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The potential of plants as a source of anti-malarial agents Dr Geoffrey M. Rukunga Kenya Medical Research Institute PO

The potential of plants as a source of anti-malarial agents Dr Geoffrey M. Rukunga Kenya Medical Research Institute PO BOX 54840 NAIROBI E-mail <grukunga@kemri.org>. Global statistics of Malaria. 1.5 – 2.7 million deaths annually Over 1 billion clinical episodes

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The potential of plants as a source of anti-malarial agents Dr Geoffrey M. Rukunga Kenya Medical Research Institute PO

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  1. The potential of plants as a source of anti-malarial agents Dr Geoffrey M. Rukunga Kenya Medical Research Institute PO BOX 54840 NAIROBI E-mail <grukunga@kemri.org>

  2. Global statistics of Malaria • 1.5 – 2.7 million deaths annually • Over 1 billion clinical episodes • 300 – 500 million people infected • Every 10 – 30 seconds a child dies of malaria

  3. Impact of malaria in Africa • Major health problem in the tropics • About 90 million clinical cases annually. • Malaria leads to economic loss. • Most affected are pregnant women and children Under 5 years.

  4. What contributes to the problem? • Resistance to conventional drugs. • Affordability of available drugs. There for need to continue searching for new agents

  5. Plant drugs • Approximately 80% of the people in the developing countries depend on traditional medicine. • The discovery of quinine and artemisinin has stimulated interest in medicinal plants as sources of new antimalarial drugs.

  6. Selection of plants for antimalarial activity • Ethno medical bases • Random selection

  7. Methodologies • Extractions – water or organic solvent • In vitro assays – IC 50s • Cytotoxicity assays CC50’s • Selectivity index (S.I) = IC 50/CC50 • In vivo assays – percentage chemosuppression of parasitaemia. • Toxicity in animals. • Activity guided isolation of the active compound (?)

  8. So many publications yet few candidates anti-malarial agents • Anti-malarial compounds rare. • Most studies ends up with only in vitro assays. • If beyond in vitro assay – then toxicity - problem • Usually because of lack of resources • trained personnel • equipment • Finances

  9. Categorization of plants extracts with in vitro anti-plasmodial activity • Category 1: High activity IC 50 equal or less than 10 g/mL • Category 2: Moderate activity IC 50 between 10 and 100 g/mL • Category 3: Low or no activity IC 50 Above 100 g/mL

  10. Category 1 (High activities) 120 plant extracts from 74 plant species, belonging to 34 families. Some of the families with more species than others: Annonaceae (alkaloids) Apocynaceae (Alkaloids) Asteracea (sesquiterpenes) Celestraceae (Triterpenes) Meliaceae (limonoids) Simaroubaceae (quassinoids) Menispermaceae (Alkaloids) Rutaceae (Alkaloids) Rubiaceae (alkaloids)

  11. Category 2 – moderate activities 203 plant extracts from 129 plant species, belonging to 50 families. Some of the families with more species than others: Annonaceae Asteraceae Meliaceae Loganiacea Fabaceae

  12. Classes of compounds with high anti-malarial activities • Alkaloids • Basic compounds -highly bioactive compounds. • The structures are very diverse • Families containing the compounds includes Annonaceae Loganiaceae Menispermaceae Asclepiadaceae Dioncophyllaceae Rubiacea Rutaceae Apocynaceae

  13. Quinine – An alkaloidal compound

  14. Quassinoids • Heavily oxygenated lactones majority with C-20 basic skeleton. • The structures are very diverse • Simaroubaceae – is the family associated with quassinoids

  15. A quassinoid from Simaba guianensis (Simaroubaceae) IC 50 < 1.7 ng/mL

  16. Sesquiterpenes • Biosynthetically made from three 5-carbon isoprene units skeleton • Among the most active terpenoids • Artemisinin belongs to thisd class of compounds. • Families identified with highly active sesquiterpenes includes • Asteraceae Siparunaceae • Cyperaceae Valerianaceae • Rosaceae

  17. Artemisinin and Mustakone

  18. Triterpenes • Triterpenes. • Biosynthetically made from 6 units isoprene units • Diverse sructures. • Some triterpenes have exhibited high • anti-plasmodial activity. • Families associated includes: • Ancistrocladaceae • Meliaceae • Simaroubaceae • Celestraceae

  19. pristimerin – triterpene from Maytenus senegalensis - Celestraceae IC 50 < 200 ng/mL

  20. Limonoids Tetranoterpenoids a class of compounds highly active. Family associated with these compounds – Meliaceae IC 50s < 1ug/mL

  21. Discussions • Points to consider in the categorization of the • plant extracts with anti-plasmodial activity. • Type of extract • Strain of Plasmodium parasite used in the assay • Part of the plant extracted • Geographical location of plant • Time of the year harvested • Thus categorization is a guide

  22. Way forward • Prioritization of plants as source of • anti-malarial agents. • Families whose exts have high anti-malarial activity (cat 1&2). • Families that contain class of compounds with known potent anti-malarial activity e.g liminoids, alkaloids, quassinoids etc. • Cytotoxicity after in vitro anti-plasmodial assays. • Confirm activity in vivo • Toxicity studies in animals. • plant part: leaves > stems > roots • Ease of propagation, cultivation etc • Team work – the only answer.

  23. End Thank you

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