The development and application of a method for the estimation of mouth level exposure (MLE) to four tobacco specific nitrosamines
Tobacco specific nitrosamines (TSNA) in cigarette smoke are an important class of toxicants. Therefore the quantification of TSNA via spent filters from smokers is a valuable addition to the filter analysis method. Previous research has shown that analysis of nicotine in filters gives good correlations to the levels of TSNA measured in smoke. We have recently described an LC-MS/MS method for the quantitation of four TSNA (NNK, NNN, NAB, NAT); calibration equations with linear correlations were obtained by measuring the mainstream smoke TSNA yields and nicotine levels in filters using six regimes to cover yields that span those expected from human smoked cigarettes. Good correlation was found between TSNA yields and levels of tip nicotine (r2>0.93) for both a commercial 6 mg (ISO tar yield) product and a 6 mg test product with different tobacco blend and substantially lower mainstream TSNA yields. In order to demonstrate the methodology, TSNA yields were estimated from filter samples from a previous study where 73 smokers smoked the commercial product from days 1 to 15 and days 51 to 71 and the test product from days 16 to 50. Mean (SD) NNK MLE levels were 51.1 (17.5) and 51.3 (16.7) ng/cig for the control cigarette and 14.8 (6.0) ng/cig for the test cigarette. Other TSNA (NNN, NAB, NAT) were consistent with this trend. Urinary TSNA biomarker data supported these results showing reductions in TSNA excretion (e.g. total NNAL) during the consumption of the test product and returned to the previous levels when the smokers resumed smoking the commercial product. The MLE method is thus able to discriminate the TSNA exposure of smokers following switching to a cigarette with reduced blend TSNA test product.