Α4β2 Nicotinic Acetylcholine Receptor Agonist Research Articles

Cytisine is neuroprotective in female but not male 6-hydroxydopamine lesioned parkinsonian mice and acts in combination with 17-β-estradiol to inhibit apoptotic endoplasmic reticulum stress in dopaminergic neurons.

Apoptotic endoplasmic reticulum (ER) stress is a major mechanism for dopaminergic (DA) loss in Parkinson's disease (PD). We assessed if low doses of the partial α4β2 nicotinic acetylcholine receptor agonist, cytisine attenuates apoptotic ER stress and exerts neuroprotection in substantia nigra pars compacta (SNc) DA neurons. Alternate day intraperitoneal injections of 0.2mg/kg cytisine were administered to female and male mice with 6-hydroxydopamine (6-OHDA) lesions in the dorsolateral striatum, which caused unilateral degeneration of SNc DA neurons. Cytisine attenuated 6-OHDA-induced PD-related behaviors in female, but not in male mice. We also found significant reductions in tyrosine hydroxylase (TH) loss within the lesioned SNc of female, but not male mice. In contrast to female mice, DA neurons within the lesioned SNc of male mice showed a cytisine-induced pathological increase in the nuclear translocation of the pro-apoptotic ER stress protein, C/EBP homologous protein (CHOP). To assess the role of estrogen in cytisine neuroprotection in female mice, we exposed primary mouse DA cultures to either 10nM 17-β-estradiol and 200nM cytisine or 10nM 17-β-estradiol alone. 17-β-estradiol reduced expression of CHOP, whereas cytisine exposure reduced 6-OHDA-mediated nuclear translocation of two other ER stress proteins, activating transcription factor 6 and x-box-binding protein 1, but not CHOP. Taken together, these data show that cytisine and 17-β-estradiol work in combination to inhibit all three arms (activating transcription factor 6, x-box-binding protein 1, and CHOP) of apoptotic ER stress signaling in DA neurons, which can explain the neuroprotective effect of low-dose cytisine in female mice.

Involvement of Proton-Coupled Organic Cation Antiporter in Varenicline Transport at Blood-Brain Barrier of Rats and in Human Brain Capillary Endothelial Cells

Varenicline is a selective partial α4β2 nicotinic acetylcholine receptor agonist, which is used to help achieve smoking cessation. Here, we investigated varenicline transport at the blood-brain barrier by means of in vivo microdialysis, in situ brain perfusion, and brain efflux index measurements in rats, and in vitro uptake studies in human brain capillary endothelial cells. Microdialysis demonstrated that varenicline is actively transported from blood to brain in rats. Blood-to-brain uptake transport of varenicline, as measured by the in situ brain perfusion technique, was strongly inhibited by diphenhydramine, a potent inhibitor of proton-coupled organic cation (H+/OC) antiporter. However, brain efflux index study showed that brain-to-blood efflux transport of varenicline was not inhibited by diphenhydramine. In human brain capillary endothelial cells, varenicline was taken up time- and concentration-dependently. The uptake was dependent on an oppositely directed proton gradient, but was independent of extracellular sodium and membrane potential. The uptake was inhibited by a metabolic inhibitor, and by substrates of H+/OC antiporter, but not by substrates or inhibitors of OCTs, OCTNs, PMAT, and MATE1, which are known organic cation transporters. The present results suggest that the H+/OC antiporter contributes predominantly to varenicline uptake at the blood-brain barrier.

Chemistry and Pharmacology of a Series of Unichiral Analogues of 2-(2-Pyrrolidinyl)-1,4-benzodioxane, Prolinol Phenyl Ether, and Prolinol 3-Pyridyl Ether Designed as α4β2-Nicotinic Acetylcholine Receptor Agonists.

Some unichiral analogues of 2R,2'S-2-(1'-methyl-2'-pyrrolidinyl)-7-hydroxy-1,4-benzodioxane, a potent and selective α4β2-nAChR partial agonist, were designed by opening dioxane and replacing hydroxyl carbon with nitrogen. The resulting 3-pyridyl and m-hydroxyphenyl ethers have high α4β2 affinity and good subtype selectivity, which get lost if OH is removed from phenyl or the position of pyridine nitrogen is changed. High α4β2 affinity and selectivity are also attained by meta hydroxylating the 3-pyridyl and the phenyl ethers of (S)-N-methylprolinol and the phenyl ether of (S)-2-azetidinemethanol, known α4β2 agonists, although the interaction mode of the aryloxymethylene substructure cannot be assimilated to that of benzodioxane. Indeed, the α4β2 and α3β4 functional tests well differentiate behaviors that the binding tests homologize: both the 3-hydroxyphenyl and the 5-hydroxy-3-pyridyl ether of N-methylprolinol are α4β2 full agonists, but only the latter is highly α4β2/α3β4 selective, while potent and selective partial α4β2 agonism characterizes the hydroxybenzodioxane derivative and its two opened semirigid analogues.

TC-2559, an α4β2 nicotinic acetylcholine receptor agonist, suppresses the expression of CCL3 and IL-1β through STAT3 inhibition in cultured murine macrophages

The anti-inflammatory properties of TC-2559, an α4β2 nicotinic acetylcholine receptor (nAChR) agonist, on cultured murine macrophages was investigated. TC-2559 suppressed the upregulation of CC-chemokine ligand 3 (CCL3) and interleukin-1β (IL-1β) following lipopolysaccharide (LPS) treatment in J774A.1 cells. TC-2559 inhibited the phosphorylation of signal transducer and activator of transcription 3 (pSTAT3) but not nuclear factor-κB p65 after LPS. Blockade of pSTAT3 by AG490 inhibited the upregulation of CCL3 and IL-1β after LPS. In conclusion, TC-2559-driven α4β2 nAChR signaling suppressed the upregulation of CCL3 and IL-1β by inhibiting pSTAT3 in inflammatory macrophages, resulting in the suppression of neuropathic pain.

Peripheral alpha4beta2 nicotinic acetylcholine receptor signalling attenuates tactile allodynia and thermal hyperalgesia after nerve injury in mice.

Neuropathic pain is often refractory to conventional analgesics including opioids and non-steroidal anti-inflammatory drugs. Evidence suggests nicotinic acetylcholine receptor ligands regulate pain transmission. Effects of α4β2 nicotinic acetylcholine receptor activation on pain behaviours after nerve injury were studied. Mice were subjected to partial sciatic nerve ligation (PSL). Nicotinic acetylcholine receptor α4 and β2 subunits localization in injured nerves were evaluated by immunohistochemistry. Neuropathic pain, assessed by tactile allodynia and thermal hyperalgesia, was examined by von Frey test and Hargreaves test respectively. Nicotinic acetylcholine receptor α4 and β2 subunits were up-regulated in injured nerves and were expressed on F4/80-positive macrophages. When nicotine was perineurally administered daily for 4 days (day 7-10; maintenance phase) after nerve injury, pain behaviours were significantly alleviated. The inhibitory effects of nicotine were reversed by co-administration of mecamylamine (non-selective nicotinic acetylcholine receptor antagonist) and dihydro-β-erythroidine (selective α4β2 nicotinic acetylcholine receptor antagonist). Likewise, when α4β2 nicotinic acetylcholine receptor agonists (TC2559 or ABT418) were administered daily for 4 days (day 7-10) after nerve injury, pain behaviours were significantly attenuated. On the other hand, nicotine administered daily for 4 days (day 0-3; initiation phase) after nerve injury alleviated pain behaviours, which were antagonized by co-administration of dihydro-β-erythroidine. TC2559 administered daily for 4 days (day 0-3) also attenuated nerve injury-induced pain behaviours. The activation of α4β2 nicotinic acetylcholine receptor expressed on infiltrating macrophages in injured nerves may participate in the relief of PSL-induced neuropathic pain during maintenance and initiation phases.

Differential effects of subtype-specific nicotinic acetylcholine receptor agonists on early and late hippocampal LTP

Brain nicotinic acetylcholine receptors are involved in several neuropsychiatric disorders, e.g. Alzheimer's and Parkinson's diseases, Tourette's syndrome, schizophrenia, depression, autism, attention deficit hyperactivity disorder, and anxiety. Currently, approaches selectively targeting the activation of specific nicotinic acetylcholine receptors are in clinical development for treatment of memory impairment of Alzheimer's disease patients. These are α4β2 and α7 nicotinic acetylcholine receptor agonists which are believed to enhance cholinergic and glutamatergic neurotransmission, respectively. In order to gain a better insight into the mechanistic role of these two nicotinic acetylcholine receptors in learning and memory, we investigated the effects of the α4β2 nicotinic acetylcholine receptor agonist TC-1827 and the α7 nicotinic acetylcholine receptor partial agonist SSR180711 on hippocampal long-term potentiation (LTP), a widely accepted cellular experimental model of memory formation. Generally, LTP is distinguished in an early and a late form, the former being protein-synthesis independent and the latter being protein-synthesis dependent. TC-1827 was found to increase early LTP in a bell-shaped dose dependent manner, but did not affect late LTP. In contrast, the α7 nicotinic acetylcholine receptor partial agonist SSR180711 showed enhancing effects on both early and late LTP in a bell-shaped manner. Furthermore, SSR180711 not only increased early LTP, but also transformed it into late LTP, which was not observed with the α4β2 nicotinic acetylcholine receptor agonist. Therefore, based on these findings α7 nicotinic acetylcholine receptor (partial) agonists appear to exhibit stronger efficacy on memory improvement than α4β2 nicotinic acetylcholine receptor agonists.

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.

Clinical Summaries

Clinical Summaries

12th International Conference on Alzheimer's Disease (ICAD), Vienna, Austria

21 July 2009. In like a lamb, out like a lion. It’s a full season too late for this variation on the March weather proverb, but hopefully our generous readers will forgive their roving reporter for bending it anyway, because starting meekly and finishing with a roar is exactly what the Alzheimer’s Association’s 12th International Conference on Alzheimer’s Disease (ICAD) did when it unfolded in Vienna 11-16 July. And it is not about changing weather, either. All week, the Austrian capital bathed meeting attendees in sparkling sunshine (which seemed to seduce many into sneaking off for daytrips into this beautiful city as attendance seemed a bit sparse at times, but no names shall be named). No, the scientific program started with humbling reports of the failure – abject and otherwise – of the latest round of clinical trials. The program continued with confirmatory studies on the ability of exercise, a heart-healthy diet, and modest drinking while one is cognitively healthy, to modify one’s risk of cognitive decline somewhat. This is an important life message people should take to heart, but it is not the kind of news close followers of the field are looking for. But then the last morning – when many had departed, the exhibit hall was emptied out, and the press room had closed up shop – featured within the space of three hours arguably the biggest news in Alzheimer’s disease (AD) genetics research in the past decade. Three independent genomewide association studies, one being the largest performed to date on some 4,000 cases, together reported three new genes for late-onset AD. Hence, overall comments about ICAD in Vienna went from a plaintive “I haven’t heard anything really new” at the beginning to a confident “We can declare three new genes for Alzheimer’s” at the end. Most remarkable from an observer’s perspective was the consensus among independent genetics groups that the new genes would likely hold up to scrutiny in future studies even if their individual effect was small. When is the last time you remember applause and nodding faces, not skepticism or criticism, greeting the first introduction of a new candidate gene at a major AD conference? The genes reported today are ApoJ (aka clusterin), CR1 (which encodes a complement receptor), and PICALM (which encodes an endocytic gene). Together, they point partly to amyloid-β (Aβ) generation/clearance playing a role in late-onset AD, said Philippe Amouyel of the Institute Pasteur in Lille, France, but more broadly, they also implicate other upstream processes as leading to AD pathology and symptoms. “The GWAS data suggest that innate immunity and cholesterol are key themes in the disease,” said Julie Williams of Cardiff University, UK. Regarding clinical trials, the news in Vienna was mostly dire. Among the trials that reported results, GSK’s Phase 3 rosiglitazone program failed, the ADCS’s valproate and DHA trials were negative, as were the Phase 2b trials of AstraZeneca’s α4β2 nicotinic acetylcholine receptor agonist AZD3480 and of a monthly implant formulation of donepezil called mimopezil. The large anti-amyloid trials are many months to years away from yielding results, and without substantiation the rumors that inevitably fly in such periods of suspended animation are not worth reporting. The presentation by Bengt Winblad of the Karolinska Institute in Stockholm, Sweden, of Novartis’s CAD106 ac-

Randomized placebo-controlled study of the nicotinic agonist SIB-1508Y in Parkinson disease

This randomized, placebo-controlled, 5-week Phase II trial evaluated the safety and tolerability of SIB-1508Y, a selective alpha4beta2 nicotinic acetylcholine receptor agonist, in 77 individuals with early Parkinson disease. Lightheadedness was a common dosage-related adverse effect at higher dosages, leading to frequent dosage reduction, drug discontinuation, and eventual trial redesign. A maximally tolerated dosage of 10 mg daily was identified. No antiparkinsonian or cognitive-enhancing effects were demonstrated in this trial.