Disease is defined as a state of disorder that lays the groundwork for conditions of ill health. Even the most complex disease begins with cellular imbalance, and scientists are looking to discover biomarkers that can detect the earliest signs of pathogenesis.

The mitochondrion, coined the “powerhouse of the cell”, comprises a powerful factory for cellular energy production.
Photo credit: National Institutes of Health

Immunoglobulin A (IgA) is an essential antibody which acts as a first line of defense for epithelial cells; it functions to eliminate pathogens, neutralize toxins, and impede viral and bacterial adhesion to mucous membranes.

IgA nephropathy (IgAN) occurs when IgA gradually accumulates in the kidneys leading to inflammation and subsequent impairment of the kidney’s ability to filter out toxins and waste from the blood. This inflammation can lead to mitochondrial damage, ultimately resulting in the pathogenesis of kidney disease. Mitochondrial injury leads to cellular damage and death, wherein mitochondrial DNA (mtDNA) fragments are released into the circulation and can eventually be found in bodily substances such as urine. 

Researchers are actively studying the utility of urinary mtDNA as an alternative biomarker for assessing mitochondrial injury. Physicians are attempting to move away from tissue biopsies due to its invasiveness and are discovering that mtDNA found in urine can be used as an essential biomarker for kidney disease.

A group of researchers from the Soonchunyhang University in South Korea investigated whether patients with IgAN exhibited an increased level of urinary mtDNA and how their results would correlate to existing prognostic markers. Hyo Kwon et al. isolated urinary DNA using Norgen Biotek’s Urine DNA Isolation Micro Kit (#18100) and subsequently measured mtDNA genes COX3 and ND1 by RT-PCR.

They found that in their comparison with healthy volunteers, urinary mtDNA levels were indeed elevated in patients with IgAN (Figure 1b), demonstrating a clear association of mitochondrial injury with IgAN. 

Figure 1. IgA nephropathy is associated with elevated urinary mitochondrial DNA copy numbers. - 2019

The researchers’ analysis of the effects of various traditional medical treatments on mtDNA levels of IgA patients failed to show a decrease in urinary COX3 and ND1, highlighting the need to further investigate and reassess existing treatment protocols. By examining structural changes in mitochondria, the researchers observed that in comparison to healthy kidney donors whose mitochondria appeared organized with densely stacked cristae membranes, samples from IgAN patients exhibited mitochondria that were clearly disorganized and smaller in size (Figure 5). 

Figure 5. IgA nephropathy is associated with elevated urinary mitochondrial DNA copy numbers. - 2019

Hyo Kwon et al. demonstrate the presence of ultrastructural changes within IgA patients, providing insights into mitochondrial injury and its role in pathogenesis of kidney disease. They emphasize that further investigation is required to quantitatively assess the extent and location of mitochondrial damage, clarifying its role in the development of IgA nephropathy prior to its manifestation. Further studies may also elucidate the precise mechanisms of mitochondrial dysfunction, and thereby create a new perspective in pre-pathogenesis diagnosis and improving existing treatments and protocols.  

It is expected that concentrations of mtDNA will be low and highly variable among patients. As a way to optimize future studies in this field, a higher starting volume of urine could be used to increase urinary mtDNA yields. This can be obtained using Norgen’s Urine DNA Isolation Maxi Kit (#50100) wherein up to 80mL of urine can be processed for isolation. Since mtDNA is located in the circulation outside the cell, another option to explore is cell-free urine sampling and isolation—for which a kit is also offered by Norgen. This carries the additional benefit of removing cellular genomic DNA that could potentially mask the mtDNA present. In summary, this study suggests the utility of urinary mtDNA as a biomarker, offering insights into mitochondrial injury and its pathological association with IgA nephropathy.

Check out Norgen’s Urine Collection and Preservation tubes for details on the only preservative that efficiently stabilizes RNA, DNA and protein at room temperature for two years.