Nicotine-enhanced epithelial differentiation in reconstructed human oral mucosa in vitro

Nicotine mediated epithelial modulations: An in-vitro evidence

Introduction

Nicotine, the main ingredient in tobacco, acts as a key alkaloid of nearly all tobacco products and has been demonstrated to facilitate tumorigenesis and accelerate metastasis. Further traditional tobacco products have shown to give systemic oral effects such as vasoconstriction, inflammation, and delayed wound healing, however; none of the reports have confirmed the significant knowledge of oral sequel of the effect of nicotine on oral epithelial cells. So, the current study aimed to investigate the effect of nicotine on epithelial transformation to a malignant state.

Material & methods

Through in-vitro experiments, the effects of nicotine on epithelial cells obtained from nicotine never exposed buccal mucosa were analyzed using total count and viability test, proliferation assay, cell cycle distribution assay, and PI3K/MAPK dual pathway activation assay.

Result & conclusion

MTT assay demonstrated that the proliferation of epithelial cells takes place at a 150 mM concentration of nicotine. Further, we identified the significantly increased cell count and viability in nicotine-exposed cells. Further, cell cycle distribution assay results demonstrated that nicotine forced the epithelial cells to enter the first growth phase. The same influence of nicotine was observed on the PI3K/MAPK dual pathway activation assay where a greater number of nicotine exposed cells showed dual pathway activation. In conclusion, the current study determined the potential mechanism of action of nicotine on oral epithelial cell proliferation through activating the oncogenic pathway. This may help to develop novel therapeutic strategies for the prevention of malignant transformation from smokeless tobacco-caused oral cancer.

A 3D Model of Human Buccal Mucosa for Compatibility Testing of Mouth Rinsing Solutions

Oral mucositis is the most common and severe non-hematological complication associated with cancer radiotherapy, chemotherapy, or their combination. Treatment of oral mucositis focuses on pain management and the use of natural anti-inflammatory, sometimes weakly antiseptic mouth rinses in combination with optimal oral cavity hygiene. To prevent negative effects of rinsing, accurate testing of oral care products is necessary. Due to their ability to mimic realistic in-vivo conditions, 3D models may be an appropriate option in compatibility testing of anti-inflammatory and antiseptically effective mouth rinses. We present a 3D model of oral mucosa based on the cell line TR-146 with a physical barrier, characterized by high transepithelial electrical resistance (TEER) and confirmed cell integrity. Histological characterization of the 3D mucosa model showed a stratified, non-keratinized multilayer of epithelial cells similar to that of human oral mucosa. By means of immuno-staining, tissue-specific expression of cytokeratin 13 and 14 was shown. Incubation of the 3D mucosa model with the rinses had no effects on cell viability, but TEER decreased 24h after incubation in all solutions except ProntOral®. Analogous to skin models, the established 3D model meets the quality control criteria of OECD guidelines and may therefore be suitable for comparing the cytocompatibility of oral rinses.

N-Acetylcysteine modulates the effects of composites on human gingival keratinocytes

OBJECTIVE

The aim of this study was to evaluate, if antioxidants, like N-Acetylcysteine, can modulate effects of composite eluates on human gingival keratinocytes.

METHODS

Composite samples of ceram.x® universal, Filtek™ Supreme XTE, and Admira® Fusion were stored 72h in cell culture medium to prepare eluates, according to ISO 10993-12:2012. Human gingival keratinocytes were exposed to these eluates with or without 3mM N-Acetylcysteine. Following cell observation by iCELLigence®, exposure periods were determined at 1d and 4d. Cell morphological analysis combined with live/dead staining was performed. Tissue-specific biomarkers of terminal differentiation, Involucrin and Filaggrin, were analyzed by indirect immunofluorescence (IIF) and Western blot (WB). qPCR profiling was performed on genes encoding for: inflammation, apoptosis, turn-over of extracellular matrix, adhesion, proliferation and differentiation. For statistical analysis one-way Anova was used (p<0.05).

RESULTS

Cells exposed to N-Acetylcysteine exhibited morphological changes but no cell death. After adding 3mM N-Acetylcysteine to HGK cultures, increased fluorescence intensity and protein amounts of Involucrin and Filaggrin indicated enhanced differentiation (p<0.05). Gene expression was modulated by: (i) composition of the composite eluates, (ii) NAC and (iii) exposure time. Filtek™ Supreme XTE showed a significant increased gene expression in inflammatory genes (p<0.05), which was amplified by the addition of NAC at 1d. Concerning exposure time, modulated gene expression showed eluate dependency, substantiated by Filtek™ Supreme XTE modulation at day 1 and Admira® Fusion at day 4.

SIGNIFICANCE

N-Acetylcysteine-emerging effects on gingival keratinocytes were threefold: (i) increase of differentiation, (ii) modulation of composite-related effects and (iii) in parts counteraction of eluate-induced effects.

Evaluation of the epithelial cells of lower lip mucosa after debonding of fixed orthodontic appliances

BACKGROUND

Orthodontic appliances (ligatures, braces, wires, etc.), are one of the main sources of trauma in the oral cavity. Friction between brackets and mucosa is a kind of chronic trauma that may cause buccal mucosal proliferation and ulceration and is one of the most common complaints of patients during orthodontic treatment. The aim of this study was to evaluate the changes of the lower lip epithelial cells after the removal of orthodontic fixed appliances.

METHODS

Cells of lower lip oral mucosa of 31 orthodontic patients were collected by exfoliative cytology in three times: immediately (T0), 30(T1) and 60 (T2) days after debonding. Nuclear (NA) and cytoplasmic (CA) areas, NA/CA ratio, cell morphology and cellularity of smears were evaluated using cytomorphometric and cytomorphologic methods. Friedman test followed by the Wilcoxon test was used to compare the NA, CA and NA/CA values in three different times. Cell morphology and cellularity were analyzed by the Chi-square test. All statistical tests were performed with SPSS version 20.

RESULTS

The NA and CA values increased significantly (P<0.001) after the removal of friction and irritation of orthodontic appliances in T1 and T2 and reached their highest level in T2. The NA/CA values did not change significantly (P=0.25). Class I smears, according to Papanicolaou classification, were observed in T0, T1, and T2. Superficial epithelial cells were predominant cell types in the lower incisor region in all times without statistically significant difference in three intervals.

CONCLUSIONS

Orthodontic appliances increase keratinization of lip mucosa which is considered an adaptive reaction to the mechanical stimulus, but after removing of the appliances cellular activity rapidly increases. Keratinization is the main change observed at the end of orthodontic treatment.

A Review of In Vitro Modelling Approaches to the Identification and Modulation of Squamous Metaplasia in the Human Tracheobronchial Epithelium

Squamous metaplasia in the tracheobronchial epithelium (TBE) involves the replacement of the normal pseudostratified mucociliary epithelium with a stratified squamous epithelium. Squamous metaplasia is considered to be an adaptive response that protects the lumen from the effects of inhaled airborne pollutants, but which might also feature as a pre-neoplastic lesion preceding squamous cell carcinoma. With the exception of transglutaminase I, involucrin, and cytokeratins 5, 6 and 13, few markers that contribute to the squamous phenotype have been identified in human TBE that can be used in diagnosis or to monitor its development in laboratory investigations, and current models are inadequate to provide statistically meaningful data. Therefore, new predictive markers have been identified, and new techniques established, in epithelial in vitro models capable of expressing squamous characteristics, which will be used to identify hazardous exposures and elucidate the mechanisms by which they induce their effects. A protocol for the quantitative detection of transglutaminase activity has been standardised in keratinocytes, based on the enzymatic incorporation of fluorescein–cadaverine (FC) into bis(γ-glutamyl) polyamine cross-links. The specificity of this compound as a transglutaminase substrate was demonstrated by using a range of competitive transglutaminase inhibitors, and by modulation of the squamous pathway. FC incorporation was localised to the cell membrane of terminally differentiating cells, and was not visible in basal, proliferating cells. High calcium-containing medium, nicotine and cigarette smoke condensates (CSC) induced an increase in FC incorporation, providing evidence of their role in enhancing the squamous pathway. Analysis by flow cytometry was used to provide a quantitative assessment of a range of optimised squamous differentiation markers, identified in normal human bronchial epithelia and in a bronchial cell line. Transglutaminase I was induced in a time-dependent manner, in post-confluent cells induced to differentiate down the squamous pathway, whereas involucrin was ubiquitously expressed and the levels of cytokeratins 5, 6 and 18 were reduced. The response of these and other differentiation markers to squamous-inducing conditions is being explored.

The Development of a Standardised Protocol to Measure Squamous Differentiation in Stratified Epithelia, by using the Fluorescein Cadaverine Incorporation Technique

Fluorescein cadaverine (FC) incorporation into cornified envelopes during squamous differentiation in stratified epithelia acts as a fluorescent substitute for endogenous transglutaminase substrates that can be visualised and quantified. The FC incorporation technique has been used to evaluate squamous differentiation in keratinocytes cultured in a medium that stimulates differentiation and in response to modulation by chemicals. A Standard Operating Procedure for the measurement of squamous differentiation is required as part of the prevalidation procedure for in vitro assays. In the present study, keratinocytes were isolated from the epidermis of 34 human donors. Cellular metabolic activity (resorufin production), total protein (kenacid blue uptake) and transglutaminase activity (FC incorporation) were measured in 87 and 21 independent runs at 6 and 12 days, respectively. Analysis of the control data showed that the cultures had a mean resorufin production that decreased over 12 days. This was inversely related to FC incorporation, which increased over 12 days. Mean protein concentration was reduced over the 12 days, but not in analyses that used donors for whom both 6-day and 12-day data were available. This information was used to define the normal limits within which the data should fall (mean +/- 1 SD). Data sets falling outside the normal limits performed statistically no differently from the normal responders, in experiments conducted to investigate the effects of chemicals on the modulation of squamous differentiation in keratinocytes. This was demonstrated by using compounds that modify transglutaminase expression and/or activity. All-trans retinoic acid significantly inhibited FC incorporation, but stimulated resorufin production at 1 x 10(-7)M and above. Nicotine significantly up-regulated both FC incorporation and resorufin production at 125 microg/ml. Hence, it was concluded that this robust assay approach, in which keratinocytes from a range of donors respond predictably to the test chemicals employed, did not justify the limitations that would be imposed by setting criteria that eliminated all data lying outside the normal range.

Heavy Cigarette Smokers in a Chinese Population Display a Compromised Permeability Barrier

Cigarette smoking is associated with various cutaneous disorders with defective permeability. Yet, whether cigarette smoking influences epidermal permeability barrier function is largely unknown. Here, we measured skin biophysical properties, including permeability barrier homeostasis, stratum corneum (SC) integrity, SC hydration, skin surface pH, and skin melanin/erythema index, in cigarette smokers. A total of 99 male volunteers were enrolled in this study. Smokers were categorized as light-to-moderate (<20 cigarettes/day) or heavy smokers (≥20 cigarettes/day). An MPA5 was used to measure SC hydration and skin melanin/erythema index on the dorsal hand, forehead, and cheek. Basal transepidermal water loss (TEWL) and barrier recovery rates were assessed on the forearm. A Skin-pH-Meter pH900 was used to measure skin surface pH. Our results showed that heavy cigarette smokers exhibited delayed barrier recovery after acute abrogation (1.02% ± 13.06 versus 16.48% ± 6.07), and barrier recovery rates correlated negatively with the number of daily cigarettes consumption (p = 0.0087). Changes in biophysical parameters in cigarette smokers varied with body sites. In conclusion, heavy cigarette smokers display compromised permeability barrier homeostasis, which could contribute, in part, to the increased prevalence of certain cutaneous disorders characterized by defective permeability. Thus, improving epidermal permeability barrier should be considered for heavy cigarette smokers.

Occluded Cigarette Smoke Exposure Causing Localized Chloracne-Like Comedones

Many environmental acne disorders, including chloracne and oil acne, were previously thought to occur predominantly in occupational settings following polycyclic aromatic hydrocarbon exposure. Cigarette smoke has also been shown to contain a large number of these toxic polycyclic aromatic hydrocarbon components and strictly correlates with noninflammatory acneiform lesion development in postadolescent patients. We report a case of localized open comedones associated with occluded cigarette smoke exposure near the nasal cavity due to infrequently changed gauze following rhinectomy. The dermal uptake of polycyclic aromatic hydrocarbon components in cigarette smoke has the potential to function as a contributing factor in chloracne development. Several of these environmental and noninflammatory acne subtypes may share a common molecular propensity for enhanced comedogenesis originating from aryl hydrocarbon receptor pathway effects in the skin. Additional studies are needed to further elucidate the exact mechanistic pathways through which tobacco smoke impacts the integumentary system.

Preclinical alterations of oral epithelial cells in contact with orthodontic appliances

AIM

This study evaluated the behavior of oral epithelial cells in contact with orthodontic appliances.

METHODS

Oral epithelial cells of clinically normal buccal mucosa were obtained by liquid-based exfoliative cytology from 22 orthodontic patients. The following regions were evaluated: a) oral mucosa exposed to friction from orthodontic brackets; b) oral mucosa exposed to friction from the tube on the orthodontic band, and c) oral mucosa not exposed to friction (control area). Nuclear (NA) and cytoplasmic (CA) areas and NA/CA ratio were assessed by an image analysis system. Cell morphology and cellularity were also analyzed by Papanicolaou technique.

RESULTS

The NA of the cells in contact with orthodontic brackets and bands were smaller than the control area. Cells in contact with the brackets showed the greatest reduction in CA in comparison with the cells subjected to friction from the tube, and the control group. Smears classified as type I predominated in all regions analyzed, although type II were predominant, together with superficial epithelial cells, mainly in the oral mucosa in contact with the band tube.

CONCLUSION

Preclinical alterations in the epithelial cells of oral mucosa, caused by orthodontic appliances, are reduction in NA, increase in cell keratinization and inflammatory features, especially in the band tube area.

Chronic exposure to cigarette smoke increases matrix metalloproteinases and Filaggrin mRNA expression in oral keratinocytes: role of nicotine stimulation

The vegetal alkaloid nicotine has been proved to modify the expression of many keratinocyte markers. In this study, the basal expression of MMP-2, MMP-9, MMP-28, and Filaggrin has been evaluated in oral keratinocytes, in order to collect information about the ability of cigarette smoke to modify the basal expression pattern of these key enzymes in the absence of evident clinical signs in the oral epithelium. MMP-2, MMP-9, MMP-28, and Filaggrin basal expression was investigated by RT-PCR in oral keratinocytes derived from smokers (n=11), non-smokers (n=11), and ex-smokers (n=6) healthy volunteers. Moreover keratinocytes from non-smokers volunteers were stimulated in vitro by a single dose administration of nicotine (10 μM) in order to estimate the effect of nicotinic receptors activation on the basal expression of the studied markers. RT-PCR analysis showed that all the markers studied were overexpressed in keratinocytes from smoker donors compared to control keratinocytes, while a single dose of nicotine was able to induce only Filaggrin expression in keratinocytes from non-smoking donors. Markers expression in ex-smoker donors was similar to that observed in normal non-smoker donors. These data indicate for the first time that cigarette smoking affects basal expression of some important markers in oral mucosa keratinocytes in vivo in the absence of clinical signs and that smoke quitting restores basal expression levels of these markers.

Influence of the mesenchymal cell source on oral epithelial development

The extent of the influence of mesenchymal tissue on epithelial development is still debated, and elucidation of epithelial-mesenchymal interactions should be of relevance for controlling normal as well as pathological growth and development. The aim of the present study was to elucidate the influence of the mesenchymal cell type on oral mucosa epithelial development in vitro, using tissue-engineering principles, by including three different sources for mesenchymal cell type, viz. oral mucosa, skin and cornea, each of them presenting a distinct type of epithelium in situ. We investigated epithelial-mesenchymal interactions, considering both morphological criteria and protein expression (filaggrin, keratin 10, keratin 12, keratin 13 and laminin 5). The results of the histology, immunohistochemistry and transmission electron microscopy of the three types of tissue-engineered constructs composed of mesenchymal cells of different sources (oral, dermal and corneal fibroblasts) and of the same oral epithelial cells showed that the mesenchymal cell source had a significant influence on the thickness and ultrastructure of the epithelium, but not on the differentiation of oral epithelial cells, which might be an intrinsic property of these cells due to their genetic programming.

Nicotine induces upregulated expression of beta defensin-2 via the p38MAPK pathway in the HaCaT human keratinocyte cell line

Human beta-defensins (hBDs), a group of antimicrobial peptides, are involved in the protective barrier of the oral epithelium. Nicotine induces periodontal and oral epithelial diseases. The purpose of the present study was to investigate the effect of nicotine on the expression pattern of hBD-2 in keratinocytes. HaCaT cells, a keratinocyte cell line, were incubated with 8, 15, 30, or 80 μM nicotine for 24 h. Expression of hBD-2 was observed by RT-PCR, qRTPCR, and ELISA assay. The cells were treated with inhibitors for intracellular pathways (p38MAP kinase, NF-κB, JNK, MAPK-ERK) and with nicotinic acetylcholine receptor (nAChR) inhibitors in a series of experiments. Data were analyzed using Student's t test. qRT-PCR revealed that the expression level of hBD-2 mRNA was significantly higher at 30 and 80 μM nicotine than the control without nicotine (P < 0.05). The 80 μM cell extraction contained significantly higher hBD-2 peptide levels than the control (P < 0.05). The p38MAP kinase inhibitor abolished the upregulated expression of hBD-2 by nicotine. Both nAChR inhibitors also abolished the upregulation of hBD-2 by nicotine. The present study demonstrated that nicotine causes upregulated expression of hBD-2 via the p38MAP kinase pathway in keratinocytes.

Receptor-mediated tobacco toxicity: acceleration of sequential expression of alpha5 and alpha7 nicotinic receptor subunits in oral keratinocytes exposed to cigarette smoke

Tobacco products and nicotine alter the cell cycle and lead to squamatization of oral keratinocytes (KCs) and squamous cell carcinoma. Activation of nicotinic acetylcholine receptors (nAChRs) elicits Ca(2+) influx that varies in magnitude between different nAChR subtypes. Normal differentiation of KCs is associated with sequential expression of the nAChR subtypes with increasing Ca(2+) permeability, such as alpha5-containing alpha3 nAChR and alpha7 nAChR. Exposure to environmental tobacco smoke (ETS) or an equivalent concentration of nicotine accelerated by severalfold the alpha5 and alpha7 expression in KCs, which could be abolished by mecamylamine and alpha-bungarotoxin with different efficacies, suggesting the following sequence of autoregulation of the expression of nAChR subtypes: alpha3(beta2/beta4) > alpha3(beta2/beta4)alpha5 > alpha7 > alpha7. This conjecture was corroborated by results of quantitative assays of subunit mRNA and protein levels, using nAChR-specific pharmacologic antagonists and small interfering RNAs. The genomic effects of ETS and nicotine involved the transcription factor GATA-2 that showed a multifold increase in quantity and activity in exposed KCs. Using protein kinase inhibitors and dominant negative and constitutively active constructs, we characterized the principal signaling cascades mediating a switch in the nAChR subtype. Cumulative results indicated that the alpha3(beta2/beta4) to alpha3(beta2/beta4)alpha5 nAChR transition predominantly involved protein kinase C, alpha3(beta2/beta4)alpha5 to alpha7 nAChR transition-Ca(2+)/calmodulin-dependent protein kinase II and p38 MAPK, and alpha7 self-up-regulation-the p38 MAPK/Akt pathway, and JAK-2. These results provide a mechanistic insight into the genomic effects of ETS and nicotine on KCs and characterize signaling pathways mediating autoregulation of stepwise overexpression of nAChR subtypes with increasing Ca(2+) permeability in exposed cells. These observations have salient clinical implications, because a switch in the nAChR subunit composition can bring about a corresponding switch in receptor function, leading to profound pathobiologic effects observed in KCs exposed to tobacco products.

Nicotine and biochanin A, but not cigarette smoke, induce anti-inflammatory effects on keratinocytes and endothelial cells in patients with Behçet's disease

During periods of smoking, patients with Behçet's disease have less oral aphthae than in abstinence. To elucidate this observation, human keratinocytes and dermal microvascular endothelial cells (HMEC-1) were incubated with serum of 20 patients with Behçet's disease and 20 healthy controls for 4 hours. Maximum non-toxic concentrations were determined and the cells were further treated with 6 microM nicotine, 3.3% cigarette smoke extract (CES), 100 microM biochanin A, and 6.25/12.5 microM pyrrolidine dithiocarbamate alone and in combinations for 24 hours. Serum IL-8 levels of patients were significantly lower than those of controls. However, after 4 hours incubation with patients' sera, IL-8 release by both cell types was markedly increased when compared with the corresponding serum levels. The levels of IL-6 and vascular endothelial growth factor (VEGF) release were after 4 hours similar with the corresponding levels in serum. IL-1 was not detected. Nicotine significantly decreased IL-8 and -6 release by HMEC-1 maintained in both patients' and controls' sera, but only IL-6 release by keratinocytes maintained in patients' sera. VEGF release by both cells was markedly increased after nicotine treatment in either serum. CES significantly decreased IL-8 release and increased production of VEGF in keratinocytes maintained in patients' serum. The phytoestrogen biochanin A alone and in combination with nicotine further decreased the secretion of IL-8, -6, and VEGF in all experimental settings. Our data support a specific anti-inflammatory effect of nicotine on keratinocytes and endothelial cells maintained in the serum of patients with Behçet's disease. Moreover, biochanin A is likely to exhibit similar and even more profound results than nicotine.

Receptor-mediated tobacco toxicity: cooperation of the Ras/Raf-1/MEK1/ERK and JAK-2/STAT-3 pathways downstream of alpha7 nicotinic receptor in oral keratinocytes

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.

Effects of nicotine on proliferation, cell cycle, and differentiation in immortalized and malignant oral keratinocytes

BACKGROUND

Numerous epidemiological studies have reported that tobacco smoking is a major risk factor for oral cancer, but relatively little is known about the effect of nicotine, a major product of cigarette smoking, on immortalized oral keratinocytes and cancer cells.

METHODS

We investigated the effects of nicotine on the growth and differentiation of immortalized human oral keratinocytes (IHOK), primary oral cancer cells (HN4), metastatic oral cancer cells (HN12), and human skin keratinocytes (HaCaT), in the monolayer and in the three-dimensional (3D) raft cultures using the MTT assay, Western blotting, and cell cycle analysis.

RESULTS

Nicotine inhibited the proliferation of immortalized and malignant keratinocytes in dose- and time-dependent manners as determined by MTT assay. The 3D organotypic culture showed that nicotine at high concentration (300 microM) inhibits epithelial maturation, surface keratinization, and decreased epithelial thickness. Flow cytometry showed that nicotine inhibited cell cycle progression by inducing G(0)/G(1) arrest of HaCaT, IHOK, HN4, and HN12 cells without causing apoptosis. Nicotine treatment increased p21 expression in immortalized cells (HaCaT, IHOK) and oral cancer cells (HN4, HN12), but decreased pRb and p53 expression in oral cancer cells. Moreover, after high-dose nicotine treatment, the involucrin expression increased markedly in immortalized cells, but not in oral cancer cells.

CONCLUSIONS

We demonstrated that nicotine inhibits growth through cell cycle arrest at G(0)/G(1) phase probably by increasing the expression of p21(WAF1/CIP1). Nicotine also affects epithelial differentiation in immortalized and malignant oral keratinocytes. Malignant oral keratinocytes appear to be more resistant to the effects of nicotine on epithelial growth and differentiation as compared to the immortalized cells.

Receptor-mediated tobacco toxicity: regulation of gene expression through alpha3beta2 nicotinic receptor in oral epithelial cells

Tobacco is a known cause of oral disease but the mechanism remains elusive. Nicotine (Nic) is a likely culprit of pathobiological effects because it displaces the local cytotransmitter acetylcholine from the nicotinic receptors (nAChRs) expressed by oral keratinocytes (KCs). To gain a mechanistic insight into tobacco-induced morbidity in the oral cavity, we studied effects of exposures to environmental tobacco smoke (ETS) versus equivalent concentration of pure Nic on human and murine KCs. Both ETS and Nic up-regulated expression of cell cycle and apoptosis regulators, differentiation marker filaggrin, and signal transduction factors at both the mRNA and protein levels. These changes could be abolished in cultured human oral KCs transfected with anti-alpha3 small interfering RNA or treated with the alpha3beta2-preferring antagonist alpha-conotoxin MII. Functional inactivation of alpha3-mediated signaling in alpha3-/- mutant KCs prevented most of the ETS/Nic-dependent changes in gene expression. To determine relevance of the in vitro findings to the in vivo situation, we studied gene expression in oral mucosa of neonatal alpha3+/+ and alpha3-/- littermates delivered by heterozygous mice soon after their exposures to ETS or equivalent concentration of pure Nic in drinking water. In addition to reverse transcriptase-polymerase chain reaction and Western blot, the ETS/Nic-dependent alterations in gene expression were also detected by semiquantitative immunofluorescence assay directly in KCs comprising murine oral mucosa. Only wild-type mice consistently developed significant (P < 0.05) changes in the gene expression. These results identified alpha3beta2 nAChR as a major receptor mediating effects of tobacco products on KC gene expression. Real-time polymerase chain reaction demonstrated that in all three model systems the common genes targeted by alpha3beta2-mediated ETS/Nic toxicity were p21, Bcl-2, NF-kappaB, and STAT-1. The expression of the nAChR subunits alpha5 and beta2 and the muscarinic receptor subtypes M(2) and M(3) was also altered. This novel mechanism offers innovative solutions to ameliorate the tobacco-related cell damage and intercede in disease pathways, and may shed light on general mechanisms regulating and driving tobacco-related morbidity in human cells.

Nicotine effects on skin: Are they positive or negative?

The adverse effects of tobacco on the skin are well known but the role of nicotine is more controversial. Nicotinic receptors are expressed in the skin, on keratinocytes, fibroblasts and blood vessels. Nicotine induces vasoconstriction associated with local hyperaemia. It inhibits inflammation through effects on central and peripheral nervous system and through direct effect on immune cells. It delays wound healing and accelerates skin aging. The role of nicotine on skin diseases remains unclear. Therapeutic effects of nicotine could be possible and this a new stimulating field of research.

Effects of individual characteristics on healthy oral mucosa autofluorescence spectra

Autofluorescence spectroscopy is a tool for detecting tissue alterations in vivo. In a previous study, we found spectral differences between clinically normal mucosa of different patient groups. These are possibly caused by associated patient characteristics. In the present study, we explore the influences of volunteer characteristics on healthy oral mucosa autofluorescence. Autofluorescence spectra were recorded in 96 volunteers with no clinically observable oral lesions. We applied principal components analysis to extract the relevant information. We used multivariate linear regression techniques to estimate the effect of volunteer characteristics on principal component scores. Statistically significant differences were found for all factors but age. Skin color strongly affected autofluorescence intensity. Gender differences were found in blood absorption. Alcohol consumption was associated with porphyrin-like peaks. However, all differences but those associated with skin color were of the same order of magnitude as standard deviations within categories. The effects of volunteer characteristics on autofluorescence spectra of the oral mucosa are measurable. Only the effects of skin color were large. Therefore, in lesion classification, skin color should be taken into account.

Synergistic control of keratinocyte adhesion through muscarinic and nicotinic acetylcholine receptor subtypes

The biological mechanisms involved in initiating, coordinating, and ultimately terminating cell-cell adhesion in the stratified epithelium are not well understood at present. This study was designed to elucidate the roles of the muscarinic M3, the nicotinic alpha3, and the mixed muscarinic-nicotinic alpha9 acetylcholine receptors in physiologic control of keratinocyte adhesion. Both muscarinic and nicotinic antagonists caused keratinocyte detachment and reversibly increased the permeability of keratinocyte monolayers, indicative of the involvement of both muscarinic and nicotinic pathways in the cholinergic control of keratinocyte adhesion. Since phosphorylation of adhesion proteins plays an important role in rapid assembly and disassembly of intercellular junctions, we measured muscarinic and nicotinic effects on phosphorylation of keratinocyte adhesion molecules. The phosphorylation levels of E-cadherin, beta-catenin, and gamma-catenin increased following pharmacological blockage of muscarinic receptors. Long-term blocking of alpha3, alpha9, and M3 receptor signaling pathways with antisense oligonucleotides resulted in cell-cell detachment and changes in the expression levels of E-cadherin, beta-catenin, and gamma-catenin in cultured human keratinocytes. Simultaneous inhibition of several receptor subtypes with a mixture of antisense oligonucleotides produced intensified abnormalities with cell adhesion. Moreover, altered cell-cell adhesion was found in the stratified epithelium of alpha3, alpha9, and M3 receptor knockout mice. Keratinocytes from these mice exhibited abnormal expression of adhesion molecules at both the protein and the mRNA levels. Thus, our data indicate that the alpha3, alpha9, and M3 acetylcholine receptors play key roles in regulating in a synergistic mode keratinocyte adhesion, most probably by modulating cadherin and catenin levels and activities. These findings may aid in the development of novel methods useful for the treatment of skin adhesion diseases and tumor metastasis.

Effects of snuff extract on epithelial growth and differentiation in vitro

Snuff is a locally irritative agent causing hyperkeratinization and hyperplasia of the oral epithelium. The aim of the study was to investigate the effects of snuff on epithelial cell growth and differentiation in vitro. Three-dimensional HaCaT cell cultures were grown for 6, 12, 14, and 18 days in the presence of 1% snuff extract. Ki-67, p53 and cytokeratins (Cks) 5, 13, 10, 19, 18, involucrin and filaggrin were studied by means of immunohistochemistry. Ki-67 indices were assessed, and the results analyzed statistically. Marked morphologic changes were seen with advanced culture time in the snuff group, probably as a result of increased toxic effects. Snuff exposure decreased the percentage of Ki-67 positive cells on days 6, 12, and 14, suggesting that snuff does not stimulate proliferation activity in this in vitro model. Cornification-related Ck 10 decreased after snuff exposure, indicating disturbances in the epithelial differentiation process.

Central role of fibroblast alpha3 nicotinic acetylcholine receptor in mediating cutaneous effects of nicotine

Smoking is associated with aberrant cutaneous tissue remodeling, such as precocious skin aging and impaired wound healing. The mechanism is not fully understood. Dermal fibroblasts (DF) are the primary cellular component of the dermis and may provide a target for pathobiologic effects of tobacco products. The purpose of this study was to characterize a mechanism of nicotine (Nic) effects on the growth and tissue remodeling function of DF. We hypothesized that the effects of Nic on DF result from its binding to specific nicotinic acetylcholine receptors (nAChRs) expressed by these cells and that downstream signaling from the receptors alters normal cell functioning, leading to changes in skin homeostasis. Using RT-PCR and Western blotting, we found that a 24-hour exposure of human DF to 10 micro M Nic causes a 1.9- to 28-fold increase of the mRNA and protein levels of the cell cycle regulators p21, cyclin D1, Ki-67, and PCNA and a 1.7- to 2-fold increase of the apoptosis regulators Bcl-2 and caspase 3. Nic exposure also up-regulated expression of the dermal matrix proteins collagen type Ialpha1 and elastin as well as matrix metalloproteinase-1. Mecamylamine (Mec), the specific antagonist of nAChRs, abolished Nic-induced alterations, indicating that they resulted from a pharmacologic stimulation of nAChRs expressed by DF. To establish the relevance of these findings to a specific nicotinergic pathway, we studied human DF transfected with anti-alpha3 antisense oligonucleotides and murine DF from alpha3 nAChR knockout mice. In both cases, lack of alpha3 was associated with alterations in fibroblast growth and function that were opposite to those observed in DF treated with Nic, suggesting that the nicotinic effects on DF were mostly mediated by alpha3 nAChR. In addition to alpha3, the nAChR subunits detected in human DF were alpha5, alpha7, beta2, and beta4. The exposure of DF to Nic altered the relative amounts of each of these subunits, leading to reciprocal changes in [(3)H]epibatidine-binding kinetics. Thus, some of the pathobiologic effects of tobacco products on extracellular matrix turnover in the skin may stem from Nic-induced alterations in the physiologic control of the unfolding of the genetically determined program of growth and the tissue remodeling function of DF as well as alterations in the structure and function of fibroblast nAChRs.

Nicotine permeability across the buccal TR146 cell culture model and porcine buccal mucosa in vitro: effect of pH and concentration

The present study was conducted to investigate and compare the effect of pH and drug concentration on nicotine permeability across the TR146 cell culture model and porcine buccal mucosa in vitro. As a further characterization of the TR146 cell culture model, it was explored whether the results were comparable for bi-directional and uni-directional transport in the presence of a transmembrane pH gradient. Nicotine concentrations between 10(-5) and 10(-2) M were applied to the apical side of the TR146 cell culture model or the mucosal side of porcine buccal mucosa. Buffers with pH values of 5.5, 7.4 and 8.1 were used to obtain different fractions of non- and mono-ionized nicotine. The apparent permeability (P(app)) of nicotine across both models increased significantly with increasing pH, and the P(app) values obtained with the two models could be correlated in a linear manner. With increasing concentrations of nicotine, the P(app) values decreased, which can partly be explained by an effect on the paracellular pathway. Similar results were also obtained when using the models for bi-directional as well as for uni-directional studies. The TR146 cell culture model may be used as model for buccal epithelium in studies with ionized drugs and a transmembrane pH gradient.

A receptor-mediated mechanism of nicotine toxicity in oral keratinocytes

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 alpha3, alpha5, alpha7, beta2, and beta4 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.

Organotypic cultures of gingival cells: an epithelial model to assess putative local effects of orthodontic plate and occlusal splint materials under more tissue-like conditions

This article explores whether organotypic cultures of immortalized gingival keratinocytes constitute a suitable model for assessing the epithelial cell compatibility of two groups of dental resins, each of them representing one group used in orthodontics and temporo-mandibular disorders (TMD) therapy under conditions more closely resembling the actual tissue situation. The resins were tested with the agar diffusion assay (ADA) in conventional monolayer and organotypic cultures. Compared to the control exhibiting a neutral red destaining index of 3, the index of 4 obtained after exposure of monolayers to one soft permanent resin (Durabase) indicated the presence of a non-lytic but physiologically active substance. In contrast, the adaptation of the ADA to organotypic cultures revealed no apparent lesions at the epithelial surface by performing scanning electron microscopy, while histoarchitecture indicated the development of stratified surface epithelia. This was substantiated by undamaged cells in the uppermost cell layers and by the preservation of cell-to-cell contacts. Furthermore, indirect immunofluorescence for Ki-67 and the cytokeratins ck 14 and ck4 revealed that cell proliferation and epithelial structure were maintained, while differentiation was enhanced, possibly increasing epithelial resistance. The results obtained from the organotypic cultures suggest that (i) cell-affecting effects of materials visible in monolayer cultures may not be seen in epithelia resembling that in vivo and that (ii) enhanced differentiation may be associated with increased stability of the epithelial cells. Thus, organotypic cultures of gingival cells constitute a tissue model allowing short-term tissue compatibility studies of dental materials and rendering a potential candidate also for long-term studies.

Choline acetyltransferase, acetylcholinesterase, and nicotinic acetylcholine receptors of human gingival and esophageal epithelia

A non-neuronal cholinergic system that includes neuronal-like nicotinic acetylcholine receptors (nAChRs) has recently been described in epithelial cells that line the skin and the upper respiratory tract. Since the use of nicotine-containing products is associated with morbidity in the upper digestive tract, and since nicotine may alter cellular functions directly via nAChRs, we sought to identify and characterize a non-neuronal cholinergic system in the gingival and esophageal epithelia. mRNA transcripts for alpha3, alpha5, alpha7, and beta2 nAChR subunits, choline acetyltransferase, and the asymmetric and globular forms of acetylcholinesterase were amplified from gingival keratinocytes (KC) by means of polymerase chain-reactions. These proteins were visualized in the gingival and esophageal epithelia by means of specific antibodies. Variations in distribution and intensity of immunostaining were found, indicating that the repertoire of cholinergic enzymes and receptors expressed by the cells changes during epithelial maturation, and that an upward concentration gradient of free acetylcholine exists. Blocking of the nAChRs with mecamylamine resulted in reversible loss of cell-to-cell adhesion, and shrinking and rounding of cultured gingival KC. Activation of the receptors with acetylcholine or carbachol caused stretching and peripheral ruffling of the cytoplasmic aprons, and formation of new intercellular contacts. These results demonstrate that both the keratinizing epithelium of attached gingiva and the non-keratinizing epithelium lining the upper two-thirds of the esophageal mucosa possess a non-neuronal cholinergic system. The nAChRs expressed by these epithelia are coupled to regulation of cell adhesion and motility, and may provide a target for the deleterious effects of nicotine.