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(Circulation Research. 2004;95:162.)
© 2004 American Heart Association, Inc.

Molecular Medicine

Novel Mechanism of Action for Hydralazine

Induction of Hypoxia-Inducible Factor-1 , Vascular Endothelial Growth Factor, and Angiogenesis by Inhibition of Prolyl Hydroxylases

Helen J. Knowles, Ya-Min Tian, David R. Mole, Adrian L. Harris

From the Cancer Research UK Molecular Oncology Laboratory (H.J.K., A.L.H.), Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford; and the Henry Wellcome Building of Genomic Medicine (Y.-M.T., D.R.M.), University of Oxford, Roosevelt Drive, Oxford, UK.

Correspondence to Prof Adrian L Harris, Cancer Research UK Molecular Oncology Laboratory, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford OX3 9DS, UK. E-mail harrisa{at}cancer.org.uk

The vasodilator hydralazine, used clinically in cardiovascular therapy, relaxes arterial smooth muscle by inhibiting accumulation of intracellular free Ca²⁺ via an unidentified primary target. Collagen prolyl hydroxylase is a known target of hydralazine. We therefore investigated whether inhibition of other members of this enzyme family, namely the hypoxia-inducible factor (HIF)-regulating O₂-dependent prolyl hydroxylase domain (PHD) enzymes, could represent a novel mechanism of action. Hydralazine induced rapid and transient expression of HIF-1 and downstream targets of HIF (endothelin-1, adrenomedullin, haem oxygenase 1, and vascular endothelial growth factor [VEGF]) in endothelial and smooth muscle cells and induced endothelial cell-specific proliferation. Hydralazine dose-dependently inhibited PHD activity and induced nonhydroxylated HIF-1, evidence for HIF stabilization specifically by inhibition of PHD enzyme activity. In vivo, hydralazine induced HIF-1 and VEGF protein in tissue extracts and elevated plasma VEGF levels. In sponge angiogenesis assays, hydralazine increased stromal cell infiltration and blood vessel density versus control animals. Thus, hydralazine activates the HIF pathway through inhibition of PHD activity and initiates a pro-angiogenic phenotype. This represents a novel mechanism of action for hydralazine and presents HIF as a potential target for treatment of ischemic disease.

Key Words: cardiovascular disease • iron chelation • ischemia • endothelial cells

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