Size-dependent dextran transport across rat alveolar epithelial cell monolayers

The transport of dextrans (approximately 4 to approximately 150 kDa) across an in vitro model of the alveolar epithelial barrier was studied to determine the effects of molecular size on pulmonary absorption of macromolecular drugs. Fluorescein isothiocyanate (FITC)-labeled dextrans (FDs) with average molecular weights (all in kDa) of 3.86 (FD4), 9 (FD10), 19.8 (FD20), 40.5 (FD40), 71.6 (FD70), and 156.9 (FD150) were utilized as model macromolecular drugs. Unidirectional fluxes of FDs at 37 and 4 degrees C were measured from the appearance rates of FD in the receiver fluid of open-circuited monolayers (>2000 omega-cm2) of rat alveolar epithelial cells. Apparent permeability coefficients (P(app)) were estimated from the observed flux and the corresponding concentration gradient of FD. Results showed that FD fluxes were the same in both apical-to-basolateral (AB) and opposite (BA) directions at each molecular weight studied. The P(app) was not significantly different at 0.5 and 1.0 mg/mL FD40 donor concentrations. The FD P(app) (x 10(-8)cm/s) decreased gradually from 1.35 for FD4 to 0.32 for FD40, indicating an apparent inverse relationship between P(app) and molecular weight of FD. By contrast, P(app) was about the same at 0.13 for both FD70 and FD150. When experimental temperature was lowered to 4 degrees C, P(app) decreased by approximately 40% for FDs of 4 through 40 kDa, whereas the decrease in P(app) was by approximately 80% for larger FDs of both 70 and 150 kDa. Moreover, these FDs were found to be relatively intact (approximately 90%) in either receiver fluid after 5-h flux experiments without detectable levels of metabolites in the respective donor fluid, suggesting that alveolar epithelial cells allow translocation of FDs intact across the barrier. Equivalent pore analysis, assuming restricted diffusion of FDs of 4-40 kDa via cylindrical, water-filled pores across the cell monolayer revealed a population of large equivalent pores with approximately 5.6 nm radius. These data suggest that smaller macromolecules (radius <5 nm) traverse the alveolar epithelial barrier via paracellular pathways, and that larger (i.e., radius > or = 6 nm) macromolecules likely cross the barrier via other pathways (e.g., pinocytosis).

Effects of Mycobacterium tuberculosis on the bioelectric properties of the alveolar epithelium

To investigate the hypothesis that Mycobacterium tuberculosis penetrates the alveolar epithelium by downregulating its barrier properties, we evaluated the interactions between M. tuberculosis and rat alveolar epithelial cell monolayers that are believed to share electrophysiologic properties of the human alveolar epithelium. Nonproteinaceous components of M. tuberculosis caused marked declines in electrical resistance and equivalent short-circuit current of the alveolar epithelial cell monolayers, indicating a reduction in the capacity to maintain tight intercellular junctions and to actively reabsorb sodium. M. tuberculosis elicited production of TNF-alpha mRNA and protein by alveolar epithelial cells, and the effects of recombinant TNF-alpha on the bioelectric properties of the alveolar epithelial paralleled those of M. tuberculosis. Furthermore, the effects of M. tuberculosis on alveolar epithelial resistance were abrogated by neutralizing anti-TNF-alpha antibodies. These results indicate that M. tuberculosis elicits production of TNF-alpha, which in turn reduces the bioelectric barrier properties of the alveolar epithelium. These findings provide insight into potential mechanisms by which M. tuberculosis establishes infection and disease in the lung.

Comparison of three rodent neuropathic pain models

To characterize various animal models of neuropathic pain, we compared three previously developed rat models using the same behavioral testing methods. These models involve: (1) chronic constriction injury by loose ligation of the sciatic nerve (CCI); (2) tight ligation of the partial sciatic nerve (PSL); and (3) tight ligation of spinal nerves (SNL). Comparisons were made for the time course of behavioral signs representing various components of neuropathic pain as well as for the effects of surgical sympathectomy. In general, all three methods of peripheral nerve injury produced behavioral signs of both ongoing and evoked pain with similar time courses. However, there was a considerable difference in the magnitude of each pain component between models. Signs of mechanical allodynia were largest in the SNL injury and smallest in the CCI model. On the other hand, behavioral signs representing ongoing pain were much more prominent in the CCI model than in the other two. Although the behavioral signs of neuropathic pain tended to decrease after sympathectomy in all three models, the change was most evident in the SNL model. The results of the present study suggest that the three rat models tested have contrasting features, yet all are useful neuropathic pain models, possibly representing different populations of human neuropathic pain patients.

The vesico-urethral pressuregram analysis of urethral function under stress

About one-third of older multiparous women are prone to stress urinary incontinence (SUI): unwanted urine loss during activities which suddenly raise intra-abdominal pressure. In this paper we describe and test a method for visualizing and analyzing the function of the urinary continence control system (CCS) under stress. Intravesical and intraurethral pressure changes from the resting state were recorded at proximal, mid-, and distal urethral locations during increasingly severe coughs and cross-plotted on a 'vesico-urethral pressuregram.' The slope (alpha) and intercept (chi zero) resulting from a linear regression analysis of these data were used to develop a continence equation which can be used to predict the equilibrium point pressure (PE): the intravesical pressure at which urine will leak to the intraurethral pressure recording site. We tested the null hypothesis that these parameters would not differ in six young, nulliparous continent women (mean +/- S.D. age: 30 +/- 3.5 yr) and six multiparous SUI women (52.3 +/- 8.0 yr, parity: 1.7 +/- 0.8), or between urethral locations. Significant differences in continence equation parameters were found between groups and in different urethral locations. In the SUI group static factors calculated from the term (1 - alpha) contributed 27% of the mean (S.D.) midurethral PE value, 145 (46) cm H2O, while dynamic factors, estimated from alpha, contributed 73% of this value. Valuable insights for improving the diagnosis and treatment of SUI may be obtained by analyzing the relative contributions of alpha and chi 0 to urethral closure during physical stress.

The factors related to recurrence after transcatheter arterial embolization for the treatment of hemoptysis

OBJECTIVES

Massive hemoptysis is a major clinical problem associated with high morbidity and mortality. Transcatheter arterial embolization is widely used for the treatment of massive hemoptysis, but it was reported that the recurrence rate after embolization is 12-54% in the previous studies. We evaluated the therapeutic effect of transcatheter arterial embolization for the treatment of massive hemoptysis and the factors related to recurrence.

METHODS

We reviewed 51 patients (M:F = 36:15) of transcatheter arterial embolization for the treatment of massive hemoptysis from Jan 1988 to Dec 1994, retrospectively.

RESULTS

After arterial embolization, immediate successful control (< 1 wk) of massive hempotysis was achieved in 48 of 51 patients (94.1%) and recurrence of hemoptysis was observed in 17 of 51 patients (33.3%) during the follow-up period. The patients with non-bronchial artery hemoptysis and multiple artery bleeding had increased tendency of recurrence (77.7%). On the previous history of hemoptysis, the patients with massive hemoptysis (> 400 ml/24hr) or frequent history of hemoptysis had increased tendency of recurrence (87.5%, 72.7%).

CONCLUSION

Transcatheter arterial embolization is a useful and safe procedure for immediate control in massive hemoptysis. However, the patients with this procedure had a potentiality for recurrence. We suggest that close follow-up and caution will be needed in the patients with multiple artery bleeding or with large amounts of hemoptysis or with previous episodes more than 3 times.

Large amounts of polyethylene debris in the interface tissue surrounding bipolar endoprostheses. Comparison to total hip prostheses

A histologic and biochemical comparison of interface membranes around femoral components of bipolar endoprostheses (n = 17) and total hip prostheses (n = 17) inserted without cement was conducted. The patients' profiles were similar in both groups with respect to age, sex, primary diagnosis, weight, and the interval between primary and revision arthroplasty. Macroscopically, marked circumferential abrasion of the polyethylene insert in the retrieved bipolar cups was noted. Histologic analysis revealed significantly larger amounts of polyethylene debris in the bipolar group. The membranes from the bipolar group also produced significantly greater amounts of prostaglandin E2 (P < .05). The inflammatory membranes associated with large amounts of polyethylene debris may have contributed to aseptic loosening and osteolysis in patients with a bipolar hip prosthesis.

Permeability characteristics of primary cultured rabbit conjunctival epithelial cells to low molecular weight drugs

PURPOSE

To evaluate the permeability characteristics of primary cultured rabbit conjunctival epithelial cell (RCEC) layers to low molecular weight drugs of varying lipophilicity.

METHODS

3H-mannitol; hydrophilic sotalol and atenolol; moderately lipophilic metoprolol, timolol, propranolol; and highly lipophilic betaxolol were used as model compounds.

RESULTS

The conjunctival apparent permeability coefficient (Papp) of mannitol (1 x 10(-7) cm/s) was 2.4 times lower than that of the most hydrophilic beta-blocker, sotalol (Papp = 2.4 x 10(-7) cm/s). Differences in the degree of tightness of the epithelial cell layers brought about a 30-fold difference in the transport of atenolol in favor of the leaky cell layers, while not affecting the transport of the lipophilic drug, propranolol. Within the log partition coefficient (PC) range of -0.62 (sotalol) and 3.44 (betaxolol), there was a hundred-fold difference in the Papp. A sigmoidal curve was used to depict the influence of lipophilicity on solute permeation across conjunctival epithelial cell layers. An effective half-maximal Papp was observed at a log PC value of 1.2.

CONCLUSIONS

These findings on the lipophilicity effect on drug transport are generally similar to those reported for the isolated rabbit conjunctiva, suggesting the utility of cultured rabbit conjunctival epithelial cell layers as an in vitro model for evaluating drug transport.

A primary culture model of rabbit conjunctival epithelial cells exhibiting tight barrier properties

PURPOSE

The present study was conducted to develop and characterize a functional primary culture of pigmented rabbit conjunctival epithelial cells on permeable support exhibiting tight barrier properties.

METHODS

Conjunctival epithelial cells were isolated by 0.2% protease treatment, cultured at 0.5-1.8 x 10(6) cells/cm2 onto collagen-treated Transwell filters, and were maintained either in the presence of 1% fetal bovine serum throughout or serum-free media from day 3 onwards. Transepithelial potential difference (PD) and transepithelial electrical resistance (TEER) were measured and equivalent short-circuit current (Ieq = PD/TEER) estimated.

RESULTS

There appears to be a critical plating density of 1.5 x 10(6) cells/cm2 for functional development of tight epithelial cell cultures. The culture conditions as noted above did not affect either the time when peak bioelectric parameters were attained (days 8-10) or the magnitude of these parameters at a plating density of 1.5 x 10(6) cells/cm2. Specifically, cells grown in a serum-free media showed a peak TEER of 1.9 +/- 0.2 k omega.cm2, a PD of 14.2 +/- 1.6 V (apical side negative), and and Ieq of 8.0 +/- 0.4 microA/cm2 (mean +/- SEM, n = 45). Electron microscopy of serum-weaned cultures revealed a multilayered epithelium with numerous microvilli on the outermost layer of cells, while sporadic positive Periodic Acid Schiff (PAS) staining under light microscopy suggested the presence of mucin-secretory goblet cells.

CONCLUSIONS

A functional, tight, epithelial barrier of the pigmented rabbit conjunctiva on a permeable support has been developed, which may be useful for mechanistic studies of ion and drug transport at the cellular level.

Horseradish peroxidase transport across rat alveolar epithelial cell monolayers

PURPOSE

To evaluate the transport characteristics of horseradish peroxidase (HRP, a nonspecific fluid-phase endocytosis marker) across an in vitro model of tight (> 2,000 ohm-cm2) rat alveolar epithelial cell monolayers grown on tissue culture-treated polycarbonate filters.

METHODS

Unidirectional HRP fluxes were estimated from the appearance rate of HRP in the receiver fluid following instillation in the donor fluid as a function of donor [HRP] and temperature. Molecular species present in either bathing fluid were determined at the end of flux experiments using fluorescein isothiocyanate (FITC)-labeled HRP by gel permeation chromatography. Cell-associated HRP activity at the end of the transport experiment was determined, as were the rates of recycling and transcellular movement of HRP. An enzymatic assay was uses to quantify HRP activity in the bathing fluid and cells.

RESULTS

Unidirectional HRP fluxes were symmetric and increased linearly with up to 50 microM donor [HRP]. The apparent permeability coefficient of HRP was reduced by 3.5 times upon lowering the temperature from 37 to 4 degrees C. About 50% of the FITC-labeled species present in either receiver fluid was intact HRP. Cell-associated HRP estimated from apical HRP incubation was about 4 times greater than that from basolateral incubation. Recycling into apical fluid of cell-associated HRP following apical incubation occurred rapidly with a half-time (T1/2) of approximately 5 min, reaching a plateau at approximately 67% of the initial cell-associated HRP, while transcellular movement of HRP (into basolateral fluid) took place with a T1/2 of approximately 20 min, attaining a steady-state at approximately 13% of the initial cell-associated HRP. Basolateral recycling of HRP was also rapid (T1/2 = approximately 5 min) reaching a steady-state at approximately 35% of the initial basolaterally-bound HRP. Transcellular movement of HRP following basolateral incubation was slower (T1/2 = approximately 70 min), leveling off at 50% of the initial cell-associated HRP.

CONCLUSIONS

HRP appears to be transported relatively intact (approximately 50%) across rat alveolar epithelial barrier via nonspecific fluid-phase endocytosis. The transepithelial pinocytotic rate of alveolar epithelial cells is estimated to be about 25 nL/cm2/h.

Activation of osteoclast-mediated bone resorption by the supernatant from a rabbit synovial cell line in response to polyethylene particles

It is unknown whether the soluble factors produced from cells activated by wear particles in the fibrous tissue around failed joint prostheses really activate osteoclastic bone resorption. In this study, the activation of osteoclast-mediated bone resorption by the products from a rabbit synovial cell line (HIG-82) stimulated by various particles was investigated using rabbit unfractionated bone cells cultured on a dentin slice. The HIG cells were challenged with the following laboratory-made particles: high-density polyethylene (PE), cobalt alloy (Co-Cr), titanium alloy (Ti6Al4V), pure titanium (Ti), and sintered hydroxyapatite (HA). The size of each particle was < 2 microns. The supernatants from HIG cells cultured with the appropriate concentration of wear particles were added to unfractionated bone cells on a dentin slice, and then resorbed areas were determined for each particle. Interestingly, resorbed areas significantly increased only when the culture medium from HIG cells with PE particles was added to unfractionated bone cells. This study demonstrates that PE particles stimulate the rabbit synovial cells to produce soluble factors that induce osteoclast-mediated bone resorption. Moreover, this experimental model is a useful method sensitively to evaluate the effects of soluble factors from the cells stimulated by particulate biomaterials from joint prostheses on osteoclastic bone resorption.

Liarozole inhibits human epidermal retinoic acid 4-hydroxylase activity and differentially augments human skin responses to retinoic acid and retinol in vivo

Metabolic inactivation of all-trans retinoic acid to 4-hydroxy retinoic acid occurs via a cytochrome P-450 enzyme. We investigated the effects of liarozole on the retinoic acid 4-hydroxylase activity of human epidermis and its ability to modify in vivo human skin responses to retinoic acid and all-trans retinol. Retinoic acid 4-hydroxylase activity induced in vivo by 4 d treatment with retinoic acid (0.1%) was inhibited in vitro by liarozole in a concentration-dependent manner. Comparable micromolar concentrations of liarozole were extracted from stratum corneum-free epidermis treated with 3% liarozole. Retinoic acid levels in liarozole-treated skin increased to 19 +/- 5 ng/g wet wt (mean +/- SEM, p < 0.002, n = 17) at 18 h and to 6 +/- 2 ng/g wet wt (p = 0.38, n = 17) at 48 h as compared to vehicle (not detectable). At 48 h, retinoic acid 4-hydroxylase activity was induced 9-fold over vehicle (p < 0.03, n = 8). At 96 h, no significant erythema or increased epidermal thickness was found when either retinoic acid (0.001%), all-trans retinol (0.0250%), or liarozole (3%) was applied individually, but when 0.001% retinoic acid and 3% liarozole were applied together, both erythema and increased epidermal thickness occurred. In contrast, 0.025% all-trans retinol and 3% liarozole together caused increased epidermal thickness but no erythema. These data demonstrate that, at doses used here, liarozole, although an effective inhibitor of retinoic acid 4-hydroxylase, cannot function alone like a retinoid in vivo, probably because of retinoic acid 4-hydroxylase induction. In the presence of a low dose retinoic acid or all-trans retinol, however, liarozole can amplify human skin responses to each retinoid in a manner characteristic of the retinoid at a higher dose (erythema and hyperplasia with retinoic acid; no erythema but hyperplasia with all-trans retinol).

Generation of glycolaldehyde from guinea pig airway epithelial monolayers exposed to nitrogen dioxide and its effects on sodium pump activity

Pulmonary injury from nitrogen dioxide (NO2) may in part be related to the generation of aldehydic compounds, which bind with cellular proteins and subsequently impair or inhibit cell function. We examined the generation of aldehydes from guinea pig tracheobronchial epithelial (GPTE) cell monolayers exposed to NO2. With the use of dinitrophenylhydrazine (DNP) to derivatize aldehydic compounds, glycolaldehyde, a two carbon alpha-hydroxyaldehyde, was identified in elevated levels in the basolateral fluid from monolayers exposed to NO2. DNP-glycolaldehyde levels were 81.2 +/- 2.7 and 234.0 +/- 42.6 nM in response to a 1-hr exposure to 1 and 5 ppm NO2, respectively, as compared to an air-control value of 20.3 +/- 6.8 nM. Taking into account dilution and reactivity, cellular glycolaldehyde levels could have reached as high as 3 mM for the 60-min exposure period (i.e., 0.05 mM/min). The effects of exogenous glycolaldehyde on GPTE ouabain-sensitive basolateral 86Rb uptake (an index of Na+,K(+)-ATPase activity) were examined and compared with the actions of NO2 exposure. Bolus addition of glycolaldehyde to the basolateral fluid at concentrations > or = 5 mM led to an inhibition of ouabain-sensitive 86Rb uptake, while lower concentrations had no effect. the effects of exogenous glycolaldehyde differ from NO2 exposure, which led to a sustained elevation of ouabain-sensitive 86Rb uptake with presumed generation of glycolaldehyde at a continuous low level. Glycolaldehyde does not appear to play a significant role in the acute alterations of sodium pump activity, suggesting that the NO2-induced changes in Na+,K(+)-ATPase activity of GPTE monolayers probably are further mediated by other lipid peroxidation products/oxidation processes yet to be identified.

Age-dependent expression of P-glycoprotein gp170 in Caco-2 cell monolayers

PURPOSE

To determine whether the expression and activity of the P-glycoprotein (P-GP) drug efflux pump vary with the culture age of Caco-2 cell monolayers.

METHODS

Caco-2 cell monolayers were grown for 3-27 days on tissue culture-treated Transwells. P-GP efflux function was determined by measuring transmonolayer fluxes of cyclosporin A (CsA) and verapamil, while P-GP expression level was evaluated by Western blot analysis using monoclonal antibody C219.

RESULTS

The apparent permeability coefficient (Papp) of CsA (0.5 microM) in the basolateral-to-apical (B-->A) direction increased with culture age and was higher than the apical-to-basolateral (A-->B) direction at all times. Net secretory Papp significantly increased from day 17 onward compared to that observed during day 3 through 13. Verapamil (100 microM) significantly inhibited CsA transport in the B-->A direction from day 17 to 27, while elevating CsA transport in the A-->B direction from day 6 to 27. Interestingly, the Papp of verapamil (0.5 microM) in the B-->A direction was significantly higher than in the A-->B direction from day 6 to 27, rendering increases in net secretory Papp of verapamil with culture age. Western analysis revealed that P-GP expression level was in the order of 4 weeks approximately 1 week > 3 weeks > 2 weeks at equal loading of cell proteins.

CONCLUSIONS

P-GP is continuously expressed throughout the culture period, but it may not be fully functional at an early age. Caco-2 cell monolayers of day 17 to 27 appear to be a good model to evaluate the functional role of P-GP in drug efflux.

Release of leukemia inhibitory factor in primate sepsis. Analysis of the role of TNF-alpha

Leukemia inhibitory factor (LIF), a pleiotropic cytokine with many biologic effects overlapping with those of IL-6, has been implicated in the pathogenesis of sepsis. We here analyzed the kinetics of LIF in 13 baboons challenged with a lethal (n=6) or sublethal (n=7) dose of Escherichia coli. In addition, to assess the role of TNF-alpha in the induction of LIF in vivo, seven baboons were studied that had either received a bolus injection of recombinant human TNF-alpha (100 micrograms/kg, n=3), or to whom 15 mg/kg of an anti-TNF mAB before lethal E. coli challenge was administered (n=4). LIF levels increased 2 h after E coli challenge, and reached maximum values at 4 and 8 h after a sublethal (4.4 +/- 1.6 ng/ml) or lethal (40.9 +/- 3.8 ng/ml) dose, respectively. TNF-alpha injection induced a modest rise in LIF concentrations, peaking after 6 h (228 +/- 46 pg/ml). Circulating LIF correlated with plasma levels of IL-6, both after E. coli challenge (Spearman Rank coefficient of correlation (r) = 0.849, p&lt;0.001), as well as upon TNF-alpha injection (r=0.863, p&lt;0.001). Moreover, the E. coli-induced release of either cytokine was reduced 6- to 10-fold after pretreatment with anti-TNF mAb, except in one nonsurviving animal, which exhibited a progressive increase of LIF and IL-6 levels despite the absence of TNF immunoreactivity. These results show that TNF-alpha is an intermediate factor in concerted release of LIF and IL-6 in vivo, and indicate that the enhanced elaboration of these cytokines may predict disease outcome in severe sepsis.

Release of leukemia inhibitory factor in primate sepsis. Analysis of the role of TNF-alpha

Leukemia inhibitory factor (LIF), a pleiotropic cytokine with many biologic effects overlapping with those of IL-6, has been implicated in the pathogenesis of sepsis. We here analyzed the kinetics of LIF in 13 baboons challenged with a lethal (n=6) or sublethal (n=7) dose of Escherichia coli. In addition, to assess the role of TNF-alpha in the induction of LIF in vivo, seven baboons were studied that had either received a bolus injection of recombinant human TNF-alpha (100 micrograms/kg, n=3), or to whom 15 mg/kg of an anti-TNF mAB before lethal E. coli challenge was administered (n=4). LIF levels increased 2 h after E coli challenge, and reached maximum values at 4 and 8 h after a sublethal (4.4 +/- 1.6 ng/ml) or lethal (40.9 +/- 3.8 ng/ml) dose, respectively. TNF-alpha injection induced a modest rise in LIF concentrations, peaking after 6 h (228 +/- 46 pg/ml). Circulating LIF correlated with plasma levels of IL-6, both after E. coli challenge (Spearman Rank coefficient of correlation (r) = 0.849, p<0.001), as well as upon TNF-alpha injection (r=0.863, p<0.001). Moreover, the E. coli-induced release of either cytokine was reduced 6- to 10-fold after pretreatment with anti-TNF mAb, except in one nonsurviving animal, which exhibited a progressive increase of LIF and IL-6 levels despite the absence of TNF immunoreactivity. These results show that TNF-alpha is an intermediate factor in concerted release of LIF and IL-6 in vivo, and indicate that the enhanced elaboration of these cytokines may predict disease outcome in severe sepsis.

Topical tretinoin (retinoic acid) improves early stretch marks

BACKGROUND AND DESIGN

Stretch marks are disfiguring lesions usually caused by excessive stretching of skin. We investigated the response of early, clinically active stretch marks to topical 0.1% tretinoin (retinoic acid) cream. In a double-blind, randomized, vehicle-controlled study, 22 patients applied either 0.1% tretinoin (n = 10) or vehicle (n = 12) daily for 6 months to the affected areas. Patients were evaluated by physical examination monthly and by analysis of biopsy specimens of stretch marks obtained before and at the end of therapy in comparison with untreated normal skin.

RESULTS

After 2 months, patients treated with tretinoin had significant improvements in severity scores of stretch marks compared with patients who received vehicle (P < .05). After 6 months, eight (80%) of the 10 tretinoin-treated patients had definite or marked improvement compared with one (8%) of the 12 vehicle-treated patients (P = .002). Targeted stretch marks in patients treated with tretinoin had a decrease in mean length and width of 14% and 8%, respectively, compared with an increase of 10% (P < .001) and 24% (P = .008), respectively, in patients who received vehicle. There were no significant differences in various measures of quality and quantity of dermal collagen and elastic fibers in stretch marks when tretinoin and vehicle treatments were compared.

CONCLUSIONS

Topical application of tretinoin significantly improves the clinical appearance of early, active stretch marks. The processes that are responsible for the clinical improvement remain unknown.

Alveolar epithelial clearance of protein

Substantial progress has been made in understanding the rate, the pathways, and the mechanisms regulating alveolar protein removal from the uninjured lung. Whole animal studies and cellular studies have demonstrated that the majority of alveolar epithelial protein clearance occurs by passive nondegradative diffusional pathways. Some evidence, however, has been recently presented that alveolar epithelial cells express an albumin-binding receptor as well as a polymeric immunoglobulin receptor, both of which might be important for alveolar epithelial clearance of protein. However, the contribution of these receptors requires further studies. Little is known about alveolar clearance of protein during pathological conditions; further studies are required to determine the roles of the different cell types in the lung for removal of protein from the alveolar spaces of the lung. Alveolar macrophages are likely to play an important role in the degradation and removal of insoluble protein from the distal air spaces after acute lung injury. In conclusion, the present data suggest that most proteins and peptides deposited on the epithelial surfaces in the distal air spaces are cleared as intact molecules, predominantly via paracellular routes. The contribution of pinocytic processes appear to be of minor importance for translocation of bulk quantities of proteins or peptides across the alveolar epithelium.

Effects of EGF on alveolar epithelial junctional permeability and active sodium transport

We evaluated the effects of epidermal growth factor (EGF) on transepithelial resistance (Rt) and active ion transport by alveolar epithelial cell (AEC) monolayers on tissue culture-treated polycarbonate filters. Rat type II cells were cultured in completely defined serum-free medium (MDSF) or MDSF supplemented with EGF. The addition of EGF from either day 0 (chronic) or day 4 (subacute) resulted in significant increases in Rt and short-circuit current (ISC) on day 5. After subacute exposure, these effects were delayed in onset by 6-12 h and sustained for > 24 h. Basolateral (but not apical) EGF was responsible for these effects, which were prevented by preincubation with tyrphostin RG-50864, a reversible specific inhibitor of the EGF receptor tyrosine kinase. ISC decreased, with a sensitivity to apical inhibitors of sodium transport in the order benzamil > amiloride > 5-(N-ethyl-N-isopropyl) amiloride in MDSF +/- EGF, and was completely inhibited by the addition of basolateral ouabain. Net sodium flux and Na+, K+ -ATPase activity both increased approximately 50% in the presence of EGF. These results indicate that 1) EGF decreases tight junctional permeability and increases active sodium transport by AEC monolayers via basolaterally located EGF receptors, and 2) the pathways for AEC sodium entry and exit (+/- EGF) are apical high amiloride affinity sodium channels and basolateral sodium pumps.

Contribution of Na(+)-glucose cotransport to the short-circuit current in the pigmented rabbit conjunctiva

The objective of this study was to determine whether Na(+)-glucose cotransport contributed to the residual short-circuit current (Isc) in the pigmented rabbit conjunctiva not accounted for by Cl- secretion. The Isc of the pigmented rabbit conjunctiva was measured following exposure of its mucosal or serosal side to varying concentrations of D-glucose or phloridzin in a glutathione-bicarbonated Ringer's solution (GBR). Addition of D-glucose to the mucosal side of the conjunctiva bathed in glucose-free GBR elevated Isc up to 26 +/- 6% in a dose-dependent manner (K0.5 = 1.2 mM), while mucosal (but not serosal) addition of phloridzin reduced the Isc (IC50 = 0.05 mM) of the conjunctiva bathed in regular GBR. In a mucosal Na(+)-free medium, neither 20 mM D-glucose nor 0.5 mM phloridzin was effective. In a mucosal glucose-containing medium, deletion of Na+ reduced Isc up to 27 +/- 4%. It was, however, restored to its initial value upon the addition of 17.5-141 mM Na+ to a medium containing 5 mM D-glucose. Hill plot analysis of Isc elevation at 141 mM Na+ in the presence of varying D-glucose concentrations in the mucosal bathing fluid yielded a Hill coefficient of 0.86. There is, therefore, evidence for the apical localization of phloridzin-sensitive Na(+)-coupled D-glucose transport that exhibits apparent 1:1 stoichiometry, being responsible for the maximal 26% increase in the Isc.

Vascular endothelial growth factor promotes tumor dissemination by a mechanism distinct from its effect on primary tumor growth

Tumor growth is dependent on new blood vessel formation. Inhibition of vascular endothelial growth factor (VEGF), an endothelial cell mitogen and angiogenic factor secreted by a variety of tumors and tumor cell lines, is sufficient to inhibit primary tumor growth. In the present study, we examined the effect of inhibiting VEGF on tumor cell micrometastasis. A transfectant of A431 (a human epidermoid carcinoma cell line) expressing chloramphenicol acetyltransferase (CAT) was injected s.c. into severe combined immunodeficiency (scid) mice, which were then sacrificed after 6 weeks. The presence of A431 metastases at distant sites was demonstrated by detection of CAT activity in whole-organ lysates. Treatment of animals with VEGF-neutralizing antibodies not only inhibited primary tumor growth but also suppressed metastases, as determined by CAT activity in organ lysates. In experiments to determine the mechanism by which anti-VEGF antibody inhibited metastasis, control animals were sacrificed when their tumors had reached the same size as tumors in VEGF antibody-treated animals. Metastases were uniformly present in these control animals. These findings show that inhibition of VEGF alone is sufficient to prevent tumor growth and dissemination in vivo. The inhibitory effect on metastases appears to be distinct from that on primary tumor growth.

Enhancement of airway epithelial Na+,K(+)-ATPase activity by NO2 and protective role of nordihydroguaiaretic acid

We examined the effects of nitrogen dioxide (NO2) on guinea pig tracheobronchial (GPTE) ouabain-sensitive 86Rb uptake, as an index of Na+,K(+)-ATPase activity, and specific [3H]ouabain binding. A 1-h exposure of GPTE monolayers to 5 ppm NO2 increased ouabain-sensitive 86Rb uptake (nmol.mg protein-1.30 min-1) to 512 +/- 39 compared with an air-control value of 278 +/- 20. Similarly, 1 ppm NO2 increased 86Rb uptake to 336 +/- 19 from an air control of 219 +/- 31. The specific [3H]ouabain-binding capacity (Bmax) for monolayers exposed to 5 ppm NO2 was increased to 23.2 +/- 1.2 pmol/mg protein in comparison with an air-control value of 18.4 +/- 0.4; however, there was no change at 1 ppm NO2. Binding constants (Kd) for 1 or 5 ppm NO2 were increased to 0.64 +/- 0.02 and 0.79 +/- 0.08 microM, respectively, in comparison with an air-control value of 0.53 +/- 0.02 microM. Changes of Bmax and Kd may be consistent with a recruitment of latent pumps to the basolateral cell plasma membrane and/or increased turnover of the sodium pump. However, the increase of Bmax was no more than 126% of the air control, while 86Rb uptake increased to 184%, suggesting that an increased turnover is the more predominant effect. Incubation of GPTE monolayers during NO2 exposure with nordihydroguaiaretic acid, an antioxidant, blocked the increase of ouabain-sensitive 86Rb uptake almost completely and partially protected transepithetial resistance, suggesting that lipid peroxidation processes may play a role in alterations of airway epithelial barrier and active ion transport properties.