Investigation of nicotine binding to THP-1 cells: evidence for a non-cholinergic binding site

Endogenous CHRNA7-ligand SLURP1 as a potential tumor suppressor and anti-nicotinic factor in pancreatic cancer

Smoking is associated with increased risk and poorer prognosis of pancreatic ductal adenocarcinoma (PDAC). Nicotine acts through cholinergic nicotinic receptors, preferentially α7 (CHRNA7) that also binds the endogenous ligand SLURP1 (Secreted Ly-6/uPAR-Related Protein 1). The clinical significance of SLURP1 and its interaction with nicotine in PDAC are unclear. We detected similar levels of SLURP1 in sera from healthy donors and patients with chronic pancreatitis or PDAC; higher preoperative values were associated with significantly better survival in patients with resected tumors. Pancreatic tissue was not a source of circulating SLURP1 but contained diverse CHRNA7-expressing cells, preferentially epithelial and immune, whereas stromal stellate cells and a quarter of the tumor cells lacked CHRNA7. The CHRNA7 mRNA levels were decreased in PDAC, and CHRNA7^high-PDAC patients lived longer. In CHRNA7^high COLO357 and PANC-1 cultures, opposing activities of SLURP1 (anti-malignant/CHRNA7-dependent) and nicotine (pro-malignant/CHRNA7-infidel) were exerted without reciprocally interfering with receptor binding or downstream signaling. These data suggested that the ligands act independently and abolish each other’s effects through a mechanism resembling functional antagonism. Thus, SLURP1 might represent an inborn anti-PDAC defense being sensitive to and counteracting nicotine. Boosting SLURP1-CHRNA7 interaction might represent a novel strategy for treatment in high-risk individuals, i.e., smokers with pancreatic cancer.

A filtration-based protocol to isolate human plasma membrane-derived vesicles and exosomes from blood plasma

The methods of Plasma Membrane-derived Vesicle (PMV) isolation and quantification vary considerably in the literature and a new standard needs to be defined. This study describes a novel filtration method to isolate PMVs in plasma, which avoids high speed centrifugation, and to quantify them using a Becton Dickinson (BD) FACS Calibur™ flow cytometer, as annexin V-positive vesicles, larger than 0.2 μm in diameter. Essentially microvesicles (which comprise a mixture of PMVs and exosomes) from citrate plasma were sonicated to break up clumped exosomes, and filtered using Millipore 0.1 μm pore size Hydrophilic Durapore membranes in Swinnex 13 mm filter holders. Phosphatidylserine-positive PMVs detected with annexin V-PE were quantified using combined labelling and gating strategies in conjunction with Polysciences Polybead Microspheres (0.2 μm) and BDTrucount tubes. The PMV absolute count was calculated on the analysis template using the Trucount tube lot number information and expressed in PMV count/ml. Having estimated a normal reference range (0.51×10(5)-2.82×10(5) PMVs/ml) from a small sample of human donors, using the developed method, the effect of certain variables was investigated. Variations such as freezing of samples and gender status did not significantly alter the PMV absolute count, and with age plasma PMV levels were only marginally reduced. Smokers appeared to have reduced PMV levels. Nicotine, as for calpeptin was shown to dose-dependently (from 10 up to 50 μM) reduce levels of early apoptosis in THP-1 monocytes and to decrease the level of PMV release. Fasting individuals had 2-3 fold higher PMV absolute counts compared to non-fasting subjects.

Auto/paracrine control of inflammatory cytokines by acetylcholine in macrophage-like U937 cells through nicotinic receptors

Although acetylcholine (ACh) is well known for its neurotransmitter function, recent studies have indicated that it also functions as an immune cytokine that prevents macrophage activation through a 'cholinergic (nicotinic) anti-inflammatory pathway'. In this study, we used the macrophage-like U937 cells to elucidate the mechanisms of the physiologic control of cytokine production by auto/paracrine ACh through the nicotinic class of ACh receptors (nAChRs) expressed in these cells. Stimulation of cells with lipopolysaccharide up-regulated expression of alpha1, alpha4, alpha5, alpha7, alpha10, beta1 and beta3 subunits, down-regulated alpha6 and beta2 subunits, and did not alter the relative quantity of alpha9 and beta4 mRNAs. Distinct nAChR subtypes showed differential regulation of the production of pro- and anti-inflammatory cytokines. While inhibition of the expression of the TNF-alpha gene was mediated predominantly by the alpha-bungarotoxin sensitive nAChRs, that of the IL-6 and IL-18 genes-by the mecamylamine-sensitive nAChRs. Both the Mec- and alphaBtx-sensitive nAChRs regulated expression of the IL-1beta gene equally efficiently. Upregulation of IL-10 production by auto/paracrine ACh was mediated predominantly through alpha7 nAChR. These findings offer a new insight on how nicotinic agonists control inflammation, thus laying a groundwork for the development of novel immunomodulatory therapies based on the nAChR subtype selectivity of nicotinic agonists.

A novel signaling pathway: fibroblast nicotinic receptor alpha1 binds urokinase and promotes renal fibrosis

The nicotinic acetylcholine receptor alpha1 (nAChRalpha1) was investigated as a potential fibrogenic molecule in the kidney, given reports that it may be an alternative urokinase (urokinase plasminogen activator; uPA) receptor in addition to the classical receptor uPAR. In a mouse obstructive uropathy model of chronic kidney disease, interstitial fibroblasts were identified as the primary cell type that bears nAChRalpha1 during fibrogenesis. Silencing of the nAChRalpha1 gene led to significantly fewer interstitial alphaSMA(+) myofibroblasts (2.8 times decreased), reduced interstitial cell proliferation (2.6 times decreased), better tubular cell preservation (E-cadherin 14 times increased), and reduced fibrosis severity (24% decrease in total collagen). The myofibroblast-inhibiting effect of nAChRalpha1 silencing in uPA-sufficient mice disappeared in uPA-null mice, suggesting that a uPA-dependent fibroblastic nAChRalpha1 pathway promotes renal fibrosis. To further establish this possible ligand-receptor relationship and to identify downstream signaling pathways, in vitro studies were performed using primary cultures of renal fibroblasts. (35)S-Labeled uPA bound to nAChRalpha1 with a K(d) of 1.6 x 10(-8) m, which was displaced by the specific nAChRalpha1 inhibitor d-tubocurarine in a dose-dependent manner. Pre-exposure of uPA to the fibroblasts inhibited [(3)H]nicotine binding. The uPA binding induced a cellular calcium influx and an inward membrane current that was entirely prevented by d-tubocurarine preincubation or nAChRalpha1 silencing. By mass spectrometry phosphoproteome analyses, uPA stimulation phosphorylated nAChRalpha1 and a complex of signaling proteins, including calcium-binding proteins, cytoskeletal proteins, and a nucleoprotein. This signaling pathway appears to regulate the expression of a group of genes that transform renal fibroblasts into more active myofibroblasts characterized by enhanced proliferation and contractility. This new fibrosis-promoting pathway may also be relevant to disorders that extend beyond chronic kidney disease.

Hypothesis about mechanisms through which nicotine might exert its effect on the interdependence of inflammation and gut barrier function in ulcerative colitis

Ulcerative colitis (UC) is characterized by impairment of the epithelial barrier and the formation of ulcer-type lesions, which result in local leaks and generalized alterations of mucosal tight junctions. Ultimately, this results in increased basal permeability. Although disruption of the epithelial barrier in the gut is a hallmark of inflammatory bowel disease and intestinal infections, it remains unclear whether barrier breakdown is an initiating event of UC or rather a consequence of an underlying inflammation, evidenced by increased production of proinflammatory cytokines. UC is less common in smokers, suggesting that the nicotine in cigarettes may ameliorate disease severity. The mechanism behind this therapeutic effect is still not fully understood, and indeed it remains unclear if nicotine is the true protective agent in cigarettes. Nicotine is metabolized in the body into a variety of metabolites and can also be degraded to form various breakdown products. It is possible these metabolites or degradation products may be the true protective or curative agents. A greater understanding of the pharmacodynamics and kinetics of nicotine in relation to the immune system and enhanced knowledge of gut permeability defects in UC are required to establish the exact protective nature of nicotine and its metabolites in UC. This review suggests possible hypotheses for the protective mechanism of nicotine in UC, highlighting the relationship between gut permeability and inflammation, and indicates where in the pathogenesis of the disease nicotine may mediate its effect.

Prenatal nicotine exposure and pulmonary barotrauma of newborns

Smoking in adults increases the relative risk of contracting spontaneous pneumothorax, a form of pulmonary barotrauma. Maternal smoking habits affect the fetus. Pregnant females attend the antenatal clinic at the 8th to 12th weeks of pregnancy. There is a participation rate of 99% of all births in Sweden. Their smoking habits were registered at this stage. This study supported the hypothesis that the registered maternal smoking habits covariated with the risk of contracting pulmonary barotrauma in newborn infants. The infants of smokers do not seem to be at higher risk (95% C.I. of RR: 0.78-0.99) for contracting pulmonary barotrauma than those of nonsmokers. Thus far, the hypothesis is even rejected at the 5% significance level. However, after considering other factors, especially mother's education, it seems to be an open question whether or not a weak covariation is present. Newborn boys run almost twice the risk of contracting pulmonary barotrauma than girls. Furthermore, we found an increased risk for contracting pulmonary barotrauma in the subcohort of newborns whose mothers' smoking habits were not reported.