Modulation of NSAID-induced antinociceptive and anti-inflammatory effects by alpha2-adrenoceptor agonists with gastroprotective effects

Tizanidine, an alpha2-adrenergic receptor agonist with myospasmolytic action, is indicated for the treatment of back pain either as monotherapy or in combination with nonsteridal anti-inflammatory drugs (NSAIDs). Tizanidine (0.25-1.0 mg/kg) significantly produced analgesic and anti-inflammatory effect in acetic acid induced writhing in mice and carrageenan-induced paw edema in rats, respectively. The effects were comparable with clonidine (0.25 and 0.50 mg/kg), another alpha2-agonist. Yohimbine (1 mg/kg), alpha2-adrenergic antagonist reversed the effect of tizanidine. Tizanidine (0.25 mg/kg) and clonidine (0.25 mg/kg) significantly potentiated the antinociceptive and anti-inflammatory effect of NSAIDs (nimesulide, meloxicam and naproxen). Tizanidine (1 mg/kg) did not alter basal pH, acidity (free and total) of gastric content and did not produce any mucosal injury in fasted rats. Tizanidine (1 mg/kg) significantly reduced meloxicam (UD50 3.21 mg/kg), nimesulide (UD50 24.52 mg/kg) and naproxen (UD50 14.10 mg/kg)-induced ulcerogenic effect (ulcer index, pH and free/total acidity). It is expected that tizanidine exerted gastrotprotection through stimulation of gastric and central alpha2-adrenergic receptors. Present investigation suggested that tizanidine not only enhance the analgesic and anti-inflammatory effect of NSAIDs but also improved gatstrointestinal tolerability of NSAIDs through modulation of central alpha-2-receptors. From this study, it can be speculated that tizanidine and NSAID combination therapy would prove to be a novel approach to treat nociceptive/inflammatory conditions with improved gastric tolerability of NSAIDs.     

Action of nereistoxin on recombinant neuronal nicotinic acetylcholine receptors expressed in<Emphasis Type="Italic"> Xenopus laevis</Emphasis> oocytes

Nereistoxin (NTX), a natural neurotoxin from the salivary glands of the marine annelid worm Lumbriconereis heteropoda, is highly toxic to insects. Its synthetic analogue, Cartap, was the first commercial insecticide based on a natural product. We have used voltage-clamp electrophysiology to compare the actions of NTX on recombinant nicotinic acetylcholine receptors (nicotinic AChRs) expressed in Xenopus laevis oocytes following nuclear injection of cDNAs. The recombinant nicotinic AChRs investigated were chicken 7, chicken 42 and the Drosophila melanogaster/chicken hybrid receptors SAD/2 and ALS/2. No agonist action of NTX (0.1–100 M) was observed on chicken 7, chicken 42 and the Drosophila/chicken hybrid nicotinic AChRs. Currents elicited by ACh were reduced in amplitude by NTX in a dose-dependent manner. The toxin was slightly more potent on recombinant Drosophila/vertebrate hybrid receptors than on vertebrate homomeric (7) or heteromeric (42) nicotinic AChRs. Block by NTX of the chicken 7, chicken 42 and the SAD/2 and ALS/2 Drosophila/chicken hybrid receptors is in all cases non-competitive. Thus, the site of action on nicotinic AChRs of NTX, to which the insecticide Cartap is metabolised in insects, differs from that of the major nicotinic AChR-active insecticide, imidacloprid.     

Effect of ecdysone agonists on vitellogenesis and the expression of EcR and USP in codling moth (Cydia pomonella)

The effects of tebufenozide and methoxyfenozide on vitellogenin (Vg) synthesis/release in the fat body, translocation in hemolymph, uptake by the ovary, and the expression of the ecdysone receptor (EcR) and its heterodimer partner, ultraspiracle protein (USP) in fat body, were investigated in Cydia pomonella. The results indicated that both ecdysone agonists significantly increased the Vg level in the adult hemolymph when the moths were exposed to agonist-treated surfaces. However, these agonists did not affect Vg release from the fat body nor Vg deposition in the first batch oocytes. Western blot analysis revealed that the expression of EcR and USP was significantly increased in tebufenozide- and methoxyfenozide-treated samples compared to the control, suggesting that ecdysone agonists regulated the Vg synthesis via the EcR and USP proteins complex.     

P2Y6 nucleotide receptor activates PKC to protect 1321N1 astrocytoma cells against tumor necrosis factor-induced apoptosis

1. We recently reported that the activation by UDP of rat P2Y₆ nucleotide receptors expressed in 1321N1 astrocytoma cells protected them from TNF-induced apoptosis by suppressing activation of caspase 3 and 8. This study aims to characterize the involvement of intracellular signaling pathways, including kinases, involved in the antiapoptotic effect of UDP.2. Cell death was induced in 1321N1 astrocytoma cells permanently expressing the rat P2Y₆ receptor by exposure to TNF in the presence of cycloheximide. The apoptotic fraction was analyzed using flow cytometry.3. The activation of P2Y₆ receptors by UDP both protected the astrocytes from TNF- induced apoptosis and activated protein kinase C (PKC) isotypes. The phorbol ester PMA also activated PKC and protected the cells from TNF-induced cell death. The - and -isotypes of PKC were both activated in a persistent fashion upon 5-min exposure to either UDP (10 M) or the phorbol ester PMA (100 nM). The PKC isotype was markedly activated upon UDP treatment.4. The addition of PKC inhibitors, GF109203X or Gö6976, partially antagonized the protective effect of UDP and reduced the UDP-induced phosphorylation of extracellular signal-regulated protein kinases (Erk). The inhibitors of Erk, PD98,059 or U0126, antagonized UDP-induced protection.5. The antiapoptotic protein, Akt, was not affected by P2Y₆ receptor activation. Incubation of the astrocytes with calcium modifiers, BAPTA-AM or dantrolene, did not affect the UDP-induced protection from apoptosis.6. The addition of phospholipase C (PLC) inhibitors, D609 or U73122, partially antagonized both UDP-induced protection and PKC activation.7. Therefore, it is suggested that P2Y₆ receptors in 1321N1 cells, through coupling to PC-PLC and PI-PLC, activate PKC to protect against TNF -induced apoptosis, in which the activation of Erk is involved in part.     

Novel applications of feather tip extracts from MDV-infected chickens; diagnosis of commercial broilers, whole genome separation by PFGE and synchronic mucosal infection

Marek's disease virus (MDV) productive replication occurs in the feather follicle epithelium and the feather tips are valuable both for research and disease diagnosis. Three novel applications of feather tip extracts are described now: (A). As a source of DNA for amplifying either MDV and/or ALV-J. In two clinical situations a marked advantage was obtained compared to blood and organs; in broiler breeder flocks with a mixed MDV and ALV-J infection, and in young broilers with neurological Marek's disease (MD). (B). Separation of the large ( approximately 200 kbp) MDV genome directly from the infected chickens. Using pulsed field gel electrophoresis, the DNA extracted from tumors or feather tips was separated and hybridized to a 132 bp tandem repeat MDV probe. Compared to 2/55 polymerase chain reaction (PCR) positive tumor samples, 15/61 feather tip extracts contained whole MDV genomes. (C). Experimental MDV infection was induced by the mucosal route by dripping feather tip extract to the eye and mouth of the bird. That attempted to reproduce the native infection process, however the use of extracts, instead of dry feather dust was a compromise, aimed to synchronize the infection. In one trial, tumors were induced 6 weeks after dripping day-old broilers, while in another, feather tips were PCR positive 16 days after dripping of 2-month-old layers.     

N-Acetylaspartylglutamate: the most abundant peptide neurotransmitter in the mammalian central nervous system

In the progress of science, as in life, timing is important. The acidic dipeptide, N-acetylaspartylglutamate (NAAG), was discovered in the mammalian nervous system in 1965, but initially was not considered to be a neurotransmitter candidate. In the mid-1980s, a few laboratories revisited the question of NAAG's role in the nervous system and pursued hypotheses regarding its function that ranged from a precursor for the transmitter pool of glutamate to a direct role as a peptide transmitter. Since that time, NAAG has been tested against nearly all of the established criteria for identification of a neurotransmitter. It successfully meets each of these tests, including a concentrated presence in neurons and synaptic vesicles, release from axon endings in a calcium-dependent manner following initiation of action potentials, and extracellular hydrolysis by membrane-bound peptidase activity. NAAG is the most prevalent and widely distributed neuropeptide in the mammalian nervous system. NAAG activates NMDA receptors with a low potency that may vary among receptor subtypes, and it is a highly selective agonist at the type 3 metabotropic glutamate receptor (mGluR3). Acting through this receptor, NAAG reduces cyclic AMP levels, decreases voltage-dependent calcium conductance, suppresses excitotoxicity, influences long-term potentiation and depression, regulates GABA(A) receptor subunit expression, and inhibits synaptic release of GABA from cortical neurons. Cloning of peptidase activities against NAAG provides opportunities to study the cellular and molecular mechanisms by which synaptic NAAG peptidase activity is controlled. Given the codistribution of this peptide with a spectrum of traditional transmitters and its ability to activate mGluR3, we speculate that one role for NAAG following synaptic release is the activation of metabotropic autoreceptors that inhibit subsequent transmitter release. A second role is the production of extracellular glutamate following NAAG hydrolysis.     

Biotransformation of l-DOPA to Dopamine in the Substantia Nigra of Freely Moving Rats: Effect of Dopamine Receptor Agonists and Antagonists

Abstract: We investigated the effects of continuous intranigral perfusion of dopamine D1 and D2 receptor agonists and antagonists on the biotransformation of locally applied l -DOPA to dopamine in the substantia nigra of freely moving rats by means of in vivo microdialysis. The "dual-probe" mode was used to monitor simultaneously changes in extracellular dopamine levels in the substantia nigra and the ipsilateral striatum. Intranigral perfusion of 10 µ M l -DOPA for 20 min induced a significant 180-fold increase in extracellular nigral dopamine level. No effect of the intranigral l -DOPA administration was observed on dopamine levels in the ipsilateral striatum, suggesting a tight control of extracellular dopamine in the striatum after enhanced nigral dopamine levels. Continuous nigral infusion with the D1 receptor agonist CY 208243 (10 µ M ) and with the D2 receptor agonist quinpirole at 10 µ M (a nonselective concentration) attenuated the l -DOPA-induced increase in dopamine in the substantia nigra by 85 and 75%, respectively. However, perfusion of the substantia nigra with a lower concentration of quinpirole (1 µ M ) and the D1 antagonist SCH 23390 (10 µ M ) did not affect the nigral l -DOPA biotransformation. The D2 antagonist (−)-sulpiride (10 µ M ) also attenuated the l -DOPA-induced dopamine release in the substantia nigra to ∼10% of that of the control experiments. We confirm that there is an important biotransformation of l -DOPA to dopamine in the substantia nigra. The high concentrations of dopamine formed after l -DOPA administration may be the cause of dyskinesias or further oxidative stress in Parkinson's disease. Simultaneous administration of D1 receptor agonists with l -DOPA attenuates the biotransformation of l -DOPA to dopamine in the substantia nigra. The observed effects could occur via changes in nigral GABA release that in turn influence the firing rate of the nigral dopaminergic neurons.     

Biochemical pharmacology of total retro-inverso analogues of bradykinin and angiotensin II: Molecular recognition by G-protein-coupled receptors and angiotensin converting enzyme

Total retro-inverso (TRI) analogues of bradykinin (BK), the B₂a-selective kinin antagonist d-Arg⁰[Hyp₃,d-Phe⁷,Leu⁸]BK, angiotensin II (AT II) and the AT II antagonist Saralasin ([Sar¹,Val⁵,Ala⁸]AT II) were prepared by conventional solid-phase synthesis. Molecular recognition of TRI peptidomimetics by G-protein-coupled receptors was studied by competitive radioligand displacement experiments. TRI analogues of d-Arg⁰[Hyp³,d-Phe⁷,Leu⁸]BK specifically bound to the kidney medulla B₂a bradykinin receptor with affinities (K_d) ranging from 64 M to 4 M. Conversely, TRI analogues of BK, AT II and Saralasin did not bind to either the B_2a bradykinin receptor or the rat AT_1a AT II receptor, respectively. These studies indicate that the TRI strategy is more compatible with the synthesis of antagonists than agonists. Three TRI peptidomimetics of d-Arg⁰[Hyp³,d-Phe⁷,Leu⁸]BK were weak inhibitors of angiotensin converting enzyme. All other TRI peptidomimetics had no effect upon ACE activity. These data endorse the utility of the TRI strategy for the synthesis of protease-resistant antagonists of peptide hormones and neuropeptides.     

Cytotoxic Peptides: Naphthoquinonyl Derivatives of Luteinizing Hormone-Releasing Hormone

In an attempt to produce efficient cytotoxic derivatives of luteinizing hormone-releasing hormone (LH-RH), two novel 1,4-naphthoquinone derivatives of [D-Lys⁶]-LH-RH were synthesized primarily by solid-phase peptide synthesis, in good yield and high purity. The ability of each analog to produce reactive oxygen species using enzymatic reduction, i.e. NADPH-cytochrome P-450 reductase, was evaluated employing electron spin resonance (ESR) spectroscopy and spin-trapping techniques. The ESR results suggest that the novel cytotoxic analogs are extremely effective in generating oxygen radicals.