Deletion of betaine-homocysteine S-methyltransferase in mice perturbs choline and 1-carbon metabolism, resulting in fatty liver and hepatocellular carcinomas

Role of hyperhomocysteinemia in atherosclerosis: from bench to bedside

BACKGROUND

Atherosclerosis is a leading cause of global mortality, driven by complex interactions between genetic, metabolic, and environmental factors. Among these, hyperhomocysteinemia (HHcy) has emerged as a significant and modifiable risk factor, contributing to endothelial dysfunction, oxidative stress, and vascular inflammation. Despite increasing recognition of its role in atherogenesis, the precise mechanisms and clinical implications of HHcy remain incompletely understood, necessitating a comprehensive review to connect recent mechanistic insights with practical applications.

METHODS

We analyzed the various mechanisms whereby HHcy accelerates the progression of atherosclerosis, and conducted a comprehensive review of publications in the fields of HHcy and atherosclerosis.

RESULTS

HHcy promotes atherosclerosis through several mechanisms, including inflammation, oxidative stress, epigenetic modification, and lipoprotein metabolism alteration. Moreover, this discussion extends to current strategies for the prevention and clinical management of HHcy-induced atherosclerosis.

CONCLUSION

This review consolidates and elucidates the latest advancements and insights into the role of HHcy in atherosclerosis. The comprehensive narrative connects fundamental research with clinical applications. Contemporary studies highlight the complex interplay between HHcy and atherosclerosis, establishing HHcy as not only a contributing risk factor but also an accelerator of various atherogenic processes.

LncRNA H19 promoted alcohol-associated liver disease through dysregulation of alternative splicing and methionine metabolism

BACKGROUND AND AIMS

Long noncoding RNAs constitute a significant portion of the human genome. Among these, lncRNA H19, initially identified for its high expression during fetal development followed by a decline in the liver postnatally, re-emerges in various liver diseases. However, its specific role in alcohol-associated liver disease (ALD) remains unclear.

APPROACH AND RESULTS

Elevated H19 levels were detected in peripheral blood and livers of patients with alcohol-associated cirrhosis and hepatitis, as well as in livers of ethanol-fed mice. Hepatic overexpression of H19 exacerbated ethanol-induced liver steatosis and injury. Metabolomics analysis revealed decreased methionine levels in H19-overexpressed mouse livers, attributable to H19-mediated inhibition of betaine homocysteine methyltransferase (BHMT), a crucial enzyme in methionine synthesis. H19 regulated BHMT alternative splicing through polypyrimidine tract-binding protein 1 (PTBP1), resulting in a reduced Bhmt protein-coding variant. The maternally specific knockout of H19 ( H19Mat+/- ) or liver-specific knockout of the H19 differentially methylated domain ( H19DMDHep-/- ) in ethanol-fed mice upregulated BHMT expression and ameliorated hepatic steatosis. Furthermore, BHMT restoration counteracted H19-induced ethanol-mediated hepatic steatosis.

CONCLUSIONS

This study identifies a novel mechanism whereby H19, via PTBP1-mediated BHMT regulation, influences methionine metabolism in ALD. Targeting the H19-PTBP1-BHMT pathway may offer new therapeutic avenues for ALD.

Transcriptome Profiling and Viral-Human Interactome Insights Into HBV-Driven Oncogenic Alterations in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the primary form of liver cancer that poses a significant global health concern due to its increasing incidence rates and diverse etiology. Chronic infection induced by hepatitis B virus (HBV) is a prominent etiological factor influencing the development of HCC. Although recent advances in multi-omics approaches have facilitated extensive exploration of HCC molecular characteristics, translating the characteristics of subtypes into clinical applications has been challenging due to parameters like limited sample size and complex classifiers for early detection. In the present study, we performed transcriptomics profiling of HBV-infected HCC patient tissue data to gather comprehensive insights into the intricate molecular mechanisms underlying HBV-associated HCC, specifically, viral protein interactions that influence the expression of oncogenes. The 1059 differentially expressed genes (DEGs) identified across two GEO data sets revealed upregulation of cell cycle and mitosis-related genes, alongside downregulation of genes involved in fatty acid degradation and cytochrome P450 activity. CDK1 and CDC20 which are part of the top cluster and hub gene from interactome analysis were identified as potential markers for HBV-positive HCC through gene expression pattern and overall survival analysis. Additionally, 19 DEGs showing significance in HCC development were identified as interacting partners with HBV proteins. Among them, the interaction of HBsAg with ALB and SHBG and their downregulation correlates to the lower testosterone levels identified in HBV and HCC patients. Together, the study enhances the understanding of the heterogeneity and molecular pathogenesis of HBV-positive HCC.

Identification of methionine metabolism related prognostic model and tumor suppressive functions of BHMT in hepatocellular carcinoma

Given the resistance to conventional treatments and limitations of immune checkpoint blockade therapy in hepatocellular carcinoma (HCC), it is imperative to explore novel prognostic models and biomarkers. The dependence of cancer cell on exogenous methionine, known as Hoffman effect, is a hallmark of HCC, with numerous studies reporting a strong correlation between methionine metabolism and tumor development. Betaine-homocysteine S-methyltransferase (BHMT), a critical component of methionine metabolism pathway, has polymorphisms linking to poor prognosis in multiple cancers. Nevertheless, there is little literature regarding the relationship between methionine metabolism and incidence, mortality of HCC, as well as the function of BHMT in HCC progression. In this study, by analyzing multiple datasets, we constructed a methionine metabolism-related prognostic model and thoroughly investigated the influence of BHMT on the prognosis of HCC. Bioinformatics analysis revealed a marked decrease in BHMT expression in HCC, which was linked to adverse clinical outcomes. CIBERSORT results suggest that BHMT promotes infiltration of M1 macrophages. Our results suggest its potential as an ideal prognostic biomarker for anti PD-L1 immunotherapy. In summary, this study innovatively provides first methionine metabolism-related prognostic model and unveils the tumor suppressive function of BHMT in HCC, providing potential mechanism by which BHMT exert its function.

Eggs, Dietary Choline, and Nonalcoholic Fatty Liver Disease in the Framingham Heart Study

BACKGROUND

Eggs are rich in bioactive compounds, including choline and carotenoids that may benefit cardiometabolic outcomes. However, little is known about their relationship with nonalcoholic fatty liver disease (NAFLD).

OBJECTIVES

We investigated the association between intakes of eggs and selected egg-rich nutrients (choline, lutein, and zeaxanthin) and NAFLD risk and changes in liver fat over ∼6 y of follow-up in the Framingham Offspring and Third Generation cohorts.

METHODS

On 2 separate occasions (2002-2005 and 2008-2011), liver fat was assessed using a computed tomography scan to estimate the average liver fat attenuation relative to a control phantom to create the liver phantom ratio (LPR). In 2008-2011, cases of incident NAFLD were identified as an LPR ≤0.33 in the absence of heavy alcohol use, after excluding prevalent NAFLD (LPR ≤0.33) in 2002-2005. Food frequency questionnaires were used to estimate egg intakes (classified as <1, 1, and ≥2 per week), dietary choline (adjusted for body weight using the residual method), and the combined intakes of lutein and zeaxanthin. Multivariable modified Poisson regression and general linear models were used to compute incident risk ratios (RR) of NAFLD and adjusted mean annualized liver fat change.

RESULTS

NAFLD cumulative incidence was 19% among a total of 1414 participants. We observed no associations between egg intake or the combined intakes of lutein and zeaxanthin with an incident NAFLD risk or liver fat change. Other diet and cardiometabolic risk factors did not modify the association between egg intake and NAFLD risk. However, dietary choline intakes were inversely associated with NAFLD risk (RR for tertile 3 compared with tertile 1: 0.69, 95% CI: 0.51, 0.94).

CONCLUSIONS

Although egg intake was not directly associated with NAFLD risk, eggs are a major source of dietary choline, which was strongly inversely associated with NAFLD risk in this community-based cohort.

The complex role of glycine N-methyltransferase in metabolism-a review

BACKGROUND

Glycine N-methyltransferase (GNMT) is an enzyme predominantly found in the liver, playing a crucial role in various metabolic pathways. GNMT is involved in transmethylation, transsulfuration, one-carbon metabolism, energy metabolism, and DNA methylation. Deletion or Knockdown of GNMT influences the expression of several key metabolic enzymes by accumulating S-adenosylmethionine (SAM). Dysregulation of GNMT and these metabolic enzymes can lead to metabolic dysfunction and chronic diseases.

OBJECTIVE

To provide a comprehensive review of the impact of Glycine N-methyltransferase (GNMT) on metabolism, focusing on its epigenetic and genetic mechanisms, its role in metabolic pathways, and its association with chronic diseases.

RESULTS

GNMT is highly expressed in the liver and exerts direct and indirect effects on various metabolic pathways, including transmethylation, transsulfuration, one-carbon metabolism, energy metabolism, and global DNA methylation. Current understanding suggests that GNMT operates through both epigenetic and genetic mechanisms, influencing the expression of key metabolic enzymes such as BHMT, NNMT, PEMT, DNMTs, CBS, and MTHFR through the accumulation of S-adenosylmethionine. Dysregulation of these proteins not only affects metabolic function but also contributes to the development of several chronic diseases. Furthermore, the level of GNMT protein has been directly linked to non-alcoholic fatty liver disease, with its function being gender, age, and organ specific. At the same time, GNMT and disease progression correlate, dietary supplementation and pharmacological approaches have shown promise in controlling GNMT levels.

CONCLUSION

GNMT plays a multifaceted role in metabolism, influencing various pathways and contributing to chronic disease development. Understanding its mechanisms and interactions opens avenues for targeted dietary and pharmacological therapies to manage GNMT-related metabolic dysfunction.

One carbon metabolism supplementation in maturation medium but not embryo culture medium improves the yield of blastocysts from bovine oocytes

Optimizing oocyte maturation and embryo culture media could enhance in vitro embryo production. The purpose of the present study was to investigate the role of supplementing one carbon metabolism (OCM) substrates and its cofactors (Cystine, Zinc, Betaine, B2, B3, B6, B12 and 5-methyltetrahydrofolate) in maturation and/or embryo culture media on the rate of blastocyst formation and pregnancy outcomes following the transfer of the resulting blastocysts in bovines. In the first experiment, 2537 bovine oocytes were recovered from slaughterhouse ovaries and then matured either in conventional maturation medium (IVM) or IVM supplemented with OCM substrates (Sup-IVM). After in vitro fertilization, the putative zygotes from each treatment (IVM or Sup-IVM) were cultured in the media either without (IVM/IVC or Sup-IVM/IVC) or with (IVM/Sup-IVC or Sup-IVM/Sup-IVC) OCM supplementation. The blastocyst rate, assessed on day 8, was significantly increased in Sup-IVM/IVC group (34.90 ± 2.52) as compared to IVM/IVC (17.06 ± 1.69; P = 0.0001) and Sup-IVM/Sup-IVC (20.29 ± 2.75; P = 0.004) and non-significantly as compared to IVM/Sup-IVC (24.86 ± 5.37). In the second experiment, non-matured bovine oocytes were collected by transvaginal ovum pick up after FSH stimulation, randomly allocated into IVM/IVC (n = 275) and Sup-IVM/IVC (n = 260) and the blastocysts achieved at day 7 were transferred in recipient cattle. The blastocyst rate was significantly higher in Sup-IVM/IVC group (38.85%) as compared to the IVM/IVC group (23.64%; P < 0.0001). After single embryo transfer, the supplemented blastocysts were at least as competent as non-supplemented ones with a non-significantly higher (20% vs. 14%) pregnancy rate and the advantage of several good quality blastocysts available for future use. In conclusion, optimizing the maturation medium with OCM substrates and its cofactors could enhance the formation of viable blastocysts with the potential to increase the cumulative birth rate in cattle.

Chemogenomic Screening in a Patient-Derived 3D Fatty Liver Disease Model Reveals the CHRM1-TRPM8 Axis as a Novel Module for Targeted Intervention

Metabolic dysfunction-associated steatohepatitis (MASH) is a leading cause of chronic liver disease with few therapeutic options. To narrow the translational gap in the development of pharmacological MASH treatments, a 3D liver model from primary human hepatocytes and non-parenchymal cells derived from patients with histologically confirmed MASH was established. The model closely mirrors disease-relevant endpoints, such as steatosis, inflammation and fibrosis, and multi-omics analyses show excellent alignment with biopsy data from 306 MASH patients and 77 controls. By combining high-content imaging with scalable biochemical assays and chemogenomic screening, multiple novel targets with anti-steatotic, anti-inflammatory, and anti-fibrotic effects are identified. Among these, activation of the muscarinic M1 receptor (CHRM1) and inhibition of the TRPM8 cation channel result in strong anti-fibrotic effects, which are confirmed using orthogonal genetic assays. Strikingly, using biosensors based on bioluminescence resonance energy transfer, a functional interaction along a novel MASH signaling axis in which CHRM1 inhibits TRPM8 via Gq/11 and phospholipase C-mediated depletion of phosphatidylinositol 4,5-bisphosphate can be demonstrated. Combined, this study presents the first patient-derived 3D MASH model, identifies a novel signaling module with anti-fibrotic effects, and highlights the potential of organotypic culture systems for phenotype-based chemogenomic drug target identification at scale.

Metabolomics at the cutting edge of risk prediction of MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a major public health threat globally. Management of patients afflicted with MASLD and research in this domain are limited by the lack of robust well-established non-invasive biomarkers for diagnosis, prognostication, and monitoring. The circulating metabolome reflects both the systemic metabo-inflammatory milieu and changes in the liver in affected individuals. In this review we summarize the available literature on changes in the different components of the metabolome in MASLD with a focus on changes that are linked to the presence of underlying steatohepatitis, severity of disease activity, and fibrosis stage. We further summarize the existing literature around biomarker panels that are derived from interrogation of the metabolome. Their relevance to disease biology and utility in practice are also discussed. We further highlight potential direction for future studies particularly to ensure they are fit for purpose and suitable for widespread use.

The rate of muscle wasting in liver transplant recipients on waiting list: post-transplant outcomes and associated serum metabolite patterns

Background

Sarcopenia at the time of liver transplantation (LT) is an established risk factor for mortality following LT. However, most studies in this context have defined sarcopenia by one-time, static measurements. The aims of this study were (I) to determine the impact of the rate of muscle loss in waitlisted LT recipients on post-LT outcomes and (II) to identify patterns of serum metabolites associated with patients with more progressive sarcopenia.

Methods

Patients undergoing liver transplant from 2008 to 2018 who received more than one computed tomography (CT) scans within 12 months prior to liver transplant were included (n=61). The psoas muscle index (PMI) was calculated using Slice-O-Matic software and corrected for patient height (m2). Patients were classified into two groups based the rate of reduction in PMI-high wasting [HW; change in PMI (ΔPMI) ≤-1%/month] and low wasting (LW; ΔPMI >-1%/month). Pre-transplant serum metabolic profiles were collected using nuclear magnetic resonance (NMR) spectroscopy. Living kidney donor sera was used as healthy controls.

Results

Median ΔPMI was -2.0%/month in HW and -0.15%/month in LW patients (P<0.001). Post-transplant 1-year mortality was significantly higher in HW patients. There were no significant differences in metabolite concentrations between HW and LW patients. However, perturbations in taurine, sarcosine, betaine and the aromatic amino acids (AAAs), were observed in patients with liver disease as compared to healthy controls. Liver disease was also associated with a decrease in lipoprotein profiles, especially high-density lipoprotein (HDL) particles.

Conclusions

In patients undergoing LT, the rate of progression of sarcopenia is a strong prognostic indicator of post-LT death. Serum metabolite profiles were not characteristically unique to HW patients, and most closely resemble derangements associated with chronic liver disease.

4-Hydroxynonenal from Mitochondrial and Dietary Sources Causes Lysosomal Cell Death for Lifestyle-Related Diseases

Excessive consumption of vegetable oils such as soybean and canolla oils containing ω-6 polyunsaturated fatty acids is considered one of the most important epidemiological factors leading to the progression of lifestyle-related diseases. However, the underlying mechanism of vegetable-oil-induced organ damage is incompletely elucidated. Since proopiomelanocortin (POMC) neurons in the hypothalamus are related to the control of appetite and energy expenditure, their cell degeneration/death is crucial for the occurrence of obesity. In patients with metabolic syndrome, saturated fatty acids, especially palmitate, are used as an energy source. Since abundant reactive oxygen species are produced during β-oxidation of the palmitate in mitochondria, an increased amount of 4-hydroxy-2-nonenal (4-HNE) is endogenously generated from linoleic acids constituting cardiolipin of the inner membranes. Further, due to the daily intake of deep-fried foods and/or high-fat diets cooked using vegetable oils, exogenous 4-HNE being generated via lipid peroxidation during heating is incorporated into the blood. By binding with atheromatous and/or senile plaques, 4-HNE inactivates proteins via forming hybrid covalent chemical addition compounds and causes cellular dysfunction and tissue damage by the specific oxidation carbonylation. 4-HNE overstimulates G-protein-coupled receptors to induce abnormal Ca2+ mobilization and µ-calpain activation. This endogenous and exogenous 4-HNE synergically causes POMC neuronal degeneration/death and obesity. Then, the resultant metabolic disorder facilitates degeneration/death of hippocampal neurons, pancreatic β-cells, and hepatocytes. Hsp70.1 is a molecular chaperone which is crucial for both protein quality control and the stabilization of lysosomal limiting membranes. Focusing on the monkey hippocampus after ischemia, previously we formulated the 'calpain-cathepsin hypothesis', i.e., that calpain-mediated cleavage of carbonylated Hsp70.1 is a trigger of programmed neuronal death. This review aims to report that in diverse organs, lysosomal cell degeneration/death occurs via the calpain-cathepsin cascade after the consecutive injections of synthetic 4-HNE in monkeys. Presumably, 4-HNE is a root substance of lysosomal cell death for lifestyle-related diseases.

Integration of epigenomic and transcriptomic profiling uncovers EZH2 target genes linked to cysteine metabolism in hepatocellular carcinoma

Enhancer of zeste homolog 2 (EZH2), a key protein implicated in various cancers including hepatocellular carcinoma (HCC), is recognized for its association with epigenetic dysregulation and pathogenesis. Despite clinical explorations into EZH2-targeting therapies, the mechanisms underlying its role in gene suppression in HCC have remained largely unexplored. Here, we integrate epigenomic and transcriptomic analyses to uncover the transcriptional landscape modulated by selective EZH2 inhibition in HCC. By reanalyzing transcriptomic data of HCC patients, we demonstrate that EZH2 overexpression correlates with poor patient survival. Treatment with the EZH2 inhibitor tazemetostat restored expression of genes involved in cysteine-methionine metabolism and lipid homeostasis, while suppressing angiogenesis and oxidative stress-related genes. Mechanistically, we demonstrate EZH2-mediated H3K27me3 enrichment at cis-regulatory elements of transsulfuration pathway genes, which is reversed upon inhibition, leading to increased chromatin accessibility. Among 16 EZH2-targeted candidate genes, BHMT and CDO1 were notably correlated with poor HCC prognosis. Tazemetostat treatment of HCC cells increased BHMT and CDO1 expression while reducing levels of ferroptosis markers FSP1, NFS1, and SLC7A11. Functionally, EZH2 inhibition dose-dependently reduced cell viability and increased lipid peroxidation in HCC cells. Our findings reveal a novel epigenetic mechanism controlling lipid peroxidation and ferroptosis susceptibility in HCC, providing a rationale for exploring EZH2-targeted therapies in this malignancy.

Development of a chemiluminescent immunoassay based on magnetic solid phase for quantification of homocysteine in human serum

BACKGROUND

Homocysteine (HCY) is a sulfur-containing amino acid that is an independent or important risk factor for the occurrence of many chronic diseases and is one of the most important indicators for determining health risks. However, existing HCY detection methods do not meet the requirements of clinical diagnosis. Therefore, there is an urgent need to establish new detection methods to meet the needs of clinical detection.

RESULTS

In this study, we used the principle of competitive method to establish a new method for the determination of HCY in human serum using a chemiluminescent enzyme immunoassay in conjunction with a chemiluminescent assay instrument that uses magnetic microparticles as the solid phase of the immunoreaction. The established method achieved satisfactory results in terms of minimum detection limit, specificity, accuracy, and clinical application. The limit of detection was 0.03 ng/mL. The intra-assay coefficient of variation (CV) was 1.94-5.05%, the inter-assay CV was 2.29-6.88%, and the recovery rate was 88.60-93.27%. Cross-reactivity with L-cysteine ranged from 0.0100 to 0.0200 μmol/L, and cross-reactivity with glutathione ranged from 0.0100 to 0.200 μmol/L, all of which were less than the limit of detection (LoD) of this method. The linear factor R of this method was greater than 0.99.

CONCLUSIONS

In summary, the developed method showed a good correlation with the product from Abbott. A total of 996 clinical patients with cardiovascular diseases were evaluated using the method developed in this study.

Ribosomal modification protein rimK-like family member A activates betaine-homocysteine S-methyltransferase 1 to ameliorate hepatic steatosis

Nonalcoholic fatty liver disease (NAFLD) is a serious threat to public health, but its underlying mechanism remains poorly understood. In screening important genes using Gene Importance Calculator (GIC) we developed previously, ribosomal modification protein rimK-like family member A (RIMKLA) was predicted as one essential gene but its functions remained largely unknown. The current study determined the roles of RIMKLA in regulating glucose and lipid metabolism. RIMKLA expression was reduced in livers of human and mouse with NAFLD. Hepatic RIMKLA overexpression ameliorated steatosis and hyperglycemia in obese mice. Hepatocyte-specific RIMKLA knockout aggravated high-fat diet (HFD)-induced dysregulated glucose/lipid metabolism in mice. Mechanistically, RIMKLA is a new protein kinase that phosphorylates betaine-homocysteine S-methyltransferase 1 (BHMT1) at threonine 45 (Thr45) site. Upon phosphorylation at Thr45 and activation, BHMT1 eliminated homocysteine (Hcy) to inhibit the activity of transcription factor activator protein 1 (AP1) and its induction on fatty acid synthase (FASn) and cluster of differentiation 36 (CD36) gene transcriptions, concurrently repressing lipid synthesis and uptake in hepatocytes. Thr45 to alanine (T45A) mutation inactivated BHMT1 to abolish RIMKLA's repression on Hcy level, AP1 activity, FASn/CD36 expressions, and lipid deposition. BHMT1 overexpression rescued the dysregulated lipid metabolism in RIMKLA-deficient hepatocytes. In summary, RIMKLA is a novel protein kinase that phosphorylates BHMT1 at Thr45 to repress lipid synthesis and uptake. Under obese condition, inhibition of RIMKLA impairs BHMT1 activity to promote hepatic lipid deposition.

Deficiency of betaine-homocysteine methyltransferase activates glucose-6-phosphate dehydrogenase (G6PD) by decreasing arginine methylation of G6PD in hepatocellular carcinogenesis

Betaine-homocysteine methyltransferase (BHMT) regulates protein methylation and is correlated with tumorigenesis; however, the effects and regulation of BHMT in hepatocarcinogenesis remain largely unexplored. Here, we determined the clinical significance of BHMT in the occurrence and progression of hepatocellular carcinoma (HCC) using tissue samples from 198 patients. BHMT was to be frequently found (86.6%) expressed at relatively low levels in HCC tissues and was positively correlated with the overall survival of patients with HCC. Bhmt overexpression effectively suppressed several malignant phenotypes in hepatoma cells in vitro and in vivo, whereas complete knockout of Bhmt (Bhmt-/-) produced the opposite effect. We combined proteomics, metabolomics, and molecular biological strategies and detected that Bhmt-/- promoted hepatocarcinogenesis and tumor progression by enhancing the activity of glucose-6-phosphate dehydrogenase (G6PD) and PPP metabolism in DEN-induced HCC mouse and subcutaneous tumor-bearing models. In contrast, restoration of Bhmt with an AAV8-Bhmt injection or pharmacological inhibition of G6PD attenuated hepatocarcinogenesis. Additionally, coimmunoprecipitation identified monomethylated modifications of the G6PD, and BHMT regulated the methylation of G6PD. Protein sequence analysis, generation and application of specific antibodies, and site-directed mutagenesis indicated G6PD methylation at the arginine residue 246. Furthermore, we established bidirectionally regulated BHMT cellular models combined with methylation-deficient G6PD mutants to demonstrate that BHMT potentiated arginine methylation of G6PD, thereby inhibiting G6PD activity, which in turn suppressed hepatocarcinogenesis. Taken together, this study reveals a new methylation-regulatory mechanism in hepatocarcinogenesis owing to BHMT deficiency, suggesting a potential therapeutic strategy for HCC treatment.

The origin of betaine in mouse oocytes and preimplantation embryos†

Betaine has important roles in preimplantation mouse embryos, including as an organic osmolyte that functions in cell volume regulation in the early preimplantation stages and as a donor to the methyl pool in blastocysts. The origin of betaine in oocytes and embryos was largely unknown. Here, we found that betaine was present from the earliest stage of growing oocytes. Neither growing oocytes nor early preantral follicles could take up betaine, but antral follicles were able to transport betaine and supply the enclosed oocyte. Betaine is synthesized by choline dehydrogenase, and female mice lacking Chdh did not have detectable betaine in their oocytes or early embryos. Supplementing betaine in their drinking water restored betaine in the oocyte only when supplied during the final stages of antral follicle development but not earlier in folliculogenesis. Together with the transport results, this implies that betaine can only be exogenously supplied during the final stages of oocyte growth. Previous work showed that the amount of betaine in the oocyte increases sharply during meiotic maturation due to upregulated activity of choline dehydrogenase within the oocyte. This betaine present in mature eggs was retained after fertilization until the morula stage. There was no apparent role for betaine uptake via the SIT1 (SLC6A20) betaine transporter that is active at the 1- and 2-cell stages. Instead, betaine was apparently retained because its major route of efflux, the volume-sensitive organic osmolyte - anion channel, remained inactive, even though it is expressed and capable of being activated by a cell volume increase.

Regulation of Betaine Homocysteine Methyltransferase by Liver Receptor Homolog-1 in the Methionine Cycle

Betaine-homocysteine S-methyltransferase (BHMT) is one of the most abundant proteins in the liver and regulates homocysteine metabolism. However, the molecular mechanisms underlying Bhmt transcription have not yet been elucidated. This study aimed to assess the molecular mechanisms underlying Bhmt transcription and the effect of BHMT deficiency on metabolic functions in the liver mediated by liver receptor homolog-1 (LRH-1). During fasting, both Bhmt and Lrh-1 expression increased in the liver of Lrh-1f/f mice; however, Bhmt expression was decreased in LRH-1 liver specific knockout mice. Promoter activity analysis confirmed that LRH-1 binds to a specific site in the Bhmt promoter region. LRH-1 deficiency was associated with elevated production of reactive oxygen species (ROS), lipid peroxidation, and mitochondrial stress in hepatocytes, contributing to hepatic triglyceride (TG) accumulation. In conclusion, this study suggests that the absence of an LRH-1-mediated decrease in Bhmt expression promotes TG accumulation by increasing ROS levels and inducing mitochondrial stress. Therefore, LRH-1 deficiency not only leads to excess ROS production and mitochondrial stress in hepatocytes, but also disrupts the methionine cycle. Understanding these regulatory pathways may pave the way for novel therapeutic interventions against metabolic disorders associated with hepatic lipid accumulation.

SHMT2 reduces fatty liver but is necessary for liver inflammation and fibrosis in mice

Non-alcoholic fatty liver disease is associated with an irregular serine metabolism. Serine hydroxymethyltransferase 2 (SHMT2) is a liver enzyme that breaks down serine into glycine and one-carbon (1C) units critical for liver methylation reactions and overall health. However, the contribution of SHMT2 to hepatic 1C homeostasis and biological functions has yet to be defined in genetically modified animal models. We created a mouse strain with targeted SHMT2 knockout in hepatocytes to investigate this. The absence of SHMT2 increased serine and glycine levels in circulation, decreased liver methylation potential, and increased susceptibility to fatty liver disease. Interestingly, SHMT2-deficient mice developed simultaneous fatty liver, but when fed a diet high in fat, fructose, and cholesterol, they had significantly less inflammation and fibrosis. This study highlights the critical role of SHMT2 in maintaining hepatic 1C homeostasis and its stage-specific functions in the pathogenesis of NAFLD.

Comprehensive analysis of epigenetic and epitranscriptomic genes' expression in human NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a multifactorial condition with a complex etiology. Its incidence is increasing globally in parallel with the obesity epidemic, and it is now considered the most common liver disease in Western countries. The precise mechanisms underlying the development and progression of NAFLD are complex and still poorly understood. The dysregulation of epigenetic and epitranscriptomic mechanisms is increasingly recognized to play pathogenic roles in multiple conditions, including chronic liver diseases. Here, we have performed a comprehensive analysis of the expression of epigenetic and epitranscriptomic genes in a total of 903 liver tissue samples corresponding to patients with normal liver, obese patients, and patients with non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH), advancing stages in NAFLD progression. We integrated ten transcriptomic datasets in an unbiased manner, enabling their robust analysis and comparison. We describe the complete landscape of epigenetic and epitranscriptomic genes' expression along the course of the disease. We identify signatures of genes significantly dysregulated in association with disease progression, particularly with liver fibrosis development. Most of these epigenetic and epitranscriptomic effectors have not been previously described in human NAFLD, and their altered expression may have pathogenic implications. We also performed a comprehensive analysis of the expression of enzymes involved in the metabolism of the substrates and cofactors of epigenetic and epitranscriptomic effectors. This study provides novel information on NAFLD pathogenesis and may also guide the identification of drug targets to treat this condition and its progression towards hepatocellular carcinoma.

Association between dietary intakes of B vitamins and nonalcoholic fatty liver disease in postmenopausal women: a cross-sectional study

Background

Non-alcoholic fatty liver disease (NAFLD) is increasingly common globally, particularly among postmenopausal women. Diet plays a fundamental role in the treatment of NAFLD. However, clinical research on the dietary intakes of B vitamins, specifically in postmenopausal women, is scant. Hence, it is imperative to study the impact of B vitamin dietary intake in postmenopausal women.

Methods

This study utilized National Health and Nutrition Examination Survey (NHANES) data for 668 postmenopausal women. Logistic regression analysis was conducted to investigate the association of the intakes of B vitamins with hepatic steatosis and liver fibrosis prevalence. The analysis accounted for various covariates and employed restricted cubic spline analysis to examine potential nonlinear relationships. Additionally, interactions among age, diabetes, and B-vitamin intakes, as well as the interaction between folate and vitamin B12 intake, were explored.

Results

Higher intakes of folate [0.30 (0.10-0.88)], choline [0.26 (0.07-0.95)], vitamin B1, and vitamin B2 were associated with a reduced risk of hepatic steatosis in postmenopausal women. The associations of niacin (P-nonlinear = 0.0003), vitamin B1 (P-nonlinear = 0.036), and vitamin B2 (P-nonlinear<0.0001) intakes with hepatic steatosis showed a nonlinear pattern. However, no significant associations were observed between the intakes of niacin, vitamin B6 and vitamin B12 and hepatic steatosis. Furthermore, there were no significant associations between B-vitamin intakes and liver fibrosis. No interaction effects were observed.

Conclusion

Dietary intakes of folate, choline, vitamin B1, and vitamin B2 may be associated with liver steatosis in postmenopausal women, these results suggest that optimizing the intake of these specific B vitamins may have a protective effect against liver steatosis in postmenopausal women, offering valuable insights into potential dietary strategies to promote their well-being.

Gut microbiome and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become the most prevalent chronic liver disease globally and imposed a heavy economic burden on society and individuals. To date, the pathological process of NAFLD is not yet fully elucidated. Compelling evidences have demonstrated the pivotal role of gut microbiota in the pathogenesis of NAFLD, and gut dysbiosis has been commonly observed in patients with NAFLD. Gut dysbiosis impairs gut permeability, allowing the translocation of bacterial products such as lipopolysaccharides (LPS), short-chain fatty acids (SCFAs), and ethanol to the liver via portal blood flow. This review aimed to shed light on the underlying mechanisms by which gut microbiota influences the development and progression of NAFLD. In addition, the potential application of gut microbiome as a non-invasive diagnostic tool and a novel therapeutical target was reviewed.

Sulfur-Element containing metabolic pathways in human health and crosstalk with the microbiome

In humans, methionine derived from dietary proteins is necessary for cellular homeostasis and regeneration of sulfur containing pathways, which produce inorganic sulfur species (ISS) along with essential organic sulfur compounds (OSC). In recent years, inorganic sulfur species have gained attention as key players in the crosstalk of human health and the gut microbiome. Endogenously, ISS includes hydrogen sulfide (H2S), sulfite (SO32-), thiosulfate (S2O32-), and sulfate (SO42-), which are produced by enzymes in the transsulfuration and sulfur oxidation pathways. Additionally, sulfate-reducing bacteria (SRB) in the gut lumen are notable H2S producers which can contribute to the ISS pools of the human host. In this review, we will focus on the systemic effects of sulfur in biological pathways, describe the contrasting mechanisms of sulfurylation versus phosphorylation on the hydroxyl of serine/threonine and tyrosine residues of proteins in post-translational modifications, and the role of the gut microbiome in human sulfur metabolism.

Sources and Sinks of Serine in Nutrition, Health, and Disease

Amino acid dysregulation has emerged as an important driver of disease progression in various contexts. l-Serine lies at a central node of metabolism, linking carbohydrate metabolism, transamination, glycine, and folate-mediated one-carbon metabolism to protein synthesis and various downstream bioenergetic and biosynthetic pathways. l-Serine is produced locally in the brain but is sourced predominantly from glycine and one-carbon metabolism in peripheral tissues via liver and kidney metabolism. Compromised regulation or activity of l-serine synthesis and disposal occurs in the context of genetic diseases as well as chronic disease states, leading to low circulating l-serine levels and pathogenesis in the nervous system, retina, heart, and aging muscle. Dietary interventions in preclinical models modulate sensory neuropathy, retinopathy, tumor growth, and muscle regeneration. A serine tolerance test may provide a quantitative readout of l-serine homeostasis that identifies patients who may be susceptible to neuropathy or responsive to therapy.

Metabolic liver cancer: associations of rare and common germline variants in one-carbon metabolism and DNA methylation genes

Animal studies implicate one-carbon metabolism and DNA methylation genes in hepatocellular carcinoma (HCC) development in the setting of metabolic perturbations. Using human samples, we investigated the associations between common and rare variants in these closely related biochemical pathways and risk for metabolic HCC development in a multicenter international study. We performed targeted exome sequencing of 64 genes among 556 metabolic HCC cases and 643 cancer-free controls with metabolic conditions. Multivariable logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs), adjusting for multiple comparisons. Gene-burden tests were used for rare variant associations. Analyses were performed in the overall sample and among non-Hispanic whites. The results show that among non-Hispanic whites, presence of rare functional variants in ABCC2 was associated with 7-fold higher risk of metabolic HCC (OR = 6.92, 95% CI: 2.38-20.15, P = 0.0004), and this association remained significant when analyses were restricted to functional rare variants observed in ≥2 participants (cases 3.2% versus controls 0.0%, P = 1.02 × 10-5). In the overall multiethnic sample, presence of rare functional variants in ABCC2 was nominally associated with metabolic HCC (OR = 3.60, 95% CI: 1.52-8.58, P = 0.004), with similar nominal association when analyses were restricted to functional rare variants observed in ≥2 participants (cases 2.9% versus controls 0.2%, P = 0.006). A common variant in PNPLA3 (rs738409[G]) was associated with higher HCC risk in the overall sample (P = 6.36 × 10-6) and in non-Hispanic whites (P = 0.0002). Our findings indicate that rare functional variants in ABCC2 are associated with susceptibility to metabolic HCC in non-Hispanic whites. PNPLA3-rs738409 is also associated with metabolic HCC risk.

Vegetable Oil-Peroxidation Product 'Hydroxynonenal' Causes Hepatocyte Injury and Steatosis via Hsp70.1 and BHMT Disorders in the Monkey Liver

Hsp70.1 has a dual function as a chaperone protein and lysosomal stabilizer. In 2009, we reported that calpain-mediated cleavage of carbonylated Hsp70.1 causes neuronal death by inducing lysosomal rupture in the hippocampal CA1 neurons of monkeys after transient brain ischemia. Recently, we also reported that consecutive injections of the vegetable oil-peroxidation product 'hydroxynonenal' induce hepatocyte death via a similar cascade in monkeys. As Hsp70.1 is also related to fatty acid β-oxidation in the liver, its deficiency causes fat accumulation. The genetic deletion of betaine-homocysteine S-methyltransferase (BHMT) was reported to perturb choline metabolism, inducing a decrease in phosphatidylcholine and resulting in hepatic steatosis. Here, focusing on Hsp70.1 and BHMT disorders, we studied the mechanisms of hepatocyte degeneration and steatosis. Monkey liver tissues with and without hydroxynonenal injections were compared using proteomics, immunoblotting, immunohistochemical, and electron microscopy-based analyses. Western blotting showed that neither Hsp70.1 nor BHMT were upregulated, but an increased cleavage was observed in both. Proteomics showed a marked downregulation of Hsp70.1, albeit a two-fold increase in the carbonylated BHMT. Hsp70.1 carbonylation was negligible, in contrast to the ischemic hippocampus, which was associated with ~10-fold increments. Although histologically, the control liver showed very little lipid deposition, numerous tiny lipid droplets were seen within and around the degenerating/dying hepatocytes in monkeys after the hydroxynonenal injections. Electron microscopy showed permeabilization/rupture of lysosomal membranes, dissolution of the mitochondria and rough ER membranes, and proliferation of abnormal peroxisomes. It is probable that the disruption of the rough ER caused impaired synthesis of the Hsp70.1 and BHMT proteins, while impairment of the mitochondria and peroxisomes contributed to the sustained generation of reactive oxygen species. In addition, hydroxynonenal-induced disorders facilitated degeneration and steatosis in the hepatocytes.

A new view on functions of the lysine demalonylase activity of SIRT5

AIMS

The specificity of the lysine demalonylation substrates of the pharmaceutically attractive tumor promoter/suppressor SIRT5 is not comprehensively clarified. The present study re-analyses publicly available data and highlights potentially pharmaceutically interesting outcomes by the use of bioinformatics.

MATERIALS AND METHODS

The interaction networks of SIRT5 malonylome from the wild-type and ob/ob (obese pre-diabetic type) mice were subjected to the pathway enrichment and gene function prediction analysis using GeneMania (3.5.2) application run under Cytoscape (3.9.1) environment.

KEY FINDINGS

The analysis in the wild-type mice revealed the involvement of SIRT5 malonylome in Eukaryotic translation elongation (ETE; the nodes EF1A1, EEF2, EEF1D, and EEF1G), Amino acid and derivative metabolism (AADM), and Selenoamino acid metabolism (SAM). The tumor promoter/suppressor activity of SIRT5 is mediated through the tumor promoter substrates included in AADM (GLUD1, SHMT1, ACAT1), and the tumor suppressor substrates involved in AADM and SAM (ALDH9A1, BHMT, GNMT). Selen stimulates the expression of SIRT5 and other sirtuins. SIRT5 in turn regulates the selenocysteine synthesis, which creates a regulatory loop. The analysis of SIRT5 malonylome in pre-diabetic ob/ob mice identifies the mTORC1 pathway as a mechanism, which facilitates SIRT5 functions. The comparison of the outcomes of SIRT5 malonylome, succinylome, and glutarylome analysis disclosed several differences.

SIGNIFICANCE

The analysis showed additional aspects of SIRT5 malonylome functions besides the control of glucose metabolism. It defined several unique substrates and pathways, and it showed differences compared to other enzymatic activities of SIRT5, which could be used for pharmaceutical benefits.

Homocysteine-induced endoplasmic reticulum stress activates FGF21 and is associated with browning and atrophy of white adipose tissue in Bhmt knockout mice

Betaine-homocysteine methyltransferase (BHMT) catalyzes the transfer of methyl groups from betaine to homocysteine (Hcy), producing methionine and dimethylglycine. In this work, we characterize Bhmt wild type (Bhmt-WT) and knockout (Bhmt-KO) mice that were fully backcrossed to a C57Bl6/J background. Consistent with our previous findings, Bhmt-KO mice had decreased body weight, fat mass, and adipose tissue weight compared to WT. Histological analyses and gene expression profiling indicate that adipose browning was activated in KO mice and contributed to the adipose atrophy observed. BHMT is not expressed in adipose tissue but is abundant in liver; thus, a signal must originate from the liver that modulates adipose tissue. We found that, in Bhmt-KO mice, homocysteine-induced endoplasmic reticulum (ER) stress is associated with activation of the hepatic transcription factor cyclic AMP response element binding protein (CREBH), and an increase in hepatic and plasma concentrations of fibroblast growth factor 21 (FGF21), which is known to induce adipose browning. Our data indicate that the deletion of a single gene in one-carbon metabolism modifies adipose biology and energy metabolism. Future studies could focus on identifying if functional polymorphisms in BHMT result in a similar adipose atrophy phenotype.

Ionomics-metabolome association analysis as a new approach to the impact of dietary copper levels in suckling piglets model

Ionomics-metabolomics association analysis is a novel method to elucidating the potential mechanisms underlying the effects of dietary copper on the overall health parameters of suckling piglets model. Few studies have elucidated the relationship between the changes of ionic and metabolic homeostasis responses to dietary copper level. The growth performance data was obtained from 180 suckling piglets which access to different copper levels: 6 (low copper diet, LC), 20 (control diet, CON), and 300 (high copper diet, HC) mg·kg^-1 copper (based on diet, supplementation from CuSO₄), and offered ad libitum from d 14 until weaning at 40 d of age. Dietary high level copper (300 mg·kg^-1) increased the ADG and ADFI during d 14 to 28 of piglets. Six elements (Mg, Na, K, P, Cu, and Mn) concentrations significantly changes in hair among the three treatment diets. The significant increased concentrations of Na and K, and decreased concentration of Mg and Mn in 300 mg·kg^-1 than 20 mg·kg^-1 copper diet was observed. In current study, with the increase in copper level from 20 to 300 mg·kg^-1 in diet, the correlation between hair Na, K and Cu, Mn, Zn vanish. Hair Na and K were positively correlated with serum total antioxidant capacity (T-AOC) and negatively correlated with tumor necrosis factor-α (TNF-α). The hair Cu was negatively correlated with serum malondialdehyde (MDA), total bile acid (TBA). The fecal Cu was positively correlated with serum growth hormone (GH). The results suggested that the average daily gain (ADG) in 6 mg·kg^-1 copper diet and the average daily feed intake (ADFI) in 20 mg·kg^-1 copper diet were decreased than 300 mg·kg^-1 copper diet during d 14 to 28 and the ADG was decreased in 6 and 20 mg·kg^-1 copper diets in d 29 to 40 of piglets. Dietary 20 mg·kg^-1 copper maintain ion homeostasis due to increase the number of positive correlations between macroelements-microelements in hair and serum. Significantly changed Na, K, Mg, Mn and Cu concentrations in hair can reflect the adverse effects of dietary 300 mg·kg^-1 copper of suckling piglets. We believe our results may benefit people to gain a better understanding of the ion interactions and metabolic homeostasis of heavy metal elements that are critical to human and animal health.

Metabolic enhancement of the one carbon metabolism (OCM) in bovine oocytes IVM increases the blastocyst rate: evidences for a OCM checkpoint

The one carbon metabolism (OCM) has a primary role in the process of oocyte maturation. In this study bovine oocytes were cultured for 24 h, up to MII stage, with standard medium supplemented or not with 8 metabolic enhancers of the OCM and the MII and blastocyst rate were compared. Additional analyses were performed on matured oocytes, cumulus cells, zygotes and blastocysts. The OCM supplementation increased the blastocyst rate derived from in vitro fertilization. The mitochondrial mass and DNMT3a protein expression were increased whereas DNA fragmentation decreased in matured oocytes. DNA methylation in female pronucleus of zygotes was increased. The supplementation did not directly affect the redox balance as ROS and GSH in matured oocytes and homocysteine in the spent medium were unchanged. The supplementation of the oocytes with metabolic enhancers of the OCM may increase the yield from the culture, likely due to improved DNA methylation and epigenetic programming. The lack of effects on MII rate with huge differences appearing at the blastocyst stage suggest the existence of a OCM metabolic check point that hampers oocytes progression to blastocyst post-fertilization, if they were not properly primed at the time of maturation.

Neuronally produced betaine acts via a ligand-gated ion channel to control behavioral states

Trimethylglycine, or betaine, is an amino acid derivative found in diverse organisms, from bacteria to plants and animals, with well-established functions as a methyl donor and osmolyte in all cells. In addition, betaine is found in the nervous system, though its function there is not well understood. Here, we show that betaine is synthesized in the nervous system of the nematode worm, Caenorhabditis elegans, where it functions in the control of different behavioral states. Specifically, we find that betaine can be produced in a pair of interneurons, the RIMs, and packed into synaptic vesicles by the vesicular monoamine transporter, CAT-1, expressed in these cells. Mutant animals defective in betaine synthesis are unable to control the switch from local to global foraging, a phenotype that can be rescued by restoring betaine specifically to the RIM neurons. These effects on behavior are mediated by a newly identified betaine-gated chloride channel, LGC-41, which is expressed broadly in the navigation circuit. These results implicate neuronally produced betaine as a neuromodulator in vivo and suggest a potentially similar role for betaine in nervous systems of other animals.

iPLA2β-Null Mice Show HCC Protection by an Induction of Cell-Cycle Arrest after Diethylnitrosamine Treatment

Group VIA phospholipase A2 (iPLA2β) play diverse biological functions in epithelial cells and macrophages. Global deletion in iPLA2β-null (KO) mice leads to protection against hepatic steatosis in non-alcoholic fatty liver disease, in part, due to the replenishment of the loss of hepatocellular phospholipids. As the loss of phospholipids also occurs in hepatocellular carcinoma (HCC), we hypothesized that global deletion in KO mice may lead to protection against HCC. Here, HCC induced by diethylnitrosamine (DEN) was chosen because DEN causes direct injury to the hepatocytes. Male wild-type (WT) and KO mice at 3-5 weeks of age (12-13 mice/group) were subjected to a single intraperitoneal treatment with 10 mg/kg DEN, and mice were killed 12 months later. Analyses of histology, plasma cytokines, and gene expression were performed. Due to the low-dose DEN used, we observed a liver nodule in 3 of 13 WT and 2 of 12 KO mice. Only one DEN-treated WT mouse was confirmed to have HCC. DEN-treated KO mice did not show any HCC but showed suppressed hepatic expression of cell-cycle cyclinD2 and BCL2 as well as inflammatory markers IL-1β, IL-10, and VCAM-1. Notably, DEN-treated KO mice showed increased hepatic necrosis and elevated levels of plasma lactate dehydrogenase suggesting an exacerbation of liver injury. Thus, global iPLA2β deficiency in DEN-treated mice rendered HCC protection by an induction of cell-cycle arrest. Our results suggest the role of iPLA2β inhibition in HCC treatment.

One Carbon Metabolism and S-Adenosylmethionine in Non-Alcoholic Fatty Liver Disease Pathogenesis and Subtypes

One carbon metabolism (1CM) can be defined as the transfer of a carbon unit from one metabolite to another and its replenishment by different sources of labile methyl-group nutrients: primarily choline, methionine, betaine, and serine. This flow of carbon units allows the biosynthesis of nucleotides, amino acids, formylated methionyl-tRNA, polyamines, glutathione, phospholipids, detoxification reactions, maintenance of the redox status and the concentration of NAD, and methylation reactions including epigenetic modifications. That is, 1CM functions as a nutrient sensor and integrator of cellular metabolism. A critical process in 1CM is the synthesis of S-adenosylmethionine (SAMe), the source of essentially all the hundreds of millions of daily methyl transfer reactions in a cell. This versatility of SAMe imposes a tight control in its synthesis and catabolism. Much of our knowledge concerning 1CM has been gained from studies in the production and prevention of nonalcoholic fatty liver disease (NAFLD). Here, we discuss in detail the function of the most important enzymes for their quantitative contribution to maintaining the flux of carbon units through 1CM in the liver and discuss how alterations in their enzymatic activity contribute to the development of NAFLD. Next, we discuss NAFLD subtypes based on serum lipidomic profiles with different risk of cardiovascular disease. Among the latter, we highlight the so-called subtype A for its serum lipidomic profile phenocopying that of mice deficient in SAMe synthesis and because its high frequency (about 50% of the NAFLD patients).

Betaine consumption as a new clinical approach to treatment and prophylaxis of folate-related pathologies

The most important pathway in the development of folate-related pathologies is an increase in the level of homocysteine (HC). HC, a cytotoxic and neurotoxic amino acid (when its level is ≥12 μmol/L), is 1 of the most widely studied compounds in cardiology, neurobiology, oncology, and embryology for the last 20 years. Given its toxicity, the processes of endogenous detoxification of HC are of particular interest to medicine. To date, the most studied pathway is that of remethylation (the conversion of HC to methionine), with the participation of B12- and B9-dependent methionine synthase. Less studied is remethylation with the participation of the choline derivatives betaine and betaine-HC-S-methyltransferase (BHMT). Therefore, the aim of this review was to conduct a theoretical analysis of available information regarding the contribution of betaine metabolism, its enzyme, and its genetic polymorphism to folate metabolism disturbances, and the development of folate-related pathologies. This review emphasizes the potential clinical significance of 2 factors that can influence the remethylation reaction of HC: the use of betaine and identifying the BHMT gene variants and their impact on the risk for developing certain folate-related pathologies, and treatment options. Moreover, with a high level of methylation of the BHMT gene and in the presence of its low-function variants (eg, rs3733890), it is necessary to use betaine as an additional methyl donor, especially during folate therapy. More clinical research is needed to identify the effects of the different BHMT gene variants on the individual risk for folate-related pathologies to better assess the clinical significance, the need for genetic testing, and betaine consumption.

Implications of trimethylamine N-oxide (TMAO) and Betaine in Human Health: Beyond Being Osmoprotective Compounds

Osmolytes are naturally occurring small molecular weight organic molecules, which are accumulated in large amounts in all life forms to maintain the stability of cellular proteins and hence preserve their functions during adverse environmental conditions. Trimethylamine N-oxide (TMAO) and N,N,N-trimethylglycine (betaine) are methylamine osmolytes that have been extensively studied for their diverse roles in humans and have demonstrated opposing relations with human health. These osmolytes are obtained from food and synthesized endogenously using dietary constituents like choline and carnitine. Especially, gut microbiota plays a vital role in TMAO synthesis and contributes significantly to plasma TMAO levels. The elevated plasma TMAO has been reported to be correlated with the pathogenesis of numerous human diseases, including cardiovascular disease, heart failure, kidney diseases, metabolic syndrome, etc.; Hence, TMAO has been recognized as a novel biomarker for the detection/prediction of several human diseases. In contrast, betaine acts as a methyl donor in one-carbon metabolism, maintains cellular S-adenosylmethionine levels, and protects the cells from the harmful effects of increased plasma homocysteine. Betaine also demonstrates antioxidant and anti-inflammatory activities and has a promising therapeutic value in several human diseases, including homocystinuria and fatty liver disease. The present review examines the multifarious functions of TMAO and betaine with possible molecular mechanisms towards a better understanding of their emerging and diverging functions with probable implications in the prevention, diagnosis, and treatment of human diseases.

Homocysteinylation and Sulfhydration in Diseases

Homocysteine (Hcy) is an important intermediate in methionine metabolism and generation of one-carbon units, and its dysfunction is associated with many pathological states. Although Hcy is a non-protein amino acid, many studies have demonstrated protein-related homocysteine metabolism and possible mechanisms underlying homocysteinylation. Homocysteinylated proteins lose their original biological function and have a negative effect on the various disease phenotypes. Hydrogen sulfide (H₂S) has been recognized as an important gaseous signaling molecule with mounting physiological properties. H₂S modifies small molecules and proteins via sulfhydration, which is supposed to be essential in the regulation of biological functions and signal transduction in human health and disorders. This review briefly introduces Hcy and H₂S, further discusses pathophysiological consequences of homocysteine modification and sulfhydryl modification, and ultimately makes a prediction that H₂S might exert a protective effect on the toxicity of homocysteinylation of target protein via sulfhydration. The highlighted information here yields new insights into the role of protein modification by Hcy and H₂S in diseases.

Methyl Metabolism and the Clock: An Ancient Story With New Perspectives

Methylation, that is, the transfer or synthesis of a –CH₃ group onto a target molecule, is a pervasive biochemical modification found in organisms from bacteria to humans. In mammals, a complex metabolic pathway powered by the essential nutrients vitamin B9 and B12, methionine and choline, synthesizes S-adenosylmethionine, the methyl donor in the methylation of nucleic acids, proteins, fatty acids, and small molecules by over 200 substrate-specific methyltransferases described so far in humans. Methylations not only play a key role in scenarios for the origin and evolution of life, but they remain essential for the development and physiology of organisms alive today, and methylation deficiencies contribute to the etiology of many pathologies. The methylation of histones and DNA is important for circadian rhythms in many organisms, and global inhibition of methyl metabolism similarly affects biological rhythms in prokaryotes and eukaryotes. These observations, together with various pieces of evidence scattered in the literature on circadian gene expression and metabolism, indicate a close mutual interdependence between biological rhythms and methyl metabolism that may originate from prebiotic chemistry. This perspective first proposes an abiogenetic scenario for rhythmic methylations and then outlines mammalian methyl metabolism, before reanalyzing previously published data to draw a tentative map of its profound connections with the circadian clock.

Methionine cycle in nonalcoholic fatty liver disease and its potential applications

As a chronic metabolic disease affecting epidemic proportions worldwide, the pathogenesis of Nonalcoholic Fatty Liver Disease (NAFLD) is not clear yet. There is also a lack of precise biomarkers and specific medicine for the diagnosis and treatment of NAFLD. Methionine metabolic cycle, which is critical for the maintaining of cellular methylation and redox state, is involved in the pathophysiology of NAFLD. However, the molecular basis and mechanism of methionine metabolism in NAFLD are not completely understood. Here, we mainly focus on specific enzymes that participates in methionine cycle, to reveal their interconnections with NAFLD, in order to recognize the pathogenesis of NAFLD from a new angle and at the same time, explore the clinical characteristics and therapeutic strategies.

Optimal Dietary Intake Composition of Choline and Betaine Is Associated with Minimized Visceral Obesity-Related Hepatic Steatosis in a Case-Control Study

Few studies on humans have comprehensively evaluated the intake composition of methyl-donor nutrients (MDNs: choline, betaine, and folate) in relation to visceral obesity (VOB)-related hepatic steatosis (HS), the hallmark of non-alcoholic fatty liver diseases. In this case-control study, we recruited 105 patients with HS and 104 without HS (controls). HS was diagnosed through ultrasound examination. VOB was measured using a whole-body analyzer. MDN intake was assessed using a validated quantitative food frequency questionnaire. After adjustment for multiple HS risk factors, total choline intake was the most significant dietary determinant of HS in patients with VOB (Beta: -0.41, p = 0.01). Low intake of choline (<6.9 mg/kg body weight), betaine (<3.1 mg/kg body weight), and folate (<8.8 μg/kg body weight) predicted increased odds ratios (ORs) of VOB-related HS (choline: OR: 22, 95% confidence interval [CI]: 6.5-80; betaine: OR: 14, 95% CI: 4.4-50; and folate: OR: 19, 95% CI: 5.2-74). Combined high intake of choline and betaine, but not folate, was associated with an 81% reduction in VOB-related HS (OR: 0.19, 95% CI: 0.05-0.69). Our data suggest that the optimal intake of choline and betaine can minimize the risk of VOB-related HS in a threshold-dependent manner.

Gut microbiota modulates weight gain in mice after discontinued smoke exposure

Cigarette smoking constitutes a leading global cause of morbidity and preventable death¹, and most active smokers report a desire or recent attempt to quit². Smoking-cessation-induced weight gain (SCWG; 4.5 kg reported to be gained on average per 6-12 months, >10 kg year^-1 in 13% of those who stopped smoking³) constitutes a major obstacle to smoking abstinence⁴, even under stable^5,6 or restricted⁷ caloric intake. Here we use a mouse model to demonstrate that smoking and cessation induce a dysbiotic state that is driven by an intestinal influx of cigarette-smoke-related metabolites. Microbiome depletion induced by treatment with antibiotics prevents SCWG. Conversely, fecal microbiome transplantation from mice previously exposed to cigarette smoke into germ-free mice naive to smoke exposure induces excessive weight gain across diets and mouse strains. Metabolically, microbiome-induced SCWG involves a concerted host and microbiome shunting of dietary choline to dimethylglycine driving increased gut energy harvest, coupled with the depletion of a cross-regulated weight-lowering metabolite, N-acetylglycine, and possibly by the effects of other differentially abundant cigarette-smoke-related metabolites. Dimethylglycine and N-acetylglycine may also modulate weight and associated adipose-tissue immunity under non-smoking conditions. Preliminary observations in a small cross-sectional human cohort support these findings, which calls for larger human trials to establish the relevance of this mechanism in active smokers. Collectively, we uncover a microbiome-dependent orchestration of SCWG that may be exploitable to improve smoking-cessation success and to correct metabolic perturbations even in non-smoking settings.

Combined Analysis of Expression Profiles in a Mouse Model and Patients Identified BHMT2 as a New Regulator of Lipid Metabolism in Metabolic-Associated Fatty Liver Disease

Metabolic associated fatty liver disease (MAFLD) is associated with obesity, type 2 diabetes mellitus, and other metabolic syndromes. Farnesoid X receptor (FXR, NR1H4) plays a prominent role in hepatic lipid metabolism. This study combined the expression of liver genes in FXR knockout (KO) mice and MAFLD patients to identify new pathogenic pathways for MAFLD based on genome-wide transcriptional profiling. In addition, the roles of new target genes in the MAFLD pathogenic pathway were also explored. Two groups of differentially expressed genes were obtained from FXR-KO mice and MAFLD patients by transcriptional analysis of liver tissue samples. The similarities and differences between the two groups of differentially expressed genes were analyzed to identify novel pathogenic pathways and target genes. After the integration analysis of differentially expressed genes, we identified 134 overlapping genes, many of which have been reported to play an important role in lipid metabolism. Our unique analysis method of comparing differential gene expression between FXR-KO mice and patients with MAFLD is useful to identify target genes and pathways that may be strongly implicated in the pathogenesis of MAFLD. The overlapping genes with high specificity were screened using the Gene Expression Omnibus (GEO) database. Through comparison and analysis with the GEO database, we determined that BHMT2 and PKLR could be highly correlated with MAFLD. Clinical data analysis and RNA interference testing in vitro confirmed that BHMT2 may a new regulator of lipid metabolism in MAFLD pathogenesis. These results may provide new ideas for understanding the pathogenesis of MAFLD and thus provide new targets for the treatment of MAFLD.

Cross-comparison of systemic and tissue-specific metabolomes in a mouse model of Leigh syndrome

INTRODUCTION

The value of metabolomics in multi-systemic mitochondrial disease research has been increasingly recognized, with the ability to investigate a variety of biofluids and tissues considered a particular advantage. Although minimally invasive biofluids are the generally favored sample type, it remains unknown whether systemic metabolomes provide a clear reflection of tissue-specific metabolic alterations.

OBJECTIVES

Here we cross-compare urine and tissue-specific metabolomes in the Ndufs4 knockout mouse model of Leigh syndrome-a complex neurometabolic MD defined by progressive focal lesions in specific brain regions-to identify and evaluate the extent of common and unique metabolic alterations on a systemic and brain regional level.

METHODS

Untargeted and semi-targeted multi-platform metabolomics were performed on urine, four brain regions, and two muscle types of Ndufs4 KO (n≥19) vs wildtype (n≥20) mice.

RESULTS

Widespread alterations were evident in alanine, aspartate, glutamate, and arginine metabolism in Ndufs4 KO mice; while brain-region specific metabolic signatures include the accumulation of branched-chain amino acids, proline, and glycolytic intermediates. Furthermore, we describe a systemic dysregulation in one-carbon metabolism and the tricarboxylic acid cycle, which was not clearly reflected in the Ndufs4 KO brain.

CONCLUSION

Our results confirm the value of urinary metabolomics when evaluating MD-associated metabolites, while cautioning against mechanistic studies relying solely on systemic biofluids.

Protein Targets of Acetaminophen Covalent Binding in Rat and Mouse Liver Studied by LC-MS/MS

Acetaminophen (APAP) is a mild analgesic and antipyretic used commonly worldwide. Although considered a safe and effective over-the-counter medication, it is also the leading cause of drug-induced acute liver failure. Its hepatotoxicity has been linked to the covalent binding of its reactive metabolite, N-acetyl p-benzoquinone imine (NAPQI), to proteins. The aim of this study was to identify APAP-protein targets in both rat and mouse liver, and to compare the results from both species, using bottom-up proteomics with data-dependent high resolution mass spectrometry and targeted multiple reaction monitoring (MRM) experiments. Livers from rats and mice, treated with APAP, were homogenized and digested by trypsin. Digests were then fractionated by mixed-mode solid-phase extraction prior to liquid chromatography-tandem mass spectrometry (LC-MS/MS). Targeted LC-MRM assays were optimized based on high-resolution MS/MS data from information-dependent acquisition (IDA) using control liver homogenates treated with a custom alkylating reagent yielding an isomeric modification to APAP on cysteine residues, to build a modified peptide database. A list of putative in vivo targets of APAP were screened from data-dependent high-resolution MS/MS analyses of liver digests, previous in vitro studies, as well as selected proteins from the target protein database (TPDB), an online resource compiling previous reports of APAP targets. Multiple protein targets in each species were found, while confirming modification sites. Several proteins were modified in both species, including ATP-citrate synthase, betaine-homocysteine S-methyltransferase 1, cytochrome P450 2C6/29, mitochondrial glutamine amidotransferase-like protein/ES1 protein homolog, glutamine synthetase, microsomal glutathione S-transferase 1, mitochondrial-processing peptidase, methanethiol oxidase, protein/nucleic acid deglycase DJ-1, triosephosphate isomerase and thioredoxin. The targeted method afforded better reproducibility for analysing these low-abundant modified peptides in highly complex samples compared to traditional data-dependent experiments.

SLC38A4 functions as a tumour suppressor in hepatocellular carcinoma through modulating Wnt/β-catenin/MYC/HMGCS2 axis

BACKGROUND

Many molecular alterations are shared by embryonic liver development and hepatocellular carcinoma (HCC). Identifying the common molecular events would provide a novel prognostic biomarker and therapeutic target for HCC.

METHODS

Expression levels and clinical relevancies of SLC38A4 and HMGCS2 were investigated by qRT-PCR, western blot, TCGA and GEO datasets. The biological roles of SLC38A4 were investigated by functional assays. The downstream signalling pathway of SLC38A4 was investigated by qRT-PCR, western blot, immunofluorescence, luciferase reporter assay, TCGA and GEO datasets.

RESULTS

SLC38A4 silencing was identified as an oncofetal molecular event. DNA hypermethylation contributed to the downregulations of Slc38a4/SLC38A4 in the foetal liver and HCC. Low expression of SLC38A4 was associated with poor prognosis of HCC patients. Functional assays demonstrated that SLC38A4 depletion promoted HCC cellular proliferation, stemness and migration, and inhibited HCC cellular apoptosis in vitro, and further repressed HCC tumorigenesis in vivo. HMGCS2 was identified as a critical downstream target of SLC38A4. SLC38A4 increased HMGCS2 expression via upregulating AXIN1 and repressing Wnt/β-catenin/MYC axis. Functional rescue assays showed that HMGCS2 overexpression reversed the oncogenic roles of SLC38A4 depletion in HCC.

CONCLUSIONS

SLC38A4 downregulation was identified as a novel oncofetal event, and SLC38A4 was identified as a novel tumour suppressor in HCC.

Transcriptomic analysis links hepatocellular carcinoma (HCC) in HZE ion irradiated mice to a human HCC subtype with favorable outcomes

High-charge, high-energy ion particle (HZE) radiations are extraterrestrial in origin and characterized by high linear energy transfer (high-LET), which causes more severe cell damage than low-LET radiations like γ-rays or photons. High-LET radiation poses potential cancer risks for astronauts on deep space missions, but the studies of its carcinogenic effects have relied heavily on animal models. It remains uncertain whether such data are applicable to human disease. Here, we used genomics approaches to directly compare high-LET radiation-induced, low-LET radiation-induced and spontaneous hepatocellular carcinoma (HCC) in mice with a human HCC cohort from The Cancer Genome Atlas (TCGA). We identified common molecular pathways between mouse and human HCC and discovered a subset of orthologous genes (mR-HCC) that associated high-LET radiation-induced mouse HCC with a subgroup (mrHCC2) of the TCGA cohort. The mrHCC2 TCGA cohort was more enriched with tumor-suppressing immune cells and showed a better prognostic outcome than other patient subgroups.

Ability of dietary factors to affect homocysteine levels in mice: a review

Homocysteine is associated with several diseases, and a series of dietary factors are known to modulate homocysteine levels. As mice are often used as model organisms to study the effects of dietary hyperhomocysteinemia, we collected data about concentrations of vitamin B₁₂, vitamin B₆, folate, methionine, cystine, and choline in mouse diets and the associated plasma/serum homocysteine levels. In addition, we more closely examined the composition of the control diet, the impact of the mouse strain, sex and age, and the duration of the dietary intervention on homocysteine levels. In total, 113 out of 1103 reviewed articles met the inclusion criteria. In the experimental and control diets, homocysteine levels varied from 0.1 to 280 µmol/l. We found negative correlations between dietary vitamin B₁₂ (rho = − 0.125; p < 0.05), vitamin B₆ (rho = − 0.191; p < 0.01) and folate (rho = − 0.395; p < 0.001) and circulating levels of homocysteine. In contrast, a positive correlation was observed between dietary methionine and homocysteine (methionine: rho = 0.146; p < 0.05). No significant correlations were found for cystine or choline and homocysteine levels. In addition, there was no correlation between the duration of the experimental diets and homocysteine levels. More importantly, the data showed that homocysteine levels varied widely in mice fed control diets as well. When comparing control diets with similar nutrient concentrations (AIN-based), there were significant differences in homocysteine levels caused by the strain (ANOVA, p < 0.05) and age of the mice at baseline (r = 0.47; p < 0.05). When comparing homocysteine levels and sex, female mice tended to have higher homocysteine levels than male mice (9.3 ± 5.9 µmol/l vs. 5.8 ± 4.5 µmol/l; p = 0.069). To conclude, diets low in vitamin B₁₂, vitamin B₆, or folate and rich in methionine are similarly effective in increasing homocysteine levels. AIN recommendations for control diets are adequate with respect to the amounts of homocysteine-modulating dietary parameters. In addition, the mouse strain and the age of mice can affect the homocysteine level.

Thiamethoxam induces nonalcoholic fatty liver disease in mice via methionine metabolism disturb via nicotinamide N-methyltransferase overexpression

Thiamethoxam (TMX) is one of the major compounds of neonicotinoids, the most widely used class of insecticides worldwide. Previously, TMX was considered a non-toxic neonicotinoid insecticide to mammals. However, the genotoxicity, cytotoxicity, and hepatotoxicity of TMX in mammals were recently reported. Thus far, the effects of TMX on the mouse liver and its detailed mechanism remain unclear. NNMT, strongly expressed in the liver, plays a critical role in body energy expenditure. To confirm the potential pathogenesis of liver dysfunction induced by TMX, ICR mice were exposed to TMX at a dose of 4 mg/kg and 20 mg/kg by gavage administration for 12 weeks. The data showed that chronic TMX exposure caused dyslipidemia and nonalcoholic fatty liver disease (NAFLD) in mice. Moreover, aggravated oxidative stress, dysfunction, and disorganized structure were also observed in TMX-treated mouse livers. In addition, increases of PPARγ, fatty acid synthase, and NNMT expression, as well as decreases of PPARα and GNMT expression, S-adenosylmethionine deficiency, and methionine metabolism disorder were also observed in TMX-treated mouse livers. These results suggest that chronic TMX exposure induces dyslipidemia and NAFLD in mice. Moreover, inhibition of NNMT in hepatocytes significantly reversed the effects of TMX. The molecular mechanism of TMX-induced NAFLD is mostly through NNMT-mediated methionine metabolism and methyl donor balance, which ultimately regulates PPARα signaling pathway. Inhibition of NNMT could be a potentially novel strategy for blocking the progression of NAFLD induced by TMX.

Tumor methionine metabolism drives T-cell exhaustion in hepatocellular carcinoma

T-cell exhaustion denotes a hypofunctional state of T lymphocytes commonly found in cancer, but how tumor cells drive T-cell exhaustion remains elusive. Here, we find T-cell exhaustion linked to overall survival in 675 hepatocellular carcinoma (HCC) patients with diverse ethnicities and etiologies. Integrative omics analyses uncover oncogenic reprograming of HCC methionine recycling with elevated 5-methylthioadenosine (MTA) and S-adenosylmethionine (SAM) to be tightly linked to T-cell exhaustion. SAM and MTA induce T-cell dysfunction in vitro. Moreover, CRISPR-Cas9-mediated deletion of MAT2A, a key SAM producing enzyme, results in an inhibition of T-cell dysfunction and HCC growth in mice. Thus, reprogramming of tumor methionine metabolism may be a viable therapeutic strategy to improve HCC immunity.

Intratumoral CD8+ T cells commonly display a dysfunctional state, however it remains unclear whether tumor cell metabolism actively promotes T-cell exhaustion. Here, the authors show that the tumor methionine recycling pathway has a central role in promoting T-cell dysfunction in hepatocellular carcinoma, contributing to tumor immune evasion.

Tumor methionine metabolism drives T-cell exhaustion in hepatocellular carcinoma

T-cell exhaustion denotes a hypofunctional state of T lymphocytes commonly found in cancer, but how tumor cells drive T-cell exhaustion remains elusive. Here, we find T-cell exhaustion linked to overall survival in 675 hepatocellular carcinoma (HCC) patients with diverse ethnicities and etiologies. Integrative omics analyses uncover oncogenic reprograming of HCC methionine recycling with elevated 5-methylthioadenosine (MTA) and S-adenosylmethionine (SAM) to be tightly linked to T-cell exhaustion. SAM and MTA induce T-cell dysfunction in vitro. Moreover, CRISPR-Cas9-mediated deletion of MAT2A, a key SAM producing enzyme, results in an inhibition of T-cell dysfunction and HCC growth in mice. Thus, reprogramming of tumor methionine metabolism may be a viable therapeutic strategy to improve HCC immunity.

Urine proteomics analysis of patients with neuronal ceroid lipofuscinoses

The neuronal ceroid lipofuscinoses (NCL) are a group of 13 rare neurodegenerative disorders characterized by accumulation of cellular storage bodies. There are few therapeutic options, and existing tests do not monitor disease progression and treatment response. However, urine biomarkers could address this need. Proteomic analysis of CLN2 patient urine revealed activation of immune response pathways and pathways associated with the unfolded protein response. Analysis of CLN5 and CLN6 sheep model urine showed subtle changes. To confirm and investigate the relevance of candidate biomarkers a targeted LC-MS/MS proteomic assay was created. We applied this assay to additional CLN2 samples as well as other patients with NCL (CLN1, CLN3, CLN5, CLN6, and CLN7) and demonstrated that hexosaminidase-A, aspartate aminotransferase-1, and LAMP1 are increased in NCL samples and betaine-homocysteine S-methyltransferase-1 was specifically increased in patients with CLN2. These proteins could be used to monitor the effectiveness of future therapies aimed at treating systemic NCL disease.

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The urine proteome is altered in humans and animals with NCL

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Hexosaminidase A and LAMP1 are increased in patients with NCL

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Betaine-homocysteine S-methyltransferase 1 is elevated in CLN2 patients

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Proteins altered in CLN5 and CLN6 sheep models are not affected in humans