Experimental lung injury induced by trimellitic anhydride inhalation on guinea pigs

Immunologic effector mechanisms in animal models of occupational asthma

Occupational asthma is a form of immunotoxicity resulting from an exaggerated immune response to substances encountered in the workplace. Symptoms include reversible airway obstruction, airway hyperresponsiveness, airway remodeling, mucus production and cellular infiltration into the lung, particularly eosinophilia. The asthmatic response is divided into the induction phase, occurring after initial exposure to allergen, followed by the effector phase where a subsequent exposure to the allergen results in the respiratory symptoms. Animal models have been used to investigate the asthmatic response and this review will focus on mechanistic studies of the effector phase. Variables that may impact the effector phase include strain and species of animal, dose of allergen, route of exposure, and developmental stage of the animal. Both trimellitic anhydride (TMA) and ovalbumin are known causes of occupational asthma. Ovalbumin is also a reference protein allergen in immunology, and TMA is used as a prototype of a low molecular weight respiratory allergen. Differences in effector mechanisms for TMA and ovalbumin have been noted in different animal models. Studies in the guinea pig provide the most direct comparisons of effector mechanisms of TMA and ovalbumin, with differences in the role of the complement system and arachidonate metabolites being noted. Besides the guinea pig, the Brown Norway rat, and various mouse strains provide useful asthma models for TMA and ovalbumin. However, studies of effector mechanisms are somewhat lacking in either of these species using TMA as the allergen. Continued studies are indicated to determine if unique effector mechanisms can be identified for the many different causes of occupational asthma.

Animal models to test respiratory allergy of low molecular weight chemicals: a guidance

At present, there are no widely applied or fully validated test methods to identify respiratory LMW allergens, i.e. compounds that are considered capable of inducing allergic asthma. Most tests have been investigated using strong respiratory allergens. Moreover, they are meant to detect the potential of a chemical to induce respiratory sensitisation at relatively high doses. Consequently, the sensitivity of the tests is not well-known, and they do not provide information on low doses such as generally found in occupational situations, and on threshold levels to be used in risk assessment. In addition, the various test methods use different application routes, i.e. intradermal, topical or inhalation exposure, and different parameters. Therefore standardised and validated dose-response test methods are urgently required in order to be able to identify respiratory allergens and to recommend safe exposure levels for consumers and workers. In the present paper, methods or testing strategies are described to detect respiratory sensitisation and/or allergy. Overall, assays that utilize only an induction phase may serve as indicators of respiratory sensitisation potential whereas assays that use both an induction and an elicitation or challenge phase may provide information on potency and presence of thresholds. The dermal route as sensitisation route has the advantage of the respiratory tract not being exposed to the allergen prior to challenge which facilitates the distinction between irritant and allergic effects.

Approaches to induce and elicit respiratory allergy: impact of route and intensity of exposure

Although a number of test protocols have been developed to predict respiratory allergenic potential, none of these are widely applied or fully accepted. However, given the serious health problems caused by respiratory allergy and the ever-increasing stream of new chemicals into workplaces, early identification of chemical respiratory allergens is important. Inhalation exposure as well as skin application have been used in predictive tests to induce respiratory tract sensitisation. While there are good indications in laboratory animals and humans that skin exposure can act as a route for respiratory tract sensitisation and vice versa, less is known about the effect of the route on the type of allergy evoked and on dose-response relationships. Although, the responses were in general more vigorous after dermal sensitisation than after inhalation sensitisation, the nature of the immune responses seemed to be qualitatively comparable. As to the intensity of exposure, dose or concentration-response relationships have been observed both during respiratory sensitisation and challenge, suggesting that assessment of safe exposure levels is feasible. Finally, a correct distinction between respiratory allergens and non-sensitising airway irritants is needed for effective risk assessment and management.

Trimellitic anhydride (TMA) dust induces airway obstruction and eosinophilia in non-sensitized guinea pigs

Trimellitic anhydride (TMA) causes asthma after a latency period of sensitization. In non-sensitized humans and animals, limited studies indicate that TMA exposure may also cause symptoms of asthma without a latency period. Our previous studies (J. Pharmacol. Exp. Ther. 296 (2001) 284) in a guinea pig model of TMA-induced asthma demonstrated that sensitization and the complement system were required for eosinophilia. TMA conjugated to guinea pig serum albumin (TMA-GPSA) was used to elicit the response. Since occupational exposure to TMA occurs by inhalation of dust, the present studies determined if exposure to TMA dust in a non-sensitized guinea pig elicited airway obstruction and inflammation, and whether a significantly greater response occurred after a latency period of sensitization. Guinea pigs were intradermally injected with either corn oil (non-sensitized animals) or 30% TMA (sensitized animals). Three weeks later they were challenged by intratracheal insufflation with 1 mg TMA dust or lactose dust (control) using a dry powder delivery device. Pulmonary resistance, dynamic lung compliance, mean arterial blood pressure and heart rate were monitored for 10 min. In non-sensitized guinea pigs, significant increases in pulmonary resistance and decreases in dynamic lung compliance and blood pressure occurred after TMA challenge. In sensitized animals, the same dose of TMA caused significantly greater effects compared to non-sensitized animals. In a separate experiment, cellular infiltration into the lung was determined 24 h after challenge with TMA dust or lactose dust. In both non-sensitized and sensitized animals, eosinophils in the lung tissue were increased after TMA dust challenge compared to controls. Thus, these studies suggest that the response in non-sensitized animals differs depending on whether TMA dust or TMA-GPSA is used to elicit the response. TMA dust elicits significant airway obstruction and eosinophilia in a non-sensitized animal, with even greater airway obstruction occurring in a sensitized animal.

Trimellitic anhydride-induced cellular infiltration into Guinea pig lung varies with age but not gender

BACKGROUND

In humans the incidence of asthma changes with age and gender. Immature guinea pigs have been used to model the allergic response to the occupational allergen trimellitic anhydride (TMA) where exposure to adults is paramount. We hypothesized that the TMA-induced allergic response in immature guinea pigs was similar to mature animals, regardless of gender.

METHODS

Sexually immature and mature female and male guinea pigs were sensitized intradermally with TMA. Three weeks after sensitization they were challenged intratracheally with TMA conjugated to guinea pig serum albumin (TMA-GPSA) or GPSA as a control. Twenty-four hours later cell infiltration into the lung was determined. TMA-specific IgG(1) and IgG(2) were measured in plasma and the complement activation product C3a was measured in the bronchoalveolar lavage fluid.

RESULTS

In control animals, numbers of eosinophils and neutrophils varied with age and gender. The TMA-GPSA- induced cellular infiltration was similar in all age/gender groups. However, neutrophils in the lung tissue increased only in immature animals. IgG antibodies differed between groups but did not account for differences in cell infiltration. C3a correlated with the extent of cell infiltration in all groups except mature females.

CONCLUSIONS

TMA-induced neutrophilia differs with age. TMA-induced changes in eosinophils and macrophages did not vary with age or gender. The relationship between complement activation and inflammation in mature females differs from that in the other groups, suggesting mediators of the response may change with age and gender. Effects of age and gender need to be considered in animal models of the allergic response.

The role of IgG1 and IgG2 in trimellitic anhydride-induced allergic response in the guinea pig lung

Trimellitic anhydride (TMA) is a small molecular weight chemical used in the paint and plastics industry that can cause asthma-like symptoms in humans. Guinea pigs sensitized intradermally with TMA will respond to antigen challenge with asthma-like symptoms, including an immediate bronchoconstriction and a delayed cellular infiltration into the lung, particularly eosinophil infiltration. Sensitized guinea pigs produce TMA-specific IgG1, which is thought to be important in asthmatic reactions in this animal model; however, they also produce TMA-specific IgG2 antibody. The purpose of the present study was to determine the role of IgG1 and IgG2 in the TMA-induced immediate bronchoconstriction and delayed cellular infiltration in the guinea pig. Guinea pigs were passively sensitized by intratracheal instillation of TMA-specific IgG2, an antibody preparation enriched with TMA-specific IgG1, or a combination of the two. The allergic response was induced by intratracheal instillation of TMA conjugated to guinea pig serum albumin (TMA-GPSA). A significantly greater bronchoconstrictor response was observed in animals sensitized with a combination of the IgG2 and IgG1 preparation compared to those sensitized with IgG2 or the IgG1 preparation alone. Cellular infiltration was quantified 24 h after antigen challenge by differential cell counts of bronchoalveolar lavage (BAL) cells as well as by using eosinophil peroxidase (EPO) and myeloperoxidase (MPO) activity as a measure of the numbers of eosinophils and neutrophils, respectively. In the BAL, passively sensitizing with IgG2 alone resulted in an increase in both TMA-induced MPO and EPO activity. In contrast, in the lung, passively sensitizing with a partially purified preparation of TMA-specific IgG1 alone resulted in a significant increase in TMA-induced EPO activity. Passively sensitizing with IgG2 in conjunction with the IgG1 preparation resulted in an enhanced cellular infiltration and lung injury over that seen with either antibody preparation alone. These data demonstrate an augmentation of IgG1-mediated responses by the addition of IgG2 and suggest a significant role for both subclasses of IgG antibodies in this guinea pig model of TMA-induced occupational asthma.

Anaphylactic bronchoconstriction in immunized guinea pigs provoked by inhalation and intravenous administration of hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride

We established a guinea-pig model of anaphylactic bronchoconstriction provoked in immunized animals by inhalation and intravenous administration of 4,4-methyltetrahydrophthalic anhydride (MTHPA) and hexahydrophthalic anhydride (HHPA). Guinea pigs were immunized intradermally with either MTHPA (n = 8) or HHPA (n = 8) suspended in olive oil. Control animals (n = 8) were injected with olive oil alone. After 4 weeks, the animals were challenged during mechanical ventilation by inhalation or intravenous administration of MTHPA or HHPA conjugated with guinea-pig serum albumin (GPSA). Airway flow, and airway and esophageal pressures were measured. Resistance (R) and static compliance (Cst) of the respiratory system (rs), lung (1), and chest wall were studied with the flow-interruption technique. After challenge with MTHPA-GPSA or HHPA-GPSA, R,rs and R,1 increased dramatically while Cst,rs and Cst,1 decreased, and severe arterial hypoxia developed. The reaction occurred at a well-defined dose of anhydride and lasted about 30 min. When the same dose was repeated after 30 min, the response was much attenuated. MTHPA and HHPA can induce asthma in guinea pigs. The dose-response curve at antigen challenge is steep. Once a threshold dose is reached, a severe reaction occurs. The reactivity is then exhausted. This model may be suitable for assessing occupational asthma caused by acid anhydrides and possibly by other low-molecular-weight chemicals.

Induction of type I hypersensitivity in guinea pigs after inhalation of phthalic anhydride

Guinea pigs were exposed through inhalation to phthalic anhydride (PA) dust at 0.5, 1.0, and 5.0 mg/m3, 3 hours/day for 5 consecutive days. Inhalation challenge with aerosolized phthalic anhydride-guinea pig serum albumin (PA-GPSA) conjugate elicited immediate-onset respiratory reactions in animals exposed to all three levels of dust. Inhalation challenge of a subgroup of animals with phthalic anhydride dust did not elicit an immediate response, as measured by changes in respiratory frequency and plethysmograph pressure. Serologic studies showed that these animals had allergic IgG1a antibody to PA-GPSA. There was a dose-dependent increase in specific IgG antibody activity, as measured by ELISA. Animals exposed to and challenged with 5.0 mg/m3 PA dust had significant numbers of hemorrhagic lung foci. Those animals with the greatest number of foci had high IgG antibody activity to PA, as measured by ELISA. This study showed that exposure to levels of PA dust as low as 0.5 mg/m3, below the current threshold limit value of 6.0 mg/m3, can sensitize animals to produce allergic antibody.

Guinea pig model of immunologic asthma induced by inhalation of trimellitic anhydride

We established a model of asthma induced by trimellitic anhydride (TMA) in guinea pigs and assessed the role of sensitization in the development of their bronchial hyperresponsiveness, and relationship between bronchial responsiveness and bronchial inflammation. Fourteen guinea pigs (sensitized group) were administered 1 mg/0.5 ml of trimellity 36-bovine serum albumin intramuscularly and 0.5 ml of complete Freund adjuvant on Day 1 as the priming dose. Booster doses were repeated on Day 15. By Day 28, all of the sensitized animals showed a high passive hemagglutination titer against trimellityl 14-ovalbumin. On Day 29, they were challenged by an inhalation of TMA (150 mg/m3) for 30 min, and respiratory resistance (Rrs) was monitored by the oscillation method. In all sensitized animals, Rrs increased immediately upon challenge and returned to baseline within 6 h. The bronchial reactivity to acetylcholine (Ach), measured 6 h after TMA challenge in the sensitized animals, increased significantly (p < 0.01) compared with that measured 24 h before challenge; that measured 24 h later was not different from that before challenge. There was also a significant difference (p < 0.01) in the number of eosinophils in the lamina propria and the epithelium 6 and 24 h after the challenge inhalation in the sensitized group. The increased airway responsiveness to Ach in the sensitized animals was correlated with an increase in the number of eosinophils in the lamina propria and the epithelium. These observations suggest that humoral antibody and eosinophils are involved in the pathogenesis of TMA-induced asthma.