Evidence for a role of metformin in preventing olfactory dysfunction among older adults.

BACKGROUND: Olfactory dysfunction (OD) is increasingly recognized as a hallmark of unhealthy aging and is intimately associated with mortality, but therapies remain elusive. Recognizing the increased prevalence of OD in individuals with diabetes, and the potential anti-aging effects of metformin, we studied the association of metformin use with OD. METHODS: Cross-temporal study of participants from Waves 2 (2010-11) and 3 (2015-16) of the National Social Life, Health, and Aging Project (NSHAP), a nationally representative cohort study of community-dwelling older adults. We included participants with diabetes who had complete data on olfaction and relevant covariates at Wave 2 and were not lost to follow-up at Wave 3. Olfactory identification (OI), the ability to identify the odorant, and olfactory sensitivity (OS), the ability to detect the presence of an odorant, were tested. Weighted multivariable logistic regression was used to study the association between metformin use at Wave 2 (baseline) and odds of having impaired OI/OS at Wave 3, adjusted for age, sex, race/ethnicity, education, smoking, BMI, HbA1c, years since diabetes diagnosis, and insulin use. RESULTS: Among 228 participants with diabetes (mean age=70 years, 53% female, 21% Black), 112 (49%) used metformin at baseline. Relative to nonusers, users had 58% lower odds of impaired OI and 67% lower odds of impaired OS at Wave 3. Among participants with normal baseline OS (N=62), users had 97% lower odds of impaired OS at Wave 3. CONCLUSIONS: Metformin use is associated with lower odds of OD among individuals with diabetes, suggesting a potential protective effect on olfaction. Future work including a larger sample and additional information on metformin use is needed to establish whether these findings are independent of diabetic control.

Central role of the CNGA4 channel subunit in Ca2+-calmodulin-dependent odor adaptation.

Heteromultimeric cyclic nucleotide-gated (CNG) channels play a central role in the transduction of odorant signals and subsequent adaptation. The contributions of individual subunits to native channel function in olfactory receptor neurons remain unclear. Here, we show that the targeted deletion of the mouse CNGA4 gene, which encodes a modulatory CNG subunit, results in a defect in odorant-dependent adaptation. Channels in excised membrane patches from the CNGA4 null mouse exhibited slower Ca2+-calmodulin-mediated channel desensitization. Thus, the CNGA4 subunit accelerates the Ca2+-mediated negative feedback in olfactory signaling and allows rapid adaptation in this sensory system.

Allergy testing and immunotherapy in an academic otolaryngology practice: a 20-year review.

OBJECTIVE: Allergic disease plays a central role in the clinical practice of otolaryngology. The purpose of this study was to review the 20-year experience of an allergy clinic integrated within an otolaryngology practice at a major academic institution. STUDY DESIGN: We performed a retrospective database review of over 3300 otolaryngology patients referred for allergy skin testing between 1979 and 1999. RESULTS: Approximately 80% of patients referred for allergy testing in our clinic had positive test results, of which 75.7% went on to undergo desensitization. The most common allergen was house dust, with allergies to mites, ragweed, and grass also prevalent. Among current allergy immunotherapy patients, 30.8% have undergone nasal septal, turbinate, and/or endoscopic sinus procedures in addition to allergy management. Nasal obstruction was the symptom most frequently persistent despite immunotherapy and the one most frequently reported to be improved by surgery. CONCLUSIONS: The otolaryngologist-head and neck surgeon is uniquely qualified to perform comprehensive medical and surgical management for patients with complex disease processes involving a component of allergy. We believe that an integrated approach to allergy within an otolaryngology practice optimizes the treatment of such patients.

Blocking adenylyl cyclase inhibits olfactory generator currents induced by "IP(3)-odors".

Vertebrate olfactory receptor neurons (ORNs) transduce odor stimuli into electrical signals by means of an adenylyl cyclase/cAMP second messenger cascade, but it remains widely debated whether this cAMP cascade mediates transduction for all odorants or only certain odor classes. To address this problem, we have analyzed the generator currents induced by odors that failed to produce cAMP in previous biochemical assays but instead produced IP(3) ("IP(3)-odors"). We show that in single salamander ORNs, sensory responses to "cAMP-odors" and IP(3)-odors are not mutually exclusive but coexist in the same cells. The currents induced by IP(3)-odors exhibit identical biophysical properties as those induced by cAMP odors or direct activation of the cAMP cascade. By disrupting adenylyl cyclase to block cAMP formation using two potent antagonists of adenylyl cyclase, SQ22536 and MDL12330A, we show that this molecular step is necessary for the transduction of both odor classes. To assess whether these results are also applicable to mammals, we examine the electrophysiological responses to IP(3)-odors in intact mouse main olfactory epithelium (MOE) by recording field potentials. The results show that inhibition of adenylyl cyclase prevents EOG responses to both odor classes in mouse MOE, even when "hot spots" with heightened sensitivity to IP(3)-odors are examined.

Ultrasensitive pheromone detection by mammalian vomeronasal neurons.

The vomeronasal organ (VNO) is a chemoreceptive organ that is thought to transduce pheromones into electrical responses that regulate sexual, hormonal and reproductive function in mammals. The characteristics of pheromone signal detection by vomeronasal neurons remain unclear. Here we use a mouse VNO slice preparation to show that six putative pheromones evoke excitatory responses in single vomeronasal neurons, leading to action potential generation and elevated calcium entry. The detection threshold for some of these chemicals is remarkably low, near 10(-11) M, placing these neurons among the most sensitive chemodetectors in mammals. Using confocal calcium imaging, we map the epithelial representation of the pheromones to show that each of the ligands activates a unique, nonoverlapping subset of vomeronasal neurons located in apical zones of the epithelium. These neurons show highly selective tuning properties and their tuning curves do not broaden with increasing concentrations of ligand, unlike those of receptor neurons in the main olfactory epithelium. These findings provide a basis for understanding chemical signals that regulate mammalian communication and sexual behaviour.

Use of computed tomography in the assessment of mandibular invasion in carcinoma of the retromolar trigone.

Carcinomas originating in the retromolar trigone (RMT) are uncommon and characterized by early spread. Determination of mandibular invasion is significant for planning therapy and determining prognosis. For oral cavity cancers in general, CT is reasonably accurate in assessing bone invasion. However, there is a paucity of information specifically addressing the value of CT in the RMT. In this study, the records of patients with biopsy-proven RMT carcinomas treated between 1984 and 1998 were reviewed with attention to preoperative CT scans and histopathologic findings during surgery. Half of the patients who were treated with primary resection had mandibular invasion. Bone invasion was not identified radiographically in 27% of patients with preoperative CT scans. The sensitivity of CT for bone involvement in RMT cancers was 50%, with a negative predictive value of 61.1%. The positive predictive value was 91.1%. These findings suggest that CT is a useful, but potentially inaccurate, predictor of bone invasion in the RMT.

Nitric oxide is a mediator of the late-phase response in an animal model of nasal allergy.

The presence of nitric oxide (NO) in the nose is well documented; however, the role of this molecule in nasal physiology is still poorly understood. Our laboratory has previously demonstrated that NO is a mediator of the immediate secretory response to an intranasal histamine challenge in a rat model of nasal allergy. Histamine challenge, however, does not elicit a late-phase response (LPR). To study the role of NO in the LPR, we developed a model of nasal allergy in which brown Norway rats are actively sensitized to the allergen ovalbumin and later challenged intranasally with either phosphate-buffered saline solution (vehicle), ovalbumin in vehicle, or ovalbumin and the NO synthase inhibitor N -nitro-l -arginine methyl ester. In each experiment, nasal lavage samples were collected 30, 120, 240, and 360 minutes after challenge. Lavage samples were analyzed for albumin content by ELISA, inflammatory cell concentration with a hemocytometer, and evidence of inflammation by light microscopy. Blocking NO synthesis with N -nitro-l -arginine methyl ester significantly inhibited both albumin exudation and inflammatory cell influx into the nasal cavity during the LPR. These data suggest that NO plays a role in the LPR of nasal allergy.

Perceptual and physiologic effects of histamine challenge on nasal breathing.

The purpose of this study is to determine the effect of histamine-induced nasal congestion on nasal airflow and the perception of externally applied resistance to nasal breathing. Nasal cross-sectional area and nasal airflow during free breathing were measured in 15 adult subjects before and after histamine challenge. The threshold for perception of resistance to nasal breathing was determined using a dynamic perturbator device, with both free breathing and controlled nasal air-flow. The average threshold for perception of nasal resistance was 0.383 Pa/cm3/s at baseline. After histamine application, there was a significant decrease in nasal cross-sectional area (p = 0.0001), associated with a decrease in nasal airflow (r = 0.6). The average threshold of perception increased to 1.373 Pa/cm3/s (p < 0.0001). When nasal airflow was controlled at the baseline rate, the threshold of perception improved to 0.638 Pa/cm3/s (p = 0.024). These findings indicate that nasal congestion causes a reduction in both nasal airflow and the perception of resistance to nasal breathing. The ability to detect nasal airway impairment is improved with increased nasal airflow. An improved understanding of the physiology of the subjective perception of nasal patency may lead to innovative methods for the treatment of nasal obstruction.

The role of nitric oxide in the neural control of nasal fluid production.

The production of nasal fluids serves an important role in the protection of the upper respiratory system, but can also be a troublesome symptom of rhinitis. The chief sources of nasal fluids are serous and mucous glandular secretion, epithelial goblet cell exocytosis, and exudation from submucosal blood vessels. This study was designed to investigate the role of nitric oxide in neurogenically mediated nasal vascular exudation and mucus secretion. A rat model of the naso-nasal reflex was developed in which one nasal cavity was challenged with histamine while albumin and mucin production were measured in the continuously perfused contralateral side. Histamine challenge was associated with a significant rise in contralateral albumin and mucin content. Perfusion with a nitric oxide synthase inhibitor (L-NAME) in the nasal cavity contralateral to nasal challenge was found to block albumin leakage, but not mucin secretion, on that side. The inhibition of vascular exudation was overcome by the addition of L-arginine, the natural substrate of nitric oxide synthase, to the perfusate. Treatment of the ipsilateral nasal of the ipsilateral nasal cavity with L-NAME did not significantly after the contralateral response. A high correlation was observed between albumin and mucin concentration in the perfusate. These findings indicate that NO is a mediator of the effector arm of the naso-nasal reflex that increases vascular permeability, but is not involved in the sensory nerve afferent pathway or in reflex mucin release. Further elucidation of the role of NO in nasal physiology may lead to novel pharmacotherapeutic approaches to the treatment of allergic and non-allergic rhinitis.

Nitric oxide is a mediator of neurogenic vascular exudation in the nose.

Rhinorrhea is a troublesome symptom of rhinitis seen commonly by otolaryngologists. The sources of nasal fluid production are glandular secretions and exudation from submucosal blood vessels. This study was designed to investigate the role of nitric oxide in neurogenically mediated vascular exudation in the nose. A rat model of the nasonasal reflex was developed in which one nasal cavity was challenged with histamine while albumin exudation was measured on the contralateral side. Histamine challenge was associated with a significant rise in albumin leakage, indicating an increase in vascular permeability. Perfusion with a nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester (L-NAME)) in the nasal cavity contralateral to nasal challenge was found to block albumin exudation on that side. This inhibition was overcome by the addition of L-arginine, the natural substrate of nitric oxide synthase, to the perfusate. Treatment of the ipsilateral nasal cavity with L-NAME did not significantly decrease the contralateral response. These findings indicate that NO is an important mediator of the effector arm of the nasonasal reflex that increases vascular permeability but is not involved in the sensory nerve afferent pathway. Further elucidation of the role of NO in nasal physiology may lead to novel pharmacotherapeutic approaches to the treatment of allergic and nonallergic rhinorrhea.

Nitric oxide mediates mucin secretion in endotoxin-induced otitis media with effusion.

The mechanisms that regulate mucin release in chronic otitis media with effusion, a leading cause of hearing loss in children, remain largely unknown. We developed an animal model using Sprague-Dawley rats to determine the factors responsible for mucin production in chronic otitis media with effusion. N-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of nitric oxide synthase, was used to investigate the role of nitric oxide in mucin secretion by the middle ear epithelium. All rats underwent eustachian tube obstruction. In the first set of rats, the middle ear was then injected transtympanically with 35 microl of either 300 mOsm Krebs-Ringer bicarbonate buffer (control group) or 1 mg/ml lipopolysaccharide in Krebs-Ringer (experimental group 1). In a second set of rats, the middle ear space was injected with lipopolysaccharide and then infused at a continuous rate for 7 days with either Krebs-Ringer (experimental group 2) or 1 mmol/L L-NAME in Krebs-Ringer (experimental group 3) through an osmotic infusion pump. After 7 days the volume of effusion and the quantity of mucin collected were significantly greater in lipopolysaccharide-exposed ears than in controls. In addition, antimucin immunostaining demonstrated mucous cell hyperplasia in response to lipopolysaccharide. The lipopolysaccharide-induced production of mucin and mucous cell hyperplasia was inhibited in ears treated with lipopolysaccharide and L-NAME. These results suggest that nitric oxide is a mediator in the pathway of mucin secretion in chronic otitis media with effusion.

The role of glucocorticoids in endotoxin-mediated otitis media with effusion.

OBJECTIVE: To understand the actions of glucocorticoids on the development and progression of endotoxin-mediated otitis media with effusion. METHODS AND DESIGN: The middle ears of 20 Sprague-Dawley rats were exposed to 35 microL of either 300-mOsm Krebs-Ringer solution (control; n = 5) or lipopolysaccharide, 1 mg/mL, dissolved in Krebs-Ringer solution (n = 15). Among the group that received lipopolysaccharide, 10 rats were randomly selected to receive dexamethasone (1 mg/kg intramuscularly), either 2 hours (n = 5) or 24 hours (n = 5) before the introduction of lipopolysaccharide. Middle ear fluid was sampled after 2, 4, and 6 hours of exposure. OUTCOME MEASURES: Middle ear fluid volume and albumin content were determined as measures of vascular extravasation. Histological sections of the middle ear mucosa were used to quantify the degree of leukocyte exudation. Data were analyzed by 1- or 2-way analysis of variance with the significance level set at P < .05. RESULTS: Lipopolysaccharide exposure caused a significant increase in the mean +/- SEM middle ear fluid volume from 29.9 +/- 0.99 to 45.8 +/- 1.4 microL between the 2- and 6-hour samplings. Lipopolysaccharide exposure caused a significant increase in the albumin content of middle ear fluid from 70.1 +/- 19.2 to 271.0 +/- 93.1 micrograms between the 2- and 6-hour samplings. Both increases were significant compared with controls. Lipopolysaccharide also caused a significant increase in leukocytes localized to the middle ear mucosa. Pretreatment of animals with dexamethasone for either 2 or 24 hours inhibited the lipopolysaccharide-induced changes. There were no differences between 2- and 24-hour pretreatment with dexamethasone. CONCLUSIONS: Dexamethasone inhibits the development of endotoxin-induced otitis media with effusion.

Acoustic rhinometry in the study of the acute nasal allergic response.

Acoustic rhinometry is a recently developed method for the objective assessment of nasal patency. In this study, acoustic rhinometry was used to measure changes in nasal cavity dimensions in the immediate response to nasal allergen challenge in eight pollen-sensitive subjects. Acoustic rhinometric changes were compared with subjective symptoms, as well as histamine in nasal secretions, cytology of nasal mucosal scrapings, and changes in olfactory function. A significantly greater decrease in nasal airway caliber occurred following allergen challenge as compared to buffer diluent challenge in the same individuals (70% +/- 7% versus 22% +/- 5%). During an allergic response, a strong correlation was found between the minimum cross-sectional area and the volume of the nasal cavity measured by acoustic rhinometry (r = .9). However, no correlation was observed between nasal airway caliber and concomitant subjective congestion reported by the subjects. A modest decrease in olfactory function was seen following allergen challenge (3.1 +/- 1.4 fewer odors identified correctly out of 20; p = .08). However, the alterations of olfactory function did not correlate with changes in nasal patency. The results presented in this study demonstrate that acoustic rhinometry has great potential as a reproducible method for the objective assessment of nasal obstruction occurring in nasal allergen challenge studies.

Fc-mediated endocytosis by human neutrophils. Ultrastructural studies.

Fc Receptors (FcR) mediate the binding and uptake by polymorphonuclear leukocytes (PMN) of antibody-coated particles and soluble immune complexes. We have studied Fc-mediated endocytosis by PMN ultrastructurally using a gold-conjugated monoclonal antibody (3G8) to block or to mark the location of FcR. Phagocytosis of antibody-coated erythrocytes (EIgG) was initiated rapidly after binding to discrete foci on the PMN plasma membrane. After the phagocytosis of EIgG, we examined the distribution of FcR remaining on the PMN plasma membrane. 3G8-Colloidal gold continued to bind to PMN after ingestion of up to three EIgG, demonstrating that all PMN FcR are not utilized during a brief phagocytic event. The endocytosis of soluble immune complexes was examined by labeling plasma membrane-bound rabbit immune complexes with goat anti-rabbit IgG conjugated to colloidal gold. Gold was found in clusters randomly distributed over the plasma membrane at 4 degrees C. When cells were warmed to 37 degrees C, numerous endocytic vesicles were observed as early as 2.5 minutes after warming. After 30 minutes at 37 degrees C, large vesicles, 1 micron in diameter, were found to contain 20 to 30 gold particles. The endocytosis of 3G8 was also examined using colloidal gold. After binding of 3G8-gold at 4 degrees C, clusters of large vesicles, up to 2 micron in diameter, were rapidly formed at 37 degrees C.