Hypolipidemic activity of (−)-hydroxycitrate

The influence of (−)-hydroxycitrate, a potent competitive inhibitor of adenosine triphosphate (ATP) citrate lyase, on serum triglyceride and cholesterol levels, and in vitro and in vivo rates of hepatic fatty acid and cholesterol synthesis was investigated in normal and hyperlipidemic rat model systems. (−)-Hydroxycitrate reduced equivalently the biosynthesis of triglycerides, phospholipids, cholesterol, diglycerides, cholesteryl esters, and free fatty acids in isolated liver cells. In vivo hepatic rates of fatty acid and cholesterol synthesis determined in meal-fed normolipidemic rats were suppressed significantly by the oral administration of (−)-hydroxycitrate for 6 hr, when control animals exhibited maximal rates of lipid synthesis; serum triglyceride and cholesterol levels were significantly reduced by (−)-hydroxycitrate. In two hypertryglyceridemic models—the genetically obese Zucker rat and the fructose-treated rat—elevated triglyceride levels were due, in part, to enhanced hepatic rates of fatty acid synthesis. (−)-Hydroxycitrate significantly reduced the hypertriglyceridemia and hyperlipogenesis in both models. The marked hypertriglyceridemia exhibited by the triton-treated rat was only minimally due to increased hepatic lipogenesis; (−)-hydroxycitrate significantly inhibited both serum triglyceride levels and lipogenesis in this model.     

Role of ATP in the inhibition of lipogenesis in fasted animals

This study was undertaken to obtain information both in vivo and in vitro on the role of adenosine triphosphate (ATP) in the inhibition of fatty acid synthesis in fasted mice. Fasted mice were injected intravenously with glucose or fructose or intraperitoneally with insulin to increase the supply of endogenous ATP. They then received acetate 1−¹⁴C, glucose 6−³H or fructose U−¹⁴C intravenously and were killed at various intervals. The controls received the labeled tracers only. The radioactivities of liver and carcass fatty acids were determined. The action of ATP on homogenized livers from fasted mice was also determined. The stimulation of lipogenesis was obtained under all these conditions, but only in animals fasted for 4 hr. Insulin was active only on the extrahepatic tissues. Fructose, as well as glucose, restored hepatic lipogenesis. In vitro, ATP restored lipogenesis by homogenized livers of mice fasted for 4 hr, but it inhibited the fatty acid synthesis by homogenized livers from unfasted mice. The significance of the results is discussed.     

Action of three bile acids on hepatic and intestinal cholesterogenesis in the rat

Incorporation of [1¹⁴−C] acetate into cholesterol by subcellular particles from the liver and the small intestine of rats with a biliary diversion and a duodenal perfusion of sodium taurocholate, taurochenodeoxycholate or taurodehydrocholate, was studied in vitro. In the liver, taurochenodeoxycholate prevented the increase of cholesterol synthesis induced by biliary drainage. Taurocholate had no action on cholesterol synthesis at any time, day or night. Intestinal synthesis of cholesterol was reduced by taurocholate and taurochenodeoxycholate but was not modified by taurodehydrocholate infusion.     

Linoleic acid-induced fatty acid changes in platelet and aorta of the rat: Effect of age and cholesterol

The influence of age and cholesterol on polyunsaturated fatty acids (PUFa) levels was studied in young and old male Sprague-Dawley rats. Animals were fed a fat-free diet supplemented with 10% (by wt) safflower oil with or without 1% cholesterol for 8 wk. As a result of cholesterol feeding, proportions of linoleic acid (18∶2n−6) and dihomo-γ-linolenic acid (30∶3n−6) were increased and and that of arachidonic acid (20∶4n−6) was decreased in the liver and platelet phospholipids in 64-wk-old rats, suggesting inhibitory effects of cholesterol on 20∶4n−6 synthesis from 18∶2n−6. The prominent age-dependent effect on the levels of PUFA was a retention of C−22 n−3 PUFA, accompanied by decreased C−22 n−6 PUFA and increased 20∶3n−6 in the liver and platelet phospholipids. Ratio of 20∶3n−6/20∶4n−6 increased in 64-wk-old rats regardless of dietary cholesterol, suggesting depressed Δ5-desaturase with age. In aorta phospholipids, 20∶3n−6 content and 20∶3n−6/20∶4n−6 ratio increased with cholesterol supplementation, but not with age. These results suggest that changes of PUFA composition of platelet phospholipids with age are closely linked with changes in liver phospholipids. The 20∶4n−6 content in both platelet and aorta phospholipids is kept constant, despite other n−6 and n−3 PUFA being affected by age.     

Comparative effects of (−)-hydroxycitrate and (+)-allo-hydroxycitrate on acetyl CoA carboxylase and fatty acid and cholesterol synthesis in vivo

(−)-Hydroxycitrate and (+)-allo-hydroxycitrate were investigated for their effects on lipid synthesis in vivo under conditions of either high carbohydrate feeding or 24 hr fasting. Changes in rates of lipid synthesis resulting from the oral administration of these compounds were monitored with the use of radiolabeled H₂O, alanine, and acetate. In the fed rat, (−)-hydroxycitrate significantly reduced the incorporation of H₂O and alanine into fatty acids and cholesterol. An increased incorporation of labeled H₂O into fatty acids but no change in cholesterol synthesis in the fasted rat suggested that (−)-hydroxycitrate may be an activator of acetyl CoA carboxylase. With (−)-hydroxycitrate administration, acetate incorporation into fatty acids and cholesterol was subject to pool dilution effects under fed or fasted states. (+)-allo-Hydroxycitrate was ineffective in modulating the rates of fatty acid synthesis under either nutritional condition. Both (−)-hydroxycitrate and (+)-allo-hydroxycitrate were shown to be in vitro activators of acetyl CoA carboxylase, the former being a much stronger activator than the latter. Thus, stereospecificity of the hydroxycitrate isomers was demonstrated in both the inhibition of lipid synthesis (previously shown to occur at adenosine triphosphate citrate lyase) and the stimulation of fatty acid synthesis (possibly occurring at acetyl CoA carboxylase).     

Effects of dietary protein and cholesterol on phosphatidylcholine and phosphatidylethanolamine molecular species in mouse liver

The present study examined the effects of two atherogenic factors, animal protein and cholesterol, on the distribution of fatty acids and the molecular species of major liver phospholipids in mice. Weanling mice were fed a semisynthetic diet supplemented with either casein or soy protein (20%, w/w) in the presence or absence of 0.5% cholesterol for 4 wk. Results from mouse liver showed that animal protein and, more so, dietary cholesterol modified the fatty acid profiles of the phospholipids. Animal protein had no significant effect on the concentration of lipids, but it altered the relative distribution and fatty acid profiles of the phospholipids, phosphatidylcholine and phosphatidylethanolamine. Dietary cholesterol, on the other hand, significantly increased the concentration of liver lipids, but it did not alter the relative distribution of phosphatidylcholine and phosphatidylethanolamine. In cholesterol-fed mice, the proportions of molecular species containing 18∶2n−6 were increased, whereas those containing 20∶4n−6 were decreased, indicating that dietary cholesterol suppressed linoleic acid metabolism. Since cholesterol feeding selectively decreased the ratio of 18∶0/20∶4n−6 in phosphatidylcholine, whereas it increased the 18∶0/18∶2n−6 ratio in phosphatidylethanolamine, this finding suggests that dietary cholesterol may affect the incorporation of fatty acids but not the rate of synthesis of phosphatidylcholine and phosphatidylethanolamine.     

Cholesterol oxidation in heated lard enriched with two levels of cholesterol

Cholesterol oxidation in lard containing two levels of added cholesterol was monitored using capillary gaschromatography. Loss of cholesterol and formation of cholesterol oxidation products (COPs) were measured. Lard samples with 10 times (Test I) and 2 times (Test II) the amount of cholesterol originally found in each batch of lard were heated at 180°C for 10 hr a day for 240 and 160 hr, respectively. Cholesterol steadily decreased throughout the heating period in both tests. Cholesterol loss followed a first-order reaction rate, with a rate constant (k) of −1.18×10⁻³ h⁻¹ for Test I and −9.45×10⁻³ h⁻¹ for Test II. The COPs accumulated during both heating tests. But the amount of COPs formed did not total the amount of cholesterol lost. During heating, thermal degradation of cholesterol likely occurred, and those products were not detected. During cooling, hydroperoxides formed, which further oxidized into the COPs that were detected. The 7-ketocholesterol and 5α,6α-epoxycholesterol were the predominant COPs formed. The isomeric 7α-and 7β-hydroxycholesterols also accumulated in the heating tests. The 3β,5α,6β-cholestantriol was found in very small amounts and the 25-hydroxycholesterol was not detected. Presented in part at the 80th AOCS Annual Meeting, Cincinnati, OH, in May, 1989.     

A colorimetric assay for measuring cell-free and cell-bound cholesterol oxidase

Cholesterol oxidase (cholesterol:oxygen oxidoreductase, EC 1.1.3.6) catalyzes the conversion of sterol Δ⁵-3β-alcohol to the corresponding Δ⁴-3-ketone with the reduction of oxygen to hydrogen peroxide.Rhodococcus species GK 1, a soil isolated microbe, produces an extracellular and a membrane-bound cholesterol oxidase; the latter is bound to the outer surface of the microbial cell membrane. A simple and sensitive assay is described to measure the two enzyme types; no enzyme extraction is needed for measuring the membrane-bound cholesterol oxidase. In this assay, hydrogen peroxide is reduced by the chromogen 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) in the presence of horseradish peroxidase, and the increased absorbance is followed continuously at 600 nm (ε_m = 1.82×10⁴ M⁻¹·cm⁻¹ at pH 7.0 and 30°C). The standardized assay medium contained 46.9 mM sodium-potassium phosphate buffer pH 7.0, 0.16% Triton X-100, 312.5 μM ABTS, 50 μg peroxidase (12.5 units at 25°C), 6.25% isopropanol, 306.3 μM cholesterol or other sterols (kept in solution with isopropanol), and cholesterol oxidase. Oxidation of one molecule of cholesterol by cholesterol oxidase gives one molecule of hydrogen peroxide which reacts with two molecules of ABTS. The method is reproducible and the results correlate well with those obtained by measuring the absorbance of Δ⁴-cholest-3-one at 240 nm (ε_m = 1.40×10⁴ M⁻¹·cm⁻¹ at pH 7.0 and 30°C) and by the method of Allainet al. (Clin. Chem. 20, 470–475, 1974). In terms of efficiency, simplicity, and time saved, this coupled assay is expected to be a useful method for monitoring microbial production of cholesterol oxidase on an industrial scale, and for determining cholesterol or other sterols in biological fluids.     

Influence of temperature and high dietary linoleic acid content on esterification,elongation, and desaturation of PUFA in atlantic salmon hepatocytes

The esterification, desaturation, and elongation of [1-¹⁴C]18∶3n−3, [1-¹⁴C]18∶2n−6, and [1-¹⁴C]20∶5n−3 at 5 and at 12°C were studied using cultivated hepatocytes from Atlantic salmon. The salmon were fed diets, in which 0, 50, or 100% of the supplementary fish oil had been replaced by soybean oil, for 950 day-degrees at 5 and 12°C. The endogenous percentage of 18∶2n−6 in hepatocyte lipids was 2% in cells from fish fed a diet with 100% of the supplemental lipid from fish oil, and it was slightly less than 25% in cells from fish fed the diet with 100% of the supplemental lipid from soybean oil. Furthermore, the percentages of 20∶3n−6 and 20∶4n−6 were significantly higher in hepatocytes from fish fed on soybean oil than they were in those of fish fed on fish oil. The percentages of 20∶5n−3 and 22∶6n−3, on the other hand, were lower. The endogenous levels of n−6 FA were not significantly correlated with the total amounts of radiolabeled FA esterified in hepatocyte lipids. The main radiolabeled products formed from 18∶2n−6 were 20∶2n−6 and 20∶3n−6. The level of the important eicosanoid precursor 20∶4n−6 was twice as high in hepatocyte phospholipids from fish fed the 100% soybean oil diet as it was in hepatocytes from fish fed the diet with 100% of supplemental lipid from fish oil. The main products formed from 18∶3n−3 were 20∶4n−3, 20∶5n−3, and 22∶6n−3. High levels of dietary 18∶2n−6 do allow, or even seem to increase, the production of 22∶6n−3 from 18∶3n−3 in hepatocytes. The main products formed from 20∶5n−3 were 22∶5n−3 and 22∶6n−3. The production of 22∶6n−3 from 20∶5n−3 was higher at 5°C than at 12°C. The percentage of 24∶5n−3 was higher at 5°C than it was at 12°C, as was the ratio of 24∶5 to 22∶5. These results suggest that the elongation rate of 22∶5n−3 to 24∶5n−3 is higher at the lower temperature.     

A new short-path distillation system applied to the reduction of cholesterol in butter and lard

A molecular distillation plant, built particularly to increase the separation efficiency and to obtain safer working conditions, was tested to remove cholesterol from anhydrous butter and lard. A preliminary experiment was carried out with butter to evaluate the fractionation obtained at temperatures between 190 and 250°C and residual pressures between 10⁻³ and 10⁻⁴ torr. A second experiment was carried out at 185°C and at the maximum operational vacuum, evaluating the fractionation achieved within a time scale between 30 and 180 min. Cholesterol was almost completely removed during the second hour with minimal loss of low-molecular weight triglycerides. An experiment was carried out with lard at 250°C and maximum achievable operational vacuum (10⁻⁴ Torr), lasting approximately 6 h, and cholesterol was removed almost completely during the second hour without significant modifications in the triglyceride composition. This situation remained constant throughout the duration of the test.     

Cholesterol biosensor based on electrochemically prepared polyaniline conducting polymer film in presence of a nonionic surfactant

Cholesterol biosensor has been fabricated by covalently coupling cholesterol oxidase (ChOx) via glutaraldehyde onto electrochemically prepared polyaniline film in presence of TritonX-100 [4-(1,1,3,3-tetramethylbutyl) phenyl polyethylene glycol], a non-ionic surfactant onto indium-tin-oxide (ITO) glass substrate. These ChOx/PANI-TX-100/ITO bioelectrodes have been characterized using Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV) and scanning electron microscopy (SEM) techniques. The results of response measurements carried out on ChOx/PANI-TX-100/ITO bioelectrodes using amperometric and photometric techniques, reveal detection limit as 5 mg/dl, linearity from 5 to 400 mg/dl of cholesterol and sensitivity as 131 μA/(mg/dl cm⁻²). These biosensing electrodes are thermally stable up to 65 °C, can be used about 20 times and have a shelf-life of about 10 weeks when stored at 4 °C. Attempts have also been made to utilize the ChOx/PANI-TX-100/ITO bioelectrodes for estimation of free cholesterol concentration in serum samples.     

Pharmacological modulation of fatty acid desaturation and of cholesterol biosynthesis in THP-1 cells

In THP-1 cells, simvastatin decreases, in a concentration-dependent manner, cholesterol synthesis and increases linoleic acid (LA) conversion to its long-chain derivatives, in particular to arachidonic acid, activating Δ6 and Δ5 fatty acid (FA) desaturases. The intermediates in cholesterol synthesis, mevalonate and geranylgeraniol, partially reverse the effects of simvastatin on the LA conversion. The aims of this work were to evaluate: (i) the correlation between cholesterol synthesis and desaturase activity and (ii) the possible involvement of protein isoprenylation in desaturase activity, assessed through pharmacological treatments. THP-1 cells were incubated with [1-¹⁴C]LA or with [1-¹⁴C]di-homo-γ-linolenic acid (DHGLA) and treated with simvastatin or with curcumin and nicardipine, inhibitors of desaturases. Curcumin was more active than nicardipine in inhibiting LA and DHGLA conversion: 20 μM curcumin, alone or with simvastatin, totally inhibited Δ6 and Δ5 desaturation steps; 10 μM nicardipine only partially inhibited the enzymes, being more active on Δ5 desaturase. Simvastatin treatment decreased the incorporation of acetate in cholesterol (−93.8%) and cholesterol esters (−70.2%), as expected. Curcumin and nicardipine also decreased cholesterol synthesis and potentiated simvastatin. Finally, the isoprenylation inhibitors (perillic acid and GGTI-286) neither affected the conversion of LA nor inhibited the Δ5 desaturase activity. In conclusion, our results indicate that there is no direct relationship between cholesterol synthesis and desaturase activity. In fact, simvastatin decreased cholesterol synthesis and enhanced LA conversion (mainly Δ5 desaturation), whereas curcumin and nicardipin decreased Δ5 desaturation, with a limited effect on cholesterol synthesis.     

Dietary phospholipid alters biliary lipid composition in formula-fed piglets

Plasma cholesterol, arachidonic acid (AA, 20∶4n−6), and docosahexaenoic acid (DHA, 22∶6n−3) are higher in breast-fed infants than in infants fed formula without cholesterol, AA, or DHA. This study investigated differences in plasma, hepatic, and bile lipids and phospholipid fatty acids, and expression of hepatic proteins involved in sterol metabolism that result from feeding formula with cholesterol with egg phospholipid to provide AA and DHA. For this study, three groups of piglets were evaluated: piglets fed formula with 0.65 mmol/L cholesterol, the same formula with 0.8% AA and 0.2% DHA from egg phospholipid, and piglets fed sow milk. Piglets fed the formula with phospholipid AA and DHA had higher plasma high density lipoprotein, but not apoprotein (apo) B cholesterol or triglyceride; higher bile acid and phospholipid concentrations in bile; and higher liver and bile phospholipid AA and DHA than piglets fed formula without AA and DHA (P<0.05). Hydroxy methylglutaryl (HMG)-CoA reductase and 7-α-hydroxylase, the rate-limiting enzymes of cholesterol and bile acid synthesis, respectively, and low density lipoprotein receptor mRNA levels were not different between piglets fed formula without and with phospholipid AA and DHA, but HMG-CoA reductase and 7α-hydroxylase mRNA were higher, and plasma apo B containing lipoprotein cholesterol was lower in all piglets fed formula than in piglets fed milk. These studies show that supplementing formula with AA and DHA from egg phospholipid alters bile metabolism by increasing the bile AA and DHA, and bile acid and phospholipid.     

Effects of ketoconazole on cholesterol synthesis and precursor concentrations in the rat liver

Ketoconazole, an antimycotic agent, given to rats for a week as 0.05% food addition had no effect on the hepatic concentrations of free and esterified cholesterol or on the activity of acyl coenzyme A: cholesterol-acyltransferase (ACAT). However, the levels of free methylated cholesterol precursors, especially lanosterols, less markedly Δ^8,24 and Δ⁸-dimethyl sterols and monomethyl sterols, were increased after only one day's treatment, while those of esterified methyl sterols were increased inconsistently, and those of free and esterified Δ⁸-lathosterol, lathosterol and desmosterol were not affected at all. Cholestyramine treatment had no significant effect on ACAT in spite of a decrease in the hepatic content of esterified cholesterol and caused a marked increase in the free cholesterol precursor levels, especially in those of lathosterols. Cholestyramine given to ketoconazole-treated rats increased the hepatic levels of Δ⁸ and Δ⁷-lathosterols but not desmosterol or methylated cholesterol precursors. Ketoconazole increased and cholestyramine markedly decreased plantssterols, sitosterol and campesterol in the liver. In serum, the contents of both lanosterols and lathosterol were increased but that of cholesterol tended to be decreased by ketoconazole (−19%). The results indicate that ketoconazole impairs demethylation processes at C-14 and to some extent at C-4 in the rat liver, resulting in lowered serum cholesterol level.     

Inhibition of cytolytic T lymphocyte activity by oxysterols

The objective of this study was to investigate the effects of oxysterols (OS), namely 5α-hydroxy-6-ketocholestanol, 6-ketocholestanol and 25-hydroxycholesterol, on specific cell-mediated cytotoxicity by C57BL/6 spleen cells against P815-X2 (a DBA/2 mastocytoma) target cells. Cytolytic T lymphocytes (CTL) were generated by intraperitoneally injecting C57BL/6 mice with P815-X2 tumor cells 10 d prior to the cytotoxicity experiments. Preincubation of CTL with 10⁻⁵ M 5α-hydroxy-6-ketocholestanol and 6-ketocholestanol for 45 min in lipoprotein-depleted medium resulted in an inhibition of cytolytic activity (73 and 43%, respectively) as measured by 4-h⁵¹Cr release. At a concentration of 5×10⁻⁶ M, 5α-hydroxy-6-ketocholestanol inhibited CTL activity by 65%, whereas 6-ketocholestanol did not elicit any inhibition. By contrast, 25-hydroxycholesterol did not inhibit CTL at either concentration, although it is known to be a potent inhibitor of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway. When CTL were preincubated with OS in lipoprotein-replete medium, there was no inhibition of CTL activity at the respective concentrations. The results suggest that the inhibition of CTL activity upon short-term incubation with OS is not due to the inhibition of cholesterol synthesis, but may be due to the insertion of OS into the plasma membrane to replace cholesterol and alteration of membrane physical properties.     

Stimulation of lipid absorption in young rats by cholesterol: Early time changes and effects on pentobarbital sleeping time

Four groups of young male and female rats were fed a chow diet (0), chow plus 10% corn oil (F), chow plus 1% cholesterol (C), or chow plus 1% cholesterol plus 10% corn oil (CF) for 1, 2, 4 and 8 days. After 2 dats, male F, C and CF rats exhibited a shorter anesthesia period (−20 to −30%) when given pentobarbital. By 4 days, male F and C rats had pentobarbital sleeping times (PB-ST) 20% less than 0 rats. These effects were additive and CF rats had 40% shorter PB-ST. Reduction of PB-ST by cholesterol and corn oil was similar but slightly less in female rats. Liver lipid content doubled in 4 days in CF rats, and liver cholesterol was 4 times that of 0 rats. These changes and the increases in metabolism of barbiturate suggested changes in liver microsomal enzyme activities. Serum glutamic oxaloacetic and glutamic pyruvic transaminase, two enzymes reflective of liver damage, did not increase after 8 days on C, F or CF diets. Our results suggest that consumption of an animal sterol and a high lipid diet by laboratory rats, normally consuming a diet low in fat (3–4%), increases the ability of the animal to detoxify a barbiturate. Storage of absorbed dietary cholesterol in the liver may represent a major mechanism for maintaining extra hepatic cholesterol homeostasis.     

Dietary fat ratios and liver plasma membrane lipid composition

Male Sprague-Dawley weanling rats were fed isocaloric diets consisting of 10% (by wt) fat. The six groups differed in the ratio of corn oil and butter fat present in the diets such that: 10C, 10% corn oil (C); 8C2B, 8% C/2% butter fat (B); 6C4B, 6% C/4% B; 4C6B, 4% C/6% B; 2C8B, 2% C/8% B; and 10B, 10% B. Liver plasma membranes were analyzed for fatty acid composition and cholesterol/phospholipid molar ratio. The 18∶2n−6 content was constant in the 10C and 8C2B diets and then decreased linearly through the 2C8B diet. The 20∶4n−6 and 18∶1n−9 contents were constant except in the 10B diet, in which a significant decrease and increase, respectively, were observed. The cholesterol/phospholipid molar ratio increased between the 10C and 6C4B diets and subsequently (4C6B and 10B diets) remained constant. This data indicates that changes in n−6 fatty acid content in the liver plasma membrane are directly related to dietary intake only for 18∶2n−6. Arachidonic acid content in the membrane is maintained at a constant level until the linoleic acid content of the diet is reduced to 0.5% of calories. It also indicates that the cholesterol content of the membrane becomes saturated and does not increase with increasing concentrations of saturated fat in the diet. Presented in part at the FASEB Meeting, Washington, D.C., April, 1987.     

Quantitation of cholesterol oxidation products in unirradiated and irradiated meats

A method to detect 7-ketocholesterol, cholesterol-5β,6β-epoxide, cholesterol-5α,6α-epoxide, 4-cholesten-3-one, 4,6-cholestadien-3-one and 4-cholestene-3,6-dione in unirradiated and irradiated beef, pork and veal was developed by use of chloroform-methanol-water extraction, solid-phase extraction, column separation, thin-layer chromatography and gas chromatography. This method recovered 78–88% of the cholesterol oxidation products and detected the cholesterol oxidation products at 10 ppb or higher. Irradiation of the meats to a dose of 10 kGy increased these compounds, except 4,6-cholestadien-3-one for all three types of meat, over unirradiated, and except cholesterol-5α,6α-epoxide and 4-cholesten-3-one for the pork. All the cholesterol oxidation products in the unirradiated meats increased during storage at 0–4°C for 2 wk with some exceptions for the pork. The increases of cholesterol oxidation products in stored irradiated meats were greater than those in the unirradiated.     

Preferential labeling of brain cholesterol by {3-14C}D(−)-3-hydroxybutyrate

{3-¹⁴C}D(−)-3-hydroxybutyrate or {2-¹⁴C}glucose was injected subcutaneously into 15-day old suckling rats. The animals were killed 3, 6 and 24 hr later by decapitation. Brain proteins, cholesterol, glycolipids, and phospholipids were extracted and prepared for counting. The {3-¹⁴C}D(−)-3-hydroxybutyrate injected animals showed ca. twofold greater labeling (p<.001) of brain cholesterol compared to {2-¹⁴C}glucose; whereas the {2-¹⁴C}glucose injected animals showed ca. fourfold greater labeling (p<.001) of brain proteins than {3-¹⁴C}D(−)-3-hydroxybutyrate at all time points. The difference in labeling of brain glycolipids and phospholipids was less striking, but greater labeling was apparent at each time point in the {2-¹⁴C}glucose injected animals compared to the {3-¹⁴C}D(−)-3-hydroxybutyrate injected animals. These data suggest that D(−)-3-hydroxybutyrate behaves differently than glucose, being a more direct precursor for brain cholesterol biosynthesis and a less effective precursor for brain protein synthesis. Further studies ascertaining the specific activities of the precursors are necessary to quantitatite the respective contributions of D(−)-3-hydroxybutyrate and glucose to lipid and protein synthesis in the rat brain during development.     

Effect of (−)-hydroxycitrate upon the accumulation of lipid in the rat: I. Lipogenesis

The purpose of these investigations was to ascertain the effect of (−)-hydroxycitrate on the accumulation of lipid in the meal fed rat by examining the rates of lipogenesis after acute and chronic treatment. Oral administration of (−)-hydroxycitrate depressed significantly the in vivo lipogenic rates in a dose-dependent manner in the liver, adipose tissue, and small intestine. The hepatic inhibition was significant for the 8 hr period, when control animals demonstrated elevated rates of lipid synthesis. The kinetics of this reduction of in vivo hepatic lipogenesis were identical after acute or chronic administration of (−)-hydroxycitrate. However, in vitro rates of lipogenesis were elevated after chronic administration of (−)-hydroxycitrate for 30 days. Rats receiving (−)-hydroxycitrate consumed less food than the untreated controls; however, this decreased caloric intake was not responsible for the drug induced depression of hepatic lipogenesis, as shown by studies using pair fed rats. One of six papers presented in the symposium “Effect of Drugs on Lipid Metabolism,” AOCS Spring Meeting, New Orleans, April 1973.