Protective effect of alpha-lipoic acid on bisphenol A-induced learning and memory impairment in developing mice: nNOS and keap1/Nrf2 pathway

Health risks of Bisphenol-A exposure: From Wnt signaling perspective

Human beings are routinely exposed to chronic and low dose of Bisphenols (BPs) due to their widely pervasiveness in the environment. BPs hold similar chemical structures to 17β-estradiol (E2) and thyroid hormone, thus posing threats to human health by rendering the endocrine system dysfunctional. Among BPs, Bisphenol-A (BPA) is the best-known and extensively studied endocrine disrupting compound (EDC). BPA possesses multisystem toxicity, including reproductive toxicity, neurotoxicity, hepatoxicity and nephrotoxicity. Particularly, the central nervous system (CNS), especially the developing one, is vulnerable to BPA exposure. This review describes our current knowledge of BPA toxicity and the related molecular mechanisms, with an emphasis on the role of Wnt signaling in the related processes. We also discuss the role of oxidative stress, endocrine signaling and epigenetics in the regulation of Wnt signaling by BPA exposure. In summary, dysfunction of Wnt signaling plays a key role in BPA toxicity and thus can be a potential target to alleviate EDCs induced damage to organisms.

Raddeanin A isolated from Anemone raddeana Regel improves pathological and cognitive deficits of the mice model of Alzheimer's disease by targeting β-amyloidosis

BACKGROUND

Raddeanin A is a triterpenoid isolated from Anemone raddeana Regel. It exhibits a broad spectrum of biological activities such as anti-tumor and anti-inflammatory, however, its neuroprotective effect in targeting Alzheimer's disease (AD) remains uninvestigated.

PURPOSE

To provide scientific base for the development of novel AD drug by clarifying the neuroprotective effect and molecular mechanisms of raddeanin A in both in vitro and in vivo AD model.

STUDY DESIGN

To confirm the neuroprotective role of raddeanin A in the treatment of AD, its mechanisms and effects on β-amyloidosis and Aβ fibrillation was studied in U87 cells. Besides, the improvement on cognitive deficit, pathological defects, reactive astrocyte clusters, inhibition on neuronal inflammation and apoptosis were further studied in 3 x Tg-AD mice model of AD.

METHODS

Real-time PCR, western blot, dot blot, biolayer interferometry and bioinformatics analysis were used to confirm the in vitro effect and targets of raddeanin A on β-amyloidosis and its associated protein network. A series of experiments including Morris water maze, H&E staining, nissl staining and immunofluorescence analysis were conducted to confirm the protective behavioral effect of raddeanin A in the in vivo AD mice model.

RESULTS

Raddeanin A was identified to reduce β-amyloidosis in U87 cells and 3 x Tg-AD mice model of AD by decreasing level of BACE1, APP, APP-β and Aβ. Raddeanin A improved behavioral, spatial memory and learning ability in the AD mice. In the cortex and hippocampus, raddeanin A improved the morphology and arrangement of neurons, lower the level of reactive astrocyte marker GFAP and apoptotic marker proteins Bax/Bcl2 ratio. Moreover, raddeanin A upregulated the mRNA and protein level of Prkcα in the hippocampus of AD mice whose neuroprotective effect was exerted possibly via the activation of protein kinase C.

CONCLUSION

As a novel natural agent targeting β-amyloidosis, our results provide the first evidence of the multiple in vitro and in vivo neuroprotective effect of raddeanin A, suggesting its potential therapeutic application in preventing or alleviating the symptoms of AD.

Nrf2-mediated protective effect of alpha-lipoic acid on synaptic oxidative damage and inhibition of PKC/ERK/CREB pathway in bisphenol A-exposed HT-22 cells

The harmful effects of bisphenol A (BPA) on learning and memory may involve hippocampal oxidative damage; however, the underlying mechanism remains unclear. Antioxidants that antagonize BPA-induced neuronal oxidative damage lack research. This study aimed to develop an in vitro model using the HT-22 mouse hippocampal neuronal cell line to investigate the neurotoxic mechanism of BPA and the protective effect of alpha-lipoic acid (ALA) on nuclear factor erythroid 2-related factor 2 (Nrf2) inhibition. The results showed that ALA reduced BPA-induced reactive oxygen species and neuronal nitric oxide synthase (nNOS) levels; however, inhibiting Nrf2 weakened the protective effects of ALA. BPA reduced mitochondrial complex I/III activity and ATP levels, but ALA ameliorated this damage. ALA improved the BPA-induced downregulation of the kelch-like ECH-associated protein 1 (keap1)/Nrf2 system, synaptic-related proteins, and the protein kinase C (PKC)/extracellular signal-regulated kinase (ERK)/cAMP response element binding protein (CREB) pathway; however, the protective effects of ALA were weakened when Nrf2 was inhibited. Our results suggest that BPA causes oxidative damage to HT-22 cells by damaging mitochondrial function, nNOS, and the keap1/Nrf2 system, thereby impairing synaptic-related proteins and the PKC/ERK/CREB pathway. ALA counters BPA-induced damage via Nrf2, which may be a significant target for the protective action of ALA.

Synergistic Effect of Combined Walnut Peptide and Ginseng Extracts on Memory Improvement in C57BL/6 Mice and Potential Mechanism Exploration

This work aimed to investigate whether there are synergistic effects between walnut peptide (WNP) and ginseng extracts (GSE) treatments to ameliorate the memory impairment caused by scopolamine (SCOP). The Morris water maze trial, hippocampal neuron morphology, neurotransmitters, and synaptic ultrastructure were examined, along with brain-derived neurotrophic factor (BDNF)-related signaling pathway proteins. The results of the Morris water maze trial demonstrated that the combined administration of WNP and GSE effectively alleviated memory impairment in C57BL/6 rats caused by SCOP. Improvement in the morphology of hippocampal neurons, dendritic spines, and synaptic plasticity and upregulation of neurotransmitters AChE, ACh, ChAT, Glu, DA, and 5-HT supported the memory improvement effects of WNP + GSE. In addition, compared with the model group, WNP + GSE significantly enhanced the protein levels of VAChT, Trx-1, and the CREB/BDNF/TrkB pathway in hippocampal and PC12 cells induced by SCOP (p < 0.05). Notably, WNP + GSE boosted memory via multiple pathways, not only the BDNF/TrkB/CREB target.

The molecular mechanisms of alpha-lipoic acid on ameliorating aflatoxin B1-induced liver toxicity and physiological dysfunction in northern snakehead (Channa argus)

This research aimed to evaluate the protective mechanism of alpha-lipoic acid (α-LA) on the food-borne aflatoxin B₁ (AFB₁) exposure-induced liver toxicity and physiological dysfunction in the northern snakehead (Channa argus). 480 fish (9.24±0.01 g) were randomly assigned to four treatment groups and fed with four experimental diets for 56 d including the control group (CON), AFB₁ group (200 ppb AFB₁), 600 α-LA group (600 ppm α-LA+200 ppb AFB₁), and 900 α-LA group (900 ppm α-LA+200 ppb AFB₁). The results revealed that 600 and 900 ppm α-LA attenuated AFB₁-induced growth inhibition and immunosuppression in northern snakehead. 600 ppm α-LA significantly decreased the serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and lactate dehydrogenase levels, and AFB₁ bioaccumulation, and attenuated the changes of hepatic histopathological and ultrastructure induced by AFB₁. Moreover, 600 and 900 ppm α-LA significantly up-regulated phase I metabolism genes (cytochrome P450-1a, 1b, and 3a) mRNA expression, inhibited the levels of malondialdehyde, 8‑hydroxy-2 deoxyguanosine and reactive oxygen species in the liver. Notably, 600 ppm α-LA significantly up-regulated the expression levels of nuclear factor E2 related factor 2 and its related downstream antioxidant molecules (heme oxygenase 1 and NAD(P)H: quinone oxidoreductase 1, etc.), increased the phase II detoxification enzyme-related molecules (glutathione-S-transferase and glutathione), antioxidant parameters (catalase and superoxide dismutase, etc.), and the expressions of Nrf2 and Ho-1 protein in the presence of AFB₁ exposure. Furthermore, 600 and 900 ppm α-LA significantly reduced the characteristic indices of AFB₁-induced endoplasmic reticulum stress (glucose-regulated protein 78 and inositol requiring enzyme 1, etc.), apoptosis (caspase-3 and cytochrome c, etc.) and inflammation (nuclear factor kappa B and tumor necrosis factor α, etc.), while increased the B-cell lymphoma-2 and inhibitor of κBα in the liver after being exposed to AFB₁. To summarize, the above results indicate that dietary α-LA could modulate the Nrf2 signaling pathway to ameliorate AFB₁-induced growth inhibition, liver toxicity, and physiological dysfunction in northern snakehead. Although the concentration of α-LA increased to 900 ppm from 600 ppm, the protective effects of the 900 ppm α-LA do not show an advantage over the 600 ppm α-LA, and even show inferiority in some respects. So that the recommended concentration of α-LA is 600 ppm. The present study provides the theoretical foundation for developing α-LA as the prevention and treatment of AFB₁-induced liver toxicity in aquatic animals.

E prostanoid receptor-3 promotes oxidized low-density lipoprotein-induced human aortic smooth muscle cells inflammation

AIM

The progression of atherosclerosis can lead to the occurrence of multiple cardiovascular diseases (coronary heart disease, etc.). E prostanoid receptor-3 (EP3) is known to participate in the progression of atherosclerosis. This study aimed to investigate the mechanism by which EP3 modulates the development of atherosclerosis.

METHODS AND RESULTS

ApoE^-/- mice were used to construct in vivo model of atherosclerosis. Human aortic smooth muscle cells (HASMCs) were stimulated with oxidized low-density lipoprotein (ox-LDL) to construct in vitro model of atherosclerosis. mRNA expressions were assessed by qRT-PCR, and western blot was applied to assess the protein levels. CCK-8 assay was applied to assess the cell viability. The inflammatory cytokines levels were assessed by enzyme-linked immunosorbent assay, and flow cytometry was applied to assess cell apoptosis. In vivo experiment was constructed to investigate the impact of EP3 in atherosclerosis development. L-798106 (EP3 inhibitor) significantly inhibited the levels of pro-inflammatory cytokines in atherosclerosis in vivo. EP3 inhibitor (L-798106) significantly reversed ox-LDL-caused HASMCs injury via inhibiting the apoptosis and inflammatory responses (P < 0.05). The levels of interleukin-17 (IL-17) and intercellular adhesion molecule-1 (ICAM-1) in HASMCs were elevated by ox-LDL, whereas L-798106 or knockdown of cyclic AMP (cAMP) response element-binding protein (CREB) notably restored this phenomenon (P < 0.05). EP3 overexpression further aggravated ox-LDL-induced inflammation in HASMCs, and EP3 up-regulated the levels of IL-17 and ICAM-1 in ox-LDL-treated HASMCs (P < 0.05). EP3 up-regulation promoted the inflammatory responses in ox-LDL-treated HASMCs through mediation of cAMP/protein kinase A (PKA)/CREB/IL-17/ICAM-1 axis (P < 0.05).

CONCLUSIONS

EP3 inhibitor alleviates ox-LDL-induced HASMC inflammation via mediation of cAMP/PKA/CREB/IL-17/ICAM-1 axis. Our study might shed new lights on discovering novel strategies against atherosclerosis.

Bisphenol S induces oxidative stress-mediated impairment of testosterone synthesis by inhibiting the Nrf2/HO-1 signaling pathway

Bisphenol S (BPS) is an environmental endocrine disruptor widely used in industrial production. BPS induces oxidative stress and exhibits male reproductive toxicity in mice, but the mechanisms by which BPS impairs steroid hormone synthesis are not fully understood. Nuclear factor erythroid 2-related factor 2(Nrf2)/HO-1 signaling is a key pathway in improving cellular antioxidant defense capacities. Therefore, this study explored the effects of exposure to BPS on testosterone synthesis in adult male mice and its mechanisms with regard to the Nrf2/HO-1 signaling pathway. Adult male C57BL/6 mice were orally exposed to BPS (2, 20, and 200 mg/kg BW) with sesame oil as a vehicle (0.1 ml/10 g BW) per day for 28 consecutive days. The results showed that compared with the control group, serum testosterone levels were substantially reduced in the 20 and 200 mg/kg BPS treatment groups, and testicular testosterone levels were reduced in all BPS treatment groups. These changes were accompanied by a prominent decrease in the expression levels of testosterone synthesis-related enzymes (STAR, CYP11A1, CYP17A1, HSD3B1, and HSD17B3) in the mouse testis. In addition, BPS induced oxidative stress in the testis by upregulating the messenger RNA and protein levels of Keap1 and downregulating the levels of Nrf2, HO-1, and downstream antioxidant enzymes (CAT, SOD1, and Gpx4). In summary, our results indicate that exposure of adult male mice to BPS can inhibit Nrf2/HO-1 signaling and antioxidant enzyme activity, which induces oxidative stress and thereby may impair testosterone synthesis in testicular tissues, leading to reproductive damage.

The Effects of Antioxidant Nutraceuticals on Cellular Sulfur Metabolism and Signaling

Significance: Nutraceuticals are ingested for health benefits, in addition to their general nutritional value. These dietary supplements have become increasingly popular since the late 20th century and they are a rapidly expanding global industry approaching a half-trillion U.S. dollars annually. Many nutraceuticals are promulgated as potent antioxidants. Recent Advances: Experimental support for the efficacy of nutraceuticals has lagged behind anecdotal exuberance. However, accumulating epidemiological evidence and recent, well-controlled clinical trials are beginning to support earlier animal and in vitro studies. Although still somewhat limited, encouraging results have been suggested in essentially all organ systems and against a wide range of pathophysiological conditions. Critical Issues: Health benefits of "antioxidant" nutraceuticals are largely attributed to their ability to scavenge oxidants. This has been criticized based on several factors, including limited bioavailability, short tissue retention time, and the preponderance of endogenous antioxidants. Recent attention has turned to nutraceutical activation of downstream antioxidant systems, especially the Keap1/Nrf2 (Kelch like ECH associated protein 1/nuclear factor erythroid 2-related factor 2) axis. The question now becomes, how do nutraceuticals activate this axis? Future Directions: Reactive sulfur species (RSS), including hydrogen sulfide (H2S) and its metabolites, are potent activators of the Keap1/Nrf2 axis and avid scavengers of reactive oxygen species. Evidence is beginning to accumulate that a variety of nutraceuticals increase cellular RSS by directly providing RSS in the diet, or through a number of catalytic mechanisms that increase endogenous RSS production. We propose that nutraceutical-specific targeting of RSS metabolism will lead to the design and development of even more efficacious antioxidant therapeutic strategies. Antioxid. Redox Signal. 38, 68-94.

Alpha lipoic acid reverses scopolamine-induced spatial memory loss and pyramidal cell neurodegeneration in the prefrontal cortex of Wistar Rats

Neurodegenerative disorders are linked to oxidative tissue damage characterized by gradual loss of cognitive functions and neuronal cells. Alpha-lipoic acid (AHA) has a strong antioxidant property. Scopolamine is an anti-muscarinic agent used to study the mechanism of memory loss in an animal model. This study is aimed at evaluating the antioxidant role of alpha lipoic acid in reversing scopolamine induced memory loss and neurodegenerative process in the prefrontal cortex of Wistar rats. Twenty adult male Wistar rats used were divided into four groups (n = 5): Group 1 received vehicle (Control), Group 2 had scopolamine (1 mg/kg, i.p) for 4 days, Group 3 received AHA (200 mg/kg, p.o) for 10 days while Group 4 were pretreated with scopolamine (1 mg/kg, i.p) for 4 days followed by oral administration of 200 mg/kg of AHA for 10 days. The rats were subjected to Y-maze test to assess their spatial memory. The rats were euthanized, the prefrontal area was excised and fixed in 10% formol-calcium and processed for Haematoxylin and Eosin, Cresyl fast violet for Nissl Bodies (Ribosome), and Glial Fibrillary Acidic Protein (GFAP) stains. Scopolamine caused a significant decline in spatial working memory, prefrontal neuron cell loss, and increased proliferation of reactive astrocytes (astrogliosis) when compared with the control and AHA treated group. AHA process of reversing scopolamine-induced memory deficit, prefrontal neuron cell loss, and generation of reactive astrocytes (astrogliosis) is mediated by its antioxidant mediated positive modulation of astrocyte-neuronal interaction during neuroinflammation in response to oxidative tissue damage.

Naringenin protects swine testis cells from bisphenol A-induced apoptosis via Keap1/Nrf2 signaling pathway

Bisphenol A (BPA) has caused serious pathologies in varying organs of humans and animals, especially reproductive organs. Naringenin (NRG) is a flavanone compound that has shown protective effects against several environmental chemicals through suppression of oxidative stress and activation of nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. Herein, we described the discovery path of NRG inhibition on apoptosis in BPA exposed swine testis (ST) cells through targeting Kelch-like ech-associated protein (Keap1). We found that NRG could specifically bound to the active residues of DGR domain in Keap1, thereby activating Nrf2 signaling pathway, and then increasing the levels of SOD, GPx and CAT, and finally inhibiting oxidative stress and mitochondrial apoptosis induced by BPA in ST cells. Altogether, our results showed that NRG inhibits oxidative stress and mitochondrial apoptosis induced by BPA in ST cells by targeting Keap1/Nrf2 signaling pathway, indicating that NRG could serve as an antagonistic therapy against BPA.