Depletion of glutathione and ascorbate in lung lining fluid by respirable fibres

Objective - The use of synthetic vitreous fibres has increased along with a decline in the utilisation of asbestos. There remains concern that these synthetic fibres pose a health risk to workers because of the generation of respirable fibres which can enter the lung and cause adverse health effects. An improved understanding of the mechanism of fibre pathogenicity should allow more rational short-term testing regimes for new fibres as they are developed. We hypothesised that carcinogenic fibres have greater free radical activity compared with non-carcinogenic fibres and that they contribute to disease by causing oxidative stress in the lung. We examined a panel of respirable fibres, designated as being carcinogenic or non-carcinogenic based on previous animal studies for ability to deplete antioxidants from lung lining fluid. 

Methods - On the basis of inhalation studies, a panel of fibres was divided into three carcinogenic fibres - amosite asbestos, silicon carbide, and refractory ceramic fibre 1 (RCF1) and three non-carcinogenic fibres - man-made vitreous fibre 10 (a glass fibre MMVF10), Code 100/475 glass fibre, and refractory ceramic fibre 4 (RCF4). We measured the levels of glutathione (GSH) and ascorbate, two antioxidants present in lung lining fluid (LLF) after fibre treatment. All of the experiments were carried out at equal fibre number.

Results - Fibres had the ability to deplete both GSH and ascorbate from both LLF and pure solutions, an effect which was fibre number dependent. The greatest depletion of antioxidants was observed with the two non-carcinogenic glass fibres, and this effect was observed when A549 lung epithelial cells were treated with fibres.

Conclusions - Our results show that antioxidant depletion in cell free solution and lung lining fluid solely is not a simple indicator of the ability of fibres to cause lung pathology and that other biological events in the lung are involved.