Phenolic lipids are a very diversified group of compounds derived from mono and dihydroxyphenols, i.e., phenol, catechol, resorcinol, and hydroquinone. Due to their strong amphiphilic character, these compounds can incorporate into erythrocytes and liposomal membranes. In this review, the antioxidant, antigenotoxic, and cytostatic activities of resorcinolic and other phenolic lipids are described. The ability of these compounds to inhibit bacterial, fungal, protozoan and parasite growth seems to depend on their interaction with proteins and/or on their membrane-disturbing properties.

The effects induced by natural phenolic and resorcinolic lipids on membrane permeability were investigated. All of the compounds tested perturbed the phospholipid bilayer and stabilized erythrocytes against hypoosmotically induced hemolysis. Dipalmitoylphosphatidylcholine liposomes with two preincorporated fluorescent dyes (1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatrien p-toluenesulfonate (TMA-DPH) and N-(-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoetanolamine triethylammonium salt (NBD-PE)) were used to determine the effects of tested compounds on the core and surface of the bilayer. Resorcinolic lipids from rye and cardol increased the polarization of TMA-DPH fluorescence more than that of NBD-PE, but anacardic acid, methylocardol, and alkylphenol increased NBD-PE dye fluorescence.

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Merulinic acid (heptadecenylresorcinolic acid, resorcinolic acid) is one of the members of resorcinolic lipids, the natural amphiphilic long-chain homologues of orcinol (1,3-dihydroksy-5-methylbenzene). In the present study, membrane properties of merulinic acid were investigated. Merulinic acid exhibits strong haemolytic activity against sheep erythrocytes (EH50 of 5+/-2 microM) regardless of the form of its application-direct injection into the erythrocyte suspension or injection as merulinic acid-enriched liposomes. The lysis of erythrocytes induced by merulinic acid was inhibited by the presence of divalent cations. The effectivity of the protection of erythrocytes was highest for Zn2+ and weakest for Mn2+. Merulinic acid at low concentrations also exhibits the ability for protection of cells against their lysis in hypoosmotic solutions. This protective effect is significant as, at 10 microM concentration of merulinic acid, the extent of osmotically induced cell lysis is reduced by approximately 40%. Merulinic acid induces increased permeability of liposomal vesicles. This effect was shown to be dependent on the composition of liposomal bilayer and it was stronger when lipid bilayer contained glycolipids (MGDG and DGDG) and sphingomyelin. Changes of TMA-DPH and NBD-PE fluorescence polarization show that the degree of merulinic acid incorporation into liposomal membrane is not very high. The polar "heads" of the molecules of investigated compounds are localized on the level of fatty acid's ester bonds in phospholipid molecules. Merulinic acid caused the increased fluorescence of the membrane potential fragile probe. This indicated an alteration of the surface charge and a decrease of the local pH at the membrane surface. This effect was visible in both low- and high-ionic strength environment. Merulinic acid causes also a decrease in activity of the membrane-bound enzyme acetylcholinesterase.