A Novel Ruthenium-based Molecular Sensor to Detect Endothelial Nitric Oxide

Biological Sensing of Nitric Oxide in Macrophages and Atherosclerosis Using a Ruthenium-Based Sensor

Macrophage-derived nitric oxide (NO) plays a critical role in atherosclerosis and presents as a potential biomarker. We assessed the uptake, distribution, and NO detection capacity of an irreversible, ruthenium-based, fluorescent NO sensor (Ru-NO) in macrophages, plasma, and atherosclerotic plaques. In vitro, incubation of Ru-NO with human THP1 monocytes and THP1-PMA macrophages caused robust uptake, detected by Ru-NO fluorescence using mass-cytometry, confocal microscopy, and flow cytometry. THP1-PMA macrophages had higher Ru-NO uptake (+13%, p < 0.05) than THP1 monocytes with increased Ru-NO fluorescence following lipopolysaccharide stimulation (+14%, p < 0.05). In mice, intraperitoneal infusion of Ru-NO found Ru-NO uptake was greater in peritoneal CD11b+F4/80+ macrophages (+61%, p < 0.01) than CD11b+F4/80− monocytes. Infusion of Ru-NO into Apoe−/− mice fed high-cholesterol diet (HCD) revealed Ru-NO fluorescence co-localised with atherosclerotic plaque macrophages. When Ru-NO was added ex vivo to aortic cell suspensions from Apoe−/− mice, macrophage-specific uptake of Ru-NO was demonstrated. Ru-NO was added ex vivo to tail-vein blood samples collected monthly from Apoe−/− mice on HCD or chow. The plasma Ru-NO fluorescence signal was higher in HCD than chow-fed mice after 12 weeks (37.9%, p < 0.05). Finally, Ru-NO was added to plasma from patients (N = 50) following clinically-indicated angiograms. There was lower Ru-NO fluorescence from plasma from patients with myocardial infarction (−30.7%, p < 0.01) than those with stable coronary atherosclerosis. In conclusion, Ru-NO is internalised by macrophages in vitro, ex vivo, and in vivo, can be detected in atherosclerotic plaques, and generates measurable changes in fluorescence in murine and human plasma. Ru-NO displays promising utility as a sensor of atherosclerosis.

Metal Peptide Conjugates in Cell and Tissue Imaging and Biosensing

Metal complex luminophores have seen dramatic expansion in application as imaging probes over the past decade. This has been enabled by growing understanding of methods to promote their cell permeation and intracellular targeting. Amongst the successful approaches that have been applied in this regard is peptide-facilitated delivery. Cell-permeating or signal peptides can be readily conjugated to metal complex luminophores and have shown excellent response in carrying such cargo through the cell membrane. In this article, we describe the rationale behind applying metal complexes as probes and sensors in cell imaging and outline the advantages to be gained by applying peptides as the carrier for complex luminophores. We describe some of the progress that has been made in applying peptides in metal complex peptide-driven conjugates as a strategy for cell permeation and targeting of transition metal luminophores. Finally, we provide key examples of their application and outline areas for future progress.

Determination and Imaging of Small Biomolecules and Ions Using Ruthenium(II) Complex-Based Chemosensors

Luminescence chemosensors are one of the most useful tools for the determination and imaging of small biomolecules and ions in situ in real time. Based on the unique photo-physical/-chemical properties of ruthenium(II) (Ru(II)) complexes, the development of Ru(II) complex-based chemosensors has attracted increasing attention in recent years, and thus many Ru(II) complexes have been designed and synthesized for the detection of ions and small biomolecules in biological and environmental samples. In this work, we summarize the research advances in the development of Ru(II) complex-based chemosensors for the determination of ions and small biomolecules, including anions, metal ions, reactive biomolecules and amino acids, with a particular focus on binding/reaction-based chemosensors for the investigation of intracellular analytes’ evolution through luminescence analysis and imaging. The advances, challenges and future research directions in the development of Ru(II) complex-based chemosensors are also discussed.

Cardiovascular bioimaging of nitric oxide: Achievements, challenges, and the future

Nitric oxide (NO) is a ubiquitous, volatile, cellular signaling molecule that operates across a wide physiological concentration range (pM-µM) in different tissues. It is a highly diffusible messenger and intermediate in various metabolic pathways. NO plays a pivotal role in maintaining optimum cardiovascular function, particularly by regulating vascular tone and blood flow. This review highlights the need for accurate, real-time bioimaging of NO in clinical diagnostic, therapeutic, monitoring, and theranostic applications within the cardiovascular system. We summarize electrochemical, optical, and nanoscale sensors that allow measurement and imaging of NO, both directly and indirectly via surrogate measurements. The physical properties of NO render it difficult to accurately measure in tissues using direct methods. There are also significant limitations associated with the NO metabolites used as surrogates to indirectly estimate NO levels. All these factors added to significant variability in the measurement of NO using available methodology have led to a lack of sensors and imaging techniques of clinical applicability in relevant vascular pathologies such as atherosclerosis and ischemic heart disease. Challenges in applying current methods to biomedical and clinical translational research, including the wide physiological range of NO and limitations due to the characteristics and toxicity of the sensors are discussed, as are potential targets and modifications for future studies. The development of biocompatible nanoscale sensors for use in combination with existing clinical imaging modalities provides a feasible opportunity for bioimaging NO within the cardiovascular system.