Palmitic acid induces the opening of a Ca2+-dependent pore in the plasma membrane of red blood cells: the possible role of the pore in erythrocyte lysis

The Short-Term Opening of Cyclosporin A-Independent Palmitate/Sr2+-Induced Pore Can Underlie Ion Efflux in the Oscillatory Mode of Functioning of Rat Liver Mitochondria

Mitochondria are capable of synchronized oscillations in many variables, but the underlying mechanisms are still unclear. In this study, we demonstrated that rat liver mitochondria, when exposed to a pulse of Sr2+ ions in the presence of valinomycin (a potassium ionophore) and cyclosporin A (a specific inhibitor of the permeability transition pore complex) under hypotonia, showed prolonged oscillations in K+ and Sr2+ fluxes, membrane potential, pH, matrix volume, rates of oxygen consumption and H2O2 formation. The dynamic changes in the rate of H2O2 production were in a reciprocal relationship with the respiration rate and in a direct relationship with the mitochondrial membrane potential and other indicators studied. The pre-incubation of mitochondria with Ca2+(Sr2+)-dependent phospholipase A2 inhibitors considerably suppressed the accumulation of free fatty acids, including palmitic and stearic acids, and all spontaneous Sr2+-induced cyclic changes. These data suggest that the mechanism of ion efflux from mitochondria is related to the opening of short-living pores, which can be caused by the formation of complexes between Sr2+(Ca2+) and endogenous long-chain saturated fatty acids (mainly, palmitic acid) that accumulate due to the activation of phospholipase A2 by the ions. A possible role for transient palmitate/Ca2+(Sr2+)-induced pores in the maintenance of ion homeostasis and the prevention of calcium overload in mitochondria under pathophysiological conditions is discussed.

Lipotoxicity Disrupts Erythrocyte Function: A Perspective

BACKGROUND

Lipid accumulation in the liver, skeletal and cardiac muscle, kidneys and pancreas causes cell dysfunction, death and inflammation, a biological phenomenon named lipotoxicity. Erythrocytes participate in the transport of lipids in the circulation, and their lipidome is determined by exchange with blood components.

OBJECTIVE

The objective of this study is to summarize the current knowledge regarding the effect of toxic lipid accumulation in erythrocytes.

RESULTS

Erythrocyte lipidome is altered in lipotoxic diseases, such as fatty liver disease, heart failure and diabetes. In addition, ceramide, lysophosphatidylcholine, lysophosphatidic acid, palmitic acid and free cholesterol induce erythrocyte malfunction.

CONCLUSION

Erythrocytes are an additional cell target of lipotoxicity. Further exploration of the implicated molecular mechanisms could lead to novel therapeutic targets for cardiometabolic and hematological diseases.

Anti-Diabetic and Antioxidant Activities of Red Wine Concentrate Enriched with Polyphenol Compounds under Experimental Diabetes in Rats

We obtained red wine concentrate, which was enriched with natural polyphenolic compounds (PC concentrate). The main purpose was to study the hypoglycemic and antioxidant effects of the red wine concentrate, and its impact on key hematological parameters of rats with experimental diabetes mellitus. While administrating the red wine concentrate to rats with diabetes, partial recovering of glucose tolerance was promoted, as well as normalization of glycated hemoglobin level, an increase in the quantity of erythrocytes and hemoglobin concentration. PC concentrate had anti-radical effect, which was determined using 2,2-diphenyl-1-picrylhydrazylradical (DPPH) method and effectively inhibited oxidation of phosphatidylcholine liposomes, induced by 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) as a free radical generator. It was also confirmed that PC concentrate had antioxidant properties in vivo. The contents of lipid peroxidation and protein oxidation products, the activity of catalase, and glutathione peroxidase (GPx) were increased in the plasma of rats with diabetes mellitus. At the same time, the activity of superoxide dismutase (SOD) was decreased. The concentrate of red wine had a corrective effect on investigated indicators and caused their normalization in plasma of diabetic animals.

Mitochondrial Cyclosporine A-Independent Palmitate/Ca2+-Induced Permeability Transition Pore (PA-mPT Pore) and Its Role in Mitochondrial Function and Protection against Calcium Overload and Glutamate Toxicity

A sharp increase in the permeability of the mitochondrial inner membrane known as mitochondrial permeability transition (or mPT) occurs in mitochondria under the conditions of Ca²⁺ and ROS stress. Permeability transition can proceed through several mechanisms. The most common mechanism of mPT is based on the opening of a cyclosporine A (CSA)-sensitive protein channel in the inner membrane. In addition to the CSA-sensitive pathway, mPT can occur through the transient opening of lipid pores, emerging in the process of formation of palmitate/Ca²⁺ complexes. This pathway is independent of CSA and likely plays a protective role against Ca²⁺ and ROS toxicity. The review considers molecular mechanisms of formation and regulation of the palmitate/Ca²⁺-induced pores, which we designate as PA-mPT to distinguish it from the classical CSA-sensitive mPT. In the paper, we discuss conditions of its opening in the biological membranes, as well as its role in the physiological and pathophysiological processes. Additionally, we summarize data that indicate the involvement of PA-mPT in the protection of mitochondria against calcium overload and glutamate-induced degradation in neurons.

Mitochondrial Ca2+ Transport: Mechanisms, Molecular Structures, and Role in Cells

Mitochondria are among the most important cell organelles involved in the regulation of intracellular calcium homeostasis. During the last decade, a number of molecular structures responsible for the mitochondrial calcium transport have been identified including the mitochondrial Ca2+ uniporter (MCU), Na+/Ca2+ exchanger (NCLX), and Ca2+/H+ antiporter (Letm1). The review summarizes the data on the structure, regulation, and physiological role of such structures. The pathophysiological mechanism of Ca2+ transport through the cyclosporine A-sensitive mitochondrial permeability transition pore is discussed. An alternative mechanism for the mitochondrial pore opening, namely, formation of the lipid pore induced by saturated fatty acids, and its role in Ca2+ transport are described in detail.

Effect of surface-potential modulators on the opening of lipid pores in liposomal and mitochondrial inner membranes induced by palmitate and calcium ions

The effect of surface-potential modulators on palmitate/Ca2+-induced formation of lipid pores was studied in liposomal and inner mitochondrial membranes. Pore formation was monitored by sulforhodamine B release from liposomes and swelling of mitochondria. ζ-potential in liposomes was determined from electrophoretic mobility. Replacement of sucrose as the osmotic agent with KCl decreased negative ζ-potential in liposomes and increased resistance of both mitochondria and liposomes to the pore inducers, palmitic acid, and Ca2+. Micromolar Mg2+ also inhibited palmitate/Ca2+-induced permeabilization of liposomes. The rate of palmitate/Ca2+-induced, cyclosporin A-insensitive swelling of mitochondria increased 22% upon increasing pH from 7.0 to 7.8. At below the critical micelle concentration, the cationic detergent cetyltrimethylammonium bromide (10 μM) and the anionic surfactant sodium dodecylsulfate (10-50 μM) made the ζ-potential less and more negative, respectively, and inhibited and stimulated opening of mitochondrial palmitate/Ca2+-induced lipid pores. Taken together, the findings indicate that surface potential regulates palmitate/Ca2+-induced lipid pore opening.

Interaction of phospholipase A of the E. coli outer membrane with the inhibitors of eucaryotic phospholipases A₂ and their effect on the Ca²⁺-induced permeabilization of the bacterial membrane

Phospholipase A of the bacterial outer membrane (OMPLA) is a β-barrel membrane protein which is activated under various stress conditions. The current study examines interaction of inhibitors of eucaryotic phospholipases A₂--palmitoyl trifluoromethyl ketone (PACOCF₃) and aristolochic acid (AA)--with OMPLA and considers a possible involvement of the enzyme in the Ca²⁺-dependent permeabilization of the outer membrane of Escherichia coli. Using the method of molecular docking, it has been predicted that PACOCF₃ and AA bind to OMPLA at the same site and with the same affinity as the OMPLA inhibitors, hexadecanesulfonylfluoride and bromophenacyl bromide, and the substrate of the enzyme palmitoyl oleoyl phosphatidylethanolamine. It has also been shown that PACOCF₃, AA, and bromophenacyl bromide inhibit the Ca²⁺-induced temperature-dependent changes in the permeability of the bacterial membrane for the fluorescent probe propidium iodide and suppressed the transformation of E. coli cells with plasmid DNA induced by Ca²⁺ and heat shock. The cell viability was not affected by the eucaryotic phospholipases A₂ inhibitors. The study discusses a possible involvement of OMPLA in the mechanisms of bacterial transmembrane transport based on the permeabilization of the bacterial outer membrane.