Dietary-Induced Obesity and Changes in the Biodistribution and Metabolism of Amiodarone in the Rat.

The metabolism and biodistribution of the antiarrhythmic drug amiodarone (AM) was assessed in male Sprague-Dawley rats given either normal chow or high-fat and high-fructose diets for 14 weeks. After the feeding period, microsomes were prepared from liver and intestine, and the metabolism of AM to desethylamiodarone was determined. Intrinsic clearance (CL) was reduced by hepatic microsomes isolated from rats given high-calorie diets. In intestinal microsomes, there was no change or a small increase in metabolic rate in obese rats. A biodistribution study was also undertaken in a group of control and high-fat + high fructose-fed rats. Excess calories led to a significant increase in plasma AM compared to normal chow-fed control animals. A population pharmacokinetic analysis of AM confirmed that its oral CL was reduced. In plasma, there was a decrease in the metabolite to drug ratio. Some tissue:plasma ratios of AM in high calorie-fed rats were aligned with a decrease in plasma unbound fraction. It is concluded that the findings reinforced those of a recent report where we found decreases in expressions of enzymes involved in AM dealkylation, in showing greater exposure and lower oral CL, and generally decreases in liver microsomal metabolism of AM after high-calorie diets.

Cytochrome P450 2U1, a very peculiar member of the human P450s family.

Cytochrome P450 2U1 (CYP2U1) exhibits several distinctive characteristics among the 57 human CYPs, such as its presence in almost all living organisms with a highly conserved sequence, its particular gene organization with only five exons, its major location in thymus and brain, and its protein sequence involving an unusually long N-terminal region containing 8 proline residues and an insert of about 20 amino acids containing 5 arginine residues after the transmembrane helix. Few substrates, including fatty acids, N-arachidonoylserotonin (AS), and some drugs, have been reported so far. However, its biological roles remain largely unknown, even though CYP2U1 mutations have been involved in some pathological situations, such as complicated forms of hereditary spastic paraplegia. These data together with its ability to hydroxylate some fatty acids and AS suggest its possible role in lipid metabolism.