Nam Weng Sit

Bio: Nam Weng Sit is an academic researcher from Universiti Tunku Abdul Rahman. The author has contributed to research in topics: Phytochemical & DPPH. The author has an hindex of 7, co-authored 17 publications receiving 305 citations. Previous affiliations of Nam Weng Sit include Universiti Sains Malaysia.

Pharmacokinetics of Artemisinin-Type Compounds

Abstract: Various compounds of the artemisinin family are currently used for the treatment of patients with malaria worldwide. They are characterised by a short half-life and feature the most rapidly acting antimalarial drugs to date. They are increasingly being used, often in combination with other drugs, although our knowledge of their main pharmacological features (including their absorption, distribution, metabolism and excretion) is still incomplete. Such data are particularly important in the case of combinations. Artemisinin derivatives are converted primarily, but to different extents, to the bioactive metabolite artenimol after either parenteral or gastrointestinal administration. The rate of conversion is lowest for artelinic acid (designed to protect the molecule against metabolism) and highest for the water-soluble artesunate. The absolute and relative bioavailability of these compounds has been established in animals, but not in humans, with the exception of artesunate. Oral bioavailability in animals ranges, approximately, between 19 and 35%. A first-pass effect is highly probably for all compounds when administered orally. Artemisinin compounds bind selectively to malaria-infected erythrocytes to yet unidentified targets. They also bind modestly to human plasma proteins, ranging from 43% for artenimol to 81.5% for artelinic acid. Their mode of action is still not completely understood, although different theories have been proposed. The lipid-soluble artemether and artemotil are released slowly when administered intramuscularly because of the 'depot' effect related to the oil formulation. Understanding the pharmacokinetic profile of these 2 drugs helps us to explain the characteristics of the toxicity and neurotoxicity. The water-soluble artesunate is rapidly converted to artenimol at rates that vary with the route of administration, but the processes need to be characterised further, including the relative contribution of pH and enzymes in tissues, blood and liver. This paper intends to summarise contemporary knowledge of the pharmacokinetics of this class of compounds and highlight areas that need further research.

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

The Antibacterial Potential of Honeydew Honey Produced by Stingless Bee (Heterotrigona itama) against Antibiotic Resistant Bacteria

Abstract: Scientific studies about the antibacterial effects of honeydew honey produced by the stingless bee are very limited. In this study, the antibacterial activities of 46 blossom and honeydew honeys produced by both honey bees and stingless bees were evaluated and compared. All bacterial isolates showed varying degrees of susceptibility to blossom and honeydew honeys produced by the honey bee (Apis cerana) and stingless bee (Heterotrigona itama and Geniotrigona thoracica) in agar-well diffusion. All stingless bee honeys managed to inhibit all the isolates but only four out of 23 honey bee honeys achieved that. In comparison with Staphylococcus aureus, Escherichia coli was found to be more susceptible to the antibacterial effects of honey. Bactericidal effects of stingless bee honeys on E. coli were determined with the measurement of endotoxins released due to cell lysis. Based on the outcomes, the greatest antibacterial effects were observed in honeydew honey produced by H. itama. Scanning electron microscopic images revealed the morphological alteration and destruction of E. coli due to the action of this honey. The combination of this honey with antibiotics showed synergistic inhibitory effects on E. coli clinical isolates. This study revealed that honeydew honey produced by H. itama stingless bee has promising antibacterial activity against pathogenic bacteria, including antibiotic resistant strains.

In vitro antidermatophytic activity and cytotoxicity of extracts derived from medicinal plants and marine algae.

Abstract: Objectives This study was conducted to evaluate the antidermatophytic activity of 48 extracts obtained from medicinal plants (Cibotium barometz, Melastoma malabathricum, Meuhlenbeckia platyclada, Rhapis excelsa, Syzygium myrtifolium, Vernonia amygdalina) and marine algae (Caulerpa sertularioides, Kappaphycus alvarezii) against Trichophyton rubrum and Trichophyton interdigitale (ATCC reference strains), and the cytotoxicity using African monkey kidney epithelial (Vero) cells. Active plant extracts were screened for the presence of phytochemicals and tested against clinical isolates of Trichophyton tonsurans. Methods Six different extracts (hexane, chloroform, ethyl acetate, ethanol, methanol and water) were obtained from each plant or algae sample using sequential solvent extraction. The antidermatophytic activity for the extracts was assessed using a colourimetric broth microdilution method. The viability of Vero cells was measured by Neutral Red uptake assay. Results All the extracts (except the water extracts of V. amygdalina, C. sertularioides and K. alvarezii) showed antidermatophytic activity against Trichophyton spp. The minimum fungicidal concentration (MFC) ranges for the plant extracts against T. rubrum and T. interdigitale are 0.0025–2.50 and 0.005–2.50 mg/mL, respectively. The algae extracts exhibited lower potency against both species, showing MFC ranges of 0.08–2.50 and 0.31–2.50 mg/mL, respectively. The ethanol and methanol extracts from the leaves of R. excelsa, and the methanol and water extracts from the leaves of S. myrtifolium were highly active (MFC 2.8) against reference strains of T. rubrum and T. interdigitale, and most of the clinical isolates of T. tonsurans. Phytochemical analysis indicates the presence of alkaloids, anthraquinones, flavonoids, saponins, tannins, phenolics and triterpenoids in the extracts. Conclusions The medicinal plant extracts exhibited stronger antidermatophytic activity compared to the algae extracts. The leaves of R. excelsa and S. myrtifolium are potential sources of new antidermatophytic agents against Trichophyton spp.

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...

WHO Guidelines for the treatment of malaria

Abstract: Early diagnosis and prompt treatment with effective antimalarials is a vital component of malaria control strategies. The second edition of the World Health Organization (WHO) Guidelines for the treatment of malaria revisits the global recommendations on the case management of malaria on updated evidence compared to the earlier 2006 edition. Though the recommendations are targeted at the country level policy makers providing a framework for the development of specific and more detailed national treatment protocols, it is a valuable read for all clinicians and post-graduate students.

Artemisone—A Highly Active Antimalarial Drug of the Artemisinin Class†

Abstract: Artemisinin - the next generation: Efficacies of artemisone against the malaria parasite are substantially greater than those of the current artemisinin "gold standard", artesunate. Also, in contrast to most current artemisinins it displays low lipophilicity and negligible neuro- and cytotoxicity in in vitro and in vivo assays. Thus, the drug offers promise for use in artemisinin-based combination therapy. (Chemical Equation Presented). © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.

Toxicity of the antimalarial artemisinin and its dervatives

Abstract: As long as no effective malaria vaccine is available, chemotherapy belongs to the most important weapons fighting malaria. One of the most promising new drug developments is the sesquiterpene artemisinin (ARS) and its derivatives, e.g., artemether, arteether, and sodium artesunate. Large clinical studies and meta-analyses did not show serious side effects, although proper monitoring of adverse effects in developing countries might not be a trivial task. There is a paucity of large-scale clinical trials suitable to detect rare but significant toxicity. Therefore, a final and definitive statement on the safety of artemisinins still cannot be made. In contrast, animal experiments show considerable toxicity upon application of artemisinins. In the present review, the authors give a comprehensive overview on toxicity studies in cell culture and in animals (mice, rats, rabbits, dogs, monkeys) as well as on toxicity reported in human clinical trials. The authors emphasize the current knowledge on neurotoxicity, embryotoxicity, genotoxicity, hemato- and immunotoxicity, cardiotoxicity, nephrotoxicity, and allergic reactions. The lesson learned from animal and human studies is that long-term availability rather than short-term peak concentrations of artemisinins cause toxicity. Rapid elimination of artemisinins after oral intake represents a relatively safe route of administration compared to delayed drug release after intramuscular (i.m.) injection. This explains why considerable toxicities were found in the majority of animal experiments, but not in human studies. In addition, there are drug-related differences, i.e., intramuscular application of artemether or arteether, but not to artesunate, which is safe and gives good profiles after i.m. administration in severe malaria. Although there is no need to increase doses of artemisinins for uncomplicated malaria, this has to be taken into account for cerebellar involvement in severe malaria. It might also be important in determining dose limitations for treatment of other diseases such as cancer.

Reduced Susceptibility of Plasmodium falciparum to Artesunate in Southern Myanmar

Abstract: Background Plasmodium falciparum resistance to artemisinins, the first line treatment for malaria worldwide, has been reported in western Cambodia. Resistance is characterized by significantly delayed clearance of parasites following artemisinin treatment. Artemisinin resistance has not previously been reported in Myanmar, which has the highest falciparum malaria burden among Southeast Asian countries.