Angiotensin Receptor Type 1 Inhibition in Lymphopenia and in Neutropenia After Traumatic Brain Injury In Mice: a Randomized Controlled Study (ATLANTIS)

Abstract Background: Cerebral inflammation with invasion of neutrophils and lymphocytes is an important factor in the process of secondary brain damage expansion after traumatic brain injury (TBI). Depletion of neutrophils in mice has been shown to reduce neurologic impairment after TBI. The intrinsic cerebral renin-angiotensin system is an important mediator of cerebral inflammation, as inhibition of the angiotensin II receptor type 1 (AT1) with candesartan improves neurologic recovery, and reduces secondary brain damage and cerebral neutrophil invasion after TBI. The present study was therefore designed to determine the role of immune cells in AT1 inhibition-mediated neuroprotection after TBI. Methods: In study A we assessed the effect of neutrophil depletion in mice after TBI. In study B we investigated the impact of RAG1 deficiency (RAG1-/-; mice without mature B- and T-lymphocytes) after TBI. In study C we investigated the role of neutrophils in candesartan mediated protection after TBI in wild-type mice with and without neutrophil depletion. In study D we examined the role of lymphocytes in AT1 inhibition mediated neuroprotection after TBI in RAG1-/-.Results: Neutropenic and RAG1-/- mice showed reduced brain damage compared to control groups. In control antibody treated wild type mice AT1 inhibition reduced lesion volumes and inflammation compared to vehicle, while in neutropenic mice, candesartan had no effect. In RAG1-/- mice AT1 inhibition resulted in reduction of brain damage and neuroinflammation compared to vehicle group. Conclusion: The present results demonstrate, that reduction of neutrophils and of lymphocytes as well as AT1 inhibition in wild type and RAG1-/- mice reduce brain damage and inflammation after TBI. However, AT1 inhibition was neuroprotective in RAG1-/- mice, but not in neutropenic mice. Therefore, the results indicate that AT1 inhibition mediated neuroprotection may be exerted by anti-inflammatory effects on neutrophils, with a subsequent reduction of neutrophil invasion.