| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2005: ¥1,800,000 (Direct Cost: ¥1,800,000)
|
|---|
| Research Abstract |
Erythropoietin (EPO) protects against ischemic brain injury in experimental models and in a human stroke trial. The neurotrophic mechanisms of EPO might be attributed to its antioxidant properties. The generation of reactive oxygen species (ROS) is a potential causative factor in uremic encephalopathy, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is a major source of ROS in tissues such as kidney and liver in uremia. Astrocyte, a major class of non-neuronal brain cell, subserves a wide range of adaptive functions. Recent studies have demonstrated that astrocytes are the main cellular source of EPO in the brain, and low oxygen tension stimulates EPO mRNA expression in astrocytes. Thus, we investigated whether EPO acts against ROS, and whether NADPH oxidase is involved in generating ROS in the brain of uremic rats in vivo. We also investigated whether EPO and astrocyte play a protective role against neuronal damage induced by uremic toxin in vitro. Male Sprague-Dawley
… More
rats were divided into three groups : 1) sham-operated rats (Sham) ; 2) 5/6 nephrectomized rats (Nx) ; and, 3) 5/6 nephrectomized rats treated with recombinant human erythropoietin (rHuEPO)(Nx+EPO). Accumulation in the brain of 8-oxo-2'-deoxyguanosine (8-oxo-dG), a product of oxidative DNA damage, and acrolein, a product of lipid peroxidation reaction, was examined by immunohistochemistry. Activation of NADPH oxidase was evaluated by immunohistochemistry for p67^<phox> and by measuring the amount of p67^<phox>, a cytoplasmic subunit of NADPH oxidase that translocates to the plasma membrane on activation, in the membrane fraction of brain extracts using Western blotting. The amount of astrocytes was examined by immunohistochemistry for glial fibrillary acid protein (GFAP), a marker of astrocyte. In vitro, we investigated whether the treatment with rHuEPO ameliorates p-cresol-induced neuronal damage, and also examined whether astrocyte acts as a neuroprotector against such damage by employing co-culture system of neuroblasts and astrocytes. Immunoreactivity for 8-oxo-dG, acrolein, p67^<phox>, and GFAP in the hippocampus, and the amount of p67^<phox> in the membrane fraction of brain extracts were increased in Nx compared with in sham-operated rats, but not in the treated Nx+EPO rats. In vitro, both administration of rHuEPO and co-culture with astrocytes increased neuronal cell viability after exposure to p-cresol. Our results suggest that ROS derived from NADPH oxidase induces oxidative damage in the brain during chronic renal failure and that the neuroprotective action of EPO is based on its antioxidant activity. Astrocyte acts as a neuroprotector in uremic encephalopathy, probably through its production of EPO. Less
|
