In vivo effects of hyperthermia on the functional and conformational characteristics of antithrombin.

BACKGROUND

High temperatures produce in vitro transitions of antithrombin to its inactive latent and polymeric forms. Accordingly, high body temperatures might contribute in vivo to conformational changes in antithrombin associated with increased thrombotic risk.

METHODS

We assessed the in vivo effects of different hyperthermic stimuli on antithrombin. We studied two mouse models of hyperthermia. (i) Febrile syndrome induced by turpentine. (ii) Heat stroke generated by exposure to 42 degrees C. Body temperatures were measured. Antigen, anti-factor Xa activity and conformational features of plasma antithrombin were studied. Furthermore, structural and ultrastructural features from livers were analyzed. Intracellular retention of serpins (antithrombin and alpha1-antitrypsin) was studied by western-blotting, immunohistochemistry, and immunogold-labeling-electron microscopy.

RESULTS

Hyperthermic stimuli caused a moderate deficiency of circulating antithrombin and a slight increase in its latent form. Moreover, hyperthermia caused intracellular retention of antithrombin into aggregates within the lumen of the endoplasmic reticulum of hepatocytes. This effect was similar for alpha1-antitrypsin.

CONCLUSIONS

Hyperthermia causes minor conformational changes on circulating antithrombin in vivo, although it has severe consequences for intracellular antithrombin and other hepatic serpins, inducing the intracellular retention of the nascent protein. These effects may contribute to the moderate plasma deficiency of antithrombin and the increased thrombotic risk detected in hyperthermic conditions.