Hirudo medicinalis: avascular tissues for clear-cut angiogenesis studies?

Basic studies on angiogenesis in normal and pathologic conditions, as well as research on drugs or genes/proteins that stimulate or regulate the angiogenic process, can rely on an increasing number of experimental models. Among non-mammalian models, Zebrafish is adopted by an increasing number of research groups. Moreover, angiogenesis and vasculogenesis in invertebrates like the leech Hirudo medicinalis share a high degree of similarity with the same processes occurring in humans, both under the structural/functional and biochemical points of view. Interestingly, Hirudo angiogenic growth factor receptors respond to corresponding human/mammalian recombinant growth factors and cytokines; in addition, Hirudo endogenous angiogenic growth factors and receptors react with antibodies against their human/mammalian counterparts. Furthermore, as it will be shown in this review, Hirudo has the unique advantage of having a virtually avascular muscular body wall, whereas the reliability of such a peculiar feature as a model for physiologically vascularised mammalian tissues has to be thoroughly investigated. Hirudo has proven so far to allow unambiguous, clear-cut studies on the angiogenic potential of gene-products or drugs, as well as on the anti-angiogenic compounds. This article will review the biology of angiogenesis in Hirudo and the data so far collected on angiogenesis stimulation/modulation in this model; an example describing a study on the biological activity of a naked DNA vector for angiogenesis gene therapy will also be provided.