Effects of alpha 1-acid glycoprotein on erythrocyte deformability and membrane stabilization

The effects of alpha(1)-acid glycoprotein (AGP) on human erythrocyte membrane were examined in vitro. Bovine and dog AGP, in addition to human AGP or asialo human AGP were used, and the collected data were compared with that for human serum albumin (HSA). A new technique developed by Kikuchi was used to investigate erythrocyte deformability. The addition of AGPs including human AGP facilitated the passage of human erythrocytes with an average diameter of 7.2 microm suspended in phosphate buffered saline (PBS) through a 5 microm wide microchannel; hemolysis was suppressed after the passage. The stabilizing effects of AGPs on membrane were evaluated. Human AGP prevented hemolysis induced by hypotonic phosphate buffer solution. The effects of human AGP on the oxidative changes in erythrocytes exposed to oxygen radicals were investigated. Human AGP protected erythrocytes from H(2)O(2) and prevented the oxidation of dihydrorhodamine 123 to rhodamine 123 from H(2)O(2). We propose that the antioxidant activity of human AGP is due to the binding of free radicals. In all studies, the effects of human AGP on erythrocytes might not be a function of the negative charge associated with sialyl residues, because the presence of N-acetylneuraminic acid had no effect. However, human AGP may promote microcirculation and antioxidant activity compared with HSA. No species differences in the physiological function of AGP were found. These results suggest that an increase in the AGP content of serum above the normal value found under pathological conditions facilitates the passage of erythrocytes through capillaries, stabilizes erythrocyte membranes and protects against oxidative stress, all of which are favorable for microcirculation.