Macromolecular properties and polymeric structure of canine tracheal mucins

Sulforhodamine B and exogenous surfactant effects on alveolar surface tension under acute respiratory distress syndrome conditions

In the acute respiratory distress syndrome (ARDS), alveolar surface tension, T, may be elevated. Elevated T should increase ventilation-induced lung injury. Exogenous surfactant therapy, intended to lower T, has not reduced mortality. Sulforhodamine B (SRB) might, alternatively, be used to lower T. We test whether substances suspected of elevating T in ARDS raise T in the lungs and test the abilities of exogenous surfactant and SRB to reduce T. In isolated rat lungs, we micropuncture a surface alveolus and instill a solution of a purported T-raising substance: control saline, cell debris, secretory phospholipase A₂ (sPLA₂), acid, or mucins. We test each substance alone; with albumin, to model proteinaceous edema liquid; with albumin and exogenous surfactant; and with albumin and SRB. We determine T in situ in the lungs by combining servo-nulling pressure measurement with confocal microscopy and applying the Laplace relation. With control saline, albumin does not alter T, additional surfactant raises T, and additional SRB lowers T. The experimental substances, without or with albumin, raise T. Excepting under aspiration conditions, addition of surfactant or SRB lowers T. Exogenous surfactant activity is concentration and ventilation dependent. Sulforhodamine B, which could be delivered intravascularly, holds promise as an alternative therapeutic.NEW & NOTEWORTHY In the acute respiratory distress syndrome (ARDS), lowering surface tension, T, should reduce ventilation injury yet exogenous surfactant has not reduced mortality. We show with direct T determination in isolated lungs that substances suggested to elevate T in ARDS indeed raise T, and exogenous surfactant reduces T. Further, we extend our previous finding that sulforhodamine B (SRB) reduces T below normal in healthy lungs and show that SRB, too, reduces T under ARDS conditions.

Tailoring Formulations for Intranasal Nose-to-Brain Delivery: A Review on Architecture, Physico-Chemical Characteristics and Mucociliary Clearance of the Nasal Olfactory Mucosa

The blood-brain barrier and the blood-cerebrospinal fluid barrier are major obstacles in central nervous system (CNS) drug delivery, since they block most molecules from entering the brain. Alternative drug delivery routes like intraparenchymal or intrathecal are invasive methods with a remaining risk of infections. In contrast, nose-to-brain delivery is a minimally invasive drug administration pathway, which bypasses the blood-brain barrier as the drug is directed from the nasal cavity to the brain. In particular, the skull base located at the roof of the nasal cavity is in close vicinity to the CNS. This area is covered with olfactory mucosa. To design and tailor suitable formulations for nose-to-brain drug delivery, the architecture, structure and physico-chemical characteristics of the mucosa are important criteria. Hence, here we review the state-of-the-art knowledge about the characteristics of the nasal and, in particular, the olfactory mucosa needed for a rational design of intranasal formulations and dosage forms. Also, the information is suitable for the development of systemic or local intranasal drug delivery as well as for intranasal vaccinations.

Tracheal acid or surfactant instillation raises alveolar surface tension

Whether alveolar liquid surface tension, T, is elevated in the acute respiratory distress syndrome (ARDS) has not been demonstrated in situ in the lungs. Neither is it known how exogenous surfactant, which has failed to treat ARDS, affects in situ T. We aim to determine T in an acid-aspiration ARDS model before and after exogenous surfactant administration. In isolated rat lungs, we combine servo-nulling pressure measurement and confocal microscopy to determine alveolar liquid T according to the Laplace relation. Administering 0.01 N (pH 1.9) HCl solution by alveolar injection or tracheal instillation, to model gastric liquid aspiration, raises T. Subsequent surfactant administration fails to normalize T. Furthermore, in normal lungs, tracheal instillation of control saline or exogenous surfactant raises T. Lavaging the trachea with saline and injecting the lavage solution into the alveolus raises T, suggesting that tracheal instillation may wash T-raising airway contents to the alveolus. Adding 0.01 N HCl or 5 mM CaCl₂-either of which aggregates mucins-to tracheal lavage solution reduces or eliminates the effect of lavage solution on alveolar T. Following tracheal saline instillation, liquid suctioned directly out of alveoli through a micropipette contains mucins. Additionally, alveolar injection of gastric mucin solution raises T. We conclude that 1) tracheal liquid instillation likely washes T-raising mucins to the alveolus and 2) even exogenous surfactant that could be delivered mucin-free to the alveolus might not normalize T in acid-aspiration ARDS. NEW & NOTEWORTHY We demonstrate in situ in isolated lungs that surface tension is elevated in an acid-aspiration acute respiratory distress syndrome (ARDS) model. Following tracheal liquid instillation, also in isolated lungs, we directly sample alveolar liquid. We find that liquid instillation into normal lungs washes mucins to the alveolus, thereby raising alveolar surface tension. Furthermore, even if exogenous surfactant could be delivered mucin-free to the alveolus, exogenous surfactant might fail to normalize alveolar surface tension in acid-aspiration ARDS.

Immunopathology of the Respiratory System

Respiratory immunity is accomplished using multiple mechanisms including structure/anatomy of the respiratory tract, mucosal defense in the form of the mucociliary apparatus, innate immunity using cells and molecules and acquired immunity. There are species differences of the respiratory immune system that influence the response to environmental challenges and pharmaceutical, industrial and agricultural compounds assessed in nonclinical safety testing and hazard identification. These differences influence the interpretation of respiratory system changes after exposure to these challenges and compounds in nonclinical safety assessment and hazard identification and their relevance to humans.

Barrier properties of mucus

Mucus is tenacious. It sticks to most particles, preventing their penetration to the epithelial surface. Multiple low-affinity hydrophobic interactions play a major role in these adhesive interactions. Mucus gel is also shear-thinning, making it an excellent lubricant that ensures an unstirred layer of mucus remains adherent to the epithelial surface. Thus nanoparticles (NP) must diffuse readily through the unstirred adherent layer if they are to contact epithelial cells efficiently. This article reviews some of the physiological and biochemical properties that form the mucus barrier. Capsid viruses can diffuse through mucus as rapidly as through water and thereby penetrate to the epithelium even though they have to diffuse 'upstream' through mucus that is being continuously secreted. These viruses are smaller than the mucus mesh spacing, and have surfaces that do not stick to mucus. They form a useful model for developing NP for mucosal drug delivery.

Self-association of mucin

Aggregation phenomena in aqueous solutions of purified human tracheobronchial mucin have been studied by rheological methods, steady-state fluorescence, quasielastic light scattering, and spin probe techniques. At temperatures below 30 degrees C and concentrations above 15 mg/mL and in the absence of chaotropic agents, mucin solutions are viscoelastic gels. A gel-sol transition is observed at temperatures above 30 degrees C that is manifested by the diminishing storage modulus and a loss tangent above unity throughout the studied frequency range of the oscillatory shear. No decline in the mucin molecular weight is observed by size-exclusion chromatography above 30 degrees C in the absence of redox agents or proteolytic enzymes. Aggregation of hydrophobic protein segments of the mucin chains at 37 degrees C is indicated by QELS experiments. The decreasing polarity of the microenvironment of pyrene solubilized into mucin solutions at temperatures above 30 degrees C, concomitant with the gel-sol transition, shows the hydrophobicity of the formed aggregates. ESR spectra of the fatty acid spin probe, 16-doxylstearic acid indicate that the aggregate-aqueous interface becomes more developed at elevated temperatures.

Immunological characterization of a mucin-associated protein from hamster tracheal epithelial cell culture

Airway mucins are high molecular mass (>10(6) dalton) glycoproteins with various types of associated molecules including glycoproteins, lipoproteins, and lipids. The study of mucin-associated proteins is limited largely due to the lack of specific probes. In this study, we produced a monoclonal antibody, MAbHT10, against a 190-kDa mucin associated-protein by immunizing mice with hamster airway mucin purified in nondissociative condition. Using HT10, the 190-kDa mucin-associated protein was characterized immunologically. The 190-kDa mucin-associated protein is glycoprotein and HT10 recognized carbohydrate containing portion of the protein. The association of 190-kDa protein with mucin is strong enough that heat and detergent treatment is required to dissociate it from mucin as evidenced by gel filtration chromatography, Western blot, enzyme-linked immunoadsorbent assay (ELISA), and co-immunoprecipitation. The expression of the 190-kDa protein is increased with the development of hamster tracheal epithelial cells in culture, but showed differences with the pattern of the regulation of mucin expression. Adenosine triphosphate (ATP), a known strong mucin secretagogue, dose-dependently increased mucin release but caused only marginal increase in the release of the 190-kDa protein. The MAb should be useful in the structural and functional analysis of the 190-kDa mucin-associated proteins in physiological and pathological situations such as chronic airway diseases.

Nucleotide sequence of a cDNA for canine beta-spectrin reveals high evolutionary conservation

A cDNA coding for the carboxy-terminus of canine beta-spectrin was isolated from a canine tracheal cDNA library. Analysis of the 3267 nucleotide sequence revealed a single open reading frame coding for 707 amino acids. Comparison of the deduced amino acid sequence to that of the recently reported general isoform of human beta-spectrin (beta G) revealed 98% identity. This high degree of conservation of the general isoform of beta-spectrin illustrates a strong evolutionary selection and should help in identification of sites that are candidates to mediate specialized functions of this general isoform. This is the first report of a cDNA encoding canine beta-spectrin.

Molecular cloning of the carboxy terminus of a canine tracheobronchial mucin

A cDNA library constructed from canine tracheal mRNA was screened with polyclonal antiserum specific to canine tracheal apomucin (CTM-A). Eight antibody reactive clones were isolated and purified to clonality. One of the clones, designated pCTM-A, had a 1.7 kb insert and included a single open reading frame with a poly (A)+ tail. The amino acid composition of the encoded protein was consistent with that expected for CTM-A. The fusion protein produced by cloning the 1.7 kb insert in the pMALc expression vector reacted with the purified anti-apomucin CTM-A antibody. Also, polyclonal antibodies raised to the purified protein product encoded by pCTM-A reacted with deglycosylated CTM-A confirming that this clone does indeed code for apomucin CTM-A. This is the first report of a cDNA encoding the C-terminus of a canine tracheal mucin.

Evidence for secretion of high molecular weight mucins by canine tracheal epithelial cells in primary culture: effects of select secretagogues in mucin secretion

The purpose of this investigation was to provide evidence for the secretion of high molecular weight mucins, CTM-A and CTM-B, in primary culture of canine tracheal epithelial (CTE) cells. The cells were isolated from tracheas of mongrel dogs by pronase treatment. Primary cultures of the epithelial cells were established using ICN collagen inserts in Dulbecco's modified Eagle's/F12 medium supplemented with growth factors and could be maintained for up to 23 days. The evidence for the mucin secretion in culture medium and their localization in the cells was established by a) positive immunocytochemical staining using specific antibodies developed against purified native as well as deglycosylated CTM-A and CTM-B; b) incorporation of labeled amino acids, followed by electrophoresis and autoradiography detection of glycoconjugates purified from the culture medium; c) comparison of the amino acid compositions of mucin purified from canine tracheal pouch secretions and that purified from the culture medium; and d) Western blot analyses using specific polyclonal antibodies directed against deglycosylated CTM-A and CTM-B. Immunoaffinity purified secreted labeled glycoconjugates were resistant to hyaluronidase treatment. The effects of cyclic AMP (1 x 10(-5) M), dibutyryl cyclic AMP (1 x 10(-5) M), 8-bromocyclic AMP (1 x 10(-5) M), and prostaglandin E1 (1 x 10(-6) M) on mucin secretion by CTE cells were also investigated. Secretion of mucins by CTE cells in culture was considerably more enhanced by 8-bromocyclic AMP than that observed for other secretagogues used in this study.