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Drug Binding (drug + binding)
Terms modified by Drug Binding Selected AbstractsBlood,brain barrier damage and brain penetration of antiepileptic drugs: Role of serum proteins and brain edemaEPILEPSIA, Issue 4 2009Nicola Marchi Summary Purpose:, Increased blood,brain barrier (BBB) permeability is radiologically detectable in regions affected by drug-resistant epileptogenic lesions. Brain penetration of antiepileptic drugs (AEDs) may be affected by BBB damage. We studied the effects of BBB damage on brain distribution of hydrophilic [deoxy-glucose (DOG) and sucrose] and lipophilic (phenytoin and diazepam) molecules. We tested the hypothesis that lipophilic and hydrophilic drug distribution is differentially affected by BBB damage. Methods:, In vivo BBB disruption (BBBD) was performed in rats by intracarotid injection of hyperosmotic mannitol. Drugs (H3-sucrose, 3H-deoxy-glucose, 14C-phenytoin, and C14-diazepam) or unlabeled phenytoin was measured and correlated to brain water content and protein extravasation. In vitro hippocampal slices were exposed to different osmolarities; drug penetration and water content were assessed by analytic and densitometric methods, respectively. Results:, BBBD resulted in extravasation of serum protein and radiolabeled drugs, but was associated with no significant change in brain water. Large shifts in water content in brain slices in vitro caused a small effect on drug penetration. In both cases, total drug permeability increase was greater for lipophilic than hydrophilic compounds. BBBD reduced the amount of free phenytoin in the brain. Discussion:, After BBBD, drug binding to protein is the main controller of total brain drug accumulation. Osmotic BBBD increased serum protein extravasation and reduced free phenytoin brain levels. These results underlie the importance of brain environment and BBB integrity in determining drug distribution to the brain. If confirmed in drug-resistant models, these mechanisms could contribute to drug brain distribution in refractory epilepsies. [source] Comparison of the inward- and outward-open homology models and ligand binding of human P-glycoproteinFEBS JOURNAL, Issue 23 2009Ilza K. Pajeva An homology model of human P-glycoprotein, based on the X-ray structure of the recently resolved mouse P-glycoprotein, is presented. The model corresponds to the inward-facing conformation competent for drug binding. From the model, the residues involved in the protein-binding cavity are identified and compared with those in the outward-facing conformation of human P-glycoprotein developed previously based on the Sav1866 structure. A detailed analysis of the interactions of the cyclic peptides QZ59- RRR and QZ59- SSS is presented in both the X-ray structures of mouse P-glycoprotein and the human P-glycoprotein model generated by ligand docking. The results confirm the functional role of transmembrane domains TM4, TM6, TM10 and TM12 as entrance gates to the protein cavity, and also imply differences in their functions. The analysis of the cavities in both models suggests that the ligands remain bound to the same residues during the transition from the inward- to the outward-facing conformations. The analysis of the ligand,protein interactions in the X-ray complexes shows differences in the residues involved, as well as in the specific interactions performed by the same ligand within the same protein. This observation is supported by docking of the QZ59 ligands into human P-glycoprotein, thus aiding in the understanding of the complex behavior of P-glycoprotein substrates and inhibitors. The results confirm the possibility for multispecific drug interactions of the protein, and are important for elucidating the P-glycoprotein function and ligand interactions. [source] Allosteric modulation of anti-HIV drug and ferric heme binding to human serum albuminFEBS JOURNAL, Issue 24 2005Alessio Bocedi Human serum albumin (HSA), the most prominent protein in plasma, is best known for its exceptional capacity to bind ligands (e.g. heme and drugs). Here, binding of the anti-HIV drugs abacavir, atazanavir, didanosine, efavirenz, emtricitabine, lamivudine, nelfinavir, nevirapine, ritonavir, saquinavir, stavudine, and zidovudine to HSA and ferric heme,HSA is reported. Ferric heme binding to HSA in the absence and presence of anti-HIV drugs was also investigated. The association equilibrium constant and second-order rate constant for the binding of anti-HIV drugs to Sudlow's site I of ferric heme,HSA are lower by one order of magnitude than those for the binding of anti-HIV drugs to HSA. Accordingly, the association equilibrium constant and the second-order rate constant for heme binding to HSA are decreased by one order of magnitude in the presence of anti-HIV drugs. In contrast, the first-order rate constant for ligand dissociation from HSA is insensitive to anti-HIV drugs and ferric heme. These findings represent clear-cut evidence for the allosteric inhibition of anti-HIV drug binding to HSA by the heme. In turn, anti-HIV drugs allosterically impair heme binding to HSA. Therefore, Sudlow's site I and the heme cleft must be functionally linked. [source] Designed Multifunctional Nanocomposites for Biomedical ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Humphrey H. P. Yiu Abstract The assembly of multifunctional nanocomposite materials is demonstrated by exploiting the molecular sieving property of SBA-16 nanoporous silica and using it as a template material. The cages of the pore networks are used to host iron oxide magnetic nanoparticles, leaving a pore volume of 0.29,cm3,g,1 accessible for drug storage. This iron oxide,silica nanocomposite is then functionalized with amine groups. Finally the outside of the particle is decorated with antibodies. Since the size of many protein molecules, including that of antibodies, is too large to enter the pore system of SBA-16, the amine groups inside the pores are preserved for drug binding. This is proven using a fluorescent protein, fluorescein-isothiocyanate-labeled bovine serum albumin (FITC-BSA), with the unreacted amine groups inside the pores dyed with rhodamine B isothiocyanate (RITC). The resulting nanocomposite material offers a dual-targeting drug delivery mechanism, i.e., magnetic and antibody-targeting, while the functionalization approach is extendable to other applications, e.g., fluorescence,magnetic dual-imaging diagnosis. [source] Extracellular Acidosis Modulates Drug Block of Kv4.3 Currents by Flecainide and QuinidineJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 6 2003Suresh Singarayar M.D. Introduction: As a molecular model of the effect of ischemia on drug block of the transient outward potassium current, the effect of acidosis on the blocking properties of flecainide and quinidine on Kv4.3 currents was studied. Methods and Results: Kv4.3 channels were stably expressed in Chinese hamster ovary cells. Whole-cell, voltage clamp techniques were used to measure the effect of flecainide and quinidine on Kv4.3 currents in solutions of pH 7.4 and 6.0. Extracellular acidosis attenuated flecainide block of Kv4.3 currents, with the IC50 for flecainide (based on current-time integrals) increasing from7.8 ± 1.1 ,Mat pH 7.4 to125.1 ± 1.1 ,Mat pH 6.0. Similar effects were observed for quinidine (IC50 5.2 ± 1.1 ,Mat pH 7.4 and22.1 ± 1.3 ,Mat pH 6.0). Following block by either drug, Kv4.3 channels showed a hyperpolarizing shift in the voltage sensitivity of inactivation and a slowing in the time to recover from inactivation/block that was unaffected by acidosis. In contrast, acidosis attenuated the effects on the time course of inactivation and the degree of tonic- and frequency-dependent block for both drugs. Conclusion: Extracellular acidosis significantly decreases the potency of blockade of Kv4.3 by both flecainide and quinidine. This change in potency may be due to allosteric changes in the channel, changes in the proportion of uncharged drug, and/or changes in the kinetics of drug binding or unbinding. These findings are in contrast to the effects of extracellular acidosis on block of the fast sodium channel by these agents and provide a molecular mechanism for divergent modulation of drug block potentially leading to ischemia-associated proarrhythmia.(J Cardiovasc Electrophysiol, Vol. 14, pp. 641-650, June 2003) [source] On the possibility of self-induction of drug protein bindingJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2010Leonid M. Berezhkovskiy Abstract The equilibrium unbound drug fraction (fu) is an important pharmacokinetic parameter, which influences drug elimination and distribution in the body. Commonly the drug plasma concentration is substantially less then that of drug binding proteins, so that fu can be assumed constant independent of drug concentration. A general consideration of protein binding based on the mass-action law provides that the unbound drug fraction increases with the increase of drug concentration, which is also a usual experimental observation. For several drugs, though, a seemingly unusual sharp decrease of the unbound drug fraction with the increase of total drug concentration (Ro) in the interval 0,<,Ro,,,5,µM was experimentally observed. A possible explanation of this apparently strange phenomenon is presented. The explanation is based on the consideration of a two-step mechanism of drug protein binding. The first step occurs as a drug binding to the site with relatively low affinity. Consequently this binding leads to the activation of a high affinity site, which otherwise is not available for binding. The suggested binding scheme yields the curves for fu dependence on the total drug concentration that are in good agreement with experimental measurements. The interpretation of pharmacokinetic data for the drugs with such unusual concentration dependence of fu appears to be a formidable problem. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4400,4405, 2010 [source] On the calculation of the concentration dependence of drug binding to plasma proteins with multiple binding sites of different affinities: Determination of the possible variation of the unbound drug fraction and calculation of the number of binding sites of the proteinJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2007Leonid M. Berezhkovskiy Abstract The measurement of the unbound drug fraction in plasma is routinely performed at drug concentrations much less than that of plasma proteins. Commonly, the protein has several binding sites of different affinities. The obtained value of the unbound drug fraction does not yield the affinity of each binding site separately. For drug binding to a single type of protein, it is shown that the assumption that all binding sites of the protein have the same affinity yields the slowest possible concentration increase of the unbound drug fraction, while the assumption that a drug binds to a single binding site yields the highest possible value of the unbound fraction for a given drug concentration. The conditions to be imposed on the affinities of binding sites, to provide the fastest and the slowest possible concentration increase of the unbound drug fraction are also obtained for the case of drug binding to several types of plasma proteins. The suggested approach is applied to the determination of the number of binding sites of the protein from the measured values of the unbound drug fraction at different drug concentrations. ©2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:249,257, 2007 [source] The evolutionarily conserved residue A653 plays a key role in HERG channel closingTHE JOURNAL OF PHYSIOLOGY, Issue 11 2009Svetlana Z. Stepanovic Human ether-a-go-go- related gene (HERG) encodes the rapid, outwardly rectifying K+ current IKr that is critical for repolarization of the cardiac action potential. Congenital HERG mutations or unintended pharmaceutical block of IKr can lead to life-threatening arrhythmias. Here, we assess the functional role of the alanine at position 653 (HERG-A653) that is highly conserved among evolutionarily divergent K+ channels. HERG-A653 is close to the ,glycine hinge' implicated in K+ channel opening, and is flanked by tyrosine 652 and phenylalanine 656, which contribute to the drug binding site. We substituted an array of seven (I, C, S, G, Y, V and T) amino acids at position 653 and expressed individual variants in heterologous systems to assess changes in gating and drug binding. Substitution of A653 resulted in negative shifts of the V1/2 of activation ranging from ,23.6 (A653S) to ,62.5 (A653V) compared to ,11.2 mV for wild-type (WT). Deactivation was also drastically altered: channels with A653I/C substitutions exhibited delayed deactivation in response to test potentials above the activation threshold, while A653S/G/Y/V/T failed to deactivate under those conditions and required hyperpolarization and prolonged holding potentials at ,130 mV. While A653S/G/T/Y variants showed decreased sensitivity to the IKr inhibitor dofetilide, these changes could not be correlated with defects in channel closure. Homology modelling suggests that in the closed state, A653 forms tight contacts with several residues from the neighbouring subunit in the tetramer, playing a key role in S6 helix packing at the narrowest part of the vestibule. Our study suggests that A653 plays an important functional role in the outwardly rectifying gating behaviour of HERG, supporting channel closure at membrane potentials negative to the channel activation threshold. [source] Molecular impact of MinK on the enantiospecific block of IKs by chromanolsBRITISH JOURNAL OF PHARMACOLOGY, Issue 8 2000C Lerche Slowly activating IKs (KCNQ1/MinK) channels were expressed in Xenopous oocytes and their sensitivity to chromanols was compared to homomeric KCNQ1 channels. To elucidate the contribution of the ,-subunit MinK on chromanol block, a formerly described chromanol HMR 1556 and its enantiomer S5557 were tested for enantio-specificity in blocking IKs and KCNQ1 as shown for the single enantiomers of chromanol 293B. Both enantiomers blocked homomeric KCNQ1 channels to a lesser extent than heteromeric IKs channels. Furthermore, we expressed both WT and mutant MinK subunits to examine the involvement of particular MinK protein regions in channel block by chromanols. Through a broad variety of MinK deletion and point mutants, we could not identify amino acids or regions where sensitivity was abolished or strikingly diminished (>2.5 fold). This could indicate that MinK does not directly take part in chromanol binding but acts allosterically to facilitate drug binding to the principal subunit KCNQ1. British Journal of Pharmacology (2000) 131, 1503,1506; doi:10.1038/sj.bjp.0703734 [source] Modeling hERG and its Interactions with Drugs: Recent Advances in Light of Current Potassium Channel SimulationsCHEMMEDCHEM, Issue 4 2008Maurizio Recanatini Prof. Abstract The hERG K+ channel is responsible for the rapid delayed rectifier current in cardiac myocytes, and a block of its functioning may be related with the (inherited or drug-induced) long QT syndrome. For this reason, in recent times, some interest has arisen around computational studies aimed at developing hERG/drug models for the prediction of drug binding (docking) modes, in view of the assessment of the hERG blocking potential. On the other hand, voltage-gated K+ channels have been the subject of molecular simulations for several years, and rigorous protocols for studying the main aspects of their functions (permeation, gating, voltage sensing) have been published. In this article, we briefly introduce these classical computational works on K+ channels, and then review in depth the reports on the latest advanced modeling studies on hERG. The aim is to put the hERG modeling work in the more general context of the ion channel simulations field, to show the peculiarity of hERG on the one side, and also to indicate some possible new avenues in the use of modeling techniques to increase our knowledge of this important channel. [source] | |||||||||||||