Comparison of 3 methods of exposing rats to cigarette smoke

Air Pollution and the Airways: Lessons from a Century of Human Urbanization

Since the industrial revolution, air pollution has become a major problem causing several health problems involving the airways as well as the cardiovascular, reproductive, or neurological system. According to the WHO, about 3.6 million deaths every year are related to inhalation of polluted air, specifically due to pulmonary diseases. Polluted air first encounters the airways, which are a major human defense mechanism to reduce the risk of this aggressor. Air pollution consists of a mixture of potentially harmful compounds such as particulate matter, ozone, carbon monoxide, volatile organic compounds, and heavy metals, each having its own effects on the human body. In the last decades, a lot of research investigating the underlying risks and effects of air pollution and/or its specific compounds on the airways, has been performed, involving both in vivo and in vitro experiments. The goal of this review is to give an overview of the recent data on the effects of air pollution on healthy and diseased airways or models of airway disease, such as asthma or chronic obstructive pulmonary disease. Therefore, we focused on studies involving pollution and airway symptoms and/or damage both in mice and humans.

Impact of whole-body versus nose-only inhalation exposure systems on systemic, respiratory, and cardiovascular endpoints in a 2-month cigarette smoke exposure study in the ApoE-/- mouse model

Cigarette smoking is one major modifiable risk factor in the development and progression of chronic obstructive pulmonary disease and cardiovascular disease. To characterize and compare cigarette smoke (CS)-induced disease endpoints after exposure in either whole-body (WB) or nose-only (NO) exposure systems, we exposed apolipoprotein E-deficient mice to filtered air (Sham) or to the same total particulate matter (TPM) concentration of mainstream smoke from 3R4F reference cigarettes in NO or WB exposure chambers (EC) for 2 months. At matching TPM concentrations, we observed similar concentrations of carbon monoxide, acetaldehyde, and acrolein, but higher concentrations of nicotine and formaldehyde in NOEC than in WBEC. In both exposure systems, CS exposure led to the expected adaptive changes in nasal epithelia, altered lung function, lung inflammation, and pronounced changes in the nasal epithelial transcriptome and lung proteome. Exposure in the NOEC caused generally more severe histopathological changes in the nasal epithelia and a higher stress response as indicated by body weight decrease and lower blood lymphocyte counts compared with WB exposed mice. Erythropoiesis, and increases in total plasma triglyceride levels and atherosclerotic plaque area were observed only in CS-exposed mice in the WBEC group but not in the NOEC group. Although the composition of CS in the breathing zone is not completely comparable in the two exposure systems, the CS-induced respiratory disease endpoints were largely confirmed in both systems, with a higher magnitude of severity after NO exposure. CS-accelerated atherosclerosis and other pro-atherosclerotic factors were only significant in WBEC.

Pulmonary hypertension in chronic obstructive pulmonary disease

Even mild pulmonary hypertension (PH) is associated with increased mortality and morbidity in patients with chronic obstructive pulmonary disease (COPD). However, the underlying mechanisms remain elusive; therefore, specific and efficient treatment options are not available. Therapeutic approaches tested in the clinical setting, including long-term oxygen administration and systemic vasodilators, gave disappointing results and might be only beneficial for specific subgroups of patients. Preclinical studies identified several therapeutic approaches for the treatment of PH in COPD. Further research should provide deeper insight into the complex pathophysiological mechanisms driving vascular alterations in COPD, especially as such vascular (molecular) alterations have been previously suggested to affect COPD development. This review summarizes the current understanding of the pathophysiology of PH in COPD and gives an overview of the available treatment options and recent advances in preclinical studies. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc.

State-of-the-art methods and devices for the generation, exposure, and collection of aerosols from heat-not-burn tobacco products

Tobacco harm reduction is increasingly recognized as a promising approach to accelerate the decline in smoking prevalence and smoking-related population harm. Potential modified risk tobacco products (MRTPs) must undergo a rigorous premarket toxicological risk assessment. The ability to reproducibly generate, collect, and use aerosols is critical for the characterization, and preclinical assessment of aerosol-based candidate MRTPs (cMRTPs), such as noncombusted cigarettes, also referred to as heated tobacco products, tobacco heating products, or heat-not-burn (HNB) tobacco products. HNB tobacco products generate a nicotine-containing aerosol by heating tobacco instead of burning it. The aerosols generated by HNB products are qualitatively and quantitatively highly different from cigarette smoke (CS). This constitutes technical and experimental challenges comparing the toxicity of HNB aerosols with CS. The methods and experimental setups that have been developed for the study of CS cannot be directly transposed to the study of HNB aerosols. Significant research efforts are dedicated to the development, characterization, and validation of experimental setups and methods suitable for HNB aerosols. They are described in this review, with a particular focus on the Tobacco Heating System version 2.2. This is intended to support further studies, the objective evaluation and verification of existing evidence, and the development of scientifically substantiated HNB MRTPs.

Comprehensive review of epidemiological and animal studies on the potential carcinogenic effects of nicotine per se

The effects of long-term use of nicotine per se on cancer risk, in the absence of tobacco extract or smoke, are not clearly understood. This review evaluates the strength of published scientific evidence, in both epidemiological and animal studies, for the potential carcinogenic effects of nicotine per se; that is to act as a complete carcinogen or as a modulator of carcinogenesis. For human studies, there appears to be inadequate evidence for an association between nicotine exposure and the presence of or lack of a carcinogenic effect due to the limited information available. In animal studies, limited evidence suggests an association between long-term nicotine exposure and a lack of a complete carcinogenic effect. Conclusive studies using current bioassay guidelines, however, are missing. In studies using chemical/physical carcinogens or transgenic models, there appears to be inadequate evidence for an association between nicotine exposure and the presence of or lack of a modulating (stimulating) effect on carcinogenesis. This is primarily due to the large number of conflicting studies. In contrast, a majority of studies provides sufficient evidence for an association between nicotine exposure and enhanced carcinogenesis of cancer cells inoculated in mice. This modulating effect was especially prominent in immunocompromized mice. Overall, taking the human and animal studies into consideration, there appears to be inadequate evidence to conclude that nicotine per se does or does not cause or modulate carcinogenesis in humans. This conclusion is in agreement with the recent US Surgeon General's 2014 report on the health consequences of nicotine exposure.

Animal models of chronic obstructive pulmonary disease

The mechanisms involved in the genesis of chronic obstructive pulmonary disease (COPD) are poorly defined. This area is complicated and difficult to model because COPD consists of four separate anatomic lesions (emphysema, small airway remodeling, pulmonary hypertension, and chronic bronchitis) and a functional lesion, acute exacerbation; moreover, the disease in humans develops over decades. This review discusses the various animal models that have been used to attempt to recreate human COPD and the advantages and disadvantages of each. None of the models reproduces the exact changes seen in humans, but cigarette smoke-induced disease appears to come the closest, and genetically modified animals also, in some instances, shed light on processes that appear to play a role.

Toxicological evaluation of an electrically heated cigarette. Part 4: Subchronic inhalation toxicology

The biological activity of mainstream smoke from an electrically heated cigarette (EHC) with controlled combustion and from the University of Kentucky Reference Cigarette 1R4F was determined in Sprague Dawley rats exposed nose-only for 90 days, 6 h a day, 7 days per week. For an equivalent response comparison between the two cigarette types, two doses were chosen for the EHC where the anticipated results were in the dynamic range of the 1R4F dose-response curve (four concentrations) for most end points. The number of cigarettes smoked per m(3) of diluted smoke resulted in total particulate matter concentrations of 40 and 90 microg l (-1) for the EHC and 40-170 microg l (-1) for the 1R4F. Biomonitoring indicated achievement of target doses. Mainstream smoke yields were lower for the EHC, with the exception of formaldehyde. No smoke-related mortality, remarkable in-life observations or abnormal gross pathological findings were observed. Smoke- and dose-related clinical pathology and organ weight changes included: increases in segmented neutrophils, some liver parameters and lung and adrenal weight relative to body weight; and decreases in lymphocytes, glucose concentration and spleen weight. Smoke-related histopathological findings in the respiratory tract included epithelial cell hyperplasia, squamous metaplasia, atrophy and accumulation of pigmented alveolar macrophages; they were mostly dose-dependent, more pronounced in the upper than lower respiratory tract and completely or partially reversed by 6 weeks post-inhalation. Qualitatively, the biological effects seen for the EHC and the 1R4F were comparable and similar to those observed in other mainstream smoke inhalation studies. Quantitatively, the biological activity of the EHC mainstream smoke was, on average, 65% lower than that of the 1R4F mainstream smoke on an equal cigarette basis and equivalent activity on an equal TPM basis.

Failure of cigarette smoke to induce or promote lung cancer in the A/J mouse

A six-month bioassay in A/J mice was conducted to test the hypothesis that chronically inhaled mainstream cigarette smoke would either induce lung cancer or promote lung carcinogenicity induced by the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Groups of 20 female A/J mice were exposed to filtered air (FA) or cigarette smoke (CS), injected with NNK, or exposed to both CS and NNK. At 7 weeks of age, mice were injected once with NNK; 3 days later, they were exposed to CS for 6 h/day, 5 days/week, for 26 weeks at a mean 248 mg total particulate matter/m3 concentration. Animals were sacrificed 5 weeks after exposures ended for gross and histological evaluation of lung lesions. No significant differences in survival between exposure groups was observed. A biologically significant level of CS exposure was achieved as indicated by CS-induced body weight reductions, lung weight increases, and carboxyhemoglobin levels in blood of about 17%. Crude tumor incidences, as determined from gross observation of lung nodules, were similar between the CS-exposed and FA groups, and the NNK and CS + NNK groups. Incidences in either of these latter groups were greater than either the CS or FA groups. Furthermore, tumor multiplicity in tumor-bearing animals was not significantly different among any of the three groups (FA, NNK, CS + NNK) in which tumors were observed. Thus, CS exposure neither induced lung tumors nor promoted NNK-induced tumors. Because the CS exposure concentration was probably near the maximally tolerable level, longer exposures should be evaluated to potentially establish a CS-induced model of lung carcinogenesis in the A/J mouse.