Cigarette Smoke Decreases Salivary 18 kDa Translocator Protein Binding Affinity – in Association with Oxidative Stress

Abstract

Reactive oxygen species (ROS) generated by cigarette smoke may contribute to lung and oral cancer. The 18 kDa Translocator protein (TSPO) has been reported to be affected by ROS as well as to participate in ROS generation at mitochondrial levels, and has been implicated in pro-apoptotic and anti-carcinogenic functions. The present study reports the presence of TSPO in the cellular fraction of human saliva. In cells collected from untreated saliva, the specific TSPO ligand [(3)H]PK 11195 showed saturable binding with high affinity, with mean B(max) and K(d) values of 6,471 +/- 501 fmol/mg protein and 6.2 +/- 0.5 nM, respectively. Our study further indicates that the cellular fraction of human saliva possesses TSPO with binding characteristics similar to that of cells from other tissues of human origin. Following exposure of saliva to cigarette smoke a three-fold decrease in the affinity of salivary TSPO to its specific ligand, [(3)H]PK 11195 (p < 0.01) occurred in the cellular fraction of the saliva, in comparison to sham treated control, without significant accompanying changes in TSPO B(max), TSPO protein levels, or general protein levels. The changes in affinity of TSPO from the cellular fraction of saliva exposed to cigarette smoke were accompanied by changes in the mean levels of protein oxidation products (carbonyls) and lipid peroxides, which were three-fold higher (p < 0.01) and two-fold higher (p < 0.01), respectively, compared to those of sham treated controls. Thus, our study shows that TSPO is present in the cellular component of saliva. Interestingly, in vitro this cellular TSPO is affected by exposure of the whole saliva to cigarette smoke, in negative correlation with oxidative stress.