Albumin and other serum and plasma proteins may be nonenzymatically glycosylated in vitro and in vivo. Chromatographie and colorimetrie measurement of these nonenzymatically glycosylated proteins shows that levels are approximately two to three times higher in diabetic than nondiabetic subjects. In diabetic patients levels appear to reflect glycemia in the preceding several days and correlate with other established parameters of glycemia such as fasting serum glucose, mean of several capillary blood glucose measurements, and glycosylated hemoglobin. Because serum and plasma proteins have shorter half-lives than hemoglobin, nonenzymatically glycosylated proteins are altered more rapidly than glycosylated hemoglobin in response to prolonged decreases or increases in blood glucose levels.
Acetylsalicylic acid significantly inhibits in vitro glycosylation of albumin and other serum proteins incubated for up to 7 days in glucose. It is not known whether such inhibition occurs in vivo.
Glycosylation of albumin appears to reduce its solubility, and glycosylation of low-density lipoprotein may increase its catabolism. Whether nonenzymatic glycosylation of other serum proteins alters their functions or may contribute to some of the long-term complications of diabetes is unknown at present.