Assessment of the deamination of aminoacetone, an endogenous substrate for semicarbazide-sensitive amine oxidase

The Impact of Semicarbazide Sensitive Amine Oxidase Activity on Rat Aortic Vascular Smooth Muscle Cells

Semicarbazide-sensitive amine oxidase (SSAO) is both a soluble- and membrane-bound transmembrane protein expressed in the vascular endothelial and in smooth muscle cells. In vascular endothelial cells, SSAO contributes to the development of atherosclerosis by mediating a leukocyte adhesion cascade; however, its contributory role in the development of atherosclerosis in VSMCs has not yet been fully explored. This study investigates SSAO enzymatic activity in VSMCs using methylamine and aminoacetone as model substrates. The study also addresses the mechanism by which SSAO catalytic activity causes vascular damage, and further evaluates the contribution of SSAO in oxidative stress formation in the vascular wall. SSAO demonstrated higher affinity for aminoacetone when compared to methylamine (Km = 12.08 µM vs. 65.35 µM). Aminoacetone- and methylamine-induced VSMCs death at concentrations of 50 & 1000 µM, and their cytotoxic effect, was reversed with 100 µM of the irreversible SSAO inhibitor MDL72527, which completely abolished cell death. Cytotoxic effects were also observed after 24 h of exposure to formaldehyde, methylglyoxal and H₂O₂. Enhanced cytotoxicity was detected after the simultaneous addition of formaldehyde and H₂O₂, as well as methylglyoxal and H₂O₂. The highest ROS production was observed in aminoacetone- and benzylamine-treated cells. MDL72527 abolished ROS in benzylamine-, methylamine- and aminoacetone-treated cells (**** p < 0.0001), while βAPN demonstrated inhibitory potential only in benzylamine-treated cells (* p < 0.05). Treatment with benzylamine, methylamine and aminoacetone reduced the total GSH levels (**** p < 0.0001); the addition of MDL72527 and βAPN failed to reverse this effect. Overall, a cytotoxic consequence of SSAO catalytic activity was observed in cultured VSMCs where SSAO was identified as a key mediator in ROS formation. These findings could potentially associate SSAO activity with the early developing stages of atherosclerosis through oxidative stress formation and vascular damage.

Association of α-Dicarbonyls and Advanced Glycation End Products with Insulin Resistance in Non-Diabetic Young Subjects: A Case-Control Study

α-Dicarbonyls and advanced glycation end products (AGEs) may contribute to the pathogenesis of insulin resistance by a variety of mechanisms. To investigate whether young insulin-resistant subjects present markers of increased dicarbonyl stress, we determined serum α-dicarbonyls-methylglyoxal, glyoxal, 3-deoxyglucosone; their derived free- and protein-bound, and urinary AGEs using the UPLC/MS-MS method; soluble receptors for AGEs (sRAGE), and cardiometabolic risk markers in 142 (49% females) insulin resistant (Quantitative Insulin Sensitivity Check Index (QUICKI) ≤ 0.319) and 167 (47% females) age-, and waist-to-height ratio-matched insulin-sensitive controls aged 16-to-22 years. The between-group comparison was performed using the two-factor (sex, presence/absence of insulin resistance) analysis of variance; multiple regression via the orthogonal projection to latent structures model. In comparison with their insulin-sensitive peers, young healthy insulin-resistant individuals without diabetes manifest alterations throughout the α-dicarbonyls-AGEs-sRAGE axis, dominated by higher 3-deoxyglucosone levels. Variables of α-dicarbonyls-AGEs-sRAGE axis were associated with insulin sensitivity independently from cardiometabolic risk markers, and sex-specifically. Cleaved RAGE associates with QUICKI only in males; while multiple α-dicarbonyls and AGEs independently associate with QUICKI particularly in females, who displayed a more advantageous cardiometabolic profile compared with males. Further studies are needed to elucidate whether interventions alleviating dicarbonyl stress ameliorate insulin resistance.

Aerobic co-oxidation of hemoglobin and aminoacetone, a putative source of methylglyoxal

Aminoacetone (1-aminopropan-2-one), a putative minor biological source of methylglyoxal, reacts like other α-aminoketones such as 6-aminolevulinic acid (first heme precursor) and 1,4-diaminobutanone (a microbicide) yielding electrophilic α-oxoaldehydes, ammonium ion and reactive oxygen species by metal- and hemeprotein-catalyzed aerobic oxidation. A plethora of recent reports implicates triose phosphate-generated methylglyoxal in protein crosslinking and DNA addition, leading to age-related disorders, including diabetes. Importantly, methylglyoxal-treated hemoglobin adds four water-exposed arginine residues, which may compromise its physiological role and potentially serve as biomarkers for diabetes. This paper reports on the co-oxidation of aminoacetone and oxyhemoglobin in normally aerated phosphate buffer, leading to structural changes in hemoglobin, which can be attributed to the addition of aminoacetone-produced methylglyoxal to the protein. Hydroxyl radical-promoted chemical damage to hemoglobin may also occur in parallel, which is suggested by EPR-spin trapping studies with 5,5-dimethyl-1-pyrroline-N-oxide and ethanol. Concomitantly, oxyhemoglobin is oxidized to methemoglobin, as indicated by characteristic CD spectral changes in the Soret and visible regions. Overall, these findings may contribute to elucidate the molecular mechanisms underlying human diseases associated with hemoglobin dysfunctions and with aminoacetone in metabolic alterations related to excess glycine and threonine.

Association between metabolically healthy central obesity in women and levels of soluble receptor for advanced glycation end products, soluble vascular adhesion protein-1, and the activity of semicarbazide-sensitive amine oxidase

AIM

To determine the levels of circulating soluble receptor for advanced glycation end products (sRAGE), as a biomarker of risk of metabolic syndrome and cardiovascular disease development in centrally obese (CO) women considered metabolically healthy (COH) in comparison with those metabolically unhealthy (COU).

METHODS

47 lean healthy, 17 COH (presenting waist-to-height ratio ≥0.5 but not elevated blood pressure, atherogenic lipid profile, and insulin resistance), and 50 COU (CO presenting ≥2 risk factors) women aged 40-45 years were included. Anthropometric characteristics, blood chemistry and hematology data, adipokines, markers of inflammation, sRAGE, soluble vascular adhesion protein-1 (sVAP-1), and the activity of semicarbazide sensitive amine oxidase (SSAO) were determined.

RESULTS

Central obesity associated with low sRAGE levels (lean healthy: 1503±633 pg/mL; COH: 1103±339 pg/mL, P<0.05; COU: 1106±367 ng/mL, P<0.0.1), hyperleptinemia, and elevated markers of inflammation irrespective of the presence or absence of cardiometabolic risk factors. COU women presented high adiponectin levels. SVAP-1 concentrations and the activity of SSAO were similar in all 3 groups.

CONCLUSION

COH women present abnormalities in non-standard markers of cardiometabolic risk (sRAGE, leptin, high sensitive C-reactive protein), supporting the view that there is no healthy pattern of obesity. The clinical impact of our findings for future prognosis of metabolically healthy obese subjects remains to be elucidated in longitudinal studies.

Correlation among soluble receptors for advanced glycation end-products, soluble vascular adhesion protein-1/semicarbazide-sensitive amine oxidase (sVAP-1) and cardiometabolic risk markers in apparently healthy adolescents: a cross-sectional study

In non-diabetics, low levels of soluble receptor for advanced glycations end products (sRAGE) associate with an increased risk of development of diabetes, cardiovascular afflictions, or death. The majority of studies in non-diabetics report an inverse relationship between measures of obesity, cardiometabolic risk factors and sRAGE and/or endogenous secretory RAGE (esRAGE) levels. To elucidate whether this inconsistency is related to the metabolically healthy obese phenotype, or a different impact of the risk factors in presence and absence of obesity, we analyzed data from 2206 apparently healthy adolescents (51 % girls) aged 15-to-19 years. The association of sRAGE levels with soluble vascular adhesion protein-1/semicarbazide sensitive amine oxidase (sVAP-1/SSAO) was also investigated. Centrally obese, including metabolically healthy, adolescents present significantly lower sRAGE and esRAGE, but not sVAP-1, levels in comparison with their lean counterparts. An increasing number of cardiometabolic risk factors did not associate with significant changes in sRAGE, esRAGE or sVAP-1 levels either in lean or in obese subjects. In multivariate analyses, WHtR, hsCRP, markers of glucose homeostasis, renal function, adiponectin, and sVAP-1 associated significantly with sRAGE and esRAGE. SVAP-1 correlated significantly with glycemia, adiponectin, hsCRP, and sRAGE. Thus, in adolescents, a decline in sRAGE and esRAGE precedes the development of metabolic syndrome. When combined, standard and non-standard cardiometabolic risk factors explain only minor proportion in a variability of sRAGE and esRAGE (8 %-11 %); or sVAP-1 (12 %-20 %). Elucidation of pathogenetic mechanisms underlying early decline in sRAGE and esRAGE levels in obese adolescents and their clinical impact with regard to future cardiometabolic health requires further studies.

Is vitamin D deficiency related to accumulation of advanced glycation end products, markers of inflammation, and oxidative stress in diabetic subjects?

OBJECTIVES

In diabetes accumulated advanced glycation end products (AGEs) are involved in the striking cardiovascular morbidity/mortality. We asked whether a hypovitaminosis D associates with an increased formation and toxicity of AGEs in diabetes.

METHODS

In 276 diabetics (160 M/116 F, age: 65.0 ± 13.4; 43 type 1,T1DM, and 233 type 2 patients, T2DM) and 121 nondiabetic controls (60 M/61 F; age: 58.6 ± 15.5 years) routine biochemistry, levels of 25-hydroxyvitamin D3 (25-(OH)D), skin autofluorescence (SAF), plasma AGE-associated fluorescence (AGE-FL), N (ε) -(carboxymethyl)lysine (CML), soluble receptor for AGEs (sRAGE), soluble vascular adhesion protein-1 (sVAP-1), high sensitive C-reactive protein (hs-CRP), and renal function (eGFR) were determined.

RESULTS

In the diabetics SAF and AGE-Fl were higher than those of the controls and correlated with age, duration of diabetes, and degree of renal impairment. In T2DM patients but not in T1DM the age-dependent rise of SAF directly correlated with hs-CRP and sVAP-1. 25-(OH)D levels in diabetics and nondiabetics were lowered to a similar degree averaging 22.5 ng/mL. No relationship between 25-(OH)D and studied markers except for sVAP-1 was observed in the diabetics.

CONCLUSION

In diabetics hypovitaminosis D does not augment accumulation of AGEs and studied markers of microinflammation and oxidative stress except for sVAP-1.

Differential effects of glyoxalase 1 overexpression on diabetic atherosclerosis and renal dysfunction in streptozotocin-treated, apolipoprotein E-deficient mice

The reactive dicarbonyls, glyoxal and methylglyoxal (MG), increase in diabetes and may participate in the development of diabetic complications. Glyoxal and MG are detoxified by the sequential activities of glyoxalase 1 (GLO1) and glyoxalase 2. To determine the contribution of these dicarbonyls to the etiology of complications, we have genetically manipulated GLO1 levels in apolipoprotein E‐null (Apoe^−/−) mice. Male Apoe^−/− mice, hemizygous for a human GLO1 transgene (GLO1TGApoe^−/− mice) or male nontransgenic Apoe^−/− litter mates were injected with streptozotocin or vehicle and 6 or 20 weeks later, aortic atherosclerosis was quantified. The GLO1 transgene lessened streptozotocin (STZ)‐induced increases in immunoreactive hydroimidazolone (MG‐H1). Compared to nondiabetic mice, STZ‐treated GLO1TGApoe^−/− and Apoe^−/− mice had increased serum cholesterol and triglycerides and increased atherosclerosis at both times after diabetes induction. While the increased GLO1 activity in the GLO1TGApoe^−/− mice failed to protect against diabetic atherosclerosis, it lessened glomerular mesangial expansion, prevented albuminuria and lowered renal levels of dicarbonyls and protein glycation adducts. Aortic atherosclerosis was also quantified in 22‐week‐old, male normoglycemic Glo1 knockdown mice on an Apoe^−/− background (Glo1KDApoe^−/− mice), an age at which Glo1KD mice exhibit albuminuria and renal pathology similar to that of diabetic mice. In spite of ~75% decrease in GLO1 activity and increased aortic MG‐H1, the Glo1KDApoe^−/− mice did not show increased atherosclerosis compared to age‐matched Apoe^−/− mice. Thus, manipulation of GLO1 activity does not affect the development of early aortic atherosclerosis in Apoe^−/− mice but can dictate the onset of kidney disease independently of blood glucose levels.

Increased levels of methylglyoxal and methylglyoxal‐derived advanced glycation end products may contribute to the development of diabetic complications. We show that overexpression of an enzyme that participates in the pathway of methylglyoxal detoxification, glyoxalase 1, protects streptozotocin‐treated, apolipoprotein E‐deficient mice from diabetic kidney disease but not from diabetes‐induced accelerated aortic atherosclerosis.

Methylglyoxal, obesity, and diabetes

Methylglyoxal (MG) is a highly reactive compound derived mainly from glucose and fructose metabolism. This metabolite has been implicated in diabetic complications as it is a strong AGE precursor. Furthermore, recent studies suggested a role for MG in insulin resistance and beta-cell dysfunction. Although several drugs have been developed in the recent years to scavenge MG and inhibit AGE formation, we are still far from having an effective strategy to prevent MG-induced mechanisms. This review summarizes the mechanisms of MG formation, detoxification, and action. Furthermore, we review the current knowledge about its implication on the pathophysiology and complications of obesity and diabetes.

Ferricytochrome (c) directly oxidizes aminoacetone to methylglyoxal, a catabolite accumulated in carbonyl stress

Age-related diseases are associated with increased production of reactive oxygen and carbonyl species such as methylglyoxal. Aminoacetone, a putative threonine catabolite, is reportedly known to undergo metal-catalyzed oxidation to methylglyoxal, NH4(+) ion, and H2O2 coupled with (i) permeabilization of rat liver mitochondria, and (ii) apoptosis of insulin-producing cells. Oxidation of aminoacetone to methylglyoxal is now shown to be accelerated by ferricytochrome c, a reaction initiated by one-electron reduction of ferricytochrome c by aminoacetone without amino acid modifications. The participation of O2(•-) and HO (•) radical intermediates is demonstrated by the inhibitory effect of added superoxide dismutase and Electron Paramagnetic Resonance spin-trapping experiments with 5,5'-dimethyl-1-pyrroline-N-oxide. We hypothesize that two consecutive one-electron transfers from aminoacetone (E0 values = -0.51 and -1.0 V) to ferricytochrome c (E0 = 0.26 V) may lead to aminoacetone enoyl radical and, subsequently, imine aminoacetone, whose hydrolysis yields methylglyoxal and NH4(+) ion. In the presence of oxygen, aminoacetone enoyl and O2(•-) radicals propagate aminoacetone oxidation to methylglyoxal and H2O2. These data endorse the hypothesis that aminoacetone, putatively accumulated in diabetes, may directly reduce ferricyt c yielding methylglyoxal and free radicals, thereby triggering redox imbalance and adverse mitochondrial responses.

Role of operon aaoSo-mutT in antioxidant defense in Streptococcus oligofermentans

Previously, we have found that an insertional inactivation of aao_So, a gene encoding L-amino acid oxidase (LAAO), causes marked repression of the growth of Streptococcus oligofermentans. Here, we found that aao_So and mutT, a homolog of pyrophosphohydrolase gene of Escherichia coli, constituted an operon. Deletion of either gene did not impair the growth of S. oligofermentans, but double deletion of both aao_So and mutT was lethal. Quantitative PCR showed that the transcript abundance of mutT was reduced for 13-fold in the aao_So insertional mutant, indicating that gene polarity derived from the inactivation of aao_So attenuated the expression of mutT. Enzymatic assays were conducted to determine the biochemical functions of LAAO and MutT of S. oligofermentans. The results indicated that LAAO functioned as an aminoacetone oxidase [47.75 nmol H₂O₂ (min·mg protein)^–1]; and MutT showed the pyrophosphohydrolase activity, which removed mutagens such as 8-oxo-dGTP. Like paraquat, aao_So mutations increased the expression of SOD, and addition of aminoacetone (final concentration, 5 mM) decreased the mutant’s growth by 11%, indicating that the aao_So mutants are under ROS stress. HPLC did reveal elevated levels of cytoplasmic aminoacetone in both the deletion and insertional gene mutants of aao_So. Electron spin resonance spectroscopy showed increased hydroxyl radicals in both types of aao_So mutant. This demonstrated that inactivation of aao_So caused the elevation of the prooxidant aminoacetone, resulting the cellular ROS stress. Our study indicates that the presence of both LAAO and MutT can prevent endogenous metabolites-generated ROS and mutagens. In this way, we were able to determine the role of the aao_So-mutT operon in antioxidant defense in S. oligofermentans.

Occurrence and distribution of salsolinol-like compound, 1-acetyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (ADTIQ) in parkinsonian brains

Parkinson's disease (PD) arises from the loss of dopaminergic neurons in the substantia nigra. 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) is well known to cause Parkinsonism in humans with neurotoxicity specific for dopaminergic neurons. The experience with MPTP supports the hypothesis that endogenous or xenobiotic neurotoxins are involved in the pathogenesis of PD in humans. In our study, 1-acetyl-6, 7-dihydroxy-1, 2, 3, 4-tetrahydro-isoquinoline (ADTIQ), a novel compound, was found in frozen human brain tissues. The formation of ADTIQ was demonstrated using dopamine and methylglyoxal under physiological conditions. Methylglyoxal is a by-product of glycolysis. ADTIQ and its precursors, dopamine and methylglyoxal, were detected in different regions of frozen human brains such as the substantia nigra, caudate nucleus, putamen, frontal cortex, and the cerebellum. A significant difference in ADTIQ levels between control and Parkinson's patients was found; for instance, the ADTIQ level in putamen of PD patients was 0.76 ± 0.27 nmol/g compared to 0.10 ± 0.01 nmol/g in control. Our results might indicate that ADTIQ is possibly related to Parkinson's disease.

Evidence for increased methylglyoxal in the vasculature of women with preeclampsia: role in upregulation of LOX-1 and arginase

Preeclampsia is characterized by vascular endothelial dysfunction partly attributed to oxidative stress. In the vasculature of preeclamptic women, we have shown increased lectin-like oxidized low-density lipoprotein receptor 1 (LOX-1) and arginase expression, which can contribute to vascular oxidative stress. However, the mechanisms of such upregulation are unknown. Methylglyoxal (MG) that plays a role in the vascular complications of diabetes mellitus and the development of hypertension can be one potential factor that can affect LOX-1 and arginase through its ability to induce oxidative stress in vascular cells. MG also reacts with lysine residues in proteins to generate advanced glycation end product, N(epsilon)-carboxy ethyl lysine, which also serves as a marker of MG. We hypothesized that markers of MG formation will be increased in the vasculature of preeclamptic women and that exogenous MG will induce oxidative stress by the upregulation of LOX-1 via arginase. We observed increased N(epsilon)-carboxy ethyl lysine expression in the vasculature of women with preeclampsia in comparison with normotensive pregnant women. Moreover, glyoxalase I and II, enzymes that detoxify MG, and glutathione reductase, which generates reduced glutathione, a cofactor for glyoxalase, are also reduced in preeclampsia. In cultured endothelial cells, MG increased arginase expression by 6 hours and LOX-1 expression by 24 hours. Inhibition of arginase or NO synthase significantly reduced MG-induced LOX-1 expression, superoxide levels, and nitrotyrosine staining. In conclusion, MG-induced LOX-1 expression is mediated via arginase upregulation likely because of uncoupling of NO synthase, which may have implications in preeclampsia.

Aminoacetone, a putative endogenous source of methylglyoxal, causes oxidative stress and death to insulin-producing RINm5f cells

Aminoacetone (AA), triose phosphates, and acetone are putative endogenous sources of potentially cytotoxic and genotoxic methylglyoxal (MG), which has been reported to be augmented in the plasma of diabetic patients. In these patients, accumulation of MG derived from aminoacetone, a threonine and glycine catabolite, is inferred from the observed concomitant endothelial overexpression of circulating semicarbazide-sensitive amine oxidases. These copper-dependent enzymes catalyze the oxidation of primary amines, such as AA and methylamine, by molecular oxygen, to the corresponding aldehydes, NH4(+) ion and H2O2. We recently reported that AA aerobic oxidation to MG also takes place immediately upon addition of catalytic amounts of copper and iron ions. Taking into account that (i) MG and H2O2 are reportedly cytotoxic to insulin-producing cell lineages such as RINm5f and that (ii) the metal-catalyzed oxidation of AA is propagated by O2(*-) radical anion, we decided to investigate the possible pro-oxidant action of AA on these cells taken here as a reliable model system for pancreatic beta-cells. Indeed, we show that AA (0.10-5.0 mM) administration to RINm5f cultures induces cell death. Ferrous (50-300 microM) and Fe(3+) ion (100 microM) addition to the cell cultures had no effect, whereas Cu(2+) (5.0-100 microM) significantly increased cell death. Supplementation of the AA- and Cu(2+)-containing culture medium with antioxidants, such as catalase (5.0 microM), superoxide dismutase (SOD, 50 U/mL), and N-acetylcysteine (NAC, 5.0 mM) led to partial protection. mRNA expression of MnSOD, CuZnSOD, glutathione peroxidase, and glutathione reductase, but not of catalase, is higher in cells treated with AA (0.50-1.0 mM) plus Cu(2+) ions (10-50 microM) relative to control cultures. This may imply higher activity of antioxidant enzymes in RINm5f AA-treated cells. In addition, we have found that AA (0.50-1.0 mM) plus Cu(2+) (100 microM) (i) increase RINm5f cytosolic calcium; (ii) promote DNA fragmentation; and (iii) increase the pro-apoptotic (Bax)/antiapoptotic (Bcl-2) ratio at the level of mRNA expression. In conclusion, although both normal and pathological concentrations of AA are probably much lower than those used here, it is tempting to propose that excess AA in diabetic patients may drive oxidative damage and eventually the death of pancreatic beta-cells.

Evidence for in Vivo Scavenging by Aminoguanidine of Formaldehyde Produced via Semicarbazide-Sensitive Amine Oxidase-Mediated Deamination

Aminoguanidine (AG) is capable of preventing advanced protein glycation and inhibiting the activity of enzymes with carbonyl groups as cofactors, such as nitric-oxide synthase (NOS) and semicarbazide-sensitive amine oxidase (SSAO). The hydrazide moiety of AG can also interact with different endogenous carbonyl metabolites and potentially harmful endogenous aldehydes. Aldehydes can be generated via different pathways, such as lipid peroxidation (malondialdehyde and 4-hydroxynonenal), oxidative deamination (aldehydes), and carbohydrate metabolism (methylglyoxal). Formaldehyde and methylglyoxal are produced via SSAO-catalyzed deamination of methylamine and aminoacetone, respectively. An increase in SSAO-mediated deamination is known to be associated with various vascular disorders, such as diabetic complications. The present study demonstrates that AG is not only capable of rapidly interacting with aldehydes in vitro but also scavenging aldehydes in vivo. The AG-formaldehyde adducts were traced, and their structures were elucidated by high-performance liquid chromatography-mass spectrometry. AG has also been shown to block formaldehyde-induced beta-amyloid aggregation. Thus, AG can be an aldehyde scavenger in addition to blocking advanced glycation and inhibition of SSAO and NOS activity. Such reactions may contribute to its pharmacological effects in the treatment of vascular disorders associated with diabetic complications and other disorders.

Modifications of arterial phenotype in response to amine oxidase inhibition by semicarbazide

Semicarbazide-sensitive amine oxidase (SSAO)-deficient mice present no alteration in elastin cross-linking processes and carotid mechanical properties. In contrast, previous studies have shown that SSAO inhibitors induced marked anomalies in arterial structure and function. The aim of the present study was to examine the effect of semicarbazide (SCZ), an efficient SSAO inhibitor, on the arterial phenotype of the carotid artery in relation to modulation of SSAO and lysyl oxidase activities in growing rats. We first show that after 6 weeks of SCZ treatment (100 mg/kg per day), SSAO activity was reduced by 90%, whereas lysyl oxidase activity was only partially inhibited (<60%) in carotid artery, compared with controls. There was significant growth inhibition and no difference in mean arterial pressure but an increase in pulse pressure with a smaller arterial diameter in SCZ-treated rats. SCZ decreased aortic insoluble elastin without a change in total collagen. In addition, extracellular proteins other than insoluble elastin and collagen were increased in SCZ-treated rats. All of the elastic lamellae presented globular masses along their periphery, and focal disorganization was observed in the ascending aorta. Carotid artery mechanical strength was lower in SCZ-treated rats, and the elastic modulus-wall stress curve was shifted leftward compared with controls, indicating increased stiffness. Thus, SCZ modifies arterial geometry and mechanical properties, alters elastic fiber structure, and reduces the content of cross-linked elastin. Because these abnormalities are essentially absent in SSAO-deficient mice, our results suggest that lysyl oxidase inhibition is responsible for the major part of the vascular phenotype of SCZ-treated rats.

Diabetes and semicarbazide-sensitive amine oxidase (SSAO) activity: A review

The enzyme of semicarbazide-sensitive amine oxidase (SSAO) activity has been reported to be elevated in blood from diabetic patients. SSAO are widely distributed in plasma membranes of various tissues and blood plasma. SSAO-mediated production of toxic aldehydes has been proposed to be related to pathophysiological conditions. Cytotoxic metabolites by SSAO may cause endothelial injury and subsequently induce atherosclerosis. The precise physiological functions of SSAO could play an important role in the control of energy balance in adipose tissue. It is possible that the increased SSAO activity in diabetes may be a result of up-regulation due to increase of SSAO substrates, such as methylamine or aminoacetone. SSAO could play an important role in the regulation of adipocyte homeostasis. Inhibition of SSAO could be of therapeutic value for treatment of diabetic patient.

Endogenous semicarbazide-sensitive amine oxidase (SSAO) inhibitor increases 1-methyl-4-phenylpyridinium ion (MPP+)-induced dopamine efflux by immobilization stress in rat striatum

The present study examined whether or not immobilization stress (IMMO)-inducible semicarbazide-sensitive amine oxidase (SSAO) inhibitor by separated gel filtration from 105,000 g supernate in rat brain cytosol contribute to the dopamine (DA) efflux by 1-methyl-4-phenylpyridinium ion (MPP(+)) in the rat striatum. The isoelectric point (pI) value of this inhibitor was determined by isoelectric focusing (IEF)-gel electrophoresis to about 3.8. The application of IMMO-induced SSAO inhibitor (3 microg) by IEF-gel electrophoresis increased DA efflux by MPP(+) in rat striatum. These results suggest that IMMO-inducible endogenous SSAO inhibitor enhances DA efflux by MPP(+).

Tamoxifen protect against hydroxyl radical generation induced by phenelzine in rat striatum

The present study was examined whether tamoxifen, a synthetic nonsteroidal antiestrogen, could suppress antidepressant drug phenelzine can increase an active dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP(+))-induced hydroxyl radical (OH) generation in the extracellular fluid of rat striatum, using in vivo microdialysis system. Rats were anesthetized, and sodium salicylate (0.5 nmol/microl/min) was infused through a microdialysis probe to detect the generation of OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Infusion of phenelzine (100 microM or 0.1 nmol/microl/min) into the striatum drastically increased dopamine (DA) efflux and the OH formation, trapped as 2,3-DHBA by the possible increased production of MPP(+). However, tamoxifen (100 microM) significantly suppressed phenelzine enhanced DA efflux and OH formation by MPP(+). These results in the present study is the first demonstration showing the protective effect of tamoxifen on OH generation induced by phenelzine enhanced MPP(+) by suppressing DA efflux.

Effects of Subchronic Treatment With Selegiline on L-DOPA-Induced Increase in Extracellular Dopamine Level in Rat Striatum

Selegiline is used an adjunct to L-DOPA therapy. We investigated extracellular striatal dopamine (DA) level in awake rats treated with L-DOPA and/or selegiline using a microdialysis method. Rats given 10 mg/kg, i.p. per day selegiline for 7 days were administered with a single dose of 100 mg/kg, i.p. L-DOPA 0 (3 h), 1, 3, 7, 14, 21, or 28 days after the last selegiline treatment. Carbidopa was administered 0.5 h before L-DOPA administration. The significant increase in basal DA level before L-DOPA treatment persisted until 1 day after the last selegiline treatment, and the significant decrease in basal DOPAC level persisted for more than 28 days. Thus, selegiline affected DA catabolism for more than 28 days. Total monoamine oxidase (MAO) and MAO-B activities at day 0 decreased by 22% and 5.7%, respectively. The significant enhancement of L-DOPA-induced increase in DA level was observed until 3 days after the last selegiline treatment. Next, the effects of reducing L-DOPA dose by 25% were examined 3 h after the last selegiline treatment. A dose-dependent decrease in DA level was observed, indicating that DA level in selegiline-treated rats can be controlled by L-DOPA dose.

Involvement of SSAO-mediated deamination in adipose glucose transport and weight gain in obese diabetic KKAy mice

Semicarbazide-sensitive amine oxidase (SSAO) is located on outer surfaces of adipocytes and endothelial and vascular smooth muscle cells. This enzyme catalyzes deamination of methylamine and aminoacetone, leading to production of toxic formaldehyde and methylglyoxal, respectively, as well as hydrogen peroxide and ammonium. Several lines of evidence suggest that increased SSAO activity is related to chronic inflammation and vascular disorders related to diabetic complications. We found that a highly potent and selective SSAO inhibitor, (E)-2-(4-fluorophenethyl)-3-fluoroallylamine (FPFA), was capable of reducing numbers of atherosclerotic lesions as well as weight gain in obese KKAy mice fed an atherogenic diet. SSAO inhibitors cause a moderate and long-lasting hyperglycemia. Such an increase in serum glucose is a result of reduction of glucose uptake by adipocytes. SSAO-mediated deamination of endogenous methylamine substrates induces adipocyte glucose uptake and lipogenesis. Highly selective SSAO inhibitors can effectively block induced glucose uptake. The results suggest that increased SSAO-mediated deamination may be concomitantly related to obesity and vascular disorders associated with type 2 diabetes.

Physiological and pathological implications of semicarbazide-sensitive amine oxidase

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the deamination of primary amines. Such deamination has been shown capable of regulating glucose transport in adipose cells. It has been independently discovered that the primary structure of vascular adhesion protein-1 (VAP-1) is identical to SSAO. VAP-1 regulates leukocyte migration and is related to inflammation. Increased serum SSAO activities have been found in patients with diabetic mellitus, vascular disorders and Alzheimer's disease. The SSAO-catalyzed deamination of endogenous substrates, that is, methylamine and aminoacetone, led to production of toxic formaldehyde and methylglyoxal, hydrogen peroxide and ammonia, respectively. These highly reactive aldehydes have been shown to initiate protein cross-linkage, exacerbate advanced glycation of proteins and cause endothelial injury. Hydrogen peroxide contributes to oxidative stress. 14C-methylamine is converted to 14C-formaldehyde, which then forms labeled long-lasting protein adduct in rodents. Chronic methylamine treatment increased the excretion of malondialdehyde and microalbuminuria, and enhanced the formation of fatty streaks in C57BL/6 mice fed with an atherogenic diet. Treatment with selective SSAO inhibitor reduces atherogenesis in KKAy diabetic mice fed with high-cholesterol diet. Aminoguanidine, which blocks advanced glycation and reduces nephropathy in animals, is in fact more potent at inhibiting SSAO than its effect on glycation. It suggests that SSAO is involved in vascular disorders under certain pathological conditions. Although SSAO has been known for several decades, its physiological and pathological implications are just beginning to be recognized.

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.

Semicarbazide-sensitive amine oxidase in aortic smooth muscle cells mediates synthesis of a methylglyoxal-AGE: implications for vascular complications in diabetes

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes formation of methylglyoxal (MG) from aminoacetone; MG then reacts with proteins to form advanced glycation end products or AGEs. Because of its potential to generate MG, SSAO may contribute to AGE-associated vascular complications of aging and diabetes. We developed a method to measure SSAO activity in bovine aortic smooth muscle cells (BASMC) based on the oxidation of 2',7'-dichlorofluorescin by hydrogen peroxide and horseradish peroxidase. The SSAO activity was completely inhibited by 10 mM semicarbazide. Argpyrimidine is a readily detectable fluorescent product of the reaction between MG and arginine. Cell lysates incubated with aminoacetone formed argpyrimidine in a reaction that was inhibited by 20 mM semicarbazide. Immunostaining of tissue sections showed that aminoacetone-treated rats (normal as well as diabetic) formed more argpyrimidine in aortic smooth muscle than untreated controls. We believe that SSAO can enhance AGE synthesis in the macrovasculature of diabetic individuals by production of MG.

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.

Aerobic oxidation of aminoacetone, a threonine catabolite: iron catalysis and coupled iron release from ferritin

Aminoacetone (AA) is a threonine and glycine catabolite long known to accumulate in cri-du-chat and threoninemia syndromes and, more recently, implicated as a contributing source of methylglyoxal (MG) in diabetes mellitus. Oxidation of AA to MG, NH(4)(+), and H(2)O(2) has been reported to be catalyzed by a copper-dependent semicarbazide sensitive amine oxidase (SSAO) as well as by Cu(II) ions. We here study the mechanism of AA aerobic oxidation, in the presence and absence of iron ions, and coupled to iron release from ferritin. Aminoacetone (1-7 mM) autoxidizes in Chelex-treated phosphate buffer (pH 7.4) to yield stoichiometric amounts of MG and NH(4)(+). Superoxide radical was shown to propagate this reaction as indicated by strong inhibition of oxygen uptake by superoxide dismutase (SOD) (1-50 units/mL; up to 90%) or semicarbazide (0.5-5 mM; up to 80%) and by EPR spin trapping studies with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), which detected the formation of the DMPO-(*)OH adduct as a decomposition product from the DMPO-O(2)(*)(-) adduct. Accordingly, oxygen uptake by AA is accelerated upon addition of xanthine/xanthine oxidase, a well-known enzymatic source of O(2)(*)(-) radicals. Under Fe(II)EDTA catalysis, SOD (<50 units/mL) had little effect on the oxygen uptake curve or on the EPR spectrum of AA/DMPO, which shows intense signals of the DMPO-(*)OH adduct and of a secondary carbon-centered DMPO adduct, attributable to the AA(*) enoyl radical. In the presence of iron, simultaneous (two) electron transfer from both Fe(II) and AA to O(2), leading directly to H(2)O(2) generation followed by the Fenton reaction is thought to take place. Aminoacetone was also found to induce dose-dependent Fe(II) release from horse spleen ferritin, putatively mediated by both O(2)(*)(-) and AA(*) enoyl radicals, and the co-oxidation of added hemoglobin and myoglobin, which may be viewed as the initial step for potential further iron release. It is thus tempting to propose that AA, accumulated in the blood and other tissues of diabetics, besides being metabolized by SSAO, may release iron and undergo spontaneous and iron-catalyzed oxidation with production of reactive H(2)O(2) and O(2)(*)(-), triggering pathological responses. It is noteworthy that noninsulin-dependent diabetes has been frequently associated with iron overload and oxidative stress.

2-Bromoethylamine as a potent selective suicide inhibitor for semicarbazide-sensitive amine oxidase

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the deamination of methylamine and aminoacetone to produce toxic aldehydes, i.e. formaldehyde and methylglyoxal, as well as hydrogen peroxide and ammonia. An increase of SSAO activity was detected by different laboratories in patients suffering from vascular disorders, i.e. diabetes and myocardial infarction. The enzyme has been suggested to play a role in vascular endothelial damage and atherogenesis. To date, there are no selective SSAO inhibitors. In the present study, 2-bromoethylamine (2-BrEA) was found to be a highly effective and selective inhibitor of SSAO obtained from different sources. The inhibition was irreversible and time dependent. It was competitive when the enzyme was not preincubated with the inhibitor, but became noncompetitive after incubation of the enzyme with 2-BrEA. The aldehyde trapping agent o-phenylenediamine was capable of preventing 2-BrEA-induced inhibition of SSAO activity. An aldehyde product was detected to be an initial product of 2-BrEA after it was incubated with SSAO. The inhibition, therefore, is mechanism-based. The SSAO inhibitory effects of eight structural analogues of 2-BrEA were assessed. It was concluded that a bromine atom at the beta position is quite important for exerting high potency of SSAO inhibition. The inhibition of SSAO activity by 2-BrEA was also demonstrated in vivo. It increased the urinary excretion of methylamine, an endogenous substrate for SSAO, in mice. 2-BrEA can be employed as a very useful tool in the investigation of SSAO.

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.

The role of alpha,beta -dicarbonyl compounds in the toxicity of short chain sugars

The extent to which sugars serve as targets for superoxide was examined using glycolaldehyde as the simplest sugar and using superoxide dismutase (SOD)-replete and SOD-null strains growing under aerobic and anaerobic conditions. Glycolaldehyde was more toxic to the SOD-null strain than to its SOD-replete parent, and this differential effect was oxygen-dependent. The product, glyoxal, could be trapped in the medium by 1,2-diaminobenzene and assayed as quinoxaline. The SOD-null strain produced more glyoxal and eliminated it more slowly than the SOD-replete parent strain. Glyoxal was approximately 10 times more toxic than glycolaldehyde and was more toxic to the SOD-null strain than to the parental strain. 1,2-Diaminobenzene protected against the toxicity of glycolaldehyde. These Escherichia coli strains contained the glutathione-dependent glyoxalases I and II, as well as the glutathione-independent glyoxalase III. Of these enzymes, glyoxalase III was most abundant, and it was inactivated within the aerobic SOD-null strain and also in extracts when exposed to the flux of superoxide and hydrogen peroxide imposed by the xanthine oxidase reaction. Thus, it appears that short chain sugars are oxidized by superoxide yielding toxic dicarbonyls. Moreover, the defensive glyoxalase III is also inactivated by the oxidative stress imposed by the lack of SOD, thereby exacerbating the deleterious effect of sugar oxidation.

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.