Inducible receptors

Natural antiinflammatory agents for pain relief in athletes

Most athletes experience musculoskeletal injuries during their sports activity that require rest at a minimum, and occasionally injuries are severe enough to necessitate surgical repair. Neurosurgeons are often consulted for athletically sustained injuries and prescribe medications for the associated pain. The use of both over-the-counter and prescription nonsteroidal medications is frequently recommended, but recent safety concerns must now be considered. The authors discuss the biochemical pathways of nonsteroidal drugs and review the potentially serious side effects of these medications. They also review the use of natural supplements, which may be a safer, and often as effective, alternative treatment for pain relief.

Kinin B1 receptors: key G-protein-coupled receptors and their role in inflammatory and painful processes

Kinins are a family of peptides implicated in several pathophysiological events. Most of their effects are likely mediated by the activation of two G-protein-coupled receptors: B(1) and B(2). Whereas B(2) receptors are constitutive entities, B(1) receptors behave as key inducible molecules that may be upregulated under some special circumstances. In this context, several recent reports have investigated the importance of B(1) receptor activation in certain disease models. Furthermore, research on B(1) receptors in the last years has been mainly focused in determining the mechanisms and pathways involved in the process of induction. This was essentially favoured by the advances obtained in molecular biology studies, as well as in the design of selective and stable peptide and nonpeptide kinin B(1) receptor antagonists. Likewise, development of kinin B(1) receptor knockout mice greatly helped to extend the evidence about the relevance of B(1) receptors during pathological states. In the present review, we attempted to remark the main advances achieved in the last 5 years about the participation of kinin B(1) receptors in painful and inflammatory disorders. We have also aimed to point out some groups of chronic diseases, such as diabetes, arthritis, cancer or neuropathic pain, in which the strategic development of nonpeptidic oral-available and selective B(1) receptor antagonists could have a potential relevant therapeutic interest.

Kinin B1 receptor up-regulation after lipopolysaccharide administration: role of proinflammatory cytokines and neutrophil influx

Several studies have now clearly established the ability of LPS to induce bradykinin B(1) receptor up-regulation in vivo and the functional relevance of this up-regulation for the pathophysiological effects of LPS. Using an in vivo system in which LPS is injected locally into the rat paw, we have examined the potential contribution of proinflammatory cytokines, NF-kappaB activation, and neutrophil influx for the functional and molecular up-regulation of the bradykinin B(1) receptor. Treatment with LPS resulted in a rapid and sustained functional up-regulation of B(1) receptors in the rat paw that correlated with the increase in B(1) receptor mRNA levels. B(1) receptor up-regulation is preceded by the rapid activation of the transcription factor NF-kappaB and the production of proinflammatory cytokines, including TNF-alpha and IL-1beta. More importantly, blockade of NF-kappaB translocation, TNF-alpha, or IL-1beta prevented the functional and molecular up-regulation of B(1) receptors. Injection of LPS also induced the influx of neutrophils that followed the peak of cytokine production and associated with the persistent activation of NF-kappaB and functional B(1) receptor up-regulation. Blockade of neutrophil influx with platelet-activating factor receptor antagonists or cell adhesion molecule blockers prevented B(1) receptor up-regulation. Thus, by acting in cooperation and in a coordinated, timely manner, TNF-alpha, IL-1beta, neutrophils, and the transcription factor NF-kappaB are major and essential players in the ability of LPS to induce B(1) receptor expression in vivo.

Mediator caused induction of a human bradykinin B1 receptor minigene: participation of c-Jun in the process

The bradykinin B1 receptor (BKB1R) gene is expressed in selected tissues such as lung and kidney. In these tissues it is expressed at a very low level until induced by inflammatory mediators. Our aim has been to understand the mechanism of this regulatory process. A human BKB1R minigene was constructed. It contained a 1.8 kb promoter, the entire exon I, 1.5 kb of intron I, the entire exon II and intron II, and the luciferase gene as a reporter. Transient transfection of the minigene into SV40-transformed IMR90 cells (IMRSV) resulted in a promoter activity which was activated by the mediators, lipopolysaccharide and (LPS) desArg(10)-kallidin. In contrast, these mediators did not induce the activity of the 1.8 kb promoter construct alone. Thus, motifs exclusive of the promoter such as 5'-UTR and/or intron regions are required for mediator-induced expression of this gene. Promoter activities of both the minigene and the 1.8 kb promoter construct were enhanced in a dose-dependent manner upon cotransfection with c-Jun. Furthermore, cotransfecting c-Jun with the minigene achieved the maximal promoter activity with no further increase in response to mediators. Conversely, the induction of the minigene promoter activity by mediators was abolished upon cotransfection with a dominant negative mutant of c-Jun. Other experiments suggest that multiple AP-1 sites are interactive with the c-Jun upregulation of this gene. Taken together, these results point to c-Jun as a key intermediary in the activation of the expression of this gene by mediators. However, participation of motifs outside of the promoter are necessary to obtain this inducible expression.

Postnatal development of opioid receptors modulating acetylcholine release in hippocampus and septum of the rat

The postnatal development of presynaptic opioid receptors inhibiting the release of acetylcholine (ACh) was studied in rat brain hippocampus, medial septum (MS) and diagonal band of Broca (DB). To this end, the corresponding brain slices (350 microm thick) of rats of various postnatal ages (postnatal day 4 [P4] to P16, and adult) were preincubated with [(3)H]choline and stimulated twice for 2 min (S(1), S(2): at 3 Hz, 2 ms, 60 mA) during superfusion with physiological buffer containing hemicholinium-3. In parallel, the activity of choline acetyltransferase (ChAT) was determined in crude homogenates of the tissues as a marker for the development of cholinergic neurons. At any postnatal age, the electrically evoked overflow of tritium from slices preincubated with [(3)H]choline was highest in the DB, followed by the MS and the hippocampus. The evoked [(3)H]overflow increased with postnatal age, reached about 50% (MS, DB) or 30% (hippocampus) of the corresponding adult levels at P16 and correlated significantly with the corresponding ChAT activities. Presence of the preferential mu-opioid receptor agonist DAMGO during S(2) significantly inhibited the evoked overflow of tritium already at P4 in DB and MS, whereas in the hippocampus significant inhibitory effects were first observed at P8 only. Moreover, adult levels of inhibition due to DAMGO were reached at P16 in the DB and MS but not in the hippocampus. In septal areas, also the effect of the preferential delta-opioid receptor agonist DPDPE on the evoked [(3)H]overflow was studied: in contrast to DAMGO, however, significant inhibitory effects of DPDPE were first observed at P12 only. In conclusion, the postnatal development of presynaptic mu-opioid receptors on cholinergic neurons in the DB and MS starts earlier than in the hippocampus and precedes that of presynaptic delta-opioid receptors.

Induction of prostaglandin I(2) receptor by tumor necrosis factor alpha in osteoblastic MC3T3-E1 cells

Mouse osteoblastic cells MC3T3-E1 produced prostaglandin E(2) via the reaction of cyclooxygenase-2 enzyme induced by tumor necrosis factor alpha (TNFalpha). Originally, the mRNA level for prostaglandin I(2) receptor (IP) was low in the cells. However, the addition of TNFalpha brought about a marked increase in the IP mRNA with a lag of about 3 h up to an about 8-fold higher level for 24 h. In addition, the induction of IP was supported by a binding experiment of [(3)H]iloprost (a stable analogue of prostaglandin I(2)). The amount of iloprost bound to the TNFalpha-stimulated cell membranes increased to a saturation level around 30 nM. Dexamethasone, cycloheximide and cyclooxygenase inhibitor suppressed the IP mRNA induction. The finding with the latter two compounds suggested a TNFalpha-dependent de novo synthesis of a protein, which is involved in the IP mRNA induction and may be attributed partially to the induced cyclooxygenase-2.

In vivo B1 kinin-receptor upregulation. Evidence for involvement of protein kinases and nuclear factor kappaB pathways

1. Intradermal (i.d.) injection of cytokines, IL-1beta and TNFalpha (5 ng, 60 and 30 min prior) produces a rapid onset up-regulation of des-Arg9-BK-mediated rat paw oedema. Here we analyse the mechanisms involved in des-Arg9-BK-induced oedema in animals pre-treated with IL-1beta or TNFalpha. 2. Co-injection of anti-IL-1beta, anti-TNFalpha and anti-IL-8 (50 ng) significantly inhibited des-Arg9-BK-induced oedema in animals pre-treated with IL-1beta (65, 37 and 42%) or TNFalpha (39, 64, 25%). IL-1 receptor antagonist (IRA, 100 microg) or IL-10 (10 ng) inhibited the oedema caused by des-Arg9-BK, in rats that had received either IL-1beta (67 and 63%) or TNFalpha (46 and 35%). 3. Co-injection of the PKC inhibitors, staurosporine (10 nmol) or RO 318220 (30 nmol) inhibited des-Arg9-BK-induced paw oedema (44 and 42% for IL-1beta and, 53 and 30% for TNFalpha, respectively). Genistein (tyrosine kinase inhibitor, 2.5 mg kg-1, s.c.) or PD 098059 (MAP-kinase inhibitor, 30 nmol) produced marked inhibition of des-Arg9-BK-induced oedema (58 and 39% for IL-1beta and 31 and 35% for TNFalpha respectively). 4. The NF-kappaB inhibitors TLCK (2 mg kg-1, i.p.) and PDCT (100 mg kg-1, i.p.) significantly inhibited the oedema of des-Arg9-BK in IL-1beta (27 and 83%) or TNFalpha (28 and 80%) pre-treated animals. 5. It is concluded that up-regulation of B1 receptors modulated by IL-1beta or TNFalpha involves the release of other cytokines, activation of PKC and tyrosine kinase pathways, co-ordinated with the activation of MAP-kinase and nuclear factor kappaB, reinforcing the view that B1 receptors may exert a pivotal role in modulating chronic inflammatory processes.

Posttranscriptional destabilization of the bradykinin B1 receptor messenger RNA: cloning and functional characterization of the 3'-untranslated region

We showed previously that the inducible bradykinin B1 receptor (BKB1R) gene expression is regulated, in part, through mRNA stabilization. Here we clone the 3'-untranslated region (3'-UTR) of the BKB1R. This region proves to be very short, containing only 14 bases with an alternative polyadenylation signal (AUUAAA) which overlaps with the stop codon. Reverse transcription confirms the presence of this alternative polyadenylation signal. Northern blot shows a single species of BKB1R mRNA of approximately 1.4 kb in agreement with its calculated length. The BKB1R mRNA induced by TNFalpha, phorbol ester, bradykinin, and desArg10-kallidin contain the same 3'-UTR species. To test the role of this region in the regulation of mRNA stability, we generated a chimeric luciferase construct containing the BKB1R 3'-UTR. The mRNA transcribed from the wild-type luciferase gene displayed a half-life of approximately 6 h. The mRNA transcribed from the chimeric construct displayed a half-life of only 1 h. This decrease was also reflected at the level of enzyme activity. Luciferase activity from cells transfected with the chimeric construct was 10 times less than from cells transfected with wild-type luciferase. The data presented provide compelling evidence that the 3'-UTR is participating in the regulation of BKB1R mRNA stability and its ultimate expression.

5-HT2B-receptor antagonist LY-272015 is antihypertensive in DOCA-salt-hypertensive rats

We previously demonstrated a change in the receptors mediating 5-hydroxytryptamine (5-HT)-induced contraction in arteries of deoxycorticosterone acetate (DOCA)-salt-hypertensive rats. Specifically, contraction to 5-HT is mediated primarily by 5-HT2A receptors in arteries from normotensive sham rats and by both 5-HT2A and 5-HT2B receptors in arteries from hypertensive rats. We hypothesized that the 5-HT2B receptor may play a role in maintaining the high blood pressure of DOCA-salt-hypertensive rats, and herein we provide data connecting in vitro and in vivo findings. The endothelium-denuded isolated superior mesenteric artery of DOCA-salt rats displayed a marked increase in maximum contraction to the newly available 5-HT2B-receptor agonist BW-723C86 compared with that of arteries from sham rats, confirming that the 5-HT2B receptor plays a greater role in 5-HT-induced contraction in arteries from DOCA-salt rats. In chronically instrumented rats, the 5-HT2B-receptor antagonist LY-272015 (0.3, 1.0, and 3.0 mg/kg iv at 30-min intervals) was given cumulatively 1 time/wk during 4 wk of continued DOCA-salt treatment. LY-272015 did not reduce blood pressure of the sham-treated rats at any time or dose. However, LY-272015 (1.0 and 3. 0 mg/kg) significantly reduced mean blood pressure in a subgroup of week 3 (-20 mmHg) and week 4 DOCA-salt (-40 mmHg) rats that had extremely high blood pressure (mean arterial blood pressure approximately 200 mmHg). Blockade of 5-HT2B receptors by in vivo administration of LY-272015 (3.0 mg/kg) was verified by observing reduced 5-HT-induced contraction in rat stomach fundus, the tissue from which the 5-HT2B receptor was originally cloned. These data support the novel hypothesis that 5-HT2B-receptor expression is induced during the development of DOCA-salt hypertension and contributes to the maintenance of severe blood pressure elevations.

Heat stress-induced B1 receptor synthesis in the rat: an ex vivo study

1. This ex vivo study was performed to characterize B1 receptor induction in rats submitted to heat stress. Changes in aortic isometric tension were recorded after a 90 min in vitro incubation with [des-Arg9]-bradykinin. B1 receptor mRNA were detected in aorta and heart using RT-PCR technique. 2. Aortic rings from sham rats did not respond to [des-Arg9]-bradykinin. In contrast, this agonist induced a concentration-dependent relaxation of aortic rings from rats submitted to lipopolysaccharide (LPS) treatment or to heat stress 24 h earlier. 3. The concentration-dependent relaxation induced by [des-Arg9]-bradykinin on aortic rings from heat-stressed rats was abolished by [des-Arg10]-HOE 140, a selective B1 receptor antagonist. 4. In endothelium denuded aortic rings from heat-stress rats, [des-Arg9]-bradykinin induced a concentration-dependent constriction. 5. Pretreatment of intact aortic rings from heat-stress rats with the cyclo-oxygenase inhibitor, diclofenac (1 microM) did not prevent the concentration-dependent relaxation in response to [des-Arg9]-bradykinin. In contrast. NO synthase inhibition with N(omega)-nitro-L-arginine methyl ester (30 microM) totally prevented the vasorelaxant response. 6. B1 receptor mRNA were not detected in aorta and heart from sham animals but were present in tissue from heat-stressed and LPS-treated rats. 7. In conclusion, our results suggest that heat stress induces a transcriptional activation of the B1 receptor gene. The induction of B1 receptors leads to an endothelium- and NO-dependent vasorelaxant response to [des-Arg9]-bradykinin.

Mechanisms in the transcriptional regulation of bradykinin B1 receptor gene expression. Identification of a minimum cell-type specific enhancer

To investigate the mechanisms of bradykinin B1 (BKB1) receptor gene expression, transient DNA transfection analyses of human BKB1 receptor gene promoter were performed in SV-40 transformed IMR90 cells. A positive regulatory element (PRE) located at position -604 to -448 base pair (bp) upstream of the transcription start site consistently exhibited, by far, the highest level of relative luciferase activity. A negative regulatory element, at position -682 to -604 bp, was able to completely ablate the function of the PRE. Transfection combined with deletion and mutation analyses illustrated that the PRE contains a classic, powerful enhancer. This enhancer was minimized to a 100-bp element at position -548 to -448 bp. A 78-bp fragment of negative regulatory element functioned as a silencer. Transient transfection of the enhancer construct, driven by heterologous herpes simplex thymidine kinase promoter, into a variety of cell types, showed that this enhancer presents a cell-type specific feature. In the characterization of the enhancer, motifs A (-548 to -532) and B (-483 to -477) were found to be essential for full enhancer activity. Motif D (-472 to -467) played a smaller role in enhancer activation. Gel shift and antibody supershift assays determined that an AP-1 factor binds with motif B. The nuclear protein which binds to motif A has yet to be identified. Both factors are the critical regulators for this enhancer activation.