Inhibition of microbiota-dependent TMAO production attenuates chronic kidney disease in mice.

Patients with chronic kidney disease (CKD) have elevated circulating levels of trimethylamine N-oxide (TMAO), a metabolite derived from gut microbes and associated with cardiovascular diseases. High circulating levels of TMAO and its dietary precursor, choline, predict increased risk for development of CKD in apparently healthy subjects, and studies in mice fed TMAO or choline suggest that TMAO can contribute to kidney impairment and renal fibrosis. Here we examined the interactions between TMAO, kidney disease, and cardiovascular disease in mouse models. We observed that while female hyperlipidemic apoE KO mice fed a 0.2% adenine diet for 14 weeks developed CKD with elevated plasma levels of TMAO, provision of a non-lethal inhibitor of gut microbial trimethylamine (TMA) production, iodomethylcholine (IMC), significantly reduced multiple markers of renal injury (plasma creatinine, cystatin C, FGF23, and TMAO), reduced histopathologic evidence of fibrosis, and markedly attenuated development of microalbuminuria. In addition, while the adenine-induced CKD model significantly increased heart weight, a surrogate marker for myocardial hypertrophy, this was largely prevented by IMC supplementation. Surprisingly, adenine feeding did not increase atherosclerosis and significantly decreased the expression of inflammatory genes in the aorta compared to the control groups, effects unrelated to TMAO levels. Our data demonstrate that inhibition of TMAO production attenuated CKD development and cardiac hypertrophy in mice, suggesting that TMAO reduction may be a novel strategy in treating CKD and its cardiovascular disease complications.

Hyodeoxycholic acid improves HDL function and inhibits atherosclerotic lesion formation in LDLR-knockout mice.

We examined the effects of a natural secondary bile acid, hyodeoxycholic acid (HDCA), on lipid metabolism and atherosclerosis in LDL receptor-null (LDLRKO) mice. Female LDLRKO mice were maintained on a Western diet for 8 wk and then divided into 2 groups that received chow, or chow + 1.25% HDCA, diets for 15 wk. We observed that mice fed the HDCA diet were leaner and exhibited a 37% (P<0.05) decrease in fasting plasma glucose level. HDCA supplementation significantly decreased atherosclerotic lesion size at the aortic root region, the entire aorta, and the innominate artery by 44% (P<0.0001), 48% (P<0.01), and 94% (P<0.01), respectively, as compared with the chow group. Plasma VLDL/IDL/LDL cholesterol levels were significantly decreased, by 61% (P<0.05), in the HDCA group as compared with the chow diet group. HDCA supplementation decreased intestinal cholesterol absorption by 76% (P<0.0001) as compared with the chow group. Furthermore, HDL isolated from the HDCA group exhibited significantly increased ability to mediate cholesterol efflux ex vivo as compared with HDL of the chow diet group. In addition, HDCA significantly increased the expression of genes involved in cholesterol efflux, such as Abca1, Abcg1, and Apoe, in a macrophage cell line. Thus, HDCA is a candidate for antiatherosclerotic drug therapy.

A role for FXR and human FGF-19 in the repression of paraoxonase-1 gene expression by bile acids.

Paraoxonase-1 (PON1), an enzyme that metabolizes organophosphate insecticides, is secreted by the liver and transported in the blood complexed to HDL. In humans and mice, low plasma levels of PON1 have also been linked to the development of atherosclerosis. We previously reported that hepatic Pon1 expression was decreased when C57BL/6J mice were fed a high-fat, high-cholesterol diet supplemented with cholic acid (CA). In the current study, we used wild-type and farnesoid X receptor (FXR) null mice to demonstrate that this repression is dependent upon CA and FXR. PON1 mRNA levels were also repressed when HepG2 cells, derived from a human hepatoma, were incubated with natural or highly specific synthetic FXR agonists. In contrast, fibroblast growth factor-19 (FGF-19) mRNA levels were greatly induced by these same FXR agonists. Furthermore, treatment of HepG2 cells with recombinant human FGF-19 significantly decreased PON1 mRNA levels. Finally, deletion studies revealed that the proximal -230 to -96 bp region of the PON1 promoter contains regulatory element(s) necessary for promoter activity and bile acid repression. These data demonstrate that human PON1 expression is repressed by bile acids through the actions of FXR and FGF-19.