Beta blockade in TBI: Dose-dependent reductions in BBB leukocyte mobilization and permeability in vivo.

BACKGROUND: Traumatic brain injury (TBI) is accompanied by a hyperadrenergic catecholamine state that can cause penumbral neuroinflammation. Prospective human studies demonstrate improved TBI survival with beta blockade (bb), although mechanisms remain unclear. We hypothesized that deranged post-TBI penumbral blood brain barrier (BBB) leukocyte mobilization and permeability are improved by bb.
METHODS: CD1 male mice (n = 64) were randomly assigned to severe TBI-controlled cortical impact: 6 m/s velocity, 1 mm depth, 3 mm diameter-or sham craniotomy, and IP injection of either saline or propranolol (1, 2, or 4 mg/kg) every 12 hours for 2 days. At 48 hours, in vivo pial intravital microscopy visualized live endothelial-leukocyte (LEU) interactions and BBB microvascular leakage. Twice daily clinical recovery was assessed by regaining of lost body weight and the Garcia Neurological Test (motor, sensory, reflex, balance assessments). Brain edema was determined by hemispheric wet-to-dry ratios.
RESULTS: Propranolol after TBI reduced both in vivo LEU rolling and BBB permeability in a dose-dependent fashion compared with no treatment (p < 0.001). Propranolol reduced cerebral edema (p < 0.001) and hastened recovery of lost body weight at 48 hours (p < 0.01). Compared with no treatment (14.9 ± 0.2), 24-hour Garcia Neurologic Test scores were improved with 2 (15.8 ± 0.2, p = 0.02) and 4 (16.1 ± 0.1, p = 0.001) but not with 1 mg/kg propranolol.
CONCLUSION: Propranolol administration reduces post-TBI LEU mobilization and microvascular permeability in the murine penumbral neurovasculature and leads to reduced cerebral edema. This is associated with hastened recovery of post-TBI weight loss and neurologic function with bb treatment. Dose-dependent effects frame a mechanistic relationship between bb and improved human outcomes after TBI.