Paul S. Bachorik

Association of hyperapobetalipoproteinemia with endogenous hypertriglyceridemia and atherosclerosis

Researchers disagree on whether plasma triglyceride levels are an independent risk factor for atherosclerotic coronary artery disease. We hypothesized that patients with endogenous hypertriglyceridemia would differ: Some would have normal values of plasma low-density lipoprotein (LDL) B protein; others, despite their normal level of LDL cholesterol, would have increased levels of LDL B protein. We believe the latter patients--those with hyperapobetalipoproteinemia--would be the ones at risk for atherosclerosis. We studied two populations. Group 1, consisting of 162 patients with type IV lipoprotein patterns, was divided into two groups. One subgroup (A), which included 38 patients with elevated plasma LDL B atherosclerotic disease than the other subgroup (B) of 36 patients with normal levels of plasma LDL B protein (10 patients versus two, p less than 0.02). Group 2 consisted of 100 patients who had had myocardial infarction. Eighty-one percent of the 47 hypertriglyceridemic and 70% of the 53 normotriglyceridemic patients had elevated plasma LDL B protein levels (129 mg/dL or greater)--a proportion significantly higher than that in Group 1 (p less than 0.001). Thus, an elevated plasma level of LDL B protein not only identifies subgroups of patients with type IV lipoprotein patterns, but also may be an important marker for atherosclerotic disease.

Prevalence of hyperapobetalipoproteinemia and other lipoprotein phenotypes in men (aged ≤50 years) and women (≤60 years) with coronary artery disease☆

The prevalence and clinical characteristics of hyperapobetalipoproteinemia (hyperapoB) and other phenotypes of dyslipoproteinemia were examined in 99 men (aged < or = 50 years) and 104 women (< or = 60 years) undergoing elective diagnostic coronary arteriography. HyperapoB was the most common phenotype (34%) associated with premature coronary artery disease (CAD). Only 20.2% of patients with CAD had a normal lipoprotein phenotype. The significant odds ratios for CAD were as follows: hypertriglyceridemic hyperapoB 17.45 (p < 0.0001), type IV 6.54 (p = 0.0001), type IIa 4.73 (p = 0.008), normotriglyceridemic hyperapoB 2.54 (p = 0.03) and type IIb 8.73 (p = 0.05). The strong association of hypertriglyceridemic hyperapoB with CAD reflected the multiplicative effect of increased low-density lipoprotein apolipoprotein B and endogenous hypertriglyceridemia, and was independent of the effects of age, sex, diabetes mellitus, systemic hypertension, body mass index and cigarette smoking. The ratio of apolipoprotein B to A-1 was better than those of low-density to high-density lipoprotein cholesterol and total to high-density lipoprotein cholesterol at discriminating dyslipidemic phenotypes from normal. Obesity was increased approximately 1.5 to two-fold in the hypertriglyceridemic phenotypes, diabetes was more prevalent in hypertriglyceridemic hyperapoB (6.8-fold; p < 0.001) and type IV (4.4-fold; p = 0.02), and hypertension was increased 1.5- to twofold in most dyslipidemic groups. The data indicate that hyperapoB and endogenous hypertriglyceridemia both contribute to the risk of premature CAD.

Novel Effects of the Acyl-Coenzyme A:Cholesterol Acyltransferase Inhibitor 58-035 on Foam Cell Development in Primary Human Monocyte–Derived Macrophages

We examined the effect of acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitors on intracellular cholesterol stores in primary human monocyte-derived macrophages (HMMs) during foam cell formation. HMMs were exposed to acetylated low density lipoprotein (acLDL, 500 microg protein per mL) with or without 58-035 (1 to 10 microg/mL) or CI-976 (2 microg/mL) for 2 to 48 hours. Total cholesterol (TC) and esterified cholesterol (EC) mass was significantly lower while unesterified cholesterol (UC) increased slightly in cells incubated with acLDL plus ACAT inhibitors. Sterol mass was also measured in cells coincubated with acLDL (500 microg protein per mL) with or without 58-035 (2 microg/mL), high density lipoprotein (HDL, 400 microg protein per mL), or HDL+58-035 for 48 hours. TC and EC were 23% and 55% lower, respectively (P<0.0004), while UC was 11% higher (P<0.04) in cells incubated with acLDL plus 58-035. In contrast, coincubation with HDL alone did not significantly affect TC, EC, or UC mass compared with acLDL alone. The effect of 58-035 could not be explained by cytotoxicity, because adenine release, secreted lactate dehydrogenase, glucose utilization, and cell protein were similar in cells exposed to acLDL regardless of the presence of 58-035. We investigated several potential mechanisms for the decreased TC mass, including increased UC efflux and decreased acLDL binding and uptake. Efflux was measured in cells exposed to [1,2-(3)H]cholesteryl oleate-labeled acLDL, unlabeled control acLDL, and native untreated acLDL (500 microg protein per mL) with or without 58-035 (5 microg/mL) for 24 or 48 hours. UC efflux increased in a time-dependent manner from cells exposed to acLDL plus 58-035 compared with cells exposed to acLDL alone (P<0. 04). High-affinity binding was measured in cells exposed to (125)I-acLDL (5 microg protein per mL) with or without excess unlabeled acLDL (100 or 500 microg protein per mL) for 4 hours at 4 degrees C. Specific acLDL binding, uptake, and total degradation were significantly lower when 58-035 was present during cholesterol enrichment compared with cells exposed to acLDL alone (P<0.001). Unlike the effects of ACAT inhibitors on foam cell formation in rodent macrophages, these compounds lowered TC accumulation in HMMs during foam cell formation by limiting the uptake of acLDL and enhancing UC efflux. They may offer promise as drug therapies for atherosclerosis.

Hyperapobetalipoproteinemia in a kindred with familial combined hyperlipidemia and familial hypercholesterolemia.

A child showed a type lib llpoproteln pattern and triglycerlde-enrlched cutaneous xanthomas before 1 year of age. The proband and 9 of 18 relatives had elevated plasma levels of low density llpoproteln (LDL) B protein; of these nine relatives, four had elevated LDL of Increased density while five had elevated LDL of normal density. Compared with normal LDL, LDL of Increased density had less cholesteryl ester and free cholesterol, more apollpoproteln B and triglycerlde, and a lower molecular weight and flotation rate (S1°). Patients with LDL of Increased density had higher mean plasma levels of trlglycerldes, very low density llpoprotelns, and intermediate density llpoprotelns, but lower levels of high density llpoprotelns than those with elevated LDL of normal density. Multiple llpoproteln patterns in the fathers family suggested the presence of familial combined hyperlipidemia (FCH). The mother of the proband and two of her relatives had type lla lipoprotein patterns and tendon xanthomas, compatible with familial hypercholesterolemia (FH). High affinity binding, Internalizatlon, and degradation of 12SI LDL In cultured fibroblasts from the proband and his mother were reduced twoto threefold compared with normal cells, while LDL receptor activity In the probands father was normal. This unusual proband has apparently Inherited both FCH and FH.

Effect of gemfibrozil in men with primary isolated low high-density lipoprotein cholesterol: A randomized, double-blind, placebo-controlled, crossover study

PURPOSE To evaluate the efficacy of gemfibrozil in men with primary isolated low high-density lipoprotein cholesterol (HDL-C) levels. PATIENTS AND METHODS Fourteen men with low levels of HDL-C but desirable total cholesterol levels received gemfibrozil in a randomized, double-blind, placebo-controlled, crossover trial. The men were placed on a National Cholesterol Education Program Step-Two Diet. They were randomly assigned to receive placebo and gemfibrozil each for 3 months, with a 1-month washout period between phases. RESULTS Overall, gemfibrozil increased the total HDL-C concentration by 9.2% (p = 0.001), reduced triglyceride (TG) levels by 38% (p < 0.01), and significantly lowered the total cholesterol:HDL-C ratio (p = 0.01). Those with fasting TG levels of 1.07 mmol/L (95 mg/dL) or greater had a significant elevation in the HDL-C level (14.6%, p = 0.005) and a reduction in TG levels (50%, p = 0.002) with gemfibrozil; those with fasting TG levels less than 1.07 mmol/L had a smaller increase in the HDL-C level (4.1%, p > 0.05) and a smaller reduction in TG levels (15%, p = 0.02). There were no significant differences in the plasma levels of low density lipoprotein-cholesterol, HDL2-C, apolipoproteins (apo) A-I and B, or Lp(a). HDL3-C and apo A-II levels rose slightly. The adverse effects attributable to gemfibrozil were minimal. CONCLUSION In men with desirable total cholesterol levels, gemfibrozil raises HDL-C and lowers TG levels to a similar extent as reported for hyperlipidemic men in the Helsinki Heart Study. These lipid-altering effects were most pronounced in those with the highest fasting TG levels.

Lipoprotein-cholesterol analysis during screening: Accuracy and reliability

OBJECTIVE To evaluate the accuracy and reliability of lipoprotein-cholesterol measurements obtained during screening. DESIGN Cross-sectional study. PARTICIPANTS From November 1989 to January 1990, 154 adults were screened. MEASUREMENTS Split venous samples from fasting participants were analyzed for total cholesterol, triglyceride, and high-density-lipoprotein (HDL) cholesterol with screening and standardized laboratory methods. Low-density-lipoprotein (LDL)-cholesterol levels were calculated using the Friedewald equation. Split venous samples from nonfasting participants were analyzed for total cholesterol. Capillary blood samples were analyzed for total cholesterol with the screening method. MAIN RESULTS Total cholesterol measurements in screening venous blood samples were 5.4% and 3.8% lower than the laboratory values in samples from fasting and nonfasting participants, respectively. Triglyceride and HDL-cholesterol values in venous samples obtained from fasting participants were, on average, 9.8% and 11.2% lower than the respective laboratory measurements. Screening HDL-cholesterol values varied, differing from the laboratory values by as much as 40% in 95% of participants. In fasting participants, total cholesterol in capillary samples averaged 5.5% higher than in venous samples; in nonfasting participants the capillary samples were 3.1% higher. Screening for either total cholesterol or LDL cholesterol identified 93% of the persons with LDL-cholesterol values of 3.36 mmol/L (130 mg/dL) or higher. CONCLUSIONS Total cholesterol can be reliably measured in samples from fasting or nonfasting persons. The values in capillary blood samples were slightly higher than those in venous samples. Screening HDL-cholesterol values were too variable to establish the HDL-cholesterol level reliably. Participants with high LDL-cholesterol levels were identified as accurately by measuring total cholesterol only when compared with calculating the LDL-cholesterol level from total cholesterol, triglyceride, and HDL-cholesterol concentrations.

Reversible high affinity uptake of apo E-free high density lipoproteins in cultured pig hepatocytes

We examined the high affinity binding, uptake, and degradation of apo E-free 125I-high density Iipoprotein (HDL) in cultured pig hepatocytes. At steady state, the cells degraded 9.4% of cell-associated 125I-HDL/hour, compared with 41.7%/hour for 125I-LDL. Pulse-chase experiments at 4° C revealed that high affinity 125I-HDL binding was reversible. Similar experiments at 37° C revealed that about 70% of the cell-associated 125I-HDL was released as a macromolecule; the remainder was degraded to acidsoluble products. In contrast, over 75% of the 125I-LDL that was released had been degraded to acid soluble products. The amount of macromolecular 125I-HDL released at 37° C was similar to the amount that was bound to the cell surface, as estimated from measurements of trypsin-releasable radioactivity. Density gradient ultracentrifugation and SDS-polyacrylamide gel electrophoretic analysis of macromolecular 125I-HDL released to the medium revealed an increase in density, and the apparent partial proteoiysis of apo A-l (Mr 25,000) to products of apparent Mr 12,000–14,000. The findings suggest that high affinity 125I-HDL uptake had a reversible component in which HDL was concentrated temporarily at the cell surface, modified, and then released as a somewhat denser Iipoprotein particle. Measurement of 125I-HDL and 125I-LDL degradation in cell homogenates revealed no difference in the inherent susceptibility of the two lipoproteins to proteoiysis by lysosomai enzymes. The overall slower rate of degradation of 125I-HDL compared to 125I-LDL was therefore due in part to the smaller fraction of HDL that was committed to irreversible catabolism. The rate of catabolism of this fraction, however, was considerable. Cells pulsed at 4° C and subsequently warmed to 37° C released one-half the acid-soluble products from 125I-HDL within about 4 hours, compared with 2 hours for cells pulsed with 125I-LDL. These findings indicate that HDL was internalized, transported to lysosomes, and degraded at about one-half the rate of LDL.

Decreased postprandial response to a fat meal in normotriglyceridemic men with hypoalphalipoproteinemia.

The plasma level of high density lipoprotein cholesterol (HDL-C) has been reported to be inversely correlated with the level of triglycerides (TGs) and the magnitude of postprandial lipemia because subjects with low HDL-C accompanying high TG levels often have an increased postprandial response to a fat load. However, information is limited regarding the postprandial response to a fat load in subjects with low HDL-C and normal fasting TG values (hypoalphalipoproteinemia [hypoalpha]). We administered an oral fat load (70 g/m2 of body surface area) to six subjects with hypoalpha and six aged-matched control subjects. Plasma levels of lipids and lipoproteins and the mass of triglyceride-rich lipoproteins (TRLs: Sf > 100 and Sf 20-100) were measured every 2 hours for 8 hours. The mass and chemical composition of Sf > 100 or Sf 20-100 TRLs were not different between the fasting groups; postprandial Sf > 100 but not Sf 20-100 TRLs (mean +/- SD) was significantly lower in subjects with hypoalpha (200.4 +/- 64.8 mg/dL versus 110.6 +/- 50.9 mg/dL; analysis of variance, F test, p = 0.04). In the hypoalpha subjects, the compositions of postprandial Sf > 100 TRLs were TG poor and cholesterol and phospholipid enriched (p < 0.001) while the Sf 20-100 TRLs were enriched in cholesterol and phospholipid but relatively protein depleted (p = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood cholesterol screening in several environments using a portable, dry-chemistry analyzer and fingerstick blood samples

A multicenter study of blood cholesterol screening was performed in several typical environments, such as community sites (shopping malls and a supermarket), health care sites, work sites, a blood bank and a school. Cholesterol was measured with a portable, dry-chemistry analyzer using capillary blood obtained by fingerstick. Data are reported from a total of 13,824 participants, spanning the entire age spectrum. Overall, 25% of screened subjects had blood cholesterol levels above the age-specific cutpoints used in the current study. Although in the aggregate this screening experience very closely approximates the expected level of referrals, the proportion of referred screened subjects differed significantly among the 5 types of screening environments and by gender. Follow-up telephone interviews indicated that 53% of referrals had initiated a physician contact. More than 75% of those who had seen a physician reported that the diagnosis of hypercholesterolemia had been confirmed, and almost 72% had been prescribed a diet. A large proportion of referred screened subjects reported having modified their diet, particularly when recommended to do so by a physician. This study has yielded encouraging evidence that physicians gave referred screened subjects appropriate initial advice for managing hypercholesterolemia. The new technology for blood cholesterol measurement evaluated in the current study has proven to be a feasible and reliable means for measuring blood cholesterol in typical screening settings.

Enzymatic analysis of total- and HDL-cholesterol: Comparison with the standardized Liebermann-Burchard method used by the lipid research clinics program

We compared two enzymatic cholesterol methods with the standardized chemical method used in the Lipid Research Clinics (LRC) program. The methods were used to measure total cholesterol and high density lipoprotein (HDL) cholesterol in heparin-MnCl2 supernatants of 1,812 sera collected over a 16-mth period from subjects who were sampled as part of the Hispanic Health and Nutrition Examination Survey. Thirty percent of the subjects had fasted for 12 h or more before venepuncture. The enzymatic total cholesterol values were 1.4-1.8% lower than the LRC method and both enzymatic methods correlated highly with the LRC method (r greater than 0.97). The enzymatic HDL cholesterol values were 2.4 and 6.4% higher than the LRC method, and the correlation between the enzymatic and LRC methods was greater than 0.93. The differences between the enzymatic and LRC methods were the same in samples from fasting and non-fasting subjects.