István Kárpáti

The Serum Paraoxonase Activity in Patients with Chronic Renal Failure and Hyperlipidemia

Human serum paraoxonase is physically associated with an apolipoprotein (Apo-A1) and clusterin-containing high-density lipoprotein (HDL) and prevents low-density lipoprotein from lipid peroxidation. The aim of our study was to determine whether paraoxonase activity or phenotype is altered in patients with chronic renal failure and in hyperlipidemic subjects without renal insufficiency and to compare the values with those of healthy controls. We investigated the serum paraoxonase activity and polymorphism in 119 hemodialyzed uremic patients, 107 patients with primary hyperlipoproteinemia, and in 110 healthy control subjects. The serum paraoxonase activity was significantly decreased both in hyperlipidemic (p < 0.01) and uremic patients (p < 0.001) as compared with controls. On comparison, the serum paraoxonase activity was significantly lower (p < 0.001) in uremic than in hyperlipoproteinemic patients. The HDL and Apo-A1 levels were as follows: uremic < hyperlipidemic < control. To assess whether the observed reduction in paraoxonase activity was due to HDL and Apo-A1 level decreases, we standardized the enzyme activity for HDL and Apo-A1 concentrations. We found that the standardized paraoxonase activity (paraoxonase/HDL ratio) was also lower in the uremic patients (103.3 ± 69.5) as compared with hyperlipidemic patients (137.64 ± 81.0) and controls (194.45 ± 94.45). The standardized values for Apo-A1 showed a similar tendency: paraoxonase/Apo-A1 ratio in uremic patients 89.64 ± 47.8, in hyperlipidemic patients 128.12 ± 69.83, and in controls 161.40 ± 47.35. The phenotypic distribution of paraoxonase (AA, AB, BB) did not change significantly in the patient groups. These results suggest that HDL concentration and phenotypic distribution of paraoxonase may not be the only determining factors, but that other as yet undetermined factors could be involved in the enzyme activity changes.

Serum paraoxonase activity changes in uremic and kidney-transplanted patients

Serum paraoxonase (PON) is a high-density lipoprotein (HDL)-associated hydrolase, which inhibits low-density lipoprotein oxidation. Uremic and kidney-transplanted patients have an increased risk of atherosclerosis, to which an increased lipoprotein oxidation may contribute. The aim of our study was to determine whether the PON activity or phenotype is altered in uremic and kidney-transplanted patients, and to compare the values with those of healthy controls. 117 uremic patients on long-term hemodialysis treatment, 115 renal-transplanted patients, and 110 healthy controls were involved in the study. The PON activity was significantly reduced in the uremic patients compared to controls (PON 101.36±30.12 vs. control 188.05±58.96 U/ml; p < 0.001), while in kidney-transplanted patients the values were almost identical to those of controls (PON 161.5±35.39 U/ml). The different immunosuppressive drug combinations did not influence PON activity. To assess whether the altered PON activity was due to a decrease HDL level, we standardized the enzyme activity for the HDL concentration (PON/HDL ratio). We found that the standardized enzyme activity was lower in the uremic (102.7±54.8) and kidney-transplanted patients (144.5±32.7) when compared to controls (194.5±94.5; p < 0.001). The phenotypic distribution of PON in uremic, renal transplant and control patients are as follows: AA 66.67, 56.48 and 66.67%; AB 31.62, 33.3 and 26.67%; BB 1.71, 10.19 and 6.67%. We conclude that the decreased PON/HDL and PON/apoA-1 ratios may lead to a reduction in the antioxidant capacity of HDL, which might contribute to the accelerated development of atherosclerosis in uremic and kidney-transplanted patients.

Altered signal pathway in angiotensin II-stimulated neutrophils of patients with hypercholesterolaemia

Angiotensin II (AII) in 1-10 nM concentrations has an in vivo immunostimulating effect on human neutrophils. The release of superoxide anions and leukotrienes (LTs) is significantly increased by 10 nM AII-stimulated neutrophils of patients with hypercholesterolaemia (HCH). These oxidizing agents may be involved in the damage of vessel walls, i.e., in atherosclerotic plaque formation. To clarify the receptor types and signal pathways in neutrophils of healthy controls and patients, inositol trisphosphate (IP(3)) production and Ca(2+) signalling were studied. Neutrophils were pretreated before AII stimulation with different inhibitory drugs. In control cells, the stimulation occurred predominantly through pertussis toxin-sensitive, type angiotensin 1 receptors. This induced IP(3) production and Ca(2+) signalling from intracellular pools. In neutrophils of hypercholesterolaemic patients, the enhanced release of oxidizing agents was dependent more on type angiotensin 2 than type angiotensin 1 receptors. After stimulation, there was no IP(3) production detected. The Ca(2+) signalling was lower than in control cells and was dependent on extracellular Ca(2+).

Discordance in human paraoxonase-1 gene between phenotypes and genotypes in chronic kidney disease.

Background: Human serum paraoxonase-1 (PON1) is a high-density lipoprotein-associated ester hydrolase which can inhibit low-density lipoprotein oxidation and has an antiatherogenic effect. Two common polymorphisms are known in the PON1 gene in humans (at positions 55 and 192), from which the latter gene alteration has been mainly attributed to alter the activity of the protein. Moreover, significantly reduced PON1 activity was found in chronic kidney disease (CKD) and renal transplant patients. Methods: The aim of the present study was to investigate the genotype and phenotype distribution of the PON1 gene as well as its end product activity in patients with CKD (n = 117), in renal transplant recipients (n = 146) and in reference subjects (n = 1,180). Results: Unexpectedly high discordances between phenotype and genotype assessments were observed in all studied groups (28.2% in the CKD, 20.55% in the transplant and 30.9% in the reference group). Arylesterase activity was significantly lower in the CKD group compared to the reference sample. There were no significant differences between patients and the reference group in the frequencies of polymorphisms PON1–55 and PON1–192. PON1 activity did not differ in patients compared to the reference group. Conclusions: Both PON1 phenotype and genotype determinations are necessary to estimate PON1 status.

Serum cystatin C is a determinant of paraoxonase activity in hemodialyzed and renal transplanted patients

Background: Human paraoxonase-1 (PON1) inhibits LDL-oxidation and atherogenesis, and possesses lactonase activity. Decreased PON1 activity was found in hemodialyzed and renal transplanted patients. Cystatin C plays a protective role in atherosclerosis, and is a new, sensitive marker of renal function. The relationship between these two markers in renal failure has not been investigated. Aims: The goal of this study was to clarify the relationship between PON1 activity, cystatin C and homocysteine in chronic renal failure. We also determined the levels of oxidatively modified LDL (oxLDL) and thiobarbituric acid reactive substances (TBARS) to characterize lipid peroxidation. Patients and methods: 74 hemodialized (HD), 171 renal transplanted patients (TRX), and 110 healthy controls (C) were involved in the study. PON1 activity and TBARS levels were measured spectrophotometrically. OxLDL level was determined with sandwich ELISA. Results: There was a negative correlation between PON1 activity and cystatin C level. Homocysteine level correlated negatively with PON1 activity, and positively with cystatin C level. OxLDL and TBARS levels were significantly higher in the HD and TRX groups compared to C. Conclusions: Cystatin C may be a good predictive factor not only for homocysteine levels but for the antioxidant status in patients with renal failure and renal transplantation.

Relationship between Serum Nickel and Homocysteine Concentration in Hemodialysis Patients

Severe hyperhomocysteinemia (HHC) is associated with atherosclerosis. In hemodialysis (HD) patients, one of the main causes of death is cardiovascular disease. In animals, trace elements such as cobalt, copper, iron, and nickel ameliorated vitamin B12 deficiency-induced HHC. However, correlations between plasma total homocysteine (tHcy) and trace elements in HD patients have not been investigated. Therefore, tHcy, folate, vitamin B12, trace elements (cobalt, copper, iron, and nickel), and some laboratory parameters such as serum total protein, albumin, transferrin, ferritin, C-reactive protein (CRP), and interleukin-6 concentrations were determined in 122 hemodialysis patients. When patients were divided into groups according to their tHcy, we found no significant differences in concentrations of cobalt, copper, and total protein, while nickel was higher, and folate, vitamin B12, and iron were lower in patients with lower than higher tHcy. In univariate regression analysis, tHcy negatively correlated with concentrations of folate (r = −0.302, p < 0.006), vitamin B12 (r = −0.347, p < 0.0001), nickel (r = −0.289, p < 0.006), and CRP (r = −0.230, p < 0.02) and positively with serum albumin (r = 0.316, p < 0.0004) and hemoglobin (r = 0.329, p < 0.0001) values. No relationship between tHcy and serum concentrations of cobalt, copper, iron, or other laboratory parameters was found in HD patients. The effect of cobalt and nickel on homocysteine production was assessed in human peripheral mononuclear cells (PBMCs). Nickel but not cobalt at concentrations found in HD patients significantly inhibited homocysteine, cysteine, and S-adenosylhomocysteine production in human PBMCs. These results suggest that nickel might also be involved in the regulation of the methionine–folate cycle in humans, as was demonstrated in animal experiments.

The epidemic of chronic kidney disease requires the estimation of glomerular filtration rate

Nowadays chronic kidney disease has become a major public health problem due to the great increase in atherogenic nephropathies. In the absence of classic renal symptoms, chronic kidney disease is mostly diagnosed when renal failure is already advanced, although it can be revealed by laboratory tests in the earlier stages. When diagnosis is late, the progression to end-stage renal failure is unavoidable and renal replacement therapy is needed. Even early-moderate renal failure significantly increases the risks for atherosclerosis, thereby leading to the deaths of patients from cardiovascular disease before initiation of dialysis. Therefore screening for asymptomatic chronic kidney disease is urgently needed. Estimated glomerular filtration rate has the greatest importance in the screening and in the timely intervention to slow down the progression of renal failure and cardiovascular disease. In 2005, the Hungarian Society of Nephrologists and the Hungarian Society of Laboratory Medicine suggested the automatic estimation and reporting of glomerular filtration rate, each time serum creatinine measurements were made. This practice is used more frequently by laboratories in Hungary. This article aims to help facilitate the utilization and evaluation of estimated glomerular filtration rate.

Low High-Density Lipoprotein Cholesterol Is Not Responsible for Decreased Paraoxonase Activity in Chronic Renal Failure

Background/Aims: Human paraoxonase-1 (PON1) is responsible for the antioxidant effect of high-density lipoprotein (HDL) by inhibiting low-density lipoprotein oxidation. Previous studies discovered dyslipidemia (DL) and decreased PON1 activity in chronic renal failure (CRF). We aimed to determine PON and arylesterase activity, phenotypic distribution of the PON1 enzyme, and lipid profile in low and normal HDL cholesterol (HDL-C) patients with CRF, and renal transplant (TX), compared to primary DL. Methods: 116 CRF (low or normal HDL-C), 52 TX (low or normal HDL-C), and 62 DL patients (low or normal HDL-C) were included. PON and arylesterase activities were measured spectrophotometrically. Phenotype was determined using the dual substrate method. Results: Aryl/HDL-C was significantly higher in low HDL-C patients. Patients with CRF had significantly lower arylesterase activity compared to DL, independent of HDL-C. PON activity and PON/HDL-C did not differ significantly in CRF compared to TX and DL. Phenotypic distribution was similar in patient groups. Low HDL-C CRF patients had significantly lower cholesterol and triglyceride than DL. Conclusion: Decreased arylesterase activity, correlating with PON1 enzyme protein quantity, is not explicable by decreased HDL-C in CRF. Low HDL-C CRF patients’ increased cardiovascular morbidity is not attributable to changes in PON1 activity, or phenotypic distribution.

CSN Society News

Nephrology has a long tradition in the Czech Republic. The first acute dialysis was performed in 1955, a chronic dialysis programme started in the early 60ies, and a transplantation programme in 1966. This was reflected by many important international meetings held in Prague: The 2nd Congress of the International Society of Nephrology (1963), 17th Congress of the European Dialysis and Transplantation Association (1980) and the 15th Congress of the European Society of Artificial Organs (1988). More recently, the 17th and 25th meetings of the International Society of Blood Purification (1999 and 2007), 11th ANCA and Vasculitis Workshop (2003), 7th European Peritoneal Dialysis Meeting (2005), 13th Congress of the European Society of Organ Transplantation (2007) and finally, this year, the 48th Congress of ERA-EDTA.

Serum paraoxonase activity changes in uremic and kidney transplanted patients

Serum paraoxonase (PON) is a high-density lipoprotein (HDL)-associated hydrolase, which inhibits low-density lipoprotein oxidation. Uremic and kidney-transplanted patients have an increased risk of atherosclerosis, to which an increased lipoprotein oxidation may contribute. The aim of our study was to determine whether the PON activity or phenotype is altered in uremic and kidney-transplanted patients, and to compare the values with those of healthy controls. 117 uremic patients on long-term hemodialysis treatment, 115 renal-transplanted patients, and 110 healthy controls were involved in the study. The PON activity was significantly reduced in the uremic patients compared to controls (PON 101.36+/-30. 12 vs. control 188.05+/-58.96 U/ml; p < 0.001), while in kidney-transplanted patients the values were almost identical to those of controls (PON 161.5+/-35.39 U/ml). The different immunosuppressive drug combinations did not influence PON activity. To assess whether the altered PON activity was due to a decrease HDL level, we standardized the enzyme activity for the HDL concentration (PON/HDL ratio). We found that the standardized enzyme activity was lower in the uremic (102.7+/-54.8) and kidney-transplanted patients (144.5+/-32.7) when compared to controls (194.5+/-94.5; p < 0.001). The phenotypic distribution of PON in uremic, renal transplant and control patients are as follows: AA 66.67, 56.48 and 66.67%; AB 31. 62, 33.3 and 26.67%; BB 1.71, 10.19 and 6.67%. We conclude that the decreased PON/HDL and PON/apoA-1 ratios may lead to a reduction in the antioxidant capacity of HDL, which might contribute to the accelerated development of atherosclerosis in uremic and kidney-transplanted patients.