Circulating Heme Oxygenase-1 and Complement Activation in Transplant-Associated Thrombotic Microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) is a severe complication in patients after hematopoietic stem cell transplantation. The pathogenesis of TA-TMA is still unclear. Previous studies showed that complement activation plays an important role in the development of TA-TMA. However, no data showed which kind of complement component triggers this process. In this study we found that heme oxygenase-1, which could induce decay-accelerating factor (DAF) and inhibit the membrane-attack complex, was significantly decreased in patients with TA-TMA. DAF levels in the TA-TMA group were in line with the levels in the myocardial infarction group but were lower than levels in the healthy, noncomplication, infection, and graft-versus-host disease groups (P < .05). Human umbilical vein endothelial cells (HUVECs) incubated with TA-TMA plasma showed lower DAF levels compared with that incubated with normal human plasma. Notably, treatment with N-acetylcysteine (NAC), a drug against oxidation, increased the level of DAF. NAC could also inhibit complement activation in HUVECs incubated with TA-TMA plasma. Taken together, we propose that NAC represents a new potential therapy for patients facing TA-TMA.