Sex differences in ochratoxin a toxicity in F344 rats after 7 and 21 days of daily oral administration.

Ochratoxin A (OTA) is a potent renal carcinogen in male rats but not in females. The mechanisms underlying these differences are unknown. The sex-dependent response of F344 rats after a repeated OTA oral administration for 7 (0.50 mg/kg bw) or 21 days (0.21 and 0.50 mg/kg bw) was evaluated. General toxicity, sex and thyroid hormones and histopathology were studied. OTA was quantified (HPLC-FLD) in plasma, kidney and liver and the expression of kidney transporters (RT-qPCR) was studied. After 7 days, kidney histopathology showed more pronounced signs of toxicity in males than in females. After 21 days, a higher toxicity was observed but sex differences disappeared. OTA concentration in plasma and tissues was similar in both sexes. Downregulation was the general OTA-induced effect. Oats' downregulation was slow in males and Oat3 did not change in females. Oatp1 was strongly downregulated in males after 21 days. An opposite effect was observed in Bcrp after 21 days: downregulation in males and upregulation in females. Females showed a dose- and time-dependent decrease of progesterone. Despite the sex differences, the final balance in OTA toxicokinetics at renal cell level does not seem to support a higher accumulation of OTA in male kidneys.

Genotoxicity of Aflatoxin B1 and Ochratoxin A after simultaneous application of the in vivo micronucleus and comet assay.

Aflatoxin B1 (AFB1) and Ochratoxin A (OTA) are genotoxic mycotoxins that can contaminate a variety of foodstuffs, the liver and the kidney being their target organs, respectively. The micronucleus (MN) assay (bone marrow) and the comet assay (liver and kidney) were performed simultaneously in F344 rats, treated with AFB1 (0.25 mg/kg b.w.), OTA (0.5 mg/kg b.w.) or both mycotoxins. After AFB1 treatment, histopathology and biochemistry analysis showed liver necrosis, focal inflammation and an increase in Alanine Aminotransferase and Aspartate Aminotransferase. OTA alone did not cause any alteration. The acute hepatotoxic effects caused by AFB1 were less pronounced in animals treated with both mycotoxins. With regard to the MN assay, after 24 h, positive results were obtained for AFB1 and negative results were obtained for OTA, although both toxins caused bone marrow toxicity. In the combined treatment, OTA reduced the toxicity and the number of MN produced by AFB1. In the comet assay, after 3 h, positive results were obtained for AFB1 in the liver and for OTA in the kidney. The combined treatment reduced DNA damage in the liver and had no influence in the kidney. Altogether, these results may be indicative of an antagonistic relationship regarding the genotoxicity of both mycotoxins.

Gene expression changes induced by ochratoxin A in renal and hepatic tissues of male F344 rat after oral repeated administration.

Ochratoxin A (OTA), a naturally occurring mycotoxin, is nephrotoxic in all animal species tested and is considered a potent renal carcinogen, particularly in male rats. Its mechanism of toxicity is still unknown, although oxidative stress appears to be a plausible mechanism. Therefore, the objective of this study was to identify the biological pathways that are modulated in vivo by OTA in male F344 rats in order to gain further insight into its mechanism of renal toxicity. Rats were gavaged daily with OTA (500 microg/kg bw) and gene expression profiles in target and non-target organs were analyzed after 7 and 21 days administration. As was expected, a time-dependent increase of OTA concentrations was found in plasma, kidney and liver, with the concentrations found in both tissues being quite similar. However, histopathological examinations only revealed changes in kidney; signs of nephrotoxicity involving single cell necrosis and karyomegalic nuclei were observed in the treated rats. The number of differentially expressed genes in kidney was much higher than in liver (541 versus 11 at both time points). Several similarities were observed with other in vivo gene expression data. However, great differences were found with previous in vitro gene expression data, with the exception of DNA damage response which was not observed at mRNA level in any of our study conditions. Down-regulation was the predominant effect. Oxidative stress response pathway and genes involved in metabolism and transport were inhibited at both time points. RGN (regucalcin) - a gene implicated in calcium homeostasis - was strongly inhibited at both time points and genes implicated in cell survival and proliferation were up-regulated at day 21. Moreover, translation factors and annexin genes were up-regulated at both time points. Apart from oxidative stress, alterations of the calcium homeostasis and cytoskeleton structure may be present at the first events of OTA toxicity.

Comparative acute systemic toxicity of several quinoxaline 1,4-di-N-oxides in Wistar rats.

The acute toxicity of six quinoxaline 1,4-di-N-oxides has been evaluated in an attempt to determine: a) the feasibility of testing systemic toxicity of these compounds in a very preliminary phase without an adequate formulation for in vivo administration, b) the LD50 range and the toxic target organ of these compounds in order to have an approximation of the structure-activity relationship. Quinoxaline 1,4-di-N-oxides have shown a great variety of biological activities with potential therapeutic application in cancer, malaria, etc. Problems of toxicity hinder the progression of these compounds to clinical phases. The compounds dissolved in DMSO at their solubility limit were administered i.v. to female Wistar rats (8 weeks, 160 g), using an infusion pump (300 microL; 20 microl/min). Animals were observed for a period of 14 days. This dose of the vehicle (1.7 ml/kg) was well tolerated by the animals. The LD50 could not be determined, but a marked hypoactivity was induced by the treatment. The same compounds were also injected intraperitoneally, suspended in 0.01% Tween 80/0.09 % saline, and the animals that did not die were observed for a period of 14 days. The LD50 could be estimated to be in a range between 30 and 120 mg/kg, except for one of the compounds. A decrease in the evolution of body weight and hypoactivity were the principal symptoms induced by the treatment. In both assays, histopathologic study of heart, liver, kidney, lung, spleen and ovaries indicated that the target organs may be heart and spleen. In conclusion, the i.v. route is not adequate for estimating the LD50 of these compounds due to solubility problems; by i.p. route, the LD50 interval is between 30 and 120 mg/kg. The data did not permit the deduction of any specific structure-activity relationship.