Mary Frances Sorrels

Biosynthesis of fatty acids and cholesterol as related to diet fat.

The objective of this study was to explore the influence of a series of simple triglycerides and natural fats on cholesterogenesis and lipogenesis. Male rats were given a partially synthetic diet containing no added fat or 30% of tributyrin, tricaproin, tricaprylin, tricaprin, trilaurin, trimyristin, tripalmitin, triolein, trilinolein, lard, butter oil, safflower oil, or a synthetic triglyceride made of one part palmitic and two parts oleic acids. After 2 weeks, the rats were administered 0.2 mc. acetate-1-C14/kg. of body weight (intraperitoneally) and were sacrificed 1 hr. later. Various tissues were removed for analysis. When compared to the low fat diet, all of the non-linoleic acid diet fats caused increases in liver 16:1 and 18:1 acids at the expense of the polyene acids, mainly 18:2 and 20:4. Stearic acid was also reduced in all cases except after tricaprin and triolein. In addition to the above, the tripalmitin diet compensated for a pronounced loss in the polyunsaturated acids with an increase in the 16:0 and 18:0 acids. Unexpectedly, dietary laurate was not deposited in the liver but resulted in a larger increase in liver myristate than after the ingestion of myristate itself. The animals on the low fat diet incorporated over 7% of the labeled acetate into liver fatty acids, those on the short-chain fat diet about 5%, those on the medium chain length fat diet 2.5%, those on the longer chain length saturated fat diet 1.5%, and those on the safflower oil and trilinolein diets only 0.3 and 0.2%, respectively. During the ingestion of the short-chain fatty acids, a very high level of palmitic acid synthesis occurred, suggesting that the short-chain acids do not inhibit its synthesis and are themselves converted to palmitic to a significant degree. During the ingestion of the long-chain fatty acids, all synthesis of fatty acids was strongly inhibited. In all cases there was a lower degree of incorporation of acetate into oleic than into palmitic. The concentration of liver cholesterol was only 2.3 mg./g. in animals on the low fat diet, approximately 4–5 mg./g. in animals on the saturated triglyceride diets, about 6 mg./g. in those on the triolein diet, and above 7 mg./g. in those on the trilinolein diet. However, only tripalmitin ingestion increased the level of liver cholesterol synthesis, as measured by the percentage of injected labeled acetate incorporated. Two weeks of dietary tripalmitin sharply decreased the amount of newly synthesized cholesterol transported into the aorta during the first hour after labeled acetate injection.

Influence of High Levels of Dietary Fats and Cholesterol on Atherosclerosis and Lipid Distribution in Swine

The degree of incorporation of injected 1-C14-acetate into tissue cholesterol on cholesterol free diets was much higher in the liver and plasma of swine ingesting saturated than unsaturated fat. The levels of cholesterol in all tissues increased with the presence of fat or cholesterol in the diet. In most cases, especially in the presence of cholesterol, cholesterol levels were highest in the presence of unsaturated fat. The combination of unsaturated fat with cholesterol in the diet produced the greatest degree of typical atheromatosis and the highest levels of cholesterol in the tissues, while saturated fat with cholesterol produced diffuse atypical lesions.

Tissue cholesterol transport as modified by diet cholesterol and the nature of diet fat

Summary Groups of rats were fed purified diets ad libitum for 10 weeks after weaning. Three diets contained no fat, 20 % safHower oil or 20 % stripped tallow respectively. Three corresponding diets contained 1 % cholesterol in addition. Five animals in each group were sacrificed at each of 1/2 periods between and 96 hours after intraperitoneal injection of [1- 14 C]-sodium acetate and gastric intubation of tritium-labeled cholesterol. Examination of the tissues led to the following conclusions: Diet cholesterol and fat each play roles in the transport of cholesterol in serum and other tissues. The roles, however, are different. Diet cholesterol decreases the concentration of high-density lipoproteins and S f 0–12 low-density lipoproteins but increases the concentration of the S f 12–20 and S f 20–400 fractions. At the same time serum cholesterol concentration increases. It is postulated that this is a result of the inhibition of cholesterol synthesis by diet cholesterol: the exogenous cholesterol transported on the low-density lipoproteins and chylomicrons replaces the endogenous, the synthesis of which may be related to high-density lipoprotein origins. Diet fat, both tallow and safflower oil, in the cholesterol-free diets increases the S f 0–12 lipoproteins. Only tallow increases the S f 20–400 fraction also. In diets containing cholesterol, tallow and safflower oil increase the S f 12–20 and Sf 20–400 fractions while tallow decreases and safflower oil increases the S f 0–12 fraction. Diet fat has no direct effect on serum cholesterol levels but enhances the responses to diet cholesterol, probably by increasing its degree of absorption. In addition, however, diet fat also decreases the time required for exogenous cholesterol to reach maximum levels in tissues, unsaturated fat being more effective than saturated. Diet fat also affects tissue cholesterol half-life, unsaturated fat reducing it and saturated fat increasing it. Low levels of tissue exogenous cholesterol radioactivities on low fat as compared to high fat diets are explained as being due to diversion of labeled acetate to fat synthesis rather than to relatively low levels of cholesterol synthesis. The aorta synthesizes cholesterol and such synthesis is not inhibited by dietary cholesterol, in contrast to the liver but similar to the intestinal mucosa.

Dietary regulation of phosphatidic acid synthesis from dihydroxyacetone phosphate and fatty acid by rat liver microsomes

Phosphatidic acid synthesis from dihydroxyacetone phosphate and 1-14C-palmitate was studied in liver microsomes of rats maintained on a stock diet (5% fat), fasted for three days after being fed the stock diet, or given a high fat diet (15% fat) or a fat free diet for a week after being fed the stock diet. The amounts of phosphatidic acid synthesized per minute per milligram of microsomal protein in rats ingesting a stock diet or a fat free diet were at least twice the levels observed in rats either fasting or maintained on a high fat diet. Following fasting, realimentation with either a fat free or high fat diet returned the microsomal capacity for phosphatidic acid synthesis to approximately the same level, which was higher than that observed in rats maintained on a stock diet. Analogous results were observed when glyceraldehyde 3-phosphate was used as the glyceride-glycerol precursor, probably because microsomes convert glyceraldehyde 3-phosphate to dihydroxy-acetone phosphate. These studies demonstrate that phosphatidic acid synthesis from dihydroxyacetone phosphate by particulate enzymes is influenced by diet.

Biosynthesis of triglycerides from triose phosphates by microsomes of intestinal mucosa.

Microsomes of hamster intestinal mucosa synthesize triglycerides from dihydroxyacetone phosphate or DL-glyceraldehyde 3-phosphate in the presence of palmitate, ATP, CoASH and NADPH or NADH but in the absence of soluble enzymes. An inhibitor of triose phosphate isomerase, 1-hydroxy-3-chloro-2-propanone phosphate, completely inhibits glyceride synthesis from glyceraldehyde 3-phosphate. This compound does not inhibit glyceride synthesis from dihydroxyacetone phosphate. These reactions confirm the conversion of glyceraldehyde 3-phosphate to dihydroxyacetone phosphate prior to glyceride synthesis.

Identification of some marine oil constituents by chromatography

Summary and ConclusionA scheme for the separation and identification of some constituents of marine oils was developed. A preliminary separation on a silicic acid column with five solvent systems was followed by further separation and identification on silicic acid impregnated glass-fiber filter paper. This method can be used successfully for qualitative determinations, but the irregularities in the density of the glass paper prevent an accurate quantitative assay.

Tissue lipide relationships from their composition and acetate incorporation.

Abstract Groups of male “miniature” swine were reared on diets very low in fat or containing 20% myristoyllaurin or 20% cottonseed oil. After approximately 11 months on the test diets they were injected intraperitoneally with acetate-1-C 14 . Twenty-four hours later they were sacrificed by exsanguination through the femoral artery, and blood plasma, liver, and adipose tissue lipide fatty acids were examined for fatty acid composition and C 14 incorporation.

Production and preferential utilization of dihydroxyacetone phosphate for glyceride synthesis in the presence of glycerol 3-phosphate

Summary The mitochondria-free supernatant of rat livers contains glycerol 3-phosphate in concentrations 20–30 times higher than that of dihydroxy-acetone phosphate. It catalyzes glyceride synthesis from added fatty acids in the absence of exogenous glycerol 3-phosphate. The synthesis of glycerides is stimulated two- to threefold in the presence of NADH or NADPH. That the enhanced synthesis is due to the endogenous production and utilization of dihydroxyacetone phosphate was shown by the conversion of 14 C-fructose 1,6-diphosphate to glycerides, a process which requires NADH or NADPH and is unaffected by the presence of glycerol 3-phosphate.

Isomerization of L-glyceraldehyde to dihydroxyacetone during glyceride synthesis by rat liver microsomes.

L-glyceraldehyde is converted to phosphatidic acid by the action of rat liver microsomal enzymes and glycerol kinase in the presence of fatty acid, ATP, CoASH and NADH. L-glycerol 3-phosphate is not an intermediate in this synthesis since microsomes in the presence of NADH neither reduce L-glyceraldehyde nor, in the additional presence of glycerol kinase and ATP, convert it to L-glycerol 3-phosphate. However dihydroxyacetone is produced when L-glyceraldehyde is incubated with microsomes. This was shown enzymatically by the subsequent conversion to dihydroxyacetone phosphate which was confirmed by the oxidation of NADH in the presence of glycerol 3-phosphate dehydrogenase. Isomerization of L-glyceraldehyde and the synthesis of dihydroxyacetone phosphate may be one of several possible mechanisms in the conversion of the triose to either glucose or glycerideglycerol which has been reported to occur in tissue.