Evidence of free and bound leptin in human circulation - Studies in lean and obese subjects and during short-term fasting
Evidence of free and bound leptin in human circulation - Studies in lean and obese subjects and during short-term fasting
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DOI：
10.1172/jci118913
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发表时间：
1996-09-15
影响因子：
15.9
通讯作者：
Caro, JF
中科院分区：
文献类型：
--
作者：
Sinha, MK;Opentanova, I;Caro, JF
人们对瘦素与其他循环蛋白的相互作用知之甚少，而这对其生物学效应可能很重要。 I-125-瘦素-血清复合物的 Sephadex G-100 凝胶过滤洗脱曲线表明，I-125-瘦素洗脱的比例与大分子相关。 I-125-瘦素与循环大分子的结合是特异性的、可逆的，并且可被未标记的瘦素取代（ED(50)：0.73+/-0.09 nM，平均值+/-SEM，n = 3）。通过瘦素亲和层析检测到几种假定的瘦素结合蛋白，其中 80-或 100-kD 蛋白质可能是可溶性瘦素受体，类似于 10% 的结合 I-125-瘦素可与瘦素受体抗体进行免疫沉淀。在瘦肉中以结合形式循环的总瘦素比例显着更高 (P < 0.001) (46.5+/-6.6%) 与肥胖受试者 (21.4+/-3.4%) 相比。在体脂 21% 或更少的瘦受试者中，总瘦素的 60-98% 处于结合形式。短期禁食显着降低了三名瘦受试者（P < 0.0005）和三名肥胖受试者（P < 0.005）的基础瘦素水平，而重新进食则将其恢复到基础水平。与肥胖受试者相比，禁食对游离瘦素水平的影响在瘦受试者中更为明显（基础与 24 小时禁食：19.6+/-1.9 与 1.3+/-0.4 ng/ml）（28.3+/-9.8 与 14.7+/-5.3）。两组中结合瘦素均未观察到显着（P > 0.05）下降。这些研究表明，在肥胖个体中，大多数瘦素以游离形式（可能是生物活性蛋白）循环，因此肥胖受试者对游离瘦素有抵抗力。在脂肪组织相对较少的瘦受试者中，大多数循环瘦素处于结合形式，因此在正常和食物匮乏状态下，大脑受体可能无法利用其对食物摄入的抑制作用。
Little is known about leptin's interaction with other circulating proteins which could be important for its biological effects. Sephadex G-100 gel filtration elution profiles of I-125-leptin-serum complex demonstrated I-125-leptin eluting in significant proportion associated with macromolecules. The I-125-leptin binding to circulating macromolecules was specific, reversible, and displaceable with unlabeled leptin (ED(50): 0.73+/-0.09 nM, mean+/-SEM, n = 3). Several putative leptin binding proteins were detected by leptin-affinity chromatography of which either 80- or 100-kD proteins could be the soluble leptin receptor as similar to 10% of the bound I-125-leptin was immunoprecipitable with leptin receptor antibodies.Significantly higher (P < 0.001) proportions of total leptin circulate in the bound form in lean (46.5+/-6.6%) compared with obese (21.4+/-3.4%) subjects. In lean subjects with 21% or less body fat, 60-98% of the total leptin was in the bound form, Short-term fasting significantly decreased basal leptin levels in three lean (P < 0.0005) and three obese (P < 0.005) subjects while refeeding restored it to basal levels. The effects of fasting on free leptin levels were more pronounced in lean subjects (basal vs. 24-h fasting: 19.6+/-1.9 vs, 1.3+/-0.4 ng/ml) compared with those in obese subjects (28.3+/-9.8 vs. 14.7+/-5.3). No significant (P > 0.05) decrease was observed in bound leptin in either group. These studies suggest that in obese individuals the majority of leptin circulates in free form, presumably bioactive protein, and thus obese subjects are resistant to free leptin. In lean subjects with relatively low adipose tissue, the majority of circulating leptin is in the bound form and thus may not be available to brain receptors for its inhibitory effects on food intake both under normal and food deprivation states.