No abstract

Activated alveolar macrophages secrete both nitric oxide and superoxide in the alveolar lining fluid which combine rapidly to form peroxynitrite, a potent oxidizing agent capable of damaging lipids and proteins in biological membranes. Peroxynitrite (1 mM) plus 100 microM Fe3+EDTA inhibited calf lung surfactant extract (CLSE) from reaching a minimum surface tension below 10 mN/m on dynamic compression. Peroxynitrite and its by-products reacted with the unsaturated lipid components of CLSE, as evidenced by the appearance of conjugated dienes and thiobarbituric acid products, and damaged all surfactant proteins. A mixture of the hydrophobic proteins [surfactant protein B (SP-B) and surfactant protein C (SP-C)] exposed to peroxynitrite became incapable of lowering phospholipid minimum surface tension on dynamic compression. Exposure of SP-A to peroxynitrite decreased its ability to cause lipid aggregation and to act synergistically with SP-B and SP-C in lowering surface tension of surfactant lipids. Western blot analysis of SP-A exposed to peroxynitrite was consistent with fragmentation and polymerization of the 28- to 36-kDa triplet band, and amino acid analysis revealed the presence of significant levels of 3-nitro-L-tyrosine. We conclude that peroxynitrite and its reactive intermediates inhibit pulmonary surfactant function by lipid peroxidation and damaging surfactant proteins.

No abstract

We studied the mechanisms by which C16:0 lysophosphatidylcholine (LPC) and albumin inhibit the surface activity of calf lung surfactant extract (CLSE) by using a pulsating bubble apparatus with a specialized hypophase exchange system, plus adsorption and Wilhelmy balance measurements. In the absence of inhibitors, CLSE (1 mg phospholipid/mL) reached minimum surface tension (gamma(min)) < 1 mN/m within 5 min of bubble pulsation at 20 cycles/min at 37 degrees C. Mixtures of CLSE:LPC had impaired surface activity depending on LPC content: gamma(min) was raised to 5 mN/m by 14 wt % LPC, to 15 mN/m by 25-30 wt% LPC, and to >20 mN/m (67 wt % LPC), even at high CLSE concentrations (3 and 6 mg phospholipid/mL). In contrast, inhibition of CLSE by albumin was more easily abolished when surfactant concentration was raised. Mixtures of albumin (3 mg/mL) and CLSE (1 mg phospholipid/mL) had gamma(min) >20 mN/m, but normal values of gamma(min) < 1 mN/m were reached at higher CLSE concentration (3 mg phospholipid/mL) even when albumin concentration was increased 8-fold to 24 mg/mL. In hypophase exchange studies, LPC, but not albumin, was able to penetrate preformed CLSE surface films and raise gamma(min) CLSE surface films with gamma(min) < 1 mN/m were isolated by an initial hypophase exchange with saline, and a second exchange with an LPC-containing hypophase raised gamma(min) to approximately 10 mN/m. CLSE surface films retained the ability to reach gamma(min) < 1 mN/m in analogous hypophase exchange studies with albumin. The ability of LPC to penetrate surface films of CLSE, although albumin could not, was also demonstrated in adsorption experiments in a Teflon dish, where diffusion was minimized by subphase stirring. Wilhelmy balance experiments also demonstrated that LPC could mix and interact with CLSE or dipalmitoyl phosphatidylcholine in solvent-spread surface films. The ability of LPC or other cell membrane lipids to penetrate interfacial films and raise gamma(min) even at high surfactant concentration may increase their inhibitory actions during acute lung injury.

The biophysical properties and physiologic effects of a series of clinical exogenous pulmonary surfactants was compared to determine the importance of the hydrophobic apoproteins (SP-B and C) as constituents of these preparations. The three exogenous surfactants studied, calf lung surfactant extract (CLSE), Survanta (Surfactant-TA), and Exosurf, all contain dipalmitoyl phosphatidylcholine (DPPC) as their major constituent. CLSE and Survanta also contain 1 to 2% of SP-B,C but Exosurf has the additives hexadecanol and tyloxapol instead to enhance the activity of DPPC. In adsorption experiments, CLSE reached a final surface tension of 22 mN/m, and Survanta and Exosurf reached 28 and 38 mN/m, respectively. Addition of 1% by weight of an apoprotein isolate containing both SP-B and C to Exosurf slightly improved its adsorption. In oscillating bubble studies, CLSE and Survanta decreased surface tension to low values of less than 1 and 2 mN/m, respectively, but Exosurf achieved a minimum value of only 29 mN/m. Addition of SP-B,C to Exosurf improved this minimum to 1 mN/m and approached the behavior of mixtures of synthetic DPPC with SP-B,C. In both adsorption and pulsating bubble experiments, the minimum surface tensions found for Exosurf were almost identical to those generated by tyloxapol alone. In studies of physiologic activity, 20 mg of CLSE or Survanta restored the pressure-volume mechanics of lavaged, surfactant-deficient excised rat lungs to 95 and 50%, respectively, of normal prelavage levels. Instillation of Exosurf (37.5 mg) produced a minimal improvement of only 10% compared to 70% for mixtures containing 1% SP-B,C with either Exosurf or DPPC.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

These experiments characterize the effects of hemoglobin and erythrocyte membrane lipids on the dynamic surface activity and adsorption facility of whole lung surfactant (LS) and a calf lung surfactant extract (CLSE) used clinically in surfactant replacement therapy for the neonatal respiratory distress syndrome (RDS). The results show that, at concentrations from 25 to 200 mg/ml, hemoglobin (Hb) increased the minimum dynamic surface tension of LS or CLSE mixtures (0.5 and 1.0 mumol/ml) from less than 1 to 25 dyn/cm on an oscillating bubble apparatus at 37 degrees C. Similarly, erythrocyte membrane lipids (0.5-3 mumol/ml) also prevented LS and CLSE suspensions (0.5-2.0 mumol/ml) from lowering surface tension below 19 dyn/cm under dynamic compression on the bubble. Surface pressure-time adsorption isotherms for LS suspensions (0.084 and 0.168 mumol phospholipid/ml) were also adversely affected by Hb (0.3-2.5 mg/ml), having a slower adsorption rate and magnitude. Significantly, these inhibitory effects of Hb and membrane lipids could be abolished if LS and CLSE concentrations were raised to high levels. In complementary physiological experiments, instillation of Hb, membrane lipids, or albumin into excised rat lungs was shown to cause a decrease in pressure-volume compliance. This decreased compliance was most prominent in lungs made partially surfactant deficient before inhibitor delivery and could be reversed by supplementation with active exogenous surfactant. Taken together, these data show that molecular components in hemorrhagic pulmonary edema can biophysically inactivate endogenous LS and adversely affect lung mechanics. Moreover, exogenous surfactant replacement can reverse this process even in the continued presence of inhibitor molecules and thus has potential utility in therapy for adult as well as neonatal RDS.

No abstract