Rabbit pregnane X receptor is activated by rifampicin

Area of Science:

• Pharmacology
• Molecular Biology
• Genetics

Background:

• The pregnane X receptor (PXR) is a nuclear receptor that regulates genes involved in drug metabolism and detoxification.
• Understanding species-specific differences in PXR function is crucial for accurate preclinical drug testing and predicting human responses.

Purpose of the Study:

• To isolate and characterize the rabbit pregnane X receptor (PXR) ortholog.
• To investigate the ligand-binding and activation profile of rabbit PXR.
• To compare rabbit PXR function with that of other species, particularly rat and human.

Main Methods:

• Reverse transcriptase-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) were used to isolate rabbit PXR cDNA.
• Sequence analysis was performed to determine amino acid identity with known PXR orthologs.
• Functional assays involved cell transfection with rabbit PXR expression plasmids and reporter constructs, followed by treatment with various ligands (e.g., rifampicin, pregnenolone 16alpha-carbonitrile).

Main Results:

• A rabbit PXR ortholog was identified with high sequence identity to mouse and human PXR.
• Rabbit PXR exhibited distinct ligand activation compared to rat PXR; it was activated by rifampicin but not pregnenolone 16alpha-carbonitrile.
• The activation profile of rabbit PXR more closely resembled that of human PXR, aligning with observed cytochrome P450 3A6 induction in rabbits.

Conclusions:

• The cloned cDNA represents the rabbit PXR ortholog.
• Rabbit PXR displays a ligand activation profile distinct from rat PXR and similar to human PXR.
• These findings have implications for using rabbits as models for studying drug metabolism and predicting human drug responses.