apoA- AND apoB-CONTAINING LIPOPROTEINS AND Lp(A) CONCENTRATION IN NON-DIALYZED PATIENTS WITH CHRONIC RENAL FAILURE

Abstract

Background: End-Stage renal disease is associated with accelerated atherosclerosis and a high incidence of cardiovascular disease. Methods: The serum levels of lipids and apolipoproteins and Lp(a) were determined in 51 patients with chronic renal failure (CRF) with various advancement, without interference of factors which might disturb Lp(a) metabolism and with proteinuria less than 0.5 g/24 h. The patients studied were divided into two groups: patients with moderate renal failure (CRF-M) and creatinine levels of 2–6 mg/dL n = 27; and predialysis patients with end stage renal disease (ESRD) and creatinine levels higher than 8.5 mg/dL n = 24. Results: In both studied groups serum concentrations of triglycerides (TG), total apoCIII, apoCIIInonB, apoB:CIII were statistically increased, (except total cholestrol (TC) and LDL-cholestrol (LDL-C), apoB, total apoE, apoEnonB, apoB:E), while the levels of HDL-cholestrol (HDL-C) and apoAI significantly decreased. Lipid and lipoprotein ratios as risk factors of atherosclerosis were similar in both groups. The TC/HDL-C ratio increased, while that of HDL-C/apoAI and apoAI/apoCIII decreased. Serum Lp(a) concentrations were significantly increased in both studied groups. The medians and ranges of Lp(a) concentration were similar in both groups. Serum Lp(a) levels correlated with total cholesterol (r = 0.295; p < 0.05), LDL-C (r = 0.312; p < 0.05) and apoB (r = 0.215; p < 0.05). In addition, no correlation was found between Lp(a) levels and albumin concentrations (r = 0.126; p = 0.421). Conclusion: Our results may indicate that the reduced levels of apoA-containing lipoproteins and increased TG-rich apoB-containing lipoproteins and Lp(a) indicated a clear atherogenic pattern in early renal disease. Increased Lp(a) concentration may result in nonspecific synthesis or catabolism disturbances. Measurement and monitoring of lipoprotein family profiles offers a new means for selecting appropriate therapies targeted for normalizing dyslipidemia in non-dialyzed patients.

• Lipids
• Lipoproteins
• Moderate
• Renal failure

INTRODUCTION

Dyslipoproteinemia and lipoprotein(a) as an independent risk factor for coronary artery diseases and is a predictor for cardiovascular mortality of patients with chronic renal failure.[[1]], [[2]], [[3]]

Lp(a) levels were reported to be markedly increased in continuous ambulatory peritoneal dialysis,[[4]] and in hemodialysis patients (HD).[[5]] Markedly elevated Lp(a) concentrations were consistently reported in patients with renal diseases, especially in those patients with proteinuria.[[6]] There are reports of an increased serum lipoproteins concentration in predialytic patients, but less is known about apoA- and apoB-containing lipoproteins and Lp(a) concentrations in early renal insufficiency.[[7]], [[8]]

In this study we determined serum levels of Lp(a), apoA- and apoB-containing lipoproteins in patients with moderate renal failure (CRF-M) with creatinine 2–6 mg/dL as well as end stage renal disease (ESRD) with creatinine higher than 8.5 mg/dL before dialysis without factors which might disturb Lp(a) metabolism and proteinuria less than 0.5 g/24 h.

PATIENTS AND METHODS

Serum levels of lipids, apolipoproteins and Lp(a) were determined in 51 patients with chronic renal failure (CRF) with various advancement. These patients were without the following factors inducing lipoprotein metabolism: diabetes, endocrine disease, liver disease, active inflammatory disease, glucose intolerance, strong and median urinary protein, malignancy, and obesity. The patients did not take medicines influencing lipid economy and were on an average diet and treated using furosemide, calcium carbonium and vitamins.

The patients studied were divided into two groups: CRF-M with creatinine 2–6 mg/dL n = 27, and ESRD with creatinine higher than 8.5 mg/dL n = 24.

The diagnosis of the patients is presented in Table 1.

Table 1. Diagnosis of Patients

	CRF-M Patients n = 27 Creatinine 2–6 mg/dL	ESRD Patients n = 24 Creatinine > 8.5 mg/dL
Glomerulonephritis	M-6, F-7	M-4, F-5
Interstitial nephritis	M-1, F-1	M-1
Obstructive nephropathy	M-1, F-1	M-2, F-1
Hypertensive nephrosclerosis	M-2, F-1	M-2, F-2
Polycystic disease	F-1
Pyelonephritis	M-3, F-4	M-3, F-3

M – male; F – female.

All patients had proteinuria of less than 0.5 g/24 h. The reference group consisted of 30 persons (15 males and 15 females) recruited from apparently healthy normolipidemic subjects. Blood samples were taken from healthy persons and patients by antecubital venipuncture after 14 h fasting.

The selected routine laboratory parameters (creatinine, urea, uric acid, albumin and electrolytes) were determined using the Cobas Intagra analyzer (Roche Diagnostics, Indianapolis). Lipids and apolipoproteins AI (apoAI) as well as apoB were also determined on a Cobas Integra analyzer. Total cholesterol (TC) was determined by the enzymatic-colorimetric methods (cholesterol CHOD-PAP, Roche), HDL-cholesterol (HDL-C) after precipitation with phosphotungstic acid and magnesium ions, and LDL-cholesterol (LDL-C) was calculated according to the Friedewald formula. Triglycerides (TG) were determined using the standard enzymatic technique (Roche kit) ApoAI. ApoB were measured by a Roche kit, using the turbidimetric methods. The total apoCIII (apoCIII), apoCIII present in the particles without apoB (apoCIII non B), and total apoE (apoE) and apoE present in the particles without apoB (apoEnonB) were measured by electroimmunodiffusion according to Laurell using a commercial kit Sebia, Issy les Moulineaux, France. However, apoB containing apoCIII (apoB: CIII) was calculated from the difference between total apoCIII and apoCIIInonB, and apoB containing apoE (apoB: E) was calculated from the difference between total apoE and apoEnonB. The concentration of Lp(a) was determined by electroimmunodiffusion using the commercial Hydragel Lp(a) kit (Sebia, Issy les Moulinex, France).

STATISTICAL ANALYSIS

Statistical analysis was performed using one-way analysis of the ANOVA variance and multiple comparisons for assessment of the mean ± standard deviation (SD). Lp(a) was expressed in terms of the medians and min–max ranges, and the difference between median values was assessed by nonparametric statistics (Mann-Whitney U test). Correlation between variables was analyzed using Spearman's correlation coefficient. Statistical significance of all variables was established at the level p < 0.05.

RESULTS

The selected clinical and routine laboratory parameters are presented in Table 2. Lipid and lipoprotein parameters of patients and the reference group are shown in Table 3. The CRF-M patients with creatinine 2–6 mg/dL and ESRD patients with creatinine higher than 8.5 mg/dL had statistically increased serum concentration of TG, but not TC and LDL-C, and significantly decreased HDL-C levels. Moreover, statistically significant changes were shown in the profile of apolipoproteins. In CRF-M and ESRD patients the apoAI level decreased significantly, but apoB, total apoE, apoEnonB and apoB:E did not change compared to the reference group. On the other hand, in both groups a statistically significant increase of total apoCIII, apoCIIInonB and apoB: CIII levels were observed in comparison to healthy subjects. Lipid and lipoprotein ratios as risk factors of atherosclerosis were analyzed. The TC/HDL-C ratio increased significantly in CRF-M and ESRD patients, while HDL-C/apoAI and apoAI/apoCIII ratios decreased as compared with the reference group. Serum Lp(a) concentrations significantly increased in the CRF-M and ESRD group. The medians and ranges of Lp(a) concentrations were similar in both groups of patients. Serum Lp(a) levels correlated with TC (r = 0.295; p<0.05), LDL-C (r = 0.312; p<0.05) and apoB (r = 0.215; p<0.05). In addition, no correlation was found between Lp(a) levels and albumin concentrations (r = 0.126; p = 0.421).

Table 2. Clinical and Laboratory Parameters in the Reference Group and Patients with Moderate Renal Failure (CRF-M) and Predialysis Patients with End-Stage Renal Disease (ESRD) (mean ± SD)

Parameters	Reference Group n = 30	CRF-M Patients n = 27 Creatinine 2–6 mg/dL	ESRD Patients n = 24 Creatinine >8.5 mg/dL
Age	38.5±14.2	40.3±12.5	41.2±14.7
BMI	24.3±2.5	23.7±2.8	22.8±3.2
Years of disease		5.5±2.57	7.3±2.71
Proteinuria g/24 h	Negative	0.31±0.19	0.34±0.17
GFR mL/min	117.1±5.2	29.8±18.52***	8.4±2.52, 5***††
Urea mg/dL	26.58±6.19	103.68±32.672***	191.51±50.762, 5***††
Uric acid mg/dL	4.01±1.00	6.11±1.692***	6.62±2.042***
Albumin g/dL	4.58±0.38	4.37±0.46	4.1±0.52
Na mmol/L	139.84±1.62	142.48±3.39	140.99±4.39
K mmol/L	4.37±0.23	4.48±0.49	4.77±0.53
P mg/dL	3.23±0.44	4.73±1.242***	6.76±1.59234***†

*versus reference group, *** p< 0.001;

†versus CRF-M,

†p< 0.05,

††p< 0.01.

BMI – body mass index, GFR – glomerular filtration.

Table 3. Lipoprotein Profiles in the Reference Group and Patients with Moderate Renal Failure (CRF-M) and Predialysis Patients with End-Stage Renal Disease (ESRD) (mean ± SD)

Parameters	Reference Group n = 30	CRF-M Patients n = 27 Creatinine 2–6 mg/dL	ESRD Patients n = 24 Creatinine >8.5 mg/dL
TG mg/dL	90.28±34.89	168.54±65.459***	172.81±61.399***
TC mg/dL	186.34±24.01	197.72±21.23	187.71±44.64
LDL mg/dL	105.93±30.03	128.44±27.03	120.60±39.19
HDL-C mg/dL	57.17±11.45	36.40±6.699***	31.99±8.399***
apoAI mg/dL	153.16±17.41	130.14±16.098**	122.33±19.299***
apoB mg/dL	91.49±12.76	103.14±13.86	101.62±24.92
apoE mg/dL	4.43±1.48	4.36±0.61	4.40±1.52
apoEnonB mg/dL	3.42±1.05	3.24±0.66	3.35±1.39
apoB:E mg/dL	1.00±0.82	1.11±0.62	0.99±0.53
apoCIII mg/dL	2.61±0.51	3.71±0.989***	3.79±1.329***
apoCIIInonB mg/dL	1.99±0.49	2.69±0.968**	2.89±1.229***
apoB:CIII mg/dL	0.63±0.23	1.01±0.428**	0.99±0.468**
TC/HDL-C	3.30±0.75	5.47±1.649***	6.03±1.849***
HDL-C/apoAI	0.37±0.04	0.28±0.039***	0.26±0.059***
apoAI/apoCIII	57.84±10.10	41.32±11.809***	35.83±10.409***
Lp(a)mg/dL medians, ranges	9 (5.7–13)	22 (5.7–90)8**	22 (5.7–94)8**

*versus reference group,

**p< 0.01,

***p< 0.001.

DISCUSSION

Renal failure is associated with abnormal concentration and composition of plasma lipoprotein.[[1]] This dyslipoproteinemia can already be detected at the early asymptomatic stages of renal insufficiency.[[9]], [[10]], [[11]] Our findings confirm that renal dyslipoproteinemia in non-dialyzed patients is characterized to a greater extent by abnormal apolipoprotein rather than lipid profile, including decreased levels of apoA-containing lipoproteins (apoAI) and increased concentrations of apoB-containing lipoproteins (apoB:CIII), but did not change the levels of apoB and ApoB-containing apoE (apoB:E). This finding suggested that at the early stage of renal failure cholesterol-rich lipoprotein particles did not change but the levels of intact or partially delipidized TG-rich lipoprotein particles were higher. Compositional changes of the apoB-containing lipoproteins, as reflected in their apolipoprotein compositions may be another important contribution factor. Such alterations may render the apoB-containing lipoproteins less suitable as substrates for lipolysis.[[12]] The increased content of apoCIII could be one of the crucial abnormalities, the cause of which is still unexplained.[[12]], [[13]] Apart from alterations in substrate characteristics the abnormal lipoprotein composition, may also result in a reduced cellular uptake of lipoproteins mediated by the LDL pathways. ApoE is a ligand for this receptor-mediated uptake, whereas apoCIII may interfere with these processes. An increased apoCIII but normal apoE in renal dyslipidemia could contribute to reduced cellular uptake of apoB-containing lipoproteins in patients with renal failure. As a consequence, an accumulation of both intact or partially delipidized TG-rich lipoproteins can be anticipated.[[12]] It was demonstrated that TG-rich apoB-containing lipoproteins have atherogenic properties and can play a role in the development of cardiovascular disease in renal patients.[[14]] It was suggested that the reduced levels of apoA-containing lipoproteins and apoAI/apoB, HDL-C/apoAI and apoAI/apoCIII ratios, and increased TG-rich apoB-containing lipoproteins and TC/HDL-C and LDL-C/HDL-C ratios indicated a clear atherogenic pattern in early renal disease. Alaupovic reported that measurement of lipoprotein family profiles offers a new means for selecting appropriate therapies targeted in individual subjects, at decreasing undesirable and/or increasing beneficial lipoproteins families.[[15]]

It was presented that serum Lp(a) concentrations increased significantly relatively early in renal insufficiency. Moreover, the medians and ranges of serum Lp(a) concentrations were similar in both studied groups. This finding, excluding induction of a general increase in hepatic protein synthesis, may play an important role in determining serum Lp(a) concentration in renal disease because these patients had proteinuria lower than 0.5 mg/dL.[[7]] Recently Stenvinkel suggested that increased Lp(a) levels in non-dialyzed patients with chronic renal failure can be modulated depending on inflammatory and/or nutritional parameters.[[16]] Our results as well as those obtained previously[[7]], [[13]], [[17]] indicated that uremia “per se” may influence Lp(a) metabolism. It should be mentioned that the weak positive correlation between TC and LDL-C as well as ApoB and Lp(a) is likely to reflect the possible, even though disputable, role of the LDL receptor in the Lp(a) catabolism.[[7]], [[17]] Increased Lp(a) concentration occurs in early renal failure and may result in nonspecific synthesis or catabolism disturbances in patients with mild/moderate renal insufficiency.[[17]]

We concluded that the reduced levels of apoA-containing lipoproteins and increased TG-rich apoB-containing lipoproteins and Lp(a), indicated a clear atherogenic pattern in early renal disease. Increased Lp(a) levels may result in nonspecific synthesis or catabolism disturbances. These findings may be of importance for selecting and monitoring the appropriate preventive measures for normalizing dyslipidemia in non-dialyzed patients.

ACKNOWLEDGMENT

This work was supported by Prof. L. Janicka and Prof. A. Książek with the Department of Clinical Nephrology, University of Medicine, Lublin and Head of S. Wyszyński Technical Hospital, Lublin.