Ambrose Okem | University of KwaZulu-Natal (original) (raw)

Papers by Ambrose Okem

Journal of Pharmacological and Toxicological Methods, 2019

Journal of Pharmacological and Toxicological Methods, Jun 18, 2019

Medicine in Drug Discovery

South African Journal of Botany, 2017

Abstract The global demand for medicinal plant products has increased in the last two decades lea... more Abstract The global demand for medicinal plant products has increased in the last two decades leading to overexploitation and sometimes extinction of indigenous medicinal plants. Plant biotechnology offers an efficient approach to enhanced biosynthesis of essential and/or bioactive compounds in plants. This study was aimed at developing a micropropagation protocol for Agathosma betulina Berg. (Buchu), one of the most highly utilized aromatic medicinal plants in South Africa. The study also aimed to develop a technique that will enhance the biosynthesis of some bioactive compounds by manipulating the media composition. Seeds and nodal explants from Buchu were decontaminated, germinated and sub-cultured on Murashige and Skoog (1962) (MS) media adjusted with different concentrations of N6-Benzyladenine (BA), 1-naphthaleneacetic acid (NAA) and dichlorophenoxy acetic acid (2,4-D). Dried samples from in vitro cultures were extracted using dichloromethane and analyzed for phytochemical compositions using GC–MS. In vitro seed germination produced healthy seedlings that can be transplanted ex vitro. Significantly higher shoot proliferation was recorded in nodal explants grown in 1/2 strength MS supplemented with 2,4-D and a combination of NAA and BA. Phytochemical analysis revealed significantly higher amounts of limonene accumulated in callus compared to other plant parts. The most abundant phytochemicals were recorded in plants grown on media supplemented with NAA 2.7 μM; these include limonene, pulegone and isomenthone (68, 39 and 33 μg kg− 1 DW respectively). Biosynthesis of certain compounds in in vitro culture of Buchu was induced by plant growth regulator application compared to the control. The plants possess a number of pharmacological properties including anticancer, antimicrobial and antioxidant. These activities are linked to inherent phytochemical contents. Hence, the use of micropropagation techniques that will enhance the biosynthesis of some bioactive compounds in Buchu will be an efficient means to meet the high demands for this plant.

Plant Biology, 2016

Hypoxis hemerocallidea is a highly utilized medicinal plant in South Africa. Its cultivation has ... more Hypoxis hemerocallidea is a highly utilized medicinal plant in South Africa. Its cultivation has received considerable attention in order to meet the high demand. High levels of cadmium (Cd) and aluminum (Al) in H. hemerocallidea plants sold in traditional medicinal markets was previously reported. The present study used an in vitro propagation model to investigate the uptake of Cd and Al by H. hemerocallidea and their effect on plant growth, elemental uptake and some stress-induced responses such as pigment, malondialdehyde (MDA), proline content and ultrastructural changes. Shoot and root growth of plantlets exposed to Cd, Cd:Al and high concentrations of Al was significantly reduced. Highest concentrations of Cd accumulated in the corms of Cd-treated plantlets while highest Al concentrations occurred in the leaves and roots. There was higher accumulation of Cd and Al when applied singularly compared to the Cd:Al combination treatments. Cd and Al also reduced accumulation of trace elements in micropropagted H. hemerocallidea with lowest concentrations in the Cd:Al combination treatments. Exposure to Cd, Al and Cd:Al significantly reduced the level of chlorophyll but increased the levels of carotenoids, MDA and proline. Ultrastructural changes were also observed in H. hemerocallidea exposed to Cd and Al. All these factors contributed to the inhibition of plant growth and could potentially affect the ability of this important medicinal plant to synthesize bioactive compounds. It is thus necessary to understand heavy metal stress-induced responses in this highly valued medicinal plant to ensure a high quality product for the consumer.

South African Journal of Botany, 2016

South African Journal of Botany, 2015

Drimia elata (Jacq.) is a bulbous plant that is extensively utilized in South African traditional... more Drimia elata (Jacq.) is a bulbous plant that is extensively utilized in South African traditional medicine. This study investigated the effects of cadmium (Cd) and aluminum (Al) on growth, heavy metal bioaccumulation, metabolite content and antibacterial activity in D. elata. Seeds were germinated and after seven months, plants were exposed to various concentrations of Cd and Al both singly and in combinations for six weeks. Thereafter, the experiment was terminated and the mean fresh (FW) and dry weights (DW) of the bulb and shoot biomass recorded. Dried samples (0.5 g DW) were analyzed for Cd and Al accumulation using Inductively Coupled Plasma-Optical Emission Spectroscopy. In addition, total chlorophyll, free-proline, total phenolic and flavonoid content were quantified as a measure of plant stress. Antibacterial activity was assessed using the microdilution assay and the activity was correlated to heavy metal and secondary metabolite content. Plants exposed to heavy metals generally exhibited a marked reduction in plant biomass. The highest Cd content (83 mg/kg) was recorded in bulbs grown in Cd 5:Al 1000 mg/l. There was a significant increase in free-proline and a significant reduction in the chlorophyll, phenolic and flavonoid content in plants exposed to increasing concentrations of Cd and Al. This decrease in secondary metabolite content may account for the poor antibacterial activity of plants grown in most of the heavy metal treatments. This results indicate that exposure of D. elata to heavy metal contaminated soil may potentially compromise the health of the consumer due to heavy metal bioaccumulation as well as reduced efficacy of the herbal product.

International Journal of Phytoremediation, 2015

The use of plant growth regulators (PGRs) and biostimulants to enhance phytoextraction is gaining... more The use of plant growth regulators (PGRs) and biostimulants to enhance phytoextraction is gaining popularity in phytoremediation technology. This study investigated the stimulatory effects of smoke-water (SW), a smoke-derived compound karrikinolide (KAR1) and other known plant growth regulators (PGRs) [gibberellic acid (GA3), kinetin (Kin) and indole-3-butyric acid (IBA)] to enhance the phytoextraction potential of Pennisetum clandestinum. Pennisetum clandestinum seedlings were grown for 10 weeks in vermiculite using Hoagland&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s nutrient solution and were treated with cadmium (Cd) (2, 5 and 10 mg L(-1)) and SW, KAR1 and PGRs. KAR1exhibited positive effects on shoot and root dry weight (140 and 137 mg respectively) at the highest concentration of Cd (10 mg L(-1)) compared to all the other treatments. KAR1 and SW treatments used in the present study significantly improved the phytoextraction potential of P. clandestinum (602 and 575 mg kg(-1) respectively) compared to the other tested PGRs. This is the first report on the use of SW and KAR1to enhance phytoremediation potential in P. clandestinum. Further studies are needed to elucidate the exact mechanisms of smoke constituents involved in phytoextraction potential of plant species.

South African Journal of Botany, 2012

In South Africa, the use of commercial herbal concoctions is becoming very popular. However, due ... more In South Africa, the use of commercial herbal concoctions is becoming very popular. However, due to lack of Good Manufacturing Practices there is a possibility of heavy metal contamination in these commercial herbal concoctions. The aim of this investigation was to screen for heavy metal and trace elements in commercial herbal concoctions used in traditional medicine to treat various kinds of ailments in South Africa. This is the first investigation in which metal concentrations in commercial herbal concoctions was measured. Fourteen herbal concoctions were obtained from traditional herbal (muthi) shops and were subjected to analysis for total and bioavailable metal concentrations using Inductively Coupled Plasma-Optical Emission Spectrophotometry (ICP-OES). Of all the concoctions tested only Vusa umzimba and Sejeso herbal mixture contained high amounts of Cd (2.2 and 0.6 mg/kg) respectively, exceeding the safety limit of 0.3 mg/kg (WHO, 1998). Vusa umzimba also exhibited high amounts of bioavailable Cd (1.2 mg/kg) thereby making it unsafe for human consumption. Surprisingly very high amounts of Hg were detected in Ingwe muthi mixture and Sejeso herbal mixture (14.9 and 12.3 mg/kg) respectively. These by far exceeds the weekly allowance limit of 2 μg/kg given by WHO/UN committee (2007). Relatively high amounts of Pb were found in Sejeso herbal mixture. The levels of bioavailable metals detected in this study raise concerns, not only for consumer safety, but also the quality of herbal concoctions available as part of the traditional medicinal practice in South Africa.

Food and Chemical Toxicology, 2013

South African Journal of Botany, 2014

The quality and safety of herbal medicines is becoming a major concern worldwide particularly due... more The quality and safety of herbal medicines is becoming a major concern worldwide particularly due to contamination by heavy metals. The present study quantified the levels of heavy metals in frequently used South African medicinal plants and determined the variations in certain biological activities and phytochemical compositions. Eleven plant species were obtained from both muthi shops (MS) (commercial outlets) and from open street markets (OSM) for comparison. Samples were dried, powdered and digested using microwave acid-assisted digestion. The digested solutions were analysed for heavy metals using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Plants were classified based on their elemental composition using chemometric techniques. Powdered plant samples were extracted using 70% acetone and screened for antibacterial activity against E. coli and S. aureus. Phytochemical analyses were carried out to determine total phenolic and flavonoid content. Of the 22 samples analysed, Bulbine natalensis obtained from OSM and Alepidea amatymbica obtained from MS exhibited high levels of Al [5559 and 4392 mg/kg dry weight (DW)] and Fe (4164 and 4465 mg/kg DW) respectively. Levels of As and Hg were above the World Health Organization permissible limits in most of the samples analysed. Hierarchical cluster analysis classified the samples into four groups based on their metallic analyte concentrations. Group one having low metal content and group four having a high metal content. In general, plant samples with high levels of metals yielded greater antibacterial activity. However, antibacterial activity recorded in this study is not an indicator of high levels of heavy metal contamination as some samples despite the high levels of metal exhibited low antibacterial activity. The variations in the amounts of phenolics and flavonoids in the evaluated samples could have probably been that some of the plant samples may have been harvested from different localities or at different times of the year, perhaps plant age or degree of storage. The results highlighted the need for in-depth risk and quality assessments.

Biomedicines, 2020

Melanoma is the least common form of skin cancer and is associated with the highest mortality. Wh... more Melanoma is the least common form of skin cancer and is associated with the highest mortality. Where melanoma is mostly unresponsive to conventional therapies (e.g., chemotherapy), BRAF inhibitor treatment has shown improved therapeutic outcomes. Photodynamic therapy (PDT) relies on a light-activated compound to produce death-inducing amounts of reactive oxygen species (ROS). Their capacity to selectively accumulate in tumor cells has been confirmed in melanoma treatment with some encouraging results. However, this treatment approach has not reached clinical fruition for melanoma due to major limitations associated with the development of resistance and subsequent side effects. These adverse effects might be bypassed by immunotherapy in the form of antibody–drug conjugates (ADCs) relying on the ability of monoclonal antibodies (mAbs) to target specific tumor-associated antigens (TAAs) and to be used as carriers to specifically deliver cytotoxic warheads into corresponding tumor cell...

Pharmacological activities of selected South African medicinal plants I, Ambrose Okem, student nu... more Pharmacological activities of selected South African medicinal plants I, Ambrose Okem, student number: 210551070 i. The research reported in this dissertation, except where otherwise indicated, is the result of my own endeavours in the Research Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of KwaZulu-Natal Pietermaritzburg; ii. This dissertation has not been submitted for any degrees or examination at any other University; iii. This thesis does not contain data, Figures or writing, unless specifically acknowledged, copied from other researchers.

African Journal of Traditional, Complementary and Alternative medicines, Oct 1, 2017

Background: Gnidia capitata L. F. belongs to the family Thymelaeaceae, and has been widely report... more Background: Gnidia capitata L. F. belongs to the family Thymelaeaceae, and has been widely reported for its ethnobotanical uses, especially for the treatment of several human ailments which include skin conditions. However, there is limited information about the pharmacological properties of this plant as a potential cosmetic agent or pharmaceutical. The aim of this study was to evaluate the therapeutic potential of G. capitata for its anti-tyrosinase, antibacterial, antioxidant, anticancer and anti-mycobacterial properties. Materials and methods: G. capitata was extracted with methanol (MeOH), ethyl acetate (EtOAc), dichloromethane (DCM) and hexane (n-Hex). All extracts were tested in vitro for activities against Propionibacterium acnes (ATCC 11827) and Mycobacterium tuberculosis H37Rv (ATCC 27294). Tyrosinase inhibitory activity was screened using tyrosinase from Agaricus bispor. Antioxidant activity was investigated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Results: EtOAc, DCM and n-Hex extracts of the plant showed antibacterial activity against P. acnes with MICs of 125 µg/ml. The DCM and n-Hex extracts showed anti-mycobacterial activity with MICs of 500µg/ml. The methanolic extract showed the highest antioxidant activity with an IC 50 of 41.83µg/ml. Conclusion: The findings presented in this study may explain the potential use of G. capitata for the treatment of certain skin conditions. The potent antioxidant activity could help control the negative effects associated with inflammatory mediators that are produced during the immune response in people that are affected by skin conditions.

HortScience

The effect of drip irrigation regimen on growth, physiological parameters, and crop yield in Cucu... more The effect of drip irrigation regimen on growth, physiological parameters, and crop yield in Cucumis sativus L. was investigated using a drip irrigation system. The experimental design comprised eight various water regimens (2, 4, 6, 8, 10, 12, 14, and 16 L·h−1). Plants received water five times a day, making a total of 10, 20, 30, 40, 50, 60, 70, and 80 L per day. Growth and photosynthetic parameters were analyzed on a weekly base for a period of 8 weeks. Crop yield was measured at the end of the experiment. In general, photosynthetic rate (A), intercellular CO2 concentration (Ci), stomatal conductance (gS) and the transpiration rate (E) of the cucumber plants were enhanced by increasing water quantities compared with the control. Overall, the total chlorophyll content was significantly enhanced between week 7 and 8 in plants treated with high irrigation volume. Significant improvements were recorded in plant height and number of leave from week 3 to 8 in plants supplied with high ...