Modulation of copper transporters in protection against cisplatin-induced cochlear hair cell damage

Abstract

Cisplatin belongs to platinum-based drugs and is widely used in cancer chemotherapy. Ototoxicity is one of the major dose limiting side-effects of cisplatin. For toxicity to occur cisplatin must first be transported from the bloodstream into cochlear cells. Three copper transporters are considered pathways for regulating the uptake and translocation of cisplatin into cells: Ctr1, ATP7A and ATP7B. Our recent study with cochlear organotypic cultures shows that cochlear hair cells can be destroyed by cisplatin at low concentrations from 10μm to 100μn. However, high doses of cisplatin cannot damage hair cells, maybe due to intrinsic feedback reactions that increase export of platinum by ATP7B when the platinum concentration is high in extracellular space. Cimitidine is a specific copper transporter inhibitor that can block the entrance of copper and platinum, and may prevent cisplatin-induced cochlear hair cell injury. To evaluate this hypothesis, we treated cochlear organotypic cultures with cisplatin (10 μm or 50 μm) alone, or cisplatin combined with cimitidine at concentrations ranging from 10-2000 μm for 48 hours. cisplatin at 10 μm damaged about 20% hair cells. In contrast, when cimitidine (10 μm, 100 μm and 2000 μm) was added to the culture, near 100% cochlear hair cell survived. At higher concentration (50 μm), cisplatin destroyed about 80% of cochlear hair cells. However, 100 μmcimitidine rescued about 50% hair cells from cisplatin damage, and 2000μm cimitidine protected about 80% hair cells. The data of western blot showed that CTR1 and ATP7B expressions were increased in cisplatin treated cochlear tissue, but cimitidine significantly reduced CTR1 and ATP7B. In addition, ATP7A expression was depressed a little after cisplatin treatment. Considering that Ctr1 is involved in copper and platinum influx, but the ATP7A and ATP7B are copper export transporters, the results suggest that cimitidine can effectively block the entrance by copper transporters and stop the influx of cisplatin.