Role of nitric oxide in the induction of apoptosis by smokeless tobacco extract

Cytotoxicity, oxidative stress, and inflammatory response of smokeless tobacco extracts and cytotoxicity of combustible cigarette whole smoke in a 3D oral organotypic buccal cell model

Oral disease is frequently associated with viral and environmental exposures and oral hygiene. The use of tobacco is a risk factor in the development of oral disease. Cytotoxicity, inflammatory response, and oxidative stress have been reported to have a role in the development of oral disease. These three endpoints were evaluated in a 3D human oral buccal model, EpiOral™, following exposure to CORESTA reference smokeless tobacco products (CRPs) and cigarette whole smoke. CRPs for Swedish style snus (CRP1), moist snuff (CRP2), and dry snuff (CRP3) were each extracted in complete artificial saliva (CAS) with a ratio of 300 mg CRP to 1 mL of CAS. Each of the CRP extracts (15-300 mg/ml) were applied to the apical side of a 3D organotypic buccal cell model for 24 or 48 h continuously, then cytotoxicity (LDH), oxidative stress (8-isoprostane), and inflammatory response (IP10, IL-1α, and IL-8) were measured. Experiments with 3R4F cigarettes were conducted by exposing the buccal tissues to whole smoke for a maximum of 2.5 h. Cytotoxicity (MTT) was measured 24 h post-exposure. Exposure of buccal tissues to whole smoke from a cigarette induced a dose-dependent cytotoxic response. In contrast, the CRP extracts elicited minimal cytotoxicity (<15%) when compared to CAS (vehicle control), but time- and dose-dependent effects on oxidative stress and inflammatory response were observed. Collectively, these data demonstrate that a 3D organotypic buccal human model may be used to assess biological mechanisms (MOAs) involved in the development of oral disease following exposure to smokeless tobacco products and may be applicable for differentiation between tobacco product categories.

Aqueous extract of tobacco induces mitochondrial potential dependent cell death and epithelial-mesenchymal transition in gingival epithelial cells

Smokeless tobacco habits are detrimental to oral health. A correlation between tobacco use and local epithelial tissue damage exists. Yet, the underlying cellular mechanism is not precisely characterized. This study assessed the dose-dependent action of Smokeless tobacco extract on gingival epithelial cells. Gingival tissue was taken from 5 healthy donors. Gingival epithelial cells were isolated by an enzymatic method and cultured up to passage 2. The cultured cells were treated with smokeless tobacco extract at 10%, 25%, 50%, and 75% volume concentration. After 48 h of incubation, MTT assay, Annexin V/PI assay, and DiIC1(5) assay were used to evaluate viability, apoptosis, and mitochondrial potential of the cells. RT-qPCR was used to determine the expression of BAX, BCL2, ECAD, NCAD, and TWIST. The Smokeless tobacco extract reduced cell viability by disrupting the mitochondrial potential and inducing apoptosis. Further, the Smokeless tobacco extract induced a dose-dependent epithelial-mesenchymal-transition in gingival epithelial cells. Apoptotic cellular death caused by tobacco extract on the gingival epithelial system was dependant on the mitochondrial potential of the cell. The results demonstrate that smokeless tobacco causes detrimental metabolic alterations of the periodontium.

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This study elucidates the mechanism by which Smokeless tobacco products cause cellular damage to the gingival epithelium. The use of Smokeless tobacco products can lead to major cellular and surface changes in the gingiva and its appearance. The consequences of these changes are not limited to oral cancer but also increases a person's risk for dental and periodontal disease.

Effects of smokeless tobacco on cell viability, reactive oxygen species, apoptosis, and inflammatory cytokines in human umbilical vein endothelial cells

Smokeless tobacco products provide an alternative to cigarettes; however, smokeless tobacco is carcinogenic and harmful to human health. This study evaluated the toxicological effects of snus extracts and cigarette smoke total particulate matter (TPM) on human umbilical vein endothelial cells (HUVECs). Treated cells were examined for cell viability, reactive oxygen species (ROS), apoptosis, and inflammatory cytokines. Moreover, we explored the mechanism of programmed cell death induced by snus. The results showed that snus extracts significantly inhibited cell viability in a dose-dependent manner. ROS was significantly increased in treatment groups, and anti-oxidant treatment could not prevent snus extract-induced cell death. Snus extracts induced apoptosis, DNA damage, activation and cleavage of caspase-3 and caspase-8, pathway-related gene change, and interleukin (IL)-6 and IL-8 release in HUVECs. Snus extracts exposure may induce cytotoxicity, ROS generation, inflammatory cytokines release, and apoptosis or DNA damage through intrinsic and extrinsic pathways in HUVECs.

N, K. S, C. VK, K. ND, C. SK, Maddu N. Smokeless tobacco induced biophysical and biochemical alterations in the plasma, erythrocytes, and platelets of panmasala users: Subsequent biological effects

AIM & BACKGROUND

Smokeless tobacco (SLT) products are extensively consumed throughout the world including India. These products act as the primary addictive agents, due to the presence of nicotine among other tobacco products to humans and animals and its quitting is difficult. Higher the exposure of SLT products more is the toxic effects and alterations in erythrocytes and platelets.

OBJECTIVES

The products of smokeless tobacco could cause increase in the concentrations of oxidants (free radicals), decrease the activities antioxidant enzymes, activate the process of programmed cell death through enhanced expression of inducible nitric oxide synthase. Smokeless tobacco products represent a major modifiable risk factor for the development of redox imbalance through the enhanced production of reactive oxygen species and diminished activities of antioxidant enzymes in plasma, bio-membranes of erythrocytes, and platelets and induction of apoptosis in the blood.

MATERIALS AND METHODS

The protein expression of inducible nitric oxide synthase (iNOS) was studied by western blot and gene expression of apoptotic proteins, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) was evaluated by RT-PCR technique. Membrane fluidity of erythrocytes and platelets was studied by the fluorescence method.

RESULTS

The results of the present study revealed that significantly elevated levels of iNOS enzyme in plasma, erythrocyte, and platelet membranes of panmasala users. We found that gene expression levels of Bcl2, Bax, IL-6, caspase proteins (Caspase 8, Caspase 10, and Caspase 12) are greater and decreased levels of TNF-α with no significant change in blood of smokeless tobacco users in comparison with normal controls. In addition, there were substantial significantly higher in concentrations of nicotine, cotinine, and epinephrine in the plasma of panmasala users than non-tobacco users. Panmasala can be caused a significant increase in nitroxidative stress marker (LPO, NO, and ONOO-) values and significant decrease in the levels of antioxidant enzymes in erythrocytes and platelets.

CONCLUSION

On the basis of the present study results, it may be concluded that the chronic use of panmasala than any smokeless tobacco products may be a contributory risk factor or may give conclusive idea and has been associated with the expansion of the development of structural and functional alterations in the erythrocyte and platelet membranes induced oxidative damage and apoptosis, possibly further enhanced by nicotine and tobacco-specific N-nitrosamines. SLT exposure had implicated a threat and enormous implications on public health and is required to prove that may not be viewed as a safe alternative to any tobacco products.

Smokeless tobacco extract inhibits proliferation and promotes apoptosis in oral mucous fibroblasts

The consumption of smokeless tobacco extract (STE) is growing rapidly, and it has been implicated in several human diseases including diabetes, inflammation and a number of types of cancer. The toxicity of STE requires evaluation, as it is known to induce numerous public health issues. To investigate whether STE serves a role in cultured human oral mucosa fibroblasts (hOMFs), the present study examined HOMF morphology with inverted microscopy and immunofluorescence staining. The cell viability was measured with MTT assays, which detected the cell apoptosis rate via flow cytometry. The activities of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) were measured via flow cytometry and commercial kits, subsequent to exposing the cells to various concentrations of STE. Reverse transcription quantitative polymerase chain reaction and western blot analyses were used to demonstrate that the mRNA and the protein expression levels of cell cycle-associated genes (cyclin-dependent kinase inhibitor 1 and cyclin D1), apoptosis-associated genes [B cell lymphoma 2 (Bcl-2) and Bcl-2-associatied X protein], tumor protein (p53), nuclear factor kappa light chain enhancer of activated B cells (NF-κB)-transcription factor (p65) signaling pathways, NF-E2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and NAD(P)H: quinoneoxidoreductase1 (NQO1). The results indicated that the hOMF cells were positive for cytokeratin staining. STE induced G1-S cell cycle progression and cell apoptosis by regulating the cell cycle or apoptosis-associated proteins. STE treatment increased the concentrations of ROS and MDA, and decreased the concentrations of SOD and CAT. STE unregulated phosphorylated-p53, NF-κB p65, Nrf2, HO-1, and NQO1 expression levels in the hOMF cells. The present study demonstrated that STE appears to promote oral disease.

Evaluation of in vitro assays for assessing the toxicity of cigarette smoke and smokeless tobacco

BACKGROUND

In vitro toxicology studies of tobacco and tobacco smoke have been used to understand why tobacco use causes cancer and to assess the toxicologic impact of tobacco product design changes. The need for toxicology studies has been heightened given the Food and Drug Administration's newly granted authority over tobacco products for mandating tobacco product performance standards and evaluate manufacturers' health claims about modified tobacco products. The goal of this review is to critically evaluate in vitro toxicology methods related to cancer for assessing tobacco products and to identify related research gaps.

METHODS

PubMed database searches were used to identify tobacco-related in vitro toxicology studies published since 1980. Articles published before 1980 with high relevance also were identified. The data were compiled to examine (a) the goals of the study, (b) the methods for collecting test substances, (c) experimental designs, (d) toxicologic end points, and (e) relevance to cancer risk.

RESULTS

A variety of in vitro assays are available to assess tobacco smoke that address different modes of action, mostly using non-human cell models. However, smokeless tobacco products perform poorly in these assays. Although reliable as a screening tool for qualitative assessments, the available in vitro assays have been poorly validated for quantitative comparisons of different tobacco products. Assay batteries have not been developed, although they exist for nontobacco assessments. Extrapolating data from in vitro studies to human risks remains hypothetical.

CONCLUSIONS

In vitro toxicology methods are useful for screening toxicity, but better methods are needed for today's context of regulation and evaluation of health claims.

Adverse effects of Sudanese toombak vs. Swedish snuff on human oral cells

BACKGROUND

The high incidence of oral cancer in Sudan has been associated with the use of toombak, the local type of smokeless tobacco. However, its specific effects on human oral cells are not known. We aimed to investigate the effects of toombak on primary normal human oral keratinocytes, fibroblasts, and a dysplastic oral keratinocytic cell line, and to compare them with the effects induced by Swedish snuff.

METHOD

Aqueous extracts were prepared from moist toombak and Swedish snuff and added in serial dilutions on in vitro monolayer cultured cells. Cell viability, morphology and growth, DNA double-strand breaks (gammaH2AX staining), expression of phosphatidylserine (Annexin V staining), and cell cycle were assessed after various exposure time periods.

RESULTS

Significant decrease in cell number, occurrence of DNA double-strain breaks, morphological and biochemical signs of programmed cell death were detected in all oral cell types exposed to clinically relevant dilutions of toombak extract, although to a lesser extent in normal oral fibroblasts and dysplastic keratinocytes. G2/M-block was also detected in normal oral keratinocytes and fibroblasts exposed to clinically relevant dilutions of toombak extract. Swedish snuff extract had less adverse effects on oral cells, mainly at non-clinically relevant dilutions.

CONCLUSION

This study indicates a potential for toombak, higher than for Swedish snuff, to damage human oral epithelium. Dysplastic oral keratinocytes were less sensitive than their normal counterparts, suggesting that they might have acquired a partially resistant phenotype to toombak-induced cytotoxic effects while still being prone to DNA damage that could lead to further malignant progression.

Increased inducible nitric oxide synthase in lung carcinoma of smokers

BACKGROUND

Cigarette smoking is well known to play an important role in the development of lung cancer. Inducible nitric oxide synthase (iNOS) can either promote or inhibit cell proliferation and growth, which makes its role in the development of malignant tumors controversial. The relation between cigarette smoking and iNOS in human lung cancer is unknown.

METHODS

The study examined the levels of iNOS/NO in nonsmall-cell lung cancer (NSCLC) tissues of smokers and nonsmokers and in NSCLC cells (NCI-H23) treated by 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a potent tobacco-specific carcinogen.

RESULTS

The level of iNOS/NO was significantly higher in lung cancer tissues of smokers than that of nonsmokers. Unlike iNOS/NO, the activity of caspase-3 was reduced in the former compared with the latter. The expression of the cleaved caspase-3 was deceased in NCI-H23 cells treated with S-Nitroso-N-acetylpenicillamine (SNAP), an NO donor, whereas treatment with NG-methyl-L-arginine (NMA), an NO inhibitor, caused an increase in cleaved caspase-3. Consistent with the change in caspase-3, SNAP treatment inhibited cell death induced by UCN01, a potent cell death-inducer. NMA treatment greatly enhanced the sensitivity of the cells to UCN01. Further, the cells treated by NNK showed an increase in iNOS protein, accompanied by an elevation of cell proliferation.

CONCLUSIONS

The study demonstrates that cigarette smoking promotes the level of iNOS/NO but suppresses the activity of caspase-3, which may lead to the proliferation and growth of lung cancer cells.

Inhibition of nitric oxide-induced apoptosis by nicotine in oral epithelial cells

Development of oral cancer is clearly linked to the usage of smokeless tobacco. The molecular mechanisms involved in this process are however not well understood. Toward this goal, we investigated the effect of smokeless tobacco exposure on apoptosis of oral epithelial cells. Exposure of oral epithelial cells to smokeless tobacco extract (STE) induces apoptosis in a dose-dependent manner, until a threshold level of nicotine is achieved upon which apoptosis is inhibited. 1 mM of nicotine is able to inhibit apoptosis significantly induced by STE in these oral cells. Exposure of cells to nicotine alone has no effect on apoptosis, but nicotine inhibits apoptosis induced by other agents present in STE. In this study we show that, the anti-apoptotic action of nicotine is specifically associated with down-regulation of nitric oxide (NO) production. Using specific inducers of NO, we have demonstrated that inhibition of apoptosis by nicotine is through down-regulation of NO production. Further, we observed that nicotine clearly acts as a sink of NO radicals, shown using peroxynitrite generator (SIN-1) in conjunction or absence of radical scavengers. Nicotine thus causes most damage in transformed epithelial cells as depicted by accumulation of nitrotyrosine in a 3-NT ELISA assay. Inhibition of apoptosis is a hallmark in tumor progression and propels development of cancer. It may further result in functional loss of apoptotic effector mechanisms in the transformed cells. Thus, our data clearly indicates that inhibition of NO-induced apoptosis by nicotine may lead to tobacco-induced oral carcinogenesis, and implies careful development of modalities in tobacco cessation programs.

Clinical, pathological, cellular and molecular lesions caused by oral smokeless tobacco - a review

While carcinogenicity of smokeless tobacco (ST) to humans is well established the oral lesions that precede development of cancer are less well characterized. The clinical appearances of ST-associated lesions are variable. Epidemiological studies show a strong significant association of risk with chronic daily use but population differences are noted because of various commercial products in use. Morphological features observed are some what different to oral lesions caused by smoking and oral dysplasia in ST-associated lesions is less common. Effects of ST on oral keratinocytes observed in vitro include alterations in cell proliferation, apoptosis and activation of inflammatory markers. Genetic aberrations caused by ST include activation of ras, uncommon in smokers but mutational hot spots in p53 encountered are similar to those in smokers.

Modulation of annexin I and cyclooxygenase-2 in smokeless tobacco-induced inflammation and oral cancer

Smokeless tobacco usage is a growing public health concern in the United States. Epidemiological evidence shows a correlation between use of chewing tobacco, lesions of the oral cavity and the incidence of oral and other cancers. However, the molecular mechanism(s) underlying the oral cancer causation are yet unknown. The major constituents of tobacco are known to cause inflammation, DNA damage and cell death. We propose modulation of inflammatory mediators by smokeless tobacco as a novel mechanism for the development of oral cancer. Exposure of hamster cheek pouches to smokeless tobacco extract (STE) results in cleavage of the anti-inflammatory peptide from the anti-inflammatory protein annexin I. Annexin I is produced from cultured oral epithelial cells and its expression is modulated by STE. We further show that STE exposure of oral epithelial cells results in upregulation of the pro-inflammatory protein COX-2. COX-2 is also upregulated in immortalized human oral epithelial cells, human squamous cell carcinoma cells and in primary tumor tissues from head and neck cancer. In summary, we find that exposure to smokeless tobacco results in loss of the anti-inflammatory activity of annexin I and upregulation of the pro-inflammatory COX-2 in oral cells. The dual effect of these regulatory events leads the cells down the carcinogenic pathway.