Mary C. Ritter

Accelerated cholesteryl ester transfer in plasma of patients with hypercholesterolemia.

To discern the mechanism(s) that underlie abnormal cholesteryl ester transfer (CET) in patients with hypercholesterolemia, we have studied this dysfunctional step in reverse cholesterol transport in 13 subjects with genetically heterogeneous forms of hypercholesterolemia (HC). In all HC patients, the mass of CE transferred in whole plasma from HDL to VLDL and LDL increased rapidly initially and was significantly greater than in controls at 1, 2, and 4 h (P less than 0.005). To further characterize this disturbance, we performed a series of recombination experiments. Combining HC d less than 1.063 containing acceptor VLDL + LDL with the d greater than 1.063 fraction from controls containing donor HDL + CE-transfer protein (CETP) and not the converse combination showed the same characteristics of accelerated CET noted with intact HC plasma, indicating that abnormal transfer was associated with the HC acceptor lipoproteins. When HC VLDL and its subfractions and LDL were isolated separately and then combined with control d greater than 1.063 fractions, accelerated CET was only associated with VLDL1. Consistent with an acceleration of the neutral lipid transfer reaction occurring between HDL and VLDL1 in HC in vivo, we found that the triglyceride/CE ratio was decreased in HC VLDL1 (P less than 0.001), and increased in HDL (P less than 0.25). CETP mass was significantly increased in HC plasma (HC 2.3 +/- 4 micrograms/ml vs. control 1.3 +/- 0.3 micrograms/ml; mean +/- SD; P less than 0.025). This series of observations demonstrate that CET is accelerated in the plasma of HC patients, and this disturbance results from dysfunction of the VLDL1 subfraction rather than an elevation of CETP levels. Since an abnormality of this type in vivo can lead to the accumulation of potentially atherogenic CE-enriched apoB-containing lipoproteins in plasma, it may be an additional previously unrecognized factor that increases cardiovascular risk in HC patients.

Accelerated cholesteryl ester transfer in patients with insulin-dependent diabetes mellitus.

Abstract. Abnormalities in cholesteryl ester transfer (CET) may play a role in the development of diabetic arterial vascular complications. To assess this important step systematically in reverse cholesterol transport, we have studied 20 treated, clinically stable, normolipidaemic patients. Contrary to the impairment in CET described previously in NIDDM, the mass of CE transferred from HDL to VLDL+LDL was significantly greater in IDDM patients than in controls at 1,2, and 4 h (P<0.001). When the d<1.063 plasma fractions from IDDM subjects were combined with controls d<1.063 fractions, an accelerated CET response was observed which was identical to that found in intact IDDM plasma. This finding, which indicates that this disturbance in CET was associated with the acceptor lipoproteins, was confirmed when we found that it was reproduced by the addition of IDDM VLDL and not LDL to control d>1.063 fractions.

Accelerated cholesteryl ester transfer in noninsulin-dependent diabetes mellitus

Alterations in core lipid composition of lipoproteins in noninsulin-dependent diabetes mellitus (NIDDM) patients have suggested that the heteroexchange of neutral lipids between HDL and the apo B-containing lipoproteins may be enhanced. For this reason, we studied cholesteryl ester transfer (CET) in ten sulfonylurea-treated patients with stable NIDDM. CET measured in all NIDDM subjects with an assay of mass transfer was significantly greater than that of controls at 1 and 2 h (P < 0.001); the transfer of radiolabeled CE also was increased in a subset of four of the NIDDM group (NIDDM k = 0.21 +/- 0.04 vs. control k = 0.10 +/- 0.05; P < 0.05). A weak correlation was demonstrable between the mass of CE transferred at 1 h and diabetic control expressed as plasma fructosamine (r = 0.58, P < 0.09). To characterize this disturbance in CET further, the donor (HDL + VHDL) and acceptor (VLDL + LDL) lipoprotein fractions were isolated by ultracentrifugation at d 1.063 g/ml from NIDDM and control plasma and a series of recombination experiments were performed. Combining NIDDM acceptor with control donor fractions that contained HDL and CETP and not the combination of NIDDM donor and control acceptor lipoproteins resulted in an accelerated CET response identical to that observed in NIDDM whole plasma. This observation indicated that the abnormality in CET in NIDDM was associated with the VLDL + LDL fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraperitoneal insulin therapy corrects abnormalities in cholesteryl ester transfer and lipoprotein lipase activities in insulin-dependent diabetes mellitus.

Patients with insulin-dependent diabetes mellitus (IDDM) have proatherogenic disturbances in cholesteryl ester transfer (CET) despite intensive subcutaneous insulin therapy (ISC). Since CET is activated by insulin-sensitive lipoprotein lipase (LPL), which normally increases postprandially, we queried whether iatrogenic hyperinsulinism from ISC stimulated LPL and CET by studying well-controlled IDDM patients after ISC and then 6 months after lowering systemic insulin levels by intraperitoneal (IP) insulin delivery. Although glycemic control (HbA1c IDDM, 6.9 +/- 1.7%; control, 4.5% to 8%) was excellent during ISC, CET was accelerated (P < .001) and both systemic insulin levels and LPL specific activity were increased (P < .05). Following IP, basal systemic insulin levels declined by more than one half (ISC, 8.22 +/- 6.5 versus IP, 2.77 +/- 2.4 microU/mL; mean +/- SD; P < .025), and both LPL and CET activities returned to normal. Plasma triglyceride, cholesterol, high-density lipoprotein-2 (HDL2) cholesterol, HDL3 cholesterol, cholesteryl ester transfer protein mass, and glycemic control (HbA1c, 6.3 +/- 0.8%) were unchanged and remained normal. These findings indicate that ISC is associated with high levels of basal CET and LPL. These alterations both appear to be closely linked to iatrogenic hyperinsulinemia resulting from ISC. The fact that they are both reversed when systemic insulin levels are reduced by IP suggests that insulin, acting through LPL, influences the nature of the interaction of the lipoproteins engaged in CET.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary supplementation with marine lipid concentrate on the plasma lipoprotein composition of hypercholesterolemic patients

Although the triglyceride-lowering actions of n-3 fatty acids of marine lipids are now well-recognized, their effects on plasma lipoproteins have not been studied systematically in patients with hypercholesterolemia. To address this question, we supplemented the Phase 1 American Heart Association diets of 14 hypercholesterolemic ambulatory outpatients with a commercially available preparation of marine lipid concentrate (SuperEPA) containing 7.5 g n-3 fatty acids per day and studied their plasma lipids and lipoproteins before and after 30 days of treatment. Both plasma triglyceride and cholesterol levels fell uniformly in all patients while the mean VLDL- and LDL-cholesterol decreased by 58% (P less than 0.005) and 13% (P less than 0.025) respectively. The decrease in whole plasma cholesterol was significantly correlated with the fall in LDL-cholesterol (r = 0.85, P less than 0.01), and not VLDL-cholesterol (r = 0.39, NS). Among the other potentially beneficial actions observed was an increase in HDL2 in all patients (mean increment 41%, P less than 0.005), and an increase in the HDL2/HDL3 ratio (+46%, P less than 0.001) and decreases in the LDL/HDL ratio (-14%, P less than 0.005) and in the unesterified cholesterol/lecithin ratio (-17%; P less than 0.001) in plasma. The increase in the unesterified cholesterol/esterified cholesterol ratio in VLDL and HDL3 suggested that marine lipid therapy resulted in a reduction in the size of lipoprotein particles in these fractions. Since these changes may reduce cardiovascular risk, these findings suggest that marine lipids may prove useful in the treatment of certain patients with hypercholesterolemia.

Differing Effects of Pancreas-kidney Transplantation With Systemic Versus Portal Venous Drainage on Cholesteryl Ester Transfer in IDDM Subjects

OBJECTIVE Cholesteryl ester transfer (CET) is accelerated in patients with IDDM treated with conventional (subcutaneous) insulin therapy (CIT) and a number of other disorders associated with premature cardiovascular disease. We have shown that in IDDM this disturbance is closely linked to iatrogenic hyperinsulinemia (HI), because it was reversed when insulin was administered by the intraportal (IP) route. In this study, we sought to determine whether HI after successful pancreas-kidney transplantation (PKT) has the same adverse effect on CET. RESEARCH DESIGN AND METHODS CET was measured by both mass and isotopic assays and compared in two groups of euglycemic non-insulin-requiring IDDM PKT patients with either systemically draining allografts and persistent HI or grafts with portal vein anastomoses that were normoinsulinemic (PK-P). A third group of eight nondiabetic kidney transplant (KT) patients receiving the same immunosuppressive drugs served as control subjects. RESULTS CET in pancreas-kidney transplantation subjects with systemic venous drainage (PK-S) was increased (P < 0.001) to the same level we have reported previously in IDDM patients receiving CIT and was significantly higher (P < 0.001) than in those subjects with PK-P. CET in the PK-P group did not differ from that of the KT control patients. CONCLUSIONS CET is affected by variations in systemic insulin levels in pancreas transplant patients with allografts that have differing venous drainage. Because high systemic insulin levels are linked to the activation of (ET, euglycemic HI IDDM pancreas allograft recipients may continue to be at high risk for macrovascular complications.

Contribution of glycaemic control, endogenous lipoproteins and cholesteryl ester transfer protein to accelerated cholesteryl ester transfer in IDDM

Abstract In an earlier study we demonstrated that the transfer of cholesteryl ester (CET) estimated as the net mass of CE lost from HDL to the apoB‐containing lipoproteins (VLDL + LDL) during incubation of plasma is accelerated in normolipidaemic patients with insulin‐dependent diabetes mellitus (IDDM). Recombination experiments with isolated lipoprotein fractions employing this same mass transfer assay indicated that this disturbance resulted from dysfunction of VLDL and not from changes in the activity of CE transfer protein (CETP).

Probucol treatment in hypercholesterolemic patients: effects on lipoprotein composition, HDL particle size, and cholesteryl ester transfer☆

Despite probucols capacity to induce regression of tendinous xanthomata and reduce whole plasma and LDL cholesterol (LDL-C) in patients with hypercholesterolemia, its therapeutic use in the United States has been limited because of concern about its HDL-lowering effects. To assess the possibility that probucol might facilitate mobilization of tissue cholesterol in the presence of low HDL levels as a consequence of favorable changes in lipoprotein composition and function, we have analyzed lipoproteins and studied cholesteryl ester transfer (CET) in hypercholesterolemic patients before and after treatment. Prior to treatment, the free cholesterol (FC)/lecithin (L) ratio in plasma, a new index of cardiovascular risk, and the mass of cholesteryl ester transferred from HDL to the apo B-containing lipoproteins (CET) both were significantly increased (P less than 0.001). As previously shown, plasma cholesterol, LDL-C, HDL-C, HDL2, and apolipoproteins A-I, A-II, and B all fell significantly following probucol treatment. The FC/L ratio in plasma (P less than 0.01) and HDL2 (P less than 0.01) both fell significantly also, as did the sphingomyelin/lecithin ratio in VLDL + LDL (P less than 0.001) which is typically increased in untreated patients with hypercholesterolemia. Nondenaturing gradient gel electrophoresis in 6 patients revealed that the quantitative changes in HDL were associated with a redistribution of particles characterized by a decrease in the prevalence of the largest (HDL2b) and a relative increase in the number of the smallest (HDL3b) particles. Moreover, CET following probucol therapy returned to levels which were indistinguishable from those of normolipidemic controls. These results indicate that untreated patients with hypercholesterolemia have abnormalities in (1) lipoprotein composition which have been shown to retard the movement of cholesterol from tissues to HDL, and in (2) CET which is accelerated and can potentially lead to the formation in plasma of atherogenic CE-enriched apo B-containing lipoproteins. Probucols capacity to reverse these specific alterations suggests that it may have beneficial effects on cholesterol transport in patients with hypercholesterolemia.

Effects of ω-3 Fish Oils on Plasma Lipids, Lipoprotein Composition, and Postheparin Lipoprotein Lipase in Women With IDDM

Because the apparent reduction in cardiovascular risk noted in nondiabetic populations that ingest diets rich in marine lipids containing ω-3 fatty acids is believed to result in part from their capacity to modify the composition and physicochemical behavior of lipoproteins, we sought to determine whether dietary supplementation with marine lipids might favorably affect lipoprotein composition in insulin-dependent diabetes mellitus (IDDM). Eight normolipidemic IDDM women (mean ± SD age 29.8 ± 4.7 yr) were studied before and 3 mo after receiving a marine-lipid concentrate (Super-EPA) containing 6 g ω-3 fatty acids and a total of 12 mg of cholesterol daily. Weight, insulin requirements, and glycosylated hemoglobin remained stable. After treatment, mean ± SD plasma triglyceride (TG) levels fell (before, 81.7 ± 22 mg/dl; after, 69.19 ± 17; P < 0.025). High-density lipoprotein2 (HDL2) cholesterol (before, 10.98 ± 5.45 mg/dl; after, 18.43 ± 7.93; P < 0.01), its major apolipoprotein A-I (apoAl), and the major phospholipids (sphingomyelin and lecithin) all rose significantly. ApoB and plasma and low-density lipoprotein cholesterol levels and HDL3 composition were unchanged. Postheparin hepatic and lipoprotein lipase activities were unaffected by marine lipids. These data indicate that women with IDDM experience apparently beneficial effects on TG and HDL2 from dietary supplementation with ω-3 fatty acids administered in a low-cholesterol–containing oil without adversely affecting overall diabetes management. If these changes in lipoprotein concentration and composition prove to have antiatherogenic consequences and are free of long-term toxicity, these agents may have a role in the therapy of IDDM patients.

Effect of marine lipids on cholesteryl ester transfer and lipoprotein composition in patients with hypercholesterolemia.

While the effects of omega-3 (n-3) fatty acids present in marine lipids on plasma lipoprotein levels have been intensively studied, less is known about their impact on reverse cholesterol transport. For this reason, for a 3-month period we studied the effects of the administration of n-3 fatty acids (6 g/day) as a dietary supplement on cholesteryl ester transfer (CET), a key step in this process, and lipoprotein composition in 12 outpatients with genetically heterogeneous forms of hypercholesterolemia. Before treatment, CET in hypercholesterolemic patients, estimated as the mass of cholesteryl ester (CE) transferred from high density lipoprotein (HDL) to very low density lipoprotein (VLDL) plus low density lipoprotein (LDL), was markedly accelerated, peaking after only 1-2 hours of incubation of whole plasma; this response differed significantly (p < 0.001) from the initial delayed curvilinear response of control subjects. Consistent with the accelerated CET occurring in vivo, their triglyceride to esterified cholesterol core lipid ratio before treatment was reduced in the intact VLDL fraction and VLDL1 but not in VLDL2 or VLDL3 and was reciprocally increased in HDL. In addition, the free (unesterified) cholesterol to lecithin ratio of VLDL1 was abnormally increased. Recombination experiments performed with individual lipoprotein fractions revealed that accelerated CET was specifically associated with the VLDL1 subfraction and not LDL, HDL, and cholesteryl ester transfer protein (CETP), although pretreatment levels of CETP were significantly increased (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)