Homeostasis between lipid peroxidation and antioxidant enzyme activities in healthy human aging.

In healthy people the plasma malondialdehyde increases with age, however there is a simultaneous rise in the activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in red blood cells, although both enzymes show a biphasic behaviour, that is, reaching the lowest values at 40-50 years of age to rise remarkably later on. No significant changes were found in the case of glutathione peroxidase but the age-dependent behaviour is similar to the other enzymes mentioned above. The activity of glutathione reductase shows a clear increase depending on age, up to middle age, with or without flavin adenine dinucleotide. We conclude that the increase in the activities of the anti-oxidant enzymes of the red blood cells during aging, could be interpreted as a positive feedback mechanism in response to rising lipid peroxidation. Consequently, from the point of view of the parameters used the homeostasis between the production of free radicals and anti-oxidant systems seems to be maintained in the common, normal aging pattern.