The importance of brain PGE2 inhibition versus paw PGE2 inhibition as a mechanism for the separation of analgesic and antipyretic effects of lornoxicam in rats with paw inflammation

Analyzing the Antinociceptive Effect of Interleukin-31 in Mice

The theory that an itch inhibits pain has been refuted; however, previous research did not investigate this theory for an interleukin-31 (IL-31)-induced itch. Previously, we have found that morphine-induced antinociception was partially reduced in IL-31 receptor A (IL-31RA)-deficient (IL-31RAKI) mice, indicating that IL-31RA may play an important role in morphine-induced peripheral antinociception. In the present study, we evaluated the effect of IL-31-induced analgesia on a 2,4,6-trinitrochlorobenzene (TNCB)-sensitized mice using a hot-plate test. This test evaluated the antinociceptive activity of morphine and non-steroidal anti-inflammatory drugs (NSAIDs). Repeated pretreatment with IL-31 showed significant antinociceptive action. Furthermore, its combination with morphine, but not with NSAIDs, increased the analgesic action. In contrast, treatment with TNCB and capsaicin decreased antinociception. Moreover, TNCB increased IL-31RA expression in the dorsal root ganglia at 24 h, whereas capsaicin inhibited it. The comparative action of several analgesics on TNCB or capsaicin was evaluated using a hot-plate test, which revealed that the antinociceptive activity was decreased or disappeared in response to capsaicin-induced pain in IL-31RAKI mice. These results indicate that the analgesic action of IL-31 involves the peripheral nervous system, which affects sensory nerves. These results provide a basis for developing novel analgesics using this mechanism.

Intra-articular Injection of Lornoxicam and MicroRNA-140 Co-loaded Cationic Liposomes Enhanced the Therapeutic Treatment of Experimental Osteoarthritis

Osteoarthritis is a chronic joint disease characterized by chronic inflammation, progressive destruction of articular cartilage, and subchondral bone sclerosis. When compared to individual treatment, the combined administration of genes and small-molecule drugs for osteoarthritis may not only provide superior inflammation control and pain relief, but may also repair cartilage damage. Here, cationic liposomes (CL) were used to deliver small hydrophobic drugs and microRNA into chondrocytes to treat osteoarthritis. Lornoxicam cationic liposomes (Lnxc-CL) were prepared by film dispersion, and loaded with microRNA-140 (miR-140) by electrostatic interaction to obtain cationic liposomes co-loaded with lornoxicam and miR-140 (Lnxc-CL/miR-140). The prepared Lnxc-CL/miR-140 had a particle size of 286.6 ± 7.3 nm, polydispersity index (PDI) of 0.261 ± 0.029 and zeta potential of 26.5 ± 0.5 mV and protected miR-140 from RNase degradation for 24 h. Lnxc-CL/miR-140 was evaluated for its ability to regulate gene expression in chondrocytes in vitro and to provide in vivo therapeutic effects for knee osteoarthritis in rats. The results of in vitro uptake experiments and polymerase chain reaction (PCR) analysis showed that Lnxc-CL/miR-140 efficiently delivered miR-140 into chondrocytes and up-regulated the expression of miR-140 and COL2A1 mRNA. Pharmacodynamics studies demonstrated that Lnxc-CL/miR-140 effectively treated osteoarthritis by eliminating joint inflammation and repairing damaged cartilage cells, with superior therapeutic effects compared to Lnxc or miR-140 alone. Overall, the findings of this study support the co-delivery of Lnxc and miR-140 with cationic liposomes as a potential new therapeutic strategy for the treatment of osteoarthritis.

Antinociception by fluoro-loxoprofen, a novel non-steroidal anti-inflammatory drug with less ulcerogenic effects, in rat models of inflammatory pain

The use of non-steroidal anti-inflammatory drugs (NSAIDs) for the treatment of inflammatory pain is limited by gastrointestinal complications. The rapid action of NSAIDs is associated with better pain relief. Previously, we demonstrated that fluoro-loxoprofen, a novel NSAID, has less ulcerogenic potential than other NSAIDs, attributable to its gastroprotective properties. The aim of this study was to investigate and compare the effects of fluoro-loxoprofen on inflammatory pain in rats with those of other NSAIDs. Oral administration of fluoro-loxoprofen, loxoprofen, and celecoxib resulted in equivalent analgesic action against yeast-induced inflammatory pain. The antinociceptive effect of fluoro-loxoprofen was maximized within 1 h after administration, which is less time than that observed for loxoprofen (2 h) and celecoxib (3 h). We confirmed that both fluoro-loxoprofen and loxoprofen suppressed the increases in prostaglandin E₂ in inflamed paws. In addition to yeast-induced pain, fluoro-loxoprofen produced a similar effect against adjuvant-induced inflammatory pain, with faster peak analgesic effects than those observed for loxoprofen and celecoxib. Taken together, these results suggest that the analgesic effect of fluoro-loxoprofen is equivalent to that of loxoprofen and celecoxib. Moreover, the analgesic effect of fluoro-loxoprofen against inflammatory pain was more rapid than that of other NSAIDs, and this may be associated with its rapid absorption property.

Alleviating CYP and hERG liabilities by structure optimization of dihydrofuran-fused tricyclic benzo[d]imidazole series - Potent, selective and orally efficacious microsomal prostaglandin E synthase-1 (mPGES-1) inhibitors: Part-2

In an effort to identify CYP and hERG clean mPGES-1 inhibitors from the dihydrofuran-fused tricyclic benzo[d]imidazole series lead 7, an extensive structure-activity relationship (SAR) studies were performed. Optimization of A, D and E-rings in 7 afforded many potent compounds with human whole blood potency in the range of 160-950 nM. Selected inhibitors 21d, 21j, 21m, 21n, 21p and 22b provided selectivity against COX-enzymes and mPGES-1 isoforms (mPGES-2 and cPGES) along with sufficient selectivity against prostanoid synthases. Most of the tested analogs demonstrated required metabolic stability in liver microsomes, low hERG and CYP liability. Oral pharmacokinetics and bioavailability of lead compounds 21j, 21m and 21p are discussed in multiple species like rat, guinea pig, dog, and cynomolgus monkey. Besides, these compounds revealed low to moderate activity against human pregnane X receptor (hPXR). The selected lead 21j further demonstrated in vivo efficacy in acute hyperalgesia (ED₅₀: 39.6 mg/kg) and MIA-induced osteoarthritic pain models (ED₅₀: 106 mg/kg).

Discovery of furan and dihydrofuran-fused tricyclic benzo[d]imidazole derivatives as potent and orally efficacious microsomal prostaglandin E synthase-1 (mPGES-1) inhibitors: Part-1

This letter describes the synthesis and biological evaluation of furan and dihydrofuran-fused tricyclic benzo[d]imidazole derivatives as novel mPGES-1 inhibitors, capable of inhibiting an increased PGE₂ production in the disease state. Structure-activity optimization afforded many potent mPGES-1 inhibitors having <50 nM potencies in the A549 cellular assay and adequate metabolic stability in liver microsomes. Lead compounds 8l and 8m demonstrated reasonable in vitro pharmacology and pharmacokinetic properties over other compounds. In particular, 8m revealed satisfactory oral pharmacokinetics and bioavailability in multiple species like rat, guinea pig, dog and cynomolgus monkey. In addition, the representative compound 8m showed in vivo efficacy by inhibiting LPS-induced thermal hyperalgesia with an ED₅₀ of 14.3 mg/kg in guinea pig.

Sensory and signaling mechanisms of bradykinin, eicosanoids, platelet-activating factor, and nitric oxide in peripheral nociceptors

Peripheral mediators can contribute to the development and maintenance of inflammatory and neuropathic pain and its concomitants (hyperalgesia and allodynia) via two mechanisms. Activation or excitation by these substances of nociceptive nerve endings or fibers implicates generation of action potentials which then travel to the central nervous system and may induce pain sensation. Sensitization of nociceptors refers to their increased responsiveness to either thermal, mechanical, or chemical stimuli that may be translated to corresponding hyperalgesias. This review aims to give an account of the excitatory and sensitizing actions of inflammatory mediators including bradykinin, prostaglandins, thromboxanes, leukotrienes, platelet-activating factor, and nitric oxide on nociceptive primary afferent neurons. Manifestations, receptor molecules, and intracellular signaling mechanisms of the effects of these mediators are discussed in detail. With regard to signaling, most data reported have been obtained from transfected nonneuronal cells and somata of cultured sensory neurons as these structures are more accessible to direct study of sensory and signal transduction. The peripheral processes of sensory neurons, where painful stimuli actually affect the nociceptors in vivo, show marked differences with respect to biophysics, ultrastructure, and equipment with receptors and ion channels compared with cellular models. Therefore, an effort was made to highlight signaling mechanisms for which supporting data from molecular, cellular, and behavioral models are consistent with findings that reflect properties of peripheral nociceptive nerve endings. Identified molecular elements of these signaling pathways may serve as validated targets for development of novel types of analgesic drugs.

Effect of celecoxib and L-NAME on global ischemia-reperfusion injury in the rat hippocampus

Transient global ischemia continues to be an important clinical problem with limited treatment options. The present study aimed to investigate the possible protective effects of celecoxib [a selective cyclooxygenase (COX-2) inhibitor] and N-omega-nitro-L-arginine methyl ester (L-NAME) [a nonselective nitric oxide synthase (NOS) inhibitor] against global ischemia-reperfusion (IR) induced biochemical and histological alterations in the rat hippocampus. Global ischemia was induced by bilateral clamping of the common carotid arteries for 60 minutes. Hippocampal cysteinyl aspartate-specific protease-3 (caspase-3) activity, nitrite/nitrate contents (NOX), as well as COX-2 immunoreactivity in the hippocampal Cornu Ammonis 1 (CA1) subregion were dramatically increased 24 hours after global ischemia. After 72-hour of reperfusion, ischemia induced a selective, extensive neuronal loss in the hippocampus CA1 subregion. Celecoxib (3 and 5 mg/kg, intraperitoneally; i.p.), administered 30 minutes before ischemia and at 6, 12, and 22 hours of 24-hour reperfusion, caused significant reductions in hippocampal caspase-3 activity as well as the number of COX-2 immunoreactive (COX-2 ir) neurons in the CA1 subregion. Further, celecoxib (3 or 5 mg/kg, i.p.), administered 30 minutes before ischemia and at 6, 12, 22, and 48 hours of 72-hour reperfusion, provided a notable histological protection of hippocampal CA1 neurons. Meanwhile, L-NAME (3 mg/kg, i.p.), administered twice (immediately after ischemia and 45 minutes after starting the reperfusion period), effectively reduced the elevated NOX level, decreased hippocampal caspase-3 activity and COX-2 immumoreactivity, and ameliorated ischemia-induced damage in the hippocampal CA1 subregion. The present study indicates that celecoxib and L-NAME might be neuroprotective agents of potential benefit in the treatment of cerebral ischemia.

The antipyretic effect of dipyrone is unrelated to inhibition of PGE(2) synthesis in the hypothalamus

BACKGROUND AND PURPOSE

Bacterial lipopolysaccharide (LPS) induces fever through two parallel pathways; one, prostaglandin (PG)-dependent and the other, PG-independent and involving endothelin-1 (ET-1). For a better understanding of the mechanisms by which dipyrone exerts antipyresis, we have investigated its effects on fever and changes in PGE(2) content in plasma, CSF and hypothalamus induced by either LPS or ET-1.

EXPERIMENTAL APPROACH

Rats were given (i.p.) dipyrone (120 mg·kg(-1)) or indomethacin (2 mg·kg(-1)) 30 min before injection of LPS (5 µg·kg(-1), i.v.) or ET-1 (1 pmol, i.c.v.). Rectal temperature was measured by tele-thermometry. PGE(2) levels were determined in the plasma, CSF and hypothalamus by elisa.

KEY RESULTS

LPS or ET-1 induced fever and increased CSF and hypothalamic PGE(2) levels. Two hours after LPS, indomethacin reduced CSF and hypothalamic PGE(2) but did not inhibit fever, while at 3 h it reduced all three parameters. Three hours after ET-1, indomethacin inhibited the increase in CSF and hypothalamic PGE(2) levels but did not affect fever. Dipyrone abolished both the fever and the increased CSF PGE(2) levels induced by LPS or ET-1 but did not affect the increased hypothalamic PGE(2) levels. Dipyrone also reduced the increase in the venous plasma PGE(2) concentration induced by LPS.

CONCLUSIONS AND IMPLICATIONS

These findings confirm that PGE(2) does not play a relevant role in ET-1-induced fever. They also demonstrate for the first time that the antipyretic effect of dipyrone was not mechanistically linked to the inhibition of hypothalamic PGE(2) synthesis.