Peer-Reviewed PublicationApril 2022

Ascorbic acid specifically reduces the misclassification of nonirritating reactive chemicals in the OptiSafe™ macromolecular eye irritation test

Toxicology In Vitro, Vol. 80, April 2022 · Lebrun Labs Research Team

Overview

A persistent challenge for any in vitro eye irritation test is the false-positive problem: some chemicals react with test substrates in ways that mimic irritation signals, even though they pose no real hazard to the eye. This study demonstrates that adding ascorbic acid, a key antioxidant naturally present in ocular fluid, to the OptiSafe™ reaction mixture selectively neutralizes those misleading signals without affecting the test's ability to detect true irritants. The result is a meaningful improvement in specificity, reducing unnecessary hazard classifications for reactive-but-safe ingredients such as certain aldehydes and reducing agents commonly found in cosmetic and personal care formulations.

Abstract

The OptiSafe™ macromolecular eye irritation test (EIT) is a nonanimal, shelf-stable assay that detects ocular irritants by measuring the interaction of a test substance with a surrogate macromolecular substrate. A known limitation of macromolecular-based assays is that some reactive chemicals, particularly aldehydes and reducing agents, can produce false-positive results by reacting with the substrate through mechanisms unrelated to ocular irritation. This study investigated whether the addition of ascorbic acid, an antioxidant present in the aqueous humor of the eye, could reduce these false positives without compromising sensitivity. A panel of reactive nonirritants and confirmed irritants was tested with and without ascorbic acid supplementation. Results showed that ascorbic acid specifically reduced the false-positive rate for reactive nonirritants while maintaining sensitivity for true GHS Category 1 and Category 2 irritants. The modification improves the overall accuracy of the OptiSafe™ test and better models the antioxidant environment of the living eye.

Relevance to Lebrun Labs Services

This refinement is built into the current version of the OptiSafe™ Eye Irritation Test (EIT) that Lebrun Labs runs as a contract testing service. For clients formulating with reactive ingredients, including aldehydes, reducing agents, or oxidizing compounds, this improvement means fewer unnecessary Category 1 or Category 2 eye irritation classifications and a more accurate picture of real-world ocular hazard. Industries that benefit most include cosmetics, personal care, household cleaning products, and industrial chemical manufacturers seeking GHS or EU CLP classification data. Our team can advise on whether your specific formulation chemistry is likely to benefit from this protocol refinement.

Research reported in this publication was supported by the National Institute of Environmental Health Sciences of the National Institutes of Health under Award Number SB1ES025501. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.