INHIBITION OF NEUTROPHIL AND MONOCYTE DEFENSIVE FUNCTIONS BY NICOTINE

TO LEARN MORE ABOUT THE EFFECTS OF SMOKELESS TOBACCO on the defensive functions of neutrophils, we studied the influence of nicotine on thes e cells in vitro, looking at their bactericidal activity against oral pathogens, and at their ability to produce microbicidal reactive oxyge n species (oxygen radicals). Exposure of human blood neutrophils to ni cotine (0.01% to 0.1%) inhibited their ability to kill Actinomyces nae slundii, Actinobacillus actinomycetemcomitans, and Fusobacterium nucle atum. Although these concentrations of nicotine are high, such concent rations are relevant to phagocytes in the gingival sulcus, because smo keless tobacco contains 0.5% to 3.5% nicotine by dry weight. Nicotine had no such inhibitory effect when the killing assay was performed in an anaerobic environment, implying that nicotine preferentially affect ed oxygen-dependent killing mechanisms. To further investigate the eff ects of nicotine on production of oxygen radicals, neutrophils were pr imed with lipopolysaccharide and triggered with f-met-leu-phe or phorb ol ester in the presence of nicotine. Nicotine inhibited production of superoxide anion (measured by reduction of cytochrome c) and hydrogen peroxide (measured by oxidation of phenol red). Nicotine inhibition o f superoxide production was reversible by washing away the nicotine. B y observing that nicotine inhibited the reduction of cytochrome c by r eagent potassium superoxide, we determined that nicotine directly abso rbed superoxide. In addition, by examining nicotine inhibition of the uptake of oxygen by neutrophils, we determined that nicotine also inte rfered with the production of oxygen radicals by these cells. Nicotine also inhibited production of superoxide and interleukin-1 beta by mon ocytes. Nicotine did not affect the viability of neutrophils and monoc ytes, as determined by their ability to exclude trypan blue dye. Inhib ition of the aerobic antimicrobial funct ions of neutrophils and monoc ytes by nicotine may alter the microbial ecology of the oral cavity, a nd this might be one mechanism by which nicotine compromises the oral health of users of tobacco products.