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Toxicological information

Respiratory sensitisation

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Administrative data

Endpoint:
respiratory sensitisation
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: No suitable guideline

Data source

Reference
Reference Type:
publication
Title:
Assessment of respiratory hypersensitivity in guinea pigs sensitized to toluene diisocyanate: a comparison of sensitization protocols
Author:
Pauluhn J & Mohr U
Year:
1998
Bibliographic source:
Inhal.Toxicol. 10: 131-54

Materials and methods

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Toluene Diisocyanate, Desmodur T80, an 80:20 mixture of the 2,4 and 2,6 isomers (purity >99.9%)

Test animals

Species:
guinea pig
Strain:
Dunkin-Hartley
Sex:
female

Test system

Route of induction exposure:
intradermal
Route of challenge exposure:
inhalation
Vehicle:
corn oil
Concentration:
0.3% TDI in 100µl corn oil (intradermal)
0, 3.8, 11, 26, 46 and 51mg TDI/m3
Details on study design:
For comparison, groups of guinea pigs were sensitized to TDI by combined single intradermal injection (0.3% TDI in 100 microlitres corn oil) and repeated inhalation exposure (3h/day for 5 consecutive days) to 0, 3.8, 11, 26, 46, and 51 mg TDI/m3 air. One group of animals was sensitized by intradermal injection only. Naive and polyisocyanate resin (50 and 250 mg dust/m3 air) sensitized animals served as controls. Three weeks after the first encounter with the inducing agent, animals were challenged with the free TDI (ca 0.5 mg/m3), and 1 week later with the TDI-protein conjugate.Animals induced with the polyisocyanate resin were similarly challenged with the free chemical (ca 50 mg/m3) and TDI- as well as resin-protein conjugates.

Results and discussion

Results:
Two groups were exposed by inhalation of 136 or 220 mg TDI/m3 for 15 min. They experienced bradypnoea on the day of exposure.

The bradypnoea experienced by the animals exposed to 3.8 mg TDI/m3 was accompanied by a laboured/irregular breathing pattern and breathing sounds at higher concentrations. Those exposed to >11 mg TDI/m3 displayed reduced motility.

The animals sensitized by a single, brief, high-level exposure appeared to be mildly more responsive to TDI challenge than those in the other groups.

The guinea pigs receiving the id and the inhalation exposure, showed a longer, more intense response to TDI-GPSA, than those which received only the injection.

The guinea pigs were sacrificed 1 day after the conjugate challenge.Tissue sections from TDI exposed animals showed the presence of epithelial disruption, pulmonary inflammation and activation of the lung associated lymph nodes (LALN). Inflammation was characterised by infiltration of eosinophils and polymorphonuclear leucocytes. Histological analysis of the lungs, and LALN, revealed an association of the influx of polymorphonuclear and eosinophilic granulocytes, and the TDI level at induction. The 15 min exposure to 220 mg TDI/m3 caused a statistically significant increase of polymorphonuclear and eosinophilic granulocytes. Infiltrations of these granulocytes were seen in the tracheae of the animals exposed to TDI by inhalation, with the exception of those receiving 138 mg TDI/m3 for 15 min.

The guinea pigs exposed to the polyisocyanate resin had IgG1 antibodies to both TDI-GPSA and resin-GPSA; apparently cross-reactivity.

Any other information on results incl. tables

The inhalation challenge with TDI failed to elicit pulmonary responses, while during the TDI-protein conjugate challenge characteristic changes in breathing patterns occurred. Animals sensitized to higher concentrations of TDI by inhalation displayed increased responsiveness to ACh and an influx of eosinophilic granulocytes in airways or lung-associated lymph nodes (LALN). Guinea pigs of the TDI resin groups did not respond to any challenge, nor was there any influx of eosinophils in airways or LALN; that is, they were indistinguishable from naive controls. IgG1 antibodies were observed in all groups receiving TDI or TDI resin.

In summary, it could be demonstrated that the intradermal injection, in addition to the 5 x 3 h inhalation exposures, did not increase markedly the sensitivity of this animal model. However, the outcome of test appeared to be less dependent on the exposure concentration used for sensitization of the animals when the combined protocol was used. Therefore, it is believed that the combined induction protocol improves the robustness of this animal model. Accordingly, in order to classify a low-molecular-weight substance as a respiratory sensitizer, a triad of responses should be considered: (1) positive respiratory response upon challenge with the hapten, and if negative, also challenge with the conjugate of the hapten, (2) an influx of eosinophilic granulocytes, and (3) increased specific IgG1 response.

Applicant's summary and conclusion