Effects of 2-methoxyestradiol on hydrogen peroxide induced neuronal cell death and tau hyperphosphorylation

Alzheimer's Disease (AD) is characterized by progressive cognitive impairment, and memory loss. It has been shown that depletion of estrogens renders women vulnerable to AD with menopause women presenting higher risk for AD development than men. However, women under hormone replacement therapy (HRT) with 17β-estradiol (E2) show lower risk for AD, implying that E2 may be protective. It has been shown that E2 exerts its effects through the estrogen receptor (ER) but also via its biologically active metabolites, 2-hydroxyestradiol (2OH), and 2-methoxyestradiol (2ME). We hypothesized that the neuroprotective effects of E2 are partly attributed to its metabolites. SH-SY5Y neuronal cells were subjected oxidative stress (OS) cell death by hydrogen peroxide (H2O2), in the presence or absence of E2, 2ME and 2OH. Viability was assessed by trypan blue and thiazolyl blue tetrazolium bromide assays, intracellular OS with the Dichlorodihydrofluorescein Diacetate (DCFDA) assay, and Bax, p53 and PUMA quantified by RT-PCR. Tau hyperphosphorylation was studied by western blot. E2 and its metabolites 2OH and 2ME protect from cell death as assessed by the viability assays. Their effect was partly attributed to their antioxidant properties evidenced by the reduction of intracellular OS. Treatment with 2ME resulted in a reduction of Bax, but not p53 or PUMA in cells challenged with OS. Finally, 2ME was able to inhibit tau hyperphosphorylation as well. E2 protects neuron cells partly through its metabolites. Further studies are needed to fully delineate the mechanism for this protection.