Effects of in vivo treatments of nicotine and benzo[a]pyrene on the epidermal growth factor receptor in hamster buccal pouch

In vitro testing of the responses of human gingival fibroblasts and L-929 cells to nicotine

Tobacco smoke is considered to be a major risk factor in the development of cardiac diseases and lung cancer. It has also been shown that periodontitis is more prevalent and more severe in smokers than in non-smokers. Nicotine, the major pyridine alkaloid in tobacco, has been shown to participate in periodontal disease, exerting both local and systemic effects. In the present study, the effects of nicotine (6μg/ml, 60μg/ml and 600μg/ml) on human gingival fibroblasts (HGF) were assessed by using various exposure protocols. The responses of HGF cultures obtained from smokers and non-smokers were compared to those found when using a continuous cell line (L-929). Neutral red uptake (NRU) and the measurement of DNA content with bis-benzimide dye were used to assess cell viability and cell number, respectively. NRU was the most sensitive technique for the detection of cytotoxic effects. L-929 cells were found to be affected by nicotine in the NRU assay, with a strong cytotoxic effect with 600μg/ml nicotine, and a "response" with 60μg/ml nicotine when prolonged or double challenge was applied. Non-smoker HGF and smoker HGF reacted to nicotine in different ways, depending on the concentrations and the exposure times used, but had identical reactions following double exposure. With the Hoechst DNA assay, 600μg/ml nicotine was found to affect the growth of non-smoker HGF after long or repeated exposure, while smoker HGF were affected only by repeated exposure; growth of L-929 cells was not affected. It was concluded that HGF from smokers are able to sustain higher concentrations of nicotine without adverse effects than are non-smoker HGF and L-929 cells. If this occurs in vivo, nicotine would not be considered to be a major toxicant to HGF in smokers.

Nicotine induces resistance to epidermal growth factor receptor tyrosine kinase inhibitor by α1 nicotinic acetylcholine receptor-mediated activation in PC9 cells

INTRODUCTION

Nicotine, the major component among the 4000 identified chemicals in cigarette smoke, binds to nicotinic acetylcholine receptors (nAChRs) on non-small-cell lung cancer (NSCLC) cells and regulates cellular proliferation by activating mitogen-activated protein kinases [AQ: MAPK has been expanded to mitogen-activated protein kinases. Please approve.]and PI3K/Akt pathways. In patients with smoking-related lung cancer who continue smoking, the anticancer effect of epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) is weaker than that in nonsmokers; however, the precise reason for this difference remains unclear. We investigated the role of α1 nAChR subunit in this phenomenon.

METHODS

We screened for α1 nAChR mRNA in three NSCLC cell lines and analyzed the protein in resected primary NSCLC tissues. We used Western blot and RNA interference (siRNA) methodology to confirm the results.

RESULTS

We determined that α1 nAChR plays an essential role in nicotine-induced cell signaling and nicotine-induced resistance to EGFR-TKI. In addition, we showed that silencing of α1 nAChR subunit in NSCLC may suppress the nicotine-induced resistance to EGFR-TKI.

CONCLUSIONS

These results further implicate nicotine in lung carcinogenesis, and suggest that α1 nAChR may be a biomarker for EGFR-TKI treatment and also a personalizing target molecule for patients with smoking-related lung cancer.

Nicotine promotes mammary tumor migration via a signaling cascade involving protein kinase C and CDC42

Nicotine, one of the major components in tobacco, is at high concentrations in the bloodstream of cigarette smokers. However, the mechanisms of how nicotine affects tumor development and whether nicotine is a potential carcinogen for malignancies induced by secondhand smoking are not fully understood yet. Here, we investigate the signaling pathways by which nicotine potentiates tumorigenesis in human mammary epithelial-like MCF10A or cancerous MCF7 cells. We show that human MCF10A and MCF7 cells both express four subunits of nicotine acetylcholine receptor (nAChR). The treatment of these cells with nicotine enhances the activity of protein kinase C (PKC) alpha without altering the expression level of this kinase. Nicotine also stimulates [(3)H]thymidine incorporation into the genome of these cells as well as forces serum-starved cells to enter S phase of the cell cycle, resulting in growth promotion. Importantly, on nicotine treatment, the mobility of MCF10A and MCF7 cells is enhanced, which can be blocked by the addition of nAChR or PKC inhibitor. Experiments using small interfering RNA knockdown or ectopic expression of cdc42 showed that cdc42 functions as a downstream effector of PKC and is crucial in the regulation of nicotine-mediated migratory activity in the cells. Together, our findings suggest that nicotine, through interacting with its receptor, initiates a signaling cascade that involves PKC and cdc42 and consequently promotes migration in mammary epithelial or tumor cells.

Nicotine promoted colon cancer growth via epidermal growth factor receptor, c-Src, and 5-lipoxygenase-mediated signal pathway

Nicotine [3-(1-methyl-2-pyrrolidinyl)-pyridine], a major alkaloid in tobacco, has been implicated as playing a role in carcinogenesis. Our previous study showed that passive cigarette smoking promoted inflammation-associated colonic adenoma formation in mice, and 5-lipoxygenase (5-LOX) plays an important role in this process. In the present study, we aimed to investigate whether nicotine could stimulate colon cancer cell proliferation and tumor growth in nude mice xenograft model and the possible mechanisms involved. Results showed that nicotine stimulated SW1116 colon cancer cell proliferation in a dose-dependent manner. Epidermal growth factor receptor (EGFR) and c-Src phosphorylation levels together with protein expression of 5-LOX were also significantly enhanced in this proliferation process. Inhibitors of EGFR and c-Src alleviated the actions of nicotine on cell proliferation and 5-LOX protein expression. Combination of both agents produced additive effect. In contrast, 5-LOX inhibitor had no direct effect on the phosphorylation levels of EGFR and c-Src and yet inhibited cell proliferation. In the colon cancer xenograft model, nicotine also significantly enhanced tumor growth. This acceleration of tumor growth corresponded well with increased vascularization and its proangiogenic factors. Inhibitors of EGFR, c-Src, and 5-LOX all significantly impeded the tumor growth induced by nicotine. Together, nicotine can promote colonic tumorigenesis both in vitro and in vivo. Activation of the phosphorylated form of EGFR and c-Src followed by an increased 5-LOX expression are the prime pathogenic mechanisms in the tumorigenic process in the colon.

Nicotine effects on proliferation and the bombesin-like peptide autocrine system in human small cell lung carcinoma SHP77 cells in culture

OBJECTIVES

To determine whether nicotine affects the proliferation and expression of the bombesin-like peptide autocrine system in human small cell lung carcinoma (SCLC) SHP77 cells compared with nonmalignant human bronchial epithelial BEAS 2B cells as non-neuroendocrine controls.

METHODS

Human lung cells were cultured in defined serum-free medium with various concentrations of nicotine added for various times. Proliferation was measured by cell counts and colorimetric assay, bombesin-like peptide receptor expression was assayed by specific binding assays and quantitative competitive PCR, and bombesin-like peptides determined by ELISA.

RESULTS

Nicotine significantly stimulated the growth of human SCLC SHP77 and NCI-H865 cells, but not BEAS 2B cells. Bombesin-like peptide receptor specific binding and mRNA expression were not affected by nicotine exposure in SHP77 cells or BEAS 2B cells. An increase in SHP77 cellular bombesin-like peptide content was observed.

CONCLUSIONS

Human SCLC SHP77 cells express the components of the bombesin-like peptide autocrine system. Increased proliferation in the presence of nicotine may be due in part to increased levels of bombesin-like peptides in SHP77 cultured in nicotine. Nicotine effects on nonmalignant pulmonary neuroendocrine cells may provide additional insight into how nicotine itself may promote lung carcinogenesis.

Animal models used to test the interactions between infectious agents and products of cigarette smoked implicated in sudden infant death syndrome

Animal test systems are reviewed that have relevance to sudden infant death syndrome (SIDS) are reviewed. These test interactions between infectious agents (or their toxins) and products of cigarette smoke. Infectious agents implicated in SIDS include members of the enterobacteria and clostridia, Staphylococcus aureus and Streptococcus pyogenes. Smoking is thought to be the single most preventable cause of SIDS. Tobacco smoke contains many extremely toxic products including cyanide and nicotine. Many animal test systems are available to examine the potency of bacterial toxins and smoke-derived components. These include mice, hamsters, rats and chick embryos. Such systems reveal synergy between bacterial toxins, especially endotoxin and superantigens. They have also demonstrated potentiation of low levels of bacterial toxin by low levels of both nicotine and its primary metabolite, cotinine. These findings suggest a possible causal explanation for the fact that passive exposure to cigarette smoke is a risk factor in sudden infant death syndrome.