AFRICAN POTATO (Hypoxis hemerocallidea): DRUG INTERACTIONS
3.5 Pharmacological Activity of AP
44 3.4.8 Sterols and Sterolins
Some sterols and sterolins have been identified, and in some cases, quantified in the extracts of Hypoxis. In 1975, a patent was registered with the British patents office, on the extraction of sterols and sterolins from plant material, in particular Hypoxis [174]. These were identified as β-sitosterol and β-sitosterol glucoside. Four years later, another patent was registered by Pegel et al [175] in America, on methods of extraction of these sterols and sterolins from Hypoxis plants. In both cases, the amount of sterols and sterolins recovered were claimed to be high, while another study reported far much lower amounts [176].
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quercetin, but hypoxoside did not exhibit similar activity. In the same study, the antioxidant activity was assessed using Ferric Reducing Activity Plasma (FRAP), and rooperol exhibited high antioxidant activity, while hypoxoside did not exhibit any activity. It was suggested that the slight antioxidant activity of AP aqueous extract could be due to other compounds, and not to hypoxoside. Methanolic and aqueous extracts of Hypoxis hemerocallidea were found to possess free radical scavenging activity which was comparable to that of vitamin C, which was the control [179]. This study assessed antioxidant properties, using free radical scavenging method, while the former employed FRAP, lipid peroxidation assay, superoxide anion oxidation assay, as well as free radical scavenging method. Therefore, the antioxidant property report by Nair et al [87] provides a comprehensive assessment of potential antioxidant activity, since each test provides a different insight on potential antioxidant activity.
3.5.3 Anti-inflammatory Properties
It is reported that hypoxoside and Hypoxis rooperi did not inhibit activity of COX-1 and COX-2 enzymes in vitro, but rooperol noticeably inhibited both these enzymes [180].
Methanolic extracts of Hypoxis hemerocallidea were assessed for prostaglandin-synthesis inhibition, and found to inhibit synthesis of prostaglandins. In 2006, Steenkamp et al [179]
assessed the anti-inflammatory activity of Hypoxis extracts, and indomethacin was used as a control and reported that ethanolic extracts exhibited higher inhibitory effects than aqueous extracts.
In experimental models of rat oedema, aqueous Hypoxis extract was evaluated for anti inflammatory activity and compared to diclofenac [181]. The model was rat hind paw oedema, which was induced by injection of intra-plantar injection of fresh egg albumin. This pholgistic agent resulted in acute inflammation of the paw, and an aqueous extract of Hypoxis hemerocallidea is reported to have produced significant reduction in inflammation [181].
3.5.4 Antinociceptive Properties
Thermal and chemical tests were used to assess antinociceptive properties of aqueous Hypoxis hemerocallidea extracts in mice [181]. The thermal pain was induced by placing the
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mice in a beaker which was heated by a hot plate, and the pain stimulus (jumping out of beaker) was assessed. There was a significant increase in the time taken to respond to pain in mice dosed with extract compared to control group. However, this was less than the response from the morphine group. Based on this result, it is reported that the AP aqueous extract may have centrally- and peripherally-mediated analgesic properties [181]. Chemical pain was induced by intra-peritonially administering 0.2 ml of 3% acetic acid solution to the mice. The mice were divided into three groups: control, AP aqueous extract, and diclofenac. AP aqueous extract significantly relieved pain more than the control, but was less than diclofenac. These investigations concluded that an AP aqueous extract exhibited analgesic properties.
3.5.5 Antidiabetic/Hypoglycaemic Effects
The hypoglycaemic effects of methanolic extracts of Hypoxis hemerocallidea were evaluated in male Wistar rats weighing 250-300 g [182]. The doses of AP extract were 100-800 mg/kg orally and were compared to placebo and standard treatments of glibenclamide (5 mg/kg) administered orally and insulin 5 µU/kg subcutaneously. The AP extracts produced significant reduction in blood glucose concentration. In another study, Ojewole et al [181]
compared the hypoglycaemic effects AP aqueous extracts to control and chlorpropamide (a first generation sulphonylurea). The AP aqueous extract was found to significantly reduce blood glucose levels. However, the mechanism of this hypoglycaemic effect is not reported.
3.5.6 Anticonvulsant Activity
Plant species traditionally used in the treatment of epilepsy and convulsions were selected and assessed for binding to GABAA – benzodiazepine receptor complex. Hypoxis hemerocallidea, Hypoxis angustifolia and Hypoxis colchicifolia species were some of the species and extracts which were prepared with both ethanol and water [183]. All the hypoxis leaves and corms showed dose-dependent anti-convulsant activity.
3.5.7 Antibacterial Activity
One of the traditional uses of AP is the treatment of wounds where both leaves and the corm have been used [165]. The antibacterial properties of Hypoxis hemerocallidea leaves and
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corm were assessed by Katerere et al [184] after extraction with acetone and methanol. The important nocosomial organisms tested were Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Enterococcus faecalis. The dried corm extract was the most effective against S. aureus. The antibacterial activity of ethanolic and aqueous extracts of Hypoxis hemerocallidea against Escherichia coli were assessed and found to inhibit growth of the organism but this inhibition was reportedly less than the inhibition induced by ciprofloxacin [179].
Laporta et al [180] reported on antibacterial activity of Hypoxis rooperi extract, hypoxoside and rooperol against Staphaylococcus aureus and Escherichia coli. The antibacterial effect observed was comparatively less than that of neomycin which was used a reference. It was also reported that the gram-positive strain S. aureus was the most sensitive bacteria.
Inhibition of motility and multiplication of bacteria by agglutinins of lectins in some plants were assessed. Lectins are non-enzymatic proteins which bind to mono- and oligosaccharides reversibly with high selectivity. Hypoxis hemerocallidea reportedly produced some agglutinins which resulted in precipitation and inhibition of the growth of S. aureus and Bacillus subtilis [185].