Impact of Heat-Not-Burn Mainstream on Oxidative Stress and Neuroinflammatory Pathways in the Rat Prefrontal Cortex

Background Heat-not-Burn (HnB) devices provide nicotine by heating tobacco without combustion. For this reason, these devices reached high popularity in recent years, especially among never-smokers and young people, bringing more people closer to smoking and becoming an emergent public health problem. Indeed, due to its electronic heat-not-burn technology, HnB devices have been proposed as a safer alternative to conventional cigarettes and as a possible approach to smoking cessation. Although users are exposed to lower levels of toxic compounds, the overall health effects of employing these products have not been adequately assessed yet. Recently, some evidence suggested how HnB mainstream contains various harmful constituents typical of tobacco smoke and have shown some toxicological outcomes similar to those elicited by traditional cigarettes. Based on this evidence, the aim of this study was to investigate the HnB impact on oxidative stress and antioxidant enzymatic machinery, as well as on key signalling pathways involved in DNA damage, in the rat prefrontal cortex. Methods To this end, male Sprague Dawley rats were exposed to HnB mainstream using a whole-body mode. After four weeks, animals were sacrificed, the prefrontal cortex (PFCx) was collected, and the measurement of reactive radical species (RRS) content was performed using electron paramagnetic resonance. The mRNA and protein levels of pro-inflammatory cytokines, antioxidant enzymes and some markers of neuroinflammation, as well as of DNA damage were assessed by quantitative RT-PCR and Western Blot assay. Results Results showed the HnB exposure enhanced RRS production and the protein level of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) as well as oxidative injury markers (OGG1 and 8-OHdG). The exposure to HnB mainstream induced an increase of the expression of antioxidant enzymes, like SOD1 and CAT, and altered the gene expression of peroxisome proliferator-activated receptors (PPARs) and KDM6A, a lysine 27 histone demethylating enzyme involved in the neuroinflammation response. Moreover, animals exposed to HnB showed a marked increment of drug-metabolism enzymes cytochrome P450, involved in the metabolism of nicotine as well as of aldehydes and polycyclic aromatic present in the HnB mainstream. This induction of monooxygenase P450-linked system together with the RRS increase could promote oxidative stress, leading to CNS damage. Conclusions This study highlighted the ability of HnB to promote neuroinflammation in the rat PFCx. Indeed, these results showed that aerosol generated from HnB devices may induce inflammatory and oxidative processes, as indicated by alterations in pro- and anti-inflammatory genes, as well as antioxidant enzymes and DNA damage markers.