Effects of low dosage progestin-only administration upon plasma triglycerides and lipoprotein metabolism in postmenopausal women.

Oral administration to five postmenopausal women of dl-norgestrel (0.075 mg/d for 7 wk) reduced mean fasting plasma levels of triglycerides by 29% (P < 0.001), VLDL triglycerides by 39% (P < 0.01), and VLDL apo B by 26% (P < 0.05), while lowering mean total cholesterol by 7% (P < 0.06). To explain these observations the kinetics of VLDL and LDL apo B turnover were studied by injecting autologous 125I-labeled VLDL and 131I-labeled LDL under control conditions and again in the fourth week of a 7-wk course of dl-norgestrel. VLDL apo B pool size fell by an average of 27% (1.2 vs 1.7 mg/kg, P < 0.06) and production of apo B by 18% (18 vs 22 mg/kg per d, P < 0.05) with unchanged fractional catabolic rate. Production of LDL apo B increased 36% with dl-norgestrel (12 vs 9.4 mg/kg per d, P < 0.05), but this was compensated by a 36% increase in fractional catabolic rate of LDL apo B (0.33 vs 0.25 pools/d, P < 0.005), thereby maintaining pool size. Lipoprotein (a) fell by an average of 12% (16 vs 18 mg/dl, P < 0.06). dl-Norgestrel reduced VLDL triglycerides (40 vs 64 mg/dl, P < 0.05), intermediate density lipoprotein cholesterol (14 vs 19 mg/dl, P < 0.02), IDL apo B (5.3 vs 7.2 mg/dl, P < 0.05), and VLDL cholesterol (3.1 vs 5.1 mg/dl, 0.10 > P > 0.05), in parallel with the reductions in VLDL apo B production and pool size. dl-Norgestrel significantly lowered the production rate of VLDL apo B, thereby decreasing plasma VLDL and intermediate density lipoprotein concentrations.     

Effects of combined estrogen and progestin administration on plasma lipoprotein metabolism in postmenopausal women.

Treatment of postmenopausal women with low doses of estradiol-17 beta (1 mg/d) and dl-norgestrel (0.075 [corrected] mg/d) significantly reduced fasting serum levels of low density lipoprotein (LDL) cholesterol and lowered very low density lipoprotein (VLDL) triglycerides in four of five subjects. To explain these results, the kinetics of VLDL and LDL apolipoprotein (apo) B turnover were studied by injecting autologous 125I-labeled VLDL and 131I-labeled LDL into subjects before discontinuing long-term (4-yr) treatment with the estradiol-17 beta and dl-norgestrel and again 7 wk after stopping treatment. The 24% mean decrease in VLDL apo B pool size during treatment was associated with a significant increase in VLDL apo B fractional catabolic rate (15 +/- 1 vs. 11 +/- 1 pools/d), whereas production rate was similar to control (24 +/- 3 vs. 21 +/- 2 mg/kg per d). There was a significant 25% mean decrease in LDL apo B pool size (27 +/- 2 vs. 36 +/- 3 mg/kg) due to a significant decrease in total (8.3 +/- 0.3 vs. 11 +/- 1 mg/kg per d) and independent (3.3 +/- 0.5 vs. 6.6 +/- 0.8 mg/kg per d, P less than 0.05) LDL apo B production. Estradiol-17 beta together with dl-norgestrel lowered plasma VLDL by enhancing their clearance and LDL by reducing their production.     

Combined hyperlipidemia in transgenic mice overexpressing human apolipoprotein Cl.

We have generated transgenic mice over-expressing human apolipoprotein CI (apo CI) using the native gene joined to the downstream 154-bp liver-specific enhancer that we defined for apo E. Human apo CI (HuCI)-transgenic mice showed elevation of plasma triglycerides (mg/dl) compared to controls in both the fasted (211 +/- 81 vs 123 +/- 52, P = 0.0001) and fed (265 +/- 105 vs 146 +/- 68, P < 0.0001) states. Unlike the human apo CII (HuCII)- and apo CIII (HuCIII)-transgenic mouse models of hypertriglyceridemia, plasma cholesterol was disproportionately elevated (95 +/- 23 vs 73 +/- 23, P = 0.002, fasted and 90 +/- 24 vs 61 +/- 14, P < 0.0001, fed). Lipoprotein fractionation showed increased VLDL and IDL + LDL with an increased cholesterol/triglyceride ratio (0.114 vs 0.065, P = 0.02, in VLDL). The VLDL apo E/apo B ratio was decreased 3.4-fold (P = 0.05) and apo CII and apo CIII decreased in proportion to apo E. Triglyceride and apo B production rates were normal, but clearance rates of VLDL triglycerides and postlipolysis lipoprotein "remnants" were significantly slowed. Plasma apo B was significantly elevated. Unlike HuCII- and HuCIII-transgenic mice, VLDL from HuCI transgenic mice bound heparin-Sepharose, a model for cell-surface glycosaminoglycans, normally. In summary, apo CI overexpression is associated with decreased particulate uptake of apo B-containing lipoproteins, leading to increased levels of several potentially atherogenic species, including cholesterol-enriched VLDL, IDL, and LDL.     

Suppression of apolipoprotein B production during treatment of cholesteryl ester storage disease with lovastatin. Implications for regulation of apolipoprotein B synthesis.

Cholesteryl ester storage disease (CESD) is characterized by the deficient activity of lysosomal cholesteryl ester (CE) hydrolase, accumulation of LDL-derived CE in lysosomes, and hyperlipidemia. We studied the kinetics of VLDL and LDL apolipoprotein B (apoB), using 125I-VLDL and 131I-LDL, in a 9-yr-old female with CESD and elevated total cholesterol (TC) (271.0 +/- 4.4 mg/dl), triglyceride (TG) (150.0 +/- 7.8 mg/dl), and LDL cholesterol (184.7 +/- 3.4 mg/dl). These studies demonstrated a markedly elevated production rate (PR) of apoB, primarily in LDL, with normal fractional catabolism of apoB in VLDL and LDL. Urine mevalonate levels were elevated, indicative of increased synthesis of endogenous cholesterol. Treatment with lovastatin, a competitive inhibitor of hydroxymethylglutaryl coenzyme A reductase, resulted in significant reductions in TC (196.8 +/- 7.9 mg/dl), TG (100.8 +/- 20.6 mg/dl), and LDL cholesterol (102.0 +/- 10.9 mg/dl). Therapy reduced VLDL apoB PR (5.2 vs. 12.2 mg/kg per d pretreatment) and LDL apoB PR (12.7 vs. 24.2 mg/kg per d pretreatment). Urine mevalonate levels also decreased during therapy. These results indicate that, in CESD, the inability to release free cholesterol from lysosomal CE resulted in elevated synthesis of endogenous cholesterol and increased production of apoB-containing lipoproteins. Lovastatin reduced both the rate of cholesterol synthesis and the secretion of apoB-containing lipoproteins.     

Influence of age on the metabolism of plasma low density lipoproteins in healthy males.

The plasma concentration of the atherogenic low density lipoproteins (LDL) increases with age. To clarify the mechanism of this change, we studied the kinetics of autologous 125I-LDL apolipoprotein B (apo B) in 41 normolipidemic, nonobese healthy males. For comparison, they were divided into three age groups: young, 21-39 yr (n = 18), middle-aged, 40-59 yr (n = 11), and old, 60-80 yr (n = 12). The levels of plasma LDL cholesterol and LDL apo B increased from respectively 3.4 +/- 0.1 (SEM) mmol/liter and 86 +/- 2 mg/dl in the young to 4.1 +/- 0.1 mmol/liter and 95 +/- 3 mg/dl in the old (P less than 0.01), and this increase was linked to a progressively decreased (r = -0.38, P less than 0.02) fractional catabolic rate of LDL apo B (0.348 +/- 0.010 pools per day in the young vs. 0.296 +/- 0.009 pools per day in the old, P less than 0.01). The production rate of LDL apo B did not differ significantly between the groups. The reduced fractional catabolic rate of LDL apo B in the old was not associated with a decrease in binding affinity of the LDL particle to its receptor, as judged from its ability to compete for 125I-LDL fibroblast binding. When hepatic LDL receptor expression was stimulated by cholestyramine treatment in six old males, their LDL apo B fractional catabolic rate increased to the levels observed in the young subjects. We conclude that the increase in LDL which normally occurs with age is explained by a reduced capacity for its removal, and hypothesize that this is mediated via a reduced hepatic LDL receptor expression.     

Measurement of very low density and low density lipoprotein apolipoprotein (Apo) B-100 and high density lipoprotein Apo A-I production in human subjects using deuterated leucine. Effect of fasting and feeding.

Six normolipidemic male subjects, after an 8-h overnight fast, were given a bolus injection and then a 15-h constant intravenous infusion of [D3]L-leucine. Subjects were studied in the fasted state and on a second occasion in the fed state (small, physiological meals were given every hour for 15 h). Apolipoproteins were isolated by preparative gradient gel electrophoresis from plasma lipoproteins separated by sequential ultracentrifugation. Incorporation of [D3]L-leucine into apolipoproteins was monitored by negative ionization, gas chromatography-mass spectrometry. Production rates were determined by multiplying plasma apolipoprotein pool sizes by fractional production rates (calculated as the rate of isotopic enrichment [IE] of each protein as a fraction of IE achieved by VLDL (d less than 1.006 g/ml) apo B-100 at plateau. VLDL apo B-100 production was greater, and LDL (1.019 less than d less than 1.063 g/ml) apo B-100 production was less in the fed compared with the fasted state (9.9 +/- 1.7 vs. 6.4 +/- 1.7 mg/kg per d, P less than 0.01, and 8.9 +/- 1.2 vs. 13.1 +/- 1.2 mg/kg per d, P less than 0.05, respectively). No mean change was observed in high density lipoprotein apo A-I production. We conclude that: (a) this stable isotope, endogenous-labeling technique, for the first time allows for the in vivo measurement of apolipoprotein production in the fasted and fed state; and (b) since LDL apo B-100 production was greater than VLDL apo B-100 production in the fasted state, this study provides in vivo evidence that LDL apo B-100 can be produced independently of VLDL apo B-100 in normolipidemic subjects.     

Effect of a high-carbohydrate, low-saturated-fat diet on apolipoprotein B and triglyceride metabolism in Pima Indians.

The mechanisms by which high-carbohydrate, low-saturated-fat diets lower LDL cholesterol (LDLC) concentrations are unknown. In this study, kinetics of VLDL, intermediate density lipoprotein (IDL), and LDL apoprotein B and VLDL triglyceride were determined in seven nondiabetic (ND) and seven non-insulin-dependent diabetic (NIDDM) Pima Indian subjects on high-fat and high-carbohydrate (HICHO) diets. Metabolic changes were similar in ND and NIDDM. On the HICHO diet, LDLC decreased (131 +/- 8 vs. 110 +/- 7 mg/dl, P less than 0.0001) in all subjects. Mean fasting and 24-h triglyceride (TG) concentrations were unchanged, as were mean production rates and fractional clearance rates (FCR) of VLDL apoB and VLDL TG. The mean VLDL apoB pool size (303 +/- 20 vs. 371 +/- 38 mg, P = 0.01) increased owing to a decrease in the mean transport rate (10.7 +/- 1.1 vs. 8.4 +/- 0.9 mg/kg fat-free mass (ffm) per day, P less than 0.0001) and the mean rate constant (2.3 +/- 0.2 vs. 1.5 +/- 0.2, P less than 0.001) for the VLDL apoB to IDL apoB conversion pathway. The mean transport rate of VLDL apoB to LDL apoB via IDL (10.2 +/- 0.9 vs. 8.0 +/- 0.8 mg/kg ffm per day, P less than 0.001) decreased. Mean LDL apoB concentrations decreased (70 +/- 5 vs. 61 +/- 5 mg/dl, P less than 0.001) on the HICHO diet. Means for total LDL apoB transport rate, LDL apoB FCR, and LDLC/apoB ratios were unchanged. In summary, the HICHO diet decreased the activity of mechanisms that convert VLDL to LDL, which contributed to the decrease in LDLC in all subjects. There was also evidence in some subjects for increased activity of LDL apoB clearance mechanisms, and a decrease in the LDLC to apoB ratio.     

Malondialdehyde-modified low density lipoproteins in patients with atherosclerotic disease.

The murine monoclonal antibody mAb-1H11 raised against malondialdehyde (MDA)-modified LDL, was used to detect cross-reacting material in human atheromatous tissue and in plasma. MDA-modified LDL levels in plasma were 0.19 +/- 0.02 mg/dl (mean +/- SEM) in 44 control subjects, 0.24 +/- 0.02 mg/dl in 15 patients with chronic stable angina pectoris (P = NS vs LDL cholesterol matched controls), 1.4 +/- 0.1 mg/dl in 60 patients with acute myocardial infarction (P < 0.001 vs controls), and 0.86 +/- 0.11 mg/dl in 22 patients with carotid atherosclerosis (P < 0.001 vs controls). Modified LDL, isolated from pooled LDL of 10 patients, showed a higher electrophoretic mobility on agarose gels, a higher content of thiobarbituric acid reactive substances, and a higher cholesterol/protein ratio than native LDL and had a similar reactivity (antigen/protein ratio) in the assay as the in vitro MDA-modified LDL used for calibration. Its apo B-100 moiety was not fragmented. Uptake of this modified LDL by macrophages resulted in foam cell generation. In conclusion, elevated plasma levels of atherogenic MDA-modified LDL may be a marker for unstable atherosclerotic cardiovascular disease.     

Increase in plasma total and lipoprotein cholesterol during incubation of whole blood samples at 37 degrees C--influence of LCAT inhibitors.

Incubation of whole blood samples at 37 degrees C caused a time-dependent increase in plasma cholesterol concentrations. In samples from 40 fasting healthy males, plasma cholesterol rose by 13.6 +/- 3% during 24 h (P less than 0.001). Changes in cholesterol concentrations were found in both the HDL fraction and the VLDL/LDL fraction. The increase in lipoprotein cholesterol concentrations correlated positively with the initial levels of HDL cholesterol and apo A-I; and with the original levels of VLDL/LDL cholesterol, apo B and triglycerides. The increase in plasma total cholesterol was not related to the HDL cholesterol and apo A-I concentrations. It was more pronounced in samples with elevated plasma concentrations of total cholesterol, VLDL/LDL cholesterol, apo B and triglycerides. The elevation in plasma total cholesterol resulted from an increase in cholesteryl esters, whereas free cholesterol decreased. After LCAT inhibition no changes in total, free and esterified cholesterol were observed. Therefore, increase in plasma cholesterol seems to represent a LCAT-dependent cholesterol transport out of blood cells.     

High protein diet complements resin therapy of familial hypercholesterolemia.

The intermediate-term effects on plasma lipoprotein lipids of substituting meat and dairy protein for carbohydrate in the diets of five subjects (three women, two men) with familial hypercholesterolemia receiving cholestyramine (mean dose, 18 g/d) were studied. Subjects were randomly allocated to either the high or low protein diets (mean 27 versus 10% of energy as protein, 25% as fat, and 48 versus 65% as carbohydrate) for 4 to 5 weeks and then switched to the other diet for another 4 to 5 weeks. Mean fasting plasma HDL cholesterol rose significantly by 17 +/- 3% (1.11 +/- 0.12 vs 0.95 +/- 0.11 mmol/L, p less than 0.005, n = 5), whereas total triglycerides fell by 23 +/- 2% (1.7 +/- 0.3 vs 2.2 +/- 0.3 mmol/L, p less than 0.005, n = 5), VLDL triglycerides fell by 28 +/- 5% (0.88 +/- 0.15 vs 1.18 +/- 0.19 mmol/L, p less than 0.02, n = 5), VLDL cholesterol fell by 32 +/- 7% (0.39 +/- 0.08 vs 0.56 +/- 0.09 mmol/L, p less than 0.01, n = 5), the ratio of LDL cholesterol: HDL cholesterol by 19 +/- 5% (4.7 +/- 0.7 vs 5.7 +/- 0.7, p less than 0.05) and that of total cholesterol: HDL cholesterol by 16 +/- 5% (6.6 +/- 0.5 vs 8.0 +/- 0.7, p less than 0.05) on the high versus low protein diet. Increasing dietary protein intake at the expense of carbohydrate may be useful in treating hypoalphalipoproteinemia and/or hypertriglyceridemia in patients with familial hypercholesterolemia.     

Significance of low density lipoprotein production in the regulations of plasma cholesterol level in man.

To determine whether production or catabolism of low density lipoprotein (LDL) is the major factor controlling LDL concentrations in subjects with plasma cholesterol levels from low-normal to mildly elevated, measurements of apoprotein of LDL (apoLDL) turnover were performed in 16 patients with various plasma cholesterol concentrations. Cholesterol balance studies were done simultaneously in 13 of these patients. Plasma concentrations of apoLDL and LDL-cholesterol were positively correlated with synthetic rates of apoLDL (r = 0.74, P less than 0.001; r = 0.50, P less than 0.05, respectively). No correlation was noted between the fractional catabolic rate for apoLDL and apoLDL levels (or LDL-cholesterol). For further analysis, the patients were divided into three groups with stepwise increases in apoLDL concentrations. When apoLDL levels rose significantly, from 83 +/- 5 SEM to 122 +/- 2 to 149 +/- 5 mg/dl, synthetic rates for apoLDL also increased significantly from 11.6 +/- 12. to 17.0 +/- 0.9 to 23.8 +/- 1.8 mg/d/kg ideal weight. In contrast, the fractional catabolic rate of apoLDL was not different among the three groups (0.32 +/- 0.03 vs. 0.29 +/- 0.02 vs. 0.33 +/- 0.03/d). No relation was noted between synthesis of total body cholesterol (or bile acids) and concentrations, production rates, or removal of apoLDL. Thus, concentrations of apoLDL and LDL-cholesterol in these subjects with plasma cholesterol levels from low-normal to mildly elevated were regulated mainly by synthetic rates of apoLDL and not by LDL catabolism.     

Genetic analysis of a kindred with familial hypobetalipoproteinemia. Evidence for two separate gene defects: one associated with an abnormal apolipoprotein B species, apolipoprotein B-37; and a second associated with low plasma concentrations of apolipoprotein B-100.

In 1979 Steinberg and colleagues recognized a unique kindred with normotriglyceridemic hypobetalipoproteinemia (1979. J. Clin. Invest. 64:292-301). We have undertaken an intensive reexamination of this kindred and have studied 41 family members in three generations. In this family we document the presence of two distinct apo B alleles associated with low plasma concentrations of apolipoprotein (apo) B and low density lipoprotein (LDL) cholesterol and we trace the inheritance of these two alleles over three generations. One of the alleles resulted in the production of an abnormal, truncated apo B species, apo B-37. The other apo B allele was associated with reduced plasma concentrations of the normal apo B species, apo B-100. H.J.B., the proband, and two of his siblings had both abnormal apo B alleles and were therefore compound heterozygotes for familial hypobetalipoproteinemia. Their average LDL-cholesterol level was 6 +/- 9 mg/dl. All of the offspring of the three compound heterozygotes had hypobetalipoproteinemia, and each had evidence of only one of the abnormal apo B alleles. In the entire kindred, we identified six heterozygotes for familial hypobetalipoproteinemia who had only the abnormal apo B-37 allele and their average LDL cholesterol was 31 +/- 12 mg/dl. We identified 10 heterozygotes who had only the allele for reduced plasma concentrations of apo B-100 and their LDL cholesterol level was 31 +/- 15 mg/dl. Unaffected family members (n = 22) had LDL cholesterol levels of 110 +/- 27 mg/dl. This report describes the first kindred in which two distinct abnormal apo B alleles have been identified, both of which are associated with familial hypobetalipoproteinemia.     

Apolipoprotein B-100 deficiency. Intestinal steatosis despite apolipoprotein B-48 synthesis

We describe a child, the issue of phenotypically normal parents, who had fat malabsorption, both intestinal and hepatic steatosis, and serum cholesterol and triglyceride concentrations of 38 and 63 mg/dl, respectively. Lipoprotein electrophoresis, Ouchterlony double diffusion, and electron microscopy demonstrated that normal low density lipoproteins (LDL: 1.006 less than rho less than 1.063 g/ml) were absent. Lipoprotein particles in the rho less than 1.006-g/ml fraction were triglyceride rich, very large (93.2 +/- 35.1 nm), and contained the B-48 but not the B-100 apoprotein; both species of apolipoprotein (apo) B were found in the parents' lipoproteins. These chylomicrons and chylomicron remnants were present even in the patient's fasting plasma, which suggested prolonged dietary fat absorption. Plasma levels of high density lipoprotein lipids and proteins were low, and the phosphatidylcholine/sphingomyelin ratio was reduced as in typical abetalipoproteinemia. The monosialylated form of apo C-III was not identified on polyacrylamide gel electrophoresis, which suggested that this protein was elaborated only with very low density lipoproteins (VLDL). A radioimmunoassay for apo B employing a polyclonal antisera to plasma LDL gave apparent plasma apo B levels of 0.6, 66, and 57 mg/dl in the patient and his father and mother, respectively. The displacement curve generated by the parents' VLDL and LDL did not did not differ from control lipoproteins. The patient's chylomicron-chylomicron remnant fraction displaced normal LDL over the entire radioimmunoassay range, but the efficiency of displacement was strikingly less than with B-100 containing lipoproteins. If the patient's B-48 protein is not qualitatively abnormal, these results confirm very limited immunochemical cross-reactivity between at least one major epitope on B-100 and the epitopes expressed on B-48. The apo B defect in this patient appears to be recessive. It abolishes B-100 production and may additionally limit the formation of B-48.     

Lipoprotein composition and HDL particle size distribution in women with non-insulin-dependent diabetes mellitus and the effects of probucol treatment

To further characterize the spectrum of potentially atherogenic disturbances in lipoprotein composition in non-insulin-dependent diabetes mellitus (NIDDM), we have studied a subset of women with NIDDM before and after treatment with the lipophilic lipid-lowering drug probucol (1 gm day), which we have shown corrects certain compositional abnormalities these women share with subjects who have hypercholesterolemia. Before treatment, the NIDDM group had a somewhat higher plasma triglyceride level (154 +/- 58.3 mg/dl, vs control, 80.0 +/- 21 mg/dl [mean +/- SD]; p less than 0.025) than controls but their cholesterol and high-density lipoprotein cholesterol (HDL-C) levels did not differ from control levels. A number of significant disturbances, however, were present in the surface and core lipid composition of their lipoproteins. Although the cholesterol content of NIDDM low-density lipoprotein (LDL) was similar to that of controls, its content of sphingomyelin and phosphatidylinositol plus phosphatidylserine and sphingomyelin-to-lecithin ratio all were significantly reduced. Moreover, their very-low-density lipoprotein (VLDL) and HDL2 tended to have reduced amounts of free (unesterified) cholesterol (FC) relative to lecithin, and their HDL2 and HDL3 tended to be triglyceride enriched. Probucol therapy resulted in significant decreases in total plasma cholesterol (-15%), FC (-28%), HDL-C (-22%), and triglyceride (-16%) and in apoproteins A-I, B, and E (apo A-I, B, and E), without changing diabetic control (before probucol: hemoglobin A1, cholesterol, 10.7% +/- 2.7%; after probucol: 10.9% +/- 3.0%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Abnormal concentrations of CII, CIII, and E apolipoproteins among apolipoprotein B-containing, B-free, and A-I-containing lipoprotein particles in hemodialysis patients

Serum concentrations of total cholesterol, triglycerides, and apolipoproteins (apo) A-I, B, CII, CIII, and E in 36 hemodialysis patients and nine anephric patients were compared with the concentrations in 34 normolipidemic subjects. The dialysis patients displayed a moderate hypertriglyceridemia (1.94 +/- 0.12 vs 1.09 +/- 0.11 mmol/L in controls, mean +/- SEM; P less than 0.001), apo CIII concentrations were also increased (130.2 +/- 2.1 vs 108.4 +/- 0.7 mg/L; P less than 0.001), whereas apo CII (34.5 +/- 0.5 vs 36 +/- 0.5 mg/L; P less than 0.05), apo E (22.7 +/- 0.3 vs 27.9 +/- 0.2 mg/L; P less than 0.001), and apo A-I (1.18 +/- 0.05 vs 1.31 +/- 0.04 g/L; P less than 0.05) were decreased. Concentrations of serum apo B were normal (0.86 +/- 0.03 vs 0.97 +/- 0.07 g/L). In the hemodialysis patients, apo CIII concentrations were increased in apo B-containing lipoproteins (30.1 +/- 0.5 vs 25.0 +/- 0.1 mg/L; P less than 0.001), whereas CII and E were decreased below control values (14.4 +/- 0.2 vs 16.8 +/- 0.1, and 8.2 +/- 0.2 vs 11.4 +/- 0.1 mg/L, respectively; P less than 0.001 each). By calculation, non-B-containing lipoproteins in the hemodialysis group had increased concentrations of apo CIII (100.1 +/- 2.1 vs 83.3 +/- 0.7 mg/L; P less than 0.001) and decreased amounts of apo E (14.5 +/- 0.4 vs 16.4 +/- 0.3 mg/L; P less than 0.001); apo CII content was unchanged (20.1 +/- 0.5 vs 19.3 +/- 0.5 mg/L). Results for apo CII, CIII, and E among apo A-I-containing lipoproteins in both normolipidemic and hemodialysis groups were similar to those in non-B-containing lipoproteins. Finally, the sole significant (P less than 0.01) difference between the anephric and hemodialysis groups was the lower apo E concentrations in the former group. Accumulation of triglyceride-rich lipoproteins in hemodialysis patients may thus be related to the enrichment of apo CIII in apo B-containing lipoproteins and to a marked decrease in the apo CII and E contents.     

Chylomicronemia due to apolipoprotein CIII overexpression in apolipoprotein E-null mice. Apolipoprotein CIII-induced hypertriglyceridemia is not mediated by effects on apolipoprotein E.

The mechanism of apolipoprotein (apo) CIII-induced hypertriglyceridemia remains uncertain. We crossed apoCIII transgenic and apoE gene knockout (apoE0) mice, and observed severe hypertriglyceridemia with plasma triglyceride levels of 4,521+/-6, 394 mg/dl vs. 423+/-106 mg/dl in apoE0 mice, P < 0.00001 for log(triglycerides [TG]). Cholesterols were 1,181+/-487 mg/dl vs. 658+/-151 mg/dl, P < 0.0001. Lipoprotein fractionation showed a marked increase in triglyceride-enriched chylomicrons+VLDL. This increase was limited to the lowest density (chylomicrons and Sf 100-400) subfractions. Intermediate density lipoproteins (IDL)+LDL increased moderately, and HDL decreased. There was no significant increase in triglyceride production in apoCIII transgenic/apoE0 mice. The clearance of VLDL triglycerides, however, was significantly decreased. Lipoprotein lipase in postheparin plasma was elevated, but activation studies suggested LPL inhibition by both apoCIII transgenic and apoCIII transgenic/apoE0 plasma. ApoCIII overexpression also produced a marked decrease in VLDL glycosaminoglycan binding which was independent of apoE. The predominant mechanism of apoCIII-induced hypertriglyceridemia appears to be decreased lipolysis at the cell surface. The altered lipoprotein profile that was produced also allowed us to address the question of the direct atherogenicity of chylomicrons and large VLDL. Quantitative arteriosclerosis studies showed identical results in both apoCIII transgenic/apoE0 and apoE0 mice, supporting the view that very large triglyceride-enriched particles are not directly atherogenic.     

Inference of a molecular defect of apolipoprotein B in hypobetalipoproteinemia by linkage analysis in a large kindred.

Heterozygous hypobetalipoproteinemia is characterized by reduced plasma concentrations of LDL cholesterol, total triglycerides, and apo B to less than 50% of normal values. The molecular basis of this disorder remains unknown. The phenotype cosegregates with a DNA haplotype of the apo B gene in an Idaho pedigree, with a maximum decimal logarithm of the ratio (LOD) score of 7.56 at a recombination rate of zero. Individuals carrying this haplotype had total cholesterol levels of 96 mg/dl, LDL cholesterol levels of 37 mg/dl, triglycerides levels of 51 mg/dl, and apo B levels of 38 mg/dl. This study strongly suggests that apo B mutations underlie hypobetalipoproteinemia, and demonstrates the power of the candidate gene approach in linkage analysis for unraveling genetic determinants in metabolic disorders of undefined etiology.     

Low-dose effect of simvastatin (MK-733) on serum lipids, lipoproteins, and apolipoproteins in patients with hypercholesterolemia

The effects of simvastatin (MK-733), a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on serum lipids, lipoproteins, and apolipoproteins were investigated in 29 patients (12 men, 17 women, aged 37 to 73) with moderate to severe hypercholesterolemia. It was given in doses of 2.5 mg/day for four months and 5 mg/day for the succeeding four months. Total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and apolipoprotein (apo) B decreased by 18% (263 +/- 7 mg/dl to 216 +/- 7 mg/dl, P less than 0.01), 24% (180 +/- 7 mg/dl to 136 +/- 7 mg/dl, P less than 0.01), and 21% (133 +/- 4 mg/dl to 104 +/- 3 mg/dl, P less than 0.01), respectively, four months after treatment. Similar reductions (17%, 24%, and 23%, respectively, P less than 0.01) were observed at eight months. A significant reduction in triglyceride (TG) was observed (173 +/- 15 mg/dl to 136 +/- 11 mg/dl at eight months, P less than 0.01), as was a significant increase in serum high-density lipoprotein cholesterol (HDL-C) (48 +/- 2 mg/dl to 52 +/- 2 mg/dl at eight months, P less than 0.01). However, apo AI and apo AII remained unchanged. Atherogenic indices of (TC--HDL-C)/ HDL-C, LDL-C/HDL-C, and apo B/Apo AI ratios were significantly (P less than 0.01) reduced after treatment. No significant changes were observed in lipoprotein lipase, hepatic TG lipase, and lecithin: cholesterol acyltransferase (LCAT) activities. Simvastatin was well tolerated and no critical side effects were noted in the eight-month study period. These data indicate that simvastatin, even at a low dose of 2.5 to 5 mg daily, causes consistent reductions in serum TC, LDL-C, apo B, and TG, and a rise in HDL-C and antiatherogenic lipoproteins.     

Metabolic basis of hyperapobetalipoproteinemia. Turnover of apolipoprotein B in low density lipoprotein and its precursors and subfractions compared with normal and familial hypercholesterolemia.

The turnover of apolipoprotein B (apo B) in very low density, intermediate density, and low density lipoproteins (VLDL, IDL, and LDL) and in the light and heavy fractions of LDL was determined in seven patients with hyperapobetalipoproteinemia (hyperapo B), six normolipidemic subjects, and five patients with heterozygous familial hypercholesterolemia (FH). After receiving an injection of 125I-VLDL, hyperapo B patients were found to have a higher rate of synthesis of VLDL-apo B than controls (40.1 vs. 21.5 mg/kg per d, P less than 0.05) but a reduced fractional catabolic rate (FCR) (0.230 vs. 0.366/h, P less than 0.01). After receiving an injection of 131I-LDL, hyperapo B patients had higher rates of LDL-apo B synthesis than controls (23.1 vs. 13.0 mg/kg per d, P less than 0.001), as did FH patients (22.7 mg/kg per d). The FCR of LDL was similar in hyperapo B patients and controls (0.386 vs. 0.366/d) but was markedly decreased in FH patients (0.192/d). Most subjects exhibited precursor-product relationships between VLDL and IDL, and all did between IDL and light LDL; an analogous relationship between light and heavy LDL was evident in most hyperapo B patients and controls but not in FH patients. Simultaneous injection of differentially labeled LDL fractions and deconvolution analysis showed increased light LDL synthesis with normal conversion into heavy LDL in hyperapo B, whereas in FH conversion of light LDL was reduced and there was independent synthesis of heavy LDL. These data show that the increased concentration of LDL-apo B in hyperapo B is solely due to increased LDL synthesis, which is secondary to increased VLDL synthesis; in contrast, in FH there is both an increase in synthesis of LDL (which is partly VLDL-independent) and reduced catabolism.     

Serum and lipoprotein apolipoprotein B levels in normal subjects and patients with hyperlipoproteinaemia.

Apolipoprotein B (apo B) levels were measured by radioimmunoassay in the serum and lipoproteins from normal subjects and patients with hyperlipoproteinaemia. The total serum apo B concentration in normal subjects was 0.91 +/- 0.16 g/l (mean +/- S.D.); in type IIa hyperlipoproteinaemia it was 2.24 +/- 0.61 g/l; in type IIb, 3.05 +/- 1.24 g/l; in type IV, 2.24 +/- 0.99 g/l; and in type V, 1.30 +/- 0.16 g/l. In normal subjects 5.6 +/- 2.1% (mean +/- S.D.) of total apo B was present in very low density lipoproteins (VLDL) and 93 +/- 9% in low density lipoproteins (LDL). Corresponding values for type IIa were 3.8 +/- 1.9% and 93 +/- 3%, for type IIb, 9.9 +/- 7.5% and 91 +/- 1%, for type IV, 16.9 +/- 9.5% and 81 +/- 9%, and for type V, 38.4 +/- 11.0% and 52 +/- 8%. The ratio of cholesterol to apo B in serum was decreased in types IIa, IIb and IV, and increased in type V whereas the ratio of triglyceride to apo B in serum was decreased in type IIa, normal in type IIb and increased in types IV and V. The ratio of cholesterol to apo B in VLDL was increased in types IIa, IIb and V, but normal in type IV, whereas in LDL, this ratio was normal in types IIa and V but reduced in types IIb and IV. The ratio of triglycerides to apo B in VLDL was normal in types IIa, IIb and IV but raised in type V. In LDL, this ratio was increased in types IIb and IV but normal in types IIa and V.