Inhibition of sickle red cell adhesion and vasoocclusion in the microcirculation by antioxidants

Abstract

In sickle cell anemia (SCA), inflammatory (i.e., intravascular sickling and transient vasoocclusive) events result in chronic endothelial activation. In addition to sickling behavior, sickle (SS) red blood cells exhibit abnormal interaction with the vascular endothelium, which is considered to have an important role in initiation of vasoocclusion. Upregulation of endothelial adhesion molecules caused by oxidants (and cytokines) may lead to increased SS red cell adhesion. We hypothesize that endothelial activation is indispensable in SS red cell adhesion to the endothelium and that antioxidants will have an inhibitory effect on this interaction. We examined the effect of selected antioxidants in ex vivo mesocecum vasculature, a well-established model that allows measurement of hemodynamic parameters and, by intravital microscopy, can allow quantification of adhesion. We tested antioxidant enzymes (SOD and catalase) and an intravascular SOD mimetic, polynitroxyl albumin (PNA), in the presence of platelet-activating factor (PAF); the latter causes endothelial oxidant generation and endothelial activation, which characterize SCA. In ex vivo preparations, PAF not only induced marked endothelial oxidant generation, it also enhanced SS red cell adhesion, resulting in frequent blockage of small-diameter venules. The adhesion, inversely related to venular diameter, and vasoocclusion were markedly inhibited by antioxidants, resulting in improved hemodynamics. PNA, the most effective antioxidant, also abolished SS red cell adhesion in non-PAF-activated preparations. Thus SS red cell adhesion and related vasoocclusion may be ameliorated by antioxidant therapy with a stable and long-acting molecule (e.g., PNA).

Resuscitation of Traumatic Brain Injury and Hemorrhagic Shock with Polynitroxylated Albumin, Hextend, Hypertonic Saline, and Lactated Ringer's: Effects on Acute Hemodynamics, Survival, and Neuronal Death in Mice

“…PNA is a colloid with beneficial effects across numerous experimental paradigms. It has been shown to reduce infarct size in experimental stroke in rats (Beaulieu et al, 1998;Sugawara et al, 2001), attenuate damage in experimental myocardial ischemia in rats (Li et al, 2002) and in murine models of sickle cell crisis (Kaul et al, 2006), and highly germane to our work, it reduces mortality in experimental HS in rats (Kentner et al, 2002). These beneficial effects may result from the potent intravascular antioxidant and nitric oxide-sparing effects conferred by the covalently linked nitroxide moieties in PNA.…”

Hemopexin Therapy Improves Cardiovascular Function by Preventing Heme-Induced Endothelial Toxicity in Mouse Models of Hemolytic Diseases

“…The administration of antioxidants, 49,50 endothelial activation inhibitors, 51 or NO donors 52,53 has been shown to positively affect vascular function in hemolytic diseases. In this scenario, Hx therapy could contribute to restoration of cardiovascular homeostasis, targeting multiple steps involved in the pathogenesis of vasculopathy and consequent cardiac decay.…”

Erythrocyte NADPH oxidase activity modulated by Rac GTPases, PKC, and plasma cytokines contributes to oxidative stress in sickle cell disease

“…48 Trials of antioxidant agents in mouse models of SCD also appear to reduce markers of acute and chronic inflammation. 49,50 Of note, all of these studies attempt scavenging of free radicals rather than inhibition of their production. On the basis of the data we present in this study, NADPH oxidase activity is implicated not only as a source of oxidative stress in SCD coming from WBC and endothelial cells but also as an endogenous, erythrocyte-specific mechanism that contributes to RBC rigidity and fragility.…”