A new approach for treatments against central nervous disease : Structure of albumin-derived microglial activating factor

Microglial activation has recently been recognized as a cause of damage in various neurodegenerative diseases.A possible mechanism underlying this damage is the activation of microglia by serum factors leaked through a disruption of the blood-brain barrier，which in turn trigger microglial cell proliferation and the release of various substances toxic to neurons，such as superoxide(O ii D22齐埃D2)。We recently reported that serum albumin enhanced O I D22文件D2 production in cultured rat microglia stimulated by phorbol ester(Si e al.，1997，Glia21：413-418)。In the present report，we identify the active site of this enhancement within the albumin molecule。We purified an active subfragment from trypsin-treated bovine serum albumin(BSA)that was composed of 12-mer and 33-mer peptides connected by a disulfide bond.The chemically synthesized12-mer peptide showed activity within a concentration range(ca.10I D1-7I D1M)equivalent to that of albumin.The activities of a series of synthesized peptides conclusively indicated that the minimum active sequence was Leu-His-Thr-Leu。Enhancement of O I D22文件D2 production by this peptide was also observed in macrophages quiescently prepared from rat peritoneal fluid。The present study may contribute toward the development of a tool to suppress the pathological activation of microglia and may also shed light on albumin‘s role in the biological defense system。

Microglial activation has recently been recognized as a cause of damage in various neurodegenerative diseases. A possible mechanism underlying this damage is the activation of microglia by serum factors leaked through a disruption of the blood-brain barrier, which in turn trigger microglial cell proliferation and the release of various substances toxic to neurons, such as superoxide (OィイD22ィエD2). We recently reported that serum albumin enhanced OィイD22ィエD2 production in cultured rat microglia stimulated by phorbol ester (Si e al., 1997, Glia 21 : 413-418). In the present report, we identify the active site of this enhancement within the albumin molecule. We purified an active subfragment from trypsin-treated bovine serum albumin (BSA) that was composed of 12-mer and 33-mer peptides connected by a disulfide bond. The chemically synthesized 12-mer peptide showed activity within a concentration range (ca. 10ィイD1-7ィエD1 M) equivalent to that of albumin. The activities of a series of synthesized peptides conclusively indicated that the minimum active sequence was Leu-His-Thr-Leu. Enhancement of OィイD22ィエD2 production by this peptide was also observed in macrophages quiescently prepared from rat peritoneal fluid. The present study may contribute toward the development of a tool to suppress the pathological activation of microglia and may also shed light on albumin's role in the biological defense system.