In vivo collagen metabolism in spontaneously diabetic (db/db) mice

The role of extracellular matrix in the pathophysiology of diabetic wounds

Impaired healing leading to the formation of ulcerated wounds is a critical concern in patients with diabetes. Abnormalities in extracellular matrix (ECM) production and remodeling contribute to tissue dysfunction and delayed healing. Specifically, diabetes-induced changes in the expression and/or activity of structural proteins, ECM-modifying enzymes, proteoglycans, and matricellular proteins have been reported. In this review, we provide a summary of the key ECM molecules and associated changes in skin and diabetic wounds. Such information should allow for new insights in the understanding of impaired wound healing and lead to the development of ECM-based therapeutic strategies.

Poly(methacrylic acid-co-methyl methacrylate) beads promote vascularization and wound repair in diabetic mice

Topical application of beads made from poly(methacrylic acid-co-methyl methacrylate) (45 mol % methacrylic acid, MAA) increased the number of blood vessels and improved 1.5 x 1.5 cm full thickness wound closure in a diabetic mouse (db/db) model. Three groups were compared: MAA beads, control poly(methyl methacrylate) beads (PMMA), and no bead blanks. MAA bead treatment significantly increased percent wound closure at all timepoints (7, 14, and 21 days) with MAA bead-treated wounds almost closed at day 21 (91 +/- 5.4% MAA vs. 79 +/- 3.2% PMMA or 76 +/- 4.8% no beads; p < 0.05). This was consistent with the expected significant increase in vascularity in the MAA group at days 7 and 14. For example at day 14, MAA bead-treated wounds had a vascular density of 22.7 +/- 2.6 vessels/hpf compared with 17.0 +/- 2.0 vessels/hpf in the PMMA bead group (p < 0.05). Epithelial gap and migration measurements suggested that the increased vascularity leads to enhanced epithelial cell migration as a principal means of wound closure. Although studies are underway to elucidate the mechanism of this angiogenic response, the results presented here support the notion that such materials, perhaps in other forms, may be useful in wound care or in other situations where vascularity is to be enhanced without the use of exogenous growth factors.

Repair of full-thickness bowel injury

OBJECTIVE

Colon surgery is more and more often performed in complex situations such as after trauma, under immunosuppression, or in the elderly. Even under optimal conditions, anastomosis fails in certain situations. The objective of this study was to demonstrate the normal phases of bowel healing and to review the local and systemic factors affecting healing with special attention to critical care variables such as major surgery, acute hemorrhage, and infections.

DATA SOURCE

MEDLINE cited and/or published articles.

DESIGN

Review analysis.

RESULTS

Colon healing is a structured cascade of different phases that can be affected by a multitude of local (infection, ischemia) and systemic (diabetes, malnutrition, anemia, hypothermia, trauma) factors. The normal phases of repair, the resulting bursting pressure as an experimental index of healing, and the available published data on local and systemic factors affecting healing are summarized.

CONCLUSION

Several local and systemic factors negatively affect bowel healing; there is still a small portion of patients who fail to heal, suggesting that intrinsic factors need to be analyzed.

Blockade of receptor for advanced glycation end-products restores effective wound healing in diabetic mice

Receptor for advanced glycation end-products (RAGE), and two of its ligands, AGE and EN-RAGEs (members of the S100/calgranulin family of pro-inflammatory cytokines), display enhanced expression in slowly resolving full-thickness excisional wounds developed in genetically diabetic db+/db+ mice. We tested the concept that blockade of RAGE, using soluble(s) RAGE, the extracellular ligand-binding domain of the receptor, would enhance wound closure in these animals. Administration of sRAGE accelerated the development of appropriately limited inflammatory cell infiltration and activation in wound foci. In parallel with accelerated wound closure at later times, blockade of RAGE suppressed levels of cytokines; tumor necrosis factor-alpha; interleukin-6; and matrix metalloproteinases-2, -3, and -9. In addition, generation of thick, well-vascularized granulation tissue was enhanced, in parallel with increased levels of platelet-derived growth factor-B and vascular endothelial growth factor. These findings identify a central role for RAGE in disordered wound healing associated with diabetes, and suggest that blockade of this receptor might represent a targeted strategy to restore effective wound repair in this disorder.

Diabetes impairs the development of early strength, but not the accumulation of collagen, during intestinal anastomotic healing in the rat

The evidence that diabetes mellitus adversely affects healing is derived from data on skin, where diminished wound strength is accompanied by a reduced collagen content. As no such data are available on intestinal anastomotic repair, and it has been reported that collagen metabolism in skin and intestine is affected differently by the diabetic state, anastomotic healing in the rat intestine during uncontrolled diabetes was examined. Wistar rats underwent resection and anastomosis of both ileum and colon 1 week after a single injection of streptozotocin (diabetic group) or citrate (control group). After 3 days the mean bursting pressure of ileal anastomoses was 4.1 kPa in controls and 1.0 kPa in diabetic animals (P < 0.05). For colon, these values were 12.0 and 4.9 kPa respectively (P < 0.05). This negative effect of diabetes persisted after 7 days in ileum but not in colon. Diabetic animals had more anastomotic abscesses, especially in the ileum: nine of 16 animals at 3 days after operation versus one of 15 in the control group (P < 0.01). Anastomotic hydroxyproline concentration and content in diabetic animals were not reduced. The postoperative collagen synthetic capacity, as measured in tissue explants, was strongly stimulated in the wound area and appeared essentially unchanged in the diabetic animals. Uncontrolled streptozotocin-induced diabetes severely impairs the development of anastomotic strength in the rat intestine but, unlike impaired wound healing in skin, this phenomenon is not caused by deficient accumulation of collagen.

Aminoguanidine treatment reduces the increase in collagen stability of rats with experimental diabetes mellitus

Alterations in the biophysical properties of connective tissues in diabetes mellitus have been attributed to the nonenzymatic glycation of the collagens and the subsequent formation of browning products, cross-linking the proteins. Aminoguanidine may bind to carbonyl groups of these nonenzymatic glycation products and thereby block the process. Rats with streptozotocin-induced diabetes were treated with aminoguanidine, 25 mg.kg-1.day-1, for 120 days. The aminoguanidine treatment did not counteract the increase in blood glucose concentrations, nor did it prevent the arrest in weight gain of diabetic rats. The increased stability in 7 mol/l urea and increased tensile strength of tail tendons from the diabetic rats, however, were prevented by the aminoguanidine treatment. Aminoguanidine did not reduce the formation of early nonenzymatic glycation products (aldimine and Amadori rearrangement products), whereas the amount of browning products (fluorescent compounds) was reduced in the tail tendon collagen of the diabetic rats. Aminoguanidine treatment of intact rats did not influence these parameters. These findings indicate that the biophysical alterations of collagens induced by experimental diabetes are caused by cross-links derived from the nonenzymatic glycation, and furthermore, that aminoguanidine treatment may prevent the concomitant changes in biophysical properties of connective tissues.

Wound collagenase activity correlates directly with collagen glycosylation in diabetic rats

Extracellular glycosylation of proteins in diabetics may contribute to observed impairments in wound healing. We investigated the interactions of blood glucose concentration and wound collagen glycosylation, collagen content, and proteolytic activity during wound healing in diabetic animals. Rats were made differentially hyperglycemic with intraperitoneal injection of streptozotocin (0-65 mg/kg body weight). Animals with blood glucose concentrations greater than 240 mg glucose/dL were classified as diabetic, those with blood glucose concentrations less than 160 were grouped as nondiabetic. Polytetrafluoroethelene (PTFE) wound cylinders were surgically implanted in 32 rats and removed on postoperative day 5. Harvested cylinders were analyzed for hydroxyproline content, collagen glycosylation, and collagenase and protease activity. Collagenase activity was 14% higher in diabetics than nondiabetics (P less than .001). Glycosylation of wound collagen averaged 48.0% higher in diabetics (P less than .001). Wound hydroxyproline content was 39% lower in diabetics (P less than .05). Studies show a high degree of correlation (Pearson) of wound collagen nonenzymatic extracellular glycosylation (NEG) with mean blood glucose concentration (r = .98, P less than .001). Wound collagen glycosylation correlates strongly with both protease activity (r = .86, P less than .001) and collagenase activity (r = .83, P less than .001). This study demonstrates a significant blood glucose concentration dependent increase of glycosylation in newly synthesized collagen in hyperglycemic animals that is associated with increased collagenase activity and decreased wound collagen content.

Streptozotocin-induced diabetes and the rat periodontium: decreased relative collagen production

This is the first study concerning the extent to which relative collagen production (RCP) in rat periodontal tissues is affected by diabetes. Determination of RCP, rather than individual production rates for collagen or for non-collagen protein, was deemed necessary because saturation of all proline pools in tissues of diabetics (and non-diabetic controls) was not achieved. Such non-saturation occurred despite the injection of a pool-expanding dose of proline (400-1150 mg/rat), non-saturation indicated by the lesser specific radioactivity (S.R.) of free-[3H]proline in tissues than that of the injected solution. RCP was decreased in five periodontal tissues (incisor and molar gingiva, incisor and molar periodontal ligament, antemolar palatal mucosa) and in skin. Diabetes-decreased RCP seems to result from decreased collagen synthesis and increased intracellular degradation, although some evidence is presented for increased extracellular degradation of recently secreted collagen.