Toxicity of aerosols of nicotine and pyruvic acid (separate and combined) in Sprague–Dawley rats in a 28-day OECD 412 inhalation study and assessment of systems toxicology

Abstract

Toxicity of nebulized nicotine (Nic) and nicotine/pyruvic acid mixtures (Nic/Pyr) was characterized in a 28-day Organization for Economic Co-operation and Development 412 inhalation study with additional transcriptomic and lipidomic analyses. Sprague-Dawley rats were nose-only exposed, 6 h/day, 5 days/week to filtered air, saline, nicotine (50 µg/l), sodium pyruvate (NaPyr, 33.9 µg/l) or equimolar Nic/Pyr mixtures (18, 25 and 50 µg nicotine/l). Saline and NaPyr caused no health effects, but rats exposed to nicotine-containing aerosols had decreased body weight gains and concentration-dependent increases in liver weight. Blood neutrophil counts were increased and lymphocyte counts decreased in rats exposed to nicotine; activities of alkaline phosphatase and alanine aminotransferase were increased, and levels of cholesterol and glucose decreased. The only histopathologic finding in non-respiratory tract organs was increased liver vacuolation and glycogen content. Respiratory tract findings upon nicotine exposure (but also some phosphate-buffered saline aerosol effects) were observed only in the larynx and were limited to adaptive changes. Gene expression changes in the lung and liver were very weak. Nic and Nic/Pyr caused few significant changes (including Cyp1a1 gene upregulation). Changes were predominantly related to energy metabolism and fatty acid metabolism but did not indicate an obvious toxicity-related response. Nicotine exposure lowered plasma lipids, including cholesteryl ester (CE) and free cholesterol and, in the liver, phospholipids and sphingolipids. Nic, NaPyr and Nic/Pyr decreased hepatic triacylglycerol and CE. In the lung, Nic and Nic/Pyr increased CE levels. These data suggest that only minor biologic effects related to inhalation of Nic or Nic/Pyr aerosols were observed in this 28-day study.

Acute pulmonary effects of aerosolized nicotine

“…In one study, 50% of rats inhaling very high concentrations of nicotine (30%) aerosol became acutely apneic and died (65). In another very low-dose study no adverse effects were obtained (54). The nicotine concentrations we used are normally found in e-cigs, and they generate plasma levels that are comparable to e-cig or cigarette smoking users.…”

“…Therefore, the effects of nicotine are less clear. Tobacco companies however continue to promote and report that inhaled nicotine has no adverse effect (54). It is imperative to mention that these studies were carried out at nicotine levels far less than what is used in e-cig refills.…”

Animal Inhalation Models to Investigate Modulation of Inflammatory Bowel Diseases

“…In addition, because of stress associated with restraint in nose-only exposure systems, training is required to adapt animals to the technical procedures. Vehicle or fresh air exposures are also needed to help distinguish such stress-related effects from treatment effects [33]. The daily execution of nose-only exposures requires that animals be individually inserted into the exposure tubes, a technical aspect that may limit the numbers of animals that can be used in the experiments.…”

“…Finally, to elucidate the molecular mechanisms of IBD-CS interactions, beyond the current knowledge, it will be necessary to combine robust IBD models (UC and CD), well-controlled, state-of-the-art inhalation exposure design and technology and disease-specific endpoints with systems-wide molecular profiling. We conducted systems toxicology-oriented inhalation studies using mouse models to investigate effects of CS and candidate modified risk tobacco products in chronic obstructive and cardiovascular diseases [33,[88][89][90][91]. These studies demonstrated the feasibility and suitability of this approach for identifying the molecular basis of disease mechanisms and the biological impacts of CS.…”

“…The study design and inhalation exposure technology were based on the OECD guidelines TG412 and TG413 for 28 and 90 days inhalation toxicity studies, respectively [92,93]. Satellite groups were included to provide material for the additional molecular investigations and a similar study was conducted on rats exposed to nicotine aerosols [33]. A very detailed description of the study design and methodology was provided [94] and this might serve as a template for new IBD inhalation studies.…”