Effect of 5-aminosalicylic acid (5-ASA) and other salicylates on short-chain fat metabolism in the colonic mucosa. Pharmacological implications for ulcerative colitis

Fatty acids and lipid mediators in inflammatory bowel disease: from mechanism to treatment

Inflammatory Bowel Disease (IBD) is a chronic, relapsing inflammatory disorder of the gastrointestinal tract. Though the pathogenesis of IBD remains unclear, diet is increasingly recognized as a pivotal factor influencing its onset and progression. Fatty acids, essential components of dietary lipids, play diverse roles in IBD, ranging from anti-inflammatory and immune-regulatory functions to gut-microbiota modulation and barrier maintenance. Short-chain fatty acids (SCFAs), products of indigestible dietary fiber fermentation by gut microbiota, have strong anti-inflammatory properties and are seen as key protective factors against IBD. Among long-chain fatty acids, saturated fatty acids, trans fatty acids, and ω-6 polyunsaturated fatty acids exhibit pro-inflammatory effects, while oleic acid and ω-3 polyunsaturated fatty acids display anti-inflammatory actions. Lipid mediators derived from polyunsaturated fatty acids serve as bioactive molecules, influencing immune cell functions and offering both pro-inflammatory and anti-inflammatory benefits. Recent research has also highlighted the potential of medium- and very long-chain fatty acids in modulating inflammation, mucosal barriers, and gut microbiota in IBD. Given these insights, dietary intervention and supplementation with short-chain fatty acids are emerging as potential therapeutic strategies for IBD. This review elucidates the impact of various fatty acids and lipid mediators on IBD and delves into potential therapeutic avenues stemming from these compounds.

Nutrition and gut health: the impact of specific dietary components - it's not just five-a-day

The health benefits of fruit, vegetables and dietary fibre have been promoted for many years. Much of the supporting evidence is circumstantial or even contradictory and mechanisms underlying health benefits of specific foods are poorly understood. Colorectal cancer shows marked geographical differences in incidence, probably linked with diet, and explanations for this require knowledge of the complex interactions between diet, microbiota and the gut epithelium. Dietary fibres can act as prebiotics, encouraging growth of saccharolytic bacteria, but other mechanisms are also important. Some but not all soluble fibres have a 'contrabiotic' effect inhibiting bacterial adherence to the epithelium. This is particularly a property of pectins (galacturonans) whereas dietary fructans, previously regarded as beneficial prebiotics, can have a proinflammatory effect mediated via toxic effects of high butyrate concentrations. This also suggests that ulcerative colitis could in part result from potentially toxic faecal butyrate concentrations in the presence of a damaged mucus layer. Epithelial adherence of lectins, either dietary lectins as found in legumes, or bacterial lectins such as the galactose-binding lectin expressed by colon cancer-associated Fusobacterium nucleatum, may also be important and could be inhibitable by specific dietary glycans. Conversely, emulsifiers in processed foods may increase bacterial translocation and alter the microbiota thus promoting inflammation or cancer. Focusing on one condition is of limited value although in developing public health messages and growing evidence for impacts of dietary components on all-cause mortality is gaining more attention. We are only just starting to understand the complex interactions between food, the microbiota and health.

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.

Effect of a new de-N-acetyl-lysoglycosphingolipid on chemically-induced inflammatory bowel disease: possible mechanism of action

A new, orally active de-N-acetylated lysoglycosphingolipid (WILD20) was evaluated as antiinflammatory agent using a model of chemically-induced inflammatory bowel disease (IBD) in the rat to mimic human ulcerative colitis and Chron's disease. IBD was induced by hapten trinitrobenzenesulphonic acid (TNB). WILD20, orally administered as preventive or curative, was demonstrated to be efficacious at daily dosages of 0.1-1 mg/kg for 4-5 days. Damage scores, body weight, spleen weight, colonic tissular levels of LTB4, myeloperoxidase (MPO) and malondialdehyde (MDA) are influenced and brought into parameters of normality. Histological observation demonstrated quicker healing, better repair, reduced inflammation, and poor eosinophil degranulation. The mechanisms underlying WILD20 antiinflammatory effects were investigated: whereas WILD20 fails to show a direct effect on PKC, it reduces PKC translocation to the membrane; cellular PLA2 was consequently greatly reduced through this mechanism and thought to be responsible for WILD20 efficacy towards chemically-induced IBD.

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.

Effect of 5-aminosalicylic acid and analogous substances on superoxide generation and intracellular free calcium in human neutrophilic granulocytes

Activated polymorphonuclear leukocytes (PMNs), which are found in the inflammatory lesions of chronic inflammatory bowel disease, produce tissue-destructive oxygen-derived free radicals. The influence of 5-aminosalicylic acid (5-ASA), its acetylated metabolite (Ac-5-ASA), sulfasalazine (SAZ), and olsalazine (OLZ) (5-ASA dimer linked by an azo group) in pharmacologically relevant concentrations (0.1-10 mM) were tested on PMN superoxide production with either the receptor-specific agent formyl-methionyl-leucyl-phenylalanine (fMLP) or the protein kinase C activator phorbol myristate acetate (PMA). Inhibition of receptor-specific superoxide production occurred at 0.07, 0.32, and 0.63 mM (IC50 values) for 5-ASA, SAZ, and OLZ, respectively. No inhibitory effects of SAZ and OLZ were observed when PMA was applied as stimulus for PMN superoxide production. The results indicate that the signal to which PMNs respond by generating superoxide is primarily due to calcium release from intracellular stores. They further suggest that SAZ and OLZ may affect the oxygen-derived free radical production in human PMNs by unspecific cytotoxicity or by interference with the nicotinamide adenine dinucleotide phosphate, reduced (NADPH) oxidase system, whereas 5-ASA itself is a free radical scavenger.

Olsalazine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in inflammatory bowel disease

Olsalazine (sodium azodisalicylate; azodisal sodium) is an anti-inflammatory agent designed to deliver its active moiety, mesalazine (5-aminosalicylic acid; mesalamine), to the colon while avoiding the adverse effects associated with the use of a sulfapyridine carrier. As a prodrug, olsalazine is an effective oral treatment for both active ulcerative colitis and for maintenance of disease remission and may possibly be of benefit in patients with Crohn's colitis. Findings from both short and long term noncomparative and comparative studies demonstrate that olsalazine 1 to 3g daily in divided doses improves clinical signs and symptoms of colitis in approximately 60 to 80% of patients with acute ulcerative colitis of mild to moderate severity. This improvement rate was similar to that obtained with sulfasalazine. Lower doses of olsalazine, usually 1g daily in divided doses, also maintained remission in patients with chronic ulcerative colitis. While olsalazine effectively delivers mesalazine to the colon, the prodrug itself increases net luminal water secretion and accelerates gastrointestinal transit of a meal. The resulting diarrhoea (occurring in approximately 17% of patients and resulting in withdrawal from therapy in 6% of patients) is distinguishable from that associated with inflammatory bowel disease by the high water content and the absence of blood. Olsalazine-induced diarrhoea usually occurred soon after initiation of olsalazine therapy or dosage increase, was more frequent with higher doses and was usually transient. Dosage reduction, increases in frequency of dosing and concomitant administration with food reduced the severity in many patients with persistent olsalazine-induced diarrhoea. With the exception of diarrhoea, olsalazine was generally well tolerated. Fewer than 14% of patients allergic to or intolerant of sulfasalazine had similar reactions to olsalazine. Olsalazine appears to be a suitable therapy for the treatment of first attacks as well as acute exacerbation of mild to moderate acute ulcerative colitis, and for the maintenance of remission in patients with chronic ulcerative colitis.

Mesalazine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in chronic inflammatory bowel disease

Mesalazine (5-aminosalicylic acid; mesalamine), the active moiety of sulphasalazine (salazosulfapyridine), is available in specially formulated oral and rectal forms for the treatment of active ulcerative colitis of mild to moderate severity and for maintenance therapy during disease remission. Tablets or capsules coated with acrylic-based resin and tablets containing microgranules coated with ethylcellulose deliver mesalazine to the distal small intestine and colon, thus avoiding the need for the carrier, sulphapyridine, which is responsible for many of the adverse effects associated with sulphasalazine. Since mesalazine is released in the small intestine from some coated preparations in contrast to sulphasalazine, these oral formulations have therapeutic potential in Crohn's disease. A limited number of therapeutic trials suggest that orally administered mesalazine 1.5 to 2.4g daily is of similar efficacy to sulphasalazine 2 to 3g daily in patients with mild to moderate ulcerative colitis. The efficacy of mesalazine enemas has been more widely investigated, a dose of 1 to 4g once daily being consistently more effective than placebo and apparently similar to enemas of prednisone 25mg or oral sulphasalazine 3g. Initial results suggest that mesalazine 4g enemas may be more effective than those containing hydrocortisone 100mg. Mesalazine and sulphasalazine in approximately equivalent oral dosages are similarly effective in maintaining remission in ulcerative colitis. Orally administered coated mesalazine is generally well tolerated by about 85% of patients allergic to or intolerant of sulphasalazine, the remainder experiencing similar reactions to both drugs. Adverse effects of mesalazine enemas are confined to local irritation and effects resulting from enema-tip insertion. Thus, orally administered coated mesalazine is a suitable alternative to sulphasalazine in the treatment of patients with mild to moderate active distal ulcerative colitis and for maintaining remission particularly in patients allergic to or intolerant of sulphasalazine. In patients who find enema therapy acceptable, mesalazine enemas are effective and well tolerated.

Possible mode of action of 5-aminosalicylic acid

Despite the extensive use of sulfasalazine (SAS) and/or 5-aminosalicylic acid (5-ASA) in patients with inflammatory bowel disease and, more recently, rheumatoid arthritis, their mode of action has not been elucidated so far. None of the numerous pharmacological and biochemical effects described, including immunosuppressive, antifolate, and modulatory actions on lymphocyte and leukocyte functions, could be defined unequivocally as mediating their beneficial activity. Recently, interest has focused on actions of SAS and 5-ASA on the various enzymes of the arachidonic acid cascade. Mucosa of patients with inflammatory bowel disease generates excessive amounts of cyclooxygenase products such as prostaglandins (PG) as well as 5-lipoxygenase products such as leukotriene (LT) B4 and sulfidopeptide-LT. Both PG and LT exert proinflammatory actions and are potentially important mediators of mucosal inflammation. SAS and 5-ASA, however, have been found to inhibit PG synthesis under certain experimental conditions only, while increasing PG formation under other conditions. While SAS was found to inhibit colonic LTB4 synthesis, 5-ASA was reported to selectively affect the cyclooxygenase pathway of arachidonate metabolism in this tissue. Our results demonstrate that, like the parent compound, the metabolite 5-ASA in a dose-dependent manner inhibits release of LTB4 and sulfidopeptide-LT from normal human colonic mucosa (IC50 3.5 and 3.7 mmol/liter, respectively). Indomethacin, which has no efficacy in the treatment of patients with inflammatory bowel disease, on the other hand, selectively inhibited PGE2 formation in normal and inflamed colonic mucosa (IC50 1.7 and 1.0 mmol/liter, respectively) without reducing synthesis of LTB4 or sulfidopeptide-LT.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of 5-lipoxygenase pathway of arachidonic acid metabolism in human neutrophils by sulfasalazine and 5-aminosalicylic acid

The possible effect of sulfasalazine, 5-aminosalicylic acid, and acetyl-5-aminosalicylic acid on endogenous arachidonic acid release and metabolism was studied in human polymorphonuclear leukocytes (PMNs). A new in vitro assay was used by which [1-14C]arachidonic acid is incorporated by purified peripheral PMNs until steady state was obtained (5 hr). After preincubation with the test drugs prior to activation with calcium ionophore A23187, the released eicosanoids were isolated by extraction and thin-layer chromatography (TLC) and quantitated by autoradiography and laser densitometry. Median drug concentrations needed for 50% inhibition of leukotriene B4 and 5-hydroxyeicosatetraenoic acid (5-HETE) release was 4-5 mM (range 1-9 mM) for both sulfasalazine and 5-aminosalicylic acid. The acetylated derivative of 5-aminosalicylic acid was ineffective. The present data suggest that inhibition of arachidonic acid lipoxygenation may be an essential action of sulfasalazine and its active metabolite, 5-aminosalicylic acid. Interference with lipoxygenase enzymes, rather than a steroid-like inhibition of arachidonic acid release from intracellular phospholipids, seems to be the mode of action.

The antiinflammatory moiety of sulfasalazine, 5-aminosalicylic acid, is a radical scavenger

Using a novel spectrophotometric assay to detect free radical scavengers, the effects of sulfasalazine, a compound frequently administered in the treatment of chronic inflammatory bowel disease, and its main metabolites, 5-aminosalicylic acid (5-ASA), sulfapyridine, and N-acetyl-5-ASA, were compared with biological antioxidants (nordihydroguaiaretic acid (NDGA), alpha-tocopherol, and ascorbic acid) and antiinflammatory salicylates (acetylsalicylic acid and sodium salicylate). The results show that 5-ASA, but neither sulfasalazine and its other metabolites, nor the salicylates, shares with the biological antioxidants the property of being a potent scavenger of free radicals. Since 5-ASA is formed in millimolar concentrations in the colon of sulfasalazine-treated patients this mode of action may explain the beneficial effect of sulfasalazine in inflammatory bowel disease. Locally formed 5-ASA may break the free radical chain reaction initiated and maintained by activated phagocytes, thus arresting the perpetuating tissue destruction. This mechanism may indicate a general potential for radical scavengers in chronic inflammation.