Anxiogenic activity of isatin, a putative biological factor, in rodents

Metabolite interactions between host and microbiota during health and disease: Which feeds the other?

Metabolites produced by the host and microbiota play a crucial role in how human bodies develop and remain healthy. Most of these metabolites are produced by microbiota and hosts in the digestive tract. Metabolites in the gut have important roles in energy metabolism, cellular communication, and host immunity, among other physiological activities. Although numerous host metabolites, such as free fatty acids, amino acids, and vitamins, are found in the intestine, metabolites generated by gut microbiota are equally vital for intestinal homeostasis. Furthermore, microbiota in the gut is the sole source of some metabolites, including short-chain fatty acids (SCFAs). Metabolites produced by microbiota, such as neurotransmitters and hormones, may modulate and significantly affect host metabolism. The gut microbiota is becoming recognized as a second endocrine system. A variety of chronic inflammatory disorders have been linked to aberrant host-microbiota interplays, but the precise mechanisms underpinning these disturbances and how they might lead to diseases remain to be fully elucidated. Microbiome-modulated metabolites are promising targets for new drug discovery due to their endocrine function in various complex disorders. In humans, metabolotherapy for the prevention or treatment of various disorders will be possible if we better understand the metabolic preferences of bacteria and the host in specific tissues and organs. Better disease treatments may be possible with the help of novel complementary therapies that target host or bacterial metabolism. The metabolites, their physiological consequences, and functional mechanisms of the host-microbiota interplays will be highlighted, summarized, and discussed in this overview.

Tryptophan metabolites in depression: Modulation by gut microbiota

Clinical depression is a multifactorial disorder and one of the leading causes of disability worldwide. The alterations in tryptophan metabolism such as changes in the levels of serotonin, kynurenine, and kynurenine acid have been implicated in the etiology of depression for more than 50 years. In recent years, accumulated evidence has revealed that gut microbial communities, besides being essential players in various aspects of host physiology and brain functioning are also implicated in the etiology of depression, particularly through modulation of tryptophan metabolism. Therefore, the aim of this review is to summarize the evidence of the role of gut bacteria in disturbed tryptophan metabolism in depression. We summed up the effects of microbiota on serotonin, kynurenine, and indole pathway of tryptophan conversion relevant for understanding the pathogenesis of depressive behavior. Moreover, we reviewed data regarding the therapeutic effects of probiotics, particularly through the regulation of tryptophan metabolites. Taken together, these findings can open new possibilities for further improvement of treatments for depression based on the microbiota-mediated modulation of the tryptophan pathway.

Tryptophan Metabolites as Mediators of Microbiota-Gut-Brain Communication: Focus on Isatin

Isatin (indole-2,3-dione) is an endogenous regulator, exhibiting various behavioral, biological, and pharmacological activities. Synthesis of isatin includes several crucial stages: cleavage of the tryptophan side chain and subsequent oxidation of the indole nucleus. Although these stages require concerted action of bacterial and host enzymes, there are two pathways of isatin formation: the host and bacterial pathways. Isatin acts as a neuroprotector in different experimental models of neurodegeneration. Its effects are realized via up- and downregulation of isatin-responsive genes and via interaction with numerous isatin-binding proteins identified in the brain. The effect of isatin on protein-protein interactions in the brain may be important for realization of weak inhibition of multiple receptor targets.

Relation between Mood and the Host-Microbiome Co-Metabolite 3-Indoxylsulfate: Results from the Observational Prospective NutriNet-Santé Study

Gut microbiota metabolizes tryptophan into indole, which can influence brain and behavior. Indeed, some oxidized derivatives of indole, formed in the liver, have neuroactive properties, and indole overproduction by the gut microbiota induces an anxio-depressive phenotype in rodents. The aim of this study was to investigate in humans whether there was a relationship between recurrent depressive symptoms and indole production by the gut microbiota. A case-control study was conducted in 45–65-year-old women, who were participants in the observational prospective NutriNet-Santé Study. Cases were defined as having two Center for Epidemiological Studies-Depression Scales (CES-D) scores ≥ 23 at a two-year interval (recurrent depressive symptoms, n = 87). Each case was matched with two controls (two CES-D <23; n = 174). Urinary excretion of 3-indoxylsulfate, the major final metabolite of indole, was used as a biomarker of indole production by the gut microbiota. Conditional logistic regression models for paired data showed a positive association between urinary 3-indoxylsulfate concentrations, grouped in tertiles, and recurrent depressive symptoms (odds ratio = 2.46, p for trend = 0.0264 in the final model adjusted for confounding factors). This association suggested that indole production by the gut microbiota may play a role in the onset of mood disorders in humans.

An enriched biosignature of gut microbiota-dependent metabolites characterizes maternal plasma in a mouse model of fetal alcohol spectrum disorder

Prenatal alcohol exposure (PAE) causes permanent cognitive disability. The enteric microbiome generates microbial-dependent products (MDPs) that may contribute to disorders including autism, depression, and anxiety; it is unknown whether similar alterations occur in PAE. Using a mouse PAE model, we performed untargeted metabolome analyses upon the maternal–fetal dyad at gestational day 17.5. Hierarchical clustering by principal component analysis and Pearson’s correlation of maternal plasma (813 metabolites) both identified MDPs as significant predictors for PAE. The majority were phenolic acids enriched in PAE. Correlational network analyses revealed that alcohol altered plasma MDP-metabolite relationships, and alcohol-exposed maternal plasma was characterized by a subnetwork dominated by phenolic acids. Twenty-nine MDPs were detected in fetal liver and sixteen in fetal brain, where their impact is unknown. Several of these, including 4-ethylphenylsulfate, oxindole, indolepropionate, p-cresol sulfate, catechol sulfate, and salicylate, are implicated in other neurological disorders. We conclude that MDPs constitute a characteristic biosignature that distinguishes PAE. These MDPs are abundant in human plasma, where they influence physiology and disease. Their altered abundance here may reflect alcohol’s known effects on microbiota composition and gut permeability. We propose that the maternal microbiome and its MDPs are a previously unrecognized influence upon the pathologies that typify PAE.

A Neuroprotective Dose of Isatin Causes Multilevel Changes Involving the Brain Proteome: Prospects for Further Research

Isatin (indole-2,3-dione) is an endogenous regulator, exhibiting a wide range of biological and pharmacological activities. At doses of 100 mg/kg and above, isatin is neuroprotective in different experimental models of neurodegeneration. Good evidence exists that its effects are realized via interaction with numerous isatin-binding proteins identified in the brain and peripheral tissues studied. In this study, we investigated the effect of a single dose administration of isatin to mice (100 mg/kg, 24 h) on differentially expressed proteins and a profile of the isatin-binding proteins in brain hemispheres. Isatin administration to mice caused downregulation of 31 proteins. However, these changes cannot be attributed to altered expression of corresponding genes. Although at this time point isatin influenced the expression of more than 850 genes in brain hemispheres (including 433 upregulated and 418 downregulated genes), none of them could account for the changes in the differentially expressed proteins. Comparative proteomic analysis of brain isatin-binding proteins of control and isatin-treated mice revealed representative groups of proteins sensitive to isatin administration. Control-specific proteins (n = 55) represent specific targets that interact directly with isatin. Appearance of brain isatin-binding proteins specific to isatin-treated mice (n = 94) may be attributed to the formation of new clusters of protein–protein interactions and/or novel binding sites induced by a high concentration of this regulator (ligand-induced binding sites). Thus, isatin administration produces multiple effects in the brain, which include changes in gene expression and also profiles of isatin-binding proteins and their interactomes. Further studies are needed for deeper insight into the mechanisms of the multilevel changes in the brain proteome induced by isatin. In the context of the neuroprotective action, these changes may be aimed at interruption of pathological links that begin to form after initiation of pathological processes.

Synthesis, characterization, and antimicrobial activity of some new N-aryl-N'-(2-oxoindolin-3-ylidene)-benzohydrazonamides

A green approach was developed for synthesizing a series of (isatin-3-ylidene)-hydrazonamides 3a-j from the reaction between isatin, (isatin-3-ylidene)malononitrile, or 2-cyano-2-(2-isatin-3-ylidene)acetate and benzohydrazonamide in ethyl acetate solutions at ambient temperature. The structures of the new compounds were confirmed on the basis of spectral data. In this eco-friendly medium, a variety of (isatin-3-ylidene)hydrazonamides were obtained free of catalyst in good to excellent yields. All the synthesized products were evaluated for their antimicrobial activity. Among the compounds tested, 3b and 3d exhibited good antibacterial activity against Staphylococcus aureus, whereas others responded moderately with reference to the standard drug ciprofloxacin.

Gut microbial metabolites in depression: understanding the biochemical mechanisms

Gastrointestinal and central function are intrinsically connected by the gut microbiota, an ecosystem that has co-evolved with the host to expand its biotransformational capabilities and interact with host physiological processes by means of its metabolic products. Abnormalities in this microbiota-gut-brain axis have emerged as a key component in the pathophysiology of depression, leading to more research attempting to understand the neuroactive potential of the products of gut microbial metabolism. This review explores the potential for the gut microbiota to contribute to depression and focuses on the role that microbially-derived molecules – neurotransmitters, short-chain fatty acids, indoles, bile acids, choline metabolites, lactate and vitamins – play in the context of emotional behavior. The future of gut-brain axis research lies is moving away from association, towards the mechanisms underlying the relationship between the gut bacteria and depressive behavior. We propose that direct and indirect mechanisms exist through which gut microbial metabolites affect depressive behavior: these include (i) direct stimulation of central receptors, (ii) peripheral stimulation of neural, endocrine, and immune mediators, and (iii) epigenetic regulation of histone acetylation and DNA methylation. Elucidating these mechanisms is essential to expand our understanding of the etiology of depression, and to develop new strategies to harness the beneficial psychotropic effects of these molecules. Overall, the review highlights the potential for dietary interventions to represent such novel therapeutic strategies for major depressive disorder.

Indole, a Signaling Molecule Produced by the Gut Microbiota, Negatively Impacts Emotional Behaviors in Rats

Gut microbiota produces a wide and diverse array of metabolites that are an integral part of the host metabolome. The emergence of the gut microbiome-brain axis concept has prompted investigations on the role of gut microbiota dysbioses in the pathophysiology of brain diseases. Specifically, the search for microbe-related metabolomic signatures in human patients and animal models of psychiatric disorders has pointed out the importance of the microbial metabolism of aromatic amino acids. Here, we investigated the effect of indole on brain and behavior in rats. Indole is produced by gut microbiota from tryptophan, through the tryptophanase enzyme encoded by the tnaA gene. First, we mimicked an acute and high overproduction of indole by injecting this compound in the cecum of conventional rats. This treatment led to a dramatic decrease of motor activity. The neurodepressant oxidized derivatives of indole, oxindole and isatin, accumulated in the brain. In addition, increase in eye blinking frequency and in c-Fos protein expression in the dorsal vagal complex denoted a vagus nerve activation. Second, we mimicked a chronic and moderate overproduction of indole by colonizing germ-free rats with the indole-producing bacterial species Escherichia coli. We compared emotional behaviors of these rats with those of germ-free rats colonized with a genetically-engineered counterpart strain unable to produce indole. Rats overproducing indole displayed higher helplessness in the tail suspension test, and enhanced anxiety-like behavior in the novelty, elevated plus maze and open-field tests. Vagus nerve activation was suggested by an increase in eye blinking frequency. However, unlike the conventional rats dosed with a high amount of indole, the motor activity was not altered and neither oxindole nor isatin could be detected in the brain. Further studies are required for a comprehensive understanding of the mechanisms supporting indole effects on emotional behaviors. As our findings suggest that people whose gut microbiota is highly prone to produce indole could be more likely to develop anxiety and mood disorders, we addressed the issue of the inter-individual variability of indole producing potential in humans. An in silico investigation of metagenomic data focused on the tnaA gene products definitively proved this inter-individual variability.

Isatin, an endogenous nonpeptide biofactor: A review of its molecular targets, mechanisms of actions, and their biomedical implications

Isatin (indole-2,3-dione) is an oxidized indole. It is widely distributed in mammalian tissues and body fluids, where isatin concentrations vary significantly from <0.1 to > 10 µM. Isatin output is increased under conditions of stress. Exogenously administered isatin is characterized by low toxicity, mutagenicity, and genotoxicity in vivo. Cytotoxic effects of isatin on various cell cultures are usually observed at concentrations exceeding 100 µM. Binding of [³ H]isatin to rat brain sections is consistent with its physiological concentrations. Proteomic analysis of mouse and rat brain isatin-binding proteins revealed about 90 individual proteins, which demonstrated significant interspecies differences (rat versus mouse). Certain evidence exist that redox state(s) and possibly other types of posttranslational modifications regulate affinity of target proteins to isatin. Recent data suggest that interacting with numerous intracellular isatin binding proteins, isatin can act as a regulator of complex protein networks in norm and pathology. Physiological concentrations of isatin in vitro inhibit monoamine oxidase B and natriuretic peptide receptor guanylate cyclase, higher (neuroprotective) concentrations (50-400 μM) cause apoptosis of various (including malignant tumor) cell lines and influence expression of certain apoptosis-related genes. Being administered in vivo, isatin exhibits various behavioral effects; it attenuates manifestations of MPTP-induced parkinsonism and tumor growth in experimental animal models. © 2017 BioFactors, 44(2):95-108, 2018.

Are the Traditional Medical Uses of Muricidae Molluscs Substantiated by Their Pharmacological Properties and Bioactive Compounds?

Marine molluscs from the family Muricidae hold great potential for development as a source of therapeutically useful compounds. Traditionally known for the production of the ancient dye Tyrian purple, these molluscs also form the basis of some rare traditional medicines that have been used for thousands of years. Whilst these traditional and alternative medicines have not been chemically analysed or tested for efficacy in controlled clinical trials, a significant amount of independent research has documented the biological activity of extracts and compounds from these snails. In particular, Muricidae produce a suite of brominated indoles with anti-inflammatory, anti-cancer and steroidogenic activity, as well as choline esters with muscle-relaxing and pain relieving properties. These compounds could explain some of the traditional uses in wound healing, stomach pain and menstrual problems. However, the principle source of bioactive compounds is from the hypobranchial gland, whilst the shell and operculum are the main source used in most traditional remedies. Thus further research is required to understand this discrepancy and to optimise a quality controlled natural medicine from Muricidae.

Synthesis, characterization and antimicrobial activities of mixed ligand transition metal complexes with isatin monohydrazone Schiff base ligands and heterocyclic nitrogen base

Mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with various uninegative tridentate ligands derived from isatin monohydrazone with 2-hydroxynapthaldehyde/substituted salicylaldehyde and heterocyclic nitrogen base 8-hydroxyquinoline have been synthesized and characterized by elemental analysis, conductometric studies, magnetic susceptibility and spectroscopic techniques (IR, UV-VIS, NMR, mass and ESR). On the basis of these characterizations, it was revealed that Schiff base ligands existed as monobasic tridentate ONO bonded to metal ion through oxygen of carbonyl group, azomethine nitrogen and deprotonated hydroxyl oxygen and heterocyclic nitrogen base 8-hydroxyquinoline existed as monobasic bidentate ON bonded through oxygen of hydroxyl group and nitrogen of quinoline ring with octahedral or distorted octahedral geometry around metal ion. All the compounds have been tested in vitro against various pathogenic Gram positive bacteria, Gram negative bacteria and fungi using different concentrations (25, 50, 100, 200 μg/mL) of ligands and their complexes. Comparative study of antimicrobial activity of ligands, and their mixed complexes indicated that complexes exhibit enhanced activity as compared to free ligands and copper(II) Cu(LIV)(Q)⋅H2O complex was found to be most potent antimicrobial agent.

Highly Monodispersed PEG-stabilized Ni Nanoparticles: Proficient Catalyst for the Synthesis of Biologically Important Spiropyrans

A convenient and efficient synthesis of biologically and pharmacologically important spiropyrans from the condensation of malononitrile, 1,3-dicarbonyl compounds and ninhydrin/acenaphthequinone/isatin has been reported using recyclable heterogeneous polyethylene glycol (PEG)-stabilized Ni nanoparticles in ethylene glycol. This new protocol affords products in high yields and less reaction time.

Design, synthesis, computational and biological evaluation of new anxiolytics

New anxiolytics have been discovered by prediction of biological activity with computer programs pass and derek for a heterogeneous set of 5494 highly chemically diverse heterocyclic compounds (thiazoles, pyrazoles, isatins, a-fused imidazoles and others). The majority of tested compounds exhibit the predicted anxiolytic effect. The most potent activity was found in 2-(4-nitrophenyl)-3-(4-phenylpiperazinomethyl)imidazo[1,2-a]pyridine 8, 1-[(4-bromophenyl)-2-oxoethyl]-3-(1,3-dioxolano)-2-indolinone 3, 5-hydroxy-3-methoxycarbonyl-1-phenylpyrazole 5 and 2-(4-fluorophenyl)-3-(4-methylpiperazinomethyl)imidazo[1,2-a]pyridine 7. The application of the computer-assisted approach significantly reduced the number of synthesized and tested compounds and increased the chance of finding new chemical entities (NCEs).

Isatin, an endogenous monoamine oxidase inhibitor, triggers a dose- and time-dependent switch from apoptosis to necrosis in human neuroblastoma cells

Isatin is an endogenous indole that is increased in stress, inhibits monoamine oxidase (MAO) B and improves bradykinesia and striatal dopamine levels in rat models of Parkinson's disease. Consequently, it has been suggested that isatin might be a possible treatment for Parkinson's disease although little is known about its effects on neural cell growth and survival. The aim of this study was to investigate the survival of dopaminergic human neuroblastoma (SH-SY5Y) cells following treatment with increasing concentrations of isatin. SH-SY5Y cells were exposed to isatin for defined time points, after which cell survival was determined by MTT assay. A combination of Annexin V binding and propidium iodide (PI) exclusion was used to distinguish apoptosis from necrosis in flow cytometry experiments and FACS profiles of permeabilised PI-labelled cells were employed for the assessment of cell cycle distribution. Isatin treatment (1-400 microM) for 24h induced a significant dose-dependent increase in MTT metabolism by SH-SY5Y cells in culture, but this was not due to an increase in cell division. At the higher concentrations (200-400 microm) isatin triggered cell death, although MTT metabolism was still increased in the culture, suggesting that surviving cells were hypermetabolic. Following a longer (48 h) exposure, isatin was found to cause cell death in a dose-dependent manner; at lower concentrations (50 microM), the predominant mode of cell death was apoptosis while at the highest concentration (400 microm) increasing numbers of necrotic cells were also evident. Thus, in dopaminergic SH-SY5Y cells isatin induces cell death in dose- and time-dependent manner. This death occurred as a continuum of survival, apoptosis and necrosis. Our results re-emphasise that caution should be exercised when considering high doses of isatin as a putative anti-Parkinson's disease therapeutic.

Effect of acute stress and gender on isatin in rat tissues and serum

Isatin is an endogenous indole present in mammalian tissues and fluids. This study was designed to test the effect of both acute stress (AS) and gender on isatin's levels in rat serum, heart and brain, using a HPLC-UV detection method. Basal brain isatin levels were higher in females than in males. AS resulted in increased isatin levels in male serum, heart and brain, and in female serum and heart, but not in the brain. The percentage increases were greater in males than in females in all three sources. After stress, there were significant correlations between isatin levels in the serum and the heart. However, there were no correlations between brain levels and those in the other sources. These results consolidate previous evidence that isatin levels are altered by stress and suggest that brain isatin is under separate control from that in the periphery.

Anticonvulsant activity of hydrazones, Schiff and Mannich bases of isatin derivatives

In the present study, anticonvulsant activity of hydrazones, Schiff and Mannich bases of isatin were evaluated by maximal electroshock method (MES) and metrazol-induced convulsions (MET) at 30, 100 and 300 mg/kg dose levels. Neurotoxicity of the compounds was also assessed at the same dose levels. Eight compounds of the series exhibited significant anticonvulsant activity at 30 mg/kg dose level. 3-(4-chloro-phenylimino)-5-methyl-1,3-dihydro-indol-2-one (compound 10) was found to be the most potent compound of the series with 87% protection at 100 mg/kg and an ED(50) of 53.61 mg/kg (MET). All the compounds exhibited lesser neurotoxicity compared to phenytoin. All the active compounds showed greater protection than sodium valproate. The essential structural features responsible for interaction with receptor site are established within a suggested pharmacophore.

Effects of isatin on rotational behavior and DA levels in caudate putamen in Parkinsonian rats

Isatin was a potent endogenous monoamine oxidase (MAO) inhibitor that is more active against MAO-B than MAO-A. The acute effects of isatin on apomorphine (APO)-induced rotations were evaluated in Parkinsonian rats induced by 6-hydroxydopamine (6-OHDA) lesion. Furthermore, the effects of isatin on DA release in caudate putamen (CPu) of model and normal rats were monitored using fast cyclic voltammetry (FCV). The contents of monoamine transmitters and their metabolites in CPu of model and normal rats were also analyzed by high performance liquid chromatography with electrochemical detection after administration of isatin. Here we show that isatin (100 mg/kg, i.p.) apparently inhibited APO-induced rotations of Parkinsonian rats to 39.1+/-3.7% of the control (n=12), while it had no apparent effects on electrical stimuli-induced DA release either in normal rats or in model rats. In addition, the content of 5-hydroxytryptamine but not DA was increased in both normal rats and model rats after isatin (100 mg/kg, i.p.) was administered (P<0.01, n=6). The content of 5-hydroxyindole acetic acid was not changed. These results suggest that isatin cannot increase DA levels in rat CPu. Therefore, the effects of isatin on APO-induced rotations of our Parkinsonian rats could not attribute to its inhibition of DA catabolism as a MAO inhibitor.

Is there a future for neuropeptide receptor ligands in the treatment of anxiety disorders?

This review provides an overview of preclinical and clinical evidence of a role for the neuroactive peptides cholecystokinin (CCK), corticotropin-releasing factor (CRF), neuropeptide Y (NPY), tachykinins (i.e., substance P, neurokinin [NK] A and B), and natriuretic peptides in anxiety and/or stress-related disorders. Results obtained with CCK receptor antagonists in animal studies have been highly variable, and clinical trials with several of these compounds in anxiety disorders have been unsuccessful so far. However, future investigations using CCK receptor antagonists with better pharmacokinetic characteristics and animal models other than those validated with the classical anxiolytics benzodiazepines may permit a more precise evaluation of the potential of these compounds as anti-anxiety agents. Results obtained with peptide CRF receptor antagonists in animal models of anxiety convincingly demonstrated that the blockade of central CRF receptors may yield anxiolytic-like activity. However, the discovery of nonpeptide and more lipophilic CRF receptor antagonists is essential for the development of these agents as anxiolytics. Similarly, there is clear preclinical evidence that the central infusion of NPY and NPY fragments selective for the Y1 receptor display anxiolytic-like effects in a variety of tests. However, synthetic nonpeptide NPY receptor agonists are still lacking, thereby hampering the development of NPY anxiolytics. Unlike selective NK1 receptor antagonists, which have variable effects in anxiety models, peripheral administration of selective NK2 receptor antagonists and central infusion of natriuretic peptides produce clear anxiolytic-like activity. Taken as a whole, these findings suggest that compounds targeting specific neuropeptide receptors may become an alternative to benzodiazepines for the treatment of anxiety disorders.

Stress-induced increase in urinary isatin excretion in rats: reversal by both dexamethasone and alpha-methyl-P-tyrosine

The effects of acute food deprivation and acute cold exposure on 24-hr urinary isatin excretion in rats and a mechanism responsible for changes in urinary isatin excretion during stress were investigated. This is the first study to demonstrate by HPLC that urinary isatin excretion is increased by stress. Both types of stress induced a marked increase in urinary isatin excretion during the 24 hr following the initiation of stress. Dexamethasone administration prevented the increase in urinary isatin excretion induced by both of the different types of stress. Furthermore, administration of either the benzodiazepine receptor agonist diazepam or the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine prevented the increase in urinary isatin excretion induced by acute food deprivation, whereas the dopamine-beta-hydroxylase inhibitor diethyldithiocarbamate proved ineffective. These observations suggest that during stress, activated catecholamine-synthesizing cells and corticotropin-releasing factor cells, both of which play central roles in stress responses, may be involved in total isatin production. Isatin may serve as an endogenously generated marker for some types of stress.

Function of endogenous monoamine oxidase inhibitors (tribulin)

Recent research on tribulin [low molecular weight endogenous inhibitory activity of monoamine oxidase (MAO)] has confirmed that its level is increased in both human urine and rat tissues by stress or anxiety, and by anxiogenic drugs. However tribulin is now known to contain several different molecules. The raised inhibitory activity in rat tissues is selective for MAO-A. There is a parallel decrease in MAO-A activity ex vivo, suggesting a possible functional effect. Increase in endogenous MAO I may competitively inhibit the binding of irreversible MAO I drugs, and may also help to mediate some mood altering effects of other drugs, or procedures such as ECT. In human urine both MAO-A I and MAO-B I have been found to be increased in mild stress. Similar findings have been made with human saliva. Selective inhibitors of MAO-A have been identified from human urine, and pig brain, but it is not yet clear to what extent they account for the MAO-A I activity increased in stress. Isatin is an endogenous selective inhibitor of MAO-B (K1 approximately 3 microM). It has a distinct distribution in rat brain, with highest concentration in the hippocampus of 0.1 microgram/g. Its level is increased by pentylene tetrazole, and isatin is itself anxiogenic in rodent models. Its administration also increases monoamine levels in the brain. It is a potent antagonist of the ANP receptor, and it may act to link the control of monoamine function and natriuresis.

Anxiogenic action of caffeine: an experimental study in rats

The anxiogenic action of caffeine (10, 25 and 50 mg/kg, i.p.) was investigated in rats and compared with that of yohimbine (2 mg/kg, i.p.). The experimental methods used were the open-field, elevated plus-maze, social interaction and novelty-suppressed feeding latency tests. Caffeine produced a dose-related profile of behavioural changes, which were qualitatively similar to those induced by yohimbine and which indicate an anxiogenic activity in rodents. Thus, both the drugs reduced ambulation and rears, and increased immobility and defaecation in the open-field test. They decreased the number of entries and time spent on the open arms of the elevated-plus maze, reduced social interaction in paired rats and increased the feeding latency in an unfamiliar environment in 48-h food-deprived rats. Lorazepam, a well known benzodiazepine anxiolytic agent, attenuated the anxiogenic effects of caffeine and yohimbine. Subchronic administration of caffeine (50 mg/kg, i.p.) for 21 days, in different groups of animals, induced a significant degree of tolerance in the elevated plus-maze test, which was statistically significant after 14 and 21 days' treatment. Yohimbine, however, did not induce similar tolerance. When caffeine (50 mg/kg, i.p.) was withdrawn after 21 days' administration, to a separate group of rats, significant withdrawal anxiety was observed 48 h later as noted in the elevated plus-maze test. The investigations support clinical evidence of caffeine-induced anxiety, tolerance to anxiety on continued use, and withdrawal anxiety in chronic caffeine-containing beverage users.

Isatin: a link between natriuretic peptides and monoamines?

Isatin is an endogenous indole with a distinctive distribution in brain and tissues. In the brain, the highest levels have been found in the hippocampus (0.1 microgram/g), and an immunocytochemical stain has shown specific localization within particular cells. In vitro, its most potent known actions are as an inhibitor of monoamine oxidase B (IC50 approximately 3 microM), and of atrial natriuretic peptide (ANP) receptor binding and ANP-induced guanylate cyclase (both with an IC50 approximately 0.4 microM). In vivo, isatin administration (10-200 mg/kg) causes an increase of monoamine neurotransmitter levels in the brain. Isatin is anxiogenic in animal models at doses of 10-20 mg/kg and sedative at higher doses. Its anxiogenic effects are unlikely to be due to inhibition of monoamine oxidase, but may possibly stem from interaction with the ANP system. Isatin may mediate a link between monoamines and the natriuretic peptide system, and its analogues may provide new pharmacological tools.

Anxiogenic activity of centrally administered scorpion (Mesobuthus tamulus) venom in rats

The anxiogenic action of intracerebroventricularly (i.c.v.) administered Mesobuthus tamulus venom (MTV) was investigated in rats. MTV (1, 3 and 5 g/rat, i.c.v.) induced a dose-related anxiogenic response which was qualitatively comparable to that produced by yohimbine (2 mg/kp, i.p.), an established anxiogenic agent. Both MTV and yohimbine reduced exploratory activity and rears, while increasing immobility and defaecation, in the open-field test. Likewise, both the drugs decreased the number of entries and time spent on the open arms of the elevated plus-maze, reduced social interaction and increased feed-latency in a novel environment. Rat brain levels of tribulin, a postulated endocoid indicator of anxiety, assessed in terms of endogenous monoamine oxidase (MAO) A and B inhibitor activity, were increased by both MTV and yohimbine. The results indicate that the venom has significant anxiogenic activity, which is consonant with some of the clinical symptoms seen after scorpion sting.

Rat brain monoamine oxidase A and B inhibitory (tribulin) activity during drug withdrawal anxiety

Morphine (10 mg/kg), ethanol (8% w/v, 2 ml/kg), nicotine (0.1 mg/kg), cannabis extract (200 mg/kg), lorazepam (10 mg/kg) and ondansetron (0.1 mg/kg) were each administered to rats twice daily i.p. for 14 days and the anxiogenic response following their withdrawal was monitored by the elevated plus-maze test 24 h later. Brains were removed and endogenous monoamine oxidase (MAO) A and B inhibitory activity (tribulin) levels measured on day 14 and 24 h after drug withdrawal in different groups of animals. Morphine, ethanol, lorazepam and nicotine withdrawal was associated with significant anxiety and corresponding increase in brain tribulin activity, particularly its MAO A inhibitory component. Cannabis and ondansetron withdrawal were neither associated with anxiety or change in tribulin levels. The investigation supports the postulated role of tribulin as an endogenous correlate of anxiety, its MAO A inhibitory component accounting for a major part of this effect.

Isatin is a potent endogenous antagonist of guanylate cyclase-coupled atrial natriuretic peptide receptors

Isatin (indole-2,3-dione) is an endogenous compound with anxiogenic properties. In the brain, highest levels (0.1 microgram/g) have been found in the rat hippocampus. In the present study, we show that isatin has little effect on a wide range of neurotransmitter and hormonal receptors but that it acts as an inhibitor of atrial natriuretic peptide (ANP) binding, with an IC50 of 4x 10(-7) M. It also inhibits ANP-activated particulate guanylate cyclase from rat kidney, heart and brain membranes in dose-dependent fashion, varying also with ANP concentration. These findings suggest that isatin is a new endogenous regulator of mammalian ANP activity, with potential implications for the control of both anxiety and natriuresis.

Anxiogenic activity of intraventricularly administered bradykinin in rats

The anxiogenic action of bradykinin was investigated in rats and compared with that of yohimbine, a known anxiogenic agent. Bradykinin (0.5, 1 and 2 μg/rat) was administered intracerebroventricularly (i.c.v.), whereas yohimbine (2 mg/kg) was administered i.p. The experimental methods used were the open- field, elevated plus-maze, social interaction and novelty suppressed feeding latency tests, and estimation of brain tribulin activity in terms of endogenous monoamine oxidase (MAO) A and MAO B inhibition. The behavioural and biochemical effects induced by bradykinin were qualitatively similar to those of yohimbine. Thus, both the drugs reduced ambulation and rears, and increased immobility and defecation, in the open-field test. They decreased the number of entries and time spent on the open arms of the elevated plus-maze, reduced social interaction in paired rats and increased the feeding latency in an unfamiliar environment in 48 h food-deprived rats. These effects are known to be associated with anxiety in animals. Bradykinin and yohimbine increased rat brain tribulin activity, the effect on the MAO A inhibitor component being more marked than that on the MAO B inhibitor component. The MAO A inhibitor component has been postulated to be the major anxiogenic moiety of tribulin. Lorazepam, a well known benzodiazepine anxiolytic agent, attenuated the anxiogenic effects of bradykinin and yohimbine, which may not be a functional effect. The investigation indicates that, like cholecystokinin (CCK), bradykinin may function as an endogenous anxiogenic peptide.

Increase of brain endogenous monoamine oxidase inhibitory activity (tribulin) in experimental audiogenic seizures in rats: evidence for a monoamine oxidase A inhibiting component of tribulin

Brain tribulin activity in rats with an inherited predisposition to audiogenic epilepsy was studied after seizures of different intensity were induced by an electric bell. Weak seizures (from 0 to 2 arbitrary units) did not produce any changes in endogenous inhibitory activity towards either monoamine oxidase (MAO) A or B. Moderate seizures were characterized by increases in both MAO A and MAO B inhibitory activity (up to 1.9-fold). Complete tonic epileptiform seizures with total areflexia (4 arbitrary units) induced further augmentation (up to 2.5-fold) of MAO A but not of MAO B inhibitory activity. This dissociation between the two inhibitory activities points to the existence of a separate MAO A-inhibiting component of brain tribulin which is different from isatin.

Inhibitory potency of some isatin analogues on human monoamine oxidase A and B

Isatin is an endogenous compound which acts as a selective inhibitor of monoamine oxidase (MAO) B. In this study a range of isatin analogues were tested for their in vitro inhibition of human MAO A and B. Most of the analogues were less potent than isatin. Hydroxylation of the aromatic ring changed the inhibitory potency in favour of MAO A, with 5-hydroxyisatin being a potent and selective MAO A inhibitor (IC50 8 microM). Isatinic acid, which is formed reversibly from isatin at alkaline pH, showed no inhibition.

Pergolide can induce soluble superoxide dismutase in rat striata

Pergolide, a dopamine receptor agonist, given daily i.p. for three weeks at 0.04 mg/kg and 0.4 mg/kg, significantly induced soluble (Cu-Zn) superoxide dismutase in the rat striatum, while having no effect on the mitochondrial (Mn) form of the enzyme. Such induction, which can also be effected by (-)-deprenyl, may help to protect against nigrostriatal degeneration.