Effects of 17β-estradiol on proliferation, cell viability and intracellular redox status in native human lens epithelial cells

Purpose: The purpose of this study was to examine the effects of 17β-estradiol on proliferation, cell death and redox status in cultured human lens epithelial cells (HLECs). Methods: HLECs were exposed to 17β-estradiol after which cell viability was measured by 3-(4,5dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) and the number of mitotic and apoptotic cell nuclei was determined after staining with Hoechst 33342. Apoptosis was also determined by measuring caspase-3 activity and propidium iodide was used to determine the proportion of non-viable cells. Pro- and antioxidative effects of 17β-estradiol was investigated by measuring peroxides, superoxides and glutathione, using dichlorofluorescein diacetate (DCFH-DA), dihydroethidium (HET), and monochlorobimane (MCB), respectively. Effects on mitochondrial membrane potential were determined using 5,5′,6,6’-tetrachloro-1,1’,3,3′- tetraethylbenzimidazolylcarbocyanine iodide (JC-1). The ability of 17β-estradiol to prevent reactive oxygen species (ROS)-production in HLECs after exposure to 25 µM H2O2 for 24h was also measured. Results: This study demonstrates increased mitotic activity in HLECs exposed to physiologic concentrations of 17βestradiol (1 nM). Pharmacological concentrations of 17β-estradiol caused increased number of apoptotic cell nuclei and caspase-3 activation. Physiologic concentrations of 17β-estradiol (0.1–10 nM) stabilized the mitochondrial membrane potential. Similar or slightly higher concentrations of 17β-estradiol (0.01–1 µM) protected against H2O2-induced oxidative stress as evident by decreased levels of peroxides and superoxides. Conclusions: The present study demonstrates mitogenic and anti-oxidative effects of 17β-estradiol at physiologic concentrations, whereas pharmacological levels induced oxidative stress and acted pro-apoptotic in cultured lens cells. Several studies indicate a higher prevalence of cataract among women as compared to men at the same age. Epidemiologic studies and data from National Quality Registers demonstrate a higher incidence of cataract extraction in women [1,2]. It has been suggested that there are gender-related differences in self-assessment of visual function and/or different demands for good visual acuity for men and women depending on their respective everyday activities or differences in longevity, which could contribute to this difference [2,3]. However, several population-based studies report on higher prevalence of lens opacities in women [4-7], thus indicating that female gender is indeed a “true” risk factor for cataract. There is accumulating evidence that hormonal status and the duration of life-time exposure to estrogen influence the risk of cataract formation. Older age at menarche has been associated with increased risk for cataract and a decreased risk