Insulin-status-dependent modulation of FoF1-ATPase activity in rat liver mitochondria

The phloroglucinol calcitrinone A, a novel mitochondria-targeting agent, induces cell death in breast cancer cells

Breast cancer is the most common cancer and the leading cause of cancer-related mortality among females worldwide. From the leaves of Callistemon citrinus, we have isolated a novel phloroglucinol dimer, calcitrinone A, and analyzed its potential anticancer activity using the triple-negative breast cancer cell line MDA-MB-231. Calcitrinone A decreased the total intracellular ATP levels, inhibited proliferation, and induced apoptosis in MDA-MB-231 cells, but was less toxic to peripheral blood mononuclear cells. The antiproliferative and apoptosis-inducing effects of calcitrinone A were confirmed in vivo using breast cancer xenografts grown on chick chorioallantoic membranes. Mechanistic analysis showed mitochondrial membrane-potential dissipation and interference with energy-yielding processes resulting in cell accumulation in the S phase of the cell cycle. Seahorse assay analysis revealed an early inhibition of mitochondrial oxidative phosphorylation (OXPHOS). At the molecular level, calcitrinone A inhibited activity of the succinate-coenzyme Q reductase (SQR) (mitochondrial complex II). In silico docking identified the coenzyme Q binding pocket as a possible high affinity binding site for calcitrinone A in SQR. Inhibition of complex II was accompanied by strong elevation of mitochondrial superoxide and cytoplasmic ROS. Calcitrinone A might be a promising anticancer lead compound acting through the interference with the mitochondrial complex II activity.

Type 2 diabetes differentially affects the substrate saturation kinetic attributes of erythrocyte hexokinase and phosphofructokinase

The substrate kinetic parameters of hexokinase (HK) and phosphofructokinase (PFK)-the key irreversible enzymes of glycolysis-in erythrocytes from type 2 diabetic subjects were examined in comparison with control subjects. It was observed that the kinetic parameters such as K_m , V_max , Apparent K_cat , K_cat /K_m , and substrate (ATP) inhibition kinetic and substrate binding characteristics are significantly altered in the diabetic group. The observed changes are suggestive of compositional changes in the subunit makeup of HK and PFK. The implication of these findings in relation to energy status of the diabetic erythrocyte and its interrelationship with loss of cell deformability are discussed here.

Anti-angiogenic drugs: direct anti-cancer agents with mitochondrial mechanisms of action

Components of the mitochondrial electron transport chain have recently gained much interest as potential therapeutic targets. Since mitochondria are essential for the supply of energy that is required for both angiogenic and tumourigenic activity, targeting the mitochondria represents a promising potential therapeutic approach for treating cancer. Here we investigate the established anti-angiogenesis drugs combretastatin A4, thalidomide, OGT 2115 and tranilast that we hypothesise are able to exert a direct anti-cancer effect in the absence of vasculature by targeting the mitochondria. Drug cytotoxicity was measured using the MTT assay. Mitochondrial function was measured in intact isolated mitochondria using polarography, fluorimetry and enzymatic assays to measure mitochondrial oxygen consumption, membrane potential and complex I-IV activities respectively. Combretastatin A4, OGT 2115 and tranilast were both shown to decrease mitochondrial oxygen consumption. OGT 2115 and tranilast decreased mitochondrial membrane potential and reduced complex I activity while combretastatin A4 and thalidomide did not. OGT 2115 inhibited mitochondrial complex II-III activity while combretastatin A4, thalidomide and tranilast did not. Combretastatin A4, thalidomide and OGT 2115 induced bi-phasic concentration-dependent increases and decreases in mitochondrial complex IV activity while tranilast had no evident effect. These data demonstrate that combretastatin A4, thalidomide, OGT 2115 and tranilast are all mitochondrial modulators. OGT 2115 and tranilast are both mitochondrial inhibitors capable of eliciting concentration-dependent reductions in cell viability by decreasing mitochondrial membrane potential and oxygen consumption.

Cardioprotection induced by remote ischemic preconditioning preserves the mitochondrial respiratory function in acute diabetic myocardium

A 2×2 factorial design was used to evaluate possible preservation of mitochondrial functions in two cardioprotective experimental models, remote ischemic preconditioning and streptozotocin-induced diabetes mellitus, and their interaction during ischemia/reperfusion injury (I/R) of the heart. Male Wistar rats were randomly allocated into four groups: control (C), streptozotocin-induced diabetic (DM), preconditioned (RPC) and preconditioned streptozotocin-induced diabetic (DM+RPC). RPC was conducted by 3 cycles of 5-min hind-limb ischemia and 5-min reperfusion. DM was induced by a single dose of 65 mg/kg streptozotocin. Isolated hearts were exposed to ischemia/reperfusion test according to Langendorff. Thereafter mitochondria were isolated and the mitochondrial respiration was measured. Additionally, the ATP synthase activity measurements on the same preparations were done. Animals of all groups subjected to I/R exhibited a decreased state 3 respiration with the least change noted in DM+RPC group associated with no significant changes in state 2 respiration. In RPC, DM and DM+RPC group, no significant changes in the activity of ATP synthase were observed after I/R injury. These results suggest that the endogenous protective mechanisms of RPC and DM do preserve the mitochondrial function in heart when they act in combination.

The mitochondrial-targeted antioxidant, MitoQ, increases liver mitochondrial cardiolipin content in obesogenic diet-fed rats

Cardiolipin (CL), a unique mitochondrial phospholipid, plays a key role in several processes of mitochondrial bioenergetics as well as in mitochondrial membrane stability and dynamics. The present study was designed to determine the effect of MitoQ, a mitochondrial-targeted antioxidant, on the content of liver mitochondrial membrane phospholipids, in particular CL, and its fatty acid composition in obesogenic diet-fed rats. To do this, twenty-four 6week old male Sprague Dawley rats were randomized into three groups of 8 animals and fed for 8weeks with either a control diet, a high fat diet (HF), or a HF diet with MitoQ (HF+MitoQ). Phospholipid classes and fatty acid composition were assayed by chromatographic methods in liver and liver mitochondria. Mitochondrial bioenergetic function was also evaluated. While MitoQ had no or slight effects on total liver fatty acid composition and phospholipid classes and their fatty acid composition, it had major effects on liver mitochondrial phospholipids and mitochondrial function. Indeed, MitoQ both increased CL synthase gene expression and CL content of liver mitochondria and increased 18:2n-6 (linoleic acid) content of mitochondrial phospholipids by comparison to the HF diet. Moreover, mitochondrial CL content was positively correlated to mitochondrial membrane fluidity, membrane potential and respiration, as well as to ATP synthase activity, while it was negatively correlated to mitochondrial ROS production. These findings suggest that MitoQ may decrease pathogenic alterations to CL content and profiles, thereby preserving mitochondrial function and attenuating the development of some of the features of metabolic syndrome in obesogenic diet-fed rats.

Cannabinoid receptor agonists are mitochondrial inhibitors: a unified hypothesis of how cannabinoids modulate mitochondrial function and induce cell death

Time-lapse microscopy of human lung cancer (H460) cells showed that the endogenous cannabinoid anandamide (AEA), the phyto-cannabinoid Delta-9-tetrahydrocannabinol (THC) and a synthetic cannabinoid HU 210 all caused morphological changes characteristic of apoptosis. Janus green assays of H460 cell viability showed that AEA and THC caused significant increases in OD 595 nm at lower concentrations (10-50 microM) and significant decreases at 100 microM, whilst HU 210 caused significant decreases at all concentrations. In rat heart mitochondria, all three ligands caused significant decreases in oxygen consumption and mitochondrial membrane potential. THC and HU 210 caused significant increases in mitochondrial hydrogen peroxide production, whereas AEA was without significant effect. All three ligands induced biphasic changes in either mitochondrial complex I activity and/or mitochondrial complex II-III activity. These data demonstrate that AEA, THC, and HU 210 are all able to cause changes in integrated mitochondrial function, directly, in the absence of cannabinoid receptors.

Consumption of soy protein isolate modulates the phosphorylation status of hepatic ATPase/ATP synthase beta protein and increases ATPase activity in rats

ATPase/ATP synthase plays important roles in the regulation of carbohydrate, protein, and lipid metabolism through modulating energy homeostasis. The purpose of this study was to examine the effects of feeding soy proteins and isoflavones (ISF) on the enzymatic activity and protein modification of hepatic mitochondrial ATPase/ATP synthase. In Expt. 1, Sprague-Dawley rats aged 50 d were fed diets containing either 20% casein or 20% alcohol-washed soy protein isolate (SPI) with or without supplemental ISF (770.7 micromol/kg diet) for 70 d. In Expt. 2, weanling Sprague-Dawley rats were fed diets containing 20% casein with or without added ISF (154.1 micromol/kg diet) or 20% SPI for 90 d. Hepatic mitochondrial ATPase activity was significantly higher in the rats fed SPI than in those fed casein. Addition of ISF to SPI eliminated the action of SPI. ATPase/ATP synthase beta protein contents in the liver were unchanged; however, its patterns measured by 2-dimensional Western blot were different among dietary groups. The rats fed SPI or SPI plus ISF had 3 more major protein spots with the same molecular weights (80 kDa and 55 kDa) as those presented in the rats fed casein but with different isoelectric points. Pretreatment of hepatic mitochondrial proteins from the rats fed casein with alkaline phosphatase produced the same ATPase/ATP synthase beta patterns as observed in the SPI-fed rats and significantly elevated the ATPase activity. These results suggest that consumption of soy proteins increases hepatic ATPase activity, which might be a consequence of increased dephosphorylation or decreased phosphorylation of the mitochondrial ATPase/ATP synthase beta protein.

Diabetic modulation of the temperature kinetics properties of cytochrome oxidase activity in rat brain mitochondria

The effects of alloxan-diabetes and subsequent treatment with insulin on temperature kinetics properties of cytochrome oxidase activity from rat brain mitochondria were examined. The enzyme activity decreased only at the late stage of diabetes which was not normalized by insulin treatment; however at early stage of diabetes hyper-stimulation occurred. In the control animals the Arrhenius plot was chair shaped with three energies of (E1, E2 and E3) and two phase transition temperatures (Tt1 and Tt2). At early diabetic stage the Arrhenius plot became biphasic and E1)and E2 decreased; insulin treatment reversed chair-shaped pattern with increase in E2. These changes correlated with transient changes in the phospholipids profiles especially decreased acidic phospholipids. The temperature kinetics parameters were minimally affected at the late stage of diabetes or by insulin treatment. Thus at the late stage the brain tissue seems to have readjusted to its insulin homeostasis.

Effect of alloxan diabetes and subsequent insulin treatment on temperature kinetics properties of succinate oxidase activity in rat kidney mitochondria

Early and late effects of alloxan diabetes and subsequent treatment with insulin on the temperature kinetics properties of succinate oxidase (SO) activity in rat kidney mitochondria were examined. In diabetic animals SO activity increased significantly and the increase was more pronounced at the late stage. Insulin treatment partially restored SO activity. However, the effect was temperature-dependent. In diabetic animals the energy of activation in the low temperature range (E(L)) increased significantly while that in the high temperature range (E(H)) decreased. The latter seems to be responsible for improving catalytic efficiency in the diabetic state. Insulin treatment normalized E(H) only in the 1-month diabetic group. The phase transition temperature (Tt), decreased in diabetic animals. Insulin treatment caused an increase beyond the control value in Tt in 1-month diabetic animals. The results suggest that insulin status-dependent modulation of SO activity is a complex process.

Insulin status-dependent alterations in lipid/phospholipid composition of rat kidney microsomes and mitochondria

Early and late effects of alloxan-diabetes on lipid/phospholipid composition in rat kidney microsomes and mitochondria were examined. In microsomes, early diabetic state resulted in an increase in contents of total phospholipids (TPL), cholesterol (CHL), with an increase in the lysophospholipids (Lyso), phosphatidylcholine (PC), and phosphatidylinositol (PI) components. The sphingomyelin (SPM), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidic acid (PA) content decreased. Treatment with insulin had no effect on PC but PE increased and the other components decreased. In the 1-month diabetic group PI, PS, PE, and PA components decreased, whereas Lyso and PC increased. Treatment with insulin had restorative effects on PE, PI, and PS; Lyso was further elevated whereas PA decreased. In mitochondria, at an early stage of diabetes marginally increased CHL content was restored by insulin treatment. Long-term diabetes lowered the TPL and elevated the CHL content. Treatment with insulin partially restored the TPL and CHL content. A diabetic state decreased the proportion of PE and diphosphatidylglycerol (DPG) components but increased the Lyso, SPM, PC, PI, and PS components in the mitochondria. Treatment with insulin had a partial restorative effect. The membrane fluidity of both microsomes and mitochondria decreased in general in the diabetic condition and was not corrected by insulin treatment at a late stage. However, at an early stage, treatment with insulin fluidized both membranes.