Determinants of drug entry into the developing brain.

Area of Science:

• Neuroscience
• Pharmacology
• Developmental Biology

Background:

• Drug safety in pregnancy and neonates is a clinical concern, especially regarding long-term neurodevelopment.
• Limited knowledge exists on placental and blood-brain barrier drug permeability during development.
• The role of ATP-binding cassette (ABC) transporters in limiting brain drug entry during development is poorly understood.

Purpose of the Study:

• To investigate developmental differences in drug transfer across the blood-brain barrier and placenta.
• To assess the impact of acute versus chronic drug exposure on drug entry into the brain at different developmental stages.
• To explore the role of ABC transporters in mediating age-dependent drug permeability.

Main Methods:

• Radiolabeled paracetamol, digoxin, and cimetidine were administered to Sprague Dawley rats at fetal (E19), neonatal (P4), and adult stages.
• Drug entry into brain and cerebrospinal fluid (CSF) was measured after acute or chronic (5-day) intraperitoneal exposure.
• Placental transfer and brain/CSF drug levels were compared to passive diffusion markers (L-glucose, sucrose, glycerol).
• ABC transporter gene expression in brain, choroid plexus, and placenta was analyzed using RT-qPCR.

Main Results:

• Developing brains and CSF showed higher drug entry compared to adult brains and CSF.
• In adults, chronic treatment decreased digoxin and paracetamol brain entry, correlating with ABCB1a (P-glycoprotein) upregulation.
• No such downregulation or decreased transfer was observed in fetal or neonatal animals.
• Chronic paracetamol exposure paradoxically increased drug transfer into the fetal brain.

Conclusions:

• The developing brain exhibits reduced efflux capacity, increasing vulnerability to acute drug exposure.
• Adult brains develop regulatory capacity for efflux transporters, offering protection against chronic drug exposure.
• Neonatal brains lack this regulatory capacity, posing a greater risk from chronic drug administration.
• These findings highlight critical developmental differences in drug transport and safety.