Semicarbazide-sensitive Amine Oxidase Expression Research Articles

The Biological Implication of Semicarbazide-Sensitive Amine Oxidase (SSAO) Upregulation in Rat Systemic Inflammatory Response under Simulated Aerospace Environment.

The progress of space science and technology has ushered in a new era for humanity's exploration of outer space. Recent studies have indicated that the aerospace special environment including microgravity and space radiation poses a significant risk to the health of astronauts, which involves multiple pathophysiological effects on the human body as well on tissues and organs. It has been an important research topic to study the molecular mechanism of body damage and further explore countermeasures against the physiological and pathological changes caused by the space environment. In this study, we used the rat model to study the biological effects of the tissue damage and related molecular pathway under either simulated microgravity or heavy ion radiation or combined stimulation. Our study disclosed that ureaplasma-sensitive amino oxidase (SSAO) upregulation is closely related to the systematic inflammatory response (IL-6, TNF-α) in rats under a simulated aerospace environment. In particular, the space environment leads to significant changes in the level of inflammatory genes in heart tissues, thus altering the expression and activity of SSAO and causing inflammatory responses. The detailed molecular mechanisms have been further validated in the genetic engineering cell line model. Overall, this work clearly shows the biological implication of SSAO upregulation in microgravity and radiation-mediated inflammatory response, providing a scientific basis or potential target for further in-depth investigation of the pathological damage and protection strategy under a space environment.

Simulated microgravity alters the expression of plasma SSAO and its enzymatic activity in healthy rats and increases the mortality in high-fat diet/streptozotocin-induced diabetes

Semicarbazide-sensitive amine oxidase (SSAO) activity is known to be associated with certain pathologies including diabetes. In this study, SSAO expression and enzymatic activity in blood plasma of healthy rats were significantly upregulated under simulated microgravity (SMG) condition. Significant mortality was observed in SMG group of diabetic rats. Results indicate that microgravity might increase the risks of SSAO-associated alterations.

Semicarbazide-Sensitive Amine Oxidase Increases in Calcific Aortic Valve Stenosis and Contributes to Valvular Interstitial Cell Calcification.

Introduction Calcific aortic valve stenosis (CAVS) is a common disease associated with aging. Oxidative stress participates in the valve calcification process in CAVS. Semicarbazide-sensitive amine oxidase (SSAO), also referred to as vascular adhesion protein 1 (VAP-1), transforms primary amines into aldehydes, generating hydrogen peroxide and ammonia. SSAO is expressed in calcified aortic valves, but its role in valve calcification has remained largely unexplored. The aims of this study were to characterize the expression and the activity of SSAO during aortic valve calcification and to establish the effects of SSAO inhibition on human valvular interstitial cell (VIC) calcification. Methods Human aortic valves from n = 80 patients were used for mRNA extraction and expression analysis, Western blot, SSAO activity determination, immunohistochemistry, and the isolation of primary VIC cultures. Results SSAO mRNA, protein, and activity were increased with increasing calcification within human aortic valves and localized in the vicinity of the calcified zones. The valvular SSAO upregulation was consistent after stratification of the subjects according to cardiovascular and CAVS risk factors associated with increased oxidative stress: body mass index, diabetes, and smoking. SSAO mRNA levels were significantly associated with poly(ADP-ribose) polymerase 1 (PARP1) in calcified tissue. Calcification of VIC was inhibited in the presence of the specific SSAO inhibitor LJP1586. Conclusion The association of SSAO expression and activity with valvular calcification and oxidative stress as well as the decreased VIC calcification by SSAO inhibition points to SSAO as a possible marker and therapeutic target to be further explored in CAVS.

Inhibition of semicarbazide-sensitive amine oxidase reduces atherosclerosis in apolipoprotein E-deficient mice

Inflammation, oxidative stress, and formation of advanced glycated end products (AGEs) and advanced lipoxidation end products (ALEs) are important for atherosclerosis. Vascular adhesion protein-1 (VAP-1) participates in inflammation and has semicarbazide-sensitive amine oxidase (SSAO) activity, which catalyzes oxidative deamination to produce hydrogen peroxide and aldehydes, leading to generation of AGEs and ALEs. However, the effect of VAP-1/SSAO inhibition on atherosclerosis remains controversial, and no studies used coronary angiography to evaluate if plasma VAP-1/SSAO is a biomarker for coronary artery disease (CAD). Here, we examined if plasma VAP-1/SSAO is a biomarker for CAD diagnosed by coronary angiography in humans and investigated the effect of VAP-1/SSAO inhibition by a specific inhibitor PXS-4728A on atherosclerosis in cell and animal models. In the study, VAP-1/SSAO expression was increased in plaques in humans and in apolipoprotein E (ApoE)-deficient mice, and colocalized with vascular endothelial cells and smooth muscle cells (SMCs). Patients with CAD had higher plasma VAP-1/SSAO than those without CAD. Plasma VAP-1/SSAO was positively associated with the extent of CAD. In ApoE-deficient mice, VAP-1/SSAO inhibition reduced atheroma and decreased oxidative stress. VAP-1/SSAO inhibition attenuated the expression of adhesion molecules, chemoattractant proteins, and proinflammatory cytokines in the aorta, and suppressed monocyte adhesion and transmigration across human umbilical vein endothelial cells. Consequently, the expression of markers for macrophage recruitment and activation in plaques was decreased by VAP-1/SSAO inhibition. Besides, VAP-1/SSAO inhibition suppressed proliferation and migration of A7r5 SMC. Our data suggest that plasma VAP-1/SSAO is a novel biomarker for the presence and the extent of CAD in humans. VAP-1/SSAO inhibition by PXS-4728A is a potential treatment for atherosclerosis.

Expression of the semicarbazide-sensitive amine oxidase in articular cartilage: its role in terminal differentiation of chondrocytes in rat and human

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the oxidation of primary amines into ammonia and reactive species (hydrogen peroxide, aldehydes). It is highly expressed in mammalian tissues, especially in vascular smooth muscle cells and adipocytes, where it plays a role in cell differentiation and glucose transport. The study aims at characterizing the expression and the activity of SSAO in rat and human articular cartilage of the knee, and to investigate its potential role in chondrocyte terminal differentiation. SSAO expression was examined by immunohistochemistry and western blot. Enzyme activity was measured using radiolabeled benzylamine as a substrate. Primary cell cultures of rat chondrocytes were treated for 21 days by a specific SSAO inhibitor, LJP 1586. Terminal chondrocyte differentiation markers were quantified by RT-qPCR. The basal and IL1β-stimulated glucose transport was monitored by the entrance of (3)[H]2-deoxyglucose in chondrocytes. SSAO was expressed in chondrocytes of rat and human articular cartilage. SSAO expression was significantly enhanced during the hypertrophic differentiation of chondrocytes characterized by an increase in MMP13 and in alkaline phosphatase (ALP) expressions. SSAO inhibition delayed the late stage of chondrocyte differentiation without cell survival alteration and diminished the basal and IL1β-stimulated glucose transport. Interestingly, SSAO activity was strongly increased in human osteoarthritic cartilage. SSAO was expressed as an active form in rat and human cartilage. The results suggest the involvement of SSAO in rat chondrocyte terminal differentiation via a modulation of the glucose transport. In man, the increased SSAO activity detected in osteoarthritic patients may trigger hypertrophy and cartilage degeneration.

Abstract P626: Amine Oxidase Activity in Mesenteric Perivascular Adipose Tissue Adipocytes is Mediated by Semicarbazide Sensitive Amine Oxidase

Perivascular adipose tissue (PVAT) is important in regulating vascular tone and reduces contraction of vessels to various agonists. PVAT is composed of adipocytes and the stromal vascular fraction (SVF), which contains immune cells, neurons, endothelial cells, fibroblasts and preadipocytes. Adipocytes, the main cell type in PVAT, contain various amine oxidases. We hypothesized that amine oxidases in mesenteric PVAT would metabolize vasoactive amines. To determine the primary enzyme(s) responsible for the amine oxidase activity in PVAT, an Amplex Red assay was performed. We added tyramine, a substrate for monoamine oxidase-A & B (MAO-A, MAO-B) and semicarbazide sensitive amine oxidase (SSAO), to cell and tissue fractions from male Sprague Dawley rats to test for H 2 O 2 production as an indicator of oxidase activity. Oxidase activity in mesenteric PVAT increased from 7.92±2.27 (vehicle) to 20.83±5.30 with the addition of tyramine (p<0.05) and from 9.30±2.55 to 24.60±6.38 in adipocytes (p<0.05; pmol/min·mg±SEM; N=5). In both the mesenteric PVAT and isolated adipocytes, the oxidase activity was reduced to baseline levels (vehicle) by pre-incubating with the SSAO inhibitor semicarbazide (1 mM; PVAT: 8.49±2.56, adipocytes: 9.43±3.21; p<0.05; N=4-5). No reduction in oxidase activity in both the mesenteric PVAT and the isolated adipocytes was observed when the MAO-A inhibitor clorgyline or the MAO-B inhibitor pargyline (1 μM; a concentration at which each drug is specific for their respective enzyme) were used. Westerns revealed that mesenteric PVAT adipocytes had the highest expression of monomeric SSAO (~80 kDa; 124.75±30.71%) compared to the whole PVAT (66.15±9.92%), blood vessels (48.2±6.89%) and the SVF (38.76±11.65%) as quantified by percent density relative to β-actin using protein isolated from male Sprague Dawley rats (p<0.05; values given as %β-actin±SEM, N=4). Oxidase activity within the SVF remains to be determined. These findings support that most of the oxidase activity in mesenteric PVAT can be attributed to SSAO and the adipocyte is an abundant source of SSAO. Due to the proximity of PVAT to the blood vessel, oxidase activity in PVAT through SSAO may alter vascular tone by metabolizing vasoactive amines and through the production of H 2 O 2 .

A cross-talk between Aβ and endothelial SSAO/VAP-1 accelerates vascular damage and Aβ aggregation related to CAA-AD

An association between semicarbazide-sensitive amine oxidase (SSAO) and cerebral amyloid angiopathy (CAA) related to Alzheimer's disease (AD) has been largely postulated. Increased SSAO activity and expression have been detected in cerebrovascular tissue and plasma of AD patients, colocalizing with cerebrovascular amyloid-beta (Aβ) deposits. As an enzyme, SSAO metabolizes primary amines generating hydrogen peroxide, ammonia, and aldehydes. The ability of these products to generate oxidative stress, to enhance the advanced glycation end-product generation, to promote the Aβ aggregation in vitro, and to induce apoptosis supports its role in CAA-related vascular pathology. However, whether the SSAO increase constitutes a cause or it is a consequence of the pathologic process has not been elucidated so far. To set up the nature of this relationship, vascular cell models expressing SSAO were treated with different Aβ forms, simulating the CAA conditions in vitro. It was found that the presence of the vasculotropic Dutch-mutated Aβ1–40 increases (Aβ1–40 D) the SSAO-dependent toxicity, which is accompanied by an increase of SSAO protein availability in endothelial cell membranes. In addition, SSAO enhances Aβ1–40 D and Aβ1–42 deposition on vascular cells by both activity-dependent and -independent mechanisms. Thus, we provide evidences indicating that Aβ itself could be one of the factors inducing SSAO increase in AD, enhancing its toxic effect, and inducing the vascular dysfunction and, in turn, that SSAO stimulates Aβ deposition on the vascular walls, thereby contributing to the CAA-AD progression. Therefore, molecules inhibiting SSAO could provide an alternative treatment for preventing/delaying the progress of CAA-AD–associated vasculopathy.

Arterial vascular cell line expressing SSAO: a new tool to study the pathophysiology of vascular amine oxidases

Semicarbazide-sensitive amine oxidase (SSAO) widely exists in nature, mainly expressed at significant levels in vasculature. It plays a detrimental role in vascular diseases, particularly atherosclerosis, which occurs mainly in arteries. Herein we for the first time present SSAO expression in arterial lineage of vascular cell line, i.e., human umbilical arterial endothelial cell (HUAEC). Firstly, two commercially available gene transfection reagents were compared to determine high transfection efficiency and then the expression behavior of HUAEC:SSAO was characterized. Furthermore, our model was also been compared with commonly used human embryonic kidney (HEK) cell transfected with the same vector. For enzymatic assay, an in-house developed highly sensitive high performance liquid chromatography electron spray ionization mass spectrometry method was applied. Results indicated that the maximal transfection efficiency in HUAEC was detected by JetPEI™ and transfected protein was expressed at membrane and cytosol of different clones. No significant variations were observed in HUAEC between cell passages 1 and 7, although HEK cell displayed twofold higher SSAO expression level than HUAEC. The transfected SSAO was shown to be released into the cell-culture medium. Both cellular and released types of SSAO exhibited monomer and dimer structural forms. The cytotoxicity determination exhibited large number of viable cells after transfection with JetPEI™. Differential expression characterization of this new cell line demonstrates the correct behavior of SSAO in arterial endothelial cells and also provides a real physiological environment to elucidate the unclear role of this enzyme. In addition, our cellular model could partly solve the problems raised by the loss of enzyme expression found in cultured endothelial cells. This model could also be a useful tool for proteomic base study, screening of interacting protein and analysis of compounds that could modify its activity for therapeutic purposes.

Benzylamine antihyperglycemic effect is abolished by AOC3 gene invalidation in mice but not rescued by semicarbazide-sensitive amine oxidase expression under the control of aP2 promoter

Semicarbazide-sensitive amine oxidase (SSAO) is a transmembrane enzyme that metabolizes primary amines from endogenous or dietary origin. SSAO is highly expressed in adipose, smooth muscle and endothelial cells. In each of these cell types, SSAO is implicated in different biological functions, such as glucose transport activation, extracellular matrix maturation and leucocyte extravasation, respectively. However, the physiological functions of SSAO and their involvement in pathogenesis remain uncompletely characterized. To better understand the role of adipose tissue SSAO, we investigated whether it was necessary and/or sufficient to produce the antihyperglycemic effect of the SSAO-substrate benzylamine, already reported in mice. Therefore, we crossed SSAO-deficient mice invalidated for AOC3 gene and transgenic mice expected to express human SSAO in an adipocyte-specific manner, under the control of aP2 promoter. The aP2-human AOC3 construct (aP2-hAOC3) was equally expressed in the adipose tissue of mice expressing or not the native murine form and almost absent in other tissues. However, the corresponding SSAO activity found in adipose tissue represented only 20 % that of control mice. As a consequence, the benzylamine antihyperglycemic effect observed during glucose tolerance test in control was abolished in AOC3-KO mice but not rescued in mice expressing aP2-hAOC3. The capacity of benzylamine or methylamine to activate glucose uptake in adipocytes exhibited parallel variations in the corresponding genotypes. Although the aP2-hAOC3 construct did not allow a total rescue of SSAO activity in adipose tissue, it could be assessed from our observations that adipocyte SSAO plays a pivotal role in the increased glucose tolerance promoted by pharmacological doses of benzylamine.

P4-299: Neuron-binding autoantibodies in human sera enhance Abeta42 accumulation in adult mouse brain neurons

of Alzheimer’s disease (AD), and it is characterized by the deposition of beta-amyloid (A ) in cerebral cortical and meningeal blood vessels (Kawai M. et al., 1993), inducing degeneration of vascular cells. Semicarbazide-sensitive amine oxidase (SSAO) [E.C. 1.4.3.6] is present in vascular cells and in plasma. It metabolizes primary amines (Lyles GA., 1996) generating hydrogen peroxide (H2O2), ammonia (NH3) and the corresponding aldehyde, that contribute to the oxidative stress, advanced glycation end-product generation (GubisneHaberle D. et al., 2004), and beta amyloid aggregation (Chen K. et al., 2006). Furthermore in endothelial cells, SSAO is induced under inflammatory conditions (Smith D.J. et. al., 1998). We have reported that SSAO is overexpressed in cerebrovascular tissue of patients with CAA-AD, and that it colocalizes with beta-amyloid deposits (Ferrer I. et al., 2002). This over-expression correlates with high SSAO activity in plasma of severe AD patients (del Mar Hernandez M. et al., 2005). We have also described that plasma SSAO is able to induce apoptosis in vascular cells (Hernandez M. et.al., 2006). The aim of this work is to demonstrate whether A is able to induce SSAO overexpression in HUVEC cells as vascular cell type. Methods: Because of the SSAO/ VAP-1 expression fenotype is lost in cultured cells, HUVEC (human umbilical vein endothelial cells) cells, were stably transfected with vector pcDNA 3.1 containing hVAP-1/SSAO. Cells were treated with A 1-40 Dutch type (mutation E22Q) and/or Methylamine as SSAO substrate. Cell viability, SSAO activity and its expression were determined using specific antibodies against SSAO. Results: Herein we report that A 1-40 E22Q induces the SSAO activity and expression in HUVEC cells. This increasing activity promotes oxidative stress that enhances the toxicity generated by A alone. This toxicity is reverted by specific SSAO inhibitors, confirming SSAO as the responsible of such effect. Conclusions: These results allow us to postulate that deposits of A in cerebrovascular tissue, induce SSAO expression that may contribute to the vascular damage associated to CAA-AD.

The contribution of cerebral vascular semicarbazide‐sensitive amine oxidase to cerebral amyloid angiopathy in Alzheimer's disease

Semicarbazide-sensitive amine oxidase (SSAO) catalyses the oxidative deamination of a variety of endogenous substrates, such as methylamine and aminoacetone, to produce highly reactive aldehydes, which are capable of inducing protein cross-linkage, beta amyloid (Abeta) aggregation and advanced glycation end-product formation. In the brain, SSAO is exclusively located on the blood vessels. Deposits of Abeta, the hallmark of Alzheimer's disease (AD), are closely associated with cerebral blood vessels, that is, cerebral amyloid angiopathy (CAA). In the present study, we examined whether SSAO-mediated deamination contributes to CAA in AD. We employed immunohistochemistry to examine the colocalization of SSAO and Abeta in post mortem brains of AD patients. To assess the role of SSAO-mediated deamination in the deposition of Abeta on blood vessel walls, we developed an in vitro blood vessel model using sections of human umbilical cord. We found a strong expression of SSAO colocalized with Abeta deposits on the blood vessels in AD brains. We also demonstrated that SSAO-mediated deamination increases the deposition of Abeta onto blood vessel walls. Our results support the hypothesis that cerebral vascular SSAO-catalysed deamination contributes to CAA in AD brains.

Adipogenesis-related increase of semicarbazide-sensitive amine oxidase and monoamine oxidase in human adipocytes

A strong induction of semicarbazide-sensitive amine oxidase (SSAO) has previously been reported during murine preadipocyte lineage differentiation but it remains unknown whether this emergence also occurs during adipogenesis in man. Our aim was to compare SSAO and monoamine oxidase (MAO) expression during in vitro differentiation of human preadipocytes and in adipose and stroma-vascular fractions of human fat depots. A human preadipocyte cell strain from a patient with Simpson–Golabi–Behmel syndrome was first used to follow amine oxidase expression during in vitro differentiation. Then, human preadipocytes isolated from subcutaneous adipose tissues were cultured under conditions promoting ex vivo adipose differentiation and tested for MAO and SSAO expression. Lastly, human adipose tissue was separated into mature adipocyte and stroma-vascular fractions for analyses of MAO and SSAO at mRNA, protein and activity levels. Both SSAO and MAO were increased from undifferentiated preadipocytes to lipid-laden cells in all the models: 3T3-F442A and 3T3-L1 murine lineages, human SGBS cell strain or human preadipocytes in primary culture. In human subcutaneous adipose tissue, the adipocyte-enriched fraction exhibited seven-fold higher amine oxidase activity and contained three- to seven-fold higher levels of mRNAs encoded by MAO-A, MAO-B, AOC3 and AOC2 genes than the stroma-vascular fraction. MAO-A and AOC3 genes accounted for the majority of their respective MAO and SSAO activities in human adipose tissue. Most of the SSAO and MAO found in adipose tissue originated from mature adipocytes. Although the mechanism and role of adipogenesis-related increase in amine oxidase expression remain to be established, the resulting elevated levels of amine oxidase activities found in human adipocytes may be of potential interest for therapeutic intervention in obesity.

Influence of high-fat diet on amine oxidase activity in white adipose tissue of mice prone or resistant to diet-induced obesity

Decreased monoamine oxidase (MAO) activity has been observed in adipose tissue of obese patients. Since substrates of MAO and semicarbazide-sensitive amine oxidase (SSAO) can modify adipocyte metabolism, this work investigates whether changes in amine oxidase activity may occur during white adipose tissue (WAT) development. We evaluated MAO and SSAO activities in WAT of high-fat diet (HFD) and low-fat diet fed mice. To distinguish the effect of HFD on its own from the effect of fat mass enlargement, obesity-prone transgenic line of the FVBn strain lacking beta3-adrenergic receptors (AR) but expressing human beta3-AR and alpha2-AR (mbeta3-/-, hbeta3+/+, halpha2+/-) was compared to its obesity-resistant control (mbeta3-/-, hbeta3+/+). As already reported, the former mice became obese while the latter resisted to HFD. No significant change in SSAO or MAO activity was found in WAT of both strains after HFD when expressing oxidase activity per milligram of protein. However, when considering the overall capacity of the fat depots to oxidize tyramine or benzylamine, there was an increase in MAO and SSAO activity only in the enlarged WAT of HFD-induced obese mice. Therefore, the comparison of these models allowed to demonstrate that the higher amine oxidase capacity hold in enlarged fat stores of obese mice is more likely the consequence of increased fat cell number rather than the result of an increased expression of MAO or SSAO in the adipocyte.

Semicarbazide-sensitive Amine Oxidase in Annulo-aortic Ectasia Disease: Relation to Elastic Lamellae-associated Proteins

Lysyl oxidases (Lox), which are members of the amine oxidase family, are involved in the maturation of elastic lamellae and collagen fibers. Modifications of amine oxidases in idiopathic annulo-aortic ectasia disease (IAAED) have never been investigated. Our aim was to examine the expression of several proteins that might interfere with elastic fiber organization in control (n=10) and IAAED (n=18) aortic tissues obtained at surgery. Expression of amine oxidases and semicarbazide-sensitive amine oxidase (SSAO), and cellular phenotypic markers were examined by immunohistopathology and confocal microscopy. The expression of these proteins was assessed in relation to clinical and histomorphological features of the arterial wall. In control aorta, SSAO staining was expressed along elastic lamellae, whereas in aneurysmal areas of IAAED, SSAO was markedly decreased, in association with severe disorganization of elastic lamellae. Smooth muscle myosin heavy chain was also decreased in IAAED compared with controls, indicating smooth muscle cell dedifferentiation. Multiple regression analysis showed that elastic lamellar thickness (ELT) was correlated positively with the SSAO:elastin ratio and negatively with the Lox:elastin ratio, and that the clinical features of IAAED (aneurysm, thoracic aorta diameter, and aortic insufficiency) were positively correlated with ELT but not with SSAO. The relationship between SSAO expression and ELT suggests that this amine oxidase may be involved in elastic fiber organization. However, in advanced IAAED, the deficit in SSAO expression could be secondary to the decrease and fragmentation of elastic fibers and/or to vascular smooth muscle cell dedifferentiation.

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.

Overexpression of Semicarbazide-Sensitive Amine Oxidase in Smooth Muscle Cells Leads to an Abnormal Structure of the Aortic Elastic Laminas

Elevated semicarbazide-sensitive amine oxidase (SSAO) activity has been observed in several human conditions, eg, diabetes, and it has been speculated that SSAO contributes to the development of vasculopathies associated with this disease. To investigate in vivo consequences of elevated expression of SSAO in vascular tissues, we have developed a transgenic model for overexpression of human SSAO in mice. A smooth muscle-specific promoter, smooth muscle alpha-actin promoter 8 (SMP8) was used. Transgenic expression of human SSAO in tissues with a high content of smooth muscle cells was confirmed by Northern blot analysis. Enzymatic analysis of homogenates from transgenic tissues showed elevated levels of SSAO activity compared to non-transgenic littermates. Furthermore, when plasma SSAO activity was analyzed, much higher activity was detected compared to plasma from control mice, indicating that plasma SSAO may originate from smooth muscle cells. Histopathological evaluation of aorta and renal artery from transgenic mice revealed an abnormal structure of the elastin tissue. Instead of the regularly folded elastic laminae normally found in tunica media of sacrificed mice, the elastic laminae were straight and unfolded with irregularly arranged elastic fibers, forming tangled webs, between the intercalating elastic laminae. These alterations of the elastin structures suggest that overexpression of SSAO has led to a reduced elasticity of the arteries. Moreover, the mean femoral arterial pressure of the SMP8 SSAO transgenic mice was significantly lower in comparison to non-transgenic littermates. This suggests that the transgenic mice have a defect in their ability to regulate blood pressure.

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.

Semicarbazide-sensitive amine oxidase in pre-eclampsia: no relation with markers of endothelial cell activation

Background: Semicarbazide sensitive amine-oxidase (SSAO) is an adhesion molecule and thought to play a role in endothelial cell dysfunction (ECD). SSAO has never been associated with markers of ECD. Pre-eclampsia (PE) is, like the early stages of atherosclerosis, characterised by ECD. SSAO could contribute to ECD in PE. Methods: Plasma samples were obtained in 14 pre-eclamptic patients and 14 matched controls. In these SSAO-activity, von Willebrand factor (vWF) levels and ED1 fibronectin levels were determined. Placental tissue was collected of 12 pre-eclamptic pregnancies, 8 preterm deliveries and 12 term controls. In these samples, SSAO activity was assessed. In a subset of these placentas, immunohistochemical staining was performed for SSAO, ICAM-1 and VCAM-1. Results: Plasma SSAO activity was not significantly different between pre-eclamptic subjects and controls. VWF and ED1 fibronectin were both significantly increased in the pre-eclamptic subjects. There was no correlation between SSAO activity and vWF or ED1 fibronectin levels. Placental SSAO activity was not different between pre-eclamptic pregnancies, preterm deliveries and term controls. There was strong staining of SSAO in vascular smooth muscle cells (VSM) and moderate staining of trophoblast in all three groups. Endothelial cell expression of SSAO was only seen in term controls and the placentas of pre-eclamptic patients. There was no association between the expression of SSAO, ICAM-1 or VCAM-1 in the placentas of pre-eclamptic patients. Conclusion: SSAO expression and activity are not related to markers of ECD.

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.

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 βA4 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.