Elsevier

Neuroscience Research

Volume 76, Issue 3, July 2013, Pages 125-132
Neuroscience Research

Blockade of interleukin-6 receptor suppresses inflammatory reaction and facilitates functional recovery following olfactory system injury

https://doi.org/10.1016/j.neures.2013.03.015Get rights and content

Highlights

  • Anti-IL-6R antibody decreased astrocytes and macrophages in damaged olfactory bulbs.

  • Anti-IL-6R antibody contributes to olfactory nerve regeneration morphologically.

  • Anti-IL-6R antibody contributes to functional recovery of the olfactory system.

  • Blockade of IL-6R could be a new treatment for traumatic olfactory dysfunction.

Abstract

We previously reported that anti-inflammatory treatment with steroids improves recovery outcome in an olfactory nerve injury model. Clinically, however, steroid administration is not recommended in the acute phase of head injury because of concerns regarding side effects and no evidence of its efficacy. Recently, it has been reported that interleukin-6 (IL-6) plays an important role in the inflammatory reaction. The present study investigates if anti-IL-6 receptor (IL-6R) antibody can facilitate functional recovery in the olfactory system following injury. Rat anti-mouse IL-6R antibody (MR16-1) was intraperitoneally injected to severe olfactory nerve injury model mice immediately after the nerve transection (NTx). Histological assessment of recovery within the olfactory bulb was made at 5–70 days. X-gal staining labeled the degenerating and regenerating olfactory nerve fibers and immunohistochemical staining detected the presence of reactive astrocytes and macrophages/microglia. MR16-1-injected animals showed significantly smaller areas of injury-associated tissue, fewer astrocytes and macrophages/microglia, and an increase in regenerating nerve fibers. Olfactory function assessments using both an olfactory avoidance behavioral test and evoked potential testing showed improved functional recovery in MR16-1-injected mice. These findings suggest that blockade of IL-6R could provide a new therapeutic strategy for the treatment of olfactory dysfunction following head injuries.

Introduction

Olfactory dysfunction is relatively common following head trauma. Early estimates of the incidence of posttraumatic olfactory dysfunction based on 32 clinical reports average around 8% (Hendriks, 1988). Recently, new reports suggest the incidence is higher averaging 11–22% (De Kruijk et al., 2003, Haxel et al., 2008, Sigurdardottir et al., 2010). Since loss of olfactory function lowers patients’ quality of life and can be life threatening due to the inability to detect hazardous events such as fire, gas leak, and spoiled food intake (Miwa et al., 2001, Santos et al., 2004), therapeutic management of patients aimed at improving olfactory dysfunction is an important clinical objective.

Head trauma can cause olfactory dysfunction by overextension, distortion and tearing of the olfactory nerves and contusions of the olfactory bulbs and orbitofrontal regions of the brain (Costanzo et al., 2012). Although the olfactory system has a remarkable capacity for neural regeneration and recovery following injury, olfactory function does not recover in many cases of severe head injury. The prognosis for recovery from olfactory dysfunction after head trauma is only 10–38% (Sumner, 1964, Zusho, 1982, Costanzo and Becker, 1986, Jimenez et al., 1997, London et al., 2008), while that caused by inflammatory diseases as chronic rhinosinusitis and allergic rhinitis are reported to have a relatively better prognosis, with recovery rates of up to 68–86% (Delank and Stoll, 1998, Kobayashi et al., 2005, Miwa et al., 2005). We previously demonstrated using olfactory nerve injury model in mice that recovery in the olfactory system depends on the severity of the damage. We found that anti-inflammatory treatment with steroids during the acute phase of injury is effective in suppressing the inflammatory reaction and local glial scar formation and improves recovery outcome after olfactory nerve transection (NTx) (Kobayashi and Costanzo, 2009). In clinical practice, however, steroids are not typically used for the treatment of head injury patients since several studies reported that steroids do not have a significant efficacy on morbidity and mortality in patients with severe head injury and there are concerns that steroids may cause serious side effects such as hypertension, hyperglycemia, infection, bone necrosis and psychosis (Cooper et al., 1979, Braakman et al., 1983, Dearden et al., 1986).

Interleukin-6 (IL-6) has proven to play an important role in regulating the inflammatory reaction and the anti-IL-6 receptor (IL-6R) antibody has been reported to be effective inhibitor of the inflammatory reaction by preventing IL-6 from combining with the IL-6 receptor (Taga and Kishimoto, 1997, Rose-John et al., 2006). Recently anti-human IL-6R antibody (tocilizumab) has been used instead of steroids for the treatment of refractory inflammatory diseases such as rheumatoid arthritis, Castleman's disease and juvenile idiopathic arthritis (Nishimoto et al., 2000, Nishimoto et al., 2004, Yokota et al., 2005). For the central nervous system, a recent study reported that administration of anti-IL-6R antibody suppresses glial scar formation and ameliorates functional recovery of experimentally injured spinal cord in mice (Okada et al., 2004). The present study was designed to investigate if therapeutic intervention using anti-IL-6R antibody is effective on recovery outcomes in olfactory system following injury in mice. In this study, we used histological techniques to examine recovery outcome by following the amount of injury-associated tissue (glial scar), reactive astrocytes (GFAP) and macrophages/microglia (CD68) and the degree of degeneration and regeneration of olfactory nerve fibers. We also administered an olfactory function test using avoidance conditioning behavior to odorants and electrophysiological recording of field potential responses to electrical stimulation of the olfactory mucosa to determine if morphological recovery would parallel functional recovery in the olfactory system following therapeutic intervention.

Section snippets

Experimental animals

This study was performed using a transgenic strain of mice (OMP-tau-lacZ mice) obtained from the Jackson Laboratory (Bar Harbor, ME, USA). This strain is derived from C57BL/6 mice. In OMP-tau-lacZ mice, the gene sequence encoding the olfactory marker protein (OMP) has been replaced with a tau-lacZ reporter gene (Mombaerts et al., 1996). The OMP is expressed in all mature olfactory neurons (Farbman and Margolis, 1980) and the replacement with tau-lacZ reporter gene allows for the visualization

Effects of anti-IL-6R antibody injection

To determine if anti-IL-6R antibody treatment can facilitate recovery of the olfactory nerves after NTx injury, MR16-1 was injected intraperitoneally in the severe injury model mice. Fig. 2 gives results of MR16-1 treatment compared to effects of control IgG. In X-gal stained tissues, blue glomeruli on the NTx side decreased at Day 5 and 14 after the NTx, indicating that degeneration of the olfactory nerves at the nerve lesion continued until Day 14 (Fig. 2C). However, the reappearance of blue

Discussion

Olfactory receptor cells located in the olfactory epithelium are bipolar cells and their axons are connected to secondary neurons with synapse formation in the glomeruli on the olfactory bulb. Previous studies reported that olfactory bulbectomy or axotomy induced apoptosis in olfactory receptor neurons, resulting in their degeneration (Nan et al., 2001, Miwa et al., 2002). These degenerative neurons release chemical signals that initiate programmed cell death. Regeneration of olfactory receptor

Acknowledgments

We would like to thank Chugai Pharmaceutical Co. Ltd. (Tokyo, Japan) and Dr. Tadamitsu Kishimoto (Immunology Frontier Research Center, Osaka University, Japan) for providing MR16-1, and Dr. Richard M. Costanzo (Virginia Commonwealth University School of Medicine, USA) for reading the manuscript and giving invaluable comments. This study was supported by the Mie University Medical Research Award for Young Investigators.

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    These authors contributed equally to this work.

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