Induced ototoxicity in guinea pigs: dose-effect and morphofunctional evaluation

Abstract

Cisplatin is a chemotherapic broadly used for treatment of solid tumors with excellent results, however, it possesses many side effects as the nefrotoxicity, the suppression medular, the neuropathy and the ototoxicity. Although we have measures to avoid the first three, that doesn't happen with the coclear lesion, that doesn't present preventive measures and most of the time is irreversible. This way, a great interest exists in studying the ototoxicity’s mechanism. The scientific literature has shown conflicting evidences in relation to the ideal dose, the time at the beginning of the coclear lesion, the application way (acute or chronic) and the methodology for the ideal study on the ototoxicity induced by the cisplatina in humans or animals. The lack of more researches on the otoacoustic emissions (ideal exam to endorse the function of the cells external ciliadas) and its correlation with the ototoxic dose induced the idealization of this paper. Aim: to verify the dose and the ideal administration dose of cisplatin, with the purpose of obtain a significant lesion, consequently making possible its use for tests with otoproteting agents in albine guinea pigs, to ratify as methods morphofunctional ideals, the otoacoustic emissions and the electronic microscopy, and to define the best method for the morphometric study in the electronic microscopy. Material and Method: Female albine guinea pigs will be studied, with average from 350 to 400 g, in a total of 48 animals composing 4 study groups in agreement with the dose. All of the groups will count with a control animal for each one of the interventions. The study groups were divided in the following doses: Group 1: 9 animals with one dose of 7,5 mg/kg/d, intraperitoneal. Group 2: 9 animals with two doses of 7,5 mg/kg/d, in the first and fifth day, intraperitoneal. Group 3: 9 animals with 3 doses of 7,5 mg/kg/d in the first, fifth day, and seventh day, intraperitoneal. Group 4: 9 animals with doses 6 of 2,5 mg/kg/d in the first, second, third, fifth, sixth and eighth day, intraperitoneal. The otoacoustic emission by distortion products will be accomplished in all the animals, for being an exam highly sensitive for lesions in cells external ciliadas provoked by the cisplatina. After the accomplishment of the second otoacoustic emissions, the guinea pigs will be sacrificed by intracardiac injection with ketamine and xilasine, and their temporary bones removed. Afer the cochleae exposed, it will be perfund through the round window with glutaraldeide solution to 2,5% in cacodilate of sodium 0,1 M pH 7,2 for three times and later submerged in this same solution for more 48 hours in room temperature. At the end of this period the sample will be washed three times with during one hour, being proceeded the retreat of the optic capsule, and submerging the remaining material in the lid for other 12 hours. After it is made the dehydration in gradual series of etanol 50%, 70%, 90% (30 minutes each) and 100% (twice of 30 minutes), following by drying of critical point and bath of gold 25nm for the sputtering method. After that processing the cochleae will be observed under electronic microscopy over magnification of 350, 1500 and 2000 times. (AU)