Comparative Effects of Cholesterol and β‐Sitosterol on the Liposome Membrane Characteristics

Abstract

The influence of different phospholipid types (pure phospholipids 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine, POPC, 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine, DPPC, and one commercial phospholipid mixture, Lipoid H100), sterol types (cholesterol vs. β‐sitosterol), and various sterol concentrations (5–50 mol%) on liposomal membrane fluidity, thermotropic properties, liposome size, zeta potential, and lipid oxidation kinetics using fluorescent lipid probe BODIPY 581/591 C11 (4,4‐difluoro‐5‐[4‐phenyl‐1,3‐butadienyl]‐4‐bora‐3a,4a‐diaza‐s‐indacene‐3‐undecanoic acid) are investigated. DPPC bilayer is more rigid than POPC and phospholipids mixture membranes. Pure DPPC gives the smallest liposomes, while liposomes of Lipoid H100 have the largest diameter. Both sterols reduce membrane fluidity of all liposomes, increase absolute zeta potential, cause significant changes in particle size, and decrease phase transition temperature (Tm) and enthalpy of DPPC. POPC/β‐sitosterol liposomes exhibit the most significant lipid oxidation of the lipophilic probe. Along with beneficial effects of phytosterols on human health, better membrane fluidity, more favorable and stabilizing interactions with phospholipids, smaller vesicle size, and enhanced physical stability in comparison to cholesterol are some of the encouraging results for the use of β‐sitosterol in liposome formulations for potential application in foods, pharmaceutics, and cosmetics. Practical Applications: Adjusting the composition of liposomal membrane (lipid type, sterol type, and concentration) can be used as a tool to control membrane fluidity, permeability, and thermotropic properties, and thus predict release properties, physical, thermal, and oxidative stability. A commercial phospholipid mixture of different natural phospholipids with impurities creates less uniform liposomal membrane that is characterized by higher fluidity in comparison to DPPC. The type of phospholipid has huge influence on MLVs size. β‐sitosterol, which is a phytosterol with beneficial effects on human health can be used as a replacement for cholesterol in liposomal formulations, but with the following in mind: β‐sitosterol reduces fluidity of the phospholipid bilayer to a lesser extent than cholesterol, β‐sitosterol gives smaller MLVs than cholesterol, DPPC/β‐sitosterol SUVs are bigger than 100 nm in diameter (relevant for intravenous administration), MLVs with ≥30 mol% of β‐sitosterol can be considered as physically stable (unlike those with cholesterol), irrespective to the phospholipid type. The influence of different phospholipid types, sterol types, and various sterol concentrations on liposomal membrane fluidity, thermo tropic properties, liposomesize, zeta potential, and lipid oxidation kinetics are investigated.

‐sitosterol and gentisic acid loaded 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine liposomal particles

“…As can be seen from Figure 4, the main phase transition temperature and enthalpy of liposomes containing 10 mol % of β-sitosterol were lower than the same parameters of liposomes without sterol. Namely, the addition of β-sitosterol induced a decrease in T m (40.3 • C, both in the absence and in the presence of gentisic acid), whereas ∆H values were 5.3 and 6.1 kcal/mol in the absence and in the presence of gentisic acid, respectively; β-sitosterol caused a significant decrease in enthalpy compared to pure DPPC liposomes, which is in agreement with previous studies (Jovanović et al 2018;Wu et al 2012). Comparing the incorporation of β-sitosterol and gentisic acid into liposomal particles, it could be concluded (via the changes in enthalpy) that gentisic acid had more favourable, stabilizing interactions with phospholipids than β-sitosterol.…”

“…Liposomes represent spherical micrometric or nanometric particles comprising a central aqueous compartment, encircled by one or more bilayers which are composed mainly of phospholipids and sterols. Biocompatible and biodegradable liposomal particles are suitable for delivery of various bioactive components, including vitamins, polyphenols, carotenoids, peptides, enzymes, essential oils (Hammoud, Gharib, Fourmentin, Elaissari, & Greige-Gerges 2019;Jovanović et al 2018;Reidel, Camussone, Archilla, Calvinho, & Veaute 2019). During the encapsu-lation of active principles in liposomal vesicles, lipophilic compounds can be located within the lipid bilayer, hydrophilic substances in the aqueous internal cavity, whereas amphiphilic components are found at the waterlipids interface (Hammoud et al 2019).…”

Modification of hydrophilic polymer network to design a carrier for a poorly water‐soluble substance

“…A negative value of surface potential indicated that a phosphate group was presented in an outer part with respect to the choline groups. [37] Such high absolute value of the zeta potential meant that the prepared liposomal particles were stable due to a large repulsion between them. [37] The FTIR spectra of the PMAC samples of different formulations are presented in Figure 1A,B.…”

“…[37] Such high absolute value of the zeta potential meant that the prepared liposomal particles were stable due to a large repulsion between them. [37] The FTIR spectra of the PMAC samples of different formulations are presented in Figure 1A,B. A FTIR spectrum of neat caffeine is reported on each plot for comparison.…”

Preparation of nanoliposomes by microfluidic mixing in herring-bone channel and the role of membrane fluidity in liposomes formation

“…It is known that various sterols, especially cholesterol, affect structure and fluidity of phospholipid membranes. The influence of sterols like cholesterol or β-sitosterol at various concentrations up to 50 mol% on liposomal membrane fluidity, liposome size and thermal transition was tested on small unilamellar liposomes (SUV) prepared by lipid hydration methods and sonication 30,31 . The authors confirmed concentration dependent impact of sterols on membrane fluidity, but only small effect was observed with respect to the final size of SUV liposomes prepared by ultrasonication.…”