EFFECT OF ADVANCED GLYCATION END PRODUCT-MODIFIED ALBUMIN ON TISSUE FACTOR EXPRESSION BY MONOCYTES - ROLE OF OXIDANT STRESS AND PROTEIN-TYROSINE KINASE ACTIVATION

Diabetes is associated with a hypercoagulable state that contributes t o macrovascular complications, including cardiovascular events. The gl ycation reaction, a consequence of chronic hyperglycemia, has also bee n implicated in the pathogenesis of diabetic complications. Glycated p roteins have receptors on monocytes and generate reactive oxygen speci es that can regulate the expression of a number of genes. As abnormal monocyte expression of tissue factor (TF), the main initiator of the c oagulation cascade, is responsible for thrombosis in a number of clini cal settings, we studied the effect of glycated albumin on monocyte TF expression. Mononuclear cells were incubated with glycated albumin fo r 24 hours, and monocyte TF activity was measured with a plasma recalc ification time assay; TF antigen was measured by ELISA and TF mRNA by RT-PCR. Glycated albumin induced blood monocyte expression of the proc oagulant protein TF at the mRNA level. Oxidative stress appeared to be involved in this effect, as the antioxidant N-acetylcysteine diminish ed TF mRNA accumulation in stimulated monocytes. Hydroxyl radicals, wh ich may be generated inside cells from H2O2 via the Fenton reaction, a lso appeared to be involved in this effect, as hydroxyl radical scaven gers downregulated TF activity and antigen levels (but not TF mRNA). F inally, the involvement of activated protein tyrosine kinase in the tr ansmission of the signal from the membrane to the nucleus was suggeste d by the inhibitory effect of herbimycin A. These results point to a n ew mechanism for the hypercoagulability often described in diabetic pa tients and suggest that antioxidants or protein tyrosine kinase inhibi tors might be of therapeutic value in this setting.