The Effect of Glucose Fluctuation on Apoptosis and Function of INS-1 Pancreatic Beta Cells.
BACKGROUND
Blood glucose level continuously fluctuates within a certain range in the human body. In diabetes patients, the extent of such fluctuation is large, despite the strict control of blood glucose. Blood glucose fluctuation has been shown to mediate more adverse effects on vascular endothelial cells and diabetes complications than chronic hyperglycemia, which has been explained as due to oxidative stress. As few previous studies have reported the effects of chronic and intermittent hyperglycemia on the apoptosis and function of pancreatic beta cells, this study reported herein was performed to investigate such effects on these cells.


METHODS
For chronic hyperglycemia, INS-1 cells were cultured for 5 days with changes of RPMI 1640 medium containing 33 mM glucose every 12 hours. For intermittent hyperglycemia, the medium containing 11 mM glucose was exchanged with the medium containing 33 mM glucose every 12 hours. Apoptosis was assessed by TUNEL assay Hoechst staining and cleaved caspase 3. Insulin secretory capacity was assessed, and the expression of Mn-SOD and Bcl-2 was measured by Western blotting.


RESULTS
In comparison to the control group, INS-1 cells exposed to chronic hyperglycemia and intermittent hyperglycemia showed an increase in apoptosis. The apoptosis of INS-1 cells exposed to intermittent hyperglycemia increased significantly more than the apoptosis of INS-1 cells exposed to chronic hyperglycemia. In comparison to the control group, the insulin secretory capacity in the two hyperglycemic states was decreased, and more with intermittent hyperglycemia than with chronic hyperglycemia. The expression of Mn-SOD and Bcl-2 increased more with chronic hyperglycemia than with intermittent hyperglycemia.


CONCLUSIONS
Intermittent hyperglycemia induced a higher degree of apoptosis and decreased the insulin secretory capacity more in pancreatic beta cells than chronic hyperglycemia. This activity may be mediated by the anti-oxidative enzyme Mn-SOD and the anti-apoptotic signal Bcl-2.
Department of Internal Medicine, Maryknoll Medical Center, Busan, Korea.
Mi Kyung
MK
Kim
Hye Sook
HS
Jung
Chang Shin
CS
Yoon
Jung Hae
JH
Ko
Hae Jung
HJ
Jun
Tae Kyun
TK
Kim
Min Jeong
MJ
Kwon
Soon Hee
SH
Lee
Kyung Soo
KS
Ko
Byoung Doo
BD
Rhee
Jeong Hyun
JH
Park