Prevention of venous thrombotic events in brain injury: review of current practices

A Systematic Review and Meta-Analysis on the Therapeutic Efficacy of Heparin and Low Molecular Weight Heparins in Animal Studies of Traumatic Brain Injury

The identification of effective pharmacotherapies for traumatic brain injury (TBI) remains a major challenge. Treatment with heparin and its derivatives is associated with neuroprotective effects after experimental TBI; however, the optimal dosage and method of administration, modes of action, and effects on hemorrhage remain unclear. Therefore, this review aimed to systematically evaluate, analyze, and summarize the available literature on the use of heparin and low molecular weight heparins (LMWHs) as treatment options for experimental TBI. We searched two online databases (PubMed and ISI Web of Science) to identify relevant studies. Data pertaining to TBI paradigm, animal subjects, drug administration, and all pathological and behavior outcomes were extracted. Eleven studies met our pre-specified inclusion criteria, and for outcomes with sufficient numbers, data from seven publications were analyzed in a weighted mean difference meta-analysis using a random-effects model. Study quality and risk of bias were also determined. Meta-analysis revealed that heparin and its derivatives decreased brain edema, leukocyte rolling, and vascular permeability, and improved neurological function. Further, treatment did not aggravate hemorrhage. These findings must be interpreted with caution, however, because they were determined from a limited number of studies with substantial heterogeneity. Also, overall study quality was low based on absences of data reporting, and potential publication bias was identified. Importantly, we found that there are insufficient data to evaluate the variables we had hoped to investigate. The beneficial effects of heparin and LMWHs, however, suggest that further pre-clinical studies are warranted.

Cerebral Edema and Neurological Recovery after Traumatic Brain Injury Are Worsened if Accompanied by a Concomitant Long Bone Fracture

Progression of severe traumatic brain injury (TBI) is associated with worsening cerebral inflammation, but it is unknown how a concomitant bone fracture (FX) affects this progression. Enoxaparin (ENX), a low molecular weight heparin often used for venous thromboembolic prophylaxis, decreases penumbral leukocyte (LEU) mobilization in isolated TBI and improves neurological recovery. We investigated if TBI accompanied by an FX worsens LEU-mediated cerebral inflammation and if ENX alters this process. CD1 male mice underwent controlled cortical impact (CCI) or sham craniotomy with or without an open tibial FX, and received either ENX (1 mg/kg, three times/day) or saline for 2 days following injury. Randomization defined four groups (Sham, CCI, CCI+FX, CCI+FX+ENX, n = 10/group). Two days after CCI, neurological recovery was assessed with the Garcia Neurological Test (GNT); intravital microscopy (LEU rolling and adhesion, microvascular leakage) and blood hemoglobin levels were also evaluated. Penumbral cerebral neutrophil sequestration (Ly-6G immunohistochemistry [IHC]) were evaluated post-mortem. In vivo LEU rolling was greater in CCI+FX (45.2 ± 4.8 LEUs/100 μm/min) than in CCI alone (26.5 ± 3.1, p = 0.007), and was suppressed by ENX (23.2 ± 5.5, p = 0.003 vs. CCI + FX). Neurovascular permeability was higher in CCI+FX (71.1 ± 2.9%) than CCI alone (42.5 ± 2.3, p < 0.001). GNT scores were lower in CCI+FX (15.2 ± 0.2) than in CCI alone (16.3 ± 0.3, p < 0.001). Hemoglobin was lowest in the CCI+FX+ENX group, lower than in Sham or CCI. IHC demonstrated greatest polymorphonuclear neutrophil (PMN) invasion in CCI+FX in uninjured cerebral territories. A concomitant long bone FX worsens TBI-induced cerebral LEU mobilization, microvascular leakage, and cerebral edema, and impairs neurological recovery at 48 h. ENX suppresses this progression but may increase bleeding.

Unfractionated heparin after TBI reduces in vivo cerebrovascular inflammation, brain edema and accelerates cognitive recovery

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.