The mechanism of palmitoyl-CoA inhibition of Ca2+ uptake in liver and heart mitochondria

Inhibitors of succinate: quinone reductase/Complex II regulate production of mitochondrial reactive oxygen species and protect normal cells from ischemic damage but induce specific cancer cell death

Succinate:quinone reductase (SQR) of Complex II occupies a unique central point in the mitochondrial respiratory system as a major source of electrons driving reactive oxygen species (ROS) production. It is an ideal pharmaceutical target for modulating ROS levels in normal cells to prevent oxidative stress-induced damage or alternatively,increase ROS in cancer cells, inducing cell death.The value of drugs like diazoxide to prevent ROS production,protecting normal cells, whereas vitamin E analogues promote ROS in cancer cells to kill them is highlighted. As pharmaceuticals these agents may prevent degenerative disease and their modes of action are presently being fully explored. The evidence that SDH/Complex II is tightly coupled to the NADH/NAD+ ratio in all cells,impacted by the available supplies of Krebs cycle intermediates as essential NAD-linked substrates, and the NAD+-dependent regulation of SDH/Complex II are reviewed, as are links to the NAD+-dependent dehydrogenases, Complex I and the E3 dihiydrolipoamide dehydrogenase to produce ROS. This review collates and discusses diverse sources of information relating to ROS production in different biological systems, focussing on evidence for SQR as the main source of ROS production in mitochondria, particularly its relevance to protection from oxidative stress and to the mitochondrial-targeted anti cancer drugs (mitocans) as novel cancer therapies [corrected].

Effects of palmitoyl CoA and palmitoyl carnitine on the membrane potential and Mg2+ content of rat heart mitochondria

Palmitoyl CoA and palmitoyl carnitine added to rat heart mitochondria in amounts above 20 and 50 nmoles/mg protein, respectively, induced a fall in transmembrane potential and loss of endogenous Mg2+. The dissipation of membrane potential by low concentrations of palmitoyl CoA in the presence of Ca2+, but not that of high concentrations of palmitoyl CoA alone, was prevented by either ruthenium red, Cyclosporin A or Mg2+, but reversed only by Mg2+. The fall of membrane potential induced by palmitoyl carnitine was not prevented by any of these factors. It is suggested that the action of both palmitoyl CoA and palmitoyl carnitine at high concentrations is due to a non specific disruption of membrane architecture, while that of low concentrations of palmitoyl CoA in the presence of Ca2+ is associated specifically with energy dissipation due to Ca2+ cycling.

Ca2+-mediated action of long-chain acyl-CoA on liver mitochondria energy-linked processes

The decrease of steady-state transmembrane potential (delta psi) and loss of accumulated Ca2+ are magnified if palmitoyl-CoA is added to rat liver mitochondria exposed to Ca2+ and phosphate. The extent of this damage increases with increasing concentration of long-chain acyl-CoA. Addition of L-carnitine with or without the addition of palmitoyl-CoA considerably delays the deenergization. In the latter case, there is a substantial decrease in the assayed endogenous long-chain acyl-CoA content. This protective action of L-carnitine is abolished by L-aminocarnitine, a powerful inhibitor of carnitine palmitoyl transferase (palmitoyl-CoA: L-carnitine O-palmitoyltransferase, EC 2.3.1.21.). The removal of Ca2+ by EGTA, or the inhibition of its uptake by Ruthenium red or Mg2+ further enhances the degree of protection.

Mitochondrial Ca2+ fluxes: role of free fatty acids, acyl-CoA and acylcarnitine

It has been suggested that accumulation of lipid metabolites, such as fatty acids, fatty acyl-CoA and acylcarnitine, in the ischaemic myocardium, may be responsible for disturbances in mitochondrial Ca2+ fluxes. In view of the presence of an intracellular fatty acid binding protein, the question arose whether these intermediates affect mitochondrial Ca2+ uptake and release similarly in vivo. In this study the effects of linoleic acid, palmitic acid, palmitoyl-CoA and palmitoylcarnitine were studied on mitochondrial Ca2+ fluxes in the absence and presence of albumin, an avid binder of fatty acid derivatives. Albumin reversed the effects of the above compounds on mitochondrial Ca2+ uptake and release, suggesting that the presence of an intracellular fatty acid binding protein may protect the ischaemic myocardial cell against the deleterious effects of accumulated fatty acid derivatives.

beta-Hydroxy acyl-CoA inhibition of mitochondrial ATP production

beta-Hydroxypalmitoyl-CoA and beta-hydroxystearoyl-CoA were synthesized, purified and quantitated. beta-Hydroxypalmitoyl-CoA and beta-hydroxystearoyl-CoA instantly and reversibly inhibited oxidative phosphorylation by rabbit heart mitochondria oxidizing pyruvate. [8-14C]ADP uptake studies showed that the beta-hydroxy acyl-CoA species linearly inhibited the adenine nucleotide translocase system. Free beta-hydroxy fatty acids at comparable concentrations (0.005 mM) did not affect ADP uptake or state III respiration.

Metabolic relationship between arachidonate activation and its transfer to lysophospholipids by brain microsomes

Evidence is presented to indicate a metabolic relationship between arachidonic acid activation and its transfer to lysophospholipids by brain microsomes. Thus, in the presence of 1-acylglycerophosphocholines or 1-acyl-glycerophosphoinositols, the activation of labeled arachidonate to its acyl-CoA was enhanced, and the acyl-CoA formed was, in turn, transferred to the lysophospholipids to form the respective diacyl-glycerophospholipids. The "coupling effect" seems to pertain mainly to the lysophospholipids which are good substrates of the acyltransferase. Other lyso-compounds were either not effective or inhibitory to the arachidonate activation process. The activation-transfer activity mediated by the fatty acid ligase and acyltransferase could be dissociated by Triton X-100, which apparently stimulated the acyl-CoA ligase activity but inhibited the acyltransferase. These results suggest that fatty acid ligase and acyltransferase are located in close proximity within the membrane domain. The existence of a close metabolic relationship between these two enzymic reactions is important for maintaining a dynamic equilibrium between the free fatty acids and the membrane phospholipids. The mechanism is also useful in regulating the cellular acyl-CoA and lysophospholipid metabolism, because both compounds have membrane perturbing properties when present in excessive quantity.

Acyl-carnitine effects on isolated cardiac mitochondria and erythrocytes

The effects of various long-chain acyl-carnitines (AC) on mitochondrial functions and red cell membrane stability were studied. Lower concentrations slightly stimulate respiration-dependent functions such as phosphorylation rate and Ca++ uptake velocity, whereas higher concentrations inhibit these functions with concomitant depression of the ATP/O ratio. The order of effectiveness among the AC is very similar for different mitochondrial functions. The differences among AC in their actions on red cell stability in hypotonic media and their differences in influence on mitochondrial functions exhibit less resemblance. The relative order of erythrolytic concentrations of AC follows the order of their critical micellar concentrations. Model calculations indicate that the concentrations of AC found in ischemic hearts are below those which exhibit inhibitory effects in vitro. Ultrastructural changes in mitochondria incubated with AC are different from those found in ischemic tissue. From this, it seems questionable whether the elevated AC levels in ischemic hearts are indeed as important for the development of membrane damage as is often supposed.

The interaction of long-chain acyl CoA with membranes

Published data regarding the interaction of long-chain acyl CoA derivatives with the protein and phospholipid constituents of biological membranes is reviewed and discussed in relationship to the premise that such interactions may lead to membrane damage during pathological situations. The topics considered include: the detergent properties of long-chain CoA, the interaction with membrane-associated enzymes, biological membranes, or model membrane systems, and the binding to a soluble protein that may facilitate intracellular transport. The effects of long-chain acyl CoA on heart mitochondria and the relevance of such studies to myocardial ischemia also is emphasized.