Chronic dexamethasone treatment potentiates insult to olfactory receptor cells produced by 3-methylindole

The influence of head injury on olfactory and gustatory function

Head injury, particularly that resulting in brain injury, is a significant public health concern. For example, annual incidence rates of traumatic brain injury, a common consequence of head injury, range from 54 to 60 million people worldwide, including 2.2-3.6 million people whose trauma is moderate to severe. Trauma to the face and brain, including blast injuries common in modern warfare, can result in alterations in the ability to both smell and taste. In the case of smell, these include total loss of function (anosmia), decreased sensitivity (hyposmia), alterations in odor quality (dysosmia), and hallucination (phantosmia). Although taste dysfunction, i.e., altered perception of such basic taste-bud-mediated sensations as sweet, sour, bitter, salty, and savory (umami), can be similarly influenced by head trauma, the effects are typically more subtle and less studied. The present review provides an up-to-date assessment of what is known about the impact of head injury on quantitative measures of taste and smell function, including the influences of severity, type of injury, location of insults, prognosis, and approaches to therapy.

Burning odor-elicited anxiety in OEF/OIF combat veterans: Inverse relationship to gray matter volume in olfactory cortex

Despite the anatomical overlap between the brain's fear/threat and olfactory systems, a very limited number of investigations have considered the role of odors and the central olfactory system in the pathophysiology of PTSD. The goal of the present study was to assess structural differences in primary and secondary olfactory cortex between combat veterans with and without PTSD (CV + PTSD, CV-PTSD, respectively). An additional goal was to determine the relationship between gray matter volume (GMV) in olfactory cortex and the distressing properties of burning-related odors. A region of interest voxel-based morphometric (VBM) approach was used to measure GMV in olfactory cortex in a well-characterized group of CV + PTSD (n = 20) and CV-PTSD (n = 25). Prior to the MRI exam, combat-related (i.e., burning rubber) and control odors were systematically sampled and rated according to their potential for eliciting PTSD symptoms. Results showed that CV + PTSD exhibited significantly reduced GMV in anterior piriform (primary olfactory) and orbitofrontal (secondary olfactory) cortices compared to CV-PTSD (both p < .01). For the entire group, GMV in bilateral anterior piriform cortex was inversely related to burning rubber odor-elicited memories of trauma (p < .05). GMV in orbitofrontal cortex was inversely related to both clinical and laboratory measures of PTSD symptoms (all p < .05). In addition to replicating an established inverse relationship between GMV in anxiety-associated brain structures and PTSD symptomatology, the present study extends those findings by being the first report of volumetric decreases in olfactory cortex that are inversely related to odor-elicited PTSD symptoms. Potential mechanisms underlying these findings are discussed.

Dexamethasone affects mouse olfactory mucosa gene expression and attenuates genes related to neurite outgrowth

BACKGROUND

Olfaction is one of the important senses for humans. Systemic glucocorticoids are the most commonly used medications for olfactory loss because of their strong anti-inflammatory effects. However, their effect on olfactory function is still controversial and the precise mechanism is not clear. To gain a global view of the effect of systematic glucocorticoid treatment on gene expression in the olfactory mucosa (OM), we profiled these changes in a murine model of olfaction in order to identify underlying molecular mechanisms.

METHODS

C57BL/6 mice were injected daily for 2 weeks (WK2) with dexamethasone (DEX, intraperitoneally, 1 mg/kg body weight) vs 1 day of DEX (D1) vs controls, which received saline (Ctrl) (n = 9/group). Total RNA from the OM was used to analyze global gene expression. Genes showing changes in expression were compared using the Database for Annotation, Visualization and Integrated Discovery (DAVID, v6.7) and the General Olfactory Sensitivity Database (GOSdb; http://genome.weizmann.ac.il/GOSdb).

RESULTS

Between the WK2 and Ctrl groups, 3351 genes were differentially expressed, of which 236 genes were related to olfactory function. Genes involved in axon guidance, cell projection, and inflammation were enriched and overlapped significantly with those in the GOSdb.

CONCLUSION

Systemic glucocorticoids exert effects on transcription of a notable number of genes in the OM and appear to orchestrate changes related to axon guidance, cell projection, and inflammation. Further examination may allow targeted therapies that lack the side effects of this category of medication.

Neurotoxic exposure and impairment of the chemical senses of taste and smell

The chemical senses of taste and smell determine the flavor of foods and beverages, guide appropriate food intake, and warn of such environmental hazards as spoiled or poisonous food, leaking natural gas, smoke, and airborne pollutants. This chapter addresses the influences of neurotoxic exposures on human chemoreception and provides basic information on the adverse influences of such exposures on rodent epithelia. The focus of the chapter is in olfaction, given dearth of empiric research on the effects of neurotoxic chemical exposures on the sense of taste, i.e., sweet, sour, bitter, salty, and savory sensations. As will be apparent from the chapter, numerous neurotoxins--many of which are encountered in industrial workplaces--alter the ability to smell, including solvents, metals, and particulate matter. The olfactory system is particularly vulnerable to such agents since its receptors are more or less directly exposed to the outside environment. Importantly, some such agents can enter the brain via the olfactory nerve or surrounding perineural spaces, bypassing the blood-brain barrier and damaging central nervous system structures and inducing pathologic processes that appear to be similar to those seen in neurodegenerative diseases such as Alzheimer's and Parkinson's.

Relationship between olfactory function and olfactory neuronal population in C57BL6 mice injected intraperitoneally with 3-methylindole

OBJECTIVE

It is not known how many olfactory receptor neurons should be intact to maintain olfaction in mouse models treated with 3-methylindole. The aim of this study is to investigate the relationship between a simple olfactory test outcome and the olfactory neuronal population.

STUDY DESIGN

Mouse model.

SETTING

Animal laboratory of the Seoul National University Bundang Hospital.

SUBJECTS AND METHODS

Olfactory dysfunction was induced by intraperitoneal injection of 3-methylindole in 38 six-week-old female C57BL6 mice. Olfactory function was evaluated by a food-finding test following 72-hour starvation. The olfactory neuronal population was quantified by olfactory marker protein (OMP) expression.

RESULTS

The average time for finding food was 8.1 seconds in control mice. It was 13.4, 84.4, 90.1, and 111.4 seconds for mice injected with 100, 200, 300, and 400 μg/g of 3-methylindole, respectively. Harvesting the whole olfactory neuroepithelium, densitometric analysis showed significant decrease of OMP in the 300- and 400-μg/g groups as compared with controls (18.8% and 17.5% of relative density, respectively). In the olfactory bulb, there was a significant decrease of OMP in the 200-, 300-, and 400-μg/g groups (44.5%, 37.0%, and 9.0% of relative density, respectively). The food-finding time had a significant reverse correlation with the relative density of OMP both in the olfactory bulb and in the olfactory neuroepithelium.

CONCLUSION

Our study showed that olfactory impairment was correlated with olfactory neuronal population in mice treated with 3-methylindole. The food-finding test would be a useful tool that could be easily performed without special training in the 3-methylindole-treated C57BL6 anosmic mouse model.

Effects of statins on regeneration of olfactory epithelium

BACKGROUND

This study was performed to investigate whether statins can enhance the recovery of the olfactory epithelium (OE) damaged by 3-methylindole (3MI), an olfactotoxicant, and to compare the effects with those of steroids.

METHODS

Randomized placebo-controlled trial was performed. Fifty-four healthy female Sprague-Dawley rats (aged 9-10 weeks and weighing 160-180 g each) were randomly allocated to the statin-treated, steroid-treated, or control groups. Olfactory loss was induced using i.p. injection of 3MI in adult rats. Atorvastatin (10 mg/kg for 4 weeks), prednisolone (1 mg/kg for 2 weeks), or normal saline (1 cc for 4 weeks) was then administered per os with a gastric tube. Hematoxylin and eosin (H&E) staining and immunohistochemical staining were performed to evaluate the change of thickness and the arrangement of the OE, and immunoreactivity to protein gene product (PGP) 9.5 and proliferating cell nuclear antigen (PCNA).

RESULTS

The statin-treated group showed the earliest increase of the thickness of the OE (p = 0.002 at 7 days after 3MI injection) and the immunoreactivity to PCNA (p = 0.032 at 7 days after 3MI injection) among the three groups. The immunoreactivity to PGP 9.5 showed significantly better improvement at the 7th and 28th days after 3MI injection compared with the steroid-treated or control groups (p = 0.002 and p < 0.001, respectively).

CONCLUSION

Statins might enhance the proliferation and neuroregenesis of the OE after 3MI injection.

Effects of typical inducers on olfactory xenobiotic-metabolizing enzyme, transporter, and transcription factor expression in rats

Several xenobiotic-metabolizing enzymes (XMEs) have been identified in the olfactory mucosa (OM) of mammals. However, the molecular mechanisms underlying the regulation of these enzymes have been little explored. In particular, information on the expression of the transcriptional factors in this tissue is quite limited. The aim of the present study was to examine the impact of five typical inducers, Aroclor 1254, 3-methylcholanthrene, dexamethasone, phenobarbital, and ethoxyquin, on the activities and mRNA expression of several XMEs in the OM and in the liver of rats. We also evaluated the effects of these treatments on the mRNA expression of transcription factors and transporters. On the whole, the intensities of the effects were lower in the OM than in the liver. Dexamethasone was found to be the most efficient treatment in the OM. Dexamethasone induced the transcription of several olfactory phase I, II, and III genes [such as cytochromes P450 2A3 and 3A9, UDP-glucuronosyltransferase (UGT) 2A1, and multidrug resistance-related protein type 1] and increased UGT activities. We observed that dexamethasone up-regulated sulfotransferase 1C1 expression in the OM but down-regulated it in the liver. Aroclor and ethoxyquin induced the gene expression of CYP1A and quinone reductase, respectively, in the OM. The transcription factors aryl hydrocarbon receptor, nuclear factor E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor α, pregnane X receptor, and glucocorticoid receptor were detected in the OM, but no constitutive androstane receptor expression was observed. Dexamethasone and Aroclor enhanced olfactory Nrf2 expression. These results demonstrate that olfactory XME can be modulated by chemicals and that the mechanisms involved in the regulation of these enzymes are tissue-specific.

The effect of Ginkgo biloba on the expression of intermediate-early antigen (c-fos) in the experimentally induced anosmic mouse

OBJECTIVE

Treatment of olfactory dysfunction is very difficult and has limited modality. Treatment with steroids has been used in patients with olfactory dysfunction but the side effects of steroid need to be weighed against its potential benefits. In the present study, the effect of systemic administration of dexamethasone and EGb 761 on damage to olfactory mucosa produced by zinc sulfate was examined. Expression of the immediate-early antigen (IEG), c-fos, in the olfactory bulb and piriform cortex was used to determine the effects of treatment.

METHODS

Young adult CD1 mice (6 to 8 weeks old, male) were used. After anosmic mice were made by bilateral intranasal irrigation with 0.2 ml of 5% (0.17 M) zinc sulfate, anosmia was confirmed by a food finding test. Four groups of anosmic mice were studied: a steroid group (steroid injection group, n=12), an EGb group (EGb injection group, n=12), a steroid-EGb group (steroid and EGb injection group, n=12), and a control group (anosmic mice and no Tx. n=12). The olfactory bulb and piriform cortex of four mice in each group were obtained at 1, 2, and 3 weeks after instillation of zinc sulfate by cardiac perfusion, and immunohistochemical staining for c-fos was also performed to evaluate brain activity. In approximately 10 well-defined glomeruli of the olfactory bulb and in one side of the piriform cortex, c-fos (+) cells were counted. Statistical analyses were performed by Kruskal-Wallis one-way analysis of variance (ANOVA) by rank.

RESULTS

In all experimental groups, c-fos (+) cells increased in a time-dependent manner. The combination treatment of steroid and EGb was the most effective and the no-treatment group the least effective 1 week later after zinc sulfate irrigation. However, 3 weeks later after zinc sulfate irrigation, there was no statistically significant differences in the number of c-fos positive cells among all 4 groups (3 treatment groups and the control group).

CONCLUSION

The combination treatment of EGb and steroid enhanced the regeneration of the olfactory pathway after olfactory mucosal injury by zinc sulfate. Our study suggests that EGb could be an effective treatment option for olfactory dysfunction.

Effect of ginkgo biloba and dexamethasone in the treatment of 3-methylindole-induced anosmia mouse model

BACKGROUND

Olfactory loss is a challenging disease. Although glucocorticoid is sometimes used for the treatment of anosmia, it has been reported that it potentiated neural damage in the early phase of treatment. This study is designed to identify the effect of ginkgo biloba, an antioxidant that acts as a free radical scavenger, in the treatment of olfactory injury aggravated by dexamethasone.

METHODS

Anosmia mouse model was induced by i.p. injection of 3-methylindole (3-MI). Twenty-five mice were divided into one control group without anosmia and four anosmia treatment groups (given treatments of dexamethasone and/or ginkgo biloba). The effects of treatment were evaluated by behavioral test, Western blot, and immunohistochemistry 2 weeks after 3-MI injection.

RESULTS

Induction of anosmia was confirmed by behavioral tests. The thickness and cell number of olfactory neuroepithelium were decreased more significantly in the dexamethasone treatment group than in the combination treatment group. The expression of olfactory marker protein (OMP) in olfactory epithelium was more decreased also in the dexamethasone treatment group than in the combination treatment group. The expression of OMP was decreased significantly in the olfactory bulbs of anosmia groups but there were no differences between the anosmia treatment groups.

CONCLUSION

Dexamethasone treatment was associated with further deterioration of olfactory injury by 3-MI and it was recovered by combination treatment of dexamethasone and ginkgo biloba. The antioxidant effect of ginkgo biloba might play a role in restoration of olfactory loss and it was effective only when oxidative stress is maximized by dexamethasone.

Drug-induced taste disorders

Numerous drugs have the potential to adversely influence a patient's sense of taste, either by decreasing function or producing perceptual distortions or phantom tastes. In some cases, such adverse effects are long lasting and cannot be quickly reversed by drug cessation. In a number of cases, taste-related adverse effects significantly alter the patient's quality of life, dietary choices, emotional state and compliance with medication regimens. In this review, we describe common drug-related taste disturbances and review the major classes of medications associated with them, including antihypertensives, antimicrobials and antidepressants. We point out that there is a dearth of scientific information related to this problem, limiting our understanding of the true nature, incidence and prevalence of drug-related chemosensory disturbances. The limited data available suggest that large differences exist among individuals in terms of their susceptibility to taste-related adverse effects, and that sex, age, body mass and genetic variations in taste sensitivity are likely involved. Aside from altering drug usage, management strategies for patients with taste-related adverse effects are sorely needed. Unfortunately, stopping a medication is not always an easy option, particularly when one is dealing with life-threatening conditions such as seizures, cancer, infection, diabetes mellitus and uncontrolled hypertension. Hopefully, the information contained in this review will sensitize physicians, researchers and drug manufacturers to this problem and will result in much more research on this pressing topic.

Steroid-dependent anosmia

OBJECTIVE

To document the response to steroids in patients remaining anosmic following endoscopic nasal and sinus polypectomy.

STUDY DESIGN

A prospective study of 24 patients with nasal and sinus polyps who were anosmic prior to endoscopic nasal and sinus surgery. Those who remained anosmic after surgery were treated with steroids. Most patients had asthma, allergic rhinitis, or both. A few had aspirin sensitivity.

METHODS

All 24 patients had testing of their sense of smell before and after surgery. Those who remained anosmic postoperatively were first treated with topical nasal and then oral steroids and then tested again.

RESULTS

Twelve of the 24 remained anosmic after surgery and were found to be unresponsive to nasal steroids, but oral steroids were found to restore the sense of smell to normal in most patients. Few patients continued to take the medication for long periods of time mainly because of a fear of side effects. Recent studies have suggested the role of systemic steroids in olfactory secretion, which may explain the mechanism for this response.

CONCLUSION

Patients who remain anosmic after the removal of nasal and sinus polyps can be treated with oral steroids resulting in improvement of their sense of smell. Further research is needed on a molecular level to determine the reason for this and also why oral but not nasal steroids are helpful in these patients.