The attenuation effect of potassium 2-(1-hydroxypentyl)-benzoate in a mouse model of diabetes-associated cognitive decline: The protein expression in the brain.

AIMS: dl-PHPB (potassium 2-(1-hydroxypentyl)-benzoate) has been shown to have neuroprotective effects against acute cerebral ischemia, vascular dementia, and Alzheimer's disease. The aim of this study was to investigate the effects of dl-PHPB on memory deficits and preliminarily explore the underlying molecular mechanism. METHODS: Blood glucose and behavioral performance were evaluated in the KK-Ay diabetic mouse model before and after dl-PHPB administration. Two-dimensional difference gel electrophoresis (2D-DIGE)-based proteomics was used to identify differentially expressed proteins in brain tissue. Western blotting was used to study the molecular mechanism of the related signaling pathways. RESULTS: Three-month-old KK-Ay mice were given 150 mg/kg dl-PHPB by oral gavage for 2 months, which produced no effect on the level of serum glucose. In the Morris water maze test, KK-Ay mice treated with dl-PHPB showed significant improvements in spatial learning and memory deficits compared with vehicle-treated KK-Ay mice. Additionally, we performed 2D-DIGE to compare brain proteomes of 5-month KK-Ay mice treated with and without dl-PHPB. We found 14 altered proteins in the cortex and 11 in the hippocampus; two of the 25 altered proteins and another four proteins that were identified in a previous study on KK-Ay mice were then validated by western blot to further confirm whether dl-PHPB can reverse the expression levels of these proteins. The phosphoinositide 3-kinase/protein kinase B/glycogen synthase kinase-3ß (PI3K/Akt/GSK-3ß) signaling pathway was also changed in KK-Ay mice and dl-PHPB treatment could reverse it. CONCLUSIONS: These results indicate that dl-PHPB may play a potential role in diabetes-associated cognitive impairment through PI3K/Akt/GSK-3ß signaling pathway and the differentially expressed proteins may become putative therapeutic targets.

Inhibitory effects of antidepressant fluoxetine on cloned Kv2.1 potassium channel expressed in HEK293 cells.

It is well demonstrated that antidepressant fluoxetine has significant inhibitory effects on voltage-gated potassium channels. So far, the concise regulation of fluoxetine on Kv2.1, the predominant delayed rectifier potassium channel subtype in the central nervous system, are rarely reported. Here patch-clamp recording was used to investigate the inhibitory effects of fluoxetine on Kv2.1 potassium channels stably expressed in HEK293 cells. The results showed fluoxetine dose-dependently suppressed Kv2.1 currents with an IC50 of 51.3 µM. At the test potential positive to +50 mV, fluoxetine 50 µM voltage-dependently suppressed Kv2.1 currents with an electrical distance δ of 0.28. Moreover, fluoxetine 50 µM did not affect the activation process of Kv2.1, but reduced the decay time constant τinact and obviously accelerated the inactivation process of Kv2.1 and left-shifted the half-maximal inactivation potential of Kv2.1 potassium channel by 9.8 mV. Fluoxetine 50 µM notably delayed the recovery process of Kv2.1 from inactivation with increased time constants. In addition, fluoxetine 50 µM use-dependently inhibited Kv2.1 currents at different frequencies. In conclusion, the inhibition of Kv2.1 by fluoxetine was concentration-dependent, voltage-dependent and use-dependent. The accelerated steady-state inactivation of Kv2.1 channels induced by fluoxetine might be ascribed to the delay of the recovery process of Kv2.1.

Studies of pathology and pharmacology of diabetic encephalopathy with KK-Ay mouse model.

AIMS: Pathogenesis of diabetic encephalopathy (DE) is not completely understood until now. The purposes of this study were to illustrate the changes in morphology, function, and important transporters in neurons and glia during DE, as well as to reveal the potential therapeutic effects of medicines and the diet control on DE. METHODS: Spontaneous obese KK-Ay mice were used to investigate diabetes-induced cognitive disorder, the morphology, function, and protein expression changes in impact animal and the cell level studies. The new drug candidate PHPB, donepezil, and low-fat food were used to observe the therapeutic effects. RESULTS: KK-Ay mice at 5 months of age showed typical characteristics of type 2 diabetes mellitus (T2DM） and appeared significant cognitive deficits. Morphological study showed microtubule-associated protein 2 (MAP2) expression was increased in hippocampal neurons and glial fibrillary acidic protein (GFAP) expression decreased in astrocytes. Meanwhile, the vesicular glutamate transporter 1 (vGLUT1) expression was increased and glucose transporter 1 (GLUT1) decreased, and the expression of brain-derived neurotrophic factor (BDNF) and glial cell-derived neurotrophic factor (GDNF) was also reduced in KK-Ay mice. Microglia were activated, and IL-1ß and TNF-α were increased obviously in the brains of the KK-Ay mice. Most of the above changes in the KK-Ay mice at 5 months of age could be relieved by diet intervention (DR) or by treatment of donepezil or new drug candidate PHPB. CONCLUSION: KK-Ay mouse is a useful animal model for studying DE. The alterations of morphology, structure, and function of astrocyte and microglia in KK-Ay mice might be rescued by DR and by treatment of medicine. The proteins we reported in this study could be used as biomarkers and the potential drug targets for DE study and treatment.

2-(4-methyl-thiazol-5-yl) ethyl nitrate maleate-potentiated GABAA receptor response in hippocampal neurons.

AIMS: 2-(4-methyl-thiazol-5-yl) ethyl nitrate maleate (NMZM), a derivative of clomethiazole (CMZ), had been investigated for the treatment of Alzheimer's disease (AD). The beneficial effects of NMZM in AD included reversing cognitive deficit, improving learning and memory as well as neuroprotection. The pharmacological effects of NMZM on GABAA receptors were reported previously; however, the mechanisms were unclear and were explored therefore. RESULTS: In this study, we demonstrated that NMZM improved learning and memory by alleviating scopolamine-induced long-term potentiation (LTP) suppression in the dentate gyrus of rats, indicating that NMZM had protective effects against scopolamine-induced depression of LTP. Next, we investigated the action of NMZM on GABAA receptors in hippocampal neurons and the binding site of NMZM on GABAA receptors. NMZM directly activated GABAA receptors in hippocampal neurons in a weak manner. However, NMZM could potentiate the response of GABAA receptors to GABA and NMZM positively modulated GABAA receptors with an EC50 value of 465 µmol/L at 3 µmol/L GABA while this potentiation at low concentration of GABA (1, 3 µmol/L) was more significant than that at high concentration (10, 30 µmol/L). In addition, NMZM could enhance GABA currents after using diazepam and pentobarbital, the positive modulators of GABAA receptors. NMZM could not affect the etomidate-potentiated GABAA current. It suggested that the binding site of NMZM on GABAA receptors is the same as etomidate. CONCLUSIONS: These results provided support for the neuroprotective effect of NMZM, which was partly dependent on the potentiation of GABAA receptors. The etomidate binding site might be a new target for neuronal protection and for drug development.

The pathological roles of NDRG2 in Alzheimer's disease, a study using animal models and APPwt-overexpressed cells.

AIMS: To investigate the roles of N-myc downstream-regulated gene 2 (NDRG2) in the pathology of aging and neurodegenerative disease such as Alzheimer's disease (AD). RESULTS: In this study, we confirmed the upregulation of NDRG2 in the brains of aging and AD animal models. To explore the role of NDRG2 in the pathology of AD at molecular level, we conducted a cell-based assay of highly expressed wild-type human APP695 SK-N-SH cells (SK-N-SH APPwt). By silencing and overexpressing gene of NDRG2, we demonstrated that NDRG2-mediated increase in Aß1-42 was through the pathways of BACE1 and GGA3. NGRG2 improved tau phosphorylation via enhanced activity of CDK5 and decreased Pin1, but it was not affected by GSK3ß pathway. NDRG2 might also induce cell apoptosis through the extrinsic (caspase 8) apoptotic pathway by interaction with STAT3. CONCLUSION: Our study confirmed the upregulation of NDRG2 in AD animal models and demonstrated its important roles in AD pathology. NDRG2 might be a potential target for studying and treatment of AD.

Changes in Synaptic Plasticity and Glutamate Receptors in Type 2 Diabetic KK-Ay Mice.

In the present study, the progressive alteration of cognition and the mechanisms of reduction in long-term potentiation (LTP) in spontaneous obese KK-Ay type 2 diabetic mice were investigated. In the study, 3-, 5-, and 7-month-old KK-Ay mice were used. The results indicated that KK-Ay mice showed cognitive deficits in the Morris water maze test beginning at the age of 3 months. LTP was significantly impaired in KK-Ay mice during whole study period (3 to 7 months). The above deficits were reversible at an early stage (3 to 5 months old) by diet intervention. Moreover, we found the underlying mechanisms of LTP impairment in KK-Ay mice might be attributed to abnormal phosphorylation or expression of postsynaptic glutamate receptor subunits instead of alteration of basal synaptic transmission. The expression levels of NR1, NR2A, and NR2B subunits of N-methyl-d-aspartate receptors (NMDARs) were unchanged while the Tyr-dependent phosphorylation of both NR2A and NR2B subunits were significantly reduced in KK-Ay mice. The level of p-Src expression mediating this process was decreased, and the level of αCaMKII autophosphorylation was also reduced. Meanwhile, the GluR1 of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) was decreased, and GluR2 was significantly increased. These data suggest that deficits in synaptic plasticity in KK-Ay mice may arise from the abnormal phosphorylation of the NR2 subunits and the alteration of subunit composition of AMPARs. Diet intervention at an early stage of diabetes might alleviate the cognitive deficits and LTP reduction in KK-Ay mice.

Over-expressed human TREK-1 inhibits CHO cell proliferation via inhibiting PKA and p38 MAPK pathways and subsequently inducing G1 arrest.

AIM: Recent studies have shown that the two-pore-domain potassium channel TREK-1 is involved in the proliferation of neural stem cells, astrocytes and human osteoblasts. In this study, we investigated how TREK-1 affected the proliferation of Chinese hamster ovary (CHO) cells in vitro. METHODS: A CHO cell line stably expressing hTREK-1 (CHO/hTREK-1 cells) was generated. TREK-1 channel currents in the cells were recorded using whole-cell voltage-clamp recording. The cell cycle distribution was assessed using flow cytometry analysis. The expression of major signaling proteins involved was detected with Western blotting. RESULTS: CHO/hTREK-1 cells had a high level of TREK-1 expression, reached up to 320%±16% compared to the control cells. Application of arachidonic acid (10 µmol/L), chloroform (1 mmol/L) or etomidate (10 µmol/L) substantially increased TREK-1 channel currents in CHO/hTREK-1 cells. Overexpression of TREK-1 caused CHO cells arresting at the G1 phase, and significantly decreased the expression of cyclin D1. The TREK-1 inhibitor l-butylphthalide (1-100 µmol/L) dose-dependently attenuated TREK-1-induced G1 phase cell arrest. Moreover, overexpression of TREK-1 significantly decreased the phosphorylation of Akt (S473), glycogen synthase kinase-3ß (S9) and cAMP response element-binding protein (CREB, S133), enhanced the phosphorylation of p38 (T180/Y182), but did not alter the phosphorylation and expression of signal transducer and activator of transcription 3 (STAT3). CONCLUSION: TREK-1 overexpression suppresses CHO cell proliferation by inhibiting the activity of PKA and p38/MAPK signaling pathways and subsequently inducing G1 phase cell arrest.