# Evaluation of Ototoxic Effects of Cisplatin in a Rat Model: A Dose-Response Study
## 1 Introduction  
In 2022, approximately 20 million new cancer cases and 9.7 million deaths occurred worldwide [1]. Despite well-documented side effects, cisplatin (cis-dclorodiamminoplatin, CDDP) chemotherapy is widely used as single-agent or combination therapy for induction and neoadjuvant therapy in several solid tumors. The therapeutic and side effects of CDDP are influenced by various pharmacological factors, including dose and method of administration (single and cumulative dose) [2; 3; 4]. In particular, the therapeutic effects of CDDP can be achieved through cytotoxic lesions in cancer cells, as it can form bonds with DNA and possibly also interact with proteins and RNA, leading to the destruction of cell functions and induction of apoptosis [5; 6]. Nausea and vomiting (currently treated with an antiemetic regimen) are the main side effects followed by neurotoxicity, nephrotoxicity, and ototoxicity, as well as less frequent but notable liver, respiratory, and hematological effects [2; 5; 7]. CDDP ototoxicity manifests itself in vertigo, tinnitus, and hearing loss. In severe cases, hearing loss can become bilateral either temporarily or permanently [3; 8]. The onset of hearing loss occurs at high frequencies within the cochlea and then progresses to the frequency range of spoken language [4]. The use of animal models has validated that this type of hearing loss is caused by CDDP ototoxicity, as it is capable of interacting and forming adducts with DNA strands, causing an inflammatory response and generating reactive oxygen species (ROS) [3; 9; 10; 11]. ROS production in the basal turn of the cochlea causes the loss of outer hair cells, resulting in an influx of calcium in the cochlear cells, which ultimately leads to cell apoptosis [3]. In mammals, hair cell loss is not repairable due to the lack of stem cell niches in the cochlea to replace damaged sensory tissue [12; 13]. CDDP-induced nephrotoxicity is common and frequently severe due to tubular dysfunction. The development of acute kidney injury usually occurs after a few days of treatment. The occurrence of hypomagnesemia is possible, especially after multiple doses of CDDP [14; 15]. Risk factors for CDDP nephrotoxicity include single and cumulative dose, frequency of administration [16], female sex, advanced age, smoking and hypoalbuminemia, as well as preexisting kidney problems [17; 18]. Nephrotoxicity caused by cisplatin is complex and involves multiple processes that are directed toward cell death. In vitro experiments conducted in the primary culture cells of the mouse proximal tubule have shown that low concentrations of CDDP lead to apoptosis, while high concentrations lead to necrosis. However, in vivo administration causes death by both necrosis and apoptosis [17]. To date, it has become clear that toxicity is due to oxidative stress in both cases of nephrotoxicity and ototoxicity [6; 8; 19]. Oxidative stress occurs when there is a discrepancy between the amount of ROS in an organism and its ability to counteract them through detoxification or damage repair. ROS are divided into two categories: radical molecules such as superoxide anion (O\({}^{2-}\)) and hydroxyl radical (OH-) and non-radical molecules such as hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) [20]. The superoxide radical is very reactive, so it has a very short half-life (-1 ns), while H\({}_{2}\)O\({}_{2}\) has such low reactivity that the molecule can enter the cell nucleus, generating peroxide ions and hydroxyl radicals that can cause serious damage to DNA, membrane proteins, and lipids [20]. H\({}_{2}\)O\({}_{2}\) has already been shown to be a dangerous reactive species in in vitro cells derived from the organ of [PERSON] (ODC) [21]. ROS-induced oxidative stress can be addressed by cells that produce certain molecules with defense functions, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) [20]. Antioxidants become active when reduced and are reactivated by specific enzymes.