Effects of enzyme inducers and inhibitors on the pharmacokinetics of metformin in rats: involvement of CYP2C11, 2D1 and 3A1/2 for the metabolism of metformin

METFORMIN: FROM DIABETES TO CANCER TO PROLONGATION OF LIFE

The metformin molecule dates back to over a century, but its clinical use started in the '50s. Since then, its use in diabetics has grown constantly, with over 150 million users today. The therapeutic profile also expanded, with improved understanding of novel mechanisms. Metformin has a major activity on insulin resistance, by acting on the insulin receptors and mitochondria, most likely by activation of the adenosine monophosphate-activated kinase. These and associated mechanisms lead to significant lipid lowering and body weight loss. An anti-cancer action has come up in recent years, with mechanisms partly dependent on the mitochondrial activity and also on phosphatidylinositol 3-kinase resistance occurring in some malignant tumors. The potential of metformin to raise life-length is the object of large ongoing studies and of several basic and clinical investigations. The present review article will attempt to investigate the basic mechanisms behind these diverse activities and the potential clinical benefits. Metformin may act on transcriptional activity by histone modification, DNA methylation and miRNAs. An activity on age-associated inflammation (inflammaging) may occur via activation of the nuclear factor erythroid 2 related factor and changes in gut microbiota. A senolytic activity, leading to reduction of cells with the senescent associated secretory phenotype, may be crucial in lifespan prolongation as well as in ancillary properties in age-associated diseases, such as Parkinson's disease. Telomere prolongation may be related to the activity on mitochondrial respiratory factor 1 and on peroxisome gamma proliferator coactivator 1-alpha. Very recent observations on the potential to act on the most severe neurological disorders, such as amyotrophic lateral sclerosis and frontotemporal dementia, have raised considerable hope.

Mechanisms and effects of metformin on skeletal muscle disorders

Skeletal muscle disorders are mostly genetic and include several rare diseases. With disease progression, muscle fibrosis and adiposis occur, resulting in limited mobility. The long course of these diseases combined with limited treatment options affect patients both psychologically and economically, hence the development of novel treatments for neuromuscular diseases is crucial to obtain a better quality of life. As a widely used hypoglycemic drug in clinical practice, metformin not only has anti-inflammatory, autophagy-regulating, and mitochondrial biogenesis-regulating effects, but it has also been reported to improve the symptoms of neuromuscular diseases, delay hypokinesia, and regulate skeletal muscle mass. However, metformin's specific mechanism of action in neuromuscular diseases requires further elucidation. This review summarizes the evidence showing that metformin can regulate inflammation, autophagy, and mitochondrial biogenesis through different pathways, and further explores its mechanism of action in Duchenne muscular dystrophy, statin-associated muscle disorders, and age-related sarcopenia. This review clarifies the directions of future research on therapy for neuromuscular diseases.

Metformin-loaded nanoerythrosomes: An erythrocyte-based drug delivery system as a therapeutic tool for glioma

Glioma is an intra-cranial malignancy with the origin of neural stem cells or precursor cells, the most prevalent brain tumor worldwide. Glioblastoma, the fourth-grade glioma, is a common brain tumor whose incidence rate is 5-7 people per 100,000 populations annually. Despite their high mortality rate, all efforts for treatment have yet to achieve any desirable clinical outcome. The Wnt signaling pathway is a conserved pathway among species that seems to be a candidate for cancer therapy by its inhibition. Metformin is a known inhibitor of the Wnt signaling pathway. Its effects on glioma treatment have been observed in cellular, animal, and clinical experiments. Nanoerythrosomes are drug carriers obtained from the cellular membrane of red blood cells in nano size which can offer several characteristics to deliver metformin to brain tumors. They are good at loading and carrying hydrophilic drugs, they can protect metformin from its metabolizing enzymes, which are present in the blood-brain barrier, and they can extend the period of metformin presence in circulation. In this study, nanoerythrosomes were prepared by using the hypotonic buffer. They had particle sizes in the range of 97.1 ± 34.2 nm, and their loading efficiency and loading capacity were 72.6% and 1.66%, respectively. Nanoerythrosomes could reserve metformin in their structure for a long time, and only 50% of metformin was released after 30 h. Moreover, they released metformin at a low and approximately constant rate. Besides, nanoerythrosomes could tolerate various kinds of stress and maintain most of the drug in their structure. Altogether, nanoerythrosome can be a suitable drug delivery system to deliver therapeutic amounts of metformin to various tissues.

Impact of Pomegranate Juice on the Pharmacokinetics of CYP3A4- and CYP2C9-Mediated Drugs Metabolism: A Preclinical and Clinical Review

The Punica granatum L. (pomegranate) fruit juice contains large amounts of polyphenols, mainly tannins such as ellagitannin, punicalagin, and punicalin, and flavonoids such as anthocyanins, flavan-3-ols, and flavonols. These constituents have high antioxidant, anti-inflammatory, anti-diabetic, anti-obesity, and anticancer activities. Because of these activities, many patients may consume pomegranate juice (PJ) with or without their doctor's knowledge. This may raise any significant medication errors or benefits because of food-drug interactions that modulate the drug's pharmacokinetics or pharmacodynamics. It has been shown that some drugs exhibited no interaction with pomegranate, such as theophylline. On the other hand, observational studies reported that PJ prolonged the pharmacodynamics of warfarin and sildenafil. Furthermore, since it has been shown that pomegranate constituents inhibit cytochrome P450 (CYP450) activities such as CYP3A4 and CYP2C9, PJ may affect intestinal and liver metabolism of CYP3A4 and CYP2C9-mediated drugs. This review summarizes the preclinical and clinical studies that investigated the impact of oral PJ administration on the pharmacokinetics of drugs that are metabolized by CYP3A4 and CYP2C9. Thus, it will serve as a future road map for researchers and policymakers in the fields of drug-herb, drug-food and drug-beverage interactions. Preclinical studies revealed that prolonged administration of PJ increased the absorption, and therefore the bioavailability, of buspirone, nitrendipine, metronidazole, saquinavir, and sildenafil via reducing the intestinal CYP3A4 and CYP2C9. On the other hand, clinical studies are limited to a single dose of PJ administration that needs to be protocoled with prolonged administration to observe a significant interaction.

Meta-Assessment of Metformin Absorption and Disposition Pharmacokinetics in Nine Species

The objective of this study was to systematically assess literature datasets and quantitatively analyze metformin PK in plasma and some tissues of nine species. The pharmacokinetic (PK) parameters and profiles of metformin in nine species were collected from the literature. Based on a simple allometric scaling, the systemic clearances (CL) of metformin in these species highly correlate with body weight (BW) (R2 = 0.85) and are comparable to renal plasma flow in most species except for rabbit and cat. Reported volumes of distribution (VSS) varied appreciably (0.32 to 10.1 L/kg) among species. Using the physiological and anatomical variables for each species, a minimal physiologically based pharmacokinetic (mPBPK) model consisting of blood and two tissue compartments (Tissues 1 and 2) was used for modeling metformin PK in the nine species. Permeability-limited distribution (low fd1 and fd2) and a single tissue-to-plasma partition coefficient (Kp) value for Tissues 1 and 2 were applied in the joint mPBPK fitting. Nonlinear regression analysis for common tissue distribution parameters along with species-specific CL values reasonably captured the plasma PK profiles of metformin across most species, except for rat and horse with later time deviations. In separate fittings of the mPBPK model to each species, Tissue 2 was considered as slowly-equilibrating compartment consisting of muscle and skin based on in silico calculations of the mean transit times through tissues. The well-fitted mPBPK model parameters for absorption and disposition PK of metformin for each species were compared with in vitro/in vivo results found in the literature with regard to the physiological details and physicochemical properties of metformin. Bioavailability and absorption rates decreased with the increased BW among the species. Tissues such as muscle dominate metformin distribution with low permeability and partitioning while actual tissue concentrations found in rats and mice show likely transporter-mediated uptake in liver, kidney, and gastrointestinal tissues. Metformin has diverse pharmacologic actions, and this assessment revealed allometric relationships in its absorption and renal clearance but considerable variability in actual and modeled tissue distribution probably caused by transporter differences.

Pharmacokinetics of metformin in collagen-induced arthritis rats

Due to the elevated presence of cytokines, the expressions of metabolic enzymes and drug transporters are altered in rheumatoid arthritis (RA). Given the high incidence of diabetes in patients with RA, the aim of the present study was to investigate the metformin pharmacokinetics of a single oral dose in rats with collagen-induced arthritis (CIA). Blood and urine samples were collected at different timepoints, and analyzed by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Tissue samples were also collected to investigate the expression of metabolic enzymes and drug transporters by quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and western blot. The results indicated that the bioavailability of metformin was markedly decreased in the CIA rats. Moreover, metformin was not metabolized by enzymes of rat liver microsomes, suggesting that the decreased bioavailability of metformin was independent of the liver metabolism. In addition, the mRNA, protein expression level and activity of the renal organic cation transporter 2 (OCT2) was markedly increased, suggesting that the enhanced renal clearance of metformin in CIA rats may be due to the up-regulated activity of OCT2. In conclusion, our study suggested that the reduced bioavailability of metformin in CIA rats is possibly related to the up-regulated function of the renal protein OCT2.

Enhanced Intestinal Permeability and Plasma Concentration of Metformin in Rats by the Repeated Administration of Red Ginseng Extract

We aimed to assess the potential herb-drug interactions between Korean red ginseng extract (RGE) and metformin in rats in terms of the modulation of metformin transporters, such as organic cation transporter (Oct), multiple toxin and extrusion protein (Mate), and plasma membrane monoamine transporter (Pmat). Single treatment of RGE did not inhibit the in vitro transport activity of OCT1/2 up to 500 µg/mL and inhibited MATE1/2-K with high IC₅₀ value (more than 147.8 µg/mL), suggesting that concomitant used of RGE did not directly inhibit OCT- and MATE-mediated metformin uptake. However, 1-week repeated administration of RGE (1.5 g/kg/day) (1WRA) to rats showed different alterations in mRNA levels of Oct1 depending on the tissue type. RGE increased intestinal Oct1 but decreased hepatic Oct1. However, neither renal Oct1/Oct2 nor Mate1/Pmat expression in duodenum, jejunum, ileum, liver, and kidney were changed in 1WRA rats. RGE repeated dose also increased the intestinal permeability of metformin; however, the permeability of 3-O-methyl-d-glucose and Lucifer yellow was not changed in 1WRA rats, suggesting that the increased permeability of metformin by multiple doses of RGE is substrate-specific. On pharmacokinetic analysis, plasma metformin concentrations following intravenous injection were not changed in 1WRA, consistent with no significant change in renal Oct1, Oct2, and mate1. Repeated doses of RGE for 1 week significantly increased the plasma concentration of metformin, with increased half-life and urinary excretion of metformin following oral administration of metformin (50 mg/kg), which could be attributed to the increased absorption of metformin. In conclusion, repeated administration of RGE showed in vivo pharmacokinetic herb-drug interaction with metformin, with regard to its plasma exposure and increased absorption in rats. These results were consistent with increased intestinal Oct1 and its functional consequence, therefore, the combined therapeutic efficacy needs further evaluation before the combination and repeated administration of RGE and metformin, an Oct1 substrate drug.

A dosing algorithm for metformin based on the relationships between exposure and renal clearance of metformin in patients with varying degrees of kidney function

PURPOSE

The aims of this study were to investigate the relationship between metformin exposure, renal clearance (CL_R), and apparent non-renal clearance of metformin (CL_NR/F) in patients with varying degrees of kidney function and to develop dosing recommendations.

METHODS

Plasma and urine samples were collected from three studies consisting of patients with varying degrees of kidney function (creatinine clearance, CL_CR; range, 14-112 mL/min). A population pharmacokinetic model was built (NONMEM) in which the oral availability (F) was fixed to 0.55 with an estimated inter-individual variability (IIV). Simulations were performed to estimate AUC_0-τ, CL_R, and CL_NR/F.

RESULTS

The data (66 patients, 327 observations) were best described by a two-compartment model, and CL_CR was a covariate for CL_R. Mean CL_R was 17 L/h (CV 22%) and mean CL_NR/F was 1.6 L/h (69%).The median recovery of metformin in urine was 49% (range 19-75%) over a dosage interval. When CL_R increased due to improved renal function, AUC_0-τ decreased proportionally, while CL_NR/F did not change with kidney function. Target doses (mg/day) of metformin can be reached using CL_CR/3 × 100 to obtain median AUC_0-12 of 18-26 mg/L/h for metformin IR and AUC_0-24 of 38-51 mg/L/h for metformin XR, with C_max < 5 mg/L.

CONCLUSIONS

The proposed dosing algorithm can be used to dose metformin in patients with various degrees of kidney function to maintain consistent drug exposure. However, there is still marked IIV and therapeutic drug monitoring of metformin plasma concentrations is recommended.

Transcriptomic effects of metformin in skeletal muscle arteries of obese insulin-resistant rats

We examined the effects of metformin, a commonly used antidiabetic drug, on gene expression in multiple arteries. Specifically, transcriptional profiles of feed arteries and second branch order arterioles in the soleus, gastrocnemius, and diaphragm muscles as well as aortic endothelial scrapes were examined from obese insulin-resistant Otsuka Long-Evans Tokushima Fatty rats treated with ( n = 9) or without ( n = 10) metformin from 20 to 32 weeks of age. Metformin-treated rats exhibited a reduction in body weight, adiposity, and HbA1c ( P < 0.05). The greatest number of differentially expressed genes (FDR < 15%) between those treated with and without metformin was found in the red gastrocnemius 2a arterioles (93 genes), followed by the diaphragm 2a arterioles (62 genes), and soleus 2a arterioles (15 genes). We also found that two genes were differentially expressed in aortic endothelial cells (LETMD1 and HMGCS2, both downregulated), one gene in the gastrocnemius feed artery (BLNK, downregulated), and no genes in the soleus and diaphragm feed arteries and white gastrocnemius 2a arterioles. No single gene was altered by metformin across all vessels examined. This study provides evidence that metformin treatment produces distinct gene expression effects throughout the arterial tree in a rat model of obesity and insulin resistance. Genes whose expression was modulated with metformin do not appear to have a clear connection with its known mechanisms of action. These findings support the notion that vascular gene regulation in response to oral pharmacological therapy, such as metformin, is vessel specific. Impact statement This study provides evidence that metformin treatment produces artery-specific gene expression effects. The genes whose expression was modulated with metformin do not appear to have a clear connection with its known mechanisms of action.

Pharmacokinetics of metformin in the rat: assessment of the effect of hyperlipidemia and evidence for its metabolism to guanylurea

Metformin pharmacokinetics are highly dependent upon organic cationic transporters. There is evidence of a change in its renal clearance in hyperlipidemic obese patients, and no information on its metabolic fate. To study some of these aspects, the influence of poloxamer 407 (P407)-induced hyperlipidemia on metformin pharmacokinetics was assessed. Control and P407-treated adult male rats were administered 30 mg/kg metformin intravenously (i.v.). The pharmacokinetic assessments were performed at 2 time points, 36 and 108 h, following the intraperitoneal dose of P407 (1 g/kg). mRNA and protein expressions of cationic drug transporters were also measured. There was no evidence of a change in metformin pharmacokinetics after i.v. doses as a consequence of short-term hyperlipidemia, and a change in transporter mRNA but not protein expression was observed in the P407- treated rats 108 h after P407 injection. Urinary recovery of unchanged drug was high (>90%) but incomplete. Presumed metabolite peaks were detected in chromatograms of hepatocytes and microsomal protein spiked with metformin. Comparative chromatographic elution times and mass spectra suggested that one of the predominant metabolites was guanylurea. Hyperlipidemia by itself did not affect the pharmacokinetics of metformin. Guanylurea is a putative metabolite of metformin in rats.

Bio-enhancing Effect of Piperine with Metformin on Lowering Blood Glucose Level in Alloxan Induced Diabetic Mice

Background:

Diabetes mellitus is the most rampant metabolic pandemic of the 21^st century. Piperine, the chief alkaloid of Piper nigrum (black pepper) is widely used in alternative and complementary therapies has been extensively studied for its bio-enhancing property.

Objective:

To evaluate the bio-enhancing effect of piperine with metformin in lowering blood glucose levels in alloxan-induced diabetic mice.

Materials and Methods:

Piperine was isolated from an extract of fruits of P. nigrum. Alloxan-induced (150 mg/kg intraperitoneal) diabetic mice were divided into four groups. Group I (control 2% gum acacia 2 g/100 mL), Group II (metformin 250 mg/kg), Group III (metformin and piperine 250 mg/kg + 10 mg/kg), and Group IV (metformin and piperine 125 mg/kg + 10 mg/kg). All the drugs were administered orally once daily for 28 days. Blood glucose levels were estimated at day 0, day 14, and end of the study (day 28).

Results:

The combination of piperine with therapeutic dose of metformin (10 mg/kg + 250 mg/kg) showed significantly more lowering of blood glucose level as compared to metformin alone on both 14^th and 28^th day (P < 0.05). Piperine in combination with sub-therapeutic dose of metformin (10 mg/kg + 125 mg/kg) showed significantly more lowering of blood glucose as compared to control group and also showed greater lowering of blood glucose as compared to metformin (250 mg/kg) alone.

Conclusion:

Piperine has the potential to be used as a bio-enhancing agent in combination with metformin which can help reduce the dose of metformin and its adverse effects.

SUMMARY

Piperine is known for its bioenhancing property. This study evaluates the effect of piperine in combination with oral antidiabetic drug metformin. Drugs were administered for 28 days in alloxan induced diabetic mice and blood glucose lowering effect was seen. Results showed significantly better effect of combination of piperine with therapeutic dose of metformin in comparison to metformin alone. Piperine in combination with subtherapeutic dose of metformin also showed better effect than therapeutic dose of metformin. Piperine, thus shows potential to be used as bioenhancer in combination with metformin.

Advances in epilepsy treatment: lacosamide pharmacokinetic profile

Lacosamide (LCM) is a functionalized amino acid specifically developed for use as an antiepileptic drug (AED) and is currently indicated as adjunctive treatment for partial-onset seizures in adults with focal epilepsy (maximum approved dose 400 mg/day). Characterization of the pharmacokinetic profile is an important aspect in the development of LCM. Studies in healthy subjects and in patients with focal epilepsy have established that LCM has several favorable pharmacokinetic characteristics, including rapid absorption and high oral bioavailability not affected by food, linear and dose-proportional pharmacokinetics, low inter- and intraindividual variability, low plasma protein binding, renal elimination, and a low potential for clinically relevant pharmacokinetic drug-drug interactions both with AEDs and other common medications. Studies have demonstrated bioequivalence among the three LCM formulations (oral tablets, oral solution, and solution for intravenous (IV) infusion), allowing direct conversion to or from oral and IV administration without titration. Thus, the favorable and predictable pharmacokinetic profile and bioequivalence of LCM formulations, coupled with the low potential for clinically relevant pharmacokinetic drug-drug interactions, make LCM an easy-to-use adjunctive treatment for the management of patients with focal epilepsy.

Effects of Korean red ginseng extract on acute renal failure induced by gentamicin and pharmacokinetic changes by metformin in rats

AIM OF THE STUDY

Korean red ginseng is one of the best selling dietary supplements and its individual constituents enhance renal function. Acute renal failure (ARF) is a predisposing complication of diabetes mellitus as a result of combination drug therapy. The combination of antibiotic-antidiabetic drugs can entail toxicities and drug interactions because of the antibiotic resistance in patients with severe bacterial infection. Currently, gentamicin-metformin combination therapy is commonly prescribed for treating bacterial infections and diabetes, even though both drugs are mainly excreted via the kidney. Thus, this study was designed to investigate whether a Korean red ginseng extract (KRG) prevents renal impairment and pharmacokinetic changes by metformin in rats with renal failure induced by gentamicin.

MATERIALS AND METHODS

The in vivo pharmacokinetics and in vitro hepatic/intestinal metabolism of metformin were assessed using control (CON), control with Korean red ginseng extract (KRG-CON), acute renal failure induced by gentamicin (ARF), and ARF with Korean red ginseng (KRG-ARF) rats.

RESULTS AND CONCLUSIONS

Pharmacokinetic changes of metformin did not occur in KRG-ARF rats because KRG reduce the renal accumulation of gentamicin compared to ARF rats. Thus, KRG seemed to prevent acute renal failure induced by gentamicin treatment.

Reduced clearance of ε-acetamidocaproic acid in rats with acute renal failure induced by uranyl nitrate

Objectives

Anti-ulcer drugs are frequently used in patients with acute renal failure (ARF). Zinc acexamate is ionized to zinc and ε-acetamidocaproic acid and free EACA exerts a potent therapeutic effect in treating gastric or duodenal ulcers with few side effects. Thus, pharmacokinetic changes in rats with acute renal failure induced by uranyl nitrate (U-ARF rats) were investigated in this study.

Methods

The in-vivo pharmacokinetics and in-vitro hepatic/intestinal metabolism of EACA were assessed using control and U-ARF rats. The mechanism of urinary excretion of EACA was further investigated in rats.

Key findings

After intravenous and oral administration of zinc acexamate to U-ARF rats, there were significant increases in the values of the area under the curve (AUC) and decreases in the values for time-averaged renal and nonrenal clearances (Clr and Clnr, respectively) compared with control rats. Slower Clnr was partly due to a decrease in the metabolism in liver and/or intestine. Slower Clr could have been due to urine flow rate-dependent timed-interval renal clearance, decrease in organic anion transporter-mediated renal excretion (drug interaction with probenecid and decrease in the relative contribution of net secretion compared with glomerular filtration in U-ARF rats) and/or impaired kidney function.

Conclusions

The pharmacokinetics were significantly altered in U-ARF rats due to the changes in both the hepatic/intestinal metabolism and urinary excretion.

Silymarin regulates the cytochrome P450 3A2 and glutathione peroxides in the liver of streptozotocin-induced diabetic rats

This study aimed to investigate the protective and regulatory effects of silymarin (SMN) and melatonin (MEL) on streptozotocin (STZ)-induced diabetic changes in cytochrome P450 3A2 (CYP 3A2) and glutathione peroxidase (GPX) expression and antioxidant status in the liver. Male Wistar rats were divided into five groups, including: control (C), untreated diabetic animals (D), SMN-treated diabetics (S, 50 mg/kg, orally), MEL-treated diabetics (M, 10 mg/kg, i.p.), and SMN plus MEL-treated diabetics (S+M). Diabetes was induced by a single intraperitoneal injection of STZ (50 mg/kg). The blood glucose level, daily urinary volume and body weight changes were measured. After the 28 days treatment period, antioxidant status was analyzed by means of the determination of malondialdehyde (MDA) content, nitric oxide (NO) and total thiol molecules (TTM) levels in the liver. The glycogen depletion in the liver was examined by histochemical staining. The CYP 3A2 and GPX expression at mRNA level was determined using RT-PCT technique. SMN and MEL both individually or in combination prevented from diabetes-induced weight loss and lowered daily urinary volume significantly (p<0.05). None of the test compounds could lower the blood glucose level significantly (p>0.05). Both SMN and MEL could convert the diabetes induced elevated levels of MDA and NO and the diabetes-reduced TTM content to the control level. Moreover, the diabetes-up regulated CYP 3A2 and down regulated GPX, returned to normal values after SMN treatment. Histochemical and histopathological examinations revealed that the diabetes-induced glycogen-depletion and single cell necrosis markedly improved with the SMN and SMN plus MEL treatment. Our data suggest that the STZ-induced diabetes in addition of disturbing the antioxidant status, alters the expression levels of CYP 3A2 and GPX. Moreover, the SMN and SMN plus MEL treatment was able to normalize both the antioxidant status and the expression of CYP 3A2 and GPX in the liver of diabetic rats.

Pharmacokinetic and pharmacodynamic interaction between nifedipine and metformin in rats: competitive inhibition for metabolism of nifedipine and metformin by each other via CYP isozymes

It has been reported that hypertension exponentially increases in the patients with type 2 diabetes mellitus. Thus, this study was performed to investigate the pharmacokinetic and pharmacodynamic interactions between nifedipine and metformin, since both drugs were commonly metabolized via hepatic CYP2C and 3A subfamilies in rats. Nifedipine (3 mg/kg) and metformin (100 mg/kg) were simultaneously administered intravenously or orally to rats. Concentrations (I) of each drug in the liver and intestine, maximum velocity (V(max)), Michaelis-Menten constant (K(m)), and intrinsic clearance (CL(int)) for the disappearance of each drug, apparent inhibition constant (K(i)) and [I]/K(i) ratios of each drug in liver and intestine were determined. Also the metabolism of each drug in rat and human CYPs and blood pressure were also measured. After the simultaneous single intravenous administration of both drugs together, the AUCs of each drug were significantly greater than that in each drug alone due to the competitive inhibition for the metabolism of nifedipine by metformin via hepatic CYP3A1/2 and of metformin by nifedipine via hepatic CYP2C6 and 3A1/2. After the simultaneous single oral administration of both drugs, the significantly greater AUCs of each drug than that in each drug alone could have mainly been due to the competitive inhibition for the metabolism of nifedipine and metformin by each other via intestinal CYP3A1/2 in addition to competitive inhibition for the hepatic metabolism of each drug as same as the intravenous study.

Pharmacokinetic interaction between itraconazole and metformin in rats: competitive inhibition of metabolism of each drug by each other via hepatic and intestinal CYP3A1/2

BACKGROUND AND PURPOSE

Fungal infection is prevalent in patients with diabetes mellitus. Thus, we investigated whether a pharmacokinetic interaction occurs between the anti-fungal agent itraconazole and the anti-glycaemic drug metformin, as both drugs are commonly administered together to diabetic patients and are metabolized via hepatic CYP3A subfamily in rats.

EXPERIMENTAL APPROACH

Itraconazole (20 mg·kg(-1)) and metformin (100 mg·kg(-1)) were simultaneously administered i.v. and p.o. to rats. Concentrations (I) of each drug in the liver and intestine, maximum velocity (V(max)), Michaelis-Menten constant (K(m)) and intrinsic clearance (CL(int) ) for the disappearance of each drug, apparent inhibition constant (K(i) ) and [I]/K(i) ratios of each drug in the liver and intestine were determined. Also the metabolism of each drug in rat and human CYPs was measured in vitro.

KEY RESULTS

After simultaneous administration of both drugs, either i.v. or p.o., the total area under the plasma concentration-time curve from time zero to infinity (AUC)s of itraconazole and metformin were significantly greater than that of either drug administered alone. The metabolism of itraconazole and metformin was significantly inhibited by each other via CYP3A1 and 3A2 in rat and 3A4 in human microsomes.

CONCLUSIONS AND IMPLICATIONS

The significantly greater AUCs of itraconazole and metformin after i.v. administration of both drugs are probably due to competitive inhibition of the metabolism of each drug by each other via hepatic CYP3A1/2. Whereas after oral administration of both drugs, the significantly greater AUCs of each drug administered together than that of either drug alone is mainly due to competitive inhibition of intestinal metabolism of each drug by each other via intestinal CYP3A1/2.

Effects of cytochrome P450 (CYP) inducers and inhibitors on ondansetron pharmacokinetics in rats: involvement of hepatic CYP2D subfamily and 3A1/2 in ondansetron metabolism

The types of hepatic microsomal cytochrome P450 (CYP) isozymes responsible for the in-vivo metabolism of ondansetron in rats have not been reported. In this study, ondansetron at a dose of 8 mg kg−1 was administered intravenously to rats pretreated with various inducers of CYP isozymes, such as 3-methylcholanthrene, orphenadrine citrate, isoniazid and dexamethasone phosphate (the main inducers of CYP1A1/2, 2B1/2, 2E1 and 3A1/2 in rats, respectively), and inhibitors, such as SKF-525A (a non-specific inhibitor of CYP isozymes), sulfaphenazole, quinine hydrochloride and troleandomycin (the main inhibitors of CYP2C6, 2D subfamily and 3A1/2 in rats, respectively). In rats pretreated with quinine hydrochloride and troleandomycin, the time-averaged non-renal clearance of ondansetron was significantly slower (48.9 and 13.2% decrease, respectively) than that in control rats. In rats pretreated with dexamethasone phosphate, the time-averaged non-renal clearance was significantly faster (18.2% increase) than that in control rats. The results suggest that ondansetron is primarily metabolized via the CYP2D subfamily and 3A1/2 in rats.

Effects of cysteine on metformin pharmacokinetics in rats with protein-calorie malnutrition: partial restoration of some parameters to control levels

Metformin is metabolized primarily via hepatic microsomal cytochrome P450 (CYP)2C11, CYP2D1 and CYP3A1/2 in rats. The expression and mRNA levels of hepatic CYP2C11 and CYP3A1/2 are decreased in rats with protein-calorie malnutrition (PCM), but these levels are fully or partially restored to control levels in PMC rats by oral cysteine supplementation (PCMC rats). Thus, it would be expected that the pharmacokinetic parameters of metformin in PCM rats would be returned to control levels in PCMC rats. Metformin was administered i.v. (100 mg kg−1) and orally (100 mg kg−1) to control, CC (control rats with oral cysteine supplementation), PCM and PCMC rats. The following pharmacokinetic parameters of metformin following i.v. administration were restored from levels in PCM rats to levels in control rats in PCMC rats: intrinsic clearance (0.0350, 0.0309, 0.0253 and 0.0316 mL min−1 mg−1 protein for control, CC, PCM, and PCMC rats, respectively), total area under the plasma concentration-time curve from time zero to time infinity (AUC; 4110, 4290, 5540 and 4430 μg min mL−1, respectively), and time-averaged non-renal clearance (8.12, 7.95, 5.94 and 8.17 mL min−1 kg−1, respectively). AUC values following oral administration were comparable between control and PCMC rats (1520, 1480, 2290 and 1680 μg min mL−1, respectively).

Pharmacokinetics of itraconazole in diabetic rats

After intravenous or oral administration of 10 mg/kg itraconazole to rats with streptozotocin-induced diabetes mellitus and to control rats, the total area under the plasma concentration-time curve from time 0 to 24 h (AUC0-24) for itraconazole and that for its metabolite, 7-hydroxyitraconazole, were similar between the two groups of rats. This may be explained by the comparable hepatic and intestinal intrinsic clearance rates for the disappearance of itraconazole and the formation of 7-hydroxyitraconazole in both groups of rats.

Effects of cytochrome P450 inducers and inhibitors on the pharmacokinetics of intravenous furosemide in rats: involvement of CYP2C11, 2E1, 3A1 and 3A2 in furosemide metabolism

Objectives

It has been reported that the non-renal clearance of furosemide was significantly faster in rats pretreated with phenobarbital but was not altered in rats pretreated with 3-methylcholanthrene. However, no studies on other cytochrome P450 (CYP) isozymes have yet been reported in rats.

Method

Furosemide 20 mg/kg was administered intravenously to rats pretreated with various CYP inducers –3-methylcholanthrene, orphenadrine citrate and isoniazid, inducers of CYP1A1/2, 2B1/2 and 2E1, respectively, in rats – and inhibitors – SKF-525A (a nonspecific inhibitor of CYP isozymes), sulfaphenazole, cimetidine, quinine hydrochloride and troleandomycin, inhibitors of CYP2C6, 2C11, 2D and 3A1/2, respectively, in rats.

Key findings

The non-renal clearance of furosemide was significantly faster (55.9% increase) in rats pretreated with isoniazid, but slower in those pretreated with cimetidine or troleandomycin (38.5% and 22.7% decreases, respectively), than controls. After incubation of furosemide with baculovirus-infected insect cells expressing CYP2C11, 2E1, 3A1 or 3A2, furosemide was metabolized via CYP2C11, 2E1, 3A1 and 3A2.

Conclusions

These findings could help explain possible pharmacokinetic changes of furosemide in various rat disease models (where CYP2C11, 2E1, 3A1 and/or CYP3A2 are altered) and drug–drug interactions between furosemide and other drugs (mainly metabolized via CYP2C11, 2E1, 3A1 and/or 3A2).

Pharmacokinetics of drugs in rats with diabetes mellitus induced by alloxan or streptozocin: comparison with those in patients with type I diabetes mellitus

Objectives

In rats with diabetes mellitus induced by alloxan (DMIA) or streptozocin (DMIS), changes in the cytochrome P450 (CYP) isozymes in the liver, lung, kidney, intestine, brain, and testis have been reported based on Western blot analysis, Northern blot analysis, and various enzyme activities. Changes in phase II enzyme activities have been reported also. Hence, in this review, changes in the pharmacokinetics of drugs that were mainly conjugated and metabolized via CYPs or phase II isozymes in rats with DMIA or DMIS, as reported in various literature, have been explained. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized in the kidney, and that were excreted mainly via the kidney or bile in DMIA or DMIS rats were reviewed also. For drugs mainly metabolized via hepatic CYP isozymes, the changes in the total area under the plasma concentration–time curve from time zero to time infinity (AUC) of metabolites, AUCmetabolite/AUCparent drug ratios, or the time-averaged nonrenal and total body clearances (CLNR and CL, respectively) of parent drugs as reported in the literature have been compared.

Key findings

After intravenous administration of drugs that were mainly metabolized via hepatic CYP isozymes, their hepatic clearances were found to be dependent on the in-vitro hepatic intrinsic clearance (CLint) for the disappearance of the parent drug (or in the formation of the metabolite), the free fractions of the drugs in the plasma, or the hepatic blood flow rate depending on their hepatic extraction ratios. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized via the kidney in DMIA or DMIS rats were dependent on the drugs. However, the biliary or renal CL values of drugs that were mainly excreted via the kidney or bile in DMIA or DMIS rats were faster.

Summary

Pharmacokinetic studies of drugs in patients with type I diabetes mellitus were scarce. Moreover, similar and different results for drug pharmacokinetics were obtained between diabetic rats and patients with type I diabetes mellitus. Thus, present experimental rat data should be extrapolated carefully in humans.

Effects of cytochrome P450 inhibitors on the biotransformation of fluorogenic substrates by adult male rat liver microsomes and cDNA-expressed rat cytochrome P450 isoforms

We have evaluated the use of a panel of six fluorogenic cytochrome P450 (CYP) substrates as a potential tool for rapid screening for global changes in CYP activity in rats under different physiological conditions. The biotransformation of 3-[2-(N,N-diethyl-N-methylammonium)ethyl]-7-methoxy-4-methylcoumarin (AMMC), 7-benzyloxy-4-(trifluoromethyl)-coumarin, 7-benzyloxyquinoline, 3-cyano-7-ethoxycoumarin, 7-methoxy-4-(trifluoromethyl)-coumarin, and 7-ethoxy-4-trifluoromethyl-coumarin by microsomes from adult male rat liver were characterized, their sensitivities to 15 putative inhibitors were determined and compared to similar experiments using nine different complementary DNA (cDNA)-expressed rat CYPs. Inhibitory profiles of the substrates in microsomes were different from each other, with some overlap, suggesting that each substrate is to some extent biotransformed by a different CYP isoform. Ketoconazole and clotrimazole were nonselective inhibitors, while ticlopidine selectively inhibited biotransformation of AMMC. CYP2A1 did not biotransform any of the substrates, and CYP2E1 was insensitive to all the inhibitors tested. Some inhibitors did not affect the biotransformation of the fluorogenic substrates by cDNA-expressed isoforms as predicted by their effects on conventional substrates, e.g., chlorzoxazone and diethyldithiocarbamate were inactive against CYP2E1, and CYP2C6 was not inhibited by sulfaphenazole. When results in microsomes and cDNA-expressed CYPs were compared, only the majority of the biotransformation of AMMC by microsomes could be assigned with full confidence to a specific CYP isoform, namely CYP2D2. Nevertheless, different inhibitory profiles of the substrates indicate that the panel will be useful for rapid functional quantification of global CYP activity in rats under different experimental conditions. Our results also demonstrate the inappropriateness of extrapolating inhibitory data between conventional and fluorogenic CYP substrates.

Effects of water deprivation on drug pharmacokinetics: correlation between drug metabolism and hepatic CYP isozymes

Male Sprague-Dawley rats deprived of water for 72 h (a rat model of dehydration) showed no change in protein expression of the hepatic microsomal cytochrome P450 (CYP) 1A2, 2B1/2, 2C11, or 3A1/2, but an increase in protein expression (3-fold) and mRNA level (2.6-fold) of CYP2E1. Glucose feeding instead of food normalized CYP2E1 protein expression during dehydration. Here, we review how dehydration can change the pharmacokinetics of drugs reported in the literature via changing CYP isozyme levels. We also discuss how dehydration changes the pharmacokinetics of drugs that are metabolized via renal DHP-I, or are mainly excreted in the urine and bile, and form conjugates.

Effects of CYP inducers and inhibitors on the pharmacokinetics of intravenous theophylline in rats: involvement of CYP1A1/2 in the formation of 1,3-DMU

The types of hepatic cytochrome P450 (CYP) isozymes responsible for the metabolism of theophylline and for the formation of 1,3-dimethyluric acid (1,3-DMU) in rats in-vivo does not seem to have been studied at the dose ranges of dose-independent metabolic disposition of theophylline in rats (up to 10 mg kg(-1)). Therefore, theophylline (5 mg kg(-1)) was administered i.v. to male Sprague-Dawley rats pretreated with various inducers and inhibitors of CYP isozymes. In rats pretreated with 3-methylcholanthrene (3-MC), orphenadrine or dexamethasone (main inducers of CYP1A1/2, CYP2B1/2 and CYP3A1/2, respectively, in rats), the time-averaged non-renal clearance (CLNR) of theophylline was significantly faster than in their respective controls (1260, 42.7 and 69.0% increases, respectively). However, in rats pretreated with troleandomycin (a major inhibitor of CYP3A1/2 in rats), CLNR was significantly slower than in the controls (50.7% decrease). The 24 h urinary excretion of 1,3-DMU was increased significantly only in rats pretreated with 3-MC. The ratio of area under the curve for 1,3-DMU and theophylline (AUC1,3-DMU/AUCtheophylline) was increased significantly in rats pretreated with 3-MC (160% increase) and decreased significantly in rats pretreated with troleandomycin (50.1% decrease); however, the ratio was not increased in rats pretreated with dexamethasone. These data suggest that theophylline is primarily metabolized via CYP1A1/2, CYP2B1/2, and CYP3A1/2, and that 1,3-DMU is primarily formed via CYP1A1/2, and possibly CYP3A1/2, in rats.

Pharmacokinetic interaction between DA-8159, a new erectogenic, and metformin in rats: competitive inhibition of metabolism via hepatic CYP3A1/2

BACKGROUND AND PURPOSE

Erectile dysfunction is highly prevalent in diabetic patients and PDE V inhibitors are effective and safe for the treatment of erectile dysfunction in men with diabetes. Therefore, in this study we investigated whether a pharmacokinetic interaction occurs between DA-8159 and metformin, as both drugs are metabolized via hepatic CYP3A1/2 in rats.

EXPERIMENTAL APPROACH

DA-8159 (30 mg kg(-1)) and metformin (100 mg kg(-1)), both separately and together, were administered to rats either intravenously or orally. The V (max), K (m), CL(int), apparent inhibition constants (K (i)), [I]/K (i) and concentrations of each drug in the liver and intestine were then measured.

KEY RESULTS

After i.v. administration of both drugs simultaneously, the AUC of DA-8159 and metformin was significantly greater (21.2 and 33.9% increase for DA-8159 and metformin, respectively) than that of each drug alone. After p.o. administration of the drugs, the AUC of metformin was also significantly greater (20.7% increase) in the presence of DA-8159 than in its absence. However, the AUC of DA-8159 was similar in the absence and presence of metformin.

CONCLUSIONS AND IMPLICATIONS

The significantly greater AUC of metformin and DA-8159 after i.v. administration of both drugs and of metformin after p.o. administration of both drugs is probably due to competitive inhibition for the metabolism of these drugs via hepatic CYP3A1/2. However, the similar AUCs of DA-8159 in the absence and presence of metformin, after p.o. administration, indicates that the dose of metformin used was insufficient to inhibit the hepatic and intestinal metabolism of DA-8159.

Why insulin sensitizers but not secretagogues should be retained when initiating insulin in type 2 diabetes

The stringent targets set for HbA(1c) levels in type 2 diabetes are currently achieved by fewer than half the patients in the United States. Failure to manage hyperglycaemia in the early stages of disease results in progressive loss of beta-cell function, which ultimately necessitates the initiation of insulin therapy. At this point, choices have to be made on whether to continue oral anti-diabetic drug therapy and, if so, with which agent(s). Historically, sulfonylureas have been the mainstay of oral anti-diabetic drug therapy; however, their long-term efficacy in patients with depleted beta-cell capacity is doubtful, and other classes of oral anti-diabetic drugs, notably the insulin sensitizers, may prove more reliable. These agents (metformin and thiazolidinediones) appear to provide various benefits over and above sustained glycaemic control, which may variably include reduced loss of beta-cell function as well as improvements to cardiovascular risk factors, morbidity, and mortality. Metformin also limits weight gain associated with insulin therapy. This manuscript presents the case that when insulin therapy is initiated it should be tailored to individual needs through combination with one or more insulin sensitizers rather than a secretagogue.

Effects of bacterial lipopolysaccharide on the pharmacokinetics of metformin in rats

It was reported that the hepatic microsomal cytochrome P450 (CYP) 2C11, 2D1, and 3A1 (not via the CYP1A2, 2B1/2, and 2E1) were involved in the metabolism of metformin in rats. It was also reported that the expressions of CYP2C11 and 3A2 decreased in rats pretreated with Klebsiella pneumoniae lipopolysaccharide (KPLPS). Therefore, the pharmacokinetic parameters of metformin could be changed in rats pretreated with KPLPS. Hence, the pharmacokinetic parameters of metformin were compared after both intravenous and oral administration of the drug at a dose of 100mg/kg to control rats and rats pretreated with KPLPS. After intravenous administration of metformin to rats pretreated with KPLPS, the total area under the plasma concentration-time curve from time 0 to infinity (AUC) of the drug was significantly greater (40.5% increase) than the controls due to significantly smaller CL value (27.7% decrease) than the controls. The significantly smaller CL value could be due to significantly smaller both the CL(R) and CL(NR) values (34.0% and 18.1% decrease, respectively) than the controls. The significantly smaller CL(NR) value could be due to decrease in the expressions of CYP2C11 and 3A2 in rats pretreated with KPLPS. After oral administration of metformin, the AUC of the drug was not significantly different between two groups of rats, and this may be at least partly due to decrease in absorption from the gastrointestinal tract compared with the controls.

Dose-independent pharmacokinetics of metformin in rats: Hepatic and gastrointestinal first-pass effects

Pharmacokinetic parameters of metformin were evaluated after intravenous and oral administration (50, 100, and 200 mg/kg) in rats. The hepatic, gastric, and intestinal first-pass effects were also measured after intravenous, intraportal, intragastric, and intraduodenal administration (100 mg/kg) in rats. The total area under the plasma concentration-time curve from time zero to time infinity (AUC) values were dose-proportional after both intravenous and oral dose ranges studied. After oral administration (100 mg/kg), approximately 4.39% of oral dose was not absorbed and extent of absolute oral bioavailability (F) value was approximately 29.9%. The gastrointestinal first-pass effect of metformin was approximately 53.8% of oral dose in rats (the gastric and intestinal first-pass effects were approximately 23.1 and 30.7%, respectively), and the hepatic first-pass effect was approximately 27.1% after absorption into the portal vein. Since approximately 41.8% of oral metformin was absorbed into the portal vein, the value of 27.1% is equivalent to 11.3% of oral dose. The first-pass effects of metformin in the lung and heart were almost negligible in rats. The low F value of metformin in rats was mainly due to considerable gastrointestinal first-pass effects. The stability of metformin, distribution of metformin between plasma and blood cells, and factors affecting protein binding of metformin to 4% human serum albumin were also discussed.

Effects of water deprivation on the pharmacokinetics of metformin in rats

It was reported that metformin was mainly metabolized via hepatic CYP2C11, 2D1 and 3A1/2 in rats, and in a rat model of dehydration, the expressions of hepatic CYP2C11 and 3A1/2 were not changed. Hence, it could be expected that the Cl(nr) of metformin is comparable between two groups of rats if the contribution of CYP2D1 in the rat model of dehydration is not considerable. It was also reported that the timed-interval renal clearance of metformin was dependent on the urine flow rate in rats. In the rat model of dehydration, the 24 h urine output was significantly smaller than in the controls. Hence, the urinary excretion of metformin was expected to be smaller than the controls. The above expectations were proven as follows. After intravenous administration of metformin (100 mg/kg) to the rat model of dehydration, the Cl(nr) were comparable between the two groups of rats. After both intravenous and oral administration of metformin (both 100 mg/kg) to the rat model of dehydration, the 24 h urinary excretion of the drug was significantly smaller than in the controls. After oral administration of metformin to the rat model of dehydration, the AUC was significantly greater (99.2% increase) than the controls.