In vivo fluorescence imaging of biomaterial-associated inflammation and infection in a minimally invasive manner

Positron Emission Tomography of Nitric Oxide by a Specific Radical-Generating Dihydropyridine Tracer

Nitric oxide (NO) plays a pivotal role as a biological signaling molecule, presenting challenges in its specific detection and differentiation from other reactive nitrogen and oxygen species within living organisms. Herein, a 18F-labeled (fluorine-18, t1/2 = 109.7 min) small-molecule tracer dimethyl 4-(4-(4-[18F]fluorobutoxy)benzyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate ([18F]BDHP) is developed based on the dihydropyridine scaffold for positron emission tomography (PET) imaging of NO in vivo. [18F]BDHP exhibits a highly sensitive and efficient C-C cleavage reaction specifically triggered by NO under physiological conditions, leading to the production of a 18F-labeled radical that is readily retained within the cells. High uptakes of [18F]BDHP are found within and around NO-generating cells, such as macrophages treated with lipopolysaccharide or benzo(a)pyrene. MicroPET/CT imaging of arthritic animal model mice reveals distinct tracer accumulation in the arthritic legs, showcasing a higher distribution of NO compared with the control legs. In summary, a specific radical-generating dihydropyridine tracer with a unique radical retention strategy has been established for the marking of NO in real-time in vivo.

A Naked Eye-Invisible Ratiometric Fluorescent Microneedle Tattoo for Real-Time Monitoring of Inflammatory Skin Conditions

The field of portable healthcare monitoring devices has an urgent need for the development of real-time, noninvasive sensing and detection methods for various physiological analytes. Currently, transdermal sensing techniques are severely limited in scope (i.e., measurement of heart rate or sweat composition), or else tend to be invasive, often needing to be performed in a clinical setting. This study proposes a minimally invasive alternative strategy, consisting of using dissolving polymeric microneedles to deliver naked eye-invisible functional fluorescent ratiometric microneedle tattoos directly to the skin for real-time monitoring and quantification of physiological and pathological parameters. Reactive oxygen species are overexpressed in the skin in association with various pathological conditions. Here, one demonstrates for the first time the microneedle-based delivery to the skin of active fluorescent sensors in the form of an invisible, ratiometric microneedle tattoo capable of sensing reactive oxygen species in a reconstructed human-based skin disease model, as well as an in vivo model of UV-induced dermal inflammation. One also elaborates a universal ratiometric quantification concept coupled with a custom-built, multiwavelength portable fluorescence detection system. Fully realized, this approach presents an opportunity for the minimally invasive monitoring of a broad range of physiological parameters through the skin.

Small-molecule fluorescent probes: big future for specific bacterial labeling and infection detection

Bacterial infections remain a global healthcare problem that is particularly attributed to the spread of antibiotic resistance and the evolving pathogenicity. Accurate and swift approaches for infection diagnosis are urgently needed to facilitate antibiotic stewardship and effective medical treatment. Direct optical imaging for specific bacterial labeling and infection detection offers an attractive prospect of precisely monitoring the infectious disease status and therapeutic response in real time. This feature article focuses on the recent advances of small-molecule probes developed for fluorescent imaging of bacteria and infection, which covers the probe design, responsive mechanisms and representative applications. In addition, the perspective and challenges to advance small-molecule fluorescent probes in the field of rapid drug-resistant bacterial detection and clinical diagnosis of bacterial infections are discussed. We envision that the continuous advancement and clinical translations of such a technique will have a strong impact on future anti-infective medicine.

Recent Advances in the Evaluation of Antimicrobial Materials for Resolution of Orthopedic Implant-Associated Infections In Vivo

While orthopedic implant-associated infections are rare, revision surgeries resulting from infections incur considerable healthcare costs and represent a substantial research area clinically, in academia, and in industry. In recent years, there have been numerous advances in the development of antimicrobial strategies for the prevention and treatment of orthopedic implant-associated infections which offer promise to improve the limitations of existing delivery systems through local and controlled release of antimicrobial agents. Prior to translation to in vivo orthopedic implant-associated infection models, the properties (e.g., degradation, antimicrobial activity, biocompatibility) of the antimicrobial materials can be evaluated in subcutaneous implant in vivo models. The antimicrobial materials are then incorporated into in vivo implant models to evaluate the efficacy of using the material to prevent or treat implant-associated infections. Recent technological advances such as 3D-printing, bacterial genomic sequencing, and real-time in vivo imaging of infection and inflammation have contributed to the development of preclinical implant-associated infection models that more effectively recapitulate the clinical presentation of infections and improve the evaluation of antimicrobial materials. This Review highlights the advantages and limitations of antimicrobial materials used in conjunction with orthopedic implants for the prevention and treatment of orthopedic implant-associated infections and discusses how these materials are evaluated in preclinical in vivo models. This analysis serves as a resource for biomaterial researchers in the selection of an appropriate orthopedic implant-associated infection preclinical model to evaluate novel antimicrobial materials.

Cyanine-Dyad Molecular Probe for the Simultaneous Profiling of the Evolution of Multiple Radical Species During Bacterial Infections

Real-time monitoring of the evolution of bacterial infection-associated multiple radical species is critical to accurately profile the pathogenesis and host-defense mechanisms. Here, we present a unique dual wavelength near-infrared (NIR) cyanine-dyad molecular probe (HCy5-Cy7) for simultaneous monitoring of reactive oxygen and nitrogen species (RONS) variations both in vitro and in vivo. HCy5-Cy7 specifically turns on its fluorescence at 660 nm via superoxide or hydroxyl radical (O₂ ^.- , ^. OH)-mediated oxidation of reduced HCy5 moiety to Cy5, while peroxynitrite or hypochlorous species (ONOO^- , ClO^- )-induced Cy7 structural degradation causes the emission turn-off at 800 nm. Such multispectral but reverse signal responses allow multiplex manifestation of in situ oxidative and nitrosative stress events during the pathogenic and defensive processes in both bacteria-infected macrophage cells and living mice. Most importantly, this study may also provide new perspectives for understanding the bacterial pathogenesis and advancing the precision medicine against infectious diseases.

Comprehensive characterization method for a fluorescence imaging system

Fluorescence imaging systems are regularly characterized by their ability to distinguish varying concentrations of fluorophores in a solution or tissue phantom. However, there is inadequate standardization in the field for fluorescence characterization. In this study, we characterize a fluorescence imaging system developed for pathogen detection, regarding its ability to detect a near-infrared dye. During this process, we vary a number of key factors involved in fluorescence imaging, such as the excitation intensity, background level, working distance, volume of fluorescent solution, and type of container used to hold the fluorescent solution. We then analyze the results, with statistical rigor, to determine which factors result in significant changes in fluorescence detection. Notably, we found that using different types of containers to hold the dye solution can have a significant impact on fluorescence detection, while the effects of working distance and excitation intensity can vary. Based on our findings, greater standardization, or at least more thorough reporting of the experimental setup, is recommended to researchers when publishing characterization results of new imaging systems.

Options and Limitations in Clinical Investigation of Bacterial Biofilms

Bacteria can form single- and multispecies biofilms exhibiting diverse features based upon the microbial composition of their community and microenvironment. The study of bacterial biofilm development has received great interest in the past 20 years and is motivated by the elegant complexity characteristic of these multicellular communities and their role in infectious diseases. Biofilms can thrive on virtually any surface and can be beneficial or detrimental based upon the community's interplay and the surface. Advances in the understanding of structural and functional variations and the roles that biofilms play in disease and host-pathogen interactions have been addressed through comprehensive literature searches. In this review article, a synopsis of the methodological landscape of biofilm analysis is provided, including an evaluation of the current trends in methodological research. We deem this worthwhile because a keyword-oriented bibliographical search reveals that less than 5% of the biofilm literature is devoted to methodology. In this report, we (i) summarize current methodologies for biofilm characterization, monitoring, and quantification; (ii) discuss advances in the discovery of effective imaging and sensing tools and modalities; (iii) provide an overview of tailored animal models that assess features of biofilm infections; and (iv) make recommendations defining the most appropriate methodological tools for clinical settings.

Photonic monitoring of treatment during infection and sepsis: development of new detection strategies and potential clinical applications

Despite the strong decline in the infection-associated mortality since the development of the first antibiotics, infectious diseases are still a major cause of death in the world. With the rising number of antibiotic-resistant pathogens, the incidence of deaths caused by infections may increase strongly in the future. Survival rates in sepsis, which occurs when body response to infections becomes uncontrolled, are still very poor if an adequate therapy is not initiated immediately. Therefore, approaches to monitor the treatment efficacy are crucially needed to adapt therapeutic strategies according to the patient's response. An increasing number of photonic technologies are being considered for diagnostic purpose and monitoring of therapeutic response; however many of these strategies have not been introduced into clinical routine, yet. Here, we review photonic strategies to monitor response to treatment in patients with infectious disease, sepsis, and septic shock. We also include some selected approaches for the development of new drugs in animal models as well as new monitoring strategies which might be applicable to evaluate treatment response in humans in the future. Figure Label-free probing of blood properties using photonics.

* A Paradigm for the Evaluation of Tissue-Engineering Biomaterials and Templates

Procedures for the evaluation of tissue-engineering processes, including those used for the testing of the relevant biomaterials, have not been developed in a logical manner. This perspectives paper discusses the limitations of testing regimes and recommends a very different approach. The main emphasis is on the existing methods for assessing the biological safety of these biomaterials, which, it is suggested, are irrelevant for evaluating materials that are intended to facilitate the generation of new tissue. An algorithm is proposed that sets out the pathway from materials design and characterization through to the production of a file that sets out full biocompatibility, functionality, and tissue incorporation data that are suitable for regulatory consideration for first-in-man experiences. Central to this algorithm is the choice of animal models and the real-time monitoring of the implanted construct performance.

Highly specific C-C bond cleavage induced FRET fluorescence for in vivo biological nitric oxide imaging

A novel Förster resonance energy transfer (FRET) fluorescence "off-on" system based on the highly specific, sensitive and effective C-C bond cleavage of certain dihydropyridine derivatives was reported for real-time quantitative imaging of nitric oxide (NO). 1,4-Dihydropyridine was synthesized as a novel linker which could connect customized fluorophores and their corresponding quenchers. The specific and quantitative response to NO is confirmed using fluorescence spectrometry with the classical example of fluorescein isothiocyanate (FITC) and [4'-(N,N'-dimethylamino)phenylazo] benzoyl (DABCYL). The fluorescence intensity increased linearly with the increase in the amount of NO. Cells incubated with an exogenous NO donor emitted fluorescence as expected. A high fluorescence intensity was detected in macrophages which generate NO when incubated with lipopolysaccharide (LPS). The in vivo imaging shows about an 8-fold contrast between Freund's adjuvant stimulated feet and normal feet in mice after intravenous injection, which was the first example of in vivo semiquantitative fluorescence imaging of NO in mammals.

Imaging of radicals following injury or acute stress in peripheral nerves with activatable fluorescent probes

Peripheral nerve injury evokes a complex cascade of chemical reactions including generation of molecular radicals. Conversely, the reactions within nerve induced by stress are difficult to directly detect or measure to establish causality. Monitoring these reactions in vivo would enable deeper understanding of the nature of the injury and healing processes. Here, we utilized near-infrared fluorescence molecular probes delivered via intra-neural injection technique to enable live, in vivo imaging of tissue response associated with nerve injury and stress. These initially quenched fluorescent probes featured specific sensitivity to hydroxyl radicals and become fluorescent upon encountering reactive oxygen species (ROS). Intraneurally delivered probes demonstrated rapid activation in injured rat sciatic nerve but minimal activation in normal, uninjured nerve. In addition, these probes reported activation within sciatic nerves of living rats after a stress caused by a pinprick stimulus to the abdomen. This imaging approach was more sensitive to detecting changes within nerves due to the induced stress than other techniques to evaluate cellular and molecular changes. Specifically, neither histological analysis of the sciatic nerves, nor the expression of pain and stress associated genes in dorsal root ganglia could provide statistically significant differences between the control and stressed groups. Overall, the results demonstrate a novel imaging approach to measure ROS in addition to the impact of ROS within nerve in live animals.

In Vivo Imaging of Retinal Oxidative Stress Using a Reactive Oxygen Species-Activated Fluorescent Probe

PURPOSE

In vivo methods for detecting oxidative stress in the eye would improve screening and monitoring of the leading causes of blindness: diabetic retinopathy, glaucoma, and age-related macular degeneration.

METHODS

To develop an in vivo biomarker for oxidative stress in the eye, we tested the efficacy of a reactive oxygen species (ROS)-activated, near-infrared hydrocyanine-800CW (H-800CW) fluorescent probe in light-induced retinal degeneration (LIRD) mouse models. After intravitreal delivery in LIRD rats, fluorescent microscopy was used to confirm that the oxidized H-800CW appeared in the same retinal layers as an established ROS marker (dichlorofluorescein).

RESULTS

Dose-response curves of increasing concentrations of intravenously injected H-800CW demonstrated linear increases in both intensity and total area of fundus hyperfluorescence in LIRD mice, as detected by scanning laser ophthalmoscopy. Fundus hyperfluorescence also correlated with the duration of light damage and functional deficits in vision after LIRD. In LIRD rats with intravitreal injections of H-800CW, fluorescent labeling was localized to photoreceptor inner segments, similar to dichlorofluorescein.

CONCLUSIONS

Hydrocyanine-800CW detects retinal ROS in vivo and shows potential as a novel biomarker for ROS levels in ophthalmic diseases.

Cyanine polyene reactivity: scope and biomedical applications

Cyanines are indispensable fluorophores that form the chemical basis of many fluorescence-based applications. A feature that distinguishes cyanines from other common fluorophores is an exposed polyene linker that is both crucial to absorption and emission and subject to covalent reactions that dramatically alter these optical properties. Over the past decade, reactions involving the cyanine polyene have been used as foundational elements for a range of biomedical techniques. These include the optical sensing of biological analytes, super-resolution imaging, and near-IR light-initiated uncaging. This review surveys the chemical reactivity of the cyanine polyene and the biomedical methods enabled by these reactions. The overarching goal is to highlight the multifaceted nature of cyanine chemistry and biology, as well as to point out the key role of reactivity-based insights in this promising area.

Scaffold-based anti-infection strategies in bone repair

Bone fractures and non-union defects often require surgical intervention where biomaterials are used to correct the defect, and approximately 10% of these procedures are compromised by bacterial infection. Currently, treatment options are limited to sustained, high doses of antibiotics and surgical debridement of affected tissue, leaving a significant, unmet need for the development of therapies to combat device-associated biofilm and infections. Engineering implants to prevent infection is a desirable material characteristic. Tissue engineered scaffolds for bone repair provide a means to both regenerate bone and serve as a base for adding antimicrobial agents. Incorporating anti-infection properties into regenerative medicine therapies could improve clinical outcomes and reduce the morbidity and mortality associated with biomaterial implant-associated infections. This review focuses on current animal models and technologies available to assess bone repair in the context of infection, antimicrobial agents to fight infection, the current state of antimicrobial scaffolds, and future directions in the field.