New concepts in tissue repair: skin as an example.

Several heparin-binding growth factors (HBGFs) are thought to play a key role in natural processes of tissue regeneration or repair after release from inflammatory or circulating cells and extracellular matrix-associated heparan sulfate proteoglycosaminoglycans. To clarify how the bioavailability of these HBGFs can help regulate wound-healing processes, we studied the healing effect of various chemically substituted dextrans (RGTA) selected for their affinity for HBGFs. One member of the RGTA family, RGTA11, obtained by substitution of carboxymethyl (CM), benzylamide (B) and benzylamide sulfonate (S) groups in a proportion of 110% (CM), 2.6% (B) and 36.5% (S) respectively was used in these studies. RGTA11 may potentiate the biological activity of fibroblast growth factors 1 and 2 and protect them against heat or pH inactivation and proteolytic degradation. RGTA11 was tested in a rat punch-biopsy skin-healing model for its ability to enhance wound repair. Wounds were filled with collagen plaster alone or soaked with RGTA, and skin regeneration was studied by histological analysis. In collagen plaster, RGTA11 affected both the kinetics and quality of restored skin. It seems likely that endogenous growth factors naturally released during the regeneration process are trapped and protected against natural proteases, thereby preserving their ability to stimulate tissue repair. Since most known growth factors have a nearly ubiquitous distribution and blind to heparin, our hypothesis was verified by studying the ability of RGTA to induce repair in damaged tissue. We demonstrated the RGTA could stimulate wound repair in various models, including bone, muscle, nerve, cornea and colonic anastomosis. The data presented here concern wound-healing in a deep skin model and suggest that heparan-like biopolymers constitute a new family of tissue-repair agents with a wide variety of potential uses. The efficiency of this approach in cases in which impaired healing is associated with a pathology, as in diabetes, remains to be determined.

Induction of choriogenesis by 20-hydroxyecdysone in the German cockroach.

Experiments in vitro have shown that 20-hydroxyecdysone (at a concentration of 0.2 and 2 microM and after 12 and 24 hr of incubation) is able to induce the precocious deposition of chorion materials by the follicular epithelium of young oocytes of the cockroach Blattella germanica. Since previous studies had shown that 20-hydroxyecdysone levels in B. germanica ovaries increase with oocyte maturation to reach a peak just before oviposition, we therefore hypothesize that ovarian ecdysteroids trigger Choriogenesis in this species through an autocrine action.