G.Russell Warnick

Contrasting effects of unmodified and time-release forms of niacin on lipoproteins in hyperlipidemic subjects: Clues to mechanism of action of niacin

To minimize the cutaneous flushing symptoms associated with niacin use, a time-release capsule form of niacin has been formulated. Thus study compares the effects of time-release niacin with those of unmodified niacin on lipoprotein lipids, including HDL2 and HDL3, apoproteins A-I and A-II, clinical chemistries, symptomatic side effects, and adherence to the medication regimen. Seventy-one primarily hypercholesterolemic subjects were randomized to either unmodified niacin or time-release niacin ad took medication for a six-month period. The two groups were closely matched on anthropomorphic and lipid variables. Adherence to the therapeutic regimen at a dose of 1.5 g/d in the first month of treatment was similar in the two groups. Thereafter, at a dose of 3.0 g/d, adherence was in excess of 90% among subjects taking unmodified niacin but only 64% among those taking time-release niacin, chiefly because of aggravated gastrointestinal symptoms; cutaneous flushing side effects, however, were slightly less common with time-release niacin. At these levels of adherence, LDL cholesterol (C) was reduced 21% by unmodified niacin and 13% by the time release form. Plasma total triglyceride was reduced more with unmodified niacin (27%) than with time-release niacin (8% maximum), and HDL-C and HDL2-C were increased significantly with unmodified niacin (26% and 36%) and were not significantly changed by time-release niacin. Increased to a similar degree on both regimens were HDL3-C (approximately 35%) and apoA-I (approximately 12%). ApoA-II was not affected by either drug regimen.(ABSTRACT TRUNCATED AT 250 WORDS)

Lp(a) lipoprotein: Relationship to sinking pre-β lipoprotein, hyperlipoproteinemia, and apolipoprotein B

To assess the relationship between the Lp(a) and the sinking pre-beta (d smaller than 1.006) lipoprotein, the concentration of Lp(a) was quantified by radial immunodiffusion and the presence or absence of sinking pre-beta was assessed by agarose electrophoresis in overnight fasting plasma samples from 485 adults, comprised of 320 with normal lipid levels, 48 with type IIa, 40 with type IIb, and 77 with type IV lipoprotein phenotypes. The median Lp(a) level was 7.6 mg/100 ml, 89% (433 of 485) having detectable Lp(a) levels. Twenty-two per cent (107 of 485) had detectable pre-beta lipoprotein in the d greater than 1.006 plasma fraction (sinking pre-beta). Of the sinking pre-beta positive plasma samples, 96% (102 and 107) exceeded the median Lp(a) level, and sinking pre-beta was detected in all 44 samples with an Lp(a) concentration exceeding 40 mg/100 ml. The relationship of Lp(a) and sinking pre-beta to lipoprotein phenotype was assessed. Compared to the normolipidemic group, the type IIa group had higher Lp(a) percentile values (p smaller than 0.02), whereas the IIb and type IV groups had significantly lower Lp(a) values than the normolipidemic group. Ninety-two per cent (296 of 320) of the normolipidemic subjects had detectable levels of Lp(a) and 22% (70 of 320) had detectable sinking pre-beta lipoprotein. Ninety-four per cent (45 of 48) of the type IIa plasmas had detectable Lp(a) levels and 27% (13 of 48) had sinking pre-beta lipoproteins. Contrasted with the IIa group, only 80% (32 of 40) of the IIb plasmas had detectable Lp(a) levels and 18% (7 of 40) had sinking pre-beta lipoprotein. In the type IV plasmas 78% (60 of 77) had detectable Lp(a) and 22% (17 of 77) had sinking pre-beta lipoprotein. Lp(a) or log Lp(a) levels were not correlated with apolipoprotein B levels (n = 485, r = 0.002 or 0.037, respectively). Furthermore, Lp(a) levels remained essentially constant in three subjects whose aprptein B levels were altered in response to pharmacological and/or dietary manipulation. A fourth subject had a 50% increase in Lp(a) but this change did not correlate with apoprotein B changes. Thus, these findings suggest that Lp(a) is metabolically independnet of low density lipoprotein even though it shares the same structural protein, apoprotein B.

Reduction in high density lipoproteins by anabolic steroid (stanozolol) therapy for postmenopausal osteoporosis.

The effects of stanozolol, 17-methyl-2H-5 alpha-androst-2-eno [3,2-c] pyrazol-17 beta-ol, on lipoprotein levels were assessed in a short-term (6 wk) prospective study of 10 normolipidemic, postmenopausal, osteoporotic women. While total cholesterol and triglyceride levels remained constant, equal and offsetting responses were seen in low density lipoprotein (LDL) cholesterol (+30.9 +/- 28.1 mg/dl [mean +/- S.D.], p less than 0.01, a 21% increase) and high density lipoprotein (HDL) cholesterol (-32.5 +/- 11.9 mg/dl [mean +/- S.D.], p less than 0.001, a 53% decline). Hence the LDL/HDL ratio increased dramatically, from 2.5 +/- 0.7 to 6.8 +/- 2.5. Within HDL, stanozolol was associated with a greater decline in HDL2 (from 26.0 +/- 7.4 mg/dl to 3.8 +/- 1.9 mg/dl, p less than 0.001, an 85% decrease) than HDL3 (which diminished from 35.7 +/- 3.2 to 24.1 +/- 5.8 mg/dl. p less than 0.001, a 35% decrease). The major HLD apolipoproteins also declined (A-I by a mean of 41% and A-II by 24%, both p less than 0.001). Postheparin hepatic triglyceride lipase increased (off treatment 74 +/- 42 nmole free fatty acid min-1 mole-1, on treatment 242 +/- 110, n = 6, p = 0.06). All changes were reversed by 5 wk following termination of the drug. These lipoprotein changes suggest caution in the long term prescription of stanozolol, particularly in those without overriding clinical indications for its use.

Quantitation of high density lipoproteins

The demand for high density lipoprotein (HDL) quantitation has dramatically increased with the renewed awareness of the importance of HDL as a negative risk factor for coronary heart disease. HDL is usually estimated by specific precipitation of the non-HDL apoB-containing lipoproteins by polyanions and divalent cations followed by measurement of cholesterol in the supernatant. A common procedure involves precipitation with sodium heparin at 1.3 mg/ml and MnCl2 at 0.046 M (final concentrations). This method is appropriate for serum but less than ideal for plasma because of incomplete precipitation and sedimentation of the apoB-containing lipoproteins. A two-fold increase in Mn2+ to 0.096 M improves precipitation of the apoB-associated lipoproteins from plasma without excessive precipitation of HDL. This modified heparin-Mn2+ procedure gives results nearly identical to the results with the ultracentrifugal reference method (cholesterol in the d>1.063 fraction corrected for losses and the presence of apoB-associated cholesterol). The dextran sulfate 500-Mg2+ and the sodium phosphotungstate-Mg2+ procedures give results consistently 2–4 mg/dl lower than does the reference method. In contrast, a heparin-Ca2+ method gives results 5–8 mg/dl higher than does the reference method. Immunochemical analysis of apoA-I in the precipitate and apoB in the supernatant indicates that lower values for the phosphotungstate-Mg2+ procedure is due to partial precipitation of the A-I-containing lipoproteins, while higher values by the heparin-Ca2+ method are due to incomplete precipitation of the apoB-containing lipoproteins. Quantitation of the principal apoproteins of HDL, A-I and A-II, represent an important additional index of HDL concentrations and composition. Quantitation of plasma A-I and A-II concentrations by radial immunodiffusion indicates that women generally have higher HDL concentrations than men (women, A-I, 135±25, A-II, 36±6; men, A-I, 120±20, A-II, 33±5; mean±S.D., in mg/dl). A-I and A-II do not increase with age in men but show a slight increase with age in women. Estrogen increases HDL cholesterol and protein and may in part account for the higher HDL in women. The lighter density HDL subclass has a higher A-I/A-II ratio than the denser HDL subclass, with women generally having significantly more of the lighter HDL subclass. Density-gradient ultracentrifugation in CsCl2 gradients indicates that HDL contains subpopulations of differing hydrated density which vary in the A-I/A=II ratio. Immunoassay of A-I and A-II when used in combination with HDL cholesterol analysis is a powerful tool for studies of HDL structure, epidemiology and metabolism.

Genetic transmission of isoapolipoprotein E phenotypes in a large kindred: Relationship to dysbetalipoproteinemia and hyperlipidemia☆☆☆

The largest reported kindred of a proband with type III hyperlipoproteinemia was investigated by assessment of lipid and lipoprotein levels and very low density lipoprotein (VLDL) isoapolipoprotein E distributions in all accessible family members (56% of the 124 living blood relatives and 59% of the 37 spouses). The results confirm in this kindred a trimodal distribution of apoE3/E2 ratios, and segregation analysis of 16 informative matings classified according to E3/E2 ratio demonstrated classical Mendelian inheritance of the autosomal codominant type: the E3/E2 ratio is determined by two alleles, apoE3d and apoE3n, which produce three phenotypes apoE3-D, apoE3-ND, and apoE3-N, corresponding to the low, intermediate, and high modes, respectively. Vertical transmission of the apoE3-D phenotype occurred in two branches of the second generation. In both instances this represented pseudodominance; i.e., products of heterozygous (apoE3-ND) x homozygous (apoE3-D) matings. Hyperlipidemia (defined as a low density lipoprotein cholesterol and/or plasma triglyceride level exceeding the respective age-, sex-, and sex-steroid-specific 95th percentiles derived from Lipid Research Clinics population studies) was present in 15 blood relatives in multiple lipoprotein patterns, consistent with the presence of familial combined hyperlipidemia in this kindred. Eight of nine members with the apoE3-D phenotype had either type III hyperlipoproteinemia or, in the absence of hyperlipidemia, beta-VLDL and at least marginally cholesterol-rich VLDL (VLDL-cholesterol/plasma triglyceride greater than 0.25) (defined as dysbetalipoproteinemia). The ninth such member, the only child with this phenotype, was normal. beta-VLDL and marginally cholesterol-rich VLDL was seen in but one of six hyperlipidemic family members of phenotype apoE3-ND, in none of seven hyperlipidemic blood relatives of phenotype apoE3-N, in no normolipidemic family members of phenotype apoE3-ND or apoE3-N, and in no spouses (three of whom were hyperlipidemic and nine of phenotype apoE3-ND). Thus, among adult members of the OD kindred the apo3-D phenotype was nearly specifically associated with dysbetalipoproteinemia or, when hyperlipidemia was present, type III hyperlipoproteinemia.

Distribution of lipoprotein triglyceride and lipoprotein cholesterol in an adult population by age, sex, and hormone use: The pacific northwest bell telephone company health survey☆

This report describes the distribution of lipoprotein triglyceride and lipoprotein cholesterol in employees of the Pacific Northwest Bell Telephone Company. Means, medians, and selected percentiles are presented for very low, low, and high density lipoproteins (VLDL, LDL, and HDL, respectively) in 606 randomly selected white subjects aged 20-59. Results are specific for age decade, sex, and female sex hormone usage. Women who use sex hormones have significantly higher concentrations of triglycerides in all of the fractions across all age decades from 20 to 59 than do women not taking hormones. The average VLDL, LDL, and HDL triglyceride levels in women taking hormones are 69, 25 and 18 mg/dl which are considerably higher than the corresponding averages of 44, 17 and 12 mg/dl noted in women not taking hormones. Men have the highest average VLDL triglyceride value (85 mg/dl) but their average triglyceride concentrations in the LDL and HDL fractions (18 and 12 mg/dl) approximate those of women not taking hormones. This study in a well-defined population provides references standards for lipoprotein triglyceride concentrations. These results can be used to evaluate the effect of sex hormone treatment on the lipoprotein triglyceride content in VLDL, LDL and HDL, and to assess triglyceride content as a potential risk factor in men and older women.

Physiological and analytical variation in cholesterol and triglycerides

Plasma cholesterol and triglyceride levels were determined, on each of two AutoAnalyzer systems in 11 healthy subjects, weekly over a 10-week and monthly over a 12-month period. Analytical variation was 1–2% for cholesterol and 2–5% for triglyceride. Cholesterol and triglyceride values on frozen quality control serum pools were not indicative of absolute values on fresh plasma. Even though the two AutoAnalyzer systems averaged within 1–2 mg/dl for triglyceride and cholesterol on the serum quality control pools during the 12-month period, the two systems differed by 7–8 mg/dl on fresh or frozen plasma samples. The coefficient of physiological variation on the 10 weekly samples averaged 5% (range 3–10%) for plasma cholesterol and 18% (range 9–27%) for plasma triglyceride. Analysis of the monthly samples suggested significant (P<0.05) seasonal trends: cholesterol was highest in the winter months and lowest in October, whereas triglyceride was highest in January and February and lowest in May and December. We conclude that intra-individual variation can be an important source of error in attempting to make a genetic diagnosis of hyperlipidemia and/or in evaluating hypolipidemic regimens in a given subject.

Effect of fenofibrate treatment on plasma lipoprotein lipids, high-density lipoprotein cholesterol subfractions, and apolipoproteins B, AI, AII, and E☆

In this segment of a multicenter study, 36 hypercholesterolemic patients were randomly assigned to fenofibrate or placebo treatment to assess effects on plasma concentrations of lipoprotein cholesterol and triglyceride, high-density lipoprotein-cholesterol subfractions, and apolipoproteins E, B, Al, and All. All of these factors are of known or potential value in determining the patients risk of arteriosclerosis. Observations were made during initial screening and placebo phases, a 24-week, double-blind treatment phase, and a subsequent 24-week, open-label fenofibrate phase. There were three possible expressions of fenofibrate efficacy. Changes in lipoprotein cholesterol and total triglyceride concentrations observed in these patients were very similar to those seen with the larger multicenter cohort: total triglyceride levels decreased 38 to 46 percent, low-density lipoprotein cholesterol levels decreased 13 to 20 percent, and high-density lipoprotein cholesterol levels increased 4 to 13 percent. Triglyceride concentrations were significantly reduced (p less than 0.01) in very low-density lipoprotein (50 to 56 percent, similar to those of total triglyceride and very low-density lipoprotein cholesterol), and in low-density lipoprotein cholesterol levels (17 to 21 percent). A slight but statistically insignificant decrease in high-density lipoprotein triglyceride was observed (9 to 15 percent). High-density lipoprotein2 cholesterol levels did not change significantly, whereas high-density lipoprotein3 cholesterol levels increased 8 to 16 percent, accounting for all of the increase in high-density lipoprotein cholesterol. Apoprotein All levels increased significantly (13 to 20 percent) whereas those of apolipoprotein Al did not, consistent with an increase in high-density lipoprotein3 levels, where apolipoprotein All is more abundant relative to apolipoprotein Al than in high-density lipoprotein2. Apolipoprotein B levels decreased 20 to 26 percent and those of apolipoprotein E went from 29 to 34 percent, relative to the 16 to 20 percent decreases in very low-density lipoprotein and low-density lipoprotein triglyceride and cholesterol levels. Five patients with combined elevations of triglyceride and low-density lipoprotein cholesterol treated with fenofibrate, had reductions primarily in triglyceride, total apolipoprotein E (50 percent reduction), and apolipoprotein B (18 percent) levels. High-density lipoprotein3 cholesterol levels increased 19 percent and high-density lipoprotein2 cholesterol levels were unchanged. Low-density lipoprotein cholesterol levels declined slightly in four patients and a slight rise was observed in a fifth patient.(ABSTRACT TRUNCATED AT 400 WORDS)

ASSOCIATION OF ISOAPOLIPOPROTEIN-E3 DEFICIENCY WITH HETEROZYGOUS FAMILIAL HYPERCHOLESTEROLAEMIA: IMPLICATIONS FOR LIPOPROTEIN PHYSIOLOGY

A prepubertal girl with both homozygous isoapolipoprotein-E3 deficiency (the genetic defect underlying type-III hyperlipoproteinaemia) and heterozygous familial hypercholesterolaemia (familial type-IIa hyperlipoproteinaemia) presented with severe hypercholesterolaemia and antecubital and popliteal planar xanthomas. She responded dramatically to clofibrate. Her mother was normolipidaemic and heterozygous for apo-E3-deficiency. Her father, an obligate apo-E3-deficient heterozygote, and his similarly affected brother died prematurely with severe hypercholesterolaemia which had been refractory to clofibrate. Her paternal grandfather, who had the same combination of disorders as the proband, also responded to clofibrate, whereas her grandmother was normolipidaemic. Hence homozygous apo-E3 deficiency may present during childhood as severe hypercholesterolaemia when combined with familial hypercholesterolaemia, suggesting that the low-density-lipoprotein receptor may represent one mechanism whereby apo-E3-deficient remnants of very-low-density lipoproteins and chylomicrons are cleared from the plasma compartment. The removal of such apo-E3-deficient remnants is especially facilitated by clofibrate.

Type III hyperlipoproteinemia: a comparative study of current diagnostic techniques.

Research into the prevalence, genetic transmission and pathophysiology of Type III hyperlipoproteinemia has suffered from the lack of a practical specific diagnostic procedure. In this study, very low density lipoprotein (VLDL) compositional criteria were established in a population lacking the beta-migrating VLDL characteristic of this disorder. Diagnosis by these criteria was compared to diagnosis using current criteria for the Type III lipoprotein pattern. In addition two techniques for detecting Type III without preliminary VLDL isolation by ultracentrifugation were evaluated. Plasma triglyceride (TG) concentration dependent cutlines for the compositional criteria reduced false positives at low TG levels and false negatives at high TG levels. Furthermore, an agarose electrophoresis heparin-manganese precipitation technique was effective for screening for a possible Type III pattern in plasma whereas the combination agarose-polyacrylamide gel electrophoresis system was not effective.