A comparison between radiometric and fluorimetric methods for measuring SSAO activity

Non-Ceruloplasmin Copper as a Stratification Biomarker of Alzheimer's Disease Patients: How to Measure and Use It

Alzheimer's disease (AD) is a type of dementia very common in the elderly. A growing body of recent evidence has linked AD pathogenesis to copper (Cu) dysmetabolism in the body. In fact, a subset of patients affected either by AD or by its prodromal form known as Mild Cognitive Impairment (MCI) have been observed to be unable to maintain a proper balance of Cu metabolism and distribution and are characterized by the presence in their serum of increased levels of Cu not bound to ceruloplasmin (non-ceruloplasmin Cu). Since serum non-ceruloplasmin Cu is a biomark- er of Wilson's disease (WD), a well-known condition of Cu-driven toxicosis, in this review, we pro- pose that in close analogy with WD, the assessment of non-ceruloplasmin Cu levels can be exploit- ed as a cost-effective stratification and susceptibility/risk biomarker for the identification of some AD/MCI individuals. The approach can also be used as an eligibility criterion for clinical trials aim- ing at investigating Cu-related interventions against AD/MCI.

Development of a HPLC-FL method to determine benzaldehyde after derivatization with N-acetylhydrazine acridone and its application for determination of semicarbazide-sensitive amine oxidase activity in human serum

A novel fluorescence labeling reagent N-acetylhydrazine acridone (AHAD) was designed and synthesized. A highly sensitive high performance liquid chromatography (HPLC) method coupled with fluorescence detection to determine benzaldehyde after derivatization with AHAD was developed. Optimum derivatization was obtained at 40 °C for 30 min with trichloroacetic acid as catalyst. Benzaldehyde derivative was separated on a reversed-phase SB-C18 column in conjunction with a gradient elution and detected by fluorescence detection at excitation and emission wavelengths of 371 nm and 421 nm. The established method exhibited excellent linearity over the injected amount of benzaldehyde of 0.003 to 5 nmol mL⁻¹. The method was successfully applied to the determination of serum semicarbazide-sensitive amine oxidase (SSAO) activity in humans. SSAO is a significant biomarker because serum SSAO activity is elevated in patients with Alzheimer's disease, vascular disorders, heart disease and diabetes mellitus. It was demonstrated that the SSAO activity of the hyperglycemic group (60 ± 4 nmol mL⁻¹ h⁻¹) was significantly higher than that of normal blood sugar group (44 ± 4 nmol mL⁻¹ h⁻¹) with P < 0.05.

A highly sensitive HPLC-FL method to determine semicarbazide-sensitive amine oxidase activity was developed utilizing AHAD as the novel fluorescence labeling reagent.

Anatomical distribution of primary amine oxidase activity in four adipose depots and plasma of severely obese women with or without a dysmetabolic profile

Semicarbazide-sensitive amine oxidase (SSAO), identical to primary amine oxidase or vascular adhesion protein-1, is a membrane enzyme that generates hydrogen peroxide. SSAO is highly expressed at the adipocyte surface, and its plasma levels increase with type 2 diabetes. Since visceral adipose tissue (AT) is more tightly associated with obesity complications than subcutaneous (SC) abdominal fat, we compared SSAO activity in plasma and 4 distinct AT locations in 48 severely obese women (body mass index (BMI), averaging 54 ± 11 kg/m²), with or without a dysmetabolic profile. Higher glucose and triacylglycerol levels vs lower high-density lipoprotein (HDL)-cholesterol characterized dysmetabolic women (DYS; n = 25) from non-dysmetabolic (NDYS; n = 23), age- and weight-matched subjects. SC, mesenteric (ME), omental (OM), and round ligament (RL) fat locations were collected during bariatric surgery. SSAO capacity to oxidize up to 1 mM benzylamine was determined in AT and plasma with radiometric and fluorimetric methods. Plasma SSAO was higher in the DYS group. SSAO activity was higher in fat than in plasma, when expressed as radiolabeled benzaldehyde per milligram of protein. In ATs from DYS women, protein content was 10 % higher, and basal hydrogen peroxide release lower than in NDYS subjects, except for RL location. The SSAO affinity towards benzylamine did not exhibit regional variation and was not altered by a dysmetabolic profile (K _m averaging 184 ± 7 μM; n = 183). Although radiometric and fluorimetric methods gave different estimates of oxidase activity, both indicated that AT SSAO activity did not vary according to anatomical location and/or metabolic status in severely obese women.

Glitazones inhibit human monoamine oxidase but their anti-inflammatory actions are not mediated by VAP-1/semicarbazide-sensitive amine oxidase inhibition

Glitazones are peroxisome proliferator-activated receptor gamma (PPARγ) agonists widely used as antidiabetic drugs also known as thiazolidinediones. Most of them exert other effects such as anti-inflammatory actions via mechanisms supposed to be independent from PPARγ activation (e.g., decreased plasma monocyte chemoattractant protein-1 (MCP-1) levels). Recently, pioglitazone has been shown to inhibit the B form of monoamine oxidase (MAO) in mouse, while rosiglitazone and troglitazone were described as non-covalent inhibitors of both human MAO A and MAO B. Since molecules interacting with MAO might also inhibit semicarbazide-sensitive amine oxidase (SSAO), known as vascular adhesion protein-1 (VAP-1), and since VAP-1/SSAO inhibitors exhibit anti-inflammatory activity, our aim was to elucidate whether VAP-1/SSAO inhibition could be a mechanism involved in the anti-inflammatory behaviour of glitazones. To this aim, MAO and SSAO activities were measured in human subcutaneous adipose tissue biopsies obtained from overweight women undergoing plastic surgery. The production of hydrogen peroxide, an end-product of amine oxidase activity, was determined in tissue homogenates using a fluorometric method. The oxidation of 1 mM tyramine was inhibited by pargyline and almost resistant to semicarbazide, therefore predominantly MAO-dependent. Rosiglitazone was more potent than pioglitazone in inhibiting tyramine oxidation. By contrast, benzylamine oxidation was only abolished by semicarbazide: hence SSAO-mediated. Pioglitazone hampered SSAO activity only when tested at 1 mM while rosiglitazone was inefficient. However, rosiglitazone exhibited anti-inflammatory activity in human adipocytes by limiting MCP-1 expression. Our observations rule out any involvement of VAP-1/SSAO inhibition and subsequent limitation of leukocyte extravasation in the anti-inflammatory action of glitazones.

Semicarbazide-sensitive amine oxidase (SSAO) inhibition ameliorates kidney fibrosis in a unilateral ureteral obstruction murine model

Semicarbazide-sensitive amine oxidase (SSAO) is an enzyme known for its dual function in mediating inflammation and reactive oxygen species production. However, the role of SSAO inhibitors in limiting kidney fibrosis is unclear. We aimed to determine the effectiveness of a SSAO inhibitor (SSAOi; PXS4728A) as an antifibrotic agent using a 7-day unilateral ureteric obstruction (UUO) model of acute kidney fibrosis in 6- to 8-wk-old mice. The experimental groups were 1) Sham operated; 2) UUO; 3) UUO+SSAOi (2 mg/kg); 4) UUO+telmisartan, an angiotensin receptor blocker (3 mg/kg); and 5) UUO+SSAOi+telmisartan. Kidney tissue was analyzed for histological evidence of tubulointerstitial fibrosis, nitrotyrosine staining, and mRNA expression of markers associated with fibrosis and inflammation. Kidney SSAO activity was determined by radiometric [14C]benzylamine methodology. Our results show that SSAOi effectively suppresses UUO-mediated SSAO activity. Extracellular matrix markers, namely, fibronectin, collagen IV protein, and nitrotyrosine staining, were lower in UUO+SSAOi mice compared with untreated UUO mice. This was consistent with the attenuated mRNA expression of collagen IV and fibronectin. SSAOi effectively inhibited transforming growth factor-β1 (TGF-β1) and monocyte chemoattractant protein-1 (MCP-1) expression to a similar extent to that observed with telmisartan. Individually, SSAOi and telmisartan induced a reduction in interstitial leukocyte and macrophage accumulation. However, the combination of SSAOi and telmisartan was more effective at reducing inflammatory cell infiltration. These results demonstrate that SSAO inhibition significantly suppresses profibrotic and proinflammatory cytokine secretion, reduces oxidative stress, and limits inflammatory cell accumulation and extracellular matrix expression in an acute model of renal fibrosis.