EFFECT OF SIALIC-ACID ON GLYCATION-INDUCED FLUORESCENCE OF ALBUMIN

The aims of this study were to determine whether in vitro nonenzymatic glycation of proteins by sialic acid (sialylation) induces the genera tion of fluorescence, and whether the presence of this keto sugar may affect the generation of fluorescence induced by other sugars. Incubat ion of bovine serum albumin (BSA; 1.5 mM) with sugars (50 mM in 0.2 M phosphate buffer, pH 7.4, at 37 degrees C) resulted in a time-dependen t increase of formaldehyde release (moles/moles of protein). On the 17 th day of incubation, the value was 0.53+/-0.06, 0.78+/-0.15 and 1.23/-0.18 for sialic acid, fructose and glucose respectively, compared wi th 0.37+/-0.05 for BSA. The fluorescence intensity (arbitrary units/mg protein) was higher after 17 days of incubation with fructose (16.9+/ -1.8) than with glucose (12.7+/-1.3), while no significant increase wa s noted with sialic acid compared with BSA (3.8+/-0.4). Fluorescence i ntensity increase by incubation with glucose (50 mM) was significantly reduced by sialic acid (20 mM) after both 10 (P<0.001) and 14 (P<0.00 1) days of incubation, while inhibition was weaker after 14 (P<0.05) t han after 10 (P<0.001) days when fructose (50 mM) was used as the glyc ating agent. This indicates that sialic acid can be potentially used t o limit the damage from adverse glycation-induced processes.