Trihydroxycholanoyl-taurine in brains of rodents with hepatic encephalopathy

Further evidence for blood-to-brain influx of unconjugated bile acids by passive diffusion: Determination of their brain-to-serum concentration ratios in rats by LC/MS/MS

Bile acids (BAs) reside in the brain and are probably involved in some neurological disorders. The view that most of unconjugated BAs in the brain are derived across the blood-brain barrier from the periphery by passive diffusion depending on their hydrophobicity is currently dominant, but some studies have made conflicting claims. In this study, the correlation analysis between the rat brain and serum levels of unconjugated BAs with a wider range of hydrophobicity was conducted to obtain further evidence about the blood-to-brain influx of unconjugated BAs by passive diffusion. We first developed the precise, accurate and matrix effect-free LC/ESI-MS/MS methods for quantifying eight major unconjugated BAs in the rat brain and serum. Derivatization was employed for increasing the assay sensitivity and specificity. The analysis using these methods reproduced the strong positive correlations between the brain and serum levels, and significant higher concentrations in the serum than in the brain for all the unconjugated BAs. The BA with the higher logPow (hydrophobicity) had the higher brain-to-serum concentration ratio (mono- > di- > trihydroxy BAs). Furthermore, the hydrophobicity was considered as the stronger factor for the blood-to-brain influx of the BAs than the serum protein binding ratio. Thus, this study provided further evidence supporting that passive diffusion is the major mechanism for the blood-to-brain influx of the unconjugated BAs.

A critical review of bile acids and their receptors in hepatic encephalopathy

Hepatic encephalopathy describes an array of neurological complications that arise due to liver insufficiency. The pathogenesis of hepatic encephalopathy shares a longstanding association with hyperammonemia and inflammation, and recently, aberrant bile acid signaling has been implicated in the development of key features of hepatic encephalopathy. These key features include neuronal dysfunction, neuroinflammation and blood-brain barrier permeability. This review summarizes the findings of recent studies demonstrating a role for bile acids in the pathogenesis of hepatic encephalopathy via one of three main bile acid receptors and speculates on the possible downstream consequences of aberrant bile acid signaling.