Analysis of Draize eye irritation testing and its prediction by mining publicly available 2008-2014 REACH data

Abstract

Public data from ECHA online dossiers on 9,801 substances encompassing 326,749 experimental key studies and additional information on classification and labeling were made computable. Eye irritation hazard, for which the rabbit Draize eye test still represents the reference method, was analyzed. Dossiers contained 9,782 Draize eye studies on 3,420 unique substances, indicating frequent retesting of substances. This allowed assessment of the test’s reproducibility based on all substances tested more than once. There was a 10% chance of a non-irritant evaluation after a prior severe-irritant result according to UN GHS classification criteria. The most reproducible outcomes were the results negative (94% reproducible) and severe eye irritant (73% reproducible). To evaluate whether other GHS categorizations predict eye irritation, we built a dataset of 5,629 substances (1,931 “irritant” and 3,698 “non-irritant”). The two best decision trees with up to three other GHS classifications resulted in balanced accuracies of 68% and 73%, i.e., in the rank order of the Draize rabbit eye test itself, but both use inhalation toxicity data (“May cause respiratory irritation”), which is not typically available. Next, a dataset of 929 substances with at least one Draize study was mapped to PubChem to compute chemical similarity using 2D conformational fingerprints and Tanimoto similarity. Using a minimum similarity of 0.7 and simple classification by the closest chemical neighbor resulted in balanced accuracy from 73% over 737 substances to 100% at a threshold of 0.975 over 41 substances. This represents a strong support of read-across and (Q)SAR approaches in this area.

Keywords: animal testing alternatives; chemical safety; dataset; in silico; ocular toxicity.

Fig. 1. Prevalence of outcomes for substances tested with OECD TG 405 (Draize rabbit eye test) in REACH registrations 2008–2014

Mode outcome was used for substances with multiple OECD TG 405 studies.

Fig. 2

Number of Draize rabbit eye tests per year found in REACH registrations 2008–2014

Fig. 3. Eye irritation category endpoint scores

Built from 4,134 Draize studies where the result could be mapped to a standard Draize category. Box plots describe score distributions for iris, cornea, conjunctivae and chemosis endpoints given different Draize categories and are based on the “score” parameter for Draize tests. Reversibility is not considered in this analysis. Scores outside of Draize definitions (given in Tab. 1) are the results of incorrect inputs in ECHA dossiers.

Fig. 4. Draize endpoint classification strategy as represented by IDRI

The flowchart shows how eye irritation classifications are made for Type 1, Type 2A, Type 2B and non-irritant categories. Corn = cornea score, chem = chemosis score, 7 Day Reverse = Status of 7 day phenotype reversibility, 21 Day reverse = Status of 21 day phenotype reversibility. It should be noted that substances causing serious or irreversible eye damage (“corrosion”) that persists within 21 days post-exposure are also considered Type 1.

Fig. 5. GHS Draize category decision tree from Draize endpoint data

Decision tree trained using CART algorithm from severity and reversibility features using 391 substances for which eye irritation category could be defined. Note that this decision tree closely matches the criteria defined in GHS hazards. Cornea μ stands for the mean cornea score from Draize studies for a chemical, cornea max is the maximum observed cornea score from Draize studies for a chemical (see Section 2.3).

Fig. 6. Decision trees built from subset analysis of hazards dataset

Subsets generated from substances with hazard classifications for all hazards in decision tree. These decision trees indicate strong relationships between GHS hazard classifications.

Fig. 7. Fruchterman Reingold layout of a chemical similarity map for substances with rabbit eye irritation data in REACH registrations 2008–2014

929 substances with at least one Draize study and a mapping to PubChem were included. Chemical similarity was expressed as Jaccard (Tanimoto) index. Red = Type1, Orange = Type2A, Yellow = Type2B, Blue = non-irritant. Size of node is proportional to number of neighbors (larger nodes have more neighbors).