Airway responsiveness measured by barometric plethysmography in guinea pigs

Therapeutic effects of soluble guanylate cyclase stimulation on pulmonary hemodynamics and emphysema development in guinea pigs chronically exposed to cigarette smoke

We have analyzed the effect of the soluble guanylate cyclase (sGC) stimulator BAY 41-2272 in a therapeutic intervention in guinea pigs chronically exposed to cigarette smoke (CS). The effects of sGC stimulation on respiratory function, pulmonary hemodynamics, airspace size, vessel remodeling, and inflammatory cell recruitment to the lungs were evaluated in animals that had been exposed to CS for 3 mo. CS exposure was continued for an additional 3 mo in half of the animals and withdrawn in the other half. Animals that stopped CS exposure had slightly lower pulmonary artery pressure (PAP) and right ventricle (RV) hypertrophy than those who continued CS exposure, but they did not recover from the emphysema and the inflammatory cell infiltrate. Conversely, oral BAY 41-2272 administration stopped progression or even reversed the CS-induced emphysema in both current and former smokers, respectively. Furthermore, BAY 41-2272 produced a reduction in the RV hypertrophy, which correlated with a decrease in the PAP values. By contrast, the degree of vessel remodeling induced by CS remained unchanged in the treated animals. Functional network analysis suggested perforin/granzyme pathway downregulation as an action mechanism capable of stopping the progression of emphysema after sGC stimulation. The pathway analysis also showed normalization of the expression of cGMP-dependent serine/kinases. In conclusion, in guinea pigs chronically exposed to CS, sGC stimulation exerts beneficial effects on the lung parenchyma and the pulmonary vasculature, suggesting that sGC stimulators might be a potential alternative for chronic obstructive pulmonary disease treatment that deserves further evaluation.

Preparation of a Sustained-Release Nebulized Aerosol of R-terbutaline Hydrochloride Liposome and Evaluation of Its Anti-asthmatic Effects via Pulmonary Delivery in Guinea Pigs

An aerosolized liposome formulation for the pulmonary delivery of an anti-asthmatic medication was developed. Asthma treatment usually requires frequent administration of medication for a sustained bronchodilator response. Liposomes are known for their sustained drug release capability and thus would be a suitable delivery system for prolonging the therapeutic effect of anti-asthmatic medication. Liposomes prepared by thin film hydration were loaded with a model drug, R-terbutaline hydrochloride(R-TBH), using an ammonium sulfate-induced transmembrane electrochemical gradient. This technique provided an encapsulation efficiency of up to 71.35% and yielded R-TBH liposomes with a particle size of approximately 145 ± 20 nm. According to stability studies, these R-TBH liposomes should be stored at 4°C before usage. Compared to R-TBH solution, which showed 90.84% release within 8 h, liposomal R-TBH had a cumulative release of 73.53% at 37°C over 192 h. A next generation impactor (NGI) was used to analyze the particle size distribution in the lungs of R-TBH liposome aerosol in vitro at 5°C. The therapeutic efficacy of the nebulized aerosol of the R-TBH liposomes was assessed via pulmonary delivery in guinea pigs. The results showed that, compared to the R-TBH solution group, the R-TBH liposome group had a prolonged anti-asthma effect.

Inhalation of concentrated PM2.5 from Mexico City acts as an adjuvant in a guinea pig model of allergic asthma

Exposure to Particulate Matter (PM) could function as an adjuvant depending on the city of origin in mice allergic asthma models. Therefore, our aim was to determine whether inhalation of fine particles (PM2.5) from Mexico City could act as an adjuvant inducing allergic sensitization and/or worsening the asthmatic response in guinea pig, as a suitable model of human asthma. Experimental groups were Non-Sensitized (NS group), sensitized with Ovalbumin (OVA) plus Aluminum hydroxide (Al(OH)3) as adjuvant (S + Adj group), and sensitized (OVA) without adjuvant (S group). All the animals were exposed to Filtered Air (FA) or concentrated PM2.5 (5 h/daily/3 days), employing an aerosol concentrator system, PM2.5 composition was characterized. Lung function was evaluated by barometric plethysmography (Penh index). Inflammatory cells present in bronchoalveolar lavage were counted as well as OVA-specific IgG1 and IgE were determined by ELISA assay. Our results showed in sensitized animals without Al(OH)3, that the PM2.5 exposure (609 ± 12.73 μg/m3) acted as an adjuvant, triggering OVA-specific IgG1 and IgE concentration. Penh index increased ∼9-fold after OVA challenge in adjuvant-sensitized animals as well as in S + PM2.5 group (∼6-fold), meanwhile NS + FA and S + FA lacked response. S + Adj + PM2.5 group showed an increase significantly of eosinophils and neutrophils in bronchoalveolar lavage. PM2.5 composition was made up of inorganic elements and Polycyclic Aromatic Hydrocarbons, as well as endotoxins and β-glucan, all these components could act as adjuvant. Our study demonstrated that acute inhalation of PM2.5 acted as an adjuvant, similar to the aluminum hydroxide effect, triggering allergic asthma in a guinea pig model. Furthermore, in sensitized animals with aluminum hydroxide an enhancing influence of PM2.5 exposure was observed as specific-hyperresponsiveness to OVA challenge (quickly response) and eosinophilic and neutrophilic airway inflammation. Fine particles from Mexico City is a complex mix, which play a significant role as adjuvant in allergic asthma.

Characteristic plethysmographic findings in a guinea pig model of COPD

AIM OF THE STUDY

Long-term exposure to cigarette smoke generates chronic obstructive pulmonary disease (COPD) in guinea pigs, but a comprehensive evaluation of changes in lung function, as assessed by barometric whole body plethysmography (WBP), is lacking.

MATERIALS AND METHODS

Female guinea pigs were exposed to the smoke of 20 cigarettes/day, 5 days/week, during 10 weeks (COPD group, n = 8), and were compared with unexposed female guinea pigs of the same age (control group, n = 8). WBP was performed in both groups, followed by lung histology.

RESULTS

At the end of the exposure period, guinea pigs in the COPD group had higher respiratory frequency, while duty cycle (Ti/Ttot) was unaffected. There was a trend toward minute ventilation (MV) and expiratory flow at the mid-tidal volume (EF50) to be higher in the COPD group. Enhanced pause (Penh) was lower, while time of braking (TB) and time to PEF relative to Te (Rpef) were higher in the COPD group. All guinea pigs exposed to tobacco smoke developed emphysematous lesions in their lungs and gained less body weight than controls.

CONCLUSIONS

In this COPD model, exposure to cigarette smoke produced changes in WBP characterized by a shallow breathing pattern with decreased Penh and a trend toward increasing EF50 (probably due to decreased elastic recoil), increased TB (suggesting dynamic laryngeal narrowing), and a trend of increasing MV (probably due to a higher metabolic rate). Many of these functional changes resemble those observed in patients with COPD and corroborate the suitability of this guinea pig model for the study of COPD.

Allergic sensitization modifies the pulmonary expression of 5-hydroxytryptamine receptors in guinea pigs

There is mounting evidence that 5-hydroxytryptamine (5-HT) plays a role in asthma. However, scarce information exists about the pulmonary expression of 5-HT receptors and its modification after allergic sensitization. In the present work, we explored the expression of 5-HT1A, 5-HT2A, 5-HT3, 5-HT4, 5-ht5a, 5-HT6, and 5-HT7 receptors in lungs from control and sensitized guinea pigs through qPCR and Western blot. In control animals, mRNA from all receptors was detectable in lung homogenates, especially from 5-HT2A and 5-HT4 receptors. Sensitized animals had decreased mRNA expression of 5-HT2A and 5-HT4 receptors and increased that of 5-HT7 receptor. In contrast, they had increased protein expression of 5-HT2A receptor in bronchial epithelium and of 5-HT4 receptor in lung parenchyma. The degree of airway response to the allergic challenge was inversely correlated with mRNA expression of the 5-HT1A receptor. In summary, our results showed that major 5-HT receptor subtypes are constitutively expressed in the guinea pig lung, and that allergic sensitization modifies the expression of 5-HT2A, 5-HT4, and 5-HT7 receptors.

An aerosol formulation of R-salbutamol sulfate for pulmonary inhalation

An aerosol formulation containing 7.5 mg of R-salbutamol sulfate was developed. The aerosol was nebulized with an air-jet nebulizer, and further assessed according to the new European Medicines Agency (EMA) guidelines. A breath simulator was used for studies of delivery rate and total amount of the active ingredient at volume of 3 mL. A next generation impactor (NGI) with a cooler was used for analysis of the particle size and in vitro lung deposition rate of the active ingredient at 5 °C. The anti-asthmatic efficacy of the aerosol formulation was assessed in guinea pigs with asthma evoked by intravenous injection of histamine compared with racemic salbutamol. Our results show that this aerosol formulation of R-salbutamol sulfate met all the requirements of the new EMA guidelines for nebulizer. The efficacy of a half-dose of R-salbutamol equaled that of a normal dose of racemic salbutamol.

Using plethysmography to determine erythropoietin's impact on neural control of ventilation

The evaluation of respiratory parameters often requires the use of anesthetics (that depress the neural -network controlling respiration), and/or ways to restrain the animal's mobility (that produces a stress-dependent increase of respiration). Consequently, the establishment of plethysmography represented an invaluable technique in respiratory physiology. Plethysmography, indeed, allows the assessment of ventilatory parameters on living, unanesthetized, and unrestrained animals. The conception of the barometric plethysmography relies on the fact that an animal placed inside a hermetically closed chamber generates through its breathing a fluctuation of pressure in the chamber than can be recorded. Thus, the respiratory frequency and the tidal volume can be directly measured, while the animal's ventilation is calculated indirectly by the multiplication of these two parameters. In our hands, plethysmography was a key tool to investigate the impact of erythropoietin (Epo) on the neural control of hypoxic ventilation in mice.

Effects of cigarette smoke and chronic hypoxia on airways remodeling and resistance. Clinical significance

Previously we have reported that association of cigarette smoke (CS) and chronic hypoxia (CH) interact positively to physiopathologically remodel pulmonary circulation. In present study we have exposed guinea pigs to CS smoke (four cigarettes/day; 3 months; CS) and to chronic hypoxia (12% O(2), 15 days; CH) alone or in combination (CSCH animals) and evaluated airways remodeling and resistance assessed as Penh (enhance pause). We measured Penh while animals breathe air, 10% O(2) and 5% CO(2) and found that CS and CH animals have higher Penh than controls; Penh was even larger in CSCH animals. A rough parallelism between Penh and thickness of bronchiolar wall and muscular layer and Goblet cell number was noticed. We conclude that CS and CH association accelerates CS-induced respiratory system damage, evidenced by augmented airway resistance, bronchial wall thickness and muscularization and Goblet cell number. Our findings would suggest that appearance of hypoxia would aggravate any preexisting pulmonary pathology by increasing airways resistance and reactivity.