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Pharmacokinetics of artemisinin-type compounds

Navaratnam V, Mansor SM, Sit NW, Grace J, Li Q, Olliaro P

Clin Pharmacokinet, 2000 Oct;39(4):255-70.
PMID: 11069212

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.
Bioactivity of medicinal plant extracts against human fungal pathogens and evaluation of toxicity using Vero cells

Oon YN, Chen RJ, Kuan JM, Sit NW

Trop Biomed, 2021 Sep 01;38(3):469-475.
PMID: 34608121 DOI: 10.47665/tb.38.3.090

Medicinal plants are a potential source of new antifungal agents to combat the development of drug-resistant fungi. This study aims to investigate the aerial parts of Alternanthera sessilis (Amaranthaceae) and Ipomoea aquatica (Convolvulaceae), and the leaves of Catunaregam spinosa (Rubiaceae) and Tradescantia spathacea (Commelinaceae) for antifungal activity and cytotoxicity. The plant materials were extracted sequentially using hexane, chloroform, ethyl acetate, ethanol, methanol, and distilled water. The antifungal activity was evaluated against four species of yeasts and two species of filamentous fungi using a colorimetric broth microdilution method. The toxicity of the extracts was assessed using African monkey kidney epithelial (Vero) cells. All 24 extracts from the four medicinal plants showed inhibitory activity against all fungal species, except Aspergillus fumigatus, with a minimum inhibitory concentration range of 0.04-2.50 mg/mL. The antifungal activity of these plants was more prominent on the yeasts than the filamentous fungi. Generally, the less polar extracts (hexane, chloroform, and ethyl acetate) of the plants had stronger antifungal activity than the more polar extracts (ethanol, methanol, and water). In contrast, toxicity assessment revealed that the less polar extracts showed relatively higher toxicity towards the Vero cells than the more polar extracts. The lowest median cytotoxic concentration was shown by the chloroform extract of A. sessilis (17.4 ± 0.4 μg/mL). All water extracts, the methanol extract of I. aquatica, and the ethyl acetate, ethanol, and methanol extracts of T. spathacea did not show significant toxicity (P>0.05) towards the Vero cells. The results suggested that Tradescantia spathacea has the most promising potential for pharmaceutical developments due to its broad spectrum and selective activity against human fungal pathogens.
Fulltext High performance liquid chromatography profiling of health-promoting phytochemicals and evaluation of antioxidant, anti-lipoxygenase, iron chelating and anti-glucosidase activities of wetland macrophytes

Ooh KF, Ong HC, Wong FC, Sit NW, Chai TT

Pharmacogn Mag, 2014 Aug;10(Suppl 3):S443-55.
PMID: 25298659 DOI: 10.4103/0973-1296.139767

The phytochemistry and bioactivity of wetland macrophytes are underexplored. Plants are known as the natural sources of phytochemical beneficial to health.
Fulltext Botanical Origin Differentiation of Malaysian Stingless Bee Honey Produced by Heterotrigona itama and Geniotrigona thoracica Using Chemometrics

Ng WJ, Sit NW, Ooi PA, Ee KY, Lim TM

Molecules, 2021 Dec 16;26(24).
PMID: 34946710 DOI: 10.3390/molecules26247628

Stingless bee honey, specifically honeydew honey, is generally valued for its better health benefits than those of most blossom types. However, scientific studies about the differentiation of stingless bee honey based on honeydew and blossom origins are very limited. In this study, 13C NMR spectroscopy was employed to quantify the seven major sugar tautomers in stingless bee honey samples, and the major sugar compositions of both honeydew and blossom types were found not significantly different. However, several physicochemical properties of honeydew honey including moisture content, free acidity, electrical conductivity, ash content, acetic acid, diastase, hydrogen peroxide, and mineral elements levels were significantly higher; while total soluble solid, proline, and hydroxymethylfurfural were significantly lower than blossom honey. Greater antioxidant capacity in honeydew honey was proven with higher total phenolic compounds, ABTS, DPPH, superoxide radical scavenging activities, peroxyl radical inhibition, iron chelation, and ferric reducing power. Using principal component analysis (PCA), two clusters of stingless bee honey from the honeydew and blossom origin were observed. PCA also revealed that the differentiation between honeydew and blossom origin of stingless bee honey is possible with certain physicochemical and antioxidant parameters. The combination of NMR spectroscopy and chemometrics are suggested to be useful to determine the authenticity and botanical origin of stingless bee honey.
Fulltext Chemical composition, antioxidant, antimicrobial and antiviral activities of the leaf extracts of Syzygium myrtifolium

Ahmad MA, Lim YH, Chan YS, Hsu CY, Wu TY, Sit NW

Acta Pharm, 2022 Jun 01;72(2):317-328.
PMID: 36651512 DOI: 10.2478/acph-2022-0013

This study was conducted to evaluate the chemical composition and biological activities of the leaf extracts of Syzygium myrtifolium Walp. (Myrtaceae). The results indicate that the leaf extracts of S. myrtifolium contain various classes of phytochemicals (alkaloids, anthraquinones, flavonoids, phenolics, saponins, tannins and triterpenoids) and possess antioxidant, antibacterial, antifungal and antiviral activities. Ethyl acetate, ethanol, methanol, and water extracts exhibited significantly higher (p < 0.05) oxygen radical absorbance capacity and ferric-reducing antioxidant power than the hexane and chloroform extracts. However, all extracts exhibited stronger inhibitory activity against four tested species of yeasts (minimal inhibitory concentration: 0.02-0.31 mg mL-1) than against six tested species of bacteria (minimal inhibitory concentration: 0.16-1.25 mg mL-1). The ethanolic extract offered the highest protection of Vero cells (viability > 70 %) from the cytopathic effect caused by the Chikungunya virus while the ethyl acetate extract showed significant replication inhibitory activity against the virus (p < 0.001) using the replicon-enhanced green fluorescent protein reporter system.
Fulltext Self-management using crude herbs and the health-related quality of life among adult patients with hypertension living in a suburban setting of Malaysia

Joachimdass RJ, Subramaniam K, Sit NW, Lim YM, Teo CH, Ng CJ, et al.

PLoS One, 2021;16(9):e0257336.
PMID: 34506588 DOI: 10.1371/journal.pone.0257336

PURPOSE: To determine the prevalence of crude herbs' use in the self-management of hypertension and the health-related quality of life (HRQOL) in patients with hypertension.
METHODS: This cross-sectional study was performed among patients with hypertension attending a government health clinic. Socio-demographic characteristics, lifestyle modifications, medical history and predictors of crude herbs users were obtained. The diversity of crude herbs used was assessed using a modified international complementary and alternative medicine questionnaire (I-CAM-Q) and the HRQOL was assessed using the SF36 instrument.
RESULTS: Out of the 294 patients recruited, 52.4% were female, 41.5% were Malay and 38.8% were within the 60 to69 age category. The prevalence of crude herbs users was 30.6% and the most common herbs used were pegaga (Centella asiatica), peria (Momordica charantia) and betik (Carica papaya). Using the regression analysis, significantly higher odds of using crude herbs are noted among Malay or Indian patients who have these characteristics: attained secondary education, experienced falls or muscle pain, and had systolic blood pressure of more than 140 mmHg. There was no significant difference in HRQOL domains between the crude herb users and non-users (p>0.05).
CONCLUSION: Besides taking allopathic medications, certain patients with hypertension use crude herbs as a form of self-management. Although patients are adamant about integrating crude herbs as a form of self-management, the effects of doing so have not been properly investigated. This implies that the healthcare staff members need to communicate with the patients regarding the use of crude herbs together with conventional drugs.
Antifungal and cytotoxic activities of selected medicinal plants from Malaysia

Chan YS, Cheah YH, Chong PZ, Khor HL, Teh WS, Khoo KS, et al.

Pak J Pharm Sci, 2018 Jan;31(1):119-127.
PMID: 29348093

This study was conducted to investigate the antifungal potential and cytotoxicity of selected medicinal plants from Malaysia. The extracts from the stem of Cissus quadrangularis and the leaves of Asplenium nidus, Pereskia bleo, Persicaria odorata and Sauropus androgynus were assayed against six fungi using p-iodonitrotetrazolium-based on colorimetric broth microdilution method. All the plant extracts were found to be fungicidal against at least one type of fungus. The strongest fungicidal activity (minimum fungicidal concentration=0.16 mg/mL) were exhibited by the hexane extract of C. quadrangularis, the hexane, chloroform, ethanol and methanol extracts of P. bleo, the hexane and ethyl acetate extracts of P. odorata, and the water extract of A. nidus. In terms of cytotoxicity on the African monkey kidney epithelial (Vero) cells, the chloroform extract of P. odorata produced the lowest 50% cytotoxic concentration (100.3 ± 4.2 μ g/mL). In contrast, none of the water extracts from the studied plants caused significant toxicity on the cells. The water extract of A. nidus warrants further investigation since it showed the strongest fungicidal activity and the highest total activity (179.22 L/g) against Issatchenkia orientalis, and did not cause any toxicity to the Vero cells.
Fulltext Dengue vector surveillance in insular settlements of Pulau Ketam, Selangor, Malaysia

Lim KW, Sit NW, Norzahira R, Sing KW, Wong HM, Chew HS, et al.

Trop Biomed, 2010 Aug;27(2):185-92.
PMID: 20962714 MyJurnal

A year-long ovitrap surveillance was conducted between November 2007 and October 2008 in two insular settlements (Kampung Pulau Ketam and Kampung Sungai Lima) within the Malaysian island of Pulau Ketam. Eighty standard ovitraps were placed indoors and outdoors of randomly selected houses/locations. Results demonstrated an endemic baseline Aedes population throughout the year without weekly large fluctuations. Kampung Pulau Ketam has high Aedes aegypti and Aedes albopictus population, but only Ae. aegypti was found in Kampung Sungai Lima. Aedes aegypti showed no preference for ovitraps placed indoor versus outdoor. However, as expected, significantly more outdoor ovitraps were positive for Ae. albopictus (p<0.05). Trends in Ae. albopictus and Ae. aegypti populations mirrored each other suggesting that common factors influenced these two populations.
In vitro antidermatophytic activity and cytotoxicity of extracts derived from medicinal plants and marine algae

Sit NW, Chan YS, Lai SC, Lim LN, Looi GT, Tay PL, et al.

J Mycol Med, 2018 Sep;28(3):561-567.
PMID: 30060991 DOI: 10.1016/j.mycmed.2018.07.001

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 0.005-2.50mg/mL, respectively. The algae extracts exhibited lower potency against both species, showing MFC ranges of 0.08-2.50 and 0.31-2.50mg/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<0.1mg/mL) and with high selectivity indices (SI>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.