.3; 0.0), P=.05) and total grain intake tended to be positively associated with SAM and SAH (2.4% (-0.5; 5.5), P=.08; 5.8% (-0.2; 12.1), P=.06, respectively, per SD increase in cereal intake). Fish intake was inversely associated with plasma Hcy and SAH concentrations (-5.4% (-9.7; -0.8), P=.02 and -7.0% (-12.1; -1.5), P=.01, respectively) and positively associated with the SAM:SAH ratio (6.2% (1.6; 11.0), P=.008). In conclusion, intake and fish and whole-grain appear to be associated with a beneficial one-carbon metabolism profile. This indicates that dietary components could play a role in regulation of one-carbon metabolism with a potential impact on disease prevention.

Amino acid changes during transition to a vegan diet supplemented with fish in healthy humans

Purpose

To explore whether changes in dietary protein sources can lower plasma branched-chain amino acids (BCAAs), aromatic amino acids and sulfur amino acids (SAAs) that are often elevated in the obese, insulin-resistant state and in type 2 diabetes.

Methods

Thirty-six subjects (mean age 31 ± 2 years) underwent a voluntary abstinence from meat, poultry, eggs, and dairy products for 6 weeks, while enriching the diet with fish, in fulfillment of a religious fast. Subjects were assessed 1 week before the fast (V1), 1 week after initiation of the fast (V2) and in the last week of the fast (V3). Thirty-four subjects completed all three visits.

Results

Fasting plasma BCAAs decreased at V2 and remained low at V3 (P < 0.001 for all). Valine showed the greatest decline, by 20 and 19 % at V2 and V3, respectively. Phenylalanine and tryptophan, but not tyrosine, also decreased at V2 and V3. The two proteinogenic SAAs, methionine and cysteine, remained stable, but the cysteine product, taurine, decreased from 92 ± 7 μmol/L to 66 ± 6 (V2; P = 0.003) and 65 ± 6 μmol/L (V3; P = 0.003). A progressive decline in plasma glutamic acid, coupled with an increase in glutamine, was observed. Plasma total and LDL cholesterol decreased at V2 and V3 (P < 0.001 for all).

Conclusion

Changing dietary protein sources to plant- and fish-based sources in an ad libitum setting lowers the plasma BCAAs that have been linked to diabetes risk. These findings point to habitual diet as a potentially modifiable determinant of fasting plasma BCAA concentrations.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-016-1237-6) contains supplementary material, which is available to authorized users.

Serum S-adenosylmethionine, but not methionine, increases in response to overfeeding in humans

BACKGROUND

Plasma concentration of the methyl donor S-adenosylmethionine (SAM) is linearly associated with body mass index (BMI) and fat mass. As SAM is a high-energy compound and a sensor of cellular nutrient status, we hypothesized that SAM would increase with overfeeding.

METHODS

Forty normal to overweight men and women were overfed by 1250 kcal per day for 28 days.

RESULTS

Serum SAM increased from 106 to 130 nmol/l (P=0.006). In stratified analysis, only those with weight gain above the median (high-weight gainers; average weight gain 3.9±0.3 kg) had increased SAM (+42%, P=0.001), whereas low-weight gainers (weight gain 1.5±0.2 kg) did not (Pinteraction=0.018). Overfeeding did not alter serum concentrations of the SAM precursor, methionine or the products, S-adenosyl-homocysteine and homocysteine. The SAM/SAH (S-adenosylhomocysteine) ratio was unchanged in the total population, but increased in high-weight gainers (+52%, P=0.006, Pinteraction =0.005). Change in SAM correlated positively with change in weight (r=0.33, P=0.041) and fat mass (r=0.44, P=0.009), but not with change in protein intake or plasma methionine, glucose, insulin or low-density lipoprotein (LDL)-cholesterol.

CONCLUSION

Overfeeding raised serum SAM in proportion to the fat mass gained. The increase in SAM may help stabilize methionine levels, and denotes a responsiveness of SAM to nutrient state in humans. The role of SAM in human energy metabolism deserves further attention.

Serum Lipid and Serum Metabolite Components in relation to anthropometric parameters in EPIC-Potsdam participants

BACKGROUND/AIM

Lipidomic and metabolomic techniques become more and more important in human health research. Recent developments in analytical techniques enable the investigation of high amounts of substances. The high numbers of metabolites and lipids that are detected with among others mass spectrometric techniques challenge in most cases the statistical processes to bring out stable and interpretable results. This study targets to use the novel non-established statistical method treelet transform (TT) to investigate high numbers of metabolites and lipids and to compare the results with the established method principal component analysis (PCA). Serum lipid and metabolite profiles are investigated regarding their association to anthropometric parameters associated to obesity.

METHODS

From 226 participants of the EPIC (European Prospective Investigation into Cancer and Nutrition)-Potsdam study blood samples were investigated with an untargeted metabolomics approach regarding serum metabolites and lipids. Additionally, participants were surveyed anthropometrically to assess parameters of obesity, such as body mass index (BMI), waist-to-hip-ratio (WHR) and body fat mass. TT and PCA are used to generate treelet components (TCs) and factors summarizing serum metabolites and lipids in new, latent variables without too much loss of information. With partial correlations TCs and factors were associated to anthropometry under the control for relevant parameters, such as sex and age.

RESULTS

TT with metabolite variables (p=121) resulted in 5 stable and interpretable TCs explaining 18.9% of the variance within the data. PCA on the same variables generated 4 quite complex, less easily interpretable factors explaining 37.5% of the variance. TT on lipidomic data (p=353) produced 3 TCs as well as PCA on the same data resulted in 3 factors; the proportion of explained variance was 17.8% for TT and 39.8% for PCA. In both investigations TT ended up with stable components that are easier to interpret than the factors from the PCA. In general, the generated TCs and factors were similar in their structure when the factors are considered regarding the original variables loading high on them. Both TCs and factors showed associations to anthropometric measures.

CONCLUSIONS

TT is a suitable statistical method to generate summarizing, latent variables in data sets with more variables than observations. In the present investigation it resulted in similar latent variables compared to the established method of PCA. Whereby less variance is explained by the summarizing constructs of TT compared to the factors of PCA, TCs are easier to interpret. Additionally the resulting TCs are quite stable in bootstrap samples.

Role of S-adenosylhomocysteine in cardiovascular disease and its potential epigenetic mechanism

Transmethylation reactions utilize S-adenosylmethionine (SAM) as a methyl donor and are central to the regulation of many biological processes: more than fifty SAM-dependent methyltransferases methylate a broad spectrum of cellular compounds including DNA, histones, phospholipids and other small molecules. Common to all SAM-dependent transmethylation reactions is the release of the potent inhibitor S-adenosylhomocysteine (SAH) as a by-product. SAH is reversibly hydrolyzed to adenosine and homocysteine by SAH hydrolase. Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. However, a major unanswered question is if homocysteine is causally involved in disease pathogenesis or simply a passive and indirect indicator of a more complex mechanism. A chronic elevation in homocysteine levels results in a parallel increase in intracellular or plasma SAH, which is a more sensitive biomarker of cardiovascular disease than homocysteine and suggests that SAH is a critical pathological factor in homocysteine-associated disorders. Previous reports indicate that supplementation with folate and B vitamins efficiently lowers homocysteine levels but not plasma SAH levels, which possibly explains the failure of homocysteine-lowering vitamins to reduce vascular events in several recent clinical intervention studies. Furthermore, more studies are focusing on the role and mechanisms of SAH in different chronic diseases related to hyperhomocysteinemia, such as cardiovascular disease, kidney disease, diabetes, and obesity. This review summarizes the current role of SAH in cardiovascular disease and its effect on several related risk factors. It also explores possible the mechanisms, such as epigenetics and oxidative stress, of SAH. This article is part of a Directed Issue entitled: Epigenetic dynamics in development and disease.

Arsenic Exposure, Arsenic Metabolism, and Incident Diabetes in the Strong Heart Study

OBJECTIVE

Little is known about arsenic metabolism in diabetes development. We investigated the prospective associations of low-moderate arsenic exposure and arsenic metabolism with diabetes incidence in the Strong Heart Study.

RESEARCH DESIGN AND METHODS

A total of 1,694 diabetes-free participants aged 45-75 years were recruited in 1989-1991 and followed through 1998-1999. We used the proportions of urine inorganic arsenic (iAs), monomethylarsonate (MMA), and dimethylarsinate (DMA) over their sum (expressed as iAs%, MMA%, and DMA%) as the biomarkers of arsenic metabolism. Diabetes was defined as fasting glucose ≥ 126 mg/dL, 2-h glucose ≥ 200 mg/dL, self-reported diabetes history, or self-reported use of antidiabetic medications.

RESULTS

Over 11,263.2 person-years of follow-up, 396 participants developed diabetes. Using the leave-one-out approach to model the dynamics of arsenic metabolism, we found that lower MMA% was associated with higher diabetes incidence. The hazard ratios (95% CI) of diabetes incidence for a 5% increase in MMA% were 0.77 (0.63-0.93) and 0.82 (0.73-0.92) when iAs% and DMA%, respectively, were left out of the model. DMA% was associated with higher diabetes incidence only when MMA% decreased (left out of the model) but not when iAs% decreased. iAs% was also associated with higher diabetes incidence when MMA% decreased. The association between MMA% and diabetes incidence was similar by age, sex, study site, obesity, and urine iAs concentrations.

CONCLUSIONS

Arsenic metabolism, particularly lower MMA%, was prospectively associated with increased incidence of diabetes. Research is needed to evaluate whether arsenic metabolism is related to diabetes incidence per se or through its close connections with one-carbon metabolism.

Body composition in gene knockouts of sulfur amino acid-metabolizing enzymes

Plasma concentrations of several amino acids are elevated in human obesity and insulin resistance, but there is no conclusive evidence on whether the amino acid alterations are causal. Dietary restriction of the essential SAA methionine (MR) in rats produces a hypermetabolic phenotype, with an integrated set of transcriptional changes in lipid enzymes in liver and adipose tissue. MR also induces an array of changes in methionine metabolites, including elevated plasma homocysteine and decreased cystathionine, cysteine, glutathione, and taurine. Several knockouts of enzymes acting downstream of methionine recapitulate the phenotypic results of MR, suggesting that the MR phenotype may be driven by changes distal to methionine. Here we review the changes in SAA and body composition in seven relevant knockout mouse models. All seven models feature decreased body weight, which in five of these have been further explored and shown to result from predominantly decreased fat mass. Common to several models is increased energy expenditure, enhanced insulin sensitivity, and protection against dietary obesity, as occurs in MR. A decrease in plasma total cysteine concentrations is also seen in most models. The lean phenotype could often be reversed by dietary supplementation of cysteine or choline, but not taurine, betaine or a H2S donor. Importantly, the plasma concentrations of both cysteine and choline are positively associated with fat mass in large populations studies, while taurine, betaine, and H2S are not. Collectively, the emerging data from dietary and knockout models are in harmony with human epidemiologic data, suggesting that the availability of key nutrients in the SAA pathway regulates fat storage pathways.

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.