The molecular initiating event in the adverse outcome pathway for skin sensitization is the covalent binding of the sensitizer to skin proteins, and a first method to address this key event was adopted as OECD TG 442C in 2015. This method, the direct peptide reactivity assay (DPRA), uses two synthetic peptides (one containing a cysteine, one containing a lysine residue) that are incubated with a single concentration of the test substance. After 24 hours incubation, the concentrations of remaining, non-depleted peptide are determined using HPLC.All currently adopted non-animal OECD TGs to assess skin sensitization, including the DPRA, provide information on the
An express (3-minute) test for acute toxicity determination by using the oligochaete annelid, Tubifex tubifex, is described. The EC50(Tubifex tubifex) [EC50(Tt)] for movement inhibition was calculated by using a concentration–response dependence. The reproducibility of the test was checked over several years and by several workers. Its applicability is limited to compounds which are soluble in water. The calculated EC50(Tt) indices correlate with LC50 values determined by using the fish, Pimephales promelas (96hour assay), and with ICG50 values determined by using the ciliate, Tetrahymena pyriformis (48-hour assay) with high statistical significance (r = 0.822, n = 35, and r = 0.927, n = 80, respectively). The correlation between the EC50(Tt) indices and rat oral LD50 values (48-hour assay) was r = 0.519 (n = 67). The correlation within organic compounds was closer (r = 0.635, n = 60) than with the heterogeneous series of chemicals. A similar trend was noticed for the correlation with mouse oral LD50 values (r = 0.479, n = 56) with the heterogeneous series of chemicals, as compared that with the series without inorganic salts (r = 0.605, n = 42), and similarly with mouse intraperitoneal LD50 values, where r = 0.543 (n = 50) with the heterogeneous series of chemicals and r = 0.893 (n = 33) with the series of organic chemicals.
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