Protection and Spontaneous Recovery from Cisplatin-Induced Hearing Loss
Cisplatin [cis-diamminechloroplatinum(II)] has proved itself as a potent antineoplastic agent. However, nephrotoxicity, neurotoxicity, gastrointestinal toxicity, myelosuppression, and ototoxicity interfere with its therapeutical efficacy. Forced diuresis reduces nephrotoxicity, effectively leaving neurotoxicity and ototoxicity as the major side effects of concern, and gastrointestinal toxicity and myelosuppression as the secondary side effects.
So far, attempts to reduce these side effects by developing equally potent platinum analogs have been unsuccessful. Some success has been achieved, however, by cotreatment with protective agents. Nearly all these agents are sulfuror sulfhydryl-containing compounds (thio compounds), known as antioxidants and potent heavy metal chelators. These thio compounds may provide protection from cisplatin toxicity either (1) by direct interaction between the cisplatin and the thio moiety, (2) by displacing platinum from its site of toxic action, (3) by preventing platinum from interfering with superoxide dismutase, or (4) by scavenging of cisplatin-induced free radicals. In particular the first two protective mechanisms bear the risk of reducing the antineoplastic activity of cisplatin.
Since nephrotoxicity can be controlled effectively by forced diuresis, a more specific approach of coping with ototoxicity by focusing on protection at the sensorineural level was chosen. Being familiar with the neuroprotective and neurotrophic properties of ACTH-related neuropeptides, specifically against cisplatin-induced peripheral neuropathies, it was judged expedient to test for a possible otoprotective action of these neuropeptides. The results were positive, although tainted with high interanimal variability.
When testing for the possibility that the neuropeptides would merely delay cisplatin-induced ototoxicity rather than reduce it, it was discovered in control series without neuropeptide cotreatment that the ear can recover spontaneously from cisplatin-induced hearing loss. This was found both electrophysiologically and in outer hair cell (OHC) counts. Although these preliminary findings require further investigation, they strongly suggest that spontaneous recovery of cochlear injury can occur in the mature mammalian cochlea. Moreover, the otoprotective action of the ACTH-related neuropeptides suggests that it may be possible to stimulate recovery from acute hearing loss using neuropeptides.