Impact of polynitroxylated albumin (PNA) and tempol on ischemia/reperfusion injury: intravital microscopic study in the dorsal skinfold chamber of the Syrian golden hamster.

Nitric oxide-releasing drugs have been shown to reduce ischemia/reperfusion (I/R) injury by acting as radical scavengers. However, their therapeutic application is hampered by specific side effects and rapid bioreduction in vivo. The half-life and antioxidant activity of nitroxides may be enhanced by their covalent binding to human serum albumin, resulting in polynitroxyl albumin (PNA). Thus, PNA may represent a novel antioxidative drug. The objectives of this study were to elucidate 1) whether PNA is able to diminish I/R injury; 2) the most effective dose of PNA in vivo; and 3) whether the addition of the nitroxide tempol enhances and/or prolongs the effect of PNA. Experiments were performed using a 4-h tourniquet-induced ischemia model in the hamster dorsal skinfold chamber. In the first part, five groups (n = 6) of animals received an infusion of 1) 1% body weight (b.w.) saline (0.9%); 2) 0.5% b.w. albumin (20%); 3) 0.5% b.w. PNA (20%); 4) 1% b.w. albumin (20%); and 5) 1% b.w. PNA (20%) 15 min prior to reperfusion. In the second part of the study, tempol (17 mg/mL) was added either to albumin or PNA (1:9), and 0.5% b.w. of this solution was infused (Group 6: tempol + albumin 0.5% b.w.; Group 7: tempol + PNA 0.5% b.w.). Intravital fluorescence microscopy allowed for quantification of functional capillary density (FCD), leukocyte adherence, extravasation of fluorescein isothiocyanate-labeled Dextran and non-viable (Propidium-positive) cell count prior to ischemia and 0.5 h, 2 h, and 24 h after reperfusion. PNA and--to a lesser extent albumin--effectively reduced postischemic microvascular perfusion failure, leukocyte adhesion, and tissue injury. PNA was most effective in the dose 1% b.w. Although free oxygen radical scavenging seems to be an underlying mechanism leading to the beneficial effects of PNA on I/R injury, hemodilution and known radical scavenging properties of pure albumin contribute in part to the observed effects. Although the combination of tempol and PNA revealed further short-term effects on microvascular perfusion and leukocyte adhesion, it did not result in a long-term improvement of tissue injury.