2-Pyrrolidinone in human cerebrospinal fluid: a major constituent of total gamma-aminobutyric acid

Interpretable machine learning-derived nomogram model for early detection of diabetic retinopathy in type 2 diabetes mellitus: a widely targeted metabolomics study

Objective

Early identification of diabetic retinopathy (DR) is key to prioritizing therapy and preventing permanent blindness. This study aims to propose a machine learning model for DR early diagnosis using metabolomics and clinical indicators.

Methods

From 2017 to 2018, 950 participants were enrolled from two affiliated hospitals of Wenzhou Medical University and Anhui Medical University. A total of 69 matched blocks including healthy volunteers, type 2 diabetes, and DR patients were obtained from a propensity score matching-based metabolomics study. UPLC-ESI-MS/MS system was utilized for serum metabolic fingerprint data. CART decision trees (DT) were used to identify the potential biomarkers. Finally, the nomogram model was developed using the multivariable conditional logistic regression models. The calibration curve, Hosmer–Lemeshow test, receiver operating characteristic curve, and decision curve analysis were applied to evaluate the performance of this predictive model.

Results

The mean age of enrolled subjects was 56.7 years with a standard deviation of 9.2, and 61.4% were males. Based on the DT model, 2-pyrrolidone completely separated healthy controls from diabetic patients, and thiamine triphosphate (ThTP) might be a principal metabolite for DR detection. The developed nomogram model (including diabetes duration, systolic blood pressure and ThTP) shows an excellent quality of classification, with AUCs (95% CI) of 0.99 (0.97–1.00) and 0.99 (0.95–1.00) in training and testing sets, respectively. Furthermore, the predictive model also has a reasonable degree of calibration.

Conclusions

The nomogram presents an accurate and favorable prediction for DR detection. Further research with larger study populations is needed to confirm our findings.

Metabolomics Profile in ABAT Deficiency Pre- and Post-treatment

Metabolomic profiling is an emerging technology in the clinical setting with immediate diagnostic potential for the population of patients with Inborn Errors of Metabolism. We present the metabolomics profile of two ABAT deficiency patients both pre- and posttreatment with flumazenil. ABAT deficiency, also known as GABA-transaminase deficiency, is caused by recessive mutations in the gene ABAT and leads to encephalopathy of variable severity with hypersomnolence, hypotonia, hypomyelination, and seizures. Through metabolomics screening of multiple patient tissues, we identify 2-pyrrolidinone as a biomarker for GABA that is informative in plasma, urine, and CSF. These data will enable noninvasive diagnostic testing for the population of patients with disorders of GABA metabolism.

Free-GABA levels in the cerebrospinal fluid of patients suffering from several neurological diseases Its potential use for the diagnosis of diseases which course with inflammation and tissular necrosis

Free GABA levels were measured in the cerebrospinal fluid (CSF) of 74 neurological patients suffering from cerebral cysticercosis (n = 9), Parkinson's disease (n = 5), multiple sclerosis (n = 6), epilepsy (n = 24), meningeal tuberculosis (n = 6), viral encephalitis (n = 3), cerebrovascular disease (n = 8) and several kinds of dystonia (n = 5). A statistical significant four-fold elevation in free GABA levels was found in patients with cerebral cysticercosis. A non statistical significant two-fold increase in free GABA levels was also encountered in the CSF of patients affected by cerebrovascular disease and viral encephalitis. No changes in CSF free GABA levels were found in patients suffering from any of the other disorders. It is suggested that free GABA levels may be elevated in the CSF of patients suffering from neurological diseases which course with inflammation and tissular necrosis such as cerebral cysticercosis. Much work is needed however to establishd whether CSF free GABA levels can be used as a diagnostic tool in at least some type of these patients.

Formation of Vinylogous Compounds in Model Maillard Reaction Systems

The thermal degradation over temperature and time of selected amino acids (Asp, Gln, and Glu) in the presence of reducing sugars was investigated in low moisture model systems. Copyrolysis of glucose-Asp mixtures led to the release of acrylic acid, attaining >5 mmol/mol Asp at 230 degrees C after 5 min. Spurious amounts of 3-butenamide were detected upon heating Gln together with a carbonyl source. Apparently, intramolecular cyclization is favored to procure 2-pyrrolidinone, reaching levels >3 mmol/mol above 230 degrees C. 2-Pyrrolidinone was also formed in comparable amounts in pyrolyzed sugar-Glu mixtures, indicating that the Maillard reaction may be an important contributor to the formation of 2-pyrrolidinone in certain cooked foods. The chemical route to acrylic acid and 3-butenamide is probably analogous to that described for acrylamide recently. Evidence is also presented that acrylic acid may be an intermediate in the formation of acrylamide, and yields could be augmented by coincubation of fructose-Asp with certain amino acids such as Gln, reaching approximately 5% of the yield obtained by the Asn route. A computational study to determine the reactivity of the vinylogous products indicated a reduced ability of 3-butenamide as compared to acrylamide to form stable intermediates by Michael nucleophilic addition. Acrylamide and acrylic acid exhibited a similar theoretical reactivity potential toward nucleophiles. No information is as yet available on the occurrence of acrylic acid in cooked foods. Extensive toxicological evaluation indicates that acrylic acid is of no concern at the amounts to be expected in foods.

GABA and glutamate in the human brain

Cortical excitability reflects a balance between excitation and inhibition. Glutamate is the main excitatory and GABA the main inhibitory neurotransmitter in the mammalian cortex. Changes in glutamate and GABA metabolism may play important roles in the control of cortical excitability. Glutamate is the metabolic precursor of GABA, which can be recycled through the tricarboxylic acid cycle to synthesize glutamate. GABA synthesis is unique among neurotransmitters, having two separate isoforms of the rate-controlling enzyme, glutamic acid decarboxylase. The need for two separate genes on two chromosomes to control GABA synthesis is unexplained. Two metabolites of GABA are present in uniquely high concentrations in the human brain. Homocarnosine and pyrrolidinone have a major impact on GABA metabolism in the human brain. Both of these GABA metabolites have anticonvulsant properties and can have a major impact on cortical excitability.

Acute effects of vigabatrin on brain GABA and homocarnosine in patients with complex partial seizures

PURPOSE

The acute, subacute, and chronic effects of vigabatrin (VGB) were studied in patients with refractory complex partial seizures. VGB increases human brain gamma-aminobutyric acid (GABA) and the related metabolites, homocarnosine and 2-pyrrolidinone.

METHODS

In vivo measurements of GABA and homocarnosine were made of a 14-cc volume in the occipital cortex by using 1H spectroscopy with a 2.1-Tesla magnetic resonance spectrometer and an 8-cm surface coil. Six patients (three women) were studied serially during the initiation and maintenance of VGB as adjunct therapy.

RESULTS

The first, 3 g dose of VGB increased brain GABA by 2.0 micromol/g within 81 min of oral administration. After 2 h, median edited GABA remained essentially the same for 2 days. The response to the second, 3-g dose of VGB given at 48 h was considerably less than that to the first dose, with a median increase of 0.5 micromol/g within 72 min. After 2-3 months, rechallenging patients taking 1.5-g VGB twice daily with 6 g increased GABA by 0.4 micromol/g within 87 min. Homocarnosine increased more gradually than GABA to above-normal levels after a week of VGB therapy.

CONCLUSIONS

VGB promptly elevates brain GABA and presumably offers partial protection against further seizures within hours of the first oral dose. Once-a-day dosing is sufficient to increase GABA. Patients may be expected to experience the effects of increased homocarnosine within 1 week.

Localized 1H NMR measurements of 2-pyrrolidinone in human brain in vivo

Localized 1H NMR homonuclear J editing spectroscopy was used to measure the concentration of 2-pyrrolidinone (PRDN) in the human occipital lobe of five normal and six epileptic subjects taking vigabatrin. PRDN is a lactam cyclization product of gamma-aminobutyric acid (GABA). From a localized volume of 13.5 cm3 in the occipital cortex, the concentration of PRDN ranged from 0.2 to 0.3 micromol/g in normal subjects, whereas in epileptic subjects on vigabatrin PRDN was elevated to 0.6 +/- 0.1 micromol/g. The elevated PRDN in patients on vigabatrin was in accord with raised GABA levels compared with normals. 1H NMR measurements of PRDN will be important in assessment of the role of this metabolite for improved seizure control.

Vigabatrin increases human brain homocarnosine and improves seizure control

Homocarnosine, a dipeptide of gamma-aminobutyric acid (GABA) and histidine, is thought to be an inhibitory neuromodulator synthesized in subclasses of GABAergic neurons. Homocarnosine is present in human brain in greater amounts (0.4-1.0 micromol/g) than in other animals. The antiepileptic drug vigabatrin increases human cerebrospinal fluid homocarnosine linearly with daily dose. By using 1H nuclear magnetic resonance spectroscopy, serial occipital lobe GABA and homocarnosine concentrations were measured in 11 patients started on vigabatrin. Daily low-dose (2 g) vigabatrin increased both homocarnosine and GABA. Larger doses of vigabatrin (4 g) further increased homocarnosine but changed GABA levels minimally. Seizure control improved with increasing homocarnosine and GABA concentrations. Patients whose seizure control improved with the addition of vigabatrin had higher mean homocarnosine, but the same mean GABA concentrations, than those whose seizure control did not improve. Increased homocarnosine may contribute to improved seizure control.

Evidence for the presence, synthesis, immunoreactivity, and uptake of GABA in the nervous system of the snail Helisoma trivolvis

In the present study several techniques were employed to test the hypothesis that gamma-aminobutyric acid (GABA) is a neurotransmitter in the central nervous system (CNS) of the pond snail Helisoma trivolvis (Mollusca, Pulmonata). First, by using chromatographic techniques, the presence of GABA and its differential distribution among the ganglia constituting the CNS was demonstrated. Second, de novo synthesis of 3H-GABA from 3H-glutamate was shown by the CNS. Levels of both endogenous and newly synthesized GABA were greatest in the buccal, cerebral, and pedal ganglia. Third, indirect immunohistochemistry of wholemounts revealed a central network of GABA-like immunoreactive neurons. With the possible exceptions of two pairs of fibers in nerve trunks, all projections from GABA-immunoreactive neurons were confined to the CNS, suggesting a predominantly central role for GABA. Stained neurons were found on the dorsal surface of the buccal ganglia and throughout the cerebral and pedal ganglia. No GABA-immunoreactive cell bodies were observed in the parietal, pleural, or visceral ganglia. Finally, uptake of 3H-GABA was examined autoradiographically in sectioned ganglia. A pattern of radiolabelled cells was observed that closely resembled the distribution of GABA-immunoreactive neurons. The data described above fulfill several criteria necessary to establish GABA as a transmitter in the nervous system of Helisoma. Taken together with previously obtained pharmacological evidence demonstrating that GABA acts on Helisoma central neurons, GABA is considered to be a strong candidate for a neurotransmitter in Helisoma.

Detection of several novel gamma-aminobutyric acid-containing compounds in human CSF

gamma-Aminobutyric acid (GABA) concentrations in human CSF are known to increase significantly after hydrolysis; however, the source of this increase has been unknown. Using either ion-exchange or reverse-phase chromatography coupled with on-line alkaline hydrolysis, we have shown 2-pyrrolidinone, the lactam of GABA, to be present in insufficient quantity to account for this increase. Subsequent experiments involving fraction collection of column eluents followed by acid hydrolysis and rechromatography demonstrated the presence of several previously undetected GABA-containing compounds.

Clinical relevance of measuring GABA concentrations in cerebrospinal fluid

Determination of GABA concentrations in human cerebrospinal fluid can be used to assess GABAergic activity in the central nervous system. As CSF free GABA concentrations may vary with age, sex, CSF fraction, and collection and storage conditions, careful attention to these factors are necessary to allow interpretation of results. Longitudinal studies to investigate the influence of pharmacological agents on CSF GABA have proven especially useful to define clinical biochemical activity and have been utilized to attribute the anti-epileptic action of vigabatrin, a selective inhibitor of GABA-transaminase, to its effects on brain GABA metabolism.

Inborn errors of carnosine and homocarnosine metabolism

Serum carnosinase deficiency with carnosinuria has been reported in 23 children with neurological signs and/or mental retardation. In adults four cases in one family had serum carnosinase deficiency, carnosinuria, and in addition elevated homocarnosine in CSF and in the brain. The mother was one of these cases but had no clinical symptoms; however her three children have spastic paraparesis, retinitis pigmentosa and mental retardation. Serum carnosinase deficiency alone is not the cause of the neurological symptoms. When two of the affected children consumed carnosine, anserine or homocarnosine, they metabolized these compounds much less rapidly than did two normal control individuals.

Review: Normal and abnormal central nervous system GABA metabolism in childhood

The metabolism and function of central nervous system GABA is briefly reviewed. Hereditary disorders of the GABA metabolism presenting in childhood are discussed with particular emphasis on the recently identified succinic semialdehyde dehydrogenase deficiency and GABA-transaminase deficiency, and on diseases associated with low CSF GABA which await further unravelling. Low CSF GABA concentrations are not always associated with convulsions. A separate section is devoted to the CSF as a tool in the diagnosis of these disorders. Finally, we present a few diagnostic and therapeutic guidelines.

Regional in vivo superfusion of the spinal cord and KC1-induced amino acid release

In vivo push-pull superfusion was used to sample the regional release of amino acids into spinal superfusates of urethane-anesthetized rats. By collecting superfusates from the intrathecal space surrounding the sacral-lower thoracic spinal cord, it was possible to achieve a stable release of amino acids in one- and five-minute superfusate fractions. Introducing the depolarizing agent, potassium chloride (KC1) (40 mM), into the superfusion medium significantly increased GLU, GLY, and TAU concentrations in superfusates compared to pre-KCl values. The findings that these three amino acids were the only ones (out of 20) that showed a significant increase in response to KCl administration, suggest that they mediate neurotransmission in this region of the spinal cord. Amino acid concentrations were determined in spinal superfusates by high performance liquid chromatography (HPLC), utilizing an automated ortho-phthaldialdehyde precolumn derivatization system. The regional superfusion system described in this paper provides a technique for measuring KC1-produced release of neurochemicals that may mediate neurotransmission in delimited spinal regions.

Clinical pharmacology of vigabatrin

1. Upon oral administration vigabatrin is rapidly absorbed. Plasma elimination half-life ranges between 5 and 7 h in normal volunteers. Vigabatrin is eliminated primarily via the kidneys with about 65% of the administered dose found unchanged in the urine within 24 h. Kinetics are dose-linear within the range of usual therapeutic doses. 2. At therapeutic doses in man vigabatrin produces dose-related increases in CSF concentrations of free and total GABA, homocarnosine (the GABA-histidine dipeptide) and beta-alanine. These biochemical changes are consistent with an inhibition of GABA-transaminase activity in brain. 3. Thus, with systemic availability upon oral administration and biochemical activity in the CNS, the prerequisites for potential uses of vigabatrin in neurological disorders have been demonstrated in clinical pharmacological studies.

Levels of total gamma-aminobutyric acid (GABA), free GABA and homocarnosine in cerebrospinal fluid of epileptic patients before and during gamma-vinyl-GABA (vigabatrin) treatment

Levels of total gamma-aminobutyric acid (TGABA), free GABA (FGABA), and homocarnosine (HC) were studied in CSF taken from 12 controls and 28 patients with drug-refractory epilepsy before and during 7 months of gamma-vinyl-GABA (GVG) administration. At baseline TGABA and FGABA in CSF of epileptic patients did not differ from that of the controls. In epileptic patients HC was 127% of that in controls. During GVG treatment TGABA was 283%, FGABA 197%, and HC 310% of the levels at baseline in the same patients. The patients who had over 50% reduction in seizure frequency during GVG (responders, 46% of the study population) at baseline had higher TGABA and HC in CSF than patients with less than 50% reduction in seizures (non-responders). During GVG the responders and nonresponders had similar levels of different GABAergic markers. The present study shows that in man GVG treatment effectively suppresses seizures in nearly half of the epileptic patients who had previously been drug-refractory. The elevated levels of GABAergic markers in CSF are not, however, necessarily related to good seizure control during GVG.