Native serotonin membrane receptors recognize 5-hydroxytryptophan-functionalized substrates: enabling small-molecule recognition

Recognition of small diffusible molecules by large biomolecules is ubiquitous in biology. To investigate these interactions, it is important to be able to immobilize small ligands on substrates; however, preserving recognition by biomolecule-binding partners under these circumstances is challenging. We have developed methods to modify substrates with serotonin, a small-molecule neurotransmitter important in brain function and psychiatric disorders. To mimic soluble serotonin, we attached its amino acid precursor, 5-hydroxytryptophan, via the ancillary carboxyl group to oligo(ethylene glycol)-terminated alkanethiols self-assembled on gold. Anti-5-hydroxytryptophan antibodies recognize these substrates, demonstrating bioavailability. Interestingly, 5-hydroxytryptophan-functionalized surfaces capture membrane-associated serotonin receptors enantiospecifically. By contrast, surfaces functionalized with serotonin itself fail to bind serotonin receptors. We infer that recognition by biomolecules evolved to distinguish small-molecule ligands in solution requires tethering of the latter via ectopic moieties. Membrane proteins, which are notoriously difficult to isolate, or other binding partners can be captured for identification, mapping, expression, and other purposes using this generalizable approach.

Expression and functional role of adenosine receptors in regulating inflammatory responses in human synoviocytes

BACKGROUND AND PURPOSE

Adenosine is an endogenous modulator, interacting with four G-protein coupled receptors (A(1), A(2A), A(2B) and A(3)) and acts as a potent inhibitor of inflammatory processes in several tissues. So far, the functional effects modulated by adenosine receptors on human synoviocytes have not been investigated in detail. We evaluated mRNA, the protein levels, the functional role of adenosine receptors and their pharmacological modulation in human synoviocytes.

EXPERIMENTAL APPROACH

mRNA, Western blotting, saturation and competition binding experiments, cyclic AMP, p38 mitogen-activated protein kinases (MAPKs) and nuclear factor (NF)-kappaB activation, tumour necrosis factor alpha (TNF-alpha) and interleukin-8 (IL-8) release were assessed in human synoviocytes isolated from patients with osteoarthritis.

KEY RESULTS

mRNA and protein for A(1), A(2A), A(2B) and A(3) adenosine receptors are expressed in human synoviocytes. Standard adenosine agonists and antagonists showed affinity values in the nanomolar range and were coupled to stimulation or inhibition of adenylyl cyclase. Activation of A(2A) and A(3) adenosine receptors inhibited p38 MAPK and NF-kappaB pathways, an effect abolished by selective adenosine antagonists. A(2A) and A(3) receptor agonists decreased TNF-alpha and IL-8 production. The phosphoinositide 3-kinase or G(s) pathways were involved in the functional responses of A(3) or A(2A) adenosine receptors. Synoviocyte A(1) and A(2B) adenosine receptors were not implicated in the inflammatory process whereas stimulation of A(2A) and A(3) adenosine receptors was closely associated with a down-regulation of the inflammatory status.

CONCLUSIONS AND IMPLICATIONS

These results indicate that A(2A) and A(3) adenosine receptors may represent a potential target in therapeutic modulation of joint inflammation.

Conformational effects of Lys191 in the human GnRH receptor: mutagenesis and molecular dynamics simulations studies

In the present study, we analyzed the role of Lys191 on function, structure, and dynamic behavior of the human GnRH receptor (hGnRHR) and the formation of the Cys14-Cys200 bridge, which is essential for receptor trafficking to the plasma membrane. Several mutants were studied; mutants lacked either the Cys14-Cys200 bridge, Lys191 or both. The markedly reduced expression and function of a Cys14Ser mutant lacking the 14-200 bridge, was nearly restored to wild-type/DeltaLys191 levels upon deletion of Lys191. Lys191 removal resulted in changes in the dynamic behavior of the mutants as disclosed by molecular dynamics simulations: the distance between the sulfur- (or oxygen-) sulfur groups of Cys (or Ser)14 and Cys200 was shorter and more constant, and the conformation of the NH(2)-terminus and the exoloop 2 exhibited fewer fluctuations than when Lys191 was present. These data provide novel information on the role of Lys191 in defining an optimal configuration for the hGnRHR intracellular trafficking and function.

The importance of brain banks for molecular neuropathological research: The New South Wales Tissue Resource Centre experience

New developments in molecular neuropathology have evoked increased demands for postmortem human brain tissue. The New South Wales Tissue Resource Centre (TRC) at The University of Sydney has grown from a small tissue collection into one of the leading international brain banking facilities, which operates with best practice and quality control protocols. The focus of this tissue collection is on schizophrenia and allied disorders, alcohol use disorders and controls. This review highlights changes in TRC operational procedures dictated by modern neuroscience, and provides examples of applications of modern molecular techniques to study the neuropathogenesis of many different brain disorders.

Insulin resistance in experimental alcohol-induced liver disease

BACKGROUND AND AIM

Chronic ethanol consumption impairs liver regeneration due, in part, to inhibition of insulin signaling. This study characterizes the mechanisms and consequences of ethanol-impaired insulin signaling in relation to oxidative injury and altered gene expression.

METHODS

Long-Evans rats were fed for 8 weeks with isocaloric liquid diets containing 0% (control) or 37% ethanol (caloric content). Livers were used to examine histopathology, indices of oxidative stress, gene expression required for insulin and insulin-like growth factor (IGF) signaling, insulin-responsive gene expression, i.e. glyceraldehydes-3-phosphate dehydrogenase (GAPDH) and aspartyl-asparaginyl-beta-hydroxylase (AAH), and competitive equilibrium binding to the insulin, IGF-I, and IGF-II receptors.

RESULTS

Chronic ethanol exposure caused liver injury with increased hepatocellular steatosis, inflammation, apoptosis, and increased immunoreactivity for activated caspase-3, 8-hydroxy-2'-deoxyguanosine, and 4-hydroxy-2,3-nonenol. These effects were associated with increased expression of IGF-I receptor, IGF-II, and IGF-II receptor, and expression of IGF-I, AAH, and GAPDH, which mediate energy metabolism and cell motility/remodeling, and reduced binding to the insulin receptor.

CONCLUSIONS

Chronic ethanol-induced liver injury causes insulin resistance with inhibition of insulin-responsive genes needed for metabolism, remodeling, and regeneration. In contrast, the IGF-I and IGF-II signaling mechanisms remain relatively preserved, suggesting that insulin-regulated hepatic functions may be selectively vulnerable to the toxic effects of ethanol.

Structure-activity relationships of 2,N(6),5'-substituted adenosine derivatives with potent activity at the A2B adenosine receptor

2, N6, and 5'-substituted adenosine derivatives were synthesized via alkylation of 2-oxypurine nucleosides leading to 2-arylalkylether derivatives. 2-(3-(Indolyl)ethyloxy)adenosine 17 was examined in both binding and cAMP assays and found to be a potent agonist of the human A2BAR. Simplification, altered connectivity, and mimicking of the indole ring of 17 failed to maintain A2BAR potency. Introduction of N6-ethyl or N6-guanidino substitution, shown to favor A2BAR potency, failed to enhance potency in the 2-(3-(indolyl)ethyloxy)adenosine series. Indole 5' '- or 6' '-halo substitution was favored at the A2BAR, but a 5'-N-ethylcarboxyamide did not further enhance potency. 2-(3' '-(6' '-Bromoindolyl)ethyloxy)adenosine 28 displayed an A2BAR EC50 value of 128 nM, that is, more potent than the parent 17 (299 nM) and similar to 5'-N-ethylcarboxamidoadenosine (140 nM). Compound 28 was a full agonist at A2B and A2AARs and a low efficacy partial agonist at A1 and A3ARs. Thus, we have identified and optimized 2-(2-arylethyl)oxo moieties in AR agonists that enhance A2BAR potency and selectivity.

Dexmethylphenidate hydrochloride in the treatment of attention deficit hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) affects a large number of children. For decades, the stimulants have been the mainstay of pharmacological treatment for ADHD. Dexmethylphenidate (d-MPH), the d-isomer of the traditional racemic mixtures of d,l-threo-(R,R)-MPH, was recently introduced as another potential option in the stimulant class of medications. This paper reviews and summarizes the available research literature on d-MPH regarding pharmacodynamic, pharmacokinetic, chemical structure, receptor binding, toxicology, and clinical perspectives. d-MPH potentially may offer some advantages in the realms of absorption and duration of action compared with its racemic counterpart. The differences in pharmacokinetics and clinical implications of the immediate-release and extended-release forms of d-MPH are also compared and contrasted.

RO1138452 and RO3244794: characterization of structurally distinct, potent and selective IP (prostacyclin) receptor antagonists

Prostacyclin (PGI2) possesses various physiological functions, including modulation of nociception, inflammation and cardiovascular activity. Elucidation of these functions has been hampered by the absence of selective IP receptor antagonists. Two structurally distinct series of IP receptor antagonists have been developed: 4,5-dihydro-1H-imidazol-2-yl)-[4-(4-isopropoxy-benzyl)-phenyl]-amine (RO1138452) and R-3-(4-fluoro-phenyl)-2-[5-(4-fluoro-phenyl)-benzofuran-2-ylmethoxycarbonylamino]-propionic acid (RO3244794).RO1138452 and RO3244794 display high affinity for IP receptors. In human platelets, the receptor affinities (pKi) were 9.3 +/- 0.1 and 7.7 +/- 0.03, respectively; in a recombinant IP receptor system, pKi values were 8.7 +/- 0.06 and 6.9 +/- 0.1, respectively. Functional antagonism of RO1138452 and RO3244794 was studied by measuring inhibition of carbaprostacyclin-induced cAMP accumulation in CHO-K1 cells stably expressing the human IP receptor. The antagonist affinities (pKi) of RO1138452 and RO3244794 were 9.0 +/- 0.06 and 8.5 +/- 0.11, respectively. Selectivity profiles for RO1138452 and RO3244794 were determined via a panel of receptor binding and enzyme assays. RO1138452 displayed affinity at I2 (8.3) and PAF (7.9) receptors, while RO3244794 was highly selective for the IP receptor: pKi values for EP1 (< 5), EP3 (5.38), EP4 (5.74) and TP (5.09). RO1138452 (1-10 mg kg(-1), i.v.) and RO3244794 (1-30 mg kg(-1), i.v.) significantly reduced acetic acid-induced abdominal constrictions. RO1138452 (3-100 mg kg(-1), p.o.) and RO3244794 (0.3-30 mg kg(-1), p.o.) significantly reduced carrageenan-induced mechanical hyperalgesia and edema formation. RO3244794 (1 and 10 mg kg(-1), p.o.) also significantly reduced chronic joint discomfort induced by monoiodoacetate. These data suggest that RO1138452 and RO3244794 are potent and selective antagonists for both human and rat IP receptors and that they possess analgesic and anti-inflammatory potential.

A2B adenosine receptor activity is reduced in neutrophils from patients with systemic sclerosis

We conducted the present study to investigate protein expression and functioning of A2A and A2B adenosine receptors (ARs) in neutrophils of patients affected by systemic sclerosis (SSc). The presence of A2A and A2B ARs was assessed by immunoblotting using specific antibodies. Equilibrium A2A and A2B ARs binding parameters were evaluated by radioligand binding assay. Functional studies were conducted to investigate coupling of the A2B AR to the adenylyl cyclase pathway. This is the first report of the use of Western blot analysis to confirm the presence of A2A and A2B ARs in human neutrophils. No significant changes in A2A AR binding parameters or expression levels were detected between SSc patients and healthy control individuals. A significant decrease (65%) in the maximum density of A2B AR binding sites occurred in SSc neutrophils, whereas no changes in the affinity constant values were found. Moreover, a decrease in A2B AR mediated adenylyl cyclase activity was observed in patients with SSc. Our findings demonstrate the occurrence of selective alterations in A2B AR density and signalling in SSc.

N6-Substituted adenosine derivatives: selectivity, efficacy, and species differences at A3 adenosine receptors

The activation of the human A(3) adenosine receptor (AR) by a wide range of N(6)-substituted adenosine derivatives was studied in intact CHO cells stably expressing this receptor. Selectivity of binding at rat and human ARs was also determined. Among N(6)-alkyl substitutions, small N(6)-alkyl groups were associated with selectivity for human A(3)ARs vs. rat A(3)ARs, and multiple points of branching were associated with decreased hA(3)AR efficacy. N(6)-Cycloalkyl-substituted adenosines were full (</=5 carbons) or partial (>/=6 carbons) hA(3)AR agonists. N(6)-(endo-Norbornyl)adenosine 13 was the most selective for both rat and human A(1)ARs. Numerous N(6)-arylmethyl analogues, including substituted benzyl, tended to be more potent in binding to A(1) and A(3) vs. A(2A)ARs (with variable degrees of partial to full A(3)AR agonisms). A chloro substituent decreased the efficacy depending on its position on the benzyl ring. The A(3)AR affinity and efficacy of N(6)-arylethyl adenosines depended highly on stereochemistry, steric bulk, and ring constraints. Stereoselectivity of binding was demonstrated for N(6)-(R-1-phenylethyl)adenosine vs. N(6)-(S-1-phenylethyl)adenosine, as well as for the N(6)-(1-phenyl-2-pentyl)adenosine, at the rat, but not human A(3)AR. Interestingly, DPMA, a potent agonist for the A(2A)AR (K(i)=4nM), was demonstrated to be a moderately potent antagonist for the human A(3)AR (K(i)=106nM). N(6)-[(1S,2R)-2-Phenyl-1-cyclopropyl]adenosine 48 was 1100-fold more potent in binding to human (K(i)=0.63nM) than rat A(3)ARs. Dual acting A(1)/A(3) agonists (N(6)-3-chlorobenzyl- 29, N(6)-(S-1-phenylethyl)- 39, and 2-chloro-N(6)-(R-phenylisopropyl)adenosine 53) might be useful for cardioprotection.

Desensitization of alpha 2A-adrenoceptor signalling by modest levels of adrenaline is facilitated by beta 2-adrenoceptor-dependent GRK3 up-regulation

(1) Adrenaline (ADR) and noradrenaline (NA) can simultaneously activate inhibitory alpha(2)- and stimulatory beta-adrenoceptors (AR). However, ADR and NA differ significantly in that ADR is a potent beta(2)-AR agonist while NA is not. Only recently has the interaction resulting from the simultaneous activation of alpha(2)- and beta(2)-AR been examined at the cellular level to determine the mechanisms of alpha(2)-AR regulation following concomitant activation of both alpha(2)- and beta(2)-ARs by chronic ADR. (2) This study evaluates beta(2)-AR regulation of alpha(2A)-AR signalling following chronic ADR (300 nM) and NA (1 and 30 micro M) treatments of BE(2)-C human neuroblastoma cells that natively express both beta(2)- and alpha(2A)-ARs. (3) Chronic (24 h) treatment with ADR (300 nM) desensitized the response to the alpha(2A)-AR agonist, brimonidine, in BE(2)-C cells. Addition of the beta-AR antagonist, propranolol, blocked the ADR-induced alpha(2A)-AR desensitization. Unlike ADR, chronic NA (1 micro M) treatment had no effect on the alpha(2A)-AR response. However if NA was increased to 30 micro M for 24 h, alpha(2A)-AR desensitization was observed; this desensitization was partially reversed by propranolol. (4) Chronic ADR (300 nM) treatment reduced alpha(2A)-AR binding levels, contributing to the alpha(2A)-AR desensitization. This decrease was prevented by addition of propranolol during ADR treatment. Chronic NA (30 micro M), like ADR, treatment lowered specific binding, whereas 1 micro M NA treatment was without effect. (5) Chronic ADR treatment produced a significant increase in GRK3 levels and this was blocked by propranolol or GRK2/3 antisense DNA treatment. This antisense DNA, common to both GRK2 and GRK3, also blocked chronic ADR-induced alpha(2A)-AR desensitization and down-regulation. (6) Acute (1 h) ADR (300 nM) or NA treatment (1 micro M) produced alpha(2A)-AR desensitization. The desensitization produced by acute treatment was beta-AR independent, as it was not blocked by propranolol. (7) We conclude that chronic treatment with modest levels of ADR produces alpha(2A)-AR desensitization by mechanisms that involve up-regulation of GRK3 and down-regulation of alpha(2A)-AR levels through interactions with the beta(2)-AR.

Glycosaminoglycans in human retinoblastoma cells: heparan sulfate, a modulator of the pigment epithelium-derived factor-receptor interactions

BACKGROUND

Pigment epithelium-derived factor (PEDF) has binding affinity for cell-surface receptors in retinoblastoma cells and for glycosaminoglycans. We investigated the effects of glycosaminoglycans on PEDF-receptor interactions.

RESULTS

125I-PEDF formed complexes with protease-resistant components of medium conditioned by human retinoblastoma Y-79 cells. Using specific glycosaminoglycan degrading enzymes in spectrophotometric assays and PEDF-affinity chromatography, we detected heparin and heparan sulfate-like glycosaminoglycans in the Y-79 conditioned media, which had binding affinity for PEDF. The Y-79 conditioned media significantly enhanced the binding of 125I-PEDF to Y-79 cell-surface receptors. However, enzymatic and chemical depletion of sulfated glycosaminoglycans from the Y-79 cell cultures by heparitinase and chlorate treatments decreased the degree of 125I-PEDF binding to cell-surface receptors.

CONCLUSIONS

These data indicate that retinoblastoma cells secrete heparin/heparan sulfate with binding affinity for PEDF, which may be important in efficient cell-surface receptor binding.

Differential allosteric modulation by amiloride analogues of agonist and antagonist binding at A(1) and A(3) adenosine receptors

The diuretic drug amiloride and its analogues were found previously to be allosteric modulators of antagonist binding to A(2A) adenosine receptors. In this study, the possibility of the allosteric modulation by amiloride analogues of antagonist binding at A(1) and A(3) receptors, as well as agonist binding at A(1), A(2A), and A(3) receptors, was explored. Amiloride analogues increased the dissociation rates of two antagonist radioligands, [3H]8-cyclopentyl-1,3-dipropylxanthine ([3H]DPCPX) and [3H]8-ethyl-4-methyl-2-phenyl-(8R)-4,5,7,8-tetrahydro-1H-imidazo[2,1-i]purin-5-one ([3H]PSB-11), from A(1) and A(3) receptors, respectively. Amiloride and 5-(N,N-dimethyl)amiloride (DMA) were more potent at A(1) receptors than at A(3) receptors, while 5-(N,N-hexamethylene)amiloride (HMA) was more potent at A(3) receptors. Thus, amiloride analogues are allosteric inhibitors of antagonist binding at A(1), A(2A), and A(3) adenosine receptor subtypes. In contrast to their effects on antagonist-occupied receptors, amiloride analogues did not affect the dissociation rates of the A(1) agonist [3H]N(6)-[(R)-phenylisopropyl]adenosine ([3H]R-PIA) from A(1) receptors or the A(2A) agonist [3H]2-[p-(2-carboxyethyl)phenyl-ethylamino]-5'-N-ethylcarboxamidoadenosine ([3H]CGS21680) from A(2A) receptors. The dissociation rate of the A(3) agonist radioligand [125I]N(6)-(4-amino-3-iodobenzyl)adenosine-5'-N-methyluronamide ([125I]I-AB-MECA) from A(3) receptors was decreased significantly by amiloride analogues. The binding modes of amiloride analogues at agonist-occupied and antagonist-occupied receptors differed markedly, which was demonstrated in all three subtypes of adenosine receptors tested in this study. The effects of the amiloride analogues on the action of the A(3) receptor agonist were explored further using a cyclic AMP functional assay in intact CHO cells expressing the human A(3) receptor. Both binding and functional assays support the allosteric interactions of amiloride analogues with A(3) receptors.

Allosteric modulation of [3H]-CGP39653 binding through the glycine site of the NMDA receptor: further studies in rat and human brain

Binding of D,L-(E)-2-amino-4-[(3)H]-propyl-5-phosphono-3-pentenoic acid ([(3)H]-CGP39653), a selective antagonist at the glutamate site of the NMDA receptor, is modulated by glycine in rat brain tissue. We have further investigated this phenomenon in rodent and human brain by means of receptor binding and quantitative autoradiography techniques. In rat cerebral cortical membranes the glycine antagonist 3-[2-(Phenylaminocarbonyl)ethenyl]-4,6-dichloro-indole-2-carboxylic acid sodium salt (GV150526A) did not change basal [(3)H]-CGP39653 binding, but competitively reversed the high affinity component of [(3)H]-CGP39653 binding inhibition by glycine, with a pK(B) value of 8.38, in line with its affinity for the glycine site (pK(i)=8.49 vs. [(3)H]-glycine). Glycine (10 microM) significantly decreased [(3)H]-CGP39653 affinity for the NMDA receptor (with no change in the B(max)), whereas enhanced L-glutamate affinity (P<0.05, paired-samples Student's t-test). In rat brain sections the addition of GV150526A (30 microM) to the incubation medium increased [(3)H]-CGP39653 binding to 208% of control (average between areas), indicating the presence of endogenous glycine. The enhancement presented significant regional differences (P<0.05, two-way ANOVA), with striatum higher than cerebral cortex (282 and 187% of control, respectively; P<0.05, Fisher's LSD). On the contrary, there was not any significant variation in affinity values of [(3)H]-CGP39653, L-glutamate, glycine and GV150526A in striatal and cortical membranes. These results confirmed the existence of regionally distinct NMDA receptors subtypes with different glycine/glutamate allosteric modulation. Whole brain autoradiography revealed an uneven distribution of [(3)H]-CGP39653 binding sites in human brain. High levels of binding were determined in hippocampus and in cingulate, frontoparietal and insular cortex. Intermediate to low levels of binding were found in diencephalic nuclei and basal ganglia. [(3)H]-CGP39653 binding was increased to 216% of control (mean between areas) by 30 microM GV150526A. The enhancement, however, did not present significant regional differences. These results introduce GV150526A as a useful tool to identify NMDA receptor subtypes by means of receptor autoradiography; moreover, they demonstrate that the allosteric inhibition of [(3)H]-CGP39653 binding by glycine parallels an increase in receptor affinity to the endogenous ligand L-glutamate. Finally, this study provides the first detailed anatomical description of the regional distribution of [(3)H]-CGP39653 binding sites in human brain.

Receptor binding studies of soft anticholinergic agents

Receptor binding studies were performed on 24 soft anticholinergic agents and 5 conventional anticholinergic agents using 4 cloned human muscarinic receptor subtypes. The measured pK(i) values of the soft anticholinergic agents ranged from 6.5 to 9.5, with the majority being in the range of 7.5 to 8.5. Strong correlation was observed between the pK(i) s determined here and the pA 2 values measured earlier in guinea pig ileum contraction assays. The corresponding correlation coefficients (r2) were 0.80, 0.73, 0.81, and 0.78 for pK(i) (m1), pK(i) (m2), pK(i) (m3), and pK(i) (m4), respectively. Quantitative structure-activity relationship (QSAR) studies were also performed, and good characterization could be obtained for the soft anticholinergics containing at least 1 tropine moiety in their structure. For these compounds, the potency as measured by the pK i values was found to be related to geometric, electronic, and lipophilicity descriptors. A linear regression equation using ovality (O(e)), dipole moment (D), and a calculated log octanol-water partition coefficient (QLogP) gave reasonably good descriptions (r = 0.88) for the pK(i) (m3) values.

Effect of dexamethasone treatment on maturational changes in the NMDA receptor in sheep brain

The objective of the present study was to examine the effect of antenatal or postnatal treatment with corticosteroids on the NMDA receptor, one of the mediators of both normal brain development and hypoxic-ischemic injury, by determining the characteristics of the receptor MK-801 binding site in untreated and corticosteroid-treated fetal and newborn lambs. (3)H-MK-801 binding was performed in cerebral cortical cell membranes from fetal sheep at 88, 120, and 136 d gestation (term = 150 d), and from 5-d-old lambs and adult ewes. Animals were randomized to receive dexamethasone [fetuses: 6 mg, i.m. every 12 hr for four doses to mother; lambs: 0.01 mg/kg (low dose) or 0.25 mg/kg (high dose) every 12 hr for four doses] or placebo. During development, B(max) (apparent number of receptors) increased, reaching a maximum in 5-d-old lambs (p < 0.05) and decreasing in the adult brain. K(d) (dissociation constant) did not change, suggesting that receptor affinity was not altered during maturation. Dexamethasone treatment had no effect on MK-801 binding in the fetus or adult, but in lambs was associated with a significant decrease in B(max) from 2.17 +/- 0.18 pmol/mg protein in placebo-treated animals to 1.65 +/- 0.8 and 1.62 +/- 0.07 pmol/mg protein in low-dose and high-dose animals, respectively. Affinity for (3)H-MK-801 decreased 20% after dexamethasone treatment in lambs only (p < 0.05). Thus, dexamethasone treatment appears to modify the NMDA receptor only during a specific period of brain development.

Characterization of a novel nonpeptide vasopressin V(2)-agonist, OPC-51803, in cells transfected human vasopressin receptor subtypes

We discovered the first nonpeptide arginine-vasopressin (AVP) V(2)-receptor agonist, OPC-51803. Pharmacological properties of OPC-51803 were elucidated using HeLa cells expressing human AVP receptor subtypes (V(2), V(1a) and V(1b)) and compared with those of 1-desamino-8-D-arginine vasopressin (dDAVP), a peptide V(2)-receptor agonist. OPC-51803 and dDAVP displaced [(3)H]-AVP binding to human V(2)- and V(1a)-receptors with K(i) values of 91.9+/-10.8 nM (n = 6) and 3.12+/-0.38 nM (n = 6) for V(2)-receptors, and 819+/-39 nM (n = 6) and 41.5+/-9.9 nM (n = 6) for V(1a)-receptors, indicating that OPC-51803 was about nine times more selective for V(2)-receptors, similar to the selectivity of dDAVP. OPC-51803 scarcely displaced [(3)H]-AVP binding to human V(1b)-receptors even at 10(-4) M, while dDAVP showed potent affinity to human V(1b)-receptors with the K(i) value of 13.7+/-3.2 nM (n = 4). OPC-51803 concentration-dependently increased cyclic adenosine 3', 5'-monophosphate (cyclic AMP) production in HeLa cells expressing human V(2)-receptors with an EC(50) value of 189+/-14 nM (n = 6). The concentration-response curve for cyclic AMP production induced by OPC-51803 was shifted to the right in the presence of a V(2)-antagonist, OPC-31260. At 10(-5) M, OPC-51803 did not increase the intracellular Ca(2+) concentration ([Ca(2+)](i)) in HeLa cells expressing human V(1a)-receptors. On the other hand, dDAVP increased [Ca(2+)](i) in HeLa cells expressing human V(1a)- and V(1b)-receptors in a concentration-dependent fashion. From these results, OPC-51803 has been confirmed to be the first nonpeptide agonist for human AVP V(2)-receptors without agonistic activities for V(1a)- and V(1b)-receptors. OPC-51803 may be useful for the treatment of AVP-deficient pathophysiological states and as a tool for AVP researches.

Characterization and distribution of prolactin releasing peptide (PrRP) binding sites in the rat--evidence for a novel binding site subtype in cardiac and skeletal muscle

Prolactin releasing peptide (PrRP) was recently purified from bovine hypothalamus and binds to the orphan receptor, UHR-1. We examined the distribution and kinetics of (125)I-PrRP binding in rat tissues together with molecular characterization by chemical cross-linking and Northern blotting. In this study (125)I-PrRP binding showed specificity and rapid association and dissociation. Specific binding was found in membranes from rat tissues including brain (hypothalamus, medulla oblongata and cerebellum), pituitary, heart, soleus muscle, adipose tissue, kidney, adrenal gland, testis and small intestine. In hypothalamus, pituitary, heart and soleus competition analysis indicated only one class of binding site in each tissue. Binding affinity for PrRP (IC(50)) and binding site density (B(max)) respectively were 5.2+/-0.9 nM and 674+/-97 fmol mg protein(-1) in hypothalamus (n = 5), 1.4+/-0.6 nM and 541+/-126 fmol mg protein(-1) in pituitary (n = 3), 6.6+/-0.7 nM and 628+/-74 fmol mg protein(-1) in heart (n = 4) and 9.8+/-0.9 nM and 677+/-121 fmol mg protein(-1) in soleus muscle (n = 4). Analysis of (125)I-PrRP-binding site complexes by chemical cross-linking showed a binding site M(r) of 69,000 in hypothalamus and 41,000 in heart and soleus. Northern analysis of polyA(+) RNA from hypothalamus showed a 4.2 kb band as expected for UHR-1, but heart and soleus showed a 4.8 kb band. Taken together these results indicate that there may be different subtypes of PrRP binding sites in rat tissues which may differ from UHR-1.

Estradiol modulates bcl-2 in cerebral ischemia: a potential role for estrogen receptors

We have shown that physiological levels of estradiol exert profound protective effects on the cerebral cortex in ischemia induced by permanent middle cerebral artery occlusion. The major goal of this study was to begin to elucidate potential mechanisms of estradiol action in injury. Bcl-2 is a proto-oncogene that promotes cell survival in a variety of tissues including the brain. Because estradiol is known to promote cell survival via Bcl-2 in non-neural tissues, we tested the hypothesis that estradiol decreases cell death by influencing bcl-2 expression in ischemic brain injury. Furthermore, because estradiol may protect the brain through estrogen receptor-mediated mechanisms, we examined expression of both receptor subtypes ERalpha and ERbeta in the normal and injured brain. We analyzed gene expression by RT-PCR in microdissected regions of the cerebral cortex obtained from injured and sham female rats treated with estradiol or oil. We found that estradiol prevented the injury-induced downregulation of bcl-2 expression. This effect was specific to bcl-2, as expression of other members of the bcl-2 family (bax, bcl-x(L), bcl-x(S), and bad) was unaffected by estradiol treatment. We also found that estrogen receptors were differentially modulated in injury, with ERbeta expression paralleling bcl-2 expression. Finally, we provide the first evidence of functional ERbeta protein that is capable of binding ligand within the region of the cortex where estradiol-mediated neuroprotection was observed in cerebral ischemia. These findings indicate that estradiol modulates the expression of bcl-2 in ischemic injury. Furthermore, our data suggest that estrogen receptors may be involved in hormone-mediated neuroprotection.

Synthesis and biological evaluation of cytotoxic analogs of somatostatin containing doxorubicin or its intensely potent derivative, 2-pyrrolinodoxorubicin

To create cytotoxic hybrid analogs of somatostatin (SST), octapeptides RC-160 (D-Phe-Cys-Tyr-D-Trp- Lys-Val-Cys-Trp-NH2) and RC-121 (D-Phe-Cys-Tyr-D-Trp- Lys-Val-Cys-Thr-NH2) were linked to doxorubicin (DOX) or its superactive derivative, 2-pyrrolino-DOX (AN-201). The conjugation was performed by coupling N-9-fluorenylmethoxycarbonyl (N-Fmoc)-DOX-14-O-hemiglutarate or 2-pyrrolino-DOX-14-O-hemiglutarate to the amino terminus of [Lys(Fmoc)5]RC-160 yielding AN-163 and AN-258, respectively, after deprotection. The respective cytotoxic conjugates of RC-121 (AN-162 and AN-238) were prepared similarly. In vitro tests on human cancer cell lines-MKN-45 gastric cancer, MDA-MB-231 breast cancer, PC-3 prostate cancer, and MIA PaCa-2 pancreatic cancer-demonstrated that the antiproliferative activity of the cytotoxic radicals in these conjugates was virtually retained. In H-345 human small cell lung carcinoma cell line, conjugates of RC-121 preserved the cytotoxic activity of their radicals, but the hybrids with RC-160 showed approximately 10 times lower activity. The ability of the carriers and the hybrids to inhibit the binding of 125I-labeled RC-160 to receptors for SST on rat pituitary membrane preparation was also determined. The cytotoxic conjugates inhibited 50% of the specific binding of the radioligand in the nanomolar concentration range (IC50 < 80 nM). When SST-like activities of AN-238 and its carrier, RC-121, were compared in the rat pituitary superfusion system, both compounds were found to suppress a stimulated growth hormone release at nanomolar concentrations. Preliminary studies in animal models of breast and prostate cancers showed that AN-238 is less toxic than AN-201 and more potent in inhibiting tumor growth. These highly active cytotoxic analogs of SST have been designed as targeted antitumor agents for the treatment of various cancers expressing receptors for SST octapeptides.

Human vascular kinin receptors of the B2 type characterized by radioligand binding

1. The human umbilical vein responds to bradykinin (BK) with contractions that are mediated by B2 receptors. In the present study, the corresponding vascular smooth muscle B2 binding sites have been investigated. 2. [3H]-BK, a full agonist labelled ligand, was used to demonstrate a single binding site giving a Kd value of 0.51+/-0.02 nM and a Bmax of 24+/-1 fmol mg(-1) protein. Scatchard plots were linear (r=0.98) in the 0.05-5 nM range of concentrations. Non-specific binding was found to be 30% of total binding. 3. Competition binding curves gave the following order of potency for various B2 receptor agonists: BK-[Hyp3]-BK > or = Lys-BK >> [Aib7]-BK >>> [desArg9]-BK, which is typical of B2 receptors. There was no binding to B1 receptors since the selective B1 receptor ligand, Lys-[desArg9]BK was inactive up to 10 microM (n=4). 4. Characterization of the binding site with antagonists, performed with three chemically distinct series of peptide and non-peptide compounds, revealed a high affinity of Hoe 140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-BK) (Ki 0.17 nM; n=4) which was more potent that FR 173657 ([(E)-3-(6-acetamido-3-pyridyl)-N-[N-[2,4-dichloro-3-[(2-methyl-8-quinol inyl)oxymethyl]phenyl]-N-methylaminocarbonylmethyl] acrylamide]) (Ki 1.94 nM; n=4), D-Arg-[Hyp3,D-Phe7,Leu8]-BK (Ki 256 nM; n=4) and Win 64338 (phosphonium, [[4[[2[[bis(cyclohexylamino)methylene]amino]-3-(2-naphthalenyl)-1-oxopro pyl]amino]phenyl]methyl]tributyl, chloride, monohydrochloride) (Ki 1,450 nM; n=4). 5. The present study describes and characterises B2 receptor binding sites in the vascular smooth muscle of the human umbilical vein. The binding assay appears to be suitable for studying new agonists or antagonists designed to activate or block the B2 receptor class that mediate the majority of the physiopathological effects of kinins in man.

Adenosine A1 receptor-mediated activation of phospholipase C in cultured astrocytes depends on the level of receptor expression

Adenosine A1 receptors induce an inhibition of adenylyl cyclase via G-proteins of the Gi/o family. In addition, simultaneous stimulation of A1 receptors and of receptor-mediated activation of phospholipase C (PLC) results in a synergistic potentiation of PLC activity. Evidence has accumulated that Gbetagamma subunits mediate this potentiating effect. However, an A1 receptor-mediated increase in extracellular glutamate was suggested to be responsible for the potentiating effect in mouse astrocyte cultures. We have investigated the synergistic activation of PLC by adenosine A1 and alpha1 adrenergic receptors in primary cultures of astrocytes derived from different regions of the newborn rat brain. It is reported here that (1) adenosine A1 receptor mRNA as well as receptor protein is present in astrocytes from all brain regions, (2) A1 receptor-mediated inhibition of adenylyl cyclase is of similar extent in all astrocyte cultures, (3) the A1 receptor-mediated potentiation of PLC activity requires higher concentrations of agonist than adenylyl cyclase inhibition and is dependent on the expression level of A1 receptor, and (4) the potentiating effect on PLC activity is unrelated to extracellular glutamate. Taken together, our data support the notion that betagamma subunits are the relevant signal transducers for A1 receptor-mediated PLC activation in rat astrocytes. Because of the lower affinity of betagamma, as compared with alpha subunits, more betagamma subunits are required for PLC activation. Therefore, only in cultures with higher levels of adenosine A1 receptors is the release of betagamma subunits via Gi/o activation sufficient to stimulate PLC. It is concluded that variation of the expression level of adenosine A1 receptors may be an important regulatory mechanism to control PLC activation via this receptor.

Irreversible antagonism of 5HT2c receptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ)

To determine if N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), a carboxyl group activating agent, can inactivate 5HT2c receptors, we have examined the effects of EEDQ on 5HT2c receptor-mediated responses to 5-hydroxytryptamine (5HT) in Xenopus oocytes, and on the binding of [3H]5HT to 5HT2c receptors in transfected HeLa cells. In oocytes expressing rat 5HT2c receptors, EEDQ inhibited the 5HT2c receptor-mediated Cl- currents; and the response did not recover more than 24 h after removal of the EEDQ. To see if this effect of EEDQ was on the receptor itself, the binding of 5HT to 5HT2c receptors was studied in transfected HeLa cells. EEDQ decreased the specific binding of [3H]5HT to 5HT2c receptors. At approximately 22 degrees C, incubating the membranes with 2 x 10(-4) M EEDQ for 1 h caused a 40% decrease in the Bmax, without changing the K(d). At 37 degrees C, the same treatment with EEDQ blocked [3H]5HT binding completely. Half-maximal inhibition occurred at 5 microM EEDQ at both temperatures, and washing for 1.5 h did not restore the binding, suggesting that the inactivation of 5HT2c receptor binding was practically irreversible. Results from both systems showed clearly that EEDQ is an irreversible antagonist of 5HT2c receptors and therefore can be used for many studies of this receptor.

Blockage of 5HT2C serotonin receptors by fluoxetine (Prozac)

Fluoxetine (Prozac) inhibited the membrane currents elicited by serotonin (5-hydroxytryptamine; 5HT) in Xenopus oocytes expressing either cloned 5HT2C receptors or 5HT receptors encoded by rat cortex mRNA. Responses of 5HT2C receptors, elicited by nM concentrations of 5HT, were rapidly and reversibly blocked by micromolar concentrations of fluoxetine. For responses elicited by 1 microM 5HT, the IC50 of fluoxetine inhibition was approximately 20 microM. In accord with the electrophysiological results, fluoxetine inhibited the binding of [3H]5HT to 5HT2C receptors expressed in HeLa cells (Ki approximately 65-97 nM), and the binding to 5HT receptors in rat cortex membranes was also inhibited but less efficiently (Ki approximately 56 microM). Our results show that fluoxetine is a competitive and reversible antagonist of 5HT2C receptors and suggest that some therapeutic effects of fluoxetine may involve blockage of 5HT receptors, in addition to its known blockage of 5HT transporters. Similar work may help to design more selective compounds for use in the treatment of brain disorders.

Design, synthesis, and in vitro evaluation of cytotoxic analogs of bombesin-like peptides containing doxorubicin or its intensely potent derivative, 2-pyrrolinodoxorubicin

Five peptide fragments, based on the C-terminal sequence of bombesin (BN)-(6-14) or BN-(7-14), were selected as carriers for radicals doxorubicin (DOX) and 2-pyrrolino-DOX to create hybrid cytotoxic analogs. All these compounds had a reduced peptide bond (CH2-NH or CH2-N) between positions 13 (Phe or Leu) and 14 (Phe, Leu, or Tac) (Tac = thiazolidine-4-carboxylic acid). Three pseudononapeptide carriers contained N-terminal D-Phe or D-Tpi at position 6 (Tpi = 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid). Two pseudooctapeptides had Gln7 at the N terminus. The conjugation of N-(9-fluorenylmethoxycarbonyl) doxorubicin (N-Fmoc-DOX)-14-O-hemiglutarate to the peptide carriers at the N terminus resulted in cytotoxic hybrids of BN-like peptides containing DOX. These hybrids could then be converted to analogs with 2-pyrrolino-DOX by a reaction with 4-iodobutyraldehyde. The ability of the carriers and the conjugates to inhibit the binding of 125I-labeled [Tyr4]BN to receptors for BN/gastrin releasing peptide (GRP) on Swiss 3T3 cells was determined. Cytotoxic conjugates of pseudooctapeptide carrier analogs displayed the highest binding affinity (KD approximately 1 nM). The cytotoxic BN analogs and their corresponding cytotoxic radicals exerted similar inhibitory effects on the in vitro growth of CFPAC-1 human pancreatic cancer, DMS-53 human lung cancer, PC-3 human prostate cancer, and MKN-45 human gastric cancer cell lines that have receptors for BN/GRP. In DMS-53 cells, the activity of 2-pyrrolino-DOX and its conjugates was approximately 2500 times higher than that of DOX and its hybrids. These highly potent cytotoxic analogs of BN have been designed as targeted anti-tumor agents for the treatment of various cancers that possess receptors for BN/GRP.