Effects of 17 beta-estradiol and its isomer 17 alpha-estradiol on learning in rats with chronic cholinergic deficiency in the brain

Kinetic Study of 17α-Estradiol Activity in Comparison with 17β-Estradiol and 17α-Ethynylestradiol

17α-estradiol (αE2), an endogenous stereoisomer of the hormone 17β-estradiol (E2), is capable of binding to estrogen receptors (ER). We aimed to mathematically describe, using experimental data, the possible interactions between αE2 and sperm ER during the process of sperm capacitation and to develop a kinetic model. The goal was to compare the suggested kinetic model with previously published results of ER interactions with E2 and 17α-ethynylestradiol (EE2). The HPLC-MS/MS method was developed to monitor the changes of αE2 concentration during capacitation. The calculated relative concentrations Bt were used for kinetic analysis. Rate constants k and molar ratio n were optimized and used for the construction of theoretical B(t) curves. Modifications in αE2–ER interactions were discovered during comparison with models for E2 and EE2. These new interactions displayed autocatalytic formation of an unstable adduct between the hormone and the cytoplasmic receptors. αE2 accumulates between the plasma membrane lipid bilayer with increasing potential, and when the critical level is reached, αE2 penetrates through the inner layer of the plasma membrane into the cytoplasm. It then rapidly reacts with the ER and creates an unstable adduct. The revealed dynamics of αE2–ER action may contribute to understanding tissue rejuvenation and the cancer-related physiology of αE2 signaling.

17α-Estradiol: a candidate neuroserm and non-feminizing estrogen for postmenopausal neuronal complications

Extensive evidence suggests that decline in ovarian function with menopause is associated with neuronal dysfunction. Major cause of this is rise in oxidative stress and inflammatory cytokines because of estrogen deficiency. 17β-Estradiol (E2, hormone with potent antioxidant and anti-inflammatory activity) has profound protective actions on multiple organ systems, but feminizing side effects of β-estradiol limits its clinical efficacy. 17α-Estradiol (E2α), a non feminizing congener, gives a ray of hope to the scientific community as an alternative strategy to treat menopause associated neuronal pathologies. We assessed the protective actions of 17α-estradiol (5, 10μg/kg) against cognitive deficits, depression and motor coordination after 4weeks of ovariectomy in rats and compared its efficacy with E2 at same doses. After the behavioral assay animals were sacrificed and their brains were harvested for biochemical studies. Uterine weights were also assessed. E2 and E2α (5, 10μg/kg) were equally protective against attenuating cognitive deficits, depressive symptoms and motor incoordination in OVX rats. Both demonstrated significant antioxidant activity and E2, but not E2α, increased serum estradiol levels and proliferated uterine weights, markers of feminizing action. It can thus be concluded that E2α offers safe alternative to E2 in protecting against menopausal neuropathologies.

Development of 17alpha-estradiol as a neuroprotective therapeutic agent: rationale and results from a phase I clinical study

17alpha-estradiol (17alpha-E2) differs from its isomer, the potent feminizing hormone 17beta-estradiol (17beta-E2), only in the stereochemistry at one carbon, but this is sufficient to render it at least 200-fold less active as a transactivating hormone. Despite its meager hormonal activity, 17alpha-E2 is as potent as 17beta-E2 in protecting a wide variety of cell types, including primary neurons, from a diverse array of lethal and etiologically relevant stressors, including amyloid toxicity, serum withdrawal, oxidative stress, excitotoxicity, and mitochondrial inhibition, among others. Moreover, both estradiol isomers have shown efficacy in animal models of stroke, Alzheimer's disease (AD), and Parkinson's disease (PD). Data from many labs have yielded a mechanistic model in which 17alpha-E2 intercalates into cell membranes, where it terminates lipid peroxidation chain reactions, thereby preserving membrane integrity, and where it in turn is redox cycled by glutathione or by NADPH through enzymatic coupling. Maintaining membrane integrity is critical to mitochondrial function, where loss of impermeability of the inner membrane initiates both necrotic and apoptotic pathways. Thus, by serving as a mitoprotectant, 17alpha-E2 forestalls cell death and could correspondingly provide therapeutic benefit in a host of degenerative diseases, including AD, PD, Friedreich's ataxia, and amyotrophic lateral sclerosis, while at the same time circumventing the common adverse effects elicited by more hormonally active analogues. Positive safety and pharmacokinetic data from a successful phase I clinical study with oral 17alpha-E2 (sodium sulfate conjugate) are presented here, and several options for its future clinical assessment are discussed.