Relationship of non-LDL-bound apo(a), urinary apo(a) fragments and plasma Lp(a) in patients with impaired renal function.

BACKGROUND: Plasma lipoprotein (a) [Lp(a)] has been shown to be a risk factor for atherosclerosis in numerous studies. However, the catabolism of this lipoprotein is not very clear. We and others have shown that Lp(a) is excreted into urine in the form of fragments. Lp(a) has also been shown to exist in a low-density non-lipoprotein (LDL)-bound form. Since Lp(a) is increased in all forms of kidney disease with reduced excretory kidney function and decreased excretion of apo(a) fragments could be partially responsible for this increase, we investigated the relationship of non-LDL-bound apo(a), urinary apo(a) fragments and plasma Lp(a) in patients with impaired renal function. METHODS: Plasma Lp(a), non-LDL-bound apo(a) and urinary apo(a) fragments were measured in 55 kidney disease patients (28 males and 27 females) and matched controls. RESULTS: Plasma Lp(a) and non-LDL-bound apo(a) were increased in patients, whereas urinary apo(a) was decreased, especially in patients with a creatinine clearance < 70 ml/min. There was a significant correlation between plasma Lp(a) and non-LDL-bound apo(a) in patients and controls. CONCLUSION: We conclude that decreased urinary apo(a) excretion could be one possible mechanism of increased plasma Lp(a) and non-LDL-bound apo(a) in patients with decreased kidney function.