Feature Articles

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

Sanders, Robert D. BSc, MBBS, PhD, FRCA^1,2,3; Godlee, Alexandra MSc¹; Fujimori, Toshifumi BSc¹; Goulding, John PhD¹; Xin, Gang PhD¹; Salek-Ardakani, Samira PhD¹; Snelgrove, Robert J. PhD¹; Ma, Daqing MD, PhD²; Maze, Mervyn FRCA, FRCP, FMedSci^2,4; Hussell, Tracy PhD¹

Author Information

¹Department of Leukocyte Biology, Imperial College, London, UK.

²Department of Anaesthetics, Intensive Care & Pain Medicine, Imperial College, London, London, UK.

³Magill Department of Anaesthetics, Intensive Care & Pain Medicine, Chelsea & Westminster Hospital, London, UK.

⁴Department of Anesthesia & Perioperative Care, University of California, San Francisco, CA.

*See also p. 1807.

Current address for John Goulding: La Jolla Institute for Allergy and Immunology, San Diego, CA 92037.

Dr. Sanders developed the hypothesis with Drs. Maze and Hussell. Drs. Sanders, Godlee, Fujimori, Goulding, Xin, Salek-Ardakani, Snelgrove, Ma, Maze, and Hussell designed and/or conducted the animal experiments. Dr. Sanders wrote the manuscript with input from all authors.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website (http://journals.lww.com/ccmjournal).

This work was supported, in part, by grant G0802353 to Dr. Sanders, grant G0802752 to Dr. Hussell, and grant G0802392 to Dr. Ma from the Medical Research Council, Swindon, United Kingdom, and grant 095707/Z/11/Z to Dr. Sanders from the Wellcome Trust. Dr. Sanders has received an honorarium for speaking on behalf of Hospira about immune effects of sedatives at the Canadian Society of Anesthesiology meeting. Hospira had no input into the design of the talk or this manuscript. There is no on-going relationship. Prof. Mervyn Maze has acted as a consultant for Hospira and Orion on the development of dexmedetomidine and received research funding from these organizations. These companies had no role in the work in this manuscript. Neurosearch supplied NS11394 at no cost.

Drs. Snelgrove and Ma received grant support from Wellcome Trust. Dr. Maze received grant support from MRC and the National Institutes of Health, receives royalties from Xenon Neuroprotection, and has patents with Dexmeditomidine (Stanford University).. Dr. Godlee received funding support from Wellcome Trust. Dr. Hussell received grant support from the Medical Research Council (Clinical Fellowship to Dr. Sanders). Dr. Fujimori is employed by the Imperial College London. Dr. Sanders received grant support, consulted for, and received honoraria from Hospira. The remaining authors have disclosed that they do not have any potential conflicts of interest.

For information regarding this article, E-mail: [email protected]

Critical Care Medicine 41(7):p 1627-1636, July 2013. | DOI: 10.1097/CCM.0b013e31827c0c8d

Abstract

Objectives:

Benzodiazepines are used for treating anxiety, epilepsy, muscle spasm, alcohol withdrawal, palliation, insomnia, and sedation as they allosterically modulate γ-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 (α1-γ2) 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 α1 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.