Ca(2+)-dependent nonspecific permeability of the inner membrane of liver mitochondria in the guinea fowl (Numida meleagris)

Synthesis and comparative analysis of the cytotoxicity and mitochondrial effects of triphenylphosphonium and F16 maslinic and corosolic acid hybrid derivatives

The cytotoxic profile and antiproliferative and mitochondrial effects of triterpene acid conjugates with mitochondriotropic lipophilic triphenylphosphonium (TPP+) and F16 cations were evaluated. Maslinic and corosolic acids chosen as the investigation objects were synthesized from commercially available oleanolic and ursolic acids. Study of the cytotoxic activity of TPP+ and F16 triterpenoid derivatives against six tumor cell lines demonstrated a comparable synergistic effect in the anticancer activity, which was most pronounced in the case of MCF-7 mammary adenocarcinoma cells and Jurkat and THP-1 leukemia cells. The corosolic and maslinic acid hybrid derivatives caused changes in the progression of tumor cell cycle phases when present in much lower doses than their natural triterpene acid precursors. The treatment of tumor cell lines with the conjugates resulted in the cell cycle arrest in the G1 phase and increase in the cell population in the subG1 phase. The cationic derivatives of the acids were markedly superior to their precursors as inducers of hyperproduction of reactive oxygen species and more effectively decreased the mitochondrial potential in isolated rat liver mitochondria. We concluded that the observed cytotoxic effect of TPP+ and F16 triterpenoid conjugates is attributable to the ability of these compounds to initiate mitochondrial dysfunctions. Their cytotoxicity, antiproliferative action, and mitochondrial effects depend little on the type of cationic groups used.

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.

Enhanced resistance to Ca2+-induced mitochondrial permeability transition in the long-lived red-footed tortoise Chelonoidis carbonaria

The interaction between supraphysiological cytosolic Ca2+ levels and mitochondrial redox imbalance mediates the mitochondrial permeability transition (MPT). The MPT is involved in cell death, diseases and aging. This study compared the liver mitochondrial Ca2+ retention capacity and oxygen consumption in the long-lived red-footed tortoise (Chelonoidis carbonaria) with those in the rat as a reference standard. Mitochondrial Ca2+ retention capacity, a quantitative measure of MPT sensitivity, was remarkably higher in tortoises than in rats. This difference was minimized in the presence of the MPT inhibitors ADP and cyclosporine A. However, the Ca2+ retention capacities of tortoise and rat liver mitochondria were similar when both MPT inhibitors were present simultaneously. NADH-linked phosphorylating respiration rates of tortoise liver mitochondria represented only 30% of the maximal electron transport system capacity, indicating a limitation imposed by the phosphorylation system. These results suggested underlying differences in putative MPT structural components [e.g. ATP synthase, adenine nucleotide translocase (ANT) and cyclophilin D] between tortoises and rats. Indeed, in tortoise mitochondria, titrations of inhibitors of the oxidative phosphorylation components revealed a higher limitation of ANT. Furthermore, cyclophilin D activity was approximately 70% lower in tortoises than in rats. Investigation of critical properties of mitochondrial redox control that affect MPT demonstrated that tortoise and rat liver mitochondria exhibited similar rates of H2O2 release and glutathione redox status. Overall, our findings suggest that constraints imposed by ANT and cyclophilin D, putative components or regulators of the MPT pore, are associated with the enhanced resistance to Ca2+-induced MPT in tortoises.

New quaternized pyridinium derivatives of betulin: Synthesis and evaluation of membranotropic properties on liposomes, pro- and eukaryotic cells, and isolated mitochondria

The present study describes the synthesis of pyridinium derivatives of betulin, including new 4-methyl- and 3,5-methyl-pyridinium analogs, their effect on artificial membrane systems (liposomes), cytotoxicity in models of prokaryotic (E. coli K-12 MG1655) and eukaryotic cells (rat thymocytes), as well as their effect on the functioning of membrane systems of rat liver mitochondria. We have shown that the presence of methyl groups in the pyridine ring of compounds determines the ability of the derivatives to effectively permeabilize the artificial membrane of lecithin liposomes for the fluorescent probe sulforhodamine B. The 4-methyl- and 3,5-methyl-pyridinium analogs inhibit the growth of E. coli K-12 MG1655 and, at the same time, did not have a cytotoxic effect on rat thymocytes. However, in the latter case, we noted a decrease in the mitochondrial potential of cells. The studied compounds reduced the functional activity of mitochondria, suppressing the activity of complexes of the respiratory chain and reducing the membrane potential. In addition, compounds containing methyl groups in the p- and m-positions of the pyridine ring were also able to permeabilize the inner membrane of mitochondria, causing them to swell. In this case, the most lipophilic compound containing two methyl substituents at the m-position of the pyridine fragment was most effective and had a protonophore effect on mitochondria. The paper discusses the dependence of the membranotropic and biological actions of the quaternized pyridine derivatives of betulin on their structure and lipophilicity.

ATP synthase: Evolution, energetics, and membrane interactions

The synthesis of ATP, life’s “universal energy currency,” is the most prevalent chemical reaction in biological systems and is responsible for fueling nearly all cellular processes, from nerve impulse propagation to DNA synthesis. ATP synthases, the family of enzymes that carry out this endless task, are nearly as ubiquitous as the energy-laden molecule they are responsible for making. The F-type ATP synthase (F-ATPase) is found in every domain of life and has facilitated the survival of organisms in a wide range of habitats, ranging from the deep-sea thermal vents to the human intestine. Accordingly, there has been a large amount of work dedicated toward understanding the structural and functional details of ATP synthases in a wide range of species. Less attention, however, has been paid toward integrating these advances in ATP synthase molecular biology within the context of its evolutionary history. In this review, we present an overview of several structural and functional features of the F-type ATPases that vary across taxa and are purported to be adaptive or otherwise evolutionarily significant: ion channel selectivity, rotor ring size and stoichiometry, ATPase dimeric structure and localization in the mitochondrial inner membrane, and interactions with membrane lipids. We emphasize the importance of studying these features within the context of the enzyme’s particular lipid environment. Just as the interactions between an organism and its physical environment shape its evolutionary trajectory, ATPases are impacted by the membranes within which they reside. We argue that a comprehensive understanding of the structure, function, and evolution of membrane proteins—including ATP synthase—requires such an integrative approach.

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 F16-Betulin Conjugate on Mitochondrial Membranes and Its Role in Cell Death Initiation

This work demonstrates the effects of a newly synthesized conjugate of the plant triterpenoid betulin and the penetrating cation F16 used for mitochondrial targeting. The resulting F16-betulin conjugate revealed a mitochondria-targeted effect, decreasing the mitochondrial potential and inducing superoxide overproduction in rat thymocytes in vitro. It has been suggested that this may cause the cytotoxic effect of the conjugate, which significantly exceeds the effectiveness of its precursors, betulin and F16. Using isolated rat liver mitochondria, we found that the F16-betulin conjugate has a surface-active effect on mitochondrial membranes, causing organelle aggregation. This effect of the derivative resulted in a dose-dependent decrease in mitochondrial transmembrane potential, as well as suppression of respiration and oxidative phosphorylation, especially in the case of nicotinamide adenine dinucleotide (NAD)-fueled organelles. In addition, the F16-betulin conjugate caused an increase in H₂O₂ generation by mitochondria fueled with glutamate and malate. These effects of the derivative can presumably be due to the powerful suppression of the redox activity of complex I of the mitochondrial electron transport chain. The paper discusses how the mitochondria-targeted effects of the F16-betulin conjugate may be related to its cytotoxic effects.

Structure of the Complete Dimeric Human GDAP1 Core Domain Provides Insights into Ligand Binding and Clustering of Disease Mutations

Charcot-Marie-Tooth disease (CMT) is one of the most common inherited neurological disorders. Despite the common involvement of ganglioside-induced differentiation-associated protein 1 (GDAP1) in CMT, the protein structure and function, as well as the pathogenic mechanisms, remain unclear. We determined the crystal structure of the complete human GDAP1 core domain, which shows a novel mode of dimerization within the glutathione S-transferase (GST) family. The long GDAP1-specific insertion forms an extended helix and a flexible loop. GDAP1 is catalytically inactive toward classical GST substrates. Through metabolite screening, we identified a ligand for GDAP1, the fatty acid hexadecanedioic acid, which is relevant for mitochondrial membrane permeability and Ca2+ homeostasis. The fatty acid binds to a pocket next to a CMT-linked residue cluster, increases protein stability, and induces changes in protein conformation and oligomerization. The closest homologue of GDAP1, GDAP1L1, is monomeric in its full-length form. Our results highlight the uniqueness of GDAP1 within the GST family and point toward allosteric mechanisms in regulating GDAP1 oligomeric state and function.

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.

Effect of Triclosan on the Functioning of Liver Mitochondria and Permeability of Erythrocyte Membranes of Marsh Frog (Pelophylax ridibundus (Pallas, 1771))

The paper examines the effects of the antimicrobial agent triclosan on the functioning of the liver mitochondria of marsh frog (Pelophylax ridibundus (Pallas, 1771)). It was established that triclosan inhibits DNP-stimulated respiration of mitochondria and decreases respiratory control ratio. In addition, triclosan causes the collapse of the mitochondrial membrane potential on both types of substrates. Such an action of triclosan can be mediated by both a protonophore effect and suppression of the activity of complex II and combined activity of complexes II + III (and, to a lesser degree, the combined activity of complexes I + III) of the mitochondrial respiratory chain. It is shown that high concentrations of triclosan enhance the production of hydrogen peroxide during the oxidation of substrates of the complex I by mitochondria, and decrease it in the case of succinate oxidation. It is found that triclosan is able to induce nonspecific permeability of the liver mitochondria of these amphibians, as well as the plasma membrane of erythrocytes. The possible mechanisms of triclosan effect on marsh frog liver mitochondria and red blood cells are discussed.