C.R. Treadwell

Absorption of α- and β-octadecyl glyceryl ethers.

Abstract Lymph fistula rats were fed test meals containing 35 mg of α- or β-octadecyl-1-C14-glyceryl ether. The β-glyceryl ether was absorbed into the lymph to a greater extent (96%) than the α-glyceryl ether (76%). Fractionation of the lymph lipids indicated that 37–48% of the C14-activity was in the form of C14-fatty acid, and from 55 to 63% as free and esterified C14-glyceryl ethers. The α-glyceryl ether was split in the intestine to a greater extent than the β-glyceryl ether. Most of the C14-activity of the lymph lipids was in the alkoxydiglyceride fraction. The β-glyceryl ether was more efficiently converted to the alkoxydiglyceride than the α-glyceryl ether. More alkoxymonoglyceride appeared in the lymph when the α-glyceryl ether was fed than when the β-glyceryl ether was administered.

Hydrolysis and utilization of cholesterol esters for steroid synthesis by canine adrenal homogenates

Cholesterol-4-C14 esters of palmitic, oleic, linoleic, and arachidonic acids were incubated with canine adrenal homogenates. All of the esters were hydrolyzed independently of exogenous cofactors. C14 activity was incorporated into adrenal steroids best when a TPNH-generating system was added to the incubation mixture. n nThe rate of hydrolysis of cholesteryl-4-C14 palmitate was less than that of the esters of the unsaturated fatty acids when compared in a homogenate prepared from the adrenals of a single dog. n nThe possibility that the exogenous tracer esters did not mix with the endogenous pool of cholesterol esters is discussed.

Esterification of cholesterol in rat liver microsomes

Washed rat liver microsomes esterify cholesterol in the presence of added ATP and CoA; net synthesis of cholesterol esters was demonstrated. The optimum pH of the reaction was between 6.8 and 7.2; the effects of time and concentration of substrate were investigated. The composition of the C 14 -cholesterol esters synthesized by rat liver microsomes with added ATP and CoA was similar to that present in the microsomes before incubation and consisted predominantly of saturated and monounsaturated esters. A series of CoA esters (palmityl-CoA, oleyl-CoA, linoleyl-CoA, and arachidonyl-CoA) were tested for their effect on the esterification reaction. All of these CoA esters gave much lower levels of esterification than added ATP and CoA. The addition of fatty acid CoA derivatives, fatty acids, or fatty acid-albumin complexes to systems with ATP and CoA inhibited cholesterol esterification. This inhibition was not neutralized by the addition of fatty acid-poor serum albumin. The inhibition by fatty acid CoA esters could not be adequately explained in terms of free fatty acid liberated from the CoA esters by a deacylase in the microsomes. The data suggest that the major pathway for cholesterol esterification in liver microsomes does not involve a simple condensation between cholesterol and fatty acid CoA esters.

Role of the liver in the metabolism of exogenous cholesterol esters.

Abstract Rats were fed a test meal containing cholesterol, no fatty acids, or different fatty acids. A control group received a test meal with only a tracer amount of cholesterol-4-C 14 . Substantial amounts of cholesterol esters accumulated in the liver in 24 hours. The degree of accumulation was greatest when unsaturated fatty acids were fed. The cholesterol ester which accumulated to the greatest extent, irrespective of the fatty acid fed, was cholesterol oleate. The fatty acid composition of the serum cholesterol esters was essentially unchanged by cholesterol feeding. The cholesterol-C 14 ester pattern in the liver at 24 hours was similar in all groups irrespective of the fatty acid fed and showed a general shift toward C 14 -monounsaturated esters. In all groups, the principal cholesterol-C 14 ester found in the blood at the end of 24 hours was cholesterol arachidonate. The specific activity data on the free and individual cholesterol esters; of the liver indicate that a major portion of the incoming cholesterol esters undergoes transferase reactions with fatty acid donors to form other cholesterol esters. The specific activity of the serum cholesterol esters did not exceed the specific activity of the corresponding liver cholesterol esters. The results of the present study suggest that intestinal cholesterol esters are rapidly removed by the liver. A portion of these esters undergoes hydrolysis to free cholesterol while another portion appears to participate in a series of transferase reactions with fatty acid donors to form other cholesterol esters. A major ester formed in this fashion is cholesterol arachidonate, which is then released into the blood in association with the lipoproteins.

Enzymic preparation of labeled unsaturated fatty acid esters of cholesterol

Abstract An enzymic procedure is described which utilizes pancreatic cholesterol esterase for the synthesis of unsaturated fatty acid esters of cholesterol in amounts from 1 to 75 mg. The procedure is particularly suitable for the synthesis of very small amounts of labeled, high specific activity cholesteryl esters. A number of cholesteryl-4-C 14 esters were obtained in good yield (from 70 to 75% starting with 1 mg of cholesterol and 50 to 60% starting with 75 mg of cholesterol) and with a degree of purity ranging from 93 to 99%.

Esterification of cholesterol by canine adrenal homogenates

Abstract Tracer amounts of cholesterol-4-C11 were incorporated into sterol esters and adrenal steroids by whole homogenates of dog adrenal glands. The esterification reaction was stimulated by addition of ATP, CoA, DPN and a TPNH-generating system (TPN and G6P). Esterification induced by ATP and CoA was inhibited by the addition of oleic acid. Palmityl-CoA stimulated esterification above control levels, but its effect was less than that of ATP and CoA. Maximum incorporation of labeled cholesterol into adrenal steroids was obtained with the addition of a TPNH-generating system. Addition of ATP, CoA, and DPN to this system resulted in diminished labeled steroid formation and increased esterification.

Intestinal metabolism of epicholesterol-4-C14☆

Abstract Epicholesterol-4-C 14 (46.1 mg.) was fed in a physiological test meal to lymph-fistula rats and found to be poorly absorbed into the lymph. Free epicholesterol-4-C 14 was identified as the major C 14 sterol in the lymph and feces plus intestinal contents at the end of 6 and 24 hr., and at 6 hr. in the small intestine. No esterified epicholesterol could be found in those areas. A portion of the fed epicholesterol was converted to a saturated digitonin-precipitable sterol (probably dihydrocholesterol) in its transfer from the lumen of the intestine to the lymph. Lymph, small intestine, and feces plus intestinal contents showed the presence of 3β-C 14 sterols at the end of 6 and 24 hr., with the largest amounts of those sterols present at the latter time. Up to 84% of the 3β-C 14 sterols found in the lymph were present in the esterified form, whereas the major portion of the 3β-C 14 sterols in the small intestine and feces plus intestinal contents was present in the free form. Up to 50% of the C 14 sterols present in the intestinal wall at the end of 24 hr. were digitonin precipitable. The transformation of epicholesterol to 3β-sterol probably occurs in the intestinal wall.

Concerning the identity of pancreatic cholesterol esterase.

Abstract Lipase and cholesterol esterase activity were measured in pancreas homogenates which were pretreated with acid, alkali, and heat. Lipase was stable when pretreated for 15 min. at temperatures from 37 to 55 °. From 55 to 65 ° there was a partial loss in activity and complete inactivation at 70 °. Cholesterol esterase was progressively inactivated above 37 ° with complete inactivation at 65 °. Lipase was more stable at acid and alkaline pHs than cholesterol esterase. Tributyrin, olive oil, methyl butyrate, and ethyl oleate were split in the absence of bile salts. No cholesterol esterase activity was obtained in the absence of bile salts.

Intestinal absorption of cholesterol-4-C14-d-glucoside☆

Abstract The properties, estimation, and intestinal absorption of cholesterol-4-C 14 - d -glucoside were investigated. A technique for the separation of cholesterol- d -glucoside from free and esterified cholesterol was devised based on the differential solubility of those substances in petroleum ether and 2:1 chloroform-methanol. Cholesterol-4-C 14 - d -glucoside, when fed to lymph-fistula animals, was found to be poorly absorbed. A portion of the C 14 sterol glucoside was hydrolyzed in the intestinal lumen, and the free cholesterol liberated entered the intestinal wall. Both free and esterified C 14 sterols were detected in the lymph. No intact cholesterol- d -glucoside could be detected in the small intestine, lymph, or serum following its feeding.