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At least 811 records · Page 45Linked to original sources
PubMed2002

Esterification does not impair lutein bioavailability in humans.

Age-related macular degeneration (ARMD) is inversely associated with the accumulation of lutein + zeaxanthin in the macula, but higher lutein intakes are inconsistently related to reduced risk of ARMD in epidemiologic studies. Resolution of efficacy awaits clinical trials designed with knowledge of lutein supplement pharmacokinetics. Lutein bioavailability was determined for lutein diester and unesterified lutein formulations as they might be incorporated into dietary supplements. Healthy subjects (n = 18) consumed a single dose of each formulation (either 0.5 or 0.67 micro mol lutein/kg body, 10 and 8 subjects, respectively) in random order, and the appearance of free lutein + zeaxanthin was measured in serum from 0 to 408 h. Areas under the serum concentration x time curves (AUC), as a measure of bioavailability, were independent of gender, body mass index and lutein dose. The lutein diester formulation was 61.6% more bioavailable than the unesterified lutein formulation with higher mean AUC, maximum serum concentration and ascending slope (P < 0.05). The AUC was greater in 14 of 18 subjects when they consumed the lutein diester formulation. Comparison with data from previous studies suggested that dissolution was a greater limitation to bioavailability than lutein ester hydrolysis because an oil-solubilized unesterified lutein preparation, given at 0.5 micro mol/kg body, resulted in greater mean peak concentrations and AUC compared with either the unesterified or lutein diester formulations used in our study. In conclusion, the lutein diester formulation poses no impediment to lutein bioavailability at the doses tested, but formulation dissolution is an important factor in lutein bioavailability and should be evaluated before a supplement and dose are selected for use in clinical trials.

Adult↗
PubMedDate not supplied

Intestinal retinol esterification and serum retinol in children with cystic fibrosis.

Children with cystic fibrosis (CF) often have a poor vitamin A status. We found in the present work a reduced level of serum retinol in older children with this disease. As retinol enters intestinal lymph as retinyl esters, the enzyme acyl-CoA:retinol acyltransferase (ARAT) may be of importance for retinol absorption. We have assayed ARAT activity in duodenal mucosal homogenate from children with CF. There was a large variation within the group. However, mean ARAT activity was not significantly decreased, as compared with controls. Thus, the lack of pancreatic enzymes probably is the main reason for reduced vitamin A absorption in CF. In celiac disease and in lactose intolerance--both mucosal disorders--a significant reduction of mean ARAT activity was found.

Acyltransferases↗
PubMed1992

The esterification of fatty acids by Staphylococcus aureus fatty acid modifying enzyme (FAME) and its inhibition by glycerides.

Fifty-five randomly selected Staphylococcus aureus strains were examined for fatty acid modifying enzyme (FAME) production. Of these, 20.4% did not elaborate the enzyme. Amongst the remaining strains, the lowest level produced in culture was 0.1 unit/10(9) cocci and the maximum was 2.01 U/10(9) cocci; the median level was 0.4 U/10(9) cocci. In a series of straight-chain saturated fatty acids with 11-24 carbons, all could be esterified by FAME. However, those with 15-19 carbons were generally better substrates than the others. For a particular chain length, the unsaturated forms were better substrates than the saturated form. Triglycerides with unsaturated fatty acid side chains were potent inhibitors of FAME. Diglycerides were almost as active as triglycerides, but monoglycerides were much less inhibitory. FAME was purified by gel filtration followed by hydrophobic interaction chromatography on hexyl agarose. FAME and lipase may have a role in determining the survival of S. aureus in lesions.

Acyltransferases↗
PubMed1991

Methanol esterification reactions catalyzed by snake venom and bovine intestinal 5'-nucleotide phosphodiesterases. Formation of nucleoside 5'-monophosphate methyl esters from guanosine 5'-triphosphate and other nucleoside 5'-polyphosphates.

It is not known whether the enzymes 5'-nucleotide phosphodiesterase/nucleotide pyrophosphatase (EC 3.1.4.1/EC 3.6.1.9) catalyze the transfer of nucleotides to acceptors other than water. We have investigated the action of snake venom and bovine intestinal mucosa phosphodiesterases on nucleoside 5'-polyphosphates in the presence of methanol. In those conditions, GTP was converted by snake venom phosphodiesterase to a mixture of GMP and another compound with a different retention time in reverse-phase high-performance liquid chromatography. That compound, by ultraviolet, 1H- and 13C-nuclear magnetic resonance spectroscopic analysis, and by enzyme analysis, was characterized as the methyl ester of GMP (GMP-OMe). The molar fraction [GMP-OMe]/[GMP + GMP-OMe] formed was higher than the molar fraction of methanol as a solvent in reaction mixtures. Similar reactions took place at comparable rates with snake venom and bovine intestinal mucosa phosphodiesterases using several nucleoside 5'-polyphosphates as substrates. The ability of 5'-nucleotide phosphodiesterases to catalyze transfer reactions to a non-water acceptor is relevant to the mechanism of the enzymes, to their use as analytical tools, and to their possible use/role in the preparative/in vivo synthesis of nucleotide esters.

Animals↗
PubMed2001

Retinoic acid homeostasis: retinoic acid regulates liver retinol esterification as well as its own catabolic oxidation in liver.

Retinol is stored in liver in the form of its esters. The retinol-esterifying enzyme lecithin:retinol acyltransferase (LRAT) catalyzes the conversion of retinol into its storage form. Expression of the LRAT mRNA is induced by retinoic acid (RA), or by dietary vitamin A, and is downregulated upon vitamin A depletion. RA also induces the expression in liver of the mRNA for CYP26, the enzyme that disposes of excess RA by oxidizing RA to 4-oxo-RA. CYP26 is downregulated upon vitamin A depletion.

Acyltransferases↗
PubMed2003

Tamoxifen is a potent inhibitor of cholesterol esterification and prevents the formation of foam cells.

Tamoxifen is a selective estrogen receptor modulator (SERM) used for the treatment and prevention of breast cancer. Tamoxifen has been reported to protect against the progression of coronary artery diseases in human and different atherosclerosis animal models by blocking the appearance of the atheromatous plaque. However, the molecular mechanism of this effect remains unknown. Acyl-CoA:cholesterol acyl transferase (ACAT) catalyzes the biosynthesis of cholesteryl esters, which are the major lipids found in the atheromatous plaque. In this paper we have tested whether ACAT might be inhibited by tamoxifen. We show, using molecular modeling, that tamoxifen displays three-dimensional structural homology with Sah 58-035 (3-[decyldimethylsilyl]-N-[2-(4-methylphenyl)-1-phenylethyl]-propanamide), a prototypical inhibitor of ACAT. We report that tamoxifen inhibits ACAT in a concentration-dependent manner on rat liver microsomal extract. We show that the presence on estrogen receptor ligands of a backbone isosteric to the diphenyl ethane backbone of Sah 58-035 constitutes a pharmacophore for ACAT inhibition. More importantly, tamoxifen was able to inhibit ACAT on intact macrophages stimulated with acetylated low-density lipoproteins and blocked the formation of foam cells, a step that precedes the formation of the atheromatous plaque. This work constitutes the first evidence that tamoxifen is an inhibitor of ACAT and foam cell formation at therapeutic doses and that this may account for its atheroprotective action.

Animals↗