Pharmacokinetic interactions of pioglitazone

Pioglitazone is a thiazolidinedione compound used in the treatment of type 2 diabetes. It has been reported to be metabolised by multiple cytochrome P450 (CYP) enzymes, including CYP2C8, CYP2C9 and CYP3A4 in vitro. The aims of this work were to identify the CYP enzymes mainly responsible for the elimination of pioglitazone in order to evaluate its potential for in vivo drug interactions, and to investigate the effects of CYP2C8- and CYP3A4-inhibiting drugs (gemfibrozil, montelukast, zafirlukast and itraconazole) on the pharmacokinetics of pioglitazone in healthy volunteers. In addition, the effect of induction of CYP enzymes on the pharmacokinetics of pioglitazone in healthy volunteers was investigated, with rifampicin as a model inducer. Finally, the effect of pioglitazone on CYP2C8 and CYP3A enzyme activity was examined in healthy volunteers using repaglinide as a model substrate. Study I was conducted in vitro using pooled human liver microsomes (HLM) and human recombinant CYP isoforms. Studies II to V were randomised, placebo-controlled cross-over studies with 2-4 phases each. A total of 10-12 healthy volunteers participated in each study. Pretreatment with clinically relevant doses with the inhibitor or inducer was followed by a single dose of pioglitazone or repaglinide, whereafter blood and urine samples were collected for the determination of drug concentrations. In vitro, the elimination of pioglitazone (1 µM) by HLM was markedly inhibited, in particular by CYP2C8 inhibitors, but also by CYP3A4 inhibitors. Of the recombinant CYP isoforms, CYP2C8 metabolised pioglitazone markedly, and CYP3A4 also had a significant effect. All of the tested CYP2C8 inhibitors (montelukast, zafirlukast, trimethoprim and gemfibrozil) concentration-dependently inhibited pioglitazone metabolism in HLM. In humans, gemfibrozil raised the area under the plasma concentration-time curve (AUC) of pioglitazone 3.2-fold (P < 0.001) and prolonged its elimination half-life (t½) from 8.3 to 22.7 hours (P < 0.001), but had no significant effect on its peak concentration (Cmax) compared with placebo. Gemfibrozil also increased the excretion of pioglitazone into urine and reduced the ratios of the active metabolites M-IV and M-III to pioglitazone in plasma and urine. Itraconazole had no significant effect on the pharmacokinetics of pioglitazone and did not alter the effect of gemfibrozil on pioglitazone pharmacokinetics. Rifampicin decreased the AUC of pioglitazone by 54% (P < 0.001) and shortened its dominant t½ from 4.9 to 2.3 hours (P < 0.001). No significant effect on Cmax was observed. Rifampicin also decreased the AUC of the metabolites M-IV and M-III, shortened their t½ and increased the ratios of the metabolite to pioglitazone in plasma and urine. Montelukast and zafirlukast did not affect the pharmacokinetics of pioglitazone. The pharmacokinetics of repaglinide remained unaffected by pioglitazone. These studies demonstrate the principal role of CYP2C8 in the metabolism of pioglitazone in humans. Gemfibrozil, an inhibitor of CYP2C8, increases and rifampicin, an inducer of CYP2C8 and other CYP enzymes, decreases the plasma concentrations of pioglitazone, which can necessitate blood glucose monitoring and adjustment of pioglitazone dosage. Montelukast and zafirlukast had no effects on the pharmacokinetics of pioglitazone, indicating that their inhibitory effect on CYP2C8 is negligible in vivo. Pioglitazone did not increase the plasma concentrations of repaglinide, indicating that its inhibitory effect on CYP2C8 and CYP3A4 is very weak in vivo.

MIPS: metal interactions in protein structures

MIPS (metal interactions in protein structures) is a database of metals in the three-dimensional acromolecular structures available in the Protein Data Bank. Bound metal ions in proteins have both catalytic and structural functions. The proposed database serves as an open resource for the analysis and visualization of all metals and their interactions with macromolecular (protein and nucleic acid) structures. MIPS can be searched via a user-friendly interface, and the interactions between metals and protein molecules, and the geometric parameters, can be viewed in both textual and graphical format using the freely available graphics plug-in Jmol. MIPS is updated regularly, by means of programmed scripts to find metal-containing proteins from newly released protein structures. The database is useful for studying the properties of coordination between metals and protein molecules. It also helps to improve understanding of the relationship between macromolecular structure and function. This database is intended to serve the scientific community working in the areas of chemical and structural biology, and is freely available to all users, around the clock, at http://dicsoft2.physics.iisc.ernet.in/mips/.

Phage lambda beta protein, a component of general recombination, is associated with host ribosomal S1 protein

We have purified phage lambda beta protein produced by a recombinant plasmid carrying bet gene and confirm that it forms a complex with a protein of relative molecular mass 70 kDa. Therefore, beta protein, a component of general genetic recombination, is associated with two functionally diverse complexes; one containing exonuclease and the other 70 kDa protein. Using a number of independent methods, we show that 70 kDa protein is the ribosomal S1 protein of E. coli. Further, the association of 70 kDa protein with beta protein is biologically significant, as the former inhibits joining of the terminal ends of lambda chromosome and renaturation of complementary single stranded DNA promoted by the latter. More importantly, these findings initiate an understanding of an important mode of host- virus interaction in general with specific implication(s) in homologous genetic recombination.

Concise review: Humanized models of tumor immunology in the 21st century: Convergence of cancer research and tissue engineering

Despite positive testing in animal studies, more than 80% of novel drug candidates fail to proof their efficacy when tested in humans. This is primarily due to the use of preclinical models that are not able to recapitulate the physiological or pathological processes in humans. Hence, one of the key challenges in the field of translational medicine is to “make the model organism mouse more human.” To get answers to questions that would be prognostic of outcomes in human medicine, the mouse's genome can be altered in order to create a more permissive host that allows the engraftment of human cell systems. It has been shown in the past that these strategies can improve our understanding of tumor immunology. However, the translational benefits of these platforms have still to be proven. In the 21st century, several research groups and consortia around the world take up the challenge to improve our understanding of how to humanize the animal's genetic code, its cells and, based on tissue engineering principles, its extracellular microenvironment, its tissues, or entire organs with the ultimate goal to foster the translation of new therapeutic strategies from bench to bedside. This article provides an overview of the state of the art of humanized models of tumor immunology and highlights future developments in the field such as the application of tissue engineering and regenerative medicine strategies to further enhance humanized murine model systems.

Pharmacokinetic interactions affecting the antidiabetic repaglinide

Introduction Repaglinide is a short-acting drug, used to reduce postprandial hyperglycaemia in type 2 diabetic patients. Repaglinide is extensively metabolised, and its oral bioavailability is about 60%; its metabolites are mainly excreted into bile. In previous studies, the cytochrome P450 (CYP) 3A4 inhibitors itraconazole and clarithromycin have moderately increased the area under the concentration-time curve (AUC) of repaglinide. Gemfibrozil, a CYP2C8 inhibitor, has greatly increased repaglinide AUC, enhancing and prolonging its blood glucose-lowering effect. Rifampicin has decreased the AUC and effects of repaglinide. Aims The aims of this work were to investigate the contribution of CYP2C8 and CYP3A4 to the metabolism of repaglinide, and to study other potential drug interactions affecting the pharmacokinetics of repaglinide, and the mechanisms of observed interactions. Methods The metabolism of repaglinide was studied in vitro using recombinant human CYP enzymes and pooled human liver microsomes (HLM). The effect of trimethoprim, cyclosporine, bezafibrate, fenofibrate, gemfibrozil, and rifampicin on the metabolism of repaglinide, and the effect of fibrates and rifampicin on the activity of CYP2C8 and CYP3A4 were investigated in vitro. Randomised, placebo-controlled cross-over studies were carried out in healthy human volunteers to investigate the effect of bezafibrate, fenofibrate, trimethoprim, cyclosporine, telithromycin, montelukast and pioglitazone on the pharmacokinetics and pharmacodynamics of repaglinide. Pretreatment with clinically relevant doses of the study drug or placebo was followed by a single dose of repaglinide, after which blood and urine samples were collected to determine pharmacokinetic and pharmacodynamic parameters. Results In vitro, the contribution of CYP2C8 was similar to that of CYP3A4 in the metabolism of repaglinide (< 2 μM). Bezafibrate, fenofibrate, gemfibrozil, and rifampicin moderately inhibited CYP2C8 and repaglinide metabolism, but only rifampicin inhibited CYP3A4 in vitro. Bezafibrate, fenofibrate, montelukast, and pioglitazone had no effect on the pharmacokinetics and pharmacodynamics of repaglinide in vivo. The CYP2C8 inhibitor trimethoprim inhibited repaglinide metabolism by HLM in vitro and increased repaglinide AUC by 61% in vivo (P < .001). The CYP3A4 inhibitor telithromycin increased repaglinide AUC 1.8-fold (P < .001) and enhanced its blood glucose-lowering effect in vivo. Cyclosporine inhibited the CYP3A4-mediated (but not CYP2C8-mediated) metabolism of repaglinide in vitro and increased repaglinide AUC 2.4-fold in vivo (P < .001). The effect of cyclosporine on repaglinide AUC in vivo correlated with the SLCO1B1 (encoding organic anion transporting polypeptide 1, OATP1B1) genotype. Conclusions The relative contributions of CYP2C8 and CYP3A4 to the metabolism of repaglinide are similar in vitro, when therapeutic repaglinide concentrations are used. In vivo, repaglinide AUC was considerably increased by inhibition of both CYP2C8 (by trimethoprim) and CYP3A4 (by telithromycin). Cyclosporine raised repaglinide AUC even higher, probably by inhibiting the CYP3A4-mediated biotransformation and OATP1B1-mediated hepatic uptake of repaglinide. Bezafibrate, fenofibrate, montelukast, and pioglitazone had no effect on the pharmacokinetics of repaglinide, suggesting that they do not significantly inhibit CYP2C8 or CYP3A4 in vivo. Coadministration of drugs that inhibit CYP2C8, CYP3A4 or OATP1B1 may increase the plasma concentrations and blood glucose-lowering effect of repaglinide, requiring closer monitoring of blood glucose concentrations to avoid hypoglycaemia, and adjustment of repaglinide dosage as necessary.

Inter-helical Interactions in Membrane Proteins: Analysis Based on the Local Backbone Geometry and the Side Chain Interactions

The availability of a significant number of the Structures of helical membrane proteins has prompted us to investigate the mode of helix-helix packing. In the present study, we have considered a dataset of alpha-helical membrane proteins representing Structures solved from all the known superfamilies. We have described the geometry of all the helical residues in terms of local coordinate axis at the backbone level. Significant inter-helical interactions have been considered as contacts by weighing the number of atom-atom contacts, including all the side-chain atoms. Such a definition of local axis and the contact criterion has allowed us to investigate the inter-helical interaction in a systematic and quantitative manner. We show that a single parameter (designated as alpha), which is derived from the parameters representing the Mutual orientation of local axes, is able to accurately Capture the details of helix-helix interaction. The analysis has been carried Out by dividing the dataset into parallel, anti-parallel, and perpendicular orientation of helices. The study indicates that a specific range of alpha value is preferred for interactions among the anti-parallel helices. Such a preference is also seen among interacting residues of parallel helices, however to a lesser extent. No such preference is seen in the case of perpendicular helices, the contacts that arise mainly due to the interaction Of Surface helices with the end of the trans-membrane helices. The Study Supports the prevailing view that the anti-parallel helices are well packed. However, the interactions between helices of parallel orientation are non-trivial. The packing in alpha-helical membrane proteins, which is systematically and rigorously investigated in this study, may prove to be useful in modeling of helical membrane proteins.

Investigation of inter-ion interactions in N,N,N',N'-tetramethylethylenediammonium dithiocyanate via experimental and theoretical charge density studies

The crystal structure of the N,N,N',N'-tetramethylethylenediammonium dithiocyanate salt has been examined by experimental charge density studies from high-resolution X-ray diffraction data. The corresponding results are compared with multipole refinements, using theoretical structure factors obtained from a periodic density functional theory calculation at the B3LYP level with a 6-31G** basis set. The salt crystallizes in space group P (1) over bar and contains only a single ion pair with an inversion center in the cation. The salt has thus one unique classical N+-H center dot center dot center dot(NCS)(-) hydrogen bond but also has six other weaker interactions: four C-H center dot center dot center dot S, one C-H center dot center dot center dot N, and one C-H center dot center dot center dot C-pi. The nature of all these interactions has been examined topologically using Bader's quantum theory of "atoms in molecules" and all eight of the Koch-Popelier criteria. The experimental and theoretical approaches agree well and both show that the inter-ion interactions, even in this simplest of systems, play an integrated and complex role in the packing of the ions in the crystal. Electrostatic potential maps are derived from experimental charge densities. This is the first time such a system has been examined in detail by these methods.

Electromechanical interactions in a carbon nanotube based thin film field emitting diode

Carbon nanotubes (CNTs) have emerged as promising candidates for biomedical x-ray devices and other applications of field emission. CNTs grown/deposited in a thin film are used as cathodes for field emission. In spite of the good performance of such cathodes, the procedure to estimate the device current is not straightforward and the required insight towards design optimization is not well developed. In this paper, we report an analysis aided by a computational model and experiments by which the process of evolution and self-assembly (reorientation) of CNTs is characterized and the device current is estimated. The modeling approach involves two steps: (i) a phenomenological description of the degradation and fragmentation of CNTs and (ii) a mechanics based modeling of electromechanical interaction among CNTs during field emission. A computational scheme is developed by which the states of CNTs are updated in a time incremental manner. Finally, the device current is obtained by using the Fowler–Nordheim equation for field emission and by integrating the current density over computational cells. A detailed analysis of the results reveals the deflected shapes of the CNTs in an ensemble and the extent to which the initial state of geometry and orientation angles affect the device current. Experimental results confirm these effects.

Low-temperature Er3+ emission in Ge-S-Ga glasses excited by host absorption

The photoluminescence (PL) of a series of (GeS2)(80)(Ga2S3)(20) glasses doped with different amounts of Er (0.17, 0.35, 0.52, 1.05 and 1.39 at.%) at 77 and 4.2 K has been studied. The influence of the temperature on the emission cross-section of the PL bands at -> 1540, 980 and 820 nm under host excitation has been defined. A quenching effect of the host photoluminescence has been established from the compositional dependence of the PL intensity. It has been found that the present Er3+-doped Ge-S-Ga glasses posses PL lifetime values about 3.25 ms. (C) 2007 Elsevier B.V. All rights reserved.