Methylation of Phenyl Rings in Ester-Stabilized Phosphorus Ylides Vastly Enhances Their Protonophoric Activity

We have recently discovered that ester-stabilized phosphorus ylides, resulting from deprotonation of a phosphonium salt such as [Ph3PCH2COOR], can transfer protons across artificial and biological membranes. To create more effective cationic protonophores, we synthesized similar phosphonium salts with one ((heptyloxycarbonylmethyl)(p-tolyl)bromide) or two ((butyloxycarbonylmethyl)(3,5-xylyl)osphonium bromide) methyl substituents in the phenyl groups. The methylation enormously augmented both protonophoric activity of the ylides on planar bilayer lipid membrane (BLM) and uncoupling of mammalian mitochondria, which correlated with strongly accelerated flip-flop of their cationic precursors across the BLM.

Synthesis of Triphenylphosphonium-Linked Derivative of 3,5-Ditert-butyl-4-hydroxybenzylidene-malononitrile (SF6847) via Knoevenagel Reaction Yields an Effective Mitochondria-Targeted Protonophoric Uncoupler

Mitochondrial uncouplers are actively sought as potential therapeutics. Here, we report the first successful synthesis of mitochondria-targeted derivatives of the highly potent uncoupler 3,5-ditert-butyl-4-hydroxybenzylidene-malononitrile (SF6847), bearing a cationic alkyl(triphenyl)phosphonium (TPP) group. As a key step of the synthesis, we used condensation of a ketophenol with malononitrile via the Knoevenagel reaction. SF-C5-TPP with a pentamethylene linker between SF6847 and TPP, stimulating respiration and collapsing membrane potential of rat liver mitochondria at submicromolar concentrations, proved to be the most effective uncoupler of the series. SF-C5-TPP showed pronounced protonophoric activity on a model planar bilayer lipid membrane. Importantly, SF-C5-TPP exhibited rather low toxicity in fibroblast cell culture, causing mitochondrial depolarization in cells at concentrations that only slightly affected cell viability. SF-C5-TPP was more effective in decreasing the mitochondrial membrane potential in the cell culture than SF6847, in contrast to the case of isolated mitochondria. Like other zwitterionic uncouplers, SF-C5-TPP inhibited the growth of Bacillus subtilis in the micromolar concentration range.

The critical role of mitochondrial lipid peroxidation in ferroptosis: insights from recent studies

Ferroptosis is a regulated form of necrotic cell death reliant on iron-catalyzed lipid peroxidation. Although the precise involvement of mitochondria in ferroptosis remains incompletely elucidated, recent research indicates that mitochondrial oxidative events wield a pivotal influence in this mechanism. This article centers on the most recent discoveries, spotlighting the significance of mitochondrial lipid peroxidation in the occurrence of ferroptosis. Modern investigative tools, such as mitochondria-specific dyes responsive to lipid peroxidation and antioxidants targeting mitochondria, have been employed to delve into this phenomenon. The authors' recent empirical evidence demonstrates that mitochondrial lipid peroxidation, quantified using the innovative fluorescent ratiometric probe MitoCLox, takes place prior to the onset of ferroptotic cell death. The mitochondria-targeted antioxidant SkQ1 hinders mitochondrial lipid peroxidation and thwarts ferroptosis, all while leaving unaffected the buildup of reactive oxygen species within the cytoplasm, an antecedent to mitochondrial lipid peroxidation. Similarly, the redox agent methylene blue, impeding the genesis of reactive oxygen species in complex I of the electron transport chain, also imparts a comparable protective effect. These findings collectively imply that reactive oxygen species originating from complex I might hold particular significance in fomenting mitochondrial lipid peroxidation, a pivotal trigger of ferroptosis.

Ester-stabilized phosphorus ylides as protonophores on bilayer lipid membranes, mitochondria and chloroplasts

Triphenylphosphonium ylides are commonly used as key intermediates in the Wittig reaction. Based on the known acidities of stabilized ylide precursors, we proposed that a methylene group adjacent to phosphorus in these compounds can ensure proton shuttling across lipid membranes. Here, we synthesized (decyloxycarbonylmethyl)triphenylphosphonium bromide (CMTPP-C₁₀) by reaction of triphenylphosphine with decyl bromoacetate. This phosphonium salt precursor of the ester-stabilized phosphorus ylide along with its octyl (CMTPP-C₈) and dodecyl (CMTPP-C₁₂) analogues was found to be a carrier of protons in mitochondrial, chloroplast and artificial lipid membranes, suggesting that it can reversibly release hydrogen ions and diffuse through the membranes in both zwitterionic (ylide) and cationic forms. The CMTPP-C₁₀-mediated electrical current across planar bilayer lipid membranes exhibited pronounced proton selectivity. Similar to conventional protonophores, known to uncouple electron transport and ATP synthesis, CMTPP-C_n (n = 8, 10, 12) stimulated mitochondrial respiration, while decreasing membrane potential, at micromolar concentrations, thereby showing the classical uncoupling activity in mitochondria. CMTPP-C₁₂ also caused dissipation of transmembrane pH gradient on chloroplast membranes. Importantly, CMTPP-C₁₀ exhibited substantially lower toxicity in cell culture, than C₁₂TPP. Thus, we report the finding of a new class of ylide-type protonophores, which is of substantial interest due to promising therapeutic properties of uncouplers.

Mitochondrial Lipid Peroxidation Is Responsible for Ferroptosis

Ferroptosis induced by erastin (an inhibitor of cystine transport) and butionine sulfoximine (an inhibitor of glutathione biosynthesis) was prevented by the mitochondria-targeted antioxidants SkQ1 and MitoTEMPO. These effects correlate with the prevention of mitochondrial lipid peroxidation, which precedes cell death. Methylene blue, a redox agent that inhibits the production of reactive oxygen species (ROS) in complex I of the mitochondrial electron transport chain, also inhibits ferroptosis and mitochondrial lipid peroxidation. Activation of ROS production in complex I with rotenone in the presence of ferrous iron stimulates lipid peroxidation in isolated mitochondria, while ROS produced by complex III are ineffective. SkQ1 and methylene blue inhibit lipid peroxidation. We suggest that ROS formed in complex I promote mitochondrial lipid peroxidation and ferroptosis.

[The Expression of Genes Encoding ABCA1 and ABCG1 Transporters and PPARγ, LXRβ, and RORα Transcriptional Factors in Subcutaneous and Visceral Adipose Tissue in Women with Metabolic Syndrome]

The study aimed to investigate tissue-specific gene expression of ABCA1 and ABCG1, encoding cholesterol transporters, as well as PPARG, LXRβ (NR1H2), and RORA, encoding the most important transcriptional regulators of lipid metabolism, in subcutaneous and visceral adipose tissue (SAT and VAT) in women with metabolic syndrome. It was shown that the ABCG1 mRNA SAT/VAT ratio decreases with age and correlates with the development of metabolic syndrome. After age adjustment, women have reduced chances of metabolic syndrome development when ABCG1 gene expression in SAT is higher relative to VAT than women with VAT ABCG1 gene expression higher or comparable to SAT: OR = 0.15 (95% CI 0.03-0.76), p = 0.023. The ABCA1 mRNA SAT/VAT ratio positively correlated with HDL cholesterol levels (after age adjustment β = 0.350, p = 0.046), therefore individuals with higher ABCA1 mRNA level in SAT relative to VAT had elevated HDL levels. The ABCA1 mRNA level in SAT was decreased in smokers (p = 0.001). There was a negative correlation between the PPARG mRNA level in SAT with body mass index and waist circumference in the general sample (β = -0.602, p = 0.003 and β = -0.642, p = 0.001, respectively, after age adjustment). A decrease of the PPARG mRNA SAT/VAT ratio was associated with elevated plasma insulin level and the insulin resistance index HOMA-IR β = -0.819, p = 0.004 and β = -1.053, p = 0.008, respectively, after age adjustment). Thus, the study has shown that the ratio of ABCA1, ABCG1, and PPARG genes expression in different types of adipose tissue (SAT/VAT) could be a significant factor that predicts the development of atherogenic dyslipidemia, metabolic syndrome, and insulin resistance in obesity.

[Epicardial and subcutenious adipose tissue adiponectin gene expression in coronary artery disease patients]

Aim To determine the expression of adiponectin gene (ADIPOQ) and the content of high-molecular-weight adiponectin (HMWA) in epicardial (EAT) and subcutaneous adipose tissue (SCAT) in patients with ischemic heart disease (IHD).Material and methods Paired samples of EAT and SCAT and blood serum were withdrawn from patients with IHD after bypass surgery and 16 subjects without IHD (comparison group). Matrix RNA (mRNA) level was measured using real-time polymerase chain reaction. HMWA levels in EAT and SCAT were evaluated by Western blotting. Serum adiponectin concentration was measured immunoenzymatically. For all patients, echocardiography was performed to measure the EAT thickness; coronarography was performed to determine severity of coronary atherosclerosis.Results Serum adiponectin concentration was lower in IHD patients than in the comparison group (p<0.001). Levels of ADIPOO gene mRNA and HMWA in SCAT were lower in IHD patients than in the comparison group (р=0.020 and p=0.003, respectively). The HMWA level in EAT was lower with the EAT thickness of 8 mm compared to the HMWA level in IHD patients with EAT ≤8 mm (p=0.034).Conclusion The decreased serum concentration of antiatherogenic adiponectin and the reduced expression of ADIPOQ gene in SCAT (mRNA, HMWA) are associated with IHD.

NMDA and GABA receptor presence in rat heart mitochondria

The purpose of this study is to demonstrate the presence of three more receptors in mitochondria. Two N-methyl-d-aspartate receptor (NMDAR) subunits (NR1 and NR2B) are found by protein immunoblot and immunogold labeling in mitochondria fraction isolated from rat heart. These data allow supposing NMDAR presence and functioning in the inner mitochondrial membrane. There are no signs of receptor presence obtained in heart tissue lysate, that indicates the receptor localization exactly in mitochondria. The possible receptor functions discussed are its participation in calcium transport and in excitation-metabolism coupling. Besides, preliminary evidence is obtained of GABA_A and GABA_B receptors presence in heart mitochondria. One can surmise their role in metabolism regulation and their possible co-operation with NMDAR just as in the nervous system.

Induction of autophagy by depolarization of mitochondria

Mitochondrial dysfunction plays a crucial role in the macroautophagy/autophagy cascade. In a recently published study Sun et al. described the induction of autophagy by the membranophilic triphenylphosphonium (TPP)-based cation 10-(6'-ubiquinonyl) decyltriphenylphosphonium (MitoQ) in HepG2 cells (Sun C, et al. "MitoQ regulates autophagy by inducing a pseudo-mitochondrial membrane potential [PMMP]", Autophagy 2017, 13:730-738.). Sun et al. suggested that MitoQ adsorbed to the inner mitochondrial membrane with its cationic moiety remaining in the intermembrane space, adding a large number of positive charges and establishing a "pseudo-mitochondrial membrane potential," which blocked the ATP synthase. Here we argue that the suggested mechanism for generation of the "pseudo-mitochondrial membrane potential" is physically implausible and contradicts earlier findings on the electrophoretic displacements of membranophilic cations within and through phospholipid membranes. We provide evidence that TPP-cations dissipated the mitochondrial membrane potential in HepG2 cells and that the induction of autophagy in carcinoma cells by TPP-cations correlated with the uncoupling of oxidative phosphorylation. The mild uncoupling of oxidative phosphorylation by various mitochondria-targeted penetrating cations may contribute to their reported therapeutic effects via inducing both autophagy and mitochondria-selective mitophagy.

[Regulation of ABCA1 and ABCG1 gene expression in the intraabdominal adipose tissue]

Tissue specific expression of genes encoding cholesterol transporters ABCA1 and ABCG1 as well as genes encoding the most important transcriptional regulators of adipogenesis - LXRa, LXRb, PPARg and RORa has been investigated in intraabdominal adipose tissue (IAT) samples.A direct correlation between the content of ABCA1 and ABCG1 proteins with RORa protein level (r=0.480, p<0.05; r=0.435, p<0.05, respectively) suggests the role of the transcription factor RORa in the regulation of IAT ABCA1 and ABCG1 protein levels. ABCA1 and ABCG1 gene expression positively correlated with obesity indicators such as body mass index (BMI) (r=0.522, p=0.004; r=0.594, p=0.001, respectively) and waist circumference (r=0.403, p=0.033; r=0.474, p=0.013, respectively). The development of obesity is associated with decreased IAT levels of RORa and LXRb mRNA (p=0.016 and p=0.002, respectively). These data suggest that the nuclear factor RORa can play a significant role in the regulation of cholesterol metabolism and control IAT expression of ABCA1 and ABCG1, while the level of IAT LXRb gene expression may be an important factor associated with the development of obesity.

[Genetic Risk Factors of Macrovascular Complications in Patients With Type 2 Diabetes]

High risk of macrovascular complications in patients with type 2 diabetes mellitus (T2DM) is caused by insulin resistance and atherogenic dyslipidemia that may be genetically determined. The aim of this study was to assess the association of polymorphic genetic variants APOA5 (S19W/rs3135506), CETP (Taq1B/rs708272), PON1 (Q192R /rs662) and PPARG (Pro12Ala /rs1801282) with T2DM and macrovascular complications in patients with T2DM resident in Northwestern Russia. We examined 386 patients with T2DM and 199 healthy controls. Genotyping was performed by polymerase chain reaction followed by restriction analysis. The study revealed the protective role of allele 12Ala of PPARG gene against T2DM development (odds ratio [OR]=0.58; 95% confidence interval [CI] 0.39-0.85). B1B1 genotype of CETP was associated with increased risk of stroke in T2DM patients (OR=1.85; 95%CI1.07-3.21). RR genotype of PON1 was associated with increased risk of T2DM with stroke (OR=2.98; 95%CI1.01-8.84). According to study results Pro12Ala (rs1801282) variant of PPARG affected the risk of T2DM; polymorphic variants of CETP (Taq1B/rs708272) and PON1 (Q192R/rs662) contributed to the risk of macrovascular complications of T2DM.

ITLN1, PPARg AND TNFa GENE EXPRESSION IN VISCERAL ADIPOSE TISSUE

The adipose tissue is considered today as an endocrine organ in which tissue-specific regulation of gene expression plays a key role in the processes of development of obesity and comorbidities, such as diabetes and cardiovascular disease. The present study is focused on ITLN1, PPARã and TNFá gene expression in intra-abdominal adipose tissue and its effect on the serum levels of omentin 1 and TNFa in individuals with different body mass. It has been shown that serum TNFa level is significantly higher in the subgroup of patients with overweight and obesity (BMI ≥ 25 kg/m2) as compared to individuals with normal body weight (BMI < 25 kg/m2)( p < 0.03). We have demonstrated that the expression level of the PPARã gene is positively correlated with the ITLN1 gene expression level in the intra-abdominal adipose tissue (r = 0.516, p = 0.020). Serum level of omentin 1 positively correlates with PPARã mRNA and protein levels in intra-abdominal adipose tissue (r = 0.550, p < 0.05 and r = 0.581, p < 0.03, respectively). For the subgroup of patients with overweight and obesity, we have shown negative correlation of the level of TNFá mRNA with PPARã and ITLN1 mRNA levels was shown (r = –0.549, p < 0.05 and r = –0.475, p < 0.05, respectively). This study is the first to show a correlation relationship between PPARã gene expression level in the intra-abdominal adipose tissue and the expression and secretion levels of omentin 1.

Low Concentrations of Uncouplers of Oxidative Phosphorylation Prevent Inflammatory Activation of Endothelial Cells by Tumor Necrosis Factor

In endothelial cells, mitochondria play an important regulatory role in physiology as well as in pathophysiology related to excessive inflammation. We have studied the effect of low doses of mitochondrial uncouplers on inflammatory activation of endothelial cells using the classic uncouplers 2,4-dinitrophenol and 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole, as well as the mitochondria-targeted cationic uncoupler dodecyltriphenylphosphonium (C12TPP). All of these uncouplers suppressed the expression of E-selectin, adhesion molecules ICAM1 and VCAM1, as well as the adhesion of neutrophils to endothelium induced by tumor necrosis factor (TNF). The antiinflammatory action of the uncouplers was at least partially mediated by the inhibition of NFκB activation due to a decrease in phosphorylation of the inhibitory subunit IκBα. The dynamic concentration range for the inhibition of ICAM1 expression by C12TPP was three orders of magnitude higher compared to the classic uncouplers. Probably, the decrease in membrane potential inhibited the accumulation of penetrating cations into mitochondria, thus lowering the uncoupling activity and preventing further loss of mitochondrial potential. Membrane potential recovery after the removal of the uncouplers did not abolish its antiinflammatory action. Thus, mild uncoupling could induce TNF resistance in endothelial cells. We found no significant stimulation of mitochondrial biogenesis or autophagy by the uncouplers. However, we observed a decrease in the relative amount of fragmented mitochondria. The latter may significantly change the signaling properties of mitochondria. Earlier we showed that both classic and mitochondria-targeted antioxidants inhibited the TNF-induced NFκB-dependent activation of endothelium. The present data suggest that the antiinflammatory effect of mild uncoupling is related to its antioxidant action.