Neovascularization may contribute to functional recovery after neural injury. Combination treatment of stroke with a nitric oxide donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1, 2-diolate (DETA-NONOate) and bone marrow stromal cells promotes functional recovery. However, the mechanisms underlying functional improvement have not been elucidated. In this study, we tested the hypothesis that combination treatment upregulates angiopoietin-1 and its receptor Tie2 in the ischemic brain and bone marrow stromal cells, thereby enhancing cerebral neovascularization after stroke. Adult wild type male C57BL/6 mice were i.v. administered PBS, bone marrow stromal cells 5x10(5), DETA-NONOate 0.4 mg/kg or combination DETA-NONOate with bone marrow stromal cells (n=12/group) after middle cerebral artery occlusion. Combination treatment significantly upregulated angiopoietin-1/Tie2 and tight junction protein (occludin) expression, and increased the number, diameter and perimeter of blood vessels in the ischemic brain compared with vehicle control (mean+ or -S.E., P<0.05). In vitro, DETA-NONOate significantly increased angiopoietin-1/Tie2 protein (n=6/group) and Tie2 mRNA (n=3/group) expression in bone marrow stromal cells. DETA-NONOate also significantly increased angiopoietin-1 protein (n=6/group) and mRNA (n=3/group) expression in mouse brain endothelial cells (P<0.05). Angiopoietin-1 mRNA (n=3/group) was significantly increased in mouse brain endothelial cells treated with DETA-NONOate in combination with bone marrow stromal cell-conditioned medium compared with cells treated with bone marrow stromal cell-conditioned medium or DETA-NONOate alone. Mouse brain endothelial cell capillary tube-like formation assays (n=6/group) showed that angiopoietin-1 peptide, the supernatant of bone marrow stromal cells and DETA-NONOate significantly increased capillary tube formation compared with vehicle control. Combination treatment significantly increased capillary tube formation compared with DETA-NONOate treatment alone. Inhibition of angiopoietin-1 significantly attenuated combination treatment-induced tube formation. Our data indicated that combination treatment of stroke with DETA-NONOate and bone marrow stromal cells promotes neovascularization, which is at least partially mediated by upregulation of the angiopoietin-1/Tie2 axis.