Enhanced anti-amnestic effect of donepezil by Ginkgo biloba extract (EGb 761) via further improvement in pro-cholinergic and antioxidative activities

ETHNOPHARMACOLOGICAL RELEVANCE

EGb 761 is a standardized dry extract of Ginkgo biloba L. leaves traditionally used by Eastern Asia and has been associated with beneficial effects on neurodegeneration disorders, including Alzheimer's disease.

AIM OF THE STUDY

Since beneficial interactions between EGb 761 and donepezil have been observed in previous clinical studies, the current study was proposed aiming to further explore related mechanisms from both pharmacokinetics and pharmacodynamics aspects.

MATERIALS AND METHODS

Pharmacodynamic interactions were studied in scopolamine-induced cognitive impairment rats received two-weeks treatment of vehicle, EGb 761 and/or donepezil by the Morris water maze test and ex vivo evaluation of biomarkers of cholinergic transmission and oxidative stress in rat brain. In the meantime, pharmacokinetic profiles of donepezil and bilobalide were obtained and compared among all treatment groups. In addition, impact of the bioavailable EGb 761 components on donepezil brain penetration was evaluated with the hCMEC/D3 cell monolayer model.

RESULTS

Scopolamine-induced rats with co-treatment of EGb 761 and donepezil had significantly improved cognitive function in the Morris water maze test with increased brain levels of superoxide dismutase and decreased brain levels of acetylcholinesterase and malondialdehyde than that with treatment of only EGb 761 or donepezil. Despite such beneficial pharmacodynamics outcomes, the two-week co-treatment of EGb 761 and donepezil did not alter the plasma pharmacokinetics and brain uptake of donepezil or bilobalide, which was further verified in the hCMEC/D3 monolayer model.

CONCLUSION

Co-administration of EGb 761 and donepezil exerted better anti-amnestic effect via further enhanced pro-cholinergic and antioxidative effects of EGb 761 or donepezil in scopolamine-induced cognitive impairment rat without alteration in their systemic/brain exposure.

Extraction-free spectrophotometric assay of the antitussive drug pentoxyverine citrate using sulfonephthalein dyes

Pentoxyverine citrate (PEN-citrate) is an antitussive (cough suppressant) drug used for cough associated with illnesses like common cold. In this work, PEN-citrate is quantified by applying a simple, direct and accurate spectrophotometric method in pure form, pharmaceutical formulation (Cabella®, 2.13 mg/mL) and human serum samples. The formation of a stable yellow ion-pair with sulfonephthalein dyes; bromocresol green (BCG), bromophenol blue (BPB), bromothymol blue (BTB), bromocresol purple (BCP), bromochlorophenol blue (BChPB) and bromoxylenol blue (BXB), in three nonpolar solvents (chloroform, dichloromethane, acetonitrile) is used as the basis for this method. This is the first assay method reported for the quantification of PEN-citrate using the sulfonephthaleins as coloring agents. Diverse parameters were investigated in order to optimize the calibration curve conditions. The strategy was validated with respect to linearity range, precision, accuracy, specificity, robustness and limits of detection (LOD) and quantification (LOQ). In addition, solvents of different polarities were utilized to investigate the color reaction, light absorption and to allow for increasing the method sensitivity. Beer's law is obeyed over a wide concentration range (up to 42.05 μg/mL in case of BTB method). LOD and LOQ values reached 0.22 and 0.72 μg/mL, respectively, upon using BChPB. The relative standard deviation (%RSD) was ≤1.91% while correlation coefficient values (r) were ≥ 0.9974. High molar absorptivity values and low values of Sandell's sensitivity were obtained indicating that the proposed methods are highly sensitive. The validated methods were applied to the analysis of PEN-citrate in the dosage form and human serum samples where the drug was successfully resolved from the pharmaceutical additives and serum components with recoveries ≥98.98%.

Influence of organic anion transporter 1/3 on the pharmacokinetics and renal excretion of ginkgolides and bilobalide

ETHNOPHARMACOLOGICAL RELEVANCE

The major terpene lactones of ginkgo biloba extract (GBE) include ginkgolide A, B, C and bilobalide are used for the protection of cardiovascular, cerebrovascular and neurodegenerative diseases. Terpene lactones are orally bioavailable and predominantly eliminated via the renal pathway. However, information on the transporters involved in the pharmacokinetics (PK) and renal excretion of terpene lactones is limited.

AIM OF THE STUDY

The objective of this study is to assess the role of OAT1/3 which are important transporters in the human kidney in the PK and renal excretion ginkgolide A, B, C and bilobalide.

MATERIALS AND METHODS

Uptake of ginkgolide A, B, C and bilobalide in Madin-Darby Canine Kidney (MDCK) and human embryonic kidney 293 (HEK293) cells overexpressing OAT1 or OAT3, respectively were studied. To verify the result from in vitro cell models, the studies on PK, kidney accumulation and urinary excretion of ginkgolide A, B, C and bilobalide were carried out in rats.

RESULTS

The result showed that ginkgolide A, B, C and bilobalide are low-affinity substrates of OAT1/3. Following co-administration with probenecid, a typical inhibitor of OAT1/3, the rat plasma concentrations of ginkgolide A, B, C and bilobalide increased significantly. AUC showed a significant increase in the probenecid-treated rats compared to control rats (893.48 vs. 1123.85, 314.91 vs. 505.74, and 2724.97 vs. 3096.40 μg/L*h for ginkgolide A, B and bilobalide, respectively), while the clearance of these compounds significantly decreased. The accumulation of ginkgolide A, B and bilobalide in the kidney of the probenecid-treated rats was reduced by 1.8, 2.4, and 1.5-fold, respectively; further reducing the cumulative urinary recovery of these compounds.

CONCLUSION

The findings indicated that ginkgolide A, B and bilobalide are excreted via OAT1/3-mediated transport in the kidney and OAT1/3 inhibitor significantly influence the PK ginkgolides and bilobalide.

[Quantification of pentoxyverine citrate in human plasma by LC-ESI/MS method and its application]

A rapid and sensitive liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI/ MS) method for quantification of pentoxyverine citrate in human plasma has been developed and applied for the bioequivalence and pharmacokinetics study. After extracted from plasma samples with ethyl acetate, analysis was performed in selected ion monitoring (SIM) mode with a positive electrospray ionization (ESI) interface with a mobile phase consisted of methanol and water (0.4% glacial acetic acid and 4 mmol x L(-1) ammonium acetate, 43 : 57, v/v). The linear concentration range of the calibration curves was 1.0-160.0 ng x mL(-1) for pentoxyverine citrate, inter- and intra-precision (RSD) was less than 12.5%, accuracy (RE) was in +/- 13.5% and absolute recovery was more than 80%. The method was proved simple, rapid, sensitive, specific and suitable for pharmacokinetic and bioequivalence study of Yufenweilin capsule containing pentoxyverine citrate.

F15063, a potential antipsychotic with dopamine D2/D3 antagonist, 5-HT1A agonist and D4 partial agonist properties: (IV) duration of brain D2-like receptor occupancy and antipsychotic-like activity versus plasma concentration in mice

F15063 (N-[(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)ethyl]-3-(cyclopent-1-enyl)-benzylamine fumarate salt) is a novel potential antipsychotic with dopamine D(2)/D(3) blocking properties and agonist activity at 5-HT(1A) and D(4) receptors. The pertinent parameter for pharmacological activity of antipsychotics appears to be central D2-like receptor occupancy. However, its duration is not necessarily correlated with drug plasma levels, on which clinical dosing regimens are often based. Thus, we compared in mice the duration of actions of F15063 and haloperidol to (1) inhibit apomorphine-induced climbing and sniffing (behavioural measures of D2-like receptor antagonism) and (2) occupy D2-like receptors in vivo in the striatum and olfactory tubercles (inhibition of [(3)H]nemonapride binding). Finally, we measured plasma levels of F15063. D2-like receptor occupancy in the striatum remained elevated at 1, 4 and 8 h postadministration, with both F15063 (ID(50): 7.1, 3.6 and 16.5 mg/kg p.o., respectively) and the typical antipsychotic, haloperidol (ID(50): 1.4, 0.52 and 0.53 mg/kg p.o., respectively). This was paralleled by a protracted inhibition of apomorphine-induced climbing (ED(50): 0.9, 2.8 and 3.6 mg/kg p.o., and 0.21, 0.37 and 0.87 mg/kg p.o., respectively, for F15063 and haloperidol). In contrast, after administration of 10 mg/kg p.o. of F15063, its plasma levels decreased rapidly: 15.2, 2.1 and 0.6 ng/ml, 1, 4 and 8 h after administration, respectively. A similar pattern of results was observed when F15063 and haloperidol were administered i.p. and s.c., respectively. To summarise, the time-course of D2-like receptor occupancy and inhibition of apomorphine-climbing (and sniffing) behaviours was similarly long lasting with F15063 and haloperidol. In addition, the durations of action of F15063 and haloperidol in a behavioural model of antipsychotic-like activity were closely correlated to their occupancy of central D2-like receptors, and much longer than their presence in plasma.

Extrapolating from animal studies to the efficacy in humans of a pretreatment combination against organophosphate poisoning

The extrapolation from animal data to therapeutic effects in humans, a basic pharmacological issue, is especially critical in studies aimed to estimate the protective efficacy of drugs against nerve agent poisoning. Such efficacy can only be predicted by extrapolation of data from animal studies to humans. In pretreatment therapy against nerve agents, careful dose determination is even more crucial than in antidotal therapy, since excessive doses may lead to adverse effects or performance decrements. The common method of comparing dose per body weight, still used in some studies, may lead to erroneous extrapolation. A different approach is based on the comparison of plasma concentrations at steady state required to obtain a given pharmacodynamic endpoint. In the present study, this approach was applied to predict the prophylactic efficacy of the anticholinergic drug caramiphen in combination with pyridostigmine in man based on animal data. In two species of large animals, dogs and monkeys, similar plasma concentrations of caramiphen (in the range of 60-100 ng/ml) conferred adequate protection against exposure to a lethal-dose of sarin (1.6-1.8 LD(50)). Pharmacokinetic studies at steady state were required to achieve the correlation between caramiphen plasma concentrations and therapeutic effects. Evaluation of total plasma clearance values was instrumental in establishing desirable plasma concentrations and minimizing the number of animals used in the study. Previous data in the literature for plasma levels of caramiphen that do not lead to overt side effects in humans (70-100 ng/ml) enabled extrapolation to expected human protection. The method can be applied to other drugs and other clinical situations, in which human studies are impossible due to ethical considerations. When similar dose response curves are obtained in at least two animal models, the extrapolation to expected therapeutic effects in humans might be considered more reliable.

Influence of pharmaceutical quality on the bioavailability of active components from Ginkgo biloba preparations

To be effective, herbal medicinal products are expected to meet comparable standards concerning the assessment of efficacy, safety and biopharmaceutical quality as chemically defined synthetic drugs as food supplements. However, these requirements are often not fulfilled, particularly regarding the characterization of biopharmaceutical properties such as in-vitro dissolution and in-vivo bioavailability. With respect to the relevance of biopharmaceutical quality of herbal medicinal products, two different Ginkgo biloba brands (test product: Ginkgo biloba capsules; reference product: Ginkgold) were analysed for dissolution rates and bioavailability of the most relevant active ingredients. Dissolution rates at pH 1 and 4.5 were determined according to the USP 23. The relative bioavailability of ginkgolide A, ginkgolide B and bilobalide was investigated after single oral administration of 120 mg Ginkgo biloba extract as tablets or capsules. Bioavailability data (area under the curve and peak concentration in plasma) were clearly different and did not show bioequivalence of test and reference products. The slow in-vitro dissolution of the test product resulted in a large decrease in bioavailability. These results indicate for the first time that the pharmaceutical properties of a herbal medicinal product have a significant impact on the rate and extent of drug absorption, and very likely on efficacy in humans.

Fluorescence properties of albumin blue 633 and 670 in plasma and whole blood

We have determined the fluorescence characteristics of two long wavelength dyes, albumin blue 633 (AB633) and 670 (AB670), in plasma and blood to evaluate the possibility of making direct fluorescence sensing measurements in blood. Using binding and lifetime measurements we were also able to show that these dyes bind selectively to human serum albumin (HSA) in plasma and blood. By measuring changes in the mean lifetime of AB670 with changes in the HSA concentration, we showed that lifetime-based sensing can be used to monitor HSA concentrations using these albumin blue dyes. Anisotropy measurements for AB633 and AB670 in plasma and blood revealed high anisotropy values for these dyes in these media. Exploiting these high anisotropies, we were also able to determine HSA concentrations in plasma and blood mimics using changes in AB670 anisotropy with HSA concentration. These results show that, apart from being able to make fluorescence measurements directly in plasma and blood, it is possible to sense directly for specific plasma/blood components using fluorescent probes that bind preferentially to them.

Liquid chromatography/atmospheric pressure chemical ionization mass spectrometry of terpene lactones in plasma of volunteers dosed with Ginkgo biloba L. extracts

Liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI-ITMS) was applied to evaluate the levels of ginkgolides A and B and bilobalide in plasma of volunteers after administration of Ginkgo biloba extracts in free (Ginkgoselect) or phospholipid complex (Ginkgoselect Phytosome) forms, providing 9.6 mg of total terpene lactones. The maximum plasma concentrations, C(max), of total ginkgolides A, B and bilobalide were 85.0 and 181.8 microg/mL for Ginkgoselect and Ginkgoselect Phytosome, respectively. The C(max) values were reached at 120 min for the free form and at 180--240 min for the phospholipid complex form. In both cases, the mean elimination half-life of each terpene lactone was in the range 120--180 min. Due to its sensitivity (about 1 ng/mL) and specificity, LC/APCI-ITMS proved to be a very powerful tool for pharmacokinetic studies of these phytochemicals.

Analysis of brefeldin A in plasma by gas chromatography with electron capture detection

The National Cancer Institute (NCI) is pursuing preclinical development of Brefeldin A (BFA), a macrolide isolated from Penicillium brefeldianum, as an antitumor agent. BFA exhibits a unique spectrum of activity against the human tumor cell line panel that composes the NCI's recently established in vitro antitumor screen. A specific method to assay the compound in biological fluids has been developed in which BFA and 1-eicosanol, added as the internal standard, are extracted from plasma specimens with diethyl ether. The residue afforded by evaporation of the organic solvent is dried in vacuo and derivatized with heptafluorobutyrylimidazole prior to analysis by capillary gas chromatography with electron capture detection. Derivatization of both secondary hydroxyl groups of BFA is rapid and quantitative, as confirmed by mass spectrometry. The lowest concentration of BFA quantified with acceptable reproducibility in 50 microliters of plasma is 0.1 microgram/ml, for which a 5.6% coefficient of variation has been determined from six standard curves assayed on separate days. Detector response exhibits a positive deviation from linearity for samples with BFA concentrations greater than 2.5 micrograms/ml. The assay is shown by application to be suitable for preliminary investigations of BFA plasma pharmacokinetics in mice. These studies reveal that BFA is subject to rapid elimination from the mouse, with plasma levels declining in an apparent biphasic manner from an initial concentration of 33 to 0.2 micrograms/ml at 60 min after intravenous treatment with a 26.3 mg/kg dose.

[Pentoxyverine poisoning via maternal milk in a fully breast-fed newborn infant]

A four-week-old male infant who had been exclusively breast-fed by his mother developed acute respiratory failure with intermittent arrest of breathing for up to 15 sec, in between sighing breaths and normal ones. For two weeks his mother had been taking pentoxyverine-containing cough drops for an upper respiratory tract infection. Pentoxyverine was demonstrated in maternal serum and breast milk, as well as the child's serum and urine, in some in very high concentrations. The course of the illness and comparison with reported instances of pentoxyverine poisoning in infants makes it likely that this, too, was such a case.

Quantitative determination of N-[trans-2-(dimethylamino)-cyclopentyl]-N-(3',4'-dichlorophenyl)propan amide, its 2H5-labeled analogue and their N-dealkylated metabolites in dog serum by capillary gas chromatography-mass spectrometry

This paper describes the development of a capillary gas chromatographic--mass spectrometric method for the determination of N-[trans-2-(dimethylamino)cyclopentyl]-N-(3',4'-dichlorophenyl)propan amide and its metabolites in serum. The method utilizes an automated sample preparation whereby drug, metabolites and internal standard are extracted from polar serum components by adsorption chromatography onto an XAD-type resin. The N-demethylated metabolites are derivatized by acetylation prior to chromatography. Detection is by mass spectrometry with chemical ionization. This method was utilized to determine levels of unlabeled and pentadeuterated drug and their respective metabolites in canine serum after oral co-administration. No significant kinetic isotope effects were observed for either absorption or metabolism.

Quantitative determination of N-(trans-2-dimethylaminocyclopentyl)-N-(3',4'-dichlorophenyl) propanamide and its N-demethyl metabolite in dog serum by gas chromatography

A gas chromatographic-electron capture (GC-EC) method has been developed for the determination of N-(trans-2-dimethylaminocyclopentyl)-N-(3',4'-dichlorophenyl)pr opanamide, a potential antidepressant drug, and its N-demethyl metabolite in serum. The GC-EC system employed a 3% OV-17 on 100/120 mesh Supelcoport, 2-m X 2-mm i.d. glass column and an isothermal temperature of 195 degrees C. The parent drug and metabolite were extracted from alkalinized serum (pH approximately 13) with toluene, back-extracted into an acidic solution (pH approximately 1), and finally, after adjusting to pH 13, extracted again with toluene. The extensive sample cleanup was necessary to remove serum components which interfered with the analysis. The analytical method was shown to give quantitative recovery of the drug and metabolite, to be linear over a 100-fold concentration range, and to have the necessary precision and sensitivity to detect and quantify as little as 1 ng/mL of the drug or its metabolite. The method has been employed to determine the serum level of drug and metabolite in dogs receiving a single oral dose and to determine the possible correlation between the administered dose and serum levels.

Use of nitrogen-specific detector for GLC determination of caramiphen in whole blood

A sensitive GLC determination of caramiphen in whole blood was developed using a nitrogen-specific detector. The method permits the determination of levels of caramiphen as low as 2.5 ng/ml of blood and provides sufficient sensitivity and reproducibility for clinical use.

Gas chromatographic determination of methylcyclopentadienylmanganesetricarbonyl in biological tissues and fluids

The procedure described for quantitating methylcyclopentadienylmanganese-tricarbonyl (MMT, a fuel additive) in small samples of biological fluids and tissues is based on extracting the MMT into hexane containing biphenyl as internal standard, followed by gas chromatographic analysis. With flame ionisation detection, as little as 1-2 ppm of MMT in tissue can be determined relatively easily. The method is also applicable to in vitro investigations of MMT metabolism, and it has been used to show that the enzymic oxidation of MMT by rat-liver microsomes is a cytochrome P-450-dependent process.

Development of a procedure for the assay of an experimental steroid drug in dog plasma

Studies of the estimation of 16alpha-cyano-3beta-cyclopentyloxypregn-5-en-20-one (an experimental drug) in dog plasma are described. Extraction using a salt/solvent pair (ammonium carbonate/ethyl acetate) is followed by a rapid chromatographic procedure employing Lipidex 5000, which affords a substantially purified fraction. After preparation of the t-butyldimethylsilyloxime, quantification of the drug is performed by selected ion monitoring. The [2H9]cyclopentyloxyl analogue is used as an internal standard. In a preliminary experiment, the advantages (in terms of both sensitivity and selectivity) of the use of an open tubular GLC column are demonstrated.

Comparative beta-adrenoceptor blocking effects and pharmacokinetics of penbutolol and propranolol in man

1 The beta-adrenoceptor blocking effects of penbutolol were compared with those of propranolol and a placebo in a double-blind trial involving six healthy volunteers. 2 Heart rate (HR), systolic blood pressure (SBP) and peak expiratory flow rate (PEFR) were measured at rest and during vigorous exercise before and at intervals up to 7 h after oral administration of the drugs. In addition, plasma renin activity (PRA) at rest and plasma levels of penbutolol and propranolol were determined. 3 Penbutolol proved to be a non-cardioselective beta-adrenoceptor blocking drug, antagonizing exercise-induced tachycardia, reducing exercise-induced increase in PEFR and decreasing PRA. The beta-adrenolytic potency of penbutolol was shown to be four-fold that of propranolol but the duration of its effect was similar. 4 The peak plasma level of penbutolol was reached 1 h after administration and its half-life was 4.5 h. 5 Comparison of plasma levels and biological activity of penbutolol revealed that after oral administration this drug is transformed into an active metabolite in man.

Plasma level studies of penbutolol after oral dose in man

Plasma levels of penbutolol (HOE 893d) were determined in eight healthy adult male subjects after oral administration of 50-mg capsules. Fast absorpiton of the drug from the gastrointestinal tract was indicated by the rapid increase in plasma levels during the absorption phase, with a peak time at about 1 hour after dosing in all subjects. After the peak level, plasma concentrations declined biexponentially, with an average half-life of 2.5 and 27 hours for the fast and slow disposition phases, respectively. These values were in good agreement with data previously found for this drug. Cumulative excretion of intact drug in the urine of the eight subjects during 72 hours after dosing was less than 4 per cent, except for one subject who excreted 9.82 per cent of the dose. Large individual variations were found for area under the plasma level curves, disposition rates, and amounts of intact drug excreted in the urine. Significant pharmacologic effects were noted in all eight subjects at the 50-mg dose level, and mild side effects were evident in one half of these subjects. The average drop in blood pressure and pulse rate for all subjects was 26/18 mm Hg and 19 beats per minute, respectively.

Detection and analysis of Parpanit in blood by gas-liquid chromatography

A method has been developed for the extraction of Parpanit free base (caramiphen) from human blood and for determination of the drug by gas–liquid chromatography. The method is reliable and nearly quantitative but insufficiently sensitive for use in peak build-up and clearance studies in humans. Factors such as the age of the blood and time of contact of the drug with the blood on the efficiency of recovery were examined. The Parpanit content of fresh rabbit blood could be measured accurately, but there was considerable variability in the results obtained with fresh blood from different rabbits. The drug was degraded or absorbed by contact with rabbit blood in vitro and in vivo, more rapidly by the serum than by the cells.