Two-week inhalation toxicity of polymeric diphenylmethane-4, 4'-diisocyanate (PMDI) in rats: analysis of biochemical and morphological markers of early pulmonary response

Evaluation of animal toxicity studies with diisocyanates regarding presence of thresholds for induction and elicitation of respiratory allergy by quantitative weight of evidence

Animal toxicity studies on diisocyanates were evaluated using quantitative weight of evidence (QWoE) to test the hypothesis that the dose-response curve shows a threshold for the induction and/or elicitation of respiratory sensitization. A literature search identified 59 references that included at least two concentration groups of the diisocyanate and a vehicle-exposed concurrent control in the study design. These studies were subjected to a QWoE-assessment applying scoring criteria for quality and relevance/strength of effects relevant to the selected endpoint of respiratory sensitization. Overall, the studies assessing dose/concentration-response for diisocyanates with the endpoint, respiratory sensitization, were heterogenous regarding study design, animal models used, endpoints assessed, and quality. Only a limited number of the studies subjected to the QWoE-assessment allowed drawing conclusions about possible thresholds for respiratory sensitization. Highest quality and relevance/strength of effects scores were obtained by a series of studies specifically designed to investigate a potential threshold for elicitation of respiratory sensitization in the Brown Norway (BN) rat. These studies applied an elaborate study design to optimize induction of respiratory sensitization and reduce interference by respiratory tract irritation. In summary, the available studies provided moderate to good support for the existence of a threshold for elicitation and limited to moderate support for a threshold regarding induction of respiratory allergy by diisocyanates in experimental animals. However, a quantitative extrapolation of threshold values established in rodents to humans remains complex.

General and genetic toxicology studies of Aleurites moluccana (L.) Willd. seeds in vitro and in vivo assays

ETHNOPHARMACOLOGY RELEVANCE

Aleurites moluccana is popularly used for the diseases like ulcers, fever, headache, asthma, conjunctivitis, gonorrhea, inflammation, hepatitis, and rheumatism. The seed, also known as "noz da Índia", has been popularly consumed for weight loss purposes but reports of toxicity have been associated with its ingestion. In the literature, there are not enough studies to elucidate its toxicology, so evaluating the general and genetic toxicological of A. moluccana seeds can provide data to ensure their intake.

AIM OF THE STUDY

The objective of the present study was to elucidate the oral toxicity, mutagenicity, genotoxicity and cytotoxicity of A. moluccana seeds in vitro and in vivo assays.

MATERIALS AND METHODS

The chemical composition of the aqueous extract of A. moluccana seeds (AEAMS) was analyzed in relation to phenolic compounds, tannins, flavonoids and fatty acid. For the in vitro assays, the cytotoxic potential was assessed by the MTS assay whereas the mutagenic potential was assessed by the Ames test. For in vivo assays, was conducted an acute oral toxicity study, with "Up-and-Down Procedure" and repeated dose toxicity with "Repeated Dose 28-Day Oral Toxicity". To assess genetic damage, mutagenic potential was assessed by the micronucleus test whereas the polychromatic erythrocyte/normochromatic erythrocyte ratio was obtained with bone marrow cells to determine the cytotoxic potential and genotoxic potential was assessed by the comet assay using peripheral blood cells.

RESULTS

AEAMS did not show cytotoxic and mutagenic potential in vitro. No clinical signs of toxicity were observed in animals after the acute oral toxicity test, suggesting that the LD₅₀ of aqueous extract of A. moluccana seeds > 2000 mg/kg in a single dose by intragastric route. However, in toxicity at repeated doses for 28 days, the doses initially established (250; 500 and 750 mg/kg/day by intragastric route) caused mortality in the animals and the reestablished doses (25, 50 and 100 mg/kg/day by intragastric route) showed no changes in parameters or clinical signs attributed to toxicity. Furthermore, AEAMS also did not show mutagenic, genotoxic and cytotoxic potential in vivo.

CONCLUSIONS

AEAMS did not show cytotoxic, genotoxic and mutagenic potential in vitro and in vivo. And although the AEAMS has an LD₅₀ > 2000 mg/kg, and does not have physiological, biochemical, hematological, histopathological changes or clinical signs related to toxicity when administered in low concentrations and for a short period, in high concentrations and continued use caused toxicity and mortality in Wistar rats. In order to obtain complementary results, is recommended highly that further mid and long-term toxicological studies are investigated, and in no-rodent specie.

Immunotoxicological impact and biodistribution assessment of bismuth selenide (Bi2Se3) nanoparticles following intratracheal instillation in mice

Variously synthesized and fabricated Bi2Se3 nanoparticles (NPs) have recently been explored for their theranostic properties. Herein, we investigated the long term in-vivo biodistribution of Bi2Se3 NPs and systematically screened its immune-toxic potential over lungs and other secondary organs post intratracheal instillation. X-Ray CT scan and ICP MS results revealed significant particle localization and retention in lungs monitored for 1 h and 6 months time period respectively. Subsequent particle trafficking was observed in liver, the major reticuloendothelial organ followed by gradual but incomplete renal clearance. Pulmonary cytotoxicity was also found to be associated with persistent neutrophilic and ROS generation at all time points following NP exposure. The inflammatory markers along with ROS generation further promoted oxidative stress and exaggerated additional inflammatory pathways leading to cell death. The present study, therefore, raises serious concern about the hazardous effects of Bi2Se3 NPs and calls for further toxicity assessments through different administration routes and doses as well.

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 18h/day while in all other studies a 6h/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.

Antibiotic acyldepsipeptides activate ClpP peptidase to degrade the cell division protein FtsZ

The worldwide spread of antibiotic-resistant bacteria has lent urgency to the search for antibiotics with new modes of action that are devoid of preexisting cross-resistances. We previously described a unique class of acyldepsipeptides (ADEPs) that exerts prominent antibacterial activity against Gram-positive pathogens including streptococci, enterococci, as well as multidrug-resistant Staphylococcus aureus. Here, we report that ADEP prevents cell division in Gram-positive bacteria and induces strong filamentation of rod-shaped Bacillus subtilis and swelling of coccoid S. aureus and Streptococcus pneumoniae. It emerged that ADEP treatment inhibits septum formation at the stage of Z-ring assembly, and that central cell division proteins delocalize from midcell positions. Using in vivo and in vitro studies, we show that the inhibition of Z-ring formation is a consequence of the proteolytic degradation of the essential cell division protein FtsZ. ADEP switches the bacterial ClpP peptidase from a regulated to an uncontrolled protease, and it turned out that FtsZ is particularly prone to degradation by the ADEP-ClpP complex. By preventing cell division, ADEP inhibits a vital cellular process of bacteria that is not targeted by any therapeutically applied antibiotic so far. Their unique multifaceted mechanism of action and antibacterial potency makes them promising lead structures for future antibiotic development.

Extensive Analysis of Elastase-Induced Pulmonary Emphysema in Rats: ALP in the Lung, a New Biomarker for Disease Progression?

It is accepted that pulmonary exposure of rodents to porcine pancreatic elastase (ELT) induces lesions that morphologically resemble human emphysema. Nonetheless, extensive analysis of this model has rarely been conducted. The present study was designed to extensively examine the effects of ELT on lung inflammation, cell damage, emphysematous change, and cholinergic reactivity in rats. Intratracheal administration of two doses of ELT induced 1) a proinflammatory response in the lung that was characterized by significant infiltration of macrophages and an increased level of interleukin-1beta in lung homogenates, 2) lung cell damage as indicated by higher levels of total protein, lactate dehydrogenase, and alkaline phosphatase (ALP) in lung homogenates, 3) emphysema-related morphological changes including airspace enlargement and progressive destruction of alveolar wall structures, and 4) airway responsiveness to methacholine including an augmented Rn value. In addition, ELT at a high dose was more effective than that at a low dose. This is the novel study to extensively analyze ELT-induced lung emphysema, and the analysis might be applied to future investigations that evaluate new therapeutic agents or risk factors for pulmonary emphysema. In particular, ALP in lung homogenates might be a new biomarker for the disease progression/exacerbation.

Comparative Analysis of Pulmonary Irritation by Measurements of Penh and Protein in Bronchoalveolar Lavage Fluid in Brown Norway Rats and Wistar Rats Exposed to Irritant Aerosols

The object of this study was to compare in two strain of rats (Brown Norway and Wistar) that were acutely exposed (1 x 6 hrs) to aerosols of polymeric methylenediphenyl-4,4'-diisocyanate (MDI), the relative sensitivity of the functional endpoint "enhanced pause (Penh)" with endpoints in bronchoalveolar lavage fluid (BALF) indicative of lower respiratory tract irritation. This approach included an analysis of both the concentration-response and the time-course of effects. Penh was measured repeatedly prior to (baseline) and during a stepped methacholine (MCh) bronchoprovocation challenge in barometric plethysmographic chambers on postexposure days 1, 3, and 7. Results show that total protein in BALF was a sensitive endpoint to probe early effects caused by exposure to irritant polyisocyanate aerosol. Baseline Penh increased in a concentration-dependent manner and paralleled closely the magnitude of increased BALF-protein on postexposure day 1. The time-course of changes in Penh complemented those of BALF-protein observed in previous studies. The incremental increase of Penh during a stepped MCh-challenge was attenuated with increasing baseline Penh values. In summary, these data show that the exposure to irritant concentrations of this aerosolized polyisocyanate caused a transient perturbation of the blood/air-barrier, which can suitably be probed by measurements of protein in BALF. Although Penh appears to parallel these changes, it displays substantially greater variability. The increase in Penh is apparently more related to changes in breathing patterns either caused by stimulation of receptors or changes in the mechanical properties of lung parenchyma. In regard to Penh and BALF-protein, both strains of rats were equally susceptible, although some endpoints displayed a higher variability in Brown Norway rats when compared to Wistar rats. This supports the conclusion that Wistar rats afford a higher diagnostic resolution than BN rats.

Brown Norway rat asthma model of diphenylmethane-4,4'-diisocyanate (MDI): analysis of the elicitation dose-response relationship

The known human asthmagen polymeric diphenylmethane-diisocyanate (MDI) was investigated in the Brown Norway rat skin asthma model. Two types of dose-response relationships are addressed with the following focus: (1) does sensitization dose and surface area influence the subsequent elicitation response and (2) is the elicitation response more dependent on previous elicitation doses or more on skin sensitizing dose? These two aims are investigated in two elaborated experiments, using inflammatory (bronchoalveolar lavage, BAL) and physiologic (Penh) endpoints to characterize asthma-like responses in rats. Postchallenge measurements of Penh focused on responses delayed in onset. Inflammatory endpoints in BAL were performed one day after the fourth challenge. Both protocols utilized a dermal sensitization phase with two administrations on days 0 and 7 followed by four inhalation challenges with approximately 38 mg MDI/m(3) in intervals of 2 weeks. In the first protocol three groups of rats were topically dosed with 40, 10, and 2.5 mul of MDI per rat. Each dose group consisted of three subgroups with dosed surface areas of 3.1-12.6 cm(2), 0.8-3.1 cm(2), and 0.4-0.8 cm(2), respectively. In the second protocol groups of rats were topically dosed with 40 microl of MDI per rat followed by three challenges with 37 mg MDI/m(3). At the fourth challenge subgroups of rats were either challenged with 8, 18, or 39 mg MDI/m(3). Independent of the protocol used, response was characterized by increased influx of neutrophilic granulocytes in BAL and delayed respiratory response. All groups from the first study sensitized to and challenged with MDI elicited a distinct response relative to similarly challenged naive rats. A sensitization dose dependence of the elicitation response was not found. The second protocol revealed that the elicitation dose correlates with increased neutrophils in BAL and delayed-onset respiratory responses. In summary, these data suggest that the vigor of asthma-like responses appear to be more dependent on the inhalation elicitation dose of previously challenged rats rather than the dermal induction dose.

Absorption, distribution, metabolism and excretion of an inhalation dose of [14C] 4,4'-methylenediphenyl diisocyanate in the male rat

The received dose, tissue distribution, metabolism, routes and rates of excretion of [(14)C]-4, 4(')-methylenediphenyl diisocyanate (MDI) were investigated in the male rat following a 6-h inhalation exposure to [(14)C]-MDI at a target concentration of 2 mg m(-3). The mean dose received was equivalent to 0.078 mg MDI per animal, of this between 25 and 32% of radiolabelled material was available systemically. Radioactivity was distributed to all tissues examined with the highest proportions present in the respiratory and gastrointestinal tracts, suggesting that both oral ingestion and pulmonary absorption contributed to the systemic dose of [(14)C]-MDI derived material, with the oral ingestion and the majority of the internal dose resulting from ingestion of radiolabelled material by grooming the pelt after exposure. Radioactivity was excreted mainly via faeces (about 80% of the received dose). Excretion in bile and urine each accounted for less than 15% of the dose. MDI was extensively metabolized after uptake, with two routes of transformation evident; the proposed spontaneous formation of mixed molecular weight polyureas and the enzyme catalysed metabolism of systemically available MDI or MDI derivatives to give N-acetylated and N-acetylated hydroxylated products. No free MDA was detected in any of the biomatrices (urine, faeces, bile) investigated.

Alveolar macrophages have a dual role in a rat model for trimellitic anhydride-induced occupational asthma

Occupational exposure to low molecular weight chemicals, like trimellitic anhydride (TMA), can result in occupational asthma. Alveolar macrophages (AMs) are among the first cells to encounter inhaled compounds. These cells can produce many different mediators that have a putative role in asthma. In this study, we examined the role of AMs in lung function and airway inflammation of rats exposed to TMA. Female Brown Norway rats were sensitized by dermal application of TMA or received vehicle alone on days 0 and 7. One day before challenge, rats received intratracheally either empty or clodronate-containing liposomes to deplete the lungs of AMs. On day 21, all rats were challenged by inhalation of TMA in air. Lung function parameters were measured before, during, within 1 h after, and 24 h after challenge. IgE levels and parameters of inflammation and tissue damage were assessed 24 h after challenge. Sensitization with TMA led to decreased lung function parameters during and within 1 h after challenge as compared to non-sensitized rats. AM depletion alleviated the TMA-induced drop in lung function parameters and induced a faster recovery compared to sham-depleted TMA-sensitized rats. It also decreased the levels of serum IgE 24 h after challenge, but did not affect the sensitization-dependent increase in lung lavage fluid IL-6 and tissue TNF-alpha levels. In contrast, AM depletion augmented the TMA-induced tissue damage and inflammation 24 h after challenge. AMs seem to have a dual role in this model for TMA-induced occupational asthma since they potentiate the immediate TMA-induced decrease in lung function but tended to dampen the TMA-induced inflammatory reaction 24 h later.

Inhaled cationic amphiphilic drug-induced pulmonary phospholipidosis in rats and dogs: time-course and dose–response of biomarkers of exposure and effect

This study compares the pulmonary response to an inhaled highly soluble hydrochloride (CAD-HCl) with a low soluble sulphate salt (CAD-SO4) of a dicationic amphiphilic drug (CAD). These salts are known to accumulate in the lung. The bioavailability through gastrointestinal uptake is poor. Wistar rats and beagle dogs received repeated 1 h/day inhalation exposures over 1-4 weeks. The focus of this analysis is to appraise the correlation of markers of effects related to pulmonary phospholipidosis and cytotoxicity relative to the concentration of CAD in the lung tissue, alveolar macrophages and serum. Rats and dogs are known to experience remarkable differences in their respiratory minute volumes and respiratory patterns. In order to facilitate dosimetric comparisons, identical exposure paradigms and methodological procedures were selected. Over a wide range of cumulative dosages, the CADs bound to lung tissue and cells in bronchoalveolar lavage (BAL) paralleled, whilst no clear association existed in terms of plasma concentrations. This suggests that analysis of the fractional loading of BAL-cells (mainly alveolar macrophages) with CAD or CAD-surfactant complexes is amenable to monitor the accumulation of CADs in the lung. In terms of the comparative phospholipidosis-inducing potency, the CAD-HCl was more potent as compared to CAD-SO4. Following dosimetric adjustments, rats and dogs appeared to be equally susceptible to phospholipidosis. In summary, when exposed to equivalent concentrations of CADs, dogs did not demonstrate a markedly different susceptibility than rats. With regard to the relative intensity of changes, the increase of phospholipids in BAL-fluid and especially BAL-cells correlated with the cumulative exposure dose. Thus, with regard to probing the extent of CAD-induced 'overloading' of alveolar macrophages pharmacokinetic determinations in BAL-cells are considered superior to determinations in plasma. Additional advantages of using the alveolar macrophage as denominator to normalize pulmonary drug concentrations include comparisons across species, and exposure regimens are feasible based on almost readily available endpoints in both pre-clinical and selected clinical studies.

Respiratory allergy and pulmonary irritation to trimellitic anhydride in Brown Norway rats

Occupational exposure to low-molecular-weight (LMW) allergens such as acid anhydrides can result in occupational asthma, an allergic disease characterized by episodic airway obstruction, airways inflammation, and non specific airways hyperresponsiveness. Since LMW irritants can provoke rather similar effects and since most, if not all, LMW allergens have irritant properties, this study addressed the distinction between allergenic and irritant effects of the respiratory allergen trimellitic anhydride (TMA). BN rats were sensitized by dermal application of TMA or vehicle alone and 3 weeks later were challenged by inhalation of a slightly irritating concentration of TMA or the vehicle. Lung function was measured before, during, and shortly after challenge. One day after challenge, in vivo and in vitro nonspecific airways hyperresponsiveness to methacholine was measured, and bronchoalveolar lavage was performed to measure total protein, lactate dehydrogenase, N-acetyl-glucosaminidase, and total and differential leukocyte numbers in the fluid. In addition, IgE measurements and histopathological examinations of the respiratory tract were carried out. TMA challenge of sensitized, but not sham-sensitized, BN rats reduced breathing frequency during challenge, elevated total and TMA-specific serum IgE levels, and caused a typical allergic asthma-associated airway pathology, as observed earlier. Vehicle challenge did not cause these effects, irrespective of sensitization. Hyperresponsiveness to methacholine was only seen in TMA-sensitized and -challenged rats. These rats also showed increased levels of the biochemical parameters and increased numbers of eosinophils and neutrophils in the lung lavage fluid; TMA challenge of sham-sensitized rats caused similar but markedly less pronounced effects. During TMA challenge of sham-sensitized rats, a breathing pattern typical of irritation was noticed but a clearly distinct pattern was seen upon TMA challenge of sensitized rats. In conclusion, TMA challenge of sensitized rats caused sensitization-dependent asthma-like early changes in breathing pattern that clearly could be distinguished from irritant-induced changes and non-specific airways hyperresponsiveness 24 h after challenge. Sensitization-dependent functional changes were accompanied by inflammatory changes characteristic of asthma and biochemical evidence of airway damage.

Analysis of markers of exposure to polymeric methylene-diphenyl diisocyanate (pMDI) in rats: a comparison of dermal and inhalation routes of exposure

Rats received polymeric methylenediphenyl-diisocyanate (pMDI) or a mixture of methylenediphenyl-4,4'-diamine (4,4'-MDA) and amino-di(aminophenylmethylene)-benzene (3-core MDA) by single inhalation or dermal exposure. The ratio of 4,4'-MDA and 3-core MDA used in this study mirrored that of 4,4'-MDI and 3-core MDI present in pMDI. The yields of the corresponding markers of exposure in hydrolyzed blood (Hb-adducts) and urine were determined. For the inhalation exposure, rats were acutely exposed for a duration of 6 h to 3.7 mg pMDI/m3 and 2.7 mg MDA/m3, respectively. Furthermore, C x t products of approximately 1200 mg pMDI/m3 x h were examined, ranging from 3 h x 6.2 mg/m3, 1.5 h x 12.7 mg/m3, 45-min x 25.1 mg/m3, and 23-min x 58.1 mg/m3. Additional groups of rats received equimolar doses of pMDI and MDA by epicutaneous exposure, i.e., 100 mg pMDI/kg bw, equivalent to approximately 50 mg 4,4'-MDI/kg bw and 34 mg 3-core MDI/kg bw or 79 mg MDA-mixture/kg bw, equivalent to 46 mg 4,4'-MDA/kg bw and 33 mg 3-core-MDA/kg bw. The biomarkers measured in this study suggest that the kind and yield of biomarkers are dependent on the route of exposure and differ markedly for MDI and MDA. This isocyanate appears to undergo reactions specific to the site of first contact (e.g., formation of adducts, conjugates and/or polyureas), suggesting that these markers of 'total body burden' can neither predict the local dose at that site nor does it provide any means to identify the route receiving the most critical dose. Similarly, it appears that the formation of biomarkers is governed by reactions requiring an intact isocyanate group rather than hydrolysis. In contrast, for MDA this type of portal-of-entry specificity was not observed. Moreover, trace amounts of diamines available to dermal contact, with respect to the isocyanate, may cause false-positive readings. Thus, in spite of the recognized advantages of biomonitoring to identify cryptic exposures not readily detected by conventional analytical sampling procedures, in regard to pMDI this technique appears to be potentially biased to overestimate exposure, i.e., results obtained from integrating dosimeters of exposure need to be verified by adequate air monitoring.

Carcinogenic risk of toluene diisocyanate and 4,4'-methylenediphenyl diisocyanate: epidemiological and experimental evidence

Diisocyanates are highly reactive compounds widely used, for example, in the production of polyurethane foams, elastomers, paints, and adhesives. The high chemical reactivity of these compounds is also reflected in their toxicity: diisocyanates are one of the most important causes of occupational asthma but also other adverse effects, such as irritation and toxic reactions, have been described in exposed subjects. One of the open questions is whether occupational isocyanate exposure is a carcinogenic hazard. The few epidemiological studies available have been based on young cohorts and short follow-up and are not conclusive. Toluene diisocyanate (TDI) has been classified as carcinogenic in animals on the basis of gavage administration studies, but no conclusions are available on inhalation exposure. For 4,4'-methylene diphenyldiisocyanate (MDI) there is suggestive evidence for carcinogenicity in rats. The possible carcinogenic mechanism of TDI and MDI is not clear. Both chemicals have been positive in a number of short-term tests inducing gene mutations and chromosomal damage. The reactive form could be either the diisocyanate itself or may derive from the metabolic activation of the aromatic diamine derivatives formed by hydrolysis. TDI and MDI react with DNA in vivo and in vitro. However, the structure of the adducts has not been identified. Especially from the in vivo experiment it is not known if the adducts are a product from the reaction with the isocyanate or the corresponding amine. In conclusion, both TDI and MDI are highly reactive chemicals that bind to DNA and are probably genotoxic. The alleged animal carcinogenicity of TDI and MDI would suggest that occupational exposure to these compounds is a carcinogenic risk. The few epidemiological studies available have not, however, been able to clarify if TDI and MDI are occupational carcinogens.

Inhalation toxicity of 1,6-hexamethylene diisocyanate homopolymers (HDI-IC and HDI-BT): results of subacute and subchronic repeated inhalation exposure studies

This article addresses results of two 13-wk inhalation toxicity studies in Wistar rats with aerosolized 1,6-hexamethylene diisocyanate (HDI) homopolymers using either the isocyanurate (HDI-IC) type or biuret (HDI-BT) type. Groups of 10 rats/sex/level were exposed nose-only to breathing zone concentrations of 0.5, 3.3, and 26.4 mg HDI-IC/m(3) or 0.4, 3.4, and 21.0 mg HDI-BT/m(3) (MMAD = 1.4-3.3 microm). The exposure regimen was 6 h/day, 5 days/wk for 13 wk. Two control groups were used in each study; one was exposed to filtered air, and the other to the vehicle acetone. In subacute pilot studies, groups of rats were exposed under identical conditions for 3 consecutive weeks using concentrations of approximately 4, 15-18, and 77-90 mg homopolymer/m(3). All studies demonstrated that adverse effects were caused by irritation-related responses occurring predominantly in the lower respiratory tract. Following subchronic exposure, compound-related effects were found only at the highest concentrations used and were confined to mild respiratory distress, marginally decreased body weights, and increased lung weights. Hematological evaluation showed a marginal increase in leukocyte counts. Pulmonary function testing revealed minimal changes indicative of increases in functional residual capacity and total lung capacity but without evidence of increased bronchial hyperreactivity to acetylcholine aerosol. Histopathology demonstrated an increased recruitment of alveolar macrophages, focal interstitial fibrosis with round-cell infiltrations, and bronchiolo-alveolar proliferations at the high-level exposure groups. The no-observable-adverse-effect levels (NOAELs) of both the 3- and 13-wk studies were in the range of 3-4 mg/m(3). Appreciable differences between the two types of polyisocyanates were not observed.

Inhalation studies in laboratory animals--current concepts and alternatives

Highly standardized and controlled inhalation studies are required for hazard identification to make test results reproducible and comparable and to fulfill general regulatory requirements for the registration of new drugs, pesticides, or chemicals. Despite significant efforts, the results of inhalation studies have to be analyzed judiciously due to the great number of variables. These variables may be related to technical issues or to the specific features of the animal model. Although inhalation exposure of animals mimics human exposure best, ie, error-prone route-to-route extrapolations are not necessary, not all results obtained under such very rigorous test conditions may necessarily also occur under real-life exposure conditions. Attempts are often made to duplicate as closely as possible these real-life exposure conditions of humans in appropriate bioassays. However, this in turn might affect established baseline data, rendering the interpretation of new findings difficult. In addition, specific use patterns, eg, of inhalation pharmaceuticals or pesticide-containing consumer products, may impose test agent-specific constraints that challenge traditional approaches. Moreover, specific modes of action of the substance under investigation, the evaluation of specific endpoints, or the clarification of equivocal findings in common rodent species may require exposure paradigms or the use of animal species not commonly used in inhalation toxicology. However, particularly in inhalation toxicology, the choice of animal models for inhalation toxicity testing is usually based on guideline requirements and practical considerations, such as exposure technology, expediency, and previous experience rather than validity for use in human beings. Larger animal species, apart from the welfare aspects, may require larger inhalation chambers to accommodate the animals, but for technical reasons and the difficulty of generating homogeneous exposure atmospheres in such inhalation chambers, this may jeopardize the outcome of the study. Some of the many variables and possible artifacts likely to occur in animal inhalation studies are addressed in this paper.