Glutathione depletion upregulates P-glycoprotein expression at the blood-brain barrier in rats

Glutathione (GSH) depletion has been implicated in the pathogenesis of neurological diseases. During GSH depletion, cells of the blood-brain barrier are subjected to chronic oxidative stress. Using an in-vivo system, we have investigated whether glutathione depletion changed expression of P-glycoprotein at the blood-brain barrier in rats.

Diethyl maleate was intraperitoneally injected to induce GSH depletion in rats. P-glycoprotein expression at the blood-brain barrier was examined by Western blotting and RT-PCR, and its function was assessed by measuring the brain-to-plasma concentration ratios (Kp values) of rhodamine 123 (Rh123). Evans Blue dye was used as a blood-brain barrier indicator for examining the extravasation from the blood to the brain.

Four hours after treatment of rats with diethyl maleate, the brain GSH content significantly reduced. The mdr1a mRNA expression at the blood-brain barrier was upregulated, whereas no significant change in mdr1b mRNA expression was found. The P-glycoprotein level was significantly increased compared with control rats. At the same time, the Kp values of Rh123 suggested that function of P-glycoprotein was significantly enhanced at the blood-brain barrier in rats with GSH depletion induced by diethyl maleate. No significant difference of the Evans Blue dye concentration in the brain cortex was found between GSH depletion rats and control rats. Treatment of rats with N-acetylcysteine decreased P-glycoprotein upregulation induced by diethyl maleate.

The oxidative stress induced by GSH depletion played a positive role in the regulation of function and expression of P-glycoprotein at the blood-brain barrier in rats.