Inhibition of bovine lung semicarbazide-sensitive amine oxidase (SSAO) by some hydrazine derivatives

Network-based drug repurposing for potential stroke therapy

Stroke is the leading cause of death and disability worldwide, with a growing number of incidences in developing countries. However, there are currently few medical therapies for this disease. Emerged as an effective drug discovery strategy, drug repurposing which owns lower cost and shorter time, is able to identify new indications from existing drugs. In this study, we aimed at identifying potential drug candidates for stroke via computationally repurposing approved drugs from Drugbank database. We first developed a drug-target network of approved drugs, employed network-based approach to repurpose these drugs, and altogether identified 185 drug candidates for stroke. To validate the prediction accuracy of our network-based approach, we next systematically searched for previous literature, and found 68 out of 185 drug candidates (36.8 %) exerted therapeutic effects on stroke. We further selected several potential drug candidates with confirmed neuroprotective effects for testing their anti-stroke activity. Six drugs, including cinnarizine, orphenadrine, phenelzine, ketotifen, diclofenac and omeprazole, have exhibited good activity on oxygen-glucose deprivation/reoxygenation (OGD/R) induced BV2 cells. Finally, we showcased the anti-stroke mechanism of actions of cinnarizine and phenelzine via western blot and Olink inflammation panel. Experimental results revealed that they both played anti-stroke effects in the OGD/R induced BV2 cells via inhibiting the expressions of IL-6 and COX-2. In summary, this study provides efficient network-based methodologies for in silico identification of drug candidates toward stroke.

Overview of the Neuroprotective Effects of the MAO-Inhibiting Antidepressant Phenelzine

Phenelzine (PLZ) is a monoamine oxidase (MAO)-inhibiting antidepressant with anxiolytic properties. This multifaceted drug has a number of pharmacological and neurochemical effects in addition to inhibition of MAO, and findings on these effects have contributed to a body of evidence indicating that PLZ also has neuroprotective/neurorescue properties. These attributes are reviewed in this paper and include catabolism to the active metabolite β-phenylethylidenehydrazine (PEH) and effects of PLZ and PEH on the GABA-glutamate balance in brain, sequestration of reactive aldehydes, and inhibition of primary amine oxidase. Also discussed are the encouraging findings of the effects of PLZ in animal models of stroke, spinal cord injury, traumatic brain injury, and multiple sclerosis, as well other actions such as reduction of nitrative stress, reduction of the effects of a toxin on dopaminergic neurons, potential anticonvulsant actions, and effects on brain-derived neurotrophic factor, neural cell adhesion molecules, an anti-apoptotic factor, and brain levels of ornithine and N-acetylamino acids.

Comparison of Inhibitor and Substrate Selectivity between Rodent and Human Vascular Adhesion Protein-1

Vascular adhesion protein-1 (VAP-1) is an ectoenzyme that functions as a copper-containing amine oxidase and is involved in leukocyte adhesion at sites of inflammation. Inhibition of VAP-1 oxidative deamination has become an attractive target for anti-inflammatory therapy with demonstrated efficacy in rodent models of inflammation. A previous comparison of purified recombinant VAP-1 from mouse, rat, monkey, and human gene sequences predicted that rodent VAP-1 would have higher affinity for smaller hydrophilic substrates/inhibitors because of its narrower and more hydrophilic active site channel. An optimized in vitro oxidative deamination fluorescence assay with benzylamine (BA) was used to compare inhibition of five known inhibitors in recombinant mouse, rat, and human VAP-1. Human VAP-1 was more sensitive compared to rat or mouse VAP-1 (lowest IC₅₀ concentration) to semicarbazide but was least sensitive to hydralazine and LJP-1207. Hydralazine had a lower IC₅₀ in rats compared to humans, although not significant. However, the IC₅₀ of hydralazine was significantly higher in the rat compared to mouse VAP-1. The larger hydrophobic compounds from Astellas (compound 35c) and Boehringer Ingelheim (PXS-4728A) were hypothesized to have higher binding affinity for human VAP-1 compared to rodent VAP-1 since the channel in human VAP-1 is larger and more hydrophobic than that in rodent VAP-1. Although the sensitivity of these two inhibitors was the lowest in the mouse enzyme, we found no significant differences between mouse, rat, and human VAP-1. Michaelis-Menten kinetics of the small primary amines phenylethylamine and tyramine were also compared to the common marker substrate BA demonstrating that BA had the highest affinity among the substrates. Rat VAP-1 had the highest affinity for all three substrates and mouse VAP-1 had intermediate affinity for BA and phenylethylamine, but tyramine was not a substrate for mouse VAP-1 under these assay conditions. These results suggest that comparing oxidative deamination in mouse and rat VAP-1 may be important if using these species for preclinical efficacy models.

Attenuation of Weight Gain and Prevention of Associated Pathologies by Inhibiting SSAO

Obesity is a worldwide prevalent metabolic disorder that is associated with diabetes, among many other diseases. Bearing this in mind, prevention and treatment ways need to be improved. Notably, activity of the enzyme semicarbazide-sensitive amine oxidase (SSAO) is found to be elevated in overweight subjects. Moreover, SSAO inhibition has resulted in an increase of histamine activity in adipose tissue and the limitation of body fat. The current review aims to overview the risks of obesity, rationalize the molecular ways of SSAO activity, and outline the strategies of inhibiting upregulated enzyme levels. It describes the differences between SSAO inhibitors and advances the prospective agents. Based on evidence, caffeine is proposed as an effective, safe, and reliable choice to inhibit SSAO activity. Furthermore, the histamine in adipocytes has been associated with SSAO activity. Therefore, it is suggested as one of the key compounds to be studied for obesity management. To conclude, inhibiting SSAO may attenuate weight gain and prevent related diseases.

Attenuation of the effects of oxidative stress by the MAO-inhibiting antidepressant and carbonyl scavenger phenelzine

Phenelzine (β-phenylethylhydrazine) is a monoamine oxidase (MAO)-inhibiting antidepressant with anxiolytic properties. It possesses a number of important pharmacological properties which may alter the effects of oxidative stress. After conducting a comprehensive literature search, the authors of this review paper aim to provide an overview and discussion of the mechanisms by which phenelzine may attenuate oxidative stress. It inhibits γ-aminobutyric acid (GABA) transaminase, resulting in elevated brain GABA levels, inhibits both MAO and primary amine oxidase and, due to its hydrazine-containing structure, reacts chemically to sequester a number of reactive aldehydes (e.g. acrolein and 4-hydroxy-2-nonenal) proposed to be implicated in oxidative stress in a number of neurodegenerative disorders. Phenelzine is unusual in that it is both an inhibitor of and a substrate for MAO, the latter action producing at least one active metabolite, β-phenylethylidenehydrazine (PEH). This metabolite inhibits GABA transaminase, is a very weak inhibitor of MAO but a strong inhibitor of primary amine oxidase, and sequesters aldehydes. Phenelzine may ameliorate the effects of oxidative stress by reducing formation of reactive metabolites (aldehydes, hydrogen peroxide, ammonia/ammonia derivatives) produced by the interaction of MAO with biogenic amines, by sequestering various other reactive aldehydes and by inhibiting primary amine oxidase. In PC12 cells treated with the neurotoxin MPP⁺, phenelzine has been reported to reduce several adverse effects of MPP⁺. It has also been reported to reduce lipid peroxidative damage induced in plasma and platelet proteins by peroxynitrite. In animal models, phenelzine has a neuroprotective effect in global ischemia and in cortical impact traumatic brain injury. Recent studies reported in the literature on the possible involvement of acrolein in spinal cord injury and multiple sclerosis indicate that phenelzine can attenuate adverse effects of acrolein in these models. Results from studies in our laboratories on effects of phenelzine and PEH on primary amine oxidase (which catalyzes formation of toxic aldehydes and is overexpressed in Alzheimer's disease), on sequestration of the toxic aldehyde acrolein, and on reduction of acrolein-induced toxicity in mouse cortical neurons are also reported.

Tranylcypromine in mind (Part I): Review of pharmacology

It has been over 50 years since a review has focused exclusively on the monoamine oxidase (MAO) inhibitor tranylcypromine (TCP). A new review has therefore been conducted for TCP in two parts which are written to be read preferably in close conjunction: Part I - pharmacodynamics, pharmacokinetics, drug interactions, toxicology; and Part II - clinical studies with meta-analysis of controlled studies in depression, practice of TCP treatment, place in therapy. Pharmacological data of this review part I characterize TCP as an irreversible and nonselective MAO-A/B inhibitor at low therapeutic doses of 20mg/day with supplementary norepinephrine reuptake inhibition at higher doses of 40-60mg/day. Serotonin, norepinephrine, dopamine, and trace amines, such as the "endogenous amphetamine" phenylethylamine, are increased in brain, which leads to changes in neuroplasticity by e.g. increased neurotrophic growth factors and translates to reduced stress-induced hypersecretion of corticotropin releasing factor (CRF) and positive testing in animal studies of depression. TCP has a pharmacokinetic half-life (t_1/2) of only 2h which is considerably lower than for most other antidepressant drugs. However, a very long pharmacodynamic half-life of about one week is found because of the irreversible MAO inhibition. New studies show that, except for cytochrome P450 (CYP) 2A6, no other drug metabolizing CYP-enzymes are inhibited by TCP at therapeutic doses which defines a low potential of pharmacokinetic interactions in the direction from TCP to other drugs. Insufficient information is available, however, for plasma concentrations of TCP influenced by comedication. More quantitative data are also needed for TCP metabolites such as p-hydroxytranylcypromine and N-acetyltranylcypromine. Pharmacodynamic drug interactions comprise for instance severe serotonin toxicity (SST) with serotonergic drugs and hypertensive crisis with indirect sympathomimetics. Because of the risk of severe food interaction, TCP treatment remains beset with the need for a mandatory tyramine-restricted diet. Toxicity in overdose is similar to amitriptyline and imipramine according to the distance of therapeutic to toxic doses. In conclusion, TCP is characterized by an exceptional pharmacology which is different to most other antidepressant drugs, and a more special evaluation of clinical efficacy and safety may therefore be needed.

Perivascular Adipose Tissue's Impact on Norepinephrine-Induced Contraction of Mesenteric Resistance Arteries

Background: Perivascular adipose tissue (PVAT) can decrease vascular contraction to NE. We tested the hypothesis that metabolism and/or uptake of vasoactive amines by mesenteric PVAT (MPVAT) could affect NE-induced contraction of the mesenteric resistance arteries. Methods: Mesenteric resistance vessels (MRV) and MPVAT from male Sprague-Dawley rats were used. RT-PCR and Western blots were performed to detect amine metabolizing enzymes. The Amplex® Red Assay was used to quantify oxidase activity by detecting the oxidase reaction product H2O2 and the contribution of PVAT on the mesenteric arteries' contraction to NE was measured by myography. Results: Semicarbazide sensitive amine oxidase (SSAO) and monoamine oxidase A (MAO-A) were detected in MRV and MPVAT by Western blot. Addition of the amine oxidase substrates tyramine or benzylamine (1 mM) resulted in higher amine oxidase activity in the MRV, MPVAT, MPVAT's adipocyte fraction (AF), and the stromal vascular fraction (SVF). Inhibiting SSAO with semicarbazide (1 mM) decreased amine oxidase activity in the MPVAT and AF. Benzylamine-driven, but not tyramine-driven, oxidase activity in the MRV was reduced by semicarbazide. By contrast, no reduction in oxidase activity in all sample types was observed with use of the monoamine oxidase inhibitors clorgyline (1 μM) or pargyline (1 μM). Inhibition of MAO-A/B or SSAO individually did not alter contraction to NE. However, inhibition of both MAO and SSAO increased the potency of NE at mesenteric arteries with PVAT. Addition of MAO and SSAO inhibitors along with the H2O2 scavenger catalase reduced PVAT's anti-contractile effect to NE. Inhibition of the norepinephrine transporter (NET) with nisoxetine also reduced PVAT's anti-contractile effect to NE. Conclusions: PVAT's uptake and metabolism of NE may contribute to the anti-contractile effect of PVAT. MPVAT and adipocytes within MPVAT are a source of SSAO.

Construction of a D-amino acid oxidase reactor based on magnetic nanoparticles modified by a reactive polymer and its application in screening enzyme inhibitors

Developing facile and high-throughput methods for exploring pharmacological inhibitors of D-amino acid oxidase (DAAO) has triggered increasing interest. In this work, DAAO was immobilized on the magnetic nanoparticles, which were modified by a biocompatible reactive polymer, poly(glycidyl methacrylate) (PGMA) via an atom transfer radical polymerization technique. Interestingly, the enzyme immobilization process was greatly promoted with the assistance of a lithium perchlorate catalyst. Meanwhile, a new amino acid ionic liquid (AAIL) was successfully synthesized and employed as the efficient chiral ligand in a chiral ligand exchange capillary electrophoresis (CLE-CE) system for chiral separation of amino acids (AAs) and quantitation of methionine, which was selected as the substrate of DAAO. Then, the apparent Michaelis-Menten constants in the enzyme system were determined with the proposed CLE-CE method. The prepared DAAO-PGMA-Fe3O4 nanoparticles exhibited excellent reusability and good stability. Moreover, the enzyme reactor was successfully applied in screening DAAO inhibitors. These results demonstrated that the enzyme could be efficiently immobilized on the polymer-grafted magnetic nanoparticles and that the obtained enzyme reactor has great potential in screening enzyme inhibitors, further offering new insight into monitoring the relevant diseases.

Monoamine oxidase inhibitors and neuroprotection: a review

Monoamine oxidase inhibitors have been available for more than 50 years, initially developed as antidepressants but currently used in a variety of psychiatric and neurological conditions. There has been a recent surge of interest in monoamine oxidase inhibitors because of their reported neuroprotective and/or neurorescue properties. Interestingly, it seems that often these properties are independent of their ability to inhibit monoamine oxidase. This review article presents an overview of the neuroprotective/neurorescue properties of these multifaceted drugs and focuses on phenelzine, (-)-deprenyl, rasagiline, ladostigil, tranylcypromine, moclobemide, and clorgyline and their possible neuroprotective mechanisms.

Comparison of phenelzine and geometric isomers of its active metabolite, β-phenylethylidenehydrazine, on rat brain levels of amino acids, biogenic amine neurotransmitters and methylamine

Phenelzine is a monoamine oxidase (MAO) inhibitor used in treatment of depression and anxiety disorders. It also elevates brain levels of γ-aminobutyric acid (GABA) and inhibits primary amine oxidase (PrAO), an enzyme whose activity and/or expression has been reported to be increased in diabetes mellitus, Alzheimer's disease and cardiovascular disorders. Phenelzine is not only an inhibitor of, but also a substrate for, MAO and it has been suggested that an active metabolite, namely β-phenylethylidenehydrazine (PEH), is responsible for phenelzine's effects on amino acids. PEH is also a strong inhibitor of PrAO but has weak effects on MAO. PEH has a double bond and can thus exist as (E)- and (Z)-geometric isomers, but to date the two isomers have not been compared with regard to their neurochemical effects. We have investigated the effects of phenelzine, (E)- and (Z)-PEH on rat whole brain levels of amino acids, biogenic amine neurotransmitters and methylamine (an endogenous substrate of PrAO). Under the conditions used in the study, (E)- and (Z)-PEH appear to be equivalent in their neurochemical properties. Both PEH isomers and phenelzine produced marked increases in rat brain levels of GABA and alanine while decreasing brain levels of glutamine. Phenelzine increased brain levels of biogenic amine neurotransmitters (noradrenaline, dopamine and serotonin), whereas neither PEH isomer altered levels of these neurotransmitters to a considerable extent. All three drugs significantly increased rat brain levels of methylamine, with (E)- and (Z)-PEH causing a greater increase than phenelzine. These results are discussed in relation to the possible therapeutic applications of these drugs.

A therapeutic approach to cerebrovascular diseases based on indole substituted hydrazides and hydrazines able to interact with human vascular adhesion protein-1, monoamine oxidases (A and B), AChE and BuChE

Herein, we report the biological evaluation of a series of indole substituted hydrazides and hydrazines throughout the assessment of their multipotent inhibitory potency towards monoamine oxidase (MAO) A and B, semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1), and the cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Hydrazine JL72 (3-(3-hydrazinylpropyl)-1H-indole) showed a potent, reversible and non-time-dependent inhibition of MAO-A, which suggests its capacity in restoring serotoninergic neurotransmission being devoid of the side effects observed for classic MAO-A inhibitors. In addition, JL72 behaved as a moderate BuChE inhibitor. Finally, both hydrazines and hydrazides derivatives showed high affinity towards SSAO/VAP-1. Among them, JL72 behaved as a noncompetitive and the most potent inhibitor (IC50 = 0.19 ± 0.04 μM), possessing also a significant anti-inflammatory activity. The combined inhibition of SSAO/VAP-1, MAO (A and B), AChE and BuChE appear as an important therapeutic target to be considered in the treatment of cerebrovascular and neurological disorders such as Alzheimer's disease.

Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1: a patent survey

INTRODUCTION

Vascular adhesion protein-1 (VAP-1)/semicarbazide-sensitive amine oxidase (SSAO) is an adhesion protein involved in leukocyte trafficking and inflammatory processes, with a special amine oxidase activity. Inhibitors have been mainly developed for treating chronic inflammatory disorders. The utility of inhibitors as antiangiogenic agents in ophthalmological and oncological diseases is currently under evaluation. SSAO substrates may mimic several insulin effects, although their utility for the treatment of diabetes is still far from being fully understood.

AREAS COVERED

This paper reviews the patent literature of SSAO/VAP-1 inhibitors and substrates, for the period of 1990 - 2010. The current stage of SSAO/VAP-1-interacting agents published in patents is described, along with their chemical structures and pharmacological uses.

EXPERT OPINION

SSAO/VAP-1 is a promising anti-inflammatory target. Another important field for therapeutic application of these inhibitors may be ophthalmology, due to their antiangiogenic effects. SSAO substrates might also be of therapeutic value in the treatment of diabetes; however, more extensive research has to be undertaken to validate this approach.

Ralstonia solanacearum induces soluble amine-oxidase activity in Solanum torvum stem calli

Solanum torvum is reported to carry resistance to bacterial wilt caused by Ralstonia solanacearum. So, this wild species is used as rootskock for eggplants or tomatoes in naturally infected soil. This study aimed to investigate the involvement of the polyamine metabolism pathway in the resistance mechanisms of this species. Calli induced from Solanum torvum stem explants were inoculated with the bacteria under partial vacuum. All calli showed a hypersensitive response after infiltration. Furthermore, amine oxidase activity with aldehyde and H(2)O(2) production was detected in soluble protein extracts of calli infiltrated by the bacteria. Due to its preferential affinity for aliphatic amines, this enzyme was supposed to have amine oxidase-like (AO-like) activity. Moreover, the length of aliphatic chain cycle altered the oxidative deamination kinetics of potential substrates. The AO-like catalytic activity was significantly inhibited by chelator agents such as ethylene-diamine-tretraacetic (EDTA), and also by semi-carbazide as aminoguanidine. These results suggested that (i) the prosthetic group of the AO-like enzyme could be a tyrosine-derived 6-hydroxytopaquinone structure, copper containing; (ii) this enzyme could be a semi-carbazide sensitive amine oxidase (SSAO).

Structure-activity relationships of SSAO/VAP-1 arylalkylamine-based substrates

Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) substrates show insulin-mimetic effects and are therefore potentially valuable molecules for the treatment of diabetes mellitus. Herein we review several structural and electronic aspects of SSAO arylalkylamine-based substrates. Two main modifications directly affect amine oxidase (AO) activity: 1) variation in ring substitution modulates the biological activity of the arylalkylamine ligand by converting a substrate into a substrate-like inhibitor, and 2) variation in the number of methylene units between the aromatic ring and the ammonium groups of the arylalkylamine substrates dramatically alters the oxidation rate between species. Furthermore, we review relevant information about mammalian SSAO/VAP-1 substrate selectivity and specificity over monoamine oxidases (MAOs).

Antidepressant phenelzine alters differentiation of cultured human and mouse preadipocytes

Change in body weight is a frequent side effect of antidepressants and is considered to be mediated by central effects on food intake and energy expenditure. The antidepressant phenelzine (Nardil) potently inhibits both monoamine oxidase and semicarbazide-sensitive amine oxidase activities, two enzymes that are highly expressed in adipose tissue, raising the possibility that it could directly alter adipocyte biology. Treatment with this compound is rather associated with weight gain. The aim of this work was to examine the effects of phenelzine on differentiation and metabolism of cultured human and mouse preadipocytes and to characterize the mechanisms involved in these effects. In all preadipocyte models, phenelzine induced a time- and dose-dependent reduction in differentiation and triglyceride accumulation. Modulation of lipolysis or glucose transport was not involved in phenelzine action. This effect was supported by the reduced expression in the key adipogenic transcription factors peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and CCAAT/enhancer binding protein-alpha, which was observed only at the highest drug concentrations (30-100 microM). The PPAR-gamma agonists thiazolidinediones did not reverse phenelzine effects. By contrast, the reduction in both cell triglycerides and sterol regulatory element-binding protein-1c (SREBP-1c) was detectable at lower phenelzine concentrations (1-10 microM). Phenelzine effect on triglyceride content was prevented by providing free fatty acids to the cells and was partially reversed by overexpression of a dominant-positive form of SREBP-1c, showing the privileged targeting of the lipogenic pathway. When considered together, these findings demonstrate that an antidepressant directly and potently inhibits adipocyte lipid storage and differentiation, which could contribute to psychotropic drug side effects on energy homeostasis.

Arylalkylamine vanadium salts as new anti-diabetic compounds

Vanadium compounds show insulin-like effects in vivo and in vitro. Several clinical studies have shown the efficacy of vanadium compounds in type 2 diabetic subjects. However, a major concern is safety, which calls for the development of more potent vanadium compounds. For that reason different laboratories develop strategies to decrease the therapeutic dose of vanadate. One of these strategies use substrates of semicarbazide-sensitive amine oxidase (SSAO)/vascular adhesion protein-1 (VAP-1), a bifunctional protein with amine oxidase activity and adhesive properties implicated in lymphocyte homing at inflammation sites. Substrates of SSAO combined with low concentrations of vanadate strongly stimulate glucose transport and GLUT4 glucose transporter recruitment to the plasma membrane in 3T3-L1 adipocytes and in rat adipocytes. This combination also shows anti-diabetic effects in various animal models of type 1 and type 2 diabetes. Benzylamine/vanadate administration generates peroxovanadium locally in pancreatic islets, which stimulates insulin secretion, and also produces peroxovanadium in adipose tissue, thereby activating glucose metabolism in adipocytes and in neighboring muscle. This opens up the possibility of using the SSAO/VAP-1 activity as a local generator of protein tyrosine phosphatase inhibitors in anti-diabetic therapy. More recently a novel class of arylalkylaminevanadium salts have shown potent insulin-mimetic effects downstream of the insulin receptor. Administration of these compounds lowers glycemia and normalizes the plasma lipid profile in type 1 and type 2 models of diabetes. The combination of different approaches to decrease vanadium doses, among them chelating agents and SSAO substrates, should permit to develop safe and efficient vanadium based agents safe for diabetes treatment.

Interaction of rat lung SSAO with the novel 1-N-substituted thiocarbamoyl-3-substituted phenyl-5-(2-pyrolyl)-2-pyrazoline derivatives

Interactions of twelve new synthesized 1-N-substituted thiocarbamoyl-3-substituted phenyl-5-pyrolyl-2-pyrazoline derivatives with rat lung semicarbazide-sensitive amine oxidase (SSAO) were assessed. Pyrazoline derivatives were synthesized according to previous methods and SSAO was purified from the crude microsomal fractions of rat lung.Three compounds (3e, 3f, 3k) with a p-methoxy group at the phenyl ring inhibited rat lung SSAO non-competitively and irreversibly, and showed higher affinity towards SSAO when expressed in terms of IC(50) for SSAO/Monoamine oxidase B (MAO-B). Since these novel pyrazoline derivatives have been found to act as suicide inhibitors of SSAO, the semicarbazide group in these molecules may be responsible for the SSAO inhibitory action. It is suggested that these compounds cannot enter the first small active site cavity of SSAO and may interact tightly with another binding site or with some other reactive groups present in the molecule. Compound 3e showed the highest inhibitory activity on rat lung SSAO. The novel pyrazoline derivatives may be used to discriminate between Cu- and FAD-containing amine oxidases and may have promising features as anti-Parkinson agents if the SSAO-inhibitory effects can be supported by in vivo studies.

Absence of tissue-bound semicarbazide-sensitive amine oxidase activity in carp tissues

We have previously reported that carp (Cyprinus carpio) tissue mitochondria contain a novel form of monoamine oxidase (MAO), which belongs neither to MAO-A nor to MAO-B of the mammalian enzyme. This conclusion results from the findings that the carp MAO was equally sensitive to a selective MAO-A inhibitor clorgyline and to the MAO-B selective inhibitor l-deprenyl, when tyramine, a substrate for both forms, serotonin or beta-phenylethylamine, a substrate for either A or B-form of mammalian MAO, was used. In the present study, we tried to detect another amine oxidase, termed tissue-bound semicarbazide-sensitive amine oxidase (SSAO), activity in carp tissues. As definition of SSAO was used, such as insensitivity to inhibition of the kynuramine oxidizing activity by an MAO inhibitor pargyline and high sensitivity to the SSAO inhibitor semicarbazide. The results indicated that the oxidizing activity was selectively and almost completely inhibited by 0.1 mM pargyline alone or a combination of 0.1 mM pargyline plus 0.1 mM semicarbazide, but not by 0.1 mM semicarbazide alone. We also tried to detect any SSAO activity by changing experimental conditions, such as lower incubation temperature, higher enzyme protein concentration, a lower substrate concentration and different pH's in the reaction, as the enzyme source. However, still no SSAO activity could be detected in the tissues. These results conclusively indicate that carp tissues so far examined do not contain SSAO activity.

Aldehyde load in ischemia-reperfusion brain injury: neuroprotection by neutralization of reactive aldehydes with phenelzine

In ongoing studies of the neuroprotective properties of monoamine oxidase inhibitors, we found that phenelzine provided robust neuroprotection in the gerbil model of transient forebrain ischemia, with drug administration delayed up to 3 h post reperfusion. Since ischemia-reperfusion brain injury is associated with large increases in the concentrations of reactive aldehydes in the penumbra area, we investigated if the hydrazine function of phenelzine was capable of sequestering reactive aldehydes. Both aminoaldehydes and acrolein are generated from the metabolism of polyamines to putrescine by polyamine oxidase. These toxic aldehydes in turn compromise mitochondrial and lysosomal integrity and initiate apoptosis and necrosis. Previous studies have demonstrated that pharmacological neutralization of reactive aldehydes via the formation of thioacetal derivatives results in significant neuroprotection in ischemia-reperfusion injury, in both focal and global ischemia models. In our studies of acrolein and 3-aminopropanal toxicity, using an immortalized retinal cell line, we found that aldehyde sequestration with phenelzine was neuroprotective. The neuroprotection observed with phenelzine is in agreement with previous studies of aldehyde sequestering agents in the treatment of ischemia-reperfusion brain injury and supports the concept that "aldehyde load" is a major factor in the delayed cell losses of the ischemic penumbra.

Decreased serum semicarbazide sensitive aminooxidase (SSAO) activity in patients with major depression

Semicarbazide sensitive aminooxidase (SSAO) is known to interplay with monoamine oxidases (MAO) and several antidepressants. Taking into account the monoamine hypothesis concerning the pathophysiology of depression, the aim of the present pilot study was to evaluate serum SSAO activity in depressed patients. A total of 21 inpatients with major depression and 41 healthy controls were studied. Serum SSAO activity was determined by HPLC on days 1, 5 and 10 of inpatient treatment. At baseline without medication including antidepressants, highly depressed patients (MADRS score>or=30) had significantly decreased serum SSAO activity (mean 385+/-161 mU/l) when compared to healthy controls (mean 526+/-141 mU/l; p=0.003). This SSAO decrease was less pronounced at day 5 and day 10 under an antidepressive drug regime. Decreased serum SSAO activity was observed in patients with major depression, especially in those with high MADRS scores. The present results support the hypothesis of dysfunctional monoaminergic metabolism in the pathogenesis of depressive disorders. The disputable association between depression and monoamine metabolism requires further investigation, particularly with regard to SSAO activity and medication status.

2-bromoethylamine, a suicide inhibitor of semicarbazide-sensitive amine oxidase, increases hydralazine hypotension in rats

Previous work has shown that inhibitors of the predominantly vascular enzyme semicarbazide-sensitive amine oxidase (SSAO) potentiate the hypotensive response to hydralazine, itself a SSAO inhibitor, in anesthetized rats. The present study was carried out to determine whether the recently described suicide SSAO inhibitor 2-bromoethylamine shares this effect. Hypotensive responses to hydralazine, 0.1 mg/kg IV, were obtained in chloralose-urethane-anesthetized rats, either unpretreated or receiving bromoethylamine at different doses and pretreatment intervals. Parallel experiments were run with semicarbazide, the prototypical hydrazine SSAO inhibitor. Both inhibitors potentiated hydralazine hypotension, bromoethylamine having a longer latency and a shorter duration of action than semicarbazide. High doses of bromoethylamine did not produce potentiation, a phenomenon attributed to SSAO inactivation by excess substrate and decreased formation by the enzyme of the inhibitor product. Experiments with combined administration of both inhibitors were also carried out. When semicarbazide was administered before bromoethylamine, potentiaton was prevented, apparently by a mechanism similar to the above; when it was given after the amine, potentiation was increased. This was attributed to enzyme inhibition by interaction with 2 different active sites. The charactertistics of hydralazine potentiation by bromoethylamine were considered compatible with the mechanism of SSAO inhibition by the amine.

Stimulation of glucose transport by semicarbazide-sensitive amine oxidase activity in adipocytes from diabetic rats

Semicarbazide-sensitive amine oxidase (SSAO) is highly expressed in adipose cells, and substrates of SSAO such as benzylamine in combination with low concentrations of vanadate strongly stimulate glucose transport and GLUT4 recruitment in mouse 3T3-L1 adipocytes and in isolated rat adipocytes. Here we examined whether this combination of molecules also stimulates glucose transport in adipocytes from streptozotocin-induced diabetic rats and from Goto-Kakizaki diabetic rats. As previously reported, adipocytes obtained from streptozotocin-induced diabetic rats, showed a reduced stimulation of glucose transport in response to insulin. Under these conditions, the combination of benzylamine and vanadate caused a marked stimulation of glucose transport that was similar to the stimulation detected in control adipocytes. Adipocytes isolated from Goto-Kakizaki diabetic rats also showed a defective response to insulin; however, acute incubation in the presence of benzylamine and vanadate stimulated glucose transport in these cells to the same extent than in adipocytes from non-diabetic rats. These data indicate that adipocytes obtained from two different models of animal diabetes do not show resistance to the activation of glucose transport by SSAO activity, which is in contrast to the well reported resistance to insulin action. It seems to suggest that SSAO activity in combination with vanadate triggers a glucose transport-activating intracellular pathway that remains intact in the diabetic state. Further, our data support the view that the combination of benzylamine and vanadate could be an effective therapy in diabetes.

Semicarbazide-sensitive amine oxidases: enzymes with quite a lot to do

The semicarbazide-sensitive amine oxidases (SSAO) (EC 1.4.3.6) were believed to be detoxifying enzymes, primarily involved in the oxidative deamination of endogenous amines, such as methylamine and aminoacetone, together with some xenobiotic amines. However, it appears that the reaction products may have important signalling functions in the regulation of cell development and glucose homeostasis. Furthermore, enzyme, from some sources, behaves as a cellular adhesion protein under inflammatory and it may also be involved in lipid transport. This review considers what is known about the activities and potential functions of this hardworking protein.

Semicarbazide-sensitive amine oxidase: role in the vasculature and vasodilation after in situ inhibition

1. The characteristics of semicarbazide-sensitive amine oxidase (SSAO) are reviewed and the unknown physiological or pathological role of this enzyme emphasized. 2. The various mechanisms of action proposed for the vasodilator drug hydralazine are considered. In particular, the inhibitory action on various enzymes, related or not to cardiovascular function, are discussed. 3. Studies linking inhibition of SSAO to hydralazine hypotension are reviewed and a general hypothesis relating both actions is presented. The hypothesis postulates that (a). vascular SSAO is involved in the regulation of vascular tone, and (b). hydralazine vasodilation is the consequence of vascular SSAO inhibition. 4. Evidence supporting these postulates is presented and vascular SSAO inhibition is proposed as a novel mechanism of vasodilation.

Semicarbazide-sensitive amine oxidase (SSAO) in the brain

Semicarbazide-sensitive amine oxidase (SSAO) is widely distributed in almost tissues. However, its presence in brain microvessels is still controversial. The affinity of SSAO towards benzylamine (Bz) is considerably higher than that of monoamine oxidase (MAO). SSAO plays a role in the toxicity of several environmental and endogenous amines. SSAO-mediated production of toxic aldehydes has been proposed to be related to pathophysiological conditions. The most potent of inhibition of SSAO in monkey brain was observed by tricyclic antidepressant drug imipramine, as compared to tetracyclic drug maprotiline or non-cyclic drug nomifensine. An endogenous SSAO modulator in rat brain cytosol after immobilization stress (IMMO) was found and that this inhibitor could be induced by IMMO. SSAO activity in rat brain might be regulated by the level of this inhibitor. Semicarbazide, a SSAO inhibitor, enhances the formation of .OH products of efflux/oxidation due to 1-methyl-4-phenylpyridinium ion (MPP+). The precise physiological functions of SSAO could play an important role in the control of energy balance in adipose tissue. SSAO could play an important role in the regulation of adipocyte homeostasis.

Substrates of semicarbazide-sensitive amine oxidase co-operate with vanadate to stimulate tyrosine phosphorylation of insulin-receptor-substrate proteins, phosphoinositide 3-kinase activity and GLUT4 translocation in adipose cells

It has been shown that the combination of benzylamine or tyramine and low concentrations of vanadate markedly stimulates glucose transport in rat adipocytes by a mechanism that requires semicarbazide-sensitive amine oxidase (SSAO) activity and H(2)O(2) formation. Here we have further analysed the insulin-like effects of the combination of SSAO substrates and vanadate and we have studied the signal-transduction pathway activated in rat adipocytes. We found that several SSAO substrates (benzylamine, tyramine, methylamine, n-decylamine, histamine, tryptamine or beta-phenylethylamine), in combination with low concentrations of vanadate, stimulate glucose transport in isolated rat adipocytes. Furthermore, SSAO substrates together with vanadate stimulated the recruitment of GLUT4 to the cell surface in isolated rat adipocytes. Benzylamine plus vanadate also stimulated glucose transport and GLUT4 translocation in 3T3-L1 adipocytes. Benzylamine or tyramine in combination with vanadate potently stimulated the tyrosine phosphorylation of both insulin receptor substrate (IRS)-1 and IRS-3. In contrast, benzylamine and vanadate caused only a weak stimulation of insulin receptor kinase. Benzylamine or tyramine in combination with vanadate also stimulated phosphoinositide 3-kinase activity; wortmannin abolished the stimulatory effect of benzylamine and vanadate on glucose transport in adipose cells. Furthermore, the administration of benzylamine and vanadate in vivo caused a rapid lowering of plasma glucose levels, which took place in the absence of alterations in plasma insulin. On the basis of these results we propose that SSAO activity regulates glucose transport in adipocytes. SSAO oxidative activity stimulates glucose transport via the translocation of GLUT4 carriers to the cell surface, resulting from a potent tyrosine phosphorylation of IRS-1 and IRS-3 and phosphoinositide 3-kinase activation. Our results also indicate that substrates of SSAO might regulate glucose disposal in vivo.

Evidence for existence of immobilization stress-inducible semicarbazide-sensitive amine oxidase inhibitor in rat brain cytosol

An endogenous inhibitor of semicarbazide-sensitive amine oxidase (SSAO) was separated by gel filtration from 105000xg supernate in rat brain cytosol following immobilization stress (IMMO). The molecular weight of this inhibitor was estimated to be 500-700 by gel filtration. This inhibitor was proved to be heat-stable resistant to protease treatment. These results suggest that this inhibitor is induced by IMMO. SSAO activity in rat brain might be regulated by the level of this inhibitor.

Enhancement of hydralazine hypotension by low doses of isoniazid. Possible role of semicarbazide-sensitive amine oxidase inhibition

The influence of pretreatment with 1 through 300 mg/kg ip of isoniazid (ISO) on blood pressure and heart rate responses to 0.1 mg/kg iv of hydralazine (HYD) was assessed in rats anesthetized with chloralose--urethane. HYD hypotension was significantly enhanced by ISO at doses between 3 and 300 mg/kg ip. Heart rate was not influenced by HYD in control or pretreated animals. Depressor responses to 0.2 mg/kg iv of pinacidil (PIN) were also potentiated by ISO at 100 and 300, but not at 30 mg/kg. Similarly, ISO decreased cerebral gamma-aminobutyric acid (GABA) at the two highest doses; 30 mg/kg was without effect. Pretreatment of rats with ISO at 1 through 300 mg/kg failed to influence HYD-induced relaxation of aortic rings. These results were interpreted as indicating that potentiation of HYD hypotension by high doses of ISO is not specific for that vasodilator and is related to decreased cerebral GABA, as postulated previously. Lower doses could specifically potentiate the HYD-induced hypotensive effect by inhibition of semicarbazide-sensitive amine oxidase (SSAO), since both ISO and HYD are potent inhibitors of this enzyme. In support of this hypothesis, the SSAO inhibitors, benserazide (100 mg/kg ip) and mexiletine (50 mg/kg ip), were also found to enhance HYD hypotension.

Inhibition of monkey brain semicarbazide-sensitive amine oxidase by various antidepressants

We examined whether the antidepressant drugs, such as the dicyclic drug zimeldine, the tricyclic drug imipramine, tetracyclic drug maprotiline, and the non-cyclic drug nomifensine, inhibit in vitro semicarbazide-sensitive amine oxidase (SSAO) activity in monkey brain. The deamination of 1 microM benzylamine was not inhibited at high concentrations of clorgyline or deprenyl, while it was highly sensitive for semicarbazide. When corresponding experiments were performed with 100 microM benzylamine, the opposite results were obtained. The most potent of inhibition of SSAO was observed by imipramine, followed by maprotiline, zimeldine and nomifensine. Inhibition of SSAO was not enhanced by varying the time of preincubation of the enzyme and various antidepressant drugs, indicating direct action on and reversible inhibition of SSAO. We found the tricyclic antidepressant drug to be the most selective inhibitors of SSAO activity in monkey brain, as compared with other type of antidepressant drugs.

Molecular cloning of a major mRNA species in murine 3T3 adipocyte lineage. differentiation-dependent expression, regulation, and identification as semicarbazide-sensitive amine oxidase

In an effort to identify novel mRNAs modulated during the course of adipose conversion, we have used a simplified differential display technique and have isolated a cDNA encoding an amine oxidase tremendously expressed in the adipocyte, the semicarbazide-sensitive amine oxidase (SSAO). The predicted amino acid sequence (765 amino acids) is likely to be the homologue of the human placental amine oxidase and of the partially known sequence of the rat adipocyte membrane amine oxidase. SSAO mRNAs are present in several tissues, but strikingly, the highest levels of gene expression are found in adipose tissue and aorta. Enzyme transcript levels are barely detectable in preadipocytes but are induced several hundred-fold during the adipocyte differentiation of 3T3-L1 or 3T3-F442A cells and of rat precursor primary cultures. These changes in transcript levels parallel a sharp increase in SSAO enzyme activity. The biochemical properties of the SSAO present in 3T3-L1 or 3T3-F442A adipocytes closely resemble the features of the SSAO activity previously described in white and brown adipose tissues. Interestingly, SSAO mRNA levels and enzyme activity drop in response to effectors of the cAMP pathway and to the cytokine tumor necrosis factor-alpha, indicating that two major signaling molecules of adipose tissue development and metabolism can control SSAO function. Moreover, the expression of SSAO transcripts and activity are clearly down-regulated in white adipose tissue from obese Zücker rats. Because of its known stimulatory effect on glucose transport, its biochemical properties and its pattern of expression and regulation, SSAO could play an important role in the regulation of adipocyte homeostasis.

Developmental vasculotoxicity associated with inhibition of semicarbazide-sensitive amine oxidase

The endogenous substrate(s) and physiological function(s) of semicarbazide-sensitive amine oxidase (SSAO), a group of enzymes exhibiting highest activity in vascular smooth muscle cells of the mammalian aortic wall, remain undetermined. This study examines the pathophysiological effects in the thoracic aortic wall resulting from specific in vivo SSAO inhibition. Weanling Sprague-Dawley rats were treated acutely or chronically with either semicarbazide hydrochloride or the allylamine derivatives MDL-72274 or MDL-72145 (Marion Merrell Dow Research Institute, Cincinnati, OH). Treatment with these compounds produced acute (6 and 24 h) and chronic (21 day) lowering of SSAO activity in aorta and lung with little effect on the activity of the vital matrix-forming enzyme, lysyl oxidase, in aortas of chronically treated animals. Chronic SSAO inhibition produced lesions consisting of striking disorganization of elastin architecture within the aortic media accompanied by degenerative medial changes and metaplastic changes in vascular smooth muscle cells. No significant difference in the total weight of dry, lipid-extracted aortic elastin and collagen components were observed between chronically SSAO inhibited and control animals. However, the amount of mature elastin was lowered and mature collagen was raised in the aortas of animals treated chronically with semicarbazide. Descending thoracic aortic rings isolated from chronically SSAO-inhibited animals had larger cross-sectional diameters (i.e., exhibited dilation) when compared to corresponding rings from control animals. This study demonstrates that developmental toxicity, characterized by striking vascular lesions and dilated thoracic aortas, can result from specific in vivo SSAO inhibition, suggesting a role for SSAO in connective tissue matrix development and maintenance, and specifically in the development of normal elastin.

Purification and characterization of a novel cyclohexylamine oxidase from the cyclohexylamine-degrading Brevibacterium oxydans IH-35A

Cyclohexylamine oxidase (CHAO) from a cell extract of Brevibacterium grown on cyclohexylamine was purified 50.2-fold, to electrophoretic homogeneity, by serial chromatographies. The molecular mass of the native enzyme was estimated to be approximately 50 kDa by gel filtration and SDS-PAGE. The optimum pH was 7.4 and the stable pH range was 6.0 to 7.0. The enzyme was thermostable up to 30 degrees C. The enzyme was found to be highly specific for the deamination of alicyclic monoamines such as cyclopentylamine, cycloheptylamine, and N-methylcyclohexylamine and aliphatic monoamines, such as sec-butylamine. The apparent K(m) value for cyclohexylamine was 1.23 mM. The enzyme was inhibited by flavin enzyme inhibitors such as quinine and quinacrine. The N-terminal 27 amino acid residues were determined as Gly-Ser-Val-Thr-Pro-Asp-Pro-Asp-Val-Asp-Val-Ile-Ile-His-Gly-Ala-Gly-Ile-Ser-Gly-Ser-Ala-Ala-Ala-Lys-Ala-Leu-, revealing homology to conventional flavin-containing amine oxidases (EC 1.4.3.4).

Autoradiographic imaging of formaldehyde adducts in mice: possible relevance for vascular damage in diabetes

The activity of semicarbazide-sensitive amine oxidase (SSAO) has been reported to be elevated in blood from diabetic patients. It has been suggested that the enzyme is involved in the development of complications such as retinopathies, nephropathies and neuropathies, which are associated with advanced diabetes, possibly by the formation of toxic metabolites. Under the influence of SSAO, methylamine is deaminated to formaldehyde which is known to react with various macromolecules. It has therefore been proposed that specific inhibition of SSAO could be of therapeutic value for treatment of diabetic patients. The present results provide evidence that treatment with an SSAO inhibitor potently reduces the levels of irreversible adducts. In this study, 14C-methylamine was given intraperitoneally to NMRI mice, and the tissue distribution of irreversibly bound methylamine metabolites was estimated by an autoradiographic method. Such radioactive residues occurred in high concentrations in the intestinal wall, brown adipose tissue, spleen and bone marrow. By inhibiting SSAO irreversibly with hydralazine before giving 14C-methylamine to the mice, it was possible to determine the resynthesis rate of SSAO in different tissues. A complete recovery of SSAO activity was seen in the intestinal wall after 6 days, whereas only about 60% was recovered in adipose tissue after 14 days. This suggests that factors controlling the synthesis of SSAO differ in these tissues, or that these tissues express different forms of enzymes.

Role of semicarbazide-sensitive amine oxidase on glucose transport and GLUT4 recruitment to the cell surface in adipose cells

The previous characterization of an abundant population of non-adrenergic imidazoline-I2 binding sites in adipocytes and the recent demonstration of the interplay between these binding sites and amine oxidases led us to analyze the amine oxidase activity in membranes from isolated rat adipocytes. Adipocyte membranes had substantial levels of semicarbazide-sensitive amine oxidase (SSAO). SSAO activity and immunoreactive SSAO protein were maximal in plasma membranes, and they were also detectable in intracellular membranes. Vesicle immunoisolation analysis indicated that GLUT4-containing vesicles from rat adipocytes contain substantial levels of SSAO activity and immunoreactive SSAO protein. Immunotitration of intracellular GLUT4 vesicles indicated that GLUT4 and SSAO colocalize in an endosomal compartment in rat adipocytes. SSAO activity was also found in GLUT4 vesicles from 3T3-L1 adipocytes and rat skeletal muscle. Benzylamine, a substrate of SSAO activity, caused a marked stimulation of glucose transport in isolated rat adipocytes in the presence of very low vanadate concentrations that by themselves were ineffective in exerting insulin-like effects. This synergistic effect of benzylamine and vanadate on glucose transport was totally abolished in the presence of semicarbazide, a specific inhibitor of SSAO. Subcellular membrane fractionation revealed that the combination of benzylamine and vanadate caused a recruitment of GLUT4 to the plasma membrane of adipose cells. The stimulatory effects of benzylamine and vanadate on glucose transport were blocked by catalase, suggesting that hydrogen peroxide production coupled to SSAO activity plays a crucial regulatory role. Based on these results we propose that SSAO activity might contribute through hydrogen peroxide production to the in vivo regulation of GLUT4 trafficking in adipose cells.

Purification and characterization of membrane-bound semicarbazide-sensitive amine oxidase (SSAO) from bovine lung

Semicarbazide-sensitive amine oxidase (SSAO) has been purified from bovine lung microsomes in a form which is catalytically active and stable to storage. The enzyme, an integral membrane protein, was solubilized with Triton X-100 and purification was achieved, in the presence of detergent, by chromatography with Cibacron Blue 3GA-agarose, hydroxylapatite, Lens culinaris-agarose, Resource Q-FPLC and gel filtration on Superdex 200 HR-FPLC. This is the first reported procedure for the extensive purification of a membrane-bound SSAO. The purified enzyme had an apparent Mr of 400000 but exhibited microheterogeneity with SDS/PAGE and isoelectric focusing, probably as a result of its glycoprotein nature. It behaved as a tetramer with subunits with apparent Mr values of 100. Antibodies raised towards the purified enzyme cross-reacted with the enzymes from human lung and bovine plasma. Redox-cycling staining and reaction with carbonyl reagents were consistent with the presence of a quinone cofactor, possibly topa quinone. The enzyme was also shown to contain two mol of Cu/mol of enzyme and removal of half of this bound copper resulted essentially in complete inhibition of enzyme activity. In contrast to the reported behaviour of the SSAO enzymes from plasma, the bovine lung enzyme was relatively insensitive to inhibition by cyanide, copper-chelating agents and amiloride. The specificity of the bovine lung enzyme was also narrower than reported for soluble SSAO. It catalysed the oxidative deamination of benzylamine, methylamine, 2-phenylethylamine and histamine but had no significant activity towards dopamine, 5-hydroxytryptamine, tryptamine or tyramine.

Conversion of taurine into N-chlorotaurine (taurine chloramine) and sulphoacetaldehyde in response to oxidative stress

N-Chlorotaurine (taurine chloramine), formed by treating taurine with hypochlorous acid, was shown to decompose to sulphoacetaldehyde with a first-order rate constant of 9.9+/-0.5 x 10(-4).h-1 at 37 degrees C in 0.1 M phosphate buffer, pH 7.4. Rat liver homogenates accelerated this decay in a process that was proportional to tissue-protein concentration and saturable, with maximum velocity (Vmax) and Km values of 0.28+/-0.01 nmol/min per mg of protein and 37+/-9 microM respectively. This activity was found to be lost on heat denaturation, but retained after dialysis. There was no detectable formation of sulphoacetaldehyde when taurine itself was incubated with the tissue homogenates under the same conditions. Activation of human neutrophils (1.67 x 10(6) cells/ml) with latex beads resulted in a respiratory burst of oxygen-radical production, the products of which were partially sequestered by 12.5 mM taurine. Under these conditions sulphoacetaldehyde was generated at a constant rate of 637+/-18 pmol/h per ml for over 7 h. A non-activated neutrophil suspension contained constant levels of 1.42+/-0.02 nmol/ml sulphoacetaldehyde, as did activated cells incubated in the absence of taurine, a basal level which may indicate a steady turnover of taurine in these cells. Such formation of chlorotaurine and its decay to the aldehyde may be the first steps in the metabolism of taurine to isethionate (2-hydroxyethanesulphonate) that has been demonstrated by various authors to occur in vivo.

Allylamine and beta-aminopropionitrile induced aortic medial necrosis: mechanisms of synergism

We have developed a model of aortic smooth muscle necrosis in adult Sprague Dawley rats by feeding them two vascular toxins (allylamine HCl, or AA, and beta-aminopropionitrile, or betaAPN) in concert for 10 days. Either toxin given alone does not cause aortic lesions. In order to shed light on the mechanism of the synergistic action of these two toxins we fed known modulators of AA or betaAPN toxicity to rats concurrently with the two toxins. As modulators we used (a) semicarbazide (98 mg/kg/day, given 4 h prior to toxins), a known inhibitor of the vascular enzyme SSAO which metabolizes AA; (b) L-cysteine (1.5% in rat chow, beginning 3 days prior to toxins), which has been shown to reduce the toxic effects of betaAPN; and (c) phenelzine sulphate (3 mg/kg/day, given 4 h prior to toxins), an inhibitor of SSAO and potentiator of betaAPN toxicity. Rats were fed various combinations of the toxins and modulators by gavage: water (n = 8); (AA, 100 mg/kg/day) AA + phenelzine (n = 8); AA + semicarbazide (n = 8); AA + L-cysteine (n = 11); (betaAPN, 1 g/kg/day) betaAPN + phenelzine (n = 8); betaAPN + semicarbazide (n = 8); betaAPN + L-cysteine (n = 8); (AA, 100 mg + betaAPN, 1 g/kg/day) AA + betaAPN + phenelzine (n = 9), AA + betaAPN + semicarbazide (n = 8); AA + betaAPN + L-cysteine (n = 12); phenelzine (3 mg/kg/day) (n = 4); semicarbazide (98 mg/kg/day) (n = 4) and L-cysteine (1.5% in rat chow) (n = 4). We found that phenelzine sulphate (a drug previously used in the treatment of hypertension) when given with AA reproduced the AA + betaAPN induced aortic lesions. Phenelzine + betaAPN caused no lesions, but when combined with AA + betaAPN, aortic lesions were intensified and included marked secondary degeneration of the vascular wall. Semicarbazide was found to completely obviate the vascular toxicity of AA + betaAPN. L-Cysteine feeding markedly decreased the incidence and severity of vascular lesions in AA + betaAPN treated rats, but did not change the incidence or severity of heart lesions caused by AA alone. These data indicate that the synergistic necrotizing toxicity of AA + betaAPN is primarily an AA effect. We postulate that some modulating influence of betaAPN (or phenelzine) on tissue distribution, metabolism, or detoxification pathways of AA increases AA's acute vascular toxicity, whereas semicarbazide offers protection by inhibiting the initial deamination of AA to a highly reactive aldehyde.