Roberto Motterlini

Human Sickle Cell Blood Modulates Endothelial Heme Oxygenase Activity: Effects on Vascular Adhesion and Reactivity

Objective—Sickle cell disease (SCD) is characterized by extensive hemolysis, increased cellular adhesion, and vaso-occlusion. Tissues from sickle patients express heme oxygenase-1 (HO-1), the enzyme that degrades free heme/hemoglobin to the signaling molecule carbon monoxide, and the antioxidants biliverdin/bilirubin. Here, we examined the HO response in endothelial cells exposed to human sickle blood and determined whether this response is beneficial for SCD. Methods and Results—We measured HO activity in human and bovine aortic endothelial cells incubated with human sickle or normal blood. Sickle blood increased HO activity, which was enhanced by hypoxia and was caused mainly by the red cell components of sickle blood. Oxidized hemoglobin was higher in sickle blood and increased markedly over time. Interestingly, HO activity correlated inversely with patients hemoglobin levels and positively with bilirubin and lactate dehydrogenase. HO-1 induction, exogenous biliverdin, or carbon monoxide markedly decreased adhesion of sickle blood to the endothelium, and sickle red cells partially inhibited relaxation mediated by carbon monoxide in isolated aortas. Conclusions—Our results highlight important associations between SCD and HO byproducts, which may counteract vascular complications of SCD.

Heme Oxygenase in Skeletal Muscle

Sepsis is a common cause of morbidity and mortality, particularly in elderly, immunocompromised, and critically ill patients. Indeed, severe sepsis is at present the most common cause of death in intensive care unit in the United States (Bone et al., 1992).Respiratory failure is a major clinical manifestation of sepsis, greatly contributing to the mortality of this pathologic condition (Montgomery et al., 1985). In this context, respiratory failure has been traditionally related to the development of adult respiratory distress syndrome (Montgomery et al., 1985). However, different experimental studies demonstrated that an impaired contractile function of respiratory muscles, including the diaphragm, is another important mechanism of respiratory failure during sepsis (Boczkowski et al., 1990 and Boczkowski et al. 1996; El Dwairi et al., 1998; Shindoh et al., 1992; Hussain et al., 1985; Van Surell et al., 1992). Diaphragmatic dysfunction during sepsis appears to be mediated mainly by oxidative stress (Shindoh et al., 1992; Supinski et al., 1996; Van Surell et al., 1992). In fact, we and others have recently shown an increased production of oxidants, such as superoxide anion and peroxynitrite, in the diaphragm of endotoxemic rats (El Dwairi et al, 1998; Boczkowski et al., 1999). The expression of the inducible isoform of nitric oxide (NO) synthase (NOS2) is partly responsible for this effect (Boczkowski et al., 1999).

Heme Oxygenase and the Novel Tumour-Specific Anti-Vascular Compound Combretastatin A4-Phosphate

In recent years there has been increasing interest in exploiting the tumour vasculature as a target for cancer therapy. It is now well established that the growth and expansion of malignant tumours is critically dependent on the establishment of a vascular network assuring nutritive blood flow (Folkman, 1990). However, a number of solid tumours are now known to be characterised by an inadequate vascularisation consisting of a temporally and spatially heterogeneous blood supply (Vaupel et al., 1989). Vascular targeting has received increasing interest in the past few years. This strategy aims at targeting the established tumour vasculature causing direct shut down in tumour blood flow, leading to secondary tumour cell death (Chaplin et al., 1998). Combretastatin A4-phosphate (CA-4-P) is the lead compound of a number of tubulin binding agents which cause selective vascular shut down in experimental tumours. It entered clinical trial in 1998.