Activation of PPARgamma reverses a defect of surfactant synthesis in mice lacking two types of fatty acid binding protein.

Lung surfactant is a lipid-protein-film covering the inner alveolar surface. We have previously shown that double knock-out (d-ko) mice lacking both the epidermal-type (E-) and the heart-type (H-) fatty acid binding protein (FABP) exhibit a defect of surfactant synthesis in alveolar type II cells that can be corrected by feeding pioglitazone, a drug that activates peroxisome proliferator-activated receptor gamma (PPARgamma). Here, we demonstrate first that healthy surfactant at collapse pressure produces protrusions composed of bilayers but not folds, second that the d-ko effect profoundly perturbs lipid/hydrophobic protein composition, pressure-area isotherm, and structural organisation of the surfactant at nanoscale, parameters that are critical for the normal breathing cycle. In support of these data in vivo measurements of lung function reveal that maximum compliance in d-ko vs. wild-type mice is significantly reduced. Further, we show that the biophysical phenotype can be corrected substantially with pioglitazone. Finally, we show that d-ko alveolar cells up-regulate liver-type (L-) FABP, a member of the FABP family that we have previously shown to interact with PPARgamma. Taken together, these data suggest that PPARgamma agonists could be a tool to repair surfactant damage caused by dysfunctional alveolar lipid metabolism, and provide in vivo support for L-FABP aided signaling.

Epileptogenic drugs in a model nervous system: electrophysiological effects and incorporation into a phospholipid layer.

Mechanisms of epileptiform activity in a model nervous system (buccal ganglia of Helix pomatia) are presented. The ganglia contain the identified giant neurons B1 through B4. For epileptiform activity, pentylenetetrazol (1 mmol/L to 40 mmol/L) or etomidate (12.5 micromol/L to 500 micromol/L) were applied. Membrane pressure was measured using a Wilhelmy film balance. In electrophysiological experiments, both drugs induced several effects in all studied neurons: membrane resistance increased, down-stroke of action potentials declined, and all types of chemical synaptic potentials decreased (the latter concerns pentylenetetrazol only). The threshold was 1 mmol/L of pentylenetetrazol and 12.5 micromol/L of etomidate. Epileptiform potentials developed in neurons that had expressed the membrane mechanisms underlying pacemaker potentials. The threshold of this development was again 1 mmol/L of pentylenetetrazol and 12.5 micromol/L of etomidate. Epileptiform depolarizations appeared with 40 mmol/L of pentylenetetrazol and 500 micromol/L of etomidate. In biochemical experiments, both drugs incorporated into an artificial phospholipids membrane and increased pressure in the membrane. The threshold of pressure increase was 1 mmol/L of pentylenetetrazol and 12.5 micromol/L of etomidate. Pressure increased dose-dependently and was 69% and 63% above starting pressure of 10 mN/m with epileptogenic concentrations of pentylenetetrazol (40 mmol/L) and of etomidate (500 micromol/L), respectively. It is postulated that amphiphilic substances incorporate into cell membranes and increase intramembranous pressure, and that this disturbs several membrane processes mechanically and leads to epileptic depolarizations in pacemaker neurons.

Multilayer structures in lipid monolayer films containing surfactant protein C: effects of cholesterol and POPE.

The influence of cholesterol and POPE on lung surfactant model systems consisting of DPPC/DPPG (80:20) and DPPC/DPPG/surfactant protein C (80:20:0.4) has been investigated. Cholesterol leads to a condensation of the monolayers, whereas the isotherms of model lung surfactant films containing POPE exhibit a slight expansion combined with an increased compressibility at medium surface pressure (10-30 mN/m). An increasing amount of liquid-expanded domains can be visualized by means of fluorescence light microscopy in lung surfactant monolayers after addition of either cholesterol or POPE. At surface pressures of 50 mN/m, protrusions are formed which differ in size and shape as a function of the content of cholesterol or POPE, but only if SP-C is present. Low amounts of cholesterol (10 mol %) lead to an increasing number of protrusions, which also grow in size. This is interpreted as a stabilizing effect of cholesterol on bilayers formed underneath the monolayer. Extreme amounts of cholesterol (30 mol %), however, cause an increased monolayer rigidity, thus preventing reversible multilayer formation. In contrast, POPE, as a nonbilayer lipid thought to stabilize the edges of protrusions, leads to more narrow protrusions. The lateral extension of the protrusions is thereby more influenced than their height.