The Mastic Tree (Pistacia lentiscus L.) Leaves as Source of BACs: Effect of Growing Location, Phenological Stage and Extraction Solvent on Phenolic Content.

RESEARCH BACKGROUND: Mastic tree (Pistacia lentiscus L.) of the Anacardiaceae family is an evergreen shrub from Mediterranean countries where it is used in traditional medicine. Analysis of P. lentiscus leaf, stem, fruit and root extracts showed high concentrations of principal groups of secondary metabolites (flavonoids, phenolic acids and tannins), suggesting the plant possesses great biological potential. Therefore, the aim of this research is to evaluate the impact of environmental parameters and the extraction solvent type on the concentration of phenols in mastic tree leaf extracts grown at four different locations along the Adriatic coast (Barbariga, Lun, Hvar and Vela Luka) during three phenological stages (early flowering, early fruiting and late fruiting). EXPERIMENTAL APPROACH: Since mastic tree plant has phenolic compounds with different structures and chemical properties, ethanolic and methanolic leaf extracts were analysed using high-performance liquid chromatography (HPLC) coupled with UV/Vis PDA detector. Phenolic compounds were identified by comparing the retention times and spectral data with those of standards at 280 and 340 nm. RESULTS AND CONCLUSIONS: In all samples, phenolic acids and flavonol glycosides were quantified, while catechin was quantified only in methanolic extracts. The 5-O-galloylquinic acid was determined as a predominant phenolic compound in all samples followed by monogalloyl glucose, 3,5-di-O-galloylquinic acid, 3,4,5-tri-O-galloylquinic acid and gallic acid, respectively. Myricetin-3-O-rhamnoside was found to be the predominant flavonol glycoside followed by myricetin-3-O-glucoside, myricetin-3-O-glucuronide, quercetin-3-O-rhamnoside and derivative of flavonol glycoside. The mass concentration of these compounds significantly varied during different phenological stages, at different growing locations and used extraction solvents. The highest phenolic mass concentration was determined in the samples harvested at Hvar growing location and extracted in 80% methanol. The highest total phenolic acid mass concentration was obtained in the samples harvested during the flowering phenological stage and the highest total flavonoid mass concentration in the samples harvested during the early fruiting stage. NOVELTY AND SCIENTIFIC CONTRIBUTION: The obtained data provide a better understanding of the P. lentiscus species phenolic concentration, which can lead to further investigations regarding the valorisation of mastic tree leaves as pharmaceutical products or as food products with added value.

Evaluation of Polyphenolic Profile and Antioxidant Activity of Pistacia lentiscus L. Leaves and Fruit Extract Obtained by Optimized Microwave-Assisted Extraction.

Pistacia lentiscus L. is a Mediterranean shrub known for its health promoting effects attributed to a large extent to polyphenols accumulated in all parts of the plant. Microwave-assisted extraction is a green extraction technique enabling fast and effective isolation of plant polyphenols. Therefore, the aim of this research was to optimize the microwave-assisted extraction of polyphenols from Pistacia lentiscus L. leaves and fruit in terms of temperature, extraction time and microwave power and to evaluate their polyphenolic profile by UPLC/ESI-MS2 and antioxidant capacity by ORAC assay. Optimal extraction conditions for leaf polyphenols were 69 °C, 512 W and 12 min, while for fruit were slightly more intensive-75 °C, 602 W and 15 min. Obtained total phenolic content in leaves and fruit was similar to that obtained after 30 min of the heat-reflux method. The polyphenolic profile of extracts included 34 compounds, with myricetin glycosides being the most abundant compounds among flavonoids in Pistacia lentiscus L. leaves and fruit and gallic acid and its derivates among the phenolic acids. ORAC assay showed higher antioxidant capacity for Pistacia lentiscus L. leaves extract than for fruit, which is in correlation with their respective phenolic content.

Essential Oil Composition of Different Plant Parts from Croatian Petasites albus (L.) Gaertn. and Petasites hybridus (L.) G.Gaertn., B.Mey. & Scherb. (Asteraceae).

Essential oil compositions of fresh leaves, flower stems and rhizomes obtained by hydrodistillation from different Croatian populations of Petasites albus (L.) Gaertn. and Petasites hybridus (L.) G.Gaertn., B.Mey. & Scherb. (four of each species) were investigated using gas chromatography-flame ionization detection and gas chromatography-mass spectrometry. Altogether, 118 constituents were identified, accounting for 81.19-96.81 % of total oil composition. All essential oils were characterized by oxygenated sesquiterpenes, with distinct compounds recorded for both investigated species. Clear separation between the two species was confirmed by principal component analysis and hierarchical cluster analysis. This is the first study that recorded intraspecific variations of essential oil constituents from P. albus and P. hybridus. Obtained results could contribute to the understanding of their medicinal and nutritional value.

Long-term seizure outcome following epilepsy surgery in the parietal lobe: a meta-analysis.

Due to a limited number of patients with drug-resistant parietal lobe epilepsy in surgical series, there are insufficient data about long-term seizure outcome following surgery restricted to the parietal lobe. We performed a meta-analysis to asses long-term outcomes in patients with parietal lobe epilepsy who underwent surgery confined to the parietal lobe or resection with major involvement of the parietal cortex. An English language literature search for studies on parietal lobe surgery and outcome was conducted using the MEDLINE database, followed by a manual search based on specific criteria. An inverse variance random effect meta-analysis model was used to estimate the pooled proportion of Engel Class I. Meta-regression models were used to examine the association between outcome and potential predictors. The search yielded seven retrospective studies with a total sample size of 253 patients (mean follow-up: 104.9±74.8 months). Following surgery, Engel Class I surgical outcome was achieved in 62.4% (95% CI: 0.492-0.755). Two independent predictors were identified for positive long-term outcome: interictal EEG localized to the parietal region (p=0.007) and the presence of tumour (p=0.022). Following surgery confined to the parietal lobe or resection with major involvement of the parietal cortex, the long-term prognosis of patients with parietal lobe epilepsy is favourable.

Evidence-based selection of training compounds for use in the mechanism-based integrated prediction of drug-induced liver injury in man.

The current test systems employed by pharmaceutical industry are poorly predictive for drug-induced liver injury (DILI). The 'MIP-DILI' project addresses this situation by the development of innovative preclinical test systems which are both mechanism-based and of physiological, pharmacological and pathological relevance to DILI in humans. An iterative, tiered approach with respect to test compounds, test systems, bioanalysis and systems analysis is adopted to evaluate existing models and develop new models that can provide validated test systems with respect to the prediction of specific forms of DILI and further elucidation of mechanisms. An essential component of this effort is the choice of compound training set that will be used to inform refinement and/or development of new model systems that allow prediction based on knowledge of mechanisms, in a tiered fashion. In this review, we focus on the selection of MIP-DILI training compounds for mechanism-based evaluation of non-clinical prediction of DILI. The selected compounds address both hepatocellular and cholestatic DILI patterns in man, covering a broad range of pharmacologies and chemistries, and taking into account available data on potential DILI mechanisms (e.g. mitochondrial injury, reactive metabolites, biliary transport inhibition, and immune responses). Known mechanisms by which these compounds are believed to cause liver injury have been described, where many if not all drugs in this review appear to exhibit multiple toxicological mechanisms. Thus, the training compounds selection offered a valuable tool to profile DILI mechanisms and to interrogate existing and novel in vitro systems for the prediction of human DILI.

Effect of human glutathione S-transferase hGSTP1-1 polymorphism on the detoxification of reactive metabolites of clozapine, diclofenac and acetaminophen.

Recent association studies suggest that genetically determined deficiencies in GSTs might be a risk factor for idiosyncratic adverse drug reactions resulting from the formation of reactive drug metabolites. hGSTP1-1 is polymorphic in the human population with a number of single nucleotide polymorphisms that yield an amino acid change in the encoded protein. Three allelic variants of hGSTP1-1 containing an Ile105Val or Ala114Val substitution, or a combination of both, have been the most widely studied and showed different activity when compared to wild-type hGSTP1-1*A (Ile105/Ala114). In the present study, we studied the ability of these allelic variants to catalyze the GSH conjugation of reactive metabolites of acetaminophen, clozapine, and diclofenac formed by bioactivation in in vitro incubations by human liver microsomes and drug metabolizing P450 BM3 mutants. The results show that effects of the change of amino acid at residue 105 and 114 on conjugation reactions were substrate dependent. A single substitution at residue 105 affects the ability to catalyze GSH conjugation, while when both residue 105 and 114 were substituted the effect was additionally enhanced. Single mutation at position 114 did not show a significant effect. The different hGSTP1-1 mutants showed slightly altered regioselectivities in formation of individual GSH conjugates of clozapine which suggests that the binding orientation of the reactive nitrenium ion of clozapine is affected by the mutations. For diclofenac, a significant decrease in activity in GSH-conjugation of diclofenac 1',4'-quinone imine was observed for variants hGSTP1-1*B (Val105/Ala114) and hGSTP1-1*C (Val105/Val114). However, since the differences in total GSH conjugation activity catalyzed by these allelic variants were not higher than 30%, differences in inactivation of reactive intermediates by hGSTP1-1 are not likely to be a major factor in determining interindividual difference in susceptibility to adverse drug reactions induced by the drugs studied.

Effect of human glutathione S-transferases on glutathione-dependent inactivation of cytochrome P450-dependent reactive intermediates of diclofenac.

Idiosyncratic adverse drug reactions due to the anti-inflammatory drug diclofenac have been proposed to be caused by the generation of reactive acyl glucuronides and oxidative metabolites. For the oxidative metabolism of diclofenac by cytochromes P450 at least five different reactive intermediates have been proposed previously based on structural identification of their corresponding GSH-conjugates. In the present study, the ability of four human glutathione S-transferases (hGSTs) to catalyze the GSH-conjugation of the different reactive intermediates formed by P450s was investigated. Addition of pooled human liver cytosol and recombinant hGSTA1-1, hGSTM1-1, and hGSTP1-1 to incubations of diclofenac with human liver microsomes or purified CYP102A1M11 L437N as a model system significantly increased total GSH-conjugation. The strongest increase of total GSH-conjugation was observed by adding hGSTP1-1, whereas hGSTM1-1 and hGSTA1-1 showed lower activity. Addition of hGSTT1-1 only showed a minor effect. When considering the effects of hGSTs on GSH-conjugation of the different quinoneimines of diclofenac, it was found that hGSTP1-1 showed the highest activity in GSH-conjugation of the quinoneimine derived from 5-hydroxydiclofenac (5-OH-DF). hGSTM1-1 showed the highest activity in inactivation of the quinoneimine derived from 4'-hydroxydiclofenac (4'-OH-DF). Separate incubations with 5-OH-DF and 4'-OH-DF as substrates confirmed these results. hGSTs also catalyzed GSH-conjugation of the o-iminemethide formed by oxidative decarboxylation of diclofenac as well as the substitution of one of the chlorine atoms of DF by GSH. hGSTP1-1 showed the highest activity for the formation of these minor GSH-conjugates. These results suggest that hGSTs may play an important role in the inactivation of DF quinoneimines and its minor reactive intermediates especially in stress conditions when tissue levels of GSH are decreased.

Human precision-cut liver slices as an ex vivo model to study idiosyncratic drug-induced liver injury.

Idiosyncratic drug-induced liver injury (IDILI) is a major problem during drug development and has caused drug withdrawal and black-box warnings. Because of the low concordance of the hepatotoxicity of drugs in animals and humans, robust screening methods using human tissue are needed to predict IDILI in humans. According to the inflammatory stress hypothesis, the effects of inflammation interact with the effects of a drug or its reactive metabolite, precipitating toxic reactions in the liver. As a follow-up to our recently published mouse precision-cut liver slices model, an ex vivo model involving human precision-cut liver slices (hPCLS), co-incubated for 24 h with IDILI-related drugs and lipopolysaccharide (LPS), was developed to study IDILI mechanisms related to inflammatory stress in humans and to detect potential biomarkers. LPS exacerbated the effects of ketoconazole and clozapine toxicity but not those of their non-IDILI-related comparators, voriconazole and olanzapine. However, the IDILI-related drugs diclofenac, carbamazepine, and troglitazone did not show synergistic toxicity with LPS after incubation for 24 h. Co-incubation of ketoconazole and clozapine with LPS decreased the levels of glutathione in hPCLS, but this was not seen for the other drugs. All drugs affected LPS-induced cytokine release, but interestingly, only ketoconazole and clozapine increased the level of LPS-induced TNF release. Decreased levels of glutathione and cysteine conjugates of clozapine were detected in IDILI-responding livers following cotreatment with LPS. In conclusion, we identified ketoconazole and clozapine as drugs that exhibited synergistic toxicity with LPS, while glutathione and TNF were found to be potential biomarkers for IDILI-inducing drugs mediated by inflammatory stress. hPCLS appear to be suitable for further unraveling the mechanisms of inflammatory stress-associated IDILI.

Characterization of human cytochrome P450s involved in the bioactivation of clozapine.

Clozapine is known to cause hepatotoxicity in a small percentage of patients. Oxidative bioactivation to reactive intermediates by hepatic cytochrome P450s (P450s) has be proposed as a possible mechanism. However, in contrast to their role in formation of N-desmethylclozapine and clozapine N-oxide, the involvement of individual P450s in the bioactivation to reactive intermediates is much less well characterized. The results of the present study show that 7 of 14 recombinant human P450s were able to bioactivate clozapine to a glutathione-reactive nitrenium ion. CYP3A4 and CYP2D6 showed the highest specific activity. Enzyme kinetical characterization of these P450s showed comparable intrinsic clearance of bioactivation, implicating that CYP3A4 would be more important because of its higher hepatic expression, compared with CYP2D6. Inhibition experiments using pooled human liver microsomes confirmed the major role of CYP3A4 in hepatic bioactivation of clozapine. By studying bioactivation of clozapine in human liver microsomes from 100 different individuals, an 8-fold variability in bioactivation activity was observed. In two individuals bioactivation activity exceeded N-demethylation and N-oxidation activity. Quinidine did not show significant inhibition of bioactivation in any of these liver fractions, suggesting that CYP2D6 polymorphism is not an important factor in determining susceptibility to hepatotoxicity of clozapine. Therefore, interindividual differences and drug-drug interactions at the level of CYP3A4 might be factors determining exposure of hepatic tissue to reactive clozapine metabolites.

AMAP, the alleged non-toxic isomer of acetaminophen, is toxic in rat and human liver.

N-acetyl-meta-aminophenol (AMAP) is generally considered as a non-toxic regioisomer of the well-known hepatotoxicant acetaminophen (APAP). However, so far, AMAP has only been shown to be non-toxic in mice and hamsters. To investigate whether AMAP could also be used as non-toxic analog of APAP in rat and human, the toxicity of APAP and AMAP was tested ex vivo in precision-cut liver slices (PCLS) of mouse, rat and human. Based on ATP content and histomorphology, APAP was more toxic in mouse than in rat and human PCLS. Surprisingly, although AMAP showed a much lower toxicity than APAP in mouse PCLS, AMAP was equally toxic as or even more toxic than APAP at all concentrations tested in both rat and human PCLS. The profile of proteins released into the medium of AMAP-treated rat PCLS was similar to that of APAP, whereas in the medium of mouse PCLS, it was similar to the control. Metabolite profiling indicated that mouse PCLS produced the highest amount of glutathione conjugate of APAP, while no glutathione conjugate of AMAP was detected in all three species. Mouse also produced ten times more hydroquinone metabolites of AMAP, the assumed proximate reactive metabolites, than rat or human. In conclusion, AMAP is toxic in rat and human liver and cannot be used as non-toxic isomer of APAP. The marked species differences in APAP and AMAP toxicity and metabolism underline the importance of using human tissues for better prediction of toxicity in man.

Mass spectrometric characterization of protein adducts of multiple P450-dependent reactive intermediates of diclofenac to human glutathione-S-transferase P1-1.

Use of the nonsteroidal anti-inflammatory drug diclofenac (DF) is associated with serious idiosyncratic hepatotoxicity. Covalent binding of reactive intermediates of DF to proteins is considered to initiate the process leading to this severe side-effect. The aim of this study was to characterize the nature of covalent protein modifications by reactive metabolites of DF which result from bioactivation by cytochrome P450. DF and its major monohydroxylated metabolites 4'-hydroxydiclofenac (4'-OH-DF) and 5-hydroxydiclofenac (5-OH-DF) were bioactivated using a highly active P450 BM3 mutant (CYP102A1M11H) in the presence of the model target protein human glutathione-S-transferase P1-1 (hGST P1-1). Protein-adducts were subsequently identified by LC-MS/MS analysis of tryptic digests of hGST P1-1. In total, 10 different peptide adducts were observed which result from modifications of Cys-47 and Cys-14 of hGST P1-1. The majority of the protein thiol modifications appeared to be derived from 5-OH-DF, which produced seven different peptide adducts with mass increments of 289.0, 309.0, and 339.0 Da. Remarkably, no peptide adducts were observed upon the bioactivation of 4'-OH-DF. Incubations of P450 BM3 with DF also showed the peptide adducts derived from 5-OH-DF and peptide adducts that are not derived from quinone imine. A peptide adduct with a mass increment of 249.0 Da most likely results from the o-imine methide formed by oxidative decarboxylation of DF. In addition, a peptide adduct was observed with a mass increment of 259.0 Da, which corresponds to the substitution of one of the chlorine atoms of DF by protein thiol. A corresponding GSH-conjugate with a similar mass increment was only observed if incubations of DF with P450 and GSH were supplemented by human GST P1-1. The results of this study not only confirm the importance of 5-OH-DF in covalent protein-binding but also suggest that the nature of protein adduction is not necessarily reflected by chemical conjugation with GSH.

Role of residue 87 in the activity and regioselectivity of clozapine metabolism by drug-metabolizing CYP102A1 M11H: application for structural characterization of clozapine GSH conjugates.

In the present study, a site-saturation mutagenesis library of drug-metabolizing CYP102A1 M11H with all 20 amino acids at position 87 was applied as a biocatalyst for the production of stable and reactive metabolites of clozapine. Clozapine is an atypical antipsychotic drug in which formation of reactive metabolites is considered to be responsible for several adverse drug reactions. Reactive intermediates of clozapine can be inactivated by GSH to multiple GSH conjugates by nonenzymatic and glutathione transferase (GST)-mediated conjugation reactions. The structures of several GST-dependent metabolites have not yet been elucidated unequivocally. The present study shows that the nature of the amino acid at position 87 of CYP102A1 M11H strongly determines the activity and regioselectivity of clozapine metabolism. Some mutants showed preference for N-demethylation and N-oxidation, whereas others showed high selectivity for bioactivation to reactive intermediates. The mutant containing Phe87 showed high activity and high selectivity for the bioactivation pathway and was used for the large-scale production of GST-dependent GSH conjugates by incubation in the presence of recombinant human GST P1-1. Five human-relevant GSH adducts were produced at high levels, enabling structural characterization by (1)H NMR. This work shows that drug-metabolizing CYP102A1 mutants, in combination with GSTs, are very useful tools for the generation of GSH conjugates of reactive metabolites of drugs to enable their isolation and structural elucidation.

Diclofenac inhibits tumor necrosis factor-α-induced nuclear factor-κB activation causing synergistic hepatocyte apoptosis.

UNLABELLED: Drug-induced liver injury (DILI) is an important clinical problem. It involves crosstalk between drug toxicity and the immune system, but the exact mechanism at the cellular hepatocyte level is not well understood. Here we studied the mechanism of crosstalk in hepatocyte apoptosis caused by diclofenac and the proinflammatory cytokine tumor necrosis factor α (TNF-α). HepG2 cells were treated with diclofenac followed by TNF-α challenge and subsequent evaluation of necrosis and apoptosis. Diclofenac caused a mild apoptosis of HepG2 cells, which was strongly potentiated by TNF-α. A focused apoptosis machinery short interference RNA (siRNA) library screen identified that this TNF-α-mediated enhancement involved activation of caspase-3 through a caspase-8/Bid/APAF1 pathway. Diclofenac itself induced sustained activation of c-Jun N-terminal kinase (JNK) and inhibition of JNK decreased both diclofenac and diclofenac/TNF-α-induced apoptosis. Live cell imaging of GFPp65/RelA showed that diclofenac dampened the TNF-α-mediated nuclear factor kappaB (NF-κB) translocation oscillation in association with reduced NF-κB transcriptional activity. This was associated with inhibition by diclofenac of the TNF-α-induced phosphorylation of the inhibitor of NF-κB alpha (IκBα). Finally, inhibition of IκB kinase ß (IKKß) with BMS-345541 as well as stable lentiviral short hairpin RNA (shRNA)-based knockdown of p65/RelA sensitized hepatocytes towards diclofenac/TNF-α-induced cytotoxicity. CONCLUSION: Together, our data suggest a model whereby diclofenac-mediated stress signaling suppresses TNF-α-induced survival signaling routes and sensitizes cells to apoptosis.

Metabolism related toxicity of diclofenac in yeast as model system.

Diclofenac is a widely used drug that can cause serious hepatotoxicity, which has been linked to metabolism by cytochrome P450s (P450). To investigate the role of oxidative metabolites in diclofenac toxicity, a model for P450-related toxicity was set up in Saccharomyces cerevisiae. We expressed a drug-metabolizing mutant of cytochrome P450 BM3 (BM3 M11) in yeast. Importantly, BM3 M11 yielded similar oxidative metabolite profiles of diclofenac as human P450s. It was found that yeast strains expressing BM3 M11 grew significantly slower when exposed to diclofenac than strains without BM3 M11. Furthermore, the amount of reactive oxygen species (ROS) after incubation with diclofenac was higher in strains expressing BM3 M11 than in strains without this enzyme, confirming that P450 activity increases diclofenac toxicity. Interestingly, 4'- and 5-hydroxydiclofenac had no effect on cell growth or ROS formation in cells expressing BM3 M11, although hydroxydiclofenac-derived quinone imines were identified in these strains by detection of their glutathione conjugates. This suggests that 4'- and 5-hydroxydiclofenac, as well as their quinone imines, are not involved in toxicity in yeast. Rather, the P450-related toxicity of diclofenac is caused by primary metabolites such as arene oxides resulting in hydroxydiclofenac or radical species formed during decarboxylation.

Role of human glutathione S-transferases in the inactivation of reactive metabolites of clozapine.

The conjugation of reactive drug metabolites to GSH is considered an important detoxification mechanism that can be spontaneous and/or mediated by glutathione S-transferases (GSTs). In case GSTs play an important role in GSH conjugation, genetically determined deficiencies in GSTs may be a risk factor for adverse drug reactions (ADRs) resulting from reactive drug metabolites. So far, the role of GSTs in the detoxification of reactive intermediates of clozapine, a drug-causing idiosyncratic drug reactions (IDRs), has not been studied. In the present study, we studied the ability of four recombinant human GSTs (hGST A1-1, hGST M1-1, hGST P1-1, and hGST T1-1) to catalyze the GSH conjugation of reactive metabolites of clozapine, formed in vitro by human and rat liver microsomes and drug-metabolizing P450 BM3 mutant, P450 102A1M11H. Consistent with previous studies, in the absence of GSTs, three GSH conjugates were identified derived from the nitrenium ion of clozapine. In the presence of three of the GSTs, hGST P1-1, hGST M1-1, and hGST A1-1, total GSH conjugation was strongly increased in all bioactivation systems tested. The highest activity was observed with hGST P1-1, whereas hGST M1-1 and hGST A1-1 showed slightly lower activity. Polymorphic hGST T1-1 did not show any activity in catalyzing GSH conjugation of reactive clozapine metabolites. Interestingly, the addition of hGSTs resulted in major changes in the regioselectivity of GSH conjugation of the reactive clozapine metabolite, possibly due to the different active site geometries of hGSTs. Two GSH conjugates found were completely dependent on the presence of hGSTs. Chlorine substitution of the clozapine nitrenium ion, which so far was only observed in in vivo studies, appeared to be the major pathway of hGST P1-1-catalyzed GSH conjugation, whereas hGST A1-1 and hGST M1-1 also showed significant activity. The second GSH conjugate, previously also only found in in vivo studies, was also formed by hGST P1-1 and to a small extent by hGST A1-1. These results demonstrate that human GSTs may play a significant role in the inactivation of reactive intermediates of clozapine. Therefore, further studies are required to investigate whether genetic polymorphisms of hGST P1-1 and hGST M1-1 contribute to the interindividual differences in susceptibility to clozapine-induced adverse drug reactions.

Development of a validated liquid chromatographic method for the determination of related substances and assay of tenofovir disoproxil fumarate.

The present study describes the development and validation of a selective liquid chromatographic (LC) method for the analysis of tenofovir disoproxil fumarate (TDF) and its related substances. The gradient method uses a base deactivated C18 column (Hypersil BDS column; 25 cmx4.6 mm I.D.) maintained at a temperature of 30 degrees C. The mobile phases consist of acetonitrile, tetrabutylammonium/phosphate buffer pH 6.0 and water: (A; 2:20:78 v/v/v) and (B; 65:20:15 v/v/v). The flow rate is 1.0 mL/min and UV detection is performed at 260 nm. Good separation of TDF and 21 impurities was achieved. A system suitability test (SST) to check the quality of separation is also specified. The developed method was further validated with respect to robustness, precision, sensitivity and linearity. The method is proved to be robust, precise, sensitive and linear between 0.1 microg/mL and 0.15 mg/mL. The limit of detection and limit of quantification are 0.03 and 0.1 microg/mL, respectively. The method was successfully applied to the quantification of related substances and assay of commercial TDF samples (bulk substances and tablets).

Evaluation of two approaches to characterise liquid chromatographic columns using pharmaceutical separations.

In this paper a comparison of two column characterisation systems is reported: the method based on the hydrophobic-subtraction model of Dolan and Snyder (HS method) versus the method developed at the Katholieke Universiteit Leuven (KUL method). Comparison was done for seven different pharmaceutical separations (fluoxetine, gemcitabine, erythromycin, tetracycline, tetracaine, amlodipine and bisacodyl), using a set of 59 columns. A ranking was built based on an F value (KUL) or F(s) value (HS) versus a (virtual) reference column. Both methods showed similar probabilities of ranking patterns. Correlation of the respective test parameters of both approaches was poor. Both methods are not perfect and do not match well, but anyhow yield results which allow, with a relatively high certainty, the selection of similar or dissimilar columns as compared to a reference column. An analyst that uses either of the two methods will end up with a similar probability to choose an adequate column. From a practical point of view, it must be noted that the KUL method is easier to use.

Silica-based monolithic columns versus conventional particle-packed columns for liquid chromatographic analysis of tetracycline, oxytetracycline and chlortetracycline.

The rise of monolithic stationary phases offers to routine and research laboratories several advantages. In spite of their recent discovery, they have rapidly become highly popular separation media for liquid chromatography. Time reduction and economic reasons like e.g. a diminished use of mobile phase are the most important ones. At the same time, it was reported that these columns offer a faster and better separation. The aim of this article was to investigate the transferability of methods originally developed on conventional particle-packed C(18) columns (XTerra RP18 and Zorbax RX), onto the more recent monolithic columns. Both types, conventional particle-packed and monolithic columns, were able to separate tetracycline, oxytetracycline and chlortetracycline from their respective impurities with sufficient resolution, but showed remarkably shorter analysis times and lower backpressures, improving the lifetime of the column.

Effect of long-term storage and use on the properties of reversed-phase liquid chromatographic columns.

In order to study column deterioration as a result of long-term storage and/or usage in liquid chromatography analyses, 55 pairs (same batch) of different commercial reversed-phase C(18) columns were examined using an already existing column characterisation system. After initial testing, one column was stored and the other was used to analyse different pharmaceuticals. All columns were characterized by four chromatographic parameters reflecting hydrophobicity, silanol activity, metal impurity and steric selectivity at the beginning and at the end of the test. An F-value was calculated to express the change of column properties with one single number. After performing analyses, higher F-values were obtained as compared to the non-used, stored columns. Although the time during which the columns were used to perform analyses was relatively short, an obvious influence was noticed, mainly resulting from small changes in silanol activity and hydrophobicity. Most of the affected columns have no endcapping and/or no base deactivation, making them more vulnerable for degradation, resulting in higher silanol activity and faster ageing. This effect is observed less with columns equipped with polar-embedded groups and/or polar endcapping, protecting the column by blocking the silanol groups and attracting a shielding water layer. Also columns with higher coverages and bulky or long chains show more resistance towards degradation.

Development of a liquid chromatographic method for the determination of related substances and assay of d-cycloserine.

d-cycloserine or d-4-amino-3-isoxazolidinone is an antibiotic produced by Streptomyces garyphalus and Streptomyces orchidaceus. d-Cycloserine is used in the second line treatment of tuberculosis and is often used in developing countries. Therefore, expensive high-tech techniques are not recommended for analysis. Here, a liquid chromatography method with ultraviolet detection (LC-UV) is described using a base deactivated column (Hypersil BDS column; 25 cm x 4.6 mm I.D.) kept at 45 degrees C. The gradient method uses mobile phases containing acetonitrile (ACN), 20mM sodium octane sulphonate (SOS), 0.2M potassium dihydrogen phosphate buffer pH 2.8, water: A: (4:70:10:16v/v/v/v) and B: (17:70:10:3v/v/v/v). The method proved to be robust, linear, repeatable, sensitive, selective and easy to perform. For the related substances test 50 microl of a 0.5 mg/ml d-cycloserine solution is injected. For assay, a concentration of 0.1 mg/ml is proposed to avoid overloading of the detector.