Reduced Cleavage of Von Willebrand Factor By ADAMTS13 Exacerbates Acute Kidney Injury Secondary to Traumatic Injury

Introduction: Increases in plasma von Willebrand Factor (vWF) antigen levels, accompanied by decreases in its respective metalloprotease, ADAMTS13, have been demonstrated following severe injury. We hypothesized that following traumatic injury, endothelial damage and activation would result in the release of high molecular weight multimeric (HMWM) vWF forms into circulation with a concominant decrease in ADAMTS13. We further hypothesized that the alterations in circulating levels and functions of these factors, following traumatic injury, promote an increased thrombogenic and inflammatory response, which exacerbates the risk of developing post traumatic acute kidney injury (AKI).

Methods: Plasma samples from a cohort of patients with trauma induced AKI, collected at 0-, 24-, and 72-hours after admission, were evaluated against plasma samples from trauma patients that were matched for injury characteristics, but were without AKI. VWF and ADAMTS13 activity and antigen levels were evaluated. Circulating vWF multimeric composition was determined by vertical agarose gel electrophoresis.

We further evaluated the effects of traumatic injury on ADAMTS13 and vWF by means of a pre-clinical model of trauma and hemorrhage, which is comprised of a liver laceration, cardiac puncture, and soft tissue injury. Following this polytrauma model, hepatic ADAMTS13 RNA expression was evaluated by qRT-PCR of total liver RNA; analyzed liver samples were taken immediately before, 24-, and 72-hours after injury. The impact of the polytrauma model on renal function was evaluated via changes in plasma cystatin C, while the effect on the renal microvasculature was evaluated by means of immunofluorescent staining of vWF and fibrinogen in kidney sections.

Results: VWF antigen was increased in trauma patients when compared to healthy controls upon admission (11.0 ± 3.72 ug/mL vs. 4.64 ± 0.91 ug/mL), persisting through 72-hours (13.11 ± 3.16 ug/mL). The percentage of HMWM vWF forms in trauma patient samples was elevated at all time points compared to pooled normal plasma (PNP) (27.9 ± 4.5% and 15.9 ± 0.8). Trauma patient ADAMTS13 activity was decreased at all time points (0.48 ± 0.14 IU/mL vs. 1.27 ± 0.26 IU/mL). AKI patients showed a 1.54 ± 0.48-fold increase in vWF antigen levels over the 72-hour period (p=0.016), while there was no change in the control trauma group. Those who developed AKI demonstrated a larger proportion of HMWM vWF at 72-hours than their non-AKI counterparts (32.9 ± 2.4% vs 28.8 ± 3.2%).

qRT-PCR of murine total liver RNA, following the polytrauma model, exhibited ADAMTS13 RNA expression levels that were 35% of normal at 24-hours and 60% of normal at 72 hours post-injury. A matched analysis of murine plasma cystatin C levels demonstrated a marked elevation 24-hours post polytrauma model (sham: 510ng/mL (435-561) vs trauma: 550 (479-701)). H&E staining of kidney sections, which were harvested following the polytrauma model, demonstrated generalized renal tubule dilation and denudation, suggestive of post-traumatic acute tubular necrosis. Immunofluorescent studies of kidney sections from the same mice exhibited 8-15µm microvascular plugs that were positive for fibrinogen with a vWF core; renal immunofluorescent studies of control mice demonstrated no microvascular depositions.

Conclusions: These data indicate that traumatic injury alters the circulating composition of ADAMTS13 and its target, vWF, shifting their equilibrium to one that promotes inflammation and thrombosis. In the immediate moments following injury, these mechanisms support life-saving hemostasis; however, as these changes extend into the following days, the early hemostatic benefit quickly shifts to a burden that may produce microvascular clot deposition, exacerbating pathologic states such as acute kidney injury.