Nonenzymatically glycated serum albumin: interaction with galactose-specific liver lectins

The critical role of dimer formation in monosaccharides binding to human serum albumin

Monosaccharides are found to bind tightly to human serum albumin when a dimeric structure is formed in the binding pocket.

Evaluation of 99mTc-labeled modified serum albumin for tumor detection

Serum albumin (SA) modified and labeled with 131I-tyramine N-1'-desoxysorbitol (131I-TDS) has been shown to localize in tumors [Sinn et al., (1990) Nucl. Med. Biol. Part B 17, 819-827]. We prepared similar TDS complexes labeled with 99mTc and evaluated their potential for tumor imaging. Derivatization of SA with TDS was optimized using cyanuric chloride or 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDAC) as coupling agents. A high TDS loading yield of 38 mol/mol SA was obtained with the latter reagent. Modified SA (8 and 38 mol TDS/mol SA) were labeled with 99mTc via the stannous reduction method and injected i.v. into EMT-6 tumor bearing mice. 125I-TDS-SA (8 mol 125I-TDS/mol SA) revealed a high tumor uptake of 10% ID/g at 3 h post-injection. The 99mTc-labeled SA and TDS-SA complexes lacked tumor specificity, instead TDS loading of SA resulted in increased liver/spleen uptake, suggesting colloid formation. This study confirms the potential of modified SA for tumor imaging but highlights the importance of choice of radioisotope, as well as site of attachment of the radiolabel to the modified SA for optimal tumor localization.

Binding sites for short-term glycated albumin on peritoneal cells of the rat

The interaction of in vitro short-term glycated rat serum albumin with rat peritoneal cells (40% macrophages) was investigated. Using 125I-labeled albumins the following results were obtained. Glycated albumins showed a binding reaction at 4 degrees C, which appeared to reach equilibrium within 2 h. The concentration-dependent binding of glycated albumin showed saturation. Binding data evaluated for glycated albumin using the Sips equation are: average association constant Ko = 3.15 x 10(7) M-1 with a heterogeneity index of a = 0.8 and 1.12 x 10(4) binding sites per cell. Such binding sites were identified in 40% of the peritoneal cell preparations studied. Native albumins, maleylated albumin, chondroitinsulfates, polylysine, lysine, fructose, glucose and hexitol-lysine could not compete with radio-labeled glycated rat albumin for its binding site on peritoneal cells. Effective competitors were glycated human serum albumin, glycated polylysine and fructose-lysine. Although the contamination with minute amounts of advanced glycosylation end products (AGE) could not be excluded, short-term glycated albumin was found to be bound to membranes of peritoneal phagocytotic cells by fructose-lysine specific proteins, whose approximately defined molecular masses of 290 kDa are distinct from hitherto described binding proteins for AGE- and aldehyde-modified proteins or for the scavenger receptors.