Copyright © 2004 by Institute of Pharmacology
`Polish Academy of Sciences
`
`Polish Journal of Pharmacology
`Pol. J. Pharmacol., 2004, 56, 43–49
`ISSN 1230-6002
`
`REVIEW
`
`g-HYDROXYBUTYRIC ACID (GHB) AND ITS CHEMICAL
`MODIFICATIONS: A REVIEW OF THE GHBergic SYSTEM
`
`Anna Waszkielewicz#, Jacek Bojarski
`
`,AF=HJAJ B HC=E? +DAEIJHO =CEAE= 7ELAHIEJO A@E?= +ACA A@O?= ' 2 !$&& H= M 2=@
`
`-Hydroxybutyric acid (GHB) and its chemical modifications: a review
`the GHBergic system. A. WASZKIELEWICZ, J. BOJARSKI. Pol.
`of
`J. Pharmacol., 2004, 56, 43–49
`
`g-Hydroxybutyric acid (GHB) is a naturally occurring substance with
`function of an inhibitory neurotransmitter in the central nervous system in
`mammals. GHB can be used as a medicine in narcolepsy (Xyrem) and for
`general anesthesia (sodium oxybate). It is also a popular drug of abuse, caus-
`ing coma, addiction and severe withdrawal syndrome, and, therefore, de-
`manding thorough studies on the GHBergic system and expanded research
`on toxicology of this compound. The aim of this review is to present the
`proved and some suggested mechanisms of its action from pharmacological
`point of view, which may help to properly treat intoxication or other patho-
`logical states caused by GHB ingestion. Some new GHB derivatives studied
`for analogous action and their present use are also described.
`
`Key words:
`NCS-382
`
`-hydroxybutyric acid, 1,4-butanediol, g-butyrolactone,
`
`
`
`correspondence; e-mail: AM.Waszkielewicz@interia.pl
`
`AMN1011
`IPR of Patent No. 8,772,306
`
`

`
`Introduction
`
`The g-hydroxybutyric acid (GHB) is a structural
`analog of the g-aminobutyric acid (GABA).
`
`NH
`
`OH
`
`O
`
`OH
`
`OH
`
`O
`
`GABA
`
`GHB
`
`It is an endogenous substance with function of
`an inhibitory neurotransmitter in the central nerv-
`ous system in mammals. Its natural concentration
`in the human brain is 0.3 mmol/g. However, the
`compound is able to pass the blood-brain barrier,
`which is unique for a neurotransmitter, and, thus,
`its concentration in cerebrospinal fluid (CSF) can
`be enlarged. The main mechanism of its action con-
`sists in binding to a specific presynaptic GHB re-
`ceptor which is coupled to a G protein [34]. Its fur-
`
`A. Waszkielewicz, J. Bojarski
`
`ther effect relies upon a decrease in adenyl cyclase
`activity.
`A receptor complex of GHB-GABA* has also
`been reported and GHB was proved to be an ago-
`nist of most GABA* receptors [5]. The third obser-
`ved mechanism involves an allosteric action on the
`calcium channels [19].
`Under physiological conditions, GHB origi-
`nates from GABA which is metabolized by a trans-
`aminase to succinic semialdehyde and then by a de-
`hydrogenase to GHB. Nevertheless, most of GABA
`is transformed to succinic acid which enters the
`Krebs cycle (Fig. 1).
`
`Neuropharmacological action
`
`GHB can be found in both nerve and somatic
`cells and in body fluids such as blood and CSF.
`However, its function in the body outside the nerv-
`ous system remains unknown.
`
`1,4- Butanediol
`
`OH
`
`Oxidation
`
`4-Hydroxybutanal
`
`OH
`
`OH
`
`O
`
`H
`
`Dehydratation
`
`O
`
`O
`
`g-Butyrolactone
`
`Oxidation
`
`g-Hydroxybutyric acid
`
`OH
`
`O
`
`OH
`
`Oxidation
`
`Reduction
`
`Succinic semialdehyde
`
`H
`
`O
`
`Oxidation
`
`OH
`
`O
`
`Succinic acid
`
`O
`
`OH
`
`O
`
`OH
`
`Hydrolysis
`
`Transamination
`
`NH2
`
`O
`
`Oxidative
`transamination
`
`OH
`g-Aminobutyric acid
`
`Krebs cycle
`
`Fig. 1. Metabolism of g-hydroxybutyric acid, g-aminobutyric acid, 1,4-butanediol and g-butyrolactone
`
`44
`
`Pol. J. Pharmacol., 2004, 56, 43–49
`
`AMN1011
`IPR of Patent No. 8,772,306
`
`

`
`C0;,4:;*76;41+ )+1, ), 165 ,-418)618-5
`
`The cerebral cortex
`
`Stimulation of the GHB-GABA* receptor com-
`plex in the frontal lobe of the cerebral cortex proba-
`bly leads to absence seizures [2] due to inhibition
`of Ca  uptake (stimulated by K ions). Moreover,
`agonism at presynaptic GABA* receptor results in
`lowered GABA release leading to the absence sei-
`zures mentioned above [14, 33]. Another result of
`the GABA* agonism is the hypnotic effect [37].
`An increase in endogenous acetylcholine level
`has been reported after GHB administration as well
`as an increase in serotonin synthesis and metabo-
`lism [31].
`In the 1970s it was observed that morphine ele-
`vated the GHB level and that GHB and morphine had
`synergic effect in producing euphoria [30]. Later, it
`was demonstrated that GHB increased synthesis of
`enkephalins, and that GHB-induced EEG change was
`reversed by naloxone [29]. Moreover, GHB was
`proved not to stimulate the m, d and k opioid recep-
`tors [25].
`in the hippocampus,
`lobe,
`In the temporal
`which is responsible for memory and learning, ago-
`nistic action at
`the GABA* receptors leads to
`guanyl cyclase activation, increase in cGMP level,
`and consequently to hyperpolarization of hippo-
`campal neurons. Such action is responsible for am-
`nesia due to GHB ingestion.
`
`The thalamus
`
`A decrease in the excitatory postsynaptic poten-
`tials in the thalamus has been reported. Such action
`is responsible for the anesthetic effect of GHBNa
`used as sodium oxybate (Somsanit) [9]. It is sus-
`pected that the GHB-GABA* receptor complex also
`can be formed in the ventrobasal nucleus in the
`thalamus and is responsible for absence seizures [1].
`
`The hypothalamus
`
`Administration of GHB results in activation of
`tyrosine hydroxylase and, as a result, the larger
`amount of dopamine is synthesized. Nevertheless,
`small doses of the drug decrease and its large doses
`increase secretion of dopamine [5].
`Secretion of dopamine in the striatum is de-
`creased independently of the GHB dose.
`
`The limbic system
`
`The limbic system is responsible for the mood.
`Frequent stimulation of the reward system, espe-
`
`cially the extended amygdala, which includes the
`shell and the nucleus accumbens, with the same
`substance leads to addiction [27]. Such mechanism
`also concerns GHB ingestion [16].
`
`The cerebellum
`
`There are so few GHB receptors in the cerebel-
`lum that the effect of their stimulation is merely no-
`ticeable. What is observed in this structure is that
`GHB decreases the synthesis of nitric oxide, result-
`ing in sudden reversible increase in blood pressure
`in the brain.
`
`The spinal cord
`
`Intraspinal GHB administration leads to hyper-
`polarization of neurons in the spinal cord [26].
`
`The metabolic and endocrinologic effects
`
`Inhibitory effect of GHB on the GABA-keto-
`glutaric acid transaminase leads to a decrease in
`glucose catabolism and greater tolerance of hypo-
`xia [35]. Such an action can be considered as an ad-
`vantage of GHB use in resuscitation [17].
`Another effect of the drug consists in increasing
`the growth hormone level, which was the reason why
`GHB became popular among body-builders [31].
`
`Toxicology
`
`Only 1% of GHB is excreted with urine in the
`unchanged form [13]. Therefore, in order to meas-
`ure its concentration in blood or urine, it is essential
`to use advanced chromatographic methods. One of
`them, using gas chromatography/mass spectrome-
`try (GC/MS), allows to measure as small drug con-
`centrations as 0.1 mg/l in plasma and 0.2 mg/l in
`urine, however, it requires conversion of GHB to
`g-butyrolactone (GBL) (acidification of samples)
`[10]. Another GC/MS analysis, which does not re-
`quire the mentioned conversion, can be used for
`samples within the concentration range between
`0.5–2.0 mg/l [8, 18]. If a patient has ingested GBL
`which was partially converted to GHB in blood, it
`may be the easiest to use high performance liquid
`chromatography (HPLC) [13]. Another analytical
`procedure has recently been developed by Kimura
`et al. [15] due to the need for higher sensitivity of
`tests. In addition, a new ultra-rapid procedure seems
`promising, because a valid result of the test is ac-
`cessible within 1 h [36].
`
`155  !$
`
`45
`
`AMN1011
`IPR of Patent No. 8,772,306
`
`

`
`A. Waszkielewicz, J. Bojarski
`
`GHB is rapidly metabolized to succinic semialde-
`hyde and then to succinic acid which enters the Krebs
`cycle (Fig. 1) and the final metabolic products are
`CO and H O. Therefore, 4–6 h after the GHB in-
`gestion it may be impossible to measure its concen-
`tration in urine [20, 28].
`Acute intoxication can be entirely cured within
`6 h in cases when it does not impair respiratory ac-
`tivity [22].
`Some dose- and blood concentration-effect re-
`lationships are summarized in Tables 1 and 2.
`
`Chemical modifications of GHB
`
`Trans-4-hydroxycrotonic acid (T-HCA) (I)
`
`T-HCA was proved to be an endogenous sub-
`stance in the CNS [3]. It is able to bind to the GHB
`receptor and it was the first compound that showed
`properties required for a substance to be capable of
`reacting with the GHB receptor. Firstly, the active
`
`form of the compound must be non-lactonic. Sec-
`ondly, there is small tolerance of the distance be-
`tween the carboxyl and the hydroxyl groups.
`
`1,4-Butanediol (II)
`
`1,4-Butanediol is much more lipophilic than
`GHB. Therefore, it passes through the blood-brain
`barrier much faster and clinical effects are observed
`sooner than after GHB ingestion. However, in the
`CNS it is transformed to GHB as it is shown in Fig-
`ure 2. It should be noticed that administration of
`any alcohol dehydrogenase inhibitor, such as etha-
`nol or 4-methylpyrazole, prevents the sedative ef-
`fect from development after GHB ingestion. Disul-
`firam, which is an inhibitor of aldehyde dehydroge-
`nase, partially abolishes
`the
`sedative
`effect.
`Therefore, it seems that 1,4-butanediol (1,4-BD)
`acts after being metabolized to GHB and/or to
`GABA [4, 38].
`
`alcohol
`dehydrogenase
`
`OH
`
`OH
`
`OH
`
`aldehyde
`dehydrogenase
`
`OH
`
`H
`
`O
`
`OH
`
`O
`
`Fig. 2. 1,4-Butanediol metabolism to g-hydroxybutyric acid
`
`OH
`
`OH
`
`O
`trans-4-hydroxycrotonic acid (I)
`
`Cl
`
`OH
`
`O
`4-chlorobutyric acid (III)
`
`Cl
`
`ONa
`
`OH
`
`OH
`
`OH
`1,4-butanediol (II)
`
`O
`
`OH
`
`CH3
`
`O
`4-metoxybutyric acid (IV)
`
`O
`NCS-356
`sodium 4-hydroxy-5-p-chlorophenylpentanoate (V)
`
`OH
`
`ONa
`
`O
`
`UMB68
`sodium 4-hydroxy-4-methylpentanoate (VI)
`
`Fig. 3. GHB-related compounds
`
`OH
`
`OH
`
`O
`
`UMB58
`5- hydroxypentanoic acid (VII)
`
`46
`
`Pol. J. Pharmacol., 2004, 56, 43–49
`
`AMN1011
`IPR of Patent No. 8,772,306
`
`

`
`NH
`
`O
`
`OH
`
`NH
`
`CH
`
`N-benzylamide of
`
`(benzylamine)-g-hydroxybutyric acid (VIII)
`
`O
`
`Cl
`
`NH
`
`OH
`
`NH
`
`CH
`
`N-(o-chlorobenzyl)-amide of
`
`-(benzylamine)-g-hydroxybutyric acid (IX)
`
`(CH )m
`
`R
`
`NH
`
`O
`
`N
`
`N
`(CH )n
`
`OH
`-(4-Phenylpiperazine)-g-hydroxybutyric acid and
`-(4-benzylpiperazine)-g-hydroxybutyric acid derivatives (X)
`
`n = 0 or 1
`m = 1 or 2 (for m = 2 R = H)
`R = H, 2-Cl, 4-Cl, 4-F, 4-CH3, 4-OCH3, 3,4-(OCH3)2
`
`C0;,4:;*76;41+ )+1, ), 165 ,-418)618-5
`
`Table 1. The relationship between the dose and the effect of
`GHB in patients [6]
`
`Dose (g)
`
`Effect
`
`below 0.7
`
`euphoria, sociability
`
`0.7–1.4
`
`1.5–2.1
`
`2.1–3.5
`
`3.5–4.9
`
`short amnesia
`
`weariness and sleep
`
`intensification of the above effects
`
`hypnosis, hypotonia, weak analgesia
`
`Table 2. The relationship between the GHB concentration in
`blood and the state of consciousness in patients [12]
`
`GHB concentration
`in blood (mg/l)
`
`State of consciousness
`
`over 260
`
`156-260
`
`52-156
`
`patients in coma and did not react to
`pain stimuli
`
`patients asleep and did react to pain
`stimuli
`
`patients showed spontaneous
`movements and occasionally opened
`their eyes
`
`below 52
`
`patients woke up
`
`C"-substituted derivatives
`
`Fig. 4. Antiepileptic derivatives of g-hydroxybutyric acid
`
`Both 4-chlorobutyric acid (III) and 4-metho-
`xybutyric acid (IV) have stronger ability to cause
`absence seizures [21] (Fig. 3).
`sodium 4-hydroxy-5-p-chlorophe-
`NCS-356,
`nylpentanoate (V), is a specific GHB receptor ago-
`nist used for receptor studies. However, it is rapidly
`metabolized in the organism [37].
`The following compounds have been studied
`for both GHB receptor agonism and their potential
`metabolism [37]. Both UMB68 (VI) and UMB58
`(VII) are specific GHB receptor agonists. UMB68,
`sodium 4-hydroxy-4-methylpentanoate, is not me-
`tabolized by oxidases due to a change in the pri-
`mary alcohol group (GHB) into the tertiary one
`(UMB68). Therefore, it is used for GHB receptor
`studies. UMB58, 5-hydroxypentanoic acid, can be
`another compound proving the tolerance of the dis-
`tance between the carboxyl and the hydroxyl group
`in the acid for the GHB receptor agonism.
`Both compounds: N-benzyl-a-(benzylamine)
`-g-hydroxybutanamide (VIII) and N-(o-chloroben-
`zyl)-a-(benzylamine)-g-hydroxybutanamide
`(IX)
`(Fig. 4) have been synthesized within the American
`Antiepileptic Drug Development (ADD) program
`
`and chosen as effective and the least toxic among
`this group of substances. Within the range of
`promising compounds, there are also a-(4-phenyl-
`piperazine)-g-hydroxybutyric acid and a-(4-benzyl-
`piperazine)-g-hydroxybutyric acid derivatives (X)
`[19].
`
`Cyclic compounds
`
`Among cyclic compounds tested for their influ-
`ence on different seizures, there are g-thiobutyrola-
`ctone (XI) and GBL (XII) (Fig. 5). The former has
`the potential of causing grand mal seizures [21]
`and the latter, as GHB precursor, causes petit mal
`seizures. It is suspected that GBL is first hydro-
`lyzed to GHB in blood by the serum esterases, then
`the GHB passes through the blood-brain barrier
`and in the CNS it reacts with the GHB receptor.
`
`NCS-382
`
`The pharmacological GHB receptor antagonist,
`NCS-382 (6,7,8,9-tetrahydro-5-[H]benzocyclo-he-
`pten-5-ol-4-ylideneacetic acid) (XIII) (Fig. 5), and
`especially its (R)-isomer [7], is accessible in NIDA
`
`155  !$
`
`47
`
`AMN1011
`IPR of Patent No. 8,772,306
`
`

`
`S
`
`O
`
`O
`
`O
`
`procedures to test GHB, 1,4-BD and/or GBL is im-
`pressive as it seems to meet requirements of emer-
`gency toxicology departments.
`
`g-Thiobutyrolactone (XI)
`
`g-Butyrolactone (GBL) (XII)
`
`REFERENCES
`
`A. Waszkielewicz, J. Bojarski
`
`OH
`
`O
`
`OH
`
`NCS-382 (6,7,8,9 tetrahydro-5-[H]benzocyclohepten-
`5-ol-4-ylideneacetic acid) (XIII)
`
`Fig. 5. Cyclic derivatives of GHB
`
`(National Institute on Drug Abuse) for studies on
`the GHBergic system. It is able to antagonize GHB
`action, up to a certain GHB dose, due to the other
`mechanisms of action reported for GHB [24].
`NCS-382 is also able to antagonize seizures of dif-
`ferent sources other than those caused by GHB, al-
`though clinical data do not suggest that the effec-
`tiveness is always satisfactory [32].
`
`Valproic acid and ethosuximide
`
`The GHB dehydrogenase inhibitors, valproic
`acid (Depakene, Valproate, Valrelease) and etho-
`suximide (Zarontin), which are common antiepi-
`leptic medicines, intensify all the effects observed
`after administration of GHB [11, 23]. The effect is
`observed due to inhibited GHB metabolism.
`
`Conclusions
`
`The recent 40 years of studies on pharmacologi-
`cal aspects of GHB action in mammalian brain
`have brought a large amount of information con-
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`still
`remain unsolved. Certain substances with
`proved action on the GHBergic system require fur-
`ther studies and much more specific data are ex-
`pected. Nevertheless, the development of analytical
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`Received: July 21, 2003; in revised form: November 26,
`2003.
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`155  !$
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`49
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`AMN1011
`IPR of Patent No. 8,772,306