SummaryObesity and oral estrogens are independent risk factors for venous thrombosis, and their combined effect is stronger than the sum of the isolated factors. It was the objective of this study to investigate the interaction between obesity and estrogens at the level of venous thrombotic tendency, coagulation and inflammation in a mouse model.Female C57Bl/6J mice were fed a standard fat diet (SFD) or a high fat diet (HFD) to induce nutritional obesity.After 14 weeks, while maintaining their diet, mice were orally treated eight days with 1 µg ethinylestradiol or vehicle (n=25 per group), and subsequently subjected to an inferior caval vein (ICV) thrombosis model.The ICV thrombosis model resulted in an increased thrombus weight in vehicle-treated HFD mice (3.0 ± 0.7 mg) compared to vehicle-treated SFD mice (1.4 ± 0.4 mg; p=0.064). Surprisingly, estrogens reduced thrombus weight, which was significant for the HFD group (0.8 ± 0.5 mg; p=0.013).As compared to SFD feeding, HFD feeding significantly increased plasma levels of coagulation factor VIII, combined factor II/VII/X (p<0.001), and plasminogen activator inhibitor-1 (p=0.009), causing a prothrombotic shift of the coagulation profile. Estrogens had no significant effects on this profile with either diet,whereas serum amyloidA and hepatic inflammatory cytokines were minimally affected.The synergistic effect of obesity and estrogens on the venous thrombotic risk in women could not be translated into the mouse context. Short-term ethinylestradiol administration in a mouse ICV thrombosis model counteracts the prothrombotic phenotype associated with nutritionally induced obesity, despite a comparable activated plasma coagulation profile in estrogen-treated and untreated obese mice.
