Cigarette smoke, but not novel tobacco vapor products, causes epigenetic disruption and cell apoptosis

Heat-Not-Burn (HNB) products, generating vapor without combusting tobacco leaves, have been developed with the expectation that the number and quantity of chemicals in the vapor of these products would be reduced compared with the smoke from conventional combustible cigarettes. However, whether the lower chemical levels correlate with lower toxicity remains to be determined. Here we examined differences in the biological effects of conventional cigarette smoke (CS) and two HNB products, Ploom TECH and Ploom TECH+, using the cultured cancer cell line A549 and the normal bronchial epithelium cell line BEAS-2B. The conventional CS 3R4F extract (0.5%) markedly decreased cell proliferation of both A549 and BEAS-2B cells; however, 0.5% extracts of these commercially available HNB products did not affect cell growth. To determine the cause of decreased cell proliferation, a TUNEL assay was performed, and the results indicated that apoptosis had occurred in both A549 and BEAS-2B cells at 24 h after exposure to 3R4F. To further explore the effect of CS on epigenetics, we performed western blotting to detect histone H2A phosphorylation, which is known to affect transcriptional regulation. Only the 3R4F extract decreased histone H2A phosphorylation in both A549 and BEAS-2B cells. Next, we examined alterations in gene expression after treatment of A549 cells with Ploom TECH, Ploom TECH+, or 3R4F extracts. It was found that 339, 107, and 103 genes were upregulated more than 2 fold in A549 cells treated with 3R4F, Ploom TECH, or Ploom TECH + extracts, respectively. Among the 339 genes that were upregulated in response to 3R4F, we focused on EGR1, FOS, and FOSB, since they were upregulated more than 100 fold, which was confirmed using RT-qPCR. These results suggest that CS, but not HNB products, cause epigenetic disruption and cell apoptosis, possibly by elevating transcription of genes such as EGR1.