Acetaminophen‐induced hepatotoxicity of cultured hepatocytes depends on timing of isolation from light‐cycle controlled mice

Most physiological changes follow a daily cycle in animals because their circadian rhythm is adjusted to and synchronized with sunlight. In particular, the circadian rhythm affects liver functions, including pharmacokinetics and metabolism. The influence of circadian rhythm has not been included in hepatotoxicity assays used in drug discovery and development. In this study, the contribution of circadian rhythm was investigated in acetaminophen‐induced hepatotoxicity in mice and primary cultured hepatocytes. Hepatotoxicity was induced via the intraperitoneal administration of acetaminophen to a greater extent at night than during the day in mice. The sensitivity of acetaminophen‐induced hepatotoxicity was consistent with the expression levels of acetaminophen‐metabolizing enzyme and circadian genes. The host‐derived circadian rhythm was still evident in the primary cultured hepatocytes within a day after their isolation from the liver. Primary cultured hepatocytes isolated at night were significantly more sensitive to acetaminophen than those isolated during the day. The sensitivity toward acetaminophen‐induced hepatotoxicity depended on the circadian rhythm of the expression of acetaminophen‐metabolizing genes and intracellular glutathione levels in primary cultured hepatocytes. These results obtained from cultured cells correspond to those in mice, suggesting that the timing of hepatocyte isolation is important when investigating drug metabolism and toxicity tests in culture. The host‐derived circadian rhythm was still evident in the primary cultured hepatocytes within a day after their isolation from the liver. Primary cultured hepatocytes isolated at night were significantly more sensitive to acetaminophen than those isolated during the day. The sensitivity toward acetaminophen‐induced hepatotoxicity depended on the circadian rhythm of the expression of acetaminophen‐metabolizing genes and intracellular glutathione levels in primary cultured hepatocytes.