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Abstract
Background
Hyperglycemia is a well-recognized pathogenic factor of long term complications in diabetes mellitus and hyperglycemia also generates reactive oxygen species (ROS) in β cells when ROS accumulate in excess for prolonged periods of time, they cause chronic oxidative stress and adverse effects. Unfortunately, the islet contacts low capacity of endogenous antioxidant effects. But, γ-glutamylcysteine synthetase (γ-GCS), the rate-limiting enzyme for glutathione synthesis, is well represented in islets.
Methods
This study is to evaluate the changes in the activity of γ-GCS, glutathione in β-cells exposed to high glucose, in pancreatic tissue of OLETF (Otsuka Long Evans Tokushima Fatty) and LETO (Long-Evans Tokushima Otsuka) rats, in leukocytes from patients with Korean type 2 DM (T2DM) and to disclose the effects of high blood glucose on this impairment in patients with T2DM. We divided our patients into 3 groups by HbA1c (controls: n = 20, well controls diabetes: n=24, poorly controlled diabetes: n = 36).
Results
We observed that decreased glutathione level, γ-GCS expression, glucose-stimulated (GSIS) and increased intracellular peroxide level in the INS-1 cells exposed to 30 mM glucose condition. Also decreased glutathione level at erythrocytes, γ-GCS expression at leukocytes and increased oxidized LDL, MDA (malondialdehyde) level at plasma from patients with T2DM compared to controls (esp, poorly controlled patients).
Figures and Tables
Fig. 1
The effects of high glucose on the intracellular peroxide level, PDX-1, MafA, insulin mRNA and glucose stimulated insulin secretion (GSIS) in the INS-1 cells. A, INS-1 cells incubated for 72 hours at 30 mM glucose increased levels of intracellular peroxides compared with the 5.6 mM glucose (P < 0.05). And, INS-1 cells incubated at 30 mM glucose decreased GSIS compared with the 5.6 mM glucose. *P < 0.05 vs. 5.6 mM glucose; B, INS-1 cells incubated for 72 hours at 30 mM glucose decreased PDX-1, MafA, insulin mRNA compared with the 5.6 mM glucose. *P < 0.05; C, INS-1 cells incubated for 72 hours at 30 mM glucose decreased the expression of γ-GCS mRNA and GSH level compared with the 5.6 mM glucose in INS-1 cell (P < 0.05). *P < 0.05 vs. 30 mM glucose. Data are mean ± SE from 3 separate experiments.
Fig. 2
GSH level at pancreatic tissues in OLETF (n = 5) and LETO rats (n = 5). GSH level at pancreatic tissues in OLETF rats was significantly decreased compared with LETO rats. *P < 0.05 vs. LETO rats.
Fig. 3
Expression of γ-GCS mRNA in leukocytes and GSH level in erythrocytes from patients with T2DM. Expression of γ-GCS mRNA in leukocytes and GSH level in erythrocytes from patients with T2DM (n = 60) were significantly decreased compared with controls (n = 20). *P < 0.05 vs. Diabetics.
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