Gut derived chronic inflammation in HIV-1 and chronic kidney disease : the role of the microbial metabolite TMAO and immunomodulatory effects of Vitamin D

Abstract

Persistent immune activation with premature ageing and increased risk of cardiovascular disease (CVD) are features shared by HIV-1 infected individuals and patients with chronic kidney disease (CKD). Underlying dysbiosis, a failing mucosal barrier function and microbial translocation (MT) are contributing factors in both conditions. Vitamin D supplementation might prove valuable by its modulatory effects on innate and adaptive immunity, including induction of antimicrobial peptides (AMPs), regulation of epithelial barrier integrity and gut microbial composition. The main objective of this thesis was to assess gut-derived immune activation and investigate the modulatory effects of vitamin D supplementation in HIV-1. Additionally we wanted to explore Trimethylamine-N-Oxid (TMAO), a microbial metabolite with newly ascribed pro-atherosclerotic properties, as a novel link between gut microbiome and inflammaging in CKD and in HIV-1.

In an observational study on HIV-1 infected individuals on antiretroviral treatment (ART) and non-HIV controls, we found that, whereas HIV-1 infected individuals demonstrated increased immune activation in the form of elevated levels of hsCRP and sCD14 with HIV as an independent risk factor, they did not differ from controls in degree of MT measured by LPS. We next assessed the role of TMAO in cross-sectional and retrospective cohorts of CKD and HIV-1 patients of various disease stages. We found that TMAO levels correlated with increased systemic inflammation measured by hsCRP and was an independent predictor of mortality in CKD. TMAO levels were strongly associated with renal function and normalized after renal transplantation. In HIV-1, we found that TMAO levels were lower in untreated HIV-1 and normalized with treatment, but held no association with markers of immune activation or MT. Higher TMAO-levels in well controlled HIV-1 were not significantly associated with cardiovascular events. Nor was TMAO levels clearly associated with gut microbiome, or degree of dysbiosis. Finally, in a randomized, double-blind and placebo-controlled trial of daily supplementation with vitamin D and phenylbutyrate in treatment-naïve HIV-1 infected individuals, we found no significant effects on circulating immune activation markers or TMAO and kynurenine/tryptophan ratio. Nor was there a significant treatment effect on the colonic mucosal microbiome.

In conclusion, vitamin D did not associate with biomarkers of immune activation in well controlled HIV-1. Further, we found no support that supplementation with vitamin D and PBA could modulate gut-derived immune activation and dysbiosis in treatment-naïve HIV-1. Our results suggest that TMAO may have a contributory role in immune activation and all-cause mortality in CKD. However, the role of TMAO in cardiovascular pathogenesis in CKD was not specifically addressed. Moreover, elevated TMAO levels were strongly related to kidney functions and the effects should be interpreted with caution. In HIV-1, or data did not support TMAO as a significant link between gut dysbiosis and inflammaging. TMAO levels were disparately confounded by HIV-1, microbial composition and ART, thus limiting its role as a cardiovascular marker in HIV-1.