ABSTRACT
Double stranded RNA (dsRNA) activated protein kinase R (PKR), a ubiquitously expressed serine/threonine kinase is a key inducer of inflammation, insulin resistance and glucose homeostasis in obesity. Recent studies have demonstrated that PKR can respond to metabolic stress in mice as well as in humans. However the underlying molecular mechanism is not fully understood. The aim of the present study was to examine the effect of high glucose on cultured rat L6 muscle cells and to investigate whether inhibition of PKR could prevent any deleterious effects of high glucose in these cells. PKR expression was determined by immunofluorescence and immunoblotting. The expression of different insulin signaling gene markers were measured by RT-PCR. Oxidative stress and apoptosis were determined by flow cytometry. High glucose treated L6 muscle cells developed a significant increase in PKR expression. Impaired insulin signaling as well as reduced insulin stimulated glucose uptake was observed in high glucose treated L6 muscle cells. A significant increase in reactive oxygen species generation and apoptosis formation was also observed in high glucose treated cultured L6 muscle cells. All these effects of high glucose were attenuated by a selective PKR inhibitor imoxin. Our study demonstrates PKR may have an additive role against the deleterious effects of high glucose in diabetes. Prevention of PKR activation, by safer and specific inhibitors is a therapeutic option in metabolic disorders that needs to be explored further.
Subject(s)
Glucose/toxicity , Insulin/pharmacology , Muscle Cells/drug effects , Signal Transduction/genetics , eIF-2 Kinase/genetics , Animals , Apoptosis/drug effects , Cell Line , Gene Expression Regulation , Imidazoles/pharmacology , Indoles/pharmacology , Insulin/metabolism , Muscle Cells/cytology , Muscle Cells/metabolism , Oxidative Stress/drug effects , Protein Kinase Inhibitors/pharmacology , Rats , Reactive Oxygen Species/agonists , Reactive Oxygen Species/metabolism , eIF-2 Kinase/antagonists & inhibitors , eIF-2 Kinase/metabolismABSTRACT
BACKGROUND: Methylglyoxal (MG) is a byproduct of glucose metabolism and an inducer of advanced glycation end products (AGEs). AGEs are implicated in the pathogenesis of diabetes as well as hypertension. Most of the currently available MG scavengers are non-specific and have other effects as well. Alagebrium (ALA), developed by Alteon Corporation is a MG scavenger. Thus the aim of the present study was to investigate the potential of novel ALA analogs as possible MG scavengers and whether they could prevent any deleterious effects of MG. METHODS AND RESULTS: MG levels were measured by HPLC. The different biochemical and molecular parameters were measured by assay kits, RT-PCR and immunocytochemistry. Out of the 15 ALA analogs tested in vitro, compound no. 13 was found to be an effective inhibitor of MG in a concentration and time dependent manner. Compound no. 13 significantly attenuated the MG levels in vitro in MG treated cultured H9C2 cardiomyocytes as well as in vivo in MG treated SD rats. MG induced oxidative stress and apoptosis were attenuated by pretreatment of H9C2 cardiac myocytes with compound no. 13. MG induced cardiac hypertrophy and apoptosis were also attenuated by treating MG treated SD rats with compound no. 13. CONCLUSION: Our results indicate compound 13 as an effective inhibitor of MG in vitro in cultured cardiomyocytes and in vivo in SD rats and thus it may prove very useful in blocking the multiple deleterious effects of MG, including AGEs and vascular complications of diabetes.
