LIPID PEROXIDATION

Figure
Lipid peroxidation - chain reaction
Unsaturated fatty acids with isolated double bonds are converted into lipid hydroperoxides with conjugated double bonds.
One degradation product of lipid peroxidation is MDA (malondialdehyde). MDA is one of the TBARS - Thiobarbituric acid reactive substances. MDA is very reactive and is potentially mutagenic, as it can attack DNA. MDA and other TBARS are used as markers of oxidative stress.

Defence:
Endogenous antioxidants protect the unsaturated fatty acids against oxidation by scavenging lipid peroxy radicals and thereby prevent the chain reaction.

Cholesterol oxidation
LDL particles contain vitamin E, see chapter II.

In vitro study showing cholesterol oxidation:

Role of vitamin E in preventing the oxidation of low-density lipoprotein
(Esterbauer et al, American Journal of Clinical Nutrition, 1990)

Blood samples were collected from healthy human donors.

The graph shows the endogenous antioxidants in LDL, together with the increase of lipid peroxides (blue curve) measured by absorption of UV light at 232 nm.
(Conjugated double bonds have an absorption maximum at 234 nm.)
The lag phase (the phase where there is no or little oxidation of LDL) ends at ~ 50 minutes.

What conclusions can be drawn from this graph?

-See QUIZ at the end of the e-lecture.