title: Seasonal modulation of the 8-and 24-hour rhythms of ondansetron tolerance in mice.
abstract: Ondansetron (Zophren((R))) is a serotonin 5HT(3)-receptor antagonist used primarily to control nausea and vomiting caused by cytotoxic chemo-and radio-therapy. Tolerance to this drug shows both 24 and 8 h periodicities. In this framework, this study aimed to determine whether these ondansetron tolerance rhythms are modulated by season. The chronotoxic effect of a fixed dose (3.5 mg/kg, i.p.) of the drug was investigated with reference to both time of the day and year dependencies. Season-related studies were performed on 560 male Swiss mice, 10 to 12 wks old, synchronized with L:D=12:12 for three weeks. During a 1 yr span (2005), four 24 h studies were performed with a single dosing time at 1, 7, 13, and 19 hours after light onset (HALO), respectively. Tolerance was assessed daily during a 40-day span after acute ondansetron treatment. Both chi(2) test and cosinor methods were used to analyze the time series data. Statistically significant dosing time-dependent changes were validated in both yearly and daily time scales. The 24 h mean survival rate peaked in spring (92%) compared to fall (72%), the 20% difference being statistically significant (chi(2) test with p<0.05 and cosinor with p<0.0001 for seasonal rhythm detection and with a peak time, Ø,=April 3+/-6.6 days). A 24 h rhythm was also detected in each of the seasonal time points. However, the curve pattern was monophasic in fall as well as spring. In fall, a large amplitude (A) circadian rhythm was detected that peaked at 19 HALO, while in the spring, a small circadian rhythm was detected that peaked at 1 HALO. The curve pattern was biphasic in summer (with large A) and in winter (with a small A). The existence of two peaks of equal magnitude in winter (100% survival rate) and in summer (100% and 90%) suggests the presence of both circadian and ultradian rhythms rather than an ultradian component of the 24 h period. The seasonal modulation of ondansetron circadian chronotolerance seems to involve several rhythm parameters: season-related changes in the 24 h mean (M), amplitude (A), acrophase location (Ø), as well as bimodal curve patterns including the coexistence of rhythms with respectively 24 and 8 h periods in winter and summer. In conclusion, tolerance to ondansetron varies not only according to the 24 and 8 h periods but also according to seasons, which suggests the complexity of ondansetron toxicity rhythms. Seasonal modulation of ondansetron tolerance may also influence the strategies of chemo-and chrono-therapy, and it is therefore necessary to take it into account in clinical drug-delivery protocols to minimize side effects of cytotoxic anticancer and antiemetic agents.
authors: Faculté de Médecine, Laboratoire d'Immuno-Oncologie Moléculaire, Monastir, Tunisia.
authors: Achraf
authors: A
authors: Khedhaier
authors: Mossadok
authors: M
authors: Ben-Attia
authors: Wafa
authors: W
authors: Gadacha
authors: Mamane
authors: M
authors: Sani
authors: Alain
authors: A
authors: Reinberg
authors: Naceur A
authors: NA
authors: Boughattas
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D004361:Drug Tolerance; D008297:Male; D051379:Mice; D017294:Ondansetron / Q000494:pharmacology* / Q000633:toxicity; D010507:Periodicity; D012621:Seasons; D012702:Serotonin Antagonists / Q000494:pharmacology / Q000633:toxicity; D016019:Survival Analysis
chemical_list: D012702:Serotonin Antagonists; D017294:Ondansetron