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

SSAO/VAP-1 in Cerebrovascular Disorders: A Potential Therapeutic Target for Stroke and Alzheimer's Disease

The semicarbazide-sensitive amine oxidase (SSAO), also known as vascular adhesion protein-1 (VAP-1) or primary amine oxidase (PrAO), is a deaminating enzyme highly expressed in vessels that generates harmful products as a result of its enzymatic activity. As a multifunctional enzyme, it is also involved in inflammation through its ability to bind and promote the transmigration of circulating leukocytes into inflamed tissues. Inflammation is present in different systemic and cerebral diseases, including stroke and Alzheimer’s disease (AD). These pathologies show important affectations on cerebral vessels, together with increased SSAO levels. This review summarizes the main roles of SSAO/VAP-1 in human physiology and pathophysiology and discusses the mechanisms by which it can affect the onset and progression of both stroke and AD. As there is an evident interrelationship between stroke and AD, basically through the vascular system dysfunction, the possibility that SSAO/VAP-1 could be involved in the transition between these two pathologies is suggested. Hence, its inhibition is proposed to be an interesting therapeutical approach to the brain damage induced in these both cerebral pathologies.

Novel starter cultures Virgibacillus spp. selected from grasshopper sub shrimp paste to inhibit biogenic amines accumulation

Controlling the content of biogenic amines (BAs) is critical to guarantee the safety of fermented aquatic products. The degradation characteristics and application potential of amine-negative starter cultures (Virgibacillus halodenitrificans CGMCC 1.18601: G25, Virgibacillus pantothenticus CGMCC 1.18602: G38) screened from grasshopper sub shrimp paste (Gssp) were studied. The enzymes of the two strains G25 and G38 that degrade BAs were amine oxidases (AOs) located on their respective cell membranes. The conditions that promoted the AO activity of Virgibacillus spp. were NaCl concentrations 5–10%, temperature 37 °C, pH 7.0 and ethanol concentrations 0–2%. Safety assessments (antibiotic susceptibility, biofilm activity and hemolytic activity) indicated that Virgibacillus spp. do not present a risk to human health, and this isolate can be confidently recommended as safe starter cultures for the food industry. Then, the two strains were cultured separately as starters and applied to the Gssp to analyze their influence on the flavor and quality of the product. As far as the bad flavors in Gssp such as sulfur-organic and sulf-chlor were concerned, the response values in the starter groups by G25 and G38 were significantly reduced by 39% and 65%, respectively. For the ability of strains to degrade BAs in Gssp, G25 degraded 11.1% of histamine, 11.3% of tyramine, 15.5% of putrescine and 4.1% of cadaverine; G38 significantly degraded 10.1% of histamine, 21.8% of tyramine, 18.1% of putrescine and 5.0% of cadaverine. These results indicated that the selected species could be used as starter cultures for the control of BA accumulation and degradation in Gssp.

Methylxanthines Inhibit Primary Amine Oxidase and Monoamine Oxidase Activities of Human Adipose Tissue

Background: Methylxanthines including caffeine and theobromine are widely consumed compounds and were recently shown to interact with bovine copper-containing amine oxidase. To the best of our knowledge, no direct demonstration of any interplay between these phytochemicals and human primary amine oxidase (PrAO) has been reported to date. We took advantage of the coexistence of PrAO and monoamine oxidase (MAO) activities in human subcutaneous adipose tissue (hScAT) to test the interaction between several methylxanthines and these enzymes, which are involved in many key pathophysiological processes. Methods: Benzylamine, methylamine, and tyramine were used as substrates for PrAO and MAO in homogenates of subcutaneous adipose depots obtained from overweight women undergoing plastic surgery. Methylxanthines were tested as substrates or inhibitors by fluorimetric determination of hydrogen peroxide, an end-product of amine oxidation. Results: Semicarbazide-sensitive PrAO activity was inhibited by theobromine, caffeine, and isobutylmethylxanthine (IBMX) while theophylline, paraxanthine, and 7-methylxanthine had little effect. Theobromine inhibited PrAO activity by 54% at 2.5 mM. Overall, the relationship between methylxanthine structure and the degree of inhibition was similar to that seen with bovine PrAO, although higher concentrations (mM) were required for inhibition. Theobromine also inhibited oxidation of tyramine by MAO, at the limits of its solubility in a DMSO vehicle. At doses higher than 12 % v/v, DMSO impaired MAO activity. MAO was also inhibited by millimolar doses of IBMX, caffeine and by other methylxanthines to a lesser extent. Conclusions: This preclinical study extrapolates previous findings with bovine PrAO to human tissues. Given that PrAO is a potential target for anti-inflammatory drugs, it indicates that alongside phosphodiesterase inhibition and adenosine receptor antagonism, PrAO and MAO inhibition could contribute to the health benefits of methylxanthines, especially their anti-inflammatory effects.

Oxidative Deamination of Emixustat by Human Vascular Adhesion Protein-1/Semicarbazide-Sensitive Amine Oxidase

Emixustat potently inhibits the visual cycle isomerase retinal pigment epithelium protein 65 (RPE65) to reduce the accumulation of toxic bisretinoid by-products that lead to various retinopathies. Orally administered emixustat is cleared rapidly from the plasma, with little excreted unchanged. The hydroxypropylamine moiety that is critical in emixustat's inhibition of RPE65 is oxidatively deaminated to three major carboxylic acid metabolites that appear rapidly in plasma. These metabolites greatly exceed the plasma concentrations of emixustat and demonstrate formation-rate-limited metabolite kinetics. This study investigated in vitro deamination of emixustat in human vascular membrane fractions, plasma, and recombinant human vascular adhesion protein-1 (VAP-1), demonstrating single-enzyme kinetics for the formation of a stable aldehyde intermediate (ACU-5201) in all in vitro systems. The in vitro systems used herein established sequential formation of the major metabolites with addition of assay components for aldehyde dehydrogenase and cytochrome P450. Reaction phenotyping experiments using selective chemical inhibitors and recombinant enzymes of monoamine oxidase, VAP-1, and lysyl oxidase showed that only VAP-1 deaminated emixustat. In individually derived human vascular membranes from umbilical cord and aorta, rates of emixustat deamination were highly correlated to VAP-1 marker substrate activity (benzylamine) and VAP-1 levels measured by enzyme-linked immunosorbent assay. In donor-matched plasma samples, soluble VAP-1 activity and levels were lower than in aorta membranes. A variety of potential comedications did not strongly inhibit emixustat deamination in vitro.

Blood-brain barrier dysfunction underlying Alzheimer's disease is induced by an SSAO/VAP-1-dependent cerebrovascular activation with enhanced Aβ deposition

Dysfunctions of the vascular system directly contribute to the onset and progression of Alzheimer's disease (AD). The blood-brain barrier (BBB) shows signs of malfunction at early stages of the disease. When Abeta peptide (Aβ) is deposited on brain vessels, it induces vascular degeneration by producing reactive oxygen species and promoting inflammation. These molecular processes are also related to an excessive SSAO/VAP-1 (semicarbazide-sensitive amine oxidase) enzymatic activity, observed in plasma and in cerebrovascular tissue of AD patients. We studied the contribution of vascular SSAO/VAP-1 to the BBB dysfunction in AD using in vitro BBB models. Our results show that SSAO/VAP-1 expression is associated to endothelial activation by altering the release of pro-inflammatory and pro-angiogenic angioneurins, most highly IL-6, IL-8 and VEGF. It is also related to a BBB structure alteration, with a decrease in tight-junction proteins such as zona occludens or claudin-5. Moreover, the BBB function reveals increased permeability and leukocyte adhesion in cells expressing SSAO/VAP-1, as well as an enhancement of the vascular Aβ deposition induced by mechanisms both dependent and independent of the enzymatic activity of SSAO/VAP-1. These results reveal an interesting role of vascular SSAO/VAP-1 in BBB dysfunction related to AD progression, opening a new window in the search of alternative therapeutic targets for fighting AD.

Simvastatin blocks soluble SSAO/VAP-1 release in experimental models of cerebral ischemia: Possible benefits for stroke-induced inflammation control

Beyond cholesterol reduction, statins mediate their beneficial effects on stroke patients through pleiotropic actions. They have shown anti-inflammatory properties by a number of different mechanisms, including the inhibition of NF-κB transcriptional activity and the consequent increase and release of adhesion molecules. We have studied simvastatin's effects on the vascular enzyme semicarbazide-sensitive amine oxidase/vascular adhesion protein 1 (SSAO/VAP-1), which is involved in stroke-mediated brain injury. SSAO/VAP-1 has leukocyte-binding capacity and mediates the expression of other adhesion proteins through signaling molecules generated by its catalytic activity. Our results indicate that soluble SSAO/VAP-1 is released into the bloodstream after an ischemic stimulus, in parallel with an increase in E-selectin and VCAM-1 and correlating with infarct volume. Simvastatin blocks soluble SSAO/VAP-1 release and prevents E-selectin and VCAM-1 overexpression as well. Simvastatin also effectively blocks SSAO/VAP-1-mediated leukocyte adhesion, although it is not an enzymatic inhibitor of SSAO in vitro. In addition, simvastatin-induced changes in adhesion molecules are greater in human brain endothelial cell cultures expressing SSAO/VAP-1, compared to those not expressing it, indicating some synergic effect with SSAO/VAP-1. We think that part of the beneficial effect of simvastatin in stroke is mediated by the attenuation of the SSAO/VAP-1-dependent inflammatory response.

Characterisation and application of Halomonas shantousis SWA25, a halotolerant bacterium with multiple biogenic amine degradation activity

Biogenic amines are identified as toxicological substances in foods and may have detrimental effects on consumers’ health. In recent years, the application of microorganisms that can degrade biogenic amines has become an emerging method for their reduction. The degradation characteristics and application potential of a salt-tolerant bacterium Halomonas shantousis SWA25 were investigated in this study. H. shantousis SWA25 exhibited degradation activity against eight biogenic amines at 10–40°C (optimum, 30–40°C) and pH 3.0–9.0 (optimum, 6.0–7.0) in the presence of 0–20% (w/v) NaCl (optimum, 0%). Specifically, H. shantousis SWA25 degraded all tryptamine (TRY) and tyramine (TYR) in 6 h, all phenethylamine (PHE) in 9 h, 66.7% of histamine (HIM), 52.4% of cadaverine (CAD), 48.0% of spermidine (SPD), 42.9% of putrescine (PUT) and 42.0% of spermine (SPM) in 20 h at 30°C and pH 7.0 with shaking at 120 r min−1. The enzymes from H. shantousis SWA25 responsible for degradation of biogenic amines were mainly amine oxidases located on the cell membrane. Further studies showed that H. shantousis SWA25 effectively degraded TRY, PHE, PUT, CAD, HIM and TYR in commercial fish sauce and soy sauce samples. Nevertheless, significant SPD and SPM degradation were not observed due to low initial concentrations. Therefore, H. shantousis SWA25 can be applied as a potential biogenic amines degradation bacterium in foods.

Protective effect of the multitarget compound DPH-4 on human SSAO/VAP-1-expressing hCMEC/D3 cells under oxygen-glucose deprivation conditions: an in vitro experimental model of cerebral ischaemia

BACKGROUND AND PURPOSE

Stroke and Alzheimer's disease (AD) are related pathologies in which the cerebrovascular system is involved. Plasma levels of semicarbazide-sensitive amine oxidase/vascular adhesion protein 1 (SSAO/VAP-1, also known as Primary Amine Oxidase -PrAO) are increased in both stroke and AD patients and contribute to the vascular damage. During inflammation, its enzymatic activity mediates leukocyte recruitment to the injured tissue, inducing damage in the blood-brain barrier (BBB) and neuronal tissue. We hypothesized that by altering cerebrovascular function, SSAO/VAP-1 might play a role in the stroke-AD transition. Therefore, we evaluated the protective effect of the novel multitarget-directed ligand DPH-4, initially designed for AD therapy, on the BBB.

EXPERIMENTAL APPROACH

A human microvascular brain endothelial cell line expressing human SSAO/VAP-1 was generated, as the expression of SSAO/VAP-1 is lost in cultured cells. To simulate ischaemic damage, these cells were subjected to oxygen and glucose deprivation (OGD) and re-oxygenation conditions. The protective role of DPH-4 was then evaluated in the presence of methylamine, an SSAO substrate, and/or β-amyloid (Aβ).

KEY RESULTS

Under our conditions, DPH-4 protected brain endothelial cells from OGD and re-oxygenation-induced damage, and also decreased SSAO-dependent leukocyte adhesion. DPH-4 was also effective at preventing the damage induced by OGD and re-oxygenation in the presence of Aβ as a model of AD pathology.

CONCLUSIONS AND IMPLICATIONS

From these results, we concluded that the multitarget compound DPH-4 might be of therapeutic benefit to delay the onset and/or progression of the neurological pathologies associated with stroke and AD, which appear to be linked.

Vascular cell lines expressing SSAO/VAP-1: a new experimental tool to study its involvement in vascular diseases

BACKGROUND INFORMATION

PrAO (primary amine oxidase), also known as SSAO (semicarbazide-sensitive amine oxidase)/VAP-1 (vascular adhesion protein-1), is an enzyme (EC 1.4.3.21) that is highly expressed in blood vessels and participates in many cell processes, including glucose handling or inflammatory leucocyte recruitment. High activity levels of this enzyme are associated with diabetes, atherosclerosis, AD (Alzheimer's disease) or stroke, among others, thus meaning that studies concerning SSAO as a therapeutic target are becoming more frequent. However, the study of this enzyme is difficult, owing to its loss of expression in cell cultures.

RESULTS

We have developed an endothelial cell line that stably expresses the human SSAO/VAP-1 to be used as endothelial cell model for the study of this enzyme. The transfected protein is mainly expressed as a dimer in the membrane of these cells, and we demonstrate its specific localization in the lipid rafts of endothelial cells. The protein shows levels of enzymatic activity and kinetic parameters comparable with those observed in vivo by the same cell type. The transfected SSAO/VAP-1 is also able to mediate the adhesion of leucocytes to the endothelium, a known function of this protein under inflammatory conditions. This distinctive function is not exerted by the SSAO/VAP-1 transfected protein in a smooth muscle cell line that expresses 3-fold higher protein levels. These differences have been widely reported to exist in vivo. Furthermore, using this endothelial cell model, we describe for the first time the involvement of the leucocyte-adhesion activity of SSAO/VAP-1 in the Aβ (amyloid β-peptide)-mediated pro-inflammatory effect.

CONCLUSIONS

The characterization of this new cell line shows the correct behaviour of the transfected protein and endorses the use of these cellular models for the in-depth study of the currently poorly understood functions of SSAO/VAP-1 and its involvement in the above-mentioned pathologies. This cellular model will be also useful for the evaluation of potential compounds that could modulate its activity for therapeutic purposes.

VAP-1/SSAO plasma activity and brain expression in human hemorrhagic stroke

BACKGROUND

Vascular adhesion protein-1 (VAP-1) is a cell surface and circulating enzyme that belongs to the semicarbazide-sensitive amine oxidase (SSAO) family, which oxidatively deaminates primary amines and is implicated in leukocyte extravasation. Our aim was to investigate the alteration of soluble VAP-1/SSAO activity in plasma samples after acute intracerebral hemorrhage (ICH) and its presence in human ICH brain tissue.

METHODS

VAP-1/SSAO activity was determined in plasma of 66 ICH patients and 58 healthy controls. In addition, we assessed the expression of VAP-1/SSAO in postmortem brain tissue from hemorrhagic stroke patients by Western blot and immunohistochemistry.

RESULTS

We observed significantly higher levels of plasma VAP-1/SSAO activity in patients with ICH compared to matched elderly controls (p = 0.001). Plasma VAP-1/SSAO activity <2.7 pmol/min·mg and baseline ICH volume <17 ml were independent predictors of neurological improvement after 48 h (OR 6.8, 95% CI 1.14-41.67, p = 0.035, and OR 10.64, 95% CI 1.1-100, p = 0.041, respectively), after adjustment for baseline stroke severity. We also found that membrane-bound VAP-1/SSAO levels were lower in the perihematoma region than in the corresponding contralateral brain areas of patients deceased due to ICH (p = 0.024).

CONCLUSIONS

Our data demonstrate that plasma VAP-1/SSAO activity is increased in ICH and predicts neurological outcome, suggesting a possible contribution of the soluble protein in secondary brain damage. Furthermore, anti-VAP-1/SSAO strategies might be a promising approach to prevent neurological worsening following ICH.

Plasma VAP-1/SSAO activity predicts intracranial hemorrhages and adverse neurological outcome after tissue plasminogen activator treatment in stroke

BACKGROUND AND PURPOSE

Vascular adhesion protein-1 (VAP-1) is a cell surface and circulating enzyme involved in recruitment of lymphocytes and neutrophils through its semicarbazide-sensitive amine oxidase (SSAO) activity. We aimed to study plasma VAP-1/SSAO activity in relation to the risk for intracranial bleeding complications in patients with stroke treated with tissue plasminogen activator (tPA), the greatest safety concern with this treatment.

METHODS

In 141 patients with ischemic stroke, we measured VAP-1/SSAO activity in plasma taken before tPA administration. Hemorrhagic events were classified according to brain CT criteria and functional outcomes evaluated using the National Institutes of Health Stroke Scale. We also assessed the potential therapeutic effect of blocking VAP-1/SSAO activity in a rat embolic stroke model treated with tPA.

RESULTS

We saw significantly higher levels of plasma VAP-1/SSAO activity in patients who subsequently experienced hemorrhagic transformation. Elevated plasma VAP-1/SSAO activity also predicted worse neurological outcome in these patients. In the rat model, we confirmed that use of the inhibitor semicarbazide prevented adverse effects caused by delayed tPA administration, leading to a smaller infarct volume.

CONCLUSIONS

Our data demonstrate that baseline VAP-1/SSAO activity predicts parenchymal hemorrhage after tPA, suggesting the safety of thrombolytic agents could be improved by considering VAP-1/SSAO activity. Furthermore, anti-VAP-1/SSAO drugs given with tPA may prevent neurological worsening in patients with ischemic stroke.

Drug interactions

Drugs for allergy are often taken in combination with other drugs, either to treat allergy or other conditions. In common with many pharmaceuticals, most such drugs are subject to metabolism by P450 enzymes and to transmembrane transport. This gives rise to considerable potential for drug-drug interactions, to which must be added consideration of drug-diet interactions. The potential for metabolism-based drug interactions is increasingly being taken into account during drug development, using a variety of in silico and in vitro approaches. Prediction of transporter-based interactions is not as advanced. The clinical importance of a drug interaction will depend upon a number of factors, and it is important to address concerns quantitatively, taking into account the therapeutic index of the compound.

Fluorinated phenylcyclopropylamines. Part 6: Effects of electron withdrawing or donating aryl substituents on the inhibition of tyramine oxidase from Arthrobacter sp. by diastereomeric 2-aryl-2-fluoro-cyclopropylamines

Diastereomeric arylcyclopropylamines substituted with fluorine in the 2-position and with electron donating or electron withdrawing groups at the aromatic ring were evaluated as inhibitors of microbial tyramine oxidase. The trans-isomers were consistently more potent inhibitors of the enzyme than the cis-isomers. Electron donating substituents increased the potency of tyramine oxidase inhibition, while electron withdrawing substituents decreased the activity. The results obtained are discussed in terms of pK(a) and log D values of the inhibitors as well as the mechanism of action of tranylcypromines and the geometry of the active site of the enzyme.

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.

SSAO/VAP-1 protein expression during mouse embryonic development

SSAO/VAP-1 is a multifunctional enzyme depending on in which tissue it is expressed. SSAO/VAP-1 is present in almost all adult mammalian tissues, especially in highly vascularised ones and in adipocytes. SSAO/VAP-1 is an amine oxidase able to metabolise various endogenous or exogenous primary amines. Its catalytic activity can lead to cellular oxidative stress, which has been implicated in several pathologies (atherosclerosis, diabetes, and Alzheimer's disease). The aim of this work is to achieve a study of SSAO/VAP-1 protein expression during mouse embryogenesis. Our results show that SSAO/VAP-1 appears early in the development of the vascular system, adipose tissue, and smooth muscle cells. Moreover, its expression is strong in several epithelia of the sensory organs, as well as in the development of cartilage sites. Altogether, this suggests that SSAO/VAP-1 enzyme could be involved in the differentiation processes that take place during embryonic development, concretely in tissue vascularisation.

Purification and characterization of a copper-containing amine oxidase from Mycobacterium sp. strain JC1 DSM 3803 grown on benzylamine

A bacterial semicarbazide-sensitive amine oxidase (SSAO) was purified and characterized from Mycobacterium sp. strain JC1 DSM 3803 grown on benzylamine. During the purification procedures, the enzyme was tending to aggregate and exhibited heterogeneity in native PAGE. The heterogeneous forms having amine oxidase (AO) activity could be separated by their native molecular weights using gel-filtration chromatography. Most of the AOs behaved as dimers (M(r) 150,000) composed of a 75-kDa subunit, but some aggregated to form tetramers (M(r) 300,000). Besides their native molecular weight, subunit composition and V(max) value, both forms (dimer and tetramer) have almost identical biochemical properties (e.g. subunit size, optimum pH and temperature, activation energy, K(m) value on benzylamine, substrate and inhibitor specificities). When AO activity was observed by activity staining, the best-oxidized substrate was benzylamine, although the AO also oxidized tyramine and histamine. The AO was strongly inhibited by semicarbazide and isoniazid, but KCN did not affect its activity. The purified enzyme was shown to contain 2.39 mol of copper per mole of subunit, but there were no evidences of topaquinone co-factor involvement, when tested by absorption spectrum analysis and redox-cycling staining for quinoprotein detection.

Inhibition of amine oxidases by the histamine-1 receptor antagonist hydroxyzine

The effects of the drug hydroxyzine on the activities of the rat liver monoamine oxidases (EC 1.4.3.6; MAO) and the membrane-bound and soluble forms of bovine semicarbazide-sensitive amine oxidase (EC 1.4.3.6; SSAO) were studied. Hydroxyzine was found to be a competitive inhibitor of MAO-B (Ki - 38 microM), whereas it had a low potency towards MAO-A (IC50 > 630 microM). Although it was a relatively potent competitive inhibitor of bovine plasma SSAO (Ki approximately 1.5 microM), it was a weak inhibitor of the membrane-bound form of the enzyme from bovine lung (IC50 approximately 1 mM). These findings extend our knowledge of the drug binding capabilities of the amine oxidases and suggest that these interactions may contribute to the complex actions of this drug.

Semicarbazide-sensitive amine oxidase (SSAO) and its possible contribution to vascular damage in Alzheimer's disease

One of the key pathological features of the progressive neurodegenerative disorder Alzheimer's disease (AD) is cerebral amyloid angiopathy (CAA). CAA is present in most cases of AD, and it is characterized by the deposition of beta-amyloid (Abeta) in brain vessels, inducing the degeneration of vascular smooth muscle cells and endothelial cells. Herein we report that semicarbazide-sensitive amine oxidase (SSAO) is overexpressed in cerebrovascular tissue of patients with AD-CAA, and that it colocalizes with beta-amyloid deposits. This over-expression correlates with high SSAO activity in plasma of severe AD patients. In addition, we have observed that the catalytic activity of SSAO is able to induce apoptosis in smooth muscle cells in vitro. Taken together, these results allow us to postulate that SSAO may contribute to the vascular damage associated to AD.

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.

The role of amine oxidases in xenobiotic metabolism

The amine oxidases of mammalian tissues are a heterogeneous family of enzymes that metabolise various monoamines, diamines and polyamines produced endogenously, or being absorbed as dietary or xenobiotic substances. The heterogeneous class of amine oxidases can be divided on an arbitrary basis of the chemical nature of their cofactors into two types. Monoamine oxidase (MAO) and an intracellular form of polyamine oxidase (PAO) contain flavin adenine dinucleotide (FAD) as their cofactor, whereas a second group of amine oxidases without FAD contain a cofactor possessing one or more carbonyl groups, making them sensitive to inhibition by carbonyl reagents such as semicarbazide; this group includes semicarbazide-sensitive amine oxidase (SSAO) and the connective tissue enzyme, lysyl oxidase. This article focuses on the general aspects of MAO's contribution to the metabolism of foreign toxic substances including toxins and illegal drugs. Another main objective of this review is to discuss the properties of PAO and SSAO and their involvement in the metabolism of xenobiotics.

Vascular adhesion protein-1 plays an important role in postischemic inflammation and neuropathology in diabetic, estrogen-treated ovariectomized female rats subjected to transient forebrain ischemia

Endothelial vascular adhesion protein-1 (VAP-1) facilitates leukocyte adhesion and infiltration. This relates partly to the function of VAP-1 as a semicarbazide-sensitive amine oxidase (SSAO). We examined the effects of VAP-1/SSAO inhibition [via LJP-1207 (N'-(2-phenyl-allyl)-hydrazine hydrochloride)] on pial venular leukocyte adhesion and infiltration (at 2-10 h of reperfusion) and neuropathology (at 72 h of reperfusion) after transient forebrain ischemia (TFI). A model associated with increased postischemic inflammation was used-i.e., diabetic ovariectomized (OVX) female rats given chronic estrogen replacement therapy (ERT). We compared rats treated, either at the onset or at 6 h of reperfusion, with saline or LJP-1207. Additional rats, rendered neutropenic 24 h before TFI, were studied. In saline-treated controls, intravascular accumulation of adherent leukocytes gradually increased, reaching 15 to 20% of the venular area, at which point neutrophil infiltration commenced (at approximately 6 h). In the rats given LJP-1207 at the onset of reperfusion, limited neutrophil adhesion ( approximately 5% maximum) and no infiltration were observed. These results generally paralleled those in neutropenic rats. In rats treated at 6 h of reperfusion, the pattern of neutrophil adhesion was similar to that of the saline-treated group up to 6 h, but further infiltration was essentially prevented. Neurologic outcomes and histopathology were similar to one another in the LJP-1207-treated and neutropenic groups and significantly improved over those in saline-treated controls. Thus, VAP-1-mediated post-TFI leukocyte adhesion/infiltration in diabetic OVX females given chronic ERT contributes substantially to neuropathology. One implication is that specifically preventing leukocyte infiltration provides a substantial measure of neuroprotection. This could explain the finding of LJP-1207 having at least a 6-h therapeutic window in this model.

Production of a truncated soluble human semicarbazide-sensitive amine oxidase mediated by a GST-fusion protein secreted from HEK293 cells

Elevated levels of semicarbazide-sensitive amine oxidase (SSAO) activity have been observed in several human conditions such as congestive heart failure, diabetes mellitus, and inflammation. The reactive aldehydes and hydrogen peroxide produced by SSAO have been suggested to contribute to the progression of vascular complications associated with these conditions. In addition, SSAO activity has been shown to be involved in the leukocyte extravasation process at sites of inflammation. To facilitate characterization and development of specific and selective inhibitors of SSAO, we have developed a method for production of recombinant human SSAO. The extracellular region (residues 29-763) of human SSAO was expressed in HEK293 cells in fusion with a mutated Schistosoma japonicum glutathione S-transferase (GST) and secreted to the culture medium. The mutGST-SSAO fusion protein was purified in a single step by glutathione-affinity chromatography followed by site-specific cleavage using a GST-3C protease fusion protein to remove the mutGST fusion partner. A second glutathione-affinity chromatography step was then used to capture both the mutGST fusion partner and the GST-3C protease, resulting in milligram quantities of pure, enzymatically active, and soluble recombinant human SSAO.

Anti-inflammatory effects of inhibiting the amine oxidase activity of semicarbazide-sensitive amine oxidase

Human semicarbazide-sensitive amine oxidase (SSAO) or vascular adhesion protein-1 (VAP-1) is a copper-containing amine oxidase (AOC3, EC 1.4.3.6) that has both enzymatic and adhesive function. SSAO catalyzes the oxidative deamination of primary amines, resulting in the formation of the corresponding aldehyde and release of hydrogen peroxide and ammonia. Membrane-bound SSAO is an inflammation-inducible endothelial cell adhesion molecule that mediates the interaction between leukocytes and activated endothelial cells in inflamed vessels. Both the direct adhesive and enzymatic functions seem to be involved in the adhesion cascade. LJP 1207 [N'-(2-phenyl-allyl)-hydrazine hydrochloride] is a potent (human SSAO IC(50) = 17 nM), selective, and orally available SSAO inhibitor that blocks both the enzymatic and adhesion functions of SSAO/VAP-1. In a mouse model of ulcerative colitis, LJP 1207 significantly reduces mortality, loss of body weight, and colonic cytokine levels. Quantitative histopathological assessment of colitis activity in this model showed a highly significant suppression of inflammation, injury, and ulceration scores in the animals treated with the SSAO/VAP-1 inhibitor. LJP 1207 also reduced serum levels of tumor necrosis factor-alpha and interleukin 6 in lipopolysaccharide (LPS)-challenged mice and prolonged survival post-LPS-induced endotoxemia. Therapeutic and prophylactic administration of LJP 1207 in the rat carrageenan footpad model also markedly inhibited swelling and inflammation. Overall, the data suggest that small molecule SSAO/VAP-1 inhibitors may provide clinical benefit in the treatment of acute and chronic inflammatory diseases.

Molecular cloning and characterization of rat semicarbazide-sensitive amine oxidase

Semicarbazide-sensitive amine oxidase (SSAO) (EC 1.4.3.6) is widely distributed in nature and catalyzes the oxidative deamination of primary amines. Although SSAO full-length cDNA sequences have been reported for some mammalian species, only a partial 5'-terminal sequence has been confirmed in the rat. In this study we isolated full-length SSAO cDNA from rat aorta and examined its mRNA expression in various rat tissues by real-time PCR, as well as the subcellular and tissue distributions of SSAO activity. The deduced amino acid sequence showed 91% and 80% identity with mouse and human SSAO, respectively. The mRNA was expressed in many rat tissues. Those findings were supported by the broad distribution of SSAO in the body. Thus, a high level of SSAO was shown in adipocytes by both mRNA expression and enzyme activity measurement. The results suggest that SSAO may play an important role in the degradation of biologically active amines in adipocytes.

Characterization of semicarbazide-sensitive amine oxidase in human subcutaneous adipocytes and search for novel functions

Numerous studies have characterized semicarbazide-sensitive amine oxidase activity (SSAO) in rat fat cells but this oxidase is scarcely documented in human adipose tissue. Our aim was to further characterize SSAO in human adipose tissue (activity, mRNA and protein abundance) and to investigate whether SSAO activity can interplay with glucose and lipid metabolism in human adipocytes via the hydrogen peroxide it generates. Polyclonal antibodies directed against bovine lung SSAO allowed the detection of a substantial amount of immunoreactive protein (apparent molecular mass 100 kDa) in human subcutaneous adipocytes from either mammary or abdominal fat depots. A 4-kb mRNA was detected in fat depots using a cDNA probe designed from the placenta SSAO sequence. Almost all the oxidation of benzylamine found in adipose tissue homogenates was due to fat cells and was located in the adipocyte membrane fraction. The oxidation of benzylamine and methylamine were similar and totally inhibited by semicarbazide or hydralazine but resistant to pargyline. Histamine was poorly oxidized. Benzylamine and methylamine dose-dependently stimulated glucose transport in intact adipocytes. This insulin-like effect of amines did not increase in the presence of 0.1 mM vanadate but was inhibited by semicarbazide and antioxidants. Benzylamine and methylamine also exhibited antilipolytic effects, with complete inhibition of lipolysis at 1 mM. These results show that fat cells from non-obese subjects express a membrane-bound SSAO which readily oxidizes exogenous amines, generates hydrogen peroxide and exerts short-term insulin-like actions on glucose and lipid metabolism.

Localization of monoamine oxidase A and B and semicarbazide-sensitive amine oxidase in human peripheral tissues

Monoamine oxidase (MAO) A and B and semicarbazide-sensitive amine oxidase (SSAO) localizations in peripheral human tissues were compared by immunohistochemistry. The primary antibodies used were mouse monoclonal anti-human MAO-A (6G11/E1) and anti-human MAO-B (3F12/G10/2E3) and a rabbit polyclonal anti-bovine SSAO antibody. Immunoreactivities of the samples, obtained from 6 routine autopsy cases, showed different distributions in the tissues studied (heart, lung, duodenum, liver, pancreas, spleen, thyroid gland, adrenal gland and kidney). The relative MAO-A, MAO-B and SSAO distributions indicated a widespread distribution of these enzymes in the human body that is characterized by a matching cellular pattern in only few tissues. These differences suggest that each amine oxidase may play a specific function in, at least some, peripheral tissues.

Long-term high copper intake: effects on indexes of copper status, antioxidant status, and immune function in young men

BACKGROUND

Short-term high copper intake does not appear to affect indexes of copper status or functions related to copper status, but the effects of long-term high copper intake are unknown.

OBJECTIVE

A study was conducted in men to determine the effect of long-term high copper intake on indexes of copper status, oxidant damage, and immune function.

DESIGN

Nine men were confined to a metabolic research unit (MRU) for 18 d and were fed a 3-d rotating menu providing an average of 1.6 mg Cu/d. The men continued the study under free-living conditions for 129 d and supplemented their usual diets with 7 mg Cu/d. The men then returned to the MRU for 18 d of the same diet as during the first period, except that copper intake was 7.8 mg/d. Plasma copper, ceruloplasmin activity, ceruloplasmin protein, plasma malondialdehyde, benzylamine oxidase activity, erythrocyte superoxide dismutase, hair copper, urinary copper, and urinary thiobarbituric acid-reactive substances were measured during each MRU period.

RESULTS

Ceruloplasmin activity, benzylamine oxidase, and superoxide dismutase were significantly higher at the end of the second MRU period than at the end of the first. Urinary copper excretion, hair copper concentrations, and urinary thiobarbituric acid-reactive substances were significantly higher during the second MRU period than during the first. Polymorphonuclear cell count, the percentage of white blood cells, lymphocyte count, and interleukin 2R were affected by copper supplementation. Antibody titer for the Beijing strain of influenza virus was significantly lower in supplemented subjects after immunization than in unsupplemented control subjects.

CONCLUSIONS

Under highly controlled conditions, long-term high copper intake results in increases in some indexes of copper status, alters an index of oxidant stress, and affects several indexes of immune function. The physiologic implications of these changes are unknown.

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.

Overexpression of semicarbazide-sensitive amine oxidase in human myopathies

Oxidative stress has been implicated in the pathogenesis of several muscle diseases. Semicarbazide-sensitive amine oxidase (SSAO) metabolizes oxidative deamination of primary aromatic and aliphatic amines. In the oxidative reactions, amine substrates are converted into the aldehyde, followed by the production of ammonia and H(2)O(2). Although normal levels in muscle are very low, SSAO is expressed in almost all mammalian tissues. In this study, we examined the possible implication of SSAO as an additional source of oxidative stress in the pathogenesis of muscle disorders. The expression of SSAO was examined immunohistochemically in muscle biopsy specimens from patients with inclusion-body myositis (IBM; n = 5), desmin-related myopathy (DRM; n = 3), dermatomyositis (n = 3), granulomatous (sarcoid) myopathy (n = 2), muscle denervation-reinnervation (n = 3), and rhabdomyolysis (n = 2), as well as from control subjects (n = 3). Strong SSAO immunoreactivity was present in vacuolated and nonvacuolated fibers in IBM, in abnormal fibers in DRM, and in degenerating and regenerating fibers in dermatomyositis and rhabdomyolysis. In addition, SSAO overexpression was observed in muscle fibers adjacent to granulomas in sarcoid myopathy. These results suggest that SSAO is a source of oxidative stress in diseased human skeletal muscle and that it contributes to oxidative stress-induced damage in various inflammatory and other myopathies. Alternatively, the expression of SSAO in muscle fibers may be a consequence of muscle fiber injury.

Synthesis of 4-methyl-thio-phenyl-propylamine and the evaluation of its interaction with different amine oxidases

A new molecule, the 4-methyl-thio-phenyl-propylamine (PrNH(2)) was synthesized and its biological interaction with different amine oxidases such as semicarbazide sensitive amine oxidase (SSAO) [E.C.1.4.3.6], and monoamine oxidase [E.C.1.4.3.4] under its two isoforms, MAO A and MAO B, has been assessed. The substrate specifities of MAO and SSAO overlap to some extent. In this context, the search of new molecules, able to discriminate between these different amine oxidases is very important as it will allow greater elucidation of the SSAO's role in physiological and pathological conditions. We report for the first time, the synthesis and evaluation of a new molecule which has a high affinity towards the SSAO family of enzymes, more so than previously described and furthermore an ability to discriminate between the different amine oxidases.

Oxidative stress-dependent inhibition of yeast cell growth by farnesylamine and its possible relation to amine oxidase in the mitochondrial fraction

Among various analogs of the isoprenoid farnesol (FOH), farnesylamine (FNH2) inhibited the growth of the budding yeast Saccharomyces cerevisiae by accelerating cellular reactive oxygen species (ROS) generation. Unlike the case with FOH, however, FNH2 did not cause mitochondrial transmembrane potential (mtDeltaPsi) hyperpolarization so that FNH2-treated cells were not protected against ROS production by inhibiting the proton pumping function of mitochondrial F(O)F1-ATPase. FNH2 promoted ROS generation even in cells of a respiration-deficient mutant, indicating a yeast metabolic pathway other than mitochondrial electron transport as the origin of ROS. FNH2 oxidase activity was detected in the yeast mitochondrial fraction, which produces hydrogen peroxide (H2O2) in the reaction with either FNH2 or geranylgeranylamine (GGNH2), in addition to polyamine oxidase activity specific for spermine. GGNH2 also exhibited the growth inhibitory effect with the accompanying induction of ROS generation, while such an activity was not detected with any of the polyamines tested or geranylamine. FNH2 oxidase, which was sensitive to a typical copper-chelating agent, diethyldithiocarbamic acid (DDC), could be solubilized with Triton X-100, and detected as a single band upon activity staining with FNH2 but not with spermine in polyacrylamide gel electrophoresis. FNH2-treated cells were partly protected against ROS production by the additional supplementation of DDC in the medium. Our results suggest the involvement of H2O2 production due to direct oxidation of FNH2 by copper amine oxidase in oxidative stress-dependent inhibition of yeast cell growth.

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.

Activation of human lung semicarbazide sensitive amine oxidase by a low molecular weight component present in human plasma

Semicarbazide-sensitive amine oxidase (SSAO) encodes a wide family of enzymes named E.C.1.4.3.6 [amine:oxygen oxidoreductase (deaminating) (copper containing)] that metabolises primary aliphatic and aromatic amines. It is present in almost all vascularised and nonvascularised mammalian tissues, and it is also present in soluble form in plasma. SSAO appears to show different functions depending on the tissue where it is expressed. Here we describe, for the first time, the activation of the SSAO from human lung by human plasma. The extent of activation was greater when the human plasma came from diabetic and heart infarcted patients. A kinetic mechanism of such effect is proposed. The activation was lost after the plasma was dialysed, indicating a low molecular weight component (MW <3800 Da) to be responsible. The activator component is heat stable and resistant to proteolysis by chymotrypsin and trypsin and also resistant to perchloric acid treatment. However, treatment with 35% formic acid, completely abolished activation, suggesting involvement of lipid material. The possibility of that lysophosphatidylcholine (LPC), an amphiphilic phospholipid derived from the phosphatidylcholine, the major component in plasma accumulated in pathological conditions, was studied. LPC was shown to behave as a "competitive activator" of human lung SSAO at concentrations below its critical micellar concentration (CMC value=50 microM). Thus LPC may be a component of the SSAO activatory material present in human plasma.

Plasma amine oxidase: a postulated cardiovascular risk factor in nondiabetic obese patients

Increased activity of semicarbazide-sensitive plasma amine oxidase (SSAO), an enzyme converting various amines, has been implicated in the generation of endothelial damage through formation of cytotoxic reaction products. We investigated if SSAO activity is elevated in morbidly obese patients, which might contribute to the increased cardiovascular risk associated with obesity. SSAO activity was determined in 74 nondiabetic, obese patients (median body mass index [BMI]: 42.9 kg/m(2)) and in 32 healthy, non-obese controls (median BMI: 23.3 kg/m(2)) using a radiometric assay based on the conversion of [(14)C]benzylamine. SSAO and parameters of glucose and lipid metabolism were compared for subgroups of obese patients with normal (n = 49) and impaired (n = 25) glucose tolerance using nonparametric statistical tests. Median SSAO activity was 434 microU/mL in obese patients, which was significantly higher than in healthy, non-obese controls (median SSAO activity: 361 microU/mL). Median SSAO activity in patients with normal and impaired glucose tolerance was 423 and 464 microU/mL, respectively. SSAO activity was not correlated with any other clinical or laboratory parameters characteristic of the metabolic alterations associated with obesity. Elevated SSAO activity is found in nondiabetic, morbidly obese patients and might be an interesting independent risk factor for obesity-related cardiovascular morbidity. Long-term follow-up of SSAO and its possible role in pathogenic events is warranted since intervention with specific SSAO inhibitors is available.

Autonomous histamine metabolism in human melanoma cells

Melanoma cells constitutively produce various cytokines as well as growth factors and express their corresponding receptors. Exogenous histamine is known to be a growth factor for some tumours while in other cases histamine inhibits tumour growth, and acts on G protein-coupled H1 and H2 histamine receptors. In previous studies we have detected the expression of the l-histidine decarboxylase (HDC) gene and the presence of HDC protein in human melanoma cell lines. In the present study, the activities of the histamine-forming enzyme HDC and of the degrading enzymes diamine oxidase (DAO) and histamine N-methyltransferase (HNMT) were measured in primary (WM35 and WM983) and metastatic (M1 and HT168) human melanoma cell lines. HDC activity was found in WM35 and WM983 cell lines, while detectable HNMT activity was measured in WM983, M1 and HT168 lines. In contrast, DAO showed very low activity in melanoma cell lines. Melanoma cells release a detectable amount of histamine into the medium without external stimuli. These findings support the possibility of autonomous histamine metabolism in melanoma cells. Our results suggest that not only exogenous histamine but also histamine produced and released by the melanoma cells and acting as an autocrine and paracrine factor may influence cell proliferation and modulate the in situ immune response of the host.

The inhibition of semicarbazide-sensitive amine oxidase by aminohexoses

Semicarbazide-sensitive amine oxidase (EC 1.4.3.6; amine:oxygen oxidoreductase (deaminating) (copper-containing); SSAO) is a multifunctional protein. It acts under inflammatory conditions as a vascular-adhesion protein (VAP-1), mediating the adhesion of lymphocytes to vascular endothelial cells. The relationships, if any, between this adhesion function and the enzymatic functions (amine-substrate specificity and catalysis) of SSAO have not yet been defined. Since cell surface amino sugars and their derivatives are known to be involved in cell-to-cell recognition, we have investigated their possible effects on the enzyme activity of SSAO. The aminohexoses galactosamine, glucosamine and mannosamine were not oxidatively deaminated by SSAO. However, their presence during the assay of benzylamine oxidation resulted in a time-dependent inhibition. This inhibition was shown to follow saturation kinetics with respect to hexosamine concentration. Although time-dependent, the inhibition of SSAO activity was found to be reversible by dilution. In contrast, there is no such inhibition when the N-acetylamino sugar derivatives or the parent sugars (galactose, glucose and mannose) replaced the amino sugars in the reaction mixture. These results suggest that the interactions between SSAO and aminohexoses are specific and, therefore, that the cell-adhesion functions and amine-recognition functions of VAP-1/SSAO may be interlinked.

Regulation of semicarbazide-sensitive amine oxidase expression by tumor necrosis factor-alpha in adipocytes: functional consequences on glucose transport

Membrane-associated semicarbazide-sensitive amine oxidase (SSAO) is mainly present in the media of aorta and in adipose tissue. Recent works have reported that SSAO activation can stimulate glucose transport of fat cells and promote adipose conversion. In this study, the murine 3T3-L1 preadipose cell line was used to investigate SSAO regulation by tumor necrosis factor-alpha (TNF-alpha), a cytokine that is synthesized in fat cells and known to be involved in obesity-linked insulin resistance. SSAO mRNA and protein levels, and enzyme activity were decreased by TNF-alpha in a dose- and time-dependent manner, without any change of SSAO affinity for substrates or inhibitors. SSAO inhibition caused by TNF-alpha was spontaneously reversed along the time after TNF-alpha removal. The decrease in SSAO expression also occurred in white adipose tissue of C57BL/6 mice treated with mTNF-alpha. Overall, we demonstrated that reduction in SSAO expression induced by the cytokine had marked repercussions on amine-stimulated glucose transport, in a dose- and time-dependent manner. This effect was more pronounced than the inhibiting effect of TNF-alpha on insulin-stimulated glucose transport. Moreover, the peroxisome proliferator-activated receptor gamma agonists thiazolidinediones did not reverse either TNF-alpha effect on amine-sensitive glucose transport or the inhibition of SSAO activity, whereas they antagonized TNF-alpha effects on insulin-sensitive glucose transport. These results demonstrate that TNF-alpha can strongly down-regulate SSAO expression and activity, and through this mechanism can dramatically reduce amine-stimulated glucose transport. This suggests a potential role of this regulatory process in the pathogenesis of glucose homeostasis dysregulations observed during diseases accompanied by TNF-alpha overproduction, such as cachexia or obesity.

Homocysteine promotes the LDL oxidase activity of ceruloplasmin

Ceruloplasmin (CP) oxidises low density lipoprotein (LDL). The oxidising potential depends on the formation of Cu(+)-CP which is redox-cycled during oxidation. Homocysteine (HCY) reduces free Cu(2+), potentiating its cell-damaging property. We show that HCY enhanced LDL oxidation by CP, but did not activate the LDL oxidising potential of Cu(2+)-diamine oxidase. Selective removal of the redox-active Cu(2+) abolished the LDL oxidase activity of CP. However, HCY partially restored the LDL oxidase activity of redox-copper depleted CP, indicating that the remaining six copper atoms in CP may also be involved in the process. Spectroscopic and oxidation inhibition studies using the Cu(+)-reagent bathocuproine revealed that HCY induced Cu(+)-CP formation, thus promoting its LDL oxidase activity.

Activity staining of plasma amine oxidase after polyacrylamide gel electrophoresis and its application to natural inhibitor screening

Plasma amine oxidase (plasma AO, EC 1.4.3.6) is a copper-containing AO which converts benzylamine (BZ) to benzaldehyde, generating hydrogen peroxide and ammonia. The peroxidase was used as an ancillary enzyme to couple hydrogen peroxide to 3-amino-9-ethylcarbazole (AEC) to achieve plasma AO activity after electrophoresis on native polyacrylamide gels. It was confirmed that plasma AO is inhibited by semicarbazide but neither by clorgyline nor by deprenyl. We also used plasma AO activity staining for the screening of natural inhibitors. This fast and sensitive method can be used in the process of plasma AO purification, characterization, and inhibitor screening.

Immunolocalization of semicarbazide-sensitive amine oxidase in human dental pulp and its activity towards serotonin

The semicarbazide-sensitive amine oxidase (EC 1.4.3.6; SSAO) from crude homogenates of human dental pulp was shown to catalyse the oxidative deamination of 5-hydroxytryptamine (serotonin; 5-HT) with a K(m) of 318+/-52 microM. In this respect the human enzyme resembles that in pig dental pulp, but differs from SSAO in all other tissues studied, which are inactive towards 5-HT. A method is described for obtaining intact dental pulp in which the anatomical details are preserved. Extracted teeth are frozen in dry ice and later defrosted rapidly before being fractured in a mechanical vice, facilitating pulp removal. Immunohistochemistry showed SSAO in the odontoblast layer, nerve fibres and blood vessels. The presence of SSAO in nerves in dental pulp appears to be unique. Tryptophan hydroxylase, a key enzyme in 5-HT synthesis, was also demonstrated in nerves and the odontoblast layer of human dental pulp.

Overexpression of semicarbazide sensitive amine oxidase in the cerebral blood vessels in patients with Alzheimer's disease and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy

Semicarbazide sensitive amine oxidase (SSAO) metabolizes oxidative deamination of primary aromatic and aliphatic amines, and, in the brain, it is selectively expressed in blood vessels. SSAO expression is examined, by immunohistochemistry with a purified polyclonal antibody to SSAO from bovine lung, in the brains of subjects with Alzheimer disease (AD; n=10), cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL; n=2), and age-matched controls (n=8). SSAO immunoreactivity is restricted to meningeal and parenchymal blood vessels in control and diseased brains. Yet, a marked and selective increase in SSAO immunoreactivity occurs in association with betaA4 vascular amyloid deposits in patients with AD, and in the vicinity of the typical granular deposits in the blood vessels of gray and white matter in patients with CADASIL. Oxidative deamination of primary aromatic and aliphatic amines by SSAO produces ammonia, hydrogen peroxide and the corresponding aldehyde. Moreover, increased SSAO immunoreactivity is associated with increased Cu/Zn superoxide dismutase 1 expression restricted to abnormal blood vessels in diseased brains. Therefore, it is suggested that increased SSAO expression is a source of oxidative stress in the blood vessel wall in AD and CADASIL.

Semicarbazide-sensitive amine oxidase in vascular smooth muscle cells: differentiation-dependent expression and role in glucose uptake

Cultured vascular smooth muscle cells (VSMCs) derived from rat aortic media were used to examine semicarbazide-sensitive amine oxidase (SSAO) expression during their differentiation process. In a defined serum-free medium permissive for in vitro VSMC differentiation, there was a large increase in SSAO mRNA and protein levels and in the related enzyme activity during the course of cell culture. This pattern of expression was concomitant with that of some smooth muscle-specific mRNA markers of differentiation. mRNAs in differentiated cultured VSMCs were comparable to those detected in total aorta and media. Pharmacological properties of SSAO present in VSMCs were similar to enzyme activities previously described in the aortic wall. In this model, we also demonstrated that methylamine, a physiological substrate of SSAO, activated 2-deoxyglucose transport in a time- and dose-dependent manner. This methylamine effect was reproduced by other SSAO substrates and was prevented by the SSAO inhibitor semicarbazide. It was antagonized in the presence of catalase, suggesting that SSAO-activated glucose transport was mediated through H(2)O(2) production. In addition, methylamine promoted glucose transporter 1 accumulation at the cell surface. Thus, we demonstrate for the first time the differentiation-dependent expression of SSAO in VSMCs and its role in the regulation of VSMC glucose uptake.

Oxygen dependency of monoamine oxidase activity in the intact lung

Hydrogen peroxide generated by monoamine oxidase (MAO)-mediated deamination of biogenic amines has been implicated in cell signaling and oxidative injury. Because the pulmonary endothelium is a site of metabolism of monoamines present in the venous return, this brings into question a role for MAO in hyperoxic lung injury. The objective of this study was to evaluate the O(2) dependency of the MAO reaction in the lung. To this end, we measured the pulmonary venous effluent concentrations of the MAO substrate [(14)C]phenylethylamine and its metabolite [(14)C]phenylacetic acid after the bolus injection of either phenylethylamine or phenylacetic acid into the pulmonary artery of perfused rabbit lungs over a range of PO(2) values from 16 to 518 Torr. The apparent Michaelis constant for O(2) was approximately 18 microM, which is more than an order of magnitude less that measured for purified MAO. The results suggest a minimal influence of high O(2) on MAO activity in the normal lung and demonstrate the importance of measuring reaction kinetics in the intact organ.

Semicarbazide-sensitive amine oxidase activation promotes adipose conversion of 3T3-L1 cells

Semicarbazide-sensitive amine oxidase (SSAO) is an amine oxidase related to the copper-containing amine oxidase family. The tissular form of SSAO is located at the plasma membrane, and is mainly expressed in vascular smooth muscle cells and adipocytes. Recent studies have suggested that SSAO could activate glucose transport in fat cells. In the present work, we investigated the potential role of a chronic SSAO activation on adipocyte maturation of the 3T3-L1 pre-adipose cell line. Exposure of post-confluent 3T3-L1 pre-adipocytes to methylamine, a physiological substrate of SSAO, promoted adipocyte differentiation in a time- and dose-dependent manner. This effect could be related to SSAO activation, since it was antagonized in the presence of the SSAO inhibitor semicarbazide, but not in the presence of the monoamine oxidase inhibitor pargyline. In addition, methylamine-induced adipocyte maturation was mimicked by 3T3-L1 cell treatment with other SSAO substrates. Finally, the large reversion of methylamine action by catalase indicated that hydrogen peroxide generated by SSAO was involved, at least in part, in the modulation of adipocyte maturation. Taken together, our results suggest that SSAO may contribute to the control of adipose tissue development.

Amine oxidase substrates mimic several of the insulin effects on adipocyte differentiation in 3T3 F442A cells

We have previously reported that substrates of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO) exert short-term insulin-like effects in rat adipocytes, such as stimulation of glucose transport. In the present work, we studied whether these substrates could also mimic long-term actions of insulin. Adipose differentiation of 3T3 F442A cells, which is highly insulin-dependent, served as a model to test the effects of sustained administration of amine oxidase substrates. Daily treatment of confluent cells with 0.75 mM tyramine (a substrate of MAO and SSAO) or benzylamine (a substrate of SSAO) over 1 week caused the acquisition of typical adipocyte morphology. The stimulation of protein synthesis and triacylglycerol accumulation caused by tyramine or benzylamine reached one half of that promoted by insulin. This effect was insensitive to pargyline (an MAO inhibitor), but was inhibited by semicarbazide (an SSAO inhibitor) and by N-acetylcysteine (an antioxidant agent), suggesting the involvement of the H(2)O(2) generated during SSAO-dependent amine oxidation. Chronic administration of amine oxidase substrates also induced the emergence of adipose conversion markers, such as aP2, glycerol-3-phosphate dehydrogenase, the glucose transporter GLUT4, and SSAO itself. Moreover, cells treated with amines acquired the same insulin sensitivity regarding glucose transport as adipocytes classically differentiated with insulin. In all, most of the adipogenic effects of amines were additive to insulin. Our data reveal that amine oxidase substrates partially mimic the adipogenic effect of insulin in cultured preadipocytes. Furthermore, they suggest that SSAO not only represents a novel late marker of adipogenesis, but could also be directly involved in the triggering of terminal adipocyte differentiation.