Platelet aggregation is inhibited by phycolectins.

Lectins from four marine algal species were examined for interaction with human platelets. The lectin designated hypnin A, from the red alga Hypnea japonica, inhibited adenosine diphosphate (ADP)- or collagen-induced human platelet aggregation in a dose-dependent manner. Complete inhibition was observed at concentrations of 100 and 5 micrograms/ml of the lectin with ADP (2 microM) and collagen (0.2 microgram/ml)-induced platelet aggregation, respectively. At the inhibitory concentration of 0.5 to 100 micrograms/ml, the lectin did not induce aggregation of resting platelets. Lectins from the other three algal species also inhibited ADP-induced human platelet aggregation. These results indicate that the algal lectins are a new group of inhibitors and may be useful to study glycoconjugates on platelet membranes and to design novel platelet aggregation inhibitors.