Improvement in ARDS experimental model installation: low mortality rate and maintenance of hemodynamic stability

IntroductionMany experimental models using lung lavage have been developed for the study of acute respiratory distress syndrome (ARDS). The original technique has been modified by many authors, resulting in difficulties with reproducibility. There is insufficient detail on the lung injury models used, including hemodynamic stability during animal preparation and drawbacks encountered such as mortality. The authors studied the effects of the pulmonary recruitment and the use of fixed tidal volume (Vt) or fixed inspiratory pressure in the experimental ARDS model installation.MethodsAdult rabbits were submitted to repeated lung lavages with 30 ml/kg warm saline until the ARDS definition (PaO₂/FiO₂ ≤ 100) was reached. The animals were divided into three groups, according to the technique used for mechanical ventilation: 1) fixed Vt of 10 ml/kg; 2) fixed inspiratory pressure (IP) with a tidal volume of 10 ml/kg prior to the first lung lavage; and 3) fixed Vt of 10 ml/kg with pulmonary recruitment before the first lavage.ResultsThe use of alveolar recruitment maneuvers, and the use of a fixed Vt or IP between the lung lavages did not change the number of lung lavages necessary to obtain the experimental model of ARDS or the hemodynamic stability of the animals during the procedure. A trend was observed toward an increased mortality rate with the recruitment maneuver and with the use of a fixed IP.DiscussionThere were no differences between the three study groups, with no disadvantage in method of lung recruitment, either fixed tidal volume or fixed inspiratory pressure, regarding the number of lung lavages necessary to obtain the ARDS animal model. Furthermore, the three different procedures resulted in good hemodynamic stability of the animals, and low mortality rate.     

Poorly soluble particulates: searching for a unifying denominator of nanoparticles and fine particles for DNEL estimation

Under the new European chemicals regulation, REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) a Derived No-Effect Level (DNEL), i.e., the level of exposure above which humans should not be exposed, is defined. The focus of this paper is to develop a weight-of-evidence-based DNEL-approach for inhaled poorly soluble particles. Despite the common mode of action of inhaled insoluble, spherical particulate matter (PM), a unifying, most appropriate metric conferring pulmonary biopersistence and toxicity has yet not been demonstrated. Nonetheless, there is compelling evidence from repeated rat inhalation exposure studies suggesting that the particle displacement volume is the most prominent unifying denominator linking the pulmonary retained dose with toxicity. Procedures were developed to analyze and model the pulmonary toxicokinetics from short-term to long-term exposure. Six different types of poorly soluble nano- to submicron PMs were compared: ultrafine and pigmentary TiO₂, synthetic iron oxide (Fe₃O₄, magnetite), two aluminum oxyhydroxides (AlOOH, Boehmite) with primary isometric particles approximately of either 10 or 40 nm, and MWCNT. The specific agglomerate densities of these materials ranged from 0.1 g/cm³ (MWCNT) to 5 g/cm³ (Fe₃O₄). Along with all PM, due to their long retention half-times and associated biopersistence in the lung, even short-term inhalation studies may require postexposure periods of at least 3 months to reveal PM-specific dispositional and toxicological characteristics. This analysis provides strong evidence that pulmonary toxicity (sustained inflammation) is dependent on the volume-based cumulative lung exposure dose. Lung toxicity, evidenced by PMN in BAL occurred at lung doses exceeding 10-times the overload threshold. Furthermore, the conclusion is supported that repeated inhalation studies on rats should utilize an experimental window of cumulative volume loads of respirable PM in the range of 1 μl/lung (no-adverse-effect range); however, not exceeding ≈10 μl/lung that would lead to retention half-times increasing 1 year. This can be targeted best by computational toxicology, i.e., the modeling of particle deposition and lung retention biokinetics during the exposure and recovery periods. Inhalation studies exceeding that threshold volume may lead to meaningless findings difficult to extrapolate to any real-life scenario. In summary, this analysis supports a volume-based generic mass concentration of 0.5 μl PM_respirable/m³ × agglomerate density, independent on nano- or submicron-sized properties, as a generic no-adverse effect level in both rats and humans.     

H3K9 acetylation change patterns in rats after exposure to traffic-related air pollution

Traffic-related air pollution (TRAP) has been acknowledged as a potential risk factor for numerous respiratory disorders including lung cancer; however, the exact mechanisms involved are still unclear. Here we investigated the effects of TRAP exposure on the H3K9 acetylation in rats. The exposure was performed in both spring and autumn with identical study procedures. In each season, 48 healthy Wistar rats were exposed to different levels of TRAP for 4 h, 7 d, 14 d, and 28 d, respectively. H3K9 acetylation levels in both the peripheral blood mononuclear cells (PBMCs) and lung tissues were quantified. Multiple linear regression was applied to assess the influence of air pollutants on H3K9 acetylation levels. The levels of PM_2.5, PM₁₀, and NO₂ in the tunnel and crossroad groups were significantly higher than in the control group. The H3K9 acetylation levels were not significantly different between spring and autumn. When spring and autumn data were analyzed together, no significant association between the TRAP and H3K9 acetylation was found in 4 h exposure window. However, in the 7 d exposure window, PM_2.5 and PM₁₀ exposures were associated with changes in H3K9 acetylation ranging from 0.276 (0.053, 0.498) to 0.475 (0.103, 0.848) per 1 μg/m³ increase in the pollutant concentration. In addition, prolonged exposure of the rats in the tunnel showed that both PM_2.5 and PM₁₀ concentrations were positively associated with H3k9 acetylation in both PBMCs and lung tissues. The findings showed that 7-d and prolonged TRAP exposure could effectively increase the H3K9 acetylation level in both PBMCs and lung tissues of rats.     

Dry Powder Aerosols Generated by Standardized Entrainment Tubes From Drug Blends With Lactose Monohydrate: 1. Albuterol Sulfate and Disodium Cromoglycate

The major objective of this study was: discriminatory assessment of dry powder aerosol performance using standardized entrainment tubes (SETs) and lactose-based formulations with two model drugs. Drug/lactose interactive physical mixtures (2%w/w) were prepared. Their properties were measured: solid-state characterization of phase behavior and molecular interactions by differential scanning calorimetry and X-ray powder diffraction; particle morphology and size by scanning electron microscopy and laser diffraction; aerosol generation by SETs and characterization by twin-stage liquid impinger and Andersen cascade impactor operated at 60 L/min. The fine particle fraction (FPF) was correlated with SET shear stress (τ_s), using a novel powder aerosol deaggregation equation (PADE). Drug particles were < 5 μm in volume diameter with narrow unimodal distribution (Span < 1). The lowest shear SET (τ_s = 0.624 N/m²) gave a higher emitted dose (ED ~ 84–93%) and lower FPF (FPF_6.4 ~ 7–25%). In contrast, the highest shear SET (τ_s = 13.143 N/m²) gave a lower ED (ED ~ 75–89%) and higher FPF (FPF_6.4 ~ 15–46%). The performance of disodium cromoglycate was superior to albuterol sulfate at given τ_s, as was milled with respect to sieved lactose monohydrate. Excellent correlation was observed (R² ~ 0.9804–0.9998) when pulmonary drug particle release from the surface of lactose carriers was interpreted by PADE linear regression for dry powder formulation evaluation and performance prediction.     

Towards the bioequivalence of pressurised metered dose inhalers 1: Design and characterisation of aerodynamically equivalent beclomethasone dipropionate inhalers with and without glycerol as a non-volatile excipient

A series of semi-empirical equations were utilised to design two solution based pressurised metered dose inhaler (pMDI) formulations, with equivalent aerosol performance but different physicochemical properties. Both inhaler formulations contained the drug, beclomethasone dipropionate (BDP), a volatile mixture of ethanol co-solvent and propellant (hydrofluoroalkane-HFA). However, one formulation was designed such that the emitted aerosol particles contained BDP and glycerol, a common inhalation particle modifying excipient, in a 1:1 mass ratio. By modifying the formulation parameters, including actuator orifice, HFA and metering volumes, it was possible to produce two formulations (glycerol-free and glycerol-containing) which had identical mass median aerodynamic diameters (2.4 μm ± 0.1 and 2.5 μm ± 0.2), fine particle dose (⩽5 μm; 66 μg ± 6 and 68 μg ± 2) and fine particle fractions (28% ± 2% and 30% ± 1%), respectively. These observations demonstrate that it is possible to engineer formulations that generate aerosol particles with very different compositions to have similar emitted dose and in vitro deposition profiles, thus making them equivalent in terms of aerosol performance. Analysis of the physicochemical properties of each formulation identified significant differences in terms of morphology, thermal properties and drug dissolution of emitted particles. The particles produced from both formulations were amorphous; however, the formulation containing glycerol generated particles with a porous structure, while the glycerol-free formulation generated particles with a primarily spherical morphology. Furthermore, the glycerol-containing particles had a significantly lower dissolution rate (7.8% ± 2.1%, over 180 min) compared to the glycerol-free particles (58.0% ± 2.9%, over 60 min) when measured using a Franz diffusion cell. It is hypothesised that the presence of glycerol in the emitted aerosol particles altered solubility and drug transport, which may have implications for BDP pharmacokinetics after deposition in the respiratory tract.     

Proposal for a revised Reference Concentration (RfC) for manganese based on recent epidemiological studies

In 1993, based on observations of subclinical neurological effects in workers, the United States Environmental Protection Agency (US EPA) published a Reference Concentration (RfC) of 0.05 μg/m³ for manganese (Mn). The geometric mean exposure concentration, 150 μg/m³ respirable Mn, was considered the lowest observable adverse effect level (LOAEL), and uncertainty factors (UFs) were applied to account for sensitive populations, database limitations, a LOAEL, subchronic exposure, and potential differences in toxicity of different forms of Mn. Based on a review of more recent literature, we propose two alternate Mn RfCs. Of 12 more recent occupational studies of eight cohorts with chronic exposure durations, examining subclinical neurobehavioral effects, predominantly on the motor system, three were considered appropriate for development of an RfC. All three studies yielded no observable adverse effect levels (NOAELs) of approximately 60 μg/m³ respirable Mn. Converting the occupational NOAEL to a human equivalent concentration (HEC) of 21 μg/m³ (for continuous exposure) and applying a UF of 10 to account for intraspecies variability yielded an RfC of 2 μg/m³. We also derived a similar RfC (7 μg/m³) using an Mn benchmark dose (BMD) as the point of departure. Overall confidence in both RfCs is medium.     

Assessment of pulmonary toxicity of gold nanorods following intra-tracheal instillation in rats

The present investigation was aimed to evaluate the pulmonary toxicity of 10 and 25 nm gold nanorods (GNRs) following intra-tracheal instillation in rats using bronchoalveolar lavage (BAL) fluid and lung histopathological analysis. The GNRs displayed that the dose-dependent toxicity via elevated lactate dehydrogenase leakage, alkaline phosphatase, lipid peroxidation and total microprotein levels in BAL fluids after 1 day, 1 week and 1 month post exposure periods. All the parameters were returned to normal values after 3 months post exposure period may be due to recovery. The rat lung histopathology displayed that accumulation of macrophages, inflammatory response and tissue thickening for both sizes of GNRs. 10 nm GNRs increased all BAL fluid parameters significantly following 1 day, 1 week and 1 month post exposure periods whereas 25 nm GNRs have shown similar effects but less extent. These investigations proposed that the dose and size dependent pulmonary toxicity of GNRs.     

Inhalation of chlorine causes long-standing lung inflammation and airway hyperresponsiveness in a murine model of chemical-induced lung injury

Chlorine is highly irritating when inhaled, and is a common toxic industrial gas causing tissue damage in the airways followed by an acute inflammatory response. In this study, we investigated mechanisms by which chlorine exposure may cause reactive airways dysfunction syndrome (RADS) and we examined the dose-dependency of the development of symptoms. Mice were exposed to 50 or 200 ppm Cl₂ during a single 15 min exposure in a nose-only container. The experiment terminated 2, 6, 12, 24, 48, 72 h and 7, 14, 28 and 90 days post exposure. Inflammatory cell counts in bronchoalveolar lavage (BAL), secretion of inflammatory mediators in BAL, occurrence of lung edema and histopathological changes in lung tissue was analyzed at each time-point. Airway hyperresponsiveness (AHR) was studied after 24 and 48 h and 7, 14, 28 and 90 days. The results showed a marked acute response at 6 h (50 ppm) and 12 h (200 ppm) post exposure as indicated by induced lung edema, increased airway reactivity in both central and peripheral airways, and an airway inflammation dominated by macrophages and neutrophils. The inflammatory response declined rapidly in airways, being normalized after 48 h, but inflammatory cells were sustained in lung tissue for at least seven days. In addition, a sustained AHR was observed for at least 28 days. In summary, this mouse model of chlorine exposure shows delayed symptoms of hyperreactive airways similar to human RADS. We conclude that the model can be used for studies aimed at improved understanding of adverse long-term responses following inhalation of chlorine.     

Preparation and Evaluation of Controlled Release Microparticles for Respiratory Protein Therapy

A series of microparticle formulations, designed for controlled release pulmonary therapy, were evaluated in terms of their physical properties, aerosol performance, lung epithelial cell toxicity, and controlled release profile. A protein, bovine serum albumin (BSA) was chosen as a model macromolecule active ingredient which was coprocessed, using spray drying, with varying concentrations of the release modifier, polyvinyl alcohol (PVA). The spray dried microparticles were tested for their physico-chemical characteristics (e.g., size distribution, morphology and density), in vitro aerosolisation performance using a 5-stage Marple Miller Impactor (MMI) and in vitro release profiles by a custom-built diffusion cell (in 100 mL phosphate buffer pH 7.4). The toxicity of PVA on lung epithelial cells was investigated using a human alveolar basal epithelium A549 cell line. Analysis of the particle size data indicated that all the spray dried BSA/PVA samples had similar size distributions with a median particle diameter (d_0.5) across all samples of 2.79 ± 0.11 µm. All formulations had relatively good aerosolisation performance when compared to conventional dry powder inhalation (DPI) formulations although increasing PVA percentage had a negative effect on the aerosol performance in vitro. Analysis of the difference and similarity factors for the release profiles indicated significant differences with respect to PVA concentration. Furthermore, cell toxicity analysis indicated PVA to have limited effect on cell viability after 24 h exposure. A series of protein-based inhalation formulations have been developed and tested, and shown to be suitable for controlled release in the respiratory tract. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2709–2717, 2009     

Effects of Th1 and Th2 cells balance in pulmonary injury induced by nano titanium dioxide

To explore the potential immunoregulatory mechanisms linking nano TiO₂ and pulmonary injury, Sprague Dawley rats were exposed by intra-tracheal instillation to nano TiO₂ with the individual doses of 0.5, 4.0 and 32 mg/kg b.w., micro TiO₂ with 32 mg/kg b.w. and 0.9% NaCl, respectively. The exposure was conducted twice a week, for four consecutive weeks. The results of lung histology demonstrated increased macrophages accumulation, extensive disruption of alveolar septa, slight alveolar thickness and expansion hyperemia. Mitochondria tumefaction organelles dissolution, endoplasmic reticulum expansion and the gap of nuclear broadening were shown. The changes of IFN-γ and IL-4 level showed no statistical difference. The mRNA expression of GATA-3 was up-regulated, whereas T-bet was significantly down-regulated. The protein expression of T-bet decreased and there were significant differences in nano 4 and 32 mg/kg groups. The imbalance of Th1/Th2 cytokines might be one of the mechanisms of immunotoxicity of respiratory system induced by nano TiO₂ particles.     

Altered lung function in rats after subacute exposure to n-butyl isocyanate

The objectives of this study were to use pulmonary function tests, blood gas measurements and bronchoalveolar lung lavage (BAL) to characterize lesions in the respiratory tract of young adult male Wistar rats as a result of a 5-day exposure (6 h/day) to 0, 1.1, 6.2, 15 or 26 mg n-butyl isocyanate (n-BIC)/m³ air. Further objectives were to probe the diagnostic sensitivities of these procedures in comparison with more traditional evaluations (clinical observation, lung weight, histopathology). Measurements were performed during post-exposure weeks 2 and 5. Most rats exposed to 26 mg/m³ died or were sacrificed in a moribund state during post-exposure week 2. All other rats survived the exposure regimen. In rats exposed to 15 and 26 mg/m³ a significant decrease in body weight, laboured breathing, hypoactivity, nasal discharge, cyanosis, and hypothermia were observed. Pulmonary function measurements revealed increased total lung capacity (TLC) and residual volume (RV), decreased forced expiratory flow rates and quasistatic compliance in rats exposed to 26 mg/m³. At the end of the observation period rats exposed to 6.2 and 15 mg/m³ air were hyperresponsive to an acetylcholine bronchoprovocation aerosol. Arterial blood gas measurements revealed an arterial hypoxia and an increase in venous admixture, suggesting a severe mismatch of the ventilation-perfusion relationship, Biochemical and cellular components in BAL fluid (BALF) indicated a concentration dependent and protracted increase of polymorphonuclear leucocytes and further inflammatory parameters. In the 1.1 mg/m³ group BALF parameters were not significantly elevated. The major histopathological lesions of the lung were thickening of septa, emphysema, and intra-alveolar oedema in rats exposed to 26 mg/m³. Collectively, these results demonstrate obstructive and progressive lung disease with associated gas trapping and severe disturbance of the ventilation perfusion relationship which is considered to be the cause of delayed mortality. In terms of variability and sensitivity the increase in BALF parameters was most sensitive in indicating the diseased state of the lung.     

Modifications of breathing pattern induced by inhaled sulphur mustard in mice

A head-only exposure assembly was used for exposing mice to vapours of sulphur mustard (SM). The respiration was monitored using an on-line computer program, capable of recognizing the breathing pattern as sensory irritation, airflow limitation and pulmonary irritation. SM was dissolved in acetone and vapourized using a compressed air nebulizer. Mice were exposed to the vapours (8.5, 16.9, 21.3, 26.8, 42.3 and 84.7 mg/m³) for 1h in a body plethysmograph fitted with a 20-gauge needle and a microphone for sensing the respiratory flow signals. The signals were amplified, digitized and integrated to give tidal volume, and stored in a computer for further analysis. The respiration of the mice was followed for modifications in the breathing pattern until 7 days post-exposure. SM induced sensory irritation during exposure, and there was a concentration dependent decrease in the respiratory frequency and an increase in tidal volume. Lower concentrations showed recovery after stopping the exposure. RD₅₀, the concentration that depresses 50% of the respiration was estimated to be 27.4 mg/m³. Following exposure to higher concentrations the animals started dying after 6␣days. The LC₅₀ was estimated to be 42.5 mg/m³ (14␣days observation period). The respiratory frequency decreased on subsequent days of exposure depending upon the exposure concentration, and the breathing pattern was characteristic of airflow limitation. The ratio of flow/tidal volume was decreased following exposure to concentrations of 26.8 and 42.3 mg/m³. The ratio of flow/tidal volume may be a better measurement than the measurements based on flow alone for the assessment of airflow limitation. Pulmonary irritation was not observed showing that the lungs were not affected. The body weight of the animals decreased progressively. The present methodology will be useful for identifying the effects of SM on the respiratory system, one of the end-points considered when establishing occupational exposure limits. Received: 12 April 1996 / Accepted: 21 August 1996     

Effects of particulate matter from straw burning on lung fibrosis in mice

ObjectiveTo investigate the impacts of particulate matter 2.5 (PM2.5) from straw burning on the acute exacerbation of lung fibrosis in mice and the preventive effects of N-acetylcysteine (NAC).MethodsThe composition, particle size, and 30-min concentration change in an exposure system of the PM2.5 from straw-burning were determined. Forty C57BL male mice were equally randomized to two groups: bleomycin (BLM)-induced lung fibrosis with an exposure to air (BLM + air) and BLM + PM2.5 groups. On day 7 after receiving intratracheal injection of BLM, mice were exposed to air or PM2.5 in an exposure system for 30 min twice daily and then sacrificed after one-week or four-week exposure (10 mice/group). Mouse survival, lung histopathology, macrophage accumulation in the lung, and pro-inflammatory cytokine levels in alveolar lavage fluid (ALF) were determined.ResultsPM2.5 from straw burning were mainly composed of organic matter (74.1%); 10.92% of the inorganic matter of the PM2.5 were chloride ion; 4.64% were potassium ion; other components were sulfate, nitrate, and nitrite. Particle size was 10nm–2 μm. Histopathology revealed a greater extent of inflammatory cell infiltration in the lung, widened alveolar septum, and lung fibrosis in the BLM + PM2.5 group than in the BLM + air group and a greater extent of those adverse effects after four-week than after one-week exposure to PM2.5. The BLM + PM2.5 group also showed macrophages containing particular matter and increased pulmonary collagen deposition as the exposure to PM2.5 increased. Interleukin (IL)-6 and TNF-α levels in ALF were significantly higher in the BLM + PM2.5 group than in the BLM + air group (P < 0.05) and significantly higher after four-week exposure than after one-week exposure to PM2.5 (P < 0.05). TGF-β levels in ALF after four-week exposure were significantly higher in the BLM + PM2.5 group than in the BLM + air group (P < 0.05). The levels of IL-6, TNF-α, and TGF-β in peripheral serum were not significantly different in the BLM + PM2.5 and BLM + air groups. Lung hydroxyproline contents increased as the exposure to PM2.5 increased and were significantly higher after four-week than after one-week exposure (P = 0.019). Exposure to PM2.5 did not affect the survival of normal mice (100%) but reduced the survival of mice with BLM-induced IPF (30%), whereas NAC extended the survival (70%, vs. BLM + PM2.5, P = 0.032).ConclusionExposure of mice with BLM-induced IPF to PM2.5 from straw burning exacerbated lung inflammation and fibrosis and increased mortality; NAC increased the mouse survival, indicating protective effects.     

Sensory irritation, pulmonary irritation, and acute lethality of a polymeric isocyanate and sensory irritation of 2,6-toleune diisocyanate

The use of monomeric and polymeric isocyanates in a wide variety of industries has been increasing. Little is known about the toxicity of polymeric isocyanates and the widely used 2,6-toluene diisocyanate (TDI) isomer. The pulmonary and sensory irritation of an aliphatic polyisocyanate (DES-N) based on hexamethylene diisocyanate (HDI) was studied in Swiss-Webster male mice during aerosol exposures in the range of 25 to 131 mg/m³. The sensory irritation of 2,6-TDI vapor was studied in the range of 0.37 to 7.6 mg/m³ (0.05 to 1.1 ppm). The aerodynamic equivalent diameter and geometric standard deviation for the DES-N aerosol were 0.6 μm and 2.4, respectively. High-speed liquid chromatography was used to determine both free HDI in DES-N and HDI in the exposure chamber. Each exposure was for 3 hr during which the tidal volume pattern and respiratory rate of groups of four mice were recorded. Unlike the monomeric isocyanates, DES-N acted predominantly as a pulmonary irritant, evoking little sensory irritation. The concentration needed to reduce the respiratory rate 50% due to pulmonary irritation was 57.1 mg/m³. The LC50, determined by counting the number of deaths within the 24 hr period following a 4-hr exposure, was 91.2 mg/m³. In groups of animals killed 2 hr after the 4-hr exposure, the concentration of DES-N needed to increase lung weight by 50% was 45 mg/m³. Based on comparisons with another pulmonary irritant, nitrogen dioxide, the maximum concentration for DES-N permitted in industry should be 1 mg/m³ with a time-weighted average for an 8-hr period of 0.5 mg/m³. From the concentration-response relationship due to sensory irritation for 2,6-TDI, the RD50 was determined to be 1.8 mg/m³ (0.26 ppm) which is close to the value of 1.4 mg/m³ (0.20 ppm) determined previously for 2,4-TDI. No pulmonary irritation was observed. For industrial applications the exposure limit for 2,4-TDI of 0.04 mg/m³ (0.006 ppm) is also suggested as appropriate for the 2,6-TDI isomer.     

Preexposure to Amorphous Silica Particles Attenuates but also Enhances Allergic Reactions in Trimellitic Anhydride-Sensitized Brown Norway Rats

Irritant-induced inflammation of the airways may aggravate respiratory allergy induced by chemical respiratory allergens. Therefore, the effect of airway irritation by synthetic amorphous silica (SAS) on respiratory allergy to trimellitic anhydride (TMA) was studied. Brown Norway (BN) rats were topically sensitized on day 0 and on day 7, subsequently exposed for 6 h/day for 6 days to 27 mg/m³ SAS, and challenged by inhalation to a minimally irritating concentration of 12 mg/m³ TMA, 24 h after the last SAS exposure. An additional group was exposed to SAS before a second challenge to TMA. Control groups were treated with vehicle, and/or did not receive SAS exposure. Breathing parameters, cellular and biochemical changes in bronchoalveolar lavage (BAL) fluid, and histopathological airway changes 24 h after challenge were the main parameters studied. Exposure to SAS alone resulted in transient changes in breathing parameters during exposure, and in nasal and alveolar inflammation with neutrophils and macrophages. Exposure to SAS before a single TMA challenge resulted in a slightly irregular breathing pattern during TMA challenge. SAS also diminished the effect of TMA on tidal volume, laryngeal ulceration, laryngeal inflammation, and the number of BAL (lung) eosinophils in most animals, but aggravated laryngeal squamous metaplasia and inflammation in a single animal. The pulmonary eosinophilic infiltrate and edema induced by a second TMA challenge was diminished by the preceding SAS exposure, but the number of lymphocytes in BAL was increased. Thus, a respiratory particulate irritant like SAS can reduce as well as aggravate certain aspects of TMA-induced respiratory allergy.     

Measurement of various respiratory dynamics parameters following acute inhalational exposure to soman vapor in conscious rats

Abstract

Respiratory dynamics were investigated in head-out plethysmography chambers following inhalational exposure to soman in untreated, non-anesthetized rats. A multipass saturator cell was used to generate 520, 560 and 600?mg?×?min/m³ of soman vapor in a customized inhalational exposure system. Various respiratory dynamic parameters were collected from male Sprague-Dawley rats (300--350?g) during (20?min) and 24?h (10?min) after inhalational exposure. Signs of CWNA-induced cholinergic crisis were observed in all soman-exposed animals. Percentage body weight loss and lung edema were observed in all soman-exposed animals, with significant increases in both at 24?h following exposure to 600?mg?×?min/m³. Exposure to soman resulted in increases in respiratory frequency (RF) in animals exposed to 560 and 600?mg?×?min/m³ with significant increases following exposure to 560?mg?×?min/m³ at 24?h. No significant alterations in inspiratory time (IT) or expiratory time (ET) were observed in soman-exposed animals 24?h post-exposure. Prominent increases in tidal volume (TV) and minute volume (MV) were observed at 24?h post-exposure in animals exposed to 600?mg?×?min/m³. Peak inspiratory (PIF) and expiratory flow (PEF) followed similar patterns and increased 24?h post-exposure to 600?mg?×?min/m³ of soman. Results demonstrate that inhalational exposure to 600?mg?×?min/m³ soman produces notable alterations in various respiratory dynamic parameters at 24?h. The following multitude of physiological changes in respiratory dynamics highlights the need to develop countermeasures that protect against respiratory toxicity and lung injury.     

Derivation of an occupational exposure limit for inorganic borates using a weight of evidence approach

Inorganic borates are encountered in many settings worldwide, spurring international efforts to develop exposure guidance (US EPA, 2004; WHO, 2009; ATSDR, 2010) and occupational exposure limits (OEL) (ACGIH, 2005; MAK, 2011). We derived an updated OEL to reflect new data and current international risk assessment frameworks. We assessed toxicity and epidemiology data on inorganic borates to identify relevant adverse effects. International risk assessment frameworks (IPCS, 2005, 2007) were used to evaluate endpoint candidates: reproductive toxicity, developmental toxicity, and sensory irritation. For each endpoint, a preliminary OEL was derived and adjusted based on consideration of toxicokinetics, toxicodynamics, and other uncertainties. Selection of the endpoint point of departures (PODs) is supported by dose–response modeling. Developmental toxicity was the most sensitive systemic effect. An OEL of 1.6 mg B/m³ was estimated for this effect based on a POD of 63 mg B/m³ with an uncertainty factor (UF) of 40. Sensory irritation was considered to be the most sensitive effect for the portal of entry. An OEL of 1.4 mg B/m³ was estimated for this effect based on the identified POD and an UF of 1. An OEL of 1.4 mg B/m³ as an 8-h time-weighted average (TWA) is recommended.     

Interrelating the acute and chronic mode of action of inhaled methylenediphenyl diisocyanate (MDI) in rats assisted by computational toxicology

Polymeric methylenediphenyl diisocyanate (MDI) is a high production volume chemical intermediate consisting of monomeric 4,4′-MDI, its 2,2′- and 2,4′-isomers, and higher oligomeric homologues. The toxicity of pMDI has systematically been investigated in previous regulatory and mechanistic studies. One cornerstone of toxicological risk assessment is to understand the critical Mode of Action (MoA) of inhaled MDI aerosol. This paper compares the no-observed-adverse effect levels (NOAELs) in rats from two published whole-body exposure chronic inhalation bioassays with the lung irritation-based point of departures (PODs) from acute and subacute nose-only inhalation studies. Acute irritation was related to elevated concentrations of protein in bronchoalveolar lavage fluid (short-term studies), whilst the chronic events were characterized by histopathology. In the chronic bioassay the exposure duration was either 6 or 18 h/day while in all other studies a 6 h/day regimens were applied. The major objective of this paper is to analyze the interrelationship of acute pulmonary irritation and the acute-on-chronic manifestations of pulmonary disease following recurrent chronic inhalation exposure. This included considerations on the most critical metrics of exposure with regard to the acute concentration × exposure duration per day (C × T_day) and the chronic cumulative dose metrics. In summary, this analysis supports the conclusion that the C × T_day relative to the acute pulmonary irritation threshold is more decisive for the chronic outcome than the concentration per se or the time-adjusted cumulative dose. For MDI aerosols, the acute threshold C × T_day was remarkably close to the NOAELs of the chronic inhalation studies, independent on their differing exposure mode and regimens. This evidence is supportive of a simple, direct MoA at the site of initial deposition of aerosol. Accordingly, for chemicals reactive to the endogenous nucleophilic agents contained in the lining fluid of the lung, one unifying essential prerequisite for pulmonary injury appears to be a C × T_day that exhausts the homeostatic pool of MDI-scavenging agents. In the case that threshold is exceeded, the secondary compensatory chronic response may then cause additional superimposed types of chronic pathologies.     

Nitric oxide mediated effects on reproductive toxicity caused by carbon disulfide in male rats

This study investigated nitric oxide (NO) mediation of carbon disulfide (CS₂) toxicity that compromised male rat spermatogenesis and endocrine function. Rats were exposed to multiple levels of CS₂ concentration (0, 50, 250, 1250 mg/m³). A 1250 mg/m³ CS₂ + sodium nitroprusside (SNP) group and a 1250 mg/m³ CS₂ + NG-monomethyl-l-arginine (l-NMMA) group were established to explore the role of NO in mediating CS₂ toxicity. NO concentrations, NO synthase (NOS) activity, and sex hormone levels were measured, and sperm characteristics were observed and analyzed. Our data show that CS₂ exposure decreased: NOS activity; tissue NO concentrations; serum levels of gonadotropin-releasing hormones, luteinizing hormones, and testosterone; and sperm count and activity. In contrast, increased serum follicle-stimulating hormone concentrations and teratospermia were observed with CS₂ exposure. SNP reduced some of the toxic effects of CS₂, while l-NMMA treatment showed no effect. The results suggests that NO mediates compromised reproductive system function caused by CS₂ exposure.