Session Speaker
Discovery of the Biologically Active Compounds from the Insect Salivary Glands as a Potential Drugs
Peter Takac
Slovakia

Blood-feeding arthropods have developed effective mechanisms that inhibit haemostatic responses of their vertebrate hosts. Antihaemostatic factors are contained in saliva and injected into the vertebrate hosts during blood-feeding. Platelet aggregation and vasoconstriction are key haemostatic responses, particularly in small wounds. Every haematophagous arthropod examined to date has been found to secrete some type of vasodilator. Vasodilators help to maintain blood flow during feeding and increase the probability of finding blood by increasing the size of the target venules and arterioles. The vasodilators in blood-feeding arthropod saliva are generally thought to cause the erythema (reflecting increased capillary permeability) observed following the bite of an arthropod. Vasodilation is most significant in vectors that have short feeding stylets (e.g. sand flies) or chewing mouthparts (e.g. biting flies). Horse flies feed from superficial haematomas and probably rely heavily on the pharmacological properties of their saliva to find blood. We described the first evidence of vasodilators in horse fly Hybomitra bimaculata (Diptera, Tabanidae)salivary gland extract and clone and express one of the active peptides (termed vasotab). Physiological tests using crude salivary gland extracts and reverse-phase HPLC fractions demonstrated positive inotropism in isolated rat hearts, vasodilatation of coronary and peripheral vessels, and Na, K-ATPase inhibition. One of the vasoactive fractions was analysed by N-terminal Edman degradation and a 47 amino acid sequence obtained. A full-length cDNA encoding the peptide was cloned from a phage library using degenerate primer PCR and the peptide expressed in insect cells. A 20 amino acid signal sequence precedes the mature 56 amino acid vasotab peptide which is a member of the Kazal-type protease inhibitor family. The peptide has a unique 7 amino acid insertion between the third and fourth cysteine residues. The recombinant peptide prolonged the action potential and caused positive inotropism of isolated rat heart myocytes and may be an ion channel modulator. At the same time we would like to introduce our first observations of the biologically active compounds from some other insects and our experience with the Maggot debridement therapy in Slovakia.