Food Lipids: Chemistry, Nutrition, and Biotechnology

[53–55]. However, other studies did not demonstrate an effect of dietary fish oil
relative to oils rich in lineolic acid on in vitro LDL oxidation [56,57]. Currently,
there is no explanation for these contradictory results.
c. Antioxidants. Fat-soluble antioxidants, especially �-tocopherol (vitamin E),
are a main protecting factor against in vitro LDL oxidation. Supplementation of
vitamin E increases the tocopherol content of LDL, resulting in a higher oxidation
resistance of LDL, as evidenced from an increased lag time [58]. Other antioxidants,
such as carotenoids, ascorbic acid, and ubiquinol-10, also have an important impact
on the oxidative resistance of LDL.
Ascorbic acid, a hydrophilic antioxidant, and ubiquinol-10, a lipophilic antioxidant,
are capable of regenerating tocopherols, and addition of these antioxidants
to the test tube results in a longer lag time [59–61].
Oils rich in polyunsaturated fatty acids by nature contain relatively high concentrations
of antioxidants. An exception are fish oils, which have relatively low
levels of fat-soluble antioxidants, but their potentially harmful effects on LDL oxidation
can be counteracted by addition of vitamin E to these oils.
B. Conclusion
Several studies now strongly suggest that oxidation of LDL in vivo takes place,
which results in even more harmful LDL particles. Therefore, LDL oxidation may
play an important role in the formation of atherosclerotic lesions.
Replacing saturated fatty acids in the diet with linoleic acid reduces plasma
LDL cholesterol concentrations. However, this dietary intervention will also increase
the proportion of linoleic acid in the LDL particle thereby its in vitro oxidizability.
As monosaturated fatty acids are less readily oxidized and have comparable beneficial
effects on the plasma lipoprotein profile, oleic acid might be preferred over
linoleic acid. Increased in vitro oxidizability of the LDL particle might also be observed
when n-3 polyunsaturated fatty acids from fish oils are added to the diet,
which can be overcome by simultaneously increasing the intake of vitamin E. Although
these studies clearly demonstrate that diet affects in vitro LDL oxidizability,
the importance of these findings for the in vivo situation are less evident.
VIII. HEMOSTASIS
Hemostasis, derived from the Greek words for blood and standing, is a complex,
delicately balanced system of interactions to keep the blood circulating as a fluid
through the blood vessels. In case of imbalance, such as when a vessel is damaged,
the blood stands, starts to clot, and a stable thrombus forms. This, of course, is
necessary to stop a wound from bleeding. However, if a stable thrombus is formed
in a small coronary artery, the artery becomes occluded, blood and oxygen supply
are hampered, and a heart attack results.
The hemostatic system involves interacting processes for the formation of a
stable thrombus—platelet aggregation and blood clotting—but also a mechanism to
dissolve the thrombus, i.e., fibrinolysis (Fig. 12). In vivo these processes are associated
and the interplay defines the prethrombotic state of the blood.
Hemostatic factors are difficult to measure. Due to the venipuncture and subsequent
blood sampling and plasma preparation, platelets might become activated,
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.