Evaluation of Cytotoxic, Oxidative, and Pro-Inflammatory Effects of Aqueous Cigarette Smoke Extract on Human Monocytes: A Potential Model System for Assessment of Next-Generation Tobacco and Nicotine Products

Abstract

Tobacco smoking is a risk factor for the development of atherosclerosis. One strategy to reduce the harmful side effects of tobacco smoking is the development of next-generation tobacco and nicotine products. A crucial step in the development of atherosclerosis is the activation and adhesion of monocytes. Remarkably, little is known about the direct effects of cigarette smoking on monocytes. In this study, we developed methods to determine the detrimental effects of aqueous cigarette smoke extract (CSEaq) from 3R4F reference cigarettes on human monocytes in vitro. First, we tested the cytotoxic effects of CSEaq on human peripheral blood monocyte cell line derived from an acute monocytic leukemia patient (THP-1) and primary monocytes. Treatment of THP-1 cells with CSEaq reduced cell viability at dosages ≥40% in a dose-dependent manner. Cell viability of primary monocytes was reduced by CSEaq at dosages ≥10%. CSEaq activated the antioxidative NRF2 system and its target gene NAD(P)H dehydrogenase, quinone 1 in a dose-dependent manner in both cell types. Expression of target gene HMOX1 was increased only in THP-1 cells. In addition, we showed an increased expression of NADPH oxidase subunit NOX2 in response to CSEaq in THP-1 cells, but not in primary monocytes. Furthermore, CSEaq strongly induced adhesion molecule intercellular adhesion molecule 1 in THP-1 cells, but not in primary monocytes. Pro-inflammatory markers CCL2 and CD31 showed a strong induction in response to CSEaq in THP-1 cells, but they remained unchanged in primary monocytes. In conclusion, we have developed in vitro test systems allowing the evaluation of cytotoxic, oxidative, and pro-inflammatory effects of CSEaq on monocytes. These test systems can be considered potential model systems for assessment of next-generation tobacco and nicotine products. Although THP-1 cells were more susceptible to changes of gene expression, primary monocytes showed a stronger reduction of cell viability in response to CSEaq.