# Evaluation of Ototoxic Effects of Cisplatin in a Rat Model: A Dose-Response Study
## 4 Discussion
It was probable that the border region, which encompasses the terminal portion of PCT, was more susceptible to ototoxic agents, and the medulla and cortex can stimulate other cells to generate SOD1 in the nucleus, allowing epithelial cells to be prepared to counteract potential oxidative damage. In rats treated with CDDP, nuclear staining was present in PCT cells throughout the cortex, while detached and necrotic cells were not detected in the damaged region; although, degenerate nuclei and necrotic nuclear fragments were observed. Stress-induced cells located in the border region between the medulla and cortex can stimulate other cells to generate SOD1 to be prepared for oxidative stress, and cells in areas with negative staining may have lost their mechanism of protection against oxidative stress and died through apoptosis or necrosis. Comparable results were observed in other animal models treated with cisplatin, where the investigation focused on the role of cisplatin in the induction of drug-induced liver injury (DILI), a significant concern due to its potential to precipitate acute liver failure [98; 99]. In mice, it was shown that the hepatotoxic effects of cisplatin are predominantly mediated through the generation of reactive oxygen species (ROS), such as the superoxide anion (O\({}^{2-}\)), which induce oxidative stress, apoptosis, and subsequent liver damage [98]. Additionally, the expression levels of superoxide dismutase 1 (SOD1) and glutathione peroxidase, another antioxidant enzyme, were found to be reduced. Furthermore,histopathological analyses revealed that exposure to cisplatin results in hepatocellular necrosis, particularly in the centrilobular regions of the liver [99]. In cisplatin-induced ototoxicity, both the Haber-Weiss and Fenton reactions are involved. These reactions contribute to the generation of reactive oxygen species (ROS), which play a significant role in oxidative stress leading to cochlear cell damage [3; 4; 5; 6]. Regarding CYI isoforms, the involvement of cytochrome P450 enzymes (CYPs) in cisplatin-induced ototoxicity has been studied, but specific CYI isoforms (such as CYP1A1 and CYP1A2) are typically not highlighted in the context of ototoxicity [100; 101]. The focus is more on oxidative stress and inflammatory pathways. The Haber-Weiss reaction produces hydroxyl radicals (OH-) from hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) and superoxide (O\({}^{2-}\)). The Fenton reaction generates hydroxyl radicals (OH-) from hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) and ferrous ions (Fe\({}^{2+}\)). We describe the ROS involvement investigating nitrotyrosine and superoxide dismutase 1 (SOD1). Nitrotyrosine formation indicates nitrosative stress, resulting from the reaction of tyrosine with peroxynitrite (ONOO-). SOD1 catalyzes the dismutation of superoxide (O\({}^{2-}\)) into oxygen (O\({}_{2}\)) and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)), mitigating oxidative stress. In summary, the cumulative dose of CDDP of 14 mg/kg administered in three doses (IP-3) used in our experimental rat model was found to be the most effective way to study the ototoxicity and nephrotoxicity induced by exposure to this chemotherapeutic agent: due to the evidence of well-characterized induced ototoxic and nephrotoxic damage, along with the absence of mortality. Ototoxic damage in the IP-3 group was characterized by significant hearing loss, particularly at high frequencies, and loss of hair cells, especially OHCs, both related to the basal region of the cochlea. The stria vascularis and spiral ganglion did not show any morphological changes. CDDP causes oxidative stress in the cochlear area by increasing the number of nitrosylated proteins, specifically in the stria vascularis, spiral ligament, and organ of Corti. CDDP had a significant impact on SOD1 expression in OHCs, resulting in an increase in reactive nitrogen species, enzyme dysfunction, and cell death. The stria vascularis was not affected by these effects, probably due to the abundance of SOD and other antioxidant enzymes.