PubMed Health⌕ Search

Biomedical subjects

N Qureshi

Publications and source records attributed to N Qureshi.

At least 19 recordsLinked to original sources
PubMed1992

Rhodopseudomonas sphaeroides lipid A derivatives block in vitro induction of tumor necrosis factor and endotoxin tolerance by smooth lipopolysaccharide and monophosphoryl lipid A.

Rhodopseudomonas (Rhodobacter) sphaeroides diphosphoryl lipid A is a relatively inert species of lipid A but has been shown to antagonize the effects of toxic lipopolysaccharide (LPS) both in vivo and in vitro. The antagonist and its monophosphoryl derivative were examined for the ability to block tumor necrosis factor synthesis and reverse tolerance induction in vitro in macrophage cultures stimulated with bioactive preparations of smooth LPS, rough LPS, diphosphoryl lipid A, and monophosphoryl lipid A. Inhibition of agonist activity and reversal of tolerance by these novel penta-acylated lipid A antagonists provides new insight into macrophage-LPS interactions.

Animals↗
PubMed1992

In vivo inhibition of lipopolysaccharide-induced lethality and tumor necrosis factor synthesis by Rhodobacter sphaeroides diphosphoryl lipid A is dependent on corticosterone induction.

Diphosphoryl lipid A from the lipopolysaccharide (LPS) of Rhodobacter sphaeroides (Rs-DPLA) has been demonstrated to block in mice and guinea pigs the increase in the serum tumor necrosis factor (TNF) response induced by highly purified deep rough chemotype LPS from Escherichia coli D31m4 (ReLPS). The present study was designed to determine the role of corticosterone induction by Rs-DPLA and its effect on TNF regulation and survival in lethal endotoxin shock models and to evaluate the ability of Rs-DPLA to induce endotoxin tolerance. Administration of a 100-fold excess of Rs-DPLA 1 h prior to ReLPS administration inhibited the characteristic peak in serum TNF levels induced by LPS. Inhibition was apparent in normal and D-galactosamine (GalN)-sensitized mice and occurred at the pretranslational level, as splenic TNF and interleukin-1 beta mRNAs were present in lower amounts in LPS-stimulated mice pretreated with Rs-DPLA. Consistent with its effects in reducing serum TNF levels, Rs-DPLA pretreatment protected GalN-sensitized mice from a lethal ReLPS challenge. In contrast, Rs-DPLA did not inhibit the increase in the serum TNF response or protect against a lethal ReLPS challenge in parallel experiments with adrenalectomized (Adrex) mice, for which the 50% lethal dose of ReLPS was comparable to that for GalN-sensitized mice. Furthermore, Rs-DPLA appeared to prime Adrex animals and increase the magnitude of the serum TNF response to a suboptimal LPS stimulus. Priming by Rs-DPLA, however, was not observed in normal or GalN-sensitized mice. Although Rs-DPLA by itself was nontoxic and unable to elevate serum TNF levels in any of the models investigated, it did induce a significant increase in the serum corticosterone response and was capable of inducing endotoxin tolerance in normal mice. The inability of Rs-DPLA to protect Adrex mice from a lethal ReLPS stimulus or to inhibit the increase in the serum TNF response suggests that the protective effect of Rs-DPLA in normal or GalN-sensitized animals occurs through corticosterone induction. These results support the concept that endogenous glucocorticoids can modulate the endotoxic effects of LPS by inhibiting the synthesis of inflammatory cytokines.

Animals↗
PubMed1992

Structural features that influence the ability of lipid A and its analogs to abolish expression of suppressor T cell activity.

Lipid A preparations derived from the lipopolysaccharides of several gram-negative bacteria, as well as chemically defined synthetic lipid A's and their analogs (both glucosamine mono- and disaccharides), were used to establish the chemical structures required for (i) abolishing the expression of suppressor T cell (Ts) function and (ii) inducing polyclonal activation of B cells. Salmonella minnesota R595 lipid A (diphosphoryl lipid A) possesses both of these activities. Decreasing the number of phosphate groups in lipid A from two to one (monophosphoryl lipid A) as well as decreasing the fatty acyl content, primarily by removing the residue at the 3 position, resulted in a progressive reduction in toxicity; however, these structural modifications did not influence its ability to abolish the expression of Ts function. Reducing the fatty acyl content from five to four (lipid A precursor IVA or Ia) eliminated the capacity to influence Ts function but not to induce polyclonal activation of B cells. None of the monosaccharide analogs of lipid A examined influenced the expression of Ts activity, although some were able to activate B cells polyclonally. Thus, in order to be able to abolish the expression of Ts function, lipid A (i) must be a glucosamine disaccharide, (ii) may have either one or two phosphate groups, and (iii) must have at least five fatty acyl groups. Also, the chain length of the nonhydroxylated fatty acid, as well as the location of acyloxyacyl groups (2' versus 3' position), may play an important role. These findings indicate that the chemical structures responsible for the toxicity of lipid A differ from those that influence its capacity to abolish the expression of Ts function and to induce polyclonal activation of B cells.

Animals↗
PubMed1991

Lipopolysaccharide-induced stimulation of CD11b/CD18 expression on neutrophils. Evidence of specific receptor-based response and inhibition by lipid A-based antagonists.

Gram-negative bacterial septicemia is a common clinical syndrome resulting, in part, from the activation of phagocytic leukocytes by LPS. By using flow cytometry, we have characterized LPS-induced expression of the beta 2 integrin CD11b/CD18. After exposure to Salmonella minnesota R595 LPS, expression of neutrophil CD11b/CD18 is rapidly upregulated, beginning within 5 min and achieving a peak fluorescence (typically two- to threefold over base line) by 30 min. The increase in CD11b/CD18 expression was similar in kinetics and magnitude to that produced by FMLP, PMA, and human rTNF-alpha. Concentrations of LPS necessary to stimulate a response were as low as 1 ng/ml of R595 LPS; a maximal response was observed between 30 and 100 ng/ml. The upregulation of CD11b/CD18 due to LPS was not interrupted by protein synthesis inhibitors. A group of glucosamine disaccharide lipid A-like molecules: Rhodobacter sphaeroides lipid A, lipid IVA, KDO2IVA, and deacylated LPS were able to block the stimulatory effect of LPS. This inhibition was specific for the actions of LPS as stimulation of polymorphonuclear leukocytes (PMN) by FMLP, human rTNF alpha, PMA, and rewarming were not altered by the disaccharide inhibitors. PMN which were exposed to the specific disaccharide LPS antagonists and then washed, were refractory to stimulation by LPS. The monosaccharide lipid A precursor lipid X also blocked stimulation of neutrophils by LPS, although with a 100-fold reduction in potency. Unlike the disaccharide inhibitors, PMN exposed to lipid X were still responsive to LPS stimulation after washing. The PMN response to LPS was less sensitive in the absence of serum, although upregulation of CD11b/CD18 could still be seen using higher concentrations of LPS. Monoclonal antibody directed against CD14 (clone 3C10), also specifically inhibited LPS induced PMN CD11b/CD18 expression both in the presence and absence of serum. These findings support the hypothesis that LPS stimulates neutrophils by interacting with specific cellular receptors.

Antigens, CD↗
PubMed1991

Lipid A-like molecules that antagonize the effects of endotoxins on human monocytes.

Lipopolysaccharide (LPS) endotoxin is implicated as the bacterial product responsible for the clinical syndrome of Gram-negative septicemia. Although the lipid A domain of LPS appears to be responsible for the toxicity of endotoxin, lipid A from the photosynthetic bacterium Rhodobacter sphaeroides (RSLA) and a disaccharide precursor of lipid A from enteric bacteria, termed lipid IVA, have little activity on human cells. Using the human promonomyelocytic cell line THP-1 and human monocytic cells, we now show that both lipid IVA and RSLA are antagonists of LPS. Complete, apparently competitive, inhibition of LPS activity is possible at a 10-100-fold excess of antagonist, as judged by measuring the release of cytokines and prostaglandin E2. Both antagonists prevent monocyte stimulation by endotoxin extracted from a variety of Gram-negative bacteria. Cells pretreated with either inhibitor and subsequently washed still show attenuated responses to LPS. Stimulation of monocytes by whole Gram-negative bacteria is also antagonized in a dose-dependent manner. Lipid X has no inhibitory effect in the same dose range as lipid IVA and RSLA. These findings rule out LPS sequestration as the explanation for the observed antagonism. Neither inhibitor alters monocyte stimulation by phorbol 12-myristate 13-acetate, Staphylococcus aureus, or purified protein derivative, demonstrating specificity for LPS. Although RSLA appears to inhibit LPS when tested with macrophages from both humans and mice, lipid IVA had the unique ability to act as an LPS antagonist with human-derived cells but to exhibit LPS-like effects with murine-derived cells. Like LPS, lipid IVA stimulated the release of both tumor necrosis factor alpha and arachidonic acid from murine-derived RAW 264.7 macrophage tumor cells. The range of concentrations necessary for lipid IVA to induce LPS-like effects in murine cells was similar to that necessary to antagonize the actions of LPS in human monocytes. The agonist activities of lipid IVA were completely inhibitable by RSLA. This unique species-dependent pharmacology observed with lipid IVA may reflect differences between human and murine LPS receptors. RSLA and lipid IVA may be useful in defining the role of LPS in Gram-negative bacterial infections and may prove to be prototypical therapeutic agents for the treatment of Gram-negative septicemia.

Animals↗
PubMed1991

Chemical reduction of 3-oxo and unsaturated groups in fatty acids of diphosphoryl lipid A from the lipopolysaccharide of Rhodopseudomonas sphaeroides. Comparison of biological properties before and after reduction.

Unlike the diphosphoryl lipid A (DPLA) derived from toxic lipopolysaccharide of Escherichia coli and Salmonella strains, the DPLA from nontoxic lipopolysaccharide of Rhodopseudomonas sphaeroides ATCC 17023 is biologically inactive. This could be due to the presence of 3-oxotetradecanoic and delta 7-tetradecenoic acids. These two fatty acids in R. sphaeroides DPLA were catalytically reduced in platinum oxide/H2 to the 3-hydroxy and saturated fatty acids, respectively. The biologically active E. coli DPLA was also treated with platinum oxide/H2, but as expected, the reduction step did not change the structure. These two preparations were then compared with the untreated samples for biological activity in three select in vitro assays. Over a range of 0.01-100 ng/ml, both normal and reduced DPLA from R. sphaeroides were inactive in priming phorbol myristate acetate-stimulated superoxide anion release in human alveolar macrophages. Over a range of 10-10(3) ng/ml, both samples failed to induce tumor necrosis factor in the RAW 264.7 murine macrophage cell line. The reduced DPLA marginally activated 70Z/3 pre-B cells at concentrations of 0.1-30 micrograms/ml. In every case, both normal and platinum oxide/H2-treated E. coli DPLA were biologically active. These results indicate that the lack of biological activity of R. sphaeroides DPLA is not due to the presence of 3-oxo and unsaturated fatty acids, but rather to one or more of the following: (i) presence of only five fatty acyl groups (compared to six in active lipid A); (ii) presence of 3-hydroxydecanoic acids (rather than 3-hydroxytetradecanoic, in active lipid A); (iii) greater variation in size of the fatty acids.

Catalysis↗
PubMed1991

Lowering of serum cholesterol in hypercholesterolemic humans by tocotrienols (palmvitee).

A double-blind, crossover, 8-wk study was conducted to compare effects of the tocotrienol-enriched fraction of palm oil (200 mg palmvitee capsules/day) with those of 300 mg corn oil/d on serum lipids of hypercholesterolemic human subjects (serum cholesterol 6.21-8.02 mmol/L). Concentrations of serum total cholesterol (-15%), LDL cholesterol (-8%), Apo B (-10%), thromboxane (-25%), platelet factor 4 (-16%), and glucose (-12%) decreased significantly only in the 15 subjects given palmvitee during the initial 4 wk. The crossover confirmed these actions of palmvitee. There was a carry over effect of palmvitee. Serum cholesterol concentrations of seven hypercholesterolemic subjects (greater than 7.84 mmol/L) decreased 31% during a 4-wk period in which they were given 200 mg gamma-tocotrienol/d. This indicates that gamma-tocotrienol may be the most potent cholesterol inhibitor in palmvitee capsules. The results of this pilot study are very encouraging.

Adult↗
PubMed1991

Dietary tocotrienols reduce concentrations of plasma cholesterol, apolipoprotein B, thromboxane B2, and platelet factor 4 in pigs with inherited hyperlipidemias.

Normolipemic and genetically hypercholesterolemic pigs of defined lipoprotein genotype were fed a standard diet supplemented with 50 micrograms/g tocotrienol-rich fraction (TRF) isolated from palm oil. Hypercholesterolemic pigs fed the TRF supplement showed a 44% decrease in total serum cholesterol, a 60% decrease in low-density-lipoprotein (LDL)-cholesterol, and significant decreases in levels of apolipoprotein B (26%), thromboxane-B2 (41%), and platelet factor 4 (PF4; 29%). The declines in thromboxane B2 and PF4 suggest that TRF has a marked protective effect on the endothelium and platelet aggregation. The effect of the lipid-lowering diet persisted only in the hypercholesterolemic swine after 8 wk feeding of the control diet. These results support observations from previous studies on lowering plasma cholesterol in animals by tocotrienols, which are naturally occurring compounds in grain and palm oils and may have some effect on lowering plasma cholesterol in humans.

Animals↗
PubMed1991

Diphosphoryl lipid A derived from lipopolysaccharide (LPS) of Rhodopseudomonas sphaeroides inhibits activation of 70Z/3 cells by LPS.

Diphosphoryl lipid A derived from nontoxic lipopolysaccharide (LPS) of Rhodopseudomonas sphaeroides ATCC 17023 did not stimulate the murine pre-B cell line 70Z/3 to synthesize surface immunoglobulin or kappa mRNA. However, it effectively blocked Escherichia coli LPS-induced activation of 70Z/3 cells in a concentration-dependent manner. This inhibition was specific only to cells activated by LPS, since it did not inhibit activation of 70Z/3 cells by gamma interferon. Maximal inhibitory effect occurred when the antagonist was added within 2 h before adding the LPS. These results strongly suggested that R. sphaeroides diphosphoryl lipid A is competing with E. coli LPS for physiological lipid A receptors on the 70Z/3 cells.

Animals↗
PubMed1991

Diphosphoryl lipid A obtained from the nontoxic lipopolysaccharide of Rhodopseudomonas sphaeroides is an endotoxin antagonist in mice.

Diphosphoryl lipid A (DPLA) obtained from the nontoxic lipopolysaccharide (LPS) of Rhodopseudomonas sphaeroides ATCC 17023 did not induce interleukin-1 release by murine peritoneal macrophages. However, it blocked this induction by toxic deep-rough chemotype LPS (ReLPS) from Escherichia coli D31m4. Previously, we obtained similar results on the induction of tumor necrosis factor (TNF) by macrophages. These results showed that DPLA is able to block in vitro the induction of two important mediators of gram-negative bacterial sepsis. We then wanted to determine whether DPLA could also block the induction of TNF by LPS in animals. Mice were treated with 100 micrograms of R. sphaeroides DPLA and challenged 60 min later with 1.0 micrograms of ReLPS from E. coli. The serum TNF level was measured after 60 min. Treatment of mice with this DPLA blocked the rapid and transient rise of TNF caused by ReLPS. This result suggested that R. sphaeroides DPLA might be able to protect animals against endotoxin shock caused by gram-negative bacterial infection.

Animals↗
PubMed1990

Inactivation of suppressor T cell activity by the nontoxic lipopolysaccharide of Rhodopseudomonas sphaeroides.

Antibody responses of mice immunized with type III pneumococcal polysaccharide were examined with and without treatment with nontoxic lipopolysaccharide from Rhodopseudomonas sphaeroides (Rs-LPS). The results obtained were similar to those described previously for mice treated with monophosphoryl lipid A (MPL) except that lower amounts of Rs-LPS were needed. Both were without effect when given at the time of immunization with type III pneumococcal polysaccharide but elicited significant enhancement when given 2 to 3 days later. Such enhancement was T cell dependent and not due to polyclonal activation of immunoglobulin M synthesis by B cells. Treatment with either Rs-LPS or MPL abolished the expression but not induction of low-dose paralysis, a form of immunological unresponsiveness known to be mediated by suppressor T cells (Ts). The in vitro treatment of cell suspensions containing Ts with extremely small amounts of Rs-LPS or MPI completely eliminated the capacity of such cells to transfer suppression to other mice. These findings indicate that the immunomodulatory effects of both MPL and Rs-LPS are mainly the result of eliminating the inhibitors effects of Ts; this permits the positive effects of amplifier T cells to be more fully expressed, thereby resulting in an increased antibody response. The significance of these and other findings to the use of Rs-LPS as a pharmacotherapeutic agent for gram-negative bacterial sepsis is discussed.

Animals↗
PubMed1989

Diphosphoryl lipid A from Rhodopseudomonas sphaeroides ATCC 17023 blocks induction of cachectin in macrophages by lipopolysaccharide.

Purified diphosphoryl lipid A (DPLA) obtained from the nontoxic lipopolysaccharide of Rhodopseudomonas sphaeroides ATCC 17023 was shown to block the induction of cachectin (tumor necrosis factor) in the RAW 264.7 macrophage cell line by toxic deep-rough-chemotype lipopolysaccharide (ReLPS) of Escherichia coli in a concentration-dependent manner. The ReLPS-to-DPLA mass ratios of 1:10 and 1:100 (when 1.0 ng of ReLPS per ml was used) gave 55 and 95% inhibitions, respectively, of the induction of cachectin. Since the structure of the DPLA from R. sphaeroides is so similar to that of the lipid A moiety of the toxic ReLPS from E. coli, we suggest that this inhibition could have been due to competitive binding by DPLA to the active sites on the macrophage. This DPLA could become a useful reagent to study the nature of lipopolysaccharide/lipid A binding in macrophages and perhaps other responding cells.

Animals↗
PubMed1988

Complete structural determination of lipopolysaccharide obtained from deep rough mutant of Escherichia coli. Purification by high performance liquid chromatography and direct analysis by plasma desorption mass spectrometry.

Lipopolysaccharide (LPS) extracted from the deep rough mutant of Escherichia coli D31m4 was disaggregated with 0.1 M EDTA, pH 7.0, and fractionated on a diethylaminoethyl-cellulose column to yield the biphosphate form of LPS. After methylation, the derivative was purified by reverse-phase high performance liquid chromatography using a C18-bonded silica cartridge. A linear gradient of 50-100% isopropyl alcohol/water (93:7, v/v) in acetonitrile/water (93:7, v/v) was used over a period of 60 min. The derivatized LPS showed a single major peak by high performance liquid chromatography, and this hexamethyl hexaacyl LPS was recovered and subjected to chemical analysis, plasma desorption mass spectrometry, and nuclear magnetic resonance (NMR) spectroscopy. Chemical analysis of the purified hexamethyl LPS quantitated certain key chemical compositions. Plasma desorption mass spectrometry showed a molecular ion (M + CH2 + Na)+ at m/z 2360, which established the molecular formula and Mr to be C116H214N2O39P2 and 2323, respectively. Thus, it contained two each of glucosamine, 2-keto-3-deoxyoctonate, and phosphate; four beta-hydroxymyristates; one laurate; and one myristate. NMR spectroscopy confirmed the locations of the four ester-linked fatty acyl groups. Based on these results and the known structure of free lipid A, the complete structure of the deep-rough chemotype LPS from E. coli can now be presented with confidence. This is the first report of a successful purification to homogeneity and the characterization of the simplest of the LPS at the intact level. This study shows that the natural distribution of the lipid A moiety of LPS from E. coli D31m4 is hexaacyl/pentaacyl in a molar ratio of greater than 90:less than 10. Acid hydrolysis of LPS causes the formation of the lower homologues of the free lipid A.

Chemical Fractionation↗
PubMed1988

Location of fatty acids in lipid A obtained from lipopolysaccharide of Rhodopseudomonas sphaeroides ATCC 17023.

Monophosphoryl lipid A (MLA) obtained from the lipopolysaccharide of Rhodopseudomonas sphaeroides ATCC 17023 was initially purified by silicic acid column chromatography to yield a single major pentaacyl MLA fraction. This fraction was methylated and further purified by reverse-phase high performance liquid chromatography to yield three prominent peak fractions. Laser desorption mass spectrometry of these three fractions allowed us to complete the important structural analysis of lipid A from this source. Three structurally distinct forms of dimethyl MLA were identified where Mr = 1447, 1449, and 1451 atomic mass units. These forms differed only by the presence or absence of unsaturation and keto group in the fatty acids. We established that the acyloxyacyl group (either delta 7-tetradecenoyloxytetradecanoate or tetradecanoyloxytetradecanoate) and the 3-ketotetradecanoate or hydroxytetradecanoate occupied the 2'- and 2-positions of the glucosamine disaccharide, respectively. Analysis of several minor fractions suggests that there is considerable structural heterogeneity in the MLA. With this new knowledge, the study of the structure-to-function relationship of the reported lack of toxicity of lipopolysaccharide from R. sphaeroides can be completed.

Chemical Phenomena↗
PubMed1988

Stimulation of rabbit synoviocyte prostaglandin E2 synthesis by lipopolysaccharides and their subunit structures.

Lipopolysaccharides (LPS) induce synoviocyte activation and may lead to destruction of synovial joint tissues. We assessed the production of prostaglandin E2 (PGE2) as a measure of synoviocyte activation by LPS and their subunit structures. Diphosphoryl lipid A was the smallest portion of lipid A tested that stimulated PGE2 production. The polysaccharide fraction of LPS, containing the O antigen, was also active. Intraarticular injections of the polysaccharide resulted in a synovitis very similar to that found in association with the intact LPS molecule. These observations suggest that both parts of LPS might be involved in gram-negative, organism-associated synovitis.

Animals↗
PubMed1987

Substitution of phosphatidylserine by lipid A in the activation of purified rabbit brain protein kinase C.

Three lipid A derivatives (hexaacyl monophosphoryl lipid A, hexaacyl diphosphoryl lipid A, and disaccharide precursor IVA) were shown to activate protein kinase C from rabbit brain. These derivatives substituted for phosphatidylserine in a concentration-dependent manner and did not compete for binding of [3H]phorbol dibutyrate to its receptor site. Instead, phorbol dibutyrate binding was increased on raising the concentration of the derivatives in a similar manner to phosphatidylserine. The phorbol ester 12-0-tetra-decanol 13-acetate augmented the activation of protein kinase C by the lipid A derivatives.

Animals↗
PubMed1987

Structural determination of lipid A from gram negative bacteria using laser desorption mass spectrometry.

Laser desorption mass spectrometry has been employed for the structural determination of lipid A components derived from the lipopolysaccharides (LPS) of gram-negative bacteria. Mass spectra were obtained for methylated monophosphoryl lipid A from Neisseria gonorrhoeae and Rhodopseudomonas sphaeroides, for diphosphoryl lipid A from Escherichia coli and for the intact LPS from the Re Mutant of E. coli consisting of triphosphoryl lipid A and two KDO (2-keto-3-deoxyoctonate) units. Fragmentation of the phosphate (or pyrophosphate) on the reducing glucosamine is followed by fragmentation of acyl-linked fatty acids. Also observed are fragment ions which correspond to the distal portion of the molecule.

Escherichia coli↗