Effect of Kidney Disease and Gut-Derived Uremic Toxins on Flavin Monooxygenases: Clinical and Translational Research StudiesProkopienko, Alexander (2019) Effect of Kidney Disease and Gut-Derived Uremic Toxins on Flavin Monooxygenases: Clinical and Translational Research Studies. Doctoral Dissertation, University of Pittsburgh. (Unpublished)
AbstractCardiovascular disease (CVD) is the leading cause of death in patients with kidney disease. Unfortunately, therapeutic strategies targeting traditional risk factors have limited impact on reducing CVD outcomes, suggesting that non-traditional CVD risk factors may play an important role in kidney disease. In fact, the altered kidney disease gut microbiome is a source of several non-traditional CVD risk factors. In particular, trimethylamine-N-oxide (TMAO) is formed from gut microbiota production of trimethylamine and hepatic flavin monooxygenase (FMO) metabolism. The overarching objective of this dissertation was to investigate the effect of kidney disease and gut-derived toxins on flavin monooxygenase activity. To achieve these goals, an analytical method was developed and validated to measure gut-derived toxins including kynurenic acid, hippuric acid, indoxyl sulfate and p-cresol sulfate. In vitro studies utilizing rat microsomes demonstrated significant increases in the formation of TMAO in the kidney disease group versus the control, suggesting increased FMO activity. Although gene and protein expression of FMO were not changed, metabolic activation elicited by octylamine and presence of human uremic serum increased FMO-mediated TMAO formation. Ex vivo translational studies using primary cultures of human hepatocytes demonstrated that exposure to indoxyl sulfate, a gut-derived toxin, increases FMO3 expression and FMO-mediated TMAO formation. The findings suggest that metabolic activation and indoxyl sulfate exposure increase FMO activity and represent novel mechanisms that contribute to increased TMAO formation in kidney disease and may be a therapeutic target to reduce TMAO exposure and CVD. In a pilot clinical study, a novel strategy to reduce formation of TMAO with diindolylmethane was investigated in Stage 3-4 kidney disease patients. Gut-derived uremic toxins and corresponding intestinal microbiome profiles were also assessed. The findings demonstrated that diindolylmethane reduced serum TMAO concentrations in males compared to females. The microbiota composition was also significantly altered in the kidney disease patients compared to control. Furthermore, the microbiota was a strong predictor of gut-derived toxin exposure. Collectively, this work advances our understanding of potential increases in FMO activity and microbiota alterations in kidney disease that will facilitate future work to develop therapeutic strategies to reduce CVD. Share
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