Cytogenetic damage in peripheral lymphocytes of mitochondrial disease patients

The molecular origins and pathophysiological consequences of micronuclei: New insights into an age-old problem

Micronuclei (MN), the small nucleus-like bodies separated from the primary nucleus, can exist in cells with numerical and/or structural chromosomal aberrations in apparently normal tissues and more so in tumors in humans. While MN have been observed for over 100 years, they were merely and constantly considered as passive indicators of chromosome instability (CIN) for a long time. Relatively little is known about the molecular origins and biological consequences of MN. Rapid technological advances are helping to close these gaps. Very recent studies provide exciting evidence that MN act as key platform for chromothripsis and a trigger of innate immune response, suggesting that MN could affect cellular functions by both genetic and nongenetic means. These previously unappreciated findings have reawakened widespread interests in MN. In this review, the diverse mechanisms leading to MN generation and the complex fate profiles of MN are discussed, together with the evidence for their contribution to CIN, inflammation, senescence and cell death. Moreover, we put this knowledge together into a speculative perspective on how MN may be responsible for cancer development and how their presence may influence the choice of treatment. We suggest that the heterogeneous responses to MN may function physiological to ensure the arrestment, elimination and immune clearance of damaged cells, but pathologically, may enable the survival and oncogenic transformation of cells bearing CIN. These insights not only underscore the complexity of MN biology, but also raise a host of new questions and provide fertile ground for future research.

Electron transfer mediators and other metabolites and cofactors in the treatment of mitochondrial dysfunction

Mitochondrial disorders (MDs) are caused by impairment of the mitochondrial electron transport chain (ETC). The ETC is needed for oxidative phosphorylation, which provides the cell with the most efficient energy outcome in terms of ATP production. One of the pathogenic mechanisms of MDs is the accumulation of reactive oxygen species. Mitochondrial dysfunction and oxidative stress appear to also have a strong impact on the pathogenesis of neurodegenerative diseases and cancer. The treatment of MDs is still inadequate. Therapies that have been attempted include ETC cofactors, other metabolites secondarily decreased in MDs, antioxidants, and agents acting on lactic acidosis. However, the role of these dietary supplements in the treatment of the majority of MDs remains unclear. This article reviews the rationale for their use and their role in clinical practice in the context of MDs and other disorders involving mitochondrial dysfunction.

Advances in molecular diagnostics for mitochondrial diseases

BACKGROUND

Mitochondrial disorders (MD) are diseases caused by impairment of the mitochondrial respiratory chain. Phenotypes are polymorphous and may range from pure myopathy to multisystemic disorders. The genetic defect can be located on mitochondrial or nuclear DNA. At present, diagnosis of MD requires a complex approach: measurement of serum lactate, electromyography, muscle histology and enzymology, and genetic analysis. Magnetic resonance spectroscopy allows the assessment of tissue metabolic alterations, thus providing useful information for the diagnosis and monitoring of MD. Molecular soluble markers of mitochondrial dysfunction, at rest and during exercise, can identify the impairment of the aerobic system in MD, but a reliable biomarker for the screening or diagnosis of MD is still needed.

OBJECTIVE

Molecular and genetic characterization of MD, together with other experimental approaches, contribute to add new insights to these diseases. Here, the role and advances of diagnostic techniques for MD are reviewed.

CONCLUSION

Possible applications of the results obtained by new molecular investigative approaches could in future guide therapeutic strategies.

Functional Diagnostics in Mitochondrial Diseases

Mitochondrial diseases (MD) with respiratory chain defects are caused by genetic mutations that determine an impairment of the electron transport chain functioning. Diagnosis often requires a complex approach with measurements of serum lactate, magnetic resonance spectroscopy (MRS), muscle histology and ultrastructure, enzymology, genetic analysis, and exercise testing. The ubiquitous distribution of the mitochondria in the human body explains the multiple organ involvement. Exercise intolerance is a common symptom of MD, due to increased dependence of skeletal muscle on anaerobic metabolism, with an excess lactate generation, phosphocreatine depletion, enhanced free radical production, reduced oxygen extraction and electron flux through the respiratory chain. MD treatment has included antioxidants (vitamin E, alpha lipoic acid), coenzyme Q10, riboflavin, creatine monohydrate, dichloroacetate and exercise training. Exercise is a particularly important tool in diagnosis as well as in the management of these diseases.