Usha Mishra

N-acetylcysteine boosts brain and blood glutathione in gaucher and Parkinson diseases

Objective This study aimed to determine if the antioxidant N-acetylcysteine (NAC) is able to alter peripheral and central redox capabilities in patients with Parkinson disease (PD) or Gaucher disease (GD). Methods The study included nondemented adult subjects: 3 with PD, 3 with GD, and 3 healthy controls. Baseline brain glutathione (GSH) concentrations were measured using 7-T magnetic resonance spectroscopy (MRS). Baseline blood reduced-to-oxidized GSH ratios were determined for each subject. Brain GSH concentrations and blood redox ratios were then determined during and at specified time points after a single, 150-mg/kg NAC infusion. Results N-acetylcysteine increased blood GSH redox ratios in those with PD and GD and healthy controls, which was followed by an increase in brain GSH concentrations in all subjects. Conclusions This is the first demonstration that with MRS, it is possible to directly measure and monitor increases in brain GSH levels in the human brain in response to a single, intravenous administration of NAC. This work shows the potential utility of MRS monitoring, which could assist in determining dosing regimens for clinical trials of this potentially useful antioxidant therapy for PD disease, GD, and other neurodegenerative disorders.

Simultaneous analysis of flunixin, naproxen, ethacrynic acid, indomethacin, phenylbutazone, mefenamic acid and thiosalicycic acid in plasma and urine by high-performance liquid chromatography and gas chromatography—mass spectrometry

Simple and reproducible high-performance liquid chromatographic (HPLC) and gas chromatographic-mass spectrometric (GC-MS) methods have been developed for the simultaneous analysis of several acidic drugs in horse plasma and urine. Although the capillary GC-MS column provided better separation of the drugs than the reversed-phase C8 (3 microns, 75 mm) HPLC column, the total analysis time with HPLC was shorter than the total analysis time with GC-MS. The HPLC system equipped with a diode-array detector provided simultaneous screening (limit of detection 100-500 ng/ml) and confirmation (limit 1.0 micrograms/ml) of the drugs. The HPLC system equipped with fixed-wavelength ultraviolet and fluorescence detectors provided a relatively sensitive screening [limit of detection 50-150 ng/ml for ultraviolet and 10 ng/ml for fluorescence (naproxen only) detectors] of the drugs. However, the positive samples had to be confirmed by using either the diode-array detector or the GC-MS system. The GC-MS system provided simultaneous screening and confirmation of the drugs at very low concentrations (20-50 ng/ml).

Steady-State Carbamazepine Pharmacokinetics Following Oral and Stable-Labeled Intravenous Administration in Epilepsy Patients: Effects of Race and Sex

Carbamazepine is a widely prescribed antiepileptic drug. Owing to the lack of an intravenous formulation, its absolute bioavailability, absolute clearance, and half‐life in patients at steady state have not been determined. We developed an intravenous, stable‐labeled (SL) formulation in order to characterize carbamazepine pharmacokinetics in patients. Ninety‐two patients received a 100‐mg infusion of SL‐carbamazepine as part of their morning dose. Blood samples were collected up to 96 hours after drug administration. Plasma drug concentrations were measured with liquid chromatography–mass spectrometry, and concentration–time data were analyzed using a noncompartmental approach. Absolute clearance (l/hr/kg) was significantly lower in men (0.039 ± 0.017) than in women (0.049 ± 0.018; P = 0.007) and in African Americans (0.039 ± 0.017) when compared with Caucasians (0.048 ± 0.018; P = 0.019). Half‐life was significantly longer in men than in women as well as in African Americans as compared with Caucasians. The absolute bioavailability was 0.78. Sex and racial differences in clearance may contribute to variable dosing requirements and clinical response.

Intravenous topiramate: comparison of pharmacokinetics and safety with the oral formulation in healthy volunteers.

Although oral topiramate (TPM) products are widely prescribed for migraines and epilepsy, injectable TPM is not available for human use. We have developed a solubilized TPM formulation using a cyclodextrin matrix, Captisol with the long‐term goal of evaluating its safety and efficacy in neonatal seizures. This study in healthy adult volunteers was performed as required by the U.S. Food and Drug Administration (FDA) to demonstrate the pharmacokinetics and safety prior to initiation of studies involving children. This study allowed investigation of absolute bioavailability, absolute clearance, and distribution volume of TPM, information that could not be obtained without using an intravenous TPM formulation.

Screening and confirmation of drugs in horse urine by using a simple column extraction procedure

A simple and reproducible column (Clean Screen-DAU, copolymeric bonded-phase silica column) extraction procedure has been described for the screening and confirmation of drugs in horse urine. The recovery of drugs by the column extraction was better than or comparable to the recovery by the liquid-liquid extraction, which is commonly used in the equine analytical laboratories. The column extraction provided broad coverage of drugs, separated extracts into three fractions (acidic/neutral, steroids, basic), produced a cleaner extract, and eliminated the need for special liquid-liquid extraction procedures for different drugs. The column extract was cleaner and did not contain impurities, whereas, the liquid-liquid extract was relatively impure and the extract required further thin-layer chromatographic cleanup. The column extraction procedure was used to confirm the presence of several potent drugs, such as fentanyl, etorphine, and mazindol.

Interaction of N-acetylcysteine and Cysteine in Human Plasma

N-acetyl-L-cysteine (NAC), a well-known antioxidant, has been successfully used as adjuvant therapy for late-stage childhood cerebral adrenoleukodystrophy (c-ALD); however, the mechanisms of NAC action are poorly understood. Previous research indicates that NAC serves as a precursor to L-cysteine (Cys), the rate-limiting substrate in the biosynthesis of glutathione (GSH), a potent, endogenous antioxidant. We hypothesized that NAC acts by liberating protein-bound Cys in plasma in an NAC concentration-dependent manner, which increases unbound Cys available for GSH biosynthesis. Human plasma was incubated for 1 h with varying, clinically relevant concentrations of NAC (0-1000 µg/mL). The effect of this interaction over time was evaluated by incubating plasma for 5-90 min with 100 µg/mL NAC. Unbound and bound Cys and NAC were separated by ultrafiltration, and concentrations were measured using high-performance liquid chromatography-mass spectrometry. Significant increases in unbound Cys were observed with increasing NAC concentrations. Also, Cys plasma protein binding decreased from 85% (10 µg/mL NAC) to approximately 0% (1000 µg/mL). Total endogenous Cys was 66% unbound at 5 min after incubation. These results demonstrate that NAC liberates endogenous, protein-bound Cys in human plasma at clinically relevant NAC concentrations. A greater understanding of NAC actions will aid in the optimization of NAC therapy including its use in c-ALD.

Intravenous Administration of Stable-Labeled N-Acetylcysteine Demonstrates an Indirect Mechanism for Boosting Glutathione and Improving Redox Status

There is an increasing interest in using N-acetylcysteine (NAC) as a treatment for neurodegenerative disorders to increase glutathione (GSH) levels and its redox status. The purpose of this study was to characterize the biosynthesis of NAC to GSH using a novel stable isotope-labeled technique, and investigate the pharmacodynamics of NAC in vivo. Female wild-type mice were given a single intravenous bolus dose of 150 mg kg(-1) stable-labeled NAC. Plasma, red blood cells (RBC), and brain tissues were collected at predesignated time points. Stable-labeled NAC and its metabolite GSH (both labeled and unlabeled forms) were quantified in blood and brain samples. Molar ratios of the reduced and oxidized forms of GSH (GSH divided by glutathione disulfide, redox ratio) were also determined. The elimination phase half-life of NAC was approximately 34 min. Both labeled and unlabeled GSH in RBC were found to increase; however, the area under the curve above baseline (AUCb0-280 ) of labeled GSH was only 1% of the unlabeled form. These data indicate that NAC is not a direct precursor of GSH. In addition, NAC has prolonged effects in brain even when the drug has been eliminated from systemic circulation.

Repeated‐Dose Oral N‐Acetylcysteine in Parkinson's Disease: Pharmacokinetics and Effect on Brain Glutathione and Oxidative Stress

Parkinsons disease (PD) is associated with oxidative stress and decreased nigral glutathione (GSH), suggesting that therapies that boost GSH may have a disease‐modifying effect. Intravenous administration of a high dose of N‐acetylcysteine (NAC), a well‐known antioxidant and GSH precursor, increases blood and brain GSH in individuals with PD and with Gaucher disease and in healthy controls. To characterize the pharmacokinetics of repeated high oral doses of NAC and their effect on brain and blood oxidative stress measures, we conducted a 4‐week open‐label prospective study of oral NAC in individuals with PD (n = 5) and in healthy controls (n = 3). Brain GSH was measured in the occipital cortex using 1H‐MRS at 3 and 7 tesla before and after 28 days of 6000 mg NAC/day. Blood was collected prior to dosing and at predetermined collection times before and after the last dose to assess NAC, cysteine, GSH, catalase, malondialdehyde (MDA) and 4‐hydroxynonenal (4‐HNE) concentrations and the reduced‐to‐oxidized GSH ratio (GSH/ glutathione disulfide [GSSG]). Symptomatic adverse events were reported by 3 of the 5 subjects with PD. NAC plasma concentration–time profiles were described by a first‐order absorption, 1‐compartment pharmacokinetic model. Although peripheral antioxidant measures (catalase and GSH/GSSG) increased significantly relative to baseline, indicators of oxidative damage, that is, measures of lipid peroxidation (4‐HNE and MDA) were unchanged. There were no significant increases in brain GSH, which may be related to low oral NAC bioavailability and small fractional GSH/GSSG blood responses. Additional studies are needed to further characterize side effects and explore the differential effects of NAC on measures of antioxidant defense and oxidative damage.

Analysis of detomidine in horse blood, plasma and urine samples utilizing a sensitive gas chromatography-mass spectrometry method

Chemical ionization- and electron impact ionization-selective ion monitoring provided a simple and sensitive method for measuring detomidine (Domosedan), a potent sedative-analgesic drug for horses and cattle. Chemical ionization was at least 10 times more sensitive than electron impact ionization. By using propranolol as an internal standard, we found that the recovery of detomidine from the extraction procedure used in this study was greater than 75% for plasma, whole blood, or urine samples. Approximately 68% of detomidine was bound to plasma protein and 53% was bound to red blood cells.

Screening of steroids in horse urine and plasma by using electron impact and chemical ionization gas chromatography-mass spectrometry

Gas chromatography with chemical ionization mass spectrometry and selected-ion monitoring provided a sensitive method for the screening and confirmation of steroids in horse urine and plasma. Chemical ionization mass spectrometry was more sensitive than the electron impact ionization mass spectrometry for most of the steroids except for testosterone, prednisone-metabolite-2 and prednisolone-metabolite-2. The chromatographic conditions used in this study provided clean separation of different natural and synthetic steroids. Approximately 75-85% of the steroids added to plasma and approximately 65-70% of the steroids added to urine were recovered by the extraction procedure used in this study.