Early steps of insulin action in the skin of intact rats

Melatonin promotes the development of the secondary hair follicles by regulating circMPP5

BACKGROUND

The quality and yield of cashmere fibre are closely related to the differentiation and development of secondary hair follicles in the skin of cashmere goats. The higher the density of secondary hair follicles, the higher the quality and yield of cashmere from the fleece. Development of secondary hair follicles commences in the embryonic stage of life and is completed 6 months after birth. Preliminary experimental results from our laboratory showed that melatonin (MT) treatment of goat kids after their birth could increase the density of secondary hair follicles and, thus, improve the subsequent yield and quality of cashmere. These changes in the secondary hair follicles resulted from increases in levels of antioxidant and expression of anti-apoptotic protein, and from a reduction in apoptosis. The present study was conducted to explore the molecular mechanism of MT-induced secondary hair follicle differentiation and development by using whole-genome analysis.

RESULTS

MT had no adverse effect on the growth performance of cashmere kids but significantly improved the character of the secondary hair follicles and the quality of cashmere, and this dominant effect continued to the second year. Melatonin promotes the proliferation of secondary hair follicle cells at an early age. The formation of secondary hair follicles in the MT group was earlier than that in the control group in the second year. The genome-wide data results involved KEGG analysis of 1044 DEmRNAs, 91 DElncRNAs, 1054 DEcircRNAs, and 61 DEmiRNAs which revealed that the mitogen-activated protein kinase (MAPK) signaling pathway is involved in the development of secondary hair follicles, with key genes (FGF2, FGF21, FGFR3, MAPK3 (ERK1)) being up-regulated and expressed. We also found that the circMPP5 could sponged miR-211 and regulate the expression of MAPK3.

CONCLUSIONS

We conclude that MT achieves its effects by regulating the MAPK pathway through the circMPP5 sponged the miR-211, regulating the expression of MAPK3, to induce the differentiation and proliferation of secondary hair follicle cells. In addition there is up-regulation of expression of the anti-apoptotic protein causing reduced apoptosis of hair follicle cells. Collectively, these events increase the numbers of secondary hair follicles, thus improving the production of cashmere from these goats.

Effects of topical insulin on wound healing: a meta-analysis of animal and clinical studies

Various researches have reported that the application of topical insulin improves wound healing. Considering the lack of a quantitative comprehensive research on this matter, we conducted a meta-analysis of clinical research and experimental animal studies. Prospective and randomized controlled trials of PubMed, Embase, and Cochrane Library were conducted using appropriate search strategies to compare the effectiveness of topical application of saline and insulin on wounds. The standardized mean difference was calculated as follows: wound healing time, wound healing rate, wound area, and the percentage of wound contraction. Each study used the Cochrane risk-of-bias tool and RevMan 5.3 software to create aggregated assessments and forest plots. The quality of evidence was evaluated in accordance with the methods of the Grading of Recommendations, Assessment, Development and Evaluation working group. Four clinical and nine animal studies eligible for inclusion were included in the meta-analysis. The assessments for clinical studies were as follows: wound healing time, -2.48 [-3.44, -1.51] and wound healing rate, 22.23 [18.17, 26.28]. Meanwhile, for animal studies, the following assessments were noted: wound healing time, -1.27 [-1.75, -0.79]; wound contraction rate, 15.91 [13.88, 17.95]; and wound area, -19.3 [-21.16, -17.44]. For the measurement of the following results, only one animal study was performed, pericyte recruitment of microvessels. Based on the analysis, it can be preliminarily judged that application of topical insulin can aid wound healing.

Wound healing treatment using insulin within polymeric nanoparticles in the diabetes animal model

The aim of this work was to prepare chitosan nanoparticles containing insulin and to evaluate its therapeutic activity during wound healing in diabetic rats. The hypothesis that guided this study was that the combination of insulin within chitosan nanoparticles could stimulate the signaling pathway for wound healing. The chitosan nanoparticles were prepared by the ionotropic gelation method presenting average size of 183.3 ± 8.32 nm, polydispersity index (PDI) 0.397 ± 0.07 and zeta potential of 33.7 ± 2.45 mV for empty chitosan nanoparticles (EC) and 245.9 ± 25.46 nm and PDI 0.463 ± 0.01, and zeta potential of 39.3 ± 4.88 mV for chitosan nanoparticles containing insulin (IC). The insulin association efficiency was 97.19% ± 2.18. These nanoparticles and free insulin (FI) were incorporated within a hydrogel (Sepigel®) for topical application in the wound of 72 diabetic rats distributed in four groups: Sepigel® (S, control), free insulin (FI), empty chitosan nanoparticles (EC), and chitosan nanoparticles containing insulin (IC). The animals in each group were reorganized into three subgroups (n = 6) to assess their clinical signs after days 3, 7, and 14 from the beginning of treatments. Intense fibroplasias were observed in the free or insulin-chitosan nanoparticles groups. In the latter, a large number of blood vessels were observed at day 7th. Our data indicated that both empty and insulin-containing chitosan nanoparticles were able to stimulate inflammatory cell proliferation, and angiogenesis, followed by wound maturation.

Insulin promotes macrophage phenotype transition through PI3K/Akt and PPAR-γ signaling during diabetic wound healing

Overactivation and persistent chronic inflammation are the major pathogenic characteristics of diabetic-impaired healing, and diabetic wound healing can be promoted by stimulating the transition of macrophage phenotype from pro-inflammatory (M1) to anti-inflammatory (M2). Our previous studies found that the application of insulin induced an advanced initiation and resolution of inflammatory response. To further explore the mechanism, we have investigated the effect of insulin on macrophage phenotype switch utilizing a diabetic rat model and a human monocytic THP-1 cell. We have utilized the high glucose (HG) and HG plus insulin to stimulate the M1 macrophages derived from lipopolysaccharide-treated THP-1 cells. We studied the secretion of inflammatory mediator and related signaling pathways by using western blot test, immunofluorescence, and Rac1 pull-down assay. We have found that the production of pro-inflammatory mediators, which thereafter induced macrophage polarization toward M1 phenotype, has been elevated due to consistent HG exposure. HG plus insulin stimulation, on the other hand, promoted anti-inflammatory effects. Experiments performed on diabetic burn wounds indicated that the insulin modulated macrophages transition from M1 to M2 phenotype. We found that PI3K/Akt/Rac-1 and PPAR-γ signaling pathways are involved in the anti-inflammatory effect of insulin. Insulin inhibited HG-induced activation of p38, NF-κB, and STAT1 transcriptional activity by activating Akt-Rac-1 signaling. Moreover, insulin performs anti-inflammatory effects through upregulation of PPAR-γ expression and induced P38-mediated dephosphorylation of PPAR-γ (Ser112). In conclusion, insulin downregulates inflammatory response, regulates M1 macrophage transition in response to HG, and thus improves chronic wound healing.

In vivo effects of diabetes, insulin and oleanolic acid on enzymes of glycogen metabolism in the skin of streptozotocin-induced diabetic male Sprague-Dawley rats

The skin is the largest organ in the body and diabetes induces pathologic changes on the skin that affect glucose homeostasis. Changes in skin glycogen and glucose levels can mirror serum glucose levels and thus the skin might contribute to whole body glucose metabolism. This study investigated the in vivo effects of diabetes, insulin and oleanolic acid (OA) on enzymes of glycogen metabolism in skin of type 1 diabetic rats. Diabetic and non-diabetic adult male Sprague-Dawley rats were treated with a single daily dose of insulin (4 IU/kg body weight), OA (80 mg/kg body weight) and a combination of OA + insulin for 14 days. Glycogen phosphorylase (GP) expression; and GP, glycogen synthase (GS) and hexokinase activities as well glycogen levels were evaluated. The results suggest that diabetes lowers hexokinase activity, GP activity and GP expression with no change in GS activity whilst the treatments increased GP expression and the activities of hexokinase, GP and GS except for the GS activity in OA treated rats. Glycogen levels were increased slightly by diabetes as well as OA treatment. In conclusion diabetes, OA and insulin can lead to changes in GS and GP activities in skin without significantly altering the glycogen content. We suggest that the skin may contribute to whole body glucose homeostasis particularly in disease states.

Transdermal delivery of insulin by amidated pectin hydrogel matrix patch in streptozotocin-induced diabetic rats: effects on some selected metabolic parameters

PURPOSE

Studies in our laboratory are concerned with developing optional insulin delivery routes based on amidated pectin hydrogel matrix gel. We therefore investigated whether the application of pectin insulin (PI)-containing dermal patches of different insulin concentrations sustain controlled release of insulin into the bloodstream of streptozotocin (STZ)-induced diabetic rats with concomitant alleviation of diabetic symptoms in target tissues, most importantly, muscle and liver.

METHODS

Oral glucose test (OGT) responses to PI dermal matrix patches (2.47, 3.99, 9.57, 16.80 µg/kg) prepared by dissolving pectin/insulin in deionised water and solidified with CaCl2 were monitored in diabetic rats given a glucose load after an 18-h fast. Short-term (5 weeks) metabolic effects were assessed in animals treated thrice daily with PI patches 8 hours apart. Animals treated with drug-free pectin and insulin (175 µg/kg, s.c.) acted as untreated and treated positive controls, respectively. Blood, muscle and liver samples were collected for measurements of selected biochemical parameters.

RESULTS

After 5 weeks, untreated diabetic rats exhibited hyperglycaemia and depleted hepatic and muscle glycogen concentrations. Compared to untreated STZ-induced diabetic animals, OGT responses of diabetic rats transdermally applied PI patches exhibited lower blood glucose levels whilst short-term treatments restored hepatic and muscle glycogen concentrations. Plasma insulin concentrations of untreated diabetic rats were low compared with control non-diabetic rats. All PI treatments elevated plasma insulin concentrations of diabetic rats although the levels induced by high doses (9.57 and 16.80 µg/kg) were greater than those caused by low doses (2.47 and 3.99 µg/kg) but comparable to those in sc insulin treated animals.

CONCLUSIONS

The data suggest that the PI hydrogel matrix patch can deliver physiologically relevant amounts of pharmacologically active insulin.

NOVELTY OF THE WORK

A new method to administer insulin into the bloodstream via a skin patch which could have potential future applications in diabetes management is reported.

Local use of insulin in wounds of diabetic patients: higher temperature, fibrosis, and angiogenesis

BACKGROUND

Clinical trials have shown the effectiveness of systemic and local insulin therapy in improving wound healing. Diabetic wounds remain a challenge for healthcare providers. Impaired angiogenesis and reduced granulation tissue formation contribute to inadequate wound healing. The aim of this study was to investigate the effect of local insulin administration in acute and chronic diabetic wounds.

METHODS

Eight diabetic patients presenting with full-thickness wounds, of different causes, were included in this study. Five wounds were due to necrobiosis, one to trauma, and two to postneoplasm resection. All wounds were treated with regular bedside treatment. In addition, half of the wound surface was treated with insulin and the other half did not receive insulin. Thermographic and biopsy specimens of the two sides were obtained on days 0 and 14. The presence of fibrosis, change in temperature, and amount of blood were evaluated.

RESULTS

Significant differences in the number of vessels were observed on the insulin-treated side (96 ± 47) when compared with the no-insulin side (32.88 ± 45) (p < 0.026). The percentage of fibrosis (insulin: 44.42 ± 30.42 percent versus no insulin: 12.38 ± 36.17 percent; p < 0.047) and the mean temperature (insulin: 1.27 ± 1.12°C versus no-insulin: 0.13 ± 1.22°C; p < 0.001) were also significantly different between sides. No adverse events related to the study occurred.

CONCLUSION

The use of local insulin improves the formation of new blood vessels, increases fibrosis, and correlates with increased temperature.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

Pseudomonas aeruginosa biofilms perturb wound resolution and antibiotic tolerance in diabetic mice

Diabetic patients are more susceptible to the development of chronic wounds than non-diabetics. The impaired healing properties of these wounds, which often develop debilitating bacterial infections, significantly increase the rate of lower extremity amputation in diabetic patients. We hypothesize that bacterial biofilms, or sessile communities of bacteria that reside in a complex matrix of exopolymeric material, contribute to the severity of diabetic wounds. To test this hypothesis, we developed an in vivo chronic wound, diabetic mouse model to determine the ability of the opportunistic pathogen, Pseudomonas aeruginosa, to cause biofilm-associated infections. Utilizing this model, we observed that diabetic mice with P. aeruginosa-infected chronic wounds displayed impaired bacterial clearing and wound closure in comparison with their non-diabetic littermates. While treating diabetic mice with insulin improved their overall health, it did not restore their ability to resolve P. aeruginosa wound infections or speed healing. In fact, the prevalence of biofilms and the tolerance of P. aeruginosa to gentamicin treatment increased when diabetic mice were treated with insulin. Insulin treatment was observed to directly affect the ability of P. aeruginosa to form biofilms in vitro. These data demonstrate that the chronically wounded diabetic mouse appears to be a useful model to study wound healing and biofilm infection dynamics, and suggest that the diabetic wound environment may promote the formation of biofilms. Further, this model provides for the elucidation of mechanistic factors, such as the ability of insulin to influence antimicrobial effectiveness, which may be relevant to the formation of biofilms in diabetic wounds.

Topical insulin accelerates wound healing in diabetes by enhancing the AKT and ERK pathways: a double-blind placebo-controlled clinical trial

BACKGROUND

Wound healing is impaired in diabetes mellitus, but the mechanisms involved in this process are virtually unknown. Proteins belonging to the insulin signaling pathway respond to insulin in the skin of rats.

OBJECTIVE

The purpose of this study was to investigate the regulation of the insulin signaling pathway in wound healing and skin repair of normal and diabetic rats, and, in parallel, the effect of a topical insulin cream on wound healing and on the activation of this pathway.

RESEARCH DESIGN AND METHODS

We investigated insulin signaling by immunoblotting during wound healing of control and diabetic animals with or without topical insulin. Diabetic patients with ulcers were randomized to receive topical insulin or placebo in a prospective, double-blind and placebo-controlled, randomized clinical trial (NCT 01295177) of wound healing.

RESULTS AND CONCLUSIONS

Expression of IR, IRS-1, IRS-2, SHC, ERK, and AKT are increased in the tissue of healing wounds compared to intact skin, suggesting that the insulin signaling pathway may have an important role in this process. These pathways were attenuated in the wounded skin of diabetic rats, in parallel with an increase in the time of complete wound healing. Upon topical application of insulin cream, the wound healing time of diabetic animals was normalized, followed by a reversal of defective insulin signal transduction. In addition, the treatment also increased expression of other proteins, such as eNOS (also in bone marrow), VEGF, and SDF-1α in wounded skin. In diabetic patients, topical insulin cream markedly improved wound healing, representing an attractive and cost-free method for treating this devastating complication of diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01295177.

Insulin enhances proliferation and viability of human umbilical vein endothelial cells

This investigation is a follow-up to our previous in vivo studies revealing that rapid stretch increases tissue insulin in murine skin flaps, coincident with the up-regulation of key angiogenic effectors and enhanced vascularization. In the present study, we used human umbilical vein endothelial cells (HUVECs) as an in vitro model system to determine the role of insulin in the chemical signals regulating the processes of proliferation and viability (survival). MTT-based colorimetric methods demonstrated that insulin enhances proliferation and survival of HUVECs. Western blot analysis revealed that protein kinase B (pAkt [Thr(308)]) and vascular endothelial growth factor (VEGF) were the insulin-responsive intermediates in proliferating endothelial cells (ECs). In insulin-enhanced survival, both pAkt (Thr(308)) and pAkt (Ser(473)) were activated in HUVECs. However, no change in VEGF expression accompanied pAkt activation. The beneficial effects of insulin were abrogated by insulin receptor (IR)/insulin-like growth factor receptor (IGFR) or phosphoinositide-3 kinase (PI3-K) blockade, suggesting that insulin-induced EC proliferation and viability are mediated through pIR/pIGFR and PI3-K effectors. These data provide new insights into the beneficial effects of insulin on vascularization and tissue viability, providing a mechanistic link to the enhancement of healing in acutely stretched skin.

Acute stretch promotes endothelial cell proliferation in wounded healing mouse skin

We have developed a novel in vivo model utilizing acute stretch to investigate endothelial cell proliferation as a marker of vascular growth in healing mouse skin. This study is a follow-up to ones revealing immediate stretch improves blood flow, decreases total tissue necrosis, and induces tissue insulin transcription. Dorsal distally based flaps of skin were stretched for 3 min using linear (skin hook) plus hemispherical load cycling (inflated subcutaneous silicone catheter). Unstretched, wounded skin along the back and sternum served as postoperative controls. Laser Doppler flowmetry demonstrated a threefold increase in flap perfusion at postoperative day 7. A stretch-induced sixfold increase in endothelial cell mitogenesis accompanied enhancements in blood flow and extracorporal wound healing over the sternum. Western blots revealed up-regulation/activation of insulin and mitogenic signaling intermediates in stretched skin. Activated insulin and insulin growth factor receptors (pIR/pIGFR), protein kinase B (Akt, pAkt), vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor 2 (flk-1) were among the identified stretch-responsive intermediates. These results indicate the benefits of acute stretch are mediated through enhanced vascularity as evidenced by endothelial cell mitogenesis and up-regulation/activation of insulin and key angiogenic effectors in dorsal distally based skin flaps.

Local insulin-zinc injection accelerates skin donor site wound healing

BACKGROUND

Systemically administered insulin has been shown to accelerate wound healing. To minimize the hypoglycemic and hypokalemic effects of insulin, we investigated a new route of insulin administration by local injection into skin wounds.

MATERIALS AND METHODS

Partial thickness skin donor site wounds were created on the backs of adult rabbits with a dermatome set at 0.015 inch. The wounds were covered by Aquaphor gauze (Smith and Nephew, Largo, FL), and OpSite membrane (Smith and Nephew, Hull, United Kingdom) and protected by rabbit jackets. Long-acting insulin-zinc suspension was selected for local injection. In study 1, insulin was injected into the wound at different doses, and the concentrations of blood glucose and wound insulin were measured to determine the proper dose and injection frequency. In study 2, wound healing days were compared between two groups (n = 7 each) receiving local injection of either insulin-zinc or zinc alone as control. Based on the results from study 1, a dose of 0.25 units of long-acting insulin-zinc suspension was injected into the wound every other day in the insulin group.

RESULTS

After injection, 0.25 units of insulin decreased blood glucose concentration (minimum 60 mg/dL) during the first 3 h, which then returned to the preinjection level (80 mg/dL). One injection maintained wound insulin concentration above 50 muU/mL for more than 24 h. With local injection of 0.25 units insulin-zinc every other day, the wound healing time was 11.2 +/- 2.3 d, which was faster (P = 0.02) than 15.1 +/- 4.1 d in the control group.

CONCLUSION

Local injection of long-acting insulin-zinc suspension accelerated skin wound healing without major systemic side effects, demonstrating its potential usefulness in burn treatment.

Local injection of insulin-zinc stimulates DNA synthesis in skin donor site wound

Our group has reported the ability of local insulin-zinc injection to accelerate skin wound healing. This experiment was conducted to investigate the metabolic mechanisms of locally injected insulin-zinc in accelerating wound healing. A partial thickness skin donor site wound was created on the back, and indwelling catheters were placed in the carotid artery and jugular vein in anesthetized rabbits. On day 7 after injury, the wound was either injected with 0.2 U of insulin-zinc, 0.4 microg zinc (the amount of zinc in 0.2 U of insulin-zinc), or not injected; stable isotope tracers were infused for measurement of wound DNA synthetic rate as a reflection of cell proliferation. Wound protein synthetic and breakdown rates were also measured. The local insulin-zinc injection increased wound insulin concentration from below 5 pmol/L to 1,260+/-780 pmol/L with minor changes in blood glucose concentration that did not require exogenous glucose replacement. In the insulin-zinc-injected wound, the total DNA synthetic rate was increased by approximately 50% (p<0.05 vs. control). In the zinc-injected wound, whereas total DNA synthetic rate was increased (p<0.05 vs. control), net protein deposition (synthesis-breakdown) was less (p<0.05) than those in the control and insulin-zinc groups. We conclude that local insulin-zinc injection stimulates wound DNA synthesis, which would be expected to accelerate wound reepithelialization.

A novel function of insulin in rat dermis

In this study we present a novel function of insulin in rat dermis. We investigated local effects of insulin on interstitial fluid pressure (Pif), and capillary albumin leakage and pro-inflammatory cytokine production in skin and serum after intravenous lipopolysaccharide (LPS), tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) challenge treated with a glucose-insulin-potassium regimen (GIK). The main objective for this study was to investigate anti-inflammatory effects of insulin. Work by others shows that insulin stimulates cell adhesion, and that this effect is dependent upon phosphatidylinositol 3-kinase (PI3K) activity. Cytokines like platelet-derived growth factor BB (PDGF-BB) attenuate lowering of Pif, possibly via PI3K. LPS and pro-inflammatory cytokines contribute to oedema development during acute inflammation by lowering the Pif. Intravenous injection of LPS, TNF-alpha or IL-1beta to Wistar Møller rats caused a lowering of Pif, but after local injection of insulin in the paw, Pif increased back to control values. IL-1beta caused a lowering in control from -0.5 +/- 0.2 mmHg to -3.0 +/- 0.2 mmHg after 20 min (mean +/- S.E.M.) (P < 0.05). Within 50 min after insulin injection the pressure was increased to -0.6 +/- 0.2 mmHg (P > 0.05 compared with control). Insulin was given together with a PI3K inhibitor (wortmannin) locally in the skin, almost abolishing the effect of insulin on Pif. A GIK regimen was given as a continuous intravenous infusion, significantly attenuating the oedema formation after LPS or TNF-alpha/IL-1beta challenge. The same GIK regimen caused a significant reduction in pro-inflammatory cytokines in serum and in interstitial fluid in skin of endotoxaemic rats. These experiments show a possible role for insulin in the interstitium during inflammation induced by LPS and TNF-alpha/IL-1beta. Insulin can attenuate a lowering of Pif possibly via PI3K, and it has an anti-inflammatory effect by inhibiting production of pro-inflammatory cytokines.