Michelle Schaper

Characteristic modifications of the breathing pattern of mice to evaluate the effects of airborne chemicals on the respiratory tract

A system was developed for exposure of unanesthetized mice to airborne chemicals and for continuous measurement of their breathing pattern prior to, during and following exposure. By measuring inspiratory and expiratory airflows (VI and VE), and integration with time to yield tidal volume (VT), we obtained characteristic modifications to the normal breathing pattern. These permitted recognition that a specific portion of the respiratory tract was affected by the selected airborne chemicals. Following recognition, we also quantitated the degree of effect using one specific measurement in each case. An effect on the upper respiratory tract, induced by the sensory irritant, 2-chlorobenzylchloride, was quantitated by measuring a decrease in respiratory frequency. An effect on the conducting airways, induced by the airway constrictor, carbamylcholine, was quantitated by a decrease in VE at the mid-point of VT. An effect at the alveolar level, induced either by the vagal nerve ending stimulant, propranolol, or by the pulmonary irritant, machining fluid G, was quantitated by an increase in the length of a pause induced at the end of expiration. The system is easy to construct and operate and can be used to rapidly evaluate the effects of airborne chemicals on the respiratory tract.

Development of a database for sensory irritants and its use in establishing occupational exposure limits.

A database was developed for chemicals whose sensory-irritating properties had been investigated using a previously described animal bioassay. In this bioassay, mice were exposed to an airborne chemical, and changes in their respiratory pattern were determined. For each chemical tested, the concentration capable of producing a 50% decrease in respiratory rate (RD50) was obtained and its relative potency estimated. For the current study, 295 such airborne materials, including single chemicals and mixtures, were found in the literature. A total of 154 RD50 values were obtained in male mice of various strains for the 89 chemicals in the database for which there were also TLVs. An examination of the TLVs and RD50 values demonstrated, as previously with the smaller dataset (n = 40), a high correlation (R2 = 0.78) of the TLVs with 0.03 x RD50. This supports the continued use of the animal bioassay for establishing exposure limits to prevent sensory irritation in the workplace. No other bioassay provides this type of information or has been used so extensively to suggest guidelines for occupational exposures.

Computer assisted recognition and quantitation of the effects of airborne chemicals acting at different areas of the respiratory tract in mice.

The pattern and timing of a normal breath in unanesthetized mice was analyzed from measurement of inspiratory and expiratory airflows (VI and VE). Airflow was measured via a differential pressure transducer, attached to a pneumotachograph, which itself was attached to a body plethysmograph into which a mouse was placed. The analog voltage from the differential pressure transducer was digitized and stored for analysis on a microcomputer. Criteria were developed to classify each breath as normal (N) or belonging into one of seven abnormal categories. The abnormal categories were arrived at by computer analysis, recognizing specific modifications of the normal pattern into patterns of: sensory irritation of the upper respiratory tract (S), airflow limitation within the conducting airways of the lungs (A) or pulmonary irritation at the alveolar level (P). Combinations of these effects, i.e., S+A, P+A, P+S and P+S+A were also recognized. Computer analysis of each breath also permitted quantitative evaluation of the degree of S, A or P abnormalities. To induce each type of effect we used inhalation exposures to 2-chlorobenzylchloride, carbamylcholine or propranolol. We propose that this approach will permit rapid evaluation of the possible effects of airborne chemicals at three levels of the respiratory tract, with the classification of the type of effect easily obtained in an objective way using well defined criteria, followed by quantitation of the degree of each effect.

Sensory and pulmonary irritation with exposure to methyl isocyanate

Methyl isocyanate (MIC) was tested for its potency as a sensory irritant and as a pulmonary irritant in mice. To evaluate sensory irritation, animals were exposed to MIC at concentrations between 0.5 and 7.6 ppm for a period of 90 min. A characteristic reflex decrease in respiratory rate indicating sensory irritation was observed. The concentration evoking a 50% decrease in respiratory rate (RD50) was found to be 1.3 ppm. To evaluate pulmonary irritation, animals were first anesthetized and fitted with a tracheal cannula. Following recovery from anesthesia, they were exposed to MIC at concentrations between 0.4 and 7.3 ppm for a period of 90 min. A characteristic decrease in respiratory rate indicating pulmonary irritation in tracheally cannulated (TC) mice was observed. The concentration evoking a 50% decrease in respiratory rate (RD50TC) was found to be 1.9 ppm. Thus, MIC was found to be a potent sensory and pulmonary irritant.

Structure-activity relationships of volatile organic chemicals as sensory irritants

Abstract We used a database of 145 volatile organic chemicals for which the sensory irritation potency (RD50) has been reported in mice. Chemicals were first separated into two groups: nonreactive and reactive, using Fergusons rule. This rule suggests that nonreactive chemicals induce their effect via a physical ( p) mechanism (i.e., weak forces or interactions between a chemical and a biological receptor). Therefore, appropriate physicochemical descriptors can be used to estimate their potency. For reactives, a chemical (c) mechanism (i.e., covalent bonding with the receptor) would explain their potency. All chemicals were also separated on the basis of functional groups and subgroups into 24 classifications. Our results indicated that the potency of nonreactive chemicals, regardless of their chemical structure, can be estimated using a variety of physicochemical descriptors. For reactive chemicals, we identified five basic reactivity mechanisms which explained why their potency was higher than that estimated from physicochemical descriptors. We concluded that Fergusons proposed rule is adequate initially to classify two separate mechanisms of receptor interactions, p vs c. Several physicochemical descriptors can be used to estimate the potency of p chemicals, but chemical reactivity descriptors are needed to estimate the potency for c chemicals. At present, this is the largest database for nonreactive-reactive chemicals in toxicology. Because of the wide variety of c chemicals presented, a semi-quantitative estimate of the potency of new, or not previously evaluated, c chemicals can be arrived at via comparison with those presented and the basic chemical reactivity mechanisms presented.

Improved immunosuppression with aerosolized cyclosporine in experimental pulmonary transplantation

Rejection remains a major obstacle to long-term success of pulmonary transplantation. Direct delivery of cyclosporine to lung allografts may produce better control of rejection by generating high intragraft concentrations of drug with decreased systemic delivery and toxicity. The efficacy of inhaled cyclosporine in preventing allograft rejection was compared with systemic delivery by intramuscular injections in a rat model of lung transplantation (Brown-Norway to Lewis). Group 1 animals were given no immunosuppression. Group 2 received a single i.m. injection of 25 mg/kg CsA on the day of operation while group 3 received daily doses on postoperative days 0–3. Groups 4–7 received aerosolized CsA daily for seven days. The aerosol generator produced an airborne concentration of CsA of 180 mg/ m3 with a mean particle size of 0.7 μ and estimated pulmonary depositions of CsA of 0.98–3.6 mg/kg/day. Animals were killed on POD 7, and the transplanted lungs graded histologically in a blinded fashion. All control animals showed destructive grade 4 changes by POD 7. Animals receiving high-dose aerosolized CsA (groups 6 and 7) showed minimal changes with a mean rejection grade of 1.3. A single i.m. dose of CsA (group 2) failed to prevent rejection; the mean grade was 2.2. Animals given four i.m. doses of CsA had a mean grade of 1.8. Aerosolized CsA provided significantly better control of rejection than did systemic CsA (groups 6 and 7 vs. groups 2 and 3; P<0.0002 and <0.0054, respectively). Local delivery of CsA by aerosol inhalation is effective in limiting acute rejection of the rat lung allograft.

Estimating the Sensory Irritating Potency of Airborne Nonreactive Volatile Organic Chemicals and Their Mixtures

This article describes the possibility of estimating whether or not a mixture of nonreactive volatile organic chemicals (NRVOC) is likely to elicit complaints of sensory irritation in humans. For this estimation we rely on: a) the sensory irritating potency of individual NRVOC can be estimated from a variety of physicochemical properties of these chemicals, b) at low exposure concentrations, the additivity rule can be applied using the potency of each chemical in a mixture and c) a threshold concentration exists below which no sensory irritation will occur. We used this estimating approach and we compared the results obtained with those obtained experimentally in humans exposed to a well defined mixture. The approach presented can be used to arrive at a decision as to whether or not exposure to a mixture of NRVOC is likely to result in sensory irritation complaints by humans, either in the general indoor air situation or for industrial workers.

Evaluation of airborne particulates and fungi during hospital renovation

This study was conducted over 30 weeks on a hospital floor undergoing partial renovation. Some patients housed on the floor were immunosuppressed, including bone marrow transplant recipients. The construction zone was placed under negative pressure and was separated from patient rooms by existing hospital walls and via erection of a temporary barrier. Other control measures minimized patient exposure to airborne materials. Air sampling was done for 3 weeks prior to construction, 24 weeks during construction, and 3 weeks after renovation was completed. Airborne particulate concentrations, total spore counts, particle size, and fungal species were assessed. At the beginning of the renovation there were increases in airborne particulates (from 0.2 to 2.0 mg/m3) and fungal spores (from 3.5 to 350 colony forming units (CFU/m3), but only in the construction zone. Throughout the remainder of the renovation, particulate and fungal spore levels fluctuated inside the construction zone but remained close to baseline values in the patient area. When renovation was completed, particulates and spore counts inside the construction zone decreased to preconstruction levels. The primary fungus isolated from air samples was Penicillium. This study demonstrated that control measures were effective in reducing exposures of hospitalized patients to airborne particulates and spores and in reducing the increased risk of aspergillosis and other fungal infections associated with hospital construction projects. The data from this study may be useful in establishing exposure guidelines for other health care settings.

Respiratory effects of trimellitic anhydride aerosols in mice

Groups of mice were exposed to trimellitic anhydride (TMA) aerosols for 30 min at concentrations ranging from approximately 2 to 150 mg/m3. The sensory and pulmonary irritating properties of TMA were assessed during these exposures. Sensory irritation, as evidenced by a lengthening of the time of expiration (TE), was not evoked in any exposure. However, TMA aerosols evoked other rapid, reversible alterations of respiratory cycle timing, suggestive of pulmonary irritation. The time of inspiration (TI) and expiration (TE) decreased as TMA exposure concentration was increased. Also, characteristic pauses (i. e., apneic periods) occurred between breaths. The length of these pauses (TP) increased as TMA exposure concentration was raised. Respiratory frequency (f) was dependent upon the magnitude of increase in TP. At lower TMA concentrations, TP was short and f was elevated, whereas at higher concentrations, TP was long and f was reduced. Interestingly, there was no other evidence of pulmonary irritation besides the alterations in respiratory cycle timing. Histopathological evaluation of the respiratory tracts of TMA-exposed animals revealed no changes from those of controls. Finally, there was no evidence of cumulative or delayed pulmonary effects in mice repeatedly exposed to TMA aerosols. These acute changes in respiratory cycle timing may have occurred as a result of stimulation of vagal nerve endings along the conducting airways and in the deep lung, directly produced by TMA aerosols.

Immunosuppression with aerosolized cyclosporine for prevention of lung rejection in a rat model

The efficacy of local delivery of aerosol cyclosporine (CsA) for prevention of lung rejection was compared with the intramuscular route (IM) in a fully allogeneic rat model (BN/LEW) of lung transplantation (LTx). Control rats (group 1, n = 6) received no CsA after LTx. Rats in group 2 (n = 10) received 4 doses of CsA in olive oil (25 mg/kg) intramuscularly starting on postoperative day (POD) 0. Group 3 (n = 9) was treated with aerosolized CsA for 3 h/day for 7 days starting on POD 0. All animals were sacrificed on POD 6. Transplanted lungs were graded histologically in a blind manner on a 0-4 scale. Control animals all showed grade 4 rejection. i.m. CsA therapy reduced lung rejection with a rejection grade of 1.8 +/- 0.35 (mean +/- SD) but was associated with a 50% incidence of pneumonia. Aerosol CsA provided better control of rejection with a rejection grade of 1.2 +/- 0.4 (group 3 vs. group 2: P less than 0.05 Wilcoxon) and none of these animals had penumonia. Trough blood levels of CsA were significantly lower in the group treated with aerosolized CsA when compared with the IM group (P less than 0.05). Therefore we conclude that: (1) aerosol CsA is effective in preventing lung allograft rejection following lung transplantation in rats, and (2) local delivery of aerosol CsA is superior to the i.m. route because better control of rejection is achieved with a lower systemic delivery of CsA.