Circulating mitochondrial DNA (mtDNA), widely studied as a disease biomarker, comprises of mtDNA located within mitochondria, indicative of mitochondrial function, and cell‐free (cf) mtDNA linked to inflammation. The purpose of this study was to determine the ranges of, and relationship between, cellular and cf mtDNA in human blood. Whole blood from 23 controls (HC) and 20 patients with diabetes was separated into peripheral blood mononuclear cells (PBMCs), plasma, and serum. Total DNA was isolated and mtDNA copy numbers were determined using absolute quantification. Cellular mtDNA content in PBMCs was higher than in peripheral blood and a surprisingly high level of cf mtDNA was present in serum and plasma of HC, with no direct relationship between cellular and cf mtDNA content within individuals. Diabetes patients had similar levels of cellular mtDNA compared to healthy participants but a significantly higher cf mtDNA content. Furthermore, only in patients with diabetes, we observed a correlation between whole blood and plasma mtDNA levels, indicating that the relationship between cellular and cf mtDNA content is affected by disease status. In conclusion, when evaluating mtDNA in human blood as a biomarker of mitochondrial dysfunction, it is important to measure both cellular and cf mtDNA.

中文翻译：

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测量细胞和无细胞线粒体 DNA 作为人类血液中疾病生物标志物的案例

循环线粒体 DNA (mtDNA) 作为疾病生物标志物被广泛研究，包括位于线粒体内的 mtDNA，指示线粒体功能，以及与炎症相关的无细胞 (cf) mtDNA。本研究的目的是确定人类血液中细胞和 cf mtDNA 的范围和关系。来自 23 名对照 (HC) 和 20 名糖尿病患者的全血被分离成外周血单核细胞 (PBMC)、血浆和血清。分离总 DNA 并使用绝对定量确定 mtDNA 拷贝数。PBMC 中的细胞 mtDNA 含量高于外周血，并且在 HC 的血清和血浆中存在令人惊讶的高水平 cf mtDNA，在个体中的细胞和 cf mtDNA 含量之间没有直接关系。与健康参与者相比，糖尿病患者的细胞 mtDNA 水平相似，但 mtDNA 含量明显更高。此外，仅在糖尿病患者中，我们观察到全血和血浆 mtDNA 水平之间的相关性，表明细胞和 cf mtDNA 含量之间的关系受疾病状态的影响。总之，在评估人类血液中的 mtDNA 作为线粒体功能障碍的生物标志物时，测量细胞和 cf mtDNA 很重要。