Antiinflammatory peptides (antiflammins) inhibit synthesis of platelet-activating factor, neutrophil aggregation and chemotaxis, and intradermal inflammatory reactions

Antiinflammatory peptides: current knowledge and promising prospects

BACKGROUND

Inflammation is part of the regular host reaction to injury or infection caused by toxic factors, pathogens, damaged cells, irritants, and allergens. Antiinflammatory peptides (AIPs) are present in all living organisms, and many peptides from herbal, mammalian, bacterial, and marine origins have been shown to have antimicrobial and/or antiinflammatory properties.

METHODS

In this study, we investigated the effects of antiinflammatory peptides on inflammation, and highlighted the underlying mechanisms responsible for these effects.

RESULTS

In multicellular organisms, including humans, AIPs constitute an essential part of their immune system. In addition, numerous natural and synthetic AIPs are effective immunomodulators and can interfere with signal transduction pathways involved in inflammatory cytokine expression. Among them, some peptides such as antiflammin, N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), and those derived from velvet antler proteins, bee venom, horse fly salivary gland, and bovine β-casein have received considerable attention over the past few years.

CONCLUSION

This article presents an overview on the major properties and mechanisms of action associated with AIPs as immunomodulatory, chemotactic, antioxidant, and antimicrobial agents. In addition, the results of various studies dealing with effects of AIPs on numerous classical models of inflammation are reviewed and discussed.

The roles of a ribosomal protein S19 polymer in a mouse model of carrageenan-induced acute pleurisy

C5-deficient mice usually present moderate neutrophil activation during the initiation phase of acute inflammation. Conversely, C5a receptor (C5aR)-deficient mice show unusually excessive activation of neutrophils. We identified the ribosomal protein S19 (RP S19) polymer, which is cross-linked at Lys122 and Gln137 by transglutaminases in apoptotic neutrophils, as a second C5aR ligand during the resolution phase of acute inflammation. The RP S19 polymer promotes apoptosis via the neutrophil C5aR and phagocytosis via the macrophage C5aR. To confirm the roles of the RP S19 polymer, we employed a carrageenan-induced acute pleurisy mouse model using C57BL/6J mice with a knock-in of the Gln137Glu mutant RP S19 gene and replaced the RP S19 polymer with either an S-tagged C5a/RP S19 recombinant protein or the RP S19^122-145 peptide monomer and dimer (as functional C5aR agonists/antagonists) and the RP S19^122-145 peptide trimer (as a functional C5aR antagonist). Neutrophils and macrophages were still present in the thoracic cavities of the knock-in mice at 24h and 7days after carrageenan injection, respectively. Knock-in mice showed structural organization and severe hemorrhaging from the surrounding small vessels of the alveolar walls in the lung parenchyma. In contrast to the RP S19^122-145 peptide monomer and trimer, the simultaneous presence of S-tagged C5a/RP S19 and the RP S19^122-145 peptide dimer completely improved the physiological and pathological acute inflammatory cues. The RP S19 polymer, especially the dimer, appears to play a role at the resolution phase of carrageenan-induced acute pleurisy in C57BL/6J model mice.

Methods for Testing Immunological Factors

Hypersensitivity reactions can be elicited by various factors: either immunologically induced, i.e., allergic reactions to natural or synthetic compounds mediated by IgE, or non-immunologically induced, i.e., activation of mediator release from cells through direct contact, without the induction of, or the mediation through immune responses. Mediators responsible for hypersensitivity reactions are released from mast cells. An important preformed mediator of allergic reactions found in these cells is histamine. Specific allergens or the calcium ionophore 48/80 induce release of histamine from mast cells. The histamine concentration can be determined with the o-phthalaldehyde reaction.

Uteroglobin, a possible ligand of the lipoxin receptor inhibits serum amyloid A-driven inflammation

Serum amyloid A (SAA) production is increased by inflamed arthritic synovial tissue, where it acts as a cytokine/chemoattractant for inflammatory and immune cells and as an inducer of matrix degrading enzymes. SAA has been shown to bind lipoxin A4 receptor, a member of the formyl-peptide related 2 G-protein coupled receptor family (ALX) and elicit proinflammatory activities in human primary fibroblast-like synoviocytes (FLS). We report on the identification of uteroglobin, a small globular protein with potent anti-inflammatory activities, as a possible ligand of ALX. Uteroglobin-specific association with ALX was demonstrated by an enzyme immunoassay experiment employing a cell line engineered to express the human ALX receptor. Uteroglobin's interaction with ALX resulted in the inhibition of SAA responses, such as attenuation of phospholipase A2 activation and cellular chemotaxis. In FLS, uteroglobin showed an antagonism against SAA-induced interleukin-8 release and decreased cell migration. These novel roles described for uteroglobin via ALX may help elucidate genetic and clinical observations indicating that a polymorphism in the uteroglobin promoter is linked to disease outcome, specifically prediction of bone erosion in patients with rheumatoid arthritis or severity of IgA glomerulonephritis and sarcoidosis.

Foam cell formation of alveolar macrophages in Clara cell ablated mice inhaling crystalline silica

We investigated the function of Clara cells in vivo during exposure to inhaled crystalline silica by morphological and immunohistochemical examination of intra-alveolar cells and alveolar macrophages in Clara cell-ablated mice. The Clara cells of male FVB/n mice (8-12 weeks old) were ablated by intraperitoneal administration of naphthalene (300 mg/kg). The mice were then exposed to crystalline silica (Min-U-Sil-5, 97.1 ± 9.5 mg/m³, 6 hours/day, 5 days/week) for up to two weeks. The lungs were assessed by morphometry, as well as by immunohistochemistry of CD36, lectin-like oxygenated low-density lipoprotein receptor (LOX)-1, and matrix metalloproteinases (MMPs) -2, -9 and -12. There was a significantly greater number of intra-alveolar cells in Clara cell-ablated mouse groups than in wild-type mouse groups that were exposed to crystalline silica. A marked number of foamy alveolar macrophages were only detected in the Clara cell-ablated group exposed to crystalline silica, indicating that Clara cells inhibit infiltration and foam cell formation of alveolar macrophages. Immunohistochemical analysis indicated that foamy alveolar macrophages in the Clara cell-ablated group that inhaled crystalline silica overexpress CD36 and LOX-1, indicating upregulation of scavenger receptors of alveolar macrophages. These cells also express MMP-2, -9 and -12, suggesting increased gelatinolytic and elastolytic activities. Our findings suggest that Clara cells not only inhibit infiltration of alveolar macrophages but also their phagocytotic and gelatinolytic functions in silica-induced pulmonary injury.

Evidence for an anti-inflammatory loop centered on polymorphonuclear leukocyte formyl peptide receptor 2/lipoxin A4 receptor and operative in the inflamed microvasculature

The importance of proresolving mediators in the overall context of the resolution of acute inflammation is well recognized, although little is known about whether these anti-inflammatory and proresolving molecules act in concert. In this article, we focused on lipoxin A(4) (LXA(4)) and annexin A1 (AnxA1) because these two very different mediators converge on a single receptor, formyl peptide receptor type 2 (FPR2/ALX). Addition of LXA(4) to human polymorphonuclear leukocytes (PMNs) provoked a concentration- and time-dependent mobilization of AnxA1 onto the plasma membrane, as determined by Western blotting and flow cytometry analyses. This property was shared by another FPR2/ALX agonist, antiflammin-2, and partly by fMLF or peptide Ac2-26 (an AnxA1 derivative that can activate all three members of the human FPR family). An FPR2/ALX antagonist blocked AnxA1 mobilization activated by LXA(4) and antiflammin-2. Analysis of PMN degranulation patterns and phospho-AnxA1 status suggested a model in which the two FPR2/ALX agonists mobilize the cytosolic (and not the granular) pool of AnxA1 through an intermediate phosphorylation step. Intravital microscopy investigations of the inflamed mesenteric microvasculature of wild-type and AnxA1(-/-) mice revealed that LXA(4) provoked leukocyte detachment from the postcapillary venule endothelium in the former (>50% within 10 min; p < 0.05), but not the latter genotype (∼15%; NS). Furthermore, recruitment of Gr1(+) cells into dorsal air-pouches, inflamed with IL-1β, was significantly attenuated by LXA(4) in wild-type, but not AnxA1(-/-), mice. Collectively, these data prompt us to propose the existence of an endogenous network in anti-inflammation centered on PMN AnxA1 and activated by selective FPR2/ALX agonists.

Annexin-1 modulates repair of gastric mucosal injury

Annexin-1 is a glucocorticoid-inducible protein that plays an important effector role in the resolution of inflammation and has recently been shown to contribute to the resistance of the stomach to injury. Using an integrated genetic and pharmacological approach, we have tested the hypothesis that annexin-1 contributes to the healing of mucosal injury, given that such injury is accompanied by an inflammatory response, which is often associated with an overexpression of annexin-1 expression. Gastric ulcers were induced in mice through serosal application of acetic acid. Annexin-1 expression during the healing of the ulcers was examined. The effects on gastric ulcer healing of treatment with an annexin-1 mimetic (Ac2-26), an antagonist of the annexin-1 receptor (Boc2), or a glucocorticoid (dexamethasone) were examined. Finally, susceptibility to and healing of indomethacin-induced gastric lesions were compared in wild-type and annexin-1-deficient mice. Expression of annexin-1 was significantly increased in the gastric ulcer margin throughout the healing process. Treatment with an annexin-1 mimetic (Ac2-26) significantly enhanced gastric ulcer healing. In contrast, both dexamethasone and an formyl peptide receptor-like-1 (FPRL-1) antagonist impaired the early phase of ulcer healing. Annexin-1-deficient mice exhibited the same susceptibility as wild-type mice to indomethacin-induced gastric damage, but the healing of that damage was impaired in the former. These data support the hypothesis that annexin-1 contributes significantly to the process of healing of gastric mucosal damage.

Uteroglobin: a steroid-inducible immunomodulatory protein that founded the Secretoglobin superfamily

Blastokinin or uteroglobin (UG) is a steroid-inducible, evolutionarily conserved, secreted protein that has been extensively studied from the standpoint of its structure and molecular biology. However, the physiological function(s) of UG still remains elusive. Isolated from the uterus of rabbits during early pregnancy, UG is the founding member of a growing superfamily of proteins called Secretoglobin (Scgb). Numerous studies demonstrated that UG is a multifunctional protein with antiinflammatory/ immunomodulatory properties. It inhibits soluble phospholipase A(2) activity and binds and perhaps sequesters hydrophobic ligands such as progesterone, retinols, polychlorinated biphenyls, phospholipids, and prostaglandins. In addition to its antiinflammatory activities, UG manifests antichemotactic, antiallergic, antitumorigenic, and embryonic growth-stimulatory activities. The tissue-specific expression of the UG gene is regulated by several steroid hormones, although a nonsteroid hormone, prolactin, further augments its expression in the uterus. The mucosal epithelia of virtually all organs that communicate with the external environment express UG, and it is present in the blood, urine, and other body fluids. Although the physiological functions of this protein are still under investigation, a single nucleotide polymorphism in the UG gene appears to be associated with several inflammatory/autoimmune diseases. Investigations with UG-knockout mice revealed that the absence of this protein leads to phenotypes that suggest its critical homeostatic role(s) against oxidative damage, inflammation, autoimmunity, and cancer. Recent studies on UG-binding proteins (receptors) provide further insight into the multifunctional nature of this protein. Based on its antiinflammatory and antiallergic properties, UG is a potential drug target.

Antiflammin-2 activates the human formyl-peptide receptor like 1

The anti-inflammatory actions of the nonapeptide antiflammin-2, identified by homology with uteroglobin and annexin-A1 sequences, have been described in some detail, yet its mechanisms of action remain elusive. Since recent data indicate an involvement of the formyl peptide receptor (FPR)-like 1 (or FPRL-1) in the effects of annexin-A1, we have tested here the effect of antiflammin-2 with respect to this receptor family. Using HEK-293 cells expressing either human FPR and FPRL-1, and an annexin-A1 peptide as tracer ([¹²⁵I-Tyr]-Ac2-26), we found that antiflammin-2 competed for binding only at FPRL-1, and not FPR, with an approximate EC₅₀ of 1 μM. In line with data produced for the full-length protein, genuine receptor activation by antiflammin-2 was confirmed by rapid phosphorylation of extracellular-regulated kinase 1 and 2. Finally, study of the neutrophil interaction with activated endothelium under flow demonstrated an inhibitory effect of antiflammin-2, thus providing functional support to a role for the antiflammin-2/FPRL-1 anti-inflammatory axis.

Platelet-Activating Factor Synthesis and Response on Pancreatic Islet Endothelial Cells: Relevance for Islet Transplantation

BACKGROUND

Recent data suggest that donor intraislet endothelial cells may survive islet transplantation and participate to the events that influence islet engraftment. However, the mechanisms that regulate islet endothelial behavior in this setting are poorly known.

METHODS

We obtained immortalized human (hIECs) and mouse (mIECs) islet endothelial cells by transfection with SV40-T-large antigen and studied the synthesis and response to Platelet-activating factor (PAF), a multipotent phospholipid that acts as endothelial mediator of both inflammation and angiogenesis.

RESULTS

HIECs showed typical endothelial markers such as expression of vWF, CD31, and CD105, uptake of acetylated-LDL and binding to ULE-A lectin. Moreover, they expressed nestin, the PAF-receptor and possess surface fenestrations and in vitro angiogenic ability of forming tubular structures on Matrigel. Likewise, mIECs showed expression of vWF, CD31, nestin, PAF-receptor and CD105, and uptake of acetylated-LDL. HIECs and mIECs rapidly produced PAF under stimulation with thrombin in a dose-dependent way. Exogenous PAF or thrombin-induced PAF synthesis increased leukocyte adhesion to hIECS and mIECs and cell motility of both endothelial cell lines. Moreover, PAF or thrombin-induced PAF synthesis accelerated in vitro formation of vessel-like tubular structures when hIECs are seeded on Matrigel. Notably, gene-microarray analysis detected up-regulation of beta3 integrin gene on hIECs stimulated with PAF, that was confirmed at the protein level.

CONCLUSIONS

Based on the novel development of immortalized islet endothelium, these results suggest that PAF may have a dual role that links inflammation to angiogenesis in the early events of islet transplantation.

Novel C5a regulators in inflammatory disease

Complement is part of the innate immune system, acting to protect the host from microorganisms such as bacteria, and other foreign and abnormal cells. Although primarily protective, complement activation can also cause damage to the host. In a number of inflammatory diseases, including rheumatoid arthritis and dermatitis, there is excessive and inappropriate complement activation. Many of the toxic effects seen in these conditions are attributable to the excessive production of the anaphylatoxin C5a, which may contribute to both the initiation and progression of the disease. Therefore, the regulation of C5a production and modulation of its function are good pharmacological targets in these disorders. As yet, there are no effective agents for the therapeutic regulation of C5a in routine clinical practice. This review describes the role of C5a in inflammatory disease, animal models used to study C5a-related effects, and current strategies aimed at regulating C5a. There is also a discussion of the strengths and weaknesses of these approaches, and an outline of the likely progress of this class of drugs in the future.

Clara cell secretory protein modulates lung inflammatory and immune responses to respiratory syncytial virus infection

Clara cell secretory protein (CCSP) has been shown to have anti-inflammatory and immunomodulatory functions in the lung. Respiratory syncytial virus (RSV) is the most common cause of respiratory infection in infants and young children. RSV usually infects small airways and likely interacts with the Clara cells of bronchioles. To determine a possible role for CCSP during acute RSV infection, CCSP-deficient (CCSP(-/-)) and wild-type (WT) mice were intratracheally infected with RSV and the lung inflammatory and immune responses to RSV infection were assessed. RSV-F gene expression was increased in the lungs of CCSP(-/-) mice as compared with WT mice following RSV infection, consistent with increased viral persistence. Lung inflammation was significantly increased in CCSP(-/-) mice as compared with WT mice after infection. Moreover, although the levels of Th1 cytokines were similar, the levels of Th2 cytokines and neutrophil chemokines were increased in the lungs of CCSP(-/-) mice following infection. Physiologic endpoints of exacerbated lung disease, specifically airway reactivity and mucus production, were increased in CCSP(-/-) mice after RSV infection. Importantly, restoration of CCSP in the airways of CCSP(-/-) mice abrogated the increased viral persistence, lung inflammation, and airway reactivity. These findings suggest a role for CCSP and Clara cells in regulating lung inflammatory and immune responses to RSV infection.

Lys 43 and Asp 46 in alpha-helix 3 of uteroglobin are essential for its phospholipase A2 inhibitory activity

Uteroglobin (UG) is an anti-inflammatory, secreted protein with soluble phospholipase A2 (sPLA2)-inhibitory activity. However, the mechanism by which UG inhibits sPLA2 activity is unknown. UG is a homodimer in which each of the 70-amino acid subunits forms four alpha-helices. We previously reported that sPLA2-inhibitory activity of UG may reside in a segment of alpha-helix 3 that is exposed to the solvent. In addition, it has been suggested that UG may inhibit sPLA2 activity by binding and sequestering Ca++, essential for sPLA2 activation. By site-specific mutation, we demonstrate here that Lys 43 Glu, Asp 46 Lys or a combination of the two mutations in the full-length, recombinant human UG (rhUG) abrogates its sPLA2-inhibitory activity. We demonstrate further that recombinant UG does not bind Ca++ although when it is expressed with histidine-tag (H-tag) it is capable of binding Ca++. Taken together our results show that: (i) Lys 43 and Asp 46 in rhUG are critical residues for the sPLA2-inhibitory activity of UG and (ii) Ca++-sequestration by rhUG is not likely to be one of the mechanisms responsible for its sPLA2-inhibitory activity.

Advances in ocular allergy: basic mechanisms, clinical patterns and new therapies

Ocular allergy presents unsolved mysteries in molecular and cellular mechanisms, and at the same time continues to challenge ophthalmologists daily in a wide array of disease forms. The recent understanding of the key role of the T helper type 2 cytokines, adhesion molecules and chemokines may provide future avenues for pharmacological targeting of releasable inflammatory mediators. More potent topical mast cell stabilizers and H1 receptor antagonists have become commercially available for the management of the prevalent and benign forms of allergic conjunctivitis. Immunostimulatory DNA sequences present an innovative and promising route for the treatment of ocular allergy, but clinical studies are needed to demonstrate their efficacy in humans. Surgical methods are suggested to reconstruct the ocular surface in the sight-threatening diseases vernal keratoconjunctivitis and atopic keratoconjunctivitis. This review presents an update of the major advances in both the basic mechanisms and clinical and therapeutic aspects of ocular allergic diseases that were reported during the past year.

Natural inhibitors of neutrophil function in acute respiratory distress syndrome

OBJECTIVE

Neutrophils play a key role in the physiopathogenesis of acute lung injury in general and acute respiratory distress syndrome (ARDS) in particular. To identify the anti-inflammatory mediators with a protective effect on lung tissue damage in ARDS, we correlated the concentration of the Clara cell 16-kD protein (CC16; an inhibitor of neutrophil chemotaxis), angiogenin (an inhibitor of degranulation), and the total radical oxygen neutralizing activity with the amount of elastase (a marker of neutrophil activation) and with the Pao2/Fio2 ratio, which is inversely related to lung injury.

SETTING

University hospital.

PATIENTS

Patients with ARDS (n = 12) and patients at risk for developing ARDS (n = 14).

INTERVENTIONS

Patients underwent bronchoalveolar lavage 12 hrs after diagnosis of ARDS or at-risk status.

MEASUREMENTS AND MAIN RESULTS

The amount of CC16 and radical oxygen neutralizing activity was not significantly different in patients with or at risk for ARDS. In contrast, the amount (mean +/- sem) of angiogenin in the bronchoalveolar lavage of ARDS patients (45 +/- 14 ng/mL, n = 12) was increased 11-fold (p <.05) compared with patients at risk for ARDS (4 +/- 1 ng/mL, n = 14). In patients with ARDS, the amount of protein and angiogenin in bronchoalveolar lavage increased with decreasing concentration of CC16 (p <.05). In addition, CC16 correlated with the Pao2/Fio2 ratio (p <.05) and inversely with the amount of elastase (p <.05) and thus may be regarded as a reliable protective agent for lung injury.

CONCLUSION

A high concentration of CC16, a natural inhibitor of neutrophil function, decreases neutrophil-mediated lung damage of patients with ARDS. Strategies to increase natural anti-inflammatory agents, and thus influence the disruption of the balance between natural inflammatory and anti-inflammatory or protective factors, could be useful to modulate the tissue destruction and the course of ARDS.

Therapeutic applications of antiflammin peptides in experimental ocular inflammation

Antiflammins are synthetic peptides derived from the region of highest local similarity between uteroglobulin and lipocortin. These peptides have shown anti-inflammatory activity on carrageenan-induced rat footpad edema. They are potent inhibitors for phospholipase A2 activation both in vitro and in vivo. Previously, we have demonstrated the effectiveness of topical antiflammins in suppressing acute ocular inflammation and allergic response in rodent endotoxin-induced uveitis and murine allergic conjunctivitis. The mechanisms by which antiflammins protect against inflammation and allergy in these ocular models may involve inhibition of phospholipase A2 and inducible nitric oxide synthase (iNOS) as well as the production of proinflammatory cytokine, interleukin-6.

Antiflammin peptides in the regulation of inflammatory response

This review focuses on the role of antiflammins in the regulation of the inflammatory response, in particular acute inflammation. The results show that antiflammins were effective on several classical models of inflammation. Preliminary data suggest that antiflammin action may be due to their ability to suppress leukocyte trafficking to the lesion.

Antiflammins. Bioactive peptides derived from uteroglobin

Uteroglobin/Clara cell 10-kDa protein (UG/CC10) is a hormonally regulated small secretory protein that has a variety of in vitro and in vivo pharmacological effects. These include a potent anti-inflammatory activity and inhibitory effects on neutrophil migration, thrombin-induced platelet aggregation, in vitro chemoinvasion, as well as "tumor suppressor"-like effects and other properties. Several mechanisms of action have been proposed for these effects. Pharmacological properties suggest that UG itself or substances derived from it may be used as experimental drugs for several indications. The group of oligopeptides collectively known as "antiflammins" (AFs) were originally described in 1988. Their design was derived from the region of highest sequence similarity between UG and another group of proteins with anti-inflammatory properties, the lipocortins or annexins. Nanomolar concentrations of these peptides can reproduce several of the pharmacological activities of UG, including its in vivo anti-inflammatory effects and inhibition of platelet aggregation. The AFs have been safely and effectively used to suppress inflammation and fibrosis in several animal models. Progress in clarifying the mechanism of action of the AFs may facilitate the structure-based design of a novel class of potent anti-inflammatory, antichemotactic drugs.

Uteroglobin reverts the transformed phenotype in the endometrial adenocarcinoma cell line HEC-1A by disrupting the metabolic pathways generating platelet-activating factor

Uteroglobin, originally named blastokinin, is a protein synthesized and secreted by most epithelia, including the endometrium. Uteroglobin has strong anti-inflammatory properties that appear to be due, at least in part, to its inhibitory effect on the activity of the enzyme phospholipase A(2). In addition, recent experimental evidence indicates that uteroglobin exerts antiproliferative and antimetastatic effects in different cancer cells via a membrane receptor. The human endometrial adenocarcinoma cell line HEC-1A does not express uteroglobin. Thus, we transfected HEC-1A cells with human uteroglobin cDNA. The transfectants showed a markedly reduced proliferative potential as assessed by impaired plating efficiency as well as by reduced growth in soft agar. Cytofluorimetric analysis clearly indicated that in uteroglobin-transfected cells the time for completion of the cell cycle was increased. We previously demonstrated that HEC-1A cells actively synthesize platelet-activating factor, one of the products of phospholipase A(2) activity. In addition, we demonstrated that platelet-activating factor stimulates the proliferation of these cells through an autocrine loop. In uteroglobin transfectants, the activity of phospholipase A(2) and platelet-activating factor acetyl-transferase, which are involved in the synthesis of platelet-activating factor, was significantly reduced compared with wild-type and vector-transfected cells (p < 0.05). Our results indicate that enforced expression of uteroglobin in HEC-1A cells markedly reduced their growth potential and significantly impaired the synthesis of platelet-activating factor, an autocrine growth factor for these cells. These data suggest that one possible mechanism for the recently observed antineoplastic properties of uteroglobin may be the inhibition of the synthesis of platelet-activating factor.

The anti-inflammatory peptides, antiflammins, regulate the expression of adhesion molecules on human leukocytes and prevent neutrophil adhesion to endothelial cells

Antiflammin-1 and antiflammin-2 are nonapeptides corresponding to the region of highest similarity between glucocorticoid-inducible proteins lipocortin-1 and uteroglobin. We have studied whether antiflammins could affect expression of adhesion molecules on human leukocytes and coronary artery endothelial cells (HCAEC) and binding of neutrophils (PMNs) to HCAEC. Although neither antiflammin-1 nor antiflammin-2 affected expression of adhesion molecules on resting PMNs, monocytes, and lymphocytes in whole blood, they attenuated changes in L-selectin and CD11/CD18 expression evoked by platelet-activating factor or interleukin-8 with IC(50) values of 4-20 micromol/l. The maximum inhibition was similar to those seen with human recombinant lipocortin-1 (100 microgram/ml). Unlike dexamethasone (100 nmol/l), the antiflammins had little effect on LPS-stimulated expression of E-selectin and ICAM-1 on HCAEC. Consistently, culture of HCAEC with dexamethasone, but not with antiflammins, decreased PMN binding to endothelial cells. Preincubation of PMNs with antiflammins markedly decreased their adhesion to LPS-activated HCAEC. Inhibition of adhesion was additive with function blocking anti-E-selectin and anti-L-selectin antibodies, but was not additive with anti-CD18 antibody. These results show that antiflammins inhibit PMN adhesion to HCAEC by attenuating activation-induced up-regulation of CD11/CD18 expression on leukocytes, and suggest that antiflammins may represent a novel therapeutic approach in blocking leukocyte trafficking in host defense and inflammation.

Clara cell protein-positive epithelial cells are reduced in small airways of asthmatics

Clara cell 10 kilodalton protein (CC10), the predominant product from nonciliated cells in the epithelial lining of bronchioles (Clara cells), has been shown to have immunomodulatory and anti-inflammatory activity, and may play roles in controlling inflammation in the airway. This study was designed to examine immunohistochemical expression of CC10 in epithelial cells in small airways (perimeter < 6 mm) of asthmatic and control nonsmokers who underwent lung resection because of peripheral lung carcinoma and to compare CC10-positive epithelial cell proportions with numbers of inflammatory cells in small airways of asthmatics. Significantly decreased proportions of CC10-positive epithelial cells and significantly increased numbers of T cells, activated eosinophils, and mast cells in small airways of asthmatics were found compared with those of control subjects. CC10-positive epithelial cell proportions inversely correlated with numbers of T cells and mast cells in small airways of asthmatics. Decreases of CC10-producing cells may give an accelerating cause for further aggravation of inflammatory responses in chronic asthma.

Loss of transformed phenotype in cancer cells by overexpression of the uteroglobin gene

Uteroglobin (UG) is a multifunctional, secreted protein that has receptor-mediated functions. The human UG (hUG) gene is mapped to chromosome 11q12.2-13.1, a region frequently rearranged or deleted in many cancers. Although high levels of hUG expression are characteristic of the mucosal epithelia of many organs, hUG expression is either drastically reduced or totally absent in adenocarcinomas and in viral-transformed epithelial cells derived from the same organs. In agreement with these findings, in an ongoing study to evaluate the effects of aging on UG-knockout mice, 16/16 animals developed malignant tumors, whereas the wild-type littermates (n = 25) remained apparently healthy even after 11/2 years. In the present investigation, we sought to determine the effects of induced-expression of hUG in human cancer cells by transfecting several cell lines derived from adenocarcinomas of various organs with an hUG-cDNA construct. We demonstrate that induced hUG expression reverses at least two of the most important characteristics of the transformed phenotype (i.e., anchorage-independent growth on soft agar and extracellular matrix invasion) of only those cancer cells that also express the hUG receptor. Similarly, treatment of the nontransfected, receptor-positive adenocarcinoma cells with purified recombinant hUG yielded identical results. Taken together, these data define receptor-mediated, autocrine and paracrine pathways through which hUG reverses the transformed phenotype of cancer cells and consequently, may have tumor suppressor-like effects.

Inhibitory effect of peptides derived from the N-terminus of lipocortin 1 on arachidonic acid release and proliferation in the A549 cell line: identification of E-Q-E-Y-V as a crucial component

1. The ability of the glucocorticoid-induced protein lipocortin 1 (LC1) to inhibit arachidonic acid release and cell proliferation in A549 cells may be mimicked by a sequence taken from the N-terminal, LC1(13-25) (FIENEEQEYVQTV). We have now synthesized and tested for biological activity a library of 25 smaller peptides derived from this sequence. 2. Peptides were tested in two assays: A549 cells were prelabelled with tritiated arachidonic acid and thapsigargin (50 nM) and EGF (10 nM) used to stimulate the release of this fatty acid. Cell proliferation was determined by counting cell numbers following 3 day incubation with these peptides, or controls. 3. Many of the peptides were highly insoluble but could be more readily dissolved in aqueous solution in the presence of commercial liposomes or phosphatidyl serine (5 microM). Since neither of these agents alone had any effect on arachidonic acid release or cell proliferation, all peptides were tested in the presence of 5 microM phosphatidyl serine. Under these conditions LC1(13-25) was active in both assay systems with an IC40 of 40.7 and 57.0 microM respectively. 4. Deletion of amino acids from the C-terminus of the peptide progressively diminished (2-3 fold) the molar potency of LC1(13-25) in both assays: after the removal of Val22 biological activity was virtually undetectable or very weak (< 30% of LC1[13-25]). 5. Removal of amino acids from the N-terminus also lead to a progressive reduction (3-5 fold) in the molar potency of the peptides and biological activity became undetectable, or very weak, after the removal of Glu18. 6. All active peptides contained the core sequence EQEYV(Glu-Gln-Glu-Tyr-Val) which seems to represent a crucial component of the pharmacophore, although this sequence on its own was inactive and the shortest peptide with significant activity was LC1(18-25) (EQEYVQTV). 7. Methoxylation of Tyr21 abolished the ability of LC1(18-25) to inhibit cell proliferation and arachidonic acid release. A cyclized version of LC1(18-25) was also tested and found to be inactive. 8. LC1(18-25) (178 microM) inhibits cPLA2 activation in A549 cells as judged by a band-shift assay, whereas equimolar concentrations of an inactive peptide LC1(19-25) were without effect in this assay system. 9. Several possible mechanisms whereby these peptides act are discussed in the light of LC1 biology and of the effect of glucocorticoids on cell function.

Antiflammin 1 peptide delivered non-invasively by iontophoresis reduces irritant-induced inflammation in vivo

The potential of an anti-inflammatory peptide (antiflammin 1) to reduce irritation when delivered transdermally by iontophoresis was examined. A model drug irritant, chlorpromazine, was co-delivered with and without antiflammin 1 by iontophoresis to hairless guinea pigs transdermally. Quantitative skin irritation measurements were obtained by monitoring erythema by skin color reflectance with the Minolta Chromameter. Antiflammin 1 delivered by iontophoresis significantly decreased, but did not eliminate, the erythema associated with co-delivery of an irritating drug compound. Lesion formation was also reduced in the presence of antiflammin 1. In vitro flux across hairless guinea pig skin demonstrated no significant differences in flux of the irritant compound in the presence or absence of antiflammin 1. In vivo generation and efflux of the inflammation mediator Prostaglandin E2 increased during 24-h application of irritant and was unchanged in the presence of antiflammin 1. This result is discussed with respect to recent evidence that antiflammins may act on the lipo-oxygenase pathway. In summary, antiflammin 1, an anti-inflammatory peptide, can be delivered transdermally by iontophoresis with retention of its biological activity in vivo.

Antiflammins: endogenous nonapeptides with regulatory effect on inflammation

1. Antiflammins are a new family of peptides that share a common sequence with uteroglobin and lipocortin-1, which retain the anti-inflammatory action of these proteins. 2. However, it is controversial whether or not the antiflammins have any effect on enzymes involved in arachidonic acid mobilization and/or arachidonic acid metabolism. 3. This review summarizes our current knowledge of the properties and activity of antiflammins.

Human uteroglobin gene: structure, subchromosomal localization, and polymorphism

Human uteroglobin (hUG) or Clara cell 10-kD protein (cc10 kDa) is a steroid-dependent, immunomodulatory, cytokine-like protein. It is secreted by mucosal epithelial cells of all vertebrates studied. The cDNA encoding hUG and the 5' promoter region of the gene have been characterized previously. Here, we report that the structure of the entire hUG gene is virtually identical to those of rabbit, rat, and mouse. It is localized on human chromosome 11q12.3-13.1, a region in which several important candidate disease genes have been mapped by linkage analyses. Our data indicate that candidate genes for atopic (allergic) asthma and Best's vitelliform macular dystrophy are in closest proximity to the hUG gene. To determine whether hUG gene mutation may be involved in the pathogenesis of these diseases, we studied two isolated groups of patients, each afflicted with either atopy or Best's disease, respectively. We detected a single base-pair change in the hUG gene in Best's disease patients and normal controls but no such change was detected in atopy patients. This alteration in hUG gene-sequence in Best disease family appears to be a polymorphism. Although the results of our investigation did not uncover mutations in hUG gene that could be causally related to the pathogenesis of either of these diseases, its conservation throughout vertebrate phyla implies that this gene is of physiological importance. Moreover, the close proximity of this gene to several candidate disease genes makes it an important chromosomal marker in cloning and characterization of those genes.

Resonance assignment and secondary structure determination and stability of the recombinant human uteroglobin with heteronuclear multidimensional NMR

Human uteroglobin (h-UG) or Clara cell 10kDa (cc10kDa) is a steroid-dependent, 17 kDa homodimeric, secretory protein with potent anti-inflammatory/immunomodulatory properties. However, the exact physiological role still remains to be determined. It has been hypothesised that its activity is exerted through the binding of a specific target represented by a small molecule (still unknown), and that the binding is regulated by the formation/disruption of two cysteine bonds. The binding properties of the reduced UG have been proved in vitro for several different molecules, but no in vivo data are available to date. However, binding has been observed between reduced rabbit UG and a protein of an apparent molecular mass of 90 kDa and, more recently, we found an h-UG-binding protein

Antiflammin-2, a nonapeptide of lipocortin-1, inhibits leukocyte chemotaxis but not arachidonic acid mobilization

We have studied the effects of antiflammin-2, a fragment corresponding to amino acids 246-254 of lipocortin-1 (HDMNKVLDL), on arachidonate mobilization and metabolism and we also determined the effect of antiflammin-2 on the chemotaxis of phagocytes. Our results demonstrated that the antiflammin-2 was not able to diminish significantly [3H]arachidonic acid mobilization stimulated by 4 beta-phorbol-12-myristate 13-acetate or calcium ionophore A23187 in murine 3T6 fibroblasts or resident peritoneal macrophages. Further, antiflammin-2 had no effect on arachidonate metabolism. In contrast, a glucocorticoid such as dexamethasone reduced significantly [3H]arachidonic acid release and arachidonate metabolism induced in both cells. This study confirms the inhibitory effect of antiflammin on leukocyte migration and suggests that it acts partly through the inhibition of leukocyte binding to endothelial cells.

Degradation of antiflammin 2 under acidic conditions

Antiflammin 2 (HDMNKVLDL, AF2) is a synthetic peptide derived from the region of highest sequence similarity of lipocortin I and uteroglobin, and is a potent antiinflammatory agent without any known side effects of corticosteroids. The antiinflammatory activity of AF2 has been demonstrated, but is not reproducible between laboratories. It has been suggested that the chemical instability of this peptide is responsible for the loss of activity. The degradation of AF2 in aqueous solutions at a pH range of 3 to 10 has been reported. In this study, the degradation of AF2 at acidic pHs was monitored by reversed-phase HPLC. The reactions were studied as functions of buffer concentration and temperature. The rates of loss of AF2 followed apparent pseudo-first-order kinetics. Several products were isolated and identified by fast atom bombardment mass spectroscopy and tandem mass spectroscopy, and were the result of C- and N-terminus hydrolyses of aspartyl peptide bonds in AF2. The peptide bonds at C-termini of the aspartyl residues were most susceptible to hydrolysis, resulting in the formation of major degradation products, HDMNKVLD, MNKVLDL, and MNKVLD. The minor products from the N-terminus hydrolysis were HDMNKVL and MNKVL and formed at much slower rates.

Role of platelet-activating factor in pathogenesis of galactosamine-lipopolysaccharide-induced liver injury

In an attempt to clarify the role of platelet-activating factor (PAF) in the pathogenesis of hepatic injury induced by galactosamine (GalN) plus lipopolysaccharide (LPS), effects of WEB 2086 (PAF receptor antagonist) on hepatic injury in vivo as well as on neutrophil adherence to hepatic endothelial cells in vitro have been investigated, as we have recently clarified the role of neutrophils in this experimental model of hepatic injury. Although an enhanced serum TNF-alpha level after GalN-LPS administration was not reduced by WEB 2086, hepatic injury and hepatic neutrophil accumulation in the liver after GalN-LPS administration were attenuated by WEB 2086. An in vitro study revealed that an enhanced neutrophil adhesion to hepatic endothelial cells by stimulation with the sera that were collected from the GalN-LPS-treated rats, was reduced in the presence of WEB 2086 in a dose-dependent manner. In addition, LPS, TNF-alpha, and PAF were found to enhance the neutrophil adherence to hepatic endothelial cells, which was reduced in the presence of WEB 2086. These results suggest that PAF play an important role in the GalN-LPS induced hepatic injury and that PAF receptor antagonist reduces the neutrophil adherence to hepatic endothelial cells in the liver.

Oxidative degradation of antiflammin 2

PURPOSE

To study the oxidation of the methionine residue of antiflammin 2 (HDMNKVLDL, AF2) as a function of pH, buffer concentration, ionic strength, and temperature using different concentrations of hydrogen peroxide and to determine the accessibility of methionine residue to oxidation.

METHODS

Reversed-phase high-performance liquid chromatography (RPHPLC) was used as the main analytical method in determining the oxidation rates of AF2. Calibration curves for AF2 and the oxidation product, methionine sulfoxide of AF2 (Met(O)-3-AF2), were constructed for each measurement using standard materials. Fast Atom Bombardment Mass Spectroscopy (FABMS) was used to characterize the product.

RESULTS

Met(O)-3-AF2 was the only oxidation product detected at pH 3.0 to 8.0. The oxidation rates were independent of buffer concentrations, ionic strength, and pH from 3.0 to 7.0. However, there was an acceleration of the rates at basic pHs, and small amounts of degradation products other than Met(O)-3-AF2 were observed in this alkaline region.

CONCLUSIONS

Oxidation of methionine in AF2 does not cause the biological inactivation reported by other laboratories since this drug is relatively stable under neutral conditions in the absence of oxiding agent.

Effects of an anti-inflammatory peptide (antiflammin 2) on cell influx, eicosanoid biosynthesis and oedema formation by arachidonic acid and tetradecanoyl phorbol dermal application

Antiflammins are synthetic peptides with sequence homology to proteins inhibitory for phospholipase A2 (EC 3.1.1.4). The effect of antiflammin 2 on murine arachidonate or 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced ear oedema has been studied. Topical application of arachidonic acid (AA) produced a short-lived oedema response with rapid onset associated with marked increases in prostaglandin E2 levels. TPA produced a longer-lasting oedema associated with marked influx of neutrophils and mononuclear cells as well as predominant formation of leukotriene B4 (LTB4). Topical pretreatment with indomethacin or dexamethasone reduced plasma leakage, oedema and prostaglandin E2 biosynthesis in AA-induced oedema, whereas antiflammin 2 had no effect. However, topical pretreatment with antiflammin 2 dose-dependently reduced plasma leakage, cell influx, oedema and LTB4 levels in response to TPA. These results indicate that the anti-inflammatory effect of antiflammins can be attributed to AA mobilization and/or 5 lipoxygenase inhibition but can be dissociated from an effect on arachidonic acid metabolism by the cyclooxygenase pathway.

Effect of nonapeptide fragments of uteroglobin and lipocortin I on oedema and mast cell degranulation

The anti-inflammatory action of nonapeptide fragments of uteroglobin or lipocortin I known as antiflammins, was tested in the carrageenan or phospholipase A2 rat paw oedema model. The development of carrageenan-induced oedema in rats was significantly inhibited during the early and late phases of the oedema by the local administration of antiflammins 1 and 2. However, the peptides were not able to inhibit phospholipase A2-induced oedema. The time course of the anti-oedematous activity of nonapeptides after intradermal carrageenan injection may be attributed to their effect on mast cell degranulation and accumulation and activation of leukocytes. Naja naja phospholipase A2 exhibited strong histamine release-inducing activity, which may have contributed to the rat paw oedema induction. Surprisingly, antiflammins had a limited but significant inhibitory effect on histamine secretion.

Crystallization and characterization of the recombinant human Clara cell 10-kDa protein

Crystals of recombinant human Clara cell 10-kDa protein were grown both from ammonium sulfate and polyethylene glycol (PEG) solutions. Crystals grown from ammonium sulfate solution have been characterized by X-ray diffraction studies as monoclinic with the space group C2 and lattice constants a = 69.2 A, b = 83.0 A, c = 58.3 A, and beta = 99.7 degrees. The monoclinic crystals diffract to beyond 2.5 A. Some of the crystals grown from PEG were of a similar habit to those grown from ammonium sulfate, but others were triclinic with the space group P1 and cell constants a = 40.3 A, b = 46.3 A, c = 51.3 A, alpha = 117.7 degrees, beta = 102.3 degrees, and gamma = 71.4 degrees. These crystals diffract to beyond 3.2 A.

Tissue-specific expression of the gene coding for human Clara cell 10-kD protein, a phospholipase A2-inhibitory protein

Clara cell 10-kD protein (cc10kD), a secretory phospholipase A2 inhibitor, is suggested to be the human counterpart of rabbit uteroglobin (UG). Because cc10kD is expressed constitutively at a very high level in the human respiratory epithelium, the 5' region of its gene may be useful in achieving organ-specific expression of recombinant DNA in gene therapy of diseases such as cystic fibrosis. However, it is important to establish the tissue-specific expression of this gene before designing gene transfer experiments. Since the UG gene in the rabbit is expressed in many other organs besides the lung and the endometrium, we investigated the organ and tissue specificity of human cc10kD gene expression using polymerase chain reaction, nucleotide sequence analysis, immunofluorescence, and Northern blotting. Our results indicate that, in addition to the lung, cc10kD is expressed in several nonrespiratory organs, with a distribution pattern very similar, if not identical, to that of UG in the rabbit. These results underscore the necessity for more detailed analyses of the 5' region of the human cc10kD gene before its usefulness in gene therapy could be fully assessed. These data also suggest that cc10kD and UG may have similar physiological function(s).

Differentiation and uteroglobin gene expression by novel rabbit endometrial cell lines

A clear understanding of the mechanism of differentiation of mammalian endometrial epithelia would significantly improve our knowledge of embryo implantation and placentation. An ideal model for such studies would be immortal endometrial epithelial cell lines which express a well characterized, steroid-responsive, differentiation-specific gene in vitro. We characterized two cell lines which are temperature-sensitive for differentiation. At the non-permissive temperature (39.5 degrees C), in presence of ovarian steroids, these cells express the gene coding for uteroglobin, a steroid-dependent, immunomodulatory/antiinflammatory protein in the rabbit. In addition, when cultured on artificial basement membrane (Matrigel), in presence of ovarian steroids both cell lines developed organized, tubular structures with lumens, reminiscent of an intact endometrium and secreted 33-fold more uteroglobin than the untreated controls. Thus, these immortal cell lines provide a unique model to study endometrial epithelial cell differentiation and steroid hormone action in vitro.

In vitro and in vivo effects of the anti-inflammatory peptides, antiflammins

The anti-inflammatory synthetic polypeptides referred to as antiflammins are thought to be inhibitors of phospholipase A2 (PLA2) (EC 3.1.1.4). These peptides are from the sequence of amino acids of greatest similarity between uteroglobin and lipocortin I. The effect of these peptides was studied on PLA2 activation in rat platelets and on acute inflammatory models after local or parenteral administration of drug. We found that antiflammins decreased collagen-induced platelet activation, but had no effect when arachidonic acid was used as activator. The peptides were able to inhibit acute inflammatory processes induced by carrageenan or phorbol esters when administered locally or parenterally. However, antiflammins had no effect on inflammation induced by exogenous PLA2 administration. These results indicate that the antiflammins may have a direct inhibitory effect on PLA2 activation but not on the enzyme or enzyme-substrate interaction.

Antiflammins. Anti-inflammatory activity and effect on human phospholipase A2

Two anti-inflammatory peptides (antiflammins) corresponding to a high amino acid similarity region between lipocortin I and uteroglobin were tested for their ability to inhibit purified human synovial fluid phospholipase A2 (HSF-PLA2). No inhibitory activity was observed, even at such high concentrations of peptides as 50 microM. When antiflammins were preincubated with the enzyme and/or the substrate, no HSF-PLA2 inhibition was detected. In vivo anti-inflammatory activity of these peptides was evaluated in several experimental models of inflammation induced by carrageenan, croton-oil, oxazolone and Naja naja naja venom phospholipase A2 (PLA2). In contrast to the in vitro results, anti-inflammatory activity was observed in all tests, except when inflammation was induced by snake venom PLA2. Taken together, our results do not support the hypothesis that the in vivo anti-inflammatory effect of antiflammins is directly related to inhibition of PLA2 activity.

Regulation of extracellular phospholipase A2 activity: implications for inflammatory diseases

Phospholipases A2 (PLA2s; E.C.3.1.1.4) are a family of esterases that are involved in myriads of physiological and pathological processes. The involvement of these enzymes, especially the extracellular PLA2s, in the generation of proinflammatory lipid mediators makes them a very important target for investigation. These PLA2s have been suggested to be involved in the pathogenesis of several human inflammatory diseases. Thus, delineating the mechanism(s) of regulation of the activity of these enzymes may provide a better understanding of the pathophysiology of these diseases and allow the rational design and development of novel therapeutic agents. In this article, we provide a brief description of PLA2s in general with a special emphasis on extracellular enzymes, their mechanism(s) of action, and possible role in the pathogenesis of inflammatory diseases. Additionally, we describe: (i) a novel mechanism of activation of extracellular PLA2s by transglutaminases and (ii) the development of one class of antiinflammatory agents, antiflammins, derived from the active site structure of endogenous PLA2-inhibitory proteins.

Leukotriene B4 and platelet-activating factor in human skin

Acute inflammatory reactions are characterized by leukocyte infiltration associated with increases in vascular permeability and in local blood flow. Leukocyte infiltration can be induced by chemotactic factors such as leukotriene B4 (LTB4) and paf-acether (formerly known as platelet-activating factor) that can be generated within inflammatory lesions. Vascular permeability and increase in blood flow are also affected by LTB4 and paf-acether, as well as by several other substances, including histamine and prostaglandins. Derived from arachidonic acid via the 5 lipo-oxygenase pathway, LTB4 is one of the most potent leukocyte chemotactic substances known. Intradermal injections of LTB4 induce dermal neutrophil infiltration in animal models and in humans. Topical application of LTB4 to human skin induces intraepidermal micro-abscesses containing numerous intact neutrophils. LTB4 has been found to be increased in psoriatic lesions, but its synthesis by epidermal cells remains undecided. Like other leukotrienes, LTB4 can stimulate DNA synthesis in cultured human epidermal keratinocytes. However, receptors for LTC4 but not for LTB4 have been found on human keratinocytes in culture. Paf-acether is an ether-linked phospholipid identified as 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine and is considered to be one of the most potent mediators of acute allergic and inflammatory reactions. For instance, intradermal injection of paf-acether induces inflammatory events such as neutrophil infiltration and increase in vascular permeability. Recent data suggest that cutaneous cells, such as fibroblasts and keratinocytes, are capable of producing paf and that paf is released during the development of allergic cutaneous reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective inhibition by antiflamrnin-2 of thromboxane B(2) release from isolated and perfused guinea-pig lung

Antiflammin-2 (AF2) is a nonapeptide corresponding to the amino acid residues 246–254 of lipocortin-1 showing anti-inflammatory activity both in vitro and in vivo. The effect of AF2 on the thromboxane B₂ (TXB₂) and histamine release from isolated and perfused guinea-pig lungs has been studied. AF-2 (10–100 nM) inhibited leukotriene C₄- (LTC₄) (3 ng) and antigen-induced (ovalbumin, 1 mg) TXB₂ release in normal and sensitized lungs, respectively. In contrast AF-2 (100 nM) did not modify TXB₂ release induced by histamine (5 μg) or bradykinin (5 μg) in normal lungs. Antigen-induced histamine release was not affected by 100 nM AF-2 infusion. When tested in chopped lung fragments AF-2 (0.1–25 μM) did not modify the release of histamine and TXB₂ induced by antigen (ovalbumin, 10 μg ml⁻¹) or calcium ionophore A 23187 (1 μM). Our results show that the inhibitory effect of AF-2 on TXB₂ release is selective and depends on the stimulus applied. In this respect AF-2 mimics, at least in part, the actions of both glucocorticoids and lipocortin-1.

The molecular action of tumor necrosis factor-alpha

Tumor necrosis factor-alpha (TNF-alpha) is a polypeptide hormone newly synthesized by different cell types upon stimulation with endotoxin, inflammatory mediators (C5a anaphylatoxin), or cytokines such as interleukin-1 and, in an autocrine manner, TNF itself. The net biological effect of TNF-alpha may vary depending on relative concentration, duration of cell exposure and presence of other mediators which may act in synergism with this cytokine. TNF-alpha may be relevant either in pathological events occurring in cachexia and endotoxic shock and inflammation or in beneficial processes such as host defense, immunity and tissue homeostasis. The biological effects of TNF-alpha are triggered by the binding to specific cell surface receptors. The formation of TNF-alpha-receptor complex activates a variety of biochemical pathways that include the transduction of the signal at least in part controlled by guanine-nucleotide-binding regulatory proteins (G proteins), its amplification through activation of adenyl cyclase, phospholipases and protein kinases with the generation of second messenger pathways. The transduction of selected genes in different cell types determines the characteristics of the cell response to TNF-alpha. The full understanding of the molecular mechanisms of TNF-alpha will provide the basis for a pharmacological approach intended to inhibit or potentiate selected biological actions of this cytokine.