Circadian variation in anticonvulsant activity of valproic acid in mice.

PURPOSE: This study aims to investigate whether valproic acid (VPA) anticonvulsant activity varied according to circadian dosing-time in mice. METHODS: VPA was administered to mice at four circadian stages (1, 7, 13 and 19h after light onset, (HALO)). The controls received a saline injection followed by a s.c. injection of pentylenetetrazol (PTZ) 30min later. In pretreated animals, VPA was administered 30min before PTZ administration. RESULTS: The results obtained showed that VPA-induced anticonvulsant activity depends on circadian dosing-time in mice. VPA has significantly increased the latency of the first clonic seizure at all circadian stages. This increase varied depending on the time of VPA pre-treatment, the highest and the lowest increases were recorded respectively at 7 and 19 HALO. The Cosinor analysis has also validated a circadian rhythm of this increase. The intensity of seizures in pretreated mice varied significantly according to circadian stage. The highest seizure intensity was recorded at 19 HALO. A circadian rhythm of the seizure intensity in VPA pretreated mice was detected, with an acrophase located at the middle of the dark span (Ø=18.09 HALO±2.27h). CONCLUSION: The present findings provide evidence for a pronounced anticonvulsant effect of VPA when administered in the 2nd middle of the light-rest span in mice. These results might probably be due to the circadian variation of VPA pharmacokinetic since our previous studies showed that the optimal tolerance corresponded to the middle of the rest span, the time which induces the highest total plasma clearance.

Hepatoprotective effect of Opuntia microdasys (Lehm.) Pfeiff flowers against diabetes type II induced in rats.

Opuntia sp. has long been used as a folk medicine to treat hepatitis and diabetes in Sicile (Italy). To extract the polyphenols from the flower of Opuntia microdasys Lehm. at post flowring stage and evaluate the antidiabetic activity in vitro and in vivo. The hepatoprotective activity of Opuntia microdasys aqueous flowers extract at post flowering stage (OFP) has been tested for their antidiabetic activity. On fructose-alloxan induced diabete in rat model, evaluating the inhibitory effects of OFP on some carbohydrate metabolizing enzymes, pancreatic α-amylase and intestinal α-glucosidase activities in vitro. The OFP extract showed inhibitory activity against α-glucosidase (IC50=0.17±0.012mg/ml) and α-amylase (IC50=2.55±0.41mg/ml). The inhibitory potential of OFP extract on these enzymes suggests a positive and probable role of this extract in the management and treatment of diabetes mellitus, particularly, for type 2. Oral administration of the OFP at 200mg/kg to diabetic male rats for 28days demonstrated a significant protective effect by lowering the levels of glucose (123.21±1.38mg/dL) and hepatic marker enzymes (AST, ALT, LDH, γ-GT, BT, PAL, TC, LDL-C, HDL-C and TG). OFP attenuated oxidative stress by decreasing the SOD, CAT, GPX activity and the levels of PC and MDA in the liver and restored the histological architecture of the rat liver. OFP has protective effects on the protection of liver, thereby reducing some of the causes of diabetes in experimental animals.

Dosing-time dependent oxidative effects of an immunosuppressive drug "Mycophenolate Mofetil" on rat kidneys.

This study investigates whether the toxicity in kidneys as well as oxidative stress varied according to the dosing time of an immunosuppressive agent "mycophenolate mofetil (MMF)" in Wistar Rat. 300mg/kg of MMF was injected by intraperitonal at four different circadian stages (1, 7, 13 and 19h after light onset, HALO). Rats were sacrificed after 3days, and the kidneys were removed for determination of oxidative stress and histological analysis. Biochemical variable (creatinine, urea) was performed. Statistical analysis showed that MMF administration at 7 HALO produced a renal toxicity assessed by the significant increase in both blood creatinine and urea and antioxidant activity assessed by malondialdehyde and protein carbonyl levels indicating an induction of lipid peroxidation in oxidative damage. Whereas, at this time MMF induced a decrease the enzyme activities of renal catalase and superoxide dismutase, with a renal histopathology alterations (glomerular atrophy and lesions within proximal tubules). However, when MMF was injected in the middle of the dark-activity phase it produced a very mild renal toxicity and low oxidative stress. The obtained data indicate that the maximum of renal toxicity is observed when MMF was injected in the middle of the light- rest span in rats.

Circadian variation of cytotoxicity and genotoxicity induced by an immunosuppressive agent "Mycophenolate Mofetil" in rats.

Immunosuppressive drugs such as Mycophenolate Mofetil (MMF) are used to suppress the immune system activity in transplant patients and reduce the risk of organ rejection. The present study investigates whether the potential cytotoxicity and genotoxicity varied according to MMF dosing-time in Wistar Rat. A potentially toxic MMF dose (300 mg/kg) was acutely administered by the i.p. route in rats at four different circadian stages (1, 7, 13 and 19 hours after light onset, HALO). Rats were sacrificed 3 days following injection, blood and bone marrow were removed for determination of cytotoxicity and genotoxicity analysis. The genotoxic effect of this pro-drug was investigated using the comet assay and the micronucleus test. Hematological changes were also evaluated according to circadian dosing time. MMF treatment induced a significant decrease at 7 HALO in red blood cells, in the hemoglobin rate and in white blood cells. These parameters followed a circadian rhythm in controls or in treated rats with an acrophase located at the end of the light-rest phase. A significant, thrombocytopenia was observed according to MMF circadian dosing time. Furthermore, abnormally shaped red cells, sometimes containing micronuclei, poikilocytotic in red cells and hypersegmented neutrophil nuclei were observed with MMF treatment. The micronucleus test revealed damage to chromosomes in rat bone marrow; the comet assay showed significant DNA damage. This damage varied according to circadian MMF dosing time. The injection of MMF in the middle of the dark-activity phase produced a very mild hematological toxicity and low genotoxicity. Conversely, it induced maximum hematological toxicity and genotoxicity when the administration occurred in the middle of the light-rest phase, which is physiologically analogous to the end of the activity of the diurnal phase in human patients.

Gastrointestinal toxicity of mycophenolate mofetil in rats: Effect of administration time.

This study investigates whether the intestinal toxicity of the immunosuppressive agent "mycophenolate mofetil (MMF)" varied according to the circadian dosing-time in rats. MMF (300 mg/kg) was acutely administered by i.p. route in rats at four different circadian stages (1, 7, 13 and 19 hours after light onset, HALO). The results obtained showed that MMF-induced intestinal toxicity depends on circadian dosing-time in rats. A severe toxicity in the duodenum and jejunum was observed when the drug was administered at 7 HALO compared to controls and to other circadian times. This toxicity appeared in the form of villous and Liberkhun gland atrophy and nodular inflammation. At this dosing-time, MMF induced a significant increase of phosphatase alkaline activity and a significant decrease of gut mucosa weight, protein content and disaccharidases activities. Conversely, MMF dosing at 19 HALO induced lower gut toxicity, irrespective of type of toxicity explored. These data suggest the existence of a circadian rhythm of gut toxicity for this immunosuppressive agent and the best time of gastrointestinal tolerance (chronotolerance) of this agent was observed in the middle of the dark-activity span of rats.

Circadian variation of mycophenolate mofetil pharmacokinetics in rats.

The present work aims to investigate whether the pharmacokinetics of the active metabolite mycophenolic acid (MPA) varies according to the circadian dosing-time of mycophenolate mofetil (MMF). A total of 180 male Wistar rats aged 8 weeks and synchronized for 3 weeks to 12 h light and 12 h dark were used. A single dose of 200 mg/kg of MMF was administrated in rats by i.p route at either of the four different circadian stages (1, 7, 13, and 19 Hours After Light Onset, HALO) (45 rats/circadian time). At each circadian stage, blood samples were collected at 5, 10, 15, 20, 30 min, 1 h, 1 h 30 min, 2 h, 3 h, 4 h, 6 h, 8 h, 12 h and 24 h following drug injection. Plasma MPA concentrations were analyzed for each sample using a validated high-performance liquid chromatography (RP-HPLC) method. Tmax of MPA remained similar whatever the circadian time of injection mean Tmax=30 min). However, the peak of plasma concentration Cmax varied significantly according to the circadian dosing-time. Maximum and minimum Cmax were obtained when MMF was injected at 7 HALO (69.1 µg/ml) and at 19 HALO (22.7 ± 1.74 µg/ml) respectively. AUC0-24 varied significantly according to the circadian-time of injection (166.33 ± 10.54 mg h/L at 7 HALO vs 80.27 ± 2.33 mg h/L at 19 HALO) (p<0.05). The highest and lowest mean values of plasma clearance (CL calculated as Dos/AUC) were observed at 19 HALO (2.45 ± 0.07 L/h/kg) and at 7 HALO (1.08 ± 0.06 L/h/kg) respectively (p<0.05). Cosinor showed a circadian rhythm in the pharmacokinetic parameters Cmax, AUC0-24 and plasma clearance. The mechanism of circadian rhythm in MMF tolerance might be partly explained by the circadian variation of pharmacokinetics since the time (7 HALO) of maximum hematological and digestive toxicity corresponds to that of the lowest plasma clearance on the highest Cmax and AUC0-24 of MMF.

Circadian variation of Valproic acid pharmacokinetics in mice.

Valproic acid (VPA) is currently one of the most commonly used antiepileptic drugs. This study aims to investigate whether VPA pharmacokinetics varied according to circadian dosing-time. A single dose of VPA (350 mgkg(-1)) was administered by intraperitonally (i.p.) route to a total of 132 mice synchronized for 3 weeks to 12h light (rest span) and 12 h dark (activity span). Four different circadian times (1, 7, 13 and 19 HALO) of drug injection were used (33 mice/circadian time). At each circadian time, blood samples were withdrawn at (0 h) and at 0.083, 0.166, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2 and 3h after VPA injection. Plasma VPA concentrations were determined by an EMIT method. There were no significant differences in T(max) of VPA whatever the circadian-time of injections (T(max)=0.166 h). However, there were relevant differences in C(max) between the four circadian groups (p<0.005), it varied between 386 ± 30.86 mg L(-1) in mice treated at 7 HALO and 824 ± 39.85 mg L(-1) in mice treated at 19 HALO. The AUC(0-∞) was significantly two times higher when VPA was administered at 19 HALO as compared to the injection at 7 HALO. Drug dosing at 7 HALO resulted in highest Cl(T) value: 0.405 ± 0.006 L h(-1)kg(-1), whereas Cl(T) was significantly slower when VPA was administered at 19 HALO (0.157 ± 0.009 L h(-1)kg(-1)) (p<0.0001). The AUC(0-∞) was significantly 2-fold higher when VPA was administered at 19 HALO (2216.65 ± 138.91 mg h(-1)L(-1)) as compared to the injection at 7 HALO (864.09 ± 16.82 mg h(-1)L(-1)) (p<0.0001). Cosinor analysis showed circadian rhythm in different pharmacokinetic parameters. C(max) and AUC(0-∞) have a significant circadian rhythm with an acrophase located at 20.16 HALO ± 0.16 h (the middle of the active span) (p<0.001), whereas Cl(T) and Vd showed a significant circadian rhythm with an acrophase located respectively at 7.86 HALO ± 0.57 h and 6.13 HALO ± 0.07 h (the middle of the rest span) (p<0.001). The large circadian variation of VPA pharmacokinetic processes might be involved in the mechanisms of circadian rhythm in murine toxicity since the optimal tolerance corresponded to the time which induces lowest C(max) and AUC values.

Chronotolerance study of the antiepileptic drug valproic acid in mice.

BACKGROUND: Valproic acid (VPA) is an antiepileptic drug widely used for the treatment of absence seizures and generalized tonic-clonic seizures. The present work aims to study whether VPA-induced toxicity varies according to the dosing-time in the 24 hour-scale. METHODS: The influence of dosing-time on tolerance to VPA was investigated in 120 male Swiss mice synchronized under a light-dark cycle (12:12). The mean VPA lethal dose was first determined to be 850 ± 0.2 mg/kg, i.p.. Such a dose was administered by i.p. route to a total of 90 mice divided in six circadian stages [1, 5, 9, 13, 17 and 21 Hours After Light Onset (HALO)] (15 mice/circadian time); 30 mice were used as control (5 mice / circadian time). RESULTS: The surviving treated mice exhibited a significant circadian variation in rectal temperature and body weight loss (p < 0.001). The least rectal temperature change and body weight loss occurred when VPA was injected at 9 HALO. Drug dosing at 9 HALO resulted in -9 % weight loss whereas drug dosing at 17 HALO was -15 % (Ø = 20.3 HALO ± 1.1 h, p ≤ 0.0001). Lethal toxicity also varied according to circadian dosing-time (χ2 = 42.1, p < 0.0001). The highest (60 %) and the lowest (6.67 %) survival rates were observed at 9 HALO and 17 HALO respectively. Cosinor analyses validated a significant circadian rhythm in survival duration with an acrophase at 8.4 HALO ± 0.75 h (p < 0.001). CONCLUSIONS: With regards to these data the optimal tolerance to VPA occurred when the drug was administered in the second half of the light-rest span of mice which is physiologically analogous to the second half of the night for human patients.