Effect of free and esterified ω-3 docosahexaenoic acid on the interfacial properties of phase-segregated monolayers

ROMINA F. VAZQUEZ; M. LUCRECIA LONGARZO; OSVALDO N. OLIVEIRA JR; SABINA M. MATÉ

Córdoba

Congreso; LI Reunión Anual de la Sociedad Argentina de Biofísica (SAB); 2023

Sociedad Argentina de Biofísica

Docosahexaenoic acid (DHA, 22:6) is an ω-3 polyunsaturated fatty acid that influences immunological, metabolic, and neurological responses through still unknown mechanisms. Upon incorporation into plasma membranes, DHA acyl chains are proposed to reorganize the phospholipid-protein spatial distribution, particularly remodeling the architecture of sphingomyelin (SM)- and Cholesterol (Chol)-enriched raft domains. In this study, we explored the organization and physical properties of monolayers of the phase-segregated mixture phosphatidylcholine (PC)/SM/Chol in the presence of free DHA or DHA esterified in PC (SDPC). Incorporating either lipid produced an expansion of the monolayers to higher areas and enhanced the compressibility of the films. Brewster angle microscopy imaging revealed changes in the microscopic organization of the films with smaller liquid-ordered domains in the presence of free or esterified DHA. Polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) measurements showed a decrease in the conformational order of the hydrocarbon chains when DHA was incorporated whether in its free form or as an esterified compound, pointing to the cis-double bonds of these polyunsaturated lipids as the main responsible for this effect. Incorporating the ω-3 lipids also affected the interfacial region, increasing the hydration levels and inducing changes in the orientation of the phospholipids headgroups. In addition, PM-IRRAS spectra revealed changes in SM H-bonding patterns; free DHA-containing monolayers presented weaker SM H-bonding networks, while stronger H-bonded SM species were detected in SDPC-containing films. These results confirmed the disordering effect introduced by polyunsaturated chains of ω-3 lipids, showing its consequences on the hydration levels of the monolayers and the organization of the SM/Chol-enriched domains.