Erol Şener

Brain mast cells and therapeutic potential of vasoactive intestinal peptide in a Parkinson's disease model in rats: brain microdialysis, behavior, and microscopy.

In the present study, the effect of systemically administered vasoactive intestinal peptide (VIP) (25 ng/kg i.p.) was investigated on drug-induced rotational behavior, extra-cellular dopamine levels and histology of corpus striatum in a 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinsons disease. After 15 days of 6-OHDA lesion, apomorphine-induced (0.05 mg/kg s.c.) rotational behavior of the animals significantly increased and extra-cellular dopamine levels of corpus striatum were significantly reduced. VIP reversed the rotational deficits but did not alter the decrease in striatal dopamine levels. On the other hand, histological data indicate that VIP significantly reduced neuronal death and demyelination. Electron microscopic appearance of mast cells showed ultra-structural variety between VIP-treated and 6-OHDA lesioned groups. VIP activates mast cells without any evidence of typical exocytosis, and possibly mast cells could participate in neuroprotection. Our results suggest that systemically administered VIP can attenuate the motor response changes, neuronal cell death, and myelin sheet loss characteristically associated with 12 microg 6-OHDA administration into the rat striatum. Brain mast cells seem to participate in neuronal protection. Possibly, protective cues could be produced by brain mast cells.

A simple and sensitive LC–ESI-MS (ion trap) method for the determination of bupropion and its major metabolite, hydroxybupropion in rat plasma and brain microdialysates

A specific and highly sensitive liquid chromatography-electrospray mass spectrometry (LC-ESI-MS) method for the direct determination of bupropion (BUP) and its main metabolite hydroxybupropion (HBUP) in rat plasma and brain microdialysate has been developed and validated. The analysis was performed on a Bonus RP C18 (100 mm × 2.1mm i.d., 3.5 μm particles) column using gradient elution with the mobile phase consisting of acetonitrile and ammonium formate buffer (10mM, pH 4). Plasma samples were analyzed after a simple, one-step protein precipitation clean-up with trichloroacetic acid (TCA), however clean-up for microdialysis samples was not necessary, enabling direct injection of the samples into the LC-ESI-MS system. Signals of the compounds were monitored under the multiple reaction monitoring (MRM) mode of the LC-ESI-MS (ion trap) for quantification. The precursor to product ion transitions of m/z 240-184 and m/z 256-238 were used to measure BUP and HBUP, respectively. The method was validated in both plasma and microdialysate samples, and the obtained lower limit of quantification (LLOQ) was 1.5 ng mL(-1) for BUP and HBUP in both matrices. The intra- and inter-day assay variability was less than 15% for both analytes. This LC-ESI-MS method provided simple sampling, rapid clean-up and short analysis time (<9 min), applicable to the routine therapeutic monitoring and pharmacokinetic studies of BUP and HBUP.

A sensitive capillary LC-UV method for the simultaneous analysis of olanzapine, chlorpromazine and their FMO-mediated N-oxidation products in brain microdialysates

A specific and sensitive capillary liquid chromatography-ultraviolet detection (cap-LC-UV) method in combination with a micro-extraction by packed sorbent (MEPS) sample clean-up procedure has been developed and validated for the simultaneous analysis of chlorpromazine, olanzapine and their flavin-containing monooxygenase (FMO) mediated N-oxides in rat brain microdialysates. Chromatographic separation was obtained on an Acclaim Pepmap RP C18 column with an ID of 300µm. An injection volume of 20µL was used to inject the largely aqueous samples and was shown to have no influence on the obtained peak shape of the compounds of interest. Optimal conditions for MEPS extraction were obtained on a mixed-mode M1 (80% C8, 20% SCX) cartridge after diluting microdialysate samples with phosphate buffer pH 2.5 (1:3 v/v). The method was validated and lower limits of quantification (LLOQ) were determined at 0.5nM for all compounds. Linearity was demonstrated between the LLOQ and 1µM for all compounds (R2>0.995). MEPS recoveries were between 92% and 98%, with intra- and interday variabilities below 15%. The applicability of the developed method was successfully demonstrated by analysing rat brain microdialysates. The capillary LC-UV method in combination with MEPS sample treatment provides a simple, sensitive method to quantify all compounds of interest in 45min and can be applied for routine therapeutic monitoring and pharmacokinetic studies of olanzapine, chlorpromazine and their respective N-oxides.

Determination of Carbamazapine by Flow‐Injection Analysis: Its Application to Tablet Analysis and Dissolution Studies

Abstract Flow injection analysis (FIA) of carbamazepine (CBZ) and its relevant application to the conventional CBZ tablets, e.g., content uniformity test and tablet dissolution, is described in this study. An aqueous solution of 1% sodium dodecyl sulphate (SDS) was employed as a carrier solvent. The best parameters were determined for FIA analysis; flow‐rate of 1 mL · min−1, detection wavelength of 288 nm, and an injection volume of 20 µL. Validation tests (intra‐ and inter‐day) were realized with highly good repeatability (RSD%=1.92) and linearity, limit of detection (LOD) and limit of quantification (LOQ) were calculated to be 8.34×10−7 M and 2.5×10−6 M, respectively. Results of analysis which were achieved on the tablets were compared to those methods that were suggested by USP 28. Each step was examined by statistical testing, and it seems that the proposed method is applicable, as well as the methods in the pharmacopoeia.

DEVELOPMENT OF A SIMPLE AND SPECIFIC UHPLC ASSAY FOR THE DETERMINATION OF ARIPIPRAZOLE AND DEHYDROARDPDPRAZOLE IN RAT PLASMA

ABSTRACT A new, simple, specific, and rapid ultra high performance liquid chromatography method was developed and validated for the determination of aripiprazole and its active metabolite dehydroaripiprazole in rat plasma. The analysis was performed on a Zorbax Eclipse Plus C18 (50 mm × 2.1 mm, 1.8 µm particles) column using gradient elution with a mobile phase consisting of acetonitrile and acetate buffer (30 mM, pH 5). Plasma samples were analyzed after a simple, one-step protein precipitation with acetonitrile. The method was validated and the specificity, linearity, limit of detection, limit of quantitation, precision, accuracy, recoveries, matrix effect, stability and robustness were determined. The analytes and internal standard were separated in 3.5 min and the total analysis time including the clean-up step was 8 min. Limit of detection was 0.012 µg mL -1 and 0.009 µg mL for aripiprazole and dehydroaripiprazole, respectively. Limit of quantitation was 0.039 µg mL -1 and 0.029 µg mL for aripiprazole and dehydroaripiprazole, respectively.The intra- and inter-day assay variability was less than 2% for the analytes. The proposed method is rapid, reproducible and accurate to quantify both aripiprazole and dehydroaripiprazole. It involves a simple plasma deproteination technique using one step protein precipitation with acetonitrile. This validated method was successfully used to quantify plasma concentrations of the analytes in rat plasma.