Absorption and esterification of micellar free and esterified cholesterol-4-C14

Other relevant components of nuts: phytosterols, folate and minerals

Nuts contain significant amounts of essential micronutrients that are associated with an improved health status when consumed at doses beyond those necessary to prevent deficiency states. Nuts do not contain cholesterol, but they are rich in chemically related phytosterols, a class of compounds that interfere with intestinal cholesterol absorption and thus help lower blood cholesterol. Nuts also contain folate, a B-vitamin necessary for normal cellular function that plays an important role in detoxifying homocysteine, a sulphur-containing amino acid with atherothrombotic properties that accumulates in plasma when folate status is subnormal. Compared to other common foodstuffs, nuts have an optimal nutritional density with respect to healthy minerals, such as calcium, magnesium and potassium. Like that of most vegetables, the sodium content of nuts is very low. A high intake of calcium, magnesium and potassium, together with a low sodium intake, is associated with protection against bone demineralisation, arterial hypertension, insulin resistance, and overall cardiovascular risk. Phytosterols might justify part of the cholesterol-lowering effect of nut intake beyond that attributable to fatty acid exchange, while the mineral richness of nuts probably contributes to the prevention of diabetes and coronary heart disease observed in epidemiological studies in association with frequent nut consumption.

Micellar distribution of cholesterol and phytosterols after duodenal plant stanol ester infusion

Properties of the intestinal digestion of the dietary phytosterols, cholesterol and cholestanol, and the mechanisms by which phytosterols inhibit the intestinal absorption of cholesterol in healthy human subjects are poorly known. We have studied the hydrolysis of dietary plant sterol and stanol esters and their subsequent micellar solubilization by determining their concentrations in micellar and oil phases of the jejunal contents. Two liquid formulas with low (formula 1) and high (formula 2) plant stanol concentrations were infused via a nasogastric tube to the descending duodenum of 8 healthy human subjects, and intestinal contents were sampled for gas-liquid chromatographic sterol analysis 60 cm more distally. During the duodenal transit, phytosterol esters were hydrolyzed. This was especially profound for sitostanol, as its esterified fraction per milligram of sitosterol decreased 80% (P < 0.001) in formula 1 and 61% (P < 0.001) in formula 2. Contrary to that, esterified fraction of cholesterol per milligram of sitosterol was increased fourfold (P < 0.001) in formula 1 and almost sixfold (P < 0.001) in formula 2, whereas that of cholestanol remained unchanged. Percentages of esterified sterols and stanols in total intestinal fluid samples were higher after the administration of formula 2 than of formula 1. Esterified cholesterol and stanols accumulated in the oil phase, and free stanols replaced cholesterol in the micellar phase. At high intestinal plant stanol concentrations, cholesterol looses its micellar solubility possibly by replacement of its free fraction in the micellar phase by hydrolyzed plant stanols, which leads to a decreased intestinal absorption of cholesterol.

Sterol ester hydrolase in Fusarium oxysporum

Two electrophoretically different forms of sterol ester hydrolase (EC 3.1.1.13) were obtained from the cytoplasmic extract of the mycelia of Fusarium oxysporum. The entities, estimated at 60,000 (I) and 15,000 (II) molecular weights, were obtained in Sephadex G100 column chromatography of the ammonium sulfate precipitate from the cytoplasmic extract. A third form III, 75,000 MW, was obtained from the culture filtrate. The activity of the enzyme was increased by Triton X-100 and was not inhibited by p-chloromercuribenzoate (PCMB), a sulfhydryl reagent. The enzymes I and II were inhibited differentially by NaCl. The optimal activities of forms I, II and III occurred at pH 4.8, pH 8.0 and pH 7.0, respectively. The apparent Km values of 7.7 X 10(-5), 8.3 X 10(-5) and 10.5 X 10(-5), respectively, indicate a similar order of affinity for cholesteryl oleate at pH 7.1. The rate of hydrolysis of cholesteryl esters were in the order: linoleate greater than oleate greater than valerate greater than butyrate greater than acetate. Cholesteryl benzoate and palmitate were not hydrolyzed. The properties of the microbial enzyme are discussed in relation.

The effect of lecithin on intestinal cholesterol uptake by rat intestine in vitro

1. Sacs 20 cm long were obtained from the upper half of the small intestine of bile fistula rats (bile duct cannulated 48 hours previously). The sacs were everted, filled with oxygenated phosphate buffer and incubated 1 hr at 37 degrees C in 25 ml. of a buffered micellar solution of oleic acid (0.6 mM), mono-olein (0.3 mM), sodium taurocholate (4.8 mM) and (3)H-labelled cholesterol (0.15 mM) plus glucose (28 mM).2. After incubation the amount of [(3)H]cholesterol taken up by the mucosal tissue was measured. It averaged 200 n-mole/hr.g tissue wet wt. +/- 6 (S.E.).3. Adding 3 ml. whole rate bile with other factors unchanged caused cholesterol uptake to decrease by 50% in confirmation of previous studies.4. Adding purified lecithin obtained from rat liver tissue, and from egg yolks, similarly decreased cholesterol uptake. A significant response was obtained with 2.5 mg liver lecithin (concentration 0.13 mM) and a near maximum response with 15 mg (concentration 0.80 mM). 10 mg lecithin decreased uptake by an amount equivalent to that obtained with 3 ml. whole bile.5. Lecithin is an active component of whole bile causing reduced intestinal cholesterol uptake from micelles.6. The decreased uptake of cholesterol in the presence of lecithin may have been the result of expansion of the cholesterol-containing micelles with consequent reduction in cholesterol permeability.

[Pancreatectomy in the eel: effects on serum glucose and cholesterol]

Pancreatectomy in the eel causes a slight tendency toward hyperglycemia; total and partial pancreatectomies cause a drop of total serum cholesterol. Thus, complete removal of the islet tissue in this teleost is not followed by diabetes mellitus, and also the endocrine control of the cholesterol-containing serum components seems to differ from that in mammals.

Bile salt malabsorption in regional ileitis, ileal resection and mannitol-induced diarrhea

Fecal bile salt excretion was studied in healthy volunteers, patients with regional ileitis, and patients with ileal resection. 10 muc of carboxyl-(14)C-cholic acid was given orally. Stools and urine were collected daily for 5-10 days, the bile salts extracted, and the radioactivity assayed. Urinary excretion was negligible. All patients with ileal resection excreted bile salts in the feces significantly faster than controls, and five of the six excreted 50% of the radioactivity within 24 hr. Their mean intestinal transit time was 5.6 hr compared to 26 hr for the controls. Two of the three patients with regional ileitis excreted bile salts almost as rapidly as patients with ileal resection. Vitamin B(12) absorption was also defective in those patients, but the intestinal transit time was not decreased. To study the effect of rapid intestinal transit on bile salt excretion, four of the control subjects were given orally 1200 ml of 10% mannitol for 7 days, and the labeled cholic acid excretion rate was again studied. The mean intestinal transit time was markedly shortened, mild steatorrhea developed, and the fecal bile salt excretion rate increased slightly. It is concluded that ileal resection and ileal disease are major factors and rapid intestinal transit is a minor factor in causing excessive fecal bile salt loss. The relevance of bile salt wastage to lipid malabsorption is unknown because of insufficient information about compensatory jejunal absorption, maximum rate of hepatic bile salt synthesis, and the minimum necessary intraluminal concentration of conjugated bile salt.