New perspectives in biomonitoring liver function by means of serum bile acids: experimental and hypothetical biochemical basis.

The functional activity of the liver and the variety of its responses to injury makes the choice of appropriate tests of function a difficult task. Because of the highly efficient uptake of bile acids by the normal hepatocyte, the determination of serum bile acid (SBA) concentration has been proposed as a test to detect early changes of liver function not associated with cytotoxicity. Several biomonitoring studies have been carried out on subjects occupationally exposed to hepatotoxic substances, by evaluating SBAs as indicators of early liver dysfunction. Even though these studies are not exactly comparable because of the different protocols adopted, most of them show a significant increase in SBA concentrations among the exposed subjects compared with unexposed controls. Furthermore, higher prevalences of subjects with abnormal SBA concentrations occur in those exposed to mixtures of organic solvents. Increased SBA concentrations among the subjects exposed to various xenobiotics have been explained by assuming a change in function of hepatocytes. As regards the nature of the mechanisms involved in the increase in SBA concentrations, recent experimental observations pointed out that some chlorinated aliphatics were able to inhibit cell membrane ATPases and alter cytosolic calcium homeostasis. The lack of any relation, however, between exposure and SBA concentrations remains an important point to clarify and at present prevents the use of measurement of SBA concentrations as an index of effect.