beta-Alanine uptake by mouse brain slices

The dihydropyrimidine dehydrogenase gene contributes to heritable differences in sleep in mice

Many aspects of sleep are heritable, but only a few sleep-regulating genes have been reported. Here, we leverage mouse models to identify and confirm a previously unreported gene affecting sleep duration-dihydropyrimidine dehydrogenase (Dpyd). Using activity patterns to quantify sleep in 325 Diversity Outbred (DO) mice-a population with high genetic and phenotypic heterogeneity-a linkage peak for total sleep in the active lights off period was identified on chromosome 3 (LOD score = 7.14). Mice with the PWK/PhJ ancestral haplotype at this location demonstrated markedly reduced sleep. Among the genes within the linkage region, available RNA sequencing data in an independent sample of DO mice supported a highly significant expression quantitative trait locus for Dpyd, wherein reduced expression was associated with the PWK/PhJ allele. Validation studies were performed using activity monitoring and EEG/EMG recording in Collaborative Cross mouse strains with and without the PWK/PhJ haplotype at this location, as well as EEG and EMG recording of sleep and wake in Dpyd knockout mice and wild-type littermate controls. Mice lacking Dpyd had 78.4 min less sleep during the lights-off period than wild-type mice (p = 0.007; Cohen's d = -0.94). There was no difference in other measured behaviors in knockout mice, including assays evaluating cognitive-, social-, and affective-disorder-related behaviors. Dpyd encodes the rate-limiting enzyme in the metabolic pathway that catabolizes uracil and thymidine to β-alanine, an inhibitory neurotransmitter. Thus, data support β-alanine as a neurotransmitter that promotes sleep in mice.

Comparison of taurine, hypotaurine and β-alanine uptake in brain synaptosomal preparations from developing and adult mouse

The properties of taurine, hypotaurine and β-alanine uptakes were compared in brain synaptosomal preparations from 6-day-old and adult mice. The uptakes of these structurally related amino acids resembled each other, being concentrative, sodium-dependent and inhibited by the same analogues. The absolute sodium requirement of uptake was already evident in developing brain. The affinity of the lowaffinity uptake for taurine was higher in immature than in adult brain. Both affinity and maximal velocity increased in hypotaurine uptake during development, whereas in β-alanine uptake only the maximal velocity did so. The efficient synaptosomal taurine and hypotaurine transport systems in immature brain could contribute to the high taurine level in developing brain.

Two new reactive targets of 2,5-hexanedione in vitro – beta-alanine and glycine

In this study, we found that two amino acids reacted with 2,5-hexanedione to form new reaction products in vitro, respectively. In the reaction of beta-alanine and 2,5-hexanedione, a reaction product was obtained and analyses of obtained results showed it was 3-(2,5-dimethyl-1H-pyrrol-1-yl)propanoic acid; in the reaction of glycine and 2,5-hexanedione, a reaction product was also obtained and analyses showed it was (2,5-dimethyl-1H-pyrrol-1-yl)acetic acid. Two reaction products were found to be oxidized easily; in addition, the latter was more easily to be oxidized than the former in the air. Our discoveries demonstrated that reactions between amino acids and 2,5-hexanedione could exist possibly in vitro. At present, it is clear that 2,5-hexanedione causes either axon atrophy or swelling, but the underlying molecular mechanism is still unclear. Since both beta-alanine and glycine are considered as neurotransmitter in the central nervous system, the reaction products remain to be identified in vivo.

New insights in dihydropyrimidine dehydrogenase deficiency: a pivotal role for beta-aminoisobutyric acid?

DPD (dihydropyrimidine dehydrogenase) constitutes the first step of the pyrimidine degradation pathway, in which the pyrimidine bases uracil and thymine are catabolized to beta-alanine and the R-enantiomer of beta-AIB (beta-aminoisobutyric acid) respectively. The S-enantiomer of beta-AIB is predominantly derived from the catabolism of valine. It has been suggested that an altered homoeostasis of beta-alanine underlies some of the clinical abnormalities encountered in patients with a DPD deficiency. In the present study, we demonstrated that only a slightly decreased concentration of beta-alanine was present in the urine and plasma, whereas normal levels of beta-alanine were present in the cerebrospinal fluid of patients with a DPD deficiency. Therefore the metabolism of beta-alanine-containing peptides, such as carnosine, may be an important factor involved in the homoeostasis of beta-alanine in patients with DPD deficiency. The mean concentration of beta-AIB was approx. 2-3-fold lower in cerebrospinal fluid and urine of patients with a DPD deficiency, when compared with controls. In contrast, strongly decreased levels (10-fold) of beta-AIB were present in the plasma of DPD patients. Our results demonstrate that, under pathological conditions, the catabolism of valine can result in the production of significant amounts of beta-AIB. Furthermore, the observation that the R-enantiomer of beta-AIB is abundantly present in the urine of DPD patients suggests that significant cross-over exists between the thymine and valine catabolic pathways.

Identification of a G Protein-coupled Receptor Specifically Responsive to β-Alanine

We isolated a cDNA encoding an orphan G protein-coupled receptor, TGR7, which has been recently reported to correspond to MrgD. To search for ligands for TGR7, we screened a series of small molecule compounds by detecting the Ca2+ influx in Chinese hamster ovary cells expressing TGR7. Through this screening, we found that beta-alanine at micromolar doses specifically evoked Ca2+ influx in cells expressing human, rat, or mouse TGR7. A structural analogue, gamma-aminobutyric acid, weakly stimulated cells expressing human or rat TGR7, but another analogue, glycine, did not. In addition, beta-alanine decreased forskolin-stimulated cAMP production in cells expressing TGR7, suggesting that TGR7 couples with G proteins Gq and Gi. In guanosine 5'-O-3-thiotriphosphate binding assays conducted using a membrane fraction of cells expressing TGR7, beta-alanine specifically increased the binding of guanosine 5'-O-3-thiotriphosphate. When a fusion protein composed of TGR7 and green fluorescent protein was expressed in cells, it localized at the plasma membrane but internalized into the cytoplasm after treatment with beta-alanine. In addition, we found that beta-[3H]alanine more efficiently bound to TGR7-expressing cells than to control cells. From these results, we concluded that TGR7 functioned as a specific membrane receptor for beta-alanine. Quantitative PCR analysis revealed that TGR7 mRNA was predominantly expressed in the dorsal root ganglia in rats. By in situ hybridization and immunostaining, we confirmed that TGR7 mRNA was co-expressed in the small diameter neurons with P2X3 and VR1, both in rat and monkey dorsal root ganglia. Our results suggest that TGR7 participates in the modulation of neuropathic pain.

Beta-alanine release from the adult and developing hippocampus is enhanced by ionotropic glutamate receptor agonists and cell-damaging conditions

The release of the inhibitory amino acid beta-alanine was investigated in hippocampal slices from adult (3-month-old) and developing (7-day-old) mice, using a superfusion system. The release was enhanced by beta-alanine itself and the structural analogs taurine and y-aminobutyrate. It was dependent on Na+, but independent of Ca2+ in both mature and immature hippocampus, being thus mostly mediated by uptake carriers operating in an outward direction. The release was potentiated in the developing mice, but not affected in the adults, by the ionotropic glutamate receptor agonists N-methyl-D-aspartate, kainate, 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and tetrazolylglycine in a receptor-mediated manner. Cell-damaging conditions, including hypoxia, hypoglycemia, ischemia, oxidative stress and the presence of free radicals, greatly enhanced beta-alanine release at both ages, but more markedly in the adults. The great amounts of beta-alanine, together with the inhibitory amino acids taurine and gamma-aminobutyrate, released simultaneously with the excitatory amino acids in the hippocampus may constitute an important protective mechanism against excitotoxicity, which leads to neuronal death.

beta-alanine uptake is upregulated in FeCl3-induced cortical scars

Glial uptake of beta-[14C]alanine (beta-Ala) was studied in male Sprague-Dawley rats after sub-pial iontophoresis of FeCl3 into the right motor strip. Models bearing a 15-day-old scar were selected because of the presence of strongly reactive glia induced by FeCl3. Behavioral seizures were observed by daily visual inspection in one third of the animals. The effects of intraperitoneal (i.p.) injections of DL-alpha-aminoadipic acid (DLaAA), which exerts specific gliotoxicity through glutamine synthetase (GS) inhibition, and of 3-mercaptoproprionic acid (3MP), a potent inhibitor of glutamic acid decarboxylase (GAD: the rate-limiting enzyme in the biosynthesis of gamma-aminobutyric acid [GABA]), were also examined. There was significant enhancement of beta-Ala uptake in the margins of the scars. Further increases of uptake were triggered by 3MP, and there was extensive recruitment of astrocytes within isocortex even at a distance from the edges of the scar. DL-alpha-Aminoadipic acid caused a slight decrease of beta-Ala uptake, which was selectively localized to the scar margins. Seizure activity was unchanged by high i.p. doses of DL alpha AA. Our results strongly suggest that beta-Ala has high affinity for normal and reactive astrocytes, and that the uptake can be significantly enhanced by lowering endogenous GABA levels in abnormal cortical tissues in and around FeCl3-lesions by inhibition of GAD. Enhancement of glial beta-Ala uptake appeared to depend heavily on increased endothelial transport of small neutral amino acids, in a process modulated by perivascular glia. This model of free radical neurotoxicity may help gain more insight into abnormal neuronal-glial interactions caused by lipid peroxidation.

Characterization of sodium-independent beta-alanine binding to cerebral cortical membranes from 7-day-old and adult mice

The sodium-independent binding of beta-alanine to cerebral cortical membranes from adult (3- and 12-month-old) and developing (7-day-old) mice was characterized for the first time. The binding was saturable in each age group, consisting of only one component. The affinity for beta-alanine was highest and the number of available binding sites greatest in young animals. The binding was not affected by strychnine, but inhibited by beta-alanine itself, glycine, L-alanine and L-serine, the IC50 values being lower in immature mice. Glycine was shown to be a competitive inhibitor. The binding was also inhibited, albeit only in adults, by N-methyl-D-aspartate receptor antagonists acting at the glycine modulatory site and by some GABAergic substances. It is concluded that even though beta-alanine may possess binding sites of its own, particularly in the immature cerebral cortex, beta-alanine could at least partly bind to strychnine-insensitive glycine sites in the N-methyl-D-aspartate receptor complex.

Excitatory and inhibitory amino acids in the cerebral cortex of nucleus basalis magnocellularis lesioned rats

It is well known that pathways arising from the nucleus basalis magnocellularis in the basal forebrain which terminate in the cerebral cortex are involved in cognitive function. The cholinergic system is generally thought to play a large part in these processes from lesion, pharmacological and transplantation studies. With increasing evidence suggesting the involvement of amino acid transmitters in learning and memory processes, it is of interest to also evaluate possible changes in the levels of amino acid transmitters in the cortex of nucleus basalis magnocellularis-lesioned rats. In the present study, 9 cortical amino acids were measured in rats with bilateral lesions of the nucleus basalis magnocellularis. We measured significant reductions in aspartate, alanine and gamma-aminobutyric acid; these were 80%, 75%, and 81%, respectively, of control brain values. These results suggest that changes in the amino acid content of the cerebral cortex following lesion of the nucleus basalis magnocellularis-lesioned rat should perhaps also be considered when evaluating behavioral effects in this model.

Uptake and release of beta-alanine in cerebellar granule cells in primary culture: regulation of release by glutamatergic and GABAergic receptors

The uptake and release of beta-[3H]alanine were studied in cultured glutamatergic cerebellar granule cells of the rat. The uptake of beta-alanine was saturable and sodium-dependent, comprising one high-affinity transport component. It was inhibited by hypotaurine, taurine, GABA and homotaurine but not by glycine or glutamate. The release was enhanced by homoexchange, veratridine and high K+ concentrations (50 mM). The K(+)-stimulated release was at least partially Ca(2+)-dependent. The release was shown to be subject to regulation by GABAA receptors and glutamate receptors of the kainate type. The results signify that beta-alanine may have a functional role in cerebellar granule cells.

Release of GABA and taurine from brain slices

In brain slices the mechanisms of release of GABA have been extensively studied, but those of taurine markedly less. The knowledge acquired from studies on GABA is, nevertheless, still fragmentary, not to speak of that obtained from the few studies on taurine, and firm conclusions are difficult, even impossible, to draw. This is mainly due to methodological matters, such as the diversity and pitfalls of the techniques applied. Brain slices are relatively easy to prepare and they represent a preparation that may most closely reflect relations prevailing in vivo, since the tissue structure and cellular integrity are largely preserved. In our opinion the most recommendable method at present is to superfuse freely floating agitated slices in continuously oxygenated medium. Taurine is metabolically rather inert in the brain, whereas the metabolism of GABA must be taken into account in all release studies. The use of inhibitors of GABA catabolism is discouraged, however, since a block in GABA metabolism may distort relations between different releasable pools of GABA in tissue. It is not known for sure how well, and homogeneously, incubation of slices with radioactive taurine labels the releasable pools but at least in the case of GABA there may prevail differences in the behavior of labeled and endogenous GABA. It is suggested therefore that the results obtained with radioactive GABA or taurine should be frequently checked and confirmed by analyzing the release of respective endogenous compounds. The spontaneous efflux of both GABA and taurine from brain slices is very slow. The magnitude of stimulation of GABA release by homoexchange is greater than that of taurine under the same experimental conditions. However, the release of both amino acids is generally enhanced by a great number of structural analogs, the most potent being those which are simultaneously the most potent inhibitors of uptake. This may result in part from inhibition of reuptake of amino acid molecules released from slices but the findings may also signify that the efflux of GABA and taurine is at least partially mediated by the membrane carriers operating in an outward direction. It is thus advisable not to interpret that stimulation of release in the presence of uptake inhibitors solely results from the block of reuptake of exocytotically released molecules, since changes in the carrier-mediated transport are also likely to occur upon stimulation. The electrical and K+ stimulation evoke the release of both GABA and taurine. The evoked release of GABA is several-fold greater than that of taurine in slices from the adult brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Purification and characterization of dihydropyrimidine dehydrogenase from pig liver

Dihydropyrimidine dehydrogenase was isolated from cytosolic pig liver extracts and purified 3100-fold to apparent homogeneity. Purification made use of ammonium sulfate fractionation, precipitation with acetic acid and chromatography on DEAE-cellulose and 2',5'-ADP-Sepharose with 28% recovery of total activity. The native enzyme has a molecular mass of 206 kDa and is apparently composed of two similar, if not identical, subunits. Proteolytic cleavage reveals two fragments with apparent molecular masses of 92 kDa and 12 kDa. The C-terminal 12-kDa fragment seems to be extremely hydrophobic. The enzyme contains tightly associated compounds including four flavin nucleotide molecules and 32 iron atoms/206-kDa molecule. The iron atoms are probably present in iron-sulfur centers. The flavins released from the enzyme were identified as FAD and FMN in equal amounts. An isoelectric point of 4.65 was determined for the dehydrogenase. Apparent kinetic parameters were obtained for the substrates thymine, uracil, 5-aminouracil, 5-fluorouracil and NADPH.

A re-examination of the Na+-independent binding of [3H]beta-alanine to rat brain stem-spinal cord

The Na+-independent binding of [3H]beta-alanine to rat brain stem plus spinal cord was reinvestigated, in order to study in more detail the characteristics of previously described beta-alanine binding processes. Binding was absent when amino acid-free postnuclear supernatants or crude synaptic membranes were used. Experiments performed with several other Na+-free preparations showed a sole binding component, irrespective of the preparation used. Biochemical characterization of this Na+-independent binding, using frozen/thawed/washed synaptosomal-mitochondrial fractions, showed that binding reached a plateau between 7 min and 13 min, increasing thereafter. Binding was linear with fraction protein over a range of 200-415 micrograms/ml incubation medium. Binding was completely inhibited by glycine, alanine, alpha-aminobutyric acid, beta-aminoisobutyric acid, hypotaurine and strychnine, and to a lesser extent by 2,2-dimethyl-beta-alanine, brucine and gelsemine. It was insensitive to taurine, gamma-aminobutyric acid (GABA), 2-guanidinoethanesulfonic acid (GES), carnosine, and bicuculline methiodide. Binding was reversible, saturable (KD 20 microM), and heat sensitive.

Taurine and beta-alanine uptake in primary astrocytes differentiating in culture: effects of ions

The effects of ions on taurine and beta-alanine uptake were studied in astrocytes during cellular differentiation in primary cultures. The uptakes were strictly Na+-dependent and also inhibited by the omission of K+ and in the presence of ouabain suggesting that their transport is fuelled mainly by these cation gradients. Two sodium ions were associated in the transport of one taurine and beta-alanine molecule across cell membranes. A reduction in Cl- concentration also markedly inhibited the uptake of both amino acids, indicating that this anion is of importance in the transport processes. The similar ion dependency profiles of taurine and beta-alanine uptake corroborate the assumption that the uptake of these amino acids in astrocytes is mediated by the same carrier. In Na+- and K+-free media both taurine and beta-alanine uptakes were reduced significantly more in 14-day-old or older than in 7-day-old cultures. No significant changes occurred in the coupling ratio between Na+ and taurine or beta-alanine as a function of spontaneous cellular differentiation or upon dBcAMP treatment. These results suggest that the uptake systems of these structurally related amino acids in astrocytes have reached a relatively high degree of functional maturity by two weeks in culture.

Taurine and GABA release from mouse cerebral cortex slices: effects of structural analogues and drugs

The effects of structural analogues, excitatory amino acids and certain drugs on spontaneous and potassium-stimulated exogenous taurine and GABA release were investigated in mouse cerebral cortex slices using a superfusion system. Spontaneous efflux of both amino acids was rather slow but could be enhanced by their uptake inhibitors. Taurine efflux was facilitated by exogenous taurine, hypotaurine, beta-alanine and GABA, whereas GABA, nipecotic acid and homotaurine effectively enhanced GABA release. The stimulatory potency of the analogues closely corresponded to their ability to inhibit taurine and GABA uptake, respectively, indicating that these efflux processes could be mediated by the carriers operating outwards. Glutamate induced GABA release, whereas taurine efflux was potentiated by aspartate, glutamate, cysteate, homocysteate and kainate. The centrally acting drugs, including GABA agonists and antagonists, as well as the proposed taurine antagonist TAG (6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine-1,1-dioxide), had no marked effects on spontaneous taurine and GABA release. Potassium ions stimulated dose-dependently both taurine and GABA release from the slices, the responses of taurine being strikingly slow but sustained. Exogenous GABA and nipecotic acid accelerated the potassium-stimulated GABA release, whereas picrotoxin and bicuculline were ineffective. The potassium-stimulated taurine release was unaltered or suppressed by exogenous taurine and analogues, differing in this respect from GABA release. The apparent magnitude of the depolarization-induced GABA release is thus influenced by the function of membrane transport sites, but the same conclusion cannot be drawn with regard to taurine. Haloperidol and imipramine were able to affect the evoked release of both taurine and GABA.

High-affinity uptake of taurine and beta-alanine in primary cultures of rat astrocytes

The kinetics and specificity of taurine and beta-alanine uptake were studied in primary cultures of rat astrocytes under identical experimental conditions. The uptake consisted of nonsaturable penetration and saturable high-affinity transport that was strictly sodium dependent. The cells accumulated taurine more effectively than beta-alanine, both the affinity and uptake capacity being greater for taurine. Taurine uptake was competitively inhibited by beta-alanine and GABA, the former being more potent. Also, hypotaurine and 2-guanidinoethanesulphonic acid strongly reduced taurine uptake, but L-2,4-diaminobutyric acid had no significant effect. beta-Alanine uptake was also competitively inhibited by GABA, but the most potent inhibitors were hypotaurine and 2-guanidinoethanesulphonic acid. L-2,4-Diaminobutyric acid was moderately active. The uptake systems for taurine and beta-alanine were thus in principle similar, and they exhibited certain characteristics typical for a neurotransmitter amino acid. The inhibition studies further suggest the existence of only one common transport system for taurine, beta-alanine, and GABA in cultured primary astrocytes. The same uptake system may also be used for hypotaurine.

Taurine and hypotaurine transport by a single system in cultured neuroblastoma cells

The kinetics of mutual inhibition of taurine and hypotaurine uptake were studied using neuroblastoma C1300 cells as neuronal model. Hypotaurine and GABA inhibited taurine uptake competitively, increasing the apparent Km. High-affinity uptake of hypotaurine was completely abolished and the low-affinity component competitively inhibited by taurine. GABA affected noncompetitively low-affinity hypotaurine uptake, whereas the effect on high-affinity uptake was competitive, with an increase in the apparent Km. All structural analogues tested inhibited taurine and hypotaurine uptakes similarly. The most potent inhibitors were beta-alanine and 2-guanidinoethanesulphonic acid. The mutual inhibition and similar specificity profiles of taurine and hypotaurine uptakes showed that these amino acids employ a single transport system in neuroblastoma cells. Competitive inhibition by GABA of the high-affinity uptake of taurine and hypotaurine further suggests that also GABA uses the same carrier system.

beta-Alanine transport into plasma membrane vesicles derived from rat brain synaptosomes

Transport of beta-alanine has been demonstrated in membrane vesicles isolated from rat brain, using artificially imposed ion gradients as the sole energy source. The uptake of beta-alanine is strictly dependent on the presence of Na+ and Cl- in the medium, and the process can be driven either by an Na+ gradient (out greater than in) or by a Cl- gradient (out greater than in) when the other essential ion is present. The process is stimulated by a membrane potential (negative inside) as demonstrated by the effect of ionophore valinomycin and anions with different permeabilities. beta-Alanine uptake is inhibited by the presence of GABA.