Vitamin A transporting proteins in human epidermis and blister fluids

In connection with studies on vitamin A transport to keratinocytes in vivo, the retinol, retinol-binding protein (RBP), and prealbumin contents of blister fluid obtained subepidermally (suction) or intraepidermally (friction) were analyzed. The median concentrations of the three components in suction blister fluid (SBF) were all about 33% of the serum concentrations. Corresponding values for alpha 2-macroglobulin and total protein, measured as controls, were 27 and 30%, respectively. The relative amounts of retinol and prealbumin in friction blister fluid (FBF) were the same as those in SBF. By contrast, FBF contained more RBP (median value 40%; P less than 0.01 vs SBF value). It is suggested that apo-RBP (RBP without retinol) is generated within the epidermis and contributes to the high RBP value in FBF. FBF constituents are probably derived from the intercellular space of the epidermis, at least during the initial phase of blister formation. Accordingly, RBP and prealbumin were identified in homogenates of pure epidermis. During the later stages of blister formation, FBF resembles an ultrafiltrate of dermal fluid, although different in this respect from SBF.