LIPOPROTEIN ( a ) AS AN ACUTE PHASE REACTANT IN PATIENTS ON CHRONIC HEMODIALYSIS

Lipoprotein (a) [Lp(a)], is an independent risk factor for atherosclerotic cardiovascular disease in patients on chronic hemodialysis. A low concentration of high density lipoprotein cholesterol (HDL-C) and serum albumin are another potential risk factors. U e purpose of this study was to explore in patients on chronic hemodialysis, whether Lp(a) elevated levels are infl uenced by activated acute phase response (APR) and the correlation of Lp(a) with HDL-C and serum albumin. In  hemodialysis patients with C-reactive protein (CRP) levels over than  mg/L and  hemodialysis patients with CRP levels in the normal range, Lp(a), HDL-C and serum albumin were determined in relation to CRP, as a sensitive marker of an APR. Results showed that serum concentration of CRP in  hemodialysis patients was signifi cantly higher than in controls (, mg/L versus , mg/L, p<,).Patients with elevated CRP had signifi cantly higher serum levels of Lp(a) and lower serum levels of HDL-C and albumin, than patients with CRP in the normal range ( , mg/dl versus , mg/dl, p<,, , mmol/L versus , mmol/L, p<, and , g/L versus , g/L, p<,). Lp(a) levels correlated positively with CRP and negatively with HDL-C and serum albumin, in patients with elevated CRP, but not in healthy controls. According to the results Lp(a) reacts as an acute phase protein, in patients with APR.


Introduction
e morbidity and mortality of cardiovascular disease are substantially higher among hemodialysis patients, than in the general population ().Atherosclerotic cardiovascular disease accounts for approximately half of deaths in end-stage renal disease and contributes to the extraordinarily high total annual mortality of  observed in such patients ().Lipoprotein(a)[Lp(a)], is an independent risk factor for clinical events attributed to atherosclerotic cardiovascular disease in patients receiving chronic hemodialysis treatment of end-stage renal disease.Lp(a) is a low density lipoprotein (LDL)like lipoprotein containing a unique apolipoprotein called apo(a).Serum levels of Lp(a) are determined largely by genetic variation in the gene encoding for apo(a).Apo(a) is very homologous to plasminogen () and exhibits an extreme size polymorphism with the apo(a) isoproteins, ranging in size from  to  kDa.Inherited in an autosomal co dominant fashion, the apo(a) isoprotein is closely correlated with serum Lp(a) concentrations, with an inverse correlation between the size of the apo(a) isoprotein and the serum Lp(a) concentrations.Lp(a) has been implicated in the regulation of plasminogen activator inhibitor- expression in endothelial cells and shown to inhibit endothelial cell surface fi brinolysis to attenuate plasminogen binding to platelets and to bind to plaque matrix components (,).Autopsy studies in humans have documented the presence of Lp(a) in aortic and coronary atherosclerotic plaques and an apparent co localization with fi brin(ogen).High plasma concentrations of Lp(a) are considered a major risk factor for atherosclerosis and cardiovascular disease (,).Lp(a) levels are frequently elevated in patients receiving chronic hemodialysis treatment of end-stage renal disease (,).Elevated plasma Lp(a) levels in chronic renal failure patients, have been associated with a frequency distribution of apolipoprotein (a) -Lp(a) isoforms, similar to those found in general population. is indicates that elevated Lp(a) levels in these patients are not due to the genetic origin ().It has been suggested that kidneys have an important role in Lp(a) metabolism.ere is decrease in Lp(a) catabolism or increase in Lp(a) production by liver ().Although it has not been fully explained, high Lp(a) levels in hemodialysis patients may also be due to activated acute phase reactants ().Approximately  of patients on hemodialysis, have evidence of chronic infl ammation due to uremia and dialysis.e uremic state is associated with an altered immune response (,,) and intermittent stimulation by endotoxins originating from the dialysis water supply and artifi cial vein grafts or bioincompatibility caused the increased circulating infl ammatory proteins, such as plasma CRP (,,), a sensitive marker of an APR.CRP is the prototypical acute phase response protein, produced by the liver under the control of various proinfl ammatory cytokines, namely interleukin- (IL-), interleukin- (IL-) and TNF-.Its uniqueness is due to rapid (within  hours) and dramatic increases (up to -fold) in circulating concentrations after a cytokine-mediated response to infl ammation.Chronic renal failure results in profound lipid disorders.Decreased HDL-C is one of the main metabolic abnormalities of the lipoprotein profile in chronically uremic patients.Several mechanisms, working in concert, may underlie the reduction in HDL (high density lipoproteins) levels, which is usually indicative of impaired reverse cholesterol transport.Specifi cally, maturation of HDL is impaired and its composition is altered.us, uremic patients usually exhibit decreased levels of apolipoproteins AI and AII (the main protein constituents of HDL), diminished activity of lecithincholesterol acyl-transferase, the enzyme responsible for the esterifi cation of free cholesterol in HDL particles, as well as increased activity of cholesteryl ester transfer protein that facilitates the transfer of cholesterol esters from HDL to triglyceride-rich lipoproteins, thus reducing the serum concentration of high density lipoprotein cholesterol ().Today the interest on infl ammatory biomarkers predicting the risk of clinical event increases ().Main function of acute phase proteins is expressed by remodeling of HDL creating dysfunction and reduced serum concentration of HDL-C as a result (,).Previous longitudinal studies showed that hypoalbuminemia was associated with cardiovascular disease.Richard and colleagues () fi rst reported this association in the general population.ey did serum electrophoresis in  middle-aged men free of an atherosclerotic disease at entry, and they monitored the development of cardiovascular disease, during , years on average.Albumin level was signifi cantly lower among myocardial infarction or sudden death.In hemodialysis patients, hypoalbuminemia is also known to be associated with cardiovascular disease (,) and is a powerful risk factor for cardiovascular mortality.Since albumin is a negative acute-phase reactant, non-nutritional factors like infl ammation depress albumin synthesis in hemodialysis patients.Infl ammation causes a decrease in albumin synthesis and an increase in albumin fractional rate, providing two mechanisms for hypoalbuminemia ().Some studies have demonstrated a signifi cant inverse relationship between serum Lp(a) and albumin concentration in hemodialysis patients (,).We therefore hypothesize that an activated acute phase response is responsible for the atherogenic condition in hemodialysis patients and besides Lp(a) we decided to determines serum HDL and albumin, starting from their antiaterogenic eff ects.e aim of this study was to explore, in patients on chronic hemodialysis treatment, whether the changes in Lp (a) is infl uenced by activated acute phase reaction and to study the relationship of Lp(a) with CRP, HDL-C and serum albumin.

Materials and Methods
In this study were examined  blood samples of patients with chronic renal failure ( age range from  to  years ) who were treated by hemodialysis in the Clinic of Internal Diseases in Clinical Centre in Prishtina, more than  months, which is considered as chronic hemodialysis.In the samples initially were determined CRP and sedimentation rate by two measurements, in a period of - month, to be sure that CRP levels were not occasionally elevated, but remain elevated over time, as a chronic infl ammation.an the patients were divided in two groups: group of  patients with elevated CRP levels over than  mg/L and sedimentation rate of over mm/h, in both blood samples and group of  patients with CRP levels in the normal range.For the fi rst group, based in patients history, angina, possible myocardial infraction, cerebrovascular events were excluded and the concentrations of the second measurement of CRP, were taken in consider.A part of CRP, among all the patients, serum levels of Lp (a), HDL-C and albumin were determined. healthy people, were included as a control group.Measurements of serum CRP, Lp(a) and albumin were performed on fresh samples.The serum concentration of CRP was measured by the turbidimetric method based in combines of CRP with specific antibody to form insoluble antigen antibody complexes.Diazyme's Lipoprotein (a) assay is based on a latex enhanced immunoturbidimetric method.e normal range for CRP is less than  mg/L, and the range for Lp(a) is less than mg/dl.HDL-C was measured directly with detergent which solubilizes the HDL lipoprotein particles, releasing HDLcholesterol.Measurement of serum albumin was carried out on serum using the bromocresol green method.

Statistical analysis
The data were analysed using the descriptive statistics for each biochemical parameter that was followed.Statistically significant differences were ana-lysed using the student's t-test, with the acceptance of statistical signifi cance at the level p<,.Relationships and correlations between biochemical parameters were analysed using Pearson Chi-square(χ) test.

Results
Mean serum CRP concentration in  hemodialysis patients was signifi cantly higher than in controls (, ±, mg/L versus , ± ,, respectively p<,; Table .).Mean value of Lp(a) was signifi cantly higher in hemodialysis patients than in healthy controls (, ¶mg/ dl versus , mg/dl, respectively p<,; Table .).Result showed that mean value of Lp(a) was significantly higher in patients exhibiting elevated CRP than to those patients with CRP levels in the normal range (, mg/L versus , mg/L ; p<,; Table 

Discussion
During recent years, substantial evidence has accumulated suggesting that Lp(a) is another important risk factor for cardiovascular disease in the general population, as well as in dialysis patients.e mechanism of Lp (a) atherogenicity has not been elucidated, but likely involves both its ability to infl uence plasminogen activation as well as its atherogenic potential as a lipoprotein particle after receptor mediated uptake.Though the concentration of serum Lp(a) is mostly determined by genetic factors, secondary factors such as APR and end stage renal disease also contributes to its increase.Lp (a) levels are frequently elevated in patients receiv-ing chronic hemodialysis treatment (,).In this study mean serum Lp (a) value in hemodialysis patients was signifi cantly higher, in compare with a control group (Table .), which confi rm that kidney have an important role in Lp(a) metabolism ().In addition, patients with end-stage renal disease, including dialysis patients, often have infl ammation and it has been suggested that impaired renal function may influence the inflammatory response.According to the results considerable number of patients exhibited an activated acute phase response, characterized by an increase of CRP concentration (,,).Mean serum CRP value, in  patients was signifi cantly higher than in controls (Table .) respectively this group of patients, have evidence of chronic infl ammation due to uremia and dialysis.Some studies have demonstrated a close relationship between high Lp(a) levels and the APR, as shown by correlations with CRP and IL- (,)..Because seven IL--responsive element sequence motifs can be identifi ed in the ' fl anking regulatory region of the apo(a) gene on chromosome , it is likely that apo(a) responds as an acute phase reactant ().Uremia can be considered to be a state of activated acute phase response and in the microinfl ammatory milieu, a number of atherogenic proteins like Lp(a) are elevated and a number of anti-atherogenic factors like HDL-C and serum albumin are diminished.
In this study Lp(a) mean value was signifi cantly higher in patients with elevated CRP than to those patients with CRP levels in the normal range (Table .).Based on results, APR exhibited higher serum levels of Lp(a), respectively Lp(a) reacts as an acute phase protein in patients with high CRP levels ().For this reason Lp(a) levels correlated in the positive way with CRP (Figure .).It is well known that many hemodialysis patients have low levels of HDL, which is a crucial risk factor for atherosclerosis.Recently, Barter et al. () have demonstrated that the serum HDL level is a signifi cant inverse predictor of subsequent major cardiovascular events.In end stage renal disease HDL-C is now emerging as a key entity in both determining risk and providing protection, although none as yet specifi es HDL as a target for treatment ().Infl ammation is one of the powerful factors also contribute to its decreased levels (,).Study results showed signifi cantly lower levels of HDL-C in the group of patients with elevated CRP, in compare with the patients with CRP in the normal range (Table .), and negative correlation of HDL and CRP (  serum albumin characteristics of an acute phase reactant, it is meaningful that Lp(a) levels correlated negatively with HDL-C.This correlation is also presented in the published results ().Hypoalbuminemia is known to be strongly associated with ischemic heart disease in dialysis patients and it is thought to be one of the cardiovascular risk factors (,).Infl ammation is an important factor which has an infl uence on albumin levels ().Albumin concentration in hemodialysis patients changes with infl ammation through its eff ects on albumin catabolism and synthesis, respectively.According to the results there was the signifi cant diff erence in albumin levels between a group of the patients with elevated CRP and those patients with CRP values in the normal range.(Table .) Albumin levels correlated in the negative way with CRP (Figure .), which proved that hypoalbuminemia in hemodialysis patients is partially a consequence of infl ammation.Diff erent studies have reported, that by increasing serum albumin levels, in renal failure, serum Lp(a) levels were decreased ().Based on our results a signifi cant inverse relationship existed between serum albumin and Lp(a) in hemodialysis patients, respectively serum albumin levels correlated in the negative way with Lp(a) in patients with elevated CRP (Figure .).According to the literature it is a signifi cant indicator for cardiovascular death of hemodialysis patients ().
Figure .).ese results indicate that the infl ammatory condition may be responsible for low HDL-C.While serum Lp(a) levels showed a positive correlation with CRP, with HDL-C correlated negatively (Figure .).Because of the

TABLE 6
.).HDL-C levels were signifi cantly lower in hemodialysis patients than in healthy controls, as well as serum albumin (, mmol/L versus , mmol/L; p< , and ,g/L versus , g/L; p< ,; Table.)Patients with elevated CRP had significantly lower serum levels of HDL-C and albumin, in compare with patients with CRP in the normal range (, mmol/L versus , mmol/L ; p<, and , g/L versus , g/L ; p<,; Table.).
. Correlation of Lp(a) and HDL-C in hemodialysis patients with elevated CRP levels and in healthy controls TABLE 7. Correlation of CRP and serum albumin in hemodialysis patients with elevated CRP levels and in healthy controls

TABLE 4
. Correlation of CRP and Lp(a) in hemodialysis patients with elevated CRP levels and in healthy controls TABLE 5. Correlation of CRP and HDL-C in hemodialysis patients with elevated CRP levels and in healthy controls

TABLE 8 .
Correlation of Lp(a)and serum albumin in hemodialysis patients with elevated CRP levels and in healthy controlsConclusionAccording to the study results, end stage renal disease contributes to Lp (a) increases.Changes of the atherogenic risk profi le, in hemodialysis patients, namely elevated Lp (a), as well as decreased HDL-C and serum albumin, are partially the consequence of an activated APR. e results further show that Lp (a) reacts as an acute phase reactant in hemodialysis patients with high CRP levels.For this reason Lp (a) correlated positively with CRP and negatively with HDL-C and serum albumin.It is suggested that these correlations might show high cardiovascular risk.