Circadian variation of plasma cortisol and whole blood reduced glutathione levels in nasopharyngeal carcinoma patients.

Background & Objective: Glutathione is involved in cellular protection against radiation damage and drug detoxification. This study was to investigate the circadian variation of plasma cortisol and whole blood reduced glutathione (GSH) levels in nasopharyngeal carcinoma (NPC) patients to provide references for chronotherapy for NPC.

Methods: A total of 13 NPC patients and 14 healthy volunteers were involved. Peripheral venous blood was sampled every 4 h during one 24-hour period starting at 12:00 am. The plasma cortisol concentration was determined by radioimmunoassay; the GSH concentration was determined by high performance liquid chromatography.

Results: Plasma cortisol levels of both groups displayed clear and similar circadian rhythms. The cortisol level peaked in both groups in the morning and was the lowest at mid-night. In both groups, GSH concentrations showed significant differences according to sampling time (ANOVA for Repeated Measures, F=5.18, P=0.02). By cosinor analysis, the circadian variation of the GSH level in NPC group was marginally statistically significant (Cosinor analysis, P=0.06) with the acrophase appeared at 05:02; the GSH level in control group displayed an obvious circadian rhythm and the acrophase appeared at 07:44+/-01:56 (P<0.01). The rhythm-adjust mean value of glutathione was (19.60+/-1.11) nmol/mg protein in NPC group and (8.95+/-0.46) nmol/mg protein in control group.

Conclusions: The circadian rhythm of the plasma cortisol level is maintained in NPC patients, even in some patients at advanced stages. In NPC patients, GSH shows a trend of circadian variation which is similar to that in healthy controls. These results could be used to select special schedules for chrono-radiotherapy and chrono-chemotherapy for NPC patients.