Quantification of total mitochondrial DNA and the 4977-bp common deletion in Pearson's syndrome lymphoblasts using a fluorogenic 5'-nuclease (TaqMan) real-time polymerase chain reaction assay and plasmid external calibration standards

SOD2 Alleviates Hearing Loss Induced by Noise and Kanamycin in Mitochondrial DNA4834-deficient Rats by Regulating PI3K/MAPK Signaling

Superoxide dismutase 2 (SOD2)-mediated gene therapy has significant protective effects against kanamycin-induced hearing loss and hair cell loss in the inner ear, but the underlying mechanisms are still unclear. Herein, an in vivo aging model of mitochondrial DNA (mtDNA)4834 deletion mutation was established using D-galactose, and the effects of noise or kanamycin on inner ear injury was investigated. Rats subjected to mtDNA4834 mutation via D-galactose administration showed hearing loss characterized by the disruption of inner ear structure (abnormal cell morphology, hair cell lysis, and the absence of the organ of Corti), increased SOD2 promoter methylation, and an increase in the degree of apoptosis. Exposure to noise or kanamycin further contributed to the effects of D-galactose. SOD2 overexpression induced by viral injection accordingly counteracted the effects of noise and kanamycin and ameliorated the symptoms of hearing loss, suggesting the critical involvement of SOD2 in preventing deafness and hearing-related conditions. The PI3K and MAPK signaling pathways were also regulated by noise/kanamycin exposure and/or SOD2 overexpression, indicating that they may be involved in the therapeutic effect of SOD2 against age-related hearing loss.

Rosiglitazone Protects Endothelial Cells From Irradiation-Induced Mitochondrial Dysfunction

Background and Purpose

Up to 50–60% of all cancer patients receive radiotherapy as part of their treatment strategy. However, the mechanisms accounting for increased vascular risks after irradiation are not completely understood. Mitochondrial dysfunction has been identified as a potential cause of radiation-induced atherosclerosis.

Materials and Methods

Assays for apoptosis, cellular metabolism, mitochondrial DNA content, functionality and morphology were used to compare the response of endothelial cells to a single 2 Gy dose of X-rays under basal conditions or after pharmacological treatments that either reduced (EtBr) or increased (rosiglitazone) mitochondrial content.

Results

Exposure to ionizing radiation caused a persistent reduction in mitochondrial content of endothelial cells. Pharmacological reduction of mitochondrial DNA content rendered endothelial cells more vulnerable to radiation-induced apoptosis, whereas rosiglitazone treatment increased oxidative metabolism and redox state and decreased the levels of apoptosis after irradiation.

Conclusion

Pre-existing mitochondrial damage sensitizes endothelial cells to ionizing radiation-induced mitochondrial dysfunction. Rosiglitazone protects endothelial cells from the detrimental effects of radiation exposure on mitochondrial metabolism and oxidative stress. Thus, our findings indicate that rosiglitazone may have potential value as prophylactic for radiation-induced atherosclerosis.

Salivary Mitochondrial DNA Copy Number Is Associated With Exercise Ventilatory Efficiency

Chen, Y, Hill, HZ, Lange, G, and Falvo, MJ. Salivary mitochondrial DNA copy number is associated with exercise ventilatory efficiency. J Strength Cond Res 31(7): 2000-2004, 2017-Mitochondrial DNA copy number (mtDNAcn) is an index of mitochondrial content and is responsive to changes in exercise training volume. Therefore, assessment of mtDNAcn may help to optimize exercise prescription and aid in athlete monitoring. Although previous work has assessed mtDNAcn derived from skeletal muscle and blood using invasive approaches, no study has examined salivary mtDNAcn and its relationship with sport performance. Fifteen adults (32.2 ± 7.1 years) volunteered to participate in this study. Each participant provided a saliva sample for the analysis of mtDNAcn via real-time polymerase reaction. In addition, participants completed an exercise challenge test to assess oxygen consumption relative to body weight (V[Combining Dot Above]O2·kg) and ventilatory efficiency (VE/V[Combining Dot Above]CO2). Using multiple linear regression, we examined the association of V[Combining Dot Above]O2·kg and VE/V[Combining Dot Above]CO2 with salivary mtDNAcn, adjusting for self-reported physical activity (min·wk). Greater mtDNAcn was associated with lower VE/V[Combining Dot Above]CO2 (p < 0.01) and higher V[Combining Dot Above]O2·kg (p < 0.05). In our model adjusted for physical activity, greater mtDNAcn remained associated with lower VE/V[Combining Dot Above]CO2 (β = -0.186; 95% confidence interval [CI], -0.348 to -0.025; p < 0.05), but not with V[Combining Dot Above]O2·kg (β = -0.022; 95% CI, -0.113 to 0.063). Our findings suggest that salivary mtDNAcn is associated with ventilatory efficiency, which may reflect enhanced exercise efficiency as a consequence of greater total mitochondrial content. As saliva collection is noninvasive, stable at room temperature, and less costly in comparison to skeletal muscle and blood, future studies may consider using saliva for the evaluation of mitochondrial content for the purposes of monitoring exercise training as well as optimizing exercise prescription.

Increased mitochondrial DNA deletions and copy number in transfusion-dependent thalassemia

BACKGROUND

Iron overload is the primary cause of morbidity in transfusion-dependent thalassemia. Increase in iron causes mitochondrial dysfunction under experimental conditions, but the occurrence and significance of mitochondrial damage is not understood in patients with thalassemia.

METHODS

Mitochondrial DNA (mtDNA) to nuclear DNA copy number (Mt/N) and frequency of the common 4977-bp mitochondrial deletion (ΔmtDNA⁴⁹⁷⁷) were quantified using a quantitative PCR assay on whole blood samples from 38 subjects with thalassemia who were receiving regular transfusions.

RESULTS

Compared with healthy controls, Mt/N and ΔmtDNA⁴⁹⁷⁷ frequency were elevated in thalassemia (P = 0.038 and P < 0.001, respectively). ΔmtDNA⁴⁹⁷⁷ was increased in the presence of either liver iron concentration > 15 mg/g dry-weight or splenectomy, with the highest levels observed in subjects who had both risk factors (P = 0.003). Myocardial iron (MRI T2* < 20 ms) was present in 0%, 22%, and 46% of subjects with ΔmtDNA⁴⁹⁷⁷ frequency < 20, 20-40, and > 40/1 × 10⁷ mtDNA, respectively (P = 0.025). Subjects with Mt/N values below the group median had significantly lower Matsuda insulin sensitivity index (5.76 ± 0.53) compared with the high Mt/N group (9.11 ± 0.95, P = 0.008).

CONCLUSION

Individuals with transfusion-dependent thalassemia demonstrate age-related increase in mtDNA damage in leukocytes. These changes are markedly amplified by splenectomy and are associated with extrahepatic iron deposition. Elevated mtDNA damage in blood cells may predict the risk of iron-associated organ damage in thalassemia.

Ultraviolet B, melanin and mitochondrial DNA: Photo-damage in human epidermal keratinocytes and melanocytes modulated by alpha-melanocyte-stimulating hormone

Alpha-melanocyte-stimulating hormone (alpha-MSH) increases melanogenesis and protects from UV-induced DNA damage. However, its effect on mitochondrial DNA (mtDNA) damage is unknown. We have addressed this issue in a pilot study using human epidermal keratinocytes and melanocytes incubated with alpha-MSH and irradiated with UVB. Real-time touchdown PCR was used to quantify total and deleted mtDNA. The deletion detected encompassed the common deletion but was more sensitive to detection. There were 4.4 times more mtDNA copies in keratinocytes than in melanocytes. Irradiation alone did not affect copy numbers. Alpha-MSH slightly increased copy numbers in both cell types in the absence of UVB and caused a similar small decrease in copy number with dose in both cell types. Deleted copies were nearly twice as frequent in keratinocytes as in melanocytes. Alpha-MSH reduced the frequency of deleted copies by half in keratinocytes but not in melanocytes. UVB dose dependently led to an increase in the deleted copy number in alpha-MSH-treated melanocytes. UVB irradiation had little effect on deleted copy number in alpha-MSH-treated keratinocytes. In summary, alpha-MSH enhances mtDNA damage in melanocytes presumably by increased melanogenesis, while α-MSH is protective in keratinocytes, the more so in the absence of irradiation.

Mitochondrial DNA 4977-base pair common deletion in blood leukocytes and melanoma risk

The 4977-base pair common deletion DmtDNA4977 is the most frequently observed mitochondrial DNA mutation in human tissues. Because mitochondrial DNA mutations are mainly caused by reactive oxygen species (ROS), and given that oxidative stress plays an important role in melanoma carcinogenesis, the investigation of DmtDNA4977 may be particularly relevant to the development of melanoma. In this study, we compared DmtDNA4977 levels in blood leukocytes from 206 melanoma patients and 219 healthy controls. Overall, melanoma cases had significantly higher levels of DmtDNA4977 than healthy controls (median: 0.60 vs 0.20, P = 0.008). The difference was evident among individuals who were older than 47 yrs, women, and had pigmentation risk factors (e.g., blond or red hair, blue eye, fair skin, light, or none tanning ability after prolonged sun exposure, and freckling in the sun as a child). The difference was also evident among those who had at least one lifetime sunburn with blistering and had no reported use of a sunlamp. Interestingly, among controls, DmtDNA4977 levels differed by phenotypic index and reported use of a sunlamp. In the risk assessment, increased levels of DmtDNA4977 were associated with a 1.23-fold increased risk of melanoma (odds ratio (OR): 1.23, 95% confidence interval (90% CI): 1.01, 1.50). A significant dose-response relationship was observed in quartile analysis (P = 0.001). In summary, our study suggests that high levels of DmtDNA4977 in blood leukocytes are associated with increased risk of melanoma and that association is affected by both pigmentation and personal history of sun exposure.

Mitochondrial DNA 4977 bp deletion is a common phenomenon in hair and increases with age

Mitochondrial DNA (mtDNA) is believed to be particularly susceptible to oxidative damage during aging, resulting in mtDNA point mutations, duplications, and deletions. Although mtDNA deletions have been reported in various human tissues, e.g., the brain, heart, and skeletal muscle, little is known about the occurrence in hair. Therefore, we screened for the presence of mtDNA 13162 bp, 10422 bp, 7663 bp, 7436 bp, 4989 bp, and 4977 bp deletions in 90 hair samples from subjects aged 5 days to 91 years by using polymerase chain reaction (PCR) and investigated the deletion load by TaqMan probe-based real-time PCR. We detected the mtDNA 4977 bp deletion in hair samples, but none of the other deletions that were screened for. The proportion of mtDNA 4977 deletion carriers was 98.3% (89/90) and the deletion loads increased from 0 to 1.436 ± 0.2086% of the total mtDNA with an exponential increase with age (r = 0.677, p < 0.05). These results suggest that mtDNA 4977 bp deletion is a common phenomenon in hair and increases with age. These findings expand our understanding of the tissue-specific distribution of mtDNA deletions.

Detection and quantification of a radiation-associated mitochondrial DNA deletion by a nested real-time PCR in human peripheral lymphocytes

In this study we implemented a new assay using a nested real-time polymerase chain reaction (PCR) to detect radiation-induced common deletion (CD) in mitochondrial DNA (mtDNA) of human peripheral lymphocytes. A standard curve for real-time PCR was established by applying a plasmid DNA containing human normal mtDNA or mutated mtDNA. Human peripheral lymphocyte DNA was amplified and quantified by real-time PCR using primer sets for total damaged or mutated mtDNA, plus probes labeled with the fluorescent dyes. The first-round PCR generated multiple products were used as the template for a second-round PCR. We herein describe a nested real-time PCR assay capable of quantifying mtDNA bearing the CD in human peripheral lymphocytes following exposure (in vitro) to (137)Cs γ-rays in a dose range of 0.5 up to 5Gy. The reproducibility of this assay was evident for both unirradiated and irradiated samples by examining human blood lymphocytes from 14 donors. This technique was sensitive enough to detect deletions in mtDNA at low dose levels, as low as 0.5Gy, and higher levels of CD mtDNA were evident at higher doses (≥1Gy), however, there was no consistent dose-response relationship.

Combined OXPHOS complex I and IV defect, due to mutated complex I assembly factor C20ORF7

Defects of the mitochondrial oxidative phosphorylation (OXPHOS) system are frequent causes of neurological disorders in children. Linkage analysis and DNA sequencing identified a new founder p.G250V substitution in the C20ORF7 complex I chaperone in five Ashkenazi Jewish patients from two families with a combined OXPHOS complex I and IV defect presenting with Leigh's syndrome in infancy. Complementation with the wild type gene restored complex I, but only partially complex IV activity. Although the pathogenic mechanism remains elusive, a C20ORF7 defect should be considered not only in isolated complex I deficiency, but also in combination with decreased complex IV. Given the significant 1:290 carrier rate for the p.G250V mutation among Ashkenazi Jews, this mutation should be screened in all Ashkenazi patients with Leigh's syndrome prior to muscle biopsy.

Analysis of the common deletions in the mitochondrial DNA is a sensitive biomarker detecting direct and non-targeted cellular effects of low dose ionizing radiation

One of the key issues of current radiation research is the biological effect of low doses. Unfortunately, low dose science is hampered by the unavailability of easily performable, reliable and sensitive quantitative biomarkers suitable detecting low frequency alterations in irradiated cells. We applied a quantitative real time polymerase chain reaction (qRT-PCR) based protocol detecting common deletions (CD) in the mitochondrial genome to assess direct and non-targeted effects of radiation in human fibroblasts. In directly irradiated (IR) cells CD increased with dose and was higher in radiosensitive cells. Investigating conditioned medium-mediated bystander effects we demonstrated that low and high (0.1 and 2Gy) doses induced similar levels of bystander responses and found individual differences in human fibroblasts. The bystander response was not related to the radiosensitivity of the cells. The importance of signal sending donor and signal receiving target cells was investigated by placing conditioned medium from a bystander response positive cell line (F11-hTERT) to bystander negative cells (S1-hTERT) and vice versa. The data indicated that signal sending cells are more important in the medium-mediated bystander effect than recipients. Finally, we followed long term effects in immortalized radiation sensitive (S1-hTERT) and normal (F11-hTERT) fibroblasts up to 63 days after IR. In F11-hTERT cells CD level was increased until 35 days after IR then reduced back to control level by day 49. In S1-hTERT cells the increased CD level was also normalized by day 42, however a second wave of increased CD incidence appeared by day 49 which was maintained up to day 63 after IR. This second CD wave might be the indication of radiation-induced instability in the mitochondrial genome of S1-hTERT cells. The data demonstrated that measuring CD in mtDNA by qRT-PCR is a reliable and sensitive biomarker to estimate radiation-induced direct and non-targeted effects.

Mitochondrial DNA alterations of peripheral lymphocytes in acute lymphoblastic leukemia patients undergoing total body irradiation therapy

Background

Mitochondrial DNA (mtDNA) alterations, including mtDNA copy number and mtDNA 4977 bp common deletion (CD), are key indicators of irradiation-induced damage. The relationship between total body irradiation (TBI) treatment and mtDNA alterations in vivo, however, has not been postulated yet. The aim of this study is to analyze mtDNA alterations in irradiated human peripheral lymphocytes from acute lymphoblastic leukemia (ALL) patients as well as to take them as predictors for radiation toxicity.

Methods

Peripheral blood lymphocytes were isolated from 26 ALL patients 24 hours after TBI preconditioning (4.5 and 9 Gy, respectively). Extracted DNA was analyzed by real-time PCR method.

Results

Average 2.31 times mtDNA and 0.53 fold CD levels were observed after 4.5 Gy exposure compared to their basal levels. 9 Gy TBI produced a greater response of both mtDNA and CD levels than 4.5 Gy. Significant inverse correlation was found between mtDNA content and CD level at 4.5 and 9 Gy (P = 0.037 and 0.048). Moreover, mtDNA content of lymphocytes without irradiation was found to be correlated to age.

Conclusions

mtDNA and CD content may be considered as predictive factors to radiation toxicity.

Quantification of human mitochondrial DNA using synthesized DNA standards

Successful mitochondrial DNA (mtDNA) forensic analysis depends on sufficient quantity and quality of mtDNA. A real-time quantitative PCR assay was developed to assess such characteristics in a DNA sample, which utilizes a duplex, synthetic DNA to ensure optimal quality assurance and quality control. The assay's 105-base pair target sequence facilitates amplification of degraded DNA and is minimally homologous to nonhuman mtDNA. The primers and probe hybridize to a region that has relatively few sequence polymorphisms. The assay can also identify the presence of PCR inhibitors and thus indicate the need for sample repurification. The results show that the assay provides information down to 10 copies and provides a dynamic range spanning seven orders of magnitude. Additional experiments demonstrated that as few as 300 mtDNA copies resulted in successful hypervariable region amplification, information that permits sample conservation and optimized downstream PCR testing. The assay described is rapid, reliable, and robust.

The interplay between SUCLA2, SUCLG2, and mitochondrial DNA depletion

SUCLA2-related mitochondrial DNA (mtDNA) depletion syndrome is a result of mutations in the β subunit of the ADP-dependent isoform of the Krebs cycle succinyl-CoA synthase (SCS). The mechanism of tissue specificity and mtDNA depletion is elusive but complementation by the GDP-dependent isoform encoded by SUCLG2, and the association with mitochondrial nucleoside diphosphate kinase (NDPK), is a plausible link. We have investigated this relationship by studying SUCLA2 deficient fibroblasts derived from patients and detected normal mtDNA content and normal NDPK activity. However, knockdown of SUCLG2 by shRNA in both patient and control fibroblasts resulted in a significant decrease in mtDNA amount, decreased NDPK and cytochrome c oxidase activities, and a marked growth impairment. This suggests that, SUCLG2, to a higher degree than SUCLA2, is crucial for mtDNA maintenance and that mitochondrial NDPK is involved. Although results pertain to a cell culture system, the findings might explain the pathomechanism and tissue specificity in mtDNA depletion caused by defective SUCLA2.

Differential regulation of full-length genome and a single-stranded 7S DNA along the cell cycle in human mitochondria

Mammalian mitochondria contain full-length genome and a single-stranded 7S DNA. Although the copy number of mitochondrial DNA (mtDNA) varies depending on the cell type and also in response to diverse environmental stresses, our understanding of how mtDNA and 7S DNA are maintained and regulated is limited, partly due to lack of reliable in vitro assay systems that reflect the in vivo functionality of mitochondria. Here we report an in vitro assay system to measure synthesis of both mtDNA and 7S DNA under a controllable in vitro condition. With this assay system, we demonstrate that the replication capacity of mitochondria correlates with endogenous copy numbers of mtDNA and 7S DNA. Our study also shows that higher nucleotide concentrations increasingly promote 7S DNA synthesis but not mtDNA synthesis. Consistently, the mitochondrial capacity to synthesize 7S DNA but not mtDNA noticeably varied along the cell cycle, reaching its highest level in S phase. These findings suggest that syntheses of mtDNA and 7S DNA proceed independently and that the mitochondrial capacity to synthesize 7S DNA dynamically changes not only with cell-cycle progression but also in response to varying nucleotide concentrations.

Detection of mitochondrial DNA variation in human cells

The ability to detect mitochondrial DNA (mtDNA) variation within human cells is important not only to identify mutations causing mtDNA disease, but also as mtDNA mutations are being increasingly described in many ageing tissues and in complex diseases such as diabetes, neurodegeneration and cancer. In this review, we discuss the main molecular genetic techniques that can be applied to study the two main types of mtDNA mutation: point mutations and large-scale mtDNA rearrangements. We then describe in detail protocols routinely used within our laboratory to analyse mtDNA mutations in individual human cells such as single muscle fibres and individual neurons to study the relationship between mtDNA mutation load and respiratory chain dysfunction.

Patterns of persistent DNA damage associated with sun exposure and the glutathione S-transferase M1 genotype in melanoma patients

Solar radiation can lead to changes affecting DNA metabolism resulting in loss of DNA integrity. Skin specimens obtained from melanoma patients treated at the Memorial Sloan-Kettering Cancer Center were used to study patterns of DNA fragmentation using the comet assay and levels of deletions in mitochondrial DNA (mtDNA) using real-time PCR. Skin specimens were classified according to the glutathione S-transferase M1 (GSTM1) genotype (either wild type [WT] or null) and patient sunburn history. GSTM1 null individuals with a sunburn history showed increased levels of both DNA fragmentation by comet assays and mtDNA deletions relative to GSTM1 WT patients with little or no sunburn history. Microarray analyses identified a number of genes whose expression was upregulated >or=5-fold in cells from GSTM1-null patients or from those reporting histories of sunburn. These genes encoded small molecule transporters, various growth factor/chemokine receptors, transcription factors and tumor suppressors. Of 17 genes directly involved in DNA repair, three DNA ligases were highly upregulated while the RAD23 UV excision repair gene and the Growth Arrest and DNA Damage gene (GADD45) were downregulated. These findings support the idea that exposure to solar radiation early in life may induce long-term cellular changes that lead to persistent DNA damage and altered patterns of gene expression.

Collection of isolated cells for studying mitochondrial DNA mutations within individual cells

Mitochondrial genome integrity is an important issue in somatic mitochondrial genetics. Development of quantitative methods is indispensable to somatic mitochondrial genetics as quantitative studies are required to characterize heteroplasmy and mutation processes, as well as their effects on phenotypic developments. This chapter outlines the methods for collecting individual cells appropriate for analysis of mtDNA mutations by single-molecule PCR. In addition, we describe the protocols for respiratory complexes II and IV in these cells. Together, the identification of respiratory deficiency and mtDNA mutations within single cells provides a powerful means of evaluating the importance of these events in disease and aging.

Mitochondrial deoxyribonucleotide pools in deoxyguanosine kinase deficiency

Mutated deoxyguanosine kinase (dGK), which catalyses the first step of the mitochondrial deoxypurine salvage pathway, accounts for a hepatocerebral variant of mitochondrial DNA (mtDNA) depletion syndromes. In order to elucidate the pathogenic mechanism of dGK deficiency, mitochondrial and cytoplasmic deoxyribonucleoside triphosphate (dNTP) pools in cycling and quiescent fibroblasts from a dGK deficient patient were measured. The mitochondrial dNTP pools were found to be imbalanced, mainly in quiescent cells due to decreased dGTP while mtDNA content and mitochondrial respiratory chain activities were concomitantly decreased. Supplementation of deoxyguanosine and deoxyadenosine normalized mitochondrial dNTP pools, mtDNA content and partially restored the MRC function. It is suggested that the cytoplasmic deoxycytine kinase supplemented with external substrates may compensate for the deficient dGK.

Detection of mitochondrial DNA deletions in the cochlea and its structural elements from archival human temporal bone tissue

Large-scale deletions of mitochondrial DNA (mtDNA) have been associated with aging and disease in post-mitotic tissues. These post-mitotic tissues, including skeletal muscle, heart and brain, are heavily dependent on intact functional mitochondria. The cochlear tissues are known to contain an abundance of mitochondria. This observation stimulated a search for mtDNA deletions in the cochlea and its elements using a sensitive nested PCR methodology and long range PCR to explain the functional deficits observed in age-related hearing loss. The presence of the so-called "common" deletion (CD) was detected in cochlear tissue from two individuals with age-related hearing loss, 73 and 78 years of age. Three additional deletions, that to our knowledge have not been previously reported, were also identified in these two individuals, including a 5354 bp deletion flanked with a 3 bp repeat, a 9682 bp deletion flanked by a 10 bp repeat and a 5142 bp deletion without a flanking repeat. The 9682 and 5142 bp deletions were also detected in an individual 39 years of age with normal hearing, however, these two deletions were not detected in a normal hearing individual 9 years of age. In contrast, the 5354 bp deletion was detected in all four of the individuals studied. To localize the deletions within the cochlea, the cochlear elements were removed by laser capture microdissection (LCM) and the mtDNA from these tissues was studied. The 5142 and 5354 bp deletions were detected in the organ of corti, spiral ligament, and ganglion cells, but not in the stria vascularis. These findings correlate with the reduction in the number of spiral ganglion cells and outer hair cells, and the normal stria vascularis volume observed in this individual. All four of these deletions involve the cytochrome c oxidase (COX) subunit III gene, encoded by mtDNA. These observations suggest that multiple mtDNA deletions may contribute to a deficit in mitochondrial function in the cochlea and result in hearing loss if a level of physiological significance is reached.

Depletion of mitochondrial DNA in leukocytes of patients with poly-Q diseases

Polyglutamine (poly-Q) diseases are late-onset neurodegenerative disorders arising from the expansion of an unstable CAG repeat in the affected gene, which is translated to a tract of glutamine residues. This kind of mutant proteins may be aggregated and accumulated, and thereby enhance cellular oxidative stress. In one of our previous studies (Free Radic. Res. 2003;37:1307-17), we found that alteration in the leukocyte mtDNA content is very sensitive to the level of oxidative stress in blood. Thus, we proposed that leukocyte mtDNA content may be used as a biomarker to predict the severity of clinical manifestation of poly-Q diseases. We recruited 50 healthy subjects and 114 patients with poly-Q diseases, including spinal cerebellar atrophy 2/3, spinal bulbar muscular atrophy, and Huntington chorea. We found that mtDNA in leukocytes was depleted in patients with poly-Q diseases (P<0.05). Moreover, the results showed that patients with lower mtDNA content more frequently manifested multiple-symptom disorders and had high CAG repeat numbers in the mutant genes. In conclusion, we suggest that leukocyte mtDNA content correlates with the length of GAG repeat and may serve as an index of the severity of poly-Q diseases.

Quantitative analysis of mitochondrial DNA 4977-bp deletion in sporadic breast cancer and benign breast diseases

The mitochondrial DNA (mtDNA) 4977-bp deletion (DeltamtDNA(4977) mutation) is one of the most frequently observed mtDNA mutations in human tissues and may play a role in carcinogenesis. Only a few studies have evaluated DeltamtDNA(4977) mutation in breast cancer tissue, and the findings have been inconsistent, which may be due to methodological differences. In this study, we developed a quantitative real-time PCR assay to assess the level of the DeltamtDNA(4977) mutation in tumor tissue samples from 55 primary breast cancer patients and 21 patients with benign breast disease (BBD). The DeltamtDNA(4977) mutation was detected in all of the samples with levels varying from 0.000149% to 7.0%. The DeltamtDNA(4977) mutation levels were lower in tumor tissues than in adjacent normal tissues in both breast cancer and BBD subjects. The differences, however, were not statistically significant. No significant difference between breast cancer and BBD patients was found in the DeltamtDNA(4977) mutation levels of tumor tissues and adjacent normal tissues. The DeltamtDNA(4977) mutation levels were not significantly associated with clinicopathological characteristics (age, histology, tumor stage, and ER/PR status) in breast cancer or BBD patients. These results do not support the notion that the mitochondrial DNA 4977-bp deletion plays a major role in breast carcinogenesis.

Novel selective human mitochondrial kinase inhibitors: Design, synthesis and enzymatic activity

Selective and effective TK2 inhibitors can be obtained by introduction of bulky lipophilic chains (acyl or alkyl entities) at the 2' position of araT and BVaraU, nucleoside analogues naturally endowed with a low TK2 affinity. These derivatives showed a competitive inhibitory activity against TK2 in micromolar range. BVaraU nucleoside analogues, modified on the 2'-O-acyl chain with a terminal N-Boc amino-group, conserved or increased the inhibitory activity against TK2 (7l and 7m IC(50): 6.4 and 3.8 microM, respectively). The substitution of an ester for a carboxamide moiety at the 2' position of araT afforded a consistent reduction of the inhibitory activity (25, IC(50): 480 microM). On the contrary, modifications at 2'-OH position of araC and araG, have provided inactive derivatives against TK2 and dGK, respectively. The biological activity of a representative compound, 2'-O-decanoyl-BVaraU, was also investigated in normal human fibroblasts and was found to impair mitochondrial function due to TK2 inhibition.

The plasmids of Chlamydia trachomatis and Chlamydophila pneumoniae (N16): accurate determination of copy number and the paradoxical effect of plasmid-curing agents

A 7·5 kbp cryptic plasmid is found in almost all isolates of Chlamydia trachomatis. Real-time PCR assays, using TaqMan chemistry, were set up to quantify accurately both the chlamydial plasmid and the single copy, chromosomal omcB gene in the infectious, elementary bodies (EBs) of C. trachomatis L1 440. Plasmid copy number was also determined in the EBs of six other lymphogranuloma venereum (LGV) isolates (serovars L1–L3), ten trachoma isolates (serovars A–C) and nine urogenital isolates (serovars D–J). The results indicated an average plasmid copy number of 4·0±0·8 (mean±95 % confidence interval) plasmids per chromosome. During the chlamydial developmental cycle, up to 7·6 plasmids per chromosome were detected, indicating an increased plasmid copy number in the actively replicating reticulate bodies. Attempts to eliminate the plasmid from strain L1 440 using the plasmid-curing agents ethidium bromide, acridine orange or imipramine/novobiocin led to a paradoxical increase in plasmid copy number. It is speculated that the stress induced by chemical curing agents may stimulate the activity of plasmid-encoded replication (Rep) proteins. In contrast to C. trachomatis, only a single isolate of Chlamydophila pneumoniae bears a plasmid. C. pneumoniae strain N16 supports a 7·4 kbp plasmid in which ORF1, encoding one of the putative Rep proteins, is disrupted by a deletion and split into two smaller ORFs. Similar assay techniques revealed 1·3±0·2 plasmids per chromosome (mean±95 % confidence interval) in EBs of this strain. These findings are in agreement with the hypothesis that the ORF1-encoded protein is involved in, but not essential for, plasmid replication and control of copy number.