Effect of cyclooxygenase-2 inhibition on renal function in elderly persons receiving a low-salt diet. A randomized, controlled trial.

BACKGROUND: Most nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit both cyclooxygenase-1 (COX-1), whose inhibition is associated with gastrointestinal ulceration, and COX-2, whose inhibition is associated with therapeutic benefits. Although agents that do not produce COX-1 activity may have fewer adverse effects, targeted disruption of the COX-2 allele in mice has resulted in severe renal problems, suggesting that COX-2 inhibition may also produce adverse effects. OBJECTIVE: To determine the effect of rofecoxib, a member of the coxib class of drugs and a specific inhibitor of the COX-2 enzyme, on renal function in elderly patients. DESIGN: A randomized, three-period, single-dose crossover study and a randomized, parallel-group, multiple-dose study. SETTING: Clinical research units. PATIENTS: 75 patients 60 to 80 years of age. INTERVENTION: In the first study, single doses of rofecoxib, 250 mg (about 5-fold to 20-fold the recommended dose); indomethacin, 75 mg; and placebo were administered to 15 patients. In the second study, multiple doses of rofecoxib, 12.5 or 25 mg/d; indomethacin, 50 mg three times daily; or placebo were administered to 60 patients. Patients in both studies received a low-sodium diet MEASUREMENTS: Glomerular filtration rate, creatinine clearance, and urinary and serum sodium and potassium values. RESULTS: Compared with placebo, single doses of rofecoxib and indomethacin decreased the glomerular filtration rate by 0.23 m/s (P < 0.001) and 0.18 mL/s (P = 0.003), respectively. In contrast, respective decreases of 0.14, 0.13, and 0.10 mL/s were observed after multiple doses of rofecoxib, 12.5 mg/d (P = 0.019); rofecoxib, 25 mg (P = 0.029), and indomethacin (P = 0.086) were administered. Changes in creatinine clearance and serum and urinary sodium and potassium were less pronounced. CONCLUSIONS: The effects of COX-2 inhibition on renal function are similar to those observed with nonselective NSAIDs. Thus, COX-2 seems to play an important role in human renal function.

Effects of simvastatin and pravastatin on gonadal function in male hypercholesterolemic patients.

Inhibition of cholesterol biosynthesis by hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors could, in theory, adversely affect male gonadal function because cholesterol is a precursor of steroid hormones. The objective of this randomized double-blind trial was to compare the effects of simvastatin, pravastatin, and placebo on gonadal testosterone production and spermatogenesis. After a 6-week placebo and lipid-lowering diet run-in period, 159 male patients aged 21 to 55 years with type IIa or IIb hypercholesterolemia, low-density lipoprotein (LDL) cholesterol between 145 and 240 mg/dL, and normal basal levels of testosterone were randomly assigned to treatment with simvastatin 20 mg (n = 40), simvastatin 40 mg (n = 41), pravastatin 40 mg (n = 39), or placebo (n = 39) once daily. After 24 weeks of treatment, mean total cholesterol levels were decreased 24% to 27% and mean LDL cholesterol was decreased 30% to 34% in the 3 active-treatment groups (P < .001 for all comparisons to placebo). At 24 weeks, there were no statistically significant differences between the placebo group and any of the active-treatment groups for the change from baseline in testosterone, human chorionic gonadotropin (hCG)stimulated testosterone, free testosterone index, follicle-stimulating hormone (FSH), luteinizing hormone (LH), or sex hormone-binding globulin (SHBG). Moreover, there were no statistically significant differences at week 12 or week 24 for the change from baseline in sperm concentration, ejaculate volume, or sperm motility for any active treatment relative to placebo. Both simvastatin and pravastatin were well tolerated. In summary, we found no evidence for clinically meaningful effects of simvastatin or pravastatin on gonadal testosterone production, testosterone reserve, or multiple parameters of semen quality.

Reduced coronary events in simvastatin-treated patients with coronary heart disease and diabetes or impaired fasting glucose levels: subgroup analyses in the Scandinavian Simvastatin Survival Study.

BACKGROUND: Patients with diabetes mellitus (DM) have a marked increase in coronary heart disease (CHD) events relative to those without DM. In a previous report from the Scandinavian Simvastatin Survival Study using a clinical case definition of DM (n = 202), simvastatin-treated patients had significantly fewer CHD events compared with placebo-treated control subjects. OBJECTIVE: To examine the effect of simvastatin therapy on CHD in patients with DM and impaired fasting glucose levels. METHODS: Using the 1997 American Diabetes Association diagnostic criteria, we assessed the effect of simvastatin therapy post hoc for an average of 5.4 years in Scandinavian Simvastatin Survival Study patients with normal fasting glucose (n = 3237), impaired fasting glucose (n = 678), and DM (n = 483). RESULTS: Simvastatin-treated patients with DM had significantly reduced numbers of major coronary events (relative risk [RR] = 0.58; P = .001) and revascularizations (RR = 0.52; P = .005). Total (RR = 0.79; P = .34) and coronary (RR = 0.72; P = .26) mortality were also reduced in DM, but not significantly, due to small sample size. In impaired fasting glucose (IFG) subjects, simvastatin use significantly reduced the number of major coronary events (RR = 0.62; P = .003), revascularizations (RR = 0.57; P = .009), and total (RR = 0.57; P = .02) and coronary (RR = 0.45; P = .007) mortality. CONCLUSION: Our results extend previous findings in patients with DM to a larger cohort, confirming the benefit of cholesterol lowering with simvastatin treatment on CHD events. In addition, significant decreases in total mortality, major coronary events, and revascularizations were observed in simvastatin-treated patients with impaired fasting glucose levels. These results strongly support the concept that cholesterol lowering with simvastatin therapy improves the prognosis of patients with elevated fasting glucose levels (> or =6.0 mmol/L [> or =110 mg/ dL]) or DM and known CHD.

Effect of simvastatin treatment on cardiovascular resource utilization in impaired fasting glucose and diabetes. Findings from the Scandinavian Simvastatin Survival Study.

OBJECTIVE: The Scandinavian Simvastatin Survival Study showed that simvastatin treatment reduced cardiovascular events in hypercholesterolemic subjects with coronary heart disease. The clinical benefits of therapy were similar in all three subgroups: normal fasting glucose (NFG, n = 3,237), impaired fasting glucose (IFG, n = 678), and diabetes (n = 483). This analysis compared the costs of simvastatin treatment with the costs of cardiovascular disease-related hospitalizations in the three subgroups. RESEARCH DESIGN AND METHODS: The cost of simvastatin treatment was defined as the average retail price and the cost of drug safety monitoring and adverse experiences. The costs of cardiovascular disease-related hospitalizations were determined by actual rates of hospitalization and 1995 MEDSTAT diagnosis-related group costs. RESULTS: Within trial, simvastatin treatment cost approximately $6,000 per patient. Simvastatin treatment reduced cardiovascular disease-related hospitalizations by 23% in NFG (P = 0.001), 30% in IFG (P = 0.015), and 40% in diabetic subjects (P = 0.007) within trial (median follow-up of 5.4 years). Average length of stay was reduced by 2.4 days in diabetic subjects (P = 0.021). Total cardiovascular disease-related hospital days were reduced by 28% (P < 0.001) in NFG, 38% (P = 0.005) in IFG, and 55% (P < 0.001) in diabetic subjects. For NFG subjects, simvastatin reduced the average cost of cardiovascular disease-related hospitalizations by $3,585, which offset 60% of the cost of simvastatin therapy. For IFG subjects, average cardiovascular disease-related hospitalization costs were reduced by $4,478, which offset 74% of the drug cost. For diabetic subjects, there was a net cost savings of $1,801 per subject within trial. CONCLUSIONS: Simvastatin significantly reduced cardiovascular disease-related hospitalizations and total hospital days for all three groups and significantly reduced length of stay for the diabetic group in addition to providing significant clinical benefits. The benefits were greatest in the diabetic group, with estimated cost savings within trial from simvastatin treatment.

Lipoprotein changes and reduction in the incidence of major coronary heart disease events in the Scandinavian Simvastatin Survival Study (4S)

BACKGROUND: The Scandinavian Simvastatin Survival Study (4S) randomized 4444 patients with coronary heart disease (CHD) and serum cholesterol 5.5 to 8.0 mmol/L (213 to 310 mg/dL) with triglycerides < or =2.5 mmol/L (220 mg/dL) to simvastatin 20 to 40 mg or placebo once daily. Over the median follow-up period of 5.4 years, one or more major coronary events (MCEs) occurred in 622 (28%) of the 2223 patients in the placebo group and 431 (19%) of the 2221 patients in the simvastatin group (34% risk reduction, P<.00001). Simvastatin produced substantial changes in several lipoprotein components, which we have attempted to relate to the beneficial effects observed. METHODS AND RESULTS: The Cox proportional hazards model was used to assess the relationship between lipid values (baseline, year 1, and percent change from baseline at year 1) and MCEs. The reduction in MCEs within the simvastatin group was highly correlated with on-treatment levels and changes from baseline in total and LDL cholesterol, apolipoprotein B, and less so with HDL cholesterol, but there was no clear relationship with triglycerides. We estimate that each additional 1% reduction in LDL cholesterol reduces MCE risk by 1.7% (95% CI, 1.0% to 2.4%; P<.00001). CONCLUSIONS: These analyses suggest that the beneficial effect of simvastatin in individual patients in 4S was determined mainly by the magnitude of the change in LDL cholesterol, and they are consistent with current guidelines that emphasize aggressive reduction of this lipid in CHD patients.

Effect of simvastatin on ischemic signs and symptoms in the Scandinavian simvastatin survival study (4S).

In patients participating in the Scandinavian Simvastatin Survival Study, cholesterol lowering with simvastatin reduced the incidence of carotid bruits and cerebrovascular events as well as new-onset or worsening of angina pectoris and intermittent claudication. These effects suggest that simvastatin may have a general antiatherosclerotic effect not limited to the coronary bed.

Effect of alendronate on risk of fracture in women with low bone density but without vertebral fractures: results from the Fracture Intervention Trial.

CONTEXT: Alendronate sodium reduces fracture risk in postmenopausal women who have vertebral fractures, but its effects on fracture risk have not been studied for women without vertebral fractures. OBJECTIVE: To test the hypothesis that 4 years of alendronate would decrease the risk of clinical and vertebral fractures in women who have low bone mineral density (BMD) but no vertebral fractures. DESIGN: Randomized, blinded, placebo-controlled trial. SETTING: Eleven community-based clinical research centers. SUBJECTS: Women aged 54 to 81 years with a femoral neck BMD of 0.68 g/cm2 or less (Hologic Inc, Waltham, Mass) but no vertebral fracture; 4432 were randomized to alendronate or placebo and 4272 (96%) completed outcome measurements at the final visit (an average of 4.2 years later). INTERVENTION: All participants reporting calcium intakes of 1000 mg/d or less received a supplement containing 500 mg of calcium and 250 IU of cholecalciferol. Subjects were randomly assigned to either placebo or 5 mg/d of alendronate sodium for 2 years followed by 10 mg/d for the remainder of the trial. MAIN OUTCOME MEASURES: Clinical fractures confirmed by x-ray reports, new vertebral deformities detected by morphometric measurements on radiographs, and BMD measured by dual x-ray absorptiometry. RESULTS: Alendronate increased BMD at all sites studied (P<.001) and reduced clinical fractures from 312 in the placebo group to 272 in the intervention group, but not significantly so (14% reduction; relative hazard [RH], 0.86; 95% confidence interval [CI], 0.73-1.01). Alendronate reduced clinical fractures by 36% in women with baseline osteoporosis at the femoral neck (>2.5 SDs below the normal young adult mean; RH, 0.64; 95% CI, 0.50-0.82; treatment-control difference, 6.5%; number needed to treat [NNT], 15), but there was no significant reduction among those with higher BMD (RH, 1.08; 95% CI, 0.87-1.35). Alendronate decreased the risk of radiographic vertebral fractures by 44% overall (relative risk, 0.56; 95% CI, 0.39-0.80; treatment-control difference, 1.7%; NNT, 60). Alendronate did not increase the risk of gastrointestinal or other adverse effects. CONCLUSIONS: In women with low BMD but without vertebral fractures, 4 years of alendronate safely increased BMD and decreased the risk of first vertebral deformity. Alendronate significantly reduced the risk of clinical fractures among women with osteoporosis but not among women with higher BMD.

Cholesterol-lowering therapy in women and elderly patients with myocardial infarction or angina pectoris: findings from the Scandinavian Simvastatin Survival Study (4S)

BACKGROUND: The Scandinavian Simvastatin Survival Study (4S) demonstrated pronounced reductions in mortality and major coronary events in a cohort of patients with established coronary heart disease (CHD). The present study provides a detailed, post hoc assessment of the efficacy and safety of simvastatin therapy in the following subgroups of 4S patients: those > or = 65 years of age, those < 65 years of age, women, and men. METHODS AND RESULTS: The 4S cohort of 4444 CHD patients included 827 women and 1021 patients > or = 65 years of age. Total cholesterol at baseline was 5.5 to 8.0 mmol/L with triglycerides < or = 2.5 mmol/L. Patients were randomized to therapy with simvastatin 20 to 40 mg daily or placebo for a median follow-up period of 5.4 years. End points consisted of all-cause and CHD mortality, major coronary events (primarily CHD death and nonfatal myocardial infarction), other acute CHD and atherosclerotic events, hospitalizations for CHD and cardiovascular events, and coronary revascularization procedures. Mean changes in serum lipids were similar in the different subgroups. In patients > or = 65 years of age in the simvastatin group, relative risks (95% confidence intervals) for clinical events were as follows: all-cause mortality, 0.66 (0.48 to 0.90); CHD mortality, 0.57 (0.39 to 0.83); major coronary events, 0.66 (0.52 to 0.84); any atherosclerosis-related event, 0.67 (0.56 to 0.81); and revascularization procedures, 0.59 (0.41 to 0.84). In women, the corresponding figures were 1.16 (0.68 to 1.99); 0.86 (0.42 to 1.74), 0.66 (0.48 to 0.91), 0.71 (0.56 to 0.91), and 0.51 (0.30 to 0.86), respectively. CONCLUSIONS: Cholesterol lowering with simvastatin produced similar reductions in relative risk for major coronary events in women compared with men and in elderly (> or = 65 years of age) compared with younger patients. There were too few female deaths to assess the effects on mortality in women. Because mortality rates increased substantially with age, the absolute risk reduction for both all-cause and CHD mortality in simvastatin-treated subjects was approximately twice as great in the older patients.

Safety and tolerability of cholesterol lowering with simvastatin during 5 years in the Scandinavian Simvastatin Survival Study.

BACKGROUND: Long-term safety is an important consideration in the selection and use of drugs, such as lipid-lowering agents, that are prescribed to reduce the risk of clinical events during long periods. METHODS: The Scandinavian Simvastatin Survival Study was designed to evaluate the effects of cholesterol lowering with simvastatin on mortality and morbidity in patients with coronary heart disease. The 4444 patients aged 35 to 70 years (mean, 58.9 years) with angina pectoris or previous myocardial infarction and serum cholesterol levels of 5.5 to 8.0 mmol/L (213-310 mg/dL) receiving a lipid-lowering diet were randomly assigned to take double-blind treatment with simvastatin, 20 to 40 mg once daily, or placebo. In addition to previously reported end-point events, detailed clinical and laboratory safety data were collected during a median follow-up period of 5.4 years (range in survivors, 4.9-6.2 years). RESULTS: The only clearly drug-related serious adverse event during the 5.4-year median follow-up period was a single reversible case of myopathy. The frequencies of persistent elevations of hepatic aminotransferase levels above 3 times the upper limit of normal and of nonviral hepatitis in the simvastatin and placebo treatment groups were not significantly different. Examination of the lens showed no between-group differences, and no previously unrecognized adverse effects of the drug were observed. There were no significant between-group differences in adverse events in any body system. In particular, the frequency of adverse events related to the central nervous system was similar in both groups. CONCLUSION: The safety profile of simvastatin, 20 to 40 mg daily, over 5 years was excellent.

Biochemical and radiologic improvement in Paget's disease of bone treated with alendronate: a randomized, placebo-controlled trial.

PURPOSE: The potent bisphosphonates offer great promise in the management of Paget's disease of bone, but are currently available only as parenteral preparations in most countries. There is a need for a well-tolerated, oral therapy. Furthermore, none of the currently available therapies have been rigorously demonstrated to heal the lytic bone lesions characteristic of this condition. Alendronate is a potent new oral aminobisphosphonate that has shown promising effects on Paget's disease in preliminary studies. METHODS: We report a double-blind, randomized comparison of oral alendronate 40 mg/day and placebo over 6 months in 55 patients with Paget's disease. Efficacy was determined from measurements of biochemical indices of bone turnover (serum alkaline phosphatase and urine N-telopeptide) and blinded radiologic assessment of lytic bone lesions. RESULTS: N-telopeptide excretion declined by 86% and serum alkaline phosphatase by 73% in patients receiving alendronate, but remained stable in patients receiving placebo (P < 0.001 between groups for both indices). Responses were similar whether or not patients had previously received bisphosphonate treatment. Alendronate treatment normalized alkaline phosphatase in 48% of patients. Forty-eight percent of alendronate-treated patients showed radiologic improvement in osteolysis whereas in the placebo group only 4% improved (P = 0.02 for between-groups comparison). No patient in either group showed worsening of osteolysis. Bone histomorphometry indicated that alendronate tended to normalize turnover indices. There was no evidence of abnormal mineralization in bone biopsies taken from 12 alendronate-treated subjects. The treatment was well tolerated. CONCLUSION: Oral alendronate appears to be a safe and effective therapy for Paget's disease and results in healing of lytic bone lesions.

Size transformations of intermediate and low density lipoproteins induced by unesterified fatty acids.

Plasma from individual human subjects is known to contain multiple discrete subpopulations of low (LDL) and intermediate (IDL) density lipoproteins that differ in particle size and density. The metabolic origins of these subpopulations are unknown. Transformation of IDL and larger LDL to smaller, denser LDL particles had been postulated to occur as a result of the combined effects of triglyceride hydrolysis and lipid transfer. However, the presence of multiple small LDL subspecies has been described in patients lacking cholesteryl ester transfer protein. We have characterized an alternative pathway in which size decrements in IDL or LDL are produced in the presence of unesterified fatty acids and a source of apolipoprotein (apo) A-I. Incubation of IDL or LDL subfractions with palmitic acid and either high density lipoproteins (HDL), apoHDL, or purified apoA-I gives rise to apoA-I, apoB-containing complexes that can dissociate into two particles, an apoB-containing lipoprotein with particle diameter 10-30 A smaller than the starting material, and a still smaller species (apparent peak particle diameter 140-190 A) containing lipid and apoA-I but no apoB. The newly formed IDL or LDL are depleted in phospholipid and free cholesterol with no change in apoB-100 as assessed by SDS gel electrophoresis. We hypothesize that this reaction may contribute to the formation of discrete IDL and LDL subpopulations of varying size during the course of hydrolysis of triglyceride-rich lipoproteins in plasma.

Dissociation of high density lipoprotein precursors from apolipoprotein B-containing lipoproteins in the presence of unesterified fatty acids and a source of apolipoprotein A-I.

Incubation of low (LDL), intermediate (IDL), or very low density lipoproteins (VLDL) with palmitic acid and either high density lipoproteins (HDL), delipidated HDL, or purified apolipoprotein (apo) A-I resulted in the formation of lipoprotein particles with discoidal structure and mean particle diameters ranging from 146 to 254 A by electron microscopy. Discs produced from IDL or LDL averaged 26% protein, 42% phospholipid, 5% cholesteryl esters, 24% free cholesterol, and 3% triglycerides; preparations derived from VLDL contained up to 21% triglycerides. ApoA-I was the predominant protein present, with smaller amounts of apoA-II. Crosslinking studies of discs derived from LDL or IDL indicated the presence of four apoA-I molecules per particle, while those derived from large VLDL varied more in size and contained as many as six apoA-I molecules per particle. Incubation of discs derived from IDL or LDL with purified lecithin:cholesterol acyltransferase (LCAT), albumin, and a source of free cholesterol produced core-containing particles with size and composition similar to HDL2b. VLDL-derived discs behaved similarly, although the HDL products were somewhat larger and more variable in size. When discs were incubated with plasma d greater than 1.21 g/ml fraction rather than LCAT, core-containing particles in the size range of normal HDL2a and HDL3a were also produced. A variety of other purified free fatty acids were shown to promote disc formation. In addition, some mono and polyunsaturated fatty acids facilitated the formation of smaller, spherical particles in the size range of HDL3c. Both discoidal and small spherical apoA-I-containing lipoproteins were generated when native VLDL was incubated with lipoprotein lipase in the presence of delipidated HDL. We conclude that lipolysis product-mediated dissociation of lipid-apoA-I complexes from VLDL, IDL, or LDL may be a mechanism for formation of HDL subclasses during lipolysis, and that the availability of different lipids may influence the type of HDL-precursors formed by this mechanism.

Regulation of cholesterol metabolism in the ethionine-induced premalignant rat liver.

The early premalignant liver provides a model in which to study metabolic alterations that may be permissive for the development of full malignancy. Although there are biochemical changes in this model, there are no detectable morphological ones when compared with a normal, fully differentiated liver. The maintenance of cholesterol homeostasis, essential for proper functioning of mammalian cells, is known to be altered in malignancy. We used the ethionine-induced premalignant liver model to study the effects of the premalignant state on cellular parameters involved in the maintenance of hepatic cholesterol homeostasis. Cholesterol synthesis was elevated about twofold in the livers of rats treated with ethionine as was the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, its rate limiting enzyme. There was no change in reductase activation state. Acyl coenzyme A:cholesterol acyl-transferase (ACAT) was decreased about 30%, and cholesterol 7 alpha-hydroxylase, about 50%. There was no significant change in neutral cholesteryl ester hydrolase activity, but acid hydrolase activity was decreased. There was little change in low density lipoprotein receptor protein as determined by immunoblotting. Biliary lipid secretion was in the normal range when expressed per gram liver; however, bile flow was doubled. The ethionine-fed animals were mildly hypocholesterolemic and had an altered serum lipoprotein pattern. Cholesterol synthesis and HMG-CoA reductase activity exhibited decreased sensitivities to inhibition by dietary cholesterol when compared to control livers. However, sensitivity to intragastrically administered mevalonolactone was not altered. Although ACAT activity was increased by mevalonolactone administration to levels similar to those in untreated animals, it was not increased in the ethionine-fed animals by feeding cholesterol. The ethionine-induced premalignant liver responded to ethinyl estradiol treatment in a manner similar to that of the control, i.e., profound hypolipidemia, increased low density lipoprotein receptors, decreased reductase activity, and increased cholesterol esterification. Thus, these livers retained their estrogen responsiveness. Taken together, the data demonstrate that the major elements involved in maintaining hepatic cholesterol homeostasis are present in the premalignant liver, although in some cases at levels that are different from the control. However, the susceptibility to regulation was altered in these livers to suggest markedly decreased availability of cholesterol of exogenous origin to the regulatory compartment(s). Further, coupling of the different elements involved in maintenance of hepatic cholesterol homeostasis appeared to have been changed.

Interactions of high density lipoproteins with very low and low density lipoproteins during lipolysis.

Interactions of high density lipoproteins (HDL) with very low (VLDL) and low (LDL) density lipoproteins were investigated during in vitro lipolysis in the presence of limited free fatty acid acceptor. Previous studies had shown that lipid products accumulating on lipoproteins under these conditions promote the formation of physical complexes between apolipoprotein B-containing particles (Biochim. Biophys. Acta, 1987. 919: 97-110). The presence of increasing concentrations of HDL or delipidated HDL progressively diminished VLDL-LDL complex formation. At the same time, association of HDL-derived apolipoprotein (apo) A-I with both VLDL and LDL could be demonstrated by autoradiography of gradient gel electrophoretic blots, immunoblotting, and apolipoprotein analyses of reisolated lipoproteins. The LDL increased in buoyancy and particle diameter, and became enriched in glycerides relative to cholesterol. Both HDL2 and HDL3 increased in particle diameter, buoyancy, and relative glyceride content, and small amounts of apoA-I appeared in newly formed particles of less than 75 A diameter. Association of apoA-I with VLDL or LDL could be reproduced by addition of lipid extracts of lipolyzed VLDL or purified free fatty acids in the absence of lipolysis, and was progressively inhibited by the presence of increasing amounts of albumin. We conclude that lipolysis products promote multiple interactions at the surface of triglyceride-rich lipoproteins undergoing lipolysis, including physical complex formation with other lipoprotein particles and transfers of lipids and apolipoproteins. These processes may facilitate remodeling of lipoproteins in the course of their intravascular metabolism.

Lipoprotein subspecies and risk of coronary disease.

This review summarizes physical and chemical properties of major subspecies of very-low-, low-, intermediate, and high-density lipoproteins. Hypotheses regarding the metabolic origins of these subspecies and evidence for their associations with risk of coronary artery disease are presented.

Metabolism of human intermediate and very low density lipoprotein subfractions from normal and dysbetalipoproteinemic plasma. In vivo studies in rat.

Subfractions of radioiodinated d less than 1.019 g/ml lipoproteins were isolated by nonequilibrium density gradient ultracentrifugation (DGU) from normal and dysbetalipoproteinemic human plasma and were injected into rats. Size and density (d) of lipoprotein products formed over 8 hours were assessed by gradient gel electrophoresis and equilibrium DGU, respectively. Subfractions containing a subspecies of very low density lipoproteins (VLDL) of particle diameter greater than 350 A were cleared rapidly from the plasma and formed only small amounts of low density lipoproteins (LDL). Fractions containing VLDL subspecies of smaller diameter (300 to 350 A) were cleared much more slowly, and formed greater amounts of a discrete LDL product with the characteristics of human LDL-II (peak particle diameter 255 to 265 A, d = 1.030 to 1.040 g/ml). A similar LDL product was formed from subfractions containing intermediate density lipoproteins (IDL). Cholesterol-enriched subspecies within the smaller, denser portion of the IDL spectrum, however, yielded two additional products. One had size and density characteristic of the major human LDL-I subclass reported previously (265 to 275 A, d = 1.025 to 1.030 g/ml), while the other was yet larger (275 to 285 A) and overlapped normal IDL in size and density. In dysbetalipoproteinemic plasma, the metabolic precursors of the largest product were shifted from the IDL to the small VLDL (beta-VLDL) particle distribution. Since beta-VLDL are known to predispose to accelerated atherosclerosis in dysbetalipoproteinemia, it may be that metabolically homologous cholesterol-enriched IDL subspecies in other subjects have similar atherogenic properties.

Lipolysis products promote the formation of complexes of very-low-density and low-density lipoproteins.

In the course of lipolysis, surface lipid products may accumulate on very-low-density lipoproteins (VLDL). To investigate potential lipoprotein interactions mediated by such products, radiolabeled low-density lipoproteins (LDL) were incubated with VLDL and bovine milk lipoprotein lipase in the presence of limited free fatty acid acceptor. With partial VLDL degradation, association of radiolabeled LDL with VLDL remnants or larger aggregates of VLDL density was demonstrated by gradient gel electrophoresis, agarose chromatography, and density gradient ultracentrifugation. VLDL-LDL complex formation was also observed in incubations with lipid extracts from lipolyzed VLDL or with purified palmitic acid in the absence of lipolysis. Complex formation was inhibited by addition of increasing amounts of albumin as free fatty acid acceptor, but could be detected at molar ratios of free fatty acids/albumin that occur in vivo. Composition analysis of LDL reisolated following incubation with VLDL and lipase under conditions favoring partial complex formation revealed enrichment in glycerides and depletion of cholesterol. We conclude that lipolysis products can promote the formation of stable complexes of LDL and VLDL, and that physical interactions of this nature may play a role in the transfer of lipids and apolipoproteins between lipoprotein particles.

Presence of multiple subpopulations of lipoproteins of intermediate density in normal subjects.

Analysis of human plasma by gradient gel electrophoresis (GGE) revealed multiple distinct bands in the size range between very low density (VLDL) and low density lipoproteins (LDL). GGE of intermediate density lipoproteins (IDL) from normal subjects consistently showed two major bands with particle diameters in the range of 275 to 300 A. The larger, usually predominant subspecies was designated IDL-1, and the smaller, IDL-2. GGE also demonstrated two sizes of subpopulations in the VLDL density range in all subjects. A discontinuous nonequilibrium density gradient ultracentrifugation technique was devised to isolate a series of fractions containing progressively smaller lipoproteins. Successive fractions showed progressive enrichment in cholesteryl-esters, depletion of triglyceride, slower migration on agarose, and depletion of apo E and the C apolipoproteins relative to apo B. The IDL-1 and IDL-2 subspecies appeared to represent two distributions of lipoproteins overlapping in size (particle diameter 280-300 A and 268-284 A, respectively) and buoyant density (d = 1.008-1.022 g/ml and d = 1.013-1.028 g/ml, respectively). Plasma from two patients with dysbetalipoproteinemia showed predominant increases in fractions normally containing small VLDL and IDL-1, while patients with severe hypertriglyceridemia had increases primarily in levels of larger VLDL. Heterogeneity of lipoprotein precursors could account for the discrete subspecies of LDL observed in human plasma.

Immunonephelometry of apolipoprotein A-II in plasma.

A quantitative assay based on endpoint immunonephelometry was developed for human apolipoprotein A-II (apoA-II) in plasma or serum. Dilution of plasma samples with a 0.1 mol/L solution of sodium cholate enhanced the quantification. We used either purified apoA-II as the primary standard or plasma as a secondary standard. Results correlated well (r = 0.90) with those by a double-antibody radioimmunoassay for 63 serum samples from both normal and hyperlipemic individuals. The interassay coefficient of variation for the immunonephelometric assay was 7% within a working range between 0.05 and 0.7 microgram of apoA-II per sample (corresponding to a 1500-fold final dilution of serum). No extraction of samples with organic solvent is necessary if the triglyceride concentration is less than 4 g/L.