Strain differences in purified rat hepatic 3 alpha-hydroxysteroid UDP-glucuronosyltransferase

Area of Science:

• Biochemistry
• Pharmacology
• Toxicology

Background:

• Hepatic UDP-glucuronosyltransferases (UGTs) are crucial for metabolizing xenobiotics and endogenous compounds.
• Individual differences in UGT activity can significantly affect drug efficacy and toxicity.
• Rat models are commonly used to study UGTs, but strain-specific variations require careful consideration.

Purpose of the Study:

• To investigate qualitative and quantitative differences in hepatic 3 alpha-hydroxysteroid UDP-glucuronosyltransferase (3α-HSD UGT) between Wistar and Sprague-Dawley rats.
• To characterize the kinetic properties of purified 3α-HSD UGT from different rat populations.
• To understand the implications of these variations for steroid glucuronidation.

Main Methods:

• Purification of hepatic 3α-HSD UGT from Wistar and Sprague-Dawley rats using Chromatofocusing and affinity chromatography.
• Assay of glucuronidation rates for various substrates (androsterone, chenodeoxycholic acid, testosterone, p-nitrophenol, oestrone).
• Determination of kinetic parameters (Km) for androsterone and UDP-glucuronic acid.

Main Results:

• Wistar rats exhibited significant individual variations in the glucuronidation rates of androsterone and chenodeoxycholic acid, while Sprague-Dawley rats did not.
• The amount of 3α-HSD UGT in low-activity Wistar rats was approximately 10% of that in high-activity Wistar rats.
• Purified 3α-HSD UGT from high-activity Wistar rats and Sprague-Dawley rats showed similar apparent Km for androsterone (6 µM), but low-activity Wistar rats had a substantially higher Km (120 µM).
• Apparent Km for UDP-glucuronic acid was consistent across all groups (0.3 mM).

Conclusions:

• Significant inter-individual variability exists in hepatic 3α-HSD UGT activity in Wistar rats, particularly for androsterone and chenodeoxycholic acid glucuronidation.
• These variations are primarily due to differences in enzyme amount and kinetic properties (Km for androsterone), not UDP-glucuronic acid affinity.
• Strain-specific differences and intra-strain variability in 3α-HSD UGT activity should be considered in toxicological and pharmacological studies using rat models.