Circulating Mitochondrial DNA as Biomarker Linking Environmental Chemical Exposure to Early Preclinical Lesions Elevation of mtDNA in Human Serum after Exposure to Carcinogenic Halo-Alkane-Based Pesticides

Abstract

There is a need for a panel of suitable biomarkers for detection of environmental chemical exposure leading to the initiation or progression of degenerative diseases or potentially, to cancer. As the peripheral blood may contain increased levels of circulating cell-free DNA in diseased individuals, we aimed to evaluate this DNA as effect biomarker recognizing vulnerability after exposure to environmental chemicals. We recruited 164 individuals presumably exposed to halo-alkane-based pesticides. Exposure evaluation was based on human biomonitoring analysis; as biomarker of exposure parent halo-methanes, -ethanes and their metabolites, as well as the hemoglobin-adducts methyl valine and hydroxyl ethyl valine in blood were used, complemented by expert evaluation of exposure and clinical intoxication symptoms as well as a questionnaire. Assessment showed exposures to halo alkanes in the concentration range being higher than non-cancer reference doses (RfD) but (mostly) lower than the occupational exposure limits. We quantified circulating DNA in serum from 86 individuals with confirmed exposure to off-gassing halo-alkane pesticides (in storage facilities or in home environment) and 30 non-exposed controls, and found that exposure was significantly associated with elevated serum levels of circulating mitochondrial DNA (in size of 79 bp, mtDNA-79, p = 0.0001). The decreased integrity of mtDNA (mtDNA-230/mtDNA-79) in exposed individuals implicates apoptotic processes (p = 0.015). The relative amounts of mtDNA-79 in serum were positively associated with the lag-time after intoxication to these chemicals (r = 0.99, p<0.0001). Several months of post-exposure the specificity of this biomarker increased from 30% to 97% in patients with intoxication symptoms. Our findings indicate that mitochondrial DNA has a potential to serve as a biomarker recognizing vulnerable risk groups after exposure to toxic/carcinogenic chemicals.

Plasma Mitochondrial DNA Levels as a Biomarker of Lipodystrophy Among HIV-infected Patients Treated with Highly Active Antiretroviral Therapy (HAART).

“…Plasma mtDNA levels are also significantly increased in patients with tissue injury and various tumors [15,20,21]. The mechanism that cells use to release free circulating DNA into the blood is still not elucidated.…”

Release of bulk cell free DNA during physical exercise occurs independent of extracellular vesicles

“…The steady mitochondrial DNA level in plasma, also shown by others (Beiter et al 2011), most likely excludes apoptosis as main mechanism of DNA release following exhaustive exercise. The different nature and release mechanisms of cell free mtDNA and nuclear DNA could be also reflected by their lack of correlation in some diseases (Budnik et al 2013). It was suggested that cfDNA concentrations increase by unknown active or passive mechanisms in response to acute stress during exercise (Breitbach et al 2012).…”

Impact of Intravenous Ascorbic Acid Infusion on Novel Biomarkers in Patients with Severe Sepsis

“…Estimation of mtDNA levels was performed by quantitative real-time PCR (QPCR) essentially as described by Budnik et al [11]. Briefly two primer sets specific for the mitochondrial ribosomal 16S RNA were used: One pair amplified a 74-bp fragment that represented total mtDNA and included DNA released by apoptotic cells (mtDNA-74).…”