Original ContributionCytochrome P450-2E1 promotes aging-related hepatic steatosis, apoptosis and fibrosis through increased nitroxidative stress
Graphical abstract
Introduction
Aging is a physiological process, that is characterized by a progressively decreased capacity to maintain internal homeostasis, with decreased ability to respond to various endogenous and exogenous stresses and increased risk of morbidity and mortality [1]. Many mechanistic theories for aging-related pathophysiological changes were proposed earlier [2] and have still been debated till to date [3], [4]. The prevailing mechanistic explanation for the aging process is “the free radical theory of aging” [5], despite being controversial [6]. This theory states that the increased damage in aged tissues is caused by the reaction of the free radicals with cellular macromolecules such as lipids, proteins, and nucleic acid, leading to compromised cellular functions and tissue injury [7]. Indeed, reactive oxygen species (ROS) and reactive nitrogen species (RNS) were reported to increase with aging. Consequently, accumulation of oxidized and/or nitrated proteins as well as lipid peroxides and oxidatively-damaged DNA are frequently observed in the aged tissues compared to the young counterparts [8], [9].
The liver was thought to exhibit minimal aging-dependent changes compared to other tissues [10]. This may be due to high contents of antioxidants and other defensive enzymes in the liver. However, recent reports showed that the liver also undergoes significant changes during aging process, since aged livers, especially in rodents after 12 months of age and older, contain less volume and regenerative capacity with elevated accumulation of insoluble oxidized proteins (e.g., lipofuscin) in the cytoplasm, altered nuclear shapes, and increased apoptosis, steatosis, fibrosis, and carcinoma, compared to the young counterparts [11], [12]. Interestingly, many studies showed a positive relationship between increased oxidative stress levels and deterioration of liver functions during the aging process [13], [14].
The cytochrome P450-2E1 (CYP2E1) enzyme, constitutively expressed in many tissues including the liver and extrahepatic organs, can oxidize a variety of small molecule substrates such as alcohol (ethanol), drugs, solvents, procarcinogens, and fatty acids [15], [16], [17]. It is induced by ethanol, acetone, and other small molecule substrates. CYP2E1 can also be regulated by age, gender, genetic factors, nutrition, hormones, as well as pathophysiological conditions such as diabetes and obesity [18], [19]. The superoxide anion can be produced from the CYP2E1-related catalytic activity even in the absence of its substrates [15], [16], [17]. The superoxide anion can become a potent oxidative radical that can cause severe tissue damage through interaction with other free radicals such as nitric oxide (NO) to produce a more potently toxic peroxynitrite [20]. It can be also converted to a more toxic hydroxyl radical in the presence of transition metals [21].
CYP2E1 levels have been evaluated both in aged people (usually≥55 years) and animals (usually≥2 months) and through the entire life span in animals [22], [23], [24], [25]. The results of these studies revealed that CYP2E1 protein levels were unchanged or decreased, or CYP2E1 activities were decreased with aging. Furthermore, other reports showed increased levels of hepatocyte apoptosis and liver fibrosis in the aged mice [11], [26], [27]. However, to the best of our knowledge, the role of CYP2E1 in promoting hepatic steatosis, apoptosis, and fibrosis observed in aged rodents has never been evaluated. Thus, this study was aimed to investigate the role of CYP2E1 in promoting nitroxidative stress and hepatic changes by comparing the various parameters in young versus aged wild-type (WT) mice. To further verify the causal role of CYP2E1 in aging-related hepatic changes, we also evaluated the histological and biochemical characteristics of the livers in young and aged Cyp2e1-null mice compared to those of the WT counterparts.
Section snippets
Materials
All chemicals used in this study were from Sigma Chemical (St. Louis, MO, USA), unless indicated otherwise. Specific antibodies against CYP2E1, inducible nitric oxide synthase (iNOS), 3-nitrotyrosine (3-NT), and β-actin were from Abcam Inc. (Cambridge, MA, USA). Respective antibodies against collagen 1A1 and 4-hydroxynonenal (HNE) were from Millipore (Billerica, MA, USA) and the sources of other primary antibodies are listed in Table 1. Secondary antibodies conjugated with horse radish
More prominent hepatic histopathological changes in aged WT mice
To investigate the age-related hepatic histological and/or structural changes, we compared the respective liver tissues of young (7-weeks) and aged (16-months) WT and Cyp2e1-null groups (n≥10/group). The livers of the aged WT mice were pale and the margins of the livers were blunt. The dilated gall bladders filled with bile were only observed in the aged WT. Hepatocyte vacuolation, ballooning degeneration, and inflammatory cell infiltration mostly with lymphocytes and neutrophils were markedly
Discussion
Mice have been widely used as a suitable model to study the underlying mechanism(s) of aged-related hepatic steatosis, apoptosis, and fibrosis since they are short-lived and share many similarities with human conditions [11], [26], [27]. Constitutive expression of CYP2E1, involved in ROS production, has been reported to be significantly higher in female mice than males, suggesting a more potentially pronounced pathophysiological outcomes in females than males possibly resulting from
Conflict of interest
The authors declared no conflict of interest.
Acknowledgment
This research was supported by the Intramural Research Program of National Institute on Alcohol Abuse and Alcoholism and by a Grant to Youngshim Choi from the KRIBB Research Initiative Program (Korean Biomedical Scientist Fellowship Program), and Korea Research institute of Bioscience and Biotechnology, Republic of Korea. We are thankful to Dr. Frank J. Gonzalez (National Cancer Institute, NIH, Bethesda, MD, USA) and Dr. James P. Hardwick (Northeastern Ohio University College of Medicine,
References (78)
Understanding the odd science of aging
Cell
(2005)Theories and mechanisms of aging
Clin. Geriatr. Med.
(2011)- et al.
Trends in oxidative aging theories
Free Radic. Biol. Med.
(2007) - et al.
Increased expression of cytochrome P450 2E1 in nonalcoholic fatty liver disease: mechanisms and pathophysiological role
Clin. Res. Hepatol. Gastroenterol.
(2011) - et al.
The role of intracellular signaling in insulin-mediated regulation of drug metabolizing enzyme gene and protein expression
Pharmacol. Ther.
(2007) Iron and CYP2E1-dependent oxidative stress and toxicity
Alcohol
(2003)- et al.
Effect of normal aging on the activity of human hepatic cytochrome P450IIE1
Biochem. Pharmacol.
(1990) - et al.
Role of CYP2E1 in the hepatotoxicity of acetaminophen
J. Biol. Chem.
(1996) - et al.
PPARalpha expression protects male mice from high fat-induced nonalcoholic fatty liver
J. Nutr.
(2011) - et al.
Critical role of cytochrome P450 2E1 (CYP2E1) in the development of high fat-induced non-alcoholic steatohepatitis
J. Hepatol.
(2012)
Role of peroxisome proliferator-activated receptor-alpha in fasting-mediated oxidative stress
Free Radic. Biol. Med.
Role of cytochrome P450 2E1 in protein nitration and ubiquitin-mediated degradation during acetaminophen toxicity
Biochem. Pharmacol.
Defects of the respiratory chain in the normal human liver and in cirrhosis during aging
Hepatology
Circulating biologically active oxidized phospholipids show on-going and increased oxidative stress in older male mice
Redox Biol.
Lifespan extension in the spontaneous dwarf rat and enhanced resistance to hyperoxia-induced mortality
Exp. Gerontol.
Mitochondrial dysfunction in NASH: causes, consequences and possible means to prevent it
Mitochondrion
Protein homeostasis and aging: the importance of exquisite quality control
Ageing Res. Rev.
Inverse correlation of protein oxidation and proteasome activity in liver and lung
Mech. Ageing Dev.
Model of nonalcoholic steatohepatitis
Am. J. Clin. Nutr.
Cordycepin (3′-deoxyadenosine) attenuates age-related oxidative stress and ameliorates antioxidant capacity in rats
Exp. Gerontol.
CYP2E1 potentiates binge alcohol-induced gut leakiness, steatohepatitis, and apoptosis
Free Radic. Biol. Med.
The natural history of nonalcoholic fatty liver disease: a population-based cohort study
Gastroenterology
Oxidative inactivation of key mitochondrial proteins leads to dysfunction and injury in hepatic ischemia reperfusion
Gastroenterology
Robust protein nitration contributes to acetaminophen-induced mitochondrial dysfunction and acute liver injury
Free Radic. Biol. Med.
Mitochondrial dysfunction and tissue injury by alcohol, high fat, nonalcoholic substances and pathological conditions through post-translational protein modifications
Redox Biol.
Hydrogen peroxide release by mitochondria increases during aging
Mech. Ageing Dev.
Heme oxygenase-1 protects HepG2 cells against cytochrome P450 2E1-dependent toxicity
Free Radic. Biol. Med.
Decreased proteolysis caused by protein aggregates, inclusion bodies, plaques, lipofuscin, ceroid, and’‘aggresomes’ during oxidative stress, aging, and disease
Int. J. Biochem. Cell. Biol.
Critical role of c-jun N-terminal protein kinase in promoting mitochondrial dysfunction and acute liver injury
Redox Biol.
An attempt at a rational classification of theories of ageing
Biol. Rev. Camb. Philos. Soc.
Theories of aging: an ever-evolving field
Acta Naturae
Aging: a theory based on free radical and radiation chemistry
J. Gerontol.
The free radical theory of aging is dead. Long live the damage theory!
Antioxid. Redox Signal.
Does oxidative damage to DNA increase with age?
Proc. Natl. Acad. Sci. USA
Age-dependent accumulation of 8-oxoguanine in the DNA and RNA in various rat tissues
Oxid. Med. Cell. Longev.
Aging and the liver: an update
J. Gerontol. A: Biol. Sci. Med. Sci.
Aging and liver disease
Curr. Opin. Gastroenterol.
Hepatic steatosis, fibrosis, and cancer in elderly cadavers
Anat. Rec. (Hoboken)
Evidence of oxidative injury during aging of the liver in a mouse model
J. Am. Aging Assoc.
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