NOS1AP genetic variation is associated with impaired healing of diabetic foot ulcers and diminished response to healing of circulating stem/progenitor cells

The wound microbiota: microbial mechanisms of impaired wound healing and infection

The skin barrier protects the human body from invasion by exogenous and pathogenic microorganisms. A breach in this barrier exposes the underlying tissue to microbial contamination, which can lead to infection, delayed healing, and further loss of tissue and organ integrity. Delayed wound healing and chronic wounds are associated with comorbidities, including diabetes, advanced age, immunosuppression and autoimmune disease. The wound microbiota can influence each stage of the multi-factorial repair process and influence the likelihood of an infection. Pathogens that commonly infect wounds, such as Staphylococcus aureus and Pseudomonas aeruginosa, express specialized virulence factors that facilitate adherence and invasion. Biofilm formation and other polymicrobial interactions contribute to host immunity evasion and resistance to antimicrobial therapies. Anaerobic organisms, fungal and viral pathogens, and emerging drug-resistant microorganisms present unique challenges for diagnosis and therapy. In this Review, we explore the current understanding of how microorganisms present in wounds impact the process of skin repair and lead to infection through their actions on the host and the other microbial wound inhabitants.

Molecular Pathophysiology of Chronic Wounds: Current State and Future Directions

Venous leg ulcers, diabetic foot ulcers, and pressure ulcers are complex chronic wounds with multifactorial etiologies that are associated with high patient morbidity and mortality. Despite considerable progress in deciphering the pathologies of chronic wounds using "omics" approaches, considerable gaps in knowledge remain, and current therapies are often not efficacious. We provide a comprehensive overview of current understanding of the molecular mechanisms that impair healing and current knowledge on cell-specific dysregulation including keratinocytes, fibroblasts, immune cells, endothelial cells and their contributions to impaired reepithelialization, inflammation, angiogenesis, and tissue remodeling that characterize chronic wounds. We also provide a rationale for further elucidation of ulcer-specific pathologic processes that can be therapeutically targeted to shift chronic nonhealing to acute healing wounds.

Circulating endothelial precursor cells are associated with a healed diabetic foot ulcer evaluated in a prospective cohort study

The goal of this multicentre study was to evaluate whether circulating endothelial precursor cells and microparticles can predict diabetic foot ulcer healing by the 16th week of care. We enrolled 207 subjects, and 40.0% (28.4, 41.5) healed by the 16th week of care. Using flow cytometry analysis, several circulating endothelial precursor cells measured at the first week of care were associated with healing after adjustment for wound area and wound duration. For example, CD34+ CD45dim , the univariate odds ratio was 1.19 (95% confidence interval: 0.88, 1.61) and after adjustment for wound area and wound duration, the odds ratio was (1.67 (1.16, 2.42) p = 0.006). A prognostic model using CD34+ CD45dim , wound area, and wound duration had an area under the curve of 0.75 (0.67, 0.82) and CD34+ CD45dim per initial wound area, an area under the curve of 0.72 (0.64, 0.79). Microparticles were not associated with a healed wound. Previous studies have indicated that circulating endothelial precursor cells measured at the first office visit are associated with a healed diabetic foot ulcer. In this multicentred prospective study, we confirm this finding, show the importance of adjusting circulating endothelial precursor cells measurements by wound area, and show circulating endothelial precursor cells per wound area is highly predictive of a healed diabetic foot ulcer by 16th week of care.

Blood-Borne Microparticles Are an Inflammatory Stimulus in Type 2 Diabetes Mellitus

The proinflammatory state associated with diabetes mellitus (DM) remains poorly understood. We found patients with DM have 3- to 14-fold elevations of blood-borne microparticles (MPs) that bind phalloidin (Ph; Ph positive [+] MPs), indicating the presence of F-actin on their surface. We hypothesized that F-actin-coated MPs were an unrecognized cause for DM-associated proinflammatory status. Ph+MPs, but not Ph-negative MPs, activate human and murine (Mus musculus) neutrophils through biophysical attributes of F-actin and membrane expression of phosphatidylserine (PS). Neutrophils respond to Ph+MPs via a linked membrane array, including the receptor for advanced glycation end products and CD36, PS-binding membrane receptors. These proteins in conjunction with TLR4 are coupled to NO synthase 1 adaptor protein (NOS1AP). Neutrophil activation occurs because of Ph+MPs causing elevations of NF-κB and Src kinase (SrcK) via a concurrent increased association of NO synthase 2 and SrcK with NOS1AP, resulting in SrcK S-nitrosylation. We conclude that NOS1AP links PS-binding receptors with intracellular regulatory proteins. Ph+MPs are alarmins present in normal human plasma and are increased in those with DM and especially those with DM and a lower-extremity ulcer.

Translational development of ABCB5+ dermal mesenchymal stem cells for therapeutic induction of angiogenesis in non-healing diabetic foot ulcers

Background

While rapid healing of diabetic foot ulcers (DFUs) is highly desirable to avoid infections, amputations and life-threatening complications, DFUs often respond poorly to standard treatment. GMP-manufactured skin-derived ABCB5⁺ mesenchymal stem cells (MSCs) might provide a new adjunctive DFU treatment, based on their remarkable skin wound homing and engraftment potential, their ability to adaptively respond to inflammatory signals, and their wound healing-promoting efficacy in mouse wound models and human chronic venous ulcers.

Methods

The angiogenic potential of ABCB5⁺ MSCs was characterized with respect to angiogenic factor expression at the mRNA and protein level, in vitro endothelial trans-differentiation and tube formation potential, and perfusion-restoring capacity in a mouse hindlimb ischemia model. Finally, the efficacy and safety of ABCB5⁺ MSCs for topical adjunctive treatment of chronic, standard therapy-refractory, neuropathic plantar DFUs were assessed in an open-label single-arm clinical trial.

Results

Hypoxic incubation of ABCB5⁺ MSCs led to posttranslational stabilization of the hypoxia-inducible transcription factor 1α (HIF-1α) and upregulation of HIF-1α mRNA levels. HIF-1α pathway activation was accompanied by upregulation of vascular endothelial growth factor (VEGF) transcription and increase in VEGF protein secretion. Upon culture in growth factor-supplemented medium, ABCB5⁺ MSCs expressed the endothelial-lineage marker CD31, and after seeding on gel matrix, ABCB5⁺ MSCs demonstrated formation of capillary-like structures comparable with human umbilical vein endothelial cells. Intramuscularly injected ABCB5⁺ MSCs to mice with surgically induced hindlimb ischemia accelerated perfusion recovery as measured by laser Doppler blood perfusion imaging and enhanced capillary proliferation and vascularization in the ischemic muscles. Adjunctive topical application of ABCB5⁺ MSCs onto therapy-refractory DFUs elicited median wound surface area reductions from baseline of 59% (full analysis set, n = 23), 64% (per-protocol set, n = 20) and 67% (subgroup of responders, n = 17) at week 12, while no treatment-related adverse events were observed.

Conclusions

The present observations identify GMP-manufactured ABCB5⁺ dermal MSCs as a potential, safe candidate for adjunctive therapy of otherwise incurable DFUs and justify the conduct of a larger, randomized controlled trial to validate the clinical efficacy.

Trial registration: ClinicalTrials.gov, NCT03267784, Registered 30 August 2017, https://clinicaltrials.gov/ct2/show/NCT03267784

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03156-9.

Further evidence that wound size and duration are strong prognostic markers of diabetic foot ulcer healing

Diabetic foot ulcers (DFU) are a critical problem for those with diabetes mellitus. Predicting the healing likelihood of a DFU is important to implementing appropriate care, allocating resources, having access to advanced therapies, having successful clinical trials, calibrating clinical trial results, and providing information to administrative entities on patient and provider outcomes. Prognostic modeling can also be important when attempting to compare results across trials or care centers. In a prospective cohort study, we demonstrate and replicate that simple wound characteristics like wound area and wound duration can be used to predict wound healing by the 16^th week of care. The models were based on previous literature and replicated using a machine learning algorithm. The use of wound duration and wound area in a prognostic model continues to be important when comparing study results, center-based outcomes, as well as designing clinical trials.

Role of growth factors and cytokines in diabetic foot ulcer healing: A detailed review

The aim of the review is to examine the role of growth factors and cytokines in the management of Diabetic Foot Ulcers, such as platelet derived growth factor (PDGF), vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and Insulin like growth factor (IGF). Taking this a step further, the role of Hypoxia-inducible factors (HIFs), Transforming growth factor beta 1 (TGF-β-1) and other growth factors have also been examined, with regard to the treatment of diabetic foot ulcers. The roles of these above-mentioned growth cytokines have been analyzed by studying various scholastic articles. The complete process of wound healing is implemented and regulated by numerous cytokines and human growth factors. The findings of the study indicate that wound healing of diabetic foot ulcers is a complex and extremely challenging biological and molecular process that involves coordinated efforts of multiple cell types. The therapeutic effects of various growth factors in the clinical management of wounds are chronic venous ulcers, pressure ulcers, and diabetic foot ulcers. It has been concluded that altercations of various cytokines are found in patients enduring diabetic foot ulcers. In a similar way, changes in the level of cytokines are also found in patients suffering from other diabetic complications such as diabetic nephropathy, retinopathy, and neuropathy. Subsequently, the diabetic wound healing process can be accelerated by regulating the levels of the cytokines.

Differentiation of diabetic foot ulcer-derived induced pluripotent stem cells reveals distinct cellular and tissue phenotypes

Diabetic foot ulcers (DFUs) are a major complication of diabetes, and there is a critical need to develop novel cell- and tissue-based therapies to treat these chronic wounds. Induced pluripotent stem cells (iPSCs) offer a replenishing source of allogeneic and autologous cell types that may be beneficial to improve DFU wound-healing outcomes. However, the biologic potential of iPSC-derived cells to treat DFUs has not, to our knowledge, been investigated. Toward that goal, we have performed detailed characterization of iPSC-derived fibroblasts from both diabetic and nondiabetic patients. Significantly, gene array and functional analyses reveal that iPSC-derived fibroblasts from both patients with and those without diabetes are more similar to each other than were the primary cells from which they were derived. iPSC-derived fibroblasts showed improved migratory properties in 2-dimensional culture. iPSC-derived fibroblasts from DFUs displayed a unique biochemical composition and morphology when grown as 3-dimensional (3D), self-assembled extracellular matrix tissues, which were distinct from tissues fabricated using the parental DFU fibroblasts from which they were reprogrammed. In vivo transplantation of 3D tissues with iPSC-derived fibroblasts showed they persisted in the wound and facilitated diabetic wound closure compared with primary DFU fibroblasts. Taken together, our findings support the potential application of these iPSC-derived fibroblasts and 3D tissues to improve wound healing.-Kashpur, O., Smith, A., Gerami-Naini, B., Maione, A. G., Calabrese, R., Tellechea, A., Theocharidis, G., Liang, L., Pastar, I., Tomic-Canic, M., Mooney, D., Veves, A., Garlick, J. A. Differentiation of diabetic foot ulcer-derived induced pluripotent stem cells reveals distinct cellular and tissue phenotypes.

Descriptive vs mechanistic scientific approach to study wound healing and its inhibition: Is there a value of translational research involving human subjects?

The clinical field of wound healing is challenged by numerous hurdles. Not only are wound-healing disorders complex and multifactorial, but the corresponding patient population is diverse, often elderly and burdened by multiple comorbidities such as diabetes and cardiovascular disease. The care of such patients requires a dedicated, multidisciplinary team of physicians, surgeons, nurses and scientists. In spite of the critical clinical need, it has been over 15 years since a treatment received approval for efficacy by the FDA in the United States. Among the reasons contributing to this lack of effective new treatment modalities is poor understanding of mechanisms that inhibit healing in patients. Additionally, preclinical models do not fully reflect the disease complexity of the human condition, which brings us to a paradox: if we are to use a "mechanistic" approach that favours animal models, we can dissect specific mechanisms using advanced genetic, molecular and cellular technologies, with the caveat that it may not be directly applicable to patients. Traditionally, scientific review panels, for either grant funding or manuscript publication purposes, favour such "mechanistic" approaches whereby human tissue analyses, deemed "descriptive" science, are characterized as a "fishing expedition" and are considered "fatally flawed." However, more emerging evidence supports the notion that the use of human samples provides significant new knowledge regarding the molecular and cellular mechanisms that control wound healing and contribute to inhibition of the process in patients. Here, we discuss the advances, benefits and challenges of translational research in wound healing focusing on human subject research.

Neutrophil microparticle production and inflammasome activation by hyperglycemia due to cytoskeletal instability

Microparticles are lipid bilayer-enclosed vesicles produced by cells under oxidative stress. MP production is elevated in patients with diabetes, but the underlying cellular mechanisms are poorly understood. We hypothesized that raising glucose above the physiological level of 5.5 mm would stimulate leukocytes to produce MPs and activate the nucleotide-binding domain, leucine-rich repeat pyrin domain-containing 3 (NLRP3) inflammasome. We found that when incubated in buffer with up to 20 mm glucose, human and murine neutrophils, but not monocytes, generate progressively more MPs with high interleukin (IL)-1β content. Enhanced MP production required generation of reactive chemical species by mitochondria, NADPH oxidase, and type 2 nitric-oxide synthase (NOS-2) and resulted in S-nitrosylation of actin. Depleting cells of capon (C-terminal PDZ ligand of neuronal nitric-oxide synthase protein), apoptosis-associated speck-like protein containing C-terminal caspase recruitment domain (ASC), or pro-IL-1β prevented the hyperglycemia-induced enhancement of reactive species production, MP generation, and IL-1β synthesis. Additional components required for these responses included inositol 1,3,5-triphosphate receptors, PKC, and enhancement of filamentous-actin turnover. Numerous proteins become localized to short filamentous actin in response to S-nitrosylation, including vasodilator-stimulated phosphoprotein, focal adhesion kinase, the membrane phospholipid translocation enzymes flippase and floppase, capon, NLRP3, and ASC. We conclude that an interdependent oxidative stress response to hyperglycemia perturbs neutrophil cytoskeletal stability leading to MP production and IL-1β synthesis.