Carolyn Knight-Gibson

Apolipoprotein-B-Containing Lipoproteins and the Progression of Renal Insufficiency

Hyperlipidemia is associated with accelerated glomerular sclerosis in experimental renal insufficiency. To investigate whether the dyslipoproteinemia seen in human renal failure also influences the future course of renal insufficiency, we have correlated plasma levels of lipids and apolipoproteins at start of follow-up with the subsequent change in renal function in 34 adult patients with chronic renal disease. Nineteen patients had primary renal disease, and 15 patients had diabetic nephropathy. Except for antihypertensive therapy no specific treatment to modify the progression of the disease was given during the follow-up. The rate of progression was determined by repeated measurements of the glomerular filtration rate (GFR). The time of follow-up ranged from 12 to 91 months with an average of 39.7 +/- 16.7 months. The mean initial GFR was 34.7 +/- 13.9 ml/min x 1.73 m2 body surface area and the average decline in renal function was -0.27 +/- 0.26 ml/min/month. The entry levels of triglycerides (TG; p = 0.04), very-low-density lipoprotein cholesterol (p = 0.03), apolipoprotein-B (ApoB; p = 0.008) and systolic blood pressure (SBP; p = 0.04) were significantly correlated with the rate of progression. Among lipoprotein variables, ApoB showed the strongest correlation with the decline in GFR. Patients with a progressive course of their disease also tended to have initially higher levels of total cholesterol (TC) and low-density lipoprotein cholesterol (NS), whereas the initial plasma concentration of high-density lipoprotein cholesterol did not show an association with the progression of renal insufficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of lovastatin on ApoA- and ApoB-containing lipoproteins. Families in a subpopulation of patients participating in the Monitored Atherosclerosis Regression Study (MARS).

To establish whether lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, exhibits a specific effect on apolipoprotein (apo) A- and apoB-containing lipoproteins, 63 subjects, a subset of the 270 Monitored Atherosclerosis Regression Study (MARS) patients with hypercholesterolemia (190 to 295 mg/dL) and documented coronary artery disease, were randomized into either lovastatin 40 mg twice daily or matching placebo tablets twice daily. Both groups consumed a diet containing 27% calories as fat (polyunsaturated fat/saturated fat ratio, 2.85) and a daily cholesterol intake of less than 250 mg. The plasma lipid and apolipoprotein profiles were determined at the time of randomization and after 2 years of treatment, and the levels of apoA- and apoB-containing lipoprotein families were measured after 2 years of treatment. After this treatment period, the drug group was characterized in comparison with the placebo group by significantly reduced levels of total cholesterol (33%), triglycerides (30%), very-low-density lipoprotein cholesterol (36%), low-density lipoprotein cholesterol (43%), apoB (36%), apoC-III (18%), and apoE (17%) and slightly but insignificantly increased levels of high-density lipoprotein cholesterol (6%) and apoA-I (1%). The 2-year levels of lipoprotein containing apoA-I but no apoA-II (LpA-I) and lipoprotein containing both apoA-I and apoA-II (LpA-I/A-II) particles separated by immunoaffinity chromatography on an anti-apoA-II immunosorber did not differ between the two treatment groups. However, the apoB-containing lipoprotein (Lp) families defined by apolipoprotein composition and separated by immunoaffinity chromatography on anti-apoA-II and anti-apoC-III immunosorbers were affected in a selective manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein C-I induces apoptosis in human aortic smooth muscle cells via recruiting neutral sphingomyelinase

Objectives—Apolipoprotein C-I (apoC-I) influences lipoprotein metabolism, but little is known about its cellular effects in aortic smooth muscle cells (ASMC). Methods and Results—In cultured human ASMC, apoC-I and immunoaffinity purified apoC-I–enriched high-density lipoproteins (HDL) markedly induced apoptosis (5- to 25-fold), compared with control cells, apoC-I–poor HDL, and apolipoprotein C-III (apoC-III) as determined by 4′, 6-diamidino-2-phenylindole dihydrochloride staining and DNA ladder assay. Preincubation of cells with GW4869, an inhibitor of neutral sphingomyelinase (N-SMase), blocked apoC-I–induced apoptosis, an effect that was bypassed by C-2 ceramide. The activity of N-SMase was increased 2- to 3-fold in ASMC by apoC-I, apoC-I–enriched HDL, and tumor necrosis factor &agr; (TNF-&agr;) (positive control) after 10 minutes and then decreased over 60 minutes, which is a kinetic pattern not seen with controls, apoC-III, and apoC-I–poor HDL. ApoC-I and apoC-I–enriched HDL stimulated the generation of ceramide, the release of cytochrome c from mitochondria, and activation of caspase-3 greater than that found in controls, apoC-III, and apoC-I–poor HDL. GW4869 inhibited apoC-I–induced production of ceramide and cytochrome c release. Conclusions—ApoC-I and apoC-I–enriched HDL activate the N-SMase-ceramide signaling pathway, leading to apoptosis in human ASMC, which is an effect that may promote plaque rupture in vivo.

The Plasma Levels of Homocysteine Are Elevated in Moderate Renal Insufficiency but Do Not Predict the Rate of Progression

Background: Chronic renal failure is characterized by specific alterations of the lipoprotein metabolism. It is also characterized by elevated plasma levels of total homocysteine (tHcy). Hyperhomocysteinemia has been shown to be a risk factor for atherosclerosis in both the general population and in patients with end-stage renal disease. Aim: To analyze whether elevated tHcy levels also may contribute to a higher rate of progression of renal insufficiency in patients with moderately advanced renal failure. Methods: To investigate whether tHcy concentrations are associated with an accelerated rate of progression of renal insufficiency, we have correlated baseline plasma concentrations of tHcy with the progressive decline of renal function in an observational study of human chronic renal disease. Results: Sixty-three nondiabetic patients (49 men, 14 women) were studied as part of an observational study of patients with moderately advanced renal insufficiency. The average follow-up time of the patient population was 3.0 years, and the mean rate of decline in glomerular filtration rate (51Cr- EDTA clearance) was –3.2 ± (SD) 3.9 ml/min × 1.73 m2 body surface area. The mean plasma concentration of tHcy at the beginning of the study was 28.3 ± 12.0 µmol/l. Plasma tHcy concentrations correlated significantly with the glomerular filtration rate (r = –0.32, p < 0.01). However, there was no association between the initial plasma level of tHcy and the rate of progression as assessed by linear regression analysis (r = 0.02; NS). In contrast, increased levels of apolipoprotein B, low-density lipoprotein cholesterol, and proteinuria were all significantly associated with a more rapid decline in renal function. Conclusions: Patients with moderately advanced chronic renal insufficiency have elevated plasma levels of homocysteine. The tHcy plasma levels increase in parallel with the degree of reduction in renal function. However, the hyperhomocysteinemia is not prospectively associated with a higher rate of progression of the renal functional impairment. Hence, there is no indication that elevated homocysteine levels play a contributing role for an accelerated glomerulosclerotic process.

Apolipoprotein C-III, Hypertriglyceridemia and Triglyceride-Rich Lipoproteins in Uremia

Apolipoprotein C-III (ApoC-III) plays an important role in the metabolism of triglyceride-rich lipoproteins and is known to be elevated in patients with uremia. To investigate the role of apoC-III in uremic dyslipidemia, we examined apoC-III, triglyceride levels and lipoprotein particles containing both apoB and apoC-III (LP-Bc) in 27 uremic patients prior to dialysis (predialysis), 30 patients on hemodialysis (HD) and 31 patients on peritoneal dialysis (PD). All three groups of patients had elevated levels of plasma apoC-III (20±7 mg/dl for predialysis, 18±5 for HD and 22±8 for PD, compared to 11±3 mg/dl for control subjects [p<0/01 for all comparisons]). ApoC-III was positively correlated with plasma triglycerides in PD patients (r = 0.86, p<0.0001), HD patients (r = 0.67, p<0.0001) and predialysis patients (r = 0.60, p<0.001) as well as in all patients combined (r = 0.75, p<0.0001). ApoC-III was also positively correlated with levels of LP-Bc in all three groups of patients, although this correlation was less strong (r = 0.46, p<0.0001 for all patients combined). In predialysis and PD patients, the majority of apoC-III was found in heparin precipitable lipoproteins, whereas the majority of apoC-III in HD patients was found in HDL, indicating less efficient lipolysis in predialysis and PD patients in comparison with HD. These data support the hypothesis that the elevation of apoC-III in uremia can alter the metabolism of triglyceride-rich lipoproteins, leading to an elevation in triglycerides and LP-Bc. Understanding the mechanism(s) of elevated apoC-III in uremia may help to clarify the causes of uremic dyslipidemia.

Isolation and partial characterization of lipoprotein A-II (LP-A-II) particles of human plasma

High density lipoproteins (HDL) consist of a mixture of chemically and functionally distinct families of particles defined by their characteristic apolipoprotein (Apo) composition. The two major lipoprotein families are lipoprotein A-I (LP-A-I) and lipoprotein A-I:A-II (LP-A-I:A-II). This study describes the isolation of a third minor HDL family of particles referred to as lipoprotein A-II (LP-A-II) because it lacks ApoA-I and contains ApoA-II as its main or sole apolipoprotein constituent. Because ApoA-II is an integral protein constituent of three distinct lipoprotein families (LP-A-I:A-II, LP-A-II: B:C:D:E and LP-A-II), LP-A-II particles were isolated from whole plasma by sequential immunoaffinity chromatography on immunosorbers with antisera to ApoA-II, ApoB and ApoA-I, respectively. In normolipidemic subjects, the concentration of LP-A-II particles, based on ApoA-II content, is 4-18 mg/dl accounting for 5-20% of the total ApoA-II not associated with ApoB-containing lipoproteins. The lipid composition of LP-A-II particles is characterized by low percentage of triglycerides and cholesterol esters and a high percentage of phospholipids in comparison with lipid composition of LP-A-I and LP-A-II: A-II. The major part of LP-A-II particles contain ApoA-II as the sole apolipoprotein constituent; however, small subsets of LP-A-II particles may also contain ApoD and other minor apolipoproteins. The lipid/protein ratio of LP-A-II is higher than those of LP-A-I and LP-A-I:A-II. In homozygous ApoA-I and ApoA-I/ApoC-III deficiencies, LP-A-II particles are the only ApoA-containing high density lipoprotein with levels found to be within the same range (7-13 mg/dl) as those of normolipidemic subjects. However, in contrast to normal LP-A-II, their lipid composition is characterized by higher percentages of triglycerides and cholesterol esters and a lower percentage of phospholipids and their apolipoprotein composition by the presence of ApoC-peptides and ApoE in addition to ApoA-II and ApoD. These results show that LP-A-II particles are a minor HDL family and suggest that, in the absence of ApoA-I-containing lipoproteins, they become an efficient acceptor/donor of ApoC-peptides and ApoE required for a normal metabolism of triglyceride-rich lipoproteins. Their other possible functional roles in lipid transport remain to be established in future experiments.

Effect of Gemfibrozil on Lipoprotein Abnormalities in Chronic Renal Insufficiency: A Controlled Study in Human Chronic Renal Disease

BACKGROUND Renal dyslipoproteinemia is characterized by the accumulation of intact and partially metabolized triglyceride-rich lipoproteins. Reduced lipolytic enzyme activities may be one of the major pathophysiological mechanisms contributing to a retarded catabolism of these lipoproteins in patients with renal insufficiency. OBJECTIVE To evaluate the effect of gemfibrozil treatment on renal dyslipoproteinemia. STUDY DESIGN A randomized, controlled open study with 2 parallel groups. OUTCOME VARIABLES Plasma concentrations of lipids, apolipoproteins and lipoprotein particles. PATIENTS AND METHODS Fifty-seven non-nephrotic, non-diabetic patients with moderately advanced renal insufficiency were randomized to either treatment with gemfibrozil at dosages from 300 to 900 mg/day (n = 28) or dietary counseling (n = 29). The intervention period was 12 months. Plasma concentrations of lipids, apolipoproteins and apoA- and apoB-containing lipoprotein particles were determined at the entry and after 6 and 12 months of treatment. RESULTS No serious adverse effects occurred during the study. Six patients experienced mild gastrointestinal symptoms and prematurely withdrew from the drug treatment. In the group treated with gemfibrozil the plasma concentrations of triglycerides, total cholesterol, very low density lipoprotein (VLDL) and low density (LDL) cholesterol decreased significantly by 47, 13, 43 and 14%, respectively, in comparison to baseline. High density lipoprotein (HDL) cholesterol increased significantly by 18%. ApoB, apoC-III, apoC-III in heparin-manganese precipitate (reflecting apoC-III in VLDL and LDL) and apoE decreased significantly by 21, 18, 26 and 49%, respectively. Furthermore, gemfibrozil treatment resulted in the reduction of plasma concentrations of complex (LP-Bc) and simple (LP-B) apoB-containing lipoprotein particles by 22 and 7%, respectively. However, these changes were not statistically significant. There was a slight, insignificant increase in the levels of LP-A-I:A-II particles and no change in the levels of LP-A-I particles. In contrast to the effect of the pharmacological intervention, the dietary counseling only resulted in minor changes in the plasma lipid and apolipoprotein profiles. The only significant changes were a 10% increase in HDL cholesterol and a 35% decrease in apoE. CONCLUSIONS Gemfibrozil treatment significantly reduces both plasma lipids and apoB, apoC-III and apoE concentrations in patients with moderately advanced renal insufficiency. The results of this study indicate that gemfibrozil enhances the clearance of apoB-containing triglyceride-rich lipoproteins.

Plasma levels of lipoprotein (a) do not predict progression of human chronic renal failure

Chronic renal failure is frequently accompanied by elevated plasma levels of lipoprotein (a) [Lp(a)]. Elevated Lp(a) levels have been proposed to contribute not only to increased risk of atherosclerotic and thrombotic complications but also to the progression of renal insufficiency. To investigate whether higher Lp(a) plasma concentrations are associated with an accelerated rate of progression of renal insufficiency, we have correlated baseline plasma concentrations of Lp(a) with the progressive decline of renal function in an observational study of human chronic renal disease. Forty-nine non-diabetic patients (40 men, nine women) were studied as part of an observational study of patients with moderately advanced renal insufficiency. The average follow-up time of the patient population was 3.1 years, and the mean rate of decline in glomerular filtration rate (51Cr-EDTA clearance) was -2.8 (SD 4.1) ml/min/1.73 m2. The mean plasma concentration of Lp(a) at the beginning of the study was 19.2 (SD 18.6) mg/100 ml with a median value of 12.2 mg/100 ml. There was no association between the initial plasma concentration of Lp(a) and the rate of progression as assessed by linear regression analysis. Furthermore, the progression rate in patients within the highest quartile of the Lp(a) distribution (> or = 30 mg/100 ml) did not differ from that in patients with lower levels of Lp(a). In contrast, increased levels of apolipoprotein (apo) B, low-density lipoprotein (LDL)-cholesterol, and proteinuria were all significantly associated with a more rapid decline in renal function. Based on these results, it was concluded that elevated plasma levels of Lp(a) are not associated with an increased rate of progression of renal insufficiency in human chronic renal disease. However, the results of this study suggest that other apoB-containing lipoproteins may play a significant role in this process.

Lipoprotein Particles in Hypertriglyceridemic States

The compositional and metabolic heterogeneity of operationally defined plasma lipoprotein classes (1-3) has necessitated the introduction of a classification system that utilizes apolipoproteins as specific markers for identifying and distinguishing discrete lipoprotein particles (1,4). In this system, lipoprotein particles are characterized and defined by their apolipoprotein composition (1,4). Studies on the quantification and distribution of apolipoproteins (4,5) have shown that apolipoprotein (Apo)B and ApoA (A-I 4- A-II) form two major groups of plasma lipoproteins. These two major lipoprotein groups may be separated (6) by immunoprecipitation or immunoaffinity chromatography of whole plasma (6). The use of these procedures results in the isolation of ApoA-containing lipoproteins free of ApoB. The fractionation of ApoA-containing lipoproteins into two major discrete lipoprotein particles LP-A-I and LP-A-I:A-II by immunoaffinity chromatography on an immunosorber with polyclonal antibodies to ApoA-II has already been described by Cheung and Albers (7). To identify discrete lipoprotein particles of the ApoB group of lipoproteins, we have developed a procedure based on sequential immunoprecipitation of ApoB-containing lipoproteins with polyclonal antisera to apolipoproteins B, E, C-III and, if necessary, C-II and C-I (6,8). The fractionation of very low density (VLDL, d < 1.006 g/ml) and two subtractions of low density (LDL.., d = 1.006-1.019 g/ml; LDL?, d = 1.019-1.063 g/ml lipoproteins from normolipidemic subjects by sequential immunoprecipitation showed that each of these density classes consists of a mixture of distinct lipoprotein particles including cholesterol ester-rich LP-B and triglyceride- rich LP-B:C-I:C-II:C-III:E (LP-B:C:E) and LP-B:C-I: C-II:C-III (LP-B:C) particles (8). The LP-B:C:E family of particles in some normolipidemic and hypercholesterolemic subjects also contained varying amounts of LP-B:E particles. In addition, small amounts of LP-B:C-I:E, LP-B:C-II, LP-C-III and LP-E particles were detected in some but not all-subjects or density classes. Each of the major ApoB-containing families of particles was shown to represent a polydisperse system of particles heterogeneous with respect to size, hydrated density, and lipid/protein ratio, but homogeneous with respect to the qualitative apolipoprotein composition.

Changes in plasma lipid and apolipoprotein levels between heparin-induced extracorporeal low-density lipoprotein precipitation (HELP) treatments

Heparin-induced extracorporeal low-density lipoprotein (LDL) precipitation (HELP) treatments selectively remove LDL with minimal effects on high-density lipoproteins (HDL), but limited data are available on effects between treatments. The levels of factors associated with increased coronary artery disease risk (atherogenic) among treatments may have therapeutic significance, especially for combined HELP and lipid-lowering drug therapy. Hypercholesterolemic and combined hyperlipidemic patients resistant to diet/drug therapy were treated with biweekly HELP therapy. Hypercholesterolemic patients received either lovastatin or no drug, whereas combined hyperlipidemic patients received gemfibrozil. Plasma lipid (total cholesterol, triglycerides, LDL cholesterol, and HDL cholesterol) and apolipoprotein A-I, A-II, B, C-III, and E levels were measured before treatment, then immediately, and 2, 4, 7, and 14 days after treatments (n = 28). Atherogenic factor (LDL cholesterol, total cholesterol, apolipoprotein B) levels decreased > 50% with treatment, gradually increasing over 14 days to pretreatment levels. Factors associated with reduced coronary artery disease risk (HDL cholesterol and apolipoproteins A-I and A-II) decreased 8% to 16% but recovered by 2 days. Components of triglyceride-rich lipoproteins (triglycerides and apolipoproteins C-III and E) decreased 38% to 55% with variable post-treatment recoveries. Lovastatin reduced pretreatment levels of atherogenic and triglyceride-rich lipoprotein components and slowed post-treatment increases compared with no drug therapy. Gemfibrozil produced changes similar to lovastatin. Drug therapy had little effect on factors associated with reduced coronary artery disease risk. HELP apheresis produced large reductions in plasma atherogenic factor levels with gradual return to pretreatment levels over 14 days, whereas antiatherogenic factors were minimally reduced and recovered rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)