Clinical characteristics and coronary risk factors of patients with low concentrations of serum low-density lipoprotein cholesterol and total cholesterol

We investigated the clinical characteristics and coronary risk factors of Chinese patients with suspected coronary artery disease (CAD) having low serum concentrations of both low-density lipoprotein cholesterol (LDL-C) and total cholesterol (TC). Of 1,450 patients with suspected CAD (age range, 30-92 years; 948 men and 502 women), 760 had established CAD. The patients were divided into three groups according to lipid profile patterns. Group 1 patients (n = 138) had low LDL-C concentrations (< 100 mg/dL) and low TC concentrations (< 160 mg/dL). They were characterized by lower triglyceride concentrations, lower frequencies of high TC/high-density lipoprotein cholesterol (HDL-C) ratios (> 5) and LDL-C/HDL-C ratios (> 5), and lower frequencies of a family history of CAD and obesity. Group 3 patients (n = 610) had LDL-C concentrations of 130 mg/dL or above and TC concentrations of 200 mg/dL or above, much higher than in group 1. The prevalence of CAD was 41.3% (57/138) in group 1. 46.7% (328/702) in group 2, and 61.5% (375/610) in group 3. Groups with higher TC and LDL-C concentrations had a higher CAD prevalence. Coronary risk factors of group 1 patients appeared to be low HDL-C concentration, high TC/HDL-C ratio, advanced age, cigarette smoking, hypertension, and diabetes mellitus. Among these risk factors, HDL-C and hypertension were independent predictors of CAD. Unlike in the other two groups, hypertension was the only independent nonlipid risk factor. We conclude that in therapy or prevention of CAD, the goals should be to reduce LDL-C concentration to below 100 mg/dL and the TC concentration to below 160 mg/dL. However, other risk factors should also be considered.     

Absorption, metabolism, and serum concentrations of cholesterol in vegetarians: effects of cholesterol feeding

Serum concentrations and metabolism of cholesterol were studied in vegetarians basally and during a dietary cholesterol load. Cholesterol absorption efficiency was normal and synthesis was slightly enhanced, even though serum cholesterol precursors were not increased. The serum concentrations of total and low-density-lipoprotein cholesterol were decreased proportionally to the reduced intake and absolute absorption of cholesterol. Fecal plant sterols were negatively correlated with the absorption efficiency of cholesterol and positively with fecal sterols and cholesterol synthesis, suggesting interference of high plant sterol intakes with cholesterol absorption. Cholesterol saturation and bile acid composition of the bile were not changed. The increased serum plant sterol-cholesterol ratios were positively related to the intake and negatively to the biliary secretion of plant sterols. Cholesterol feeding increased absolute cholesterol absorption and serum concentrations of total and low-density-lipoprotein cholesterol, did not change absorption efficiency or synthesis of cholesterol, but increased fecal cholestanol excretion.     

Use of cholesterol oxidase for assay of total and free cholesterol in serum by continuous-flow analysis

Idescribe an assay for total cholesterol in serum, with use of the AutoAnalyzer ii (Technicon), in which cholesterol esters are saponified by alkali, cholesterol is held in aqueous micellar solution with a surfactant (Triton X-100) and oxidized by cholesterol oxidase, and the hydrogen peroxide produced is measured by chelation with Ti4+ and xylenol orange. An assay for free cholesterol in serum, based on similar principles, is also described, and the two can be run simultaneously on a dual-channel AutoAnalyzer II. Standard solutions of cholesterol in isopropanol have poorer carryover characteristics than sera, and therefore do not reach the same continuous-flow steady state as sera of equivalent concentrations. Consequent potential calibration errors are avoided by using micellar solutions of cholesterol containing albumin for standardization. The formation of cholesterol peroxide in solutions of cholesterol in isopropanol is demonstrated, and this constitutes another potential source of error in the calibration of enzymic cholesterol assays. In analyzing patients' sera, results of the total cholesterol assay correlate well with those of a mechanized method in which cholesterol esterase and cholesterol oxidase are used; an automated Abell method, calibrated with solutions of cholesterol in isopropanol, gave slightly higher values. Determinations of the ratio of free cholesterol to total cholesterol by our automated cholesterol exidase assays given values that agree well with published results in which digitonin precipitation is used.     

Intra-individual variations in triglyceride and total cholesterol levels in serum in mixed hyperlipidemia

Swings in serum concentrations of total cholesterol and triglycerides were assessed retrospectively in 12 of 60 patients with mixed hyperlipidaemia (ten men, two women; mean age 44 [38-55] years). A second disease as a cause of the hyperlipidaemia had been excluded. Despite clinical stability and unchanged drug therapy the fasting values of triglycerides, measured enzymatically, in a minimum of four different samples (over several months) differed by more than 5 mmol/l, a mean of 16.6 (5-41.9) mmol/l. The lowest values were 2.7 (1.3-7.5) mmol/l, the highest 17.9 (6.4-44.6) mmol/l. Total cholesterol concentrations varied around 5.5 (1.6-31.7) mmol/l, minimal values 5.7 (4.2-8.9) mmol/l, maximal ones 12.0 (6.9-37.4) mmol/l. Six of the twelve patients consumed more than 60 g alcohol daily. The cause of the marked variations between individual samples is uncertain. Marked swings in triglyceride and total cholesterol concentrations are likely in mixed hyperlipidaemia. It is, therefore, essential to measure these concentrations repeatedly to assess correctly the diagnosis and treatment.     

Effects of spinach leaf protein concentrate on the serum cholesterol and amino acid concentrations in rats fed a cholesterol-free diet

The effects of spinach leaf protein concentrate (SPPC) on serum and liver lipid concentrations and on serum free amino acid concentrations were examined in rats fed a cholesterol-free diet containing 2 and 10% fats. The serum total cholesterol, triacylglycerol and phospholipid concentrations in the rats fed an SPPC diet containing 2% corn oil were significantly lower than those of the rats fed a corresponding casein diet. When 10% corn oil or lard was used, the serum cholesterol-lowering effect of the SPPC became insignificant, but the serum and liver triacylglycerol concentrations were kept at significantly lower levels. Both the amounts of fecal neutral steroids and bile acids were significantly higher in the rats fed the SPPC than those of the casein-fed rats. The concentrations of serum threonine, serine, glutamine, glycine, cystine, and isoleucine were significantly higher in the rats fed the SPPC diet containing 2% corn oil compared with those of the control rats, but when the dietary fat was raised to 10%, only glycine showed a higher serum concentration. These results indicate that the SPPC has a stronger cholesterol-lowering effect at a lower dietary fat level, 2%, and the activity is partly due to the inhibition of intestinal absorption of cholesterol and bile acid, and partly due to an increase in the concentration of some of the serum amino acids.     

Fat-modified diets influence serum concentrations of cholesterol precursors and plant sterols in hypercholesterolemic subjects

Serum noncholesterol sterols, cholesterol precursors and plant sterols, are indicators of cholesterol absorption and synthesis. Serum plant sterol concentrations correlate positively with cholesterol absorption, but have also been found to correlate with dietary unsaturated to saturated fatty acid ratios. We studied the concentration of serum noncholesterol sterols during four different fat-modified diets, (1) high-fat, saturated fat-enriched (control), (2) reduced-fat, sunflower oil-enriched (SO-enriched), (3) rapeseed oil-enriched (RO-enriched), and (4) reduced-fat, saturated fat-enriched (reduced-fat), followed for 6 months in hypercholesterolemic subjects in a parallel design. The proportion of lathosterol (micrograms per 100 mg cholesterol), a precursor of cholesterol synthesis, increased significantly (P < .05) in both SO-enriched (mean +/- SD 147 +/- 57 v 167 +/- 76, 0 v 6 months) and RO-enriched (147 +/- 54 v 157 +/- 52) groups, where the reduction in low-density lipoprotein (LDL) cholesterol was also significant. The proportion of sitosterol, a plant sterol, decreased significantly in the control group (137 +/- 48 v 122 +/- 42), and the proportion of another plant sterol, campesterol, increased in the RO-enriched group (280 +/- 141 v 333 +/- 162), reflecting changes in the use of vegetable oils in these two groups rather than increased cholesterol absorption. In the whole study population, the proportion of linoleic and alpha-linolenic acid (a marker of the use of RO) in cholesterol esters (CEs) correlated (P < .001) with the proportion of sitosterol (r = .43) and campesterol (r = .36) in serum at the end of the study. In conclusion, serum cholesterol precursors were found to be useful indicators of cholesterol metabolism, but changes in serum plant sterols reflected dietary changes rather than cholesterol metabolism during long-term dietary intervention with fat-modified diets.     

Relation of serum total cholesterol, serum triglycerides and fasting plasma glucose to colorectal carcinoma in situ

BACKGROUND: No one has previously examined the relation of serum total cholesterol, serum triglycerides and fasting plasma glucose to colorectal carcinoma in situ. METHODS: A case-control study was performed with 129 cases of colorectal carcinoma in situ and 258 matched controls among examinees undergoing a health check-up in Tokyo from January 1991 to March 1993. RESULTS: There was a significant, positive association between serum total cholesterol levels and the risk of colorectal carcinoma in situ after adjustment for age, sex, body mass index, smoking status and alcohol consumption. Serum triglyceride levels were significantly and positively associated with colorectal carcinoma in situ risk regardless of adjustment for the above covariates. Although there was no clear relation between colorectal carcinoma in situ and fasting plasma glucose levels, a modest increase of colorectal carcinoma in situ risk was observed in the highest category (> or =116 mg/dl) of fasting plasma glucose levels. CONCLUSIONS: The findings suggest a positive association between serum total cholesterol levels and the risk of colorectal cancer, rather than an inverse relation. The strong association with serum triglyceride levels and the weak association with fasting plasma glucose levels support the hypothesis that hyperinsulinaemia may play an important role in colorectal carcinogenesis.     

Cohort study of serum total cholesterol and in-hospital incidence of infectious diseases

A multiethnic cohort of adult members of the Kaiser Permanente Medical Care Program (55300 men and 65271 women) was followed for 15 years (1979-93) to assess the association between total cholesterol and risk of infections (other than respiratory and HIV) diagnosed in the in-patient setting. Using multivariate Cox regression, total cholesterol was inversely and significantly related to urinary tract, venereal, musculo-skeletal, and all infections among men; and to urinary tract, all genito-urinary, septicaemia or bacteraemia, miscellaneous viral site unspecified, and all infections among women. The reduction of risk of all infections associated with a 1 S.D. increase in total cholesterol was 8% in both men (95% CI, 4-12 %) and women (95% CI, 5-11%). For urinary tract infections among men, as for septicaemia or bacteraemia and nervous system infections among women, the risk relation was restricted to persons aged 55-89 years. Nervous system infections were positively related to total cholesterol among women aged 25-54. In both genders, the significant inverse association with all infections persisted after excluding the first 5 years of follow-up. Collectively, these data are suggestive of an inverse association, although not entirely consistent, between total cholesterol and incidence of infections either requiring hospitalization or acquired in the hospital. Further research is needed to elucidate whether these associations are biologically plausible or represent uncontrolled confounding by unmeasured risk factors.     

Variations in plasma volume affect total and low-density lipoprotein cholesterol concentrations during the menstrual cycle

Serum lipids are known to vary during the menstrual cycle. To determine if changes in plasma volume contribute to this effect, we determined serum lipids, lipoproteins, and estimated changes in plasma volume in 18 premenopausal women at the start of and at 5-day intervals after menstruation. Eleven men served as a comparison group. Changes in plasma volume were estimated from changes in hemoglobin and hematocrit. Total and low-density lipoprotein (LDL) cholesterol (mean +/- SD) increased 15 +/- 14 mg/dL (9% +/- 10%) and 11 +/- 13 (11% +/- 14%) within 10 days after the start of menstruation (P < .05) and then decreased toward baseline during the rest of the cycle. High-density lipoprotein (HDL) cholesterol increased 3 mg/dL, or 5%, (P < .05) on days 10 and 15 after menstruation. Plasma volume decreased 4% +/- 9% (P < .06) 10 days after the start of menstruation, and this maximum decrease in plasma volume coincided with peak increases in total, LDL, and HDL cholesterol. Except for an 8-mg/dL increase in LDL cholesterol at day 5, lipid changes were no longer significant after adjusting for changes in plasma volume. We conclude that alterations in plasma volume account for approximately half of the increase in total and LDL cholesterol during the menstrual cycle.     

Determination of total cholesterol in serum by liquid chromatography-isotope dilution mass spectrometry

We have developed a liquid chromatography-isotope dilution mass spectrometry procedure to quantify total cholesterol in serum. A particle-beam interface was used for coupling the liquid chromatograph and the mass spectrometer. After electron impact ionization the ions m/z = 386 and m/z = 389 were used for selective ion monitoring of cholesterol and the internal standard [25,26,27-(13)C]cholesterol. The sample preparation steps required for serum materials are alkaline hydrolysis and an extraction of the cholesterol into the cyclohexane phase. Imprecision for the determination of cholesterol in control materials is typically <1.0%. The deviation from the certified reference values was <0.75% for all control materials tested. A method comparison of the results obtained by this method with those obtained by gas chromatography-isotope dilution mass spectrometry for n = 28 pooled human sera derived from samples analyzed in our routine laboratory did not show differences >2.5%.     

Longitudinal trends in total serum cholesterol levels in a Japanese cohort, 1958-1986

This study is a preliminary examination of the reliability of adolescent self-reported pretreatment alcohol and other drug (AOD) use frequency. Assessments of self-reported pretreatment AOD use were conducted at admission and discharge (approximately a 1-month time period) at an adolescent drug misuser treatment program. The sample consisted of 197 male and female adolescents. There were statistically significant increases between admission and discharge assessments of pretreatment AOD use frequency. The greatest discrepancy was found for alcohol use, in which three-fourths (76%) of the sample reported a higher level of pretreatment alcohol use frequency at discharge assessment as compared to their admission assessment. Over one-third (35%) of the sample was found to have a significantly higher level of pretreatment alcohol use frequency at discharge assessment. The cause of this response discrepancy is unknown, but if it represents underreporting at admission, it may cause diagnostic and referral errors, as well as attenuate effect sizes in treatment outcome studies.     

Elevated total cholesterol in bulimia nervosa

c-erbB-2, a member of the tyrosine kinase oncogene family, is overexpressed in about 30% of human breast tumors where it correlates with poor prognosis. In vitro studies have suggested that increased expression of the receptor plays an important role in malignant progression. To better understand the direct effects of p185HER2 overexpression, a human c-erbB-2 expression vector was transfected into the hormone-dependent MCF-7 human breast carcinoma cell line and cell growth was analysed. Unexpectedly, colony formation assay revealed a reduction in the number and size of colonies as compared with mock-transfected cells. In hormone-deprived medium, c-erbB-2 transfected cells acquired growth capability, consistent with previous reports. By contrast, two c-erbB-2-transfected clones grown in complete medium showed a reduced proliferation rate despite the activation of a fully functional oncoprotein capable of autophosphorylation and induction of the MAPK pathway. The number of c-erbB-2-overexpressing cells in the S phase of the cell cycle was about one-half the number of control and mock-transfected cells. Also, overexpression of c-erbB-2 induced overexpression of p21WAF1, pRB hypophosphorylation and a mature differentiated cell phenotype with production of lipid droplets. Functional inactivation of p185HER2 by means of a specific single chain antibody indicated the c-erbB-2-dependence of the observed alterations. These data show that the exogenous overexpression of the c-erbB-2 gene in hormone-dependent breast cancer cells inhibits proliferation and induces differentiation.     

Dietary inulin lowers plasma cholesterol and triacylglycerol and alters biliary bile acid profile in hamsters

The mechanisms by which inulin may elicit its lipid-lowering effect are not well elucidated. To examine the lipid-lowering potential of inulin and especially its effect on bile acid metabolism, male golden Syrian hamsters were fed semipurified diets containing 20 g/100 g fat, 0.12 g/100 g cholesterol and 0 (control), 8, 12 or 16% inulin for 5 wk. Plasma total cholesterol concentrations were significantly lowered by 18, 15 and 29% in hamsters fed 8, 12 and 16% inulin, respectively. Dietary inulin specifically decreased VLDL cholesterol, which was significantly lower in hamsters fed 16% inulin compared with controls (1.1 +/- 0.3 vs. 2.9 +/- 0.6 mmol/L). LDL and HDL cholesterol were not significantly affected by dietary inulin. Plasma triacylglycerol was significantly reduced by 40 and 63% in hamsters fed 12 and 16% inulin, respectively. Hepatic total cholesterol and particularly esterified cholesterol accumulation were significantly lower in hamsters fed 8% inulin compared with controls. All three levels of dietary inulin caused distinct alterations in the bile acid profile of gallbladder bile. Taurochenodeoxycholic acid was significantly lower, whereas glycocholic and glycodeoxycholic acid were greater in hamsters fed inulin. Daily fecal bile acid excretion (micromol/d) tended to be greater (P = 0.056) in inulin-fed hamsters compared with controls, whereas daily neutral sterol excretion was not affected. These data demonstrate that the lipid-lowering action of inulin is possibly due to several mechanisms, including altered hepatic triacylglycerol synthesis and VLDL secretion and impaired reabsorption of circulating bile acids.     

Linkage between cholesterol 7alpha-hydroxylase and high plasma low-density lipoprotein cholesterol concentrations

Interindividual differences in plasma low-density lipoprotein cholesterol (LDL-C) levels reflect both environmental variation and genetic polymorphism, but the specific genes involved and their relative contributions to the variance in LDL-C are not known. In this study we investigated the relationship between plasma LDL-C concentrations and three genes with pivotal roles in LDL metabolism: the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and cholesterol 7alpha-hydroxylase (CYP7). Analysis of 150 nuclear families indicated statistically significant linkage between plasma LDL-C concentrations and CYP7, but not LDLR or APOB. Further sibling pair analyses using individuals with high plasma LDL-C concentrations as probands indicated that the CYP7 locus was linked to high plasma LDL-C, but not to low plasma LDL-C concentrations. This finding was replicated in an independent sample. DNA sequencing revealed two linked polymorphisms in the 5' flanking region of CYP7. The allele defined by these polymorphisms was associated with increased plasma LDL-C concentrations, both in sibling pairs and in unrelated individuals. Taken together, these findings indicate that polymorphism in CYP7 contributes to heritable variation in plasma LDL-C concentrations. Common polymorphisms in LDLR and APOB account for little of the heritable variation in plasma LDL-C concentrations in the general population.     

Variations of cholesterol and total lipid concentrations in sera of healthy young men. Differentiating analytic error from biologic variability

Three major sources of variation affecting serum cholesterol and serum total lipid concentration values were studied in a group of healthy men. The first source of variation, analytic error, was separated into pre-instrumental and instrumental components. The pre-instrumental component, which consisted of all uncertainties occurring from the instant of venipuncture to the entrance of the sample into the instrument, was statistically significant for total lipids. The second major source of variation-preparation of the subject-was evaluated for four major stresses: diet, exercise, posture prior to venipuncture, and duration of tourniquet application. Diet affected total lipids, while the specifics of posture and tourniquet application were statistically significant for both serum cholesterol and total lipids. The third source of variation considered was the within-day and the day-to-day changes. Within-day changes were divided into within-hour and hour-to-hour effects. Day-to-day changes occurred over a two-week period. The magnitude and statistical significance of the changes were evaluated using an ANOVA model. The C.V.'s of day-to-day changes for cholesterol and total lipids (biologic) were 5.3% and 10.2%, respectively while the hour-to-hour within-day C.V.'s were 3.8% for cholesterol and 10.4% for serum total lipids. In all cases the biologic variation was in far excess of the analytic variation. The significance of these factors affecting intraindividual variation in healthy subject is discussed.     

Long-term supplementation with a high cholesterol diet decreases the release of ATP from the caudal artery in aged rats

We examined the effects of high cholesterol (HC) diet on the spontaneous and noradrenaline-induced release of ATP, ADP, AMP and adenosine from caudal arteries and on the plasma levels of these adenyl purines in aged (100-week-old) Wistar rats. Administration of this diet for 12 weeks significantly reduced spontaneous and noradrenaline (1 micromol/L)-evoked release of adenyl purines from the caudal arteries relative to rats given the control diet The unsaturation index of fatty acids (UI), which gives the average number of double bonds, of both the plasma and the caudal artery was significantly less in the HC diet-fed rats than in those fed the control diet. The HC diet for 12 weeks produced a slight but significant increase in systolic and diastolic blood pressure with advancing age. Regression analysis revealed a significant inverse relationship between the total amount of purines released from the artery and diastolic blood pressure, and also a positive relationship between the total amount of purines released and the UI of the caudal artery. These results suggest that the high cholesterol diet decreased the release of adenyl purines from the caudal arteries of aged rats, leading to an increase in blood pressure.     

An HPLC-GC/MS reference method for serum total cholesterol with control for ester hydrolysis

Currently used isotope-dilution mass spectrometry methods for serum total cholesterol are performed without control in each sample for completeness of hydrolysis of cholesterol esters. In order to monitor this step in the analysis, we developed a method based on both high-pressure liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS). 13C3-cholesterol and cholesteryl [1-14C] oleate were added to serum that was saponified and extracted into hexane. The extract was subjected to HPLC with collection of the fractions corresponding to cholesterol and cholesteryl oleate. The radio-activity of the latter was counted in order to estimate the nonhydrolysed fraction that on average amounted to less than 0.1% for commonly used ester hydrolysis procedures. The cholesterol fraction was subjected to GC/MS for quantitation using the traditional isotope-dilution principle. Evaluation of accuracy by assaying sera from the National Institute of Standards and Technology showed a deviation from the target value of < 1% with a coefficient of variation of < or = 1.0%. In conclusion, the present reference method for serum total cholesterol assures results based on complete hydrolysis of the cholesterol ester fraction.     

Nephrectomy decreases amylin and pramlintide clearance in rats

Amylin is a 37 amino acid hormone, co-secreted with insulin from the pancreatic beta-cell in response to nutrient stimuli. Because the human amylin analog, pramlintide, is being tested in patients with diabetes mellitus, a known risk factor for nephropathy, we examined the role of the kidney on amylin and pramlintide metabolism and action in functionally nephrectomized rats. Nephrectomy markedly altered amylin metabolism: it increased incremental area under the plasma amylin concentration curve 3.6-fold (P<0.001) and increased the elimination half-life from 17+/-1 to 26+/-2 minutes (P < 0.01) after subcutaneous injection of 100 microg amylin. Nephrectomy decreased plasma amylin clearance from 20.3+/-1.1 to 7.9+/-0.4 mL/min (P < 0.0001). Thus, at these doses in the rat, the kidney is important for metabolizing amylin and pramlintide.