90-day nose-only inhalation toxicity study of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in Sprague-Dawley rats.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is one of the key tobacco-specific nitrosamines that plays an important role in human lung carcinogenesis. Repeated dose inhalation toxicity data on NNK, particularly relevant to cigarette smoking, however, is surprisingly limited. Hence, there is a lack of direct information available on the carcinogenic and potential non-carcinogenic effects of NNK via inhalational route exposure. In the present study, the subchronic inhalation toxicity of NNK was evaluated in Sprague Dawley rats. Both sexes (9-10 weeks age; 23 rats/sex/group) were exposed by nose-only inhalation to air, vehicle control (75% propylene glycol), or 0.2, 0.8, 3.2, or 7.8 mg/kg body weight (BW)/day of NNK (NNK aerosol concentrations: 0, 0, 0.0066, 0.026, 0.11, or 0.26 mg/L air) for 1 h/day for 90 consecutive days. Toxicity was evaluated by assessing body weights; food consumption; clinical pathology; histopathology; organ weights; blood, urine, and tissue levels of NNK, its major metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and their glucuronides (reported as total NNK, tNNK, and total NNAL, tNNAL, respectively); tissue levels of the DNA adduct O6-methylguanine; blood and bone marrow micronucleus (MN) frequency; and bone marrow DNA strand breaks (comet assay). The results showed that NNK exposure caused multiple significant adverse effects, with the most sensitive endpoint being non-neoplastic lesions in the nose. Although the genotoxic biomarker O6-methylguanine was detected, genotoxicity from NNK exposure was negative in the MN and comet assays. The Lowest-Observed-Adverse-Effect-Level (LOAEL) was 0.8 mg/kg BW/day or 0.026 mg/L air of NNK for 1 h/day for both sexes. The No-Observed-Adverse-Effect-Level (NOAEL) was 0.2 mg/kg BW/day or 0.0066 mg/L air of NNK for 1 h/day for both sexes. The results of this study provide new information relevant to assessing the human exposure hazard of NNK.

Advancement of the Infant Air-Jet Dry Powder Inhaler (DPI): Evaluation of Different Positive-Pressure Air Sources and Flow Rates.

PURPOSE: In order to improve the delivery of dry powder aerosol formulations to the lungs of infants, this study implemented an infant air-jet platform and explored the effects of different air sources, flow rates, and pulmonary mechanics on aerosolization performance and aerosol delivery through a preterm nose-throat (NT) in vitro model. METHODS: The infant air-jet platform was actuated with a positive-pressure air source that delivered the aerosol and provided a full inhalation breath. Three different air sources were developed to provide highly controllable positive-pressure air actuations (using actuation volumes of ~10 mL for the preterm model). While providing different flow waveform shapes, the three air sources were calibrated to produce the same flow rate magnitude (Q90: 90th percentile of flow rate). Multiple air-jet DPI designs were coupled with the air sources and evaluated with a model spray-dried excipient enhanced growth formulation. RESULTS: Compared to other designs, the D1-Single air-jet DPI provided improved performance with low variability across all three air sources. With the tested D1-Single air-jet and Timer air source, reducing the flow rate from 4 to 1.7 L/min marginally decreased the aerosol size and significantly increased the lung delivery efficiency above 50% of the loaded dose. These results were not impacted by the presence of downstream pulmonary mechanics (resistance and compliance model). CONCLUSIONS: The selected design was capable of providing an estimated >50% lung delivery efficiency of a model spray-dried formulation and was not influenced by the air source, thereby enabling greater flexibility for platform deployment in different environments.

Visual loss from dermal fillers.

BACKGROUND: An increasing number of people are undergoing non-surgical aesthetic procedures, especially injections of botulinum toxin and dermal fillers. While toxin injections have lower rates of complications, profound and serious consequences can arise with the use of dermal fillers. CASE: A 29-year-old woman presented to the eye casualty department with sudden visual loss, ptosis and ophthalmoplegia after having had non-surgical rhinoplasty in a beauty salon in West London. The filler was administered by a healthcare professional not registered with the General Medical Council (GMC) or similar governing body. DISCUSSION: Despite prompt measures on arrival at our service, the symptoms of visual loss, ptosis and ophthalmoplegia persisted. Attempts from the patient and medical services to report the incident (to trading standards and the police) were to no avail. CONCLUSION: This case highlights the poor treatment response to filler-related ophthalmic complications. It is also evident that in the United Kingdom, there appears to be poor regulation in the use of these products, a lack of clear guidelines for the management of their complications and finally no recourse for patients to challenge practitioners who lack medical registration and are not held accountable.

Formaldehyde-induced hematopoietic stem and progenitor cell toxicity in mouse lung and nose.

Formaldehyde (FA), an economically important and ubiquitous chemical, has been classified as a human carcinogen and myeloid leukemogen. However, the underlying mechanisms of leukemogenesis remain unclear. Unlike many classical leukemogens that damage hematopoietic stem/progenitor cells (HSC/HPC) directly in the bone marrow, FA-as the smallest, most reactive aldehyde-is thought to be incapable of reaching the bone marrow through inhalation exposure. A recent breakthrough study discovered that mouse lung contains functional HSC/HPC that can produce blood cells and travel bi-directionally between the lung and bone marrow, while another early study reported the presence of HSC/HPC in rat nose. Based on these findings, we hypothesized that FA inhalation could induce toxicity in HSC/HPC present in mouse lung and/or nose rather than in the bone marrow. To test this hypothesis, we adapted a commercially available protocol for culturing burst-forming unit-erythroid (BFU-E) and colony-forming unit-granulocyte, macrophage (CFU-GM) colonies from bone marrow and spleen to also enable culture of these colonies from mouse lung and nose, a novel application of this assay. We reported that in vivo exposure to FA at 3 mg/m3 or ex vivo exposure up to 400 µM FA decreased the formation of both colony types from mouse lung and nose as well as from bone marrow and spleen. These findings, to the best of our knowledge, are the first empirically to show that FA exposure can damage mouse pulmonary and olfactory HSC/HPC and provide potential biological plausibility for the induction of leukemia at the sites of entry rather than the bone marrow.

Advances in the field of intranasal oxytocin research: lessons learned and future directions for clinical research.

Reports on the modulatory role of the neuropeptide oxytocin on social cognition and behavior have steadily increased over the last two decades, stimulating considerable interest in its psychiatric application. Basic and clinical research in humans primarily employs intranasal application protocols. This approach assumes that intranasal administration increases oxytocin levels in the central nervous system via a direct nose-to-brain route, which in turn acts upon centrally-located oxytocin receptors to exert its behavioral effects. However, debates have emerged on whether intranasally administered oxytocin enters the brain via the nose-to-brain route and whether this route leads to functionally relevant increases in central oxytocin levels. In this review we outline recent advances from human and animal research that provide converging evidence for functionally relevant effects of the intranasal oxytocin administration route, suggesting that direct nose-to-brain delivery underlies the behavioral effects of oxytocin on social cognition and behavior. Moreover, advances in previously debated methodological issues, such as pre-registration, reproducibility, statistical power, interpretation of non-significant results, dosage, and sex differences are discussed and integrated with suggestions for the next steps in translating intranasal oxytocin into psychiatric applications.

Maturation of nasal microbiota and antibiotic exposures during early childhood: a population-based cohort study.

OBJECTIVES: Little is known about maturation of the airway microbiota during early childhood and the consequences of early-life antibiotic exposure. METHODS: In a population-based birth cohort of 902 healthy Finnish children, we applied deep neural network models to investigate the relationship between the nasal microbiota (measured by 16S rRNA gene sequencing at up to three time points) and child age during the first 24 months. We also performed stratified analyses according to antibiotic exposure during the age period 0-2 months. RESULTS: The dense deep neural network analysis successfully modelled the relationship between 232 bacterial genera and child age with a mean absolute error of 4.3 (95%CI 4.0-4.7) months. Similarly, the recurrent neural network analysis also successfully modelled the relationship between 215 genera and child age with a mean absolute error of 0.45 (95%CI 0.42-0.47) months. Among the genera, Staphylococcus spp. and members of the Corynebacteriaceae decreased with age, while Dolosigranulum and Moraxella increased with age in the first 2 years of life (all false discovery rate (FDR) = 0.001). In children without early-life antibiotic exposure, Dolosigranulum increased with age (FDR = 0.001). By contrast, in those with early-life antibiotic exposure, Haemophilus increased with age (FDR = 0.002). CONCLUSIONS: In this prospective birth cohort of healthy children, we demonstrated the development of the nasal microbiota, with shifts in specific genera constituting maturation, in the first 2 years of life. Antibiotic exposures during early infancy were related to different age-discriminatory bacteria.

Nonsurgical Rhinoplasty Using Injectable Fillers: A Safety Review of 2488 Procedures.

Background: Injectable fillers are used worldwide to improve the appearance of the nose by nonsurgical methods. The procedure is not without risks, as blindness and skin necrosis have been reported as a consequence of filler injections in the nose. Objective: To determine an overall adverse event (AE) rate for the nonsurgical rhinoplasty (NSR) procedure and to assess whether previous surgical rhinoplasty increases the odds of an AE. Methods: A retrospective chart review of 2275 patients and 2488 NSR procedures for a 10-year period from a single physician injector was conducted. Results: The overall procedural AE rate was 7.6%, with five cases (0.20%) considered serious (ischemia and necrosis). Previous surgical rhinoplasty patients had a greater AE rate (10.8%) than those patients without previous surgery (7.4%), with a significant odds ratio of 1.51 (95% confidence interval: 1.03-2.18); p = 0.032. Injecting the tip and sidewall of the nose had the highest AE rates for both categories of patients. Conclusions: NSR is a relatively safe procedure with the majority of AEs common injection site reactions. Patients with previous surgical rhinoplasty demonstrated significantly increased odds of an AE potentially due to surgical changes in anatomy.

Nasal respiration is necessary for ketamine-dependent high frequency network oscillations and behavioral hyperactivity in rats.

Changes in oscillatory activity are widely reported after subanesthetic ketamine, however their mechanisms of generation are unclear. Here, we tested the hypothesis that nasal respiration underlies the emergence of high-frequency oscillations (130-180 Hz, HFO) and behavioral activation after ketamine in freely moving rats. We found ketamine 20 mg/kg provoked "fast" theta sniffing in rodents which correlated with increased locomotor activity and HFO power in the OB. Bursts of ketamine-dependent HFO were coupled to "fast" theta frequency sniffing. Theta coupling of HFO bursts were also found in the prefrontal cortex and ventral striatum which, although of smaller amplitude, were coherent with OB activity. Haloperidol 1 mg/kg pretreatment prevented ketamine-dependent increases in fast sniffing and instead HFO coupling to slower basal respiration. Consistent with ketamine-dependent HFO being driven by nasal respiration, unilateral naris blockade led to an ipsilateral reduction in ketamine-dependent HFO power compared to the control side. Bilateral nares blockade reduced ketamine-induced hyperactivity and HFO power and frequency. These findings suggest that nasal airflow entrains ketamine-dependent HFO in diverse brain regions, and that the OB plays an important role in the broadcast of this rhythm.

Rapid Ex-Vivo Ciliogenesis and Dose-Dependent Effect of Notch Inhibition on Ciliogenesis of Respiratory Epithelia.

Background: Cilia are actin based cellular protrusions conserved from algae to complex multicellular organisms like Homo sapiens. Respiratory motile cilia line epithelial cells of the tracheobronchial tree, beat in a synchronous, metachronal wave, moving inhaled pollutants and pathogens cephalad. Their role in both congenital disorders like primary ciliary dyskinesia (PCD) to acquired disorders like chronic obstructive pulmonary disease (COPD) continues to evolve. In this current body of work we outline a protocol optimized to reciliate human nasal epithelial cells and mouse tracheal cells in vitro. Using this protocol, we knocked down known cilia genes, as well as use a small molecule inhibitor of Notch, N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl Ester (DAPT), to assess the effect of these on ciliogenesis in order to show the validity of our protocol. Methods: Tracheas were harvested from wild-type, adult C57B6 mice, pronase digested and sloughed off epithelial cells grown to confluence in stationary culture on rat-tail collagen coated wells. Upon reaching confluence, collagen was digested and cells placed suspension culture protocol to reciliate the cells. Using this suspension culture protocol, we employed siRNA gene knockdown to assay gene functions required for airway ciliogenesis. Knock down of Dynein axonemal heavy chain 5 (Dnah5), a ciliary structural protein, was confirmed using immunostaining. Mouse tracheal cells were treated in suspension with varying doses of DAPT, an inhibitor of Notch, with the purpose of evaluating its effect and dose response on ciliogenesis. The optimum dose was then used on reciliating human nasal epithelial cells. Results: siRNA knockdown of Foxj1 prevented ciliation, consistent with its role as a master regulator of motile cilia. Knockdown of Dnai1 and Dnah5 resulted in immotile cilia, and Cand1 knockdown, a centrosome protein known to regulate centrosome amplification, inhibited airway ciliogenesis. Dnah5 knockdown was confirmed with significantly decreased immunostaining of cilia for this protein. Inhibiting Notch signaling by inhibiting gamma secretase with DAPT enhanced the percentage of ciliation, and resulted in longer cilia that beat with higher frequency in both mouse and human airway epithelia. Conclusions: Modifying existing reciliation protocols to suit both human nasal epithelial and mouse tracheal tissue, we have shown that knockdown of known cilia-related genes have the expected effects. Additionally, we have demonstrated the optimal dosage for significantly improving reciliation of airway epithelia using DAPT. Given that cilia length and function are significantly compromised in COPD, these findings open up interesting avenues for further exploration.

Characterization and Treatment of SARS-CoV-2 in Nasal and Bronchial Human Airway Epithelia.

In the current COVID-19 pandemic context, proposing and validating effective treatments represents a major challenge. However, the scarcity of biologically relevant pre-clinical models of SARS-CoV-2 infection imposes a significant barrier for scientific and medical progress, including the rapid transition of potentially effective treatments to the clinical setting. We use reconstituted human airway epithelia to isolate and then characterize the viral infection kinetics, tissue-level remodeling of the cellular ultrastructure, and transcriptional early immune signatures induced by SARS-CoV-2 in a physiologically relevant model. Our results emphasize distinctive transcriptional immune signatures between nasal and bronchial HAE, both in terms of kinetics and intensity, hence suggesting putative intrinsic differences in the early response to SARS-CoV-2 infection. Most important, we provide evidence in human-derived tissues on the antiviral efficacy of remdesivir monotherapy and explore the potential of the remdesivir-diltiazem combination as an option worthy of further investigation to respond to the still-unmet COVID-19 medical need.

Nose-to-brain drug delivery system with ligand/cell-penetrating peptide-modified polymeric nano-micelles for intracerebral gliomas.

We previously developed a nose-to-brain delivery system using poly(ethylene glycol)-polycaprolactone block polymeric micelles modified by a cell-penetrating peptide, Tat (PEG-PCL-Tat). This system showed excellent delivery of the anti-cancer drug camptothecin to the brain and improved therapeutic efficacy in a brain tumor model. However, improvements are necessary to selectively deliver drugs to tumor sites once they enter the brain, and avoid toxic side effects to normal brain tissue. In this study, to develop tumor-selective novel polymeric micelles, mixed micelles consisting of Tat-conjugated polymer micelles and stearoyl-modified bombesin (Bom/PEG-PCL-Tat) were designed. The GRPR selectivity, cellular uptake, and cytotoxicity in C6 glioma cells as well as the intracerebral drug distribution and therapeutic efficacy of Bom/PEG-PCL-Tat mixed micelles after intranasal administration in C6 glioma orthotropic grafted rats were evaluated. Selective cellular uptake and marked cytotoxic effects against GRPR-expressing C6 glioma cells were observed, as well as C6 tumor tissue-specific accumulation in vivo. Rats treated with camptothecin subsequent to a brain tumor graft survived longer when the drug was delivered by Bom/PEG-PCL-Tat mixed micelles than by PEG-PCL-Tat micelles.

Nasal timosaponin BII dually sensitive in situ hydrogels for the prevention of Alzheimer's disease induced by lipopolysaccharides.

Alzheimer's disease (AD) is a common and severe brain disease with a high mortality among the elders, but no highly efficient medications are currently available. For example, timosaponin BII, an efficient anti-AD agent, has low oral bioavailability. Here, timosaponin BII was formulated in a temperature/ion-sensitive in situ hydrogel (ISG) that was well transformed into gels in the nasal environment. Timosaponin BII protected the PC12 cells injured by lipopolysaccharides (LPS) by decreasing TNF-α and IL-1ß and stabilizing F-actin. Timosaponin BII ISGs were intranasally administered to the mice every day for 38 days. On Day 36, LPS was injected to the mice to establish an AD model. Morris water maze experiments showed that the number of the animals that were able to cross the platform returned to normal and the total distance over which the animals moved in the open field also increased, which demonstrated that the spatial memory and spontaneous behavior were improved after treatment compared to the model. Moreover, an AD improver, inducible nitric oxide synthase (iNOS) in the brain, was reduced after treatment. High brain targeting effect of timosaponin BII ISGs was confirmed by in vivo fluorescence imaging. The nasal timosaponin BII dually sensitive ISGs can serve as a promising medication for local prevention of AD.

Can a Pretreatment Visual Analog Scale Predict Treatment Outcome in Allergic Rhinitis?

BACKGROUND: The visual analogue scale (VAS) is a simple and useful tool to assess the severity of allergic rhinitis. Whether a pretreatment VAS score can guide appropriate medication is unclear. OBJECTIVE: The aim of this study was to evaluate whether a pretreatment VAS score could be used to predict therapeutic response. METHODS: A prospective 4-week cohort study involving 101 allergic rhinitis patients was carried out. All patients were treated with triamcinolone acetonide aqueous nasal spray 220 µg once daily for 28 days. The treatment outcomes were evaluated using VAS scores (0-10 cm), total nasal symptoms scores (TNSSs), nasal mucociliary clearance times (NMCCTs), and global symptom controls (GSCs). The minimal clinically important differences (MCIDs) method was used to separate the patients into with and without improvement groups. Receiver operating characteristic curve analysis was performed to evaluate the predictive value of pretreatment VAS scores in relation to MCIDs after treatment. RESULTS: Pretreatment VAS scores showed a positive correlation with pretreatment TNSSs and NMCCTs (ρ = 0.66, p < 0.001 and r = 0.44, p < 0.001, respectively), and a negative correlation with GSCs after treatment (r = -0.53, p < 0.001). The MCID values of TNSSs and NMCCTs were 3.19 and 2.78, respectively. The cutoff value of pretreatment VAS ranged between 6.5 and 7.7 points, with an average value of 7.1. CONCLUSION: A pretreatment VAS score of 7 or higher was associated with an unfavorable treatment outcome, which suggests the potential therapeutic predictive value of VAS scoring.

Nitinol actuated soft structures towards transnasal drug delivery: a pilot cadaver study.

Sudden hearing loss can be treated noninvasively by administering drugs to the middle ear (≈1 ml) via the eustachian tube. The nasopharyngeal cavity requires high dexterity manipulation as it is restricted by the nasal vestibule, and precise drug delivery through the small cavity can allow previously unreachable areas to be reconsidered for localized delivery. Nitinol has shape memory capabilities and can be used for distal actuation accessed from small lumen and a tortuous path. The drug delivery device (DDD) is a soft and needle-sized (2 mm) and comprises of Nitinol, ribbon spring, and a drug delivery tube. By controlling the input voltage to the Nitinol, bending of the device at different angles could be achieved, and the ribbon spring works antagonistically to the Nitinol to revert to the initial position once deactivated. The actuation of the device and its corresponding bending are calculated in vitro and found to have a bending angle ranging between 36.2 and 66.8° for applied voltages of 1.2-2.0 V, with surface temperature of 45.6-154 °C. The DDD is able to actuate 200 cycles with ≈91-76% retention of bending performance, with a temperature increase of ≈8.5-9% when 1.2-2.0 V is applied. Addition of soft insulating material shows ≈34-62% reduction in the surface temperature in the first cycle and ≈37-59% over 200 cycles when actuated at 1.2-2.0 V. The active steering and navigation capabilities of the DDD are demonstrated in simulated environments (based on the eustachian tube dimensions of adult and infant). Preclinical testing in human cadavers is demonstrated and suggests the developed DDD controlled by varying the input voltages for bending, and mechanically varied drug delivery may be a feasible option for localized drug delivery in eustachian tube. Graphical abstract.

Use of Nasal Pathology in the Derivation of Inhalation Toxicity Values for Hydrogen Sulfide.

Nasal pathology can play an important role in the risk assessment process. For example, olfactory neuron loss (ONL) is one of the most sensitive end points seen in subchronic rodent hydrogen sulfide (H2S) studies and has been used by several agencies to derive health-protective toxicity values. Alternative methods that rely on computational fluid dynamics (CFD) models to account for the influence of airflow on H2S-induced ONL have been proposed. The use of CFD models result in toxicity values that are less conservative than those obtained using more traditional methods. These alternative approaches rely on anatomy-based CFD models. Model predictions of H2S delivery (flux) to the olfactory mucosal wall are highly correlated with ONL in rodents. Three major areas of focus for this review include a brief description of nasal anatomy, H2S-induced ONL in rodents, derivation of a chronic inhalation reference concentration for H2S, and the use of CFD models to derive alternative toxicity values for this gas.

Development of nose-to-brain delivery of ketoconazole by nanostructured lipid carriers against cryptococcal meningoencephalitis in mice.

Cryptococcus neoformans-mediated meningoencephalitis is a critical infectious disorder of the human central nervous system. However, efficient treatment for the disease is limited due to the poor penetration across the blood brain barrier (BBB). Here, we develop a nose-to-brain drug delivery system utilizing nanostructured lipid carriers (NLCs). We demonstrated that fluorescent-dye-loaded NLCs efficiently uptake into the cytoplasm of encapsulated C. neoformans cells. In comparison with current antifungal drugs, the ketoconazole (keto)-NLCs show significantly increased antifungal activity against C. neoformans in vivo under various growth conditions. The NLCs show enhanced tissue colonization properties. Importantly, using animal imaging analyses, NLCs are able to enter brain tissues via the olfactory bulb region by intranasal administration, bypassing the BBB. In addition, NLCs maintain prolonged residence in tissues. In mouse brain tissue, keto-NLCs showed significantly enhanced antifungal activity when administered intranasally, drastically dampening the C. neoformans burden. Taken together, NLCs not only improve the ketoconazole penetration efficiency against capsulated C. neoformans cells, but also boost the efficacy of antifungal drugs. Most importantly, keto-NLCs significantly contribute to the treatment of cryptococcal meningoencephalitis in mice by bypassing the BBB via the olfactory system.

ORKAMBI-Mediated Rescue of Mucociliary Clearance in Cystic Fibrosis Primary Respiratory Cultures Is Enhanced by Arginine Uptake, Arginase Inhibition, and Promotion of Nitric Oxide Signaling to the Cystic Fibrosis Transmembrane Conductance Regulator Channel.

ORKAMBI, a combination of the corrector, lumacaftor, and the potentiator, ivacaftor, partially rescues the defective processing and anion channel activity conferred by the major cystic fibrosis-causing mutation, F508del, in in vitro studies. Clinically, the improvement in lung function after ORKAMBI treatment is modest and variable, prompting the search for complementary interventions. As our previous work identified a positive effect of arginine-dependent nitric oxide signaling on residual F508del-Cftr function in murine intestinal epithelium, we were prompted to determine whether strategies aimed at increasing arginine would enhance F508del-cystic fibrosis transmembrane conductance regulator (CFTR) channel activity in patient-derived airway epithelia. Now, we show that the addition of arginine together with inhibition of intracellular arginase activity increased cytosolic nitric oxide and enhanced the rescue effect of ORKAMBI on F508del-CFTR-mediated chloride conductance at the cell surface of patient-derived bronchial and nasal epithelial cultures. Interestingly, arginine addition plus arginase inhibition also enhanced ORKAMBI-mediated increases in ciliary beat frequency and mucociliary movement, two in vitro CF phenotypes that are downstream of the channel defect. This work suggests that strategies to manipulate the arginine-nitric oxide pathway in combination with CFTR modulators may lead to improved clinical outcomes. SIGNIFICANCE STATEMENT: These proof-of-concept studies highlight the potential to boost the response to cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulators, lumacaftor and ivacaftor, in patient-derived airway tissues expressing the major CF-causing mutant, F508del-CFTR, by enhancing other regulatory pathways. In this case, we observed enhancement of pharmacologically rescued F508del-CFTR by arginine-dependent, nitric oxide signaling through inhibition of endogenous arginase activity.