Mild and reversible nephrotoxicity following repeated administration of damnacanthal in nude mice.

Damnacanthal was previously shown to be a promising colorectal cancer therapeutic candidate. Its efficacy relied on multiple administrations. This study, therefore, aims to assess the renal toxicity of 20 mg/kg damnacanthal (DAM20) in nude mice following three, seven and 14 repeated administrations. No clinical signs of renal toxicity and abnormal renal tissue histopathology were demonstrated. Seven repeated doses of DAM20 resulted in a decrease in BUN, increased urine-serum creatinine ratio, and urine microalbumin leakage (p-value = 0.031, 0.016 and 0.028, respectively), indicating the perturbation of kidney and liver functions. Some of these abnormalities were reversible to the normal ranges when the treatment continued to 14 repeated doses. However, significant kidney enlargement and increased urine creatinine (p- value = 0.032 and 0.030) were observed, indicating fluid retention and chronic kidney disease. Immunohistochemical analysis and TUNEL assay consistently demonstrated the absence of cleaved caspase-3 expression, DNA fragmentation, and infiltration of pan-macrophages (F4/80) and M2 macrophages (CD206) in the renal tissues of all mice subjected to three, seven, and 14 repeated doses of DAM20. A single exception was observed in one mouse from the 14-dose group, which exhibited minimal cleaved caspase-3 activation (0.14 % positive area). However, a significant increase in KIM-1 expression in renal tissue following 14 repeated doses of DAM20 (p- value = 0.012) indicated the presence of renal tubular injury. Interestingly, the absence of DNA fragmentation and macrophage infiltration in the renal cortex suggests that the DAM20-induced injury was mild, successfully resolved through endogenous repair mechanisms, and did not progress to irreversible damage or tissue remodeling. In conclusion, this study demonstrated that repeated administration of DAM20 in nude mice resulted in mild and reversible nephrotoxicity. However, further large-scale investigations are warranted to gain a more comprehensive understanding of damnacanthal toxicity profile and to ensure its safe use in potential therapeutic applications.