Leukotriene B4 is involved in hemodialysis-associated neutropenia

New and promising type of leukotriene B4 (LTB4) antagonists based on the 1,4-benzodioxine structure

New leukotriene B4 (LTB4) antagonists have been synthesized that can be considered as potential anti-inflammatory drugs. Structures containing the dioxygenated nucleus of 1,4-benzodioxine constitute a potential group of leukotriene B4 (LTB4) antagonists. The objective of this study was to access efficient and selective LTB4 antagonists as a way to elucidate the role of LTB4 in inflammatory processes and therefore allow the development of new types of structures based on 1,4-benzodioxine. Forty-one new 1,4-benzodioxine molecules substituted at different positions of the heterocyclic nucleus were synthesized to determine the minimum structural requirements by studying structure-activity relationships. Eighteen of them were tested in vitro and in vivo for their anti-inflammatory activity related to the antagonist character of LTB4. Pharmacological tests have shown satisfactory in vitro activity for compounds 24b, 24c and 24e with IC50's of 288, 439, 477 nM respectively. The results of the in vivo tests, carried out with the compound that presented greater activity in the in vitro tests 24b, have shown significant anti-inflammatory properties.

Cell cycle-dependent localization of the proteasome to chromatin

An integrative understanding of nuclear events including transcription in normal and cancer cells requires comprehensive and quantitative measurement of protein dynamics that underlie such events. However, the low abundance of most nuclear proteins hampers their detailed functional characterization. We have now comprehensively quantified the abundance of nuclear proteins with the use of proteomics approaches in both normal and transformed human diploid fibroblasts. We found that subunits of the 26S proteasome complex were markedly down-regulated in the nuclear fraction of the transformed cells compared with that of the wild-type cells. The intranuclear proteasome abundance appeared to be inversely related to the rate of cell cycle progression, with restraint of the cell cycle being associated with an increase in the amount of proteasome subunits in the nucleus, suggesting that the nuclear proteasome content is dependent on the cell cycle. Furthermore, chromatin enrichment for proteomics (ChEP) analysis revealed enrichment of the proteasome in the chromatin fraction of quiescent cells and its apparent dissociation from chromatin in transformed cells. Our results thus suggest that translocation of the nuclear proteasome to chromatin may play an important role in control of the cell cycle and oncogenesis through regulation of chromatin-associated transcription factors.

Vitamin E suppresses 5-lipoxygenase-mediated oxidative stress in peripheral blood mononuclear cells of hemodialysis patients regardless of administration route

A number of pathological conditions caused by oxidative stress have been reported in uremic patients undergoing maintenance hemodialysis (HD). Enhanced lipid peroxidation was previously observed in peripheral blood mononuclear cells (PBMCs) of HD patients. Upregulation of 5-lipoxygenase (5-Lox) activity and protein content with enhanced production of leukotriene B(4) (LTB(4)) and membrane lipoperoxides was also shown in PBMCs of HD patients. Administration of free vitamin E specifically inhibited 5-Lox activity without affecting gene expression at the protein level. To assess whether oral or intramuscular (IM) administration of vitamin E may suppress 5-Lox in HD patients, PBMCs from 16 subjects on maintenance HD therapy for at least 6 months were investigated before and after a short course of IM or oral administration of vitamin E (8 patients per group). PBMCs from 13 healthy controls were also evaluated and assumed as the reference standard. Vitamin E significantly reduced lipid peroxidation, LTB(4) content, and 5-Lox activity in PBMCs, whereas 5-Lox gene expression at the protein level was not affected. There were no significant differences in these parameters between patients treated with IM or oral vitamin E. PBMCs of HD patients showed enhanced membrane lipid peroxidation and release of LTB(4), both linked to upregulation of 5-LOX: 5-Lox activity and related oxidative stress were significantly (although not completely) suppressed by vitamin E regardless of the administration route.

Activation of 5-lipoxygenase and related cell membrane lipoperoxidation in hemodialysis patients

Lipid peroxidation was shown at the membrane level in peripheral blood cells of patients hemodialyzed on cuprophan dialyzers, and was mainly attributable to the generation of conjugated hydroperoxides in the lipid bilayer. The oxidative index (i.e., the A234/205 ratio) of membrane lipids was 3.2-fold higher in hemodialysis patients than in healthy control subjects, and also the level of leukotriene B4 was significantly increased (up to 1.7-fold over control). Both membrane peroxidation and release of leukotriene B4 were linked to upregulation of 5-lipoxygenase activity (up to 2.4-fold over control) and expression at the protein level (up to 1.9-fold). Vitamin E, the most important lipophilic antioxidant, prevented both membrane peroxidation and release of leukotriene B4 by inhibiting 5-lipoxygenase activity without affecting enzyme expression. Similar results were observed in patients hemodialyzed on polymethylmetacrylate membranes, but in this case the activation of 5-lipoxygenase was less pronounced. The use of a purified 5-lipoxygenase demonstrated that vitamin E was a reversible inhibitor of enzyme activity (IC50 = 35 +/- 4 microM), further characterized as noncompetitive (Ki = 30 +/- 3 microM). Taken together, the results reported here shed some light on the mechanism responsible for the oxidative damage in hemodialysis. Moreover, the beneficial effect of vitamin E described here may have relevance for the therapy of patients with kidney disease.

5-Lipoxygenase gene expression in hemodialysis

Leukotrienes (LTs), the end products of the eicosanoid pathway released during inflammation, are markers of polymorphonuclear cell and monocyte activation. The present study focused on the possibility that 5-lipoxygenase (5-LO), the key enzyme for LT synthesis, was involved in the interaction between blood and the hemodialysis (HD) membrane. 5-LO gene expression was examined by reverse transcriptase polymerase chain reaction (RT-PCR) in samples of mononuclear cells isolated from peripheral blood withdrawn at the start and at 15 min of HD from 10 chronic HD patients, 5 treated with Cuprophan and 5 with polymethylmethacrylate (PMMA) membrane. An increased 5-LO gene expression was detected at 15 min in 4 of 5 patients using the Cuprophan membrane but in none of the 5 PMMA treated patients. Our results showed for the first time that the interaction between blood and the HD membrane upregulates 5-LO messenger ribonucleic acid (mRNA).

A highly sensitive and selective method for the determination of Leukotriene B4 in human plasma by negative ion chemical ionization/gas chromatography/tandem mass spectrometry

We have developed a highly sensitive and highly selective method for the determination of Leukotriene B4 (LTB4) in human plasma using negative ion chemical ionization/gas chromatography/tandem mass spectrometry (NICI/GS/MS/MS) analysis. The developed method was summarized as follows. Deuterated LTB4 (d4-LTB4) was added to human plasma samples as an internal standard, and samples were extracted by a Sep-pak C18 column. Extracted LTB4 was derivatized into the pentafluorobenzyl ester of bis-trimethylsilyl ether (PFB-TMS-LTB4) and quantified on the basis of selected reaction monitoring (SRM) at m/z 299 of [M-PFB-2TMSOH]- by NICI/GC/MS/MS analysis, which was the product ion of [M-PFB]-. The detection limit for the quantification of LTB4 in human plasma was 10 pg ml-1, sufficiently sensitive to determine the concentrations of endogenous LTB4 in human plasma. The plasma level of LTB4 measured in healthy male volunteers was 33.85 +/- 33.91 pg ml-1 (mean +/- S.D. in six volunteers). The technique of MS/MS used in this method offers much greater sensitivity and selectivity than single-stage mass spectrometry. The developed method showed good reproducibility with a simple and rapid extraction procedure, and would be useful for examining the relationship between various disease states and the levels of LTB4 in biological fluids.

Preserved antioxidative defense of lipoproteins in renal failure and during hemodialysis

Contact to artificial surfaces during hemodialysis activates leukocytes, which then form oxidized arachidonic acid products and free radicals. This might promote the oxidative modification of low-density lipoproteins (LDL) that play a key role in the initiation of atherosclerosis. Thus, leukocyte activation could specifically contribute to the high mortality from atherosclerotic complications on long-term hemodialysis. Therefore monitored LDL and high-density lipoprotein (HDL) resistance to copper-stimulated oxidation in patients with end-stage renal disease on maintenance hemodialysis with cellulose acetate or polysulfone membranes (n = 12), in patients with chronic renal failure (n = 13) and in healthy controls (n = 12). Six of the dialysis patients were restudied during a single cuprophane dialysis. Circulating leukocytes were reversibly reduced early in hemodialysis with cellulose acetate (minimum, 83.6% +/- 7.4% of baseline values at 30 minutes after dialysis start), polysulfone (minimum, 80.4% +/- 10.5% at 15 minutes; P < 0.05) and cuprophane (minimum, 24.5% +/- 8.5% at 60 minutes; P < 0.0001). Despite the leukocyte activation, LDL oxidation lag time was not shortened in comparison with healthy controls and was even prolonged at the end of cellulose acetate (P < 0.05) and cuprophane (P < 0.05) dialysis. HDL oxidation lag time increased (12.6% +/- 0.9%; P < 0.0001) 15 to 60 minutes after start of hemodialysis and returned to predialysis values thereafter. In patients with chronic renal failure, the lag time of HDL oxidation was significantly prolonged (13.34 minutes +/- 0.9) compared with healthy controls (10.91 +/- 2.0 minutes; P < 0.01) as well as compared with the dialysis patients at baseline (9.9 minutes +/- 1.4; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatible membranes in acute renal failure: prospective case-controlled study

The mortality of critically ill patients with acute renal failure has been halved through intervention by haemodialysis. However, several reports suggest that the course of the disorder may be prolonged by this procedure. Our prospective randomised study was done to see whether the generation of inflammatory mediators by bio-compatible membranes has an adverse effect on the outcome of acute renal failure. 52 patients, similar in age, severity of acute renal failure, general disease status (APACHE II), and management of acute renal failure or its related conditions, were divided into two groups. Haemodialysis was done with cuprophane or polyacrylonitrile membranes. Cuprophane membranes induced intense activation of the complement system (as judged by measurement of C3a) and lipooxygenase pathway (leukotriene B4) resulting in alterations of neutrophil kinetics and function. The cuprophane group had a lower survival rate (38 vs 65%), a higher proportion of patients dying from sepsis (71 vs 40%), required more haemodialysis sessions (12 vs 9), and demonstrated delayed resolution and recovery from acute renal failure than the polyacrylonitrile group. The difference in mortality regarding lethal sepsis as cause of death was statistically significant. Our observations indicate that the outcome of critically ill patients with acute renal failure may be influenced by bio-incompatibility reactions to the dialysis membrane. These results have direct implications for such patients on haemodialysis.

Generation of leukotriene B4 by hemodialyzer membranes: a novel index of biocompatibility

Leukotriene B4 (LTB4) plays an important role in acute and chronic inflammatory and hypersensitive reactions. We studied the time course of LTB4 biosynthesis in whole blood in 18 patients with end-stage renal failure maintained on regular hemodialysis with two different membranes, cuprophane and polyacrylonitrile (AN 69). The basal levels of LTB4 from dialysis patients did not differ significantly from a normal control group. Compared to predialytic values, the cuprophane membrane caused a maximal release of LTB4 by a factor of about 4.5 (p less than 0.01) within the first 10 to 20 minutes. Thereafter the level fell and returned to baseline range at the end of the hemodialysis session. With the use of the AN 69 membrane no significant increase of LTB4 could be demonstrated. The changes in LTB4 concentration showed a close temporal correlation to the alterations in white blood cell count. We conclude that (1) LTB4 is a biologically important mediator of neutrophil activation during hemodialysis, and (2) LTB4 may be a sensitive marker of biocompatibility in vivo.