The macrophage stimulating anti-cancer agent, RRx-001, protects against ischemia-reperfusion injury

Abstract

Background: RRx-001, a clinical macrophage-stimulating anti-cancer agent that also produces nitric oxide (NO) was studied in a model of ischemia-reperfusion injury.

Methods: The production of NO is dependent on the oxygen tension because nitric oxide synthases convert l-arginine to NO and l-citrulline in the presence of O₂. Since the P450 enzymes, which metabolize nitrate esters such as nitroglycerin are dependent on oxygen, the generation of 'exogenous' NO is also sensitive to alterations in tissue PO₂. I/R injury was studied in a hamster chamber window, with compression of the periphery of the window for 1 h to induce ischemia. Animals received RRx-001 (5 mg/kg) 24 h before ischemia and sodium nitrite (10 nmols/kg) was supplemented 10 min after the start of reperfusion. Vessel diameter, blood flow, adherent leukocytes, and functional capillary density were assessed by intravital microscopy at 0.5, 2, and 24 h following the release of the ischemia.

Results: The results demonstrated that, compared to control, RRx-001 preconditioning increased blood flow and functional capillary density, and preserved tissue viability in the absence of side effects over a sustained time period.

Conclusion: Thus, RRx-001 may serve as a long-lived protective agent during postsurgical restoration of flow and other ischemia-reperfusion associated conditions, increasing blood flow and functional capillary density as well as preserving tissue viability in the absence of side effects.

Keywords: Ischemia-reperfusion injury; RRx-001; functional capillary density; nitric oxide; oncology.

Figure 1.

Impact of leukocyte activation on blood flow and rheology in the microcirculation. In ischemia-reperfusion, peripheral resistance is elevated due to leukocyte obstruction due to pseudopod projections or cell adhesion to the vascular wall. (a) Normal Blood Flow. (b) Vessel during ischemia-reperfusion. (c) Vessel during ischemia reperfusion, treated with nitric oxide.

Figure 2.

Experimental Model.

Figure 3.

Arteriolar diameter and blood flow following the release of the ischemia. *p < 0.05 compared to control.

Figure 4.

Functional capillary density (FCD) and immobilized leukocytes following the release of the ischemia. †, p < 0.05 compared to control.

Figure 5.

Immobilized leukocytes following the release of the ischemia. †, p < 0.05 compared to control.

Figure 6.

Tissue viability 24 following the release of the ischemia. **p < 0.05 for both the number of apoptotic and necrotic in the RRx-001 treatment group compared to control.

Figure 7.

RRx-001 binds to a thiol residue on βeta-Cys-93.