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Biomedical subjects

C W Davis

Publications and source records attributed to C W Davis.

At least 19 recordsLinked to original sources
PubMed2002

Pharmacology of INS37217 [P(1)-(uridine 5')-P(4)- (2'-deoxycytidine 5')tetraphosphate, tetrasodium salt], a next-generation P2Y(2) receptor agonist for the treatment of cystic fibrosis.

INS37217 [P(1)-(uridine 5')-P(4)-(2'-deoxycytidine 5')tetraphosphate, tetrasodium salt] is a deoxycytidine-uridine dinucleotide with agonist activity at the P2Y(2) receptor. In primate lung tissues, the P2Y(2) receptor mRNA was located by in situ hybridization predominantly in epithelial cells and not in smooth muscle or stromal tissue. The pharmacologic profile of INS37217 parallels that of UTP, leading to increased chloride and water secretion, increased cilia beat frequency, and increased mucin release. The combined effect of these actions was confirmed in an animal model of tracheal mucus velocity that showed that a single administration of INS37217 significantly enhanced mucus transport for at least 8 h after dosing. This extended duration of action is consistent with the ability of INS37217 to resist metabolism by airway cells and sputum enzymes. The enhanced metabolic stability and resultant increased duration of improved mucociliary clearance may confer significant advantages to INS37217 over other P2Y(2) agonists in the treatment of diseases such as cystic fibrosis.

Animals↗
PubMed2001

The CF salt controversy: in vivo observations and therapeutic approaches.

There is controversy over whether abnormalities in the salt concentration or volume of airway surface liquid (ASL) initiate cystic fibrosis (CF) airway disease. In vivo studies of CF mouse nasal epithelia revealed an increase in goblet cell number that was associated with decreased ASL volume rather than abnormal [Cl(-)]. Aerosolization of osmolytes in vivo failed to raise ASL volume. In vitro studies revealed that osmolytes and pharmacological agents were effective in producing isotonic volume responses in human airway epithelia but were typically short acting and less effective in CF cultures with prolonged volume hyperabsorption and mucus accumulation. These data show that (1) therapies can be designed to normalize ASL volume, without producing deleterious compositional changes in ASL, and (2) therapeutic efficacy will likely depend on development of long-acting pharmacologic agents and/or an increased efficiency of osmolyte delivery.

Aerosols↗
PubMed2001

The relative roles of passive surface forces and active ion transport in the modulation of airway surface liquid volume and composition.

Two hypotheses have been proposed recently that offer different views on the role of airway surface liquid (ASL) in lung defense. The "compositional" hypothesis predicts that ASL [NaCl] is kept low (<50 mM) by passive forces to permit antimicrobial factors to act as a chemical defense. The "volume" hypothesis predicts that ASL volume (height) is regulated isotonically by active ion transport to maintain efficient mechanical mucus clearance as the primary form of lung defense. To compare these hypotheses, we searched for roles for: (1) passive forces (surface tension, ciliary tip capillarity, Donnan, and nonionic osmolytes) in the regulation of ASL composition; and (2) active ion transport in ASL volume regulation. In primary human tracheobronchial cultures, we found no evidence that a low [NaCl] ASL could be produced by passive forces, or that nonionic osmolytes contributed substantially to ASL osmolality. Instead, we found that active ion transport regulated ASL volume (height), and that feedback existed between the ASL and airway epithelia to govern the rate of ion transport and volume absorption. The mucus layer acted as a "reservoir" to buffer periciliary liquid layer height (7 microm) at a level optimal for mucus transport by donating or accepting liquid to or from the periciliary liquid layer, respectively. These data favor the active ion transport/volume model hypothesis to describe ASL physiology.

Biological Transport, Active↗
PubMed2001

Differential effects of UTP, ATP, and adenosine on ciliary activity of human nasal epithelial cells.

The purinergic regulation of ciliary activity was studied using small, continuously superfused explants of human nasal epithelium. The P2Y(2) purinoceptor (P2Y(2)-R) was identified as the major purinoceptor regulating ciliary beat frequency (CBF); UTP (EC(50) = 4.7 microM), ATP, and adenosine-5'-O-(3-thiotriphosphate) elicited similar maximal responses, approximately twofold over baseline. ATP, however, elicited a post-peak sustained plateau in CBF (1.83 +/- 0.1-fold), whereas the post-peak CBF response to UTP declined over 15 min to a low-level plateau (1.36 +/- 0.16-fold). UDP also stimulated ciliary beating, probably via P2Y(6)-R, with a maximal effect approximately one-half that elicited by P2Y(2)-R stimulation. Not indicated were P2Y(1)-R-, P2Y(4)-R-, or P2Y(11)-R-mediated effects. A(2B)-receptor agonists elicited sustained responses in CBF approximately equal to those from UTP/ATP [5'-(N-ethylcarboxamido)adenosine, EC(50) = 0.09 microM; adenosine, EC(50) = 0.7 microM]. Surprisingly, ADP elicited a sustained stimulation in CBF. The ADP effect and the post-peak sustained portion of the ATP response in CBF were inhibited by the A(2)-R antagonist 8-(p-sulfophenyl)theophylline. Hence, ATP affects ciliary activity through P2Y(2)-R and, after an apparent ectohydrolysis to adenosine, through A(2B)AR.

Adenosine↗
PubMed2000

Experiences at a large teaching hospital with levofloxacin for the treatment of community-acquired pneumonia.

Costs, patient outcomes, and susceptibility patterns of selected organisms after the implementation of guidelines for the treatment of community-acquired pneumonia (CAP) at a large community teaching hospital were analyzed to assess the benefit of the guidelines. The guidelines, implemented in September 1998, included recommendations for the use of levofloxacin as the preferred antimicrobial, with rapid intravenous (i.v.) to oral (p.o.) conversion. Purchase data for levofloxacin, ceftriaxone, and azithromycin were analyzed, as well as susceptibilities and demographic and outcome data for patients admitted in 1999 in diagnosis-related groups (DRGs) 89 and 90 (simple pneumonia with and without comorbidities, respectively). Patients in each DRG were divided into a levofloxacin use only (LUO) group and an all other therapies (AOT) group. Average length of stay (LOS), hospital costs, death rate, age, and ratio of oral to intravenous dosage administration were analyzed. A total of 571 patients in DRG 89 and 110 patients in DRG 90 were included. The average LOS for DRG 89 was not significantly different between LUO patients and AOT patients (3.56 +/- 2.23 days and 3.88 +/- 2.65 days, respectively). Average total costs were significantly higher for AOT patients ($3385 +/- $2937 versus $2892 +/- $2397 for LUO patients); similar trends but no significant differences were found in the DRG 90 group. In the LUO groups in both DRGs, patients were more than five times as likely to receive an oral dosage form than patients in the AOT group. For DRG 89, the death rate was significantly lower for the LUO group (1.29%) than the AOT group (7.1%). Susceptibility data for all organisms remained stable from 1998 to 1999. The average costs in the AOT groups suggest that total hospital costs for 1999 in the LUO group were $241,516 less than costs would have been before guideline implementation. Combined drug acquisition cost savings in 1999 for levofloxacin, ceftriaxone, and azithromycin were $21,115. The use of CAP treatment guidelines was associated with reductions in antimicrobial costs, total hospitalization costs, LOS, and death rate, without a detrimental effect on organism susceptibility.

Administration, Oral↗
PubMed2000

Telepathology networking in VISN-12 of the Veterans Health Administration.

The Veterans Integrated Service Network (VISN)-12, headquartered in Chicago, has implemented a telepathology network between the eight VISN-12 hospital laboratories and Loyola University Medical School linked by an economical, high-speed wide-area network (WAN). Implementation of the WAN has reduced monthly telecommunications costs in VISN-12 by approximately 67%. In addition to telepathology, the WAN enables real-time teleradiology (general, computer tomography, and ultrasound), telefluoroscopy, telenuclear medicine imaging, telepsychiatry, and other forms of teleconsultation. Current applications of telepathology in VISN-12 include: primary diagnosis and consultation in surgical pathology, interpretation of serum protein electrophoresis and immunofixation gels, provision of support for consolidated microbiology laboratories, review of problematic peripheral blood smears, and distance learning. We have learned a variety of lessons from telepathology. The enthusiasm and technical skill of providers are essential for success. As well, frequent communication and rapid technical support are necessary. Finally, in a supportive environment, telepathology is a tool that can help bring together clinical laboratories with shared missions and goals.

Computer Communication Networks↗
PubMed2000

Osmotic water permeabilities of cultured, well-differentiated normal and cystic fibrosis airway epithelia.

Current hypotheses describing the function of normal airway surface liquid (ASL) in lung defense are divergent. One theory predicts that normal airways regulate ASL volume by modulating the flow of isosmotic fluid across the epithelium, whereas an alternative theory predicts that ASL is normally hyposmotic. These hypotheses predict different values for the osmotic water permeability (P(f)) of airway epithelia. We measured P(f) of cultures of normal and cystic fibrosis (CF) airway epithelia that, like the native tissue, contain columnar cells facing the lumen and basal cells that face a basement membrane. Xz laser scanning confocal microscopy recorded changes in epithelial height and transepithelial volume flow in response to anisosmotic challenges. With luminal hyperosmotic challenges, transepithelial and apical membrane P(f) are relatively high for both normal and CF airway epithelia, consistent with an isosmotic ASL. Simultaneous measurements of epithelial cell volume and transepithelial water flow revealed that airway columnar epithelial cells behave as osmometers whose volume is controlled by luminal osmolality. Basal cell volume did not change in these experiments. When the serosal side of the epithelium was challenged with hyperosmotic solutions, the basal cells shrank, whereas the lumen-facing columnar cells did not. We conclude that (a) normal and CF airway epithelia have relatively high water permeabilities, consistent with the isosmotic ASL theory, and the capacity to restore water on airway surfaces lost by evaporation, and (b) the columnar cell basolateral membrane and tight junctions limit transepithelial water flow in this tissue.

Bronchi↗
PubMed1999

Incidence of invasive pneumococcal disease in Sydney children, 1991-96.

OBJECTIVE: Few data are available on invasive disease due to Streptococcus pneumoniae in representative Australian childhood populations. This study aimed to determine the age-specific incidence of invasive pneumococcal disease in Sydney children. METHODOLOGY: Population-based prospective study where isolates of Streptococcus pneumoniae from normally sterile sites were identified through an established laboratory surveillance network. Isolates came from children aged under 15 years living within the boundaries of Central, Eastern. Southern, Western and South-western Sydney Area Health Services from 1 July 1991 to 30 June 1996. RESULTS: Invasive pneumococcal disease was identified in 320 children during a 5-year period, of whom 193 (60%) were under 2 years of age. The incidence per 100,000 children was 12.7 per 100,000 (95% CI: 11.4-14.2/100,000) under 15 years; 31.7 (95% CI 28.1-35.7) under 5 years, and 45.5 (95% CI 38.9-53.3) under 2 years. The incidence of pneumococcal meningitis in children aged under 2 years was 10.5 per 100,000 (95% CI: 7.4-14.5/100,000). CONCLUSIONS: The incidence of childhood invasive pneumococcal disease in Sydney was stable during 1991-96 and comparable to rates reported from other industrialized countries. There was no evidence of any change in pneumococcal disease incidence with reduction in invasive Haemophilus influenzae type b (Hib) disease following introduction of Hib immunization.

Adolescent↗
PubMed1999

Mucin gene expression during differentiation of human airway epithelia in vitro. Muc4 and muc5b are strongly induced.

Mucus hypersecretion is characteristic of chronic airway diseases. However, regulatory mechanisms are poorly understood. Human airway epithelial cells grown on permeable supports at the air-liquid interface (ALI) develop a mucociliary morphology resembling that found in vivo. Such cultures provide a model for studying secretory cell lineage, differentiation, and function, and may provide insight regarding events leading to mucus hypersecretion. The mucin gene expression profile of well-differentiated human airway epithelial cells in culture has not yet been established. We compared expression of all the currently described mucin genes in poorly differentiated (conventional cultures on plastic) and well-differentiated (ALI) human nasal and bronchial epithelial cells. Differentiation-dependent upregulation of MUC3, MUC5AC, MUC5B, and MUC6 messenger RNA (mRNA) was demonstrated using reverse transcriptase-polymerase chain reaction (RT-PCR). Northern blot analysis showed a similar increase for MUC4 and demonstrated that induction of MUC4 and MUC5B expression depended on retinoic acid. MUC1, MUC2, MUC7, and MUC8 mRNAs were also detected by RT-PCR, but these genes did not appear to be strongly regulated as a function of differentiation. Mucin gene expression was similar in bronchial and nasal cells. Thus, mucociliary differentiation of human airway epithelia in vitro entails upregulation of several mucin genes.

Cell Differentiation↗
PubMed1998

Evidence for periciliary liquid layer depletion, not abnormal ion composition, in the pathogenesis of cystic fibrosis airways disease.

The pathogenesis of cystic fibrosis (CF) airways infection is unknown. Two hypotheses, "hypotonic [low salt]/defensin" and "isotonic volume transport/mucus clearance," attempt to link defects in cystic fibrosis transmembrane conductance regulator-mediated ion transport to CF airways disease. We tested these hypotheses with planar and cylindrical culture models and found no evidence that the liquids lining airway surfaces were hypotonic or that salt concentrations differed between CF and normal cultures. In contrast, CF airway epithelia exhibited abnormally high rates of airway surface liquid absorption, which depleted the periciliary liquid layer and abolished mucus transport. The failure to clear thickened mucus from airway surfaces likely initiates CF airways infection. These data indicate that therapy for CF lung disease should not be directed at modulation of ionic composition, but rather at restoring volume (salt and water) on airway surfaces.

Absorption↗
PubMed1998

Coordinated clearance of periciliary liquid and mucus from airway surfaces.

Airway surface liquid is comprised of mucus and an underlying, watery periciliary liquid (PCL). In contrast to the well-described axial transport of mucus along airway surfaces via ciliary action, theoretical analyses predict that the PCL is nearly stationary. Conventional and confocal microscopy of fluorescent microspheres and photoactivated fluorescent dyes were used with well-differentiated human tracheobronchial epithelial cell cultures exhibiting spontaneous, radial mucociliary transport to study the movements of mucus and PCL. These studies showed that the entire PCL is transported at approximately the same rate as mucus, 39.2+/-4.7 and 39.8+/-4.2 micrometer/sec, respectively. Removing the mucus layer reduced PCL transport by > 80%, to 4.8+/-0.6 micrometer/sec, a value close to that predicted from theoretical analyses of the ciliary beat cycle. Hence, the rapid movement of PCL is dependent upon the transport of mucus. Mucus-dependent PCL transport was spatially uniform and exceeded the rate expected for pure frictional coupling with the overlying mucus layer; hence, ciliary mixing most likely accelerates the diffusion of momentum from mucus into the PCL. The cephalad movement of PCL along airway epithelial surfaces makes this mucus-driven transport an important component of salt and water physiology in the lung in health and disease.

Biological Transport↗
PubMed1998

Ca2+ and protein kinase C activation of mucin granule exocytosis in permeabilized SPOC1 cells.

Mucin secretion by airway goblet cells is under the control of apical P2Y2, phospholipase C-coupled purinergic receptors. In SPOC1 cells, the mobilization of intracellular Ca2+ by ionomycin or the activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) stimulates mucin secretion in a fully additive fashion [L. H. Abdullah, J. D. Conway, J. A. Cohn, and C. W. Davis. Am. J. Physiol. 273 (Lung Cell. Mol. Physiol. 17): L201-L210, 1997]. This apparent independence between PKC and Ca2+ in the stimulation of mucin secretion was tested in streptolysin O-permeabilized SPOC1 cells. These cells were fully competent to secrete mucin when Ca2+ was elevated from 100 nM to 3.1 microM for 2 min following permeabilization; the Ca2+ EC50 was 2.29 +/- 0.07 microM. Permeabilized SPOC1 cells were exposed to PMA or 4alpha-phorbol at Ca2+ activities ranging from 10 nM to 10 microM. PMA, but not 4alpha-phorbol, increased mucin release at all Ca2+ activities tested: at 10 nM Ca2+ mucin release was 2.1-fold greater than control and at 4.7 microM Ca2+ mucin release was maximal (3.6-fold increase). PMA stimulated 27% more mucin release at 4.7 microM than at 10 nM Ca2+. Hence, SPOC1 cells possess Ca2+-insensitive, PKC-dependent, and Ca2+-dependent PKC-potentiated pathways for mucin granule exocytosis.

Adenosine Triphosphate↗
PubMed1997

Protein kinase C and Ca2+ activation of mucin secretion in airway goblet cells.

Airway goblet cells secrete mucin in response to ATP and uridine 5'-triphosphate (UTP), but the underlying signal transduction pathways are poorly understood. Cultures of SPOC1 cells (L. H. Abdullah, S. W. Davis, L. Burch, M. Yamauchi, S. H. Randell, P. Nettesheim, and C. W. Davis. Biochem. J. 316: 943-951, 1996) secreted mucin on exposure to phorbol 12-myristate 13-acetate (PMA) [apparent affinity (K0.5) approximately 100 nM] and ionomycin (K0.5 approximately 5 microM) almost fivefold over baseline. Thapsigargin also elicited secretion (K0.5 approximately 20 nM). Ionomycin and PMA together elicited approximately twice the secretion of either agent alone. Overnight exposure to half-maximal PMA abolished the response to maximal doses of UTP and PMA, whereas ionomycin was fully effective. Protein kinase C (PKC) activity in the membrane fraction was increased by maximal doses of PMA and UTP, whereas ionomycin had no effect. PKC inhibitors were relatively ineffective against PMA- and UTP-induced mucin secretion. Human and canine goblet cells in epithelial explants, by video microscopy, underwent exocytosis with ionomycin (1 microM) and PMA (0.1 or 1 microM). SPOC1 cell mucin secretion was not stimulated by forskolin, 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate, or 8-bromoguanosine 3',5'-cyclic monophosphate. Cystic fibrosis transmembrane conductance regulator was not detected in SPOC1 cells by Western blotting, and its mRNA was detected by reverse transcriptase polymerase chain reaction (PCR) only as a very weak band and after 55 PCR cycles. Multidrug resistance (MDR1), however, was readily detected by Western blotting, and its mRNA was detected as a major band after 35 PCR cycles. Thus airway goblet cell mucin secretion, distal to receptor activation, may be regulated independently by Ca(2+)- and PKC-dependent pathways. Cystic fibrosis transmembrane conductance regulator and cyclic nucleotides, however, may not play a major role in this secretion.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

P2u purinoceptor regulation of mucin secretion in SPOC1 cells, a goblet cell line from the airways.

The SPOC1 cell, a novel goblet cell line derived from rat trachea, was tested for its ability to exhibit regulated mucin secretion in response to purinergic (P2) agonists. High-molecular mass glycoconjugates (HMMGs) purified by CsCl-density-gradient centrifugation had a buoyant density of 1.45 g/ml. The purified HMMG material exhibited a single major band with an apparent molecular mass of greater than 1000 kDa in SDS/ polyacrylamide gels stained with silver or blotted and stained with soya-bean agglutinin. [3H]HMMG was resistant to proteoglycan-degrading enzymes, but was susceptible to neuraminidase. The HMMG was approx. 91% carbohydrate by weight, and the glycosides were O-linked. The HMMG amino acid composition was enriched in Ser and Thr (sum 27%). Thus SPOC1-cell HMMG possess the characteristics of mucin. Mucin secretion by SPOC1 cells, grown on permeable supports and perfused luminally, was stimulated by ATP, UTP and adenosine 5'-[gamma-thio]triphosphate (100 microM) 4-5-fold over a baseline of 4 ng/min. The three dose-effect relations were nearly identical (K0.5 approximately 4 microM). SPOC1 cells grown on plastic and rat tracheal epithelial primary cells responded similarly to ATP and/or UTP. SPOC1 cells failed to respond to other purinergic agonists, either luminally or serosally, and consequently seem to possess an apical membrane P2u purinoceptor. SPOC1-cell total RNA was probed for P2u purinoceptor mRNA. Using conserved primers for both reverse transcriptase and PCR, a single band of the predicted size was observed, which had a nucleotide base sequence identical with the rat P2u purinoceptor mRNA. Thus SPOC1 cells secrete mucin under the control of a P2u purinoceptor; they should prove useful in dissecting the associated cellular regulatory pathways.

Adenosine Triphosphate↗
PubMed1996

Moisture-dependent crystallization of amorphous lamotrigine mesylate.

A commercially available computer-controlled vacuum moisture balance was used for determining moisture sorption isotherms of freeze-dried and spray-dried lamotrigine mesylate drug substance and freeze dried drug product containing mannitol. The presence or absence of desorption hysteresis and the characteristics of the weight-versus-time profile as a sample was exposed to a defined relative humidity ramp were sensitive indicators of moisture-induced crystallization. Combination of the moisture sorption data with polarized light microscopy, differential scanning calorimetry, and X-ray powder diffraction provided qualitative verification of the crystallization with < 50 mg of sample. The normalized water loss during crystallization was used to detect as little as 2% amorphous content in physical mixtures of amorphous and crystalline lamotrigine mesylate. Moisture sorption, water plasticization, and crystallization properties of amorphous forms prepared by spray drying and freeze drying were nearly identical. Cofreeze-drying lamotrigine mesylate with D-mannitol resulted in a mixture of amorphous lamotrigine mesylate with properties similar to those of spray-dried or freeze-dried materials and crystalline D-mannitol. The amount of water needed for crystallization over a time scale observable in the moisture balance was considerably more than the amount needed to lower the glass transition temperature of the sample to the operating temperature of the instrument. This result illustrated the importance of time scale effects in determining critical moisture levels for crystallization from the amorphous state.

Crystallization↗
PubMed1996

Mucociliary differentiation of serially passaged normal human tracheobronchial epithelial cells.

The goal of our studies was to establish procedures for subculturing normal human tracheobronchial epithelial (NHTBE) cells without compromising their ability to differentiate into mucous and ciliated cells (i.e., differentiation competence) and to study the regulation of airway secretions by epidermal growth factor (EGF) and retinoic acid (RA). Primary NHTBE cells were obtained from a commercial source and subcultured repeatedly in serum-free medium on plastic tissue culture dishes. The subcultured cells were tested after every passage for differentiation competence in air-liquid interface (ALI) cultures. The apical secretions of cultured NHTBE cells were characterized by immunoblotting, Western blotting, or enzyme-linked immunosorbent assay using a variety of antibodies. They contained mucin-like materials as well as lysozyme, lactoferrin, and secretory leukocyte protease inhibitor (SLPI). We found that an EGF concentration of 25 ng/ml, which is commonly used in airway cell cultures, adversely affected growth, mucin production, and morphology of ALI cultures and that RA was essential for mucociliary differentiation. Without RA, the epithelium became squamous and mucin secretions decreased 300- to 900-fold. In contrast, secretion of lysozyme, lactoferrin, and SLPI was significantly increased in RA-depleted cultures. Cells of passage 2 (P-2) through P-4 remained competent to differentiate into mucous and ciliated cells when grown in ALI cultures. However, mucin secretion and ciliagenesis decreased in P-3 and P-4 cell cultures and P-3 but not P-4 cell cultures exhibited bioelectric properties characteristic of airway epithelium. We concluded that P-2 and P-3 NHTBE cell cultures retain many important features of normal airway epithelium. This enables one to conduct many studies of airway cell biology with a greatly expanded (6,000-fold) cell pool.

Bronchi↗