James F. Mead

Uptake and transport of fatty acids into the brain and the role of the blood-brain barrier system.

Publisher Summary This chapter discusses the uptake and transport of fatty acids into the brain and describes the role of the blood–brain barrier system. In addition to the usual saturated and unsaturated fatty acids such as palmitic, stearic, and oleic acids, the brain contains a rather large amount of polyunsaturated fatty acids with four, five, and six double bonds. Another class of fatty acids found largely in the brain is that of the α-hydroxy long-chain fatty acids. The brain has the necessary enzymes for synthesis of the required fatty acids, thus, reducing the demand on transport of fatty acids synthesized elsewhere or ingested in the diet. The essential fatty acids, which cannot be synthesized by the mammalian systems, must come from the diet and transported into the brain by the circulating blood. Both of these fatty acids are found in trace amounts in the rat brain; however, their polyunsaturated products occur abundantly. Dietary fatty acids can influence the composition of brain lipids.

Epoxides as products of lipid autoxidation in rat lungs.

The nature and content of lipid epoxides in rat lung were examined in air-breathing control rats and those exposed to nitrogen dioxide. Exposure to 6.5 ppm NO2 for 24 hr resulted in significantly greater epoxide content in a number of lipid classes. It is proposed that lipid autoxidation in lung tissues may contribute to the levels of epoxide-containing lipids. Furthermore, the processes involved in epoxide formation may be predicted from autoxidation studies utilizing a system of unsaturated fatty acid monolayers on silica gel which serves as a model for biomembranes. The findings indicate that exposure to oxidizing gases can lead to an accumulation of lipid epoxides in both lung parenchymal tissue and on the alveolar surface.

Isoprene — The main hydrocarbon in human breath

Abstract Isoprene was found to be the main endogenous hydrocarbon of human breath. It was also identified in nursing Long-Evans and Sprague Dawley rats, as well as for a short-time post weaning. Several preliminary data, regarding the source of isoprene are also available. We have been able to find small amounts of isoprene production by rats liver and kidney tissue slices.

The effect of the environmental temperature on the fatty acid composition and on thein vivo incorporation of 1-14C-acetate in goldfish (Carassius auratus L.)

Two-year-old goldfish were adapted to 10C and 35C environmental temperatures during a three-week period, and the fatty acids from triglycerides and certain phospholipids were analyzed by gas-liquid chromatography. Over-all unsaturation of the major fatty acids increased with lower temperature in all lipids which were examined although fish maintained at 10C actually had less polyenoic acid in their tissues than did those maintained at 35C.Fish acclimated to 10C and 30C were injected with 1-14C-acetate, and the activities of the isolated fatty acids were counted. The incorporation of14C into the fatty acids was much greater at the lower temperature. A comparison of the activities of saturated and unsaturated fatty acids within each temperature group revealed a tendency toward higher incorporation into the unsaturated acids at lower temperature. The possible correlations between accelerated biosynthesis of polyenoic acids and the lower tissue levels of these acids in the cold-adapted fish are discussed.

Metabolism of epoxidized phosphatidylcholine by phospholipase A2 and epoxide hydrolase

The isolation and measurement of phospholipid epoxides as major peroxidation products in biomembrane preparations prompted an investigation of enzymatic mechanisms which may be responsible for their elimination. Analysis of microsomal epoxide hydrolase and phospholipase A2 activity against a phospholipid epoxide commonly encountered in tissues indicated it to be a poor substrate for epoxide hydrolase, but rapidly hydrolyzed by phospholipase A2. Microsomal and purified phospholipase A2 preparations hydrolyzed the phospholipid epoxide at rates 2-fold greater than were observed with a monoenoic phospholipid from which the epoxide would be derived. The product fatty acid epoxide,cis-9,10-epoxystearic acid, was rapidly hydrated by microsomal and cytosolic epoxide hydrolase. On the basis of earlier reports demonstrating increased phospholipase activity against oxidized phospholipids, and on the results of the present study, a model for the metabolism of oxidized membrane phospholipids is proposed.

Chromatographic separation of the plasma lipids.

Summary By chromatography on a silicic acid column, artificial lipid mixtures and plasma lipids have been separated into fractions composed mainly of the following groups: sterol esters, triglycerides, sterols, fatty acids and phospholipids. By this tech-nic eleostearic acid is found exclusively in the triglyceride fraction after having been fed as the methyl ester.

Influence of temperature on the fatty acid pattern of mosquitofish (Gambusia affinis) and guppies (Lebistes reticulatus)

Adult male mosquitofish were adapted to 14–15C and 26–27C water temperature over a 14-day period and the fatty acids from their total lipids analyzed by gasliquid chromatography.Newly born guppies were raised at the same temperature for eight weeks and analyzed in the same way. Some fish in the warm water group were subjected to a sudden drop in temperature and the changes of the fatty acids studied after two and eight days, and after two and four weeks.In all fish the tendency is toward higher unsaturation at lower temperature, but the acids involved in the change differ with the species of fish. A distinct difference is also obvious when guppies are raised at, or when they are adapted to the low temperature. The diet, too, influences the kind and amount of fatty acid synthesis and deposition.

A lipid mobilizing factor in serum of tumor-bearing mice.

There is considerable evidence that the growing tumor requires a source of unsaturated fatty acids, but the nature of this source and the mechanism of mobilizing the fatty acids from it are obscure. These experiments make use of AKR mice with implanted adipose tisue labeled with 1-14C linoleic acid. With this experimental animal, it has been found that: (a) in the normal, fed mouse, fat is mobilized slowly and appears largely as respiratory CO2, following oxidation, (b) in the normal, fasted mouse, fat is mobilized rapidly and appears largely as respiratory CO2; (c) in the tumor-bearing, fed mouse, fat is mobilized rapidly and appears largely in the tumor; and (d) the serum from tumor-bearin mice, when injected into normal mice, produces an immediate massive fat mobilization that does not respond to feeding, whereas the serum from normal, fed mice does not. It is concluded that a mobilizing factor of unknown nature is present in the serum of tumor-bearing AKR mice.

Role of oleic acid in the metabolism of essential fatty acids

Groups of young male guinea pigs were fed diets containing corn oil, coconut oil, coconut oil plus elaidic acid, and coconut oil plus oleic acid. The oleic acid-fed group showed signs of essential fatty acid deficiency after four weeks and severe signs after eight weeks. The elaidic acid-fed group did not show these symptoms. It is proposed that oleic acid competes competitively with linoleic acid as a substrate for the enzymes involved in linoleate transformations when only a very limited supply of linoleic acid is available to the animals and oleic acid is made available in relatively large amounts.A detailed analysis of the serum, liver, and adipose tissue lipid and a study of the incorporation of acetate-1-C14 into different lipids is presented.

The bacterial origin of rat breath pentane

Abstract Vitamin E-deficient rats or rats subjected to other conditions thought to lead to peroxidation of tissue lipids produce pentane and other hydrocarbon gases in the breath. However, pentane production is found to depend on the linoleate content of the recent diet. It is decreased or eliminated by inclusion of ascorbic acid in the food or water, by removal of linoleate from the diet, by starvation and by the antibiotic, clindamycin. It is enhanced by feeding linoleate hydroperoxide or by removal of vitamin E from the diet for a short period. These findings lead to the conclusion that the major source of pentane is not membrane lipid peroxidation but is from the action of intestinal bacteria on linoleate hydroperoxide.