María Teresa Ronco

Hyperglycemia induces apoptosis in rat liver through the increase of hydroxyl radical: new insights into the insulin effect

In this study, we analyzed the contribution of hydroxyl radical in the liver apoptosis mediated by hyperglycemia through the Bax-caspase pathway and the effects of insulin protection against the apoptosis induced by hyperglycemia. Male adult Wistar rats were randomized in three groups: control (C) (sodium citrate buffer, i.p.), streptozotocin (STZ)-induced diabetic (SID) (STZ 60 mg/kg body weight, i.p.), and insulin-treated SID (SID+I; 15 days post STZ injection, SID received insulin s.c., twice a day, 15 days). Rats were autopsied on day 30. In liver tissue, diabetes promoted a significant increase in hydroxyl radical production which correlated with lipid peroxidation (LPO) levels. Besides, hyperglycemia significantly increased mitochondrial BAX protein expression, cytosolic cytochrome c levels, and caspase-3 activity leading to an increase in apoptotic index. Interestingly, the treatment of diabetic rats with desferoxamine or tempol (antioxidants/hydroxyl radical scavengers) significantly attenuated the increase in both hydroxyl radical production and in LPO produced by hyperglycemia, preventing apoptosis by reduction of mitochondrial BAX and cytosolic cytochrome c levels. Insulin treatment showed similar results. The finding that co-administration of antioxidants/hydroxyl radical scavengers together with insulin did not provide any additional benefit compared with those obtained using either inhibitors or insulin alone shows that it is likely that insulin prevents oxidative stress by reducing the effects of hydroxyl radicals. Importantly, insulin significantly increased apoptosis inhibitor protein expression by induction of its mRNA. Taken together, our studies support that, at least in part, the hydroxyl radical acts as a reactive intermediate, which leads to liver apoptosis in a model of STZ-mediated hyperglycemia. A new anti-apoptosis signal for insulin is shown, given by an increase of apoptosis inhibitor protein.

Tumor necrosis factor alpha pathways develops liver apoptosis in type 1 diabetes mellitus.

We analyzed the contribution of TNF-α intracellular pathway in the development of apoptosis in the liver of streptozotocin-induced diabetic rats. In liver tissue, diabetes promoted a significant increase of TNF-α/TNF-R1, and led to the activation of caspase-8, of nuclear factor kappa B (NFκB), and JNK signaling pathways. The activation of NFκB led to an induction of iNOS and consequent increase in NO production. As a consequence of such changes a significant increase of caspase-3 activity and of apoptotic index were observed in the liver of diabetic animals. Importantly, the treatment in vivo of diabetic rats with etanercept (TNF-α blocking antibody) or aminoguanidine (selective iNOS inhibitor) significantly attenuated the induction of apoptosis by reduction of caspase-3 activity. Overall, we demonstrated that in the diabetes enhances TNF-α in the liver, which may be a fundamental key leading to apoptotic cell death, through activation of caspase-8, NFκB and JNK pathways.

Interferon α-induced apoptosis on rat preneoplastic liver is mediated by hepatocytic transforming growth factor β1

In previous work we showed that interferon alfa‐2b (IFN‐α2b) increases apoptosis on rat hepatic preneoplastic foci. The aim of this study was to determine if transforming growth factor β1 (TGF‐β1) was involved in the programmed cell death on the foci. Animals were divided into 6 groups: subjected to a 2‐phase model (diethylnitrosamine plus 2‐acetylaminofluorene) of preneoplasia development (group 1); treated with IFN‐α2b during the 2 phases (group 2); treated with IFN‐α2b during initiation with diethylnitrosamine (group 3); treated with IFN‐α2b during 2‐acetylaminofluorene administration (group 4); subjected only to an initiation stage (group 5); and treated with IFN‐α2b during the initiation period (group 6). Serum TGF‐β1 levels were increased in IFN‐α2b–treated rats. Immunohistochemical studies showed that IFN‐α2b significantly increased the quantity of TGF‐β1–positive hepatocytes in groups 2 to 4. Phosphorylated‐Smads‐2/3 (p‐Smads‐2/3) proteins in liver nuclear extracts were significantly elevated. To determine the source of TGF‐β1, isolated hepatocytes, Kupffer cells, and peritoneal macrophages from animals in groups 1 and 5 were cultured with or without IFN‐α2b. IFN‐α2b stimulus induced several‐fold increases of TGF‐β1 secretion from hepatocytes. Neither Kupffer cells nor peritoneal macrophages secreted detectable TGF‐β1 levels when they were treated with IFN‐α2b. IFN‐α2b–stimulated cultured hepatocytes from preneoplastic livers showed enhanced apoptosis, measured by fluorescence microscopy and caspase‐3 activity. They presented higher nuclear accumulation of p‐Smads‐2/3, indicating increased TGF‐β1 signaling. When anti–TGF‐β1 was added to the culture media, TGF‐β1 activation and apoptosis induced by IFN‐α2b were blocked. In conclusion, IFN‐α2b–induced production of TGF‐β1 by hepatocytes from preneoplastic liver is involved in the apoptotic elimination of altered hepatic foci. (HEPATOLOGY 2004;40:394–402.)

Quercetin prevents liver carcinogenesis by inducing cell cycle arrest, decreasing cell proliferation and enhancing apoptosis

SCOPE Quercetin is the most abundant flavonoid in human diet. It has special interest as it holds anticancerous properties. This study aims to clarify the mechanisms involved in quercetin effects during the occurrence of preneoplastic lesions in rat liver. METHODS AND RESULTS Adult male Wistar rats were subjected to a two-phase model of hepatocarcinogenesis (initiated-promoted group). Initiated-promoted animals also received quercetin 10 and 20 mg/kg body weight (IPQ10 and IPQ20 groups, respectively). Antioxidant defenses were modified by quercetin administration at both doses. However, only IPQ20 group showed a reduction in number and volume of preneoplastic lesions. This group showed increased apoptosis and a reduction in the proliferative index. In addition, IPQ20 group displayed a reduction of cell percentages in G₁ and S phases, accumulation in G₂, and decrease in M phase, with reduced expression of cyclin D1, cyclin A, cyclin B, and cyclin-dependent kinase 1. Interestingly, peroxisome proliferator activated receptor-α levels were reduced in IPQ20 group. CONCLUSION The outcomes of this study represent a significant contribution to the current understanding on the preventive mechanisms of quercetin during the early stages of liver cancer development, demonstrating that in addition to its known proapoptotic characteristics, the flavonoid modulates the expression of critical cell cycle regulators and peroxisome proliferator activated receptor-α activity.

Tumor necrosis factor alpha induced by Trypanosoma cruzi infection mediates inflammation and cell death in the liver of infected mice

Trypanosoma cruzi (T. cruzi) infected C57BL/6 mice developed a progressive fatal disease due to an imbalance in the profile of circulating related compounds accompanying infection like tumor necrosis factor alpha (TNFalpha). TNFalpha has been proposed as an important effector molecule in apoptosis. In this work, we evaluate inflammation and the proteins involved in apoptotic process in liver of infected mice and the role of TNFalpha. C57BL6/mice were infected subcutaneously with 100 viable trypomastigotes of Tulahuén strain of T cruzi. One set of these animals were treated with 375 microg of antihuman TNFalpha blocking antibody. Animals were sacrificed at 14 days post-infection (p.i).The analyses of Bcl-2 family proteins revealed an increase of the pro-apoptotic proteins Bax and tBid in T. cruzi-infected mice. Compared with control animals, cytochrome c release was increased. Apoptosis was also induced in infected mice. Anti-TNFalpha treatment decreases hepatic apoptosis. Our results suggest that T. cruzi infection induces programmed cell death in the host liver by increase of TNFalpha production, associated with TNF-R1 over-expression, that set in motion the Bid cleavage and mitochondrial translocation, Bax mitochondrial translocation, cytochrome c release, and ultimately apoptosis induction.

Benznidazole treatment attenuates liver NF-κB activity and MAPK in a cecal ligation and puncture model of sepsis.

Recent studies have shown that Benznidazole (BZL), known for its antiparasitic action on Trypanosoma cruzi, modulates pro-inflammatory cytokines and nitric oxide (NO) release in activated macrophages by blocking NF-κB through inhibition of IKK in vitro. As so far, little is known about the mechanism by which BZL provokes the inhibition of inflammatory response in sepsis in vivo, we aimed to delineate the possible role of BZL as a modulator in liver inflammation in mice with sepsis induced by cecal ligation and puncture (CLP). Specifically, we analyzed leukocytes, liver production of TNF-α and NO and the intracellular pathways modulated by these mediators, including NF-κB and MAPKs, in the liver of mice 24 h post-CLP. Our results show that BZL reduces leukocytes in peripheral blood accompanied by an increase in peritoneal macrophages 24h after CLP. In the liver of these septic mice, BZL decreased expression of mRNA and protein for TNF-α and NOS-2 by inhibition of NF-κB and MAPK (p-38 and ERK). The body of evidence suggests that the immunomodulatory effects of BZL could act selectively, as it is able to decrease the systemic inflammatory reaction and the hepatic response but it can increase the number of cells in the site of infection.

Cross-talk between IFN-α and TGF-β1 signaling pathways in preneoplastic rat liver

Interferon-γ/transforming growth factor-β (IFN-γ/TGF-β) pathways have opposite effects on diverse cellular functions. However, little is known about interactions between IFN-α/TGF-β. In previous studies, we showed that IFN-α2b increases TGF-β1 production and secretion in hepatocytes from preneoplastic rat livers. Here, the interaction between IFN-α/TGF-β1 pathways was explored. We observed a positive cross-talk between IFN-α and TGF-β1 signaling, with activation of both pathways. p300 protein levels in hepatocytes from preneoplastic livers were enough to interact with both activated Stat1 and Smad2/3. Besides, Smad7 was not directly related with TGF-β1 and IFN-α signals. Interestingly, we reported the novel finding that the autocrine TGF-β1 up-regulates TGF-βRII at protein and mRNA levels. In conclusion, the intracellular signals triggered by IFN-α2b and by autocrine TGF-β1 are integrated at the nuclear level, where activated Stat1 and Smad2/3 are capable of interact with p300, present in no restrictive cellular amounts.

Interferon-α2b (IFN-α2b)-induced apoptosis is mediated by p38 MAPK in hepatocytes from rat preneoplastic liver via activation of NADPH oxidase

It is still unclear how Interferon-alfa (IFN-α) acts on preventing the appearance of hepatocarcinogenesis. We have demonstrated that IFN-α2b induces hepatocytic transforming growth factor-beta1 (TGF-β1) production and secretion by inducing reactive oxygen species (ROS) formation through the activation of NADPH oxidase. This TGF-β1, alters antioxidant defences and induces programmed cell death. Since it was demonstrated that IFN-α induces apoptosis through the activation of p38 mitogen-activated protein kinase (p38 MAPK), this study was aimed to assess the role of this kinase in the IFN-α2b-induced apoptosis in rat liver preneoplasia; and to further evaluate the participation of NADPH oxidase. p38 MAPK pathway was activated during the IFN-α2b-induced apoptosis in rat liver preneoplasia. This activation was accompanied with phosphorylation of different transcription factors, depending on the time of IFN-α2b stimulus. Our data suggest that NADPH oxidase is activated by IFN-α2b through p38 MAPK. p38 MAPK-induced activation of NADPH oxidase is accomplished by a two-step pathway: first, ROS-independent and second ROS- and TGF-β1-dependent.

Hepatocytes isolated from preneoplastic rat livers are resistant to ethacrynic acid cytotoxicity

Glutathione S-transferases (GSTs) are involved in the detoxification of xenobiotics, such as several cytostatic drugs, through conjugation with glutathione (GSH). Pi class GST (GST P) liver expression is associated with preneoplastic and neoplastic development and contributes with the drug-resistance phenotype. Ethacrynic acid (EA) is an inhibitor of rat and human GSTs. In addition, causes lipid peroxidation in isolated rat hepatocytes. Therefore, we decided to evaluate the role of the GST/GSH system in isolated hepatocytes from preneoplastic rat livers (IP) in the presence of EA and determine the cytotoxicity of the drug. Our results showed a resistance to the toxic effects of EA since viability and cellular integrity values were significantly higher than control. Initial levels of thiobarbituric acid reactive substances (TBARS) in IP hepatocytes were significantly higher than control and the presence of EA did not change TBARS levels. A diminution in intracellular total GSH was observed by treating with EA isolated hepatocytes from both groups. However, the initial total GSH levels were higher in IP hepatocytes than in control. Immunoblotting analysis showed the presence of GST P in IP animals only. Although alpha and mu class isoenzymes levels were decreased in IP hepatocytes, total GST activity was 1.5-fold higher than in control. In addition, multidrug-resistance protein 2 (Mrp2) showed fivefold decreased levels in IP hepatocytes. In conclusion, increased total GSH, decreased Mrp2 levels and the presence of GST P could be critical factors involved in the resistance of IP hepatocytes to the toxicity of EA.

Role of reactive oxygen species in the early stages of liver regeneration in streptozotocin-induced diabetic rats

Abstract Diabetes mellitus is a risk factor for prognosis after liver resection. In previous work, we found a pro-apoptotic state in the diabetic rat liver. In this work, this was also observed 1 hour post-partial hepatectomy (PH) and resulted in a deficient regenerative response 24 hours post-PH. Treatment with insulin and/or Desferoxamine (DES) (iron chelator) or Tempol (TEM) (free radicals scavenger) was effective in preventing the liver reactive oxygen species (ROS) production induced by diabetic state. High levels of ROS play a role in hepatic lipid peroxidation in diabetes before and after PH, and lead to increased pro-apoptotic events, which contribute to a reduced regenerative response. This becomes of relevance for the potential use of antioxidants/free radical scavengers plus insulin for improvement of post-surgical recovery of diabetic patients subjected to a PH.