Role of oxidative stress in alcohol-induced liver injury

Concerted action of sulfiredoxin and peroxiredoxin I protects against alcohol-induced oxidative injury in mouse liver

Peroxiredoxins (Prxs) are peroxidases that catalyze the reduction of reactive oxygen species (ROS). The active site cysteine residue of members of the 2-Cys Prx subgroup (Prx I to IV) of Prxs is hyperoxidized to cysteine sulfinic acid (Cys-SO(2) ) during catalysis with concomitant loss of peroxidase activity. Reactivation of the hyperoxidized Prx is catalyzed by sulfiredoxin (Srx). Ethanol consumption induces the accumulation of cytochrome P450 2E1 (CYP2E1), a major contributor to ethanol-induced ROS production in the liver. We now show that chronic ethanol feeding markedly increased the expression of Srx in the liver of mice in a largely Nrf2-dependent manner. Among Prx I to IV, only Prx I was found to be hyperoxidized in the liver of ethanol-fed wildtype mice, and the level of Prx I-SO(2) increased to ≈30% to 50% of total Prx I in the liver of ethanol-fed Srx(-/-) mice. This result suggests that Prx I is the most active 2-Cys Prx in elimination of ROS from the liver of ethanol-fed mice and that, despite the up-regulation of Srx expression by ethanol, the capacity of Srx is not sufficient to counteract the hyperoxidation of Prx I that occurs during ROS reduction. A protease protection assay revealed that a large fraction of Prx I is located together with CYP2E1 at the cytosolic side of the endoplasmic reticulum membrane. The selective role of Prx I in ROS removal is thus likely attributable to the proximity of Prx I and CYP2E1.

CONCLUSION

The pivotal functions of Srx and Prx I in protection of the liver in ethanol-fed mice was evident from the severe oxidative damage observed in mice lacking either Srx or Prx I.

Management of alcoholic liver disease: an update

Treatment of alcoholic liver disease is for the most part based on the stage of the disease and the pathogenic event that is being targeted. The primary treatment modalities that are considered in the treatment of alcoholic liver disease include abstinence, agents that suppress inflammation, anticytokine therapy, nutritional support, modifiers of alcohol metabolism, anti-oxidants, and inhibitors of hepatic fibrosis. Future therapeutic options include exploration of new pathways such as the patatin-like phospholipase domain containing 3 protein (PNPLA-3).

Investigating the pathobiology of alcoholic pancreatitis

Alcohol abuse is one of the most common causes of pancreatitis. The risk of developing alcohol-induced pancreatitis is related to the amount and duration of drinking. However, only a small portion of heavy drinkers develop disease, indicating that other factors (genetic, environmental, or dietary) contribute to disease initiation. Epidemiologic studies suggest roles for cigarette smoking and dietary factors in the development of alcoholic pancreatitis. The mechanisms underlying alcoholic pancreatitis are starting to be understood. Studies from animal models reveal that alcohol sensitizes the pancreas to key pathobiologic processes that are involved in pancreatitis. Current studies are focussed on the mechanisms responsible for the sensitizing effect of alcohol; recent findings reveal disordering of key cellular organelles including endoplasmic reticulum, mitochondria, and lysosomes. As our understanding of alcohol's effects continue to advance to the level of molecular mechanisms, insights into potential therapeutic strategies will emerge providing opportunities for clinical benefit.

Animal products, diseases and drugs: a plea for better integration between agricultural sciences, human nutrition and human pharmacology

Eicosanoids are major players in the pathogenesis of several common diseases, with either overproduction or imbalance (e.g. between thromboxanes and prostacyclins) often leading to worsening of disease symptoms. Both the total rate of eicosanoid production and the balance between eicosanoids with opposite effects are strongly dependent on dietary factors, such as the daily intakes of various eicosanoid precursor fatty acids, and also on the intakes of several antioxidant nutrients including selenium and sulphur amino acids. Even though the underlying biochemical mechanisms have been thoroughly studied for more than 30 years, neither the agricultural sector nor medical practitioners have shown much interest in making practical use of the abundant high-quality research data now available. In this article, we discuss some specific examples of the interactions between diet and drugs in the pathogenesis and therapy of various common diseases. We also discuss, using common pain conditions and cancer as specific examples, how a better integration between agricultural science, nutrition and pharmacology could lead to improved treatment for important diseases (with improved overall therapeutic effect at the same time as negative side effects and therapy costs can be strongly reduced). It is shown how an unnaturally high omega-6/omega-3 fatty acid concentration ratio in meat, offal and eggs (because the omega-6/omega-3 ratio of the animal diet is unnaturally high) directly leads to exacerbation of pain conditions, cardiovascular disease and probably most cancers. It should be technologically easy and fairly inexpensive to produce poultry and pork meat with much more long-chain omega-3 fatty acids and less arachidonic acid than now, at the same time as they could also have a similar selenium concentration as is common in marine fish. The health economic benefits of such products for society as a whole must be expected vastly to outweigh the direct costs for the farming sector.

Epimorphin protects hepatocytes from oxidative stress by inhibiting mitochondrial injury

BACKGROUND AND AIMS

Many investigations have demonstrated that cell injuries caused by generation of reactive oxygen species (ROS) is a common mechanism of various hepatic disorders. Recently, we have demonstrated that epimorphin, originally cloned as a mesenchymal protein, protects cultured intestinal epithelial cells from ROS. We therefore examine whether epimorphin protects primary cultured hepatocytes from ROS-induced cell injury.

METHODS

We explored the cell viability and the intracellular ROS levels of purified murine hepatocytes after exposure to 0.5 mM H(2)O(2) with or without pretreatment of epimorphin. Then, we observed mitochondrial permeability transition (MPT) and depolarization using confocal microscopy to make clear the mechanism that epimorphin inhibited cell injuries after exposure to H(2)O(2). In addition, to clarify the signaling pathways related to cell survival, we carried out Western blotting analysis with phosphorylated stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) polyclonal antibody to evaluate the inhibition of JNK by epimorphin. Finally, we evaluated the cell viability in hepatocytes administered JNK inhibitor.

RESULTS

Epimorphin protected primary cultured hepatocytes from H(2)O(2)-induced cell injuries independent of intracellular ROS levels. Epimorphin also inhibited onset of MPT, depolarization of the mitochondrial membrane potential, and eventually cell killing. The cell protective function of epimorphin after exposure to H(2)O(2) was not dependent on Akt signaling but on JNK signaling.

CONCLUSION

Epimorphin can protect hepatocytes from MPT-dependent cell injury induced by ROS. Since hepatic disorders could be caused by MPT-dependent cell injuries with excessive ROS, epimorphin might open a new therapeutic avenue for hepatic disorders.

Acetaldehyde adducts in alcoholic liver disease

Chronic alcohol abuse causes liver disease that progresses from simple steatosis through stages of steatohepatitis, fibrosis, cirrhosis, and eventually hepatic failure. In addition, chronic alcoholic liver disease (ALD), with or without cirrhosis, increases risk for hepatocellular carcinoma (HCC). Acetaldehyde, a major toxic metabolite, is one of the principal culprits mediating fibrogenic and mutagenic effects of alcohol in the liver. Mechanistically, acetaldehyde promotes adduct formation, leading to functional impairments of key proteins, including enzymes, as well as DNA damage, which promotes mutagenesis. Why certain individuals who heavily abuse alcohol, develop HCC (7.2-15%) versus cirrhosis (15-20%) is not known, but genetics and co-existing viral infection are considered pathogenic factors. Moreover, adverse effects of acetaldehyde on the cardiovascular system and hematologic systems leading to ischemia, heart failure, and coagulation disorders, can exacerbate hepatic injury and increase risk for liver failure. Herein, we review the role of acetaldehyde adducts in the pathogenesis of chronic ALD and HCC.

Cellular and mitochondrial effects of alcohol consumption

Alcohol dependence is correlated with a wide spectrum of medical, psychological, behavioral, and social problems. Acute alcohol abuse causes damage to and functional impairment of several organs affecting protein, carbohydrate, and fat metabolism. Mitochondria participate with the conversion of acetaldehyde into acetate and the generation of increased amounts of NADH. Prenatal exposure to ethanol during fetal development induces a wide spectrum of adverse effects in offspring, such as neurologic abnormalities and pre- and post-natal growth retardation. Antioxidant effects have been described due to that alcoholic beverages contain different compounds, such as polyphenols as well as resveratrol. This review analyzes diverse topics on the alcohol consumption effects in several human organs and demonstrates the direct participation of mitochondria as potential target of compounds that can be used to prevent therapies for alcohol abusers.

Ethanol induction of CYP2A5: permissive role for CYP2E1

CYP2A5 metabolizes xenobiotics and activates hepatocarcinogens, and induction occurs in response to hepatic damage and cellular stress. We evaluated whether ethanol can elevate CYP2A5 and whether CYP2E1 plays a role in the ethanol induction of CYP2A5. Wild-type (WT), CYP2E1 knockout (KO), and CYP2E1 knockin (KI) mice were fed ethanol for 3 weeks. Ethanol increased CYP2E1 and CYP2A5 protein and activity in WT mice but not in the KO mice. Induction of CYP2A5 (and CYP2E1) was restored in the KI mice. Ethanol induction of CYP2A5 occurred only after CYP2E1 was first induced. Immunohistochemical staining revealed that CYP2E1 and CYP2A5 colocalize to the same zones in the liver. Ethanol also elevated CYP2A5 mRNA levels in WT and KI mice but not in KO mice. Induction of CYP2A5 by cadmium was partially decreased in KO mice compared with WT or KI mice. Ethanol elevated CYP2A4 mRNA levels in all mice although the extent of induction was lowest in the KO mice. In summary, ethanol elevated mouse hepatic CYP2A5 levels, which may be of toxicological significance because CYP2A5 metabolizes nicotine and other drugs and activates hepatocarcinogens. Induction of CYP2A5 by ethanol is potentiated by the induction of CYP2E1. We speculate that ethanol induction of CYP2E1 followed by increases in reactive oxygen species and activation of Nrf2 are important steps in the mechanism by which ethanol induces CYP2A5. The possibility that induction of CYP2E1 is permissive for the induction of CYP2A5 may reflect a new contribution by CYP2E1 to the actions of ethanol.

Cell-based assay to quantify the antioxidant effect of food-derived carotenoids enriched in postprandial human chylomicrons

We developed a new method to evaluate the antioxidant effect of food products in a biological system. The antioxidant status of HepG2 cells was quantified after incubation with postprandial human chylomicrons after the intake of vegetable products. Three subjects consumed in a meal a vegetable soup containing 8.4 mg of β-carotene and 9 mg of lycopene. After 5 h, the subjects consumed a second meal without carotenoids. Blood samples were collected at basal time and every hour for 9 h. Chylomicrons were isolated from serum samples and used for both carotenoid quantification and HepG2 stimulation. Carotenoid in chylomicrons followed an inter-individual and bimodal carotenoid response. We demonstrated the antioxidant effect of postprandial chylomicrons in HepG2 at the time of maximum carotenoid concentration of chylomicrons with respect to basal time. This cell-based assay seems to be a useful method to evaluate the antioxidant effect of fruit and vegetable products in a biological system.

CYP2E1 enhances ethanol-induced lipid accumulation but impairs autophagy in HepG2 E47 cells

The regulation and function of autophagy and lipid metabolism have recently been reported to be reciprocally related. Macroautophagy mediates the breakdown of lipids stored in lipid droplets. An inhibition of autophagy leads to the development of a fatty liver. We evaluated the ability of CYP2E1 to modulate the effects of ethanol on lipid accumulation and autophagy in vitro. The E47 HepG2 cell which expresses CYP2E1 was treated with ethanol at 50, 100 and 150mM for 4 or 5days. Ethanol-induced lipid accumulation and an increase of triglycerides (TG) in E47 cells to a greater extent than in control C34 cells which do not express CYP2E1. In contrast, autophagy (LC3 II/LC3 I ratio) was significantly induced by ethanol in C34 cells to a greater extent than in E47 cells. P62 was significantly increased in E47 cells after ethanol treatment. Thus, there is a reciprocal relationship between the effects of ethanol on lipid accumulation and autophagy in the CYP2E1-expressing cells. Inhibition of autophagy by 3-methyladenine (3MA), increased lipid accumulation and TG levels in C34 cells which display elevated autophagy, but enhanced lipid accumulation and TG level to a lesser extent in E47 cells which displayed lower autophagy. Ethanol induced CYP2E1 activity and oxidative stress in E47 cells compared with C34 cells. These experiments suggest that the expression of CYP2E1 may impair autophagy formation which contributes to lipid accumulation in the liver. We hypothesize that CYP2E1-induced oxidative stress promotes the accumulation of lipid droplets by ethanol and this may be responsible for the suppression of autophagy in the liver.

Bimodal targeting of microsomal cytochrome P450s to mitochondria: implications in drug metabolism and toxicity

IMPORTANCE OF THE FIELD

Microsomal CYPs are critical for drug metabolism and toxicity. Recent studies show that these CYPs are also present in the mitochondrial compartment of human and rodent tissues. Mitochondrial CYP1A1 and 2E1 show both overlapping and distinct metabolic activities compared to microsomal forms. Mitochondrial CYP2E1 also induces oxidative stress. The mechanisms of mitochondria targeting of CYPs and their role in drug metabolism and toxicity are important factors to consider while determining the drug dose and in drug development.

AREAS COVERED IN THIS REVIEW

This review highlights the mechanisms of bimodal targeting of CYP1A1, 2B1, 2E1 and 2D6 to mitochondria and microsomes. The review also discusses differences in structure and function of mitochondrial CYPs.

WHAT THE READERS WILL GAIN

A comprehensive review of the literature on drug metabolism in the mitochondrial compartment and their potential for inducing mitochondrial dysfunction.

TAKE HOME MESSAGE

Studies on the biochemistry, pharmacology and pharmacogenetic analysis of CYPs are mostly focused on the molecular forms associated with the microsomal membrane. However, the mitochondrial CYPs in some individuals can represent a substantial part of the tissue pool and contribute in a significant way to drug metabolism, clearance and toxicity.

Aldehyde dehydrogenase 3B1 (ALDH3B1): immunohistochemical tissue distribution and cellular-specific localization in normal and cancerous human tissues

Aldehyde dehydrogenase (ALDH) enzymes are critical in the detoxification of endogenous and exogenous aldehydes. Our previous findings indicate that the ALDH3B1 enzyme is expressed in several mouse tissues and is catalytically active toward aldehydes derived from lipid peroxidation, suggesting a potential role against oxidative stress. The aim of this study was to elucidate by immunohistochemistry the tissue, cellular, and subcellular distribution of ALDH3B1 in normal human tissues and in tumors of human lung, colon, breast, and ovary. Our results indicate that ALDH3B1 is expressed in a tissue-specific manner and in a limited number of cell types, including hepatocytes, proximal convoluted tubule cells, cerebellar astrocytes, bronchiole ciliated cells, testis efferent ductule ciliated cells, and histiocytes. ALDH3B1 expression was upregulated in a high percentage of human tumors (lung > breast = ovarian > colon). Increased ALDH3B1 expression in tumor cells may confer a growth advantage or be the result of an induction mechanism mediated by increased oxidative stress. Subcellular localization of ALDH3B1 was predominantly cytosolic in tissues, with the exception of normal human lung and testis, in which localization appeared membrane-bound or membrane-associated. The specificity of ALDH3B1 distribution may prove to be directly related to the functional role of this enzyme in human tissues.

Macroautophagy and chaperone-mediated autophagy are required for hepatocyte resistance to oxidant stress

The function of the lysosomal degradative pathway of autophagy in cellular injury is unclear, because findings in nonhepatic cells have implicated autophagy as both a mediator of cell death and as a survival response. Autophagic function is impaired in steatotic and aged hepatocytes, suggesting that in these settings hepatocellular injury may be altered by the decrease in autophagy. To delineate the specific function of autophagy in the hepatocyte injury response, the effects of menadione-induced oxidative stress were examined in the RALA255-10G rat hepatocyte line when macroautophagy was inhibited by a short hairpin RNA (shRNA)-mediated knockdown of the autophagy gene atg5. Loss of macroautophagy sensitized cells to apoptotic and necrotic death from normally nontoxic concentrations of menadione. Loss of macroautophagy led to overactivation of the c-Jun N-terminal kinase (JNK)/c-Jun signaling pathway that induced cell death. Death occurred from activation of the mitochondrial death pathway with cellular adenosine triphosphate (ATP) depletion, mitochondrial cytochrome c release, and caspase activation. Sensitization to death from menadione occurred despite up-regulation of other forms of autophagy in compensation for the loss of macroautophagy. Chaperone-mediated autophagy (CMA) also mediated resistance to menadione. CMA inhibition sensitized cells to death from menadione through a mechanism different from that of a loss of macroautophagy, because death occurred in the absence of JNK/c-Jun overactivation or ATP depletion.

CONCLUSION

Hepatocyte resistance to injury from menadione-induced oxidative stress is mediated by distinct functions of both macroautophagy and CMA, indicating that impaired function of either form of autophagy may promote oxidant-induced liver injury.

Nrf2-Keap1 antioxidant system and hepatic diseases

NF-E2-related factor 2 (Nrf2) is an important transcription factor. When oxidative stress occurs, Nrf2 dissociates from Keap1 (Kelch-like ECH-associating protein 1), translocates to the nucleus, and regulates the expression of genes encoding phase II detoxifying enzymes and antioxidant proteins, thereby increasing the resistance to oxidative stress and electrophilic agents. Reactive oxygen species and oxidative stress play an important role in the development of hepatic diseases. In this article, we will summarize the relationship between the Nrf2-Keap1 system and hepatic diseases.

Effects of blueberry on hepatic fibrosis and transcription factor Nrf2 in rats

AIM: To investigate the effects of blueberry on hepatic fibrosis and NF-E2-related factor 2 (Nrf2) transcription factor in rats.

METHODS: Forty-five male Sprague-Dawley rats were randomly divided into control group (A); CCl₄-induced hepatic fibrosis group (B); blueberry prevention group (C); Dan-shao-hua-xian capsule (DSHX) prevention group (D); and blueberry + DSHX prevention group (E). Liver fibrosis was induced in rats by subcutaneous injection of CCl₄ and a high-lipid/low-protein diet for 8 wk (except the control group). The level of hyaluronic acid (HA) and alanine aminotransferase (ALT) in serum was examined. The activity of superoxide dismutase (SOD), glutathione-S-transferase (GST) and malondialdehyde (MDA) in liver homogenates was determined. The degree of hepatic fibrosis was evaluated by hematoxylin and eosin and Masson staining. Expression of Nrf2 and NADPH quinone oxidoreductase 1 (Nqo1) was detected by real-time reversed transcribed-polymerase chain reaction, immunohistochemical techniques, and western blotting.

RESULTS: Compared with group B, liver indices, levels of serum HA and ALT of groups C, D and E were reduced (liver indices: 0.038 ± 0.008, 0.036 ± 0.007, 0.036 ± 0.005 vs 0.054 ± 0.009, P < 0.05; HA: 502.33 ± 110.57 ng/mL, 524.25 ± 255.42 ng/mL, 499.25 ± 198.10 ng/mL vs 828.50 ± 237.83 ng/mL, P < 0.05; ALT: 149.44 ± 16.51 U/L, 136.88 ± 10.07 U/L, 127.38 ± 11.03 U/L vs 203.25 ± 31.62 U/L, P < 0.05), and SOD level was significantly higher, but MDA level was lower, in liver homogenates (SOD: 1.36 ± 0.09 U/mg, 1.42 ± 0.13 U/mg, 1.50 ± 0.15 U/mg vs 1.08 ± 0.19 U/mg, P < 0.05; MDA: 0.294 ± 0.026 nmol/mg, 0.285 ± 0.025 nmol/mg, 0.284 ± 0.028 nmol/mg vs 0.335 ± 0.056 nmol/mg, P < 0.05). Meanwhile, the stage of hepatic fibrosis was significantly weakened (P < 0.05). Compared with group A, the activity of GST liver homogenates and expression levels of Nrf2 and Nqo1 in group B were elevated (P < 0.05). The expression level of Nrf2 and Nqo1 in groups C, D, and E were increased as compared with group B, but the difference was not significant.

CONCLUSION: Blueberry has preventive and protective effects on CCl₄-induced hepatic fibrosis by reducing hepatocyte injury and lipid peroxidation. However, these effects may not be related to the activation of Nrf2 during long-term of CCl₄.

Oxidative stress is important in the pathogenesis of liver injury induced by sulindac and lipopolysaccharide cotreatment

Among currently prescribed nonsteroidal anti-inflammatory drugs, sulindac (SLD) is associated with the greatest incidence of idiosyncratic hepatotoxicity in humans. Previously, an animal model of SLD-induced idiosyncratic hepatotoxicity was developed by cotreating rats with a nonhepatotoxic dose of LPS. Tumor necrosis factor-alpha (TNF) was found to be critically important to the pathogenesis. In this study, the mechanism of liver injury induced by SLD/LPS cotreatment was further explored. Protein carbonyls, products of oxidative stress, were elevated in liver mitochondria of SLD/LPS-cotreated rats. The results of analyzing gene expression in livers of rats before the onset of liver injury indicated that genes associated with oxidative stress were selectively regulated by SLD/LPS cotreatment. Antioxidant treatment with either ebselen or dimethyl sulfoxide attenuated SLD/LPS-induced liver injury. The role of oxidative stress was further investigated in vitro. SLD sulfide, the toxic metabolite of SLD, enhanced TNF-induced cytotoxicity and caspase 3/7 activity in HepG2 cells. SLD sulfide also increased dichlorofluorescein fluorescence, suggesting generation of reactive oxygen species (ROS). Hydrogen peroxide and TNF cotreatment of HepG2 cells caused greater cytotoxicity than either treatment alone. Either antioxidant tempol or a pancaspase inhibitor Z-VAD-FMK decreased cell death as well as caspase 3/7 activity induced by SLD sulfide/TNF coexposure. These results indicate that SLD/LPS treatment causes oxidative stress in livers of rats and suggest that ROS are important in SLD/LPS-induced liver injury in vivo. Furthermore, ROS contribute to the cytotoxic interaction of SLD and TNF by activating caspase 3/7.

Alcohol and acetaldehyde in public health: from marvel to menace

Alcohol abuse is a serious medical and social problem. Although light to moderate alcohol consumption is beneficial to cardiovascular health, heavy drinking often results in organ damage and social problems. In addition, genetic susceptibility to the effect of alcohol on cancer and coronary heart disease differs across the population. A number of mechanisms including direct the toxicity of ethanol, its metabolites [e.g., acetaldehyde and fatty acid ethyl esters (FAEEs)] and oxidative stress may mediate alcoholic complications. Acetaldehyde, the primary metabolic product of ethanol, is an important candidate toxin in developing alcoholic diseases. Meanwhile, free radicals produced during ethanol metabolism and FAEEs are also important triggers for alcoholic damages.

PPAR/RXR Regulation of Fatty Acid Metabolism and Fatty Acid omega-Hydroxylase (CYP4) Isozymes: Implications for Prevention of Lipotoxicity in Fatty Liver Disease

Fatty liver disease is a common lipid metabolism disorder influenced by the combination of individual genetic makeup, drug exposure, and life-style choices that are frequently associated with metabolic syndrome, which encompasses obesity, dyslipidemia, hypertension, hypertriglyceridemia, and insulin resistant diabetes. Common to obesity related dyslipidemia is the excessive storage of hepatic fatty acids (steatosis), due to a decrease in mitochondria β-oxidation with an increase in both peroxisomal β-oxidation, and microsomal ω-oxidation of fatty acids through peroxisome proliferator activated receptors (PPARs). How steatosis increases PPARα activated gene expression of fatty acid transport proteins, peroxisomal and mitochondrial fatty acid β-oxidation and ω-oxidation of fatty acids genes regardless of whether dietary fatty acids are polyunsaturated (PUFA), monounsaturated (MUFA), or saturated (SFA) may be determined by the interplay of PPARs and HNF4α with the fatty acid transport proteins L-FABP and ACBP. In hepatic steatosis and steatohepatitis, the ω-oxidation cytochrome P450 CYP4A gene expression is increased even with reduced hepatic levels of PPARα. Although numerous studies have suggested the role ethanol-inducible CYP2E1 in contributing to increased oxidative stress, Cyp2e1-null mice still develop steatohepatitis with a dramatic increase in CYP4A gene expression. This strongly implies that CYP4A fatty acid ω-hydroxylase P450s may play an important role in the development of steatohepatitis. In this review and tutorial, we briefly describe how fatty acids are partitioned by fatty acid transport proteins to either anabolic or catabolic pathways regulated by PPARs, and we explore how medium-chain fatty acid (MCFA) CYP4A and long-chain fatty acid (LCFA) CYP4Fω-hydroxylase genes are regulated in fatty liver. We finally propose a hypothesis that increased CYP4A expression with a decrease in CYP4F genes may promote the progression of steatosis to steatohepatitis.

Oxidative damage to RNA: mechanisms, consequences, and diseases

Overproduction of free radicals can damage cellular components resulting in progressive physiological dysfunction, which has been implicated in many human diseases. Oxidative damage to RNA received little attention until the past decade. Recent studies indicate that RNA, such as messenger RNA and ribosomal RNA, is very vulnerable to oxidative damage. RNA oxidation is not a consequence of dying cells but an early event involved in pathogenesis. Oxidative modification to RNA results in disturbance of the translational process and impairment of protein synthesis, which can cause cell deterioration or even cell death. In this review, we discuss the mechanisms of oxidative damage to RNA and the possible biological consequences of damaged RNA. Furthermore, we review recent evidence suggesting that oxidative damage to RNA may contribute to progression of many human diseases.