Lipoprotein(a) levels in relation to albumin concentration in childhood nephrotic syndrome

Abstract

Background. Lipoprotein(a) [Lp(a)] is a lipoprotein consisting of a low- density lipoprotein (LDL) particle linked to a polymorphic glycoprotein, apoprotein(a) [apo(a)]. Prior studies have reported high Lp(a) levels in the nephrotic syndrome, but it is still controversial whether this is due to the degree of hypoalbuminemia or proteinuria. Methods. To investigate a model of nephrotic syndrome in the absence of renal failure, we studied a group of 84 children in different clinical stages of the disease for a period of five years. We evaluated the direct relationships between lipoproteins, including Lp(a), and/or plasma albumin and proteinuria. Results. Lp(a) levels were significantly higher in the subjects with the active disease compared with patients in remission, and were also significantly different when subjects were ranked by albumin quartiles. Multiple regression analysis revealed that Lp(a) levels were inversely correlated with apo(a) isoform size and plasma albumin levels but not with the proteinuria/creatinine clearance ratio. Among subjects in complete remission, Lp(a) levels were different in patients with albumin levels below or above the fifth percentile. After the improvement of the clinical stage of the disease, the Δ% variation of albumin levels was related to the Δ% of apoB and LDL cholesterol (LDL-C), but not with the Δ% variation of Lp(a), whereas the Δ% variation of LDL-C was, in turn, related to the Δ% of Lp(a) levels. Conclusions. These results suggest that in the childhood nephrotic syndrome, the increased Lp(a) levels are mainly related to hypoalbuminemia, probably through a mechanism involving apoB overproduction, which leads to an increased number of LDL particles to be converted into Lp(a).