S. M. Greenfield

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.

A randomized controlled study of evening primrose oil and fish oil in ulcerative colitis

In a placebo‐controlled study, 43 patients with stable ulcerative colitis were randomized to receive either MaxEPA (n= 16), super evening primrose oil (n= 19), or olive oil as placebo (n= 8) for 6 months, in addition to their usual treatment. Treatment with MaxEPA increased red‐cell membrane concentrations of eicosapentaenoic acid (EPA) at 3 months by three‐fold and at 6 months by four‐fold (both P < 0.01), and doubled docosahexaenoic acid (DHA) levels at 6 months (P < 0.05). Treatment with super evening primrose oil increased red‐cell membrane concentrations of dihomogamma‐linolenic acid (DGLA) by 40% at 6 months (P < 0.05), whilst treatment with placebo reduced levels of DGLA and DHA at 6 months (both P < 0.05). Clinical outcome was assessed by patient diary cards, sigmoidoscopy and histology of rectal biopsy specimens. Super evening primrose oil significantly improved stool consistency compared to MaxEPA and placebo at 6 months, and this difference was maintained 3 months after treatment was discontinued (P < 0.05). There was however, no difference in stool frequency, rectal bleeding, disease relapse, sigmoidoscopic appearance or rectal histology in the three treatment groups. Despite manipulation of cell‐membrane fatty acids, fish oils do not exert a therapeutic effect in ulcerative colitis, while evening primrose oil may be of some benefit.

Lack of efficacy of a reduced microparticle diet in a multi-centred trial of patients with active Crohn's disease.

Background and aims Dietary microparticles, which are bacteria-sized and non-biological, found in the modern Western diet, have been implicated in both the aetiology and pathogenesis of Crohns disease. Following on from the findings of a previous pilot study, we aimed to confirm whether a reduction in the amount of dietary microparticles facilitates induction of remission in patients with active Crohns disease, in a single-blind, randomized, multi-centre, placebo controlled trial. Methods Eighty-three patients with active Crohns disease were randomly allocated in a 2×2 factorial design to a diet low or normal in microparticles and/or calcium for 16 weeks. All patients received a reducing dose of prednisolone for 6 weeks. Outcome measures were Crohns disease activity index, Van Hees index, quality of life and a series of objective measures of inflammation including erythrocyte sedimentation rate, C-reactive protein, intestinal permeability and faecal calprotectin. After 16 weeks patients returned to their normal diet and were followed up for a further 36 weeks. Results Dietary manipulation provided no added effect to corticosteroid treatment on any of the outcome measures during the dietary trial (16 weeks) or follow-up (to 1 year); e.g., for logistic regression of Crohns disease activity index based rates of remission (P=0.1) and clinical response (P=0.8), in normal versus low microparticle groups. Conclusions Our adequately powered and carefully controlled dietary trial found no evidence that reducing microparticle intake aids remission in active Crohns disease.

Gastro-intestinal availability of aluminium from tea

The in vitro speciation of aluminium (Al) in black tea infusion (pH 4.8) was assessed using 3000, 10,000 and 30,000 Da cut-off ultrafilters, and the effect of adding human gastric juice (pH 2.3) and then raising the pH to 6.5 were also studied. 78% Al in the tea infusion passed through the 3000-Da ultrafilter; this percentage increased to more than 90% with the addition of gastric juice at pH 2.3, but then reduced to approximately 5% when the incubate was adjusted to pH 6.5. The breakdown of tea-derived polyphenols to low molecular weight phenols in vivo was measured using high-resolution 1H nuclear magnetic resonance spectroscopic analysis of ileostomy effluent, but there was no evidence of low molecular weight breakdown products from the polyphenols of ingested tea in this effluent. These results suggest that only a small proportion of Al in tea is potentially available for absorption throughout the small bowel. It may be misleading to estimate systemic Al absorption from tea drinking simply from total urinary aluminium excretion as has been done previously.

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.

Lipid peroxidation in rats chronically fed ethanol.

Chronic alcohol consumption induces cytochrome P450IIE1, enabling habitual abusers to consume far greater quantities of alcohol than normal subjects. This pathway of metabolism leads to the production of free radical species, which cause tissue damage through peroxidation of cell membranes. Groups of Wistar rats of equal male: female ratio (n = 24) were fed alcohol by gavage twice daily to achieve a dosage of 15 g/kg body weight. Mean peak blood alcohol concentrations of 186 mg% were produced in males and 156 mg% in females. The animals were allowed free access to standard laboratory chow and water. Control animals were pair-fed to the alcoholic group and fed isocaloric glucose by gavage. Groups of animals were killed between 9 and 11 am on consecutive mornings, after nocturnal feeding, since it has previously been shown that fasting rapidly depletes hepatic glutathione concentrations. Hepatic glutathione was measured by a spectrophotometric enzymatic recycling procedure. As a marker of lipid peroxidation hepatic malonaldehyde (MDA) was measured by high performance liquid chromatography. Hepatic MDA was increased in the alcoholic group (p < 0.001), as was total hepatic glutathione (p < 0.0001). Plasma concentrations of alpha-tocopherol were increased in the alcoholic group, but ascorbic acid and superoxide dismutase values were not affected. No sex differences were detected. The increased MDA production in the alcohol group is strong evidence that lipid peroxidation is a mechanism of alcoholic tissue damage. The rise in hepatic glutathione may be an adaptive response to free radical production that protects the rat against tissue damage.

Inhibition of red cell membrane lipid peroxidation by sulphasalazine and 5-aminosalicylic acid.

The effects of sulphasalazine, 5-aminosalicylic acid (5-ASA), and sulphapyridine on peroxidation of red cell membrane lipids, measured as malondialdehyde production, were assessed. Sulphasalazine and 5-ASA, at concentrations of 10(-5)-10(-3) M significantly inhibit lipid peroxidation, suggesting an antioxidant action that may explain the efficacy of these drugs in treating inflammatory bowel disease. Sulphapyridine, which is not effective in inflammatory bowel disease inhibited malondialdehyde production at a concentration of 10(-3) M only.

Concentrations of metals in gastric juice in health and peptic ulcer disease.

The concentrations of essential metal cations in gastric juice, collected at endoscopy from 17 normal patients and 11 with peptic ulcer disease, were determined by inductively coupled plasma emission spectrometry. Mean fasting levels in normal gastric juice were as follows: sodium 47.7 mM, potassium 14.6 mM, calcium 0.8 mM, magnesium 0.36 mM, zinc 13 microM, and copper 1.2 microM: these did not differ significantly in health or disease. Because samples were contaminated with iron, the concentration of this metal was only estimated (ca 3.5 microM in normal subjects), and this secretion could represent a significant proportion of the daily loss of endogenous iron. The pH of gastric juice predicted the concentrations of magnesium and calcium, but not copper or zinc, in the juice. It is concluded that previously reported values for trace metals in gastric juice have been incorrect and that the very low amounts secreted in the gastric juice will not interfere with the absorption of other trace metals from the diet. In contrast, the concentrations of macroelements in gastric juice may be sufficient to stimulate the absorption of trace metals from the gut.

The effects of sulphasalazine and its metabolites on prostaglandin production by human mononuclear cells

Although it has been proposed that sulphasalazine (SASP) and its metabolite 5-aminosalicylic acid (5-ASA) act therapeutically by inhibiting production of vasoactive and immunoregulatory prostaglandins (PGs), in previous in vitro studies these drugs have both inhibited and promoted PG production. This study demonstrates that SASP and 5-ASA promote or inhibit peripheral blood mononuclear cell PG production depending upon the PG measured, the concentration of the drug, and whether the cells were stimulated. Sulphapyridine, the other constituent of SASP, only inhibited production. At high concentrations of SASP and 5-ASA the viability of mononuclear cells was reduced. The enhancement of PG production and toxicity was greater with SASP than 5-ASA, while the PGs most affected by SASP were not those most affected by 5-ASA. Thus, in vitro SASP may possess properties other than those of 5-ASA and this may explain the different therapeutic properties of these two compounds.

The effects of 5-aminosalicylic acid and acetyl-5-aminosalicylic acid on lipid peroxidation in erythrocytes and prostaglandin production by mononuclear cells

In parallel studies, the effects of 5‐aminosalicylic acid (5‐ASA) and acetyl‐5‐aminosalicylic acid (acetyl‐5‐ASA) on peroxidation of red‐cell membrane lipids and production of prostaglandins by peripheral blood mononuclear cells were assessed. 5‐ASA at concentrations of 10‐5, 10‐4 and 10‐3m significantly inhibited erythrocyte lipid peroxidation, measured as malondialdehyde production, by 20%, 56% and 63%, respectively, (P < 0.05, P < 0.002, P < 0.001, respectively) while acetyl‐ 5‐ASA had no effect. 10‐5 and 10‐4m 5‐ASA significantly increased production by stimulated peripheral blood mononuclear cells of PGE2 (by 31% and 30%, P < 0.01, P < 0.05, respectively) and PGF2α (by 30% and 25%, P < 0.05, P < 0.01, respectively). 10‐4 M 5‐ASA also significantly stimulated prostacyclin production measured as 6KF1α by 10% (P < 0.05). At 10‐3 M 5‐ASA there were significant falls in 6KF1α (by 37%) PGE2 (by 45%) and PGF2α (by 47%) (P < 0.01, P < 0.001, P < 0.001, respectively) although this was accompanied by a decrease in cell viability. Acetyl‐5‐ASA had little effect upon prostaglandin production. 5‐ASA scavenges free radicals and stimulates production of cyto‐protective prostaglandins.