Decoding the nature and complexity of extracellular mtDNA: Types and implications for health and disease.

The mitochondrial DNA (mtDNA) is replicated and canonically functions within intracellular mitochondria, but recent discoveries reveal that the mtDNA has another exciting extracellular life. mtDNA fragments and mitochondria-containing vesicular structures are detected at high concentrations in cell-free forms, in different biofluids. Commonly referred to as cell-free mtDNA (cf-mtDNA), the field is currently without a comprehensive classification system that acknowledges the various biological forms of mtDNA and whole mitochondria existing outside the cell. This absence of classification hampers the creation of precise and consistent quantification methods across different laboratories, which is crucial for unraveling the molecular and biological characteristics of mtDNA. In this article, we integrate recent findings to propose a classification for different types of Extracellular mtDNA [ex-mtDNA]. The major biologically distinct types include: Naked mtDNA [N-mtDNA], mtDNA within non-mitochondrial Membranes [M-mtDNA], Extracellular mitochondria [exM-mtDNA], and mtDNA within Mitochondria enclosed in a Membrane [MM-mtDNA]. We outline the challenges associated with accurately quantifying these ex-mtDNA types, suggest potential physiological roles for each ex-mtDNA type, and explore how this classification could establish a foundation for future research endeavors and further analysis and definitions for ex-mtDNA. By proposing this classification of circulating mtDNA forms, we draw a parallel with the clinically recognized forms of cholesterol, such as HDL and LDL, to illustrate potential future significance in a similar manner. While not directly analogous, these mtDNA forms may one day be as biologically relevant in clinical interpretation as cholesterol fractions are currently. We also discuss how advancing methodologies to reliably quantify distinct ex-mtDNA forms could significantly enhance their utility as health or disease biomarkers, and how their application may offer innovative therapeutic approaches.

Powering prescription: Mitochondria as "Living Drugs" - Definition, clinical applications, and industry advancements.

Mitochondria's role as engines and beacons of metabolism and determinants of cellular health is being redefined through their therapeutic application as "Living Drugs" (LDs). Artificial mitochondrial transfer/transplant (AMT/T), encompassing various techniques to modify, enrich, or restore mitochondria in cells and tissues, is revolutionizing acellular therapies and the future of medicine. This article proposes a necessary definition for LDs within the Advanced Therapeutic Medicinal Products (ATMPs) framework. While recognizing different types of LDs as ATMPs, such as mesenchymal stem cells (MSCs) and chimeric antigen receptor T (CAR T) cells, we focus on mitochondria due to their unique attributes that distinguish them from traditional cell therapies. These attributes include their inherent living nature, diverse sources, industry applicability, validation, customizability for therapeutic needs, and their capability to adapt and respond within recipient cells. We trace the journey from initial breakthroughs in AMT/T to the current state-of-the-art applications by emerging innovative companies, highlighting the need for manufacturing standards to navigate the transition of mitochondrial therapies from concept to clinical practice. By providing a comprehensive overview of the scientific, clinical, and commercial landscape of mitochondria as LDs, this article contributes to the essential dialogue among regulatory agencies, academia, and industry to shape their future in medicine.