ABSTRACT
Background: elevated level of plasma homocysteine has been related to various diseases. Patients with hyperhomocysteinemia can develop hepatic steatosis and fibrosis. We hypothesized that oxidative stress induced by homocysteine might play an important role in pathogenesis of liver injury. Also, the cellular response designed to combat oxidative stress is primarily controlled by the transcription factor Nrf2, a principal inducer of anti-oxidant and phase II-related genes
Methods: hepG2 cells were treated with homocysteine in different time periods. Glutathione content was measured by flowcytometry. Using electrophoretic mobility shift assay [EMSA] and Western-blotting, anti-oxidant response element [ARE]-binding activity of Nrf2 for heme ocygenase-1 [HO-1] was demonstrated. Real time RT-PCR and Western-blotting were performed to evaluate whether homocysteine was able to induce mRNA and protein expression of HO-1
Results: the role of Nrf2 in cellular response to homocysteine is substantiated by the following observations in HepG2 cells exposed to homocysteine [i] Western-blotting revealed that Nrf2 is strongly stabilized and became detectable in nuclear extracts. [ii] EMSA demonstrated increased binding of Nrf2 to oligomers containing HO-1 promoter-specific ARE-binding site. [iii] Real time RT-PCR and Western-blotting revealed increased mRNA and protein expression of inducible gene HO-1 after treatment with Homocysteine
Conclusion: data presented in the current study provide direct evidence that the immediate cellular response to oxidative stress provoked by homocysteine is orchestrated mainly by the Nrf2-ARE pathway. Therefore, induction of Nrf2-ARE-dependent expression of HO-1 could be a therapeutic option for hepatic cells damage induced by homocysteine. Iran. Biomed. J. 17 [2]: 93-100, 2013
ABSTRACT
The worldwide prevalence of insulin resistant states such as the metabolic syndrome has grown rapidly over the past few decades. The metabolic syndrome is a constellation of common metabolic disorders that promote the development of atherosclerosis and cardiovascular disease. Studies in both human and animal models suggest that hepatic inflammation and insulin resistance are key initiating factors in the development of the metabolic syndrome. Chronic inflammation is known to be associated with visceral obesity and is characterized by production of abnormal adipokines and cytokines such as tumor necrosis factor a, interleukin-1 [IL-1], IL-6, leptin, and resistin. These factors inhibit insulin signaling in the liver [hepatocytes] by activating suppressors of cytokine signalling proteins; several kinases such as c-Jun N-terminal kinases, IKK-beta, and Protein kinase C; and protein tyrosine phosphatase 1B, that in turn impair insulin signaling at insulin receptor and insulin receptor substrate level. Hepatic insulin resistance in turn causes impaired suppression of glucose production by insulin in hepatocytes leading to hyperglycemia, induction of very low density lipoprotein production, and de novo lipogenesis. Increased production of C-reactive protein [CRP] and plasminogen activator inhibitor-1, both markers of an inflammatory state, is also observed in insulin resistance. All of the above metabolic abnormalities can directly or indirectly promote atherosclerosis. In particular, hyperglycemia induces endothelial dysfunction, cellular proliferation, changes in extracellular matrix conformation, and impairment of low density lipoproteins [LDL]-receptor-mediated lipoprotein uptake. Small dense LDLs have higher affinity to the intimal proteoglycans, leading to the penetration of more LDL particles into the arterial wall. CRP can also accelerate atherosclerosis by increasing the expression of PAI-1 and adhesion molecules in endothelial cells, inhibition of nitric oxide formation, and increasing LDL uptake into macrophages. In summary, hepatic insulin resistance is a critical early event that underlies the development of the metabolic syndrome and progression to atherosclerosis and cardiovascular disease