Effect of a 2-hydroxylated fatty acid on Cholesterol-rich membrane domains

2-Hydroxyoleic acid-inserted liposomes as a multifunctional carrier of anticancer drugs

Studies have shown that insertion of oleic acid into lipid bilayers can modulate the membrane properties of liposomes so as to improve their function as drug carriers. Considering that 2-hydroxyoleic acid (2OHOA), a potential antitumor agent currently undergoing clinical trials, is a derivative of oleic acid, we explored the possibility of developing 2OHOA-inserted liposomes as a multifunctional carrier of antitumor drugs in the present study. The insertion of 2OHOA into lipid bilayers was confirmed by surface charge determination and differential scanning calorimetry. 2OHOA insertion greatly decreased the order of dimyristoylphosphatidylcholine packing, produced a nanosized (<100 nm) dispersion, and improved the colloidal stability of liposomes during storage. Moreover, 2OHOA-inserted liposome forms exhibited greater growth inhibitory activity against cancer cells compared with free 2OHOA, and the growth-inhibitory activity of liposomal 2OHOA was selective for tumor cells. 2OHOA insertion greatly increased the liposome-incorporated concentration of hydrophobic model drugs, including mitoxantrone, paclitaxel, and all-trans retinoic acid (ATRA). The in vitro anticancer activity of ATRA-incorporated/2OHOA-inserted liposomes was significantly higher than that of ATRA-incorporated conventional liposomes. In a B16-F10 melanoma syngeneic mouse model, the tumor growth rate was significantly delayed in mice treated with ATRA-incorporated/2OHOA-inserted liposomes compared with that in the control group. Immunohistochemical analyses revealed that the enhanced antitumor activity of ATRA-incorporated/2OHOA-inserted liposomes was due, at least in part, to increased induction of apoptosis. Collectively, our findings indicate that 2OHOA-inserted liposomes exhibit multiple advantages as antitumor drug carriers, including the ability to simultaneously deliver two anticancer drugs - 2OHOA and incorporated drug - to the tumor tissue.

Changes in membrane organization upon spontaneous insertion of 2-hydroxylated unsaturated fatty acids in the lipid bilayer

Recent research regarding 2-hydroxylated fatty acids (2OHFAs) showed clear evidence of their benefits in the treatment of cancer, inflammation, and neurodegenerative disorders such as Alzheimer's disease. Monolayer compressibility isotherms and isothermal titration calorimetry of 2OHFA (C18-C22) in phosphatidylcholine/phosphatidylethanolamine/sphingomyelin/cholesterol (1:1:1:1 mole ratio), a mixture that mimics the composition of mammalian plasma membrane, were performed to assess the membrane binding capacity of 2OHFAs and their natural, nonhydroxylated counterparts. The results show that 2OHFAs are surface-active substances that bind membranes through exothermic, spontaneous processes. The main effects of 2OHFAs are a decrease in lipid order, with a looser packing of the acyl chains, and a decreased dipole potential, regardless of the 2OHFAs' relative affinity for the lipid bilayer. The strongest effects are usually observed for 2-hydroxyarachidonic (C20:4) acid, and the weakest one, for 2-hydroxydocosahexaenoic acid (C22:6). In addition, 2OHFAs cause increased hydration, except in gel-phase membranes, which can be explained by the 2OHFA preference for membrane defects. Concerning the membrane dipole potential, the magnitude of the reduction induced by 2OHFAs was particularly marked in the liquid-ordered (lo) phase (cholesterol/sphingomyelin-rich) membranes, those where order reduction was the smallest, suggesting a disruption of cholesterol-sphingolipid interactions that are responsible for the large dipole potential in those membranes. Moreover, 2OHFA effects were larger than for both lo and ld phases separately in model membranes with liquid disordered (ld)/lo coexistence when both phases were present in significant amounts, possibly because of the facilitating effect of ld/lo domain interfaces. The specific and marked changes induced by 2OHFAs in several membrane properties suggest that the initial interaction with the membrane and subsequent reorganization might constitute an important step in their mechanisms of action.

Membrane composition and dynamics: a target of bioactive virgin olive oil constituents

The endogenous synthesis of lipids, which requires suitable dietary raw materials, is critical for the formation of membrane bilayers. In eukaryotic cells, phospholipids are the predominant membrane lipids and consist of hydrophobic acyl chains attached to a hydrophilic head group. The relative balance between saturated, monounsaturated, and polyunsaturated acyl chains is required for the organization and normal function of membranes. Virgin olive oil is the richest natural dietary source of the monounsaturated lipid oleic acid and is one of the key components of the healthy Mediterranean diet. Virgin olive oil also contains a unique constellation of many other lipophilic and amphipathic constituents whose health benefits are still being discovered. The focus of this review is the latest evidence regarding the impact of oleic acid and the minor constituents of virgin olive oil on the arrangement and behavior of lipid bilayers. We highlight the relevance of these interactions to the potential use of virgin olive oil in preserving the functional properties of membranes to maintain health and in modulating membrane functions that can be altered in several pathologies. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.