Autologous Low Density Lipoprotein Research Articles

Functionalized Low-Density Lipoprotein Nanoparticles for in Vivo Enhancement of Atherosclerosis on Magnetic Resonance Images

To allow visualization of macrophage-rich and miniature-sized atheromas by magnetic resonance (MR) imaging, we have converted low-density lipoprotein (LDL) into MR-active nanoparticles via the intercalation of a 1,4,7,10-tetraazacyclodecane-1,4,7-triacetic acid (DO3A) derivative and the subsequent coordination reaction with Gd(3+). After careful removal of nonchelated Gd(3+), an MR-active LDL (Gd(3+)-LDL) with a remarkably high payload of Gd(3+) (in excess of 200 Gd(3+) atoms per particle) and a high relaxivity (r(1) = 20.1 s(-1) mM(-1) per Gd(3+) or 4040 s(-1) mM(-1) per LDL) was obtained. Dynamic light-scattering photon correlation spectroscopy (DLS) and cryo transmission electron microscope (cryoTEM) images showed that Gd(3+)-LDL particles did not aggregate and remained of a similar size (25-30 nm) to native LDL. Intravenous injection of Gd(3+)-LDL into an atherosclerotic mouse model (ApoE(-/-)) resulted in an extremely high enhancement of the atheroma-bearing aortic walls at 48 h after injection. Free Gd(3+) dissociation from Gd(3+)-LDL was not detected over the imaging time window (96 h). Because autologous LDL can be isolated, modified, and returned to the same patient, our results suggest that MR-active LDL can potentially be used as a noninfectious and nonimmunogenic imaging probe for the enhancement of atheroplaques presumably via the uptake into macrophages inside the plaque.

Transendothelial lipoprotein exchange and microalbuminuria.

Microalbuminuria associates with increased risk of atherosclerosis in individuals without diabetes. We hypothesized that transendothelial lipoprotein exchange is elevated among such individuals, possibly explaining increased intimal lipoprotein accumulation and thus atherosclerosis. Using an in vivo isotope technique, transendothelial exchange of low density lipoprotein (LDL) was measured in 77 non-diabetic individuals. Autologous 131-iodinated LDL was reinjected intravenously, and the 1-h fractional escape rate was calculated as index of transendothelial exchange. There was no difference in transendothelial LDL exchange between subjects with microalbuminuria versus normoalbuminuria (mean (95% confidence interval) 3.8%/h (3.3-4.3%/h) versus 4.2%/h (3.7-4.7%/h); P=0.33). In contrast, there was a positive correlation between transendothelial LDL exchange and (logarithmically transformed) plasma insulin: beta=0.6 (95% CI: 0.1-1.1); R=0.22; P<0.05. This correlation was independent of age, sex, blood pressure, plasma concentration of lipoproteins, LDL size, body mass index, plasma volume, and use of medicine, and it was unlikely caused by altered hepatic LDL receptor expression, or glycosylation of LDL. In non-diabetic individuals, transendothelial LDL exchange is not associated with microalbuminuria, but possibly with hyperinsulinemia.

Transvascular lipoprotein transport in patients with chronic renal disease

While increased plasma cholesterol is a well-established cardiovascular risk factor in the general population, this is not so among patients with chronic renal disease. We hypothesized that the transvascular lipoprotein transport, in addition to the lipoprotein concentration in plasma, determines the degree of atherosclerosis among patients with chronic renal disease. We used an in vivo method for measurement of transvascular transport of low-density lipoprotein (LDL) in 21 patients with chronic renal disease and in 42 healthy control patients. Autologous 131-iodinated LDL was reinjected intravenously, and the 1-hour fractional escape rate was taken as index of transvascular transport. Transvascular LDL transport tended to be lower in patients with chronic renal disease than in healthy control patients [3.3 (95% CI 2.4-4.2) vs. 4.2 (3.7-4.2)%/hour; NS]. However, this tendency disappeared when transvascular LDL transport was corrected for distribution volume of LDL [1.7 (1.2-2.2) vs. 1.8 (1.6-2.0) %/(hour x (L/m(2))); NS]. There was significant variation in transvascular LDL transport between diabetic patients with chronic renal disease, nondiabetic patients with chronic renal disease, and healthy control patients [5.0 (3.2-7.8) vs. 3.0 (2.2-3.8) vs. 4.2 (3.6-4.8) %/hour; P < 0.01 after adjustment for distribution volume of LDL]. This variation was unlikely caused by altered hepatic LDL receptor expression or glycosylation of LDL in diabetes patients. Transvascular LDL transport may be increased in diabetic patients with chronic renal disease, suggesting that lipoprotein flux into the arterial wall is increased. A similar mechanism does not operate in nondiabetic patients with chronic renal disease.

Increased transvascular low density lipoprotein transport in insulin dependent diabetes: a mechanistic model for development of atherosclerosis

Background: The increased risk of atherosclerosis associated with diabetes cannot be explained by conventional cardiovascular risk factors alone. We hypothesized that transvascular lipoprotein transport may be increased in patients with diabetes, possibly explaining increased intimal lipoprotein accumulation and thus atherosclerosis. Methods: We used an in vivo method for measurement of transvascular transport of low density lipoprotein (LDL) and applied it in 24 patients with insulin dependent diabetes mellitus (type 1) and in 30 healthy controls. LDL was individually sampled and autologous 131-iodinated LDL was reinjected intravenously in addition to 125-iodinated albumin, and the 1-h fractional escape rates were taken as indices of transvascular transport. Results: Transvascular LDL transport was 5.7±2.2 and 4.0±1.8%/h in patients with diabetes and controls ( P<0.005); equivalent values for albumin were 6.8±2.5 and 5.4±2.0%/h ( P<0.05). This difference most likely was not caused by altered hepatic LDL receptor expression, glycosylation of LDL, small LDL size, nephropathy, statin use, or different plasma insulin levels in diabetes patients. Conclusion: Transvascular LDL transport may be increased in patients with type 1 diabetes. This suggests that lipoprotein flux into the arterial wall is increased in people with type 1 diabetes, possibly explaining accelerated development of atherosclerosis.

The susceptibility of lipoprotein(a) to copper oxidation is correlated with the susceptibility of autologous low density lipoprotein to oxidation

Objectives Lipoprotein(a) [Lp(a)] can be oxidized by copper in vitro in a way comparable to low-density lipoprotein (LDL). We sought to determine whether the susceptibility of Lp(a) to oxidation is correlated with the susceptibility of autologous heterogeneous LDL, with apolipoprotein(a) [apo(a)] molecular size, or with both factors. Design and methods We examined shifts in electrophoretic mobility of Lp(a) and LDL caused by copper oxidation in plasma samples from 81 healthy men. The effect of copper oxidation on different-sized apo(a) was also evaluated. Results There was a close correlation between the relative electrophoretic mobilities of oxidized Lp(a) and oxidized LDL in subjects, especially with small-sized apo(a) ( n = 25, r = 0.72, p < 0.0001). Oxidative processes in Lp(a) resulted in the degradation of large-, but not small-sized apo(a). Conclusions The susceptibility of Lp(a) to oxidation is correlated with that of autologous LDL. Large-sized apo(a) may be involved in the Lp(a) oxidation.

The Effect of Vitamin E and Vitamin C Supplementation on LDL Oxidizability and Neutrophil Respiratory Burst in Young Smokers

Objective: The purpose of this study was to determine the effect of vitamin E and/or vitamin C supplementation on low-density lipoprotein (LDL) oxidizability and neutrophil (PMN) superoxide anion production in young smokers.Methods: Thirty smokers with a <5 pack-year history were randomly assigned to take placebo; vitamin C (1 g/day); vitamin E (400 IU/day); or both vitamins in a double-blind fashion. Subjects took the supplements for 8 weeks. At weeks 0 and 8, blood was collected for isolation of LDL and PMN, and for antioxidant vitamin analysis. LDL was oxidized with a copper (Cu) catalyst, and oxidation was measured by formation of conjugated dienes over a 5-hour time course. Lag times and maximum oxidation rates were calculated from the time course data. PMN superoxide anion release was assessed by respiratory burst after stimulation with phorbol ester and opsonized zymosan, and their ability to oxidize autologous LDL following treatment with the above stimuli was measured with the conjugated diene assay.Results: Subjects who received vitamin E alone had a significant increase in the lag phase of Cu-catalyzed LDL oxidation (week 0, 118 ± 31 min vs. week 8, 193 ± 80 min, mean ± SD, p < 0.05), whereas the vitamin C and placebo groups had no changes in LDL oxidation kinetics. The group receiving both vitamins E and C had a significant reduction in oxidation rate (week 0, 7.4 ± 2.3 vs. week 8, 5.1 ± 2.1, p < 0.05). There were no significant changes for any group in PMN superoxide anion production or PMN LDL oxidation after stimulation with either phorbol ester or opsonized zymosan. Plasma and LDL vitamin E concentrations were significantly increased in both groups that received vitamin E. The subjects who received vitamin C alone had no significant change in plasma vitamin C concentrations; however, when data were pooled from both groups who received vitamin C, the increases were significant.Conclusion: Vitamin E supplementation of young smokers was effective in reducing Cu-catalyzed LDL oxidizability; however, vitamin E and/or C supplementation showed few significant effects on the more physiologically relevant PMN function. This casts doubt on the ability of antioxidant supplementation to reduce oxidative stress in smokers in vivo. Therefore, smoking cessation remains the only means by which young smokers can prevent premature coronary heart disease.

Effects of continuous conjugated estrogen and micronized progesterone therapy upon lipoprotein metabolism in postmenopausal women

AbstractThe effects of continuously administering both conjugated equine estrogens (CEE) and micronized progesterone (MP) on the concentration, composition, production and catabolism of very low density (VLDL) and low density lipoproteins (LDL) have not previously been reported. The mechanism of the hormonally induced reductions of plasma LDL cholesterol of Sf 0–20 (mean 16%, P < 0.005) and LDL apoB (mean 6%, P < 0.025) were investigated by studying the kinetics of VLDL and LDL apolipoprotein (apo) B turnover after injecting autologous 131I-labeled VLDL and 125I-labeled LDL into each of the 6 moderately hypercholesterolemic postmenopausal subjects under control conditions and again in the fourth week of a 7-week course of therapy (0.625 mg/d of CEE + 200 mg/d of MP). The combined hormones significantly lowered plasma LDL apoB by increasing the mean fractional catabolic rate of LDL apoB by 20% (0.32 vs. 0.27 pools/d, P < 0.03). Treatment also induced a significant increase in IDL production (6.3 vs. 3.7 mg/kg/d, P = 0.028). However, this did not result in an increase in LDL production because of an increase in IDL apoB direct catabolism (mean 102%, P = 0.033). VLDL kinetic parameters were unchanged and the concentrations of plasma total triglycerides (TG), VLDL-TG, VLDL-apoB did not rise as often seen with estrogen alone. Plasma HDL-cholesterol rose significantly (P < 0.02). Our major conclusion is that increased fractional catabolism of LDL underlies the LDL-lowering effect of the combined hormones. —Wolfe, B. M., P. H. R. Barrett, L. Laurier, and M. W. Huff. Effects of continuous conjugated estrogen and micronized progesterone therapy upon lipoprotein metabolism in postmenopausal women. J. Lipid Res. 2000. 41: 368–375.

Variation of apolipoprotein B as a possible cause of decreased low density lipoprotein clearance and hypercholesterolemia

The fractional catabolic rate (FCR) for low density lipoprotein (LDL) apolipoprotein B (apo B) was studied to explore the variations in apo B as a possible cause of hypercholesterolemia. The FCR of radioiodine labelled autologous LDL and homologous LDL isolated from a normocholesterolemic subject were compared in forty-nine type II hypercholesterolemic males and females with the mean plasma concentration of total cholesterol of 7.78 mmol/l, LDL-cholesterol 5.41 mmol/l and triglycerides 2.09 mmol/l. In most patients the autologous LDL was catabolized at an equal rate and sometimes even faster than the homologous LDL. However, twelve out of forty-nine patients catabolized homologous LDL 0.8–19.3% faster than autologous LDL and several apo B polymorphisms were determined. No apo B-3500 or apo B-3531 mutations were detected. Patients with XbaI −/− (absence of cutting site) had lower total, IDL and LDL cholesterol and LDL apoB than the other genotypes. Patients with EcoRI +/+(presence of cutting site) had higher total, VLDL and LDL cholesterol and slower FCR for autologous LDL, and their VLDL was richer in cholesterol than that of patients with the EcoRI +/−. The MspI and ins/del polymorphisms were not associated with variations in the measured parameters. The apo E 4 was associated with higher VLDL and IDL cholesterol, higher triglycerides and LDL apo B than E 3/3. Overall, the determined apo B polymorphisms were not related to the slow clearance of autologous LDL among the 12 patients, in whom autologous LDL was cleared at a slower rate than homologous LDL. In conclusion, hypercholesterolemia can be due to particle-related slow clearance of LDL in some patients. However, this is not a common cause of hypercholesterolemia.

Vascular 131I-low-density lipoprotein imaging in patients with hypertension and early atherosclerotic lesions in the carotid artery.

The reinjection of autologous 131I-labelled low-density lipoprotein (LDL) followed by vascular scintigraphy has been used to investigate lipid-containing plaques, but no information is available on the early stages of plaques in hypertensives. Vascular scintigraphy after re-injection of autologous 131I-labelled LDL was used to investigate early atherosclerotic lesions visualized by sonography in the carotid arteries of patients with hypertension. 10 male patients (4 smokers; mean age 56 +/- 8 years;) with early carotid atherosclerosis (mono- or bilateral; intima-media-thickness ranging from 1.5 to 3.5 mm) as shown by sonography were studied. All these normolipemic patients suffered from primary hypertension and were treated with diuretics. As controls 6 healthy male subjects (3 smokers; mean age 54 +/- 9 years;), with normal blood pressure and lipid pattern were recruited. Hot spots appeared in the areas with early atherosclerosis in 7 patients, while none were seen in controls. Positive kinetic curves were observed in 4 patients. No significant differences emerged in the target/non-target ratios. Vascular lipoprotein uptake in hypertensive patients is apparently late and rather limited; the uptake pattern may depend on plaque composition.

Dietary beef tallow alters the fatty acid profiles of bile and liver membranes, but not secretion of cholesterol in bile

To test the hypothesis that type and amount of dietary fat has a regulatory effect on secretion of cholesterol in bile, young growing pigs were fed diets containing either 20% or 40% of energy as primarily either beef tallow or soybean oil or as a 50:50 (wt:wt) blend of tallow and soybean oil. After week 6, pigs were injected with autologous low-density lipoproteins containing 3H-cholesterol. Serial bile samples were collected for 24 hours; then tissues were collected. Amount of tallow in dietary fat correlated positively (P < 0.05) with amounts of palmitoleic and oleic and negatively with linoleic and linolenic fatty acids in biliary phospholipids. In addition, amount of tallow in dietary fat correlated positively with amounts of myristic, palmitoleic and oleic acids but negatively with stearic acid in membranes of liver. Composition of dietary fat, however, did not affect concentration or daily secretion of cholesterol, bile acids or phospholipids in bile. Furthermore, secretion of 3H-cholesterol as biliary cholesterol or bile acids was not affected by type or amount of dietary fat. Concentration of cholesterol in liver tended to be greater in pigs fed diets containing tallow (P<0.10); no differences in cholesterol concentrations, however, were seen in aorta, heart, skeletal muscle, or gastrointestinal tract. Percentage of injected 3H-cholesterol was greater (P<0.001) in perirenal adipose tissue from pigs fed diets containing soy oil than from pigs fed diets containing tallow. There were no significant differences (P<0.05) seen in percentage of injected 3H-cholesterol deposition in several other organs. In summary, type of dietary fat altered fatty acid composition of biliary phospholipids and liver membranes but had no effect on cholesterol secretion into bile and no major effects on cholesterol distribution in major organs of young pigs.

Delayed Low Density Lipoprotein (LDL) Catabolism Despite a Functional Intact LDL-Apolipoprotein B Particle and LDL-Receptor in a Subject with Clinical Homozygous Familial Hypercholesterolemia

We identified a 38-yr-old male patient with the clinical expression of homozygous familial hypercholesterolemia presenting as severe coronary artery disease, tendon and skin xanthomas, arcus lipoides, and joint pain. The genetic trait seems to be autosomal recessive. Interestingly, serum concentrations of cholesterol responded well to diet and statins. We had no evidence of an abnormal low density lipoprotein (LDL)-apolipoprotein B (apoB) particle, which was isolated from the patient using the U937 proliferation assay as a functional test of the LDL-binding capacity. The apoB 3500 and apoB 3531 defects were ruled out by PCR. In addition, we found no evidence for a defect within the LDL-receptor by skin fibroblast analysis, linkage analysis, single-strand conformational polymorphism and Southern blot screening across the entire LDL-receptor gene. The in vivo kinetics of radioiodinated LDL-apoB were evaluated in the proband and three normal controls, subsequently. The LDL-apoB isolated from the patient showed a normal catabolism, confirming an intact LDL particle. In contrast the fractional catabolic rate (d−1) of autologous LDL in the subject and the normal controls revealed a remarkable delayed catabolism of the patient’s LDL (0.15 vs. 0.33–0.43 d−1). In addition, the elevation of LDL-cholesterol in the patient resulted from an increased production rate with 22.8 mg/kg per day vs. 12.7–15.7 mg/kg per day. These data indicate that there is another catabolic defect beyond the apoB and LDL-receptor gene causing familial hypercholesterolemia.

The influence of age on low density lipoprotein metabolism: effects of cholestyramine treatment in young and old healthy male subjects.

The plasma concentration of low density lipoproteins (LDL) increases with age, mainly as the result of a reduced clearance of LDL. Because the conversion of cholesterol to bile acids is reduced with age, we hypothesized that the response of plasma LDL to stimulation of bile acid production would be different in young and old subjects. Comparison of the response to cholestyramine treatment in two groups of normolipidaemic, normal weight males: seven young (23-34 years) and eight old (64-73 years). Outpatients at the metabolic ward of a university hospital given a standardized diet of natural type. Cholestyramine was given 8 g b.i.d. for 3 weeks and continued during the second LDL turnover study. Kinetics of autologous radiolabelled LDL before and during treatment. Mean values of lipoprotein lipid levels obtained during the two turnover studies. Changes in LDL particle composition and LDL receptor affinity between the two study periods. Both age groups responded with decreased levels of LDL cholesterol and apolipoprotein-B (apoB), the change being more pronounced in the old subjects. The LDL apoB fractional catabolic rate was increased by approximately 11% in both groups. In contrast, there was a reduced ability in the old subjects to sustain their production rates for LDL apoB with resin therapy, resulting in a 23% reduction in LDL input. No effect on the apparent LDL apoB synthesis rate was observed in the young subjects. LDL particles isolated from cholestyramine-treated subjects were triglyceride-enriched and cholesterol-depleted, and showed a lowered affinity for the LDL receptor in tissue culture studies. The results demonstrate that stimulation of bile acid production by cholestyramine treatment decreases LDL cholesterol levels in both young and old subjects. This therapy increases LDL apoB elimination in both age groups, but reduction of apparent LDL apoB production is only seen in old subjects.

Erdheim-chester disease: Low low-density lipoprotein levels due to rapid catabolism

We have identified a 44-year-old patient with symmetrically excessive xanthomatosis, called Erdheim-Chester disease (ECD), and simultaneously decreased levels of low-density lipoprotein (LDL) cholesterol. Clinically, this patient presents lipoidgranulomatosis of numerous long and flat bones with involvement of the liver, spleen, pericardium, pleura, thyroid, skin, conjunctiva, and gingiva. However, the patient does not have any signs of atherosclerosis. So far, the underlying defect has not been elucidated. We performed a LDL—apolipoprotein B (apoB) kinetic study in the ECD patient and a normal control to determine the etiology of the low LDL level in ECD. LDL was isolated from both subjects, radioiodinated with either 131I or 125I, and injected simultaneously into the ECD patient and the normal control. Normal and ECD LDL was catabolized at the same rate after injection into the control subject (fractional catabolic rate [FCR], 0.43/d and 0.46/d, respectively). Therefore, LDL isolated from an ECD subject is metabolically normal. In contrast, autologous LDL injected into the ECD subject showed a markedly increased catabolism (FCR, 0.69/d) compared with that in the control subject (FCR, 0.43/d). This is the first report about increased catabolism of LDL cholesterol in a patient.

Preparation and biodistribution of 99mtechnetium labelled oxidized LDL in man

Radiolabelled autologous low density lipoprotein (LDL) has previously been used to study in vivo distribution and metabolism of native-LDL. Non-invasive imaging of atherosclerotic lesions using 99mTc-LDL was shown to be feasible in animal models and patients but the clinical utility remains to be assessed. Since recent reports suggest that oxidized LDL may play a major role in the pathogenesis of atherosclerosis, we developed a technique to oxidize autologous LDL and compared the biodistribution of oxidized-LDL with that of native-LDL in man. In addition, we evaluated the uptake in vivo of oxidized- and native-LDL by atherosclerotic plaques. LDL, obtained from human plasma was treated with various combinations of copper ions and H 2O 2 to induce oxidative modification by increasing the content of lipid peroxidation products and electrophoretic mobility. When LDL (0.3 mg/ml) was incubated with 100 μM Cu 2+ and 500 μM H 2O 2 oxidation occurred rapidly within 1 h, and was labelled with 99mTc efficiently as native LDL. In vivo distribution studies revealed a faster plasma clearance of oxidized-LDL compared to native-LDL, and a higher uptake by the reticuloendothelial system. Tomographic scintigraphy of the neck in patients suffering from transient ischemic attacks, revealed accumulation of radiolabelled LDL preparations in the carotid artery affected by atherosclerotic lesions. We developed a technique to rapidly oxidize LDL using copper and H 2O 2. Biodistribution data demonstrate that oxidized-LDL is rapidly cleared from circulation, is taken up mostly by organs rich in macrophages, and can be detected at the level of carotid plaques.

Preparation and biodistribution of 99mtechnetium labelled oxidized LDL in man

Radiolabelled autologous low density lipoprotein (LDL) has previously been used to study in vivo distribution and metabolism of native-LDL. Non-invasive imaging of atherosclerotic lesions using 99mTc-LDL was shown to be feasible in animal models and patients but the clinical utility remains to be assessed. Since recent reports suggest that oxidized LDL may play a major role in the pathogenesis of atherosclerosis, we developed a technique to oxidize autologous LDL and compared the biodistribution of oxidized-LDL with that of native-LDL in man. In addition, we evaluated the uptake in vivo of oxidized- and native-LDL by atherosclerotic plaques. LDL, obtained from human plasma was treated with various combinations of copper ions and H2O2 to induce oxidative modification by increasing the content of lipid peroxidation products and electrophoretic mobility. When LDL (0.3 mg/ml) was incubated with 100 μM Cu2+ and 500 μM H2O2 oxidation occurred rapidly within 1 h, and was labelled with 99mTc efficiently as native LDL. In vivo distribution studies revealed a faster plasma clearance of oxidized-LDL compared to native-LDL, and a higher uptake by the reticuloendothelial system. Tomographic scintigraphy of the neck in patients suffering from transient ischemic attacks, revealed accumulation of radiolabelled LDL preparations in the carotid artery affected by atherosclerotic lesions. We developed a technique to rapidly oxidize LDL using copper and H2O2. Biodistribution data demonstrate that oxidized-LDL is rapidly cleared from circulation, is taken up mostly by organs rich in macrophages, and can be detected at the level of carotid plaques.

Dietary fish oil decreases low-density-lipoprotein clearance in nonhuman primates

To assess whether fish oil-induced alterations in low-density-lipoprotein (LDL) composition have distinct and important effects on LDL metabolism, we evaluated LDL kinetic behavior in cynomolgus macaques fed an atherogenic diet supplemented with either fish oil (1.6 g n-3 fatty acids; n = 10) or olive oil (n = 9) for > or = 6 mo. LDL from monkeys supplemented with fish oil or olive oil was isolated, labeled with either 125I or 131I, and simultaneously reinjected so that each monkey received its own (autologous injection) and donor (homologous injection) LDL. For LDL injected autologously (monkeys that received their own LDL), the LDL fractional clearance rate (FCR) was reduced in fish oil-supplemented monkeys compared with the olive oil-supplemented controls (0.42 +/- 0.03 compared with 0.56 +/- 0.05 pools/d, P = 0.04). The cholesteryl ester content of fish oil LDL increased compared with olive oil LDL (43 +/- 2% and 36 +/- 3%, respectively, P = 0.03), and the LDL cholesteryl ester content was strongly correlated with autologous LDL clearance (r = -0.76, P = 0.0001). Compared with olive oil LDL, fish oil LDL had a reduced dissociation constant (KD) for binding to the LDL receptor in vitro (KD for fish oil LDL compared with olive oil LDL: 13.9 +/- 1.8 and 7.4 +/- 1.0 mg LDL protein/L, P = 0.03). When both fish oil LDL and olive oil LDL were simultaneously injected into fish oil-supplemented monkeys, the FCR of fish oil LDL was decreased compared with olive oil LDL (0.42 +/- 0.03 and 0.52 +/- 0.04 pools/d, P = 0.006). These data suggest that dietary supplementation with fish oil decreases LDL clearance, and that this effect is mediated, at least in part, by altering LDL structure and reducing the affinity of LDL for its receptor.

Effects of continuous low-dosage hormonal replacement therapy on lipoprotein metabolism in postmenopausal women

The effects on lipoprotein metabolism of female hormone replacement therapy (HRT) for 7 weeks with combined low dosages of a widely used oral progestin and estrogen combination, medroxyprogesterone acetate ([MPA] 2.5 mg/d) and conjugated equine estrogen ([CEE] 0.625 mg/d), were studied in six postmenopausal women. To investigate the mechanism of the reduction of low-density lipoprotein (LDL) cholesterol by HRT, the kinetics of very-low-density lipoprotein (VLDL) and LDL apolipoprotein (apo) B turnover were studied by injection of autologous 131l-labeled VLDL and 125l-labeled LDL under control conditions and again in the fourth week of HRT. HRT induced (1) a 12% ± 4% ( P < .02) reduction of the cholesterol content of LDL of S f 0–12, which was attributable to a 15% ± 5% decrease in the mean ratio of cholesterol to apo B (1.3 ± 0.1 v 1.5 ± 0.1, P < .025), and (2) a 13% ± 4% increase in the mean fractional catabolic rate (FCR) of LDL apo B (0.34 ± 0.03 v 0.30 ± 0.02 pools/d, respectively, P ± .05). However, there were no significant changes in mean values for (1) pool size (42 ± 4 v 43 ± 3 mg/kg) or production rate (14 ± 0.5 v 13 ± 0.9 mg/kg/d, P > .1) of LDL apo B or (2) pool size (2.5 ± 0.6 v 2.8 ± 0.6 mg/kg), FCR (8.0 ± 2.0 v 8.1 ± 1.7 pools/d) or production rate (16 ± 4 v 19 ± 2 mg/kg/d, P > .04) of VLDL apo B. HRT increased high-density lipoprotein (HDL) cholesterol concentration significantly (by 16% to 18%, P < .05), whereas the mean ratio of plasma total cholesterol to HDL cholesterol decreased by 19% ± 3% ( P < .005). HRT favorably influenced the overall plasma lipoprotein lipid vascular risk profile while significantly altering both the composition and fractional catabolism of LDL.

Hypercholesterolemia in postmenopausal women: Metabolic defects and response to low-dose lovastatin

Objective. —To determine the metabolic mechanisms underlying hypercholesterolemia in postmenopausal women and to determine whether a low dose of lovastatin will correct this abnormality. Design. —In the first part of the study, turnover rates of autologous low-density lipoprotein (LDL) were measured in hypercholesterolemic and control women. In the second part, hypercholesterolemic women participated in a placebo-controlled, randomized, double-blind study using lovastatin as the therapeutic agent. Setting. —The General Clinical Research Center of the University of Texas Southwestern Medical Center, Dallas, utilizing inpatient and outpatient facilities, and the Veterans Affairs Medical Center, Dallas, Tex. Patients. —For the LDL turnover study, 26 postmenopausal women with moderate hypercholesterolemia (mean±SD LDL cholesterol, 4.78±0.59 mmol/L [185 ±23 mg/dL]) and 13 postmenopausal women with normal levels of plasma lipids and lipoproteins (mean±SD LDL cholesterol, 3.31 ±0.39 mmol/L [128±15 mg/dL]) were studied. Sixteen postmenopausal women participated in the drug study. Interventions. —In the drug study, patients received blindly both lovastatin (10 mg/d) and placebo. Main Outcome Measures. —In the first study, kinetic parameters of LDL metabolism; in the second study, response in lipids and lipoproteins to lovastatin therapy. Results. —In the LDL turnover study, mean (±SD) input (production) rates for LDL apolipoprotein B (apo B) were similar for hypercholesterolemic women and control women (12.4 [±3.2] mg/kg per day and 11.1 [±2.2] mg/kg per day, respectively). In contrast, mean (±SD) fractional catabolic rates for LDL apo B in hypercholesterolemic women (0.29 [±0.04] pools per day) were significantly lower than those in normolipidemic women (0.35 [±0.03] pools per day). In the drug trial, lovastatin therapy reduced mean (±SD) total cholesterol and LDL cholesterol from 7.03 (±1.16) mmol/L (272 [±45] mg/dL) and 4.42 (±0.80) mmol/L (171 [±31] mg/dL, respectively, to 5.70 (±1.03) mmol/L (221 [±40] mg/dL) and 3.46 (±0.85) mmol/L (134 [±33] mg/dL). Conclusions. —The turnover data suggest that hypercholesterolemia in postmenopausal women is primarily attributable to a reduced activity of LDL receptors. In accord, the hypercholesterolemia in these women was effectively lowered by low doses of lovastatin. Thus, a low dose of lovastatin appears highly effective for treatment of moderate hypercholesterolemia in most postmenopausal women, presumably because it reverses the reduction in LDL receptor activity associated with menopause. (JAMA. 1994;271:453-459)

Hypercholesterolemia in Postmenopausal Women

<h3>Objective.</h3> —To determine the metabolic mechanisms underlying hypercholesterolemia in postmenopausal women and to determine whether a low dose of lovastatin will correct this abnormality. <h3>Design.</h3> —In the first part of the study, turnover rates of autologous low-density lipoprotein (LDL) were measured in hypercholesterolemic and control women. In the second part, hypercholesterolemic women participated in a placebo-controlled, randomized, double-blind study using lovastatin as the therapeutic agent. <h3>Setting.</h3> —The General Clinical Research Center of the University of Texas Southwestern Medical Center, Dallas, utilizing inpatient and outpatient facilities, and the Veterans Affairs Medical Center, Dallas, Tex. <h3>Patients.</h3> —For the LDL turnover study, 26 postmenopausal women with moderate hypercholesterolemia (mean±SD LDL cholesterol, 4.78±0.59 mmol/L [185 ±23 mg/dL]) and 13 postmenopausal women with normal levels of plasma lipids and lipoproteins (mean±SD LDL cholesterol, 3.31 ±0.39 mmol/L [128±15 mg/dL]) were studied. Sixteen postmenopausal women participated in the drug study. <h3>Interventions.</h3> —In the drug study, patients received blindly both lovastatin (10 mg/d) and placebo. <h3>Main Outcome Measures.</h3> —In the first study, kinetic parameters of LDL metabolism; in the second study, response in lipids and lipoproteins to lovastatin therapy. <h3>Results.</h3> —In the LDL turnover study, mean (±SD) input (production) rates for LDL apolipoprotein B (apo B) were similar for hypercholesterolemic women and control women (12.4 [±3.2] mg/kg per day and 11.1 [±2.2] mg/kg per day, respectively). In contrast, mean (±SD) fractional catabolic rates for LDL apo B in hypercholesterolemic women (0.29 [±0.04] pools per day) were significantly lower than those in normolipidemic women (0.35 [±0.03] pools per day). In the drug trial, lovastatin therapy reduced mean (±SD) total cholesterol and LDL cholesterol from 7.03 (±1.16) mmol/L (272 [±45] mg/dL) and 4.42 (±0.80) mmol/L (171 [±31] mg/dL, respectively, to 5.70 (±1.03) mmol/L (221 [±40] mg/dL) and 3.46 (±0.85) mmol/L (134 [±33] mg/dL). <h3>Conclusions.</h3> —The turnover data suggest that hypercholesterolemia in postmenopausal women is primarily attributable to a reduced activity of LDL receptors. In accord, the hypercholesterolemia in these women was effectively lowered by low doses of lovastatin. Thus, a low dose of lovastatin appears highly effective for treatment of moderate hypercholesterolemia in most postmenopausal women, presumably because it reverses the reduction in LDL receptor activity associated with menopause. (<i>JAMA</i>. 1994;271:453-459)

Lovastatin enhances hepatic uptake of low density lipoprotein in humans.

A noninvasive method for visualizing the uptake of low density lipoprotein (LDL) was used to investigate the effect of hypolipidemic drugs on LDL uptake by the human liver in vivo. Fourteen hypercholesterolemic patients (six with familial hypercholesterolemia and eight with common hypercholesterolemia) were studied. Autologous LDL particles were isolated and divided into two aliquots; one was labeled with 99mTC and the other with 131I, and both preparations were reinjected simultaneously. The labeled LDL was visualized 24 h later by scanning the thorax and abdomen with a gamma camera, and the liver/heart ratio was calculated as an estimate of the hepatic uptake of LDL. The results of 99mTC-labeled LDL scintigraphy were compared with conventional determinations of the fractional catabolic rate (FCR) for 131I-labeled LDL. The latter correlated best with the liver/heart ratio (r = 0.80, P < 0.001). Lovastatin treatment increased the liver/heart ratio (15%, P < 0.01) in the patients with polygenic hypercholesterolemia and the FCR for LDL in both groups (22%, P < 0.05, for those with familial hypercholesterolemia and 37%, P < 0.01 for those with polygenic hypercholesterolemia). Scanning of the liver using the 99mTC-labeled LDL method provides a noninvasive method for visualizing the hepatic uptake of LDL in vivo in humans. This study also provides direct proof that lovastatin, a drug that enhances LDL receptor activity in the liver, also increases the hepatic uptake of LDL in humans.