Celastrus paniculatus seed extract exhibits neuroprotective effects against MPP+‑induced apoptotic cell death via GSK‑3β in a Parkinson's disease model

Parkinson's disease (PD) is a common neurodegenerative disease induced by the death of dopaminergic neurons. Seed oil of Celastrus paniculatus (CP) Willd. has protective and antioxidant properties; however, to the best of our knowledge, no studies have analyzed the neuroprotective effect of CP seeds on PD. The present study aimed to investigate the neuroprotective effects and mechanism of CP seed extract (CPSE) using an in vitro 1-methyl-4-phenylpyridinium ion (MPP+)-induced PD model. The effect of CPSE on the expression levels of apoptotic marker proteins, such as Bcl-2 and its upstream pathway protein, glycogen synthase kinase-3β (GSK-3β), was investigated in human neuroblastoma SH-SY5Y cells. The effect of CPSE on the viability of SH-SY5Y cells was evaluated using MTT assay. To investigate the potential neuroprotective effect of CPSE, SH-SY5Y cells were treated with MPP+ to induce PD-associated cytotoxicity. SH-SY5Y cells were treated with 2 mM MPP+ before or after CPSE treatment to determine the protective effect of CPSE against MPP+-induced neurotoxicity using MTT, WST-1 and lactate dehydrogenase assays. Moreover, it was investigated whether CPSE could promote survival signals by regulating the protein expression levels of apoptotic markers (Bcl-2 and GSK-3β) using western blotting. High concentrations and prolonged treatment of CPSE did not have any adverse effect on SH-SY5Y cell viability. Furthermore, MPP+-induced dopaminergic neuron damage was ameliorated by CPSE treatment. CPSE also showed anti-apoptotic activity by reversing the inhibitory effects of MPP+ on Bcl-2 expression. Moreover, CPSE abolished MPP+-induced decreases in phosphorylated-GSK-3β (Ser9) expression. Taken together, the present findings suggested that CPSE may exert a neuroprotective effect in PD.

Current opinion on the regulation of small intestinal magnesium absorption

Magnesium (Mg²⁺) has an important role in numerous biological functions, and Mg²⁺ deficiency is associated with several diseases. Therefore, adequate intestinal absorption of Mg²⁺ is vital for health. The small intestine was previously thought to absorb digested Mg²⁺ exclusively through an unregulated paracellular mechanism, which is responsible for approximately 90% of total Mg²⁺ absorption. Recent studies, however, have revealed that the duodenum, jejunum, and ileum absorb Mg²⁺ through both transcellular and paracellular routes. Several regulatory factors of small intestinal Mg²⁺ uptake also have been explored, e.g., parathyroid hormone, fibroblast growth factor-23, apical acidity, proton pump inhibitor, and pH-sensing channel and receptors. The mechanistic factors underlying proton pump inhibitor suppression of small intestinal Mg²⁺, such as magnesiotropic protein dysfunction, higher mucosal bicarbonate secretion, Paneth cell dysfunction, and intestinal inflammation, are currently being explored. The potential role of small intestinal microbiomes in Mg²⁺ absorption has also been proposed. In this article, we reviewed the current knowledge on the mechanisms and regulatory factors of small intestinal Mg²⁺ absorption.

Hippocampal synaptic dysfunction and spatial memory impairment in omeprazole-treated rats

Although the association of prolonged use of proton pump inhibitors, such as omeprazole, with memory impairment has been reported more than two decades ago, its underlying molecular mechanism is yet to be determined. Thus, in this study, we aimed to determine the mechanisms underlying the effect of prolonged omeprazole treatment on hippocampal synaptic function and spatial memory in male rats. Adult rats were subcutaneously administered with omeprazole for 12 or 24 weeks. Spatial memory was assessed using the Morris water maze (MWM) test. We examined the hippocampal protein expression of synaptic plasticity proteins, including the AMPA receptor subunit GluA1, postsynaptic density-95 (PSD-95), and activity-regulated cytoskeleton-associated protein (Arc), and the hippocampal expression and localization of androgen receptor (AR). In the MWM test, the escape latency was found to be significantly higher, and the number of platform crossings and the time spent in the target quadrant were significantly lower in the rats treated with omeprazole compared to the control rats. Hypomagnesemia and lower bone and brain Mg²⁺ content were also detected in the omeprazole-treated groups compared with the control group. The expression of GluA1, PSD-95, and Arc in the hippocampus and the expression of AR in the dentate gyrus and CA1 of the hippocampus were significantly lower in the omeprazole-treated groups than in the control group. These results suggest that prolonged omeprazole treatment might lead to memory deficit by impairing glutamate receptor trafficking or synaptic anchoring. Hypomagnesemia and brain Mg²⁺ deficiency may be, at least in part, involved in omeprazole-induced memory impairment.

The effects of okadaic acid-treated SH-SY5Y cells on microglia activation and phagocytosis

The activation of microglia is found to be associated with neurodegenerative disorders including Alzheimer's disease (AD). Several studies have shown that okadaic acid (OA) induced deposition of tau hyperphosphorylation, and subsequent neuronal degeneration, loss of synapses, and memory impairment, all of which resemble the pathology of AD. Although OA is a powerful tool available for mechanisms of the neurotoxicity associated with AD, the exact mechanism underlying the activation of microglial cells remains unrevealed. The aim of this study was to determine the effect of both OA and OA-treated neuroblastoma SH-SY5Y cells on microglial HAPI cell viability, activation, and phagocytosis. The results showed that both OA and OA-treated neurons did not induce any detectable cytotoxicity of microglial cells. Furthermore, incubation with OA-treated SH-SY5Y cells could increase the expression of ionized calcium-binding adapter molecule 1 (Iba1) on microglial HAPI cells. This result indicated that OA may induce microglial activation through the toxicity of neurons. Moreover, we also demonstrated that OA-treated SH-SY5Y cells were engulfed by CD11b/c-labeled microglial HAPI cells, which were abolished after treatment with 10 mM O-phospho- l-serine ( L-SOP) for 30 min before co-culture with OA-treated SH-SY5Y cells, indicating cells experiencing phagocytic activity. We also confirmed that OA treatment for 24 h significantly increased tau hyperphosphorylation at S396 in SH-SY5Y cells. In conclusion, our findings indicate that OA is a potential toxic inducer underlying the role of microglia in AD pathogenesis.

Ultrastructural intestinal mucosa change after prolonged inhibition of gastric acid secretion by omeprazole in male rats

Omeprazole is a potent inhibitor of gastric acid secretion. It was reported that omeprazole induced dramatic gastric mucosa morphologic changes from the resting state to the stimulated state. However, the effect of omeprazole administration on the ultrastructure and absorptive function of small intestines was largely unknown. Here, male Sprague-Dawley rats were daily treated with a single dose of omeprazole for 12 or 24 weeks. Ultrastructure intestinal mucosal change in duodenum, jejunum, and ileum was observed. We also determined small intestine inflammation, using intraepithelial lymphocytes activation. Finally, magnesium levels were measured in plasma, urine, feces, muscle, and bone to determine systemic magnesium balance. Omeprazole-treated rats had significantly decreased the width of tight junction, villous length, and absorptive area of duodenum, jejunum, and ileum compared to control rats. The small intestine of the omeprazole-treated group showed significantly higher intraepithelial lymphocytes activation levels compared with the control group. Lower secretory granules of Paneth cells at the base of the crypts were showed in omeprazole-treated rats. They also had significantly lower plasma, urinary, bone, and muscle Mg2+ contents indicating hypomagnesemia with systemic magnesium deficiency. In conclusion, prolonged omeprazole treatment-induced small intestinal inflammation and villous atrophy, which led to decrease small intestinal magnesium absorption in the condition of proton pump inhibitor-induced hypomagnesemia.

Effect of prolonged omeprazole administration on segmental intestinal Mg2+ absorption in male Sprague-Dawley rats

BACKGROUND

The exact mechanism of proton pump inhibitors (PPIs)-induced hypomagnesemia (PPIH) is largely unknown. Previous studies proposed that PPIH is a consequence of intestinal Mg²⁺ malabsorption. However, the mechanism of PPIs-suppressed intestinal Mg²⁺ absorption is under debate.

AIM

To investigate the effect of 12-wk and 24-wk omeprazole injection on the total, transcellular, and paracellular Mg²⁺ absorption in the duodenum, jejunum, ileum, and colon of male Sprague-Dawley rats.

METHODS

The rats received 20 mg/kg∙d subcutaneous omeprazole injection for 12 or 24 wk. Plasma and urinary Mg²⁺, Ca²⁺, and PO₄³⁻ levels were measured. The plasma concentrations of 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF-23), epidermal growth factor (EGF), and insulin were also observed. The duodenum, jejunum, ileum, and colon of each rat were mounted onto individual modified Using chamber setups to study the rates of total, transcellular, and paracellular Mg²⁺ absorption simultaneously. The expression of transient receptor potential melastatin 6 (TRPM6) and cyclin M4 (CNNM4) in the entire intestinal tract was also measured.

RESULTS

Single-dose omeprazole injection significantly increased the intraluminal pH of the stomach, duodenum, and jejunum. Omeprazole injection for 12 and 24 wk induced hypomagnesemia with reduced urinary Mg²⁺ excretion. The plasma Ca²⁺ was normal but the urinary Ca²⁺ excretion was reduced in rats with PPIH. The plasma and urinary PO₄³⁻ levels increased in PPIH rats. The levels of 1α,25(OH)₂D₃ and FGF-23 increased, whereas that of plasma EGF decreased in the omeprazole-treated rats. The rates of the total, transcellular, and paracellular Mg²⁺ absorption was significantly lower in the duodenum, jejunum, ileum, and colon of the rats with PPIH than in those of the control rats. The percent suppression of Mg²⁺ absorption in the duodenum, jejunum, ileum, and colon of the rats with PPIH compared with the control rats was 81.86%, 70.59%, 69.45%, and 39.25%, respectively. Compared with the control rats, the rats with PPIH had significantly higher TRPM6 and CNNM4 expression levels throughout the intestinal tract.

CONCLUSION

Intestinal Mg²⁺ malabsorption was observed throughout the intestinal tract of rats with PPIH. PPIs mainly suppressed small intestinal Mg²⁺ absorption. Omeprazole exerted no effect on the intraluminal acidic pH in the colon. Thus, the lowest percent suppression of total Mg²⁺ absorption was found in the colon. The expression levels of TRPM6 and CNNM4 increased, indicating the presence of a compensatory response to Mg²⁺ malabsorption in rats with PPIH. Therefore, the small intestine is an appropriate segment that should be modulated to counteract PPIH.

The inhibitory role of purinergic P2Y receptor on Mg2+ transport across intestinal epithelium-like Caco-2 monolayer

The mechanism of proton pump inhibitors (PPIs) suppressing intestinal Mg2+ uptake is unknown. The present study aimed to investigate the role of purinergic P2Y receptors in the regulation of Mg2+ absorption in normal and omeprazole-treated intestinal epithelium-like Caco-2 monolayers. Omeprazole suppressed Mg2+ transport across Caco-2 monolayers. An agonist of the P2Y2 receptor, but not the P2Y4 or P2Y6 receptor, suppressed Mg2+ transport across control and omeprazole-treated monolayers. Omeprazole enhanced P2Y2 receptor expression in Caco-2 cells. Forskolin and P2Y2 receptor agonist markedly enhanced apical HCO3- secretion by control and omeprazole-treated monolayers. The P2Y2 receptor agonist suppressed Mg2+ transport and stimulated apical HCO3- secretion through the Gq-protein coupled-phospholipase C (PLC) dependent pathway. Antagonists of cystic fibrosis transmembrane conductance regulator (CFTR) and Na+-HCO3- cotransporter-1 (NBCe1) could nullify the inhibitory effect of P2Y2 receptor agonist on Mg2+ transport across control and omeprazole-treated Caco-2 monolayers. Our results propose an inhibitory role of P2Y2 on intestinal Mg2+ absorption.

Age-Related Memory Impairment Associated With Decreased Endogenous Estradiol in the Hippocampus of Female Rats

It is widely known that not only the gonadal estradiol (E2) but also hippocampal E2 plays an essential role in memory process. However, the role of hippocampal E2-enhanced memory mechanism during aging is largely unknown. The aim of the present study was to investigate the effect of age on E2 concentration, the expression level of its receptors, and key steroidogenic enzymes in hippocampus. We also investigated the effect of microglia activation on E2 synthesis in hippocampal neurons. The results showed that serum E2 was higher in 19-month-old (aged) rats, which exhibited spatial memory decline in the Morris water maze (MWM) test when compared to the younger rats. Hence, serum E2 may not be associated with the reduced spatial memory performance in aging. In contrast, the level of E2 and the expressions of its receptors were significantly decreased in hippocampus of aged female rat compared to younger females. Furthermore, the expressions of key hippocampal steroidogenic enzymes, steroidogenic acute regulatory protein (StAR), and cytochrome P450 (P450) also significantly decreased with age, which resulted in lower hippocampal E2 levels. In addition, we found that the microglia of aged brain highly expressed interleukin 6 (IL-6), which directly inhibited E2 synthesis in hippocampal neurons via suppression of P450 synthesis. Taken together, we summarized that the microglia-derived IL-6 inhibited hippocampal E2 synthesis in aged rats which, in turn, contributed to the deficit of spatial memory performance.

Inhibition of hippocampal estrogen synthesis by reactive microglia leads to down-regulation of synaptic protein expression

Activation of microglia may facilitate age-related impairment in cognitive functions including hippocampal-dependent memory. Considerable evidence indicates that hippocampal-derived estrogen improves hippocampal-dependent learning and memory. We hypothesize that activated microglia may inhibit de novo hippocampal estrogen synthesis and in turn suppress hippocampal synaptic protein expression. The present study aimed to elucidate the role of lipopolysaccharide (LPS)-activated microglial HAPI cells on estrogen synthesis and expression of synaptic proteins using H19-7 hippocampal neurons with a neuron-microglia co-culture system. LPS induced expression of the microglial activation markers major histocompatibility complex II (MHC II), CD11b, and ionized calcium-binding adapter molecule 1 (Iba1). Prolonged LPS exposure also enhanced the secretion of interleukin (IL)-6 and nitric oxide (NO) from microglial HAPI cells. Exposure to either LPS-activated microglia or IL-6, significantly suppressed the expression of synaptic proteins and the secretion of de novo hippocampal estrogen in H19-7 hippocampal neurons. In addition, LPS-activated microglia also decreased the expression of estrogen receptors (ERα and ERβ) in H19-7 hippocampal neurons. Our findings demonstrate a potential mechanism of microglia activation underlying the reduction in estrogen-mediated signaling on synaptic proteins in hippocampal neurons, which may be involved in hippocampal-dependent memory formation.

A priming role of local estrogen on exogenous estrogen-mediated synaptic plasticity and neuroprotection

The localization of estrogen (E2) has been clearly shown in hippocampus, called local hippocampal E2. It enhanced neuronal synaptic plasticity and protected neuron form cerebral ischemia, similar to those effects of exogenous E2. However, the interactive function of hippocampal and exogenous E2 on synaptic plasticity activation and neuroprotection is still elusive. By using hippocampal H19-7 cells, we demonstrated the local hippocampal E2 that totally suppressed by aromatase inhibitor anastrozole. Anastrozole also suppressed estrogen receptor (ER)β, but not ERα, expression. Specific agonist of ERα (PPT) and ERβ (DPN) restored ERβ expression in anastrozole-treated cells. In combinatorial treatment with anastrozole and phosphoinositide kinase-3 (PI-3K) signaling inhibitor wortmannin, PPT could not improve hippocampal ERβ expression. On the other hand, DPN induced basal ERβ translocalization into nucleus of anastrozole-treated cells. Exogenous E2 increased synaptic plasticity markers expression in H19-7 cells. However, exogenous E2 could not enhance synaptic plasticity in anastrozole-treated group. Exogenous E2 also increased cell viability and B-cell lymphoma 2 (Bcl2) expression in H₂O₂-treated cells. In combined treatment of anastrozole and H₂O₂, exogenous E2 failed to enhance cell viability and Bcl2 expression in hippocampal H19-7 cells. Our results provided the evidence of the priming role of local hippocampal E2 on exogenous E2-enhanced synaptic plasticity and viability of hippocampal neurons.

Genomic and non-genomic actions of estrogen on synaptic plasticity in SH-SY5Y cells

Estrogen modulates synaptic plasticity, an important mechanism of memory storage. Previously, we have reported that estrogen rapidly increases the expression of Arc (activity-regulated cytoskeleton associated protein), a key protein for synaptic plasticity, via non-genomic phosphoinositide-3 kinase (PI-3K)-, mitogen-activated protein kinase (MAPK)-, and estrogen receptor (ER)-dependent pathways in SH-SY5Y cells. The present study aimed to investigate the role of each ER subtype, alpha and beta, in synaptic plasticity in SH-SY5Y cells. The specific agonist of ER beta (DPN) markedly induced Arc expression that mimics treatment with estrogen, but not ER alpha (PTT). Determination of subcellular localization of ER beta using immunocytochemistry shows that ER beta was retained in the cytoplasm of the untreated cells. In estrogen-treated cells, the membrane and cytosolic ER beta gradually decreased, while nuclear ER beta progressively increased in time-dependent manner, suggesting estrogen-dependent nuclear translocation of ER beta. Nuclear accumulation of ER beta at 6-12h post-estrogen treatment, leads to increased PSD-95 and SYP mRNA expression, indicating the classical genomic estrogenic action on synaptic plasticity. However, the block of PI-3K signaling by Wortmannin partially suppressed estrogen (48 h)-induced PSD-95 and SYP expression, suggesting a crosstalk mechanism between genomic and non-genomic actions of estrogen on synaptic plasticity. Therefore, the estrogen-enhanced synaptic plasticity is ER beta-dependent and involves the crosstalk mechanism of non-genomic and genomic estrogenic actions.

Estrogen stimulates activity-regulated cytoskeleton associated protein (Arc) expression via the MAPK- and PI-3K-dependent pathways in SH-SY5Y cells

Activity-regulated cytoskeleton associated protein (Arc) is known to be induced by synaptic plasticity following memory consolidation. Since estrogen has been shown to play an important role in synaptogenesis, a key aspect of the synaptic plasticity, we aimed to study the effects of estrogen on Arc expression in SH-SY5Y human neuroblastoma cells. Using quantitative real-time PCR, Western blot, and confocal immunocytochemistry techniques we found that estrogen markedly increased Arc mRNA and protein expression in SH-SY5Y cells. Estrogen-activated Arc expression was mediated via mitogen-activated protein kinase (MAPK) and phosphoinositide-3 kinase (PI-3K), but not protein kinase C (PKC) and Rho-associated kinase (ROCK), and in the estrogen receptor (ER)-dependent manner. Estrogen also significantly upregulated the dendritic spine scaffolding protein, postsynaptic density-95 (PSD-95), as well as expression of the presynaptic vesicle protein, synaptophysin. Our findings demonstrate the possible mechanisms of estrogen-induced synaptic plasticity, as well as memory consolidation.