Mechanisms of cisplatin-induced chronotoxicity in mice

<p>【Purpose】Living organisms are controlled by the circadian rhythms. It has become clear that these circadian differences affect the frequency of diseases. Additionally, time-dependent differences in the pharmacokinetics of medications are also reported. Therefore, it is now notable to take care of chronobiology-based medication. Our research, which we describe as “chronotoxicology” has focused on the relationship between injection timings and the degree of onset metal toxicity. We recently investigated that the chronotoxicity of seven metals, including Ni and Cu, showed specific patterns of diurnal variation (Yoshioka et al, J Toxicol Sci, 43 (2), 129-134, 2018). These results present the possibility that each elements or compounds can exhibit a unique chronotoxicity. As for medication, since reports about chronotoxicity were limited, it is important to investigate the chronotoxicity of various medicinal drugs for improving the quality of life.</p><p>Cisplatin (CDDP) has using abroad in the way of platinum complex on anticancer drugs. However, it is known that CDDP exhibit serious side effects, such as acute renal damage (AKD). Although the diurnal variation of CDDP-induced nephrotoxicity has been reported, mechanisms of these differentiations were not elucidated. In this study, we investigated the circadian variations in CDDP-induced toxicity focused on toxicity and its mechanism using mouse model.</p><p> 【Method】(1) For the mortality assays, 7-week-old ICR mice were divided into six groups of five animals each. Each group was administered 20 mg/kg CDDP by an intraperitoneal injection at one of six different time points (clock time; 10:00, 14:00, 18:00, 22:00, 2:00, or 6:00), described here as zeitgeber times (ZT); ZT2, ZT6, ZT10, ZT14, ZT18, or ZT22, respectively. Injections were performed under red light during the dark period (ZT14, ZT18, or ZT22). Surviving numbers of mice was monitored until 14 days after the injection (2) We measured expression levels of OCT2 (intracellular incorporation transporter) in kidney from six different times points. (3) For analysis of circadian variations in the renal injury, the mice received intraperitoneal injections of 20 mg/kg CDDP at ZT2 or ZT14. After 72 h, the animals were euthanized and bled for plasma collection. Kidneys were harvested from each of these animals. Using plasma, we determined creatinine and blood urea nitrogen (BUN). In addition, we performed qPCR, western blotting, and histological analysis in the each kidney. </p><p> 【Results and Discussion】(1) We showed, mice were tolerant at ZT22 and ZT2 10:00, whereas at ZT6, ZT10, ZT14, and ZT18, mice indicated higher susceptibility to CDDP-induced toxicity These results suggest that injection timings affected the severity of CDDP-induced toxicity. (2) Expression levels of OCT2 was no significant change in all 6 groups. This result indicated that the chronotoxicity of CDDP would be occurred after incorporation in the kidney. (3) We showed that the levels of nephrotoxicity indicators (BUN, creatinine, renal levels of inflammatory cytokines, necrosis, and DNA adducts) significantly increased as ZT14 (dark phase) but not at ZT2 (light phase). These results suggest that the chronotoxicology of CDDP might provide valuable information regarding the importance of injection timings for toxicity evaluation tests and undesirable side effects.</p>