Ichrak Dridi

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 At each circadian time, blood samples were withdrawn at (0 h) and at 0.083, 0.166, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2 and 3h after VPA injection.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.

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.

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.

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 time-dependent hepatic and renal toxicities to valproic acid in mice

This study aims to investigate whether hepatic and renal valproic acid (VPA) toxicities varied according to the dosing time in the 24-h scale in mice. VPA was administered by i.p. route to different groups of animals at four different circadian stages (1, 7, 13, and 19 h after light onset (HALO)). Biochemical study and histopathological examinations on liver and kidney sections were performed. The results showed that the hepatic and renal toxicity induced by VPA was time related. Animals treated at 19 HALO showed vacuolar degenerative changes, congestions, and inflammatory areas on liver parenchyma. Lesions within proximal tubules were observed in the kidney in groups treated at 19 HALO. The largest increases in alanine aminotransferase, alkaline phosphatase and plasma creatinine activities were also observed at 19 HALO. The obtained data indicate that the optimal hepatic and renal tolerance is observed when VPA was injected in the middle of the light-rest span of mice.

Temporal influence of experimental exposure of wistar rats to hexachlorobenzene on the morphology and some enzyme activities of intestinal mucosae

The intestinal reactivity to the oral administration to rats of 16 mg of Hexachlorobenzene (HCB) kg−1 b.w. (1.6% of LD50) for 30 days was explored in the beginning and at the end of the rest light phase of animals to check whether the presence of food in the intestine could lessen the impact of this pesticide. The treatment caused a mucosa layer hypertrophy and consequently a severe reduction of the intestinal lumen. The morphometric measurements presented a positive correlation with the values of the mucosa weight. The specific activities of alkaline phosphatase, gamma glutamyl transferase, sucrase, maltase and lactase were measured and used to estimate the functional state of the organ. The observed effects could reflect an inflammatory process without significant impact on the absorptive function of the organ. And, the influence of the HCB-dosing time on the reactivity of the intestine was not confirmed and appeared not to be related to the level of filling of the intestinal lumen with alimentary bolus.

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.

Circadian variation in hepatic toxicity of the immunosuppressive agent “Mycophenolate Mofetil” in rats

Immunosuppressive drugs may have varying toxicity or efficacy depending on the administration time. This study investigates whether the liver toxicity of the mycophenolate mofetil (MMF) varies according to the circadian dosing-time in rats. 300 mg/kg of MMF was injected by intraperitonal route to different groups of animals at four different circadian stages (1, 7, 13, and 19 h after light onset, HALO). Biochemical variable (transaminase, alkaline phosphatase) and histopathological examinations on liver section were performed. The results obtained showed that MMF treatment induced hepato-toxicity depending on the circadian time. A severe toxicity in the liver was observed when the drug was injected at 7 HALO. The data obtained indicate that the maximum of hepato-toxicity is observed when MMF was injected in the middle of the light-rest span of rats which is physiologically analogous to the end of the activity of the diurnal phase in human patients.

Murine circadian time-dependent tolerance to the immunosuppressive agent mycophenolate mofetil (MMF)

The present work aims to investigate whether the tolerance to mycophenolate mofetil (MMF) varies according to the circadian dosing time in rats. A total of 120 male Wistar rats were synchronized for three weeks to 12 h light/12 h dark. A potentially lethal dose of MMF (450 mg/kg, i.p.) was injected to different groups of animals at six different circadian stages (1, 5, 9, 13, 17, and 21 hours after light onset, HALO). Survival rate, body weight, and rectal temperature were used as three toxicity end-points. Drug dosing at 13 HALO resulted in 80% survival rate as compared to drug dosing at 17 HALO (20%). The Cosinor analysis revealed a significant ultradian rhythm (t = 8 h) in survival. The surviving treated rats exhibited a significant hyperthermia and body weight loss on days 3, 5, and 9. An ultradian component of τ = 8 h (p < 0.001) in the circadian body weight rhythm was detected by Cosinor (p < 0.0001).