The alpha 4 integrin chain is a ligand for alpha 4 beta 7 and alpha 4 beta 1

The heterodimeric alpha 4 integrins alpha 4 beta 7 lymphocyte Peyer's patch adhesion molecule ([LPAM]-1) and alpha 4 beta 1 (very late antigen-4) are cell surface adhesion molecules involved in lymphocyte trafficking and lymphocyte-cell and matrix interactions. Known cellular ligands include vascular cell adhesion molecule (VCAM)-1, which binds to alpha 4 beta 1 and alpha 4 beta 7, and the mucosal addressin cell adhesion molecule (MAdCAM)-1, which binds to alpha 4 beta 7. Here we show that the alpha 4 chain of these integrins can itself serve as a ligand. The alpha 4 chain, immunoaffinity purified and immobilized on glass slides, binds thymocytes and T lymphocytes. Binding exhibits divalent cation requirements and temperature sensitivity which are characteristic of integrin-mediated interactions, and is specifically inhibited by anti-alpha 4 integrin antibodies, which exert their effect at the cell surface. Cells expressing exclusively alpha 4 beta 7 (TK-1) or alpha 4 beta 1 (L1-2) both bound avidly, whereas alpha 4-negative cells did not. A soluble 34-kD alpha 4 chain fragment retained binding activity, and it inhibited lymphocyte adhesion to alpha 4 ligands. It has been shown that alpha 4 integrin binding to fibronectin involves an leucine-aspartic acid-valine (LDV) motif in the HepII/IIICS region of fibronectin (CS-1 peptide), and homologous sequences are important in binding to VCAM-1 and MAdCAM-1. Three conserved LDV motifs occur in the extracellular sequence of alpha 4. A synthetic LDV-containing alpha 4- derived oligopeptide supports alpha 4-integrin-dependent lymphocyte adhesion and blocks binding to the 34-kD alpha 4 chain fragment. Our results suggest that alpha 4 beta 7 and alpha 4 beta 1 integrins may be able to bind to the alpha 4 subunit on adjacent cells, providing a novel mechanism for alpha 4 integrin-mediated and activation-regulated lymphocyte interactions during immune responses.     

Alpha(4)beta(7)/alpha(4)beta(1) dual integrin antagonists block alpha(4)beta(7)-dependent adhesion under shear flow

The alpha(4) integrin, alpha(4)beta(7), plays an important role in recruiting circulating lymphocytes to the gastrointestinal tract, where its ligand mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is preferentially expressed on high endothelial venules (HEVs). Dual antagonists of alpha(4)beta(1) and alpha(4)beta(7), N-(2,6-dichlorobenzoyl)-(L)-4-(2',6'-bis-methoxyphenyl)phenylalanine (TR14035) and N-(N-[(3,5-dichlorobenzene)sulfonyl]-2-(R)-methylpropyl)-(D)-phenylalanine (compound 1), were tested for their ability to block the binding of alpha(4)beta(7)-expressing cells to soluble ligand in suspension and under in vitro and in vivo shear flow. Compound 1 and TR14035 blocked the binding of human alpha(4)beta(7) to an (125)I-MAdCAM-Ig fusion protein with IC(50) values of 2.93 and 0.75 nM, respectively. Both compounds inhibited binding of soluble ligands to alpha(4)beta(1) or alpha(4)beta(7) on cells of human or rodent origin with similar potency. Under shear flow in vitro, TR14035 and compound 1 blocked binding of human alpha(4)beta(7)-expressing RPMI-8866 cells or murine mesenteric lymph node lymphocytes to MAdCAM-Ig with IC(50) values of 0.1 and 1 microM, respectively. Intravital microscopy was used to quantitate alpha(4)-dependent adhesion of fluorescent murine lymphocytes in Peyer's patch HEVs. When cells were prestimulated with 2 mM Mn(2+) to activate alpha(4)beta(7) binding to ligand, anti-alpha(4) monoclonal antibody (mAb) [10 mg/kg (mpk) i.v.] blocked adhesion by 95%, and anti-beta(1) mAb did not block adhesion, demonstrating that this interaction was dependent on alpha(4)beta(7). TR14035 blocked adhesion to HEVs [ED(50) of 0.01-0.1 mpk i.v.], and compound 1 blocked adhesion by 47% at 10 mpk i.v. Thus, alpha(4)beta(7)/alpha(4)beta(1) antagonists blocked alpha(4)beta(7)-dependent adhesion of lymphocytes to HEVs under both in vitro and in vivo shear flow.     

An assessment of the mechanistic differences between two integrin alpha 4 beta 1 inhibitors,the monoclonal antibody TA-2 and the small molecule BIO5192, in rat experimental autoimmune encephalomyelitis

Integrin alpha 4 beta 1 plays an important role in inflammatory processes by regulating the migration of lymphocytes into inflamed tissues. Here we evaluated the biochemical, pharmacological, and pharmacodynamic properties and efficacy in experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, of two types of alpha 4 beta 1 inhibitors, the anti-rat alpha 4 monoclonal antibody TA-2 and the small molecule inhibitor BIO5192 [2(S)-[[1-(3,5-dichloro-benzenesulfonyl)-pyrrolidine-2(S)-carbonyl]-amino]-4-[4-methyl-2(S)-(methyl-[2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl]-amino)-pentanoylamino]-butyric acid]. TA-2 has been extensively studied in rats and provides a benchmark for assessing function. BIO5192 is a highly selective and potent (KD of <10 pM) inhibitor of alpha 4 beta 1. Dosing regimens were identified for both inhibitors, which provided full receptor occupancy during the duration of the study. Both inhibitors induced leukocytosis, an effect that was used as a pharmacodynamic marker of activity, and both were efficacious in the EAE model. Treatment with TA-2 caused a decrease in alpha 4 integrin expression on the cell surface, which resulted from internalization of alpha 4 integrin/TA-2 complexes. In contrast, BIO5192 did not modulate cell surface alpha 4 beta 1. Our results with BIO5192 indicate that alpha 4 beta 7 does not play a role in this model and that blockade of alpha 4 beta 1/ligand interactions without down-modulation is sufficient for efficacy in rat EAE. BIO5192 is highly selective and binds with high affinity to alpha 4 beta 1 from four of four species tested. These studies demonstrate that BIO5192, a novel, potent, and selective inhibitor of alpha 4 beta 1 integrin, will be a valuable reagent for assessing alpha 4 beta 1 biology and may provide a new therapeutic for treatment of human inflammatory diseases.     

N-n-alkylnicotinium analogs,a novel class of nicotinic receptor antagonists: interaction with alpha4beta2* and alpha7* neuronal nicotinic receptors

The current study demonstrates that N-n-alkylnicotinium analogs with increasing n-alkyl chain lengths from 1 to 12 carbons have varying affinity (Ki = 90 nM-20 microM) for S-(-)-[3H]nicotine binding sites in rat striatal membranes. A linear relationship was observed such that increasing n-alkyl chain length provided increased affinity for the alpha4beta2* nicotinic acetylcholine receptor (nAChR) subtype, with the exception of N-n-octylnicotinium iodide (NONI). The most potent analog was N-n-decylnicotinium iodide (NDNI; Ki = 90 nM). In contrast, none of the analogs in this series exhibited high affinity for the [3H]methyllycaconitine binding site, thus indicating low affinity for the alpha7* nAChR. The C8 analog, NONI, had low affinity for S-(-)-[3H]nicotine binding sites but was a potent inhibitor of S-(-)-nicotine-evoked [3H]dopamine (DA) overflow from superfused striatal slices (IC50 = 0.62 microM), thereby demonstrating selectivity for the nAChR subtype mediating S-(-)-nicotine-evoked [3H]DA overflow (alpha3alpha6beta2* nAChRs). Importantly, the N-n-alkylnicotinium analog with highest affinity for the alpha4beta2* subtype, NDNI, lacked the ability to inhibit S-(-)-nicotine-evoked [3H]DA overflow and, thus, appears to be selective for alpha4beta2* nAChRs. Furthermore, the present study demonstrates that the interaction of these analogs with the alpha4beta2* subtype is via a competitive mechanism. Thus, selectivity for the alpha4beta2* subtype combined with competitive interaction with the S-(-)-nicotine binding site indicates that NDNI is an excellent candidate for studying the structural topography of alpha4beta2* agonist recognition binding sites, for identifying the antagonist pharmacophore on the alpha4beta2* nAChR, and for defining the role of this subtype in physiological function and pathological disease states.     

Expression of mucosal homing receptor alpha4beta7 by circulating CD4+ cells with memory for intestinal rotavirus.

The integrin alpha4beta7 mediates lymphocyte binding to mucosal addressin cell adhesion molecule-1, and its expression defines lymphocytes capable of trafficking through the intestines and the intestinal lymphoid tissues. We examined the ability of discrete alpha4beta7(hi) and alpha4beta7- subsets of circulating memory phenotype (CD45RA-) CD4+ T cells to proliferate in response to rotavirus, a ubiquitous intestinal pathogen. alpha4beta7(hi) memory (CD45RA-) CD4+ T cells displayed much greater reactivity to rotavirus than alpha4beta7- memory or naive (CD45RA+) CD4+ T cells. In contrast, alpha4beta7- memory cells were the predominant population responsive to mumps antigen after intramuscular vaccination. Our results are consistent with the conclusion that natural rotavirus infection, an enteric pathogen, results in a specific circulating memory CD4+ response that is largely limited to the gut-homing alpha4beta7+ subpopulation. This phenotype is not shared with memory cells elicited by intramuscular immunization (shown here) or by skin contact allergens. The results support the hypothesis that gut trafficking memory CD4+ T cells comprise cellular memory for intestinal antigens and suggest that regulated expression of alpha4beta7 helps target and segregate intestinal versus systemic immune response.     

Design, synthesis, and analysis of a polyethelene glycol-modified (PEGylated) small molecule inhibitor of integrin {alpha}4{beta}1 with improved pharmaceutical properties

Integrin alpha4beta1 plays an important role in inflammatory processes by regulating the migration of leukocytes into inflamed tissues. Previously, we identified BIO5192 [2(S)-{[1-(3,5-dichloro-benzenesulfonyl)-pyrrolidine-2(S)-carbonyl]-amino}-4-[4-methyl-2(S)-(methyl-{2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl}-amino)-pentanoylamino]-butyric acid], a highly selective and potent (K(D) of 9 pM) small molecule inhibitor of alpha4beta1. Although BIO5192 is efficacious in various animal models of inflammatory disease, high doses and daily treatment of the compound are needed to achieve a therapeutic effect because of its relatively short serum half-life. To address this issue, polyethylene glycol modification (PEGylation) was used as an approach to improve systemic exposure. BIO5192 was PEGylated by a targeted approach in which derivatizable amino groups were incorporated into the molecule. Two sites were identified that could be modified, and from these, five PEGylated compounds were synthesized and characterized. One compound, 2a-PEG (K(D) of 19 pM), was selected for in vivo studies. The pharmacokinetic and pharmacodynamic properties of 2a-PEG were dramatically improved relative to the unmodified compound. The PEGylated compound was efficacious in a rat model of experimental autoimmune encephalomyelitis at a 30-fold lower molar dose than the parent compound and required only a once-a-week dosing regimen compared with a daily treatment for BIO5192. Compound 2a-PEG was highly selective for alpha4beta1. These studies demonstrate the feasibility of PEGylation of alpha4beta1-targeted small molecules with retention of activity in vitro and in vivo. 2a-PEG, and related compounds, will be valuable reagents for assessing alpha4beta1 biology and may provide a new therapeutic approach to treatment of human inflammatory diseases.     

Aberrant activation of integrin alpha4beta7 suppresses lymphocyte migration to the gut

Integrin adhesion molecules mediate lymphocyte migration and homing to normal and inflamed tissues. While the ligand-binding activity of integrins is known to be modulated by conformational changes, little is known about how the appropriate balance of integrin adhesiveness is maintained in order to optimize the migratory capacity of lymphocytes in vivo. In this study we examined the regulation of the gut homing receptor alpha4beta7 integrin by manipulating at the germline level an integrin regulatory domain known as adjacent to metal ion-dependent adhesion site (ADMIDAS). ADMIDAS normally serves to raise the activation threshold of alpha4beta7, thereby stabilizing it in the default nonadhesive state. Lymphocytes from knockin beta7 (D146A) mice, which harbor a disrupted ADMIDAS, not only expressed an alpha4beta7 integrin that persistently adhered to mucosal addressin cell adhesion molecule-1 (MAdCAM-1), but also exhibited perturbed cell migration along MAdCAM-1 substrates resulting from improper de-adhesion of the lymphocyte trailing edge. In vivo, aberrantly activated alpha4beta7 enhanced adhesion to Peyer's patch venules, but suppressed lymphocyte homing to the gut, diminishing the capacity of T cells to induce colitis. Our results underscore the importance of a proper balance in the adhesion and de-adhesion of the alpha4beta7 integrin, both for lymphocyte trafficking to the gut and for colitis progression.     

Novel peptide ligands for integrin alpha 4 beta 1 overexpressed in cancer cells

Using the "one-bead one-peptide" combinatorial technology, a library of random cyclic octapeptides and nonapeptides, consisting of natural and unnatural amino acids, was synthesized on polystyrene beads. This library was used to screen for peptides that promoted attachment and proliferation of bronchioloalveolar carcinoma cells (H1650), employing a "cell growth on bead" assay. Consensus peptide sequences of cNleDXXXXc and cXNleDXXXXc (where Nle is norleucine) were identified. With alanine scanning and site-directed deletion, a typical ligand consisted of a motif of -NleDI/V/Nle- with two flanking cysteines. These peptide ligands were specific for promoting cell attachment of the H1650 cells and the cells of lymphoid cancers (Jurkat and Raji) but not other selected human cell lines of lung cancer and fibroblast. In an antibody blocking assay, integrin alpha(4)beta(1), which was overexpressed in H1650, Jurkat, and Raji, was identified as a putative receptor for these peptide ligands. Using Chinese hamster ovary cells transfected with either wild-type or mutant integrin alpha(4), a critical binding site for these peptides was localized to the glycine residue at position 190 of integrin alpha(4).     

Identification of a high-affinity receptor for interleukin 1 alpha and interleukin 1 beta on cultured human rheumatoid synovial cells

In this report the binding of recombinant human interleukins 1 alpha and 1 beta (rIL-1 alpha and rIL-1 beta) to primary cultures of human rheumatoid synovial cells is measured and compared to the concentrations of these mediators required for stimulation of PGE2 production by these same cells. The average concentration of IL-1 alpha required for half-maximal stimulation of PGE2 was 4.6 +/- 1.5 pM (+/- SEM) (n = 6), whereas for IL-1 beta half-maximal stimulation was observed at a concentration of 1.3 +/- 0.24 pM (n = 6). Both direct and competitive binding experiments were performed. In direct binding experiments, IL-1 alpha bound with a Kd of 66 pM (n = 1), while IL-1 beta bound with a Kd of 4 pM (n = 2). In competitive binding experiments, IL-1 alpha inhibited binding of 125I-IL-1 alpha with a Ki of 33-36 pM (n = 2) and binding of 125I-IL-1 beta with a Ki of 51-63 pM (n = 2). IL-1 beta inhibited binding of 125I-IL-1 alpha with a Ki of 2-3 pM (n = 2) and binding of 125I-IL-1 beta with a Ki of 7 pM (n = 2). The binding data were best fit by a model specifying a single class of receptors with homogeneous affinity for either IL-1 alpha or IL-1 beta and with an abundance of 3,000-14,000 sites per cell. Autoradiography showed that the vast majority of the synoviocytes within the cultures possessed IL-1 receptors. Comparison of biological response curves with the binding curves indicates that the observed receptors exhibit sufficiently high affinity to mediate the response of human synoviocytes to low picomolar concentrations of IL-1 alpha and IL-1 beta.     

Effects of prolonged nicotinic ligand exposure on function of heterologously expressed,human alpha4beta2- and alpha4beta4-nicotinic acetylcholine receptors

Effects of prolonged nicotinic ligand exposure on the function of human alpha4beta2- and alpha4beta4-nicotinic acetylcholine receptor (nAChR) subtypes were studied using receptors heterologously expressed in SH-EP1 human epithelial cells. Magnitudes of acute, nAChR-mediated, specific 86Rb+ efflux responses to 1 mM carbamylcholine were reduced after pretreatment with specific nAChR ligands in effects that depended on pretreatment drug dose, duration of drug pretreatment, and duration of drug-free recovery. Fifty percent inhibition of alpha4beta2-nAChR function following 5 min of recovery occurred after 1 min of pretreatment with 1 mM nicotine but also after 1-h pretreatment at 10 nM nicotine. Seventy-five percent loss in function persisted 1 h after drug removal following 15 min or more of exposure to 1 mM nicotine. However, functional recovery was nearly complete after 1 h in drug-free medium following 1 min to 24 h pretreatment with 0.1 to 1 microM nicotine, i.e., in the range of smoker plasma nicotine levels. alpha4beta4-nAChR was similarly sensitive to persistent inactivation by prolonged nicotine exposure. Carbamylcholine exhibited slightly lower persistent inactivation potency than nicotine at both alpha4beta2- and alpha4beta4-nAChR. The nAChR antagonist, mecamylamine, exhibited persistent inactivation potency and efficacy similar to nicotine at alpha4beta2-nAChR but had a reduced effect on alpha4beta4-nAChR. These studies illustrate persistent inactivation of human alpha4beta2- or alpha4beta4-nAChR induced by prolonged exposure to nicotine and show that other ligands induce nAChR persistent inactivation in a subtype-specific manner.     

Pulmonary eosinophilia in a murine model of allergic inflammation is attenuated by small molecule alpha4beta1 antagonists

Inhibition of alpha4beta1/vascular cell adhesion molecule-1 (VCAM-1) interactions have therapeutic potential in treating allergic airway disease because of the importance of these adhesion molecules in the trafficking of eosinophils, lymphocytes, and monocytes. We examined several small molecule inhibitors of alpha4beta1/VCAM-1 interactions with in vitro potencies (IC(50) values) ranging from 0.52 nM (CP-664511; 3-[3-(1-[2-[3-methoxy-4-(3-O-tolyl-ureido)phenyl]-acetylamino]-3-methyl-butyl)isoxazol-5-yl]-propionic acid) to 38.5 nM (CP-609643; 3-[3-methyl-1-[2-[4-(3-O-tolyl-ureido)-phenyl]-acetylamino]-butyl)-isoxazol-5-yl]-propionic acid). The same compounds were evaluated in vivo using a murine model of ovalbumin-induced pulmonary eosinophilia. In this model, systemic administration of antibodies against alpha4 reduced bronchoalveolar lavage (BAL) eosinophilia approximately 60%. Small molecule alpha4beta1 antagonists were administered by intratracheal instillation and demonstrated dose-dependent inhibition of BAL eosinophil numbers and achieved a maximum inhibition of approximately 60%. In general, the rank order of potency for these compounds in vitro was consistent with that observed in vivo, which confirms that their efficacy is likely via blockade of alpha4beta1/VCAM-1 interactions. The most potent compound, CP-664511, also inhibited BAL eosinophilia following s.c. administration (1-10 mg/kg, s.c.). These data support the utility of small molecule alpha4beta1 antagonists in the treatment of relevant diseases, such as asthma.     

Genetic approaches identify differential roles for alpha4beta2* nicotinic receptors in acute models of antinociception in mice

The effects of nicotine on the tail-flick and hot-plate tests were determined to identify nicotinic receptor subtypes responsible for spinally and supraspinally mediated nicotine analgesia in knockin mice expressing hypersensitive alpha(4) nicotinic receptors (L9'S), in seven inbred mouse strains (C57BL/6, DBA/2, A/2, CBA/2, BALB/cByJ, C3H/HeJ, and 129/SvEv), and in two F1 hybrids (B6CBAF1 and B6D2F1). L9'S heterozygotes were approximately 6-fold more sensitive to the antinociceptive effects of nicotine than the wild-type controls in the hot-plate test but not in the tail-flick assay. Large differences in the effects of nicotine were also observed with both tests for the seven mouse strains. A/J and 129 mice were 6- to 8-fold more sensitive than CBA and BALB mice. In addition, B6CBAF1 hybrid mice were even less sensitive than CBA mice. Nicotinic binding sites were measured in three spinal cord regions and the hindbrain of the inbred strains. Significant differences in cytisine-sensitive, high affinity [(125)I]epibatidine binding site levels (alpha(4)beta(2)(*) subtypes), but not in (125)I-alpha-bungarotoxin binding (alpha(7)(*) subtypes), were observed. Significant negative correlations between cytisine-sensitive [(125)I]epibatidine binding and nicotine ED(50) for both tests were noted. Our results indicate that alpha(4)beta(2)(*) acetylcholine nicotinic receptors (nAChR) are important in mediating nicotine analgesia in supraspinal responses, while also showing that alpha(4)beta(2)(*)-nAChR and at least one other nAChR subtype appear to modulate spinal actions.     

The novel alpha7 nicotinic acetylcholine receptor agonist N-[(3R)-1-azabicyclo[2.2.2]oct-3-yl]-7-[2-(methoxy)phenyl]-1-benzofuran-2-carboxamide improves working and recognition memory in rodents

The relative contribution of alpha4beta2, alpha7 and other nicotinic acetylcholine receptor (nAChR) subtypes to the memory enhancing versus the addictive effects of nicotine is the subject of ongoing debate. In the present study, we characterized the pharmacological and behavioral properties of the alpha7 nAChR agonist N-[(3R)-1-azabicyclo[2.2.2]oct-3-yl]-7-[2-(methoxy)phenyl]-1-benzofuran-2-carboxamide (ABBF). ABBF bound to alpha7 nAChR in rat brain membranes (Ki=62 nM) and to recombinant human 5-hydroxytryptamine (5-HT)3 receptors (Ki=60 nM). ABBF was a potent agonist at the recombinant rat and human alpha7 nAChR expressed in Xenopus oocytes, but it did not show agonist activity at other nAChR subtypes. ABBF acted as an antagonist of the 5-HT3 receptor and alpha3beta4, alpha4beta2, and muscle nAChRs (at higher concentrations). ABBF improved social recognition memory in rats (0.3-1 mg/kg p.o.). This improvement was blocked by intracerebroventricular administration of the alpha7 nAChR antagonist methyllycaconitine at 10 microg, indicating that it is mediated by alpha7 nAChR agonism. In addition, ABBF improved working memory of aged rats in a water maze repeated acquisition paradigm (1 mg/kg p.o.) and object recognition memory in mice (0.3-1 mg/kg p.o.). Rats trained to discriminate nicotine (0.4 mg/kg s.c.) from vehicle did not generalize to ABBF (0.3-30 mg/kg p.o.), suggesting that the nicotine cue is not mediated by the alpha7 nAChR and that selective alpha7 nAChR agonists may not share the abuse liability of nicotine. Our results support the hypothesis that alpha7 nAChR agonists may provide a novel therapeutic strategy for the treatment of cognitive deficits with low abuse potential.     

In vivo optical imaging of human lymphoma xenograft using a library-derived peptidomimetic against alpha4beta1 integrin

Increasing literature suggests that cell adhesion molecule alpha4beta1 integrin plays a pivotal role in autoimmune diseases and cancer development. Noninvasive visualization of alpha4beta1 integrin in vivo will facilitate the understanding of its involvement in disease progression and development of targeted therapies. Due to the lack of high-affinity targeting ligands, molecular imaging of alpha4beta1 integrin is much less explored than that of alphavbeta3 and alphavbeta5 integrins. We have recently reported using the one bead-one compound combinatorial library method to identify a peptidomimetic, LLP2A, that preferentially binds to activated alpha4beta1 integrin. Here, we described the use of LLP2A-Cy5.5 conjugate as an in vivo optical imaging probe in a human lymphoma xenograft model. This univalent LLP2A-Cy5.5 conjugate retained the binding activity and specificity to alpha4beta1 integrin as shown by cell binding assays using alpha4beta1-positive Molt-4 T-leukemia cells. The subcutaneous Molt-4 tumor was clearly visualized from 1 to 24 h after tail vein injection of the conjugate. Direct imaging and confocal microscopic examination of excised tumors and organs confirmed the accumulation of LLP2A in tumors and revealed very little or no uptake in normal organs except for lymph nodes. Kidney uptake was high when the whole organ was scanned but it was negative when examined microscopically, suggesting that LLP2A bound to the renal tubules loosely. Tumor uptake of LLP2A-Cy5.5 conjugate was blocked by excess unlabeled LLP2A. This study showed that the combinatorial chemical library-derived peptidomimetic LLP2A can be easily developed into an optical imaging probe for noninvasively monitoring of activated alpha4beta1 integrin in vivo.     

The development of experimental autoimmune encephalomyelitis in the mouse requires alpha4-integrin but not alpha4beta7-integrin.

Because monoclonal antibodies (mAbs) directed against alpha4-integrin and VCAM-1 inhibit the development of experimental autoimmune encephalomyelitis (EAE) in vivo, it has been concluded that the successful therapeutic effect is due to interference with alpha4beta1/VCAM-1-mediated interaction of autoaggressive T cells with the blood-brain barrier. A possible role for alpha4beta7-integrin, or interference with other T cell mediated events during the pathogenesis of EAE, has not been considered. We have compared the effects of mAb therapy on the development of EAE in the SJL/N mouse, using a large panel of mAbs directed against alpha4, beta7, the alpha4beta7-heterodimer, and against VCAM-1. Although encephalitogenic T cells express both alpha4-integrins, mAbs directed against the alpha4beta7-heterodimer or against the beta7-subunit did not interfere with the development of EAE. In contrast, mAbs directed against alpha4 and VCAM-1 inhibited or diminished clinical or histopathological signs of EAE. Our data demonstrate for the first time that alpha4beta7 is not essential for the development of EAE. Furthermore, our in vitro studies suggest that the therapeutic effect of anti-alpha4-treatment of EAE might also be caused by inhibition of antigen-specific T cell proliferation.     

Differential regulation of mesolimbic alpha 3/alpha 6 beta 2 and alpha 4 beta 2 nicotinic acetylcholine receptor sites and function after long-term oral nicotine to monkeys

Because the mesolimbic dopamine system plays a critical role in nicotine addiction/reinforcement and because nicotinic receptors regulate dopamine release, we initiated a study to evaluate the long-term effects of nicotine (>6 months at the final dose) on nicotinic acetylcholine receptor (nAChR) sites and function in the nucleus accumbens of nonhuman primates. Nicotine was given in the drinking water as this mode of administration is long-term but intermittent, thus resembling smoking in this aspect. We determined the effects of nicotine treatment on function and binding of the alpha3/alpha6beta2* and alpha4beta2* nAChRs subtypes in nucleus accumbens, a region directly implicated in the addictive effects of nicotine. To evaluate function, we measured nicotine and K+-evoked [3H]dopamine release from nucleus accumbens synaptosomes. Changes in alpha4beta2* and alpha3/alpha6beta2* nAChRs were measured using 125I-epibatidine, [125I]A85380 [5-[125I]iodo-3(2(S)-azetidinylmethoxy) pyridine] and 125I-alpha-conotoxin MII autoradiography. Chronic nicotine treatment, which led to plasma nicotine levels in the range of smokers, significantly increased nucleus accumbens alpha4beta2* nAChR sites and function compared with control. By contrast, this treatment did not significantly change alpha3/alpha6beta2* nAChR sites or evoked dopamine release in this region compared with control. Thus, these data are distinct from previous results in striatum in which the same nicotine treatment paradigm decreased striatal alpha3/alpha6beta2* nAChR sites and function. The finding that long-term nicotine treatment selectively modulates alpha4beta2* and not alpha3/alpha6beta2* nAChR expression in primate nucleus accumbens is consistent with the results of studies in nicotinic receptor mutant mice implicating the alpha4beta2* nAChR subtype in nicotine-mediated addiction.     

Chronic treatment with flumazenil enhances binding sites for convulsants at recombinant alpha(1)beta(2)gamma(2S) GABA(A) receptors.

GABA(A) receptors mediate most of the fast inhibitory neurotransmission in the brain. Prolonged occupancy of these receptors by ligands leads to regulatory changes often resulting in reduction of receptor function. The mechanism of these changes is still unknown. In this study, stably transfected human embryonic kidney (HEK) 293 cells were used as a model to study the effects of prolonged flumazenil (antagonist of benzodiazepine binding sites at GABA(A) receptors) exposure on the recombinant alpha(1)beta(2)gamma(2S) GABA(A) receptors, the most common type of GABA(A) receptors found in the brain. Exposure (48 h) of HEK 293 cells stably expressing recombinant alpha(1)beta(2)gamma(2S) GABA(A) receptors to flumazenil (1 or 5 microM) in the presence of GABA (1 microM), enhanced the maximum number (B(max)) without affecting the affinity (K(d)) of [(3)H]TBOB labeled binding sites for convulsants. Diazepam (1 nM-1 mM) in the presence of GABA (1 microM) modulated [(3)H]TBOB binding to control and flumazenil pretreated cells according to a two-site model. No significant differences between the groups were observed in either the potency or efficacy of diazepam to modulate [(3)H]TBOB binding, as evidenced by a lack of significant changes between their IC(50) and I(max) values. The results suggest that chronic exposure of HEK 293 cells stably expressing recombinant alpha(1)beta(2)gamma(2S) GABA(A) receptors to flumazenil up-regulates the binding sites for convulsants, but it does not appear to affect the functional coupling between these sites and benzodiazepine binding sites. Along with our recent data, these results suggest that chronic treatment with flumazenil enhances the number of GABA(A) receptors.     

Constitutive activation of integrin alpha 4 beta 1 defines a unique stage of human thymocyte development

Our understanding of thymocyte development and of the positive and negative selection events involved in shaping the repertoire of mature T lymphocytes has been greatly facilitated by the use of transgenic and gene knockout animals. Much less is known about the factors that control the homing and population of the thymus by T cell precursors and the subsequent migration of developing thymocytes through the thymic architecture. As the integrins represent a candidate group of cell surface receptors that may regulate thymocyte development, we have analyzed the expression and function of alpha 4 beta 1 and alpha 5 beta 1 on human thymocytes. A major portion of double positive (CD4+ CD8+) human thymocytes express alpha 4 beta 1 in a constitutively active form and adhere to fibronectin and vascular cell adhesion molecule 1. alpha 4 beta 1 expression is similar on adherent and nonadherent populations, thus, activity reflects the receptor state and not simple expression. The adherent cells are immature, expressing high levels of CD4/CD8 and low levels of CD3 and CD69. In contrast, nonadherent cells possess the phenotype of thymocytes after positive selection, expressing intermediate levels of CD4 and/or CD8 and high levels of CD3 and CD69. The adherent population fails to respond to activation with anti-CD3 and fibronectin, whereas nonadherents exhibit an alpha 5 beta 1- dependent proliferation. Differential regulation of alpha 4 beta 1 and alpha 5 beta 1 receptors may provide a mechanism controlling cellular traffic, differentiation, and positive selection of thymocytes.     

Cotinine selectively activates a subpopulation of alpha3/alpha6beta2 nicotinic receptors in monkey striatum

The nicotine metabolite cotinine is an abundant long-lived bio-active compound that may contribute to the overall physiological effects of tobacco use. Although its mechanism of action in the central nervous system has not been extensively investigated, cotinine is known to evoke dopamine release in the nigrostriatal pathway through an interaction at nicotinic receptors (nAChRs). Because considerable evidence now demonstrates the presence of multiple nAChRs in the striatum, the present experiments were done to determine the subtypes through which cotinine exerts its effects in monkeys, a species that expresses similar densities of striatal alpha4beta2* (nAChR containing the alpha4 and beta2 subunits, but not alpha3 or alpha6) and alpha3/alpha6beta2* (nAChR composed of the alpha3 or alpha6 subunits and beta2) nAChRs. Competition binding studies showed that cotinine interacts with both alpha4beta2* and alpha3/alpha6beta2* nAChR subtypes in the caudate, with cotinine IC(50) values for inhibition of 5-[(125) I]iodo-3-[2(S)-azetinylmethoxy]pyridine-2HCl ([(125)I]A-85380) and (125)I-alpha-conotoxinMII binding in the micromolar range. This interaction at the receptor level is of functional significance because cotinine stimulated both alpha4beta2* and alpha3/alpha6beta2* nAChR [(3)H]dopamine release from caudate synaptosomes. Our results unexpectedly showed that nicotine evokes [(3)H]dopamine release from two alpha3/alpha6beta2* nAChR populations, one of which was sensitive to cotinine and the other was not. This cotinine-insensitive subtype was only present in the medial caudate and was preferentially lost with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced nigrostriatal damage. In contrast, cotinine and nicotine elicited equivalent levels of alpha4beta2* nAChR-mediated dopamine release. These data demonstrate that cotinine functionally discriminates between two alpha3/alpha6beta2* nAChRs in monkey striatum, with the cotinine-insensitive alpha3/alpha6beta2* nAChR preferentially vulnerable to nigrostriatal damage.