Effect of Fusidic Acid and Some Nitrogen-Containing Derivatives on Liposomal and Mitochondrial Membranes.

The paper assesses the membranotropic action of the natural antibiotic fusidic acid (FA) and its derivatives. It was found that a FA analogue with ethylenediamine moiety (derivative 2), in contrast to native FA and 3,11-dioxime analogue (derivative 1), is able to increase the mobility of the lipid bilayer in the zone of lipid headgroups, as well as to induce permeabilization of lecithin liposome membranes. A similar effect of derivative 2 is also observed in the case of rat liver mitochondrial membranes. We noted a decrease in the microviscosity of the mitochondrial membrane and nonspecific permeabilization of organelle membranes in the presence of this agent, which was accompanied by a decrease in mitochondrial Δψ and OXPHOS efficiency. This led to a reduction in mitochondrial calcium retention capacity. The derivatives also reduced the production of H2O2 by mitochondria. The paper considers the relationship between the structure of the tested compounds and the observed effects.

Bile Acids as Inducers of Protonophore and Ionophore Permeability of Biological and Artificial Membranes.

It is now generally accepted that the role of bile acids in the organism is not limited to their participation in the process of food digestion. Indeed, bile acids are signaling molecules and being amphiphilic compounds, are also capable of modifying the properties of cell membranes and their organelles. This review is devoted to the analysis of data on the interaction of bile acids with biological and artificial membranes, in particular, their protonophore and ionophore effects. The effects of bile acids were analyzed depending on their physicochemical properties: namely the structure of their molecules, indicators of the hydrophobic-hydrophilic balance, and the critical micelle concentration. Particular attention is paid to the interaction of bile acids with the powerhouse of cells, the mitochondria. It is of note that bile acids, in addition to their protonophore and ionophore actions, can also induce Ca2+-dependent nonspecific permeability of the inner mitochondrial membrane. We consider the unique action of ursodeoxycholic acid as an inducer of potassium conductivity of the inner mitochondrial membrane. We also discuss a possible relationship between this K+ ionophore action of ursodeoxycholic acid and its therapeutic effects.

Effect of Modified Levopimaric Acid Diene Adducts on Mitochondrial and Liposome Membranes.

This paper demonstrates the membranotropic effect of modified levopimaric acid diene adducts on liver mitochondria and lecithin liposomes. We found that the derivatives dose-dependently reduced the efficiency of oxidative phosphorylation of mitochondria due to inhibition of the activity of complexes III and IV of the respiratory chain and protonophore action. This was accompanied by a decrease in the membrane potential in the case of organelle energization both by glutamate/malate (complex I substrates) and succinate (complex II substrate). Compounds 1 and 2 reduced the generation of H2O2 by mitochondria, while compound 3 exhibited a pronounced antioxidant effect on glutamate/malate-driven respiration and, on the other hand, caused ROS overproduction when organelles are energized with succinate. All tested compounds exhibited surface-active properties, reducing the fluidity of mitochondrial membranes and contributing to nonspecific permeabilization of the lipid bilayer of mitochondrial membranes and swelling of the organelles. Modified levopimaric acid diene adducts also induced nonspecific permeabilization of unilamellar lecithin liposomes, which confirmed their membranotropic properties. We discuss the mechanisms of action of the tested compounds on the mitochondrial OXPHOS system and the state of the lipid bilayer of membranes, as well as the prospects for the use of new modified levopimaric acid diene adducts in medicine.

Mitochondria-targeted prooxidant effects of betulinic acid conjugated with delocalized lipophilic cation F16.

The paper examines the molecular mechanisms of the cytotoxicity of conjugates of betulinic acid with the penetrating cation F16. The in vitro experiments on rat thymocytes revealed that all the obtained F16-betulinic acid derivatives showed more than 10-fold higher cytotoxicity as compared to betulinic acid and F16. In this case, 0.5-1 µM of all conjugates showed mitochondria-targeted action, inducing superoxide overproduction and reducing the mitochondrial potential of cells. Experiments on isolated rat liver mitochondria revealed the ability of conjugates to dose-dependently reduce the membrane potential of organelles, as well as the intensity of respiration and oxidative phosphorylation, which is also accompanied by an increase in the production of hydrogen peroxide by mitochondria. It was shown that these actions of derivatives may be due to several effects: the reversion of ATP synthase, changes in the activity of complexes of the respiratory chain and permeabilization of the inner mitochondrial membrane. All compounds also demonstrated the ability to induce aggregation of isolated rat liver mitochondria. Using the model of lecithin liposomes, we found that the F6 conjugate (2 µM) induces the permeability of vesicle membranes for the fluorescent probe sulforhodamine B. High concentrations (25 µM) of the F6 derivative have been found to induce dynamic processes in the liposome membrane leading to aggregation and/or fusion of vesicle membranes. The paper discusses the relationship between the mitochondria-targeted effects of F16-betulinic acid conjugates and their cytotoxicity.

Effect of betulin and betulonic acid on isolated rat liver mitochondria and liposomes.

The paper considers the effects of plant triterpenoid betulin and its derivative betulonic acid on rat liver mitochondria and liposomes. It was found that betulonic acid and, to a lesser extent, betulin, activate mitochondrial respiration in states 2 and 4 and inhibit ADP- and DNP-stimulated (uncoupled) respiration. The effect of betulonic acid resulted in a significant decrease of the respiratory control and ADP/O ratios and decrease in Δψ. The effects of both compounds were most pronounced in the case of succinate-fueled mitochondrial respiration. This may include both the possible protonophore effect of betulonic acid and the inhibition of respiratory chain complexes by both compounds. Both agents enhanced H2O2 production in succinate-fueled mitochondria, while betulonic acid exerted an antioxidant effect with NAD-dependent substrates. Betulin was found to induce mitochondrial aggregation, but had no effect on membrane permeability. A similar pattern was found on liposomes. As revealed by the laurdan generalized polarization (GP) technique, betulin increased laurdan GP in lecithin liposomes, indicating a decrease in membrane fluidity. Measurements of GP as a function of fluorescence excitation wavelength gave an ascending line for high concentrations of betulin, which can be interpreted as phase heterogeneity of the lipid/betulin system. High concentrations of betulin (> 60 mol%) was also demonstrated to cause permeabilization of lecithin liposomes. Betulonic acid was much less effective in inducing the aggregation of mitochondria and liposomes and had no effect on membrane permeability. The possible mechanisms of betulin and betulonic acid effect on rat liver mitochondria and liposomes are discussed.

Membranotropic effects of ω-hydroxypalmitic acid and Ca2+ on rat liver mitochondria and lecithin liposomes. Aggregation and membrane permeabilization.

The paper examines membranotropic Ca2+-dependent effects of ω-hydroxypalmitic acid (HPA), a product of ω-oxidation of fatty acids, on the isolated rat liver mitochondria and artificial membrane systems (liposomes). It was established that in the presence of Ca2+, HPA induced aggregation of liver mitochondria, which was accompanied by the release of cytochrome c from the organelles. It was further demonstrated that the addition of Ca2+ to HPA-containing liposomes induced their aggregation and/or fusion. Ca2+ also caused the release of the fluorescent dye sulforhodamine B from liposomes, indicating their permeabilization. HPA was shown to induce a high-amplitude swelling of Ca2+-loaded mitochondria, to decrease their membrane potential, to induce the release of Ca2+ from the organelles and to result in the oxidation of the mitochondrial NAD(P)H pool. Those effects of HPA were not blocked by the MPT pore inhibitor CsA, but were suppressed by the mitochondrial calcium uniporter inhibitor ruthenium red. The effects of HPA were also observed when Ca2+ was replaced with Sr2+ (but not with Ba2+ or Mg2+). A supposition is made that HPA can induce a Ca2+-dependent aggregation of mitochondria, as well as Ca2+dependent CsA-insensitive permeabilization of the inner mitochondrial membrane - with the subsequent lysis of the organelles.