Targeted cytotoxic analogs of luteinizing hormone-releasing hormone: a reply

Targeting gonadotropins: an alternative option for Alzheimer disease treatment

Recent evidence indicates that, alongside oxidative stress, dysregulation of the cell cycle in neurons susceptible to degeneration in Alzheimer disease may play a crucial role in the initiation of the disease. As such, the role of reproductive hormones, which are closely associated with the cell cycle both during development and after birth, may be of key import. While estrogen has been the primary focus, the protective effects of hormone replacement therapy on cognition and dementia only during a “crucial period” led us to expand the study of hormonal influences to other members of the hypothalamic pituitary axis. Specifically, in this review, we focus on luteinizing hormone, which is not only increased in the sera of patients with Alzheimer disease but, like estrogen, is modulated by hormone replacement therapy and also influences cognitive behavior and pathogenic processing in animal models of the disease. Targeting gonadotropins may be a useful treatment strategy for disease targeting multiple pleiotropic downstream consequences.

Down-regulation of serum gonadotropins is as effective as estrogen replacement at improving menopause-associated cognitive deficits

Declining levels of estrogen in women result in increases in gonadotropins such as luteinizing hormone (LH) through loss of feedback inhibition. LH, like estrogen, is modulated by hormone replacement therapy. However, the role of post-menopausal gonadotropin increases on cognition has not been evaluated. Here, we demonstrate that the down-regulation of ovariectomy-driven LH elevations using the gonadotropin releasing hormone super-analogue, leuprolide acetate, improves cognitive function in the Morris water maze and Y-maze tests in the absence of E2. Furthermore, our data suggest that these effects are independent of the modulation of estrogen receptors alpha and beta, or activation of CYP19 and StAR, associated with the production of endogenous E2. Importantly, pathways associated with improved cognition such as CaMKII and GluR1-Ser831 are up-regulated by leuprolide treatment but not by chronic long-term E2 replacement suggesting independent cognition-modulating properties. Our findings suggest that down-regulation of gonadotropins is as effective as E2 in modulating cognition but likely acts through different molecular mechanisms. These findings provide a potential novel protective strategy to treat menopause/age-related cognitive decline and/or prevent the development of AD.

Gonadotropin-releasing hormone (GnRH)-I and GnRH-II induce cell growth inhibition in human endometrial cancer cells: involvement of integrin beta3 and focal adhesion kinase

Endometrial carcinoma is the most common neoplasm of the female genital tract, accounting for nearly one half of all gynecologic cancers in the Western world. Although intensive research on pathological phenomena of endometrial cancer is currently going on, but exact cause and biological aspects of this disease are not well described yet. In addition to well-documented roles of gonadotropin-releasing hormone (GnRH) in hypopituitary ovarian (HPO) axis, the agonistic or antagonistic analogs (or both) of GnRH have been shown to inhibit the proliferation of a variety of human gynecologic cancers. Thus, in the present study, we further examined the possibility that GnRH induces integrin beta3 and activation of focal adhesion kinase (FAK) through mitogen-activated protein kinases (MAPKs), ERK1/2 and p38, to inhibit the growth of HEC1A endometrial cancer cell line. As a result, both GnRH-I and GnRH-II resulted in a significant increase in integrin beta3 expression and evoked the activation of FAK in a time-dependent manner in these cells. In addition, these analogs induced an activation of ERK1/2 and p38 MAPK in a time-dependent manner as downstream pathways of FAK. It appears that GnRH-II has much greater effect on the activation of FAK, ERK1/2 and p38 compared to GnRH-I in these cells. Further, we demonstrated that the growth inhibition of HEC1A cells by GnRH-I or GnRH-II is involved in the activation of integrin-FAK and ERK1/2 and p38 MAPK pathways. Taken together, these results suggest that GnRH may be involved in the inhibition of endometrial cancer cell growth via activation of integrin beta3 and FAK as a direct effect. This knowledge could contribute to a better understanding of the mechanisms implicated in the therapeutic action of GnRH and its biomedical application for the treatment against endometrial cancer.

Menopause, estrogen, and gonadotropins in Alzheimer's disease

For decades, Alzheimer's disease (AD) has been linked to aging, gender, and menopause. Not surprisingly, this led most investigators to focus on the role of estrogen. While undoubtedly important, estrogen is unlikely the key determinant of disease pathogenesis. Rather, it appears that estrogen may work in conjunction with a novel determinant of disease pathogenesis, namely gonadotropins. The fact that gonadotropins, specifically luteinizing hormone, play a pivotal role in disease is apparent from significant etiological, epidemiological, and pathological evidences. Moreover, targeting gonadotropins appears to have beneficial actions as a therapeutic regimen.

Increases in luteinizing hormone are associated with declines in cognitive performance

Questions surrounding estrogen therapy for post-menopausal cognitive decline and dementia led us to examine the role of luteinizing hormone that becomes elevated after menopause. We examined hippocampal-associated cognitive performance, as measured with the Y-maze task, in two strains of transgenic mice, one (Tg-LHbeta) which over-expresses luteinizing hormone and another (LHRKO), which has increased circulating luteinizing hormone levels, but its receptors are silenced. Our results demonstrate that Tg-LHbeta, but not LHRKO mice, show decreased Y-maze performance when compared to aged-matched wild-type animals. These findings indicate that increased luteinizing hormone levels, in the presence of functional receptors may, at least in part, be responsible for cognitive decline after menopause. As such, modulation of luteinizing hormone or its receptor levels may prove to be useful therapeutic strategies for cognitive decline associated with aging and age-related neurodegenerative diseases such as Alzheimer disease.