**1. Introduction**

#### **1.1. Hematophagous animals**

On the search for niches to ensure the survival of their populations, some animal species adapted as parasites on other species, retrieving nutrients directly from the inner mediums

of their hosts. In this way, these animals acquired the capacity to mediate the host defenses in order to succeed on their search for food [1, 2].

bleeding. First, after injury, circulating platelets bind to collagen in the exposed vessel wall and aggregate, and second, the clotting factors are activated in the coagulation cascade, resulting in the formation of a fibrin clot. Thus, hemostasis coagulation reactions and fibrinolysis

Anticoagulants from Hematophagous http://dx.doi.org/10.5772/intechopen.78025 41

Hematophagous animals such as bloodsuckers (leeches, mosquitoes, and ticks) are rich sources of anticoagulant molecules; among them, clotting inhibitors, fibrinogenolytics, plasminogen activators, and platelet inhibitors, all are present in their fluids and secretions, with roles on physiological processes such as feeding, digestion, self-defense, etc. Bloodsuckers access the blood fluid through the wound made by specialized structures targeting blood coagulation components, specially thrombin, factor Xa and the prothrombinase and tissue factor/FVIIa complexes, as a strategy to maintain blood incoagulable over a relatively long period of time. These new anticoagulants from hematophagous animals have opened new perspectives in the scientific area for basic and applied researches, having applications in the therapeutic area, as anticoagulant medication. Therefore, hematophagous animals have been

Leeches are annelids (Annelida, Hirudinea), and feature over 650 known species found on many parts of the planet, including the oceans. Some species do not suck blood, but prey on worms and other small animals. Many sensorial organs are deployed to detect feeding opportunities, such as receptors over the body sensitive to movements and vibrations of water and soil, and also the "ocelli," light-sensitive cells. Some receptors of these animals can detect very

Even before the medicinal principles of leeches were studied in depth, it was known that these animals had powerful anticlotting and antiprotease substances as the blood found in their intestines remained liquid for weeks [27]. The most studied substances come from the salivary glands of hematophagous leeches. As an example, we have the European leech *Hirudo medicinalis*, for over a century, reaching its highest popularity on the XIX century in Europe. These leeches feature three adapted jaws in their mouth system that perforate the host's skin [6].

Other well-studied leech is the *Haementeria ghilianii*, popularly named as Giant Leech, found mainly in the North of Brazil and in the French Guyana, reaching up to a 50 cm length. However, differently from the European ones, leeches of the *Haementeria* genus have a proboscis on the mouth system, which is introduced on the pores of the host animal to find

The salivary secretions of leeches have different roles, which are more important for the sucking process than for digestion itself. Some of these functions are performed by substances that have not even been isolated and/or studied, such as an anesthetic agent that causes the "bite" of the mandibular leeches to be painless and also a vasodilator of the histamine type that prolongs the bleeding of the host [6]. Many other substances of pharmacological interest

are crucial for the proper functioning of the hemostatic system [24].

an excellent target for studies, including pharmacologists [3, 25, 26].

small quantities of some substances such as oils and blood [6].

peripheral blood vessels, from which they then feed [6].

have been characterized and described [28].

**2. Anticoagulant from leeches**

Among the arthropods, there are more than 14,000 species which are classified in around 400 genders of blood sucking animals with specific need to suck the host's blood, mostly vertebrate. These types of ectoparasites are called hematophagous animals and their saliva feature a rich array of substances capable to keep the ingested blood unclotted in their digestive system [3, 4].

The hematophagous animals feature exquisite and highly specialized mouthparts and a saliva rich in anti-hemostatic components. These substances are able to interfere on different stages of the blood coagulation mechanism and fibrinolysis. There are different groups of hematophagous animals, such as annelids, like leeches [5, 6] and intestinal worms [7], including arthropods, like mosquitoes [8] and ticks (arachnids) [9], and even mammals such as vampire bats [10].
