Induction of circulating phospholipase A2 activity by intravenous infusion of endotoxin in patients with neoplasia

Calculating therapeutic indices and therapeutic advantages for endotoxins and monophosphoryl lipid A: an evaluation of data from the scientific literature

This review article addresses the question of whether or not monophosphoryl lipid A offers a therapeutic advantage over smaller doses of endotoxin. Biological data were collected from a literature review and these were used to calculate therapeutic indices for monophosphoryl lipid A and endotoxin. Subsequent calculations yielded results which showed that, in humans and in other animals, monophosphoryl lipid A did have a therapeutic advantage over smaller doses of endotoxin.

Changes in group II phospholipase A2 gene expression in rat heart during sepsis

BACKGROUND

This study was undertaken to investigate alterations of group II phospholipase A2 (PLA2) gene expression and its underlying mechanism in rat heart during different phases of sepsis.

MATERIALS AND METHODS

Sepsis was induced by cecal ligation and puncture (CLP). Experiments were divided into three groups, control, early sepsis, and late sepsis. Early and late sepsis refers to those animals sacrificed at 9 and 18 h, respectively, after CLP. PLA2 enzyme activity, group II PLA2 protein level, messenger RNA (mRNA) abundance, transcription rate, and half-life were measured.

RESULTS

PLA2 activity was decreased by 29% during early sepsis but it was increased by 49% during late sepsis. Group II PLA2 protein level was decreased by 27% during early sepsis but it was increased by 35.3% during late sepsis. Group II PLA2 mRNA was decreased by 21% during early sepsis but it was increased by 141% during late sepsis. The transcription rate of group II PLA2 mRNA was reduced by 25% during early sepsis but it was elevated by 67% during late sepsis. The half-life of group II PLA2 mRNA remained unaltered during early and late phases of sepsis.

CONCLUSIONS

These results demonstrate that PLA2 activity, group II PLA2 protein level, the mRNA abundance, and transcription rate were concurrently underexpressed during early sepsis, while they were overexpressed during late sepsis, with no change in the degradation of gene transcript. These data indicate that the biphasic changes in group II PLA2 gene expression are regulated transcriptionally during sepsis.

Dexamethasone modulates hypotension induced by opioids in anaesthetised rats

The effect of dexamethasone on hypotension induced by mu-, kappa- and delta-opioid receptor agonists was investigated in pentobarbital-anaesthetised rats. Morphine (nonselective opioid receptor agonist), DAGO (D-Ala2-N-methyl-[Phe4-Gly5-ol]enkephalin; mu-opioid receptor-selective agonist), U50-488H (trans(+/-)-3,4-dichloro-N-methyl-N-(2[1pyrrolidynyl]cyclohexyl)-benzeneacetamide; kappa-opioid receptor-selective agonist) and deltorphin II (delta-opioid receptor-selective agonist), given intravenously, 5 micromol/kg, induced hypotension in rats. This hypotension was characterised by a fall in mean arterial blood pressure in 1-2 min that recovered in 30 min for morphine and U50-488H and in 5 or 20 min for DAGO and deltorphin II, respectively. Dexamethasone per se at a dose of 7.5 micromol/kg, i.v. did not significantly modify the mean arterial blood pressure of animals. Dexamethasone administration 90 min, but not 30 or 60 min, before the opioid agonists injection, prevented the hypotension induced by morphine or U50-488H, but not that induced by DAGO or deltorphin II. Pretreatment with RU-38486 (mifepristone; 7.5 micromol/kg, i.v.), a glucocorticoid receptor antagonist, 15 min before the steroid, prevented dexamethasone inhibition of hypotension induced by morphine and U50-488H. Furthermore, pretreatment with cycloheximide, a protein synthesis inhibitor (3.5 micromol/kg, i.v.), was also able to abolish the effects of dexamethasone on morphine- and U50-488H-induced hypotension. Results of the present study indicate that dexamethasone inhibited kappa-opioid receptor-mediated hypotension in rats, indicating a further important functional interaction between corticosteroids and the opioid system at kappa receptors. The ability of cycloheximide and RU-38486 to block dexamethasone effects indicates that steroid interference with kappa-opioid receptor-mediated hypotension involves a protein synthesis-dependent mechanism via glucocorticoid receptors.

Serum phospholipases A2 in patients undergoing panproctocolectomy because of severe ulcerative colitis

A major role has been proposed for group II phospholipase A2 in the pathogenesis of local and generalised inflammatory reactions. Elevated catalytic activity and mass concentrations of this enzyme have been found in serum and tissue samples of the colon in patients with active ulcerative colitis. The cellular source(s) of group II phospholipase A2 in the blood circulation is (are) unknown. In the current prospective study, we investigated the mass concentration of group II phospholipase A2 and the catalytic activity concentration of phospholipase A2 in serial serum samples of 15 consecutive patients who underwent a standard panproctocolectomy operation for severe ulcerative colitis. Both the catalytic activity concentrations of phospholipase A2 and the mass concentrations of group II phospholipase A2 increased rapidly in serum samples to maximum values on the first postoperative day and then decreased (p = 0.002 and p < 0.001, respectively) in patients who recovered uneventfully. Three patients had postoperative complications that further increased the enzyme concentrations at the time of respective complications. The pattern of group II phospholipase A2 mass concentration profiles was similar to the profiles of C-reactive protein. The results show that the removal of the large bowel does not eliminate the potential to secrete group II phospholipase A2 into the blood circulation in these patients. Secretion of group II phospholipase A2 into the circulation after surgery seems to be a normal host response to a major abdominal operation and postoperative complications. Consequently, we conclude that the large bowel is not an important source of group II phospholipase A2 in sera of patients with ulcerative colitis. The results also support the assumptions that the catalytic activity of phospholipase A2 in serum is attributable to group II phospholipase A2 and that this enzyme is an acute phase protein.

Cytosolic phospholipase A2 and cyclooxygenase-2 mediate release and metabolism of arachidonic acid in tumor necrosis factor-alpha-primed cultured intestinal epithelial cells (INT 407)

BACKGROUND

We have recently reported that tumor necrosis factor-alpha (TNF-alpha), a pro-inflammatory cytokine that has been suggested to play a role in the pathogenesis of inflammatory bowel disease, potentiates phospholipase A2 (PLA2)-stimulated arachidonic acid (AA) release and prostaglandin E2 (PGE2) formation in cultured intestinal epithelial cells (INT 407). The aim of the present study was to investigate which particular isoforms of PLA2 and cyclooxygenase (COX) are involved in these processes.

METHODS

Cells were labeled with 14C-AA or 14C-oleic acid, and the amounts of released fatty acid and PGE2 were analyzed by thin-layer chromatography. mRNA was analyzed by reverse transcription and polymerase chain reaction.

RESULTS

The cells contained mainly mRNA for cytosolic PLA2 (cPLA2) and only trace amounts of mRNA for group I and II PLA2. TNF-alpha potentiated the release of 14C-AA but not of 14C-oleic acid. The TNF-alpha-potentiated PGE2 release was reduced after inhibition of cellular COX activity or mRNA synthesis. TNF-alpha increased the amounts of mRNA for COX-2 but not for COX-1.

CONCLUSIONS

The results point to the possibility that TNF-alpha may modulate the intestinal mucosal content of biologically active AA metabolites by priming cPLA2- and COX-2-mediated processes in the epithelial cells.

Prolonged expression of lipopolysaccharide (LPS)-induced inflammatory genes in whole blood requires continual exposure to LPS

Blood-borne lipopolysaccharide (LPS) is thought to be a major inducer of sepsis; however, it remains controversial whether an ongoing exposure to LPS is required to maintain the underlying systemic inflammatory response. To address this question, we have studied the expression of tumor necrosis factor alpha (TNF-alpha), interleukin 1-beta (IL-1 beta), and the procoagulant protein tissue factor induced by LPS ex vivo in whole human blood. The addition of a 1-ng/ml bolus of LPS to blood rapidly induced mRNA expression of all three genes. The mRNA levels peaked after 1 to 2 h, depending on the gene, and then declined to baseline after approximately 5 h. The decline in mRNA expression was not caused by a loss of responsiveness of the blood cells to LPS but rather correlated with the neutralization of LPS inflammatory activity by plasma components. Furthermore, administering a 1-ng/ml dose of LPS in six hourly aliquots of 167 pg/ml greatly prolonged the expression of mRNAs and induced a much greater release of TNF-alpha and IL-1 beta protein than did a single bolus. Dosing by repeated additions was more effective than a single bolus in inducing secretion of TNF-alpha and IL-1 beta at LPS levels of < or = 10 ng/ml, which corresponded to the LPS neutralization capacity of plasma. Finally, both mRNA expression and protein secretion induced by repeated administration of LPS were rapidly reversed by the addition of the LPS-neutralizing protein, bactericidal/permeability-increasing protein, even after several hours of stimulation. These results indicate that continuous or repeated exposure to LPS is required to maintain the expression of inflammatory genes and that the activated state is rapidly reversed with LPS neutralization.

Induction of cytosolic phospholipase A2 in human leukocytes by lipopolysaccharide

Stimulation of peripheral blood leukocytes with lipopolysaccharide results in the synthesis of inflammatory cytokines including interleukin-1 beta, interleukin-6, tumor necrosis factor-alpha and prostaglandin E2 correlating with an increase in phospholipase A2 activity. Mammalian cells contain several phospholipase A2 isoforms including the 14-kDa secretory isoform and the more recently described high-molecular-mass cytosolic isoform. It is commonly believed that during inflammatory responses secretory phospholipase A2 becomes activated. However, we could not detect secretory phospholipase A2 nor its corresponding mRNA after lipopolysaccharide-induced activation. By contrast, we found increased mRNA levels for cytosolic phospholipase A2 following activation of peripheral blood leukocytes when levels were compared to non-stimulated controls. Our results demonstrate that cytosolic phospholipase A2, rather than the secretory isoform may be the mediator of the lipopolysaccharide-induced inflammatory cascade in human peripheral blood leukocytes.

Immunohistologic detection of non-pancreatic phospholipase A2 (type II) in human placenta and its possible involvement in normal parturition at term

Placenta is one of the richest sources of non-pancreatic phospholipase A2 (npPLA2) (type II) in the human body, and the enzyme is the key enzyme releasing unsaturated fatty acids from membrane phospholipids. Prostaglandins (PGs) play a critical role in the initiation and progression of parturition. Cytokines are presumed to play a central role in the initiation of normal labor at term, and cytokines are also found to regulate both synthesis and secretion of npPLA2 enzyme. In an attempt to resolve the physiologic function of the npPLA2 enzyme in placental tissue, immunohistologic localization and enzymatic activity measurements of npPLA2 enzyme were performed. NpPLA2 protein was detected in vascular smooth muscle, endothelial cells and connective tissue cells in placenta and umbilical cord, and the protein was weakly stained in trophoblast cells in placenta. Enzymatic activity was not increased in sera from mother nor child compared to sera from healthy individuals, but the activity in amniotic fluid was considerably higher. Our findings support the candidacy for npPLA2 in enzymatic arachidonic acid release from foetal membranes.

Coley's toxins, tumor necrosis factor and cancer research: a historical perspective

As far back as the 1700s, it was recorded that certain infectious disease processes could exert a beneficial therapeutic effect upon malignancy. Most prominent among the numerous deliberate efforts made to take advantage of these observations was that of a pioneering New York surgeon, William B. Coley, active career 1891-1936. Using a bacterial vaccine to treat primarily inoperable sarcoma. Coley accomplished a cure rate of better than 10%. This review examines the history of these efforts and presents a discussion of their corresponding relevance to present day immunotherapy.

Phospholipase A2-induced hypotension in the rat and its pharmacological modulation

1. An increase in circulating levels of extracellular group II phospholipase A2 (PLA2) has been detected in patients with septic shock as well as in rats, rabbits and human volunteers following intravenous endotoxin administration. 2. Group II PLA2 from Naja mocambique mocambique (NajaPLA2) snake venom (1-10 micrograms i.v.) induced a dose-dependent hypotension and leucopenia in the rat similar to that induced by intravenous administration of endotoxin. 3. NajaPLA2 did not aggregate rat platelet, but did aggregate purified rat neutrophils in vitro. However intravenous PLA2 caused rat platelets to aggregate in vivo. 4. The hypotensive effect was reduced either by inactivating NajaPLA2 in vitro with para-bromophenacyl bromide or by infusing in vivo polyclonal rabbit antiPLA2 antisera. Neither the hypotension nor the leucopenia was affected by several agonists and inhibitors. 5. The leukotriene D4 antagonist L-649,923 produced a dose-related (5-20 mg/kg i.v.) inhibition of NajaPLA2-induced hypotension while the dual inhibitor of lipo- and cyclooxygenase BW755c (5-50 mg/kg i.v.) was ineffective. 6. In rats rendered leucopenic with methotrexate the L-649,923 was ineffective implying that the L-649,923 effect could be partially mediated through its action on neutrophils.