Nicotinic receptors of rat lymphocytes during adjuvant polyarthritis

The controversial effect of smoking and nicotine in SARS-CoV-2 infection

The effects of nicotine and cigarette smoke in many diseases, notably COVID-19 infection, are being debated more frequently. The current basic data for COVID-19 is increasing and indicating the higher risk of COVID-19 infections in smokers due to the overexpression of corresponding host receptors to viral entry. However, current multi-national epidemiological reports indicate a lower incidence of COVID-19 disease in smokers. Current data indicates that smokers are more susceptible to some diseases and more protective of some other. Interestingly, nicotine is also reported to play a dual role, being both inflammatory and anti-inflammatory. In the present study, we tried to investigate the effect of pure nicotine on various cells involved in COVID-19 infection. We followed an organ-based systematic approach to decipher the effect of nicotine in damaged organs corresponding to COVID-19 pathogenesis (12 related diseases). Considering that the effects of nicotine and cigarette smoke are different from each other, it is necessary to be careful in generalizing the effects of nicotine and cigarette to each other in the conducted researches. The generalization and the undifferentiation of nicotine from smoke is a significant bias. Moreover, different doses of nicotine stimulate different effects (dose-dependent response). In addition to further assessing the role of nicotine in COVID-19 infection and any other cases, a clever assessment of underlying diseases should also be considered to achieve a guideline for health providers and a personalized approach to treatment.

Effect of nicotine on body composition in mice

Nicotine induces weight loss in both humans and rodents consuming a regular diet; however, the effect of nicotine on body weight and fat composition in rodents consuming a high-fat diet (HFD) has not been well studied. Thus, this study examined the effect of nicotine vs saline on body weight and fat composition in mice fed with either an HFD (62% of kcal from fat) or a standard normal chow diet (NCD) for 7 weeks. Nicotine dose dependently reduced body weight gain in mice that consumed both diets, but this effect was significantly greater in mice on the HFD. Caloric intake was decreased in nicotine-treated mice. Estimates of energy intake suggested that decreased caloric intake accounted for all the reduced weight gain in mice on an NCD and 66% of the reduced weight gain on an HFD. Computed tomography analysis for fat distribution demonstrated that nicotine was effective in reducing abdominal fat in mice that consumed the HFD, with nicotine treatment leading to lower visceral fat. The effect of nicotine on weight loss in mice on an HFD was completely blocked by mecamylamine, a nonselective nicotinic acetylcholine receptor (nAChR) antagonist, but only partially blocked by the α4β2 nAChR partial agonist/antagonist, varenicline. We conclude that nicotine is effective in preventing HFD-induced weight gain and abdominal fat accumulation.

Nicotinic receptors regulate B lymphocyte activation and immune response

The presence of nicotinic acetylcholine receptors (nicotinic receptors) composed of either alpha7 or alpha4 and beta2 subunits is revealed in B lymphocytes by means of radioligand binding assay and Cell ELISA. Mouse B lymphocytes contained 12,200+/-3200 of epibatidine-binding sites and 3130+/-750 of alpha-Bungarotoxin-binding sites per cell. Mice lacking nicotinic receptor subunits alpha4, beta2 or alpha7 had less serum IgG and IgG-producing cells in the spleen, but showed stronger immune response to both protein antigen in vivo and CD40-specific antibody in vitro than wild-type mice. Anti-CD40-stimulated proliferation of B lymphocytes from beta2 knockout, but not wild-type mice was inhibited with nicotine. Our results indicate that signalling through nicotinic receptors affects both the pre-immune state and activation of B lymphocytes in the immune response, possibly via CD40-dependent pathway. This could contribute to immune depression found in tobacco smokers.

Evidence for functional nicotinic receptors on pancreatic beta cells

Epidemiological studies associate smoking with reduced insulin secretion. We hypothesized that nicotine could negatively affect pancreatic beta-cell function. Acute or 48-hour exposures to nicotine (10(-4) to 10(-6) mol/L) moderately inhibited insulin release at basal (3.3 mmol/L) and/or elevated (27 mmol/L) glucose in rat and human islets. Acute exposure to nicotine (10(-6) mol/L) inhibited tolbutamide (200 micromol/L)-induced insulin release by 41% (P < .05), but did not affect secretion induced by KCl (20 mmol/L) or 3-isobutyl-1-methylxanthine (1 mmol/L) (tested in rat islets). Specific binding of [3H]nicotine was demonstrated in rat islets and in a beta -cell line of rat origin, INS-1. Such binding was enhanced by 48 hours of coculture with nicotine (10(-7) mol/L). Expression of mRNA for the nicotinic receptor subunits alpha 2, alpha 3, alpha 4, alpha 5, alpha 7, and beta 2 was detected in INS-1 cells by reverse transcriptase polymerase chain reaction. Acute exposure to cytisine (10(-6) mol/L), an agonist of alpha 4, beta 2 subunits, partially inhibited tolbutamide-induced insulin release. Specific binding of alpha bungarotoxin (10(-10) mol/L), an antagonist of the alpha 7 subunit, could be demonstrated in INS-1 cells, and culture with alpha bungarotoxin modestly increased insulin release in postculture incubations at basal and elevated glucose, P < .05. Our data indicate that functional nicotinic receptors are present in pancreatic islets and beta cells.

The expression and functional role of nicotinic acetylcholine receptors in rat adipocytes

To clarify whether nicotine has a direct effect on the function of adipocytes, we evaluated nicotinic acetylcholine receptor (nAChR) expression in adipocytes by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry and the direct effects of nicotine on the production of adipocytokines by enzyme-linked immunosorbent assay and Western blot analysis. Receptor binding assays were performed using [3H]nicotine. RT-PCR studies revealed that alpha1-7, 9, 10, beta1-4, delta, and epsilon subunit mRNAs are expressed in adipocytes. Immunocytochemical experiments also suggested the presence of alpha7 and beta2 subunits. The receptor binding assay revealed a binding site for nicotine (Kd = 39.2 x 10(-9) M) on adipocytes. Adipocytes incubated with nicotine for 12 and 36 h released tumor necrosis factor-alpha (TNF-alpha), adiponectin, and free fatty acid (FFA) into the medium in a dose-dependent manner with increasing nicotine concentration from 6 x 10(-8) to 6 x 10(-4) M. However, TNF-alpha protein levels in adipocytes incubated for 12 and 36 h decreased in a dose-dependent manner with increasing nicotine concentration from 6 x 10(-8) to 6 x 10(-4) M. These results show that adipocytes have functional nAChRs and suggest that nicotine reduces TNF-alpha protein production in adipocytes through the activation of nAChRs. Nicotine may temporarily lower insulin sensitivity by stimulating the secretion of TNF-alpha and FFA, whereas long-term direct stimulation of nAChRs by nicotine in addition to autonomic nervous system stimulation may contribute to better insulin sensitivity in vivo through a modulated secretion of adipocytokines.

Functional Nicotinic Acetylcholine Receptors Are Expressed in B Lymphocyte-Derived Cell Lines

Nicotine has been shown to affect B lymphocyte immune response. In this study, we have explored the presence of nicotinic receptors in B lymphocyte-derived cell lines, myeloma X63-Ag8 and hybridoma 1D6. We found that myeloma expressed on average 10,170 +/- 1,100 [3H]epibatidine and 6,730 +/- 370 125I-alpha-bungarotoxin binding sites per cell, thus reflecting the presence of both homomeric and heteromeric nicotinic receptors. More specifically, the presence of alpha4- and alpha7-containing nicotinic receptor subunits was demonstrated in both myeloma and hybridoma cells with subunit-specific antibodies. It was significantly higher in dividing than in resting cells. Long-term exposure to nicotine, at physiological concentration found in smokers, resulted in up-regulation of both alpha4 and alpha7 subunits in hybridoma cells. Additionally, nicotine stimulated hybridoma cell proliferation, whereas it decreased antibody production. In contrast, alpha7-specific snake toxins inhibited cell proliferation but increased antibody production. It is concluded that myeloma and hybridoma cells express alpha4- and alpha7-containing nicotinic receptors, which participate in regulating cell proliferation and function.

Immunochemical and immunocytochemical characterization of cholinergic markers in human peripheral blood lymphocytes

Cholinergic markers and the expression of M(2)-M(5) muscarinic cholinergic receptor subtypes were investigated in human peripheral blood lymphocytes by Western blot analysis and immunocytochemistry. The totality of peripheral blood lymphocytes express acetylcholine (ACh) immunoreactivity, choline acetyltransferase (ChAT), acetylcholinesterase (AChE), vesicular ACh transporter (VAChT) and M(2)-M(5) muscarinic cholinergic receptor protein immunoreactivity. Western blot analysis performed independently on T and B lymphocytes using anti-ChAT and anti-AChE antibodies revealed labelling of single bands of approximately 68-70 and 70 kDa, respectively, whereas VAChT was bound to two bands of approximately 80 and 45 kDa. The pattern of immunoblotting was similar in membranes of lymphocytes and striatum, used as a reference brain tissue. Western blot analysis using anti M(2)-M(5) receptor antibodies revealed labelling of single bands of approximately 55, 85-90, 50 and 81 kDa, respectively. Confocal laser immunofluorescence showed the localization of ACh and VAChT immunoreactivity in punctiform areas likely corresponding to cytoplasmic vesicles. ChAT and AChE were diffused to the cytoplasm and plasma membrane. Muscarinic receptor immunoreactivity was located in lymphocyte plasma membrane. Although the role of lymphocyte cholinergic system is still unclear, the demonstration of cholinergic markers in T and B human blood lymphocytes supports the view that a cholinergic systems may contribute to the regulation of immune function. The characterization of these cholinergic markers may also contribute to define if their evaluation can be used for assessing the status of brain cholinergic system.

Differential expression of nicotinic acetylcholine receptor subunits in fetal and neonatal mouse thymus

Studies were initiated to identify nicotinic acetylcholine receptor (nAChR) subunits and subtypes expressed in the developing immune system and cell types on which nAChR are expressed. Reported here are reverse transcription-polymerase chain reactions (RT-PCR) studies of nAChR alpha2-alpha7 and beta2-beta4 subunit gene expression using fetal or neonatal regular or scid/scid C57BL/6 mouse thymus. Findings are augmented with studies of murine fetal thymic organ cultures (FOTC) and of human peripheral lymphocytes. Novel partial cDNA sequences were derived for mouse nAChR alpha2, alpha3, beta3 and beta4 subunits, polymorphisms were identified in mouse nAChR alpha4, alpha7 and beta2 subunits, and recently derived sequences for mouse nAChR alpha5 and alpha6 subunits were confirmed. Thymic stromal cells appear to express nAChR alpha2, alpha3, alpha4, alpha7 and beta4 subunits, perhaps in addition to alpha5 and beta2 subunits, in a pattern reminiscent of expression in the developing brain. Immature T cells appear to express alpha3, alpha5, alpha7, beta2 and beta4 subunits, just as do neural crest-derived cells targeted by cholinergic innervation. Peripheral T cells seem to express an unusual profile of alpha2, alpha5 and alpha7 subunits, perhaps indicating that their nAChR express yet-to-be-identified assembly partners or that T cell nicotinic responsiveness occurs through homomeric nAChR composed of alpha7 subunits. Our findings are consistent with published work but show a much wider array of nAChR subunit gene expression in mouse thymic stromal and/or lymphoid cells and evidence for developmental regulation of nAChR subunit expression. These studies suggest important roles for nAChR in immune system development and function and in the neuroimmune network.

Nicotine reduces the incidence of type I diabetes in mice

Nicotine has been previously shown to have immunosuppressive actions. Type I diabetes is an autoimmune disease resulting from the specific destruction of the insulin-producing pancreatic beta-cells. Thus, we hypothesized that nicotine may exert protective effects against type I diabetes. The multiple low-dose streptozotocin (MLDS)-induced model and spontaneous nonobese diabetic (NOD) mouse model of type I diabetes were used to assess whether nicotine could prevent this autoimmune disease. Blood glucose levels, diabetes incidence, pancreas insulin content, and cytokine levels were measured in both models of diabetes, both to asses the level of protection exerted by nicotine and to further investigate its mechanism of action. Nicotine treatment reduced the hyperglycemia and incidence of disease in both the MLDS and NOD mouse models of diabetes. Nicotine also protected against the diabetes-induced decrease in pancreatic insulin content observed in both animal models. The pancreatic levels of the Th1 cytokines interleukin (IL)-12, IL-1, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma were increased in both MLDS-induced and spontaneous NOD diabetes, an effect prevented by nicotine treatment. Nicotine treatment increased the pancreatic levels of the Th2 cytokines IL-4 and IL-10. Nicotine treatment reduces the incidence of type I diabetes in two animal models by changing the profile of pancreatic cytokine expression from Th1 to Th2.

Relative amounts of mRNA encoding four subtypes of muscarinic receptors (m2-m5) in human peripheral blood mononuclear cells

It is known that lymphocytes express functional muscarinic cholinergic receptors. In this study, RT-PCR method was applied to study the presence and relative levels of mRNA encoding muscarinic receptor subtypes in human peripheral blood mononuclear cells (PBMCs). Our results, confirmed by DNA sequencing, demonstrate the presence of m2, m3, m4, and m5 receptor subtypes in human PBMCs. The relative levels of muscarinic receptor subtypes fit the following pattern: m3 > m5 > m4 > m2. Our data provide strong evidence confirming previous pharmacological studies that suggested the existence of several subtypes of muscarinic receptors on human PBMCs. We cannot exclude the possibility that expression of receptor subtype depends on the lineage and/or activation status of the cell.

Rat lymphocytes produce and secrete acetylcholine in dependence of differentiation and activation

Previous data from this laboratory suggested for the first time that immune cells of the immune system of different species are capable to synthesize the neurotransmitter acetylcholine. In the present study we detected the RNA message for choline acetyltransferase in thymic, splenic and peripheral blood lymphocytes of rats using RT-PCR. Furthermore, using a sensitive radioimmunoassay, we measured acetylcholine in thymic, splenic and peripheral blood lymphocytes. T-cells were found to contain about three times the amount of acetylcholine as compared to B-cells, and CD4+ cells showed significantly higher levels as compared to CD8+ cells. Mitogenic stimulation with PHA increased the acetylcholine levels in lymphoid cells as well as the release into the supernatants.

The acetylcholine receptor ligand-gated channel as a molecular target of disease and therapeutic agents

Over the last two decades a convergence of techniques from various scientific disciplines has led to enormous growth in our comprehension of the structure, evolutionary trends and the multiplicity of functions performed by ligand- and voltage-gated ion channels and receptors. It is probably the combination of single-channel resolution through the introduction of the patch-clamp technique with the insights provided by genetic engineering (especially site-directed mutagenesis), that have had the clearest impact in the field by disclosing the mechanisms of action of an ever increasing number of ion channels. These large protein molecules underlie a variety of cell functions; correspondingly they can be affected by a variety of pathological conditions leading to abnormal function, either by mutation or in an acquired form. The nicotinic acetylcholine receptor (AChR), the best studied ligand-gated ion channel, is no exception to this rule, and is known to be the target of several inherited and acquired diseases. The convergence of methodological approaches that proved so successful in unraveling the normal function of ion channels in general is now being extended to include the description of pathological conditions affecting these proteins, and is already filling in hitherto missing details which will lead to improved understanding of the molecular mechanisms of channel gating, ion permeation and block in disease states affecting the receptor/channel proper or induced by exogenous ligands. More such disease states, from which mechanisms of channel function can be revealed, are likely to be discovered in the near future.

Sympathetically induced paradoxical increases of the cutaneous blood flow in chronically inflamed rats

In adjuvant arthritic (AA) rats, an abnormal responsiveness of nociceptors (C-fibre polymodal receptors) to sympathetic activities, i.e., alpha 2-adrenoceptor mediated activation of C-fibre polymodal receptors (CPRs), has been observed. The present investigations were undertaken to determine if a similar plastic change would occur in the cutaneous vascular system in the rat chronic inflammation model. The vascular responses were measured by a laser-Doppler flowmeter in the hindpaw skin of the AA rats after electrical stimulation of lumbar sympathetic trunk (sympathetic stimulation). In control non-arthritic rats, the sympathetic stimulation caused decrease in blood flow of the skin (SkBF) in all animals tested (n = 7). On the other hand, the sympathetic stimulation in the AA rats caused both increase (n = 15) as well as decrease (n = 11) in SkBF. In contrast to the abnormal responsiveness of CPRs, the intra-arterial injection of noradrenaline caused the expected decrease in SkBF in all animals tested, and in no instances increases in SkBF were observed. To determine whether activation of nitric oxide (NO), which is known to be a potent endogenous vasodilatation substance, was involved in the vasodilating effect to sympathetic stimulation, an inhibitor of NO synthase, NG-monomethyl-L-arginine (L-NMMA), was applied systemically. L-NMMA significantly increased baseline blood pressure in the control and the AA rats, but it did not significantly alter the SkBF in the control or the AA rats after the sympathetic stimulation, suggesting that NO is not a mediator in the vasoactive responses. The results of the current studies showed for the first time that electrical stimulation of the lumbar sympathetic trunk causes vasodilatation in the skin of the AA rats. This abnormal responsiveness of regional SkBF after sympathetic stimulation was not mediated by adrenergic or NO system.