Influence of chronic nicotine intake and acute ethanol challenge on gastric mucus level and blood flow in rabbits

Nicotine/cigarette smoke promotes metastasis of pancreatic cancer through α7nAChR-mediated MUC4 upregulation

Despite evidence that long-term smoking is the leading risk factor for pancreatic malignancies, the underlying mechanism(s) for cigarette-smoke (CS)-induced pancreatic cancer (PC) pathogenesis has not been well-established. Our previous studies revealed an aberrant expression of the MUC4 mucin in PC as compared to the normal pancreas and its association with cancer progression and metastasis. Interestingly, here we explore a potential link between MUC4 expression and smoking-mediated PC pathogenesis and report that both cigarette-smoke-extract (CSE) and nicotine, which is the major component of CS, significantly up-regulates MUC4 in PC cells. This nicotine-mediated MUC4 overexpression was via α7 subunit of nicotinic acetylcholine receptor (nAChR) stimulation and subsequent activation of the JAK2/STAT3 downstream signaling cascade in cooperation with the MEK/ERK1/2 pathway; this effect was blocked by the α7nAChR antagonists, α-bungarotoxin and mecamylamine, and by specific siRNA-mediated STAT3 inhibition. Additionally, we demonstrated that nicotine-mediated MUC4 up-regulation promotes the PC cell migration through the activation of the downstream effectors such as HER2, c-Src and FAK; this effect was attenuated by shRNA-mediated MUC4 abrogation, further implying that these nicotine-mediated pathological effects on PC cells are MUC4 dependent. Furthermore, the in-vivo studies demonstrated a dramatic increase in the mean pancreatic tumor weight [low-dose (100 mg/m³ TSP), p=0.014; high-dose (247 mg/m³ TSP), p=0.02] and significant tumor metastasis to various distant organs in the CS-exposed-mice, orthotopically implanted with luciferase-transfected PC cells, as compared to the sham-controls. Moreover, the CS-exposed mice had elevated levels of serum cotinine [low-dose, 155.88±35.96 ng/ml; high-dose, 216.25±29.95 ng/ml] and increased MUC4, α7nAChR and pSTAT3 expression in the pancreatic tumor tissues. Altogether, our findings revealed for the first time that CS up-regulates the MUC4 mucin in PC via α7nAChR/JAK2/STAT3 downstream signaling cascade, thereby promoting metastasis of pancreatic cancer.

Nicotine suppresses inflammatory factors in HBE16 airway epithelial cells after exposure to cigarette smoke extract and lipopolysaccharide

Cigarette smoke is a major cause of chronic inflammatory pulmonary disease, leading to inflammation, mucin (MUC) production, tissue damage, and remodeling. It is also well known that the major addictive component of cigarette smoke is nicotine. This study focused on the role of nicotine in the development of inflammatory pulmonary disease induced by cigarette smoke. HBE16 human airway epithelial cells were treated with serial dilutions of cigarette smoke chloroform extract (CE), lipopolysaccharide (LPS), and nicotine. The release of MUC5AC, tumor necrosis factor (TNF)-α, interleukin (IL)-8, and IL-6 protein were assayed by enzyme-linked immunosorbent assay. The MUC5AC protein also was observed by immunofluorescence. The expression of MUC5AC, TNF-α, IL-8, and IL-6 mRNA were detected by real-time polymerase chain reaction. We found that the mRNA of the proinflammatory mediators TNF-α, IL-8, and IL-6, as well as MUC5AC was highly expressed after CE and LPS stimulation. Nicotine did not cause an excessive expression of TNF-α, IL-8, and IL-6, nor did it affect protein production from the MUC5AC gene. Nicotine not only failed to stimulate production of TNF-α, IL-8, and IL-6, but its presence was shown to suppress the activation resulting from exposure to CE and LPS (P < 0.05). Preincubation with nicotine also would reduce the level of MUC5AC protein in culture supernatants of CE- and LPS-treated cells. However, mRNA expression of MUC5AC showed no significant change in nicotine-treated cells when compared with normal control cells. This distinctive pattern implies that nicotine may have potential to suppress airway inflammation and maintain the mucus over retention in airway secretory cells to some extent, thus forming a balance between mucus hyperproduction and hypersecretion in airways exposed to smoking and LPS.

Cigarette smoke and its extract delays ulcer healing and reduces nitric oxide synthase activity and angiogenesis in rat stomach

1. The purpose of the present study was to examine whether cigarette smoke and its extract could affect ulcer healing, angiogenesis and nitric oxide synthase (NOS) activity in the gastric mucosa. 2. Ulcerated rats were either exposed to cigarette smoke or given smoke extract once daily for 3 days. Rats were killed and stomachs were removed for the measurement of ulcer size, angiogenesis and NOS activity. 3. Angiogenesis and constitutive NOS activity were concomitantly and dose-dependently reduced by cigarette smoke or its extract. The same treatments also delayed ulcer healing. 4. These results indicate that cigarette smoke and its extract repress the processes of new blood vessel formation and NOS activity during tissue repair in the gastric mucosa. These could, in turn, retard the healing process in the gastric mucosa.

Effects of selective beta-adrenoceptor antagonists on gastric ulceration in the rat

Metoprolol and butoxamine, beta-adrenoceptor antagonists which act selectively at the beta 1- and beta 2-adrenoceptors, respectively, have been investigated for their actions on the ethanol, indomethacin and cold-restraint stress ulcer models. Oral administration of butoxamine but not metoprolol significantly attenuated gastric mucosal damage in the three types of ulcer model. Intraperitoneal injection of butoxamine reduced indomethacin ulceration but not that of the other two models. The stimulatory effect of butoxamine on the gastric mucosal potential difference and intramucosal mucus level correlated positively with its anti-ulcer action. Only oral administration of butoxamine significantly increased the mucosal prostaglandin E2 (PGE2) level but not after intraperitoneal injection. Oral administration of butoxamine also significantly increased the mucosal PGE2 level in the three types of ulcer model but this drug was only effective in the indomethacin ulcer model after intraperitoneal injection. Gastric acid and pepsin output were not affected by either drug. Metoprolol significantly reduced systemic blood pressure; this could be attributed to a reduction in gastric mucosal blood flow. These results imply that beta 2-adrenoceptors play a significant role in the pathogenesis of gastric ulceration. We suggest that the anti-ulcer effect of butoxamine was in part a result of strengthening of the mucosal barrier but that this was not effected by modification of acid or pepsin secretions in the stomach. Stimulation of PGE2 in the gastric mucosa could contribute in part to the anti-ulcer action of the drug, especially when given by the oral route.

A study of the antiulcer mechanisms of propranolol in rats

Although propranolol has been shown to protect against ethanol and stress ulceration, the antiulcer mechanisms are still unclear. The present study examined the antiulcer mechanisms of propranolol in three different types of ulceration induced respectively by ethanol (60%), indomethacin (30 mg/kg) and stress (cold-restraint). Propranolol pretreatment in the highest dose (10 mg/kg) given either intraperitoneally (i.p.) or orally (p.o.) prevented gastric mucosal damage in these three ulcer models. The three doses of the drug (2.5, 5 or 10 mg/kg) dose-dependently decreased systemic blood pressure which was accompanied by a reduction of gastric mucosal blood flow. These findings suggest that the protection was unrelated to an improvement of local circulation in the stomach. However, propranolol preserved the mucus levels in the three types of ulcer models. The beta-adrenoceptor blocker also increased the basal gastric mucosal potential difference. These findings indicate that propranolol strengthens the mucosal barrier by the preservation of mucosal mucus and enhancement of the mucosal integrity in the stomach.