Wound healing is an evolutionarily conserved, complex, multicellular process that, in skin, aims at barrier restoration. This process involves the coordinated efforts of several cell types including keratinocytes, fibroblasts, endothelial cells, macrophages, and platelets. The migration, infiltration, proliferation, and differentiation of these cells will culminate in an inflammatory response, the formation of new tissue and ultimately wound closure. This complex process is executed and regulated by an equally complex signaling network involving numerous growth factors, cytokines and chemokines. Of particular importance is the epidermal growth factor (EGF) family, transforming growth factor beta (TGF-beta) family, fibroblast growth factor (FGF) family, vascular endothelial growth factor (VEGF), granulocyte macrophage colony stimulating factor (GM-CSF), platelet-derived growth factor (PDGF), connective tissue growth factor (CTGF), interleukin (IL) family, and tumor necrosis factor-alpha family. Currently, patients are treated by three growth factors: PDGF-BB, bFGF, and GM-CSF. Only PDGF-BB has successfully completed randomized clinical trials in the Unites States. With gene therapy now in clinical trial and the discovery of biodegradable polymers, fibrin mesh, and human collagen serving as potential delivery systems other growth factors may soon be available to patients. This review will focus on the specific roles of these growth factors and cytokines during the wound healing process.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1524-475X.2008.00410.x

Growth factors and cytokines in wound healing.

In the last few decades, a great deal of progress has been made in understanding the cellular and biochemical interplay that comprises the normal wound healing response. This response is a complex process involving intricate interactions among a variety of different cell types, structural proteins, growth factors, and proteinases. The normal wound repair process consists of three phases--inflammation, proliferation, and remodeling--that occur in a predictable sequence and comprise a series of cellular and biochemical events. A review of the biochemical and physiologic processes that regulate wound healing and the cascade of cellular events that gives rise to the healing process is presented here.

Physiology and Healing Dynamics of Chronic Cutaneous Wounds

Uncontrolled macrophage activation is now considered to be a critical event in the pathogenesis of chronic inflammatory diseases such as atherosclerosis, multiple sclerosis, and chronic venous leg ulcers. However, it is still unclear which environmental cues induce persistent activation of macrophages in vivo and how macrophage-derived effector molecules maintain chronic inflammation and affect resident fibroblasts essential for tissue homeostasis and repair. We used a complementary approach studying human subjects with chronic venous leg ulcers, a model disease for macrophage-driven chronic inflammation, while establishing a mouse model closely reflecting its pathogenesis. Here, we have shown that iron overloading of macrophages — as was found to occur in human chronic venous leg ulcers and the mouse model — induced a macrophage population in situ with an unrestrained proinflammatory M1 activation state. Via enhanced TNF-α and hydroxyl radical release, this macrophage population perpetuated inflammation and induced a p16INK4a-dependent senescence program in resident fibroblasts, eventually leading to impaired wound healing. This study provides insight into the role of what we believe to be a previously undescribed iron-induced macrophage population in vivo. Targeting this population may hold promise for the development of novel therapies for chronic inflammatory diseases such as chronic venous leg ulcers.

/pdf/an-unrestrained-proinflammatory-m1-macrophage-population-2d5kqjmun0.pdf

An unrestrained proinflammatory M1 macrophage population induced by iron impairs wound healing in humans and mice

The role of vascular endothelial growth factor in wound healing.

General principles of wound healing

The stability of peptide growth factors exposed to fluids from healing surgical wounds and from nonhealing chronic wounds was examined in vitro. (125)I-Labeled transforming growth factor-beta1 or platelet-derived growth factor-BB was incubated with fluids from healing surgical wounds and fluids from venous stasis or pressure ulcers. Fluids from healing surgical wounds had no appreciable effect on the level of (125)I corresponding to intact growth factor. In contrast, incubation with fluids from several venous stasis or pressure ulcers resulted in significant degradation of these growth factors. Degradation was blocked by broad-spectrum serine proteinase inhibitors and by specific inhibitors of neutrophil elastase. Levels of elastase activity in wound fluids correlated with the ability to degrade peptide growth factors. Further comparisons showed qualitative and quantitative differences in the endogenous proteinase inhibitors, alpha2-macroglobulin and alpha1-antiproteinase. These results could explain, in part, the variable growth factor levels which have been found in chronic wounds. More importantly, the ability of some chronic nonhealing wounds to rapidly degrade exogenously added growth factors has important implications with regard to past and future clinical attempts to use peptide growth factors to treat these types of problem wounds.

Ability of chronic wound fluids to degrade peptide growth factors is associated with increased levels of elastase activity and diminished levels of proteinase inhibitors.

Interleukin-1-alpha (IL-1alpha) is a member of a family of proinflammatory polypeptide mediators that has been shown in vitro to stimulate collagenase production. Collagenase is a proteolytic enzyme classified as one of the matrix metalloproteinases (MMP-1) that specifically recognizes and cleaves collagen. Therefore, the objective of this study was to compare the levels of these two proteins in chronic wounds as possible factors in the pathogenesis of chronic wounds. Fluids from 10 chronic wounds were collected before and after a 1-week treatment with a hydroactive dressing (Cutinova cavity). In addition, fluids were collected from 20 acute wounds for comparison. IL-1alpha and MMP-1 levels were quantified using sandwich ELISA. Collagenase activity was measured using a radiolabeled collagen as substrate. Clinically, the chronic wounds showed decreased area (-21.0 cm2) and reduced volume (-134.5 cm3) by 4 weeks after treatment with the hydroactive dressing. There were no significant differences in the protein concentrations between acute wound fluids (21.0 +/- 3.0 mg/ml) and chronic wound fluids before and after treatment with the hydroactive dressing (18.3 +/- 5.5 and 25.2 +/- 7.6 mg/ml, respectively). Levels of IL-1alpha in the acute wound fluids were low (0.019 pg/mg), whereas in the chronic wound fluid before treatment they had been significantly elevated (44.9 + 21.8 pg/mg). Following treatment with the hydroactive dressing, the IL-1alpha levels dropped to 10.3 + 3.3 pg/mg (p < 0.05). Collagenase activity was not detectable in acute wound fluid, elevated in pretreatment chronic wounds (12.9 + 3.4 units), and decreased in chronic wounds after treatment (11.4 + 3.3 units). This study correlated clinical healing of chronic wounds with biochemical changes in the ulcer microenvironment. As the chronic wounds began to heal, there was a significant decrease in the IL-1alpha levels and collagenase activity, thus suggesting that these two proteins may contribute to the lack of healing characteristic of chronic wounds.

Oluyinka O. Olutoye

Papers

Ability of chronic wound fluids to degrade peptide growth factors is associated with increased levels of elastase activity and diminished levels of proteinase inhibitors.

Interleukin-1alpha and collagenase activity are elevated in chronic wounds

Lower cytokine release by fetal porcine platelets: A possible explanation for reduced inflammation after fetal wounding

Hyaluronic acid inhibits fetal platelet function: Implications in scarless healing

Aggregatory characteristics and expression of the collagen adhesion receptor in fetal porcine platelets