Journal of Clinical & Experimental Dermatology Research
Open Access

Abstract

Factors Affecting the Concentration of Diphenylmethane-4,4′-Diisocyanate in Freund’s Complete Adjuvant. Can They Affect the Outcome of the Guinea-Pig Maximization Test?

Haneen Hamada, Magnus Bruze, Erik Zimerson, Marléne Isaksson, Malin Engfeldt

Background: The animal assay Guinea Pig Maximization Test (GPMT) uses Freund’s complete adjuvant (FCA) to enhance the dermal sensitization in the animals. In a previous study, the degree of sensitization when investigating diphenylmethane-4,4′-diisocyanate (4,4′-MDI) varied. 4,4′-MDI is known to be a reactive diisocyanate and concern was risen that its instability and reaction with FCA might affect the outcome.
Objectives: To investigate the stability of 4,4′-MDI and its possible reaction with components in FCA.
Methods: The same preparations as used in the GPMT were prepared, i.e. 1.0% w/v 4,4ʹ-MDI in FCA/paraffin oil (40/60 v/v) and stored under different conditions for 48 hours. The content of 4,4′-MDI in both FCA/paraffin oil mixtures as well as in samples of pure substance were monitored by chemical analysis using gel permeation chromatography (GPC).
Results: The 4,4′-MDI content in pure substance can decrease substantially within a few months. A rapid decrease in 4,4′-MDI concentration was also seen in 4,4′-MDI/FCA preparations stored in refrigerator and room temperature.
Conclusion: The outcome of 4,4ʹ-MDI sensitization in GPMT might be affected by the instability of the pure substance as well as its reaction with FCA. Major effects can be expected if these two factors are interacting. Hence, fresh 4,4ʹ-MDI should be used and preparations of induction substances should be prepared in close connection to the intradermal injection.