Soluble receptors for IL-1 and IL-4: biological activity and therapeutic potential

Interleukin-6 and interleukin-6 receptor secretion by chronic lymphatic leukaemia and normal B lymphocytes: effect of PMA and PWM

Interleukin-6 (IL-6) and soluble interleukin-6 receptor (sIL-6R) were detected in supernatants of cultures of B chronic lymphatic leukaemia (CLL) lymphocytes. Phorbol-12-myristate 13 acetate (PMA) caused a decrease in the levels of IL-6 in 14 out of 16 cultures and an increase in levels of sIL6R in all 15 cases. The effect of pokeweed mitogen (PWM) was variable and not significant. The levels of IL-6 were below the detection limit (60 pg/ml) in sera of 13 CLL patients whereas sIL-6R was detected (13 ng/ml to 97 ng/ml) in the 13 sera. IL6 was not detected in cultures of unstimulated or stimulated with PMA or PWM normal human B cells. Levels of sIL-6R were minimal in cultures of normal B lymphocytes and were increased in PMA stimulated cultures. The results are consistent with the view that B-CLL cells produce spontaneously IL-6 which could act in an autocrine fashion to cause shedding of surface IL-6R and account for the correlation found between serum levels of sIL-6R and B-CLL lymphocyte numbers. The fall in levels of IL-6 in PMA stimulated CLL cultures might express masking or degradation of IL-6 after combination with the receptor.

Widespread production of novel soluble protein isoforms by alternative splicing removal of transmembrane anchoring domains

We have investigated the effects of alternative splicing on transcripts encoding membrane proteins in 1001 human genes. Out of a total of 464 alternatively spliced genes encoding single-pass transmembrane (TM) proteins, in 188 we observed a splice form that specifically removed the TM domain, producing a soluble protein isoform. For example, in syndecan-4, the new alternative splice form closely parallels the proteolytic ectodomain shedding previously shown in this protein, and recognized as an important regulatory mechanism of receptor function. While many of the soluble isoforms produced by alternative splicing have already been validated, most are novel, and in 57 genes showed a statistically significant association (P-value<0.01) with a specific tissue.

Soluble antagonists to interleukin-1 (IL-1) and tumor necrosis factor (TNF) inhibits loss of tissue attachment in experimental periodontitis

BACKGROUND, AIMS

Periodontal disease is a significant cause of tooth loss among adults and is characterized by the alteration and permanent destruction of the deeper periodontal tissues. Although the presence of pathologic microbes is required to trigger this process, the amplification and progression of the diseased state is believed to rely heavily on the production of host mediators in response to bacteria or their metabolic products. The inflammatory response is effective in preventing large-scale colonization of the gingival tissues by bacteria that lie in close proximity to the tooth surface or within the gingival sulcus. It has been postulated that the host-response in some individuals may lead to an over-reaction to invading oral pathogens resulting in the destruction of periodontal tissues.

METHODS

Several host-derived mediators are believed to contribute to this response. Two agents considered to be essential in periodontal destruction are interleukin-1 (IL-1) and tumor necrosis factor (TNF). We investigated the role of IL-1 and TNF in the loss of connective tissue attachment in a Macaca fascicularis primate model of experimental periodontitis. Silk ligatures impregnated with the periodontal pathogen, Porphyromonas gingivalis were wrapped around the posterior teeth and the activity of IL-1 and TNF were inhibited by soluble receptors to these proinflammatory cytokines via local injection into interdental papillae.

RESULTS

Histomorphometric analysis indicates that IL-1 and TNF antagonists significantly reduced the loss of connective tissue attachment by approximately 51% and the loss of alveolar bone height by almost 91%, both of which were statistically significant.

CONCLUSION

This investigation demonstrates that the loss of connective tissue attachment and progression of periodontal disease can be retarded by antagonists to specific host mediators such as IL-1 and TNF and may provide a potential treatment modality to combat the disease process.

Interleukin-1 and tumor necrosis factor antagonists inhibit the progression of inflammatory cell infiltration toward alveolar bone in experimental periodontitis

Periodontal disease is a significant cause of tooth loss in humans and is one of the most prevalent diseases associated with bone loss. Following bacterial colonization, the gingiva becomes inflamed and, in some cases, progresses to destruction of alveolar bone. To investigate the temporal movement of inflammatory cells toward alveolar bone and the role of interleukin-1 (IL-1) and tumor necrosis factor (TNF) in this process, studies were carried out in a Macaca fascicularis primate model of experimental periodontitis. IL-1 and TNF activity was inhibited by local application of soluble receptors to IL-1 and TNF by injection into interdental papillae. The results indicate that following induction of experimental periodontitis, the front of inflammatory cells progresses toward alveolar bone and is associated with osteoclast formation. These processes are inhibited by blockers to IL-1 and TNF. These studies suggest that the conversion from gingivitis to periodontitis is directly associated with the movement of an inflammatory infiltrate toward alveolar bone, and that this activity is at least partially dependent upon IL-1 and/ or TNF.

IL-1 and TNF Antagonists Inhibit the Inflammatory Response and Bone Loss in Experimental Periodontitis

Periodontal disease is the most frequent cause of tooth loss in humans and is the most prevalent disease associated with bone loss, including osteoporosis. Periodontal destruction is initiated by bacteria that colonize the tooth surface, leading to inflammation and bone resorption. To assess the roles of IL-1 and TNF in this process, studies were conducted in a Macaca fascicularis primate model of experimental periodontitis. Function-blocking soluble receptors to IL-1 and TNF were applied by local injection to sites with induced periodontal destruction and compared with similar sites injected with vehicle alone. The results indicate that injection of soluble receptors to IL-1 and TNF inhibited by approximately 80% the recruitment of inflammatory cells in close proximity to bone. The formation of osteoclasts was reduced by 67% at the experimental sites compared with that at the control sites, and the amount of bone loss was reduced by 60%. All results were statistically significant (p &lt; 0.01). These findings indicate that a significant component of the pathologic process of periodontitis is due to IL-1/TNF activity, since inhibiting IL-1/TNF reduces both inflammatory cell recruitment and bone loss. The data also suggest that inflammation associated with gingivitis is actively protective, since blocking further up-regulation of the host response with IL-1/TNF inhibitors does not cause periodontal damage. Furthermore, these results coupled with recent evidence that IL-1 and TNF participate in endocrine-associated osteoporosis suggest that multiple pathologies involving excessive loss of bone may operate through a common mechanism involving IL-1 and/or TNF.

Receptor cloning and heterologous expression--towards a new tool for drug discovery

The explosion in the number of cloned receptors presents the pharmaceutical industry with challenges to discover new drugs targeting those receptors; to find more-selective drugs for all novel receptor subtypes; and to learn more about the function of the receptors in order to discern the conditions where such drugs may be applied usefully as therapeutics. At the same time, receptor cloning affords an unprecedented opportunity to address these challenges: heterologously expressed recombinant human receptors can be used for drug screening and - through an improved understanding of structure-function relationship - possibly for drug design, while the receptor clones permit mobilization of the full power of molecular biology to elucidate the function of the receptors in health and disease.

Pharmacokinetic parameters and biodistribution of soluble cytokine receptors

The potential use of soluble cytokine receptors as therapeutics in disease states when excessive or prolonged cytokine expression leads to pathogenesis is just beginning (Van Brunt, 1989). The inhibitory effects of soluble receptors have been found to be highly potent and specific for their respective cytokines (Maliszewski and Fanslow, 1990; Maliszewski et al., 1990). Recent in vivo data have shown that exogenously administered soluble receptors can function as cytokine antagonists and suppress autoimmune inflammatory responses (Jacobs et al., 1991a), allograft rejection, and alloreactivity (Fanslow et al., 1990b). The proposed frequency of administration and dosage of a therapeutic agent is dependent on the half-life of the agent and the route of administration. The elimination or half-life of a drug usually depends on its physiochemical properties (molecular size, glycosylation, isoelectric point, and hydrophobic/hydrophilic properties) (DiPalma and DiGregorio, 1990; Katzung, 1984). The half-life will also depend on the mechanism of clearance for that specific receptor. Once pharmacokinetic data are available for soluble receptors, the therapeutic potential of these molecules can be better evaluated. Only limited pharmacokinetic data are currently available for soluble cytokine receptors (Jacobs et al., 1991b). For sIL-1R, the majority of an intravenously administered dose was cleared in the second elimination phase, with a reasonably long half-life (6.3 hr), such that the entire dose was not eliminated until 35 hr. If administration is by subcutaneous injection, the half-life was even more prolonged. One explanation for the prolonged half-life is the minimal distribution to liver and kidneys and thus low levels of clearance by these organs. In contrast, elimination of intravenously administered sIL-4R was relatively rapid, with a short half-life (2.3 hr). This appeared mainly due to liver distribution and clearance, which has been the highest observed for any soluble cytokine receptor. Administering sIL-4R by subcutaneous injection significantly prolonged the half-life. This was most likely due to delaying the rate of liver distribution by slowing the rate of sIL-4R absorption into the circulation. Thus, subcutaneous injection would be the recommended route of administration for this receptor. Construction of a larger dimeric sIL-4R fusion protein did not prolong the i.v. half-life compared to that of the monomer, as the sIL-4R fusion protein was distributed to, and was cleared by, the liver to a greater degree.(ABSTRACT TRUNCATED AT 400 WORDS)

Soluble interferon-alpha receptor molecules are present in body fluids

Soluble forms of the interferon-alpha receptor (sIFN-alpha R) were identified in human serum and urine by Western blotting with monoclonal antibodies (MAb) directed against IFN-alpha R, and by immunoprecipitation (Iptn) of a covalently cross-linked complex of IFN-alpha R and [125I]IFN-alpha with anti IFN-alpha MAb. Elevated levels of sIFN-alpha R were found in sera of hairy cell leukemia patients. The soluble receptor from serum migrated as a 55 kDa protein in SDS-PAGE, and, as expected, the cross-linked product migrated as a 75 kDa protein. The soluble receptor from urine was found to be a protein of mol. wt. 45 kDa and its cross-linked complex migrated as a 65 kDa protein. The calculated mol. wt. of the entire extracellular domain of the IFN-alpha R prior to post-translational modifications is 47,000. Since there are 12 potential glycosylation points in this extracellular domain, its actual mol. wt. may be as high as 70,000 Da. It is therefore concluded that sIFN-alpha R molecules, corresponding to truncated forms of the extracellular domain of the cell surface IFN-alpha R, are present in human serum and in normal human urine.

Production and ligand-binding characteristics of the soluble form of murine erythropoietin receptor

A recombinant soluble form (sEPO-R) of erythropoietin (EPO) receptor (EPO-R) was produced by Chinese hamster ovary cells and isolated in high yield with the EPO-fixed gel. Ligand binding assays were done using three methods; precipitation of sEPO-R radiolabeled EPO complex and competition of sEPO-R for the binding of radiolabeled EPO with the cellular EPO-R. The results showed a Kd of 17 nM which was much lower than those for cellular EPO-R. One N-glycosylation site exists in sEPO-R but the glycosylation did not affect the binding affinity to EPO. A complex with a molecular size that corresponded to a 1:1 complex of EPO and sEPO-R was detected.

Therapeutic potential of cytokine manipulation

Interleukin 1 is just one of a large, growing, collection of potent cytokines that are produced by a variety of cells and have a myriad of overlapping activities. Many of these cytokines have important pathophysiological actions in diseases ranging from rheumatoid arthritis to AIDS. Selective inhibition of the synthesis or of the action of specific cytokines may have therapeutic benefit. In this review, Brian Henderson and Simon Blake discuss the ways in which cytokine function could be manipulated pharmacologically for therapeutic benefit.

Cytokines, receptors, and inhibitors

Cytokines are endogenous mediators in inflammatory and immunologic host defense reactions. In various diseases cytokines produced in excess cause systemic or local toxic effects. Cytokines therefore are tightly controlled by regulation of their biosynthesis and release and by counteracting mechanisms which limit their activities. Two new cytokine inhibitory mechanisms have recently been discovered. First, the generation of soluble receptors which compete with cellular receptors for cytokine binding has been recognized as a general phenomenon. Second, a receptor antagonist polypeptide binding to the receptor but not eliciting biological activity has been discovered in the IL-1 system. These polypeptides, when expressed in various recombinant forms, are not only research tools but may find also direct clinical use.

Interleukin-1 receptor antagonist: discovery, structure and properties

Interleukin-1 receptor antagonist (IL-1ra) is a recently-described member of the IL-1 family. This unique human protein has 30% amino acid sequence homology to IL-1 beta and binds to human types I and II IL-1 receptors without apparent cellular activation. IL-1ra blocks the in vitro stimulatory effects of IL-1 on thymocytes, fibroblasts, endothelial cells and bone cells. In addition, IL-1ra is a potent inhibitor of the inflammatory effects of IL-1 in vivo. IL-1ra represents the first naturally-occurring cytokine inhibitor and may be important in modulating IL-1 effects in both normal and abnormal physiology.