Haourigui M, Martin M E, Thobie N, Benassayag C, Nunez E A
U-224 INSERM, Faculté de Médecine Xavier Bichat, Laboratoire de Biochimie, Paris, France.
Endocrinology. 1993 Jul;133(1):183-91. doi: 10.1210/endo.133.1.8319565.
In vitro studies have shown that FFA induce conformational changes in human corticosteroid-binding globulin (CBG). We increased the plasma FFA concentrations of adult male rats by injecting heparin to determine whether such changes in CBG binding and immunological properties also occur in vivo. The in vivo transient activation of lipase by heparin produced a large increase in plasma FFA at 10 and 20 min (P < 0.01), which was maximal at 60 min (P < 0.005) and remained elevated at 120 min (P < 0.01) postinjection. This rise in FFA was associated with a 2- to 3-fold increase in the binding indices (C values; liters per g) of corticosterone (B) and progesterone to CBG 60-120 min postinjection (P < 0.001). There was a good positive correlation (r = 0.85) between the increase in B binding and the rise in plasma FFA in heparin-treated rats. The enhanced B binding to CBG resulted from a 2-fold increase in the apparent number of binding sites, without any significant change in the affinity constant (Ka). FFA extracted from postheparin plasma and a standard FFA mixture induced similar changes in B binding to purified mature rat CBG. The immunological behavior of CBG was not significantly changed after heparin-induced lipolysis, but the immunoreactivity of CBG from heparin-treated rats was more reduced by incubation with exogenous FFA than that from controls. FFA extracted from the plasma of heparin-treated rats and a standard FFA mixture both produced a dose-dependent drop in the immunodetection of pure CBG. These binding and immunological studies indicate that FFA mediate conformational changes in rat CBG in vivo. Thus, FFA, in addition to their roles as metabolic energy sources and components of complex lipids, can be rapid potent endogenous modulators of steroid-protein interactions.
体外研究表明，游离脂肪酸（FFA）可诱导人皮质类固醇结合球蛋白（CBG）发生构象变化。我们通过注射肝素提高成年雄性大鼠的血浆FFA浓度，以确定CBG结合和免疫特性的此类变化在体内是否也会发生。肝素在体内对脂肪酶的短暂激活使血浆FFA在注射后10分钟和20分钟大幅增加（P < 0.01），在60分钟时达到最大值（P < 0.005），并在注射后120分钟仍保持升高（P < 0.01）。注射后60 - 120分钟，FFA的这种升高与皮质酮（B）和孕酮与CBG的结合指数（C值；升/克）增加2至3倍相关（P < 0.001）。在肝素处理的大鼠中，B结合的增加与血浆FFA的升高之间存在良好的正相关（r = 0.85）。B与CBG结合增强是由于结合位点的表观数量增加了2倍，而亲和常数（Ka）没有任何显著变化。从肝素后血浆中提取的FFA和标准FFA混合物在B与纯化的成熟大鼠CBG的结合中诱导了类似的变化。肝素诱导的脂解后，CBG的免疫行为没有显著变化，但与对照组相比，肝素处理大鼠的CBG与外源性FFA孵育后的免疫反应性降低得更多。从肝素处理大鼠的血浆中提取的FFA和标准FFA混合物均使纯CBG的免疫检测呈剂量依赖性下降。这些结合和免疫研究表明，FFA在体内介导大鼠CBG的构象变化。因此，FFA除了作为代谢能量来源和复合脂质的成分外，还可以是类固醇 - 蛋白质相互作用的快速有效内源性调节剂。
