*2.1.5.1. Collagen-binding proteins*

Leech antiplatelet protein (LAPP) is a specific inhibitor by collagen pathway from *Haementeria officinalis* leech salivary glands. It has around 13 kDa and pI 4.0. Recombinant LAPP (rLAPP) is able to inhibit collagen-mediated platelet aggregation under test-tube stirring conditions (IC50 ∼ 60–100 nM) and, also, it is able to block platelet adhesion to soluble collagen under static conditions, a step mediated by integrin α2β1 [96, 97]. There are reports demonstrating that this recombinant prevents integrin α-I domain binding to collagen with IC50 ∼ 125 nM [98]. The platelet adhesion to collagen type I is inhibited by rLAPP at high shear rate (1600 s−1) and this inhibitor is also able to prevent the binding of vWF to collagen type III [99]. In spite of this, rLAPP inhibits platelet deposition to cross sections of human atherosclerotic coronary arteries [99], and studies in baboons proved that rLAPP did not block collagen graft thrombosis, suggesting that inhibition of collagen alone is not enough to prevent thrombosis, possibly because TF exposure plays an important role in the model [100]. The crystal structure of LAPP has been determined and consists of a C-terminal domain which is very compact and a disordered N-terminal region [101].

Calin is isolated from the salivary secretion of the European leech *H. medicinalis,* as well as the rLAPP; it is able to inhibit the vWF-binding and platelet adhesion to collagen both under static and flow conditions [102]. Similarly, Saratin, from *Haementeria ghilianii* leeches, has been described as a platelet aggregation inhibitor that acts on collagen preventing the binding to integrin α2β1 and vWF [103]. The recombinant Saratin was obtained in yeasts (*Hansenula polymorpha*) [104] and it is being commercialized by BioVascular which has developed this product to GMP standards and is evaluating the effects in clinical studies [105]. To date, in the literature, only a few animal studies have been published, where it has been given alone or together with other drugs in glaucoma rabbit models [106, 107]. Saratin, when administrated alone in rat carotid endarterectomy model, significantly decreased platelet adhesion, intimal hyperplasia, luminal stenosis, and thrombosis. This inhibitor did not increase suture line bleeding or bleeding times, and did not decrease platelet counts. In this study, the authors also have concluded that Saratin may serve as a topical agent to be used for the site-specific inhibition of thrombosis and intimal hyperplasia after vascular manipulation [108].
