Weak and non-independent association between plasma TAFI antigen levels and the insulin resistance syndrome

Increased plasma thrombin-activatable fibrinolysis inhibitor (TAFI) levels were recently shown to be a part of the insulin resistance syndrome. We investigated the relationship between plasma TAR antigen levels and insulin resistance markers and compared these results with those obtained for PAI-1 and fibrinogen which are known to be closely related to insulin resistance syndrome and fat mass, respectively. Eighty-nine obese females had 1.3-, 1.2-, and 3-fold higher circulating TAFI. fibrinogen and PAI-1, respectively, compared with 64 lean females. Univariate analysis showed that the significance level for association between TAFI or fibrinogen concentrations and insulin resistance markers was lower than the significance level for association between PAI-1 and insulin resistance markers. Nevertheless. TAR fibrinogen, and PAI-1 plasma levels were significantly associated to each other. In linear stepwise ascendant analysis, insulin resistance markers accounted for 50% of the interindividual variability of plasma PAI-1 and only for 10% of plasma TAFI and 13% of fibrinogen variability. The contribution of insulin resistance markers to plasma TAFI antigen levels variability disappeared when PAI-1 or fibrinogen was entered in the statistical model. TAR mRNA was detected in the liver but not in adipose tissue and endothelial cells. No TAFI mRNA was detected in normal or atherosclerotic vessels either. These results suggest that elevated TAR antigen levels found in obese subjects are not independently associated with the metabolic markers of the insulin resistance syndrome. Increased plasma TAFI antigen levels in obesity might reflect a specific pathway of regulation at the liver level.