The use of tobacco products is associated with an increased incidence of periodontal disease, poor response to periodontal therapy, and a high risk for developing head and neck cancer. Nicotine and tobacco-derived nitrosamines have been shown to exhibit their pathobiologic effects due in part to activation of the nicotinic acetylcholine (ACh) receptors (nAChRs), mainly alpha7 nAChR, expressed by oral keratinocytes (KCs). This study was designed to gain mechanistic insight into alpha7-mediated morbidity of tobacco products in the oral cavity. We investigated the signaling pathways downstream of alpha7 nAChR in monolayers of oral KCs exposed for 24 h to aged and diluted sidestream cigarette smoke (ADSS) or an equivalent concentration of pure nicotine. By both real-time polymerase chain reaction (PCR) and In-cell Western, the KCs stimulated with ADSS or nicotine showed multifold increases of STAT-3. These effects could be completely blocked or significantly (P<0.05) diminished if the cells were pretreated with the alpha7 antagonist alpha-bungarotoxin (alphaBTX) or transfected with anti-alpha7 small interfering RNA (siRNA-alpha7). The use of pathway inhibitors revealed that signaling through the Ras/Raf-1/MEK1/ERK steps mediated alpha7-dependent up-regulation of STAT-3. Targeted mutation of the alpha7 gene prevented ERK1/2 activation by nicotine. Using the gel mobility shift assay, we demonstrated that an increased protein binding activity of STAT-3 caused by ADSS or pure nicotine was mediated by janus-activated kinase (JAK)-2. Activation of JAK-2/STAT-3 pathway could be prevented by alphaBTX or siRNA-alpha7. Thus, nuclear transactivation of STAT-3 in KCs exposed to tobacco products is mediated via intracellular signaling downstream from alpha7, which proceeds via two complementary pathways. The Ras/Raf-1/MEK1/ERK cascade culminates in up-regulated expression of the gene encoding STAT-3, whereas recruitment and activation of tyrosine kinase JAK-2 phosphorylates it. Elucidation of this novel mechanism of nicotine-dependent nuclear transactivation of STAT-3 identifies oral alpha7 nAChR as a promising molecular target to prevent, reverse, or retard tobacco-related periodontal disease and progression of head and neck cancer by receptor inhibitors.

The biologic role of novel cholinergic toxin-like signaling peptides termed SLURP (secreted mammalian Ly-6/uPAR-related protein) in the mucocutaneous epithelium is a subject of intense research. Previous studies demonstrated that SLURP-1 activates the alpha7 subtype of keratinocyte nicotinic acetylcholine receptors (nAChRs) and facilitates keratinization and programmed cell death, and that the level of SLURP-2 was found to be upregulated several fold in the hyperproliferative skin of patients with psoriasis. In this study, we demonstrated for the first time that human epidermal and oral keratinocytes secrete SLURP-2. We cloned human SLURP-2 and produced the mouse monoclonal antibody 341F10-1F12 that visualized SLURP-2 in the cytoplasm of normal human epidermal and oral keratinocytes grown in culture. In epidermis, SLURP-2 was found predominantly in the suprabasal compartment, whereas in the attached gingiva-in the lowermost epithelial layers. Recombinant SLURP-2 (rSLURP-2) competed with nicotinic radioligands for binding to keratinocytes, showing a higher affinity to the [3H]epibatidine- than [3H]nicotine-labeled sites. Treatment with rSLURP-2 significantly (P < 0.05) increased the number of keratinocytes in culture and their resistance to apoptosis, which could be abolished by mecamylamine more efficiently than alpha-bungarotoxin. By real-time PCR and in-cell western, rSLURP-2 significantly (P < 0.05) downregulated gene expression of the differentiation markers loricrin, filaggrin, and cytokeratins 1 and 10, and pro-apoptotic Bax, Bad, and caspase 3 which were elevated by high extracellular calcium, and rSLURP-2 also abolished activation of caspases 3 and 8 caused by camptothecin. These results indicated that SLURP-2 competes with acetylcholine predominantly at the alpha3 nAChR, and that receptor ligation with SLURP-2 delays keratinocyte differentiation and prevents apoptosis. Thus, the different effects observed for SLURP-1 and -2 can be explained by their differential binding to the nAChR subtypes expressed in keratinocytes. These findings present a novel paradigm of the physiologic regulation of mucocutaneous epithelial cells by locally produced small hormone-like peptide molecules, and open novel directions toward better understanding and treating of skin and mucosal diseases.

To gain a mechanistic insight into nicotinic receptor-dependent morbidity of tobacco products in the oral cavity, we studied effects of exposures of normal human oral keratinocytes (KCs) for 24 h to environmental tobacco smoke (ETS) vs. equivalent concentration of pure nicotine. The exposed KCs showed a multifold increase of nuclear factor-κB (NF-κB) at the mRNA and protein levels, which could be significantly (p<0.05) diminished by α-bungarotoxin or transfection with anti-α7 small interfering RNA. An increased protein-binding activity of NF-κB also could be prevented by blocking α7 signaling. The use of pathway inhibitors demonstrated that the Ras/Raf-1/MEK1/ERK steps mediated α7-dependent upregulation of NF-κB. Thus, exposure of KCs to tobacco may lead to the pathobiologic effects via an intracellular signaling pathway downstream of α7 that proceeds through the Ras/Raf-1/MEK1/ERK steps leading to upregulated expression and transactivation of NF-κB.

SUMMARY:Smoking and smokeless tobacco cause morbidity that originates from the epithelium lining of the skin and upper digestive tract. Oral keratinocytes (OKC) express nicotinic acetylcholine receptors (nAChRs) that bind nicotine (Nic). We studied the mechanism of the receptor-mediated toxicity of tobacco products on OKC. Preincubation of normal human OKC with Nic altered the ligand-binding kinetics of their nAChRs, suggesting that the nAChRs underwent structural changes. This hypothesis was confirmed by the finding that exposure of OKC to Nic causes transcriptional and translational changes. Through RT-PCR and immunoblotting, we found a 1.5-to 2.9-fold increase in the mRNA and protein levels of ␣3, ␣5, ␣7, ␤2, and ␤4 nAChR subunits. Exposure of OKC to Nic also changed the mRNA and protein levels of the cell cycle and cell differentiation markers Ki-67, PCNA, p21, cyclin D1, p53, filaggrin, loricrin, and cytokeratins 1 and 10. The nicotinic antagonist mecamylamine prevented these changes, which indicates that the Nic-induced changes in the expression of both the nAChR and the cell cycle and cell differentiation genes resulted from pharmacologic stimulation of nAChRs with Nic. To establish the relevance of these findings to the pathobiologic effects of tobacco products in vivo, we studied the above parameters in the oral tissue of rats and mice after their exposure for 3 weeks to environmental cigarette smoke or drinking water containing equivalent concentrations of Nic that are pathophysiologically relevant. The changes of the nAChRs and the cell cycle and cell differentiation genes were similar to those found in vitro. The results of indirect immunofluorescence assay of tissue specimens validated these findings. Thus, some pathobiologic effects of tobacco products in oral tissues may stem from Nic-induced alterations of the structure and function of keratinocyte nAChRs responsible for the physiologic regulation of the cell cycle by the cytotransmitter acetylcholine. (Lab Invest 2001, 81:1653-1668.T he epithelial cells lining human attached gingiva and the upper two-thirds portion of the esophagus have recently been shown to express cholinergic enzymes and receptors that mediate acetylcholine (ACh) signaling (Nguyen et al, 2000a(Nguyen et al, , 2000b. The cholinergic system of oral epithelium includes the synthesizing enzyme choline acetyltransferase, two molecular forms of the degrading enzyme acetylcholinesterase, the asymmetric and the globular forms, and two classes of ACh receptors, the nicotinic and the muscarinic receptors. The heteromeric nicotinic ACh receptor (nAChRs) channels on the cell membrane of oral keratinocytes (OKC) can be composed of ␣3, ␣5, ␤2, and ␤4 subunits, eg, ␣3␤2(␤4) Ϯ ␣5, and the homomeric channels can be made of several ␣7 or ␣9 subunits (Conti-Tronconi et al, 1994). The diversity of nAChRs expressed by OKC in the course of their development could allow a single cytotransmitter ACh to exert different effects on these cells at various stages of their development, which helps explai...

Recent interest in the local delivery of antimicrobial and anti-inflammatory agents has stimulated interest in the efficacy of various treatment regimens. Chlorhexidine gluconate (CHX) delivered daily by home-applied marginal irrigation as a 0.04% solution in combination with a single professional irrigation of 0.12% CHX was tested over a 3-month period. Sixty periodontal maintenance patients each having at least 2 pockets greater than or equal to 4 mm probing depth, and bleeding on probing were assigned to either Group 1: one professional subgingival 0.12% CHX (Peridex) irrigation (Perio Pik) followed by adjunctive daily home marginal 0.04% CHX irrigation (Pik Pocket); Group 2: one professional subgingival 0.12% CHX irrigation followed by adjunctive daily home marginal water irrigation; Group 3: one professional subgingival water irrigation followed by adjunctive daily home marginal water irrigation; or Group 4: control. At baseline and 3 month visits, subgingival plaque samples were taken from 2 sites per patient. Cultural microbiological analysis was performed using non-selective and selective media. Plaque Index, Gingival Index, pocket probing depths, and gingival recession were assessed. Scaling and root planing (supportive periodontal treatment) was provided for each patient followed by subgingival irrigation as outlined above. At 3 months the Gingival Index and pocket probing depths were both significantly reduced (P less than .05) in all irrigation groups compared to baseline. There were no significant changes in clinical parameters in the control group from baseline to 3 months. In Group 1 the GI was significantly reduced (P less than .05) compared to Group 4 at 3 months.(ABSTRACT TRUNCATED AT 250 WORDS)