Drug metabolic enzyme genotype-phenotype discrepancy: High phenoconversion rate in patients treated with antidepressants

Cytochromes from the P450 family (CYP) play a central role in the primary metabolism of frequently prescribed antidepressants, potentially affecting their efficacy and tolerance. There are however important differences in the drug metabolic capacities of each individual resulting from a combination of intrinsic and environmental factors. This variability can present an important risk for patients and increases the difficulty of drug prescription in clinical practice. Pharmacogenetic studies have uncovered a number of alleles defining the intrinsic metabolizer status, however, additional factors affecting cytochrome activity can modify this activity and result in a phenoconversion. The present study investigates the discrepancy between the genetically predicted and actually measured activities for the six most important liver cytochromes (CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6 and CYP3A4) in a cohort of patients under antidepressant treatment, previously shown to have a high proportion of patients with low metabolizing activities. We now performed the genetic characterization of this cohort to determine the extent of the genetic versus environmental contribution in these decreased activities. For all enzyme tested, we observed an important rate of phenoconversion, affecting between 33 % and 65 % of the patients, as well as a significant (p < 1E-06) global reduction in the effective but not predicted activities of CYP2D6, CYP2C9 and CYP2C19 compared to the general population. Our results highlight the advantages of phenotyping versus genotyping as well as the increased risk of treatment failure or adverse effect occurrence in a polymedicated population.

Simultaneous determination of melatonin and 6-hydroxymelatonin in human overnight urine by LC-MS/MS

For the quantification of the pineal hormone melatonin and its metabolite, 6-hydroxymelatonin, in human overnight urine, a single accurate method by liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed. Urine samples were deconjugated using β-glucuronidase/arylsulfatase from Helix pomatia before solid phase extraction (SPE) purification. Chromatographic separation was performed using a reverse phase C18 column with a 7-minute gradient elution. Water was used as matrix to prepare the calibration standards, and deuterated analogues of melatonin and 6-hydroxymelatonin were used as internal standards. This newly developed method was validated in terms of linearity, accuracy, repeatability, intermediate precision, recovery, matrix effect, and stability according to the guidelines of the European Medicines Agency. The method was successfully applied to the analysis of overnight urine samples from 12 healthy volunteers, showing significant correlations of urinary melatonin and 6-hydroxymelatonin excretion rates with age. The urinary 6-hydroxymelatonin to melatonin ratio was also established and will be assessed in further studies as a potential endogenous metric of CYP1A2 activity.

Coadministration of ticagrelor and ritonavir: Toward prospective dose adjustment to maintain an optimal platelet inhibition using the PBPK approach

Ticagrelor is a potent antiplatelet drug metabolized by cytochrome (CYP)3A. It is contraindicated in patients with human immunodeficiency virus (HIV) because of the expected CYP3A inhibition by most protease inhibitors, such as ritonavir and an increased bleeding risk. In this study, a physiologically based pharmacokinetic (PBPK) model was created for ticagrelor and its active metabolite (AM). Based on the simulated interaction between ticagrelor 180 mg and ritonavir 100 mg, a lower dose of ticagrelor was calculated to obtain, when coadministered with ritonavir, the same pharmacokinetic (PK) and platelet inhibition as ticagrelor administered alone. A clinical study was thereafter conducted in healthy volunteers. Observed PK profiles of ticagrelor and its AM were successfully predicted with the model. Platelet inhibition was nearly complete in both sessions despite administration of a fourfold lower dose of ticagrelor in the second session. This PBPK model could be prospectively used to broaden the usage of ticagrelor in patients with ritonavir-treated HIV regardless of the CYP3A inhibition.

Prediction of Metabolic Interactions With Oxycodone via CYP2D6 and CYP3A Inhibition Using a Physiologically Based Pharmacokinetic Model

Evaluation of a potential risk of metabolic drug–drug interactions (DDI) is of high importance in the clinical setting. In this study, a physiologically based pharmacokinetic (PBPK) model was developed for oxycodone and its two primary metabolites, oxymorphone and noroxycodone, in order to assess different DDI scenarios using published in vitro and in vivo data. Once developed and refined, the model was able to simulate pharmacokinetics of the three compounds and the DDI extent in case of coadministration with an inhibitor, as well as the oxymorphone concentration variation between CYP2D6 extensive metabolizers (EM) and poor metabolizers (PM). The reliability of the model was tested against published clinical studies monitoring different inhibitors and dose regimens, and all predicted area under the concentration–time curve (AUC) ratios were within the twofold acceptance range. This approach represents a strategy to evaluate the impact of coadministration of different CYP inhibitors using mechanistic incorporation of drug-dependent and system-dependent available in vitro and in vivo data.

The association of cytochrome P450 genetic polymorphisms with sulfolane formation and the efficacy of a busulfan-based conditioning regimen in pediatric patients undergoing hematopoietic stem cell transplantation

Cytochrome P450 enzymes (CYPs) and flavin-containing monooxygenases (FMOs) likely have a role in the oxidation of intermediate metabolites of busulfan (Bu). In vitro studies to investigate the involvement of these enzymes are cumbersome because of the volatile nature of the intermediate metabolite tetrahydrothiophene (THT) and the lack of sensitive quantitation methods. This study explored the association between the CYP2C9, CYP2C19, CYP2B6 and FMO3 genotypes and sulfolane (Su, a water soluble metabolite of Bu) plasma levels in children undergoing hematopoietic stem cell transplantation (HSCT). The relationship between these genotypes and the effectiveness of myeloablative conditioning was also analyzed. Sixty-six children receiving an intravenous Bu-based myeloablative conditioning regimen were genotyped for common functional variant alleles in CYP2C9 (*2 and *3), CYP2C19 (*2 and *17), FMO3 (rs2266780, rs2266782 and rs1736557) and CYP2B6 (*5 and *9). The plasma levels of Bu and its metabolite Su were measured after the ninth Bu dose in a subset of 44 patients for whom plasma samples were available. The ratio of Bu to Su was considered the metabolic ratio (MR) and was compared across the genotype groups. Higher MRs were observed in CYP2C9*2 and *3 allele carriers (mean±s.d.: 7.8±3.6 in carriers vs 4.4±2.2 in non-carriers; P=0.003). An increased incidence of graft failure was observed among patients with an MR>5 compared with those with MR values <5 (20% vs 0%; P=0.02). In contrast, a significantly higher incidence of relapse and graft failure (evaluated as event-free survival) was observed in patients with malignant disease who carried CYP2B6 alleles with reduced function on both chromosomes compared with carriers of at least one normal allele (100% vs 40%; P=0.0001). These results suggest that CYP2C9 has a role in the oxidation reactions of THT and indicate that it may be possible to predict the efficacy of Bu-based myeloablative conditioning before HSCT on the basis of CYP genotypes and Bu MRs.

Applications of CYP450 testing in the clinical setting

Interindividual variability in drug response is a major clinical problem. Polymedication and genetic polymorphisms modulating drug-metabolising enzyme activities (cytochromes P450, CYP) are identified sources of variability in drug responses. We present here the relevant data on the clinical impact of the major CYP polymorphisms (CYP2D6, CYP2C19 and CYP2C9) on drug therapy where genotyping and phenotyping may be considered, and the guidelines developed when available. CYP2D6 is responsible for the oxidative metabolism of up to 25% of commonly prescribed drugs such as antidepressants, antipsychotics, opioids, antiarrythmics and tamoxifen. The ultrarapid metaboliser (UM) phenotype is recognised as a cause of therapeutic inefficacy of antidepressant, whereas an increased risk of toxicity has been reported in poor metabolisers (PMs) with several psychotropics (desipramine, venlafaxine, amitriptyline, haloperidol). CYP2D6 polymorphism influences the analgesic response to prodrug opioids (codeine, tramadol and oxycodone). In PMs for CYP2D6, reduced analgesic effects have been observed, whereas in UMs cases of life-threatening toxicity have been reported with tramadol and codeine. CYP2D6 PM phenotype has been associated with an increased risk of toxicity of metoprolol, timolol, carvedilol and propafenone. Although conflicting results have been reported regarding the association between CYP2D6 genotype and tamoxifen effects, CYP2D6 genotyping may be useful in selecting adjuvant hormonal therapy in postmenopausal women. CYP2C19 is responsible for metabolising clopidogrel, proton pump inhibitors (PPIs) and some antidepressants. Carriers of CYP2C19 variant alleles exhibit a reduced capacity to produce the active metabolite of clopidogrel, and are at increased risk of adverse cardiovascular events. For PPIs, it has been shown that the mean intragastric pH values and the Helicobacter pylori eradication rates were higher in carriers of CYP2C19 variant alleles. CYP2C19 is involved in the metabolism of several antidepressants. As a result of an increased risk of adverse effects in CYP2C19 PMs, dose reductions are recommended for some agents (imipramine, sertraline). CYP2C9 is responsible for metabolising vitamin K antagonists (VKAs), non-steroidal anti-inflammatory drugs (NSAIDs), sulfonylureas, angiotensin II receptor antagonists and phenytoin. For VKAs, CYP2C9 polymorphism has been associated with lower doses, longer time to reach treatment stability and higher frequencies of supratherapeutic international normalised ratios (INRs). Prescribing algorithms are available in order to adapt dosing to genotype. Although the existing data are controversial, some studies have suggested an increased risk of NSAID-associated gastrointestinal bleeding in carriers of CYP2C9 variant alleles. A relationship between CYP2C9 polymorphisms and the pharmacokinetics of sulfonylureas and angiotensin II receptor antagonists has also been observed. The clinical impact in terms of hypoglycaemia and blood pressure was, however, modest. Finally, homozygous and heterozygous carriers of CYP2C9 variant alleles require lower doses of phenytoin to reach therapeutic plasma concentrations, and are at increased risk of toxicity. New diagnostic techniques made safer and easier should allow quicker diagnosis of metabolic variations. Genotyping and phenotyping may therefore be considered where dosing guidelines according to CYP genotype have been published, and help identify the right molecule for the right patient.

The paraoxonase-1 pathway is not a major bioactivation pathway of clopidogrel in vitro

BACKGROUND AND PURPOSE

Clopidogrel is a prodrug bioactivated by cytochrome P450s (CYPs). More recently, paraoxonase-1 (PON1) has been proposed as a major contributor to clopidogrel metabolism. The purpose of this study was to assess the relative contribution of CYPs and PON1 to clopidogrel metabolism in vitro.

EXPERIMENTAL APPROACH

Clopidogrel metabolism was studied in human serum, recombinant PON1 enzyme (rePON1), pooled human liver microsomes (HLMs), HLMs with the CYP2C19*1/*1 genotype and HLMs with the CYP2C19*2/*2 genotype. Inhibition studies were also performed using specific CYP inhibitors and antibodies. Clopidogrel and its metabolites were measured using LC/MS/MS method.

KEY RESULTS

PON1 activity was highest in the human serum and there was no difference in PON1 activity between any of the HLM groups. The production of clopidogrel's active metabolite (clopidogrel-AM) from 2-oxo-clopidogrel in pooled HLMs was approximately 500 times that in serum. When 2-oxo-clopidogrel was incubated with rePON1, clopidogrel-AM was not detected. Clopidogrel-AM production from 2-oxo-clopidogrel was lower in CYP2C19*2/*2 HLMs compared with CYP2C19*1/*1 HLMs, while PON1 activity in HLMs with both genotypes was similar. Moreover, incubation with inhibitors of CYP3A, CYP2B6 and CYP2C19 significantly reduced clopidogrel bioactivation while a PON1 inhibitor, EDTA, had only a weak inhibitory effect.

CONCLUSION AND IMPLICATIONS

This in vitro study shows that the contribution of PON1 to clopidogrel metabolism is limited at clinically relevant concentrations. Moreover, CYP2C19, CYP2B6 and CYP3A play important roles in the bioactivation of clopidogrel.

Liver kidney microsomal type 1 antibodies reduce the CYP2D6 activity in patients with chronic hepatitis C virus infection

Liver kidney microsomal type 1 (LKM-1) antibodies have been shown to decrease the CYP2D6 activity in vitro and are present in a minority of patients with chronic hepatitis C infection. We investigated whether LKM-1 antibodies might reduce the CYP2D6 activity in vivo. All patients enrolled in the Swiss Hepatitis C Cohort Study and tested for LKM-1 antibodies were assessed (n = 1723): 10 eligible patients were matched with patients without LKM-1 antibodies. Patients were genotyped for CYP2D6 variants to exclude individuals with a poor metabolizer genotype. CYP2D6 activity was measured by a specific substrate using the dextromethorphan/dextrorphan metabolic ratio to classify patients into four activity phenotypes. All patients had a CYP2D6 extensive metabolizer genotype. The observed phenotype was concordant with the CYP2D6 genotype in most LKM-negative patients, whereas only three LKM-1 positive patients had a concordant phenotype (six presented an intermediate and one a poor metabolizer phenotype). The median DEM/DOR ratio was sixfold higher in LKM-1 positive than in LKM-1 negative patients (0.096 vs. 0.016, P = 0.004), indicating that CYP2D6 metabolic function was significantly reduced in the presence of LKM-1 antibodies. In chronic hepatitis C patients with LKM-1 antibodies, the CYP2D6 metabolic activity was on average reduced by 80%. The impact of LKM-1 antibodies on CYP2D6-mediated drug metabolism pathways warrants further translational studies.

Influence of the paraoxonase-1 Q192R genetic variant on clopidogrel responsiveness and recurrent cardiovascular events: a systematic review and meta-analysis

BACKGROUND

A poor biological response to clopidogrel is associated with an increased risk of major cardiovascular ischemic events (MACE). Paraoxonase 1 (PON1) enzyme activity is modulated by the PON1-Q192R variant (rs662) and was recently suggested to be strongly involved in clopidogrel bioactivation, but the influence of the PON1-Q192R variant on the risk of MACE in clopidogrel-treated patients is controversial.

OBJECTIVES

To determine whether the PON1-Q192R variant influences clopidogrel biological responsiveness and the risk of MACE in patients treated with clopidogrel.

METHODS

Systematic review and meta-analysis of studies of the association between the PON1-Q192R polymorphism and the biological response to clopidogrel and/or the risk of MACE during clopidogrel administration.

RESULTS

Seventeen studies were included. In the 12 studies of the biological response to clopidogrel (n = 5302 patients), there was no significant difference between 192QQ and 192QR + 192RR subjects, whatever the laboratory method used (global mean standardized difference = 0.10 [-0.06; 0.25], P = 0.22). Eleven studies assessed the risk of MACE, four using a case-control design (n = 2739 patients) and seven a prospective design (n = 5353 patients). Overall, MACE occurred in 19% of patients in case-control studies and in 6% of patients in prospective cohort studies, with no significant difference between 192QQ and 192QR + 192RR patients (OR = 1.28 [0.97; 1.68], P = 0.08). Similar results were obtained when study design was taken into account. Heterogeneity was mainly driven by one publication.

CONCLUSIONS

This meta-analysis suggests that the PON1-Q192R polymorphism has no major impact on the risk of MACE and does not alter the biological response to clopidogrel in clopidogrel-treated patients.

Oral flurbiprofen metabolic ratio assessment using a single-point dried blood spot

We investigated whether a single blood measurement using the minimally invasive technique of a finger prick to draw a blood sample of 5 µl (to yield a dried blood spot (DBS)) is suitable for the assessment of flurbiprofen (FLB) metabolic ratio (MR). Ten healthy volunteers who had been genotyped for CYP2C9 were recruited as subjects. They received FLB alone in session 1 and FLB with fluconazole in session 2. In session 3, the subjects were pretreated for 4 days with rifampicin and received FLB with the last dose of rifampicin on day 5. Plasma and DBS samples were obtained between 0 and 8 h after FLB administration, and urine was collected during the 8 h after administration. The pharmacokinetic profiles of the drugs were comparable in DBS and plasma. FLB's apparent clearance values decreased by 35% in plasma and DBS during session 2 and increased by 75% in plasma and by 30% in DBS during session 3. Good correlations were observed between MRs calculated from urine, plasma, and DBS samples.

Genetic polymorphisms and drug interactions modulating CYP2D6 and CYP3A activities have a major effect on oxycodone analgesic efficacy and safety

BACKGROUND AND PURPOSE

The major drug-metabolizing enzymes for the oxidation of oxycodone are CYP2D6 and CYP3A. A high interindividual variability in the activity of these enzymes because of genetic polymorphisms and/or drug-drug interactions is well established. The possible role of an active metabolite in the pharmacodynamics of oxycodone has been questioned and the importance of CYP3A-mediated effects on the pharmacokinetics and pharmacodynamics of oxycodone has been poorly explored.

EXPERIMENTAL APPROACH

We conducted a randomized crossover (five arms) double-blind placebo-controlled study in 10 healthy volunteers genotyped for CYP2D6. Oral oxycodone (0.2 mg x kg(-1)) was given alone or after inhibition of CYP2D6 (with quinidine) and/or of CYP3A (with ketoconazole). Experimental pain (cold pressor test, electrical stimulation, thermode), pupil size, psychomotor effects and toxicity were assessed.

KEY RESULTS

CYP2D6 activity was correlated with oxycodone experimental pain assessment. CYP2D6 ultra-rapid metabolizers experienced increased pharmacodynamic effects, whereas cold pressor test and pupil size were unchanged in CYP2D6 poor metabolizers, relative to extensive metabolizers. CYP2D6 blockade reduced subjective pain threshold (SPT) for oxycodone by 30% and the response was similar to placebo. CYP3A4 blockade had a major effect on all pharmacodynamic assessments and SPT increased by 15%. Oxymorphone C(max) was correlated with SPT assessment (rho(S)= 0.7) and the only independent positive predictor of SPT. Side-effects were observed after CYP3A4 blockade and/or in CYP2D6 ultra-rapid metabolizers.

CONCLUSIONS AND IMPLICATIONS

The modulation of CYP2D6 and CYP3A activities had clear effects on oxycodone pharmacodynamics and these effects were dependent on CYP2D6 genetic polymorphism.

The effects of CYP2D6 and CYP3A activities on the pharmacokinetics of immediate release oxycodone

BACKGROUND AND PURPOSE

There is high interindividual variability in the activity of drug-metabolizing enzymes catalysing the oxidation of oxycodone [cytochrome P450 (CYP) 2D6 and 3A], due to genetic polymorphisms and/or drug-drug interactions. The effects of CYP2D6 and/or CYP3A activity modulation on the pharmacokinetics of oxycodone remains poorly explored.

EXPERIMENTAL APPROACH

A randomized crossover double-blind placebo-controlled study was performed with 10 healthy volunteers genotyped for CYP2D6 [six extensive (EM), two deficient (PM/IM) and two ultrarapid metabolizers (UM)]. The volunteers randomly received on five different occasions: oxycodone 0.2 mg x kg(-1) and placebo; oxycodone and quinidine (CYP2D6 inhibitor); oxycodone and ketoconazole (CYP3A inhibitor); oxycodone and quinidine+ketoconazole; placebo. Blood samples for plasma concentrations of oxycodone and metabolites (oxymorphone, noroxycodone and noroxymorphone) were collected for 24 h after dosing. Phenotyping for CYP2D6 (with dextromethorphan) and CYP3A (with midazolam) were assessed at each session.

KEY RESULTS

CYP2D6 activity was correlated with oxymorphone and noroxymorphone AUCs and C(max) (-0.71 < Spearman correlation coefficient rhos < -0.92). Oxymorphone C(max) was 62% and 75% lower in PM than EM and UM. Noroxymorphone C(max) reduction was even more pronounced (90%). In UM, oxymorphone and noroxymorphone concentrations increased whereas noroxycodone exposure was halved. Blocking CYP2D6 (with quinidine) reduced oxymorphone and noroxymorphone C(max) by 40% and 80%, and increased noroxycodone AUC(infinity) by 70%. Blocking CYP3A4 (with ketoconazole) tripled oxymorphone AUC(infinity) and reduced noroxycodone and noroxymorphone AUCs by 80%. Shunting to CYP2D6 pathway was observed after CYP3A4 inhibition.

CONCLUSIONS AND IMPLICATIONS

Drug-drug interactions via CYP2D6 and CYP3A affected oxycodone pharmacokinetics and its magnitude depended on CYP2D6 genotype.

Two structurally different T-type Ca 2+ channel inhibitors, mibefradil and pimozide, protect CA1 neurons from delayed death after global ischemia in rats

Recent in vitro evidence suggests that T-type Ca(2+) channels are implicated in the mechanisms of ischemia-induced delayed neuronal cell death. The aim of this work was to study the neuroprotective potential of mibefradil and pimozide, both T-type Ca(2+) channel inhibitors, in an in vivo rat model of global ischemia. We performed blinded and randomized placebo vs. treatment experiments using 57 animals to test mibefradil and fourteen animals to test pimozide. Each treated animal received a single stereotactic intraventricular injection of mibefradil or intraperitoneal injection of pimozide prior to transient global cerebral ischemia. The primary endpoint was the number of neurons surviving in the CA1 region 72 h after insult as evaluated by NeuN-labeled cell counts. All physiological variables monitored immediately before and after ischemic insult were equivalent between all groups. Surviving neurons in the CA1 region were significantly more frequent in the treated groups compared to the placebo group (mibefradil: 36.8 ± 2.8 cells in a 200 × 100 μm counting area vs. placebo: 25.2 ± 3.2 [P < 0.01]; pimozide: 39.4 ± 1.12 vs. placebo: 27.8 ± 0.7 [P < 0.0001]). Thus, administration of mibefradil or pimozide effectively prevents neuronal death after ischemia in a rat model of global ischemia. This study provides further support for a neuroprotective effect of T-type Ca(2+) current inhibition during ischemia.

Development and validation of a new reversed-phase ion pairing liquid chromatographic method with fluorescence detection for penciclovir analysis in plasma and aqueous humor

A simple, sensitive and reliable HPLC ion-pairing method with fluorescence detection, was developed for penciclovir determination in plasma and aqueous humor, with a Zorbax SB-aq C18 (100 mmx2.1 mm) column. Plasma samples were treated by solid-phase extraction with Oasis MCX (30 mg) cartridges. Ganciclovir, an antiviral drug structurally related to penciclovir, was used as internal standard (I.S.). Aqueous humor samples were directly injected into the chromatographic system. Separation was performed by a gradient elution with a mobile phase consisting of a mixture of acetonitrile and phosphate buffer 50mM containing 5mM of sodium octanesulfonate, pH 2.0, at a flow rate of 0.3 ml/min. The method was validated and showed good performances in terms of linearity, sensitivity, precision and trueness. Quantification limit was obtained at 0.05 microg/ml for aqueous humor and at 0.1 microg/ml for plasma. Finally, the proposed analytical method was used to measure penciclovir in clinical samples for a pharmacokinetic study, after oral administration of famciclovir.

Not all statins interfere with clopidogrel during antiplatelet therapy

BACKGROUND

Clopidogrel and statins are frequently coadministered in patients with ischemic heart diseases. Recent reports suggested that clopidogrel's effectiveness in inhibiting adenosine diphosphate (ADP)-induced platelets aggregation is attenuated by co-administration of certain statins. The objective of the present study was to define which statin might interfere with the antiaggregation property of clopidogrel.

METHODS

We designed a pharmacokinetic study and tested ex vivo platelet function on 21 healthy volunteers who received clopidogrel and all currently commercially available statins: rosuvastatin [10 mg o.d.], simvastatin [20 mg o.d.], fluvastatin [80 mg o.d.], pravastatin [40 mg o.d.], and atorvastatin [20 mg o.d.]. Each statin was administered for 7 days followed by 1 week of wash-out period with clopidogrel treatment alone. Detection of the statins in the plasma was performed on all blood samples, using HPLC analytical method.

RESULTS

All individuals, except one, were responders to clopidogrel with inhibition of ex vivo ADP induced platelet aggregation. All statins, except pravastatin, were detectable in the plasma at the end of each treatment period in all patients, and no statin was detectable after any of the wash-out periods. Clopidogrel was significantly less efficient to prevent platelet aggregation when coadministrated with simvastatin or fluvastatin. No difference was observed in clopidogrel efficacy when coadministered with rosuvastatin, pravastatin or atorvastatin.

CONCLUSIONS

This is the first study investigating clopidogrel-statin interactions on ex vivo platelet function with all commercially available statins and which were administered to the same individuals. It demonstrates in healthy volunteers that at the doses used in this study, simvastatin and fluvastatin, but not atorvastatin, pravastatin or rosuvastatin interfere with the anti-aggregation effect of clopidogrel.

Calystegine distribution in some solanaceous species

The distribution of eight calystegines (A(3), A(5), B(1), B(2), B(3), B(4), C(1) and N(1)) and their content was investigated by gas chromatography coupled to mass spectrometry (GC-MS) in Datura metel, Atropa belladonna, Hyoscyamus albus, Mandragora autumnalis, Solanum sodomaeum, Withania somnifera, Withania frutescens and Brunfelsia nitida. The most frequently encountered calystegines were A(3), B(1), B(2) and B(3), while distribution of N(1) and C(1) was more limited. In all the investigated samples, calystegines A(5) and B(4) were never detected. This report focuses for the first time on calystegines in Withania and Brunfelsia genera and in Mandragora autumnalis and Solanum sodomaeum species.

Routine o-glycan characterization in nutritional supplements--a comparison of analytical methods for the monitoring of the bovine kappa-casein macropeptide glycosylation

Analytical procedures, including capillary isoelectric focusing (CIEF), high-performance anion-exchange chromatography coupled to amperometric detection (HPAEC-PAD) and normal-phase chromatography with fluorescence detection are presented for the characterization of a highly O-glycosylated caseinomacropeptide (CGMP) and the detection of subtle glycosylation differences between CGMP Batches obtained with two different preparation procedures. Modified two-step CIEF allowed monitoring of glycopeptide heterogeneity and determination of the isoelectric points of acidic glycoforms. The mixture of wide and narrow pH range ampholytes was optimized to improve glycoform resolution. The pI of the different CGMP glycoforms was evaluated with pI internal standards and found to range between 3.08 and 3.58, which indicates a very acidic glycopeptide. Moreover, the monosaccharide composition was determined with HPAEC-PAD after neutral and amino sugars release by using adequate acidic hydrolysis of CGMP. Results indicated a similar composition for Batches I and II, but the monosaccharide percentages were 3-4 fold higher in Batch I, particularly for galactose and glucose. This likely reflects a higher content in lactose in the case of Batch I. Finally, O-linked oligosaccharides were released with an automated hydrazinolysis and derivatized with a sensitive labelling reagent, 2-aminobenzamide. The derivatives were then analyzed by normal-phase HPLC coupled with fluorescence detection, and separated on the basis of hydrophilic interaction, which allowed oligosaccharide mapping of the two CGMP. It appeared that the two CGMP preparations had an almost identical O-glycan population, but CGMP Batch I was more glycosylated than Batch II. Additionally, the sizes of the separated glycans, expressed as the number of glucose units, were tentatively assigned using calibration with a partial hydrolysate of dextran. In conclusion, a combination of electrophoretic and chromatographic techniques was found powerful in studying glycoprotein heterogeneity and assessing batch-to-batch consistency.

Capillary electrophoresis and high-performance anion exchange chromatography for monitoring caseinoglycomacropeptide sialylation

Capillary zone electrophoresis was applied to separate caseinoglycomacropeptide glycoforms and characterize microheterogeneity of the glycopeptide. Particular attention was paid to the sialic acid content in caseinoglycomacropeptide obtained through different manufacturing processes. A chemometric approach was used to simultaneously study effects of acid concentration, hydrolysis time and temperature on sialic acid release from caseinoglycomacropeptide. Hydrolysis conditions that maximize sialic acid release were chosen. Sialic acid was determined using high performance anion exchange chromatography coupled with pulsed amperometric detection. Results were compared to those obtained by alternative techniques, such as colorimetric and enzymatic methods.

Use of borate complexation for the separation of non-UV-absorbing calystegines by capillary electrophoresis

A capillary zone electrophoresis method was developed for the simultaneous analysis of seven closely related polyhydroxyalkaloids called calystegines. Successful results were obtained with a fused-silica capillary, 80 mM sodium tetraborate at pH 9.2 and temperature of 50 degrees C. Detection of non-UV-absorbing calystegines was achieved through in-situ complexation with borate ions. To further improve method sensitivity, a capillary with a bubble cell was used and detection performed at low wavelength (191 nm). Effects of buffer concentration, pH and temperature on migration times and efficiency are discussed. Migration behavior of selected compounds was significantly affected by their chemical structure (i.e., number and position of hydroxy groups). Under optimized conditions, baseline separation of the selected compounds was achieved in less than 12 min. Precision was evaluated by measuring repeatability and intermediate precision of migration times and corrected peak areas. Finally, the method was applied to the qualitative analysis of calystegines in plant extracts and results were confirmed by GC-MS.

Partial solubility parameters of lactose, mannitol and saccharose using the modified extended Hansen method and evaporation light scattering detection

The modified extended Hansen method was tested for the first time to determine partial solubility parameters of non-polymeric pharmaceutical excipients. The method was formerly tested with drug molecules, and is based upon a regression analysis of the logarithm of the mole fraction solubility of the solute against the partial solubility parameters of a series of solvents of different chemical classes. Two monosaccharides and one disaccharide (lactose monohydrate, saccharose and mannitol) were chosen. The solubility of these compounds was determined in a series of solvents ranging from nonpolar to polar and covering a wide range of the solubility parameter scale. Sugars do not absorb at the UV-vis region, and the saturated solutions were assayed with a recent chromatographic technique coupled to an evaporative light scattering detector. This technique was suitable to determine the concentration dissolved in most solvents. The modified extended Hansen method provided better results than the original approach. The best model was the four parameter equation, which includes the dispersion delta d, dipolar delta p, acidic delta a and basic delta b partial solubility parameters. The partial solubility parameters obtained, expressed as MPa1/2, were delta d = 17.6, delta p = 28.7, delta h = 19, delta a = 14.5, delta b = 12.4, delta T = 32.8 for lactose, delta d = 16.2, delta p = 24.5, delta h = 14.6, delta a = 8.7, delta b = 12.2, delta T = 32.8 for mannitol and delta d = 17.1, delta p = 18.5, delta h = 13, delta a = 11.3, delta b = 7.6, delta T = 28.4 for saccharose. The high total solubility parameters delta T obtained agree with the polar nature of the sugars. The dispersion parameters delta d are quite similar for the three sugars indicating that the polar delta p and hydrogen bonding parameters (delta h, delta a, delta b) are responsible for the variation in the total solubility parameters delta T obtained, as also found for drugs. The results suggest that the method could be extended to determine the partial solubility parameters of other non-polymeric pharmaceutical excipients.

Experimental design for enantioselective separation of celiprolol by capillary electrophoresis using sulfated beta-cyclodextrin

A capillary zone electrophoresis method was developed for the enantioseparation of celiprolol enantiomers, using a sulfated beta-cyclodextrin (beta-CD) as a chiral selector. The use of a coated capillary was necessary to achieve stable and reproducible enantioseparations. A central composite design was applied to optimize the method and four parameters were selected for this study: the buffer pH, the buffer concentration, the sulfated beta-CD concentration and the temperature. Resolution between celiprolol enantiomers as well as analysis time and generated current were established as responses. For each response, a model was obtained by a second-degree mathematical expression. From the models, the most favorable conditions were determined by optimizing the resolution between celiprolol enantiomers and by setting the two other responses at threshold values. Response surfaces were also used to assess the robustness of the analytical method around the optimal region. Successful results were obtained with a 52 mM acetate buffer at pH 4.0 in the presence of 3.0 mM sulfated beta-CD at a temperature of 19.5 degrees C. Under these optimized conditions, baseline separation of the celiprolol enantiomers was achieved in less than 10 min. The method showed good validation data in terms of precision, accuracy and linearity, and was found to be suitable in determining celiprolol enantiomers in pharmaceutical preparations and in biological fluids.

Development and validation of liquid chromatography and capillary electrophoresis methods for acarbose determination in pharmaceutical tablets

Liquid chromatography and capillary zone electrophoresis, respectively coupled to an evaporative light scattering detector and a UV detector have been developed for the analysis of acarbose without any derivatization procedure. The electrophoretic separation of acarbose anomers was achieved through the manipulation of the working temperature. Both methods were validated and showed good validation data in terms of precision, accuracy and linearity. The validated methods were successfully applied to the dosage of acarbose in commercially available Glucobay tablets.