Anti-high mobility group box 1 antibody suppresses local inflammatory reaction and facilitates olfactory nerve recovery following injury.

BACKGROUND: Refractory olfactory dysfunction is a common finding in head trauma due to olfactory nerve injury. Anti-inflammatory treatment using steroids is known to contribute to functional recovery of the central and peripheral nervous systems in injury models, while there is a concern that steroids can induce side effects. The present study examines if the inhibition of proinflammatory cytokine, high mobility group box 1 (HMGB1), can facilitate olfactory functional recovery following injury. METHODS: Olfactory nerve transection (NTx) was performed in OMP-tau-lacZ mice to establish injury models. We measured HMGB1 gene expression in the olfactory bulb using semi-quantitative polymerase chain reaction (PCR) assays and examined HMGB1 protein localization in the olfactory bulb using immunohistochemical staining. Anti-HMGB1 antibody was intraperitoneally injected immediately after the NTx and histological assessment of recovery within the olfactory bulb was performed at 5, 14, 42, and 100 days after the drug injection. X-gal staining labeled OMP in the degenerating and regenerating olfactory nerve fibers, and immunohistochemical staining detected the presence of reactive astrocytes and macrophages/microglia. Olfactory function was assessed using both an olfactory avoidance behavioral test and evoked potential recording. RESULTS: HMGB1 gene and protein were significantly expressed in the olfactory bulb 12 h after NTx. Anti-HMGB1 antibody-injected mice showed significantly smaller areas of injury-associated tissue, fewer astrocytes and macrophages/microglia and an increase in regenerating nerve fibers. Both an olfactory avoidance behavioral test and evoked potential recordings showed improved functional recovery in the anti-HMGB1 antibody-injected mice. CONCLUSIONS: These findings suggest that inhibition of HMGB1 could provide a new therapeutic strategy for the treatment of olfactory dysfunction following head injuries.

Electrical properties of cells from human olfactory epithelium.

OBJECTIVE: The electrical properties of olfactory cells (OCs) are typically examined using animals such as newts, mice, and frogs, with few studies on human OCs. This study investigated the electrical properties of human cells from olfactory epithelium (hCOEs) obtained from subjects of olfactory epithelium showing no clinical symptoms during endoscopic sinus surgery. METHODS: hCOEs were isolated by collagenase treatment for whole-cell patch clamp recording. The identity of the cells was confirmed by immunohistochemistry with an antibody against olfactory maker protein. Under the voltage clamp with the whole-cell recording configuration, the voltage-gated currents of isolated hCOEs were recorded when the membrane potential was depolarized from a holding potential of -100 mV in a stepwise manner between -90 mV and + 40 mV. RESULTS: Only one of 14 hCOE samples expressed a transient inward current at the depolarizing voltage step that was activated by depolarization beyond -40 mV and reached a peak at -30 mV. Delayed and sustained outward currents (444 ± 106 pA at + 40 mV pulse; n = 20) were suppressed by tetraethyl ammonium (n = 3), which is consistent with the properties of newt OCs. CONCLUSIONS: Most hCOEs did not exhibit the transient inward current observed in animal models. These findings provide insight into the physiological basis of the unique aspects of human olfactory signal transduction.

A Time Limit for Initiating Anti-Inflammatory Treatment for Improved Olfactory Function after Head Injury.

We previously reported that treatment with an anti-inflammatory drug, specifically a steroid, is effective in improving recovery during the acute phase of head injury. Clinically, however, patients with head injury usually become aware of their olfactory loss several weeks or months after the injury, which may be a critical factor in poor recovery from olfactory dysfunction. This raises an important question: When should steroid administration begin in order to achieve optimum improvement of olfactory dysfunction? The present study was designed to reveal the time limit for starting anti-inflammatory treatment for better improvement of post-traumatic olfactory dysfunction. Olfactory nerve transection (NTx) was performed in olfactory marker protein (OMP)-tau-lacZ mice and subcutaneous injections of dexamethasone sodium phosphate for 5 consecutive days was started at 7, 14, 28, and 42 days after the NTx (7-, 14-, 28-, and 42-day time-points). Histological assessment of olfactory nerve recovery in the olfactory bulb was made at 5, 14, and 42 days after the start of drug treatment. Olfactory function assessments using both an olfactory avoidance behavioral test and evoked potential testing also were performed. Animals treated at 7 days post-injury had less injury-associated tissue with fewer astrocytes and macrophages and better histological and functional nerve recovery, compared with control mice. However, those treated at 14, 28, or 42 days post-injury did not show significant histological or functional differences between saline control and treatment groups. These findings suggest that an anti-inflammatory treatment using steroids for traumatic olfactory dysfunction may be effective if started at least by 7 days, but may be ineffective at 14 days or later after head injury.

Tumor necrosis factor-α antagonist suppresses local inflammatory reaction and facilitates olfactory nerve recovery following injury.

OBJECTIVE: Olfactory dysfunction is a common finding in head trauma due to injury to the olfactory nerve. We previously reported that anti-inflammatory treatment with steroids improves recovery outcome in olfactory nerve injury models. Clinically, however, steroid administration is not recommended in the acute phase of head injury cases because of concerns regarding its side effects. Tumor necrosis factor (TNF-α) is known to play a key role in inflammatory response to injury. The present study examines if the inhibition of TNF-α can facilitate functional recovery in the olfactory system following injury. MATERIALS AND METHODS: Olfactory nerve transection (NTx) was performed in olfactory marker protein (OMP-tau-lacZ) mice to establish injury models. We measured TNF-α gene expression in the olfactory bulb using semi-quantitative and real time polymerase chain reaction (PCR) assays and found that they increase within hours after NTx injury. A TNF-α antagonist (etanercept) was intraperitoneally injected immediately after the NTx and histological assessment of recovery within the olfactory bulb was performed at 5-70 days. X-gal staining labeled OMP in the degenerating and regenerating olfactory nerve fibers, and immunohistochemical staining detected the presence of reactive astrocytes and macrophages/microglia. RESULTS: Etanercept-injected mice 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 recordings showed improved functional recovery in etanercept-injected animals. CONCLUSION: These findings suggest that inhibition of TNF-α could provide a new therapeutic strategy for the treatment of olfactory dysfunction following head injuries.

Suppression and recovery of voltage-gated currents after cocaine treatments of olfactory receptor cells.

OBJECTIVE: Cocaine (1-5% concentrations) is commonly used as a local anesthetic for the otorhinolaryngeal surgery of the nasal cavity. Recent reports indicate that some patients complain of olfactory deficits after surgery, and decreased olfaction is found in cocaine abusers. In spite of these reports, the effects of cocaine on the olfactory receptor cells are unknown. METHODS: Effect of cocaine was examined in olfactory receptor cells isolated from the newt. Under the voltage clamp with the whole-cell recording configuration, the voltage-gated currents were recorded when the membrane potential was depolarized from a holding potential of -100 mV in a step wise between -90 mV and +40 mV. RESULTS: When cocaine was applied by a puff pressure (5%) and the extracellular solution, the voltage-gated currents, including inward and outward components, were significantly reduced. The dose-suppression curves of cocaine for sodium and potassium currents could be fitted by the Hill equation. Half-blocking concentration of sodium and potassium currents were 43 µM and 557 µM; Hill coefficient was 1.1 and 0.9, respectively. CONCLUSION: This rapid and complete recovery from the suppression was confirmed even after the treatments with the high concentration cocaine. This fact implies that cocaine does not affect olfactory ability after locally high dose treatments of nasal cavity in surgical operation.

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

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.