supported by the Natural Science Foundation of Hubei Province(No. 2005ABA081);the Foundation of Educational Commission of Hubei Province(No. D20074004);the Foundation of Health Department of Hubei Province(No. 2007JX3B29);the Science and Technology Key Projects of Hubei Province(No. 2007AA301C14-1);Excellent Youth Foundation of Health Department of Hubei Province(No. QJX2008-40);Youth Team of Science and Technology Innovation Foundation of Yunyang Medical College(No. 2008CXX02)