BACKGROUND Enoxaparin (ENX) has been shown to reduce cerebral edema and improve neurologic recovery after traumatic brain injury (TBI), through blunting of cerebral leukocyte (LEU) recruitment. High mobility group box 1 (HMGB1) protein may induce inflammation through LEU activation. We hypothesized that ENX after TBI reduces LEU-mediated edema through blockade of HMGB1 signaling. METHODS Twenty-three CD1 mice underwent severe TBI by controlled cortical impact and were randomized to one of four groups receiving either monoclonal antibody against HMGB1 (MAb) or isotype (Iso) and either ENX (1 mg/kg) or normal saline (NS): NS + Iso (n = 5), NS + MAb (n = 6), ENX + Iso (n = 6), ENX + MAb (n = 6). ENX or NS was administered 2, 8, 14, 23 and 32 hours after TBI. MAb or Iso (25 μg) was administered 2 hours after TBI. At 48 hours, cerebral intravital microscopy served to visualize live LEU interacting with endothelium and microvascular fluorescein isothiocyanate–albumin leakage. The Neurological Severity Score (NSS) graded neurologic recovery; wet-to-dry ratios determined cerebral/lung edema. Analysis of variance with Bonferroni correction was used for statistical analyses. RESULTS ENX and MAb similarly reduced in vivo pial LEU rolling without demonstrating additive effect. In vivo albumin leakage was greatest in vehicle-treated animals but decreased by 25% with either MAb or ENX but by 50% when both were combined. Controlled cortical impact–induced cerebral wet-to-dry ratios were reduced by MAb or ENX without additive effect. Postinjury lung water was reduced by ENX but not by MAb. Neurologic recovery at 24 hours and 48 hours was similarly improved with ENX, MAb, or both treatments combined. CONCLUSION Mirroring ENX, HMGB1 signaling blockade reduces LEU recruitment, cerebrovascular permeability, and cerebral edema following TBI. ENX further reduced lung edema indicating a multifaceted effect beyond HMGB1 blockade. Further study is needed to determine how ENX may play a role in blunting HMGB1 signaling in brain injury patients.

BACKGROUND Severe traumatic brain injury (TBI) may increase the risk of venous thromboembolic complications; however, early prevention with heparinoids is often withheld for its anticoagulant effect. New evidence suggests low molecular weight heparin reduces cerebral edema and improves neurological recovery after stroke and TBI, through blunting of cerebral leukocyte (LEU) recruitment. It remains unknown if unfractionated heparin (UFH) similarly affects brain inflammation and neurological recovery post-TBI. We hypothesized that UFH after TBI reduces cerebral edema by reducing LEU-mediated inflammation and improves neurological recovery. METHODS CD1 male mice underwent either TBI by controlled cortical impact (CCI) or sham craniotomy. UFH (75 U/kg or 225 U/kg) or vehicle (VEH, 0.9% saline) was administered 2, 11, 20, 27, and 34 hours after TBI. At 48 hours, pial intravital microscopy through a craniotomy was used to visualize live brain LEUs interacting with endothelium and microvascular fluorescein isothiocyanate–albumin leakage. Neurologic function (Garcia Neurological Test, GNT) and body weight loss ratios were evaluated 24 and 48 hours after TBI. Cerebral and lung wet-to-dry ratios were evaluated post mortem. ANOVA with Bonferroni correction was used to determine significance (p < 0.05). RESULTS Compared to positive controls (CCI), both UFH doses reduced post-TBI in vivo LEU rolling on endothelium, concurrent cerebrovascular albumin leakage, and ipsilateral cerebral water content after TBI. Additionally, only low dose UFH (75 U/kg) improved GNT at both 24 and 48 hours after TBI. High dose UFH (225 U/kg) significantly increased body weight loss above sham at 48 hours. Differences in lung water content and blood pressure between groups were not significant. CONCLUSIONS UFH after TBI reduces LEU recruitment, microvascular permeability, and brain edema to injured brain. Lower UFH doses concurrently improve neurological recovery whereas higher UFH may worsen functional recovery. Further study is needed to determine if this is caused by increased bleeding from injured brain with higher UFH doses.