Apolipoprotein(a) isoform-specific changes of lipoprotein(a) after kidney transplantation

The atherogenic lipoprotein(a) (Lp(a)) is significantly increased in patients with kidney disease. Some studies in hemodialysis patients described this increase to be dependent on the genetic apolipoprotein(a) (apo(a)) isoforms. Only patients who express high molecular weight (HMW) apo(a) isoforms but not those with low molecular weight (LMW) isoforms show a relative increase of Lp(a) when compared to healthy controls matched for apo(a) isoforms. However, this was not confirmed by all studies. We therefore prospectively investigated the changes of Lp(a) deriving from each apo(a) isoform in heterozygotes following kidney transplantation. Lp(a) concentrations were measured by ELISA. To calculate the isoform-specific concentrations and the changes of Lp(a) deriving from each isoform, we densitometrically scanned the apo(a) bands from immunoblots before and after transplantation in 20 patients expressing two apo(a) isoforms. Of these, 10 patients expressed both an LMW and an HMW apo(a) isoform. The other 10 patients expressed only HMW isoforms. Densitometric scanning of apo(a) bands and calculation of isoform-derived Lp(a) concentrations clearly demonstrated that the decrease of Lp(a) following kidney transplantation is caused by changes in the expression of HMW apo(a) isoforms. In some patients, we observed an almost complete disappearance of the HMW apo(a) isoform after transplantation. This study clearly demonstrates that the changes of Lp(a) plasma concentrations in kidney disease depend on the genetically determined size of apo(a). This provides evidence for an interaction of apo(a) genetic variability and kidney function on Lp(a) concentrations.