Gamma-hydroxybutyric acid: neurobiology and toxicology of a recreational drug

Abrupt awakening phenomenon associated with gamma-hydroxybutyrate use: A case series

Case reports mention a sudden awakening from GHB-associated coma but do not specify its time course. The aim of the present case series was to investigate the time course of the awakening from GHB intoxication and the relationship to plasma concentrations of GHB and the presence of other drugs. Unconscious (GCS <or=8) participants at six large rave parties who were treated at medical stations were included. Serial blood samples were taken every 10 to 30 minutes for toxicological analysis. At the same time-points, the depth of coma was scored with the Glasgow Coma Score (GCS). Fifteen out of 21 unconscious patients proved to be positive for GHB. Fourteen of these had ingested one or more other drugs. The median GHB plasma concentration upon arrival in the medical station was 212 microg/ml (range 112 to 430 microg/ml). In 10 patients the GCS was scored more than twice, allowing study of the time course. The GCS of these patients remained <or=8 for a median time of 90 minutes (range 30 to 105 minutes). The duration of the transition between GCS of <or=8 and >or=12 was 30 minutes (range 10 to 50 minutes). A subgroup of five patients had a GCS of 3 upon arrival and remained at 3 for a median time of 60 minutes (range 30 to 110 minutes), while the median time for the transition between the last point with GCS 3 and the first with GCS 15 was 30 minutes (range 20 to 60 minutes). This case series illustrates that patients with GHB intoxications remain in a deep coma for a relatively long period of time, after which they awaken over about 30 minutes. This awakening is accompanied by a small change in GHB concentrations. A confounding factor in these observations is co-ingested illicit drugs.

Drug abuse and dependency during pregnancy: anaesthetic issues

Drug abuse is a significant social problem that can lead to serious obstetric complications, some of which may be confused with pregnancy-related disease states. Substance abuse poses a number of challenges with respect to the management of pain and the conduct of anaesthesia in the peripartum period. This review was based on information from a literature search of epidemiological, research and review papers on substance abuse during pregnancy, obtained for the purpose of preparing a background paper for the Ministerial Council on Drug Strategy, Commonwealth Government of Australia. Given that almost 80% of substance-abusing parturients require anaesthetic services in the perinatal period, early antenatal referral for anaesthetic review is recommended. To optimise the care of these vulnerable patients, obstetricians, general practitioners and midwives should attempt to identify substance-abusing parturients and refer them to an anaesthetist. A careful anaesthetic evaluation with non-judgemental questioning is essential, with management tailored to individual patient needs and the urgency of obstetric intervention for vaginal delivery or caesarean section. Opioid-dependent women, in particular, benefit from antenatal pain management planning. Patients recovering from drug addiction should also have a well-documented analgesic strategy. A multidisciplinary approach will involve obstetricians, anaesthetists and staff of the Drug and Alcohol Service. In acute admissions of women by whom antenatal care was not accessed, a high index of suspicion for illicit drug use should arise. Because illicit substance use is so prevalent, if untoward reactions occur during an otherwise uneventful anaesthetic, the possibility of drug abuse should be considered.

Effects of gamma hydroxybutyric acid on inhibition and excitation in rat neocortex

The mechanism by which the sedative and amnestic recreational drug gamma hydroxybutyric acid (GHB) acts is controversial. Some studies indicate that it acts at its unique receptor, while others demonstrate effects mediated through the GABAB receptor. We examined the effect of GHB on evoked GABAA receptor-mediated mono- and polysynaptic inhibitory postsynaptic currents (IPSCs) as well as on N-methyl-d-aspartate (NMDA) and AMPA-mediated excitatory postsynaptic currents (EPSCs) in layers II/III pyramidal cells of the frontal cortex of rat brain. One millimolar (mM) GHB suppressed monosynaptic IPSCs by 20%, whereas polysynaptic IPSCs were reduced by 56%. GHB (1 mM) also produced a significant suppression of NMDA-mediated EPSCs by 53% compared with 27% suppression of AMPA-mediated EPSCs. All effects of GHB on IPSCs and EPSCs were reversed by the specific GABAB antagonist CGP 62349, but not by the GHB receptor antagonist (2E)-5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene ethanoic acid. Consistent with a presynaptic site of action, GHB reduced the frequency but not the amplitude of AMPA receptor-mediated mEPSCs and had no effect on postsynaptic currents evoked by direct application of NMDA. Finally, even though GHB appeared to be acting at presynaptic GABAB receptors, GHB and the GABAB agonist baclofen appeared to have opposite potencies for depression of NMDA- vs. AMPA-mediated EPSCs. GHB showed a preference for depressing NMDA responses while baclofen more potently suppressed AMPA responses. The suppression of NMDA more than AMPA responses by GHB at intoxicating doses may make it attractive as a recreational drug and may explain why GHB is abused and baclofen is not.

Therapeutic concepts in succinate semialdehyde dehydrogenase (SSADH; ALDH5a1) deficiency (gamma-hydroxybutyric aciduria). Hypotheses evolved from 25 years of patient evaluation, studies in Aldh5a1-/- mice and characterization of gamma-hydroxybutyric acid pharmacology

We overview the pathophysiological bases, clinical approaches and potential therapeutic options for succinate semialdehyde dehydrogenase (SSADH; EC1.2.1.24) deficiency (gamma-hydroxybutyric aciduria, OMIM 271980, 610045) in relation to studies on SSADH gene-deleted mice, outcome data developed from 25 years of patient evaluation, and characterization of gamma-hydroxybutyric acid (GHB) pharmacology in different species. The clinical picture of this disorder encompasses a wide spectrum of neurological and psychiatric dysfunction, such as psychomotor retardation, delayed speech development, epileptic seizures and behavioural disturbances, emphasizing the multifactorial pathophysiology of SSADH deficiency. The murine SSADH-/- (e.g. Aldh5a1-/-) mouse model suffers from epileptic seizures and succumbs to early lethality. Aldh5a1-/- mice accumulate GHB and gamma-aminobutyric acid (GABA) in the central nervous system, exhibit alterations of amino acids such as glutamine (Gln), alanine (Ala) and arginine (Arg), and manifest disturbances in other systems including dopamine, neurosteroids and antioxidant status. Therapeutic concepts in patients with SSADH deficiency and preclinical therapeutic experiments are discussed in light of data collected from research in Aldh5a1-/- mice and animal studies of GHB pharmacology; these studies are the foundation for novel working approaches, including pharmacological and dietary trials, which are presented for future evaluation in this disease.

Proteomic analysis of γ-butyrolactone-treated mouse thalamus reveals dysregulated proteins upon absence seizure

Absence seizure has been of interest because the symptom is related to sensory processing. However, the mechanism that causes the disease is not understood yet. To better understand the molecular mechanism related to the disease progress at protein level, we performed proteomic studies using the thalamus of mice for which absence seizure was induced by gamma-butyrolactone (GBL). Differential proteome expression between GBL-treated mice and control mice was examined by fluorescence 2D difference gel electrophoresis (DIGE) at three different time points (5, 10, and 30 min) after GBL-administration. We identified 16 proteins differentially expressed by >1.4-fold at any of the three time points. All proteins besides the serine protease inhibitor EIA were down-regulated in absence seizure-induced mice. The down-regulated proteins can be classified into five groups by their biological functions: cytoskeleton rearrangement, neuroprotection, neurotransmitter secretion, calcium binding, and metabolism. The maximum level of change was reached by 10 min after GBL-treatment, with the expression level returning back to the original at 30 min when mice were awakened from absence seizure thereby demonstrating the proteomic response is reversible. Our results suggest that absence seizures are associated with restricted functional sets of proteins, whose down-regulation may interfere with general function of neuronal cells.

Lipid abnormalities in succinate semialdehyde dehydrogenase (Aldh5a1-/-) deficient mouse brain provide additional evidence for myelin alterations

Earlier work from our laboratory provided evidence for myelin abnormalities (decreased quantities of proteins associated with myelin compaction, decreased sheath thickness) in cortex and hippocampus of Aldh5a1(-/-) mice, which have a complete ablation of the succinate semialdehyde dehydrogenase protein [E.A. Donarum, D.A. Stephan, K. Larkin, E.J. Murphy, M. Gupta, H. Senephansiri, R.C. Switzer, P.L. Pearl, O.C. Snead, C. Jakobs, K.M. Gibson, Expression profiling reveals multiple myelin alterations in murine succinate semialdehyde dehydrogenase deficiency, J. Inher. Metab. Dis. 29 (2006) 143-156]. In the current report, we have extended these findings via comprehensive analysis of brain phospholipid fractions, including quantitation of fatty acids in individual phospholipid subclasses and estimation of hexose-ceramide in Aldh5a1(-/-) brain. In comparison to wild-type littermates (Aldh5a1(+/+)), we detected a 20% reduction in the ethanolamine glycerophospholipid content of Aldh5a1(-/-)mice, while other brain phospholipids (choline glycerophospholipid, phosphatidylserine and phosphatidylinositol) were within normal limits. Analysis of individual fatty acids in each of these fractions revealed consistent alterations in n-3 fatty acids, primarily increased 22:6n-3 levels (docosahexaenoic acid; DHA). In the phosphatidyl serine fraction there were marked increases in the proportions of polyunsaturated fatty acids with corresponding decreases of monounsaturated fatty acids. Interestingly, the levels of hexose-ceramide (glucosyl- and galactosylceramide, principal myelin cerebrosides) were decreased in Aldh5a1(-/-) brain tissue (one-tailed t test, p=0.0449). The current results suggest that lipid and myelin abnormalities in this animal may contribute to the pathophysiology.

Metabolism of gamma-hydroxybutyrate to d-2-hydroxyglutarate in mammals: further evidence for d-2-hydroxyglutarate transhydrogenase

gamma-Hydroxybutyratic acid (GHB), and its prodrugs 4-butyrolactone and 1,4-butanediol, represent expanding drugs of abuse, although GHB is also used therapeutically to treat narcolepsy and alcoholism. Thus, the pathway by which GHB is metabolized is of importance. The goal of the current study was to examine GHB metabolism in mice with targeted ablation of the GABA degradative enzyme succinic semialdehyde dehydrogenase (SSADH(-/-) mice), in whom GHB persistently accumulates, and in baboons intragastrically administered with GHB immediately and persistently. Three hypotheses concerning GHB metabolism were tested: (1) degradation via mitochondrial fatty acid beta-oxidation; (2) conversion to 4,5-dihydroxyhexanoic acid (a putative condensation product of the GHB derivative succinic semialdehyde); and (3) conversion to d-2-hydroxyglutaric acid (d-2-HG) catalyzed by d-2-hydroxyglutarate transhydrogenase (a reaction previously documented only in rat). Both d-2-HG and 4,5-dihydroxyhexanoic acid were significantly increased in neural and nonneural tissue extracts derived from SSADH(-/-) mice. In vitro studies demonstrated the ability of 4,5-dihydroxyhexanoic acid to displace the GHB receptor ligand NCS-382 (IC(50) = 38 micromol/L), although not affecting GABA(B) receptor binding. Blood and urine derived from baboons administered with GHB also accumulated d-2-HG, but not 4,5-dihydroxyhexanoic acid. Our results indicate that d-2-HG is a prominent GHB metabolite and provide further evidence for the existence of d-2-hydroxyglutarate transhydrogenase in different mammalian species.

Synthesis and Biological Activity of Allosteric Modulators of GABAB Receptors, Part 2. 3-(2,6-Bis-tert-butyl-4-hydroxyphenyl)propanols

A series of 13 2,2-disubstituted 3-(3,5-di-t-butyl-4-hydroxyphenyl)propan-1-ol derivatives have been prepared for evaluation as allosteric modulators of GABAB receptors. The activity (EC50, 4–7 μM) was greatest for the cyclohexyl and cyclopentyl analogues.

Diversification of catalytic activities and ligand interactions in the protein fold shared by the sugar isomerases, eIF2B, DeoR transcription factors, acyl-CoA transferases and methenyltetrahydrofolate synthetase

Evolution of diverse catalytic and ligand-binding activities in a given protein fold is a widely observed phenomenon in the protein-domain universe. However, the details of this evolutionary process, general principles, if any, and implications for origins of particular catalytic mechanisms are poorly understood in many common protein folds. Taking advantage of the wealth of currently available protein structure and sequence data, we explore these issues in the context of a large assemblage of biochemically diverse protein domains sharing a common origin, namely the sugar isomerases, translation factor eIF2B, ligand-binding domains of the DeoR-family transcription factors, acetyl-CoA transferases and methenyltetrahydrofolate synthetase. We show that in at least three independent instances, including the sugar-binding domains of the DeoR family transcription factors, this domain has been used as small molecule sensor coupled to helix-turn-helix DNA-binding domains. In at least two of these instances the domain functions as a non-catalytic sensor of ligands. We provide evidence that the ancestral version of this fold was a distinct version of the Rosmann-like folds, which probably possessed two distinct ligand-binding areas that were differentially utilized in different descendents. Analyzing the sequences and structures of proteins in this fold we show that there are two principal factors related to the origin of catalytic diversity in this fold. Firstly, specific inserts and extension added to the core domain on multiple occasions in evolution have affected the access to the active site regions, and thereby allowed for different substrates and allosteric regulators. The second major factor appears to be the emergence of considerable diversity of family-specific residues with important biochemical roles. Interestingly, proteins of this fold, which catalyze similar reactions on similar substrates, might possess very distinctive sets of active residues required for substrate binding catalysis. In particular, different sugar isomerases or acyl transferases in this fold might show distinct constellations of active site residues. These findings suggest that whereas ligand-binding, and even generic catalytic ability emerged early in the evolution of the fold, the specific catalytic mechanisms appear to have independently emerged on multiple occasions in the generic precursors of this fold.

Determination of the GABA analogue succinic semialdehyde in urine and cerebrospinal fluid by dinitrophenylhydrazine derivatization and liquid chromatography-tandem mass spectrometry: application to SSADH deficiency

Succinic semialdehyde (SSA) accumulates in the inborn error of meta- bolism succinic semialdehyde dehydrogenase deficiency owing to impaired enzymatic conversion to succinic acid. We developed a stable-isotope dilution liquid chromato- graphy-tandem mass spectrometry method for the determination of SSA in urine and cerebrospinal fluid samples. Stable-isotope-labelled [13C4]SSA, serving as internal standard, was prepared by reaction of ninhydrin with L-[13C5]glutamic acid. SSA in body fluids was converted to its dinitrophenylhydrazine (DNPH) derivative, without sample purification prior to the derivatization procedure. The DNPH derivative of SSA was injected onto a C18 analytical column and chromatography was performed by isocratic elution. Detection was accomplished by tandem mass spectrometry operating in the negative multiple-reaction monitoring mode. The limit of detection was 10 nmol/L and the calibration curves over the range 0-500 pmol of SSA showed good linearity (r2 > 0.99). The intra-day coefficient of variation (n = 10) for urine was 2.7% and inter-day coefficient of variation (n = 5) for urine was 8.5%. The average recoveries performed on two levels by enriching urine and cerebrospinal fluid samples ranged between 85 and 115%, with coefficients of variation < 8%. The method enabled the first determination of normal values for SSA in urine and pathological values of SSA in urine and cerebrospinal fluid samples derived from patients with succinic semialdehyde dehydrogenase deficiency.