Inhibition of neutrophil degranulation and superoxide production by sulfasalazine. Comparison with 5-aminosalicylic acid, sulfapyridine and olsalazine

Discovery of putative inhibitors of human Pkd1 enzyme: Molecular docking, dynamics and simulation, QSAR, and MM/GBSA

Polycystic kidney disease is the most prevalent hereditary kidney disease globally and is mainly linked to the overexpression of a gene called PKD1. To date, there is no effective treatment available for polycystic kidney disease, and the practicing treatments only provide symptomatic relief. Discovery of the compounds targeting the PKD1 gene by inhibiting its expression under the disease condition could be crucial for effective drug development. In this study, a molecular docking and molecular dynamic simulation, QSAR, and MM/GBSA-based approaches were used to determine the putative inhibitors of the Pkd1 enzyme from a library of 1379 compounds. Initially, fourteen compounds were selected based on their binding affinities with the Pkd1 enzyme using MOE and AutoDock tools. The selected drugs were further investigated to explore their properties as drug candidates and the stability of their complex formation with the Pkd1 enzyme. Based on the physicochemical and ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) properties, and toxicity profiling, two compounds including olsalazine and diosmetin were selected for the downstream analysis as they demonstrated the best drug-likeness properties and highest binding affinity with Pkd1 in the docking experiment. Molecular dynamic simulation using Gromacs further confirmed the stability of olsalazine and diosmetin complexes with Pkd1 and establishing interaction through strong bonding with specific residues of protein. High biological activity and binding free energies of two complexes calculated using 3D QSAR and Schrodinger module, respectively further validated our results. Therefore, the molecular docking and dynamics simulation-based in-silico approach used in this study revealed olsalazine and diosmetin as potential drug candidates to combat polycystic kidney disease by targeting Pkd1 enzyme.

Non-surgical interventions for late rectal problems (proctopathy) of radiotherapy in people who have received radiotherapy to the pelvis

BACKGROUND

This is an update of a Cochrane review first published in 2002, and previously updated in 2007. Late radiation rectal problems (proctopathy) include bleeding, pain, faecal urgency, and incontinence and may develop after pelvic radiotherapy treatment for cancer.

OBJECTIVES

To assess the effectiveness and safety of non-surgical interventions for managing late radiation proctopathy.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 11, 2015); MEDLINE (Ovid); EMBASE (Ovid); CANCERCD; Science Citation Index; and CINAHL from inception to November 2015.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing non-surgical interventions for the management of late radiation proctopathy in people with cancer who have undergone pelvic radiotherapy for cancer. Primary outcomes considered were: episodes of bowel activity, bleeding, pain, tenesmus, urgency, and sphincter dysfunction.

DATA COLLECTION AND ANALYSIS

Study selection, 'Risk of bias' assessment, and data extraction were performed in duplicate, and any disagreements were resolved by involving a third review author.

MAIN RESULTS

We identified 1221 unique references and 16 studies including 993 participants that met our inclusion criteria. One study found through the last update was moved to the 'Studies awaiting classification' section. We did not pool outcomes for a meta-analysis due to variation in study characteristics and endpoints across included studies.Since radiation proctopathy is a condition with various symptoms or combinations of symptoms, the studies were heterogeneous in their intended effect. Some studies investigated treatments targeted at bleeding only (group 1), some investigated treatments targeted at a combination of anorectal symptoms, but not a single treatment (group 2). The third group focused on the treatment of the collection of symptoms referred to as pelvic radiation disease. In order to enable some comparison of this heterogeneous collection of studies, we describe the effects in these three groups separately.Nine studies assessed treatments for rectal bleeding and were unclear or at high risk of bias. The only treatments that made a significant difference on primary outcomes were argon plasma coagulation (APC) followed by oral sucralfate versus APC with placebo (endoscopic score 6 to 9 in favour of APC with placebo, risk ratio (RR) 2.26, 95% confidence interval (CI) 1.12 to 4.55; 1 study, 122 participants, low- to moderate-quality evidence); formalin dab treatment (4%) versus sucralfate steroid retention enema (symptom score after treatment graded by the Radiation Proctopathy System Assessments Scale (RPSAS) and sigmoidoscopic score in favour of formalin (P = 0.001, effect not quantified, 1 study, 102 participants, very low- to low-quality evidence), and colonic irrigation plus ciprofloxacin and metronidazole versus formalin application (4%) (bleeding (P = 0.007, effect not quantified), urgency (P = 0.0004, effect not quantified), and diarrhoea (P = 0.007, effect not quantified) in favour of colonic irrigation (1 study, 50 participants, low-quality evidence).Three studies, of unclear and high risk of bias, assessed treatments targeted at something very localised but not a single pathology. We identified no significant differences on our primary outcomes. We graded all studies as very low-quality evidence due to unclear risk of bias and very serious imprecision.Four studies, of unclear and high risk of bias, assessed treatments targeted at more than one symptom yet confined to the anorectal region. Studies that demonstrated an effect on symptoms included: gastroenterologist-led algorithm-based treatment versus usual care (detailed self help booklet) (significant difference in favour of gastroenterologist-led algorithm-based treatment on change in Inflammatory Bowel Disease Questionnaire-Bowel (IBDQ-B) score at six months, mean difference (MD) 5.47, 95% CI 1.14 to 9.81) and nurse-led algorithm-based treatment versus usual care (significant difference in favour of the nurse-led algorithm-based treatment on change in IBDQ-B score at six months, MD 4.12, 95% CI 0.04 to 8.19) (1 study, 218 participants, low-quality evidence); hyperbaric oxygen therapy (at 2.0 atmospheres absolute) versus placebo (improvement of Subjective, Objective, Management, Analytic - Late Effects of Normal Tissue (SOMA-LENT) score in favour of hyperbaric oxygen therapy (HBOT), P = 0.0019) (1 study, 150 participants, moderate-quality evidence, retinol palmitate versus placebo (improvement in RPSAS in favour of retinol palmitate, P = 0.01) (1 study, 19 participants, low-quality evidence) and integrated Chinese traditional plus Western medicine versus Western medicine (grade 0 to 1 radio-proctopathy after treatment in favour of integrated Chinese traditional medicine, RR 2.55, 95% CI 1.30 to 5.02) (1 study, 58 participants, low-quality evidence).The level of evidence for the majority of outcomes was downgraded using GRADE to low or very low, mainly due to imprecision and study limitations. 

AUTHORS' CONCLUSIONS

Although some interventions for late radiation proctopathy look promising (including rectal sucralfate, metronidazole added to an anti-inflammatory regimen, and hyperbaric oxygen therapy), single small studies provide limited evidence. Furthermore, outcomes important to people with cancer, including quality of life (QoL) and long-term effects, were not well recorded. The episodic and variable nature of late radiation proctopathy requires large multi-centre placebo-controlled trials (RCTs) to establish whether treatments are effective. Future studies should address the possibility of associated injury to other gastro-intestinal, urinary, or sexual organs, known as pelvic radiation disease. The interventions, as well as the outcome parameters, should be broader and include those important to people with cancer, such as QoL evaluations.

Mechanism of action of 5-arninosalicylic acid

5-Aminosalicylic Acid (5-ASA) has been used for over 50 years in the treatment of inflammatory bowel disease in the pro-drug form sulphasalazine (SASP). SASP is also used to treat rheumatoid arthritis. However whether the therapeutic properties of SASP are due to the intact molecule, the 5-ASA or sulphapyridine components is unknown. Several mechanisms of action have been proposed for 5-ASA and SASP including interference in the metabolism of arachidonic acid to prostaglandins and leukotrienes, scavenging,of reactive oxygen species, effects on leucocyte function and production of cytokines. However, it is unlikely that the anti-inflammatory properties of SASP and 5-ASA are due to several different properties but more likely that a single property of 5-ASA explains the theraapeutic effects of 5-ASA and SASP. Reactive oxygen species (ROS) are involved in the metabolism of prostaglandins and leukotrienes and can act as second messengers, and so the scavenging of ROS may be the single mechanism of action of 5-ASA that gives rise to its antiinflammatory effects in both inflammatory bowel disease and rheumatoid arthritis.

Immunotherapies in rheumatologic disorders

Over the past several decades, rheumatology has directed its focus to understanding and countering the immune dysregulation underlying autoimmune diseases with rheumatologic manifestations. Older therapies, effective though poorly understood, are being scrutinized anew and are yielding the immune-modulating mechanisms behind their efficacy. New therapies, the "biologics," are drugs tailored to address specific immune defects and imbalances. This article discusses the current standard and biologic immunotherapies of the rheumatic diseases, correlating our current understanding of their mechanisms with dysfunctions believed to be present in the major autoimmune syndromes, especially rheumatoid arthritis and systemic lupus erythematosus.

Ulcerative colitis: current treatment strategies and future prospects

Ulcerative colitis (UC) is a disease of unknown etiology characterized by inflammation of the mucosa and occasionally the submucosa of the colon. Conventional drug therapy for UC involves use of aminosalicylates, corticosteroids, azathioprine/6-mercaptopurine, cyclosporine and anti-tumor necrosis factor therapy. Alternative therapies include probiotics, nicotine and fish oil. Drugs like tacrolimus, rosiglitazone and Trichuris suis ova are being evaluated for use in UC patients. With the new biologic agents, new treatment options for UC continue to evolve. In this article we will discuss the conventional drugs, the alternative therapies and the management strategies according to the severity and extent of UC.

Scavenging of reactive oxygen and nitrogen species by the prodrug sulfasalazine and its metabolites 5-aminosalicylic acid and sulfapyridine

Sulfasalazine is a prodrug composed by a molecule of 5-aminosalicylic acid (5-ASA) and sulfapyridine (SP), linked by an azo bond, which has been shown to be effective in the therapy of inflammatory bowel diseases (IBD) such as ulcerative colitis and Crohn's disease, as well as of rheumatic diseases, such as rheumatoid arthritis and ankylosing spondylitis. The precise mechanism of action of sulfasalazine and/or its metabolites has not been completely elucidated, though its antioxidant effects are well established and are probably due to its scavenging effects against reactive oxygen and nitrogen species (ROS and RNS), as well as metal chelating properties, in association to its inhibitory effects over neutrophil oxidative burst. The present work was focused on screening and comparing the potential scavenging activity for an array of ROS (O(2)(•-), H(2)O(2), (1)O(2), ROO(•) and HOCl) and RNS ((•)NO and ONOO(-)), mediated by sulfasalazine and its metabolites 5-ASA and SP, using validated in vitro screening systems. The results showed that both 5-ASA and sulfasalazine were able to scavenge all the tested ROS while SP was practically ineffective in all the assays. For HOCl, (1)O(2), and ROO(•), 5-ASA showed the best scavenging effects. A new and important finding of the present study was the strong scavenging effect of 5-ASA against (1)O(2). 5-ASA was shown to be a strong scavenger of (•)NO and ONOO(-). Sulfasalazine was also able to scavenge these RNS, although with a much lower potency than 5-ASA. SP was unable to scavenge (•)NO in the tested concentrations but was shown to scavenge ONOO(-), with a higher strength when the assay was performed in the presence of 25 mM bicarbonate, suggesting further scavenging of oxidizing carbonate radical. In conclusion, the ROS- and RNS-scavenging effects of sulfasalazine and its metabolites shown in this study may contribute to the anti-inflammatory effects mediated by sulfasalazine through the prevention of the oxidative/nitrative/nitrosative damages caused by these species.

The neutrophil respiratory burst and bacterial digestion in Crohn's disease

BACKGROUND

Neutrophils are a key part of the innate immune defence against microbes, using the respiratory burst (RB) to optimise killing and digestion. Previous studies of the neutrophil RB in Crohn's disease (CD) have yielded conflicting results.

METHODS

Superoxide production in response to phorbol-myristyl acetate (PMA) was measured in neutrophils from 100 patients with CD compared to 50 healthy controls (HCs) and 50 patients with ulcerative colitis (UC). A further 22 CD and 10 HCs were studied using f-Met-Leu-Phe (fMLP), and digestion of E. coli by neutrophils was also evaluated.

RESULTS

The mean ± SEM PMA-stimulated RB (nmol O(2)/10(6) cells/min) was 10.86 ± 0.26 in HCs, 9.76 ± 0.23 in CD (P=0.02) and 10.04 ± 0.28 in UC (P=0.09 vs HC and 0.47 vs CD). No significant effect of age, gender or medication was observed. The RB in three patients with presumed CD was found to be in the range expected in patients with inherited neutrophil disorders. Stimulation with fMLP was calcium dependent and attenuated in patients on 5-ASA. Digestion of E. coli by neutrophils was not different in HC vs CD (21.6 vs 20.53%, P=0.60).

CONCLUSION

The significant reduction in neutrophil RB in CD does not appear to result in defective bacterial digestion and is therefore unlikely play a major role in pathogenesis. Three patients in this cohort of patients with presumed idiopathic CD were found to have a profound defect of the neutrophil RB. A high index of suspicion for such patients is prudent, as their prognosis can be improved by altering or augmenting the conventional treatment regimens employed for CD.

Improving delivery of aminosalicylates in ulcerative colitis: effect on patient outcomes

Developments in drug delivery technology have expanded the formulations of 5-aminosalicylic acid (5-ASA) available to clinicians over the last 50 years. Delivery of adequate doses of 5-ASA to the colon can be achieved by pH-dependent, delayed-release or pro-drug formulations. Despite some variations in the pharmacokinetics between individual preparations, the clinical effects in induction of response and maintenance of remission in ulcerative colitis appear to be consistent. Direct comparison studies between different preparations have yielded similar results in primary endpoints, although differences in secondary endpoints or post hoc analyses have been noted. The development of delivery methods that allow once-daily administration represents a potential means to improve the low medication adherence rates reported in patients with ulcerative colitis.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Antioxidant effects of aminosalicylates and potential new drugs for inflammatory bowel disease: assessment in cell-free systems and inflamed human colorectal biopsies

BACKGROUND

The therapeutic efficacy of 5-aminosalicylic acid in inflammatory bowel disease may be related to its antioxidant properties.

AIM

To compare in vitro the antioxidant effects of conventional drugs (5-aminosalicylic acid, corticosteroids, metronidazole), with new aminosalicylates (4-aminosalicylic acid, balsalazide) and other potential therapies (ascorbate, N-acetylcysteine, glutathione, verapamil).

METHODS

Compounds were assessed for efficacy in reducing the in vitro production of reactive oxygen species by cell-free systems (using xanthine/xanthine oxidase, with or without myeloperoxidase) and by colorectal biopsies from patients with ulcerative colitis using luminol-amplified chemiluminescence.

RESULTS

5-aminosalicylic acid and balsalazide were more potent antioxidants than 4-aminosalicylic acid or N-acetyl-5-aminosalicylic acid in cell-free systems. 5-aminosalicylic acid (20 mM) and balsalazide (20 mM) inhibited rectal biopsy chemiluminescence by 93% and 100%, respectively, compared with only 59% inhibition by 4-aminosalicylic acid (20 mM). Hydrocortisone, metronidazole and verapamil had no significant effect on chemiluminescence in any system. Ascorbate (20 mM) inhibited chemiluminescence by 100% in cell-free systems and by 60% in rectal biopsies. N-acetyl cysteine (10 mM), and both oxidized and reduced glutathione (10 mM), completely inhibited chemiluminescence in cell-free systems, but not with rectal biopsies.

CONCLUSIONS

The antioxidant effects of compounds varies between cell-free systems and inflamed colorectal biopsies. The effect of drugs on the chemiluminescence produced by these two assay systems is useful for screening potentially new antioxidant treatments for inflammatory bowel disease. Ascorbate seems worth further study as a novel therapy.

Effects of antirheumatic drugs on adhesiveness of endothelial cells and neutrophils

Because disease-modifying antirheumatic drugs might exert part of their effects on adhesion of polymorphonuclear neutrophils (PMN) to endothelial cells, this being the first step for PMN migration to inflammatory lesions, we evaluated such drug effects in vitro. Gold sodium thiomalate (GSTM) impaired the ability of interleukin 1beta (IL-1beta)-stimulated human umbilical vein endothelial cells (HUVEC) to express E-selectin and to bind PMN but had no effect on the expression of intercellular adhesion molecule 1 (ICAM-1) or on hyperadhesivity of N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN. Auranofin (AF) interacted with HUVEC and PMN adhesiveness but in opposite directions: this drug hampered IL-1beta-induced HUVEC hyperadhesiveness and expression of E-selectin and intercellular adhesion molecule 1, but augmented PMN adherence and CD18 expression. The net effect of auranofin was a reduction of cytokine-driven adhesiveness and enhancement of formylpeptide-induced adhesion. Salazopyrin did not affect HUVEC or PMN adhesiveness or E-selectin and intercellular adhesion molecule 1 expression. Thus, the gold-containing drugs modulated HUVEC and PMN adhesiveness by different mechanisms but ones involving surface adhesion molecules.

Inhibition of neutrophil-dependent cytotoxicity for human endothelial cells by antirheumatic drugs

Because polymorphonuclear (PMN) neutrophils are major effector cells in vasculitides, we assessed whether disease-modifying antirheumatic drugs impaired the ability of human PMNs to lyse human umbilical vein endothelial cells (HUVECs) in vitro. HUVECs were grown to confluence and labeled with chromium 51. PMNs, stimuli, and antirheumatic drugs were added stepwise, and the release of 51Cr was subsequently assessed. Lipoxin A4 (LXA4) and the oligopeptide fMLP, activating PMNs by surface receptors, conferred highly significant cytolysis that was dose-dependently reduced when auranofin, gold sodium aurothiomalate (GSTM), and sulfasalazine and its metabolites sulfapyridine and 5-ASA were added to the assay system. This protection remained, but with stimulus- and drug-specific variations, when either PMNs or HUVECs alone were treated with drugs before washings and PMN activation. In contrast, methotrexate did not protect HUVECs. Cytotoxicity conferred by the ionophore A23187 was inhibited by auranofin and GSTM only. Likewise, when HUVEC cytolysis was induced by two major cytotoxic mechanisms of PMNs, exogenous H2O2, or PMN lysates, auranofin and GSTM hampered lysis significantly. Thus in this in vitro model of vasculitis, auranofin, GSTM, sulfasalazine, sulfapyridine, and 5-ASA--but not methotrexate--dose-dependently reduced the PMN-dependent endothelial cell damage by effects on the PMNs as well as effects on the HUVECs.

Effect of allopurinol, sulphasalazine, and vitamin C on aspirin induced gastroduodenal injury in human volunteers

BACKGROUND

The mechanisms of aspirin induced gastroduodenal injury are not fully understood. Aspirin induces the release of reactive oxygen metabolites in animal models, which may contribute to mucosal injury.

AIMS

To investigate the effects of aspirin administered with placebo or antioxidants on gastric mucosal reactive oxygen metabolite release and gastroduodenal injury in human volunteers.

SUBJECTS

Fourteen healthy volunteers participated in the study (seven male; mean age 27 years, range 20-40).

METHODS

In a double blind, randomised, crossover study, volunteers received aspirin 900 mg twice daily and either placebo, allopurinol 100 mg twice daily, sulphasalazine 1 g twice daily or vitamin C 1 g twice daily for three days. Injury was assessed endoscopically and by quantifying mucosal reactive oxygen metabolite release by measuring chemiluminescence before and after each treatment. The effect on prostanoids was determined by measuring ex vivo antral prostaglandin E2 (PGE2) synthesis and serum thromboxane B2 (TXB2).

RESULTS

No drug reduced any parameter of gastric injury but vitamin C reduced duodenal injury assessed by Lanza score (p < 0.005). Chemiluminescence increased after aspirin both with placebo (p < 0.05) and vitamin C (p < 0.05). Post-treatment chemiluminescence was lower in subjects taking allopurinol (p < 0.05) or sulphasalazine (p < 0.005) than in those taking placebo with aspirin.

CONCLUSIONS

In this study, aspirin induced gastric injury was associated with reactive oxygen metabolite release. This was reduced by sulphasalazine and allopurinol, although macroscopic injury was not affected. Vitamin C, however, was shown to have a previously unrecognised protective effect against aspirin induced duodenal injury.

Circulating neutrophils from patients with ulcerative colitis have a normal respiratory burst

The hallmark of ulcerative colitis is a diffuse infiltration of neutrophils from the circulation into the colonic mucosa. The underlying mechanism for neutrophil tissue infiltration is unknown. One possible hypothesis is abnormal circulating neutrophils. This hypothesis has been previously tested with conflicting results. The aim of our study was to re-evaluate circulating neutrophil function in the absence of several possible confounding factors. To this end, we measured the respiratory burst of circulating neutrophils in response to two different stimuli by chemiluminescence in patients with active and inactive ulcerative colitis being off all medications. Our results show no significant difference between ulcerative colitis patients and controls in peak chemiluminescence, area-under-the-curve and time to peak comparisons. However, 27% of patients with active ulcerative colitis had an abnormally elevated chemiluminescence to stimuli. In addition, no correlations were seen between disease activity and peak chemiluminescence. Thus circulating neutrophils in the majority of patients with ulcerative colitis do not appear to be either "primed" or hyperactive. This may suggest the presence of local colonic factors that lead to neutrophil tissue infiltration and activation.

Salicylates for ulcerative colitis--their mode of action

Delivery of 5-aminosalicylic acid to the colon by sulphasalazine, other azo-bonded compounds and controlled-release preparations is introduced in the context of metabolism by epithelial cells and therapeutic efficacy in ulcerative colitis. Potential modes of action are then reviewed, including actions on luminal bacteria, epithelial cell surface receptors, cellular events (such as nitric oxide release or butyrate oxidation), electrolyte transport and epithelial permeability. Evidence for an influence of salicylates on circulating and lamina propria inflammatory cells is presented, as well as actions on adhesion molecules, chemotactic peptides and inflammatory mediators, such as eicosanoids, platelet-activating factor, cytokines or reactive oxygen metabolites. The precise mechanism will remain uncertain as long as the aetiology of ulcerative colitis is unknown, but a pluripotential mode of action of salicylates is an advantage when influencing the network of events that constitute chronic inflammation.

Treatment of inflammatory bowel disease from now to the millennium

After decades of therapeutic stasis, treatment advances are occurring in inflammatory bowel disease. Recognition that mesalazine was the active moiety of sulphasalazine has led to a number of new methods of delivering mesalazine without sulphapyridine, with improved toxicity ratios. Current attempts to deliver topical steroids directly to the large bowel have yet to be established as therapeutically effective. Immunosuppressive treatment has been used for many years but recent evidence has firmly established its value and cyclosporin has recently been added to the therapeutic armamentarium. Increasing understanding of the basic processes of inflammation has yielded targets for anti-inflammatory treatments aimed both at the processes of immune activation and of attraction by chemotaxis of neutrophils from the circulation to the lamina propria. Some of these novel treatments, which will be assessed in forthcoming years, involve large molecular weight bioengineered peptides and antibodies that are likely to be expensive and difficult to administer. Other treatment, e.g. 5-lipoxygenase or thromboxane synthesis inhibitors or platelet-activating factor antagonists, are conventional lower molecular weight compounds that are easier to produce and are orally active. It is predicted that 5-lipoxygenase inhibitors will be the next therapeutic advance in inflammatory bowel disease. Such a prediction may founder if blanket suppression of multiple inflammatory mechanisms, rather than targeted actions, is required in inflammation.

Review article: the mode of action of the aminosalicylates in inflammatory bowel disease

Sulphasalazine and other 5-aminosalicylic acid (5-ASA)-containing drugs are used in the treatment of acute inflammatory bowel disease and in the maintenance of clinical remission. Despite their use for over 50 years, the mechanism of action of this class of drugs remains uncertain, although a number of possibilities are discussed in this review. It seems likely that the aminosalicylates are important free radical scavengers, can reduce leukotriene production and can inhibit the cellular release of interleukin-1, all of which are likely to be important in reducing the acute inflammatory response in inflammatory bowel disease. The effects of these drugs on prostaglandin production are more contentious, but it appears that 10(-5) to 10(-4) M concentrations stimulate production of prostaglandins which may be cytoprotective, while higher doses of these drugs inhibit prostaglandin production. The aminosalicylates may maintain remission in inflammatory bowel disease by preventing leucocyte recruitment into the bowel wall. The drugs inhibit the chemotactic response to leukotriene B4, reduce the synthesis of platelet activating factor and also inhibit leucocyte adhesion molecule upregulation.

Inhibition of leucocyte adhesion molecule upregulation by tumor necrosis factor alpha: a novel mechanism of action of sulphasalazine

The effects of the cytokine tumour necrosis factor alpha and the calcium ionophore A23187 upon CD11a, CD11b, CD11c and CD18 leucocyte membrane expression was analysed in whole blood using monoclonal antibodies and flow cytometry. Both agents significantly increased the density of CD11b/CD18 membrane expression on monocytes and granulocytes, but had no effects on adhesion molecule expression on lymphocytes. The effects of sulphasalazine, 5-aminosalicylic acid (5-ASA) and sulphapyridine upon adhesion molecule upregulation were then examined; 10(-3) and 10(-4) M sulphasalazine and 5-ASA significantly reduced tumour necrosis factor alpha induced CD11b/CD18 upregulation on monocytes and granulocytes but had no effects upon A23187 mediated upregulation. Sulphapyridine was inactive. These results suggest that sulphasalazine and 5-ASA may interfere with mechanisms of leucocyte recruitment in inflammatory bowel disease.

Influence of anti-inflammatory drugs and free radical scavengers on intestinal ischemia induced oxidative tissue damage

The influence of oxygen free radical scavengers and anti-inflammatory drugs on postischemic lipid peroxidation and myeloperoxidase activity was shown. The best results were obtained from vitamin E and the antiinflammatory treatment with CP and SUL, whereas an iron elimination only showed slight effects on myeloperoxidase activity above all. In experiments without therapy a linear increase of lipid peroxides dependent on reperfusion durance was found, whereas myeloperoxidase already showed a remarkable increase during ischemia and early reperfusion. This difference can be interpreted by scavenging mechanisms, which are overcharged after an appointed durance of reperfusion.

Free radicals and other reactive oxygen metabolites in inflammatory bowel disease: cause, consequence or epiphenomenon?

Oxygen-derived free radicals and other reactive oxygen metabolites have emerged as a common pathway of tissue injury in a wide variety of otherwise disparate disease processes. This has given rise to the hope that efforts directed towards the pharmacologic control of free radical-mediated tissue injury (Reilly, P.M., Schiller, H. J. and Bulkley, G. B. (1991) Pharmacologic approach to tissue injury mediated by free radicals and other reactive oxygen metabolites. Am. J. Surg. 161: 488-503) may have particular application to patients suffering from Crohn's disease and/or ulcerative colitis. However, because tissue injury by any mechanism, even direct mechanical trauma, can elicit an inflammatory response which entails the secondary generation of toxic oxidants by neutrophils and tissue macrophages, it is important that the evidence for this association be examined critically, so as to discriminate the possibility of an etiologic role for these toxic compounds from their presence as a reflection of injury caused primarily by other agents. Similarly, in considering the therapeutic potential of free radical ablation for the treatment of patients with IBD it is important to distinguish between interventions that might specifically block the fundamental injury mechanism from those which would act in a more nonspecific, anti-inflammatory role.

The production of an amine-modified derivative of 5-aminosalicylic acid by activated neutrophils. Roles for myeloperoxidase and chloride ions

Following incubation with activated neutrophils, two metabolites of 5-aminosalicyclic acid (5-ASA) were identified by HPLC. These two metabolites accounted for approximately 60% and 20% of the original 5-ASA. The formation of the major metabolite was prevented by pre-incubation with the peroxidase inhibitor, azide, and reduced by the omission of chloride ions from the incubation medium, or the presence of catalase. A similar product was generated by sodium hypochlorite or myeloperoxidase/H2O2, mass spectroscopical analysis being consistent with it being 5-nitroso-salicylate. Our finding suggests that the efficacy of 5-ASA results from its ability to react with and so scavenge hypochlorite ions. The amount of amine-modified 5-ASA in the faecal stream may thus provide an indicator for hypochlorite production in the bowel.

Modulation of arachidonic acid metabolism by olsalazine and other aminosalicylates in leukocytes

We investigated the action of the new aminosalicylate olsalazine (disodium azodisalicylate) on arachidonic acid metabolism in comparison with 5-aminosalicylic acid (5-ASA) and sulphasalazine (SASP) by in vitro incubation of cellular homogenates from human polymorphonuclear (PMNL) and mononuclear (MNL) leukocytes with 14C-labelled arachidonic acid. Olsalazine reduced the synthesis of leukotriene B4 (LTB4), 5-hydroxyeicosatetraenoic acid (5-HETE), 11-HETE, 12-HETE, and 15-HETE in PMNL and MNL slightly less than SASP. 5-ASA was significantly less inhibitory than olsalazine and SASP on the formation of lipoxygenase products in PMNL and on LTB4 synthesis in MNL. In contrast, in MNL the formation of 5-HETE was unaffected, and the production of 11-HETE, 12-HETE, and 15-HETE was even slightly activated by 5-ASA. Total prostaglandin synthesis was dose-dependently reduced by the aminosalicylates (SASP greater than olsalazine greater than 5-ASA), but only SASP markedly altered the prostaglandin (PG) profile, with an increase in PGE2 and PGF2 alpha at the expense of other cyclooxygenase products. It may be concluded that olsalazine resembled SASP with regard to the inhibition of the lipoxygenase but had effects intermediate between the other salicylates on cyclooxygenase. Furthermore, the alteration of the prostaglandin profile by SASP points to an overlying cofactor effect of this drug.

Scavenger effect of sulfasalazine, 5-aminosalicylic acid, and olsalazine on superoxide radical generation

The in vitro antioxidant capacity of sulfasalazine (SASP), its metabolites (SP, 5-ASA), and olsalazine (OAZ), was studied by evaluating their effects on superoxide (O2-.) production. Assay systems were the xanthine-xanthine oxidase (X/XOD) reaction and phorbol myristate acetate (PMA)-activated polymorphonuclear leukocytes (PMNs), using the cytochrome c (cyt-c) reduction assay and a luminol-dependent chemiluminescence method. 5-ASA, SASP, and OAZ showed a dose-dependent scavenger effect in both O2-. generating systems, 5-ASA being the most powerful (greater than 50% of inhibition in the PMNs system and greater than 70% in the X/XOD system at 10 microM concentration). SP had an inhibitory effect only in the PMNs system but did not modify the activity of xanthine oxidase, thus excluding a scavenger action. These data suggest that the scavenger effect of 5-ASA, SASP, and OAZ may be an important mechanism of action.

Reactive oxygen metabolites and colitis: a disturbed balance between damage and protection. A selective review

Enhanced local production of reactive oxygen metabolites has been found in association with colitis, both experimentally and in humans. Cellular and biochemical systems involved have been identified, and 5-aminosalicylic acid-containing drugs but, more effectively, specific scavengers have been found to reduce the intestinal inflammatory process. The multitude of reactions in which oxygen metabolites participate provides a new area of research in intestinal inflammation. These basic studies might bring related clinical studies in an era of new anti-inflammatory drugs for inflammatory bowel disease specifically designed to scavenge toxic oxygen metabolites.

Luminal concentrations of orally ingested 4-aminosalicylic acid as determined by in-vivo equilibrium dialysis

We measured 4-aminosalicylic acid (4-ASA) levels in faecal water by in-vivo equilibrium dialysis during oral ingestion of drug by two different dose protocols (A and B). In Protocol A, 5 normal subjects ingested 3 g of 4-ASA as the free acid and 20 mg of metaclopromide per day. On Day 5, small dialysis sacs filled with dextran 40 were ingested and the oral drug was continued until the sacs were retrieved from the stool. Protocol B followed the same format except that 3 g of 4-ASA was ingested twice daily and metaclopromide was omitted. In both protocols concentrations of 4-ASA and N-acetylated 4-ASA in sac contents were measured by HPLC. In-vitro dialysis studies showed bi-directional equilibrium was reached within 120 min. During Protocol A, intraluminal concentrations of total 4-ASA ranged from 14.0 to 32.2 mmol/L with a mean of 20.6 mmol/L. With Protocol B, total 4-ASA levels ranged from 20.1 to 41.3 mmol/L with a mean of 33.9 mmol/L. From 90 to 99% of the drug in the dialysates was N-acetylated. These concentrations of total 4-ASA are similar to those of 5-ASA after ingestion of therapeutic doses of sulphasalazine or absorption-resistant formulations of 5-ASA. Thus, oral 4-ASA could have a role in the treatment of inflammatory bowel disease.

Effect of sulphasalazine and sulphapyridine on neutrophil superoxide production: role of cytosolic free calcium

As the neutrophil granulocyte plays an important part in rheumatoid inflammation the effect of sulphasalazine on neutrophil function was studied. The results show that sulphasalazine, and its metabolite sulphapyridine, inhibit neutrophil superoxide production elicited by the receptor mediated stimulus N-formyl-methionyl-leucyl-phenyl-alanine (fMLP) and by the calcium ionophore A23187. This effect seems to be dependent on inhibition of intracellular Ca++ increase as both substances reduce this increase upon cell activation with fMLP and A23187. Sulphasalazine and sulphapyridine do not inhibit superoxide production after stimulation with the ester phorbol myristate acetate, a stimulus response coupling which is independent of intracellular Ca++ increase. The reported inhibition of superoxide generation may explain, at least partly, the antirheumatic property of sulphasalazine.

Clinical evidence supporting the radical scavenger mechanism of 5-aminosalicylic acid

5-Aminosalicylic acid, the therapeutically active metabolite of sulfasalazine, was exposed to oxygen-derived free radicals produced by the Fenton reaction in vitro, and several metabolites were detected and characterized by high performance liquid chromatography and ultraviolet spectrophotometry. The majority of these metabolites were present in methanolic extracts of feces samples from sulfasalazine-treated patients with inflammatory bowel disease but not in rheumatoid arthritis patients with normal bowel function. The presence of these metabolites, which have not been demonstrated in vivo before, provides evidence of an interaction between 5-aminosalicylic acid and oxygen-derived free radicals in sulfasalazine-treated patients with inflammatory bowel disease. Since the concentration of lipid peroxides, which is dependent on the release of oxygen-derived free radicals, was significantly increased in pretreatment rectal biopsies of the patients, and further was normalized concomitantly with a significant improvement in disease activity over the 5-wk treatment period, an important role of the radical scavenger mechanism of 5-aminosalicylic acid in sulfasalazine therapy of chronic inflammatory bowel disease is strongly suggested.

Reversible drug effects on the metabolic activation of polymorphonuclear leukocytes

Polymorphonuclear leukocytes (PMNs) stimulated by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (FMLP) were effectively inhibited by chlorpromazine (10 microM) and azelastine (20 microM) in terms of superoxide generation, and restored by the addition of dodecylbenzenesulfonic acid (DBS) in a range of concentrations from 20 to 40 microM. The stimulation of superoxide generation by DBS was also inactivated by dodecylamine (DA) but was restored by the subsequent addition of DBS. A dose dependent competitive inhibition and activation of leukocytes was observed between azelastine (10 microM) and DBS (20 microM). The release of arachidonic acid from leukocytes activated by the chemotactic peptide was decreased by DA or chlorpromazine, but could be restored by DBS. The changes in membrane potential of leukocytes as monitored by cyanine dye were also decreased by DA, chlorpromazine or azelastine. These observations indicate that some cationic drugs reversibly inhibit membrane bound enzymes or receptors. The physiological responses of these inhibited PMNs can then be restored by appropriate anionic amphiphiles.

Simple and rapid method for the simultaneous determination of the eight main metabolites and conjugates of sulphasalazine in human plasma, urine and faeces using dynamically modified silica

A simple and rapid method for the simultaneous determination of sulphapyridine, N-acetylsulphapyridine, 5-aminosalicylic acid, N-acetyl-5-aminosalicylic acid, hydroxysulphapyridine, N-acetylhydroxysulphapyridine, sulphapyridine O-glucuronide and N-acetylsulphapyridine O-glucuronide in plasma, urine and faeces is presented. After precipitation of plasma proteins by addition of methanol the samples are injected directly into the liquid chromatographic system. The limit of detection is 1 microgram/ml or less at a signal-to-noise ratio of 5 for all compounds using ultraviolet, fluorescence or electrochemical detection. The advantages of the dynamically modified silica approach in this reversed-phase high-performance liquid chromatographic method are demonstrated with respect to regulation and reproducibility of the selectivity.

The enhancing effect of cyclosporine A and sulfasalazine on the prevention of rejection in rat cardiac allografts

Sulfasalazine (SASP) has been used for many years as a disease-modifying agent in inflammatory bowel disease and in rheumatoid arthritis. However, its mode of action is not entirely clear. Evidence has been accumulated which indicates that its efficacy is due to an immunomodulatory effect. In the present communication, we report that SASP has an immunomodulatory capacity in an experimental rat cardiac allograft model. A combination of 100 mg/kg per day of SASP given orally until rejection and 10 mg/kg per day of cyclosporine A (CyA) given orally for 10 days resulted in a significantly increased graft survival time as compared to that in animals given CyA alone.