Abstract P552: Mendelian Randomization Analysis of Metabolites Associated With Severe Obesity in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL)
Authors: Young Kristin , Buchanan Victoria L , Graff Mariaelisa , Krishnan Mohanrah , Highland Heather , Yu Bing , Avery Christy L , Buyske Steve , Cai Jianwen , Daviglus Martha L , Howard Annie Green , Isasi Carmen R , Kaplan Robert , Loos Ruth , Qi Qibin , Rohde Rebecca , Rotter Jerome I , Van Horn Linda , Gordon-Larsen Penny , Boerwinkle Eric , North Kari E 
Published: March 2023

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.