Effects of 4-hydroxynonenal on mitochondrial 3-hydroxy-3-methylglutaryl (HMG-CoA) synthase

Astaxanthin Protects against Alcoholic Liver Injury via Regulating Mitochondrial Redox Balance and Calcium Homeostasis

Increasing evidence points to the critical role of calcium overload triggered by mitochondrial dysfunction in the development of alcoholic liver disease (ALD). As an important organelle for aerobic respiration with a double-layered membrane, mitochondria are pivotal targets of alcohol metabolism-mediated lipid peroxidation, wherein mitochondria-specific phospholipid cardiolipin oxidation to 4-hydroxynonenal (4-HNE) ultimately leads to mitochondrial integrity and function impairment. Therefore, it is absolutely essential to identify effective nutritional intervention targeting mitochondrial redox function for an alternative therapy of ALD, in order to compensate for the difficulty in achieving alcohol withdrawal due to addiction. In this study, we confirmed the significant advantages of astaxanthin (AX) against alcohol toxicity among various carotenoids via cell experiments and identified the potential in mitochondrion morphogenesis and calcium signaling pathway by bioinformatics analysis. The ALD model of Sprague-Dawley (SD) rats was also generated to investigate the effectiveness of AX on alcohol-induced liver injury, and the underlying mechanisms were further explored. AX intervention attenuated alcohol-induced oxidative stress and lipid peroxidation as well as mitochondrial dysfunction characterized by degenerative morphology changes and collapsed membrane potential. Also, AX reduced the production of 4-HNE by activating the Nrf2-ARE signaling pathway, which is closely associated with the redox balance of mitochondria. In addition, relieved mitochondrial Ca2+ accumulation caused by AX was observed both in vivo and in vitro. Furthermore, we revealed the structure-activity relationship of AX and mitochondrial membrane channel proteins MCU and VDAC1, implying potential acting targets. Altogether, our data indicated a new mechanism of AX intervention which protects against alcohol-induced liver injury through restoring redox balance and Ca2+ homeostasis in mitochondria, as well as provided novel insights into the development of AX as a therapeutic option for the management of ALD.

Electrophilic Aldehyde 4-Hydroxy-2-Nonenal Mediated Signaling and Mitochondrial Dysfunction

Reactive oxygen species (ROS), a by-product of aerobic life, are highly reactive molecules with unpaired electrons. The excess of ROS leads to oxidative stress, instigating the peroxidation of polyunsaturated fatty acids (PUFA) in the lipid membrane through a free radical chain reaction and the formation of the most bioactive aldehyde, known as 4-hydroxynonenal (4-HNE). 4-HNE functions as a signaling molecule and toxic product and acts mainly by forming covalent adducts with nucleophilic functional groups in proteins, nucleic acids, and lipids. The mitochondria have been implicated as a site for 4-HNE generation and adduction. Several studies clarified how 4-HNE affects the mitochondria's functions, including bioenergetics, calcium homeostasis, and mitochondrial dynamics. Our research group has shown that 4-HNE activates mitochondria apoptosis-inducing factor (AIFM2) translocation and facilitates apoptosis in mice and human heart tissue during anti-cancer treatment. Recently, we demonstrated that a deficiency of SOD2 in the conditional-specific cardiac knockout mouse increases ROS, and subsequent production of 4-HNE inside mitochondria leads to the adduction of several mitochondrial respiratory chain complex proteins. Moreover, we highlighted the physiological functions of HNE and discussed their relevance in human pathophysiology and current discoveries concerning 4-HNE effects on mitochondria.

High omega arachidonic acid/docosahexaenoic acid ratio induces mitochondrial dysfunction and altered lipid metabolism in human hepatoma cells

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a common cause of liver disease worldwide and is a growing epidemic. A high ratio of omega-6 fatty acids to omega-3 fatty acids in the diet has been implicated in the development of NAFLD. However, the inflicted cellular pathology remains unknown. A high ratio may promote lipogenic pathways and contribute to reactive oxygen species (ROS)-mediated damage, perhaps leading to mitochondrial dysfunction. Therefore, these parameters were investigated to understand their contribution to NAFLD development.

AIM

To examine the effect of increasing ratios of omega-6:3 fatty acids on mitochondrial function and lipid metabolism mediators.

METHODS

HepG2-derived VL-17A cells were treated with normal (1:1, 4:1) and high (15:1, 25:1) ratios of omega-6: omega-3 fatty acids [arachidonic acid (AA): docosahexaenoic acid (DHA)] at various time points. Mitochondrial activity and function were examined via MTT assay and Seahorse XF24 analyzer, respectively. Triglyceride accumulation was determined by using EnzyChrom™ and levels of ROS were measured by fluorescence intensity. Protein expression of the mediators of lipogenic, lipolytic and endocannabinoid pathways was assessed by Western blotting.

RESULTS

High AA:DHA ratio decreased mitochondrial activity (P < 0.01; up to 80%) and promoted intracellular triglyceride accumulation (P < 0.05; 40%-70%). Mechanistically, it altered the mediators of lipid metabolism; increased the expression of stearoyl-CoA desaturase (P < 0.05; 22%-35%), decreased the expression of peroxisome proliferator-activated receptor-alpha (P < 0.05; 30%-40%) and increased the expression of cannabinoid receptor 1 (P < 0.05; 31%). Furthermore, the high ratio increased ROS production (P < 0.01; 74%-115%) and reduced mitochondrial respiratory functions such as basal and maximal respiration, ATP production, spare respiratory capacity and proton leak (P < 0.01; 35%-68%).

CONCLUSION

High AA:DHA ratio induced triglyceride accumulation, increased oxidative stress and disrupted mitochondrial functions. Stimulation of lipogenic and steroidal transcription factors may partly mediate these effects and contribute to NAFLD development.

Effects of Prolonged Dietary Curcumin Exposure on Skeletal Muscle Biochemical and Functional Responses of Aged Male Rats

Oxidative stress resulting from decreased antioxidant protection and increased reactive oxygen and nitrogen species (RONS) production may contribute to muscle mass loss and dysfunction during aging. Curcumin is a phenolic compound shown to upregulate antioxidant defenses and directly quench RONS in vivo. This study determined the impact of prolonged dietary curcumin exposure on muscle mass and function of aged rats. Thirty-two-month-old male F344xBN rats were provided a diet with or without 0.2% curcumin for 4 months. The groups included: ad libitum control (CON; n = 18); 0.2% curcumin (CUR; n = 18); and pair-fed (PAIR; n = 18) rats. CUR rats showed lower food intake compared to CON, making PAIR a suitable comparison group. CUR rats displayed larger plantaris mass and force production (vs. PAIR). Nuclear fraction levels of nuclear factor erythroid-2 related-factor-2 were greater, and oxidative macromolecule damage was lower in CUR (vs. PAIR). There were no significant differences in measures of antioxidant status between any of the groups. No difference in any measure was observed between CUR and CON rats. Thus, consumption of curcumin coupled with reduced food intake imparted beneficial effects on aged skeletal muscle. The benefit of curcumin on aging skeletal muscle should be explored further.

Biological Activities, Health Benefits, and Therapeutic Properties of Avenanthramides: From Skin Protection to Prevention and Treatment of Cerebrovascular Diseases

Oat (Avena sativa) is a cereal known since antiquity as a useful grain with abundant nutritional and health benefits. It contains distinct molecular components with high antioxidant activity, such as tocopherols, tocotrienols, and flavanoids. In addition, it is a unique source of avenanthramides, phenolic amides containing anthranilic acid and hydroxycinnamic acid moieties, and endowed with major beneficial health properties because of their antioxidant, anti-inflammatory, and antiproliferative effects. In this review, we report on the biological activities of avenanthramides and their derivatives, including analogs produced in recombinant yeast, with a major focus on the therapeutic potential of these secondary metabolites in the treatment of aging-related human diseases. Moreover, we also present recent advances pointing to avenanthramides as interesting therapeutic candidates for the treatment of cerebral cavernous malformation (CCM) disease, a major cerebrovascular disorder affecting up to 0.5% of the human population. Finally, we highlight the potential of foodomics and redox proteomics approaches in outlining distinctive molecular pathways and redox protein modifications associated with avenanthramide bioactivities in promoting human health and contrasting the onset and progression of various pathologies. The paper is dedicated to the memory of Adelia Frison.

ALDH2 Inhibition Potentiates High Glucose Stress-Induced Injury in Cultured Cardiomyocytes

Aldehyde dehydrogenase (ALDH) gene superfamily consists of 19 isozymes. They are present in various organs and involved in metabolizing aldehydes that are biologically generated. For instance, ALDH2, a cardiac mitochondrial ALDH isozyme, is known to detoxify 4-hydroxy-2-nonenal, a reactive aldehyde produced upon lipid peroxidation in diabetic conditions. We hypothesized that inhibition of ALDH leads to the accumulation of unmetabolized 4HNE and consequently exacerbates injury in cells subjected to high glucose stress. H9C2 cardiomyocyte cell lines were pretreated with 10 μM disulfiram (DSF), an inhibitor of ALDH2 or vehicle (DMSO) for 2 hours, and then subjected to high glucose stress {33 mM D-glucose (HG) or 33 mM D-mannitol as an osmotic control (Ctrl)} for 24 hrs. The decrease in ALDH2 activity with DSF pretreatment was higher in HG group when compared to Ctrl group. Increased 4HNE adduct formation with DSF pretreatment was higher in HG group compared to Ctrl group. Pretreatment with DSF leads to potentiated HG-induced cell death in cultured H9C2 cardiomyocytes by lowering mitochondrial membrane potential. Our results indicate that ALDH2 activity is important in preventing high glucose induced cellular dysfunction.

Impaired ALDH2 activity decreases the mitochondrial respiration in H9C2 cardiomyocytes

Reactive oxygen species (ROS)-mediated reactive aldehydes induce cellular stress. In cardiovascular diseases such as ischemia-reperfusion injury, lipid-peroxidation derived reactive aldehydes such as 4-hydroxy-2-nonenal (4HNE) are known to contribute to the pathogenesis. 4HNE is involved in ROS formation, abnormal calcium handling and more importantly defective mitochondrial respiration. Aldehyde dehydrogenase (ALDH) superfamily contains NAD(P)(+)-dependent isozymes which can detoxify endogenous and exogenous aldehydes into non-toxic carboxylic acids. Therefore we hypothesize that 4HNE afflicts mitochondrial respiration and leads to cell death by impairing ALDH2 activity in cultured H9C2 cardiomyocyte cell lines. H9C2 cardiomyocytes were treated with 25, 50 and 75 μM 4HNE and its vehicle, ethanol as well as 25, 50 and 75 μM disulfiram (DSF), an inhibitor of ALDH2 and its vehicle (DMSO) for 4 h. 4HNE significantly decreased ALDH2 activity, ALDH2 protein levels, mitochondrial respiration and mitochondrial respiratory reserve capacity, and increased 4HNE adduct formation and cell death in cultured H9C2 cardiomyocytes. ALDH2 inhibition by DSF and ALDH2 siRNA attenuated ALDH2 activity besides reducing ALDH2 levels, mitochondrial respiration and mitochondrial respiratory reserve capacity and increased cell death. Our results indicate that ALDH2 impairment can lead to poor mitochondrial respiration and increased cell death in cultured H9C2 cardiomyocytes.

Keratin 8 absence down-regulates colonocyte HMGCS2 and modulates colonic ketogenesis and energy metabolism

Absence of colonic keratin 8 causes intestinal inflammation and decreased levels of the ketogenic enzyme HMGCS2. Upstream, the butyrate transporter MCT1 is decreased, leading to increased luminal butyrate. Ketogenic conditions fail to induce HMGCS2 in the keratin 8–knockout colon, suggesting a role for keratins in colonocyte energy homeostasis.

Simple-type epithelial keratins are intermediate filament proteins important for mechanical stability and stress protection. Keratin mutations predispose to human liver disorders, whereas their roles in intestinal diseases are unclear. Absence of keratin 8 (K8) in mice leads to colitis, decreased Na/Cl uptake, protein mistargeting, and longer crypts, suggesting that keratins contribute to intestinal homeostasis. We describe the rate-limiting enzyme of the ketogenic energy metabolism pathway, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), as a major down-regulated protein in the K8-knockout (K8^−/−) colon. K8 absence leads to decreased quantity and activity of HMGCS2, and the down-regulation is not dependent on the inflammatory state, since HMGCS2 is not decreased in dextran sulfate sodium-induced colitis. Peroxisome proliferator–activated receptor α, a transcriptional activator of HMGCS2, is similarly down-regulated. Ketogenic conditions—starvation or ketogenic diet—increase K8^+/+ HMGCS2, whereas this response is blunted in the K8^−/− colon. Microbiota-produced short-chain fatty acids (SCFAs), substrates in the colonic ketone body pathway, are increased in stool, which correlates with decreased levels of their main transporter, monocarboxylate transporter 1 (MCT1). Microbial populations, including the main SCFA-butyrate producers in the colon, were not altered in the K8^−/−. In summary, the regulation of the SCFA-MCT1-HMGCS2 axis is disrupted in K8^−/− colonocytes, suggesting a role for keratins in colonocyte energy metabolism and homeostasis.

Effect of N-acetylcysteine plus deferoxamine on oxidative stress and inflammation in dystrophic muscle cells

OBJECTIVES

Oxidative stress and inflammatory process play an important role in the pathogenesis of Duchenne muscular dystrophy (DMD). We investigated whether deferoxamine (DFX) improves the antioxidant effects of N-acetylcysteine (NAC) on primary cultures of dystrophic muscle cells from mdx mice, the experimental model of DMD.

METHODS

Primary cultures of skeletal muscle cells from mdx mice were treated with either NAC (10 mM), DFX (5 mM), or NAC plus DFX for 24 hours. The muscle cells of C57BL/10 mice were used as controls.

RESULTS

Production of hydrogen peroxide (H2O2) and levels of 4-hydroxynonenal (4-HNE), tumor necrosis factor alpha (TNF-α), and nuclear factor kappa-B (NF-κB) were significantly higher in mdx muscle cells than in C57BL/10 muscle cells. Treatment with NAC, DFX, or NAC plus DFX significantly decreased H2O2 production (24, 58, and 72%, respectively), and levels of 4-HNE-protein adducts (62, 33, and 71%, respectively), TNF-α (32, 29, and 31%, respectively), and NF-κB (34, 38, and 52%, respectively) on dystrophic muscle cells.

DISCUSSION

This study demonstrates that mdx muscle cells are able to produce key oxidative stress and inflammatory markers, without the interference of inflammatory cells, and shows that NAC plus DFX reduced the inflammatory and oxidative stress indicators, mainly H2O2 production and NF-κB levels by dystrophic fibers.

Proteomic analysis of 4-hydroxynonenal (4-HNE) modified proteins in liver mitochondria from chronic ethanol-fed rats

Chronic ethanol-mediated oxidative stress and lipid peroxidation increases the levels of various reactive lipid species including 4-hydroxynonenal (4-HNE), which can subsequently modify proteins in the liver. It has been proposed that 4-HNE modification adversely affects the structure and/or function of mitochondrial proteins, thereby impairing mitochondrial metabolism. To determine whether chronic ethanol consumption increases levels of 4-HNE modified proteins in mitochondria, male rats were fed control and ethanol-containing diets for 5 weeks and mitochondrial samples were analyzed using complementary proteomic methods. Five protein bands (approx. 35, 45, 50, 70, and 90kDa) showed strong immunoreactivity for 4-HNE modified proteins in liver mitochondria from control and ethanol-fed rats when proteins were separated by standard 1D SDS-PAGE. Using high-resolution proteomic methods (2D IEF/SDS-PAGE and BN-PAGE) we identified several mitochondrial proteins immunoreactive for 4-HNE, which included mitofilin, dimethylglycine dehydrogenase, choline dehydrogenase, electron transfer flavoprotein α, cytochrome c1, enoyl CoA hydratase, and cytochrome c. The electron transfer flavoprotein α consistently showed increased 4-HNE immunoreactivity in mitochondria from ethanol-fed rats as compared to mitochondria from the control group. Increased 4-HNE reactivity was also detected for dimethylglycine dehydrogenase, enoyl CoA hydratase, and cytochrome c in ethanol samples when mitochondria were analyzed by BN-PAGE. In summary, this work identifies new targets of 4-HNE modification in mitochondria and provides useful information needed to better understand the molecular mechanisms underpinning chronic ethanol-induced mitochondrial dysfunction and liver injury.

Regulation and therapeutic strategies of 4-hydroxy-2-nonenal metabolism in heart disease

4-Hydroxy-2-nonenal (4-HNE), a reactive aldehyde, is generated from polyunsaturated fatty acids (PUFAs) in biological membranes. Reactive oxygen species (ROS) generated during oxidative stress react with PUFAs to form aldehydes like 4-HNE, which inactivates proteins and DNA by forming hybrid covalent chemical addition compounds called adducts. The ensuing chain reaction results in cellular dysfunction and tissue damage. It includes a wide spectrum of events ranging from electron transport chain dysfunction to apoptosis. In addition, 4-HNE directly depresses contractile function, enhances ROS formation, modulates cell signaling pathways, and can contribute to many cardiovascular diseases, including atherosclerosis, myocardial ischemia-reperfusion injury, heart failure, and cardiomyopathy. Therefore, targeting 4-HNE could help reverse these pathologies. This review will focus on 4-HNE generation, the role of 4-HNE in cardiovascular diseases, cellular targets (especially mitochondria), processes and mechanisms for 4-HNE-induced toxicity, regulation of 4-HNE metabolism, and finally strategies for developing potential therapies for cardiovascular disease by attenuating 4-HNEinduced toxicity.

Overexpression of hydroxymethylglutaryl CoA synthase 2 and 2,4-dienoyl-CoA reductase in rat pancreas following chronic alcohol consumption

OBJECTIVES

The mechanism of alcohol-induced pancreatic damage is unclear. The aim of this study was to clarify the effects of chronic alcohol intake on the pancreatic proteome.

METHODS

Rats were fed an alcohol-containing Lieber-DeCarli liquid diet, and the pancreatic proteome was compared with that of pair-fed control rats using agarose 2-dimensional gel electrophoresis followed by liquid chromatography-tandem mass spectrometry.

RESULTS

The expression of 3 proteins was consistently altered in alcohol-fed rats: 1 protein was down-regulated, and 2 proteins were up-regulated. The 2 up-regulated proteins were identified as 2,4-dienoyl-CoA reductase and hydroxymethylglutaryl-CoA synthase (HMGCS2). The combined concentration of malondialdehyde and 4-hydroxyalkenals was significantly greater in alcohol-fed rats. It is noteworthy that the reactivity of anti-4-hydroxy-2-nonenal antibody was significantly higher toward HMGCS2 isolated from alcohol-fed rats. The activity of HMGCS2 was higher in alcohol-fed rats, but the relative increase in enzyme activity in alcohol-fed rats was less than the relative increase in HMGCS2 expression.

CONCLUSIONS

Chronic alcohol consumption results in distinct alterations in the expression of 3 pancreatic proteins. The reactivity of 4-hydroxy-2-nonenal toward one of the up-regulated proteins, HMGCS2, increased markedly following chronic alcohol intake, suggesting that up-regulation of HMGCS2 is connected with alterations of lipid peroxidation induced by alcohol.

Hepatic mitochondrial dysfunction induced by fatty acids and ethanol

Understanding the key aspects of the pathogenesis of alcoholic fatty liver disease particularly alterations to mitochondrial function remains to be resolved. The role of fatty acids in this regard requires further investigation due to their involvement in fatty liver disease and obesity. This study aimed to characterize the early effects of saturated and unsaturated fatty acids alone on liver mitochondrial function and during concomitant ethanol exposure using isolated liver mitochondria and VA-13 cells (Hep G2 cells that efficiently express alcohol dehydrogenase). Liver mitochondria or VA-13 cells were treated with increasing concentrations of palmitic or arachidonic acid (1 to 160 μM) for 24 h with or without 100 mM ethanol. The results showed that in isolated liver mitochondria both palmitic and arachidonic acids significantly reduced state 3 respiration in a concentration-dependent manner (P<0.001), implicating their ionophoric activities. Increased ROS production occurred in a dose-dependent manner especially in the presence of rotenone (complex I inhibitor), which was significantly more prominent in arachidonic acid at 80 μM (+970%, P<0.001) than palmitic acid (+40%, P<0.01). In VA-13 cells, ethanol alone and both fatty acids (40 μM) were able to decrease the mitochondrial membrane potential and cellular ATP levels and increase lipid formation. ROS production was significantly increased with arachidonic acid (+110%, P<0.001) exhibiting a greater effect than palmitic acid (+39%, P<0.05). While in the presence of ethanol, the drop in the mitochondrial membrane potential, cellular ATP levels, and increased lipid formation were further enhanced by both fatty acids, but with greater effect in the case of arachidonic acid, which also correlated with significant cytotoxicity (P<0.001). This study confirms the ability of fatty acids to promote mitochondrial injury in the development of alcoholic fatty liver disease.

N-acetylcysteine treatment reduces TNF-α levels and myonecrosis in diaphragm muscle of mdx mice

BACKGROUND & AIMS

Duchenne muscular dystrophy (DMD) is a genetic muscle disease caused by the absence of dystrophin. An established animal model of DMD is the mdx mouse, which is unable to express dystrophin. Inflammation, particularly the proinflammatory cytokine tumor necrosis factor alpha (TNF-α), strongly contributes to necrosis in the dystrophin-deficient fibers of the mdx mice and in DMD. In this study we investigated whether the antioxidant N-acetylcysteine (NAC) decreases TNF-α levels and protects the diaphragm muscle of mdx mice against necrosis.

METHODS

Mdx mice (14 days old) received daily intraperitoneal injections of NAC for 14 days, followed by removal of the diaphragm muscle. Control mdx mice were injected with saline.

RESULTS

NAC reduced TNF-α and 4-HNE-protein adducts levels, inflammation, creatine kinase levels, and myonecrosis in diaphragm muscle.

CONCLUSIONS

NAC may be used as a complementary treatment for dystrophinopathies. However, clinical trials are needed to determine the appropriate dose for patients with Duchenne muscular dystrophy.

Associations between functional polymorphisms in antioxidant defense genes and urinary oxidative stress biomarkers in healthy, premenopausal women

Functional polymorphisms in endogenous antioxidant defense genes including manganese superoxide dismutase (MnSOD), catalase (CAT), and glutathione peroxidase (GPX-1) have been linked with risk of cancer at multiple sites. Although it is presumed that these germline variants impact disease risk by altering the host's ability to detoxify mutagenic reactive oxygen species, very few studies have directly examined this hypothesis. Concentrations of 8-isoprostane F2α (8-iso-PGF2α) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxoxdG)-sensitive indicators of lipid peroxidation and DNA oxidation, respectively-were measured in 24-h urine samples obtained from 93 healthy, premenopausal women participating in a dietary intervention trial. In addition, DNA was extracted from blood for genotyping of MnSOD Val16Ala, CAT-262 C > T, and GPX1 Pro198Leu genotypes by Taqman assay. Although geometric mean concentrations of 8-iso-PGF2(α) and 8-oxoxdG varied across several study characteristics including race, education level, body mass index, and serum antioxidant levels, there was little evidence that these biomarkers differed across any of the examined genotypes. In summary, functional polymorphisms in endogenous antioxidant defense genes do not appear to be strongly associated with systemic oxidative stress levels in young, healthy women.

Nectarine promotes longevity in Drosophila melanogaster

Fruits containing high antioxidant capacities and other bioactivities are ideal for promoting longevity and health span. However, few fruits are known to improve the survival and health span in animals, let alone the underlying mechanisms. Here we investigate the effects of nectarine, a globally consumed fruit, on life span and health span in Drosophila melanogaster. Wild-type flies were fed standard, dietary restriction (DR), or high-fat diet supplemented with 0-4% nectarine extract. We measured life span, food intake, locomotor activity, fecundity, gene expression changes, and oxidative damage indicated by the level of 4-hydroxynonenal-protein adduct in these flies. We also measured life span, locomotor activity, and oxidative damage in sod1 mutant flies on the standard diet supplemented with 0-4% nectarine. Supplementation with 4% nectarine extended life span, increased fecundity, and decreased expression of some metabolic genes, including a key gluconeogenesis gene, PEPCK, and oxidative stress-response genes, including peroxiredoxins, in female wild-type flies fed the standard, DR, or high-fat diet. Nectarine reduced oxidative damage in wild-type females fed the high-fat diet. Moreover, nectarine improved the survival of and reduced oxidative damage in female sod1 mutant flies. Together, these findings suggest that nectarine promotes longevity and health span partly by modulating glucose metabolism and reducing oxidative damage.

Mitochondrial c-Jun N-terminal kinase (JNK) signaling initiates physiological changes resulting in amplification of reactive oxygen species generation

The JNK signaling cascade is critical for cellular responses to a variety of environmental and cellular stimuli. Although gene expression aspects of JNK signal transduction are well studied, there are minimal data on the physiological impact of JNK signaling. To bridge this gap, we investigated how JNK impacted physiology in HeLa cells. We observed that inhibition of JNK activity and JNK silencing with siRNA reduced the level of reactive oxygen species (ROS) generated during anisomycin-induced stress in HeLa cells. Silencing p38 had no significant impact on ROS generation under anisomycin stress. Moreover, JNK signaling mediated amplification of ROS production during stress. Mitochondrial superoxide production was shown to be the source of JNK-induced ROS amplification, as an NADPH oxidase inhibitor demonstrated little impact on JNK-mediated ROS generation. Using mitochondrial isolation from JNK null fibroblasts and targeting the mitochondrial scaffold of JNK, Sab, we demonstrated that mitochondrial JNK signaling was responsible for mitochondrial superoxide amplification. These results suggest that cellular stress altered mitochondria, causing JNK to translocate to the mitochondria and amplify up to 80% of the ROS generated largely by Complex I. This work demonstrates that a sequence of events exist for JNK mitochondrial signaling whereby ROS activates JNK, thereby affecting mitochondrial physiology, which can have effects on cell survival and death.

A mass spectrometric analysis of 4-hydroxy-2-(E)-nonenal modification of cytochrome c

Cytochrome c is a key mitochondrial respiratory protein that is particularly susceptible to modification during oxidative stress. The nature of this susceptibility is linked to the mitochondrial membrane being rich in esterified linoleic acid, which predisposes this organelle to the formation of lipid peroxidation products such as 4-hydroxy-2-(E)-nonenal (4-HNE). To better understand the nature of cytochrome c modification by 4-HNE, we initiated an in vitro study utilizing a combination of MALDI-TOF mass spectrometry, LC-ESI-MS/MS and isotope labeling to monitor 4-HNE modification of cytochrome c under various conditions. The overwhelming reaction observed is Michael addition by Lys side-chains in addition to the modification of His 33. While the Lys-4-HNE adducts were generally observed to be reversible, the 4-HNE-His 33 was observed to be stable with half of the formed adduct surviving the denaturation and proteolysis protocols used to generate proteolytic peptides for LC-ESI-MS/MS.

Acetoacetate as regulator of palmitic acid-induced uncoupling involving liver mitochondrial ADP/ATP antiporter and aspartate/glutamate antiporter

The effect of acetoacetate on palmitate-induced uncoupling with the involvement of ADP/ATP antiporter and aspartate/glutamate antiporter has been studied in liver mitochondria. The incubation of mitochondria with acetoacetate during succinate oxidation in the presence of rotenone, oligomycin, and EGTA suppresses the accumulation of conjugated dienes. This is considered as a display of antioxidant effect of acetoacetate. Under these conditions, acetoacetate does not influence the respiration of mitochondria in the absence or presence of palmitate but eliminates the ability of carboxyatractylate or aspartate separately to suppress the uncoupling effect of this fatty acid. The action of acetoacetate is eliminated by beta-hydroxybutyrate or thiourea, but not by the antioxidant Trolox. In the absence of acetoacetate, the palmitate-induced uncoupling is limited by a stage sensitive to carboxyatractylate (ADP/ATP antiporter) or aspartate (aspartate/glutamate antiporter); in its presence, it is limited by a stage insensitive to the effect of these agents. In the presence of Trolox, ADP suppresses the uncoupling action of palmitate to the same degree as carboxyatractylate. Under these conditions, acetoacetate eliminates the recoupling effects of ADP and aspartate, including their joint action. This effect of acetoacetate is eliminated by beta-hydroxybutyrate or thiourea. It is supposed that the stimulating effect of acetoacetate is caused both by increase in the rate of transfer of fatty acid anion from the inner monolayer of the membrane to the outer one, which involves the ADP/ATP antiporter and aspartate/glutamate antiporter, and by elimination of the ability of ADP to inhibit this transport. Under conditions of excessive production of reactive oxygen species in mitochondria at a high membrane potential and in the presence of small amounts of fatty acids, such effect of acetoacetate can be considered as one of the mechanisms of antioxidant protection.

Olive leaf extract prevents spontaneous occurrence of non-alcoholic steatohepatitis in SHR/NDmcr-cp rats

AIMS

Oxidative stress may play an important role in the pathogenesis of non-alcoholic steatohepatitis (NASH). Oleuropein, the active constituent of olive leaf, possesses anti-oxidant, hypoglycaemic, and hypolipidaemic activities. We aimed to investigate the preventive effects of olive leaf extract on hepatic fat accumulation in a rat model of NASH.

METHODS

Spontaneously hypertensive/NIH-corpulent rats were fed a diet of AIN-93G with or without olive leaf extract (500, 1000, 2000 mg/kg diet, and control; 5 rats each) for 23 weeks. Serological and histopathological findings, anti-oxidative activity, and the alteration of fatty acid synthesis in the liver were evaluated.

RESULTS

Histopathologically, a diet of AIN-93G containing more than 1000 mg/kg olive leaf extract had a preventive effect for the occurrence of NASH. Thioredoxin-1 expression in the liver was more evident in rats fed this diet, and 4-hydroxynonenal expression in the liver was less evident in these rats. There were no significant differences in the activities of hepatic carnitine palmitoyltransferase, fatty acid synthase, malic enzyme, and phosphatidic acid phosphohydrolase among the groups.

CONCLUSIONS

Our data suggest that olive leaf extract may help prevent NASH, presumably through its anti-oxidative activity.

Formation of gamma-ketoaldehyde-protein adducts during ethanol-induced liver injury in mice

Ethanol metabolism promotes the formation of a variety of reactive aldehydes in the liver. These aldehydes can rapidly form covalent protein adducts. Accumulating evidence indicates that these protein adducts may contribute to ethanol-mediated liver injury. Overproduction of gamma-ketoaldehydes, levuglandins (LGs) and isolevuglandins, is implicated in the pathogenesis of several chronic inflammatory diseases. gamma-Ketoaldehydes can form protein adducts orders of magnitude more quickly than 4-hydroxynonenal (4-HNE) or malondialdehyde. We hypothesized that ethanol-induced oxidative stress in vivo results in overproduction of LGE(2)- and iso[4]LGE(2)-protein adducts in mouse liver. Female C57BL/6 mice were allowed free access to an ethanol-containing diet for up to 39 days or pair-fed control diets. Pathological markers of ethanol-induced hepatic injury including serum alanine aminotransferase, hepatic triglyceride, and CYP2E1 were elevated in response to ethanol feeding. Ethanol-induced formation of iso[4]LGE(2)-, LGE(2)-, and 4-HNE-protein adducts in mouse liver was dependent on both dose and duration of ethanol feeding. Deficiency of cyclooxygenase 1 or 2 did not prevent ethanol-induced iso[4]LGE(2) or LGE(2) adducts in the liver, but adduct formation was reduced in both TNFR1- and CYP2E1-deficient mice. In summary, ethanol feeding enhanced gamma-ketoaldehyde-protein adduct production via a TNFR1/CYP2E1-dependent, but cyclooxygenase-independent, mechanism in mouse liver.

Mitochondrial protein thiol modifications in acetaminophen hepatotoxicity: effect on HMG-CoA synthase

Acetaminophen (APAP) overdose is the leading cause of drug related liver failure in many countries. N-acetyl-p-benzoquinone imine (NAPQI) is a reactive metabolite that is formed by the metabolism of APAP. NAPQI preferentially binds to glutathione and then cellular proteins. NAPQI binding is considered an upstream event in the pathophysiology, especially when binding to mitochondrial proteins and therefore leads to mitochondrial toxicity. APAP caused a significant increase in liver toxicity 3h post-APAP administration as measured by increased serum alanine aminotransferase (ALT) levels. Using high-resolution mitochondrial proteomics techniques to measure thiol and protein changes, no significant change in global thiol levels was observed. However, 3-hydroxy-3-methylglutaryl coenzyme A synthase 2 (HMG-CoA synthase) had significantly decreased levels of reduced thiols and activity after APAP treatment. HMG-CoA synthase is a key regulatory enzyme in ketogenesis and possesses a number of critical cysteines in the active site. Similarly, catalase, a key enzyme in hydrogen peroxide metabolism, also showed modification in protein thiol content. These data indicate post-translational modifications of a few selected proteins involved in mitochondrial and cellular regulation of metabolism during liver toxicity after APAP overdose. The pathophysiological relevance of these limited changes in protein thiols remains to be investigated.