In vivo conversion of gamma-aminobutyric acid and 1,4-butanediol to gamma-hydroxybutyric acid in rat brain. Studies using stable isotopes

Early Events after Herpes Simplex Virus-Type 1 Entry Are Necessary for the Release of Gamma-Hydroxybutyrate upon Acute Infection

We reported that gamma-hydroxybutyrate (GHB) is released upon Herpes Simplex Virus Type-1 (HSV-1) acute infection. However, the cellular biochemical processes involved in the production of GHB in infected cells are unclear. This study aims to shed light on the biochemical pathway and the stage within the viral life cycle responsible for the release of GHB in infected cells. UV-inactivation, acyclovir (ACV), and cycloheximide (CHX) treatments were used to inhibit HSV-1 replication at various stages. Vero cells treated with UV-inactivated HSV-1 significantly decreased GHB production. However, ACV or CHX treatments did not affect GHB production. We also showed that inhibition of glycolytic enzyme enolase by sodium fluoride (NaF) significantly reduces GHB production upon infection. This finding suggests that suppression of glycolytic activity negatively affects cellular GHB production. Our data also indicated that succinic semialdehyde dehydrogenase, an enzyme involved in the shunt of the tricarboxylic acid (TCA) cycle to generate succinic acid, was decreased upon infection, suggesting that infection may trigger the accumulation of succinic semialdehyde, causing the production of GHB. Although the precise mechanism has yet to be defined, our results suggest that early events following infection modulates the release of GHB, which is generated through the metabolic pathways of glycolysis and TCA cycle.

Method validation of gamma-Hydroxybutyric acid detection upon Herpes Simplex Virus-Type 1 infection using LC-MRM-MS with 3-nitrophenylhydrazine derivatization

Volatile organic compounds (VOCs) release triggered by infection of DNA virus has not been studied extensively. Previously, we reported that gamma-butyrolactone (GBL), a VOC, was released upon Herpes Simplex Virus Type-1 (HSV-1) acute infection. Based on the metabolic pathway and chemical conversion of GBL, we hypothesized that infected cells produce gamma-Hydroxybutyric acid (GHB) as a key pathway intermediate for the subsequent production of GBL. An analytical technique for the rapid detection of GHB is crucial for further understanding its role in the cellular response to HSV-1 infection. To address this, we developed a sensitive, reliable, and specific method for the detection and quantification of GHB in mammalian cell culture using a pre-column derivatization approach. Our data showed that the carboxylic acid functional group of GHB could be derivatized with 3-nitrophenylhydrazine hydrochloride (3-NPH) to produce its hydrazineyl derivative. Unlike GHB, the derivative could be detected seamlessly in HPLC-MS. We also demonstrate quantitive conversion of GHB into the derivative with over 95% yield at a range of 1 μg/mL- 6 μg/mL GHB concentration. This method offers a rapid quantification of GHB in aqueous mixtures, especially in cultured extracts.

γ-Hydroxybutyric Acid: Pharmacokinetics, Pharmacodynamics, and Toxicology

Gamma-hydroxybutyrate (GHB) is a short-chain fatty acid present endogenously in the brain and used therapeutically for the treatment of narcolepsy, as sodium oxybate, and for alcohol abuse/withdrawal. GHB is better known however as a drug of abuse and is commonly referred to as the "date-rape drug"; current use in popular culture includes recreational "chemsex," due to its properties of euphoria, loss of inhibition, amnesia, and drowsiness. Due to the steep concentration-effect curve for GHB, overdoses occur commonly and symptoms include sedation, respiratory depression, coma, and death. GHB binds to both GHB and GABAB receptors in the brain, with pharmacological/toxicological effects mainly due to GABAB agonist effects. The pharmacokinetics of GHB are complex and include nonlinear absorption, metabolism, tissue uptake, and renal elimination processes. GHB is a substrate for monocarboxylate transporters, including both sodium-dependent transporters (SMCT1, 2; SLC5A8; SLC5A12) and proton-dependent transporters (MCT1-4; SLC16A1, 7, 8, and 3), which represent significant determinants of absorption, renal reabsorption, and brain and tissue uptake. This review will provide current information of the pharmacology, therapeutic effects, and pharmacokinetics/pharmacodynamics of GHB, as well as therapeutic strategies for the treatment of overdoses. Graphical abstract.

Lack of evidence for synaptic high-affinity γ-hydroxybutyric acid (GHB) transport in rat brain synaptosomes and 11 Na+ -dependent SLC neurotransmitter transporters

γ-Hydroxybutyric acid (GHB) is an endogenous compound proposed to act as a neurotransmitter. Na⁺ -dependent, high-affinity GHB transport has long been considered important evidence supporting this hypothesis. However, the molecular identity of such a high-affinity transporter remains unknown. In this study, we sought to identify and characterize GHB synaptic transport through a series of studies using both native and recombinant systems with the ultimate aim of providing evidence to clarify the proposed role of GHB as a neurotransmitter in the mammalian brain. Native [³ H]GHB transport was studied in isolated rat brain synaptosomes and compared to synaptic membranes. As a targeted approach, GHB was also screened against a panel of Na⁺ -dependent SLC6 neurotransmitter transporters recombinantly expressed in Xenopus laevis oocytes or tsA201 cells. Finally, the low-affinity GHB transporters, MCT1/2 and SMCT1, were probed as GHB transporters in L-[¹⁴ C]lactate uptake assays in synaptosomes. We found no evidence of high-affinity [³ H]GHB transport in purified rat brain cortical or striatal synaptosomes or at any of the 11 SLC6 transporters tested. Instead, our results indicate the binding of [³ H]GHB to an unidentified membrane component, distinct from any of the known GHB targets. In accordance with others, we found that GHB and the analog 3-hydroxycyclopent-1-enecarboxylic acid (HOCPCA) can, in millimolar concentrations, inhibit L-[¹⁴ C]lactate uptake at MCT1 and/or MCT2 and that this also can occur in synaptosomes. In conclusion, through a variety of in vitro pharmacological studies, we were unsuccessful in identifying a specific synaptic high-affinity transporter for GHB. Our findings emphasize the need to reevaluate GHB's role as a potential neurotransmitter. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

New catalytic strategies for α,ω-diols production from lignocellulosic biomass

Catalytic strategies for the synthesis of 1,5-pentanediol (PDO) with 69% yield from hemicellulose and the synthesis of 1,6-hexanediol (HDO) with 28% yield from cellulose are presented. Fractionation of lignocellulosic biomass (white birch wood chips) in gamma-valerolactone (GVL)/H₂O generates a pure cellulose solid and a liquid stream containing hemicellulose and lignin, which is further dehydrated to furfural with 85% yield. Furfural is converted to PDO with sequential dehydration, hydration, ring-opening tautomerization, and hydrogenation reactions. Acid-catalyzed cellulose dehydration in tetrahydrofuran (THF)/H₂O produces a mixture of levoglucosenone (LGO) and 5-hydroxymethylfurfural (HMF), which are converted with hydrogen to tetrahydrofuran-dimethanol (THFDM). HDO is then obtained from hydrogenolysis of THFDM. Techno-economic analysis demonstrates that this approach can produce HDO and PDO at a minimum selling price of $4090 per ton.

The Neurobiological Mechanisms of Gamma-Hydroxybutyrate Dependence and Withdrawal and Their Clinical Relevance: A Review

OBJECTIVE

x03B3;-Hydroxybutyrate (GHB) has gained popularity as a drug of abuse. In the Netherlands the number of patients in treatment for GHB dependence has increased sharply. Clinical presentation of GHB withdrawal can be life threatening. We aim, through this overview, to explore the neurobiological pathways causing GHB dependency and withdrawal, and their implications for treatment choices.

METHODS

In this work we review the literature discussing the findings from animal models to clinical studies focused on the neurobiological pathways of endogenous but mainly exogenous GHB.

RESULTS

Chronic abuse of GHB exerts multifarious neurotransmitter and neuromodulator effects on x03B3;-aminobutyric acid (GABA), glutamate, dopamine, serotonin, norepinephrine and cholinergic systems. Moreover, important effects on neurosteroidogenesis and oxytocin release are wielded. GHB acts mainly via a bidirectional effect on GABAB receptors (GABABR; subunits GABAB1 and GABAB2), depending on the subunit of the GIRK (G-protein-dependent ion inwardly rectifying potassium) channel involved, and an indirect effect of the cortical and limbic inputs outside the nucleus accumbens. GHB also activates a specific GHB receptor and β1-subunits of α4-GABAAR. Reversing this complex interaction of neurobiological mechanisms by the abrupt cessation of GHB use results in a withdrawal syndrome with a diversity of symptoms of different intensity, depending on the pattern of GHB abuse.

CONCLUSION

The GHB withdrawal symptoms cannot be related to a single mechanism or neurological pathway, which implies that different medication combinations are needed for treatment. A single drug class, such as benzodiazepines, gabapentin or antipsychotics, is unlikely to be sufficient to avoid life-threatening complications. Detoxification by means of titration and tapering of pharmaceutical GHB can be considered as a promising treatment that could make polypharmacy redundant.

Volatile Organic Compound Gamma-Butyrolactone Released upon Herpes Simplex Virus Type -1 Acute Infection Modulated Membrane Potential and Repressed Viral Infection in Human Neuron-Like Cells

Herpes Simplex Virus Type -1 (HSV-1) infections can cause serious complications such as keratitis and encephalitis. The goal of this study was to identify any changes in the concentrations of volatile organic compounds (VOCs) produced during HSV-1 infection of epithelial cells that could potentially be used as an indicator of a response to stress. An additional objective was to study if any VOCs released from acute epithelial infection may influence subsequent neuronal infection to facilitate latency. To investigate these hypotheses, Vero cells were infected with HSV-1 and the emission of VOCs was analyzed using two-dimensional gas chromatograph/mass spectrometry (2D GC/MS). It was observed that the concentrations of gamma-butyrolactone (GBL) in particular changed significantly after a 24-hour infection. Since HSV-1 may establish latency in neurons after the acute infection, GBL was tested to determine if it exerts neuronal regulation of infection. The results indicated that GBL altered the resting membrane potential of differentiated LNCaP cells and promoted a non-permissive state of HSV-1 infection by repressing viral replication. These observations may provide useful clues towards understanding the complex signaling pathways that occur during the HSV-1 primary infection and establishment of viral latency.

Mechanisms for the Specific Properties of γ-Hydroxybutyrate in Brain

γ-Hydroxybutyrate (GHB) is both a natural brain compound with neuromodulatory properties at central GABAergic synapses (micromolar concentration range) and also a drug (Xyrem(R) ) clinically used for the treatment of various neurological symptoms (millimolar dose range). However, this drug has abuse potential and can be addictive for some patients. Here, we review the basic mechanistic role of endogenous GHB in brain as well as the properties and mechanisms of action for therapeutic clinical doses of exogenous GHB. Several hypotheses are discussed with a preference for a molecular mechanism that conciliates most of the findings available. This conciliatory model may help for the design of GHB-like drugs active at lower doses and devoid of major side effects.

Modular isotopomer synthesis of γ-hydroxybutyric acid for a quantitative analysis of metabolic fates

Herein we report a study combining metabolomics and mass isotopomer analysis used for investigation of the biochemical fate of γ-hydroxybutyric acid (GHB). Using various (13)C incorporation labeling patterns into GHB, we have discovered that GHB is catabolized by previously unknown processes that include (i) direct β-oxidation to acetyl-CoA and glycolate, (ii) α-oxidation to 3-hydroxypropionyl-CoA and formate, and (iii) cleavage of C-4 to yield 3-hydroxypropionate and CO2. We further utilized the unique attributes of our labeling patterns and the resultant isotopomers to quantitate relative flux down the identified pathways.

Physical dependence on gamma-hydroxybutrate (GHB) prodrug 1,4-butanediol (1,4-BD): time course and severity of withdrawal in baboons

BACKGROUND

1,4-Butanediol (1,4-BD) is a gamma-hydroxybutyrate (GHB) pro-drug, with multiple commercial uses, and a drug of abuse. Although there are case reports of a withdrawal syndrome following 1,4-BD use, no studies have evaluated the physical dependence potential of 1,4-BD and characterized the time course of withdrawal.

METHODS

Vehicle and then 1,4-BD were administered continuously 24 h/day via intragastric catheters in male baboons (Papio anubis, n=3). Dosing was initiated at 100 mg/kg and increased by 100mg/kg/day to 400mg/kg. After a stabilization period, doses of 500 and then 600 mg/kg/day were each maintained for 3-4 weeks. Plasma levels of 1,4-BD and GHB were determined for each dose condition. Physical dependence was assessed via administration of a GABA-B antagonist (precipitated withdrawal test) during administration of the 600 mg/kg dose and via abrupt termination of chronic 1,4-BD administration (spontaneous withdrawal test). Outcome measures included the number of food pellets earned, performance on a fine-motor task, observed behaviors, and plasma levels of GHB and 1,4-BD.

RESULTS

Following maintenance of 1,4-BD 600 mg/kg for 3 weeks, the number of food pellets earned was significantly decreased. At the end of chronic 1,4-BD dosing, the levels of GHB in plasma ranged from 1290 to 2300 μmol/L and levels of 1,4-BD in plasma ranged from 13.1 to 37.9 μmol/L. Signs of physical dependence were observed following precipitated and spontaneous withdrawal tests. Seizures were not observed.

CONCLUSIONS

These data indicate chronic 1,4-BD produced physical dependence in baboons and the withdrawal syndrome can be characterized as mild to intermediate.

Self-administration of gamma-hydroxybutyric acid (GHB) precursors gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) in baboons

RATIONALE

Gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) are gamma-hydroxybutyrate (GHB) pro-drugs and drugs of abuse.

OBJECTIVE

Given the reports of abuse, and the ease at which GBL and 1,4-BD may be obtained, we investigated the reinforcing effects of GBL (n = 5) and 1,4-BD (n = 4) in baboons using IV self-administration procedures.

METHODS

Sessions ran 24 h/day. Each injection was contingent upon completion of a fixed number (120 or 160) of lever responses. A 3-h timeout period followed each injection, limiting the total number of injections to eight per day. Self-administration was first established with cocaine (0.32 mg/kg/injection). GBL (10-130.0 mg/kg/injection), 1,4-BD (10-100 mg/kg/injection), or vehicle was substituted for cocaine for at least 15 days. Food pellets were available ad libitum 24 h/day and were contingent upon completion of ten lever responses.

RESULTS

GBL (32-100 mg/kg/injection) maintained significantly greater numbers of injections when compared to vehicle in four of five baboons, and the mean rates of injection were high (more than six per day) in three baboons and moderate in the fourth baboon (four to six per day). 1,4-BD (78-130 mg/kg/injection) maintained significantly greater numbers of injections when compared to vehicle in only two out of four baboons, and mean rates were moderate to high in both baboons. Self-injection of these doses of GBL and 1,4-BD generally inhibited food-maintained responding.

CONCLUSIONS

GBL and 1,4-BD have abuse liability. Given that GBL and 1,4-BD are self-administered, are easier to obtain than GHB, and are detected in seized samples, additional legal control measures of these GHB pro-drugs may be needed.

Possible long-term effects of γ-hydroxybutyric acid (GHB) due to neurotoxicity and overdose

In several countries, including the Netherlands, the use of GHB seems to be rising. GHB is regarded by recreational users as an innocent drug without any side effects. Recently, the number of patients in treatment due to GHB addiction sharply increased. In addition, various studies report incidents following risky GHB use or GHB overdosing. Other sedative drugs, like ketamine and alcohol have been shown to result in unintended neurotoxic harm at the level of memory and cognitive function. As outlined in the present review, GHB and ketamine have a common mode of action, which suggests that GHB may also lead to similar neurotoxicity as ketamine. GHB overdosing, as well as binge drinking (and high ketamine doses), induce profound coma which is probably neurotoxic for the brain especially in the maturing brain of young adults. It is therefore advocated to investigate possible long-term neurotoxic effects in recreational GHB users e.g. by studying the residual effects on cognition and memory.

Behavioral effects and pharmacokinetics of gamma-hydroxybutyrate (GHB) precursors gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) in baboons

RATIONALE

Gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) are prodrugs for gamma-hydroxybutyrate (GHB). Like GHB, GBL and 1,4-BD are drugs of abuse, but their behavioral effects may differ from GHB under some conditions.

OBJECTIVES

The first study compared the behavioral effects of GBL (32-240 mg/kg) and 1,4-BD (32-240 mg/kg) with each other and to effects previously reported for GHB (32-420 mg/kg). A second study determined GHB pharmacokinetics following intragastric administration of GHB, GBL, and 1,4-BD.

METHODS

Operant responding for food, observed behavioral effects, and a fine-motor task occurred at multiple time intervals after administration of drug or vehicle. In a separate pharmacokinetics study, blood samples were collected across multiple time points after administration of GHB, GBL, and 1,4-BD.

RESULTS

Like GHB, GBL, and 1,4-BD impaired performance on the fine-motor task, but the onset of motor impairment differed across drugs. GBL and 1,4-BD dose dependently decreased the number of food pellets earned, but at lower doses than previously observed for GHB. Similar to GHB, both GBL and 1,4-BD produced sedation, muscle relaxation, gastrointestinal symptoms, and tremors/jerks. Administration of GBL and 1,4-BD produced higher maximum concentrations of GHB with shorter times to maximum concentrations of GHB in plasma when compared to GHB administration.

CONCLUSIONS

GBL and 1,4-BD produced behavioral effects similar to those previously reported with GHB and the time course of effects were related to blood levels of GHB. Given their higher potency and faster onset of effects, the abuse liability of GBL and 1,4-BD may be greater than GHB.

Effects of 1,4-butanediol administration on oxidative stress in rat brain: study of the neurotoxicity of gamma-hydroxybutyric acid in vivo

gamma-Hydroxybutyric acid (GHB) is a naturally occurring compound in the central nervous system (CNS) whose tissue concentration are highly increased in the neurometabolic-inherited deficiency of succinic semialdehyde dehydrogenase (SSADH) activity or due to intoxication. SSADH deficiency is biochemically characterized by increased concentrations of GHB in tissues, cerebrospinal fluid, blood and urine of affected patients. Clinical manifestations are variable and include retardation of mental, motor, and language development along with other neurological symptoms, such as hypotonia, ataxia and seizures, whose underlying mechanisms are practically unknown. The precursor of GHB, 1,4-butanediol (1,4-BD) has been used to study the mechanisms of in vivo GHB neurotoxicity. Therefore, in the present work, the effect of acute administration of 20 or 120 mg/Kg 1,4-BD was investigated on various parameters of oxidative stress, such as spontaneous chemiluminescence, thiobarbituric acid-reactive substances (TBA-RS), total antioxidant reactivity (TAR), sulfhydryl and protein carbonyl contents, as well as the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in homogenates from cerebral cortex of 14-day-old Wistar rats. Acute administration of 120 mg/Kg 1,4-BD significantly increased spontaneous chemiluminescence and TBA-RS levels, while TAR measurement was markedly diminished, whereas injection of a lower dose (20 mg/Kg) did not change the parameters examined. Other parameters of oxidative stress evaluated were not affected by administration of 1,4-BD. These results indicate that 1,4-BD induces in vivo oxidative stress by stimulating lipid peroxidation and decreasing the non-enzymatic antioxidant defenses in cerebral cortex of young rats. If these effects also occur in humans, it is possible that they might contribute to the brain damage found in SSADH-deficient patients and possibly in individuals intoxicated by GHB or its prodrugs (gamma-butyrolactone or 1,4-BD).

Cardiovascular responses elicited by intragastric administration of BDL and GHB

Gamma-hydroxybutyrate (GHB) and its metabolic precursor, 1,4-butanediol (BDL), are widely used recreational drugs. Although most commonly described as CNS depressants, GHB and BDL elicit significant sympathomimetic cardiovascular responses [increases in mean arterial pressure (MAP) and heart rate] when administered parenterally. Given that humans most commonly ingest both drugs orally, we examined the dose-response relationships for intragastrically administered GHB and BDL on MAP and heart rate in conscious rats using radiotelemetry. The intragastric administration of GHB increased MAP. BDL increased both MAP and heart rate and was approximately 10-fold more potent as a cardiovascular stimulant than GHB when administered intragastrically. Pretreatment with ethanol prevented the lethality of BDL. These data indicate that 1) both GHB and BDL produce cardiovascular responses when administered intragastrically and 2) BDL is more potent and potentially more dangerous than GHB when administered via this route.

Lack of effects of GHB precursors GBL and 1,4-BD following i.c.v. administration in rats

Gamma-hydroxybutyrate (GHB) is used therapeutically and recreationally worldwide. Since the scheduling of GHB by the USA and the United Nations in 2000-2001, the recreational use of GHB precursors has reportedly increased. The aim of this study was to examine if potency differences of GHB and GHB-like compounds are due to their blood-brain barrier permeability. The effects of peripheral and central administration of GHB, GHB precursors gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD), and the gamma-aminobutyric acid (GABA)(B) receptor agonist baclofen on schedule-controlled responding were examined in rats. GHB and baclofen were 276- and 253-fold more potent, respectively, after intracerebroventricular (i.c.v.) administration than after intraperitoneal (i.p.) administration, whereas GBL and 1,4-BD, up to a dose of 1780 microg were without effect after i.c.v. administration. These data suggest that GBL and 1,4-BD are not metabolically converted to GHB in the brain, that enhanced brain penetration cannot account for potency differences between compounds, and that baclofen, like GHB, can readily cross the blood-brain barrier.

GC/MS profiling of gamma-hydroxybutyrate and precursors in various animal tissues using automatic solid-phase extraction. Preliminary investigations of its potential interest in postmortem interval determination

To quantify gamma-hydroxybutyrate (GHB) and its physiological metabolites, gamma-aminobutyric acid (GABA), 1,4-butanediol (1,4-BD), and gamma-butyrolactone (GBL) in various animal tissues (kidney, muscle, heart, liver, blood, brain cortex, thalamus, hypothalamus, hippocampus, or pons), an original gas chromatographic/mass spectrometric method with a automated solid-phase extraction by Oasis MCX cartridges on a Gilson Aspec Xli was developed. Using such apparatus allowed the limit of detection (LOD) of target compounds to be significantly lowered (LOD: 0.027, 0.025, and 5.7 microg/mL for GHB, 1,4-BD, and GABA, respectively, in 200 microL or microg of sample). After validation of each analytical step, the satisfactory performances of the apparatus in conjunction with the rapidity and ease of the extraction step make it suitable for simultaneous assay of GHB, 1,4-BD, GBL, and GABA. The method was used to test the correlation between GHB levels in tissues obtained at different times after death of male Sprague-Dawley rats and the postmortem interval. Preliminary results show a linear increase of GHB levels in relation to time of death in thoracic blood and central nervous system of animals kept at 15 and 20 degrees C.

Detection of gamma-hydroxybutyrate in striatal microdialysates following peripheral 1,4-butanediol administration in rats

The illicit use and abuse of 1,4-butanediol (1,4-BD) results from its presumed conversion to gamma-hydroxybutyrate (GHB) and subsequent pharmacological effects via action on GABA-B and GHB-specific receptors. Using in vivo microdialysis we measured the appearance of GHB in the striata of rats after peripheral 1,4-BD administration. We developed and utilized an HPLC-UV (215 nm) detection of GHB that yielded a limit of quantification (S/N=10) of 2.0 micro g/mL (40 ng/injection) and a limit of detection (S/N=3) of 0.75 micro g/mL (15 ng/injection). GHB appeared in the striatal microdialysates within 20 min after intraperitoneal (i.p.) administration of varying doses of 1,4-BD. GHB concentrations reached dose-dependent maxima 80-100 min post-1,4-BD administration, with peak values of 10.6+/-2.9, 25.3+/-3.4 and 48.1+/-7.1 micro g/mL (mean+/-S.E.M.), corresponding to 1,4-BD doses of 250, 500 and 750 mg/kg, respectively. The conversion of 1,4-BD to GHB was completely prevented by the alcohol dehydrogenase inhibitor 4-methylpyrazole (4MP), administered prior to 1,4-BD, as evidenced by the failure of GHB to appear in the striatal microdialysates. Sleep times in animals were similarly correlated with GHB concentrations in the microdialysates.

Succinic Semialdehyde Dehydrogenase Deficiency: GABAB receptor-mediated function

The succinic semialdehyde dehydrogenase (SSADH) null mouse (SSADH(-/-)) represents a viable animal model for human SSADH deficiency and is characterized by markedly elevated levels of both gamma-hydroxybutyric acid (GHB) and gamma-aminobutyric acid (GABA) in brain, blood, and urine. In physiological concentrations, GHB acts at the GHB receptor (GHBR), but in high concentrations such as those observed in the brains of children with SSADH deficiency, GHB is thought to be a direct agonist at the GABABR receptor (GABABR). We tested the hypothesis that both GHBR and GABABR-mediated function are perturbed in SSADH deficiency. Therefore, we examined the high affinity binding site for GHB as well as the expression and function of the GABABR in mutant mice made deficient in SSADH (SSADH(-/-)). There was a significant decrease in binding of the specific GABABR antagonist, [3H]CGP-54626A at postnatal day (PN)7 and PN14 in SSADH(-/-) when compared to wild type control animals (SSADH(+/+)), particularly in hippocampus. GABABR-mediated synaptic potentials were decreased in SSADH(-/-). Immunoblot analysis of GABABR1a, R1b, and R2 in SSADH(-/-) indicated a trend towards a region-specific and time-dependent decrease of GABABR subunit protein expression. There was no difference between SSADH(-/-) and wild type in binding of either [3H]GHB or a specific GHBR antagonist to the GHBR. These data suggest that the elevated levels of GABA and GHB that occur in SSADH(-/-) lead to a use-dependent decrease in GABABR-mediated function and raise the possibility that this GHB- and GABA-induced perturbation of GABABR could play a role in the pathogenesis of the seizures and mental retardation observed in SSADH deficiency.

A review of evidence leading to the prediction that 1,4-butanediol is not a carcinogen

1,4-Butanediol is an industrial chemical used primarily as an intermediate in the manufacture of other organic chemicals. It has recently been associated with deaths, addiction and withdrawal related to its promotion and use as a dietary supplement. The rapid absorption and conversion of 1,4-butanediol to gamma-hydroxybutyric acid (GHB, or date rape drug) in animals and humans is well documented and is the basis for its abuse potential. A disposition and metabolism study conducted in F344 rats by the National Toxicology Program (NTP) confirmed the rapid conversion of 1-(14)C-1,4-butanediol to (14)CO2. Because of this, the toxicological profile of 1,4-butanediol resembles that of gamma-hydroxybutyric acid. Gamma-hydroxybutyric acid occurs naturally in the brain and peripheral tissues and is converted to succinate and metabolized through the TCA cycle. Although the function of gamma-hydroxybutyric acid in peripheral tissues is not known, the presence of specific high affinity receptors for gamma-hydroxybutyric acid suggests that it functions as a neuromodulator in the brain and neuronal tissue. Gamma-hydroxybutyric acid readily crosses the blood-brain barrier and elicits characteristic neuropharmacologic responses after oral, i.p., or i.v. administration. The same responses are observed after administration of 1,4-butanediol. The cyclic lactone of gamma-hydroxybutyric acid, gamma-butyrolactone, is also rapidly converted to gamma-hydroxybutyric acid by enzymes in the blood and liver in animals and humans, and produces pharmacological effects identical to those produced by 1,4-butanediol and gamma-hydroxybutyric acid. Gamma-butyrolactone was previously evaluated by the NTP in 14-day and 13-week prechronic toxicology studies and in 2-year chronic toxicology and carcinogenesis studies in F344 rats and B6C3F1 mice. No organ specific toxicity occurred. In the carcinogenesis studies there was an equivocal response in male mice based on a marginal increase in the incidence of pheochromocytomas of the adrenal medulla. Because the absence of chronic toxicity and significant carcinogenicity of gamma-hydroxybutyric acid were established in NTP prechronic and chronic studies with gamma-butyrolactone, it is concluded that similar results would be obtained in a 2-year study with 1,4-butanediol, and that 1,4-butanediol is not a carcinogen.

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.

Resuscitative Treatments on 1,4-Butanediol Mortality in Mice

STUDY OBJECTIVE

Recent reports on fatalities associated with overdoses from 1,4-butanediol (1,4-BD), a precursor of the drug of abuse gamma-hydroxybutyric acid (GHB), pose the need for investigations focusing on possible pharmacologic remedies. Accordingly, the present study investigates whether 4-methylpyrazole (4-MP; also termed fomepizole and Antizol), an inhibitor of alcohol dehydrogenase (the enzyme involved in the first step of the conversion of 1,4-BD into GHB), and the gamma-aminobutyric acid B (GABAB) receptor antagonist (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911), provides protection against 1,4-BD-induced mortality in CD1 mice.

METHODS

Two sets of experiments were conducted with mortality as the outcome measure. In all experiments, mice were initially treated with a lethal dose of 1,4-BD (3 g/kg, intragastric [i.g.]). In the first set of experiments (dose-response curves), once mice had displayed clear signs of 1,4-BD intoxication, animals were randomly allocated in separate groups (n=10) and treated acutely with either 4-MP (vehicle, 3, 10, 30, and 100 mg/kg, intraperitoneal [i.p.]) or SCH 50911 (vehicle, 75, 150, and 300 mg/kg, i.p.). Mortality was recorded every hour for the first 9 hours and 12, 18, and 24 hours after 1,4-BD injection. In the second set of experiments (time course), mice were randomly allocated in separate groups (n=10). A single dose of either 4-MP (30 mg/kg, i.p.) or SCH 50911 (150 mg/kg, i.p.) was administered 15, 30, 60, 90, or 120 minutes after administration of 3 g/kg 1,4-BD (i.g.). Again, mortality was recorded every hour for the first 9 hours and 12, 18, and 24 hours after 1,4-BD injection.

RESULTS

In the dose-response experiments, the acute administration of 4-MP and SCH 50911 exerted a dose-dependent resuscitative effect in mice acutely intoxicated by 3 g/kg 1,4-BD. Specifically, 30 and 100 mg/kg 4-MP and 150 mg/kg SCH 50911 protected all treated mice against 1,4-BD-induced mortality. Conversely, all mice treated with 4-MP- and SCH 50911-vehicle died. In the time-course experiments, protection induced by 30 mg/kg 4-MP was complete when administered up to 90 minutes after 1,4-BD injection. Vice versa, the complete protection induced by 150 mg/kg SCH 50911 progressively diminished as the time between 1,4-BD and SCH 50911 administration was increased from 15 to 120 minutes.

CONCLUSION

These results indicate that both 4-MP and SCH 50911 protected against mortality induced by 1,4-BD. Further, these results suggest that 1,4-BD-induced mortality in mice is a result of conversion of 1,4-BD into GHB and GHB-induced activation of the GABAB receptor. Because both 4-MP and GABAB receptor antagonists are available for human use, clinical studies on their ability to reverse the consequences of 1,4-BD and GHB intoxication, including fatal events, might be considered.

Survival of massive γ-hydroxybutyrate/ 1,4-butanediol overdose

Gamma-hydroxybutyrate and its metabolic precursors gamma butyrolactone and 1,4-butanediol are widely used recreational drugs known to cause short periods of deep sedation with rapid recovery. We present a case of survival with good neurological outcome following massive ingestion in which the patient remained sedated for 14 h.

Gamma-hydroxybutyric acid (GHB) and gamma-aminobutyric acidB receptor (GABABR) binding sites are distinctive from one another: molecular evidence

gamma-Hydroxybutyric Acid (GHB) is thought to be a weak partial agonist at the gamma-aminobutyric acid(B) Receptor (GABA(B)R), but the precise relationship of the GHB receptor (GHBR) to the GABA(B)R remains unclear. In order to test the hypothesis that the GHBR is not identical to the GABA(B)R, we conducted two groups of experiments. First, GABA(B)R subtype 1 (R1) and/or subtype 2 (R2) were over expressed in HEK 293 cells and membrane binding studies on the transfected cells done using [(3)H]GHB and [(3)H] (2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene) ethanoic acid ([(3)H]NCS-382). The latter is a specific antagonist at the GHB binding site. Second, [(3)H]GHB and [(3)H]NCS-382 autoradiographic binding studies were done on the brains of mice in which the gene for GABA(B)R1a was deleted. Such mice do not have a functioning GABA(B)R. There was no detectable specific [(3)H]GHB or [(3)H]NCS-382 binding in HEK 293 cells transfected with GABA(B)R1, R2, or R1/R2. Binding to [(3)H]CGP54626A, a high affinity GABA(B)R antagonist, was absent in GABA(B)R1a(-/-) mice. There was no difference in [(3)H]NCS-382 binding observed in the brains of GABA(B)R1a(-/-), GABA(B)R1a(+/-) or GABA(B)R1a(+/+) mice. Specific [(3)H]GHB binding was observed in the brain of GABA(B)R1a(-/-) mice but was significantly lower than in wild type mice. These data support the hypothesis that the GHB binding site is separate and distinct from the GABA(B)R.

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

gamma-Hydroxybutyric acid (GHB) is a short-chain fatty acid that occurs naturally in mammalian brain where it is derived metabolically from gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the brain. GHB was synthesised over 40 years ago and its presence in the brain and a number of aspects of its biological, pharmacological and toxicological properties have been elucidated over the last 20-30 years. However, widespread interest in this compound has arisen only in the past 5-10 years, primarily as a result of the emergence of GHB as a major recreational drug and public health problem in the US. There is considerable evidence that GHB may be a neuromodulator in the brain. GHB has multiple neuronal mechanisms including activation of both the gamma-aminobutyric acid type B (GABA(B)) receptor, and a separate GHB-specific receptor. This complex GHB-GABA(B) receptor interaction is probably responsible for the protean pharmacological, electroencephalographic, behavioural and toxicological effects of GHB, as well as the perturbations of learning and memory associated with supra-physiological concentrations of GHB in the brain that result from the exogenous administration of this drug in the clinical context of GHB abuse, addiction and withdrawal. Investigation of the inborn error of metabolism succinic semialdehyde deficiency (SSADH) and the murine model of this disorder (SSADH knockout mice), in which GHB plays a major role, may help dissect out GHB- and GABA(B) receptor-mediated mechanisms. In particular, the mechanisms that are operative in the molecular pathogenesis of GHB addiction and withdrawal as well as the absence seizures observed in the GHB-treated animals.

Comparison of the actions of gamma-butyrolactone and 1,4-butanediol in Swiss-Webster mice

The abuse of gamma-hydroxybutyrate (GHB) and two of its precursors, gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) are recognized as a public health concern. Here, we report dose-response and time-course analyses for effects of GBL and 1,4-BD on locomotor activity and body temperature in Swiss-Webster mice. Locomotor activity was measured for 2 h following a single injection of one of four doses of each agent plus a saline vehicle control. At 50 mg/kg, GBL produced an initial depression of locomotor activity which was followed by stimulation of locomotor activity. In contrast, 1,4-BD at 50 mg/kg stimulated locomotor activity without producing any depression of activity. At higher doses, GBL produced primarily a dose-dependent decrease in locomotor activity that returned to baseline within 50 min. In contrast, 1,4-BD produced an initial depression which was followed by stimulation of activity. Body temperature was measured rectally across a 2.5-h time course following injection with either agent. Both drugs produced hypothermia with peak effects occurring at 20 and 30 min for both drugs for the lower and higher dose, respectively. At 150 mg/kg, GBL produced a greater hypothermic response; however, no differences in hypothermic response were observed at 100 mg/kg. These studies demonstrate that the precursor drugs to GHB have some differential actions from each other.

4-Methylpyrazole Decreases 1,4-Butanediol Toxicity by Blocking Itsin VivoBiotransformation to γ-Hydroxybutyric Acid

1,4-Butanediol (1,4-BD), a prodrug converted in vivo to gamma-hydroxybutyric acid by alcohol dehydrogenase, has resulted in life-threatening overdoses and deaths. We investigated whether 4-methylpyrazole (4-MP), an alcohol dehydrogenase antagonist, can be used as an antidote in a murine model of 1,4-BD overdose. CD-1 mice were overdosed with 1,4-BD, 600 mg/kg i.p. Mice then received 4-MP, 25 mg/kg i.p., or control injections after 1 min, 5 min, and symptom appearance. Mice were then evaluated for toxicity by the righting reflex and rotarod test every 10 min after intervention. When 4-MP was administered 1 and 5 min after 1,4-BD overdose, mice completely maintained their righting reflex. Conversely, control mice lost their righting reflex for 110 and 130 min, respectively (P < 0.05). When 4-MP was administered after symptomatic 1,4-BD overdose, mice lost their righting reflex but recovered it by 60 min. Conversely, control mice lost their righting reflex and recovered it by 140 min (P < 0.05). When 4-MP was administered at 1 min after 1,4-BD overdose, mice never failed the rotarod test. Conversely, control mice failed the rotarod test for 210 min (P < 0.05). When 4-MP was administered 5 min after 1,4-BD and after symptomatic 1,4-BD overdose, mice failed the rotarod test for 100 and 110 min, respectively. Conversely, control mice failed the rotarod test for 210 and 180 min, respectively (P < 0.05). In addition, treatment of mice with 4-MP significantly attenuated increases in blood gamma-hydroxybutyric acid concentrations and prevented loss of the righting reflex and failure of the rotarod test. In this murine model of 1,4-BD overdose, 4-MP conferred antidotal effects by inhibiting alcohol dehydrogenase-mediated biotransformation of 1,4-BD to gamma-hydroxybutyric acid.

Photosensitive absence epilepsy with myoclonias and heterozygosity for succinic semialdehyde dehydrogenase (SSADH) deficiency

OBJECTIVE

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a neurometabolic disorder characterized by excessive GABA levels and seizures. There has been no clinical phenotype described to date with heterozygosity for SSADH deficiency.

METHODS

A patient heterozygous for SSADH deficiency presented with absence and myoclonic seizures. EEG monitoring and enzymatic, metabolic, and molecular studies for SSADH were obtained on the patient and family members.

RESULTS

EEG recordings yielded generalized 3-4 Hz spike-wave paroxysms and trains of multiple spikes in the heterozygous patient, and photosensitivity in the heterozygous patient and parent as well as in the sibling with homozygous deficiency. The heterozygous patient and parents did not manifest 4-OH-butyric aciduria but SSADH levels were low and a splice site mutation of the SSADH gene was identified in each.

CONCLUSIONS

Heterozygosity for SSADH deficiency may be associated with an epilepsy syndrome characterized by absence and myoclonic seizures, photoparoxysmal EEG and generalized epileptiform discharges

SIGNIFICANCE

Heterozygous SSADH deficiency may be suspected, given an appropriate family history in the setting of an apparently idiopathic generalized epilepsy. Pathogenic explanations may relate to regional elevations in GABA or GHB concentrations.

The Discriminative Stimulus Effects of γ-Hydroxybutyrate and Related Compounds in Rats Discriminating Baclofen or Diazepam: The Role of GABAB and GABAA Receptors

The discriminative stimulus effects of gamma-hydroxybutyrate (GHB) can be mimicked by GABA(A) receptor-positive modulators (e.g., diazepam) and GABA(B) receptor agonists (e.g., baclofen). The purposes of this study were to see whether stimulus control could be established with baclofen and to further characterize the role of GABAergic mechanisms in the behavioral actions of GHB by evaluating GHB and related compounds in rats discriminating either diazepam or baclofen. Training criteria were satisfied with baclofen and diazepam after 69 and 44 sessions, respectively. GHB and its precursors gamma-butyrolactone and 1,4-butanediol occasioned >80% responding on the drug-associated lever in rats discriminating baclofen and <11% in rats discriminating diazepam. Diazepam and other GABA(A) receptor-positive modulators occasioned intermediate levels of responding on the baclofen lever, whereas baclofen occasioned less than 4% responding on the diazepam lever. The GABA(B) receptor antagonist CGP 35348 [(3-aminopropyl)(diethoxymethyl) phosphinic acid] partially antagonized the effects of baclofen as well as the baclofen-like effects of GHB, and flumazenil partially antagonized the effects of diazepam. This study established stimulus control with baclofen, and substitution data provided direct evidence for a role of GABAergic, especially GABA(B), mechanisms in the discriminative stimulus effects of GHB. The lack of substitution by GHB or its metabolic precursors for diazepam indicates a comparatively smaller role of GABA(A) mechanisms in these effects of GHB. The inability of CGP 35348 to completely attenuate the effects of baclofen and GHB suggests that multiple receptors could be involved in the discriminative stimulus effects of GHB.

Chronic 1,4-butanediol treatment in rats: cross-tolerance to γ-hydroxybutyrate and (±)-baclofen

The effects of 1,4-butanediol, gamma-hydroxybutyrate (GHB), and (+/-)-baclofen on food-maintained responding in rats were assessed before, during, and after chronic treatment with 1,4-butanediol. Six weeks of treatment with 1,4-butanediol (twice daily, 320 mg/kg for 3 weeks followed by 560 mg/kg for 3 weeks) decreased sensitivity to the rate-decreasing effects of (+/-)-baclofen and GHB without changing sensitivity to 1,4-butanediol. Sensitivity to (+/-)-baclofen and GHB returned to control values 2-3 weeks after discontinuation of treatment. These data suggest that tolerance to the effects of GHB or its precursors might result from changes in GABA(B) mechanisms.

The ??-Hydroxybutyrate Withdrawal Syndrome

gamma-Hydroxybutyrate (GHB) is endogenous inhibitory transmitter that, when administered in pharmacological doses, has sedative-hypnotic properties. It is used in anaesthesia for the treatment of narcolepsy/catalepsy and in alcohol/opioid detoxification treatment regimens. Based on its purported anabolic effects, GHB use became established among bodybuilders. As the euphorigenic effects of GHB became publicised, attendees at dance clubs and rave parties began to use it alone or in combination with other psychoactive drugs. Following the ban of GHB in 1990, several precursor products (e.g. gamma-butyrolactone, butanediol) became widely used as replacement drugs until their ultimate proscription from lawful use in 2000. GHB and its precursors, like most sedative-hypnotic agents, can induce tolerance and produce dependence. Although many GHB users will experience a mild withdrawal syndrome upon drug discontinuation, those with chronic heavy GHB use can experience severe withdrawal. This syndrome clinically resembles the withdrawal syndrome noted from alcohol and other sedative-hypnotic drugs (e.g. benzodiazepines). Distinct clinical features of GHB withdrawal are its relatively mild and brief autonomic instability with prolonged psychotic symptoms. Patients with fulminant GHB withdrawal require aggressive treatment with cross-tolerant sedative hypnotics, such as benzodiazepines.

GABA, gamma-hydroxybutyric acid, and neurological disease

gamma-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. GABA is converted from glutamic acid by the action of glutamic acid decarboxylase (GAD) of which two isoforms exist GAD65 and GAD67. GABA then is broken down, both within the cell and in the synaptic cleft by GABA transaminase to form succinic semialdehyde. In turn, succinic semialdehyde is converted either to succinic acid by succinic semialdehyde dehydrogenase or into gamma-hydroxybutyric acid (GHB) by succinic semialdehyde reductase. Because GABA modulates the majority of inhibition that is ongoing in the brain, perturbations in GABAergic inhibition have the potential to result in seizures. Therefore, the most common disorder in which GABA is targeted as a treatment is epilepsy. However, other disorders such as psychiatric disease, spasticity, and stiff-person syndrome all have been related to disorders of GABAergic function in the brain. This review covers the roles of GABAergic neurotransmission in epilepsy, anxiety disorders, schizophrenia, stiff-person syndrome, and premenstrual dysphoric disorder. In the final section of this review, the GABA metabolite GHB is discussed in terms of its physiological significance and its role in epilepsy, sleep disorders, drug and alcohol addiction, and an inborn error of GABA metabolism, succinic semialdehyde dehydrogenase deficiency.

Drosophila metabolize 1,4-butanediol into gamma-hydroxybutyric acid in vivo

A solvent, 1,4-butanediol, is also abused as a recreational drug. In mammals, 1,4-butanediol is metabolized into gamma-hydroxybutyric acid (GHB), which stimulates metabotropic gamma-aminobutyric acid (GABA) GABAB and putative GHB receptors. Here we show that in vivo injection of 1,4-butanediol into adult Drosophila leads to GHB synthesis (GHB was detectable 5 min after 1,4-butanediol injection and increased dramatically 1-2 h later). This synthesis of GHB was accompanied by an impairment of locomotor activity that was mimicked by a direct injection of GHB into flies. We propose Drosophila as a model to study the molecular actions of 1,4-butanediol and GHB.

Interactions of gamma-hydroxy butyrate with ethanol and NCS 382

We examined the effects of gamma-hydroxy butyrate (GHB) alone and in combination with either ethanol or NCS 382 [(2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene], a purported antagonist at the GHB receptor. These effects were examined on the responding of rats under a fixed-ratio (FR) 10 schedule of sugar solution (14%, w/v; 0.1 ml) presentation. GHB dose-relatedly decreased responding. When GHB was combined with ethanol, the effects of the two drugs were less than additive. NCS 382 did not antagonize the rate-decreasing effects of GHB. These observations are consistent with the notion that many of the behavioral actions of exogenously administered GHB result from GHB's actions at sites other than the GHB receptor, and are inconsistent with the popular notion that the effects of GHB and ethanol are synergistic.

Intoxication due to 1,4-butanediol

We report a case of intoxication resulting from the ingestion of a liquid, sold in the illicit market as "liquid ecstasy," which was found to contain 1,4-butanediol, a metabolic precursor of gamma-hydroxybutiric acid (GHB). Identification of the substance in the liquid was performed by gas chromatography-mass spectrometry (GC-MS). The toxicological analysis of blood, urine and gastric content of the victim was performed by immunoassay and gas chromatography with nitrogen-phosphorus detection as screening techniques and by means of GC-MS for confirmation and quantitation of 1,4-butanediol and GHB. The following drug concentrations were found: 82 microg/ml (blood), 401 microg/ml (urine) and 7.4 microg/ml (gastric content) for 1,4-butanediol and 103 microg/ml (blood), 430.0 microg/ml (urine) for GHB. In addition to these, other drugs detected and their blood concentration found in this case were methylenedioxymethylamphetamine (MDMA) 0.23 microg/ml and its metabolite methylenedioxyphenylamphetamine (MDA) 0.10 microg/ml. In the urine, a concentration of 0.10 microg/ml of benzoylecgonine was also found.

The role of GABAB receptors in the discriminative stimulus effects of gamma-hydroxybutyrate in rats: time course and antagonism studies

gamma-Hydroxybutyrate (GHB) is a neurotransmitter in brain and an emerging drug of abuse, although its mechanism of action is poorly understood. This study characterized the role of GABA(A), GABA(B), and other receptors in the discriminative stimulus effects of GHB. Eight rats reliably discriminated 200 mg/kg GHB from saline after a median of 35 (range: 23-41) training sessions. GHB, a metabolic precursor 1,4-butanediol (1,4-BDL), and the GABA(B) agonist (+/-)baclofen all occasioned greater than 83% responding on the GHB lever. The onset of action was similar for GHB and 1,4-BDL; however, 1,4-BDL exhibited a longer duration of action than GHB. The GHB precursor gamma-butyrolactone, the benzodiazepine diazepam, the neuroactive steroid pregnanolone, the opioid agonist morphine, and the N-methyl-d-aspartate antagonist ketamine elicited substantial GHB-appropriate responding, although none occasioned greater than 66% drug-lever responding. The barbiturate pentobarbital and the GABA(A) receptor agonist muscimol did not occasion greater than 17% drug-lever responding at any dose tested. The benzodiazepine antagonist flumazenil attenuated GHB-lever responding occasioned by diazepam, but not GHB. The GABA(B) receptor antagonist CGP 35348 antagonized GHB-lever responding occasioned by baclofen or GHB. Small doses of the purported GHB receptor antagonist (2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene ethanoic acid (NCS-382) attenuated partially the effects of GHB, whereas larger doses of NCS-382 alone occasioned partial GHB-lever responding. These results implicate GABA(B) mechanisms in the discriminative stimulus effects of GHB and further suggest that the effects of 1,4-BDL under these conditions result from its conversion to GHB. That NCS-382 shares effects with GHB could explain the lack of antagonism reported for NCS-382 in some studies.

Evaluation of the reinforcing and discriminative stimulus effects of 1,4-butanediol and gamma-butyrolactone in rhesus monkeys

Metabolic precursors and prodrugs of gamma-hydroxybutyrate (GHB), including 1,4-butanediol (BDL) and gamma-butyrolactone (GBL), have sedative and anesthetic effects and might have positive reinforcing effects. BDL and GBL were evaluated using behavioral procedures that measure positive reinforcing effects and discriminative stimulus effects of drugs that modulate gamma-aminobutyric acid (GABA) at the GABA(A) receptor complex. One group of rhesus monkeys could respond for saline or the barbiturate methohexital (i.v.) in a self-administration paradigm. Two other groups of monkeys discriminated the barbiturate pentobarbital (i.g.) or the benzodiazepine midazolam (s.c.) from saline in a drug discrimination paradigm; another group of monkeys was treated with the benzodiazepine diazepam (5.6 mg/kg/day, p.o.) and discriminated the benzodiazepine antagonist flumazenil (s.c.) from vehicle. In self-administration experiments, methohexital and not BDL (0.1-3.2 mg/kg/injection) or GBL (0.1-3.2 mg/kg/injection) reliably maintained responding above saline levels. BDL and GBL, up to doses that suppressed responding, did not substitute for pentobarbital, midazolam or flumazenil. The onset of action for both drugs to decrease response rate was delayed (90 min for GBL and 150 min for BDL). These results suggest that any abuse-related effects of BDL and GBL are qualitatively different from the abuse-related effects of GABA(A) receptor modulators and further indicate that BDL and GBL do not have positive reinforcing effects in rhesus monkeys experienced with self-administration of a short-acting sedative-hypnotic.

Enzyme and receptor antagonists for preventing toxicity from the gamma-hydroxybutyric acid precursor 1,4-butanediol in CD-1 mice

1,4-Butanediol (1,4-BD), the diol alcohol precursor of gamma-hydroxybutyric acid (GHB), undergoes in vivo enzymatic biotransformation to GHB by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase. The subsequent metabolite, GHB, is pharmacologically active at GABA(B) and GHB receptors. GHB can be metabolized in vivo to gamma-aminobutyric acid (GABA) and trans-4-hydroxycrotonic acid (T-HCA), which are also pharmacologically active at GABA(B) receptors and GHB receptors, respectively. Therefore, we speculate that 1,4-BD overdose toxicity can be prevented or attenuated with the ADH enzyme inhibitor 4-methylpyrazole (4-MP) as well as with CGP-35348 and NCS-382, novel high-affinity receptor antagonists of GABA(B) receptors and GHB receptors, respectively. In our murine model of acute 1,4-BD overdose, pretreatment of CD-1 mice with 4-MP significantly attenuated increases in blood GHB concentrations and prevented loss of the righting reflex and failure of the rotarod test. Also, pretreatment with CGP-35348 and its combination with NCS-382 significantly decreased the duration of failure for the rotarod test and the percentage of animals failing the rotarod test, respectively. However, pretreatment of CD-1 mice with NCS-382 alone produced prolonged failure of the rotarod test, an unexpected synergistic effect with 1,4-BD and presumably GHB, which has not previously been demonstrated.

Repeated administration of gamma-hydroxybutyric acid (GHB) to mice: assessment of the sedative and rewarding effects of GHB

Because of the sedative/hypnotic and euphoric effects of gamma-hydroxybutyric acid (GHB), the recreational use of the drug has increased significantly. In the current study we investigated the sedative and rewarding effects of GHB in Swiss Webster mice. Although the acute administration of GHB (200 mg/kg) caused marked hypolocomotion, repeated administration of the drug for 6 or 14 days produced tolerance to this effect. In addition, the administration of GHB 300 mg/kg to naive mice caused catalepsy, which dissipated in mice pre-exposed to GHB (200 mg/kg). Consequently, after repeated treatment with GHB, tolerance developed to both the hypolocomotion and cataleptic effects of the drug. The administration of GHB or its precursor gamma-butyrolactone for 14 days increased the striatal content of dopamine. The sedative effects of GHB may be due to hypodopaminergic activity from inhibition of dopamine release and a subsequent increase in the intraneuronal dopamine level. The rewarding effect of GHB was assessed in the conditioned place preference paradigm. Mice treated repeatedly with 250 mg/kg for 7 days developed conditioned preference for the GHB-paired compartment of the cage, suggesting that the GHB cue is rewarding. The development of tolerance to the sedative effects of GHB coupled with the rewarding properties of the drug support the abuse potential of GHB. Further studies are necessary to determine the mechanism underlying the development of tolerance to GHB and the rewarding effect of the drug.

Central effects of 1,4-butanediol are mediated by GABA(B) receptors via its conversion into gamma-hydroxybutyric acid

The aliphatic alcohol 1,4-butanediol in converted into gamma-hydroxybutyric acid (GHB) via two enzymatic steps: first, it is oxidised by alcohol dehydrogenase in gamma-hydroxybutyraldehyde; second, the latter is transformed, likely by aldehyde dehydrogenase, into GHB. Initially, the present study compared the sedative/hypnotic effect of GHB and 1,4-butanediol, measured as loss of righting reflex. 1,4-Butanediol was more potent than GHB, presumably because of a more rapid penetration of the blood brain barrier. Further alcohol dehydrogenase inhibitors, 4-methylpyrazole and ethanol, totally prevented the sedative/hypnotic effect of 1,4-butanediol; the aldehyde dehydrogenase inhibitor disulfiram partially blocked the sedative/hypnotic effect of 1,4-butanediol. Finally, the sedative/hypnotic effect of 1,4-butanediol was antagonised by the GABA(B) receptor antagonists, SCH 50911 [(2S)(+)-5,5-dimethyl-2-morpholineacetic acid] and CGP 46381 [(3-aminopropyl)(cyclohexylmethyl)phosphinic acid], but not by the putative GHB receptor antagonist NCS-382 (6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid), indicating that it is mediated by GABA(B) but not GHB receptors. Taken together, these results suggest that the sedative/hypnotic effect of 1,4-butanediol is mediated by its conversion in vivo into GHB which, in turn, binds to GABA(B) receptors. Accordingly 1,4-butanediol, unlike GHB, failed to displace [(3)H]GHB and [(3)H]baclofen in brain membranes.

Capillary gas chromatographic determination of 1,4-butanediol and gamma-hydroxybutyrate in human plasma and urine

This article describes two methods for the determination of 1,4-butanediol and gamma-hydroxybutyrate in human plasma and urine using capillary gas chromatography. For 1,4-butanediol, plasma or urine samples (500 microl) were extracted by protein precipitation whereas for gamma-hydroxybutyrate, plasma or urine samples (500 microl) were extracted and derivatised with BF3-butanol. The compounds were separated on a Supelcowax-10 column and detection was achieved using a flame ionization detector. The methods are linear over the specific ranges investigated, accurate (with a percentage of the nominal concentration <109.8%) and showed intra-day and inter-day precision within the ranges of 5.0-12.0 and 7.0-10.1%, respectively. No interferences were observed in plasma and urine from hospitalized patients.

Brain amino acid metabolism and ketosis

The relationship between ketosis and brain amino acid metabolism was studied in mice that consumed a ketogenic diet (>90% of calories as lipid). After 3 days on the diet the blood concentration of 3-OH-butyrate was approximately 5 mmol/l (control = 0.06-0.1 mmol/l). In forebrain and cerebellum the concentration of 3-OH-butyrate was approximately 10-fold higher than control. Brain [citrate] and [lactate] were greater in the ketotic animals. The concentration of whole brain free coenzyme A was lower in ketotic mice. Brain [aspartate] was reduced in forebrain and cerebellum, but [glutamate] and [glutamine] were unchanged. When [(15)N]leucine was administered to follow N metabolism, this labeled amino acid accumulated to a greater extent in the blood and brain of ketotic mice. Total brain aspartate ((14)N + (15)N) was reduced in the ketotic group. The [(15)N]aspartate/[(15)N]glutamate ratio was lower in ketotic animals, consistent with a shift in the equilibrium of the aspartate aminotransferase reaction away from aspartate. Label in [(15)N]GABA and total [(15)N]GABA was increased in ketotic animals. When the ketotic animals were injected with glucose, there was a partial blunting of ketoacidemia within 40 min as well as an increase of brain [aspartate], which was similar to control. When [U-(13)C(6)]glucose was injected, the (13)C label appeared rapidly in brain lactate and in amino acids. Label in brain [U-(13)C(3)]lactate was greater in the ketotic group. The ratio of brain (13)C-amino acid/(13)C-lactate, which reflects the fraction of amino acid carbon that is derived from glucose, was much lower in ketosis, indicating that another carbon source, i.e., ketone bodies, were precursor to aspartate, glutamate, glutamine and GABA.