Intranasal zinc and anosmia: the zinc-induced anosmia syndrome

Association between dietary zinc intake and olfactory dysfunction: a study based on the NHANES database

OBJECTIVE

The primary objective of this study was to find the association between dietary zinc intake and the prevalence of olfactory disorders using data from the National Health and Nutrition Examination Survey (NHANES).

METHODS

A cross-sectional study was conducted using the 2013-2014 NHANES data. A linear regression model was constructed with dietary zinc intake as the independent variable and olfactory dysfunction as the dependent variable. Initially, in the unadjusted model, weighted logistic regression analysis was carried out for continuous variables, and stratified analysis was conducted for categorical variables. Subsequently, three models were created to perform subgroup analysis by adjusting for different confounding factors, further investigating the relationship between dietary zinc intake and olfactory dysfunction. Finally, restricted cubic spline (RCS) models adjusting for all confounding factors were utilized to study the nonlinear associations of age and dietary zinc intake with olfactory dysfunction and their relevant thresholds.

RESULTS

A total of 2958 samples were analyzed in this study. Weighted logistic regression analysis displayed a negative relationship between dietary zinc intake and the prevalence of olfactory dysfunction in the population of non-Hispanic whites and other Hispanics, as well as in individuals with body mass index (BMI) ≥ 25 kg/m2 (OR < 1, P < 0.05). The P values for the multiplicative interaction terms adjusting for all confounding factors were not significant (P for interaction > 0.05). In the three regression models adjusting for different confounding factors, dietary zinc intake was significantly negatively related to olfactory dysfunction in all populations (Crude: OR 0.63, 95% CI 0.44-0.91; Model I: OR 0.58, 95% CI 0.38-0.90; Model II: OR 0.59, 95% CI 0.35-1.00). Subgroup analysis based on BMI showed a remarkable negative relationship between dietary zinc intake and olfactory dysfunction in the group with BMI of 25-30 kg/m2 (Crude: OR 0.50, 95% CI 0.28-0.90, P = 0.012; Model I: OR 0.49, 95% CI 0.24-1.00, P = 0.021) and the group with BMI ≥ 30 kg/m2 (Crude: OR 0.55, 95% CI 0.33-0.92, P = 0.013; Model I: OR 0.51, 95% CI 0.29-0.88, P = 0.005; Model II: OR 0.51, 95% CI 0.29-0.91, P = 0.004). RCS analysis revealed a remarkable nonlinear association of age and dietary zinc intake with olfactory dysfunction (P-non-linear < 0.05). The prevalence of olfactory dysfunction was considerably higher in individuals aged 60 and above compared to those under 60 years old. Daily dietary zinc intake within the range of 9.60-17.45 mg was a protective factor for olfactory dysfunction, while intake outside this range increased the prevalence of olfactory dysfunction.

CONCLUSION

Daily dietary zinc intake within the range of 9.60-17.45 mg has a protective effect against olfactory dysfunction. Intake outside this range increases the prevalence of olfactory dysfunction. The prevalence of olfactory dysfunction is significantly higher in individuals aged 60 and above compared to those under 60 years old. For individuals with a BMI of 25-30 kg/m2 and a BMI ≥ 30 kg/m2, dietary zinc intake is negatively correlated with olfactory dysfunction. Therefore, it is recommended that these populations increase their dietary zinc intake to develop healthier lifestyles and maintain olfactory health.

Efficacy of Normalising Serum Zinc Level for Patients with Olfactory Dysfunction and Zinc Deficiency

INTRODUCTION

Zinc deficiency may worsen the severity of olfactory dysfunction; however, the relationship between serum zinc levels and therapeutic effects on olfactory dysfunction remains uncertain. This study investigated the relationship between normalising serum zinc levels and the therapeutic effects on olfactory dysfunction.

METHODS

Forty-two patients diagnosed with post-infectious, post-traumatic, and idiopathic olfactory dysfunction, with serum zinc levels <70 μg/dL, were included in the study. All patients were treated with mecobalamin, tokishakuyakusan, and polaprezinc. The patients were divided into 2 groups: the zinc-normalised (≥70 μg/dL) and zinc-deficient (<70 μg/dL) groups, based on their post-treatment serum zinc levels. Olfactory test results were compared in each of the 2 groups.

RESULTS

The patients were treated for a median of 133 days. The zinc-normalised group had significantly better results in all olfactory tests (detection/recognition thresholds of the T&T olfactometer, odour identification test (Open Essence), Visual Analogue Scale for olfactory dysfunction, and self-administered odour questionnaire). In contrast, only the self-administered odour questionnaire showed a significant improvement in the zinc-deficient group, with no significant differences observed in the other olfactory tests. When comparing the changes in the olfactory test scores between the 2 groups, significant differences were observed in the detection/recognition thresholds of the T&T olfactometer test and Open Essence results.

CONCLUSION

These findings suggest that patients with olfactory dysfunction may have difficulty improving their olfactory function if they also have zinc deficiency. Furthermore, normalisation of zinc deficiency may contribute to the improvement of olfactory dysfunction with general treatment.

Identifying candidate genes underlying isolated congenital anosmia

An estimated 1 in 10 000 people are born without the ability to smell, a condition known as congenital anosmia, and about one third of those people have non-syndromic, or isolated congenital anosmia (ICA). Despite the significant impact of olfaction for our quality of life, the underlying causes of ICA remain largely unknown. Using whole exome sequencing (WES) in 10 families and 141 individuals with ICA, we identified a candidate list of 162 rare, segregating, deleterious variants in 158 genes. We confirmed the involvement of CNGA2, a previously implicated ICA gene that is an essential component of the olfactory transduction pathway. Furthermore, we found a loss-of-function variant in SREK1IP1 from the family gene candidate list, which was also observed in 5% of individuals in an additional non-family cohort with ICA. Although SREK1IP1 has not been previously associated with olfaction, its role in zinc ion binding suggests a potential influence on olfactory signaling. This study provides a more comprehensive understanding of the spectrum of genetic alterations and their etiology in ICA patients, which may improve the diagnosis, prognosis, and treatment of this disorder and lead to better understanding of the mechanisms governing basic olfactory function.

Nutritional deficiencies that may predispose to long COVID

Multiple nutritional deficiencies (MND) confound studies designed to assess the role of a single nutrient in contributing to the initiation and progression of disease states. Despite the perception of many healthcare practitioners, up to 25% of Americans are deficient in five-or-more essential nutrients. Stress associated with the COVID-19 pandemic further increases the prevalence of deficiency states. Viral infections compete for crucial nutrients with immune cells. Viral replication and proliferation of immunocompetent cells critical to the host response require these essential nutrients, including zinc. Clinical studies have linked levels of more than 22 different dietary components to the likelihood of COVID-19 infection and the severity of the disease. People at higher risk of infection due to MND are also more likely to have long-term sequelae, known as Long COVID.

Drug-induced olfactory and gustatory dysfunction: Analysis of FDA adverse events reporting system

OBJECTIVES

With the COVID-19 pandemic, there is growing interest and research in olfactory and gustatory dysfunction (OGD). Drug-induced dysfunction is an often overlooked etiology. While several medications include smell or taste disturbance as a side effect, there are no publications describing which medications are most frequently implicated. We aim to describe the patterns of these adverse drug reactions (ADRs) using the FDA Adverse Events Reporting System (FAERS).

METHODS

The FAERS database was queried from 2011 to 2021 for terms describing ADRs related to OGD. Terms included anosmia, hyposmia, olfactory test abnormal, olfactory nerve disorder, hallucination olfactory, parosmia, ageusia, hypogeusia, dysgeusia, and taste disorder. We identified the top reported medications associated with general smell dysfunction, general taste dysfunction, reduced smell, and altered smell.

RESULTS

From 2011 to 2021, 16,091 ADRs were reported with OGD, of which13,641 (84.8%) and 2,450 (15.2%) were associated with gustatory and olfactory reactions, respectively. Zinc products (370 reports) and fluticasone propionate (214) were most commonly associated with olfactory dysfunction, specifically reduced olfaction. Varenicline (24) and fluticasone propionate (23) were most commonly associated with altered smell. Lenalidomide (490) and sunitinib (468) were most commonly associated with gustatory dysfunction. Antineoplastic and immunomodulating medications accounted for 21.6% and 36.3% of olfactory and gustatory ADRs, respectively. Among this category, immunoglobulin drugs were the most commonly associated with OGD ADRs.

CONCLUSION

Gustatory dysfunction is more commonly reported ADR compared with olfactory dysfunction. Immunologic/rheumatologic medications are the leading culprit of reported OGD. With increasing numbers of patients presenting to otolaryngologists for OGD, it is important to consider drug-induced etiology.

LEVEL OF EVIDENCE

III.

Effects of zinc deficiency on the regeneration of olfactory epithelium in mice

The olfactory epithelium can regenerate after damage; however, the regeneration process is affected by various factors, such as viral infections, head trauma, and medications. Zinc is an essential trace element that has important roles in organ development, growth, and maturation. Zinc also helps regulate neurotransmission in the brain; nevertheless, its relationship with olfactory epithelium regeneration remains unclear. Therefore, we used a severe zinc deficiency mouse model to investigate the effects of zinc deficiency on olfactory epithelium regeneration. Male wild-type C57BL/6 mice were divided into zinc-deficient and control diet groups at the age of 4 weeks, and methimazole was administered at the age of 8 weeks to induce severe olfactory epithelium damage. We evaluated the olfactory epithelium before and 7, 14, and 28 days after methimazole administration by histologically analyzing paraffin sections. RNA sequencing was also performed at the age of 8 weeks before methimazole administration to examine changes in gene expression caused by zinc deficiency. In the zinc-deficient group, the regenerated olfactory epithelium thickness was decreased at all time points, and the numbers of Ki-67-positive, GAP43-positive, and olfactory marker protein-positive cells (i.e. proliferating cells, immature olfactory neurons, and mature olfactory neurons, respectively) failed to increase at some time points. Additionally, RNA sequencing revealed several changes in gene expression, such as a decrease in the expression of extracellular matrix-related genes and an increase in that of inflammatory response-related genes, in the zinc-deficient group. Therefore, zinc deficiency delays olfactory epithelium regeneration after damage in mice.

Interventions for the treatment of persistent post-COVID-19 olfactory dysfunction

BACKGROUND

Olfactory dysfunction is a common consequence of COVID-19 infection and persistent symptoms can have a profound impact on quality of life. At present there is little guidance on how best to treat this condition. A variety of interventions have been suggested to promote recovery, including medication and olfactory training. However, it is uncertain whether any intervention is of benefit. This is an update of the 2021 review with one additional study added.  OBJECTIVES: 1) To evaluate the benefits and harms of any intervention versus no treatment for people with persisting olfactory dysfunction due to COVID-19 infection.  2) To keep the evidence up-to-date, using a living systematic review approach.  SEARCH METHODS: The Cochrane ENT Information Specialist searched the Cochrane ENT Register; Central Register of Controlled Trials (CENTRAL); Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished trials. The date of the latest search was 20 October 2021.   SELECTION CRITERIA: We included randomised controlled trials (RCTs) in people with COVID-19 related olfactory disturbance that had persisted for at least four weeks. We included any intervention compared to no treatment or placebo.  DATA COLLECTION AND ANALYSIS: We used standard Cochrane methods. Our primary outcomes were the recovery of sense of smell, disease-related quality of life and serious adverse effects. Secondary outcomes were the change in sense of smell, general quality of life, prevalence of parosmia and other adverse effects (including nosebleeds/bloody discharge). We used GRADE to assess the certainty of the evidence for each outcome.

MAIN RESULTS

We included two studies with 30 participants. The studies evaluated the following interventions: systemic corticosteroids plus intranasal corticosteroid/mucolytic/decongestant and palmitoylethanolamide plus luteolin.  Systemic corticosteroids plus intranasal corticosteroid/mucolytic/decongestant compared to no intervention We included a single RCT with 18 participants who had anosmia for at least 30 days following COVID-19 infection. Participants received a 15-day course of oral corticosteroids combined with nasal irrigation (consisting of an intranasal corticosteroid/mucolytic/decongestant solution) or no intervention. Psychophysical testing was used to assess olfactory function at 40 days. This is a single, small study and for all outcomes the certainty of evidence was very low. We are unable to draw meaningful conclusions from the numerical results. Palmitoylethanolamide plus luteolin compared to no intervention We included a single RCT with 12 participants who had anosmia or hyposmia for at least 90 days following COVID-19 infection. Participants received a 30-day course of palmitoylethanolamide and luteolin or no intervention. Psychophysical testing was used to assess olfactory function at 30 days. This is a single, small study and for all outcomes the certainty of evidence was very low. We are unable to draw meaningful conclusions from the numerical results.

AUTHORS' CONCLUSIONS

There is very limited evidence available on the efficacy and harms of treatments for persistent olfactory dysfunction following COVID-19 infection. However, we have identified a number of ongoing trials in this area. As this is a living systematic review we will update the data regularly, as new results become available.

Interventions for the prevention of persistent post-COVID-19 olfactory dysfunction

BACKGROUND

Loss of olfactory function is well recognised as a symptom of COVID-19 infection, and the pandemic has resulted in a large number of individuals with abnormalities in their sense of smell. For many, the condition is temporary and resolves within two to four weeks. However, in a significant minority the symptoms persist. At present, it is not known whether early intervention with any form of treatment (such as medication or olfactory training) can promote recovery and prevent persisting olfactory disturbance. This is an update of the 2021 review with four studies added.

OBJECTIVES

1) To evaluate the benefits and harms of any intervention versus no treatment for people with acute olfactory dysfunction due to COVID-19 infection.  2) To keep the evidence up-to-date, using a living systematic review approach.  SEARCH METHODS: The Cochrane ENT Information Specialist searched the Cochrane ENT Register; Central Register of Controlled Trials (CENTRAL); Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished trials. The date of the latest search was 20 October 2021.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) in people with COVID-19 related olfactory disturbance, which had been present for less than four weeks. We included any intervention compared to no treatment or placebo.  DATA COLLECTION AND ANALYSIS: We used standard Cochrane methods. Our primary outcomes were the presence of normal olfactory function, serious adverse effects and change in sense of smell. Secondary outcomes were the prevalence of parosmia, change in sense of taste, disease-related quality of life and other adverse effects (including nosebleeds/bloody discharge). We used GRADE to assess the certainty of the evidence for each outcome.  MAIN RESULTS: We included five studies with 691 participants. The studies evaluated the following interventions: intranasal corticosteroid sprays, intranasal corticosteroid drops, intranasal hypertonic saline and zinc sulphate.  Intranasal corticosteroid spray compared to no intervention/placebo We included three studies with 288 participants who had olfactory dysfunction for less than four weeks following COVID-19. Presence of normal olfactory function The evidence is very uncertain about the effect of intranasal corticosteroid spray on both self-rated recovery of olfactory function and recovery of olfactory function using psychophysical tests at up to four weeks follow-up (self-rated: risk ratio (RR) 1.19, 95% confidence interval (CI) 0.85 to 1.68; 1 study; 100 participants; psychophysical testing: RR 2.3, 95% CI 1.16 to 4.63; 1 study; 77 participants; very low-certainty evidence).  Change in sense of smell The evidence is also very uncertain about the effect of intranasal corticosteroid spray on self-rated change in the sense of smell (at less than 4 weeks: mean difference (MD) 0.5 points lower, 95% CI 1.38 lower to 0.38 higher; 1 study; 77 participants; at > 4 weeks to 3 months: MD 2.4 points higher, 95% CI 1.32 higher to 3.48 higher; 1 study; 100 participants; very low-certainty evidence, rated on a scale of 1 to 10, higher scores mean better olfactory function). Intranasal corticosteroids may make little or no difference to the change in sense of smell when assessed with psychophysical testing (MD 0.2 points, 95% CI 2.06 points lower to 2.06 points higher; 1 study; 77 participants; low-certainty evidence, 0- to 24-point scale, higher scores mean better olfactory function).  Serious adverse effects The authors of one study reported no adverse effects, but their intention to collect these data was not pre-specified so we are uncertain if these were systematically sought and identified. The remaining two studies did not report on adverse effects.  Intranasal corticosteroid drops compared to no intervention/placebo We included one study with 248 participants who had olfactory dysfunction for ≤ 15 days following COVID-19. Presence of normal olfactory function Intranasal corticosteroid drops may make little or no difference to self-rated recovery at > 4 weeks to 3 months (RR 1.00, 95% CI 0.89 to 1.11; 1 study; 248 participants; low-certainty evidence). No other outcomes were assessed by this study.  Data on the use of hypertonic saline nasal irrigation and the use of zinc sulphate to prevent persistent olfactory dysfunction are included in the full text of the review.

AUTHORS' CONCLUSIONS

There is very limited evidence available on the efficacy and harms of treatments for preventing persistent olfactory dysfunction following COVID-19 infection. However, we have identified a number of ongoing trials in this area. As this is a living systematic review we will update the data regularly, as new results become available.

Enhancement of olfaction by femtomolar concentrations of zinc ions

Zinc is recognized as an important element for olfaction. Zinc nanoparticles enhance olfaction in response to odors; however, the mechanisms underlying this action remain unknown. Herein, the effect of zinc on olfactory receptors was deduced using electro-olfactogram (EOG) responses recorded from the isolated olfactory mucosae of bullfrogs (Rana catesbeiana) following the administration or chelation of zinc ions. Menthone and n-amyl acetate were used as odorants, whereas forskolin (an adenylate cyclase activator) and cholera toxin (a Gαolf activator) were used as intracellular signal transduction activators. The EOG responses provoked by the odorants and cholera toxin were suppressed by dithizone-mediated zinc ion chelation, and the EOG responses were recovered by administering non-chelated zinc. However, the EOG response to forskolin was not suppressed by dithizone. In contrast, the addition of femtomolar concentrations of zinc ions enhanced the EOG responses. The above-mentioned effects on EOG responses were examined by changing the concentration of zinc ions but not zinc nanoparticles. The results of this study suggest that Gαolf alone or both olfactory receptors and Gαolf likely require zinc ions for their activation.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Zinc for the prevention or treatment of acute viral respiratory tract infections in adults: a rapid systematic review and meta-analysis of randomised controlled trials

OBJECTIVE

To evaluate the benefits and risks of zinc formulations compared with controls for prevention or treatment of acute viral respiratory tract infections (RTIs) in adults.

METHOD

Seventeen English and Chinese databases were searched in April/May 2020 for randomised controlled trials (RCTs), and from April/May 2020 to August 2020 for SARS-CoV-2 RCTs. Cochrane rapid review methods were applied. Quality appraisals used the Risk of Bias 2.0 and Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach.

RESULTS

Twenty-eight RCTs with 5446 participants were identified. None were specific to SARS-CoV-2. Compared with placebo, oral or intranasal zinc prevented 5 RTIs per 100 person-months (95% CI 1 to 8, numbers needed to treat (NNT)=20, moderate-certainty/quality). Sublingual zinc did not prevent clinical colds following human rhinovirus inoculations (relative risk, RR 0.96, 95% CI 0.77 to 1.21, moderate-certainty/quality). On average, symptoms resolved 2 days earlier with sublingual or intranasal zinc compared with placebo (95% CI 0.61 to 3.50, very low-certainty/quality) and 19 more adults per 100 were likely to remain symptomatic on day 7 without zinc (95% CI 2 to 38, NNT=5, low-certainty/quality). There were clinically significant reductions in day 3 symptom severity scores (mean difference, MD -1.20 points, 95% CI -0.66 to -1.74, low-certainty/quality), but not average daily symptom severity scores (standardised MD -0.15, 95% CI -0.43 to 0.13, low-certainty/quality). Non-serious adverse events (AEs) (eg, nausea, mouth/nasal irritation) were higher (RR 1.41, 95% CI 1.17 to 1.69, NNHarm=7, moderate-certainty/quality). Compared with active controls, there were no differences in illness duration or AEs (low-certainty/quality). No serious AEs were reported in the 25 RCTs that monitored them (low-certainty/quality).

CONCLUSIONS

In adult populations unlikely to be zinc deficient, there was some evidence suggesting zinc might prevent RTIs symptoms and shorten duration. Non-serious AEs may limit tolerability for some. The comparative efficacy/effectiveness of different zinc formulations and doses were unclear. The GRADE-certainty/quality of the evidence was limited by a high risk of bias, small sample sizes and/or heterogeneity. Further research, including SARS-CoV-2 clinical trials is warranted.

PROSPERO REGISTRATION NUMBER

CRD42020182044.

Interventions for the prevention of persistent post-COVID-19 olfactory dysfunction

BACKGROUND

Loss of olfactory function is well recognised as a cardinal symptom of COVID-19 infection, and the ongoing pandemic has resulted in a large number of affected individuals with abnormalities in their sense of smell. For many, the condition is temporary and resolves within two to four weeks. However, in a significant minority the symptoms persist. At present, it is not known whether early intervention with any form of treatment (such as medication or olfactory training) can promote recovery and prevent persisting olfactory disturbance.  OBJECTIVES: To assess the effects (benefits and harms) of interventions that have been used, or proposed, to prevent persisting olfactory dysfunction due to COVID-19 infection. A secondary objective is to keep the evidence up-to-date, using a living systematic review approach.  SEARCH METHODS: The Cochrane ENT Information Specialist searched the Cochrane COVID-19 Study Register; Cochrane ENT Register; CENTRAL; Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished studies. The date of the search was 16 December 2020.

SELECTION CRITERIA

Randomised controlled trials including participants who had symptoms of olfactory disturbance following COVID-19 infection. Individuals who had symptoms for less than four weeks were included in this review. Studies compared any intervention with no treatment or placebo.  DATA COLLECTION AND ANALYSIS: We used standard Cochrane methodological procedures. Our primary outcomes were the presence of normal olfactory function, serious adverse effects and change in sense of smell. Secondary outcomes were the prevalence of parosmia, change in sense of taste, disease-related quality of life and other adverse effects (including nosebleeds/bloody discharge). We used GRADE to assess the certainty of the evidence for each outcome.  MAIN RESULTS: We included one study of 100 participants, which compared an intranasal steroid spray to no intervention. Participants in both groups were also advised to undertake olfactory training for the duration of the trial. Data were identified for only two of the prespecified outcomes for this review, and no data were available for the primary outcome of serious adverse effects. Intranasal corticosteroids compared to no intervention (all using olfactory training) Presence of normal olfactory function after three weeks of treatment was self-assessed by the participants, using a visual analogue scale (range 0 to 10, higher scores = better). A score of 10 represented "completely normal smell sensation". The evidence is very uncertain about the effect of intranasal corticosteroids on self-rated recovery of sense of smell (estimated absolute effect 619 per 1000 compared to 520 per 1000, risk ratio (RR) 1.19, 95% confidence interval (CI) 0.85 to 1.68; 1 study; 100 participants; very low-certainty evidence).  Change in sense of smell was not reported, but the self-rated score for sense of smell was reported at the endpoint of the study with the same visual analogue scale (after three weeks of treatment). The median scores at endpoint were 10 (interquartile range (IQR) 9 to 10) for the group receiving intranasal corticosteroids, and 10 (IQR 5 to 10) for the group receiving no intervention (1 study; 100 participants; very low-certainty evidence).

AUTHORS' CONCLUSIONS

There is very limited evidence regarding the efficacy of different interventions at preventing persistent olfactory dysfunction following COVID-19 infection. However, we have identified a small number of additional ongoing studies in this area. As this is a living systematic review, the evidence will be updated regularly to incorporate new data from these, and other relevant studies, as they become available.  For this (first) version of the living review, we identified a single study of intranasal corticosteroids to include in this review, which provided data for only two of our prespecified outcomes. The evidence was of very low certainty, therefore we were unable to determine whether intranasal corticosteroids may have a beneficial or harmful effect.

Interventions for the treatment of persistent post-COVID-19 olfactory dysfunction

BACKGROUND

Olfactory dysfunction is an early and sensitive marker of COVID-19 infection. Although self-limiting in the majority of cases, when hyposmia or anosmia persists it can have a profound effect on quality of life. Little guidance exists on the treatment of post-COVID-19 olfactory dysfunction, however several strategies have been proposed from the evidence relating to the treatment of post-viral anosmia (such as medication or olfactory training).

OBJECTIVES

To assess the effects (benefits and harms) of interventions that have been used, or proposed, to treat persisting olfactory dysfunction due to COVID-19 infection. A secondary objective is to keep the evidence up-to-date, using a living systematic review approach.  SEARCH METHODS: The Cochrane ENT Information Specialist searched the Cochrane COVID-19 Study Register; Cochrane ENT Register; CENTRAL; Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished studies. The date of the search was 16 December 2020.

SELECTION CRITERIA

Randomised controlled trials including participants who had symptoms of olfactory disturbance following COVID-19 infection. Only individuals who had symptoms for at least four weeks were included in this review. Studies compared any intervention with no treatment or placebo.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodological procedures. Primary outcomes were the recovery of sense of smell, disease-related quality of life and serious adverse effects. Secondary outcomes were the change in sense of smell, general quality of life, prevalence of parosmia and other adverse effects (including nosebleeds/bloody discharge). We used GRADE to assess the certainty of the evidence for each outcome.

MAIN RESULTS

We included one study with 18 participants, which compared the use of a 15-day course of oral steroids combined with nasal irrigation (consisting of an intranasal steroid/mucolytic/decongestant solution) with no intervention. Psychophysical testing was used to assess olfactory function at baseline, 20 and 40 days. Systemic corticosteroids plus intranasal steroid/mucolytic/decongestant compared to no intervention Recovery of sense of smell was assessed after 40 days (25 days after cessation of treatment) using the Connecticut Chemosensory Clinical Research Center (CCCRC) score. This tool has a range of 0 to 100, and a score of ≥ 90 represents normal olfactory function. The evidence is very uncertain about the effect of this intervention on recovery of the sense of smell at one to three months (5/9 participants in the intervention group scored ≥ 90 compared to 0/9 in the control group; risk ratio (RR) 11.00, 95% confidence interval (CI) 0.70 to 173.66; 1 study; 18 participants; very low-certainty evidence). Change in sense of smell was assessed using the CCCRC score at 40 days. This study reported an improvement in sense of smell in the intervention group from baseline (median improvement in CCCRC score 60, interquartile range (IQR) 40) compared to the control group (median improvement in CCCRC score 30, IQR 25) (1 study; 18 participants; very low-certainty evidence). Serious adverse events andother adverse events were not identified in any participants of this study; however, it is unclear how these outcomes were assessed and recorded (1 study; 18 participants; very low-certainty evidence).

AUTHORS' CONCLUSIONS

There is very limited evidence available on the efficacy and harms of treatments for persistent olfactory dysfunction following COVID-19 infection. However, we have identified other ongoing trials in this area. As this is a living systematic review we will update the data regularly, as new results become available. For this (first) version of the living review we identified only one study with a small sample size, which assessed systemic steroids and nasal irrigation (intranasal steroid/mucolytic/decongestant). However, the evidence regarding the benefits and harms from this intervention to treat persistent post-COVID-19 olfactory dysfunction is very uncertain.

Canine Special Senses: Considerations in Olfaction, Vision, and Audition

Canine companions have learned to aid in performing tasks and conducting work for decades. Areas where unique capabilities of working dogs are harnessed are growing. This expansion, alongside efforts to increase domestic purpose-bred stock and awareness of the important role working dogs play in society, is increasing the role veterinarians provide. This article provides a brief overview of 3 key sensory systems in working dogs and highlights considerations for care related to each olfaction, audition, and vision.

Drug Repurposing in the COVID-19 Era: Insights from Case Studies Showing Pharmaceutical Peculiarities

COVID-19 may lead to severe respiratory distress syndrome and high risk of death in some patients. So far (January 2021), only the antiviral remdesivir has been approved, although no significant benefits in terms of mortality and clinical improvement were recently reported. In a setting where effective and safe treatments for COVID-19 are urgently needed, drug repurposing may take advantage of the fact that the safety profile of an agent is already well known and allows rapid investigation of the efficacy of potential treatments, at lower costs and with reduced risk of failure. Furthermore, novel pharmaceutical formulations of older agents (e.g., aerosolized administration of chloroquine/hydroxychloroquine, remdesivir, heparin, pirfenidone) have been tested in order to increase pulmonary delivery and/or antiviral effects of potentially active drugs, thus overcoming pharmacokinetic issues. In our review, we will highlight the importance of the drug repurposing strategy in the context of COVID-19, including regulatory and ethical aspects, with a specific focus on novel pharmaceutical formulations and routes of administration.

Zinc against COVID-19? Symptom surveillance and deficiency risk groups

A wide variety of symptoms is associated with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection, and these symptoms can overlap with other conditions and diseases. Knowing the distribution of symptoms across diseases and individuals can support clinical actions on timelines shorter than those for drug and vaccine development. Here, we focus on zinc deficiency symptoms, symptom overlap with other conditions, as well as zinc effects on immune health and mechanistic zinc deficiency risk groups. There are well-studied beneficial effects of zinc on the immune system including a decreased susceptibility to and improved clinical outcomes for infectious pathogens including multiple viruses. Zinc is also an anti-inflammatory and anti-oxidative stress agent, relevant to some severe Coronavirus Disease 2019 (COVID-19) symptoms. Unfortunately, zinc deficiency is common worldwide and not exclusive to the developing world. Lifestyle choices and preexisting conditions alone can result in zinc deficiency, and we compile zinc risk groups based on a review of the literature. It is also important to distinguish chronic zinc deficiency from deficiency acquired upon viral infection and immune response and their different supplementation strategies. Zinc is being considered as prophylactic or adjunct therapy for COVID-19, with 12 clinical trials underway, highlighting the relevance of this trace element for global pandemics. Using the example of zinc, we show that there is a critical need for a deeper understanding of essential trace elements in human health, and the resulting deficiency symptoms and their overlap with other conditions. This knowledge will directly support human immune health for decreasing susceptibility, shortening illness duration, and preventing progression to severe cases in the current and future pandemics.

Intranasal Antiviral Drug Delivery and Coronavirus Disease 2019 (COVID-19): A State of the Art Review

OBJECTIVE

To provide a state of the art review of intranasal antiviral drug delivery and to discuss current applications, adverse reactions, and future considerations in the management of coronavirus disease 2019 (COVID-19).

DATA SOURCES

PubMed, Embase, and Clinicaltrials.gov search engines.

REVIEW METHODS

A structured search of the current literature was performed of dates up to and including April 2020. Search terms were queried as related to topics of antiviral agents and intranasal applications. A series of video conferences was convened among experts in otolaryngology, infectious diseases, public health, pharmacology, and virology to review the literature and discuss relevant findings.

CONCLUSIONS

Intranasal drug delivery for antiviral agents has been studied for many years. Several agents have broad-spectrum antiviral activity, but they still require human safety and efficacy trials prior to implementation. Intranasal drug delivery has potential relevance for future clinical trials in the settings of disease spread prevention and treatment of SARS-CoV-2 and other viral diseases.

IMPLICATIONS FOR PRACTICE

Intranasal drug delivery represents an important area of research for COVID-19 and other viral diseases. The consideration of any potential adverse reactions is paramount.

Zinc Exacerbates Tau Pathology in a Tau Mouse Model

Hyperphosphorylated tau protein is a key pathology in Alzheimer's disease (AD), frontotemporal dementia, chronic traumatic encephalopathy, and Parkinson's disease. The essential trace element zinc exacerbates tauopathy in vitro as well as in a Drosophila model of AD. However, the interaction has never been assessed behaviorally or biochemically in mammals. Zinc supplementation is prevalent in society, finding use as a treatment for macular degeneration and cataracts, and is also taken as an immune system booster with high levels appearing in multivitamins marketed toward the elderly. Using a transgenic mouse model that contains the human gene for tau protein (P301L), we assessed the effects of excess chronic zinc supplementation on tau pathology. Behavioral tests included nest building, circadian rhythm, Morris Water Maze, fear conditioning, and open field. Biochemically, total tau and Ser396 phosphorylation were assessed using western blot. Number of tangles were assessed by Thioflavin-S and free zinc levels were assessed by Zinpyr-1. Tau mice demonstrated behavioral deficits compared to control mice. Zinc supplementation exacerbated tauopathic deficits in circadian rhythm, nesting behavior, and Morris Water Maze. Biochemically, zinc-supplemented tau mice showed increased phosphorylation at pSer396. Zinc supplementation in tau mice also increased tangle numbers in the hippocampus while decreasing free-zinc levels, demonstrating that tangles were sequestering zinc. These results show that zinc intensified the deficits in behavior and biochemistry caused by tau.

The Olfactory System of Zebrafish as a Model for the Study of Neurotoxicity and Injury: Implications for Neuroplasticity and Disease

The olfactory system, composed of the olfactory organs and the olfactory bulb, allows organisms to interact with their environment and through the detection of odor signals. Olfaction mediates behaviors pivotal for survival, such as feeding, mating, social behavior, and danger assessment. The olfactory organs are directly exposed to the milieu, and thus are particularly vulnerable to damage by environmental pollutants and toxicants, such as heavy metals, pesticides, and surfactants, among others. Given the widespread occurrence of olfactory toxicants, there is a pressing need to understand the effects of these harmful compounds on olfactory function. Zebrafish (Danio rerio) is a valuable model for studying human physiology, disease, and toxicity. Additionally, the anatomical components of the zebrafish olfactory system are similar to those of other vertebrates, and they present a remarkable degree of regeneration and neuroplasticity, making it an ideal model for the study of regeneration, reorganization and repair mechanisms following olfactory toxicant exposure. In this review, we focus on (1) the anatomical, morphological, and functional organization of the olfactory system of zebrafish; (2) the adverse effects of olfactory toxicants and injury to the olfactory organ; and (3) remodeling and repair neuroplasticity mechanisms following injury and degeneration by olfactory toxicant exposure.

Toxic exposures and the senses of taste and smell

This review addresses the adverse influences of neurotoxic exposures on the ability to smell and taste. These chemical senses largely determine the flavor of foods and beverages, impact food intake, and ultimately nutrition, and provide a warning for spoiled or poisonous food, leaking natural gas, smoke, airborne pollutants, and other hazards. Hence, toxicants that damage these senses have a significant impact on everyday function. As noted in detail, a large number of toxicants encountered in urban and industrial air pollution, including smoke, solvents, metals, and particulate matter can alter the ability to smell. Their influence on taste, i.e., sweet, sour, bitter, salty, and savory (umami) sensations, is not well documented. Given the rather direct exposure of olfactory receptors to the outside environment, olfaction is particularly vulnerable to damage from toxicants. Some toxicants, such as nanoparticles, have the potential to damage not only the olfactory receptor cells, but also the central nervous system structures by their entrance into the brain through the olfactory mucosa.

Olfactory dysfunction revisited: a reappraisal of work-related olfactory dysfunction caused by chemicals

Occupational exposure to numerous individual chemicals has been associated with olfactory dysfunction, mainly in individual case descriptions. Comprehensive epidemiological investigations into the olfactotoxic effect of working substances show that the human sense of smell may be impaired by exposure to metal compounds involving cadmium, chromium and nickel, and to formaldehyde. This conclusion is supported by the results of animal experiments. The level of evidence for a relationship between olfactory dysfunction and workplace exposure to other substances is relatively weak.

Olfactory dysfunction revisited: a reappraisal of work-related olfactory dysfunction caused by chemicals

Occupational exposure to numerous individual chemicals has been associated with olfactory dysfunction, mainly in individual case descriptions. Comprehensive epidemiological investigations into the olfactotoxic effect of working substances show that the human sense of smell may be impaired by exposure to metal compounds involving cadmium, chromium and nickel, and to formaldehyde. This conclusion is supported by the results of animal experiments. The level of evidence for a relationship between olfactory dysfunction and workplace exposure to other substances is relatively weak.

Information Olfactation: Harnessing Scent to Convey Data

Olfactory feedback for analytical tasks is a virtually unexplored area in spite of the advantages it offers for information recall, feature identification, and location detection. Here we introduce the concept of information olfactation as the fragrant sibling of information visualization, and discuss how scent can be used to convey data. Building on a review of the human olfactory system and mirroring common visualization practice, we propose olfactory marks, the substrate in which they exist, and their olfactory channels that are available to designers. To exemplify this idea, we present VISCENT: A six-scent stereo olfactory display capable of conveying olfactory glyphs of varying temperature and direction, as well as a corresponding software system that integrates the display with a traditional visualization display. Finally, we present three applications that make use of the viScent system: A 2D graph visualization, a 2D line and point chart, and an immersive analytics graph visualization in 3D virtual reality. We close the paper with a review of possible extensions of viScent and applications of information olfactation for general visualization beyond the examples in this paper.

The role of metals in mammalian olfaction of low molecular weight organosulfur compounds

Covering: up to the end of 2017While suggestions concerning the possible role of metals in olfaction and taste date back 50 years, only recently has it been possible to confirm these proposals with experiments involving individual olfactory receptors (ORs). A detailed discussion of recent experimental results demonstrating the key role of metals in enhancing the response of human and other vertebrate ORs to specific odorants is presented against the backdrop of our knowledge of how the sense of smell functions both at the molecular and whole animal levels. This review emphasizes the role of metals in the detection of low molecular weight thiols, sulfides, and other organosulfur compounds, including those found in strong-smelling animal excretions and plant volatiles, and those used in gas odorization. Alternative theories of olfaction are described, with evidence favoring the modified "shape" theory. The use of quantum mechanical/molecular modeling (QM/MM), site-directed mutagenesis and saturation-transfer-difference (STD) NMR is discussed, providing support for biological studies of mouse and human receptors, MOR244-3 and OR OR2T11, respectively. Copper is bound at the active site of MOR244-3 by cysteine and histidine, while cysteine, histidine and methionine are involved with OR2T11. The binding pockets of these two receptors are found in different locations in the three-dimensional seven transmembrane models. Another recently deorphaned human olfactory receptor, OR2M3, highly selective for a thiol from onions, and a broadly-tuned thiol receptor, OR1A1, are also discussed. Other topics covered include the effects of nanoparticles and heavy metal toxicants on vertebrate and fish ORs, intranasal zinc products and the loss of smell (anosmia).

Zinc gluconate toxicity in wild-type vs. MT1/2-deficient mice

Previous studies have suggested that oral zinc supplementation can help reduce the duration of the common cold; however, the use of intranasal (IN) zinc is strongly associated with anosmia, or the loss of the sense of smell, in humans. Prior studies from this lab showed that upregulation of metallothioneins (MT) is a rapid and robust response to zinc gluconate (ZG). Therefore, we assessed the role of MT in the recovery of nasal epithelial damage resulting from IN zinc administration. The main studies in this investigation used a high dose of ZG (170mM) to ensure ablation of the olfactory mucosa, so that the progression of histological and functional recovery could be assessed. In vivo studies using wild-type, MT1/2 knockout mice (MT KO), and heterozygotes administered ZG by IN instillation showed profound loss of the olfactory mucosa in the nasal cavity. Recovery was monitored, and a lower percentage of the MT KO mice were able to smell 28 d after treatment; however, no significant difference was observed in the rate of cell proliferation in the basal layer of the olfactory epithelium between MT KO and wild-type mice. A lower concentration of ZG (33mM), equivalent to that found in homeopathic IN ZG preparations, also caused olfactory epithelial toxicity in mice. These studies suggest that the use of zinc in drug formulations intended for IN administration in humans must be carefully evaluated for their potential to cause olfactory functional deficits.

Environmental Toxicants-Induced Immune Responses in the Olfactory Mucosa

Olfactory sensory neurons (OSNs) are the receptor cells for the sense of smell. Although cell bodies are located in the olfactory mucosa (OM) of the nasal cavity, OSN axons directly project to the olfactory bulb (OB) that is a component of the central nervous system (CNS). Because of this direct and short connection from this peripheral tissue to the CNS, the olfactory system has attracted attention as a port-of-entry for environmental toxicants that may cause neurological dysfunction. Selected viruses can enter the OB via the OM and directly affect the CNS. On the other hand, environmental toxicants may induce inflammatory responses in the OM, including infiltration of immune cells and production of inflammatory cytokines. In addition, these inflammatory responses cause the loss of OSNs that are then replaced with newly generated OSNs that re-connect to the OB after inflammation has subsided. It is now known that immune cells and cytokines in the OM play important roles in both degeneration and regeneration of OSNs. Thus, the olfactory system is a unique neuroimmune interface where interaction between nervous and immune systems in the periphery significantly affects the structure, neuronal circuitry, and immunological status of the CNS. The mechanisms by which immune cells regulate OSN loss and the generation of new OSNs are, however, largely unknown. To help develop a better understanding of the mechanisms involved, we have provided a review of key research that has investigated how the immune response in the OM affects the pathophysiology of OSNs.

Mechanistic studies of the toxicity of zinc gluconate in the olfactory neuronal cell line Odora

Zinc is both an essential and potentially toxic metal. It is widely believed that oral zinc supplementation can reduce the effects of the common cold; however, there is strong clinical evidence that intranasal (IN) zinc gluconate (ZG) gel treatment for this purpose causes anosmia, or the loss of the sense of smell, in humans. Using the rat olfactory neuron cell line, Odora, we investigated the molecular mechanism by which zinc exposure exerts its toxic effects on olfactory neurons. Following treatment of Odora cells with 100 and 200μM ZG for 0-24h, RNA-seq and in silico analyses revealed up-regulation of pathways associated with zinc metal response, oxidative stress, and ATP production. We observed that Odora cells recovered from zinc-induced oxidative stress, but ATP depletion persisted with longer exposure to ZG. ZG exposure increased levels of NLRP3 and IL-1β protein levels in a time-dependent manner, suggesting that zinc exposure may cause an inflammasome-mediated cell death, pyroptosis, in olfactory neurons.

Position on zinc delivery to olfactory nerves in intranasal insulin phase I-III clinical trials

Zinc in pancreatic insulin is essential for processing and action of the peptide, while in commercial preparations zinc promotes hexameric structure and prevents aggregate formation. In 2002, for the first time, insulin was delivered to humans intranasally with resulting cerebrospinal fluid insulin increases, but steady peripheral insulin levels. The novel method of increasing brain insulin levels without changes in the periphery resulted in an expansion of brain insulin research in clinical trials. As pre-clinical research has shown that brain insulin modulates a number functions, including food cravings and eating behavior, learning and memory functions, stress and mood regulation; realization of beneficial effects of insulin in modulating these functions in clinical populations became a possibility with the new direct-to-brain insulin delivery methodology. However, zinc, being integral to insulin structure and function, is neurotoxic, and has resulted in adverse effects to human health. In the last century, intranasal zinc was given preventively during the time of polio outbreak, and in the 21st century intranasal zinc was widely used over the counter to prevent common cold. In both cases, patients experienced partial or complete loss of smell. This paper is the first one to analyze zinc salts and concentrations of those two epidemiological adversities and directly compare formulations distributed to the public with animal toxicity data. The information gained from animal and epidemiological data provides a foundation for the formation of opinion given in this paper regarding safety of intranasal zinc in emerging clinical trials with intranasal insulin.

The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis

BACKGROUND

A previous meta-analysis found that high dose zinc acetate lozenges reduced the duration of common colds by 42%, whereas low zinc doses had no effect. Lozenges are dissolved in the pharyngeal region, thus there might be some difference in the effect of zinc lozenges on the duration of respiratory symptoms in the pharyngeal region compared with the nasal region. The objective of this study was to determine whether zinc acetate lozenges have different effects on the duration of common cold symptoms originating from different anatomical regions.

METHODS

We analyzed three randomized trials on zinc acetate lozenges for the common cold administering zinc in doses of 80-92 mg/day. All three trials reported the effect of zinc on seven respiratory symptoms, and three systemic symptoms. We pooled the effects of zinc lozenges for each symptom and calculated point estimates and 95% confidence intervals (95% CI).

RESULTS

Zinc acetate lozenges shortened the duration of nasal discharge by 34% (95% CI: 17% to 51%), nasal congestion by 37% (15% to 58%), sneezing by 22% (-1% to 45%), scratchy throat by 33% (8% to 59%), sore throat by 18% (-10% to 46%), hoarseness by 43% (3% to 83%), and cough by 46% (28% to 64%). Zinc lozenges shortened the duration of muscle ache by 54% (18% to 89%), but there was no difference in the duration of headache and fever.

CONCLUSIONS

The effect of zinc acetate lozenges on cold symptoms may be associated with the local availability of zinc from the lozenges, with the levels being highest in the pharyngeal region. However our findings indicate that the effects of zinc ions are not limited to the pharyngeal region. There is no indication that the effect of zinc lozenges on nasal symptoms is less than the effect on the symptoms of the pharyngeal region, which is more exposed to released zinc ions. Given that the adverse effects of zinc in the three trials were minor, zinc acetate lozenges releasing zinc ions at doses of about 80 mg/day may be a useful treatment for the common cold, started within 24 hours, for a time period of less than two weeks.

The nasal approach to delivering treatment for brain diseases: an anatomic, physiologic, and delivery technology overview

The intricate pathophysiology of brain disorders, difficult access to the brain, and the complexity and high risks and costs of drug development represent major hurdles for improving therapies. Nose-to-brain drug transport offers an attractive alternative or addition to formulation-only strategies attempting to enhance drug penetration into the CNS. Although still a matter of controversy, many studies in animals claim direct nose-to-brain transport along the olfactory and trigeminal nerves, circumventing the traditional barriers to CNS entry. Some clinical trials in man also suggest nose-to-brain drug delivery, although definitive proof in man is lacking. This review focuses on new nasal delivery technologies designed to overcome inherent anatomical and physiological challenges and facilitate more efficient and targeted drug delivery for CNS disorders.

Evaluation of the toxicity of zinc in the rat olfactory neuronal cell line, Odora

Zinc (Zn) has long been touted as a panacea for common cold. Recently, there has been some controversy over whether an intranasal (IN) zinc gluconate gel, purported to fight colds, causes anosmia, or loss of the sense of smell, in humans. Previous evidence has shown that IN zinc sulfate (ZnSO4) solutions can cause anosmia in humans as well as significant damage to the olfactory epithelium in rodents. Using an in vitro olfactory neuron model (the rat Odora cell line), we tested the hypothesis that Zn toxicity was caused by inhibition of the hydrogen voltage-gated channel 1(HVCN1), leading to acidosis and apoptotic cell death. Following studies to characterize the toxicity of zinc gluconate and ZnSO4, Odora cells were grown on coverslips and loaded with 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester to measure intracellular pH in the presence and absence of Zn salts. While we found that HVCN1 is not functional in Odora cells, we found that olfactory neurons in vitro maintain their intracellular pH through a sodium/proton exchanger, specifically the sodium proton antiporter 1. ZnSO4, at nontoxic levels, had no impact on intracellular pH after acute exposure or after 24 h of incubation with the cells. In conclusion, Zn toxicity is not mediated through an acidification of intracellular pH in olfactory neurons in vitro.

A potent combination microbicide that targets SHIV-RT, HSV-2 and HPV

Prevalent infection with human herpes simplex 2 (HSV-2) or human papillomavirus (HPV) is associated with increased human immunodeficiency virus (HIV) acquisition. Microbicides that target HIV as well as these sexually transmitted infections (STIs) may more effectively limit HIV incidence. Previously, we showed that a microbicide gel (MZC) containing MIV-150, zinc acetate (ZA) and carrageenan (CG) protected macaques against simian-human immunodeficiency virus (SHIV-RT) infection and that a ZC gel protected mice against HSV-2 infection. Here we evaluated a modified MZC gel (containing different buffers, co-solvents, and preservatives suitable for clinical testing) against both vaginal and rectal challenge of animals with SHIV-RT, HSV-2 or HPV. MZC was stable and safe in vitro (cell viability and monolayer integrity) and in vivo (histology). MZC protected macaques against vaginal (p<0.0001) SHIV-RT infection when applied up to 8 hours (h) prior to challenge. When used close to the time of challenge, MZC prevented rectal SHIV-RT infection of macaques similar to the CG control. MZC significantly reduced vaginal (p<0.0001) and anorectal (p = 0.0187) infection of mice when 10(6) pfu HSV-2 were applied immediately after vaginal challenge and also when 5×10(3) pfu were applied between 8 h before and 4 h after vaginal challenge (p<0.0248). Protection of mice against 8×10(6) HPV16 pseudovirus particles (HPV16 PsV) was significant for MZC applied up to 24 h before and 2 h after vaginal challenge (p<0.0001) and also if applied 2 h before or after anorectal challenge (p<0.0006). MZC provides a durable window of protection against vaginal infection with these three viruses and, against HSV-2 and HPV making it an excellent candidate microbicide for clinical use.

A modified zinc acetate gel, a potential nonantiretroviral microbicide, is safe and effective against simian-human immunodeficiency virus and herpes simplex virus 2 infection in vivo

We previously showed that a prototype gel comprising zinc acetate (ZA) in carrageenan (CG) protected mice against vaginal and rectal herpes simplex virus 2 (HSV-2) challenge as well as macaques against vaginal simian-human immunodeficiency virus reverse transcriptase (SHIV-RT) challenge. In this work, we modified buffers and cosolvents to obtain a stable, nearly iso-osmolal formulation and evaluated its safety and efficacy against SHIV-RT and HSV-2. In vitro toxicity to lactobacilli and Candida albicans was determined. Macaques were given daily doses of ZA and CG (ZA/CG) or CG alone vaginally for 14 days and challenged with SHIV-RT 24 h later. Mice were challenged vaginally or rectally with HSV-2 immediately after a single gel treatment to measure efficacy or vaginally 12 h after daily gel treatment for 7 days to evaluate the gel's impact on susceptibility to HSV-2 infection. The modified ZA/CG neither affected the viability of lactobacilli or C. albicans nor enhanced vaginal HSV-2 infection after daily ZA/CG treatment. Vaginal SHIV-RT infection of macaques was reduced by 66% (P = 0.006) when macaques were challenged 24 h after the last dose of gel. We observed 60% to 80% uninfected mice after vaginal (P < 0.0001) and rectal (P = 0.008) high-dose HSV-2 challenge. The modified ZA/CG gel is safe and effective in animal models and represents a potential candidate to limit the transmission of HIV and HSV-2.

Anosmia does not impair the anxiolytic-like effect of lavender essential oil inhalation in mice

AIM

The inhalation of Lavandula angustifolia (lavender) essential oil has anxiolytic-like effects in animal models and humans, but its mechanism of action is still not fully understood. The inhalation of essential oils can induce anxiolytic effects through the central nervous system (e.g., lung absorption and bloodstream transport) or stimulation of the olfactory system and secondary activation of brain regions. Thus, the main objective of the present study was to evaluate whether the perception of lavender essential oil aroma, when inhaled, is necessary to obtain its anxiolytic-like effects in mice tested in the marble-burying test.

MAIN METHODS

Anosmia was induced by irrigating the nasal cavity with zinc gluconate+zinc acetate so that the mice could not detect odors in the olfactory discrimination test. The marble-burying test was used to evaluate the anxiolytic-like effects of inhaled lavender essential oil.

KEY FINDINGS

Anosmia did not interfere with the anxiolytic-like effect of lavender essential oil inhalation in the marble-burying test at concentrations of 2.5% (number of marbles buried: vehicle, 4.7±1.0; zinc, 6.2±2.2; p>0.10) and 5% (number of marbles buried: vehicle, 3.4±0.8; zinc, 4.3±0.9; p>0.10). Lavender essential oil at a concentration of 0.5% was ineffective.

SIGNIFICANCE

These results suggest that olfactory system activation is unlikely to participate in the anxiolytic-like effect of lavender essential oil inhalation.

Drug development of intranasally delivered peptides

Intranasal drug delivery has attracted increasing attention as a noninvasive route of administration for therapeutic proteins and peptides. The delivery of therapeutic peptides through the nasal route provides an alternative to intravenous or subcutaneous injections. This review highlights the drug-development considerations unique to nasal therapeutics and discusses some of the factors and strategies that affect and can improve nasal absorption of peptides. The selectivity and good safety profile typical of peptide therapeutics, along with the dose limitation for intranasal administration, can provide challenges in drug development. Therefore, nasal peptide therapeutics often require special considerations in the nonclinical safety evaluations, such as determining drug exposure in the context of the maximum feasible dose in order to adequately prepare nasal products for clinical studies.

Nasal gel and olfactory cleft

OBJECTIVE

To evaluate whether a nasal gel, administrated using a radial-hole inhaler, reaches the olfactory cleft and if a different administration method influences distribution.

MATERIAL AND METHOD

Sixteen healthy volunteers underwent a nasal endoscopy at 1 and 7minutes after the administration of a intranasal gel, with a different method in each fossa.

RESULTS

No dye deposition was identified at the olfactory cleft, middle turbinate or middle meatus. In all cases the gel was identified at the nasal vestibule. On the right side, the second most frequent dye identification area was the inferior turbinate, with a rate of 87% at the first minute and 75% at 7 minutes. It was followed by the septum (75 and 62%) and the inferior meatus (6.2 and 12.5%). On the left side, the second most frequent stained area was the septum (18.7 and 13.5%), followed by the inferior meatus (6.5 and 65%). No inferior turbinate staining was found in the left side. There was a significant difference in the deposition rate at the septum (P<.01) and inferior turbinate (P<.001), when both administration methods were compared.

CONCLUSIONS

No nasal gel, administrated using a radial-hole inhaler, was found at the olfactory cleft, middle turbinate or middle meatus. Gel distribution was located at the anterior and inferior portion of the nose, independent of the administration method used. Significantly different gel distribution rates were found at the septum and inferior turbinate when the 2 administration methods were compared.

Sniffing out pharmacology: interactions of drugs with human olfaction

Advances in the understanding of the sense of smell have increased awareness of the role of olfaction in human life. Odors are perceived via specific G protein-coupled receptors (GPCRs) with cAMP as the second messenger. Drugs that interact with this signaling cascade, such as opioids, cannabinoids and sildenafil, are known to reduce olfactory function. Drugs that are active in the central nervous system (CNS) may also hinder the complex processing of olfactory information to distinguish, via pattern recognition, thousands of odors from the signals of only ∼400 distinct olfactory receptors. Many other interactions with drug targets expressed at the olfactory bulb are also likely to occur. However, olfactory drug effects have rarely been explored in controlled studies. In the current activities of drug development and re-purposing, olfaction could become highly important because it can impact significantly upon the enjoyment of food. With an established molecular basis and using available tools, the assessment of olfaction in drug development and approval is advised.

Zinc acetate/carrageenan gels exhibit potent activity in vivo against high-dose herpes simplex virus 2 vaginal and rectal challenge

Topical microbicides that block the sexual transmission of HIV and herpes simplex virus 2 (HSV-2) are desperately needed to reduce the incidence of HIV infections worldwide. Previously we completed phase 3 testing of the carrageenan-based gel Carraguard. Although the trial did not show that Carraguard is effective in preventing HIV transmission during vaginal sex, it did show that Carraguard is safe when used weekly for up to 2 years. Moreover, Carraguard has in vitro activity against human papillomavirus (HPV) and HSV-2 and favorable physical and rheological properties, which makes it a useful vehicle to deliver antiviral agents such as zinc acetate. To that end, we previously reported that a prototype zinc acetate carrageenan gel protects macaques against vaginal challenge with combined simian-human immunodeficiency virus reverse transcriptase (SHIV-RT). Herein, we report the safety and efficacy of a series of zinc acetate and/or carrageenan gels. The gels protected mice (75 to 85% survival; P < 0.001) against high-dose (10(6)-PFU) HSV-2 vaginal or rectal challenge. In contrast, zinc acetate formulated in HEC (hydroxyethylcellulose; or the Universal Placebo) failed to protect mice against the high-dose vaginal HSV-2 challenge (similar to aqueous zinc acetate solution and the placebo controls). The gels were found to be effective spreading gels, exhibited limited toxicity in vitro, caused minimal damage to the architecture of the cervicovaginal and rectal mucosae in vivo, and induced no increased susceptibility to HSV-2 infection in a mouse model. Our results provide a strong rationale to further optimize and evaluate the zinc acetate/carrageenan gels for their ability to block the sexual transmission of HIV and HSV-2.

Human sinonasal explant system for testing cytotoxicity of intranasal agents

BACKGROUND

Intranasal agents play a critical role in the management of sinonasal disorders. There are ongoing efforts to develop new intranasal medications to combat sinonasal disease. Some intranasal agents, however, can have cytotoxic effects on human sinonasal tissue. In order to facilitate safe drug discovery, we developed a simple and reliable in vitro screening assay using human sinonasal explants to measure the cytotoxic profiles of intranasal agents.

METHODS

We obtained sinonasal tissues from several regions of the nasal cavity from 12 patients undergoing endoscopic sinonasal surgery. These tissues were cultured on polytetrafluoroethylene membrane in serum-free growth medium. We determined the biochemical properties of these explants by measuring extracellular lactate dehydrogenase (LDH) levels and performing histological analyses over a period of 1 to 2 weeks. We then examined the cytotoxic profiles of 13 intranasal agents by measuring extracellular LDH levels using the human sinonasal explant system.

RESULTS

Sinonasal explants exhibited a rapid reduction in extracellular LDH levels indicating stabilization in the culture environment within 2 days. Histological analysis showed maintenance of good cellular architecture for up to 2 weeks. The explants displayed intact epithelium and expressed βIII-tubulin and Ki-67. Of the 13 tested intranasal agents, 1% zinc sulfate (ZnSO(4) ), 5% ZnSO(4) , and Zicam application were cytotoxic.

CONCLUSION

Based on the unique biochemical properties of the human nasal explant culture system, we developed a simple and reliable in vitro screening assay to determine the cytotoxic profiles of various intranasal agents by examining extracellular LDH levels and histopathology.

The therapeutic test: an ancient malady in the 21st century

The response to treatment was the diagnostic mainstay in ancient times when diseases were poorly understood. Now that the bases of most diseases are known, appropriate diagnostic means are available. However, many physicians still rely on therapeutic tests to establish diagnoses. Since most illnesses are self-limited and because of the placebo effect, many physicians and patients attribute the improvement to the medication and believe that the correct diagnosis was made. However, inappropriate therapeutic tests often lead to diagnostic delays, rapid emergence of antibiotic-resistant bacterial pathogens, increased risks of adverse drug reactions, and unnecessary expenses. To reduce the frequency of unwarranted therapeutic tests, health-care professionals and educators must take steps to rectify the problem.

Toxin-induced chemosensory dysfunction: a case series and review

BACKGROUND

Toxic chemical exposures are estimated to account for 1-5% of all olfactory disorders. Both olfactory neurons and taste buds are in direct contact with environmental agents because of their relatively unprotected anatomic locations, thereby making them susceptible to damage from acute and chronic toxic exposures. The aim of this study was to illustrate different aspects of the diagnostic and therapeutic approach to this disorder using a series of case reports and review of the literature.

METHODS

Cases were selected for inclusion based on a retrospective chart review of patients who presented to a university-based nasal dysfunction clinic with toxin-induced olfactory or gustatory dysfunction between January 1985 and December 2008. Workup included complete history, otolaryngologic examination, psychophysical testing, and imaging.

RESULTS

Patient ages ranged from 31 to 67 years (mean, 49.3 years). Etiology of chemosensory impairment included exposure to ammonia, isodecanes, hairdressing chemicals, chemotherapy, gasoline, and intranasal zinc. Five of the seven patients (71%) presented with olfactory dysfunction alone, one patient (14%) presented with dysgeusia alone, and one patient (14%) presented with both smell and taste loss. Only one patient (14%) reported parosmias. Tests of olfaction revealed normosmia in one patient (14%), mild-to-moderate hyposmia in one patient (14%), and severe hyposmia to anosmia in five patients (72%). Both patients who reported taste disorders had hypogeusia on testing.

CONCLUSION

This case series illustrates the wide spectrum of this disorder and provides a framework for the workup and treatment of these patients.

Zicam-induced damage to mouse and human nasal tissue

Intranasal medications are used to treat various nasal disorders. However, their effects on olfaction remain unknown. Zicam (zinc gluconate; Matrixx Initiatives, Inc), a homeopathic substance marketed to alleviate cold symptoms, has been implicated in olfactory dysfunction. Here, we investigated Zicam and several common intranasal agents for their effects on olfactory function. Zicam was the only substance that showed significant cytotoxicity in both mouse and human nasal tissue. Specifically, Zicam-treated mice had disrupted sensitivity of olfactory sensory neurons to odorant stimulation and were unable to detect novel odorants in behavioral testing. These findings were long-term as no recovery of function was observed after two months. Finally, human nasal explants treated with Zicam displayed significantly elevated extracellular lactate dehydrogenase levels compared to saline-treated controls, suggesting severe necrosis that was confirmed on histology. Our results demonstrate that Zicam use could irreversibly damage mouse and human nasal tissue and may lead to significant smell dysfunction.

Treatment of naturally acquired common colds with zinc: a structured review

BACKGROUND

Over the past 20 years, the use of zinc as an over-the-counter alternative therapy for the common cold has vastly grown in popularity. Recent reports of potentially permanent anosmia caused by intranasal zinc therapy warrant careful analysis of the therapeutic effects of zinc.

METHODS

A search of the Medline database (including articles published during 1966-2006) for studies of zinc and the common cold produced 105 published reports. Fourteen were randomized, placebo-controlled studies that examined the effect of zinc lozenges, nasal sprays, or nasal gels on naturally acquired common colds. Eleven features of experimental design affecting signal quality, chance, bias, and blinding were used to evaluate the 14 placebo-controlled studies. These criteria were validated case definition, quantifiable hypothesis, sample size calculation, randomized assignment, double blinding, proof of blinding, measurement of compliance, measurement of dropout rate, analysis by intent to treat, description of methods of analysis, and measurements of probability. Equal weight was given to each criterion, because failure to meet any one could potentially invalidate the findings of a clinical trial.

RESULTS

Four studies met all 11 criteria. Three of these studies reported no therapeutic effect from zinc lozenge or nasal spray. One study reported positive results from zinc nasal gel. Of the remaining 10 studies, 6 reported a positive effect and 4 reported no effect. Intent-to-treat analysis was the most common criterion not met.

CONCLUSIONS

This structured review suggests that the therapeutic effectiveness of zinc lozenges has yet to be established. One well-designed study did report a positive effect of zinc nasal gel.

Olfaction and olfactory epithelium in mice treated with zinc gluconate

OBJECTIVE

We assessed whether a nasal spray containing zinc gluconate (ZG) compromises the integrity of olfactory epithelium and olfactory function.

METHODS

Axonal transport of horseradish peroxidase from olfactory epithelium to the olfactory bulb was studied in 2- to 21-day survival mice given intranasal injections of 2, 8, or 50 microL of ZG (approximately 4, 15, and 94 times the equivalent recommended human dose). Other similarly treated mice were tested using precision olfactometry to detect and discriminate odors.

RESULTS

Anatomic changes were graded as a function of dose and survival time. Two microliter injections had no discernable effect. while the 50 microL volume produced substantial deafferentation of input to the olfactory bulb in short-survival cases. Nearly complete restitution of input occurred within 3 weeks. At each volume and survival time, zinc sulfate (ZS) had a greater effect. Behaviorally, 2 microL and 8 microL ZG-treated mice and those given multiple injections of 2 microL ZG performed as well as controls, whereas those given 50 microL were hyposmic but not anosmic. ZS-treated mice performed more poorly, and those injected with 50 microL were anosmic for the first 8 to 10 test days.

CONCLUSIONS

A massive dose of a ZG nasal spray did cause a transient disruption of the olfactory epithelium and compromised olfaction. More moderate volumes, even those far in excess of a recommended dose, were largely without effect on odor detection and discrimination tasks. These outcomes fail to support the claims from recent clinical case reports that use of a ZG-containing nasal spray can produce anosmia.