Plasma lipoperoxides and aging. Critical assessment of the thiobarbituric acid method for the measurement of lipoperoxides and malondialdehyde.

Thiobarbituric acid reactive products were measured in plasma of 66 normal subjects ranging from 19 to 92 years of age. A significant correlation (r = 0.54, p less than 10(-6) was formed between the level of these metabolites and the age of the subjects. As a matter of fact this method analyzes two kinds of substances from two different origins, free malondialdehyde or lipid peroxides. These two fractions were identified by extracting lipids using Folch's method and leaving all free malondialdehyde in the plasma (95.6 +/- 11.8% recovery for a known amount added to the plasma). Plasma analysis prior to and after extraction showed that thiobarbituric acid reactive products were lipid peroxides for 74.8 +/- 4.3%, the remainder being free malondialdehyde. The origin of these two fractions is discussed.