One-carbon Metabolism Pathway Research Articles

Fat and proteolysis due to methionine, tryptophan, and niacin deficiency leads to alterations in gut microbiota and immune modulation in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is one of the intractable diseases. Nutritional components associated with IBD have been identified, and it is known that excessive methionine intake exacerbates inflammation, and that tryptophan metabolism is involved in inflammation. Analysis of the gut microbiota has also progressed, where Lactobacillus regulate immune cells in the intestine and suppress inflammation. However, whether the methionine and tryptophan metabolic pathways affect the growth of intestinal Lactobacillus is unknown. Here we show how transient methionine, tryptophan, and niacin deficiency affects the host and gut microbiota in mouse models of colitis (induced by dextran sodium sulfate) fed a methionine-deficient diet (1K), tryptophan and niacin-deficient diet (2K), or methionine, tryptophan, and niacin-deficient diet (3K). These diets induced body weight decrease and 16S rRNA analysis of mouse feces revealed the alterations in the gut microbiota, leading to a dramatic increase in the proportion of Lactobacillus in mice. Intestinal RNA sequencing data confirmed that the expression of several serine proteases and fat-metabolizing enzymes were elevated in mice fed with methionine, tryptophan, and niacin (MTN) deficient diet. In addition, one-carbon metabolism and peroxisome proliferator-activated receptor (PPAR) pathway activation were also induced with MTN deficiency. Furthermore, changes in the expression of various immune-related cytokines were observed. These results indicate that methionine, tryptophan, and niacin metabolisms are important for the composition of intestinal bacteria and host immunity. Taken together, MTN deficiencies may serve as a Great Reset of gut microbiota and host gene expression to return to good health.

Abstract 2756: Single cell analysis reveals treatment response-associated plastic cell state and lineage switching in aggressive variant prostate cancer

Abstract Prostate cancer (PCa) is a common malignancy in men over 65, ranking as the second leading cause of cancer-related deaths among men in the United States. While most prostate cancers respond to androgen receptor (AR) targeting therapies, Aggressive Variant Prostate Cancers (AVPCs), characterized by RB1, Tp53, and/or PTEN alterations, do not. AVPCs exhibit lineage plasticity in preclinical models, enabling the expression of non-prostate epithelial lineage markers to adapt to therapeutic pressures. However, a measurable definition of lineage plasticity as a potential therapeutic target for clinical trials is currently lacking. To arrive at said definition, we perform single-nuclei RNA sequencing (snRNA-seq) on lymph node metastases from twelve AVPC patients with matched sample pairs of both pre- and post-treatment. Additionally, we include snRNA-seq data from eight non-AVPC patients as a baseline. Expanding upon our prior establishment of tumor-specific total mRNA expression (TmS) as an indicator of tumor cell lineage plasticity (Nature Biotechnology, PMID: 35697807), we employ unique molecular identifier (UMI) counts from individual cells to quantify this plasticity. We reveal a distinct cluster of tumor cells with notably high UMI counts in resistant samples, indicative of a less differentiated state and increased transcriptional diversity. This high-UMI cluster is marked by significant enrichment in pathways associated with epithelial-mesenchymal transition (EMT), stemness, one-carbon metabolism, and arginine metabolism pathways. Concurrently, there is a reduction in activity within the androgen receptor (AR) and DNA damage repair pathways. These characteristics suggest an enhanced capacity for lineage switching in AVPC tumor cells, potentially contributing to evasion from targeted therapies. Moreover, immune components within resistant samples consistently display lower UMI counts, indicating a diminished propensity for lineage plasticity. In conclusion, we present a better understanding of lineage switching in therapeutic resistance in AVPCs, paving the way for novel treatment strategies in PCa management. Citation Format: Shuai Guo, Elavarasan Subramani, Daniel E. Frigo, Patrick G. Pilié, Sangeeta Goswami, Rama Soundararajan, Ana Aparicio, Wenyi Wang. Single cell analysis reveals treatment response-associated plastic cell state and lineage switching in aggressive variant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2756.

Serine synthesis and catabolism in starved lung cancer and primary bronchial epithelial cells

Serine and glycine give rise to important building blocks in proliferating cells. Both amino acids are either synthesized de novo or taken up from the extracellular space. In lung cancer, serine synthesis gene expression is variable, yet, expression of the initial enzyme, phosphoglycerate dehydrogenase (PHGDH), was found to be associated with poor prognosis. While the contribution of de novo synthesis to serine pools has been shown to be enhanced by serine starvation, the impact of glucose deprivation, a commonly found condition in solid cancers is poorly understood. Here, we utilized a stable isotopic tracing approach to assess serine and glycine de novo synthesis and uptake in different lung cancer cell lines and normal bronchial epithelial cells in variable serine, glycine, and glucose conditions. Under low glucose supplementation (0.2 mM, 3–5% of normal plasma levels), serine de novo synthesis was maintained or even activated. As previously reported, also gluconeogenesis supplied carbons from glutamine to serine and glycine under these conditions. Unexpectedly, low glucose treatment consistently enhanced serine to glycine conversion, along with an up-regulation of the mitochondrial one-carbon metabolism enzymes, serine hydroxymethyltransferase (SHMT2) and methylenetetrahydrofolate dehydrogenase (MTHFD2). The relative contribution of de novo synthesis greatly increased in low serine/glycine conditions. In bronchial epithelial cells, adaptations occurred in a similar fashion as in cancer cells, but serine synthesis and serine to glycine conversion, as assessed by label enrichments and gene expression levels, were generally lower than in (PHGDH positive) cancer cells. In summary, we found a variable contribution of glucose or non-glucose carbon sources to serine and glycine and a high adaptability of the downstream one-carbon metabolism pathway to variable glucose supply.

Global DNA Methylation Levels Viz-a-Viz Genetic and Biochemical Variations in One Carbon Metabolic Pathway: An Exploratory Study from North India.

Despite the importance of one carbon metabolic pathway (OCMP) in modulating the DNA methylation process, only a few population-based studies have explored their relationship among healthy individuals. This study aimed to understand the variations in global DNA methylation levels with respect to selected genetic (CBS 844ins68, MTRR A66G, MTR A2756G, and MTHFR C677T polymorphisms) and biochemical (folate, vitamin B12, and homocysteine) markers associated with OCMP among healthy North Indian adults. The study has been conducted among 1095 individuals of either sex (69.5% females), aged 30-75 years. A sample of 5 mL of blood was collected from each participant. Homocysteine, folate, and vitamin B12 levels were determined using the chemiluminescence technique. Restriction digestion was performed for genotyping MTRR A66G, MTR A2756G, and MTHFR C677T polymorphisms and allele-specific PCR amplification for CBS 844ins68 polymorphism. Global DNA methylation levels were analyzed using ELISA-based colorimetric technique. Of the selected genetic and biochemical markers, the mutant MTRR A66G allele was positively associated with global DNA methylation levels. Further, advanced age was inversely associated with methylation levels. MTRR 66GG genotype group was hypermethylated than other genotypes in folate replete and vitamin B12 deficient group (a condition prevalent among vegetarians), suggesting that the G allele may be more efficient than the wild-type allele in such conditions. Global DNA methylation levels appeared to be more influenced by genetic than biochemical factors. MTRR 66G allele may have a selective advantage in vitamin B12 deficient conditions. Further research should be undertaken to understand how genetics affects epigenetic processes.

The functional roles of S-adenosyl-methionine and S-adenosyl-homocysteine and their involvement in trisomy 21.

The one-carbon metabolism pathway is involved in critical human cellular functions such as cell proliferation, mitochondrial respiration, and epigenetic regulation. In the homocysteine-methionine cycle S-adenosyl-methionine (SAM) and S-adenosyl-homocysteine (SAH) are synthetized, and their levels are finely regulated to ensure proper functioning of key enzymes which control cellular growth and differentiation. Here we review the main biological mechanisms involving SAM and SAH and the known related human diseases. It was recently demonstrated that SAM and SAH levels are altered in plasma of subjects with trisomy 21 (T21) but how this metabolic dysregulation influences the clinical manifestation of T21 phenotype has not been previously described. This review aims at providing an overview of the biological mechanisms which are altered in response to changes in the levels of SAM and SAH observed in DS.

Abstract WP251: Dietary Methionine and Homocysteine Level Interaction and Recurrent Stroke

Background: The folate one-carbon metabolism pathway (FOCM) provides vital one-carbon units for epigenetic regulation. Genetic variants in FOCM genes may affect methionine metabolism. Elevated circulating homocysteine (Hcy), a FOCM byproduct, is linked to increased stroke risk. However, the protective effects of dietary regulation of methionine and Hcy levels against recurrent stroke are uncertain. Objective: To investigate dietary methionine (METH) and its interaction with post-methionine load Hcy levels (POST) with recurrent stroke risk; to assess if genetically determined POST and its interaction with METH predict recurrent stroke risk. Methods: We utilized the Vitamin Intervention for Stroke Prevention (VISP) trial to estimate hazards ratios of METH and its interaction with POST on recurrent stroke with a Cox proportional hazards model. We also generated a POST polygenic risk score (PRS) with ridge regression using previously identified polymorphisms, located within ALDH1L1, CPS1, GNMT, and PSPH, as indicators of FOCM function. Results: The participants (n = 2,100; 64% men) had a mean (SD) age of 67 (11) years. Ancestry consisted of 82% European, 12% African, and 5.7% Other. A small portion of participants had missing POST values (7.3%). Clinical POST (HR 1.02; 95%CI 0.98, 1.06) and its interaction with METH (HR 0.99; 95% CI 0.97, 1.01) were not associated with recurrent stroke risk. Similarly, there was no significant relationship observed between PRS POST (HR 0.96; 95%CI 0.80, 1.15) and its interaction with METH (HR 1.02; 95% CI 0.94, 1.10). Conclusion: Dietary methionine and post-methionine load Hcy levels neither interact nor predict recurrent stroke risk. Our PRS approach showed similar negative findings. The relationship of the FOCM and recurrent stroke risk may lie in epigenetics.

LAT1-dependent placental methionine uptake is a key player in fetal programming of metabolic disease

The Developmental Origins of Health and Disease hypothesis sustains that exposure to different stressors during prenatal development prepares the offspring for the challenges to be encountered after birth. We studied the gestational period as a particularly vulnerable window where different stressors can have strong implications for fetal programming of the offspring's life-long metabolic status via alterations of specific placentally expressed nutrient transporters. To study this mechanism, we used a murine prenatal stress model, human preeclampsia, early miscarriage, and healthy placental tissue samples, in addition to in vitro models of placental cells. In stressed mice, placental overexpression of L-type amino acid transporter 1 (Lat1) and subsequent global placental DNA hypermethylation was accompanied by fetal and adult hypothalamic dysregulation in global DNA methylation and gene expression as well as long-term metabolic abnormalities exclusively in female offspring. In human preeclampsia, early miscarriage, and under hypoxic conditions, placental LAT1 was significantly upregulated, leading to increased methionine uptake and global DNA hypermethylation. Remarkably, subgroups of healthy term placentas with high expression of stress-related genes presented increased levels of placental LAT1 mRNA and protein, DNA and RNA hypermethylation, increased methionine uptake capacity, one-carbon metabolic pathway disruption, higher methionine concentration in the placenta and transport to the fetus specifically in females. Since LAT1 mediates the intracellular accumulation of methionine, global DNA methylation, and one-carbon metabolism in the placenta, our findings hint at a major sex-specific global response to a variety of prenatal stressors affecting placental function, epigenetic programming, and life-long metabolic disease and provide a much-needed insight into early-life factors predisposing females/women to metabolic disorders.

Metagenomic Characterisation of the Gut Microbiome and Effect of Complementary Feeding on Bifidobacterium spp. in Australian Infants.

Complementary feeding induces dramatic ecological shifts in the infant gut microbiota toward more diverse compositions and functional metabolic capacities, with potential implications for immune and metabolic health. The aim of this study was to examine whether the age at which solid foods are introduced differentially affects the microbiota in predominantly breastfed infants compared with predominantly formula-fed infants. We performed whole-genome shotgun metagenomic sequencing of infant stool samples from a cohort of six-month-old Australian infants enrolled in a nested study within the ORIGINS Project longitudinal birth cohort. Infants born preterm or those who had been administered antibiotics since birth were excluded. The taxonomic composition was highly variable among individuals at this age. Predominantly formula-fed infants exhibited a higher microbiome diversity than predominantly breastfed infants. Among the predominantly breastfed infants, the introduction of solid foods prior to five months of age was associated with higher alpha diversity than solid food introduction after six months of age, primarily due to the loss of Bifidobacterium infantis. In contrast, the age at which solid food was introduced was not associated with the overall change in diversity among predominantly formula-fed infants but was associated with compositional changes in Escherichia abundance. Examining the functional capacity of the microbiota in relation to these changes, we found that the introduction of solid foods after six months of age was associated with elevated one-carbon compound metabolic pathways in both breastfed and formula-fed infants, although the specific metabolic sub-pathways differed, likely reflecting different taxonomic compositions. Our findings suggest that the age of commencement of solid foods influences the gut microbiota composition differently in predominantly breastfed infants than in predominantly formula-fed infants.

Exploring the complexities of 1C metabolism: implications in aging and neurodegenerative diseases.

The intricate interplay of one-carbon metabolism (OCM) with various cellular processes has garnered substantial attention due to its fundamental implications in several biological processes. OCM serves as a pivotal hub for methyl group donation in vital biochemical reactions, influencing DNA methylation, protein synthesis, and redox balance. In the context of aging, OCM dysregulation can contribute to epigenetic modifications and aberrant redox states, accentuating cellular senescence and age-associated pathologies. Furthermore, OCM's intricate involvement in cancer progression is evident through its capacity to provide essential one-carbon units crucial for nucleotide synthesis and DNA methylation, thereby fueling uncontrolled cell proliferation and tumor development. In neurodegenerative disorders like Alzheimer's and Parkinson's, perturbations in OCM pathways are implicated in the dysregulation of neurotransmitter synthesis and mitochondrial dysfunction, contributing to disease pathophysiology. This review underscores the profound impact of OCM in diverse disease contexts, reinforcing the need for a comprehensive understanding of its molecular complexities to pave the way for targeted therapeutic interventions across inflammation, aging and neurodegenerative disorders.

Oxidative stress-initiated one-carbon metabolism drives the generation of interleukin-10-producing B cells to resolve pneumonia.

The metabolic reprogramming underlying the generation of regulatory B cells during infectious diseases remains unknown. Using a Pseudomonas aeruginosa-induced pneumonia model, we reported that IL-10-producing B cells (IL-10+ B cells) play a key role in spontaneously resolving infection-mediated inflammation. Accumulated cytosolic reactive oxygen species (ROS) during inflammation were shown to drive IL-10+ B-cell generation by remodeling one-carbon metabolism. Depletion of the enzyme serine hydroxymethyltransferase 1 (Shmt1) led to inadequate one-carbon metabolism and decreased IL-10+ B-cell production. Furthermore, increased one-carbon flux elevated the levels of the methyl donor S-adenosylmethionine (SAM), altering histone H3 lysine 4 methylation (H3K4me) at the Il10 gene to promote chromatin accessibility and upregulate Il10 expression in B cells. Therefore, the one-carbon metabolism-associated compound ethacrynic acid (EA) was screened and found to potentially treat infectious pneumonia by boosting IL-10+ B-cell generation. Overall, these findings reveal that ROS serve as modulators to resolve inflammation by reprogramming one-carbon metabolism pathways in B cells.

Optic disc edema during strict 6° head-down tilt bed rest is related to one-carbon metabolism pathway genetics and optic cup volume

Some astronauts on International Space Station missions experience neuroophthalmological pathologies as part of spaceflight associated neuro-ocular syndrome (SANS). Strict head-down tilt bed rest (HDTBR) is a spaceflight analog that replicates SANS findings and those who had 3–4 risk alleles (G and C alleles from the methionine synthase reductase [MTRR] A66G and serine hydroxymethyltransferase [SHMT1] C1420T, respectively) as compared to 1-2 risk alleles, had a greater increase in total retinal thickness (TRT). The objective of this study was to identify factors that contribute to the individual variability of the development of SANS in a 60 d HDTBR at the German Aerospace Center’s:envihab facility, Cologne Germany. 22 of 24 subjects who participated in the HDTBR study provided blood samples for genetic analysis. Total retinal thickness and optic cup volume were measured before and after bed rest. Subjects with 3–4 versus 0-2 risk alleles had greater ΔTRT during and after bed rest, and the model improved with the addition of baseline optic cup volume. This bed rest study confirms that variants of MTRR and SHMT1 are associated with ocular pathologies. Subjects with more risk alleles had the greatest HDTBR-induced ΔTRT, reaffirming that genetics predispose some individuals to developing SANS. Preflight optic cup volume and genetics better predict ΔTRT than either one alone. Whether nutritional supplements can override the genetic influences on biochemistry, physiology, and pathophysiology remains to be tested. These findings have significant implications for both aerospace and terrestrial medicine.

Exploring the Interplay Between Vitamin B12-related Biomarkers, DNA Methylation, and Gene-Nutrition Interaction in Esophageal Precancerous Lesions

Vitamin B12 depletion has been suggested to be associated with esophageal precancerous lesions (EPL). However, the potential mechanisms remain unclear. This study aims to evaluate the role of vitamin B12 and its regulated epigenetic modification in EPL and provide preliminary information on the identification of potential molecular biomarkers for the early prediction of EPL. We collected information and samples from the Early Diagnosis and Early Treatment Project of Esophageal Cancer database from 200 EPL cases and 200 matched controls. Vitamin B12, one-carbon metabolism biomarkers, genetic polymorphism of TCN2 C776G, and DNA methylation were compared. Preliminarily identified candidate promoters of differentially methylated CpG positions were further verified by targeted bisulfite sequencing. EPL cases had significantly lower serum levels of vitamin B12 and transcobalamin II, and higher serum levels of homocysteine and 5-methyltetrahydrofolate than controls. The TCN2 C776G polymorphism was found to be associated with susceptibility to EPL and may interact with vitamin B12 nutritional status to influence the risk of EPL in male subjects. In addition, global hypomethylation related to vitamin B12 depletion was observed in EPL cases, along with region-specific hypermethylation of UGT2B15 and FGFR2 promoters. This study suggests that vitamin B12 depletion may be associated with aberrant DNA methylation and increased risk of EPL through the one-carbon metabolism pathway, presents that the TCN2 C776G polymorphism may interact with vitamin B12 nutritional status to affect EPL risk in males, and also identifies specific locations in the UGT2B15 and FGFR2 promoters with potential as promising molecular biomarkers.

Anaplastic thyroid cancer cells upregulate mitochondrial one-carbon metabolism to meet purine demand, eliciting a critical targetable vulnerability

Anaplastic thyroid cancer (ATC) is one of the most aggressive and lethal tumor types, characterized by loss of differentiation, epithelial-to-mesenchymal transition, extremely high proliferation rate, and generalized resistance to therapy. To identify novel relevant, targetable molecular alterations, we analyzed gene expression profiles from a genetically engineered ATC mouse model and from human patient datasets, and found consistent upregulation of genes encoding enzymes involved in the one-carbon metabolic pathway, which uses serine and folates to generate both nucleotides and glycine.Genetic and pharmacological inhibition of SHMT2, a key enzyme of the mitochondrial arm of the one-carbon pathway, rendered ATC cells glycine auxotroph and led to significant inhibition of cell proliferation and colony forming ability, which was primarily caused by depletion of the purine pool. Notably, these growth-suppressive effects were significantly amplified when cells were grown in the presence of physiological types and levels of folates. Genetic depletion of SHMT2 dramatically impaired tumor growth in vivo, both in xenograft models and in an immunocompetent allograft model of ATC.Together, these data establish the upregulation of the one-carbon metabolic pathway as a novel and targetable vulnerability of ATC cells, which can be exploited for therapeutic purposes.

Association of the DNA Methylation of Obesity-Related Genes with the Dietary Nutrient Intake in Children.

The occurrence of obesity stems from both genetic and external influences. Despite thorough research and attempts to address it through various means such as dietary changes, physical activity, education, and medications, a lasting solution to this widespread problem remains elusive. Nutrients play a crucial role in various cellular processes, including the regulation of gene expression. One of the mechanisms by which nutrients can affect gene expression is through DNA methylation. This modification can alter the accessibility of DNA to transcription factors and other regulatory proteins, thereby influencing gene expression. Nutrients such as folate and vitamin B12 are involved in the one-carbon metabolism pathway, which provides the methyl groups necessary for DNA methylation. Studies have shown that the inadequate intake of these nutrients can lead to alterations in DNA methylation patterns. For this study, we aim to understand the differences in the association of the dietary intake between normal weight and overweight/obese children and between European American and African American children with the DNA methylation of the three genes NRF1, FTO, and LEPR. The research discovered a significant association between the nutritional intake of 6-10-years-old children, particularly the methyl donors present in their diet, and the methylation of the NRF1, FTO, and LEPR genes. Additionally, the study emphasizes the significance of considering health inequalities, particularly family income and maternal education, when investigating the epigenetic impact of methyl donors in diet and gene methylation.

Differential effects of bariatric surgery and caloric restriction on hepatic one-carbon and fatty acid metabolism

Weight loss interventions, including dietary changes, pharmacotherapy, or bariatric surgery, prevent many of the adverse consequences of obesity, and may also confer intervention-specific benefits beyond those seen with decreased weight alone. We compared the molecular effects of different interventions on liver metabolism to understand the mechanisms underlying these benefits. Male rats on a high-fat, high-sucrose diet underwent sleeve gastrectomy (SG) or intermittent fasting with caloric restriction (IF-CR), achieving equivalent weight loss. The interventions were compared to ad-libitum (AL)-fed controls. Analysis of liver and blood metabolome and transcriptome revealed distinct and sometimes contrasting metabolic effects between the two interventions. SG primarily influenced one-carbon metabolic pathways, whereas IF-CR increased de novo lipogenesis and glycogen storage. These findings suggest that the unique metabolic pathways affected by SG and IF-CR contribute to their distinct clinical benefits, with bariatric surgery potentially influencing long-lasting changes through its effect on one-carbon metabolism.

One-carbon metabolism and microbial pathogenicity.

One-carbon metabolism (OCM) pathways are responsible for several functions, producing a number of one-carbon unit intermediates (formyl, methylene, methenyl, methyl) that are required for the synthesis of various amino acids and other biomolecules such as purines, thymidylate, redox regulators, and, in most microbes, folate. As humans must acquire folate from the diet, folate production is a target for antimicrobials such as sulfonamides. OCM impacts the regulation of microbial virulence such that in a number of instances, limiting the availability of para-aminobenzoic acid (pABA), an essential OCM precursor, causes a reduction in pathogenicity. Porphyromonas gingivalis, however, displays increased pathogenicity in response to lower pABA levels, and exogenous pABA exerts a calming influence on heterotypic communities of P. gingivalis with pABA-producing partner species. Differential responses to pABA may reflect both the physiology of the organisms and their host microenvironment. OCM plays an integral role in regulating the global rate of protein translation, where the alarmones ZMP and ZTP sense insufficient stores of intracellular folate and coordinate adaptive responses to compensate and restore folate to sufficient levels. The emerging interconnections between OCM, protein synthesis, and context-dependent pathogenicity provide novel insights into the dynamic host-microbe interface.

SHMT2 Promotes Gastric Cancer Development through Regulation of HIF1α/VEGF/STAT3 Signaling.

The metabolic enzymes involved in one-carbon metabolism are closely associated with tumor progression and could be potential targets for cancer therapy. Recent studies showed that serine hydroxymethyltransferase 2 (SHMT2), a crucial enzyme in the one-carbon metabolic pathway, plays a key role in tumor proliferation and development. However, the precise role and function of SHMT2 in gastric cancer (GC) remain poorly understood. In this study, we presented evidence that SHMT2 was necessary for hypoxia-inducible factor-1α (HIF1α) stability and contributed to GC cells' hypoxic adaptation. The analysis of datasets retrieved from The Cancer Genome Atlas and the experimentation with human cell lines revealed a marked increase in SHMT2 expression in GC. The SHMT2 knockdown in MGC803, SGC7901, and HGC27 cell lines inhibited cell proliferation, colony formation, invasion, and migration. Notably, SHMT2 depletion disrupted redox homeostasis and caused glycolytic function loss in GC cells under hypoxic circumstances. Mechanistically, we discovered SHMT2 modulated HIF1α stability, which acted as a master regulator of hypoxia-inducible genes under hypoxic conditions. This, in turn, regulated the downstream VEGF and STAT3 pathways. The in vivo xenograft experiments showed that SHMT2 knockdown markedly reduced GC growth. Our results elucidate the novel function of SHMT2 in stabilizing HIF1α under hypoxic conditions, thus providing a potential therapeutic strategy for GC treatment.

Abstract 6449: Association between dietary one-carbon metabolism-related nutrients and the risk of colorectal cancer: Findings from the Singapore Chinese Health Study

Abstract Background. Colorectal cancer (CRC) is a commonly diagnosed subtype of cancer with a high mortality rate. One-carbon metabolism is a set of complex pathways, responsible for providing methyl group for DNA synthesis, repair and methylation. Adequate DNA methylation maintains chromosome stability and prevents gene disruption. Diet is a major source for key substrates and co-factors (i.e., vitamin B6, choline and folate) involved in one-carbon metabolism. A majority of epidemiologic studies that have evaluated one-carbon metabolism-related nutrients in relation to CRC risk have focused on the potential role of folate only. Due to the involvement of multiple nutrients and the complexity of one-carbon metabolism pathways, a comprehensive assessment of the nutrients involved and their associations with CRC risk is needed. The purpose of the current analysis was therefore to evaluate the association between one-carbon metabolism-related nutrients with the risk of developing CRC using the Singapore Chinese Health Study (SCHS). Methods. The SCHS is an on-going population-based prospective cohort study that includes 61,321 Chinese men and women in Singapore who were 45-74 years of age at baseline. A 165-item semi-quantitative food frequency questionnaire was used to obtain information of dietary intake. Cox proportional hazard regression models were used to estimate the hazard ratios (HRs) and respective 95% confidence intervals (CIs) for CRC associated with one-carbon metabolism-related nutrients, including thiamine, riboflavin, niacin, vitamin B6, folate acid, vitamin B12, choline, methionine, and betaine, adjusting for potential confounders. Results. After an average of 17.5 years of follow-up, 2,140 participants developed CRC. An inverse association between folate acid and colon cancer. The HRs and respective 95% CIs for quarters 2, 3 and 4 vs. quarter 1 (the lowest quartile) was 0.98 (0.84-1.14), 0.93 (0.79-1.10) and 0.80 (0.64-0.98) (Ptrend=0.04). Similar pattern was observed between folate acid intake and colon cancer risk among never smokers (HRQ4vsQ1=0.67, 95% CI: 0.51-0.86; Ptrend=0.005). No association was found between other one-carbon metabolism-related nutrients and the risk of colorectal cancer Conclusions. In a large on-going prospective cohort study of more than 61,000 Chinese Singaporeans, we found inverse associations between dietary folate acid and the risk of colon cancer. This association was more obvious among never smokers. Our findings provide critical implication for primary prevention and control of colorectal cancer. Citation Format: Yen Thi-Hai Pham, Aizhen Jin, Renwei Wang, Woon-Puay Koh, Jian-Min Yuan, Hung N. Luu. Association between dietary one-carbon metabolism-related nutrients and the risk of colorectal cancer: Findings from the Singapore Chinese Health Study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6449.

Interactions of SNPs in Folate Metabolism Related Genes on Prostate Cancer Aggressiveness in European Americans and African Americans.

Studies showed that folate and related single nucleotide polymorphisms (SNPs) could predict prostate cancer (PCa) risk. However, little is known about the interactions of folate-related SNPs associated with PCa aggressiveness. The study's objective is to evaluate SNP-SNP interactions among the DHFR 19-bp polymorphism and 10 SNPs in folate metabolism and the one-carbon metabolism pathway associated with PCa aggressiveness. We evaluated 1294 PCa patients, including 690 European Americans (EAs) and 604 African Americans (AAs). Both individual SNP effects and pairwise SNP-SNP interactions were analyzed. None of the 11 individual polymorphisms were significant for EAs and AAs. Three SNP-SNP interaction pairs can predict PCa aggressiveness with a medium to large effect size. For the EA PCa patients, the interaction between rs1801133 (MTHFR) and rs2236225 (MTHFD1), and rs1801131 (MTHFR) and rs7587117 (SLC4A5) were significantly associated with aggressive PCa. For the AA PCa patients, the interaction of DHFR-19bp polymorphism and rs4652 (LGALS3) was significantly associated with aggressive PCa. These SNP-SNP interactions in the folate metabolism-related genes have a larger impact than SNP individual effects on tumor aggressiveness for EA and AA PCa patients. These findings can provide valuable information for potential biological mechanisms of PCa aggressiveness.

Abstract P552: Mendelian Randomization Analysis of Metabolites Associated With Severe Obesity in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL)

Obesity remains a global public health burden, with 4.7 million premature deaths globally attributed to obesity. Severe obesity (SevO: defined as body mass index (BMI)≥40) is a major risk factor for other comorbidities, including heart disease and Type 2 Diabetes, which disproportionately impact historically marginalized populations, including Hispanic/Latinos. Based on BRFSS data, 24.5% of US Hispanic/Latino adults are projected to have severe obesity by 2030. However, the etiology of the underlying metabolic dysfunction remains unknown. To address this gap, we identified metabolites associated with SevO in genotyped participants aged ≥20 with 25 < BMI ≥ 40 and metabolic data in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL). We investigated cross-sectional associations between Blom-transformed metabolites and baseline SevO, adjusting for age, study center, background group, smoking status, and principal components of ancestry, stratified by sex (SUGEN), and meta-analyzed (SAS 9.4). For the top 20 metabolites, we extracted publicly available HCHS/SOL metabolite GWAS (mGWAS) summary statistics to derive metaboQTLs, and summary statistics from a multi-population meta-analysis of SevO (N>70,000) and implemented forward MR analysis using the MendelianRandomization R package (v0.3.0), which provides various robust causal estimation methods for summary data. Anthropometry and data for 640 known Metabolon metabolites were available for 551 females (mean age: 43.3 years, 27% SevO) and 371 males (mean age 43.4 years, 15% SevO). We identified Bonferroni-corrected significant SevO associations (p<0.05/640) for 224 metabolites in the meta-analysis. Of the top 20 metabolites associated with SevO, we excluded six with no genome-wide significant SNPs in the mGWAS. For the remaining 14, we included independent SNPs with p<1E-6 as instrumental variables in the MR for each metabolite. After excluding SNPs ±500kb from known BMI loci, two metabolites showed causal associations with SevO, cytidine (penalized robust MR-Egger: ß (SE) =0.121 (0.051), p=0.018) and indoleproprionate (penalized weighted median-MR: ß (SE) =-0.138 (0.043), p=0.001). Cytidine is a pyrimidine nucleoside consisting of D-ribose and cytosine, which is a precursor of cytidine triphosphate required in the one-carbon metabolism pathway to convert phosphatidylcholine (PC) to phosphatidylethanolamine (PE). PC biosynthesis is higher in adipose tissue macrophages in obese mice and humans. Indoleproprionate is a microbial metabolite of tryptophan produced by gut bacteria. Indoleproprionate levels have been shown to be associated with higher microbiome diversity and lower incidence of T2D. Our work points to future efforts to validate findings in other cohorts, including reverse MR to further elucidate the causal relationship between metabolites and severe obesity.