Dilek Dogrukol-Ak

The antioxidants a-lipoic acid and N-acetylcysteine reverse memory impairment and brain oxidative stress in aged SAMP8 mice

Oxidative stress may play a crucial role in age‐related neurodegenerative disorders. Here, we examined the ability of two antioxidants, α‐lipoic acid (LA) and N‐acetylcysteine (NAC), to reverse the cognitive deficits found in the SAMP8 mouse. By 12 months of age, this strain develops elevated levels of Aβ and severe deficits in learning and memory. We found that 12‐month‐old SAMP8 mice, in comparison with 4‐month‐old mice, had increased levels of protein carbonyls (an index of protein oxidation), increased TBARS (an index of lipid peroxidation) and a decrease in the weakly immobilized/strongly immobilized (W/S) ratio of the protein‐specific spin label MAL‐6 (an index of oxidation‐induced conformational changes in synaptosomal membrane proteins). Chronic administration of either LA or NAC improved cognition of 12‐month‐old SAMP8 mice in both the T‐maze footshock avoidance paradigm and the lever press appetitive task without inducing non‐specific effects on motor activity, motivation to avoid shock, or body weight. These effects probably occurred directly within the brain, as NAC crossed the blood–brain barrier and accumulated in the brain. Furthermore, treatment of 12‐month‐old SAMP8 mice with LA reversed all three indexes of oxidative stress. These results support the hypothesis that oxidative stress can lead to cognitive dysfunction and provide evidence for a therapeutic role for antioxidants.

Passage of VIP / PACAP / Secretin Family Across the Blood-Brain Barrier: Therapeutic Effects

In recent years, VIP/PACAP/secretin family has special interest. Family members are vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), secretin, glucagon, glucagon like peptide-1 (GLP(1)), GLP(2), gastric inhibitory peptide (GIP), growth hormone releasing hormone (GHRH or GRF), and peptide histidine methionine (PHM). Most of the family members present both in central nervous system (CNS) and in various peripheral tissues. The family members that are released into blood from periphery, especially gut, circulate the brain and they can cross the blood brain barrier. On the other hand, some of the members of this family that present in the brain, can cross from brain to blood and reach the peripheral targets. VIP, secretin, GLP(1), and PACAP 27 are transported into the brain by transmembrane diffusion, a non-saturable mechanism. However, uptake of PACAP 38 into the brain is saturable mechanism. While there is no report for the passage of GIP, GLP(2), and PHM, there is only one report that shows, glucagon and GHRH can cross the BBB. The passage of VIP/PACAP/secretin family members opens up new horizon for understanding of CNS effects of peripherally administrated peptides. There is much hope that those peptides may prove to be useful in the treatment of serious neurological diseases such as Alzheimers disease, amyotropic lateral sclerosis, Parkinsons disease, AIDS related neuropathy, diabetic neuropathy, autism, stroke and nerve injury. Their benefits in various pathophysiologic conditions undoubtly motivate the development of a novel drug design for future therapeutics.

Passage of vasoactive intestinal peptide across the blood–brain barrier

We investigated the ability of vasoactive intestinal peptide (VIP) to cross the blood-brain barrier (BBB), the interface between the peripheral circulation and central nervous system (CNS). VIP labeled with 131I (I-VIP) and injected intravenously into mice was taken up by brain as determined by multiple-time regression analysis. Excess unlabeled VIP was unable to impede the entry of I-VIP, indicating that passage is by nonsaturable transmembrane diffusion. High pressure liquid chromatography (HPLC) showed the radioactivity entering the brain to be intact I-VIP. After intracerebroventricular (i.c.v.) injection, I-VIP was sequestered by brain, slowing its efflux from the CNS. In summary, VIP crosses the BBB unidirectionally from blood to brain by transmembrane diffusion.

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.

Determination of amlodipine in pharmaceutical formulations by differential-pulse voltammetry with a glassy carbon electrode

A differential‐pulse voltammetric method was developed for the determination of amlodipine based on the oxidation of the dihydropyridine group on the surface of glassy carbon electrode under stationary and rotating conditions. The experiments were conducted in a supporting electrolyte consisting of 0.2 MKCl, 0.1 Mphosphate buffer, and 10 % (v/v) methanol during investigation of initial potential and pH effects. No adsorption effect was observed on using an initial potential of 0 mVand the supporting electrolyte solution at pH 5.5 under both stationary and rotating conditions. The factor affecting the voltammetric current was diffusional in the range of 200—1000 rpm for rotating, and 2—40 mV s−1 for stationary conditions up to a concentration of 0.04 mg mL−1 amlodipine. The limit of detection (LOD) and the limit of quantitative (LOQ) for the rotating and stationary techniques were found to be 0.004 and 0.0072 mg mL−1 (for S/N = 3.3) and LOQ 0.012 and 0.022 mg mL−1 (for S/N = 10), respectively. The proposed method was applied to the tablets containing amlodipine and according to the statistical evaluations acceptable results were obtained at the 95 % probability level.

DETERMINATION OF RUTIN IN HYPERICUM PERFORATUM EXTRACT BY CAPILLARY ELECTROPHORESIS

A capillary zone electrophoretic (CZE) method for the determination of rutin in an ethanolic extract of the aerial parts of Hypericum perforatum (Hypericaceae) is described. The analysis was performed using a fused-silica capillary and a background electrolyte consisted of 10% ethanol and 20 mM borate buffer at pH 8.0 applied at a potential of 28 kV, vacuum injection of 1 s and detecting at 200 nm. Rutin had a migration time of 10.1 ± 0.2 min. Reproducibility was 1.26% for 9.37 × 10−5 M standard rutin. Detection limit was 2.7 × 10−6 M (S/N = 3). A well-correlated calibration equation was obtained for the mentioned conditions. The amount of rutin in the total plant material was found to be 0.21% ± 0.02.

The determination of lansoprazole in pharmaceutical preparation by capillary electrophoresis

SummaryA capillary electrophoretic method for the determination of lansoprazole in pharmaceutical preparations is described. The analysis was performed in a fused silica capillary using 20 mM borate buffer at pH 8.7 as a background electrolyte. The best resolution was obtained by applying a potential of 30 kV and vacuum injection of 1 s. Detection was made at 200 nm. Phenobarbital sodium was a good internal standard and the migration times were 4.1±0.2 min (lansoprazole) and 5.7±0.2 min (phenobarbital sodium). A well-correlated calibration equation was found in the range of 1.12×10−5 and 2.24×10−4 M. Limit of detection (LOD) and limit of quantitation (LOQ) were 1.4×10−6 M (RSD 1.44%) and 4.42×10−6 M (RSD 1.49%), respectively. The method was validated and applied to the capsules containing enteric coated pellets of lansoprazole. The results of the proposed method were compared those of UV spectrophotometry. Insignificant differences were found between the two methods at the 95% probability level. The described CE method is selective, rapid, sensitive and accurate for the analysis of lansoprazole in quality control laboratories.

A capillary zone electrophoretic method for the determination of nimesulide in pharmaceutical preparation and serum

A simple capillary zone electrophoretic (CZE) method was developed to determine nimesulide in pharmaceutical tablet formulations and serum. Method development was conducted in a fused-silica capillary using a background electrolyte of 10 mM borate buffer containing 10% ethanol at pH 8.1, injecting for 1 s by vacuum injection, applying 30 kV. Salicylic acid was found to be a good internal standard (IS) and detection was performed at 200 nm. Nimesulide and IS appeared at average migration times (RSD%) of 7.2 (0.75%) and 10.4 (0.91%) min, respectively. The limit of detection (S/N = 3) and limit of quantitation (S/N= 10) were 2.2 × 10 -6 M and 6.7 x 10 -6 M, respectively. The method was applied to the tablets containing 100 mg nimesulide and the results were compared to those of UV-spectrophotometry. The recoveries of methods (as mean (mg) ± RSD%) were found to be 99.6 ± 1.59 for CZE and 98.9 ± 1.04 for UV spectrophotometry. The proposed method was also applied for the determination of nimesulide in serum by the standard addition technique. The proposed method is sensitive, precise, and easy to use for the determination of nimesulide in tablets and serum.

A validated thin-layer chromatographic method for analysis of bupropion hydrochloride in a pharmaceutical dosage form

A simple and sensitive thin-layer chromatographic method has been established for analysis of bupropion hydrochloride in pharmaceutical tablets. Chromatography on silica gel 60 F254 plates with 30:10:1 (v/v) ethanol-chloroform-glacial acetic acid as mobile phase furnished compact spots at RF 0.56 ± 0.01. Densitometric analysis was performed at 254 nm. To show the specificity of the method bupropion hydrochloride was subjected to acid and alkaline hydrolysis, oxidation, photodegradation, and dry and wet heat treatment; peaks of degradation products were well resolved from that of the pure drug. Linear regression analysis revealed a good linear relationship between peak area and amount of bupropion hydrochloride in the range 200–1000 ng per band. The limits of detection and quantitation were 11.45 and 34.71 ng per band, respectively. The method was validated, in accordance with ICH guidelines, for precision, accuracy, robustness, and ruggedness. The intra-day and interday repeatability of the method, as RSD, was approximately 1–2%, showing method precision was sufficient. Method recovery was between 102.07 and 104.58% and between 97.20 and 102.19% for quality-control standards and for bupropion hydrochloride in a synthetic mixture, respectively. Statistical comparison of results with those obtained from HPLC analysis proved the method is reproducible and enables selective analysis of bupropion hydrochloride in pharmaceuticals. Because the method could effectively separate the drug from its degradation products, it can be regarded as stability indicating.

Determination of Leflunomide in Pharmaceutical Tablets by Flow‐Injection Analysis

Abstract A flow injection analysis (FIA) of leflunomide using UV‐detection is described, in this study. The most suitable carrier solvent was found to be an aqueous solution of ethanol (25%, v/v). Leflunomide was determined at the optimum conditions, such as flow rate of 0.8 mL · min−1 and detection wavelength of 260 nm. The method has been validated and linearity was examined in the range of 2.75×10−6−1.10×10−4 M. The limit of detection (LOD) and quantitation (LOQ) were calculated to be 2.60×10−7 M (S/N=3.3) and 7.87×10−7 M (S/N=10), respectively. The application of the proposed method has been performed in pharmaceutical tablets of leflunomide and excellent results were obtained. The results were compared with those obtained from UV‐spectrophotometry. Insignificant difference was found between the methods. As a result, the FIA method for the determination of leflunomide in pharmaceutical tablets can be proposed as a precise, accurate, sensitive, and cheap method for routine analysis laboratories.