Establishment of in vitro binding assay of high mobility group box-1 and S100A12 to receptor for advanced glycation endproducts: Heparin's effect on binding

Interaction between the receptor for advanced glycation end products (RAGE) and its ligands has been implicated in the pathogenesis of various inflammatory disorders. In this study, we establish an in wtro binding assay in which recombinant human high-mobility group box 1 (rhHMGBl) or recombinant human S100A12 (rhS100A12) immobilized on the microplate binds to recombinant soluble RAGE (rsRAGE). The rsRAGE binding to both rhHMGBl and rhS100A12 was saturable and dependent on the immobilized ligands. The binding of rsRAGE to rhS100A12 depended on Ca²⁺ and Zn²⁺, whereas that to rhHMGBl was not. Scatchard plot analysis showed that rsRAGE had higher affinity for rhHMGBl than for rhS100A12. rsRAGE was demonstrated to bind to heparin, and rhS100A12, in the presence of Ca²⁺, was also found to bind to heparin. We examined the effects of heparin preparations with different molecular sizes-unfractionated native heparin (UFH), low molecular weight heparin (LMWH) 5000 Da, and LMWH 3000 Da- on the binding of rsRAGE to rhHMGBl and rhS100A12. All 3 preparations concentration-dependently inhibited the binding of rsRAGE to rhHMGBl to a greater extent than did rhS100A12. These results suggested that heparin's anti-inflammatory effects can be partly explained by its blocking of the interaction between HMGB1 or S100A12 and RAGE. On the other hand, heparin would be a promising effective remedy against RAGE-related inflammatory disorders.