Wollastonite Fibers in Vitro Generate Reactive Oxygen Species Able to Lyse Erythrocytes and Activate the Complement Alternate Pathway

Wollastonite fibers were tested in vitro for their ability toproduce reactive oxygen species (ROS) with two different systems:a cell-free reactive mixture containing deoxyribose and a polymorphonuclearleukocyte suspension. After adding the fibers, we measured thethiobarbituric acid-reactive substances pduced by deoxyribosedegradation and luminol-enhanced chemiluminescence, respectively.Compared with asbestos, wollastonite fibers produced higherROS levels both in the PMN suspensions and in the cell-freereactive mixtures. A large amount of these ROS were not hydroxylradicals. Indeed we obtained remarkable differences in ROS generationbetween unground and ground wollastonite fibers and negativeresults with fibers modified with ferric chloride and dithionite.In addition, ROS generation was partially inhibited (by 46–54%)in the reactions performed in the presence of 1,3-dimethyl-2-thiourea(DMTU), a strong hydroxyl radical scavenger. Wollastonite fiberswere also analyzed for their ability to lyse erythrocytes andactivate complement. Hemolytic potency was about twice thatof chrysotile and half that of crocidolite. The levels of complementactivation (via the alternate pathway) were about four-fifthsof those measured in zyrnosan-activated plasma (a typical stimulusused to activate the alternate pathway), equal to those obtainedwith crocidolite, and two-thirds of those found with chrysotile.The addition of DMTU markedly reduced both these activities.Since asbestos fiber toxicity is mainly due to hydroxyl radicalgeneration, our results indicate that wollastonite fibers areprobably less toxic than asbestos fibers.