Metabolism of squalene in human fat cells. Demonstration of a two-pool system

Human adipose tissue has been shown to contain exceptionally high concentrations of squalene. In the present experiments, it was shown that most of adipose tissue squalene is located in the fat cells. Of this squalene, 80% is located in the central neutral lipid droplet and 20% is bound to the microsomal membranes. Upon incubation of isolated fat cells with radiolabeled substrates, both the microsomal and the droplet squalene became labeled. The specific activity of microsomal squalene increased faster than that of droplet squalene. In addition, the microsomal squalene quickly equilibrated to a maximal specific activity, whereas the droplet squalene showed a steady increase in specific activity. These observations indicate rapid turnover of microsomal squalene and slow turnover of droplet squalene. Moreover, they reflect intracellular transfer of labeled squalene from microsomes to the lipid droplet. During a 3-hour incubation of fat cells with labeled substrates, 90% of the newly formed labeled squalene was transferred to the lipid droplet and only 10% was converted into cholesterol. The results demonstrate that adipocyte squalene can be segregated anatomically and functionally into two distinct pools: a small metabolically active pool in the microsomal membranes where squalene is synthesized and a large metabolically inactive pool in the fat droplet where squalene is stored. The intracellular transfer of de novo synthesized squalene into the fat droplet of fat cells is one mechanism of squalene accumulation in adipose tissue.

Fate of intravenously administered squalene in the rat

To investigate the metabolism of serum squalene rats were given intravenously serum or isolated lipoprotein containing [3H]squalene and [14C]cholesterol. Labeled squalene disappeared multiexponentially from serum and the rate of disappearance was consistently faster than for [14C]cholesterol. [3H]Squalene given by injection did not accumulate in tissues, but was rapidly cyclized to sterols, resulting in the labeling of serum methyl sterols and cholesterol as well as biliary and fecal sterols and bile acids. Independent of the form of administration, the fractional conversion of squalene to serum cholesterol was less than one. This was caused by the fact that [3H]squalene was eliminated initially more rapidly than serum [14C]cholesterol in the feces and was converted to a greater extent than serum cholesterol to bile acids, whereas both labels were eliminated in parallel as neutral sterols. The results support the role of newly synthesized hepatic cholesterol as the preferred substrate of bile acid synthesis.

Cholesterol absorption, elimination and synthesis in coeliac disease

Hypocholesterolaemia and high faecal elimination of cholesterol was explored by measuring the percentage of cholesterol absorbed, faecal steroids, serum cholesterol and dietary cholesterol in patients with coeliac disease before and after a gluten free diet. From these data, the total and endogenous flux of cholesterol into the gut and the amount of cholesterol absorbed could be calculated. The mean faecal bile acid excretion was normal, but faecal endogenous steroids and thus faecal total steroids, and the cholesterol synthesis, were increased in the patients. The percentage of cholesterol absorbed was quite low (15.1 +/- 2.1 (SEM) v. 34.1 +/- 2.5 in the controls), and it was attributable to a mucosal damage in the upper small intestine, suggesting that this played a primary role in the high faecal sterol loss. However, the influx of endogenous cholesterol into the gut had increased, so that in absolute terms the absorption of cholesterol was low only inconsistently. The gluten-free diet caused the opposite changes in the absorption percentage and influx of cholesterol into the gut, while the amount of cholesterol absorbed was only insignificantly increased. Serum cholesterol was significantly correlated with the cholesterol absorbed (r = 0.36; P less than 0.01), faecal endogenous steroids (r = -0.30; P less than 0.05), and cholesterol synthesis (r = -0.29; P less than 0.05). Furthermore, the rise in serum cholesterol during the gluten-free diet correlated negatively with the changes in cholesterol (r = -0.55; P less than 0.05) and bile acid (r = -0.77; P less than 0.01) synthesis. These associations and the lack of correlations between the amounts of cholesterol absorbed and synthesized suggest that the serum cholesterol level and regulation of cholesterol synthesis are interrelated in coeliac disease.

In vitro synthesis of triglycerides and cholesterol in human gallbladder mucosa

Triglyceride and sterol synthesis was investigated in vitro in the gallbladder mucosa from control subjects and patients with acalculous cholesterolosis. The incorporation rate of 14C-acetate was 1.6 +/- 0.2 nmol/g/h into cholesterol (sum of squalene, methyl sterols, and cholesterol) and 5.7 +/- 0.8 nmol/g/h into triglycerides. The rates were significantly correlated with each other (r = 0.667). The conversion of 3H-mevalonate into cholesterol (49 +/- 10 nmol/g/h) and triglycerides (4.7 +/- 1.2 nmol/g/h) indicated a high activity in the postmevalonate cholesterol synthesis and an active shunt pathway of mevalonate metabolism. The synthesis rates of cholesterol, triglycerides, and sterol esters were closely interrelated, were unaltered in cholesterolosis, and were not correlated with the serum, biliary, and mucosal lipid concentrations. Thus, despite marked lipid accumulation the lipid synthesis proceeds effectively in the gallbladder mucosa with cholesterolosis.

Effects of neomycin alone and in combination with cholestyramine on serum methyl sterols and conversion of acetate and mevalonate to cholesterol

Serum free methyl sterols (cholesterol precursors) and the acetate-mevalonate test (the 14C/3H ratio in serum cholesterol after an intravenous injection of a 14C-acetate-3H-mevalonate mixture) were studied in hypercholesterolaemic patients treated with neomycin, cholestyramine or their combination so as to show whether the two tests could detect changes in cholesterol synthesis (measured with faecal steroids). During a 2-week neomycin treatment the ratio increased (+55%) proportionately with the increase in faecal steroids (+29%), the decrease in serum cholesterol (-20%) being negatively correlated with the change in serum methyl sterols. After 1 to 2 years on neomycin, faecal steroids were still high and serum cholesterol low. The ratio had fallen, however, below the initial level, the respective proportionate decrease in methyl sterols being insignificant. In cholestyramine-treated patients a marked increase in cholesterol synthesis (171% increase in faecal steroids) was reflected in a proportionate increase in the ratio (+196%) and serum methyl sterols (+134%). Inclusion of neomycin in the cholestyramine treatment increased faecal steroids (overall increase 206%) and further decreased serum cholesterol (from -25% to -38%) but tended to reduce the ratio and serum methyl sterols. The findings suggest that neomycin activates the pre- and post-mevalonate steps of cholesterol synthesis.

Lipid composition of bile and gallbladder mucosa in patients with acalculous cholesterolosis

To investigate pathogenetic factors of cholesterolosis of the gallbladder, the lipid composition of both the hepatic and gallbladder bile and gallbladder mucosa were compared with each other in 6 patients with and 5 patients without acalculous cholesterolosis. The molar percentage of biliary cholesterol and total bile acid pattern were similar in the two groups. Of the biliary cholesterol precursors, methyl sterols, but not squalene, correlated closely with cholesterol both in the hepatic (r = 0.901) and gallbladder bile (r = 0.747). Methyl sterols, expressed either per cholesterol or bile acids, were higher and squalene was lower in the gallbladder bile than in the hepatic bile. In addition, methyl sterols were increased in the hepatic and gallbladder bile of the patients with cholesterolosis, as if the hepatic production of these precursors had been enhanced--probably as a consequence of altered hepatic cholesterol synthesis. In cholesterolosis the gallbladder mucosa was characterized by a marked increase in triglycerides and significant elevations of the esterified sterols and free methyl sterols. The esterification degrees of sterols, which were consistently higher for methyl sterols than for cholesterol, were closely correlated with the respective mucosal sterol concentrations. The methyl sterols/cholesterol ratio in the bile correlated significantly with mucosal free and esterified methyl sterols, esterified cholesterol, and the methyl sterols/cholesterol ratio. The data suggest that free sterols can be transferred from the bile to the gallbladder mucosa, and that altered hepatic cholesterol synthesis is associated with the development of the cholesterolosis of human gallbladder.

Diurnal variation of cholesterol precursors squalene and methyl sterols in human plasma lipoproteins

Animal cholesterol synthesis shows a marked diurnal variation, a phenomenon, at the moment, not known to occur in man. Since cholesterol precursors in serum reflect overall cholesterol synthesis in many conditions, a 24-hr profile of squalene and methyl sterols was studied in plasma lipoproteins in order to demonstrate whether these cholesterol precursors could exhibit a diurnal cycling in healthy human subjects. During the 24-hr period, lipoproteins of density < 1.006 g/ml transported 30-50% of the plasma squalene. Free methyl sterols were found mainly in low density lipoproteins (LDL) and esterified methyl sterols in LDL and high density lipoproteins (HDL). Postprandial hyperlipidemia at noon was associated with an inconsistent increase of the squalene and free methyl sterol concentrations in the lipoproteins of density < 1.006 g/ml. In terms of micro g per mg of cholesterol, the precursor contents were, however, low in each lipoprotein during the daytime. During the night and early morning, the values were several times higher. Thus the peak plasma squalene and methyl sterol contents occurred at midnight and 4 am. The highest variation was found for squalene in the density class < 1.006 g/ml and for lanosterol and diunsaturated dimethyl sterol in LDL and HDL. For different methyl sterols, the mean diurnal variation was 3.5- to 6.9-fold in LDL, 2.0- to 4.5-fold in HDL, and 2.6- to 3.6-fold in the density class < 1.006 g/ml. The respective values for squalene were 2.2, 1.4, and 2.9. Esterified methyl sterols varied slightly in the density class < 1.006 g/ml only, and the percentage esterification exhibited a diurnal fluctuation that was the reciprocal of that of free methyl sterol levels. The rapid and marked diurnal fluctuation of squalene and free methyl sterols in plasma lipoproteins suggests that these precursors are metabolized on and off lipoproteins. The variation is most likely caused by changes in cholesterol synthesis, inferring that circadian rhythm also regulates human cholesterol production.-Miettinen, T. A. Diurnal variation of cholesterol precursors squalene and methyl sterols in human plasma lipoproteins.

HDL cholesterol and beta-adrenoceptor blocking agents in a 5 year multifactorial primary prevention trial

1 Serum HDL cholesterol measured at the end of a 5 year multifactorial primary prevention trial, aimed to reduce risk factor levels and incidence of ischaemic heart disease, revealed quite low values in drug-treated subjects. 2 Analysis of subgroups treated with beta-adrenoceptor blocking agents (mainly pindolol) alone or in different combinations with diuretics showed inconsistent effects of beta-adrenoceptors blockers on serum HDL cholesterol. HDL cholesterol levels in patients treated with pindolol with or without a diuretic were not different from those of the risk-free control group. 3 Subjects on combined beta-adrenoceptor blocker-hypolipidaemic treatments had lower HDL-cholesterol than those on hypolipidaemic agents alone. 4 Withdrawal of pindolol at the end of the trial caused a small but significant increase in serum HDL cholesterol in a small subgroup of mildly hypertensive patients. Thus, pindolol appears to have slightly reduced serum HDL cholesterol but the relevance of this small decrease on the incidence of ischaemic heart disease is questionable.

Hepatic copper in primary biliary cirrhosis: biliary excretion and response to penicillamine treatment

Excessive hepatic copper accumulation occurs in long-lasting cholestatic liver disorders especially in primary biliary cirrhosis. As in Wilson's disease, penicillamine has recently been introduced for the treatment of primary biliary cirrhosis. In Wilson's disease there is decreased biliary excretion of copper. The present study shows that as compared with controls the biliary excretion of copper is not decreased in primary biliary cirrhosis; instead it may be increased in some patients. However, when compared with high hepatic copper concentration biliary copper excretion was low. In contrast with copper, biliary secretion of bile acids was decreased in eight of the 17 patients. Treatment with oral penicillamine (600 mg/day) for one year resulted in a significant decrease of hepatic copper concentration, but had no consistent effect on the biliary excretion of copper or on the amount of histologically stainable orcein-positive copper-binding protein. The results suggest that excessive hepatic copper accumulation in primary biliary cirrhosis may not be primarily caused by a decreased biliary excretion, or that a new equilibrium is achieved in advanced primary biliary cirrhosis. D-penicillamine appears to improve significantly the biliary excretion of bile acids.

Effect of probucol on cholesterol synthesis, plasma lipoproteins and the activities of lipoprotein and hepatic lipase in the rat

The postheparin plasma lipoprotein lipase (LPL) activity and plasma HDL and LDL cholesterol concentrations, decreases significantly during probucol treatment of the rat. The reduction of the LPL activity obviously took place in adipose tissue. The activity of hepatic lipase and the in vitro synthesis of cholesterol in the liver or isolated jejunal villous cells were unaffected by the probucol treatment. Plasma triglyceride and VLDL cholesterol concentrations remained similar in the control and probucol groups despite the difference in the LPL activity, whereas the esterified VLDL cholesterol level was significantly reduced in the probucol group. The results suggest that the HDL lowering action of probucol is contributed by the reduced LPL activity probably via impaired VLDL metabolism.

Comparison of different components in the fractional conversion of mevalonate to cholesterol with cholesterol synthesis and serum methyl sterols

Serum squalene and methyl sterols (cholesterol precursors), and the fractional conversion of mevalonate to cholesterol (FCM) were determined after an i.v. injection of a labelled mevalonate-labelled cholesterol mixture in fifteen studies in eleven subjects with varying cholesterol synthesis rates (sterol balance values), including three cases with ileal dysfunction. FCM was divided in two components, FCM I and FCM II, hypothesised to represent rapidly and slowly mixing components of newly formed cholesterol, respectively. Cholesterol synthesis ranged from 1.42 to 8.75 mmol day-1 and FCM from 0.352 to 0.857. The synthesis rate was correlated with FCM, with FCM II, weakly or not at all with FCM I, highly significantly with serum methyl sterols and insignificantly with serum squalene. However, within the fairly narrow normal synthesis limits (less than 3.3 mmol day-1) the synthesis rate was not correlated significantly with FCM. Despite a marked range of obesity and a highly significant correlation between the synthesis and body weight only FCM II was correlated with body weight in subjects without ileal dysfunction. The findings suggest that FCM, and its components FCM I and FCM II reflect weakly the total cholesterol synthesis rate, and the rapidly and slowly mixing portions of newly formed cholesterol, respectively.

Biliary lipids, faecal steroids, and liver function in patients with chronic active hepatitis and primary biliary cirrhosis: significance of hepatic orcein-stained complexes

Biliary lipids, faecal steroids, and serum bile acids were studied in patients with chronic active hepatitis and primary biliary cirrhosis. The results were correlated with excretory and parenchymal liver function tests and with the presence or absence of orcein-positive copper-protein complexes in histological liver specimens. In general, faecal bile acids, but not neutral and total sterols, correlated negatively with the percentage of biliary cholic acid, serum cholesterol, and serum bile acids and positively with the percentage of biliary deoxycholic acid. In orcein-positive subjects-indicative of long-standing cholestasis-the bile was undersaturated with cholesterol, biliary deoxycholic acid was subnormal, cholic acid correspondingly increased, and serum cholesterol and bile acids were raised. Only patients with marked impairment of both excretory and parenchymal liver functions had a decreased output of neutral sterols, bile acids, and total steroids, and, thus, low bile acid and cholesterol synthesis. The findings indicate that mild disturbances in parenchymal liver function infrequently cause major changes in cholesterol metabolism, while abnormalities in secretory liver function-in orcein-positive subjects especially-are frequently associated with proportionate changes in parameters of cholesterol metabolism.

Effect of probucol on the activity of postheparin plasma lipoprotein lipase and hepatic lipase

The effect of discontinuation of long term (34-56 months) probucol treatment on serum lipids, lipoproteins and on the activity of postheparin plasma lipoprotein and hepatic lipase ahs been studied in 10 healthy males participating in a primary prevention programme of coronary heart disease. A significant increase was observed in the activity of postheparin plasma lipoprotein lipase, in the total serum cholesterol concentration and in the serum concentrations of high density lipoprotein (HDL) cholesterol, HDL phospholipids and apoprotein AI after withdrawal of the drug No changes were seen in the serum triglyceride levels or in the activity of postheparin plasma hepatic lipase. The activity of postheparin plasma hepatic lipase tended to correlate with the serum concentration of HDL. No correlations were present between the individual changes in the serum levels of HDL and in the activity of postheparin plasma triglyceride lipases.

Lack of serum cholesterol-lowering effect of skimmed milk and butter milk under controlled conditions

The effects of skimmed milk and butter milk on the plasma concentration of cholesterol, triglyceride and high density lipoprotein cholesterol were studied in voluntary male prisoners under carefully controlled conditions. No significant differences were observed in the serum lipid or lipoprotein levels between the groups ingesting the control diet and the diets containing 2.71 of skimmed milk or 2.01 of butter milk per day for 3 weeks.

Thin-layer and gas--liquid chromatographic identification of neutral steroids in human and rat feces

Natural steroids from rat and human feces were fractionated by sequential thin-layer chromatography (TLC) on Florisil, silica gel, and silver nitrate-impregnated silica gel and analyzed by gas--liquid chromatography (GLC). Cholesterol, coprostanol, and coprostanone accounted for more than 95% of the endogenous neutral steroid in human feces, the remainder being predominantly cholestanol. In addition, evidence was obtained for the presence in human feces of trace amounts of epicoprostanol and cholestanone. In rat feces, several cholesterol precursors that probably originated in the skin (and were ingested during fur=licking) were detected in relatively large amounts, accounting for as much as 27% of the total fecal neutral steroids, whereas these steroids were quantitatively trivial in human feces. As with cholesterol, the major dietary plant sterols (sitosterol, campesterol, and stigmasterol) were converted by intestinal bacteria to the corresponding coprostane and ketonic derivatives during intestinal transit in both human beings and rats. This combined use of TLC and GLC provided for the separation of steroids of endogenous and dietary origin that could not be resolved by either system alone. A majority of the fecal steroids could be tentatively identified by their chromatographic behavior in different TCL systems and on GLC, even when reference standards were unavailable.

Origins of fecal neutral steroids in rats

The origins of rat fecal neutral steroids were studied in male and female animals fed a sterol-free diet and maintained in an isotopic steady state. The specific activity of fecal cholesterol was found to be consistently lower than that of plasma cholesterol and of the fecal bile acids, indicating that a considerable portion of the fecal neutral steroids was derived from cholesterol not in equilibrium with the rapidly exchangeable pool of body cholesterol. This non-exchanging fraction of neutral steroids was larger in male than in female rats; it appeared to have at least two origins: skin surface lipids licked off fur, and sterols newly synthesized by the intestinal mucosa and secreted into the gut lumen. When the ingestion of skin sterols rich in cholesterol precursors was minimized, the proportion of the non-exchanging fraction of fecal neutral sterols fell somewhat, but the output of cholesterol precursors dropped markedly. This suggests that a significant portion of the non-exchanging fecal cholesterol fraction originated in the intestinal wall by secretion. It can be concluded that the fecal neutral steroids of rats originate primarily from three sources: 1) de novo cholesterol synthesis by the intestinal mucosa, 2) ingested dietary, skin, and fecal sterols, and 3) a rapidly exchangeable cholesterol pool excreted through bile, the intestinal wall, or both.

Cholesterol synthesis and storage in adipose tissue

A markedly-high cholesterol production characterizes human obesity. So far, the site of origin of this extra synthesis has not been defined, even though the liver may play an important role. A marked expansion of adipose tissue in obesity raises a question on the local cholesterol synthesis, particularly because this organ can store a lot of cholesterol and its precursors, methyl sterols and squalene particularly. Some aspects of cholesterol synthesis and storage in adipose tissue will be dealt with in this paper. Available data have demonstrated that human fat tissue is capable of synthesizing cholesterol at a low rate.

Squalene and sterol synthesis in isolated small-intestinal cells of the rat

To compare the synthesis rate of cholesterol in different cells of the small intestine, isolated villous and crypt cells were incubated with a mixture of 14C-acetate and 3H-mevalonate in the presence of unlabeled carriers. The synthesis rate of squalene (includes the portion converted to sterols) from acetate was tenfold higher in the crypt than villous cells. The synthesis rate of squalene from mevalonate and the cyclization rate of squalene (the portion found in sterols) were about twofold higher in crypt than in villous cells. The conversion of acetate to squalene was correlated with that to fatty acids in the crypt cells only (r = 0.823), and the ratio of the two synthesis rates (squalene/fatty acids) was threefold higher in crypt than in villous cells. Despite the significant differences in the synthesis rates of squalene and sterols the concentrations of squalene and methyl sterols were similar in the two cell types. THe cholesterol content was, however, consistently higher in villous than in crypt cells, but the concentration was not correlated with the synthesis of squalene in the two cell types. The appearance of labeled squalene was clearly lower than that of labeled sterols in the lipoprotein-free incubation medium, but no differences were found between villous and crypt cells.

Diurnal variation of LDL and HDL cholesterol

Determination of a 24-hour lipoprotein lipid profile on a mixed diet showed a typical increase in VLDL (includes chylomicrons) lipids following food intake in normal subjects. The change was less marked or absent in patients with jejuno-ileal by-pass and after cholestyramine treatment of a case with post-ileal-resection diarrhoea. Triglycerides of other lipoproteins did not fluctuate very much but free and esterified cholesterol of LDL and HDL showed a significant diurnal variation: lowest values were seen early in the morning followed by an increase before breakfast, with the highest levels during the afternoon in most cases. No clearcut precursor-product relationship could be seen between VLDL and LDL or HDL, yet the rhythmic changes in the VLDL levels and/or in cholesterol synthesis may be causally associated with the diurnal variation of cholesterol in LDL and HDL.

Effect of long-term antihypertensive and hypolipidemic treatment on high density lipoprotein cholesterol and apolipoproteins A-I and A-II

The concentrations of total serum cholesterol and triglycerides and serum HDL cholesterol, triglycerides and apoproteins A-I and A-II were measured in 119 men after 4 years of active participation in a multifactorial primary prevention trial of coronary heart disease. No difference was observed in total serum cholesterol, triglycerides, HDL lipids or apoproteins between the control subjects without medication and the men treated with antihypertensive drugs (beta-blockers alone or in combination with thiazides). The concentration of HDL cholesterol was significantly lower and that of apoprotein A-II significantly higher in the individuals treated with clofibrate than in the controls. On the other hand, the levels of both HDL cholesterol and apoprotein A-I were lower in the men treated with probucol than in the controls, whereas that of A-II was within the control limits. The ratio HDL cholesterol/apoprotein A-I was subnormal in all 3 groups treated with lipid-lowering drugs, as if the treatment had lowered the cholesterol saturation of the HDL fraction. The levels of HDL cholesterol and apoprotein A-I were negatively correlated with the length of the treatment in subjects treated with probucol but not in the other groups. These results suggest that in long-term use, probucol and possibly clofibrate lower both the concentration and the cholesterol/apoprotein ratio of the HDL fraction.

Phytosterolaemia, xanthomatosis and premature atherosclerotic arterial disease: a case with high plant sterol absorption, impaired sterol elimination and low cholesterol synthesis

A fourth case is described in which phytosterolaemia, earlier diagnosed as familial hypercholesterolaemia, was associated with normocholesterolaemia, hypersplenism and premature atherosclerotic arterial disease requiring a three-vessel coronary bypass at the age of 29 years. During a follow-up of 5 years 22-26% and 27-30% of serum and bile sterols were plant sterols, respectively. In addition to campesterol and beta-sitosterol, stigmasterol and a fourth major plant sterol, tentatively identified as avenasterol, were found in bile, and in free and esterified forms in all serum lipoproteins. Analysis of faecal steroids and measurement of biliary lipid secretion indicated that in addition to enhanced absorption of plant sterols their decreased biliary secretion contributed to the development of phytosterolaemia. Impaired biliary cholesterol secretion was compensated for by a markedly reduced cholesterol but normal bile acid synthesis and resulted in bile undersaturated with respect to cholesterol, in a reduced intestinal cholesterol pool and in a very low faecal excretion of cholesterol as neutral sterols. Cholestyramine brought about a modest increase in cholesterol elimination as bile acids, increased cholesterol synthesis as evidenced by the sterol balance value and the increased cholesterol precursors squalene and methyl sterols in plasma and bile, and reduced the plasma cholesterol by 21% and plant sterols by 16%, but had no effect on the biliary composition of main sterols.

Squalene, methyl sterol, and cholesterol levels in human organs. Postmortem analysis of their distributions

The postmortem tissue distribution of cholesterol precursors, squalene, and methyl sterols was quantitated in ten human subjects by the use of gas-liquid chromatography. Five methyl sterol subfractions were found, with each organ having a pattern of its own. The mean esterification percentage of the methyl sterol mixture tended to correlate with the methyl sterol concentration and was higher than that of cholesterol in each tissue; the ester percentage was lowest for a diunsaturated dimethyl sterol and highest for a monounsaturated dimethyl sterol. The squalene levels were very high in adipose tissues, while methyl sterols concentrated in organs that produce little cholesterol. The levels in cholesterolgenic tissues were not very high. Squalene level was not correlated with methyl sterol or cholesterol levels in any organs, while methyl sterol and cholesterol levels were highly significantly correlated in the gallbladder wall.

A lack of esterification of lanosterol and other methyl sterols in human serum in vitro

Human serum contains small amounts of free and esterified cholesterol precursors, such as lanosterol and other methyl sterols. Incubating the serum for 24 h at room temperature without and with different additions of free methyl sterols was not followed by any detectable esterification of these sterols during the subsequent 24 h incubation period, though the amount of cholesterol esters was markedly increased. [3H]dihydrolanosterol added to serum was not esterified in any lipoprotein fraction either, whereas the [14C]cholesterol added was found to be esterified during the 24 h incubation period. The lack of methyl sterol esterification in vitro suggests that these sterols are not proper substrates for serum lecithin: cholesterol acyltransferase and that esterified serum methyl sterols originate from tissues.

Relationships between serum lipids and malabsorption of bile acids, neutral sterols, and fats in exocrine pancreatic insufficiency

The relationship between serum lipids, fecal steroids, and fecal fat was studied in nine men with exocrine pancreatic insufficiency due to chronic pancreatitis. The mean fecal bile acid and fat outputs were significantly increased, the neutral sterol excretion was within normal limits, and total elimination and synthesis of cholesterol were slightly increased. A positive correlation between fecal fat and neutral sterols suggests that the patients actually had cholesterol malabsorption and that the normal neutral sterol excretion was apparently the result of a low biliary cholesterol secretion. In view of the fairly small increase in cholesterol elimination, the serum cholesterol level was surprisingly low, indicating that malnutrition may have limited compensatory increase in cholesterol synthesis. Serum triglycerides were negatively correlated with fecal fat. Thus, severe malabsorption apparently also limited the triglyceride production.

Effects of neomycin alone and in combination with cholestyramine on serum cholesterol and fecal steroids in hypercholesterolemic subjects

Effects of neomycin were studied on serum cholesterol and fecal steroids in hypercholesterolemic patients during a short treatment period (4 wk) and a long treatment period (16 mo), using small (1.5 g/d) and large (up to 6 g/d) doses alone and in combination with cholestyramine. In the short-term low-dose study the decrease in serum cholesterol by 21% was associated with a proportionate increase in fecal cholesterol elimination as neutral sterols through impaired cholesterol absorption. Serum cholesterol remained low and fecal steroid excretion remained elevated in the long-term neomycin study. Increasing the dosage from 1.5 to 6 g/d at the end of the 16-mo period brought about a further slight decrease in serum cholesterol and a small further increase in fecal neutral and acidic steroids. The increases in fecal bile acids and fat but not in neutral sterols were positively correlated with the increases in the neomycin dosage. Thus, large neomycin doses can also cause bile acid malabsorption. In another series of patients, a decrease (25%) in serum cholesterol by cholestyramine was associated with a proportional increase in the fecal elimination of cholesterol (2.5-fold) as bile acids. The inclusion of neomycin in cholestyramine therapy further increased fecal steroid output (solely as neutral sterols) by only about one-fifth of that due to cholestyramine, but further decreased serum cholesterol almost to the same extent (-17%) as cholestyramine alone. The overall decrease was 38%, no side effects occurred, and the patients found combination therapy convenient. Neomycin decreased serum cholesterol in different studies by 10+/-2, 17+/-4, and 12+/-4% per 100 mg/d of the increment in fecal steroids, the respective decrease for cholestyramine being only 2.2+/-0.5%. Thus, neomycin effectively reduced serum cholesterol by a relatively small increase in cholesterol elimination (via cholesterol malabsorption) compared with cholestyramine-induced bile acid malabsorption.

Effects of weight reduction on squalene, methyl sterols and cholesterol and on their synthesis in human adipose tissue

Quantitation of cholesterol and its precursors from human adipose tissue biopsies revealed very high squalene and moderately high methyl sterol concentrations. The squalene and cholesterol values were correlated with each other. Weight reduction in obese subjects following a jejuno-ileal bypass resulted in a significant but transient increase in adipose tissue cholesterol. The squalene concentration was also increased postoperatively, the maximum being reached about 6 months later than that of cholesterol as if the mobilization of squalene from shrunken adipocytes had been slow. Weight reduction with a 2--14 day total fast significantly reduced the adipocyte size but had no consistent effect on adipose tissue squalene, methyl sterol and cholesterol concentrations or on their adipocyte contents. Incubation of adipose tissue with labelled acetate and mevalonate revealed that the bulk of the labels in non-saponifiable lipids stayed in the large intermediate pools of methyl sterols and squalene in particular, fairly little being found in the cholesterol fraction itself. The total fast inhibited the incorporation of both 14C-acetate and 3H-mevalonate to squalene, methyl sterols and cholesterol, suggesting that cholesterol synthesis was inhibited before and after the mevalonate step.

Effects of bran on serum cholesterol, faecal mass, fat, bile acids and neutral sterols, and biliary lipids in patients with diverticular disease of the colon

Twenty-two patients with symptomatic diverticular disease of the colon were randomly allocated to control and high-fibre groups so that the long-term effect (up to 12 months) of bran on serum, faecal and biliary lipids could be studied. Even in cases of high initial values, faecal mass was increased by bran and the change was positively correlated with the change in dietary fibre. Faecal fat and dry weight were also increased. Faecal bile acids were initially slightly raised and were positively correlated with wet weight both off and on bran. The latter significantly decreased the excretion and concentration of bile acids, in particular the high initial values. The change in bile acids was not correlated with the change in dietary fibre or faecal wet weight. Sterol balance values indicated that the bran-induced decrease in faecal bile acids was associated with a lower cholesterol synthesis. Serum cholesterol decreased significantly in two hypercholesterolaemic individuals only. Correlations between different parameters revealed that the higher the initial level or the greater the drop in cholesterol synthesis, the greater the decrease in serum cholesterol. Bran had no effect on the biliary saturation of cholesterol. The percentage of biliary deoxycholate was negatively correlated with faecal mass (less so with faecal bile acid output) both before and during bran and was significantly decreased by bran. The percentage of cholic acid increased correspondingly and that of chenodeoxycholate remained unchanged. Faecal bile acids also indicated that the synthesis of the two primary bile acids was lowered by bran to the same degree.

Release of newly synthesized squalene, methyl sterols and cholesterol from human adipocytes in the presence of lipoproteins

Upon incubation of free fat cells for 3 h with labelled mevalonate, more than 90% of the radioactivity of the non-saponifiable material was found in the squalene fraction and less than 10% in the methyl sterol and cholesterol fractions. About 25, 30 and 65% of the cholesterol counts were found respectively in VLDL, LDL, or HDL added to the medium while none of the newly synthesized squalene was released into the lipoproteins. The results indicate that adipose tissue squalene can originate from local synthesis. It is not released from the cells into the medium, but can contribute to local cholesterol synthesis in both rapidly and slowly exchangeable cholesterol pools of adipose tissue.

Fecal beta-sitosterol in patients with diverticular disease of the colon and in vegetarians

Fecal sterol analysis showed that excretion of beta-sitosterol, a major component of poorly absorbable dietary vegetable sterols, is subnormal in patients with diverticular disease of the colon. Thus, the patients had evidently consumed a diet low in plant materials. The finding agrees with the current opinion that diverticular disease of the colon is associated with dietary fibre deficiency and suggests that fecal beta-sitosterol provides a rough measure of the vegetable intake. In vegetarians the beta-sitosterol excretion was actually high.

New insights into cholesterol dynamics

Kinetic aspects of cholesterol dynamics are described, with flux from the gut, to the liver, to the tissues, and back to the liver and gut, with a discussion of modifying mechanisms, synthesis, and transport. Overproduction of cholesterol, and bile acid and cholesterol malabsorption, are related to clinical problems.

Serum immunoreactive prolyl hydroxylase in liver disease

The concentration of serum immunoreactive prolyl hydroxylase (SIRPH) was measured in thirty patients with chronic active hepatitis, thirteen with primary biliary cirrhosis, four with alcoholic or idiopathic cirrhosis, and four with acute hepatitis; the values were compared with those in twenty-three control subjects. Increases in SIRPH were found in all the groups with liver diseases, individual values being highest in primary biliary cirrhosis in which about two-thirds of patients had values more than two standard deviations above the mean value in the control subjects. No correlation was found between SIRPH and other tests of liver function or some routine laboratory tests. SIRPH may reflect some hitherto unknown of unmeasured process in the diseased hepatic cells.

Cholestyramine and ileal by-pass in the treatment of familial hypercholesterolaemia

A comparison was made of the therapeutic effectiveness of cholestyramine and an ileal by-pass operation as hypocholesterolaemic measures in thirteen patients with familial xanthomatotic type II hypercholesterolaemia. Serum cholesterol and faecal steroids were measured before and at the end of a 10 day course of cholestyramine (32 g/day), and subsequently after an ileal by-pass operation. The mean decrease in serum cholesterol caused by cholestyramine (-17%) was significantly less than that caused by the surgical procedure (-33%). The increase in faecal steroid excretion, mainly as bile acids, was lower with cholestyramine (1.261 g/day) than after the ileal exclusion (2.176 g/day) and a positive correlation was found between the decrease in serum cholesterol and the increase in the faecal elimination of steroids of cholesterol origin. However, even though the increase in faecal steroids with cholestyramine was positively correlated with that resulting from ileal by-pass, the correlation between the corresponding changes in serum cholesterol level was not significant. The findings indicate that ileal by-pass decreases serum cholesterol and increases faecal elimination of cholesterol more effectively than cholestyramine, and that the decrease in the serum cholesterol level induced by ileal exclusion is not consistently predictable by the serum cholesterol response to the preceding cholestyramine treatment.

Effect of pectin on serum cholesterol, fecal bile acids and biliary lipids in normolipidemic and hyperlipidemic individuals

Pectin, 40-50 g/day for two weeks administered to nine normolipidemic and hyperlipidemic patients, had no effect on serum triglycerides but did cause a significant decrease in the serum total and unesterified cholesterol of hypercholesterolemic subjects in particular. This was associated with increased excretion of fecal bile acids and total steroids and increased concentration of plasma methyl sterols. Thus, the serum cholesterol reduction by pectin appears to be caused by increased cholesterol elimination into stools as bile acids which is then balanced by enhanced cholesterol synthesis. The composition of biliary bile acids and lipids was not changed and secondary bile acids and sterols decreased inconsistently in feces. The measurement of fecal dry weight suggested that the bulk of the pectin was degraded by bacteria during passage through the intestine. Consequently fecal mass and dry weight were not consistently increased, suggesting that pectin may not be an ideal fibre for increasing fecal bulk in functional colonic disorders.

Measurement of cholesterol synthesis in kinetically defined pools using fecal steroid analysis and double labeling technique in man

The purpose of the study was to develop a kinetic method for measurement of different parameters of cholesterol metabolism in man using labeled cholesterol precursors that could initially be incorporated even into the slowly exchangeable cholesterol pool. For this purpose, tritiated water and [2-14C]mevalonate were given to five normocholesterolemic subjects and the activities for serum cholesterol and body water were measured serially for up to eight weeks. Elimination of cholesterol was measured by fecal analysis of neutral and acidic steroids. For comparison, two subjects received a mixture of [4-14C]cholesterol and [2-3H]mevalonate. The data were subjected to multicompartmental analysis by computer, with the assumption that synthesis occurred in two compartments. The rapidly exchangeable cholesterol (pool 1) and the fractional hydrogon transport constant from body water to cholesterol could not be measured directly; therefore, the influence of two different mass transport values was tested. The best fit was obtained with the smaller mass of cholesterol in pool 1 associated with a hydrogen transport constant of 0.700 (32 out of 46 hydrogens originate from water). Kinetic analysis of the data allows estimates of the exchangeable cholesterol mass, flux rates of cholesterol between pools 1 and 2, and synthesis of cholesterol separately in the two pools. The results of computer analysis suggested that, in contrast to what has been assumed earlier on the basis of studies with radiolabelled cholesterol, 22-53% of endogenous cholesterol synthesis took place in pool 2 from body water and that this synthesis tended to correlate with the total body fat mass. The study with [2-3H]mevalonate and [4-14C]cholesterol indicated synthesis in pool 2 to be 20-22% of the total. Up to 50% of the DL[2-14C]mevalonate dose was incorporated into cholesterol. The fractional incorporation of DL-mevalonate into pool 2 was correlated with that of tritiated water, indicating that both precursors studied yielded essentially the same kinetic result.

Deaths in connection with chlormethiazole (heminevrin) therapy

Six cases are described where death occurred in connection with chlormethiazole (Heminevrin) infusion. The close time relationship and indirect evidence strongly suggest that chlormethiazole had an important role in the fatal outcome of the patients, but definite proof of this way was not possible to obtain. Present or past alcohol abuse and respiratory, liver, cardiac or CNS diseases of different degrees seemed to be features in common for the patients possibly rendering them susceptible to the suggested detrimental effect of chlormethiazole therapy. Respiratory depression is supposed to be the primary pathogenetic mechanism of the death. Considering the relatively limited use of chlormethiazole in the department in which these cases were observed and the recommended dosage applied, the risk of serious complication during chlormethiazole infusions seems to be surprisingly high.

Treatment of hypercholesterolemia with Secholex. A long-term clinical trial and comparison with cholestyramine

The efficacy of an anion-exchange gel, Secholex, as a hypocholesterolemic agent was assessed in 46 patients in 4 different studies and the effects were compared with those of cholestyramine. All patients had severe Type II-a or II-b hyperlipoproteinemia. In short-term metabolic studies Secholex (15 g/day) and cholestyramine (16 g/day) decreased serum cholesterol levels and increased total fecal sterol output and serum methyl sterol concentration to a similar extent, but cholestyramine was more effective than Secholex in increasing fecal bile acid excretion. In crossover studies, the two drugs appeared to be equally effective in lowing serum cholesterol levels but the patients mostly preferred Secholex. Twenty patients were treated with Secholex over a two-year period. The average decrease in serum cholesterol levels from the mean pretreatment value of 406 mg/100 ml was 15% during the first year, and 13% during the second year. In 5 patients the serum cholesterol was permanently lowered by more than 20% (good responders), while in 7 patients the average reduction of serum cholesterol level during Secholex administration was less than 10% (non-responders). The serum triglyceride level was slightly decreased by Secholex in Type II-b patients but was unaltered in Type II-a patients. At the end of the treatment period, serum iron and vitamin B12 levels were normal but the serum folic acid concentration was reduced in eight of 20 patients. A dose--response study indicated that a similar cholesterol-lowering effect was obtained with daily doses of 9 and 15 g of Secholex. It is concluded that Secholex is a relatively safe drug which effectively reduces serum cholesterol levels in two-thirds of patients with severe hypercholesterolemia.

Clinical correlations and significance of orceinpositivity in chronic active hepatitis and primary biliary cirrhosis

Clinical, biochemical and immunological variables were analyzed in 30 patients with orcein-negative (ON) chronic active hepatitis (CAH), 4 patients with ON primary biliary cirrhosis (PBC), 8 patients with orcein-positive (OP; intracellular copper-binding protein seen histologically in liver biopsy specimens) CAH and 15 patients with OP-PBC. A marked elevation of serum bile acids, alkaline phosphatase, leusine aminopeptidase, gammaglutamyl transpeptidase and cholesterol concentrations, and highly pathological BSP Tm values were characteristic for OP-cases. In addition the faecal fat level was increased and bile acids decreased in OP-cases. Serum levels of IgG or IgM and the occurrence of smooth muscle, mitochondrial or glomerular antibodies were identical in ON- and OP-CAH as well as also in ON- and OP-PBC. 49 patients were treated with a combination of prednisone and azathioprine from 4 to 72 months (mean 22). 26 patients with ON-CAH responded biochemically and morphologically to the treatment. No treatment failures were found in ON-CAH. In contrast treatment failure was confirmed in every treated OP-PBC or OP-CAH. The results suggest that orcein-positivity indicates a poor response to prednisone-azathioprine treatment of CAH.

Effect of oxandrolone treatment on the activity of lipoprotein lipase, hepatic lipase and phospholipase A1 of human postheparin plasma

The effect of a synthetic steroid, oxandrolone, on total postheparin plasma lipolytic activity, postherpain hepatic lipase activity, lipoprotein lipase and phospholipase A1 was studied in seven patients with hypertriglyceridemia. The mean total postheparin lipolytic activity increased 100 per cent during oxandrolone tratement (p smaller than 0.05). This change was caused mainly by postheparin hepatic lipase, whose activity increased on the average more than 2.5 times (p smaller than 0.001). The change in postheparin plasma-lipoprotein-lipase activity was insignificant. A highly significant correlation (r equals +0.87, p smaller than 0.01) was observed between the activities of postheparin hepatic lipase and phospholipase A1 before and during oxandrolone treatment. No relation was observed between serum triglyceride level and various postheparin lipase activities, or between the changes induced by oxandrolone in the level of serum lipids and the activities of postheparin lipases. We conclude that oxandrolone increases the activities of postheparin plasma hepatic lipase and phospholipase A1 but has little influence on lipoprotein lipase.

Regulation of cholesterol synthesis and storage in fat cells

The fat cells of rat epididymal adipose tissue contain an average of 0.5 mg of cholesterol per gram of triglyceride. Of this cholesterol, 90% is nonesterified and 80% is located in the lipid storage compartment. The fat cell cholesterol content correlated positively with cell size. During fasting the free cholesterol of the adipocyte decreased in parallel with triglyceride, whereas the amount of esterified cholesterol did not change. The fat cell cholesterol content is independent of the amount of dietary cholesterol. On in vitro incubation of rat fat cells with radiolabeled acetate, mevalonate, glucose, leucine, or water, labeled cholesterol was synthesized. The rate of cholesterol synthesis increased with fat cell size. Fasting suppressed cholesterol synthesis by 90%, whereas refeeding stimulated the synthesis above values found in normally fed rats. Stimulation of lipolysis with theophylline or with dibutyryl cyclic AMP markedly inhibited cholesterol synthesis in fat cells. Insulin increased the incorporation of glucose and leucine into fat cell cholesterol. The cholesterol synthesis in fat cells was not suppressed by a high cholesterol diet. Addition of very low or low density lipoprotein into the incubation medium suppressed fat cell cholesterol synthesis whereas high density lipoprotein did not. The lipoprotein-free serum stimulated cholesterol synthesis compared with serum-free medium. The rate of cholesterol synthesis in total adipose tissue of rat was estimated to be 4% of that in the liver. It seems unlikely that the increased body cholesterol turnover present in obesity is accounted for by the enhanced cholesterol formation in the enlarged adipose tissue.