N-Acetyl-Aspartyl-Glutamate in Brain Health and Disease

N-acetyl-aspartyl-glutamate (NAAG) is the most abundant dipeptide in the brain, where it acts as a neuromodulator of glutamatergic synapses by activating presynaptic metabotropic glutamate receptor 3 (mGluR3). Recent data suggest that NAAG is selectively localized to postsynaptic dendrites in glutamatergic synapses and that it works as a retrograde neurotransmitter. NAAG is released in response to glutamate and provides the postsynaptic neuron with a feedback mechanisms to inhibit excessive glutamate signaling. A key regulator of synaptically available NAAG is rapid degradation by the extracellular enzyme glutamate carboxypeptidase II (GCPII). Increasing endogenous NAAG—for instance by inhibiting GCPII—is a promising treatment option for many brain disorders where glutamatergic excitotoxicity plays a role. The main effect of NAAG occurs through increased mGluR3 activation and thereby reduced glutamate release. In the present review, we summarize the transmitter role of NAAG and discuss the involvement of NAAG in normal brain physiology. We further present the suggested roles of NAAG in various neurological and psychiatric diseases and discuss the therapeutic potential of strategies aiming to enhance NAAG levels.

Phe-Gly motifs drive fibrillization of TDP-43's prion-like domain condensates

Transactive response DNA-binding Protein of 43 kDa (TDP-43) assembles various aggregate forms, including biomolecular condensates or functional and pathological amyloids, with roles in disparate scenarios (e.g., muscle regeneration versus neurodegeneration). The link between condensates and fibrils remains unclear, just as the factors controlling conformational transitions within these aggregate species: Salt- or RNA-induced droplets may evolve into fibrils or remain in the droplet form, suggesting distinct end point species of different aggregation pathways. Using microscopy and NMR methods, we unexpectedly observed in vitro droplet formation in the absence of salts or RNAs and provided visual evidence for fibrillization at the droplet surface/solvent interface but not the droplet interior. Our NMR analyses unambiguously uncovered a distinct amyloid conformation in which Phe-Gly motifs are key elements of the reconstituted fibril form, suggesting a pivotal role for these residues in creating the fibril core. This contrasts the minor participation of Phe-Gly motifs in initiation of the droplet form. Our results point to an intrinsic (i.e., non-induced) aggregation pathway that may exist over a broad range of conditions and illustrate structural features that distinguishes between aggregate forms.

The prion-like domain of TDP-43 assembles biomolecular condensates which mature into amyloid fibrils that accumulate at the condensate/solvent interface. In vitro reconstitution of these fibrils reveals an amyloid core stabilized by residues that are not necessarily essential to create the droplet form.

Growth promotion in Arabidopsis thaliana by bacterial cyclodipeptides involves the TOR/S6K pathway activation

Cyclodipeptides (CDPs) are the smallest peptidic molecules that can be produced by diverse organisms such as bacteria, fungi, and animals. They have multiple biological effects. In this paper, we examined the CDPs produced by the bacteria Pseudomonas aeruginosa PAO1, which are known as opportunistic pathogens of humans and plants on TARGET OF RAPAMYCIN (TOR) signaling pathways, and regulation of root system architecture. This bacterium produces the bioactive CDPs: cyclo(L-Pro-L-Leu), cyclo(L-Pro-L-Phe), cyclo(L-Pro-L-Tyr), and cyclo(L-Pro-L-Val). In a previous report, these molecules were found to modulate basic cellular programs not only via auxin mechanisms but also by promoting the phosphorylation of the S6 ribosomal protein kinase (S6K), a downstream substrate of the TOR kinase. In the present work, we found that the inoculation of Arabidopsis plants with P. aeruginosa PAO1, the non-pathogenic P. aeruginosa ΔlasI/Δrhll strain (JM2), or by direct exposure of plants to CDPs influenced growth and promoted root branching depending upon the treatment imposed, while genetic evidence using Arabidopsis lines with enhanced or decreased TOR levels indicated a critical role of this pathway in the bacterial phytostimulation.

[Characteristics of the pineal gland and thymus relationship in aging]

The review presents the interference between thymus and pineal gland during their involution. The research data of thymus peptides influence on pineal gland and pineal peptides on thymus are summarized. Analysis of these data showed that pineal peptides (Epithalamin, Epitalon) had more effective geroprotective effect on thymus involution in comparison with geroprotective effect of thymic peptides (Thymalin, Thymogen) on involution of pineal gland. The key mechanisms of pineal peptides effect on thymus dystrophy is immunoendocrine cooperation, which is realized as transcription's activation of various proteins.

[Possible relation of BDNF and GDNF to neuropsychiatric disorders]

Structural abnormalities are demonstrated in various neuropsychiatric disorders, including Alzheimer's disease, Parkinson's disease, and even major depression. On the other hand, recent studies have demonstrated the structural and functional modifications in the adult brain that are associated with synaptic plasticity and neurogenesis. Accordingly, regulation of synaptic plasticity and neurogenesis may lead to the development of novel treatments for neuropsychiatric disorders. Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) have important roles not only in neuronal survival and differentiation, but also in the formation and maintenance of neural circuits and synapse plasticity. Accumulating evidence suggests that these neurotrophic factors may be applied to the treatment of neuropsychiatric disorders. In addition, compounds that increase the expression of BDNF and/or GDNF in the brain should have potential therapeutic values. We have demonstrated that systemic administration of dipeptide Leu-Ile increases BDNF and GDNF production in the brain, and has a protective role in methamphetamine and morphine dependence. In this review, we discuss the potential role of BDNF, GDNF and their inducers in the treatment for neuropsychiatric disorders.

Role of gut hormones in obesity

A critical role for the gut in energy homeostasis has emerged. Gut hormones not only have a role in digestion but several of them have been found to modulate appetite in animals and humans. Current nonendocrine drugs for obesity are limited by their modest efficacies, and bariatric surgery is confined to use in severe cases. The discovery of important appetite-signaling pathways from the gut to the brain has led to the emergence of several gut hormone-derived drugs that are being investigated for clinical use. This article summarizes the physiology of the major gut hormones implicated in appetite regulation, and reviews clinical evidence that gives us insight into their potential as clinical treatments for obesity.

Dileucine motif is sufficient for internalization and synaptic vesicle targeting of vesicular acetylcholine transporter

Efficient cholinergic transmission requires accurate targeting of vesicular acetylcholine transporter (VAChT) to synaptic vesicles (SVs). However, the signals that regulate this vesicular targeting are not well characterized. Although previous studies suggest that the C-terminus of the transporter is required for its SV targeting, it is not clear whether this region is sufficient for this process. Furthermore, a synaptic vesicle-targeting motif (SVTM) within this sequence remains to be identified. Here we use a chimeric protein, TacA, between an unrelated plasma membrane protein, Tac, and the C-terminus of VAChT to demonstrate the sufficiency of the C-terminus for targeting to synaptic vesicle-like vesicles (SVLVs) in PC12 cells. TacA shows colocalization and cosedimentation with the SV marker synaptophysin. Deletion mutation analysis of TacA demonstrates that a short, dileucine motif-containing sequence is required and sufficient to direct this targeting. Dialanine mutation analysis within this sequence suggests indistinguishable signals for both internalization and SV sorting. Using additional chimeras as controls, we confirm the specificity of this region for SVLVs targeting. Therefore, we suggest that the dileucine-containing motif is sufficient as a dual signal for both internalization and SV targeting during VAChT trafficking.

Involvement of glial cell line-derived neurotrophic factor in inhibitory effects of a hydrophobic dipeptide Leu-Ile on morphine-induced sensitization and rewarding effects

There are few efficacious medications for drug dependence at present. We have previously demonstrated that Leu-Ile, which induces the expression of not only tumor necrosis factor-alpha (TNF-alpha) but also glial cell line-derived neurotrophic factor (GDNF), inhibits methamphetamine (METH) and morphine (MOR)-induced sensitization and rewarding effects by regulating extracellular dopamine levels via the induction of TNF-alpha expression, and indicated the potential of Leu-Ile as a novel therapeutic agent for METH and MOR-induced dependence. In the present study, we investigated the involvement of GDNF in inhibitory effects of Leu-Ile on MOR-induced sensitization and rewarding effects. Repeated treatment with MOR for 9 days, which results in an enhancement of the locomotor-stimulating effects (sensitization) of MOR, increased GDNF levels in the nucleus accumbens compared with those in saline-treated mice. Repeated pre-treatment with Leu-Ile for 9 days potentiated the MOR-induced increase in GDNF levels. MOR at a low dose (3mg/kg) produced place preference in GDNF heterozygous knockout (GDNF-(+/-)) mice, but not in littermate GDNF-(+/+) mice. No inhibitory effect of Leu-Ile on MOR-induced place preference was observed in GDNF-(+/-) mice. These results suggest that GDNF is involved in the inhibitory effects of Leu-Ile on MOR-induced sensitization and rewarding effects.

Neonatal administration of N-acetyl-l-aspartyl-l-glutamate induces early neurodegeneration in hippocampus and alters behaviour in young adult rats

N-acetyl-L-aspartyl-L-glutamate (NAAG) is a dipeptide that could be considered a sequestered form of L-glutamate. As much as 25% of L-glutamate in brain may be present in the form of NAAG. NAAG is also one of the most abundant neuroactive small molecules in the CNS: it is an agonist at Group II metabotropic glutamate receptors (mGluR II) and, at higher concentrations, at the N-methyl-D-aspartate (NMDA) type of ionotropic glutamate receptors. As such, NAAG can be either neuroprotective or neurotoxic and, in fact, both characteristics have been discussed and described in the literature. In the present studies, 250 nmol NAAG was infused into each lateral cerebral ventricle of 12-day-old rat pups and, using Nissl-stained sections, neurodegeneration in the hippocampus was evaluated 24 or 96 h after the infusion. In several experiments, the neuronal death was also visualised by Fluoro-Jade B staining and studied by TUNEL technique. Some of the NAAG-treated animals were allowed to survive until 50 days post partum and subjected to behavioural (open field) tests. The administration of NAAG to 12-day-old rats resulted in extensive death of neurons particularly in the dentate gyrus of the hippocampus. The neurodegeneration was, in part, prevented by administration of an NMDA receptor antagonist MK-801 (0.1 mg/kg). The nuclear DNA-fragmentation demonstrated by TUNEL technique pointed to the presence of non-specific single-strand DNA cleavage. The NAAG-associated neonatal neuronal damage may have perturbed development of synaptic circuitry during adolescence as indicated by an altered performance of the experimental animals in the open field testing (changes in grooming activity) at postnatal day 50. The results underscore the potential neurotoxicity of NAAG in neonatal rat brain and implicate neonatally induced, NMDA receptor-mediated neuronal loss in the development of abnormal behaviour in young adult rats.

Caspase and bid involvement in Clostridium difficile toxin A-induced apoptosis and modulation of toxin A effects by glutamine and alanyl-glutamine in vivo and in vitro

Clostridium difficile is the leading cause of nosocomial bacterial diarrhea. Glutamine and its stable and highly soluble derivative alanyl-glutamine, have been beneficial in models of intestinal injury. In this study, we extend our work on the mechanisms of Clostridium difficile toxin A (TxA)-induced apoptosis in human intestinal epithelial T84 cells and evaluate the effects of glutamine and alanyl-glutamine on TxA-induced apoptosis in vitro and disruption of ileal mucosa in vivo. T84 cells were incubated with TxA (100 ng/ml) in medium with or without glutamine or alanyl-glutamine (3 to 100 mM). Apoptosis was evaluated by DNA fragmentation in vitro and the terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling method in vivo. Caspase and Bid involvement were investigated by Western blotting. Ligated rabbit ileal loops were used for the evaluation of intestinal secretion, mucosal disruption, and apoptosis. TxA induced caspases 6, 8, and 9 prior to caspase 3 activation in T84 cells and induced Bid cleavage by a caspase-independent mechanism. Glutamine or alanyl-glutamine significantly reduced TxA-induced apoptosis of T84 cells by 47% and inhibited activation of caspase 8. Both glutamine and alanyl-glutamine reduced TxA-induced ileal mucosal disruption and secretion. Altogether, we further delineated the apoptosis-signaling cascade induced by TxA in T84 cells and demonstrated the protective effects of glutamine and alanyl-glutamine. Glutamine and alanyl-glutamine inhibited the apoptosis of T84 cells by preventing caspase 8 activation and reduced TxA-induced intestinal secretion and disruption.

N-Acetylaspartate as a reservoir for glutamate

N-acetylaspartate (NAA) is an intermediary metabolite that is found in relatively high concentrations in the human brain. More specifically, NAA is so concentrated in the neurons that it generates one of the most visible peaks in nuclear magnetic resonance (NMR) spectra, thus allowing NAA to serve as "a neuronal marker". However, to date there is no generally accepted physiological (primary) role for NAA. Another molecule that is found at similar concentrations in the brain is glutamate. Glutamate is an amino acid and neurotransmitter with numerous functions in the brain. We propose that NAA, a six-carbon amino acid derivative, is converted to glutamate (five carbons) in an energetically favorable set of reactions. This set of reactions starts when aspartoacylase converts the six carbons of NAA to aspartate and acetate, which are subsequently converted to oxaloacetate and acetyl CoA, respectively. Aspartylacylase is found in astrocytes and oligodendrocytes. In the mitochondria, oxaloacetate and acetyl CoA are combined to form citrate. Requiring two steps, the citrate is oxidized in the Kreb's cycle to alpha-ketoglutarate, producing NADH. Finally, alpha-ketoglutarate is readily converted to glutamate by transaminating the alpha-keto to an amine. The resulting glutamate can be used by multiple cells types to provide optimal brain functional and structural needs. Thus, the abundant NAA in neuronal tissue can serve as a large reservoir for replenishing glutamate in times of rapid or dynamic signaling demands and stress. This is beneficial in that proper levels of glutamate serve critical functions for neurons, astrocytes, and oligodendrocytes including their survival. In conclusion, we hypothesize that NAA conversion to glutamate is a logical and favorable use of this highly concentrated metabolite. It is important for normal brain function because of the brain's relatively unique metabolic demands and metabolite fluxes. Knowing that NAA is converted to glutamate will be important for better understanding myriad neurodegenerative diseases such as Canavan's Disease and Multiple Sclerosis, to name a few. Future studies to demonstrate the chemical, metabolic and pathological links between NAA and glutamate will support this hypothesis.

Phosphoproteomic analysis of the effect of cyclo-[His-Pro] dipeptide on PC12 cells

The effects of dipeptide cyclo-[His-Pro] (CHP), known to participate in the appetite behavior and food intake control, have been investigated using PC12 cells in culture as model system. We found that only in the presence of experimental conditions that cause cellular stress the cyclic dipeptide affect cellular proliferation and protects from apoptosis. It greatly enhances the phosphorylation of hsp27, alpha-B-crystallin, Cdc2, and p-38 MAPK, whereas it decreases the phosphorylation of MEK1, Cav 2, GSK3a, PKB/Akt, PKCdelta, PKCgamma, and Erk2. PKA and PKG are involved in ERK1/2 deactivation via a receptor that appears to be dually coupled to Gs and Gq protein subfamilies.

Characterization of a dipeptide motif regulating IFN-gamma receptor 2 plasma membrane accumulation and IFN-gamma responsiveness

The IFN-gammaR complex is composed of two IFN-gammaR1 and two IFN-gammaR2 polypeptide chains. Although IFN-gammaR1 is constitutively expressed on all nucleated cells, IFN-gammaR2 membrane display is selective and tightly regulated. We created a series of fluorescent-tagged IFN-gammaR2 expression constructs to follow the molecule's cell surface expression and intracellular distribution. Truncation of the receptor immediately upstream of Leu-Ile 255-256 (254X) created a receptor devoid of signaling that overaccumulated on the cell surface. In addition, this truncated receptor inhibited wild-type IFN-gammaR2 activity and therefore exerted a dominant negative effect. In-frame deletion (255Delta2) or alanine substitution (LI255-256AA) of these amino acids created mutants that overaccumulated on the plasma membrane, but had enhanced function. Single amino acid substitutions (L255A or I256A) had a more modest effect. In-frame deletions upstream (253Delta2), but not downstream (257Delta2), of Leu-Ile 255-256 also led to overaccumulation. A truncation within the IFN-gammaR2 Jak2 binding site (270X) led to a mutant devoid of function that did not overaccumulate and did not affect wild-type IFN-gammaR2 signaling. We have created a series of novel mutants of IFN-gammaR2 that have facilitated the identification of intracellular domains that control IFN-gammaR2 accumulation and IFN-gamma responsiveness. In contrast to IFN-gammaR1, not only dominant negative, but also dominant gain-of-function, mutations were created through manipulation of IFN-gammaR2 Leu-Ile 255-256. These IFN-gammaR2 mutants will allow fine dissection of the role of IFN-gamma signaling in immunity.

Stochastic-based descriptors studying peptides biological properties: modeling the bitter tasting threshold of dipeptides

MARCH-INSIDE methodology was applied to the prediction of the bitter tasting threshold of 48 dipeptides by means of pattern recognition techniques, in this case linear discriminant analysis (LDA), and regression methods. The LDA models yielded a percentage of good classification higher than 80% with the two main families of descriptor generated by this methodology (95.8% for self return probability and 83.3% using electronic delocalization entropy). The regression models can explain more than 80% of the experimental variance of the independent variable. Two regression models were obtained with R(2) values of 0.82 and 0.88 for the whole data and the data without two outliers, respectively; having a standard deviation of 0.27 and 0.23. The predictive power of the obtained equations was assessed by the Leave-One-Out cross validation procedures, giving the same percentages of good classification as in the training set, in the LDA models, and yielding values of q(2) of 0.78 and 0.86 in the regression model, respectively. The validation of this methodology was also carried out by comparison with previous reports modeling this data with other well-known methodologies, even 3-D molecular descriptors.

Elucidation of the effect of brain cortex tetrapeptide Cortagen on gene expression in mouse heart by microarray

OBJECTIVES

Aging is associated with significant alterations in gene expression in numerous organs and tissues. Anti-aging therapy with peptide bioregulators holds much promise for the correction of age-associated changes, making a screening for their molecular targets in tissues an important question of modern gerontology. The synthetic tetrapeptide Cortagen (Ala-Glu-Asp-Pro) was obtained by directed synthesis based on amino acid analysis of natural brain cortex peptide preparation Cortexin. In humans, Cortagen demonstrated a pronounced therapeutic effect upon the structural and functional posttraumatic recovery of peripheral nerve tissue. Importantly, other effects were also observed in cardiovascular and cerebrovascular parameters.

DESIGN

Based on these latter observations, we hypothesized that acute course of Cortagen treatment, large-scale transcriptome analysis, and identification of transcripts with altered expression in heart would facilitate our understanding of the mechanisms responsible for this peptide biological effects. We therefore analyzed the expression of 15,247 transcripts in the heart of female 6-months CBA mice receiving injections of Cortagen for 5 consecutive days was studied by cDNA microarrays.

RESULTS

Comparative analysis of cDNA microarray hybridisation with heart samples from control and experimental group revealed 234 clones (1,53% of the total number of clones) with significant changes of expression that matched 110 known genes belonging to various functional categories. Maximum up- and down-regulation was +5.42 and -2.86, respectively.

CONCLUSION

Intercomparison of changes in cardiac expression profile induced by synthetic peptides (Cortagen, Vilon, Epitalon) and pineal peptide hormone melatonin revealed both common and specific effects of Cortagen upon gene expression in heart.

TCR comodulation of nonengaged TCR takes place by a protein kinase C and CD3 gamma di-leucine-based motif-dependent mechanism

One of the earliest events following TCR triggering is TCR down-regulation. However, the mechanisms behind TCR down-regulation are still not fully known. Some studies have suggested that only directly triggered TCR are internalized, whereas others studies have indicated that, in addition to triggered receptors, nonengaged TCR are also internalized (comodulated). In this study, we used transfected T cells expressing two different TCR to analyze whether comodulation took place. We show that TCR triggering by anti-TCR mAb and peptide-MHC complexes clearly induced internalization of nonengaged TCR. By using a panel of mAb against the Ti beta chain, we demonstrate that the comodulation kinetics depended on the affinity of the ligand. Thus, high-affinity mAb (K(D) = 2.3 nM) induced a rapid but reversible comodulation, whereas low-affinity mAb (K(D) = 6200 nM) induced a slower but more permanent type of comodulation. Like internalization of engaged TCR, comodulation was dependent on protein tyrosine kinase activity. Finally, we found that in contrast to internalization of engaged TCR, comodulation was highly dependent on protein kinase C activity and the CD3 gamma di-leucine-based motif. Based on these observations, a physiological role of comodulation is proposed and the plausibility of the TCR serial triggering model is discussed.

Inhibition of calpain is a component of nitric oxide-induced down-regulation of human mast cell adhesion

Nitric oxide is an important messenger that regulates mast cell activity by modifications to gene expression and intracellular pathways associated with exocytosis and adhesion. Integrin interactions with extracellular matrix components modulate an array of cell activities, including mediator production and secretion. To investigate the molecular mechanisms underlying NO regulation of mast cell function, we studied its effects on adhesion of a human mast cell line (HMC-1) to fibronectin (FN). The NO donors S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine strongly down-regulated the adhesion of HMC-1 to FN. Inhibitors of soluble guanylate cyclase and protein kinase G did not alter the response of cells to NO. A peroxynitrite scavenger did not affect modulation of adhesion by NO, nor could the effect of NO be mimicked by the peroxynitrite-producing compound 3-morpholinosydnonimine. NO donors inhibited the cysteine protease, calpain, while calpain inhibitors mimicked the effect of NO and led to a decrease in the ability of HMC-1 cells to adhere to FN. Thus, NO is an effective down-regulator of human mast cell adhesion. The mechanism for this action does not involve peroxynitrite or activation of soluble guanylate cyclase. Instead, a portion of NO-induced down-regulation of adhesion may be attributed to inhibition of the cysteine protease, calpain, an enzyme that has been associated with control of integrin activation in other cell types. The inhibition of calpain is most likely mediated via nitrosylation of its active site thiol group. Calpain may represent a novel therapeutic target for the regulation of mast cell activity in inflammatory disorders.

Amino acids are still as exciting as ever

Glutamate is probably the most important excitatory transmitter in the vertebrate central nervous system. Its multiple functional roles in the brain and spinal cord make therapeutic manipulation of these systems fraught with difficulties. There has, however, been recent progress in pharmacological manipulations of NMDA receptor subtypes and non-NMDA receptors, and understanding of the roles of NAAG, that promise rapid advances in pain control.

Functions of N-acetyl-L-aspartate and N-acetyl-L-aspartylglutamate in the vertebrate brain: role in glial cell-specific signaling

N-Acetyl-L-aspartate (NAA) and its derivative N-acetylaspartylglutamate (NAAG) are major osmolytes present in the vertebrate brain. Although they are synthesized primarily in neurons, their function in these cells is unclear. In the brain, these substances undergo intercompartmental cycles in which they are released by neurons in a regulated fashion and are then rapidly hydrolyzed by catabolic enzymes associated with glial cells. Recently, the catabolic enzyme for NAA hydrolysis has been found to be expressed only in oligodendrocytes, and the catabolic enzyme for NAAG expressed only in astrocytes. These results indicate an unusual tricellular metabolic sequence for the synthesis and hydrolysis of NAAG wherein it is synthesized in neurons from NAA and L-glutamate, hydrolyzed to NAA and L-glutamate by astrocytes, and further hydrolyzed to L-aspartate and acetate by oligodendrocytes. Since the discovery that the NAA and NAAG anabolic products of neurons are specifically targeted to oligodendrocytes and astrocytes, respectively, this unique metabolic compartmentalization also suggests that these substances may play an important role in cell-specific glial signaling. In this review, it is hypothesized that a key function of NAA and NAAG in the vertebrate brain is in cell signaling and that these substances are important in the regulation of interactions of brain cells and in the establishment and maintenance of the nervous system.

N-Acetylaspartylglutamate: the most abundant peptide neurotransmitter in the mammalian central nervous system

In the progress of science, as in life, timing is important. The acidic dipeptide, N-acetylaspartylglutamate (NAAG), was discovered in the mammalian nervous system in 1965, but initially was not considered to be a neurotransmitter candidate. In the mid-1980s, a few laboratories revisited the question of NAAG's role in the nervous system and pursued hypotheses regarding its function that ranged from a precursor for the transmitter pool of glutamate to a direct role as a peptide transmitter. Since that time, NAAG has been tested against nearly all of the established criteria for identification of a neurotransmitter. It successfully meets each of these tests, including a concentrated presence in neurons and synaptic vesicles, release from axon endings in a calcium-dependent manner following initiation of action potentials, and extracellular hydrolysis by membrane-bound peptidase activity. NAAG is the most prevalent and widely distributed neuropeptide in the mammalian nervous system. NAAG activates NMDA receptors with a low potency that may vary among receptor subtypes, and it is a highly selective agonist at the type 3 metabotropic glutamate receptor (mGluR3). Acting through this receptor, NAAG reduces cyclic AMP levels, decreases voltage-dependent calcium conductance, suppresses excitotoxicity, influences long-term potentiation and depression, regulates GABA(A) receptor subunit expression, and inhibits synaptic release of GABA from cortical neurons. Cloning of peptidase activities against NAAG provides opportunities to study the cellular and molecular mechanisms by which synaptic NAAG peptidase activity is controlled. Given the codistribution of this peptide with a spectrum of traditional transmitters and its ability to activate mGluR3, we speculate that one role for NAAG following synaptic release is the activation of metabotropic autoreceptors that inhibit subsequent transmitter release. A second role is the production of extracellular glutamate following NAAG hydrolysis.

Pseudomonas syringae phytotoxins: mode of action, regulation, and biosynthesis by peptide and polyketide synthetases

Coronatine, syringomycin, syringopeptin, tabtoxin, and phaseolotoxin are the most intensively studied phytotoxins of Pseudomonas syringae, and each contributes significantly to bacterial virulence in plants. Coronatine functions partly as a mimic of methyl jasmonate, a hormone synthesized by plants undergoing biological stress. Syringomycin and syringopeptin form pores in plasma membranes, a process that leads to electrolyte leakage. Tabtoxin and phaseolotoxin are strongly antimicrobial and function by inhibiting glutamine synthetase and ornithine carbamoyltransferase, respectively. Genetic analysis has revealed the mechanisms responsible for toxin biosynthesis. Coronatine biosynthesis requires the cooperation of polyketide and peptide synthetases for the assembly of the coronafacic and coronamic acid moieties, respectively. Tabtoxin is derived from the lysine biosynthetic pathway, whereas syringomycin, syringopeptin, and phaseolotoxin biosynthesis requires peptide synthetases. Activation of phytotoxin synthesis is controlled by diverse environmental factors including plant signal molecules and temperature. Genes involved in the regulation of phytotoxin synthesis have been located within the coronatine and syringomycin gene clusters; however, additional regulatory genes are required for the synthesis of these and other phytotoxins. Global regulatory genes such as gacS modulate phytotoxin production in certain pathovars, indicating the complexity of the regulatory circuits controlling phytotoxin synthesis. The coronatine and syringomycin gene clusters have been intensively characterized and show potential for constructing modified polyketides and peptides. Genetic reprogramming of peptide and polyketide synthetases has been successful, and portions of the coronatine and syringomycin gene clusters could be valuable resources in developing new antimicrobial agents.

Nef-induced CD4 degradation: a diacidic-based motif in Nef functions as a lysosomal targeting signal through the binding of beta-COP in endosomes

The Nef protein of primate lentiviruses downregulates the cell surface expression of CD4 through a two-step process. First, Nef connects the cytoplasmic tail of CD4 with adaptor protein complexes (AP), thereby inducing the formation of CD4-specific clathrin-coated pits that rapidly endocytose the viral receptor. Second, Nef targets internalized CD4 molecules for degradation. Here we show that Nef accomplishes this second task by acting as a connector between CD4 and the beta subunit of COPI coatomers in endosomes. A sequence encompassing a critical acidic dipeptide, located nearby but distinct from the AP-binding determinant of HIV-1 Nef, is responsible for beta-COP recruitment and for routing to lysosomes. A novel class of endosomal sorting motif, based on acidic residues, is thus revealed, and beta-COP is identified as its downstream partner.

Mechanism of dipeptide stimulation of its own transport in a human intestinal cell line

The initial objective of this study was to investigate whether the presence of dipeptide in the culture medium stimulates the uptake of dipeptide by a human intestinal cell line that expresses the oligopeptide transporter (Pept-1). The results showed that addition of glycylsarcosine (Gly-Sar) for 24 hr to the culture medium significantly increased the rate of glycylglutamine (Gly-Gln) uptake by Caco-2 cells. Furthermore, this stimulation in transport was also observed when Cefadroxil (beta-lactam antibiotic) instead of Gly-Gln was used as a probe but did not occur when Gly-Sar was added to the culture medium for only 2 hr or when Gly-Sar was substituted by a corresponding mixture of glycine plus sarcosine. The subsequent objective of the study was to investigate the mechanism of stimulation in transport described earlier. The results showed that the addition of Gly-Sar for 24 hr to the culture medium: (1) increased the Vmax of Gly-Gln transport by two-fold without affecting its Km, (2) increased the protein mass of Pept-1 by more than two-fold, (3) increased the abundance of Pept-1 mRNA by three-fold, and (4) had no effect on Gly-Gln transport when an inhibitor of trans-Golgi network (brefeldin) was added to the culture medium, but still increased the abundance of Pept-1 mRNA. In conclusion, the results show that dipeptides stimulate their own transport by increasing the membrane population of Pept-1. The molecular mechanism appears to be an increase in expression of the gene encoding Pept-1. A therapeutic application of the present results is that if bioavailability of orally administered peptidomimetic drugs is limited, patients may be tried on a high-protein diet to enhance their absorption.

Increased glutamatergic neurotransmission and oxidative stress after alcohol withdrawal

OBJECTIVE

Neurophysiological and pathological effects of ethanol may be mediated, to an important extent, via the glutamatergic system. Animal studies indicate the acute effects of ethanol disrupt glutamatergic neurotransmission by inhibiting the response of the N-methyl-D-aspartate (NMDA) receptor. Persistent attenuation of glutamatergic neurotransmission by chronic ethanol exposure results in the compensatory up-regulation of NMDA receptors. Whether glutamatergic neurotransmission and oxidative stress are enhanced during ethanol withdrawal in humans is unknown.

METHOD

CSF was obtained from 18 matched comparison subjects and from 18 patients with alcohol dependence 1 week and 1 month after cessation of ethanol ingestion. CSF samples were analyzed for excitatory neurotransmitters, gamma-aminobutyric acid (GABA), and markers for oxidative stress.

RESULTS

The alcohol-dependent patients' CSF levels of aspartate, glycine, and N-acetylaspartylglutamate were all higher than those of the comparison subjects, and their concentration of GABA was lower. In addition, there were significant correlations between excitatory neurotransmitters and oxidative stress markers, which suggest that the two mechanisms may play an interactive role in neurotoxicity mediated by ethanol withdrawal.

CONCLUSIONS

The data suggest that augmentation of excitatory neurotransmission may lead to enhanced oxidative stress, which, in concert with reduced inhibitory neurotransmission, may contribute to the symptoms of ethanol withdrawal and associated neurotoxicity in humans. Whether these abnormalities represent a trait- or state-dependent marker of ethanol dependence remains to be resolved.

Effects of gamma-glutamylcysteine ethyl ester on heart mitochondrial creatine kinase activity: involvement of sulfhydryl groups

To study the mechanism of the protective effect of gamma-glutamylcysteine ethyl ester, mitochondrial creatine kinase activity of rat heart was measured. Gamma-glutamylcysteine ethyl ester had a protective effect against the depression of creatine kinase activity induced by xanthine + xanthine oxidase or hydrogen peroxide. Gamma-glutamylcysteine ethyl ester also prevented the depression of creatine kinase activity induced by N-ethylmaleimide. It is suggested that the protective effect of gamma-glutamylcysteine ethyl ester is related to oxygen free radicals or to reduction of the sulfhydryl groups of the enzyme which were previously oxidized by oxygen free radicals.

The simplest proline-containing peptides PG, GP, PGP, and GPGG: regulatory activity and possible sources of biosynthesis

Our own data and data from the literature on the regulatory role of the simplest proline-containing peptides GP, PG, PGP, GPGG, and cyclic-PG are summarized. These peptides are involved in homeostasis of gastric mucosa and the anticoagulant and fibrinolytic potential of blood plasma. They also potentiate memory consolidation processes in the central nervous system. The most probable sources of these peptides are polypeptide precursors of collagen, elastin, and enterostatin.

The nagging question of the function of N-acetylaspartylglutamate

N-Acetylaspartylglutamate (NAAG) is a neuropeptide found in millimolar concentrations in brain that is localized to subpopulations of glutamatergic, cholinergic, GABAergic, and noradrenergic neuronal systems. NAAG is released upon depolarization by a Ca(2+)-dependent process and is an agonist at mGluR3 receptors and an antagonist at NMDA receptors. NAAG is catabolized to N-acetylaspartate and glutamate primarily by glutamate carboxypeptidase II, which is expressed on the extracellular surface of astrocytes. The levels of NAAG and the activity of carboxypeptidase II are altered in a regionally specific fashion in several neuropsychiatric disorders.

Stoichiometry and pH dependence of the rabbit proton-dependent oligopeptide transporter PepT1

1. The intestinal H(+)-coupled peptide transporter PepT1, displays a broad substrate specificity and accepts most charged and neutral di- and tripeptides. To study the proton-to-peptide stoichiometry and the dependence of the kinetic parameters on extracellular pH (pHo), rabbit PepT1 was expressed in Xenopus laevis oocytes and used for uptake studies of radiolabelled neutral and charged dipeptides, voltage-clamp analysis and intracellular pH measurements. 2. PepT1 did not display the substrate-gated anion conductances that have been found to be characteristic of members of the Na(+)- and H(+)-coupled high-affinity glutamate transporter family. In conjunction with previous data on the ion dependence of PepT1, it can therefore be concluded that peptide-evoked charge fluxes of PepT1 are entirely due to H+ movement. 3. Neutral, acidic and basic dipeptides induced intracellular acidification. The rate of acidification, the initial rates of the uptake of radiolabelled peptides and the associated charge fluxes gave proton-substrate coupling ratios of 1:1, 2:1 and 1:1 for neutral, acidic and basic dipeptides, respectively. 4. Maximal transport of the neutral and charged dipeptides Gly-Leu, Gly-Glu, Gly-Lys and Ala-Lys occurred at pHo 5.5, 5.2, 6.2 and 5.8, respectively. The Imax values were relatively pHo independent but the apparent affinity (Km(app) values for these peptides were shown to be highly pHo dependent. 5. Our data show that at physiological pH (pHo 5.5-6.0) PepT1 prefers neutral and acidic peptides. The shift in transport maximum for the acidic peptide Gly-Glu to a lower pH value suggests that acidic dipeptides are transported in the protonated form. The shift in the transport maxima of the basic dipeptides to higher pH values may involve titration of a side-chain on the transporter molecule (e.g. protonation of a histidine group). These considerations have led us to propose a model for coupled transport of neutral, acidic and basic dipeptides.

N-acetylaspartylglutamate acetoxymethyl triester (NAAG.AM) as a tool for loading the neuropeptides NAAG and succinimidyl-NAAG into intact cells: effect on [3H]-dopamine exocytosis

Although N-acetylaspartylglutamate (NAAG) is one of the neuropeptides found in highest concentrations in the mammalian central nervous system, its functional role in neuronal signaling has not been definitively established. In some neuronal populations, NAAG is concentrated in nerve terminals and thus, it may play a role in the cytoplasmic events underlying neurotransmitter exocytosis. In the present study we have validated the use of the synthetic derivative NAAG-acetoxymethyl triester (NAAG.AM) as a tool to increase the intracellular levels of the peptide and assessed the ability of NAAG to regulate [3H]-dopamine ([3H]-DA) secretion in PC12 cells. Enzymatic degradation of NAAG.AM by nonspecific brain esterases resulted in the progressive formation of NAAG and succinimidyl-NAAG (Asu-NAAG). However, only 8% of NAAG.AM was converted to NAAG. Significant amounts of NAAG (1 nmol/mg protein) were demonstrable in cultures of the neuroblastoma cell line N2A following incubation with NAAG.AM for 2 h, with the concentration of (Asu)-NAAG being at least 100-fold higher. The pheochromocytoma cell line PC12 was used to assess the influence of loaded NAAG derivatives on [3H]-DA exocytosis. Incubation with 0.1-1 mM NAAG.AM did not affect the basal efflux or total content of [3H]-DA. However, it induced a dose-dependent decrease of [3H]-DA secretion in response to 56 mM KCl depolarization reaching an inhibition of 49% with 1 mM NAAG.AM. In contrast, NAAG.AM did not affect secretion induced by the calcium ionophore A23187 (100 microM). The present study validates the use of NAAG.AM as a tool to load NAAG derivatives into intact cells and provides preliminary evidence for an intracellular role of the peptide.

Abnormal excitatory neurotransmitter metabolism in schizophrenic brains

BACKGROUND

Schizophrenia has been hypothesized to be caused by a hypofunction of glutamatergic neurons. Findings of reduced concentrations of glutamate in the cerebrospinal fluid of patients with schizophrenia and the ability of glutamate-receptor antagonists to cause psychotic symptoms lend support to this hypothesis. N-acetylaspartylglutamate (NAAG), a neuropeptide that is highly concentrated in glutamatergic neurons, antagonizes the effects of glutamate at N-methyl-D-aspartate receptors. Moreover, NAAG is cleaved to glutamate and N-acetylaspartate by a specific peptidase, N-acetyl-alpha-linked acidic dipeptidase (NAALADase). To test the glutamatergic hypothesis of schizophrenia, we studied the NAAG-related glutamatergic variables in postmortem brains from patients with schizophrenia, neuroleptic-treated controls, and normal individuals, with particular emphasis on the prefrontal cortex and hippocampus.

METHOD

Different regions of frozen brain tissue from three different groups (patients with schizophrenia, neuroleptic-treated controls, and normal controls) were assayed to determine levels of NAAG, N-acetylaspartate, NAALADase, and several amino acids, including aspartate and glutamate.

RESULTS

Our study demonstrates alterations in brain levels of aspartate, glutamate, and NAAG and in NAALADase activity. Levels of NAAG were increased and NAALADase activity and glutamate levels were decreased in the schizophrenic brains. Notably, the changes in NAAG level and NAALADase activity in schizophrenic brains were more selective than those for aspartate and glutamate. In neuroleptic-treated control brains, levels of aspartate, glutamate, and glycine were found to be increased.

CONCLUSIONS

The changes in levels of aspartate, glutamate, NAAG, and NAALADase are prominent in the prefrontal and hippocampal regions, where previous neuropathological studies of schizophrenic brains demonstrate consistent changes. These findings support the hypothesis that schizophrenia results from a hypofunction of certain glutamatergic neuronal systems. They also suggest that the therapeutic efficacy of neuroleptics may be related to increased glutamatergic activity.

Role of the conserved dipeptide Gly75 and Cys76 on HIV-1 Vpr function

Vpr is one of the accessory proteins encoded by the HIV-1 genome. Several interesting features associated with Vpr include incorporation into virus particles, ability to oligomerize, localization in the nucleus, and positive effect on virus production and replication. In order to understand the structure-function relationship of Vpr, we have analyzed the role of the Gly75 and Cys76 (GC) residues which are highly conserved in HIV-1 Vpr and in Vpr and Vpx of HIV-2/SIV. We have generated several substitution mutants involving this dipeptide and have evaluated for expression, stability, nuclear localization, and virion incorporation of Vpr. Our data demonstrate that the GC residues are not essential for virion incorporation and nuclear localization of Vpr. Serine substitution for Cys, however, restricted the localization of Vpr in the cytoplasm without affecting the Gag-directed incorporation of Vpr into virus-like particles. Interestingly, the cysteine-substituted mutants showed altered stability in comparison to the wild type, and substitution mutants for glycine showed minimal effect on stability. These results indicate that the glycine and cysteine do not play a role in nuclear localization or virion incorporation properties of Vpr and further suggest that these two functions of Vpr may not be interdependent.

[The pharmacological activity of carnosine]

The properties of the histidine-containing dipeptide carnosine (beta-alanyl-L-histidine) and its possible biological role are considered. The agent is discussed in terms of its antioxidative and immunomodulating effects on the body. A history of its discovery and investigations of the therapeutical benefits are outlined. The data given indicate that there are great perspectives in expensively using carnosine as a drug.

The immunocytochemical localization of N-acetylaspartyl glutamate, its hydrolysing enzyme NAALADase, and the NMDAR-1 receptor at a vertebrate neuromuscular junction

Although glutamate is thought to be the neurotransmitter at the invertebrate neuromuscular junction, acetylcholine is accepted as the primary neurotransmitter of the vertebrate motoneurons. N-acetylaspartylglutamate, a dipeptide localized in putative glutamatergic neurons in brain, is also found in high concentrations (> mM) in mammalian motoneurons and the ventral roots of spinal cord. N-acetylaspartylglutamate, which is released from neurons by depolarization in a Ca(2+)-dependent fashion, is implicated in glutamatergic transmission in two ways: it is a partial agonist at NMDA receptors, and it is cleaved to yield extracellular glutamate and N-acetylasparate by the specific peptidase N-acetylated alpha-linked acidic dipeptidase. Given the localization of N-acetylaspartylglutamate in motor neuronal perikarya and axons, we wondered whether N-acetylaspartylglutamate or glutamate cleaved from N-acetylaspartylglutamate by N-acetylated alpha-linked acidic dipeptidase may also play a role in neuromuscular transmission. Here we describe the immunocytochemical detection at the rat neuromuscular junction of N-acetylaspartylglutamate in terminals of motoneurons, of N-acetylated alpha-linked acidic dipeptidase in perisynaptic Schwann cells, and of the NMDAR-1 glutamate receptor subunit on postsynaptic muscle membranes. These results point to a potential role for N-acetylaspartylglutamate at the rat neuromuscular junction. Further, this is the first demonstration of a glutamate receptor protein at vertebrate neuromuscular synapses. Together with other recent findings, our results suggest that glutamate-like molecules are involved in neuromuscular transmission not only in invertebrates but also in veretebrates where they may modulate signaling by acetylcholine.

Bioactive cyclic dipeptides

Cyclic dipeptides are among the simplest peptide derivatives commonly found in nature. Most cyclic dipeptides found to date appear to have emerged as by-products of fermentation and food processing. However, many are endogenous to members of animal and plant kingdoms; these include cyclo(Pro-Leu), cyclo(Pro-Val), cyclo(Pro-Phe), cyclo(Ala-Leu), cyclo(Pro-Tyr), cyclo(Pro-Trp), and cyclo(His-Pro). Although the five cyclic dipeptides--cyclo(His-Pro), cyclo(Leu-Gly), cyclo(Tyr-Arg), cyclo(Asp-Pro), and cyclo(Pro-Phe)--exhibit interesting physiological and/or pharmacological activities in mammals, only one of these, cyclo(His-Pro), has been conclusively shown to be endogenous to mammals. On the other hand, cyclo(Leu-Gly), cyclo(Tyr-Arg), and cyclo(Asp-Pro) are structurally related to endogenous peptides Pro-Leu-Gly-NH2 (melanocyte-stimulating hormone release inhibiting factor), Tyr-Arg (kyotorphin), and Val-Pro-Asp-Pro-Arg (enterostatin), respectively, which may serve as precursor peptides. It needs to be determined, however, whether these peptides can indeed result from the processing of their respective precursors. In conclusion, it appears that cyclic dipeptides are a relatively unexplored class of bioactive peptides that may hold great promise for the future.

Gamma-L-glutamyl-L-glutamate is an endogenous dipeptide in the rat olfactory bulb which activates N-methyl-D-aspartate receptors

The concentration of gamma-L-glutamyl-L-glutamate (gamma-glu-glu), a potent displacer of excitatory amino acid receptor binding, and other structurally related dipeptides were determined in extracts of the rat olfactory bulb by a novel liquid chromatographic method. Whole-cell patch clamp recordings of currents from freshly isolated neurons showed that gamma-glu-glu produced inward currents at negative holding potentials, provided microM concentrations of glycine were added and no Mg(2+)-ions were present, indicating activation of N-methyl-D-aspartate receptors. Consistently, geometry optimization of gamma-glu-glu using molecular mechanics calculations, suggested a bent conformer with structural features supporting this view.

Actions of APGW-amide and GW-amide on identified central neurons of the snail, Helix aspersa

1. Actions of APGWamide and GWamide have been examined on identified central neurons of the snail, Helix aspersa. 2. In F1 neurons, both APGWamide and GWamide, 0.5-5 microM, reversibly inhibited the amplitude of evoked-IPSPs which were dopaminergic, but had no direct effect on membrane potential, cell firing rate, or dopamine-induced responses. These results indicate that the actions of APGWamide and GWamide in F1 neurons are at presynaptic sites. 3. At concentrations between 0.5 and 10 microM, APGWamide and GWamide had direct postsynaptic effects on F2 neurons. They inhibited the spike activity and hyperpolarized the membrane potential of F2 neurons in a dose-dependent manner with a reversal potential around -85 mV which is close to Ek. 4. In K+ free solution, the inhibitory effects of APGWamide and GWamide were potentiated, while they were reduced by increasing external K+ concentration. Either tetraethylammonium (10 mM) or 4-aminopyridine (500 microM) only partially prevented the inhibition induced by APGWamide and GWamide on F2 neurons. Combination of TEA (5 mM) and 4-AP (250 microM) could abolish this inhibition. However, neither 1 mM La2+ nor 10 mM Co2+ could prevent the inhibitory action of APGWamide and GWamide. This evidence indicates that the postsynaptic inhibition of APGWamide and GWamide on F2 neurons is due to an increase in K+ conductance and that both transient K channel (IA) and delay K+ channel (IK) were affected by these peptides. 4. APGWamide and GWamide exert both presynaptic and postsynaptic effects of Helix neurons, depending on the neuron under study. They are qualitatively and quantitatively similar in their presynaptic or postsynaptic actions.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific role of N-acetyl-aspartyl-glutamate in the in vivo regulation of dopamine release from dendrites and nerve terminals of nigrostriatal dopaminergic neurons in the cat

Levels of N-acetyl-aspartyl-glutamate measured by high-pressure liquid chromatography were found to be very high in the cat substantia nigra, particularly in the pars compacta, while those in the caudate nucleus were much lower. In halothane-anaesthetized cats implanted with push-pull cannulae, N-acetyl-aspartyl-glutamate (10(-8) M) induced a marked and prolonged release of newly synthesized [3H]dopamine, when infused into the posterior but not into the anterior part of the caudate nucleus. In contrast, in the presence of tetrodotoxin (10(-6) M), N-acetyl-aspartyl-glutamate (10(-8) M) reduced the residual release of [3H]dopamine; this effect was also more pronounced in the posterior than in the anterior part. In the conditions used, as indicated by experiments with [3H]N-acetyl-aspartyl-glutamate no glutamate was formed from the infused N-acetyl-aspartyl-glutamate. Ibotenate (10(-5) M) induced changes in [3H]dopamine release in both the absence and presence of tetrodotoxin, which were closely similar to those observed with N-acetyl-aspartyl-glutamate. Responses induced by either N-acetyl-aspartyl-glutamate or ibotenate were not mediated by N-methyl-D-aspartate receptors since N-methyl-D-aspartate stimulated the release of [3H]dopamine only when used in a high concentration (10(-4) M) and applied in a magnesium-free superfusion medium in both the presence of glycine (10(-6) M) and strychnine (10(-6) M). In addition, the stimulatory effect of N-methyl-D-aspartate persisted in the presence of tetrodotoxin; it was of similar amplitude in both parts of the caudate nucleus and of shorter duration than that evoked by either N-acetyl-aspartyl-glutamate or ibotenate alone. N-Acetyl-aspartyl-glutamate interacted with dopaminergic neurons not only presynaptically in the caudate nucleus but also in the substantia nigra since a marked increase in [3H]dopamine release was observed both from local dendrites and from nerve terminals in the ipsilateral caudate nucleus when N-acetyl-aspartyl-glutamate (10(-7) M) was infused locally into the substantia nigra pars compacta. No effect could be seen in contralateral structures. The isomer of natural N-acetyl-aspartyl-glutamate, beta-N-acetyl-aspartyl-glutamate (10(-7) M), had no effect on [3H]dopamine release when applied similarly in the substantia nigra, thus confirming the specificity of the action of N-acetyl-aspartyl-glutamate.

Production and characterization of monoclonal antibodies to N-acetyl-aspartyl-glutamate

N-acetyl-aspartyl-glutamate (NAAG) is a putative neuromodulator/neurotransmitter in the mammalian nervous system. Immunohistochemical studies with polyclonal NAAG antisera have revealed immunoreactive neurons and processes in several brain regions. However, these antisera crossreact to some degree with N-acetyl-aspartate (NAA), which is present in mM concentrations in brain, prompting the development of monoclonal antibodies (MAb) more specific for NAAG. By fusing spleen lymphocytes obtained from BALB/c mice pre-immunized with NAAG covalently linked to bovine serum albumin by carbodiimide with SP2/0-Ag 14 mouse myeloma cells, we produced three IgG2a (kappa) MAb which specifically reacted with NAAG. These MAb exhibited negligible crossreactivity with NAA or with structurally similar peptides, as shown by solid-phase radioimmunoassay. Antibody activity was absorbed out selectively by both NAAG-thyroglobulin conjugate and free NAAG. These MAb stained many nuclei of the medulla-pons and midbrain, mitral cells in the olfactory bulb, pyramidal neurons in sensorimotor cortex, locus ceruleus, and several cholinergic cranial nuclei. The staining pattern strongly correlated with NAAG levels determined by HPLC. Monoclonal antibodies significantly enhanced sensitivity of staining, allowing visualization of dorsal horn neurons in spinal cord, which were not readily detectable with polyclonal antiserum. Availability of these MAb now facilitates further clarification of the role of NAAG in the brain.

The antioxidative properties of carnosine, a natural histidine containing dipeptide

The experimental results suggest that the antioxidative function of carnosine is one of the most important manifestations of its biological role. The ability of carnosine to interact directly with lipid peroxidation products was demonstrated. The effects of carnosine on partial restoration of lens transparency in dog eyes with senile cataract which is known to be caused by lipid peroxidation were demonstrated "in vitro" and "in vivo".

[Biological role of histidine-containing dipeptides]

The biological role of histidine-containing dipeptides is reviewed. The role of carnosine and anserine in muscle function is discussed from the evolutionary viewpoint. Evidence on the antioxidative effect of carnosine and its protection of biological membranes against lipid peroxidation-induced damages is presented. The effects of presently known natural antioxidative agents and carnosine on lipid peroxidation are compared. Carnosine has been shown to be a more universal protector of membranes as compared to free radical scavengers.

Stimulation-produced spinal inhibition from the midbrain in the rat is mediated by an excitatory amino acid neurotransmitter in the medial medulla

It has been previously established that a bulbar relay plays an important role in descending inhibition of spinal dorsal horn nociceptive neurons and nociceptive reflexes produced by stimulation in the midbrain periaqueductal gray (PAG). In the present study, selected receptor antagonists were microinjected into the medial medullary nucleus raphe magnus (NRM) to determine whether descending inhibition of the tail flick (TF) reflex in the rat produced by focal electrical stimulation in the midbrain PAG was mediated by serotonin, opioid, or glutamate receptors on bulbospinal neurons in the NRM. It was determined in initial experiments that the serotonin receptor antagonist methysergide, the opioid receptor antagonist naloxone, the local anesthetic lidocaine, and the glutamate receptor antagonists gamma-D-glutamylglycine (DGG) and DL-2-amino-5-phosphonovalerate (APV) microinjected into the medulla all significantly increased the threshold of focal electrical stimulation in the medulla required to inhibit the TF reflex. The antinociceptive efficacy of agonists at opioid, serotonin, and glutamate receptors was also tested in other experiments. The microinjection of morphine (2.5-10 micrograms) into the NRM increased significantly TF latencies in a dose-dependent manner in rats in the awake or lightly anesthetized state; morphine was more potent in awake rats. Inhibition of the TF reflex produced by the microinjection of morphine was reversed by a subsequent microinjection of naloxone into the same site in the medulla. The microinjection of serotonin (5 and 10 micrograms), however, did not affect the latency of the TF reflex in either awake or lightly anesthetized rats. Glutamate (100 microM, 0.5 microliter) microinjected into the rostral ventral medulla produced an inhibition of the TF reflex of short duration that could be blocked or attenuated significantly by the glutamate receptor antagonists DGG or APV microinjected into the same site. In subsequent experiments, a nonspecific functional block was introduced adjacent to the NRM bilaterally in the medullary reticular formations (MRFs) by the microinjection of the local anesthetic lidocaine; receptor antagonists were then microinjected into the NRM and their effect on the threshold of focal electrical stimulation in the PAG to inhibit the TF reflex determined. No increase was seen in stimulation thresholds in the PAG following the microinjection of either methysergide or naloxone into the NRM. Following the microinjection of lidocaine, DGG or APV into the NRM, the stimulation threshold in the PAG for inhibition of the TF reflex was increased significantly.(ABSTRACT TRUNCATED AT 400 WORDS)

Glycyl-L-glutamine, a precursor, and glycyl-L-glutamic acid, a neurotrophic factor for maintenance of acetylcholinesterase and butyrylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat in vivo

L. W. Haynes and M. E. Smith have reported [(1985) Biochem. Soc. Trans. 13, 174-175] that glycyl-L-glutamine (Gly-Gln) increases the A12 and G4 forms of acetylcholinesterase (AcChoEase) in cultured embryonic rat skeletal muscle. Since Gly-Gln meets the criteria established for the neurotrophic factor (NF) in extracts of central nervous system/sciatic nerves that maintains AcChoEase and butyrylcholinesterase (BtChoEase) in the denervated cat superior cervical ganglion (SCG) in vivo, it was tested by the latter procedure. Solutions of Gly-Gln (10(-7)-10(-3) M) in 0.9% NaCl solution were infused for 24 hr via the right common carotid artery of cats with preganglionically denervated SCG, following ligation of the external carotid and lingual arteries. At 48 hr postdenervation, the AcChoEase and BtChoEase contents of the right SCG were within the range of similarly treated controls infused with 0.9% NaCl solution; the AcChoEase and BtChoEase contents of the left SCG, where the infused solutions arrived by way of a much more circuitous route, were significantly elevated at concentrations of Gly-Gln of 10(-5) M and higher. This suggested that the neurotrophic effect on the left SCG was produced by a metabolite of Gly-Gln. Accordingly, glycine, L-glutamine, and glycyl-L-glutamic acid (Gly-Glu) were then tested. Glycine and L-glutamine were inactive; Gly-Glu, 10(-6)-10(-5) M, exerted a significantly positive neurotrophic effect at both the right and left SCG; at 10(-4) M, the effect was absent. The method employed currently for preparation of extracts of SCG for assay of AcChoEase, BtChoEase, and protein contents (homogenization of scissor-minced ganglia in water) was compared with homogenization in molar NaCl/1% Triton X-100. Values obtained by the former procedure, in comparison with the latter, were 91% +/- 7% for AcChoEase and 83% +/- 7% for BtChoEase, expressed as substrate hydrolyzed per mg of protein per min.