Pharmacological investigation of some trees used in South African traditional medicine.
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Date
2005
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Abstract
South Africa is home to a wide diversity of cultural groups, all of which
utilize the flora for a variety of purposes. This is true with regard to traditional
medicine systems which are similar to those of the rest of Africa south of the
Sahara, with diviners (sangomas) and herbalists (inyangas) as the key health
providers. In addition, the Country is rich in plant diversity with some 30 000
species of flowering plants - almost one tenth of the worlds recorded higher plants.
This incorporates a large diversity of plants including trees, shrubs, herbs, bulbs
and corms.
The adverse effects of traditional medicinal plants and natural products
are not well documented in the literature. Recently, many plants used as food or in
traditional medicine have been shown to be potentially mutagenic using in vitro
assays. Thus, the scientific evaluation of traditional medicine and medicinal plants
is very important to validate claims made on safety and efficiency of such usages.
After a survey of the available ethnobotanical literature, ten trees used in
South African traditional medicine were selected. These species were: Acacia
niolotica subspecies kraussiana, Acacia sieberiana, Albizia adianthifolia,
Combretum kraussii, Faidherbia albida, Ficus sur, Prunus africana, Salix
mucronata, Terminalia sericea and Trichilia dregeana. Plant parts including leaf,
root and bark were collected from each of the selected trees (exceptions were
Albizia adianthifolia, Faidherbia albida, Terminalia sericea and Prunus africana)
and extracted using ethyl acetate, ethanol and water individually to ensure the
extraction of compounds over a wide range of polarities. The extracts (in total, 78)
were screened for antibacterial, anti-inflammatory (COX-1 and COX-2) and antiacetylcholinesterase
activities and investigated for their potential mutagenic effects
using the Ames test.
Antibacterial activity was detected using the disc-diffusion and microdilution
assays. The extracts were tested against Gram-positive bacteria: Bacillus
subtilis, Staphylococcus aureus, Micrococcus luteus and Gram-negative bacteria:
Escherichia coli and Klebsiella pneumoniae. Of the 78 different plant extracts
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tested (final amount of plant material was 1 mg per disc), 84% showed activity
against Gram-positive bacteria. From this percentage, 20% also showed activity
against Gram-negative bacteria. The best inhibition was observed with ethyl
acetate and ethanol root extracts of Terminalia sericea against both Gram-positive
and Gram-negative bacteria.
In the micro-dilution assay, 55% of the plant extracts showed minimum
inhibitory concentration (MIC) values ~ 1.56 mg/ml against Gram-positive and/or
Gram-negative bacteria. The ethyl acetate bark extract of Acacia sieberiana and
the root and bark ethyl acetate extracts of Acacia nilotica inhibited bacterial growth
of both Gram-positive and Gram-negative bacteria at concentrations ~ 0.8 mg/ml.
The aqueous leaf extracts of Acacia sieberiana had a low MIC value (0.3 mg/ml)
against Gram-negative Kleibsiella pneumoniae and the ethyl acetate extracts of the
root inhibited growth of Escherichia coli with an MIC value of 0.1 mg/ml. However,
these two extracts showed no activity in the disc-diffusion assay. The MIC values of
the neomycin (control) were 0.8 I-Ig/ml and 3.1 I-Ig/ml against Kleibsiella
pneumoniae and Escherichia coli respectively.
In the anti-inflammatory test, 70% of the plant extracts from different plant
parts (leaf, root, bark) of the tree investigated showed strong inhibition in both the
CQX-1 and CQX-2 bioassays. The CQX-2 inhibitory effects of aqueous extracts
were generally lower when compared to the organic solvent extracts. However,
water extracts of Acacia nilotica was an exception (~ 90%).
In the acetylcholinesterase inhibitory test, 21% of the plant extracts were
active at concentrations ~ 1 mg/ml using the micro-plate assay. The lowest IC50
value was 0.04 mg/ml obtained with an ethanol bark extract of Combretum kraussii.
The IC50 value of the galanthamine (positive control) was 2 I-IM.
None of the investigated plants showed any potential mutagenic effects
with Salmonella typhymurium strain TA 98 using the Ames test.
Using bioassay-guided fractionation, anolignan B was isolated from the
ethyl acetate root extract of Terminalia sericea. Antibacterial activity of anolignan B
was determined using the microdilution assay. The compound possessed activity
against both Gram-positive and Gram-negative bacteria. The lowest MIC value
(3.8 IJg/ml) was observed with Staphylococcus aureus. MIC value of the neomycin
was 1.5 IJg/ml.
Anti-inflammatory activity of anolignan B was detected using the CQX-1
and CQX-2 bioasays. The compound showed strong inhibitory activity against
CQX-1 and weaker activity against CQX-2. The ICso values were 1.5 mM and 7.5
mM with CQX-1 and CQX-2 respectively. The ICso values of indomethacin were
0.003 mM and 0.186 mM against CQX-1 and CQX-2 respectively.
There were no potential mutagenic effects showen by anolignan B against
Salmonella typhimurium strain TA 98 in the Ames test.
Isolation of anolignan B from Terminalia species and the antibacterial and
anti-inflammatory activities observed in this work have not been reported
previously and could therefore be recorded as novel biological activities for this
compound. These results also support the idea that the use of ethnobotanical data
can provide a valuable short cut by indicating plants with specific uses which might
likely be sources of biologically active chemicals.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
Keywords
Traditional medicine--South Africa., Medicinal plants--South Africa., Trees--South Africa., Pharmacology., Botany, Medical., Antibacterial agents., Anti-inflammatory agents., Mutagens., Terminalia sericea., Theses--Botany.