Cellular oxidative modification of low density lipoprotein does not require lipoxygenases

Area of Science:

• Biochemistry
• Cardiovascular Research
• Cell Biology

Background:

• Oxidative modification of low-density lipoprotein (LDL) is implicated in atherosclerosis development.
• Previous studies suggested lipoxygenases are necessary for cellular LDL modification.

Purpose of the Study:

• To re-evaluate the role of lipoxygenase enzymes in the oxidative modification of LDL by cultured cells.
• To determine if 5-lipoxygenase or 15-lipoxygenase activity is required for LDL modification.

Main Methods:

• Utilized specific 5-lipoxygenase inhibitors and general lipoxygenase inhibitors (reductive inactivation).
• Tested the effects of 5,8,11,14-eicosatetraynoic acid on 15-lipoxygenase activity and LDL modification in macrophages.
• Compared LDL modification efficiency between macrophages and endothelial cells (RECB4 line).

Main Results:

• 5-lipoxygenase inhibitors did not prevent LDL modification.
• General antioxidants (reductive inactivation inhibitors) blocked both cellular and copper-ion-mediated LDL modification.
• 5,8,11,14-eicosatetraynoic acid inhibited 15-lipoxygenase at concentrations much lower than those affecting LDL modification and showed cytotoxicity.
• Macrophages and endothelial cells modified LDL similarly, despite differing 15-lipoxygenase activity.

Conclusions:

• Neither 5-lipoxygenase nor 15-lipoxygenase is required for the oxidative modification of LDL by cultured cells.
• The mechanism of LDL modification by cells may not involve lipoxygenase activity.
• General antioxidant effects, rather than specific lipoxygenase inhibition, explained previous findings.