Fred H. Mattson

Enzymatic hydrolysis at an oil/water interface

Triglycerides are metabolized by most of the organs and tissues of the body. However, the conditions in the lumen of the intestinal tract are unique, for it is only here that triglycerides are metabolized in the free state. Elsewhere these lipids are associated with water-soluble materials. Since the substrate is water-insoluble and the enzyme is water-soluble, lipase, which brings about the hydrolysis of triglycerides in the intestinal tract, has the special property of being capable of functioning efficiently at an oil/water interface. Any material that can alter the nature of this oil/water interface can markedly influence the digestion of triglycerides.Because of the unusual conditions under which the hydrolysis of triglycerides occurs, the usual methods of studying enzyme kinetics are not applicable. Besides the enzyme-substrate reaction itself, one must consider also such matters as diffusion of the substrate to the oil/water interface, removal of the products of hydrolysis from the oily/water interface, and the subsequent diffusion of these into the bulk phase. All of these steps can be influenced by such variables as efficiency of agitation, electrolyte concentration, and the presence of surface-active agents, such as monoglycerides, soaps, and the bile salts.

Hydrogenation of a fatty acids is not influenced by the position it occupies on a triglyceride molecule

Randomly rearranged soybean oil (Iodine Value 128) was hydrogenated with samples being taken at decrements of 10 I.V. units. The composition of the fatty acids occupying the various positions of the triglyceride molecules of these fats was determined. The results demonstrate that the position an unsaturated fatty acid occupies on a triglyceride molecule does not influence its rate of hydrogenation.

The effect of a non-absorbable fat on the turnover of plasma cholesterol in the rat

Rats were injected with [4-14C]-cholesterol and then fed diets that contained sucrose polyester (SPE) at levels of 0 and 8% of the diet.14C was measured in neutral and acidic steroid fractions of the feces collected during days 35–39 post i.v. injection. Periodic blood samples were used to measure the specific activity of the plasma cholesterol. The plasma data were consistent with a two-pool model for the decay of the plasma specific activity. The slow component of the decay curve decreased more rapidly in animals that received SPE. The half-life corresponding to this component was approximately 20% shorter in the SPE-fed animals compared to the control group. The mass of cholesterol calculated for the first pool was similar for all groups of animals. The14C found in the feces was consistent with the more rapid removal of cholesterol from the body in the SPE-fed animals. The mass of excreted steroid was equal to the calculated rate of cholesterol production in each group of animals.

The long-term effects of dietary sucrose polyester on African green monkeys.

Abstract Sucrose polyester (SPE) is a nonabsorbable fat which has been shown to lower plasma cholesterol concentrations when incorporated into the diet of human volunteers. This study was designed to assess the long-term (15 months) effect of oral administration of SPE on plasma cholesterol concentrations, body weights, and health of African green monkeys, a species similar to man in its lipid metabolism. All animals were fed for 2 months a high-cholesterol-containing diet to induce hypercholesterolemia. To simulate therapeutic intervention, dietary cholesterol was then decreased substantially and the effects of high or low (40 or 25%) fat content and presence or absence of SPE in the diet (as about 10% of diet) were assessed. There were four groups of animals: Group I (low fat-no SPE), Group II (high fat-no SPE), Group III (low fat-SPE), and Group IV (high fat-SPE). SPE administration resulted in 36% (high fat-SPE) and 40% (low fat-SPE) reductions in mean plasma cholesterol concentrations compared to 23% (high fat-no SPE) and 19% (low fat-no SPE) mean reductions in groups not fed SPE. The effect of SPE was statistically significant (P < 0.003). The effect of SPE was maximal in those animals with a high or intermediate plasma cholesterol response to dietary cholesterol and minimal or nonexistent in animals with a low plasma cholesterol response to dietary cholesterol. No significant differences between groups could be detected in body weight gain or in animal health as determined by the frequency of clinical illness and serial clinicopathologic observations.

Distribution among tissues of intravenously administered sucrose octaoleate

The distribution of [14C]oleate label in rat tissues in the 6 hr after intravenous administration of sucrose octa-[14C]oleate (7.5 mg; SuO8) was compared with that observed after administration of [14C]triolein. The [14C]-oleate label, whether injected as triolein emulsion, or as chylomicrons obtained from donor animals, rapidly cleared from the serum; only 10% or less remained in the serum 15 min after injection. Labeled SuO8 disappeared less rapidly from the serum; about one-third of the dose was present after 15 min, and after 120 min 14% remained. In the liver, there was an initial greater accumulation of fatty acid label when and emulsion of either triolein or SuO8 was given rather than the chylomicrons. The octaester continued to accumulate in the liver throughout the 6 hr of study, and 78% of the initial dose was present at that time. By contrast, although one-third of the triolein, as of SuO8, was found in the liver shortly after injection, levels subsequently decreased; at 6 hr, 12% of the label remained associated with that organ. A small portion, up to 8% of the acid label, whether administered as chylomicrons or as a triolein emulsion, was found in the epididymal fat pads. Smaller amounts, usually 1% or less, of the [14C]oleate label were found in fat pads following the injection of labeled SuO8. In a separate study, the levels of acid label in the liver and spleen were monitored for 21 days following the intravenous administration of [14C]SuO8. There was an initial accumulation of approximately half of the injected lipid label in the liver and one-quarter in the spleen. By day 21, the level in the liver had decreased to one-third of that administered, while the level in spleen remained at one-quarter.