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Henk Timmerman

Publications and source records attributed to Henk Timmerman.

28 records · Page 2Linked to original sources
PubMed2003

Synthesis and structure-activity relationships of conformationally constrained histamine H(3) receptor agonists.

Immepip, a conformationally constrained analogue of the histamine congener imbutamine, shows high affinity and functional activity on the human H(3) receptor. Using histamine and its homologues as prototypes, other rigid analogues containing either a piperidine or pyrrolidine ring in the side chain were synthesized and tested for their activities at the human H(3) receptor and the closely related H(4) receptor. In the series of piperidine containing analogues, immepip was found to be the most potent H(3) receptor agonist, whereas its propylene analogue 13a was identified as a high-affinity neutral antagonist for the human H(3) receptor. Moreover, replacement of the piperidine ring of immepip by a pyrrolidine ring led to a pair of enantiomers that show a distinct stereoselectivity at the human H(3) and H(4) receptor.

Binding, Competitive↗
PubMed2003

Constitutively active Gq/11-coupled receptors enable signaling by co-expressed G(i/o)-coupled receptors.

Co-expression of guanine nucleotide-binding regulatory (G) protein-coupled receptors (GPCRs), such as the G(i/o)-coupled human 5-hydroxytryptamine receptor 1B (5-HT(1B)R), with the G(q/11)-coupled human histamine 1 receptor (H1R) results in an overall increase in agonist-independent signaling, which can be augmented by 5-HT(1B)R agonists and inhibited by a selective inverse 5-HT(1B)R agonist. Interestingly, inverse H1R agonists inhibit constitutively H1R-mediated as well as 5-HT(1B)R agonist-induced signaling in cells co-expressing both receptors. This phenomenon is not solely characteristic of 5-HT(1B)R; it is also evident with muscarinic M2 and adenosine A1 receptors and is mimicked by mastoparan-7, an activator of G(i/o) proteins, or by over-expression of Gbetagamma subunits. Likewise, expression of the G(q/11)-coupled human cytomegalovirus (HCMV)-encoded chemokine receptor US28 unmasks a functional coupling of G(i/o)-coupled CCR1 receptors that is mediated via the constitutive activity of receptor US28. Consequently, constitutively active G(q/11)-coupled receptors, such as the H1R and HCMV-encoded chemokine receptor US28, constitute a regulatory switch for signal transduction by G(i/o)-coupled receptors, which may have profound implications in understanding the role of both constitutive GPCR activity and GPCR cross-talk in physiology as well as in the observed pathophysiology upon HCMV infection.

Animals↗
PubMed2003

SYNOPSIS: SYNthesize and OPtimize System in Silico.

We present a de novo design program called SYNOPSIS, that includes a synthesis route for each generated molecule. SYNOPSIS designs novel molecules by starting from a database of available molecules and simulating organic synthesis steps. This way of generating molecules imposes synthetic accessibility on the molecules. In addition to a starting database, a fitness function is needed that calculates the value of a desired property for an arbitrary molecule. The values obtained from this function guide the design process in optimizing the molecules toward an optimal value of the calculated property. Two applications are described. The first uses an electric dipole moment calculation to generate molecules possessing a strong dipole moment. The second makes use of the three-dimensional structure of a viral enzyme in order to generate high affinity ligands. Twenty eight compounds designed with the program resulted in 18 synthesized and tested compounds, 10 of which showed HIV inhibitory activity in vitro.

Anti-HIV Agents↗
PubMed2003

Improgan antinociception does not require neuronal histamine or histamine receptors.

Improgan, a chemical congener of the H(2) antagonist cimetidine, induces antinociception following intracerebroventricular (i.c.v.) administration in rodents, but the mechanism of action of this compound remains unknown. Because the chemical structure of improgan closely resembles those of histamine and certain histamine blockers, and because neuronal histamine is known to participate in pain-relieving responses, the antinociceptive actions of improgan were evaluated in mice containing null mutations in the genes for three histamine receptors (H(1), H(2), and H(3)) and also in the gene for histidine decarboxylase (the histamine biosynthetic enzyme). Similar to earlier findings in Swiss-Webster mice, improgan induced maximal, reversible, dose-related reductions in thermal nociceptive responses in ICR mice, but neither pre-improgan (baseline) nor post-improgan nociceptive latencies were changed in any of the mutant mice as compared with wild-type controls. Improgan also had weak inhibitory activity in vitro (pK(i)=4.7-4.9) on specific binding to three recently-discovered, recombinant isoforms of the rat H(3) receptor (H(3A), H(3B), and H(3C)). The present findings strongly support the hypothesis that neuronal histamine and its receptors fail to play a role in improgan-induced antinociception.

Analgesics↗
PubMed2002

Identification of the first nonpeptidergic inverse agonist for a constitutively active viral-encoded G protein-coupled receptor.

Human cytomegalovirus (HCMV) encodes a G protein-coupled receptor (GPCR), named US28, which shows homology to chemokine receptors and binds several chemokines with high affinity. US28 induces migration of smooth muscle cells, a feature essential for the development of atherosclerosis, and may serve as a co-receptor for human immunodeficiency virus-type 1 entry into cells. Previously, we have shown that HCMV-encoded US28 displays constitutive activity, whereas its mammalian homologs do not. In this study we have identified a small nonpeptidergic molecule (VUF2274) that inhibits US28-mediated phospholipase C activation in transiently transfected COS-7 cells and in HCMV-infected fibroblasts. Moreover, VUF2274 inhibits US28-mediated HIV entry into cells. In addition, VUF2274 fully displaces radiolabeled RANTES (regulated on activation normal T cell expressed and secreted) binding at US28, apparently with a noncompetitive behavior. Different analogues of VUF2274 have been synthesized and pharmacologically characterized, to understand which features are important for its inverse agonistic activity. Finally, by means of mutational analysis of US28, we have identified a glutamic acid in transmembrane 7 (TM 7), which is highly conserved among chemokine receptors, as a critical residue for VUF2274 binding to US28. The identification of a full inverse agonist provides an important tool to investigate the relevance of US28 constitutive activity in viral pathogenesis.

Animals↗
PubMed2002

Role of histamine H3 receptors in control of mouse intestinal motility in vivo and in vitro: comparison with alpha2-adrenoceptors.

We tested drugs acting at histamine H3 receptors in mice on the gastrointestinal transit of a charcoal meal in vivo and on neurogenic contractions of isolated ileal preparations. The agonist (R)-alpha-methylhistamine (100 micromol/kg) caused a maximum 25% reduction of gastrointestinal transit, an effect mimicked by immepip (100 micromol/kg) and antagonized by thioperamide (20 micromol/kg) or clobenpropit (20 micromol/kg). In the isolated ileum, (R)-alpha-methylhistamine (10-100 microM) caused a slight, thioperamide-insensitive, reduction (maximum 15%) of electrically evoked cholinergic contractions. In comparison, the alpha2-adrenoceptor agonist clonidine (0.1 micromol/kg) caused a 35.2% inhibition of the gastrointestinal transit and almost completely reduced (maximum 82% at 1 microM) the cholinergic contraction of the isolated ileum, both effects being antagonized by idazoxan (0.4 micromol/kg and 1 microM, respectively). These results suggest that histamine H3 receptors, located outside the myenteric plexus, mediate an inhibition of the gastrointestinal transit in vivo. Conversely, the presence of a2-adrenoceptors in the cholinergic nerve endings and their inhibitory role in the control of gastrointestinal propulsion is confirmed.

Animals↗
PubMed2002

A novel phenylaminotetralin radioligand reveals a subpopulation of histamine H(1) receptors.

Previously, (-)-trans-1-phenyl-3-N,N-dimethylamino-1,2,3,4-tetrahydronaphthalene ([-]-trans-H(2)-PAT) was shown to activate stereospecifically histamine H(1) receptors coupled to modulation of tyrosine hydroxylase activity in guinea pig and rat forebrain in vitro and in vivo. Furthermore, the novel radioligand [(3)H](-)-trans-H(2)-PAT was shown to label selectively H(1) receptors in guinea pig and rat brain with high affinity (K(D), ~0.1 and 0.5 nM, respectively) and a B(max) about 50 and 15%, respectively, of that observed for the H(1) antagonist radioligand [(3)H]mepyramine. In the current study, [(3)H](-)-trans-H(2)-PAT-labeled cloned guinea pig and human H(1) receptors in Chinese hamster ovary (CHO) cell membranes with high affinity (K(D), ~0.08 and 0.23 nM, respectively) and a B(max) about 15% of that observed for [(3)H]mepyramine. The binding of H(2)-PAT to H(1) receptors in both CHO-H(1) cell lines was stereoselective with the (-)-trans-isomer having affinity (K(i), ~1.5 nM) about 4-, 20-, and 50-times higher than the (-)-cis-, (+)-trans-, and (+)-cis-isomers, respectively; the affinity of (-)-trans-H(2)-PAT was unaffected by excess GTP. In functional assays, (-)-trans-H(2)-PAT was a full antagonist of histamine H(1)-mediated stimulation of phospholipase C (PLC) and [(3)H]inositol phosphates (IP) formation in CHO-H(1) cells, a full inverse agonist of constitutively active H(1) receptors in COS-7-H(1) cells, and a full competitive antagonist (pA(2) = 9.2) of histamine H(1)-mediated contraction of guinea pig ileum. It is concluded that (-)-trans-H(2)-PAT is an antagonist at H(1) receptors coupled to PLC/IP formation and smooth muscle contraction. Meanwhile, the observation that [(3)H](-)-trans-H(2)-PAT labels only a subpopulation of H(1) receptors and that (-)-trans-H(2)-PAT activates H(1) receptors coupled to modulation of tyrosine hydroxylase suggests that there may be post-translational H(1) receptor heterogeneity.

Animals↗
PubMed2002

Kaposi's sarcoma-associated herpesvirus-encoded G protein-coupled receptor ORF74 constitutively activates p44/p42 MAPK and Akt via G(i) and phospholipase C-dependent signaling pathways.

The G protein-coupled receptor encoded by Kaposi's sarcoma-associated herpesvirus, also referred to as ORF74, has been shown to stimulate oncogenic and angiogenic signaling pathways in a constitutively active manner. The biochemical routes linking ORF74 to these signaling pathways are poorly defined. In this study, we show that ORF74 constitutively activates p44/p42 mitogen-activated protein kinase (MAPK) and Akt via G(i)- and phospholipase C (PLC)-mediated signaling pathways. Activation of Akt by ORF74 appears to be phosphatidylinositol 3-kinase (PI3-K) dependent but, interestingly, is also mediated by activation of protein kinase C (PKC) and p44/p42 MAPK. ORF74 may signal to Akt via p44/p42 MAPK, which can be activated by G(i), through activation of PI3-K or through PKC via the PLC pathway. Signaling of ORF74 to these proliferative and antiapoptotic signaling pathways can be further modulated positively by growth-related oncogene (GROalpha/CXCL1) and negatively by human gamma interferon-inducible protein 10 (IP-10/CXCL10), thus acting as an agonist and an inverse agonist, respectively. Despite the ability of the cytomegalovirus-encoded chemokine receptor US28 to constitutively activate PLC, this receptor does not increase phosphorylation of p44/p42 MAPK or Akt in COS-7 cells. Hence, ORF74 appears to signal through a larger diversity of G proteins than US28, allowing it to couple to proliferative and antiapoptotic signaling pathways. ORF74 can therefore be envisioned as an attractive target for novel treatment of Kaposi's sarcoma.

Animals↗