D-[3H]glucosamine labelling of epidermal and dermal glycosaminoglycans in cultured human skin.

An in vitro model is presented for the study of glycosaminoglycans in human skin. The synthesis of six glycosaminoglycan species in both dermis and epidermis was measured by D-[3H]glucosamine labelling. Punched biopsies (epidermis + entire dermis) of 3 mm in diameter were cultured at 37 degrees C in 5% carbon dioxide-95% air. When the label was added 18 h after explantation, the incorporation started immediately, and for all glycosaminoglycans the time-dependent incorporation was linear for 16 h. The experimental variation was minimized by expressing the measurements in epidermis "per explant" and in dermis "per mg of wet explant". A ratio to dermal hydroxyproline did not improve the precision. Most of the variation arose "before" isolation and separation of the glycosaminoglycans. The labelled products were macromolecules and were converted to small molecules by chondroitinase ABC + heparinase. The total incorporation in dermis was 2 1/2 times higher than in epidermis. Hyaluronic acid was the predominant synthesized product in dermis, and hyaluronic acid and heparan sulphate were the predominant products in epidermis. The proportions (%) in dermis/epidermis were as follows: hyaluronic acid, 61/44; heparan sulphate, 18/31; dermatan sulphate, 5/8; chondroitin 4/6-sulphate, 10/7 and heparin-like glycosaminoglycan, 1/2. The same species were also demonstrated as native constituents of uncultured human skin. Hyaluronic acid and dermatan sulphate predominated in dermis, whereas no single species predominated in epidermis. Their concentrations in uronic acid equivalents per mg of wet skin (pmol/mg of epidermis + dermis) were as follows in dermis/epidermis: hyaluronic acid, 243/0.48; heparan sulphate, 22/0.44; dermatan sulphate, 170/0.56; chondroitin 4/6-sulphate, 72/0.50; and heparin-like glycosaminoglycan, 5/0.22. Thus, only 0.4% of the in vivo synthesized glycosaminoglycan was present in epidermis.