Analysis of proteins in rabbit pulmonary surfactant using monoclonal antibodies

Efficacy and Safety of Combination Therapy with Tolvaptan and Furosemide in Children with Nephrotic Syndrome and Refractory Edema: A Prospective Interventional Study

OBJECTIVE

Severe edema in children with nephrotic syndrome is often refractory to conventional diuretics. Tolvaptan has been used satisfactorily for managing edema in patients with heart failure and cirrhosis. The safety and efficacy of combination therapy with oral tolvaptan and intravenous (IV) furosemide was assessed in patients with furosemide refractory edema.

METHODS

Patients, aged 5-18 y with nephrotic syndrome and severe edema, were screened for eligibility. After excluding hypovolemia, patients received IV furosemide (3-4 mg/kg/d) for 48 h. Those refractory to IV furosemide (weight loss < 3%) received tolvaptan (0.5-1 mg/kg once daily) and IV furosemide for the next 48 h. Parameters were compared between 48 h of furosemide alone and combination therapy.

RESULTS

A total of 24 patients (18 boys) with mean age of 8.0 ± 3.0 y were enrolled. Urine volume significantly increased with combination therapy as compared to furosemide therapy (mean difference: 1.2 mL/kg/h; 95% CI: 0.8-1.65 mL/kg/h) (p < 0.001). Compared to therapy with furosemide alone, combination therapy resulted in significant reduction in body weight from 26.9 ± 10.3 kg to 24.8 ± 9.7 kg (p < 0.001). Estimated glomerular filtration rate did not change (p = 0.81) but serum sodium increased from 135.7 ± 3.3 mEq/L to 140.4 ± 4.8 mEq/L (p < 0.001) with combination therapy; 2 patients showed asymptomatic hypernatremia.

CONCLUSION

The combination of oral tolvaptan and IV furosemide is effective in augmenting diuresis and reducing weight in patients with furosemide refractory edema but requires monitoring of electrolytes and volume status.

Implication of surfactant apoprotein in otitis media with effusion

A two-site simultaneous immunoassay using monoclonal antibodies against human surfactant apoprotein (SAP) was used to measure SAP in middle ear effusions (MEEs). In 130 MEE samples from children with otitis media with effusion, SAP was detected in 54 samples (SAP-positive cases, 41.5%). In the remainder, the SAP concentration was below the sensitivity of the immunoassay (SAP-negative cases, 58.5%). A significant difference in periods of observation was found between the SAP-positive cases (17.3 +/- 16.8 months) and the SAP-negative cases (26.2 +/- 22.5 months) (p less than .01). The percentage of positive cases was highest in the serous MEE group (81.2%) and decreased in the purulent MEE group (57%), the mucoid MEE group (30%), and the hyperviscous MEE group (13.6%), in that order. In the purulent MEE group and the mucoid MEE group, the period of observation was significantly shorter in the SAP-positive cases (18.3 +/- 20.4 months and 20.2 +/- 19.4 months) than in the SAP-negative cases (35.9 +/- 24.5 months and 25.4 +/- 18.7 months) (p less than .05). These results suggest that SAP is present in the middle ear cleft and may be a good prognostic predictor of otitis media with effusion in children.

Aspects of secondary and quaternary structure of surfactant protein A from canine lung

The results of a large number of studies indicate that pulmonary surfactant contains a unique protein whose principal isoform has a molecular weight of about 30,000, and whose presence in surfactant is associated with important metabolic and physicochemical properties. This protein, SP-A, as isolated from canine surfactant, contains a domain of 24 repeating triplets of Gly-X-Y, similar to that found in collagens. These studies were undertaken to determine whether SP-A forms a collagen-like triple helix when in solution, and to describe certain aspects of its size and shape. Our experiments were done on SP-A extracted by two different methods from canine surfactant, and on SP-A produced by molecular cloning. The results from all three preparations were similar. The circular dichroism of the complete protein was characterized by a relatively large negative ellipticity at 205 nm, with a negative shoulder ranging from 215 to 230 nm. There was no positive ellipticity, and the spectrum was not characteristic of collagen. Trypsin hydrolysis resulted in a fragment with peak negative ellipticity at about 200 nm, without the negative shoulder. Further hydrolysis of this fragment with pepsin resulted in a CD spectrum similar to that of collagen. The spectrum of the collagen-like fragment was reversibly sensitive to heating to 50 degrees C, and was irreversibly lost after treatment with bacterial collagenase. SP-A migrated on molecular sieving gels with an equivalent Stokes radius of 110 to 120 A, and had a sedimentation coefficient of 14 S. Using these data we calculate a molecular weight of about 700,000. The hydrodynamic characteristics can be approximated as a prolate ellipsoid of revolution having an axial ratio of about 20. We conclude that SP-A aggregates into a complex of 18 monomers, which may form six triple-helices. The shape of the complex is considerably more globular than collagen and is not consistent with end-to-end binding of the helices to form fibrous structures.

Surfactant-associated 15- and 35-kDa proteins are concentrated in different organelles in rat lung tissue

We have used isopycnic gradient ultracentrifugation to isolate a total lamellar body fraction (total-lb) from rat lung and then further subfractionated this using differential centrifugation to obtain two distinct subpopulations of organelles. When the total-lb was diluted to 0.25 M with sucrose and centrifuged at 8000 X for 30 min we obtained a fraction (lbA) that contained primarily intact classic-appearing lb. When the supernatant was then centrifuged at 80,000 X g for 60 min we obtained a vesicular fraction (lbB). Whereas both fractions had an identical phospholipid composition, their enzyme profiles differed markedly. The lbA had a higher level of beta-glycerophosphatase, while lbB had more 5'-nucleotidase. Moreover, lbB had a phospholipid:protein ratio of 9.2 while lbA had one of 6.3. An examination of the specific activity-time curves revealed that lbA had a curve that was broader and reached a peak earlier than lbB, but the downslopes of both curves were identical; they did not bear a classic precursor-product relationship to one another. The two fractions differed very significantly in their protein profiles. Whereas lbA contained a large amount of a 15-kDa protein with very small amounts of 35-, 37-, 38-, 45-, and 60-kDa proteins, lbB contained predominantly a 35-kDa protein with smaller amounts of 15-, 23-, 26-, 37-, 38-, 45-, and 60-kDa proteins. We suggest that lbB is surfactant taken back up into the alveolar type II cell, or a second release form of tissue surfactant, or a mixture of the two.

Monoclonal antibody identification of a type II alveolar epithelial cell antigen and expression of the antigen during lung development

A monoclonal antibody identifying an antigen expressed by rat type II alveolar epithelial cells, but not by type I epithelial cells or other mature lung cells, was produced by immunization of mice with cells of the rat L2 cell line. The antigen recognized by the antibody was present on the microvillous luminal surface of type II epithelial cells. In adult rat lung, only type II epithelial cells bound the antibody. During fetal development the antigen was expressed by cuboidal epithelial cells lining the respiratory ducts of the first divisions of the tracheal bud, but not by epithelial cells lining the esophagus or trachea. The antigen continued to be expressed by cuboidal epithelial cells lining the larger respiratory ducts until approximately 19 days gestational age. Thereafter, expression was increasingly limited to selected single cells or clusters of two to four cuboidal cells in the smallest ducts. By the 21st postnatal day, the antigen was expressed only by type II alveolar epithelial cells. Type II alveolar epithelial cells isolated from adult lung and the L2 cell line in culture expressed the antigen on the cell surface. A protein of approximately 146,000 Mr was isolated by immunoadsorption of the antigen from non-ionic detergent extracts of type II cells and L2 cells. Preliminary studies of the binding of the antibody to other rat tissues indicate that the antibody binds to renal proximal tubular epithelial cells of the kidney and the luminal surface of the small bowel epithelial cells.

Induction of glucose 6-phosphatase in cultured hepatoma cells by dexamethasone

The synthetic glucocorticoid, dexamethasone, induced high levels of glucose 6-phosphatase in a line of cultured hepatoma cells (2S FAZA). This conflicts with current theory that glucocorticoids induce a microsomal translocase, specific for glucose 6-phosphate, but not the hydrolase itself. The earlier conclusion was based on experiments with rat livers in vivo in which cortisone was the inducing agent. In the present study, 5 X 10(-6) M dexamethasone induced a tenfold increase in glucose 6-phosphatase activity in "intact" as well as disrupted microsomes using either glucose 6-phosphate or mannose 6-phosphate as substrate. This induction was blocked by cycloheximide (50 micrograms/ml). The broad pH maxima between 5.5 and 7.0 were similar for both "intact" and disrupted microsomes.