PubMed Health⌕ Search

Biomedical subjects

R Silverstein

Publications and source records attributed to R Silverstein.

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

Endogenous and exogenous glucocorticoids have different roles in modulating endotoxin lethality in D-galactosamine-sensitized mice.

Endotoxin sensitivity and dexamethasone protection have been assessed in mice that were adrenalectomized and also treated with D-galactosamine at the time of endotoxin challenge. Our data establish that adrenalectomy did not detectably alter the magnitude of the increased sensitivity induced by D-galactosamine alone. Furthermore, protection provided by acute exogenous glucocorticoid treatment was still demonstrable in these mice and was not influenced by chronic experimentally induced glucocorticoid deficiency. Our data confirm that the adrenalectomized mouse model of endotoxin lethality is characterized by increased sensitivity to endotoxin and establish that the magnitude of this sensitizing effect is more than 100-fold. We also show for the first time that adrenalectomy causes an appreciable kinetic shift in the endotoxic crisis and that dexamethasone, given at the time of endotoxin challenge, will significantly reverse the increased sensitivity to lethality. Our results indicate that the protective effects of corticosteroids may involve important chronic as well as acute responses. In particular, we conclude that endogenous glucocorticoid need not always increase host resistance to endotoxin, nor does such a circumstance eliminate the possibility for exogenous glucocorticoid-mediated protective effects.

Adrenalectomy↗
PubMed1993

An interleukin-6-induced acute-phase response does not confer protection against lipopolysaccharide lethality.

Lipopolysaccharide (LPS), a component of gram-negative bacterial outer cell walls, can stimulate lymphoreticular cells to produce cytokines such as tumor necrosis factor alpha (TNF-alpha), interleukin-1 (IL-1), and IL-6. One of these proinflammatory cytokines, IL-6, induces hepatic synthesis of a class of proteins termed acute-phase proteins. D-Galactosamine inhibits acute-phase protein synthesis and concurrently sensitizes mice to a lethal dose of LPS approximately 10,000-fold. From these observations, we hypothesized that the acute-phase response may serve as a defense mechanism for protection of the host against the deleterious effects of LPS. To test this hypothesis, murine recombinant IL-6 (mrIL-6) was used to induce an acute-phase response prior to a lethal LPS challenge in both D-galactosamine-treated and normal mice. Induction of the acute-phase response by mrIL-6 was quantitated by measuring the concentrations of fibrinogen and complement component C3, two well-characterized acute-phase proteins, in the circulation. The effect of acute-phase and normal serum on TNF-alpha release by peritoneal macrophages stimulated with LPS in vitro was also examined. The results of these studies confirmed the induction of the acute-phase response by mrIL-6, as reflected in an approximate doubling in circulating levels of fibrinogen and C3. However, when either D-galactosamine-sensitized or normal mice were challenged with a lethal dose of LPS at various times after mrIL-6 administration, the acute-phase response induced by mrIL-6 did not alter either cumulative lethality or the kinetics of lethality. Additionally, compared with normal serum, acute-phase serum did not affect TNF-alpha release by peritoneal macrophages following LPS-mediated stimulation in vitro. Collectively, these studies would not support a dominant role for an IL-6-mediated acute-phase response as contributing to the resistance of normal mice compared with D-galactosamine-sensitized mice in LPS-induced lethal toxicity.

Acute-Phase Reaction↗
PubMed1993

Natural adrenocorticosteroids do not restore resistance to endotoxin in the adrenalectomized mouse.

Chronic loss of adrenocorticosteroid activity by adrenalectomy (10 days) or acute inhibition of glucocorticoid receptor function by injection of an anti-progestin (RU-38486) increased sensitivity to lipopolysaccharide about 200-fold, compared to that of control animals. Daily subcutaneous injection of a mixture of the natural glucocorticoid corticosterone and the mineralocorticoid deoxycorticosterone did not restore resistance to the endotoxin. The largest dose of steroid, 400 micrograms corticosterone + 200 micrograms deoxycorticosterone, provided only partial protection against 20 micrograms LPS, which was 10% of the LD50 for animals with adrenals. The mechanisms involved in lack of effectiveness of natural corticosteroids will require further experimentation.

Adrenal Cortex Hormones↗
PubMed1992

The role of protected extracellular compartments in interactions between leukocytes, and platelets, and fibrin/fibrinogen matrices.

Polymorphonuclear leukocytes express multiple surface receptors that mediate their adhesion to extracellular matrices and to other cells. These receptors also play roles in cell migration and phagocytosis. We have studied the role of one class of polymorphonuclear leukocytes surface receptors, the beta 2 integrins, in the interactions of these cells with fibrinogen. We have found that the beta 2 integrins, CD11b/CD18 (complement receptor three) and CD11c/CD18 mediate attachment of polymorphonuclear leukocytes to fibrinogen-coated surfaces. Polymorphonuclear leukocytes must be stimulated with chemoattractants, such as fMLP, or with cytokines, such as tumor necrosis factor to bind to fibrinogen via these integrins. Moreover, each of these integrins interacts with a different segment of the fibrinogen molecule. PMN adherence to fibrinogen via CD11b/CD18 depends on the carboxy terminus of fibrinogen, whereas adherence via CD11c/CD18 depends on the amino terminus of fibrinogen's alpha-chain. One of the physiological consequences of these interactions is that polymorphonuclear leukocytes stimulated with either chemoattractants or TNF form protected compartments at their interface with fibrinogen-coated surfaces and that elastase released into these compartments is inaccessible to protease inhibitors present in the plasma. These protected compartments exclude plasma proteins of > 40,000 daltons such as alpha 1 anti-proteinase, thereby allowing polymorphonuclear leukocyte proteases to degrade matrix proteins within this compartment without interference by plasma anti-proteinases.

Animals↗
PubMed1992

Hydrazine sulfate protection against endotoxin lethality: analysis of effects on expression of hepatic cytokine genes and an acute-phase gene.

Hydrazine sulfate (HS) pretreatment protects mice against the lethal effects of bacterial endotoxin lipopolysaccharide (LPS) through mechanisms yet to be established. The liver was examined as a model organ to determine HS effects on (a) LPS activation of leukocyte (Kupffer cell) interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) genes and (b) subsequent cytokine-mediated induction of the acute-phase response as measured by hepatic metallothionein (MT) gene expression. The utility of this model was documented by in situ hybridization which showed that acute induction by LPS of the IL-1 beta gene occurred in cells found in liver sinusoids, consistent with Kupffer cells, whereas induction of the MT gene occurred in hepatocytes. The cell specific expression of these genes was further verified by Northern blot hybridization to LPS-treated liver RNA which showed that the LPS-mediated increase in hepatic cytokine mRNA levels, unlike that of MT, was not prevented by D-galactosamine (D-GalN) treatment. Northern blot hybridization established that HS pretreatment did not block the acute induction of hepatic cytokine mRNAs (IL-1 beta and TNF-alpha) by LPS nor did it induce these cytokine mRNAs in the absence of LPS. Northern blot hybridization further established that HS did not prevent LPS-mediated activation of hepatocyte MT gene expression. Thus, HS does not prevent LPS from activating liver leukocytes. These results also suggest that HS pretreatment neither prevents the general release of cytokines from LPS activated leukocytes nor the general induction of acute-phase protein gene expression in hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute-Phase Proteins↗
PubMed1991

Hydrazine sulfate protects D-galactosamine-sensitized mice against endotoxin and tumor necrosis factor/cachectin lethality: evidence of a role for the pituitary.

In previously published studies, we had demonstrated that hydrazine sulfate pretreatment protected mice against the lethal effects of endotoxin and that this protection was accompanied by a sustained increase in hepatic phosphoenolpyruvate carboxykinase activity (Silverstein, R., C.A. Christoffersen, and D.C. Morrison. 1989. Infect. Immun. 57:2072). The same hydrazine sulfate pretreatment has now been found to protect mice against endotoxin in the D-galactosamine model with an increase in the endotoxin LD50 of approximately four orders of magnitude. Elimination of the pretreatment period, or administration of an additional dose of D-galactosamine at the time of hydrazine sulfate pretreatment, renders the mice refractory to the protection. Given the sensitivity of phosphoenolpyruvate carboxykinase regulation to several hormones, we investigated the possibility that protection may have been hormone mediated. In addition to determining the effect of hydrazine sulfate on the plasma levels of phosphoenolpyruvate carboxykinase regulating hormones, we have investigated the effects of hydrazine sulfate on endotoxin lethality in mice whose capacity to respond hormonally to external stimuli has been compromised by hypophysectomy. Our results show a significant enhancement in circulating levels of plasma corticosterone 30 min after hydrazine sulfate injection. Moreover, hypophysectomy results in a marked increase in sensitivity of mice to endotoxin challenge as well as an abrogation of the protection against endotoxin lethality mediated by hydrazine sulfate. Although hydrazine sulfate protection distinguishes between sensitivity brought on, individually, by D-galactosamine and by hypophysectomy, mice sensitized by both hypophysectomy and D-galactosamine are not protected against endotoxin lethality by hydrazine sulfate. We conclude that hydrazine sulfate protection against endotoxin lethality is endocrine dependent, with the available evidence implicating a pituitary/adrenal axis, with glucocorticoid involvement. In as much as D-galactosamine is known to act directly in the liver in disrupting protein synthesis, it is proposed that events in the liver are critical to the hydrazine sulfate-mediated protection against endotoxin and are possibly the target of the endocrine involvement. Hydrazine sulfate pretreatment also protects D-galactosamine-sensitized mice against the lethal effects of injected tumor necrosis factor/cachectin.

Animals↗
PubMed1990

Monoclonal antibody to mouse lipopolysaccharide receptor protects mice against the lethal effects of endotoxin.

Specific endotoxic lipopolysaccharide (LPS) binding sites on the cell membranes of murine lymphocytes and macrophages that may serve as functional receptors for LPS have recently been identified using photoactivatable cross-linking LPS derivatives. A monoclonal antibody (Mab 5D3) with specificity for this 80-kDa protein has also been generated and characterized. The capacity of MAb 5D3 to protect mice against the lethal effects of endotoxin was investigated. Pretreatment of CF1 mice with as little as 15 micrograms of MAb 5D3 provided virtually complete protection against a dose of endotoxin 10-fold greater than that required to kill all mice in an untreated control group using the galactosamine sensitization model. Significant protection was also afforded normal mice given MAb 5D3 relative to saline. Several lines of evidence suggest that MAb 5D3-mediated protection is due to the agonist properties of this antibody rather than a receptor blockade mechanism.

Animals↗
PubMed1989

Modulation of endotoxin lethality in mice by hydrazine sulfate.

Although the precise mechanism of endotoxin lethality has yet to be defined, it is well recognized that the amount of hepatic phosphoenolpyruvate carboxykinase is reproducibly and significantly reduced after challenge with endotoxin. Hydrazine has been shown to be a specific inhibitor of gluconeogenesis, causing a metabolic crossover at the step catalyzed by phosphoenolpyruvate carboxykinase. More recently, it has also been shown that hydrazine sulfate may be of potential therapeutic value against cancer cachexia. The experiments described in this paper demonstrate that treatment of CF1 mice with hydrazine sulfate 5 h prior to challenge with endotoxin from Salmonella enteritidis significantly improved survival. Furthermore, such treatment counteracted the drop in hepatic phosphoenolpyruvate carboxykinase activity in isolated cytosol otherwise evident at 6 h and 12 h after endotoxin challenge. Despite this, there was no corresponding improvement in the plasma glucose, measured at 6, 12, and 24 h following endotoxin challenge. It is suggested that the endogenous response to the metabolic crossover initiated by hydrazine may contribute to the protection. The response to hydrazine sulfate has yet to be fully elaborated but does include the increase in phosphoenolpyruvate carboxykinase activity. In contrast with the protection seen upon hydrazine sulfate pretreatment, injecting a corresponding dose of hydrazine sulfate after the endotoxin resulted in more fatalities.

Animals↗
PubMed1983

Postnatal synaptic development of the rat.

Presynaptic boutons of the dorsomedial region of the nucleus tractus solitarius (NTS) were studied during the first 30 days of postnatal development of the rat. Electron micrographs were analyzed by conventional and stereological techniques to determine the area and volumetric density and fraction, and the number per linear length on both the dendrites and cell bodies. The numerical density and volumetric fraction of boutons in the NTS increased rapidly within the first 10 postnatal days. The number of boutons per area and volume remained stable between 10 and 30 days. Twice as many boutons synapsed on the larger dendrites than the cell bodies during the first 10 days, and then increased to 4 times the number of synapses per linear length on the cell body after the tenth postnatal day. The rapid synaptic development and shift in shift in sites of synaptic contact on neurons of the NTS suggest synaptic contacts rapidly change during early postnatal development.

Animals↗
PubMed1980

Inactivation and modification of phosphoenolpyruvate carboxykinase differentially labeled with bromopyruvate.

Phosphoenolpyruvate carboxylkinase (GTP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32) is inactivated by bromopyruvate with specific substrate protection against the inactivation. Despite the fact that the enzyme also is known to possess oxalacetate decarboxylase activity, the modification does not appear to be directed toward a pyruvate or enolpyruvate binding site, as evident from the kinetics of the inactivation and from protection studies. Thus, the reactivity of bromopyruvate is different than toward several other enzymes where pyruvate is a substrate or product. Acetopyruvate and oxalate inhibit carboxykinase activity, but neither of these compounds, nor pyruvate, protects against the inactivation. Using differentially labeled enzyme, it was shown that modification of one sulfhydryl is sufficient to cause loss of both catalytic activities. Protection by inosine nucleotides was found to be similar in each instance. It would appear that a common sulfhydryl is critical to both carboxykinase and oxalacetate decarboxylase activities, and that each utilizes the same nucleotide binding site, despite the known different roles of the nucleotide in each reaction.

Animals↗
PubMed1980

Evidence for an essential hydrophobic domain in the maintenance of phosphoenolpyruvate carboxykinase activity. Site-specific binding and inactivation by 1-anilinonaphthalene-8-sulfonate.

1-Anilinonaphthalene-8-sulfonate (ANS) binds to phosphoenolpyruvate carboxykinase with subsequent rapid inactivation. Kinetics are saturating, with an enzyme half-life of 0.29 min at 4 x 10(-4) M ANS. IDP, GDP, and phosphoenolpyruvate protect against the inactivation. The enzyme is not covalently modified and it retains an affinity for protecting substrates and substrate analogs, with the exception of oxalate. Binding of ANS occurs in a hydrophobic environment, as suggested by the changes in fluorescence emission, and is markedly pH-dependent, leading to more rapid inactivation at acid pH. Inactivation by ANS differs in this respect from inactivation by N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonate which affinity labels the enzyme (Silverstein, R., Rawitch, A.B., and Grainger, D.A. (1979) Biochem. Biophys. Res Commun. 87, 911-918). Though the mechanism by which ANS inactivates the enzyme is unclear, the effect is atypical in that ANS binding does not normally lead to irreversible inactivation.

Anilino Naphthalenesulfonates↗
PubMed1978

Iatrogenic arteriovenous fistula. An unusual complication of indwelling pericardial catheter and intrapericardial steroid instillation for the treatment of uremic pericarditis.

The drainage and instillation of poorly absorbable corticosteroids has recently been suggested as an laternative to the present modes of therapy for uremic pericarditis. One patient who underwent such a therapeutic approach subsequently had a left internal mammary artery to right internal mammary vein arteriovenous fistula develop. To our knowledge, this is the first report of the development of arteriovenous fistula after either pericardiocentesis or intrapericardial instillation of steroids.

Adult↗
PubMed1978

Purification of hepatic phosphoenolpyruvate carboxykinase by affinity and hydrophobic chromatography.

Phosphoenolpyruvate carboxykinase has been purified by a procedure involving chromatography on norleucine-Sepharose, using a decreasing (NH4)2 SO4-inorganic phosphate concentration gradient, followed by chromatography on GMP-Sepharose. The enzyme is eluted from the affinity column with 2.5 X 10(-5)m IDP. The same procedure is applicable to hog mitochondrial and cytosol enzymes yielding the enzyme as a single band on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The corresponding molecular weight is 65,000 for each enzyme. Discontinuous polyacrylamide gel electrophoresis of the mitochondrial enzyme gave two sharp bands that were found to contain carboxykinase activity upon assay of gel slices. Similar analysis of the cytosol enzyme showed a much different staining pattern and four regions of carboxykinase activity. Plots of relative mobility of the two mitochondrial bands vs. per cent polyacrylamide in the gels gave parallel lines, confirming that the two bands did not result from enzyme aggregation. Elution of the enzyme upon analytical Sephacryl S-200 chromatography did, however, produce some resolution of the two bands without change in specific activity. The purification procedure described above has been applied also to the human mitochondrial enzyme with similar results. The molecular weight, similarly is 68,000.

Animals↗