SEARCH · Search PubMed

Results for “Esterification”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources

PubMed1985

Paradoxical esterification of plasma cholesterol in fish eye disease.

The activity of lecithin: cholesterol acyl transferase (LCAT), the enzyme which catalyses the esterification of human plasma cholesterol, has been measured by two independent methods in plasma from the two known living Swedish patients with fish eye disease. The enzyme activity was in both cases about 15% of that of normal plasma. Paradoxically, however, the percentage of plasma cholesterol which was esterified was almost normal in both patients. In addition, a normal spectrum of the fatty acids of the cholesteryl esters was present indicating a normal cholesterol esterification pathway in vivo. Incubation experiments in vitro of plasma from the two patients also yielded normal cholesterol esterification rates when measured by two different methods. These paradoxical results for cholesterol esterification are discussed on the basis of the present biochemical knowledge of fish eye disease and LCAT deficiency.

Aged↗

PubMed1997

Preferential esterification of endogenously formed 5-hydroxyeicosatetraenoic acid to phospholipids in activated polymorphonuclear leukocytes.

The esterification of endogenously formed 5-hydroxyeicosatetraenoic acid (5-HETE) to cellular lipids in rat polymorphonuclear leukocytes (PMNL) was studied quantitatively by a fluorometric method using HPLC. Rapid and maximal production of free 5-HETE was observed after a 5-min stimulation of PMNL with A23187. The amount of free 5-HETE then declined rapidly, while that of 5-HETE esterified to phospholipids and triacylglycerol concomitantly increased in a time-dependent manner. Stimulation by A23187 yielded approximately 100 ng/10(7) cells esterified 5-HETE in 60 min, which corresponded to the decrease in the amount of free 5-HETE from 5 min to 60 min and indicated that free 5-HETE, which was formed endogenously, was metabolized predominantly by esterification to cellular lipids. The esterification profile of exogenous 5-HETE was different from that of endogenous 5-HETE. 5-[3H]HETE, which was added exogenously to the culture medium, was rapidly incorporated into PMNL and almost 80% of the total radioactivity was located in triacylglycerol. A quantitative study revealed that endogenous 5-HETE was esterified equally to phospholipids and triacylglycerol. Like PMNL, peritoneal macrophages treated with A23187 released significant amounts of 5-HETE. However, less 5-HETE was esterified to cellular lipids than in PMNL. Negligible amounts of 12-HETE, produced by activated peritoneal macrophages or activated platelets after a challenge with A23187, were esterified during the entire incubation. Exogenous 5-HETE was rapidly taken up by PMNL, but was incorporated into macrophages much more slowly than into PMNL. No uptake of 12-HETE into macrophages was observed. The rapid uptake of exogenous 5-HETE was strongly inhibited by the suppression of acylation of 5-HETE by triacsin C. These results suggest that esterification might be one of the factors that regulate the rate of incorporation of 5-HETE.

Animals↗

PubMed1986

Differences in uptake and esterification of saturated analogues of cholesterol by rat small intestine.

Coprostanol and cholestanol are two saturated analogues of cholesterol. The former, which is the A/B ring isomer of cholesterol, is a nonabsorbable sterol, whereas the latter, which has an A/B ring configuration closer to that of cholesterol, is absorbed only half as efficiently as cholesterol. Intestinal mucosal cell uptake and esterification, two important steps in absorption, were studied in vivo after feeding the sterols and in vitro using everted sacs of rat small intestine. The results showed that the intestinal tissue content of coprostanol, total and esterified, were significantly lower than that of cholestanol. Total cholesterol concentration in the intestinal tissue was similar throughout but the esterified cholesterol content increased significantly throughout the length of the intestine compared with controls. The study suggests that cholestanol is absorbable because its uptake and esterification are not limited, whereas coprostanol is nonabsorbable because its uptake and esterification are limited in the intestinal mucosa. Also, the two sterols stimulate the activities of cholesterol esterase, one of the cholesterol esterifying enzymes, in the intestinal mucosa. The present study along with previous studies suggests that the structure of the sterol molecule as a whole appears to be the important determinant for its uptake and esterification, and probably absorption, in the small intestine.

Animals↗

PubMed1994

A cell culture system for screening human serum for ability to promote cellular cholesterol efflux. Relations between serum components and efflux, esterification, and transfer.

A cell culture system was employed to test a large number of samples of human serum for the ability to stimulate the efflux of cell cholesterol. The extent of efflux obtained with each specimen was correlated with the serum concentrations of cholesterol, triglycerides, apoprotein (apo) B, apo A-I, apo A-II, and lipoprotein subfractions (ie, high-density lipoprotein2 [HDL2], HDL3, lipoprotein [Lp] A-I, and LpA-I:A-II). In addition, the subsequent esterification of the released cholesterol and the distribution of the synthesized exogenous cholesteryl esters between HDL and low-density lipoprotein/very-low-density lipoprotein provided estimates of the lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) activities of each serum. The values for these activities were analyzed for correlations with cell efflux and the various serum parameters. Cell cholesterol efflux best correlated with serum total HDL cholesterol values. HDL2 and HDL3 correlated about equally well with efflux, whereas LpA-I demonstrated a much greater association with efflux than did LpA-I:A-II. Analysis of the data by partial correlation analysis indicated that HDL3 and LpA-I were the HDL subfractions most closely associated with efflux. Esterification of the released radiolabeled cholesterol was strongly and positively correlated with serum triglyceride concentrations and negatively related to the serum concentrations of HDL2. There was no relation between esterification values, which reflect LCAT activity, and efflux. The transfer of the labeled cholesteryl esters between HDL and apoB-containing lipoproteins was used as a measure of CETP activity and demonstrated a pattern in which all apoB-related parameters were positively correlated to transfer of esterified cholesterol, and all HDL associated parameters, particularly HDL3, were negatively related to transfer. No relations were observed between efflux, esterification, and transfer.

Adult↗

PubMed1983

Retinol esterification by microsomes from the mucosa of human small intestine. Evidence for acyl-Coenzyme A retinol acyltransferase activity.

The mechanism of the intestinal esterification of retinol has been obscure. Recently, an acyl-Coenzyme A (CoA):retinol acyltransferase (ARAT) was found in rat intestinal microsomes, and experiments were therefore conducted to determine whether a corresponding enzyme exists in human small intestine. When microsomes were incubated with [3H]retinol and palmitoyl-CoA, or retinol and [1-14C]palmitoyl-CoA, radioactive retinyl palmitate was formed as identified by alumina column chromatography and reverse-phase high-pressure liquid chromatography. Heating the microsomes for 30 min at 60 degrees C resulted in loss of activity. The esterification was negligible without exogenous acyl-CoA and markedly stimulated by palmitoyl-, oleoyl-, and stearoyl-CoA in concentrations up to 20 microM. The acyl-CoA was successfully replaced by an acyl-CoA generating system, but not by unactivated palmitate (2.5-200 microM). The assay was dependent on the presence of albumin with optimum activity at 2-10 mg/ml. The optimal retinol concentration was 20-30 microM and pH approximately 7.4. The esterifying activity was completely inhibited by 8 mM of taurocholate and to 90% by 1 mM of 5,5'-dithiobis(2-nitrobenzoic acid). Activity was found throughout the small intestine. In jejunum the rate of retinol esterification was: 3.44 +/- 2.24 nmol [3H]retinyl ester formed . mg microsomal protein-1 . min-1 (mean +/- SD, n = 12). The corresponding activity in whole homogenates of biopsies were 1.17 +/- 0.28 (n = 8). It is concluded that human small intestine contains a microsomal acyl-CoA:retinol acyltransferase. Due to its high activity in vitro this enzyme is likely to be responsible for the intestinal esterification of retinol.

Acyltransferases↗

PubMed2001

Effects of fluvastatin and its major metabolites on low-density lipoprotein oxidation and cholesterol esterification in macrophages.

We investigated effects of fluvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, and its major metabolites, M2 and M4, on CuSO4-induced low-density lipoprotein (LDL) oxidation and cholesteryl ester accumulation in mouse peritoneal macrophages. All the test compounds inhibited LDL oxidation, and M2 had the most potent effect comparable to vitamin E. When LDL was previously incubated with the test compounds in the presence of CuSO4, the pre-treatment resulted in a marked reduction of facilitated cholesteryl ester accumulation in macrophages. Supplementation of mevalonate did not overcome the inhibitory effects of fluvastatin and its metabolites on both LDL oxidation and facilitated cholesterol esterification. Pravastatin, another HMG-CoA reductase inhibitor, did not show any inhibitory effect. Consequently, these effects of fluvastatin and its metabolites are considered to be derived from their own unique chemical structures. Moreover, fluvastatin and M2 directly inhibited cholesterol esterification induced by oxidized LDL in macrophages, but pravastatin was also found to have a weak effect. As their inhibitory effects were overcome by addition of mevalonate, the direct inhibitory effect on cholesterol esterification would be a common property of HMG-CoA reductase inhibitors. The inhibitory effects of fluvastatin and its metabolites on both LDL oxidation and cholesterol esterification in macrophages may contribute to the antiatherogenic action in vivo.

Animals↗

PubMed1997

Effects of saturation and esterification of fat sources on site and extent of digestion in steers: ruminal fermentation and digestion of organic matter, fiber, and nitrogen.

Five steers (average 526 kg) fitted with ruminal, duodenal, and ileal cannulas were used in a 5 x 6 Youden square design with 14-d periods. Diets contained chopped alfalfa hay, corn silage, and concentrate (25:35:40, DM basis). Treatments were 1) control (no added fat), 2) tallow (T), 3) partially hydrogenated tallow (PHT), 4) hydrogenated tallow (HT), 5) blend (1:1) of HT and hydrogenated free fatty acids (HTHFA), and 6) hydrogenated free fatty acids (HFA). Fats replaced cornstarch in the control diet to supply 5% added fatty acids. Intake was restricted to 90% of ad libitum; DMI was similar among diets (average 9 kg/d). Ruminal pH and molar proportion of propionate (P) were greater (P < .05) but total VFA concentration, proportion of acetate (A), A:P, and percentages of OM digested in the rumen and total tract were less (P < .05) when fat-supplemented diets were fed than when the control diet was fed. Total VFA concentration increased linearly (P < .05) as esterification of fat sources increased (HFA < HTHFA < HT). Acetate and A:P increased linearly (P < .10) but propionate and apparent total tract digestibility of OM decreased linearly (P < .05) as either saturation (T < PHT < HT) or esterification of fat sources increased. Ruminal NH3 N concentration increased linearly (P < .001) as saturation increased. Apparent ruminal digestibilities of ADF (P < .05) and NDF (P < .10) increased linearly as esterification increased. Flow of nonammonia nonmicrobial N to the duodenum was less (P < .10) but flow of microbial N was greater (P < .05) for the control diet than for fat-supplemented diets. Flows and small intestinal digestibilities of N and efficiencies of microbial protein synthesis were not altered by degree of saturation or esterification. Results confirm previous in vitro observations that T or HFA can alter ruminal digestion; however, because these effects usually are not observed in dairy cows, feed intake likely is very important in responses to supplemental fats.

Analysis of Variance↗

PubMed1984

Cholesterol esterification by mammary gland microsomes from the lactating rat.

Cholesterol esterification by fatty acyl-CoA:cholesterol acyltransferase (ACAT, EC 2.3.1.26) has been demonstrated in microsomes prepared from breast tissue of the lactating rat, employing the incorporation of [1-14C]oleoyl coenzyme-A into cholesteryl[14C]oleate. The regulation of this activity in vitro was studied by supplementing microsomes with unesterified cholesterol supplied either as a dispersion in acetone or by incubating microsomes with cholesterol-enriched serum lipoproteins prior to enzyme assay. ACAT activity was increased by more than 80% when the ratio of unesterified cholesterol to microsomal protein was increased from 29 to 48 micrograms/mg protein, indicating that the normal cholesterol content of mammary gland microsomes does not saturate this enzyme. Cholesterol esterification could be inhibited nearly completely in vitro by addition of the polar steroid progesterone (93% decrease in ACAT activity with 75 microM progesterone) and, to lesser extents, by estradiol and retinol. Enzyme assays were also performed after incubating microsomes with N-acylamides that inhibit cholesteryl ester synthesis in other systems. Under conditions where the mammary gland ACAT reaction was inhibited by more than 82%, the esterification of retinol was reduced by less than 30% and incorporation of [14C]oleoyl-CoA into triglycerides was not inhibited at all. These studies indicate that the lactating mammary gland contains ACAT activity having properties similar to ACAT in other organs. The presence of ACAT activity in the lactating mammary gland provides a possible mechanism for the synthesis of cholesteryl esters found in milk. It can also be inferred that ACAT in mammary gland microsomes is likely to be distinct from the microsomal acyltransferases that catalyze the esterification of retinol and glycerides.

Acyltransferases↗

PubMed2001

Decreased hepatic accumulation and enhanced esterification of cholesterol in mice deficient in mdr1a and mdr1b P-glycoproteins.

Class I P-glycoproteins [Pgp; MDR1 (ABCB1) in humans, mdr1a and mdr1b in mice] confer resistance to structurally diverse chemotherapeutic drugs in cultured cells and intact animals, but the function of these proteins in normal physiology remains poorly characterized. Based on studies in cell culture, a putative role for class I Pgp in absorption and intracellular trafficking of sterols has been proposed. We examined wild-type and mdr1a(-/)-/1b(-/)- mice to determine whether class I Pgp affects cholesterol absorption and esterification in vivo. Using a dual-isotope protocol, absorption of orally administered radiolabeled cholesterol into serum did not differ between wild-type and mdr1a(-/)-/1b(-/)- mice, demonstrating that class I Pgp is not essential for overall absorption of cholesterol through the intestine. However, the ratio of oral to intravenous labeled cholesterol in liver was decreased significantly in mdr1a(-/)-/1b(-/)- mice. In the liver, but not other tested organs, deletion of class I Pgp enhanced kinetics of esterification of an oral bolus of radiolabeled cholesterol without affecting esterification of cholesterol administered intravenously. Steady-state hepatic content of cholesterol and esterified cholesterol also were unaffected by absence of mdr1a and mdr1b.Thus, in normal animals, class I Pgp functions to kinetically increase hepatic accumulation and decrease esterification of orally administered cholesterol in vivo.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed1978

Relationship between high density lipoproteins and the rate of in vitro serum cholesterol esterification.

The rate of in vitro esterification of serum cholesterol and the concentrations of serum high density lipoprotein cholesterol (HDL-C) were measured in 18 women and 9 men, 74--95 years of age. Subjects in this age group can have HDL-C levels below accepted limits of normal. The subjects were divided into two groups, one with HDL-C less than 40 mg/dl and the other with HDL-C 40 mg/dl or higher. The rate of in vitro serum cholesterol esterification in the former group was 2.00 n. moles/ml/min, significantly higher (p less than 0.02) than 1.62 n. moles/ml/min present in the latter group. There was no correlation between the cholesterol esterification and a protein (s), which can produce an immune gamma globulin that completely inhibits in vitro serum cholesterol esterification. These findings are discussed with reference to the putative relationships between HDL-C and atherosclerosis.

Aged↗

PubMed1986

Esterification of exogenously derived free cholesterol by cultured fibroblasts.

The incorporation and esterification by cultured human fibroblasts of vesicle- or low density lipoprotein-derived free [3H]cholesterol was examined. The rate of the cellular uptake of free [3H]cholesterol from lipid vesicles was similar in both LDL-receptor positive lung fibroblasts and in LDL-receptor negative fibroblasts. When human LDL was used as the carrier of free [3H]cholesterol, however, the LDL-receptor positive lung fibroblasts incorporated significantly more [3H]cholesterol than did the LDL-receptor negative cells. The exchangeable free [3H]cholesterol was available for intracellular esterification. The formation of [3H]cholesteryl esters was markedly inhibited by lysosomotropic drugs, either indicating a partly lysosomal esterification reaction, or implying that free [3H]cholesterol moves through the lysosomal compartment on its way to intracellular esterification sites. Either way, the lysosomes appear to have a metabolic role in the metabolism of exchangeable free [3H]cholesterol.

Cells, Cultured↗

PubMed1982

Retinol esterification by mammary gland microsomes from the lactating rat.

Because vitamin A in milk is largely present as esterified retinol while blood plasma predominantly contains unesterified retinol, experiments were conducted to determine whether membranes from the lactating mammary gland are able to synthesize retinyl esters in vitro. When microsomes from rats lactating for 7 to 14 days were incubated with [(3)H]retinol dispersed in dimethylsulfoxide, some [(3)H]retinol esterification was observed (147 pmol/5 min per 0.5 mg protein). However, 3- to 7-fold increases in retinyl ester synthesis could be achieved by supplying either a fatty acyl CoA-generating system or preformed fatty acyl CoA thioesters; thus, the major activity in vitro has the characteristics of a fatty acyl CoA: retinol acyltransferase. Both long-chain and medium-chain fatty acyl CoA esters stimulated [(3)H]-labeled retinyl ester synthesis in vitro. Concordantly, analysis of the retinyl ester pattern of rat milk demonstrated the presence of eight different esters of retinol ranging in fatty acyl chain length from 8 to 18 carbons. Retinol esterification by microsomes was maximal at neutral pH (7.1) in the presence of approximately 50 micro M palmitoyl CoA, and was linear with time of incubation for at least 5 min. Retinyl ester synthesis increased with the apparent concentration of [(3)H]retinol to approximately 200 nmol/ml, but was also dependent on the ratio of retinol relative to total microsomal protein in the incubation mixture. These experiments demonstrate for the first time retinol esterification by mammary gland membranes and point to the hypothesis that free retinol from plasma is esterified in this organ before secretion of retinyl esters in milk.-Ross, A. C., Retinol esterification by mammary gland microsomes from the lactating rat.

Animals↗

PubMed1996

Esterification of oxysterols in human serum: effects on distribution and cellular uptake.

Oxysterols, oxidized derivatives of cholesterol, may enter the circulation as contaminants of cholesterol-containing food, arise through peroxidation of lipoproteins, or be generated by enzymatic reactions. They are found in serum associated either with lipoproteins or with albumin. In these studies, 25-hydroxycholesterol (25OHC) was used as a model oxysterol to investigate the effect of esterification on the association of oxysterols with serum components and their delivery to cultured cells. 25OHC added in vitro to fresh human serum was readily esterified during incubation at 37 degrees C, most likely by serum lecithin:cholesterol acyltransferase (LCAT) as it was blocked by known inhibitors of LCAT. The 25OHC-esters formed were identified as monoesters by comparing their elution on high performance liquid chromatography and thin-layer chromatography with that of chemically synthesized 25OHC mono- and diesters. Esterification doubled the percentage of 25OHC associated with lipoproteins, concomitantly decreasing the amount associated with albumin. Whereas unesterified 25OHC readily transferred between isolated lipoproteins, 25OHC-esters remained associated with donor lipoproteins unless human lipoprotein-deficient serum was added. That cholesteryl ester transfer protein (CETP) mediated transfer of 25OHC-esters was demonstrated by the ineffectiveness of rat lipoprotein-deficient serum as well as by the ability of IC-4, an anti-CETP monoclonal antibody, to suppress the transfer. Esterification of 25OHC in serum limited its entry into human erythrocytes and fibroblasts (GM 3468A cells) in vitro. Up-regulation of fibroblast low density lipoprotein (LDL)-receptors enhanced the uptake of esterified 25OHC from medium, but did little to enhance the total uptake of 25OHC. Thus, esterification of oxysterols in serum shifts their distribution away from albumin into LDL and high density lipoprotein (HDL) and limits their availability to cells in culture.

Biological Transport↗

PubMed1998

Role of glutamic acid residues 154, 155, and 165 of lecithin:cholesterol acyltransferase in cholesterol esterification and phospholipase A2 activities.

Previous studies have shown that cholesterol esterification activity by lecithin:cholesterol acyltransferase (LCAT) is progressively inhibited as up to three acidic acid residues are chemically modified. The purpose of this study was to determine whether three glutamic acid residues in LCAT (154, 155, and 165), that align exactly with three acidic acid residues (270, 271, and 281) in the amphipathic phospholipid binding region of apoE, were necessary for enzymatic activity. Site-directed mutagenesis was used to generate mutant constructs of LCAT in which glutamic acid residues 154, 155, and 165 were replaced with glutamine or lysine. Media harvested from transiently transfected COS cells was used as a source of LCAT for cholesterol esterification and phospholipase A2 (PLA2) assays. Cholesterol esterification for all mutant constructs (11-26 nmol CE/h/microg) was similar to or greater than that of wild type LCAT (16 nmol CE/h/microg), except for a triple mutant, in which glutamic acid residues 154, 155, and 165 were changed to lysines (5 nmol CE/h/microg). PLA2 activity followed a similar trend. There was a significant decrease in the cholesterol esterification to PLA2 activity ratio when residue 165 was mutated from its wild type negative charge (E) to an uncharged (Q) or positive (K) charged residue (10.2 vs. 6.0 vs. 4.3, respectively). We conclude that glutamic acid residues 154, 155, and 165 individually or collectively are not necessary for LCAT activity and that residue 165 may be in a region of LCAT that is involved with cholesterol binding or is sensitive to cholesterol binding at the active site of the enzyme.

Amino Acid Sequence↗

PubMed1986

Enzymatic esterification of exogenous retinol and 3,4-didehydroretinol in the retinal pigment epithelium.

The kinetics of esterification of exogenous retinol by cell membranes prepared from the crude homogenate of the frog retinal pigment epithelium was studied. The formation of retinyl palmitate from added retinol was directly assayed by high performance liquid chromatography (HPLC). A linear relationship was observed between the amount of protein (up to 2 mg) in the incubation medium and the amount of retinyl palmitate formed. At room temperature, this reaction took less than 2 hours to complete. By varying the substrate concentration in the incubation medium, the reciprocal of initial velocity of the reaction (nmol retinyl palmitate formed per hour) was plotted against the reciprocal of substrate concentration (nmol of retinol). This double-reciprocal plot shows that the apparent Km of the reaction was 10 microM with an apparent Vmax of 9.1 nmol of retinyl palmitate per hour per mg protein. When this assay was repeated in the presence of 3,4-didehydroretinol (20 microM), the kinetics of the reaction showed the pattern of that of a competitive inhibitor, suggesting that 3,4-didehydroretinol competes with retinol for the same active site for esterification. The esterification of 3,4-didehydroretinol resulted in the formation of 3,4-didehydroretinyl palmitate, which was also measured by HPLC. The amount of 3,4-didehydroretinyl palmitate formed by this reaction decreased in proportion to increased retinol concentration in the incubation mixture. This further confirms that a competition exists between the esterification of retinol and 3,4-didehydroretinol by retinal pigment epithelium of the frog.

Animals↗

PubMed1981

Interaction between macrophages and aortic smooth muscle cells. Enhancement of cholesterol esterification in smooth muscle cells by media of macrophages incubated with acetylated LDL.

Mouse peritoneal macrophages were cultured for 24 h in Dulbecco-Vogt medium containing 10% calf serum. This medium was replaced with Dulbecco-Vogt medium containing 1% bovine serum albumin to which all subsequent additions were made. Medium changes, accompanied by appropriate additions, were made every 48 or 72 h and the media were used for incubation of aortic smooth muscle cells, prelabeled with [3H]cholesterol. The amount of labeled cholesteryl ester in the smooth muscle cells incubated for 48 h with macrophage media which had been collected 48-144 h after addition of acetylated LDL was increased 3-4 times above that present prior to postincubation. A marked increment in cholesteryl ester mass occurred also after incubation of smooth muscle cells with macrophage media conditioned with acetylated LDL and this effect was shared by maleylated LDL, but not by other negatively charged compounds. The increase in labeled cholesteryl ester in smooth muscle cells was more pronounced with media collected at later time intervals of incubation with macrophages and was evident 8 hr after postincubation. Only the d less than 1.063 fraction of the medium enhanced cholesterol esterification in smooth muscle cells. The acetylated LDL reisolated from macrophage media at d less than 1.063 did not compete with native LDL for degradation by smooth muscle cells. No increase in degradation of 125I-labeled acetylated LDL preincubated with macrophages was observed above that of non-preincubated acetylated LDL. The macrophage medium conditioned with acetylated LDL depressed [14C]acetate incorporation into sterols in smooth muscle cells and this effect was abolished by extraction of the medium with diethyl ether. The ratio of free to total cholesterol in the macrophage media collected after incubation with acetylated LDL increased from 28-70%, and a decrease occurred after incubation with smooth muscle cells. The enhancement of cholesterol esterification could be abolished by addition of high density apolipoprotein/sphingomyelin mixture during incubation with macrophages, even though excretion of free cholesterol into the medium increased 3-fold. It is proposed that when smooth muscle cells are presented with a lipoprotein in which an increase in the free to esterified cholesterol ratio occurred, and which is not recognized by a specific receptor, the enhancement of cellular cholesterol esterification is due mostly to a surface transfer of lipoprotein-free cholesterol. The present results offer another view of the possible interactions between macrophages and smooth muscle cells. A modified lipoprotein, not recognized by smooth muscle cells, is ingested by macrophages, which leads to accumulation of esterified cholesterol. Part of the esterified cholesterol undergoes hydrolysis and is excreted back into the medium, leading to enrichment of the lipoproteins in the medium with free cholesterol. This enrichment with free cholesterol promotes cholesterol esterification in smooth muscle cells.

Acylation↗

PubMed1983

Esterification of cholesterol and 25-hydroxycholesterol by rat liver microsomes.

The properties of an enzyme in rat liver microsomes was described that catalyzed the formation of 25-hydroxycholesteryl ester in the presence of labeled sterol and oleoyl-CoA. The reaction was similar in several respects to that of cholesteryl ester formation by acyl-CoA: cholesterol acyltransferase. Trypsin pretreatment of microsomes inhibited the esterification of both sterols and a similar dose-dependent inhibition was produced by addition of progesterone and several androgens. Microsomes with an enhanced cholesterol content resulting from in vivo treatment with ethinyl estradiol showed increased esterifying activity towards both cholesterol and 25-hydroxycholesterol. Esterification of endogenous microsomal cholesterol was increased by the addition of 25-hydroxycholesterol, concomitant with 25-hydroxycholesteryl ester formation. To assess the relationship between the association of sterols with membranes and sterol ester formation, microsomes were preincubated with either sterol, reisolated by ultracentrifugation in a density gradient and then analyzed chemically or enzymatically. Cholesterol and 25-hydroxycholesterol both associated with microsomes and the added sterol was subsequently esterified. Maximal esterification was only partially dependent on the amount bound. Progesterone, which inhibited sterol esterification, did not bind to microsomes and no inhibition was observed in reisolated microsomes, indicating that the inhibition produced by progesterone was reversible.

Animals↗

PubMed1988

Effect of fatty acid supplementation on cholesterol and retinol esterification in J774 macrophages.

J774 macrophages exposed to medium containing cholesterol-rich phospholipid dispersions accumulate cholesteryl ester. Supplementing this medium with 100 micrograms oleate/ml increased cellular cholesteryl ester contents 3-fold. Cell retinyl ester contents increased 8-fold when medium containing retinol dispersed in dimethyl sulfoxide was supplemented with oleate. These increases were not the result of increases in total lipid uptake by the cells but rather of redistribution of cholesterol and retinol into their respective ester pools. Effective oleate concentration of 15-30 micrograms/ml increased cellular retinyl and cholesteryl ester contents. The effective oleate concentration was reduced to 5 micrograms/ml when the fatty acid/albumin molar ratio was increased. The oleate-stimulated increase in cholesterol esterification was blocked by incubating cells with Sandoz 58-035, a specific inhibitor of acyl-CoA:cholesterol acyltransferase (ACAT), indicating that the effect of fatty acid exposure is mediated through changes in ACAT activity. When cholesterol or retinol was added to cells which had been exposed to oleate for 24 h to provide a triacylglycerol store, the cellular contents of cholesteryl or retinyl ester were also significantly increased compared to cells not previously exposed to oleate. The oleate-stimulated increase in the esterification of cholesterol and/or retinol was also observed in P388D1 macrophages, human (HepG2) and rat (Fu5AH) hepatomas, human fibroblasts, rabbit aortic smooth muscle cells and MCF-7 breast carcinoma cells. In addition to oleate, a number of other fatty acids increased retinol esterification in J774 macrophages; however, cellular cholesterol esterification in these cells was increased only by unsaturated fatty acids and was inhibited in the presence of saturated fatty acids. Although the cellular uptake of radiolabeled oleate and palmitate was similar, a significant difference in the distribution of these fatty acids among the lipid classes was observed. These data demonstrate that exogenous fatty acids are one factor that regulate cellular cholesteryl and retinyl ester contents in cultured cells.

Animals↗