Effects of estrogens on oxidative protein damage in plasma and tissues in ovariectomised rats

To assess estrogen-related changes in the redox status of the brain and liver proteins as well as the systemic oxidative stress in ovarectomised (OVX) rats

Twelve-week-old, sexually mature female Sprague-Dawley rats (200-250g) were randomly divided into four groups: The following treatment combinations were administrated daily to all in 0.05 ml 96% ethanol solution by gastric gavage. (1) Sham operation (2) OVX rats (3) OVX rats [0.02 mg/kg/day of 17beta-estradiol (E2) and 0.01 mg/kg/day of norethisterone acetate] (4) OVX rats [E2 (0.01 mg/kg/day) and drospirenon (0.02 mg/kg/day)]. Estrogen levels were determined using routine clinical-chemistry methods. We also measured protein oxidation parameters such as protein carbonyl (PCO), total thiol (T-SH) and the other oxidative stress markers malondialdehyde (MDA) and glutathione (GSH).

Ovariectomy resulted in abnormal elevation of plasma and tissue oxidative stress markers and changes in redox status of the proteins in tissue dependent manner. Supplementation of various estrogens combinations partially alleviated these abnormalities and restored redox homeostasis of proteins after the ovariectomy. Among the studied protein oxidation parameters, plasma and tissue PCO levels of the OVX rats were higher than those of the control groups (P < 0.01). Hormone replacement therapies (HRT) caused a decrease in PCO and MDA in both plasma and tissue of the OVX rats (P < 0.01). HRT in OVX rats decreased plasma MDA and increased liver and brain GSH (P < 0.01). Liver MDA levels of the Drospirenon-treated rats were lower than in the norethisterone acetate group (P < 0.01). On the other hand, Drospirenon increases brain GSH s more effectively than norethisterone acetate (P < 0.01). After bilateral oopherectomy, plasma and tissue T-SH levels decreased in the OVX group compared with control (P < 0.01). Norethisterone acetate increased plasma T-SH more effectively than Drospirenon (P < 0.05)

The study showed the extent of oxidative protein damage (OPD) in this model of estrogen deficiency. The protective effect of estrogens against tissue specific OPD suggests that estrogens play an important role within the antioxidant defense systems in plasma, liver and brain. The exact molecular mechanisms leading to these findings are not yet completely known. Meanwhile, hormone replacement therapy for the prevention of OPD in a tissue specific manner may be required.