Calciprotein particles (CPP) are solid-phase calcium-phosphate bound to serum protein fetuin-A and dispersed as colloids in the blood. Recent clinical studies indicated that serum CPP levels were increased with decline of renal function and associated with inflammation and vascular calcification. However, CPP assays used in these studies measured only a part of CPP over a certain particle size and density. Here we show that such CPP are mostly artifacts generated during processing of serum samples in vitro. The native CPP in fresh plasma are smaller in size and lower in density than those artifactual CPP, composed of fetuin-A carrying amorphous and/or crystalline calcium-phosphate, and increased primarily with serum phosphate levels. We have identified several physicochemical factors that promote aggregation/dissolution of CPP and transition of the calcium-phosphate from the amorphous phase to the crystalline phase in vitro, including addition of anti-coagulants, composition of buffer for sample dilution, the number of freeze-thaw cycles, the speed for sample freezing, and how many hours the samples were left at what temperature. Therefore, it is of critical importance to standardize these factors during sample preparation in clinical studies on CPP and to investigate the biological activity of the native CPP.

中文翻译：

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慢性肾脏病患者血浆钙蛋白蛋白颗粒的鉴定和定量，其具有独特的物理特性。

钙蛋白颗粒（CPP）是固相磷酸钙，与血清蛋白胎球蛋白A结合，并以胶体形式分散在血液中。最近的临床研究表明，血清CPP水平随肾功能下降而增加，并与炎症和血管钙化有关。但是，这些研究中使用的CPP分析仅在一定粒径和密度下测量了一部分CPP。在这里，我们显示出这种CPP主要是在体外血清样品处理过程中产生的伪影。新鲜血浆中的天然CPP比那些人工CPP（由携带无定形和/或结晶性磷酸钙的胎球蛋白A组成，并且随血清磷酸盐水平的增加而增加）的尺寸更小，密度也更低。我们已经确定了几种物理化学因素，可促进CPP的聚集/溶解以及体外磷酸钙从无定形相向结晶相的转变，包括添加抗凝剂，用于样品稀释的缓冲液组成，冷冻次数。解冻循环，样品冷冻的速度以及在什么温度下样品保留了多少小时。因此，在CPP临床研究的样品制备过程中标准化这些因素并研究天然CPP的生物学活性至关重要。以及样品在什么温度下放置了几个小时。因此，在CPP临床研究的样品制备过程中标准化这些因素并研究天然CPP的生物学活性至关重要。以及样品在什么温度下放置了几个小时。因此，在CPP临床研究的样品制备过程中标准化这些因素并研究天然CPP的生物学活性至关重要。