| dc.description.abstract | In many developing countries, farmers and pastoralists still rely on their indigenous
knowledge, practices and locally available plants to control nematode parasitic
infections, both in livestock and humans. The overall aim of my thesis was to
undertake bioassay-guided phyto-chemical study of extracts and their constituents
from Ethiopian anti-parasitic plants used by healers to control gastrointestinal
nematode parasites in livestock to validate their ethno-medicinal use and to
characterise and identify their active ingredients.
As a first experiment (Chapter Three), four types of crude extracts (water, 70%
methyl-alcohol, absolute methanol and acetone) of four indigenous Ethiopian
medicinal plants (Adenia species, Cissus ruspolii, Ipomoea eriocarpa and Euphorbia
thymifolia) were screened against Teladorsagia circumcincta egg hatching in vitro,
not only as a first step to validate the traditional healers claim but also to choose the
most promising plant extract(s) for further phyto-chemical studies. The egg hatching
inhibition (EHI) test results revealed that the anti-parasitic properties of these plants
depended on plant species, dose, and solvent polarity. The water extracts of both C.
ruspolii and Adenia sp. exhibited largest, up to 100% EHI but also larval migration
inhibition activities, and were selected for further studies. The second experiment
(Chapter Four) assessed the nature of active constituents in these extracts by physico-chemical
methods. It was observed that the major constituents of both plant extracts
responsible for the EHI activities are likely highly polar, water-soluble, small and
moderately heat-labile molecules. The third and fourth experiments (Chapters Five
and Six) consisted of separating Cissus ruspolii and Adenia sp. water extracts into
discrete fractions by gel-permeation chromatography, EHI tests of Bio-Gel P-2
fractions followed by thin layer chromatography (TLC) profiling of these fractions to
detect separated spots (in day light, under UV-light or after staining with various
staining reagents) and also to see how elution patterns of separated spots affected by
column parameters. The EHI tests on the fractions obtained revealed that the active
constituents of C. ruspolii and Adenia sp. water crude extracts were eluted into few
fractions based on their molecular sizes. The TLC profilings of these fractions
identified spot patterns of active and inactive fractions, which allowed pooling of
active constituents based on their EHI and TLC profiling into three pools for each
plant. The fifth experiment (Chapter Seven) was to isolate and purify compounds
from these pools using various preparative planar and column chromatographic
methods. Sequential applications of column chromatography followed by preparative
thin layer chromatography isolated and purified five active compounds from C.
ruspolii and two active compounds from Adenia sp. The sixth experiment (Chapter
Eight) was to characterize and propose/elucidate structures of compounds from the
active fractions using chromatographic, analytical and spectroscopic methods. In this
regard, the structures of two oleanane type triterpenoid saponins isolated from one of
active fractions of Adenia sp. were proposed based on their mass spectrometry (MS)
and nuclear magnetic resonance (NMR) data with support of compounds property,
TLC and literature. Similar outcomes for C. ruspolii were not achieved due to lack of
sufficient sample to run 13C-nuclear magnetic resonance spectroscopy and
distortionless enhancement by polarization transfer (DEPT), contamination of some
purified compounds with ill-characterised substance from the preparative TLC
matrix and in some cases mass spectrometry (MS) and nuclear magnetic resonance
(NMR) data did not support each other. The last experiment (Chapter Nine) was to
assess anthelmintic efficacy and safety of C. ruspolii and Adenia sp. crude water
extracts in Heligmosomoides bakeri infected mice. This in vivo test revealed that
both plant extracts exhibited significant reduction in worm burdens and worm egg
excretion, with moderate effects on haematology and organ weights at tolerated
dosages.
In conclusion, both in vitro and in vivo data revealed that Adenia sp. and C. ruspolii
have anthelmintic properties, thus validating traditional healer claims and supporting
ethno-medicinal use. The bioassay-guided phytochemical study resulted in the
isolation of a number of active compounds from these plants, for some of which a
structure has been proposed. | en |
