Pharmacological blockage of serotonin biosynthesis and circadian changes in oxaliplatin toxicity in rats

Diurnal expression of MRP4 in bone marrow cells underlies the dosing-time dependent changes in the oxaliplatin-induced myelotoxicity

The expression and function of some xenobiotic transporters varies according to the time of day, causing the dosing time-dependent changes in drug disposition and toxicity. Multidrug resistance-associated protein-4 (MRP4), an ATP­binding cassette (ABC) efflux transporter encoded by the Abcc4 gene, is highly expressed in bone marrow cells (BMCs) and protects them against xenobiotics, including chemotherapeutic drugs. In this study, we demonstrated that MRP4 was responsible for the extrusion of oxaliplatin (L-OHP), a platinum (Pt)-based chemotherapeutic drug, from BMCs of mice, and that the efflux transporter expression exhibited significant diurnal variation. Therefore, we investigated the relevance of the diurnal expression of MRP4 in BMCs for L-OHP-induced myelotoxicity in mice maintained under standardized light/dark cycle conditions. After intravenous injection of L-OHP, the Pt content in BMCs varied according to the injection time. Lower Pt accumulation in BMCs was detected in mice after injection of L-OHP at the mid-dark phase, during which the expression levels of MRP4 increased. Consistent with these observations, the myelotoxic effects of L-OHP were attenuated when mice were injected with L-OHP during the dark phase. This dosing schedule also alleviated the L-OHP-induced reduction of the peripheral white blood cell count. The present results suggest that the myelotoxicity of L-OHP is attenuated by optimizing the dosing schedule. Diurnal expression of MRP4 in BMCs is associated with the dosing time-dependent changes in L-OHP-induced myelotoxicity.

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The Optimal Dosing Times of Corticoids. The therapeutic use of Cortisol and its derivatives, anti-inflammatory corticoids, sets delicate problems to resolve because of Cortisol's physiological roles and its circadian rhythms. Cortisol and the majority of its derivatives have desirable and undesirable effects that are time-related administration. The chronothera- peutic optimisation to increase desirable effects and safety of corticoids is shown in the treatment of adrenocortical failure, congenital adrenal hyperplasia and asthma. The knowledge of physiological and physiopathological rhythms of asthma permitted to realize oral treatment optimisation by using a number of corticoids. This knowledge puts in a prominent position the advantages of ciclesonide: a new inhaled corticoid. A chronobiologic approach could be used in a classic optimisation which involves a molecule modification and inhalation like routes of administration.

Circadian Rhythms in Toxic Effects of the Serotonin Antagonist Ondansetron in Mice

The aim of the study was to learn whether the lethal and the motor incoordination (ataxia) side effect of ondansetron (Zophren) administration is dosing-time dependent. Ondansetron is a serotonin 5-HT3 receptor antagonist used primarily to control nausea and vomiting arising from cytotoxic chemo- and radiotherapy. A total of 210 male Swiss mice 10 to 12 weeks of age were synchronized for 3 weeks by 12 h light (rest span)/12 h dark (activity span). Different doses of ondansetron were injected intraperitoneally (i.p.) at fixed times during the day to determine both the sublethal (TD50) and lethal (LD50) doses, which were, respectively, 3.7 +/- 0.6 mg/kg and 4.6 +/- 0.5 mg/kg. In the chronotoxicologic study a single dose of ondansetron (3.5 mg/kg, i.p.) was administered to different and comparable groups of animals at four different circadian stages [1, 7, 13, and 19 h after light onset (HALO)]. The lethal toxicity was statistically significantly dosing time-dependent (chi2 = 21.51, p < 0.0001). Drug dosing at 1 HALO resulted in 100% survival rate whereas drug dosing at 19 HALO was only one-half that (52%). Similarly, lowest and highest ataxia occurred when ondansetron was injected at 1 and 19 HALO, respectively (chi2 = 22.24, p < 0.0001). Effects on rectal temperature were also dosing-time related (Cosinor analysis, p < 0.0001). The characteristics of the waveform describing the temporal patterns differed between the studied variables, e.g., lethal toxicity and survival rate showing two peaks and rectal temperature showing one peak in the 24 h time series waveform pattern. Cosinor analysis also revealed a statistically significant ultradian (tau = 8 h) rhythmic component in the considered variables. Differences in curve patterns in toxicity elicited by ondansetron on a per end point basis are hypothesized to represent the phase relations between the identified 24 h and 8 h periodicities.

Involvement of serotonin in the hypoglycemic response to 2Hz electroacupuncture of zusanli acupoint (ST36) in rats

In our previous studies, an insulin-dependent hypoglycemic effect produced by electroacupuncture (EA) was shown to be mediated by endogenous opioid peptides (EOP). In the present study, we applied 2 Hz EA to both zusanli acupoints (ST36) in the test group for 30 min, and to a nonacupoint area in the control group for 30 min to compare the acupoint specific character in the hypoglycemic effect of EA. Assays of plasma beta-endorphin and insulin levels were performed by ELISA kits. The insulin-dependent mechanism of the hypoglycemic effect was also investigated in streptozotocin (STZ)-induced diabetic rats. The mediation of EOP and the role of mu-opioid receptor were examined by naloxone and mu-opioid receptor knockout mice (MOR-KOM). The serotonin depletion was carried out by injecting (i.p.) p-chlorophenylalanine (PCPA); two low doses of serotonin were also injected (i.v.) to analyze the direct effect on plasma glucose levels. The hypoglycemic effect of EA was much greater in rats stimulated at ST36 than in rats receiving the same stimulation at the nonacupoint area. The plasma levels of insulin and beta-endorphin were also significantly elevated after stimulation of both zusanli acupoints, but remained unchanged following stimulation at the nonacupoint area. There was no sharp hypoglycemic response to 2 Hz EA at zusanli acupoint of STZ-induced diabetic rats. However, the hypoglycemic effect of this EA was not totally blocked by the sufficient dose of naloxone (1 mg/kg, i.v.). Additionally, 2 Hz EA at ST36 also showed a sharp decrease in plasma glucose levels of MOR-KOM. Pretreatment with PCPA did not reproduce hypoglycemic response to 2 Hz EA in naloxone-treated rats and MOR-KOM mice. Furthermore, injection of serotonin decreased the plasma glucose levels significantly. Therefore, we suggest that serotonin also involved in the hypoglycemic action of 2 Hz EA at both zusanli acupoints of normal rats.