Efficacy of urine bile acid as a non-invasive indicator of liver damage in rats.

Estimation of liver damage is important in the pathophysiological and toxicological study of liver disease. As a novel, non-invasive marker of liver damage, we studied the efficacy of urine bile acids (UBA) in a rat model of liver disease. Thioacetamide (TAA)-treated rats were used in this study. Single intraperitoneal administration of high-dose TAA induces severe damage to the liver, and thus is used as a model of acute hepatitis. Continuous administration of low-dose TAA yields mild damage to the liver, and induces cirrhosis and hepatic tumors. In this study, it was found that both acute and chronic administration of TAA was associated with a dose-dependent elevation of UBA. The elevation of UBA content correlated with the alteration of blood biochemical indicators, and UBA screening showed a remarkable ability to distinguish liver-damaged rats from healthy rats. In particular, UBA analysis was found to have high sensitivity, specificity, and positive predictive value for the screening of rats with abnormal serum alkaline phosphatase (ALP) activity due to chronic liver damage, which was confirmed to include cholestasis and subsequent cirrhosis by liver histological analysis. In conclusion, we demonstrated that measurement of UBA is a simple, non-invasive and effective method for the screening of cholestasis in TAA-treated rats. We suggest that UBA analysis may have potent applicability for monitoring the progress of liver damage in animal models of chronic liver disease, such as cirrhosis and hepatic encephalopathy.

Toxicokinetics and toxicity of thioacetamide sulfoxide: a metabolite of thioacetamide.

Thioacetamide (TA) is bioactivated by CYP2E1 to TA sulfoxide (TASO), and to the highly reactive sulfdioxide (TASO(2)), which initiates hepatic necrosis by covalent binding. Previously, we have established that TA exhibits saturation toxicokinetics over a 12-fold dose range, which explains the lack of dose-response for bioactivation-based liver injury. In vivo and in vitro studies indicated that the second step (TASO-->TASO(2)) of TA bioactivation is less efficient than the first one (TA-->TASO). The objective of the present study was to specifically test the saturation of the second step of TA bioactivation by directly administering TASO, which obviates the contribution from first step, i.e. TA-->TASO. Male SD rats were injected with low (50mg/kg, ip), medium (100mg/kg) and high (LD(70), 200mg/kg) doses of TASO. Bioactivation-mediated liver injury that occurs in the initial time points (6 and 12h), estimated by plasma ALT, AST and liver histopathology over a time course, was not dose-proportional. Escalation of liver injury thereafter was dose dependent: low dose injury subsided; medium dose injury escalated upto 36h before declining; high dose injury escalated from 24h leading to 70% mortality. TASO was quantified in plasma by HPLC at various time points after administration of the three doses. With increasing dose (i.e., from 50 to 200mg/kg), area under the curve (AUC) and C(max) increased more than dose proportionately, indicating that TASO bioactivation exhibits saturable kinetics. Toxicokinetics and initiation of liver injury of TASO are similar to that of TA, although TASO-initiated injury occurs at lower doses. These findings indicate that bioactivation of TASO to its reactive metabolite is saturable in the rat as suggested by previous studies with TA.