A sensitive method for quantitation of gamma-hydroxybutyric acid and gamma-butyrolactone in brain by electron capture gas chromatography

Synthesis and catabolism of gamma-hydroxybutyrate in SH-SY5Y human neuroblastoma cells: role of the aldo-keto reductase AKR7A2

gamma-Hydroxybutyrate (GHB) is an endogenous metabolite synthesized in the brain. There is strong evidence to suggest that GHB has an important role as a neurotransmitter or neuromodulator. The human aldo-keto reductase AKR7A2 has been proposed previously to catalyze the NADPH-dependent reduction of succinic semialdehyde (SSA) to GHB in human brain. In this study we have used RNA interference to evaluate the role of AKR7A2 in GHB biosynthesis in human neuroblastoma SH-SY5Y cells. Quantitative reverse transcription-PCR analysis and immunoblotting revealed that short interfering RNA molecules directed against AKR7A2 led to a significant reduction in both AKR7A2 transcript and protein levels 72 h post-transfection. We have shown that reduced expression of AKR7A2 results in a 90% decrease in SSA reductase activity of cell extracts. Furthermore, we have shown using gas chromatography-mass spectrometry that a decrease in the level of AKR7A2 was paralleled with a significant reduction in intracellular GHB concentration. This provides conclusive evidence that AKR7A2 is the major SSA reductase in these cells. In contrast, short interfering RNA-dependent reduction in AKR7A2 levels had no effect on the GHB dehydrogenase activity of the extracts, and inhibitor studies suggest that another enzyme characteristic of an NAD-dependent alcohol dehydrogenase may be responsible for catalyzing this reverse reaction. Together these findings delineate pathways for GHB metabolism in the brain and will enable a better understanding of the relationship between GHB biosynthesis and catabolism in disease states and in drug overdose.

Determination of endogenous gamma-hydroxybutyric acid (GHB) levels in antemortem urine and blood

Gamma-hydroxybutyric acid's (GHB's) natural presence in the body has made the interpretation of its levels a challenging task for the forensic toxicologist. This study was designed to measure endogenous GHB levels in antemortem urine and blood samples. The range detected in urine was from 34 to 575 microg/dl and in blood from 17 to 151microg/dl. The results indicate that the concentration of endogenous GHB in urine and blood concur with the suggested cut-off levels at 1000 and 500 microg/dl, respectively.

Rapid colorimetric screening test for gamma-hydroxybutyric acid (liquid X) in human urine

A rapid colorimetric test for the detection of gamma-hydroxybutyric acid (GHB) is described. The ferric hydroxamate test for ester detection has been adapted to detect GHB in human urine samples from a healthy female and a healthy male subject. The assay can be performed within 5 min and with a GHB detection limit of 0.5 mg/ml when 0.3 ml of human urine is used and a GHB detection limit of 0.1 mg/ml when 1 ml of human urine is used. The colored complex indicating the presence of GHB is purple according to the assay conditions. Test results are free from the interference by alcohol, phenolic compounds and other biological chemicals under the assay conditions. In addition, the colorimetric test is free from the potential false-positive test result that could result from physiological concentrations of GHB.

Development and validation of a high-performance liquid chromatographic method for the determination of gamma-hydroxybutyric acid in rat plasma

A method for the determination of gamma-hydroxybutyric acid (GHB) in rat plasma was developed using solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with UV detection. GHB was isolated from plasma using strong anion-exchange SPE columns. The chromatographic separation was performed on a C18 Aqua column. The lower limit of quantification was 10 microg/ml using 60 microl of plasma. The linearity of the calibration curves was satisfactory as indicated by correlation coefficients of >0.990. The within-day and between-day precision were <10% (n=24), the accuracy was nearly 101%. Plasma concentrations in rats after GHB infusion determined by HPLC-UV were compared with the corresponding concentrations determined with a validated gas chromatographic-mass spectrometric method by orthogonal distance regression. A good correlation was observed and a t-test indicated no significant differences from 0 and 1 for the intercept and slope, respectively.

A novel method for GHB detection in urine and its application in drug-facilitated sexual assaults

A confirmation procedure for the identification and quantification of gamma-hydroxybutyric acid (GHB) in urine is presented. This method is unique in that it does not involve the conversion of GHB to the gamma-butyrolactone (GBL). The urine samples were extracted using ethyl acetate, evaporated and derivatized with N, O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane (TMCS), and analyzed by gas chromatography-mass spectrometry. Quantification was performed using selective ion monitoring (SIM), using GHB-d(6) as the internal standard. This method is simple and provides excellent linearity and sensitivity for GHB in urine.

Design and structure-activity relationship analysis of ligands of gamma-hydroxybutyric acid receptors

With the use of [3H]gamma-hydroxybutyric acid, binding experiments allowed the screening of new compounds as ligands of gamma-hydroxybutyric acid receptors. Starting from the acid-alcohol gamma-hydroxybutyric acid structure, structure-activity relation analysis and lead optimization highlighted gamma-hydroxybutyric acid derivatives with significantly increased affinities, when compared with the affinity of gamma-hydroxybutyric acid. Further pharmacological studies with the use of gamma-hydroxybutyric acid derivatives allowed the characterization of the first competitive antagonist acting at gamma-hydroxybutyric acid receptors (NCS 382).

Determination of gamma-hydroxybutyric acid (GHB) in plasma and urine by headspace solid-phase microextraction and gas chromatography/positive ion chemical ionization mass spectrometry

A new method for the qualitative and quantitative analysis of gamma-hydroxybutyric acid (GHB) in plasma and urine samples is described. It involves the conversion of GHB to gamma-butyrolactone (GBL), its subsequent headspace solid-phase microextraction (SPME), and detection by gas chromatography/positive ion chemical ionization mass spectrometry (GC/PICI-MS), using D(6)-GBL as internal standard. The assay is linear over a plasma GHB range of 1-100 microg/mL (n = 5, r = 0.999) and a urine GHB range of 5-150 microg/mL (n = 5, r = 0. 998). Relative intra- and inter-assay standard deviations, determined for plasma and urine samples at 5 and 50 microg/mL, are all below 5%. The method is simple, specific and reasonably fast. It may be applied for clinical and forensic toxicology as well as for purposes of therapeutic drug monitoring.

The gamma-hydroxybutyrate signalling system in brain: organization and functional implications

gamma-Hydroxybutyrate is a metabolite of GABA which is synthesized and accumulated by neurons in brain. This substance is present in micromolar quantities in all brain regions investigated as well as in several peripheral organs. Neuronal depolarization releases gamma-hydroxybutyrate into the extracellular space in a Ca(2+)-dependent manner. Gamma-hydroxybutyrate high-affinity receptors are present only in neurons, with a restricted specific distribution in the hippocampus, cortex and dopaminergic structures of rat brain (the striatum in general, olfactory bulbs and tubercles, frontal cortex, dopaminergic nuclei A9, A10 and A12). Stimulation of these receptors with low amounts of gamma-hydroxybutyrate induces in general hyperpolarizations in dopaminergic structures with a reduction of dopamine release. However, in the hippocampus and the frontal cortex, it seems that gamma-hydroxybutyrate induces depolarization with an accumulation of cGMP and an increase in inositol phosphate turnover. Some of the electrophysiological effects of GHB are blocked by NCS-382, a gamma-hydroxybutyrate receptor antagonist while some others are strongly attenuated by GABAB receptors antagonists. Gamma-hydroxybutyrate penetrates freely into the brain when administered intravenously or intraperitoneally. This is a unique situation for a molecule with signalling properties in the brain. Thus, the gamma-hydroxybutyrate concentration in brain easily can be increased more than 100 times. Under these conditions, gamma-hydroxybutyrate receptors are saturated and probably desensitized and down-regulated. It is unlikely that GABAB receptors could be stimulated directly by GHB. Most probably, GABA is released in part under the control of GHB receptors in specific pathways expressing GABAB receptors. Alternatively, GABAB receptors might be specifically stimulated by the GABA formed via the metabolism of gamma-hydroxybutyrate in brain. In animals and man, these GHBergic and GABAergic potentiations induce dopaminergic hyperactivity (which follows the first phase of dopaminergic terminal hyperpolarization), a strong sedation with anaesthesia and some EEG changes with epileptic spikes. It is presumed that, under pathological conditions (hepatic failure, alcoholic intoxication, succinic semialdehyde dehydrogenase defects), the rate of GHB synthesis or degradation in the peripheral organ is modified and induces increased GHB levels which could interfere with the normal brain mechanisms. This pathological status could benefit from treatments with gamma-hydroxybutyric and/or GABAB receptors antagonists. Nevertheless, the regulating properties of the endogenous gamma-hydroxybutyrate system on the dopaminergic pathways are a cause for the recent interest in synthetic ligands acting specifically at gamma-hydroxybutyrate receptors and devoid of any role as metabolic precursor of GABA in brain.

Therapeutic gamma-hydroxybutyric acid monitoring in plasma and urine by gas chromatography-mass spectrometry

A gas chromatographic-mass spectrometric (GC-MS) method for the determination of therapeutic levels of gamma-hydroxybutyric acid (GHB) in plasma and urine samples is described. GHB is converted to its lactonic form gamma-butyrolactone (GBL) which is extracted from biological fluids after the addition of the internal standard delta-valerolactone. Final GC-MS analysis is obtained under electron impact selected ion monitoring (SIM) conditions. Mean relative recoveries of GHB from plasma and urine are 75.5% (RSD% = 2.2) and 76.4% (RSD% = 2.4), respectively. The assay is linear over a plasma GHB range of 2-200 micrograms ml-1 (r = 0.999) and a urine GHB range of 2-150 micrograms ml-1 (r = 0.998). Intra- and inter-assay relative standard deviations (n = 5) determined at 10 and 100 micrograms ml-1 are below 5%. The method is simple, specific and accurate, and may be applied for analytical purposes related to pharmacokinetic studies and therapeutic drug monitoring.

A rapid and sensitive method for the determination of gamma-hydroxybutyric acid and trans-gamma-hydroxycrotonic acid in rat brain tissue by gas chromatography/mass spectrometry with negative ion detection

gamma-Hydroxybutyric acid (GHB) and trans-gamma-hydroxycrotonic acid (HCA) together with their respective internal standards were derivatized to give the pentafluorobenzyl esters of the N-tert-butyldimethylsilyl derivatives. These compounds give, under electron capture conditions, very simple negative ion mass spectra. A very sensitive and specific assay for GHB and HCA in brain tissue (detection limit of about 5 pg per injection) using gas chromatography/negative ion mass spectrometry is described. The average levels measured in the whole brain were 1.10 +/- 0.18 nmol GHB/g wet weight and 0.18 +/- 0.02 nmol HCA/g wet weight.

gamma-Hydroxybutyric acid in subcellular fractions of rat brain

The presence of gamma-hydroxybutyric acid (GHB) in synaptosome-enriched fractions of rat brain was ascertained using a GLC technique. The stability of GHB in synaptosomes was evaluated by addition of various gamma-aminobutyric acid (GABA) transaminase (GABA-T) inhibitors, GHB, or ethosuximide to the homogenizing medium. Furthermore, changes in whole brain GHB levels were compared with those in the synaptosomal fraction in animals treated with GABA-T inhibitors, GABA, or ethosuximide. GHB was present in synaptosome-enriched fractions in concentrations ranging from 40 to 70 pmol/mg of protein. There was no evidence for redistribution, leakage, or metabolism of GHB during the preparation of synaptosomes. The elevations of whole brain GHB level associated with GABA-T or ethosuximide treatment were reflected by a parallel increase in synaptosomal GHB content. These data add to the growing evidence that GHB may have neurotransmitter or neuromodulator function.

Quantification by selected ion monitoring of pipecolic acid, proline, gamma-aminobutyric acid and glycine in rat brain

A procedure for the simultaneous analysis of brain pipecolic acid, proline, gamma-aminobutyric acid and glycine--amino acids with potent inhibitory actions on the central nervous system--was developed. The identification and quantification of the amino acids were performed with a gas chromatographic--mass spectrometric--computer system using deuterium-labelled amino acids as the internal standards. After separation of the amino acids by high-performance liquid chromatography, the methyl ester heptafluorobutyryl derivatives were prepared. The lower limit of quantification for this method is at the picomole level. The usefulness of this chromatographic procedure has been demonstrated by measurement of trace amounts of pipecolic acid in rat brain.

Endogenous gamma-hydroxybutyrate in rat brain areas: postmortem changes and effects of drugs interfering with gamma-aminobutyric acid metabolism

The possibility that gamma-hydroxybutyrate (GHB), a metabolite of gamma-aminobutyric acid (GABA), may play a role in the CNS has recently come to attention. We describe here a sensitive and specific mass fragmentographic technique that allows the measurement of picomole amounts of GHB in single rat brain areas. Moreover, we show that GHB can accumulate postmortem, an effect that is blocked by the use of microwave irradiation to kill the animals. To understand further the relationship between GABA and GHB formation, we treated rats with drugs known to interfere with GABA metabolism at different levels and concomitantly measured GABA and GHB in cerebral cortex and cerebellum. Isoniazide, which blocks the formation of GABA, also decreases GHB. Blockers of the catabolism of GABA, such as aminooxyacetic acid and gamma-acetylenic GABA, increase GABA levels and decrease those of GHB. Sodium dipropylacetate increases both GABA and GHB, supporting the hypothesis that this effective antiepileptic drug also blocks in vivo the enzyme that converts succinic semialdehyde to succinic acid.

Studies on the relation of gamma-hydroxybutyric acid (GHB) to gamma-aminobutyric acid (GABA). Evidence that GABA is not the sole source for GHB in rat brain

The effects of gamma-aminobutyric acid (GABA)-alpha-oxoglutarate aminotransferase (GABA-T) inhibitors, L-glutamic acid decarboxylase (GAD) inhibitors, and antipetit mal anticonvulsants on gamma-hydroxybutyric acid (GHB) and GABA were studied. Treatment with anticonvulsants and GABA-T inhibitors resulted in an increase in steady-state brain levels of both GHB and GABA. GAD inhibitors produced markedly decreased levels of brain GABA but no change in GHB concentrations. Studies of GHB derived exclusively from GABA showed that GABA-T inhibitors which produced an elevation of steady-state levels of GHB in brain also resulted in a decrease in GABA-derived GHB. Intracerebroventricular (i.c.v.) administration of GABA, putrescine, and 1,4-butanediol all produced significant elevations in brain GHB, but GABA-T inhibitors blocked this effect of GABA and putrescine. These data suggest that there may be another source for GHB in brain in addition to GABA and raise the possibility that 1,4-butanediol may be that source.

Ontogeny of gamma-hydroxybutyric acid. I. Regional concentration in developing rat, monkey and human brain

Steady state levels of gamma-hydroxybutyrate (GHB) were measured in whole brain and discrete regions of brain in developing and adult rat, monkey, and human brain. Postmortem changes in concentration of GHB in rat and human brain were also assessed. There were no significant postmortem changes in GHB under the conditions which the ontogeny experiments were done. The concentration of GHB was uniformly higher in the immature brains of the 3 species studied. In the rat the highest concentration was in immature hypothalamus and cortex with a significant decrease occurring between postnatal day 12 and 14. In human, the highest concentration was in fetal cerebellum and adult hypothalamus. Comparison of these data with published ontogeny data for gamma-aminobutyric acid (GABA) suggest that there may be a source of GHB in brain other than GABA.