Unique sphingomyelin patches are targets of a beta-cell-specific antibody

Abstract

This article is available online at http://www.jlr.org this restoration noninvasively ( 1 ). Recent years have seen exponential progress in applying various imaging modalities (MRI, positron emission tomography, optical) for noninvasive detection and monitoring of pancreatic ␤ -cell mass ( 2-6 ). A crucial prerequisite for clinical application of these techniques is the availability of a contrast agent with high affi nity and high specifi city toward ␤ -cell surface markers.Antibodies or their fragments, owing to their high specifi city, biocompatibility and ability to carry payload to the target site, could serve as an ideal molecule for imaging applications. A number of different antibodies have been suggested for noninvasive determination of ␤ -cell mass ( 7-9 ). However, most of them suffer from lack of specifi city for islet ␤ cells. Part of this problem emanates from the fact that ␤ cells share the same lineage as other cells in the pancreas, making it diffi cult to elucidate unique targets on the ␤ -cell surface. In addition, there is a challenging requirement for imaging agents to be retained by ␤ cells at least 1,000-fold more strongly than by exocrine cells ( 10 ). No antibodies/antibody fragments have yet been described that fulfi ll all the requirements, necessitating a further search for ␤ -cell biomarkers. The single-chain antibody SCA B5 has shown promise in the past ( 11 ). However, its target and its utility for ␤ -cell imaging are unknown.In a previous study, we showed that the 125 I-labeled ␤ -cell-specifi c IC2 antibody accumulates in the pancreas of streptozotocin-induced mice in direct proportion to ␤ -cell mass ( 2 ). However, further progress toward the development of an antibody-based in vivo imaging probe was impeded due to lack of information about the nature and identity of the ␤ -cell surface antigen. IC2 is a rat monoclonal antibody of the IgM isotype, obtained by fusing lymphocytes from diabetes-prone BB rats with a rat myeloma partner and selected by screening hybridoma supernatants against Rin5F insulinoma cells ( 12 ). In this study, we present Abstract To devise successful imaging and therapeutic strategies, the identifi cation of ␤ -cell surface markers is one of the challenges in diabetes research that has to be resolved. We previously showed that IC2, a rat monoclonal IgM antibody, can be used for ex vivo determination of Increased blood glucose levels mostly accompanied by a decrease in functional ␤ -cell mass are a key characteristic of human diabetes. While type 1 diabetes results from autoimmune destruction of insulin-producing ␤ cells, type 2 diabetes is characterized by insulin resistance and relative insulin defi ciency. In both cases, pancreatic ␤ -cell mass is affected by the disease. Patients suffering from these conditions would benefi t from clinical interventions aimed at restoring functional ␤ -cell mass and methods to monitor Award JDRF 37-2009-30 (A.M.). This work was supported in part by Juvenile Diabetes Research Foundation

Sphingomyelin Patches on Pancreatic Beta-cells Are Indicative of Insulin Secretory Capacity

“…We recently reported the discovery of cholesterol-stabilized sphingomyelin patches on the surface of beta-cells that are targeted by IC2, a rat monoclonal antibody (Kavishwar et al 2011). In this study, we investigated whether the expression of these patches vary during diabetes development.…”

“…We have previously shown the utility of the IC2 antibody in determining beta cell mass ex vivo in an STZ model of diabetes (Moore et al 2001). To fully exploit the value of this antibody or its fragments for imaging and/or targeted therapy we have recently elucidated the antigen for this antibody (Kavishwar et al 2011). In particular, we showed that sphingomyelin stabilized with cholesterol forms unique patches on the surface of beta-cells that are recognized by the IC2 antibody.…”

“…We have previously identified sphingomyelin patches as an antigen for this antibody (Kavishwar et al 2011). In this study, we used sphingomyelin-coated PVDF membranes as a stationary phase.…”

“…In particular, we showed that sphingomyelin stabilized with cholesterol forms unique patches on the surface of beta-cells that are recognized by the IC2 antibody. Furthermore, these patches were unique for beta-cells and were not expressed on any other types of islet cells or in any other tissue (Kavishwar et al 2011). To further investigate the utility of SM patches as a unique betacell biomarker, we embarked on the current study.…”

“…To this end, we have recently described unique cholesterolstabilized sphingomyelin (SM) patches on the surface of betacells defined by targeting with an IC2 antibody (Kavishwar et al 2011). IC2 is a rat monoclonal IgM that was obtained by fusing splenocytes from diabetic BioBreeding (BB) rats with the Y.3 Ag 1.2.3 rat myeloma cell line.…”