Urinary organic acids in succinic semialdehyde dehydrogenase deficiency: evidence of alpha-oxidation of 4-hydroxybutyric acid, interaction of succinic semialdehyde with pyruvate dehydrogenase and possible secondary inhibition of mitochondrial beta-oxidation

Succinic semialdehyde dehydrogenase deficiency in mice and in humans: An untargeted metabolomics perspective

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare neurometabolic disorder caused by disruption of the gamma-aminobutyric acid (GABA) pathway. A more detailed understanding of its pathophysiology, beyond the accumulation of GABA and gamma-hydroxybutyric acid (GHB), will increase our understanding of the disease and may support novel therapy development. To this end, we compared biochemical body fluid profiles from SSADHD patients with controls using next-generation metabolic screening (NGMS). Targeted analysis of NGMS data from cerebrospinal fluid (CSF) showed a moderate increase of aspartic acid, glutaric acid, glycolic acid, 4-guanidinobutanoic acid, and 2-hydroxyglutaric acid, and prominent elevations of GHB and 4,5-dihydroxyhexanoic acid (4,5-DHHA) in SSADHD samples. Remarkably, the intensities of 4,5-DHHA and GHB showed a significant positive correlation in control CSF, but not in patient CSF. In an established zebrafish epilepsy model, 4,5-DHHA showed increased mobility that may reflect limited epileptogenesis. Using untargeted metabolomics, we identified 12 features in CSF with high biomarker potential. These had comparable increased fold changes as GHB and 4,5-DHHA. For 10 of these features, a similar increase was found in plasma, urine and/or mouse brain tissue for SSADHD compared to controls. One of these was identified as the novel biomarker 4,5-dihydroxyheptanoic acid. The intensities of selected features in plasma and urine of SSADHD patients positively correlated with the clinical severity score of epilepsy and psychiatric symptoms of those patients, and also showed a high mutual correlation. Our findings provide new insights into the (neuro)metabolic disturbances in SSADHD and give leads for further research concerning SSADHD pathophysiology.

Urinary markers of Mycobacterium tuberculosis and dysbiosis in paediatric tuberculous meningitis cases undergoing treatment

BACKGROUND

The pathogenesis of tuberculous meningitis (TBM) involves infection by Mycobacterium tuberculosis in the meninges and brain. However, recent studies have shown that the immune response and inflammatory processes triggered by TBM can have significant effects on gut microbiota. Disruptions in the gut microbiome have been linked to various systemic consequences, including altered immunity and metabolic dysregulation. Inflammation caused by TBM, antibiotic treatment, and changes in host immunity can all influence the composition of gut microbes. This complex relationship between TBM and the gut microbiome is of great importance in clinical settings. To gain a deeper understanding of the intricate interactions between TBM and the gut microbiome, we report innovative insights into the development of the disease in response to treatment. Ultimately, this could lead to improved outcomes, management strategies and quality of life for individuals affected by TBM.

METHOD

We used a targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach to investigate metabolites associated with gut metabolism in paediatric participants by analysing the urine samples collected from a control group (n = 40), and an experimental group (n = 35) with confirmed TBM, which were subdivided into TBM stage 1 (n = 8), stage 2 (n = 11) and stage 3 (n = 16).

FINDINGS

Our metabolomics investigation showed that, of the 78 initially selected compounds of microbiome origin, eight unique urinary metabolites were identified: 2-methylbutyrlglycine, 3-hydroxypropionic acid, 3-methylcrotonylglycine, 4-hydroxyhippuric acid, 5-hydroxyindoleacetic acid, 5-hydroxyhexanoic acid, isobutyrylglycine, and phenylacetylglutamine as urinary markers of dysbiosis in TBM.

CONCLUSION

These results - which are supported by previous urinary studies of tuberculosis - highlight the importance of gut metabolism and of identifying corresponding microbial metabolites as novel points for the foundation of improved management of TBM patients.

New gamma-hydroxybutyric acid (GHB) biomarkers: Development and validation of a liquid chromatography-tandem mass spectrometry method for the determination of GHB amino acid, carnitine, and fatty acid conjugates in urine

Gamma-hydroxybutyric acid (GHB) represents an important drug in clinical and forensic toxicology, particularly in the context of drug-facilitated crimes. Analytically, GHB remains a major challenge given its endogenous occurrence and short detection window. Previous studies identified a number of potential interesting novel conjugates of GHB with carnitine, amino acids (AA, glutamate, glycine, and taurine), or fatty acids. As a basis for comprehensive studies on the suitability of these novel biomarkers, we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in human urine. Additionally, already known markers 2,4-dihydroxy butyric acid (2,4-DHB), 3,4-DHB, glycolic acid, succinic acid, succinylcarnitine, and GHB glucuronide were included. The method was fully validated according to (inter)national guidelines. Synthetic urine proved suitable as a surrogate matrix for calibration. Matrix effects were observed for all analytes with suppression effects of about 50% at QC LOW, and approximately 20% to 40% at QC HIGH, but with consistent standard deviation of <25% at QC LOW and <15% at QC HIGH, respectively. All analytes showed acceptable intra- and inter-day imprecision of below 20%, except for inter-day variation of GHB taurine and FA conjugates at the lowest QC. Preliminary applicability studies proved the usefulness of the method and pointed towards GHB glycine, followed by other AA conjugates as the most promising candidates to improve GHB detection. FA conjugates were not detected in urine samples yet. The method can be used now for comprehensive sample analysis on (controlled) GHB administration to prove the usefulness of the novel GHB biomarkers.

Silage Fermentation: A Potential Microbial Approach for the Forage Utilization of Cyperus esculentus L. By-Product

Cyperus esculentus L. leaves (CLL) are agricultural by-products produced from Cyperus esculentus L. harvesting, and can be used as livestock feed despite their low economic value for human consumption. This study aims to develop a favorable approach to processing Cyperus esculentus L. by-product as coarse fodder. The chopped CLL was pretreated by (1) mixing with canola straw at a 4:1 ratio, or (2) wilting it for 8 h, then it ensiling with or without compounded lactic acid bacteria (LAB) additives for 60 days. Our results demonstrated that compounded LAB additives: improved CLL silage fermentation quality by increasing acetic acid and lactic acid contents and decreasing ethanol and ammonia-N contents; preserved nutrients by raising the level of crude protein and water soluble carbohydrates; modified the bacterial community by increasing the relative abundance of Lactobacillus while decreasing the relative abundance of undesirable Enterococcus; and also might improve animal health by increasing the relative concentrations of antioxidant substances (such as 7-galloylcatechin) and antibacterial compounds (such as ferulic acid). This study provides strong evidence that Cyperus esculentus L. by-product can be a potential livestock feed after being ensiled with compounded LAB additives.

GHB related acids are useful in routine casework of suspected GHB intoxication cases

GHB related acids (3,4-dihydroxy butyric acid, 2,4-dihydroxy butyric acid and glycolic acid) are produced through oxidative GHB metabolism. These analytes could be potential biomarkers to ensure the diagnosis of a GHB intoxication and even prolong the detection window. Within this study, forensic routine cases were measured to consider the potential of additional gas chromatographic mass spectrometric analysis on these acids. 17 GHB positive real cases (10 serum samples and 7 urine samples) and 40 cases with suspicion of drugging in DFC cases and negative GHB results (21 serum samples and 19 urine samples) were evaluated. Increased GHB related acid concentrations were detected in all serum and most urine samples positive on GHB. In some GHB negative cases, especially in serum samples, concentrations of GHB related acids gave hints that GHB actually was taken. We recommend to use the following cut-offs for a more reliable interpretation of potential GHB intoxication cases: 3,4-OH-BA:>3 mg/L in serum and>50 mg/L in urine; 2,4-OH-BA:>2 mg/L in serum and>25 mg/L in urine; GA:>5 mg/L in serum and>400 mg/L in urine.

Detection of γ-hydroxybutyric acid-related acids in blood plasma and urine: Extending the detection window of an exogenous γ-hydroxybutyric acid intake?

In crimes facilitated by γ-hydroxybutyric acid (GHB) administration, the frequent occurrence of anterograde amnesia of the victims as well as the short detection window and variations of endogenous GHB concentrations complicate obtaining analytical proof of GHB administration. Because elevated endogenous organic acid concentrations have been found in the urine of patients with succinic semialdehyde deficiency (leading to accumulation of GHB in human specimens) and after GHB ingestion, we searched for an alternative way to prove GHB administration via detection of elevated organic acid concentrations in blood plasma and urine. We collected blood and urine samples from narcolepsy patients (n = 5) treated with pharmaceuticals containing GHB sodium salt (1.86-3.72 g GHB as free acid per dose). Although GHB was detectable only up to 4 h in concentrations greater than the commonly used cutoff levels in blood plasma, 3,4-dihydroxybutyric acid (3,4-DHB) could be detected up to 12 h in blood plasma in concentrations exceeding initial concentrations of the same patient before GHB ingestion. Furthermore, four of the five patients showed an increase above endogenous levels described in the scientific literature. In urine, GHB concentrations above commonly used cutoff levels could be observed 4.5-9.5 h after GHB intake. Creatinine standardized initial concentrations were reached again for glycolic acid (GA), 3,4-DHB, and 2,4-dihydroxybutyric (2,4-DHB) acid at 6.5-22, 11.5-22, and 8.5-70 h after GHB intake, respectively. Therefore, 2,4-DHB, 3,4-DHB, and GA are promising and should be further investigated as potential biomarkers to prolong the detection window of GHB intake.

Towards Extending the Detection Window of Gamma-Hydroxybutyric Acid-An Untargeted Metabolomics Study in Serum and Urine Following Controlled Administration in Healthy Men

In forensic toxicology, gamma-hydroxybutyrate (GHB) still represents one of the most challenging drugs of abuse in terms of analytical detection and interpretation. Given its rapid elimination, the detection window of GHB in common matrices is short (maximum 12 h in urine). Additionally, the differentiation from naturally occurring endogenous GHB, is challenging. Thus, novel biomarkers to extend the detection window of GHB are urgently needed. The present study aimed at searching new potential biomarkers of GHB use by means of mass spectrometry (MS) metabolomic profiling in serum (up to 16.5 h) and urine samples (up to 8 h after intake) collected during a placebo-controlled crossover study in healthy men. MS data acquired by different analytical methods (reversed phase and hydrophilic interaction liquid chromatography; positive and negative electrospray ionization each) were filtered for significantly changed features applying univariate and mixed-effect model statistics. Complementary to a former study, conjugates of GHB with glycine, glutamate, taurine, carnitine and pentose (ribose) were identified in urine, with particularly GHB-pentose being promising for longer detection. None of the conjugates were detectable in serum. Therein, mainly energy metabolic substrates were identified, which may be useful for more detailed interpretation of underlying pathways but are too unspecific as biomarkers.

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.

Novel biomarkers and age-related metabolite correlations in plasma and dried blood spots from patients with succinic semialdehyde dehydrogenase deficiency

BACKGROUND

Previous work has identified age-related negative correlations for γ-hydroxybutyric acid (GHB) and γ-aminobutyric acid (GABA) in plasma of patients with succinic semialdehyde dehydrogenase deficiency (SSADHD). Using plasma and dried blood spots (DBS) collected in an ongoing natural history study, we tested the hypothesis that other biomarkers would follow a similar age-related negative correlation as seen for GHB/GABA. Samples (mixed sex) included: patients (n = 21 unique samples, 1-39.5 yrs) and parallel controls (n = 9 unique samples, 8.4-34.8 yrs). Archival control data (DBS only; n = 171, 0.5-39.9 yrs) was also included.

RESULTS

Metabolites assessed included amino acids (plasma, DBS) and acylcarnitines, creatine, creatinine, and guanidinoacetate (DBS only). Age-related negative correlations for glycine (plasma, DBS) and sarcosine (N-methylglycine, plasma) were detected, accompanied by elevated proline and decreased levels of succinylacetone, argininosuccinate, formaminoglutamate, and creatinine. Significantly low acylcarnitines were detected in patients across all chain lengths (short-, medium- and long-chain). Significant age-dependent positive correlations for selected acylcarnitines (C6-, C12DC(dicarboxylic)-, C16-, C16:1-, C18:1-, C18:2OH-carnitines) were detected in patients and absent in controls. Receiver operating characteristic (ROC) curves for all binary comparisons revealed argininosuccinate and succinylacetone to be the most discriminating biomarkers (area > 0.92).

CONCLUSIONS

Age-dependent acylcarnitine correlations may represent metabolic compensation responsive to age-related changes in GHB and GABA. Our study highlights novel biomarkers in SSADHD and expands the metabolic pathophysiology of this rare disorder of GABA metabolism.

Longitudinal metabolomics in dried bloodspots yields profiles informing newborn screening for succinic semialdehyde dehydrogenase deficiency

Analyses of 19 amino acids, 38 acylcarnitines, and 3 creatine analogues (https://clir.mayo.edu) were implemented to test the hypothesis that succinic semialdehyde dehydrogenase deficiency (SSADHD) could be identified in dried bloodspots (DBS) using currently available newborn screening methodology. The study population included 17 post-newborn SSADHD DBS (age range 0.8-38 years; median, 8.2 years; 10 M; controls, 129-353 age-matched individuals, mixed gender) and 10 newborn SSADHD DBS (including first and second screens from 3 of 7 patients). Low (informative) markers in post-newborn DBS included C2- and C4-OH carnitines, ornithine, histidine and creatine, with no gender differences. For newborn DBS, informative markers included C2-, C3-, C4- and C4-OH carnitines, creatine and ornithine. Of these, only creatine demonstrated a significant change with age, revealing an approximate 4-fold decrease. We conclude that quantitation of short-chain acylcarnitines, creatine, and ornithine provides a newborn DBS profile with potential as a first tier screening tool for early detection of SSADHD. This first tier evaluation can be readily verified using a previously described second tier liquid chromatography-tandem mass spectrometry method for γ-hydroxybutyric acid in the same DBS. More extensive evaluation of this first/second tier screening approach is needed in a larger population.

Post-mortem tissue analyses in a patient with succinic semialdehyde dehydrogenase deficiency (SSADHD). I. Metabolomic outcomes

Metabolomic characterization of post-mortem tissues (frontal and parietal cortices, pons, cerebellum, hippocampus, cerebral cortex, liver and kidney) derived from a 37 y.o. male patient with succinic semialdehyde dehydrogenase deficiency (SSADHD) was performed in conjunction with four parallel series of control tissues. Amino acids, acylcarnitines, guanidino- species (guanidinoacetic acid, creatine, creatinine) and GABA-related intermediates were quantified using UPLC and mass spectrometric methods that included isotopically labeled internal standards. Amino acid analyses revealed significant elevation of aspartic acid and depletion of glutamine in patient tissues. Evidence for disruption of short-chain fatty acid metabolism, manifest as altered C4OH, C5, C5:1, C5DC (dicarboxylic) and C12OH carnitines, was observed. Creatine and guanidinoacetic acids were decreased and elevated, respectively. GABA-associated metabolites (total GABA, γ-hydroxybutyric acid, succinic semialdehyde, 4-guanidinobutyrate, 4,5-dihydroxyhexanoic acid and homocarnosine) were significantly increased in patient tissues, including liver and kidney. The data support disruption of fat, creatine and amino acid metabolism as a component of the pathophysiology of SSADHD, and underscore the observation that metabolites measured in patient physiological fluids provide an unreliable reflection of brain metabolism.

Temporal metabolomics in dried bloodspots suggests multipathway disruptions in aldh5a1-/- mice, a model of succinic semialdehyde dehydrogenase deficiency

Succinic semialdehyde dehydrogenase (SSADH) deficiency (SSADHD; OMIM 271980) is a rare disorder featuring accumulation of neuroactive 4-aminobutyric acid (GABA; γ-aminobutyric acid, derived from glutamic acid) and 4-hydroxybutyric acid (γ-hydroxybutyric acid; GHB, a short-chain fatty acid analogue of GABA). Elevated GABA is predicted to disrupt the GABA shunt linking GABA transamination to the Krebs cycle and maintaining the balance of excitatory:inhibitory neurotransmitters. Similarly, GHB (or a metabolite) is predicted to impact β-oxidation flux. We explored these possibilities employing temporal metabolomics of dried bloodspots (DBS), quantifying amino acids, acylcarnitines, and guanidino- metabolites, derived from aldh5a1^+/+, aldh5a1^+/- and aldh5a1^-/- mice (aldehyde dehydrogenase 5a1 = SSADH) at day of life (DOL) 20 and 42 days. At DOL 20, aldh5a1^-/- mice had elevated C6 dicarboxylic (adipic acid) and C14 carnitines and threonine, combined with a significantly elevated ratio of threonine/[aspartic acid + alanine], in comparison to aldh5a1^+/+ mice. Conversely, at DOL 42 aldh5a1^-/- mice manifested decreased short chain carnitines (C0-C6), valine and glutamine, in comparison to aldh5a1^+/+ mice. Guanidino species, including creatinine, creatine and guanidinoacetic acid, evolved from normal levels (DOL 20) to significantly decreased values at DOL 42 in aldh5a1^-/- as compared to aldh5a1^+/+ mice. Our results provide a novel temporal snapshot of the evolving metabolic profile of aldh5a1^-/- mice while highlighting new pathomechanisms in SSADHD.

Allopregnanolone Treatment Improves Plasma Metabolomic Profile Associated with GABA Metabolism in Fragile X-Associated Tremor/Ataxia Syndrome: a Pilot Study

Currently, there is no effective treatment for the fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative disorder. In this pilot study, we evaluated whether allopregnanolone, a natural neurosteroid that exerts beneficial effects in neurodegenerative diseases, nervous system injury, and peripheral neuropathies, could improve lymphocytic bioenergetics and plasma pharmacometabolomics in six males with FXTAS (68 ± 3 years old; FMR1 CGG repeats 94 ± 4; FXTAS stages ranging from 3 to 5) enrolled in a 12-week open-label intervention study conducted at the University of California Davis from December 2015 through July 2016. Plasma pharmacometabolomics and lymphocytic mitochondria function were assessed at baseline (on the day of the first infusion) and at follow-up (within 48 h from the last infusion). In parallel, quantitative measurements of tremor and ataxia and neuropsychological evaluations of mental state, executive function, learning, memory, and psychological symptoms were assessed at the same time points. Allopregnanolone treatment impacted significantly GABA metabolism, oxidative stress, and some of the mitochondria-related outcomes. Notably, the magnitude of the individual metabolic response, as well as the correlation with some of the behavioral tests, was overwhelmingly carrier-specific. Based on this pilot study, allopregnanolone treatment has the potential for improving cognitive and GABA metabolism in FXTAS aligned with the concept of precision medicine.

The GC-MS metabolomics signature in patients with fibromyalgia syndrome directs to dysbiosis as an aspect contributing factor of FMS pathophysiology

INTRODUCTION

Fibromyalgia syndrome (FMS) is a chronic pain syndrome. Previous analyses of untargeted metabolomics data indicated altered metabolic profile in FMS patients.

OBJECTIVES

We report a semi-targeted explorative metabolomics study on the urinary metabolite profile of FMS patients; exploring the potential of urinary metabolite information to augment existing medical diagnosis.

METHODS

All cases were females. Patients had a medical history of persistent FMS (n = 18). Control groups were first-generation family members of the patients (n = 11), age-related individuals without indications of FMS (n = 10), and healthy, young (18-22 years) individuals (n = 41). The biofluid investigated was early morning urine samples. Data generation was done through gas chromatography-mass spectrometry (GC-MS) analysis and data processing and analyses were performed using Matlab, R, SPSS and SAS software.

RESULTS

Quantitative analysis revealed the presence of 196 metabolites. Unsupervised and supervised multivariate analyses distinguished all three control groups and the FMS patients, which could be related to 14 significantly increased metabolites. These metabolites are associated with energy metabolism, digestion and metabolism of carbohydrates and other host and gut metabolites.

CONCLUSIONS

Overall, urinary metabolite profiles in the FMS patients suggest: (1) energy utilization is a central aspect of this pain disorder, (2) dysbiosis seems to prevail in FMS patients, indicated by disrupted microbiota metabolites, supporting the model that microbiota may alter brain function through the gut-brain axis, with the gut being a gateway to generalized pain, and (3) screening of urine from FMS is an avenue to explore for adding non-invasive clinical information for diagnosis and treatment of FMS.

Inborn errors of metabolism

Inborn errors of metabolism, also known as inherited metabolic diseases, constitute an important group of conditions presenting with neurologic signs in newborns. They are individually rare but collectively common. Many are treatable through restoration of homeostasis of a disrupted metabolic pathway. Given their frequency and potential for treatment, the clinician should be aware of this group of conditions and learn to identify the typical manifestations of the different inborn errors of metabolism. In this review, we summarize the clinical, laboratory, electrophysiologic, and neuroimaging findings of the different inborn errors of metabolism that can present with florid neurologic signs and symptoms in the neonatal period.

Therapeutic relevance of mTOR inhibition in murine succinate semialdehyde dehydrogenase deficiency (SSADHD), a disorder of GABA metabolism

Aldehyde dehydrogenase 5a1-deficient (aldh5a1-/-) mice, the murine orthologue of human succinic semialdehyde dehydrogenase deficiency (SSADHD), manifest increased GABA (4-aminobutyric acid) that disrupts autophagy, increases mitochondria number, and induces oxidative stress, all mitigated with the mTOR (mechanistic target of rapamycin) inhibitor rapamycin [1]. Because GABA regulates mTOR, we tested the hypothesis that aldh5a1-/- mice would show altered levels of mRNA for genes associated with mTOR signaling and oxidative stress that could be mitigated by inhibiting mTOR. We observed that multiple metabolites associated with GABA metabolism (γ-hydroxybutyrate, succinic semialdehyde, D-2-hydroxyglutarate, 4,5-dihydrohexanoate) and oxidative stress were significantly increased in multiple tissues derived from aldh5a1-/- mice. These metabolic perturbations were associated with decreased levels of reduced glutathione (GSH) in brain and liver of aldh5a1-/- mice, as well as increased levels of adducts of the lipid peroxidation by-product, 4-hydroxy-2-nonenal (4-HNE). Decreased liver mRNA levels for multiple genes associated with mTOR signaling and oxidative stress parameters were detected in aldh5a1-/- mice, and several were significantly improved with the administration of mTOR inhibitors (Torin 1/Torin 2). Western blot analysis of selected proteins corresponding to oxidative stress transcripts (glutathione transferase, superoxide dismutase, peroxiredoxin 1) confirmed gene expression findings. Our data provide additional preclinical evidence for the potential therapeutic efficacy of mTOR inhibitors in SSADHD.

Incidence and Geographic Distribution of Succinic Semialdehyde Dehydrogenase (SSADH) Deficiency

The incidence of succinic semialdehyde dehydrogenase (SSADH) deficiency, an autosomal recessive inherited disorder of GABA degradation, is unknown. Upon a recent diagnosis of a new family of affected fraternal twins from the Punjabi ethnic group of India, case ascertainment from the literature and our database was done to determine the number of confirmed cases along with their geographic distribution. The probands presented with global developmental delay, infantile onset epilepsy, and a persistent neurodevelopmental disorder upon diagnosis at 10 years of age with intellectual disability, expressive aphasia, and behavioral problems most prominent for hyperactivity. Gamma-hydroxybutyric aciduria and homozygous ALDH5A1 c.608C>T; p.Pro203Leu mutations were confirmed. Identification of all available individual cases with clinical details available including geographic or ethnic origin revealed 182 patients from 40 countries, with the largest number of patients reported from the USA (24%), Turkey (10%), China (7%), Saudi Arabia (6%), and Germany (5%). This study provides an accounting of all published cases of confirmed SSADH deficiency and provides data useful in planning further studies of this rare inborn error of metabolism.

Adrenal cortex expression quantitative trait loci in a German Holstein × Charolais cross

Background

The importance of the adrenal gland in regard to lactation and reproduction in cattle has been recognized early. Caused by interest in animal welfare and the impact of stress on economically important traits in farm animals the adrenal gland and its function within the stress response is of increasing interest. However, the molecular mechanisms and pathways involved in stress-related effects on economically important traits in farm animals are not fully understood. Gene expression is an important mechanism underlying complex traits, and genetic variants affecting the transcript abundance are thought to influence the manifestation of an expressed phenotype. We therefore investigated the genetic background of adrenocortical gene expression by applying an adaptive linear rank test to identify genome-wide expression quantitative trait loci (eQTL) for adrenal cortex transcripts in cattle.

Results

A total of 10,986 adrenal cortex transcripts and 37,204 single nucleotide polymorphisms (SNPs) were analysed in 145 F2 cows of a Charolais × German Holstein cross. We identified 505 SNPs that were associated with the abundance of 129 transcripts, comprising 482 cis effects and 17 trans effects. These SNPs were located on all chromosomes but X, 16, 24 and 28. Associated genes are mainly involved in molecular and cellular functions comprising free radical scavenging, cellular compromise, cell morphology and lipid metabolism, including genes such as CYP27A1 and LHCGR that have been shown to affect economically important traits in cattle.

Conclusions

In this study we showed that adrenocortical eQTL affect the expression of genes known to contribute to the phenotypic manifestation in cattle. Furthermore, some of the identified genes and related molecular pathways were previously shown to contribute to the phenotypic variation of behaviour, temperament and growth at the onset of puberty in the same population investigated here. We conclude that eQTL analysis appears to be a useful approach providing insight into the molecular and genetic background of complex traits in cattle and will help to understand molecular networks involved.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0442-x) contains supplementary material, which is available to authorized users.

A case of acute onset succinic semialdehyde dehydrogenase deficiency: neuroimaging findings and literature review

BACKGROUND

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal recessive disorder of γ-aminobutyric acid metabolism, leading to elevated levels of γ-aminobutyric acid and γ-hydroxybutyric acid in cerebrospinal fluid.

PATIENT

We describe the neuroimaging findings of a previously healthy 6-month-old girl with acute onset of lethargy, hypotonia, and choreiform movements, and a subsequent diagnosis of SSADH deficiency. Magnetic resonance (MR) imaging of the brain revealed symmetric T2 hyperintense signal abnormalities and reduced diffusivity of the globus pallidi bilaterally. Arterial spin-labeling perfusion MR imaging suggested bilateral hyperperfusion of the globus pallidi. MR spectroscopy of the thalamus and frontal lobe white matter revealed increased signal intensity in the glutamate and glutamine region of the spectra between 2.1 and 2.4 ppm.

CONCLUSION

The unique early imaging findings described here may be attributable to bioenergetic failure and deficiency in mitochondrial energy metabolism and are consistent with SSADH-knockout mice studies.

Succinic semialdehyde dehydrogenase deficiency (SSADHD): Pathophysiological complexity and multifactorial trait associations in a rare monogenic disorder of GABA metabolism

Discovered some 35 years ago, succinic semialdehyde dehydrogenase deficiency (SSADHD) represents a rare, autosomal recessively-inherited defect in the second step of the GABA degradative pathway. Some 200 patients have been reported, with broad phenotypic and genotypic heterogeneity. SSADHD represents an unusual neurometabolic disorder in which two neuromodulatory agents, GABA (and the GABA analogue, 4-hydroxybutyrate), accumulate to supraphysiological levels. The unexpected occurrence of epilepsy in several patients is counterintuitive in view of the hyperGABAergic state, in which sedation might be expected. However, the epileptic status of some patients is most likely represented by broader imbalances of GABAergic and glutamatergic neurotransmission. Cumulative research encompassing decades of basic and clinical study of SSADHD reveal a monogenic disease with broad pathophysiological and clinical phenotypes. Numerous metabolic perturbations unmasked in SSADHD include alterations in oxidative stress parameters, dysregulation of autophagy and mitophagy, dysregulation of both inhibitory and excitatory neurotransmitters and gene expression, and unique subsets of SNP alterations of the SSADH gene (so-called ALDH5A1, or aldehyde dehydrogenase 5A1 gene) on the 6p22 chromosomal arm. While seemingly difficult to collate and interpret, these anomalies have continued to open novel pathways for pharmacotherapeutic considerations. Here, we present an update on selected aspects of SSADHD, the ALDH5A1 gene, and future avenues for research on this rare disorder of GABA metabolism.

Accumulated Metabolites of Hydroxybutyric Acid Serve as Diagnostic and Prognostic Biomarkers of Ovarian High-Grade Serous Carcinomas

Ovarian cancer is a heterogeneous disease of low prevalence, but poor survival. Early diagnosis is critical for survival, but it is often challenging because the symptoms of ovarian cancer are subtle and become apparent only during advanced stages of the disease. Therefore, the identification of robust biomarkers of early disease is a clinical priority. Metabolomic profiling is an emerging diagnostic tool enabling the detection of biomarkers reflecting alterations in tumor metabolism, a hallmark of cancer. In this study, we performed metabolomic profiling of serum and tumor tissue from 158 patients with high-grade serous ovarian cancer (HGSOC) and 100 control patients with benign or non-neoplastic lesions. We report metabolites of hydroxybutyric acid (HBA) as novel diagnostic and prognostic biomarkers associated with tumor burden and patient survival. The accumulation of HBA metabolites caused by HGSOC was also associated with reduced expression of succinic semialdehyde dehydrogenase (encoded by ALDH5A1), and with the presence of an epithelial-to-mesenchymal transition gene signature, implying a role for these metabolic alterations in cancer cell migration and invasion. In conclusion, our findings represent the first comprehensive metabolomics analysis in HGSOC and propose a new set of metabolites as biomarkers of disease with diagnostic and prognostic capabilities.

Hypoxia and GABA shunt activation in the pathogenesis of Alzheimer's disease

We have previously observed that the conversion of mild cognitive impairment to definitive Alzheimer's disease (AD) is associated with a significant increase in the serum level of 2,4-dihydroxybutyrate (2,4-DHBA). The metabolic generation of 2,4-DHBA is linked to the activation of the γ-aminobutyric acid (GABA) shunt, an alternative energy production pathway activated during cellular stress, when the function of Krebs cycle is compromised. The GABA shunt can be triggered by local hypoperfusion and subsequent hypoxia in AD brains caused by cerebral amyloid angiopathy. Succinic semialdehyde dehydrogenase (SSADH) is a key enzyme in the GABA shunt, converting succinic semialdehyde (SSA) into succinate, a Krebs cycle intermediate. A deficiency of SSADH activity stimulates the conversion of SSA into γ-hydroxybutyrate (GHB), an alternative route from the GABA shunt. GHB can exert not only acute neuroprotective activities but unfortunately also chronic detrimental effects which may lead to cognitive impairment. Subsequently, GHB can be metabolized to 2,4-DHBA and secreted from the brain. Thus, the activation of the GABA shunt and the generation of GHB and 2,4-DHBA can have an important role in the early phase of AD pathogenesis.

Disorders of GABA metabolism: SSADH and GABA-transaminase deficiencies

Clinical disorders known to affect inherited gamma-amino butyric acid (GABA) metabolism are autosomal recessively inherited succinic semialdehyde dehydrogenase and GABA-transaminase deficiency. The clinical presentation of succinic semialdehyde dehydrogenase deficiency includes intellectual disability, ataxia, obsessive-compulsive disorder and epilepsy with a nonprogressive course in typical cases, although a progressive form in early childhood as well as deterioration in adulthood with worsening epilepsy are reported. GABA-transaminase deficiency is associated with a severe neonatal-infantile epileptic encephalopathy.

Temperament type specific metabolite profiles of the prefrontal cortex and serum in cattle

In the past decade the number of studies investigating temperament in farm animals has increased greatly because temperament has been shown not only to affect handling but also reproduction, health and economically important production traits. However, molecular pathways underlying temperament and molecular pathways linking temperament to production traits, health and reproduction have yet to be studied in full detail. Here we report the results of metabolite profiling of the prefrontal cortex and serum of cattle with distinct temperament types that were performed to further explore their molecular divergence in the response to the slaughter procedure and to identify new targets for further research of cattle temperament. By performing an untargeted comprehensive metabolite profiling, 627 and 1097 metabolite features comprising 235 and 328 metabolites could be detected in the prefrontal cortex and serum, respectively. In total, 54 prefrontal cortex and 51 serum metabolite features were indicated to have a high relevance in the classification of temperament types by a sparse partial least square discriminant analysis. A clear discrimination between fearful/neophobic-alert, interested-stressed, subdued/uninterested-calm and outgoing/neophilic-alert temperament types could be observed based on the abundance of the identified relevant prefrontal cortex and serum metabolites. Metabolites with high relevance in the classification of temperament types revealed that the main differences between temperament types in the response to the slaughter procedure were related to the abundance of glycerophospholipids, fatty acyls and sterol lipids. Differences in the abundance of metabolites related to C21 steroid metabolism and oxidative stress indicated that the differences in the metabolite profiles of the four extreme temperament types could be the result of a temperament type specific regulation of molecular pathways that are known to be involved in the stress and fear response.

Deregulated tyrosine-phenylalanine metabolism in pulmonary tuberculosis patients

Metabolic profiling of biofluids from tuberculosis (TB) patients would help us in understanding the disease pathophysiology and may also be useful for the development of novel diagnostics and host-directed therapy. In this pilot study we have compared the urine metabolic profiles of two groups of subjects having similar TB symptoms and categorized as active TB (ATB, n = 21) and non-TB (NTB, n = 21) based on GeneXpert test results. Silylation, gas chromatography mass spectrometry, and standard chemometric methods were employed to identify the important molecules and deregulated metabolic pathways. Eleven active TB patients were followed up on longitudinally for comparative urine metabolic profiling with healthy controls (n = 11). A set of 42 features qualified to have a variable importance parameter score of > 1.5 of a partial least-squares discriminate analysis model and fold change of > 1.5 at p value < 0.05 between ATB and NTB. Using these variables, a receiver operating characteristics curve was plotted and the area under the curve was calculated to be 0.85 (95% CI: 0.72-0.96). Several of these variables that represent norepinephrine, gentisic acid, 4-hydroxybenzoic acid, hydroquinone, and 4-hydroxyhippuric acid are part of the tyrosine-phenylalanine metabolic pathway. In the longitudinal study we observed a treatment-dependent trend in the urine metabolome of follow-up samples, and subjects declared as clinically cured showed similar metabolic profile as those of asymptomatic healthy subjects. The deregulated tyrosine-phenylalanine axis reveals a potential target for diagnostics and intervention in TB.

Metabolism of gamma hydroxybutyrate in human hepatoma HepG2 cells by the aldo-keto reductase AKR1A1

Gamma hydroxybutyrate (GHB) is a recreational and date-rape drug, for which the detection following ingestion is hampered by rapid metabolism and its endogenous presence. GHB catabolism occurs mainly by its oxidation to succinic semialdehyde (SSA), which converts to succinate and enters the tricarboxylic acid cycle. A high Km aldehyde reductase has previously been reported to catalyse the NADP-dependent oxidation of GHB at high concentrations. It is assumed that this enzyme is identical to the aldo-keto reductase AKR1A1, but its role in GHB oxidation has not been fully evaluated. In this study, the extent of AKR1A1 in GHB metabolism has been determined in HepG2 cells using RNA-interference technology. The gene encoding AKR1A1 was targeted by siRNA. Results demonstrate a successful knock-down of the AKR1A1 gene with 92% reduction in total mRNA and 93% reduction in protein expression. Demolishing AKR1A1 expression in HepG2 cells leads to significant 82% decrease in NADP-dependent GHB-dehydrogenase activity at high concentration (10mM) of GHB. Moreover, when exposing the cells to 50 μM of GHB for 24h, and measuring intracellular and extracellular GHB levels by GC/MS, a significant two-fold increase was observed on GHB intracellular level in silenced cells. In contrast, measuring SSA-reductase activity in silenced cells indicated that AKR1A1 is not involved in endogenous GHB production. These findings describe a pathway for GHB metabolism in the liver which should be useful in GHB exposure cases, and will enable a better understanding of the enzymes participating in its metabolism at natural and overexposed levels.

Evidence of redox imbalance in a patient with succinic semialdehyde dehydrogenase deficiency

The pathophysiology of succinic semialdehyde dehydrogenase (SSADH) deficiency is not completely understood. Oxidative stress, mitochondrial pathology, and low reduced glutathione levels have been demonstrated in mice, but no studies have been reported in humans. We report on a patient with SSADH deficiency in whom we found low levels of blood reduced glutathione (GSH), and elevations of dicarboxylic acids in urine, suggestive of possible redox imbalance and/or mitochondrial dysfunction. Thus, targeting the oxidative stress axis may be a potential therapeutic approach if our findings are confirmed in other patients.

Metabolism of γ-hydroxybutyrate in perfused rat livers

GHB (γ-hydroxybutyrate) is both a neurotransmitter and a drug of abuse (date-rape drug). We investigated the catabolism of this compound in perfused rat livers. Using a combination of metabolomics and mass isotopomer analysis, we showed that GHB is metabolized by multiple processes, in addition to its previously reported metabolism in the citric acid cycle via oxidation to succinate. A substrate cycle operates between GHB and γ-aminobutyrate via succinic semialdehyde. Also, GHB undergoes (i) β-oxidation to glycolyl-CoA+acetyl-CoA, (ii) two parallel processes which remove C-1 or C-4 of GHB and form 3-hydroxypropionate from C-2+C-3+C-4 or from C-1+C-2+C-3 of GHB, and (iii) degradation to acetyl-CoA via 4-phosphobutyryl-CoA. The present study illustrates the potential of the combination of metabolomics and mass isotopomer analysis for pathway discovery.

Metabonomic variations associated with AOM-induced precancerous colorectal lesions and resveratrol treatment

Resveratrol (Res), 3,5,4'-trihydroxy-trans-stilbene, is an antioxidant found in the skin of red grapes and in several other plants. This phenolic compound has been recently reported to possess cancer chemopreventive activity that inhibits the process of carcinogenesis. However, the mechanisms underlying its anticancer effects remain largely unresolved. In this study, we investigated the chemoprotective effects of dietary Res in an azoxymethane (AOM) induced precancerous colorectal lesion model in male Wistar rats. The metabolic alterations in urine, sera, and colonic tissues of experimental rats perturbed by AOM intervention as well as the Res treatment were measured by a gas chromatography time-of-flight mass spectrometry (GC-TOFMS) analysis. Significant alterations of metabolites were observed in AOM group in urine, sera, and colonic tissues, which were attenuated by Res treatment and concurrent with the histopathological improvement with significantly decreased aberrant crypt foci (ACF) incidence. Representative metabolites include depleted glucose, β-hydroxybutyrate (ketone body), hypoxanthine, and elevated branched chain amino acids (isoleucine and valine) and tryptophan in colonic tissue, as well as elevated serum aminooxyacetate and urinary 4-hydroxyphenylacetate and xanthurenate. These metabolic changes suggest that the preventive effect of Res is associated with attenuation of impaired glucose and lipid metabolism and elevated protein breakdown in colonic tissues from AOM-exposed rats. It also appears that Res induced significant metabolic alterations independent of the AOM-induced metabolic changes. The significantly altered metabolites identified in Res-AOM group relative to AOM group include arachidonate, linoleate, glutamate, docosahexaenoate, palmitelaidate, 2-aminobutyrate, pyroglutamate, and threonate, all of which are involved in inflammation and oxidation processes. This suggests that Res exerts the chemopreventive effects on ACF formation by anti-inflammatory and antioxidant mechanisms in addition to amelioration of AOM-induced mitochondrial disruption.

Succinic semialdehyde dehydrogenase: biochemical-molecular-clinical disease mechanisms, redox regulation, and functional significance

Succinic semialdehyde dehydrogenase (SSADH; aldehyde dehydrogenase 5a1, ALDH5A1; E.C. 1.2.1.24; OMIM 610045, 271980) deficiency is a rare heritable disorder that disrupts the metabolism of the inhibitory neurotransmitter 4-aminobutyric acid (GABA). Identified in conjunction with increased urinary excretion of the GABA analog gamma-hydroxybutyric acid (GHB), numerous patients have been identified worldwide and the autosomal-recessive disorder has been modeled in mice. The phenotype is one of nonprogressive neurological dysfunction in which seizures may be prominently displayed. The murine model is a reasonable phenocopy of the human disorder, yet the severity of the seizure disorder in the mouse exceeds that observed in SSADH-deficient patients. Abnormalities in GABAergic and GHBergic neurotransmission, documented in patients and mice, form a component of disease pathophysiology, although numerous other disturbances (metabolite accumulations, myelin abnormalities, oxidant stress, neurosteroid depletion, altered bioenergetics, etc.) are also likely to be involved in developing the disease phenotype. Most recently, the demonstration of a redox control system in the SSADH protein active site has provided new insights into the regulation of SSADH by the cellular oxidation/reduction potential. The current review summarizes some 30 years of research on this protein and disease, addressing pathological mechanisms in human and mouse at the protein, metabolic, molecular, and whole-animal level.

4-Hydroxybutyric aciduria associated with catheter usage: a diagnostic pitfall in the identification of SSADH deficiency

Succinic semialdehyde dehydrogenase deficiency is a slowly progressive to static neurological disorder featuring elevated concentrations of 4-hydroxybutyric acid in body fluids. We present two patients with elevated 4-hydroxybutyric acid in urine which was later shown to be linked to catheter usage.

[Succinic semialdehyde dehydrogenase deficiency: decrease in 4-OH-butyric acid levels with low doses of vigabatrin]

Succinic semialdehyde dehydrogenase deficiency (gamma-hydroxybutyric aciduria) is a rare neurometabolic disease caused by a deficiency in gamma-aminobutyric degradation, resulting in an increase in gamma-hydroxybutyric acid in biological fluids. The clinical spectrum is heterogeneous, including a variety of neurological manifestations and psychiatric symptoms. The treatment usually used is vigabatrin, but its clinical efficacy is under discussion. We present two affected siblings. The older brother was examined when he was 2.5 years old due to psychomotor and developmental delay, disturbances in motor coordination, axial hypotonia and language disability. His younger brother had mild axial hypotonia when 5 months old. Metabolic studies demonstrated a high plasma and urine concentration of gamma-hydroxybutyric acid. Mutation analysis of the gene ALDH5A1 confirmed the disease. After 1 year of treatment with low-doses of vigabatrin of the older patient, a decrease in gamma-hydroxybutyric acid plasma levels and a slow clinical improvement were observed.

Visual evoked potentials in succinate semialdehyde dehydrogenase (SSADH) deficiency

In mammals, increased GABA in the central nervous system has been associated with abnormalities of visual evoked potentials (VEPs), predominantly manifested as increased latency of the major positive component P100. Accordingly, we hypothesized that patients with a defect in GABA metabolism, succinate semialdehyde dehydrogenase (SSADH) deficiency (in whom supraphysiological levels of GABA accumulate), would manifest VEP anomalies. We evaluated VEPs on two patients with confirmed SSADH deficiency. Whereas the P100 latencies and amplitudes for binocular VEP analyses were within normal ranges for both patients, the P100 latencies were markedly delayed for left eye (OS) (and right eye (OD), patient 1) and monocular OS (patient 2): 134-147 ms; normal <118 ms. We hypothesize that elevated GABA in ocular tissue of SSADH patients leads to a use-dependent downregulation of the major GABAergic receptor in eye, GABA(C), and that the VEP recordings' abnormalities, as evidenced by P100 latency and/or amplitude measurements, may be reflective of abnormalities within visual systems. This is a preliminary finding that may suggest the utility of performing VEP analysis in a larger sample of SSADH-deficient patients, and encourage a neurophysiological assessment of GABA(C) receptor function in Aldh5a1(-/-) mice to reveal new pathophysiological mechanisms of this rare disorder of GABA degradation.

Neurotransmitter alterations in embryonic succinate semialdehyde dehydrogenase (SSADH) deficiency suggest a heightened excitatory state during development

BACKGROUND

SSADH (aldehyde dehydrogenase 5a1 (Aldh5a1); gamma-hydroxybutyric (GHB) aciduria) deficiency is a defect of GABA degradation in which the neuromodulators GABA and GHB accumulate. The human phenotype is that of nonprogressive encephalopathy with prominent bilateral discoloration of the globi pallidi and variable seizures, the latter displayed prominently in Aldh5a1-/- mice with lethal convulsions. Metabolic studies in murine neural tissue have revealed elevated GABA [and its derivatives succinate semialdehyde (SSA), homocarnosine (HC), 4,5-dihydroxyhexanoic acid (DHHA) and guanidinobutyrate (GB)] and GHB [and its analogue D-2-hydroxyglutarate (D-2-HG)] at birth. Because of early onset seizures and the neurostructural anomalies observed in patients, we examined metabolite features during Aldh5a1-/- embryo development.

METHODS

Embryos were obtained from pregnant dams sacrificed at E (embryo day of life) 10-13, 14-15, 16-17, 18-19 and newborn mice. Intact embryos were extracted and metabolites quantified by isotope dilution mass spectrometry (n = 5-15 subjects, Aldh5a1+/+ and Aldh5a1-/-) for each gestational age group. Data was evaluated using the t test and one-way ANOVA with Tukey post hoc analysis. Significance was set at the 95th centile.

RESULTS

GABA and DHHA were significantly elevated at all gestational ages in Aldh5a1-/- mice, while GB was increased only late in gestation; SSA was not elevated at any time point. GHB and D-2-HG increased in an approximately linear fashion with gestational age. Correlative studies in human amniotic fluid from SSADH-deficient pregnancies (n = 5) also revealed significantly increased GABA.

CONCLUSION

Our findings indicate early GABAergic alterations in Aldh5a1-/- mice, possibly exacerbated by other metabolites, which likely induce a heightened excitatory state that may predispose neural networks to epilepsy in these animals.

Evidence for oxidative stress in tissues derived from succinate semialdehyde dehydrogenase-deficient mice

Animal models of inborn errors of metabolism are useful for investigating the pathogenesis associated with the corresponding human disease. Since the mechanisms involved in the pathophysiology of succinate semialdehyde dehydrogenase (SSADH) deficiency (Aldh5a1; OMIM 271980) are still not established, in the present study we evaluated the tissue antioxidant defences and lipid peroxidation in various cerebral structures (cortex, cerebellum, thalamus and hippocampus) and in the liver of SSADH-deficient mice. The parameters analysed were total radical-trapping antioxidant potential (TRAP) and glutathione (GSH) levels, the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), as well as thiobarbituric acid-reactive substances (TBARS). We first observed that the tissue nonenzymatic antioxidant defences were significantly reduced in the SSADH-deficient animals, particularly in the liver (decreased TRAP and GSH) and in the cerebral cortex (decreased GSH), as compared to the wild-type mice. Furthermore, SOD activity was significantly increased in the liver and cerebellum, whereas the activity of CAT was significantly higher in the thalamus. In contrast, GPx activity was significantly diminished in the hippocampus. Finally, we observed that lipid peroxidation (TBARS levels) was markedly increased in the liver and cerebral cortex, reflecting a high lipid oxidative damage in these tissues. Our data showing an imbalance between tissue antioxidant defences and oxidative attack strongly indicate that oxidative stress is involved in the pathophysiology of SSADH deficiency in mice, and likely the corresponding human disorder.

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

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

The pediatric neurotransmitter disorders

The pediatric neurotransmitter disorders represent an enlarging group of neurological syndromes characterized by abnormalities of neurotransmitter synthesis and breakdown. The disorders of dopamine and serotonin synthesis are aromatic amino acid decarboxylase deficiency, tyrosine hydroxylase deficiency, and disorders of tetrahydrobiopterin synthesis. Amino acid decarboxylase, tyrosine hydroxylase, sepiapterin reductase, and guanosine triphosphate cyclohydrolase (Segawa disease) deficiencies do not feature elevated serum phenylalanine and require cerebrospinal fluid analysis for diagnosis. Segawa disease is characterized by dramatic and lifelong responsiveness to levodopa. Glycine encephalopathy is typically manifested by refractory neonatal seizures secondary to a defect of the glycine degradative pathway. gamma-amino butyric acid (GABA) metabolism is associated with several disorders, including glutamic acid decarboxylase deficiency with nonsyndromic cleft lip/ palate, GABA-transaminase deficiency, and succinic semialdehyde dehydrogenase deficiency. The latter is characterized by elevated gamma-hydroxybutyric acid and includes a wide range of neuropsychiatric symptoms as well as epilepsy. Pyridoxine-dependent seizures have now been associated with deficiency of alpha-aminoadipic semialdehyde dehydrogenase, as well as a new variant requiring therapy with pyridoxal-5-phosphate, the biologically active form of pyridoxine.

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.

Murine succinate semialdehyde dehydrogenase (SSADH) deficiency, a heritable disorder of GABA metabolism with epileptic phenotype

Murine models of inborn errors of metabolism represent an established approach for investigating pathophysiological mechanisms associated with the corresponding human disorder. Our laboratory studies human inherited defects of GABA synthesis and degradation. One of these, succinate semialdehyde dehydrogenase (SSADH) deficiency (or gamma-hydroxybutyric aciduria; OMIM 271980; E.C. 1.2.1.24), has recently been modeled via gene targeting in the mouse. SSADH-/- mice succumb to early lethality in status epilepticus at postnatal (PN) days 20 - 26. Numerous metabolic, neurochemical and neurophysiological abnormalities have been documented using in vitro and in vivo approaches, substantially altering our thoughts about the complexity of the corresponding human condition. Moreover, novel preclinical treatment paradigms have been developed through drug trials in gene-ablated animals. The greatest utility of this animal, however, may reside in its transition from early absence seizures to generalized convulsions and eventual status epilepticus. Accurate neurochemical assessment during this transition may provide clues to the same transition process in patients, for which the underlying mechanisms remain undefined.

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.

Succinic semialdehyde dehydrogenase deficiency (SSADH) (4-hydroxybutyric aciduria, gamma-hydroxybutyric aciduria)

Succinic semialdehyde dehydrogenase deficiency is one of the disorders of GABA metabolism, so it is not surprising that seizures occur as one of the symptoms in affected patients. Other features that are described include delayed development, hypotonia, myopathy with ragged red fibres, abnormal behaviour, and ocular abnormalities. Neonatal problems include prematurity, respiratory difficulties, and hypoglycaemia. The responsible gene has been identified on the short arm of chromosome 6. There are many mutations, and there is poor genotype-phenotype correlation resulting in difficulties in diagnosis. The pathogenesis of the condition is discussed, especially the results of the disturbed GABA catabolism, and the production of the gamma-hydroxybutyric acid. The many properties of this substance suggest it may act as a neurotransmitter or neuromodulator in the brain. The diagnosis may be difficult as the clinical picture is not really suggestive, but the MRI examination can help if it shows abnormalities in the globus pallidus. It will be confirmed by finding an excess of 4-hydroxybutyric acid in the body fluids; and the methods of estimation are discussed. Prenatal diagnosis is possible using a combination of methods. Treatment possibilities are limited. Vigabatrin should be of value as it is an inhibitor of GABA transaminase, but results have been disappointing. Symptomatic treatment may well be needed for control of seizures, abnormal behaviour and other disorders; and special educational needs must be served.

Succinic semialdehyde dehydrogenase deficiency in children and adults

Succinic semialdehyde dehydrogenase deficiency is a rare disorder of the degradation pathway of gamma-aminobutyric acid. The disorder is detected when 4-hydroxybutyric aciduria is present on urine organic acid analysis, and is subsequently confirmed by enzyme measurement on leucocytes. The disorder has been identified in approximately 350 individuals worldwide. We review the clinical features in 60 patients. The most common characteristics are developmental delay maximally involving expressive language, hypotonia, mental retardation, ataxia, and behavioral problems. Seizures occur in approximately half of patients, and include tonic-clonic, absence, and myoclonic seizures, including status epilepticus. Electroencephalographic findings are background slowing and generalized and focal epileptiform discharges. Magnetic resonance imaging typically reveals increased T2-weighted signal of the globus pallidus bilaterally, with variable involvement of white matter and the cerebellar dentate nucleus. Preliminary human cerebrospinal fluid measurements are consistent with neurometabolic aberrations documented in the murine animal model, with elevations in gamma-aminobutyric acid, gamma-hydroxybutyrate, and homocarnosine, and low glutamine. Succinic semialdehyde dehydrogenase deficiency may be an underrecognized neurometabolic disorder with a nonspecific and wide phenotypic spectrum, and carries implications for a comprehensive fundamental understanding of interrelations between multiple neurotransmitter systems.

Murine succinate semialdehyde dehydrogenase deficiency

Inherited succinic semialdehyde dehydrogenase (SSADH) deficiency (gamma-hydroxybutyric aciduria) is one of the few neurogenetic disorders of GABA metabolism, and one in which tonic-clonic seizures associate with increased central nervous system GABA and gamma-hydroxybutyrate (GHB). To explore pathomechanisms and develop new preclinical treatment approaches, we developed a murine knockout model of SSADH deficiency. In the absence of intervention, SSADH(-/-) mice suffer 100% mortality at week 3 to 4 of life from generalized tonic-clonic seizures. In this report, we summarize earlier studies indicating disruption of the GABA/glutamine axis in SSADH(-/-) mouse brain, effective pharmacotherapeutic approaches, preliminary gene-therapy results, and electrophysiological analyses of mutant mice. We also present new evidence for oxidative stress in SSADH(-/-) mice, significant alterations of dopamine metabolism, and abnormal neurosteroid levels in brain, potentially implicating the GABA(A) receptor in pathogenesis. In SSADH deficiency, the accumulation of two neuroactive species, GABA and GHB, is significant because GABA is one of the earliest transmitters expressed in mammals, with key roles in synaptogenesis and myelination, whereas GHB displays a vast array of pharmacological actions. The SSADH(-/-) mouse may represent a useful model in which to explore the effect of GABA and GHB accumulation on central nervous system development and function.

Oxidation of 4-hydroxy-2-nonenal by succinic semialdehyde dehydrogenase (ALDH5A)

Elevated levels of 4-hydroxy-trans-2-nonenal (HNE) are implicated in the pathogenesis of numerous neurodegenerative disorders. Although well-characterized in the periphery, the mechanisms of detoxification of HNE in the CNS are unclear. HNE is oxidized to a non-toxic metabolite in the rat cerebral cortex by mitochondrial aldehyde dehydrogenases (ALDHs). Two possible ALDH enzymes which might oxidize HNE in CNS mitochondria are ALDH2 and succinic semialdehyde dehydrogenase (SSADH/ALDH5A). It was previously established that hepatic ALDH2 can oxidize HNE. In this work, we tested the hypothesis that SSADH oxidizes HNE. SSADH is critical in the detoxification of the GABA metabolite, succinic semialdehyde (SSA). Recombinant rat SSADH oxidized HNE and other alpha,beta-unsaturated aldehydes. Inhibition and competition studies in rat brain mitochondria showed that SSADH was the predominant oxidizing enzyme for HNE but only contributed a portion of the total oxidizing activity in liver mitochondria. In vivo administration of diethyldithiocarbamate (DEDC) effectively inhibited (86%) ALDH2 activity but not HNE oxidation in liver mitochondria. The data suggest that a relationship between the detoxification of SSA and the neurotoxic aldehyde HNE exists in the CNS. Furthermore, these studies show that multiple hepatic aldehyde dehydrogenases are able to oxidize HNE.

Rapid and sensitive detection of urinary 4-hydroxybutyric acid and its related compounds by gas chromatography-mass spectrometry in a patient with succinic semialdehyde dehydrogenase deficiency

We describe the rapid and sensitive detection of 4-hydroxybutyric acid, which is a marker compound for succinic semialdehyde dehydrogenase (SSADH) deficiency. Urinary 4-hydroxybutyric acid and 3,4-dihydroxybutyric acid were targeted, quantified by gas chromatography-mass spectrometry after simplified urease digestion in which lactone formation from gamma-hydroxy acids is minimized. The recovery of 4-hydroxybutyric acid using this method was over 93%. 2,2-Dimethylsuccinic acid was used as an internal standard. The detection limit of this method was 1 nmol ml(-1) for both 4-hydroxybutyric acid and 3,4-dihydroxybutyric acid. The urinary concentrations of 4-hydroxybutyric acid and of 3,4-dihydroxybutyric acid from the patient with an SSADH deficiency were 880-3628 mmol mol(-1) creatinine (control; 3.3+/-3.3 mmol mol(-1) creatinine) and 810-1366 mmol mol(-1) creatinine (control; 67.4+/-56.2 mmol mol(-1) creatinine), respectively. The simplified urease digestion of urine is very useful for quantifying 4-hydroxybutyric acid and its related compounds in patients with 4-hydroxybutyric aciduria.