Caracterização morfofuncional da ototoxicidade por cisplatina em ratos : avaliação do papel da apoptose e da otoproteção por amifostina

Abstract

Cisplatin (cis-diamminedicloroplatinum) is an antineoplastic drug frequently used in the treatment of a variety of cancers, specially the head-and-neck cancer. Ototoxicity, however, has been noted as a common side-effect of cisplatin, which may lead to significant interruptions in treatment, possibly impacting on local tumor control and patient survival. The aim of this work was to develop an experimental model in rats able to study the ototoxicity as a side effect of cisplatin and to perform otoprotection studies. In addition, we evaluated if apoptosis was involved in the cellular toxicity caused by cisplatin. Male Wistar rats were intraperitoneally (i.p.) treated with 24 mg/kg of cisplatin, which was divided into three equal doses (8mg/kg) or a single i.p. administration of 16 mg/kg. The animals were evaluated by distortion product otoacoustic emission (DPOAE) or brainstem evoked response audiometry (BERA) on the 3rd and 4th days after the cisplatin injection. After the functional hearing evaluation, a group of animals had their cochleas excised and processed for hematoxylin-eosin (HE) staining, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL), and immunostaining with a caspase-3 antibody. In another set of experiments, amifostine (240 mg/kg. i.p. divided in three daily doses of 80 mg/kg) was administered immediately before the cisplatin (24mg/kg). Treatment with cisplatin caused a significant body weigh loss starting on the 1st or 2nd days when compared to non-treated animals. The mortality rate remained low until the 3rd day with significant enhance on day 4. The treatment with cisplatin 24 mg/kg, but not 16 mg/kg, resulted in a significant decrease of the DPOAE. Both doses promoted an increase of the hearing limiar detected by BERA on day 3 and 4. Morphological observations indicate cochlear lesions mainly in the vascular stria and outer hair cells. Only the scores of cochlear lesions of animals treated with the highest dose of cisplatin were significant different when compared to the non-treated group. Apoptosis was involved in the cellular toxicity caused by cisplatin 16 mg/kg, on day 3. In the highest dose or for more drawn out time, however, others mechanisms of cell toxicity must be involved. Amifostine prevented the cisplatin ototoxicity detected by functional evaluation as well as the morphological analysis. Thus, in rats, the intraperitoneal injection of cisplatin 24 mg/kg, divided into 3 equal doses, consist in a viable model for study of this adverse effect of cisplatin, with ototoxicity detected by functional evaluation with BERA and morphologic evaluation by optic microscopy for HE stains, in the third day after the beginning of the administration. Moreover, it is useful for the research of the involved mechanisms with immunostaining techniques, and still for the evaluation of otoprotective drugs.