Characterisation of impaired wound healing in a preclinical model of induced diabetes using wide-field imaging and conventional immunohistochemistry assays

Nitric oxide-based treatments improve wound healing associated with diabetes mellitus

Non-healing wounds are long-term complications of diabetes mellitus (DM) that increase mortality risk and amputation-related disability and decrease the quality of life. Nitric oxide (NO·)-based treatments (i.e., use of both systemic and topical NO· donors, NO· precursors, and NO· inducers) have received more attention as complementary approaches in treatments of DM wounds. Here, we aimed to highlight the potential benefits of NO·-based treatments on DM wounds through a literature review of experimental and clinical evidence. Various topical NO·-based treatments have been used. In rodents, topical NO·-based therapy facilitates wound healing, manifested as an increased healing rate and a decreased half-closure time. The wound healing effect of NO·-based treatments is attributed to increasing local blood flow, angiogenesis induction, collagen synthesis and deposition, re-epithelization, anti-inflammatory and anti-oxidative properties, and potent broad-spectrum antibacterial effects. The existing literature lacks human clinical evidence on the safety and efficacy of NO·-based treatments for DM wounds. Translating experimental favors of NO·-based treatments of DM wounds into human clinical practice needs conducting clinical trials with well-predefined effect sizes, i.e., wound reduction area, rate of wound healing, and hospital length of stay.

Pyroxylin-based liquid bandage forms a mechanically active protective film to facilitate skin wound healing in mice

Wound healing requires interplay between cells and molecules. Recent evidence has demonstrated that liquid bandages promote wound healing by forming a protective barrier against contamination, attenuating inflammation, and enhancing re-epithelialization and angiogenesis. In this study, we evaluated the wound healing activity of pyroxylin-based liquid bandage (LiQuiPlast®) in eight-week-old C57BL/6 male mice by generating a single 4 mm diameter full-thickness excisional skin wound on the dorsum. In the LiQuiPlast® group, the liquid bandage was applied on day 0 and was replaced every four days. Wound size was monitored every day for two weeks. The results showed that LiQuiPlast® was mechanically active (induced wound contraction), which promoted a significant wound size reduction (27 %-39 %, compared to the control group) on days 1-4 postinjury. In addition, a significant reduction in wound size was observed again in the LiQuiPlast® group (25 %-29 %, compared to the controls) on days 8-9 postinjury. LiQuiPlast®-treated wounds showed no scab. Immunohistochemistry analyses displayed a reduction in neutrophils and tumor necrosis factor-α levels in LiQuiPlast®-treated wounds, compared to the control group on day 4 postinjury (the inflammatory phase). In addition, LiQuiPlast®-treated mice had enhanced keratinocyte proliferation than control mice during this time. On day 13 postinjury, LiQuiPlast® significantly reduced hypertrophic scarring and enhanced expression and reorganization of collagen fiber compared to control mice. In conclusion, we show that LiQuiPlast® acts as a mechanically active protective film, which promotes moist wound healing by promoting wound contraction, no scab formation, attenuated inflammation, enhanced keratinocyte proliferation, and decreased scarring.

Wound healing potential of Acacia catechu in streptozotocin-induced diabetic mice using in vivo and in silico approach

Background and aim

Acacia catechu Wild. (Fabaceae) barks are traditionally used in the treatment of diabetes and wounds. Therefore, the objective of the present study was to evaluate the wound healing potential of the alcoholic extract of A. catechu (EAC) in streptozotocin-induced diabetic mice.

Experimental procedures

EAC was first subjected to phytochemical estimations and standardization using (-) epicatechin as marker with the help of HPLC. Diabetes was induced in mice using streptozotocin and the wound healing potential of EAC was evaluated using excision and incision wound models on topical and oral treatment. Various biochemical parameters, in vivo antioxidants, cytokine profiling, VEGF, and histopathological examination were also performed. Further, molecular docking studies were performed using ligand (-) epicatechin on human inducible nitric oxide synthase.

Results and conclusion

Phytochemically, EAC showed the presence of tannins, flavonoids, phenolic compounds, and saponins, while the content of (-) epicatechin was reported to be 7.81% w/w. The maximum healing of wounds (91.84 ± 1.10%) was observed in mice treated with a combination of both topical (10% gel) and oral (extract at 200 mg/kg) followed by topically and orally treated groups respectively after 14 days of treatment. These groups also showed significant restoration of altered biochemical parameters, antioxidant enzymes and cytokines. The molecular docking studies confirmed the role of (-) epicatechin in stabilizing the human inducible nitric oxide synthase with inhibitor showing binding energy of -8.31 kcal/mol. The present study confirmed the role of (-) epicatechin as a major marker in diabetic wound healing potential of A. catechu.

Dasatinib Ointment Promotes Healing of Murine Excisional Skin Wound

Dasatinib, a tyrosine kinase inhibitor, has been shown to produce anti-inflammatory activity and impair vascular integrity in vivo, including during skin wound healing, potentially promoting the repair process. Given that dasatinib is a lipophilic small molecule capable of penetrating skin, topical dasatinib might provide benefits in wound healing. In the present study, we investigated the impact of dasatinib ointments in skin wound healing in mice. A full thickness excisional skin wound (4 mm diameter) was generated on the shaved dorsum of eight-week-old C57BL/6 mice. Dasatinib ointment (0.1 or 0.2% w/w) or ointment base was applied twice daily (every 12 h) for 10 days. Elizabethan collars were used to prevent animal licking. The wound size was monitored daily for 14 days. The results showed that dasatinib ointments, particularly 0.1% dasatinib, promoted a 16-23% reduction in wound size (p < 0.05) during day 2 to day 6 postinjury compared to controls. Immunohistochemistry analyses demonstrated a reduction in wound neutrophils (38% reduction, p = 0.04), macrophages (47% reduction, p = 0.005), and tumor necrosis factor-α levels (73% reduction, p < 0.01), together with an induction of vascular leakage-mediated fibrin(ogen) accumulation (2.5-fold increase, p < 0.01) in the wound during day 3 postinjury (an early phase of repair) in 0.1% dasatinib-treated mice relative to control mice. The anti-inflammatory and vascular hyperpermeability activities of dasatinib were associated with an enhanced healing process, including increased keratinocyte proliferation (1.8-fold increase in Ki67+ cells, p < 0.05) and augmented angiogenesis (1.7-fold increase in CD31+ area, p < 0.05), compared to the ointment base-treated group. Following treatment with 0.2% dasatinib ointment, minor wound bleeding and scab reformation were observed during the late phase, which contributed to delayed healing. In conclusion, our data suggest that dasatinib ointment, mainly at 0.1%, promotes the repair process by reducing inflammation and producing a local and temporal vascular leakage, leading to an increase in fibrin(ogen) deposition, re-epithelialization, and angiogenesis. Therefore, topical dasatinib might be a potential novel candidate to facilitate skin wound healing.

A Quantitative Assessment of Wound Healing With Oxygenated Micro/Nanobubbles in a Preclinical Burn Model

BACKGROUND

Burns are devastating injuries, carry significant morbidity, and require long-term treatment or multiple reconstructive procedures. Wound healing and secondary insults caused by burn wound conversion are amendable to therapeutic intervention, where ischemia has been cited as one of the major factors (Dermatol Surg. 2008;34:1159-1169). Halting injury progression in the zone of stasis is crucial as conversion creates increased burn surface area and depth, leading to local and systemic consequences (J Burns Wounds. 2006;5:e2). Oxygen-carrying micro/nanobubbles, MNB(O2), offer a novel technology that can be used to effectively deliver oxygen to burn wounds and potentially counteract burn wound ischemia.

METHODS

Topical irrigation with MNB(O2) of full-thickness burn wounds on a rodent model (n = 3) was compared against saline-treated controls (n = 3). Tissue structure (reduced scattering coefficient, μs'), oxyhemoglobin concentration (cHbO2), and tissue perfusion were quantified over the course of 28 days through spatial frequency domain imaging and laser speckle imaging. Histological samples taken at the end of the experiment were examined for evidence of wound healing.

RESULTS

Findings in this preliminary study showed hastened healing with significant differences in spatial frequency domain imaging-measured μs' during wound healing (days 11-28) in MNB(O2) group. The healing "tipping point" seemed to occur at days 9 to 11 with increased collagen organization and increased cHbO2 occurring around that period confirming the gross healing improvements observed. In addition, histological evidence indicated that only the MNB(O2) burns had reached the remodeling phase by the end of 28-day study period.

CONCLUSIONS

These preliminary findings propose the potential of MNB(O2) as a topical method for improving burn wound healing.

Use of human bone marrow mesenchymal stem cells immortalized by the expression of telomerase in wound healing in diabetic rats

Diabetes mellitus is associated with neural and micro- and macrovascular complications. Therapeutic options for these complications are limited and the delivery of mesenchymal stem cells into lesions have been reported to improve the healing process. In this work, the effects of the administration of a lineage of human bone marrow mesenchymal stem cells immortalized by the expression of telomerase (hBMSC-TERT) as a potential therapeutic tool for wound healing in diabetic rats were investigated. This is the first description of the use of these cells in diabetic wounds. Dorsal cutaneous lesions were made in streptozotocin-induced diabetic rats and hBMSC-TERT were subcutaneously administered around the lesions. The healing process was evaluated macroscopically, histologically, and by birefringence analysis. Diabetic wounded rats infused with hBMSC-TERT (DM-TERT group) and the non-diabetic wounded rats not infused with hBMSC-TERT (CW group) had very similar patterns of fibroblastic response and collagen proliferation indicating improvement of wound healing. The result obtained by birefringence analysis was in accordance with that obtained by the histological analysis. The results indicated that local administration of hBMSC-TERT in diabetic wounds improved the wound healing process and may become a therapeutic option for wounds in individuals with diabetes.

Bioreactor design and validation for manufacturing strategies in tissue engineering

The fields of regenerative medicine and tissue engineering offer new therapeutic options to restore, maintain or improve tissue function following disease or injury. To maximize the biological function of a tissue-engineered clinical product, specific conditions must be maintained within a bioreactor to allow the maturation of the product in preparation for implantation. Specifically, the bioreactor should be designed to mimic the mechanical, electrochemical and biochemical environment that the product will be exposed to in vivo. Real-time monitoring of the functional capacity of tissue-engineered products during manufacturing is a critical component of the quality management process. The present review provides a brief overview of bioreactor engineering considerations. In addition, strategies for bioreactor automation, in-line product monitoring and quality assurance are discussed.

Functional Imaging in Wounds: Imaging Modalities of Today and Tomorrow

Wound care is a multidisciplinary field with significant economic burden to our healthcare system. Not only does wound care cost the US healthcare system $20 billion annually, but wounds also remarkably impact the quality of life of patients; wounds pose significant risk of mortality, as the five-year mortality rate for diabetic foot ulcers (DFUs) and ischemic ulcers is notably higher compared to commonly encountered cancers such as breast and prostate. Although it is important to measure how wounds may or may not be improving over time, the only relative "marker" for this is wound area measurement-area measurements can help providers determine if a wound is on a healing or non-healing trajectory. Because wound area measurements are currently the only readily available "gold standard" for predicting healing outcomes, there is a pressing need to understand how other relative biomarkers may play a role in wound healing. Currently, wound care centers across the nation employ various techniques to obtain wound area measurements; length and width of a wound can be measured with a ruler, but this carries a high amount of inter- and intrapersonal error as well as uncertainty. Acetate tracings could be used to limit the amount of error but do not account for depth, thereby making them inaccurate. Here, we discuss current imaging modalities and how they can serve to accurately measure wound size and serve as useful adjuncts in wound assessment. Moreover, new imaging modalities are also discussed and how up-and-coming technologies can provide important information on "biomarkers" for wound healing.

Evaluation of Hemodynamics in a Murine Hindlimb Ischemia Model Using Spatial Frequency Domain Imaging

BACKGROUND AND OBJECTIVES

Spatial frequency domain imaging (SFDI), an optical imaging technique capable of quantitatively measuring tissue hemodynamics over a large field-of-view, has captured the interest of scientists and clinicians due to its ability to image rapidly and noninvasively. The goal of this study was to apply SFDI in a preclinical murine model to assess its ability to measure hemodynamic changes due to hindlimb ischemia in vivo longitudinally.

STUDY DESIGN/MATERIALS AND METHODS

Complete unilateral femoral artery ligation was performed on a total of nine C57BL/6J mice to induce ischemia in the left hindlimb. Changes in vascular perfusion in each mouse were monitored through SFDI acquisition of both the ischemic and control limbs throughout the course of 4 weeks. High-frequency pulsed-wave Doppler ultrasound was also acquired to confirm occlusion of the left femoral artery post-ligation compared with the control limb, while histological analysis was used to quantify femoral artery lumen shape and size.

RESULTS

Tissue oxygen saturation in the ischemic limb normalized to the control limb decreased from a ratio of 0.96 ± 0.06 at baseline to 0.86 ± 0.10 at day 1, then 0.94 ± 0.06 at day 3, followed by 0.95 ± 0.14 at day 7, 0.91 ± 0.09 at day 14, 0.90 ± 0.09 at day 21, and 1.01 ± 0.09 at day 28.

CONCLUSION

The results of this study indicate the utility of SFDI to detect hemodynamic changes in a preclinical murine model, as well as how to effectively use this tool to extract information regarding ischemia-induced hindlimb changes. In our model, we observed a decline in tissue oxygen saturation within one day post-ischemic injury, followed by a return to baseline values over the 4-week study period. While reducing skin artifacts and modifying camera hardware could still improve this murine imaging approach, our multimodality study presented here suggests that SFDI can be used to reliably characterize ischemia-mediated changes in a clinically relevant mouse model of peripheral arterial disease. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Evaluation of keratin biomaterial containing silver nanoparticles as a potential wound dressing in full-thickness skin wound model in diabetic mice

Keratin is a cytoskeletal scaffolding protein essential for wound healing and tissue recovery. The aim of the study was to evaluate the potential role of insoluble fur keratin-derived powder containing silver nanoparticles (FKDP-AgNP) in the allogenic full-thickness surgical skin wound model in diabetic mice. The scanning electron microscopy image evidenced that the keratin surface is covered by a single layer of silver nanoparticles. Data obtained from dynamic light scattering and micellar electrokinetic chromatography showed three fractions of silver nanoparticles with an average diameter of 130, 22.5, and 5 nm. Microbiologic results revealed that the designed insoluble FKDP-AgNP dressing to some extent inhibit the growth of Escherichia coli and Staphylococcus aureus. In vitro assays showed that the FKDP-AgNP dressing did not inhibit fibroblast growth or induce hemolysis. In vivo studies using a diabetic mice model confirmed biocompatible properties of the insoluble keratin dressings. FKDP-AgNP significantly accelerated wound closure and epithelization at Days 5 and 8 (p < .05) when compared with controls. Histological examination of the inflammatory response documented that FKDP-AgNP-treated wounds contained predominantly macrophages, whereas their untreated variants showed mixed cell infiltrates rich in neutrophils. Wound inflammatory response based on macrophages favors tissue remodeling and healing. In conclusion, the investigated FKDP-AgNP dressing consisting of an insoluble fraction of keratin, which is biocompatible, significantly accelerated wound healing in a diabetic mouse model.

IDE Degrades Nociceptin/Orphanin FQ through an Insulin Regulated Mechanism

Insulin-degrading enzyme (IDE) was applied to catalyze hydrolysis of Nociceptin/Orphanin 1-16 (OFQ/N) to show the involvement of the enzyme in degradation of neuropeptides engaged in pain transmission. Moreover, IDE degradative action towards insulin (Ins) was inhibited by the OFQ/N fragments, suggesting a possible regulatory mechanism in the central nervous system. It has been found that OFQ/N and Ins affect each other degradation by IDE, although in a different manner. Indeed, while the digestion of OFQ/N is significantly affected by the presence of Ins, the kinetic profile of the Ins hydrolysis is not affected by the presence of OFQ/N. However, the main hydrolytic fragments of OFQ/N produced by IDE exert inhibitory activity towards the IDE-mediated Ins degradation. Here, we present the results indicating that, besides Ins, IDE cleaves neuropeptides and their released fragments act as inhibitors of IDE activity toward Ins. Having in mind that IDE is present in the brain, which also contains Ins receptors, it cannot be excluded that this enzyme indirectly participates in neural communication of pain signals and that neuropeptides involved in pain transmission may contribute to the regulation of IDE activity. Finally, preliminary results on the metabolism of OFQ/N, carried out in the rat spinal cord homogenate in the presence of various inhibitors specific for different classes of proteases, show that OFQ/N proteolysis in rat spinal cord could be due, besides IDE, also to a cysteine protease not yet identified.

Characterisation of impaired wound healing in a preclinical model of induced diabetes using wide-field imaging and conventional immunohistochemistry assays

Major complications of diabetes lead to inflammation and oxidative stress, delayed wound healing, and persistent ulcers. The high morbidity, mortality rate, and associated costs of management suggest a need for non-invasive methods that will enable the early detection of at-risk tissue. We have compared the wound-healing process that occurs in streptozotocin (STZ)-treated diabetic rats with non-diabetic controls using contrast changes in colour photography (ie, Weber Contrast) and the non-invasive optical method Spatial Frequency Domain Imaging (SFDI). This technology can be used to quantify the structural and metabolic properties of in-vivo tissue by measuring oxyhaemoglobin concentration (HbO2 ), deoxyhaemoglobin concentration (Hb), and oxygen saturation (StO2 ) within the visible boundaries of each wound. We also evaluated the changes in inducible nitric oxide synthase (iNOS) in the dermis using immunohistochemistry. Contrast changes in colour photographs showed that diabetic rats healed at a slower rate in comparison with non-diabetic control, with the most significant change occurring at 7 days after the punch biopsy. We observed lower HbO2 , StO2 , and elevated Hb concentrations in the diabetic wounds. The iNOS level was higher in the dermis of the diabetic rats compared with the non-diabetic rats. Our results showed that, in diabetes, there is higher level of iNOS that can lead to an observed reduction in HbO2 levels. iNOS is linked to increased inflammation, leading to prolonged wound healing. Our results suggest that SFDI has potential as a non-invasive assessment of markers of wound-healing impairment.