Prostate tissue response and antioxidant defense of rats submitted to obesity during aging and treated with melatonin

Abstract

The prostate is an organ very susceptible to changes during senescence. Benign prostate hyperplasia (BPH) and adenocarcinoma incidence increase dramatically at middle-age. Clinical and experimental studies indicate that prostate pathology is induced by factors as an imbalance in estrogen/testosterone ratio, insulin resistance, and impairment of antioxidant defense. Obesity and high lipid intake are also considered risk factors for prostate cancer development. Melatonin is a hormone with multiple functions, including antioxidant activity. In vitro studies corroborate the antiproliferative action of melatonin in prostatic cancer cells, but investigations in vivo about its role in the gland are scarce. The aim of this study is to investigate if melatonin treatment influences tissue alterations and oxidative stress in the prostate of normal or obese middle-aged rats. Analyses of tissues alterations will be based on (1) prostatic histology exam, (2) proliferative activity, (3) AR-positive cells number, and (4) incidence of pathologic lesions in the prostate gland. Biochemistry oxidative stress analyses will be determined by (5) antioxidant enzymes activity and (6) lipidic peroxidation levels. Male Wistar rats at 62nd week old will be randomly distributed into groups (n=10 per group), consisting of control (C), control treated with melatonin (CM), obese (Ob), and obese treated with melatonin (OEM). Obesity will be induced at 24th weeks old, by a standardized model based on hyperlipidemic diet intake (20% lipids). Melatonin (100µg/kg body weight/day) will be provided in drinking water containing 0,01% ethanol, from the 48th week to the end of the experiment (62nd week of old). Testosterone, estrogen, and leptin levels will be evaluated by the ELISA method. Retroperitoneal fat weight will be quantified at euthanasia. The ventral prostate will be removed and processed for the general histologic exam, stereological analyses through point count methodology, immunocytochemistry, and histopathologic analyzes. Androgen receptor (AR) and cell proliferation (PCNA) estimate will be performed by immunocytochemistry, quantified, and expressed in percentage. Incidence and multiplicity of pathologic lesions will be evaluated, as hyperplasia, stromal and acinar inflammation, intraepithelial neoplasia, and adenocarcinoma. Immunocytochemistry for Bcl-2 may be used in this last case to prove malignancy. Biochemistries specific assays will be made to assess the enzymatic activity of the following oxidant enzymes - catalase, glutathione S-transferase, glutathione peroxidase, and superoxide dismutase. Acquired results will surely collaborate to elucidate of simultaneous effects of obesity and senescence on prostate and cellular mechanisms involved. The experiment will provide information about the behavior of the prostatic antioxidant system in obesity and aging conditions and reveal information about the possible role of exogenous melatonin on prostatic homeostasis under these conditions. (AU)