FREE-RADICAL ACTIVITY OF SYNTHETIC VITREOUS FIBERS - IRON CHELATION INHIBITS HYDROXYL RADICAL GENERATION BY REFRACTORY CERAMIC FIBER

Synthetic vitreous fibers are in widespread use but the parameters tha t dictate their carcinogenicity are still a matter of scientific debat e. The free radical activities of a panel comprising an asbestos sampl e and five different respirable synthetic vitreous fiber samples were determined, to address the hypothesis that carcinogenic fibers have gr eater free radical activity than noncarcinogenic fibers. On the basis of recent inhalation studies, the six samples were divided into three carcinogenic fibers-amphibole asbestos, silicon carbide, and refractor y ceramic fiber I (designated with the abbreviation RCF 1)-and three n oncarcinogenic fibers-man-made vitreous fiber 10 (a glass fiber sample designated with the abbreviation MMVF 10), Code 100/475 glass fiber, and RCF4. All experiment were carried out with equal fiber numbers. Of the two assays of free radical activity used, the plasmid assay of DN A scission showed only amosite asbestos to have free radical activity, while the salicylate assay of hydroxyl activity showed that both amos ite asbestos and RCF1 release hydroxyl radicals; silicon carbide fiber s had no free radical activity in either of the assays. None of the no ncarcinogenic fibers demonstrated free radical activity in either of t he assays. The differences in the Two assays in demonstrating free rad ical activity with RCF1 may be due to increased release of Fe from RCF 1 under the more acid conditions of the salicylate assay, which was co nfirmed by the fact that soluble iron caused hydroxylation of salicyla te. Presence of an iron chelator inhibited the ability of the RCF1 fib ers to cause hydroxylation of salicylate, demonstrating that RCF1 gene rates hydroxyl radical by Fenton chemical reaction in the same way as amphibole asbestos.