Atherogenic diet causes lethal ileo-ceco-colitis in cyclooxygenase-2 deficient mice

Regulation of Intestinal Inflammation by Dietary Fats

With the epidemic of human obesity, dietary fats have increasingly become a focal point of biomedical research. Epidemiological studies indicate that high-fat diets (HFDs), especially those rich in long-chain saturated fatty acids (e.g., Western Diet, National Health Examination survey; NHANES 'What We Eat in America' report) have multi-organ pro-inflammatory effects. Experimental studies have confirmed some of these disease associations, and have begun to elaborate mechanisms of disease induction. However, many of the observed effects from epidemiological studies appear to be an over-simplification of the mechanistic complexity that depends on dynamic interactions between the host, the particular fatty acid, and the rather personalized genetics and variability of the gut microbiota. Of interest, experimental studies have shown that certain saturated fats (e.g., lauric and myristic fatty acid-rich coconut oil) could exert the opposite effect; that is, desirable anti-inflammatory and protective mechanisms promoting gut health by unanticipated pathways. Owing to the experimental advantages of laboratory animals for the study of mechanisms under well-controlled dietary settings, we focus this review on the current understanding of how dietary fatty acids impact intestinal biology. We center this discussion on studies from mice and rats, with validation in cell culture systems or human studies. We provide a scoping overview of the most studied diseases mechanisms associated with the induction or prevention of Inflammatory Bowel Disease in rodent models relevant to Crohn's Disease and Ulcerative Colitis after feeding either high-fat diet (HFD) or feed containing specific fatty acid or other target dietary molecule. Finally, we provide a general outlook on areas that have been largely or scarcely studied, and assess the effects of HFDs on acute and chronic forms of intestinal inflammation.

Apolipoprotein A-I mimetics mitigate intestinal inflammation in COX2-dependent inflammatory bowel disease model

Cyclooxygenase 2 (Cox2) total knockout and myeloid knockout (MKO) mice develop Crohn's-like intestinal inflammation when fed cholate-containing high fat diet (CCHF). We demonstrated that CCHF impaired intestinal barrier function and increased translocation of endotoxin, initiating TLR/MyD88-dependent inflammation in Cox2 KO but not WT mice. Cox2 MKO increased pro-inflammatory mediators in LPS-activated macrophages, and in the intestinal tissue and plasma upon CCHF challenge. Cox2 MKO also reduced inflammation resolving lipoxin A4 (LXA4) in intestinal tissue, while administration of an LXA4 analog rescued disease in Cox2 MKO mice fed CCHF. The apolipoprotein A-I (APOA1) mimetic 4F mitigated disease in both the Cox2 MKO/CCHF and piroxicam-accelerated Il10-/- models of inflammatory bowel disease (IBD) and reduced elevated levels of pro-inflammatory mediators in tissue and plasma. APOA1 mimetic Tg6F therapy was also effective in reducing intestinal inflammation in the Cox2 MKO/CCHF model. We further demonstrated that APOA1 mimetic peptides: i) inhibited LPS and oxidized 1-palmitoyl-2-arachidonoyl-sn-phosphatidylcholine (oxPAPC) dependent pro-inflammatory responses in human macrophages and intestinal epithelium; and ii) directly cleared pro-inflammatory lipids from mouse intestinal tissue and plasma. Our results support a causal role for pro-inflammatory and inflammation resolving lipids in IBD pathology and a translational potential for APOA1 mimetic peptides for the treatment of IBD.

G protein-coupled estrogen receptor inhibits vascular prostanoid production and activity

Complications of atherosclerotic vascular disease, such as myocardial infarction and stroke, are the most common causes of death in postmenopausal women. Endogenous estrogens inhibit vascular inflammation-driven atherogenesis, a process that involves cyclooxygenase (COX)-derived vasoconstrictor prostanoids such as thromboxane A2. Here, we studied whether the G protein-coupled estrogen receptor (GPER) mediates estrogen-dependent inhibitory effects on prostanoid production and activity under pro-inflammatory conditions. Effects of estrogen on production of thromboxane A(2) were determined in human endothelial cells stimulated by the pro-inflammatory cytokine tumour necrosis factor alpha (TNF-α). Moreover, Gper-deficient (Gper(-/-)) and WT mice were fed a pro-inflammatory diet and underwent ovariectomy or sham surgery to unmask the role of endogenous estrogens. Thereafter, contractions to acetylcholine-stimulated endothelial vasoconstrictor prostanoids and the thromboxane-prostanoid receptor agonist U46619 were recorded in isolated carotid arteries. In endothelial cells, TNF-α-stimulated thromboxane A2 production was inhibited by estrogen, an effect blocked by the GPER-selective antagonist G36. In ovary-intact mice, deletion of Gper increased prostanoid-dependent contractions by twofold. Ovariectomy also augmented prostanoid-dependent contractions by twofold in WT mice but had no additional effect in Gper(-/-) mice. These contractions were blocked by the COX inhibitor meclofenamate and unaffected by the nitric oxide synthase inhibitor l-N(G)-nitroarginine methyl ester. Vasoconstrictor responses to U46619 did not differ between groups, indicating intact signaling downstream of thromboxane-prostanoid receptor activation. In summary, under pro-inflammatory conditions, estrogen inhibits vasoconstrictor prostanoid production in endothelial cells and activity in intact arteries through GPER. Selective activation of GPER may therefore be considered as a novel strategy to treat increased prostanoid-dependent vasomotor tone or vascular disease in postmenopausal women.

Shotgun cholanomics of ileal fluid

In this study we have developed a rapid method for the shotgun analysis of bile acids in intestinal fluid. The method is semi-quantitative, and requires little sample preparation. Bile salts might contribute to the pathogenesis of Crohn's disease. In a pilot study we demonstrate the method by analysing the bile acid content of ileal fluid from seven Crohn's disease patients and three healthy controls. The dominant bile acids observed were di and/or trihydroxycholanoates, di- and/or trihydroxycholanoylglycines, di- and/or tri-hydroxycholanoyltaurines, monosulphated dihydroxycholanoates and monosulphated dihydroxycholanoylglycine. The method can be similarly applied to samples derived from other parts of the intestine.

COX-2 is not required for the development of murine chronic pancreatitis

Chronic pancreatitis is a severe inflammation of the pancreas associated with destruction of the parenchyma, fibrosis, and persistent abdominal pain. Cyclooxygenase-2 (COX-2) and COX-2-derived prostaglandins, key mediators of the inflammatory response, are elevated in patients with chronic pancreatitis. Previous studies investigated COX-2 as a therapeutic target. These reports showed a reduced pathology in COX-2-deficient mice with a better outcome. Here we compared the role of COX-2 in acute and chronic pancreatic inflammation using the same COX-2(-/-) mouse model of cerulein-induced pancreatitis. In a setting of acute pancreatitis, juvenile COX-2(-/-) mice exhibited a reduced histopathological score compared with wild-type littermates; on the contrary, adult mice did not show any difference in the development of the disease. Similarly, in a setting of chronic pancreatitis induced over a period of 4 wk, adult mice of the two strains showed comparable histological score and collagen deposition. However, the abundance of mRNAs coding for profibrotic genes, such as collagen, α-smooth muscle actin, and transforming growth factor-β was consistently lower in COX-2(-/-) mice. In addition, comparable histological scores and collagen deposition were observed in wild-type mice treated with a COX-2 inhibitor. We conclude that, in contrast to what was observed in the rat pancreatitis models, COX-2 has a limited and age-dependent effect on inflammatory processes in the mouse pancreas. These results suggest that COX-2 modulates the inflammatory process during the development of pancreatitis in a species-specific manner. Thus the pathophysiological roles of COX-2 and its therapeutic implications in patients with pancreatitis should be reexamined.

Atherogenic diets exacerbate colitis in mice deficient in glutathione peroxidase

BACKGROUND

The proinflammatory effect of high-fat diet has been observed beyond the cardiovascular system, but there is little evidence to support its role in triggering inflammatory bowel disease. GPx1/2-double-knockout (DKO) mice deficient in 2 intracellular glutathione peroxidases, GPx1 and GPx2, on a C57BL/6 (B6) background, have mild ileocolitis on a conventional chow.

METHODS

We fed B6 DKO mice 2 atherogenic diets to test the dietary effect on atherosclerosis and ileocolitis. Both atherogenic diets have high cholesterol-the Chol+/CA diet has cholic acid (CA), and the Chol+ diet has no CA.

RESULTS

The Chol+/CA diet induced severe colitis, but not ileitis, in the DKO mice compared with the Chol+ and the Chol- control diet. On the Chol+/CA diet, the wild-type (WT) mice had levels of aortic lesions and hypercholesterolemia similar to those of DKO mice but had no intestinal pathology. The diet-associated inflammatory responses in the DKO mice included increased colonic proinflammatory serum amyloid A3 expression, plasma lipopolysaccharide, and TNF-α levels. The Chol+/CA diet lowered the expression of the unfolded protein response genes ATF6, CHOP, unspliced Xbp(U) , and Grp78/Bip, in WT and DKO mice compared with mice on the Chol- diet.

CONCLUSIONS

We concluded that a cholesterol diet weakens the colon unfolded protein response, which can aggravate spontaneous colitis, leading to gut barrier breakdown. GPx has no impact on atherosclerosis without ultrahypercholesterolemia.

Crohn's disease as an immunodeficiency

The pathogenesis of Crohn's disease (CD) has widely been regarded as the consequence of a dysregulated T-cell-mediated response to intestinal microbes, and the majority of the worldwide research effort has focused on characterizing and treating the chronic inflammatory phase of the disease. However, recent molecular biological and clinical investigations indicate that CD is actually a primary immunodeficiency. At first counter-intuitive, the apparent paradox of a pathogenic innate immune defect can be linked mechanistically to the granulomatous chronic inflammation characteristic of the disease. Genome-wide association studies have corroborated the involvement of innate immune dysfunction in the pathogenesis of CD, but less than 20% of the heritable risk is accounted for. By contrast, in vitro and in vivo stimulation of the immune system has highlighted novel areas of interest that may lead to the development of targeted therapeutic and diagnostic tools.

Novel anti-inflammatory functions for endothelial and myeloid cyclooxygenase-2 in a new mouse model of Crohn's disease

Cyclooxygenase-2 (COX-2) is an important regulator of inflammation implicated in the development of a variety of diseases, including inflammatory bowel disease (IBD). However, the regulation of intestinal inflammation by COX-2 is poorly understood. We previously reported that COX-2(-/-) mice fed a cholate-containing high-fat (CCHF) diet had high mortality of unknown mechanisms attributable to severe intestinal inflammation in the ileo-ceco-colic junction that presented characteristics similar to Crohn's disease (CD). To further characterize the role of COX-2 in intestinal inflammation, we established cell-specific conditional COX-2(-/-) mice. Endothelial cell-specific (COX-2(-E/-E)) and myeloid cell-specific (COX-2(-M/-M)) COX-2(-/-) mice, but not wild-type mice, on the CCHF diet developed localized CD-like pathology at the ileo-ceco-colic junction that was associated with cellular infiltration, increased expression of myeloperoxidase and IL-5, and decreased IL-10 expression. The CD-like pathology in COX-2(-E/-E) mice was also accompanied by increased expression of cytokines (IL-6, TNF-alpha, and INF-gamma), compared with wild-type mice and COX-2(-M/-M) mice. In contrast, the ileo-ceco-colic inflammation in COX-2(-M/-M) mice was associated with more pronounced infiltration of granulocytes and macrophages than COX-2(-E/-E) mice. COX-2(-ME/-ME) (COX-2(-M/-M) x COX-2(-E/-E)) mice on the CCHF diet developed CD-like pathology in the ileo-ceco-colic junction reminiscent of total COX-2(-/-) mice on CCHF diet and wild-type mice on CCHF diet treated with COX-2 inhibitor, celecoxib. The pathology of diet-mediated ileo-ceco-colic inflammation in COX-2(-/-) mice offers an excellent model system to elucidate the protective roles of endothelial and myeloid COX-2 and the molecular pathogenesis of CD.