Mitochondrial bioenergetics is affected by the herbicide paraquat

AbstractThe potential toxicity of the herbicide paraquat (1,1-dimethyl-4,4′-bipyridylium dichloride) was tested in bioenergetic functions of isolated rat liver mitochondria. Paraquat increases the rate of State 4 respiration, doubling at 10 mM, indicating uncoupling effects. Additionally, State 3 respiration is depressed by about 15%, at 10 mM paraquat, whereas uncoupled respiration in the presence of CCCP is depressed by about 30%. Furthermore, paraquat partially inhibits the ATPase activity through a direct effect on this enzyme complex. However, at high concentrations (5–10 mM), the ATPase activity is stimulated, probably as consequence of the described uncoupling effect. Depression of respiratory activity is mediated through partial inhibitions of mitochondrial complexes III and IV. Paraquat depresses Δψ as a function of herbicide concentration. In addition, the depolarization induced by ADP is decreased and repolarization is biphasic suggesting a double effect. Repolarization resumes at a level consistently higher than the initial level before ADP addition, for paraquat concentrations up to 10 mM. This particular effect is clear at 1 mM paraquat and tends to fade out with increasing concentrations of the herbicide

Role of mitochondrial dysfunction in combined bile acid-induced cytotoxicity: the switch between apoptosis and necrosis

The goal of this investigation was to determine whether chenodeoxycholic acid (CDCA)-induced apoptosis is prevented by ursodeoxycholic acid (UDCA) or tauroursodeoxycholic acid (TUDC) and to characterize the involvement of mitochondria in the process. Cultured human HepG2 cells were treated in a dose- and time-dependent protocol in order to establish a sufficiently low exposure to CDCA that causes apoptosis but not necrosis. Low-dose CDCA induced an S-phase block and G2 arrest of the cell cycle, as determined by flow cytometry. As a result, cell proliferation was inhibited. CDCA-induced apoptosis, as determined by fluorescence microscopy of Hoechst 33342-stained nuclei, was evident upon coincubation with TUDC. Additionally, after exposure to UDCA plus CDCA, the cell membrane was permeable to fluorescent dyes. Caspase-9-like activity, poly(ADP-ribose) polymerase (PARP) cleavage, and extensive DNA fragmentation were detected in CDCA-exposed cells and in cells coincubated with TUDC, but not UDCA. CDCA caused a decrease in mitochondrial membrane potential and depletion of ATP, both of which were potentiated by UDCA but not TUDC. The results suggest that UDCA potentiates CDCA cytotoxicity, probably at the level of induction of the mitochondrial permeability transition (MPT). Consequently, as suggested by the lack of the main hallmarks of the apoptotic pathway, in the presence of UDCA, CDCA-induced apoptosis is not properly executed but degenerates into necrosis

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

Enhanced mitochondrial testicular antioxidant capacity in Goto-Kakizaki diabetic rats: role of coenzyme Q

Because diabetes mellitus is associated with impairment of testicular function, ultimately leading to reduced fertility, this study was conducted to evaluate the existence of a cause-effect relationship between increased oxidative stress in diabetes and reduced mitochondrial antioxidant capacity. The susceptibility to oxidative stress and antioxidant capacity (in terms of glutathione, coenzyme Q, and vitamin E content) of testis mitochondrial preparations isolated from Goto-Kakizaki (GK) non-insulin-dependent diabetic rats and from Wistar control rats, 1 yr of age, was evaluated. It was found that GK mitochondrial preparations showed a lower susceptibility to lipid peroxidation induced by ADP/Fe(2+), as evaluated by oxygen consumption and reactive oxygen species generation. The decreased susceptibility to oxidative stress in diabetic rats was associated with an increase in mitochondrial glutathione and coenzyme Q9 contents, whereas vitamin E was not changed. These results demonstrate a higher antioxidant capacity in diabetic GK rats. We suggest this is an adaptive response of testis mitochondria to the increased oxidative damage in diabetes mellitu

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.http://www.sciencedirect.com/science/article/B6T1J-4292HK0-5/1/3f9b42626ac2f0c2ab80880219b5d9c

Impact of Carvedilol on the Mitochondrial Damage Induced by Hypoxanthine and Xantine Oxidase - What Role in Myocardial Ischemia and Reperfusion?

Objectivo: Os efeitos cardioprotectores do carvedilol (CV) poderão ser explicados, em parte, por interacções ao nível da mitocôndria cardíaca. O objectivo deste trabalho visou o estudo do efeito protector do CV em mitocôndrias cardíacas durante danos oxidativos induzidos por hipoxantina e xantina oxidase (HX/XO), uma conhecida fonte de estresse oxidativo no sistema cardiovascular. Métodos: As mitocôndrias foram isoladas a partir de corações de ratos Wistar (n=8) e incubadas com o par HX/XO, na presença e na ausência de cálcio. Vários métodos foram utilizados de modo a verificar a acção protectora do CV: avaliação das alterações de volume mitocondrial (variação da densidade óptica da suspensão mitocondrial), tomada e libertação de cálcio mitocondrial (com uma sonda fluorescente, Calcium Green-5N) e respiração mitocondrial (com um eléctrodo de oxigénio). Resultados: O CV reduziu os danos mitocondriais associados à produção de espécies reactivas de oxigénio (ERO) pelos prooxidantes, como verificado pela redução no entumescimento mitocondrial e aumento da capacidade de retenção do cálcio pela mitocôndria. O CV melhorou ainda a capacidade respiratória mitocondrial associada ao estado fosforilativo e aumentou o índice de controlo respiratório (p<0.05) e o quociente ADP/O (p<0.001) das mitocôndrias cardíacas sob estresse oxidativo induzido por HX/XO. Conclusões: Os dados indicam que o CV protegeu parcialmente a mitocôndria cardíaca de danos oxidativos induzidos por HX/XO, o que poderá ser de grande utilidade em situações de isquémiareperfusão do miocárdio. Os resultados também sugerem que a mitocôndria poderá ser um alvo prioritário para a acção benéfica de alguns fármacos cardioprotectores.Objectives: The cardioprotective effects of carvedilol (CV) may be explained in part by interactions with heart mitochondria. The objective of this work was to study the protection afforded by CV against oxidative stress induced in isolated heart mitochondria by hypoxanthine and xanthine oxidase (HX/XO), a well-known source of reactive oxygen species (ROS) in the cardiovascular system. Methods: Mitochondria were isolated from Wistar rat hearts (n=8) and incubated with HX/XO in the presence and in the absence of calcium. Several methods were used to assess the protection afforded by CV: evaluation of mitochondrial volume changes (by measuring changes in the optical density of the mitochondrial suspension), calcium uptake and release (with a fluorescent probe, Calcium Green 5-N) and mitochondrial respiration (with a Clark-type oxygen electrode). Results: CV decreased mitochondrial damage associated with ROS production by HX and XO, as verified by the reduction of mitochondrial swelling and increase in mitochondrial calcium uptake. In the presence of HX and XO, CV also ameliorated mitochondrial respiration in the active phosphorylation state and prevented decrease in the respiratory control ratio (p<0.05) and in mitochondrial phosphorylative efficiency (p<0.001). Conclusions: The data indicate that CV partly protected heart mitochondria from oxidative damage induced by HX and XO, which may be useful during myocardial ischemia and reperfusion. It is also suggested that mitochondria may be a priority target for the protective action of some compounds

Decomposition of the Wave Manifold into Lax Admissible Regions and its Application to the Solution of Riemann Problems

We utilize a three-dimensional manifold to solve Riemann Problems that arise from a system of two conservation laws with quadratic flux functions. Points in this manifold represent potential shock waves, hence its name wave manifold. This manifold is subdivided into regions according to the Lax admissibility inequalities for shocks. Finally, we present solutions for the Riemann Problems for various cases and exhibit continuity relative to $L$ and $R$ data, despite the fact that the system is not strictly hyperbolic. The usage of this manifold regularizes the solutions despite the presence of an elliptic region.Comment: 42 pages, 48 figures. arXiv admin note: text overlap with arXiv:1908.0187

Polyphenols characterization and toxicological evaluation of pterospartum tridentatum leaf water extracts

Pterospartum tridentatum Willk. (prickled broom) is an autochthonous and common plant in Portugal. Leaves and stems are normally used in cooking, to flavour rice, roast meat or hunting animals. Leaves are also used as a condiment in fresh salads and, despite of its traditional use, no toxicological evaluation has been performed. P. tridentatum leaves aqueous extract ESI-MS spectrum revealed the presence of several luteolin and isorhamnetin derived phenolic compounds, which can be associated to the health benefits claimed for this plant species. Still, P. tridentatum leaves extract (up to 100 µg plant extract.mg-1 protein) stimulated state 4 and FCCP-stimulated liver mitochondria respiratory rates and inhibited the state 3 respiratory rate. Respiratory control ratio was diminished, indicating a decrease in phosphorylative efficiency due to inner mitochondrial membrane induced by P. tridentatum leaves extract. Nevertheless, previous results, cytotoxicity evaluation by MTT assay (50 and 125 µg plant extract) showed no significant decrease on HepG2 cell viability. Overall, the present study suggests that the consumption of P. tridentatum leaves should be regarded as safe

Brain and liver mitochondria isolated from diabeticGoto-Kakizaki rats show different susceptibility to induced oxidative stress

Increased oxidative stress and changes in antioxidant capacity observed in both clinical and experimental diabetes mellitus have been implicated in the etiology of chronic diabetic complications. Many authors have shown that hyperglycemia leads to an increase in lipid peroxidation in diabetic patients and animals reflecting a rise in reactive oxygen species production. The aim of the study was to compare the susceptibility of mitochondria from brain and liver of Goto-Kakizaki (12-month-old diabetic) rats (GK rats), a model of non-insulin dependent diabetes mellitus, to oxidative stress and antioxidant defenses.Brain and liver mitochondrial preparations were obtained by differential centrifugation. Oxidative damage injury was induced in vitro by the oxidant pair ADP/Fe2+ and the extent of membrane oxidation was assessed by oxygen consumption, malondialdehyde (MDA) and thiobarbituric acid reactive substances (TBARS) formation. Coenzyme Q and alpha-tocopherol contents were measured by high-performance liquid chromatography (HPLC).Brain mitochondria isolated from 12-month-old control rats displayed a higher susceptibility to lipid peroxidation, as assessed by oxygen consumption and formation of MDA and TBARS, compared to liver mitochondria. In GK rats, mitochondria isolated from brain were more susceptible to invitro oxidative damage than brain mitochondria from normal rats. In contrast, liver mitochondria from diabetic rats were less susceptible to oxidative damage than mitochondria from normal rats. This decreased susceptibility was inversely related to their alpha-tocopherol and coenzyme Q (CoQ) content.The present results indicate that the diabetic state can result in an elevation of both alpha-tocopherol and CoQ content in liver, which may be involved in the elimination of mitochondrially generated reactive oxygen species. The difference in the antioxidant defense mechanisms in the brain and liver mitochondrial preparations of moderately hyperglycemic diabetic GK rats may correspond to a different adaptive response of the cells to the increased oxidative damage in diabetes. Copyright © 2001 John Wiley & Sons, Ltd

Carvedilol: Relation Between Antioxidant Activity and Inhibition of the Mitochondrial Permeability Transition

Objectivos: A transição de permeabilidade mitocondrial (TPM) é um evento associado a estresse oxidativo severo (por exemplo, durante isquémia e reperfusão do miocárdio) e acumulação excessiva de cálcio mitocondrial, podendo mesmo levar a morte celular. Neste estudo comparou-se o efeito do Carvedilol (CV) na TPM cardíaca induzida por cálcio/fosfato (Ca/Pi) e cálcio/carboxiatractilato (Ca/Catr). Para a indução da TPM por Ca/Pi, o estresse oxidativo tem um papel importante, levando a oxidação de grupos tiólicos proteicos mitocondriais, em contraste com o efeito do Ca/Catr, onde essa oxidação é secundária à indução da TPM e não é motivada por estresse oxidativo. Materiais e métodos: As mitocôndrias foram isoladas a partir do coração de rato e avaliaram-se parâmetros relacionados com a indução da TPM (n=5 para cada indutor): entumescimento mitocondrial e oxidação dos grupos tiólicos proteicos (ambos por espectrofotometria). Resultados: Com Ca/Pi, o CV protegeu a mitocôndria da indução da TPM, nomeadamente na sua forma deletéria de alta condutância. Este efeito evidenciou-se pela diminuição do entumescimento mitocondrial. Este efeito foi simultâneo com a inibição da oxidação dos grupos tiólicos proteicos carmitocondriais (p<0.001). O CV não mostrou efeitos protectores com Ca/Catr. Conclusões: O CV protegeu a mitocôndria cardíaca da TPM, mas apenas quando a oxidação dos grupos tiólicos proteicos foi causa e não consequência da TPM. Estes resultados mostram claramente que, durante agressões ao miocárdio (durante a isquémia/reperfusão, por exemplo), o efeito protector do CV é primariamente devido a um efeito antioxidante, inibindo a produção e os efeitos das espécies reactivas de oxigénio.Objectives: The mitochondrial permeability transition (MPT) is an event related to severe oxidative stress (for example, during myocardial ischemia and reperfusion) and excessive mitochondrial calcium accumulation, also being implicated in cell death. In this study, we compared the effect of carvedilol on the cardiac MPT induced by calcium and phosphate (Ca/Pi) and calcium/carboxyatractyloside (Ca/Catr). Oxidative stress plays a major role in MPT induction by Ca/Pi, leading to the oxidation of protein thiol groups, in contrast with Ca/Catr, where such oxidation is secondary to MPT induction and is not caused by oxidative stress. Materials and methods: Mitochondria were isolated from rat hearts and parameters related to MPT induction were evaluated (n=5 for each inducer): mitochondrial swelling and oxidation of protein thiol groups (both measured by spectrophotometry). Results: Using Ca/Pi, carvedilol protected mitochondria from MPT induction, particularly in its high conductance form. Its effect was demonstrated by analyzing the decrease in mitochondrial swelling amplitude. Simultaneously, we observed inhibition of protein thiol group oxidation (p<0.001). By contrast, carvedilol did not show any protective effect with Ca/Catr. Conclusions: Carvedilol was only effective against the MPT when the oxidation of protein thiol groups was the cause and not the consequence of the MPT phenomenon. The results clearly show that during myocardial aggressions (ischemia and reperfusion, for example), the protective effect of carvedilol is primarily due to an antioxidant mechanism, inhibiting the production and effects of reactive oxygen species