Effect of water-soluble polymers on the state of aggregation, vesicle size, and phase transformations in mixtures of phosphatidylcholine and sodium cholate

Kinematic viscosity of therapeutic pulmonary surfactants with added polymers

The addition of various polymers to pulmonary surfactants improves surface activity in experiments both in vitro and in vivo. Although the viscosity of surfactants has been investigated, the viscosity of surfactant polymer mixtures has not. In this study, we have measured the viscosities of Survanta and Infasurf with and without the addition of polyethylene glycol, dextran or hyaluronan. The measurements were carried out over a range of surfactant concentrations using two concentrations of polymers at two temperatures. Our results indicate that at lower surfactant concentrations, the addition of any polymers increased the viscosity. However, the addition of polyethylene glycol and dextran to surfactants at clinically used concentrations can substantially lower viscosity. Addition of hyaluronan at clinical surfactant concentrations slightly increased Infasurf viscosity and produced little change in Survanta viscosity. Effects of polymers on viscosity correlate with changes in size and distribution of surfactant aggregates and the apparent free volume of liquid as estimated by light microscopy. Aggregation of surfactant vesicles caused by polymers may therefore not only improve surface activity as previously shown, but may also affect viscosity in ways that could improve surfactant distribution in vivo.

Polyethylene glycol addition does not improve exogenous surfactant function in an experimental model of meconium aspiration syndrome

Meconium (MEC) is a potent inactivator of pulmonary surfactant. The authors studied the effects of polyethylene glycol addition to the exogenous surfactant over the lung mechanics and volumes. Human meconium was administrated to newborn rabbits. Animals were ventilated for 20 minutes and dynamic compliance, ventilatory pressure, and tidal volume were recorded. Animals were randomized into 3 study groups: MEC group (without surfactant therapy); S100 group (100 mg/kg surfactant); and PEG group (100 mg/kg porcine surfactant plus 5% PEG). After ventilation, a pulmonary pressure-volume curve was built. Histological analysis was carried out to calculate the mean alveolar size (Lm) and the distortion index (DI). Both groups treated with surfactant showed higher values of dynamic pulmonary compliance and lower ventilatory pressure, compared with the MEC group (P < .05). S100 group had a larger maximum lung volume, V(30), compared with the MEC group (P < .05). Lm and DI values were smaller in the groups treated with surfactant than in the MEC group (P < .05). No differences were observed between the S100 and PEG groups. Animals treated with surfactant showed significant improvement in pulmonary function as compared to nontreated animals. PEG added to exogenous surfactant did not improve lung mechanics or volumes.

L-histidine-based pH-sensitive anticancer drug carrier micelle: reconstitution and brief evaluation of its systemic toxicity

A doxorubicin (DOX)-carrier micellar system consisting of poly(histidine)(5K)-b-poly(ethylene glycol)(2K) and poly(l-lactic acid)(3K)-b-PEG(2K)-folate has been developed targeting the early endosomal pH and it have been convincingly proved that intracellular high dose strategy using such micelles is effective in overcoming multidrug resistance (MDR) of cancer cells. Due to the low DOX concentrations in the micelle solution obtained by dialysis and the lack of long-term stability of the micelles, stable and lyophilized micelle formulations were the subject of investigation reported here by using excipients of sucrose, PEG or Pluronic. The reconstituted micelle solutions were examined by particle size, pH sensitivity, and cytotoxicity for MDR cells and the results were compared with the non-lyophilized micelles. Among tested excipients, Pluronic F127 (33 wt%) added to the polymer/drug solution prior to dialysis resulted in a reconstituted product stable for a week and presented equivalent benefits as the fresh micelle formulation. The blank micelles did not present any apparent systemic toxicity in mice up to 2400 mg/kg i.v. injection (800 mg/kg day) for 3 days). The brief toxicity of reconstituted DOX loaded micelles was examined by the maximum tolerated dose (MTD), which was approximately 7.5-fold higher than free DOX and guaranteeing further animal toxicity and efficacy study.

Dextran or Polyethylene Glycol Added to Curosurf for Treatment of Meconium Lung Injury in Rats

BACKGROUND

In experimental lung injuries, improvement of lung function after treatment with surfactant/polymer mixtures may depend on both type of polymer and the specific surfactant. In vitro studies suggest that dextran is more effective when mixed with Curosurf, and polyethylene glycol (PEG) is more effective when mixed with Survanta. We therefore wanted to find out whether these results held true in an animal model of acute lung injury.

OBJECTIVE

To compare the response to therapy of PEG vs. dextran when added to Curosurf after meconium lung injury.

METHODS

Lung injury was produced by intratracheal instillation of meconium (30 and 4 ml/kg). One hour after injury, Curosurf (35 mg/ml) with or without 5% dextran (68 kDa) or 5% PEG (10 kDa) was given. Arterial blood gases and peak inspiratory pressures were measured for 3 h after treatment while animals were supported by volume-regulated ventilation. Then animals were sacrificed and pressure volume relationships, lung wet/dry weights, and histology were assessed.

RESULTS

Initially, improved PaO2 and inspiratory pressure occurred for both Curosurf/PEG and Curosurf/dextran groups compared with Curosurf, but at three hours, peak inspiratory pressure and PaO2 remained significantly improved for the Curosurf/dextran but not for Curosurf/PEG groups when compared with Curosurf alone. Total lung capacity at the end of the experiment was also significantly increased in the Curosurf/dextran group, but not the Curosurf/PEG group when compared with Curosurf.

CONCLUSION

Under these experimental conditions, Curosurf/dextran mixtures provided a better therapeutic response than Curosurf/PEG or Curosurf.

Physical properties of phosphatidylcholine vesicles containing small amount of sodium cholate and consideration on the initial stage of vesicle solubilization

The effects of sub-solubilizing concentrations of sodium cholate (Na-chol) on several physicochemical properties of phosphatidylcholine (PC) small unilamellar vesicles (SUV) were considered in connection with the initial stage of membrane solubilization. ESR spectra of 12-doxylstearic acid (12-DS) in phosphatidylcholine from egg yolk (EPC) or dimyristoylphosphatidylcholine (DMPC) SUV at low concentrations (insufficient to destroy the vesicles) of Na-chol were composed of two (a strongly immobilized and an additional weakly immobilized) immiscible components. The origin of the additional bands was phase separation which occurred in the hydrophobic parts of PC SUV in the presence of Na-chol. Differential scanning calorimetry measurements demonstrated that the mixed DMPC/Na-chol SUV possessed two (a sharp low-temperature and a broad high-temperature) endothermic peaks, which is consistent with the coexistence of two immiscible phases in the vesicular membranes. zeta Potentials of the EPC/Na-chol SUV revealed that high anionic densities appeared on the surfaces of the SUV at a Na-chol concentration slightly below the upper boundary of the vesicle region. Thus, the initial stage of the solubilization of PC SUV by Na-chol was caused by the aggregation of hydrophobic parts of PC membranes, followed by the occurrence of high anionic densities on the surfaces of the vesicles. The fact that removal of Na-chol from PC/Na-chol mixed systems preferentially resulted in the formation of small vesicles might originate from these anionic charges.

Polyethylene glycol/surfactant mixtures improve lung function after HCl and endotoxin lung injuries

Addition of nonionic polymers such as polyethylene glycol (PEG) and dextran ameliorates inactivation of Survanta by a variety of substances in vitro. Addition of polymers to Survanta also improves pulmonary function when used to treat rats with lung injury caused by instillation of human meconium. To find whether this approach is effective in lung injuries that more closely resemble adult respiratory distress syndrome (ARDS), we have compared the use of Survanta with Survanta + PEG in two additional models of lung injury caused by either lipopolysaccharide (LPS) or HCl in adult rats. Significant improvement of serial measures for arterial oxygenation and of postmortem pressure-volume measurements were found after treatment with Survanta + PEG compared with Survanta alone. PEG added to Survanta increased resistance to inactivation caused by tracheal fluid taken from animals injured with HCl. Other work suggests that PEG promotes surfactant aggregation, separates surfactant from surfactant inhibitors, and enhances access of surfactant to the gas-liquid interface. The addition of polymers to surfactants may also be useful in the treatment of lung injury where inactivation of surfactant has already occurred.

Nonionic polymers reverse inactivation of surfactant by meconium and other substances

A variety of substances including human meconium have been found to affect adversely the surface tension-lowering activity of pulmonary surfactants, and this effect may be important in the pathogenesis of a number of human diseases. To find whether inactivation of surfactant could be prevented or reduced by nonionic polymers, we added dextrans, polyethylene glycols (PEGs), or polyvinylpyrrolidones (PVPs) of various molecular weights to pulmonary surfactants. One to 3% human meconium or other inactivating substances were then added to the mixtures, which were tested in a modified pulsating bubble surfactometer. Polymers (3.3-500 kD) in 1-10% concentrations enhanced the ability of a commercial surfactant replacement (Survanta) to lower the minimum surface tension in the presence of meconium, serum, or lysophosphatidylcholine. Similar effects were seen when polymers were added after mixing of surfactant and meconium or other inhibitors, indicating that polymers are capable of reversing the inactivation. Results from rat experiments indicate that total lung capacity is increased when PEG is first added to the Survanta, then mixed with meconium and instilled into the lungs. We postulate that polymers separate meconium-surfactant complexes, permitting surfactant components better access to the air-liquid interface. Taeusch HW, Lu KW, Goerke J, Clements JA. Nonionic polymers reverse inactivation of surfactant by meconium and other substances.

Aggregation of phospholipid vesicles by water-soluble polymers

Water-soluble polymers such as dextran and polyethylene glycol are known to induce aggregation and size growth of phospholipid vesicles. The present study addresses the dependence of these processes on vesicle size and concentration, polymer molecular weight, temperature, and compartmentalization of the vesicles and polymers, using static and dynamic light scattering. Increasing the molecular weight of the polymers resulted in a reduction of the concentration of polymer needed for induction of aggregation of small unilamellar vesicles. The aggregation was fully reversible (by dilution), within a few seconds, up to a polymer concentration of at least 20 wt %. At relatively low phosphatidylcholine (PC) concentrations (up to approximately 1 mM), increasing the PC concentration resulted in faster kinetics of aggregation and reduced the threshold concentration of polymer required for rapid aggregation (CA). At higher PC concentrations, CA was only slightly dependent on the concentration of PC and was approximately equal to the overlapping concentration of the polymer (C*). The extent of aggregation was similar at 37 and 4 degrees C. Aggregation of large unilamellar vesicles required a lower polymer concentration, probably because aggregation occurs in a secondary minimum (without surface contact). In contrast to experiments in which the polymers were added directly to the vesicles, dialysis of the vesicles against polymer-containing solutions did not induce aggregation. Based on this result, it appears that exclusion of polymer from the hydration sphere of vesicles and the consequent depletion of polymer molecules from clusters of aggregated vesicles play the central role in the induction of reversible vesicle aggregation. The results of all the other experiments are consistent with this conclusion.