Quantitative determination of pravastatin and R-416, its main metabolite in human plasma, by liquid chromatography-tandem mass spectrometry

A quantitative method was developed and validated for rapid and sensitive analysis of pravastatin and R-416, the main metabolite of pravastatin, in human plasma. The analytes were extracted from plasma samples by a solid phase extraction method using a Bond Elut C(8). The method involved the use of liquid chromatography coupled with atmospheric pressure chemical ionization (APCI) and selected reaction monitoring (SRM) mass spectrometry. A pravastatin analog, R-122798, was used as the internal standard (I.S.). Separation of pravastatin, R-416 and the I.S. was accomplished using a reverse-phase column (C(18)). The components eluted were ionized by the APCI source (negative ion) and subsequently detected by a highly selective triple quadrupole mass spectrometer in the SRM mode. Linear standard curves were obtained from 0.1 ng/mL (lower limit of quantification, LLOQ) to 100 ng/mL. The intra-assay precisions (coefficient of variation) for the samples at the LLOQ were 1.8% for pravastatin and 1.6% for R-416. The intra-assay accuracy values were 95.8-107.6% for pravastatin, and 92.6-109.0% for R-416, respectively. Precision and accuracy of quality control (QC) samples were determined at concentrations of 0.5, 10 and 80 ng/mL for all analytes. The intra- and inter-assay precision calculated from QC samples were within 10% for pravastatin and within 11% for R-416. The overall recoveries for pravastatin and R-416 were 75.7-82.1% and 68.6-74.3%, respectively. Pravastatin and R-416 were stable in human plasma for 3 weeks at -20 degrees C in a freezer, up to 6h at room temperature, and up to 48 h at 6 degrees C. This assay method was successfully used to evaluate the pravastatin and R-416 levels in healthy volunteers following oral administration of Mevalotin.     

Existence of two alternative pathways for fructose and sorbitol metabolism in Bacillus subtilis Marburg.

Strains of Bacillus subtilis mutated for fructose phosphotransferase system (fruA), fructose-1-phosphate kinase (fruB), fructokinase (frucC) have been tested for their catabolism of sorbitol and fructose. It is shown that the previously known pathways of sorbitol and fructose degradation in B. subtilis, e.g.: (see article) may metabolize intracellular fructose produced either by sorbitol oxidation or by fructose-1-phosphate dephosphorylation. The intracellular fructore degradation via fructose-1-phosphate kinase has been found to require the fructose phosphotransferase system which ensures a vectorial transport of fructose.     

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of hydroxysafflor yellow A in human plasma: application to a pharmacokinetic study

A sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the determination of hydroxysafflor yellow A (HSYA) in human plasma. HSYA was extracted from human plasma by using solid-phase extraction technique. Puerarin was used as the internal standard. A Shim-pack VP-ODS C(18) (150mm x 4.6mm, 5 microm) column and isocratic elution system composing of methanol and 5mM ammonium acetate (80:20, v/v) provided chromatographic separation of analytes followed by detection with mass spectrometry. The mass transition ion-pair was followed as m/z 611.19-->491.19 for HSYA and m/z 415.19-->295.10 for puerarin. The proposed method has been validated with a linear range of 1-1000 ng/ml for HSYA with a correlation coefficient >/=0.999. The lower limit of quantitation was 1 ng/ml. The intra-batch and inter-batch precision and accuracy were within 10%. The average extraction recovery was 81.7%. The total run time was 5.5 min. The validated method was successfully applied to the study on pharmacokinetics of HSYA in 12 healthy volunteers after a single oral administration of safflower oral solution containing 140 mg of HSYA.     

Miniaturized hollow fiber assisted liquid-phase microextraction with in situ derivatization and gas chromatography-mass spectrometry for analysis of bisphenol A in human urine sample

A new method that involves miniaturized hollow fiber assisted liquid-phase microextraction (HF-LPME) with in situ derivatization and gas chromatography-mass spectrometry (GC-MS) is described for the determination of trace amounts of bisphenol A (BPA) in human urine samples. The detection limit and the quantification limit of BPA in human urine sample are 0.02 and 0.1 ng ml(-1) (ppb), respectively. The calibration curve for BPA is linear with a correlation coefficient of >0.999 in the range of 0.1-50 ng ml(-1). The average recoveries of BPA in human urine samples spiked with 1 and 5 ng ml(-1) BPA are 101.0 (R.S.D.: 6.7%) and 98.8 (R.S.D.: 1.8%), respectively, with correction using the added surrogate standard, bisphenol A-(13)C12. This simple, accurate, sensitive and selective analytical method can be applicable to the determination of trace amounts of BPA in human urine samples.     

Development and validation of a liquid chromatography-mass spectrometry assay for the determination of pyronaridine in human urine

A reliable method has been developed for the determination of pyronaridine in human urine using amodiaquine as an internal standard. Liquid-liquid extraction was used for sample preparation. Analysis was performed on a Shimadzu LCMS-2010 in single ion monitoring positive mode using atmospheric pressure chemical ionization (APCI) as an interface. The extracted ion for pyronaridine was m/z 518.20 and for amodiaquine was m/z 356.10. Chromatography was carried out using a Gemini 5 microm C18 3.0 mmx150 mm column using 2 mM perflurooctanoic acid and acetonitrile mixture as a mobile phase delivered at a flow rate of 0.5 mL/min. The mobile phase was delivered in gradient mode. The retention times of pyronaridine and amodiaquine were 9.1 and 8.1 min respectively, with a total run time of 14 min. The assay was linear over a range of 14.3-1425 ng/mL for pyronaridine (R2>or=0.992, weighted 1/Concentration). The analysis of quality control samples for pyronaridine at 28.5, 285, 684 and 1140 ng/mL demonstrated excellent precision with relative standard deviation of 5.1, 2.3, 3.9 and 9.2%, respectively (n=5). Recoveries at concentrations of 28.5, 285, 684 and 1140 ng/mL were all greater than 85%.This LC-MS method for the determination of pyronaridine in human urine has excellent specifications for sensitivity, reproducibility and accuracy and can reliably quantitate concentrations of pyronaridine in urine as low as 14.3 ng/mL. The method will be used to quantify pyronaridine in human urine for pharmacokinetic and drug safety studies.     

Fructose Levels Are Markedly Elevated in Cerebrospinal Fluid Compared to Plasma in Pregnant Women

Background

Fructose, unlike glucose, promotes feeding behavior in rodents and its ingestion exerts differential effects in the human brain. However, plasma fructose is typically 1/1000th of glucose levels and it is unclear to what extent fructose crosses the blood-brain barrier. We investigated whether local endogenous central nervous system (CNS) fructose production from glucose via the polyol pathway (glucose→sorbitol→fructose) contributes to brain exposure to fructose.

Methods

In this observational study, fasting glucose, sorbitol and fructose concentrations were measured using gas-chromatography-liquid mass spectroscopy in cerebrospinal fluid (CSF), maternal plasma, and venous cord blood collected from 25 pregnant women (6 lean, 10 overweight/obese, and 9 T2DM/gestational DM) undergoing spinal anesthesia and elective cesarean section.

Results

As expected, CSF glucose was ~60% of plasma glucose levels. In contrast, fructose was nearly 20-fold higher in CSF than in plasma (p < 0.001), and CSF sorbitol was ~9-times higher than plasma levels (p < 0.001). Moreover, CSF fructose correlated positively with CSF glucose (ρ 0.45, p = 0.02) and sorbitol levels (ρ 0.75, p < 0.001). Cord blood sorbitol was also ~7-fold higher than maternal plasma sorbitol levels (p = 0.001). There were no differences in plasma, CSF, and cord blood glucose, fructose, or sorbitol levels between groups.

Conclusions

These data raise the possibility that fructose may be produced endogenously in the human brain and that the effects of fructose in the human brain and placenta may extend beyond its dietary consumption.     

Simultaneous determination of cefdinir and cefixime in human plasma by RP-HPLC/UV detection method: Method development, optimization, validation, and its application to a pharmacokinetic study

A novel isocratic reversed-phase high performance liquid-chromatography/ultraviolet detection method for simultaneous determination of cefdinir and cefixime in human plasma was developed and validated after optimization of various chromatographic conditions and other experimental parameters. Sample preparation based on a simple extraction procedure consisting of deproteination and extraction with 3 parts of 6% trichloroacetic acid aqueous solution followed by volume make up with the aqueous component of the mobile phase obtained best recoveries of the two analytes. Samples were separated on a Supelco Discovery HS C(18) (150 mm × 4.6 mm, 5 μm) analytical column protected by a Perkin Elmer C(18) (30 mm × 4.6 mm, 10 μm) guard cartridge. The mobile phase, methanol/acetonitrile (50/50, v/v):0.05% trifluoroacetic acid (19:81, v/v), operated at 50°C column oven temperature was pumped at a flow rate of 2.0 mL min(-1) and the column eluents were monitored at a wavelength of 285 nm. When Sample was injected into the Perkin Elmer high performance liquid-chromatography system through Rheodyne manual (or auto-sampler) injector equipped with 20 μL loop, separation was achieved within 4 min. The present method demonstrated acceptable values for selectivity, linearity within the expected concentration range (0.004-5.0 μg mL(-1); r(2)>0.999 for both analytes), recovery (>95% for cefdinir and >96% for cefixime), precision (%RSD<2.0 for cefdinir and <2.2 for cefixime), sensitivity (limit of detection: 1 ng mL(-1) and lower limit of quantification: 4 ng mL(-1) for both analytes), stability of solutions, and robustness. The method was efficiently applied to a pharmacokinetic study in healthy volunteers.     

Quantification of sunitinib in human plasma by high-performance liquid chromatography-tandem mass spectrometry

A rapid, sensitive and specific method was developed and validated using LC/MS/MS for determination of sunitinib in human plasma. Sample preparation involved a liquid-liquid extraction by the addition of 0.2mL of plasma with 4.0mL tert-butyl-methyl-ether extraction solution containing 25ng/mL of the internal standard clozapine. Separation of compounds was achieved on a C18 (50mmx2.1mm i.d., 3.5microm) analytical column using a mobile phase consisting of acetonitrile/H20 (65:35, v/v) containing 0.1% formic acid and isocratic flow at 0.150mL/min for 3min. The analytes were monitored by tandem-mass spectrometry with electrospray positive ionization. Linear calibration curves in human plasma were generated over the range of 0.2-500ng/mL with values for the coefficient of determination of >0.9950. Within- and between day precision and accuracy were < or =10%. The method was applied to the quantitation of sunitinib in plasma samples from a patient receiving daily oral therapy with sunitinib.     

Simultaneous liquid chromatographic determination of doxorubicin and its major metabolite doxorubicinol in parrot plasma

A new microscale method is reported for the determination of doxorubicin and its active metabolite, doxorubicinol, in parrot plasma. Sample workup involved acetonitrile protein precipitation, ethyl acetate extraction, followed by back extraction into HCl. Separations were achieved on a phenyl-hexyl column at 30 degrees C using acetonitrile (17%, v/v) in 0.01 M orthophosphoric acid (83%, v/v) delivered via a linear flow program. Fluorometric detection wavelengths were 235 nm (excitation) and 550 nm (emission). Calibration plots were linear (r2>0.999), and recoveries were 71-87% from 20 to 400 ng/mL. Assay imprecision was 相似文献   

Simultaneous determination of urinary cortisol, cortisone and corticosterone in parachutists, depressed patients and healthy controls in view of biomedical and pharmacokinetic studies

A rapid and sensitive reversed-phase liquid chromatographic method (RP-LC) with UV detection has been developed for the determination of free cortisol, cortisone and corticosterone in human urine. The assay was performed after a solid-phase extraction procedure (SPE) with dexamethasone as the internal standard. Chromatographic separation was carried out on a Nucleosil 100 C(18) analytical column using a mixture of acetonitrile and water (30 : 70, v/v) as a mobile phase at a flow-rate of 1 mL min(-1). Spectrophotometric detection was performed at 240 nm. The method has been validated for accuracy, precision, selectivity, linearity, recovery and stability. The absolute recoveries of glucocorticoids were above 94.6%. The limits of detection (LOD) and quantification (LOQ) were 0.5 and 2 ng mL(-1), respectively, for all analytes. Linearity was confirmed in the range of 2-300 ng mL(-1) with a correlation coefficient greater than 0.9997 for all steroid hormones. The proposed method was sensitive, robust and specific allowing reliable quantification of steroid hormones. This method was successfully applied for determination of three endogenous glucocorticoid levels in human urine. The studies were performed on 20 sedentary healthy volunteers in comparison to two socially diversified groups, namely 10 parachutists before and after jump and 10 patients with depression. Pharmacokinetic studies performed on these groups indicated that urinary free cortisol and cortisol-to-cortisone ratios can be treated as biomarkers of stress and depressive disorders.     

Determination of talinolol in human plasma using automated on-line solid phase extraction combined with atmospheric pressure chemical ionization tandem mass spectrometry

A specific LC-MS/MS assay was developed for the automated determination of talinolol in human plasma, using on-line solid phase extraction system (prospekt 2) combined with atmospheric pressure chemical ionization (APCI) tandem mass spectrometry. The method involved simple precipitation of plasma proteins with perchloric acid (contained propranolol) as the internal standard (IS) and injection of the supernatant onto a C8 End Capped (10 mmx2 mm) cartridge without any evaporation step. Using the back-flush mode, the analytes were transferred onto an analytical column (XTerra C18, 50 mmx4.6 mm) for chromatographic separation and mass spectrometry detection. One of the particularities of the assay is that the SPE cartridge is used as a column switching device and not as an SPE cartridge. Therefore, the same SPE cartridge could be used more than 28 times, significantly reducing the analysis cost. APCI ionization was selected to overcome any potential matrix suppression effects because the analyte and IS co-eluted. The mean precision and accuracy in the concentration range 2.5-200 ng/mL was found to be 103% and 7.4%, respectively. The data was assessed from QC samples during the validation phase of the assay. The lower limit of quantification was 2.5 ng/mL, using a 250 microL plasma aliquot. The LC-MS/MS method provided the requisite selectivity, sensitivity, robustness accuracy and precision to assess pharmacokinetics of the compound in several hundred human plasma samples.     

Screening procedure for the analysis of distigmine bromide in serum by high-performance liquid chromatography-electrospray ionization mass spectrometry

A screening procedure was developed for the identification and quantification of distigmine bromide in serum samples by using liquid chromatography (LC)-electrospray ionization (ESI)-mass spectrometry (MS). In this method, distigmine bromide was analyzed in 0.5 mL serum by using pancuronium bromide as the internal standard, and gradient elution was performed using a reversed-phase column and a mixture of 10 mM-ammonium formate and methanol as the mobile phase. A highly sensitive assay could be performed with simple solid phase extraction using a cation exchange cartridge column by carrying out selected ion monitoring analysis in the positive ion detection mode. The procedure was validated in terms of linearity (0.9973 at 2.5 ng/mL). The inter- and intra-day precisions (coefficient of variation; CV%) were <8.5% and < 9.7%, respectively. The analytes were evaluated for stability and were found to be stable in serum for 1 week at 4 degrees C and 4 weeks at -30 degrees C, and successfully applied to in the analysis of two overdose cases. This method is sensitive and useful for the detection, quantification, and confirmation of distigmine bromide in serum.     

Improvement and validation the method using dispersive liquid-liquid microextraction with in situ derivatization followed by gas chromatography-mass spectrometry for determination of tricyclic antidepressants in human urine samples

A simple, rapid and sensitive method termed dispersive liquid-liquid microextraction (DLLME) combined with gas chromatography-mass spectrometry (GC/MS) was developed for the determination of tricyclic antidepressants (TCAs) in human urine sample. An appropriate mixture of methanol (disperser solvent), carbon tetrachloride (extraction solvent), and acetic anhydride (derivatization reagent) was injected rapidly into human urine sample. After extraction, the sedimented phase was analyzed by GC/MS. The calibration curves obtained with human urine were linear with a correlation coefficient of over 0.99 in the range of 2.0/5.0-100 ng mL(-1). Under the optimum conditions (carbon tetrachloride: 10 μL, methanol: 150 μL), the detection limits and the quantification limits of the tricyclic antidepressants were 0.5-2.0 ng mL(-1) and 2.0-5.0 ng mL(-1), respectively. The average recoveries of TCAs were 88.2-104.3%. Moreover, the inter- and intra-day precision and accuracy was acceptable at all concentrations. The results showed that DLLME is applicable to the determination of trace amounts of TCAs in human urine sample.     

Development and validation of an LC-MS method with electrospray ionization for quantitation of digoxin in human plasma and urine: application to a pharmacokinetic study

A highly sensitive and specific LC-MS method was developed and validated for the quantification of digoxin in human plasma and urine using d5-dihydrodigoxin as internal standard (IS). The assay procedure involved extraction of digoxin and IS from human plasma with chloroform-isopropanol (95:5, v/v). Chromatogrphic separation was achieved on a Spherisorb ODS2 column using a gradient mobile phase with 5 mmol/L ammonium acetate in water with 1% acetic acid and acetonitrile. The mass spectrometer was operated in the selected ion monitoring mode using the respective [M+K](+) ions, m/z 819.4 for digoxin and m/z 826.4 for IS. The method was proved to be accurate and precise at linearity range of 0.12-19.60 ng/mL in plasma with a correlation coefficient (r(2)) of >or=0.9968 and 1.2-196.0 ng/mL in urine. The limit of quantification achieved with this method was 0.12 ng/mL in plasma and 1.2 ng/mL in urine. The intra- and inter-assay precision and accuracy values were found to be within the assay variability limits as per the FDA guidelines. The developed assay method was successfully applied to a pharmacokinetic study in human volunteers following intravenous administration of digoxin.     

Development of a high-performance liquid chromatography-based assay for carotenoids in human red blood cells: application to clinical studies

Peroxidized phospholipid-mediated cytotoxicity is involved in the pathophysiology of many diseases; for example, there is an abnormal increase of phospholipid hydroperoxides in red blood cells (RBCs) of dementia patients. Dietary carotenoids have gained attention as potent inhibitors of RBC phospholipid hydroperoxidation, thereby making them plausible candidates for preventing disease. However, the occurrence of carotenoids in human RBCs is still unclear. This is in contradistinction to plasma carotenoids, which have been investigated thoroughly for analytical methods as well as biological significance. In this study, we developed a method to analyze RBC carotenoids using high-performance liquid chromatography (HPLC) coupled with ultraviolet (UV) diode array detection (DAD) and atmospheric pressure chemical ionization (APCI) mass spectrometry (MS). Under optimized conditions that included extraction, separation, and detection procedures, six carotenoids (lutein, zeaxanthin, β-cryptoxanthin, α-carotene, β-carotene, and lycopene) were separated, detected by DAD, and concurrently identified based on APCI/MS and UV spectra profiles when an extract from human RBCs was subjected to HPLC-DAD-APCI/MS. The amounts of carotenoids varied markedly (1.3-70.2 nmol/L packed cells), and polar oxygenated carotenoids (xanthophylls) were predominant in RBCs. The HPLC-DAD-APCI/MS method would be a useful tool for clinical studies for evaluating the bioavailability of RBC carotenoids.     

Affinity extraction combined with stable isotope dilution LC/MS for the determination of 5-methyltetrahydrofolate in human plasma

The predominant circulating folate monoglutamate in human plasma (>90%), and thus the most significant folate for accurately diagnosing folate deficiency, is 5-methyltetrahydrofolic acid (5 MT). Folate deficiency is typically indicated when circulating folate levels are < or = 3 ng/mL. The quantitative determination of plasma folates in general, and of 5 MT in particular, is complicated by their naturally low levels (pg/mL to ng/mL), their instability, and their tendency to interconvert. Highly specific and sensitive analytical methods are needed to accurately quantify endogenous 5 MT in human plasma. A method that utilizes the specific high-affinity binding sites of bovine folate binding protein (FBP) and the selectivity and sensitivity of selected ion monitoring mode isotope-dilution liquid chromatography/mass spectrometry (LC/MS) to quantify plasma 5 MT has been developed. The method is based on the solid-phase affinity extraction (SPAE) of 5 MT and its stable isotopically labeled analogue ([13C(5)]5 MT) from plasma (1 mL) using FBP immobilized to polymeric beads. The excess high-affinity binding sites on the affinity columns enable quantitative extraction of 5 MT from plasma under optimized sample pH conditions. Additionally, it is demonstrated that plasma proteins do not hinder the determination of 5 MT; therefore, protein precipitation is not required before the affinity extraction step. Detection and quantification of the extracted 5 MT is provided by positive-ion mode LC/MS in which the protonated molecular ions [M+H](+) of the analyte and the internal standard are monitored. The method shows linearity over three orders of magnitude (0.04-40 ng/mL) and has limits of detection and quantification of 0.04 and 0.4 ng/mL, respectively. Calibration curves obtained by spiking 5 MT into plasma exhibited good linearity between 0 and 25 ng/mL and both the plasma calibration standards and the plasma samples were stable for at least 48 h at room temperature. The recovery (average +/- % RSD) of 5 MT spiked into plasma from 5 to 25 ng/mL was 98.0% +/- 1.6% (n = 15). 5 MT levels determined by SPAE-LC/MS compared to "total folate" levels determined by radioassay and microbiological assay were discordant. Reasons for the discordancy are theorized, but it is clear that there exists an urgent need for clinical reference materials containing certified folate levels.     

Simultaneous determination of lansoprazole enantiomers and their metabolites in plasma by liquid chromatography with solid-phase extraction

A simple and highly sensitive high-performance liquid chromatography (HPLC) method for the simultaneous quantitative determination of lansoprazole enantiomers and their metabolites, 5-hydroxylansoprazole enantiomers and lansoprazole sulfone, in human plasma have been developed. Chromatographic separation was achieved with a Chiral CD-Ph column using a mobile phase of 0.5M NaClO(4)-acetonitrile-methanol (6:3:1 (v/v/v)). The analysis required only 100 microl of plasma and involved a solid-phase extraction with Oasis HLB cartridge, with a high extraction recovery (>94.1%) and good selectivity. The lower limit of quantification (LOQ) of this assay was 10 ng/ml for each enantiomer of both lansoprazole and 5-hydroxylansoprazole, and 5 ng/ml for lansoprazole sulfone. The coefficient of variation of inter- and intra-day assay was <8.0% and accuracy was within 8.4% for all analytes (concentration range 10-1000 ng/ml). The linearity of this assay was set between 10 and 1000 ng/ml (r2>0.999 of the regression line) for each of the five analytes. This method is applicable for accurate and simultaneous monitoring of the plasma levels of lansoprazole enantiomers and their metabolites in the renal transplant recipients.     

Rapid determination of loratadine in small volume plasma samples by high-performance liquid chromatography with fluorescence detection

A simple and rapid high-performance liquid chromatographic method with fluorescence detection was developed for the determination of loratadine in small volume plasma samples. Liquid-liquid extraction of loratadine and diazepam (as internal standard) from plasma samples was performed with n-butyl alcohol/n-hexane (2:98, v/v) in alkaline condition followed by back-extraction into diluted perchloric acid. Chromatography was carried out using a C8 column (250 x 4.6 mm, 5 microm) under isocratic elution with acetonitrile-20 mM sodium dihydrogen phosphate-triethylamine (43:57:0.02, v/v), pH 2.4. Analyses were run at a flow-rate of 1.0 ml/min at room temperature. The method was specific and sensitive with a quantitation limit of 0.62 ng/ml and a detection limit of 0.2 ng/ml at a signal-to-noise ratio of 3:1. The mean absolute recovery of loratadine from plasma was 84%, while the intra-and inter-day coefficient of variation and percent error values of the assay method were all less than 9.7%. Linearity was assessed in the range of 0.62-20 ng/ml in plasma with a correlation coefficient of greater than 0.999. The method has been used to analyze several hundred human plasma samples for bioavailability studies.     

Metabolic fluxes in Corynebacterium glutamicum during lysine production with sucrose as carbon source

Metabolic fluxes in the central metabolism were determined for lysine-producing Corynebacterium glutamicum ATCC 21526 with sucrose as a carbon source, providing an insight into molasses-based industrial production processes with this organism. For this purpose, 13C metabolic flux analysis with parallel studies on [1-(13C)Fru]sucrose, [1-(13C)Glc]sucrose, and [13C6Fru]sucrose was carried out. C. glutamicum directed 27.4% of sucrose toward extracellular lysine. The strain exhibited a relatively high flux of 55.7% (normalized to an uptake flux of hexose units of 100%) through the pentose phosphate pathway (PPP). The glucose monomer of sucrose was completely channeled into the PPP. After transient efflux, the fructose residue was mainly taken up by the fructose-specific phosphotransferase system (PTS) and entered glycolysis at the level of fructose-1,6-bisphosphate. Glucose-6-phosphate isomerase operated in the gluconeogenetic direction from fructose-6-phosphate to glucose-6-phosphate and supplied additional carbon (7.2%) from the fructose part of the substrate toward the PPP. This involved supply of fructose-6-phosphate from the fructose part of sucrose either by PTS(Man) or by fructose-1,6-bisphosphatase. C. glutamicum further exhibited a high tricarboxylic acid (TCA) cycle flux of 78.2%. Isocitrate dehydrogenase therefore significantly contributed to the total NADPH supply of 190%. The demands for lysine (110%) and anabolism (32%) were lower than the supply, resulting in an apparent NADPH excess. The high TCA cycle flux and the significant secretion of dihydroxyacetone and glycerol display interesting targets to be approached by genetic engineers for optimization of the strain investigated.     

Rapid and sensitive determination of sertraline in human plasma using gas chromatography-mass spectrometry

A method for the determination of sertraline in human plasma using gas chromatography-mass spectrometry (GC-MS), with the selected ion-monitoring (SIM) mode, was described. The following was used in this study: (1) single liquid-liquid extraction at alkaline pH after deproteinization of plasma protein and (2) perfluoroacylation with HFBA, which has higher sensitivity (about 10-fold) compared with previous reported derivatization. The detection limit for the SIM of sertraline as an N-HFB derivative was 0.1 ng/ml, and its recovery was 80-85%. The linear response was obtained in the range of 0.2-10.0 ng/ml with a correlation coefficient of 0.999. The coefficient of variation (C.V.%) was less than 12.1% in the 1-30 ng/ml, and less than 18.2% at 0.2 ng/ml, and the accuracy was less than 10% at all of the concentration range. These findings indicate that this assay method has adequate precision and accuracy to determine the amount of sertraline in human plasma. After pharmacokinetics was performed with this assay method following oral administration of sertraline hydrochloride in man, moment analysis revealed that pharmacokinetic parameters for sertraline (Cmax, 10.3 ng/ml; Tmax, 8.0 h; T(1/2) 28.6 h) were similar to previously reported results. These results indicate that this simple and sensitive assay method is readily applicable to the pharmacokinetic studies of sertraline.