title: Nicotine promotes Streptococcus mutans extracellular polysaccharide synthesis, cell aggregation and overall lactate dehydrogenase activity.
abstract: Several epidemiology studies have reported a positive relationship between smoking and dental caries. Nicotine, an alkaloid component of tobacco, has been demonstrated to stimulate biofilm formation and metabolic activity of Streptococcus mutans, one of the most important pathogens of dental caries. The first aim of the present study was to explore the possible mechanisms leading to increased biofilm by nicotine treatment from three aspects, extracellular polysaccharides (EPS) synthesis, glucosyltransferase (Gtf) synthesis and glucan-binding protein (Gbp) synthesis at the mRNA and protein levels. The second aim was to investigate how nicotine affects S. mutans virulence, particular in lactate dehydrogenase (LDH) activity. Confocal laser scanning microscopy results demonstrated that both biofilm bacterial cell numbers and EPS were increased by nicotine. Gtf and GbpA protein expression of S. mutans planktonic cells were upregulated while GbpB protein expression of biofilm cells were downregulated by nicotine. The mRNA expression trends of those genes were mostly consistent with results on protein level but not statistically significant, and gtfD and gbpD of biofilm cells were inhibited. Nicotine was not directly involved in S. mutans LDH activity. However, since it increases the total number of bacterial cells in biofilm, the overall LDH activity of S. mutans biofilm is increased. In conclusion, nicotine stimulates S. mutans planktonic cell Gtf and Gbp expression. This leads to more planktonic cells attaching to the dental biofilm. Increased cell numbers within biofilm results in higher overall LDH activity. This contributes to caries development in smokers.
authors.affiliation: Department of Oral Biology and Tobacco Cessation and Biobehavioral Group, School of Dentistry, Indiana University, Indianapolis, IN, USA; Department of Pediatric Dentistry, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China; State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China. Electronic address: ruijmhuang@gmail.com.
authors.forename: R
authors.initials: R
authors.lastname: Huang
authors.affiliation: Department of Oral Biology and Tobacco Cessation and Biobehavioral Group, School of Dentistry, Indiana University, Indianapolis, IN, USA; State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China.
authors.forename: M
authors.initials: M
authors.lastname: Li
authors.affiliation: Department of Oral Biology and Tobacco Cessation and Biobehavioral Group, School of Dentistry, Indiana University, Indianapolis, IN, USA; Department of Pathology and Laboratory Medicine, School of Medicine, Indiana University, Indianapolis, IN, USA. Electronic address: rgregory@iu.edu.
authors.forename: R L
authors.initials: RL
authors.lastname: Gregory
mesh_terms: D001422:Bacterial Adhesion / Q000187:drug effects; D018441:Biofilms / Q000187:drug effects*; D015153:Blotting, Western; D002449:Cell Aggregation / Q000187:drug effects*; D045022:Lactate Dehydrogenases / Q000096:biosynthesis*; D018613:Microscopy, Confocal; D009538:Nicotine / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D011134:Polysaccharides / Q000096:biosynthesis; D013295:Streptococcus mutans / Q000187:drug effects* / Q000201:enzymology; D015854:Up-Regulation
chemical_list: D011134:Polysaccharides; D009538:Nicotine; D045022:Lactate Dehydrogenases
keywords: Dental caries; Glucan binding protein; Glucosyltransferase; Lactate dehydrogenase; Nicotine; Streptococcus mutans