Effect of neutropenia and granulocyte colony stimulating factor-induced neutrophilia on blood-brain barrier permeability and brain edema after traumatic brain injury in rats

Objective: Granulocyte colony stimulating factor (GCSF) has been used to in crease systemic absolute neutrophil count (ANC) in patients with severe tra umatic brain injury to reduce nosocomial infection risk. However, the effec t of increasing systemic ANC on the pathogenesis of experimental traumatic brain injury has not been studied. Thus, we evaluated the effect of systemi c ANC on blood-brain barrier (BBB) damage and brain edema after traumatic b rain injury in rats. Design: Experimental study. Setting: Research laboratory at the University of Pittsburgh, PA. Subjects: Forty-three adult male Sprague-Dawley rats. Interventions: Protocol I: rats were randomized to receive either vinblasti ne sulfate to reduce ANC, GCSF to increase ANC, or saline before controlled cortical impact (CCI) of moderate overall severity. Evans blue was used to assess BBB damage at 4-24 hrs after CGI. Protocol II: rats received GCSF o r saline before CCI. Brain edema was estimated at 24 hrs using (wet - dry) / wet weight method. Protocol III: rats received GCSF or saline before CCI. Brain neutrophil accumulation was estimated at 24 hrs using a myeloperoxid ase assay. Measurements and Main Results: Physiologic variables were controlled before CCI was maintained at normal in all animals before traumatic brain injury. No rats were anemic, hypoglycemic, or hypotensive before CCI. Protocol I: compared with control, systemic ANC decreased in vinblastine-treated rats a nd increased in GCSF-treated rats. BBB damage correlated with systemic ANC. Protocol II: mean systemic ANC before traumatic brain injury Increased 15- fold in rats given GCSF vs. control; however no difference in brain edema w as observed at 24 hrs after injury between groups. Protocol III: median sys temic ANC at the time of CCI was increased ten-fold in rats given GCSF vs. control. No difference in brain myeloperoxidase activity 24 hrs after CCI w as observed in rats treated with GCSF vs. control. Conclusions: Systemic ANC influences BBB damage after traumatic brain injur y produced by CGI. Because BBB damage and brain edema are discordant, mecha nisms other than BBB damage likely predominate in the pathogenesis of brain edema after contusion. The implications of increased BBB permeability with the administration of GCSF in our model remains to be determined. Increasi ng systemic ANG before CCI with GCSF administration does not increase postt raumatic brain neutrophil accumulation or brain edema after CCI in rats. Th e finding that neutrophil infiltration is not enhanced by systemic neutroph ilia suggests that the ability of GCSF-stimulated neutrophils to migrate in to injured tissue may be impaired, Further studies are needed to evaluate t he effects of GCSF administration on secondary injury and functional outcom e in experimental models of traumatic brain injury.