Targeted modulation of reactive oxygen species in the vascular endothelium

Abstract

'Endothelial cells lining vascular luminal surface represent an important site of signaling and injurious effects of reactive oxygen species (ROS) produced by other cells and endothelium itself in ischemia, inflammation and other pathological conditions. Targeted delivery of ROS modulating enzymes conjugated with antibodies to endothelial surface molecules (vascular immunotargeting) provides site-specific interventions in the endothelial ROS, unattainable by other formulations including PEG-modified enzymes. Targeting of ROS generating enzymes (e.g., glucose oxidase) provides ROS- and site-specific models of endothelial oxidative stress, whereas targeting of antioxidant enzymes SOD and catalase offers site-specific quenching of superoxide anion and H(2)O(2). These targeted antioxidant interventions help to clarify specific role of endothelial ROS in vascular and pulmonary pathologies and provide basis for design of targeted therapeutics for treatment of these pathologies. In particular, antibody/catalase conjugates alleviate acute lung ischemia/reperfusion injury, whereas antibody/SOD conjugates inhibit ROS-mediated vasoconstriction and inflammatory endothelial signaling. Encapsulation in protease-resistant, ROS-permeable carriers targeted to endothelium prolongs protective effects of antioxidant enzymes, further diversifying the means for targeted modulation of endothelial ROS.

Fig. 1

Vascular oxidative stress. Pro-inflammatory insults cause endothelial exposure of cell adhesion molecules (selectins, ICAM or VCAM) and cytokine production. Cell adhesion molecules facilitate white blood cell (WBC) adhesion and transmigration. Activation of Nox (for example by angiotensin II) leads to generation of superoxide that quenches NO and thus causes vasoconstriction. Activated WBCs bind to endothelium via cell adhesion molecules and produce reactive oxygen species (ROS) and other aggressive molecules that can result in oxidative damage and death of endothelial cells. ICAM, intercellular adhesion molecule; Nox, NADPH oxidase; PMN, polymorphonuclear neutrophils; TM, thrombomodulin; ICAM, intercellular cell adhesion molecule; VCAM, vascular cell adhesion molecule; TNF, tumor necrosis factor, IL, interleukin.

Fig. 2

Reactive oxygen species pathways, antioxidant enzymes and their role in vascular oxidative stress. Superoxide is produced by several cellular enzyme systems including NADPH-oxidases, xanthine oxidase, etc. It can react with NO producing aggressive peroxynitrite anion ONOO⁻ and decreasing NO pool. Superoxide spontaneously or by action of superoxide dismutase may be reduced into hydrogen peroxide H₂O₂. Hydrogen peroxide can produce extremely reactive hydrogen radical ·OH in the presence of transition metals or hypochlorous acid by myeloperoxidase. Catalase and glutathione peroxidases protect cells against hydrogen peroxide. ALI/ARDS, acute lung injury/acute respiratory distress syndrome; COX, cyclooxygenase; GSHPx, glutathione peroxidases; MPO, myeloperoxidase; ROS, reactive oxygen species; SOD, superoxide dismutase; XO, xanthine oxidase.

Fig. 3

Protective effects of targeted formulations of AOEs in models of oxidative stress in vitro and in vivo. Catalase and SOD were conjugated to antibodies against endothelial target. AngII, angiotensin II; GOX, glucose oxidase; LPS, lipopolysaccharide; PQ, paraquat; SOD, superoxide dismutase.