Low androgenization index in elderly women and elderly men with Alzheimer's disease

Protective actions of sex steroid hormones in Alzheimer's disease

Risk for Alzheimer's disease (AD) is associated with age-related loss of sex steroid hormones in both women and men. In post-menopausal women, the precipitous depletion of estrogens and progestogens is hypothesized to increase susceptibility to AD pathogenesis, a concept largely supported by epidemiological evidence but refuted by some clinical findings. Experimental evidence suggests that estrogens have numerous neuroprotective actions relevant to prevention of AD, in particular promotion of neuron viability and reduction of beta-amyloid accumulation, a critical factor in the initiation and progression of AD. Recent findings suggest neural responsiveness to estrogen can diminish with age, reducing neuroprotective actions of estrogen and, consequently, potentially limiting the utility of hormone therapies in aged women. In addition, estrogen neuroprotective actions are also modulated by progestogens. Specifically, continuous progestogen exposure is associated with inhibition of estrogen actions whereas cyclic delivery of progestogens may enhance neural benefits of estrogen. In recent years, emerging literature has begun to elucidate a parallel relationship of sex steroid hormones and AD risk in men. Normal age-related testosterone loss in men is associated with increased risk to several diseases including AD. Like estrogen, testosterone has been established as an endogenous neuroprotective factor that not only increases neuronal resilience against AD-related insults, but also reduces beta-amyloid accumulation. Androgen neuroprotective effects are mediated both directly by activation of androgen pathways and indirectly by aromatization to estradiol and initiation of protective estrogen signaling mechanisms. The successful use of hormone therapies in aging men and women to delay, prevent, and or treat AD will require additional research to optimize key parameters of hormone therapy and may benefit from the continuing development of selective estrogen and androgen receptor modulators.

Androgens and Alzheimer's disease

PURPOSE OF REVIEW

To discuss the relationship between androgens, cognition and Alzheimer's disease.

RECENT FINDINGS

It has been found that low circulating levels of androgens are a risk factor for Alzheimer's disease. Decreased circulating androgens are also associated with declining cognitive performance, particularly in memory-related tasks. Conversely, androgen supplementation to hypogonadal men results in improved memory performance. It has therefore been hypothesized that androgen supplementation may be beneficial in Alzheimer's disease. In recent studies, animal models have been used to elucidate the molecular mechanism behind this relationship between androgens and Alzheimer's disease. These studies have shown that androgen depletion results in increased levels of beta amyloid and hyperphosphorylated tau, changes which are thought to be associated with subsequent neuronal death.

SUMMARY

Androgen depletion results in molecular changes associated with Alzheimer's disease. Further human trials are needed to determine whether androgen modulating therapy for Alzheimer's disease has clinical significance.

Sex hormone binding globulin and incident Alzheimer's disease in elderly men and women

It has been suggested that low levels of estradiol and testosterone increase dementia risk. However, results of the existing observational studies examining associations of endogenous sex hormones with cognition and dementia are conflicting. A possible explanation for these inconsistent findings could be the involvement of sex hormone-binding globulin (SHBG) in regulating sex hormone levels. In the present study, we examined whether SHBG levels were associated with development of AD and overall dementia in a cohort of elderly men and women free of dementia at baseline. We observed that in both men and women higher levels of SHBG were associated with an increased risk for AD and overall dementia. These results were independent of vascular risk factors and bioactive hormone levels. Whether SHBG is causally related to dementia or whether it is a surrogate marker for rate of biological aging and increased risk or for preclinical stage of dementia has to be elucidated.

High tofu intake is associated with worse memory in elderly Indonesian men and women

BACKGROUND/AIMS

Cell culture studies suggest that phytoestrogens, abundant in soy products such as tempe and tofu, could protect against cognitive decline. Paradoxically, the Honolulu Asia Aging Study reported an increased risk for cognitive impairment and other dementia markers with high tofu (soybean curd) intake.

METHODS

A cross-sectional study was carried out in 2 rural sites (Borobudur and Sumedang) and 1 urban site (Jakarta) among mainly Javanese and Sundanese elderly (n = 719, 52-98 years of age). Memory was measured using a word learning test sensitive to dementia and soy consumption was assessed using Food Frequency Questionnaire items.

RESULTS

High tofu consumption was associated with worse memory (beta = -0.18, p < 0.01, 95% CI = -0.34 to -0.06), while high tempe consumption (a fermented whole soybean product) was independently related to better memory (beta = 0.12, p < 0.05, 95% CI = 0.00-0.28), particularly in participants over 68 years of age. Fruit consumption also had an independent positive association. The analyses were controlled for age, sex, education, site and intake of other foods.

CONCLUSION

The results for tofu consumption as a risk factor for low memory function may tie in with the Honolulu Asia Aging Study data. It is unclear whether these negative associations could be attributed to potential toxins or to its phytoestrogen levels. Estrogen (through which receptors phytoestrogens can exert effects) was found to increase dementia risk in women over 65 years of age. Tempe contains high levels of phytoestrogens, but (due to fermentation) also exhibits high folate levels which may exert protective effects. Future studies should validate these findings and investigate potential mechanisms.

Experience-dependent regulation of vesicular zinc in male and female 3xTg-AD mice

In the mammalian cerebral cortex, zinc is an important modulator of synaptic transmission and conversely, plasticity. Zinc is also involved, in a sex-dependent manner, in the pathogenesis of Alzheimer's disease (AD), where substantial declines in plasticity may occur. To examine this relationship further, the regulation of vesicular zinc was examined after the induction of cortical plasticity through vibrissae plucking in male and female C57Bl/6 and 3xTg-AD mice at various age points. Female C57Bl/6 mice were found to have an elevated response compared to male C57Bl/6 mice through mid-adult ages, a sex-difference likely mediated by the differential regulation of vesicular zinc by the sex hormones. Male 3xTg-AD mice had a significantly greater zincergic response compared to C57Bl/6 mice, which is likely indicative of a compensatory mechanism utilized by the male 3xTg-AD mice to combat the decline in plasticity associated with the AD state. These results exemplify how the regulation of vesicular zinc may be a significant component in the progression of AD, especially regarding the sex-dependent element.

Nonestrogen-based hormonal therapies for Alzheimer’s disease

Alzheimer’s disease (AD) is becoming increasingly more prevalent worldwide and is a costly, devastating disease. The fact that females are more likely to be diagnosed with AD than men has contributed to the large amount of research and literature on estrogen’s ability to rescue cognitive decline in aging females. However, recent results from the Women’s Health Initiative Memory Study (WHIMS) and the Research into Memory, Brain Function and Estrogen Replacement (REMEMBER) study, in which estrogen-replacement therapy is shown not to be beneficial to cognition in postmenopausal women, especially in women of more advanced ages, have opened the study of hormones and hormone-based therapies beyond that of sex steroids. As such, recent findings, and the focus of this review, indicate that gonadotropins such as luteinizing hormone have a role on cognitive function and AD. It is likely that the interplay of age, and the timing of estrogen and these other less studied hormones will allow us to gain a better understanding of hypothalamic–pituitary–gonadal axis regulation after menopause and how it relates to AD, and will hopefully lead to new avenues of treatment for AD.

Androgen cell signaling pathways involved in neuroprotective actions

As a normal consequence of aging in men, testosterone levels significantly decline in both serum and brain. Age-related testosterone depletion results in increased risk of dysfunction and disease in androgen-responsive tissues, including brain. Recent evidence indicates that one deleterious effect of age-related testosterone loss in men is increased risk for Alzheimer's disease (AD). We discuss recent findings from our laboratory and others that identify androgen actions implicated in protecting the brain against neurodegenerative diseases and begin to define androgen cell signaling pathways that underlie these protective effects. Specifically, we focus on the roles of androgens as (1) endogenous negative regulators of beta-amyloid accumulation, a key event in AD pathogenesis, and (2) neuroprotective factors that utilize rapid non-genomic signaling to inhibit neuronal apoptosis. Continued elucidation of cell signaling pathways that contribute to protective actions of androgens should facilitate the development of targeted therapeutic strategies to combat AD and other age-related neurodegenerative diseases.

Classical androgen receptors in non-classical sites in the brain

Androgen receptors are expressed in many different neuronal populations in the central nervous system where they often act as transcription factors in the cell nucleus. However, recent studies have detected androgen receptor immunoreactivity in neuronal and glial processes of the adult rat neocortex, hippocampal formation, and amygdala as well as in the telencephalon of eastern fence and green anole lizards. This review discusses previously published findings on extranuclear androgen receptors, as well as new experimental results that begin to establish a possible functional role for androgen receptors in axons within cortical regions. Electron microscopic studies have revealed that androgen receptor immunoreactive processes in the rat brain correspond to axons, dendrites and glial processes. New results show that lesions of the dorsal CA1 region by local administration of ibotenic acid reduce the density of androgen receptor immunoreactive axons in the cerebral cortex and the amygdala, suggesting that these axons may originate in the hippocampus. Androgen receptor immunoreactivity in axons is also decreased by the intracerebroventricular administration of colchicine, suggesting that androgen receptor protein is transported from the perikaryon to the axons by fast axonal transport. Androgen receptors in axons located in the cerebral cortex and amygdala and originating in the hippocampus may play an important role in the rapid behavioral effects of androgens.

Bioavailable testosterone is associated with a reduced risk of amnestic mild cognitive impairment in older men

OBJECTIVE

We investigated the risk of amnestic mild cognitive impairment (aMCI) in relation to serum bioavailable (BT) and total testosterone (TT) levels in older men.

DESIGN, SETTING AND SUBJECTS

A cross-sectional study in an ambulatory setting, with older men aged 55-93 years with normal cognition, aMCI and Alzheimer's disease (AD).

MEASUREMENTS

Morning serum BT and TT levels were determined. AD was diagnosed by the Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria for probable AD and aMCI by the Petersen criteria.

RESULTS

We recruited 203 Chinese older men (48 aMCI, 66 AD and 89 with normal cognition). Mean serum BT, but not TT, levels were significantly lower in the aMCI (mean BT +/- SEM 1.06 +/- 0.10 nmol/l) and AD (0.99 +/- 0.08 nmol/l) groups than in the normal controls (1.82 +/- 0.12 nmol/l) (P < 0.001, one-way anova) with no significant difference between the aMCI and AD groups. After adjustment for education, age and apolipoprotein E (apoE) genotype, logistic regression analyses showed that the serum BT level [adjusted odds ratio (OR) = 0.52, 95% confidence interval (CI) 0.32-0.85] was an independent protective factor for aMCI. For the combined outcome of aMCI and AD, the serum BT level was an independent protective factor but age and apoE epsilon4 were independent risk factors. There was no interaction between BT and age.

CONCLUSIONS

In older men, serum BT, but not TT, levels were associated with a lower risk of aMCI and AD.

The many faces of testosterone

Testosterone is more than a “male sex hormone”. It is an important contributor to the robust metabolic functioning of multiple bodily systems. The abuse of anabolic steroids by athletes over the years has been one of the major detractors from the investigation and treatment of clinical states that could be caused by or related to male hypogonadism. The unwarranted fear that testosterone therapy would induce prostate cancer has also deterred physicians form pursuing more aggressively the possibility of hypogonadism in symptomatic male patients. In addition to these two mythologies, many physicians believe that testosterone is bad for the male heart. The classical anabolic agents, 17-alkylated steroids, are, indeed, potentially harmful to the liver, to insulin action to lipid metabolism. These substances, however, are not testosterone, which has none of these adverse effects. The current evidence, in fact, strongly suggests that testosterone may be cardioprotective. There is virtually no evidence to implicate testosterone as a cause of prostate cancer. It may exacerbate an existing prostate cancer, although the evidence is flimsy, but it does not likely cause the cancer in the first place. Testosterone has stimulatory effects on bones, muscles, erythropoietin, libido, mood and cognition centres in the brain, penile erection. It is reduced in metabolic syndrome and diabetes and therapy with testosterone in these conditions may provide amelioration by lowering LDL cholesterol, blood sugar, glycated hemoglobin and insulin resistance. The best measure is bio-available testosterone which is the fraction of testosterone not bound to sex hormone binding globulin. Several forms of testosterone administration are available making compliance much less of an issue with testosterone replacement therapy.

The contribution of luteinizing hormone to Alzheimer disease pathogenesis

Several hypotheses have been proposed that attempt to explain the pathogenesis of Alzheimer Disease (AD) including theories involving senile plaque and neurofibrillary tangle formation, increased oxidative stress, and cell cycle abnormalities, since evidence for each of these pathological phenomena have been well documented in AD. Recent epidemiological and experimental data also support a role for the gonadotropin luteinizing hormone in AD. Paralleling the female predominance for developing AD, luteinizing hormone levels are significantly higher in females as compared to males, and furthermore, luteinizing hormone levels are higher still in individuals who succumb to AD. Luteinizing hormone, which is capable of modulating cognitive behavior, is not only present in the brain, but also has the highest receptor levels in the hippocampus, a key processor of cognition that is severely deteriorated in AD. Furthermore, we recently examined cognitive performance in a well-characterized transgenic mouse that over-expresses luteinizing hormone and found that these animals show decreased cognitive performance when compared to controls. We have also found that abolishing luteinizing hormone in amyloid-beta protein precursor transgenic mice (Tg2576) using a potent gonadotropin-lowering gonadotropin-releasing hormone agonist, leuprolide acetate, resulted in improved hippocampally-related cognitive performance and decreased amyloid-beta deposition. These findings, together with data indicating that luteinizing hormone modulates amyloid-beta protein precursor processing in vivo and in vitro, suggest that luteinizing hormone may contribute to AD pathology through an amyloid-dependent mechanism. These promising findings support the importance of luteinizing hormone in AD and bring to the forefront an alternative, and much needed, therapeutic avenue for the treatment of this insidious disease.

Can a single model explain both breast cancer and prostate cancer?

BACKGROUND

The Estradiol-Dihydrotestosterone model of prostate cancer (PC) showed how the interaction of hormones with specific hormone receptors affected apoptosis. The same hormone can produce different effects, depending on which hormone receptor it interacts with.

MODEL

This model proposes that the first step in the development of most PC and breast cancer (BC) occurs when aromatase converts testosterone to estradiol (E2). A sufficiently high enough local level of E2 results in telomerase activity. The telomerase activity allows cell division and may lead to BC or PC, which will proliferate if the rate of cell division is greater than the rate of cell death. The effect of hormones on their hormone receptors will affect the rate of cell death and determine whether or not the cancer proliferates.

CONCLUSION

By minimizing bcl-2 and maximizing apoptotic proteins, new systemic treatments for BC and PC can be developed that may be more effective than existing treatments.

Androgen regulation of beta-amyloid protein and the risk of Alzheimer's disease

Advancing age is the most significant risk factor for the development of Alzheimer's disease (AD), however the age-related changes that underlie this effect remain unclear. In men, one normal consequence of aging is a robust decline in circulating and brain levels of the sex steroid hormone testosterone. Testosterone depletion leads to functional impairments and increased risk of disease in androgen-responsive tissues throughout the body, including brain. In this review we discuss the relationship between age-related testosterone depletion and the development of AD. Specifically, we focus on androgen regulation of beta-amyloid protein (Abeta), the accumulation of which is a key initiating factor in AD pathogenesis. Emerging data suggest that the regulatory actions of androgens on both Abeta and the development of AD support consideration of androgen therapy for the prevention and treatment of AD.

Testosterone and cognitive function: current clinical evidence of a relationship

BACKGROUND

Testosterone levels decline as men age, as does cognitive function. Whether there is more than a temporal relationship between testosterone and cognitive function is unclear. Chemical castration studies in men with prostate cancer suggest that low serum testosterone may be associated with cognitive dysfunction. Low testosterone levels have also been observed in patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI). This paper reviews the current clinical evidence of the relationship between serum testosterone levels and cognitive function in older men.

METHODS

A systematic literature search was conducted using PubMed and EMBASE to identify clinical studies and relevant reviews that evaluated cognitive function and endogenous testosterone levels or the effects of testosterone substitution in older men.

RESULTS

Low levels of endogenous testosterone in healthy older men may be associated with poor performance on at least some cognitive tests. The results of randomized, placebo-controlled studies have been mixed, but generally indicate that testosterone substitution may have moderate positive effects on selective cognitive domains (e.g. spatial ability) in older men with and without hypogonadism. Similar results have been found in studies in patients with existing AD or MCI.

CONCLUSIONS

Low endogenous levels of testosterone may be related to reduced cognitive ability, and testosterone substitution may improve some aspects of cognitive ability. Measurement of serum testosterone should be considered in older men with cognitive dysfunction. For men with both cognitive impairment and low testosterone, testosterone substitution may be considered. Large, long-term studies evaluating the effects of testosterone substitution on cognitive function in older men are warranted.

Androgens, aging, and Alzheimer's disease

Testosterone depletion is a normal consequence of aging in men that is associated with senescent effects in androgen- responsive tissues. We discuss new evidence that one consequence of testosterone depletion in men is an increased risk for the development of Alzheimer's disease (AD). Furthermore, we discuss two candidate mechanisms by which testosterone may affect AD pathogenesis. First, testosterone has been identified as an endogenous regulator of beta-amyloid, a protein that abnormally accumulates in AD brain and is implicated as a causal factor in the disease. Second, findings from several different paradigms indicate that testosterone has both neurotrophic and neuroprotective functions. These new findings support the clinical evaluation of androgen-based therapies for the prevention and treatment of AD.

Luteinizing hormone modulates cognition and amyloid-beta deposition in Alzheimer APP transgenic mice

Until recently, the study of hormonal influences in Alzheimer disease was limited to the role of sex steroids. Despite numerous epidemiological studies supporting a protective role for estrogen in Alzheimer disease, recent studies show that estrogen administration in elderly women increases the risk of disease. Reconciling these contradictory reports, we previously hypothesized that other hormones of the hypothalamic-pituitary-gonadal axis, such as luteinizing hormone, may be involved in the onset and development of the disease. In this regard, luteinizing hormone is elevated in Alzheimer disease and is known to modulate amyloidogenic processing of amyloid-beta protein precursor. Therefore, in this study, to evaluate the therapeutic potential of luteinizing hormone ablation, we administered a gonadotropin-releasing hormone analogue, leuprolide acetate, to an aged transgenic mouse model of Alzheimer disease (Tg 2576) and measured cognitive Y-maze performance and amyloid-beta deposition after 3 months of treatment. Our data indicate that luteinizing hormone ablation significantly attenuated cognitive decline and decreased amyloid-beta deposition as compared to placebo-treated animals. Importantly, leuprolide acetate-mediated reduction of amyloid-beta correlated with improved cognition. Since both cognitive loss and amyloid-beta deposition are features of Alzheimer disease, leuprolide acetate treatment may prove to be a useful therapeutic strategy for this disease.

Sex, Hormones, and Alzheimer's Disease

More women than men have Alzheimer's disease (AD). Retrospective studies suggested that hormone replacement therapy (HRT) might counteract this disparity by reducing the risk of developing dementia. However, a recent, large, prospective study revealed the puzzling result that HRT increased dementia risk. A review of the literature was conducted to generate hypotheses that might explain why more women than men have AD, and how HRT may increase dementia risk. Longer life span of women than men may be the largest factor in the preponderance of women with AD. Longer duration of disease, less vascular dementia, and less testosterone in women than men may also contribute somewhat. HRT might increase dementia risk by several mechanisms: greater risk of strokes, leading to dementia; use of medroxyprogesterone acetate and estrone, which might have somewhat different possible effects on neuronal and cerebrovascular function than may progesterone and estradiol; decrease of free testosterone which might protect against AD; a dose or delivery method perhaps producing drug levels that might lie outside a hypothetical beneficial range; and down-regulation of estrogen receptors on cholinergic neurons, possibly reducing cholinergic activity. Further study is required to discern by which of several possible mechanisms HRT increases dementia risk.

Low free testosterone is an independent risk factor for Alzheimer's disease

The purpose of this study was to assess pituitary gonadotropins and free testosterone levels in a larger cohort of men with Alzheimer's disease (AD, n=112) and age-matched controls (n=98) from the Oxford Project to Investigate Memory and Ageing (OPTIMA). We measured gonadotropins (follicle stimulating hormone, FSH, and luteinizing hormone, LH), sex hormone binding globulin (SHBG, which determines the amount of free testosterone) and total testosterone (TT) using enzyme immunoassays. AD cases had significantly higher LH and FSH and lower free testosterone levels. LH, FSH and SHBG all increased with age, while free testosterone decreased. Low free testosterone was an independent predictor for AD. Its variance was overall explained by high SHBG, low TT, high LH, an older age and low body mass index (BMI). In controls, low thyroid stimulating hormone levels were also associated with low free testosterone. Elderly AD cases had raised levels of gonadotropins. This response may be an attempt to normalize low free testosterone levels. In non-demented participants, subclinical hyperthyroid disease (a risk factor for AD) which can result in higher SHBG levels, was associated with low free testosterone. Lowering SHBG and/or screening for subclinical thyroid disease may prevent cognitive decline and/or wasting in men at risk for AD.

Identification of sex hormone-binding globulin in the human hypothalamus

Gonadal steroids are known to influence hypothalamic functions through both genomic and non-genomic pathways. Sex hormone-binding globulin (SHBG) may act by a non-genomic mechanism independent of classical steroid receptors. Here we describe the immunocytochemical mapping of SHBG-containing neurons and nerve fibers in the human hypothalamus and infundibulum. Mass spectrometry and Western blot analysis were also used to characterize the biochemical characteristics of SHBG in the hypothalamus and cerebrospinal fluid (CSF) of humans. SHBG-immunoreactive neurons were observed in the supraoptic nucleus, the suprachiasmatic nucleus, the bed nucleus of the stria terminalis, paraventricular nucleus, arcuate nucleus, the perifornical region and the medial preoptic area in human brains. There were SHBG-immunoreactive axons in the median eminence and the infundibulum. A partial colocalization with oxytocin could be observed in the posterior pituitary lobe in consecutive semithin sections. We also found strong immunoreactivity for SHBG in epithelial cells of the choroid plexus and in a portion of the ependymal cells lining the third ventricle. Mass spectrometry showed that affinity-purified SHBG from the hypothalamus and choroid plexus is structurally similar to the SHBG identified in the CSF. The multiple localizations of SHBG suggest neurohypophyseal and neuroendocrine functions. The biochemical data suggest that CSF SHBG is of brain rather than blood origin.