A protective role for heme oxygenase-1 in INS-1 cells and rat islets that are exposed to high glucose conditions

Abstract

Heme oxygenase-1 (HO-1) has been described as an inducible protein that is capable of cytoprotection via radical scavenging and the prevention of apoptosis. Chronic exposure to hyperglycemia can lead to cellular dysfunction that may become irreversible over time, and this process has been termed glucose toxicity. Yet little is known about the relation between glucose toxicity and HO-1 in the islets. The purposes of the present study were to determine whether prolonged exposure of pancreatic islets to a supraphysiologic glucose concentration disrupts the intracellular balance between reactive oxygen species (ROS) and HO-1, and so this causes defective insulin secretion; we also wanted to evaluate a protective role for HO-1 in pancreatic islets against high glucose levels. The intracellular peroxide levels of the pancreatic islets (INS-1 cell, rat islet) were increased in the high glucose media (30 mM glucose or 50 mM ribose). The HO-1 expression was induced in the INS-1 cells by the high glucose levels. Both the HO-1 expression and glucose stimulated insulin secretion (GSIS) was decreased simultaneously in the islets by treatment of the HO-1 antisense. The HO-1 was upregulated in the INS-1 cells by hemin, an inducer of HO-1. And, HO-1 upregulation induced by hemin reversed the GSIS in the islets at a high glucose condition. These results suggest HO-1 seems to mediate the protective response of pancreatic islets against the oxidative stress that is due to high glucose conditions.

Fig. 1

The effects of high glucose on the intracellular peroxide level and Glucose stimulating insulin secretion (GSIS) in the INS-1 cells and rat islets. (A) INS-1 cells were incubated at 5.6, 22.2 or 30 mM glucose for 3 days. INS-1 cells incubated at 30 mM glucose increased levels of intracellular peroxides compared with the 5.6 mM concentration of glucose. (B) Isolated rat islets were incubated with 11.1 mM glucose or 30 mM ribose for 3 days. 30 mM ribose caused an increase of intracellular peroxide levels compared with the 11.1 mM glucose. Each cell at the high glucose or ribose concentrations showed decreased GSIS (p<0.05). Data are means±SD from 3 separate experiments.

Fig. 2

The HO-1 expression and activity after 3 days subculture of the INS-1 cells. Compared with the 5.6 mM glucose concentration, 30 mM glucose caused an increase in the HO-1 expression and activity in the INS-1 cells (p<0.05). Data are means±SD from 3 separate experiments.

Fig. 3

The intracellular peroxide level, HO-1 expression and GSIS after 3 days culture (5 hrs exposure to the ODNs) in the INS-1 cells. HO-1 was downregulated in the INS-1 cells by the HO-1 antisense ODNs (p<0.05). Data are means±SD from 3 separate experiments.

Fig. 4

The intracellular peroxide level and the HO-1 expression and activity after 3 days subculture (1 day pre-exposure of Hemin) in the INS-1 cells (A) and rat islets (B). HO-1 was upregulated in the INS-1 cells and rat islets by Hemin (p<0.05). Data are means±SD from 3 separate experiments.

Fig. 5

GSIS after 3 days subculture (1 day pre-exposure of Hemin) in the INS-1 cells (A) and rat islets (B). Hemin induced HO-1 upregulation and it reserved the GSIS in the islets at the high glucose condition (p<0.05). Data are means±SD from 3 separate experiments.