Anti-hyperglycemic, Anti-oxidant, and Cytotoxicity activity of selected Ethno medicinal plants from the Hardap region of Namibia
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Date
2024
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Publisher
University of Namibia
Abstract
Diabetes mellitus is a multifactorial non-communicable metabolic disorder,
characterized by the perpetual manifestation of hyperglycemia as a consequence of the
disturbed metabolism of carbohydrates, fat, and protein, due to defects in insulin
secretion and/or its effectiveness. Currently prescribed medication such as the
derivatives of Biguanides, have excellent therapeutic benefits but cause impaired liver
and kidney due to lactic acidosis. Based on the historic success of medicinal plants as
remedies for many ailments and the increasing need for alternative medication for
diabetes, plants from the Hardap region, in Namibia, were evaluated as potential
Complementary and Alternative Medicine (CAM) for diabetes. In Namibia, medicinal
plants are used as primary health care to manage diabetes, especially by those in
resource-poor settings. However, there is a paucity of data supporting the use of these
plants for this purpose. Scientific data must be generated to support the use of
Namibian plants as complementary and alternative medicines for managing diabetes.
To this end, a survey on the use of medicinal plants for the management of diabetes in
the Hardap region of Southern Namibia was conducted. The survey revealed eleven
plants belonging to nine different families, that is Asphodelaceae, Malvaceae,
Pedaliaceae, Apocynaceae, Lamiaceae, Geraniaceae, Zygophyllaceae, Tiliaceae, and
Fabaceae as authenticated by the National Herbarium. However, of the eleven plants,
only five were available for collection for laboratory analysis, namely Corchorus
tridens, Sarcocaulon salmoniflorum, Zygophylum decumbens, Hermannia fruticulosa,
and Hoodia gordonii.
The plant materials were air-dried at room temperature before being ground to a
powder for extraction using ethanol, methanol, and water. The plant extracts were
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subjected to Thin Layer Chromatography (TLC) screening, followed by quantification
of total flavonoid content (TFC) and total phenolic content (TPC). The biological
properties of the extracts; antioxidant activity involving DPPH and reducing power;
antihyperglycemic activity using α amylase and α glucosidase assay; and in vitro
cytotoxicity assay using MTT assay, were evaluated.
The study demonstrated the presence of alkaloids, flavonoids, phenols, saponins,
steroids, tannins, and terpenoids in plants. Quantification of phytochemicals showed
high TPC content in C. tridens, methanol extracts (23.58 ±0.41) mgQE/g, and ethanol
extracts (22.79 ±0.16). High TFC was observed in ethanol extracts of C.tridens
(96.90±7.04) mgGAE/g, followed by Z. decumbens (49.98±2.97) mg GAE/g then S.
salmoniflorum (44.55±0.44) mg GAE/ g. Data showed a statistically significant
difference between TFC and TPC (p < 0.05).
Plants showed free radical scavenging potential, with C. tridens ethanol extracts
exhibiting the highest scavenging activity with IC50 0.0312±21.05 mg/ml followed by
methanol extracts of H. fruticulosa with IC50 of 0.0339±24.64 mg/ml when compared
with the positive control (ascorbic acid) with IC50 of 0.0279±17.09 mg/ml. The
different solvents used for plant extraction significantly influenced the free radical
scavenging potential of plants (p < 0.05) while no significant difference was
demonstrated across the different concentrations (p >0.05). The reducing power of
extracts showed no significant concentration dependence (p > 0.05). High reducing
activity was recorded in methanol extracts of S. salmoniflorum 1.84 ± 0.025726834
and C. tridens 1.5± 0.014854405 when compared with the ascorbic acid of 3.16 ± 0.
026394.
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Antihyperglycemic potency of plant extracts was evident with the inhibition of α-
amylase recorded for aqueous extracts of Z. decumbens and H. gordonii, 96.3% and
93.9 % respectively when compared with the positive control (acarbose) inhibition
capacity of 64.2 % at 1 mg/ml. The inhibition of α-amylase is not significantly
influenced by the concentration (p > 0.05), though showed significant reliance on the
solvent used for extraction (p < 0.05). Aqueous extracts of H. gordonii revealed
potency with the lowest IC 50 of 0.1667 mg/ ml. A qualitative α-glucosidase inhibition
potential was demonstrated by all the tested plant extracts, through the ability to
prevent the degradation of starch in the presence of α-glucosidase and starch that was
evident by the stain that was produced on the agar. The cell line of 3T3 proliferated 90
% and above in the presence of the studied plant extracts. The Kruskal- Wallis test
revealed that the growth of 3T3 cell lines wassignificantly influenced by the difference
in extract concentrations (p < 0.05). Moreover, these cells proliferate differently in the
presence of the different studied plants (p < 0.05). The safety data of cytotoxicity
indicate less toxicity to none except for C. tridens with IC 50 0.2014±5.491 μg / μl.
The demonstrated anti-hyperglycemic activity of the studied plants, especially
aqueous extracts of Z.decumbens and H. gordonii can be attributed to the presence of
the tested phytochemicals and may infer that they have potential anti-hyperglycemic
agents as well as validate their use in the traditional setting. Further in vivo and detailed
phytochemical analysis is recommended to identify active components of the plants
and their mechanism of action.
Description
A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science in Biology
Keywords
Anti-hyperglycemic, Diabetes mellitus, Anti-oxidants, DPPH, TLC, 3T3 cell line, Namibia, University of Namibia