Synthesis and analgesic effects of novel ß2-tryptophan hexapeptide analogs.

Aiming to develop more potent analgesic substances a new series of hexapeptides containing ß(2)-tryptophan analogues was synthesized. The Trp in position 4 and 5, respectively in Ac-Arg-Phe-Met-Trp-Met-Lys-NH2 (opioid receptor antagonist) and Ac-Arg-Tyr-Tyr-Arg-Trp-Lys-NH2 (highly potent and selective NOP-receptor agonist) was substituted by the (S)-2-(1-methyl-1H-indol-3-yl)propionic residue or the (S)-2-(5-methoxy-1H-indol-3-yl)propionic residue. The analgesic effect of the four newly synthesized compounds has been evaluated in male Wistar rats by PP- and HP tests and compared to the native templates. Further estimation of the mechanisms of action of each compound was achieved using specific antagonists-naloxone for opioid and JTC801 for the NOP receptor. Replacement of Trp with ß(2)-tryptophan analogues in 4th position (Ac-Arg-Phe-Met-Trp-Met-Lys-NH2) led to increased and longer lasting analgesic effect. The results obtained permit us to assume that both opioid and NOP receptors take part in the newly synthesized compounds analgesic effects.

Effects of D-kyotorphin on nociception and NADPH-d neurons in rat's periaqueductal gray after immobilization stress.

D-kyotorphin (D-Kyo) is a synthetic analogue of the neuropeptide kyotorphin and produces naloxone reversible analgesia. Stress-induced analgesia (SIA) is an in-built mammalian pain-suppression response that occurs during or following exposure to a stressful stimulus. The periaqueductal gray (PAG) is implicated as a critical site for processing strategies for coping with different types of stress and pain and NO affects its activity. The objectives of the present study were twofold: (1) to examine the effects of D-Kyo (5 mg/kg) on acute immobilization SIA; (2) to investigate the effect of peptide on NO activity in rat PAG after the stress procedure mentioned above. All drugs were injected intraperitoneally in male Wistar rats. The nociception was measured by the paw pressure and hot plate tests. A histochemical procedure for nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)-reactive neurons was used as indirect marker of NO activity. Our results revealed that D-Kyo has modulating effects on acute immobilization stress-induced analgesia in rats may be by opioid and non-opioid systems. Although D-Kyo is incapable of crossing the blood-brain barrier it showed an increased number of NADPH-d reactive neurons in dorsolateral periaqueductal gray (dlPAG) in control but not in stressed groups. We may speculate that the effect of D-Kyo in the brain is due to structural and functional interaction between opioidergic and NO-ergic systems or D-Kyo appears itself as a stressor. Further studies are needed to clarify the exact mechanisms of its action.

3D-QSAR and preliminary evaluation of anti-inflammatory activity of series of N-pyrrolylcarboxylic acids.

The present study focuses on development of new potential inhibitors of cyclooxygenase-2 (COX-2): series of N-pyrrolylcarboxylic acids. 3D-QSAR (Quantitative Structure-Activity Relationship) CoMFA (Comparative Molecular Field Analysis) and CoMSIA (Comparative Molecular Similarity Index Analysis) models for predicting inhibitory activities against COX-1 and COX-2 as well as for evaluating in vivo anti-inflammatory activity were obtained and used for preliminary screening of new anti-inflammatory N-pyrrolylcarboxylic acids. Nine compounds were selected for in vivo testing and evaluated for their potency to decrease carrageenin-induced edema in rats. The compounds were applied i.p. at doses 20 mg/kg and 40 mg/kg and p.o. at doses 10 mg/kg and 40 mg/kg. Six compounds showed more than 70% protection of the edema. Indomethacin (2 mg/kg i.p.), used as a reference drug, possessed 54% anti-inflammatory activity under similar experimental conditions.

Effects of Tyr-MIF's family of peptides on immobilization stress-induced antinociception in rats.

UNLABELLED: The Tyr-MIF-1 family of peptides includes MIF-1, Tyr-MIF-1, Tyr-W-MIF-1 and Tyr-K-MIF-1, which have been isolated from bovine hypothalamus and cortex of human brain. Data in the literature suggest that peptides of Tyr-MIF-1's family have opioid-like and anti-opioid actions. All these peptides interact with opioid receptors and in addition bind to non-opiate sites specific for each of the peptides and able to inhibit the expression of some forms of stress-induced analgesia (SIA) in various species. AIM: To examined the effects of the Tyr-MIF-1's peptides on immobilization stress-induced antinociception. METHODS: Tyr-MIF-1's peptides were given to male Wistar rats intraperitoneally before or after 1 hour of restraint. The changes in the mechanical nociceptive threshold of the animals were measured by the Randall-Selitto paw pressure test. RESULTS: Immobilization of the rats increased the pain threshold at least 1 h. Tyr-MIF-1's peptides have contrasting effects on immobilization stress-induced antinociception in paw-pressure test in rats. When administered before immobilization procedure they potentiated the immobilization stress-induced antinociception, while if given after immobilization, they reduced it. Antinociceptive effects of Tyr-MIF-1, Tyr-W-MIF-1 and Tyr-K-MIF-1 were reduced in condition of stress. CONCLUSION: Tyr-MIF-1's peptides exerted antiopioide effects under condition of stress in paw-pressure test. These antiopioide effects were more pronounced when peptides were injected after stress exposure.

Effects of kyotorphin and analogues on nociception and pentylenetetrazole seizures.

UNLABELLED: Kyotorphin (Kyo) is synthesized in specific brain regions where it may modulate synaptic transmission and directly excites cortical neurons, and indirectly exerts opioid actions to produce analgesia via release of met-enkephalin. Kyo is formed by specific enzyme from L-tyrosine and L-arginine in the presence of ATP and Mg2+ in the brain. Kyo and its analogues Tyr-Cav, Tyr (Cl2)-Cav exerted naloxone-reversible antinociception by paw-pressure test. Kyo exerted anticonvulsive effect on the pentylenetetrazole (PTZ) seizure model. AIM: To investigate the analgesic and the anticonvulsive effects of Kyo, Tyr-Cav and Tyr(Cl2)-Cav during acute pain and PTZ seizure model. METHODS: Changes in the nociceptive effects were examined in male Wistar rats by the tail flick (TF) and hot plate (HP) tests. Kyo, Tyr-Cav, Tyr(Cl2)-Cav were applied in rats intracerebroventricularly (i.c.v.) at a dose of 20 microg/20 microl. The anticonvulsive effects of peptides were studied on a PTZ seizure model. The peptides were applied in male mice at a dose of 20 microg/mouse (i.c.v.). RESULTS: Kyo, Tyr-Cav, Tyr(Cl2)-Cav exerted analgesic effects in both nociceptive tests used. The effects were more pronounced for L-Arg, L-Cav, Tyr-Cav and Tyr(Cl2)-Cav. In PTZ seizure model Kyo and its analogues exerted strong inhibition on seizure intensity compared with control group. CONCLUSION: Taken together, these results reveal Kyo, Tyr-Cav and Tyr(Cl2)-Cav as a behaviorally active peptide in experimental animal models.

Synthesis of an MIF-1 analogue containing enantiopure (S)-α-trifluoromethyl-proline and biological evaluation on nociception.

The synthesis and the effect of a novel MIF-1 analogue on nociception during acute pain in rat model are reported. The synthesis of this enantiopure trifluoromethyl group containing tripeptide was performed through a peptide coupling reaction between the HCl. Leu-Gly-NH2 and the (S)-α-Tfm-proline. The analgesic effect of the CF3-(MIF-1) 2 has been evaluated in vivo on rat model by paw pressure (PP) and hot plate (HP) tests and compared to the native peptide MIF-1. Highest analgesic effect was observed with CF3-(MIF-1) 2 only in PP test. In order to study the mechanisms of nociception induced by the studied peptides, the involvement of the opioid and the nitric oxideergic systems was investigated. The results are in favor of a participation of both system since pretreatment, 20 min before injection of the CF3-(MIF-1) 2, with the non-competitive antagonist of opiate receptors naloxone, the nitric oxide synthase (NOS) inhibitor l-N(G)-nitroarginine ester (l-NAME) or the nitric oxide (NO) donor l-arginine (l-Arg) significantly decreased the pain perception in PP and HP tests.

Further evaluation of a series of anti-inflammatory N-pyrrolylcarboxylic acids: effects on the nociception in rats.

The analgesic activity of nine substituted N-pyrrolylcarboxylic acids, previously reported as anti-inflammatory agents, has been evaluated. The effects on nociception were examined in male Wistar rats by the Randall-Selitto paw-pressure test. The compounds were administrated in doses 10, 20, and 40 mg/kg both i.p. and p.o. As a whole, the activities of 3-(N-pyrrolyl)propanoic acids 3e-3h and 2-[3-(ethoxycarbonyl)-2-methyl-5-phenyl-1H-1-pyrrolyl]-3-methylpentanoic acid 3i were comparable with or superior to that of metamizole used as a reference (200 mg/kg, i.p.), whereas only 3a from among the N-pyrrolyl-acetic acids 3a-3d showed analgesic activity on the inflamed paw. The compounds found most promising to increase the pain threshold significantly were the same ones with the higher anti-inflammatory activity registered in our previous study: 3-[3-(ethoxycarbonyl)-2-methyl-5-(3-nitrophenyl)-1H-1-pyrrolyl]propanoic acid 3e, together with its 5-(4-nitrophenyl)- 3f, 5-phenyl- 3g, and 5-(4-methylphenyl)- 3h analogs. Certain parallels between the analgesic activities and some physicochemical properties were observed.

Ligand-based design, synthesis and primary in vivo screening of pyrrole derivatives as potential tricyclic anti-inflammatory agents.

Twelve new compounds were designed as 5-aryl-1H-pyrrole analogs of celecoxib (CAS 169590-42-5) and were synthesized by Paal-Knorr cyclization in three series according to 1H-substitution: derivatives with salicylic acid, pyrazolone or isonicotinamide residues. The average physico-chemical and steric similarity between the prototype and the new analogs (completed with two previously synthesized related products) was assessed to be 82 % and therefore considered as a reliable prerequisite for spatial compatibility and effective binding to the cyclooxygenase (COX) enzymes. The anti-inflammatory effects were determined in acute inflammation model using the carrageenan-induced rat paw edema assay on male Wistar rats (180-200 g) at doses of 10, 20 and 40 mg/kg, i.p. Six of the new products showed higher percent of inhibition (up to 100 %) compared to the highly selective COX-2 inhibitor celecoxib and the nonselective indometacin (CAS 53-86-1) used as reference compounds. Ethyl 1-(1,5-di-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-4-pyrazolyl)-2-methyl-5-phenyl-1H-3-pyrrolecarboxylate (2b), ethyl 5-(4-chlor-ophenyl)-2-methyl-1-[(4-pyridylcarbonyl) amino]-1H-3-pyrrolecarboxylate (3c) and 5-[3-acetyl-2-methyl-5-(4-methylphenyl)-1H-1-pyrrolyl] -2-hydroxybenzoic acid (4b) were pointed out as the most active representatives of each of the three tested sub-series.