Estimating the contribution of surfactant replacement therapy to the alveolar pool: An in vivo study based on ¹³C natural abundance in rabbits

Abstract

Variation of the isotopic abundance of selected nutrients and molecules has been used for pharmacological and kinetics studies under the premise that the administered molecule has a different isotopic enrichment from the isotopic background of the recipient subject. The aim of this study is to test the feasibility of assessing the contribution of exogenous surfactant phospholipids to the endogenous alveolar pool in vivo after exogenous surfactant replacement therapy in rabbits. The study consisted in measuring the consistency of C/ C ratio of disaturated-phosphatidylcholine palmitate (DSPC-PA) in 7 lots of poractant alfa, produced over a year, and among bronchoalveolar lavages of 20 rabbits fed with a standard chow. A pilot study was performed in a rabbit model of lavage-induced surfactant deficiency: 7 control rabbits and 4 treated with exogenous surfactant. The contribution of exogenous surfactant to the alveolar pool was assessed after intra-tracheal administration of 200 mg/kg of poractant alfa. The C content of DSPC-PA was measured by isotope ratio mass spectrometry. The mean DSPC-PA C/ C ratio of the 7 lots of poractant alfa was -18.8‰ with a SD of 0.1‰ (range: -18.9‰; -18.6‰). The mean C/ C ratio of surfactant DSPC recovered from the lung lavage of 20 rabbits was -28.8 ± 1.2‰ (range: -31.7‰; -25.7‰). The contribution of exogenous surfactant to the total alveolar surfactant could be calculated in the treated rabbits, and it ranged from 83.9% to 89.6%. This pilot study describes a novel method to measure the contribution of the exogenous surfactant to the alveolar pool. This method is based on the natural variation of C, and therefore it does not require the use of chemically synthetized tracers. This method could be useful in human research and especially in surfactant replacement studies in preterm infants.

A novel deuterium‐based model for measurement of exogenous surfactant using deuterium‐depleted water

“…Of note, our novel and noninvasive deuterium dilution method for endogenous and exogenous surfactant evaluation had a precision of 5 δ‰ and it was able to discriminate a ratio between endogenous and exogenous DSPC (and vice versa) of 1/30. This finding was similar to that previously reported with the 13 C method used as a reference, thus confirming its suitability for our study purpose 9 …”

“…Using the deuterium dilution technique, as proposed in this study, has several advantages: (1) it is simple as it entails the administration of drinking water without anesthesia or physical restrains; (2) DDW is available as commercially available drinking water approved for human use; and (3) we found a high agreement with the data obtained with the previous reference method, the natural variation in δ 13 C ratio 9,10 …”

“…Our research group has recently utilized the natural change in the 13 C/ 12 C ratio of the disaturated‐phosphatidylcholine (DSPC), the main component of pulmonary surfactant, to estimate the contribution of exogenous surfactant to the alveolar pool in a rabbit model of RDS 7,9,10 . Differences in the photosynthesis process of carbon dioxide fixation in C3 (e.g., soybean and rice) and C4 (e.g., corn, sugarcane, and sorghum) plants result in metabolites isolated from C4 plants having higher 13 C concentrations (−10 to −16 δ 13 C) compared with those isolated from C3 plants (−23 to −32 δ 13 C).…”

“…8 Our research group has recently utilized the natural change in the 13 C/ 12 C ratio of the disaturated-phosphatidylcholine (DSPC), the main component of pulmonary surfactant, to estimate the contribution of exogenous surfactant to the alveolar pool in a rabbit model of RDS. 7,9,10 Differences in the photosynthesis process of carbon dioxide fixation in C3 (e.g., soybean and rice) and C4 (e.g., corn, sugarcane, and sorghum) plants result in metabolites isolated from C4 plants having higher 13 C concentrations (−10 to −16 δ 13 C) compared with those isolated from C3 plants (−23 to −32 δ 13 C). Given that the isotopic signature of a metabolite is preserved following the incorporation from the diet, 11 we found that lipids recovered from rabbit lungs, raised on a C3 diet, had a different 13 C/ 12 C ratio than those contained in Poractant alfa, which is an extract of lung surfactant obtained from pigs raised on a corn diet (C4 plants).…”

Tracing exogenous surfactant in vivo in rabbits by the natural variation of 13C

“…We recently developed a new method to estimate the contribution of exogenous surfactant to the alveolar pool in a rabbit model of RDS based on carbon stable isotope natural abundance of the disaturated-phosphatidylcholine palmitic acid (DSPC-PA) [13], the main phospholipid component of pulmonary surfactant. Briefly, we verified the suitability of our method in lung-lavaged adult rabbits by assessing the constancy of poractant alfa DSPC-PA carbon stable isotopes ratio among different batches, the difference in carbon stable isotopes abundance between endogenous and exogenous surfactant, and the effect of poractant alfa administration on rabbit alveolar DSPC-PA 13 C content.…”