Endocrine Laboratory, Department of Clinical Chemistry, VU University Medical Center, Amsterdam, The Netherlands.
Department of Nephrology, VU University Medical Center, Amsterdam, The Netherlands.
Clin Chem Lab Med. 2018 Jan 26;56(2):249-255. doi: 10.1515/cclm-2017-0313.
Posttranslational oxidation of parathyroid hormone (PTH) modifies its biological activity. Measurement of non-oxidized PTH (n-oxPTH) could be an improvement in assessing PTH status, as intact PTH may rather reflect oxidative stress. However, it is debated whether oxidation of PTH occurs in vivo, or whether it is mainly an in vitro artifact. The aim of this study was to investigate the influence of different preanalytical conditions on the oxidation of PTH within a wide range of plasma PTH concentrations and oxidation propensity.
n-oxPTH was separated from its oxidized form using an affinity column capturing the oxidized PTH. n-oxPTH was measured in eluate using commercially available PTH assays. The study included ethylenediaminetetraacetic acid plasma samples from 17 patients undergoing hemodialysis and 32 healthy subjects. We determined effects of storage temperature, time until centrifugation and freeze-thaw cycles. PTH and n-oxPTH concentrations were measured in each sample using six different immunoassays.
n-oxPTH concentrations remained unchanged up to 180 min until centrifugation, two freeze-thaw cycles or after storage at -20°C or -80°C up to 79 days. Various methods for n-oxPTH and PTH measurements yielded highly comparable results, apart from standardization differences between various PTH and n-oxPTH assays.
n-oxPTH concentrations were stable under our study conditions, indicating negligible ex vivo oxidation of PTH. In addition, PTH immunoassays have a different sensitivity for n-oxPTH than for total PTH. For this reason, the n-oxPTH/total PTH ratio cannot be used in absence of a n-oxPTH standard. Clinical implications of determining n-oxPTH require additional study.
甲状旁腺激素 (PTH) 的翻译后氧化修饰了其生物活性。测量非氧化型 PTH（n-oxPTH）可能会改善 PTH 状态的评估，因为完整的 PTH 可能更能反映氧化应激。然而，关于 PTH 是否在体内发生氧化，或者它是否主要是体外的一种假象，目前仍存在争议。本研究旨在探讨在广泛的血浆 PTH 浓度和氧化倾向范围内，不同的预分析条件对 PTH 氧化的影响。
使用亲和柱从其氧化形式中分离 n-oxPTH，该亲和柱可捕获氧化的 PTH。使用市售的 PTH 测定法在洗脱液中测量 n-oxPTH。该研究纳入了 17 名接受血液透析的患者和 32 名健康受试者的 EDTA 血浆样本。我们确定了储存温度、离心前时间和冻融循环的影响。在每个样本中使用六种不同的免疫测定法测量 PTH 和 n-oxPTH 浓度。
直到离心前 180 分钟、两次冻融循环或在 -20°C 或 -80°C 下储存长达 79 天，n-oxPTH 浓度保持不变。除了各种 PTH 和 n-oxPTH 测定之间的标准化差异外，n-oxPTH 和 PTH 的各种测量方法得出的结果高度相似。
在我们的研究条件下，n-oxPTH 浓度稳定，表明 PTH 几乎不存在体外氧化。此外，与总 PTH 相比，PTH 免疫测定对 n-oxPTH 的灵敏度不同。因此，在没有 n-oxPTH 标准的情况下，n-oxPTH/总 PTH 比值不能使用。确定 n-oxPTH 的临床意义需要进一步研究。
