Peptide-major histocompatibility complex class II complexes with mixed agonist/antagonist properties provide evidence for ligand-related differences in T cell receptor-dependent intracellular signaling

Clonal activation of CD4+ and CD8+ T lymphocytes depends on binding of peptide-major histocompatibility complex (MHC) molecule complexes by their alpha/beta receptors, eventually resulting in sufficient aggregation to initiate second messenger generation. The nature of intracellular signals resulting from such T cell receptor (TCR) occupancy is believed to be independent of the specific structure of the ligand being bound, and to vary quantitatively, not qualitatively, with the concentration of ligand offered and the affinity of the receptor for the peptide-MHC molecule complex. In contrast to the expectations of this model, the analysis of the response of a T helper type 1 clone to mutant E alpha E beta k molecules in the absence or presence of a peptide antigen revealed that peptide inhibited the interleukin 2 (IL-2) response to an otherwise allostimulatory mutant form of this MHC class II molecule. The inhibition was not due to competition for formation of alloantigen, it required TCR recognition of peptide-mutant MHC molecule complexes, and it decreased IL-2 production without affecting receptor-dependent IL-3, IL-2 receptor alpha, or size enlargement responses. This preferential reduction in IL-2 secretion could be correlated with the costimulatory signal dependence of this cytokine response, but could not be overcome by crosslinking the CD28 molecule on the T cell. These results define a new class of TCR ligands with mixed agonist/antagonist properties, and point to a ligand-related variation in the quality of clonotypic receptor signaling events or their integration with other signaling processes. It was also found that a single TCR ligand showed greatly different dose thresholds for the elicitation of distinct effector responses from a cloned T cell population. The observations that changes in ligand structure can result in qualitative alterations in the effects of receptor occupancy and that quantitative variations in ligand density can be translated into qualitative differences in T cell responses have important implications for models of intrathymic selection and control of the results of active immunization.     

Pharmacology of a mixed 5-hydroxytryptamine1A/dopamine agonist

U-67413B (4-hydroxydipropylaminodihydrophenalene) bound with high affinity to both 5-hydroxytryptamine (HT)1A and D2-dopamine (DA) receptor sites. U-67413B depressed 5-HT and DA cell firing rates and depressed synthesis of both neurotransmitters. The drug depressed mouse body temperatures by an amount similar to that for buspirone, gepirone and ipsapirone, but less than that for 8-hydroxy-N,N-dipropyl-2-aminotetralin. In rats, it produced the 5-HT1A behavioral syndrome. In contrast to 5-HT1A agonists having DA antagonist effects, U-67413B mildly depressed rather than stimulated firing rates of noradrenaline (NA) neurons in the locus ceruleus by a non-alpha-2 receptor mechanism. In behavioral tests designed to measure anxiolytic activities, U-67413B was a slightly more effective anxiolytic than standard 5-HT1A anxiolytics (buspirone, gepirone and ipsapirone). The data are consistent with the hypothesis that effects of 5-HT1A agonists on NA neuron activity are mediated through effects on dopaminergic mechanisms, and that effects on NA neurons could modulate anxiolytic activities of 5-HT1A agonists.     

Molecular basis for cardiac functions

The cause of mechanical failure of the fixture component of an osseointegrated dental implant was investigated. The surfaces of five clinical specimens that had fractured were compared to those of new specimens fractured in the laboratory under monotonic and cyclic loads. Scanning electron microscopy revealed striations on the fractured surfaces of the clinical specimens, similar to striations on the laboratory-fatigued specimens and in contrast to the dimpled surfaces on the overloaded specimens. The investigation demonstrated that fractures of the fixture component of this dental implant occurred by fatigue under physiologic loads, with marginal alveolar bone loss around the fixture.     

Distributed moment histogram: a neurophysiology based method of agonist and antagonist trunk muscle activity prediction

A neurocortical-based technique of muscle recruitment is presented to solve the muscle indeterminacy problem for lumbar torso modeling. Cortical recordings from behaving primates have established motor cortex cells that respond to a wide range of task directions, but are tuned to a preferred direction. A characteristic activity pattern of these neurons seems to be associated with effort direction. It was hypothesized that a model which recruits muscles based on a similar distribution would predict antagonistic muscle activity with greater realism than a widely referenced optimization formulation. The predictions of the Distributed Moment Histogram (DMH) method were evaluated under common speed (< 30 degrees s-1) sagittal plane lifting conditions using five subjects. The predicted forces showed high correspondence with agonist and antagonist myoelectric patterns. The mean coefficient of determination for the erector spinae was r2 = 0.91, and 0.41 for the latissimus. For the antagonistic muscles, the rectus abdominus was found to be electrically silent (< 3% MVC) and no activity was predicted by the method. The external oblique muscle was observed to be minimally active (< 16% MVC), and the DMH method predicted its mostly constant activity with a mean standard error of 1.6% MVC. The realistic antagonistic predictions supported the hypothesis and justify this cortical based technique as an alternative for muscle tension estimation in biomechanical torso modeling. A primary advantage of this method is its computational simplicity and direct physiologic analog.     

Assessment of the kappa agonist and antagonist properties of mixed action opioids, mu opioids, and a delta opioid in pigeons.

The present study examined the kappa agonist and antagonist effects of various opioids in pigeons (Columba liva) trained to discriminate the kappa opioid bremazocine from saline. The mixed action opioids oxilorphan and (–)-cylorphan and the opioid antagonist naltrexone produced a dose-related antagonism of the bremazocine stimulus. With oxilorphan, the doses required to decrease responding were approximately 300 tomes larger than those required to antagonize the bremazocine stimulus, whereas with (–)-cylorphan and naltrexone the separation between these doses was relatively small. The mixed action opioid proxorphan substituted partially for and antagonized partially the bremazocine stimulus. Selected mu and delta opioids failed to substitute for or antagonize the bremazocine stimulus. The present findings suggest that mixed action opioids are active at the kappa receptor and that their effects can be distinguished from those of kappa, mu, and delta opioids. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Complex pharmacology of natural cannabinoids: evidence for partial agonist activity of delta9-tetrahydrocannabinol and antagonist activity of cannabidiol on rat brain cannabinoid receptors

Delta9-tetrahydrocannabinol (delta9-THC), cannabinol and cannabidiol are three important natural cannabinoids from the Marijuana plant (Cannabis sativa). Using [35S]GTP-gamma-S binding on rat cerebellar homogenate as an index of cannabinoid receptor activation we show that: delta9-THC does not induce the maximal effect obtained by classical cannabinoid receptor agonists such as CP55940. Moreover at high concentration delta9-THC exhibits antagonist properties. Cannabinol is a weak agonist on rat cerebellar cannabinoid receptors and cannabidiol behaves as an antagonist acting in the micromolar range.     

Molecular basis of leukemogenesis

Reactive arthritis was originally defined as a sterile joint inflammation after infection elsewhere in the body, but this view has been challenged in the past decade since different antigens and DNA and RNA of various triggering microbes have been shown to exist at the sites of inflammation in the joints. It has been suggested that microbial antigens, or intact pathogens, are important for the pathogenesis of reactive arthritis, at least in the early phase of the disease, but the exact mechanism of how the pathogens contribute to the development of this usually self-limiting polyarthritis has not been discovered. This article reviews the theories on the role of infectious agents as triggers of reactive arthritis.     

Pharmacological characterization of in vivo properties of putative mixed 5-HT1A agonist/5-HT2A/2C antagonist anxiolytics. I. Antipunishment effects in the pigeon

A conflict procedure in pigeons was used to characterize the antipunishment effects of the putative mixed 5-hydroxytryptamine (5-HT)1A agonist/5-HT2A/2C antagonists WY 50,324, CGS 18102A, LEK 8804 and FG 5974 and to further investigate interactions between the antipunishment effects of the 5-HT1A agonists buspirone and 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin] administered in combination with the mixed 5-HT2A/2C antagonist ritanserin and the alpha 1 antagonist prazosin. The 5-HT1A agonists, buspirone and 8-OH-DPAT, which lack affinity for 5-HT2A/2C receptors, produced dose-related increases in punished responding. Of the compounds with a mixed binding profile, only WY 50,324 showed effects that were comparable to those observed after 8-OH-DPAT, whereas FG 5974 and CGS 18102A exhibited limited effects on punished responding, and LEK 8804 was ineffective. Administration of a relatively low, behaviorally active dose of ritanserin (0.16 mg/kg) significantly enhanced the potency of 8-OH-DPAT and buspirone to increase punished responding from 8 to 50-fold without altering their effects on unpunished responding. Importantly, ritanserin failed to increase the number of doses of 8-OH-DPAT that significantly increased punished responding. In contrast, prazosin (2.5 mg/kg) significantly enhanced the potency and increased the number of doses of buspirone exerting significant effects on punished responding, but did not alter the effects of 8-OH-DPAT. Taken together, the results neither explain the suggested greater efficacy in producing anxiolytic effects of compounds with putative mixed 5-HT1A agonist and 5-HT2A/2C antagonist properties, nor confirm a proposed interaction between alpha1 adrenoreceptors and 5-HT1A agonists in preclinical tests of anxiolytic activity.     

Molecular and cellular basis of addiction

Drug addiction results from adaptations in specific brain neurons caused by repeated exposure to a drug of abuse. These adaptations combine to produce the complex behaviors that define an addicted state. Progress is being made in identifying such time-dependent, drug-induced adaptations and relating them to specific behavioral features of addiction. Current research needs to understand the types of adaptations that underlie the particularly long-lived aspects of addiction, such as drug craving and relapse, and to identify specific genes that contribute to individual differences in vulnerability to addiction. Understanding the molecular and cellular basis of addictive states will lead to major changes in how addiction is viewed and ultimately treated.     

Effect of an adrenergic agonist and a cholinergic antagonist on the airway epithelium

The ultrastructure of the rabbit tracheal epithelium was studied 30 minutes after intratracheal administration of two puffs of salbutamol and ipratropium bromide, respectively. The injury to the tracheal epithelium due to the treatment with both bronchospasmolytic drugs was considered moderate to severe. In both experimental groups, the degree of goblet cells' stimulation did not differ significantly, the ciliated cells were less damaged compared with the goblet ones and the morphological signs of the impaired self-cleaning ability were revealed.     

Molecular and cellular basis of immunosenescence

Aged persons and most animals studied show a significant decline in the immune response primarily caused by changes in the T cell compartment. This decline in T cell function is due to a combination of factors: decreased production of new naive T cells by the involuting thymus; extensive antigen-induced activation leading to replicative senescence and clonal exhaustion of certain T cells; and postmitotic aging of resting T cells, a phenomenon also observed in other non-dividing cells such as neurons or muscle cells. The relative importance of these processes in the T cell defective immune response observed in aged humans and animals remains to be established although it is very likely that all of them participate in immunosenescence. The cellular, molecular biological basis and the clinical consequences of the defective immune response in aging were extensively discussed and reviewed at the 5th EUCAMBIS meeting. This paper summarizes the main presentations at the meeting. This special issue contains selected presentations from the congress, in the form of peer-reviewed full papers and the abstracts of two papers previously published in the journal.     

Molecular basis for prokaryotic specificity of magainin-induced lysis

Magainins and mastoparans are examples of peptide antibiotics and peptide venoms, respectively. They have been grouped together as class L amphipathic helixes [Segrest, J.P., et al. (1990) Proteins 8, 103-117] because of similarities in the distribution of Lys residues along the polar face of the helix. Class L venoms lyse both eukaryotic and prokaryotic cells whereas class L antibiotics specifically lyse bacteria. The structural basis for the specificity of class L antibiotics is not well understood. Sequence analysis showed that class L antibiotics have a Glu residue on the nonpolar face of the amphipathic helix; this is absent from class L venoms. We synthesized three model class L peptides with or without Glu on the nonpolar face: 18LMG (LGSIWKFIKAFVGGIKKF), [E14]18LMG and [G5,E14]18LMG. Hemolysis, bacteriolysis, and bacteriostasis studies using these peptides showed that the specificity of lysis is due to both the presence of a Glu residue on the nonpolar face of the helix and the bulk of the nonpolar face. Studies using large unilamellar phospholipid vesicles showed that the inclusion of cholesterol greatly inhibited leakage by the two Glu-containing peptides. These results cannot be attributed to changes in the phase behavior of the lipids caused by the inclusion of cholesterol or to differences in the secondary structure of the peptides. These results suggest that eukaryotic cells are resistant to lysis by magainins because of peptide-cholesterol interactions in their membranes that inhibit the formation of peptide structures capable of lysis, perhaps by hydrogen bonding between Glu and cholesterol. Bacterial membranes, lacking cholesterol, are susceptible to lysis by magainins.     

Molecular basis of neuromuscular diseases

For many neuromuscular disorders, the chromosomal location is known, the causal gene has been identified, and direct application of this knowledge may be made in a clinical setting. The benefits resulting from molecular-based methods include improved diagnostic accuracy and genetic counseling for patients and other at risk family members. This chapter discusses in detail four of the most frequently encountered neuromuscular disorders. These diseases include spinal muscular atrophy, Charcot-Marie-Tooth neuropathy, Duchenne/Becker type muscular dystrophy, and myotonic dystrophy.     

Assessment of agonist and antagonist effects of tramadol in opioid-dependent humans.

The subjective, behavioral, and physiologic effects of racemic tramadol, an analgesic with low abuse liability and dual mu-opioid agonist and monoamine reuptake actions, were evaluated in 2 clinical pharmacology studies in dependent opioid abusers. In the withdrawal precipitation study, participants (N = 8) were maintained on methadone 60 mg/day orally and challenged with intramuscular tramadol, hydromorphone, naloxone, and placebo 20 hr after methadone administration. In the withdrawal suppression study, participants (N = 6) were maintained on hydromorphone given orally 10 mg 4 times daily, and spontaneous opioid withdrawal was produced by withholding doses for 23 hr. During the experimentally induced withdrawal, oral tramadol, hydromorphone, naltrexone, and placebo were given. In both studies a comprehensive panel of participant-rated, observer-rated, and physiologic measures were collected. In both studies, naloxone and naltrexone significantly increased measures of opioid withdrawal, whereas tramadol showed no discernible antagonist effects. In contrast, tramadol's pattern of effects was more similar to that of hydromorphone and suggestive of mild opioid-agonist effects (withdrawal suppression), though not to a statistically significant degree. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Molecular basis of V2 vasopressin receptor/Gs coupling selectivity

The molecular mechanisms governing the coupling selectivity of G protein-coupled receptors activated by peptide ligands are not well understood. To shed light on this issue, we have used the Gq/11-linked V1a and the Gs-coupled V2 vasopressin peptide receptors as model systems. To explore the structural basis underlying the ability of the V2 receptor to selectively recognize Gs, we systematically substituted distinct V2 receptor segments (or single amino acids) into the V1a receptor and studied whether the resulting hybrid receptors gained the ability to mediate hormone-dependent cAMP production. This strategy appeared particularly attractive since hormone stimulation of the V1a receptor has virtually no effect on intracellular cAMP levels. Functional analysis of a large number of mutant receptors transiently expressed in COS-7 cells indicated that the presence of V2 receptor sequence at the N terminus of the third intracellular loop is critical for efficient activation of Gs. More detailed mutational analysis of this receptor region showed that two polar V2 receptor residues, Gln225 and Glu231, play key roles in Gs recognition. In addition, a short sequence at the N terminus of the cytoplasmic tail was found to make an important contribution to V2 receptor/Gs coupling selectivity. We also made the novel observation that the efficiency of V2 receptor/Gs coupling can be modulated by the length of the central portion of the third intracellular loop (rather than the specific amino acid sequence within this domain). These findings provide novel insights into the molecular mechanisms regulating peptide receptor/G protein coupling selectivity.     

Molecular basis of Charcot-Marie-Tooth neuropathy

Charcot-Marie-Tooth neuropathy (CMT) is the most common inherited peripheral neuropathy. CMT is classified into type types on the basis of pathological and electrophysiological findings: type 1(CMT1), characterized by decreased nerve conduction velocities and by "onion bulb" formation: type 2(CMT2), in which nerve conduction velocities are normal and "onion bulb" formations are rarely seen. CMT1 loci map to chromosome 17 (CMT1A), chromosome 1(CMT1B), another unknown autosome (CMT1C) and the X chromosome (CMTX). Recent work has identified the gene products corresponding to CMT1A, CMT1B and CMTX as peripheral myelin protein-22(PMP22), Po and connexin 32, respectively. Dejerine-Sottas disease has been identified as being caused by the mutation of PMP-22 or Po gene.