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Selected plants used in Rwandan traditional medicine for the treatment of infections and/or rheumatoid diseases were investigated for antiviral activity in vitro against human immunodeficiency virus type-1 (HIV-1). Of the 38 tested 80% ethanolic extracts, belonging to plants of 21 different families only the extracts from the leaves of Aspilia pluriseta (Asteraceae) and Rumex bequaertii (Polygonaceae) had interesting selectivity indices (SI = ratio of the 50% cytotoxic concentration to the 50% effective antiviral concentration) higher than 1. Further fractionation of the initially antivirally inactive ethanolic extract of Tithonia diversifolia, however, led to an aqueous fraction with a high anti-HIV-1 activity (SI > 461), indicating that the cytotoxicity of some plant components may mask the antiviral properties of the active plant substances in total plant extracts.

Forty-two ethanolic extracts of thirty-six Rwandan medicinal plants were investigated for their influence on complement-mediated hemolysis. The plants were selected on the base of their ethnomedicinal use in infections and autoimmune diseases. Eight plant extracts showed an inhibitory activity against the classical pathway of the complement system and ten plant extracts against the alternative pathway. Three plant extracts exhibited an interesting activity against both pathways, i.e. Aspilia pluriseta, Coleus kilimandschari, and Macaranga kilimandscharica (leaves and stem). Further study indicated that the complement inhibitory activity was not caused by chelation of bivalent cations or by direct action on the target erythrocytes.

Ten saponins isolated from the leaves of Maesa lanceolata were tested for their antiviral, haemolytic and molluscicidal activities. The influence of the substitution pattern of these acylated triterpenoid saponins on their biological activities was investigated and structure-activity relationships were established. Maesasaponin VI(2) (3 beta-O-[[alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-galactopyranosyl-(1 --> 3)]-[beta-D-galactopyranosyl-(1 --> 2)]-beta-D-glucopyranuronyl]-21 beta,22 alpha-diangeloyloxy-13 beta,28-epoxyolean-16 alpha,28 alpha-diol), the most potent molluscicidal compound (LC(50) 0.5 ppm), also showed virucidal and haemolytic activity. In general, 21,22-diacylation appeared to be associated with a virucidal (reduction factor of the viral titer > or = 10(3) at 50 microg/ml) and haemolytic activity (HC(50) < or = 1 microg/ml).

Thirty-five flavonoids of seven different types, namely isoflavonoids, chalcones, dihydroflavonols, flavanols, flavanones, flavones, and flavonols were investigated for their ability to inhibit ascorbate-induced microsomal lipid peroxidation and their cytotoxicity. For each activity a structure-activity relationship was established. Subsequently, an antioxidant selectivity index, i. e., the maximal non-toxic dose divided by the IC(50) value for lipid peroxidation, was introduced. Kaempferol showed the highest antioxidant selectivity index of all flavonoids tested.