Protective role of hemopexin on heme-dependent lung oxidative stress.

Tert-butyl hydroperoxide (t-BOOH)-dependent chemiluminescence of perfused rat lungs increased by almost 500% upon addition of heme (from 297 +/- 28% to 1204 +/- 125% of control, p < 0.01 vs no heme). Preincubation with hemopexin significantly decreased the heme-stimulated chemiluminescence to 779 +/- 155% of control (p < 0.01) When hemopexin was replaced with rat albumin heme-stimulated chemiluminescence decreased to 1007 +/- 104% (not significantly different from results with heme alone). In vitro studies showed that hemopexin did not decrease chemiluminescence from bovine serum albumin oxidation (493 +/- 94% compared to 292 +/- 81% of control in the absence of hemopexin) and that the heme-hemopexin mixture also emitted light when exposed to t-BOOH (264 +/- 66% of control). These results suggest that hemopexin specifically inhibits some of the oxidative reactions catalyzed by free heme and may have a protect tissue oxidation in conditions in which heme release occurs (i.e., stroke).