Distinct gene expression changes in peripheral blood mononuclear cells exposed to combustible versus non-combustible tobacco product preparations
Cigarette smoking exerts diverse physiological effects including immune suppression. Existing epidemiological data show that consumption of smokeless tobacco products, such as moist snuff, is less harmful relative to smoking. We previously demonstrated that smokers exhibit distinct peripheral blood mononuclear cell (PBMC) gene expression patterns relative to moist snuff and non-tobacco consumers. To better characterize the biological effects associated with different tobacco products, a genome-wide gene expression study was performed using a PBMC in vitro model. We investigated global gene expression changes in PBMCs exposed to different nicotine equivalent doses (low, medium, and high) of whole smoke-conditioned media (WS-CM) or one nicotine equivalent dose of smokeless tobacco extract (STE) prepared from reference tobacco products (3R4F and 2S3, respectively). Pairwise statistical analysis did not identify significant expression changes by low WS-CM compared to media control. However, transcripts were significantly affected by medium WS-CM (479 transcripts), high WS-CM (2,703), and STE (2,156) treatments. The overlap between medium WS-CM and STE, and high WS-CM and STE, was minimal (34 and 65 transcripts, respectively), suggesting distinct effects of WS-CM and STE treatments. Hierarchical clustering showed that gene expression profiles under STE clustered with those under medium WS-CM, while the highest dose of WS-CM clustered distinctly from the medium WS-CM and STE conditions. Functional analysis revealed that WS-CM exposures, but not STE, uniquely affected genes involved in immune cell development and inflammatory response. Cascades of upstream regulators (e.g., TNF, IL1β, NFκB) were identified for the observed gene expression changes and generally suppressed by WS-CM, but not STE. Collectively, these findings suggest that combustible and non-combustible tobacco products produce distinct biological effects, which could explain the observed chronic immune suppression in smokers.