By Prof Stephen Gbedema
Background: Plasmodium falciparum drug resistance is a major public health challenge in sub-Sahara Africa. Many people are now resorting to the use of herbs in managing malaria due to the increasing treatment failures with conventional drugs.
In this study, the ethanolic extract of Polyalthia longifolia (Sonn) Thw. var. pendula, a variety fondly used in folklore medicine in Ghana was investigated for potential antimalarial drug development.
Method: The ethanolic extract of P. longifolia (Sonn) Thw. var. pendula stem bark was screened against
the multidrug-resistant, K1 strain of P. falciparum by the parasite lactate dehydrogenase (pLDH) assay and
a good antiplasmodial activity (IC50 22.04 7 4.23 mg/ml) was observed which led to further chromatographic
analysis in the search for actives.
Results: Bioassay guided fractionation of the extract yielded; three clerodane diterpenes [16-hydroxycleroda-
3,13-dien-16,15-olide (1), 16-oxocleroda-3,13E-dien-15-oic acid (2) and 3,16-dihydroxycleroda-4(18),13
(14)Z-dien-15,16-olide (3)], a steroid [beta-stigmasterol (4)] and two alkaloids [darienine (5) and stepholidine
(6)]. While compounds 4, 5, and 6 exhibited weak antiplasmodial activity (IC50 22–105 mg/ml),
the clerodane diterpenes exhibited significantly potent (po0.005) blood schizonticidal activity (IC50:
3–6 mg/ml).
This is the first report of the antiplasmodial activity of compounds 2 and 3. In combination assay
with chloroquine, compounds 1, 2, 3 and 5 antagonized the antiplasmodial activity of chloroquine while
4 and 6 demonstrated a synergistic action.
Conclusion: The potent antiplasmodial activity of the extract of P. longifolia (Sonn) Thw. var. pendula and
compounds therein strongly suggest its usefulness as an antimalarial agent and support its inclusion or
exploitation in formulations of herbal remedies for malaria in Ghana.
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