Estradiol and raloxifene protect cultured SN4741 neurons against oxidative stress

A large body of research has documented neuroprotective effects of estrogen against oxidative stress. Some neurodegenerative diseases such as Parkinson's disease, in which oxidative stress has been implicated as a contributing factor, affect more males than females, suggesting a possible protective effect of estrogen. We used the clonal substantia nigra cell line SN4741 to compare the neuroprotective properties of estrogen and raloxifene against oxidative stress, and to determine whether raloxifene acted as an estrogen agonist or antagonist in this system. We pretreated SN4741 cultures with alpha-estradiol, beta-estradiol, and raloxifene, and exposed them to hydrogen peroxide. Low nanomolar levels of raloxifene, beta-estradiol, and alpha-estradiol all significantly reduced cell death caused by oxidative stress. The estrogen receptor (ER) antagonist ICI 182,780 failed to reverse the neuroprotection by beta-estradiol, suggesting that the effect is not mediated by a classical ER. Western blotting using an antibody to the C-terminus region of ER-alpha revealed two bands, one at approximately 67 kDa (corresponding to ER-alpha) and a more prominent band at approximately 55-56 kDa. These results suggest that, in this cell line, both raloxifene and estrogen may be acting via a non-classical estrogen receptor.