New microencapsulated sunscreens: technology and comparative evaluation.

The aim of this work is to obtain new technologically improved microencapsulated sunscreens characterised by UV-radiation stability, good substantivity, low toxicity, a better tolerability and easiness to formulation. For this purpose we prepared two different systems using semisynthetic Hyaluronic Acid (HA) benzyl ester and a synthetic polymer (patent pending). We obtained these systems using two different methodologies: emulsification/solvent evaporation and emulsification/solvent extraction. The comparison between the two formulated systems was carried out in terms of their chemical-physical and biological properties.

AO 1535 inhibits O2- production by human macrophages.

AO 1535 is a semisynthetic monoglycosylceramide derived from O-glycosilated sphingosine, with a chemical structure similar to the glycolipids present in many mammalian tissues. In the epidermis monoglycosylceramides contribute to consolidate the structure of cutaneous layers. It has been recently shown that sphingosine and its derivatives are potent inhibitors of Protein kinase C, and block the 'respiratory burst' of phagocitic cells. In macrophages, like in neutrophils, the reactive oxygen intermediates are produced by a membrane associated enzymatic complex, NADPH-oxidase, which is activated by Protein kinase C. This study demonstrates that AO 1535 is able to inhibit the production of reactive oxygen intermediates in human monocytes and macrophages stimulated by phorbol ester and chemotactic tetrapeptide, suggesting a potential clinical application of AO 1535 in the treatment of inflammatory dermatoses.

In vitro studies on biocompatibility of hyaluronic acid esters.

The biocompatibility of semisynthetic polymers formed from hyaluronic acid esters has been studied using fibroblast cultures. The polymers, added to the culture medium, used either in powdered form or as thin membranes, behave as inert materials. The cells used in the experiments grow normally in the culture dishes. With regard to adhesiveness the cells were not able to spread on the biomembranes and tended to form isolated clusters of round cells. Human fibronectin, placental collagen (type I-IV) and fibrin could be stratified on biomembranes. When these molecules reacted with the biomaterial the film became suitable for fibroblasts spreading and growth.

Hyaluronate derivatives and their application to wound healing: preliminary observations.

Hyaluronic acid and its derivatives show promise as biomaterials in wound healing applications. Studies of cutaneous wound repair were carried out in two animal models to compare the biological effects of hyaluronic acid and hyaluronic acid ethyl ester, a new semisynthetic derivative. The two compounds were tested in partial-thickness excisional wounds in 40-kg pigs and full-thickness excisional wounds in the rabbit ear as 0.2% (w/w) formulations in a neutral Na alginate vehicle. All compounds were administered daily under an occlusive, polyurethane dressing. Neither hyaluronic acid nor the hyaluronic acid ethyl ester showed toxic or inflammatory influences over the observation period of about 2 weeks. Morphometric analysis of porcine wounds revealed small differences among treatment groups which may have been masked by the effect of the vehicle. The rabbit ear model data suggested a very slight inhibition of wound closure. Biochemical analysis of ear wounds showed this injury model to be a sensitive system for evaluation of vulnerary agents. The hyaluronate-treated wounds tended to accumulate collagen more slowly, which may reflect the capacity of these compounds to modify the scarring process. Given the ability to fabricate hyaluronate esters into films and fibers, these data suggest that such biomaterials will not, by themselves, exert a negative influence on the repair process and may improve healing, either alone or in combination with other soluble agents.

Hyaluronic acid prevents oxygen free-radical damage to granulation tissue: a study in rats.

Oxygen free-radicals are known to impair wound healing after ischaemia-reperfusion or polymorphonuclear cell stimulation. Furthermore, they reduce the breaking strength of all recent wounds and might be a cause of wound leakage. This study was performed to evaluate whether or not hyaluronic acid can reduce the risk of wound impairment caused by free-radicals, in rats with abdominal sepsis, polymorphonuclear cell stimulation or cytochrome C function derangement produced by xenobiotics. Male Sprague-Dawley rats with open wounds received phenazine methosulfate or zimosan, or had abdominal sepsis to induce oxygen free-radical generation. There were three groups of treatment: hyaluronic acid cream, hyaluronic acid ethyl ester gel, and placebo. The reduction in wound size was measured from the 1st to the 11th postoperative day; biopsies were taken for histological evaluation. Every other day, a gentle debridement was performed in all the groups of animals. We found that hyaluronic acid and its ethyl ester derivative significantly improved the wound healing of rats subjected to an increased generation of oxygen free-radicals. It remains to be established whether or not hyaluronic acid acts as a scavenger of free-radicals.