Oxidative stress and erythropoietin response in altitude exposure

Oxidative stress and erythropoietin (EPO) levels are increased following high altitude exposure. We hypothesized that the altitude-oxidative stress and EPO response would be associated with the presence or absence of acute mountain sickness (AMS) in subjects exposed at high altitude.

The study enrolled 29 healthy volunteers exposed at altitudes without strenuous physical exercise. Oxidative stress was determined by the spectrophotometric measurement of the colour occurring during the reaction of malondialdehyde (MDA) with thiobarbituric acid (TBA) on blood samples. Ferritin and EPO were also measured simultaneously.

During a rise in altitude at 2000 and 3000 m, there were no changes in plasma ferritin level in either of the 2 groups with or without AMS. In contrast, EPO increased at an altitude of 3000 m and after returning to sea level (28.2+/-2.7, 26.9+/-3.3 vs 12.2+/-1.4 and 17.1+/-1.6, P < 0.05, in group without AMS; 29.3+/-4.5, 22.8+/-2.7 vs 10.6+/-1.0 and 16.1+/-1.5, # P < 0.05, in group with AMS; compared with the baseline level and at the height of 2000 meters). At a height of 3000 m, plasma MDA level was elevated compared with that at the altitude of baseline and 2000 m in both groups of subjects with and without AMS (3.77+/-0.29 vs 1.14+/-0.17, and 1.64+/-0.22, P < 0.001, in subjects with AMS; 3.65+/-0.39 vs 1.71+/-0.21, and 1.73+/-0.21, P < 0.001, in subjects without AMS) . After returning to sea level, subjects without AMS had lower MDA oxidative stress compared with those with AMS (2.58+/-0.26 vs 3.51+/-0.24, P = 0.0223). Along with a rise in altitude, the oxidative stress in these both groups was not correlated with the changes in EPO (r2 = 0.0728, P = 0.1096).

High altitude-induced oxidative stress, detected by MDA assay, is not different between the two groups of subjects with and without AMS. Upon return to sea level, subjects without AMS had lower MDA oxidative stress burden and higher EPO level than those with AMS. Whether the subjects with altitude illness had delayed recovery from oxidative stress merits further investigation.