Allergenic extracts contain biologic components that are subject to degradation over time. Therefore, each lot of commercial extract is assigned a specific expiration date. Protein degradation is common for most extracts and often results in a decrease in potency. It is important to be familiar with the factors that can affect the stability of an extract in order to minimize changes in extract potency over time.
Temperature
Most proteins are susceptible to degradation at extreme temperatures so storing extracts at or near refrigeration (2-8°C) is the best way to maintain their stability. Prolonged exposure to ambient or higher temperatures will likely accelerate the degradation of allergenic proteins. Extracts that undergo a freeze-thaw cycle should not be used due to the likelihood of protein denaturation. It is important to note that most (if not all) allergenic extracts will have different stability profiles despite exposure to ideal storage conditions.
Diluent/Concentration
In most cases, allergenic extracts are more stable at higher protein concentrations and in solutions that contain 50% glycerin. Glycerin stabilizes protein structure and inhibits the enzymatic degradation of proteins that is otherwise observed in normal saline preparations. Human Serum Albumin (HSA) is another suitable diluent for allergenic extracts. HSA serves as a surrogate protein to maintain a stabilizing protein concentration at greater dilutions. It is also believed that HSA may help by coating the surface of the glass vial which presumably prevents the denaturation of allergenic proteins on the glass surface. Recent data from our laboratory indicates that HSA may be particularly beneficial when working with dilute extracts.
Mixing
Some allergens contain proteins with very high proteolytic activity (e.g. cockroach and molds). The latest stability studies from our laboratory have revealed a noticeable reduction in major allergen levels for various pollens when mixed with either cockroach or certain molds after just a short length of time. This measurable loss in major allergen may signify a clinically relevant drop in potency for those products. Further work is underway to extend and verify these findings.
For more information about our current efforts in extract stability profiling, please contact our scientific affairs team.