Semicarbazide-Sensitive Amine Oxidase/Vascular Adhesion Protein-1 Activity Exerts an Antidiabetic Action in Goto-Kakizaki Rats

Abstract

In this study we have explored whether the bifunctional protein semicarbazide-sensitive amine oxidase (SSAO)/ vascular adhesion protein-1 (VAP-1) represents a novel target for type 2 diabetes. To this end, Goto-Kakizaki (GK) diabetic rats were treated with the SSAO substrate benzylamine and with low ineffective doses of vanadate previously shown to have antidiabetic effects in streptozotocin-induced diabetic rats. The administration of benzylamine in combination with vanadate in type 2 diabetic rats acutely stimulated glucose tolerance, and the chronic treatment normalized hyperglycemia, stimulated glucose transport in adipocytes, and reversed muscle insulin resistance. Acute in vivo administration of benzylamine and vanadate stimulated skeletal muscle glucose transport, an effect that was also observed in incubated muscle preparations coincubated with adipose tissue explants or with human recombinant SSAO. Acute administration of benzylamine/vanadate also ameliorated insulin secretion in diabetic GK rats, and this effect was also observed in incubated pancreatic islets. In keeping with these observations, we also demonstrate that pancreatic islets express SSAO/ VAP-1. As far as mechanisms of action, we have found that benzylamine/vanadate causes enhanced tyrosine phosphorylation of proteins and reduced protein tyrosine phosphatase activity in adipocytes. In addition, incubation of human recombinant SSAO, benzylamine, and vanadate generates peroxovanadium compounds in vitro. Based on these data, we propose that benzylamine/vanadate administration generates peroxovanadium locally in pancreatic islets, which stimulates insulin secretion and also produces peroxovanadium in adipose tissue, activating glucose metabolism in adipocytes and in neighboring muscle. This opens the possibility of using the SSAO/VAP-1 activity as a local SSAO/VAP-1 is expressed in a variety of tissues, and under normal conditions expression is high in adipose cells. In isolated rat adipocytes, SSAO/VAP-1 is mainly at the plasma membrane, and nearly 17 ϫ 10 6 copies of this protein are present at the cell surface in a single adipocyte (5,6). In contrast, SSAO activity is very low or absent in other insulin-responsive tissues such as skeletal muscle or heart (7). In fact, it has been demonstrated that SSAO/ VAP-1 is not expressed in 3T3-L1 fibroblasts and that SSAO/VAP-1 gene expression is induced during adipogenesis (8). This finding is in complete agreement with the previous observation of an increase in the SSAO activity of stroma-vascular preadipocytes from rat adipose tissue during their conversion into adipocytes when cultured in vitro (9). This suggests that SSAO/VAP-1 is a member of the adipogenic gene program and, in addition, that SSAO/ VAP-1 may contribute to the acquisition of some final characteristics of fully differentiated adipose cells. Most of the SSAO/VAP-1 expressed in rat adipocytes is found in plasma membrane (5,6). Thus, subcellular fractionation of membranes from 3T3-L1 adipocytes or isolated rat adipocytes has demonstr...

Oral Insulin-Mimetic Compounds That Act Independently of Insulin

“…In addition, the combination of SSAO substrates and vanadate ameliorates insulin secretion in Goto-Kakizaki rats (13). During these studies, we noted the possibility of generating vanadium salts containing arylalkylamines that are also substrates of SSAO/VAP-1 such as benzylamine.…”

“…We have previously reported that the combination of semicarbazide (SCZ)-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) substrates and low doses of vanadate show antidiabetic effects in streptozotocininduced diabetic and Goto-Kakizaki diabetic rats (13,14) and significantly enhance glucose transport in adipocytes (15,16) and in skeletal muscle (17). In addition, the combination of SSAO substrates and vanadate ameliorates insulin secretion in Goto-Kakizaki rats (13).…”

“…Measurements in incubated soleus muscle. Isolated strips of soleus muscles were incubated, and 2-D-deoxyglucose uptake measurements were performed as reported previously (13). Muscle homogenates were obtained from strips of rat soleus.…”

Determination of human serum semicarbazide-sensitive amine oxidase activity via flow injection analysis with fluorescence detection after online derivatization of the enzymatically produced benzaldehyde with 1,2-diaminoanthraquinone

“…The obtained yellowish-brown compound was subjected to electron impact mass spectrometry (EI-MS) to identify the molecular ion and 1 H NMR studies to prove the structure. The EI-MS spectra were recorded using JMS DX-303 mass spectrometer (Joel Ltd., Japan) and 1 H NMR spectra were recorded using Varian5-inova500 (500 Hz) spectrometer (Varian, CA, USA).…”

“…It is a copper-containing glycoprotein possessing topa-quinone as a cofactor. These enzymes are found in most of the mammalians in two forms: tissue-bound and soluble isoforms (i.e., serum SSAO) [1,2]. The SSAO enzymes are different from the monoamine oxidases (MAO-A and MAO-B) in their inhibition pattern: they have tolerance to MAO inhibitors like clorgiline, pargyline and deprenyl, but sensitive to semicarbazide and other hydrazines [3].…”