Hepatic hypoxia-inducible factors inhibit PPARα expression to exacerbate acetaminophen induced oxidative stress and hepatotoxicity

Ethyl gallate concurrent administration protects against acetaminophen-induced acute liver injury in mice: An in vivo and in silico approach

Acetaminophen (APAP) in high doses causes acute liver injury and acute liver failure. Ethyl gallate (EG) is a natural polyphenol, possessing antioxidant, anti-inflammatory, and anti-microbial properties. Therefore, in this study, we evaluated the protective role of EG against APAP-induced acute liver injury in mice. Acute liver injury was induced by a single dose of APAP (400 mg/kg., i.p.). In separate groups, EG (10 mg/kg), EG (20 mg/kg), and N-acetylcysteine (NAC; 1200 mg/kg., i.p.) were administered concurrently with APAP. The mice were sacrificed after 24 h of treatment. Liver marker enzymes of hepatotoxicity, antioxidant markers, inflammatory markers, and histopathological studies were done. APAP administration caused a significant elevation of marker enzymes of hepatotoxicity and lipid peroxidation. APAP administration also decreased enzymic and nonenzymic antioxidants. Acute APAP intoxication induced nuclear factor κ B, tumor necrosis factor-α, interleukin-1, p65, and p52 and downregulated IκB gene expressions. Our histopathological studies have confirmed the presence of centrilobular necrosis, 24 h after APAP intoxication. All the above abnormalities were significantly inhibited in groups of mice that were concurrently administered with APAP + EG and APAP + NAC. Our in silico analysis further confirms that hydroxyl groups of EG interact with the above inflammatory proteins at the 3,4,5-trihydroxybenzoic acid region. These effects of EG against APAP-induced acute liver injury could be attributed to its antioxidative, free radical scavenging, and anti-inflammatory potentials. Therefore, this study suggests that EG can be an efficient therapeutic approach to protect the liver from APAP intoxication.

An Overview of the Role of Peroxisome Proliferator-activated Receptors in Liver Diseases

Peroxisome proliferator-activated receptors (PPARs) are a superfamily of nuclear transcription receptors, consisting of PPARα, PPARγ, and PPARβ/δ, which are highly expressed in the liver. They control and modulate the expression of a large number of genes involved in metabolism and energy homeostasis, oxidative stress, inflammation, and even apoptosis in the liver. Therefore, they have critical roles in the pathophysiology of hepatic diseases. This review provides a general insight into the role of PPARs in liver diseases and some of their agonists in the clinic.

HIF-1α-PPARγ-mTORC1 signaling pathway-mediated autophagy induces inflammatory response in pancreatic cells in rats with hyperlipidemic acute pancreatitis

OBJECTIVE

The incidence of hyperlipidemic acute pancreatitis (HLAP) has rapidly increased in recent years in China. Autophagy has been implicated in the inflammatory response of pancreatic cells in HLAP, but the molecular mechanisms remain unclear.

METHODS

In this study, the role of HIF-1α-PPARγ-mTORC1 pathway-mediated autophagy in the inflammatory response of pancreatic cells and the underlying molecular mechanism were investigated in a rat model of HLAP using immunohistochemistry, ELISA, electron microscopy, and western blot analysis.

RESULTS

The results revealed that autophagy was significantly increased and pancreatic injury was exacerbated in HLAP rats, and the inflammatory response was further exacerbated by treatment with rapamycin but relieved by treatment with 3-MA. Hyperlipidemia induced upregulation of HIF-1α and downregulation of PPARγ, which in turn led to an increase in autophagy and consequently exacerbation of the inflammatory response of pancreatic cells.

CONCLUSIONS

HIF-1α-PPARγ-mTORC1 pathway-mediated autophagy plays a critical role in the inflammatory response of pancreatic cells in HLAP, and interference with the HIF-1α-PPARγ-mTOR pathway can serve as a new strategy for the prevention and treatment of HLAP.

Bcl-2 inhibition combined with PPARα activation synergistically targets leukemic stem cell-like cells in acute myeloid leukemia

Persistence of leukemic stem cells (LSCs) is one of the determining factors to acute myeloid leukemia (AML) treatment failure and responsible for the poor prognosis of the disease. Hence, novel therapeutic strategies that target LSCs are crucial for treatment success. We investigated if targeting Bcl-2 and peroxisome proliferator activated receptor α (PPARα), two distinct cell survival regulating mechanisms could eliminate LSCs. This study demonstrate that the Bcl-2 inhibitor venetoclax combined with the PPARα agonist chiglitazar resulted in synergistic killing of LSC-like cell lines and CD34+ primary AML cells while sparing their normal counterparts. Furthermore, the combination regimen significantly suppressed AML progression in patient-derived xenograft (PDX) mouse models. Mechanistically, chiglitazar-mediated PPARα activation inhibited the transcriptional activity of the PIK3AP1 gene promoter and down-regulated the PI3K/Akt signaling pathway and anti-apoptotic Bcl-2 proteins, leading to cell proliferation inhibition and apoptosis induction, which was synergized with venetoclax. These findings suggest that combinatorial Bcl-2 inhibition and PPARα activation selectively eliminates AML cells in vivo and vitro, representing an effective therapy for patients with relapsed and refractory AML.

Hepatocyte ferroptosis contributes to anti-tuberculosis drug-induced liver injury: Involvement of the HIF-1α/SLC7A11/GPx4 axis

Anti-tuberculosis drug-induced liver injury (ATB-DILI) is a common serious adverse event observed during the clinical treatment of tuberculosis. However, the molecular mechanisms underlying ATB-DILI remain unclear. A recent study has indicated that ferroptosis and lipid peroxidation may be involved in liver injury. Therefore, this study aimed to investigate the role of ferroptosis in the molecular mechanisms underlying ATB-DILI. Our results showed that anti-TB drugs induced hepatocyte damage in vivo and in vitro and inhibited BRL-3A cell activity in a dose-dependent manner, accompanied by increased lipid peroxidation and reduced antioxidant levels. Moreover, ACSL4 expression and Fe²⁺ concentration significantly increased following anti-TB drug treatment. Interestingly, anti-TB drug-induced hepatocyte damage was reversed by ferrostatin-1 (Fer-1, a specific ferroptosis inhibitor). In contrast, treatment with erastin (a ferroptosis inducer) resulted in further elevation of ferroptosis indicators. Additionally, we also found that anti-TB drug treatment inhibited HIF-1α/SLC7A11/GPx4 signaling in vivo and in vitro. Notably, HIF-1α knockdown significantly enhanced anti-TB drug-induced ferroptotic events and the subsequent exacerbation of hepatocyte damage. In conclusion, our findings indicated that ferroptosis plays a crucial role in the development of ATB-DILI. Furthermore, anti-TB drug-induced hepatocyte ferroptosis was shown to be regulated by HIF-1α/SLC7A11/GPx4 signaling. These findings shed new light on the mechanisms underlying ATB-DILI and suggest novel therapeutic strategies for this disease.

Diabetic cardiomyopathy: The role of microRNAs and long non-coding RNAs

Diabetes mellitus (DM) is on the rise, necessitating the development of novel therapeutic and preventive strategies to mitigate the disease's debilitating effects. Diabetic cardiomyopathy (DCMP) is among the leading causes of morbidity and mortality in diabetic patients globally. DCMP manifests as cardiomyocyte hypertrophy, apoptosis, and myocardial interstitial fibrosis before progressing to heart failure. Evidence suggests that non-coding RNAs, such as long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), regulate diabetic cardiomyopathy-related processes such as insulin resistance, cardiomyocyte apoptosis and inflammation, emphasizing their heart-protective effects. This paper reviewed the literature data from animal and human studies on the non-trivial roles of miRNAs and lncRNAs in the context of DCMP in diabetes and demonstrated their future potential in DCMP treatment in diabetic patients.

Iron increases lipid deposition via oxidative stress-mediated mitochondrial dysfunction and the HIF1α-PPARγ pathway

Iron is an essential micro-element, involved in multiple biological activities in vertebrates. Excess iron accumulation has been identified as an important mediator of lipid deposition. However, the underlying mechanisms remain unknown. In the present study, we found that a high-iron diet significantly increased intestinal iron content and upregulated the mRNA expression of two iron transporters (zip14 and fpn1). Intestinal iron overload increased lipogenesis, reduced lipolysis and promoted oxidative stress and mitochondrial dysfunction. Iron-induced lipid accumulation was mediated by hypoxia-inducible factor-1 α (HIF1α), which was induced in response to mitochondrial oxidative stress following inhibition of prolyl hydroxylase 2 (PHD2). Mechanistically, iron promoted lipid deposition by enhancing the DNA binding capacity of HIF1α to the pparγ and fas promoters. Our results provide experimental evidence that oxidative stress, mitochondrial dysfunction and the HIF1α-PPARγ pathway are critical mediators of iron-induced lipid deposition.

Hepatoprotective Effect of Oplopanax elatus Nakai Adventitious Roots Extract by Regulating CYP450 and PPAR Signaling Pathway

O. elatus Nakai is a traditional medicine that has been confirmed to exert effective antioxidant and anti-inflammatory functions, and is used for the treatment of different disorders. However, its potential beneficial effects on drug induced hepatotoxicity and relevant molecular mechanisms remain unclear. This study investigated the protective effect and further elucidated the mechanisms of action of O. elatus on liver protection. O. elatus chlorogenic acids-enriched fraction (OEB), which included chlorogenic acid and isochlorogenic acid A, were identified by HPLC-MS/MS. OEB was administrated orally daily for seven consecutive days, followed by a single intraperitoneal injection of an overdose of APAP after the final OEB administration. The effects of OEB on immune cells in mice liver were analyzed using flow cytometry. APAP metabolite content in serum was detected using HPLC-MS/MS in order to investigate whether OEB affects CYP450 activities. The intestinal content samples were processed for 16 s microbiota sequencing. Results demonstrated that OEB decreased alanine aminotransferase, aspartate aminotransferase contents, affected the metabolism of APAP, and decreased the concentrates of APAP, APAP-CYS and APAP-NAC by inhibiting CYP2E1 and CYP3A11 activity. Furthermore, OEB pretreatment regulated lipid metabolism by affecting the peroxisome proliferator-activated receptors (PPAR) signaling pathway in mice and also increased the abundance of Akkermansia and Parabacteroides. This study indicated that OEB is a potential drug candidate for treating hepatotoxicity because of its ability to affect drug metabolism and regulate lipid metabolism.

Dihydroartemisinin alleviates steatosis and inflammation in nonalcoholic steatohepatitis by decreasing endoplasmic reticulum stress and oxidative stress

Nonalcoholic steatohepatitis (NASH) is a severely inflammatory subtype of nonalcoholic fatty liver. Endoplasmic reticulum stress (ERS) and oxidative stress (OS) cause metabolic abnormalities, promote liver steatosis and inflammation, and are central to the development of NASH. Dihydroartemisinin (DHA) is a compound extracted from Artemisia annua that is often used in the treatment of malaria. Recent studies have shown that DHA also has a wide range of pharmacological effects, acting on various organs throughout the body to exert anti-inflammatory, antioxidant, and anti-fibrotic effects. In this study, we demonstrated in vitro that the anti-inflammatory effect of DHA is effective against NASH and reduces liver steatosis. DHA treatment decreased the synthesis of lipids, such as cholesterol and free fatty acids, and the expression of nuclear factor kappa-B. This is accomplished by inhibiting the unfolded protein response and reducing the production of reactive oxygen species, thereby inhibiting OS and ERS. This study reveals DHA's therapeutic effect and potential mechanism in NASH, implying that DHA could be a new and promising candidate for NASH therapy.

Detailed Molecular Mechanisms Involved in Drug-Induced Non-Alcoholic Fatty Liver Disease and Non-Alcoholic Steatohepatitis: An Update

Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are some of the biggest public health challenges due to their spread and increasing incidence around the world. NAFLD is characterized by intrahepatic lipid deposition, accompanied by dyslipidemia, hypertension, and insulin resistance, leading to more serious complications. Among the various causes, drug administration for the treatment of numerous kinds of diseases, such as antiarrhythmic and antihypertensive drugs, promotes the onset and progression of steatosis, causing drug-induced hepatic steatosis (DIHS). Here, we reviewed in detail the major classes of drugs that cause DIHS and the specific molecular mechanisms involved in these processes. Eight classes of drugs, among the most used for the treatment of common pathologies, were considered. The most diffused mechanism whereby drugs can induce NAFLD/NASH is interfering with mitochondrial activity, inhibiting fatty acid oxidation, but other pathways involved in lipid homeostasis are also affected. PubMed research was performed to obtain significant papers published up to November 2021. The key words included the class of drugs, or the specific compound, combined with steatosis, nonalcoholic steatohepatitis, fibrosis, fatty liver and hepatic lipid deposition. Additional information was found in the citations listed in other papers, when they were not displayed in the original search.

Priming, Triggering, Adaptation and Senescence (PTAS): A Hypothesis for a Common Damage Mechanism of Steatohepatitis

Understanding the pathomechanism of steatohepatitis (SH) is hampered by the difficulty of distinguishing between causes and consequences, by the broad spectrum of aetiologies that can produce the phenotype, and by the long time-span during which SH develops, often without clinical symptoms. We propose that SH develops in four phases with transitions: (i) priming lowers stress defence; (ii) triggering leads to acute damage; (iii) adaptation, possibly associated with cellular senescence, mitigates tissue damage, leads to the phenotype, and preserves liver function at a lower level; (iv) finally, senescence prevents neoplastic transformation but favours fibrosis (cirrhosis) and inflammation and further reduction in liver function. Escape from senescence eventually leads to hepatocellular carcinoma. This hypothesis for a pathomechanism of SH is supported by clinical and experimental observations. It allows organizing the various findings to uncover remaining gaps in our knowledge and, finally, to provide possible diagnostic and intervention strategies for each stage of SH development.

Jekyll and Hyde: nuclear receptors ignite and extinguish hepatic oxidative milieu

Nuclear receptors (NRs) are ligand-binding transcription factors that regulate gene networks and physiological responses. Often oxidative stress precedes the onset of liver diseases, and Nrf2 is a key regulator of antioxidant pathways. NRs crosstalk with Nrf2, since NR activation can influence the oxidative milieu by modulating reductive cellular processes. Diet and xenobiotics also regulate NR expression and activity, suggesting a feedback loop. Depending on the tissue context and cues, NRs either increase or decrease toxicity and oxidative damage. Many FDA-approved drugs target NRs, and one could potentially repurpose them to ameliorate reactive oxygen species (ROS). Here, we discuss how several NRs modulate oxidative stress subsequent to diet, organic pollutants, and drug-induced injury to the liver.

Hypoxia via ERK Signaling Inhibits Hepatic PPARα to Promote Fatty Liver

BACKGROUND & AIMS

Fatty liver or nonalcoholic fatty liver disease (NAFLD) is the most common liver disease associated with comorbidities such as insulin resistance and cardiovascular and metabolic diseases. Chronic activation of hypoxic signaling, in particular, hypoxia-inducible factor (HIF)2α, promotes NAFLD progression by repressing genes involved in fatty acid β-oxidation through unclear mechanisms. Therefore, we assessed the precise mechanism by which HIF2α promotes fatty liver and its physiological relevance in metabolic homeostasis.

METHODS

Primary hepatocytes from VHL (VhlΔHep) and PPARα (Ppara-null) knockout mice that were loaded with fatty acids, murine dietary protocols to induce hepatic steatosis, and fasting-refeeding dietary regimen approaches were used to test our hypothesis.

RESULTS

Inhibiting autophagy using chloroquine did not decrease lipid contents in VhlΔHep primary hepatocytes. Inhibition of ERK using MEK inhibitor decreased lipid contents in primary hepatocytes from a genetic model of constitutive HIF activation and primary hepatocytes loaded with free fatty acids. Moreover, MEK-ERK inhibition potentiated ligand-dependent activation of PPARα. We also show that MEK-ERK inhibition improved diet-induced hepatic steatosis, which is associated with the induction of PPARα target genes. During fasting, fatty acid β-oxidation is induced by PPARα, and refeeding inhibits β-oxidation. Our data show that ERK is involved in the post-prandial repression of hepatic PPARα signaling.

CONCLUSIONS

Overall, our results demonstrate that ERK activated by hypoxia signaling plays a crucial role in fatty acid β-oxidation genes by repressing hepatocyte PPARα signaling.

MicroRNAs and long non-coding RNAs in the pathophysiological processes of diabetic cardiomyopathy: emerging biomarkers and potential therapeutics

The epidemic of diabetes mellitus (DM) necessitates the development of novel therapeutic and preventative strategies to attenuate complications of this debilitating disease. Diabetic cardiomyopathy (DCM) is a frequent disorder affecting individuals diagnosed with DM characterized by left ventricular hypertrophy, diastolic and systolic dysfunction and myocardial fibrosis in the absence of other heart diseases. Progression of DCM is associated with impaired cardiac insulin metabolic signaling, increased oxidative stress, impaired mitochondrial and cardiomyocyte calcium metabolism, and inflammation. Various non-coding RNAs, such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), as well as their target genes are implicated in the complex pathophysiology of DCM. It has been demonstrated that miRNAs and lncRNAs play an important role in maintaining homeostasis through regulation of multiple genes, thus they attract substantial scientific interest as biomarkers for diagnosis, prognosis and as a potential therapeutic strategy in DM complications. This article will review the different miRNAs and lncRNA studied in the context of DM, including type 1 and type 2 diabetes and the contribution of pathophysiological mechanisms including inflammatory response, oxidative stress, apoptosis, hypertrophy and fibrosis to the development of DCM .

TRPV1 activation inhibits phenotypic switching and oxidative stress in vascular smooth muscle cells by upregulating PPARα

The proliferation and migration of vascular smooth muscle cells (VSMCs) is one of main reasons of vascular remodeling and is the pathogenesis of atherosclerosis and other vascular diseases. Transient receptor potential vanilloid 1 (TRPV1) is the specific receptor of capsaicin. TRPV1 has been previously reported to inhibit proliferation, migration and phenotypic switching, but the regulatory mechanisms and relevant signalling pathways are not clear. The aim of this study was to investigate the effects of capsaicin-activated TRPV1 on VSMC phenotypic switching. In this study, oxidized low density lipoprotein (ox-LDL) was used to induce the proliferation and migration of VSMCs. Our data showed that the VSMC proliferation induced by ox-LDL was dependent on the concentration of ox-LDL. Nevertheless, the data showed that capsaicin activated TRPV1 significantly decreased ox-LDL-induced superoxide anion generation. Phenotypic switching of VSMCs was inhibited by the activation of TRPV1. Furthermore, capsaicin decreased ox-LDL-induced superoxide anion generation by activating peroxisome proliferator activated receptor α (PPARα). TRPV1 inhibited VSMC phenotypic switching via upregulated expression of PPARα. It may be considered a useful target for the treatment of vascular remodeling.

Nano-designed carbon monoxide donor SMA/CORM2 exhibits protective effect against acetaminophen induced liver injury through macrophage reprograming and promoting liver regeneration

Acetaminophen (APAP) induced liver injury is the most common drug-induced liver injury, accounting for the top cause of acute liver failure in the United State, however the therapeutic options for it is very limited. Excess generation of reactive oxygen species (ROS) and the subsequent inflammatory responses are the major factors of the liver injury. Carbon monoxide (CO) is an important gaseous molecule with versatile functions including anti-oxidation and anti-inflammation, and we previous reported the therapeutic potential of a nano-designed CO donor SMA/CORM2 in a dextran sulphate sodium (DSS) induced mouse colitis model. In this context, we investigated the effect of SMA/CORM2 in an APAP-induced mouse acute liver injury model and tackled the mechanisms involved. We found upregulation of heme oxygenase-1 (HO-1, endogenous CO generating enzyme) and the dynamic changes of macrophage polarization (pro-inflammatory M1/anti-inflammatory M2), which played important roles in the process of live injury. SMA/CORM2 treatment remarkably increased the CO levels in the liver and circulation, by which oxidative stresses in the liver were significantly reduced, and more importantly, it remarkably suppressed the expression of M1 macrophages but alternatively increased M2 polarization. Consequently the liver injury was significantly ameliorated, and the proliferation and regeneration were greatly promoted through the Pi3k/Akt/mTOR signaling pathway. The shift of macrophage polarization accompanied with the downregulated hypoxia-inducible factor-1α (HIF-1α) level. These findings suggested CO released from SMA/CORM2 manipulated the macrophage reprogramming toward M2 phenotype by inhibiting HIF-1α, which subsequently protected liver against inflammatory injury and benefited tissue repair. Moreover, compared to native CORM2, SMA/CORM2 exhibited superior bioavailability and protective effect. We thus anticipate the application of SMA/CORM2 as a therapeutic regimen for APAP induced liver injury as well as other inflammatory diseases and disorders.

Lycopene Prevents DEHP-Induced Liver Lipid Metabolism Disorder by Inhibiting the HIF-1α-Induced PPARα/PPARγ/FXR/LXR System

Di(2-ethylhexyl) phthalate (DEHP) is a widespread pollutant that badly affects animals and human health. Lycopene (LYC) has been used as a dietary supplement that has effective antioxidant and antiobesity functions. The present goal was to understand the molecular mechanisms of LYC preventing DEHP-induced lipid metabolism of the liver. The mice were intragastrically administered with LYC (5 mg/kg) and/or DEHP (500 mg/kg or 1000 mg/kg). Here, we found that LYC attenuated DEHP-caused hepatic histopathological lesions including steatosis. Hematological and biochemical analyses revealed that LYC ameliorated DEHP-caused liver function and lipid metabolism disorders. DEHP caused lipid metabolism disorders via activating the peroxisome proliferator activated receptor α/γ (PPARα/γ) signal transducer and Farnesoid X receptor (FXR)/liver X receptor (LXR) signaling pathway. As a major regulator of lipid metabolism, hypoxia-inducible factor-1α (HIF-1α) system was elevated with increased fatty degeneration under DEHP exposure. However, LYC could decrease the levels of HIF-1α/PPARα/PPARγ/FXR/LXR signaling pathway-related factors. Our research indicated that LYC could prevent DEHP-induced lipid metabolism disorders via inhibiting the HIF-1α-mediated PPARα/PPARγ/FXR/LXR system. This study may provide a possible molecular mechanism for fatty liver induced by DEHP.

MiR-23a-5p exacerbates intestinal ischemia-reperfusion injury by promoting oxidative stress via targeting PPAR alpha

MiR-23a-5p is involved in the occurrence and development of some serious diseases, but its effects on intestinal ischemia-reperfusion (II/R) injury is unclear. In this research, the hypoxia/reoxygenation (H/R) model on IEC-6 cells and II/R model in mice were used. The data showed that the ROS level in model group was significantly increased compared with control group. The level of intestinal MPO was increased and serum SOD was decreased in mice compared with sham group. Moreover, the expression levels of miR-23a-5p in model groups were obviously increased in vitro and in vivo, while the expression levels of PPARα, FOXO3α, PGC-1α, Nrf2, CAT, NQO1, HO-1 and SOD2 were significantly decreased. The double luciferase reporter gene assay showed that there was binding site between miR-23a-5p and PPARα. When miR-23a-5p was inhibited or PPARα gene was overexpressed, H/R-caused cell damage was alleviated and ROS level was decreased compared with NC group. PPARα expression level was increased, accompanied by the increased levels of FOXO3α, PGC-1α, Nrf2, CAT, NQO1, HO-1 and SOD2. After enhancing miR-23a-5p expression or silencing PPARα gene, H/R-caused cell damage was further aggravated compared with NC group, and ROS level was increased associated with the decreased levels of FOXO3α, PGC-1α, Nrf2, CAT, NQO1, HO-1 and SOD2. Our study demonstrated that miR-23a-5p exacerbated II/R injury by promoting oxidative stress via targeting PPARα, which should be considered as one new drug target to treat II/R injury.

Saponins derived from the stems and leaves of Panax ginseng attenuate scrotal heat-induced spermatogenic damage via inhibiting the MAPK mediated oxidative stress and apoptosis in mice

Heat stress (HS) reaction is a stress response caused by adverse conditions. Currently, the incidence of reproductive malignancies particularly in males has been constantly increasing. This work investigated the effects of saponins derived from the stems and leaves of Panax ginseng (GSLS) on testicular injury induced by scrotal hyperthermia in mice. GSLS (150, 300 mg/kg) were administered intragastrically to mice for 14 days, then exposed to a single scrotal heat treatment at 43°C for 18 min on seventh day. HS induced a significant loss of multinucleate giant cells, desquamation of germ cells in destructive seminiferous tubules. Moreover, HS reduced the serum testosterone, testicular tissue superoxide dismutase activity and glutathione (GSH) content, while significantly enhanced the production of malondialdehyde (p < .05). GSLS exhibited the protective potential against HS-induced injury not only by modulating Bcl-2 family and caspase protease family, but also by suppressing the protein levels of heme oxygenase-1 (HO-1), heat shock protein 70 (HSP70), hypoxia inducible factor-1α (HIF-1α) and activation of Mitogen-activated protein kinase (MAPK) signaling pathways (p < .05). In conclusion, we clearly demonstrated that GSLS exhibited a significant protective effect against HS-induced testicular dysfunction, mainly the inhibition of oxidative stress associated apoptosis partly via regulation of the MAPK signaling pathway.

Transcriptional regulation of CYP3A4 by nuclear receptors in human hepatocytes under hypoxia

The human hepatic cytochrome P-450 3A4 (CYP3A4), recognized as a multifunctional enzyme, has a wide range of substrates including commonly used drugs. Previous investigations demonstrated that the expression of CYP3A4 in human hepatocytes could be regulated by some nuclear receptors (NRs) at transcriptional level under diverse situations. The significance of oxygen on CYP3A4-mediated metabolism seems notable while the regulatory mode of CYP3A4 in the particular case still remains elusive. Recently, striking evidence has emerged that both CYP3A4 and its regulator NR could be inhibited by exposure to hypoxia. Therefore, it is of great importance to elucidate whether and how these NRs act in the transcriptional regulation of CYP3A4 in human hepatocytes under hypoxic conditions. In this review, we mainly summarized transcriptional regulation of the pivotal enzyme CYP3A4 by NRs and explored the possible regulatory pathways of CYP3A4 via these major NRs under hypoxia, expecting to provide favorable evidence for further clinical guidance under such pathological situations.

Rifampicin activates AMPK and alleviates oxidative stress in the liver as mediated with Nrf2 signaling

Although rifampicin could have a hepatic toxic effect, it has also been shown that this chemical acts as a cellular protectant against oxidative stress. Therefore, we wondered whether rifampicin has a beneficial effect such as an anti-oxidant in the liver, because the efficacy of some drugs sometimes relates with their toxicity as well as protective effects. The present study aimed to investigate the antioxidant effect of rifampicin against arachidonic acid (AA) plus iron (AA + iron) cotreatment and against acetaminophen (APAP, 500 mg/kg)-induced oxidative stress, in vitro and in vivo, respectively. In vivo, oral administration of rifampicin (100 or 200 mg/kg) attenuated elevation of serum alanine aminotransferase (ALT) and aspartate transaminase (AST), serum liver injury markers, against APAP treatment and, histologically, ameliorated tissue damage. Under in vitro examination, MTT assays were used to assess the cell death inhibitory effect of rifampicin against AA + iron-induced oxidative stress. In addition, DCFH-DA and Rh 123 staining showed that rifampicin treatment reduced reactive oxygen species (ROS) production and mitochondrial membrane damage, which had been induced by AA + iron treatment. Further, we explored whether rifampicin treatment enhanced phosphorylation of AMP-activated protein kinase (AMPK) by activation of liver kinase B1 (LKB1), the upstream kinase of AMPKα. Activated AMPKα induced activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1), which are proteins functioning in redox balance. Moreover, we confirmed a reversed cell protective effect of rifampicin under compound C (an AMPK inhibitor) treatment. Overall, our data demonstrate that rifampicin effectively protects the liver against cellular oxidative stress through AMPKα and Nrf2 pathway.

Hypoxia exacerbates nonalcoholic fatty liver disease via the HIF-2α/PPARα pathway

This study aimed to investigate whether hypoxia can affect nonalcoholic fatty liver disease (NAFLD) progression and the associated mechanisms, specifically regarding the hypoxia-inducible factor (HIF)-2α/peroxisome proliferator-activated receptor (PPAR)α pathway in vitro and in vivo. Recent studies have reported that, compared with HIF-1α, HIF-2α has different effects on lipid metabolism. We propose hypoxia may exacerbate NAFLD by the HIF-2α upregulation-induced suppression of PPARα in the liver. To verify this hypothesis, a steatotic human hepatocyte (L02) cell line treated with free fatty acids and a mouse model of NAFLD fed a high-fat diet were used. Steatotic hepatocytes were treated with hypoxia, HIF-2α siRNA, PPARα agonists, and inhibitors, respectively. Meanwhile, the NAFLD mice were exposed to intermittent hypoxia or intermittent hypoxia with PPARα agonists. The relative gene expression levels of HIF-1α, HIF-2α, mitochondrial function, fatty acid β-oxidation and lipogenesis were examined. Evidence of lipid accumulation was observed, which demonstrated that, compared with normal hepatocytes, steatotic hepatocytes exhibited higher sensitivity to hypoxia. This phenomenon was closely associated with HIF-2α. Moreover, lipid accumulation in hepatocytes was ameliorated by HIF-2α silencing or a PPARα agonist, despite the hypoxia treatment. HIF-2α overexpression under hypoxic conditions suppressed PPARα, leading to PGC-1α, NRF-1, ESRRα downregulation, and mitochondrial impairment. Additionally, β-oxidation genes such as CPT1α, CPT2α, ACOX1, and ACOX2 were downregulated and lipogenesis genes including LXRα, FAS, and SCD1 were upregulated by hypoxia. Therefore, we concluded that HIF-2α overexpression induced by hypoxia aggravated NAFLD progression by suppressing fatty acid β-oxidation and inducing lipogenesis in the liver via PPARα.

The role of hypoxia-inducible factors in metabolic diseases

Hypoxia-inducible factors (HIFs), a family of transcription factors activated by hypoxia, consist of three α-subunits (HIF1α, HIF2α and HIF3α) and one β-subunit (HIF1β), which serves as a heterodimerization partner of the HIFα subunits. HIFα subunits are stabilized from constitutive degradation by hypoxia largely through lowering the activity of the oxygen-dependent prolyl hydroxylases that hydroxylate HIFα, leading to their proteolysis. HIF1α and HIF2α are expressed in different tissues and regulate target genes involved in angiogenesis, cell proliferation and inflammation, and their expression is associated with different disease states. HIFs have been widely studied because of their involvement in cancer, and HIF2α-specific inhibitors are being investigated in clinical trials for the treatment of kidney cancer. Although cancer has been the major focus of research on HIF, evidence has emerged that this pathway has a major role in the control of metabolism and influences metabolic diseases such as obesity, type 2 diabetes mellitus and non-alcoholic fatty liver disease. Notably increased HIF1α and HIF2α signalling in adipose tissue and small intestine, respectively, promotes metabolic diseases in diet-induced disease models. Inhibition of HIF1α and HIF2α decreases the adverse diet-induced metabolic phenotypes, suggesting that they could be drug targets for the treatment of metabolic diseases.

Hypoxia increases chemoresistance in human medulloblastoma DAOY cells via hypoxia‑inducible factor 1α‑mediated downregulation of the CYP2B6, CYP3A4 and CYP3A5 enzymes and inhibition of cell proliferation

Medulloblastomas are among the most frequently diagnosed pediatric solid tumors, and drug resistance remains as the principal cause of treatment failure. Hypoxia and the subsequent activation of hypoxia-inducible factor 1α (HIF-1α) are considered key factors in modulating drug antitumor effectiveness, but the underlying mechanisms in medulloblastomas have not yet been clearly understood. The aim of the present study was to determine whether hypoxia induces resistance to cyclophosphamide (CPA) and ifosfamide (IFA) in DAOY medulloblastoma cells, whether the mechanism is dependent on HIF-1α, and whether involves the modulation of the expression of cytochromes P450 (CYP)2B6, 3A4 and 3A5 and the control of cell proliferation. Monolayer cultures of DAOY medulloblastoma cells were exposed for 24 h to moderate (1% O₂) or severe (0.1% O₂) hypoxia, and protein expression was evaluated by immunoblotting. Cytotoxicity was studied with the MTT assay and by Annexin V/PI staining and flow cytometry. Cell proliferation was determined by the trypan-blue exclusion assay and cell cycle by propidium iodide staining and flow cytometry. Hypoxia decreased CPA and IFA cytotoxicity in medulloblastoma cells, which correlated with a reduction in the protein levels of CYP2B6, CYP3A4 and CYP3A5 and inhibition of cell proliferation. These responses were dependent on hypoxia-induced HIF-1α activation, as evidenced by chemical inhibition of its transcriptional activity with 2-methoxyestradiol (2-ME), which enhanced the cytotoxic activity of CPA and IFA and increased apoptosis. Our results indicate that by stimulating HIF-1α activity, hypoxia downregulates the expression of CYP2B6, CYP3A4 and CYP3A5, that in turn leads to decreased conversion of CPA and IFA into their active forms and thus to diminished cytotoxicity. These results support that the combination of HIF-1α inhibitors and canonical antineoplastic agents provides a potential therapeutic alternative against medulloblastoma.

The PPARα Agonist Fenofibrate Prevents Formation of Protein Aggregates (Mallory-Denk bodies) in a Murine Model of Steatohepatitis-like Hepatotoxicity

Chronic intoxication of mice with the porphyrinogenic compound 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) leads to morphological and metabolic changes closely resembling steatohepatitis, a severe form of metabolic liver disease in humans. Since human steatohepatitis (both the alcoholic and non-alcoholic type) is characterized by reduced expression of PPARα and disturbed lipid metabolism we investigated the role of this ligand-activated receptor in the development of DDC-induced liver injury. Acute DDC-intoxication was accompanied by early significant downregulation of Pparα mRNA expression along with PPARα-controlled stress-response and lipid metabolism genes that persisted in the chronic stage. Administration of the specific PPARα agonist fenofibrate together with DDC prevented the downregulation of PPARα-associated genes and also improved the stress response of Nrf2-dependent redox-regulating genes. Moreover, oxidative stress and inflammation were strongly reduced by DDC/fenofibrate co-treatment. In addition, fenofibrate prevented the disruption of hepatocyte intermediate filament cytoskeleton and the formation of Mallory-Denk bodies at late stages of DDC intoxication. Our findings show that, like in human steatohepatitis, PPARα is downregulated in the DDC model of steatohepatitis-like hepatocellular damage. Its downregulation and the pathomorphologic features of steatohepatitis are prevented by co-administration of fenofibrate.

LAZ3 protects cardiac remodeling in diabetic cardiomyopathy via regulating miR-21/PPARa signaling

Diabetes contributes to cardiovascular complications and the pathogenesis of cardiac remodeling that can lead to heart failure. We aimed to evaluate the functional role of LAZ3 in diabetic cardiomyopathy (DCM). Streptozotocin (STZ) was used to induce a diabetic mouse model. Three months after induction, the mice were subjected to retro-orbital venous plexus injection of adeno-associated virus 9 (AAV9) that overexpressed LAZ3. Six weeks after the infection, mouse hearts were removed to assess the degree of cardiac remodeling. LAZ3 was down-regulated in the diabetic mouse hearts and high glucose stimulated cardiomyocytes. Knock-down of LAZ3 in cardiomyocytes with LAZ3 siRNA reduced cell viability, increased the inflammatory response and induced oxidative stress and cell apoptosis. Overexpression of LAZ3 by infection with adeno-associated virus (AAV9)-LAZ3 protected against an inflammatory response, oxidative stress and cell apoptosis in both a high glucose stimulated in vitro study and diabetic mouse hearts. We found that LAZ3 increased the activation of PPARa, which increased PGC-1a activation and subsequently augmented NRF2 expression and nuclear translocation. This outcome was confirmed by NRF2 siRNA and a PPARa activator, since NRF2 siRNA abrogated the protective effects of LAZ3 overexpression, while the PPARa activator reversed the deteriorating phenotype of LAZ3 knock-down in both the in vitro and vivo study. Furthermore, LAZ3 decreased miR-21 expression, which resulted in PPARa activation, NRF2 expression and nuclear translocation. In conclusion, LAZ3 protects against cardiac remodeling in DCM by decreasing miR-21, thus regulating PPARa/NRF2 signaling.

Sodium Tanshinone IIA Sulfonate Decreases Cigarette Smoke-Induced Inflammation and Oxidative Stress via Blocking the Activation of MAPK/HIF-1α Signaling Pathway

Aberrant activation of hypoxia-inducible factor (HIF)-1α is frequently encountered and promotes oxidative stress and inflammation in chronic obstructive pulmonary disease (COPD). The present study investigated whether sodium tanshinone IIA sulfonate (STS), a water-soluble derivative of tanshinone IIA, can mediate its effect through inhibiting HIF-1α–induced oxidative stress and inflammation in cigarette smoke (CS)-induced COPD in mice. Here, we found that STS improved pulmonary function, ameliorated emphysema and decreased the infiltration of inflammatory cells in the lungs of CS-exposed mice. STS reduced CS- and cigarette smoke extract (CSE)-induced upregulation of tumor necrosis factor (TNF)-α and interleukin (IL)-1β in the lungs and macrophages. STS also inhibited CSE-induced reactive oxygen species (ROS) production, as well as the upregulation of heme oxygenase (HO)-1, NOX1 and matrix metalloproteinase (MMP)-9 in macrophages. In addition, STS suppressed HIF-1α expression in vivo and in vitro, and pretreatment with HIF-1α siRNA reduced CSE-induced elevation of TNF-α, IL-1β, and HO-1 content in the macrophages. Moreover, we found that STS inhibited CSE-induced the phosphorylation of ERK, p38 MAPK and JNK in macrophages, and inhibition of these signaling molecules significantly repressed CSE-induced HIF-1α expression. It indicated that STS inhibits CSE-induced HIF-1α expression likely by blocking MAPK signaling. Furthermore, STS also promoted HIF-1α protein degradation in CSE-stimulated macrophages. Taken together, these results suggest that STS prevents COPD development possibly through the inhibition of HIF-1α signaling, and may be a novel strategy for the treatment of COPD.

Licochalcone A Upregulates Nrf2 Antioxidant Pathway and Thereby Alleviates Acetaminophen-Induced Hepatotoxicity

Acetaminophen (APAP) overdose-induced fatal hepatotoxicity is majorly characterized by overwhelmingly increased oxidative stress while enhanced nuclear factor-erythroid 2-related factor 2 (Nrf2) is involved in prevention of hepatotoxicity. Although Licochalcone A (Lico A) upregulates Nrf2 signaling pathway against oxidative stress-triggered cell injury, whether it could protect from APAP-induced hepatotoxicity by directly inducing Nrf2 activation is still poorly elucidated. This study aims to explore the protective effect of Lico A against APAP-induced hepatotoxicity and its underlying molecular mechanisms. Our findings indicated that Lico A effectively decreased tert-butyl hydroperoxide (t-BHP)- and APAP-stimulated cell apoptosis, mitochondrial dysfunction and reactive oxygen species generation and increased various anti-oxidative enzymes expression, which is largely dependent on upregulating Nrf2 nuclear translocation, reducing the Keap1 protein expression, and strengthening the antioxidant response element promoter activity. Meanwhile, Lico A dramatically protected against APAP-induced acute liver failure by lessening the lethality; alleviating histopathological liver changes; decreasing the alanine transaminase and aspartate aminotransferase levels, malondialdehyde formation, myeloperoxidase level and superoxide dismutase depletion, and increasing the GSH-to-GSSG ratio. Furthermore, Lico A not only significantly modulated apoptosis-related protein by increasing Bcl-2 expression, and decreasing Bax and caspase-3 cleavage expression, but also efficiently alleviated mitochondrial dysfunction by reducing c-jun N-terminal kinase phosphorylation and translocation, inhibiting Bax mitochondrial translocation, apoptosis-inducing factor and cytochrome c release. However, Lico A-inhibited APAP-induced the lethality, histopathological changes, hepatic apoptosis, and mitochondrial dysfunction in WT mice were evidently abrogated in Nrf2^-/- mice. These investigations firstly implicated that Lico A has protective potential against APAP-induced hepatotoxicity which may be strongly associated with the Nrf2-mediated defense mechanisms.