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

Abstract

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 .