Cooperation of docosahexaenoic acid and vitamin E in the regulation of UDP-glucuronosyltransferase mRNA expression

Docosahexaenoic acid (DHA) is a well known chemopreventive nutrient within diet formulations, but it may also exert toxic effects on cultured cells, while this is limited when also another relevant nutrient as vitamin E is present. This effect, beside the involvement of the two nutrients in oxidative processes, likely affects the expression of specific genes. To obtain information on combined activities of DHA and vitamin E on some gene products previously resulted to be in vivo regulated from dietary unsaturated fats, the effect of the two nutrients was evaluated in human cell line HepG2. Independently, DHA and vitamin E resulted to affect only slightly UDP-glucuronosyltransferase 1A1 (UGT1A1) mRNA expression. Nevertheless, their combination produced a considerable reduction of this mRNA. DHA also downregulated stearoyl-CoA desaturase (SCD) and sterol regulatory element binding protein (SREBP-1) expression, while vitamin E did not affect these products. However, their combination abolished the downregulation of SCD but did not affect that of SREBP-1. Therefore the effect of the two nutrients is related to specific gene regulation processes resulting in a cooperation which might be related to their physiological effects as dietary components.     

A targeted apolipoprotein B-38.9-producing mutation causes fatty livers in mice due to the reduced ability of apolipoprotein B-38.9 to transport triglycerides

Nonphysiological truncations of apolipoprotein (apo) B-100 cause familial hypobetalipoproteinemia (FHBL) in humans and mice. An elucidation of the mechanisms underlying the FHBL phenotypes may provide valuable information on the metabolism of apo B-containing lipoproteins and the structure-function relationship of apo B. To generate a faithful mouse model of human FHBL, a subtle mutation was introduced into the mouse apo B gene by targeting embryonic stem cells using homologous recombination followed by removal of the selection marker gene by Cre-loxP-mediated site-specific recombination. The engineered mice bear a premature stop codon at residue 1767 and a 42-base pair loxP inserted into intron 24 of the apo B gene, thus closely resembling the apo B-38.9-producing mutation in humans. Apo B-38.9 was the sole apo B protein in homozygote (apob(38.9/38.9)) plasma. In heterozygotes (apob(+/)(38. 9)), apo B-100 and apo B-48 were reduced by 75 and 40%, respectively, and apo B-38.9 represented 20% of total circulating apo B. Hepatic apo B-38.9 mRNA levels were reduced by 40%. In cultured apob(+/)(38. 9) hepatocytes, apo B-100 was produced in trace quantities, and the synthesis rate of apo B-38.9 relative to apo B-48 was reduced by 40%. However, almost equimolar amounts of apo B-38.9 and apo B-48 were secreted into the media. Pulse-chase studies revealed that apo B-38. 9 was secreted at a faster rate and more efficiently than apoB-48. Nevertheless, both apob(+/)(38.9) and apob(38.9/38.9) mice had reduced hepatic triglyceride secretion rates and fatty livers. Thus, low mRNA levels or defective secretion of apo B-38.9 may not be responsible for the FHBL phenotypes caused by the apo B-38.9 mutation. Rather, a reduced capacity of apo B-38.9 for triglyceride transport may account for the fatty livers in these mice.