[Circadian variations of plasma SOD and MDA in health subjects]

Oxygen derived free radical system has been to be implicated in the pathogenesis of many diseases, such as cardiovascular disease, tumor, trauma and radiation injury. Many studies have suggested that oxygen free radical initiate a series of events that result in cell membrane alterations leading to the development of cell injury. The objective of the present study was to examine the circadian characteristics of some parameters of this system in the blood. One parameter was superoxide dismutase (SOD), a major oxygen free radical scavenger; the other was malondialdehyde (MDA), an important product of lipid peroxidation initiated by oxygen free radicals. Blood samples were collected at 6 h intervals beginning at 08:00 over a 24 h span in nine healthy volunteers (5 females, 4 males, average age 30 +/- 5 years). All participants were synchronized for one week with diurnal activity from 07:00 to 23:00 and nocturnal rest, with three meals served at 07:30, 12:00 and 19:00. Plasma SOD, MDA levels were measured by pyrogallol autoxidation assay, thiobarbituric acid spectrophotometry respectively, and the data were fitted with a 24 h cosine curve and analyzed further by a population-mean cosinor. The results showed that the plasma SOD levels exhibited a highly significant circadian rhythm (P < 0.001) in healthy subjects, with acrophase (phi) at 21:17, mesor (M) of 3975.3 +/- 680.5 u/g Hb, and amplitude (A) of 273.62 u/g Hb. A circadian rhythm of plasma MDA was also detected (P < 0.01), phi = 15:15, M = 4.23 +/- 0.86 mumol/L, A = 2.37 mumol/L). The evaluation of circadian natures of SOD and MDA may be important in the prevention, diagnosis and treatment of associated diseases.