HUMAN ATHEROSCLEROTIC PLAQUE CONTAINS BOTH OXIDIZED LIPIDS AND RELATIVELY LARGE AMOUNTS OF ALPHA-TOCOPHEROL AND ASCORBATE

We assessed the antioxidant status and contents of unoxidized and oxid ized lipids in freshly obtained, homogenized samples of both normal hu man iliac arteries and carotid and femoral atherosclerotic plaque. Opt imal sample preparation involved homogenization of human atherosclerot ic plaque for 5 minutes, which resulted in recovery of most of the uno xidized and oxidized lipids without substantial destruction of endogen ous Vitamins C and E and 87% and 43% recoveries of added standards of alpha-tocotrienol and isoascorbate, respectively. The total protein, l ipid, and antioxidant levels obtained from human plaque varied among d onors, although the reproducibility of replicates from a single sample was within 3%, except for ubiquinone-10 and ascorbate, which varied b y 20% acid 25%, respectively. Plaque samples contained significantly m ore ascorbate and urate than control arteries, with no discernible dif ference in the vitamin C redox status between plaque and control mater ials. The concentrations of alpha-locopherol and ubiquinone-10 were co mparable in plaque samples and control arteries. However, approximatel y 9 mol percent of plaque alpha-tocopherol was present as alpha-tocoph erylquinone, whereas this oxidation product of vitamin E was not detec table in control arteries. Coenzyme Q(10) in plaque and control arteri es was only detected in the oxidized form ubiquinone 10, although coen zyme Q(10) oxidation may have occurred during processing. The most abu ndant of all studied lipids in plaque samples was free cholesterol, fo llowed by cholesteryl oleate and cholesteryl linoleate (Ch18:2). Appro ximately 30% of plaque Ch18:2 was oxidized, with 17%, 12%, and 1% pres ent as fatty acyl hydroxides, ketones, and hydroperoxides, respectivel y. In comparison, 7-ketocholesterol was detected at an approximate to 75-fold lower concentration. Normal arteries contained similar levels of protein as atherosclerotic arteries, much less free cholesterol, an d no detectable amounts of unoxidized or oxidized cholesteryl esters. Together, these results demonstrate the coexistence in human plaque of large amounts of oxidized cholesteryl esters with significant concent rations of ascorbate and Vitamin E in their reduced, antioxidant-activ e form. We conclude that compared with healthy human arteries, advance d atherosclerotic plaques are not deficient in the antioxidant vitamin s C and E, despite the occurrence of massive lipid oxidation.