Mitohormesis and metabolic health: The interplay between ROS, cAMP and sirtuins

The key role of mitochondria in oxidative metabolism and redox homeostasis explains the link between mitochondrial dysfunction and the development of metabolic disorders. Mitochondria's highly dynamic nature, based on alterations in biogenesis, mitophagy, fusion and fission, allows adjusting sequential redox reactions of the electron transport chain (ETC) and dissipation of the membrane potential by ATP synthase, to different environmental cues. With reactive oxygen species being an inevitable by-product of oxidative phosphorylation (OXPHOS), alterations on mitochondrial oxidative rate with a consequent excessive load of reactive oxygen species have been traditionally associated with pathological conditions. However, reactive oxygen species have also been suggested as promoters of mitohormesis, a process in which low, non-cytotoxic concentrations of reactive oxygen species promote mitochondrial homeostasis. Therefore, signaling systems involved in the regulation of mitochondrial homeostasis are attractive candidates for drug development for metabolic diseases triggered by mitochondrial dysfunction. Reversible phosphorylation downstream the cyclic AMP (cAMP) signaling cascade and deacetylation mediated by sirtuins are recognized as major mitochondrial regulators.

Evaluation of bioenergetic and mitochondrial function in liver transplantation

BACKGROUND/AIMS

We measured changes in mitochondrial function and bioenergetics that occur during ischemia/ reperfusion in fresh liver samples of patients undergoing liver transplantation. These variations correlated with markers of liver function and clinical outcome. Ischemia/reperfusion injury related to liver transplantation affects mitochondrial function and bioenergetics. Experimental studies were conducted to identify the role of bioenergetics and mitochondrial dysfunction. To the best of our knowledge, no investigation of these two factors' impacts on liver transplantation has been performed.

METHODS

This was a prospective study of 28 patients who underwent liver transplantation. We measured parameters of mitochondrial function and bioenergetics in biopsies performed during the procedure.

RESULTS

We observed a statistically significant reduction in mitochondrial membrane potential, an increase in lag phase, and decreases in mitochondrial respiration and adenosine triphosphate content (P<0.010). Higher postoperative aminotransferase peaks correlated with worse mitochondrial function; mitochondrial respiration correlated with arterial lactate (P<0.010).

CONCLUSION

There is a relationship between mitochondrial function and ischemia/reperfusion injury. The future use of these clinical markers as prognostic factors may allow early identification of post-transplant liver failure and may indicate the need to perform a new transplant.

Mild hypothermia during the reperfusion phase protects mitochondrial bioenergetics against ischemia-reperfusion injury in an animal model of ex-vivo liver transplantation-an experimental study

The organ preservation paradigm has changed following the development of new ways to preserve organs. The use of machine perfusion to preserve organs appears to have several advantages compared with conventional static cold storage. For liver transplants, the temperature control provided by machine perfusion improves organ preservation. In this experimental study, we measured the effects of different temperatures on mitochondrial bioenergetics during the reperfusion phase. An experimental model of ex-vivo liver transplantation was developed in Wistar rats (Rattus norvegicus). After total hepatectomy, cold static preservation occurred at 4ºC and reperfusion was performed at 37ºC and 32ºC using a Langendorff system. We measured parameters associated with mitochondrial bioenergetics in the livers. Compared with the livers that underwent normothermic reperfusion, mild hypothermia during reperfusion caused significant increases in the mitochondrial membrane potential, the adenosine triphosphate content, and mitochondrial respiration, and a significant reduction in the lag phase (all P < 0.001). Mild hypothermia during reperfusion reduced the effect of ischemia-reperfusion injury on mitochondrial activity in liver tissue and promoted an increase in bioenergetic availability compared with normothermic reperfusion.

Indirubin and NAD+ prevent mitochondrial ischaemia/reperfusion damage in fatty livers

BACKGROUND

Fatty livers are considerably more susceptible to acute stressors, such as ischaemia/reperfusion (I/R). As the incidence of I/R is high due to surgical events and some pathologies, there is an urgent need to find strategies against I/R injury (I/RI) in fatty livers. We postulate that an acute pretreatment with indirubin-3'-oxime (Ind) or NAD+ prevents mitochondrial dysfunction associated with warm I/RI in fatty livers.

MATERIALS AND METHODS

Zucker fatty rats were subjected to warm ischaemia and 12 hours of reperfusion. Ind or NAD+ was administered in the hepatic artery 30 minutes before ischaemia. Hepatic mitochondrial isolation was performed, and functional assays as well as molecular analysis were performed.

RESULTS

Pretreatment decreased markers of liver injury while preserving mitochondrial cytochrome c content, which is related to the prevention of calcium-induced mitochondrial permeability transition (mPT), the decline in mitochondrial respiratory state 3 and ATP content. The generation of reactive oxygen species (ROS) was also diminished. Inhibition of GSK-3ß by Ind resulted in the prevention of cyclophilin-D (CypD) phosphorylation, unabling it to bind to the adenine nucleotide translocator (ANT), thus, preventing mPT induction. Furthermore, deacetylation of CypD at Lys residue by sirtuin 3 (SIRT3) caused its dissociation from ANT, contributing to an increase in mPT threshold in NAD+ -pretreated animals.

CONCLUSIONS

Pretreatment with Ind or NAD+ protects fatty livers by maintaining mitochondrial calcium homoeostasis, thus, preserving mitochondrial function and energetic balance. As such, CypD might be a new protective target against I/RI in fatty livers.

Recent insights into mitochondrial targeting strategies in liver transplantation

Ischemia/reperfusion (I/R) injury in liver transplantation can disrupt the normal activity of mitochondria in the hepatic parenchyma. This potential dysfunction of mitochondria after I/R injury could be responsible for the initial poor graft function or primary nonfunction observed after liver transplantation. Thus, determining the mechanisms that lead to human hepatic mitochondrial dysfunction might contribute to improving the outcome of liver transplantation. Furthermore, early identification of novel prognostic factors involved in I/R injury could serve as a key endpoint to predict the outcome of liver grafts and also to promote the early adoption of novel strategies that protect against I/R injury. Here, we briefly review recent advances in the study of mitochondrial dysfunction and I/R injury, particularly in relation to liver transplantation. Next, we highlight various pharmacological therapeutic strategies that could be applied, and discuss their relationship to relevant mitochondrion-related processes and targets. Lastly, we note that although considerable progress has been made in our understanding of I/R injury and mitochondrial dysfunction, further investigation is required to elucidate the cellular and molecular mechanisms underlying these processes, thereby identifying biomarkers that can help in evaluating donor organs.

Hepatic and skeletal muscle mitochondrial toxicity of chitosan oligosaccharides of normal and diabetic rats

Diabetes and associated conditions are now considered a worldwide epidemic, with increasing costs and burdens with no cure yet developed. The chitin-derived glucosamine biopolymer chitosan has shown promising results when supplied to diabetic patients. However, no study has investigated the possible toxic side effects of chitosan treatments, in particular when regarding the most important bioenergetic organelle, mitochondria. As such, we aimed to understand if supplementation of chitosan to the diet of normal and diabetic rats could compromise mitochondrial function on two of the major organs involved in diabetes, obesity, and metabolic regulation, the liver and skeletal muscle. We supplemented the drinking water of normal Wistar and diabetic Goto-Kakizaki rats with 0.5% chitosan for 6 weeks. We show here that, in terms of hepatic bioenergetics, chitosan was relatively inert and had no major side effects. However, regarding skeletal muscle bioenergetics, chitosan significantly affected various bioenergetic parameters. As such, we conclude that chitosan, at the tested doses, is relatively safe for treatment of diabetic situations. Nonetheless, the potential for adverse toxicological side effects appears to be present, which might be relevant if higher doses are utilized.

The bile acid chenodeoxycholic acid directly modulates metabolic pathways in white adipose tissue in vitro: insight into how bile acids decrease obesity

Obesity is a worldwide epidemic, and associated pathologies, including type 2 diabetes and cardiovascular alterations, are increasingly escalating morbidity and mortality. Despite intensive study, no effective simple treatment for these conditions exists. As such, the need for go-to drugs is serious. Bile acids (BAs) present the possibility of reversing these problems, as various in vivo studies and clinical trials have shown significant effects with regard to weight and obesity reduction, insulin sensitivity restoration and cardiovascular improvements. However, the mechanism of action of BA-induced metabolic improvement has yet to be fully established. The currently most accepted model involves non-shivering thermogenesis for energy waste, but this is disputed. As such, we propose to determine whether the BA chenodeoxycholic acid (CDCA) can exert anti-obesogenic effects in vitro, independent of thermogenic brown adipose tissue activation. By exposing differentiated 3 T3-L1 adipocytes to high glucose and CDCA, we demonstrate that this BA has anti-obesity effects in vitro. Nuclear magnetic resonance spectroscopic analysis of metabolic pathways clearly indicates an improvement in metabolic status, as these cells become more oxidative rather than glycolytic, which may be associated with an increase in fatty acid oxidation. Our work demonstrates that CDCA-induced metabolic alterations occur in white and brown adipocytes and are not totally dependent on endocrine/nervous system signaling, as thought until now. Furthermore, future exploration of the mechanisms behind these effects will undoubtedly reveal interesting targets for clinical modulation.

Low-dose, subchronic exposure to silver nanoparticles causes mitochondrial alterations in Sprague-Dawley rats

AIM

Nanoparticles (NPs) have increasingly been studied due to their probable harmful effects to both humans and the environment. However, despite several indications of possible harmful effects, no long-term studies using a low dose of silver nanoparticles (AgNP) have been conducted in vivo.

RESULTS

Our data demonstrate that the prolonged exposure to a very low dose of AgNP was sufficient to cause alterations in hepatic mitochondrial function. Mitochondrial function compromised by AgNPs is recovered by pretreatment with the antioxidant N-acetylcysteine, which highlights the crucial role of oxidative stress in AgNPs' toxicity.

CONCLUSION

Our data show for the first time that even a very low dose of AgNP can cause harmful effects on mitochondrial function, thus compromising the normal function of the organ.

Losartan activates sirtuin 1 in rat reduced-size orthotopic liver transplantation

AIM: To investigate a possible association between losartan and sirtuin 1 (SIRT1) in reduced-size orthotopic liver transplantation (ROLT) in rats.

METHODS: Livers of male Sprague-Dawley rats (200-250 g) were preserved in University of Wisconsin preservation solution for 1 h at 4 °C prior to ROLT. In an additional group, an antagonist of angiotensin II type 1 receptor (AT1R), losartan, was orally administered (5 mg/kg) 24 h and 1 h before the surgical procedure to both the donors and the recipients. Transaminase (as an indicator of liver injury), SIRT1 activity, and nicotinamide adenine dinucleotide (NAD⁺, a co-factor necessary for SIRT1 activity) levels were determined by biochemical methods. Protein expression of SIRT1, acetylated FoxO1 (ac-FoxO1), NAMPT (the precursor of NAD+), heat shock proteins (HSP70, HO-1) expression, endoplasmic reticulum stress (GRP78, IRE1α, p-eIF2) and apoptosis (caspase 12 and caspase 3) parameters were determined by Western blot. Possible alterations in protein expression of mitogen activated protein kinases (MAPK), such as p-p38 and p-ERK, were also evaluated. Furthermore, the SIRT3 protein expression and mRNA levels were examined.

RESULTS: The present study demonstrated that losartan administration led to diminished liver injury when compared to ROLT group, as evidenced by the significant decreases in alanine aminotransferase (358.3 ± 133.44 vs 206 ± 33.61, P < 0.05) and aspartate aminotransferase levels (893.57 ± 397.69 vs 500.85 ± 118.07, P < 0.05). The lessened hepatic injury in case of losartan was associated with enhanced SIRT1 protein expression and activity (5.27 ± 0.32 vs 6.08 ± 0.30, P < 0.05). This was concomitant with increased levels of NAD⁺ (0.87 ± 0.22 vs 1.195 ± 0.144, P < 0.05) the co-factor necessary for SIRT1 activity, as well as with decreases in ac-FoxO1 expression. Losartan treatment also provoked significant attenuation of endoplasmic reticulum stress parameters (GRP78, IRE1α, p-eIF2) which was consistent with reduced levels of both caspase 12 and caspase 3. Furthermore, losartan administration stimulated HSP70 protein expression and attenuated HO-1 expression. However, no changes were observed in protein or mRNA expression of SIRT3. Finally, the protein expression pattern of p-ERK and p-p38 were not altered upon losartan administration.

CONCLUSION: The present study reports that losartan induces SIRT1 expression and activity, and that it reduces hepatic injury in a ROLT model.

Sirtuin 1 in rat orthotopic liver transplantation: An IGL-1 preservation solution approach

AIM: To investigate the possible involvement of Sirtuin 1 (SIRT1) in rat orthotopic liver transplantation (OLT), when Institute Georges Lopez 1 (IGL-1) preservation solution is enriched with trimetazidine (TMZ).

METHODS: Male Sprague-Dawley rats were used as donors and recipients. Livers were stored in IGL-1 preservation solution for 8h at 4 °C, and then underwent OLT according to Kamada’s cuff technique without arterialization. In another group, livers were stored in IGL-1 preservation solution supplemented with TMZ, at 10^-6 mol/L, for 8 h at 4 °C and then underwent OLT. Rats were sacrificed 24 h after reperfusion, and liver and plasma samples were collected. Liver injury (transaminase levels), mitochondrial damage (glutamate dehydrogenase activity) oxidative stress (malondialdehyde levels), and nicotinamide adenine dinucleotide (NAD⁺), the co-factor necessary for SIRT1 activity, were determined by biochemical methods. SIRT1 and its substrates (ac-FoxO1, ac-p53), the precursor of NAD⁺, nicotinamide phosphoribosyltransferase (NAMPT), as well as the phosphorylation of adenosine monophosphate activated protein kinase (AMPK), p-mTOR, p-p70S6K (direct substrate of mTOR), autophagy parameters (beclin-1, LC3B) and MAP kinases (p-p38 and p-ERK) were determined by Western blot.

RESULTS: Liver grafts preserved in IGL-1 solution enriched with TMZ presented reduced liver injury and mitochondrial damage compared with those preserved in IGL-1 solution alone. In addition, livers preserved in IGL-1 + TMZ presented reduced levels of oxidative stress. This was consistent with enhanced SIRT1 protein expression and elevated SIRT1 activity, as indicated by decreased acetylation of p53 and FoxO1. The elevated SIRT1 activity in presence of TMZ can be attributed to the enhanced NAMPT protein and NAD⁺/NADH levels. Up-regulation of SIRT1 was consistent with activation of AMPK and inhibition of phosphorylation of mTOR and its direct substrate (p-p70S6K). As a consequence, autophagy mediators (beclin-1 and LC3B) were over-expressed. Furthermore, MAP kinases were regulated in livers preserved with IGL-1 + TMZ, as they were characterized by enhanced p-ERK and decreased p-p38 protein expression.

CONCLUSION: Our study shows that IGL-1 preservation solution enriched with TMZ protects liver grafts from the IRI associated with OLT, through SIRT1 up-regulation.

Dibenzofuran-induced mitochondrial dysfunction: Interaction with ANT carrier

Exposure to environmental pollutants such as dibenzofurans and furans is linked to the pathophysiology of several diseases. Dibenzofuran (DBF) is listed as a pollutant of concern due to its persistence in the environment, bioaccumulation and toxicity to humans, being associated with the development of lung diseases and cancers, due to its extremely toxic properties such as carcinogenic and teratogenic. Mitochondria play a key role in cellular homeostasis and keeping a proper energy supply for eukaryotic cells is essential in the fulfillment of the tissues energy-demand. Therefore, interference with mitochondrial function leads to cell death and organ failure. In this work, the effects of DBF on isolated rat liver mitochondria were analyzed. DBF exposure caused a markedly increase in the lag phase that follows depolarization induced by ADP, indicating an effect in the phosphorylative system. This was associated with a dose-dependent decrease in ATPase activity. Moreover, DBF also increased the threshold to the induction of the mitochondrial permeability transition (MPT) by calcium. Pretreatment of mitochondria with DBF also increased the concentration of carboxyatractyloside (CAT) necessary to abolish ADP phosphorylation and to induce the MPT, suggesting that DBF may interfere with mitochondria through an effect on the adenine nucleotide translocase (ANT). By co-immunoprecipitating ANT and Cyclophilin D (CypD) following MPT induction, we observed that in the presence of DBF, the ratio CypD/ANT was decreased. This demonstrates that DBF interferes with the ANT and so prevents CypD binding to the ANT, causing decreased phosphorylative capacity and inhibiting the MPT, which is also reflected by an increase in calcium retention capacity. Clarifying the role of pollutants in some mechanisms of toxicity, such as unbalance of bioenergetics status and mitochondrial function, may help to explain the progressive and chronic evolution of diseases derived from exposure to environmental pollutants.

The NAD ratio redox paradox: why does too much reductive power cause oxidative stress?

The reductive power provided by nicotinamide adenine dinucleotides is invaluable for several cellular processes. It drives metabolic reactions, enzymatic activity, regulates genetic expression and allows for the maintenance of a normal cell redox status. Therefore, the balance between the oxidized (NAD(+)) and the reduced (NADH) forms is critical for the cell's proper function and ultimately, for its survival. Being intimately associated with the cells' metabolism, it is expected that alterations to the NAD(+)/NADH ratio are to be found in situations of metabolic diseases, as is the case of diabetes. NAD(+) is a necessary cofactor for several enzymes' activity, many of which are related to metabolism. Therefore, a decrease in the NAD(+)/NADH ratio causes these enzymes to decrease in activity (reductive stress), resulting in an altered metabolic situation that might be the first insult toward several pathologies, such as diabetes. Here, we review the importance of nicotinamide adenine dinucleotides in the liver cell and its fluctuations in a state of type 2 diabetes mellitus.

Hepatic FXR: key regulator of whole-body energy metabolism

The farnesoid X receptor (FXR) is a nuclear receptor whose activation leads to alterations in pathways involved in energy metabolism. For example, it serves as a bile acid receptor in tissues such as the liver, and as an energy metabolism regulator in liver, muscle and adipose tissue. However, the effects of FXR activation are not exclusive to the tissue where it is present, because receptor crosstalk affects tissues throughout the body. It has been demonstrated that FXR regulates the metabolism of not just bile acids, but also of fats and hydrocarbon metabolites. FXR is currently under study as a therapeutic target for the treatment of diseases of excess, such as diabetes. Here we review the effects of FXR activation in the response of an organism to excess energy.

Prevention of I/R injury in fatty livers by ischemic preconditioning is associated with increased mitochondrial tolerance: the key role of ATPsynthase and mitochondrial permeability transition

Ischemia/reperfusion (I/R) injury is a commonly encountered clinical problem and occurs probably as a consequence of irreversible mitochondrial injury. The increased susceptibility of fatty livers to ischemic injury is associated with depletion of adenosine triphosphate (ATP) content, which is preserved by preconditioning. Mitochondria being the main ATP production source for the cell, we aimed to evaluate whether ischemic preconditioning (IPC) of fatty livers prevents the impairment in mitochondrial function induced by I/R. Lean and steatotic animals were subjected to 90 min of hepatic warm ischemia and 12 h of reperfusion. IPC effect was tested in fatty livers. After reperfusion, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were measured. Mitochondrial membrane potential, mitochondrial respiration and susceptibility to mitochondrial permeability transition (MPT) were evaluated, as well as ATPase activity and adenine nucleotides. IPC of fatty livers decreased serum AST and ALT levels. Fatty animals subjected to I/R exhibited decreased mitochondrial membrane potential and a delay in the repolarization after a phosphorylation cycle, associated with increased state 4 respiration. Increased tolerance to MPT induction, preservation of F(1)F(o)-ATPsynthase activity and mitochondrial bioenergetics were observed in ischemic preconditioned fatty livers. Thus, IPC is an endogenous protecting mechanism that preserves mitochondrial function and bioenergetics in fatty livers.

Insulin Attenuates Diabetes-Related Mitochondrial Alterations: A Comparative Study

This study evaluated and compared the effect of insulin treatment on the status of brain, heart and kidney mitochondria isolated from 12-week streptozotocin (STZ)-induced diabetic rats versus STZ-diabetic animals treated with insulin during a period of 4 weeks. Mitochondria isolated from 12-week citrate (vehicle)-treated rats were used as control. Several mitochondrial parameters were evaluated: respiratory indexes (state 3 and 4 of respiration, respiratory control and ADP/O ratios), transmembrane potential, depolarization and repolarization levels, ATP, glutathione and coenzyme Q contents, production of hydrogen peroxide, superoxide dismutase, glutathione peroxidase and glutathione reductase activities and the ability of mitochondria to accumulate calcium. We observed that diabetes promoted a significant decrease in kidney and brain mitochondrial coenzyme Q9 content while this parameter was increased in heart mitochondria. Furthermore, diabetes induced a significant increase in hydrogen peroxide production in kidney mitochondria this effect being accompanied by a significant increase in glutathione peroxidase and reductase activities. Furthermore, brain mitochondria isolated from diabetic animals presented a lower ATP content and ability to accumulate calcium. In contrast, heart and kidney mitochondria presented a slight higher capacity to accumulate calcium. Insulin treatment normalized the levels of coenzyme Q9 and glutathione peroxidase and reductase activities and increased ATP content and the ability to accumulate calcium. Altogether these results suggest that insulin treatment attenuates diabetes-induced mitochondrial alterations protecting against the increase in oxidative stress and improving oxidative phosphorylation efficiency. In this line, insulin therapy, besides its well-known importance in the maintenance of glycemic control, may help to protect against mitochondrial dysfunction associated to several age-related disorders such as diabetes.

Cholestasis induced by chronic treatment with alpha-naphthyl-isothiocyanate (ANIT) affects rat renal mitochondrial bioenergetics

Chronic cholestasis is characteristic of many human liver diseases. Renal injury has been often associated with this type of disease. The aim of this study was to evaluate the effect of cholestasis on kidney mitochondrial bioenergetics following in vivo chronic administration of alpha-naphthyl-isothiocyanate (ANIT), a known cholestatic agent. Serum markers of renal injury, kidney morphology and endogenous adenine nucleotides were measured in ANIT-treated rats (80 mg/kg per week s.c. for 16 weeks). Changes in membrane potential and mitochondrial respiration as well as alterations in mitochondrial calcium homeostasis were monitored. Cholestatic animals shown no alterations in renal morphology when compared with control. Additionally, following chronic ANIT administration, no significant alterations in mitochondrial respiratory function have been shown. The phosphorylation capacity of cholestatic kidney mitochondria was enhanced. Associated with these parameters, mitochondria from treated animals exhibited a decreased susceptibility to disruption of mitochondrial calcium homeostasis, due to permeability transition induction. These data suggest that, despite being submitted to chronic treatment with ANIT, kidney mitochondria from cholestasis-induced rats present some defense mechanisms to circumvent this aggression. They show improved phosphorylative capacity and, moreover, a decreased susceptibility to mitochondrial permeability transition induction, probably due to adaptative mechanisms of calcium transport.

Carvedilol reduces mitochondrial damage induced by hypoxanthine/xanthine oxidase: relevance to hypoxia/reoxygenation injury

The cardioprotective properties of new pharmaceuticals such as carvedilol might be explained by enhanced mitochondrial protection. The aim of this work was to determine the role of carvedilol in the protection of heart mitochondria from oxidative damage induced by hypoxanthine/xanthine oxidase, a known source of oxidative stress in the vascular system. Carvedilol reduced oxidative-stress-induced mitochondrial injury, as seen by the delay in the loss of the mitochondrial transmembranar potential (Delta Psi), the decrease in mitochondrial swelling, and the increase in mitochondrial calcium uptake. Carvedilol improved the mitochondrial respiratory activity in state III and offered an overall protection in the respiratory control and in the P/O ratios in mitochondria under oxidative stress. The data indicated that carvedilol was able to partly protect heart mitochondria from oxidative stress-induced damage. Our results suggest that mitochondria can be important targets for some cardioprotective pharmaceuticals.

Protective effect of carvedilol on chenodeoxycholate induction of the permeability transition pore

Intracellular accumulation of toxic, hydrophobic bile acids has been proposed as one of the putative final common pathways leading to cholestatic liver injury. Furthermore, bile acids have been proposed as a causative factor for hepatic cardiomyopathy. Hepatic tissue concentrations of chenodeoxycholic acid (CDCA) during cholestasis are greater than those of other toxic bile acids. In the presence of calcium and phosphate, CDCA induced the permeability transition pore (PTP) in freshly isolated rat liver mitochondria. In this study, we evaluated the effects of carvedilol, a multirole cardioprotective compound, on CDCA-induced PTP. Mitochondrial membrane potential, osmotic swelling, and calcium fluxes were monitored. CDCA-induced PTP, characterized by membrane depolarization, release of matrix calcium, and osmotic swelling, was prevented by carvedilol. Under the same conditions, its hydroxylated analog BM-910228 did not reveal any protective effect. This finding reinforces carvedilol's therapeutic interest, because it may potentially prevent mitochondrial dysfunction associated with cardiomyopathy in the pathophysiology of cholestatic liver disease

Carvedilol in heart mitochondria: protonophore or opener of the mitochondrial K(ATP) channels?

Carvedilol ([1-[carbazolyl-(4)-oxy]-3-[2-methoxyphenoxyethyl) amino]-propanol-(2)]) has been shown to protect cardiac mitochondria from oxidative stress. In this work we examined the mechanisms responsible for an observed depressive effect in the mitochondrial transmembrane potential (delta psi). Two possible mechanisms were considered: a protonophoretic activity and the opening of mitochondrial ATP-sensitive potassium channels. We show that carvedilol increases mitochondrial inner membrane permeability to protons, but not to potassium, causing an increase in state IV respiration in the presence and absence of oligomycin. By contrast, a K(ATP)-channel inhibitor, 5-hydroxydecanoic acid, did not affect carvedilol-induced depolarizations. Hence, our results suggest that carvedilol depresses mitochondrial delta psi by a weak protonophoretic mechanism.

Inhibitory effect of carvedilol in the high-conductance state of the mitochondrial permeability transition pore

The mitochondrial permeability transition is a widely studied, but poorly understood, phenomenon in mitochondrial bioenergetics. It has been recognised that this phenomenon is related to the opening of a protein pore in the inner mitochondrial membrane, and that opening of this pore is the cause of some forms of mitochondrial dysfunction. In this work, we propose that carvedilol, a multi-role cardioprotective compound, may act as an inhibitor of the high-conductance state of the mitochondrial permeability transition pore, a conclusion supported by the finding that carvedilol provides differential protection against mitochondrial swelling in sucrose and KCl-based media, and that it is unable to protect against calcium-induced depolarisation of the mitochondrial membrane. We also show that carvedilol inhibits the oxidation of mitochondrial thiol groups and that, beyond causing a slight depression of the membrane potential, it has no inhibitory effect on mitochondrial calcium uptake.A decrease in the number of oxidised protein thiol groups may be the main mechanism responsible for this selective inhibition of the permeability transition pore in heart mitochondria. These effects may be important for the role of carvedilol in some cardiac pathologies.

Chenodeoxycholate is a potent inducer of the permeability transition pore in rat liver mitochondria

Several reports support the concept that bile acids may be cytotoxic during cholestatic disease process by causing mitochondrial dysfunction. Here we report additional data and findings aimed at a better understanding of the involvement of the permeability transition pore (PTP) opening in bile acids toxicity. The mitochondrial PTP is implicated as a mediator of cell injury and death in many situations. In the presence of calcium and phosphate, chenodeoxycholic acid (CDCA) induced a permeability transition in freshly isolated rat liver mitochondria, characterized by membrane depolarization, release of matrix calcium, and osmotic swelling. All these events were blocked by cyclosporine A (CyA) and the calcium uniporter inhibitor ruthenium red (RR). The results suggest that CDCA increases the sensitivity of isolated mitochondria in vitro to the calcium-dependent induction of the PTP.

Decreased susceptibility of heart mitochondria from diabetic GK rats to mitochondrial permeability transition induced by calcium phosphate

Type 2 diabetes (or non-insulin dependent diabetes mellitus, NIDDM) is a common metabolic disease in man. The Goto-Kakizaki (GK) rat has been designed as a NIDDM model. Previous studies with this strain have shown differences at the mitochondrial level. The mitochondrial permeability transition (MPT) is a widely studied phenomenon but yet poorly understood, that leads to mitochondrial dysfunction and cell death. The aim of this work was to compare the differences in susceptibility of induction of the MPT with calcium phosphate in GK and Wistar rats. Our results show that heart mitochondria from GK rats are less susceptible to the induction of MPT, and show a larger calcium accumulation before the overall loss of mitochondrial impermeability.

Bile acids affect liver mitochondrial bioenergetics: possible relevance for cholestasis therapy

It has been pointed out that intracellular accumulation of bile acids cause hepatocyte injury in cholestatic disease process. This study was aimed to test if cytotoxicity of these compounds is mediated through mitochondria dysfunction. Bile acids effects on isolated rat liver mitochondrial were analyzed by monitoring changes in membrane potential and mitochondrial respiration, as well as alterations in H(+) membrane permeability and mitochondrial permeability transition pore induction. Increasing concentrations of the bile acids litocholic (LCA), deoxycholic (DCA), ursodeoxycholic (UDCA), chenodeoxycholic (CDCA), glycochenodeoxycholic (GCDC), or taurochenodeoxycholic (TCDC) decrease transmembrane potential (delta psi) developed upon succinate energization. These compounds also decreased state 3 respiration and enhanced state 4. We have also demonstrated that the observed concentration-dependent stimulation of state 4 by LCA, DCA, CDCA, TCDC, and GCDC, is associated with an enhanced permeability of mitochondria to H(+). Addition of LCA, DCA, CDCA, TCDC, GCDC, and UDCA to mitochondria energized with succinate resulted in a dose-dependent membrane depolarization and stimulation of mitochondrial permeability transition. Tauroursodeoxycholate (TUDC) elicited no significant effect on succinate-supported mitochondrial bioenergetics. In contrast, in the presence of glycoursodeoxycholic (GUDC), delta psi increases as a function of bile salt concentration. The results of this investigation demonstrate that at toxicologically relevant concentrations, most but not all bile acids alter mitochondrial bioenergetics, so impairment of mitochondrial function can be clinically relevant for patients with cholestasis.