Abstract

The present studies were undertaken to investigate the possibility of an interaction between 17 β-estradiol (E2) and glutathione in protecting cells against the presence of β-amyloid 25–35 (βAP 25–35). We demonstrate that when evaluated individually, supraphysiological concentrations of either E2 (200 nm) or of reduced glutathione (GSH; 325 μm) can protect SK-N-SH human neuroblastoma cells from βAP 25–35 (20 μm) toxicity. This dose of βAP 25–35 was chosen based on the LD₅₀ (28.9 μm) obtained in our earlier work. However, in the presence of 3.25 μm GSH, the neuroprotective EC₅₀ of E2 was shifted from 126 ± 89 nm to 0.033 ± 0.031 nm, approximately 4000-fold. Similarly, in primary rat cortical neurons, the addition of GSH (3.25 μm) increased the potency of E2 against βAP 25–35 (10 μm) toxicity, as evidenced by a shift in the EC₅₀ values of E2 from 68 ± 79 nm in the absence of GSH to 4 ± 6 nm in its presence. The synergy between E2 and GSH was not antagonized by the addition of the estrogen receptor antagonist, ICI 182,780. Other thiol-containing compounds did not interact synergistically with E2, nor were any synergistic interactions observed between E2 and ascorbic acid or α-tocopherol. Based on these data, we propose an estrogen-receptor independent synergistic interaction between glutathione and E2 that dramatically increases the neuroprotective potency of the steroid and may provide insight for the development of new treatment strategies for neurodegenerative diseases.