Background: LPS is a potent bacterial virulence factor and is a source of considerable clinical morbidity and mortality. This endotoxin is a predominant component of the outer membrane of Gram-negative bacteria. The gut is exposed to high levels of LPS in conditions like Inflammatory Bowel Diseases, necrotizing enterocolitis, sepsis, and following infection with enteric pathogens. Studies have shown that exposure of gut epithelial/other cells to LPS exerts profound and differential effects on membrane transport processes. Nothing, however, is known about the effect of LPS on uptake of free thiamin in the small intestine (where absorption of dietary thiamin occurs), and the large intestine (where absorption of the microbiota-generated thiamin occurs). Aim: To examine the effect of LPS on the small and large intestinal uptake of free thiamin and to determine the mechanism(s) involved. Methods: We used in vitro (human duodenum-derived HuTu 80 cells and colon-derived non-transformed NCM460 cells), ex vivo (human differentiated polarized enteroid and colonoid monolayers), and in vivo (mouse) models in our studies. Uptake studies were performed using 3H-thiamin as substrate. Results: Treating intestinal HuTu 80 and colonic NCM460 epithelial cells with LPS led to a significant inhibition in carrier-mediated 3H-thiamin uptake. Similar results were obtained when human differentiated enteroid and colonoid monolayers ex vivo, and mouse in vivo were treated with LPS. No changes in total cellular levels of thiamin transporter-1 & -2 (THTR-1 and THTR-2, respectively) proteins and mRNAs were observed upon LPS treatments; however, a significant decrease in the fraction of the THTR-1 & THTR-2 proteins that are expressed at the cell membrane were observed. These findings suggest that the LPS inhibitory effect on thiamin uptake in the small and large intestine is likely mediated via a decrease in the fraction of the thiamin transporters that are expressed at the cell membrane. Conclusion: This study shows that bacterial LPS inhibits thiamin uptake along the intestinal tract, and that this inhibition is likely mediated via reduction in level of the THTR-1 & THTR-2 proteins at the cell membrane. Supported by NIH grants DK-56061 and AA-018071, and VA grants 101BX001142 & IK6BX006189. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.