In Vivo Evidence of Free Radical Formation After Asbestos Instillation: An ESR Spin Trapping Investigation

It has been postulated that the in vivo toxicity of asbestos results from its catalysis of free radical generation. We examined in vivo radical production using electron spin resonance (ESR) coupled with the spin trap α-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN); 180 day-old rats were intratracheally instilled with either 500 μg crocidolite or saline. Twenty-four hours later, histologic examination revealed a neutrophilic inflammatory response. ESR spectroscopy of the chloroform extract from lungs exposed to asbestos gave a spectrum consistent with a carbon-centered radical adduct, while those spectra from lungs instilled with saline revealed a much weaker signal. This same radical formation persisted and, even one month after instillation, could be detected in the lungs of rats exposed to asbestos. The 4-POBN adducts detected by ESR are very similar to, if not identical with, ethyl and pentyl radical adducts, providing evidence of in vivo lipid peroxidation resulting from asbestos exposure. We conclude that, after instillation of crocidolite in the rat, ESR analysis of lung tissue demonstrates in vivo free radical production.