Ascorbic acid prevents acetaminophen-induced hepatotoxicity in mice by ameliorating glutathione recovery and autophagy

Chronic Exposure to Arsenic and Fluoride Starting at Gestation Alters Liver Mitochondrial Protein Expression and Induces Early Onset of Liver Fibrosis in Male Mouse Offspring

The presence of arsenic (As) and fluoride (F-) in drinking water is of concern due to the enormous number of individuals exposed to this condition worldwide. Studies in cultured cells and animal models have shown that As- or F-induced hepatotoxicity is primarily associated with redox disturbance and altered mitochondrial homeostasis. To explore the hepatotoxic effects of chronic combined exposure to As and F- in drinking water, pregnant CD-1 mice were exposed to 2 mg/L As (sodium arsenite) and/or 25 mg/L F- (sodium fluoride). The male offspring continued the exposure treatment up to 30 (P30) or 90 (P90) postnatal days. GSH levels, cysteine synthesis enzyme activities, and cysteine transporter levels were investigated in liver homogenates, as well as the expression of biomarkers of ferroptosis and mitochondrial biogenesis-related proteins. Serum transaminase levels and Hematoxylin-Eosin and Masson trichrome-stained liver tissue slices were examined. Combined exposure at P30 significantly reduced GSH levels and the mitochondrial transcription factor A (TFAM) expression while increasing lipid peroxidation, free Fe 2+, p53 expression, and serum ALT activity. At P90, the upregulation of cysteine uptake and synthesis was associated with a recovery of GSH levels. Nevertheless, the downregulation of TFAM continued and was now associated with a downstream inhibition of the expression of MT-CO2 and reduced levels of mtDNA and fibrotic liver damage. Our experimental approach using human-relevant doses gives evidence of the increased risk for early liver damage associated with elevated levels of As and F- in the diet during intrauterine and postnatal period.

Aldo-keto reductase family 1 member A1 (AKR1A1) exerts a protective function in alcohol-associated liver disease by reducing 4-HNE accumulation and p53 activation

BACKGROUND

The development of alcohol-associated liver disease (ALD) is influenced by the amount and duration of alcohol consumption. The resulting liver damage can range from reversible stages, such as steatosis, steatohepatitis and alcoholic fibrosis, to the advanced and irreversible stage of cirrhosis. Aldo-keto reductase family 1 member A1 (AKR1A1) is a member of the aldo-keto reductase family that catalyzes the reduction of aldehyde groups to their corresponding alcohols in an NADPH-dependent manner. AKR1A1 was found to be downregulated in patients diagnosed with ALD. This study aims to interpret the protective effects of AKR1A1 on the development of ALD.

METHODS

A 5% alcohol-fed (AF) Akr1a1 knockout (Akr1a1-/-) mouse model and an AML12 hepatocyte model were used. The effects of AKR1A1 on liver function, inflammation, oxidative stress, lipid accumulation, and fibrosis were assessed by ELISA, western blotting, RT‒PCR, and a variety of histological staining methods in AF-induced wild-type (WT) and Akr1a1-/- mice compared to control liquid diet-fed (PF) WT and Akr1a1-/- mice.

RESULTS

The results demonstrated that AF-WT mice expressed higher levels of AKR1A1 than WT mice fed a control diet, and they did not show any noticeable liver steatosis. However, AF-Akr1a1-/- mice displayed a lower survival rate and more severe liver injury than AF-WT mice, as demonstrated by increased proinflammatory cytokines, oxidative stress, lipid accumulation, fibrosis, and reduced antioxidant enzymes in their livers. Additionally, elevated levels of 4-HNE and p53 phosphorylation were observed in AF-Akr1a1-/- mice, suggesting that the loss of AKR1A1 led to increased 4-HNE accumulation and subsequent activation of p53, which contributed to the progression of ALD. Furthermore, in AML12 hepatocytes, Akr1a1 knockdown aggravated oxidative stress and steatosis induced by palmitic acid/oleic acid (P/O) inflammation induced by lipopolysaccharide (LPS), and fibrosis induced by TGF-β1.

CONCLUSIONS

This loss-of-function study suggests that AKR1A1 plays a liver-protective role during chronic alcohol consumption by reducing the accumulation of 4-HNE and inhibiting 4-HNE-mediated p53 activation.

Ascorbate Is a Primary Antioxidant in Mammals

Ascorbate (vitamin C in primates) functions as a cofactor for a number of enzymatic reactions represented by prolyl hydroxylases and as an antioxidant due to its ability to donate electrons, which is mostly accomplished through non-enzymatic reaction in mammals. Ascorbate directly reacts with radical species and is converted to ascorbyl radical followed by dehydroascorbate. Ambiguities in physiological relevance of ascorbate observed during in vivo situations could be attributed in part to presence of other redox systems and the pro-oxidant properties of ascorbate. Most mammals are able to synthesize ascorbate from glucose, which is also considered to be an obstacle to verify its action. In addition to animals with natural deficiency in the ascorbate synthesis, such as guinea pigs and ODS rats, three strains of mice with genetic removal of the responsive genes (GULO, RGN, or AKR1A) for the ascorbate synthesis have been established and are being used to investigate the physiological roles of ascorbate. Studies using these mice, along with ascorbate transporter (SVCT)-deficient mice, largely support its ability in protection against oxidative insults. While combined actions of ascorbate in regulating epigenetics and antioxidation appear to effectively prevent cancer development, pharmacological doses of ascorbate and dehydroascorbate may exert tumoricidal activity through redox-dependent mechanisms.

Protective Effect of Fresh/Dry Dandelion Extracts on APAP-Overdose-Induced Acute Liver Injury

OBJECITVIE

To compare the liver protective activity of fresh/dried dandelion extracts against acetaminophen (APAP)-induced hepatotoxicity.

METHODS

Totally 90 Kunming mice were randomly divided into 10 groups according to body weight (9 mice for each group). The mice in the normal control and model (vehicle control) groups were administered sodium carboxymethyl cellulose (CMC-Na, 0.5%) only. Administration groups were pretreated with high and low-dose dry dandelion extract (1,000 or 500 g fresh herb dried and then decocted into 120 mL solution, DDE-H and DDE-L); low-, medium- and high-dose dandelion juice (250, 500, 1,000 g/120 mL, DJ-L, DJ-M, and DJ-H); fresh dandelions evaporation juice water (120 mL, DEJW); dry dandelion extract dissolved by pure water (1 kg/120 mL, DDED-PW); dry dandelion extract dissolved by DEJW (120 g/120 mL, DDED-DEJW) by oral gavage for 7 days at the dosage of 0.5 mL solution/10 g body weight; after that, except normal control group, all other groups were intraperitonealy injected with 350 mg/kg APAP to induce liver injury. Twenty hours after APAP administration, serum and liver tissue were collected and serum alanine aminotransferase (AST), aspartate transaminase (ALT), alkaline phosphatase (AKP), malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD) activities were quantified by biochemical kits; tumor necrosis factor (TNF-α), interleukin (IL)-2, and IL-1 β contents in liver tissue were determined by enzyme linked immunosorbent assay kits. Histopathological changes in liver tissues were observed by hematoxylin and eosin staining; TUNEL Assay and Hoechst 33258 staining were applied for cell apoptosis evaluation. The expressions of heme oxygenase-1 (HO-1), nuclear factor erythroid-2-related factor 2 (Nrf-2), caspase-9, B-cell leukemia/lymphoma 2 (Bcl-2), Bax and p-JNK were determined by Western blot analysis.

RESULTS

Pretreatment with fresh dandelion juice (FDJ, including DJ-L, DJ-M, DJ-H, DEJW and DDED-DEJW) significantly decreased the levels of serum ALT, AST, AKP, TNF-α and IL-1β compared with vehicle control group (P<0.05 or P<0.01). Additionally, compared with the vehicle control group, FDJ decreased the levels of hepatic MDA and restored GSH levels and SOD activity in livers (P<0.05 or P<0.01). FDJ inhibited the overexpression of pro-inflammatory factors including cyclooxygenase-2 and inducible nitric oxide synthase in the liver tissues (P<0.05 or P<0.01). Furthermore, Western blot analysis revealed that FDJ pretreatment inhibited activation of apoptotic signaling pathways via decreasing of Bax, and caspase-9 and JNK protein expression, and inhibited activation of JNK pathway (P<0.05 or P<0.01). Liver histopathological observation provided further evidence that FDJ pretreatment significantly inhibited APAP-induced hepatocyte necrosis, inflammatory cell infiltration and congestion.

CONCLUSIONS

FDJ pretreatment protects against APAP-induced hepatic injury by activating the Nrf-2/HO-1 pathway and inhibition of the intrinsic apoptosis pathway, and the effect of fresh dandelion extracts was superior to dried dandelion extracts in APAP hepatotoxicity model mice.

Ascorbate is a multifunctional micronutrient whose synthesis is lacking in primates

Ascorbate (vitamin C) is an essential micronutrient in primates, and exhibits multiple physiological functions. In addition to antioxidative action, ascorbate provides reducing power to α-ketoglutarate-dependent non-heme iron dioxygenases, such as prolyl hydroxylases. Demethylation of histones and DNA with the aid of ascorbate results in the reactivation of epigenetically silenced genes. Ascorbate and its oxidized form, dehydroascorbate, have attracted interest in terms of their roles in cancer therapy. The last step in the biosynthesis of ascorbate is catalyzed by l-gulono-γ-lactone oxidase whose gene Gulo is commonly mutated in all animals that do not synthesize ascorbate. One common explanation for this deficiency is based on the increased availability of ascorbate from foods. In fact, pathways for ascorbate synthesis and the detoxification of xenobiotics by glucuronate conjugation share the metabolic processes up to UDP-glucuronate, which prompts another hypothesis, namely, that ascorbate-incompetent animals might have developed stronger detoxification systems in return for their lack of ability to produce ascorbate, which would allow them to cope with their situation. Here, we overview recent advances in ascorbate research and propose that an enhanced glucuronate conjugation reaction may have applied positive selection pressure on ascorbate-incompetent animals, thus allowing them to dominate the animal kingdom.

Pleiotropic Actions of Aldehyde Reductase (AKR1A)

We provide an overview of the physiological roles of aldehyde reductase (AKR1A) and also discuss the functions of aldose reductase (AKR1B) and other family members when necessary. Many types of aldehyde compounds are cytotoxic and some are even carcinogenic. Such toxic aldehydes are detoxified via the action of AKR in an NADPH-dependent manner and the resulting products may exert anti-diabetic and anti-tumorigenic activity. AKR1A is capable of reducing 3-deoxyglucosone and methylglyoxal, which are reactive intermediates that are involved in glycation, a non-enzymatic glycosylation reaction. Accordingly, AKR1A is thought to suppress the formation of advanced glycation end products (AGEs) and prevent diabetic complications. AKR1A and, in part, AKR1B are responsible for the conversion of d-glucuronate to l-gulonate which constitutes a process for ascorbate (vitamin C) synthesis in competent animals. AKR1A is also involved in the reduction of S-nitrosylated glutathione and coenzyme A and thereby suppresses the protein S-nitrosylation that occurs under conditions in which the production of nitric oxide is stimulated. As the physiological functions of AKR1A are currently not completely understood, the genetic modification of Akr1a could reveal the latent functions of AKR1A and differentiate it from other family members.

Defective biosynthesis of ascorbic acid in Sod1-deficient mice results in lethal damage to lung tissue

Superoxide dismutase 1 (Sod1) plays pivotal roles in antioxidation via accelerating the conversion of superoxide anion radicals into hydrogen peroxide, thus inhibiting the subsequent radical chain reactions. While Sod1 deficient cells inevitably undergo death in culture conditions, Sod1-knockout (KO) mice show relatively mild phenotypes and live approximately two years. We hypothesized that the presence of abundant levels of ascorbic acid (AsA), which is naturally produced in mice, contributes to the elimination of reactive oxygen species (ROS) in Sod1-KO mice. To verify this hypothesis, we employed mice with a genetic ablation of aldehyde reductase (Akr1a), an enzyme that is involved in the biosynthesis of AsA, and established double knockout (DKO) mice that lack both Sod1 and Akr1a. Supplementation of AsA (1.5 mg/ml in drinking water) was required for the DKO mice to breed, and, upon terminating the AsA supplementation, they died within approximately two weeks regardless of age or gender. We explored the etiology of the death from pathophysiological standpoints in principal organs of the mice. Marked changes were observed in the lungs in the form of macroscopic damage after the AsA withdrawal. Histological and immunological analyses of the lungs indicated oxidative damage of tissue and activated immune responses. Thus, preferential oxidative injury that occurred in pulmonary tissues appeared to be primary cause of the death in the mice. These collective results suggest that the pivotal function of AsA in coping with ROS in vivo, is largely in pulmonary tissues that are exposed to a hyperoxygenic microenvironment.

Acetaminophen-Induced Rat Hepatotoxicity Based on M1/M2-Macrophage Polarization, in Possible Relation to Damage-Associated Molecular Patterns and Autophagy

Overdose of acetaminophen (APAP), an antipyretic drug, is an important cause of liver injury. However, the mechanism in the rat model remains undetermined. We analyzed APAP-induced hepatotoxicity using rats based on M1/M2-macrophage functions in relation to damage-associated molecular patterns (DAMPs) and autophagy. Liver samples from six-week-old rats injected with APAP (1000 mg/kg BW, ip, once) after 15 h fasting were collected at hour 10, and on days 1, 2, 3, and 5. Liver lesions consisting of coagulation necrosis and inflammation were seen in the affected centrilobular area on days 1 and 2, and then, recovered with reparative fibrosis by day 5. Liver exudative enzymes increased transiently on day 1. CD68⁺ M1-macrophages increased significantly on days 1 and 2 with increased mRNAs of M1-related cytokines such as IFN-g and TNF-α, whereas CD163⁺ M2-macrophages appeared later on days 2 and 3. Macrophages reacting to MHC class II and Iba1 showed M1-type polarization, and CD204⁺ macrophages tended to be polarized toward M2-type. At hour 10, interestingly, HMGB1 (representative DAMPs) and its related signals, TLR-9 and MyD88, as well as LC3B⁺ autophagosomes began to increase. Collectively, the pathogenesis of rat APAP hepatotoxicity, which is the first, detailed report for a rat model, might be influenced by macrophage functions of M1 type for tissue injury/inflammation and M2-type for anti-inflammatory/fibrosis; particularly, M1-type may function in relation to DAMPs and autophagy. Understanding the interplayed mechanisms would provide new insight into hepato-pathogenesis and contribute to the possible development of therapeutic strategies.

Cardamonin Reduces Acetaminophen-Induced Acute Liver Injury in Mice via Activating Autophagy and NFE2L2 Signaling

Cardamonin (CD), a naturally occurring chalcone derived from the Alpinia species, has been shown to exert antioxidant and anti-inflammatory activity, but its role in the prevention of acetaminophen- (APAP-) induced hepatotoxicity remains elusive. The objective of this study was to determine the protective effects of CD against APAP-induced acute liver injury (ALI) and the underlying mechanisms. Wild-type or transcription factor nuclear factor erythroid 2-related factor 2- (NFE2L2-) deficient mice were treated with CD (50 or 100 mg/kg, i.p.) or vehicle for 24 h. Subsequently, these mice were challenged with APAP (400 mg/kg, i.p.) for 6 h. Liver and blood samples were collected to evaluate liver injury and protein abundance. Treatment with CD significantly reduced APAP-induced hepatotoxicity. Furthermore, CD effectively reduced APAP-induced inflammation by inhibiting high mobility group box 1 (HMGB1), toll-like receptor 4 (TLR4), and NOD-like receptor protein 3 (NLRP3) signaling. In addition, CD induced activation of sequestosome 1 (p62) and NFE2L2 signaling and facilitated autophagy. By applying autophagy inhibitor 3-methyladenine (3-MA; 20 mg/kg, i.p.), further mechanistic exploration revealed that NFE2L2 deficiency promoted autophagic activity induced by CD treatment, which was conducive to the hepatoprotective effect of CD against APAP-induced hepatoxicity in NFE2L2^−/− mice. Overall, data suggest that CD has hepatoprotective effect against APAP-induced ALI, which might contribute to the activation of NFE2L2 and autophagy.

Testis-specific peroxiredoxin 4 variant is not absolutely required for spermatogenesis and fertility in mice

PRDX4, a member of peroxiredoxin family, is largely concentrated in the endoplasmic reticulum (ER) and plays a pivotal role in the redox relay during oxidative protein folding as well as in peroxidase reactions. A testis-specific PRDX4 variant transcript (PRDX4t) lacks the conventional exon 1, which encodes the signal peptide that is required for entry into the ER lumen, but instead carries alternative exon 1, which is transcribed from the upstream promoter in a testis-specific manner and results in the PRDX4t protein being localized in the cytosol. However, the potential roles of PRDX4t in male genital action remain unknown. Using a CRISPR/Cas9 system, we first disrupted the testis-specific promoter/exon 1 and generated mice that were specifically deficient in PRDX4t. The resulting PRDX4t knockout (KO) mice underwent normal spermatogenesis and showed no overt abnormalities in the testis. Mating PRDX4t KO male mice with wild-type (WT) female mice produced normal numbers of offspring, indicating that a PRDX4t deficiency alone had no effect on fertility in the male mice. We then generated mice lacking both PRDX4 and PRDX4t by disrupting exon 2, which is communal to these variants. The resulting double knockout (DKO) mice were again fertile, and mature sperm isolated from the epididymis of DKO mice exhibited a normal fertilizing ability in vitro. In the meantime, the protein levels of glutathione peroxidase 4 (GPX4), which plays an essential role in the disulfide bond formation during spermatogenesis, were significantly increased in the testis and caput epididymis of the DKO mice compared with the WT mice. Based on these results, we conclude that the disruption of the function of PRDX4t in the spermatogenic process appears to be compensated by other factors including GPX4.

Iron loading exerts synergistic action via a different mechanistic pathway from that of acetaminophen-induced hepatic injury in mice

Acetaminophen (APAP) overdose is a major cause of drug-induced acute liver failure. In such cases, free iron is released from lysosomes and is transported to mitochondria where it plays a pivotal role in APAP-induced liver injury. We previously reported that ascorbic acid (Asc) markedly mitigates APAP-induced hepatic damage in aldehyde reductase (Akr1a)-knockout (KO) mice that produce about 10% Asc as wild-type (WT) mice. However, the issue of the protective mechanism of Asc in association with the status of iron remains ambiguous. To gain additional insights into this issue, we examined effects of APAP (500 mg/kg) on female KO mice under conditions of iron loading. While the KO mice without AsA supplementation were more sensitive to APAP toxicity than the WT mice, FeSO₄ loading (25 mg/kg) to WT mice aggravated the hepatic injury, which was a similar extent to that of the KO mice. Supplementation of Asc (1.5 mg/ml in the drinking water) ameliorated KO mice irrespective of iron status but did not change the iron-mediated increase in the lethality in the WT mice. Hepatic cysteine and glutathione levels declined to similar extents in all mouse groups at 3 h irrespective of the iron status and largely recovered at 18 h after the APAP treatment when liver damage was evident. Asc prominently mitigated APAP toxicity in KO mice irrespective of the iron status but had no effect on the synergistic action of iron and APAP in the WT mice, suggesting that the mechanism for the deteriorating action of loaded iron is different from that of APAP toxicity.

Dandelion polyphenols protect against acetaminophen-induced hepatotoxicity in mice via activation of the Nrf-2/HO-1 pathway and inhibition of the JNK signaling pathway

We investigated the liver protective activity of dandelion polyphenols (DP) against acetaminophen (APAP; Paracetamol)-induced hepatotoxicity. Mice were acclimated for 1 week and randomly divided into the following groups (n = 9 per group): Control, APAP, APAP + DP (100 mg·kg^-1), APAP + DP (200 mg·kg^-1), and APAP + DP (400 mg·kg^-1) groups. Mice were pretreated with DP (100, 200, and 400 mg·kg^-1) by oral gavage for 7 d before being treated with 350 mg·kg^-1 APAP for 24 h to induced hepatotoxicity. Severe liver injury was observed, and hepatotoxicity was analyzed after 24 h by evaluation of biochemical markers, protein expressions levels, and liver histopathology. Pretreatment with DP was able to restore serum liver characteristics (aspartate transaminase, AST; alanine aminotransferase, ALT; alkaline phosphatase, AKP), improve redox imbalance (superoxide dismutase, SOD; glutathione, GSH; malondialdehyde, MDA), and decrease inflammatory factors (tumor necrosis factor-α, TNF-α; interleukin-1β, IL-1β). Pretreatment with DP also significantly inhibited the expression levels of nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Furthermore, DP pretreatment could inhibit the apoptosis of liver cells caused by APAP through up-regulation of Bcl-2 and down-regulation of Bax and caspase-9 protein. DP also down-regulated p-JNK protein expression levels to inhibit APAP-induced mitochondrial oxidative stress and up-regulated the expression of Nrf-2 and its target gene HO-1. The histopathological staining demonstrated that DP pretreatment could inhibit APAP-induced hepatocyte infiltration, congestion, and necrosis. Our results demonstrate that DP pretreatment could protect against APAP-induced hepatic injury by activating the Nrf-2/HO-1 pathway and inhibition of the intrinsic apoptosis pathway.

Quantitative analysis of γ-glutamylpeptides by liquid chromatography-mass spectrometry and application for γ-glutamyltransferase assays

γ-Glutamylpeptides are largely produced via the action of γ-glutamylcysteine synthetase or γ-glutamyltransferase (GGT). GGT transfers the γ-glutamyl moiety from glutathione (GSH) and other γ-glutamyl compounds to amino acids, peptides, or water. A conventional GGT assay employs a synthetic donor substrate, which facilitates monitoring cleavage activity by means of colorimetric analyses but provides no information on the resulting γ-glutamylpeptides. In this study, we report on the use of liquid chromatography-mass spectrometry (LC-MS) to quantitatively measure the levels of 21 γ-glutamylpeptides including GSH and 45 amino acids, including Cys. Authentic compounds consisting of 17 chemically synthesized and commercially available 4 γ-glutamylpeptides were adopted as references. We applied this method to the characterization of γ-glutamylpeptides in blood plasma and livers of mice that had been treated with an overdose of acetaminophen. The established LC-MS-based assay was found to be useful for characterizing the γ-glutamylation reaction under in vivo and in vitro conditions and was clearly helpful for understanding the physiological significance of the production of γ-glutamylpeptides.

Autophagy in Human Health and Disease: Novel Therapeutic Opportunities

SIGNIFICANCE

In eukaryotes, autophagy represents a highly evolutionary conserved process, through which macromolecules and cytoplasmic material are degraded into lysosomes and recycled for biosynthetic or energetic purposes. Dysfunction of the autophagic process has been associated with the onset and development of many human chronic pathologies, such as cardiovascular, metabolic, and neurodegenerative diseases as well as cancer. Recent Advances: Currently, comprehensive research is being carried out to discover new therapeutic agents that are able to modulate the autophagic process in vivo. Recent evidence has shown that a large number of natural bioactive compounds are involved in the regulation of autophagy by modulating several transcriptional factors and signaling pathways.

CRITICAL ISSUES

Critical issues that deserve particular attention are the inadequate understanding of the complex role of autophagy in disease pathogenesis, the limited availability of therapeutic drugs, and the lack of clinical trials. In this context, the effects that natural bioactive compounds exert on autophagic modulation should be clearly highlighted, since they depend on the type and stage of the pathological conditions of diseases.

FUTURE DIRECTIONS

Research efforts should now focus on understanding the survival-supporting and death-promoting roles of autophagy, how natural compounds interact exactly with the autophagic targets so as to induce or inhibit autophagy and on the evaluation of their pharmacological effects in a more in-depth and mechanistic way. In addition, clinical studies on autophagy-inducing natural products are strongly encouraged, also to highlight some fundamental aspects, such as the dose, the duration, and the possible synergistic action of these compounds with conventional therapy.

Enhanced autophagy contributes to protective effects of IL-22 against acetaminophen-induced liver injury

Acute or acute-on-chronic liver failure is a leading cause of death in liver diseases without effective treatment. Interleukin-22 (IL-22) is currently in clinical trials for the treatment of severe alcoholic hepatitis, but the underlying mechanisms remain to be explored. Autophagy plays a critical role in alleviating liver injury. The aim of the current study is to explore the role of autophagy in IL-22-mediated hepato-protective effect against acetaminophen (APAP)-induced liver injury. Methods: A model of acute liver injury induced by APAP was used in vivo. IL-22 was administrated to the APAP-treated mice. Hepatocytes were pre-incubated with IL-22, followed by exposure to APAP for in vitro analyses. Results: IL-22 administration significantly reduced serum ALT and AST, hepatic reactive oxygen species, and liver necrosis in APAP-challenged mice. APAP treatment increased hepatic autophagosomes, which was further intensified by IL-22 co-treatment. Hepatic LC3-II was moderately upregulated after APAP administration without obvious alteration of phosphorylation of AMP-activated kinase (p-AMPK). IL-22 pretreatment significantly upregulated hepatic LC3-II and p-AMPK in APAP-treated mice. IL-22 also alleviated APAP-induced cytotoxicity and upregulated LC3-II and p-AMPK expression in cultured hepatocytes treated with APAP in vitro. When p-AMPK was blocked with compound C (an AMPK inhibitor), IL-22-mediated LC3-II conversion and protection against APAP-induced cytotoxicity was weakened. Conclusions: Enhanced AMPK-dependent autophagy contributes to protective effects of IL-22 against APAP-induced liver injury.

Mice deficient in aldo-keto reductase 1a (Akr1a) are resistant to thioacetamide-induced liver injury

Aldehyde reductase (Akr1a) has been reported to be involved in detoxification of reactive aldehydes as well as in the synthesis of bioactive compounds such as ascorbic acid (AsA). Because Akr1a is expressed at high levels in the liver and is involved in xenobiotic metabolism, our objective was to investigate the hepato-protective role of Akr1a in a thioacetamide (TAA)-induced hepatotoxicity model using Akr1a-deficient (Akr1a^-/-) mice. Wild-type (WT) and Akr1a^-/- mice were injected intraperitoneally with TAA and the extent of liver injury in the acute phase was assessed. Intriguingly, the extent of TAA-induced liver damage was less in the Akr1a^-/- mice than in the WT mice. Biomarkers for the ER stress-induced apoptosis pathway were markedly decreased in the livers of Akr1a^-/- mice, whereas AsA levels in plasma did not change significantly in any of the mice. In the liver, TAA is converted to reactive metabolites such as TAA S-oxide and then to TAA S, S-dioxide via the action of CYP2E1. In Akr1a^-/- mice, CYP2E1 activity was relatively lower than WT mice at the basal level, leading to reactive TAA metabolites being produced at lower levels after the TAA treatment. The levels of liver proteins that were modified with these metabolites were also lower in the Akr1a^-/- mice than the WT mice after the TAA treatment. Furthermore, after a lethal dose of a TAA challenge, the WT mice all died within 36 h, whereas almost all of the Akr1a^-/- mice survived. These collective results suggest that Akr1a^-/- mice are resistant to TAA-induced liver injury, and it follows that the absence of Akr1a might modulate TAA bioactivation.

Paracetamol: overdose-induced oxidative stress toxicity, metabolism, and protective effects of various compounds in vivo and in vitro

Paracetamol (APAP) is one of the most widely used and popular over-the-counter analgesic and antipyretic drugs in the world when used at therapeutic doses. APAP overdose can cause severe liver injury, liver necrosis and kidney damage in human beings and animals. Many studies indicate that oxidative stress is involved in the various toxicities associated with APAP, and various antioxidants were evaluated to investigate their protective roles against APAP-induced liver and kidney toxicities. To date, almost no review has addressed the APAP toxicity in relation to oxidative stress. This review updates the research conducted over the past decades into the production of reactive oxygen species (ROS), reactive nitrogen species (RNS), and oxidative stress as a result of APAP treatments, and ultimately their correlation with the toxicity and metabolism of APAP. The metabolism of APAP involves various CYP450 enzymes, through which oxidative stress might occur, and such metabolic factors are reviewed within. The therapeutics of a variety of compounds against APAP-induced organ damage based on their anti-oxidative effects is also discussed, in order to further understand the role of oxidative stress in APAP-induced toxicity. This review will throw new light on the critical roles of oxidative stress in APAP-induced toxicity, as well as on the contradictions and blind spots that still exist in the understanding of APAP toxicity, the cellular effects in terms of organ injury and cell signaling pathways, and finally strategies to help remedy such against oxidative damage.

Effect and proposed mechanism of vitamin C modulating amino acid regulation of autophagic proteolysis

Autophagy is an intracellular bulk degradation process, induced under nutrient starvation. Failure of autophagy has been recognized as a contributor to aging and multiple age related neurodegenerative diseases. Improving autophagy is a beneficial anti-aging strategy, however very few physiological regulators have been identified. Here, we demonstrate that vitamin C is a nutritional stimulator of autophagy. Supplementation of fresh hepatocytes with vitamin C increased autophagic proteolysis significantly in the presence of amino acids in a dose- and time-dependent manner, although no effect was observed in the absence of amino acids. In addition, inhibitor studies with 3-methyladenine, chloroquine, leupeptin and β-lactone confirmed that vitamin C is active through the lysosomal autophagy and not the proteasome pathway. Furthermore, the autophagy marker LC3 protein was significantly increased by vitamin C, suggesting its possible site of action is at the formation step. Both the reduced (ascorbic acid, AsA) and oxidized form (dehydroascorbic acid, DHA) of vitamin C exhibited equal enhancing effect, indicating that the effect does not depend on the anti-oxidation functionality of vitamin C. To understand the mechanism, we established that the effective dose (50 μM) was 15× lower than the intracellular content suggesting these would be only a minor influx from the extracellular pool. Moreover, transporter inhibitor studies in an AsA deficient ODS model rat revealed more accurately that the enhancing effect on autophagic proteolysis still existed, even though the intracellular influx of AsA was blocked. Taken together, these results provide evidence that vitamin C can potentially act through extracellular signaling.

Saponins (Ginsenosides) from the Leaves of Panax quinquefolius Ameliorated Acetaminophen-Induced Hepatotoxicity in Mice

Acetaminophen (APAP) overdose is one of the most common inducements of drug-induced liver injury (DILI) in the world. The main purpose of this paper was to investigate the liver protection activity of saponins (ginsenosides) from the leaves of Panax quinquefolius (PQS) against APAP-induced hepatotoxicity, and the involved mechanisms were demonstrated for the first time. Mice were pretreated with PQS (150 and 300 mg/kg) by oral gavage for 7 days before being treated with 250 mg/kg APAP. Severe liver injury was exerted at 24 h post-APAP, and hepatotoxicity was assessed. Our results showed that pretreatment with PQS significantly decreased the serum alanine aminotransferase (ALT), aspartate transaminase (AST), tumor necrosis factor (TNF-α), and interleukin-1β (IL-1β) levels in a dose-dependent manner as compared to the APAP administration. Meanwhile, compared with that in the APAP group, PQS decreased hepatic malondialdehyde (MDA) contents and 4-hydroxynonenal (4-HNE) expression and restored reduced glutathione (GSH) content and superoxide dismutase (SOD) activity in livers of mice. PQS inhibited the overexpression of pro-inflammatory factors cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) in the liver tissues. Furthermore, Western blotting analysis revealed that PQS pretreatment inhibited the activation of apoptotic signaling pathways via increase of Bcl-2 and decrease of Bax and caspase-3 protein expression levels. Liver histopathological observation provided further evidence that PQS pretreatment significantly inhibited APAP-induced hepatocyte necrosis, inflammatory cell infiltration, and congestion. Biological indicators of nitrative stress such as 3-nitrotyrosine (3-NT) were inhibited after PQS pretreatment, compared to the APAP group. The present study clearly demonstrates that PQS exerts a protective effect against APAP-induced hepatic injury because of its antioxidant, anti-apoptotic, and anti-inflammatory activities. The findings from the present investigation show that PQS might be a promising candidate treatment agent against drug-induced ALI.

xCT deficiency aggravates acetaminophen-induced hepatotoxicity under inhibition of the transsulfuration pathway

Cystine, an oxidized form of cysteine (Cys), is imported into cells via the protein xCT, which is also associated with the export of glutamate as the counter amino acid. In the current study, we attempted to rationalize roles of xCT in the livers of male mice. While xCT was not expressed in the livers of ordinary mice, it was induced under conditions of glutathione depletion, caused by the administration of acetaminophen (AAP). To differentiate the role between xCT and the transsulfuration pathway on the supply of Cys, we employed an inhibitor of the enzyme cystathionine γ-lyase, propargylglycine (PPG). This inhibitor caused a marked aggravation in AAP-induced hepatic damage and the mortality of the xCT^-/- mice was increased to a greater extent than that for the xCT^+/+ mice. While a PPG pretreatment had no effect on liver condition or Cys levels, the administration of AAP to the PPG-pretreated mice reduced the levels of Cys as well as glutathione to very low levels in both the xCT^+/+ and xCT^-/- mice. These findings indicate that the transsulfuration pathway plays a major role in replenishing Cys when glutathione levels are low. Moreover, an ascorbic acid insufficiency, induced by Akr1a ablation, further aggravated the AAP-induced liver damage in the case of the xCT deficiency, indicating that glutathione and ascorbic acid function cooperatively in protecting the liver. In conclusion, while the transsulfuration pathway plays a primary role in supplying Cys to the redox system in the liver, xCT is induced in cases of emergencies, by compensating for Cys supply systems.