In this study, the harmful effects of exposure to the smoke of a HnB product were compared with traditional cigarette smoke using an animal model and analyzed through PEA analysis. Notably, the levels of multiple proteins, including CCL20, CXCL1, and PRDX5, consistently increased in the cigarette exposure group, with a clear consistent pattern evident in the heatmap. Importantly, these increases were also observed in mice exposed to HnB smoke. Additionally, the significant elevations of CCL2, CXCL9, and platelet-derived growth factor (PDGF) receptor in HnB-exposed mice indicate their association with the nicotine pathway. Therefore, these characteristic protein profiles may serve as potential biomarkers for understanding the harmful effects of HnB in the future, providing valuable insights for further research and clinical applications.
Both conventional cigarettes and e-cigarettes are primarily designed to deliver nicotine, providing immediate satisfaction through vapors. Traditional cigarettes contain carcinogenic chemicals such as nitrosamines, which are inhaled following combustion, whereas e-cigarettes only contain nicotine and relatively harmless organic solvents. Consequently, e-cigarettes are often portrayed as safer alternatives to tobacco16. However, the effects of nicotine on the immune system are nuanced and vary among studies. Notably, cigarette smoke comprises many harmful substances beyond nicotine that can adversely impact health. Nicotine is absorbed into the body through cigarette smoke, triggering various physiological changes, some of which are related to the immune system. Cells of the immune system generate and release various compounds, including cytokines, to regulate inflammation and immune responses in the body. Nicotine can influence the production and release of cytokines, potentially affecting immune responses17,18. However, the specific effects may depend on factors such as the dose, duration, and frequency of nicotine exposure, and individual differences. In this study, we observed elevated levels of CCL2, CXCL9, and PDGFB in mice exposed to e-cigarette smoke, indicating activation of a nicotine-related immune pathway.
CCL2, a chemokine also known as MCP1, plays a crucial role in inflammation and immune responses. It is associated with inflammatory reactions triggered by environmental factors and is released by multiple cells, including macrophages, monocytes, and epithelial cells19,20. Notably, CCL2 overexpression influences proliferation, migration, and tumor growth factor (TGF)-β1 expression in lung epithelial cells when exposed to cigarette smoke extract. Additionally, it acts as a regulator in the generation of pro-fibrotic mediators and migration in fibroblasts21. Therefore, CCL2 could be vital in controlling extracellular matrix turnover by stimulating intermediary molecules, such as TGF-β1, α-smooth muscle actin, and interleukin (IL)-6, in pulmonary fibroblasts. Hence, CCL2 could be a potential therapeutic target for managing idiopathic pulmonary fibrosis. Other studies suggest that CCL2 is a potent pro-inflammatory chemokine that serves as a chemoattractant for myeloid cells and has been extensively studied as a predictor and potential driver of tumor cell growth and metastasis22,23.
Tobacco smoking can induce inflammatory and autoimmune diseases via genetic/epigenetic changes, increased oxidative stress, and free radical production, leading to enhanced proliferation of B and T cells, reduced T regulatory cell function, elevated pro-inflammatory cytokines (IL-1β, IL-6, IL-8, and tumor necrosis factors), and increased expression of chemotactic cytokines such as recombinant human CXCL9 (MIG), thymus and activation-regulated chemokine, and interferon-inducible T cell α chemoattractant24–36. CXCL9 plays an important role in many diseases, including external infection, autoimmune diseases, tumor treatment, lymphoma37, and fatty livers38. Changes in these inflammatory markers and cytokines can lead to cancers at 18 different tumor sites and a range of other chronic diseases, including coronary heart disease, stroke, and chronic obstructive pulmonary disease39,40. Notably, research on the specific interaction between CXCL9 and nicotine/e cigarettes is still evolving, and conclusive evidence remains unavailable. Therefore, considering the broader context of nicotine and e-cigarette use, including their potential effects on overall health and immune function, is crucial.
The impact of nicotine, present in both tobacco products and e-cigarettes, on different bodily functions has been thoroughly examined. Notably, nicotine exposure may affect the generation and function of growth factors such as PDGFB. PDGFB is a signaling protein implicated in diverse cellular functions such as cell growth, proliferation, and differentiation, with a notable contribution to tissue repair and wound healing. Nonetheless, the precise relationship between PDGFB and nicotine or e-cigarettes is currently under investigation, and conclusive findings have been yet reached. Von Willebrand factor (vWF), PDGFB, HIVEP1, and GPX3 were identified as venous thromboembolism associated biomarkers in the VEBIOS cohort, and the vWF and PDGF-B associations were replicated in FARIVE41. Notably, various chemicals such as flavorants and additives in e-cigarettes may have different effects on the body, and the impact of heating these compounds and their potential toxic effects are also understudied. Furthermore, the method of delivering nicotine via e-cigarettes may differ from that of traditional tobacco products, potentially influencing its interaction with signaling proteins such as PDGFB. Current research have indicated elevate PDGFB levels in e-cigarette users, but the specific effects and mechanisms of these interactions are still actively being studied. As research progresses, a deeper understanding of the relationship between PDGF-B and nicotine/e-cigarettes will be necessary.
The limitation of the study lies in its reliance on animal models and observational data, which may not fully translate to human responses. Furthermore, the specific mechanisms underlying the observed protein elevation in response to HnB exposure require further elucidation through mechanistic studies. Nevertheless, this study is strengthened by its comprehensive evaluation of potential biomarkers associated with HnB exposure, providing valuable insights into the effects of alternative nicotine delivery systems on biological pathways and a solid foundation for future research on physiological responses to HnB exposure in humans.
In conclusion, the rise in specific proteins such as CCL20, CXCL1, and PDX5 observed in both cigarette and HnB users, along with the elevated levels of CCL2, CXCL9, and PDGFR in HnB smokers, indicates an association with the nicotine pathway and identifies potential markers for understanding the harmful effects of HnB. Although nicotine affects the immune system by initiating various bodily changes and altering cytokine release, its precise impact is intricate and can be influenced by other toxins in cigarette smoke. Therefore, the immune-modulating effects of nicotine should be analyzed in the wider context of the well-known health risks of smoking. Consequently, further investigation is imperative to fully grasp the intricate interplay between nicotine, other cigarette components, and immune function.