[Properties of milk in sleep induction]

Introduction

Sleep induction and its quality are issues of growing concern because its deterioration affects a large number of people and poses a risk to their well-being and quality of life and long-term health. There are several factors involved in the problem, but nutrition is one of them and in particular milk consumption has often been linked to sleep habits, sometimes as a promoter and sometimes as an inhibitor. The purpose of this review is to examine the matter further. On reaching the brain, tryptophan is the basis for the synthesis of serotonin and melatonin, which improve the induction and quality of sleep. But there is competition between tryptophan and other long-chain neutral amino acids (LNAA) (valine, leucine, isoleucine, tyrosine and phenylalanine) to cross the blood-brain barrier and reach the brain. In this sense, milk proteins with a high tryptophan content and the highest ratio between tryptophan and LNAA are very useful in promoting sleep. Moreover, milk also provides various micronutrients that help in the transformation of tryptophan into serotonin and melatonin, as well as antioxidant components, anti-inflammatory and bioactive peptides, and recent studies indicate that it favorably modulates the composition of the intestinal microbiota. Studies show that increasing milk consumption, up to the recommended intake and within a correct diet, favors the achievement and maintenance of quality sleep.

Aristolochic acid-induced nephropathy is attenuated in mice lacking the neutral amino acid transporter B0AT1 (Slc6a19)

B0AT1 (Slc6a19) mediates absorption of neutral amino acids in the small intestine and in the kidneys, where it is primarily expressed in early proximal tubules (S1-S2). To determine the role of B0AT1 in nephropathy induced by aristolochic acid (AA), which targets the proximal tubule, littermate female B0AT1-deficient (Slc6a19-/-), heterozygous (Slc6a19+/-), and wild-type (WT) mice were administered AA (10 mg/kg ip) or vehicle every 3 days for 3 wk, and analyses were performed after the last injection or 3 wk later. Vehicle-treated mice lacking Slc6a19 showed normal body and kidney weight and plasma creatinine versus WT mice. The urinary glucose-to-creatinine ratio (UGCR) and urinary albumin-to-creatinine ratio (UACR) were two to four times higher in vehicle-treated Slc6a19-/- versus WT mice, associated with lesser expression of early proximal transporters Na+-glucose cotransporter 2 and megalin, respectively. AA caused tubular injury independently of B0AT1, including robust increases in cortical mRNA expression of p53, p21, and hepatitis A virus cellular receptor 1 (Havcr1), downregulation of related proximal tubule amino acid transporters B0AT2 (Slc6a15), B0AT3 (Slc6a18), and Slc7a9, and modest histological tubular damage and a rise in plasma creatinine. Absence of B0AT1, however, attenuated AA-induced cortical upregulation of mRNA markers of senescence (p16), inflammation [lipocalin 2 (Lcn2), C-C motif chemokine ligand 2 (Ccl2), and C-C motif chemokine receptor 2 (Ccr2)], and fibrosis [tissue inhibitor of metallopeptidase 1 (Timp1), transforming growth factor-β1 (Tgfb1), and collagen type I-α1 (Col1a1)], associated with lesser fibrosis staining, lesser suppression of proximal tubular organic anion transporter 1, restoration of Na+-glucose cotransporter 2 expression, and prevention of the AA-induced fivefold increase in the urinary albumin-to-creatinine ratio observed in WT mice. The data suggest that proximal tubular B0AT1 is important for the physiology of renal glucose and albumin retention but potentially deleterious for the kidney response following AA-induced kidney injury.NEW & NOTEWORTHY Based on insights from studies manipulating glucose transport, the hypothesis has been proposed that inhibiting intestinal uptake or renal reabsorption of energy substrates has unique therapeutic potential to improve metabolic disease and kidney outcome in response to injury. The present study takes this idea to B0AT1, the major transporter for neutral amino acids in the intestine and kidney, and shows that its absence attenuates aristolochic acid-induced nephropathy.

Diet- and microbiota-related metabolite, 5-aminovaleric acid betaine (5-AVAB), in health and disease

5-Aminovaleric acid betaine (5-AVAB) is a trimethylated compound associated with the gut microbiota, potentially produced endogenously, and related to the dietary intake of certain foods such as whole grains. 5-AVAB accumulates within the metabolically active tissues and has been typically found in higher concentrations in the heart, muscle, and brown adipose tissue. Furthermore, 5-AVAB has been associated with positive health effects such as fetal brain development, insulin secretion, and reduced cancer risk. However, it also has been linked with some negative health outcomes such as cardiovascular disease and fatty liver disease. At the cellular level, 5-AVAB can influence cellular energy metabolism by reducing β-oxidation of fatty acids. This review will focus on the metabolic role of 5-AVAB with respect to both physiology and pathology. Moreover, the analytics and origin of 5-AVAB and related compounds will be reviewed.

The increasing importance of LNAA supplementation in phenylketonuria at higher plasma phenylalanine concentrations

BACKGROUND

Large neutral amino acid (LNAA) treatment has been suggested as alternative to the burdensome severe phenylalanine-restricted diet. While its working mechanisms and optimal composition have recently been further elucidated, the question whether LNAA treatment requires the natural protein-restricted diet, has still remained.

OBJECTIVE

Firstly, to determine whether an additional liberalized natural protein-restricted diet could further improve brain amino acid and monoamine concentrations in phenylketonuria mice on LNAA treatment. Secondly, to compare the effect between LNAA treatment (without natural protein) restriction and different levels of a phenylalanine-restricted diet (without LNAA treatment) on brain amino acid and monoamine concentrations in phenylketonuria mice.

DESIGN

BTBR Pah-enu2 mice were divided into two experimental groups that received LNAA treatment with either an unrestricted or semi phenylalanine-restricted diet. Control groups included Pah-enu2 mice on the AIN-93 M diet, a severe or semi phenylalanine-restricted diet without LNAA treatment, and wild-type mice receiving the AIN-93 M diet. After ten weeks, brain and plasma samples were collected to measure amino acid profiles and brain monoaminergic neurotransmitter concentrations.

RESULTS

Adding a semi phenylalanine-restricted diet to LNAA treatment resulted in lower plasma phenylalanine but comparable brain amino acid and monoamine concentrations as compared to LNAA treatment (without phenylalanine restriction). LNAA treatment (without phenylalanine restriction) resulted in comparable brain monoamine but higher brain phenylalanine concentrations compared to the severe phenylalanine-restricted diet, and significantly higher brain monoamine but comparable phenylalanine concentrations as compared to the semi phenylalanine-restricted diet.

CONCLUSIONS

Present results in PKU mice suggest that LNAA treatment in PKU patients does not need the phenylalanine-restricted diet. In PKU mice, LNAA treatment (without phenylalanine restriction) was comparable to a severe phenylalanine-restricted diet with respect to brain monoamine concentrations, notwithstanding the higher plasma and brain phenylalanine concentrations, and resulted in comparable brain phenylalanine concentrations as on a semi phenylalanine-restricted diet.

The zebrafish cationic amino acid transporter/glycoprotein-associated family: sequence and spatiotemporal distribution during development of the transport system b0,+ (slc3a1/slc7a9)

System b^0,+ absorbs lysine, arginine, ornithine, and cystine, as well as some (large) neutral amino acids in the mammalian kidney and intestine. It is a heteromeric amino acid transporter made of the heavy subunit SLC3A1/rBAT and the light subunit SLC7A9/b^0,+AT. Mutations in these two genes can cause cystinuria in mammals. To extend information on this transport system to teleost fish, we focused on the slc3a1 and slc7a9 genes by performing comparative and phylogenetic sequence analysis, investigating gene conservation during evolution (synteny), and defining early expression patterns during zebrafish (Danio rerio) development. Notably, we found that slc3a1 and slc7a9 are non-duplicated in the zebrafish genome. Whole-mount in situ hybridization detected co-localized expression of slc3a1 and slc7a9 in pronephric ducts at 24 h post-fertilization and in the proximal convoluted tubule at 3 days post-fertilization (dpf). Notably, both the genes showed co-localized expression in epithelial cells in the gut primordium at 3 dpf and in the intestine at 5 dpf (onset of exogenous feeding). Taken together, these results highlight the value of slc3a1 and slc7a9 as markers of zebrafish kidney and intestine development and show promise for establishing new zebrafish tools that can aid in the rapid screening(s) of substrates. Importantly, such studies will help clarify the complex interplay between the absorption of dibasic amino acids, cystine, and (large) neutral amino acids and the effect(s) of such nutrients on organismal growth.

Integration of the Microbiome, Metabolome and Transcriptomics Data Identified Novel Metabolic Pathway Regulation in Colorectal Cancer

Integrative multiomics data analysis provides a unique opportunity for the mechanistic understanding of colorectal cancer (CRC) in addition to the identification of potential novel therapeutic targets. In this study, we used public omics data sets to investigate potential associations between microbiome, metabolome, bulk transcriptomics and single cell RNA sequencing datasets. We identified multiple potential interactions, for example 5-aminovalerate interacting with Adlercreutzia; cholesteryl ester interacting with bacterial genera Staphylococcus, Blautia and Roseburia. Using public single cell and bulk RNA sequencing, we identified 17 overlapping genes involved in epithelial cell pathways, with particular significance of the oxidative phosphorylation pathway and the ACAT1 gene that indirectly regulates the esterification of cholesterol. These findings demonstrate that the integration of multiomics data sets from diverse populations can help us in untangling the colorectal cancer pathogenesis as well as postulate the disease pathology mechanisms and therapeutic targets.

B0AT1 Amino Acid Transporter Complexed With SARS-CoV-2 Receptor ACE2 Forms a Heterodimer Functional Unit: In Situ Conformation Using Radiation Inactivation Analysis

The SARS-CoV-2 receptor, angiotensin-converting enzyme-2 (ACE2), is expressed at levels of greatest magnitude in the small intestine as compared with all other human tissues. Enterocyte ACE2 is coexpressed as the apical membrane trafficking partner obligatory for expression and activity of the B0AT1 sodium-dependent neutral amino acid transporter. These components are assembled as an [ACE2:B0AT1]2 dimer-of-heterodimers quaternary complex that putatively steers SARS-CoV-2 tropism in the gastrointestinal (GI) tract. GI clinical symptomology is reported in about half of COVID-19 patients, and can be accompanied by gut shedding of virion particles. We hypothesized that within this 4-mer structural complex, each [ACE2:B0AT1] heterodimer pair constitutes a physiological "functional unit." This was confirmed experimentally by employing purified lyophilized enterocyte brush border membrane vesicles exposed to increasing doses of high-energy electron radiation from a 16 MeV linear accelerator. Based on radiation target theory, the results indicated the presence of Na+-dependent neutral amino acid influx transport activity functional unit with target size molecular weight 183.7 ± 16.8 kDa in situ in intact apical membranes. Each thermodynamically stabilized [ACE2:B0AT1] heterodimer functional unit manifests the transport activity within the whole ∼345 kDa [ACE2:B0AT1]2 dimer-of-heterodimers quaternary structural complex. The results are consistent with our prior molecular docking modeling and gut-lung axis approaches to understanding COVID-19. These findings advance understanding the physiology of B0AT1 interaction with ACE2 in the gut, and thereby contribute to translational developments designed to treat or mitigate COVID-19 variant outbreaks and/or GI symptom persistence in long-haul postacute sequelae of SARS-CoV-2.

The amino acid transporter AAP1 mediates growth and grain yield by regulating neutral amino acid uptake and reallocation in Oryza sativa

Nitrogen (N) is a major element necessary for crop yield. In most plants, organic N is primarily transported in the form of amino acids. Here, we show that amino acid permease 1 (AAP1) functions as a positive regulator of growth and grain yield in rice. We found that the OsAAP1 gene is highly expressed in rice axillary buds, leaves, and young panicles, and that the OsAAP1 protein is localized to both the plasma membrane and the nuclear membrane. Compared with the wild-type ZH11, OsAAP1 overexpression (OE) lines exhibited increased filled grain numbers as a result of enhanced tillering, while RNAi and CRISPR (clustered regularly interspaced short palindromic repeat; Osaap1) knockout lines showed the opposite phenotype. In addition, OsAAP1-OE lines had higher concentrations of neutral and acidic amino acids, but lower concentrations of basic amino acids in the straw. An exogenous treatment with neutral amino acids promoted axillary bud outgrowth more strongly in the OE lines than in the WT, RNAi, or Osaap1 lines. Transcriptome analysis of Osaap1 further demonstrated that OsAAP1 may affect N transport and metabolism, and auxin, cytokinin, and strigolactone signaling in regulating rice tillering. Taken together, these results support that increasing neutral amino acid uptake and reallocation via OsAAP1 could improve growth and grain yield in rice.

Protein Nanopore-Based Discrimination between Selected Neutral Amino Acids from Polypeptides

Nanopore probing of biological polymers has the potential to achieve single-molecule sequencing at low cost, high throughput, portability, and minimal sample preparation and apparatus. In this article, we explore the possibility of discrimination between neutral amino acid residues from the primary structure of 30 amino acids long, engineered peptides, through the analysis of single-molecule ionic current fluctuations accompanying their slowed-down translocation across the wild type α-hemolysin (α-HL) nanopore, and molecular dynamics simulations. We found that the transient presence inside the α-HL of alanine or tryptophan residues from the primary sequence of engineered peptides results in distinct features of the ionic current fluctuation pattern associated with the peptide reversibly blocking the nanopore. We propose that α-HL sensitivity to the molecular exclusion at the most constricted region mediates ionic current blockade events correlated with the volumes that are occluded by at least three alanine or tryptophan residues, and provides the specificity needed to discriminate between groups of neutral amino acids. Further, we find that the pattern of current fluctuations depends on the orientation of the threaded amino acid residues, suggestive of a conformational anisotropy of the ensemble of conformations of the peptide on the restricted nanopore region, related to its relative axial orientation inside the nanopore.

Production of 5-aminovaleric acid in recombinant Corynebacterium glutamicum strains from a Miscanthus hydrolysate solution prepared by a newly developed Miscanthus hydrolysis process

This study examined nine expired industrial Corynebacterium glutamicum strains with high lysine producing capability for enhanced production of 5-AVA. C. glutamicum KCTC 1857 exhibiting the highest lysine production was transformed with either original Pseudomonas putida davBA genes, encoding the 5-AVA biosynthesis pathway, or C. glutamicum codon-optimized davBA genes. C. glutamicum KCTC 1857 expressing the original genes had superior cell viability and 5-AVA production capability compared to the other strain. This strain produced 39.93g/L of 5-AVA, which is the highest titer reported to date in fed-batch fermentation from glucose. Indeed, Miscanthus hydrolysate solution prepared from a novel process, comprising pretreatment, hydrolysis, purification, and concentration, was used as feedstock for 5-AVA production. A total of 12.51g/L 5-AVA was produced from the Miscanthus hydrolysate; this value is 34.7% higher than that obtained from glucose in batch fermentation.

Contribution of Complementarity-Determining Region 3 of the T-Cell Receptor Vδ2 Chain to the Recognition of Aminobisphosphonates by Human γδ T-Cells

Human gammadelta T-lymphocytes expressing Vgamma2Vdelta2 T-cell receptors (TCRs) can be stimulated by aminobisphosphonates and can kill certain tumor cells. Although germline-encoded lysine residues on the Jgamma1.2 segment have been demonstrated to be essential for the recognition of nonpeptide antigens by human gammadelta T-cells, the role of the junctional sequences of the TCR delta chain in the recognition of aminobisphosphonates by Vgamma2Vdelta2+ T-cells remains unknown. We examined the structure of complementarity-determining region 3 (CDR3) of Vdelta2 chains expressed by aminobisphosphonate-stimulated human gammadelta T-cells. CDR3 size-spectratyping analysis of Vdelta2 chains revealed that risedronate did not induce a CDR3 size distribution pattern of Vdelta2 cells that was distinct from that of Vdelta2 cells cultured without risedronate. The clonality of risedronate-expanded Vdelta2 T-cells was also determined by sequencing analysis, with the result that no particular consensus sequences were observed. However, most Vdelta2 T-cells freshly isolated from peripheral blood carried a distinctive junctional motif consisting of a hydrophobic amino acid residue (valine, leucine, or isoleucine [Val/Leu/Ile]) at conserved position 97, and this feature was not altered by risedronate stimulation. A significant proportion of Vdelta1 T-cells from the same individual had Leu at position 97, but Vdelta1 T-cells did not expand in response to risedronate. Moreover, Vdelta2 T-cells from the nonresponder against risedronate also carried a Val/Leu/Ile amino acid residue at position 97. These results suggest that the presence of a hydrophobic amino acid residue at position 97 in CDR3 of the TCR delta chain is not sufficient to account for the recognition of aminobisphosphonate by human gammadelta T-cells.

Search for the optimal linker in tandem hairpin polyamides

In order to target specific DNA sequences >or=10 base pairs in size by minor groove binding ligands, a search for the optimal linker in dimers of hairpin polyamides was initiated. Two series of tandem polyamides ImPyIm-(R)[ImPyIm-(R)(H2N)gamma-PyPyPy-L](HN)gamma-PyPyPy-beta-Dp (1a-e), where L represents a series of 4-8 carbon long aliphatic amino acid linkers, and ImPyIm-(R)[ImPyIm-(R)(H2N)gamma-PyPyPyIm-L](HN)gamma-PyPyPy-beta-Dp (2a-e), where L represents a series of 2-6 carbon long aliphatic amino acid linkers, were synthesized and characterized by quantitative DNase I footprinting. beta, gamma and Dp represents beta-alanine, gamma-aminobutyric acid, and 3-(dimethylamino)propylamine, respectively. It was found that the five-carbon 5-aminovaleric acid (delta), is suitable to span one base-pair (bp) of DNA when incorporated into a tandem polyamide. ImPyIm-(R)[ImPyIm-(R)(H2N)gamma-PyPyPy-delta](HN)gamma-PyPyPy-beta-Dp (1b) binds the 10 bp binding-site 5'-AGTGAAGTGA-3' with equilibrium association constant K(a)=3.2 x 10(10) M(-1) and ImPyIm-(R)[ImPyIm-(R)(H2N)gamma-PyPyPyIm-delta](HN)gamma-PyPyPy-beta-Dp (2d) binds the 11 bp binding-site 5'-AGTGATAGTGA-3' with K(a)=9.7 x 10(9) M(-1). Tandem 1b also bind the 11 bp site but with lower affinity affording a 15-fold specificity for the shorter binding site. Replacing a methylene group in the amino acid linker with an oxygen atom to form tandem polyamide ImPyIm-(R)[ImPyIm-(R)(H2N)gamma-PyPyPy-E](HN)gamma-PyPyPy-beta-Dp (4) where E represents the ether linker, resulted in that an 80-fold specificity for the 10 bp binding site over the 11 bp site.

Site-directed mutagenesis of tyrosine 118 within the central constriction site of the LamB (Maltoporin) channel of Escherichia coli. I. Effect on ion transport

The three-dimensional structure of the malto-oligosaccharide-specific LamB-channel of Escherichia coli (also called maltoporin) is known from x-ray crystallography. The central constriction of the channel formed by the external loop 3 is controlled by a tyrosine residue (Y118). Y118 was replaced by site-directed mutagenesis by ten other amino acids (alanine, isoleucine, asparagine, serine, cysteine, aspartic acid, arginine, histidine, phenylalanine, and tryptophane) including neutral ones, negatively and positively charged amino acids to study the effect of their size, hydrophobicity, and charge on ion transport through LamB. The mutant proteins were purified to homogeneity. They were reconstituted into lipid bilayer membranes and single-channel conductance and ion selectivity were measured to get insight into the mechanism of ion transport through LamB. The mutation of Y118 to any other nonaromatic amino acid led to a substantial increase of the single-channel conductance by more than a factor of six at maximum. The highest effect was observed for Y118D. Additionally, a nonlinear relationship between the salt concentration in the aqueous phase and the channel conductance was observed for this mutant, indicating strong discrete charge effects on ion conductance. For all other mutants, with the exception of Y118R, linear relationships were found between single-channel conductance and bulk aqueous concentration. The individual hydrophobicity indices of the amino acids introduced inside the central constriction of the LamB channel had a somewhat smaller effect on the single-channel conductance as compared with the effect of their size and charge.

Differential potentiative effects of GABA receptor agonists in the production of antinociception induced by morphine and beta-endorphin administered intrathecally in the mouse

The effect of muscimol or baclofen injected intrathecally (i.t.) on the inhibition of the tail-flick response induced by morphine and beta-endorphin administered i.t. was studied in ICR mice. The i.t. injection of muscimol (100 ng) or baclofen (10 ng) alone did not affect the basal inhibition of the tail-flick response. Morphine (0.2 microg) and beta-endorphin (0.1 microg) caused only slight inhibition of the tail-flick response. Baclofen, but not muscimol, injected i.t. enhanced the inhibition of the tail-flick response induced by i.t. administered morphine. Both muscimol and baclofen injected i.t. significantly enhanced i.t. injected beta-endorphin-induced inhibition of the tail-flick response. Our results suggest that the GABA(B), but not GABA(A), receptors located in the spinal cord appear to be involved in enhancing the inhibition of the tail-flick response induced by morphine administered spinally. In addition, both GABA(A) and GABA(B) receptors are involved in enhancing the inhibition of the tail-flick response induced by beta-endorphin administered i.t.

Physiological and morphological correlates of presynaptic inhibition in primary afferents of the lamprey spinal cord

Patch-clamp recordings in a whole-cell mode were performed on dorsal sensory cells enzymatically isolated from the spinal cord of two lamprey species, Ichthyomyzon unicuspis and Lampetra fluviatilis. The voltage-activated currents through calcium channels were analysed. GABA and the specific GABA(B) receptor agonist baclofen reduced the peak amplitude of inward Ba2+ current, as a robust alternate charge carrier through voltage-dependent Ca2+ channels. These effects were dose-dependent and reversible. GABA(B) receptor antagonists, 2-hydroxysaclofen and delta-amino-n-valeric acid, blocked the reduction of Ba2+ currents by GABA and baclofen, while bicuculline, a GABA(A) receptor antagonist, had no blocking action. GABA and baclofen did not modify the dorsal sensory cell membrane conductance, indicating that they did not activate ligand-gated channels. However, GABA, but not baclofen, considerably increased membrane conductance and induced Cl- currents in isolated multipolar neurons (presumably interneurons and/or motoneurons). These findings suggest that GABA and baclofen action on lamprey dorsal sensory cells is mediated by GABA(B) receptors. We concluded that GABA-mediated presynaptic inhibition of lamprey dorsal sensory cell fibers results from GABA(B) receptor activation followed by a decrease of inward voltage-activated calcium currents. Appositions of GABA-immunoreactive boutons to horseradish peroxidase-labeled fibers from the dorsal root were observed at the ultrastructural level in the dorsal column using postembedding immunogold cytochemistry. It seems likely that these appositions represent the morphological substrate of dorsal sensory cell fiber presynaptic inhibition. In very rare cases, ultrastructural features were observed which could be interpreted as synaptic specializations between the GABA-immunoreactive boutons and the primary afferent fibers. The extrasynaptic action of GABA as a basis of presynaptic inhibition of this population of primary afferent neurons is discussed.

Surface interactions of a homologous series of alpha,omega-amino acids on colloidal silver and gold

Surface enhanced Raman spectroscopy (SERS) was used to characterize a homologous series of alpha,omega-amino acids on colloidal gold and silver. Raman and SER spectra of the alpha,omega-amino acids, NH2(CH2)nCOOH (n = 3-7), are presented and analyzed, revealing the probable conformations of the molecules on the metal surfaces. The alpha,omega-amino acids interact with silver and gold through both the amine and carboxylate end groups, and modify the conformation of the molecular backbone in order to maximize these interactions. An odd-even effect is observed for backbone conformations of molecules adsorbed to the silver substrate. The anomolous SER spectrum of 5-aminopentanoic acid on gold suggests the possibility of condensation polymerization at the gold surface.

Effect of tranexamic acid and delta-aminovaleric acid on lipoprotein(a) metabolism in transgenic mice

The assembly of lipoprotein(a) (Lp(a)) is a two-step process which involves the interaction of kringle-4 (K-IV) domains in apolipoprotein(a) (apo(a)) with Lys groups in apoB-100. Lys analogues such as tranexamic acid (TXA) or delta-aminovaleric acid (delta-AVA) proved to prevent the Lp(a) assembly in vitro. In order to study the in vivo effect of Lys analogues, transgenic apo(a) or Lp(a) mice were treated with TXA or delta-AVA and plasma levels of free and low density lipoprotein bound apo(a) were measured. In parallel experiments, McA-RH 7777 cells, stably transfected with apo(a), were also treated with these substances and apo(a) secretion was followed. Treatment of transgenic mice with Lys analogues caused a doubling of plasma Lp(a) levels, while the ratio of free:apoB-100 bound apo(a) remained unchanged. In transgenic apo(a) mice a 1. 5-fold increase in plasma apo(a) levels was noticed. TXA significantly increased Lp(a) half-life from 6 h to 8 h. Incubation of McA-RH 7777 cells with Lys analogues resulted in an up to 1. 4-fold increase in apo(a) in the medium. The amount of intracellular low molecular weight apo(a) precursor remained unchanged. We hypothesize that Lys analogues increase plasma Lp(a) levels by increasing the dissociation of cell bound apo(a) in combination with reducing Lp(a) catabolism.

The ligand-induced structural changes of human L-Arginine:Glycine amidinotransferase. A mutational and crystallographic study

Human L-arginine:glycine amidinotransferase (AT) shows large structural changes of the 300-flap and of helix H9 upon binding of L-arginine and L-ornithine, described as a closed and an open conformation (Humm, A., Fritsche, E., Steinbacher, S., and Huber, R. (1997) EMBO J. 16, 3373-3385). To elucidate the structural basis of these induced-fit movements, the x-ray structures of AT in complex with the amidino acceptor glycine and its analogs gamma-aminobutyric acid and delta-aminovaleric acid, as well as in complex with the amidino donor analogs L-alanine, L-alpha-aminobutyric acid, and L-norvaline, have been solved at 2.6-, 2.5-, 2.37-, 2.3-, 2.5-, and 2.4-A resolutions, respectively. The latter three compounds were found to stabilize the open conformer. The glycine analogs bind in a distinct manner and do not induce the transition to the open state. The complex with glycine revealed a third binding mode, reflecting the rather broad substrate specificity of AT. These findings identified a role for the alpha-amino group of the ligand in stabilizing the open conformer. The kinetic, structural, and thermodynamic properties of the mutants ATDeltaM302 and ATDelta11 (lacks 11 residues of H9) confirmed the key role of Asn300 and suggest that in mammalian amidinotransferases, the role of helix H9 is in accelerating amidino transfer by an induced-fit mechanism. Helix H9 does not add to the stability of the protein.

Mediation of the cardiovascular response of adenosine A1 receptor through a GABA(B) receptor in the spinal cord of the rat

Cardiovascular inhibitory effects induced by intrathecal (i.t.) administration of adenosine A1 receptor agonist and its modulation by cyclic AMP was suggested by our previous report. In this experiment, we examined the mediation of cardiovascular effects of adenosine A1 receptor by gamma-aminobutyric acid receptors A and B [GABA(A) and GABA(B)] in the spinal cord. I.t. administration of 10 nmol of N6-cyclohexyladenosine (CHA), an adenosine A1 receptor agonist, and pretreatment with bicuculline (10 nmol, i.t), a GABA(A) receptor antagonist, and 5-aminovaleric acid (50 nmol, i.t.), a GABA(B) receptor antagonist, prior to injection of CHA were performed in anesthetized, artificially ventilated Sprague-Dawley rats. I.t. injection of 50 nmol of 5-aminovaleric acid significantly attenuated the inhibitory cardiovascular effects of CHA but 10 nmol of bicuculline did not alter CHA-induced cardiovascular actions. It is suggested that cardiovascular responses of adenosine A1 receptor is mediated by GABA(B) receptor in the spinal cord.

Carbon dioxide laser treatment of extramammary Paget's disease guided by photodynamic diagnosis

Extramammary Paget's disease (EPD) is a rare malignancy occurring mainly in apocrine gland-bearing regions. Surgical excision is the treatment of choice. This may be very difficult or even impossible if the disease is widespread or located in a critical anatomical site. We report on the successful treatment of a 71-year-old man with EPD in the suprapubic region with CO2 laser guided by photodynamic diagnosis.

Effects of GABA receptor antagonists injected spinally on antinociception induced by opioids administered supraspinally in mice

The present study was designed to investigate the modulatory effects of blockade of spinal GABAA and GABAB receptors on antinociception induced by supraspinally administered mu- and epsilon-opioid receptor agonists. The effects of intrathecal (i.t.) injections with GABAA and GABAB receptor antagonists, SR 95531 [2-(3-carboxypropyl)-3-amino-6-(4-mehylphenyl)pyridazinium bromide] and 5-aminovaleric acid, respectively, on the antinociception induced by morphine (a mu-opioid receptor agonist) and beta-endorphin (an epsilon-opioid receptor agonist) injected intracerebroventricularly (i.c.v.) were studied. Antinociception was assayed using the tail-flick test. The i.t. injection of SR 95531 (0.04-0.16 nmol) and 5-aminovaleric acid (32.5-130 nmol), administered alone did not affect the latencies of the tail-flick response, but selectively antagonized the inhibition of the tail-flick response induced by muscimol (a GABAA receptor agonist) and baclofen (a GABAB receptor agonist), respectively. The i.t. injection of SR 95531 attenuated dose-dependently the inhibition of the tail-flick response induced by i.c.v. administered morphine, without affecting the i.c.v. administered beta-endorphin-induced response. 5-Aminovaleric acid attenuated dose-dependently the inhibition of the tail-flick response induced by beta-endorphin, without affecting the response to i.c.v. administered morphine. Our results indicate that GABAA but not GABAB receptors located at the spinal cord appears to be involved in the antinociception induced by morphine administered supraspinally whereas GABAB but not GABAA receptors located at the spinal cord may be involved in the antinociception induced by supraspinally administered beta-endorphin, supporting further the hypothesis that morphine and beta-endorphin administered supraspinally produce their antinociception via the activation of different descending pain inhibitory systems.

Activation and characterization of procarboxypeptidase B from human plasma

Recently we reported the isolation and cloning of a novel plasma procarboxypeptidase B that binds plasminogen [Eaton, D. L., Malloy, B. E., Tsai, S. P., Henzel, W., & Drayna, D. (1991) J. Biol. Chem. 266, 21833-21838]. This plasma procarboxypeptidase is structurally similar to tissue procarboxypeptidases, and initial substrate studies showed that this plasma protein behaves like a basic carboxypeptidase and is now known as human plasma procarboxypeptidase B (pro-pCPB). However, unlike the tissue procarboxypeptidases, pro-pCPB is extremely unstable to trypsin activation. Trypsin cleaves pro-pCPB at two sites: Arg-92 and Arg-330. Cleavage at Arg-92 releases the activation peptide and generates an active enzyme. However, cleavage at Arg-330 inactivates pCPB. This renders the characterization of pCPB difficult. We have found that 6-amino-n-hexanoic acid (epsilon ACA), a compeptitive inhibitor of basic carboxypeptidases, selectively limits trypsin cleavage of pro-pCPB. In the presence of epsilon ACA, trypsin cleavage at Arg-330 is significantly limited while the cleavage at Arg-92 is unaffected. Using this approach, active pCPB can now be obtained. Kinetic characterization shows that pCPB behaves like other known basic carboxypeptidases. pCPB is more specific for substrates with C-terminal arginine than those with C-terminal lysine for all the natural and synthetic peptides tested. It also hydrolyzes the synthetic ester substrate more efficiently than the synthetic peptide substrate, especially at high pH. The active site Zn2+ can be replaced with other metals with change in substrate specificity.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and use of fluorescent molecular probes for measuring cell-surface enzymatic oxidation of amino acids and amines in seawater

A method for investigating cell-surface enzymatic oxidative deamination of amino acids and amines in seawater was developed. This technique used synthetic fluorescent Lucifer Yellow derivatives of the amino acid lysine and the amine cadaverine as molecular probes to investigate oxidation pathways and rates. The probes were chemically stable under the conditions used and did not adsorb to container surfaces. The oxidative deamination of the fluorescent probes added to phytoplankton cultures and the subsequent production of their fluorescent oxidation products could be selectively detected by HPLC at 250 pM levels. This approach allows selective investigation of cell-surface enzymatic oxidation since neither transport of the probes across the cell membrane nor chemical transformation of the probes occurs. Bacteria were also capable of oxidizing the fluorescent amino acid probe.

Proposed antagonists at GABAB receptors that inhibit adenylyl cyclase in cerebellar granule cell cultures of rat

The effects of various proposed GABAB receptor antagonists on baclofen-mediated inhibition of adenylyl cyclase were studied in cultured cerebellar granule cells from rat. (+/-)-Baclofen maximally inhibited adenylyl cyclase by approximately 60% of the basal enzyme activity with an EC50 value of 10 microM. 3-Aminopropane sulfonic acid (3-APS) and 5-aminovaleric acid (5-AVA) produced similar responses to that seen with (+/-)-baclofen. Saclofen reversed the action of (+/-)-baclofen, 50 microM, with a half maximal inhibitory concentration (IC50) of about 1.0 mM. The most effective antagonist in blocking the action of (+/-)-baclofen was 3-aminopropyl-diethoxy-methyl-phosphonic acid (CGP 35,348). In the presence of (+/-)-baclofen, 50 microM, the IC50 for CGP 35,348 was 290 microM and its inhibitory constant (KA) was 180 microM. The agonist-like actions of 3-APS and 5-AVA were antagonized by CGP 35,348 suggesting that 3-APS and 5-AVA may act as weak agonists at the GABAB receptor that inhibits adenylyl cyclase. All antagonists tested, except the new compound CGP 35,348, have very low potencies at GABAB receptors that inhibit adenylyl cyclase, though these compounds have been quite effective at other GABAB receptor-mediated events. Thus, the GABAB receptor which inhibits adenylyl cyclase differs pharmacologically from other reported GABAB receptor/effector systems and supports the existence of multiple receptor subtypes.

Effect of single gallium arsenide exposure on some biochemical variables in porphyrin metabolism in rats

Gallium arsenide (GaAs) inhibited, dose dependently, delta-aminolevulinic acid dehydratase (ALAD) activity in blood (as observed on days 1, 7 and 15), liver and brain (on day 15) after a single oral treatment. Levels of blood zinc protoporphyrin (ZPP) and urinary delta-aminolevulinic acid (ALA) excretion were elevated on day 7 and day 15 following exposure to 2000 mg kg-1 GaAs. A dose-dependent increase in blood As contents was observed while blood Ga was detectable only at higher doses.

Hydroxylated analogues of 5-aminovaleric acid as 4-aminobutyric acidB receptor antagonists: stereostructure-activity relationships

The (R) and (S) forms of 5-amino-2-hydroxyvaleric acid (2-OH-DAVA) and 5-amino-4-hydroxyvaleric acid (4-OH-DAVA) were designed as structural hybrids of the 4-aminobutyric acidB (GABAB) agonist (R)-(-)-4-amino-3-hydroxybutyric acid [(R)-(-)-3-OH-GABA] and the GABAB antagonist 5-aminovaleric acid (DAVA). (S)-(-)-2-OH-DAVA and (R)-(-)-4-OH-DAVA showed a moderately potent affinity for GABAB receptor sites in rat brain and showed GABAB antagonist effects in a guinea pig ileum preparation. The respective enantiomers, (R)-(+)-2-OH-DAVA and (S)-(+)-4-OH-DAVA, were markedly weaker in both test systems. All four compounds were weak inhibitors of GABAA receptor binding in rat brain, and none of them significantly affected synaptosomal GABA uptake. Based on molecular modeling studies it has been demonstrated that low-energy conformations of (R)-(-)-3-OH-GABA, (S)-(-)-2-OH-DAVA, and (R)-(-)-4-OH-DAVA can be superimposed. These conformations may reflect the shapes adopted by these conformationally flexible compounds during their interaction with GABAB receptors. The present studies emphasize the similar, but distinct, constraints imposed on agonists and antagonists for GABAB receptors.

Direct evidence for mediation of an anticonflict effect of baclofen by GABAb receptors

The present article reports an experiment on the effects of baclofen (0, 0.5, 1.0, and 2.0 mg/kg) on punished drinking in rats and the modification of these by delta-amino-n-valeric acid (DANVA) (0 and 10.0 mg/kg). Baclofen significantly enhanced punished drinking and this increase was abolished by DANVA, which had no intrinsic anxiogenic activity. It is concluded that GABAb receptors probably mediate this effect of baclofen and that such receptors may be a potential site of anxiolytic drug action.

An investigation of the involvement of GABA in certain pharmacological effects of delta-9-tetrahydrocannabinol

Experiments were performed with mice to determine whether doses of the benzodiazepine, flurazepam, or the GABA uptake inhibitor, NO-328, known to potentiate catalepsy induced by delta-9-tetrahydrocannabinol (THC), would also interact synergistically with THC in the production of certain other effects. No synergism was detected either in the production of antinociception (tail flick test) or in a test in which the ability of flurazepam to delay onset of clonic convulsions induced by intravenous infusion of pentylenetetrazole was compared in the presence and absence of THC or cannabidiol. The hypothermic effect of THC was unaffected by NO-328 but enhanced by flurazepam, albeit only at doses higher than those needed to potentiate THC-induced catalepsy. In vitro experiments with guinea pig ileum showed that the ability of THC to inhibit electrically evoked contractions was unaffected by delta-amino-n-valeric acid, a GABA(B) receptor antagonist, and that preparations rendered tolerant to GABA responded normally to THC. Contractions induced by GABA in unstimulated ileal longitudinal muscle were attenuated by THC. We conclude that there is little evidence from our data that any of the THC effects studied were GABA mediated.

High sensitivity HPLC assay for GABA in brain dialysis studies

The measurement of GABA in brain dialysis experiments involves precolumn derivatization of the amino acid with o-phthaldehyde (OPA) in the presence of a thiol and subsequent high-pressure liquid chromatography with electrochemical detection. A method is described which employs an internal standard and coulometric preoxidation (+ 0.2 V) to eliminate unconjugated OPA/thiol prior to final oxidation (+ 0.4 V) of the derivatized sample. This allows for more efficient separation, providing a retention time for GABA of 9-10 min, a detection sensitivity of 2 to 5 x 10(-14) mol/sample and chromatographic stability for at least 2 weeks of daily use.

Effects of chlordiazepoxide and putative anxiogenics on conditioned suppression in rats

This paper reports two experiments. In Experiment 1, the effects of chlordiazepoxide alone and in combination with a series of putative antagonists at various sites on the GABA/benzodiazepine receptor complex on conditioned suppression of operant behavior in rats were assessed. Response rates during presentation of a stimulus associated with shock (CS responding) and when only positive reinforcement is effective (pre-CS responding) were analysed. Chlordiazepoxide (10 mg/kg) significantly increased CS responding. This effect was significantly antagonised by Ro15-1788 (10 mg/kg) and by picrotoxin (1.5 mg/kg), but not by bicuculline (1.5 mg/kg) or by delta-amino-n-valeric acid (10 or 20 mg/kg). Chlordiazepoxide also significantly, albeit more slightly, increased pre-CS responding and none of the other drugs tested significantly antagonised this action, though Ro15-1788 plus chlordiazepoxide resulted in pre-CS response rates not significantly different from either chlordiazepoxide alone or control. These interactions are discussed in the context of the proposed GABA/benzodiazepine receptor complex with the conclusion that drug effects at the benzodiazepine- and picrotoxin-sensitive channel sites have an important role in mediating anxiolytic action. However, behavioral evidence of an important role for GABAa or GABAb receptors remains very limited. The second experiment studied the intrinsic actions of bicuculline, picrotoxin, and Ro15-1788 on conditioned suppression. Responding during a conditioned stimulus associated with a mild (0.125 to 0.15 mA) electric shock (CS responding) and a control rate of responding (pre-CS responding) were recorded. Bicuculline (1.5 mg/kg) and Ro15-1788 (10 mg/kg) did not significantly affect either response rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonism of baclofen-induced antinociception by intrathecal administration of phaclofen or 2-hydroxy-saclofen, but not delta-aminovaleric acid in the rat

This study evaluated the ability of two new, selective antagonists of the gamma-aminobutyric acidB (GABAB) receptor, phaclofen (PHAC) and 2-hydroxy-saclofen (2-OH-S), to antagonize the increase in tail-flick latency (TFL) and hot-plate latency (HPL) produced by i.t. administered baclofen (BAC) in the rat. The putative GABAB receptor antagonist delta-aminovaleric acid (DAVA) was also examined for comparative purposes. Intrathecal (i.t.) pretreatment with increasing doses of PHAC (10-100 micrograms) shifted the dose-effect relationship of i.t. administered BAC progressively to the right in a parallel manner in both the tail-flick (TF) and hot-plate (HP) test. Schild analysis of the data yielded an apparent pA2 value of 7.3 +/- 0.1 and a slope of -0.98 +/- 0.14. By comparison, PHAC did not antagonize the increase in HPL produced by i.t. injection of the serotonin1A agonist, 8-hydroxy-N,N-dipropyl-2-aminotetralin. These observations indicate that PHAC competitively and selectively antagonizes BAC and further suggest that the antinociceptive effects of i.t. administered BAC are mediated by the PHAC-sensitive subtype of the GABAB receptor. Intrathecal injection of PHAC alone did not decrease TFL or HPL, suggesting that spinal GABAB receptors involved in nociception are not tonically activated. Although i.t. pretreatment with 2-OH-S (10-30 micrograms) also antagonized the antinociceptive effects of i.t. administered BAC, increasing doses of 2-OH-S did not produce progressive, rightward shifts in the dose-effect relationship of BAC. Indeed, i.t. administration of 2-OH-S alone modestly increased TFL, but not HPL in the rat. These observations suggest that 2-OH-S may be a partial agonist at spinal GABAB receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for functionally distinct subclasses of gamma-aminobutyric acid receptors in rabbit retina

gamma-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the mammalian retina, where it serves many roles in establishing complex response characteristics of ganglion cells. We now provide biochemical and physiological evidence that at least three subclasses of GABA receptors (A1, A2, and B) contribute to different types of synaptic integration. Receptor binding studies indicate that approximately three-fourths of the total number of [3H]GABA binding sites in retina are displaced by the GABAA receptor antagonist, bicuculline, whereas one-fourth are displaced by the GABA-B receptor agonist, baclofen. GABAA receptors can be described by a three-site binding model with KD values of 19 nM, 122 nM, and 5.7 microM. Benzodiazepines and barbiturates potentiate binding to the GABAA site, which suggests that significant numbers of GABAA receptors are coupled to regulatory sites for these compounds and thus are classified as GABAA1 receptors. The response to pentobarbital appears to involve a conversion of low-affinity sites to higher-affinity sites, and is reflected in changes in the densities of sites at different affinities. Functional studies were used to establish which of the different receptor subclasses regulate release from cholinergic amacrine cells. Our results show that GABA suppresses light-evoked [3H]acetylcholine release via GABAA2 receptors not coupled to a benzodiazepine or barbiturate regulatory site, and enhances release via GABAB receptors. GABAA1 sites do not appear to control acetylcholine release in rabbit retina.

Direct evidence for central action of PCPGABA to stimulate gastric acid secretion by intracisternal injection

PCPGABA, injected into the cisterna magna, significantly stimulated gastric acid secretion in the perfused rat stomach preparation. This secretagogue action was dose-dependent (0.5-2 micrograms/rat). The peak response occurred within 60 min and lasted up to 100 min. The secretagogue action by PCPGABA was completely reduced by truncal vagotomy. Intracisternal injection of 5-aminovaleric acid, a GABAB-receptor antagonist, did not alter basal gastric acid output, and it also failed to antagonize the acid secretory response to intracisternal PCPGABA. These results demonstrate that intracisternal PCPGABA caused hypersecretion of acid through vagal dependent mechanisms partially independent of GABAB-receptors.

3-Aminopropanephosphinic acid is a potent agonist at peripheral and central presynaptic GABAB receptors

The actions of the GABA analog 3-aminopropanephosphinic acid (3-APA) were studied in the guinea-pig isolated ileal preparation and at synapses between cultured rat hippocampal neurons. Like the GABAB receptor agonist, baclofen, 3-APA inhibited the electrically evoked ileal twitch. The EC50 for 3-APA was 0.8 microM; the EC50 for baclofen was 9 microM. In addition, the depressant responses to 3-APA and baclofen were blocked by the GABAB receptor antagonists phaclofen, saclofen, 2-hydroxy-saclofen and delta-aminovaleric acid. 3-APA also mimicked the presynaptic action of baclofen at GABAergic synapses between embryonic rat hippocampal neurons in culture. 3-APA reduced the amplitude of inhibitory postsynaptic potentials (IPSPs) and currents (IPSCs) by greater than 50% at a concentration of 1 microM, while baclofen reduced synaptic transmission to a similar degree at 10 microM. 3-APA did not alter membrane conductance, nor did the drug alter postsynaptic responses to GABA. These data show that 3-APA is a potent agonist at presynaptic GABAB receptors in the periphery and on GABAergic neurons from the central nervous system. The activity of 3-APA at central postsynaptic GABAB receptors remains to be studied.

Interactions of taurine with GABAB binding sites in mouse brain

The interactions of taurine with GABAB receptors were studied in membranes from the brain of the mouse by measuring the binding of [3H]baclofen and that of [3H]GABA in the presence of isoguvacine. Taurine displaced ligand binding to GABAB receptors concentration-dependently with an IC50 in the micromolar range. The effects of baclofen on the release of taurine and GABA from slices of cerebral cortex of the mouse were assessed using a superfusion system. Potassium-stimulated release of both [3H]taurine and [3H]GABA was unaffected by baclofen but potentiated by delta-aminovalerate. The enhancement of release of [3H]taurine by delta-aminovalerate was partially antagonized by baclofen, suggesting that baclofen-sensitive receptors could modify the release.

An in vitro study of the relationship between GABA receptor function and propulsive motility in the distal colon of the rabbit

1. The effects of gamma-aminobutyric acid (GABA), 3-aminopropane sulphonic acid (3-APS) and baclofen on spontaneous, electrically-induced and propulsive motility were investigated in rabbit distal colon. 2. In unstimulated longitudinal (LMPs) and circular muscle strip preparations (CMPs) 3-APS (10-200 microM) and GABA caused a clear-cut relaxation susceptible to desensitization. Baclofen (10-200 microM) caused relaxation in a minority (30%) of preparations. The 3-APS response was sensitive to tetrodotoxin (TTX; 1 microM), SR 95531 (a novel competitive GABAA-receptor antagonist) (10 microM), picrotoxinin (30 microM), and insensitive to hyoscine (1 microM) and to a combination of prazosin (1 microM) and propranolol (1 microM). The baclofen response was antagonized by 5-aminovaleric acid (DAVA, 500 microM), TTX and hyoscine and resistant to GABAA-receptor and adrenoceptor blockade. GABAA-receptors were therefore associated with non-adrenergic non-cholinergic (NANC) inhibitory nerve activation while GABAB-receptors were involved in depression of cholinergic tone of smooth muscle. GABA (10-200 microM) elicited both above mentioned effects. 3. In LMPs, baclofen (10-200 microM) dose-dependently inhibited submaximal responses to both cholinergic and NANC inhibitory nerve stimulation. This effect was resistant to SR 95531 and picrotoxinin and prevented by DAVA and baclofen desensitization. GABA (10-200 microM) mimicked the action of baclofen. GABA inhibitory effects persisted in the presence of GABAA-receptor blockade. 4. In segments of distal colon, GABA and baclofen (1-200 microM), but not 3-APS (1-200 microM), dose-dependently decreased the velocity of propulsion of an intraluminally-distended balloon. This effect was antagonized by DAVA and GABA or baclofen desensitization and resistant to SR 95531 and picrotoxinin. These antagonists per se had no effect on propulsion. In preparations in which propulsion was slowed by hyoscine (1 microM), baclofen caused no consistent further depression of propulsive activity. 5. Our results show that GABAA- and GABAB-receptors are present in rabbit colon. GABAA-receptor stimulation activates NANC inhibitory nerves without apparently affecting propulsion. GABAB-receptors are associated with a reduction of neural (mainly cholinergic) activity subserving muscular tone and peristalsis and appear to be located on both cholinergic and NANC inhibitory nerves. However, the persisting propulsive activity during suppression of GABAA- and GABAB-receptor function suggests that GABA in enteric neurones is not crucial for the neural circuitry subserving colonic peristalsis in this species.

Effects of the putative antagonists phaclofen and delta-aminovaleric acid on GABAB receptor biochemistry

1. Phaclofen and delta-aminovaleric acid (delta-AVA) have been reported to be antagonists at gamma-aminobutyric acidB (GABAB) receptors. Phaclofen, delta-AVA and related compounds were examined for potency and specificity at GABAB and GABAA receptors in rat cortical membranes labelled with [3H]-(-)-baclofen and [3H]-muscimol, respectively. Additionally phaclofen and delta-AVA were examined in two functional tests of central GABAB activity in rat cortical slices, namely the inhibition of forskolin-stimulated cyclic AMP accumulation, and the potentiation of isoprenaline-stimulated cyclic AMP accumulation. 2. delta-AVA (IC50 = 11.7 microM) was 20 fold more potent than phaclofen (IC50 = 229 microM) on GABAB receptor binding. All compounds possessing a phosphonic acid group, including phaclofen, which were active at GABAB receptors were inactive at GABAA receptors, while delta-AVA was equally potent at both receptors. Several compounds exhibited Hill coefficients of less than unity in displacing [3H]-(-)-baclofen binding. 3. (-)-Baclofen inhibited forskolin-stimulated cyclic AMP accumulation (IC50 = 7.9 microM) but this effect was not stereospecific. Phaclofen (1 mM) was inactive against this inhibition but produced a potentiation of the forskolin effect. delta-AVA (1 mM) failed to antagonize the effect of baclofen; rather it mimicked baclofen. 4. (-)-Baclofen (10 microM) potentiated isoprenaline-stimulated cyclic AMP accumulation, an effect antagonized by phaclofen (1 mM). delta-AVA (1 mM) may be a weak antagonist but also potentiated basal cyclic AMP accumulation. 5. We conclude that neither delta-AVA nor phaclofen are potent specific GABAB receptor antagonists.

GABA-A-mediated gastrin release induced by baclofen in the isolated vascularly perfused rat stomach

In order to investigate the role of peripheral GABA-B receptors, the effects of the putative GABA-B agonist baclofen on immunoreactive gastrin release from an isolated vascularly perfused rat stomach preparation were examined. The vascular infusion of baclofen at graded concentrations induced a dose-dependent increase in gastrin release; this was unaffected by the GABA-B antagonist delta-aminovaleric acid, but was fully prevented by the selective GABA-A antagonist bicuculline as well as by atropine or tetrodotoxin. These results suggest that the stimulant effects of baclofen are mediated by nervous cholinergic structures associated with GABA-A receptors, and indicate that this GABA-B agonist must be regarded as a partial agonist of peripheral GABA-A receptors.

GABA regulation of circadian responses to light. I. Involvement of GABAA-benzodiazepine and GABAB receptors

Light-induced phase shifts of the circadian locomotor rhythm of hamsters can be blocked by agents that alter GABA neurotransmission. The GABA antagonist bicuculline blocks phase delays induced by light and the benzodiazepine diazepam, which can potentiate GABA activity, blocks light-induced phase advances. In the experiments reported here, we found that the bicuculline blockade of phase delays was reduced by agents that mimic or potentiate GABA activity. Conversely, the diazepam blockade of phase advances was reduced by both competitive and noncompetitive antagonists of GABA. This indicates that the GABA-benzodiazepine receptor-ionophore complex is the most likely site of action for the effects of these drugs on circadian rhythms. However, competitive GABA agonists did not mimic the blocking effects of benzodiazepines, nor did the antagonist picrotoxin mimic the blocking effect of bicuculline. Therefore, the classic action of GABA, increased chloride conductance, may not be the effector mechanism in this case. We also found that the GABAB agonist baclofen blocked both phase advances and delays and that the blockade of advances was reversed by the antagonist delta-aminovaleric acid. Taken together, these results indicate that GABA is involved in the regulation of circadian responses to light and that the regulation is mediated by both GABAA and GABAB receptors.

Baclofen, gamma-aminobutyric acidB receptors and substance P in the mouse spinal cord

Antinociceptive effects of baclofen, a gamma-aminobutyric acidB (GABAB) agonist, were studied in mice along with other GABAergic agents, all administered intrathecally (i.t.): i.e., muscimol (GABAA agonist), bicuculline (GABAA antagonist) and 5-aminovaleric acid (GABAB antagonist). After i.t. administration, none of the four compounds increased the withdrawal latency in the tail-flick test. With the intradermal hypertonic saline (6% saline) behavioral test, baclofen decreased the number of behaviors in a dose-dependent and 5-aminovaleric acid-reversible manner, whereas i.t. administered muscimol was ineffective. With the i.t. substance P (SP) behavioral test, muscimol was again ineffective, whereas the SP-induced behaviors were differentially modified by baclofen depending on the temporal order of their i.t. administration. Although baclofen, coadministered with SP, decreased the number of SP-induced behaviors, baclofen pretreatment (2-100 min before i.t. administration of SP) increased the number of behaviors in a dose-dependent and 5-aminovaleric acid-reversible manner. Two minutes after several fixed doses of baclofen were administered i.t., dose-response curves for induction of behaviors by SP (i.t.) were shifted progressively to the left by increasing doses of baclofen, suggesting that hypersensitivity to SP had developed during this time frame. Decreased responsiveness to a peripheral noxious stimulus (hypertonic saline-induced behavior) is therefore associated with hypersensitivity to i.t. applied SP (SP behavioral test). The selective action of a GABAB agonist on neurokinin-elicited behaviors shown in this study is in clear contrast to the selective action of a GABA agonist against excitatory amino acid spinal activity noted in the following paper.

[Identification of 5-aminovaleric acid as a characteristic product of metabolism of various Clostridium species]

An unusual ninhydrin-positive compound has been isolated from feces of accidentally contaminated Sprague-Dawley autbred rats and identified by mass spectrometry and 1H-NMR spectroscopy techniques as 5-aminovaleric acid. The described procedure of isolation, purification and structure determination can be recommended as a general method of identification of unusual ninhydrin-positive compounds in complex mixtures of biological origin. The 5-aminovaleric acid was found to be produced by an anaerobic bacterium Clostridium bifermentans. It is shown that not all Clostridium spp. excrete his amino acid and that the majority of microorganisms, normally inhabiting intestine of rats, simians and man, do not possess this ability. On the basis of data obtained, the test for 5-aminovaleric acid is proposed to be included into the taxonomy of bacteria.

GABAB receptor antagonist and GABAA receptor agonist properties of a delta-aminovaleric acid derivative, Z-5-aminopent-2-enoic acid

The activity of Z-5-aminopent-2-enoic acid (A), a conformationally restricted analogue of delta-aminovaleric acid, was investigated in vitro in the guinea pig isolated ileum and vas deferens. A was found to be a relatively potent GABAB-receptor antagonist and a relatively weak GABAA-receptor agonist. The GABAB-receptor antagonist activity of A was at least 5 times greater than that of phaclofen, a selective GABAB-receptor antagonist. A may therefore be an important lead for the development of new potent and selective GABAB-antagonists.