Effect of Deferoxamine on Wound Healing Rate in Patients With Diabetes Foot Ulcers

Diabetes is reaching epidemic proportions and is predicted to affect 300 millions people worldwide in 2025. Chronic complications of diabetes represent the main concern for the modern therapy of diabetes and it has become a priority to further characterize their pathophysiological mechanisms to develop novel rational therapeutic strategies. It is a high need to identify additional mechanisms that contribute to the development of chronic complications of diabetes. Today's strategies aiming to improve blood glucose levels have limited efficiency mainly because they induce hypoglycemia when used in the optimal therapeutically range. It is therefore important to develop additional therapeutic strategies that can compensate the relative inefficient blood glucose control. There are other examples where "out of the box thinking" strategies such as treatment of hypertension have shown to be at least as efficient as glucose control to decrease morbidity and mortality in patients with diabetes.

Diabetic foot ulceration represents a major medical, social and economic problem. The lifetime risk of a person with diabetes for developing a foot ulcer is 25% and it is believed that every 30 seconds a lower limb is lost in the world due to diabetes. The condition is also followed by a high 5 years mortality which has been estimated to be 45% after ulceration and 79% after amputation. The mortality of the patients with DFU is worse than the mortality in patients with many common cancers.

The present clinical management for patients with DFU is limited and in consequence 40% of the ulcers are still not healed after one year of treatment. This limited efficacy of the present therapy is the consequence of the relative poor understanding of the pathophysiology of this complication. Even though prolonged exposure of the tissues to hyperglycemia seems to be the primary causative factor for chronic complications of diabetes it has recently become increasingly evident that hypoxia plays an important role in all diabetes complications and especially in chronic diabetic wounds. A low oxygen concentration is the consequence of either a deficient blood supply due to functional circulatory deficiency, micro- and macro-vascular disease but also by a poor local diffusion of the oxygen due to local oedema.

Adaptive responses of cells to hypoxia are mediated by the hypoxia-inducible factor 1 (HIF) which is a heterodimeric transcription factor composed of two subunits, HIF-1 alfa and HIF-1 alfa both of which are constitutively expressed in mammalian cells. Regulation of HIF-1 activity is critically dependent of the degradation of the HIF-1 alfa subunit in normoxia. The molecular basis of its degradation is O2 dependent hydroxylation of at least one of the two proline residues in the oxygen dependent degradation domain (ODDD) of HIF 1-alfa by specific Fe 2+-, oxoglutarate dependent prolyl 4-hydroxylases (HIF hydroxylases). In this form HIF-1 alfa binds to the von Hippel-Lindau (VHL) tumor suppressor protein that acts as an E3 ubiquitin ligase and targets HIF-1 alfa for proteasomal degradation (recently reviewed).

Under hypoxic conditions HIF-1alfa is stabilized against degradation and binds to HRE (hypoxic responsive elements) and up-regulates a series of genes involved in angiogenesis (such as VEGF, angiopoietin-2, -4), glycolytic energy metabolism, cell proliferation and survival which enable the cells to adapt to reduction in oxygen availability . The same induction and activation of HIF-1 can be achieved by inhibiting the degrading enzymes (HIF hydroxylases) with substances that compete with their cofactors i.e. iron or oxoglutarate. Deferoxamine is such a substance which stabilizes and activates HIF-1 by chelating iron.

HIF-1 alfa plays a pivotal role in wound healing, and its expression in the multistage process of normal wound healing has been well characterized. In essence, HIF-1 alfa is necessary for expression of multiple angiogenic growth factors, cell motility and recruitment of endothelial progenitor cells (EPC).

Previous studies have shown that hyperglycemia impairs HIF-1 alfa stability and function. Low levels of HIF-1 alfa expression were also found in foot ulcer biopsies in patients with diabetes. The hypothesis is that the wound healing defect present in diabetes is due to an inhibition of HIF-1. This concept has been demonstrated by showing that local activation of HIF-1 either by two structurally different HIF-hydroxylases inhibitors (deferoxamine and DMOG) or by direct adenovirus mediated transfer of stabile HIF in wounds is followed by improvement of wound healing in diabetic mice (db/db) despite of chronic hyperglycemia. The local activation of HIF induces several pivotal processes for wound healing such as recruitment of the EPCs, angiogenesis, cell migration. Same improvement of wound healing were registered using other methods to induce HIF in the wounds in different animal models.

This study is planned to investigate the efficacy of the local stimulation of HIF for improving wound healing in patients with DFU. It is proposed to use local applied deferoxamine which is the only HIF inducer that is approved for clinical use and has been already tested and proved to be effective in animal models of impaired diabetes on wound healing rate. The dose proposed was evaluated as the most effective in preliminary experiments performed in db/db mice.