Importance of peroxisome proliferator-activated receptor-gamma in hepatic ischemia/reperfusion injury in mice

Hepatocyte miR-21-5p-deficiency alleviates APAP-induced liver injury by inducing PPARγ and autophagy

Acetaminophen (APAP)-induced liver injury is one of the most frequent causes of acute liver failure worldwide. Significant increases in the levels of miRNA-21 in both liver tissues and plasma have been observed in APAP-overdosed animals and humans. However, the mechanistic effect of miRNA-21 on acute liver injury remains unknown. In this study, we generated a new hepatocyte-specific miRNA-21 knockout (miR-21-HKO) mouse line. miR-21-HKO and the background-matched sibling wild-type (WT) mice were treated with a toxic dose of APAP. Compared with WT mice, miR-21 HKO mice showed an increased survival, a reduction of necrotic hepatocytes, and an increased expression of light chain 3 beta, which suggested an autophagy activation. The expression of PPARγ was highly induced in the livers of miR-21-HKO mice after a 2-h APAP treatment, which preceded the activation of LC3B at the 12 h APAP treatment. miR-21 negatively regulated PPARγ protein expression by targeting its 3'-UTR. When PPARγ function was blocked by a potent antagonist GW9662 in miR-21-HKO mice, the autophage activation was significantly diminished, suggesting an indispensable role of PPARγ signaling pathway in miR-21-mediated hepatotoxicity. Taken together, hepatocyte-specific depletion of miRNA-21 alleviated APAP-induced hepatotoxicity by activating PPARγ and autophagy, demonstrating a crucial new regulatory role of miR-21 in APAP-mediated liver injury.

Didymin Alleviates Cerebral Ischemia-Reperfusion Injury by Activating the PPAR Signaling Pathway

PURPOSE

Cerebral ischemia-reperfusion (IR) injury is a severe secondary injury induced by reperfusion after stroke. Didymin has been reported to have a protective effect on intracerebral hemorrhage. However, the underlying mechanism of didymin on regulating cerebral IR injury remains largely unknown.

MATERIALS AND METHODS

A rat cerebral IR model and oxygen-glucose deprivation/reperfusion (OGD/R) model in PC12 cells were established. Hematoxylin and eosin (H&E) was used to detect the pathological changes in brain tissues, and TUNEL staining was performed to detect apoptosis of brain tissues. MTT and flow cytometry were used to measure the viability and apoptosis of PC12 cells. QRT-PCR and western blot were used to detect inflammation cytokines in PC12 cells. Western blot was used to measure the expression of PPAR-γ, RXRA, Bax, c-caspase-3, and Bcl-2.

RESULTS

Didymin pretreatment decreased apoptotic rates, reduced levels of Bax and c-caspase-3, and increased Bcl-2 level in vivo and in vitro. Additionally, didymin pretreatment increased viability and decreased the inflammation levels [interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, and monocyte chemotactic protein (MCP)-1] of OGD/R treated PC12 cells. Moreover, didymin activated the peroxisome proliferator-activated receptors (PPAR) signaling pathway and increased the expression of PPAR-γ and RXRA in OGD/R treated PC12 cells. Inhibition of PPAR-γ eliminated the protective effect of didymin on OGD/R treated cells.

CONCLUSION

Didymin protected neuron cells against IR injury in vitro and in vivo by activation of the PPAR pathway. Didymin may be a candidate drug for IR treatment.

PPARγ Mediates Protective Effect against Hepatic Ischemia/Reperfusion Injury via NF-κB Pathway

BACKGROUND

Hepatic ischemia/reperfusion injury (HIRI) is an unavoidable complication in liver surgery, however its pathological process is still unclear. Therefore, in this study, the role and mechanism of peroxisome proliferator-activated receptor gamma (PPARγ) was investigated in HIRI.

MATERIALS AND METHODS

We constructed mice models with HIRI and L02 cell models insulted hypoxia/re-oxygenation (H/R). PPARγ agonist rosiglitazone was administered prior to HIRI in mice and PPARγ-siRNA was to H/R treatment in L02 cells. Liver injury was measured by serum ALT, AST and LDH levels and performing H&E staining; the inflammatory injury was reflected by inflammatory markers IL-1β, IL-6 and TNF-α, which were assayed by Real-time PCR and Western blotting, MPO activity was determined using commercial kits; oxidative stress injury was evaluated by iNOS, MDA, SOD and GSH-PX levels; apoptosis was detected by cleaved-Caspase-3, TUNEL staining and flow cytometry; NF-κB signaling activation was reflected by phosphorylation of IκBα (p-IκBα) and nuclear translocation of NF-κB p65.

RESULTS

The level of PPARγ expression was obviously down-regulated both in mice liver subjected to IRI and in L02 cells to H/R. Overexpression of PPARγ presented protective effect on HIRI by reducing serum levels of aminotransferase and hepatic necrosis, inhibiting inflammation and apoptosis and alleviating oxidative stress in vivo. But PPARγ-siRNA aggravate H/R insult by promoting inflammation and apoptosis in vitro. Mechanistically, the NF-κB pathway activity was increased with PPARγ down-regulation by PPARγ-siRNA. Importantly, inhibition of NF-κB signaling abolished PPARγ knockdown-mediated hepatic injury.

CONCLUSIONS

PPARγ present protective effects on HIRI by attenuating liver injury, inflammatory response, oxidative stress and apoptosis in vivo and in vitro, and its mechanism may be related to down-regulation of NF-κB signaling.

Reactive Oxygen Species Induce Fatty Liver and Ischemia-Reperfusion Injury by Promoting Inflammation and Cell Death

Liver transplantation is the ultimate method for treating end-stage liver disease. With the increasing prevalence of obesity, the number of patients with non-alcoholic fatty liver, a common cause of chronic liver disease, is on the rise and may become the main cause of liver transplantation in the future. With the increasing gap between the number of donor livers and patients waiting for liver transplantation and the increasing prevalence of non-alcoholic fatty liver, the proportion of steatosis livers among non-standard donor organs is also increasing. Ischemia-reperfusion injury has historically been the focus of attention in the liver transplantation process, and severe ischemia-reperfusion injury leads to adverse outcomes of liver transplantation. Studies have shown that the production of reactive oxygen species and subsequent oxidative stress play a key role in the pathogenesis of hepatic ischemia and reperfusion injury and non-alcoholic fatty liver. Furthermore, the sensitivity of fatty liver transplantation to ischemia-reperfusion injury has been suggested to be related to the production of reactive oxygen species (ROS) and oxidative stress. In ischemia-reperfusion injury, Kupffer cell and macrophage activation along with mitochondrial damage and the xanthine/xanthine oxidase system promote marked reactive oxygen species production and the inflammatory response and apoptosis, resulting in liver tissue injury. The increased levels of ROS and lipid peroxidation products, vicious circle of ROS and oxidative stress along with mitochondrial dysfunction promoted the progress of non-alcoholic fatty liver. In contrast to the non-fatty liver, a non-alcoholic fatty liver produces more reactive oxygen species and suffers more serious oxidative stress when subjected to ischemia-reperfusion injury. We herein review the effects of reactive oxygen species on ischemia-reperfusion injury and non-alcoholic fatty liver injury as well as highlight several treatment approaches.

Protective mechanisms of telmisartan against hepatic ischemia/reperfusion injury in rats may involve PPARγ-induced TLR4/NF-κB suppression

Hepatic ischemia-reperfusion (I/R) is an important cause of liver damage in many clinical situations. Toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) is an inflammatory pathway activated in hepatic I/R injury. Telmisartan, a selective angiotensin II type 1 receptor antagonist and peroxisome proliferator-activated receptor-gamma (PPARγ) partial agonist, can inhibit the expression of pro-inflammatory cytokines. The present work investigated the possible protective effect of telmisartan against hepatic I/R injury and explored its possible mechanisms in rats. Rats were divided into four equal groups: sham-operated control, telmisartan-treated sham-operated control, I/R untreated, and I/R telmisartan-treated groups. Hepatic injury was evaluated biochemically by serum activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and histopathological examination. Hepatic oxidative stress biomarkers, myeloperoxidase level, PPARγ and TLR4 mRNA expression, and NF-κB and active caspase 3 immunoexpression were determined. The study showed that telmisartan attenuated hepatic I/R, as evidenced by decreased serum ALT and AST activities and confirmed by improvement of the histopathological changes. The protective effect of telmisartan was associated with modulation of oxidative stress parameters, myeloperoxidase level, PPARγ and TLR4 mRNA expression, and NF-κB and caspase 3 immunoexpression. Taken together, the current study showed that telmisartan could protect the rat liver from I/R injury. This hepatoprotective effect was attributed to, at least in part, increase in PPARγ expression and suppression of TLR4/NF-κB pathway.

Effect of Edaravone on MicroRNA Expression in Exosomes after Hepatic Ischemia-reperfusion Injury

BACKGROUND AND OBJECTIVE

Hepatic ischemia-reperfusion injury (HIRI) results in serious complications after liver resection and transplantation. Edaravone (ED) has a protective effect on IRI. This study was designed to evaluate whether ED could protect the liver of rats from HIRI injury and explored its exosomal miRNA-related mechanism.

METHODS

The sham group, hepatic ischemia/reperfusion (IR group), and hepatic ischemia/reperfusion + edaravone (ED group) models were established. We determined the protective effect of ED by measuring alanine aminotransferase (ALT), aspartate aminotransferase (AST), malondialdehyde (MDA), superoxide dismutase (SOD); enzyme-linked immunosorbent assay for tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β); hematoxylin-eosin staining and immunohistochemistry for histopathological changes. Exosomal miRNAs were subjected to second-generation sequencing to identify their differential expression. The results were analyzed using bioinformatics methods and validated using real-time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

HIRI rats showed higher levels of ALT, AST, oxidative stress, and inflammatory markers; ED attenuated these effects. The sequencing results showed 6 upregulated and 13 downregulated miRNAs in the IR vs. sham groups, 10 upregulated and 10 downregulated miRNAs in the ED vs. IR groups. PC-3p-190-42101 was screened as an overlapping differentially expressed miRNA, and RT-qPCR validation showed that its expression in HIRI rats was significantly decreased; ED prevented this downregulation. Moreover, the expression of PC-3P-190-42101 was significantly correlated with the level of inflammatory factors.

CONCLUSION

These findings indicate that ED can regulate the level of inflammatory factors by affecting the expression of miRNA PC-3p-190-42101 in plasma exosomes to protect the liver from IRI.

PPARγ Plays an Important Role in Acute Hepatic Ischemia-Reperfusion Injury via AMPK/mTOR Pathway

Background

Hepatic ischemia-reperfusion (IR) injury is one of the severe complications associated with liver surgery and leads to liver dysfunction. PPARγ is always linked with various physiologic pathways, and it can alleviate liver damage in IR injury.

Aim

In this study, we explored the potential mechanism of PPARγ in the pathogenesis of hepatic IR injury by mice model.

Methods

After treated with si-PPARγ or rosiglitazone, mice were subjected to hepatic ischemia-reperfusion. Liver tissue and blood samples were collected to evaluate liver injury and detected relative mRNA and protein expressions.

Results

The expression of PPARγ was increased after reperfusion. And the alleviation of PPARγ aggravated the liver damage in IR; at the same time, upregulation of the expression of PPARγ released the liver damage. And these effects of PPARγ in IR were related to the AMPK/mTOR/autophagy signaling pathway.

Conclusion

PPARγ plays an important role in hepatic IR injury at least partly via the AMPK/mTOR/autophagy pathway.

PGC-1α Protects against Hepatic Ischemia Reperfusion Injury by Activating PPARα and PPARγ and Regulating ROS Production

Peroxisome proliferator-activated receptors (PPARs) α and γ have been shown to be protective in hepatic ischemia/reperfusion (I/R) injury. However, the precise role of PPARγ coactivator-1α (PGC-1α), which can coactivate both of these receptors, in hepatic I/R injury, remains largely unknown. This study was designed to test our hypothesis that PGC-1α is protective during hepatic I/R injury in vitro and in vivo. Our results show that endogenous PGC-1α is basally expressed in normal livers and is moderately increased by I/R. Ectopic PGC-1α protects against hepatic I/R and hepatocyte anoxia/reoxygenation (A/R) injuries, whereas knockdown of endogenous PGC-1α aggravates such injuries, as evidenced by assessment of the levels of serum aminotransferases and inflammatory cytokines, necrosis, apoptosis, cell viability, and histological examination. The EMSA assay shows that the activation of PPARα and PPARγ is increased or decreased by the overexpression or knockdown of PGC-1α, respectively, during hepatic I/R and hepatocyte A/R injuries. In addition, the administration of specific antagonists of either PPARα (MK886) or PPARγ (GW9662) can effectively decrease the protective effect of PGC-1α against hepatic I/R and hepatocyte A/R injuries. We also demonstrate an important regulatory role of PGC-1α in reactive oxygen species (ROS) metabolism during hepatic I/R, which is correlated with the induction of ROS-detoxifying enzymes and is also dependent on the activations of PPARα and PPARγ. These data demonstrate that PGC-1α protects against hepatic I/R injury, mainly by regulating the activation of PPARα and PPARγ. Thus, PGC-1α may be a promising therapeutic target for the protection of the liver against I/R injury.

PPARγ in Ischemia-Reperfusion Injury: Overview of the Biology and Therapy

Ischemia-reperfusion injury (IRI) is a complex pathophysiological process that is often characterized as a blood circulation disorder caused due to various factors (such as traumatic shock, surgery, organ transplantation, burn, and thrombus). Severe metabolic dysregulation and tissue structure destruction are observed upon restoration of blood flow to the ischemic tissue. Theoretically, IRI can occur in various tissues and organs, including the kidney, liver, myocardium, and brain, among others. The advances made in research regarding restoring tissue perfusion in ischemic areas have been inadequate with regard to decreasing the mortality and infarct size associated with IRI. Hence, the clinical treatment of patients with severe IRI remains a thorny issue. Peroxisome proliferator-activated receptor γ (PPARγ) is a member of a superfamily of nuclear transcription factors activated by agonists and is a promising therapeutic target for ameliorating IRI. Therefore, this review focuses on the role of PPARγ in IRI. The protective effects of PPARγ, such as attenuating oxidative stress, inhibiting inflammatory responses, and antagonizing apoptosis, are described, envisaging certain therapeutic perspectives.

Ischemia reperfusion-induced metastasis is resistant to PPARγ agonist pioglitazone in a murine model of colon cancer

Ischemia reperfusion injury (IRI) during liver-metastasis resection for treatment of colon cancer may increase the risk of further metastasis. Peroxisome proliferator-activated receptor-γ (PPARγ) activation has been observed to exert a protective effect against IRI and IRI-induced metastasis of hepatocellular carcinoma. The present study aimed to investigate the effect of the PPARγ agonist pioglitazone on tumor metastasis and liver injury following IRI in a mouse model of colon cancer. Pioglitazone (30 mg/kg weight) was administered orally 1.5 h before and 2 h after the initiation of ischemia and was orally administrated daily to mice from day 0–21. SL4-cancer cells expressing red fluorescent protein (SL4-RFP) (1 × 10⁶) were injected into the spleen. Fifteen minutes after injection, the hepatoduodenal ligament was clamped with a vessel clip, and released 5 min later. Liver, blood and tumor samples were taken from mice in order to determine if inflammation was induced by IRI. The effect of pioglitazone on liver metastasis was assessed. Furthermore, the effect of pioglitazone to control the inflammatory response during IRI progression was examined. Liver metastasis along with MMP-9 activation and the production of inflammatory cytokines were resistant to pioglitazone. Our results indicate that liver metastasis and associated inflammation in mice were resistant to pioglitazone.

Dexmedetomidine preconditioning alleviated murine liver ischemia and reperfusion injury by promoting macrophage M2 activation via PPARγ/STAT3 signaling

BACKGROUND

Although a protective role of dexmedetomidine in liver ischemia and reperfusion (IR) injury has been reported, the underlying mechanism remains to be determined. The aim of this study is to analyze the effects of dexmedetomidine on the regulation of macrophage innate immune activation during liver IR.

METHODS

Mice were randomly divided into dexmedetomidine preconditioning (DEX) and phosphate buffered saline vehicle control (VEH) groups. A murine 70% warm liver IR model was used, and liver injury and intrahepatic inflammation was compared between groups. Bone marrow-derived macrophages (BMDMs) were stimulated with LPS in the presence or absence of dexmedetomidine. The inflammatory cytokine production was measured, and the macrophage M1/M2 polarization was determined in different groups. The underlying mechanism of dexmedetomidine in regulating macrophage M2 activation was also analyzed.

RESULTS

Compared to mice observed in the control group, mice in the DEX group showed reduced liver injury and diminished proinflammatory immune responses in livers post IR. In vitro, dexmedetomidine pretreatment promoted BMDMs M2 activation, as evidenced by increased Arg1 and Mrc1 gene induction, decreased iNOS gene induction, inhibited phosphorated-signal transducer and activator of transcription 1 (p-STAT1) but enhanced p-STAT6 expression, much lower levels of proinflammatory TNF-α and IL-6, and higher levels of anti-inflammatory IL-10 cytokine secretion. Signaling pathway analysis revealed that peroxisome proliferator-activated receptor-γ (PPARγ)/ STAT3 activation was upregulated in BMDMs with dexmedetomidine pretreatment. Furthermore, PPARγ knockdown by siRNA not only inhibited STAT3 activation but also abrogated the promotion effects of macrophage M2 activation in BMDMs pretreated with dexmedetomidine. Finally, in vivo PPARγ inhibition in macrophages by siRNA significantly increased liver IR injury and intrahepatic inflammation in mice from the Dex group, with no significant effect in the VEH group.

CONCLUSIONS

Our results indicate that dexmedetomidine preconditioning inhibited intrahepatic proinflammatory innate immune activation by promoting macrophage M2 activation in a PPARγ/STAT3 dependent manner. Our results demonstrate a novel innate immune regulatory mechanism by dexmedetomidine preconditioning during liver IR injury.

Suppression of microRNA‑27a protects against liver ischemia/reperfusion injury by targeting PPARγ and inhibiting endoplasmic reticulum stress

Liver ischemia‑reperfusion (I/R) injury is an important clinical issue related to liver transplantation. Recent studies suggest that microRNAs are implicated in various biological and pathological processes, including liver I/R injury. This study aimed to investigate the role and potential mechanism of miR‑27a during liver I/R injury. A liver I/R model was induced via 60 min of ischemia and reperfusion for 6 h in rats. Cells were transfected with miR‑27a mimics or the miR‑27a inhibitor to examine the effect of miR‑27a on liver I/R. Apoptotic cells were detected by flow cytometry and TUNEL staining. The expression of miR‑27a was measured by real‑time PCR. The expression of peroxisome proliferator‑activated receptor γ (PPARγ); gastrin‑releasing peptide 78 (GRP78) and C/EBP homologous protein (CHOP) were detected by western blot analysis. The results showed that miR‑27a was significantly upregulated during I/R injury in vivo and in vitro. In addition, miR‑27a inhibitors attenuated hypoxia/reoxygenation (H/R)‑induced oxidative stress, endoplasmic reticulum stress (ERS) and apoptosis in AML12 cells. By contrast, miR‑27a mimics promoted hypoxia/reoxygenation‑induced ERS, and apoptosis. Furthermore, PPARγ was identified as a target gene of miR‑27a using bioinformatic analysis and a dual‑luciferase reporter assay. Knockdown of PPARγ significantly abrogated the inhibitory effect of miR‑27a inhibitors on the ERS pathway. Moreover, the miR‑27a antagomir attenuated liver I/R injury in rats, a finding manifested by reduced ALT/AST, hepatocyte apoptosis, oxidative stress and inhibition of the ERS pathway. Taken together, these findings demonstrate that suppression of miR‑27a protects against liver I/R injury by targeting PPARγ and by inhibiting the ERS pathway.

Endothelial PPARγ Is Crucial for Averting Age-Related Vascular Dysfunction by Stalling Oxidative Stress and ROCK

Aging plays a significant role in the progression of vascular diseases and vascular dysfunction. Activation of the ADP-ribosylation factor 6 and small GTPases by inflammatory signals may cause vascular permeability and endothelial leakage. Pro-inflammatory molecules have a significant effect on smooth muscle cells (SMC). The migration and proliferation of SMC can be promoted by tumor necrosis factor alpha (TNF-α). TNF-α can also increase oxidative stress in SMCs, which has been identified to persuade DNA damage resulting in apoptosis and cellular senescence. Peroxisome proliferator-activated receptor (PPAR) acts as a ligand-dependent transcription factor and a member of the nuclear receptor superfamily. They play key roles in a wide range of biological processes, including cell differentiation and proliferation, bone formation, cell metabolism, tissue remodeling, insulin sensitivity, and eicosanoid signaling. The PPARγ activation regulates inflammatory responses, which can exert protective effects in the vasculature. In addition, loss of function of PPARγ enhances cardiovascular events and atherosclerosis in the vascular endothelium. This appraisal, therefore, discusses the critical linkage of PPARγ in the inflammatory process and highlights a crucial defensive role for endothelial PPARγ in vascular dysfunction and disease, as well as therapy for vascular aging.

PPAR gamma agonist, pioglitazone, rescues liver damage induced by renal ischemia/reperfusion injury

Remote organ damage is the major cause of death in patients with acute kidney injury (AKI) due to renal ischemia reperfusion (IR). Liver is one of the vital organs which are profoundly affected by AKI. The present study aims to investigate the role of peroxisome proliferator activator receptor gamma (PPARγ) in liver damage induced by IR injury in rats. Renal IR was induced by right nephrectomy, occlusion of left renal pedicle for 45 min to induce ischemia, and then reperfusion for 6 or 24 h. The PPARγ agonist, pioglitazone, was given orally for 7 days before renal IR procedure. Animals receiving pioglitazone showed improvement in renal and hepatic functions when compared to IR groups. Renal IR increased renal, hepatic and serum levels of tumor necrosis factor-α (TNF-α) and induced apoptotic cell death in liver. These effects were diminished with pioglitazone. In addition, pioglitazone reduced renal IR-induced oxidative stress in liver. Pioglitazone reduced malondialdehyde (MDA) content and NADPH oxidase mRNA expression and induced further increase in nuclear factor erythroid 2-related factor 2 (Nrf2) expression when compared to IR groups. Furthermore, pioglitazone increased the expression of PPARγ target genes such as renal and hepatic PPARγ1 (Pparg1), hepatic hemoxygenase-1 (Hmox1), and hepatic thioredoxin (TRx). Histological profiles for kidney and liver were also ameliorated with pioglitazone. Hence, PPARγ is a potential target to protect liver in patients with renal IR injury.

FAM3A mediates PPARγ's protection in liver ischemia-reperfusion injury by activating Akt survival pathway and repressing inflammation and oxidative stress

FAM3A is a novel mitochondrial protein, and its biological function remains largely unknown. This study determined the role and mechanism of FAM3A in liver ischemia-reperfusion injury (IRI). In mouse liver after IRI, FAM3A expression was increased. FAM3A-deficient mice exhibited exaggerated liver damage with increased serum levels of AST, ALT, MPO, MDA and oxidative stress when compared with WT mice after liver IRI. FAM3A-deficient mouse livers had a decrease in ATP content, Akt activity and anti-apoptotic protein expression with an increase in apoptotic protein expression, inflammation and oxidative stress when compared WT mouse livers after IRI. Rosiglitazone pretreatment protected against liver IRI in wild type mice but not in FAM3A-deficient mice. In cultured hepatocytes, FAM3A overexpression protected against, whereas FAM3A deficiency exaggerated oxidative stress-induced cell death. FAM3A upregulation or FAM3A overexpression inhibited hypoxia/reoxygenation-induced activation of apoptotic gene and hepatocyte death in P2 receptor-dependent manner. FAM3A deficiency blunted rosiglitazone's beneficial effects on Akt activation and cell survival in cultured hepatocytes. Collectively, FAM3A protects against liver IRI by activating Akt survival pathways, repressing inflammation and attenuating oxidative stress. Moreover, the protective effects of PPARγ agonist(s) on liver IRI are dependent on FAM3A-ATP-Akt pathway.

PPAR-gamma activation is associated with reduced liver ischemia-reperfusion injury and altered tissue-resident macrophages polarization in a mouse model

BACKGROUND

PPAR-gamma (γ) is highly expressed in macrophages and its activation affects their polarization. The effect of PPAR-γ activation on Kupffer cells (KCs) and liver ischemia-reperfusion injury (IRI) has not yet been evaluated. We investigated the effect of PPAR-γ activation on KC-polarization and IRI.

MATERIALS AND METHODS

Seventy percent (70%) liver ischemia was induced for 60mins. PPAR-γ-agonist or vehicle was administrated before reperfusion. PPAR-γ-antagonist was used to block PPAR-γ activation. Liver injury, necrosis, and apoptosis were assessed post-reperfusion. Flow-cytometry determined KC-phenotypes (pro-inflammatory Nitric Oxide +, anti-inflammatory CD206+ and anti-inflammatory IL-10+).

RESULTS

Liver injury assessed by serum AST was significantly decreased in PPAR-γ-agonist versus control group at all time points post reperfusion (1hr: 3092±105 vs 4469±551; p = 0.042; 6hr: 7041±1160 vs 12193±1143; p = 0.015; 12hr: 5746±328 vs 8608±1259; p = 0.049). Furthermore, liver apoptosis measured by TUNEL-staining was significantly reduced in PPAR-γ-agonist versus control group post reperfusion (1hr:2.46±0.49 vs 6.90±0.85%;p = 0.001; 6hr:26.40±2.93 vs 50.13±8.29%; p = 0.048). H&E staining demonstrated less necrosis in PPAR-γ-agonist versus control group (24hr:26.66±4.78 vs 45.62±4.57%; p = 0.032). The percentage of pro-inflammatory NO+ KCs was significantly lower at all post reperfusion time points in the PPAR-γ-agonist versus control group (1hr:28.49±4.99 vs 53.54±9.15%; p = 0.040; 6hr:5.51±0.54 vs 31.12±9.58%; p = 0.009; 24hr:4.15±1.50 vs 17.10±4.77%; p = 0.043). In contrast, percentage of anti-inflammatory CD206+ KCs was significantly higher in PPAR-γ-agonist versus control group prior to IRI (8.62±0.96 vs 4.88 ±0.50%; p = 0.04). Administration of PPAR-γ-antagonist reversed the beneficial effects on AST, apoptosis, and pro-inflammatory NO+ KCs.

CONCLUSION

PPAR-γ activation reduces IRI and decreases the pro-inflammatory NO+ Kupffer cells. PPAR-γ activation can become an important tool to improve outcomes in liver surgery through decreasing the pro-inflammatory phenotype of KCs and IRI.

Oryzanol Modifies High Fat Diet-Induced Obesity, Liver Gene Expression Profile, and Inflammation Response in Mice

In Western countries and China, the dietary habit of high calories usually results in hyperlipidemia, which is closely associated with cardiovascular diseases. In the study, we investigated the antihyperlipidemic effect of oryzanol and its molecular mechanism in the high fat diet (HFD) mouse model. In total, 60 ICR mice were randomly divided into control group, HFD group, and HFD+Ory group. The mice from the HFD+Ory group were additionally fed with 100 mg/kg of oryzanol by intragastric administration. Our data indicated that oryzanol treatment for 10 weeks significantly reduced bodyweight, liver weight, and adipose tissues weight of the mice; lowered the contents of total cholesterol (TC), triglycerides (TG), and low density lipoprotein-cholesterol (LDL-C); and elevated high density lipoprotein-cholesterol (HDL-C) in the plasma of HFD mice. Compared with the HFD group, H&E staining showed that oryzanol treatment decreased the size of fat droplets of liver tissues and the size of adipocytes. Gene chip data found that oryzanol administration caused 32 genes to increase expressions while 60 genes had reduced expressions in the liver tissues of HFD mice. IPA software was used to analyze the protein interaction network and found that transcript factor NF-κB located in the central role of network, meaning NF-κB may have important function in the lipid-lowering effect of oryzanol. Western blotting and RT-qPCR confirmed that lipid metabolism-related gene expressions were obviously regulated by oryzanol administration. Oryzanol also inhibited expressions of inflammatory factor in the liver tissues of HDF mice. Taken together, our data indicate that oryzanol treatment can regulate lipid metabolism-related gene expressions and inhibit HDF-caused obesity in mice.

Asiatic acid protects against hepatic ischemia/reperfusion injury by inactivation of Kupffer cells via PPARγ/NLRP3 inflammasome signaling pathway

Hepatic ischemia/reperfusion (I/R) contributes to major complications in clinical practice affecting perioperative morbidity and mortality. Recent evidence suggests the key role of nucleotide-binding oligomerization domain-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammaosme activation on the pathogenesis of I/R injury. Asiatic acid (AA) is a pentacyclic triterpene derivative presented with versatile activities, including antioxidant, anti-inflammation and hepatoprotective effects. This study was designed to determine whether AA had potential hepatoprotective benefits against hepatic I/R injury, as well as to unveil the underlying mechanisms involved in the putative effects. Mice subjected to warm hepatic I/R, and Kupffer cells (KCs) or RAW264.7 cells challenged with lipopolysaccharide (LPS)/H₂O₂, were pretreated with AA. Administration of AA significantly attenuated hepatic histopathological damage, global inflammatory level, apoptotic signaling level, as well as NLRP3 inflammasome activation. These effects were correlated with increased expression of peroxisome proliferator-activated receptor gamma (PPARγ). Conversely, pharmacological inhibition of PPARγ by GW9662 abolished the protective effects of AA on hepatic I/R injury and in turn aggravated NLRP3 inflammasome activation. Activation of NLRP3 inflammasome was most significant in nonparenchymal cells (NPCs). Depletion of KCs by gadolinium chloride (GdCl3) further attenuated the detrimental effects of GW9662 on hepatic I/R as well as NLRP3 activation. In vitro, AA concentration-dependently inhibited LPS/H₂O₂-induced NLRP3 inflammaosome activation in KCs and RAW264.7 cells. Either GW9662 or genetic knockdown of PPARγ abolished the AA-mediated inactivation of NLRP3 inflammasome. Mechanistically, AA attenuated I/R or LPS/H₂O₂-induced ROS production and phosphorylation level of JNK, p38 MAPK and IκBα but not ERK, a mechanism dependent on PPARγ. Finally, AA blocked the deleterious effects of LPS/H₂O₂-induced macrophage activation on hepatocyte viability in vitro, and improved survival in a lethal hepatic I/R injury model in vivo. Collectively, these data suggest that AA is effective in mitigating hepatic I/R injury through attenuation of KCs activation via PPARγ/NLRP3 inflammasome signaling pathway.

The molecular mechanisms of action of PPAR-γ agonists in the treatment of corneal alkali burns (Review)

Corneal alkali burns (CAB) are characterized by injury-induced inflammation, fibrosis and neovascularization (NV), and may lead to blindness. This review evaluates the current knowledge of the molecular mechanisms responsible for CAB. The processes of cytokine production, chemotaxis, inflammatory responses, immune response, cell signal transduction, matrix metalloproteinase production and vascular factors in CAB are discussed. Previous evidence indicates that peroxisome proliferator-activated receptor γ (PPAR-γ) agonists suppress immune responses, inflammation, corneal fibrosis and NV. This review also discusses the role of PPAR-γ as an anti-inflammatory, anti-fibrotic and anti-angiogenic agent in the treatment of CAB, as well as the potential role of PPAR-γ in the pathological process of CAB. There have been numerous studies evaluating the clinical profiles of CAB, and the aim of this systematic review was to summarize the evidence regarding the treatment of CAB with PPAR-γ agonists.

PPARγ activation reduces ischemia/reperfusion-induced metastasis in a murine model of hepatocellular carcinoma

Ischemia/reperfusion (I/R) injury during liver resection or transplantation for the treatment of hepatocellular carcinoma (HCC) may increase the risk of metastasis. Peroxisome proliferator-activated receptor-γ (PPARγ) activation has been observed to exert a protective effect against hepatic I/R injury. However, whether PPARγ activation exerts a protective effect against I/R-associated liver metastasis remains unknown. Therefore, the present study aimed to investigate the effects of the PPAR agonist rosiglitazone and the specific PPARγ antagonist GW9662 on tumor metastasis following hepatic I/R. An experimental mouse model of hepatic I/R-induced HCC metastasis was designed in order to determine the effects of I/R on tumor metastasis in the liver. Four groups were established: Sham, control (I/R), rosiglitazone (Ro) and rosiglitazone with GW9662 (Ro + GW) groups. In the latter two groups, the treatments were administered intravenously 1 h prior to the induction of ischemia. Tumor load was measured 12 days after the procedure. Furthermore, tissue analyses were conducted to determine the expression levels of alanine aminotransferase, myeloperoxidase (MPO), matrix metalloproteinase (MMP)-9, vascular cell adhesion molecule (VCAM)-1, nuclear factor (NF)-κB and PPARγ. Rosiglitazone pretreatment appeared to significantly mitigate hepatic I/R injury, as indicated by serological and histological analysis. The levels of VCAM-1, MPO and MMP-9 expression in the Ro group were significantly reduced at 8 h following ischemia compared with those in the control and Ro + GW groups. In addition, rosiglitazone inhibited the I/R-induced activation of NF-κB, and GW9662 attenuated the inhibitory effect. To the best of our knowledge, the present study is the first to report on the expression and the functional roles of PPARγ in I/R-associated metastasis. Short-term treatment of mice with rosiglitazone, a potent PPARγ agonist, confers protective effects against hepatic I/R-associated metastasis. Thus, PPARγ may be a potential therapeutic target for the protection of the liver against I/R-associated metastasis.

PPARγ and the Innate Immune System Mediate the Resolution of Inflammation

The resolution of inflammation is an active and dynamic process, mediated in large part by the innate immune system. Resolution represents not only an increase in anti-inflammatory actions, but also a paradigm shift in immune cell function to restore homeostasis. PPARγ, a ligand activated transcription factor, has long been studied for its anti-inflammatory actions, but an emerging body of literature is investigating the role of PPARγ and its ligands (including thiazolidinediones, prostaglandins, and oleanolic acids) in all phases of resolution. PPARγ can shift production from pro- to anti-inflammatory mediators by neutrophils, platelets, and macrophages. PPARγ and its ligands further modulate platelet and neutrophil function, decreasing trafficking, promoting neutrophil apoptosis, and preventing platelet-leukocyte interactions. PPARγ alters macrophage trafficking, increases efferocytosis and phagocytosis, and promotes alternative M2 macrophage activation. There are also roles for this receptor in the adaptive immune response, particularly regarding B cells. These effects contribute towards the attenuation of multiple disease states, including COPD, colitis, Alzheimer's disease, and obesity in animal models. Finally, novel specialized proresolving mediators-eicosanoids with critical roles in resolution-may act through PPARγ modulation to promote resolution, providing another exciting area of therapeutic potential for this receptor.

Losartan protects liver against ischaemia/reperfusion injury through PPAR-γ activation and receptor for advanced glycation end-products down-regulation

BACKGROUND AND PURPOSE

PPAR-γ has been reported to be a protective regulator in ischaemia/reperfusion (I/R) injury. The receptor for advanced glycation end-products (RAGE) plays a major role in the innate immune response, and its expression is associated with PPAR-γ activation. Several angiotensin receptor blockers possess partial agonist activities towards PPAR-γ. Therefore, this study investigated the action of losartan, particularly with regard to PPAR-γ activation and RAGE signalling pathways during hepatic I/R.

EXPERIMENTAL APPROACH

Mice were subjected to 60 min of ischaemia followed by 6 h of reperfusion. Losartan (0.1, 1, 3 and 10 mg · kg⁻¹) was administered 1 h prior to ischaemia and immediately before reperfusion. GW9662, a PPAR-γ antagonist, was administered 30 min prior to first pretreatment with losartan.

KEY RESULTS

Losartan enhanced the DNA-binding activity of PPAR-γ in I/R. Losartan attenuated the increased serum alanine aminotransferase activity, TNF-α and IL-6 levels, and nuclear concentrations of NF-κB in I/R. GW9662 reversed these beneficial effects. Losartan caused a decrease in apoptosis as assessed by TUNEL assay, in release of cytochrome c and in cleavage of caspase-3, and these effects were abolished by GW9662 administration. Losartan attenuated not only I/R-induced RAGE overexpression, but also its downstream early growth response protein-1-dependent macrophage inflammatory protein 2 level; phosphorylation of p38, ERK and JNK; and subsequent c-Jun phosphorylation. GW9662 reversed these effects of losartan administration.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that losartan ameliorates I/R-induced liver damage through PPAR-γ activation and down-regulation of the RAGE signalling pathway.

SPA0355 attenuates ischemia/reperfusion-induced liver injury in mice

Hepatic ischemia/reperfusion (I/R) injury leads to oxidative stress and acute inflammatory responses that cause liver damage and have a considerable impact on the postoperative outcome. Much research has been performed to develop possible protective techniques. We aimed to investigate the efficacy of SPA0355, a synthetic thiourea analog, in an animal model of hepatic I/R injury. Male C57BL/6 mice underwent normothermic partial liver ischemia for 45 min followed by varying periods of reperfusion. The animals were divided into three groups: sham operated, I/R and SPA0355 pretreated. Pretreatment with SPA0355 protected against hepatic I/R injury, as indicated by the decreased levels of serum aminotransferase and reduced parenchymal necrosis and apoptosis. Liver synthetic function was also restored by SPA0355 as reflected by the prolonged prothrombin time. To gain insight into the mechanism involved in this protection, we measured the activity of nuclear factor-κB (NF-κB), which revealed that SPA0355 suppressed the nuclear translocation and DNA binding of NF-κB subunits. Concomitantly, the expression of NF-κB target genes such as IL-1β, IL-6, TNF-α and iNOS was significantly downregulated. Lastly, the liver antioxidant enzymes superoxide dismutase, catalase and glutathione were upregulated by SPA0355 treatment, which correlated with the reduction in serum malondialdehyde. Our results suggest that SPA0355 pretreatment prior to I/R injury could be an effective method to reduce liver damage.

Silencing of long noncoding RNA AK139328 attenuates ischemia/reperfusion injury in mouse livers

Recently, increasing evidences had suggested that long noncoding RNAs (LncRNAs) are involved in a wide range of physiological and pathophysiological processes. Here we determined the LncRNA expression profile using microarray technology in mouse livers after ischemia/reperfusion treatment. Seventy one LncRNAs were upregulated, and 27 LncRNAs were downregulated in ischemia/reperfusion-treated mouse livers. Eleven of the most significantly deregulated LncRNAs were further validated by quantitative PCR assays. Among the upregulated LncRNAs confirmed by quantitative PCR assays, AK139328 exhibited the highest expression level in normal mouse livers. siRNA-mediated knockdown of hepatic AK139328 decreased plasma aminotransferase activities, and reduced necrosis area in the livers with a decrease in caspase-3 activation after ischemia/reperfusion treatment. In ischemia/reperfusion liver, knockdown of AK139328 increased survival signaling proteins including phosphorylated Akt (pAkt), glycogen synthase kinase 3 (pGSK3) and endothelial nitric oxide synthase (peNOS). Furthermore, knockdown of AK139328 also reduced macrophage infitration and inhibited NF-κB activity and inflammatory cytokines expression. In conclusion, these findings revealed that deregulated LncRNAs are involved in liver ischemia/reperfusion injury. Silencing of AK139328 ameliorated ischemia/reperfusion injury in the liver with the activation of Akt signaling pathway and inhibition of NF-κB activity. LncRNA AK139328 might be a novel target for diagnosis and treatment of liver surgery or transplantation.

Maraviroc attenuates trauma-hemorrhage-induced hepatic injury through PPAR gamma-dependent pathway in rats

Maraviroc is a CC-chemokine receptor 5 (CCR5) antagonist with potent antiviral and cancer preventive effects. Recent evidence suggests that the co-existence of CCR5 in various cell types is involved in inflammation. However, the effects that CCR5 antagonists produce in trauma-hemorrhage remain unknown. The peroxisome proliferator-activated receptor gamma (PPAR_γ) pathway exerts anti-inflammatory effects in injury. In this study, we hypothesized that maraviroc administration in male rats, after trauma-hemorrhage, decreases cytokine production and protects against hepatic injury through a PPAR_γ-dependent pathway. Male Sprague-Dawley rats underwent trauma-hemorrhage (mean blood pressure maintained at approximately 35-40 mmHg for 90 minutes), followed by fluid resuscitation. During resuscitation, a single dose of maraviroc (3 mg/kg, intravenously) with and without a PPAR_γ antagonist GW9662 (1 mg/kg, intravenously), GW9662 or vehicle was administered. Plasma alanine aminotransferase (ALT) with aspartate aminotransferase (AST) concentrations and various hepatic parameters were measured (n=8 rats/group) at 24 hours after resuscitation. The results showed that trauma-hemorrhage increased hepatic myeloperoxidase activity, intercellular adhesion molecule-1 and interleukin-6 levels, and plasma ALT and AST concentrations. These parameters were significantly improved in the maraviroc-treated rats subjected to trauma-hemorrhage. Maraviroc treatment also increased hepatic PPAR_γ expression compared with vehicle-treated trauma-hemorrhaged rats. Co-administration of GW9662 with maraviroc abolished the maraviroc-induced beneficial effects on the above parameters and hepatic injury. These results suggest that the protective effect of maraviroc administration on alleviation of hepatic injury after trauma-hemorrhage, which is, at least in part, through PPAR_γ-dependent pathway.

The effects of PPAR-γ agonist pioglitazone on renal ischemia/reperfusion injury in rats

BACKGROUND

Acute renal failure due to renal ischemia/reperfusion (IR) injury is a significant clinical problem in cardiovascular surgery. Reactive oxygen species and inflammation play essential roles in the pathophysiology of IR injury. Matrix metalloproteinases (MMPs) are enzymes that play important roles in inflammation and mediate extracellular matrix degradation. It is known that peroxisome proliferator-activated receptor-γ agonists have antiinflammatory and antioxidant effects. In the present study, we aimed to investigate the effects of pioglitazone, a synthetic peroxisome proliferator-activated receptor-γ agonist, on MMPs and oxidative stress in a renal IR injury model in rats.

MATERIALS AND METHODS

Male Wistar albino rats were divided into three groups: control (n = 7), placebo (n = 7; saline/p.o.), and pioglitazone (n = 7; 5 mg/kg/day/p.o.). In the control group, a right nephrectomy was conducted without left renal IR injury. In the placebo and pioglitazone groups, pretreatments were started 3 d before operation. In both groups, left renal pedicles were clamped for 60 min and then reperfused for 60 min. Paraffinized renal sections were evaluated histopathologically. Furthermore, expressions of MMP-2, MMP-9, tissue inhibitor of metalloproteinase (TIMP)-2, superoxide dismutase 1 (SOD1), and p47-phox/p67-phox subunits of NADPH oxidase were determined by immunostaining and scoring.

RESULTS

In the placebo group, renal IR injury induced diffuse tubular necrosis and intense acute inflammation, but pioglitazone inhibited these effects. MMP-2, MMP-9, and TIMP-2 expression increased in the placebo group. However, while MMP-2 and -9 expression decreased, TIMP-2 expression did not change in the pioglitazone group. p47-phox/p67-phox expression increased in the placebo group, but SOD1 expression did not change. Pioglitazone diminished p47-phox/p67-phox expression, whereas it enhanced SOD1 expression.

CONCLUSION

Our results suggest that pioglitazone might be helpful to reduce renal IR injury because of its antiinflammatory and antioxidant effects.

The Current Knowledge of the Role of PPAR in Hepatic Ischemia-Reperfusion Injury

Strategies to improve the viability of steatotic livers could reduce the risk of dysfunction after surgery and increase the number of organs suitable for transplantation. Peroxisome proliferator-activated receptors (PPARs) are major regulators of lipid metabolism and inflammation. In this paper, we review the PPAR signaling pathways and present some of their lesser-known functions in liver regeneration. Potential therapies based on PPAR regulation will be discussed. The data suggest that further investigations are required to elucidate whether PPAR could be a potential therapeutic target in liver surgery and to determine the most effective therapies that selectively regulate PPAR with minor side effects.

The current state of knowledge of hepatic ischemia-reperfusion injury based on its study in experimental models

The present review focuses on the numerous experimental models used to study the complexity of hepatic ischemia/reperfusion (I/R) injury. Although experimental models of hepatic I/R injury represent a compromise between the clinical reality and experimental simplification, the clinical transfer of experimental results is problematic because of anatomical and physiological differences and the inevitable simplification of experimental work. In this review, the strengths and limitations of the various models of hepatic I/R are discussed. Several strategies to protect the liver from I/R injury have been developed in animal models and, some of these, might find their way into clinical practice. We also attempt to highlight the fact that the mechanisms responsible for hepatic I/R injury depend on the experimental model used, and therefore the therapeutic strategies also differ according to the model used. Thus, the choice of model must therefore be adapted to the clinical question being answered.

Milk fat globule--EGF factor VIII ameliorates liver injury after hepatic ischemia-reperfusion

BACKGROUND

Hepatic ischemia-reperfusion (I/R) injury is a serious clinical complication that may compromise liver function because of extensive hepatocyte loss. Therefore, the development of novel and effective therapies for hepatic I/R is critical for the improvement of patient outcome. It has been previously shown that administration of milk fat globule-EGF factor VIII (MFG-E8), a membrane-associated secretory glycoprotein, exerts significant beneficial effects under acute inflammatory conditions through multiple physiological processes associated with tissue remodeling.

METHODS

To determine whether administration of recombinant human (rh) MFG-E8 attenuates liver injury in an animal model of hepatic I/R, male adult rats were subjected to 70% hepatic ischemia for 90 min, followed by reperfusion. At the beginning of reperfusion, rats were treated intravenously with normal saline (vehicle) or rhMFG-E8 (160 μg/kg) over a period of 30 min. MFG-E8 levels and various measurements were assessed 4 h after reperfusion. In addition, survival study was conducted in MFG-E8(-/-) and rhMFG-E8-treated wild-type (WT) mice using a total hepatic ischemia model.

RESULTS

Liver and plasma MFG-E8 protein levels were significantly decreased after hepatic I/R. Administration of rhMFG-E8 significantly improved liver injury, suppressed apoptosis, attenuated inflammation and oxidative stress, and downregulated NF-κB pathway. We also noticed that rhMFG-E8 treatment restored the downregulated PPAR-γ expression after hepatic I/R. MFG-E8(-/-) mice showed deterioration on survival and, in contrast, rhMFG-E8-treated WT mice showed a significant improvement of survival compared with vehicle-treated WT mice.

CONCLUSIONS

MFG-E8-mediated multiple physiological events may represent an effective therapeutic option in tissue injury following an episode of hepatic I/R.

Ischemia-Reperfusion Injury and Ischemic-Type Biliary Lesions following Liver Transplantation

Ischemia-reperfusion (I-R) injury after liver transplantation (LT) induces intra- and/or extrahepatic nonanastomotic ischemic-type biliary lesions (ITBLs). Subsequent bile duct stricture is a significant cause of morbidity and even mortality in patients who underwent LT. Although the pathogenesis of ITBLs is multifactorial, there are three main interconnected mechanisms responsible for their formation: cold and warm I-R injury, injury induced by cytotoxic bile salts, and immunological-mediated injury. Cold and warm ischemic insult can induce direct injury to the cholangiocytes and/or damage to the arterioles of the peribiliary vascular plexus, which in turn leads to apoptosis and necrosis of the cholangiocytes. Liver grafts from suboptimal or extended-criteria donors are more susceptible to cold and warm I-R injury and develop more easily ITBLs than normal livers. This paper, focusing on liver I-R injury, reviews the risk factors and mechanisms leading to ITBLs following LT.

Pharmacological preconditioning with nicorandil and pioglitazone attenuates myocardial ischemia/reperfusion injury in rats

The present investigation was designed to study the cardioprotective effects of nicorandil and pioglitazone preconditioning in myocardial ischemia/reperfusion-induced hemodynamic, biochemical and histological changes in rats. Oral doses of nicorandil (3 or 6 mg/kg) and pioglitazone (10 or 20mg/kg) were administered once daily for 5 consecutive days. Rats were then subjected to myocardial ischemia/reperfusion (40 min/10 min). Heart rate and ventricular arrhythmias were recorded during ischemia/reperfusion progress. At the end of reperfusion, plasma creatine kinase-MB activity and total nitrate/nitrite were determined. In addition, lactate, adenine nucleotides, thiobarbituric acid reactive substances, reduced glutathione and myeloperoxidase activity were estimated in the heart left ventricle. Finally, histological examination was performed to visualize the protective cellular effects of different pretreatments. Nicorandil (3 or 6 mg/kg) was effective in attenuating the ischemia/reperfusion-induced ventricular arrhythmias, creatine kinase-MB release, lactate accumulation and oxidative stress. Nicorandil (3 mg/kg) was more effective in improving the energy production and lowering the elevated myeloperoxidase activity. Both doses of pioglitazone (10 or 20 mg/kg) were equally effective in reducing lactate accumulation and completely counteracting the oxidative stress. Pioglitazone (10 mg/kg) was more effective in improving energy production and reducing ventricular arrhythmias, plasma creatine kinase-MB release and total nitrate/nitrite. It seems that selective mitochondrial K(ATP) channel opening by lower doses of nicorandil and pioglitazone in the present study provided more cardioprotection against ventricular arrhythmias and biochemical changes induced by ischemia/reperfusion. Histological examination revealed also better improvement by the lower dose of nicorandil than that of pioglitazone.

Pioglitazone attenuates allergic inflammation and induces production of regulatory T lymphocytes

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) agonists have been shown to be involved in the regulation of allergic inflammatory responses. The molecular mechanisms by which PPAR-gamma activation inhibits the inflammatory process have not been well understood.

METHODS

BALB/c mice received ovalbumin (OVA) sensitization followed by OVA intranasal challenge. Mice in the treatment group received intragastric administration with pioglitazone (PIO; 30 mg/kg) before each OVA challenge. Various allergic responses were then assessed.

RESULTS

The frequencies of sneezing and nose-scratching and eosinophil infiltration decreased significantly in the PIO treatment group compared with the OVA group (p < 0.05). The PIO treatment also showed that the levels of nasal cavity lavage fluid interleukin (IL)-5 and sera OVA-specific immunoglobulin E (IgE) were markedly reduced (p < 0.05). PIO significantly increased the expression of Foxp3 mRNA (p < 0.05) and induced production of regulatory T lymphocyte (p < 0.01) compared with the OVA group.

CONCLUSION

Given the potent effectiveness shown by PIO, we conclude that PPAR-gamma agonists deserve investigation as potential therapies for human allergic upper airway inflammation.

Peroxisome Proliferator-Activated Receptor–γ Agonist Induces Regulatory T Cells in a Murine Model of Allergic Rhinitis

Objective. To evaluate the effects of peroxisome proliferator-activated receptor (PPAR)–γ agonist on the induction of regulatory T cells (Tregs) in a murine model of allergic rhinitis.

Study Design. Randomized controlled trial.

Setting. Animal study.

Subjects and Methods. BALB/c mice that received ovalbumin sensitization and challenge served as the ovalbumin group (n = 6). Two separate groups of 6 mice received intragastric administration with PPAR-γ agonist pioglitazone (30 mg/kg/d) or pioglitazone plus PPAR-γ antagonist GW9662 (0.5 mg/d) before each ovalbumin challenge. The control group (n = 6) was treated with drug vehicle alone. Various allergic responses were assessed. Real-time polymerase chain reaction was performed to investigate the mRNA expression of forkhead box P3 (Foxp3), T-bet, and GATA-3. Flow cytometry was used to determine the percentage of Tregs.

Results. Mice developed typical pathophysiological allergic rhinitis features after the ovalbumin challenge. The frequencies of sneezing and scratching were significantly decreased by pioglitazone treatment ( P < .0001). Eosinophils infiltration and the levels of interleukin-5 and interferon-γ in nasal cavity lavage fluid and sera immunoglobulin E were also markedly decreased by pioglitazone ( P < .001). The expression of Foxp3 mRNA and the population of Tregs were significantly increased by pioglitazone ( P < .05). Cotreatment with GW9662 reversed the anti-inflammatory effects of pioglitazone. The effects of PPAR-γ agonist on Foxp3 mRNA expression and Tregs induction were abrogated by administration of GW9662.

Conclusion. PPAR-γ agonist attenuates upper airway allergic inflammation in a PPAR-γ-dependent fashion, and the beneficial effects of pioglitazone in airway allergic inflammation may be mediated by induction of Tregs.

Pioglitazone attenuates ischemia/reperfusion-induced liver injury in rats

INTRODUCTION

Hepatic ischemia/reperfusion (I/R) injury leads to free radical generation and acute inflammatory responses that cause liver damage, an important problem for liver transplantation. Pioglitazone is known to protect I/R injury in various tissues; however, the mechanism of cytoprotection is not well understood. This study investigated the effects of pioglitazone administration in a warm hepatic I/R model on tumor necrosis factor (TNF)-alpha level, tissue injury, and antioxidant enzyme activity.

MATERIALS AND METHODS

Eighty wistar strain rats were divided into 4 groups (n = 20): Group 1 sham hosts; Group 2 hepatic I/R; Group 3 hepatic I/R + pioglitazone (10 mg/kg); and Group 4 hepatic I/R + vehicle. Rat livers were subjected to 30 minutes of ischemia followed by 6 hours of reperfusion. After reperfusion rats were humanely killed to obtain liver tissue to study glutathione peroxidase (GPx), superoxide dysmutase (SOD), malondialdehyde (MDA) levels and for histopathologic assessment. TNF-alpha, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) were measured in serum.

RESULTS

Pioglitazone pretreatment significantly reduced liver enzyme content (ALT, 176.80 +/- 13.75 vs 235.28 +/- 31.92 and AST, 748.20 +/- 79.29 vs 944.85 +/- 101.87) and TNF-alpha level (9:8.60 +/- 8.67 vs 138.28 +/- 9.99) after I/R compared with the control group. MDA level (3.02 +/- 0.37 vs 4.36 +/- 0.38) and hepatocytic degeneration were reduced in the pioglitazone-treated group. GPx (2.40 +/- 0.25 vs 1.36 +/- 0.31) and SOD activity (2.22 +/- 0.30 vs 1.40 +/- 0.35) were significantly higher in the pioglitazone-treated group compared with the control group.

CONCLUSION

The present study showed that pioglitazone administration improved hepatic I/R injury that was associated with enhanced antioxidant enzyme activities and suppression of TNF-alpha, ALT, and AST levels. Because peroxisome proliferator-activated receptor-gamma agonists are widely used to treat diabetic patients, it may be relatively easy to expand their clinical indication. However, further investigations will be required to delineate protective mechanisms by which pioglitazone attenuates hepatic tissue injury after I/R.

Liver apoptosis is age dependent and is reduced by activation of peroxisome proliferator-activated receptor-gamma in hemorrhagic shock

A clinical observation in pediatric and adult intensive care units is that the incidence of multiple organ failure in pediatric trauma victims is lower than in adult patients. However, the molecular mechanisms are not yet defined. Recent experimental studies have shown that the nuclear peroxisome proliferator-activated receptor-gamma (PPARgamma) modulates the inflammatory process. In this study, we hypothesized that severity of liver injury may be age dependent and PPARgamma activation may provide beneficial effects. Hemorrhagic shock was induced in anesthetized young (3-5 mo old) and mature male Wistar rats (11-13 mo old) by withdrawing blood to a mean arterial blood pressure of 50 mmHg. After 3 h, rats were rapidly resuscitated with shed blood. Animals were euthanized 3 h after resuscitation. In mature rats, liver injury appeared more pronounced compared with young rats and was characterized by marked hepatocyte apoptosis, extravasation of erythrocytes, and accumulation of neutrophils. The ratio between the antiapoptotic protein Bcl-2 and the proapoptotic protein BAX was lower, whereas activity of caspase-3, the executioner of apoptosis, was higher in liver of mature rats compared with young rats. Plasma alanine aminotransferase levels were not different between the two age groups. This heightened liver apoptosis was associated with a significant downregulation of PPARgamma DNA binding in mature rats compared with young rats. Treatment with the PPARgamma ligand ciglitazone significantly reduced liver apoptosis in mature rats. Our data suggest that liver injury after severe hemorrhage is age dependent and PPARgamma activation is a novel hepatoprotective mechanism.

Evidence of anti-inflammatory effects of pioglitazone in the murine pleurisy model induced by carrageenan

Several studies have shown that the anti-inflammatory effect of Pioglitazone extends beyond the cardiovascular system. This study examines the anti-inflammatory effect of Pioglitazone in comparison to reference drugs (Dexamethasone and Indomethacin) in the mouse model of pleurisy induced by carrageenan which is characterized by two distinct phases (4 and 48 h) of inflammation. Pioglitazone (20 and 50 mg/kg, i.p., 0.5 h before pleurisy) inhibited both neutrophil (4 h) and mononuclears (48 h) influxes (P<0.01), but not exudation (P>0.05). While one dose of Pioglitazone was effective in inhibiting inflammation at 4 h, additional doses (10 or 20 mg/kg, i.p., 0.5 h before pleurisy induction followed by either a second dose at 24 h after the first one or two further doses at 12 h of time interval after the first one) were necessary to elicit inhibition of the second (48 h) inflammation phase. These effects were associated with a marked decrease in adenosine-deaminase (ADA) activity, tumor necrosis factor-alpha (TNF-alpha) and interleukin 1-beta (IL-1beta) levels (P<0.01). Myeloperoxidade (MPO) activity was inhibited only at 4 h (P<0.05). By contrast, reference drugs were able to inhibit all the studied inflammatory parameters (P<0.05). These results demonstrated an interesting anti-inflammatory property of this thiazolidinedione class and strengthen prior evidence that PPAR pathways constitute another important route of inflammatory process inhibition of this pleurisy model.

Rosiglitazone-enriched diet did not protect liver ischemia-reperfusion injury in a rat model

PURPOSE

To determine whether rosiglitazone-enriched diet offer protection in a classical model of liver ischemia-reperfusion injury in rats.

METHODS

Two days before the experiment, rats were divided into 2 groups: Control Group (n=13) rats fed with standard diet; Rosi Group (n=13): rats fed with a powdered standard diet supplemented with rosiglitazone. The animals were submitted to liver ischemia-reperfusion by clamping the pedicle of median and left anterolateral lobes. After 1 hour of partial hepatic ischemia, the clamp was removed for reperfusion. After 2 or 24 hours (Control and Rosi Groups), blood was collected for enzymes and cytokines analysis. Ischemic and non-ischemic liver were collected for malondialdehyde analysis and histological assessment. Lungs were removed for tissue myeloperoxidase quantification.

RESULTS

There were no statistical differences between groups for all analysed parameters.

CONCLUSION

In this model, rosiglitazone-enriched diet did not protect liver against ischemia-reperfusion injury.

Prostacyclin-induced peroxisome proliferator-activated receptor-alpha translocation attenuates NF-kappaB and TNF-alpha activation after renal ischemia-reperfusion injury

Prostacyclin and peroxisome proliferator-activated receptors (PPAR) protect against ischemia-reperfusion (I/R) injury by the induction of an anti-inflammatory pathway. In this study, we examined the prostacyclin-enhanced protective effect of PPARalpha in I/R-induced kidney injury. PPAR-alpha reduced the NF-kappaB-induced overexpression of TNF-alpha and apoptosis in cultured kidney cells. In a murine model, pretreating wild-type (WT) mice with a PPAR-alpha activator, docosahexaenoic acid (DHA), significantly reduced I/R-induced renal dysfunction (lowered serum creatinine and urea nitrogen levels), apoptotic responses (decreased apoptotic cell number and caspase-3, -8 activation), and NF-kappaB activation. By comparison, I/R-induced injury was exacerbated in PPAR-alpha knockout mice. This indicated that PPAR-alpha attenuated renal I/R injury via NF-kappaB-induced TNF-alpha overexpression. Overexpression of prostacyclin using an adenovirus could also induce PPAR-alpha translocation from the cytosol into the nucleus to inhibit caspase-3 activation. This prostacyclin/PPAR-alpha pathway attenuated TNF-alpha promoter activity by binding to NF-kappaB. Using a cAMP inhibitor (CAY10441) and a prostacyclin receptor antibody, we also found that there was another prostacyclin/IP receptor/cAMP pathway that could inhibit TNF-alpha production. Taken together, our results demonstrate for the first time that prostacyclin induces the translocation of PPAR-alpha from the cytosol into the nucleus and attenuates NF-kappaB-induced TNF-alpha activation following renal I/R injury. Treatments that can augment prostacyclin, PPAR-alpha, or the associated signaling pathways may ameliorate conditions associated with renal I/R injury.

Role of leptin in hepatic ischemia/reperfusion-induced intestinal injury of rats

AIM: To explore the changes of leptin in intestinal tract following hepatic ischemia/reperfusion (H-I/R), to investigate the association between these changes and H-I/R-induced intestinal injury, and to find out the role of leptin in H-I/R-induced intestinal injury.

METHODS: A 70% H-I/R model of rats was established, forming 5 groups including sham-operation and injury ones based on different reperfusion time. Enzyme-colorimetry was used to detect serum diamine oxidase activity after injury, hematoxylin-eosin staining and immunohistochemistry were applied to investigate pathological variations and leptin protein expressions in duodenum after injury, respectively, while reverse transcriptase-PCR was used to detect leptin mRNA expressions in duodenum after injury.

RESULTS: Compared with sham-operation group after injury, the four reperfusion groups showed no significant difference in serum diamine oxidase activity, but serum diamine oxidase level was significantly higher in 60 min ischemia/60 min reperfusion (I60'R60') group than in I60'R360' group (P = 0.0077). Pathological investigation suggested that duodenal impairments at the early phase of H-I/R were more serious, while the impairments at the later phase lessened gradually. Compared with leptin protein expression in duodenum of sham-operation group after injury, that of I60'R240' and I60'R360' groups increased significantly (0.126503 ± 0.005873, 0.129458 ± 0.003755 vs 0.079269 ± 0.001995, both P < 0.01), and the levels of reperfusion groups decreased in such order as I60'R360', I60'R240', I60'R60' and I60'R150' groups. Compared with leptin mRNA expression in duodenum of sham-operation group after injury, that of I60'R150' group decreased significantly (0.944 ± 0.033 vs 1.022 ± 0.011, P = 0.049), and it was significantly lower than the level of I60'R360' group.

CONCLUSION: The expression changes of leptin in intestinal tract after H-I/R are closely associated with intestinal injury, suggesting that leptin may be a protective factor of resisting H-I/R-induced intestinal injury.

Activation of peroxisome proliferator-activated receptor-gamma during hepatic ischemia is age-dependent

Hepatic ischemia/reperfusion injury is a complication of liver surgery, transplantation, and shock and is known to be age-dependent. Our laboratory has recently shown that peroxisome proliferator-activated receptor-gamma (PPARgamma) is down-regulated during hepatic ischemia and that this exacerbates injury. Here we examined whether activation of PPARgamma during ischemia was age-dependent. Male mice of different ages (young: 4-5 weeks; adult: 10-12 weeks; old: 10-12 months) were subjected to up to 90 min of hepatic ischemia. PPARgamma activation occurred throughout ischemia in young mice, whereas activation in adult and old mice was lost after 30 min. No significant differences were noted in PPARgamma ligand expression among the age groups. However, in young mice we observed a predominance of PPARgamma1 in the nucleus, whereas in old mice this isoform remained largely in the cytoplasm. Finally, the degree of PPARgamma activation was associated with autophagy in the liver, a mechanism of self-preservation. PPARgamma activation is prolonged in young mice as compared to older mice. This appears to be mediated by a selective retention of PPARgamma1 in the nucleus and is associated with increased autophagy. The data suggest that PPARgamma activation is an important component of the age-dependent response to hepatic ischemia/reperfusion injury.

Pioglitazone is as effective as dexamethasone in a cockroach allergen-induced murine model of asthma

Background

While glucocorticoids are currently the most effective therapy for asthma, associated side effects limit enthusiasm for their use. Peroxisome proliferator-activated receptor-γ (PPAR-γ) activators include the synthetic thiazolidinediones (TZDs) which exhibit anti-inflammatory effects that suggest usefulness in diseases such as asthma. How the ability of TZDs to modulate the asthmatic response compares to that of glucocorticoids remains unclear, however, because these two nuclear receptor agonists have never been studied concurrently. Additionally, effects of PPAR-γ agonists have never been examined in a model involving an allergen commonly associated with human asthma.

Methods

We compared the effectiveness of the PPAR-γ agonist pioglitazone (PIO) to the established effectiveness of a glucocorticoid receptor agonist, dexamethasone (DEX), in a murine model of asthma induced by cockroach allergen (CRA). After sensitization to CRA and airway localization by intranasal instillation of the allergen, Balb/c mice were challenged twice at 48-h intervals with intratracheal CRA. Either PIO (25 mg/kg/d), DEX (1 mg/kg/d), or vehicle was administered throughout the period of airway CRA exposure.

Results

PIO and DEX demonstrated similar abilities to reduce airway hyperresponsiveness, pulmonary recruitment of inflammatory cells, serum IgE, and lung levels of IL-4, IL-5, TNF-α, TGF-β, RANTES, eotaxin, MIP3-α, Gob-5, and Muc5-ac. Likewise, intratracheal administration of an adenovirus containing a constitutively active PPAR-γ expression construct blocked CRA induction of Gob-5 and Muc5-ac.

Conclusion

Given the potent effectiveness shown by PIO, we conclude that PPAR-γ agonists deserve investigation as potential therapies for human asthma.