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Session: Dietary Associations with Gut Microbial Community and Metabolic Changes (Poster Theater Flash Session 22)

(PTFS22-02-24) Diet Quality Impacts Circulating Tryptophan Metabolites and Diversity of Tryptophanase Harboring Bacteria

Tuesday, July 2, 2024
10:04 AM – 10:08 AM CT
Location:  W185A-C
SIG 3MT ELPC
Objectives: Tryptophan is an essential amino acid that is decreased with lower dietary quality. Tryptophan metabolism by host and microbial enzymes forms protective (indole) and deleterious (5-hydroxytryptamine—5-HT) metabolites that play critical roles in colorectal cancer (CRC). Indole is produced by tryptophanase (tnaA) harboring bacteria (THB). Our previous work revealed THB to be significantly associated with CRC in African Americans/Blacks (AA/Bs). Thus, we aimed to determine if dietary quality impacts the gut microbiome and circulating tryptophan metabolites in human participants.

Methods: Stool and fasting (~12 hr) venous blood were collected from 138 participants between 45-75 years of age living in Chicago. Plasma tryptophan and 5-HT were quantified using UPLC-MS. Microbial genomes were shotgun sequenced and differences between microbial features were assessed. Dietary quality was calculated from two 24-hour recalls using the USDA HEI-2015 with HEI < 51 set as a cut-point for poor dietary quality. Using NCBI’s open-source database, tnaA amino acid sequences were obtained and compared against the bacterial groups for relative sequence similarities. Relative changes in metabolites among the two HEI groups were validated using a non-parametric (Wilcoxon) t-test with a p-value of 0.05.

Results: Participants were 52% AA/B and 57% female with a mean age of 59.6 (±6.2). African American/Blacks had poor dietary quality, higher circulating 5-HT, and lower circulating tryptophan (p < .001). Using HEI-2015, 77 and 76 genera were associated with HEI < 51 and HEI ≥ 51, respectively. Analysis of associated genera revealed the THB Porphyromonas, Akkermansia, and Lachnospiraceae to be associated with HEI ≥ 51 and Escherichia, Fusobacterium, Odoribacter, and Lachnospiracae to be associated with HEI < 51. Homology analysis of tnaA sequences from representative species within associated genera ranged from 25% - 87%.

Conclusions: AA/Bs have lower serum tryptophan, higher serum 5-HT, and lower dietary quality as calculated by HEI-2015. The low sequence homology among THB demonstrates a need to understand THB activity among diverse bacteria that can be impacted by dietary quality.

Funding Sources: LTH, PG, EM, JR, HRH: R01CA204808, U54MD012523; MLO: T32CA057699; AC: RSG-23-1154989-01-CSCT.