Antithrombotic/anticoagulant and anticancer activities of selected medicinal plants from South Africa

Nine plants available in the Eastern Cape Province of South Africa were tested for antithrombotic and/or anticoagulant activity. Organic (methanol) and aqueous (distilled water) extractions were performed onthe various plant parts. The thrombin assay and clotting time assays (thrombin-induced and CaCl2-induced) were utilised. Several extracts displayed activity, but in most cases this was due to the presence of tannins. Only the aqueous extracts displayed activity after tannin removal. The Sutherlandia frutescens leaf extract displayed antithrombotic activity, with an IC50 value of 2.17 mg/ml. Gloriosa superba and Zantedeschia aethiopica leaf extracts displayed anticoagulant properties by inhibiting thrombin-induced clotting, with IC50 values of 2.97 and 3.05 mg/ml, respectively. The Leonotisleonurus root extract was found to decrease the CaCl2-induced clotting time by 50% at 8.88 mg/ml. A decrease in this value accompanied by a decrease in fibrin formation was preferable for the CaCl2-induced assay, since decreased fibrin formation may have a role in the prevention of cancer metastasis. As tannins were found to contribute minimally to the anticoagulant effect of L. leonurus, the cytotoxicity potential of the extracts of this species against five cell lines was determined. Only the organic extract yielded significant cytotoxity