Kong Soo Khoo

Bio: Kong Soo Khoo is an academic researcher from Universiti Tunku Abdul Rahman. The author has contributed to research in topics: DPPH & Oxygen radical absorbance capacity. The author has an hindex of 5, co-authored 10 publications receiving 67 citations.

Interactions between Plant Extracts and Cell Viability Indicators during Cytotoxicity Testing: Implications for Ethnopharmacological Studies

Abstract: Purpose: To compare the cytotoxicity of six medicinal plants ( Acmella ciliata , Amaranthus tricolor , Coriandrum sativum , Glebionis coronaria , Kyllinga brevifolia and Tradescantia zebrina ) using 3-(4, 5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and neutral red uptake (NRU) assays. Methods: Hexane, chloroform, ethyl acetate, ethanol, methanol and water extracts were obtained for each plant by sequential solvent extraction. Cytotoxicity was evaluated in triplicate, from 640 to 5 μg/mL, two-fold, serially on monkey kidney epithelial (Vero) cells. Results: The hexane, chloroform and ethyl acetate extracts of the six plants were more toxic to the Vero cells compared to the ethanol, methanol and water extracts. Thirty one percent (11/36) and 75 % (27/36) of the extracts showed significant cytotoxicity (p < 0.05) in MTT and NRU assays, respectively. The 78, 52 and 7 % cytotoxicity levels detected in 27 extracts using the MTT assay were significantly (p < 0.05) underestimated at 640, 320 and 160 μg/mL, respectively, using NRU assay. Nine extracts from five plants exhibited significantly lower (p < 0.05) 50 % cytotoxic concentration (CC 50 ) when NRU assay was employed compared to MTT assay. At 640 μg/mL, 10 of the 21 extracts were also found to react chemically with MTT, causing a 2.0 – 29.1-fold increase in the absorbance value (550 nm) compared to control. Conclusion: The plant extracts of A. ciliata , A. tricolor , C. sativum , G. coronaria , K. brevifolia and T. zebrina show concentration- and extraction method-dependent cytotoxicity using MTT and NRU assays. NRU assay appears to be more sensitive and reliable than MTT assay for cell viability evaluation of the plant extracts. Keywords: Acmella ciliata , Amaranthus tricolor , Coriandrum sativum , Glebionis coronaria , Kyllinga brevifolia and Tradescantia zebrina , Extraction, Medicinal plant, Neutral red uptake assay, Vero cell

Bioactivity-guided isolation and structural characterization of the antifungal compound, plumbagin, from Nepenthes gracilis

Abstract: Context: Despite several phytochemical studies of Nepenthes gracilis Korth (Nepenthaceae), the biological activities of this pitcher plant remain to be explored.Objective: This study evaluates the antifungal activity of N. gracilis extracts, isolates, and characterizes its bioactive compound and evaluates the cytotoxicity of the isolated compound.Materials and methods: Fresh leaves of N. gracilis were sequentially extracted. The fungistatic and fungicidal activities of the extracts were evaluated against six species of fungi of medical importance using a colorimetric broth microdilution method. The most active extract was fractionated by liquid–liquid partitioning and further purified by a preparative thin layer chromatography. Structural elucidation was carried out using FT-IR, GC-MS, and NMR. Cytotoxicity testing against rhesus monkey kidney epithelial cells (LLC-MK2) was assessed by a neutral red uptake (NRU) assay.Results: The hexane extract, which showed the lowest minimum inhibitory concentr...

Evaluation of antioxidant properties of phycobiliproteins and phenolic compounds extracted from Bangia atropurpurea

Abstract: Bangia atropurpurea is a freshwater red filamentous alga. In this study, we report on the recovery yield of purified phycobiliproteins, total phenolic content (TPC) and their antioxidant capacity. B. atropurpurea suspended in phosphate buffer (pH 7.2), saturated with ammonium sulphate and further isolated R-phycoerythrin and phycocyanin from phycobilisome structure by gel filtration with Sephadex G-200. Phenolic compounds extracted by variable polarity solvents to exhibit optimum yield. Folin–Ciocalteu method was used to determine the TPC, while 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and ferric-reducing antioxidant power ( FRAP) assays were used to quantitate the antioxidant activity of phycobiliproteins and phenolic compounds. B. atropurpurea predominantly contains R-phycoerythrin 54.80 % of the total protein extracted at purity ratio A 562 to A 280 of 4.45 while, phycocyanin displayed 16 % recovery yield at purity ratio A 615 to A 280 of 2.18. The purified R-phycoerythrin exhibited better antioxidant activity than phycocyanin extract and BHT synthetic antioxidant by exhibiting (IC 50% =7.66 ±0.81µg/mL) and 54.74 ± 0.11 mg GAE/1g extract for, DPPH scavenging and FRAP assay, respectively. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of purified R-phycoerythrin and phycocyanin proteins have showed apparent single band at molecular weight of 19.6 kDa and 17.5 kDa, respectively. The methanol-soluble extract displayed the utmost TPC, 80.97±0.53 mg GAE/1g extract compared to phenolic content in other organic solvents used for extraction. In accordance with TPC, methanol-soluble extract exhibited as the most effective DPPH radical scavenging and ferric reduction, (IC 50% =14.63±0.79 µg/mL) and 37.79±0.27 mg GAE/1g extract, respectively. The presence of R-phycoerythrin, phycocyanin and phenolic compounds in an array, amplifies the antioxidant property of B. atropurpurea.

Investigation of twenty selected medicinal plants from Malaysia for anti-Chikungunya virus activity

Abstract: Chikungunya virus is a reemerging arbovirus transmitted mainly by Aedes mosquitoes. As there are no specific treatments available, Chikungunya virus infection is a significant public health problem. This study investigated 120 extracts from selected medicinal plants for anti-Chikungunya virus activity. The plant materials were subjected to sequential solvent extraction to obtain six different extracts for each plant. The cytotoxicity and antiviral activity of each extract were examined using African monkey kidney epithelial (Vero) cells. The ethanol, methanol and chloroform extracts of Tradescantia spathacea (Commelinaceae) leaves showed the strongest cytopathic effect inhibition on Vero cells, resulting in cell viabilities of 92.6% ± 1.0% (512 μg/ml), 91.5% ± 1.7% (512 μg/ml) and 88.8% ± 2.4% (80 μg/ml) respectively. However, quantitative RT-PCR analysis revealed that the chloroform extract of Rhapis excelsa (Arecaceae) leaves resulted in the highest percentage of reduction of viral load (98.1%), followed by the ethyl acetate extract of Vernonia amygdalina (Compositae) leaves (95.5%). The corresponding 50% effective concentrations (EC50) and selectivity indices for these two extracts were 29.9 ± 0.9 and 32.4 ± 1.3 μg/ml, and 5.4 and 5.1 respectively. Rhapis excelsa and Vernonia amygdalina could be sources of anti-Chikungunya virus agents. [Int Microbiol 19(3):175-182 (2016)]Keywords: Chikungunya virus · antivirals · cytotoxicity · sequential extraction · medicinal plants

Vaccine and Therapeutic Options To Control Chikungunya Virus.

Abstract: SUMMARY Beginning in 2004, chikungunya virus (CHIKV) went from an endemic pathogen limited to Africa and Asia that caused periodic outbreaks to a global pathogen. Given that outbreaks caused by CHIKV have continued and expanded, serious consideration must be given to identifying potential options for vaccines and therapeutics. Currently, there are no licensed products in this realm, and control relies completely on the use of personal protective measures and integrated vector control, which are only minimally effective. Therefore, it is prudent to urgently examine further possibilities for control. Vaccines have been shown to be highly effective against vector-borne diseases. However, as CHIKV is known to rapidly spread and generate high attack rates, therapeutics would also be highly valuable. Several candidates are currently being developed; this review describes the multiple options under consideration for future development and assesses their relative advantages and disadvantages.

The Antifungal Activity of Naphthoquinones: An Integrative Review

Abstract: Naphthoquinones are the most commonly occurring type of quinones in nature. They are a diverse family of secondary metabolites that occur naturally in plants, lichens and various microorganisms. This subgroup is constantly being expanded through the discovery of new natural products and by the synthesis of new compounds via innovative techniques. Interest in quinones and the search for new biological activities within the members of this class have intensified in recent years, as evidenced by the evaluation of the potential antimicrobial activities of quinones. Among fungi of medical interest, yeasts of the genus Candida are of extreme importance due to their high frequency of colonization and infection in humans. The objective of this review is to describe the development of naphthoquinones as antifungals for the treatment of Candida species and to note the most promising compounds. By using certain criteria for selection of publications, 68 reports involving both synthetic and natural naphthoquinones are discussed. The activities of a large number of substances were evaluated against Candida albicans as well as against 7 other species of the genus Candida. The results discussed in this review allowed the identification of 30 naphthoquinones with higher antifungal activities than those of the currently used drugs.

Macroalgae as a Source of Valuable Antimicrobial Compounds: Extraction and Applications.

Abstract: In the last few decades, attention on new natural antimicrobial compounds has arisen due to a change in consumer preferences and the increase in the number of resistant microorganisms. Macroalgae play a special role in the pursuit of new active molecules as they have been traditionally consumed and are known for their chemical and nutritional composition and their biological properties, including antimicrobial activity. Among the bioactive molecules of algae, proteins and peptides, polysaccharides, polyphenols, polyunsaturated fatty acids and pigments can be highlighted. However, for the complete obtaining and incorporation of these molecules, it is essential to achieve easy, profitable and sustainable recovery of these compounds. For this purpose, novel liquid–liquid and solid–liquid extraction techniques have been studied, such as supercritical, ultrasound, microwave, enzymatic, high pressure, accelerated solvent and intensity pulsed electric fields extraction techniques. Moreover, different applications have been proposed for these compounds, such as preservatives in the food or cosmetic industries, as antibiotics in the pharmaceutical industry, as antibiofilm, antifouling, coating in active packaging, prebiotics or in nanoparticles. This review presents the main antimicrobial potential of macroalgae, their specific bioactive compounds and novel green extraction technologies to efficiently extract them, with emphasis on the antibacterial and antifungal data and their applications.

Decoding Antioxidant and Antibacterial Potentials of Malaysian Green Seaweeds: Caulerpa racemosa and Caulerpa lentillifera

Abstract: Seaweeds are gaining a considerable amount of attention for their antioxidant and antibacterial properties. Caulerpa racemosa and Caulerpa lentillifera, also known as ‘sea grapes’, are green seaweeds commonly found in different parts of the world, but the antioxidant and antibacterial potentials of Malaysian C. racemosa and C. lentillifera have not been thoroughly explored. In this study, crude extracts of the seaweeds were prepared using chloroform, methanol, and water. Total phenolic content (TPC) and total flavonoid content (TFC) were measured, followed by in vitro antioxidant activity determination using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Antibacterial activities of these extracts were tested against Methicillin-resistant Staphylococcus aureus (MRSA) and neuropathogenic Escherichia coli K1. Liquid chromatography–mass spectrometry (LCMS) analysis was then used to determine the possible compounds present in the extract with the most potent antioxidant and antibacterial activity. Results showed that C. racemosa chloroform extract had the highest TPC (13.41 ± 0.86 mg GAE/g), antioxidant effect (EC50 at 0.65 ± 0.03 mg/mL), and the strongest antibacterial effect (97.7 ± 0.30%) against MRSA. LCMS analysis proposed that the chloroform extracts of C. racemosa are mainly polyunsaturated and monounsaturated fatty acids, terpenes, and alkaloids. In conclusion, C. racemosa can be a great source of novel antioxidant and antibacterial agents, but isolation and purification of the bioactive compounds are needed to study their mechanism of action.