Serum lipoproteins protect isolated erythrocytes against retinol-induced haemolysis.

Under physiological conditions no evidence of haemolysis caused by hypervitaminosis A or vitamin A1 therapy was noted so far in the literature. Nevertheless, previous studies have demonstrated that isolated red blood cells were readily lysed by retinol and structurally related compounds [8]. These data are compatible with the existence of serum components with binding-properties comparable to that of retinol-binding protein. We therefore decided to identify additional acceptors for retinol in human serum. It was shown, that serum lipoproteins and to a lesser extent albumin protect red blood cells for the lytic effect of retinol. The amount of lipoproteins, serum, bovine serum albumin and lipoprotein-deficient serum needed to inhibit retinol (9.6 micrograms/ml) by 50% were 3, 58, 325, 1900 micrograms protein/ml respectively. Increasing their concentration in the incubation mixture results in a decrease in the rate of haemoglobin release and at last complete protection was achieved. Altogether, the results suggest that lipoproteins bind retinol and render it therefore non-haemolytic like retinol-binding protein. Furthermore, the latter indicates that lipoproteins act as carriers for vitamin A given parenterally, which one might expect since the lipoproteins are capable of transporting hydrophobic molecules.