Renal Lipoprotein (a) Metabolism

Abstract

The kidney plays a central role in lipoprotein(a) catabolism, acting as a “cemetery for lipoprotein(a)” through uptake, fragmentation, and excretion. Direct human evidence comes from Kronenberg et al., who found significant arteriovenous differences in lipoprotein(a) levels between the aorta and renal vein, demonstrating active renal uptake. Clinical evidence from renal replacement therapy further supports this role: lipoprotein(a) levels decrease rapidly after kidney transplantation but remain unchanged with hemodialysis, indicating that functioning renal tissue, not filtration, drives lipoprotein(a) metabolism. Animal studies by Reblin et al. provided mechanistic insights, showing rapid clearance of injected human lipoprotein(a) in rats, with apolipoprotein(a) localized in proximal tubular cells and fragments detected in urine. This supports the idea that the kidney fragments lipoprotein(a) before excretion. Kostner & Kostner proposed a model where circulating lipoprotein(a) undergoes proteolytic cleavage in the kidney, producing apolipoprotein(a) fragments that may themselves be biologically active and contribute to lipoprotein(a)’s atherogenicity. Clinical observations confirm that chronic kidney disease alters lipoprotein(a) metabolism. Patients with proteinuria or amyloidosis show elevated lipoprotein(a), often correlating with urinary albumin excretion, highlighting the kidney’s regulatory role. The mechanism of elevation varies by disease: in proteinuria and peritoneal dialysis, hepatic synthesis is upregulated, while in hemodialysis, impaired catabolism predominates. These abnormalities likely amplify the already high cardiovascular risk in chronic kidney disease, particularly in individuals with genetically determined small apolipoprotein(a) isoforms. Despite advances, the precise site and mechanisms of lipoprotein(a) clearance remain unclear. However, the consensus is that reduced clearance, not increased production, drives lipoprotein(a) accumulation in kidney disease. Understanding renal processing of lipoprotein(a) may provide therapeutic opportunities, with future strategies aiming to inhibit lipoprotein(a) assembly or enhance apolipoprotein(a) fragmentation to mitigate cardiovascular risk.