INFLUENCE OF CHOLINE DEFICIENCY ON THE EXPRESSION OF IRS-1 AND GLUT-2 IN THE LIVER OF STZ-INDUCED DIABETIC RATS.

A Kyriakaki1, M Gazouli2, H Al-Humadi1, A Strilakou1, N Tentolouris3, N Anagnou2, C Liapi1. 1University Medical School, Athens, Greece, Pharmacology, Greece, 2University Medical School, Athens, Greece, Biology, Greece, 3University Medical School, Athens, Greece, Propaedeutic Medicine, Greece

INTRODUCTION: Insulin stimulates the cellular uptake of glucose in the liver, muscle and adipose tissue promoting the glucose transport in the cells. Key players in insulin signaling and action, include insulin downstream signaling molecules such as insulin receptor substrate-1 (IRS-1) and the appropriate receptors in each tissue (glucose transporters -GLUT). In the liver those receptors are the GLUT 2. In the diabetic state because of the insulin deficiency GLUT-2 translocation does not take place efficiently and remains inside the cell where it is not functional, while IRS-1 fails in transmitting properly signals from the insulin receptors to intracellular pathways. A significant interaction between diabetes and choline metabolism has been reported but it is not fully elucidated. Choline is a quaternary amine, it belongs to the vitamin complex of B12 and has an augmentable clinical interest since it takes part to many physiological functions of vital interest of the organism. Choline deficient diet is a well studied model of non alcoholic steatohepatitis in rats, a condition usually accompanied by insulin resistance.

AIM: The aim of this study was to investigate the effect of dietary-induced choline deprivation (CD) on the changes caused by adult-onset streptozotocin (STZ) – induced diabetes on the rat liver activities of GLUT-2 and IRS-1.

MATERIALS AND METHODS: Male wistar Albino rats (N=48) divided in four groups were used: a) control group (CONTROL), b)the group taking choline deficient diet (CDD) c) diabetic group that was taking a balanced diet (DIAB) d) the group with diabetic rats that was taking a choline deficient diet (CDD+DIAB).

The adult-onset streptozotocin (STZ) – induced diabetes was induced by an intraperitoneal injection of streptozotocin 50mg/kg of BW at the beginning of the experiment.

The period of the food intervention was of one month. The analysis of the expression of the GLUT 2 and IRS-1 (m RNA) was estimated by RT-PCR.

RESULTS: The expression of the GLUT 2 was increased by 365% in the CDD group, by 186% in the DIAB group and by 33.4% in the CDD+DIAB group compared the CONTROL group (p<0.001). IRS-1 expression compared to CONTROL was reduced in CDD by 40.3%, in DIAB by 77.93% and in CDD+DIAB by 68,02%.

CONCLUSIONS: The greatest increase of GLUT 2 was found in the CDD group and the less one in the CDD+DIAB group. The IRS-1 showed the higher decrease in the DIAB group and in CDD+DIAB group. Thus choline deficiency has an influence on the mechanism of glucose homeostasis and promotes diabetes mellitus in previously healthy rats. Furthermore, in yet diabetic rats choline deficiency may have a deteriorating effect since the corresponding glucose transporters GLUT 2 are inefficient under these conditions. The present data show alterations in the insulin pathway and further studies are in progress in order to investigate the underlying mechanisms of these findings.