No abstract

The etiology of most chronic diseases involves interactions between environmental factors and genes that modulate important biological processes (Olden and Wilson, 2000). We are developing the publicly available Comparative Toxicogenomics Database (CTD) to promote understanding about the effects of environmental chemicals on human health. CTD identifies interactions between chemicals and genes and facilitates cross-species comparative studies of these genes. The use of diverse animal models and cross-species comparative sequence studies has been critical for understanding basic physiological mechanisms and gene and protein functions. Similarly, these approaches will be valuable for exploring the molecular mechanisms of action of environmental chemicals and the genetic basis of differential susceptibility.

Recent advances in the molecular cloning of membrane transport systems that determine bile formation have facilitated studies of the molecular mechanisms of cholestatic liver disease. The present review summarizes what has been learned about the molecular alterations of these membrane transporters in hepatocytes and cholangiocytes in acquired cholestatic liver disorders. Much of this information has been obtained from the study of animal models of cholestasis and from more limited studies in clinical cholestatic liver diseases. Many of these responses may be interpreted as adaptations that serve to diminish cholestatic liver injury.

One hundred fifty-one patients with primary biliary cirrhosis (PBC) grouped into four strata based on entry serum bilirubin (<2 mg/dL vs. 2 mg/dL or greater) and liver histology (stages I, 1 1 vs. stages 111, IV-Ludwig criteria) were randomized within each stratum to ursodiol or placebo given in a single dose of 10 to 12 mgkg at bedtime for 2 years. Placebo-(n = 74) and ursodioltreated (n = 77) patients were well matched at baseline for demographic and prognostic factors. Ursodiol induced major improvements in biochemical tests of the liver in strata 1 and 2 (entry bilirubin <2), but had less effect on laboratory tests in patients with entry serum bilirubin of 2 2 (strata 3 and 4). Histology was favorably affected by ursodiol in patients in strata 1 and 2 but not in strata 3 and 4. Ursodiol enrichment in fasting bile obtained at the conclusion of the trial was approximately 40% and comparable in all strata. Thus, differences in ursodiol enrichment of the bile acid pool do not explain better responses of laboratory tests and histology found in patients with less advanced PBC. Patients treated with ursodiol tended to develop a treatment failure less frequently than those who received placebo, particularly in strata 1 and 2 (ursodiol42%, placebo WO, P = .078). Development of severe symptoms (fatigue/pru-Abbreviations: PBC, primary biliary cirrhosis; M-W, Mann-Whitney. From the 'University of Texas Southwestern Medical Center a t Dallas, Dallas, Tx; '