Diabetic foot ulcers (DFUs) are one of the most common and serious complications of diabetes mellitus, as wound healing is impaired in the diabetic foot. Wound healing is a dynamic and complex biological process that can be divided into four partly overlapping phases: hemostasis, inflammation, proliferative and remodeling. These phases involve a large number of cell types, extracellular components, growth factors and cytokines. Diabetes mellitus causes impaired wound healing by affecting one or more biological mechanisms of these processes. Most often, it is triggered by hyperglycemia, chronic inflammation, micro- and macro-circulatory dysfunction, hypoxia, autonomic and sensory neuropathy, and impaired neuropeptide signaling. Research focused on thoroughly understanding these mechanisms would allow for specifically targeted treatment of diabetic foot ulcers. The main principles for DFU treatment are wound debridement, pressure off-loading, revascularization and infection management. New treatment options such as bioengineered skin substitutes, extracellular matrix proteins, growth factors, and negative pressure wound therapy, have emerged as adjunctive therapies for ulcers. Future treatment strategies include stem cell-based therapies, delivery of gene encoding growth factors, application of angiotensin receptors analogs and neuropeptides like substance P, as well as inhibition of inflammatory cytokines. This review provides an outlook of the pathophysiology in diabetic wound healing and summarizes the established and adjunctive treatment strategies, as well as the future therapeutic options for the treatment of DFUs.

Diabetic foot ulceration is a severe complication of diabetes that lacks effective treatment. Mast cells (MCs) contribute to wound healing, but their role in diabetes skin complications is poorly understood. Here we show that the number of degranulated MCs is increased in unwounded forearm and foot skin of patients with diabetes and in unwounded dorsal skin of diabetic mice (P < 0.05). Conversely, postwounding MC degranulation increases in nondiabetic mice, but not in diabetic mice. Pretreatment with the MC degranulation inhibitor disodium cromoglycate rescues diabetes-associated wound-healing impairment in mice and shifts macrophages to the regenerative M2 phenotype (P < 0.05). Nevertheless, nondiabetic and diabetic mice deficient in MCs have delayed wound healing compared with their wild-type (WT) controls, implying that some MC mediator is needed for proper healing. MCs are a major source of vascular endothelial growth factor (VEGF) in mouse skin, but the level of VEGF is reduced in diabetic mouse skin, and its release from human MCs is reduced in hyperglycemic conditions. Topical treatment with the MC trigger substance P does not affect wound healing in MC-deficient mice, but improves it in WT mice. In conclusion, the presence of nondegranulated MCs in unwounded skin is required for proper wound healing, and therapies inhibiting MC degranulation could improve wound healing in diabetes.

Nonhealing diabetic foot ulcers (DFUs) are characterized by low-grade chronic inflammation, both locally and systemically. We prospectively followed a group of patients who either healed or developed nonhealing chronic DFUs. Serum and forearm skin analysis, both at the protein expression and the transcriptomic level, indicated that increased expression of factors such as interferon-g (IFN-g), vascular endothelial growth factor, and soluble vascular cell adhesion molecule-1 were associated with DFU healing. Furthermore, foot skin single-cell RNA sequencing analysis showed multiple fibroblast cell clusters and increased inflammation in the dorsal skin of patients with diabetes mellitus (DM) and DFU specimens compared with control subjects. In addition, in myeloid cell DM and DFU upstream regulator analysis, we observed inhibition of interleukin-13 and IFN-g and dysregulation of biological processes that included cell movement of monocytes, migration of dendritic cells, and chemotaxis of antigen-presenting cells pointing to an impaired migratory profile of immune cells in DM skin. The SLCO2A1 and CYP1A1 genes, which were upregulated at the forearm of nonhealers, were mainly expressed by the vascular endothelial cell cluster almost exclusively in DFU, indicating a potential important role in wound healing. These results from integrated protein and transcriptome analyses identified individual genes and pathways that can potentially be targeted for enhancing DFU healing.

This study shows that endothelial dysfunction occurs early in the pathophysiology of diabetes and is a link between cardiovascular risk factors and DPN.

Obstructive sleep apnea (OSA) affects a large proportion of adults, and is as an independent risk factor for cerebrovascular and cardiovascular disease. The repetitive airway obstruction that characterizes OSA results in intermittent hypoxia, intrathoracic pressure swings, and sleep fragmentation, which in turn lead to sympathetic activation, oxidative stress, inflammation, and endothelial dysfunction. This review outlines the associations between OSA and vascular diseases and describes basic mechanisms that may be responsible for this association, in both the micro- and macrocirculation. It also reports on interventional studies that aim to ameliorate OSA and thereby reduce vascular disease burden. © 2016 American Physiological Society. Compr Physiol 6:1519-1528, 2016.

IntroductionDiabetic peripheral neuropathy (DPN) is one of the most common complications of diabetes and has been associated with cardiovascular disease, the leading cause of mortality in diabetes. As asymptomatic myocardial ischemia (MI) is frequent in diabetes, we hypothesized that DPN may be associated with MI in patients with type 2 diabetes mellitus and no history of cardiovascular events.MethodsEighty-two patients with DPN (n = 41) or without DPN (n = 41) were included. Among the DPN group, 15 had active foot ulcers. All subjects underwent Technetium-99 m sestamibi single-photon emission computed tomographic imaging for the estimation of myocardial ischemia, expressed as Summed Stress Score (SSS). The Neuropathy Disability Score (NDS) was used to quantify DPN and abnormal ratio of the longest electrocardiographic RR interval between the 28th and 32nd beats, after standing to the shortest interval between the 13th and 17th beats (RR ratio) was used as an index of cardiovascular autonomic neuropathy (CAN).ResultsAbnormal SSS was observed in 9.8% of patients without DPN and in 46.3% of patients with DPN (p < 0.001). In the multivariate analysis, NDS was the strongest predictor for SSS (β = 0.32, p = 0.003). When excluding patients with abnormal RR ratio (β = 0.32, p = 0.003) or with foot ulcers (β = 0.24, p = 0.04), this association remained significant. The RR ratio was also significantly associated with SSS in univariate (ρ = −0.30, p = 0.005) and multiple regressions (β = 0.24, p = 0.02).ConclusionsMI was strongly associated with DPN, and this association remained significant in patients with normal RR ratio. These results suggest that DPN assessment could help in identifying patients at risk of cardiovascular disease (CVD).Electronic supplementary materialThe online version of this article (doi:10.1007/s12325-016-0399-1) contains supplementary material, which is available to authorized users.

Changes in atrophy and metabolism appear to occur unequally between different regions of the forefoot in diabetes. The adductor hallucis region appears more capable of maintaining structural and metabolic integrity than the flexor hallucis or interosseous regions. The CV analysis suggests that the quantitative P methods have less variability than the qualitative grading. J. Magn. Reson. Imaging 2016;44:1132-1142.

This study demonstrates that linagliptin tends to improve endothelial and neurovascular microvascular function and is associated with decreased markers of inflammation in patients with type 2 diabetes. There was no significant effect of linagliptin on mitochondrial function, macrovascular function, or endothelial progenitor cells.