Effect of sulphydryl binding compounds on the inflammatory process

Ethacrynic acid decreases expression of proinflammatory intestinal wall cytokines and ameliorates gastrointestinal stasis in murine postoperative ileus

OBJECTIVES

Several compounds characterized by an olefin linkage conjugated to a carbonyl group have anti-inflammatory properties. The diuretic ethacrynic acid (EA) is a compound of this type. Herein, we tested the hypothesis that ethacrynic acid can modulate the development of ileus after bowel manipulation.

METHODS

Groups (n=9) of male C57Bl/6 mice underwent surgical manipulation of the small intestine using a pair of cotton-tipped applicators (MAN). Control animals (CONT) did not undergo any surgical intervention or receive treatment. MAN mice were pre- and post-treated with four intraperitoneal doses of phosphate buffered saline (PBS), EA1 (1mg/kg per dose), or EA10 (10mg/kg per dose). Gastrointestinal transit of non-absorbable FITC-labeled dextran was assessed by gavaging the mice with the tracer 24h after operation and assessing FD70 concentration 120 min later in the bowel contents from the stomach, 10 equally long segments of small intestine, cecum, and two equally long segments of colon. The geometric center for the tracer was calculated for each animal. Expression of interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS) transcripts in the ileal muscularis propria was assessed using semiquantitative reverse transcriptase-polymerase chain reaction.

RESULTS

In control animals, the mean (±SE) geometric center for the transit marker was 9.89±0.47, whereas it was 4.59±0.59 for PBS-treated animals (p<0.05 vs CONT). The geometric center for pre- post treatment with low (1mg/kg) and high (10mg/kg) doses of ethacrynic acid were 7.23±0.97 and 5.15±0.57, respectively. Compared to PBS, treatment with ethacrynic acid (1mg/kg) significantly decreased manipulation-induced IL-6 and iNOS mRNA expression in the wall of the small bowel.

CONCLUSIONS

Pre- and post-treatment with ethacrynic acid ameliorates ileus and modulates inflammation in the gut wall induced by bowel manipulation.

The pleiotropic effects of ethacrynic acid

Ethacrynic acid (EC), an effective loop diuretic especially in patients allergic to sulfa-containing drugs, possesses a number of potentially useful actions in addition to the inhibition of the Na⁺-K⁺-2Cl⁻ kidney symport. Inhibition of the enzyme glutathione S-transferase plays an important role in reducing chemotherapy drug resistance. Chemical modifications of EC increase inhibition of glutathione S-transferase and reduce toxicity due to diuretic action (hypotension and hypovolemia). This work may lead to effective therapies in reducing chemotherapy resistance in cancer chemotherapeutics. In addition, EC or conjurers may be a radiation enhancer, an anti-inflammatory agent, or a treatment for glaucoma.

The phase 2 enzyme inducers ethacrynic acid, DL-sulforaphane, and oltipraz inhibit lipopolysaccharide-induced high-mobility group box 1 secretion by RAW 264.7 cells

The diuretic ethacrynic acid (EA) has been shown to inhibit signaling by the proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB). Accordingly, we sought to determine whether this compound is capable of inhibiting the release of cytokines [interleukin (IL)-6 and IL-10] and NO from RAW 264.7 murine macrophage-like cells stimulated with lipopolysaccharide (LPS). Additionally, we sought to determine whether EA can inhibit secretion of high-mobility group box 1 (HMGB1), a nuclear protein that is secreted by immunostimulated macrophages and functions in the extracellular milieu as a proinflammatory mediator. In a concentration-dependent manner, EA inhibited secretion of IL-6, IL-10, nitric oxide, and HMGB1. As expected, EA inhibited NF-kappaB DNA binding in LPS-stimulated RAW 264.7 cells. Treating these cells with pyrrolidine dithiocarbamate, SN50 (amino acid sequence AAVALLPAVLLALLAPVQRKRQKLMP) or 5-(thien-3-yl)-3-aminothiophene-2-carboxamide (SC-514) also inhibited LPS-induced NF-kappaB DNA binding, but these compounds failed to inhibit LPS-induced HMGB1 secretion. These findings suggested that inhibition of HMGB1 secretion by EA might occur via a mechanism unrelated to the NF-kappaB signaling pathway. Because EA is an electrophilic compound that is known to be capable of inducing expression of so-called phase 2 proteins, we sought to determine whether two other phase 2 enzyme inducers, oltipraz and DL-sulforaphane, also are capable of inhibiting HMGB1 release from immunostimulated macrophages. Incubating RAW 264.7 cells with either oltipraz or DL-sulforaphane inhibited LPS-induced HMGB1 secretion. Moreover, both EA and DL-sulforaphane inhibited relocalization of nuclear HMGB1 into the cytoplasm of LPS-stimulated RAW 264.7 cells. These data suggest that phase 2 inducers may exert anti-inflammatory effects by inhibiting secretion of the cytokine-like nuclear protein HMGB1.

Ethacrynic acid inhibits multiple steps in the NF-kappaB signaling pathway

Ethacrynic acid has been used as a safe and effective diuretic for more than 30 years. In this study, we tested the hypothesis that ethacrynic acid is also an anti-inflammatory agent that inhibits signaling by the proinflammatory transcription factor NF-kappaB. We showed that ethacrynic acid inhibited luciferase expression in lipopolysaccharide-stimulated macrophage-like RAW 264.7 cells transfected with an NF-kappaB-dependent luciferase reporter vector and also inhibited NF-kappaB DNA binding in lipopolysaccharide-stimulated RAW 264.7 cells (electrophoretic mobility shift assay). Ethacrynic acid inhibited degradation of IkappaBalpha and IkappaBbeta in lipopolysaccharide-stimulated RAW 264.7 cells. Ethacrynic acid impaired DNA binding of wild-type p65 subunits of NF-kappaB in cells. However, DNA binding of a Cys--> Ser p65 mutant was not inhibited by ethacrynic acid, suggesting that ethacrynic acid inhibits DNA binding by alkylating p65 at Cys. In a cell-free system, binding of p50 homodimers to an NF-kappaB consensus sequence was inhibited by ethacrynic acid at concentrations from 10 to 100 microM, indicating that ethacrynic acid probably also covalently modifies the p50 subunit. These data indicate that ethacrynic acid inhibits activation of the NF-kappaB pathway at multiple points and suggest that this well-studied drug warrants further investigation as a potential therapeutic for various conditions that are associated with excessive inflammation.

Relationship between SH group reactivity and concentration of bovine serum albumin and rat plasma

This study revealed that SH group reactivity (R) and concentration (C) of bovine serum albumin (BSA) and rat plasma are proportional in the sulphydryl-disulfide (SH-SS) exchange reaction with 5-5' dithiobis (2nitrobenzoic acid) (DTNB). The existence of the R/C proportionality suggests the use of Kr ratio and C as parameters for characterizing the biological properties of plasma SH groups. Moreover it was found that the electrophilic agents, diethylmaleate (DEM) and ethacrynic acid (ETHAC) that react with SH groups, determine an in vitro decrease in plasma SH group concentration and a Kr increase. The Kr increase seemed to be independent of SH group blocking as results obtained with sodium dodecyl sulfate (SDS) and SDS plus DEM indicated. The Kr biological significance might be related to a conformational change of albumin. In vivo treatment with 0.6 and 1.2 ml/kg of DEM confirmed the plasmatic linear relationship between R and C and showed a Kr increase in accordance with in vitro results. In carrageenan paw edema, decreased SH group plasma levels and an increased Kr were obtained.

Serum sulfhydryl levels in rheumatoid patients treated with cyclophosphamide

Six months' cyclophosphamide treatment significantly increased the sulfhydryl (SH) serum levels in all 12 rheumatoid arthritis (RA) patients studied and significantly decreased the PIP joints' technetium index (Tc-index), the erythrocyte sedimentation rate (ESR), and the joint count.

Effects of antirheumatic drugs on protein sulphydryl reactivity of human serum

The effect of a number of antirheumatic drugs on sulphydryl group reactivity in human serum has been determined using the thiol reagent, 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB). Drug effects in vivo have been measured using sera from patients with rheumatoid arthritis receiving these compounds and the drugs have also been added to healthy human serum in vitro. An increased rate of sulphydryl-disulphide exchange between serum sulphydryl groups and DTNB was noted in rheumatoid disease. This finding was not associated with anti-inflammatory drug therapy. In vivo, non-steroidal anti-inflammatory drugs did not affect this reaction, but aurothiomalate, D-penicillamine and levamisole all significantly increased the rate of sulphydryl-disulphide exchange. When the drugs were added to healthy human serum in vitro, indomethacin, aurothiomalate and D-penicillamine stimulated sulphydryl reactivity with DTNB but levamisole had no effect. Aurothiomalate appeared to act in this system as a mixture of gold atoms and thiomalate molecules, the thiomalate stimulating and the gold inhibiting thiol reactivity. This study demonstrates that the stimulation of sulphydryl-disulphide exchange reactions in vivo is a property of three long-acting drugs used to treat rheumatoid arthritis, but not of non-steroidal antiinflammatory agents. This reactivity may therefore differentiate the second-line drugs showing true antirheumatic activity from ‘simple’ anti-inflammatory compounds. Comparative studies have shown that the addition of drugs to serum in vitro may give different results from those obtained with sera from rheumatoid patients receiving these agents. This may be due to in vivo metabolism of the compound, drug concentration effects or the parameters of the in vitro assay system. In view of this, caution is required in the interpretation of data obtained from in vitro studies of these compounds.

Anti-inflammatory activity of sesquiterpene lactones and related compounds

Some sesquiterpene lactones and related compounds were tested for anti-inflammatory activity in rodents. In the edema-induced carrageenan inflammation screen, the alpha-methylene-gamma-lactone moiety of the sesquiterpene lactones was required for inhibitory activity. The 6-hydroxy group of helenalin also was required for potency. In the tenulin series, the 2,3-epoxy derivatives were marginally active. The same structure was required for inhibition of the writhing reflex. In the chronic adjuvant arthritic screen, compounds containing the alpha-methylene-gamma-lactone moiety, the beta-unsubstituted cyclopentenone ring, and the alpha-epoxy cyclopentenone system afforded significant inhibition at 2.5 mg/kg/day. The sesquiterpene lactones were marginally effective against induced pleurisy. The delayed hypersensitivity was suppressed by these agents whereas immunoglobulin synthesis was slightly stimulated. No delerious side effects were observed with these agents from the limited tests performed.

Effects of various drugs on the osmotic lysis of rat mast cells

1. Rat mast cells were exposed to low osmotic pressures to produce a 'non-specific' disruption of the mast cell, with release of histamine along with other intracellular contents. 2. The effect of non-steroidal anti-inflammaotry drugs and various other drugs upon osmotically induced histamine release was examined. 3. Representative non-steroidal anti-inflammatory drugs indomethacin, phenylbutazone and flufenamic acid, the acidic compounds ethacrynic acid, iopanoic acid and probenecid, and the local anaesthetic lignocaine, all caused a dose-dependent facilitation of osmotically induced histamine release compared to controls. All drugs were active at 0.1 mmol/l. 4. The previously observed inhibition of compound 48/80 and the antigen-induced histamine release from rat mast cells by similar concentrations of the drugs used in the present study are unlikely to be due to mast cell plasma membrane stabilization.

Irritancy of cyclophosphamide-derived aldehydes (acrolein, chloracetaldehyde) and their effect on lymphocyte distribution in vivo: protective effect of thiols and bisulphite ions1)

(1) A strategy is described for investigating agents such as N-acetylcysteine or penicillamine that might be used as adjuvant therapy with cyclophosphamide, to lessen the toxic side-effects of this latter drug caused by some of its metabolites. (2) The toxic effects of acrolein and chloracetaldehyde were determined by (a) their effects on lymphocyte circulation and (b) their oedemagenic activity in rats. (3) Stable thiols and bisulphite ions antagonised this aldehyde toxicity/irritancy; thiosulphate ions did not. (4) Thiosulphate and bisulphite ions antagonised the irritancy/toxicity of a mustard, mechlorethamine (HN-2). (5) The possible relationship of intrinsic irritancy to anti-inflammatory activity is discussed briefly.

Connective tissue activation. IX. Modification by pharmacologic agents

Alpha- and beta-adrenergic blocking agents and imipramine inhibit the increased hyaluronate synthesis that may be induced in human synovial cultures by connective tissue activating peptide (CTAP). Considerations of drug concentration requirements, actions of analogues, and time studies all indicate that the adrenergic blockers do not act in this circumstance as conventional blockers of alpha or beta receptor sites. It is suggested that the membrane-stabilizing properties of these agents may be the important determinant for their limited "antiactivation" effect. Ethacrynic acid, a potent and more complete inhibitor of connective tissue activation, appears to act via a different mechanism.

Serum sulphydryl levels in rheumatoid patients treated with alclofenac

Serum sulphydryl levels, which are decreased in rheumatoid patients, are increased to near normal during treatment with alclofenac. The biochemical function of the sulphydryl group and its possible pathogenic significance in rheumatoid and other auto-immune diseases are discussed.