Effects of erythropoietin therapy on the lipid profile in end-stage renal failure

Ketoanalogs' Effects on Intestinal Microbiota Modulation and Uremic Toxins Serum Levels in Chronic Kidney Disease (Medika2 Study)

Nutritional therapy (NT) is a therapeutic option in the conservative treatment of chronic kidney disease (CKD) patients to delay the start of dialysis. The aim of this study was to evaluate the specific effect of ketoanalogs (KA)-supplemented diets for gut microbiota modulation. In a previous study we observed that the Mediterranean diet (MD) and a KA-supplemented very-low-protein diet (VLPD) modulated beneficially gut microbiota, reducing indoxyl- and p-cresyl-sulfate (IS, PCS) serum levels, and ameliorating the intestinal permeability in CKD patients. In the current study, we added a third diet regimen consisting of KA-supplemented MD. Forty-three patients with CKD grades 3B–4 continuing the crossover clinical trial were assigned to six months of KA-supplemented MD (MD + KA). Compared to MD, KA-supplementation in MD + KA determined (i) a decrease of Clostridiaceae, Methanobacteriaceae, Prevotellaceae, and Lactobacillaceae while Bacteroidaceae and Lachnospiraceae increased; (ii) a reduction of total and free IS and PCS compared to a free diet (FD)—more than the MD, but not as effectively as the VLPD. These results further clarify the driving role of urea levels in regulating gut integrity status and demonstrating that the reduction of azotemia produced by KA-supplemented VLPD was more effective than KA-supplemented MD in gut microbiota modulation mainly due to the effect of the drastic reduction of protein intake rather than the effect of KA.

No effect of 10 weeks erythropoietin treatment on lipid oxidation in healthy men

Studies indicate that erythropoietin (EPO) has effect on lipid and energy metabolism; however, the impact of EPO on lipid oxidation in vivo has not been well documented. Here, we evaluate whether long-term erythropoiesis-stimulating agent (ESA) treatment affects the oxidation of plasma very low-density lipoprotein triglycerides (VLDL-TG) fatty acids (FA), plasma free fatty acids (FFA) and non-plasma (residual) FA in healthy, young, sedentary men. Infusion of [1-14C]VLDL-TG and [9,10-3H]palmitate was used in combination with indirect calorimetry to assess resting lipid fuel utilization and kinetics, and resting energy expenditure (REE) before and after 10 weeks of ESA exposure compared with placebo. REE increased significantly during ESA compared with placebo (P = 0.023, RM-ANOVA). Oxidation rates of VLDL-TG FA, FFA, and residual FA remained unchanged during ESA compared with placebo. The relative contribution of the lipid stores was greatest for FFA (47.1%) and the total lipid oxidation rate and was not significantly different between ESA and placebo-treated subjects. We conclude that long-term ESA treatment of healthy young men increases REE but does not alter the oxidation rates of plasma and non-plasma FA sources.

Erythropoietin alleviates hepatic steatosis by activating SIRT1-mediated autophagy

Erythropoietin (EPO), besides its stimulatory effect on erythropoiesis, is beneficial to insulin resistance and obesity. However, its role in hepatic steatosis remains unexplored. Activating autophagy seems a promising mechanism for improving fatty liver disease. The present study investigated the role of EPO in alleviating hepatic steatosis and sought to determine whether its function is mediated by the activation of autophagy. Here, we show that EPO decreased hepatic lipid content significantly in vivo and in vitro. Furthermore, EPO/EPO receptor (EPOR) signalling induced autophagy activation in hepatocytes as indicated by western blot assay, transmission electron microscopy, and confocal microscopy. In addition, EPO increased the co-localization of autophagosomes and cellular lipids as shown by double labelling of the autophagy marker light chain microtubule-associated protein 3 (LC3) and lipids. Importantly, suppression of autophagy by an inhibitor or small interfering RNA (siRNA) abolished the EPO-mediated alleviation hepatic steatosis in vitro. Furthermore, EPO up-regulated sirtuin 1 (SIRT1) expression, and siRNA-mediated SIRT1 silencing abrogated the EPO-induced increases in LC3 protein and deacetylation levels, thereby preventing the alleviation of hepatic steatosis. Taken together, this study revealed a new mechanism wherein EPO alleviates hepatic steatosis by activating autophagy via SIRT1-dependent deacetylation of LC3. This finding might have therapeutic value in the treatment of hepatic steatosis.

Erythrocyte Metabolism during Renal Anemia Treatment with Recombinant Human Erythropoietin

Recombinant human erythropoietin (epoetin) is widely used for the treatment of renal anemia. The aim of our study was to determine the influence of epoetin on erythrocyte metabolism. Thirty-six hemodialysis patients (22 men, 14 female), aged from 17 to 64 years (mean age 43) and 30 healthy volunteers (12 men, 18 female), aged from 25 to 65 years (mean age 40) were studied. Epoetin (Eprex, Janssen-Cilag) was administered subcutaneously with the starting dose of 2000 IU three times per week for twelve months (range from 75 to 133 IU/kg/week, mean dose 102±21 IU/kg/week). Laboratory markers of: hematological response, iron status and erythrocyte metabolism were measured before epoetin administration. Afterwards the markers were controlled every three months. During epoetin treatment a significant increase in hemoglobin concentration was observed (100% patients responded in a positive way to epoetin). The following changes in erythrocyte metabolism were noticed: 1) in glycolytic enzymes: a significant increase in the activity of hexokinase and that of lactate dehydrogenase, 2) in glycolytic intermediates: a significant increase in the 2,3-diphosphoglycerate and adenosine triphosphate concentrations, 3) a significant increase sodium, potassium adenosine triphosphatase concentration, 4) the glucose uptake by erythrocytes significantly decreased while the lactate production remained stable.

During anemia treatment with epoetin in hemodialysis patients not only quantitative but also qualitative changes in erythrocytes were observed.

Dyslipidemia in patients with chronic kidney disease

Chronic kidney disease (CKD) is associated with high risk for cardiovascular disease (CVD). This association is multifactorial, but CKD is often associated with dyslipidemia, which likely contributes. Patients with CKD have dyslipidemia even at early stages of renal dysfunction and dyslipidemia tends to progress with deterioration of kidney function. The dyslipidemia in CKD is largely due to increased triglyceride levels, decreased HDL-C and varying levels of LDL-C. Current management of CKD may also affect lipid levels. Robust clinical trials demonstrate that statins are safe and efficacious in both lipid lowering and prevention of CVD events in pre-end stage CKD and post-transplant. However, there is no evidence of improved CVD outcomes with statin use in dialysis patients. This review will focus on mechanisms underlying dyslipidemia in CKD and clinical trial evidence for lipid lowering therapy in patients with CKD.

β Common Receptor Mediates Erythropoietin-Conferred Protection on OxLDL-Induced Lipid Accumulation and Inflammation in Macrophages

Erythropoietin (EPO), the key factor for erythropoiesis, also protects macrophage foam cells from lipid accumulation, yet the definitive mechanisms are not fully understood. β common receptor (βCR) plays a crucial role in the nonhematopoietic effects of EPO. In the current study, we investigated the role of βCR in EPO-mediated protection in macrophages against oxidized low-density lipoprotein- (oxLDL-) induced deregulation of lipid metabolism and inflammation. Here, we show that βCR expression was mainly in foamy macrophages of atherosclerotic aortas from apolipoprotein E-deficient mice. Results of confocal microscopy and immunoprecipitation analyses revealed that βCR was colocalized and interacted with EPO receptor (EPOR) in macrophages. Inhibition of βCR activation by neutralizing antibody or small interfering RNA (siRNA) abolished the EPO-conferred protection in oxLDL-induced lipid accumulation. Furthermore, EPO-promoted cholesterol efflux and upregulation of ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 were prevented by pretreatment with βCR neutralizing antibody or βCR siRNA. Additionally, blockage of βCR abrogated the EPO-conferred anti-inflammatory action on oxLDL-induced production of macrophage inflammatory protein-2. Collectively, our findings suggest that βCR may play an important role in the beneficial effects of EPO against oxLDL-elicited dysfunction of macrophage foam cells.

Plasma Lipoprotein Abnormalities in Hemodialysis Patients—Clinical Implications and Therapeutic Guidelines

Patients with advanced stages of chronic kidney disease (CKD) have an increased risk of death from cardiovascular disease (CVD). Dyslipidemias are associated with atherosclerotic vascular changes and the risk of occurrence of acute myocardial infarction in hemodialysis patients. However, management of dyslipidemia in hemodialysis patients does not appear to be actively carried out in routine practice. Presumably, there are three reasons for this reluctance to lipid-lowering in hemodialysis patients. First, there are epidemiological data showing the inverse relationship between cholesterol and mortality rate; a high cholesterol predicts a better survival. Second, lipids are not usually measured using standard fasting serum, but a non-fasting specimen. Third, although hypertriglyceridemia is the most common abnormality, fibrates are contraindicated in patients with renal failure because of a high risk of rhabdomyolysis. These issues are discussed in the current review article. Based on published work, lipid lowering would not increase the death rate if carried out without worsening malnutrition. The National Kidney Foundation K/DOQI Clinical Practice Guidelines recommend a reduction in fasting LDL-C below 100 mg/dL for the prevention of CVD in dialysis patients. Practically, however, the use of non-HDL-C measured by casual blood samples might be sufficient for the risk assessment in many hemodialysis patients. Statins are a good choice for lipid-lowering in dialysis patients. Furthermore, lipoprotein profile might be improved by an inventive use of dialyzer membranes, dialysate solutions, and other dialysis-related medications. For severe hypercholesterolemia, LDL-apheresis is another choice for consideration. Further studies are needed to clearly prove the benefit of lipid reduction in hemodialysis patients and those with CKD at earlier stages.

Long-term treatment with EPO increases serum levels of high-density lipoprotein in patients with CKD

BACKGROUND

Among lipid abnormalities observed in patients with chronic kidney disease (CKD) is a significant decrease in serum high-density lipoprotein cholesterol (HDL-C) levels. In a previously published randomized control trial, we showed that early erythropoietin (EPO) administration in a predialysis population slowed the progression of CKD. In the present nested substudy, we examine whether EPO has an influence on serum HDL-C levels in comparison to other lipid parameters in this population.

METHODS

Eighty-eight patients with CKD stages 3 and 4 were enrolled in the study. Forty-five patients (group 1) were treated with EPO (50 U/kg/wk), targeting to increase hemoglobin levels to 13 g/dL or greater (>or=130 g/L). The other patients (group 2) remained without treatment until hemoglobin levels decreased to less than 9 g/dL (<90 g/L). The duration of the study was 12 months.

RESULTS

At the end of the study, we observed a statistically significant decrease in serum levels of total cholesterol, low-density lipoprotein cholesterol (LDL-C), and triglycerides in both groups. However, serum HDL-C levels significantly increased in only group 1 (from 42.5 +/- 10.4 to 55.9 +/- 8.1 mg/dL [1.10 +/- 0.27 to 1.45 +/- 0.21 mmol/L]; P < 0.001), whereas they were unchanged in group 2. In addition, a significant decrease in atherogenic LDL-C/HDL-C ratio was observed in only group 1. Importantly, the increase in serum HDL-C levels correlated positively with the increase in hemoglobin values in EPO-treated patients.

CONCLUSION

Our results show that EPO treatment of predialysis patients with CKD significantly increases serum HDL-C levels, which may represent an important antiatherogenic effect of this hormone.

Enhanced metabolic effect of erythropoietin and keto acids in CRF patients on low-protein diet: Czech multicenter study

BACKGROUND

Our study is designed to establish whether supplementation with erythropoietin (EPO) exerts additional beneficial metabolic effects in patients with chronic renal failure (CRF) treated with keto acids (KAs) on a low-protein diet (LPD).

METHODS

A long-term, prospective, randomized study was designed to use three therapeutic protocols: (A) EPO plus KAs plus LPD (group I), (B) EPO plus LPD (group II), and (C) LPD (group III). One hundred eighty-six randomly selected patients (90 men, 96 women; age, 22 to 78 years) with a creatinine clearance of 22 to 36 mL/min were monitored at the beginning and at every 6 months for 3 years.

RESULTS

During the study period, glomerular filtration rate measured as inulin clearance decreased slightly (from 26.2 +/- 3.4 to 23.4 +/- 4.1 mL/min in group I), 27.4 +/- 4.8 to 20.2 +/- 4.4 mL/min in group II, and 26.8 +/- 3.6 to 17.4 +/- 4.1 mL/min in group III; P < 0.01). Serum urea levels also declined (P < 0.01), more pronouncedly in group I (P < 0.025). In group I, there was a significant increase in levels of leucine (P < 0.01) and albumin (P < 0.01) and a decrease in proteinuria (P < 0.01). Analysis of the lipid spectrum showed a mild, yet significant, decrease in total cholesterol and low-density lipoprotein cholesterol levels (P < 0.025), more pronounced in group I. In group I, there was a decrease in plasma triglyceride levels (from 362.85 +/- 115.05 mg/dL [4.1 +/- 1.3 mmol/L] to values as low as 203.55 +/- 70.80 mg/dL [2.3 +/- 0.8 mmol/L]; P < 0.01), whereas high-density lipoprotein cholesterol levels increased (from 34.75 +/- 7.72 mg/dL [0.9 +/- 0.2 mmol/L] to 46.33 +/- 7.72 mg/dL [1.2 +/- 0.2 mmol/L]; P < 0.025). Mean arterial blood pressure was stable.

CONCLUSION

EPO supplementation in patients with CRF administered KAs potentiates the beneficial effects on metabolism of proteins, amino acids, and lipids. Long-term coadministration of EPO, KA, and LPD was associated with a delay in progression of renal failure and reduction in proteinuria.

Erythropoietin supplement increases plasma lipoprotein lipase and hepatic triglyceride lipase levels in hemodialysis patients

BACKGROUND

We reported in previous studies that plasma triglyceride levels, as well as remnant-like particles-cholesterol (RLP-C) and -triglyceride (RLP-TG) levels, were significantly lower in maintenance hemodialysis (HD) patients treated with erythropoietin (EPO) than in HD patients treated without EPO. However, little is known about the mechanisms underlying the improvements in abnormal RLP metabolism in HD patients. This study investigates whether EPO supplement therapy in cases of uremic anemia increases the plasma lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) levels in HD patients.

METHODS

Twenty HD patients who had not previously received EPO were divided into two groups according to the stage of HD: 12 at the initial stage, defined as a mean HD duration of 0.35 +/- 0.68 months (range of 0 to 2.47 months), and 8 at the maintenance stage, defined as a mean HD duration of 114.1 +/- 91.9 months (range of 13.0 to 253.9 months). Fasting plasma was collected from the HD patients prior to the start of the EPO supplement therapy and at one month after the therapy. RLP-C levels were determined using a RLP-C JIMRO II kit. Fasting plasma was also collected from the HD patients 10 minutes after an intravenous injection of heparin (30 U/kg body wt). Plasma LPL levels were determined using an enzyme immunoassay, and HTGL levels were determined using a modified version of the Hernell et al method.

RESULTS

Plasma RLP-C levels showed a tendency to decrease after the start of the EPO supplement therapy in HD patients at the maintenance stage. Plasma LPL levels were significantly higher in the two groups of HD patients one month after the start of the EPO supplement therapy than in the same patients prior to the start of the EPO supplement therapy. Plasma HTGL levels were significantly higher in HD patients at the maintenance stage one month after the start of the EPO supplement therapy than in HD patients at the maintenance stage prior to the start of the EPO supplement therapy.

CONCLUSIONS

The results of this study suggest that the EPO supplement therapy may reduce plasma RLP-C levels by increasing the plasma LPL and HTGL levels in maintenance-stage HD patients.

Long-term effects of recombinant human erythropoietin therapy on growth hormone secretion in uremic patients undergoing peritoneal dialysis

Recombinant human erythropoietin (rhEPO) is being successfully used for the treatment of uremic anemia. Short-term studies have proved that correction of anemia with rhEPO therapy is accompanied by several changes in growth hormone (GH) secretion in uremic patients. The present study aimed to assess the influence of long-term rhEPO therapy on baseline and stimulated GH concentrations in a group of uremic patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Seven well-nourished and clinically stable CAPD patients were studied. Ten normal subjects were studied as controls. GH responses to direct pituitary stimulation with GH-releasing hormone (GHRH) (100 microg intravenously [i.v.]) and indirect hypothalamic stimulation with insulin-induced hypoglycemia (0.1 U/kg body weight i.v.) and clonidine (0.15 mg/m2 orally), were assessed before and after 3, 6, and 12 months of subcutaneously administered rhEPO therapy. After rhEPO administration, an increase of the hemoglobin concentration was observed in all patients and maintained at about 12 g/dL throughout the study period. rhEPO therapy did not induce any significant change in baseline concentrations of GH and insulin-like growth factor I. Correction of the anemia was accompanied by a clear increase in the area under the curve (AUC) and the area above the baseline (AAB) of GH secretion in response to GHRH stimulation. These changes were statistically significant after 3 and 6 months of therapy, although at 12 months no significant differences in relation to pretreatment values could be observed. rhEPO treatment was associated with a progressive decrement in the GH AUC and AAB in response to hypoglycemic challenge, reaching statistically significant values at months 6 and 12. On the other hand, compared with the control group, GH responses to clonidine were blunted at the start of the study in CAPD patients, and rhEPO therapy was not accompanied by any modification. In conclusion, long-term treatment with rhEPO in CAPD patients is associated with complex and profound effects on somatotrope cell function, characterized by diverse effects on GH responses to stimuli that release GH through different mechanisms. Some of these rhEPO-induced alterations in somatotrope function are dependent on the duration of treatment.

Influence of hematocrit on the measurement of lipoproteins demonstrated by the example of lipoprotein(a)

BACKGROUND

The measurement of many parameters of human blood is usually performed in plasma or serum. Since lipoproteins or apolipoproteins, for example, are found almost exclusively in the plasma fraction after low-speed centrifugation, these parameters can be expected to be distributed in a different plasma volume depending on the hematocrit value. Therefore, the measured plasma levels might be relatively too low or too high in comparison to the whole blood concentrations in the case of abnormal hematocrit levels. The aim of our experiments was to evaluate the extent of differences between whole blood and plasma concentrations, taking as an example lipoprotein(a) [Lp(a)] in hemodialysis patients with documented decreased hematocrit values.

METHODS

Lp(a) was measured in plasma as well as whole blood of 15 hemodialysis patients with low hematocrit values (0.29 +/- 0.02) in comparison to 11 control subjects (0.45 +/- 0.04).

RESULTS

Plasma concentrations were 27% higher in patients than in controls (19.7 vs. 15.5 mg/dl). The relative difference was twice as high (59%) when measured in whole blood (13.5 vs. 8.5 mg/dl). Similar relative differences were observed when whole blood concentrations of 125 hemodialysis patients and 256 controls were calculated with the formula [Lp(a)plasma * (1-hematocrit)].

CONCLUSIONS

Our findings clearly demonstrate that hematocrit is a strong confounding variable of lipoprotein measurement in epidemiological studies when concentrations are measured in plasma, especially in cases of abnormal hematocrit values. Furthermore, studies investigating the longitudinal changes of lipoproteins should consider potential hematocrit changes.

High density lipoprotein (HDL) particle composition in patients with end stage renal failure (ESRF) on chronic dialysis

BACKGROUND

Hypertriglyceridaemia, low high density lipoprotein (HDL) cholesterol level and reduced LDL particle size are the major features of uraemic dyslipidaemia. They are also found in the Insulin Resistance Syndrome.

AIM

To examine alterations in HDL composition in patients on chronic dialysis and their relationship with insulin resistance.

METHODS

HDL particle size was determined in 33 patients on chronic haemodialysis (HD), 27 on chronic ambulatory peritoneal dialysis (CAPD) and 32 control non-diabetic subjects (C) without renal disease by non-denaturing 3-30% polyacrylamide gradient gel electrophoresis. A weighted HDL particle size score was calculated taking into account both HDL particle size and percentage total HDL protein concentration of each HDL band of the individual. Lipid and apolipoliprotein concentrations were determined in HDL2 and HDL3 particles obtained by sequential ultracentrifugation. In a subset of 24 control subjects and 22 subjects on HD, insulin sensitivity was also determined by an intravenous glucose tolerance test (IVGTT).

RESULTS

HDL particles were found to be more triglyceride enriched and apoAI depleted in subjects on HD even though plasma triglyceride level was highest in patients on CAPD. Five subpopulations of HDL particles were identified by gradient gel electrophoresis in all subjects combined. In the subgroup of subjects who underwent IVGTT, the weighted HDL particle size score correlated positively with HDL cholesterol level (r = 0.6, p < 0.0005), LDL particle size (r = 0.47, p < 0.001), and insulin sensitivity (r = 0.48, p < 0.001), and negatively with plasma triglyceride level (r = 0.37, p < 0.01).

CONCLUSIONS

We conclude that even though HDL cholesterol is reduced to a similar level in subjects on both forms of dialysis for end stage renal failure, abnormalities of HDL composition are more marked in subjects on HD. Reduction in HDL particle size is linked with insulin resistance and accompanies reduction in LDL particle size and hypertriglyceridaemia.

Nandrolone decanoate reduces serum lipoprotein(a) concentrations in hemodialysis patients

We have studied the changes in the lipid profile of 14 chronic hemodialysis patients receiving a 6-month cycle of nandrolone decanoate as treatment for anemia. Nandrolone decanoate was administered in a weekly intramuscular dose of 200 mg and resulted in an increase in the hemoglobin concentration (baseline, 7.9 +/- 0.9 g/dL; month 6, 10.8 +/- 1.7 g/dL; P < 0.001, ANOVA) and also produced relevant modifications in the lipid concentrations. The most significant finding was a decrease in the concentration of lipoprotein(a) [Lp(a)]: baseline, 19.8 mg/dL (median), month 2, 10.6 mg/dL; month 4, 8.7 mg/dL; and month 6, 7.1 mg/dL (P < 0.001, Friedman). Other lipid changes induced by nandrolone decanoate were an increase in the concentrations of apolipoprotein B (P < 0.02, ANOVA) and triglyceride (P = NS, ANOVA) and a decrease of high-density lipoprotein (HDL) cholesterol (P < 0.001, ANOVA) and apolipoprotein A-I (P = NS, ANOVA). The decrease in HDL cholesterol was at the expense of the HDL2 cholesterol subfraction, whereas HDL3 remained unchanged. These lipid modifications were reversible; 4 months after nandrolone decanoate withdrawal, the lipid concentrations were similar to the basal values. The changes in Lp(a) levels did not correlate with those of hemoglobin or the other lipid parameters, suggesting that the underlying mechanisms are unrelated. Our findings could be clinically relevant if confirmed by further studies.

Down-regulation of VLDL receptor expression in chronic experimental renal failure

VLDL receptor (VLDL-R) is a novel member of the LDL receptor gene family with distinct tissue distribution and function. It binds and internalizes VLDL particles and is primarily expressed in skeletal muscle, heart, brain and adipose tissue, which use fatty acids for energy production or storage. CRF is associated with elevated serum triglyceride and VLDL concentrations and depressed VLDL and chylomicron clearance. We have recently shown marked down-regulation of lipoprotein lipase expression in CRF. This study was conducted to test the hypothesis that VLDL-R expression may be similarly depressed in CRF. To this end, VLDL-R mRNA (Northern blot) and protein mass (Western blot) of skeletal muscle (soleus) and heart were measured in male Sprague-Dawley rats six weeks after 5/6 nephrectomy (CRF group) or sham operation (NL group). A group of erythropoietin (EPO)-treated (150 U/kg twice weekly) CRF animals was included to determine the possible effect of EPO-deficiency anemia (EPO-CRF group). Subgroups of animals were studied at weeks 1, 3 and 6. The CRF group showed a fivefold increase in plasma triglyceride concentration. This was associated with an impressive fourfold reduction in heart and skeletal muscle VLDL-R mRNA and protein mass. VLDL-R mRNA levels in the heart and skeletal muscle were directly related to creatinine clearance and inversely related to serum triglyceride and VLDL concentrations. EPO therapy led to a mild improvement in CRF hypertriglyceridemia but failed to improve VLDL-R expression. Thus, the rise in plasma triglyceride and VLDL concentrations in CRF animals was associated with marked down-regulation of VLDL-R expression. Down-regulation of VLDL-R expression, shown here for the first time, reveals another facet of disturbed lipid metabolism in CRF.

Down-regulation of tissue lipoprotein lipase expression in experimental chronic renal failure

Chronic renal failure (CRF) is associated with hypertriglyceridemia, impaired clearance of very low density lipoproteins (VLDL) and chylomicrons and their remnants as well as triglyceride-enrichment of various lipoproteins. These abnormalities are indicative of depressed lipoprotein lipase (LPL)-mediated hydrolysis of triglycerides in VLD and chylomicrons. In fact, impaired post-heparin lipolytic activity and decreased adipose tissue LPL activity has been previously demonstrated in CRF. The reduction in LPL activity in CRF has been attributed to PTH-induced insulin resistance and the presence of excess lipase inhibitors in uremic plasma. However, the effect of CRF on gene expression of LPL has not been elucidated and was studied here. Heparin-releasable, detergent-extractable and total LPL activities, as well as LPL mRNA of the heart, soleus muscle and fat body were determined in male Sprague-Dawley rats at baseline and on weeks 1, 3 and 6 following 5/6 nephrectomy (CRF group) or sham operation (control group). The CRF group exhibited a marked and steady rise in plasma triglycerides along with a steady decline in LPL activities and mRNA levels of all tissues studied. In contrast, the study parameters remained virtually unchanged throughout the study period in the control group. A strong inverse correlation was found between plasma triglycerides and LPL activity in the study animals. LPL activity was directly related to LPL mRNA. We conclude that CRF results in marked down-regulation of LPL expression that can contribute to dyslipidemia and altered energy metabolism in uremia. The effect of depressed LPL expression is compounded by the previously demonstrated elevations in uremic plasma of Apo C-III and pre-beta-HDL, which are potent inhibitors of LPL.

Effect of serum subfractions from peritoneal dialysis patients on Hep-G2 cell apolipoprotein A-I and B metabolism

We previously showed that uremic serum subfractions isolated from hemodialysis (HD) patients inhibited the production of apolipoprotein (apo) A-I by human hepatoblastoma cells, Hep-G2. Because of the reported differences in atherogenic cardiovascular mortality between HD and peritoneal dialysis (PD) patients, we examined the effect of similar subfractions from PD patients on apo A-I and apo B synthesis. After obtaining informed consent, serum samples from five normal subjects and nine stable PD patients were applied to Sephadex G-25 columns to obtain the serum subfractions used in the various experiments. Sephadex G-25 chromatograms of PD sera showed a broad peak from fractions 30 through 60 (molecular wt 500 to 2000 Da). Control serum showed no peak in this region. PD serum subfractions decreased apo A-I synthesis, secretion, and apo A-I mRNA expression by Hep-G2 cells when compared to subfractions from control subjects. Cholesterol efflux studies showed that conditioned media obtained from Hep-G2 cells incubated with PD serum subfractions inhibited cholesterol efflux from fibroblasts, suggesting a biologically-significant decrease in apo A-I synthesis. PD serum subfractions increased protein synthesis and mRNA expressions of apo B by Hep-G2 cells. Therefore, serum subfractions obtained from PD patients decreased apo A-I and increased apo B synthesis, findings consistent with their serum lipoprotein profiles suggesting that a biologically-active component in these subfractions could contribute to the risk of atherogenic cardiovascular disease in PD.

Lipoprotein(a) in renal disease

Lipoprotein(a) [Lp(a)] is a genetically determined risk factor for atherosclerotic vascular disease. Several studies have described a correlation between high Lp(a) plasma levels and coronary heart disease, stroke, and peripheral atherosclerosis. In healthy individuals Lp(a) plasma concentrations are almost exclusively controlled by the apolipoprotein(a) [apo(a)] gene locus on chromosome 6q2.6-q2.7. More than 30 alleles at this highly polymorphic gene locus determine a size polymorphism of apo(a). There exists an inverse correlation between the size (molecular weight) of apo(a) isoforms and Lp(a) plasma concentrations. Average Lp(a) levels are high in individuals with low molecular weight isoforms and low in those with high molecular weight isoforms. Mean Lp(a) plasma levels are elevated over controls in patients with renal disease. Patients with nephrotic syndrome exhibit excessively high Lp(a) plasma concentrations, which can be reduced with antiproteinuric treatment. The mechanism underlying this elevation is unclear, but the general increase in protein synthesis caused by the liver due to high urinary protein loss is a likely explanation. Patients with end-stage renal disease (ESRD) also have elevated Lp(a) levels. These are even higher in patients treated by continuous ambulatory peritoneal dialysis than in those receiving hemodialysis. Lipoprotein(a) concentrations decrease to values observed in controls matched for apo(a) type following renal transplantation. This clearly demonstrates the nongenetic origin of Lp(a) elevation in ESRD. Both the increase in ESRD and the decrease following renal transplantation are apo(a) phenotype dependent. Only patients with high molecular weight phenotypes show the described changes in Lp(a) levels. In patients with low molecular weight types the Lp(a) concentrations remain unchanged during both phases of renal disease. As in the general population, Lp(a) is a risk factor for cardiovascular events in ESRD patients. In this patient group the apo(a) phenotype seems to be equally or better predictive of the degree of atherosclerosis than is Lp(a) concentration. Further prospective studies will be necessary to confirm these observations. Whether Lp(a) also plays a key role in the pathogenesis and progression of renal diseases needs further study. Controversial data on the role of the kidney in Lp(a) metabolism result from insufficient sample sizes of several studies. Due to the broad range and skewed distribution of Lp(a) plasma concentrations, large study groups must be investigated to obtain reliable results.

Lipid-lowering therapy in patients with renal disease

A growing number of clinical trials have examined the effects of different lipid lowering strategies in patients with renal disease. We carried out a meta-analysis to compare and contrast the relative efficacy of various antilipemic therapies in different renal disease settings. Studies that investigated one or more therapies designed to lower serum lipids were combined using weighted multiple linear regression. The analysis adjusted treatment effects for differences in baseline lipid levels and possible placebo effects. The results showed that antilipemic therapies generally had similar effects on lipids in different renal disease settings. In nephrotic syndrome the greatest and most consistent reductions in low density lipoprotein cholesterol (LDL) were seen with 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase inhibitors (regression coefficient with 95% confidence interval in mg/dl = -63, -79 to -46). Similar results were seen for LDL in renal transplant (-51, -57 to -45), renal insufficiency (-62, -82 to -42), hemodialysis (-65, -80 to -50) and continuous ambulatory peritoneal dialysis (CAPD) patients (-84, -104 to -64). Fibric acid analogues had less effect on LDL, but caused greater reductions in triglycerides: -132, -178 to -87, in nephrotic syndrome; -69, -93 to -45 in transplant: -107, -169 to -45 in renal insufficiency; -72, -120 to -24 in hemodialysis; and -96, -162 to -30 in CAPD. In general, the effects of diet and other therapies were less consistent. Despite possible limitations of this meta-analysis, the results provide a useful framework for choosing antilipemic therapy, and point to areas for future long-term studies examining the safety and efficacy of lipid lowering strategies in patients with renal disease.