新型合成三肽抑制巨噬细胞精氨酸转运

目的观察新型合成三肽Arg(NO3)-Lys(OCH3)-Arg(NO3)]对巨噬细胞株(RAW264．7)左旋-精氨酸／一氧化氮 (L-Arg／NO)途径的影响。方法培养的巨噬细胞(培养液中含L-Arg 0．5 mmol／L)加入脂多糖(LPS,1μg/L)随机分为3组 (每组n=6),分别加入双蒸水、三肽(1×10-4mol／L)、NG甲基-L-精氨酸(L-NMMA,1×10-4mol／L),对照组只含L-Arg (n=6),作用24 h后,检测亚硝酸盐(NO2-)、3H-L-Arg转运量;培养的巨噬细胞培养液中含L-Arg(0-2 mmol／L)]加入 LPS(1 μg／L)24 h后,检测NO2-;培养的巨噬细胞(培养液中含L-Arg 0．5mmol／L)加入LPS(1μg/L)后分别加三肽 (0-10)×10-4 mol／L]24 h后,检测NO2-、3H-L-Arg转运量。结果 LPS刺激细胞产生NO的量和L-Arg率转运分别为非刺激组的50倍和2．7倍,三肽(1×10-4mol／L)即可明显降低NO的生成及抑制L-Arg的转运(分别降低71％、67％),较 L-NMMA(1×10-4 mol／L)作用要强(P<0．05);NO的生成依赖于细胞外L-Arg,并成浓度依赖性,其米氏常数(Km):(0．162± 0．015) mmol／L、最大转运速率(Vmax):(91．2±2．3)μmol／(24 h·106cells);三肽成浓度依赖性的降低细胞L-Arg转运和 NO的生成,半数有效抑制剂量(EC50)分别为0．21×10-4mol／L、1．27×104mol／L。结论 LPS作用于巨噬细胞引起L-Arg转运增加:三肽通过抑制细胞L-Arg转运及与L-Arg竞争性结合一氧化氮合酶作用位点,影响NO的生成。

A new synthetic tripeptide inhibits L-arginine transport in macrophages

OBJECTIVE: To observe the effect of a new synthetic tripeptide Arg(NO(3))- Lys(OCH(3))- Arg(NO(3))] on L-arginine/NO pathway in the macrophage cell strain RAW246.7. METHODS: The cultured macrophages exposed to lipopolysaccharide (LPS, 1 microg/L) treatment were randomly divided into 3 groups (n=6) and treated with distilled water, 1x10(-4) mol/L tripeptide and 1x10(-4) mol/L L-arginine, NG-monomethyl-L-arginine (L-NMMA) for 24 h, respectively. The macrophages were incubated for 24 h with LPS (1 microg/L) and in the presence of different concentrations of L-arginine (0 to 2 mmol/L), or in normal culture medium (containing 0.5 mmol/L L-arginine) for 24 h with LPS (1 microg/L) and in the presence of tripeptide of 0 to 10x10(-4) mol/L. The changes of (3)H]-L-arginine transport and NO production from the macrophages were measured. RESULT: NO release from macrophages incubated in the LPS-containing culture medium was 50 folds, and (3)H]-L-arginine uptake 2.7 folds that in cells in normal culture medium. Tripeptide (1x10(-4) mol/L) inhibited (3)H]-L-arginine transport and NO production by 67% and 71% respectively. The effect of tripeptide was stronger than L-NMMA (P<0.05). Extracellular L-arginine caused a concentration-dependent increase in nitrite production, which reached the maximum at concentrations above 0.5 mmol/L Km for nitrite production of 0.162+/-0.015 mmol/L and Vmax of 91.2+/-2.3 micromol/(24h.10(6) cells). L-arginine transport and NO production were inhibited by tripeptide, but their dose-dependent pattern of changes was different with EC50 of 0.21x10(-4) mol/L and 1.27x10(-4) mol/L, respectively. CONCLUSIONS: Activation of macrophages with LPS induces nitrite accumulation in the culture medium, which is dependent on the presence of extracellular L-arginine. The tripeptide induces dysfunction of L-arginine/NO pathway in macrophages, potently inhibits L-arginine transport and competitively combine the active sites of nitric oxide synthase.