Biology subjects

Fling, R. R.

Publications and source records attributed to Fling, R. R..

3 recordsLinked to original sources

bioRxiv2021

Aryl hydrocarbon receptor (AhR) activation by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) dose-dependently shifts the gut microbiome consistent with the progression of steatosis to steatohepatitis with fibrosis

Gut dysbiosis with disrupted enterohepatic bile acid metabolism is commonly associated with non-alcoholic fatty liver disease (NAFLD) and recapitulated in a NAFLD-phenotype elicited by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice. TCDD induces hepatic fat accumulation and increases levels of secondary bile acids including taurolithocholic acid and deoxycholic acid, microbial modified bile acids involved in host bile acid regulation signaling pathways. To investigate the effects of TCDD on the gut microbiota, cecum contents of male C57BL/6 mice orally gavaged with sesame oil vehicle or 0.3, 3, or 30 {micro}g/kg TCDD were examined using shotgun metagenomic sequencing. Taxonomic analysis identified dose-dependent increases in Lactobacillus species (i.e., Lactobacillus reuteri). Increased species were also associated with dose-dependent increases in bile salt hydrolase sequences, responsible for deconjugation reactions in secondary bile acid metabolism. Increased L. reuteri levels were further associated with mevalonate-dependent isopentenyl diphosphate (IPP) biosynthesis and menaquinone biosynthesis genes. Analysis of gut microbiomes from cirrhosis patients identified increased abundance of these pathways as identified in the mouse cecum metagenomic analysis. These results extend the association of lactobacilli with the AhR/intestinal axis in NAFLD progression and highlight the similarities between TCDD-elicited phenotypes in mice to human NAFLD.

microbiology↗

bioRxiv2021

2,3,7,8-Tetrachlorodibenzo-p-dioxin elicited decreases in cobalamin inhibits methylmalonyl-CoA mutase activity redirecting propionyl-CoA metabolism to the β-oxidation-like pathway resulting in hepatic accumulation of the toxic intermediate acrylyl-CoA

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent environmental contaminant which induces diverse biological and toxic effects, including the reprograming of intermediate metabolism, mediated by the aryl hydrocarbon receptor (AHR). Targeted LC-MS analysis of hepatic extracts from mice gavaged with TCDD every 4 days for 28 days detected an increase in S-(2-carboxyethyl)-L-cysteine, a conjugate produced following the spontaneous reaction between the sulfhydryl group of cysteine and highly reactive acrylyl-CoA, an intermediate in the cobalamin (Cbl)-independent {beta}-oxidation-like metabolism of propionyl-CoA. In addition to repressing genes in both the canonical Cbl-dependent carboxylase and the alternate Cbl-independent {beta}-oxidation-like pathways at 30 g/kg TCDD, methylmalonyl-CoA mutase (MUT) activity was inhibited at lower doses. Moreover, TCDD decreased serum Cbl levels and hepatic cobalt levels while eliciting negligible effects on gene expression associated with Cbl absorption, transport, trafficking, or the derivatization to 5-deoxy-adenosylcobalamin (AdoCbl), the required MUT cofactor. In addition to inducing Acod1 that encodes for aconitate decarboxylase 1, the enzyme responsible for the decarboxylation cis-aconitate to itaconate, TCDD also dose-dependently increased itaconate levels in hepatic extracts. MUT inhibition is consistent with itaconate activation to itaconyl-CoA, a MUT suicide inactivator that adducts AdoCbl, that in turn, inhibits MUT activity and reduces Cbl levels. Collectively, these results suggest the decrease in MUT activity is due to Cbl depletion following TCDD treatment that redirected propionyl-CoA metabolism to the alternate Cbl-independent {beta}-oxidation-like pathway. The resulting hepatic accumulation of acrylyl-CoA likely contributes to TCDD-elicited hepatotoxicity and the multi-hit progression of steatosis to steatohepatitis with fibrosis.

pharmacology and toxicology↗

bioRxiv2021

Thioesterase induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin results in a futile cycle that inhibits hepatic β-oxidation

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a persistent environmental contaminant, induces steatosis by increasing hepatic uptake of dietary and mobilized peripheral fats, inhibiting lipoprotein export, and repressing {beta}-oxidation. In this study, the mechanism of {beta}-oxidation inhibition was investigated by testing the hypothesis that TCDD dose-dependently repressed straight-chain fatty acid oxidation gene expression in mice following oral gavage every 4 days for 28 days. Untargeted metabolomic analysis revealed a dose-dependent decrease in hepatic acyl-CoA levels, while octenoyl-CoA and dicarboxylic acid levels increased. TCDD also dose-dependently repressed the hepatic gene expression associated with triacylglycerol and cholesterol ester hydrolysis, fatty acid binding proteins, fatty acid activation, and 3-ketoacyl-CoA thiolysis while inducing acyl-CoA hydrolysis. Moreover, octenoyl-CoA blocked the hydration of crotonyl-CoA suggesting short chain enoyl-CoA hydratase (ECHS1) activity was inhibited. Collectively, the integration of metabolomics and RNA-seq data suggested TCDD induced a futile cycle of fatty acid activation and acyl-CoA hydrolysis resulting in incomplete {beta}-oxidation, and the accumulation octenoyl-CoA levels that inhibited the activity of short chain enoyl-CoA hydratase (ECHS1).

pharmacology and toxicology↗