Unprocessed serum glycosylphosphatidylinositol-anchored proteins are correlated to metabolic states

To study the possibility that components of eukaryotic plasma membranes are released in spontaneous or controlled fashion, a chip-based sensor was developed for complete glycosylphosphatidylinositol-anchored proteins (GPI-AP), which may form together with (phospho)lipids so far unknown (non-vesicular) extracellular complexes (GLEC). The sensor relies on changes in phase shift and amplitude of surface acoustic waves propagating over the chip surface upon specific capturing of the GPI-AP and detection of associated phospholipids and renders isolation of the labile GLEC unnecessary. GLEC were found to be released from isolated rat adipocyte plasma membranes immobilized on the chip, dependent on the flow rate and composition of the buffer stream. Moreover, incubation medium of isolated adipocytes and serum of rats are sources for GLEC which enables their differentiation according to cell size and genotype or body weight, respectively, as well as human serum.