Unexpected Nephrotoxicity in Male Ablactated Rats Induced by Cordyceps militaris: The Involvement of Oxidative Changes

Aristolochic acid nephropathy (AAN), a progressive renal interstitial fibrosis frequently associated with urothelial malignancies, was initially reported in a Belgian cohort of more than 100 patients after the intake of slimming pills containing a Chinese herb, Aristolochia fangchi. Although botanicals known or suspected to contain aristolochic acid (AA) were no longer permitted in many countries, several AAN cases were regularly observed all around the world. The incidence of AAN is probably much higher than initially thought, especially in Asia and the Balkans. In Asian countries, where traditional medicines are very popular, the complexity of the pharmacopoeia represents a high risk for AAN because of the frequent substitution of the botanical products by AA-containing herbs. In the Balkan regions, the exposure to AA found in flour obtained from wheat contaminated with seeds of Aristolochia clematitis could be responsible for the so-called Balkan-endemic nephropathy. Finally, despite the Food and Drug Administration's warnings concerning the safety of botanical remedies containing AA, these herbs are still sold via the Internet.

Nephrotoxicity is a common side effect of therapeutic interventions, environmental insults, and exposure to toxicants in the workplace. Although biomarkers for nephrotoxicity are available, they often lack sensitivity and are not specific as indicators of epithelial cell injury. Kidney injury molecule-1 (Kim-1) is a type 1 membrane protein with extracellular immunoglobulin and mucin domains. The mRNA and protein for Kim-1 are expressed at very low levels in normal rodent kidney, but expression increases dramatically after injury in proximal tubule epithelial cells in postischemic rodent kidney and in humans during ischemic acute renal failure. To evaluate the utility of Kim-1 as a biomarker for other types of renal injury, we analyzed tissue and urinary expression in response to three different types of nephrotoxicants in the rat: S-(1,1,2,2-tetrafluoroethyl)-l-cysteine (TFEC), folic acid, and cisplatin. Marked increases in Kim-1 expression were confirmed by immunoblotting in all three models. The protein was shown to be localized to the proximal tubule epithelial cell by immunofluorescence. Furthermore, Kim-1 protein was detected in urine of toxicant-treated rats. The temporal pattern of expression in response to TFEC is similar to the Kim-1 expression pattern in the postischemic kidney. In folic acid-treated kidneys, Kim-1 is clearly localized to the apical brush border of the well-differentiated proximal tubular epithelial cells. After folic acid treatment, expression of Kim-1 is present in the urine despite no significant increase in serum creatinine. Cisplatin treatment results in early detection of urinary Kim-1 protein and diffuse Kim-1 expression in S3 cells of the proximal tubule. Kim-1 can be detected in the tissue and urine on days 1 and 2 after cisplatin administration, occurring before an increase in serum creatinine. The upregulation of expression of Kim-1 and its presence in the urine in response to exposure to various types of nephrotoxicants suggest that this protein may serve as a general biomarker for tubular injury and repair processes.

Graphical abstract (a) The Yin and Yang symbol: The philosophical basis of some of the assumed properties and research on Cordyceps (see text)? (b) Cordyceps spp. parasitizing a dead Campanotus insect and (c) cordyheptapeptide A, a natural product from the fungus.