A network pharmacology-based approach to explore the therapeutic potential of Sceletium tortuosum in the treatment of neurodegenerative disorders.

Sceletium tortuosum (SCT) has been utilized medicinally by indigenous Koi-San people purportedly for mood elevation. SCT extracts are reported to be neuroprotective and have efficacy in improving cognition. However, it is still unclear which of the pharmacological mechanisms of SCT contribute to the therapeutic potential for neurodegenerative disorders. Hence, this study investigated two aspects-firstly, the abilities of neuroprotective sub-fractions from SCT on scavenging radicals, inhibiting some usual targets relevant to Alzheimer's disease (AD) or Parkinson's disease (PD), and secondly utilizing the network pharmacology related methods to search probable mechanisms using Surflex-Dock program to show the key targets and corresponding SCT constituents. The results indicated sub-fractions from SCT could scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, inhibit acetylcholinesterase (AChE), monoamine oxidase type B (MAO-B) and N-methyl-D-aspartic acid receptor (NMDAR). Furthermore, the results of gene ontology and docking analyses indicated the key targets involved in the probable treatment of AD or PD might be AChE, MAO-B, NMDAR subunit2B (GluN2B-NMDAR), adenosine A2A receptor and cannabinoid receptor 2, and the corresponding constituents in Sceletium tortuosum might be N-trans-feruloyl-3-methyldopamine, dihydrojoubertiamine and other mesembrine type alkaloids. In summary, this study has provided new evidence for the therapeutic potential of SCT in the treatment of AD or PD, as well as the key targets and notable constituents in SCT. Therefore, we propose SCT could be a natural chemical resource for lead compounds in the treatment of neurodegenerative disorders.

Identification of Mechanism and Pathway of the Interaction between the African Traditional Medicine, Sutherlandia Frutescens, and the Antiretroviral Protease Inhibitor, Atazanavir, in Human Subjects Using Population Pharmacokinetic (PK) Analysis.

Although the use of the indigenous Southern African plant, Sutherlandia frutescens (SF) for the treatment of HIV/AIDS has previously been described, the risk which it may pose to the safety and efficacy of ARVs and the potential mechanisms which underlie such effects may have clinical significance and relevance. The protease inhibitor (PI), atazanavir (ATV) is a substrate of the efflux transporter, P-gp which modulates absorption in the small intestine, as well as CYP3A4 and CYP3A5enzymes which facilitate metabolism in the small intestine and liver. The objective of this study was to investigate the effect of SF on the pharmacokinetics (PK) of atazanavir (ATV) and to use a population PK analysis to fit and explain plasma concentration vs. time profiles of ATV generated in a previously conducted study in healthy male subjects in order to understand and postulate on the potential mechanism(s) of the drug-drug interaction. The population PK Compartmental Analysis of ATV before and after a two-week regimen of Phyto Nova Sutherlandia SU1 tablets which contain SF plant material indicated that a two compartment model with a dual absorption mechanism best explained the data. The dual absorption mechanism is hypothesized to reflect "passive" (first-order, Ka parameter) and "active" (zero-order, K0 parameter) absorption processes. The model suggested that the mechanism by which SF reduced the overall bioavailability of ATV may be modulated via the inhibition of the "active" absorption process. This study has highlighted the utility of population PK analyses in postulating probable mechanism(s) whereby an ATM or a herbal medicine interacts with an allopathic drug.

Medicinal use of Sceletium: Characterization of Phytochemical Components of Sceletium Plant Species using HPLC with UV and Electrospray Ionization--Tandem Mass Spectroscopy.

PURPOSE: Sceletium plants have been used for its medicinal properties for centuries. However, there is a wide range of Sceletium plant species in which various alkaloidal components such as ∆7mesembrenone, mesembrenol, mesembranol, mesembrenone, mesembrine hydrochloride, epimesembranol and, sceletium A4 differ between species. Hence, to ensure the quality of Sceletium products used as a medicine, it is imperative to identify the appropriate species using both botanical and chemical methods. The chemical approach to identify and characterize the phytochemical composition of a particular species facilitates the choice of species that will provide the purported therapeutic outcome. Hence, specific analytical methods to identify relevant constituents from complex matrices are necessary. Although HPLC-UV detection is commonly used to identify and estimate phytochemical content of medicinal plants, use of mass spectroscopy (MS) and tandem mass spectroscopy (MS/MS) can unequivocally confirm their presence/absence based on characteristic ions and fragmentation patterns. METHODS: The various alkaloidal components were characterized by electrospray ionization (ESI) MS and MS/MS using an ionizing medium of 0.1% ammonium hydroxide in water mixed with acetonitrile. Compounds were purified and characterized for use as reference standards to identify the relevant alkaloidal constituents of several Sceletium plant species using HPLC with on-line UV-MS detection. RESULTS: ESI-MS provided the [M+H](+) ions with respective m/z values that related to the respective molecular weights 287, 289, 291, 287, 289, 324 and 291 for the above mentioned alkaloids, whereas, ESI MS/MS provided the characteristic fragment ions to confirm the structural identity of the individual alkaloids and subsequently used to confirm the presence and/or absence of specific alkaloids in various Sceletium plant samples. CONCLUSIONS: Whilst HPLC-UV detection has been a widely-used conventional analytical technique for both qualitative and quantitative analyses, the results highlight the necessity of ESI-MS detection to avoid erroneous identification of phytochemical components, particularly with mesembrine-type compounds which have closely related chemical structures. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Establishing the pharmaceutical quality of Chinese herbal medicine: a provisional BCS classification.

The Biopharmaceutical Classification System (BCS), which is a scientific approach to categorize active drug ingredient based on its solubility and intestinal permeability into one of the four classes, has been used to set the pharmaceutical quality standards for drug products in western society. However, it has received little attention in the area of Chinese herbal medicine (CHM). This is likely, in part, due to the presence of multiple active components as well as lack of standardization of CHM. In this report, we apply BCS classification to CHMs provisionally as a basis for establishing improved in vitro quality standards. Based on a top-200 drugs selling list in China, a total of 31 CHM products comprising 50 official active marker compounds (AMCs) were provisionally classified according to BCS. Information on AMC content and doses of these CHM products were retrieved from the Chinese Pharmacopoeia. BCS parameters including solubility and permeability of the AMCs were predicted in silico (ACD/Laboratories). A BCS classification of CHMs according to biopharmaceutical properties of their AMCs is demonstrated to be feasible in the current study and can be used to provide a minimum set of quality standards. Our provisional results showed that 44% of the included AMCs were classified as Class III (high solubility, low permeability), followed by Class II (26%), Class I (18%), and Class IV (12%). A similar trend was observed when CHMs were classified in accordance with the BCS class of AMCs. Most (45%) of the included CHMs were classified as Class III, followed by Class II (16%), Class I (10%), and Class IV (6%); whereas 23% of the CHMs were of mixed class due to the presence of multiple individual AMCs with different BCS classifications. Moreover, about 60% of the AMCs were classified as high-solubility compounds (Class I and Class III), suggesting an important role for an in vitro dissolution test in setting quality control standards ensuring consistent biopharmaceutical quality for the commercially available CHM products. That is, provisionally, more than half of the AMCs of the top-selling CHMs included in this study would be candidates for a bioequivalence (BE) biowaiver, based on WHO recommendations and EMEA guidelines. Thus a dissolution requirement on these AMCs would represent a significant advance in the pharmaceutical quality of CHM today.

Effect of the African Traditional Medicine, Sutherlandia frutescens, on the Bioavailability of the Antiretroviral Protease Inhibitor, Atazanavir.

The objective of this study was to investigate the effect of Sutherlandia frutescens (SF) on the bioavailability of atazanavir (ATV) in twelve healthy male subjects. During Phase I (Day 1), subjects ingested a single dose of ATV and blood samples were drawn before dose and at 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 6.0, 9.0, 12, 18, and 24 hours after dose. From Day 3 to Day 14, a single dose of milled SF was administered twice daily to each subject. During Phase II, Day 15, subjects ingested single doses of ATV and SF. Blood samples were drawn as previously described. Plasma was harvested from blood samples and the concentration of ATV therein was determined. For each phase, the mean ATV plasma concentration-time profile was plotted and the means of AUC0-24 and C max for ATV were computed. The geometric mean ratios and confidence intervals (CIs) for C max and AUC0-24 hr were 0.783 (0.609-1.00) and 0.801 (0.634-1.01), respectively. The CIs for both PK parameters fell below the limits of the "no-effect" boundary, set at 0.8-1.25, indicating that SF significantly reduced the bioavailability of ATV. This may potentially result in subtherapeutic plasma concentrations and thus reduced anti-HIV efficacy of ATV.

Interactions between phytochemical components of Sutherlandia frutescens and the antiretroviral, atazanavir in vitro: implications for absorption and metabolism.

PURPOSE: African traditional medicinal plants, such as Sutherlandia frutescens have the potential to interact pharmacokinetically with the protease inhibitor class of antiretrovirals, thereby impacting on their safety and efficacy. The effects of extracts and phytochemical components of Sutherlandia frutescens, on the in vitro absorption and metabolism of the protease inhibitor, atazanavir were thus investigated. METHODS: Aqueous and methanolic extracts of Sutherlandia frutescens were prepared by freeze-drying of hot water and methanol decoctions of Sutherlandia frutescens plant material respectively, whilst crude triterpenoid glycoside and flavonol glycoside fractions were isolated by solvent extraction and subsequent column chromatography. Atazanavir was quantitated in the absence or presence of these compounds as well as commercially available purported constituents of Sutherlandia frutescens, namely, L-canavanine, L-GABA and D-pinitol, after a one hour co-incubation in Caco-2 cell monolayers and human liver microsomes. RESULTS: The triterpenoid and flavonol glycoside fractions were found to be present in the aqueous and methanolic extracts of Sutherlandia frutescens and were shown to contain the sutherlandiosides and sutherlandins known to be present in Sutherlandia frutescens. The aqueous extract and D-pinitol significantly reduced atazanavir accumulation by Caco-2 cells, implying a decrease in atazanavir absorption, whilst the opposite was true for the triterpenoid glycoside fraction. Both the aqueous and methanolic extracts inhibited atazanavir metabolism in human liver microsomes, whilst enhanced atazanavir metabolism was exhibited by the triterpenoid glycoside fraction. CONCLUSIONS: The extracts and phytochemical components of Sutherlandia frutescens influenced the accumulation of atazanavir by Caco-2 cells and also affected ATV metabolism in human liver microsomes. These interactions may have important implications on the absorption and metabolism and thus the overall oral bioavailability of atazanavir.

Provisional biopharmaceutical classification of some common herbs used in Western medicine.

The aim of this study was to classify some markers of common herbs used in Western medicine according to the Biopharmaceutical Classification System (BCS). The BCS is a scientific approach to classify drug substances based upon their intestinal permeability and their solubility, at the highest single dose used, within the physiologically relevant pH ranges. Known marker components of twelve herbs were chosen from the USP Dietary Supplement Compendium Monographs. Different BCS parameters such as intestinal permeability (P(eff)) and solubility (C(s)) were predicted using the ADMET Predictor, which is a software program to estimate biopharmaceutical relevant molecular descriptors. The dose number (D0) was calculated when information from the literature was available to identify an upper dose for individual markers. In these cases the herbs were classified according to the traditional BCS parameters using P(eff) and D0. When no upper dose could be determined, then the amount of a marker that is just soluble in 250 mL of water was calculated. This value, M(x), defines when a marker is changing from highly soluble to poorly soluble according to BCS criteria. This biopharmaceutically relevant value can be a useful tool for marker selection. The present study showed that a provisional BCS classification of herbs is possible but some special considerations need to be included into the classification strategy. The BCS classification can be used to choose appropriate quality control tests for products containing these markers. A provisional BCS classification of twelve common herbs and their 35 marker compounds is presented.

Potential pharmacokinetic interactions between antiretrovirals and medicinal plants used as complementary and African traditional medicines.

The use of traditional/complementary/alternate medicines (TCAMs) in HIV/AIDS patients who reside in Southern Africa is quite common. Those who use TCAMs in addition to antiretroviral (ARV) treatment may be at risk of experiencing clinically significant pharmacokinetic (PK) interactions, particularly between the TCAMs and the protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Mechanisms of PK interactions include alterations to the normal functioning of drug efflux transporters, such as P-gp and/or CYP isoenzymes, such a CYP3A4 that mediate the absorption and elimination of drugs in the small intestine and liver. Specific mechanisms include inhibition and activation of these proteins and induction via the pregnane X receptor (PXR). Several clinical studies and case reports involving ARV-herb PK interactions have been reported. St John's Wort, Garlic and Cat's Claw exhibited potentially significant interactions, each with a PI or NNRTI. The potential for these herbs to induce PK interactions with drugs was first identified in reports of in vitro studies. Other in vitro studies have shown that several African traditional medicinal (ATM) plants and extracts may also demonstrate PK interactions with ARVs, through effects on CYP3A4, P-gp and PXR. The most complex effects were exhibited by Hypoxis hemerocallidea, Sutherlandia frutescens, Cyphostemma hildebrandtii, Acacia nilotica, Agauria salicifolia and Elaeodendron buchananii. Despite a high incidence of HIV/AIDs in the African region, only one clinical study, between efavirenz and Hypoxis hemerocallidea has been conducted. However, several issues/concerns still remain to be addressed and thus more studies on ATMs are warranted in order for more meaningful data to be generated and the true potential for such interactions to be determined.

HPLC analysis of mesembrine-type alkaloids in Sceletium plant material used as an African traditional medicine.

PURPOSE: Sceletium plant species have been reported to contain psychoactive alkaloids, specifically belonging to mesembrine-type alkaloids. Sceletium is presently marketed through health shops and on the internet as dried plant powder and as pharmaceutical dosage forms and purported to be useful in the treatment of psychological disorders. However, there are no validated analytical methods and reference standards of the relevant alkaloids are not commercially available for use in the analysis and quality control of Sceletium products and dosage forms. Hence, the objective of this research was to isolate and characterize appropriate analytical markers for use in the assay and as well as markers for fingerprinting by high performance liquid chromatography (HPLC). METHODS: The separation of the relevant alkaloids was carried out on a C18 column and detected at a UV wavelength of 228 nm. The method was validated and used to assay the mesembrine-type alkaloids namely Δ(7)mesembrenone, mesembranol, mesembrenone, mesembrine and epimesembranol. RESULTS: The calibration curves were found to be linear over the entire concentration range of 400-60,000 ng/ml with correlation coefficients >0.99. The accuracies of the relevant alkaloids were found to be between 94.8 and 103.6% with an inter-day relative standard deviation (RSD) of less than 2.8%. The precision studies showed inter-day RSD's of less than 3%. The recoveries were all within the range of 95 and 105% (RSD <4.5%) and the limits of quantitation (LOQ) and detection (LOD) were found to be 100 and 200 ng/ml respectively using the respective S/N ratios of 3 and 10. Conclusions. An HPLC method for the quantitative analysis of Δ(7)mesembrenone, mesembranol, mesembrenone, mesembrine and epimesembranol in Sceletium plant material has been developed and validated. This assay method can be applied for the quality control of Sceletium plant material which is used as an African Traditional Medicine for the treatment of psychological disorders.

Rapid method for the quantitative determination of efavirenz in human plasma.

A pharmacokinetic interaction study between efavirenz (EFV), a non-nucleoside reverse transcriptase inhibitor used in the treatment of HIV-1 infection, and an African traditional medicine, African potato in human subjects was undertaken. This necessitated the development and validation of a quantitative method for the analysis of EFV in plasma. A simple mobile phase consisting of 0.1M formic acid, acetonitrile and methanol (43:52:5) was pumped at a low flow rate of 0.3 ml/min through a reverse phase Phenomenex Luna C(18) (2) (5 microm, 150 mm x 2.0mm i.d.) column maintained at 40 degrees C. Diclofenac sodium was used as an internal standard (IS) and EFV and IS were monitored at 247 nm and 275 nm, respectively. A simple and rapid sample preparation involved the addition of mobile phase to 100 microl of plasma to precipitate plasma proteins followed by direct injection of 10 microl of supernatant onto the column. The procedures were validated according to international standards with good reproducibility and linear response (r=0.9990). The intra- and inter-day accuracies were between 12.3 and 17.7% at the LLOQ and between -5.8 and 9.1% for the QC samples. The intra- and inter-day precision of EFV determinations were 5.1 or less and 7.2% RSD or less, respectively across the entire QC concentration range. Mean recovery based on high, medium and low quality control standards ranged between 92.7 and 94.1% with %RSD values better than 3%. Plasma samples were evaluated for short-term (ambient temperature for 6h) and long-term (-10+/-2 degrees C for 60 days) storage conditions and were found to be stable. The method described is cost-effective and has the necessary accuracy and precision for the rapid quantitative determination of EFV in human plasma.

Investigations of the phytochemical content of Sceletium tortuosum following the preparation of "Kougoed" by fermentation of plant material.

AIM OF THE STUDY: Sceletium plant species that contain alkaloids are claimed to have mood elevation and anti-anxiety properties, especially after the plant material has been fermented. The fermented preparation is locally known as "kougoed" or "channa" and has been emphasized and advertised for its increased potency when incorporated in commercial products. The aim of the study was to investigate quantitative and qualitative changes in alkaloidal content following fermentation of plant samples carried out under controlled conditions and also on pure mesembrine hydrochloride (MHCl). MATERIALS AND METHODS: Samples were prepared from the aerial parts of Sceletium tortuosum. Studies were also conducted on mesembrine hydrochloride (MHCl) in aqueous and methanolic solutions under similar conditions of exposure to sunlight as well as under ambient and elevated temperature (40+/-2 degrees C). Quantitative and qualitative changes in alkaloidal content were monitored by HPLC and LC-MS, respectively. RESULTS AND CONCLUSIONS: The initial fermentation study showed transformation of mesembrine to Delta(7)mesembrenone, where the content of the former decreased from a concentration of 1.33% to 0.05% whilst the latter increased from below its limit of quantitation (LoQ) to 0.11% on the 10th day. The experiments on pure MHCl revealed similar transformations in aqueous solutions whereas no change was seen in methanolic solutions. Sunlight and aqueous conditions appear necessary to facilitate the transformation, which was confirmed by the absence of such a transformation when solutions of MHCl were kept in the dark.

Development of dissolution tests for the quality control of complementary/alternate and traditional medicines: application to African potato products.

PURPOSE: Unlike orthodox medicines, specific guidelines for dissolution testing of complementary/alternate (CAMs) and traditional medicines (TMs) have not been developed nor is dissolution testing a requirement for the quality control of such products. In this report, the dissolution of African Potato (AP) products, an African traditional medicine (ATM) which has been ingested by man for a diversity of ailments, has been investigated. A norlignan glycoside namely hypoxoside and a sterol, beta-sitosterol (BSS) are purported to be the most important phytochemicals in marketed products of AP. Dissolution testing of AP products containing labelled content of sterols and those containing only hypoxoside is proposed whereby BSS and hypoxoside are monitored as markers for the release of the contents of the abovementioned products, respectively. METHODS: The FDA dissolution guidance for industry was used to study the best dissolution condition for several formulations of AP. Buffers in the range of pH 1.2 to 7.5 were used to investigate the dissolution of AP products containing hypoxoside as a marker compound. Similarly, biorelevant dissolution media such as fasted state simulation fluid (FaSSIF) and fed state simulation fluid (FeSSIF) at different pH were used to investigate the release of BSS in AP formulations labelled to contain sterols which exhibited poor water solubility. RESULTS: Dissolution testing of AP products containing hypoxoside, conducted at pH 1.2 using USP Apparatus 1 indicated that more than 75% of hypoxoside was released within 1 hr. Dissolution testing of products containing sterols, conducted in FeSSIF at a pH of 5.0 resulted in a release of at least 75% of BSS after 1 hr for all but one of the products tested. CONCLUSIONS: Dissolution testing conditions have been developed for AP products containing two different marker compounds where one of the components, hypoxoside, is water soluble, whereas another component, BSS is poorly water soluble. This necessitated the use of different dissolution media and pHs in order to monitor the respective release of hypoxoside and BSS from AP products. The results of this study indicate the necessity and possibility of developing appropriate dissolution testing procedures for use in the quality control of CAMs/TMs.

A capillary zone electrophoresis method for the assay and quality control of mesembrine in Sceletium tablets.

The Sceletium plant has been reported to contain psychoactive alkaloids, specifically mesembrine, mesembrenone, mesembrenol and other related alkaloids. Sceletium is marketed through health shops and on the internet as dried plant powder and as pharmaceutical dosage forms. The objectives of this research was to develop and validate a capillary zone electrophoresis (CZE) method to identify five alkaloids and quantitatively determine the content of the important alkaloid, mesembrine in Sceletium tablets. Since reference standards of the relevant alkaloids are not commercially available for use in quality control of Sceletium products, it was necessary to isolate and characterize an appropriate analytical marker for use in the assay and additional markers for fingerprinting by CZE. The separation of the relevant alkaloids was carried out by CZE on a 50cm effective length, fused silica capillary tubing (50microm i.d.x360microm o.d.) using 50mM of sodium dihydrogen orthophosphate dihydrate at pH 1.5 as the background electrolyte and monitored at a UV wavelength of 228nm. All the marker alkaloids were found to be well resolved and were identified in the plant material and in commercially available Sceletium tablets based on the relative migration times (MTs) with respect to quinine hydrochloride that was used as an internal standard. The method was validated and used to assay the mesembrine content in Sceletium tablets. Calibration curves were found to be linear over the entire concentration range of 2.5-80microg/ml with correlation coefficients >0.995. The accuracy was found to be 92.5 and 104.5% (R.S.D.<3.5%) and the R.S.D.'s of the inter-day precision at low, medium and high tablet masses were better than 0.9, 2.2 and 2.7%, respectively. The recoveries were all within the range of 91.8 and 105.8% (R.S.D.<8.5%) and the limit of quantitation (LOQ) and limit of detection (LOD) values were found to be 2.5 and 1.5microg/ml, respectively.

Effect of African potato (Hypoxis hemerocallidea) on the pharmacokinetics of efavirenz.

PURPOSE: The purpose of this study was to evaluate the effect of the African potato (AP) on the pharmacokinetics of efavirenz. METHODS; A single-dose, two-phase sequential study was conducted over 31 days in 10 healthy volunteers. On day 1 of the study, volunteers were administered a 600 mg efavirenz tablet, and blood samples were collected before dosing and at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 12, 18, 24, 36 and 48 hours after dosing. From day 16, a traditionally prepared AP decoction was administered daily until day 30. On day 29, volunteers were administered a single 600 mg dose of efavirenz, as was done on day 1. Plasma samples were harvested immediately after blood sample collection and frozen at -80 degrees C until assayed. Plasma concentrations of efavirenz were determined by a validated high performance liquid chromatography (HPLC) method with UV detection, and pharmacokinetic parameters were calculated. Geometric mean ratios of C(max) and AUC(0-48) of efavirenz before and after co-administration of 14 successive daily doses of AP were compared. RESULTS: All subjects completed the study. The geometric mean ratios of C(max) and AUC(0-48) were 97.30 and 102.82 with corresponding 90% confidence intervals (CIs) of 78.81 - 120.14 and 89.04 - 118.80, respectively. CONCLUSION: Pharmacokinetic data generated during this study indicated that AP did not significantly alter the pharmacokinetics of efavirenz. Hence, co-administration of AP is unlikely to affect the clinical usage of efavirenz.

In vitro evaluation of human cytochrome P450 and P-glycoprotein-mediated metabolism of some phytochemicals in extracts and formulations of African potato.

African potato (Hypoxis hemerocallidea, AP) is a traditional herbal medicine widely used as an immune booster and also for the treatment of various ailments such as urinary diseases, prostrate hypertrophy and cancer. Amongst the chemical components contained in AP, the norlignan glycoside, hypoxoside (HYP) is purported to be the most important phytochemical in terms of AP's medicinal value. Additional constituents in AP include the sterols, beta-sitosterol (BSS), stigmasterol (STG), and the stanol, stigmastanol (STN). The potential of extracts of AP, AP formulations as well as HYP, its aglycone rooperol (ROP) and the sterols to inhibit in vitro metabolism of drug marker substrates by human cytochrome P450 (CYP) enzymes such as CYP3A4, 3A5 and CYP19 were investigated. Samples were also assessed for their effect on drug transport proteins such as P-glycoprotein (P-gp). The effects on CYP-mediated metabolism were studied by fluorometric microtitre plate assay. The potential interaction with P-gp was investigated by measuring the efflux of the fluorescent dye rhodamine 123 (Rh 123) in the CaCo-2 (colon carcinoma) cell line. Various extracts of AP, AP formulations, only STG and the norlignans, in particular the aglycone ROP, exhibited inhibitory effects on CYP3A4-, 3A5- and 19-mediated metabolism. The extracts and the formulations that contained a significant amount of HYP showed high induction of P-gp compared to the positive control, ritonavir. Whilst extrapolation of the current in vitro findings to clinical effects may well be considered speculative, these in vitro data should be heeded as a signal of possible in vivo interactions. Appropriate measures are therefore necessary to explore the possibility of such in vitro-in vivo correlations.

Impact of African herbal medicines on antiretroviral metabolism.

We examined the effects of two African herbal medicines recommended for HIV/AIDS patients on antiretroviral metabolism. Extracts from Hypoxis and Sutherlandia showed significant effects on cytochrome P450 3A4 metabolism and activated the pregnane X receptor approximately twofold. P-glycoprotein expression was inhibited, with Hypoxis showing 42-51% and Sutherlandia showing 19-31% of activity compared with verapamil. Initiating policies to provide herbal medicines with antiretroviral agents may put patients at risk of treatment failure, viral resistance or drug toxicity.

High-performance liquid chromatographic determination of selected flavonols in Ginkgo biloba solid oral dosage forms.

PURPOSE: This paper describes a validated high-performance liquid chromatographic (HPLC) - photodiode array (PDA) detection method to quantitate five flavonol components as markers; rutin, quercitrin, quercetin, kaempferol and isorhamnetin for use in the quality control of Ginkgo biloba dosage forms. METHODS: Separation was achieved using a minibore Phenomenex Luna 5microm C(18) (2) column with dimensions 250 x 2.00mm at 45 degrees C with a one step linear gradient using acetonitrile:formic acid (0.3%) at a flow rate of 0.4ml/min. RESULTS: The limits of quantitation for the flavonols were 2.76, 0.77, 1.11, 1.55 and 1.03microg/ml for rutin, quercitrin, quercetin, kaempferol and isorhamnetin, respectively. This method is linear over concentration ranges of 3-26microg/ml for all flavonols. Recoveries for rutin, quercitrin and kaempferol were above 94% while quercetin and isorhamnetin had average recoveries of 83% and 76%, respectively. Intraday precision did not exceed 6% and with-in day precision was better than 12% for all compounds. CONCLUSION: A suitable method was developed to identify and quantitate five relevant flavonol marker compounds and was successfully used to assay some commercially available solid oral dosage forms of Ginkgo biloba .