Esterified Cholesterol Levels Research Articles

Bile acid synthesis and intracellular and extracellular cholesterol concentrations in isolated rat hepatocytes: the effect of dietary cholesterol

Bile acid synthesis in isolated hepatocytes prepared from rats given 1% cholesterol in the diet and incubated for 1 h in suspension was not increased compared to that in cells from control rats. When the hepatocytes were maintained in monolayer culture for 24 h, however, increased production of bile acid (× 2.5) was observed in the cholesterol-fed group. The amount of bile acid synthesised during incubation in suspension was significantly correlated with intracellular unesterified cholesterol levels, but showed no correlation with intracellular esterified or medium cholesterol concentrations after 1 h. Bile acid production in hepatocytes maintained in monolayer culture was also significantly correlated with the intracellular unesterified, but not esterified, cholesterol content. In addition, in this case, there was a significant correlation with the levels of both unesterified and esterified cholesterol found in the medium after 24 h. These results suggest that the amount of cholesterol available to liver cells from extracellular sources has a role in the regulation of bile acid synthesis in cholesterol-fed rats, while the concentrations of esterified cholesterol stored within the cells are not important in this process.

糖尿病患者の脂質代謝異常に関する研究

The components of apoprotein A-I and B-100 containing particles isolated from 59 diabetics and 56 non-diabetics were analyzed using selected-affinity columns with monoclonal antibodies. Total cholesterol (Ch), free cholesterol (FC), and cholesterol ester (CE) in apoprotein A-I particles from the diabetes group was significantly lower (p<0.01) than the non-diabetes group. However, Ch, FC, and CE in apoprotein B-100 particles were significantly higher (p<0.01). The ratio of CE/FC in apoprotein B-100 particles was 2.74±0.16 in diabetics and 1.76±0.08 in non-diabetics. Therefore, total elevated cholesterol levels in apoprotein B-100 particles of the diabetic group was due to elevated esterified cholesterol levels. Although the ratio of CE/FC in apoprotein A-I particles was not significant between diabetics and non-diabetics. In addition, the protein content in apoprotein A-I particles was not significant between diabetics and non-diabetics. The protein content in apoprotein B-100 particles on diabetes was significantly higher than non-diabetes. But the ratio of Ch/protein content in apoprotein A-I particles was lower in diabetics than non-diabetics, and the ratio in apoprotein B-100 particles was not significant between diabetics and non-diabetics. This data indicates that the components of apoprotein A-I and B-100 particles are different between diabetes and non-diabetes.

Liv-52 protection against beryllium toxicity in female albino rats

Toxic effects of beryllium salts on the reproductive organs of cyclic adult female albino rats have been studied. An attempt was made to overcome these effects using an Ayurvedic medicien Liv-52 (Himalaya Drug Co., Bombay). Liv-52-primed rats (1 mL/rat/day for 15 days) were exposed to beryllium nitrate intravenously and were sacrificed at different time intervals. At autopsy ovary, uterus, cervix, and vagina were processed for biochemical and histophatologic examination. Histoarchitecture of the ovary, uterus, cervix, and vagina revealed severe necrotic changes with beryllium nitrate treatment. Tissue glycogen content and the activity of alkaline phosphatase were inhibited significantly after beryllium treatment. Total and esterified cholesterol levels increased significantly in these organs when exposed to beryllium salts. However, a significant improvement was observed in the biochemical parameters and histoarchitecture of these organs when beryllium was injected into Liv-52-primed animals.

Biochemical and pathological features of a modified strain of Watanabe heritable hyperlipidaemic rabbits

A modified strain of heritable hyperlipidaemic rabbit has been produced by crossing male albino rabbits homozygous for low density lipoprotein receptor deficiency into a coloured commercial colony with strong breeding characteristics The genetic deficiency has been preserved in the resulting offspring through many generations. Litter numbers, live weight gains and energy intake are similar to normal rabbits. Free and esterified cholesterol in serum, and total cholesterol in very low density plus low density lipoproteins, are markedly increased in homozygote, but only slightly raised in heterozygote, animals. High density lipoprotein-cholesterols show an opposite trend but with less marked differences between the genetic strains. Liver total and esterified cholesterol levels were substantially increased in homozygotes, and the ability of liver membranes to bind human 125I-LDL was markedly reduced, owing to a reduction of the number of high-affinity binding sites. All animals with serum cholesterol values greater than 14 mmol/l at weaning developed extensive aortic atherosclerosis within 16 weeks. The early lesions had the histological appearances of fatty streaks and progressed to complicated disease at 6–12 months. A distinctive pattern of calcific arteriosclerosis, quite different from atherosclerosis, was observed in most aging heterozygote animals and was associated with extensive renal calcium deposition. Corneal arcus developed in some homozygotes but there was no evidence of cerebral atherosclerosis. We conclude that homozygotes of this modified strain can be used for macroscopic studies of the progression of aortic atherosclerosis in the first 4 months after weaning but after this period a combination of macroscopic and microscopic techniques are required. Heterozygotes are unsuitable for studies of this nature.

Hepatic cholesterol synthesis and esterification in rats after chronic ethanol feeding.

1. Chronic (5 weeks) alcohol-fed and isocaloric glucose pair-fed control rats had similar body weights, liver weights and liver protein contents. 2. Hepatic esterified cholesterol and triacylglycerol levels were two- to three-fold higher in alcohol-fed rats than in controls. 3. Hepatic cholesterol synthesis rates measured in vivo with 3H2O were significantly reduced in alcohol-fed rats. 4. Hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (NADPH) (EC 1.1.1.34) activity was increased and the apparent Km for 3-hydroxymethyl-3-glutaryl-CoA was decreased in alcohol-fed rats. 5. Hepatic acyl-CoA:cholesterol acyltransferase (cholesterol acyltransferase; EC 2.3.1.26) activity was significantly increased in alcohol-fed rats. 6. These results indicate that there is no direct relationship between 3-hydroxy-3-methylglutaryl-CoA reductase activity and sterol synthesis in liver of alcohol-fed rats.

Ｃｈｏｌｅｓｔｅｒｏｌ負荷マウスの血清および大動脈質体に及ぼす食餌性脂肪の影響 リノール酸摂取量との相関

The effects of dietary linoleic acid on serum lipids, lipid peroxides and aortic cholesterol were studied in mice fed a purified diet enriched with 5% cholesterol for a period of 14 weeks. The diet was supplemented with 10% coconut oil (Group I), lard (Group II), corn oil (Group III) or linoleic acid (Group IV) to give various levels of linoleic acid. After 4 to 12 weeks, the increment of serum total cholesterol was retained in the following order: group IV greater than III greater than II greater than I, which was the same order as the linoleic acid content in the diet. At week 14, the levels of serum free and esterified cholesterol, HDL-cholesterol, triglycerides and phospholipids were highest in group IV and lowest in group I. The serum lipid peroxide level was higher in the order of group IV greater than III greater than II greater than I. The ester ratio of cholesterol, the atherogenic index and LCAT activity were not significantly different among the four groups. Gallstone formation was markedly observed with higher dietary linoleic acid intake. Aortic cholesterol levels also increased in the same order as the dietary linoleic acid level: group IV greater than III greater than II greater than I. There were significant positive correlations between the aortic cholesterol level and all the serum lipid levels, and also the lipid peroxide level. All these findings indicate that under hypercholesterolemic conditions, excess dietary linoleic acid can increase serum lipids and lipid peroxide levels, resulting in lipid deposition in the aorta.(ABSTRACT TRUNCATED AT 250 WORDS)

γ-BHC- and Cythion-induced alterations in lipid metabolism in a freshwater catfish, Clarias batrachus, during different phases of its annual reproductive cycle

Specimens of either sex of the freshwater catfish Clarias batrachus were exposed to safe and sublethal concentrations of γ-BHC (2 and 8 ppm) and Cythion (1 and 4 ppm) for 4 weeks during different phases of the annual reproductive cycle. Their effects on various lipid fractions, viz., triglycerides (TG), phospholipids, free cholesterol, and esterified cholesterol, were studied in liver, plasma, gonads, and muscle. These pesticides suppressed the level of hepatic TG in females during the preparatory, prespawning, and postspawning phases, while during the spawning phase they stimulated an increase in its level. However, in males, these pesticides were ineffective in having any effect on liver TG during the spawning and postspawning phases, but in the preparatory phase, as with the female, they increased its levels, while in the prespawning phase they decreased liver TG levels. Hepatic phospholipid biosynthesis was impaired by γ-BHC but Cythion had no effect on it. Cholesterol biosynthesis as such appeared to be unaffected by these pesticides but the dynamics of free and esterified cholesterol levels were disturbed in response to Cythion and γ-BHC. These pesticides greatly reduced the mobilization of these hepatic lipids to gonads. Muscle lipids were least affected by these pesticides.

Dietary cholesterol and bile acid synthesis in isolated rat hepatocytes

Studies in vivo have shown consistently that bile acid synthesis is increased 2-Hold when rats are fed a diet high in cholesterol (Wilson, 1964; Beher et ul., 1970; Raicht et al . , 1975; Mathe & Chevallier, 1979). Previous experiments in our laboratory with isolated hepatocytes in vitro, however, have failed to show a significant increase in the amount of bile acid synthesized by cells from cholesterol-fed as compared with control rats (Botham & Boyd, 1983~) . To try to resolve this conflict we have investigated the effect of dietary cholesterol on bile acid production in isolated hepatocytes from rats fed the bile acid sequestrant. cholestyramine. I t was hoped that in these animals with a high rate of bile acid synthesis any increased caused by cholesterol feeding would become more apparent. We have also investigated the relationship between the amount of bile acid formed and the esterified and unesterified cholesterol content of the cells. Rats were given a diet (Botham & Boyd, 19836) containing 10% (w/w) olive oil or 10% (w/w) olive oil and 1 % (w/w) cholesterol for 10 days before the addition of cholestyramine to both diets. to allow cholesterol to accumulate in the liver. Hepatocytes were prepared (Botham rt al., 1980) 4 days after beginning cholestyramine feeding. The amounts of conjugated cholic, chenodeoxycholic and /j-muricholic acid synthesized over 3 h of incubation were measured using radioimmunoassays (Beckett et al., 1978, 1979, Botham PI ul., 1983). Cholesterol was determined using cholesterol oxidase (Richmond, 1973). Unesterified cholesterol levels in cells from cholesterol-fed rats ( I 1.5 f 1 . 1 pg/mg of protein) were not significantly different from those in control animals (14.9 f 3.1 pg/mg of protein) but esterified cholesterol levels were increased about 40-fold by cholesterol feeding (control 0.7 f 0.7pg/mg of protein, cholesterol-fed 35.8 f 21.3 pg/mg of protein), showing that rats fed cholestyramine for 4 days in addition to cholesterol still had substantially elevated hepatic cholesterol ester levels. Despite this fact, the total amount of bile acid (conjugated cholic + chenodeoxycholic + fi-muricholic acid) produced by hepatocytes from cholesterol-fed rats during 3 h of incubation was significantly decreased ( I .69 3.36 nmol/mg of protein) compared with that in cells from control animals (2.36 0.45nmol/mg of protein, P < 0.025). This surprising result may be explained by the relationship between bile acid production and the levels of esterified and unesterified cholesterol in the cells, shown

Reduced cholesterol 7α-hydroxylase activity in hypercholesterolemic hamsters. Preventive effect of a fruit-enriched diet

The influence of a fruit-enriched diet on cholesterol 7α-hydroxylase activity was determined in two types of hypercholesterolemic hamsters, hamsters which develop hypercholesterolemia with aging (FEC hamsters) and hamsters with hypercholesterolemia artificially induced by cholesterol feeding. Cholesterol 7α-hydroxylase activity was reduced in hypercholesterolemic hamsters, the decline reached 50% in the animals fed 0.1% cholesterol diet. Addition of fruits (apples) to the standard diet normalized the activity of cholesterol 7α-hydroxylase in FEC hamsters but in the animals receiving the cholesterol-enriched diet, a wide interindividual variation was observed in response to consumption of fruits. The hepatic accumulation of cholesterol was prevented in half of the animals but persisted at a variable degree in the others. The activity of cholesterol 7α-hydroxylase was negatively correlated with the levels of free and esterified cholesterol in the liver. These findings suggested that augmented levels of cholesterol in the liver can inhibit the conversion of cholesterol into 7α-hydroxycholesterol. The fruit-enriched diet can stimulate the 7α-hydroxylation of cholesterol probably by facilitating the supply of substrate for bile acid synthesis.

Changes in tissue lipid levels in the freshwater catfishClarias batrachus associated with the reproductive cycle

The levels of free fatty acid (FFA), monoglyceride (MG), diglyceride (DG), triglyceride (TG), phospholipid (PL), free cholesterol (CF) and esterified cholesterol (CE) were measured in the liver, plasma, ovary, abdominal fat and muscle during different phases of the annual reproductive cycle in femaleClarias batrachus. During the preparatory phase, hepatic lipogenic activity predominated over mobilization and consumption. In the prespawning season, an increased hepatic lipogenic activity was maintained, but lipids were transferred from the liver to the ovary. In the spawning phase, the diminished food intake, and enhanced caloric demand for spawning behaviour and activity limited hepatic lipogenic activity, and TG lypolysis was increased as was the production of more FFA. Maximum accumulation of vitellogenin, as reflected by maximum rise in ovarian PL titre was characteristic of this phase. Marked reductions in ovarian lipid occurred during the postspawning phase. In the resting phase, there was a recovery of lipogenic activity, but PL synthesis was still inhibited. In contrast to other investigated teleosts, there were extremely high level of FFA in liver, plasma, ovary and muscle throughout the annual reproductive cycle inC. batrachus. FFA appears to be the main lipid metabolite which had a very high turnover. As evidenced by the high TG content, abdominal fat seems to be the main fat depot, not the liver and muscle.

High density lipoprotein free cholesterol and other lipids in coronary heart disease.

The cholesterol and choline-containing phospholipid fractions of high density lipoproteins (HDL) were determined in healthy males and in male patients with coronary heart disease (CHD) to ascertain which HDL parameter or combined parameters possess the greatest discriminative power. The free cholesterol fraction (HDL-fc) was found to be the most significant discriminator between controls and males with CHD, the mean levels (+/- SEM) being 6.6 (+/- 0.9) and 4.4 (+/- 0.6) mg/dl, respectively. Classification of CHD patients and controls using one-variable discriminant function analysis (DFA) yielded an error rate of 27% for plasma HDL-fc. Two-variable DFA using both the HDL esterified cholesterol levels and the HDL-fc levels of controls and patients reduced the error rate to 11%. The results obtained in this study indicate a possible role for HDL-fc as a predictor of CHD risk.

Effect of Hypoxia on Lipid Accumulation in Cultured Fibroblasts from Normal Rabbit and Watanabe Heritable Hyperlipidemic Rabbit

We studied the effect of hypoxia on lipid accumulation in cultured fibroblasts from normal rabbits (normal fibroblasts) and in low density lipoprotein (LDL) receptor-negative fibroblasts from WHHL (Watanabe heritable hyperlipidemic) rabbits (WHHL fibroblasts). These cells were incubated in medium with normolipemic rabbit serum (NRS) or hyperlipemic rabbit serum (HRS). The cells were incubated in a humidified atmosphere of either 20% O2, 75% N2, and 5% CO2 (control cells) or 2% O2, 93% N2, and 5% CO2 (hypoxic cells).After 48h incubation of normal fibroblasts in medium with 20% NRS, free fatty acid (FFA) levels were increased slightly and the triglyceride (TG) level markedly in hypoxic cells. In the medium with 20% HRS, in addition to the increased FFA and TG levels, the free cholesterol level was increased slightly and the esterified cholesterol level markedly in hypoxic cells. Moreover, in WHHL fibroblasts, which lack LDL receptors, cellular lipid accumulation was also observed after 48h incubation in the medium with 20% HRS, and hypoxic incubation enhanced the cellular cholesterol and TG accumulation, as in normal fibroblasts.These results suggest that under hyperlipemic conditions, non LDL receptor-mediated uptake of lipoproteins plays a major role in cellular lipid deposition and that tissue hypoxia promotes lipid accumulation in peripheral cells by the LDL receptor-independent mechanisms.

Serum levels of coenzyme Q10 and lipids in patients during total parenteral nutrition.

Serum levels of coenzyme Q10 (CoQ10) as well as lipids were determined in patients during total parenteral nutrition (TPN). The mean CoQ10 levels (M +/- SD) were 0.77 +/- 0.30 microgram/ml for 108 normal subjects and 0.59 +/- 0.35 microgram/ml for 95 patients before TPN. The mean CoQ10 level of the patients decreased significantly to 0.35 +/- 0.23 microgram/ml one week after the start of TPN, and then remained almost unchanged during TPN for up to 6 weeks. When the patients receiving TPN (TPN patients) were grouped according to their clinical diagnoses, the mean CoQ10 level of patients with cancer was significantly lower than that of the other patients without cancer in 4 week therapy, but there was no difference in the levels between the patients with and without diseases of the gastrointestinal tract. Serum levels of total cholesterol (T-Chol) and esterified cholesterol in TPN patients also declined below their respective normal ranges, but not to the same extent in comparison to CoQ10. The levels of triglycerides (TG), phospholipids (PL), non-esterified fatty acids, low density lipoproteins, very low density lipoproteins, chylomicrons, and cholesterol in the high density lipoprotein fraction in serum of TPN patients were within their normal ranges. The levels of CoQ10 in TPN patients were correlative to those of T-Chol, TG, and PL, and decreased rapidly prior to the latter levels.

Subcellular distribution and developmental expression of cholesterol ester hydrolases in fetal rat brain cultures.

Cholesterol ester hydrolase activities previously have been identified in brain and linked to the production of myelin, which has very low levels of esterified cholesterol. We have studied two cholesterol ester hydrolase activities (termed the pH 6.0 and pH 7.2 activities) in cultures derived from 19- to 21-day-old dissociated fetal rat brains and in developing rat brain. In vivo the levels of both the pH 6.0 and pH 7.2 activities began to increase by about 10 postnatal days, reached maximal levels at 20 days (20 and 1.5 nmol/h/mg protein, respectively), and thereafter remained nearly constant (pH 6.0) or decreased somewhat before becoming constant (pH 7.2). In contrast, in the cultures the pH 6.0 cholesterol ester hydrolase activity was low until 21 days in culture (DIC; 20 nmol/h/mg protein), increased to a peak activity at 31 DIC (60 nmol/h/mg protein), remained high for 24 days, and finally decreased (18 nmol/h/mg protein at 63 DIC); the pH 7.2 cholesterol ester hydrolase activity was very low until 20 DIC, increased to a peak activity at 31 days (3 nmol/h/mg protein), and thereafter decreased to a lower level (2 nmol/h/mg protein) that was maintained for about 24 days before decreasing (0.7 nmol/h/mg protein at 63 DIC). Therefore, the time courses of appearance of both cholesterol ester hydrolase activities were delayed by 10-14 days relative to that seen in vivo, and the specific activities observed in the cultures were transiently two- to three-fold higher than in rat brain, but then declined to levels characteristic of whole brain homogenates.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial prostaglandins and lysosomal function during atherogenesis: I. Homogenates of Diet-induced Atherosclerotic Aortas of Rabbit

Homogenates of control and diet-induced atherosclerotic aortas of rabbit were prepared and the levels of DNA, protein, free and esterified cholesterol, and six enzymes known to be associated with various subcellular organelles [ N-acetyl-β-glucosaminidase, β-galactosidase ( lysosomes); cytochrome oxidase ( mitochondria); neutral α-glucosidase ( endoplasmic reticulum); 5′-nucleotidase ( plasma membrane); catalase ( peroxisomes)] were compared between control and atherosclerotic preparations. The levels of prostaglandins I 2, E 2, and F 2α, based on DNA, also were measured by radioimmunoassay. Atherosclerotic aortas were significantly enriched in catalase activity (440%) and in each of the acid hydrolases (395 and 630%), based on DNA, as well as in free (630%) and esterified cholesterol (930%), based on tissue wet weight, compared to control aortas. The control level of prostaglandin I 2 was 10-fold higher than that of prostaglandin E 2, which was 3-fold higher than that of prostaglandin F 2α. Prostaglandin I 2 doubled in amount with advanced atherosclerosis, while prostaglandin E 2 increased over 10-fold, resulting in twice the amount of prostaglandin I 2 than E 2 in advanced atherosclerosis; the level of prostaglandin F 2α did not appear to change significantly with atherosclerosis. Increased levels of prostaglandins I 2 and E 2 were correlated significantly with increased aortic total cholesterol content (based on DNA) but not increased serum cholesterol levels. N-Acetyl-β-glucosaminidase activity also was correlated significantly to aortic total cholesterol content and β-galactosidase activity, as well as to the level of prostaglandin I 2; in contrast, N-acetyl-β-glucosaminidase was not significantly correlated to prostaglandin E 2. The association of prostaglandins I 2 and E 2 with aortic total cholesterol suggests the participation of prostaglandins in the response of arterial cells to lipid accumulation in atherosclerosis. The specific association of aortic prostaglandin I 2 level and N-acetyl-β-glucosaminidase activity further suggests a possible role for this prostaglandin during arterial intralysosomal cholesterol accumulation.

Thymic Epithelial Cells of Severely Undernourished Mice: Accumulation of Cholesteryl Esters and Absence of Cytoplasmic Vacuoles

The thymic epithelium was compared in weanling male and female CBA/J mice when fed ad libitum and when subjected to severe food intake restriction for 14 days. The restriction protocol elicited predominantly a metabolic response to caloric deficit rather than to protein deficiency. Electron microscopy revealed intracytoplasmic accumulations of large, circular, homogeneously electron-dense profiles (with no limiting membrane) in a high proportion of cortical and medullary epithelial cells of thymuses from restricted mice, but not from controls. The electron-dense material was not preserved in the absence of osmium. Thin-layer chromatography (TLC) indicated elevated levels of free and esterified cholesterol, particularly the latter, in whole thymus extracts of restricted mice. Measurements of total cholesterol levels in the thymic extracts were consistent with the results obtained by TLC. In addition, cryostat sections of thymuses from restricted mice, but not from controls, exhibited numerous stained foci throughout the cortex and medulla when treated with oil red O (a general neutral lipid stain) or by the Schultz procedure which is specific for cholesterol. Collectively the results suggest accumulations of cholesteryl esters, together with some free cholesterol, as non-membrane-bound droplets in the cytoplasm of thymic epithelial cells of undernourished mice. It is also of interest that the lipid-laden epithelial cells exhibited none of the cytoplasmic vacuoles observed in controls and believed to be important in thymic hormone secretion. This work provides the first direct evidence of thymus epithelial abnormalities in severe protein-energy malnutrition.

Effect of hypoxia on cholesterol accumulation in cultured rabbit aortic smooth muscle cells

We studied the effect of hypoxia on cholesterol accumulation in cultured rabbit aortic smooth muscle cells, which were incubated in a medium with normolipemic rabbit serum (NRS) or hyperlipemic rabbit serum (HRS). The cells were incubated in a humidified atmosphere of either 20% O2, 75% N 2 and 5% CO 2 (control cells) or 2% O 2, 93% N 2 and 5% CO 2 (hypoxic cells). In a medium containing 20% NRS, the free cholesterol level of hypoxic cells was only a little higher than that of control cells, and there was no significant difference in esterified cholesterol content. On the other hand, in a medium containing 20% HRS, the free cholesterol level was slightly higher and the esterified cholesterol level was markedly higher in hypoxic cells compared with control cells. These results show that hypoxia promotes the accumulation ,of cholesterol, especially as ester, in smooth muscle cells cultured with hyperlipemic serum. These in vitro experiments indicate that hypoxia in the arterial wall associated with hyperlipidemia may play an important role in atherogenesis, although the precise mechanism remains unclear.

Reduction of Plasma Lecithin—Cholesterol Acyltransferase Activity by Acute Magnesium Deficiency in the Rat

Weanling Wistar rats were pair-fed for 8 days control and magnesium-deficient diets. Acute magnesium deficiency increased plasma triglycerides and free cholesterol levels and decreased esterified cholesterol levels. The plasma activity of lecithin—cholesterol acyltransferase was markedly diminished in fasting magnesium-deficient rats (54% reduction) and plasma high density lipoprotein (HDL) free cholesterol was significantly increased in the HDL fraction. The results of this study showing that dietary magnesium affects the activity of the enzyme involved in the esterification of free cholesterol to cholesterol ester provide a possible basis for the reduced plasma cholesterol esterification and hyperlipidemia associated with acute magnesium deficiency.

The low-density lipoprotein pathway of cultured leydig tumor cells ultilization of low-density lipoprotein-derived cholesterol for steroidogenesis

We have previously reported that low-density lipoprotein (LDL) enhances and prolongs steroidogenesis in human choriogonadotropin (CG)-stimulated Leydig tumor cells (MA-10). The studies described herein elucidate the mechanisms by which LDL increases human CG stimulated steroidogenesis. Our results show that the MA-10 cells express the classic LDL pathway. LDL is bound to specific surface binding sites which are regulated by the level of intracellular cholesterol. The cellular processing of bound LDL is temperature-dependent and is inhibited by blocking lysosomal function. By using an LDL derivative in which the core cholesteryl esters have been replaced with [3H]cholesteryl linoleate, we show that LDL cholesterol is rapidly utilized for steroid hormone synthesis. The utilization of LDL cholesterol quantitatively accounts for the LDL-induced augmentation of steroidogenesis. We also show that the addition of LDL to human CG-stimulated MA-10 cells maintains cellular free and esterified cholesterol levels and increases progesterone biosynthesis. The addition of LDL does not, however, affect the cellular utilization of preexisting cholesterol stores for steroidogenesis.

Effect of excess dietary cystine on the biodynamics of cholesterol in the rat

Ingestion of an excess level of 5% of l-cystine produced in the rat the following effects: total cholesterol concentration was increased in the plasma (from 102 to 165 mg/100 ml) and body (from 133 to 184 mg/100 g) whereas esterified cholesterol level was decreased in the liver (from 151 to 59 mg/100 g). The absorption coefficient of dietary cholesterol and the external secretion (elimination in the feces of cholesterol biosynthetized in the intestine) were not changed. The urinary and fecal excretion, transformation into bile acids and input into the plasma of cholesterol biosynthesized in the organs (internal secretion) were enhanced. The elevation of cholesterol synthesis in the cystine-treated rats was explained by an increased hepatic cholesterol synthesis. Hence, addition of cholesterol, which inhibits hepatic cholesterol synthesis, to the cystine-enriched diet led to a significant decrease (by 50%) in cholesterol synthesis. Moreover, when the absorption coefficient of dietary cholesterol was decreased (replacement of lard by tristearin) cholesterol synthesis of the cystine-fed rats was increased. Thus, such a relationship, previously demonstrated for rats in which the intestine was the major source of biosynthesized cholesterol, exists also when the liver becomes more important in the synthetic process.