Paul R. Colville-Nash

Possible new role for NF-κB in the resolution of inflammation

Inflammation involves the sequential activation of signaling pathways leading to the production of both pro- and anti-inflammatory mediators. Although much attention has focused on pro-inflammatory pathways that initiate inflammation, relatively little is known about the mechanisms that switch off inflammation and resolve the inflammatory response. The transcription factor NF-κB is thought to have a central role in the induction of pro-inflammatory gene expression and has attracted interest as a new target for the treatment of inflammatory disease. We show here that NF-κB activation in leukocytes recruited during the onset of inflammation is associated with pro-inflammatory gene expression, whereas such activation during the resolution of inflammation is associated with the expression of anti-inflammatory genes and the induction of apoptosis. Inhibition of NF-κB during the resolution of inflammation protracts the inflammatory response and prevents apoptosis. This suggests that NF-κB has an anti-inflammatory role in vivo involving the regulation of inflammatory resolution.

Hematopoietic prostaglandin D2 synthase controls the onset and resolution of acute inflammation through PGD2 and 15-deoxyΔ12–14 PGJ2

Hematopoietic prostaglandin D2 synthase (hPGD2S) metabolizes cyclooxygenase (COX)-derived PGH2 to PGD2 and 15-deoxyΔ12–14 PGJ2 (15d-PGJ2). Unlike COX, the role of hPGD2S in host defense is ambiguous. PGD2 can be either pro- or antiinflammatory depending on disease etiology, whereas the existence of 15d-PGJ2 and its relevance to pathophysiology remain controversial. Herein, studies on hPGD2S KO mice reveal that 15d-PGJ2 is synthesized in a self-resolving peritonitis, detected by using liquid chromatography–tandem MS. Together with PGD2 working on its DP1 receptor, 15d-PGJ2 controls the balance of pro- vs. antiinflammatory cytokines that regulate leukocyte influx and monocyte-derived macrophage efflux from the inflamed peritoneal cavity to draining lymph nodes leading to resolution. Specifically, inflammation in hPGD2S KOs is more severe during the onset phase arising from a substantial cytokine imbalance resulting in enhanced polymorphonuclear leukocyte and monocyte trafficking. Moreover, resolution is impaired, characterized by macrophage and surprisingly lymphocyte accumulation. Data from this work place hPGD2S at the center of controlling the onset and the resolution of acute inflammation where it acts as a crucial checkpoint controller of cytokine/chemokine synthesis as well as leukocyte influx and efflux. Here, we provide definitive proof that 15d-PGJ2 is synthesized during mammalian inflammatory responses, and we highlight DP1 receptor activation as a potential antiinflammatory strategy.

Effects of Low-Dose Aspirin on Acute Inflammatory Responses in Humans

Aspirin is a unique nonsteroidal anti-inflammatory drug; at high doses (aspirinhigh, 1g), it is anti-inflammatory stemming from the inhibition of cyclooxygenase and proinflammatory signaling pathways including NF-κB, but is cardioprotective at lower doses (aspirinlow, 75 mg). The latter arises from the inhibition of thromboxane (Tx) B2, a prothrombotic eicosanoid also implicated in polymorphonuclear leukocyte trafficking. As a result, aspirinlow is widely used as a primary and secondary preventative against vascular disease. Despite this and its ability to synthesize proresolution 15-epi-lipoxin A4 it is not known whether aspirinlow is anti-inflammatory in humans. To address this, we generated skin blisters by topically applying cantharidin on the forearm of healthy male volunteers, causing an acute inflammatory response including dermal edema formation and leukocyte trafficking. Although not affecting blister fluid volume, aspirinlow (75 mg, oral, once daily/10 days) reduced polymorphonuclear leukocyte and macrophage accumulation independent of NF-κB-regulated gene expression and inhibition of conventional prostanoids. However, aspirinlow triggered 15-epi-lipoxin A4 synthesis and up-regulated its receptor (FPRL1, ALX). From complimentary in vitro experiments, we propose that 15-epi-lipoxin A4 exerts its protective effects by triggering antiadhesive NO, thereby dampening leukocyte/endothelial cell interaction and subsequent extravascular leukocyte migration. Since similar findings were obtained from murine zymosan-induced peritonitis, we suggest that aspirinlow possesses the ability to inhibit mammalian innate immune-mediated responses. This highlights 15-epi-lipoxin A4 as a novel anti-inflammatory working through a defined receptor and suggests that mimicking its mode of action represents a new approach to treating inflammation-driven diseases.

Inducible cyclooxygenase-derived 15-deoxy(Delta)12-14PGJ2 brings about acute inflammatory resolution in rat pleurisy by inducing neutrophil and macrophage apoptosis.

Failure of acute inflammation to resolve leads to persistence of the inflammatory response and may contribute to the development of chronic inflammation. Thus, an understanding of inflammatory resolution will provide insight into the etiology of chronic inflammation. In an acute pleurisy, polymorphonuclear leukocytes (PMNs) were found to predominate at the onset of the lesion but decreased in number by undergoing apoptosis, the principal mechanism by which PMNs died in this model. PMNs were progressively replaced by monocytes, which differentiated into macrophages. As with PMNs, macrophages also underwent programmed cell death leading to an abatement of the inflammatory response and eventual resolution. It was found that apoptosis of both these inflammatory cell types was mediated by pro‐resolving cyclooxygenase 2‐derived 15deoxy Δ 12‐14PGJ2, which is uniquely expressed during active resolution. Although PMN programmed cell death is well understood, the observation that macrophages apoptose during resolution of acute inflammation is less well described. These results provide insight into the mechanisms that switch off acute inflammation and prevent complications of wound healing and potentially the development of immune‐mediated chronic inflammation.

New insights into the role of COX 2 in inflammation.

Cyclo-oxygenase (COX) is responsible for the synthesis of bioactive prostanoids, the inhibition of which serves as the basis for the mode of action of clinically used nonsteroidal anti-inflammatory drugs. While there were suggestions as early as the 1970s that an inducible isoform of COX exists, it was only in the early 1990s that COX 2 was identified, cloned and sequenced. Not surprisingly, this new isoform was expressed at sites of inflammation and reported to contribute to the inflammatory response. Recently, however, evidence is emerging to suggest that COX 2 also has anti-inflammatory properties. In this review, the two faces of COX 2 are examined, with emphasis on its role in regulating inflammatory resolution, including possible mechanisms of action

Growth factors in angiogenesis: current interest and therapeutic potential

Angiogenesis, the process of new blood vessel development, is an essential component of the bodys physiology and contributes to the pathogenesis of a variety of diseases such as benign and malignant neoplasia and rheumatoid arthritis. Failure of this physiological response is also important in abnormalities of wound healing in diseases such as duodenal ulceration and diabetes. Angiogenesis is controlled by a variety of factors that initiate, control and terminate this complex, multi-stage process. This review covers those factors that are exciting much interest currently and have potential for incorporation into clinical medicine.

THE ROLE OF VASCULAR ENDOTHELIAL GROWTH FACTOR IN A MURINE CHRONIC GRANULOMATOUS TISSUE AIR POUCH MODEL OF ANGIOGENESIS

Chronic granulomatous inflammation may be considered an angiogenic‐dependent process. Recently it has been demonstrated that vascular endothelial growth factor (VEGF) or vascular permeability factor is essential for tumour angiogenesis. Its role in inflammation‐mediated angiogenesis has yet to be determined. In this study, the murine chronic granulomatous air pouch model was used to investigate the role of VEGF in angiogenesis. Animals were treated twice weekly with 10 μg per animal of neutralizing antibody to rh VEGF and the vascularity and granuloma dry weight were assessed after 7 days. This resulted in significant suppression of both angiogenesis and granuloma dry weight. Western blot analysis demonstrated the presence of VEGF; the levels of protein paralleled the angiogenic response. These results demonstrate for the first time that VEGF may be an important regulator of angiogenesis in inflammation.

Cyclopentenone prostaglandins-new allies in the war on inflammation.

Although the effects of anti-inflammatory drugs have been well studied, little is known about the signaling pathways involved in the inflammatory response. The recent finding that cyclopentenone prostaglandins inhibit IκB kinase provides a new explanation for the anti-inflammatory effects of these molecules.

Effects of low dose ionizing radiation on murine chronic granulomatous tissue

PurposeSubstantial clinical evidence shows the efficacy of low-dose radiotherapy in the treatment of a wide variety of benign conditions. However, experimental investigations into these empirically clinical observations remain scarce. We investigated in vivo low-dose radiation effects on chronic granulomatous tissue by using the air pouch model in mice.Material and MethodsChronic granulomatous air pouches were induced in mice and dosed according to 4 protocols: group I: sham control; group II: 2 Gy on day 2; group III: 2 Gy on day 6; group IV: 5 daily doses of 0.5 Gy from day 2 to 6. On day 7 after granuloma induction the granuloma wet and dry weight was estimated, the vascular content was assessed by the formation of vascular casts incorporating carmine, the inducible nitric oxide synthase (iNOS)- and heme oxygenase 1 (HO-1)-expression in tissue homogenates was assessed by Western blot analysis, and the immunohistochemical localization of iNOS was carried out in cryostat sections of the granulomatous tissue.ResultsWe did not observe any significant reduction in granulomatous tissue wet weight or dry weight following the different radiation treatments, which indicates that anti-proliferative effects in response to the low radiation doses used, are probably not involved in the effects of anti-inflammatory radiotherapy. A single dose of 2 Gy on day 2, as well as fractionated treatment with 5×0.5 Gy lead to an increase in vascularity. iNOS-expression in the homogenized granulomatous tissue was decreased, being most pronounced after single-dose irradiation with 2 Gy on day 2, early on in the acute phase of inflammation. In contrast, the HO-1-expression was increased in all irradiated groups.ConclusionLow doses of radiation interfere with the NO- and the HO-1 pathway. Since NO contributes to several aspects of inflammation such as oedema formation and inflammatory pain, we put forward the hypothesis, that the inhibitory effect of low doses of ionizing radiation on the NO pathway is one radiobiological mechanism underlying the clinically observed efficacy of anti-inflammatory radiotherapy and might result in the reduction of swelling as well as relief of pain. Furthermore, the suppression of iNOS activity could be due to the increase in the stress protein HO-1 by low dose radiotherapy.ZusammenfassungZielEs gibt zahlreiche klinische Beweise dafür, daß die niedrig dosierte Strahlentherapie in der Behandlung verschiedener gutartiger Erkrankungen erfolgreich ist. Experimentelle Untersuchungen dieser klinisch-empirischen Beobachtungen liegen jedoch nahezu nicht vor. Wir untersuchten in vivo die Effekte der niedrig dosierten Bestrahlung auf chronisch granulomatöses Gewebe unter Verwendung des Air-Pouch-Modells in der Maus.Material und MethodenChronisch granulomatöses Gewebe wurde induziert und bestrahlt: Gruppe I: scheinbestrahlte Kontrolle; Gruppe II: 2 Gy am Tag 2; Gruppe III: 2 Gy am Tag 6; Gruppe IV: 5×0,5 Gy an den Tagen 2 bis 6. Am Tag 7 nach Induktion des Granuloms wurden das Feucht- und Trockengewicht des Granuloms bestimmt, dessen Vaskularität wurde mit Hilfe des Carmin-Assays beurteilt, die Expression der induzierbaren Stickoxydsynthase (iNOS) und der Häm-Oxygenase 1 (HO-1) wurden in homogenisiertem granulomatösem Gewebe (Western-Blot-Analyse) sowie die iNOS-Immunlokalisation in Cryostat-Schnitten untersucht.ErgebnisseWir beobachteten unter den verschiedenen Behandlungsregimen keine signifikante Verminderung des Feucht- sowie des Trockengewichts des Granuloms, was darauf schließen läßt, daß antiproliferative Effekte in Reaktion auf die applizierten niedrigen Strahlendosen für die Effektivität der Entzündungsbestrahlung keine Rolle spielen. Einzeitbestrahlung mit 2 Gy am Tag 2 sowie fraktionierte Bestrahlung mit 5×0,5 Gy führten zu einer Erhöhung der Vaskularität. Die Western-Blot-Analyse der iNOS-Expression demonstrierte in allen bestrahlten Gruppen im Durchschnitt eine verminderte iNOS-Konzentration, die am ausgeprägtesten nach Einzeitbestrahlung mit 2 Gy am Tag 2 war, das heißt in der akuten Entzündungsphase. Die immunhistochemisch bestimmte Anzahl an iNOS-positiv markierten Zellen innerhalb der verschiedenen Bestrahlungsgruppen zeigte im wesentlichen ein vergleichbares Muster. Im Gegensatz dazu demonstrierte die Western-Blot-Analyse der HO-1-Expression erhöhte HO-1-Konzentrationen in allen bestrahlten Gruppen.SchlußfolgerungNiedrig dosierte ionisierende Strahlung interferiert mit dem NO- sowie dem HO-System. Da NO zu verschiedenen Aspekten der Entzündung wie Ödem und Schmerz beiträgt, postulieren wir, daß der inhibitorische Effekt niedriger Strahlendosen auf das NO-System einer der strahlenbiologischen Mechanismen der klinisch beobachteten Effektivität der Entzündungsbestrahlung ist und zu einem Rückgang des Entzündungsödems sowie einer Verminderung des Entzündungsschmerzes führen könnte. Des weiteren könnte die Suppression der iNOS-Aktivität auf eine strahleninduzierte Expression des Streßproteins HO-1 zurückzuführen sein.

Potential Adverse Effects of Cyclooxygenase-2 Inhibition: Evidence from Animal Models of Inflammation

Cyclooxygenase (COX; prostaglandin H synthase, prostaglandin endoper-oxidase) is the key enzyme in the synthesis of the prostaglandin and thromboxane families of eicosanoid mediators, and is the target for the nonsteroidal anti-inflammatory drugs (NSAIDs). The identification of an inducible COX isoform, COX-2, and the demonstration of its specific expression at sites of inflammation suggested that it may provide a useful therapeutic target for novel anti-inflammatory drugs. Inhibition of an enzyme that is not expressed in most healthy tissues would potentially avoid most of the adverse effects associated with NSAIDs, which target a constitutively expressed isoform, COX-1. The development of novel ‘super aspirins’ with high selectivity towards the inhibition of COX-2 showed that this hypothesis was well-founded and that high levels of these drugs could be tolerated without these serious adverse effects. The first two of these new generation NSAIDs, celecoxib and rofecoxib, are now in clinical use.More recently, however, concern has been expressed that COX-2 inhibition may in fact have a number of potential, previously hidden, pitfalls. These have arisen from the demonstration that COX-2 induction is not exclusively associated with the onset of an inflammatory reaction, with expression limited to inflammatory sites. In fact, COX-2 is expressed more chronically, and is also seen during the resolution of inflammation and in areas of wound-healing. The application of COX-2-selective inhibitors during these periods has been shown to be deleterious in that resolution of inflammation is delayed, gastric ulcer healing is delayed and, in some patients, ulcers have been shown to progress further to perforation. The suggestion has now been made that, in these situations, COX-2 may help resolve the pathology, perhaps by generating alternative series of prostaglandins such as the cyclopentenone prostaglandins. The finding that these prostaglandins can affect proteins by direct chemical modifications as well as having their own receptor families has rekindled debate on the deleterious and beneficial effects of prostanoids, and the implications of inhibiting the production of these mediators, in the body.Therefore, in this review we discuss the role of COX-2 in inflammation and the potential adverse effects of its inhibition.