Effects of insulin-like growth factor-I and insulin-like growth factor binding protein-1 on wound healing in a dermal ulcer model

Effects of insulin-like growth factor-1 on random pattern skin flap survival in rats

PURPOSE

To investigate the effects of pharmacological delay with insulin-like growth factor-1 (IGF-1) on skin flap survival.

METHODS

Thirty Sprague-Dawley rats were submitted to dorsal skin flap (3x9 cm). Seven days before the surgery, the animals were subdivided into three groups of 10 rats. In group 1 (controls), no injection was done. Seven days before the elevation, saline had been injected to the marked skin flap area in group 2 (sham group), and group 3 (experimental group) underwent a pharmacological delay with subcutaneous IGF-1 injections. On the seventh postoperative day, flap area was analyzed for survival. Tissue samples were obtained for histological and biochemical evaluations.

RESULTS

Survival rates were 43.55 ± 16%, 21.40 ± 8%, and 43.12 ± 14% in groups 1, 2, and 3, respectively. Differences between group 2 and other groups were statistically significant. No significant difference was detected between all three groups for tissue or plasma vascular endothelial growth factor (VEGF) levels. There was no significant histological difference between groups.

CONCLUSION

Although a single injection of insulin-like growth factor-1 (IGF-1) did not significantly increase flap survival, its wound healing features are still encouraging and further meticulously planned studies, especially with repeated applications or controlled-release methods, and combinations with binding protein are required.

Effects of IGFBP-1 and IGFBP-2 and their fragments on migration and IGF-induced proliferation of human dermal fibroblasts

OBJECTIVE

A family of six insulin-like growth factor (IGF) binding-proteins (IGFBP) bind to IGF-I and IGF-II with high affinity and modulate their activity. We have recently shown that a neutrophil-derived protease activity cleaved IGFBP-1, -2 and -4. IGFBP-1 and IGFBP-2 have a C-terminal Arg-Gly-Asp (RGD) sequence, and IGFBP-1 has been shown by others to stimulate migration through binding of its RGD sequence to α5β1 integrin. The aim of this study was to determine the effect of this IGFBP protease on IGF-induced proliferation and the effect of IGFBP-1 and IGFBP-2 and their proteolytic fragments on migration in normal and high glucose of human dermal fibroblasts (HDF).

DESIGN

We investigated the effect of intact or cleaved IGFBP-1 and -2 on proliferation in cultured HDFs and on HDF migration in normal and high glucose.

RESULTS

Both IGFBP-1 and IGFBP-2 and their proteolytic fragments stimulated HDF migration and the stimulatory effect was abolished by pre-treating cells with a α5β1 integrin antibody. High glucose impaired migration of HDFs; however, the addition of IGFBP-1, IGFBP-2 or fragments increased migration to levels observed in normoglycemia. IGFBP-2 inhibited IGF-II induced proliferation; however, the inhibitory effect was reduced after being cleaved. Intact native IGFBP-1 showed either potentiating or inhibitory effects on IGF-I induced proliferation depending on the confluence of cells, and proteolysis of IGFBP-1 did not change these effects. IGFBP-1 was found to increase phosphorylation of FAK and ERK1/2 and this effect was inhibited by the monoclonal integrin a5β1 ab.

CONCLUSIONS

IGFBP-1 and -2 and their proteolytic fragments may improve tissue repair under inflammatory conditions, through effects on proliferation and migration of HDFs in normal and high glucose.

Insulin-like growth factor-I in wound healing of rat skin

Growth factors play an important role in orchestrating and enabling the cellular responses required for successful wound healing. In the present study, rat surgical incision was used to investigate insulin-like growth factor-I (IGF-I) expression in skin cells as well as its systemic and cutaneous tissue concentrations during acute phase of wound healing. Thirty two animals were sacrificed at days 2, 3, 5 and 9 after surgery. Eight animals were used as control. Tissue expression of IGF-I in both incisional and periincisional skin areas, as well as in skin of control unwounded animals was determined by immunohistochemistry. Serum and tissue concentrations of IGF-I were measured using RIA. Immunohistochemical analysis revealed enhanced IGF-I immunostaining in the incisional area at day 2 post-wounding. Presence of IGF-I immunoreactivity in the epidermis, as well as in dermal fibroblasts and monocytes within perivascular inflammatory infiltrate suggests its local synthesis. Although serum levels of IGF-I were not altered during wound healing, their tissue contents in the incisional area were significantly increased compared with periincisional area at days 2 and 3 after injury, as well as compared with skin content of unwounded control rats in all examined time points. Obtained results support a paracrine role of IGF-I during the acute phase of wound healing by primary intention in the rat.

Stimulation of steroid-suppressed cutaneous healing by repeated topical application of IGF-I: different mechanisms of action based upon the mode of IGF-I delivery

BACKGROUND

Insulin-like growth factor-I (IGF-I) is accepted as a potent stimulus of wound healing when applied in combination with its binding proteins. However, there is only one study published that has investigated the effect of repeated topical application of unbound IGF-I on ischemic wound healing. The aim of this study was to show the effect of daily topical IGF-I therapy on cutaneous ulcer healing in a steroid-suppressed wound model.

MATERIALS AND METHODS

Full-thickness wounds were created on the back of 40 male Sprague-Dawley rats. Before surgery, animals received depot-steroids subcutaneously. Wounds were treated daily with either a standard hydrogel dressing (control), topical IGF-I dissolved in 0.2% methylcellulose gel (IGF-I gel), or a hydrogel dressing containing IGF-I (IGF-I dressing). After 7 days of treatment, wounds were excised and measured by photoplanimetry. SMA- and PCNA-expression as well as the formation of granulation tissue were assessed in tissue sections. Results are given as median(min-max). Differences between groups were calculated by the Mann-Whitney U test.

RESULTS

Subcutaneous injection of depot-steroids induced a significant delay in healing, as shown by an enlarged wound size [44(33-65) versus 25(20-35)] mm(2); P = 0.001). In steroid-treated rats, both IGF-I gel and IGF-I dressing enhanced excisional healing, as shown by a significant reduction in wound size (P = 0.0001), with IGF-I released from the dressing being even more effective than IGF-I gel (P = 0.03). However, in these animals only IGF-I released from the hydrogel dressing stimulated SMA- (P = 0.03) as well as PCNA-expression (P = 0.001) and increased granulation tissue formation (P = 0.018).

CONCLUSIONS

Our data indicate that a repeated application of topical IGF-I enhances cutaneous ulcer healing. In addition, only the controlled release of IGF-I from the hydrogel dressing is capable of reversing the steroid-induced delay of healing, suggesting different mechanisms of action with respect to the mode of IGF-I delivery.

Experimental ischemic wounds: correlation of cell proliferation and insulin-like growth factor I expression and its modification by different local IGF-I release systems

We investigated cell proliferation and local insulin-like growth factor-I (IGF-I) expression in ischemic wounds after topical application of IGF-I through different delivery systems. IGF-I dressings were fabricated from an IGF-I containing polyvinyl alcohol film placed on a standard hydrogel dressing. In vitro, the release of IGF-I from this dressing was assessed by enzyme-linked immunosorbent assay. For animal experiments, a standardized ischemic skin flap containing a full-thickness wound was created on the back of male Sprague-Dawley rats. An identical wound outside the flap served as control. We initially investigated intracutaneous pO2 (p(ti)O2), cell proliferation, and local IGF-I expression. In a second setting, wounds were treated either with IGF-I dissolved in methylcellulose gel or with an IGF-I dressing, and ulcer size and cell proliferation were assessed. In vitro, approximately 60% of IGF-I was released from the IGF-I dressing, compared to a 97% release from methylcellulose gel. In vivo, ischemic wounds showed less cell proliferation and decreased IGF-I expression than nonischemic wounds. A lower local p(ti)O2 correlated with larger wound size, less cell proliferation, and decreased IGF-I expression. Ulcer size was reduced after treatment with either IGF-I dressing or methylcellulose gel. However, cell proliferation only increased after treatment with IGF-I dressing, but not after methylcellulose gel treatment. We conclude that IGF-I expression is decreased in ischemic wounds and correlates with low cell proliferation. This can be reversed by local IGF-I application, but the efficacy of treatment depends on the delivery system.

The fibroblast-populated collagen matrix as a model of wound healing: a review of the evidence

The fibroblast-populated collagen matrix (FPCM) has been utilized as an in vitro model of wound healing for more than 2 decades. It offers a reasonable approximation of the healing wound during the phases of established granulation tissue and early scar. The gross and microscopic morphology of the FPCM and the healing wound are similar at analogous phases. The processes of proliferation, survival/apoptosis, protein synthesis, and contraction act in similar directions in these two models, and the response to exogenous agents also is consistent between them. If its limitations are respected, then the FPCM can be used as a model of the healing wound.

Age-dependency of insulin-like growth factors, insulin-like growth factor-binding proteins, and acid labile subunit in plasma and wounds of surgical patients

Wound problems are common in the elderly. We hypothesized that age-related decrements in blood levels of components of the insulin-like growth factor (IGF) system are reflected in the wound environment. In this prospective, observational study IGF-I, IGF-II, IGF-binding protein-2, IGF-binding protein-3, and acid labile subunit were measured by immunoassays in the wound fluid and plasma of young (23.5 +/- 3.3 years) and elderly (78.9 +/- 6.2 years) patients before and daily for 4 days after elective surgery. IGFs, IGFBP-3, and acid labile subunit in plasma were significantly lower in the elderly group (p < 0.0001). The decrements of these proteins in plasma were reflected in corresponding decrements of 25-70% in the wound fluid of elderly patients (p < 0.0001). Additionally, bioavailability of IGF-I was less in the aged. The IGF parameters in the wound displayed a constant ratio with those of blood, suggesting that blood contributes a major share of the IGF that enters the wound during the initial phase of healing. The current data adds to accumulating evidence that a decline in the IGF system in aged patients contributes to the healing deficits observed in the elderly.

Interaction between the insulin-like growth factor family and the integrin receptor family in tissue repair processes. Evidence in a rabbit ear dermal ulcer model

We have determined previously that IGF-I is dependent on the presence of IGF binding protein-1 (IGFBP-1) to act as a wound healing agent. We sought to determine the mechanism whereby IGFBP-1 is able to enhance IGF-I bioactivity. As IGFBP-1 binds both the alpha5beta1 integrin as well as IGF-I in vitro, we asked which of the following interactions were important: (a) the ability of IGFBP-1 to interact with an integrin receptor, and/or (b) the binding of IGF-I by IGFBP-1. We used an IGF-1 analogue (des(1-3)IGF-I) with a > 100-fold reduction in affinity for IGFBP-1 as well as an IGFBP-1 mutant (WGD-IGFBP-1) which does not associate with the alpha5beta1 integrin to selectively abrogate each of these interactions. We also tested the ability of IGFBP-2, a related binding protein which has an arginine-glycine-aspartate sequence but does not associate with integrin family members, to enhance IGF-I bioactivity. Full-thickness dermal wounds were created on rabbit ears; various combinations of native IGF-I, native IGFBP-1, native IGFBP-2, and their respective analogues/mutants were applied to each wound. Wounds were harvested 7 d later for analysis. Only native IGF-I in combination with native IGFBP-1 was effective as a wound healing agent, enhancing reepithelialization and granulation tissue deposition by 64+/-5 and 83+/-12% over controls (P = 0.008 and 0.016, respectively). The same doses of IGF-I/WGD-IGFBP-1, des(1-3)IGF-I/IGFBP-1, and IGF-I/IGFBP-2 were ineffective. We propose that IGF-I physically interacts with IGFBP-1 and that IGFBP-1 also binds to an integrin receptor, most likely the alpha5beta1 integrin. This interaction is unique to IGFBP-1 as the closely related IGFBP-2 had no effect, a finding consistent with its inability to bind to integrin receptors. Our results suggest that activation of both the IGF-I receptor and the alpha5beta1 integrin is required for IGF-I to stimulate wound healing.