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Biomedical subjects

R Neta

Publications and source records attributed to R Neta.

At least 37 records · Page 2Linked to original sources
PubMed1993

Increased fibrinogen synthesis in mice during the acute phase response: co-operative interaction of interleukin 1, interleukin 6, and interleukin 1 receptor antagonist.

Interleukin 6 (IL-6) stimulates fibrinogen (Fg) gene expression both in vivo and in vitro; while interleukin 1 (IL-1) paradoxically stimulates in vivo, yet inhibits in vitro, Fg synthesis. The naturally occurring interleukin 1 receptor antagonist (IL-1ra) and passive immunization with anti-IL-6 antiserum were used to study the in vivo mechanism of action of IL-1 on Fg gene expression. Changes in plasma Fg and hepatic Fg mRNA concentrations were measured following administration of exogenous IL-1ra together with IL-6 or IL-1 to CD2F1 mice. Our results suggest that in vivo, IL-1 per se inhibits Fg production since when IL-1ra was co-administered with IL-6, greater concentrations of Fg were observed than when IL-6 was administered alone. The data suggest that IL-1 stimulates Fg production through intermediate production of IL-6, since stimulation was abrogated when either IL-1ra or anti-IL-6 antiserum was co-administered with IL-1. An in vivo role for IL-1ra in the stimulation of Fg by IL-1 was supported by the observation that within 1 h of IL-1 administration to mice, IL-1ra mRNA was detectable in liver. It appears that IL-1, an early mediator of inflammation, inhibits constitutive expression of Fg genes and stimulates the IL-1ra and IL-6 genes. The inhibitory effect of IL-1 is reversed by endogenous IL-1ra and by the direct stimulation of Fg gene expression by IL-6.

Acute-Phase Reaction↗
PubMed1993

The role of interleukin-6 in lipopolysaccharide-induced weight loss, hypoglycemia and fibrinogen production, in vivo.

It was recently shown that interleukin (IL)-6 is an important mediator involved in the Colon (C)-26 model of experimental cancer cachexia. In this study, we wished to determine whether IL-6 is also involved in several metabolic changes associated with lipopolysaccharide (LPS) challenge. Administration of a relatively high amount of LPS to mice induced a transient weight loss, hypoglycemia, hypertriglyceridemia and an increase in the hepatic acute phase reactant, fibrinogen. Pretreatment of mice with the rat anti-murine IL-6 antibody (20F3), but not with a control antibody, resulted in a significant improvement of LPS-induced hypoglycemia and weight loss as well as a significant decrease of plasma fibrinogen. Anti-IL-6 antibody had no effect on LPS-induced hypertriglyceridemia. On the other hand, the pretreatment of mice with anti-murine TNF (TN3.19) antibody was able to completely inhibit elevation of triglycerides and modestly improve LPS-induced weight loss although it had no effect on hypoglycemia and fibrinogen production. Taken together, these results suggest that IL-6 plays a role in some of the metabolic changes associated with both an acute (i.e. LPS challenge) and chronic (C-26 cachexia) inflammatory conditions.

Analysis of Variance↗
PubMed1993

Synergistic roles of interleukin-6, interleukin-1, and tumor necrosis factor in the adrenocorticotropin response to bacterial lipopolysaccharide in vivo.

Administration of lipopolysaccharide (LPS) results in activation of the hypothalamic-pituitary-adrenal axis. LPS induces the release of a number of proinflammatory cytokines, i.e. interleukin-1 (IL-1), IL-6, and tumor necrosis factor (TNF), which activate the hypothalamic-pituitary-adrenal axis as well and may mediate the effects of LPS. Variations in the kinetics of appearance of IL-1, TNF, and IL-6 after LPS challenge suggested that these cytokines may play different roles at different times. To elucidate the mutual dependence and contribution of individual cytokines in the course of LPS-induced ACTH release, we used blocking antibodies to IL-6, TNF, and the IL-1 receptor. Our results demonstrate that anti-IL-6 antibody abrogated ACTH induction throughout the course of the response both 2 and 4 h after LPS challenge. In contrast, anti-IL-1 receptor and anti-TNF antibody, given individually, blocked ACTH production at 4 h, but not at 2 h. Only combined administration of these two antibodies diminished, but did not eliminate, ACTH release at 2 h. This is the first demonstration that all three inflammatory cytokines are obligatory for LPS-induced elevation of plasma ACTH. In addition, these results suggest that IL-1, IL-6, and TNF play different roles in LPS-induced ACTH release.

Adrenocorticotropic Hormone↗
PubMed1993

Hematopoietic growth factors and glucocorticoids synergize to mimic the effects of IL-1 on granulocyte differentiation and IL-1 receptor induction on bone marrow cells in vivo.

The mechanisms by which interleukin-1 (IL-1) stimulates hematopoiesis are not clear. We have previously shown that in vivo administration of IL-1 indirectly increases IL-1 receptor (IL-1R) expression on both immature and mature bone marrow (BM) cells, partly due to IL-1-induced hematopoietic growth factor (HGF) production. Because IL-1 also stimulates the hypothalamic pituitary-adrenal axis resulting in the production of glucocorticoids (GC), we assessed whether in vivo treatment with HGF and glucocorticoids upregulates IL-1R. Administration of IL-1 to adrenalectomized mice reduces by 53% IL-specific binding on light density bone marrow (LDBM) cells compared to sham-operated mice. The administration of dexamethasone (dex) alone induced only a slight increase in IL-1R expression but synergized with granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), IL-3 and IL-6 to upregulate IL-1R expression. Flow cytometry analysis using the RB6-8C5 antibody, which is differentially expressed on myeloid cells, indicated that combined G-CSF and dex treatment acts to promote increased numbers of differentiated myeloid progenitors in the bone marrow. Autoradiographic analysis confirmed that while G-CSF and dex increased IL-1R expression on all myeloid cells, it was particularly pronounced for myelocytes, promyelocytes and metamyelocytes. These results suggest that the ability of IL-1 to enhance granulocyte differentiation in vivo is partly due to its ability to induce a cascade of cytokines and steroids which in turn regulate IL-1 receptor expression.

Adrenal Cortex Hormones↗
PubMed1992

Role of interleukin 6 (IL-6) in protection from lethal irradiation and in endocrine responses to IL-1 and tumor necrosis factor.

Primary responsibility for the induction of various acute phase reactions has been ascribed to interleukin 1 (IL-1), tumor necrosis factor (TNF), or IL-6, suggesting that these cytokines may have many overlapping activities. Thus, it is difficult to identify the cytokine primarily responsible for a particular biologic effect, since IL-1 and TNF stimulate one another, and both IL-1 and TNF stimulate IL-6. In this work, the contribution of IL-6 in radioprotection, induction of adrenocorticotropic hormone (ACTH), and induction of hypoglycemia was assessed by blocking IL-6 activity. Administration of anti-IL-6 antibody to otherwise untreated mice greatly enhanced the incidence of radiation-induced mortality, indicating that like IL-1 and TNF, IL-6 also contributes to innate resistance to radiation. Anti-IL-6 antibody given to IL-1-treated or TNF-treated mice reduced survival from lethal irradiation, demonstrating that IL-6 is also an important mediator of both IL-1- and TNF-induced hemopoietic recovery. A similar IL-1/IL-6 interaction was observed in the case of ACTH induction. Anti-IL-6 antibody blocked the IL-1-induced increase in plasma ACTH, whereas recombinant IL-6 by itself did not induce such an increase. Anti-IL-6 antibody also mitigated TNF-induced hypoglycemia, but did not reverse IL-1-induced hypoglycemia. It is, therefore, likely that TNF and IL-1 differ in their mode of induction of hypoglycemia. Our results suggest that an interaction of IL-6 with IL-1 and TNF is a prerequisite for protection from radiation lethality, and its interaction with IL-1 for induction of ACTH.

Adrenocorticotropic Hormone↗
PubMed1992

Effects of interleukin-1 on the stress-responsive and -nonresponsive subtypes of corticotropin-releasing hormone neurosecretory axons.

Administration of interleukin-1 (IL-1) induces increases in plasma ACTH and glucocorticoids. Numerous experiments have implicated the hypothalamic CRH neurosecretory system in these responses, but have failed to provide evidence for involvement of the ACTH secretagogue vasopressin (VP). The rat CRH neurosecretory system contains two types of cells: VP expressing and VP deficient. Hence, the above findings suggested that IL-1 may selectively activate the VP-deficient subtype of CRH neurosecretory cells. In this study we employed postembedding electron microscopic immunocytochemistry to directly assay IL-1-induced depletion of secretory vesicles from identified VP-expressing and VP-deficient CRH neurosecretory axons. IL-1-induced depletion of secretory vesicles from these axons was correlated with increases in plasma ACTH and decreases in plasma PRL. No dose of IL-1 was found that could selectively activate one subtype of CRH neurosecretory axons; at doses of 0.67 microgram/100 g and above for both IL-1 alpha and IL-1 beta, equal depletion of vesicles from the two subtypes was observed. Similar results were previously found after the injection of bacterial lipopolysaccharide, which induces the release of IL-1 from macrophages. The findings unequivocally establish for the first time that IL-1 activates hypothalamic CRH neurosecretory cells in the absence of surgical stress, anesthesia, disruption of the infundibular area, or administration of toxic drugs. In addition, these data clearly demonstrate that IL-1 induces the release of VP from neurosecretory axons in the portal capillary zone of the external zone of the median eminence. Previous studies have shown that the VP-deficient subtype of CRH neurosecretory axons is not strongly activated by several types of stress; therefore, activation of the system by inflammatory mediators involves mechanisms different from those mediating the stress response.

Adrenocorticotropic Hormone↗
PubMed1992

Relationship of TNF to interleukins.

It is evident from this review that TNF exhibits complex interactions with other cytokines at the level of production and in its effects. Studies designed to determine the role of TNF in the animal models or cell culture system using pure recombinant molecules have revealed that TNF never operates by itself, but instead operates within a network of cytokines. First, the multitude of exogenous as well as endogenous signals, which induce TNF production, concomitantly also stimulate the production of a battery of other inflammatory cytokines: IL-1, IL-6, IL-8, multiple CSFs, IFN, and TGF-beta. Moreover, TNF itself stimulates the production of most of these cytokines. Thus even when pure recombinant TNF is used, it readily generates the production of other interactive cytokines. This apparent redundancy in the production of cytokines with overlapping effects presumably has protective advantage for the host. Furthermore, interaction of these cytokines is more economical and amplifies the responses to subtoxic doses of potentially harmful cytokines. Cytokine interaction may lead to either synergistic (as for many TNF-IL-1 interactions) or antagonistic effects (TNF and TGF-beta, for example). These may depend on (1) the modulation of receptor expression of one cytokine by another (IFN-gamma-enhancing receptor expression for TNF, and TGF-beta down-regulation of IL-1 receptors), (2) stabilization of the cytokine message by one another (induction of IL-6 by TNF or IL-1), (3) interactions at the level of signal transduction, (4) gene expression, or (5) at the posttranslational level. Thus the receptor repertoire, which is a function of the cell type and stage of development, actually determines the net effects of a particular combination of interactive cytokines. Clearly, the mechanisms of these interactions will need to be elucidated to better understand their biological function and to permit cytokines to be used clinically to the advantage of the host.

Animals↗
PubMed1991

In vivo interleukin-1 (IL-1) administration indirectly promotes type II IL-1 receptor expression on hematopoietic bone marrow cells: novel mechanism for the hematopoietic effects of IL-1.

Interleukin-1 (IL-1) has profound stimulatory effects on hematopoiesis but the mechanism(s) of action remain unknown. The direct action of IL-1 on hematopoietic progenitor cells requires the presence of a specific IL-1 receptor (IL-1R). In this report, we tested the effect of in vivo IL-1 treatment on the expression of IL-1R on bone marrow (BM) cells. Injection of mice with IL-1 results in a marked upregulation of IL-1R on light-density BM cells as on a subpopulation enriched for myeloid precursors. Pretreatment of mice with anti-type I IL-1R antibody (35F5), which has been shown to prevent the radioprotective effect of IL-1, also blocked IL-1-induced IL-1R expression on BM cells. This antibody did not directly bind and block IL-1 binding to the type II IL-1R expressed on hematopoietic cells, suggesting that IL-1R upregulation by IL-1 is indirect. It is therefore possible that IL-1 acts on type I IL-1R-expressing accessory cells such as stromal cells or T cells to induce production of hematopoietic growth factors (HGFs). In support of this, granulocyte colony-stimulating factor administration can induce the increase of IL-1R on BM cells. Thus, the increased expression of IL-1R on hematopoietic BM cells by IL-1 is indirect, probably mediated in part through endogenous HGF production. These results also suggest that the restorative hematopoietic effect of IL-1 occurs through both indirect and direct mechanisms.

Animals↗
PubMed1991

Role of cytokines (interleukin 1, tumor necrosis factor, and transforming growth factor beta) in natural and lipopolysaccharide-enhanced radioresistance.

Studies of radioresistance and radioprotection provide an excellent in vivo model for dissection of the pathophysiological role of cytokines. The availability of neutralizing antibodies to cytokines has made it possible to assess the contribution of cytokines to host defense and repair processes involved in radioresistance and radioprotection. Administration of anti-interleukin 1 receptor (IL-1R) antibody (35F5) or anti-tumor necrosis factor (TNF) antibody (TN3 19.12) reduced survival of irradiated CD2F1 mice. These results demonstrate conclusively that natural levels of IL-1 and TNF contribute to radioresistance of normal mice. Furthermore, the radioprotective effect of administered IL-1 was blocked not only with anti-IL-1R antibody but also with anti-TNF antibody. Similarly, the radioprotective effect of TNF was reduced with anti-IL-1R antibody. These data suggest that cooperative interaction of both cytokines is necessary to achieve successful radioprotection. Finally, when LPS was used as a radioprotector, the combined administration of anti-IL-1R and anti-TNF not only blocked the radioprotection with LPS, but actually revealed LPS to have a radiosensitizing effect. This effect may be due to induction of TGF-beta, since administration of this cytokine results in reduced survival of irradiated mice.

Animals↗
PubMed1991

An interleukin-1 receptor antagonist blocks lipopolysaccharide-induced colony-stimulating factor production and early endotoxin tolerance.

In this report, administration of a recombinant interleukin-1 receptor antagonist protein to mice was found to inhibit induction of colony-stimulating factor as well as induction of early endotoxin tolerance by lipopolysaccharide. These findings provide direct evidence that interleukin-1 is an intermediate in these two lipopolysaccharide-induced phenomena.

Animals↗
PubMed1991

Interleukin-1 and interleukin-6 act synergistically to stimulate the release of adrenocorticotropic hormone in vivo.

Interleukin-1 (IL-1) and interleukin-6 (IL-6) share a number of biological functions. Because IL-1 induces IL-6 in vivo, the extent to which IL-6 mediates the effects of IL-1 has come under investigation. The stimulation of the hypothalamic-pituitary-adrenal axis by IL-1 and IL-6 is a critical component of the inflammatory response. The present study was designed to compare the effects of recombinant human IL-1 alpha (rhIL-1 alpha) and recombinant human IL-6 (rhIL-6) administered in combination and alone on the release of adrenocorticotropic hormone (ACTH) in mice. We have demonstrated that the administration of rhIL-6 alone does not duplicate the stimulatory effect of rhIL-1 alpha on ACTH release. On the other hand, suboptimal amounts of rhIL-1 alpha and rhIL-6 synergize to induce an early (30-60 min) ACTH response and produce a later (2-3 h) response that is similar to the one observed after rhIL-1 alpha is administered alone. These results suggest that the 2-3 h response to rhIL-1 alpha may be dependent on synergy with the endogenous IL-6 it induces systemically and in the central nervous system (including the hypothalamus and the pituitary gland).

Adrenocorticotropic Hormone↗
PubMed1991

Radioprotection with cytokines--learning from nature to cope with radiation damage.

The quest for methods to protect cells from the damaging effects of ionizing radiation led to the observation that cytokines, endogenously produced hormone-like polypeptides, are radioprotective. Interleukin-1 and tumor necrosis factor-alpha, given before irradiation, can protect mice from doses of radiation that would be fatal to untreated animals. At lower doses of radiation, the hemopoietic growth factors, interleukin-1, interleukin-4, interleukin-6, tumor necrosis factor-alpha, interferon, and leukemia inhibitory factor can promote recovery when administered after irradiation. Exposure to ionizing radiation selectively induces expression of some cytokines. Recent work suggests that certain cytokines may initiate autocrine/paracrine regulated recovery and repair pathways. Thus, the radioprotective and therapeutic effects of supplementary pharmacological doses of cytokines may act by amplifying innate defenses to ionizing radiation.

Animals↗
PubMed1990

In vivo modulation with anti-interleukin-1 (IL-1) receptor (p80) antibody 35F5 of the response to IL-1. The relationship of radioprotection, colony-stimulating factor, and IL-6.

Interleukin-1 (IL-1) is radioprotective and induces both circulating colony-stimulating factor(s) (CSF) and IL-6 in mice. We evaluated the relationship among these three responses to IL-1 using anti-IL-1 receptor antibody 35F5. This antibody in vitro blocks responses of T cells and fibroblasts, but not of B cells or myeloid cell lines, to IL-1. Administration of 35F5 alone before irradiation reduced the number of surviving mice compared with those not treated with 35F5, demonstrating that endogenous IL-1 participates in the natural resistance to radiation. Thirty micrograms of 35F5 per mouse also reduced by 92% the survival of irradiated mice pretreated with 0.3 micrograms of IL-1. Similarly, 30 micrograms of 35F5 reduced by 96% to 98% the induction of IL-6 by IL-1. In contrast, 30 micrograms of 35F5 resulted in only moderate reduction of circulating CSF. Consequently, the level of circulating CSF after 35F5 treatment was still equivalent to levels of CSF that were induced by doses of IL-1 in the radioprotective range. Because treatment with 35F5 antibody resulted in the blocking of IL-1-reduced radioprotection, the above results suggest that circulating CSF, by itself, may not be sufficient for radioprotection. This conclusion supports our previous results which showed that granulocyte-macrophage CSF (GM-CSF) and G-CSF were radioprotective only when administered with suboptimal doses of IL-1.

Animals↗
PubMed1990

Evaluation of immunologic assays to determine the effects of differential housing on immune reactivity.

The mechanism is being investigated to determine specifically how an environmental variation such as differential housing can influence the multiple components of the host defense mechanism. Male C3H/HeJ mice were housed either one or five per cage. Cells and sera from these mice were analyzed and compared by several immunologic techniques to determine in which cells or tissues the effect of differential housing was most pronounced. The individually housed mice (a) had a greater capacity to phagocytose dead cells of Candida albicans. (b) had spleens that produced more macrophage colony stimulating factor (M-CSF). (c) were more responsive to M-CSF, (d) had peritoneal macrophages that released greater quantities of interleukin-1 in vitro into the surrounding medium and that had a greater capacity to migrate toward a chemotactic stimulus, and (e) had higher titers of IgM hemagglutination antibody to sheep erythrocytes. Differential housing of mice may therefore be a highly important modulator and indicator of the nature and extent of an animal's immunologic response to an environmental stimulus.

Animals↗
PubMed1990

Advances in radioprotection through the use of combined agent regimens.

The most effective radioprotective agents exhibit toxicities that can limit their usefulness. It may be possible to use combinations of agents with different radioprotective mechanisms of action at less toxic doses, or to reduce the toxicity of the major protective compound by adding another agent. With regard to the latter possibility, improved radioprotection and reduced lethal toxicity of the phosphorothioate WR-2721 was observed when it was administered in combination with metals (selenium, zinc or copper). The known mechanisms of action of potential radioprotective agents and varying effects of different doses and times of administration in relation to radiation exposure must be considered when using combined-agent regimens. A number of receptor-mediated protectors and other biological compounds, including endotoxin, eicosanoids and cytokines, have at least an additive effect when administered with thiol protectors. Eicosanoids and other bioactive lipids must be administered before radiation exposure, whereas some immunomodulators have activity when administered either before or after radiation exposure. For example, the cytokine interleukin-1 administered simultaneously with WR-2721 before irradiation or after irradiation enhances the radioprotective efficacy of WR-2721. The most effective single agents or combinations of protectors result in a decrement in locomotor activity, an index of behavioral toxicity. Recent evidence indicates that administration of the CNS stimulant caffeine mitigates the behavioral toxicity of an effective radioprotective dose of the phosphorothioate WR-3689 without altering its radioprotective efficacy. These examples indicate that the use of combinations of agents is a promising approach for maximizing radioprotection with minimal adverse effects.

Animals↗
PubMed1990

Radioprotection and therapy of radiation injury with cytokines.

Our results demonstrate that IL 1 promotes hematopoiesis in normal and radiation-compromised animals. IL 1 protected mice from lethal hematopoietic syndrome when given before irradiation. Given therapeutically after irradiation, IL 1 promoted recovery from radiation injury. Several activities of IL 1 may explain its bone marrow restorative properties. The induction with IL 1 of several hematopoietic growth factors (GM-CSF, G-CSF, M-CSF, IL 3, and IL 6) clearly contributes to the accelerated growth and differentiation of hematopoietic progenitor cells. The induction of scavenger proteins may reduce oxidative damage after irradiation. Our work raises a number of additional questions concerning the potential therapeutic utility of IL 1. The ability of IL 1 to promote engraftment of allogeneic bone marrow cells will require further study. The optimal dosage, schedule, and route for IL 1 induction of hematopoiesis will need to be established. The observed synergy of IL 1 with TNF, IL 6, or CSF's may be useful in reducing the requisite doses of cytokines from pharmacological to physiological levels, thus reducing toxic effects. The observation that the cyclooxygenase inhibitor, indomethacin, does not inhibit IL 1 radioprotection may allow us to combat some of the toxic manifestations of IL 1 and to preserve its beneficial actions. Clinical trials with IL 1 in patients, now in progress, should establish whether this cytokine may be useful in reversing the myelotoxic effects of radiotherapy and chemotherapy in humans.

Animals↗