Chromatographic analysis of glutamic acid decarboxylase in biological samples

An HPLC-based assay for improved measurement of glutamate decarboxylase inhibition/activation

L-Glutamic acid decarboxylase (GAD) is an enzyme that ensures the balance between the levels of two neurotransmitters, γ-aminobutyric acid (GABA) and L-glutamic acid (L-Glu), necessary for proper brain functioning. A reduction in the concentrations of GABA and/or GAD activity has been implicated in the symptoms associated with epilepsy, which could be plausibly alleviated by the application of GAD activators. As any unnecessary interference in GAD catalytic activity could be detrimental, it is important to study whether CNS (or other) drug candidates act on GAD or not. The ability to identify and reduce this risk early could significantly improve the process of drug development. Although many methods for measuring GAD activity in various biological samples have been described, only few (such as manometric and radiometric) were adopted as in vitro assays for the screening of potential GAD inhibitors/activators. However, these methods require specialized equipment and/or an expensive radiolabeled substrate, and may have sensitivity and/or reliability issues. Therefore, this study aimed to develop an HPLC-DAD-based assay that would allow a simple and more accurate measurement of GAD inhibition or activation using unpurified mice or rat brain homogenates. This assay is based on the quantification of GABA, formed during the enzymatic reaction, after its derivatization with dansyl chloride. Various parameters were evaluated to optimize the assay procedure (e.g. homogenate volume, incubation time, DMSO content, GAD, GABA, and dansyl-GABA stabilities). This assay was validated for pharmacological screenings using 3-mercaptopropionic acid and gallic acid and GAD obtained from different experimental animals.

GABA potentiate the immunoregulatory effects of Lactobacillus brevis BGZLS10-17 via ATG5-dependent autophagy in vitro

The characterization of mechanisms involved in the positive effects of probiotic bacteria in various pathophysiological conditions is a prerogative for their safe and efficient application in biomedicine. We have investigated the immunological effects of live bacteria-free supernatant collected from GABA-producing Lactobacillus brevis BGZLS10-17 on Concanavalin A-stimulated mesenteric lymph node cells (MLNC), an in vitro model of activated immune cells. We have shown that GABA containing and GABA-free supernatant of Lactobacillus brevis BGZLS10-17 have strong immunoregulatory effects on MLNC. Further, GABA produced by this strain exhibit additional inhibitory effects on proliferation, IFN-γ and IL-17 production by MLNC, and the expression of MHCII and CD80 on antigen presenting cells. At the other hand, GABA-containing supernatants displayed the strongest stimulatory effects on the expression of immunoregulatory molecules, such as Foxp3⁺, IL-10, TGF-β, CTLA4 and SIRP-α. By looking for the mechanisms of actions, we found that supernatants produced by BGZLS10-17 induce autophagy in different MLNC, such as CD4⁺ and CD8⁺ T lymphocytes, NK and NKT cells, as well as antigen presenting cells. Further, we showed that the stimulation of Foxp3⁺, IL-10 and TGF-β expression by BGZLS10-17 produced GABA is completely mediated by the induction of ATG5 dependent autophagy, and that other molecules in the supernatants display GABA-, ATG5-, Foxp3⁺-, IL-10- and TGF-β- independent, immunoregulatory effects.

GABA-Producing Natural Dairy Isolate From Artisanal Zlatar Cheese Attenuates Gut Inflammation and Strengthens Gut Epithelial Barrier in vitro

Probiotic bacteria are recognized for their health-promoting properties, including maintenance of gut epithelial integrity and host immune system homeostasis. Taking into account the beneficial health-promoting effects of GABA, the presence of the gadB gene, encoding glutamate decarboxylase that converts L-glutamate to GABA, was analyzed in Lactic Acid Bacteria (LAB) natural isolates from Zlatar cheese. The results revealed that 52% of tested Lactobacillus spp. and 8% of Lactococcus spp. isolates harbor the gadB gene. Qualitative and quantitative analysis of GABA production performed by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) revealed the highest GABA production by Lactobacillus brevis BGZLS10-17. Since high GABA-producing LAB natural isolates are the most valuable source of naturally produced GABA, the probiotic properties of BGZLS10-17 were characterized. This study demonstrated high adhesion of BGZLS10-17 strain to Caco-2 cells and the ability to decrease the adhesion of Escherichia coli ATCC25922 and Salmonella enterica C29039. Treatment of differentiated Caco-2 cells monolayer with BGZLS10-17 supernatant containing GABA alleviated inflammation (production of IL-8) caused by IL-1β and significantly stimulated the expression of tight junction proteins (zonulin, occludin, and claudin 4), as well as the expression of TGF-β cytokine leading to the conclusion that immunosuppression and strengthening the tight junctions can have significant role in the maintenance of intestinal epithelial barrier integrity. Taken together the results obtained in this study support the idea that using of GABA producing BGZLS10-17 probiotic strain could be a good strategy to modulate immunological response in various inflammatory diseases, and at the same time, it could be a good candidate for adjunct starter culture for production of GABA-enriched dairy foods and beverages offering new perspectives in designing the novel functional foods.

Characterization of glutamate decarboxylase from Lactobacillus plantarum and its C-terminal function for the pH dependence of activity

The gadB gene encoding glutamate decarboxylase (GAD) from Lactobacillus plantarum was cloned and expressed in Escherichia coli. The recombinant enzyme exhibited maximal activity at 40 °C and pH 5.0. The 3D model structure of L. plantarum GAD proposed that its C-terminal region (Ile454-Thr468) may play an important role in the pH dependence of catalysis. Accordingly, C-terminally truncated (Δ3 and Δ11 residues) mutants were generated and their enzyme activities compared with that of the wild-type enzyme at different pH values. Unlike the wild-type GAD, the mutants showed pronounced catalytic activity in a broad pH range of 4.0-8.0, suggesting that the C-terminal region is involved in the pH dependence of GAD activity. Therefore, this study may provide effective target regions for engineering pH dependence of GAD activity, thereby meeting industrial demands for the production of γ-aminobutyrate in a broad range of pH values.

Determination of glutamic acid decarboxylase activity and inhibition by an H2O2-sensing glutamic acid oxidase biosensor

The catalytic activity of the enzyme L-glutamic acid decarboxylase (GAD) is determined by an amperometric method based on a recently developed glutamate-selective biosensor. The biosensor is composed of an amperometric H2O2 electrode and a biocatalytic membrane containing the enzyme glutamic acid oxidase (GAO). The biosensor allows the direct and continuous measurement of GA levels by monitoring the H2O2 produced at the electrode interface as a coproduct of the GAO-catalyzed GA oxidation to alpha-ketoglutaric acid. Since GA is transformed to gamma-aminobutyric acid and CO2 under the catalytic activity of GAD, the rate of GA consumption in solution, monitored by the GAO biosensor, represents a reliable measure of GAD catalytic activity. Additional experiments performed in the presence of different concentrations of the GAD inhibitor valproic acid have shown the suitability of the proposed approach for the study of GAD inhibitors also. Discussion of the main experimental characteristics of this new analytical method is given in terms of sensitivity, reproducibility, and reliability of the experimental results and ease, time, and cost of operation.

Use of high-performance liquid chromatography for assay of glutamic acid decarboxylase. Its limitation in use for post-mortem brain

Rat brain, obtained 10 min after death, contained high levels of endogenous gamma-aminobutyric acid (GABA) and glutamic acid. Incubation of this brain homogenate at 37 degrees C indicated decrease of GABA with time due to degradation by GABA-transaminase. Reported high-performance liquid chromatographic (HPLC) methods for glutamic acid decarboxylase (GAD) assay depend on the difference between the GABA content of the reaction mixture after and before the incubation period. None of the methods considered the degradation of GABA during incubation. Furthermore, during determination of the Michaelis constant (KM) for the reaction none of them considered the endogenous substrate. Here we have focused on these factors which seriously affect the maximum velocity (Vmax) and KM values during GAD assay by the HPLC technique. By a simple and rapid HPLC technique we have measured GAD activity in post-mortem rat brain after removing endogenous glutamic acid by charcoal treatment and using gabaquline to prevent GABA degradation during incubation period. By this method a Vmax value of 46 +/- 4 nmol/h/mg protein and a KM value of 7.5 +/- 0.6 mM were observed for GAD activity of crude brain homogenate. For a comparative study, we have carried out radiometric assay of GAD activity from the same sample and observed a Vmax of 48 +/- 6 nmol/h/mg protein and KM of 6.9 +/- 0.4 mM.

A microassay for the determination of soluble and membrane-bound glutamate decarboxylase activity--influences of cations, lipid composition, and pyridoxal 5'-phosphate on the glutamate decarboxylase binding to liposomes

A radiochemical microassay for soluble and membrane-bound glutamate decarboxylase (GAD) is described. Up to 180 samples can be determined per day with a variation coefficient of 2%. The method detects newly synthesized gamma-amino-n-butyric acid in the picomole range and can easily be applied to other enzymes whose substrate and product differ by charge. In an aqueous homogenate of brain (1 + 10; w/v) about 15% of the total GAD activity are spun down by centrifugation (1 h, 100,000g) increasing to 35% of the total GAD activity in solutions with 8 mM calcium chloride or 100 mM potassium acetate. There is similar dependence on the cation concentration when GAD binds to phospholipid vesicles (liposomes) as well as dependence on lipid concentration and lipid composition. The coenzyme pyridoxal 5'-phosphate has no influence on GAD binding to liposomes.

Glutamic acid decarboxylase mRNA in rat brain: regional distribution and effects of intrastriatal kainic acid

Glutamic acid decarboxylase (GAD) mRNA was quantified in different regions of rat brain using an antisense RNA probe (ribo-probe) prepared from a cloned feline cDNA. In all brain regions studied a single band of GAD mRNA of approximately 3.7 kb was detected. The level of GAD mRNA was highest in the cerebellum, followed by the hypothalamus greater than thalamus greater than striatum greater than hippocampus greater than frontal cortex = parietal cortex greater than or equal to medulla = pons. Since GAD has been previously localized to intrinsic neurons of the striatum, we examined the effects of intrastriatal kainic acid administration on striatal GAD mRNA. The level of GAD mRNA in the kainic acid-lesioned striatum was reduced by 70-75% when compared to the contralateral (unlesioned) striatum. In contrast, the level of glutamine synthetase (an enzyme localized to glia) mRNA was increased approximately 290% in the kainic acid-lesioned striatum. There were no significant differences in GAD mRNA levels between the ipsilateral and contralateral cerebral cortices and hippocampi of rats injected with intrastriatal kainic acid.

Neurological manifestations and toxicities of the antituberculosis drugs. A review

The neurological manifestations and toxicities of 12 antituberculosis drugs [isoniazid, rifampicin (rifampin), ethambutol, p-aminosalicylic acid, pyrazinamide, streptomycin, kanamycin, ethionamide, cycloserine, capreomycin, viomycin and thiacetazone] are reviewed. Their effects upon the central nervous system, cranial nerves, peripheral nerves and the neuromuscular junction are examined, and drug interactions of neurological concern are briefly discussed. Isoniazid is well known to increase the concentrations of gamma-aminobutyric acid in neural tissues. Although conflicting data have been published, isoniazid may play a limited future role in reducing the degree of adventitious movements noted in certain neurological diseases such as multiple sclerosis, spasmodic torticollis, and other segmental dystonic syndromes. With rifampicin neurological complications have been observed infrequently. Rifampicin penetrates into the CSF and has been shown to have useful activity against various micro-organisms in the CSF, including certain viruses; however, contrary to earlier suggestions, it appears to have no role in the treatment of subacute sclerosing panencephalitis. A number of studies have indicated that isoniazid is associated with a large number of accidental and intentional poisonings. The highest incidence has been observed with Southwestern American Indians in which this agent was involved in 7% of all suicide attempts and 19% of the suicide deaths. Degeneration of the optic chiasma and nerve is a well-known adverse effect of ethambutol; toxicity is manifested by impairment of visual acuity, marked loss of colour discrimination, constricted visual fields, and central and peripheral scotoma. Ototoxicity is a well known problem caused by streptomycin, kanamycin, capreomycin and viomycin. The use of streptomycin in pregnant mothers is associated with congenital deafness in newborns in certain cases. The aminoglycoside antibiotics are also associated with flaccid paralysis following neuromuscular blockade. Adverse reactions to cycloserine are mainly dose-related with neurological and psychiatric syndromes noted in up to 50% of patients. Recent data indicate that isoniazid, rifampicin, ethambutol, pyrazinamide, streptomycin, kanamycin, ethionamide, and cycloserine appear in measurable quantities in the cerebrospinal fluid. Five of these compounds (isoniazid, rifampicin, ethambutol, kanamycin, cycloserine) pass to some degree through non-inflamed meninges. Other than discontinuation of the therapeutic regimen and general supportive measures, very few methods are described in the literature for treatment of acute intoxications with antituberculosis drugs.