Antiproliferative effect of GTS-21 in glioblastoma cells

Glioblastoma multiforme (GBM) is the most common malignant brain tumour in adults. The poor prognosis and short median overall survival of patients with GBM is associated with resistance to therapy after surgical and adjuvant treatment. The expression of various acetylcholine receptors (AChR) in GBM has been widely reported. The present study aimed to investigate the expression of cholinergic system-related genes in primary GBM and to explore the antiproliferative effect of 3-(2,4-dimethoxybenzylidene) anabaseine (GTS-21) in GBM cell lines. Therefore, the expression of 28 genes associated with the cholinergic system was detected using a customized RT² Profiler PCR Array in 44 GBM and 5 healthy control brain tissue samples. In addition, the activity of GTS-21, an alpha 7 subunit nicotinic AChR (α7 nAChR) agonist, and that of α-bungarotoxin (α-BTX), an α7 nAChR antagonist, was determined in primary and established GBM cells. Therefore, the A172, U87 and G28 cell lines and primary GBM cells were treated with GTS-21, ACh or nicotine. Cell viability was evaluated using MTT assay at 24, 48 and 72 h following cell treatment with the corresponding compounds. The results revealed that the expression of cholinergic system-related components was notably downregulated, except that of cholinergic receptor nicotinic alpha 7 subunit (CHRNA7), in primary GBM and U87 cells. However, the dominant-negative duplicate form of CHRNA7 was also downregulated. Furthermore, A172 and G28 cells exhibited a heterogeneous gene expression pattern. Additionally, GTS-21 inhibited the proliferation of GBM cells in a dose- and time-dependent manner. Interestingly, treatment with α-BTX restored the proliferation of U87 cells, but not that of A172 and G28 cells. Collectively, the findings of the present study suggested that GTS-21 may inhibit the proliferation of GBM cells and may therefore serve as a novel therapeutic approach to the treatment of GBM, which warrants further investigation.

Nicotinic acetylcholine receptors α7 and α9 modifies tobacco smoke risk for multiple sclerosis

INTRODUCTION

Tobacco smoke exposure is an established risk factor for multiple sclerosis (MS), yet how it confers risk is not known. Evidence from observational studies suggests nicotine may be a protective component. Animal studies further support this hypothesis, demonstrating nicotine's protective effect in MS is mediated by the presence and absence of α7 and α9 nicotinic acetylcholine receptors (nAChRs), respectively.

OBJECTIVE

To determine if variation in the genes encoding α7 and α9 nAChRs (cholinergic receptor nicotinic alpha 7 (CHRNA7) and alpha 9 (CHRNA9)) will modify MS risk conferred by tobacco smoking.

METHODS

A multi-stage gene-environment (G×E) framework was utilized, including a case-control analysis (286 cases, 176 controls) with haplotype- and gene-based analyses, followed by an extension case-only (1053 cases) analysis for overlapping variants.

RESULTS

The results suggest that CHRNA7 and CHRNA9 modifies MS risk conferred by tobacco smoke, where risk among smokers was increased in carriers of the minor CHRNA9 haplotype and in non-carriers the minor CHRNA7 haplotype. The findings are consistent with the pharmacology of these receptors and animal studies of MS.

CONCLUSION

This study implicates novel processes in MS initiation and demonstrate the need for further G×E studies to advancing our understanding of the missing heritability of MS.

Immunohistochemical Expression of the Alpha Nicotinic Acetylcholine Receptor 7 in the Human Normal, Diabetic, and Preeclamptic Placenta and Products of Conception

Preeclampsia (PE) and gestational diabetes (GD) are complications in advanced pregnancy while miscarriage for early pregnancy. However, the etiological factors are not well understood. Smoking has been associated with these complications as well as the sudden intrauterine deaths, sudden infant death, miscarriages, and still births. However, the immunolocalization of alpha 7 nicotine acetylcholine receptor (α7-nAChR) is not studied. Materials and Methods: α7-nAChR subunit expression was evaluated in 10 paraffin-embedded placental tissues after delivery and 10 tissue samples of products of conception during first trimester by immunohistochemistry. Among the placental tissues, two samples were normal placental tissue, four from PE mother, and four from GD mother. The expression of α7-nAChR was compared between the two groups in general and within the subgroups of placenta as well. Protein expression was evaluated using the nuclear labeling index (%) of villi with positive cells stained, positive cells in the decidua, and intensity of staining in the outer villous trophoblast layer. Results: The expression of α7-nAChR protein was high in all the cases of placenta and products of conception (POCs). α7-nAChR expression showed no notable differences among different cases of miscarriages irrespective of the mother's age and gestational age at which the event occurred. However, there were some changes among the normal, PE, and GD placental groups in the linings of the blood vessels. Changes were restricted to the villi (as opposed to the decidua) lining cells, both cytotrophoblast and syncytiotrophoblast, and were specific to the α7 subunit. PE blood vessel lining was thicker and showed more expression of this receptor in endothelial cells and myofibroblasts in PE and GD groups. In POCs, the strong expression was observed in the decidua myocytes of maternal blood vessels and in syncytiotrophoblast and cytotrophoblast of chronic villi. Conclusion: Nicotine acetyl choline receptors are found to be expressed highly in the placental tissues and in products of conception. They may be associated with the sudden perinatal deaths and miscarriages or complications of pregnancy.

Synthesis, Nicotinic Acetylcholine Receptor Binding, and in Vitro and in Vivo Pharmacological Properties of 2'-Fluoro-(substituted thiophenyl)deschloroepibatidine Analogues

The synthesis, nAChR in vitro and in vivo pharmacological properties of 2'-fluoro-3'-(substituted thiophenyl)deschloroepibatidine analogues (5a-f, 6a-d, and 7a-c) are presented herein. All had subnanomolar affinity at α4β2*-nAChRs. Contrary to lead structure epibatidine, a potent nAChR agonist, all were potent α4β2- and α3β4-AChR antagonists in an in vitro functional assay. In vivo, the compounds were also nAChR antagonists with various degrees of agonist activity. Compounds 5e, 5f, 6a, 6c, 6d, and 7c had no agonist effects in the tail-flick, hot-plate, hypothermia, or spontaneous activity tests, whereas 5a-d, 7a and 7b did not have agonist activity in the tail-flick and hot-plate tests but, like varenicline, were agonists in the hypothermia and spontaneous activity tests. Compound 6b had agonist activity in all four in vivo tests. All the compounds were antagonists of nicotine-induced antinociception in the tail-flick test, and all except 5c, 5d, 5f, and 6b were antagonists of nicotine-induced antinociception in the hot-plate test. Compound 7c, which had a K_i = 0.86 nM in the binding assay similar potency at α4β2/α3β4 with selectivity relative to α7 nAChRs, had an AD₅₀ value of 0.001 μg/kg in the tail-flick test with no agonist activity in the in vitro or in vivo test had one of the more interesting profiles.

Selective α4β2 nicotinic acetylcholine receptor agonists target epigenetic mechanisms in cortical GABAergic neurons

Nicotine improves cognitive performance and attention in both experimental animals and in human subjects, including patients affected by neuropsychiatric disorders. However, the specific molecular mechanisms underlying nicotine-induced behavioral changes remain unclear. We have recently shown in mice that repeated injections of nicotine, which achieve plasma concentrations comparable to those reported in high cigarette smokers, result in an epigenetically induced increase of glutamic acid decarboxylase 67 (GAD(67)) expression. Here we explored the impact of synthetic α(4)β(2) and α(7) nAChR agonists on GABAergic epigenetic parameters. Varenicline (VAR), a high-affinity partial agonist at α(4)β(2) and a lower affinity full agonist at α(7) neuronal nAChR, injected in doses of 1-5 mg/kg/s.c. twice daily for 5 days, elicited a 30-40% decrease of cortical DNA methyltransferase (DNMT)1 mRNA and an increased expression of GAD(67) mRNA and protein. This upregulation of GAD(67) was abolished by the nAChR antagonist mecamylamine. Furthermore, the level of MeCP(2) binding to GAD(67) promoters was significantly reduced following VAR administration. This effect was abolished when VAR was administered with mecamylamine. Similar effects on cortical DNMT1 and GAD(67) expression were obtained after administration of A-85380, an agonist that binds to α(4)β(2) but has negligible affinity for α(3)β(4) or α(7) subtypes containing nAChR. In contrast, PNU-282987, an agonist of the homomeric α(7) nAChR, failed to decrease cortical DNMT1 mRNA or to induce GAD(67) expression. The present study suggests that the α(4)β(2) nAChR agonists may be better suited to control the epigenetic alterations of GABAergic neurons in schizophrenia than the α(7) nAChR agonists.

Role of muscarinic cholinergic receptors in regulation of guanosine 3':5'-cyclic monophosphate content in mammalian brain, heart muscle, and intestinal smooth muscle

Effects of acetylcholine and of agents that mimic or block its physiological actions have been studied upon concentrations of guanosine 3':5'-cyclic monophosphate (cyclic GMP) and adenosine 3':5'-cyclic monophosphate (cyclic AMP) in slices of mammalian cerebral cortex, heart ventricle, and ileum. Acetylcholine, and cholinomimetic agents with a predominantly muscarinic action, such as methacholine, bethanechol, and pilocarpine, induced an increase in the concentration of cyclic GMP, accompanied by no change or a slight decrease in the concentration of cyclic AMP, in all three tissues studied. Tetramethylammonium, a cholinomimetic agent with a predominantly nicotinic action, on the other hand, did not significantly alter concentrations of either cyclic GMP or cyclic AMP. The increase in the tissue content of cyclic GMP induced by acetylcholine and its muscarinic analogs was antagonized by atropine, a muscarinic blocking agent, but not by hexamethonium, a nicotinic blocking agent. These and other results suggest the generalization that the interaction of acetylcholine with muscarinic receptors, but not with nicotinic receptors, causes an increase in the concentration of cyclic GMP. The data are compatible with the hypothesis that cyclic GMP may mediate the muscarinic actions of acetylcholine. The antagonistic actions of cholinergic and adrenergic agents on the physiology of contraction of intestinal smooth muscle and of cardiac muscle are reflected in, and may result from, antagonistic actions of these compounds on the levels of both cyclic GMP and cyclic AMP in these tissues.