J Sastre Toraño

Academisch Medisch Centrum Universiteit van Amsterdam, Amsterdamo, North Holland, Netherlands

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Publications (11)24 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A specific, accurate and precise high-performance liquid chromatographic assay was developed for the determination of riluzole, a drug used to treat patients with amyotrophic lateral sclerosis. Samples were treated by extraction with dichloromethane followed by reversed-phase chromatography with ultraviolet detection at 260 nm. Preset validation criteria were met from 20 to 2000 ng/mL with a linear response curve. Extraction recovery of riluzole was 65-76%. The accuracy of the method was 102-103%. Intra- and inter-day coefficients of variation were in the ranges 2.8-4.9% and 1.8-9.7%. A detection limit of 5 ng/mL was found. Determination of concentrations in serum and plasma resulted in similar results below 500 ng/mL. At higher values a matrix effect cannot be excluded. This presented method can be used to monitor plasma or serum levels in ALS patients treated with riluzole.
    Biomedical Chromatography 12/2004; 18(9):723-6. · 1.95 Impact Factor
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    ABSTRACT: A disturbed sleep-wake rhythm is common in Alzheimer disease (AD) patients and correlated with decreased melatonin levels and a disrupted circadian melatonin rhythm. Melatonin levels in the cerebrospinal fluid are decreased during the progression of AD neuropathology (as determined by the Braak stages), already in cognitively intact subjects with the earliest AD neuropathology (Braak stages I-II) (preclinical AD). To investigate the molecular mechanisms behind the decreased melatonin levels, we measured monoamines and mRNA levels of enzymes of the melatonin synthesis and its noradrenergic regulation in pineal glands from 18 controls, 33 preclinical AD subjects, and 25 definite AD patients. Pineal melatonin levels were highly correlated with cerebrospinal fluid melatonin levels. The circadian melatonin rhythm disappeared because of decreased nocturnal melatonin levels in both the preclinical AD and AD patients. Also the circadian rhythm of beta(1)-adrenergic receptor mRNA disappeared in both patient groups. The precursor of melatonin, serotonin was stepwise depleted during the course of AD, as indicated by the up-regulated monoamine oxidase A mRNA and activity (5-hydroxyindoleacetic acid:serotonin ratio). We conclude that a dysfunction of noradrenergic regulation and the depletion of serotonin by increased monoamine oxidase A result in the loss of melatonin rhythm already in preclinical AD.
    Journal of Clinical Endocrinology &amp Metabolism 01/2004; 88(12):5898-906. · 6.43 Impact Factor
  • Javier Sastre Toraño, Hendrikus J M van Kan
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    ABSTRACT: A method using gas chromatography (GC)-mass spectrometry (MS) for the simultaneous determination of the smoke uptake parameters thiocyanate, nicotine and cotinine in human tissues is reported. Nicotine, cotinine and thiocyanate, in combination with a phase-transfer catalyst, were extracted from urine, saliva and hair into dichloromethane (DCM). Thiocyanate was alkylated in the DCM-layer to form a pentafluorobenzyl derivative. The biochemical markers in DCM were directly injected into the GC system and separated on a DB-1MS column using a 9.4 min temperature program. The method was validated in urine and saliva between the limits of quantitation (1.0-15 microg ml(-1) thiocyanate, 0.010-3.0 microg ml(-1) nicotine and cotinine in urine, 0.010-1.0 microg ml(-1) nicotine and cotinine in saliva). The calibration curves were found to be linear (r > 0.996), the within- and between-day accuracy's were 83-120%, the repeatability coefficients of variation were 3-20% and the limits of detection were 0.060 ng ml(-1) thiocyanate and 0.60 ng ml(-1) nicotine and cotinine. The results of the analysis of the biomarkers in the urine of 44 volunteers were used to develop a predictive model for smoking status, using discriminant analysis. The classification model correctly classified 93.2% of cross-validated grouped cases. Saliva samples were used to confirm the results of the classification method.
    The Analyst 07/2003; 128(7):838-43. · 3.97 Impact Factor
  • S Kwadijk, J Sastre Toraño
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    ABSTRACT: A validated high-performance liquid chromatographic method with ultraviolet detection for the quantitative determination of dapsone (4,4'-diaminodifenyl sulfone, DDS) and a metabolite, hydroxylaminodapsone (4-amino-4-hydroxylaminodiphenyl sulfone, DDS-NOH), in human plasma is described. Human plasma was deproteinized with acetone and the clear supernatant solution after centrifugation was evaporated to dryness under a gentle stream of nitrogen at 70 degrees C. The residue was dissolved in a mixture of HPLC eluent and acetone (18:5 v/v) and an aliquot of this solution (50 microL) was injected onto the HPLC column. Dapsone, hydroxylaminodapsone and diazoxide as internal standard, were separated within 10 min by isocratic elution with water:acetonitrile:glacial acetic acid:triethylamine (80:20:1.0:0.5 by volume) as eluent. Detection was by ultraviolet at the wavelength of 295 nm. The within-day repeatability coefficients of variation were 3-5% for dapsone (0.301-20.0 mg/L, n = 5) and 3-5% for hydroxylaminodapsone (0.0948-6.32 mg/L, n = 5), whereas the between-day repeatability coefficients of variation were 3-8% (0.301-20.0 mg/L, n = 5) for dapsone and 4-10% for hydroxylaminodapsone (0.0948-6.32 mg/L, n = 5). The mean recoveries -were 92-107% (0.301-20.0 mg/L, n = 2), 80-82% (0.0948-6.32 mg/L, n = 2) and 88% (0.0200 mg/mL, n = 5), for dapsone, hydroxylaminodapsone and diazoxide, respectively. The average correlation coefficient of the calibration curve was 0.99988 (n = 5) for dapsone at a concentration range of 0.301-20.0 mg/L, whereas the average correlation coefficient of the hydroxylaminodapsone calibration curve was 0.99981 (n = 5) at a concentration range of 0.0948-6.32 mg/L. The limits of detection were 0.00200 and 0.0470 mg/L for dapsone and hydroxylaminodapsone, respectively. The method is suitable for drug level monitoring and for pharmacokinetic studies.
    Biomedical Chromatography 06/2002; 16(3):203-8. · 1.95 Impact Factor
  • British Journal of Clinical Pharmacology 01/2002; · 3.58 Impact Factor
  • J Sastre Toraño, S H van Hattum
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    ABSTRACT: A new method is presented for the quantitative analysis of compounds in pharmaceutical preparations Fourier transform (FT) mid-infrared (MIR) spectroscopy with an attenuated total reflection (ATR) module. Reduction of the quantity of overlapping absorption bands, by interaction of the compound of interest with an appropriate solvent, and the employment of an internal standard (IS), makes MIR suitable for quantitative analysis. Vigabatrin, as active compound in vigabatrin 100-mg capsules, was used as a model compound for the development of the method. Vigabatrin was extracted from the capsule content with water after addition of a sodium thiosulfate IS solution. The extract was concentrated by volume reduction and applied to the FTMIR-ATR module. Concentrations of unknown samples were calculated from the ratio of the vigabatrin band area (1321-1610 cm(-1)) and the IS band area (883-1215 cm(-1)) using a calibration standard. The ratio of the area of the vigabatrin peak to that of the IS was linear with the concentration in the range of interest (90-110 mg, in twofold; n=2). The accuracy of the method in this range was 99.7-100.5% (n=5) with a variability of 0.4-1.3% (n=5). The comparison of the presented method with an HPLC assay showed similar results; the analysis of five vigabatrin 100-mg capsules resulted in a mean concentration of 102 mg with a variation of 2% with both methods.
    Fresenius Journal of Analytical Chemistry 11/2001; 371(4):532-5.
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    ABSTRACT: All patients with amyotrophic lateral sclerosis (ALS) are treated with the same dose of riluzole: 50 mg twice daily. Reasonably large interindividual differences in clearance of the drug have been reported. The relatively small group of patients with high blood concentrations of riluzole has probably primarily influenced the efficacy and the incidence of side-effects in the previously conducted clinical trials with riluzole. Individual dosing of the drug may, in the case of large interindividual differences in serum concentrations of the drug, be necessary in the future. Exact data concerning the plasma and serum concentrations of riluzole in patients with ALS, after standardized intake of the drug, diet and blood sampling are unknown so far. In this study, inter- and intraindividual variability of serum and plasma levels of riluzole in 21 patients with "probable" or "definite" ALS were determined. The interindividual variability of peak serum levels (coefficient of variation=74%) was significantly larger than intraindividual variability (p<0.001). Serum levels were not correlated with age or smoking status. The determination of a correlation between riluzole serum concentrations and survival of patients with ALS will be the aim of further studies.
    Journal of the Neurological Sciences 11/2001; 191(1-2):121-5. · 2.24 Impact Factor
  • J S Toraño, A Vermes, H J Guchelaar
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    ABSTRACT: A validated, sensitive and precise reversed-phase high-performance liquid chromatographic method for the simultaneous determination of 5-flucytosine (5-FC) and 5-fluorouracil (5-FU) in human plasma is described. Two compounds, 5-methylcytosine (5-MC) and 5-chlorouracil (5-CU), were used as internal standards for the determination of 5-FC and 5-FU, respectively. Plasma samples were deproteinized with trichloroacetic acid and chromatographed on an octylsilica column, maintained at 30 degrees C during elution, using a 0.04 M phosphate buffer, pH 7.0, as eleunt. Spectrophotometric diode array detection was used at 266 nm. 5-FC, 5-FU, 5-MC and 5-CU were found to have retention times of 4.8, 5.8, 7.7 and 11.0 min respectively. Recoveries of 91-120% with reproducibility and repeatability coefficients of variation of 0.8-6% were obtained. Mean correlation coefficients of 0.99989 and 0.9995 were found for the linear calibration curves (n = 2) of 5-FC (4.816-192.6 mg/l) and 5-FU (0.05368-5.368 mg/l), respectively. The limits of quantitation were 0.3 mg/l for 5-FC and 0.05 mg/l for 5-FU.
    Biomedical Chromatography 05/2001; 15(2):89-94. · 1.95 Impact Factor
  • J Sastre Toraño, P v Rijn-Bikker, P Merkus, H J Guchelaar
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    ABSTRACT: A validated new and precise reversed-phase high-performance liquid chromatographic method for the determination of melatonin in human plasma and cerebrospinal fluid, with 5-fluorotryptamine as internal standard, is described. Liquid-liquid extraction with dichloromethane was performed under alkaline conditions. After evaporation of the organic solvent, the extract was dissolved in eluent and chromatographed on a base-deactivated octadecyl column, using an eluent composed of 650 mL potassium dihydrogenphosphate solution (0.07 mol/L water), adjusted to a pH of 3.0 with a 43% phosphoric acid solution, mixed with 350 mL methanol. Fluorescence detection at an excitation wavelength of 224 nm and an emission wavelength of 348 nm was used for quantitation. Melatonin and 5-fluorotryptamine chromatographed with retention times of 5.3 and 9. 3 min, respectively. Mean recoveries of 96% (n = 10) and 95% (n = 5) were found for melatonin in plasma and cerebrospinal fluid respectively. 5-Fluorotryptamine was found to have a mean recovery of 90% (n = 10) and 82% (n = 5) in plasma and cerebrospinal fluid, respectively. The repeatability coefficients of variation for both melatonin and 5-fluorotryptamine in plasma were 4-5% [five different samples (r = 5) on two consecutive days (n = 2)], with reproducibility coefficients of 1.6-7% (n = 2, r = 5) and 0.9-4% (n = 2, r = 5) for melatonin and internal standard, respectively. In cerebrospinal fluid the repeatability coefficient of variation of the extraction procedure was 5% (n = 1, r = 5) for melatonin and 7% (n = 1, r = 5) for 5-fluorotryptamine. The correlation coefficients of the calibration curves were 0.9998 (n = 2) in plasma at a concentration range of 0.108-25.9 ng/mL and 0.9994 (n = 2) at a concentration range of 0.108-25.9 ng/mL in cerebrospinal fluid. The limit of detection was determined at 8 pg/mL which enables to measure melatonin concentrations at physiological concentrations reached during daytime.
    Biomedical Chromatography 09/2000; 14(5):306-10. · 1.95 Impact Factor
  • J Sastre Toraño, H J Guchelaar
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    ABSTRACT: A validated, highly sensitive and precise high-performance liquid chromatographic (HPLC) method for the determination of the macrolides erythromycin, azithromycin, clarithromycin and roxithromycin in human serum is described. A diethyl ether extract, obtained from serum using a saturated sodium carbonate solution, was treated with 9-fluorenylmethyl-oxycarbonyl chloride (FMOC-Cl) for 40 min at 40 degrees C and chromatographed on a base-deactivated octadecyl column, maintained at 50 degrees C during elution, using an eluent composed of acetonitrile-hydrogenphosphate buffer, pH 7.5, with 0.125% triethylamine (3:2, v/v). Fluorescence detection was used at an excitation wavelength of 255 nm and an emission wavelength of 315 nm. Erythromycin, clarithromycin, roxithromycin and azithromycin were found to have retention times of 8.8, 15.7, 17.1 and 20.7 min, respectively. Recoveries ranging from 93 to 104% were found with reproducibility coefficients of variation of 1.1-5%. Mean correlation coefficients of 0.9997, 0.9998, 0.9996 and 0.9994 were found for the linear calibration curves (n = 2) of erythromycin (0.320-16.1 mg/l), roxithromycin (3.24-19.4 mg/l), clarithromycin (0.190-19.4 mg/l) and azithromycin (0.0988-4.94 mg/l), respectively.
    Journal of chromatography. B, Biomedical sciences and applications 01/1999; 720(1-2):89-97.