Benzodiazepine Augmented γ-Amino-Butyric Acid Signaling Increases Mortality From Pneumonia in Mice

Objectives: Benzodiazepines are used for treating anxiety, epilepsy, muscle spasm, alcohol withdrawal, palliation, insomnia, and sedation as they allosterically modulate -amino-butyric acid type A (GABA(A)) receptors. Despite widespread use, the importance and mechanism of their immune side-effects are poorly understood. Herein we sought to elucidate the impact and mechanism of benzodiazepine-induced susceptibility to infection at anxiolytic doses in mice. Design: Animal randomized controlled trial. Setting: Laboratory. Subjects: Adult female C57BL/6 and BALB/c mice. Interventions: The effect of a subsedative, anxiolytic dose of diazepam (2 mg kg(-1) intraperitoneal) was investigated in a murine Streptococcus pneumoniae pneumonia model. Measurement and Main Results: Mortality, bacterial and cytokine load, cell recruitment, and intracellular pH were measured. Diazepam treatment did not affect immune homeostasis in the lung. However, diazepam increased mortality and bacterial load from S. pneumoniae pneumonia. The increases in mortality and bacterial load were reversed by a GABA(A) antagonist, bicuculline, indicating dependence on GABA(A) receptor signaling. While cell recruitment was unaltered by diazepam, the cytokine response to infection was affected, suggesting that local responses to the pathogen were perturbed. Macrophage and monocytes expressed benzodiazepine sensitive (1-2) GABA(A) receptors. Interestingly macrophage GABA(A) receptor expression was regulated by bacterial toll-like receptor agonists and cytokines indicating an endogenous role in the immune response. Functionally diazepam appeared to counteract the endogenous down-regulation of GABA(A) signaling during infection. Consistent with augmented GABA(A) signaling, diazepam provoked intracellular acidosis in macrophage, leading to impaired cytokine production, bacterial phagocytosis and killing. In contrast, selective benzodiazepines that do not target the 1 GABA(A) subunit did not affect macrophage function ex vivo or increase susceptibility to pneumonia in vivo. Conclusions: Our data highlight the regulation of macrophage function by GABA(A) receptor signaling and the potential harm of benzodiazepine exposure during pneumonia. Therapeutically, selective drugs may improve the safety profile of benzodiazepines.