In vitro Investigation of Biological Activities of Secondary Metabolic Substances from Higher Plants (Case Study: Some Trees Used In African Traditional Medicine)  

Author

Eldeen IMS and J Van Staden

Proceeding

Traditional & Complementary Medicine Exhibition 2007 (TCME 2007), Putra World Trade Centre (PWTC), Kuala Lumpur, Malaysia.

Date

17/7/2007

Keyword

biological activities, metabolic substances, African traditional medicine

Abstract

Interactions between tropical plants and their natural predators are often complex and tend to involve unusual biodynamically active chemicals with pharmacological potential. Extracts obtained from some trees used in African traditional medicine for the treatment of different ailments such as infectious diseases, inflammation and central nervous disorders were screened for their biological activities. Of the 139 different plant extracts investigated, 73% showed antibacterial activity against both Gram-positive and Gram-negative bacteria. The best inhibition was observed with an ethanol root extract ofTerminalia sericea, ethyl acetate bark extract ofAcacia sieberiana,Acacia nilotica(root),Acacia seyal(leaf and root),Combretum hartmannianum(leaf and root) andErythrina latissima(Bark). Using cyclooxygenase 1 and 2 (COX-1 and 2) assays, 70% of the investigated plant extract showed activity against both cyclooxygenase enzymes. In the acetylcholinesterase inhibitory test, 25% of the plant extracts were found active. None of the investigated plants showed any potential mutagenic effects.Termenalia sericea(bark) andTrichilia dregeana(leaves) were selected for further investigation using bioassay guided fractionation. Anolignan B and a cycloartane type triterpenoid were isolated fromTerminlia sericeaandTrichilia dregeanarespectively. Anolignan B showed antibacterial activity against both Gram- positive and Gram-negative bacteria. The minimum inhibitory concentration values (MIC) ranged from 3.8 μg/ml againstBacillus subtilis(Gram-positive) to 31 μg/ml againstEscherichia coli(Gram-negative). Both anolignan B and cycloartane showed anti-inflammatory activity when tested against cyclooxygenase enzymes (COX-1 and COX-2). Anolignan B showed activity against both the COX-1 (IC50 =1.5 mM) and COX-2 (IC50=7.5 mM) enzymes. The cycloartane type triterpenoids possessed relatively strong activity against COX-2 (IC50 value was 40 μM) when compared to COX-1 (IC50 value was 97 μM). Further investigation into the secondary metabolites produced by tropical tree species as sustainable sources of bioactive constituents, is currently a focus at the Research Centre for Plant Growth and Development. Tropical forests represent more than 50% of the area of all forests throughout the world. They extend in the tropical belt of Africa, Asia, and Latin America to both the north and south of the equator approximately to the tropics of Cancer and Capricorn. They occur in lowlands, hills and mountains, which have varied amounts and different distributions of precipitation.  Plants growing in tropical forest habitats have had to develop and survive under intense competition for resources and nutrients.