Fluorescence microscopy imaging of mitochondrial metabolism in cancer cells

Measurement of Mitochondrial ROS Formation

Reactive oxygen species (ROS) play important roles in physiological and pathological processes. Mitochondria, particularly in skeletal and cardiac myocytes, are recognized as the primary site of ROS generation. Detecting oxidative modifications of intracellular or circulating molecules, such as lipids, proteins, and nucleic acids, is commonly employed to indicate ROS formation. However, this approach is indirect and provides limited insights into the spatiotemporal aspects of ROS generation. Understanding these aspects is crucial for comprehending the role of ROS in various pathophysiological conditions. To address this, fluorescent probes can be employed to measure ROS formation, offering a means to investigate ROS generation in both isolated mitochondria and intact cells. This chapter outlines three prominent examples for the use of fluorescent sensors to evaluate mitochondrial ROS formation in either isolated organelles or intact cells. The methods are explained in detail, and an analysis of the limitations of each technique is provided, underscoring potential sources of errors during the assay and the subsequent interpretation of results.

Exploring the anticancer and antioxidant potential of gold nanoparticles synthesized from Pterocarpus marsupium bark extract against oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a disease of significant concern with higher mortality rates. Conventional treatment approaches have several drawbacks, leading to the opening of new research avenues in the field of nanoparticle-based cancer therapeutics. The study aimed at the synthesis of gold nanoparticles (Pm-AuNPs) from the aqueous bark extract of Pterocarpus marsupium, followed by its characterization and in vitro anticancer evaluation against OSCC. The synthesized Pm-AuNPs were characterized using UV-visible spectroscopy, particle size analyser, zeta potential, FTIR and SEM techniques. The anticancer potential of the Pm-AuNPs was evaluated against OSCC cell lines (SCC29b, SSC154 and OECM-1) through in vitro assays. The IC50 value was found to be 25 ± 1.2, 45 ± 1.5 and 75 ± 2.1 µg/mL for the three OSCC cell lines, elucidating Pm-AuNPs cytotoxic effects and mechanism of action. Intracellular ROS and SOX detection, mitochondrial transmembrane potential analysis and apoptosis detection were used to confirm the activity of Pm-AuNPs against OSCC. Acute toxicity studies on Wistar rats confirmed the non-toxic nature of the Pm-AuNPs at a higher dose concentration up to 2000 mg/kg body weight. The findings underscore Pm-AuNPs as promising candidates for future anticancer therapeutics, providing insights into their mechanism of action and therapeutic efficacy against OSCC.

Label-Free Assessment of Key Biological Autofluorophores: Material Characteristics and Opportunities for Clinical Applications

Autofluorophores are endogenous fluorescent compounds that naturally occur in the intra and extracellular spaces of all tissues and organs. Most have vital biological functions - like the metabolic cofactors NAD(P)H and FAD+, as well as the structural protein collagen. Others are considered to be waste products - like lipofuscin and advanced glycation end products - which accumulate with age and are associated with cellular dysfunction. Due to their natural fluorescence, these materials have great utility for enabling non-invasive, label-free assays with direct ties to biological function. Numerous technologies, with different advantages and drawbacks, are applied to their assessment, including fluorescence lifetime imaging microscopy, hyperspectral microscopy, and flow cytometry. Here, the applications of label-free autofluorophore assessment are reviewed for clinical and health-research applications, with specific attention to biomaterials, disease detection, surgical guidance, treatment monitoring, and tissue assessment - fields that greatly benefit from non-invasive methodologies capable of continuous, in vivo characterization.

Facile One Pot Synthesis of Hybrid Core-Shell Silica-Based Sensors for Live Imaging of Dissolved Oxygen and Hypoxia Mapping in 3D Cell Models

Fluorescence imaging allows for noninvasively visualizing and measuring key physiological parameters like pH and dissolved oxygen. In our work, we created two ratiometric fluorescent microsensors designed for accurately tracking dissolved oxygen levels in 3D cell cultures. We developed a simple and cost-effective method to produce hybrid core-shell silica microparticles that are biocompatible and versatile. These sensors incorporate oxygen-sensitive probes (Ru(dpp) or PtOEP) and reference dyes (RBITC or A647 NHS-Ester). SEM analysis confirmed the efficient loading and distribution of the sensing dye on the outer shell. Fluorimetric and CLSM tests demonstrated the sensors' reversibility and high sensitivity to oxygen, even when integrated into 3D scaffolds. Aging and bleaching experiments validated the stability of our hybrid core-shell silica microsensors for 3D monitoring. The Ru(dpp)-RBITC microparticles showed the most promising performance, especially in a pancreatic cancer model using alginate microgels. By employing computational segmentation, we generated 3D oxygen maps during live cell imaging, revealing oxygen gradients in the extracellular matrix and indicating a significant decrease in oxygen level characteristics of solid tumors. Notably, after 12 h, the oxygen concentration dropped to a hypoxic level of PO2 2.7 ± 0.1%.

Cell Death in Leishmania donovani promastigotes in response to Mammalian Aurora Kinase B Inhibitor- Hesperadin

Deciphering how hesperadin, a repurposed mammalian aurora kinase B inhibitor, affects the cellular pathways in Leishmania donovani might be beneficial. This investigation sought to assess the physiological effects of hesperadin on promastigotes of L. donovani, by altering the duration of treatment following exposure to hesperadin. Groups pre-treated with inhibitors such as EGTA, NAC, and z-VAD-fmk before hesperadin exposure were also included. Morphological changes by microscopy, ATP and ROS changes by luminometry; DNA degradation using agarose gel electrophoresis and metacaspase levels through RT-PCR were assessed. Flow cytometry was used to study mitochondrial depolarization using JC-1 and MitoTracker Red; mitochondrial-superoxide accumulation using MitoSOX; plasma membrane modifications using Annexin-V and propidium iodide, and lastly, caspase activation using ApoStat. Significant alterations in promastigote morphology were noted. Caspase activity and mitochondrial-superoxide rose early after exposure whereas mitochondrial membrane potential demonstrated uncharacteristic variations, with significant functional disturbances such as leakage of superoxide radicals after prolonged treatments. ATP depletion and ROS accumulation demonstrated inverse patterns, genomic DNA showed fragmentation and plasma membrane showed Annexin-V binding, soon followed by propidium iodide uptake. Multilobed macronuclei and micronuclei accumulated in hesperadin exposed cells before they disintegrated into necrotic debris. The pathologic alterations were unlike the intrinsic or extrinsic pathways of classical apoptosis and suggest a caspase-mediated cell death most akin to mitotic-catastrophe. Most likely, a G2/M transition block caused accumulation of death signals, disorganized spindles and mechanical stresses, causing changes in morphology, organellar functions and ultimately promastigote death. Thus, death was a consequence of mitotic-arrest followed by ablation of kinetoplast functions, often implicated in L. donovani killing.

A novel imaging method (FIM-ID) reveals that myofibrillogenesis plays a major role in the mechanically induced growth of skeletal muscle

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e. an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e. myofibril hypertrophy) and/or the number of myofibrils (i.e. myofibrillogenesis) is not known. Electron microscopy (EM) can provide images with the level of resolution that is needed to address this question, but the acquisition and subsequent analysis of EM images is a time- and cost-intensive process. To overcome this, we developed a novel method for visualizing myofibrils with a standard fluorescence microscope (fluorescence imaging of myofibrils with image deconvolution [FIM-ID]). Images from FIM-ID have a high degree of resolution and contrast, and these properties enabled us to develop pipelines for automated measurements of myofibril size and number. After extensively validating the automated measurements, we used both mouse and human models of increased mechanical loading to discover that the radial growth of muscle fibers is largely mediated by myofibrillogenesis. Collectively, the outcomes of this study offer insight into a fundamentally important topic in the field of muscle growth and provide future investigators with a time- and cost-effective means to study it.

Potassium Ions Decrease Mitochondrial Matrix pH: Implications for ATP Production and Reactive Oxygen Species Generation

Potassium (K+) is the most abundant cation in the cytosol and is maintained at high concentrations within the mitochondrial matrix through potassium channels. However, many effects of K+ at such high concentrations on mitochondria and the underlying mechanisms remain unclear. This study aims to elucidate these effects and mechanisms by employing fluorescence imaging techniques to distinguish and precisely measure signals inside and outside the mitochondria. We stained the mitochondrial matrix with fluorescent dyes sensitive to K+, pH, reactive oxygen species (ROS), and membrane potential in plasma membrane-permeabilized C6 cells and isolated mitochondria from C6 cells. Fluorescence microscopy facilitated the accurate measurement of fluorescence intensity inside and outside the matrix. Increasing extramitochondrial K+ concentration from 2 mM to 127 mM led to a reduction in matrix pH and a decrease in the generation of highly reactive ROS. In addition, elevated K+ levels electrically polarized the inner membrane of the mitochondria and promoted efficient ATP synthesis via FoF1-ATPase. Introducing protons (H+) into the matrix through phosphate addition led to further mitochondrial polarization, and this effect was more pronounced in the presence of K+. K+ at high concentrations, reaching sub-hundred millimolar levels, increased H+ concentration within the matrix, suppressing ROS generation and boosting ATP synthesis. Although this study does not elucidate the role of specific types of potassium channels in mitochondria, it does suggest that mitochondrial K+ plays a beneficial role in maintaining cellular health.

A Novel Imaging Method (FIM-ID) Reveals that Myofibrillogenesis Plays a Major Role in the Mechanically Induced Growth of Skeletal Muscle

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e., an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e., myofibril hypertrophy) and/or the number of myofibrils (i.e., myofibrillogenesis) is not known. Electron microscopy (EM) can provide images with the level of resolution that is needed to address this question, but the acquisition and subsequent analysis of EM images is a time- and cost-intensive process. To overcome this, we developed a novel method for visualizing myofibrils with a standard fluorescence microscope (FIM-ID). Images from FIM-ID have a high degree of resolution and contrast, and these properties enabled us to develop pipelines for automated measurements of myofibril size and number. After extensively validating the automated measurements, we used both mouse and human models of increased mechanical loading to discover that the radial growth of muscle fibers is largely mediated by myofibrillogenesis. Collectively, the outcomes of this study offer insight into a fundamentally important topic in the field of muscle growth and provide future investigators with a time- and cost-effective means to study it.