Surfactant, a highly surface-active material composed of phospholipids, neutral lipids and proteins, lines the lungs' alveolar surface facilitating alveolar ventilation. The molecular organization of surfactant components isolated from calf-lungs was analyzed by differential-scanning calorimetry and dynamic light-scattering, and subsequently compared to surfactant components organized in uni and multilamellar liposomes. The respiratory distress syndrome developed in adult guinea pigs was used for assessing surfactant activity. Calorimetry studies showed that lipid-protein interactions were considerably abated in native surfactant as compared to those of surfactant in uni or multi-lamellar liposomes. Light-scattering experiments indicated that native surfactant has a fibrillar shape with limited lipid-protein interactions, suggesting that it is organized in a lattice-like structure forming a stable film. These findings underscore the importance of the native molecular organization of surfactant. When surfactant reconstituted as uni- or multilamellar liposomes was administred to animals under respiratory distress, they did not recover. In contrast, when native surfactant was used to treat sick animals, arterial pH and PaCO2 values improved, almost reaching normal values. It is important to emphasize that fewer steps in the protocol for isolation of calf lung surfactant made it possible to obtain it in a physiologically active molecular form.

El agente tensioactivo pulmonar es un material compuesto de fosfolípidos, lípidos neutros y proteínas que se encuentra en la superficie alveolar de los pulmones y facilita la ventilación alveolar. La organización molecular de los componentes del agente tensioactivo aislado de pulmones de ternera fue analizada por calorimetría diferencial de barrido y por dispersión dinámica de luz y posteriormente comparada con los componentes organizados en liposomas uni y multilamelares; además, se probó la actividad de superficie al desarrollar en cobayos el síndrome de dificultad respiratoria. Los estudios de calorimetría mostraron que las interacciones lípido-proteína fueron considerablemente abatidas en el agente tensioactivo nativo, en comparación con las del agente tensioactivo en forma de liposomas uni o multilamelares. Los experimentos de dispersión dinámica de luz indicaron que el agente tensioactivo nativo tiene forma fibrilar con interacciones limitadas entre lípidos y proteínas, lo que sugiere que se encuentra organizado en una estructura en forma de reja formando una película de estructura estable. Los resultados obtenidos resaltan la importancia de la organización molecular del agente tensioactivo. Cuando éste fue usado para tratar a los animales con síndrome de dificultad respiratoria, los valores del pH arterial y de PaCO2 mejoraron casi hasta alcanzar los valores normales; cuando se utilizó el agente tensioactivo reconstituído como liposomas uni o multilamelares, los animales no se recuperaron. Es importante enfatizar que el método seguido en el protocolo de aislamiento del agente tensioactivo pulmonar de ternera permitió obtenerlo en una forma fisiológicamente activa.

N-allyl (NAOx) and N-propyl (NPOx) oxamates were designed as inhibitors of alpha-hydroxyacid dehydrogenase (HADH) isozyme II from Trypanosoma cruzi. The kinetic studies showed that NAOx and NPOx were competitive inhibitors of HADH-isozyme II (Ki = 72 µM, IC50 = 0.33 mM and 70 µM, IC50 = 0.32 mM, respectively). The attachment of the allylic and propylic chains to nitrogen of the competitive inhibitor oxamate (Ki = 0.91 mM, IC50 = 4.25 mM), increased 12.6 and 13-folds respectively, the affinity for T. cruzi HADH-isozyme II. NAOx and NPOx were selective inhibitors of HADH-isozyme II, because other T. cruzi dehydrogenases were not inhibited by these substances. Since HADH-isozyme II participates in the energy metabolism of T. cruzi, a trypanocidal effect can be expected with these inhibitors. However, we were not able to detect any trypanocidal activity with these oxamates. When the corresponding ethyl esters of N-allyl (Et-NAOx) and N-propyl (Et-NPOx) oxamates were tested as a possible trypanocidal prodrugs, in comparison with nifurtimox and benznidazole, the expected trypanocidal effects were obtained.