Deficiency of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), a VWFcleaving protease, is the key factor in the pathogenesis of thrombotic thrombocytopenic purpura (TTP), a life-threatening thrombotic microangiopathy. It is well established that ADAMTS13 deficiency results in elevated plasma levels of ultralarge VWF multimers (ULVWF), which are prone to induce platelet aggregation; however, the actual trigger of TTP development remains uncertain. Here we de-

Mitochondria are involved in the development of organ failure in critical care diseases. However, the mechanisms underlying mitochondrial dysfunction are not clear yet. Inducible hemoxygenase (HO-1), a member of the heat shock protein family, is upregulated in critical care diseases and considered to confer cytoprotection against oxidative stress. However, one of the products of HO-1 is Fe 2 þ which multiplies the damaging potential of reactive oxygen species catalyzing Fenton reaction. The aim of this study was to clarify the relevance of free iron metabolism to the oxidative damage of the liver in endotoxic shock and its impact on mitochondrial function. Endotoxic shock in rats was induced by injection of lipopolysaccharide (LPS) at a dose of 8 mg/kg (i.v.). We observed that the pro-inflammatory cytokine TNF-a and the liver necrosis marker aspartate aminotransferase were increased in blood, confirming inflammatory response to LPS and damage to liver tissue, respectively. The levels of free iron in the liver were significantly increased at 4 and 8 h after onset of endotoxic shock, which did not coincide with the decrease of transferrin iron levels in the blood, but rather with expression of the inducible form of heme oxygenase (HO-1). The proteins important for sequestering free iron (ferritin) and the export of iron out of the cells (ferroportin) were downregulated facilitating the accumulation of free iron in cells. The temporarily increased concentration of free iron in the liver correlated with the temporary impairment of both mitochondrial function and tissue ATP levels. Addition of exogenous iron ions to mitochondria isolated from control animals resulted in an impairment of mitochondrial respiration similar to that observed in endotoxic shock in vivo. Our data suggest that free iron released by HO-1 causes mitochondrial dysfunction in pathological situations accompanied by endotoxic shock.

This study was designed to clarify whether mitochondrial function/dysfunction and reactive oxygen species (ROS) production have a temporal relationship with organ failure during endotoxic shock. Adult male Sprague-Dawley rats were divided into three groups receiving 1) isotonic saline (control group, n = 16); 2) 8 mg/kg lipopolysaccharide (LPS; n = 8); or 3) 20 mg/kg LPS (n = 8) intraperitoneally under short anesthesia with 3.5% of isoflurane. After 16 h, animals were killed to analyze plasma, rat liver mitochondria (RLM), and rat heart mitochondria (RHM). In accordance with plasma analysis, LPS-treated rats were divided into "responders" and "nonresponders" with high and low levels of alanine aminotransferase and creatine, respectively. RHM from responders had significantly lower respiratory activity in state 3, suggesting a decreased rate of ATP synthesis. In contrast, RLM from responders had significantly higher respiratory activity in state 3 than both nonresponders and the control group. This increase was accompanied by a decrease in phosphate-to-oxygen ratio values, which was not observed in RHM. ROS generation determined with a spin probe, 1-hydroxy-3-carboxypyrrolidine, neither revealed a difference in RHM between LPS and control groups nor between responders and nonresponders. In contrast, RLM isolated from responders showed a marked increase in ROS production compared with both the control group and nonresponders. Our data demonstrate that 1) RHM and RLM respond to endotoxic shock in a different manner, decreasing and increasing respiratory activity, respectively, and 2) there is a temporal relationship between ROS production in RLM (but not in RHM) and tissue damage in rats subjected to LPS shock.