Insulin prevents latent skin lesions by inhibiting the generation of advanced glycation end products in streptozotocin-induced diabetic rats

In vitro glycation of a tissue-engineered wound healing model to mimic diabetic ulcers

Diabetic foot ulcers are a major complication of diabetes that occurs following minor trauma. Diabetes-induced hyperglycemia is a leading factor inducing ulcer formation and manifests notably through the accumulation of advanced glycation end-products (AGEs) such as N-carboxymethyl-lysin. AGEs have a negative impact on angiogenesis, innervation, and reepithelialization causing minor wounds to evolve into chronic ulcers which increases the risks of lower limb amputation. However, the impact of AGEs on wound healing is difficult to model (both in vitro on cells, and in vivo in animals) because it involves a long-term toxic effect. We have developed a tissue-engineered wound healing model made of human keratinocytes, fibroblasts, and endothelial cells cultured in a collagen sponge biomaterial. To mimic the deleterious effects induced by glycation on skin wound healing, the model was treated with 300 µM of glyoxal for 15 days to promote AGEs formation. Glyoxal treatment induced carboxymethyl-lysin accumulation and delayed wound closure in the skin mimicking diabetic ulcers. Moreover, this effect was reversed by the addition of aminoguanidine, an inhibitor of AGEs formation. This in vitro diabetic wound healing model could be a great tool for the screening of new molecules to improve the treatment of diabetic ulcers by preventing glycation.

Selected elements of extracellular matrix of the skin in diabetes and insulin resistance

PURPOSE

Reconstruction of the skin extracellular matrix is a physiological phenomenon occurring on a continuous basis. The aim of this study is to evaluate the content of basic enzymes preventing oxidative stress: superoxide dismutase 2 and 3 as well as catalase, the content of hyaluronic acid, and the activity of N-acetyl-β-d-hexosaminidase and β-d-glucuronidase in the skin of rats used as animal models of diabetes and insulin resistance, before and after the treatment.

MATERIALS AND METHODS

The study was conducted on a group of sexually mature male Wistar rats divided into 7 groups of 10 animals. Insulin resistance was induced by feeding the rats with a high-fat diet, and diabetes was induced by a single injection of streptozotocin. Chosen groups of rats were treated with insulin or metformin. After 8 weeks, we excised a fragment of shaved dorsal skin from anesthetized rats in each group.

RESULTS

In the course of diabetes and insulin resistance, an intensified defensive activity of cells against the oxidative stress was observed in the undamaged skin, expressed by an increase in the relative content of superoxide dismutase 2 and 3, catalase and the activity of N-acetyl-β-d-hexosaminidase and β-d-glucuronidase. Diabetes and insulin resistance cause similar skin damage, as there are no differences in the relative contents or specific activities of the examined parameters.

CONCLUSIONS

Insulin and metformin improve the quality of the skin in rats with diabetes and insulin resistance, by restoring the content of hyaluronic acid to the healthy skin level.

Abundance, localization, and functional correlates of the advanced glycation end-product carboxymethyl lysine in human myocardium

Advanced glycation end‐products (AGEs) play a role in the pathophysiology of diabetes mellitus (DM) and possibly hypertension (HTN). In experimental DM, AGEs accumulate in myocardium. Little is known about AGEs in human myocardium. We quantified abundance, localization, and functional correlates of the AGE carboxymethyl lysine (CML) in left ventricular (LV) myocardium from patients undergoing coronary bypass grafting (CBG). Immunoelectron microscopy was used to quantify CML in epicardial biopsies from 98 patients (71 M, 27 F) with HTN, HTN + DM or neither (controls), all with normal LV ejection fraction. Myofilament contraction‐relaxation function was measured in demembranated myocardial strips. Echocardiography was used to quantify LV structure and function. We found that CML was abundant within cardiomyocytes, but minimally associated with extracellular collagen. CML counts/μm² were 14.7% higher in mitochondria than the rest of the cytoplasm (P < 0.001). There were no significant sex or diagnostic group differences in CML counts [controls 45.6 ± 3.6/μm² (±SEM), HTN 45.8 ± 3.6/μm², HTN + DM 49.3 ± 6.2/μm²; P = 0.85] and no significant correlations between CML counts and age, HgbA1c or myofilament function indexes. However, left atrial volume was significantly correlated with CML counts (r = 0.41, P = 0.004). We conclude that in CBG patients CML is abundant within cardiomyocytes but minimally associated with collagen, suggesting that AGEs do not directly modify the stiffness of myocardial collagen. Coexistent HTN or HTN + DM do not significantly influence CML abundance. The correlation of CML counts with LAV suggests an influence on diastolic function independent of HTN, DM or sex whose mechanism remains to be determined.

The skin remodeling in type 1 diabetes and insulin resistance animal models

The skin matrix metalloproteinase 3, tissue inhibitors of matrix metalloproteinase 2 and collagen III content changes in type 1 diabetes and insulin resistance treated with insulin and metformin were studied. Healthy adult male Wistar rats were obtained from experimental animal house, Department of Experimental Pharmacology, Medical University in Bialystok. The rats were divided randomly into five groups of 8 rats each. Control rats were injected intraperitoneally by NaCl. Type IDDM was induced by a single injection of Streptozocin. Insulin resistance was induced by a high-fat diet. The chosen groups of rats were also treated with insulin or metformin. ELISA Kits (USCN Life Science, China) were used to measure content of matrix metallo-proteinase 3 (ELISA Kit for Matrix Metalloproteinase 3 - MMP3), tissue inhibitor of matrix metalloproteinase 2 (ELISA Kit for Tissue Inhibitors of Metalloproteinase 2 - TIMP2) and content of collagen type 3 (ELISA Kit for Collagen Type III - COL3). The results were reported as a median. The statistical significance was defined as p<0.05. Type 1 diabetes and insulin resistance have significantly reduced the quality of the skin, shown by the increase in content of matrix metalloproteinase 3 and the decrease in content of tissue inhibitors of matrix metalloproteinase 2. Type 1 diabetes and insulin resistance have reduced the quality of the skin expressed by type III collagen content decrease but for future studies it is recommend to determine rat interstitial collagenase, MMP-13, as well. Insulin and metformin treatment improved the quality of the diabetic skin, demonstrated by the type III collagen content increase.

The unwounded skin remodeling in animal models of diabetes types 1 and 2

Diabetes mellitus types 1 and 2 are chronic diseases that cause serious health complications, including dermatologic problems. The diabetic skin is characterized by disturbances in collagen metabolism. A tissue remodeling depends on the degradation of extracellular matrix through the matrix metalloproteinases, which are regulated by e.g. the tissue inhibitors of metalloproteinases. The balance between matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) is essential to maintain homeostasis in the skin. The aim of this study was to determine the concentration of metalloproteinase 2, tissue inhibitor of metalloproteinase 3 and the concentration of collagen type 1 in unwounded skin of diabetes type 1 and 2 and healthy controls. The treatment of diabetes resulted in a significant decrease of MMP2, increase of TIMP3 and COL1 concentrations in the skin as compared to the untreated diabetic skin. The concentrations of MMP2 in the skin of treated rats did not show significant differences from the healthy control group. TIMP3 concentrations in the skin of treated rats are not returned to the level observed in the control group. Disturbances of the extracellular matrix of the skin are similar in diabetes type 1 and 2. Application of insulin in diabetes therapy more preferably affects the extracellular matrix homeostasis of the skin.

Garlic (Allium sativum) attenuate glomerular glycation in streptozotocin-induced diabetic rats: A possible role of insulin

OBJECTIVE

This study investigated the effect of fresh garlic aqueous extract on glomerular glycation in streptozotocin-induced diabetic rats.

METHOD

Serum insulin and glucose, in addition to renal corpuscles and erythrocyte hemoglobin glycation were determined in normal saline-treated normal rats (NS-NR), normal saline-treated diabetic rats (NS-DR) and garlic-treated diabetic rats (G-DR).

RESULTS

Compared to NS-NR, NS-DR showed significant decrease in serum insulin and increase in serum glucose and hemoglobin glycation. NS-DR also showed intense, diffused glomerular periodic acid Schiff activity. Compared to NS-DR, G-DR showed significant increase in serum insulin and decrease in serum glucose and hemoglobin glycation. Furthermore, the G-DR glomerular periodic acid Schiff activity and distribution was almost restored to that observed in NS-NR.

CONCLUSION

Garlic may attenuate glomerular glycation in streptozotocin-induced diabetic rats. This effect could be partially mediated via euglycemia induced by revitalization of endogenous insulin.

Reduced Dermis Thickness and AGE Accumulation in Diabetic Abdominal Skin

Dermatological problems in diabetes might play an important role in the spontaneous ulcers and impaired wound healing that are seen in diabetic patients. Investigation of the cause of diabetic skin disorders is critical for identifying effective treatment. The abdominal full-thickness skin tissues of 33 patients (14 nondiabetic and 19 diabetic) were analyzed. The cell viability and malondialdehyde (MDA) production of fibroblasts were measured after advanced glycosylation end product (AGE)–bovine serum albumin (BSA) exposure. Cutaneous histological observation showed reduced thickness of the diabetic abdominal dermis with morphological characteristics of obscured multilayer epithelium and shortened, thinned, and disorganized collagen fibrils with focal chronic inflammatory cell infiltration when compared with controls of the same age. Accumulation of AGEs in diabetic skin was prominent. Less hydroxyproline, higher myeloperoxidase activity, and increased MDA content were detected in diabetic skin. In vitro, the time- and dose-dependent inhibitory effects of AGE-BSA on fibroblast viability as well as the fact that AGE-BSA could promote MDA production of fibroblasts were shown. It is shown that the accumulation of AGEs in diabetic skin tissue induces an oxidative damage of fibroblasts and acts as an important contributor to the thinner diabetic abdominal dermis. The authors believe that diabetic cutaneous properties at baseline may increase the susceptibility to injury, and diabetic wounds possess atypical origin in the repair process.

The association between skin blood flow and edema on epidermal thickness in the diabetic foot

BACKGROUND

Skin blood flow plays an important role in maintaining the health of the skin. The development of interstitial edema may impede oxygen diffusion to the skin. The aim of this study was to evaluate the association of skin blood flow and edema and epidermal thickness in the feet of people with and without diabetic neuropathy compared with a healthy control group.

SUBJECTS AND METHODS

Eighty-seven subjects (19 people with diabetic neuropathy and foot ulceration, 35 people with diabetes but without neuropathy, and 33 healthy controls without diabetes) participated in the study. High-frequency ultrasonography was used to measure the epidermal thickness and edema in papillary skin at the big toe as reflected by the thickness of the subepidermal low echogenic band (SLEB). The capillary nutritive blood flow was measured by the use of video capillaroscopy, and skin blood flux was monitored by laser Doppler flowmetry.

RESULTS

There was a 7.2% increase in epidermal thickness in those with diabetes but without neuropathy and a 16.5% decrease in people with diabetic neuropathy and foot ulceration compared with the healthy controls (all P<0.05). The SLEB thickness increased in all subjects with diabetes to a greater degree in those with neuropathy and ulceration than in those without (64.7% vs. 11.8%, P<0.001). Skin blood flux was shown to be higher in the diabetes groups than in the controls (all P<0.05), but no significant differences were found in the resting nutritive capillary blood flow (P>0.05). A significant negative correlation (P=0.002, r=-0.366) was demonstrated between the SLEB and epidermal thickness at the pulp of the big toe, whereas no significant correlation was demonstrated between skin blood flow and epidermal thickness (all P>0.05).

CONCLUSIONS

An increase in subepidermal edema was demonstrated in people with diabetic neuropathy and ulceration, which may partly contribute to reduced epidermal thickness at the pulp of the big toe. This may subsequently lead to the breaking down of skin in the diabetic foot.

Epidermal thickness and biomechanical properties of plantar tissues in diabetic foot

Diabetic foot is a common complication for people with diabetes but it is unclear whether the change is initiated from the skin surface or underneath plantar tissues. This study compared the thickness of epidermis and the thickness and stiffness of the total plantar soft tissue among people with diabetes with or without complications. Seventy-two people with diabetes, including 22 people with neuropathies, 16 foot ulcerations, 34 pure diabetics without complications and 40 healthy controls participated in the study. The thickness of the epidermal layer of the plantar skin was examined using high-frequency ultrasonography; the thickness and stiffness of the total plantar soft tissue were measured by using tissue ultrasound palpation system at the big toe, the first, third and fifth metatarsal heads; and the heel pad. Compared with the control group, the average epidermal thickness of plantar skin was reduced by 15% in people with diabetic foot ulceration and 9% in people with neuropathy, but was increased by 6% in pure diabetics. There was an 8% increase in total thickness of plantar soft tissue in the 3 diabetic groups at all testing sites (all p < 0.05), except the first metatarsal head. The stiffness of plantar soft tissue was increased in all diabetic groups at all testing sites compared with the control (all p < 0.05). The epidermal plantar skin becomes thinner and plantar soft tissues stiffen in people with diabetes, particularly in persons who have neuropathy or ulceration, which increases the risk of tissue breakdown and ulceration formation.