Endocrine effects in the hazard assessment of drugs used in animal production.
Criteria of toxicological assessment are currently reviewed to ensure an adequate protection to susceptible groups, such as infants and children; in particular, concern arises about altered endocrine homeostasis in the developing organism, eliciting possible persistent effects such as reproductive disturbances and increased risk of tumours in target organs. Such items are obviously relevant also for veterinary drugs, whose main safety issue is potential lifetime exposure to residues. Two groups of chemicals, nitroimidazoles and imidazole antifungals, are reviewed as examples of the relevance of endocrine toxicity to the hazard assessment of compounds used in animal production. Nitroimidazoles are metabolized into genotoxic intermediates; in rodents they induce testicular toxicity and carcinogenicity. In particular, mammary neoplasms, mostly fibroadenomas, are consistently induced in rats as the most important effect in chronic studies; this may hint to possible endocrine-related mechanisms. Accordingly, evidences on other chemicals (e.g., triazines) show mammary tumorigenicity in rodents associated to hormonal alterations. In fact, nitroimidazoles affect synthesis of both pituitary and steroid hormones in vitro and rise progesterone and FSH levels in rats; also, limited clinical data in humans indicate endocrine-related effects. Overall, nitroimidazoles appear to affect the endocrine balance; however, the actual importance of such alterations, especially in regards to rat mammary tumours, has yet to be clarified. Imidazole antimycotics are broad-spectrum inhibitors of steroid synthesis; accordingly, diverse reproductive and developmental alterations are observed, depending on age and sex of animals exposed. Effects include pregnancy loss, delayed pup growth as well as reduced weight of androgen-dependent tissue; however, it is still difficult to identify the most susceptible biological phase. Overall the potential for inducing endocrine-related alterations should be carefully evaluated also for drugs used in animal production. A screening battery should produce a distinct fingerprint for each major endocrine activity, thus targeting longer-term tests (such as the two-generation study) on the most relevant endpoints. Moreover, the validation of molecular approaches would contribute to a biologically-based evaluation, by providing insights on such items as early effects and species-specificity.
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Macrì
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D032761:Animal Experimentation; D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity*; D004353:Drug Evaluation, Preclinical; D004354:Drug Screening Assays, Antitumor; D005260:Female; D006728:Hormones / Q000502:physiology*; D006801:Humans; D007093:Imidazoles / Q000633:toxicity*; D008297:Male
D000970:Antineoplastic Agents; D006728:Hormones; D007093:Imidazoles