Genistein partly eases aging and estropause-induced primary cortical neuronal changes in rats

Hyaluronic Acid Conjugated with 17β-Estradiol Effectively Alleviates Estropause-Induced Cognitive Deficits in Rats

Women are at a higher risk of cognitive impairments and Alzheimer's disease (AD), particularly after the menopause, when the estrous cycle becomes irregular and diminishes. Numerous studies have shown that estrogen deficiency, especially estradiol (E2) deficiency, plays a key role in this phenomenon. Recently, a novel polymeric drug, hyaluronic acid-17β-estradiol conjugate (HA-E2), has been introduced for the delivery of E2 to brain tissues. Studies have indicated that HA-E2 crosses the blood-brain barrier (BBB) and facilitates a prolonged E2 release profile while lowering the risk of estrogen-supplement-related side effects. In this study, we used ovariohysterectomy (OHE) rats, a postmenopausal cognitive deficit model, to explore the effect of a 2-week HA-E2 treatment (210 ng/kg body weight, twice a week) on the cholinergic septo-hippocampal innervation system, synaptic transmission in hippocampal pyramidal neurons and cognitive improvements. Our study revealed an 11% rise in choline acetyltransferase (ChAT) expression in both the medial septal nucleus (MS nucleus) and the hippocampus, along with a 14-18% increase in dendritic spine density in hippocampal pyramidal neurons, following HA-E2 treatment in OHE rats. These enhancements prompted the recovery of cognitive functions such as spatial learning and memory. These findings suggest that HA-E2 may prevent and improve estrogen-deficiency-induced cognitive impairment and AD.

Roles of genistein in learning and memory during aging and neurological disorders

Genistein (GEN) is a non-steroidal phytoestrogen that belongs to the isoflavone class. It is abundantly found in soy. Soy and its products are used as food components in many countries including India. The present review is focused to address roles of GEN in brain functions in the context of learning and memory as a function of aging and neurological disorders. Memory decline is one of the most disabling features observed during normal aging and age-associated neurodegenerative disorders namely Alzheimer's disease (AD) and Parkinson's disease (PD), etc. Anatomical, physiological, biochemical and molecular changes in the brain with advancement of age and pathological conditions lead to decline of cognitive functions. GEN is chemically comparable to estradiol and binds to estrogen receptors (ERs). GEN acts through ERs and mimics estrogen action. After binding to ERs, GEN regulates a plethora of brain functions including learning and memory; however detailed study still remains elusive. Due to the neuroprotective, anti-oxidative and anti-inflammatory properties, GEN is used to restore or improve memory functions in different animal models and humans. The present review may be helpful to understand roles of GEN in learning and memory during aging and neurological disorders, its direction of research and therapeutic perspectives.

Beneficial effects of the phytoestrogen genistein on hippocampal impairments of spontaneously hypertensive rats (SHR)

Hippocampal neuropathology is a recognized feature of the spontaneously hypertensive rat (SHR). The hippocampal alterations associate with cognitive impairment. We have shown that hippocampal abnormalities are reversed by 17β-estradiol, a steroid binding to intracellular receptors (estrogen receptor α and β subtypes) or the membrane-located G-protein coupled estradiol receptor. Genistein (GEN) is a neuroprotective phytoestrogen which binds to estrogen receptor β and G-protein coupled estradiol receptor. Here, we investigated whether GEN neuroprotection extends to SHR. For this purpose, we treated 5-month-old SHR for 2 weeks with 10 mg kg^-1 daily s.c injections of GEN. We analyzed the expression of doublecortin+ neuronal progenitors, glial fibrillary acidic protein+ astrocytes and ionized calcium-binding adapter molecule 1+ microglia in the CA1 region and dentate gyrus of the hippocampus using immunocytochemistry, whereas a quantitative real-time polymerase chain reaction was used to measure the expression of pro- and anti-inflammatory factors tumor necrosis factor α, cyclooxygenase-2 and transforming growth factor β. We also evaluated hippocampal dependent memory using the novel object recognition test. The results showed a decreased number of doublecortin+ neural progenitors in the dentate gyrus of SHR that was reversed with GEN. The number of glial fibrillary acidic protein+ astrocytes in the dentate gyrus and CA1 was increased in SHR but significantly decreased by GEN treatment. Additionally, GEN shifted microglial morphology from the predominantly activated phenotype present in SHR, to the more surveillance phenotype found in normotensive rats. Furthermore, treatment with GEN decreased the mRNA of the pro-inflammatory factors tumor necrosis factor α and cyclooxygenase-2 and increased the mRNA of the anti-inflammatory factor transforming growth factor β. Discrimination index in the novel object recognition test was decreased in SHR and treatment with GEN increased this parameter. Our results indicate important neuroprotective effects of GEN at the neurochemical and behavioral level in SHR. Our data open an interesting possibility for proposing this phytoestrogen as an alternative therapy in hypertensive encephalopathy.

Neuromodulating roles of estrogen and phytoestrogens in cognitive therapeutics through epigenetic modifications during aging

Estrogen (E2) plays important role in regulating hippocampal learning and memory. The decline of E2 after menopause affects learning and memory and increases the risk of neurodegenerative diseases like Alzheimer's disease (AD). Additionally, from the estrogen receptor (ER) mediated gene regulation; E2 also regulates gene expression at the transcriptional and posttranscriptional levels through epigenetic modifications. E2 recruits a number of proteins called co-regulators at the promoter region of genes. These co-regulators act as chromatin modifiers, alter DNA and histone modifications and regulate gene expression. Several studies show that E2 regulates learning and memory by altering chromatin at the promoters of memory-linked genes. Due to structural similarities with E2 and low side effects, phytoestrogens are now used as neuroprotective agents to recover learning and memory in animal models as well as human subjects during aging and different neurological disorders. Growing evidence suggests that apart from anti-oxidative and anti-inflammatory properties, phytoestrogens also act as epigenetic modifiers and regulate gene expression through epigenetic modifications. The epigenetic modifying properties of phytoestrogens are mostly studied in cancer cells but very little is known regarding the regulation of synaptic plasticity genes, learning and memory, and neurological disorders. In this article, we discuss the epigenetic modifying properties of E2 and the roles of phytoestrogens as epigenetic modifiers in the brain to recover and maintain cognitive functions.

Dietary genistein and 17β-estradiol implants differentially influence locomotor and cognitive functions following transient focal ischemia in middle-aged ovariectomized rats at different lengths of estrogen deprivation

Genistein possesses estrogenic activity and has been considered a potential replacement for estrogen replacement therapy after menopause. In the current study, we investigated the neuroprotective effects of dietary genistein at varied lengths of estrogen deprivation in middle-aged ovariectomized Sprague-Dawley rats under ischemic conditions. Two weeks of treatment with dietary genistein at 42 mg/kg but not 17β-estradiol implants improved cognitive flexibility (Morris water maze test) after short-term estrogen deprivation (2 weeks) but not long-term estrogen deprivation (12 weeks). 17β-estradiol implants but not dietary genistein improved locomotor asymmetry (cylinder test) after long-term but not short-term estrogen deprivation. Dietary genistein but not 17β-estradiol implant improved early phase motor learning (rotarod test) after long-term estrogen deprivation. Neither 17β-estradiol implant nor dietary genistein reduced infarct size after either short-term or long-term estrogen deprivation. Genistein, however, reduced ionized calcium-binding adaptor molecule-1 (Iba1) expression, a marker of brain inflammation, at the ipsilateral side of stroke injury after short-term but not long-term estrogen deprivation. This study suggests that the neuroprotective effects of dietary genistein on motor and cognitive functions are distinctly influenced by the length of estrogen deprivation following focal ischemia. SIGNIFICANCE: There is an increasing postmenopausal population opting for homeopathic medicines for the management of menopausal symptoms due to the perceived distrust in estrogen use as hormone replacement. Basic and clinical studies support the notion that early, but not delayed, hormone replacement after menopause is beneficial. Furthermore, evidence suggests that delaying hormone replacement augments the detrimental, rather than the beneficial effects of estrogens. Because of the active consideration of soy isoflavones including genistein as alternatives to estrogen replacement, it is necessary to understand the ramifications of soy isoflavones use when their administration is begun at various times after menopause.

Long-term hypogonadism diminishes the neuroprotective effects of dietary genistein in young adult ovariectomized rats after transient focal ischemia

Increasing age disproportionately increases the risk of stroke among women compared to men of similar age, especially after menopause. One of the reasons for this observation is a sharp drop in circulating estrogens. However, the timing of initiation of estrogen replacement after menopause is associated with mixed beneficial and detrimental effects, hence contributing to widespread mistrust of estrogen use. Agents including soy isoflavones are being assessed as viable alternatives to estrogen therapy. In this study, we hypothesized that the neuroprotective effects of genistein, a soy isoflavone are less sensitive to the length of hypogonadism in young adult ovariectomized rats following cerebral ischemia. We expected that long-term hypogonadism will worsen motor and cognitive function, increase post-stroke inflammation with no effect on the neuroprotection of genistein. We compared the effect of treatment with dietary genistein (GEN) on short-term (2 weeks) and long-term hypogonadism (12 weeks) in young adult ovariectomized Sprague-Dawley rats on sensorimotor function, cognition and inflammation after focal ischemia. Dorsal Silastic implant of 17β-estradiol (E2) was used as a control for hormone therapy. Long-term hypogonadism stroked rats performed worse than the short-term hypogonadism stroked rats on the motor and cognitive function tests. GEN did not improve neurological assessment and motor learning after either short-term or long-term hypogonadism. GEN improved cognitive flexibility after short-term hypogonadism but not after the long-term. Both GEN and E2 reduced tissue loss after short-term hypogonadism and reduced GFAP expression at the contralateral side of ischemia after long-term hypogonadism. The length of hypogonadism may differentially influence the neuroprotective effects of both GEN and E2 on the motor and cognitive functions in young adult rats.

The effects of astaxanthin treatment on a rat model of Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder characterized by memory loss and dementia, could be a consequence of the abnormalities of cortical milieu, such as oxidative stress, inflammation, and/or accompanied with the aggregation of β-amyloid. The majority of AD patients are sporadic, late-onset AD, which predominantly occurs over 65 years of age. Our results revealed that the ferrous amyloid buthionine (FAB)-infused sporadic AD-like model showed deficits in spatial learning and memory and with apparent loss of choline acetyltransferase (ChAT) expression in medial septal (MS) nucleus. In hippocampal CA1 region, the loss of pyramidal neurons was accompanied with cholinergic fiber loss and neuroinflammatory responses including glial reaction and enhanced expression of inducible nitric oxide synthase (iNOS). Surviving hippocampal CA1 pyramidal neurons showed the reduction of dendritic spines as well. Astaxanthin (ATX), a potent antioxidant, reported to improve the outcome of oxidative-stress-related diseases. The ATX treatment in FAB-infused rats decreased neuroinflammation and restored the ChAT + fibers in hippocampal CA1 region and the ChAT expression in MS nucleus. It also partly recovered the spine loss on hippocampal CA1 pyramidal neurons and ameliorated the behavioral deficits in AD-like rats. From these data, we believed that the ATX can be a potential option for slowing the progression of Alzheimer's disease.

Long-Term Genistein Consumption Modifies Gut Microbiota, Improving Glucose Metabolism, Metabolic Endotoxemia, and Cognitive Function in Mice Fed a High-Fat Diet

SCOPE

The aim of this study is to assess whether the long-term addition of genistein to a high-fat diet can ameliorate the metabolic and the cognitive alterations and whether the changes can be associated with modifications to the gut microbiota.

METHODS AND RESULTS

C57/BL6 mice were fed either a control (C) diet, a high-fat (HF) diet, or a high-fat diet containing genistein (HFG) for 6 months. During the study, indirect calorimetry, IP glucose tolerance tests, and behavioral analyses were performed. At the end of the study, plasma, liver, brain, and fecal samples were collected. The results showed that mice fed the HFG diet gained less weight, had lower serum triglycerides, and an improvement in glucose tolerance than those fed an HF diet. Mice fed the HFG diet also modified the gut microbiota that was associated with lower circulating levels of lipopolysaccharide (LPS) and reduced expression of pro-inflammatory cytokines in the liver compared to those fed HF diet. The reduction in LPS by the consumption of genistein was accompanied by an improvement of the cognitive function.

CONCLUSIONS

Genistein is able to regulate the gut microbiota, reducing metabolic endotoxemia and decreasing the neuroinflammatory response despite the consumption of a HF diet.

Reproductive experience modified dendritic spines on cortical pyramidal neurons to enhance sensory perception and spatial learning in rats

Behavioral adaptations during motherhood are aimed at increasing reproductive success. Alterations of hormones during motherhood could trigger brain morphological changes to underlie behavioral alterations. Here we investigated whether motherhood changes a rat’s sensory perception and spatial memory in conjunction with cortical neuronal structural changes. Female rats of different statuses, including virgin, pregnant, lactating, and primiparous rats were studied. Behavioral test showed that the lactating rats were most sensitive to heat, while rats with motherhood and reproduction experience outperformed virgin rats in a water maze task. By intracellular dye injection and computer-assisted 3-dimensional reconstruction, the dendritic arbors and spines of the layer III and V pyramidal neurons of the somatosensory cortex and CA1 hippocampal pyramidal neurons were revealed for closer analysis. The results showed that motherhood and reproductive experience increased dendritic spines but not arbors or the lengths of the layer III and V pyramidal neurons of the somatosensory cortex and CA1 hippocampal pyramidal neurons. In addition, lactating rats had a higher incidence of spines than pregnant or primiparous rats. The increase of dendritic spines was coupled with increased expression of the glutamatergic postsynaptic marker protein (PSD-95), especially in lactating rats. On the basis of the present results, it is concluded that motherhood enhanced rat sensory perception and spatial memory and was accompanied by increases in dendritic spines on output neurons of the somatosensory cortex and CA1 hippocampus. The effect was sustained for at least 6 weeks after the weaning of the pups.

Genistein suppresses the mitochondrial apoptotic pathway in hippocampal neurons in rats with Alzheimer's disease

Genistein is effective against amyloid-β toxicity, but the underlying mechanisms are unclear. We hypothesized that genistein may protect neurons by inhibiting the mitochondrial apoptotic pathway, and thereby play a role in the prevention of Alzheimer’s disease. A rat model of Alzheimer’s disease was established by intraperitoneal injection of D-galactose and intracerebral injection of amyloid-β peptide (25–35). In the genistein treatment groups, a 7-day pretreatment with genistein (10, 30, 90 mg/kg) was given prior to establishing Alzheimer’s disease model, for 49 consecutive days. Terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling assay demonstrated a reduction in apoptosis in the hippocampus of rats treated with genistein. Western blot analysis showed that expression levels of capase-3, Bax and cytochrome c were decreased compared with the model group. Furthermore, immunohistochemical staining revealed reductions in cytochrome c and Bax immunoreactivity in these rats. Morris water maze revealed a substantial shortening of escape latency by genistein in Alzheimer’s disease rats. These findings suggest that genistein decreases neuronal loss in the hippocampus, and improves learning and memory ability. The neuroprotective effects of genistein are associated with the inhibition of the mitochondrial apoptotic pathway, as shown by its ability to reduce levels of caspase-3, Bax and cytochrome c.

Exogenous dehydroisoandrosterone sulfate reverses the dendritic changes of the central neurons in aging male rats

Sex hormones are known to help maintaining the cognitive ability in male and female rats. Hypogonadism results in the reduction of the dendritic spines of central neurons which is believed to undermine memory and cognition and cause fatigue and poor concentration. In our previous studies, we have reported age-related regression in dendrite arbors along with loss of dendritic spines in the primary somatosensory cortical neurons in female rats. Furthermore, castration caused a reduction of dendritic spines in adult male rats. In light of this, it was surmised that dendritic structures might change in normal aging male rats with advancing age. Recently, dehydroepiandrosterone sulfate (DHEAS) has been reported to have memory-enhancing properties in aged rodents. In this study, normal aging male rats, with a reduced plasma testosterone level of 75-80%, were used to explore the changes in behavioral performance of neuronal dendritic arbor and spine density. Aging rats performed poorer in spatial learning memory (Morris water maze). Concomitantly, these rats showed regressed dendritic arbors and spine loss on the primary somatosensory cortical and hippocampal CA1 pyramidal neurons. Exogenous DHEAS and testosterone treatment reversed the behavioral deficits and partially restored the spine loss of cortical neurons in aging male rats but had no effects on the dendritic arbor shrinkage of the affected neurons. It is concluded therefore that DHEAS, has the efficacy as testosterone, and that it can exert its effects on the central neuron level to effectively ameliorate aging symptoms.