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Different Affinities (different + affinity)
Selected AbstractsValidation of a modified Flory-Huggins concept for description of hydrophobic organic compound sorption on dissolved humic substancesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2002Anett Georgi Abstract Sorption coefficients(KDOC) on dissolved organic matter (DOM) have been determined by means of solid-phase microextraction (SPME) for hydrophobic organic compounds (HOCs) of various classes, for example, polycyclic aromatic hydrocarbons (PAHs), noncondensed arenes, and alkanes. Relating the KDOC values obtained to the octanol-water partition coefficients of the solutes results in class-specific correlations. Obviously, PAHs have a higher affinity to DOM than other HOCs with equal KOW values. The different KDOC to KOW correlations can be combined into one general formula based on a modified Flory-Huggins concept. It permits the calculation of sorption coefficients from the solubility parameters (,) and KOW values of the solutes and the solubility parameter of the sorbent. The latter value, which is specific to the DOM under consideration, can be determined from a single measured sorption coefficient. By applying the proposed Flory-Huggins concept, which is based on the presumption of nonspecific interactions between HOCs and DOM, the different affinities of PAHs, noncondensed arenes, and alkanes to DOM can be accurately predicted. [source] Pharmacological characterization of cis -nitromethylene neonicotinoids in relation to imidacloprid binding sites in the brown planthopper, Nilaparvata lugensINSECT MOLECULAR BIOLOGY, Issue 1 2010X. Xu Abstract Neonicotinoid insecticides, such as imidacloprid, are selective agonists of the insect nicotinic acetylcholine receptors (nAChRs) and extensively used in areas of crop protection and animal health to control a variety of insect pest species. Here we describe that two cis -nitromethylene neonicotinoids (IPPA152002 and IPPA152004), recently synthesized in our laboratory, discriminated between the high and low affinity imidacloprid binding sites in the brown planthopper, Nilaparvata lugens, a major insect pest of rice crops in many parts of Asia. [3H]imidacloprid has two binding sites with different affinities (Kd value of 0.0035 ± 0.0006 nM for the high-affinity site and 1.47 ± 0.22 nM for the low-affinity site). Although the cis -nitromethylene neonicotinoids showed low displacement ability (Ki values of 0.15 ± 0.03 µM and 0.42 ± 0.07 µM for IPPA152002 and IPPA152004, respectively) against [3H]imidacloprid binding, low concentrations (0.01 µM) of IPPA152002 completely inhibited [3H]imidacloprid binding at its high-affinity site. In Xenopus oocytes co-injected with cRNA encoding Nl,1 and rat ,2 subunits, obvious inward currents were detected in response to applications of IPPA152002 and IPPA152004, although the agonist potency is reduced to that of imidacloprid. The previously identified Y151S mutation in Nl,1 showed significant effects on the agonist potency of IPPA152002 and IPPA152004, such as a 75.8% and 70.6% reduction in Imax, and a 2.4- and 2.1-fold increase in EC50. This data clearly shows that the two newly described cis -nitromethylene neonicotinoids act on insect nAChRs and like imidacloprid, discriminated between high and low affinity binding sites in N. lugens native nAChRs. These compounds may be useful tools to further elucidate the pharmacology and nature of neonicotinoid binding sites. [source] Effects of antipsychotic medication on muscarinic M1 receptor mRNA expression in the rat brainJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2008Mei Han Abstract Alterations in muscarinic M1 receptor protein and mRNA expression have been revealed in post-mortem brains of schizophrenia patients. Most patients had been treated with antipsychotics, so medication effects cannot be excluded as a possible explanation for these results. With in situ hybridization, this study investigated M1 receptor mRNA expression in rats treated with the typical antipsychotic haloperidol (0.3 mg/kg/day) and the atypical antipsychotics olanzapine (1.5 mg/kg/day) and aripiprazole (2.25 mg/kg/day) for 1 or 12 weeks. Compared with the control group, haloperidol significantly increased (,13,21%, P < 0.05) M1 mRNA expression in the CA1, CA2, and CA3 regions of the hippocampus after both 1 and 12 weeks of treatment, and it also increased (,17%, P < 0.01) M1 mRNA expression in the substantia nigra compacta after 1 week of treatment. Olanzapine significantly increased (14,22%, P < 0.05) M1 mRNA expression in the hippocampus (CA1, CA2, and CA3) and substantia nigra compacta after 12 weeks of treatment, but not after 1 week. Aripiprazole significantly increased (17%, P < 0.01) M1 mRNA expression in the hippocampus (CA1) after both 1 and 12 week treatments and increased (12%, P < 0.05) M1 mRNA expression in the nucleus accumbens after 1 week of treatment. Despite their different affinities for muscarinic M1 receptors, all three antipsychotic medications induced a similar trend of change in M1 mRNA expression in selected brain regions. These data suggest that the decreased M1 receptor protein and mRNA expression observed in schizophrenia patients is unlikely to be a consequence of drug treatments and implicates muscarinic M1 receptors in the pharmacotherapy of the disease. © 2007 Wiley-Liss, Inc. [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] Combined use of nuclear magnetic resonance and infrared spectroscopy for studying recognition processes between amphenicolic antibiotics and albuminMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003Silvia Martini Abstract Biological reactions are mostly concerned with selective interactions between small ligands and macromolecular receptors. The same ligands may activate responses of different intensities and/or effects in the presence of different receptors. Many approaches based on spectroscopic and non-spectroscopic methods have been used to study interactions between small ligands and macromolecular receptors, including methods based on NMR and IR spectroscopic analysis of the solution behaviour of the ligand in the presence of receptors. In this work, we investigated the interaction between ovine serum albumin with two amphenicolic antibiotics [chloramphenicol (CAP) and thiamphenicol (TAP)], using a combined approach based on NMR and IR methodologies, furnishing complementary information about the recognition process occurring within the two systems. The two ligands, despite their similar structures, showed different affinities towards albumin. NMR methodology is based on the comparison of selective () and non-selective () spin,lattice relaxation rates of the ligands in the presence and absence of macromolecular receptors and and temperature dependence analysis. From these studies, the ligand,receptor binding strength was evaluated on the basis of the ,affinity index.' The derivation of the affinity index from chemical equilibrium kinetics for both the CAP,albumin and TAP,albumin systems allowed a comparison of the abilities of the two amphenicolic antibiotics to interact with the protein. IR methodology is based on the comparison of the ligand,protein ,complex' spectra with those of the non-interacting systems. On the basis of the differences revealed, a more thorough IR analysis was performed in order to understand the structural changes which occurred on both ligand and protein molecules within the interacting system. Copyright © 2003 John Wiley & Sons, Ltd. [source] Repression of virulence genes by phosphorylation-dependent oligomerization ofCsrR at target promoters in S. pyogenesMOLECULAR MICROBIOLOGY, Issue 4 2001Alita A. Miller csrRS encodes a two-component regulatory system that represses the transcription of a number of virulence factors in Streptococcus pyogenes, including the hyaluronic acid capsule and pyrogenic exotoxin B. CsrRS-regulated virulence factors have diverse functions during pathogenesis and are differentially expressed throughout growth. This suggests that multiple signals induce CsrRS-mediated gene regulation, or that regulated genes respond differently to CsrR, or both. As a first step in dissecting the csrRS signal transduction pathway, we determined the mechanism by which CsrR mediates the repression of its target promoters. We found that phosphorylated CsrR binds directly to all but one of the promoters of its regulated genes, with different affinities. Phosphorylation of CsrR enhances both oligomerization and DNA binding. We defined the binding site of CsrR at each of the regulated promoters using DNase I and hydroxyl radical footprinting. Based on these results, we propose a model for differential regulation by CsrRS. [source] Demonstration of an orexinergic central innervation of the pineal gland of the pigTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2004Chiara Fabris Abstract Orexins/hypocretins, two isoforms of the same prepropeptide, are widely distributed throughout the brain and are involved in several physiological and neuroendocrine regulatory patterns, mostly related to feeding, sleep, arousal, and cyclic sleep-wake behaviors. Orexin-A and orexin-B bind with different affinities to two G-protein-coupled transmembrane receptors, orexin-1 and orexin-2 receptors (OR-R1 and OR-R2, respectively). Because of the similarities between the human and the swine brain, we have studied the pig to investigate the orexinergic system in the diencephalon, with special emphasis on the neuroanatomical projections to the epithalamic region. By using antibodies against orexin-A and orexin-B, immunoreactive large multipolar perikarya were detected in the hypothalamic periventricular and perifornical areas at the light and electron microscopic levels. In the region of the paraventricular nucleus, the orexinergic neurons extended all the way to the lateral hypothalamic area. Immunoreactive nerve fibers, often endowed with large varicosities, were found throughout the hypothalamus and the epithalamus. Some periventricular immunoreactive nerve fibers entered the epithalamic region and continued into the pineal stalk and parenchyma to disperse among the pinealocytes. Immunoelectron microscopy confirmed the presence of orexinergic nerve fibers in the pig pineal gland. After extraction of total mRNA from the hypothalamus and pineal gland, we performed RT-PCR and nested PCR using primers specific for porcine orexin receptors. PCR products were sequenced, verifying the presence of both OR-R1 and OR-R2 in the tissues investigated. These findings, supported by previous studies on rodents, suggest a hypothalamic regulation of the pineal gland via central orexinergic nervous inputs. J. Comp. Neurol. 471:113,127, 2004. © 2004 Wiley-Liss, Inc. [source] Simultaneous liquid chromatographic assay of amantadine and its four related compounds in phosphate-buffered saline using 4-fluoro-7-nitro-2,1,3-benzoxadiazole as a fluorescent derivatization reagentBIOMEDICAL CHROMATOGRAPHY, Issue 5 2006Yasuhiko Higashi Abstract Simultaneous HPLC assay of 1-adamantanamine hydrochloride (amantadine) and its four related compounds [2-adamantanamine hydrochloride (2-ADA), 1-adamantanmethylamine (ADAMA), 1-(1-adamantyl)ethylamine hydrochloride (rimantadine) and 3,5-dimethyl-1-adamantanamine hydrochloride (memantine)] in phosphate-buffered saline (pH 7.4) after pre-column derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was developed. Phosphate-buffered saline samples were mixed with borate buffer and NBD-F solution in acetonitrile at 60°C for 5 min and injected into HPLC. Five derivatives were well separated from each other. The lower limits of detection of amantadine, 2-ADA, ADAMA, rimantadine and memantine were 0.008, 0.001, 0.0008, 0.0015 and 0.01 µg/mL, respectively. The coefficients of variation for intra- and inter-day assay were less than 6.4 and 8.2%, respectively. The method presented was applied to a binding study of these compounds to human ,1 -acid glycoprotein. While affinity constants and capacities for ADAMA, rimantadine and memantine were calculated by means of Scatchard plots, those for the others were not determined. ADAMA, rimantadine and memantine were bound with different affinities and capacities. These results indicate that NBD-F is a good candidate as a fluorescent reagent to simultaneously determine amantadine and its four related compounds by HPLC after pre-column derivatization. Our method can be applied to binding studies for protein. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effects of tetraalkylammonium compounds with different affinities for organic cation transporters on the pharmacokinetics of metforminBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 9 2007Min-Koo Choi Abstract The study sought to investigate the effects of tetraalkylammonium (TAA), inhibitors of the organic cation transporters (OCTs) with different affinities, on the pharmacokinetics of metformin. The inhibitory potentials of TAAs on the uptake of metformin were evaluated by determining IC50 values in MDCK cells over-expressing OCTs and, to assess in vivo drug interactions, metformin and TAAs were coadministered to rats. Uptake of metformin was facilitated by over-expression of hOCT1 and hOCT2 and showed saturable processes, indicating that metformin is a substrate of hOCT1 and hOCT2. The IC50 values of TAAs for hOCT2 were lower than hOCT1 and decreased with increasing alkyl chain length, indicating that the inhibitory potential of TAAs on metformin uptake was greater in hOCT2 than in hOCT1 and increased with increasing alkyl chain length. The plasma concentration of metformin was elevated by the coadministration of tetrapropylammonium (TPrA) and tetrapentylammonium (TPeA), but not by tetramethylammonium (TMA) or tetraethylammonium (TEA). However, the plasma concentrations of TMA, TEA and TPrA were not changed by the coadministration of metformin. In conclusion, in vivo drug interactions between metformin and TAAs were caused only when metformin was coadministered with TAAs showing higher affinities for OCTs. Copyright © 2007 John Wiley & Sons, Ltd. [source] Probing Enzyme Promiscuity of SGNH HydrolasesCHEMBIOCHEM, Issue 15 2010Dr. Ivana Le Abstract Several hydrolases of the SGNH superfamily, including the lipase SrLip from Streptomyces rimosus (Q93MW7), the acyl-CoA thioesterase I TesA from Pseudomonas aeruginosa (Q9HZY8) and the two lipolytic enzymes EstA (from P. aeruginosa, O33407) and EstP (from Pseudomonas putida, Q88QS0), were examined for promiscuity. These enzymes were tested against four chemically different classes of a total of 34 substrates known to be hydrolysed by esterases, thioesterases, lipases, phospholipases, Tweenases and proteases. Furthermore, they were also analysed with respect to their amino acid sequences and structural homology, and their phylogenetic relationship was determined. The Pseudomonas esterases EstA and EstP each have an N-terminal domain with catalytic activity together with a C-terminal autotransporter domain, and so the hybrid enzymes EstAN,EstPC and EstPN,EstAC were constructed by swapping the corresponding N- and C-terminal domains, and their hydrolytic activities were compared. Interestingly, substrate specificity and kinetic measurements indicated a significant influence of the autotransporter domains on the catalytic activities of these enzymes in solution. TesA, EstA and EstP were shown to function as esterases with different affinities and catalytic efficacies towards p -nitrophenyl butyrate. Of all the enzymes tested, only SrLip revealed lipase, phospholipase, esterase, thioesterase and Tweenase activities. [source] Enantioselective Fluorescence Sensing of Amino Acids by Modified Cyclodextrins: Role of the Cavity and Sensing MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2004Sara Pagliari Dr. Abstract Two selectors based on modified cyclodextrins containing a metal binding site and a dansyl fluorophore,6-deoxy-6- N -(N, -[(5-dimethylamino-1-naphthalenesulfonyl)aminoethyl]phenylalanylamino-,-cyclodextrin,containing D -Phe (3) and L -Phe (4) moieties were synthesized. The conformations of the two selectors were studied by circular dichroism, two-dimensional NMR spectroscopy and time-resolved fluorescence spectroscopy. Cyclodextrin 4 was found to have a predominant conformation in which the dansyl group is self-included in the cyclodextrin cavity, while 3 showed a larger proportion of the conformation with the dansyl group outside the cavity. As a consequence, the two cyclodextrins were found to bind copper(II) with different affinities, as revealed by fluorescence quenching in competitive binding measurements. Addition of D - or L -amino acids induced increases in fluorescence intensity, which were dependent on the amino acid used and in some cases on its absolute configuration. The cyclodextrin 4 was found to be more enantioselective than 3, suggesting that the self-inclusion in the cyclodextrin cavity strongly increases the chiral discrimination ability of the copper(II) complex. Accordingly, a linear fluorescent ligand N, -[(5-dimethylamino-1-naphthalenesulfonyl)aminoethyl]- N1 -propyl-phenylalaninamide, which has the same binding site and absolute configuration as 4, showed very low chiral discrimination ability. The enantioselectivity in fluorescence response was found to be due to the formation of diastereomeric ternary complexes, which were detected by ESI-MS and by circular dichroism. Time-resolved fluorescence studies showed that the fluorescence of the dansyl group was completely quenched in the ternary complexes formed, and that the residual fluorescence was due to uncomplexed ligand. [source] Programming Heteropolymetallic Lanthanide Helicates: Thermodynamic Recognition of Different Metal Ions Along the StrandsCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2004Sébastien Floquet Dr. Abstract Under stoichiometric conditions, the segmental tris-tridentate ligand L9 assembles with two different lanthanide metal ions Ln1 and Ln2 (Ln1, Ln2=La, Nd, Sm, Eu, Yb, Lu, Y) to give mixtures of the heterotrimetallic triple-stranded helicates [(Ln1)x(Ln2)3,x(L9)3]9+ (x=0,3) in acetonitrile. The combination of qualitative (ESI-MS) and quantitative (1H NMR) speciations provides a set of thermodynamic data that were analysed with various statistical chemical models. A satisfying description requires the consideration of different affinities for the terminal N6O3 sites (k) and for the central N9 site (k) for each specific lanthanide. The nontrivial dependence of these parameters on the ionic radius provides size-discriminating effects that favour the formation of heterotrimetallic helicates in which the central site is occupied by the larger metal of the pair. Combining the latter enthalpic driving forces with entropic contributions due to specific stoichiometric conditions allows partial selection (i.e., programming) of a specific heterotrimetallic species in solution, which can be isolated by crystallisation, as demonstrated for [Eu2.04La0.96(L9)3](CF3SO3)9(CH3NO2)9 (1, Eu2.04La0.96C207H222N48O51S9F27, monoclinic, P21/c, Z=4) in which the cation [EuLaEu(L9)3]9+ is the major component in the crystal. The scope and limitation of this approach is discussed together with the conditions for explicitly considering intermetallic interaction parameters uLn1Ln2 in more sophisticated chemical models. [source] Hair colouring, permanent styling and hair structureJOURNAL OF COSMETIC DERMATOLOGY, Issue 3-4 2003S Harrison Summary Hair is an important component of body image and has immense psychological importance for both men and women. Women, in particular, over the ages have modified their appearance through changing their hair colour or style. Hair can be straight, wavy or curly, blonde, black, brown or red. These natural variations are an important part of our identity that can be manipulated according to the dictates of fashion, culture or society. Different types of hair have varying affinity for the different colouring and waving methods. Damaged hair also has a different affinity for hair products than normal healthy hair. The hair shaft is remarkably strong and resistant to the extremes of nature. Hair cosmetics are widely available and manipulate the structural properties of hair. Whilst most procedures are safe, there is considerable potential for damage to the hair and hair problems of acute onset, including hair breakage, hair loss and loss of condition, are frequently blamed on the last product used on the hair. Hair problems are particularly prevalent among people who repeatedly alter the natural style of their hair. [source] Enantioseparation of nuarimol by affinity electrokinetic chromatography-partial filling technique using human serum albumin as chiral selectorJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2008Maria Amparo Martínez-Gómez Abstract The present paper deals with the enantiomeric separation of nuarimol enantiomers by affinity EKC-partial filling technique using HSA as chiral selector. Firstly, a study of nuarimol interactions with HSA by CE-frontal analysis was performed. The binding parameters obtained for the first site of interaction were n1 = 0.84; K1 = 9.7 ± 0.3×103 M,1 and the protein binding percentage of nuarimol at physiological concentration of HSA was 75.2 ± 0.2%. Due to the moderate affinity of nuarimol towards HSA the possibility of using this protein as chiral selector for the separation of nuarimol using the partial filling technique was evaluated. A multivariate optimization approach of the most critical experimental variables in enantioresolution, running pH, HSA concentration and plug length was carried out. Separation of nuarimol enantiomers was obtained under the following selected conditions: electrophoretic buffer composed of 50 mM Tris at pH 7.3; 160 ,M HSA solution applied at 50 mbar for 156 s as chiral selector; nuarimol solutions in the range of 2,8×10,4 M injected hydrodynamically at 30 mbar for 2 s and the electrophoretic runs performed at 30°C applying 15 kV voltage. Resolution, accuracy, reproducibility speed and cost of the proposed method make it suitable for quality control of the enantiomeric composition of nuarimol in formulations and for further toxicological studies. The results showed a different affinity between nuarimol enantiomers towards HSA. [source] The properties of the Mn, Ni and Pb transport operating at plasma membranes of cucumber rootsPHYSIOLOGIA PLANTARUM, Issue 3 2007Magdalena Migocka To avoid metal toxicity, plants have developed mechanisms including efflux of metal ions from cells and their sequestration into cellular compartments. In this report, we present evidence for the role of plasma membrane efflux systems in metal tolerance of cucumber roots. We have identified the plasma membrane-transport system participating in Cd, Pb, Mn and Ni efflux from the cytosol. Kinetic characterization of this proton-coupled transport system revealed that it is saturable and has a different affinity for each of the metal ions used (with Km 5, 7.5 and 0.1 mM for Mn, Ni and Pb, respectively). Treatment of cucumber roots with 100 ,M Cd prior to the transport measurements caused a great increase (over 250%) in Cd antiport activity in plasmalemma vesicles. After decreasing the metal concentration to 50 ,M we still observed a large increase (over 150%) of this activity in comparison with the control. Moreover, the addition of 50 ,M Cd to the external solution stimulated not only Cd antiport in the plasmalemma vesicles but also the antiport of other metals used in the experiments. Treatment of cucumber roots with 50 ,M Ni revealed a similar effect: the antiport activity of Cd, Mn, Ni and Pb was stimulated, although to a lesser extent in comparison with stimulation by Cd. The data indicate that the root plasma membrane antiporter system is stimulated by the exogenous presence of heavy metals. [source] Comparison of tamsulosin and naftopidil for efficacy and safety in the treatment of benign prostatic hyperplasia: a randomized controlled trialBJU INTERNATIONAL, Issue 4 2005Momokazu Gotoh OBJECTIVES To compare the efficacy and safety of two ,1a/,1d adrenoceptor (AR) antagonists with different affinity for the ,1AR subtypes, tamsulosin and naftopidil, in the treatment of benign prostatic hyperplasia (BPH). PATIENTS AND METHODS Patients with BPH were randomized to receive either tamsulosin or naftopidil. The primary efficacy variables were the changes in the total International Prostate Symptom Score (IPSS), maximum flow rate on free uroflowmetry, and residual urine volume. The secondary efficacy variables were average flow rate, changes in the IPSS storage score, IPSS voiding score, and quality-of-life (QoL) Index score, from baseline to endpoint (12 weeks). Data on all randomized patients were included in the safety analyses for adverse effects and changes in blood pressure. RESULTS Of the 185 patients enrolled data for 144 who were eligible for inclusion in the efficacy analysis were analysed (75 from the tamsulosin and 69 from the naftopidil group). There was no significant difference in any variable at baseline between the groups. There were satistically significant improvements for all primary and secondary variables in both groups, except for residual urine in the tamsulosin group. However, there was no significant intergroup difference in the improvement of any efficacy variable between the groups. The adverse effects were comparable, with no significant differences in systolic and diastolic blood pressure after treatment in both groups. CONCLUSIONS This study suggests that naftopidil is as effective and safe as tamsulosin. Both drugs were effective in improving storage and voiding symptoms. However, there was no difference in clinical efficacy or adverse effects between the ,1 AR antagonists with different affinity to ,1 subtypes, ,1a and ,1d. [source] Intracellular and plasma steady-state pharmacokinetics of raltegravir, darunavir, etravirine and ritonavir in heavily pre-treated HIV-infected patientsBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 5 2010Rob Ter Heine WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT , The combination of raltegravir, etravirine and ritonavir boosted darunavir is a potent antiretroviral regimen for patients who have been heavily pre-treated for HIV-infection. All these agents have to exert their action intracellularly. However, only little is known about the cellular pharmacology of these agents. WHAT THIS STUDY ADDS , We investigated the steady-state plasma and cellular pharmacokinetics of raltegravir, etravirine, darunavir and ritonavir and the observed distinct intracellular accumulation ratios indicated that these antiretroviral drugs have different affinity for the cellular compartment. AIM To study the steady-state plasma and intracellular pharmacokinetics of raltegravir, etravirine, darunavir and ritonavir in heavily pre-treated patients. METHODS Patients on a salvage regimen containing raltegravir, etravirine, darunavir and ritonavir were eligible for inclusion. During a 12 h dosing interval plasma and peripheral blood mononuclear cells were collected. Drug concentrations were measured using a validated LC-MS/MS assay and pharmacokinetic analysis was performed using non-linear mixed effect modelling. RESULTS Irregular absorption was observed with raltegravir and darunavir, which may be caused by enterohepatic cycling. Relative bioavailability of ritonavir was low, when compared with other ritonavir regimens. Raltegravir plasma pharmacokinetics showed wide interpatient variability, while intracellular raltegravir concentrations could not be detected (<0.001 mg l,1 in cell lysate). The intracellular to plasma ratios for etravirine, darunavir and ritonavir were 12.9, 1.32 and 7.72, respectively, and the relative standard error of these estimates were 16.3%, 12.3% and 13.0%. CONCLUSIONS The observed distinct intracellular accumulation indicated that these drugs have different affinity for the cellular compartment. The relatively high intracellular accumulation of etravirine may explain its efficacy and its previously described absence of PK,PD relationships in the therapeutic concentration range, when compared with other non-nucleoside reverse transcriptase inhibitors. Lastly, the intracellular concentrations of ritonavir seem sufficient for inhibition of viral replication in the cellular compartment in PI-naive patients, but not in patients with HIV harbouring PI resistance. [source] In vitro neuromuscular activity of snake venomsCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 9 2002Wayne C Hodgson Summary 1.,Snake venoms consist of a multitude of pharmacologically active components used for the capture of prey. Neurotoxins are particularly important in this regard, producing paralysis of skeletal muscles. These neurotoxins can be classified according to their site of action (i.e. pre- or post-synaptic). 2.,Presynaptic neurotoxins, which display varying phospholipase A2 activities, have been identified in the venoms of the four major families of venomous snakes (i.e. Crotalidae, Elapidae, Hydrophiidae and Viperidae). The blockade of transmission produced by these toxins is usually characterized by a triphasic effect on acetylcholine release. Considerable work has been directed at identifying the binding site(s) on the presynaptic nerve terminal for these toxins, although their mechanism of action remains unclear. 3.,Post-synaptic neurotoxins are antagonists of the nicotinic receptor on the skeletal muscle. Depending on their sequence, post-synaptic toxins are subdivided into short- and long-chain toxins. These toxins display different binding kinetics and different affinity for subtypes of nicotinic receptors. Post-synaptic neurotoxins have only been identified in venoms from the families Elapidae and Hydrophiidae. 4.,Due to the high cost of developing new antivenoms and the reluctance of many companies to engage in this area of research, new methodologies are required to test the efficacy of existing antivenoms to ensure their optimal use. While chicken eggs have proven useful for the examination of haemorrhagic venoms, this procedure is not suited to venoms that primarily display neurotoxic activity. The chick biventer cervicis muscle has proven useful for this procedure, enabling the rapid screening of antivenoms against a range of venoms. 5.,Historically, the lethality of snake venoms has been based on murine LD50 studies. Due to ethical reasons, these studies are being superseded by in vitro studies. Instead, the time taken to produce 90% inhibition of nerve-mediated twitches (i.e. t90) in skeletal muscle preparations can be determined. However, these two procedures result in different rank orders because they are measuring two different parameters. While murine LD50 determinations are based on ,quantity', t90 values are based on how ,quick' a venom acts. Therefore, knowledge of both parameters is still desirable. 6.,In vitro neuromuscular preparations have proven to be invaluable tools in the examination of snake venoms and isolated neurotoxins. They will continue to play a role in further elucidating the mechanism of action of these highly potent toxins. Further study of these toxins may provide more highly specific research tools or lead compounds for pharmaceutical agents. [source] | ||||||||||||||||