Recent studies have raised fears that anticoagulant therapy might dampen the protective role of immunothrombosis and, thus, might worsen infectious diseases. Using a rat model of bloodstream infection with MRSA, we found that treatment with rTM neither increased bacterial burden nor worsened overall survival if rTM was used after the infection. Instead, rTM treatment alleviated oxidative stress, as evidenced by the decrease in the level of oxidized glutathione.
Bacterial passage from one compartment to another (e.g., from the intravascular space to the extravascular space) was facilitated by rTM treatment in our study. This finding might not be specific to rTM but common to various anticoagulants, including hirudin (8) and heparin (data not shown). Thus, we cannot completely deny the potential risk of bacterial dissemination by anticoagulant therapy. However, the increase of bacteria in the extravascular space seemed to be accompanied by a decrease of bacteria in the intravascular space, and so the bacterial burden in the whole organ was little-affected by rTM treatment. Considering that rTM did not worsen the survival rate of MRSA-infected rats if used after the infection, rTM treatment might not dampen the protective role of immunothrombosis.
Metabolomics analysis revealed that the increase in the level of oxidized glutathione in response to MRSA infection was alleviated by rTM administration 6 h after MRSA infection. Glutathione plays a major part in cellular defenses against oxidative stress (17). In exchange for the reduction of target proteins, glutathione (also known as reduced glutathione or GSH) is converted to glutathione disulfide (also known as oxidized glutathione or GSSG). The GSSG:GSH ratio is thought to be a marker of cellular toxicity and is associated with mortality in septic-shock patients (18). In the present study, the GSSG:GSH ratio was also increased in response to MRSA infection, and was decreased by rTM administration 6 h after MRSA infection (data not shown). These findings suggest that rTM alleviates oxidative stress, possibly through the maintenance of vascular patency or its intrinsic antioxidant properties (19).
The timing of anticoagulation might also be controversial. Anticoagulant drugs have been administered before infection in studies for immunothrombosis (8, 11) whereas rTM has been administered after infection onset in clinical settings (20). We administered rTM immediately before or 6 h after MRSA infection, and found that rTM administration 6 h after MRSA infection might be better in terms of improved survival. Although the best timing for clinical anticoagulation was not specified in our study, signs of organ dysfunction in addition to evident DIC might be important. Further studies are needed to gain insight into the appropriate timing for anticoagulation during sepsis treatment.
Our study had several limitations. First, it is not clear whether our findings in rats can be transferred to humans. Although studies have shown that rTM is effective in mitigating DIC in rats and humans (20, 21), activated protein C-dependent actions might not be fully expected in rats, unlike humans (22). Second, it is not clear whether our findings are applicable to infection models other than bloodstream infection with MRSA. Third, observation beyond 18 h was not possible in this study because rats became seriously ill at about this point. Fourth, the number of rats in each group was low due in part to the complexity of experiments using rats with jugular-vein catheterization and live bacteria. Fifth, erroneous inferences may have occurred when multiple comparisons were conducted simultaneously in metabolomics analysis. Further studies are necessary to confirm the findings of our study.