FIH-1: a novel protein that interacts with HIF-1alpha and VHL to mediate repression of HIF-1 transcriptional activity

Hypoxia-inducible factor 1 (HIF-1) is a master regulator of oxygen homeostasis that controls angiogenesis, erythropoiesis, and glycolysis via transcriptional activation of target genes under hypoxic conditions. O(2)-dependent binding of the von Hippel-Lindau (VHL) tumor suppressor protein targets the HIF-1alpha subunit for ubiquitination and proteasomal degradation. The activity of the HIF-1alpha transactivation domains is also O(2) regulated by a previously undefined mechanism. Here, we report the identification of factor inhibiting HIF-1 (FIH-1), a protein that binds to HIF-1alpha and inhibits its transactivation function. In addition, we demonstrate that FIH-1 binds to VHL and that VHL also functions as a transcriptional corepressor that inhibits HIF-1alpha transactivation function by recruiting histone deacetylases. Involvement of VHL in association with FIH-1 provides a unifying mechanism for the modulation of HIF-1alpha protein stabilization and transcriptional activation in response to changes in cellular O(2) concentration.

AP-1 transcriptional activity is regulated by a direct association between thioredoxin and Ref-1

Thioredoxin (TRX) is a pleiotropic cellular factor that has thiol-mediated redox activity and is important in regulation of cellular processes, including proliferation, apoptosis, and gene expression. The activity of several transcription factors is posttranslationally altered by redox modification(s) of specific cysteine residue(s). One such factor is nuclear factor (NF)-kappa B, whose DNA-binding activity is markedly augmented by TRX treatment in vitro. Similarly, the DNA-binding activity of activator protein 1 (AP-1) is modified by a DNA repair enzyme, redox factor 1 (Ref-1), which is identical to a DNA repair enzyme, AP endonuclease. Ref-1 activity is in turn modulated by various redox-active compounds, including TRX. We here report the molecular cascade of redox regulation of AP-1 mediated by TRX and Ref-1. Phorbol 12-myristate 13 acetate efficiently translocated TRX into the HeLa cell nucleus where Ref-1 preexists. This process seems to be essential for AP-1 activation by redox modification because co-overexpression of TRX and Ref-1 in COS-7 cells potentiated AP-1 activity only after TRX was transported into the nucleus by phorbol 12-myristate 13 acetate treatment. To prove the direct active site-mediated association between TRX and Ref-1, we generated a series of substitution-mutant cysteine residues of TRX. In both an in vitro diamide-induced cross-linking study and an in vivo mammalian two-hybrid assay we proved that TRX can associate directly with Ref-1 in the nucleus; also, we demonstrated the requirement of cysteine residues in the TRX catalytic center for the potentiation of AP-1 activity. This report presents an example of a cascade in cellular redox regulation.

Identification of thioredoxin-binding protein-2/vitamin D(3) up-regulated protein 1 as a negative regulator of thioredoxin function and expression

Recent works have shown the importance of reduction/oxidation (redox) regulation in various biological phenomena. Thioredoxin (TRX) is one of the major components of the thiol reducing system and plays multiple roles in cellular processes such as proliferation, apoptosis, and gene expression. To investigate the molecular mechanism of TRX action, we used a yeast two-hybrid system to identify TRX-binding proteins. One of the candidates, designated as thioredoxin-binding protein-2 (TBP-2), was identical to vitamin D(3) up-regulated protein 1 (VDUP1). The association of TRX with TBP-2/VDUP1 was observed in vitro and in vivo. TBP-2/VDUP1 bound to reduced TRX but not to oxidized TRX nor to mutant TRX, in which two redox active cysteine residues are substituted by serine. Thus, the catalytic center of TRX seems to be important for the interaction. Insulin reducing activity of TRX was inhibited by the addition of recombinant TBP-2/VDUP1 protein in vitro. In COS-7 and HEK293 cells transiently transfected with TBP-2/VDUP1 expression vector, decrease of insulin reducing activity of TRX and diminishment of TRX expression was observed. These results suggested that TBP-2/VDUP1 serves as a negative regulator of the biological function and expression of TRX. Treatment of HL-60 cells with 1alpha, 25-dihydroxyvitamin D(3) caused an increase of TBP-2/VDUP1 expression and down-regulation of the expression and the reducing activity of TRX. Therefore, the TRX-TBP-2/VDUP1 interaction may be an important redox regulatory mechanism in cellular processes, including differentiation of myeloid and macrophage lineages.

Molecular mechanisms of transcription activation by HLF and HIF1alpha in response to hypoxia: their stabilization and redox signal-induced interaction with CBP/p300

Hypoxia-inducible factor 1 alpha (HIF1alpha) and its related factor, HLF, activate expression of a group of genes such as erythropoietin in response to low oxygen. Transfection analysis using fusion genes of GAL4DBD with various fragments of the two factors delineated two transcription activation domains which are inducible in response to hypoxia and are localized in the C-terminal half. Their sequences are conserved between HLF and HIF1alpha. One is designated NAD (N-terminal activation domain), while the other is CAD (C-terminal activation domain). Immunoblot analysis revealed that NADs, which were rarely detectable at normoxia, became stabilized and accumulated at hypoxia, whereas CADs were constitutively expressed. In the mammalian two-hybrid system, CAD and NAD baits enhanced the luciferase expression from a reporter gene by co-transfection with CREB-binding protein (CBP) prey, whereas CAD, but not NAD, enhanced beta-galactosidase expression in yeast by CBP co-expression, suggesting that NAD and CAD interact with CBP/p300 by a different mechanism. Co-transfection experiments revealed that expression of Ref-1 and thioredoxin further enhanced the luciferase activity expressed by CAD, but not by NAD. Amino acid replacement in the sequences of CADs revealed a specific cysteine to be essential for their hypoxia-inducible interaction with CBP. Nuclear translocation of thioredoxin from cytoplasm was observed upon reducing O2 concentrations.

Distinct roles of thioredoxin in the cytoplasm and in the nucleus. A two-step mechanism of redox regulation of transcription factor NF-kappaB

Oxidative stresses such as UV irradiation to mammalian cells triggers a variety of oxistress responses including activation of transcription factors. Recently, activation of nuclear factor-kappaB (NF-kappaB) has been shown to be under oxidoreduction (redox) regulation controlled by thioredoxin (TRX), which is one of major endogenous redox-regulating molecules with thiol reducing activity. In order to elucidate where in the cellular compartment TRX participates in NF-kappaB regulation, we investigated the intracellular localization of TRX. UVB irradiation induced translocation of TRX from the cytoplasm into the nucleus. In our in vitro diamide-induced cross-linking study, we showed that TRX can associate directly with NF-kappaB p50. Overexpression of wild-type TRX suppressed induction of luciferase activity under NF-kappaB-binding sites in response to UV irradiation compared with the mock transfectant. In contrast, overexpression of nuclear-targeted TRX enhanced the luciferase activity. Thus, TRX seems to play dual and opposing roles in the regulation of NF-kappaB. In the cytoplasm, it interferes with the signals to IkappaB kinases and blocks the degradation of IkappaB. In the nucleus, however, TRX enhances NF-kappaB transcriptional activities by enhancing its ability to bind DNA. This two-step TRX-dependent regulation of the NF-kappaB complex may be a novel activation mechanism of redox-sensitive transcription factors.

Thioredoxin-dependent redox regulation of p53-mediated p21 activation

Thioredoxin (TRX) is a dithiol-reducing enzyme that is induced by various oxidative stresses. TRX regulates the activity of DNA-binding proteins, including Jun/Fos and nuclear factor-kappaB. TRX also interacts with an intranuclear reducing molecule redox factor 1 (Ref-1), which enhances the activity of Jun/Fos. Here, we have investigated the role of TRX in the regulation of p53 activity. Electrophoretic mobility shift assay showed that TRX augmented the DNA binding activity of p53 and also further potentiated Ref-1-enhanced p53 activity. Luciferase assay revealed that transfection of TRX enhanced p53-dependent expression of p21 and further intensified Ref-1-mediated p53 activation. Furthermore, Western blot analysis revealed that p53-dependent induction of p21 protein was also facilitated by transfection with TRX. Overexpression of transdominant negative mutant TRX (mTRX) suppressed the effects of TRX or Ref-1, showing a functional interaction between TRX and Ref-1. cis-Diamminedichloroplatinum (II) (CDDP) induced p53 activation and p21 transactivation. The p53-dependent p21 transactivation induced by CDDP was inhibited by mTRX overexpression, suggesting that TRX-dependent redox regulation is physiologically involved in p53 regulation. CDDP also stimulated translocation of TRX from the cytosol into the nucleus. Hence, TRX-dependent redox regulation of p53 activity indicates coupling of the oxidative stress response and p53-dependent repair mechanism.

Nucleosides. 110. Synthesis and antiherpes virus activity of some 2'-fluoro-2'-deoxyarabinofuranosylpyrimidine nucleosides

A series of 5-substituted 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)cytosines 7a-d and their corresponding uracils 9a-d,f were prepared by condensation of 3-O-acetyl-5-O-benzoyl-2-deoxy-2-fluoro-D-arabinosyl bromide (5) with appropriately trimethylsilylated pyrimidines followed by saponification of the protected nucleosides 6 or 8. 1-(2-Deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine (7e) was obtained by iodination of 7a. Iodination of 8a followed by removal of the protecting acyl-protecting groups afforded the 5-iodo nucleoside 9e. Several of these 2'-fluoro-substituted nucleosides completely obviated replication of herpes simplex virus type 1 (HSV-1) in monolayers of Vero cells at concentrations of 10-100 microgram/mL. The 5-iodocytosine analogue 7e was the most effective, showing 99.5% suppression of viral replication even at concentrations of 0.1 microgram/mL. The cytotoxicity of 7e to L5178Y or P815 cells in culture was minimal. A comparison of the efficacy of 7e against HSV-1 with other known nucleoside antiviral agents indicates that further in vitro and in vivo evaluation of 7e is warranted.

Size reduction by interpolation in fuzzy rule bases

Fuzzy control is at present still the most important area of real applications for fuzzy theory. It is a generalized form of expert control using fuzzy sets in the definition of vague/linguistic predicates, modeling a system by If...then rules. In the classical approaches it is necessary that observations on the actual state of the system partly match (fire) one or several rules in the model (fired rules), and the conclusion is calculated by the evaluation of the degrees of matching and the fired rules. Interpolation helps reduce the complexity as it allows rule bases with gaps. Various interpolation approaches are shown. It is proposed that dense rule bases should be reduced so that only the minimal necessary number of rules remain still containing the essential information in the original base, and all other rules are replaced by the interpolation algorithm that however can recover them with a certain accuracy prescribed before reduction. The interpolation method used for demonstration is the Lagrange method supplying the best fitting minimal degree polynomial. The paper concentrates on the reduction technique that is rather independent from the style of the interpolation model, but cannot be given in the form of a tractable algorithm. An example is shown to illustrate possible results and difficulties with the method.

Redox control of resistance to cis-diamminedichloroplatinum (II) (CDDP): protective effect of human thioredoxin against CDDP-induced cytotoxicity

Thioredoxin is a small ubiquitous protein with multiple biological functions, including cellular defense mechanisms against oxidative stress. In the present study, we investigated the role of human thioredoxin (hTRX) in the acquisition of cellular resistance to cis-diamminedichloroplatinum (II) (CDDP). The expression and activity of hTRX in Jurkat T cells was dose-dependently enhanced by exposure to CDDP, as determined by immunoblot analysis and insulin reducing assay. Furthermore, chloramphenicol acetyltransferase analysis using the hTRX promoter-reporter gene construct revealed that treatment of Jurkat cells with CDDP caused transcriptional activation of the hTRX gene, which might be mediated through increased generation of intracellular reactive oxygen intermediates. To examine the biological significance of hTRX induction, we established hTRX-overexpressing derivatives of L929 fibrosarcoma cells by stable transfection with the hTRX cDNA. The clones, which constitutively expressed the exogenous hTRX, displayed increased resistance to CDDP-induced cytotoxicity, compared with the control clones. After exposure to CDDP, the control cells showed a significant increase in the intracellular accumulation of peroxides, whereas the hTRX-transfected cells did not. Taken together, these results suggest that overexpressed hTRX is responsible for the development of cellular resistance to CDDP, possibly by scavenging intracellular toxic oxidants generated by this anticancer agent.

Direct association with thioredoxin allows redox regulation of glucocorticoid receptor function

The glucocorticoid receptor (GR) is considered to belong to a class of transcription factors, the functions of which are exposed to redox regulation. We have recently demonstrated that thioredoxin (TRX), a cellular reducing catalyst, plays an important role in restoration of GR function in vivo under oxidative conditions. Although both the ligand binding domain and other domains of the GR have been suggested to be modulated by TRX, the molecular mechanism of the interaction is largely unknown. In the present study, we hypothesized that the DNA binding domain (DBD) of the GR, which is highly conserved among the nuclear receptors, is also responsible for communication with TRX in vivo. Mammalian two-hybrid assay and glutathione S-transferase pull-down assay revealed the direct association between TRX and the GR DBD. Moreover, analysis of subcellular localization of TRX and the chimeric protein harboring herpes simplex viral protein 16 transactivation domain and the GR DBD indicated that the interaction might take place in the nucleus under oxidative conditions. Together these observations indicate that TRX, via a direct association with the conserved DBD motif, may represent a key mediator operating in interplay between cellular redox signaling and nuclear receptor-mediated signal transduction.

Nucleoredoxin, glutaredoxin, and thioredoxin differentially regulate NF-kappaB, AP-1, and CREB activation in HEK293 cells

Well-established mechanisms for regulation of protein activity include thiol-mediated oxidoreduction in addition to protein-protein interactions and phosphorylation. Nucleoredoxin (NRX), glutaredoxin (GRX), and thioredoxin (TRX) have been shown to act as a potent thiol reductase and reactive oxygen species regulator. They constitute a oxidoreductase superfamily and have been suggested as a candidate operating in the redox regulation of gene expression. We demonstrated here that intracellular localization of these redox molecules differ from each other and that the redox molecules differentially regulate NF-kappaB, AP-1, and CREB activation induced by TNFalpha, PMA, and forskolin and by expression of signaling intermediate kinases, NIK, MEKK, and PKA in HEK293 cells. This is a first report that describes involvement of NRX and GRX and differences from TRX in transcriptional regulation of NF-kappaB, AP-1, and CREB in living cells.

Rac1 activity is required for the activation of hypoxia-inducible factor 1

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that mediates cellular and systemic homeostatic responses (including erythropoiesis, angiogenesis, and glycolysis) to reduced O(2) availability in mammals. Hypoxia induces both the protein expression and transcriptional activity of the HIF-1alpha subunit. However, the molecular mechanisms of sensing and signal transduction by which changes in O(2) concentration result in changes in HIF-1 activity are poorly understood. We report here that the small GTPase Rac1 is activated in response to hypoxia and is required for the induction of HIF-1alpha protein expression and transcriptional activity in hypoxic cells.

Thioredoxin: a redox-regulating cellular cofactor for glucocorticoid hormone action. Cross talk between endocrine control of stress response and cellular antioxidant defense system

Adaptation to stress evokes a variety of biological responses, including activation of the hypothalamic-pituitary-adrenal (HPA) axis and synthesis of a panel of stress-response proteins at cellular levels: for example, expression of thioredoxin (TRX) is significantly induced under oxidative conditions. Glucocorticoids, as a peripheral effector of the HPA axis, exert their actions via interaction with a ligand-inducible transcription factor glucocorticoid receptor (GR). However, how these stress responses coordinately regulate cellular metabolism is still unknown. In this study, we demonstrated that either antisense TRX expression or cellular treatment with H2O2 negatively modulates GR function and decreases glucocorticoid-inducible gene expression. Impaired cellular response to glucocorticoids is rescued by overexpression of TRX, most possibly through the functional replenishment of the GR. Moreover, not only the ligand binding domain but the DNA binding domain of the GR is also suggested to be a direct target of TRX. Together, we here present evidence showing that cellular glucocorticoid responsiveness is coordinately modulated by redox state and TRX level and propose that cross talk between neuroendocrine control of stress responses and cellular antioxidant systems may be essential for mammalian adaptation processes.

Renin-dependent cardiovascular functions and renin-independent blood-brain barrier functions revealed by renin-deficient mice

Renin plays a key role in controlling blood pressure through its specific cleavage of angiotensinogen to generate angiotensin I (AI). Although possible existence of the other angiotensin forming enzymes has been discussed to date, its in vivo function remains to be elucidated. To address the contribution of renin, we generated renin knockout mice. Homozygous mutant mice show neither detectable levels of plasma renin activity nor plasma AI, lowered blood pressure 20-30 mm Hg less than normal, increased urine and drinking volume, and altered renal morphology as those observed in angiotensinogen-deficient mice. We recently found the decreased density in granular layer cells of hippocampus and the impaired blood-brain barrier function in angiotensinogen-deficient mice. Surprisingly, however, such brain phenotypes were not observed in renin-deficient mice. Our results demonstrate an indispensable role for renin in the circulating angiotensin generation and in the maintenance of blood pressure, but suggest a dispensable role for renin in the blood-brain barrier function.

Involvement of tumor necrosis factor-alpha in development of hepatic injury in galactosamine-sensitized mice

Intravenous injection of lipopolysaccharide and D-galactosamine, at doses of 0.2 micrograms/kg and 800 mg/kg, respectively, elicited massive hepatic necrosis within 24 hr in C3H/HeN mice. The plasma L-alanine aminotransferase (ALT, E.C. 2.6.1.2) or L-aspartate aminotransferase (AST, E.C. 2.6.1.1) activities at this point reached more than 2,000 IU/L. However, overt hepatic injury as evaluated by the plasma aminotransferase activities did not develop in mice in which only lipopolysaccharide or only D-galactosamine was injected. No tumor necrosis factor-like activities could be detected in the plasma of galactosamine- and lipopolysaccharide-injected mice as determined by the assay of cytotoxicity to highly tumor necrosis factor-sensitive L-P3 cells through the experimental period of 24 hr. However, passive immunization against mouse tumor necrosis factor-alpha with polyvalent rabbit anti-mouse tumor necrosis factor-alpha antiserum, which was able to neutralize the cytotoxic effects of recombinant mouse tumor necrosis factor-alpha on L-P3 cells, could protect the mice from the development of hepatic injury in a dose-dependent manner. Simultaneous injection of recombinant human tumor necrosis factor-alpha, instead of lipopolysaccharide, with 800 mg/kg of D-galactosamine in lipopolysaccharide-resistant C3H/HeJ mice sensitized the animals more than one thousand-fold to the development of hepatic injury. The livers appeared to be morphologically similar to those of galactosamine- and lipopolysaccharide-injected C3H/HeN mice.

Redox regulation of the DNA binding activity in transcription factor PEBP2. The roles of two conserved cysteine residues

Transcription factor PEBP2/CBF consists of a DNA binding subunit, alpha, and a regulatory subunit, beta. The alpha subunit has an evolutionarily conserved 128-amino acid region termed "Runt domain" that is responsible for both DNA binding and heterodimerization with the beta subunit. The Runt domain in all mammalian submembers of the alpha subunit contains two conserved cysteine residues, and its DNA binding activity undergoes redox regulation. To investigate the mechanism of this redox regulation, we performed site-directed mutagenesis of the two conserved cysteines in the Runt domain of the mouse PEBP2alphaA homolog. Substitution of Cys-115 to serine resulted in a partially impaired DNA binding, which remained highly sensitive to a thiol-oxidizing reagent, diamide. Conversely, the corresponding substitution of Cys-124 caused an increased DNA binding concomitant with an increased resistance to diamide. In contrast, substitution of either cysteine to aspartate was destructive to DNA binding to marked extents. These results have revealed that both Cys-115 and Cys-124 are responsible for the redox regulation in their own ways with low and high oxidizabilities, respectively. We have also found that two cellular thiol-reactive proteins, thioredoxin and Ref-1, work effectively and synergistically for activation of the Runt domain. Interestingly, the beta subunit further enhanced the activation by these proteins and reciprocally prevented the oxidative inactivation by diamide. These findings collectively suggest the possibility that the Runt domain's function in vivo could be dynamically regulated by the redox mechanism with Trx, Ref-1, and the beta subunit as key modulators.

Surface hardness change of restorative filling materials stored in saliva

OBJECTIVES

This study was to investigate the effect of saliva used as storage liquid and the length of storage effect on surface hardnesses of Fuji IX (GP) (FIX), Dyract (DR), Z-100 and Estio LC (ELC).

METHODS

The materials were mixed according to the manufacturers' instructions and immersed in distilled water or human parotid saliva. Vickers hardness number (HVN) was measured 1, 7, 20 and 40 days after the materials were mixed. HVN was calculated from the indentation diameter after 100 or 300g loading on their surface for 15s. The two methods of characterization used in this work were X-ray photoelectron spectroscopy (XPS) for surface chemical composition and electron probe microanalysis (EPMA) for depth profile analysis.

RESULTS

Only in FIX, did HVN increase with time at both storage conditions, distilled water and saliva. The increase rate of the value was higher when stored in saliva than distilled water. After 40 days storage in saliva, the HVN value of FIX increased by 39%. The increase for storage in saliva for DR was 22%, ELC 16%, and Z100 3%, compared to 1 day storage in distilled water. Ca and P peaks caused by saliva were detected by XPS and EPMA analysis, but these peaks did not exist in either composite resin or polyacid-modified composite resin by EPMA analysis.

SIGNIFICANCE

Saliva has the remarkable effect of increasing surface hardness of Fuji IX (GP).

SRB1, a class B scavenger receptor, recognizes both negatively charged liposomes and apoptotic cells

Scavenger receptors mediate the recognition of a wide range of negatively charged macromolecules such as acetylated low-density lipoproteins (AcLDL). We previously reported the isolation of CHO cell variants expressing a novel type of scavenger receptor, distinct from type I and II macrophage scavenger receptors, that recognize both AcLDL and negatively charged liposomes. In the present study, we found that these isolated CHO cells express class B scavenger receptors (SRB1), which have recently been identified as a new member of the CD36 family of membrane proteins. The isolated CHO cells and CHO transfectants constitutively expressing SRB1 recognized and mediated the endocytosis of cells undergoing apoptosis as well as that of negatively charged liposomes. In contrast, CHO cells constitutively expressing type I or II scavenger receptors were unable to take up these ligands.

Professional Oral Health Care Reduces the Number of Oropharyngeal Bacteria

Silent aspiration of oropharyngeal pathogenic organisms is a significant risk factor causing pneumonia in the elderly. We hypothesized that regular oral hygiene care will affect the presence of oropharyngeal bacteria. Professional cleaning of the oral cavity and/or the gargling of a disinfectant liquid solution was performed over a five-month period in three facilities for the dependent elderly. Total oropharyngeal bacteria, streptococci, staphylococci, Candida, Pseudomonas, and black-pigmented Bacteroides species were monitored. The levels of these oropharyngeal bacteria decreased or disappeared after weekly professional oral health care, i.e., cleaning of teeth, dentures, tongue, and oral mucous membrane by dental hygienists. After lunch, gargling with povidone iodine was shown to be less effective than professional oral care. These findings indicate that weekly professional mechanical cleaning of the oral cavity, rather than a daily chemical disinfection of the mouth, can be an important strategy to prevent aspiration pneumonia in the dependent elderly.

Stereoselective interaction of ketamine with recombinant mu, kappa, and delta opioid receptors expressed in Chinese hamster ovary cells

BACKGROUND

The authors examined the interaction of ketamine with recombinant mu, kappa, and delta opioid receptors and recombinant orphan opioid receptors expressed in Chinese hamster ovary cells (CHO-mu, CHO-kappa, CHO-delta, and CHO(ORL1), respectively).

METHODS

CHO-mu, CHO-kappa, and CHO-delta membranes were incubated with the opioid receptor radioligand [3H]diprenorphine at room temperature. Ketamine (racemic, R(-) and S(+)) was included at concentrations covering the clinical range. CHO(ORL1) membranes were incubated with [125I]Tyr(14)nociceptin and racemic ketamine at room temperature. The effects of racemic ketamine and selective opioid receptor agonists (mu: [D-Ala2, MePhe4, Gly(ol)5] enkephalin (DAMGO); kappa: spiradoline or delta: [D-pen2, D-pen5] enkephalin (DPDPE)) on forskolin-stimulated cyclic adenosine monophosphate formation also were examined. Data are mean +/- SEM.

RESULTS

Racemic ketamine increased the radioligand equilibrium dissociation constant for [3H]diprenorphine from 85+/-5 to 273+/-11, 91+/-6 to 154+/-16, and 372+/-15 to 855+/-42 pM in CHO-mu, CHO-kappa, and CHO-delta, respectively. The concentration of radioligand bound at saturation was unaffected. In CHO-mu and CHO-kappa cells, racemic ketamine did not slow the rate of naloxone-induced [3H]diprenorphine dissociation. Ketamine and its isomers also displaced [3H]diprenorphine binding to mu, kappa, and delta receptors in a dose-dependent manner, with pKi values for racemic ketamine of 4.38+/-0.02, 4.55+/-0.04, and 3.57+/-0.02, respectively. S(+)-ketamine was two to three times more potent than R(-)-ketamine at mu and kappa receptors. Racemic ketamine displaced [125I]Tyr(14)nociceptin with an estimated affinity constant of 0.5 mM. Racemic ketamine inhibited the formation of cyclic adenosine monophosphate (naloxone insensitive) in a dose-dependent manner (concentration producing 50% inhibition approximately 2 mM) in all cell lines, including untransfected CHO cells. Ketamine (100 microM) reversed DAMGO (mu) and spiradoline (kappa) inhibition of formation of cyclic adenosine monophosphate.

CONCLUSIONS

Ketamine interacts stereoselectively with recombinant mu and kappa opioid receptors.