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      An Increased Serum Level of Free Apo(a) in Renal Patients Is More Striking than that of Lp(a) and Is Influenced by Homocysteine

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          Lipoprotein(a) [Lp(a)] excess combined with hyperhomocysteinaemia and hyperfibrinogenaemia may contribute to the high incidence of vascular diseases in dialysis patients. This study is aimed at investigating the role of free apolipoprotein(a) [fapo(a)] in renal patients. We have been able to show that, as compared with controls (0.53 mg/l), the median serum concentrations of fapo(a) in patients with nephrotic syndrome (2.58 mg/l) and with peritoneal dialysis (3.40 mg/l) were strongly elevated (5- to 7-fold), while the fapo(a) levels in patients undergoing haemodialyis (1.02 mg/l) and after renal transplantation (0.90 mg/l) were about doubled. The observed differences in fapo(a) levels indicate that several mechanisms may increase the level of fapo(a), i.e., reduced renal clearance, enhanced hepatic synthesis, or homocysteine releasing apolipoprotein(a) from Lp(a). In the study collective, the median total homocysteine levels were significantly elevated in all patient groups, stronger in patients on haemodialysis (31.4 µmol/l) and peritoneal dialysis (31.2 µmol/l) than in patients with nephrotic syndrome (19.7 µmol/l) and after renal transplantation (19.5 µmol/l). In transplant patients with adequate renal function and without other apolipoprotein(a)-increasing factors, fapo(a) was significantly increased when total homocysteine exceeded 22 µmol/l. In conclusion, our findings let us presume that an increased fapo(a) level in renal patients possibly could be one of the reasons contributing to the high incidence of vascular diseases in these patients, because fapo(a) not covalently linked with Lp(a) is even more easily able to inhibit the fibrinolytic system than the complete Lp(a). These preliminary results have to be confirmed by further investigations.

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          Most cited references 5

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          cDNA sequence of human apolipoprotein(a) is homologous to plasminogen.

          Lipoprotein(a) is an LDL-like lipoprotein whose concentration in plasma is correlated with atherosclerosis. The characteristic protein component of lipoprotein(a) is apolipoprotein(a) which is disulphide-linked to apolipoprotein B-100. Sequencing of cloned human apolipoprotein(a) complementary DNA shows that it is very similar to human plasminogen. It contains a serine protease domain and two types of plasminogen-like kringle domains, one of which is present in 37 copies.
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            Protein composition of Lp(a) lipoprotein from human plasma.

            The apolipoprotein composition of purified human Lp(a) lipoprotein was investigated by SDS--polyacrylamide gel electrophoresis and immunochemically. The lipoprotein contains two different polypeptides. One is identical by its app. Mr of approximately 250 000 and immunologically with apolipoprotein B of LDL (B-100). The other polypeptide has a higher app. Mr (approximately 350 000) and stains strongly with the periodate-Schiff's reagent. This high-Mr glycoprotein contains the specific Lp(a) immunoreactivity but does not react with antibodies against apo B. Apo B and Lp(a)-protein seem to be linked by disulfide bonds in the native lipoprotein. The unreduced detergent delipidized protein moiety from Lp(a) lipoprotein shows a single band of Mr approximately 700 000 in SDS--polyacrylamide gel electrophoresis and the immunoprecipitates formed against anti-Lp(a) and anti-apo B by the unreduced protein show a reaction of immunological identity.
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              A two-step model for lipoprotein(a) formation


                Author and article information

                S. Karger AG
                May 2000
                21 April 2000
                : 85
                : 1
                : 41-49
                aZentrallabor der Universitätskliniken des Saarlandes, Homburg, bBaxter Deutschland, Heidelberg, Deutschland; cImmuno AG, Wien, Österreich; dKlinik für Innere Medizin IV, Universitätskliniken des Saarlandes, Homburg, Deutschland
                45628 Nephron 2000;85:41–49
                © 2000 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 3, References: 42, Pages: 9
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/45628
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