Characterization of biochemical, functional and structural changes in mice respiratory organs chronically exposed to cigarette smoke

The inflammation and oxidative status of rat lung tissue following smoke/vapor exposure via E-cigarette, cigarette, and waterpipe

BACKGROUND

Tobacco smoking is a major worldwide health issue that contributes to millions of deaths annually. Electronic cigarettes (E-cigarettes) are also harmful. Smoke/vapor from E-cigarettes and tobacco products consists of free radicals and other toxic substances. Tissue damage in smokers, such as lungs, is highly observed and is linked to oxidative damage and inflammation.

METHODS

The inflammation and oxidative status of rat lung tissues was examined following whole-body smoke/vapor exposure via E-cigarette, cigarette, and waterpipe for 2 h daily, 5 days per week for 8 weeks.

RESULTS

Lung tissue damage was higher in cigarettes and waterpipe groups compared to the E-cigarette group. Collectively, there was a significant increase (p < 0.05) in the mRNA expression of pro-inflammatory mediators (TNF-α, NF-κB, IL-1β) with the exception of IL-1β in the E-cigarettes group. As for the anti-inflammatory mediators (Nrf2 and IL-10), a significant reduction (p < 0.05) of mRNA expression was observed with the exception of Nrf2 in the E-cigarette group. As for IL-6, there was a significant increase in its mRNA expression (p < 0.05) in the cigarette and waterpipe groups. There was also a significant decrease (p < 0.05) in the antioxidant activity of all antioxidants tested (GPx, SOD, and CAT) in all groups with the exception of SOD in the cigarette group.

CONCLUSION

Smoke/vapor administered via E-cigarette, cigarette, and waterpipe elicits inflammation and oxidative stress in rat lungs that is accompanied by histopathological changes.

Impact of inhalation exposure to cigarette smoke on the pathogenesis of pulmonary hypertension primed by monocrotaline in rats

Extensive, long-term exposure to cigarette smoke (CS) was recently suggested to be a risk factor for pulmonary hypertension, although further validation is required. The vascular effects of CS share similarities with the etiology of pulmonary hypertension, including vascular inflammation and remodeling. Thus, we examined the influence of CS exposure on the pathogenesis of monocrotaline (MCT)-induced pulmonary hypertension, hypothesizing that smoking might accelerate the development of primed pulmonary hypertension. CS was generated from 3R4F reference cigarettes, and rats were exposed to CS by inhalation at total particulate matter concentrations of 100-300 μg/L for 4 h/day, 7 days/week for 4 weeks. Following 1 week of initial exposure, rats received 60 mg/kg MCT and were sacrificed and analyzed after an additional 3 weeks of exposure. MCT induced hypertrophy in pulmonary arterioles and increased the Fulton index, a measure of right ventricular hypertrophy. Additional CS exposure exacerbated arteriolar hypertrophy but did not further elevate the Fulton index. No significant alterations were observed in levels of endothelin-1 and vascular endothelial growth factor, or in hematological and serum biochemical parameters. Short-term inhalation exposure to CS exacerbated arteriolar hypertrophy in the lung, although this effect did not directly aggravate the overworked heart under the current experimental conditions.

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.

The effect of long-term doxycycline treatment in a mouse model of cigarette smoke-induced emphysema and pulmonary hypertension

Chronic obstructive pulmonary disease (COPD) is a major cause of death and a still incurable disease, comprising emphysema and chronic bronchitis. In addition to airflow limitation, patients with COPD can suffer from pulmonary hypertension (PH). Doxycycline, an antibiotic from the tetracycline family, in addition to its pronounced antimicrobial activity, acts as a matrix metalloproteinase (MMP) inhibitor and has anti-inflammatory properties. Furthermore, doxycycline treatment exhibited a beneficial effect in several preclinical cardiovascular disease models. In preclinical research, doxycycline is frequently employed for gene expression modulation in Tet-On/Tet-Off transgenic animal models. Therefore, it is crucial to know whether doxycycline treatment in Tet-On/Tet-Off systems has effects independent of gene expression modulation by such systems. Against this background, we assessed the possible curative effects of long-term doxycycline administration in a mouse model of chronic CS exposure. Animals were exposed to cigarette smoke (CS) for 8 mo and then subsequently treated with doxycycline for additional 3 mo in room air conditions. Doxycycline decreased the expression of MMPs and general pro-inflammatory markers in the lungs from CS-exposed mice. This downregulation was, however, insufficient to ameliorate CS-induced emphysema or PH. Tet-On/Tet-Off induction by doxycycline in such models is a feasible genetic approach to study curative effects at least in established CS-induced emphysema and PH. However, we report several parameters that are influenced by doxycycline and use of a Tet-On/Tet-Off system when evaluating those parameters should be interpreted with caution.

A 7-month inhalation toxicology study in C57BL/6 mice demonstrates reduced pulmonary inflammation and emphysematous changes following smoking cessation or switching to e-vapor products

Cigarette smoking causes serious diseases, including lung cancer, atherosclerotic coronary artery disease, peripheral vascular disease, chronic bronchitis, and emphysema. While cessation remains the most effective approach to minimize smoking-related disease, alternative non-combustible tobacco-derived nicotine-containing products may reduce disease risks among those unable or unwilling to quit. E-vapor aerosols typically contain significantly lower levels of smoke-related harmful and potentially harmful constituents; however, health risks of long-term inhalation exposures are unknown. We designed a 7-month inhalation study in C57BL/6 mice to evaluate long-term respiratory toxicity of e-vapor aerosols compared to cigarette smoke and to assess the impact of smoking cessation (Cessation group) or switching to an e-vapor product (Switching group) after 3 months of exposure to 3R4F cigarette smoke (CS). There were no significant changes in in-life observations (body weights, clinical signs) in e-vapor groups compared to the Sham Control. The 3R4F CS group showed reduced respiratory function during exposure and had lower body weight and showed transient signs of distress post-exposure. Following 7 months of exposure, e-vapor aerosols resulted in no or minimal increase in pulmonary inflammation, while exposure to 3R4F CS led to impairment of lung function and caused marked lung inflammation and emphysematous changes. Biological changes observed in the Switching group were similar to the Cessation group. 3R4F CS exposure dysregulated the lung and nasal tissue transcriptome, while these molecular effects were substantially lower in the e-vapor group. Results from this study demonstrate that in comparison with 3R4F CS, e-vapor aerosols induce substantially lower biological responses including pulmonary inflammation and emphysematous changes, and that complete switching from CS to e-vapor products significantly reduces biological changes associated with CS in C57BL/6 mice.

Assessment of nicotine release from nicotine-loaded chitosan nanoparticles dry powder inhaler formulations via locomotor activity of C57BL/6 mice

PURPOSE

This study aimed to assess the activity of controlled release nicotine from dry powder inhaler formulation via locomotor activity of C57BL/6 mice.

METHODS

To achieve this we built a nose-only inhalation device for pulmonary administration of nicotine to mice and determined the optimal operational parameters. We used the locomotor activity test to compare the effects of the inhaled nicotine hydrogen tartrate-loaded chitosan nanoparticles (NHT-CS) with NHT in C57BL/6 mice. The minimum inhaled dose of NHT-CS required to alter locomotor activity was compared with inhaled and subcutaneously (s.c) injected NHT. Finally, histological examination of lung tissues was performed to ensure inhalation of NHT-CS did not cause lung damage.

RESULTS

We found a flow rate of 0.9 L/min and an exposure time of 5 min achieved optimal delivery of nicotine. A minimum of 0.88 mg inhaled of NHT-CS or 0.59 mg inhaled of NHT was required to alter locomotor activity similarly to injection of 0.5 mg/kg nicotine, suggesting the reformulation process did not alter the activity of NHT-CS. No differences between untreated and NHT-CS treated lung tissue upon histological examination were observed.

CONCLUSIONS

The results indicated the inhaled NHT-CS is a viable preclinical option for developing novel inhalation formulations as a potential anti-smoking therapeutic.

Histone modification in the lung injury and recovery of mice in response to PM2.5 exposure

Epidemiological and experimental studies have progressively provided a better knowledge of the underlying mechanisms by which fine particulate matter (PM_2.5) exerts its harmful health effects. However, limited studies focused on the effect and following recovery after the particulate exposure ended. In this study, we determined PM_2.5 exposure-caused effects on the lung and their recovery in mice after terminating aspiration, and clarified the possible molecular modification. The results revealed that PM_2.5 exposure for 4 weeks significantly decreased the lung function, and the changes returned to normal levels after 1-week recovery. However, we observed persistent particle alveolar load following 2-week recovery. Interestingly, the alterations of H3K27ac expression and related enzyme activities mimicked the changes of respiratory function during the process, and chromatin immunoprecipitation-seqences (ChIP-seq) suggested that these PM_2.5-associated differential H3K27ac markers participated in immune responses and chemokine signaling pathway with stat2 and bcar1 being two important genes. Consistently, the expression of pro-inflammatory cytokines and chemokines elevated after PM_2.5 exposure for 4-week, and reversed to normal levels following 2-week recovery. The study highlighted that PM_2.5 aspiration caused histone modification associated lung dysfunction and inflammation, and the action restored after exposure ending and 2-week recovery. Also, persistent particle alveolar load might be a long-term potential risk for lung diseases.

Plausible Roles for RAGE in Conditions Exacerbated by Direct and Indirect (Secondhand) Smoke Exposure

Approximately 1 billion people smoke worldwide, and the burden placed on society by primary and secondhand smokers is expected to increase. Smoking is the leading risk factor for myriad health complications stemming from diverse pathogenic programs. First- and second-hand cigarette smoke contains thousands of constituents, including several carcinogens and cytotoxic chemicals that orchestrate chronic inflammatory responses and destructive remodeling events. In the current review, we outline details related to compromised pulmonary and systemic conditions related to smoke exposure. Specifically, data are discussed relative to impaired lung physiology, cancer mechanisms, maternal-fetal complications, cardiometabolic, and joint disorders in the context of smoke exposure exacerbations. As a general unifying mechanism, the receptor for advanced glycation end-products (RAGE) and its signaling axis is increasingly considered central to smoke-related pathogenesis. RAGE is a multi-ligand cell surface receptor whose expression increases following cigarette smoke exposure. RAGE signaling participates in the underpinning of inflammatory mechanisms mediated by requisite cytokines, chemokines, and remodeling enzymes. Understanding the biological contributions of RAGE during cigarette smoke-induced inflammation may provide critically important insight into the pathology of lung disease and systemic complications that combine during the demise of those exposed.

Time-dependency of mice lung recovery after a 4-week exposure to traffic or biomass air pollutants

The time-dependency of lung recovery after 3 intranasal instillations per week during four weeks of distilled water (C groups) or particles (15μg) from traffic (U groups) or biomass burning (B groups) was observed in BALB/c mice. Lung mechanics [static elastance (Est), viscoelastic component of elastance (ΔE), lung resistive (ΔP1) and viscoelastic/inhomogeneous (ΔP2) pressures] and histology were analyzed 1 (C1, U1, B1), 2 (C2, U2, B2), 7 (C7, U7, B7) or 14 days (C14, U14, B14) after the last instillation. Est, ΔE, ΔP1 and ΔP2 were higher in U1 and B1 than in C1, returning to control values at day 2, except for ΔP1 that normalized after 7 days. Alveolar collapse, bronchoconstriction index and alveolar lesion were larger in U1 and B1 than in C1, however collapse returned to baseline at 7 days, while the others normalized in 2 days. A 4-week exposure to U and B induced lung impairment that resolved 7 days after the last exposure.

The Role of Innate and Adaptive Immune Cells in the Immunopathogenesis of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a chronic and progressive inflammatory disease of the airways and lungs that results in limitations of continuous airflow and is caused by exposure to noxious gasses and particles. A major cause of morbidity and mortality in adults, COPD is a complex disease pathologically mediated by many inflammatory pathways. Macrophages, neutrophils, dendritic cells, and CD8+ T-lymphocytes are the key inflammatory cells involved in COPD. Recently, the non-coding small RNA, micro-RNA, have also been intensively investigated and evidence suggest that it plays a role in the pathogenesis of COPD. Here, we discuss the accumulated evidence that has since revealed the role of each inflammatory cell and their involvement in the immunopathogenesis of COPD. Mechanisms of steroid resistance in COPD will also be briefly discussed.