ABSTRACT
Smokers are more susceptible than non-smokers to persistent infection by Porphyromonas gingivalis, a causative agent of periodontitis. Patients who smoke exhibit increased susceptibility to periodontitis and are more likely to display severe disease and be refractory to treatment. Paradoxically, smokers demonstrate reduced clinical inflammation. We show that P. gingivalis cells exposed to cigarette smoke extract (CSE) induce a lower proinflammatory response (tumour necrosis factor-alpha, interleukin-6, interleukin-12 p40) from monocytes and peripheral blood mononuclear cells than do unexposed bacteria. This effect is reversed when CSE-exposed bacteria are subcultured in fresh medium without CSE. Using microarrays representative of the P. gingivalis genome, CSE-exposure resulted in differential regulation of 6.8% of P. gingivalis genes, including detoxification and oxidative stress-related genes; DNA repair genes; and multiple genes related to P. gingivalis virulence, including genes in the major fimbrial and capsular operons. Exposure to CSE also altered the expression of outer membrane proteins, most notably by inducing the virulence factors RagA and RagB, and a putative lipoprotein cotranscribed with the minor fimbrial antigen. Therefore, CSE represents an environmental stress to which P. gingivalis adapts by altering gene expression and outer membrane proteins. These changes may explain, in part, the altered virulence and host-pathogen interactions that have been documented in vivo in smokers with periodontal disease.
Subject(s)
Host-Parasite Interactions/drug effects , Host-Parasite Interactions/immunology , Porphyromonas gingivalis/drug effects , Porphyromonas gingivalis/immunology , Cell Line , Cells, Cultured , Cytokines/metabolism , Gene Expression/drug effects , Gene Expression Profiling , Gene Expression Regulation, Bacterial , Humans , Leukocytes, Mononuclear/immunology , Leukocytes, Mononuclear/microbiology , Monocytes/immunology , Monocytes/microbiology , Smoking , Stress, PhysiologicalABSTRACT
Nicotine [(S)-3-(1-methyl-2-pyrrolidinyl)pyridine] is a major component of tobacco and a highly efficient acetylcholine receptor (nAChR) agonist that triggers the cholinergic anti-inflammatory pathway. We demonstrate that pre-treatment of monocytes with the stable nicotine catabolite, cotinine [(S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone], dramatically alters the nature of the inflammatory response to Gram negative bacteria by abrogating the production of cytokines that are under the transcriptional control of the NF-kappaB system (TNF-alpha, IL-1beta, IL-6, IL-12/IL-23 p40) and shifting the response towards an IL-10-dominated anti-inflammatory profile. This anti-inflammatory phenomenon is initiated specifically by engagement of the monocytic alpha7 nAChR; and is PI3K/GSK-3beta-dependent; but NF-kappaB-independent. These mechanistic insights suggest an ability to exploit convergent, endogenous anti-inflammatory pathway(s) to either up-regulate or down-regulate the production of specific cytokine groups (pro- or anti-inflammatory cytokines) depending on the clinical necessity.