Activation of cyclic adenosine monophosphate-dependent protein kinase a signaling prevents liver ischemia/reperfusion injury in mice

Mechanistic Implications of GSK and CREB Crosstalk in Ischemia Injury

Ischemia-reperfusion (IR) injury is a damage to an organ when the blood supply is less than the demand required for normal functioning, leading to exacerbation of cellular dysfunction and death. IR injury occurs in different organs like the kidney, liver, heart, brain, etc., and may not only involve the ischemic organ but also cause systemic damage to distant organs. Oxygen-glucose deprivation in cells causes oxidative stress, calcium overloading, inflammation, and apoptosis. CREB is an essential integrator of the body's various physiological systems, and it is widely accepted that dysfunction of CREB signaling is involved in many diseases, including ischemia-reperfusion injury. The activation of CREB can provide life to a cell and increase the cell's survival after ischemia. Hence, GSK/CREB signaling pathway can provide significant protection to cells of different organs after ischemia and emerges as a futuristic strategy for managing ischemia-reperfusion injury. Different signaling pathways such as MAPK/ERK, TLR4/MyD88, RISK, Nrf2, and NF-κB, get altered during IR injury by the modulation of GSK-3 and CREB (cyclic AMP response element (CRE)-binding protein). GSK-3 (protein kinase B) and CREB are the downstream targets for fulfilling the roles of various signaling pathways. Calcium overloading during ischemia increases the expression of calcium-calmodulin-dependent protein kinase (CaMK), which subsequently activates CREB-mediated transcription, thus promoting the survival of cells. Furthermore, this review highlights the crosstalk between GSK-3 and CREB, promoting survival and rendering the cells resistant to subsequent severe ischemia.

Dexmedetomidine attenuates acute stress-induced liver injury in rats by regulating the miR-34a-5p/ROS/JNK/p38 signaling pathway

Dexmedetomidine (DEX) protects against acute stress-induced liver injury, but what's less clear lies in the specific mechanism. To elucidate the specific mechanism underlying DEX on acute stress-induced liver injury, an in vivo model was constructed on rats with acute stress-induced liver injury by 15 min of exhaustive swimming and 3 hr of immobilization. DEX (30 μg/kg) or miR-34a-5p agomir was injected into model rats. Open field test was used to verify the establishment of the model. Liver injury was observed by hematoxylin-eosin (H&E) staining. Contents of norepinephrine (NE), alanine aminotransfease (ALT) and aspartate aminotransferase (AST) in serum of rats were detected by enzyme-linked immunosorbent assay (ELISA) and those of oxidative stress markers (reactive oxygen species (ROS), Malondialdehyde (MDA), Glutathione (GSH), Superoxide Dismutase (SOD) and Glutathione Peroxidase (GPX)) were measured using commercial kits. Apoptosis of hepatocytes was detected by Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Western blot was performed to detect the expressions of SOD2, COX-2, cytochrome C, Cleaved caspase 3, Bax, Bcl-2, P-JNK, JNK, P-p38, p38 and c-AMP, p-PKA and PKA in liver tissues. As a result, liver injury in model rat was alleviated by DEX. DEX attenuated the increase in the levels of NE, ALT, AST, MDA, ROS, apoptosis, SOD2, COX-2, Cytochrome C, cleaved caspase 3, Bax, and P-JNK, P-p38, c-AMP, P-PKA and miR-34a-5p, and the decrease in the levels of SOD, GPX, GSH and Bcl-2 in model rats. Furthermore, miR-34a-5p overexpression could partly reverse the effects of DEX. Collectively, DEX could alleviate acute stress-induced liver injury through ROS/JNK/p38 signaling pathway via downregulation of miR-34a-5p.

Hepatoprotective effects of sevoflurane against hepatic ischemia-reperfusion injury by regulating microRNA-124-3p-mediated TRAF3/CREB axis

The purpose of the present study is to define the role of sevoflurane (SEV) in hepatic ischemia-reperfusion (I/R) injury as well as its underlying mechanism. Initially, hepatic I/R animal models and I/R hepatocyte models were established in C57BL/6 mice and normal mouse hepatocytes (BNL CL.2) after SEV preconditioning, respectively, followed by detection of microRNA-124-3p (miR-124-3p), TRAF3, and CREB expression by RT-qPCR and Western blot analysis. In addition, miR-124-3p, TRAF3 and CREB expression in hepatocytes was altered to identify their roles in modulating the levels of glutathione transferase (GST), aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and inflammation-related factors and hepatocyte apoptosis by ELISA and flow cytometry respectively. The effects of SEV on the miR-124-3p/TRAF3/CREB axis were also verified in vitro and in vivo. IP assay was performed to verify the effect of TRAF3 on CREB ubiquitination in BNL CL.2 cells, and the cycloheximide (CHX) intervention experiment to detect the stability of CREB protein. SEV augmented the miR-124-3p expression in I/R animal and cell models. Moreover, SEV was observed to suppress I/R-induced liver damage, GST, ALT, and AST levels, hepatocyte apoptosis and inflammation. Overexpression of miR-124-3p resulted in alleviation of hepatic I/R injury, which was countered by TRAF3 overexpression. miR-124-3p targeted TRAF3, while TRAF3 promoted CREB ubiquitination and reduced protein stability of CREB. SEV could impede I/R-induced liver damage, GST, ALT, and AST levels, hepatocyte apoptosis and inflammation via mediation of the miR-124-3p/TRAF3/CREB axis in vitro and in vivo. Collectively, SEV may upregulate miR-124-3p to inhibit TRAF3 expression, thereby reducing the ubiquitination and degradation of CREB, alleviating hepatic I/R injury.

Intravenous immunoglobulin is effective in alleviating hepatic ischemia-reperfusion injury: a rat model study

BACKGROUND

Hepatic ischemia-reperfusion injury (I/R) is an important factor affecting the prognosis of patients undergoing liver surgery. This study aimed to explore the value of intravenous immunoglobulin (IVIG) in hepatic I/R and its mechanism in a rat model.

MATERIALS AND METHODS

Forty eight adult male Sprague-Dawley (SD) rats were divided into six groups randomly: (1-2) treated with normal saline (NS) without ischemia or reperfusion; (3-4) treated with NS + 30 min ischemia; (5-6) treated with IVIG + 30 min ischemia. Rats of group 1/3/5 were euthanized at 12 h after operation (sham + NS + 12 h, I/R + NS + 12 h, I/R + IVIG + 12 h group) while group 2/4/6 were euthanized at 24 h (sham + NS + 24 h, I/R + NS + 24 h, I/R + IVIG + 24 h group). Interleukin 10 (IL-10), interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) were quantified as well as serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Hepatic pathological changes were observed while nuclear factor kappa B p65 (NF-κB p65), Inhibitory Subunit of NF Kappa B Alpha (IKB-alpha) and cleaved caspase-3 were detected.

CONCLUSION

ALT, AST, IL-6, TNF-alpha, NF-κB p65 and cleaved caspase-3 were increased by I/R whereas IL-10 and IKB-alpha were decreased. However, IVIG pretreatment reduced ALT, AST, IL-6, TNF-alpha, NF-κB p65 and cleaved caspase-3, but increased IL-10 and IKB-alpha. IVIG treatment attenuates the infiltration of inflammatory cell and cell apoptosis which were observed in I/R groups. IVIG may alleviate hepatic I/R in rats by inhibiting the classical NF-κB signaling pathway, reducing IL-6, TNF-alpha, promoting IL-10, and inhibiting cell apoptosis.

Prasugrel anti-ischemic effect in rats: Modulation of hippocampal SUMO2/3-IкBα/Ubc9 and SIRT-1/miR-22 trajectories

The beneficial role of prasugrel, a P2Y12 receptor blocker, in several neurointerventional procedures has been reviewed clinically. Beyond its antiplatelet capacity, the potential neuroprotective mechanisms of prasugrel are poorly addressed experimentally. Relevant to the imbalance between neuro-inflammation and neuroprotective pathways in cerebral ischemia/reperfusion (I/R), our study evaluated the anti-ischemic potential of prasugrel treatment through tackling novel targets. Male Wistar rats were allocated into 2 sets; set 1 (I/R 60 min/3 days) to assess the neurological deficits/biochemical impact of prasugrel and set 2 (I/R 60 min/5 days) for evaluating short memory/morphological/immunoreactive changes. Each set comprised 4 groups designated as sham, sham + prasugrel, I/R, and I/R + prasugrel. Post-administration of prasugrel for 3 and 5 days reduced neurological deficit scores and improved the spontaneous activity/short term spatial memory using the Y-maze paradigm. On the molecular level, prasugrel turned off SUMO2/3-inhibitory kappa (Iκ)Bα, Ubc9 and nuclear factor kappa (NF-κ)B. Besides, it inhibited malondialdehyde (MDA) and inactivated astrocytes by downregulating the glial fibrillary acidic protein (GFAP) hippocampal immune-expression. Conversely, it activated its target molecule cAMP, protein kinase (PK)A, and cAMP response element-binding protein (CREB) to enhance the brain-derived nuclear factor (BDNF) hippocampal content. Additionally, cAMP/PKA axis increased the hippocampal content of deacetylator silent information regulator 1 (SIRT1) and the micro RNA (miR)-22 gene expression. The crosstalk between these paths partakes in preserving hippocampal cellularity. Accordingly, prasugrel, regardless inhibiting platelets activity, modulated other cellular components; viz., SUMO2/3-IκBα/Ubc9/NF-κB, cAMP/PKA related trajectories, CREB/BDNF and SIRT1/miR-22 signaling, besides inhibiting GFAP and MDA to signify its anti-ischemic potential.

Promising drug repurposing approach targeted for cytokine storm implicated in SARS-CoV-2 complications

A global threat has emerged in 2019 due to the rapid spread of Coronavirus disease (COVID-19). As of January 2021, the number of cases worldwide reached 103 million cases and 2.22 million deaths which were confirmed as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This global pandemic galvanized the scientific community to study the causative virus (SARS-CoV2) pathogenesis, transmission, and clinical symptoms. Remarkably, the most common complication associated with this disease is the cytokine storm which is responsible for COVID-19 mortality. Thus, targeting the cytokine storm with new medications is needed to hamper COVID-19 complications where the most prominent strategy for the treatment is drug repurposing. Through this strategy, several steps are skipped especially those required for testing drug safety and thus may help in reducing the dissemination of this pandemic. Accordingly, the aim of this review is to outline the pathogenesis, clinical features, and immune complications of SARS-CoV2 in addition to suggesting several repurposed drugs with their plausible mechanism of action for possible management of severe COVID-19 cases.

Cyclic nucleotide phosphodiesterase inhibition as a potential therapeutic target in renal ischemia reperfusion injury

AIMS

Ischemia/reperfusion (I/R) occurs in renal artery stenosis, partial nephrectomy and most commonly during kidney transplantation. It brings serious consequences such as DGF (Delayed Graft Function) or organ dysfunction leading to renal failure and ultimate death. There is no effective therapy to handle the consequences of Renal Ischemia/Reperfusion (I/R) injury. Cyclic nucleotides, cAMP and cGMP are the important second messengers that stimulate intracellular signal transduction for cell survival in response to growth factors and peptide hormones in normal tissues and in kidneys plays significant role that involves vascular tone regulation, inflammation and proliferation of parenchymal cells. Renal ischemia and subsequent reperfusion injury stimulate signal transduction pathways involved in oxidative stress, inflammation, alteration in renal blood flow leading to necrosis and apoptosis of renal cell.

MATERIALS AND METHODS

An extensive literature review of various search engines like PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was carried out. To understand the functioning of Phosphodiesterases (PDEs) and its pharmacological modulation in Renal Ischemia-Reperfusion Injury.

KEY FINDINGS

Current therapeutic options may not be enough to treat renal I/R injury in group of patients and therefore, the current review has discussed the general characteristics and physiology of PDEs and preclinical-studies defining the relationship between PDEs expression in renal injury due to I/R and its outcome on renal function.

SIGNIFICANCE

The role of PDE inhibitors in renal I/R injury and the clinical status of drugs for various renal diseases have been summarized in this review.

YAP-Dependent Induction of CD47-Enriched Extracellular Vesicles Inhibits Dendritic Cell Activation and Ameliorates Hepatic Ischemia-Reperfusion Injury

Hepatic ischemia-reperfusion injury (IRI) is the most common cause of liver damage leading to surgical failures in hepatectomy and liver transplantation. Extensive inflammatory reactions and oxidative responses are reported to be the major processes exacerbating IRI. The involvement of Yes-associated protein (YAP) in either process has been suggested, but the role and mechanism of YAP in IRI remain unclear. In this study, we constructed hepatocyte-specific YAP knockout (YAP-HKO) mice and induced a hepatic IRI model. Surprisingly, the amount of serum EVs decreased in YAP-HKO compared to WT mice during hepatic IRI. Then, we found that the activation of YAP increased EV secretion through F-actin by increasing membrane formation, while inhibiting the fusion of multivesicular body (MVB) and lysosomes in hepatocytes. Further, to explore the essential elements of YAP-induced EVs, we applied mass spectrometry and noticed CD47 was among the top targets highly expressed on hepatocyte-derived EVs. Thus, we enriched CD47⁺ EVs by microbeads and applied the isolated CD47⁺ EVs on IRI mice. We found ameliorated IRI symptoms after CD47⁺ EV treatment in these mice, and CD47⁺ EVs bound to CD172α on the surface of dendritic cells (DCs), which inhibited DC activation and the cascade of inflammatory responses. Our data showed that CD47-enriched EVs were released in a YAP-dependent manner by hepatocytes, which could inhibit DC activation and contribute to the amelioration of hepatic IRI. CD47⁺ EVs could be a potential strategy for treating hepatic IRI.

PACAP neuropeptide promotes Hepatocellular Protection via CREB-KLF4 dependent autophagy in mouse liver Ischemia Reperfusion Injury

Organ ischemia reperfusion injury (IRI), associated with acute hepatocyte death, remains an unresolved problem in clinical orthotopic liver transplantation (OLT). Autophagy, an intracellular self-digesting progress, is responsible for cell reprograming required to regain post-stress homeostasis.

Methods: Here, we analyzed the cytoprotective mechanism of pituitary adenylate cyclase-activating polypeptide (PACAP)-promoted hepatocellular autophagy in a clinically relevant mouse model of extended hepatic cold storage (4 °C UW solution for 20 h) followed by syngeneic OLT.

Results: In contrast to 41.7% of liver graft failure by day 7 post-transplant in control group, PACAP treatment significantly improved graft survival (91.7% by day 14), and promoted autophagy-associated regeneration programs in OLT. In parallel in vitro studies, PACAP-enhanced autophagy ameliorated cellular damage (LDH/ALT levels), and diminished necrosis in H₂O₂-stressed primary hepatocytes. Interestingly, PACAP not only induced nuclear cAMP response element-binding protein (CREB), but also triggered reprogramming factor Kruppel-like factor 4 (KLF4) expression in IR-stressed OLT. Indeed, CREB inhibition attenuated hepatic autophagy and recreated hepatocellular injury in otherwise PACAP-protected livers. Furthermore, CREB inhibition suppressed PACAP-induced KLF4 expression, whereas KLF4 blockade abolished PACAP-promoted autophagy and neutralized PACAP-mediated hepatoprotection both in vivo and in vitro.

Conclusion: Current study documents the essential neural regulation of PACAP-promoted autophagy in hepatocellular homeostasis in OLT, which provides the emerging therapeutic principle to combat hepatic IRI in OLT.

Iron chelation by deferasirox confers protection against concanavalin A-induced liver fibrosis: A mechanistic approach

Hepatic iron overload is one of the causative factors for chronic liver injury and fibrosis. The present study aimed to investigate the potential antifibrotic effect of the iron chelator; deferasirox (DFX) in experimentally-induced liver fibrosis in rats. Male Sprague-Dawley rats were administered concanavalin A (Con A) and/or DFX for 6 consecutive weeks. Con A injection induced significant hepatotoxicity as was evident by the elevated transaminases activity, and decreased albumin level. Also, it disturbed the iron homeostasis through increasing C/EBP homologous protein (CHOP), decreasing phosphorylated cAMP responsive element binding protein(P-CREB) and hepcidin levels leading to significant serum and hepatic iron overload. In addition, it induced an imbalance in the oxidative status of the liver via upregulating NADPH oxidase 4 (NOX4), together with a marked decrease in anti-oxidant enzymes' activities. As a consequence, upregulation of nuclear factor-kappa b (NF-κB) and the downstream inflammatory mediators was observed. Those events all together precipitated in initiation of liver fibrosis as confirmed by the elevation of alpha-smooth muscle actin (α-SMA) and liver collagen content. Co-treatment with DFX protected against experimentally-induced liver fibrosis in rats via its iron chelating, anti-oxidant, and anti-inflammatory properties. These findings imply that DFX can attenuate the progression of liver fibrosis.

Inhibition of Cyclin-dependent Kinase 2 Signaling Prevents Liver Ischemia and Reperfusion Injury

BACKGROUND

Liver ischemia and reperfusion injury (IRI) is a major complication of liver transplant, hepatectomy, and hemorrhagic shock. The cyclin-dependent kinase 2 (CDK2) acts as a pivotal regulator of cell cycle and proliferation.

METHODS

This study evaluated the modulation and therapeutic potential of CDK2 inhibition in a mouse model of partial liver warm IRI.

RESULTS

Liver IR-triggered intrinsic CDK2 expression, peaking by 0.5 hour of reperfusion and maintaining a high-level throughout 1 to 24 hours. Roscovitine, a specific CDK2 inhibitor, prevented liver IR-mediated damage with abolished serum alanine aminotransferase levels and reserved liver pathology. CDK2 inhibition-mediated liver protection was accompanied by decreased macrophage/neutrophil infiltration, diminished hepatocyte apoptosis, abolished toll like receptor 4 signaling and downstream gene inductions (C-X-C motif ligand-10, Tumor necrosis factor-α, interleukin-1β, and interleukin-6), yet augmented interleukin-10 expression. In vitro, CDK2 inhibition by Roscovitine suppressed macrophage TLR4 activation and further depressed downstream inflammatory signaling (myeloid differentiation factor 88, interferon regulatory transcription factor 3, p38, c-Jun N-terminal kinase, and extracellular-regulated kinase).

CONCLUSIONS

Our novel findings revealed the critical role of CDK2 in hepatic cytoprotection and homeostasis against liver IRI. As CDK2 inhibition regulated local immune response and prevented hepatocyte death, this study provided the evidence for new treatment approaches to combat IRI in liver transplant.

Phosphodiestrase-1 and 4 inhibitors ameliorate liver fibrosis in rats: Modulation of cAMP/CREB/TLR4 inflammatory and fibrogenic pathways

BACKGROUND

Phosphodiestrase (PDE) enzymes are suggested to play a leading role in fibrogenesis of liver where studies showed the possible implication of PDE 1 & 4 in liver injury proposing them as possible targets for treating liver fibrosis.

AIM

The present study was designed to investigate, for the first time, the possible therapeutic effects of selective inhibitors of PDE-1 (vinpocetine) and PDE-4 (roflumilast) in liver fibrosis induced by diethylnitrosamine (DEN) in rats.

MAIN METHODS

Rats were given DEN (100 mg/kg, i.p.) once weekly for 6 weeks to induce liver fibrosis. Vinpocetine (10 mg/kg/day) or roflumilast (0.5 mg/kg/day) was then orally administered for 2 weeks.

KEY FINDINGS

Vinpocetine significantly suppressed the contents of hydroxyproline, transforming growth factor-beta 1 (TGF-β1), nuclear factor-kappa B (NF-κB) whereas roflumilast normalized them. Moreover, tumor necrosis factor-alpha (TNF-α) content and protein expressions of toll-like receptor 4 (TLR4) and tissue inhibitor of metalloproteinase-1 (TIMP-1) were markedly decreased whereas cAMP response element binding (CREB) protein expression was significantly elevated by both treatments. Additionally, vinpocetine and roflumilast up-regulated the gene expression of bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) receptor where roflumilast showed better results. PDE1 and 4 activities were inhibited by vinpocetine and roflumilast, respectively. The superior results offered by roflumilast could be related to the higher cAMP level obtained relative to vinpocetine.

SIGNIFICANCE

Our study manifested the up-regulation of PDE enzymes (1 & 4) in liver fibrosis and addressed the therapeutic role of vinpocetine and roflumilast as PDEIs through a cAMP-mediated TLR4 inflammatory and fibrogenic signaling pathways.

Protective effect of electro-acupuncture on liver ischemia-reperfusion injury in rats

Liver ischemia-reperfusion injury is an important clinical complication in which excessive inflammation is a key factor; however, few studies have provided effective means of its regulation. As previous studies suggested that electro-acupuncture (EA) is able control excessive inflammation, the present study aimed to explore its effects on liver ischemia-reperfusion injury in experimental rats. The animals were randomly divided into surgery and sham groups, which were further divided into four sub-groups, including a non-treatment (NT), a non-point acupuncture (NPA), the non-selective nicotinic acetylcholine receptor (AChR) agonist 1,1-dimethyl-4-phenyl L-pioperazinium iodide (DMPPI) and an EA group. The alanine aminotransferase (ALT), serum cytokine and myeloperoxidase (MP) levels and the tissue pathology were evaluated after 90 min of ischemia followed by a 4, 8 or 24 h reperfusion. The results demonstrated that EA and DMPPI suppressed serum ALT elevation at 4 and 8 h reperfusion, whereas NPA did not. I/R induced hepatocellular necrosis, and cytoplasmic vacuolization and sinusoidal congestion was ameliorated by EA treatment after an 8 and 24 h reperfusion. In addition, EA also inhibited liver neutrophil accumulation, evidenced by a decreased MPO level at 8 h reperfusion. EA also suppressed the release of serum inflammatory factors TNF-α and IL-6 for the duration of reperfusion. However, little influence on IL-10 was observed. Mechanistically, vagus block by subphrenic vagotomy or mecamylamine hydrochloride abolished EA effect on liver damage, neutrophil accumulation and inflammatory factor release. In conclusion, it was demonstrated that EA protects the liver against I/R induced injury by inhibiting the inflammatory response, which is associated with the vagus.

Sleeping Beauty Insertional Mutagenesis in Mice Identifies Drivers of Steatosis-Associated Hepatic Tumors

Hepatic steatosis is a strong risk factor for the development of hepatocellular carcinoma (HCC), yet little is known about the molecular pathology associated with this factor. In this study, we performed a forward genetic screen using Sleeping Beauty (SB) transposon insertional mutagenesis in mice treated to induce hepatic steatosis and compared the results to human HCC data. In humans, we determined that steatosis increased the proportion of female HCC patients, a pattern also reflected in mice. Our genetic screen identified 203 candidate steatosis-associated HCC genes, many of which are altered in human HCC and are members of established HCC-driving signaling pathways. The protein kinase A/cyclic AMP signaling pathway was altered frequently in mouse and human steatosis-associated HCC. We found that activated PKA expression drove steatosis-specific liver tumorigenesis in a mouse model. Another candidate HCC driver, the N-acetyltransferase NAT10, which we found to be overexpressed in human steatosis-associated HCC and associated with decreased survival in human HCC, also drove liver tumorigenesis in a steatotic mouse model. This study identifies genes and pathways promoting HCC that may represent novel targets for prevention and treatment in the context of hepatic steatosis, an area of rapidly growing clinical significance. Cancer Res; 77(23); 6576-88. ©2017 AACR.

The effects of tramadol on hepatic ischemia/reperfusion injury in rats

Objectives:

Tramadol is a centrally acting synthetic analgesic. It has a cardioprotective effect against myocardial ischemia-reperfusion (I/R) injury in isolated rat heart. We hypothesized that tramadol may exert a similar protective effect on hepatic I/R injury. Hence, the current investigation was designed to study the possible protective effects of tramadol on experimentally-induced hepatic I/R injury in rats.

Materials and Methods:

Tramadol was administered 30 min before ischemia following which the rats were subjected to 45 min of ischemia followed by 1 h of reperfusion.

Results:

Tramadol attenuated hepatic injury induced by I/R as evidenced by the reduction of transaminases, structural changes, and apoptotic cell death. It decreased the level of inflammatory markers such as tumor necrosis factor-alpha (TNF-α), TNF-α/interleukin-10 (IL-10) ratio, and nuclear factor-κB gene expression. It also increased the anti-inflammatory cytokine, IL-10 levels in hepatic tissues. Furthermore, it reduced oxidative stress parameters except manganese superoxide dismutase activity.

Conclusion:

The results suggest that tramadol has hepatoprotective effects against hepatic I/R injury via anti-inflammatory, antiapoptotic, and antioxidant effects.

Forskolin, a hedgehog signalling inhibitor, attenuates carbon tetrachloride-induced liver fibrosis in rats

BACKGROUND AND PURPOSE

Liver fibrosis is one of the leading causes of morbidity and mortality worldwide with very limited therapeutic options. Given the pivotal role of activated hepatic stellate cells in liver fibrosis, attention has been directed towards the signalling pathways underlying their activation and fibrogenic functions. Recently, the hedgehog (Hh) signalling pathway has been identified as a potentially important therapeutic target in liver fibrosis. The present study was designed to explore the antifibrotic effects of the potent Hh signalling inhibitor, forskolin, and the possible molecular mechanisms underlying these effects.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were treated with either CCl₄ and/or forskolin for 6 consecutive weeks. Serum hepatotoxicity markers were determined, and histopathological evaluation was performed. Hepatic fibrosis was assessed by measuring α-SMA expression and collagen deposition by Masson's trichrome staining and hydroxyproline content. The effects of forskolin on oxidative stress markers (GSH, GPx, lipid peroxides), inflammatory markers (NF-κB, TNF-α, COX-2, IL-1β), TGF-β1 and Hh signalling markers (Ptch-1, Smo, Gli-2) were also assessed.

KEY RESULTS

Hepatic fibrosis induced by CCl₄ was significantly reduced by forskolin, as indicated by decreased α-SMA expression and collagen deposition. Forskolin co-treatment significantly attenuated oxidative stress and inflammation, reduced TGF-β1 levels and down-regulated mRNA expression of Ptch-1, Smo and Gli-2 through cAMP-dependent PKA activation.

CONCLUSION AND IMPLICATIONS

In our model, forskolin exerted promising antifibrotic effects which could be partly attributed to its antioxidant and anti-inflammatory effects, as well as to its inhibition of Hh signalling, mediated by cAMP-dependent activation of PKA.

The glucagon-like peptide-1 analogue exendin-4 reverses impaired intracellular Ca(2+) signalling in steatotic hepatocytes

The release of Ca(2+) from the endoplasmic reticulum (ER) and subsequent replenishment of ER Ca(2+) by Ca(2+) entry through store-operated Ca(2+) channels (SOCE) play critical roles in the regulation of liver metabolism by adrenaline, glucagon and other hormones. Both ER Ca(2+) release and Ca(2+) entry are severely inhibited in steatotic hepatocytes. Exendin-4, a slowly-metabolised glucagon-like peptide-1 (GLP-1) analogue, is known to reduce liver glucose output and liver lipid, but the mechanisms involved are not well understood. The aim of this study was to determine whether exendin-4 alters intracellular Ca(2+) homeostasis in steatotic hepatocytes, and to evaluate the mechanisms involved. Exendin-4 completely reversed lipid-induced inhibition of SOCE in steatotic liver cells, but did not reverse lipid-induced inhibition of ER Ca(2+) release. The action of exendin-4 on Ca(2+) entry was rapid in onset and was mimicked by GLP-1 or dibutyryl cyclic AMP. In steatotic liver cells, exendin-4 caused a rapid decrease in lipid (half time 6.5min), inhibited the accumulation of lipid in liver cells incubated in the presence of palmitate plus the SOCE inhibitor BTP-2, and enhanced the formation of cyclic AMP. Hormone-stimulated accumulation of extracellular glucose in glycogen replete steatotic liver cells was inhibited compared to that in non-steatotic cells, and this effect of lipid was reversed by exendin-4. It is concluded that, in steatotic hepatocytes, exendin-4 reverses the lipid-induced inhibition of SOCE leading to restoration of hormone-regulated cytoplasmic Ca(2+) signalling. The mechanism may involve GLP-1 receptors, cyclic AMP, lipolysis, decreased diacylglycerol and decreased activity of protein kinase C.

Involvement of a cyclic adenosine monophosphate-dependent signal in the diet-induced canalicular trafficking of adenosine triphosphate-binding cassette transporter g5/g8

The adenosine triphosphate-binding cassette (ABC) half-transporters Abcg5 and Abcg8 promote the secretion of neutral sterol into bile. Studies have demonstrated the diet-induced gene expression of these transporters, but the regulation of their trafficking when the nutritional status changes in the liver remains to be elucidated. Here, we generated a novel in vivo kinetic analysis that can monitor the intracellular trafficking of Abcg5/Abcg8 in living mouse liver by in vivo transfection of the genes of fluorescent protein-tagged transporters and investigated how hypernutrition affects the canalicular trafficking of these transporters. The kinetic analysis showed that lithogenic diet consumption accelerated the translocation of newly synthesized fluorescent-tagged transporters to intracellular pools in an endosomal compartment and enhanced the recruitment of these pooled gene products into the bile canalicular membrane in mouse liver. Because some ABC transporters are reported to be recruited from intracellular pools to the bile canaliculi by cyclic adenosine monophosphate (cAMP) signaling, we next evaluated the involvement of this machinery in a diet-induced event. Administration of a protein kinase A inhibitor, N-(2-{[3-(4-bromophenyl)-2-propenyl]amino}ethyl)-5-isoquinolinesulfonamide, decreased the canalicular expression of native Abcg5/Abcg8 in lithogenic diet-fed mice, and injection of a cAMP analog, dibutyryl cAMP, transiently increased their levels in standard diet-fed mice, indicating the involvement of cAMP signaling. Indeed, canalicular trafficking of the fluorescent-tagged Abcg5/Abcg8 was enhanced by dibutyryl cAMP administration.

CONCLUSION

These observations suggest that diet-induced lipid loading into liver accelerates the trafficking of Abcg5/Abcg8 to the bile canalicular membrane through cAMP signaling machinery.

Role of soluble adenylyl cyclase in cell death and growth

cAMP signaling is an evolutionarily conserved intracellular communication system controlling numerous cellular functions. Until recently, transmembrane adenylyl cyclase (tmAC) was considered the major source for cAMP in the cell, and the role of cAMP signaling was therefore attributed exclusively to the activity of this family of enzymes. However, increasing evidence demonstrates the role of an alternative, intracellular source of cAMP produced by type 10 soluble adenylyl cyclase (sAC). In contrast to tmAC, sAC produces cAMP in various intracellular microdomains close to specific cAMP targets, e.g., in nucleus and mitochondria. Ongoing research demonstrates involvement of sAC in diverse physiological and pathological processes. The present review is focused on the role of cAMP signaling, particularly that of sAC, in cell death and growth. Although the contributions of sAC to the regulation of these cellular functions have only recently been discovered, current data suggest that sAC plays key roles in mitochondrial bioenergetics and the mitochondrial apoptosis pathway, as well as cell proliferation and development. Furthermore, recent reports suggest the importance of sAC in several pathologies associated with apoptosis as well as in oncogenesis. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Tumour necrosis factor-α promotes liver ischaemia-reperfusion injury through the PGC-1α/Mfn2 pathway

Tumour necrosis factor (TNF)-α has been considered to induce ischaemia-reperfusion injury (IRI) of liver which is characterized by energy dysmetabolism. Peroxisome proliferator–activated receptor-γ co-activator (PGC)-1α and mitofusion2 (Mfn2) are reported to be involved in the regulation of mitochondrial function. However, whether PGC-1α and Mfn2 form a pathway that mediates liver IRI, and if so, what the underlying involvement is in that pathway remain unclear. In this study, L02 cells administered recombinant human TNF-α had increased TNF-α levels and resulted in down-regulation of PGC-1α and Mfn2 in a rat liver IRI model. This was associated with hepatic mitochondrial swelling, decreased adenosine triphosphate (ATP) production, and increased levels of reactive oxygen species (ROS) and alanine aminotransferase (ALT) activity as well as cell apoptosis. Inhibition of TNF-α by neutralizing antibody reversed PGC-1α and Mfn2 expression, and decreased hepatic injury and cell apoptosis both in cell culture and in animals. Treatment by rosiglitazone sustained PGC-1α and Mfn2 expression both in IR livers, and L02 cells treated with TNF-α as indicated by increased hepatic mitochondrial integrity and ATP production, reduced ROS and ALT activity as well as decreased cell apoptosis. Overexpression of Mfn2 by lentiviral-Mfn2 transfection decreased hepatic injury in IR livers and L02 cells treated with TNF-α. However, there was no up-regulation of PGC-1α. These findings suggest that PGC-1α and Mfn2 constitute a regulatory pathway, and play a critical role in TNF-α-induced hepatic IRI. Inhibition of the TNF-α or PGC-1α/Mfn2 pathways may represent novel therapeutic interventions for hepatic IRI.

Equilibrative nucleoside transporter (ENT)-1-dependent elevation of extracellular adenosine protects the liver during ischemia and reperfusion

Ischemia and reperfusion-elicited tissue injury contributes to morbidity and mortality of hepatic surgery and during liver transplantation. Previous studies implicated extracellular adenosine signaling in liver protection. Based on the notion that extracellular adenosine signaling is terminated by uptake from the extracellular towards the intracellular compartment by way of equilibrative nucleoside transporters (ENTs), we hypothesized a functional role of ENTs in liver protection from ischemia. During orthotopic liver transplantation in humans, we observed higher expressional levels of ENT1 than ENT2, in conjunction with repression of ENT1 and ENT2 transcript and protein levels following warm ischemia and reperfusion. Treatment with the pharmacologic ENT inhibitor dipyridamole revealed elevations of hepatic adenosine levels and robust liver protection in a murine model of liver ischemia and reperfusion. Studies in gene-targeted mice for Ent1 or Ent2 demonstrated selective protection from liver injury in Ent1(-/-) mice. Treatment with selective adenosine receptor antagonists indicated a contribution of Adora2b receptor signaling in ENT-dependent liver protection.

CONCLUSION

These findings implicate ENT1 in liver protection from ischemia and reperfusion injury and suggest ENT inhibitors may be of benefit in the prevention or treatment of ischemic liver injury.

Vasoactive intestinal peptide attenuates liver ischemia/reperfusion injury in mice via the cyclic adenosine monophosphate-protein kinase a pathway

Hepatic ischemia/reperfusion injury (IRI), an exogenous, antigen-independent, local inflammation response, occurs in multiple clinical settings, including liver transplantation, hepatic resection, trauma, and shock. The nervous system maintains extensive crosstalk with the immune system through neuropeptide and peptide hormone networks. This study examined the function and therapeutic potential of the vasoactive intestinal peptide (VIP) neuropeptide in a murine model of liver warm ischemia (90 minutes) followed by reperfusion. Liver ischemia/reperfusion (IR) triggered an induction of gene expression of intrinsic VIP; this peaked at 24 hours of reperfusion and coincided with a hepatic self-healing phase. Treatment with the VIP neuropeptide protected livers from IRI; this was evidenced by diminished serum alanine aminotransferase levels and well-preserved tissue architecture and was associated with elevated intracellular cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling. The hepatocellular protection rendered by VIP was accompanied by diminished neutrophil/macrophage infiltration and activation, reduced hepatocyte necrosis/apoptosis, and increased hepatic interleukin-10 (IL-10) expression. Strikingly, PKA inhibition restored liver damage in otherwise IR-resistant VIP-treated mice. In vitro, VIP not only diminished macrophage tumor necrosis factor α/IL-6/IL-12 expression in a PKA-dependent manner but also prevented necrosis/apoptosis in primary mouse hepatocyte cultures. In conclusion, our findings document the importance of VIP neuropeptide-mediated cAMP-PKA signaling in hepatic homeostasis and cytoprotection in vivo. Because the enhancement of neural modulation differentially regulates local inflammation and prevents hepatocyte death, these results provide the rationale for novel approaches to managing liver IRI in transplant patients.

Neuropeptide PACAP in mouse liver ischemia and reperfusion injury: immunomodulation by the cAMP-PKA pathway

Hepatic ischemia and reperfusion injury (IRI), an exogenous antigen-independent local inflammation response, occurs in multiple clinical settings, including liver transplantation, hepatic resection, trauma, and shock. The immune system and the nervous system maintain extensive communication and mount a variety of integrated responses to danger signals through intricate chemical messengers. This study examined the function and potential therapeutic potential of neuropeptide pituitary adenylate cyclase-activating polypeptides (PACAP) in a murine model of partial liver "warm" ischemia (90 minutes) followed by reperfusion. Liver IRI readily triggered the expression of intrinsic PACAP and its receptors, whereas the hepatocellular damage was exacerbated in PACAP-deficient mice. Conversely, PACAP27, or PACAP38 peptide monotherapy, which elevates intracellular cyclic adenosine monophosphate/protein kinase A (cAMP-PKA) signaling, protected livers from IRI, as evidenced by diminished serum alanine aminotransferase levels and well-preserved tissue architecture. The liver protection rendered by PACAP peptides was accompanied by diminished neutrophil/macrophage infiltration and activation, reduced hepatocyte necrosis/apoptosis, and selectively augmented hepatic interleukin (IL)-10 expression. Strikingly, PKA inhibition readily restored liver damage in otherwise IR-resistant, PACAP-conditioned mice. In vitro, PACAP treatment not only diminished macrophage tumor necrosis factor alpha/IL-6/IL-12 levels in a PKA-dependent manner, but also prevented necrosis and apoptosis in primary mouse hepatocyte cultures.

CONCLUSION

Our novel findings document the importance of PACAP-mediated cAMP-PKA signaling in hepatic homeostasis and cytoprotection in vivo. Because the enhancement of neural modulation differentially regulates local inflammation and prevents hepatocyte death, these results provide the rationale for novel approaches to manage liver inflammation and IRI in transplant patients.

Targeting TIM-1 on CD4 T cells depresses macrophage activation and overcomes ischemia-reperfusion injury in mouse orthotopic liver transplantation

Hepatic injury due to cold storage followed by reperfusion remains a major cause of morbidity and mortality after orthotopic liver transplantation (OLT). CD4 T cell TIM-1 signaling costimulates a variety of immune responses in allograft recipients. This study analyzes mechanisms by which TIM-1 affects liver ischemia-reperfusion injury (IRI) in a murine model of prolonged cold storage followed by OLT. Livers from C57BL/6 mice, preserved at 4°C in the UW solution for 20 h, were transplanted to syngeneic recipients. There was an early (1 h) increased accumulation of TIM-1+ activated CD4 T cells in the ischemic OLTs. Disruption of TIM-1 signaling with a blocking mAb (RMT1-10) ameliorated liver damage, evidenced by reduced sALT levels and well-preserved architecture. Unlike in controls, TIM-1 blockade diminished OLT expression of Tbet/IFN-γ, but amplified IL-4/IL-10/IL-22; abolished neutrophil and macrophage infiltration/activation and inhibited NF-κB while enhancing Bcl-2/Bcl-xl. Although adoptive transfer of CD4 T cells triggered liver damage in otherwise IR-resistant RAG(-/-) mice, adjunctive TIM-1 blockade reduced Tbet transcription and abolished macrophage activation, restoring homeostasis in IR-stressed livers. Further, transfer of TIM-1(Hi) CD4+, but not TIM-1(Lo) CD4+ T cells, recreated liver IRI in RAG(-/-) mice. Thus, TIM-1 expressing CD4 T cells are required in the mechanism of innate immune-mediated hepatic IRI in OLTs.

The hypoxic testicle: physiology and pathophysiology

Mammalian spermatogenesis is a complex biological process occurring in the seminiferous tubules in the testis. This process represents a delicate balance between cell proliferation, differentiation, and apoptosis. In most mammals, the testicles are kept in the scrotum 2 to 7°C below body core temperature, and the spermatogenic process proceeds with a blood and oxygen supply that is fairly independent of changes in other vascular beds in the body. Despite this apparently well-controlled local environment, pathologies such as varicocele or testicular torsion and environmental exposure to low oxygen (hypoxia) can result in changes in blood flow, nutrients, and oxygen supply along with an increased local temperature that may induce adverse effects on Leydig cell function and spermatogenesis. These conditions may lead to male subfertility or infertility. Our literature analyses and our own results suggest that conditions such as germ cell apoptosis and DNA damage are common features in hypoxia and varicocele and testicular torsion. Furthermore, oxidative damage seems to be present in these conditions during the initiation stages of germ cell damage and apoptosis. Other mechanisms like membrane-bound metalloproteinases and phospholipase A2 activation could also be part of the pathophysiological consequences of testicular hypoxia.