The relationship of chemical structure to teratogenic activity among bisazo dyes: a re-evaluation.

Although the potency of trypan blue as a teratogenic agent in rodents has been known for almost twenty years the mechanism of its action remains obscure. The dye produces a variety of biological effects (see review by Beck & Lloyd, 1966) and most of these have at some time been suggested as possibly relevant to its teratogenicity. The investigation of such correlations would clearly be assisted by determining whether the biological effects of the dye are individually modified by small changes in its chemical structure, particularly if these changes also result in differences in its teratogenicity. The first teratological study of dyes related to trypan blue was made by Gillman, Gilbert, Spence & Gillman (1951), who obtained negative results in rats with six dyes (methylene blue, trypan red, Sudan IV, Bismarck brown, Niagara blue and sky blue), but gave no experimental details of their investigation. Later Wilson (1955) studied the effects of fourteen dyes on rat gestation by injecting 10 mg of each subcutaneously on each of days 7, 8 and 9 of pregnancy. He obtained large numbers of malformed offspring at term only from trypan blue, while Evans blue, Niagara blue 4B and Niagara sky blue 6B, the four dyes most closely related to trypan blue in structure, were found to be teratogenic but to a far lesser degree. In the same year Tuchmann-Duplessis & Mercier-Parot (1955) reported that azo blue was not teratogenic. Beaudoin & Pickering (1960) tested Niagara blue 2B (see Table 1 for formula) and sixteen specially synthesized compounds resembling all or part of the trypan blue molecule. Each dye was administered by a single injection of 140 mg/kg intraperitoneally into rats on the 8th day of gestation. Only two of these substances produced malformed offspring at term and then in very small numbers. Beaudoin (1961) also tested several dyes against the developing chick, and found that only trypan blue, Evans blue and Niagara blue 4B were more teratogenic than saline.