The inhibition of CYP1A2, CYP2C9, and CYP2D6 by pterostilbene in human liver microsomes.

This study used human liver microsomes to assess pterostilbene's effect on the metabolic activity of cytochrome P450 (CYP) 1A2, CYP2C9, and CYP2D6. The metabolism of their substrates (phenacetin, tolbutamide, and dextromethorphan) was assayed by quantifying their relevant metabolites by HPLC. The IC50 value was used to express the strength of inhibition, and the value of a volume per dose index (VDI) was used to indicate the metabolic ability of the enzyme. In this study, pterostilbene inhibited CYP1A2, CYP2C9, and CYP2D6's metabolic activities in vitro. CYP2C9's activity was most significantly inhibited by pterostilbene; its IC50 value was 0.12±0.04 µM. The IC50 value of CYP1A2 and CYP2D6 was 56.3±10.4 µM and 62.33±11.4 µM, respectively. The finding that suggests that pterostilbene has the potential to interact with CYP2C9 substrates in vivo. These results warrant clinical studies to assess the in vivo significance of these interactions.

Orally co-administrated oleo-gum resin of Commiphora myrrha decreases the bioavailability of cyclosporine A in rats.

Cyclosporine A is a narrow therapeutic indexed immunosuppressant used after organ transplantation. Several herbs have been reported to alter its pharmacokinetics. Myrrh, dried oleogum resin obtained from Commiphora myrrha (Burseraceae) has been used for many common ailments. The present study was carried out to investigate the effect of myrrh on the pharmacokinetics of cyclosporine A. The rats of the control group received 60 mg/kg, p.o. cyclosporine A, and blood samples were collected at predetermined time intervals. Rats of the test group were treated with an aqueous suspension of myrrh (380 mg/kg p.o.) for eight days and on 8th day a single dose of cyclosporine A was administered to the treated group after 1 h of myrrh administration. Blood samples were drawn at predetermined time points and the drug was analyzed in whole blood by using H-Class UPLC-TQD. Pharmacokinetic profiles of control and test group were compared. Statistically significant differences were observed between the pharmacokinetic parameters of control and treated groups. In the myrrh treated group, the AUC(0-t) and C(max) of cyclosporine A was decreased by about 45% and 48%, respectively. The time to reach maximum concentration (T(max)) remained almost unchanged in both groups. Results indicated that the bioavailability of cyclosporine A was reduced by about 45% when co-administered with myrrh. This observation suggests that concurrent consumption of myrrh and cyclosporine A should be avoided. To confirm the clinical relevance of these findings, P-gp and CYP3A based molecular investigations can be performed along with a well-planned clinical study.

Potential inhibitory effect of herbal medicines on rat hepatic cytochrome P450 2D gene expression and metabolic activity.

The aim of current study was to investigate the effect of some commonly used medicinal herbs on the regulation of rat CYP2D gene expression and its metabolic activity. Wistar albino rats were treated for seven consecutive days with selected doses of five commonly used herbs (Trigonella foenum-graecum, Ferula asafoetida, Nigella sativa, Commiphora myrrha and Lepidium sativum). Thereafter, rat livers were harvested and CYP2D mRNA levels were determined by RT-PCR. The metabolic activity of CYP2D was performed on rat hepatic microsomes using dextromethorphan as specific substrate. All investigated herbs produced inhibition of CYP2D mRNA expression and metabolic activity. The inhibitory potential of investigated herbs on rat CYP2D mRNA was in the following order: Commiphora myrrha > Nigella sativa > Lepidium sativum > Trigonella foenum-graecum > Ferula asafoetida. Whereas, the inhibitory potential of investigated herbs on CYP2D mediated enzyme metabolic activity was found in following order: Nigella sativa > Lepidium sativum > Trigonella foenum-graecum > Commiphora myrrha > Ferula asafoetida. The current study shows that only used herbs reduce CYP2D activity in rat liver microsomes at the transcriptional levels. Such effects could lead to undesirable pharmacological effects of clinically used low therapeutic index CYP2D substrate drugs.

Pioglitazone.

Pioglitazone is a thiazolidinedione antidiabetic with actions similar to those of rosiglitazone. It is used in the management of type 2 diabetes mellitus and is prepared by reducing 5-[4-[2-(5-ethyl-2-pyridyl)ethoxy]benzilidene]-2,4-thiazolidinedione with sodium borohydride in the presence of a cobalt ion and dimethyl glyoxime. Ultraviolet spectroscopy shows maximum absorption at 270nm. Infrared spectroscopy shows principal peaks at wave numbers 3082, 2964, 1736, 1690, 1472, 1331, 1254, 1040, 841, 728cm(-1) (KBr disk). The determination method by high-performance liquid chromatography was linear over the range of 25-1500ng/mL of pioglitazone in plasma (r(2)>0.999). The within- and between-day precision values were in the range of 2.4-6.8%. The limit of quantitation of the method was 25ng/mL. It is well absorbed with a mean absolute bioavailability of 83% and reaching maximum concentrations in around 1.5h. It is metabolized by the hepatic cytochrome P450 enzyme system. Following oral administration, approximately 15-30% of the pioglitazone dose is recovered in the urine. Renal elimination of pioglitazone is negligible, and the drug is excreted primarily as metabolites and their conjugates. It is presumed that most of the oral dose is excreted into the bile either unchanged or as metabolites and eliminated in the feces.

Investigating the Potential Effect of Commiphora myrrha on the Pharmacokinetics of Theophylline, a Narrow Therapeutic Index Drug.

AIM: The present study was conducted to investigate the effect of commonly used herb Commiphora myrrha on the pharmacokinetic profile of theophylline (narrow therapeutic index drug) in rabbits. METHODS: In the experimental groups, theophylline (16 mg/kg) was given orally to the rabbits. Where aqueous saline suspension of Commiphora myrrha (176 mg/kg, p.o.), was given to the rabbits and the blood samples were withdrawn at different time intervals (0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24 and 36 h) from marginal ear vein after dosing and theophylline in plasma was analyzed by HPLC method. RESULTS: It was observed that there a significant differences in the Cmax, AUC, AUMC, t1/2, and MRT of theophylline when coadministered with Commiphora myrrha which indicate that the herb affect the metabolism and elimination when coadministered with theophylline. CONCLUSION: Our results suggested that concurrent use of investigated herb alters the pharmacokinetics of theophylline. Confirmation of these results in human studies will warrant changes in theophylline dose or frequency when coadministered with herb under consideration.

Impact of Herbal Medicines like Nigella sativa, Trigonella foenum-graecum, and Ferula asafoetida, on Cytochrome P450 2C11 Gene Expression in Rat Liver.

AIM: Combined use of herbs and drugs may result in clinically important herb-drug interactions. The majorities of these interactions are thought to be metabolism-based and involve induction or inhibition of cytochrome P450 (CYP). The current study was designed to investigate the effect of some commonly used herbs on rat CYP2C11 gene expression and metabolic activity. METHODS: Wistar rats were treated for 7 days with increasing doses of 3 herbs; Nigella sativa, Trigonella foenum-graecum, and Ferula asafoetida. Thereafter, CYP2C11 mRNA and protein levels were determined by real-time polymerase chain reaction (RT-PCR) and western blot analyses, respectively. In vitro metabolic activity of CYP2C11 was performed on rat hepatic microsomes using tolbutamide as specific substrate. RESULTS: Our results showed that all the 3 herbs significantly inhibited the mRNA and protein expression levels of CYP2C11 in a dose-dependent manner. Furthermore, the in vitro enzyme metabolic activity study showed a significant decrease in the formation of 4-hyroxy-tolbutamide, a tolbutamide metabolite, at the higher doses. The inhibitory effects of the investigated herbs on rat CYP2C11 was in the order: Nigella Sativa > Trigonella foenum-graecum > Ferula asafoetida. CONCLUSIONS: The 3 herbs are strong inhibitor of CYP2C11 expression, which can lead to an undesirable pharmacological effect of clinically used CYP2C11 substrate drugs with a low therapeutic index.

Effect of different gamma radiation doses on solid crystalline insulin: hypoglycaemia in diabetic beagle dogs.

The effect of different doses of gamma radiation (25, 50 and 100 KGy) on the solid crystalline insulin was studied. The results showed that there was no significant difference (P > 0.05) between the hypoglycaemic effects of 25 kGy gamma-irradiated and the non-irradiated insulin as indicated by the plasma glucose levels and the relative hypoglycaemia. The exposure of insulin to higher doses of radiations (50 and 100 kGy) resulted in almost the same hypoglycaemic effect, which was however greater than that produced by the 25 kGy gamma-irradiated and the non-irradiated insulin. The DSC thermograms showed that the thermal behaviour of crystalline insulin was not affected by the different doses of irradiation. However, a slight colour change was noticed on samples exposed to 50 and 100 kGy of radiation but not on samples subjected to 25 KGy. In conclusion, while the routinely used dose (25 kGy) of gamma radiation for sterilization does not seem to affect the activity of insulin, higher doses of radiation (50 and 100 kGy) enhance its hypoglycaemic effect.

Enteric-coated insulin capsules: a combination with or a replacement of oral hypoglycaemic drugs.

The hypoglycaemic effect of Eudragit S100 enteric-coated insulin capsules containing sodium salicylate as an absorption promoter, oral hypoglycaemic tablets sulphonylurea (e.g. doanil 5 mg) and metformin (e.g. glucophage 500 mg) was studied in hyperglycaemic beagle dogs. The effect of the combinations of insulin capsules + doanil, insulin capsules + glucophage and the combination of doanil + glucophage is also studied. The results show that the enteric-coated insulin capsules produced the same results as the glucophage tablets with respect to Cmax, AUC and relative hypoglycaemia. While, doanil tablets produced non significant lowering (P > 0.05) of Cmax and a significant less (P < 0.05) AUC compared to that produced by insulin capsules and lower (P < 0.001) RH compared to that of insulin capsules or glucophage tablets. The combination of glucophage and doanil tablets resulted in synergistic effect producing 59 +/- 9.27% reduction in plasma glucose levels by 4h and significantly higher (P < 0.001) AUC and RH compared to either of the tablets alone. The combination of insulin capsules and doanil tablets produced only 16% lowering in plasma glucose levels by 6h and significantly (P < 0.001) lower AUC and RH compared to the combination of glucophage + doanil. The combination of insulin capsules and glucophage tablets produced about 38% reduction in plasma glucose levels and significantly (P < 0.001) higher AUC and RH compared to either glucophage, doanil tablets or enteric coated insulin capsules alone. The results show that enteric-coated insulin capsules can be a replacement of either of the oral hypoglycemic drugs. In addition, the combination of the insulin capsules and glucophage tablets could be a good therapy to Type II diabetic patients that not controlled properly by oral hypoglycemic drugs.

Effects of Nigella sativa and Lepidium sativum on cyclosporine pharmacokinetics.

The present study was conducted to investigate the effects of Nigella sativa and Lepidium sativum on the pharmacokinetics of cyclosporine in rabbits. Two groups of animals were treated separately with Nigella sativa (200 mg/kg p.o.) or Lepidium sativum (150 mg/kg p.o.) for eight consecutive days. On the 8th day, cyclosporine (30 mg/kg p.o.) was administered to each group one hour after herbal treatment. Blood samples were withdrawn at different time intervals (0.0, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, 12, and 24 hrs) from marginal ear vein. Cyclosporine was analyzed using UPLC/MS method. The coadministration of Nigella sativa significantly decreased the C(max) and AUC(0-∞) of cyclosporine; the change was observed by 35.5% and 55.9%, respectively (P ≤ 0.05). Lepidium sativum did not produce any significant change in C(max) of cyclosporine, although its absorption was significantly delayed compared with control group. A remarkable change was observed in T(max) and AUC(0-t) of Lepidium sativum treated group. Our findings suggest that concurrent consumption of Nigella sativa and Lepidium sativum could alter the pharmacokinetics of cyclosporine at various levels.

Effect of black seed on dextromethorphan O- and N-demethylation in human liver microsomes and healthy human subjects.

OBJECTIVE: To investigate the effects of black seed on the metabolic activities of CYP3A4 and CYP2D6 in human liver microsomes and in human subjects using dextromethorphan as a probe drug. METHODS: CYP2D6-mediated O-demethylation and CYP3A4-mediated N-demethylation of dextromethorphan (DEX) to dextrorphan (DOR) and 3-methoxymorphinan (3-MM), respectively, were utilized to assess the metabolic activities of the two enzymatic pathways. In the in vitro experiments, DEX was incubated with microsomes and NADPH in absence or presence of black seed extract (10-100 microg/ml) and the formation of the metabolites were measured by HPLC. In the clinical study, four healthy volunteers received a single oral dose of DEX 30 mg alone in phase I, and along with last dose of black seed (2.5 g twice daily for seven days) in phase II. Activities of the two enzymes were evaluated based on the urinary metabolic ratios (MRs), which were calculated from eight-hour urine collections. DEX and its metabolites were assayed in urine samples by HPLC following a liquid-liquid extraction. RESULTS: Black seed extracts significantly inhibited the formation of both metabolites in microsomes. The maximum inhibition was observed at the highest extract concentration (i.e., 100 microg/ml), which was about 80% and 60% for DOR and 3-MM, respectively. In the clinical study, the urinary MRs of DEX/DOR and DEX/3-MM increased by factors of 127 and 1.6-fold, respectively, after consumption of black seed. CONCLUSION: Black seed significantly inhibited CYP2D6 and CYP3A4 mediated metabolism of DEX in human liver microsomes and healthy human volunteers indicating that it has the potential to interact with CYP2D6 and CYP3A4 substrates.