MEASUREMENT OF OXIDATION IN PLASMA LP(A) IN CAPD PATIENTS USING A NOVEL ELISA

Background. LGE(2) is produced by the cyclooxygenase- or free radical- mediated modification of arachidonate and is formed during the oxidati on of low density lipoprotein (LDL) with subsequent adduction to lysin e residues in apo B. We have developed a sensitive enzyme-linked sandw ich immunosorbent assay (ELISA) for detection and measurement of LGE(2 )-protein adducts as an estimate of oxidation of plasma LDL and Lp(a). Methods. The assay employs rabbit polyclonal antibodies directed agai nst LGE(2)-protein adducts that form pyrroles, and alkaline phosphatas e-conjugated polyclonal antibodies specific for apo B or apo (a). It d emonstrates a high degree of specificity, sensitivity and validity. Re sults. Epitopes characteristic for LGE(2)-pyrroles were quantified in patients with end-stage renal disease (ESRD) that had undergone contin uous ambulatory peritoneal dialysis (CAPD) and in a gender- and age-ma tched control population. In addition to finding that both LDL and Lp( a) levels were elevated in CAPD patients, we also found that plasma Lp (a) but not LDL was more oxidized in CAPD patients when compared to co rresponding lipoproteins from healthy subjects. Using density gradient ultracentrifugation of plasma samples, we found that modified Lp(a) f loats at the same density as total Lp(a). Conclusions. The results of tis study demonstrate that oxidation of plasma Lp(a) is a characterist ic of ESRD patients undergoing CAPD. This ELISA may be useful for furt her investigations on oxidation of lipoproteins in the circulation of specific patient populations.