Cytochrome P450 activity in control and induced long-term cultures of rat hepatocyte spheroids

Long-term events such as enzyme induction or chronic toxicity require long-term liver culture models that maintain activity of xenobiotic metabolising enzymes. The levels of these enzyme activities and their responsiveness to chemical induction was studied in rat hepatocyte spheroids, a potential long-term hepatocyte culture model. In comparison with other long-term liver culture models, the basal metabolic activity of spheroids has not been well studied. Additionally, no existing data on the induction of CYP3A activity in spheroids could be found. The basal xenobiotic metabolising activity of rat hepatocyte spheroids was monitored over 14 days in culture, using testosterone as a probe substrate. When spheroids from days 2-14 in culture were compared to 24-h control spheroids, there was a differential maintenance of basal CYP activity. CYP2A and CYP3A activities were maintained over the culture period, while there were time-related decreases in CYP2C11 and CYP2C/CYP2B1/2 activities. The responsiveness of rat hepatocyte spheroids to chemical induction was studied following treatment with phenobarbitone (PB) or dexamethasone (DEX). PB treatment induced CYP2A, CYP2C, CYP2B1/2 and CYP3A activities. DEX treatment resulted in an induction of CYP3A and CYP2C11 activities. The results demonstrate that rat hepatocyte spheroids retained some of the liver-specific functions essential in a long-term hepatocyte culture model, thus making spheroids comparable to other long-term culture models available.