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

AIMS: 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 17ß-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. MATERIALS AND METHODS: 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. KEY FINDINGS: 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. SIGNIFICANCE: E2 protects neuron cells partly through its metabolites. Further studies are needed to fully delineate the mechanism for this protection.

Ginkgo biloba L. flavonoids inhibit CYP 2A5; potential dietary supplement for nicotine replacement therapy enhancement.

Smoking is a public health concern, and even though smoking cessation methods exist, nicotine replacement therapy (NRT) is often ineffective. Smoking behavior is related to the nicotine metabolizing enzyme (NME) P450 2A6 (mouse 2A5) polymorphisms. Accordingly, fast metabolizers are nicotine dependent, and have low quitting rates compared to slow metabolizers. In this study we examined the ability of Ginkgo biloba L (GB) and its constituents to inhibit the NME, using mouse liver microsomes containing the 2A5 enzyme. Our results indicate that GB can inhibit 2A5 (25% inhibition at 5%v/v), with the flavonoids quercetin, isorhamnetin, and kaempferol being responsible for this inhibition (23.5%, 10.7%, 25.2% inhibition at 60 ng/µL, respectively). Importantly, the flavonoids inhibited 2A5 via mechanism based inhibition (for quercetin 30 ng/µl inhibition increased from 20.8% to 26.9% within 15 minutes). Our results suggest that GB if consumed on a regular basis can help NRT enhancement particularly in fast nicotine metabolizers.