Biological effects of short-term, high-concentration exposure to methyl isocyanate. VI. In vitro and in vivo complement activation studies.

Abstract

The ability of MIC to induce complement activation in vitro and in vivo was investigated. For the in vitro studies, both human and guinea pig serum or EDTA-plasma samples were exposed to 1167 to 1260 ppm MIC vapor for 15 min at room temperature. The human serum samples exposed to MIC showed significant reductions in Factor B, C2, C4, C3, C5, and total hemolytic complement CH50 activity levels. C6 functional activity was unaffected. The C3, C5, and CH50 functional activities in guinea pig serum (the only functional tests conducted on these samples) were more sensitive to MIC-mediated reduction than the corresponding activity reductions observed in the human serum samples. The human and single guinea pig EDTA-plasma samples exposed to MIC vapor showed no evidence of C3 consumption but did show significant reductions in CH50 levels. Thus, MIC vapor was able to activate, and thereby reduce serum complement C3 activity in vitro by a complement-dependent process. However, the data suggest at least one complement component other than C3 was inactivated in EDTA-plasma by a complement-independent mechanism.For the in vivo studies, five pairs of guinea pigs were exposed to 644 to 702 ppm MIC vapor until one of the pair died (11-15 min). MIC exposure was then discontinued, the surviving guinea pig was sacrificed, and EDTA-plasma was obtained from both animals and analyzed for complement consumption. Clear evidence was obtained to indicate that complement activation had occurred in these animals exposed to MIC for 11 to 15 min. In addition, the complement activation profile observed in these guinea pigs was qualitatively similar to that seen in the guinea pig serum samples exposed to MIC vapor in vitro. The total protein concentration present in plasma samples obtained from guinea pigs that had died from MIC exposure was elevated significantly (p < 0.05) above the total protein concentration present in plasma samples obtained from these same animals before MIC exposure or from paired animals which had not died (sacrificed) from MIC exposure. The possible contribution of complement activation to the fatal reaction(s) observed in these MIC-treated animals is discussed.

Methyl isocyanate inhalation induces tissue factor-dependent activation of coagulation in rats

“…Studies by Kolb et al have suggested that acute toxicity of MIC could be mediated by its effects on the plasma membrane of endothelial cells, resulting in fluid loss from the vascular compartment, with subsequent hypovolemia and hypotension. [5,6] MIC toxicity due to inadequate circulating volume and perfusion is an attractive hypothesis since these events can lead to rapid endothelial damage and organ failure. However, since these latter studies were performed by subcutaneous injection of MIC, it is uncertain whether hypovolemia of the same magnitude would also occur in response to inhalation exposure.…”