Showing papers in "Journal of Pharmacology and Experimental Therapeutics in 2001"

Structure-Activity Relationships for Inhibition of Farnesyl Diphosphate Synthase in Vitro and Inhibition of Bone Resorption in Vivo by Nitrogen-Containing Bisphosphonates

Abstract: It has long been known that small changes to the structure of the R(2) side chain of nitrogen-containing bisphosphonates can dramatically affect their potency for inhibiting bone resorption in vitro and in vivo, although the reason for these differences in antiresorptive potency have not been explained at the level of a pharmacological target. Recently, several nitrogen-containing bisphosphonates were found to inhibit osteoclast-mediated bone resorption in vitro by inhibiting farnesyl diphosphate synthase, thereby preventing protein prenylation in osteoclasts. In this study, we examined the potency of a wider range of nitrogen-containing bisphosphonates, including the highly potent, heterocycle-containing zoledronic acid and minodronate (YM-529). We found a clear correlation between the ability to inhibit farnesyl diphosphate synthase in vitro, to inhibit protein prenylation in cell-free extracts and in purified osteoclasts in vitro, and to inhibit bone resorption in vivo. The activity of recombinant human farnesyl diphosphate synthase was inhibited at concentrations > or = 1 nM zoledronic acid or minodronate, the order of potency (zoledronic acid approximately equal to minodronate > risedronate > ibandronate > incadronate > alendronate > pamidronate) closely matching the order of antiresorptive potency. Furthermore, minor changes to the structure of the R(2) side chain of heterocycle-containing bisphosphonates, giving rise to less potent inhibitors of bone resorption in vivo, also caused a reduction in potency up to approximately 300-fold for inhibition of farnesyl diphosphate synthase in vitro. These data indicate that farnesyl diphosphate synthase is the major pharmacological target of these drugs in vivo, and that small changes to the structure of the R(2) side chain alter antiresorptive potency by affecting the ability to inhibit farnesyl diphosphate synthase.

Unveiling the Functions of Presynaptic Metabotropic Glutamate Receptors in the Central Nervous System

Abstract: Metabotropic glutamate (mGlu) receptors, which include mGlu1-8 receptors, are a heterogeneous family of G-protein-coupled receptors which function to modulate brain excitability via presynaptic, postsynaptic and glial mechanisms. Certain members of this receptor family have been shown to function as presynaptic regulatory mechanisms to control release of neurotransmitters. In general, Gi-coupled mGlu receptor subtypes appear to negatively modulate excitatory (and possibly also inhibitory) neurotransmitter output when activated. Localization studies have shown that mGlu7 is restricted to the presynaptic grid at the site of vesicle fusion. These studies along with other evidence suggest that mGlu7 is the nerve terminal autoreceptor that regulates physiological release of glutamate. Other mGlu subtypes, in particular mGlu2, mGlu8, and possibly mGlu4, are also localized presynaptically, but at perisynaptic sites outside the active zone of neurotransmitter release. Gi-coupled mGlu receptors also may exist on presynaptic elements of neighboring gamma-aminobutyric acid (GABA) neurons where they play a role in heterosynaptic suppressions of GABA release. This suggests that these receptors may have evolved to monitor glutamate that has "spilled" out of the synapse. Thus, they may serve as the brain's evolutionary mechanism to prevent pathological changes in neuronal excitability and thus maintain homeostasis. Recent progress on the molecular and pharmacological aspects of these presynaptic mGlu receptors is unveiling their functions and the therapeutic directions of agents designed for these novel glutamate receptor targets.

Drug Synergism: Its Detection and Applications

Abstract: Two drugs that produce overtly similar effects will sometimes produce exaggerated or diminished effects when used concurrently. A quantitative assessment is necessary to distinguish these cases from simply additive action. This distinction is based on the classic pharmacologic definition of additivity that, briefly stated, means that each constituent contributes to the effect in accord with its own potency. Accordingly, the relative potency of the agents, not necessarily constant at all effect levels, allows a calculation using dose pairs to determine the equivalent of either agent and the effect by using the equivalent in the dose-response relation of the reference compound. The calculation is aided by a popular graph (isobologram) that provides a visual assessment of the interaction but also requires independent statistical analysis. The latter can be accomplished from calculations that use the total dose in a fixed-ratio combination along with the calculated additive total dose for the same effect. Different methods may be used, and each is applicable to experiments in which a single drug is given at two different sites. When departures from additivity are found, whether in "two-drug" or "two-site" experiments, the information is useful in designing new experiments for illuminating mechanisms. Several examples, mainly from analgesic drug studies, illustrate this application. Even when a single drug (or site) is used, its introduction places it in potential contact with a myriad of chemicals already in the system, a fact that underscores the importance of this topic in other areas of biological investigation.

Rational Use of in Vitro P-glycoprotein Assays in Drug Discovery

Abstract: P-glycoprotein (Pgp) affects the absorption, distribution, and clearance of a variety of compounds. Thus, identification of compounds that are Pgp substrates can aid drug candidate selection and optimization. Our goal was to evaluate three assays used to determine whether compounds are Pgp substrates. Sixty-six compounds were tested in monolayer efflux, ATPase, and calcein-AM assays. Assay results yielded two categories of compounds. Category I (n = 35) exhibited concordance across the assays. Category II (n = 31) revealed differences among the assays that related to the apparent permeability (P(app)) of the compounds. Within category II, two groups were discerned based on the absence (group IIA, n = 10, nontransported substrates) or presence (group IIB, n = 21, transported substrates) of monolayer efflux. Detection of efflux (group IIB) was associated with compounds having low/moderate P(app) values (mean = 16.6 nm/s), whereas inability to detect efflux (group IIA) was associated with compounds having high P(app) values (mean = 535 nm/s). The calcein-AM and ATPase assays revealed Pgp interactions for highly permeable group IIA compounds but were less responsive than monolayer efflux for low/moderate P(app) compounds of group IIB. All assays detected substrates across a broad range of P(app), but the efflux assay was more prone to fail at high P(app), whereas the calcein-AM and ATPase assays were more prone to fail at low P(app). When P(app) is low, efflux is a greater factor in the disposition of Pgp substrates. The efflux assay is more reliable at low/moderate P(app) and is the method of choice for evaluating drug candidates despite low throughput and reliance on liquid chromatography with tandem mass spectrometry.

Expression of P-glycoprotein in human placenta : relation to genetic polymorphism of the multidrug resistance (MDR)-1 gene

Abstract: To evaluate whether mutations in the human multidrug resistance (MDR)-1 gene correlate with placental P-glycoprotein (PGP) expression, we sequenced the MDR-1 cDNA and measured PGP expression by Western blotting in 100 placentas obtained from Japanese women. Nine single nucleotide polymorphisms (SNPs) were observed with an allelic frequency of 0.005 to 0.420. Of these SNPs, G2677A (allelic frequency = 0.18) and G2677T (0.39) in exon 21 were associated with an amino acid conversion from Ala to Thr and to Ser, respectively. Sixty-one of 65 samples (93.8%), which had a C3435T allele, also had a mutant G2677(A,T) allele, suggesting an association between the two SNPs. Correlations of mutations with expression levels were observed; individuals having the G2677(A,T) and/or T-129C (p < 0.05) allele had less placental PGP. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-based genotyping tests were developed for the detection of these SNPs. The PCR, in which genomic DNAs obtained from healthy subjects (n = 48) are used as samples, was successful. The frequency of mutations in placental cDNA was identical with that in genomic DNA. When genotype results were compared between Caucasians and Japanese, ethnic differences in the frequency of polymorphism in the MDR-1 gene were suspected. Although it remains to be determined whether these SNPs influence the pharmacokinetic and dynamic properties of clinically useful drugs that are substrates of PGP, the polymorphism of the MDR-1 gene presented here may provide useful information in in vivo study of these issues.

Post-translational control of endothelial nitric oxide synthase: why isn't calcium/calmodulin enough?

Abstract: Endothelial nitric oxide synthase (eNOS) is important for cardiovascular homeostasis, vessel remodeling, and angiogenesis. Given the impact of endothelium- derived nitric oxide (NO) in vascular biology, much work in the past several years has focused on the control of NO synthesis by regulatory proteins that influence its function. Indeed calcium-activated calmodulin is important for regulation of NOS activity. Herein we discuss why other proteins, in addition to calmodulin, are necessary for eNOS regulation and summarize the biology of negative and positive regulators of eNOS function in vitro, in cells, and in blood vessels.

Etoricoxib (MK-0663): Preclinical Profile and Comparison with Other Agents That Selectively Inhibit Cyclooxygenase-2

Abstract: We report here the preclinical profile of etoricoxib (MK-0663) [5-chloro-2-(6-methylpyridin-3-yl)-3-(4-methylsulfonylphenyl) pyridine], a novel orally active agent that selectively inhibits cyclooxygenase-2 (COX-2), that has been developed for high selectivity in vitro using whole blood assays and sensitive COX-1 enzyme assays at low substrate concentration. Etoricoxib selectively inhibited COX-2 in human whole blood assays in vitro, with an IC(50) value of 1.1 +/- 0.1 microM for COX-2 (LPS-induced prostaglandin E2 synthesis), compared with an IC(50) value of 116 +/- 8 microM for COX-1 (serum thromboxane B2 generation after clotting of the blood). Using the ratio of IC(50) values (COX-1/COX-2), the selectivity ratio for the inhibition of COX-2 by etoricoxib in the human whole blood assay was 106, compared with values of 35, 30, 7.6, 7.3, 2.4, and 2.0 for rofecoxib, valdecoxib, celecoxib, nimesulide, etodolac, and meloxicam, respectively. Etoricoxib did not inhibit platelet or human recombinant COX-1 under most assay conditions (IC(50) > 100 microM). In a highly sensitive assay for COX-1 with U937 microsomes where the arachidonic acid concentration was lowered to 0.1 microM, IC(50) values of 12, 2, 0.25, and 0.05 microM were obtained for etoricoxib, rofecoxib, valdecoxib, and celecoxib, respectively. These differences in potency were in agreement with the dissociation constants (K(i)) for binding to COX-1 as estimated from an assay based on the ability of the compounds to delay the time-dependent inhibition by indomethacin. Etoricoxib was a potent inhibitor in models of carrageenan-induced paw edema (ID(50) = 0.64 mg/kg), carrageenan-induced paw hyperalgesia (ID(50) = 0.34 mg/kg), LPS-induced pyresis (ID(50) = 0.88 mg/kg), and adjuvant-induced arthritis (ID(50) = 0.6 mg/kg/day) in rats, without effects on gastrointestinal permeability up to a dose of 200 mg/kg/day for 10 days. In squirrel monkeys, etoricoxib reversed LPS-induced pyresis by 81% within 2 h of administration at a dose of 3 mg/kg and showed no effect in a fecal 51Cr excretion model of gastropathy at 100 mg/kg/day for 5 days, in contrast to lower doses of diclofenac or naproxen. In summary, etoricoxib represents a novel agent that selectively inhibits COX-2 with 106-fold selectivity in human whole blood assays in vitro and with the lowest potency of inhibition of COX-1 compared with other reported selective agents.

Correlation of gene expression of ten drug efflux proteins of the ATP-binding cassette transporter family in normal human jejunum and in human intestinal epithelial Caco-2 cell monolayers.

Abstract: This investigation describes the expression and interindividual variability in transcript levels of multiple drug efflux systems in the human jejunum and compares the expression profiles in these cells with that of the commonly used Caco-2 cell drug absorption model. Transcript levels of ten-drug efflux proteins of the ATP-binding cassette (ABC) transporter family [MDR1, MDR3, ABCB5, MRP1-6, and breast cancer resistance protein (BCRP)], lung resistance-related protein (LRP), and CYP3A4 were determined using quantitative polymerase chain reaction in jejunal biopsies from 13 healthy human subjects and in Caco-2 cells. All genes except ABCB5 were expressed, and transcript levels varied between individuals only by a factor of 2 to 3. Surprisingly, BCRP and MRP2 transcripts were more abundant in jejunum than MDR1 transcripts. Jejunal transcript levels of the different ABC transporters spanned a range of three log units with the rank order: BCRP approximately MRP2 > MDR1 approximately MRP3 approximately MRP6 approximately MRP5 approximately MRP1 > MRP4 > MDR3. Furthermore, transcript levels of 9 of 10 ABC transporters correlated well between jejunum and Caco-2 cells (r2 = 0.90). However, BCRP exhibited a 100-fold lower transcript level in Caco-2 cells compared with jejunum. Thus, the expression of a number of efflux protein transcripts in jejunum are equal to, or even higher than, that of MDR1, suggesting that the roles of these proteins (in particular BCRP and MRP2) in intestinal drug efflux have been underestimated. Also, we tentatively conclude that the Caco-2 cell line is a useful model of jejunal drug efflux, if the low expression of BCRP is taken into account.

Preclinical Studies to Predict the Disposition of Apo2L/Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand in Humans: Characterization of in Vivo Efficacy, Pharmacokinetics, and Safety

Abstract: Apo2L/TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) is a member of the tumor necrosis factor gene family known to induce apoptosis in a number of cancer cell lines and may have broad-spectrum activity against human malignancies. These studies have evaluated the potency of recombinant soluble human Apo2L/TRAIL in a mouse xenograft model and the disposition and safety of Apo2L/TRAIL in rodents and nonhuman primates. Mice with established COLO205 tumors were given daily i.v. injections of Apo2L/TRAIL (30-120 mg/kg/day). Control tumors doubled in size every 2 to 3 days, while time to tumor doubling in the treatment groups was significantly longer and related to dose (14-21 days). For pharmacokinetic studies, Apo2L/TRAIL was given as an i.v. bolus to mice (10 mg/kg), rats (10 mg/kg), cynomolgus monkeys (1, 5, and 50 mg/kg), and chimpanzees (1 and 5 mg/kg). Apo2L/TRAIL was rapidly eliminated from the serum of all species studied. Half-lives were approximately 3 to 5 min in rodents and approximately 23 to 31 min in nonhuman primates. Allometric scaling provided estimates of Apo2L/TRAIL kinetics in humans, suggesting that on a milligram per kilogram basis, doses significantly lower than those used in xenograft studies could be effective in humans. Apo2L/TRAIL clearance was highly correlated with glomerular filtration rate across species, indicating that the kidneys play a critical role in the elimination of this molecule. Safety evaluations in cynomolgus monkeys and chimpanzees revealed no abnormalities associated with Apo2L/TRAIL exposure. In conclusion, these studies have characterized the disposition of Apo2L/TRAIL in rodents and primates and provide information that will be used to predict the pharmacokinetics of Apo2L/TRAIL in humans.

Anti-Inflammatory and Immunomodulatory Potential of the Novel PDE4 Inhibitor Roflumilast in Vitro

Abstract: From a series of benzamide derivatives, roflumilast (3-cyclo-propylmethoxy-4-difluoromethoxy-N-[3,5-di-chloropyrid-4-yl]-benzamide) was identified as a potent and selective PDE4 inhibitor. It inhibits PDE4 activity from human neutrophils with an IC(50) of 0.8 nM without affecting PDE1 (bovine brain), PDE2 (rat heart), and PDE3 and PDE5 (human platelets) even at 10,000-fold higher concentrations. Roflumilast is almost equipotent to its major metabolite formed in vivo (roflumilast N-oxide) and piclamilast (RP 73401), however, more than 100-fold more potent than rolipram and Ariflo (cilomilast; SB 207499). The anti-inflammatory and immunomodulatory potential of roflumilast and the reference compounds was investigated in various human leukocytes using cell-specific responses: neutrophils [N-formyl-methyl-leucyl-phenylalanine (fMLP)-induced formation of LTB(4) and reactive oxygen species (ROS)], eosinophils (fMLP- and C5a-induced ROS formation), monocytes, monocyte-derived macrophages, and dendritic cells (lipopolysaccharide-induced tumor necrosis factor-alpha synthesis), and CD4+ T cells (anti-CD3/anti-CD28 monoclonal antibody-stimulated proliferation, IL-2, IL-4, IL-5, and interferon-gamma release). Independent of the cell type and the response investigated, the corresponding IC values (for half-maximum inhibition) of roflumilast were within a narrow range (2-21 nM), very similar to roflumilast N-oxide (3-40 nM) and piclamilast (2-13 nM). In contrast, cilomilast (40-3000 nM) and rolipram (10-600 nM) showed greater differences with the highest potency for neutrophils. Compared with neutrophils and eosinophils, representing the terminal inflammatory effector cells, the relative potency of roflumilast and its N-oxide for monocytes, CD4+ T cells, and dendritic cells is substantially higher compared with cilomilast and rolipram, probably reflecting an improved immunomodulatory potential. The efficacy of roflumilast in vitro and in vivo (see accompanying article in this issue) suggests that roflumilast will be useful in the treatment of chronic inflammatory disorders such as asthma and chronic obstructive pulmonary disease.

Biodegradable Nanoparticles for Targeted Drug Delivery in Treatment of Inflammatory Bowel Disease

Abstract: The use of nanoparticles for targeted oral drug delivery to the inflamed gut tissue in inflammatory bowel disease was examined. Such a strategy of local drug delivery would be a distinct improvement compared with existing colon delivery devices for this disease. An experimental colitis was induced by trinitrobenzenesulfonic acid to male Wistar rats. Rolipram, an anti-inflammatory model drug, was incorporated within poly(lactic-coglycolic acid) nanoparticles, which were administered once a day orally for five consecutive days. A clinical activity score and myeloperoxidase activity were determined to assess the inflammation, whereas an adverse effect index reflected the remaining neurotropic effect of rolipram resulting from its systemic absorption. All nanoparticle formulations proved to be as efficient as the drug in solution in mitigating the experimental colitis. The clinical activity score and myeloperoxidase activity decreased significantly after the oral administration of rolipram nanoparticles or solution. During the next 5 days when animals were kept without drug treatment the drug solution group displayed a strong relapse, whereas the nanoparticle groups continued to show reduced inflammation levels. The rolipram solution group had a high adverse effect index, whereas the rolipram nanoparticle groups proved their potential to retain the drug from systemic absorption as evidenced by a significantly reduced index. This new delivery system enabled the drug to accumulate in the inflamed tissue with higher efficiency than when given as solution. The nanoparticle deposition in the inflamed tissue should be given particular consideration in the design of new carrier systems for the treatment of inflammatory bowel disease.

SEA0400, a Novel and Selective Inhibitor of the Na+-Ca2+ Exchanger, Attenuates Reperfusion Injury in the in Vitro and in Vivo Cerebral Ischemic Models

Abstract: The effect of the newly synthesized compound 2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline (SEA0400) on the Na+-Ca2+ exchanger (NCX) was investigated and compared against that of 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea (KB-R7943). In addition, the effects of SEA0400 on reperfusion injury in vitro and in vivo were examined. SEA0400 was extremely more potent than KB-R7943 in inhibiting Na+-dependent Ca2+ uptake in cultured neurons, astrocytes, and microglia: IC50s of SEA0400 and KB-R7943 were 5 to 33 nM and 2 to 4 microM, respectively. SEA0400 at the concentration range that inhibited NCX exhibited negligible affinities for the Ca2+ channels, Na+ channels, K+ channels, norepinephrine transporter, and 14 receptors, and did not affect the activities of the Na+/H+ exchanger, Na+,K+-ATPase, Ca2+-ATPase, and five enzymes. SEA0400, unlike KB-R7943, did not inhibit the store-operated Ca2+ entry in cultured astrocytes. SEA0400 attenuated dose- dependently paradoxical Ca2+ challenge-induced production of reactive oxygen species, DNA ladder formation, and nuclear condensation in cultured astrocytes, whereas it did not affect thapsigargin-induced cell injury. Furthermore, administration of SEA0400 reduced infarct volumes after a transient middle cerebral artery occlusion in rat cerebral cortex and striatum. These results indicate that SEA0400 is the most potent and selective inhibitor of NCX, and suggest that the compound may exert protective effects on postischemic brain damage.

Cellular Thiols and Reactive Oxygen Species in Drug-Induced Apoptosis

Abstract: In higher eukaryotes, reactive oxygen species (ROS) are generated during respiration in mitochondria in the course of reduction of molecular oxygen as well as by distinct enzyme systems. ROS have been implicated in the regulation of diverse cellular functions including defense against pathogens, intracellular signaling, transcriptional activation, proliferation, and apoptosis. The reduction-oxidation (redox) state of the cell is primarily a consequence of the precise balance between the levels of ROS and endogenous thiol buffers present in the cell, such as glutathione and thioredoxin, which protect cells from oxidative damage. Dramatic elevation of ROS, exceeding compensatory changes in the level of the endogenous thiol buffers, may result in the sustained activation of signaling pathways and expression of genes that induce apoptosis in affected cells. Many cytotoxic drugs function selectively to kill cancer cells by the abrogation of proliferative signals, leading to cell death, and numerous reports have demonstrated that ROS are generated following treatment with these drugs. In this review, we will summarize recent contributions to our understanding of the importance of cytotoxic drug-induced modulation of cellular redox status for signaling and transcription leading to activation of apoptotic effector mechanisms.

Pentylenetetrazole-induced inhibition of recombinant gamma-aminobutyric acid type A (GABA(A)) receptors: mechanism and site of action.

Abstract: Pentylenetetrazole (PTZ) is a central nervous system convulsant that is thought, based on binding studies, to act at the picrotoxin (PTX) site of the gamma-aminobutyric acid type A (GABA(A)) receptor. In the present study, we have investigated the mechanism and site of action of PTZ in recombinant GABA(A) receptors. In rat alpha 1 beta 2 gamma 2 receptors, PTZ inhibited GABA-activated Cl(-) current in a concentration-dependent, voltage-independent manner, with an IC(50) of 0.62 +/- 0.13 mM. The mechanism of inhibition appeared competitive with respect to GABA in both rat and human alpha 1 beta 2 gamma 2 receptors. Varying subunit configuration (change or lack of alpha subunit isoform or lack of gamma 2 subunit) had modest effects on PTZ-induced inhibition, as evidenced by comparable IC(50) values (0.6-2.2 mM) in all receptor configurations tested. This contrasts with PTX and other PTX-site ligands, which have greater affinity in receptors lacking an alpha subunit. Using a one-site model for PTZ interaction with alpha 1 beta 2 gamma 2 receptors, the association rate (k(+1)) was found to be 1.14 x 10(3) M(-1) s(-1) and the dissociation rate (k(-1)) was 0.476 s(-1), producing a functional k(d) of 0.418 mM. PTZ could only gain access to its binding site extracellularly. Single-channel recordings demonstrated that PTZ decreased open probability by increasing the duration of closed states but had no effect on single-channel conductance or open state duration. alpha-Isopropyl-alpha-methyl-gamma-butyrolactone, a compound known to antagonize effects of PTX, also diminished the effects of PTZ. Taken together, our results indicate that pentylenetetrazole and picrotoxin interact with overlapping but distinct domains of the GABA(A) receptor.

Identification of Variants of CYP3A4 and Characterization of Their Abilities to Metabolize Testosterone and Chlorpyrifos

Abstract: CYP3A4 is the most abundant isoform of cytochrome P450 (CYP) in adult human liver. It metabolizes numerous clinically, physiologically, and toxicologically important compounds. The expression of CYP3A4 varies 40-fold in individual human livers, and metabolism of CYP3A4 substrates varies at least 10-fold in vivo. Single nucleotide polymorphisms (SNPs) in CYP3A4 were identified by direct sequencing of genomic DNA in 72 individuals from three different ethnic groups, including Caucasians, Blacks (African-Americans and African pygmies), and Asians. A total of 28 SNPs were identified, including five which produced coding changes M445T ( CYP3A4*3 ), R162Q ( CYP3A4*15 ), F189S ( CYP3A4*17 ), L293P ( CYP3A4*18 ), and P467S ( CYP3A4*19 ). The latter four represent new alleic variants. Racial variability was observed for the frequency of individual SNPs. CYP3A R162Q was identified only in Black populations with an allelic frequency of 4%. CYP3A4 F189S and CYP3A4 M445T were identified in Caucasians with allelic frequencies 2% and 4%, respectively. L293P and P467S were only observed in Asians at allelic frequencies of 2%. The cDNAs for the F189S, L293P, M445T, and P467S mutant alleles were constructed by site-directed mutagenesis and expressed in an Escherichia coli expression system. Testosterone and the insecticide chlorpyrifos were used to assess the catalytic activities of the most common CYP3A4 allele (CYP3A4*1) and its allelic variants. CYP3A4 F189S exhibited lower turnover numbers for testosterone and chlorpyrifos, while CYP3A4 L293P had higher turnover numbers for both substrates. The turnover numbers of the CYP3A4 M445T and P467S alleles to metabolize these compounds were not significantly different from those of wild-type CYP3A4 .

Comparison of Pharmacological Activities of Buprenorphine and Norbuprenorphine: Norbuprenorphine Is a Potent Opioid Agonist

Abstract: Buprenorphine (BUP) is an oripavine analgesic that is beneficial in the maintenance treatment of opiate-dependent individuals. Although BUP has been studied extensively, relatively little is known about norbuprenorphine (norBUP), a major dealkylated metabolite of BUP. We now describe the binding of norBUP to opioid and nociceptin/orphanin FQ (ORL1) receptors, and its effects on [35S]guanosine-5′-O-(γ-thio)triphosphate ([35S]GTPγS) binding mediated by opioid or ORL1 receptors and in the mouse acetic acid writhing test. Chinese hamster ovary cells stably transfected with each receptor were used for receptor binding and [35S]GTPγS binding. NorBUP exhibited high affinities for μ-, δ-, and κ-opioid receptors withKi values in the nanomolar or subnanomolar range, comparable to those of BUP. NorBUP and BUP had low affinities for the ORL1 receptor with Ki values in the micromolar range. In the [35S]GTPγS binding assay, norBUP displayed characteristics distinct from BUP. At the δ-receptor, norBUP was a potent full agonist, yet BUP had no agonist activity and antagonized actions of norBUP and DPDPE. At μ- and κ-receptors, both norBUP and BUP were potent partial agonists, with norBUP having moderate efficacy and BUP having low efficacy. At the ORL1 receptor, norBUP was a full agonist with low potency, while BUP was a potent partial agonist. In the writhing test, BUP and norBUP both suppressed writhing in an efficacious and dose-dependent manner, giving A50 values of 0.067 and 0.21 mg/kg, s.c., respectively. These results highlight the similarities and differences between BUP and norBUP, each of which may influence the unique pharmacological profile of BUP.

Alpha1-adrenergic receptors: new insights and directions

Abstract: The adrenergic receptors play a key role in the modulation of sympathetic nervous system activity as well as a site of action for many therapeutic agents. The alpha1-adrenergic receptor subtypes (alpha1A-, alpha1B-, alpha1D) are the prime mediators of smooth muscle contraction and hypertrophic growth, but their characterization in both binding and function have lagged the other adrenergic family members. Although they are derived from a related ancestral gene and all nine adrenergic receptor family members bind the endogenous ligands, epinephrine and norepinephrine, with roughly similar affinities, there are major differences in the mode of binding, second messenger utilization, and physiological effects of the alpha1-subtypes compared with beta- or alpha2-subtypes. Here, we review the recent literature on aspects of its binding pocket and how it differs from the beta-adrenergic receptor paradigms. We also review the signaling components and aspects of its function and provide new insights into its roles in smooth muscle, growth, neurological, and cardiovascular function.

Rifampin Is a Selective, Pleiotropic Inducer of Drug Metabolism Genes in Human Hepatocytes: Studies with cDNA and Oligonucleotide Expression Arrays

Abstract: We used expression microarrays to test the effects of rifampin on the overall pattern of mRNA expression of multiple metabolic enzymes in primary human hepatocytes. Two microarrays were utilized, a cDNA-based array and one that is oligonucleotide-based. The cDNA-based expression arrays showed that rifampin caused a 7.7 +/- 6.6-fold induction in CYP2A6 and a 4.0 +/- 2.0-fold increase in the CYP2C family of enzymes while having little effect on CYP2E1 or CYP2D6. Many non-P450 enzymes were also induced including FMO-4 and -5, UGT-1A, MAO-B, and GST-P1. The oligonucleotide-based array made it possible to detect different levels of induction within the CYP2C family, with rifampin causing a 6.5-fold increase in expression of CYP2C8 and a 3.7-fold increase in CYP2C9 while having no effect on the level of CYP2C18 mRNA. Rifampin also induced other CYP enzymes including CYP2B6 and all three members of the CYP3A family, with CYP3A4 showing the highest level of induction at 55.1-fold. RNase protection assays were used to validate results from the arrays and a comparison of all three methods of mRNA detection showed qualitatively similar results. These data make it clear that rifampin treatment brings about broad changes in the pattern of gene expression, rather than increased expression of a small number of metabolic enzymes. Clinicians and researchers who use and study rifampin and other drugs that induce drug metabolism should be alert to the possibility of multiple effects.

Pharmacokinetic Properties of 2′-O-(2-Methoxyethyl)-Modified Oligonucleotide Analogs in Rats

Abstract: Plasma pharmacokinetics, biodistribution, excretion, and metabolism of four modified 20-mer antisense oligonucleotides targeted to human intercellular adhesion molecule-1 mRNA have been characterized in rats and compared with a first-generation phosphorothioate oligodeoxynucleotide (PS ODN), ISIS 2302. The modified oligonucleotides contained 2'-O-(2-methoxyethyl) (2'-O-MOE) ribose sugar modifications on all or a portion of the nucleotides in the antisense sequence. The 2'-O-MOE-modified oligonucleotides were resistant to nuclease metabolism in both plasma and tissue. In general, plasma pharmacokinetics was not substantially altered by addition of the 2'-O-MOE modification to PS ODN. Thus, plasma clearance was dominated by distribution to tissues, broadly, with less than 10% of the administered dose excreted in urine or feces over 24 h. However, the 2'-O-MOE modification combined with the phosphodiester (PO) backbone exhibited 10-fold more rapid plasma clearance, with approximately 50% of the dose excreted in urine as intact oligonucleotide. Consistent with its rapid and extensive excretion, the PO 2'-O-MOE modification distributed to very few organs in any substantial amount with the exception of the kidney. Oligonucleotides that contained phosphorothioate backbones were highly bound to plasma proteins. Indeed, the primary characteristic that resulted in the most marked alterations in pharmacokinetics appeared to be the affinity and capacity of these compounds to bind plasma proteins. A balance of greater stability supplied by the 2'-O-MOE modification together with maintenance of plasma protein binding appears to be necessary to ensure favorable pharmacokinetics of this new generation of antisense oligonucleotides.

Blockade of Opioid Receptors in Rostral Ventral Medulla Prevents Antihyperalgesia Produced by Transcutaneous Electrical Nerve Stimulation (TENS)

Abstract: Although transcutaneous electrical nerve stimulation (TENS) is used extensively in inflammatory joint conditions such as arthritis, the underlying mechanisms are unclear. This study aims to demonstrate an opiate-mediated activation of descending inhibitory pathways from the rostral ventral medulla (RVM) in the antihyperalgesia produced by low- (4 Hz) or high-frequency (100 Hz) TENS. Paw withdrawal latency to radiant heat, as an index of secondary hyperalgesia, was recorded before and after knee joint inflammation (induced by intra-articular injection of 3% kaolin and carrageenan) and after TENS/no TENS coadministered with naloxone (20 μg/1 μl), naltrindole (5 μg/1 μl), or vehicle (1 μl) microinjected into the RVM. The selectivity of naloxone and naltrindole doses was tested against the μ-opioid receptor agonist [d-Ala 2 , N -Me-Phe 4 ,Gly-ol 5 ]-enkephalin (DAMGO) (20 ng, 1 μl) and the δ 2 -opioid receptor agonist deltorphin (5 μg, 1 μl) in the RVM. Naloxone microinjection into the RVM blocks the antihyperalgesia produced by low frequency ( p p > 0.05). In contrast, naltrindole injection into the RVM blocks the antihyperalgesia produced by high-frequency ( p p > 0.05) TENS. The analgesia produced by DAMGO and deltorphin is selectively blocked by naloxone ( p p

Interindividual variability in acetaminophen glucuronidation by human liver microsomes: identification of relevant acetaminophen UDP-glucuronosyltransferase isoforms.

Abstract: Interindividual variability in acetaminophen (APAP) glucuronidation may contribute to differences in susceptibility to APAP intoxication in humans. The purpose of this study was to identify the relevant UDP-glucuronosyltransferase (UGT) isoforms mediating APAP-UGT activity in human liver microsomes (HLMs). APAP-UGT activities and enzyme kinetics were determined using HLMs from 56 donors and nine recombinant human UGTs. Activities mediated by UGT1A1, UGT1A4, UGT1A9, and UGT2B7, and relative UGT1A6 protein content were quantified using 20 livers. More than 15-fold variation in liver microsomal APAP-UGT activities was observed with a distribution skewed toward lower activities. Although most UGTs could glucuronidate APAP, UGT1A1, UGT1A6, and UGT1A9 were most active. UGT1A6 was a relatively high-affinity ( K m = 2.2 mM), low-capacity enzyme; UGT1A1 was intermediate in affinity ( K m = 9.4 mM) and capacity; and UGT1A9 was a low-affinity ( K m = 21 mM), high-capacity enzyme. K m values were similar to UGT1A1 in high- and intermediate-activity HLMs (6–10 mM) and UGT1A9 in low-activity HLMs (10–55 mM). APAP-UGT activities correlated best with propofol-UGT ( r = 0.85; UGT1A9) and bilirubin-UGT ( r = 0.66; UGT1A1) activities, but poorly with UGT1A6 protein ( r = 0.30). A kinetic model was constructed from these data that identified UGT1A9 as the predominant APAP-UGT (>55% total activity) in HLMs over a clinically relevant APAP concentration range (50 μM-5 mM). UGT1A1 was also predicted to contribute substantially at toxic concentrations (>1 mM; >28% activity), whereas UGT1A6 was most active at relatively low concentrations ( 29% activity).

Regulation of adult neurogenesis by psychotropic drugs and stress.

Abstract: Proliferation and maturation of neurons has been demonstrated to occur at a significant rate in discrete regions of adult brain, including the hippocampus and subventricular zone. Moreover, adult neurogenesis is an extremely dynamic process that is regulated in both a positive and negative manner by neuronal activity and environmental factors. It has been suggested to play a role in several important neuronal functions, including learning, memory, and response to novelty. In addition, exposure to psychotropic drugs or stress regulates the rate of neurogenesis in adult brain, suggesting a possible role for neurogenesis in the pathophysiology and treatment of neurobiological illnesses such as depression, post-traumatic stress disorder, and drug abuse. As the mechanisms that control adult neurogenesis continue to be identified, the exciting prospect of developing pharmacological agents that specifically regulate the proliferation and maturation of neurons in the adult brain could be fulfilled.

Cloning and Characterization of a Novel Human Histamine Receptor

Abstract: Histamine exerts its numerous physiological functions through interaction with G protein-coupled receptors. Three such receptors have been defined at both the pharmacological and molecular level, while pharmacological evidence hints at the existence of further subtypes. We report here the cloning and characterization of a fourth histamine receptor subtype. Initially discovered in an expressed-sequence tag database, the full coding sequence (SP9144) was subsequently identified in chromosome 18 genomic sequence. This virtual coding sequence exhibited highest homology to the H(3) histamine receptor and was used to generate a full-length clone by polymerase chain reaction (PCR). The distribution of mRNA encoding SP9144 was restricted to cells of the immune system as determined by quantitative PCR. HEK-293 cells transiently transfected with SP9144 and a chimeric G protein alpha-subunit (Galpha(q/i1,2)) exhibited increases in intracellular [Ca(2+)] in response to histamine but not other biogenic amines. SP9144-transfected cells exhibited saturable, specific, high-affinity binding of [(3)H]histamine, which was potently inhibited by H(3) receptor-selective compounds. The rank order and potency of these compounds at SP9144 differed from the rank order at the H(3) receptor. Although SP9144 apparently coupled to Galpha(i), HEK-293 cells stably transfected with SP9144 did not exhibit histamine-mediated inhibition of forskolin-stimulated cAMP levels. However, both [(35)S]GTPgammaS binding and phosphorylation of mitogen-activated protein kinase were stimulated by histamine via SP9144 activation. In both of these assays, SP9144 exhibited evidence of constitutive activation. Taken together, these data demonstrate that SP9144 is a unique, fourth histamine receptor subtype.

Mechanism of pluronic effect on P-glycoprotein efflux system in blood-brain barrier: contributions of energy depletion and membrane fluidization.

Abstract: Pluronic block copolymer, P85, inhibits the P-glycoprotein (Pgp) drug efflux system and increases the permeability of a broad spectrum of drugs in the blood-brain barrier (BBB). This study examines the mechanisms by which P85 inhibits Pgp using bovine brain microvessel endothelial cells (BBMEC) as an in vitro model of the BBB. The hypothesis was that simultaneous alterations in intracellular ATP levels and membrane fluidization in BBMEC monolayers by P85 results in inhibition of the drug efflux system. The methods included the use of 1) standard Pgp substrate rhodamine 123 to assay the Pgp efflux system in BBMEC, 2) luciferin/luciferase assay for ATP intracellular levels, and 3) 1,6-diphenyl-1,3,5-hexatriene for membrane microviscosity. Using 3H-labeled P85 and fluorescein-labeled P85 for confocal microscopy, this study suggests that P85 accumulates in the cells and intracellular organelles such as the mitochondria where it can interfere with metabolic processes. Following exposure of BBMEC to P85, the ATP levels were depleted, and microviscosity of the cell membranes was decreased. Furthermore, P85 treatment decreased Pgp ATPase activity in membranes expressing human Pgp. A combination of experiments examining the kinetics, concentration dependence, and directionality of P85 effects on Pgp-mediated efflux in BBMEC monolayers suggests that both energy depletion (decreasing ATP pool available for Pgp) and membrane fluidization (inhibiting Pgp ATPase activity) are critical factors contributing to the activity of the block copolymer in the BBB.

Luteolin Inhibits an Endotoxin-Stimulated Phosphorylation Cascade and Proinflammatory Cytokine Production in Macrophages

Abstract: Flavonoids are naturally occurring polyphenolic compounds with a wide distribution throughout the plant kingdom. In the present study, we compared the ability of several flavonoids to modulate the production of proinflammatory molecules from lipopolysaccharide (LPS)-stimulated macrophages and investigated their mechanism(s) of action. Pretreatment of RAW 264.7 with luteolin, luteolin-7-glucoside, quercetin, and the isoflavonoid genistein inhibited both the LPS-stimulated TNF-alpha and interleukin-6 release, whereas eriodictyol and hesperetin only inhibited TNF-alpha release. From the compounds tested luteolin and quercetin were the most potent in inhibiting cytokine production with an IC(50) of less than 1 and 5 microM for TNF-alpha release, respectively. To determine the mechanisms by which flavonoids inhibit LPS signaling, we used luteolin and determined its ability to interfere with total protein tyrosine phosphorylation as well as Akt phosphorylation and nuclear factor-kappaB activation. Pretreatment of the cells with luteolin attenuated LPS-induced tyrosine phosphorylation of many discrete proteins. Moreover, luteolin inhibited LPS-induced phosphorylation of Akt. Treatment of macrophages with LPS resulted in increased IkappaB-alpha phosphorylation and reduced the levels of IkappaB-alpha. Pretreatment of cells with luteolin abolished the effects of LPS on IkappaB-alpha. To determine the functional relevance of the phosphorylation events observed with IkappaB-alpha, macrophages were transfected either with a control vector or a vector coding for the luciferase reporter gene under the control of kappaB cis-acting elements. Incubation of transfected RAW 264.7 cells with LPS increased luciferase activity in a luteolin-sensitive manner. We conclude that luteolin inhibits protein tyrosine phosphorylation, nuclear factor-kappaB-mediated gene expression and proinflammatory cytokine production in murine macrophages.

Propentofylline, a glial modulating agent, exhibits antiallodynic properties in a rat model of neuropathic pain.

Abstract: The present study was undertaken to determine whether propentofylline, a glial modulating agent, could both prevent the induction of mechanical allodynia and attenuate existing mechanical allodynia in a rodent L5 spinal nerve transection model of neuropathic pain. In a preventative paradigm, propentofylline (1 and 10 mg/kg intraperitoneally) was administered systemically daily, beginning 1 day prior to nerve transection. This regimen produced a dose-dependent decrease in mechanical allodynia ( p p p

Factors Affecting the Accelerated Blood Clearance of Polyethylene Glycol-Liposomes upon Repeated Injection

Abstract: Previously, we showed that long-circulating polyethylene glycol (PEG)-liposomes are cleared rapidly from the circulation when injected repeatedly in the same animal. In this article, we describe the effects of PEG-coating, the circulation time, the lipid dose, and the presence of encapsulated doxorubicin on the pharmacokinetics upon repeated injection in rats. Furthermore, the role of liver and splenic macrophages was investigated. Liposomes without PEG-coating also showed the so-called "enhanced clearance effect": blood levels at 4 h post injection decreased from 62.8 +/- 13.7% of injected dose (%ID) after the first injection to 0.54 +/- 0.21%ID after the second injection. This decrease was independent of the circulation time of the first dose. Decreasing the first lipid dose of PEG-liposomes to 0.05 micromol/kg still led to enhanced clearance of a second dose of 5 micromol/kg. No changes in pharmacokinetics were observed when the second dose was 50 micromol/kg. When hepatosplenic macrophages were depleted, no enhanced clearance of repeated liposome injections was observed. A dose of doxorubicin containing PEG-liposomes (Doxil), injected 1 week after injection of empty PEG-liposomes, was cleared rapidly from the circulation in rats. Our results indicate that hepatosplenic macrophages play an essential role in the enhanced clearance effect and that the change in pharmacokinetic behavior upon repeated injection is a general characteristic of liposomes, unrelated to the presence of PEG. Therefore, these findings may have a considerable impact on the clinical application of liposomal formulations that are administered repeatedly.

Pharmacokinetics of Celecoxib after Oral Administration in Dogs and Humans: Effect of Food and Site of Absorption

Abstract: Celecoxib pharmacokinetics was evaluated after single and multiple oral dosing; after dosing in a solution and as a solid; with and without food; and after administration into different sites of the GI tract using dog. After oral dosing in a solution, celecoxib was rapidly absorbed and reached maximum concentrations by 1 h; absorption was delayed another 1 to 2 h when administered as a solid. The absolute bioavailability of celecoxib was higher when given as a solution (64--88%) compared with capsule (22--40%). The absorption of celecoxib given in a capsule was delayed by food, although systemic exposure increased by 3- to 5-fold. The systemic availability of celecoxib given intragastrically in solution was similar to that obtained following direct instillation into the duodenum, jejunum, or colon through a chronic intestinal access port. Collectively, these data suggest that celecoxib is a highly permeable drug that can be absorbed throughout the GI tract and that dissolution may be a rate-limiting factor for absorption from solid dosage forms. Unlike dogs, celecoxib given to humans with a high fat meal exhibits only a slight increase in AUC(0--infinity) (11%) that is not clinically significant with regard to safety or efficacy. In humans, a lower dose and a longer GI residence time may promote the opportunity for absorption of a poorly soluble drug such as celecoxib that can be absorbed throughout the GI tract. This would minimize the effect of food on absorption; as such, patients with arthritis can be given celecoxib with or without food.

Analysis of Mecamylamine Stereoisomers on Human Nicotinic Receptor Subtypes

Abstract: Because mecamylamine, a nicotinic receptor antagonist, is used so often in nicotine research and because mecamylamine may have important therapeutic properties clinically, it is important to fully explore and understand its pharmacology. In the present study, the efficacy and potency of mecamylamine and its stereoisomers were evaluated as inhibitors of human α3β4, α3β2, α7, and α4β2 nicotinic acetylcholine receptors (nAChRs), as well as mouse adult type muscle nAChRs and rat N -methyl-d-aspartate (NMDA) receptors expressed in Xenopus oocytes. The selectivity of mecamylamine for neuronal nAChR was manifested primarily in terms of slow recovery rates from mecamylamine-induced inhibition. Neuronal receptors showed a prolonged inhibition after exposure to low micromolar concentrations of mecamylamine. Muscle-type receptors showed a transient inhibition by similar concentrations of mecamylamine, and NMDA receptors were only transiently inhibited by higher micromolar concentrations. Mecamylamine inhibition of neuronal nAChR was noncompetitive and voltage dependent. Although there was little difference between S -(+)-mecamylamine and R -(−)-mecamylamine in terms of 50% inhibition concentration values for a given receptor subtype, there appeared to be significant differences in the off-rates for the mecamylamine isomers from the receptors. Specifically, S -(+)-mecamylamine appeared to dissociate more slowly from α4β2 and α3β4 receptors than did R- (−)-mecamylamine. In addition, it was found that muscle-type receptors appeared to be somewhat more sensitive to R- (−)-mecamylamine than to S- (+)-mecamylamine. Together, these findings suggest that in chronic (i.e., therapeutic) application, S- (+)-mecamylamine might be preferable to R- (−)-mecamylamine in terms of equilibrium inactivation of neuronal receptors with decreased side effects associated with muscle-type receptors.

Locomotor effects of acute and repeated threshold doses of amphetamine and methylphenidate: relative roles of dopamine and norepinephrine.

Abstract: The prescribed use of methylphenidate (Ritalin) in the treatment of attention deficit hyperactivity disorder has risen dramatically in recent years. The relative roles of dopamine, norepinephrine, and serotonin in the therapeutic action of these drugs was assessed by comparing the responses of extracellular nucleus accumbens dopamine and serotonin and hippocampus norepinephrine to the acute administration of low methylphenidate and amphetamine doses. The comparative neurochemical profiles in response to methylphenidate and amphetamine suggest that the norepinephrine effects may play an important role in the therapeutic effects of low doses of psychostimulants. In addition, to assess possible long-term consequences of prolonged exposure to this drug, we examined whether changes in the locomotor response occurred with repeated administration of these stimulant doses. Threshold doses of methylphenidate (0.5-1.0 mg/kg) or amphetamine (0.1-0.25 mg/kg) were administered twice daily, and then animals were tested in response to 2.5 mg/kg methylphenidate or 0.5 mg/kg amphetamine. Our results provide evidence that low-dose stimulant administration can result in the development of behavioral sensitization, which is evident in the subsequent behavioral response to the drug. The relevance of these data to the therapeutic uses of these drugs is discussed within the context of the many variables that can affect the behavioral and neurochemical responses to stimulants.