Allen R. Hennes

Studies of incorporation of radioactivity into lipids by human blood

Abstract The incorporation of acetate 1-C 14 into discrete fatty acids of whole blood and platelets obtained from nonketotic insulin-dependent diabetics has been determined. Whole blood from diabetics incorporates significantly less acetate C 14 into fatty acids than does whole blood from controls. In addition, the pattern of incorporation of C 14 into fatty acids is abnormal. The percentage of C 14 in 16:0 (palmitic acid) and also 14:0 (myristic acid) is decreased, while the percentage of C 14 in 20 carbon saturated and unsaturated fatty acids is increased. The pattern of C 14 in fatty acids formed by whole blood returns to normal when the fasting blood sugar is normal, presumably indicating that leukocyte fatty acid formation is normal when the fasting blood sugar is normal. Incorporation of C 14 into fatty acids by platelets is also decreased, although difference from the control group is not significant. Platelets, too, incorporate a significantly smaller percentage of fatty acid C 14 into 14:0 and 16:0 and a significantly greater percentage of C 14 into saturated and unsaturated 20 carbon fatty acids. In addition, the percentage of C 14 in fatty acids with retention time corresponding to 22:0 (behenic acid) or greater is increased. These abnormalities are not corrected when the fasting blood sugar returns to normal. Some of the possible physiologic and clinical implications of these findings are discussed.

Studies of incorporation of radioactivity into lipids by human blood: I. Pattern of incorporation of radioactivity into fatty acids by blood from normal subjects and patients in diabetic acidosis☆

We have incubated whole blood from normal and comatose diabetic subjects with 1-C14 acetate to determine the pattern of incorporation of C14 into fatty acids. Fatty acid methyl esters were separated by gas liquid chromatography and incorporation of radioactivity into individual fatty acids was determined. Blood from control subjects incorporated a significantly greater percentage of total fatty acid radioactivity into lauric, myristic and palmitic acids (p < .001) and a significantly smaller percentage of C14 into stearic and oleic acids (p < .005) than did blood from comatose diabetics. These abnormalities could not be corrected by incubation of whole blood from comatose diabetics with insulin, nor could they be produced by decreasing pH of normal blood to as lows as 6.6. The pattern of incorporation of C14 into whole blood fatty acids returned to normal following treatment of diabetic acidosis. Thus, qualitative changes in fatty acid fromation, presumably reflecting a marked and relatively selective suppression of de novo synthesis of fatty acids, can be detected in whole blood from comatose diabetics. Blood cells appear to be useful for studying certain aspects of lipid metabolism in human diabetics.

Studies of Incorporation of Radioactivity into Lipids by Human Blood: II. Pattern of Incorporation of Radioactivity into Fatty Acids by Platelets from Normal Subjects and Patients in Diabetic Acidosis

Platelets from diabetics in acidosis incorporate significantly less C-14 into fatty acids than do platelets from control subjects. This decrease in incorporation of C-14 into fatty acids is not uniform. Incorporation of C-14 into myristic and palmitic acids, fatty acids presumably made by de novo synthesis, is suppressed to a much greater extent than is incorporation into other fatty acids. Since some of these abnormalities of incorporation of C-14 by platelets from comatose diabetics could represent isotope dilution effects, we have been particularly interested in the analysis of these data in terms of percentage of total fatty acid C-14 incorporated into the various groups of fatty acids. Platelets from diabetics in acidosis have a pattern of incorporation of C-14 into platelet fatty acids which is much different from that of normal platelets. There is a great decrease in percentage of C-14 in myristic and palmitic acid with a relative increase in percentage of C-14 in fatty acids with retention time corresponding to arachidic acid (20:0) or greater. A significant increase in relative percentage of C-14 in fatty acids containing ten carbons or less is also seen. These findings presumably mean that the cytoplasmic or malonyl CoA pathway, which is involved primarily in synthesis of palmitic and myristic acids, is suppressed greatly in diabetic acidosis, while the mitochondrial or chainlengthening pathway is suppressed to a much smaller degree, or is actually stimulated. It is, therefore, important to consider qualitative as well as quantitative alterations in fatty acid synthesis in diabetes.

Studies of Incorporation of Radioactivity into Lipids by Human Blood: IV. Abnormal Incorporation of Acetate 1-C-14 into Fatty Acids by Whole Blood and Platelets from Insulin Independent Diabetics

The incorporation of acetate 1-C-14 into fatty acids by whole blood and platelets from insulin independent diabetics has been determined. Whole blood from insulin independent diabetics incorporates significantly less C-14 into fatty acids than does whole blood from controls. As in previously reported studies done with blood cells from ketotic and nonketotic insulin dependent diabetics, a decreased percentage of fatty acid C-14 in palmitic acid (16:0) is found. This, however, exists as an isolated abnormality in whole bLiod from insulin independent diabetics. This abnormality may persist in some patients even when the fasting blood sugar is normal. The incorporation of acetate C-14 into fatty acids by platelets from insulin independent diabetics is quite similar to that of the control group. However, the pattern of incorporation of C-14 into fatty acids is abnormal. Percentage of C-14 in both myristic and palmitic acids is decreased, while percentage of C-14 in saturated and unsaturated fatty acids with retention time corresponding to 20:0 or greater is increased. These abnormalities bear no relationship to the fasting blood sugar at the time of study. These findings apparently mean that de novo synthesis of fatty acids is impaired in blood cells from both insulin dependent and insulin independent diabetics, while chain lengthening is relatively little affected.

Insulin-stimulated lipogenesis in rat adipose tissue in vitro. Incorporation of C14 from glucose and acetate into lipid fractions and fatty acids.

Abstract Rat epididymal adipose tissue was incubated in Krebs bicarbonate buffer in the presence and absence of insulin, and the incorporation of labeled acetate and glucose into major fractions and fatty acids was studied. Radioactive carbon from either substrate was incorporated predominantly into the saponifiable lipid fraction, a behavior that was exaggerated by the presence of insulin. Insulin also increased incorporation into both the glycerol and nonsaponifiable fractions but not to a comparable extent. While incorporation into all fatty acids characterized the distribution of C14 from both substrates, palmitic acid was favored. Insulin exaggerated this pattern, stimulating lipogenesis by new synthesis rather than by chain-lengthening in-situ fatty acids.