Article

Insulin can block apoptosis by decreasing oxidative stress via phosphatidylinositol 3-kinase- and extracellular signal-regulated protein kinase-dependent signaling pathways in HepG2 cells.

Department of Medicine, College of Medicine, Institute of Basic Science and Department of Biology, College of Natural Science, Cheju National University, Ara-1, Cheju, 690-756, South Korea.
European Journal of Endocrinology (Impact Factor: 3.69). 02/2003; 148(1):147-55. DOI: 10.1530/eje.0.1480147
Source: PubMed

ABSTRACT Insulin has well-known activities in controlling energy metabolism, cellular proliferation and biosynthesis of functional molecules to maintain a biological homeostasis. Recently, several studies have suggested that insulin may protect cells from apoptosis in different cell lines; however, little is known about the nature of its anti-apoptotic activity. In many clinical disorders, including type 2 diabetes mellitus, oxidative stress and the production of reactive oxygen species (ROS) is increased. With these facts as a background, we examined here whether insulin protects HepG2 cells from apoptosis by decreasing oxidative stress and, if so, which signaling steps are involved in this process.
Intracellular DNA content, the degree of nuclear condensation or poly(ADP-ribose) polymerase hydrolysis was measured to verify the occurrence of apoptotic events. Caspase-3 activity and ROS accumulation within cells were also measured. Western blot analysis was performed to identify signaling molecules activated in response to insulin.
Serum starvation resulted in a marked accumulation of ROS, activation of caspase-3, and subsequent apoptotic cell death which were, in turn, markedly blocked by the addition of insulin. The anti-apoptotic activity of insulin was sensitive to blockade of two different signaling steps, activations of phosphatidylinositol 3-kinase (PI3 kinase) and extracellular signal-regulated protein kinase (ERK).
Insulin exerts an anti-apoptotic activity by suppressing the excessive accumulation of ROS within cells through signaling pathways including stimulation of PI3 kinase and ERK in HepG2 cells.

0 Followers
 · 
49 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Clinical and experimental biomedical studies have shown Type 2 diabetes mellitus (T2DM) to be a risk factor for the development of Alzheimer's disease (AD). This study demonstrates the effect of metformin, a therapeutic biguanide administered for T2DM therapy, on β-amyloid precursor protein (APP) metabolism in in vitro, ex vivo and in vivo models. Furthermore, the protective role of insulin against metformin is also demonstrated. In LAN5 neuroblastoma cells, metformin increases APP and presenilin levels, proteins involved in AD. Overexpression of APP and presenilin 1 (Pres 1) increases APP cleavage and intracellular accumulation of β-amyloid peptide (Aβ), which, in turn, promotes aggregation of Aβ. In the experimental conditions utilized the drug causes oxidative stress, mitochondrial damage, decrease of Hexokinase-II levels and cytochrome C release, all of which lead to cell death. Several changes in oxidative stress-related genes following metformin treatment were detected by PCR arrays specific for the oxidative stress pathway. These effects of metformin were found to be antagonized by the addition of insulin, which reduced Aβ levels, oxidative stress, mitochondrial dysfunction and cell death. Similarly, antioxidant molecules, such as ferulic acid and curcumin, are able to revert metformin's effect. Comparable results were obtained using peripheral blood mononuclear cells. Finally, the involvement of NF-κB transcription factor in regulating APP and Pres 1 expression was investigated. Upon metformin treatment, NF-κB is activated and translocates from the cytoplasm to the nucleus, where it induces increased APP and Pres 1 transcription. The use of Bay11-7085 inhibitor suppressed the effect of metformin on APP and Pres 1 expression. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta (BBA) - Molecular Cell Research 02/2015; 1853(5). DOI:10.1016/j.bbamcr.2015.01.017 · 5.30 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Alcoholic liver disease (ALD) has become an important liver disease hazard to public and personal health. Oxidative stress is believed to be responsible for the pathological changes in ALD. Previous studies have showed that insulin, a classic regulator of glucose metabolism, has significant anti-oxidative function and plays an important role in maintaining the redox balance. For addressing the effects and mechanisms of insulin pre-administration on ethanol-induced liver oxidative injury, we investigated histopathology, inflammatory factors, apoptosis, mitochondrial dysfunction, oxidative stress, antioxidant defense system, ethanol metabolic enzymes and lipid disorder in liver of ethanol-exposed mice pretreatment with insulin or not. There are several novel findings in our study. First, we found insulin pre-administration alleviated acute ethanol exposure-induced liver injury and inflammation reflected by the decrease of serum AST and ALT activities, the improvement of pathological alteration and the inhibition of TNF-α and IL-6 expressions. Second, insulin pre-administration could significantly reduce apoptosis and ameliorate mitochondrial dysfunction in liver of mice exposed to ethanol, supporting by decreasing caspases-3 activities and the ratio of Bax/Bcl-2, increasing mitochondrial viability and mitochondrial oxygen consumption, inhibition of the decline of ATP levels and mitochondrial ROS accumulation. Third, insulin pre-administration prevented ethanol-mediated oxidative stress and enhance antioxidant defense system, which is evaluated by the decline of MDA levels and the rise of GSH/GSSG, the up-regulations of antioxidant enzymes CAT, SOD, GR through Nrf-2 dependent pathway. Forth, the modification of ethanol metabolism pathway such as the inhibition of CYP2E1, the activation of ALDH might be involved in the anti-oxidative and protective effects exerted by insulin pre-administration against acute ethanol exposure in mice. Finally, insulin pre-administration deteriorated hepatic steatosis in mice exposed to ethanol might be through SRBEP-1c activation. In summary, these results indicated that insulin pre-administration effectively alleviated liver oxidative injury through anti-inflammatory, anti-oxidative and anti-apoptotic activities but also deteriorated hepatic steatosis through SRBEP-1c activation in mice exposed to ethanol. Our study provided novel insight about the effects and mechanisms of insulin on ethanol-induced liver injury.
    International journal of biological sciences 01/2015; 11(5):569-86. DOI:10.7150/ijbs.11039 · 4.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Both, the R-enantiomer of the antioxidant alpha-lipoic acid (R-LA) and the hormone atrial natriuretic peptide (ANP) are known to exert potent hepatoprotective action. The present work characterises alpha-lipoic acid- and ANP-mediated signal transduction pathways involved in the regulation of apoptotic cell death in two different models: primary hepatocytes and ischemic isolated perfused rat livers. alpha-lipoic acid was shown to protect isolated hepatocytes from TNF-alpha-/ActinomycinD-induced apoptosis. Astonishingly, this effect did not seem to be governed neither by its well described antioxidative nor its Fe-chelating properties. In fact, the LA-mediated activation of the PI3-K/Akt survival pathway seemed to be responsible for the antiapoptotic properties of alpha-lipoic acid. Consequently, incubation with a specific PI3-K-inhibitor significantly reduced both, R-LA-mediated decrease in caspase activity and R-LA-induced BAD phosphorylation. Thus, PI3-K-mediated Akt activation and subsequent phosphorylation of the proapoptotic protein BAD at Ser136 are causally involved in the antiapoptotic signalling mediated by R-LA. Perfusion with ANP 20 min prior to the ischemic period is known to reduce apoptotic cell death occurring at the end of the ischemic period. We could previously show that this preconditioning of rat livers leads to a marked activation of p38 MAPK. Since ANP reduces apoptotic cell death, the potential connection between this ANP-induced p38 MAPK activation and apoptosis reduction was investigated. Astonishingly, liver perfusion with an p38 MAPK inhibitor even decreased apoptotic cell death, supporting a detrimental role of this kinase. PKA-specific inhibitors demonstrated the involvement of PKA in this ANP-mediated protection. Interestingly, it also turned out that PKA phosphorylates the proapoptotic protein BAD at Ser112, an effect known to contribute to the inhibition of apoptosis. In summary, the present data show for the first time that phosphorylation of BAD at either Ser136 or Ser112 turns out to be a central protective mechanism to defend from hepatocyte apoptosis.

Preview

Download
1 Download
Available from