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Pompeo A, Baldassare M, Luini A, Buccione R. Cyclosporin A, but not FK506, increases arachidonic acid release and inhibits proliferation of pituitary corticotrope tumor cells. Life Sci 1999; 64:837-46. [PMID: 10096434 DOI: 10.1016/s0024-3205(99)00005-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The selective immunosuppressants cyclosporin A (CsA) and tacrolimus (FK506) are used in the prevention of allogenic transplant rejection and in the therapy of chronic autoimmune inflammatory pathologies. Chronic treatment with CsA leads to secondary functional and trophic alterations of multiple organs and cell systems among which endocrine ones, through insofar uncharacterized mechanisms. With the recent use of FK506 there have been reports of an improved therapeutic efficacy and a reduction of side-effects, as compared to CsA. An intriguing hypothesis is that toxic damage could be due to a systemic CsA activation of arachidonic acid (AA) metabolism, through pathways as yet only partially characterized. The side-effects of both drugs have been poorly studied on cells from tissues other than blood or kidney. We have thus proceeded to study their action on AA release in corticotropic AtT-20/D16-16 cells. The results obtained are as follows: 1) during incubation times > or =12 h, basal AA release is increased by CsA, but not FK506; the acute effect (10 min) of melittin, a PLA2 activator, is significantly potentiated starting from a 30 min pretreatment with CsA but not FK506; manoalide, a PLA2 inhibitor, antagonizes the melittin potentiation of AA release by CsA whereas the inhibition of the melittin stimulus by glucocorticoids is antagonized both by CsA and FK506. 2) during longer (>2 d) incubation times, cell growth is inhibited by CsA but not FK506. These results indicate a role for CsA, not apparent for FK506, in the activation of PLA2 and in the inhibition of cell growth. They also suggest that CsA does not have a direct (i.e. not mediated by the immune system) therapeutic effect in inflammatory processes.
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Affiliation(s)
- A Pompeo
- Department of Cell Biology and Oncology, Istituto di Ricerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud, S. Maria Imbaro (Chieti), Italy.
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2
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Evans RJ, Surprenant A. Effects of phospholipase A2 inhibitors on coupling of alpha 2-adrenoceptors to inwardly rectifying potassium currents in guinea-pig submucosal neurones. Br J Pharmacol 1993; 110:591-6. [PMID: 7902174 PMCID: PMC2175922 DOI: 10.1111/j.1476-5381.1993.tb13851.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
1. Noradrenaline hyperpolarizes guinea-pig submucosal neurones by opening inwardly rectifying potassium channels. Intracellular recordings were made from submucosal neurones and the possible involvement of the phospholipase A2 pathway in this response was examined. 2. The non-specific phospholipase A2 inhibitors, quinacrine (10 microM) and 4-bromophenacyl bromide (4-BPB, 10 microM) inhibited nerve-evoked inhibitory synaptic potentials (i.p.s.ps) and hyperpolarizations to somatostatin and UK 14304. Quinacrine and 4-BPB also blocked the inward rectification present in current-voltage curves in the absence of somatostatin or UK 14304. 3. The more selective phospholipase A2 inhibitor, cyclosporin A (10 microM) and the lipoxygenase and cyclo-oxygenase inhibitor, eicosatetraynoic acid (ETYA, 20 microM) and nordihydroguairetic acid (NDGA, 20 microM) did not alter i.p.s.ps or hyperpolarizations to UK 14304. 4. Exogenously applied arachidonic acid (1-300 microM) did not mimic the i.p.s.p. or the hyperpolarization to UK 14304. 5. We conclude that arachidonic acid or its eicosanoid metabolites produced by phospholipase A2 stimulation are unlikely to be involved in the receptor G-protein coupled activation of potassium currents in submucosal neurones. The inhibition of the noradrenaline-induced hyperpolarization by quinacrine and 4-BPB is most likely due primarily to blockade of the basal inwardly rectifying potassium conductance present in these neurones.
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Affiliation(s)
- R J Evans
- Vollum Institute, Oregon Health Sciences University, Portland 97201
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3
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Abstract
The binding of cyclosporine to human peripheral blood lymphocytes (PBLs) was studied by measuring the fluorescence emission spectrum and lifetime of the fluorescent and immunosuppressive cyclosporine derivative dansyl-cyclosporine (DCs). The emission maximum and fluorescence lifetime of DCs were characterized in several solvents. The fluorescence emission maximum and lifetime of DCs increased at a high dielectric constant. The fluorescence lifetime decay curve of DCs was a monoexponential function in all solvents tested. Fluorescence micrographs of lipid vesicles and erythrocytes labeled with DCs exhibit uniform staining patterns, whereas PBLs show heterogeneous DCs labeling. DCs exhibits a relatively low emission maximum (490 nm) in erythrocyte membranes. Such an emission maximum is characteristic of a hydrophobic environment. DCs in PBLs also has a low emission maximum (484 nm). The lifetime of DCs in PBLs required two exponential terms to properly fit the lifetime decay curve and could not be attributed to light scattering. One short component (4.7 +/- 1.0 ns) and a second long component (18.5 +/- 1.0 ns) were resolved from the DCs fluorescence decay curves. Time-resolved anisotropy of DCs in PBLs revealed that the labeled drug was present in an anisotropic environment, consistent with at least some DCs being bound to a membrane. These fluorescence studies suggest that DCs interacts with multiple and/or heterogeneous sites in peripheral blood lymphocytes.
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Affiliation(s)
- C D Niebylski
- Department of Biological Sciences, Wayne State University, Detroit, Michigan 48202
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4
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Cooper KD, Voorhees JJ, Fisher GJ, Chan LS, Gupta AK, Baadsgaard O. Effects of cyclosporine on immunologic mechanisms in psoriasis. J Am Acad Dermatol 1990; 23:1318-26; discussion 1326-8. [PMID: 2277141 DOI: 10.1016/0190-9622(90)70360-t] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A major impetus for further investigation of cellular immunologic mechanisms in psoriasis has been the discovery that cyclosporine, a potent immunosuppressive, is highly effective in the treatment of psoriasis. Cyclosporine has significant inhibitory effects on the ability of T cells to become activated. However, a direct activity of this drug on human keratinocyte signal transduction or growth has been difficult to demonstrate at relevant concentrations. Nevertheless, treatment of psoriasis or of 12-O-tetradecanoyl phorbol-13-acetate-treated murine skin with cyclosporine does reverse many epidermal abnormalities that are common to these two systems. This suggests that the compound exerts an indirect effect on epidermal keratinocytes in vivo, perhaps through immunocyte inhibition. During treatment of psoriasis patients, cyclosporine therapy resulted in selective changes in the numbers and functions of certain antigen-presenting cell subsets (which were distinct from Langerhans cells) and T-cell subsets. These changes were accompanied by indirect evidence of decreased T-cell lymphokine release. Lesional activity of cyclosporine-treated psoriasis patients was closely correlated with the degree of T-cell activation caused by antigen-presenting cells. Cyclosporine inhibition of lymphokine or cytokine release may result in decreased recruitment of non-Langerhans antigen-presenting cells into the epidermis and thus decreased immunoreactivity in the lesion.
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Affiliation(s)
- K D Cooper
- Department of Dermatology, University of Michigan Medical Center, Ann Arbor 48109
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5
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Yokoo M, Oka D, Nakagawa S. Effects of topical cyclosporin A on guinea-pig toxic contact dermatitis. Arch Dermatol Res 1990; 282:408-11. [PMID: 2260884 DOI: 10.1007/bf00372093] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
It is known that the topical application of cyclosporin A (CsA) has a significant suppressive effect on allergic contact dermatitis. In this study, we investigated the effect of topical CsA on toxic (non-allergic) contact dermatitis. Topical CsA significantly suppressed the toxic contact reaction to croton oil. This suppressive effect was short-lived and reversible. Significant inhibition of the reaction to croton oil persisted for 3 days after stopping the CsA. The toxic reaction was blocked when CsA was applied within 6 h of the croton oil application, but when application of CsA was delayed until 12 h after the oil application there was no significant suppressive effect. Topical administration of CsA could become a valuable tool for treating toxic and allergic contact dermatitis without producing the adverse reactions caused by systemic therapy.
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Affiliation(s)
- M Yokoo
- Department of Dermatology, Kawasaki Medical School, Japan
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6
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Cooper KD, Baadsgaard O, Ellis CN, Duell E, Voorhees JJ. Mechanisms of cyclosporine A inhibition of antigen-presenting activity in uninvolved and lesional psoriatic epidermis. J Invest Dermatol 1990; 94:649-56. [PMID: 2324521 DOI: 10.1111/1523-1747.ep12876222] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
To elucidate how cyclosporine A affects antigen-presenting cell subsets and their function in human skin, we studied patients with psoriasis undergoing a therapeutic trial of cyclosporine A. Immunologic parameters abnormal in psoriatic epidermis were evaluated before and early in the course of therapy. We quantitated function and numbers of skin biopsy-derived epidermal cells with potential antigen-presenting cell (APC) activity. The antigen-presenting capacity of epidermal cells from normal-appearing skin to activate allogeneic T cells was profoundly inhibited (81% decrease) 7 d after the onset of therapy (p less than 0.05). Thus, cyclosporine A therapy inhibited T-cell activation mediated by Langerhans cells in uninvolved skin. By contrast, in lesional skin epidermal allo-antigen presenting activity was only partially inhibited at this early time point (55 +/- 7% decrease) (p less than 0.01, n = 8). The percentage decrease in allo-antigen-presenting cell activity correlated with reduced clinical activity of the lesions, r = 0.84. In three patients also examined at 14 d, we found an additional 42 +/- 5% decrease between day 7 and 14. Decreased allo-antigen-presenting activity in lesional skin was not associated with a decrease in the number of CD1+ Langerhans cells or epidermal cell release of detectable amounts of cyclosporine A or other soluble factors that abrogate T-cell alloreactivity. The time course and degree of inhibition of antigen-presenting capacity within involved psoriatic skin correlated best with a significant (p less than 0.01) reduction in non-Langerhans cell DR+ leukocytes (from 3.0 +/- 1.2% to 1.0 +/- 0.6% at day 7) (r = 0.71). Cyclosporine A therapy was associated with a rapid and complete loss of HLe1-DR+ keratinocytes (94% decrease at 7 d) in lesional skin despite the skin still being quite involved with psoriasis at this point and antigen-presenting cell activity being only 60% reduced. In conclusion, cyclosporine A interferes with T-cell activation by human epidermis through at least two mechanisms: 1) in uninvolved skin, rapid inhibition of Langerhans cell-mediated activation of T cells, and 2) in lesional skin, delayed inhibition of antigen-presenting activity which appears to correlate with the time course and level of reductions in non-Langerhans cell DR+ leukocytes. The antigen-presenting activity of the latter cells appears to be cyclosporine A resistant. In psoriatic lesions, early and complete loss of DR expression on lesional keratinocytes during cyclosporine A therapy is likely due to decreased lesional T-cell lymphokine production critical for keratinocyte DR expression.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- K D Cooper
- Department of Dermatology, University of Michigan Medical School, Anne Arbor 48109-0530
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7
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Griese M, Schur N, Laryea MD, Bremer HJ, Reinhardt D, Biggemann B. Fatty acid composition of phospholipids of plasma and of mononuclear blood cells in children with allergic asthma and the influence of glucocorticoids. Eur J Pediatr 1990; 149:508-12. [PMID: 2347346 DOI: 10.1007/bf01959406] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Fatty acid (FA) composition of plasma phospholipids and phospholipids extracted from peripheral mononuclear white blood cells (MNC) was investigated in 11 allergic asthmatic children (age 8.9 +/- 4.6 years), in 10 age-matched non-allergic healthy controls and in 14 allergic and non-allergic children with an acute attack of asthma, who had received prednisolone medication for 2-4 days. In allergic asthmatics eicosapentaenoic acid (20:5n-3) was significantly elevated in both plasma and MNC. The relative amount of 20:5n-3 in MNC as well as in plasma correlated positively with increasing levels of total serum IgE (P less than 0.02). The pattern of the other FAs in plasma and of MNC phospholipids did not differ between allergic asthmatic and non-allergic control children. In children with an acute attack of asthma, who had been treated with glucocorticoids (2 mg prednisolone/kg body weight for 2-4 days), distinct changes of relative FA composition of phospholipids were restricted to plasma, where some very long chain FA (22:4n-6, 22:5n-6) were elevated. No significant changes in FA from MNC phospholipids could be observed after glucocorticoid treatment. These findings may indicate a possible role of 20:5n-3, the precursor of "group 3" eicosanoids, in allergic asthmatic children.
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Affiliation(s)
- M Griese
- Universitäts-Kinderklinik, Düsseldorf, Federal Republic of Germany
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Churchill PC, Rossi NF, Ellis VR, Churchill MC, McDonald FD. Cyclosporine A inhibits prostaglandin E2 release, and has no effect on renin secretion, from rat renal cortical slices. Life Sci 1990; 47:1579-86. [PMID: 2250570 DOI: 10.1016/0024-3205(90)90187-v] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
These experiments were designed to test the hypothesis that cyclosporine A (CSA) inhibits renin secretion and stimulates renal prostaglandin E2 (PGE2) release in vitro. In rat renal cortical slices incubated at 37 degrees C in a buffered and oxygenated physiological saline solution containing 4 mM KCl, CSA concentrations ranging from 1 to 30 microM had no significant effect on renin secretion. Furthermore, partial depolarization of the cells, produced by increasing extracellular KCl concentration to 20 mM, failed to reveal any latent inhibitory or stimulatory effects of CSA on renin secretion. On the other hand, PGE2 release was significantly inhibited by CSA over the same range of concentrations. This inhibitory effect might be explained by the previous findings of others, that CSA inhibits phospholipase A2 activity, thereby decreasing arachidonic acid production, the rate-limiting step in PG synthesis. In conclusion, CSA inhibits PGE2 release but fails to affect renin secretion in vitro. These results suggest that the occasional effects of CSA on renin secretion in intact animals must be attributable to indirect and/or chronic effects.
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Affiliation(s)
- P C Churchill
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201
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Sasaki T, Ikezawa Z, Nakajima H. Treatment of severe psoriasis with low dose cyclosporin A and the effect on the helper-suppressor T cell ratio in peripheral blood. J Dermatol 1988; 15:480-6. [PMID: 2977785 DOI: 10.1111/j.1346-8138.1988.tb01195.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Niwa Y, Miyachi Y, Sakane T, Kanoh T, Taniguchi S. Methyltransferase and phospholipase A2 activity in the cell membrane of neutrophils and lymphocytes from patients with Behçet's disease, systemic lupus erythematosus, and rheumatoid arthritis. Clin Chim Acta 1988; 174:1-14. [PMID: 3383437 DOI: 10.1016/0009-8981(88)90362-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Phospholipid methylation and phospholipase A2 activation in the membrane of neutrophils and lymphocytes, which participate in the induction of cell activation, were assessed in patients with Behçet's disease, systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). [3H-methyl] incorporation and phospholipase A2 activity of neutrophils from active cases of Behçet's disease and RA were significantly increased compared with normal controls. In lymphocytes from the patients with active Behçet's disease and RA, a significant increase in methyltransferase activity and a marked enhancement of phospholipase activity were found. A modest increase in these two membrane phospholipid enzyme activities was observed in lymphocytes of patients with active SLE. In addition, these enzyme activities were significantly enhanced in normal leukocytes preincubated with serum from patients with active SLE and malignant RA. The potentiated functions of neutrophils and lymphocyte abnormalities in the patients tested thus seem to be at least partly due to an increase in these enzymatic activities in the cell membrane.
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Affiliation(s)
- Y Niwa
- Department of Internal Medicine, Shimane Medical University, Izumo, Japan
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11
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12
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Espevik T, Figari IS, Shalaby MR, Lackides GA, Lewis GD, Shepard HM, Palladino MA. Inhibition of cytokine production by cyclosporin A and transforming growth factor beta. J Exp Med 1987; 166:571-6. [PMID: 3110354 PMCID: PMC2189589 DOI: 10.1084/jem.166.2.571] [Citation(s) in RCA: 350] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
We investigated the ability of cyclosporin A (CsA) and transforming growth factor beta (TGF-beta) to modulate the production of TNF-alpha and TNF-beta and IFN-gamma by unseparated, nonadherent, and adherent PBMC. Treatment of unseparated PBMC with CsA resulted in a significant dose-dependent inhibition of all three cytokines ranging from greater than 90% inhibition for IFN-gamma and TNF-beta, to approximately 70% for TNF-alpha. Pretreatment of unseparated or nonadherent PBMC with TGF-beta inhibited the production of IFN-gamma by 60-70%. However, the inhibition of TNF-alpha and TNF-beta production by these cells was only minimally affected, and at 0.1-1 ng/ml TGF-beta could enhance TNF-alpha production by unseparated PBMC. In contrast, pretreatment of adherent PBMC with TGF-beta inhibited the production of TNF-alpha by approximately 60%. TGF-beta also inhibited both TNF-alpha production and tumor cell cytotoxicity mediated by murine peritoneal-derived macrophages. These observations indicate that the biological effects of CsA and TGF-beta on immune functions are of a wider range than previously reported.
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Abstract
Administration of cyclosporine (CS) as an immunosuppressive agent in clinical transplantation is associated with multiple side effects including nephrotoxicity and hypertension. These two effects could be related in that the renal changes may be secondary to alterations in organ blood flow. The present studies investigate the ability of CS to augment contractile responsiveness in blood vessels from normotensive rats. Isometric force generation was measured in isolated tail arteries and portal veins. CS (8.3 X 10(-6)M) potentiated tail artery contractile responses to sympathetic nerve stimulation, exogenous norepinephrine, and increases in extracellular potassium concentration. Portal veins undergo spontaneous contractions which are related to the firing of calcium-driven action potentials in the smooth muscle cells. CS significantly increased the frequency of these spontaneous contractile events. These results suggest that components of CS toxicity may involve a direct action on vascular smooth muscle and/or on vascular adrenergic neurotransmission.
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Niwa Y, Somiya K, Miyachi Y, Kanoh T, Sakane T. Luminol-independent chemiluminescence by phagocytes is markedly enhanced by dexamethasone, not by other glucocorticosteroids. Inflammation 1987; 11:163-74. [PMID: 3034782 DOI: 10.1007/bf00916018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The effect of several glucocorticosteroids on the generation of reactive oxygen species (ROS) was examined. The ROS assessed were O-2, H2O2, OH., and chemiluminescence (CL) (determined in the presence or absence of luminol), generated by both opsonized zymosan-stimulated neutrophils or monocytes and by the xanthine-xanthine oxidase system. Except for luminol-independent CL, only high concentrations (10(-4) M) of steroids could decrease each ROS. In contrast, luminol-independent CL generation in the phagocyte system was increased in a dose-dependent manner by the addition of dexamethasone, but not by any other steroid. Further, in lymphocyte cultures stimulated with Con A for four days, luminol-independent CL generation was demonstrated and enhanced by the addition of dexamethasone, although CL generation was not detected in the absence of dexamethasone. These findings provide evidence that CL does not always represent light specific to ROS, and they suggest the possibility that dexamethasone induces emission of light at sites of inflammation.
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Mahlberg K, Uusitalo H, Uusitalo R, Palkama A, Tallberg T. Suppression of experimental autoimmune uveitis in guinea pigs by ethylenediamine tetra-acetic acid, corticosteroids, and cyclosporin. JOURNAL OF OCULAR PHARMACOLOGY 1987; 3:199-210. [PMID: 3141538 DOI: 10.1089/jop.1987.3.199] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
In the present study, footpad immunization using purified bovine retinal S-antigen mixed with complete Freund's adjuvant was used to induce experimental autoimmune uveitis (EAU) in guinea-pigs. The EAU-control group, receiving no treatment, was compared with test animals which received topically and systemically administered ethylenediamine tetra-acetic acid (EDTA) or subcutaneous and topical corticosteroid treatment, as well as a test group which received cyclosporin A subcutaneously. The severity of the uveal inflammation was clinically evaluated by slit lamp examination. The phospholipase A2 (PLA2) activity and the protein content of the aqueous humour as well as the myeloperoxidase (MPO) activity in the ciliary body were also determined. Serum antibodies to retinal S-antigen were followed using an immunoassay technique. Topical or subcutaneous EDTA significantly reduced the ocular inflammatory response to S-antigen induced autoimmune uveitis in the guinea-pigs. The best clinical suppression of EAU was obtained in the group treated subcutaneously with EDTA. Steroid treatment also suppressed the inflammatory processes in the eyes but was not as effective as EDTA or cyclosporine A. PLA2 activity in the aqueous humour and the MPO levels measured from iris-ciliary body homogenate were significantly lower in the groups treated subcutaneously with EDTA or cyclosporin A as compared with the untreated EAU-controls. The guinea-pigs treated subcutaneously with EDTA and cyclosporin A showed the lowest antiserum titres to retinal S-antigen. The prevention of PLA2 activity in aqueous humour after EDTA treatment correlated well with the milder inflammatory response in the eye. Based on the present study, it is therefore suggested that EDTA both locally and systematically reduces the S-antigen induced inflammatory response by decreasing the formation of inflammatory mediators derived from the arachidonic acid cascade.
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Affiliation(s)
- K Mahlberg
- Laboratory of Immunology, Helsinki University Central Hospital, Finland
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Niwa Y, Taniguchi S. Phospholipid base exchange in human leukocyte membranes: quantitation and correlation with other phospholipid biosynthetic pathways. Arch Biochem Biophys 1986; 250:345-57. [PMID: 3022648 DOI: 10.1016/0003-9861(86)90736-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The biosynthesis of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) by base-exchange reactions, and of PC and PE by the CDP pathways, was assessed in the membrane phospholipids of human leukocytes (neutrophils, lymphocytes, T lymphocytes, non-T lymphocytes, and monocytes). Of the three base-exchange activities, ethanolamine exchange was the highest and choline exchange the lowest in each leukocyte membrane. In the CDP pathways, ethanolaminephosphotransferase (EPT) and cholinephosphotransferase (CPT) had comparable activities. Among subpopulations of leukocytes, T lymphocytes showed the highest levels of each enzyme activity, and neutrophils showed the least. In contrast to the enzymes of the CDP pathways, each base-exchange activity was directly proportional to the Ca2+ concentration, but markedly inhibited by Mg2+. Despite this Ca2+ dependence, the base-exchange activities were increased in a dose-dependent manner by calmodulin antagonists and, except for ethanolamine exchange, inhibited by the addition of calmodulin; EPT and CPT activities were only slightly inhibited by calmodulin antagonists and were unaffected by calmodulin. PE formation in both neutrophil and lymphocyte base-exchange reactions was enhanced in a dose-dependent manner by the presence of low concentrations of bioactive stimulants (zymosan, 0.05-0.2 mg/ml; Con A, 0.5-2 micrograms/ml), while EPT and CPT activities were not increased by these cell stimulants. Taken together, our data suggest that base-exchange activity, the biological significance of which has been hitherto unclear, may be related to cell activation; in contrast, the CDP pathways appear primarily to involve the constitutive biosynthesis of phospholipids. Our data further suggest that ethanolamine required for base-exchange reactions is a precursor of PE, N-transmethylation of which can serve as a source of cell activation, leading to production of arachidonic through PC by mediation of phospholipase A2 activity.
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