Elevated serum cholesterol in drug-oxidation-deficient rats

Polymorphic cytochrome P450 2D6: humanized mouse model and endogenous substrates

Cytochrome P450 2D6 (CYP2D6) is the first well-characterized polymorphic phase I drug-metabolizing enzyme, and more than 80 allelic variants have been identified for the CYP2D6 gene, located on human chromosome 22q13.1. Human debrisoquine and sparteine metabolism is subdivided into two principal phenotypes--extensive metabolizer and poor metabolizer--that arise from variant CYP2D6 genotypes. It has been estimated that CYP2D6 is involved in the metabolism and disposition of more than 20% of prescribed drugs, and most of them act in the central nervous system or on the heart. These drug substrates are characterized as organic bases containing one nitrogen atom with a distance about 5, 7, or 10 A from the oxidation site. Aspartic acid 301 and glutamic acid 216 were determined as the key acidic residues for substrate-enzyme binding through electrostatic interactions. CYP2D6 transgenic mice, generated using a lambda phage clone containing the complete wild-type CYP2D6 gene, exhibits enhanced metabolism and disposition of debrisoquine. This transgenic mouse line and its wild-type control are models for human extensive metabolizers and poor metabolizers, respectively, and would have broad application in the study of CYP2D6 polymorphism in drug discovery and development, and in clinical practice toward individualized drug therapy. Endogenous 5-methoxyindole- thylamines derived from 5-hydroxytryptamine were identified as high-affinity substrates of CYP2D6 that catalyzes their O-demethylations with high enzymatic capacity and specificity. Thus, polymorphic CYP2D6 may play an important role in the interconversions of these psychoactive tryptamines, including a crucial step in a serotonin-melatonin cycle.

High-density lipoprotein subfractions, apolipoproteins and antipyrine clearance in normal subjects

Serum high density lipoprotein (HDL) subfractions HDL2 and HDL3, apolipoproteins, and plasma antipyrine clearance (AP-CL) rate, an index of liver microsomal enzyme activity, were determined in 21 healthy subjects. High HDL cholesterol and HDL2 cholesterol concentrations and HDL cholesterol/cholesterol and HDL2/HDL3 cholesterol ratios were associated with high AP-CL. Phenobarbital enhanced antipyrine elimination and increased the apolipoprotein A-I/A-II ratio. Subjects who had high AP-CL had a more antiatherogenic HDL subfraction and apolipoprotein profile than those with low AP-CL.

Hypercholesterolemic effect of indomethacin in the rat

The effect of indomethacin on serum lipid constituents of the albino rat was investigated. Indomethacin 1 mg/kg, but not 10 mg/kg body weight, orally administered daily for 3 days, significantly raised total serum cholesterol level from a control value of 58.17 +/- 3.40 to 108.50 +/- 15.3 (N = 10; P less than 0.05) and free cholesterol level from 52.96 +/- 2.21 to 101.17 +/- 9.52 (N = 10; P less than 0.05). Indomethacin, 1 mg/kg p.o. daily for 3 days, also raised serum triglycerides from 45.0 +/- 7.33 to 118.30 +/- 9.05 (N = 10; P less than 0.001), while it reduced phospholipid content from 189.57 +/- 58.04 to 98.75 +/- 25.85 (N = 10; P less than 0.05). The higher dose of indomethacin 10 mg/kg p.o. daily for three days resulted in a significant increase in non-esterified fatty acids, triglycerides and total calcium, while it reduced total bilirubin, phosphorous and total lipid content of rat serum. The results indicate that according to the dose administered, indomethacin could lead to serious derangements in lipid profiles.

Defective bile acid transport in an animal model of defective debrisoquine hydroxylation

Bile acid transport in female DA (dark Aguti) rats, a model for debrisoquine hydroxylation deficiency in man, was investigated. Compared to hydroxylation competent male DA and Sprague-Dawley rats of either sex, the female DA rat had a significantly lower taurocholate maximal secretory rate in vivo. Studies in the perfused liver showed this to be due to a decreased extraction efficiency during exogenous taurocholate loading. To characterize further the defect, taurocholate uptake velocity into isolated hepatocytes was studied. This showed a decreased maximal uptake velocity in the female DA rat (P less than 0.02). Whether this defect in bile acid uptake is related to the defective debrisoquine hydroxylation, remains to be established.

Familial associations of lipids and lipoproteins in a highly consanguineous population: the Limone sul Garda study

The impact of genetic factors on the levels of plasma lipids and lipoproteins was evaluated in the total population of a small village. Limone sul Garda, separated up to recent years from neighboring communities, shows a high degree of consanguineity: major blood group phenotypes differ from nearby provinces for at least three gene frequencies. The absence of a difference in plasma lipid correlations between parent-pediatric offspring and parent-adult offspring, is consistent with the uniformity of living habits in the Limone community. Correlation coefficients proved highly significant only for plasma total cholesterol (range of r: 0.223 to 0.359). Differently from other reports, correlations for low density and high density cholesterolemias (LDL and HDL-C) were mostly nonsignificant in the parent-offspring comparisons. Similarly, only intersibling correlations for triglycerides (TG) were statistically significant. As indicated in other genetic studies on plasma lipoprotein levels (also in the Limone sul Garda study), TG and HDL-C were negatively correlated, whereas the correlation was positive between TG and LDL-C levels. The examined population does not, therefore, show a metabolic behavior at variance from other investigated groups. This study, offering a unique opportunity for enucleating genetic from environmental factors, suggests that most familial clusterings of lipoprotein concentrations are environmentally determined, whereas total cholesterolemia is controlled by autosomal mechanisms, without significant variations between sexes.

The effect on blood lipids of eating charcoal-grilled meat

For 9 days, 12 volunteers ate each day 8 oz of hamburgers and 6 oz of steak barbecued over charcoal. This was followed by a mean rise in high density lipoprotein (HDL) cholesterol of 25%. In addition there was a reduction in total cholesterol (the fall in total less the HDL fraction, which reflects mainly low density lipoprotein cholesterol was 20%). These changes were not seen when 6 of the subjects later ate the same quantity of meat under the same conditions except that it had been cooked in an electric oven. Benzo(a)pyrene and other polycyclic aromatic hydrocarbons have previously been shown to be produced in meat cooked over charcoal, and it is suggested that the resulting induction of the polycyclic hydrocarbon-dependent type of cytochrome P450 is responsible for inducing enzyme activity involved in lipid metabolism. Despite the beneficial effect that such changes in lipids might have on the risk of coronary heart disease, these findings should not be seen as a guide to long-term changes in cooking practice in view of the possible carcinogenic effects of benzo(a)pyrene produced in this way.