Evidence for a direct inhibitory effect of glucocorticoids on the activity of phospholipase A2 as a further possible mechanism of some actions of steroidal anti-inflammatory drugs

Haemostatic parameters in Cushing's syndrome

We have studied haemostatic parameters in 12 patients with Cushing's syndrome. Three patients had prolonged bleeding times, and in all seven patients whose bleeding times were measured 3-6 months after surgical treatment the postoperative bleeding times were shorter (mean 7.5 min) than the pretreatment times (mean 12.3 min). In ADP- or adrenaline-induced aggregation the second wave was lacking in six and the degree of aggregation was borderline or subnormal in five patients. One patient had, in addition, a severe defect in collagen-induced aggregation. However, thromboxane B2 production of the platelets from both endogenous and exogenous arachidonic acid was unaffected. Factor VIII:C, RAg and Rcof activities were all elevated, and in patients with severe disease F VIIIR:Ag and F VIII:Rcof activities were markedly more elevated than F VIII:C activity. The changes in both primary haemostasis and in factor VIII activities correlated clearly with the clinical severity of the disease.

Inhibition of serum phospholipase-A2 in acute pancreatitis by pharmacological agents in vitro

Phospholipase-A2 has been suggested as having a role in the pathophysiology of acute pancreatitis. The inhibition of phospholipase-A2 was studied in vitro using 17 pharmacological agents in the search for a specific therapy for acute pancreatitis. The inhibitory effect was tested using an isotopic assay system with 2-palmitoyl-(1-14C)-labelled dipalmitoyl phosphatidylcholine as a substrate and 10 microliters of serum from patients with acute necrotizing pancreatitis as an enzyme source. Among all agents tested, anti-inflammatory drugs inhibited enzyme activity most significantly: indomethacin (9.0 x 10(-3) mol l-1) decreased the phospholipase-A2 activity to one- tenth. The weak inhibitory effect could also be demonstrated using a lower concentration of 2 x 10(-5) mol l-1, which can be achieved after intravenous administration of 50 mg of this drug. The other drugs inhibited the enzyme activity at concentrations higher than those achieved after intravenous injections in clinical use. Diclofenac (3.1 x 10(-2) mol l-1) reduced the phospholipase-A2 activity by 93%, ketoprofen (2.0 x 10(-2) mol l-1) or chlorpromazine (1.4 x 10(-2) mol l-1) by 90%, tobramycin (1.7 x 10(-2) mol l-1) by 84%, doxycycline (9.0 x 10(-3) mol l-1) by 61%, dexamethasone (1.7 x 10(-3) mol l-1) by 62%, methylprednisolone (3.8 x 10(-2) mol l-1) by 50%, and pindolol (1.0 x 10(-4) mol l-1) by 59%. A weak inhibition of phospholipase-A2 activity was demonstrated by betamethasone, bupivacaine, digoxin, hydrocortisone, lidocaine, metoprolol, propranolol, and vancomycin. Indomethacin proved the most potent of the tested agents in inhibiting phospholipase-A2 activity in serum from patients with acute pancreatitis and should be further studied in vivo.

Effects of methylprednisolone on lesioned and uninjured mammalian spinal neurons: viability, ultrastructure, and network electrophysiology

An in vitro investigation was undertaken to provide information regarding the effectiveness of methylprednisolone sodium succinate (MPSS) as a treatment for the primary mechanical injury of spinal cord (SC) trauma. Exposure of uninjured mouse SC cells to MPSS for 24 h caused neuronal stress when the concentration exceeded 150 micrograms/mL; neuronal death occurred at concentrations above 600 micrograms/mL. The concentration range for MPSS protection of SC neurons subjected to a defined physical injury (laser microbeam transection of a primary dendrite 100 microns from the perikaryon) was very narrow: survival in the 30 micrograms/mL group differed significantly from the untreated control group (68.5% +/- 14.1 vs. 47.1% +/- 14.1), treatment with 20 or 60 micrograms/mL MPSS did not increase survival, and treatment with 100 micrograms/mL MPSS accelerated ultrastructural deterioration and increased the likelihood of death. Enhanced survival of lesioned neurons was observed when 30 micrograms/mL MPSS was applied within 15 min of dendrotomy but not when MPSS was administered 2 h after lesioning. Multimicroelectrode plate (MMEP) studies of SC network electrical activity indicated that MPSS associated readily with neuronal membranes. This finding was consistent with the hypothesis that MPSS may protect lesioned neurons by stabilizing damaged membranes, enhancing lesion resealing, and limiting the spread of ion-mediated damage. However, comparisons of neurite die-back 24 h after dendrotomy found no significant difference between MPSS-treated and control neurons. Application of 30 or 100 micrograms/mL MPSS increased the spontaneous burst activity of SC networks grown on MMEPs, however, there was no evidence that the increased excitability at these concentrations was the result of specific actions of MPSS on GABA or NMDA synapses.

Pretreatment with alpha tocopherol enhances neurologic recovery after experimental spinal cord compression injury

Lipid hydrolysis with subsequent production of eicosanoids and lipid peroxidation are two of the earliest potentially pathochemical events induced in spinal cord tissue by mechanical trauma. Although these membrane lipid disturbances are thought to contribute to the paralysis that occur subsequent to spinal cord injury, such a correlation has not been demonstrated directly. Consequently, the purpose of this study was to test the capacity of alpha tocopherol, the major lipid antioxidant in cellular membranes and a compound that limits the injury-induced lipid hydrolysis and peroxidation in spinal cord tissue, to promote functional recovery in a static loading model of spinal cord injury. After laminectomy, the L2 spinal cord of cats was compressed with 180 g for 5 min. For 5 days before injury and for 5 days postinjury, treated cats received orally 1000 IUD-alpha tocopherol acetate daily. Control cats were similarly injured but untreated. All cats were blindly evaluated weekly for 4 weeks for their neurologic recovery based on an 11 point behavioral scale that assessed walking, running, and stair climbing. By the second postinjury week, alpha tocopherol-pretreated cats demonstrated significantly better recovery than untreated controls. By 4 weeks, treated cats had recovered 72% of their preinjury function as compared with 20% for untreated controls, i.e., a 3.5-fold difference. These results strongly suggest that lipid peroxidation and/or hydrolysis is primarily involved in the genesis of posttraumatic paralysis and that alpha tocopherol exerts its protection of injured spinal cord tissue, at least in part, by its antioxidant and/or antilipolytic activity.

The relative resistance of lymphokine activated killer cells to suppression by prostaglandins and glucocorticoids

The possibility that lymphokine-activated killer (LAK) cells versus spontaneous natural killer (NK) cells show relative resistance to the suppressive effects of the immunoregulatory molecules prostaglandin E2 (PGE2) and dexamethasone (DMO) was investigated. LAK cells were produced in vitro by the incubation of human peripheral mononuclear cells (PBMC) for three days in the presence of interleukin-2 (IL-2). Cytotoxicity of NK and LAK cells were measured by conventional 4 hour Cr51 release assays using K562 and Daudi target cells. LAK cells were relatively resistant to suppression by PGE2. For example, NK cytotoxicity was significantly suppressed by 10(-6) M PGE2. In contrast, LAK cells required a 30 to 100 higher concentration of PGE2 according to the target used to achieve similar suppression. Likewise, a differential resistance to DMO was seen. NK cells were significantly suppressed by 10(-3) M DMO while a 1000 fold higher concentration was needed for similar suppression of LAK cytotoxicity. Overall, the results show that LAK cells are relatively resistant to immunoregulatory suppressive factors.

Potential therapeutic efficacy of inhibitors of human phospholipase A2 in septic shock

Soluble phospholipase A2 has been implicated in the pathogenesis of local and systemic inflammatory reactions. Elevated levels of circulating phospholipase A2 (PLA2) correlate with the severity of circulatory collapse and pulmonary dysfunction in gram-negative septic shock. Characterization of septic shock serum PLA2 revealed a calcium-dependent enzyme with absolute 2-acyl specificity with a pH optimum of 7.5. We tested a number of therapeutic agents for their ability to inhibit PLA2 from human septic shock serum. Chloroquine, chlorpromazine, dexamethasone base, dexamethasone sodium phosphate, indomethacin, lidocaine, oleic acid, palmitic acid, promethazine, trans-retinoic acid, rutin and dl-alpha-tocopherol were all studied over the range of 10(-2) to 10(-7) M. All agents, with the sole exception of dexamethasone base, inhibited PLA2 activity at concentrations greater than 10(-3) M. PLA2 inhibition by dexamethasone sodium phosphate was factitious, due to the formation of calcium-phosphate complexes. Of the 11 agents studied, chlorpromazine was the most effective, with an IC50 of 7.5 X 10(-5) M, a membrane concentration achievable within its therapeutic range. Inhibition was non-competitive with an apparent Ki of 5 nM. Since serum PLA2 levels correlate with mortality in both experimental endotoxemia and clinical gram-negative septic shock, and chlorpromazine was previously shown to improve survival in these conditions, we postulate that its therapeutic efficacy resides at least in part in its PLA2-inhibitory activity.

Partial purification and characterisation of two compounds from amniotic fluid which inhibit phospholipase activity in human endometrial cells

Two inhibitors of PGF synthesis in human endometrial cells were found in amniotic fluid from term non-labouring patients. Both inhibitors at 10(-9)M reduced the amount of arachidonic acid released from the cells but had no effect on PGF synthesis stimulated by arachidonic acid. The molecular weights were 150-165,000 and 70-80,000 daltons as estimated from gel filtration in two systems. Both compounds precipitated with ammonium sulfate, appeared thermostable and lost activity with trypsin digestion. Both inhibited phospholipase activity and had identical retention times with HPLC. We conclude that the compounds are novel endogenous proteins which inhibit endometrial cell phospholipase.

Lipid hydrolysis and peroxidation in injured spinal cord: partial protection with methylprednisolone or vitamin E and selenium

Compression trauma of the cat spinal cord induces a very rapid alteration in the lipid metabolism of cellular membranes, including lipid hydrolysis with release of fatty acids including arachidonate, production of biologically active eicosanoids, and loss of cholesterol. This disturbance of cellular membranes can directly damage cells and can lead to the secondary development of tissue ionic imbalance, ischemia, edema, and inflammation with neuronophagia. Pretreatment with either the synthetic glucocorticoid methylprednisolone sodium succinate (MPSS) or the antioxidants vitamin E and selenium (Se) completely prevented the loss of cholesterol and partially inhibited lipolysis and prostanoid production. Treatment with MPSS significantly reduced the postinjury tissue necrosis and paralysis. Preliminary evidence indicates that pretreatment with vitamin E and Se also protected against the effects of spinal cord injury (SCI). We speculate that the ability of these agents to preserve function after SCI may, in part, reside in their capacity to limit the trauma-induced changes in lipid metabolism.

Influence of glucocorticoids on histamine release and 45calcium uptake by isolated rat mast cells

Hydrocortisone and prednisolone inhibited the histamine release from isolated rat mast cells induced by antigen, the ionophore A23187, and compound 48/80 in the absence and in the presence of calcium. Hydrocortisone reduced the response to the different releasing agents by 50% in the concentration range 2-6 X 10(-4) M, whereas prednisolone was about 1.5 times more potent. The inhibitory effect of hydrocortisone had a rapid onset of action and maximal inhibition was observed after preincubation for 20 minutes. The effect of hydrocortisone was reversed by including 2 mM glucose in the medium. The reversal was only partial with antigen and the ionophore A23187, indicating a greater energy requirement of these releasing agents compared with compound 48/80. The inhibition of the histamine release was accompanied by a concentration-related inhibition of the 45Ca uptake, except with the ionophore. The inhibition of the 45Ca uptake was also reversed by glucose, but differences were noted concerning the influence of preincubation time. The observations are explained by an association of 45Ca to cellular material, e.g. granules, secondary to the release process. The effects of hydrocortisone and prednisolone were qualitatively identical and were not observed with estriol. The glucocorticoid inhibition of histamine release does not seem to be caused by effects on phospholipase activity or cyclic AMP metabolism. The present observations are fully consistent with an impaired mitochondrial function as the mechanism for the mast cell effects of the glucocorticoids.

Studies on the mechanism of human natural killer cell-mediated cytolysis. I. Modulation by dexamethasone and arachidonic acid

Natural killer (NK) cell-mediated cytotoxicity, as measured by the lysis of the human erythroleukemic cell line K562, is inhibited by the glucocorticosteroid dexamethasone (DEX). Kinetic analysis revealed that DEX inhibits an early event(s) in the lytic mechanism and that the inhibition is both transient and readily reversible if DEX is removed. The inhibition is not due to the production of a DEX-induced inhibitory protein or decreased target-cell binding. Attempts to counter the effects of DEX through the addition of inducers of NK activity were unsuccessful. Neither the calcium ionophore A23187 nor exogenous cyclic GMP was able to reverse the inhibition by DEX. The addition of arachidonic acid (AA), a pharmacologically active metabolite of phospholipase A-2 activation, was also unsuccessful in reversing the effects of DEX. In fact, AA itself inhibited NK activity in a dose-dependent fashion. This inhibition was not due to reduced target binding and was observed even in the presence of indomethacin. It is concluded that DEX blocks an early membrane-signaling event necessary to activate the lytic mechanism and that inhibition was not through some alternative mechanism. Inhibition of NK activity by arachidonic acid is not yet understood but most likely is not a result of enhanced prostaglandin synthesis. Hence, the study of DEX and AA inhibition provides a new approach to unravel some of the intricacies surrounding NK-mediated tumor target destruction.