CELLULAR BIOLOGICAL EFFECTS AND A SINGLE TRANSTRACHEAL INJECTION TEST IN THREE TYPES OF WHISKER FIBERS

Abstract

Recently, various kinds of asbestos substitutes have been used over a wide range of industrial applications. The dimensions of whisker fibers are similar to some forms ofasbestos, thus raising the concern of potential health effects for workers exposed in occupational environments. In this experiment, we compared the in vitro activity in cellular assays and the in vivo activity, focusing on lung inflammatory and fibrotic effects by a single transtracheal injection test among three well-characterized whisker fibers. The geometrical mean and SD of length (mum) and width (mum) and the numbers of fibers per microgram are: silicon carbide whisker (SC1), 6.4 +/- 2.45, 0.30 +/- 1.58, 0.3 x 106; titanium oxide whisker (TO1), 2.1 +/- 2.0, 0.14 +/- 1.5, 0.63 x 10 6; potassium titanate whisker (PT1), 6.0 +/- 2.0, 0.35 +/- 1.51, 0.51 x 10 6). The RAW 264.7 murine macrophage-like cell line was used for target cells. UICC crocidolite and TiO2 (rutile) particles were used as a positive and a negative control, respectively. Although the 3 types of whiskers caused an increase in lactic dehydrogenase (LDH) transudation and a decrease of cell viability at 24 h of incubation in a dose-dependent manner, there was no significant difference found among the 3 kinds of whiskers. Tumor necrosis factor (TNF-) in the culture medium showed a plateau at 12 h in a dose-dependent manner up to 0.1 mg/ml concentration of whiskers, and TO1 induced about double the TNF- of other whiskers, crocidolite, and TiO2 particles. All of the whiskers and the TiO2 particles did not cause a marked increase of intracellular interleukin-1 (IL-1), whereas crocidolite induced a significant increase at 12 h. In pathological findings, at 2 mo after a single intratracheal injection at high dose into rats, whiskers caused a substantial amount of inflammatory cell aggregation around the resident fibers, causing very slight fibrous reactions without marked difference among three kinds of whiskers. Obvious differences of biological effects in vitro and in vivo among the three kinds of whiskers were not observed except for TNF-. When compared on the basis of number per unit mass, the three kinds of whiskers showed very similar concentration in TNF- production, whereas TO1 showed lesser values than SC1 and PT1 in IL-1. We conclude that whiskerinduced biological effects may be caused by shape and size and not chemical composition (SiC vs. K2Ti8O17O, TO1 vs. TiO12 particles), and TNF- production may relate to whisker numbers, whereas IL-1 production may relate to whisker size in macrophagelike cells. However, the differences of size and numbers per unit mass among the three types of whiskers did not reflect the degree of inflammation and fibrosis in the lungs of whisker-inhaling rats.