Association between plasma activities of semicarbazide-sensitive amine oxidase and angiotensin-converting enzyme in patients with type 1 diabetes mellitus

Amine oxidase copper-containing 3 (AOC3) inhibition: a potential novel target for the management of diabetic retinopathy

Background

Diabetic retinopathy (DR), a microvascular complication of diabetes, is the leading cause of visual impairment in people aged 20–65 years and can go undetected until vision is irreversibly lost. There is a need for treatments for non-proliferative diabetic retinopathy (NPDR) which, in comparison with current intravitreal (IVT) injections, offer an improved risk–benefit ratio and are suitable for the treatment of early stages of disease, during which there is no major visual impairment. Efficacious systemic therapy for NPDR, including oral treatment, would be an important and convenient therapeutic approach for patients and physicians and would reduce treatment burden. In this article, we review the rationale for the investigation of amine oxidase copper-containing 3 (AOC3), also known as semicarbazide-sensitive amine oxidase and vascular adhesion protein 1 (VAP1), as a novel target for the early treatment of moderate to severe NPDR. AOC3 is a membrane-bound adhesion protein that facilitates the binding of leukocytes to the retinal endothelium. Adherent leukocytes reduce blood flow and in turn rupture blood vessels, leading to ischemia and edema. AOC3 inhibition reduces leukocyte recruitment and is predicted to decrease the production of reactive oxygen species, thereby correcting the underlying hypoxia, ischemia, and edema seen in DR, as well as improving vascular function.

Conclusion

There is substantial unmet need for convenient, non-invasive treatments targeting moderately severe and severe NPDR to reduce progression and preserve vision. The existing pharmacotherapies (IVT corticosteroids and IVT anti-vascular endothelial growth factor-A) target inflammation and angiogenesis, respectively. Unlike these treatments, AOC3 inhibition is predicted to address the underlying hypoxia and ischemia seen in DR. AOC3 inhibitors represent a promising therapeutic strategy for treating patients with DR and could offer greater choice and reduce treatment burden, with the potential to improve patient compliance.

Vascular Adhesion Protein-1: A Cell Surface Amine Oxidase in Translation

Significance: Vascular adhesion protein-1 (VAP-1) is an ectoenzyme that oxidates primary amines in a reaction producing also hydrogen peroxide. VAP-1 on the blood vessel endothelium regulates leukocyte extravasation from the blood into tissues under physiological and pathological conditions. Recent Advances: Inhibition of VAP-1 by neutralizing antibodies and by several novel small-molecule enzyme inhibitors interferes with leukocyte trafficking and alleviates inflammation in many experimental models. Targeting of VAP-1 also shows beneficial effects in several other diseases, such as ischemia/reperfusion, fibrosis, and cancer. Moreover, soluble VAP-1 levels may serve as a new prognostic biomarker in selected diseases. Critical Issues: Understanding the contribution of the enzyme activity-independent and enzyme activity-dependent functions, which often appear to be mediated by the hydrogen peroxide production, in the VAP-1 biology will be crucial. Similarly, there is a pressing need to understand which of the VAP-1 functions are regulated through the modulation of leukocyte trafficking, and what is the role of VAP-1 synthesized in adipose and smooth muscle cells. Future Directions: The specificity and selectivity of new VAP-1 inhibitors, and their value in animal models under therapeutic settings need to be addressed. Results from several programs studying the therapeutic potential of VAP-1 inhibition, which now are in clinical trials, will reveal the relevance of this amine oxidase in humans.

Vascular adhesion protein-1: Role in human pathology and application as a biomarker

Vascular adhesion protein-1 (VAP-1) is a member of the copper-containing amine oxidase/semicarbazide-sensitive amine oxidase (AOC/SSAO) enzyme family. SSAO enzymes catalyze oxidative deamination of primary amines, which results in the production of the corresponding aldehyde, hydrogen peroxide and ammonium. VAP-1 is continuously expressed as a transmembrane glycoprotein in the vascular wall during development and facilitates the accumulation of inflammatory cells into the inflamed environment in concert with other leukocyte adhesion molecules. The soluble form of VAP-1 is released into the circulation mainly from vascular endothelial cells. Over- and under-expression of sVAP-1 result in alterations of the reported reaction product levels, which are involved in the pathogenesis of multiple human diseases. The combination of enzymatic and adhesion capacities as well as its strong association with inflammatory pathologies makes VAP-1 an interesting therapeutic target for drug discovery. In this article, we will review the general characteristics and biological functions of VAP-1, focusing on its important role as a prognostic biomarker in human pathologies. In addition, the potential therapeutic application of VAP-1 inhibitors will be discussed.

Plasma semicarbazide-sensitive amine oxidase activity in type 1 diabetes is related to vascular and renal function but not to glycaemia

PURPOSE

Associations of semicarbazide-sensitive amine oxidase (SSAO) activity with renal and vascular function, oxidative stress, glycaemia and diabetes complications were determined.

METHODS

Plasma SSAO activity in 94 type 1 diabetes (T1DM) patients, including 34 with microvascular complications T1DM CX[+], and in 96 healthy subjects (CON) was measured by production of benzaldehyde using high-performance liquid chromatography (HPLC).

RESULTS

SSAO activity (mean ± SD) was greater in T1DM than in CON (1049 ± 294 vs 749 ± 204 mU/L; p < 0.00001) and was higher in T1DM CX[+] vs complication-free DM subjects (1148 ± 313 mU/L vs 982 ± 269 mU/L; p = 0.01). In T1DM, SSAO activity correlated with renal dysfunction [estimated glomerular filtration rate (eGFR): r = -0.44; p = 0.0001; cystatin C: r = 0.47; p = 0.0001] and markers of inflammation [soluble vascular cell adhesion molecule-1 (sVCAM-1): r = 0.41, p = 0.0001; soluble intercellular adhesion molecule-1 (sICAM-1): r = 0.33, p = 0.002] and was inversely related to small artery elasticity (SAE) (r = -0.23, p = 0.03). In CON, SSAO activity correlated with HbA1c (r = 0.26; p = 0.02).

CONCLUSION

In T1DM, SSAO activity correlates with renal dysfunction, but not with glycaemia, and may promote vascular inflammation and be a therapeutic target.

Distribution and accumulation of caffeine in rat tissues and its inhibition on semicarbazide-sensitive amine oxidase

Wistar rats were treated with caffeine or 2-bromoethylamine, the effect of caffeine on the activity of semicarbazide-sensitive amine oxidase (SSAO) in rat serum and tissues was studied using various LC-MS methods. Caffeine was found to present in all tissues after administration for 10 days and accumulated for 25 days. The level of caffeine was high in brain and liver, and the SSAO activity in all tissues was found to be inhibited by caffeine. As the concentration of caffeine increased, the SSAO activity decreased. The inhibition ratio was correlated to the levels of caffeine present. We presume that caffeine may treat with SSAO activity associated diseases.

Soluble vascular adhesion protein-1 correlates with cardiovascular risk factors and early atherosclerotic manifestations

OBJECTIVE

Vascular adhesion protein-1 is an endothelial enzyme that regulates leukocyte traffic and contributes to vascular damage in animal models. The relations of soluble vascular adhesion protein-1 (sVAP-1) with cardiovascular risk factors and markers of subclinical atherosclerosis at a population level have not been studied.

METHODS AND RESULTS

We developed a new high-throughput method and measured sVAP-1 activities in serum of 2183 persons (The Cardiovascular Risk in Young Finns Study). In women, sVAP-1 activity correlated indirectly with body mass index (r=-0.15, P<0.0001), triglycerides (r=-0.13, P<0.0001), C-reactive protein (r=-0.23; P<0.0001), and brachial artery flow-mediated vasodilatation (r=-0.076, P=0.0089) and directly with carotid plaques (r=0.066, P=0.023). None of these correlations was significant in men. In women, all these univariate correlations remained significant after adjustment for body mass index, and direct correlations with LDL-cholesterol (r=0.094, P=0.0014) and carotid intima-media thickness (r=0.075, P=0.010) became evident. In men, sVAP-1 activity associated directly with glucose (r=0.074, P=0.020), intima-media thickness (r=0.072, P=0.025), metabolic syndrome (P=0.016), and type 1 (P=0.0002) and type 2 (P<0.0001) diabetes. In multivariable analyses, sVAP-1 activity was an independent determinant of carotid intima-media thickness (P=0.0072) and plaques [odds ratio 1.71 (95% confidence interval 1.07-2.72, P=0.025] in women, but not in men.

CONCLUSIONS

sVAP-1 activity correlates directly with intima-media thickness and carotid plaques in general population and may play a role in the pathophysiology of preclinical atherosclerosis.

Soluble vascular adhesion protein-1: decreased activity in the plasma of trauma victims and predictive marker for severity of traumatic brain injury

BACKGROUND

This study done was to investigate the clinical significance of soluble vascular adhesion protein-1 (sVAP-1) activity in trauma patients with different patterns.

METHODS

96 patients with consecutive trauma ≥15 years who were admitted to emergency department of the Second Affiliated Hospital, Shantou University Medical College, China, between January 2007 and December 2009 were enrolled in this study. Plasma was collected at admission. Injury-severity score (ISS) and Glasgow Coma Scale (GCS) were used to determine the patient conditions. sVAP-1 activity was determined by using the high performance liquid chromatographic (HPLC) system.

RESULTS

Mean sVAP-1 activity in trauma patients was significantly lower than that of controls (P<0.0001), and the level was negatively correlated with circulating leucocytes and neutrophils (P<0.0001). There was a significant correlation between lower sVAP-1 activity and injury patterns. However, plasma sVAP-1 activity increased significantly in accordance with the severity of traumatic brain injury (TBI), and the patients with sVAP-1 value above 8.61 nmol/ml/h have much higher mortality rate (25.0%) than patients with sVAP-1 value lower than 8.61 nmol/ml/h (0.0%) (P=0.011).

CONCLUSIONS

Trauma patients had a decreased sVAP-1 activity. However, isolated TBI patients with higher activity of sVAP-1 at admission were more likely to have a poor outcome.

SSAO substrates exhibiting insulin-like effects in adipocytes as a promising treatment option for metabolic disorders

BACKGROUND

Benzylamine exerts insulin-like effects in adipocytes (e.g., glucose uptake and antilipolysis) and improves glucose handling in rodents.

RESULTS

In murine adipocytes, benzylamine mimics another insulin action: it enhances apelin expression in a manner that is blocked by the semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) inhibitor semicarbazide. It is shown that in human adipocytes, benzylamine activates glucose transport, but its effects are not additive to maximal insulin stimulation. Benzylamine effects are hydrogen peroxide dependent. They can be reproduced by novel substrates, but not by benzaldehyde.

CONCLUSION

Owing to the parallelism between the in vitro insulin mimicry and the in vivo improvement of glucose handling elicited by benzylamine in rodents, the SSAO/VAP-1 substrates, with stronger effects on human adipocytes than benzylamine, show promising applications for the treatment of insulin resistance.

A high concentration of prorenin in early pregnancy is associated with development of pre-eclampsia in women with type 1 diabetes

AIMS/HYPOTHESIS

The aim of this study was to investigate whether components of the renin-angiotensin system and semicarbazide-sensitive amine oxidase (SSAO) are associated with the development of pre-eclampsia in women with type 1 diabetes.

METHODS

This was an observational study of 107 consecutive pregnant women with type 1 diabetes (median duration 16 years [range 1-36 years], HbA(1c) 6.6% [range 4.9-10.5%]) in early pregnancy. At 8, 14, 21, 27 and 33 weeks and once within 5 days postpartum, blood was sampled for measurements of prorenin, renin, angiotensinogen, ACE and SSAO. HbA(1c), blood pressure and urinary albumin excretion were recorded. Pre-eclampsia was defined as blood pressure >140/90 mmHg and proteinuria ≥300 mg/24 h after 20 weeks.

RESULTS

Pre-eclampsia developed in nine women (8%) with longer diabetes duration (median 20 [range 10-32] vs 16 [range 1-36] years, p = 0.04), higher SSAO concentrations (592 [range 372-914] vs 522 [range 264-872] mU/l, p = 0.04) and a tendency towards higher prorenin levels (136 [range 50-296] vs 101 [range 21-316] ng angiotensin I ml(-1) h(-1), p = 0.06) at 8 weeks compared with women without pre-eclampsia. Levels of renin, angiotensinogen and ACE did not differ in the two groups. Throughout pregnancy, prorenin and SSAO levels were 30% (p = 0.004) and 16% (p = 0.04) higher, respectively, in women developing pre-eclampsia. Using multivariate logistic regression analysis, prorenin concentration at 8 weeks was associated with pre-eclampsia (OR 4.4 [95% CI 1.5-13.0], p = 0.007), i.e. an increase of prorenin of 100 ng angiotensin I ml(-1) h(-1) implies a 4.4 times higher risk of subsequent pre-eclampsia.

CONCLUSIONS/INTERPRETATION

In type 1 diabetic women with pre-eclampsia, a higher concentration of prorenin in early pregnancy and higher levels of prorenin and SSAO throughout pregnancy were seen.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Synergistic interaction between semicarbazide-sensitive amine oxidase and angiotensin-converting enzyme in diabetes: functional analysis by gene ontology

Plasma semicarbazide-sensitive amine oxidase (SSAO) and angiotensin-converting enzyme (ACE) were studied for their correlation with diabetes (DM) complication. The effect of interaction between SSAO and ACE in DM complication is of interest. Studying the functional change due to interaction between SSAO and ACE is difficult. In this work, the author used a new gene ontology technology to predict the functional change resulting from the interaction between SSAO and ACE. According to this study, there is a synergetic effect resulting from the interaction between SSAP and ACE. This can imply that co-expression of SSAP-ACE leads to more severe complication of DM. However, the author can also demonstrate that some molecular functions such as proteasome activator activity of SSAO and hydrolase activity, metallopeptidase activity, and zinc ion binding of ACE are suppressed after co-expression. These results provide good information for further study in diabetes medicine. However, further experimental works are required to support this in silico research.

Enzymes and pharmacogenetics of cardiovascular drugs

To select the best drug for a patient, physicians can use pharmacogenomics to optimize the effective drug and to minimize adverse reactions. Many enzymes are involved in the pharmacokinetic and pharmacodynamic sources of cardiovascular drugs. Taking the antihypertensive drugs as an example, the variability in blood pressure response is very high in different individuals, some of them having an increase in blood pressure. The most important proteins involved in the patient response to a drug are cytochrome P450 (CYP) 2D6, CYP2C19, CYP3A4 and the ABCB1 transporter. These enzymes, at the origin of important side effects or drug interactions, are responsible, at a great extent, of the cardiovascular drug response variability. Genotyping of the most important CYP today is easy while no reliable tool has been developed for the ABC transporters ATPase dependent and linked to the other phase I and phase II enzymes. The second relevant group of enzymes are involved in pharmacodynamic action of cardiovascular drugs: enzymes of the renin-angiotensin system and enzymes of the lipid metabolism. Angiotensin converting enzyme (ACE) is the most studied target with a relevant insertion deletion polymorphism. Contradictory reported data could be explained by ethnic differences or patient sample size which are often too small.

Plasma semicarbazide-sensitive amine oxidase is moderately decreased by pronounced exogenous hyperinsulinemia but is not associated with insulin sensitivity and body fat

OBJECTIVE

Semicarbazide-sensitive amine oxidase (SSAO) is widely expressed in adipose tissue, where it may contribute to stimulation of glucose transport via GLUT4 recruitment. We tested the relationships of soluble SSAO, as reflected by its plasma activity, with insulin sensitivity and indices of body fat, and determined whether insulin is involved in regulating plasma SSAO activity.

MATERIAL AND METHODS

In 24 non-diabetic subjects, the relationships of plasma SSAO activity with insulin sensitivity (M-value and free fatty acid (FFA) suppression during a 3-h hyperinsulinemic (8.3 microU kg-1 s-1), euglycemic clamp), body mass index (BMI 25.5 +/- 3.1 kg m-2), waist-hip ratio and fat mass were assessed. In 16 subjects, the effect of insulin infusion, administered at a rate of 8.3 microU kg-1 s-1 during 3 h, followed by 3-h insulin infusion at a high rate of 41.7 microU kg-1 s-1 on plasma SSAO activity was determined. In the other 8 subjects, the response of plasma SSAO activity to 24-h insulin infused at 8.3 microU kg-1 s-1 was assessed.

RESULTS

There were no relationships (all p > 0.10) of plasma SSAO activity (215 +/- 60 mU L-1) with the M-value or with any indices of body fat and FFA before and after insulin suppression. Plasma SSAO activity changed by -7.2 (95% CI, -14.5 to +0.2)% after 3 h (NS) and decreased by 10.1 (95% CI, 19.2 to 1)% after 6 h of insulin infusion (p < 0.05). Plasma SSAO activity did not significantly change after 8 h (change 0.4 (95% CI, -15.3 to +16.2)%, NS) and after 24 h (change -8.8 (95% CI, -27.4 to +9.7)%, NS) of insulin infusion.

CONCLUSIONS

It is unlikely that circulating SSAO is a clinically important marker of insulin sensitivity on glucose and fatty acid metabolism. The reduction in plasma SSAO activity in response to pronounced hyperinsulinemia suggests that insulin is involved in the regulation of the soluble form of this enzyme.

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.

Pharmacogenomics and cardiovascular drugs: need for integrated biological system with phenotypes and proteomic markers

Personalized medicine is based on a better knowledge of biological variability, considering the important part due to genetics. When trying to identify involved genes and their products in differential cardiovascular drug responses, a five-step strategy is to be followed: 1) Pharmacokinetic-related genes and phenotypes (2) Pharmacodynamic targets, genes and products (3) Cardiovascular diseases and risks depending on specific or large metabolic cycles (4) Physiological variations of previously identified genes and proteins (5) Environment influences on them. After summarizing the most well-known genes involved in drug metabolism, we will take as example of drugs, the statins, considered as very important drugs from a Public-Health standpoint, but also for economical reasons. These drugs respond differently in human depending on multiple polymorphisms. We will give examples with common ApoE polymorphisms influencing the hypolipemic effects of statins. These drugs also have pleiotropic effects and decrease inflammatory markers. This illustrates the need to separate clinical diseases phenotypes in specific metabolic pathways, which could propose other classifications, of diseases and related genes. Hypertension is also a good example of clinical phenotype which should be followed after various therapeutic approaches by genes polymorphisms and proteins markers. Gene products are under clear environmental expression variations such as age, body mass index and obesity, alcohol, tobacco and dietary interventions which are the first therapeutical actions taken in cardiovascular diseases. But at each of the five steps, within a pharmacoproteomic strategy, we also need to use available information from peptides, proteins and metabolites, which usually are the gene products. A profiling approach, i.e., dealing with genomics, but now also with proteomics, is to be used. In conclusion, the profiling, as well as the large amount of data, will more than before render necessary an organized interpretation of DNA, RNA as well as proteins variations, both at individual and population level.