Eleanor Clare Ransdell-Green

Opioids are potent analgesic agents, frequently being used to manage severe pain associated with musculoskeletal (MSK) trauma. The adverse effects of systemic opioids, such as respiratory depression, development of dependency and tolerance have impeded clinical opioid utility. To overcome these limitations, we have developed N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-based thermoresponsive polymeric prodrugs (ProGel-HMP) of hydromorphone (HMP) as a novel peripherally restricted analgesic agent for local management of MSK pain. In the present study, ProGel-HMP formulations were synthesized and characterized for their physicochemical properties. The localized retention and tissue biodistribution were assessed using near-infrared (NIR) optical imaging in a mouse model of closed femoral fracture. Analgesic efficacy was evaluated through static weight-bearing (incapacitance test) and dynamic gait analysis (CatWalk XT) over three weeks post-ProGel-HMP administration. Potential systemic analgesia was assessed via tail-flick latency. The risk of respiratory depression was evaluated using whole-body plethysmography in rats. Quantitative micro-computed tomography (micro-CT) was performed at 6 weeks post-ProGel-HMP treatment to screen for any potential impacts on the fracture healing process. NIR optical imaging confirmed that local intra-callus injection of ProGel-HMP resulted in its sustained retention at the fracture site for at least 14 days. A single local administration of ProGel-HMP provided sustained pain relief, maintaining balanced static weight distribution and improved dynamic gait parameters for up to 21 days post-fracture, whereas dose-equivalent free HMP lost efficacy within 2 days. Tail-flick testing demonstrated substantially reduced systemic antinociceptive activity following ProGel-HMP administration compared with dose-equivalent free HMP. Whole body plethysmography revealed no significant impairment in respiratory rate, tidal volume, or minute ventilation. Quantitative micro-CT analysis verified that ProGel-HMP treatment did not compromise the fracture healing process, with similar callus morphology, bone mineral density, and microstructural parameters when compared to controls. In conclusion, intra-callus administration of thermoresponsive ProGel-HMP provides potent and sustained local analgesia in a closed femoral fracture mouse model. These findings support ProGel-HMP’s potential as a promising peripherally restricted analgesia for pain management in orthopaedic trauma.

Thermoresponsive polymeric prodrugs represent a promising strategy for localized and sustained in vivo drug delivery. In this work, two polyethylene glycol (PEG)-based dexamethasone (Dex) prodrugs with different Dex contents were synthesized using a four-arm PEG scaffold. Prodrug 1, containing four Dex molecules, showed high aqueous solubility but no thermoresponsive gelation behavior. In contrast, eight-Dex Prodrug 2 exhibited temperature-dependent aggregation and formed hydrogels in aqueous media. The viscosity of the Prodrug 2 hydrogel was reduced by introducing 10% ethanol as a cosolvent, enabling an injectable formulation that rapidly forms a hydrogel depot upon contact with aqueous media. The hydrogel provides gradual Dex release via the cleavage of the acid-labile hydrazone bond linking Dex to the PEG. In a monosodium iodoacetate (MIA)-induced osteoarthritis (OA) pain model, intra-articular (IA) injection of Prodrug 2 produced rapid and sustained pain relief for up to 28 days. These findings indicate that the hydrogel-forming four-arm PEG-based Dex prodrug offers a potentially effective approach for prolonged local corticosteroid (CS) delivery, applicable to the treatment of many local pathologies, including OA and OA pain.

Hydroxyl radicals (^•OH), the most potent oxidants among reactive oxygen species (ROS), are a major contributor to oxidative damage of biomacromolecules, including DNA, lipids, and proteins. The overproduction of ^•OH is implicated in the pathogenesis of numerous diseases such as cancer, neurodegenerative disorders, and some cardiovascular pathologies. Given the localized nature of ^•OH-induced damage, detecting ^•OH, specifically near DNA and within organelles, is crucial for understanding their pathological roles. The major challenge of ^•OH detection results from their short half-life, high reactivity, and low concentrations within biological systems. As a result, there is a growing need for the development of highly sensitive and selective probes that can detect ^•OH in specific cellular regions. This review focuses on the advances in fluorescence probes designed to detect ^•OH near DNA and within cellular organelles and membranes. The key designs of the probes are highlighted, with emphasis on their strengths, applications, and limitations. Recommendations for future research directions are given to further enhance probe development and characterization.

Hydroxyl radicals (•OH), the most potent oxidants among reactive oxygen species (ROS), are a major contributor to oxidative damage of biomacromolecules including DNA, lipids, and proteins. The overproduction of •OH is implicated in the pathogenesis of numerous diseases such as cancer, neurodegenerative disorders, and some cardiovascular pathologies. Given the localized nature of •OH-induced damage, detecting •OH, specifically near DNA and within organelles, is crucial for understanding their pathological roles. The major challenge of •OH detection results from their short half-life, high reactivity, and low concentrations within biological systems. As a result, there is a growing need for the development of highly sensitive and selective probes that can detect •OH in specific cellular regions. This review focuses on the advances in fluorescence probes designed to detect •OH near DNA and within cellular organelles and membranes. The key designs of the probes are highlighted, with emphasis on their strengths, applications, and limitations. Recommendations for future research directions are given to further enhance probe development and characterization.

The metabolic rate (ṀO2) of eurythermal fishes changes in response to temperature, yet it is unclear how changes in mitochondrial function contribute to changes in ṀO2. We hypothesized that ṀO2 would increase with acclimation temperature in the threespine stickleback (Gasterosteus aculeatus) in parallel with metabolic remodeling at the cellular level but that changes in metabolism in some tissues, such as liver, would contribute more to changes in ṀO2 than others. Threespine stickleback were acclimated to 5, 12 and 20°C for 7 to 21 weeks. At each temperature, standard and maximum metabolic rate (SMR and MMR, respectively), and absolute aerobic scope (AAS) were quantified, along with mitochondrial respiration rates in liver, oxidative skeletal and cardiac muscles, and the maximal activity of citrate synthase (CS) and lactate dehydrogenase (LDH) in liver, and oxidative and glycolytic skeletal muscles. SMR, MMR and AAS increased with acclimation temperature, along with rates of mitochondrial phosphorylating respiration in all tissues. Low SMR and MMR at 5°C were associated with low or undetectable rates of mitochondrial complex II activity and a greater reliance on complex I activity in liver, oxidative skeletal muscle and heart. SMR was positively correlated with cytochrome c oxidase (CCO) activity in liver and oxidative muscle, but not mitochondrial proton leak, whereas MMR was positively correlated with CCO activity in liver. Overall, the results suggest that changes in ṀO2 in response to temperature are driven by changes in some aspects of mitochondrial function in some, but not all, tissues of threespine stickleback.