Therapeutic potential of α7 nicotinic acetylcholine receptor agonists to combat obesity, diabetes, and inflammation

Inflammation as a shared mechanism of chronic stress related disorders with potential novel therapeutic targets

Stress is a subjective experience that varies across individuals depending on their sensitivity, resilience, and length of exposure to stressors. Stress may be categorised as acute (positive stress) or chronic (negative stress). Acute stress is advantageous for the human body, but chronic stress results in changes in cardiovascular, neuroendocrine, autonomic, and immunological functions, eventually causing different illnesses. The specific process relating stress to chronic stress associated diseases is still a topic of continuing debate. Inflammation has been recognised as a new and fascinating physiological mechanism that connects chronic stress and its associated illnesses. This article explored the relationships between chronic stress, inflammation, and chronic illnesses, including depression, cancer, and cardiovascular disease. This article also emphasises on various possible therapeutic targets for the management of chronic stress related illnesses by targeting inflammation, namely lipoxins and alpha7 nicotinic receptors. These therapeutic targets may be useful in developing new and safe therapies for the management of chronic stress related dysfunctions.

Activation of α7 nicotinic receptors attenuated hyperalgesia and anxiety induced by palatable obesogenic diet withdrawal

Consumption of palatable food (PF) can alleviate anxiety, and pain in humans. Contrary, spontaneous withdrawal of long-term PF intake produces anxiogenic-like behavior and abnormal pain sensation, causing challenges to weight-loss diet and anti-obesity agents. Thus, we examined α7-nicotinic acetylcholine receptors (α7nAChR) involvement since it plays essential role in nociception and psychological behaviors.

METHODS

Adult male C57BL/6 mice were placed on a Standard Chow (SC) alone or with PF on intermittent or continuous regimen for 6 weeks. Then, mice were replaced with normal SC (spontaneous withdrawal). Body weight, food intake, and calories intake with and without the obesogenic diet were measured throughout the study. During PF withdrawal, anxiety-like behaviors and pain sensitivity were measured with PNU-282987 (α7nAChR agonist) administration.

RESULTS

Six weeks of SC + PF-intermittent and continuous paradigms produced a significant weight gain. PF withdrawal displayed hyperalgesia and anxiety-like behaviors. During withdrawal, PNU-282987 significantly attenuated hyperalgesia and anxiety-like behaviors.

CONCLUSION

The present study shows that a PF can increase food intake and body weight. Also, enhanced pain sensitivity and anxiety-like behavior were observed during PF withdrawal. α7nAChR activation attenuated anxiolytic-like behavior and hyperalgesia in PF abstinent mice. These data suggest potential therapeutic effects of targeting α7 nAChRs for obesity-withdrawal symptoms in obese subjects.

Alterations in Neuronal Nicotinic Acetylcholine Receptors in the Pathogenesis of Various Cognitive Impairments

Cognitive impairment is a typical symptom of both neurodegenerative and certain other diseases. In connection with these different pathologies, the etiology and neurological and metabolic changes associated with cognitive impairment must differ. Until these characteristics and differences are understood in greater detail, pharmacological treatment of the different forms of cognitive impairment remains suboptimal. Neurotransmitter receptors, including neuronal nicotinic acetylcholine receptors (nAChRs), dopamine receptors, and glutamine receptors, play key roles in the functions and metabolisms of the brain. Among these, the role of nAChRs in the development of cognitive impairment has attracted more and more attention. The present review summarizes what is presently known concerning the structure, distribution, metabolism, and function of nAChRs, as well as their involvement in major cognitive disorders such as Alzheimer's disease, Parkinson's disease, vascular dementia, schizophrenia, and diabetes mellitus. As will be discussed, the relevant scientific literature reveals clearly that the α4β2 and α7 nAChR subtypes and/or subunits of the receptors play major roles in maintaining cognitive function and in neuroprotection of the brain. Accordingly, focusing on these as targets of drug therapy can be expected to lead to breakthroughs in the treatment of cognitive disorders such as AD and schizophrenia.

α7nAChR Activation Combined with Endothelial Progenitor Cell Transplantation Attenuates Lung Injury in Diabetic Rats with Sepsis through the NF-κB Pathway

Chronic diabetes mellitus compromises the vascular system, which causes organ injury, including in the lung. Due to the strong compensatory ability of the lung, patients always exhibit subclinical symptoms. Once sepsis occurs, the degree of lung injury is more severe under hyperglycemic conditions. The α7 nicotinic acetylcholine receptor (α7nAChR) plays an important role in regulating inflammation and metabolism and can improve endothelial progenitor cell (EPC) functions. In the present study, lung injury caused by sepsis was compared between diabetic rats and normal rats. We also examined whether α7nAChR activation combined with EPC transplantation could ameliorate lung injury in diabetic sepsis rats. A type 2 diabetic model was induced in rats via a high-fat diet and streptozotocin. Then, a rat model of septic lung injury was established by intraperitoneal injection combined with endotracheal instillation of LPS. The oxygenation indices, wet-to-dry ratios, and histopathological scores of the lungs were tested after PNU282987 treatment and EPC transplantation. IL-6, IL-8, TNF-α, and IL-10 levels were measured. Caspase-3, Bax, Bcl-2, and phosphorylated NF-κB (p-NF-κB) levels were determined by blotting. Sepsis causes obvious lung injury, which is exacerbated by diabetic conditions. α7nAChR activation and endothelial progenitor cell transplantation reduced lung injury in diabetic sepsis rats, alleviating inflammation and decreasing apoptosis. This treatment was more effective when PNU282987 and endothelial progenitor cells were administered together. p-NF-κB levels decreased following treatment with PNU282987 and EPCs. In conclusion, α7nAChR activation combined with EPC transplantation can alleviate lung injury in diabetic sepsis rats through the NF-κB signaling pathway.

Vagus nerve modulates acute-on-chronic liver failure progression via CXCL9

BACKGROUND

Hepatic inflammatory cell accumulation and the subsequent systematic inflammation drive acute-on-chronic liver failure (ACLF) development. Previous studies showed that the vagus nerve exerts anti-inflammatory activity in many inflammatory diseases. Here, we aimed to identify the key molecule mediating the inflammatory process in ACLF and reveal the neuroimmune communication arising from the vagus nerve and immunological disorders of ACLF.

METHODS

Proteomic analysis was performed and validated in ACLF model mice or patients, and intervention animal experiments were conducted using neutralizing antibodies. PNU-282987 (acetylcholine receptor agonist) and vagotomy were applied for perturbing vagus nerve activity. Single-cell RNA sequencing (scRNA-seq), flow cytometry, immunohistochemical and immunofluorescence staining, and CRISPR/Cas9 technology were used for in vivo or in vitro mechanistic studies.

RESULTS

The unbiased proteomics identified C-X-C motif chemokine ligand 9 (CXCL9) as the greatest differential protein in the livers of mice with ACLF and its relation to the systematic inflammation and mortality were confirmed in patients with ACLF. Interventions on CXCL9 and its receptor C-X-C chemokine receptor 3 (CXCR3) improved liver injury and decreased mortality of ACLF mice, which were related to the suppressing of hepatic immune cells' accumulation and activation. Vagus nerve stimulation attenuated while vagotomy aggravated the expression of CXCL9 and the severity of ACLF. Blocking CXCL9 and CXCR3 ameliorated liver inflammation and increased ACLF-associated mortality in ACLF mice with vagotomy. scRNA-seq revealed that hepatic macrophages served as the major source of CXCL9 in ACLF and were validated by immunofluorescence staining and flow cytometry analysis. Notably, the expression of CXCL9 in macrophages was modulated by vagus nerve-mediated cholinergic signaling.

CONCLUSIONS

Our novel findings highlighted that the neuroimmune communication of the vagus nerve-macrophage-CXCL9 axis contributed to ACLF development. These results provided evidence for neuromodulation as a promising approach for preventing and treating ACLF.

Hypothalamic inflammation and the development of an obese phenotype induced by high-fat diet consumption is exacerbated in alpha7 nicotinic cholinergic receptor knockout mice

Hypothalamic inflammation and metabolic changes resulting from the consumption of high-fat diets have been linked to low grade inflammation and obesity. Inflammation impairs the hypothalamic expression of α7 nicotinic acetylcholine receptor (α7nAChR). The α7nAChR is described as the main component of the anti-inflammatory cholinergic pathway in different inflammation models. To assess whether the reduction in α7nAChR expression exacerbates hypothalamic inflammation induced by a high-fat diet (HFD), were used male and female global α7nAChR knockout mouse line in normal or high-fat diet for 4 weeks. Body weight gain, adiposity, glucose homeostasis, hypothalamic inflammation, food intake, and energy expenditure were evaluated. Insulin sensitivity was evaluated in neuronal cell culture. Consumption of an HFD for 4 weeks resulted in body weight gain and adiposity in male Chrna7-/- mice and the hypothalamus of male Chrna7-/- mice showed neuroinflammatory markers, with increased gene expression of pro-inflammatory cytokines and dysregulation in the nuclear factor kappa B pathway. Moreover, male Chrna7-/- mice consuming an HFD showed alterations in glucose homeostasis and serum of Chrna7-/- mice that consumed an HFD impaired insulin signalling in neuronal cell culture experiments. In general, female Chrna7-/- mice that consumed an HFD did not show the phenotypic and molecular changes found in male mice, indicating that there is sexual dimorphism in the analysed parameters. Thus, receptor deletion resulted in increased susceptibility to hypothalamic inflammation and metabolic damage associated with HFD consumption in male mice.

Epstein-Barr virus downregulates the α7 nicotinic acetylcholine receptor of CD8+ T lymphocytes might associate with coronary artery lesions in Kawasaki disease patients

OBJECTIVES

Kawasaki disease (KD) is a systemic vasculitis that is caused by immunological dysregulation in children exposed to pathogens like Epstein-Barr virus (EBV). Myocardial ischemia or infarction due to coronary artery lesions (CALs) might be lethal. However, it is unclear how pathogens, immunomodulation, and CALs interact, particularly in KD patients co-infected with the most widespread virus, EBV.

METHODS

We investigated pathogen carriage and fundamental clinical data in 281 KD patients. Immunological differences between CALs and non-CALs in KD patients under different conditions were analyzed. Then, the effect of infection by different pathogens on the immune response was excluded, and most EBV co-infected KD patients were included to assess the incidence of CALs, the level of immune modulation, and regulatory mechanisms in different EBV infection states.

RESULTS

Our results showed multiple pathogenic infections occur in KD patients, with EBV being the most prevalent. The incidence of CALs in the EBV-DNA (+) acute infection group, EBV-DNA (-) acute infection group, and EBV latent infection group was 0 (0/6), 27.27% (3/11) and 41.67% (10/24), respectively. The two groups were younger and had increased IL-6 levels and B cells, decreasing CD8+ T cells than the EBV-DNA (+) acute infection group. Interestingly, the increased B cells were not associated with immunoglobulin release. Additionally, these patients down-regulated α7 nicotinic acetylcholine receptor (α7nAChR) and downstream molecule PI3K/AKT/mTOR while activating the NF-κB.

CONCLUSION

Patients with different EBV infection statuses exhibit different incidences of CALs. In acute EBV-DNA (-) infected and latent EBV-infected patients, the number of CD8+ T cells decreased and downregulated CD8+ T cells' α7nAChR and PI3K/AKT/mTOR, which may associate with CALs, while the expression of NF-κB and the pro-inflammatory factor IL-6 was upregulated by inhibiting the anti-inflammatory molecule α7nAChR.

Central and peripheral actions of nicotine that influence blood glucose homeostasis and the development of diabetes

Cigarette smoking has long been recognized as a risk factor for type 2 diabetes (T2D), although the precise causal mechanisms underlying this relationship remain poorly understood. Recent evidence suggests that nicotine, the primary reinforcing component in tobacco, may play a pivotal role in connecting cigarette smoking and T2D. Extensive research conducted in both humans and animals has demonstrated that nicotine can elevate blood glucose levels, disrupt glucose homeostasis, and induce insulin resistance. The review aims to elucidate the genetic variants of nicotinic acetylcholine receptors associated with diabetes risk and provide a comprehensive overview of the available data on the mechanisms through which nicotine influences blood glucose homeostasis and the development of diabetes. Here we emphasize the central and peripheral actions of nicotine on the release of glucoregulatory hormones, as well as its effects on glucose tolerance and insulin sensitivity. Notably, the central actions of nicotine within the brain, which encompass both insulin-dependent and independent mechanisms, are highlighted as potential targets for intervention strategies in diabetes management.

360-Degree Perspectives on Obesity

Alarming statistics show that the number of people affected by excessive weight has surpassed 2 billion, representing approximately 30% of the world's population. The aim of this review is to provide a comprehensive overview of one of the most serious public health problems, considering that obesity requires an integrative approach that takes into account its complex etiology, including genetic, environmental, and lifestyle factors. Only an understanding of the connections between the many contributors to obesity and the synergy between treatment interventions can ensure satisfactory outcomes in reducing obesity. Mechanisms such as oxidative stress, chronic inflammation, and dysbiosis play a crucial role in the pathogenesis of obesity and its associated complications. Compounding factors such as the deleterious effects of stress, the novel challenge posed by the obesogenic digital (food) environment, and the stigma associated with obesity should not be overlooked. Preclinical research in animal models has been instrumental in elucidating these mechanisms, and translation into clinical practice has provided promising therapeutic options, including epigenetic approaches, pharmacotherapy, and bariatric surgery. However, more studies are necessary to discover new compounds that target key metabolic pathways, innovative ways to deliver the drugs, the optimal combinations of lifestyle interventions with allopathic treatments, and, last but not least, emerging biological markers for effective monitoring. With each passing day, the obesity crisis tightens its grip, threatening not only individual lives but also burdening healthcare systems and societies at large. It is high time we took action as we confront the urgent imperative to address this escalating global health challenge head-on.

Cholinergic dysfunction in COVID-19: frantic search and hoping for the best

A novel coronavirus known as severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is a potential cause of acute respiratory infection called coronavirus disease 2019 (COVID-19). The binding of SARS-CoV-2 with angiotensin-converting enzyme 2 (ACE2) induces a series of inflammatory cellular events with cytopathic effects leading to cell injury and hyperinflammation. Severe SARS-CoV-2 infection may lead to dysautonomia and sympathetic storm due to dysfunction of the autonomic nervous system (ANS). Therefore, this review aimed to elucidate the critical role of the cholinergic system (CS) in SARS-CoV-2 infection. The CS forms a multi-faceted network performing diverse functions in the body due to its distribution in the neuronal and non-neuronal cells. Acetylcholine (ACh) acts on two main types of receptors which are nicotinic receptors (NRs) and muscarinic receptors (MRs). NRs induce T cell anergy with impairment of antigen-mediated signal transduction. Nicotine through activation of T cell NRs inhibits the expression and release of the pro-inflammatory cytokines. NRs play important anti-inflammatory effects while MRs promote inflammation by inducing the release of pro-inflammatory cytokines. SARS-CoV-2 infection can affect the morphological and functional stability of CS through the disruption of cholinergic receptors. SARS-CoV-2 spike protein is similar to neurotoxins, which can bind to nicotinic acetylcholine receptors (nAChR) in the ANS and brain. Therefore, cholinergic receptors mainly nAChR and related cholinergic agonists may affect the pathogenesis of SARS-CoV-2 infection. Cholinergic dysfunction in COVID-19 is due to dysregulation of nAChR by SARS-CoV-2 promoting the central sympathetic drive with the development of the sympathetic storm. As well, nAChR activators through interaction with diverse signaling pathways can reduce the risk of inflammatory disorders in COVID-19. In addition, nAChR activators may mitigate endothelial dysfunction (ED), oxidative stress (OS), and associated coagulopathy in COVID-19. Similarly, nAChR activators may improve OS, inflammatory changes, and cytokine storm in COVID-19. Therefore, nAChR activators like varenicline in virtue of its anti-inflammatory and anti-oxidant effects with direct anti-SARS-CoV-2 effect could be effective in the management of COVID-19.

L, E. E, Qi R, Mu X, Feng L, Ba G, Li Y, Zhang J, Bai L, Fu M. Metabolomics analysis reveals amelioration effects of yellowhorn tea extract on hyperlipidemia, inflammation, and oxidative stress in high-fat diet-fed mice

Yellowhorn tea (YT) is traditionally used as a lipid-lowering beverage in Mongolian minorities. However, the pharmacological effects of YT extract and its specific metabolic changes in hyperlipidemia models are not fully understood. The aim of this study was to identify biomarkers using untargeted metabolomics techniques and to investigate the mechanisms underlying the changes in metabolic pathways associated with lipid lowering, anti-inflammation and anti-oxidant in hyperlipidemic mice. A high-fat diet (HFD)-induced hyperlipidemic mouse model was established. YT extract was administered as oral gavage at 0.15, 0.3, and 0.6 g/kg doses for 10 weeks. HFD-induced hyperlipidemia and the therapeutic effect of YT extract were evaluated based on histopathology and by assessing blood lipid levels. Liver inflammatory factors and oxidative stress indices were determined using enzyme-linked immunosorbent assays. Liver metabolites were evaluated using untargeted metabolomics. Biochemical and histological examinations showed that YT extract significantly reduced body-weight gain (p < 0.01) and fat deposition in tissues. YT extract significantly reduced the levels of serum and liver triglyceride and total cholesterol; inflammatory factors [interleukin (IL)-6, IL-1β, and tumor necrosis factor-α]; malondialdehyde; and leptin (p < 0.05) in hyperlipidemic mice. YT extract also significantly increased the levels of oxidative stress indicators (superoxide dismutase, catalase, and glutathione peroxidase) and adiponectin. Metabolomics studies revealed several endogenous molecules were altered by the high-fat diet and recovery following intervention with YT extract. The metabolites that were significantly different in the liver after YT intake included citicoline, acetylcholine, pyridoxine, and NAD. Pathway analysis indicated that YT extract ameliorated HFD-induced hyperlipidemia in mice via three major metabolic pathways, namely, glycerophospholipid metabolism, vitamin B6 metabolism, and nicotinate and nicotinamide metabolism. This study demonstrates YT extract has profound effects on the alleviation of HFD-induced hyperlipidemia, inflammation and oxidative stress.

GTS-21, a selective alpha7 nicotinic acetylcholine receptor agonist, ameliorates diabetic nephropathy in Leprdb/db mice

Diabetic nephropathy (DN) is a serious complicating factor in human type 2 diabetes mellitus (T2DM), and it commonly results in end-stage renal disease (ESRD) that requires kidney dialysis. Here, we report that the α7 nicotinic acetylcholine receptor (α7nAChR) agonist GTS-21 exerts a novel anti-inflammatory action to ameliorate DN, as studied using an inbred strain of Leprdb/db mice in which hyperglycemia and obesity co-exist owing to defective leptin receptor (Lepr) signaling. For this analysis, GTS-21 was administered to 10-12 week-old male and female mice as a 4 mg/kg intraperitoneal injection, twice-a-day, for 8 weeks. Kidney function and injury owing to DN were monitored by determination of plasma levels of BUN, creatinine, KIM-1 and NGAL. Histologic analysis of glomerular hypertrophy and mesangial matrix expansion were also used to assess DN in these mice. Concurrently, renal inflammation was assessed by measuring IL-6 and HMGB1, while also quantifying renal cell apoptosis, and apoptotic signaling pathways. We found that Leprdb/db mice exhibited increased markers of BUN, creatinine, NGAL, KIM-1, IL-6, cytochrome C, and HMGB-1. These abnormalities were also accompanied by histologic kidney injury (mesangial matrix expansion and apoptosis). Remarkably, all such pathologies were significantly reduced by GTS-21. Collectively, our results provide new evidence that the α7nAChR agonist GTS-21 has the ability to attenuate diabetes-induced kidney injury. Additional studies are warranted to further investigate the involvement of the vagal cholinergic anti-inflammatory reflex pathway (CAP) in ameliorating diabetic nephropathy.

Protective effect of α7 nicotinic acetylcholine receptor activation on experimental colitis and its mechanism

Background

Inflammatory bowel disease (IBD) is a common chronic remitting disease with no satisfactory treatment. The aim of this study was to investigate the protective effect of α7 nicotinic acetylcholine receptor (α7nAChR), and to determine the underlying mechanism of its activity.

Methods

The expression and distribution of α7nAChR in the intestinal tissue of patients with ulcerative colitis and Crohn’s disease were analyzed. The effects of vagal excitation on murine experimental colitis were investigated. The colitis model was induced in C57BL/6 mice by the administration of 3% dextran sulfate sodium (DSS). The therapeutic group received treatment with the α7nAChR agonist PNU-282987 by intraperitoneal injection.

Results

Our results showed that there was significantly increased expression of α7nAChR in colitis and Crohn’s disease intestinal tissue, and its expression was mainly located in macrophages and neutrophils, which were extensively infiltrated in the disease status. Treatment with an α7nAChR agonist potently ameliorated the DSS-induced illness state, including weight loss, stool consistency, bleeding, colon shortening, and colon histological injury. α7nAChR agonist exerted anti-inflammatory effects in DSS colitis mice by suppressing the secretion of multiple types of proinflammatory factors, such as IL6, TNFα, and IL1β, and it also inhibited the colonic infiltration of inflammatory cells by blocking the DSS-induced overactivation of the NF-κB and MAPK signaling pathways. Mechanistically, activation of α7nAChR decreased the number of infiltrated M1 macrophages in the colitis intestine and inhibited the phagocytosis ability of macrophages, which were activated in response to LPS stimulation.

Conclusion

Thus, an α7nAChR agonist ameliorated colonic pathology and inflammation in DSS-induced colitis mice by blocking the activation of inflammatory M1 macrophages.

Efficacy and Safety of Single-Dose OC-02 (Simpinicline Solution) Nasal Spray on Signs and Symptoms of Dry Eye Disease: The PEARL Phase II Randomized Trial

PURPOSE

Dry eye disease is a multifactorial disorder that affects the ocular surface, with symptoms including ocular irritation, impaired vision, and pain. Nicotinic acetylcholine receptor (nAChR) agonists are novel treatments for dry eye disease; this study investigates the nAChR agonist OC-02 (simpinicline solution) as an aqueous nasal spray.

METHODS

PEARL (Clinical Trial to Evaluate the Efficacy of OC-02 Nasal Spray on Signs and Symptoms of Dry Eye Disease) was a Phase II study that evaluated the efficacy and safety of OC-02 (simpinicline solution) nasal spray (OC-02 SNS) in adult patients with dry eye disease. Patients ≥22 years of age were eligible if they had an Ocular Surface Disease Index score ≥23, corneal fluorescein staining score ≥2 in >1 region or ≥4 for all regions, or Schirmer test score (STS) ≤10 mm; there were no restrictions on eye dryness score (EDS). Patients (N = 165) were randomly assigned 1:1:1:1 to vehicle (control; n = 42) or OC-02 SNS (0.11 mg, 0.55 mg, or 1.1 mg; n = 41 per group) and received a single dose of study drug (100 µL using a nasal spray atomizer) at visit 1 and visit 2 (15-19 days after visit 1). Primary efficacy outcomes were change in the STS from baseline to immediately after treatment administration (visit 1) and change in the EDS from before to 5 minutes after treatment during controlled adverse environment exposure (visit 2).

FINDINGS

Baseline demographic and ocular clinical characteristics were similar across all groups. Single-dose OC-02 SNS improved the signs and symptoms of dry eye disease. For the STS, statistically significant and dose-dependent improvements were found from before to after treatment with OC-02 SNS versus vehicle (least-squares mean change from baseline: vehicle, 3.0 mm; 0.11 mg OC-02 SNS, 9.0 mm; 0.55 mg, 17.5 mm; and 1.1 mg, 19.6 mm). For EDS, statistically significant and dose-dependent improvements were found from before to 5 minutes after treatment with higher doses of OC-02 SNS versus vehicle (least-squares mean change from baseline: vehicle, -6.5; 0.11 mg OC-02 SNS, -9.4; 0.55 mg, -17.4; and 1.1 mg, -20.7). OC-02 SNS was well tolerated: only 2 ocular adverse events were reported (eye pruritis and keratitis), and the most common nonocular events were cough and throat irritation.

IMPLICATIONS

Single-dose OC-02 SNS over a range of doses immediately and significantly increased tear production and improved eye dryness. Together with previous studies of OC-01 (varenicline solution) nasal spray, our findings suggest that agonist stimulation of nAChRs in the nasal cavity is a valid and effective mechanism to elicit natural tear production in patients with dry eye disease.

CLINICALTRIALS

gov identifier: NCT03452397.

Special Issue: Cholinergic Control of Inflammation

Inflammation caused by infection, tissue trauma, and disease states such as arthritis and inflammatory bowel disease is perceived by the Central nervous System (CNS) through different routes that, by means of neural reflex circuits, regulate the immune system response [...]

The alpha-7 nicotinic acetylcholine receptor agonist GTS-21 engages the glucagon-like peptide-1 incretin hormone axis to lower levels of blood glucose in db/db mice

AIM

To establish if alpha-7 nicotinic acetylcholine receptor (α7nAChR) agonist GTS-21 exerts a blood glucose-lowering action in db/db mice, and to test if this action requires coordinate α7nAChR and GLP-1 receptor (GLP-1R) stimulation by GTS-21 and endogenous GLP-1, respectively.

MATERIALS AND METHODS

Blood glucose levels were measured during an oral glucose tolerance test (OGTT) using db/db mice administered intraperitoneal GTS-21. Plasma GLP-1, peptide tyrosine tyrosine 1-36 (PYY1-36), glucose-dependent insulinotropic peptide (GIP), glucagon, and insulin levels were measured by ELISA. A GLP-1R-mediated action of GTS-21 that is secondary to α7nAChR stimulation was evaluated using α7nAChR and GLP-1R knockout (KO) mice, or by co-administration of GTS-21 with the dipeptidyl peptidase-4 inhibitor, sitagliptin, or the GLP-1R antagonist, exendin (9-39). Insulin sensitivity was assessed in an insulin tolerance test.

RESULTS

Single or multiple dose GTS-21 (0.5-8.0 mg/kg) acted in a dose-dependent manner to lower levels of blood glucose in the OGTT using 10-14 week-old male and female db/db mice. This action of GTS-21 was reproduced by the α7nAChR agonist, PNU-282987, was enhanced by sitagliptin, was counteracted by exendin (9-39), and was absent in α7nAChR and GLP-1R KO mice. Plasma GLP-1, PYY1-36, GIP, glucagon, and insulin levels increased in response to GTS-21, but insulin sensitivity, body weight, and food intake were unchanged.

CONCLUSIONS

α7nAChR agonists improve oral glucose tolerance in db/db mice. This action is contingent to coordinate α7nAChR and GLP-1R stimulation. Thus α7nAChR agonists administered in combination with sitagliptin might serve as a new treatment for type 2 diabetes.

Activation of α7 nicotinic acetylcholine receptor promotes HIV-1 transcription

Alpha7 nicotinic acetylcholine receptor (α7 nAChR), a hub of the cholinergic anti-inflammatory pathway (CAP), is required for the treatment of inflammatory diseases. HIV-1 infection can upregulate the expression of α7 nAChR in T lymphocytes and affect the role of CAP. However, whether α7 nAChR regulates HIV-1 infection in CD4+ T cells is unclear. In this study, we first found that activation of α7 nAChR by GTS-21 (an α7 nAChR agonist) can promote the transcription of HIV-1 proviral DNA. Then, through transcriptome sequencing analysis, we found that p38 MAPK signaling was enriched in GTS-21 treated HIV-latent T cells. Mechanistically, activation of α7 nAChR could increase reactive oxygen species (ROS), reduce DUSP1 and DUSP6, and consequently enhance the phosphorylation of p38 MAPK. By co-immunoprecipitation and liquid chromatography tandem mass spectrometry, we found that p-p38 MAPK interacted with Lamin B1 (LMNB1). Activation of α7 nAChR increased the binding between p-p38 MAPK and LMNB1. We confirmed that knockdown of MAPK14 significantly downregulated NFATC4, a key activator of HIV-1 transcription. Taken together, activation of the α7 nAChR could trigger ROS/p-p38 MAPK/LMNB1/NFATC4 signaling pathway enhancing HIV-1 transcription. We have revealed an unrecognized mechanism of α7 nAChR-mediated neuroimmune regulation of HIV infection.

Marine Origin Ligands of Nicotinic Receptors: Low Molecular Compounds, Peptides and Proteins for Fundamental Research and Practical Applications

The purpose of our review is to briefly show what different compounds of marine origin, from low molecular weight ones to peptides and proteins, offer for understanding the structure and mechanism of action of nicotinic acetylcholine receptors (nAChRs) and for finding novel drugs to combat the diseases where nAChRs may be involved. The importance of the mentioned classes of ligands has changed with time; a protein from the marine snake venom was the first excellent tool to characterize the muscle-type nAChRs from the electric ray, while at present, muscle and α7 receptors are labeled with the radioactive or fluorescent derivatives prepared from α-bungarotoxin isolated from the many-banded krait. The most sophisticated instruments to distinguish muscle from neuronal nAChRs, and especially distinct subtypes within the latter, are α-conotoxins. Such information is crucial for fundamental studies on the nAChR revealing the properties of their orthosteric and allosteric binding sites and mechanisms of the channel opening and closure. Similar data are provided by low-molecular weight compounds of marine origin, but here the main purpose is drug design. In our review we tried to show what has been obtained in the last decade when the listed classes of compounds were used in the nAChR research, applying computer modeling, synthetic analogues and receptor mutants, X-ray and electron-microscopy analyses of complexes with the nAChRs, and their models which are acetylcholine-binding proteins and heterologously-expressed ligand-binding domains.

α7 Nicotinic Acetylcholine Receptor Agonists Regulate Inflammation and Growth Hormone Resistance in Sepsis

ABSTRACT

During sepsis the normal induction of circulating insulin-like growth factor-I (IGF-I) by growth hormone (GH) action on liver is attenuated, a phenomenon called hepatic GH resistance. Hepatic GH resistance can be caused by cytokine-mediated activation of the NF-κB pathway which interferes with normal GH-signaling. The afferent and efferent fibers of the vagus nerve are integral to the cholinergic anti-inflammatory pathway (CAP) which attenuates hepatic TNFα production by activating the α7 nicotinic acetylcholine receptor (α7nAChR). We examined the effects of selective afferent vagotomy (SAV) and α7nAChR activation on sepsis-induced mortality, hepatic and systemic inflammation, the GH/IGF system and hepatic GH resistance using Sprague Dawley (SD) rats, C57BL/6 wild type (WT) mice, and α7nAChR knockout (KO) mice. Capsaicin was used to perform SAV and GTS-21 (α7nAChR agonist) was used to activate the α7nAChR. Sepsis-induced mortality, hepatic NF-κB activation, and plasma cytokine levels were increased in SAV rats and reduced in GTS-21-treated mice. The effects of sepsis on the GH/IGF-I system plasma IGF-I, IGF binding protein-1 (IGFBP-1), hepatic IGF-I, IGFBP-1, and GH receptor (GHR) mRNA and rhGH-responsiveness in mice were improved by GTS-21. Collectively these results confirm the protective effects of the anti-inflammatory CAP and α7nAChR activation in sepsis. They also provide evidence the CAP and α7nAChR activation could be used to attenuate hepatic GH resistance and anabolic failure in sepsis.

Endogenous α7 nAChR Agonist SLURP1 Facilitates Escherichia coli K1 Crossing the Blood-Brain Barrier

Alpha 7 nicotinic acetylcholine receptor (α7 nAChR) is critical for the pathogenesis of Escherichia coli (E. coli) K1 meningitis, a severe central nervous system infection of the neonates. However, little is known about how E. coli K1 manipulates α7 nAChR signaling. Here, through employing immortalized cell lines, animal models, and human transcriptional analysis, we showed that E. coli K1 infection triggers releasing of secreted Ly6/Plaur domain containing 1 (SLURP1), an endogenous α7 nAChR ligand. Exogenous supplement of SLURP1, combined with SLURP1 knockdown or overexpression cell lines, showed that SLURP1 is required for E. coli K1 invasion and neutrophils migrating across the blood-brain barrier (BBB). Furthermore, we found that SLURP1 is required for E. coli K1-induced α7 nAChR activation. Finally, the promoting effects of SLURP1 on the pathogenesis of E. coli K1 meningitis was significantly abolished in the α7 nAChR knockout mice. These results reveal that E. coli K1 exploits SLURP1 to activate α7 nAChR and facilitate its pathogenesis, and blocking SLURP1-α7 nAChR interaction might represent a novel therapeutic strategy for E. coli K1 meningitis.

Vagus nerve stimulation activates two distinct neuroimmune circuits converging in the spleen to protect mice from kidney injury

Acute kidney injury is highly prevalent and associated with high morbidity and mortality, and there are no approved drugs for its prevention and treatment. Vagus nerve stimulation (VNS) alleviates inflammatory diseases including kidney disease; however, neural circuits involved in VNS-induced tissue protection remain poorly understood. The vagus nerve, a heterogeneous group of neural fibers, innervates numerous organs. VNS broadly stimulates these fibers without specificity. We used optogenetics to selectively stimulate vagus efferent or afferent fibers. Anterograde efferent fiber stimulation or anterograde (centripetal) sensory afferent fiber stimulation both conferred kidney protection from ischemia-reperfusion injury. We identified the C1 neurons-sympathetic nervous system-splenic nerve-spleen-kidney axis as the downstream pathway of vagus afferent fiber stimulation. Our study provides a map of the neural circuits important for kidney protection induced by VNS, which is critical for the safe and effective clinical application of VNS for protection from acute kidney injury.

Modulation of preeclampsia by the cholinergic anti-inflammatory pathway: Therapeutic perspectives

The cholinergic anti-inflammatory pathway (CAP) is vital for the orchestration of the immune and inflammatory responses under normal and challenged conditions. Over the past two decades, peripheral and central circuits of CAP have been shown to be critically involved in dampening the inflammatory reaction in a wide array of inflammatory disorders. Additionally, emerging evidence supports a key role for CAP in the regulation of the female reproductive system during gestation as well as in the advent of serious pregnancy-related inflammatory insults such as preeclampsia (PE). Within this framework, the modulatory action of CAP encompasses the perinatal maternal and fetal adverse consequences that surface due to antenatal PE programming. Albeit, a considerable gap still exists in our knowledge of the precise cellular and molecular underpinnings of PE/CAP interaction, which hampered global efforts in safeguarding effective preventive or therapeutic measures against PE complications. Here, we summarize reports in the literature regarding the roles of peripheral and reflex cholinergic neuroinflammatory pathways of nicotinic acetylcholine receptors (nAChRs) in reprogramming PE complications in mothers and their progenies. The possible contributions of α7-nAChRs, cholinesterases, immune cells, adhesion molecules, angiogenesis, and endothelial dysfunction to the interaction have also been reviewed.

Increased oxidative stress and inflammatory markers contrasting with the activation of the cholinergic anti-inflammatory pathway in patients with metabolic syndrome

INTRODUCTION

Metabolic syndrome (MetS) is a disorder that is closely associated with risk factors that increase the chance of atherosclerosis and cardiovascular diseases. We demonstrate the presence of inflammation and oxidative stress in patients with MetS through levels of antioxidants and oxidative and inflammatory markers, in order to determine influential variables in therapy.

METHODS

In this study, lipid peroxidation, carbonylated protein content and enzymatic and non-enzymatic antioxidants were evaluated in samples obtained from 30 patients with MetS and 30 control patients. In addition, acetylcholinesterase (AChE) activity, C-reactive protein (CRP) and uric acid (UA) levels were determined to investigate the inflammatory process in patients with MetS.

RESULTS

Our results demonstrated an increase in the levels of oxidative markers, such as substances reactive to thiobarbituric acid (TBARS) and carbonyl protein. In addition, a decrease in the defense of non-enzymatic antioxidants, such as levels of vitamin C and glutathione (GSH) in patients with MetS. As for inflammatory markers, CRP and UA were increased in patients with MetS. Finally, activation of the cholinergic anti-inflammatory pathway was observed due to decreased AchE activity in patients with MetS.

CONCLUSION

The analyzes indicated oxidative stress, together with a reduction in the levels of antioxidant enzymes, corroborating the high consumption of these proteins. In addition, inflammation and activation of the cholinergic anti-inflammatory pathway was observed by the AChE analysis. Thus, the activation of this pathway can be studied as a possible route to a potential therapy. In addition, the markers AChE, CRP and UA may be used as a focus for the treatment of MetS.