Intensification and depletion of specific bulky renal DNA adducts (I-compounds) following exposure of male F344 rats to the renal carcinogen ferric nitrilotriacetate (Fe-NTA)

Abstract

The effects of the renal carcinogen ferric nitrilotriacetate (FeNTA) on kidney DNA of male F344 rats were studied to determine whether bulky DNA oxidation products (putative intrastrand crosslinks) could be detected by 32P-postlabeling in the target organ of carcinogenesis. Rats (10–11 weeks old) were given a single dose of FeNTA (15 mg Fe/kg body weight) i.p. at 3:00 pm. After 5 h, renal DNA from FeNTA-treated and vehicle control animals was assayed by 32P-postlabeling. Thin-layer chromatography and quantitative analysis of two labeled nucleotide fractions of increasing polarity, L and C, showed that three spots (L1, L2, and C3) were intensified 3.5- to 4.2-fold in treated animals. L1 consisted of subfractions L1a, L1b, and L1c, which could be resolved chromatographically. L1c, L2, and C3 were identical to DNA oxidation products generated by the Fenton reaction in vitro, while L1a and L1b apparently did not arise by this mechanism. DNA damage and toxicity appeared reduced in younger animals and animals treated in the morning, presumably due to differences in antioxidant defenses. Liver and lung (non-target organs) DNA did not exhibit enhanced L1, L2, and C3 spots. In addition to augmenting renal I-compounds, FeNTA reduced the levels of three major polar kidney I-compounds (C4, C5, and C6) to 22–53% of control. This reduction did not appear to arise by direct oxidative DNA damage, resembling the previously documented loss of liver I-compounds induced by numerous hepatocarcinogens. Two of these I-compounds (C4 and C5) have been reported to exhibit positive linear correlations with median lifespan of male F344 rats. The pleiotropic response of kidney I-compound levels to Fe-NTA was consistent with different roles of different types (I and II) of I-compounds in Fe-NTA-mediated renal carcinogenesis. The results strongly support a causal relationship between oxidative DNA lesions and Fe-NTA-mediated carcinogenesis.