Effects of genistein on neuronal apoptosis, and expression of Bcl-2 and Bax proteins in the hippocampus of ovariectomized rats

Unveiling the neuroprotective properties of isoflavones: current evidence, molecular mechanisms and future perspectives

Neurodegenerative diseases encompass a wide range of debilitating and incurable brain disorders characterized by the progressive deterioration of the nervous system's structure and function. Isoflavones, which are naturally occurring polyphenolic phytochemicals, have been found to regulate various cellular signaling pathways associated with the nervous system. The main objective of this comprehensive review is to explore the neuroprotective effects of isoflavones, elucidate the underlying mechanisms, and assess their potential for treating neurodegenerative disorders. Relevant data regarding isoflavones and their impact on neurodegenerative diseases were gathered from multiple library databases and electronic sources, including PubMed, Google Scholar, Web of Science, and Science Direct. Numerous isoflavones, including genistein, daidzein, biochanin A, and formononetin, have exhibited potent neuroprotective properties against various neurodegenerative diseases. These compounds have been found to modulate neurotransmitters, which in turn contributes to their ability to protect against neurodegeneration. Both in vitro and in vivo experimental studies have provided evidence of their neuroprotection mechanisms, which involve interactions with estrogenic receptors, antioxidant effects, anti-inflammatory properties, anti-apoptotic activity, and modulation of neural plasticity. This review aims to provide current insights into the neuroprotective characteristics of isoflavones and shed light on their potential therapeutic applications in future clinical scenarios.

Cytoprotective effect of genistein against dexamethasone-induced pancreatic β-cell apoptosis

Steroid-induced diabetes is a well-known metabolic side effect of long-term use of glucocorticoid (GC). Our group recently demonstrated dexamethasone-induced pancreatic β-cell apoptosis via upregulation of TRAIL and TRAIL death receptor (DR5). Genistein protects against pancreatic β-cell apoptosis induced by toxic agents. This study aimed to investigate the cytoprotective effect of genistein against dexamethasone-induced pancreatic β-cell apoptosis in cultured rat insulinoma (INS-1) cell line and in isolated mouse islets. In the absence of genistein, dexamethasone-induced pancreatic β-cell apoptosis was associated with upregulation of TRAIL, DR5, and superoxide production, but downregulation of TRAIL decoy receptor (DcR1). Dexamethasone also activated the expression of extrinsic and intrinsic apoptotic proteins, including Bax, NF-κB, caspase-8, and caspase-3, but suppressed the expression of the anti-apoptotic Bcl-2 protein. Combination treatment with dexamethasone and genistein protected against pancreatic β-cell apoptosis, and reduced the effects of dexamethasone on the expressions of TRAIL, DR5, DcR1, superoxide production, Bax, Bcl-2, NF-κB, caspase-8, and caspase-3. Moreover, combination treatment with dexamethasone and genistein reduced the expressions of TRAIL and DR5 in isolated mouse islets. The results of this study demonstrate the cytoprotective effect of genistein against dexamethasone-induced pancreatic β-cell apoptosis in both cell line and islets via reduced TRAIL and DR5 protein expression.

Arsenic Induces Differential Neurotoxicity in Male, Female, and E2-Deficient Females: Comparative Effects on Hippocampal Neurons and Cognition in Adult Rats

We earlier reported that arsenic induced hippocampal neuronal loss, causing cognitive dysfunctions in male rats. This neuronal damage mechanism involved an altered bone morphogenetic protein (BMP2)/Smad and brain-derived neurotrophic factor (BDNF)/TrkB signaling. Susceptibility to toxicants is often sex-dependent, and hence we studied the comparative effects of arsenic in adult male and female rats. We observed that a lower dose of arsenic reduced learning-memory ability, examined through passive avoidance and Y-maze tests, in male but not female rats. Again, male rats exhibited greater learning-memory loss at a higher dose of arsenic. Supporting this, arsenic-treated male rats demonstrated larger reduction in the hippocampal NeuN and %-surviving neurons, together with increased apoptosis and altered BMP2/Smad and BDNF/TrkB pathways compared to their female counterparts. Since the primary female hormone, estrogen (E2), regulates normal brain functions, we next probed whether endogenous E2 levels in females offered resistance against arsenic-induced neurotoxicity. We used ovariectomized (OVX) rat as the model for E2 deficiency. We primarily identified that OVX itself induced hippocampal neuronal damage and cognitive decline, involving an increased BMP2/Smad and reduced BDNF/TrkB. Further, these effects appeared greater in arsenic + OVX compared to arsenic + sham (ovary intact) or OVX rats alone. The OVX-induced adverse effects were significantly reduced by E2 treatment. Overall, our study suggests that adult males could be more susceptible than females to arsenic-induced neurotoxicity. It also indicates that endogenous E2 regulates hippocampal BMP and BDNF signaling and restrains arsenic-induced neuronal dysfunctions in females, which may be inhibited in E2-deficient conditions, such as menopause or ovarian failure.

Genistein Prevents Hypoxia-Induced Cognitive Dysfunctions by Ameliorating Oxidative Stress and Inflammation in the Hippocampus

Genistein (GE), a plant-derived isoflavone, is a polyphenolic non-steroidal compound. Studies showed that GE possesses anti-cancer, anti-inflammatory, anti-microbial, anti-oxidant, and anti-apoptotic activities. However, the neuroprotective role of GE in amnesia has not been studied. This study aimed to evaluate the anti-amnesic potential of GE in a mice model of hypoxia-induced amnesia and to understand the underlying mechanism. Mice were exposed to hypoxia (10% O2) and administered vehicle or GE (10, 20, 30 mg/kg) orally for 28 days. Thereafter, Morris water maze (MWM), novel object recognition (NOR), and passive avoidance task (PAT) were performed to evaluate cognitive behavior. Next, we performed biochemical tests and gene expression analysis to uncover the mechanism underlying GE mode of action. Our results showed that GE-treatment ameliorated hypoxia-induced cognitive dysfunctions in mice. Further, GE-treatment suppressed the oxidative stress in the hippocampus of amnesic mice as evidenced by reduced lipid peroxidation, reduced nitrite and ROS levels, and increased levels of reduced glutathione (GSH) and increased total antioxidant capacity. GE treatment reduced the expression of pro-inflammatory cytokines TNFα, IL1β, IL6, and MCP-1 and increased the expression of anti-inflammatory cytokine IL10 in the hippocampus of amnesic mice. Finally, GE treatment enhanced the expression of neuroprotective genes including BDNF, CREB, CBP, and IGF1 in the hippocampus of amnesic mice. Altogether, our results showed that GE treatment prevents hypoxia-induced cognitive dysfunction in mice by reducing oxidative stress and suppressing neuroinflammation while increasing the expression of neuroprotective genes in the hippocampus.

Neuroprotective Effects of Curcumin-Loaded Emulsomes in a Laser Axotomy-Induced CNS Injury Model

PURPOSE

Curcumin, a polyphenol isolated from the rhizomes of turmeric, holds great potential as a neuroprotective agent in addition to its anti-inflammatory and antioxidant characteristics. The poor bioavailability and low stability of curcumin are the greatest barriers to its clinical use. This study aims to investigate the neuroprotective effect of curcumin on axonal injury, by delivering the lipophilic polyphenol to a primary hippocampal neuron culture by means of a lipid-based drug delivery system, named emulsomes.

METHODS

To study neuroregeneration ex vivo, an injury model was established through single-cell laser axotomy on hippocampal neurites. Upon treatment with curcumin-loaded emulsomes (CurcuEmulsomes), curcumin and CurcuEmulsome uptake into neurons was verified by three-dimensional Z-stack images acquired with confocal microscopy. Neuron survival after axonal injury was tracked by propidium iodide (PI) and Hoechst staining. Alterations in expression levels of physiological markers, such as anti-apoptotic marker Bcl2, apoptotic marker cleaved caspase 3, neuroprotective marker Wnt3a and the neuronal survival marker mTOR, were investigated by immunocytochemistry analyses.

RESULTS

The results indicated significant improvement in the survival rate of injured neurons upon CurcuEmulsome treatment. Bcl2 expression was significantly higher for injured neurons treated with curcumin or CurcuEmulsome. Reduction in caspase 3 expression was seen in both curcumin and CurcuEmulsome treatment, whereas there were no significant changes in Wnt3a and mTOR expression.

CONCLUSION

The established laser-axotomy model was proven as a reliable methodology to study neurodegenerative models ex vivo. CurcuEmulsomes delivered curcumin to primary hippocampal neurons successfully. Treated with CurcuEmulsomes, injured hippocampal neurons benefit from the neuroprotective effects of curcumin, exhibiting a higher survival rate and increased anti-apoptotic marker levels.

Protective effects of organic extracts of Alpinia oxyphylla against hydrogen peroxide-induced cytotoxicity in PC12 cells

Alpinia oxyphylla, a traditional herb, is widely used for its neuroprotective, antioxidant and memory-improving effects. However, the neuroprotective mechanisms of action of its active ingredients are unclear. In this study, we investigated the neuroprotective effects of various organic extracts of Alpinia oxyphylla on PC12 cells exposed to hydrogen peroxide-induced oxidative injury in vitro. Alpinia oxyphylla was extracted three times with 95% ethanol (representing extracts 1–3). The third 95% ethanol extract was dried and resuspended in water, and then extracted successively with petroleum ether, ethyl acetate and n-butanol (representing extracts 4–6). The cell counting kit-8 assay and microscopy were used to evaluate cell viability and observe the morphology of PC12 cells. The protective effect of the three ethanol extracts (at tested concentrations of 50, 100 and 200 µg/mL) against cytotoxicity to PC12 cells increased in a concentration-dependent manner. The ethyl acetate, petroleum ether and n-butanol extracts (each tested at 100, 150 and 200 μg/mL) had neuroprotective effects as well. The optimum effective concentration ranged from 50–200 μg/mL, and the protective effect of the ethyl acetate extract was comparatively robust. These results demonstrate that organic extracts of Alpinia oxyphylla protect PC12 cells against apoptosis induced by hydrogen peroxide. Our findings should help identify the bioactive neuroprotective components in Alpinia oxyphylla.

The Angiotensin Type 1 Receptor Antagonist Losartan Prevents Ovariectomy-Induced Cognitive Dysfunction and Anxiety-Like Behavior in Long Evans Rats

Women who have bilateral oophorectomies prior to the age of natural menopause are at increased risk of developing mild cognitive decline, dementia, anxiety, and depressive type disorders. Clinical and animal studies indicate angiotensin type 1 receptor (AT₁R) blockers (ARBs) have blood pressure (BP)-independent neuroprotective effects. To investigate the potential use of ARBs in normotensive women at increased risk of developing neurocognitive problems, we studied a rat model of bilateral oophorectomy. Long Evans rats were sham-operated (Sham) or ovariectomized (Ovx) at 3 months of age and immediately treated continuously with vehicle (Veh) or the ARB losartan (Los) for the duration of the experiment. In contrast to many hypertensive rat models, ovariectomy did not increase mean arterial pressure (MAP) in these normotensive rats. Ovariectomized rats spent less time in the open arms of the elevated plus maze (EPM) [(% total time): Veh, 34.1 ± 5.1 vs. Ovx, 18.7 ± 4.4; p < 0.05] and in the center of the open field (OF) [(s): Veh, 11.1 ± 1.7 vs. Ovx, 6.64 ± 1.1; p < 0.05]. They also had worse performance in the novel object recognition (NOR) test as evidenced by a reduction in the recognition index [Veh, 0.62 ± 0.04 vs. Ovx, 0.45 ± 0.03; p < 0.05]. These adverse effects of ovariectomy were prevented by Los. Losartan also reduced plasma corticosterone in Ovx rats compared to Veh treatment [(ng/mL): Ovx–Veh, 238 ± 20 vs. Ovx–Los, 119 ± 42; p < 0.05]. Ovariectomy increased AT₁R mRNA expression in the CA3 region of the hippocampus (Hc) [(copies x 10⁶/µg RNA): Sham–Veh, 7.15 ± 0.87 vs. Ovx–Veh, 9.86 ± 1.7; p < 0.05]. These findings suggest the neuroprotective effects of this ARB in normotensive Ovx rats involve reduction of plasma corticosterone and blockade of increased AT₁R activity in the hippocampus. These data suggest ARBs have therapeutic potential for normotensive women at increased risk of developing cognitive and behavioral dysfunction due to bilateral oophorectomy prior to the natural age of menopause.

Effects of genistein and swimming exercise on spatial memory and expression of microRNA 132, BDNF, and IGF-1 genes in the hippocampus of ovariectomized rats

OBJECTIVES

The aim of the present study was to investigate the effects of genistein and exercise on the spatial memory and expression of microRNA-132, BDNF, and IGF-1 in the hippocampus of ovariectomized rats.

MATERIALS AND METHODS

Sixty animals were divided into six groups of control, sham, ovariectomy (OVX), ovariectomized with 8 weeks of genistein administration (OVX.G), with 8 weeks of swimming training (OVX.E), and with 8 weeks of both of them (OVX.G.E). The effect of genistein and/or exercise was evaluated by measuring microRNA-132, BDNF, and IGF-1 expression levels in the hippocampus tissue. Grafts were analyzed using Real-time polymerase chain reaction for microRNA-132, BDNF, IGF-1, and spatial memory via a Morris water maze (MWM).

RESULTS

Our findings showed that ovariectomy decreased the expression of microRNA-132, BDNF, and IGF-1 in the hippocampus (P<0.05) in comparison with the sham group as well as performance in the water maze (P<0.05). Also according to results ovariectomized groups that were treated with genistein/exercise or both of them showed significant difference in expression of microRNA-132, BDNF, and IGF-1 in the hippocampus (P<0.05) and decreased latency in MWM (P<0.05) compared with the OVX group but combination treatment was more effective in the OVX.G.E group in comparison with OVX.E and OVX.G groups.

CONCLUSION

Overall our results emphasized that combination treatment with genistein and exercise could improve microRNA-132, BDNF, and IGF-1 expression in the hippocampus as well as the spatial memory of ovariectomized rats. These effects may have beneficial impacts on the menopausal period.