Elevated plasma levels of fibrinogen are associated with the presence of cardiovascular disease, but it is controversial whether elevated fibrinogen causally imparts an increased risk, and as such is a true modifier of cardiovascular disease, or is merely associated with disease. By investigating a transgenic mouse model of hyperfibrinogenemia, we show that elevated plasma fibrinogen concentration
IntroductionNumerous epidemiological studies have documented the association of elevated plasma fibrinogen levels with cardiovascular disease. [1][2][3][4][5][6][7] Cross-sectional prospective studies imply that elevated plasma fibrinogen levels are an independent and predictive parameter for increased risk of coronary artery disease, stroke, and peripheral vascular disease. The magnitude of the increase in fibrinogen levels correlates with the presence and severity of peripheral arterial disease, the extent of myocardial necrosis in infarcted patients, and cerebrovascular accidents. The disease risk associated with hyperfibrinogenemia is disproportionally augmented in those individuals with the highest fibrinogen levels, indicating a threshold effect. Notwithstanding its recognized value as a marker for the presence of cardiovascular disease, it remains controversial whether an elevated fibrinogen level itself imparts an increased risk, and therefore represents a true modifier of vascular disease, or is merely associated with disease. Fibrinogen production in the liver is regulated by cytokines and is greatly enhanced in the acute phase response to infection and other inflammatory processes. [8][9][10][11] It is therefore possible that moderately elevated fibrinogen levels simply report a state of inflammation associated with vascular disease. On the other hand, augmented fibrinogen levels, per se, could alter the hemodynamic properties of blood or enhance concentration driven enzyme-substrate interactions between thrombin, fibrinogen, and platelets, and thus lead to increased intravascular fibrin deposition and thrombosis. These views are not mutually exclusive, as augmentation of fibrinogen levels secondary to an inflammatory challenge could nevertheless amplify or accelerate the disease process. Moreover, fibrinogen and fibrin degradation products might in turn enhance the inflammatory aspect of vascular lesions by regulating cytokine production and leukocyte-endothelial interactions. [12][13][14][15][16][17] Recently described genetically altered mice with chronically increased plasma fibrinogen levels in the absence of underlying inflammation provide a novel experimental tool to investigate the cause-effect relationship between hyperfibrinogenemia and vascular disease. 18 The mutant mouse strain (hereafter referred to as Hifib mice) was derived by pronuclear oocyte microinjection of the entire mouse fibrinogen locus, including all 3 fibrinogen chains as well as several kilobases of flanking sequence. The added transgenic fibrinogen allele is inherited in a Mendelian fashion, and the mice were reported to exhibit...