American Society of Hirudotherapy

Calin--a platelet adhesion inhibitor from the saliva of the medicinal leech

Research article published in Blood Coagul Fibrinolysis (1991)

Last Updated: June 18, 2026Reviewed by: ASH Editorial Board
Research article — evidence reviewArticle reference
Evidence: Research reportSalivary PharmacologyDrug DevelopmentMunro R et al. · Blood Coagul Fibrinolysis, 1991

Abstract

The saliva of the medicinal leech, Hirudo medicinalis, contains a potent, hitherto unsuspected, inhibitor of collagen-mediated platelet adhesion/aggregation. Calin, of molecular size approximately 65,000 (reduced), has a rapid (1-10 min) effect on collagen which is reflected in its ability to suppress collagen-induced platelet aggregation, as well as adhesion of platelets to collagen-coated microcarrier beads. It also causes flocculation of Type I collagen fibril suspensions. Calin is differentiated from leech collagenase in two ways: (1) by demonstrating, by SDS-PAGE analysis of the products of incubations of Calin with Type I collagen at 37 degrees C, that Calin binds to but does not cleave collagen; and (2) by showing that Calin cannot be purified using the methods used to isolate leech collagenase. Calin's rapid and unusual interaction with collagen makes it a prime candidate for one of the agents that are the causative factors of the prolonged bleeding phenomenon seen after leech bites.

Abstract sourced from PubMed (NCBI) for the cited record. See the original publication for the authoritative version.

Publication typeJournal ArticleResearch Support, Non-U.S. Gov't
Indexed MeSH termsAnimalsCollagenHumansInvertebrate HormonesLeechesPlatelet AdhesivenessPlatelet AggregationPlatelet Aggregation InhibitorsProtein BindingProtein ConformationSalivaSalivary Proteins and Peptides

Summary

Calin from Hirudo medicinalis saliva is a potent inhibitor of collagen-mediated platelet adhesion/aggregation with rapid effect on collagen; binds to but does not cleave collagen.

Why This Matters for Hirudotherapy

This study identifies and characterizes Calin, an approximately 65,000 Da (reduced) protein from the saliva of Hirudo medicinalis that inhibits collagen-mediated platelet adhesion and aggregation. Calin rapidly interacts with collagen (1–10 min), suppresses collagen-induced platelet aggregation, inhibits platelet adhesion to collagen-coated microcarrier beads, and flocculates Type I collagen fibril suspensions; SDS-PAGE confirmed it binds but does not cleave collagen, distinguishing it from leech collagenase. For ASH, this is directly relevant as Calin is identified as a candidate causative factor for the prolonged bleeding phenomenon after leech bites. Caveat: This is an in vitro biochemical characterization with no in vivo, animal, or clinical data presented.

Citation

Calin--a platelet adhesion inhibitor from the saliva of the medicinal leech.

Munro R et al. · Blood Coagul Fibrinolysis, 1991

DOI

Added to ASH library: May 27, 2026 · Site last updated: June 18, 2026

This website provides educational information and does not constitute medical advice, diagnosis, or treatment recommendations. Medicinal leech therapy carries clinically meaningful risks and should be performed only by qualified clinicians under institutionally approved protocols. FDA 510(k) clearance for medicinal leeches is limited to specific indications; investigational and off-label discussions are labeled accordingly. For patient-specific guidance, consult a qualified healthcare provider.