The diabetic rat as an impaired wound healing model: stimulatory effects of transforming growth factor-beta and basic fibroblast growth factor.

Two models of wound repair compared the effect of defined, recombinant growth factors on the rate of wound repair in both normal and streptozotocin-induced diabetic rats: subcutaneous implantation of polyvinyl alcohol sponges and incisional wounding. Transverse incisional wounds were made on the dorsal surface of rats and closed with steel sutures. Three days postwounding the rats received a single injection of either transforming growth factor-beta or vehicle alone directly into the wound site. Animals were sacrificed 7, 14, and 21 days postwounding, and fresh and formalin-fixed wound tensile strength were measured. Diabetic rats had expected defects in wound repair, including decreased granulation tissue and reduced amounts of collagen, protein, and DNA. Fresh tensile strength of the diabetic incisions was 53% of normal on Day 7 (p < or = .01) and 29% of normal on Day 21. Fixed tensile strength was 41% of normal on Day 7 (p < or = .01) and fell to 78% of normal by Day 21 (p < or = .01), suggesting that collagen concentrations of diabetic wounds increased towards normal but did not undergo maturation. TGF beta produced a moderate increase in tensile strength of fresh and fixed wounds of diabetic rats, but not to the levels of wounds in untreated normal rats. Sponges fill with granulation tissue, their reproducible rate of organization being measured by histological and biochemical methods. A single injection into sponges 3 days postimplantation of basic fibroblast growth factor, transforming growth factor-beta, or vehicle only, was evaluated at 7 and 9 days postimplantation. In the sponge model, bFGF and TGF beta were each able to induce significant increases in the accumulation of granulation tissue in both diabetic and normal rats. TGF beta increased the collagen content of sponges by 136% in sponges from diabetic animals (p < or = .001), thereby raising the collagen content to that of normal control wounds, while stimulating a 49% (p < or = .02) increase in sponges from normal animals on Day 9. By contrast, the response to bFGF was predominantly an increase in the protein and DNA content of the sponges. These results emphasize the differential effects of the two cytokines in accelerating healing under conditions of defective wound repair.