Structure–Function Relationships of New Lipids Designed for DNA Transfection

Abstract

Cationic liposome/DNA complexes can be used as nonviral vectors for direct delivery of DNA-based biopharmaceuticals to damaged cells and tissues. To obtain more effective and safer liposome-based gene transfection systems, two cationic lipids with identical head groups but different chain structures are investigated with respect to their in vitro gene-transfer activity, their cell-damaging characteristics, and their physicochemical properties. The gene-transfer activities of the two lipids are very different. Differential scanning calorimetry and synchrotron small- and wide-angle X-ray scattering give valuable structural insight. A subgel-like structure with high packing density and high phase-transition temperature from gel to liquid-crystalline state are found for lipid 7 (N'-2-[(2,6-diamino-1-oxohexyl)amino]ethyl-2,N-bis(hexadecyl)propanediamide) containing two saturated chains. Additionally, an ordered head-group lattice based on formation of a hydrogen-bond network is present. In contrast, lipid 8 (N'-2-[(2,6-diamino-1-oxohexyl)amino]ethyl-2-hexadecyl-N-[(9Z)-octadec-9-enyl]propanediamide) with one unsaturated and one saturated chain shows a lower phase-transition temperature and a reduced packing density. These properties enhance incorporation of the helper lipid cholesterol needed for gene transfection. Both lipids, either pure or in mixtures with cholesterol, form lamellar phases, which are preserved after addition of DNA. However, the system separates into phases containing DNA and phases without DNA. On increasing the temperature, DNA is released and only a lipid phase without intercalated DNA strands is observed. The conversion temperatures are very different in the two systems studied. The important parameter seems to be the charge density of the lipid membranes, which is a result of different solubility of cholesterol in the two lipid membranes. Therefore, different binding affinities of the DNA to the lipid mixtures are achieved.

Structures of malonic acid diamide/phospholipid composites and their lipoplexes

“…Nevertheless, due to the absence of the peak attributed to C a -C a in the WAXS pattern of OH4, while the signals q H-bond-1 and q H-bond-2 occur in the patterns of both lipids, and due to the discrepancies found between WAXS and IRRAS (see section below), an orthorhombic chain lattice with q 11 = 15.25 nm À1and q 02 = 16.52 nm À1 cannot be excluded. This would result in a cross-sectional area of A = 18.6 Å 2 and a unit cell perpendicular to the chain axis of 4.9-7.6 Å (such unit cell values were also described for a lipid with a related backbone27 and are close to the tight herringbone arrangement of hydrocarbon chains (5.0-7.5 Å)) 30. At pH 6.5, three reflexes are detected in WAXS: one peak at q H-bond = 12.98 nm À1 (reflex of repeating distances caused by hydrogen bonds), one at q 11 = 15.35 nm À1 , and one at q = 16.50 nm À1 , comparable to the scattering curve at pH 3.…”

General Synthesis and Physicochemical Characterisation of a Series of Peptide‐Mimic Lysine‐Based Amino‐Functionalised Lipids

“…X‐ray scattering data show that lipids 1 – 4 a – c build up lamellar phases at this pH value 28. The broadening of the phase transition peaks for lipids with an oleyl chain (OT; see Figure 1) was expected because the oleylamine used contains up to 30 % of other alkyl amines with different chain length and saturation 11b…”

The Use of Nanostructures for DNA Transfection

“…Gene transfection by lipoplexes is called lipofection. Lipofection is a method in which exogenous DNA is transported inside cationic liposomes to cross the plasma membrane by endocytosis [16]. However, until the internalized molecules reaching the nucleus, enzymes that degrade DNA called DNases can hydrolyse most of the transfected DNA, reducing the efficiency of this technique [7].…”