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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 <[email protected]>. 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 BOX 54840

NAIROBI

E-mail <[email protected]>


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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


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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.


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What contributes to the problem?

  • Resistance to conventional drugs.

  • Affordability of available drugs.

    There for need to continue searching

    for new agents


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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.


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Selection of plants for antimalarial activity

  • Ethno medical bases

  • Random selection


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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 (?)


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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


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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


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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)


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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


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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



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Quassinoids

  • Heavily oxygenated lactones majority with

    C-20 basic skeleton.

  • The structures are very diverse

  • Simaroubaceae – is the family associated with

    quassinoids


A quassinoid from simaba guianensis simaroubaceae l.jpg
A quassinoid from Simaba guianensis (Simaroubaceae)

IC 50 < 1.7 ng/mL


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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



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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


Pristimerin triterpene from maytenus senegalensis celestraceae l.jpg
pristimerin – triterpene from Maytenus senegalensis - Celestraceae

IC 50 < 200 ng/mL


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Limonoids

Tetranoterpenoids a class of compounds highly active.

Family associated with these compounds – Meliaceae

IC 50s < 1ug/mL


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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


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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.


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End

Thank you


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