Toxic copper level increases erythrocyte glycolytic rate, glutathione production and alters electrolyte balance in male Wistar rats.

BACKGROUND: Copper is a micronutrient vital to several cellular energy metabolic processes and drives erythropoiesis. However, it disrupts cellular biological activities and causes oxidative damage when in excess of cellular needs. This study investigated the effects of copper toxicity on erythrocyte energy metabolism in male Wistar rats. METHODS: Ten Wistar rats (150-170 g) were randomly divided into 2 groups: control (given 0.1 ml distilled water) and copper toxic (given 100 mg/kg copper sulphate). Rats were orally treated for 30 days. Blood, collected retro-orbitally after sodium thiopentone anaesthesia (50 mg/kg i.p.) into fluoride oxalate and EDTA bottles, was subjected to blood lactate assay and extraction of red blood cell respectively. Red blood cell nitric oxide (RBC NO), glutathione (RBC GSH), adenosine triphosphate (RBC ATP) levels, RBC hexokinase, glucose-6-phosphate (RBC G6P), glucose-6-phosphate dehydrogenase (RBC G6PDH), and lactate dehydrogenase (RBC LDH) activity was estimated spectrophotometrically. Values (Mean±SEM, n = 5) were compared by Student's unpaired T-test at p < 0.05. RESULTS AND CONCLUSION: Copper toxicity significantly increased RBC hexokinase (23.41 ± 2.80 µM), G6P (0.48 ± 0.03 µM), G6PDH (71.03 ± 4.76nmol/min/ml) activities, ATP (624.70 ± 57.36 µmol/gHb) and GSH (3.08 ± 0.37 µM) level compared to control (15.28 ± 1.37 µM, 0.35 ± 0.02 µM, 330.30 ± 49.58 µmol/gHb, 54.41 ± 3.01nmol/min/ml and 2.05 ± 0.14 µM respectively, p < 0.05). Also, RBC LDH activity (145.00 ± 19.88mU/ml), NO (3.45 ± 0.25 µM) and blood lactate (31.64 ± 0.91 mg/dl) level were lowered significantly compared to control (467.90 ± 94.23mU/ml, 4.48 ± 0.18 µM and 36.12 ± 1.06 mg/dl respectively). This study shows that copper toxicity increases erythrocyte glycolytic rate and glutathione production. This increase could be connected to a compensatory mechanism for cellular hypoxia and increased free radical generation.

Alcohol perturbed locomotor behavior, metabolism, and pharmacokinetics of gamma-hydroxybutyric acid in rats.

Gamma-hydroxybutyric acid (GHB), both a metabolic precursor and product of gamma-aminobutyric acid (GABA), is a central nervous system depressant used for the treatment of narcolepsy-associated cataplexy and alcohol withdrawal. However, administration of GHB with alcohol (ethanol) is a major cause of hospitalizations related to GHB intoxication. In this study, we investigated locomotor behavior as well as metabolic and pharmacokinetic interactions following co-administration of GHB and ethanol in rats. The locomotor behavior of rats was evaluated following the intraperitoneal administration of GHB (sodium salt, 500 mg/kg) and/or ethanol (2 g/kg). Further, time-course urinary metabolic profiling of GHB and its biomarker metabolites glutamic acid, GABA, succinic acid, 2,4-dihydroxybutyric acid (OH-BA), 3,4-OH-BA, and glycolic acid as well as pharmacokinetic analysis were performed. GHB/ethanol co-administration significantly reduced locomotor activity, compared to the individual administration of GHB or ethanol. The urinary and plasma concentrations of GHB and other target compounds, except for 2,4-OH-BA, were significantly higher in the GHB/ethanol co-administration group than the group administered only GHB. The pharmacokinetic analysis results showed that the co-administration of GHB and ethanol significantly increased the half-life of GHB while the total clearance decreased. Moreover, a comparison of the metabolite-to-parent drug area under the curve ratios demonstrated that the metabolic pathways of GHB, such α- and ß-oxidation, were inhibited by ethanol. Consequently, the co-administration of GHB and ethanol aggravated the metabolism and elimination of GHB and enhanced its sedative effect. These findings will contribute to clinical interpretation of GHB intoxication.

The GHB analogue HOCPCA improves deficits in cognition and sensorimotor function after MCAO via CaMKIIα.

Ca2+/calmodulin-dependent protein kinase II alpha (CaMKIIα) is a major contributor to physiological and pathological glutamate-mediated Ca2+ signals, and its involvement in various critical cellular pathways demands specific pharmacological strategies. We recently presented γ-hydroxybutyrate (GHB) ligands as the first small molecules selectively targeting and stabilizing the CaMKIIα hub domain. Here, we report that the cyclic GHB analogue 3-hydroxycyclopent-1-enecarboxylic acid (HOCPCA), improves sensorimotor function after experimental stroke in mice when administered at a clinically relevant time and in combination with alteplase. Further, we observed improved hippocampal neuronal activity and working memory after stroke. On the biochemical level, we observed that hub modulation by HOCPCA results in differential effects on distinct CaMKII pools, ultimately alleviating aberrant CaMKII signalling after cerebral ischemia. As such, HOCPCA normalised cytosolic Thr286 autophosphorylation after ischemia in mice and downregulated ischemia-specific expression of a constitutively active CaMKII kinase proteolytic fragment. Previous studies suggest holoenzyme stabilisation as a potential mechanism, yet a causal link to in vivo findings requires further studies. Similarly, HOCPCA's effects on dampening inflammatory changes require further investigation as an underlying protective mechanism. HOCPCA's selectivity and absence of effects on physiological CaMKII signalling highlight pharmacological modulation of the CaMKIIα hub domain as an attractive neuroprotective strategy.

Astrocytes regulate inhibitory neurotransmission through GABA uptake, metabolism, and recycling.

Synaptic regulation of the primary inhibitory neurotransmitter γ-aminobutyric acid (GABA) is essential for brain function. Cerebral GABA homeostasis is tightly regulated through multiple mechanisms and is directly coupled to the metabolic collaboration between neurons and astrocytes. In this essay, we outline and discuss the fundamental roles of astrocytes in regulating synaptic GABA signaling. A major fraction of synaptic GABA is removed from the synapse by astrocytic uptake. Astrocytes utilize GABA as a metabolic substrate to support glutamine synthesis. The astrocyte-derived glutamine is subsequently transferred to neurons where it serves as the primary precursor of neuronal GABA synthesis. The flow of GABA and glutamine between neurons and astrocytes is collectively termed the GABA-glutamine cycle and is essential to sustain GABA synthesis and inhibitory signaling. In certain brain areas, astrocytes are even capable of synthesizing and releasing GABA to modulate inhibitory transmission. The majority of oxidative GABA metabolism in the brain takes place in astrocytes, which also leads to synthesis of the GABA-related metabolite γ-hydroxybutyric acid (GHB). The physiological roles of endogenous GHB remain unclear, but may be related to regulation of tonic inhibition and synaptic plasticity. Disrupted inhibitory signaling and dysfunctional astrocyte GABA handling are implicated in several diseases including epilepsy and Alzheimer's disease. Synaptic GABA homeostasis is under astrocytic control and astrocyte GABA uptake, metabolism, and recycling may therefore serve as relevant targets to ameliorate pathological inhibitory signaling.

The Treatment of Parkinson's Disease with Sodium Oxybate.

Sodiun Oxybate (SO) has a number of attributes that may mitigate the metabolic stress on the substantia nigra pars compacta (SNpc) dopaminergic (DA) neurons in Parkinson's disease (PD). These neurons function at the borderline of energy sufficiency. SO is metabolized to succinate and supplies energy to the cell by generating ATP. SO is a GABAB agonist and, as such, also arrests the high energy requiring calcium pace-making activity of these neurons. In addition, blocking calcium entry impedes the synaptic release and subsequent neurotransmission of aggregated synuclein species. As DA neurons degenerate, a homeostatic failure exposes these neurons to glutamate excitotoxicity, which in turn accelerates the damage. SO inhibits the neuronal release of glutamate and blocks its agonistic actions. Most important, SO generates NADPH, the cell's major antioxidant cofactor. Excessive free radical production within DA neurons and even more so within activated microglia are early and key features of the degenerative process that are present long before the onset of motor symptoms. NADPH maintains cell glutathione levels and alleviates oxidative stress and its toxic consequences. SO, a histone deacetylase inhibitor also suppresses the expression of microglial NADPH oxidase, the major source of free radicals in Parkinson brain. The acute clinical use of SO at night has been shown to reduce daytime sleepiness and fatigue in patients with PD. With long-term use, its capacity to supply energy to DA neurons, impede synuclein transmission, block excitotoxicity and maintain an anti-oxidative redox environment throughout the night may delay the onset of PD and slow its progress.

The CaMKIIα hub ligand Ph-HTBA promotes neuroprotection after focal ischemic stroke by a distinct molecular interaction.

Ca2+/calmodulin-dependent protein kinase II alpha (CaMKIIα) is a potential target for acute neuroprotection due to its key role in physiological and pathological glutamate signaling. The hub domain organizes the CaMKII holoenzyme into large oligomers, and additional functional effects on holoenzyme activation have lately emerged. We recently reported that compounds related to the proposed neuromodulator γ-hydroxybutyrate (GHB) selectively bind to the CaMKIIα hub domain and increase hub thermal stabilization, which is believed to have functional consequences and to mediate neuroprotection. However, the detailed molecular mechanism is unknown. In this study, we functionally characterize the novel and brain permeable GHB analog (E)-2-(5-hydroxy-2-phenyl-5,7,8,9-tetrahydro-6H-benzo[7]annulen-6-ylidene)acetic acid (Ph-HTBA). Administration of a single dose of Ph-HTBA at a clinically relevant time point (3-6 h after photothrombotic stroke) promotes neuroprotection with a superior effect at low doses compared to the smaller GHB analog 3-hydroxycyclopent-1-enecarboxylic acid (HOCPCA). In contrast to HOCPCA, Ph-HTBA reduces Ca2+-stimulated CaMKIIα Thr286 autophosphorylation in primary cortical neurons and substrate phosphorylation of recombinant CaMKIIα, potentially contributing to its neuroprotective effect. Supported by previous in silico docking studies, we suggest that Ph-HTBA makes distinct molecular interactions with the hub cavity, which may contribute to its differential functional profile and superior neuroprotective effect compared to HOCPCA. Together, this highlights Ph-HTBA as a promising tool to study hub functionality, but also as a good candidate for clinical development.

Biochemical Investigation of 3-Sulfopropionaldehyde Reductase HpfD.

Sulfoquinovose is the polar headgroup of plant sulfolipids and is a globally abundant organosulfur compound, and its degradation by bacteria is an important component of the sulfur cycle. Sulfoquinovose degradation by certain bacteria, including Escherichia coli, produces dihydroxypropanesulfonate (DHPS), which is further converted by anaerobic bacteria into 3-hydroxypropanesulfonate (3-HPS), through the catalytic action of DHPS dehydratase (a member of the glycyl radical enzyme family), and sulfopropionaldehyde reductase HpfD (a member of the metal-dependent alcohol dehydrogenase family). Here we report biochemical investigation of Hungatella hathewayi HpfD. In addition to 3-HPS, HpfD also displayed high catalytic activities for NAD+ -dependent oxidation of 4-hydroxybutanesulfonate (4-HBS) and γ-hydroxybutyrate (GHB). The highest activity was obtained with Fe2+ or Mn2+ as the divalent metal cofactor. Bioinformatics studies suggest that, in addition to DHPS degradation, 3-HPS and γ-aminobutyrate (GABA) degradations also involve HpfD homologs.

GHB analogs confer neuroprotection through specific interaction with the CaMKIIα hub domain.

Ca2+/calmodulin-dependent protein kinase II alpha subunit (CaMKIIα) is a key neuronal signaling protein and an emerging drug target. The central hub domain regulates the activity of CaMKIIα by organizing the holoenzyme complex into functional oligomers, yet pharmacological modulation of the hub domain has never been demonstrated. Here, using a combination of photoaffinity labeling and chemical proteomics, we show that compounds related to the natural substance γ-hydroxybutyrate (GHB) bind selectively to CaMKIIα. By means of a 2.2-Å x-ray crystal structure of ligand-bound CaMKIIα hub, we reveal the molecular details of the binding site deep within the hub. Furthermore, we show that binding of GHB and related analogs to this site promotes concentration-dependent increases in hub thermal stability believed to alter holoenzyme functionality. Selectively under states of pathological CaMKIIα activation, hub ligands provide a significant and sustained neuroprotection, which is both time and dose dependent. This is demonstrated in neurons exposed to excitotoxicity and in a mouse model of cerebral ischemia with the selective GHB analog, HOCPCA (3-hydroxycyclopent-1-enecarboxylic acid). Together, our results indicate a hitherto unknown mechanism for neuroprotection by a highly specific and unforeseen interaction between the CaMKIIα hub domain and small molecule brain-penetrant GHB analogs. This establishes GHB analogs as powerful tools for investigating CaMKII neuropharmacology in general and as potential therapeutic compounds for cerebral ischemia in particular.

Determination of endogenous GHB levels in chest and pubic hair.

Endogenous nature of GHB represents a critical issue for forensic toxicologists, especially in alleged sexual assaults. Therefore, discrimination between physiologically and additional amounts from exogenous sources of such a substance must be effective and reliable in order to avoid severe misinterpretation. This study aimed to quantify the GHB baseline concentrations in chest and pubic hairs collected from 105 healthy volunteers, non-consumers of any drugs of abuse. The final scope was to investigate if these keratin matrices could represent valid alternative to scalp hair when not available. Moreover, we also evaluated the age and gender influences on the GHB baseline levels. 25 mg of hair were incubated overnight with NaOH at 56 °C. After acidification with H2SO4, the solution was liquid-liquid extracted with ethyl acetate and a trimethylsilyl derivatization was then achieved. Analysis was performed in gas chromatography-mass spectrometry in single ion monitoring mode (m/z 233, 234, 147 for GHB; m/z 239, 240 and 147 for GHB-d6). The endogenous amount in "blank" hair was estimated by the standard addition method (0.301 for chest hair and 0.235 ng/mg for pubic hair). GHB concentration ranged from 0.205 to 1.511 ng/mg for chest hair and from 0.310 to 1.913 ng/mg for pubic hair. These values were consistent with previous studies on scalp hair and on pubic hair. Unfortunately, research on chest hair is not available in literature. T-Test and Linear Regression highlighted no statistically significant differences for the two matrices and for all age/gender sub-groups. However, further studies are required to estimate a reliable cut-off value for these keratin matrices. For the first time, we demonstrated the suitability of chest and pubic hair to detect endogenous levels of GHB.

GHB related acids (dihydroxy butyric acids, glycolic acid) can help in the interpretation of post mortem GHB results.

Post mortem gamma hydroxy butyric acid (GHB) concentrations should be interpreted with caution since GHB concentrations can increase after death. Post mortem concentrations after the intake of GHB ante mortem do overlap with concentration ranges in cases without known exposure to GHB and make an interpretation challenging. GHB is known to undergo intensive metabolism to related acids (glycolic acid (GA), succinic acid (SA), 2,4- and 3,4-dihydroxy butyric acid (2,4-OH-BA and 3,4-OH-BA)). GHB and these related acids were analyzed using a validated gas chromatographic mass spectrometric (GC-MS) method after liquid liquid extraction and trimethylsilylation. SA concentrations were not usable post mortem due to instability. Concentrations in cases without known exposure to GHB (urine: n = 80; femoral blood: n = 103) were: for GA 4.6-121 mg/L in urine and 1.6-11.2 mg/L in blood, for 2,4-OH-BA < LoD-25,3 mg/L in urine and < LoD-3.7 mg/L in blood and for 3,4-OH-BA < LoD-54,3 mg/L in urine and < LoD-5.3 mg/L in blood. In death cases involving GHB (n = 11) concentrations of GHB related acids were increased compared to these levels (for GA in 7/10 cases and up to 391 mg/L in urine, in 6/11 cases and up to 34 mg/L in blood; for 2,4-OH-BA in 9/10 cases and up to 144 mg/L in urine, in 11/11 cases and up to 9.1 mg/L in blood; for 3,4-OH-BA in 7/10 cases and up to 665 mg/L in urine, in 11/11 cases and up to 19 mg/L in blood). Therefore, the concentrations of these GHB related acids can aid in a more reliable differentiation of GHB exposure in post mortem toxicology. We recommend to add the analysis of 2,4-OH-BA, 3,4-OH-BA and GA in femoral blood for the diagnosis of a GHB intake post mortem. Post mortem femoral blood concentrations > 4 mg/L for 2,4-OH-BA, > 5 mg/L for 3,4-OH-BA and > 12 mg/L for GA give hints for a GHB intake.

Endogenous Gamma-Hydroxybutyrate in Postmortem Samples.

Gamma-hydroxybutyrate (GHB) is a naturally occurring molecule present in the human body as a catabolite of the neurotransmitter gamma-aminobutyrate (GABA). In the USA, GHB has a history of being manufactured illicitly and abused, with misguided proposed benefits for the body-building community and a persistent party drug with reported GHB overdoses occurring worldwide. The interpretation of GHB in postmortem biological fluids is complicated by the endogenous nature of the molecule. Analysis often requires more than one biological matrix to detect exogenous exposure, typically in urine. The analysis is further complicated by the endogenous de novo production of GHB in postmortem specimens. This work sought to examine the prevalence of endogenous GHB concentrations in postmortem toxicology samples from Orange County, CA, and to establish suitable in-house secondary matrices to confirm or rule out exogenous GHB exposure. A total of 348 postmortem heart blood samples were randomly selected and analyzed for GHB using liquid-liquid extraction followed by gas chromatography-mass spectrometry with selective ion monitoring and GHB-d6 as an internal standard. Of the 348 cases analyzed, 39 cases resulted in positive GHB detection with the median concentration of 22.45 mg/L (10.4-62.16 mg/L). None of the positive samples had suspected GHB ingestion or usage from the case report. GHB concentrations were then examined in secondary matrices collected at autopsy from the positive cases that included (when available) peripheral blood, urine, vitreous humor, liver homogenate and brain homogenate. Within the secondary matrices, GHB levels in peripheral blood compared to that of heart blood, while liver homogenate levels were variable. Quantifiable GHB levels were not identified in vitreous humor and brain homogenate samples. Our findings reaffirm the importance of multi-matrix analysis in postmortem toxicology and further confirm the utility of vitreous humor and brain tissue to distinguish exogenous GHB exposure from endogenous production.

Inpatient management of GHB/GBL withdrawal.

BACKGROUND: Gamma-hydroxybutyrate (GHB) and its precursor gamma-butyrolactone (GBL) are popular drugs of abuse used for their euphoric, (potential) anabolic, sedative, and amnestic properties. Daily use of GHB/GBL can lead to addiction and the possibility of withdrawal syndrome on cessation which results in tremor, tachycardia, insomnia, anxiety, hypertension, delirium, coma. AIM: To describe the baseline characteristics, treatment and retention in patients admitted for GHB/GBL withdrawal management. METHODS: A retrospective review of 4 consecutive cases of patients reporting GHB/GBL addiction who were admitted for inpatient management of withdrawal syndrome. RESULTS: All patients were using GHB/GBL daily, 1-1.5 ml per hour. One of them was using cannabis additionally, others were using alcohol, cocaine and amphetamine type stimulants. Psychiatric comorbidities as personality disorders, depression, anxiety and bigorexia were recognized. Patients were treated with benzodiazepines and/or clomethiazole, atypical and typical antipsychotics and beta-blockers. Delirium was developed in two patients. One patient completed detoxification and finished the treatment program. One patient completed detoxification but stopped his treatment earlier, two patients did not completed detoxification and left the program. CONCLUSION: GHB/GBL withdrawal can be severe and retention in program is poor. Polysubstance use, psychiatric co-morbidities and heavier GHB/GBL use as possible predictors of poor treatment outcome need consideration in treatment planning.

Variation of intraindividual levels of endogenous GHB in segmented hair samples.

Gamma-hydroxybutyrate (GHB) belongs to a group of substances that may be used in drug-facilitated crime (DFC). It is also an endogenous substance. There is a dispute whether or not a single exposure to GHB can be detected in hair. The first aim of this study was to develop and validate a method for the sensitive detection of base levels of GHB in hair. The second aim was to collect analytical data of 88 volunteers (62 females/26 males) not claiming any exposure to GHB and discuss the results in the context of the identification of a potential single exposure in cases of DFC. Furthermore hair samples from a male volunteer, who took GHB twice within 8 weeks, were analysed and the results were discussed with regard to mean values of endogenous GHB analysed in this study. Hair was digested under alkaline conditions, and GHB was isolated using liquid-liquid extraction. LC-MS/MS was performed using Electrospray ionization in the negative mode, multiple reaction monitoring, and a deuterated internal standard (GHB-D6). Segmental hair analysis revealed mean concentrations of 0.673ng/mg or 0.676ng/mg (without first segment) in females and 0.935ng/mg or 0.932ng/mg (without first segment) in males. Combined mean values were 0.751ng/mg and 0.752ng/mg (without first segment). In one individual's hair single doses of 2g GHB did not lead to an increase compared to his base levels. The limits of detection and quantitation in human hair were 0.1ng/mg and 0.3ng/mg, respectively. Accuracy at 0,25ng/mg, 2,5ng/mg and 25ng/mg was determined to be 94% or higher for all levels and intra-assay CVs at these concentrations were always lower than 7% (n=5). ß-hydroxybutyrate (BHB) and glycine did not produce an interference. Recovery at 1ng/mg and 25ng/mg GHB was 23% and 13% and Matrix effects were calculated to be 77% and 89% respectively.

Substrate specificity of tuliposide-converting enzyme, a unique non-ester-hydrolyzing carboxylesterase in tulip: Effects of the alcohol moiety of substrate on the enzyme activity.

6-Tuliposides A (PosA) and B (PosB) are glucose esters accumulated in tulip (Tulipa gesneriana) as major defensive secondary metabolites. Pos-converting enzymes (TgTCEs), which we discovered previously from tulip, catalyze the conversion reactions of PosA and PosB to antimicrobial tulipalins A (PaA) and B (PaB), respectively. The TgTCEs, belonging to the carboxylesterase family, specifically catalyze intramolecular transesterification, but not hydrolysis. In this report, we synthesized analogues of Pos with various alcohol moieties, and measured the TgTCE activity together with a determination of the kinetic parameters for these analogues with a view to probe the substrate recognition mechanism of the unique non-ester-hydrolyzing TgTCEs. It was found that d-glucose-like structure and number of the hydroxyl group in alcohol moiety are important for substrate recognition by TgTCEs. Among the analogues examined, 1,2-dideoxy analogues of PosA and PosB were found to be recognized by the TgTCEs more specifically than the authentic substrates by lowering Km values. The present results will provide a basis for designing simple, stable synthetic substrate analogues for crystallographic analysis of TgTCEs.

Hair testing of GHB: an everlasting issue in forensic toxicology.

BACKGROUND: In this paper, the authors present a critical review of different studies regarding hair testing of endogenous γ-hydroxybutyrate (GHB), concentrations in chronic users, and values measured after a single GHB exposure in drug facilitated sexual assault (DFSA) cases together with the role of a recently identified GHB metabolite, GHB-glucuronide. CONTENT: The following databases (up to March 2017) PubMed, Scopus and Web of Science were used, searching the following key words: γ-hydroxybutyrate, GHB, GHB glucuronide, hair. The main key words "GHB" and "γ-hydroxybutyrate" were searched singularly and then associated individually to each of the other keywords. SUMMARY: Of the 2304 sources found, only 20 were considered appropriate for the purpose of this paper. Summing up all the studies investigating endogenous GHB concentration in hair, a very broad concentration range from 0 to 12 ng/mg was found. In order to detect a single GHB dose in hair it is necessary to commonly wait 1 month for collecting hair and a segmental analysis of 3 or 5 mm fragments and the calculation of a ratio between the targeted segment and the others represent a reliable method to detect a single GHB intake considering that the ratios presently proposed vary from 3 and 10. The only two studies so far performed, investigating GHB-Glucuronide in hair, show that the latter does not seem to provide any diagnostic information regarding GHB exposure. OUTLOOK: A practical operative protocol is proposed to be applied in all suspected cases of GHB-facilitated sexual assault (GHB-FSA).

Catabolism of GABA, succinic semialdehyde or gamma-hydroxybutyrate through the GABA shunt impair mitochondrial substrate-level phosphorylation.

GABA is catabolized in the mitochondrial matrix through the GABA shunt, encompassing transamination to succinic semialdehyde followed by oxidation to succinate by the concerted actions of GABA transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH), respectively. Gamma-hydroxybutyrate (GHB) is a neurotransmitter and a psychoactive drug that could enter the citric acid cycle through transhydrogenation with α-ketoglutarate to succinic semialdehyde and d-hydroxyglutarate, a reaction catalyzed by hydroxyacid-oxoacid transhydrogenase (HOT). Here, we tested the hypothesis that the elevation in matrix succinate concentration caused by exogenous addition of GABA, succinic semialdehyde or GHB shifts the equilibrium of the reversible reaction catalyzed by succinate-CoA ligase towards ATP (or GTP) hydrolysis, effectively negating substrate-level phosphorylation (SLP). Mitochondrial SLP was addressed by interrogating the directionality of the adenine nucleotide translocase during anoxia in isolated mouse brain and liver mitochondria. GABA eliminated SLP, and this was rescued by the GABA-T inhibitors vigabatrin and aminooxyacetic acid. Succinic semialdehyde was an extremely efficient substrate energizing mitochondria during normoxia but mimicked GABA in abolishing SLP in anoxia, in a manner refractory to vigabatrin and aminooxyacetic acid. GHB could moderately energize liver but not brain mitochondria consistent with the scarcity of HOT expression in the latter. In line with these results, GHB abolished SLP in liver but not brain mitochondria during anoxia and this was unaffected by either vigabatrin or aminooxyacetic acid. It is concluded that when mitochondria catabolize GABA or succinic semialdehyde or GHB through the GABA shunt, their ability to perform SLP is impaired.

Stability of endogenous GHB in vitreous humor vs peripheral blood in dead bodies.

For the first time, the stability of GHB was tested in post-mortem peripheral blood and vitreous humor samples, collected from 22 dead bodies at two different times: at the external body examination at the place of death and then during autopsy. An ad hoc method for the detection and quantification of GHB in vitreous humor by gas chromatography coupled to mass spectrometry (GC-MS) was developed and validated, with a good linearity between 0.1 and 50µg/mL (r2=0.991) and a precision and accuracy always better than 10% and an analytical recovery higher than 90%. The geometric mean of GHB concentration in the 22 peripheral blood samples at t0 was: 3.6µg/mL (95% CI: 2.3-5.9µg/mL) and at t1 it was 7.4µg/mL (95% CI: 5.0-10.9µg/mL); that of GHB in the 22 vitreous humor at t0 was: 2.5µg/mL (95% CI: 1.5-4.1µg/mL) and at t1 it was 3.0µg/mL (95% CI: 1.9-4.8µg/mL). There was no significant difference between the GHB concentrations in vitreous humor and peripheral blood at t0 in all the samples (p>0.10). Conversely at t1, the increase of GHB in the peripheral blood was significantly increased by a 102% (range: 86-120%) (p<0.001 vs t0), while in the vitreous humor only a slight increase by 19% was observed (range: 16-21%) (p>0.05 vs t0). Finally at t1, GHB values in the two matrices were statistically different, being that of peripheral blood higher (p<0.01). This study demonstrated the usefulness of vitreous humor as a more stable alternative matrix in comparison to peripheral blood for the post-mortem determination of endogenous GHB.

Evaluation of 3-hydroxypropionate biosynthesis in vitro by partial introduction of the 3-hydroxypropionate/4-hydroxybutyrate cycle from Metallosphaera sedula.

The chemical 3-hydroxypropionate (3HP) is an important starting reagent for the commercial synthesis of specialty chemicals. In this study, a part of the 3-hydroxypropionate/4-hydroxybutyrate cycle from Metallosphaera sedula was utilized for 3HP production. To study the basic biochemistry of this pathway, an in vitro-reconstituted system was established using acetyl-CoA as the substrate for the kinetic analysis of this system. The results indicated that 3HP formation was sensitive to acetyl-CoA carboxylase and malonyl-CoA reductase, but not malonate semialdehyde reductase. Also, the competition between 3HP formation and fatty acid production was analyzed both in vitro and in vivo. This study has highlighted how metabolic flux is controlled by different catalytic components. We believe that this reconstituted system would be valuable for understanding 3HP biosynthesis pathway and for future engineering studies to enhance 3HP production.