Effect of Phloretin on the Binding of 1-Anilino-8-naphtalene sulfonate (ANS) to 1,2-Dimyristoyl-sn-glycero-3-phosphocoline (DMPC) Vesicles in the Gel and Liquid-Crystalline State

Improving norbixin dispersibility and stability by liposomal encapsulation using the pH-driven method

BACKGROUND

Norbixin, a carotenoid extracted from annatto seeds, is widely utilized as a natural pigment in foods, cosmetics and medicines. Its water solubility is relatively high under neutral or alkaline conditions but low under acidic conditions, which limits its application in some food products.

RESULTS

This problem was overcome by utilizing liposomes to encapsulate the carotenoids so that they could be easily dispersed within acidic solutions. The norbixin was loaded into the liposomes using the pH-driven method. Liposomes were produced by passing aqueous phospholipid dispersions through a microfluidizer under high pressure. Norbixin was then added to the liposome dispersions at pH 7.0 and then driven into the hydrophobic domains of the phospholipid bilayers by acidifying the system. Measurements of the encapsulation efficiency showed that the norbixin was successfully loaded into the liposomes using the pH-driven method. X-ray diffraction analysis showed that the norbixin was in an amorphous state after incorporation into the liposomes. Encapsulation of norbixin within the liposomes was also shown to increase its water dispersibility and chemical stability under acidic pH conditions.

CONCLUSION

The pH-driven method therefore provides a useful means of increasing the application of this bioactive carotenoid within functional foods and other products. © 2021 Society of Chemical Industry.

Selective antibacterial activities and storage stability of curcumin-loaded nanoliposomes prepared from bovine milk phospholipid and cholesterol

Present study prepared curcumin-loaded nanoliposomes using bovine milk, krill phospholipids and cholesterol; and investigated the effects of cholesterol on membrane characteristics, storage stability and antibacterial properties of the curcumin nanoliposomes. Bovine milk phospholipids which have higher saturation than krill phospholipids resulted in formation of curcumin-loaded nanoliposomes with higher encapsulation efficiency (84.78%), larger absolute value of zeta potential and vesicle size (size: 159.15 ± 5.27 nm, zeta potential: -28.3 ± 0.62 mV). Cholesterol helps to formation of a more hydrophobic, compact and tighter bilayer membrane structure which improved the storage stability of nanoliposomes under alkaline (66.25 ± 0.46%), heat (43.25 ± 0.69%) and sunlight (49.44 ± 1.78%) conditions. In addition, curcumin-loaded nanoliposomes can effectively target infectious bacteria which secrete pore-forming toxins such as Staphylococcus aureus by causing the bacterial cell wall to lysis. Findings from present work can guide future development of novel antibacterial agents for use in food preservation.

Effect of packing density of lipid vesicles on the Aβ42 fibril polymorphism

The aggregation of amyloid-β 1-42 (Aβ42) on lipid membranes is closely related to the pathology of Alzheimer's disease (AD). Herein, we demonstrated the effect of the packing density of lipid vesicles on the Aβ42 fibrillation kinetics and fibril morphology. We used three distinct phosphatidylcholine (PC) lipids, containing different numbers of cis-double bonds in acyl chains, and therefore, a different packing density in the lipid vesicles. Our results showed that the fibrillation of Aβ42 was greatly enhanced and the formed fibrils became shorter as the number of double bonds in lipids increased. Due to the low-density characteristics of dioleoyl phosphatidylcholine (DOPC), Aβ42 monomers were able to interact with the hydrophobic acyl chain of lipids exposed to the aqueous phase, thereby inducing rapid fibrillation and short fibril morphologies. Furthermore, the effects of the anionic lipids dioleoyl phosphatidylserine (DOPS) and dioleoyl phosphatidylglycerol (DOPG), and mixed vesicles of DOPC/DOPS and DOPC/DOPG on Aβ42 fibrillations were investigated. The tight binding of Aβ42 to the lipid head groups via electrostatic interactions was able to suppress the modulation of Aβ42 fibrillations compared to accelerated fibrillations on loosely packed membranes. Our proposed mechanism regarding the influence of lipid packing density on Aβ42 fibrillations provides an advanced understanding of lipid-associated amyloid fibrillations.

The effect of sterol derivatives on properties of soybean and egg yolk lecithin liposomes: Stability, structure and membrane characteristics

The effects of three kinds of sterols (cholesterol, β-sitosterol and ergosterol) on the stability, microstructure and membrane properties of soybean and egg yolk lecithin liposomes were investigated by light scattering, transmission electron microscope (TEM), atomic force microscope (AFM), fluorescence and Fourier transform infrared spectroscopy (FTIR). The vesicle size of cholesterol or β-sitosterol incorporated liposomes was higher than that of the control and ergosterol incorporated ones, while the zeta-potential was similar when the same lecithin was used. Due to the excellent emulsifying capacity, Tween-80 was introduced into the system and which could obviously maintain the liposomal vesicle size in fetal bovine serum. According to TEM and AFM, the phenomena of membrane fusion and deformation were observed respectively in ergosterol-incorporated liposomes. Results of fluorescence probe spectra revealed the most compact membrane structure was found in cholesterol-incorporated liposomes, which was in accordance with the strongest intermolecular interaction in bilayers obtained by FTIR results. Conversely, the membrane of ergosterol-incorporated liposomes was the most fragile and fluid, which was also identified with the lowest physical stability obtained by Turbiscan. These results systematically illustrated the relationship between the structure of sterols and the liposomal membrane stability, and provided some meaningful information on the choice of sterols and lecithin in preparation of liposomes for different purposes.