Protein kinase Cδ mediates trimethyltin-induced neurotoxicity in mice in vivo via inhibition of glutathione defense mechanism.

We investigated whether protein kinase C (PKC) is involved in trimethyltin (TMT)-induced neurotoxicity. TMT treatment (2.8 mg/kg, i.p.) significantly increased PKCδ expression out of PKC isozymes (i.e., α, ßI, ßII, δ, and ς) in the hippocampus of wild-type (WT) mice. Consistently, treatment with TMT resulted in significant increases in cleaved PKCδ expression. Genetic or pharmacological inhibition (PKCδ knockout or rottlerin) was less susceptible to TMT-induced seizures than WT mice. TMT treatment increased glutathione oxidation, lipid peroxidation, protein oxidation, and levels of reactive oxygen species. These effects were more pronounced in the WT mice than in PKCδ knockout mice. In addition, the ability of TMT to induce nuclear translocation of Nrf2, Nrf2 DNA-binding activity, and upregulation of γ-glutamylcysteine ligase was significantly increased in the PKCδ knockout mice and rottlerin (10 or 20 mg/kg, p.o. × 6)-treated WT mice. Furthermore, neuronal degeneration (as shown by nuclear chromatin clumping and TUNEL staining) in WT mice was most pronounced 2 days after TMT. At the same time, TMT-induced inhibition of phosphoinositol 3-kinase (PI3K)/Akt signaling was evident, thereby decreasing phospho-Bad, expression of Bcl-xL and Bcl-2, and the interaction between phospho-Bad and 14-3-3 protein, and increasing Bax expression and caspase-3 cleavage were observed. Rottlerin or PKCδ knockout significantly protected these changes in anti- and pro-apoptotic factors. Importantly, treatment of the PI3K inhibitor LY294002 (0.8 or 1.6 µg, i.c.v.) 4 h before TMT counteracted protective effects (i.e., Nrf-2-dependent glutathione induction and pro-survival phenomenon) of rottlerin. Therefore, our results suggest that down-regulation of PKCδ and up-regulations of Nrf2-dependent glutathione defense mechanism and PI3K/Akt signaling are critical for attenuating TMT neurotoxicity.

Inhibition of protein kinase (PK) Cδ attenuates methamphetamine-induced dopaminergic toxicity via upregulation of phosphorylation of tyrosine hydroxylase at Ser40 by modulation of protein phosphatase 2A and PKA.

Recently, we proposed that inhibition of protein kinase (PK) Cδ may be a useful target for protection against methamphetamine (MA)-induced dopaminergic toxicity. We demonstrated that treatment with MA resulted in a significant decrease in phosphorylation of tyrosine hydroxylase (TH) at Ser(40) in the striatum, but not in the phosphorylation of TH at Ser(31) . In the present study, treatment with rottlerin (1.5 or 3.0 µg, i.c.v, once a day for 5 days), a PKCδ inhibitor, or a PKCδ antisense oligonucleotide (ASO; 2.5 µg/µl, i.c.v., 3 times) significantly attenuated MA-induced reductions in the phosphorylation of TH at Ser(40) and in the expression of PKA in the striatum of mice. This attenuation was significantly counteracted by H89 (10 or 30 ng, i.c.v., 1 h after the last MA administration), a PKA inhibitor. Treatment with rottlerin or ASO significantly attenuated the MA-induced increase in protein phosphatase (PP) 2A activity. FTY720 (1 or 5 mg/kg, i.p., 1 h after the last MA administration), a PP2A activator, significantly reversed the recovery in TH phosphorylation mediated by inhibition of PKCδ after MA treatment. Both H89 and FTY720 counteracted the recovery of MA-induced behavioural impairments induced by PKCδ inhibition. The effects, mediated by rottlerin or ASO in MA-treated wild-type mice were comparable with those in MA-treated PKCδ(-/-) mice. However, neither inhibition of the mitogen-activated protein kinase subfamily (extracellular signal-regulated kinase, c-Jun N-terminal kinase, p38) nor inhibition of calcium calmodulin kinase II significantly altered PKCδ inhibition-mediated attenuation of MA-induced impairment of TH phosphorylation. The results suggest that genetic or pharmacological inhibition of PKCδ requires modulation of PKA expression and/or PP2A activity to attenuate the impairment of TH phosphorylation at Ser(40) and behavioural activity induced by MA.

YY162 prevents ADHD-like behavioral side effects and cytotoxicity induced by Aroclor1254 via interactive signaling between antioxidant potential, BDNF/TrkB, DAT and NET.

Methylphenidate (MP) has become the primary drug of choice for treatment of attention-deficit/hyperactivity disorder (ADHD). However, its psychotropic effects severely hamper long-term clinical use. We evaluated the effects of YY162, which consists of terpenoid-strengthened Ginkgo biloba and ginsenoside Rg3, on the ADHD-like condition induced by Aroclor1254, because both components have been suggested to modulate oxidative stress, dopaminergic neurotransmission, and brain-derived neurotrophic factor (BDNF) signaling, which may be critical targets for understanding the pathogenesis of ADHD. YY162 attenuated the increase in reactive oxygen species (ROS) and decrease in BDNF levels induced by Aroclor1254 in SH-SY5Y neuroblastoma cells. YY162 significantly attenuated Aroclor1254-induced ADHD-like behavior and oxidative stress in ICR mice. Furthermore, YY162 attenuated reductions in p-TrkB, BDNF, dopamine transporter (DAT) and norepinephrine transporter (NET) expression. These attenuating effects of YY162 were comparable to those of MP. Importantly, K252a, a TrkB antagonist, counteracted the protective effects of YY162. Our results suggest that YY162 possesses significant protective activities against ADHD-like conditions with negligible behavioral side effects, and that interactive signaling between antioxidant potential and BDNF/TrkB receptor for the positive modulation of the DAT and NET is important for YY162-mediated neuroprotective activity.

Growth hormone releaser attenuates beta-amyloid (1 - 42)-induced memory impairment in mice.

Accumulating evidence indicates that growth hormone (GH) might be effective at preventing the development of Alzheimer's disease. However, exogenous GH treatment has exhibited side effects for clinical application; thus supplementation with amino acids to promote the release of GH could be a possible alternative treatment. In this study, mice that were fed with a diet of GH-releasing supplements had significantly attenuated memory impairments and hippocampal changes in the acetylcholinesterase activity and acetylcholine level induced by amyloid beta protein (Abeta) (1 - 42). Our results suggest that the use of GH-releasing supplement exerts beneficial effects on the memory impairment induced by Abeta (1 - 42).

Ginsenosides attenuate methamphetamine-induced behavioral side effects in mice via activation of adenosine A2A receptors: possible involvements of the striatal reduction in AP-1 DNA binding activity and proenkephalin gene expression.

Current evidence suggests that ginsenosides inhibit methamphetamine (MA)-induced changes in behavior, but the precise mechanisms that underlie this effect are yet to be determined. We examined the role of adenosine receptors in the ginsenoside-induced changes in hyperlocomotion and conditioned place preference (CPP) in mice that occurred in response to administration of MA (2 mg/kg, i.p. x 1 or 2 mg/kg, i.p. x 6). Changes in circling behavior paralleled changes in CPP in the presence of MA. Pre-treatment with ginsenosides (50 or 150 mg/kg, i.p.) attenuated the MA-induced circling behavior and CPP. This attenuation was reversed by the adenosine A2A receptor antagonist 1,3,7-trimethyl-8-(3-chrostyryl)xanthine (CSC; 0.5 and 1.0 mg/kg) in a dose-dependent manner, but neither the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT; 0.5 and 1.0 mg/kg) nor the A2B receptor antagonist alloxazine (ALX; 1.5 and 3.0 mg/kg) had any such effect. MA-induced increases in activator protein (AP)-1 DNA binding activity, Fos-related antigen immunoreactivity (FRA-IR), proenkephalin mRNA expression, and proenkephalin-like immunoreactivity were reduced consistently in the striatum of animals that were pretreated with ginsenosides. These reductions were largely prevented by CSC, but not by CPT or ALX. Our results suggest that the stimulation of A2A receptors by ginsenosides attenuates the changes in behavior and the increases in AP-1 DNA binding activity, FRA-IR, and proenkephalin gene expression in mouse striatum that are induced by MA.

The dextromethorphan analog dimemorfan attenuates kainate-induced seizures via sigma1 receptor activation: comparison with the effects of dextromethorphan.

In a previous study, we demonstrated that a dextromethorphan analog, dimemorfan, has neuroprotective effects. Dextromethorphan and dimemorfan are high-affinity ligands at sigma1 receptors. Dextromethorphan has moderate affinities for phencyclidine sites, while dimemorfan has very low affinities for such sites, suggesting that these sites are not essential for the anticonvulsant actions of dimemorfan. Kainate (KA) administration (10 mg kg(-1), i.p.) produced robust convulsions lasting 4-6 h in rats. Pre-treatment with dimemorfan (12 or 24 mg kg(-1)) reduced seizures in a dose-dependent manner. Dimemorfan pre-treatment also attenuated the KA-induced increases in c-fos/c-jun expression, activator protein (AP)-1 DNA-binding activity, and loss of cells in the CA1 and CA3 fields of the hippocampus. These effects of dimemorfan were comparable to those of dextromethorphan. The anticonvulsant action of dextromethorphan or dimemorfan was significantly counteracted by a selective sigma1 receptor antagonist BD 1047, suggesting that the anticonvulsant action of dextromethorphan or dimemorfan is, at least in part, related to sigma1 receptor-activated modulation of AP-1 transcription factors. We asked whether dimemorfan produces the behavioral side effects seen with dextromethorphan or dextrorphan (a phencyclidine-like metabolite of dextromethorphan). Conditioned place preference and circling behaviors were significantly increased in mice treated with phencyclidine, dextrorphan or dextromethorphan, while mice treated with dimemorfan showed no behavioral side effects. Our results suggest that dimemorfan is equipotent to dextromethorphan in preventing KA-induced seizures, while it may lack behavioral effects, such as psychotomimetic reactions.

Attenuation of cocaine-induced conditioned place preference by Polygala tenuifolia root extract.

A recent investigation indicated that Polygala tenuifolia Willdenow extract (PTE) possesses a potential antipsychotic effect. In this study, we examined the effects of PTE on the cocaine-induced changes in locomotor activity, conditioned place preference (CPP), fos-related antigen-immunoreactivity (FRA-IR), and activator protein (AP)-1 DNA binding activity. Cocaine-induced behavioral effects (hyperlocomotion and CPP) occurred in parallel with increases in FRA-IR and AP-1 DNA binding activity in the nucleus accumbens. These responses induced by cocaine were consistently attenuated by concurrent treatment with PTE (25 mg or 50 mg/kg/day, i.p. x 7). The adenosine A2A receptor antagonist, 1,3,7-trimethyl-8-(3-chlorostyrl)xanthine (0.5 or 1.0 mg/kg, i.p.), reversed the PTE-mediated pharmacological action in a dose related manner; neither the adenosine A(1) receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine (0.5 or 1.0 mg/kg, i.p.) nor the A2B receptor antagonist, alloxazine (1.5 or 3.0 mg/kg, i.p.) significantly affected this pharmacological action. Our results suggest that PTE prevents cocaine-induced behavioral effects, at least in part, via the activation of the adenosine A2A receptor.