Effects of N-acylethanolamines on mitochondrial energetics and permeability transition

Mediterranean Diet and Neurodegenerative Diseases: The Neglected Role of Nutrition in the Modulation of the Endocannabinoid System

Neurodegenerative disorders are a widespread cause of morbidity and mortality worldwide, characterized by neuroinflammation, oxidative stress and neuronal depletion. The broad-spectrum neuroprotective activity of the Mediterranean diet is widely documented, but it is not yet known whether its nutritional and caloric balance can induce a modulation of the endocannabinoid system. In recent decades, many studies have shown how endocannabinoid tone enhancement may be a promising new therapeutic strategy to counteract the main hallmarks of neurodegeneration. From a phylogenetic point of view, the human co-evolution between the endocannabinoid system and dietary habits could play a key role in the pro-homeostatic activity of the Mediterranean lifestyle: this adaptive balance among our ancestors has been compromised by the modern Western diet, resulting in a “clinical endocannabinoid deficiency syndrome”. This review aims to evaluate the evidence accumulated in the literature on the neuroprotective, immunomodulatory and antioxidant properties of the Mediterranean diet related to the modulation of the endocannabinoid system, suggesting new prospects for research and clinical interventions against neurodegenerative diseases in light of a nutraceutical paradigm.

In vitro and in vivo activation of mitochondrial membrane permeability transition pore using triiodothyronine

Using a novel method for evaluating mitochondrial swelling (Drahota et al. 2012a) we studied the effect of calcium (Ca(2+)), phosphate (P(i)), and triiodothyronine (T(3)) on the opening of mitochondrial membrane permeability transition pore and how they interact in the activation of swelling process. We found that 0.1 mM P(i), 50 microM Ca(2+) and 25 microM T(3) when added separately increase the swelling rate to about 10 % of maximal values when all three factors are applied simultaneously. Our findings document that under experimental conditions in which Ca(2+) and P(i) are used as activating factors, the addition of T(3) doubled the rate of swelling. T(3) has also an activating effect on mitochondrial membrane potential. The T(3) activating effect was also found after in vivo application of T(3). Our data thus demonstrate that T(3) has an important role in opening the mitochondrial membrane permeability pore and activates the function of the two key physiological swelling inducers, calcium and phosphate ions.

Lipid analogues as potential drugs for the regulation of mitochondrial cell death

The mitochondrion plays an important role in the production of energy as ATP, the regulation of cell viability and apoptosis, and the biosynthesis of major structural and regulatory molecules, such as lipids. During ATP production, reactive oxygen species are generated that alter the intracellular redox state and activate apoptosis. Mitochondrial dysfunction is a well-recognized component of the pathogenesis of diseases such as cancer. Understanding mitochondrial function, and how this is dysregulated in disease, offers the opportunity for the development of drug molecules to specifically target such defects. Altered energy metabolism in cancer, in which ATP production occurs largely by glycolysis, rather than by oxidative phosphorylation, is attributable in part to the up-regulation of cell survival signalling cascades. These pathways also regulate the balance between pro- and anti-apoptotic factors that may determine the rate of cell death and proliferation. A number of anti-cancer drugs have been developed that target these factors and one of the most promising groups of agents in this regard are the lipid-based molecules that act directly or indirectly at the mitochondrion. These molecules have emerged in part from an understanding of the mitochondrial actions of naturally occurring fatty acids. Some of these agents have already entered clinical trials because they specifically target known mitochondrial defects in the cancer cell.

Cannabinoid-induced changes in respiration of brain mitochondria

Cannabinoids exert various biological effects that are either receptor-mediated or independent of receptor signaling. Mitochondrial effects of cannabinoids were interpreted either as non-receptor-mediated alteration of mitochondrial membranes, or as indirect consequences of activation of plasma membrane type 1 cannabinoid receptors (CB1). Recently, CB1 receptors were confirmed to be localized to the membranes of neuronal mitochondria, where their activation directly regulates respiration and energy production. Here, we performed in-depth analysis of cannabinoid-induced changes of mitochondrial respiration using both an antagonist/inverse agonist of CB1 receptors, AM251 and the cannabinoid receptor agonists, Δ(9)-tetrahydrocannabinol (THC), cannabidiol, anandamide, and WIN 55,212-2. Relationships were determined between cannabinoid concentration and respiratory rate driven by substrates of complex I, II or IV in pig brain mitochondria. Either full or partial inhibition of respiratory rate was found for the tested drugs, with an IC50 in the micromolar range, which verified the significant role of non-receptor-mediated mechanism in inhibiting mitochondrial respiration. Effect of stepwise application of THC and AM251 evidenced protective role of AM251 and corroborated the participation of CB1 receptor activation in the inhibition of mitochondrial respiration. We proposed a model, which includes both receptor- and non-receptor-mediated mechanisms of cannabinoid action on mitochondrial respiration. This model explains both the inhibitory effect of cannabinoids and the protective effect of the CB1 receptor inverse agonist.

Mitochondria: a possible nexus for the regulation of energy homeostasis by the endocannabinoid system?

The endocannabinoid system (ECS) regulates numerous cellular and physiological processes through the activation of receptors targeted by endogenously produced ligands called endocannabinoids. Importantly, this signaling system is known to play an important role in modulating energy balance and glucose homeostasis. For example, current evidence indicates that the ECS becomes overactive during obesity whereby its central and peripheral stimulation drives metabolic processes that mimic the metabolic syndrome. Herein, we examine the role of the ECS in modulating the function of mitochondria, which play a pivotal role in maintaining cellular and systemic energy homeostasis, in large part due to their ability to tightly coordinate glucose and lipid utilization. Because of this, mitochondrial dysfunction is often associated with peripheral insulin resistance and glucose intolerance as well as the manifestation of excess lipid accumulation in the obese state. This review aims to highlight the different ways through which the ECS may impact upon mitochondrial abundance and/or oxidative capacity and, where possible, relate these findings to obesity-induced perturbations in metabolic function. Furthermore, we explore the potential implications of these findings in terms of the pathogenesis of metabolic disorders and how these may be used to strategically develop therapies targeting the ECS.

Reducing the oxidative stress mediates the cardioprotection of bicyclol against ischemia-reperfusion injury in rats

OBJECTIVE

To investigate the beneficial effect of bicyclol on rat hearts subjected to ischemia-reperfusion (IR) injuries and its possible mechanism.

METHODS

Male Sprague-Dawley rats were intragastrically administered with bicyclol (25, 50 or 100 mg/(kg∙d)) for 3 d. Myocardial IR was produced by occlusion of the coronary artery for 1 h and reperfusion for 3 h. Left ventricular hemodynamics was continuously monitored. At the end of reperfusion, myocardial infarct was measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining, and serum lactate dehydrogenase (LDH) level and myocardial superoxide dismutase (SOD) activity were determined by spectrophotometry. Isolated ventricular myocytes from adult rats were exposed to 60 min anoxia and 30 min reoxygenation to simulate IR injuries. After reperfusion, cell viability was determined with trypan blue; reactive oxygen species (ROS) and mitochondrial membrane potential of the cardiomyocytes were measured with the fluorescent probe. The mitochondrial permeability transition pore (mPTP) opening induced by Ca(2+) (200 μmol/L) was measured with the absorbance at 520 nm in the isolated myocardial mitochondria.

RESULTS

Low dose of bicyclol (25 mg/(kg∙d)) had no significant improving effect on all cardiac parameters, whereas pretreatment with high bicyclol markedly reduced the myocardial infarct and improved the left ventricular contractility in the myocardium exposed to IR (P<0.05). Medium dose of bicyclol (50 mg/(kg∙d)) markedly improved the myocardial contractility, left ventricular myocyte viability, and SOD activity, as well decreased infarct size, serum LDH level, ROS production, and mitochondrial membrane potential in rat myocardium exposed to IR. The reduction of ventricular myocyte viability in IR group was inhibited by pretreatment with 50 and 100 mg/(kg∙d) bicyclol (P<0.05 vs. IR), but not by 25 mg/(kg∙d) bicyclol. The opening of mPTP evoked by Ca(2+) was significantly inhibited by medium bicyclol.

CONCLUSIONS

Bicyclol exerts cardioprotection against IR injury, at least, via reducing oxidative stress and its subsequent mPTP opening.

Increasing antiproliferative properties of endocannabinoids in N1E-115 neuroblastoma cells through inhibition of their metabolism

The antitumoral properties of endocannabinoids received a particular attention these last few years. Indeed, these endogenous molecules have been reported to exert cytostatic, apoptotic and antiangiogenic effects in different tumor cell lines and tumor xenografts. Therefore, we investigated the cytotoxicity of three N-acylethanolamines – N-arachidonoylethanolamine (anandamide, AEA), N-palmitoylethanolamine (PEA) and N-oleoylethanolamine (OEA) - which were all able to time- and dose-dependently reduce the viability of murine N1E-115 neuroblastoma cells. Moreover, several inhibitors of FAAH and NAAA, whose presence was confirmed by RT-PCR in the cell line, induced cell cytotoxicity and favored the decrease in cell viability caused by N-acylethanolamines. The most cytotoxic treatment was achieved by the co-incubation of AEA with the selective FAAH inhibitor URB597, which drastically reduced cell viability partly by inhibiting AEA hydrolysis and consequently increasing AEA levels. This combination of molecules synergistically decreased cell proliferation without inducing cell apoptosis or necrosis. We found that these effects are independent of cannabinoid, TRPV1, PPARα, PPARγ or GPR55 receptors activation but seem to occur through a lipid raft-dependent mechanism. These findings further highlight the interest of targeting the endocannabinoid system to treat cancer. More particularly, this emphasizes the great potential benefit of designing novel anti-cancerous therapies based on the association of endocannabinoids and inhibitors of their hydrolysis.

Anandamide inhibits oxidative phosphorylation in isolated liver mitochondria

A study on the effect of anandamide (AEA) in energy coupling of rat liver mitochondria is presented. Micromolar concentrations of AEA, while almost ineffective on substrate supported oxygen consumption rate and on uncoupler stimulated respiration, strongly inhibited the respiratory state III. AEA did not change the rate and the extent of substrate generated membrane potential, but markedly delayed rebuilding by respiration of the potential collapsed by ADP addition. Overall, these data suggest that anandamide inhibits the oxidative phosphorylation process. Direct measurement of the F(o)F(1) ATP synthase activity showed that the oligomycin sensitive ATP synthesis was inhibited by AEA, (IC(50), 2.5 μM), while the ATP hydrolase activity was unaffected. Consistently, AEA did not change the membrane potential generated by ATP hydrolysis.

Palmitoylethanolamide and other anandamide congeners. Proposed role in the diseased brain

Acylethanolamides are formed in the brain "on demand" from membrane phospholipids called N-acylated phosphatidylethanolamines. The acylethanolamides are signaling molecules of lipid nature, and this lipofilicity suggests an autocrine function. The acylethanolamides include palmitoylethanolamide (PEA), oleoylethanolamide (OEA), stearoylethanolamide (SEA), and several other quantitative minor species including anandamide (= arachidonoylethanolamide). PEA and OEA can activate several different receptors and inhibit some ion channels, e.g., PPARalpha, vanilloid receptor, K(+) channels (Kv4.3, Kv1.5), and OEA can activate GPR119 and inhibit ceramidases. Targets for SEA are less clear, but it has some cannabimimetic actions in rats in vivo. All acylethanolamides accumulate during neuronal injury, and injected OEA has neuroprotective effects, and PEA has anti-inflammatory effects as studied in the peripheral system. Several of the pharmacological effects seem to be mediated via activation of PPARalpha. Recently, injected OEA has been found to consolidate memories in rats. Inhibitors of the acylethanolamide-degrading enzyme FAAH can increase levels of all acylethanolamides including annandamide, and some of the pharmacological effects caused by these inhibitors may be explained by increased cerebral levels of OEA and PEA, e.g., suppression of nicotine-induced activation of dopamine neurons. Furthermore, through activation of PPARalpha, OEA and PEA may stimulate neurosteroid synthesis, thereby modulating several biological functions mediated by GABA(A) receptors. The existence of acylethanolamides in the mammalian brain has been known for decades, but it is first within the last few years that the putative biological functions of the three most abundant acylethanolamides species are starting to emerge.

Fatty acids as modulators of the cellular production of reactive oxygen species

Long-chain nonesterified ("free") fatty acids (FFA) and some of their derivatives and metabolites can modify intracellular production of reactive oxygen species (ROS), in particular O(2)(-) and H(2)O(2). In mitochondria, FFA exert a dual effect on ROS production. Because of slowing down the rate of electron flow through Complexes I and III of the respiratory chain due to interaction within the complex subunit structure, and between Complexes III and IV due to release of cytochrome c from the inner membrane, FFA increase the rate of ROS generation in the forward mode of electron transport. On the other hand, due to their protonophoric action on the inner mitochondrial membrane ("mild uncoupling effect"), FFA strongly decrease ROS generation in the reverse mode of electron transport. In the plasma membrane of phagocytic neutrophils and a number of other types of cells, polyunsaturated FFA stimulate O(2)(-) generation by NADPH oxidase. These effects of FFA can modulate signaling functions of ROS and be, at least partly, responsible for their proapoptotic effects in several types of cells.

Receptor-independent actions of cannabinoids on cell membranes: Focus on endocannabinoids

Cannabinoids are a structurally diverse group of mostly lipophilic molecules that bind to cannabinoid receptors. In fact, endogenous cannabinoids (endocannabinoids) are a class of signaling lipids consisting of amides and esters of long-chain polyunsaturated fatty acids. They are synthesized from lipid precursors in plasma membranes via Ca(2+) or G-protein-dependent processes and exhibit cannabinoid-like actions by binding to cannabinoid receptors. However, endocannabinoids can produce effects that are not mediated by these receptors. In pharmacologically relevant concentrations, endocannabinoids modulate the functional properties of voltage-gated ion channels including Ca(2+) channels, Na(+) channels, various types of K(+) channels, and ligand-gated ion channels such as serotonin type 3, nicotinic acetylcholine, and glycine receptors. In addition, modulatory effects of endocannabinoids on other ion-transporting membrane proteins such as transient potential receptor-class channels, gap junctions and transporters for neurotransmitters have also been demonstrated. Furthermore, functional properties of G-protein-coupled receptors for different types of neurotransmitters and neuropeptides are altered by direct actions of endocannabinoids. Although the mechanisms of these effects are currently not clear, it is likely that these direct actions of endocannabinoids are due to their lipophilic structures. These findings indicate that additional molecular targets for endocannabinoids exist and that these targets may represent novel sites for cannabinoids to alter either the excitability of the neurons or the response of the neuronal systems. This review focuses on the results of recent studies indicating that beyond their receptor-mediated effects, endocannabinoids alter the functions of ion channels and other integral membrane proteins directly.

Calcium signals are affected by ciprofloxacin as a consequence of reduction of mitochondrial DNA content in Jurkat cells

The effects of ciprofloxacin on mitochondrial DNA (mtDNA) content, oxygen consumption, mitochondrial membrane potential, cellular ATP formation, and capacitative Ca(2+) entry into Jurkat cells were investigated. In cells incubated for several days with 25 mug/ml ciprofloxacin, a 60% reduction of mtDNA content, inhibition of the respiratory chain, and a significant decrease in mitochondrial membrane potential were observed. These changes led to a decrease in the calcium buffering capacity of mitochondria which, in turn, resulted in a gradual inhibition of the capacitative Ca(2+) entry. On days 4, 7, and 11 of incubation with ciprofloxacin, the initial rates of Ca(2+) entry were reduced by 33%, 50%, and 50%, respectively. Ciprofloxacin caused a transient decrease in the cellular capability for ATP formation. In cells incubated for 15 min with glucose, pyruvate, and glutamine as exogenous fuel, ciprofloxacin reduced ATP content by 16% and 35% on days 4 and 7, respectively, of incubation with the drug. However, on day 11 of incubation with ciprofloxacin, a recovery of cellular ATP formation was observed. In conclusion, long-term exposure of Jurkat cells to ciprofloxacin at a concentration of 25 mug/ml seriously affects cellular energy metabolism and calcium homeostasis.

Atractyloside and 5-hydroxydecanoate block the protective effect of puerarin in isolated rat heart

The aim of the present study was to determine whether the clinically effective cardioprotection conferred by puerarin (Pue) against ischemia and reperfusion is mediated by mitochondrial transmembrane pores and/or channels. Hearts isolated from male Sprague-Dawley rats were perfused on a Langendorff apparatus and subjected to 30 min of global ischemia followed by 120 min of reperfusion. The production of formazan, which provides an index of myocardial viability, was measured by absorbance at 550 nm, and the level of lactate dehydrogenase (LDH) in the coronary effluent was determined. In this model, Pue (0.0024-2.4 mmol/l) had a dose-dependent, negatively inotropic effect. Pretreatment with Pue at 0.24 mmol/l for 5 min before ischemia increased myocardial formazan content, reduced LDH release, improved recovery of left ventricular end-diastolic pressure and rate-pressure product (left ventricular developed pressure multiplied by heart rate) during reperfusion. Administration of atractyloside (20 micromol/l), an opener of the mitochondrial permeability transition pore, for the first 20 min of reperfusion, and 5-hydroxydecanoate (100 micromol/l), the mitochondrial-specific ATP-sensitive potassium channel blocker, for 20 min before ischemia, attenuated the protective effects of Pue. In mitochondria isolated from hearts pretreated with 0.24 mmol/l Pue for 5 min, a significant inhibition of Ca(2+)-induced swelling was observed, and this inhibition was attenuated by 5-hydroxydecanoate. In isolated ventricular myocytes, pretreatment with Pue prevented ischemia-induced cell death and depolarization of the mitochondrial membrane, and atractyloside and 5-hydroxydecanoate attenuated the effects of Pue. These findings indicate that puerarin protects the myocardium against ischemia and reperfusion injury via inhibiting mitochondrial permeability transition pore opening and activating the mitochondrial ATP-sensitive potassium channel.

Effects ofN-acylethanolamines on the respiratory chain and production of reactive oxygen species in heart mitochondria

Long-chain N-acylethanolamines (NAEs) have been found to uncouple oxidative phosphorylation and to inhibit uncoupled respiration of rat heart mitochondria [Wasilewski, M., Wieckowski, M.R., Dymkowska, D. and Wojtczak, L. (2004) Biochim. Biophys. Acta 1657, 151-163]. The aim of the present work was to investigate in more detail the mechanism of the inhibitory effects of NAEs on the respiratory chain. In connection with this, we also investigated a possible action of NAEs on the generation of reactive oxygen species (ROS) by respiring rat heart mitochondria. It was found that unsaturated NAEs, N-oleoylethanolamine (N-Ole) and, to a greater extent, N-arachidonoylethanolamine (N-Ara), inhibited predominantly complex I of the respiratory chain, with a much weaker effect on complexes II and III, and no effect on complex IV. Saturated N-palmitoylethanolamine had a much smaller effect compared to unsaturated NAEs. N-Ara and N-Ole were found to decrease ROS formation, apparently due to their uncoupling action. However, under specific conditions, N-Ara slightly but significantly stimulated ROS generation in uncoupled conditions, probably due to its inhibitory effect on complex I. These results may contribute to our better understanding of physiological roles of NAEs in protection against ischemia and in induction of programmed cell death.