Irradiation of rat brain reduces P-glycoprotein expression and function.

Area of Science:

• Neuroscience
• Radiology
• Pharmacology

Background:

• The blood-brain barrier (BBB) restricts drug entry into the brain.
• P-glycoprotein (P-gp) is a key efflux pump at the BBB, limiting drug delivery.
• Radiation therapy can alter BBB integrity and P-gp expression.

Purpose of the Study:

• To investigate the impact of brain irradiation on P-glycoprotein (P-gp) expression and function.
• To determine if radiation therapy can modulate P-gp activity, potentially enhancing drug delivery to the brain.

Main Methods:

• Rats were subjected to single or fractionated doses of brain irradiation.
• P-glycoprotein (P-gp) expression was assessed using immunohistochemistry.
• P-gp function was evaluated by measuring the uptake of the P-gp substrate [(11)C]carvedilol.
• The P-gp substrate cyclosporine A (CsA) was administered to assess its brain penetration post-irradiation.

Main Results:

• Irradiation increased [(11)C]carvedilol uptake in a dose-dependent manner, indicating reduced P-gp function.
• Fractionated irradiation led to decreased P-gp expression and increased [(11)C]carvedilol uptake.
• Single-dose irradiation showed a temporary decrease in P-gp expression and function between days 15 and 20 post-irradiation.
• Cyclosporine A brain levels were higher in the irradiated hemisphere, suggesting compromised P-gp efflux.

Conclusions:

• Brain irradiation causes a temporary decrease in P-glycoprotein (P-gp) function.
• This transient reduction in P-gp function may enhance the delivery of P-gp substrate drugs to the brain.
• Understanding these effects is crucial for optimizing drug delivery in brain tumor radiotherapy.