The role of arachidonic acid metabolites in gastrointestinal homeostasis. Biochemical, histological and clinical gastrointestinal effects

A diet enriched in omega-3 PUFA and inulin prevents type 1 diabetes by restoring gut barrier integrity and immune homeostasis in NOD mice

Introduction

The integrity of the gut barrier (GB) is fundamental to regulate the crosstalk between the microbiota and the immune system and to prevent inflammation and autoimmunity at the intestinal level but also in organs distal from the gut such as the pancreatic islets. In support to this idea, we recently demonstrated that breakage of GB integrity leads to activation of islet-reactive T cells and triggers autoimmune Type 1 Diabetes (T1D). In T1D patients as in the NOD mice, the spontaneous model of autoimmune diabetes, there are alterations of the GB that specifically affect structure and composition of the mucus layer; however, it is yet to be determined whether a causal link between breakage of the GB integrity and occurrence of autoimmune T1D exists.

Methods

Here we restored GB integrity in the NOD mice through administration of an anti-inflammatory diet (AID- enriched in soluble fiber inulin and omega 3-PUFA) and tested the effect on T1D pathogenesis.

Results

We found that the AID prevented T1D in NOD mice by restoring GB integrity with increased mucus layer thickness and higher mRNA transcripts of structural (Muc2) and immunoregulatory mucins (Muc1 and Muc3) as well as of tight junction proteins (claudin1). Restoration of GB integrity was linked to reduction of intestinal inflammation (i.e., reduced expression of IL-1β, IL-23 and IL-17 transcripts) and expansion of regulatory T cells (FoxP3⁺ Treg cells and IL-10⁺ Tr1 cells) at the expenses of effector Th1/Th17 cells in the intestine, pancreatic lymph nodes (PLN) and intra-islet lymphocytes (IIL) of AID-fed NOD mice. Importantly, the restoration of GB integrity and immune homeostasis were associated with enhanced concentrations of anti-inflammatory metabolites of the ω3/ω6 polyunsaturated fatty acids (PUFA) and arachidonic pathways and modifications of the microbiome profile with increased relative abundance of mucus-modulating bacterial species such as Akkermansia muciniphila and Akkermansia glycaniphila.

Discussion

Our data provide evidence that the restoration of GB integrity and intestinal immune homeostasis through administration of a tolerogenic AID that changed the gut microbial and metabolic profiles prevents autoimmune T1D in preclinical models.

RNase1 can modulate gut microbiota and metabolome after Aeromonas hydrophila infection in blunt snout bream

Pancreatic ribonuclease (RNase1) of Megalobrama amblycephala exhibits both antimicrobial and digestive activity. The gut microbiome improve the digestion and metabolic capacity and enhance the functioning of the immune system of the host against pathogenic bacteria. In this study, we aimed to assess the protective effect of RNase1 on Aeromonas hydrophila-induced inflammation and intestinal microbial metabolism. Megalobrama amblycephala were randomly divided into three groups: control (injected PBS), infection (A. hydrophila-injected), and treatment group (RNase1 pretreatment 24 h before the A. hydrophila injection). The morphological symptoms were significantly alleviated by RNase1. RNase1 reshaped the perturbed gut microbiota by upregulating Proteobacteria and Vibrio richness and downregulating Firmicutes, Chlamydiae, Bacillus, and Gemmobacter richness. The lysophosphatidylcholine, (±) 17 HETE, D- (+) -cellobiose, and PC (20:5) in the treatment group were restored by RNase 1 protein treatment to the level of the control group. In the treatment group, phospholipid metabolism, fatty acid metabolism, glucose metabolism and lipid metabolism were different from the control and infection groups. The proinflammatory factors concentration in intestinal samples significantly increased after A. hydrophila infection. Our results revealed that RNase1 plays an important role in resistance to pathogen invasion, reducing inflammation, and improving intestinal function, thus inhibiting the occurrence of disease.

Altered eicosanoid metabolism in the cystic fibrosis mouse small intestine

OBJECTIVES

Imbalances in essential fatty acid levels have been reported in cystic fibrosis (CF), which may relate to elevated proinflammatory eicosanoid generation. The aim of this work was to better define eicosanoid metabolism in the CF intestine.

MATERIALS AND METHODS

We used the small intestine of the cystic fibrosis transmembrane conductance regulator knockout mouse (CF mouse) to measure eicosanoid metabolic gene expression by quantitative reverse transcription polymerase chain reaction and Western blot, and eicosanoid levels by enzyme immunoassay, as compared with wild-type (WT) littermates.

RESULTS

In the CF small intestine, expression of the secretory phospholipase A2 Pla2g5 mRNA was upregulated to 980% of WT levels. The following were downregulated: leukotriene C4 synthase Ltc4s (mRNA 55% of WT); omega-hydroxylase cytochrome P450s Cyp2c40 (mRNA 54% of WT), and Cyp4a10 (mRNA 4% of WT); and the major prostaglandin degradative enzymes prostaglandin dehydrogenase Hpgd (mRNA 27% of WT) and leukotriene B4 12-hydroxydehydrogenase/15-oxo-prostaglandin 13-reductase Ltb4dh (mRNA 64% and protein 30% of WT). The prostaglandins PGE2 and PGF2alpha were increased to 400% to 600% of WT levels in the CF mouse intestine, and the hydroxyeicosatetraenoic acids (HETEs) 12-, 15-, and 20-HETE were decreased to 3% to 20% of WT levels.

CONCLUSIONS

There are changes in eicosanoid metabolic gene expression that are accompanied by significant changes in specific eicosanoid levels. These changes are expected to play important roles in the pathophysiology of CF in the intestine.

Does postoperative misoprostol use induce intestinal motility? A prospective randomised double-blind trial

BACKGROUND

Misoprostol has been shown to increase colonic activity and decrease colonic transit time in chronic constipation patients.

AIMS

The aim of this prospective, randomised, double-blind study was to examine the effectiveness of rectally administered misoprostol on inducing intestinal motility after gynaecological surgery.

METHODS

Eighty women who underwent hysterectomy were divided randomly into three groups. Group A received misoprostol 200 microg rectally while group B received 400 microg rectal misoprostol after surgery before leaving the operating room. Patients in group C received no drugs. Bowel sounds in four quadrants were checked every hour and possible side-effects of misoprostol like nausea, vomiting, and distension were evaluated. The time interval between surgery and flatus pass and the need of analgesics were noted. Statistical analyses were done with Mann-Whitney U-test and chi2 tests where available.

RESULTS

The time between surgery and presence of bowel sounds in four quadrants were similar in all groups (2.7 +/- 1.6, 2.9 +/- 1.2, 2.8 +/- 1.3 h, for groups A, B, and C, respectively). No difference was observed in flatus pass time. The incidence of nausea was significantly increased in group B compared to controls (P < 0.01). Additional analgesic need was significantly higher in groups A and B when compared to controls (P < 0.05 and P < 0.01, for groups A and B, respectively).

CONCLUSION

Rectally administered misoprostol does not improve intestinal motility in the early postoperative period and thus, it is not effective in providing early oral food intake. On the contrary, it causes distention that requires additional analgesics and vomiting that naturally limits oral diet intake.

Toxicity of nonsteroidal anti-inflammatory drugs in the elderly: is advanced age a risk factor?

We reviewed the pharmacokinetic, physiologic and epidemiologic data concerning nonsteroidal anti-inflammatory drug (NSAID)-induced gastropathy and renal insufficiency in the elderly through a structured critical reading of the literature. References were collected through a search of MEDLINE and consultation with experts in the field. While there is an abundance of pharmacokinetic data comparing relevant parameters in young and old subjects, methods are not uniform and findings are inconsistent. Prostaglandin physiology appears to be altered in older versus younger subjects. Most surprisingly, there is a scarcity of epidemiologic data examining the contribution of age as a risk factor for NSAID-induced ulcers and/or renal insufficiency. The data that do exist do not clearly support age as an independent risk factor; and we believe that comorbidities, comedications and past history are more important predictors of NSAID-induced toxicity than age and more relevant in regard to therapeutic decision-making for this patient population.

Aminoacetyl moiety as a potential surrogate for diacylhydrazine group of SC-51089, a potent PGE2 antagonist, and its analogs

8-Chlorodibenz[b,f][1,4]oxazepine-10(11H)-carboxylic acid, 2-[1-oxo-3-(4-pyridinyl)propyl]hydrazide, monohydrochloride (1, SC-51089) is a functional PGE2 antagonist selective for the EP1 receptor subtype with antinociceptive activity. During metabolism in cultured rat hepatocytes, SC-51089, which contains a diacylhydrazine moiety, has been shown to release hydrazine. Analogs of SC-51089, in which the diacylhydrazine functionality has been replaced by isosteric and isoelectronic groups, have been synthesized and have been shown to be analgesics and PGE2 antagonists of the EP1 subtype. This report discusses the structure-activity relationships within these series.

In vitro effects of arachidonic acid on the prostaglandin synthesizing system in gastric mucosa

Self-destruction of the prostaglandin cyclooxygenase has been suggested to be an important factor in the regulation of endogenous prostaglandin synthesis. The present study was done in order to define the role of this substrate-induced inactivation in the regulation of prostaglandin synthesis in gastric mucosa. In tissue homogenate, the prostaglandin synthesizing capacity is rapidly inactivated at 37 degrees C, even in the absence of exogenous arachidonic acid. It was shown that this inactivation can be prevented both by EDTA as a chelator of calcium-ions and by tetracaine, a specific inhibitor of the phospholipase A2. Additional exogenous arachidonic acid again inactivated prostaglandin synthesis in a dose dependent manner. In contrast, the prostaglandin synthesizing capacity in organ cultured mucosal biopsies is well preserved, although the release of endogenous substrate was activated by extracellular calcium and Ca-ionophore A23187. Furthermore, even at high concentrations of exogenous arachidonic acid present in the culture medium, the synthesizing capacity in intact biopsies was only slightly and reversibly reduced. These large differences between intact biopsies and cell free tissue preparations point to very efficient mechanisms controlling the substrate availability for the cyclooxygenase system both from endogenous and exogenous sources in intact gastric mucosa.

A report of three multiclinic trials evaluating arbaprostil in arthritic patients with ASA/NSAID gastric mucosal damage. The Upjohn Company Arbaprostil ASA/NSAID Gastric Mucosal Damage Treatment Study Groups

Three randomized, placebo-controlled multiclinic trials involving arbaprostil dosages of (a) 10 micrograms; (b) 25 micrograms; and (c) 10, 25, or 50 micrograms orally for 4 wk in patients older than 18 yr with rheumatoid arthritis or osteoarthritis who had endoscopically documented nonsteroidal antiinflammatory drug-associated gastric mucosal damage were conducted in the United States. All patients continued taking the nonsteroidal antiinflammatory drugs and were reendoscoped after 4 wk of therapy. Success at that time was defined as complete resolution of all gastric mucosal damage. Six hundred fifty-eight patients were enrolled in the three trials. Significantly more patients experienced healing in the arbaprostil treatment groups in all trials compared with those who received placebo. The healing rates in the various trials were 68% and 32% (10 micrograms vs. placebo; p = 0.007); 77% and 23% (25 micrograms vs. placebo; p less than 0.001); and 52%, 46%, 35%, and 16% (50, 25, and 10 micrograms vs. placebo; p less than 0.001, less than 0.001, and 0.002, respectively). Diarrhea, mostly of a mild nature, was the only arbaprostil-associated side effect and was found with the 25- and 50-microgram dosages (33% and 59%, respectively). No exacerbation of arthritis signs or symptoms was found. Arbaprostil at doses with varying effects on gastric acid secretion (25 and 50 micrograms) was documented in these trials to be an effective and safe agent for healing gastric mucosal damage associated with aspirin or other nonsteroidal antiinflammatory drugs in patients with either rheumatoid arthritis or osteoarthritis without adversely affecting joint symptomatology.

Effects of leukotriene D4, the antagonist L-649-923, and arachidonic acid on duodenal bicarbonate secretion in the rat in vivo

Prostaglandins of the E type stimulate bicarbonate secretion by the duodenal mucosa and inhibit gastric acid secretion, effects that have been related to their anti-ulcer activity. Leukotrienes constitute a more recently discovered branch of the arachidonic acid cascade, and C4 and D4 have been suggested to be ulcerogenic in the stomach. We have studied the effects of luminal administration of leukotriene D4 and the leukotriene C4/D4 antagonist L-649-923 on duodenal mucosal alkaline secretion in the anaesthetized rat. Leukotriene D4 (10(-8)-10(-6) M) had no significant effects, but the antagonist dose-dependently increased the bicarbonate secretion and also transiently increased the transmucosal electric potential difference. The precursor arachidonic acid (10(-7)-10(-6) M) caused a small increase in secretion. The increase in bicarbonate secretion in response to 10(-3) M of the antagonist was of about the same magnitude as that observed with 10(-5) of prostaglandin E2, and it was abolished by pretreatment with the cyclooxygenase inhibitor indomethacin. The gastroduodenal protective effects of L-649-923 in vivo may reflect an increase in mucosal prostaglandin production rather than leukotriene antagonism.