Glycation and Inactivation of Aspartate Aminotransferase in Diabetic Rat Tissues.

Abstract

SummaryGlycated cytosolic aspartate aminotransferase was detected in the liver and kidney of streptozotocin diabetic rats using a boronate affinity column for adjacent cis-hydroxyl groups and an immunoblotting technique. The enzymatic activity and amount of immunoreactive sub stance were determined in the liver, kidney, and erythrocytes of diabetic and control rats. The ratio of enzymatic activity to the amount of enzyme was lower in diabetic rat tissue than in that in the control rats. It has been suggested that there is an inactive aspartate aminotransferase molecule in the tissues of diabetic rats. We therefore suggest that the cytosolic aspartate aminotransferase was inactivated in the diabetic rat tissues by a glycation reaction, accompanied by an impairment in glucose utilization. Key Words cytosolic aspartate aminotransferase (CAST), inactivation of cAST, glycation of cAST, diabetes, streptozotocin (stz) Non-enzymatic glucosylation (glycation) was first described by Maillard (1) who observed browning of amino acids when they were heated with sugars. The first protein demonstrated to be glycated in vivo was hemoglobin (2, 3). Levels of glycohemoglobin (HbAlc) are now used as an important marker in diabetics. Many other plasma and structural proteins have been shown to be glycated in vivo with increases in diabetes, and in some cases such glycated proteins are known to impair their function (4, 5). Accumulation of so called advanced glycation end-product is thought to contribute to the pathology of diabetes and aging (6).We (7,8) have studied the effects of various carbohydrates on the glycation of cytosolic aspartate aminotransferase (cAST) [EC 2.6.1.1] in an in vitro system. We found that fructose was very reactive with cAST, and that the enzymatic activity was decreased by the glycation.In this study, we detected a glycated cAST in the liver and kidney of streptozotocin (stz) diabetic rats, and its enzymatic and antigenic activities were examined.

Abundance of Immunologically Active Alanine Aminotransferase in Sera of Liver Cirrhosis and Hepatocellular Carcinoma Patients

“…At the obtained optimal cutoff values, the diagnostic sensitivity and specificity of the ALT immunoassay method were 100% and 90.0%, respectively, for the HCC group, and 86.5% and 92.9% for the LC group; however, the P values for the ALT enzyme activities in the HCC and LC groups were 0.54 and 0.20, respectively, suggesting no ability of the enzymatic activity assay to discriminate patients with these chronic liver diseases from the control group. This result is consistent with the results of previously reported studies (8 ).…”

“…Recently, several reports described high IgA concentrations in serum and a high incidence of IgA nephropathy in LC patients and indicated that the amount of aspartate aminotransferaseIgA complexes increased as liver disease progressed (12,13 ). Other modifications of serum ALT, such as glycation or fragmentation by proteolysis, could inhibit the interaction of ALT with a cofactor or substrate or could convert the functional dimeric protein to a monomeric form (8,14 ). Sera from healthy individuals and patients have been reported to contain considerably more immunologically active aspartate aminotransferase than the catalytically active protein (15 ).…”

Altered Kidney Morphology and Enzymes in Streptozotocin Induced Diabetic Rats

“…The increase in the levels of AST and ALT in diabetic rats after 1-3 weeks treatment was also reported by many other workers (Fadillioglu et al; Sivajothi et al; Al-Shamsi et al; McAnuffHarding et al; Ohaeri et al). Okada et al (1997) reported that AST activity was lower than the amount of enzyme in diabetic rat tissues. It is suggested that this may be due to the inactivation of cytosolic AST in the diabetic rat tissues by a glycation reaction, accompanied by impairment in glucose utilization in STZ induced diabetes.…”

Anti-crosslinking properties of carnosine: Significance of histidine

“…We previously showed that carnosine protects against glycation (Seidler, 2000) and inactivation of aspartate aminotransferase, a dimeric, pyridoxal 5-phosphate-dependent protein that is known to be glycated in vivo (Okada et al, 1997). We used this target protein in the present study to examine the anticrosslinking properties of carnosine and its components and the consequence of select modification of specific functional groups.…”