Role of ERK1/2 in TNFα-induced internalization of Abcc2 in rat hepatocyte couplets

NADPH oxidase-generated reactive oxygen species are involved in estradiol 17ß-d-glucuronide-induced cholestasis

The endogenous metabolite of estradiol, estradiol 17β-D-glucuronide (E17G), is considered the main responsible of the intrahepatic cholestasis of pregnancy. E17G alters the activity of canalicular transporters through a signaling pathway-dependent cellular internalization, phenomenon that was attributed to oxidative stress in different cholestatic conditions. However, there are no reports involving oxidative stress in E17G-induced cholestasis, representing this the aim of our work. Using polarized hepatocyte cultures, we showed that antioxidant compounds prevented E17G-induced Mrp2 activity alteration, being this alteration equally prevented by the NADPH oxidase (NOX) inhibitor apocynin. The model antioxidant N-acetyl-cysteine prevented, in isolated and perfused rat livers, E17G-induced impairment of bile flow and Mrp2 activity, thus confirming the participation of reactive oxygen species (ROS) in this cholestasis. In primary cultured hepatocytes, pretreatment with specific inhibitors of ERK1/2 and p38MAPK impeded E17G-induced ROS production; contrarily, NOX inhibition did not affect ERK1/2 and p38MAPK phosphorylation. Both, knockdown of p47phox by siRNA and preincubation with apocynin in sandwich-cultured rat hepatocytes significantly prevented E17G-induced internalization of Mrp2, suggesting a crucial role for NOX in this phenomenon. Concluding, E17G-induced cholestasis is partially mediated by NOX-generated ROS through internalization of canalicular transporters like Mrp2, being ERK1/2 and p38MAPK necessary for NOX activation.

Delta-tocotrienol enhances the antitumor effects of interferon alpha through ROS and Erk/MAPK signaling pathways in hepatocellular carcinoma cells

The complexity of hepatocellular carcinoma (HCC) signaling and the failure of pharmacological therapeutics reveal the significance of establishing new anti-cancer strategies. Interferon alpha (IFN α) has been used as adjuvant therapy for reducing HCC recurrence and improving survival. Delta-tocotrienol (δ-tocotrienol), a natural unsaturated isoform of vitamin E, is a promising candidate for cancer treatment. In this study, we evaluated whether the combination of δ-tocotrienol with IFN α displays significant advantages in the treatment of HCC cells. Results showed that the combination significantly decreased cell viability, migration and invasion of HCC cells compared to single therapies. Combining δ-tocotrienol and IFN α enhanced the decrease in proliferating cell nuclear antigen (PCNA) and matrix metalloproteinases MMP-7 and MMP-9. The combination also produced an enhancement of apoptosis together with increased Bax/Bcl-xL ratio and ROS generation. δ-tocotrienol induced Notch1 activation and changes in Erk and p38 MAPK signaling status. Blocking experiments confirmed that ROS and Erk are involved, at least in part, in the anticancer effects of the combined treatment. In conclusion, the combination of δ-tocotrienol with IFN α therapy showed promising results for HCC cells treatment, which makes the combination of cytokine-based immunotherapy with natural products a potential strategy against liver cancer.

The Pathological Mechanisms of Estrogen-Induced Cholestasis: Current Perspectives

Estrogens are steroid hormones with a wide range of biological activities. The excess of estrogens can lead to decreased bile flow, toxic bile acid (BA) accumulation, subsequently causing intrahepatic cholestasis. Estrogen-induced cholestasis (EIC) may have increased incidence during pregnancy, and within women taking oral contraception and postmenopausal hormone replacement therapy, and result in liver injury, preterm birth, meconium-stained amniotic fluid, and intrauterine fetal death in pregnant women. The main pathogenic mechanisms of EIC may include deregulation of BA synthetic or metabolic enzymes, and BA transporters. In addition, impaired cell membrane fluidity, inflammatory responses and change of hepatocyte tight junctions are also involved in the pathogenesis of EIC. In this article, we review the role of estrogens in intrahepatic cholestasis, and outlined the mechanisms of EIC, providing a greater understanding of this disease.

Oxidative Stress and Localization Status of Hepatocellular Transporters: Impact on Bile Secretion and Role of Signaling Pathways

Significance: Most hepatopathies are primarily or secondarily cholestatic in nature. Oxidative stress (OS) is a frequent trait among them, and impairs the machinery to generate bile by triggering endocytic internalization of hepatocellular transporters, thus causing cholestasis. This is critical, since it leads to accelerated transporter degradation, which could explain the common post-transcriptional downregulation of transporter expression in human cholestatic diseases. Recent Advances: The mechanisms involved in OS-induced hepatocellular transporter internalization are being revealed. Filamentous actin (F-actin) cytoskeleton disorganization and/or detachment of crosslinking actin proteins that afford transporter stability have been characterized as causal factors. Activation of redox-sensitive signaling pathways leading to changes in phosphorylation status of these structures is involved, including Ca²⁺-mediated activation of "classical" and "novel" protein kinase C (PKC) isoforms or redox-signaling cascades downstream of NADPH oxidase. Critical Issues: Despite the well-known occurrence of hepatocellular transporter internalization in human hepatopathies, the cholestatic implications of this phenomenon have been overlooked. Accordingly, no specific treatment has been established in the clinical practice for its prevention/reversion. Future Directions: We need to improve our knowledge on the pro-oxidant triggering factors and the multiple signaling pathways that mediate this oxidative injury in each cholestatic hepatopathy, so as to envisage tailor-made therapeutic strategies for each case. Meanwhile, administration of antioxidants or heme oxygenase-1 induction to elevate the hepatocellular levels of the endogenous scavenger bilirubin are promising alternatives that need to be re-evaluated and implemented. They may complement current treatments in cholestasis aimed to enhance transcriptional carrier expression, by providing membrane stability to the newly synthesized carriers. Antioxid. Redox Signal. 35, 808-831.

Sphingosine 1-phosphate receptor 2/adenylyl cyclase/protein kinase A pathway is involved in taurolithocholate-induced internalization of Abcc2 in rats

Taurolithocholate (TLC) is a cholestatic bile salt that induces disinsertion of the canalicular transporter Abcc2 (Mrp2, multidrug resistance-associated protein 2). This internalization is mediated by different intracellular signaling proteins such as PI3K, PKCε and MARCK but the initial receptor of TLC remains unknown. A few G protein-coupled receptors interact with bile salts in hepatocytes. Among them, sphingosine-1 phosphate receptor 2 (S1PR2) represents a potential initial receptor for TLC. The aim of this study was to evaluate the role of this receptor and its downstream effectors in the impairment of Abcc2 function induced by TLC. In vitro, S1PR2 inhibition by JTE-013 or its knockdown by small interfering RNA partially prevented the decrease in Abcc2 activity induced by TLC. Moreover, adenylyl cyclase (AC)/PKA and PI3K/Akt inhibition partially prevented TLC effect on canalicular transporter function. TLC produced PKA and Akt activation, which were blocked by JTE-013 and AC inhibitors, connecting S1PR2/AC/PKA and PI3K/Akt in a same pathway. In isolated perfused rat liver, injection of TLC triggered endocytosis of Abcc2 that was accompanied by a sustained decrease in the bile flow and the biliary excretion of the Abcc2 substrate dinitrophenyl-glutathione until the end of the perfusion period. S1PR2 or AC inhibition did not prevent the initial decay, but they accelerated the recovery of these parameters and the reinsertion of Abcc2 into the canalicular membrane. In conclusion, S1PR2 and the subsequent activation of AC, PKA, PI3K and Akt is partially responsible for the cholestatic effects of TLC through sustained internalization of Abcc2.