Down-regulation of LPCAT expression increases platelet-activating factor level in cirrhotic rat liver: potential antiinflammatory effect of silybin

Cholestasis is one of the major causes of liver diseases. A chronic accumulation of toxic bile acids in the liver, which occurs in this condition, can induce fibrosis and cirrhosis. Inflammation is a fundamental component of acute and chronic cholestatic liver injury. Platelet-activating factor (PAF) is a proinflammatory lipid which may be generated by two independent pathways called the de novo and remodeling pathway being the last responsible for the synthesis of PAF during inflammation. In recent years a key role in PAF remodeling has been attributed to lysophosphatidylcholine acyltransferase (LPCAT) enzymes. Although the knowledge on their characteristic is growing, the exact mechanism of LPCAT in pathological conditions remains still unknown. Here, we reported that the level of lyso-PAF and PAF significantly increased in the liver of cirrhotic vs. control rats together with a significant decrease in both mRNA abundance and protein level of both LPCAT1 and LPCAT2. Acyltransferase activities of both LPCAT1 and LPCAT2 were parallel decreased in the liver of cirrhotic animals. Interestingly, treatment with silybin strongly decreased the level of both pro-inflammatory lipids and restored the activity and expression of both LPCAT1 and LPCAT2 of cirrhotic liver. Silybin effect was specific for LPCAT1 and LPCAT2 since it did not affect LPCAT3 mRNA abundance of cirrhotic liver.

Oxysterols and redox signaling in the pathogenesis of non-alcoholic fatty liver disease

Oxysterols are oxidized species of cholesterol coming from exogenous (e.g. dietary) and endogenous (in vivo) sources. They play critical roles in normal physiologic functions such as regulation of cellular cholesterol homeostasis. Most of biological effects are mediated by interaction with nuclear receptor LXRα, highly expressed in the liver as well as in many other tissues. Such interaction participates in the regulation of whole-body cholesterol metabolism, by acting as "lipid sensors". Moreover, it seems that oxysterols are also suspected to play key roles in several pathologies, including cardiovascular and inflammatory disease, cancer, and neurodegeneration. Growing evidence suggests that oxysterols may contribute to liver injury in non-alcoholic fatty liver disease. The present review focuses on the current status of knowledge on oxysterols' biological role, with an emphasis on LXR signaling and oxysterols' physiopathological relevance in NAFLD, suggesting new pharmacological development that needs to be addressed in the near future.

Many faces of mitochondrial uncoupling during age: damage or defense?

An increased mitochondrial proton leak occurs in aging, but the origin of such modification remains unclear. This study defined the cause of mitochondrial uncoupling in mitotic (liver) and postmitotic (heart) rat tissues during aging and its effects on energy homeostasis and free radical production. Proton leak in old heart mitochondria was dependent on uncoupling proteins' upregulation, whereas it was caused by alterations in the mitochondrial membrane composition in old liver. ATP homeostasis was impaired in both tissues from old animals and was associated to disrupted F0F1-ATPase activity. H2O2 production rate and 4-hydroxy-2-nonenalprotein adducts were higher in old liver mitochondria compared with young liver mitochondria, but they were similar in heart mitochondria from both groups. Moreover, key mitochondrial biogenesis regulators were upregulated in old liver but downregulated in old heart. In conclusion, uncoupling proteins mediate proton leak and avoid oxidative damage in heart, acting as a protective mechanism. This does not occur in liver, where ATP depletion and oxidative stress may stimulate mitochondrial biogenesis and eliminate damaged cells.

Sex hormones modulate circulating antioxidant enzymes: impact of estrogen therapy

OBJECTIVE

Ovarian senescence affects many tissues and produces a variety of symptoms and signs. We hypothesized that estrogens may also influence circulating redox balance by regulating activity of the cellular antioxidative enzyme system. We aimed to explore the impact of surgical estrogen deprivation and replacement (ERT) on the glutathione balance and antioxidant enzymes expression in fertile women.

STUDY DESIGN

Nineteen healthy premenopausal women who underwent total hysterectomy with bilateral salpingo-oophorectomy were evaluated at baseline, 30 days after surgery without ERT and 30 days after ERT. Redox balance was determined by measuring blood reduced (GSH) and oxidized (GSSG) glutathione, as well as the GSSG/GSH ratio. Antioxidant status was evaluated by measuring serum estrogen (E2) levels and mRNA expression of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST) in peripheral blood mononuclear cells.

RESULTS

Serum E2 significantly lowered after surgery, and increased in 12 out of 19 patients after 30 days of ERT (Responders). In such patients, an increase in oxidative stress was observed after surgery that resolved after ERT. Oxidative stress was sustained by reduction in the mRNA expression of both SOD and GSH-Px, that recovered after 30 days of therapy in responders. CAT and GST mRNA expression were not modified by surgery and replacement therapy.

CONCLUSIONS

Menopause is associated with significant change in antioxidant gene expression that in turn affects circulating redox state. Estrogens replacement therapy is able to prevent and counteract such modifications by acting as regulators of key antioxidant gene expression. These findings suggest that antioxidant genes are, almost in part, under the control of sex hormones, and that pathophysiology of the difference in gender disease may depend on the redox biology.

The impact of interferon lambda 3 gene polymorphism on natural course and treatment of hepatitis C

Host genetic factors may predict the outcome and treatment response in hepatitis C virus (HCV) infection. Very recently, three landmark genome-wide association studies identified single nucleotide polymorphisms near the interleukin 28B (IL28B) region which were more frequent in responders to treatment. IL28B encodes interferon (IFN)λ3, a type III IFN involved in host antiviral immunity. Favourable variants of the two most widely studied IL28B polymorphisms, rs12979860 and rs8099917, are strong pretreatment predictors of early viral clearance and sustained viral response in patients with genotype 1 HCV infection. Further investigations have implicated IL28B in the development of chronic HCV infection versus spontaneous resolution of acute infection and suggest that IL28B may be a key factor involved in host immunity against HCV. This paper presents an overview about the biological activity and clinical applications of IL28B, summarizing the available data on its impact on HCV infection. Moreover, the potential usefulness of IFNλ in the treatment and natural history of this disease is also discussed.

Glutamatergic alterations and mitochondrial impairment in a murine model of Alzheimer disease

Deficits in glutamate neurotransmission and mitochondrial functions were detected in the frontal cortex (FC) and hippopcampus (HIPP) of aged 3×Tg-Alzheimer's disease (AD) mice, compared with their wild type littermates (non-Tg). In particular, basal levels of glutamate and vesicular glutamate transporter 1 (VGLUT1) expression were reduced in both areas. Cortical glutamate release responded to K(+) stimulation, whereas no peak release was observed in the HIPP of mutant mice. Synaptosomal-associated protein 25 (SNAP-25), glutamate/aspartate transporter (GLAST), glutamate transporter 1 (GLT1) and excitatory amino acid carrier 1 (EAAC1) were reduced in HIPP homogenates, where the adenosine triphosphate (ATP) content was lower. In contrast, glutamate transporter 1 and glial fibrillary acidic protein (GFAP) were found to be higher in the frontal cortex. The respiration rates of complex-I, II, IV, and the membrane potential were reduced in cortical mitochondria, where unaltered proton leak, F(0)F(1)-ATPase activity and ATP content, with increased hydrogen peroxide production (H(2)O(2)), were also observed. In contrast, complex-I respiration rate was significantly increased in hippocampal mitochondria, together with increased proton leak and H(2)O(2) production. Moreover, loss of complex-IV and F(0)F(1)-ATPase activities were observed. These data suggest that impairments of mitochondrial bioenergetics might sustain the failure in the energy-requiring glutamatergic transmission.

Mitochondrial oxidative stress and respiratory chain dysfunction account for liver toxicity during amiodarone but not dronedarone administration

The role played by oxidative stress in amiodarone-induced mitochondrial toxicity is debated. Dronedarone shows pharmacological properties similar to those of amiodarone but several differences in terms of toxicity. In this study, we analyzed the effects of the two drugs on liver mitochondrial function by administering an equivalent human dose to a rat model. Amiodarone increased mitochondrial H(2)O(2) synthesis, which in turn induced cardiolipin peroxidation. Moreover, amiodarone inhibited Complex I activity and uncoupled oxidative phosphorylation, leading to a reduction in the hepatic ATP content. We also observed a modification of membrane phospholipid composition after amiodarone administration. N-acetylcysteine completely prevented such effects. Although dronedarone shares with amiodarone the capacity to induce uncoupling of oxidative phosphorylation, it did not show any of the oxidative effects and did not impair mitochondrial bioenergetics. Our data provide important insights into the mechanism of mitochondrial toxicity induced by amiodarone. These results may greatly influence the clinical application and toxicity management of these two antiarrhythmic drugs.

Mitochondrial biogenesis fails in secondary biliary cirrhosis in rats leading to mitochondrial DNA depletion and deletions

Chronic cholestasis is characterized by mitochondrial dysfunction, associated with loss of mitochondrial membrane potential, decreased activities of respiratory chain complexes, and ATP production. Our aim was to determine the molecular mechanisms that link long-term cholestasis to mitochondrial dysfunction. We studied a model of chronic cholestasis induced by bile duct ligation in rats. Key sensors and regulators of the energetic state and mitochondrial biogenesis, mitochondrial DNA (mtDNA)-to-nuclear DNA (nDNA) ratio (mtDNA/nDNA) relative copy number, mtDNA deletions, and indexes of apoptosis (BAX, BCL-2, and cleaved caspase 3) and cell proliferation (PCNA) were evaluated. Our results show that long-term cholestasis is associated with absence of activation of key sensors of the energetic state, evidenced by decreased SIRT1 and pyruvate dehydrogenase kinase levels and lack of AMPK activation. Key mitochondrial biogenesis regulators (PGC-1α and GABP-α) decreased and NRF-1 was not transcriptionally active. Mitochondrial transcription factor A (TFAM) protein levels increased transiently in liver mitochondria at 2 wk after bile duct ligation, but they dramatically decreased at 4 wk. Reduced TFAM levels at this stage were mirrored by a marked decrease (65%) in mtDNA/nDNA relative copy number. The blockade of mitochondrial biogenesis should not be ascribed to activation of apoptosis or inhibition of cell proliferation. Impaired mitochondrial turnover and loss of the DNA stabilizing effect of TFAM are likely the causative event involved in the genetic instability evidenced by accumulation of mtDNA deletions. In conclusion, the lack of stimulation of mitochondrial biogenesis leads to mtDNA severe depletion and deletions in long-term cholestasis. Hence, long-term cholestasis should be considered a secondary mitochondrial hepatopathy.

Mitochondrial dysfunction in nonalcoholic steatohepatitis

The pathogenesis of nonalcoholic steatohepatitis (NASH) is poorly understood and the mechanisms are still being elucidated. Mitochondrial dysfunction participates at different levels in NASH pathogenesis since it impairs fatty liver homeostasis and induces overproduction of free radicals that in turn trigger lipid peroxidation and cell death. In this article, we review the role of mitochondria in fat metabolism, energy homeostasis and reactive oxygen species production, with a focus on the role of mitochondrial impairment and uncoupling proteins in the pathophysiology of NASH progression. The potential effects of some molecules targeted to mitochondria are also discussed.

Oxidation of hepatic carnitine palmitoyl transferase-I (CPT-I) impairs fatty acid beta-oxidation in rats fed a methionine-choline deficient diet

There is growing evidence that mitochondrial dysfunction, and more specifically fatty acid β-oxidation impairment, is involved in the pathophysiology of non-alcoholic steatohepatitis (NASH). The goal of the present study was to achieve more understanding on the modification/s of carnitinepalmitoyltransferase-I (CPT-I), the rate-limiting enzyme of the mitochondrial fatty acid β-oxidation, during steatohepatitis. A high fat/methionine-choline deficient (MCD) diet, administered for 4 weeks, was used to induce NASH in rats.We demonstrated that CPT-I activity decreased, to the same extent, both in isolated liver mitochondria and in digitonin-permeabilized hepatocytes from MCD-diet fed rats.At the same time, the rate of total fatty acid oxidation to CO(2) and ketone bodies, measured in isolated hepatocytes, was significantly lowered in treated animals when compared to controls. Finally, an increase in CPT-I mRNA abundance and protein content, together with a high level of CPT-I protein oxidation was observed in treated rats. A posttranslational modification of rat CPT-I during steatohepatitis has been here discussed.

Principles and therapeutic relevance for targeting mitochondria in aging and neurodegenerative diseases

Aging is a physiologic state in which a progressive decline of organ functions may be accompanied by developing age-related diseases and neurodegenerative diseases. The causes of such conditions remain unknown, being probably related to a multifactor process. To date, the Free Radical and Mitochondrial theories seem to be the two most prominent that could explain both how and why aged people develop certain disorders, providing a rationale for treatment. Several reports demonstrate that mitochondria play a key role in aging and some neurodegenerative diseases. Damaged mitochondria produce increased amounts of Reactive Oxygen Species (ROS), leading, in turn, to progressive augmentation in damage. Dysfunctional mitochondria enhance susceptibility to cell death. Indeed, at cell level mitochondria act as an energetic hub determining cell final fate through caspase-dependent apoptosis. Thus, if aging results from oxidative stress, it may be corrected by environmental, nutritional and pharmacological strategies. In this review we summarize the role of mitochondria dysfunction occurring in aging and neurodegenerative disease, describing novel mitochondria-targeted therapy approach and the new selective molecules and nanocarriers technology as potentially effective in targeting mitochondrial dysfunction.

Oxidative stress and aging

The fountain of youth has always been a myth for mankind. Aging is a physiologic state in which a progressive decline of organ functions is accompanied with the development of age-related diseases. The causes of aging remain unknown, probably being related to a multifactorial process. To date, the free radical and mitochondrial theories seem to be the 2 most prominent theories on aging and have survived the test of time. Such theories claim that oxidative stress within mitochondria can lead to a vicious cycle in which damaged mitochondria produce increased amounts of reactive oxygen species, leading in turn to progressive augmentation in damage. If aging results from oxidative stress, it may be corrected by environmental, nutritional and pharmacological strategies. This review summarizes the role of free radicals and oxidative stress in developing aging in kidney and human pathologies.

A silybin-phospholipid complex prevents mitochondrial dysfunction in a rodent model of nonalcoholic steatohepatitis

Mitochondrial dysfunction and oxidative stress are determinant events in the pathogenesis of nonalcoholic steatohepatitis. Silybin has shown antioxidant, anti-inflammatory, and antifibrotic effects in chronic liver disease. We aimed to study the effect of the silybin-phospholipid complex (SILIPHOS) on liver redox balance and mitochondrial function in a dietary model of nonalcoholic steatohepatitis. To accomplish this, glutathione oxidation, mitochondrial oxygen uptake, proton leak, ATP homeostasis, and H(2)O(2) production rate were evaluated in isolated liver mitochondria from rats fed a methionine- and choline-deficient (MCD) diet and the MCD diet plus SILIPHOS for 7 and 14 weeks. Oxidative proteins, hydroxynonenal (HNE)- and malondialdehyde (MDA)-protein adducts, and mitochondrial membrane lipid composition were also measured. Treatment with SILIPHOS limited glutathione depletion and mitochondrial H(2)O(2) production. Moreover, SILIPHOS preserved mitochondrial bioenergetics and prevented mitochondrial proton leak and ATP reduction. Finally, SILIPHOS limited the formation of HNE- and MDA-protein adducts. In conclusion, SILIPHOS is effective in preventing severe oxidative stress and preserving hepatic mitochondrial bioenergetics in nonalcoholic steatohepatitis induced by the MCD diet. The modifications of mitochondrial membrane fatty acid composition induced by the MCD diet are partially prevented by SILIPHOS, conferring anti-inflammatory and antifibrotic effects. The increased vulnerability of lipid membranes to oxidative damage is limited by SILIPHOS through preserved mitochondrial function.

Targeting mitochondria: a new promising approach for the treatment of liver diseases

Mitochondrial dysfunction acts as a common pathogenetic mechanism in several acute and chronic liver diseases, such as Alcoholic and Non-Alcoholic Fatty Liver Disease (NAFLD), drug-induced steatohepatitis, viral hepatitis, biliary cirrhosis, hepatocellular carcinoma, ischemia/reperfusion injury and transplant rejection. In particular mitochondrial uncoupling,has been recently identified to play a determinant role in the pathogenesis of liver diseases by causing decrease of mitochondrial proton motive force and ATP depletion. Damaged mitochondria present defects in lipid homeostasis, bioenergetics impairment and overproduction of Reactive Oxygen Species (ROS), leading to lipid accumulation and oxidative stress. Dysfunctional and/or uncoupled mitochondria enhance the susceptibility of hepatocytes to cell death by necrosis, via ATP depletion, or by apoptosis, via membrane permeabilization. Thus, prevention of mitochondrial alterations promises to be an effective strategy for treatment of liver diseases. However, no therapy has proven to be absolutely effective, whereas those that are beneficial present several side effects. The present review summarizes the recent approaches in mitochondrial drug deliver systems and focuses on mitochondria-targeted molecules application in liver disease. New selective molecules and nanocarriers technology are also considered as potentially effective in the targeting of mitochondrial dysfunction in liver pathology.

Frailty syndrome is associated with altered circulating redox balance and increased markers of oxidative stress

Frailty syndrome (FS) is a condition described in aging and characterized by physical vulnerability to stress and lack of physiological reserve. In this study we aim to define whether circulating oxidative stress correlates to frailty in terms of glutathione balance and oxidative protein damage. In 62 elderly outpatients, classified as frail patients according to Fried's criteria, evaluation of reduced glutathione (GSH), oxidized glutathione (GSSG), tumor necrosis factor-alpha, malonaldehyde-(MDA) and 4-hydroxy-2,3-nonenal-(HNE) protein plasma adducts were performed. A significant increase in the GSSG was observed in patients with FS when compared to non-frail. No difference was shown in the GSH amount, suggesting a glutathione oxidation more than impairment of the synthesis. TNF-alpha, MDA- and HNE-adducts, were significantly higher in FS as compared to non-frail patients. A logistic regression model correlating FS with redox balance showed a close relationship between glutathione ratio (OR=1.8, 95% CI=1.2-2.5) and MDA adducts (OR=2.8, 95% CI=1.6-4.7) to frailty. Our findings show an association between oxidative imbalance and Frailty Syndrome. GSSG/GSH ratio and plasma protein adducts strongly predict the frailty conditions and seem to be reliable and easily measurable markers in the context of the multidimensional analysis of elderly patients.

Uncoupling protein-2 (UCP2) induces mitochondrial proton leak and increases susceptibility of non-alcoholic steatohepatitis (NASH) liver to ischaemia-reperfusion injury

BACKGROUND

The mechanisms of progression from fatty liver to steatohepatitis and cirrhosis are not well elucidated. Mitochondrial dysfunction represents a key factor in the progression of non-alcoholic steatohepatitis (NASH) as mitochondria are the main cellular site of fatty acid oxidation, ATP synthesis and reactive oxygen species (ROS) production.

AIMS

(1) To evaluate the role of the uncoupling protein 2 in controlling mitochondrial proton leak and ROS production in NASH rats and humans; and (2) to assess the acute liver damage induced by ischaemia-reperfusion in rats with NASH.

METHODS

Mitochondria were extracted from the livers of NASH humans and rats fed a methionine and choline deficient diet. Proton leak, H(2)O(2) synthesis, reduced glutathione/oxidised glutathione, 4-hydroxy-2-nonenal (HNE)-protein adducts, uncoupling protein-2 (UCP2) expression and ATP homeostasis were evaluated before and after ischaemia-reperfusion injury.

RESULTS

NASH mitochondria exhibited an increased rate of proton leak due to upregulation of UCP2. These results correlated with increased production of mitochondrial hydrogen peroxide and HNE-protein adducts, and decreased hepatic ATP content that was not dependent on mitochondrial ATPase dysfunction. The application of an ischaemia-reperfusion protocol to these livers strongly depleted hepatic ATP stores, significantly increased mitochondrial ROS production and impaired ATPase activity. Livers from patients with NASH exhibited UCP2 over-expression and mitochondrial oxidative stress.

CONCLUSIONS

Upregulation of UCP2 in human and rat NASH liver induces mitochondrial uncoupling, lowers the redox pressure on the mitochondrial respiratory chain and acts as a protective mechanism against damage progression but compromises the liver capacity to respond to additional acute energy demands, such as ischaemia-reperfusion. These findings suggest that UCP2-dependent mitochondria uncoupling is an important factor underlying events leading to NASH and cirrhosis.

Alterations of hepatic ATP homeostasis and respiratory chain during development of non-alcoholic steatohepatitis in a rodent model

BACKGROUND

Mitochondrial dysfunction is considered a key player in non-alcoholic steatohepatitis (NASH) but no data are available on the mitochondrial function and ATP homeostasis in the liver during NASH progression. In the present paper we evaluated the hepatic mitochondrial respiratory chain activity and ATP synthesis in a rodent model of NASH development.

MATERIALS AND METHODS

Male Wistar rats fed a High Fat/Methionine-Choline Deficient (MCD) diet to induce NASH or a control diet (SHAM), and sacrificed after 3, 7 and 11 weeks. The oxidative phosphorylation, the F(0)F(1)ATPase (ATP synthase) and the ATP content were assessed in liver mitochondria.

RESULTS

NASH mitochondria exhibited an increased rate of substrate oxidation at 3 weeks, which returned to below the normal level at 7 and 11 weeks, concomitantly with the coupling between the phosphorylation activity and the mitochondrial respiration (ADP/O). Uncoupling of NASH liver mitochondria did not allow the recovery of the maximal respiration rate at 7 and 11 weeks. The ATPase (ATP synthase) activity was similar in NASH and SHAM rats, but the mitochondrial ATP content was significantly lower in NASH livers.

CONCLUSIONS

The loss of hepatic ATP stores is not dependent on the F(0)F(1)-ATPase but resides in the respiratory chain. Dysfunction of both Complex I and II of the mitochondrial respiratory chain during NASH development implies a mitochondrial adaptive mechanism occurring in the early stages of NASH.

Mitochondrial involvement in non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is an increasing recognized condition that may progress to end-stage liver disease. There are consistent evidences that mitochondrial dysfunction plays a central role in NASH whatever its origin. Mitochondria are the key controller of fatty acids removal and this is part of an intensive gene program that modifies hepatocytes to counteract the excessive fat storage. Mitochondrial dysfunction participates at different levels in NASH pathogenesis since it impairs fatty liver homeostasis and induces overproduction of ROS that in turn trigger lipid peroxidation, cytokines release and cell death. In this review we briefly recall the role of mitochondria in fat metabolism and energy homeostasis and focus on the role of mitochondrial impairment and uncoupling proteins in the pathophysiology of NASH progression. We suggest that mitochondrial respiratory chain, UCP2 and redox balance cooperate in a common pathway that permits to set down the mitochondrial redox pressure, limits the risk of oxidative damage, and allows the maximal rate of fat removal. When the environmental conditions change and high energy supply occurs, hepatocytes are unable to replace their ATP store and steatosis progress to NASH and cirrhosis. The beneficial effects of some drugs on mitochondrial function are also discussed.

Bioenergetics in aging: mitochondrial proton leak in aging rat liver, kidney and heart

Aging is associated with a decline in performance in many organs and loss of physiological performance can be due to free radicals. Mitochondria are incompletely coupled: during oxidative phosphorylation some of the redox energy is dissipated as natural proton leak across the inner membrane. To verify whether proton leak occurs in mitochondria during aging, we measured the mitochondrial respiratory chain activity, membrane potential and proton leak in liver, kidneys and heart of young and old rats. Mitochondria from old rats showed normal rates of Complex I and Complex II respiration. However, they had a lower membrane potential compared to mitochondria from younger rats. In addition, they exhibited an increased rate of proton conductance which partially dissipated the mitochondrial membrane potential when the rate of electron transport was suppressed. This could compromise energy homeostasis in aging cells in conditions that require additional energy supply and could minimize oxidative damage to DNA.