Sequence variations of mitochondrial DNA D-loop region in patients with acute myeloid leukemia

Alterations of Mitochondria and Related Metabolic Pathways in Leukemia: A Narrative Review

Dysregulation of mitochondrial function often precedes malignant transformation of hematopoietic stem cells (HSCs). Mitochondria have a direct role in the maintenance of HSC functions. For example, D-2-hydroxyglutarate, generated due to the activity of mutated mitochondrial isocitrate dehydrogenase (IDH), has been implicated in the pathogenesis of leukemia. Furthermore, disturbances in the fatty acid breakdown and pyruvate oxidation are often seen in leukemic cells. These and other abnormalities expedite leukemogenesis and chemoresistance of leukemic cells. However, it needs to be elucidated whether these aberrations are the result or cause of leukemogenesis. Accordingly, for this review, a search was carried out in PubMed and Google Scholar databases until June 2019 to assess the relationship between metabolic pathways in altered mitochondria and leukemia development. In the present review, an overview of mitochondria-related mechanisms and their abnormalities in leukemia is presented, with mitochondrial pathways and factors, such as mitophagy, intermediary metabolism enzymes, oncometabolites and reactive oxygen species' generation, discussed as potential diagnostic and therapeutic targets in leukemia.

Mitochondrial DNA and genomic DNA ratio in embryo culture medium is not a reliable predictor for in vitro fertilization outcome

To investigate the ratio of mitochondrial DNA to genomic DNA (mt/gDNA) in embryo culture medium as a possible predictor for embryonic development and pregnancy outcome, we collected a total of 93 embryo biopsy specimens from 52 women at the corresponding Day 3 (D3) and Day 5 (D5) embryo culture medium of in vitro fertilization. With the multiple annealing and looping-based amplification cycles method of next-generation sequencing for whole genome amplification, we examined the karyotype of the biopsy samples and the mt/gDNA ratio in the culture medium. Results showed that the ratio of mt/gDNA had an upward trend with decreasing trophectoderm levels with no significant difference. At the same time, from D3 to D5, the mt/gDNA ratio in the medium of embryos that failed to become blastocysts showed an upward trend, and the mt/gDNA ratio of medium from embryos that reached blastulation with successful pregnancy showed a decreasing trend, but the differences were not statistically significant. We conclude that there is a certain correlation between mt/gDNA ratio and early embryonic development, but it does not reach a level that can be used as a clinical predictor.

Prognostic impact of mitochondrial DNA D-loop variations in pediatric acute myeloid leukemia

The role of mitochondrial DNA (mt-DNA) changes, especially those in the regulatory D-loop region in Acute Myeloid Leukemia (AML) remains investigational. Consecutive 151 de novo pediatric AML patients, (≤18 yr) were prospectively enrolled from June 2013-August 2016, to assess the prognostic impact of mt-DNA D-loop variations (somatic/germline) on survival. For each patient, D-loop region was sequenced on baseline bone marrow and buccal swab, and mother’s blood sample. In 151 AML subjects, 1490 variations were found at 237 positions; 80.9% were germline and 19.1% somatic. The mean number of variations per position was 6.3. Variations with frequency ≥6 were analyzed for their impact on survival and 4 categories were created, namely “somatic-protective”, “somatic-hazardous”, “germline-protective” and “germline- hazardous”. Although, somatic-protective could not predict event free survival (EFS) or overall survival (OS), somatic-hazardous [(OS) HR = 2.33, p = 0.06] and germline-hazardous [(OS) HR = 2.85, p < 0.01] significantly predicted OS and EFS. Notably, the germline-protective, could significantly predict EFS (HR = 0.31, p = 0.03) and OS (HR = 0.19, p < 0.01), only when variations at ≥2 positions were present. On multivariate analysis, three positions namely 16111, 16126, 16362 and karyotype were found to be predictive of EFS. A prognostic index (PI) was developed using nomogram PI = (0.8*karyotype) + (1.0*c16111) + (0.7*t16362) + (1.2*t16126). Hazard ratio for EFS increased significantly with increasing PI reaching to a maximum of 3.3 (p < 0.01). In conclusion, the impact of mt-DNA D-loop variations on outcomes in pediatric AML depends on their nature (germline/somatic), position and mutational burden, highlighting their potential role as evolving prognostic biomarkers.

Platelet mitochondrial cytochrome c oxidase subunit I variants with benzene poisoning

Background

Chronic benzene poisoning (CBP) is one of the most common chronic occupational poisoning which is associated with mitochondrial oxidative damage, and lead to increasing risk of respiratory diseases such as lung cancer. Cytochrome c oxidase subunit I (COI) is one of the key enzymes that plays an important role in oxidative damage regulation by eliminating reactive oxygen species (ROS). This study investigated the relationship between COI gene variants and the risk of CBP.

Methods

We investigated 44 non-smoking patients who were diagnosed with CBP and 57 unexposed non-smoking controls between the ages of 23 and 60 with their background including work experience, lifestyle and medical records. Peripheral blood (2 mL) was collected in EDTA tube and the platelet was purified from the collected blood. Variants of COI were analyzed by PCR and sequencing. Multivariable linear regression analysis was used to assess the association between CBP exposure and variants.

Results

The frequency of the mitochondrial DNA (mtDNA) T6392C, G6962 variants were 10, 7 out of 44 CBP group patients, which was higher when compared to that of 4, 2 out of 57 in the control group, suggesting these variants could be the risk factor for CBP [odds ratio (OR) 3.897, 95% CI: 1.131-13.425, P=0.023; OR 5.203, 95% CI: 1.024-26.442, P=0.034]. There was a significant difference (P<0.05) of COI variants, including T6392C and G6962A, in platelet mtDNA between patients and control samples. Meanwhile, the frequency of the mtDNA C7196A variant were 13 out of 44 control group, which was higher when compared to that of 2 of 57 in the CBP group patients, suggesting this variant could be the protective factor for CBP (OR 6.205, 95% CI: 1.320-29.162, P=0.010).

Conclusions

Our study suggests that T6392C, G6962A and C7196A from platelet mtDNA variants play a significant role in the etiology of CBP and facilitate the development of molecular biomarker on CBP diagnosis.