Xiao-duo Ji

Chronic administration of selective adenosine A1 receptor agonist or antagonist in cerebral ischemia

The effect of chronic administration of selective adenosine A1 receptor agonists and antagonists on the outcome of cerebral ischemia is entirely unknown. Therefore, we have investigated the impact of such regimens on the hippocampal adenosine A1 receptor density, and on the recovery from 10 min forebrain ischemia in gerbils. While acutely administered N6-cyclopentyladenosine (CPA) given at 0.02 mg/kg resulted only in a significant reduction of mortality, at 1 mg/kg it improved both survival and neuronal preservation in the hippocampal CA1 region. Acute treatment with 1,3-dipropyl-8-cyclopentylxanthine (CPX) significantly worsened the outcome and enhanced neuronal destruction. The effects of chronic administration of these drugs (15 days followed by 1 drug-free day) were opposite. Thus, although chronic CPA at 0.02 mg/kg did not have any effect at all, at 1 mg/kg both survival and neuronal preservation were significantly poorer than in controls, while chronic CPX resulted in a significant improvement of both measures. These results were not accompanied by adenosine A1 receptor up- or downregulation. Our study indicates that highly selective adenosine analogues may have therapeutic potential in treatment of cerebral ischemia/stroke and possibly other neurodegenerative disorders as well.

Chronic adenosine A1 receptor agonist and antagonist : effect on receptor density and N-methyl-D-aspartate induced seizures in mice

The effect of chronic administration of the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the adenosine A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) on N-methyl-D-aspartate (NMDA)-evoked seizures was studied in C57BL/6 mice (20/group). Animals were injected i.p. for 9 days with either 1.0 mg/kg CPA or 1.0 mg/kg CPX followed by 2 injection-free days (the washout period) and subsequent administration of a single dose of 60 mg/kg NMDA. As in our previous study, this dose of NMDA caused clonic/tonic seizures resulting in high (60%) mortality within 3 h after injection of the drug. Despite insignificant changes in seizure latency, chronic pretreatment with CPA increased the incidence of clonic/tonic episodes and end-point mortality. Conversely; chronic exposure to CPX completely eliminated clonic/tonic episodes, significantly increased average survival time, and reduced end-point mortality (P < 0.05). The results indicate that chronic treatment with adenosine A1 receptor antagonist may protect against NMDA-evoked seizures to the same degree as previously observed following a single, acute exposure to CPA. Since the density of adenosine receptor binding sites was unchanged after chronic treatment with either CPX or CPA, it is likely that the mechanism behind the observed protection may rest at the level of second messenger systems coupled to adenosine A1 receptors.

Synthesis and Structure-Activity Relationships of Pyridoxal-6-arylazo-5'-phosphate and Phosphonate Derivatives as P2 Receptor Antagonists.

Novel analogs of the P2 receptor antagonist pyridoxal‐5′‐phosphate‐6‐phenylazo‐2′,4′‐disulfonate (PPADS) were synthesized. Modifications were made through functional group substitution on the sulfophenyl ring and at the phosphate moiety through the inclusion of phosphonates, demonstrating that a phosphate linkage is not required for P2 receptor antagonism. Substituted 6‐phenylazo and 6‐naphthylazo derivatives were also evaluated. Among the 6‐phenylazo derivatives, 5′‐methyl, ethyl, propyl, vinyl, and allyl phosphonates were included. The compounds were tested as antagonists at turkey erythrocyte and guinea‐pig taenia coli P2Y1 receptors, in guinea‐pig vas deferens and bladder P2X1 receptors, and in ion flux experiments by using recombinant rat P2X2 receptors expressed in Xenopus oocytes. Competitive binding assay at human P2X1 receptors in differentiated HL‐60 cell membranes was carried out by using [35S]ATP‐γ‐S. A 2′‐chloro‐5′‐sulfo analog of PPADS (C14H12O9N3ClPSNa), a vinyl phosphonate derivative (C15H12O11N3PS2Na3), and a naphthylazo derivative (C18H14O12N3PS2Na2), were particularly potent in binding to human P2X1 receptors. The potencies of phosphate derivatives at P2Y1 receptors were generally similar to PPADS itself, except for the p‐carboxyphenylazo phosphate derivative C15H13O8N3PNa and its m‐chloro analog C15H12O8N3ClPNa, which were selective for P2X vs. P2Y1 receptors. C15H12O8N3ClPNa was very potent at rat P2X2 receptors with an IC50 value of 0.82 μM. Among the phosphonate derivatives, [4‐formyl‐3‐hydroxy‐2‐methyl‐6‐(2‐chloro‐5‐sulfonylphenylazo)‐pyrid‐5‐yl]methylphosphonic acid (C14H12O8N3ClPSNa) showed high potency at P2Y1 receptors with an IC50 of 7.23 μM. The corresponding 2,5‐disulfonylphenyl derivative was nearly inactive at turkey erythrocyte P2Y1 receptors, whereas at recombinant P2X2 receptors had an IC50 value of 1.1 μM. An ethyl phosphonate derivative (C15H15O11N3PS2Na3), whereas inactive at turkey erythrocyte P2Y1 receptors, was particularly potent at recombinant P2X2 receptors. Drug Dev. Res. 45:52–66, 1998. Published 1998 Wiley‐Liss, Inc.

Acyl‐hydrazide derivatives of a xanthine carboxylic congener (XCC) as selective antagonists at human A2B adenosine receptors

The structure–activity relationships (SAR) of 8‐phenyl‐1,3‐dipropylxanthine derivatives in binding to recombinant human A2B adenosine receptors were explored, in order to identify selective antagonists. Based on the finding of receptor selectivity in MRS 1204, containing an N‐hydroxysuccinimide ester attached through the p‐position of the 8‐phenyl substituent [Jacobson et al. (1999): Drug Dev. Res., 47:45–53], a hydrazide and its more stable imide derivatives were synthesized. The hydrazide of XCC (8‐[4‐[[[carboxy]methyl]oxy]phenyl]‐1,3‐dipropylxanthine) was acylated with a variety of mono‐ and dicarboxylic acids. Ki values were determined in the adenosine receptor binding assays. At recombinant human A2B receptors expressed in membranes of HEK‐293 cells, antagonist radioligands used were the xanthine 125I‐ABOPX (125I‐3‐(4‐amino‐3‐iodobenzyl)‐8‐oxyacetate‐1‐propyl‐xanthine) and the nonxanthine antagonist [3H]ZM 241385 ([3H]4‐(2‐[7‐amino‐2‐{furyl}{1,2,4}triazolo{2,3‐a}{1,3,5}triazin‐5‐ylamino‐ethyl)phenol). The initial screening utilized rat A1/A2A receptors and human A3 receptors, and selected compounds were examined at the human A1/A2A subtypes. A 1,2‐dimethylmaleimide derivative, 14 (MRS 1595), bound to human A2B receptors with a Ki of 19 nM and proved to be selective vs. human A1/A2A/A3 receptors by 160‐, and 35‐fold, respectively. Enprofylline (3‐propylxanthine) is slightly selective for A2B receptors, suggesting removal of the 1‐propyl group; however, combination of the 1‐H‐3‐Pr and 8‐phenyl substituents eliminated the selectivity. Other potent and moderately selective A2B antagonists were a tetrahydrophthaloyl derivative 18b (MRS 1614, Ki value 10 nM) and amino acid conjugates of the XCC‐hydrazide, i.e., the glutarimide 24b (MRS 1626, Ki value 13 nM), and protected dipeptide 27 (MRS 1615, Ki value 11 nM). Drug Dev. Res. 47:178–188, 1999. Published 1999 Wiley‐Liss, Inc.

Chronic adenosine A1 receptor agonist and antagonist: effect on receptor density and N-methyl--aspartate induced seizures in mice

The effect of chronic administration of the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the adenosine A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) on N-methyl-D-aspartate (NMDA)-evoked seizures was studied in C57BL/6 mice (20/group). Animals were injected i.p. for 9 days with either 1.0 mg/kg CPA or 1.0 mg/kg CPX followed by 2 injection-free days (the washout period) and subsequent administration of a single dose of 60 mg/kg NMDA. As in our previous study, this dose of NMDA caused clonic/tonic seizures resulting in high (60%) mortality within 3 h after injection of the drug. Despite insignificant changes in seizure latency, chronic pretreatment with CPA increased the incidence of clonic/tonic episodes and end-point mortality. Conversely; chronic exposure to CPX completely eliminated clonic/tonic episodes, significantly increased average survival time, and reduced end-point mortality (P < 0.05). The results indicate that chronic treatment with adenosine A1 receptor antagonist may protect against NMDA-evoked seizures to the same degree as previously observed following a single, acute exposure to CPA. Since the density of adenosine receptor binding sites was unchanged after chronic treatment with either CPX or CPA, it is likely that the mechanism behind the observed protection may rest at the level of second messenger systems coupled to adenosine A1 receptors.

Molecular recognition in P2 receptors: ligand development aided by molecular modeling and mutagenesis.

Publisher Summary As molecular modeling of cloned G protein-coupled receptor (GPCR) sequences using a rhodopsin template has been refined, it has become possible to generate hypotheses for location of the binding sites that are consistent with mutagenesis results and ligand specificities. To obtain an energetically refined 3-D structure of the ligand–receptor complex, the chapter introduces a new computational approach, a “cross docking” procedure, which simulates the reorganization of the native receptor induced by the ligand. The molecular basis for recognition by human P2Y 1 receptors of the selective, competitive antagonist MRS 2179 is probed using site-directed mutagenesis and molecular modeling. The model was derived from primary sequence comparison, secondary structure predictions, and 3-D homology building, using rhodopsin as a template, and was consistent with data obtained from mutagenesis studies. A putative nucleotide binding site was localized, following a cross docking procedure to obtain energetically refined 3-D structures of the ligand–receptor complexes, and used to predict which residues are likely to be in proximity to agonists and antagonists. Molecular modeling using PowerFit has suggested a possible model of superimposition of two classes of antagonists, nucleotides related to MRS 2179, and non-nucleotides related to pyridoxal phosphate.

A SURVEY OF NONXANTHINE DERIVATIVES AS ADENOSINE RECEPTOR LIGANDS

The binding affinities at rat A1, A2a, and A3 adenosine receptors of a wide range of heterocyclic derivatives have been determined. Mono-, bi-, tricyclic and macrocyclic compounds were screened in binding assays, using either [3H]PIA or [3H]CGS 21680 in rat brain membranes or [125I]AB-MECA in CHO cells stably transfected with rat A3 receptors. Several new classes of adenosine antagonists (e.g. 5-oxoimidazopyrimidines and a pyrazoloquinazoline) were identified. Various sulfonylpiperazines, 11-hydroxytetrahydrocarbazolenine, 4H-pyrido[1,2-a]pyrimidinone, folic acid, and cytochalasin H and J bound to A3 receptors selectively. Moreover, cytochalasin A, which bound to A1 adenosine receptors with Ki value of 1.9 μM, inhibited adenylyl cyclase in rat adipocytes, but not via reversible A1 receptor binding.

The Essential Oil of the Leaves of Psidium guajava L.

ABSTRACT A characterization of the compounds present in the essential oil from the leaves of Psidium guajava L. (a traditional Chinese medicinal plant) has been obtained. α-Pinene (37.8%) and 1,8-cineole (18.9%) are the major components.

Pyran Template Approach to the Design of Novel A3 Adenosine Receptor Antagonists.

A3 adenosine receptor antagonists have potential as anti‐inflammatory, anti‐asthmatic, and anti‐ischemic agents. We previously reported the preparation of chemical libraries of 1,4‐dihydropyridine (DHP) and pyridine derivatives and identification of members having high affinity at A3 adenosine receptors. These derivatives were synthesized through standard three‐component condensation/oxidation reactions, which permitted versatile ring substitution at five positions, i.e., the central ring served as a molecular scaffold for structurally diverse substituents. We extended this template approach from the DHP series to chemically stable pyran derivatives, in which the ring NH is replaced by O and which is similarly derived from a stepwise reaction of three components. Since the orientation of substituent groups may be conformationally similar to the 1,4‐DHPs, a direct comparison between the structure activity relationships of key derivatives in binding to adenosine receptors was carried out. Affinity at human A3 receptors expressed in CHO cells was determined vs. binding of [125I]AB‐MECA (N6‐(4‐amino‐3‐iodobenzyl)‐5′‐N‐methylcarbamoyladenosine). There was no potency‐enhancing effect, as was observed for DHPs, of 4‐styryl, 4‐phenylethynyl, or 6‐phenyl substitutions. The most potent ligands in this group in binding to human A3 receptors were 6‐methyl and 6‐phenyl analogs, 3a (MRS 1704) and 4a (MRS 1705), respectively, of 3,5‐diethyl 2‐methyl‐4‐phenyl‐4H‐pyran‐3,5‐dicarboxylate, which had Ki values of 381 and 583 nM, respectively. These two derivatives were selective for human A3 receptors vs. rat brain A1 receptors by 57‐fold and 24‐fold, respectively. These derivatives were inactive in binding at rat brain A2A receptors, and at recombinant human A2B receptors displayed Ki values of 17.3 and 23.2 μM, respectively. The selectivity, but not affinity, of the pyran derivatives in binding to the A3 receptor subtype was generally enhanced vs. the corresponding DHP derivatives. Drug Dev. Res. 48:171–177, 1999. Published 1999 Wiley‐Liss, Inc.

The Essential Oil of the Leaves of Callistemon rigidus R. Br.

ABSTRACT The essential oil from the leaves of Callistemon rigidus R. Br., a traditional Chinese medicinal plant, has been analyzed and found to contain thirteen compounds. The oil was predominantly 1, 8-cineole (89.9%).