Avanti lipid tools: connecting lipids, technology, and cell biology.

Lipid research is challenging owing to the complexity and diversity of the lipidome. Here we review a set of experimental tools developed for the seasoned lipid researcher, as well as, those who are new to the field of lipid research. Novel tools for probing protein-lipid interactions, applications for lipid binding antibodies, enhanced systems for the cellular delivery of lipids, improved visualization of lipid membranes using gold-labeled lipids, and advances in mass spectrometric analysis techniques will be discussed. Because lipid mediators are known to participate in a host of signal transduction and trafficking pathways within the cell, a comprehensive lipid toolbox that aids the science of lipidomics research is essential to better understand the molecular mechanisms of interactions between cellular components. This article is part of a Special Issue entitled Tools to study lipid functions.

The interaction of lipid-liganded gold clusters (Aurora ™) with lipid bilayers.

Lipid bilayers of different phospholipid compositions have been prepared, in the form of vesicles, or of supported lipid bilayers, and doped with Aurora™ at 0.1 mol%. Aurora™ consists of an Au55 gold nanoparticle (about 1.4 nm in diameter) capped with triphenylphosphine ligands and a single diglyceride (distearoyl glycerol) ligand. Gold nanoparticles have been incorporated in the past inside liposomes, or grafted onto their surfaces, with diagnostic or therapeutic aims. Including the gold nanoparticles in a stable form within the lipid bilayers has serious technical difficulties. We have tested the hypothesis that, because of the diglyceride ligand, Aurora™ would allow the easy incorporation of gold nanoclusters into cell membranes or lipid bilayers. Our results show that Aurora™ readily incorporates into lipid bilayers, particularly when they are in the fluid phase, i.e. the state in which cell membranes exist. Calorimetric, fluorescence polarization or fluorescence confocal microscopy concur in showing that bilayer-embedded Aurora™hardly changes the physical properties of the bilayers, nor does it perturb the phase equilibrium in lipid mixtures giving rise to lateral phase separation in the plane of the membrane. Atomic force microscopy shows, in fluid bilayers, well-resolved particles, 1.2-2.9 nm in height, that are interpreted as single Aurora™conjugates. Cryo-transmission electron microscopy allows the clear observation of lipid bilayers with an enhanced contrast due to the Aurora™ gold nanoparticles; the single particles can be resolved at high magnification. Our studies support the applicability of Aurora™ as a membrane-friendly form of nano-gold particles for biological research or clinical applications.

Improved oral delivery of N-(4-hydroxyphenyl)retinamide with a novel LYM-X-SORB organized lipid complex.

PURPOSE: Fenretinide [N-(4-hydroxyphenyl)retinamide (4-HPR)] is a cytotoxic retinoid that suffers from a wide interpatient variation in bioavailability when delivered orally in a corn oil capsule. The poor bioavailability of the capsule formulation may have limited responses in clinical trials, and the large capsules are not suitable for young children. To support the hypothesis that a novel organized lipid matrix, LYM-X-SORB, can increase the oral bioavailability of fenretinide, fenretinide in LYM-X-SORB matrix and in a powderized LYM-X-SORB formulation was delivered to mice. EXPERIMENTAL DESIGN: Fenretinide was delivered orally to mice as the contents of the corn oil capsule, in LYM-X-SORB matrix (4-HPR/LYM-X-SORB matrix) or in a LYM-X-SORB matrix powderized with sugar and flour (4-HPR/LYM-X-SORB oral powder). Levels of 4-HPR, and its principal metabolite, N-(4-methoxyphenyl)retinamide, were assayed in plasma and tissues. RESULTS: In a dose-responsive manner, from 120 to 360 mg/kg/d, delivery to mice of 4-HPR in LYM-X-SORB matrix, or as 4-HPR/LYM-X-SORB oral powder, increased 4-HPR plasma levels up to 4-fold (P<0.01) and increased tissue levels up to 7-fold (P<0.01) compared with similar doses of 4-HPR delivered using capsule contents. Metabolite [N-(4-methoxyphenyl)retinamide] levels mirrored 4-HPR levels. Two human neuroblastoma murine xenograft models showed increased survival (P<0.03), when treated with 4-HPR/LYM-X-SORB oral powder, confirming the bioactivity of the formulation. CONCLUSIONS: 4-HPR/LYM-X-SORB oral powder is a novel, oral drug delivery formulation, suitable for pediatric use, which warrants further development for the delivery of fenretinide in the treatment of cancer. A phase I clinical trial in pediatric neuroblastoma is in progress.