OC 45.5 - The lethality in mice treated with intravenous polyphosphate is not due to thrombosis

Background: Polyphosphate (polyP), a procoagulant released from platelets, activates coagulation via the contact system. Intravenous (IV) polyP is lethal in mice, presumably because of overwhelming thrombosis. Previously, we showed that histidine-rich glycoprotein (HRG) binds polyP and attenuates its procoagulant effects.

Aims: To determine the mechanisms responsible for the lethality of mice treated with IV polyP and the impact of HRG on this process.

Methods: Wild-type or HRG-deficient (HRG-/-) mice were given synthetic or platelet-derived polyP in doses up to 100 mg/kg; saline was used as a control. The ECG was monitored, and the levels of troponin, creatine-kinase-MB isoform (CK-MB), and creatinine were measured before and after polyP injection. To assess the role of thrombosis, IV enoxaparin (10 mg/kg) or saline was given prior to the administration of 50 mg/kg polyP. Organs were harvested for histology and fibrin quantification. The cellular toxicity of polyP was assessed by culturing mouse cardiomyocytes and HEK293 cells with polyP in the absence or presence of HRG and measuring lactate dehydrogenase (LDH) levels.

Results: IV polyP was lethal in HRG-/- mice at 30 mg/kg and lethal in wild-type mice at doses of ≥50 mg/kg. IV polyP was associated with fibrin deposition in the lungs, and ECG changes, including heart block and ST-segment changes. Compared with saline-treated mice, IV polyP-induced dose-dependent increases in troponin, CK-MB, and creatinine levels by up to 4-fold in wild-type mice and even greater in HRG-/- mice. Enoxaparin attenuated polyP-induced fibrin deposition but did not reduce mortality or prevent the ECG or biomarker changes. In cell culture, polyP increased LDH levels in a dose- and time-dependent manner, which was attenuated with supplemental HRG and abolished when polyP was pretreated with alkaline phosphatase.

Conclusion(s): The lethality in mice treated with high doses of IV polyP more likely reflects end-organ injury than thrombosis, and HRG protects against such injury.