Makoveichuk Elena, Ruge Toralph, Nilsson Solveig, Södergren Anna, Olivecrona Gunilla
Department of Medical Biosciences/Physiological Chemistry, Umeå University, Umeå, Sweden.
Department of Surgery and Perioperative Sciences/Acute Medicine, Umeå University, Umeå Sweden.
PLoS One. 2017 Jan 20;12(1):e0168922. doi: 10.1371/journal.pone.0168922. eCollection 2017.
Angiopoietin-like protein 4 (ANGPTL4) is suggested to be a master regulator of plasma triglyceride metabolism. Our aim was to study whether the previously reported high levels of ANGPTL4 detected in serum from patients with rheumatoid arthritis (RA) by ELISA was due to any specific molecular form of this protein (oligomers, monomers or fragments). ANGPTL4 levels were first determined in serum from 68 RA patients and 43 age and sex matched control subjects and the mean values differed by a factor of 5.0. Then, ANGPTL4 was analyzed after size exclusion chromatography (SEC) of serum samples. With serum from one of the RA patients with high levels of ANGPTL4, the dominant reactivity was found in fractions corresponding to high-molecular weight proteins. In addition, a minor peak of reactivity eluting late from the column was found both in the patient and in controls. By the use of HeteroBlock®, and by careful selection of antibodies, we documented non-specific reactions for ANGPTL4 in 39% of samples from the RA patients, most likely due to cross-reactivity of the antibodies with rheumatoid factor (RF). The corresponding figure for control subjects was 6.3%. After corrections for non-specific reactions, the mean level of ANGPTL4 in serum from RA patients was still significantly higher than in control individuals (mean levels were 101±62 and 67±39 ng/ml respectively, P = 0.02). We re-analyzed samples from our previously published studies on ANGPL4 levels in patients on hemodialysis and patients with diabetes type 2. These samples did not show false positive reactions. The levels of ANGPTL4 were comparable to those detected previously.
血管生成素样蛋白4（ANGPTL4）被认为是血浆甘油三酯代谢的主要调节因子。我们的目的是研究先前通过酶联免疫吸附测定（ELISA）在类风湿关节炎（RA）患者血清中检测到的高水平ANGPTL4是否归因于该蛋白的任何特定分子形式（寡聚体、单体或片段）。首先测定了68例RA患者和43例年龄及性别匹配的对照受试者血清中的ANGPTL4水平，平均值相差5.0倍。然后，对血清样本进行尺寸排阻色谱（SEC）分析后检测ANGPTL4。在其中一名ANGPTL4水平较高的RA患者血清中，主要反应性出现在对应于高分子量蛋白质的级分中。此外，在该患者和对照中均发现从柱中洗脱较晚的一个较小反应峰。通过使用HeteroBlock®并仔细选择抗体，我们记录到39%的RA患者样本中ANGPTL4存在非特异性反应，最可能是由于抗体与类风湿因子（RF）的交叉反应。对照受试者的相应比例为6.3%。校正非特异性反应后，RA患者血清中ANGPTL4的平均水平仍显著高于对照个体（平均水平分别为101±62和67±39 ng/ml，P = 0.02）。我们重新分析了我们先前发表的关于血液透析患者和2型糖尿病患者ANGPL4水平研究中的样本。这些样本未显示假阳性反应。ANGPTL4水平与先前检测到的水平相当。
