Intact human ceruloplasmin oxidatively modifies low density lipoprotein

Area of Science:

• Biochemistry
• Cardiovascular Research
• Oxidative Stress

Background:

• Ceruloplasmin (Cp) is a major copper-binding protein in plasma, often classified as an acute-phase protein.
• Its physiological role remains uncertain, with a commonly attributed antioxidant function, particularly in suppressing lipid oxidation.
• Recent focus on low-density lipoprotein (LDL) oxidation necessitates re-evaluation of Cp's function in this process.

Purpose of the Study:

• To investigate the effect of purified, undegraded human ceruloplasmin on copper ion-mediated oxidation of LDL.
• To compare the oxidative or antioxidative properties of intact versus degraded ceruloplasmin.
• To elucidate the role of copper within ceruloplasmin in its interaction with LDL.

Main Methods:

• Purification of human ceruloplasmin and preparation of degraded forms.
• Assessment of LDL oxidation using thiobarbituric acid-reacting substances (TBARS), electrophoretic mobility, conjugated dienes, and total lipid peroxides.
• Copper removal and restoration experiments using Chelex-100 and ultrafiltration.

Main Results:

• Intact ceruloplasmin significantly enhanced copper-mediated LDL oxidation (>25-fold increase in TBARS).
• Degraded ceruloplasmin and commercial preparations exhibited only mild inhibition of LDL oxidation, comparable to albumin.
• Copper is essential for ceruloplasmin's oxidant activity; its removal abolished this effect, while repletion restored it.

Conclusions:

• Ceruloplasmin's effect on LDL oxidation is dependent on its structural integrity and bound copper content.
• Intact ceruloplasmin acts as a potent oxidant of LDL, challenging its established antioxidant role.
• These findings suggest a potential pro-oxidant role for ceruloplasmin in vivo, contributing to LDL oxidation in blood and arterial walls.