In vitro studies on the biologic effects of fibers: correlation with in vivo bioassays

In vitro studies employing organ cultures, primary cell cultures, cell lines, and bacterial systems have been used to assess the toxicity, mutagenicity, and carcinogenic potential of asbestos and nonasbestos fibers. These experiments have been useful in defining mechanisms contributing to the causation of fiber-associated lung diseases. Long (greater than 8 microns), thin asbestos fibers are more active in vitro than short (less than or equal to 2 microns) fibers or nonfibrous particles, an observation supporting the importance of fiber dimension in disease. Although in vitro bioassays cannot evaluate characteristics such as clearance and/or durability of fibers which may be critical determinants of fiber toxicity in lung, they can be used both to address dosimetry at the cellular level (i.e., number of fibers per cell that elicit a measurable biologic end point) and to evaluate preventive approaches to fiber-induced cell injury. Development of in vitro models employing target cells of the lung, i.e., mesothelial cells, tracheobronchial epithelial cells, and lung fibroblasts, as well as carefully characterized preparations of fibers and particles, will be necessary to evaluate whether in vitro bioassays are amenable to predicting the pathogenic potential of synthetic and naturally occurring fibers comparatively.