Reference moist smokeless tobacco-induced apoptosis in human monocytes/macrophages cell line MM6

Moist smokeless tobacco use is associated with various types of oral injury, including leukoplakia and dipper's pouch, although the mechanism by which the injury is caused still remains unclear. One possible mechanism is that moist smokeless tobacco affects the inflammatory response. For example, a study by Johnson et al. demonstrated a reduction in the volume density of macrophages and increased inflammation and redness at the smokeless tobacco placement site when compared to non-placement site. The current study investigated the direct effect of reference moist smokeless tobacco extract (STE) exposure on the viability of MM6 monocyte/macrophage cell line. The exposure of MM6 cells to various concentrations of STE, led to a significant and dose-related decrease in cell viability. Furthermore, STE exposure resulted in an increase in Annexin V/PI positive cells, an increase in TUNEL-positive cells, and cleaved PARP staining all of which were inhibited by pre-incubation with a pan-caspase inhibitor, suggesting that the observed STE toxicity was due to the induction of apoptosis. Next, the role of various moist smokeless tobacco-derived components in STE-induced apoptosis of MM6 cells was investigated. Our findings suggest that STE-induced osmotic stress, but not exposure to nicotine, plays an important role in STE-induced apoptosis of MM6 cells. Together, these data show for the first time that STE exposure leads to the induction of apoptosis in human monocyte/macrophage cells, which appears to be induced in part, by reference STE-mediated osmotic stress.