Protective Effect of Minocycline Against Cisplatin-induced Ototoxicity

OBJECTIVES: Cisplatin, a widely used chemotherapeutic agent, has serious side effects, including nephrotoxicity and ototoxicity. Minocycline is a semisynthetic second-generation tetracycline that exerts anti-inflammatory and neuroprotective effects. The purpose of this study was to elucidate the protective effect of minocycline against cisplatin-induced ototoxicity in the auditory hair cell. METHODS: The House Ear Institute-Organ of Corti 1 (HEI-OC1) cell line and guinea pigs were used for in vitro and in vivo experiments. Cells were exposed to cisplatin with or without pre-treatment with minocycline. Cell survival was analyzed using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide). Whole-cell lysates were collected and immunoblotted with antibodies against Bcl-2, p-c-Jun, active caspase-3, cleaved poly (ADP-ribose) polymerase (PARP), and apoptosis-inducing factor (AIF). The guinea pigs received intraperitoneal injections of cisplatin alone or following minocycline pretreatment. The auditory brainstem response was tested and the cochleae were harvested and evaluated using scanning electron microscopy. RESULTS: Survival significantly increased in cells pretreated with minocycline compared with cells exposed to cisplatin alone. Cisplatin treatment increased the expression of active caspase 3, p-c Jun, PARP, and AIF, and pretreatment with minocycline attenuated this response. In animal study, the threshold shift by cisplatin injection in the auditory brainstem response was less pronounced in animals pretreated with minocycline. Scanning electron microscopy revealed more severe damage to the outer hair cells at the basal and middle turns than the apical turn. CONCLUSION: Minocycline partially protects against cisplatin-induced ototoxicity via both caspase-dependent and independent apoptosis pathways.

Changes in the Expression Pattern of Cyclooxygenase-2, Mapkinases and Related Apoptotic Markers by Different Levels of Estrogen Supplementation in Mature or Ovariectomized Female Rat Heart

The effects of different concentrations of estrogen supplementation to mature female rats or estrogen supplementation to ovariectomized rats on cyclooxygenase-2 (COX-2) expression, PGE2 production and mapkinases expression were investigated in experimentally induced atherogenic rats with feeding a high fat.high cholesterol diet. In the first experiment using 48-week old mature rats, the supplementation of three different levels of estrogen was compared to the basal diet. The high concentration of estrogen supplementation induced the marked up-regulation of COX-2 protein and the increase in plasma PGE2 production and this seems to be followed by the up-regulation of p38 among mapkinases. The regulation of bax showed in a reverse trend of COX-2 in heart tissues of mature female rats. In the second experimental system, female Sprague-Dawley rats were bilaterally ovariectomized; sham-operated animals were used as controls. Three weeks later, the animals were supplied with basal diet to sham-operated control group and ovariectomized control group, and estrogen supplemented diet to ovariectomized group for an eight-week experimental period. In a group supplemented with a medium dose of estrogen, COX-2 expression was up-regulated. This up-regulation was accompanied by the elevated expression of pERK1/2. Bax was increased in estrogen-fed animals indicating bax might be involved in estrogen feeding state in ovariectomized rats. Further investigations on the relationship between COX-2 and biological activities such as vasodilation by estrogen are required in in vivo system of female rats at the various physiological states.