Rapid enzymatic determination of free and esterified cholesterol content of serum and tissues

Antioxidant improves smooth muscle sarco/endoplasmic reticulum Ca(2+)-ATPase function and lowers tyrosine nitration in hypercholesterolemia and improves nitric oxide-induced relaxation

Antioxidants improve endothelial function in hypercholesterolemia (HC); however, whether this includes improvement of the vascular smooth muscle response to NO is unknown. NO relaxes arteries, in part, by stimulating Ca(2+) uptake via sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) in aortic smooth muscle, and HC impairs SERCA function and the response to NO. HC induces oxidative stress, which could impair SERCA function. To study the effect of antioxidants, which are known to improve endothelium-dependent relaxation in HC, smooth muscle SERCA activity and NO-induced relaxation were studied in rabbits fed normal chow or a 0.5% cholesterol diet for 13 weeks. The antioxidant t-butylhydroxytoluene (BHT, 1%) was mixed with the HC diet in the last 3 weeks. HC impaired acetylcholine- and NO-induced relaxation, and these were restored by BHT. After inhibiting SERCA with thapsigargin, no difference existed in NO-induced relaxation among the three groups. Reduced aortic SERCA activity in HC was restored by BHT without changing SERCA protein expression. 3-Nitrotyrosine was notably increased in the media of the HC aorta, where it colocalized with SERCA. Tyrosine-nitrated SERCA protein was immunoprecipitated in the aortas of HC rabbits, where it was decreased by BHT, and it was also detected in the aortas of atherosclerotic humans. Thus, the antioxidant reverses impaired smooth muscle SERCA function in HC, and this is correlated with the improved relaxation to NO. These beneficial effects may depend on reducing the direct effects on SERCA of reactive oxygen species that are augmented in HC.

Dietary omega 3 fatty acids and cholesterol modify enterocyte microsomal membrane phospholipids, cholesterol content and phospholipid enzyme activities in diabetic rats

Diabetes-associated changes in intestinal uptake of nutrients are modified by isocaloric variations in the type of dietary lipids, and are associated with alterations in the phospholipid and fatty acyl content of the intestinal brush border membrane. The present study was designed to test the hypothesis that diet- and diabetes-associated changes in enterocyte microsomal membrane phospholipids are due to variations in the activity of two phospholipid metabolizing enzymes, 1,2-diacylglycerol:CDPcholine cholinephosphotransferase (CPT) and phosphatidylethanolamine methyltransferase (PEMT). Adult female Wistar rats were fed one of four semisynthetic diets--beef tallow low in cholesterol (BT), beef tallow high in cholesterol (BTC), fish oil low in cholesterol (FO) or fish oil high in cholesterol. In half of the animals, diabetes mellitus was produced by injection of streptozotocin. Jejunal and ileal enterocyte microsomes (EMM) were isolated and analyzed for cholesterol and phospholipids, as well as for CPT and PEMT activities. In control animals, feeding FO reduced EMM total phospholipids including phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol. Feeding FO resulted in a greater than 95% reduction in the activity of CPT. Diabetes was associated with increased jejunal EMM total phospholipids including sphingomyelin (SM) and PE, without associated changes in CPT or PEMT. Dietary cholesterol supplementation did not affect EMM total cholesterol or phosphlipid composition in control rats fed BT or FO, but was associated with an increase in EMM cholesterol in diabetic rats fed BT or FO. A decrease in total phospholipids due to a decline in SM, PC and PE in diabetic rats fed FO was not associated with changes in the activities of CPT or PEMT in EMM.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential and interactive effects of calcium channel blockers and cholesterol content of the diet on jejunal uptake of lipids in rabbits

The present study was undertaken to determine the effects of two classes of calcium channel blockers (CCB), nisoldipine (N) and verapamil (V), on the jejunal uptake of lipids in rabbits. The uptake of cholesterol and long-chain fatty acids into rabbit jejunum was examined after 6 and 36 min of exposure to N or V in vitro ("acute" studies), and after 3-wk feeding of N or V ("chronic" studies). Animals were fed either a low (0.08%) cholesterol diet (LCD) or a high (2.8%) cholesterol diet (HCD), with or without N or V added. Acute in vitro exposure of the jejunum to N or V did not affect the uptake of cholesterol or palmitic acid in rabbits fed LCD or HCD. The effect of N or V feeding depended upon the cholesterol content of the diet; adding N or V to LCD increased cholesterol uptake while adding N or V to HCD enhanced or lowered cholesterol uptake, respectively. Both N and V increased the uptake of stearic acid in LCD. N in HCD had no effect on fatty acid uptake, whereas V lowered the uptake of stearic and linoleic acids and increased the uptake of oleic acid. These changes in lipid uptake were not due to variation in the animals' food intake, body weight gain, or intestinal mucosal surface area. The chronic administration of N or V results in an intestinal adaptative process that alters the jejunal uptake of lipids, the direction of which is influenced by the class of CCB, and by the cholesterol content of the diet. (ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous microanalysis of biliary cholesterol, bile acids and fatty acids in lecithin using capillary column gas chromatography: an advantage to assess bile lithogenecity

Simultaneous determination of biliary lipids was performed by alkaline hydrolysis, the formation of the methyl ester derivatives of fatty acids that are constituents of phospholipids and of the acetylated methyl ester derivatives of bile acids, and subsequent analysis by capillary column gas chromatography. Complete separation and satisfactory recovery of cholesterol, bile acids, and fatty acids were achieved. Also, the accuracy of the calculation of the bile cholesterol saturation index was enhanced by computation. Since the degree of acyl chain unsaturation affects the cholesterol-holding capacity in vesicles, this method provides a unique insight into bile metastability by the quantitative assessment of fatty acids in lecithin.

Comparative study of methods for measuring cholesterol in biological fluids

A method combining enzymatic and electrochemical detection of cholesterol in biological fluids was compared with conventional detection methods: two chromatographic methods--gas chromatography or high performance liquid chromatography--and two enzymatic methods with colorimetric detection either by kinetic measurement or at the end of the reaction. For serum, enzymatic determination is accurate with both colorimetric detection methods; but for bile, colorimetric detection is difficult to perform due to interference from bile pigments. Enzymatic cholesterol determination, combined with electrochemical detection, is simpler and gives results in good agreement with those of chromatographic methods.

Simultaneous microanalysis of bile acids and cholesterol in bile by glass capillary column gas chromatography

Simultaneous quantitative microanalysis of bile acids and cholesterol was carried out by enzymatic hydrolysis, the formation of the ethyl ester dimethylethylsilyl ether derivatives and subsequent analysis by glass capillary gas chromatography. A complete separation and satisfactory recovery of cholesterol and the five major bile acids commonly occurring in human and hamster bile were obtained. The method is applicable to individual small animal models such as hamster from which only a small amount of bile is available.

Impairment of endothelium-dependent relaxation: an early marker for atherosclerosis in the rabbit

1. Cholesterol feeding of rabbits impairs the endothelium-dependent relaxation (EDR) evoked by acetylcholine (ACh) in the aorta. The experiments described in this paper were undertaken to examine the influence of age upon this phenomenon. 2. Rabbits aged 8 weeks and 46 weeks were fed a diet containing 2% cholesterol and other lipids for 4 weeks. Age-matched control animals were fed a standard rabbit diet. The concentrations of cholesterol and triglycerides in plasma were measured and the extent of atherosclerosis was estimated by staining the aortae with Sudan Red. Light and electron microscopy were undertaken also. 3. Rings of aorta were prepared for recording isometric tension. They were contracted with noradrenaline (NA) and EDR elicited by adding ACh. 4. The young rabbits showed weight gain, hypercholesterolaemia, prominent Sudan Red staining, together with scanning and transmission electron microscopic (SEM and TEM) features of cholesterol-induced atherosclerosis. The older animals showed significant weight loss and hypercholesterolaemia. The aortae of these animals showed no significant sudanophilia or light microscopic features of atherosclerosis. The SEM appearances were similar to the young animals fed cholesterol. 5. EDR to ACh was significantly impaired in both groups of cholesterol-fed rabbits. The maximal relaxations to ACh in young control and cholesterol-fed rabbits were 46.4 +/- 2.9% and 24.0 +/- 4.3% (mean +/- s.e. mean, n = 8, P less than 0.05) of the contractile response to NA (1 mumol 1(-1]. The corresponding results in the age control and cholesterol-fed rabbits were 31.8 +/- 3.9% and 9.1 +/- 1.5% (n = 9, P less than 0.05). 6. The young rabbits were far more susceptible to cholesterol-induced atherosclerosis than older animals and these changes were accompanied by loss of EDR. In the older animals and these changes were accompanied by loss of EDR. In the older animals the loss of the latter property was not accompanied by a significant degree of atherosclerosis although hypercholesterolaemia was present.

Endothelium-dependent relaxation in experimental atherosclerosis in the rabbit

The effect of feeding a diet supplemented with lipids and containing 2% cholesterol on the endothelium-dependent relaxation of rabbit aorta to acetylcholine was assessed. The effect of feeding a standard rabbit diet after an initial period of 2% cholesterol feeding was assessed also. Age-matched male, New Zealand white rabbits were fed either a 2% cholesterol diet or a standard rabbit diet. The animals were anesthetized with pentobarbitone sodium (25 mg/kg) and killed either at the beginning of the study (0 weeks) or at 4, 8, or 10 weeks. The animals in the reversal study were fed the 2% cholesterol diet for 6 weeks and killed after an additional 14 and 32 weeks on standard diet. The extent of atherosclerosis in the aorta was assessed by Sudan Red staining, estimation of tissue cholesterol, and light and electron microscopy. The relaxation response to acetylcholine was measured in rings of the thoracic aorta following precontraction with norepinephrine (-6.0 log mol/l). The relaxation was significantly impaired in aortas from rabbits fed the 2% cholesterol diet compared to aortas from animals fed the standard diet. The impairment of relaxation was apparent as early as 4 weeks after the start of the 2% cholesterol diet and remained impaired over the next 6 weeks. No improvement in endothelium-dependent relaxation was seen in rabbits on the reversal diet for 14 and 32 weeks. Thus, endothelium-dependent relaxation is attenuated in animals fed a 2% cholesterol diet, and the loss of relaxation persists for at least 32 weeks after the animals are returned to a standard diet.

Gout in the elderly, a separate entity?

To evaluate whether the clinical pattern of gout differed between elderly women and men a retrospective study was performed in all women (22) and men (18) in our rheumatological clinics who developed gout after the age of 60. The diagnosis was made after a mean of 2.6 years of joint complaints in women and after 1.2 years in men. In about half the patients complaints started in more than one joint, often including the big toe. In five women, but none of the men, complaints started in the fingers. No correlation was found between gout and the presence of tophi or Heberden's nodes in the finger joints. The mean uric acid level was higher in women (0.61 mmol/l) than in men (0.53 mmol/l), and almost all the women (95%) used diuretics and only 56% of the men did so.

Dietary fat selectively alters transport properties of rat jejunum

The influence of dietary fatty acid composition on intestinal active and passive transport function, brush border membrane composition, and morphology was examined in rats. Animals fed a semisynthetic diet high in saturated fatty acids demonstrated enhanced in vitro jejunal uptake of decanoic, dodecanoic, palmitic, stearic, and linoleic acid, as well as cholesterol and chenodeoxycholic and taurochenodeoxycholic acid, as compared with uptake in animals fed a semisynthetic diet high in polyunsaturated fatty acids but equivalent in total content of fat and other nutrients, or as compared with Purina chow. Feeding the saturated fatty acid diet was also associated with reduced jejunal uptake of a range of concentrations of glucose, enhanced ileal uptake of leucine, unchanged uptake of galactose, and lower uptake of decanol. The semisynthetic diets did not alter brush border membrane protein, sucrase or alkaline phosphatase activities, cholesterol, or total phospholipids, although the percentage of jejunal amine phospholipids was higher than in rats fed chow. The morphologic differences between the jejunum and ileum were abolished in animals fed the high polyunsaturated fatty acid diet; in rats fed the high saturated fatty acid diet, there was reduced mean ileal villus height, width, thickness, surface area, cell size, and villus density, as well as reduced mucosal surface area. The changes in jejunal transport were not correlated with the alterations in morphology, unstirred layer resistance, food intake, or body weight gain. It is proposed that small changes in the percentage of total dietary lipids composed of essential and nonessential fatty acids (without concurrent alterations in dietary total fat, carbohydrate, or protein) influence active and passive intestinal transport processes in the rat.

Intestinal morphology, marker enzymes and lipid content of brush border membranes from rabbit jejunum and ileum: effect of aging

Aging is associated with changes in the intestinal uptake of nutrients. This study was undertaken to determine whether the morphology, enzyme markers and the lipid content of the intestinal brush border membrane (BBM) was influenced by aging. There was an increase in the height of the jejunal villi and number of cells/villus, resulting in an age-related increase in the jejunal villus and mucosal surface area in young as compared with weanling rabbits. In mature 1-year-old animals, there was a decline in villus height, number of cells/villus, and mucosal surface area, so that the jejunal characteristics of the mature animals resembled those of the weanling rabbits. In the ileum, aging was associated with an increase (weanling vs. young), then a decrease (young vs. mature) in the height of the villi, and the number of cells/villus. Aging had no effect on the size of the villus cells. At all ages there was a direct positive relationship between the height of the villi and the mucosal surface area, and between villus surface area and sucrase activity. An established technique was used to purify rabbit BBM and to measure the BBM content of enzyme markers and lipids in weanling, young and mature animals. Both the BBM sucrase (S) and alkaline phosphatase (AP) increased in young as compared with weanling rabbits, and the ratio of AP/S remained unchanged. The S remained high in mature rabbits, but AP declined, so that AP/S fell. There was a positive linear correlation between S and villus surface area. In weanling rabbits, the total BBM phospholipid content and the ratio of total phospholipid/total cholesterol were lower in the ileum than in the jejunum. In the jejunal BBM of young animals, there was more total free fatty acids and cholesterol ester than in the weanling jejunum. The jejunal BBM total phospholipids and total cholesterol were higher in the mature than in the weanling animal jejunum when expressed as nmoles/mg protein, but the ratio of total phospholipid/total cholesterol was unaffected by aging. The greatest percentage of jejunal BBM phospholipid was comprised of lecithin and phosphatidyl ethanolamine. The increased BBM total phospholipid content in mature animals was associated with a higher amount and lower proportion of lecithin, but a higher proportion of sphingomyelin and phosphatidyl serine.(ABSTRACT TRUNCATED AT 400 WORDS)

Conversion of acetate to CO2, lipids, proteins, and lipoproteins during hemodialysis in humans

Acetate-1-14C or acetate-2-14C was infused into the venous dialysis line in 17 chronic stable patients over a 4-hr period of standard hemodialysis. Radioactive CO2 in expired air was measured continuously during dialysis and for 20 hr postdialysis. Significantly more acetate-1-14C (56 +/- 2%) was recovered as 14CO2 in the expired air than was acetate-2-14C (49 +/- 3%). A total of 81% and 71% of the radioactivity was recovered from the expired air and expended dialysate from acetate-1-14C and acetate-2-14C, respectively. Of the remainder, a significant portion was incorporated into plasma lipids and proteins. Incorporation of radioactivity into phospholipids, cholesterol esters, and triglycerides increased during dialysis and continued to increase during the postdialysis period. Free fatty acid radioactivity increased during dialysis but declined afterwards. In the lipoprotein fractions radioactivities remained elevated at 24 hr in the LDL and HDL fractions, but declined in the VLDLs after this time interval.

Mass fragmentographic analysis of total cholesterol in serum using a heptadeuterated internal standard

A mass fragmentographic method for the determination of total cholesterol in serum using heptadeuterated [25,26,26,26,27,27,27-2H]cholesterol as internal standard is presented. The results obtained are compared with a colorimetric and gas chromatographic method which were previously proposed as reference methods. Criteria for the development of absolute measurement by means of mass fragmentography and stable isotopically labelled internal standards are given. The conclusion is drawn that, at present, mass fragmentographic methods for the determination of total cholesterol in serum do not fulfil the criteria required for absolute methods.

Plasma membrane phospholipid, cholesterol and fatty acyl composition of differentiated and undifferentiated L6 myoblasts

The lipid composition of plasma membranes isolated from differentialted and undifferentiated L6 myoblasts have been compared. In general, the plasma membranes of differentiated L6 myoblasts have a higher cholesterol to phospholipid molar ratio than plasma membranes of undifferentiated cells. Differentiated L6 myoblasts have increased relative amounts of phosphatidylethanolamine and phosphatidylcholine ine in their plasma membrane and a decreased relative amount of sphingomyelin when compared with the plasma membranes of undifferentiated myoblasts. In addition, preliminary results show that differentiated L6 myoblasts plasma membrane phospholipid shows differences in the fatty acyl composition, specifically there appears to be relatively more 17:0 and 24:1 and less 16:1 and 18:1 than in plasma membrane phospholipids of undifferentiated L6 myoblasts. These observations indicate that significant changes in plasma membrane lipid composition occur during myoblast differentiation. The role that changes in lipid composition play in control of cellular differentiation, however, remains to be elucidated.