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The Relative Clotting Activity of Glycated and Non-Glycated Forms of Fibrinogen

It is well known that proteins, including shortlived proteins such as fibrinogen (t,,, 5 days),' have higher levels of glycation in diabetic than in normal subjects. Lutjens et al. (1985)2 have reported that clotting function and thermal stability of fibrinogen are not affected by glycation. That work used trace amounts of glycated fibrinogen and measured clotting activity using radiochemical techniques. In the present study we re-examined this relationship using higher concentrations of fibrinogen and measuring clotting activity using a BBL fibrinometer. Fibrinogen was extracted from the blood of 11 diabetic and 18 non-diabetic subjects according to Denson (1972)3 by Al(OH), absorption of prothrombin and thrombin and washing of fibrinogen in ice cool buffers. This procedure preserves the fibrinogen and its carbohydrate moiety. The extracts were shown to be pure by electrophoresis. Samples of the extracts were analysed for clotting activity by enzymatic cleavage of two pairs of fibrinopeptides from fibrinogen to form a fibrin clot which was measured by a BBL fibrinometer. The individual results for the clotting activity of the fibrinogen were divided by the fibrinogen concentrations as measured by extinction (coefficient of 1.5) , to give a measure of clotting activity relative to the total fibrinogen concentration. Fibrinogen extracted from diabetic subjects had a mean clotting activity (SD) of 0.6(0.07) which was significantly higher (P<O.001) than that from the non-diabetic subjects, 0.47(0 -08). Commercial fibrinogen was glycated in vitro by incubation with (500 mmol/L) and without glucose at 37°C for 48 h to produce a 51:49% mixture and a 2% mixture, respectively (as measured by boronic acid gel chromatography). Glycated and non-glycated fibrinogen were separated, with 100% efficiency from the incubated glycated mixture using boronic acid gel chromatography, and the clotting activities were determined as shown in Table 1. Following the incubation at 37°C there was some loss of clotting activity by all fibrinogen solutions, but this was most pronounced for the non-glycated fibrinogen. These results suggest that the glycation of fibrinogen may enhance clotting activity or offer some protection against the loss of activity associated with incubation.