Using an original automated analyzer of double bonds we determined the rate constants for oxidation of saturated and unsaturated mono- and dienoic fatty acids (in vivo substrates for beta-oxidation in the mitochondria) by the ozone titration method. The rate constant for O(3) oxidation is maximum for oleic monoenoic acid, lower for dienoic linoleic, and very low for saturated palmitic acid. The rate constant for oxidation of oleic fatty acid, which by one order of magnitude surpasses that for oxidation of essential arachidonic acid, indicates that oleic acid is a leading in vivo acceptor of active O(2) species. By the rate of trapping active oxygen species and in the quantitative aspect, endogenously produced oleic acid can be regarded as the main biological antioxidant.

No abstract

Oxidation of arachidonic acid by ROS in vitro can be evaluated by the formation of reaction products (conjugated dienes); this is preceded by a lag period caused by the action of antioxidants (alpha-tocopherol, beta-carotene, and ascorbic acid). In case of ozone titration the oxidizer is consumed even during the lag period, when conjugated dienes are not yet forming. Comparison of the oxidation rate constants for antioxidants, arachidonic and oleic monoenic fatty acids suggests that during the lag period Cu(2+)-initiated forms of O(2) oxidize primarily oleic acid, whose reaction rate constant is much higher than those of antioxidants. Presumably, the duration of lag period during oxidation of arachidonic acid and formation of conjugated dienes is determined also by the content of triglycerides and oleic fatty acid in low density lipoproteins.

The number of the fatty acid double bonds (unsaturation degree) in the plasma lipid pool was evaluated by automated ozone titration. A positive relationship between the content of double bonds, cholesterol, and glycerol was detected. The higher was plasma cholesterol level, the more double bonds contained fatty acids. At cholesterol level of 0.8-18.9 mmol/liter the double bond/cholesterol ratio approached 4.0 and double bond/glycerol ratio was 1.3-1.5. The maximum content of double bonds was detected in LDL. It was hypothesized that the greater part of plasma cholesterol is esterified with arachidonic acid possessing 4 double bonds; three fatty acids are esterified with glycerol, which altogether have 1-3 double bonds. It seems that plasma cholesterol level indirectly but significantly reflects the level of essential polyenic fatty acids, while glycerol reflects the levels of saturated and unsaturated fatty acids. The role of cholesterol in the plasma consists in the participation in transfer of essential fatty acid in the nonpolar form and their absorption by cells. LDL are the main transmitters of essential polyenic fatty acids in the form of cholesterol esters.

No abstract