Improved stability and biological activity of bacterioruberin in nanovesicles

Abstract

Bacterioruberin (BR) is a dipolar C50 isoprenoid with 13 conjugated double bonds and four terminals hydroxyl groups produced by most members of the Haloferacaceae family of halophilic archaea. BR is a natural antioxidant with antimicrobial, antiviral, anticancer and antihaemolytic activity, but its chemical lability, poor water solubility and low bioavailability spoil many of its potential therapeutic uses. In this work, BR extracted from Halorubrum tebenquichense was loaded into liposomes (L-BR, soybean phosphatidylcholine) and archaeosomes (A-BR, sn 2,3 ether-linked archaeolipids). A-BR (125 nm; −50 mV ζ potential, 9.6 μg BR/mg lipids) preserved the antioxidant activity of BR in front of light and temperature, protected its structure against acidity and retained BR within archaeolipid bilayers for 2 years. In contrast, L-BR (154 nm; −13 mV ζ potential, 6.9 μg BR/mg lipids) failed to protect and retain BR. Besides, A-BR inhibited haemolysis induced by ROO* and was more captured by macrophages (J774A.1 cells) than L-BR. However, the anti-inflammatory (TNF-α release) and antioxidant activities (ROS reduction) from A-BR on lipopolysaccharide or H2O2-stimulated J774A.1 cells were comparable to those from L-BR. BR partitioned both in A and L, but SAXS analysis suggested that only archaeosomes mechanically trapped BR, making its partition more stable than in liposomal bilayers, and this impairs its intracytoplasmic delivery. Results postulate A-BR as a candidate for future investigations in chronic inflammatory diseases.