# Evaluation of Ototoxic Effects of Cisplatin in a Rat Model: A Dose-Response Study
## 4 Discussion  
For almost 45 years, CDDP has been the cornerstone of chemotherapy for various solid cancers. However, its use was often limited by its side effects, such as ototoxicity and nephrotoxicity [28]. Investigating these effects in animal models remains crucial in developing better prevention protocols for oncological patients. The high mortality rate in these models, which was determined by the dose used and attributed to the systemic toxic effects of CDDP, remains an important obstacle in the experimental settings of CDDP [29; 30]. Therefore, our objective was to develop an in vivo model of cisplatin ototoxicity and nephrotoxicity that exhibited measurable damage and achieved the lowest to absent mortality. Our study found that in the 1-IP group, a single intraperitoneal injection group had a mortality rate of 25%, while the 3-IP group had a mortality rate of zero, which was achieved by giving CDDP 14 mg/kg in three daily doses of 4.6 mg/kg. The physical condition of the animals in the IP-3 group was still optimal after four days after the first injection, except for a predictable weight loss. The results are consistent with those of [PERSON] and collaborators [31], who treated CBA/J mice with CDDP at 15 mg/kg in a single dose or four daily doses, with a mortality rate of 70% to 10%, respectively. Weight loss was between 9% and 16% in our Sprague Dawley rat model, with no significant differences between the two drug administration modalities. Similar findings were found in other studies, where weight loss was dose-dependent and not influenced by the mode of administration of CDDP [32; 33; 34]. The causes of CDDP-induced weight loss can be called gastrointestinal toxicity, which leads to decreased appetite and reduced food intake, as well as reduced water absorption, resulting in excessive sodium secretion by tubular cells in the kidney, leading to polyuria, dehydration, and, ultimately, weight loss [35; 36]. Ototoxicity is a common adverse effect associated with CCDP administration, with an estimated incidence of up to 36% among adult patients [37]. In both animal and human populations, frequency and severity were observed to be dose-dependent [38; 39; 40; 29]. ABR data confirm that CDDP at 14 mg/kg causes a shift in the threshold at all frequencies (Figure 4). This agrees with previous findings from previous experimental studies, particularly in the medial (8-16 kHz) and basal (32-64 kHz) regions of the cochlea [41; 32; 42]. It is worth noting that not only the dose of CDDP administered affects the extent of auditory damage, but also the way of administration [3; 39]. As we showed, compared to CDDP administered in three daily doses, a single dose of CDDP results in a reduction in hearing loss in the basal region of the cochlea (ABR: 3-IP 19.7 vs. 1-IP 34.7 dB, \(p=0.011\)). Although, the differences in the apical and medial regions were not significant between the two treated groups. The permanent hearing loss caused by CDDP was caused by irreversible damage to neurosensorial tissue [2; 11; 42; 41]. The cells most affected were OHC, with increasing damage from the apical cochlear region to the base [38; 43; 44; 31; 45]. This damage depends on both the dose and time, and the number of missing hair cells is correlated with increasing doses of CDDP [2; 39; 44; 46]. Our study confirmed these results. The 3-IP group had significantly higher cell loss than the NT group but was lower than the 1-IP group (1-IP 68.32% vs. 25.65% 3-IP). The observed damage, as expected, mainly affects hair cells (especially OHCs) in the basal region, with less extensive damage in the medial region and no damage in the apical region. Cochleograms obtained by scanning electron microscopy (SEM) or confocal TUNEL analysis facilitate accurate cell counting by correlating cell integrity with the presence of stereocilia and nuclei, respectively.