Increased prostaglandin E2 and leukotriene B4 synthesis in isolated colonic mucosal cells in inflammatory bowel disease. a preliminary report

Involvement of Proinflammatory Arachidonic Acid (ARA) Derivatives in Crohn’s Disease (CD) and Ulcerative Colitis (UC)

Recently, an increase in the incidence of inflammatory bowel disease (IBD) has been observed, especially among children and adolescents. Currently, few studies focus on the differentiation of inflammation in IBD subunits, i.e., Crohn’s Disease (CD) and Ulcerative Colitis (UC). The aim of this study was to compare the concentrations of proinflammatory mediators of arachidonic acid (ARA) and linoleic acid (LA) in patients with CD (n = 34) and UC (n = 30), in order to identify differences in inflammation in both diseases and within the same entity, according to disease activity. Sixty-four adolescents with a mean age of 13.76 ± 2.69 and 14.15 ± 3.31, for CD and UC, respectively, were enrolled in the study. Biochemical analysis of ARA and LA derivatives was performed using a liquid chromatography. A trend was observed in the concentration of 15S-HETE (hydroxyeicosatetraenoic acids) in CD relative to UC. The active phase of both diseases showed a higher 15S-HETE concentration in active CD relative to active UC. Comparing patients with CD with active and inactive disease showed a trend of increased levels of thromboxane B2, leukotriene B4 and 9S-HODE (hydroxyoctadecadienoic acid) in the active versus the inactive disease. We also observed statistically significantly higher levels of 12S-HETE in inactive CD relative to active CD. In the UC group, on the other hand, statistically significantly higher levels of prostaglandin E2 and 16RS-HETE were observed in active UC relative to inactive UC. Moreover, significantly higher concentrations of LTX A4 5S, 6R were observed in inactive UC relative to the active phase. In conclusion, the present study indicated the activity of the 15-LOX pathway in CD. Further studies involving lipid mediators in patients with IBD may contribute to the development of new therapies for the treatment of IBD. The identification of differences in the course of inflammation may help to target therapy in CD and UC, and perhaps allow the introduction of an additional diagnostic marker between the two main IBD subtypes.

Partial replacement of dietary linoleic acid with long chain n-3 polyunsaturated fatty acids protects against dextran sulfate sodium-induced colitis in rats

Imbalances in the dietary n-6 and n-3 polyunsaturated fatty acids have been implicated in the increased prevalence of inflammatory bowel disease. This study investigated the effects of substitution of linoleic acid with long chain n-3 polyunsaturated fatty acids and hence decreasing n-6:n-3 fatty acid ratio on inflammatory response in dextran sulfate sodium induced colitis. Male weanling Sprague Dawley rats were fed diets with n-6:n-3 fatty acid in the ratios of 215,50,10 or 5 for 3 months and colitis was induced by administration of dextran sulfate sodium in drinking water during last 11 days. Decreasing the dietary n-6:n-3 fatty acid ratio to 10 and 5 significantly attenuated the severity of colitis as evidenced by improvements in clinical symptoms, reversal of shortening of colon length, reduced severity of anemia, preservation of colonic architecture as well as reduced colonic mucosal myeloperoxidase activity. This protection was associated with suppression of colonic mucosal proinflammatory mediators such as TNFα, IL-1β and nitric oxide. These findings suggest that long chain n-3 polyunsaturated fatty acids at a level of 3.0 g/kg diet (n-6:n-3 ratio of 10) prevents dextran sulfate sodium induced colitis by suppressing the proinflammatory mediators.

Attenuation of colonic inflammation by partial replacement of dietary linoleic acid with α-linolenic acid in a rat model of inflammatory bowel disease

Increasing prevalence of inflammatory bowel disease may be due to imbalance in the intake of n-6 and n-3 PUFA in the diet. This study investigates the impact of varying ratios of dietary linoleic acid (LA, 18 : 2n-6) to α-linolenic acid (ALA, 18 : 3n-3) on the inflammatory response in dextran sulphate sodium (DSS)-induced colitis. Weanling male Sprague-Dawley rats were divided into five groups: a non-colitic group with a LA:ALA ratio of 215 (CON-215), and colitic groups with LA:ALA ratios of 215 (DSS-215), 50 (DSS-50), 10 (DSS-10) and 2 (DSS-2). Blends of groundnut, palmolein and linseed oils were used to provide varying LA:ALA ratios. All the rats were fed the respective experimental isoenergetic diets containing 10 % fat for 90 d and DSS was administered during the last 11 d. Colonic inflammation was evaluated by clinical, biochemical and histological parameters. The results showed attenuation of colitis in the DSS-2 group as evidenced by significant reductions in disease activity index, mucosal myeloperoxidase activity (P < 0·05), alkaline phosphatase activity (P < 0·01) and increase in colon length (P < 0·01) compared to the groups fed with higher ratios (DSS-215). This was accompanied by significant reductions in mucosal proinflammatory cytokines TNF-α (P < 0·01) and IL-1β (P < 0·01) and improvement in the histological score. Further, ALA supplementation increased long-chain (LC) n-3 PUFA and decreased LC n-6 PUFA in colon structural lipids. These data suggest that substitution of one-third of LA with ALA (LA:ALA ratio 2) mitigates experimental colitis by down-regulating proinflammatory mediators.

Hemokinin-1 stimulates prostaglandin E₂ production in human colon through activation of cyclooxygenase-2 and inhibition of 15-hydroxyprostaglandin dehydrogenase

Hemokinin-1 (HK-1) is a newly identified tachykinin, originating from the immune system rather than neurons, and may participate in the immune and inflammatory response. In colonic mucosa of patients with inflammatory bowel disease (IBD), up-regulation of the TAC4 gene encoding HK-1 and increased production of prostaglandin E₂ (PGE₂) occur. Our aim was to examine the mechanistic link between human HK-1 and PGE₂ production in normal human colon. Exogenous HK-1 (0.1 μM) for 4 h evoked an increased PGE₂ release from colonic mucosal and muscle explants by 10- and 3.5-fold, respectively, compared with unstimulated time controls. The HK-1-stimulated PGE₂ release was inhibited by the tachykinin receptor antagonists (S)1-2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)piperidin-3-yl]ethyl-4-phenyl-l azonia-bicyclo[2.2.2]octane (SR140333) [neurokinin-1 (NK₁)] and N-[(2S)-4-(4-acetamido-4-phenylpiperidin-1-yl)-2-(3,4-dichlorophenyl)butyl]-N-methylbenzamide (SR48968) [neurokinin-2 (NK₂)] and was also inhibited by the cyclooxygenase (COX)-2 inhibitor N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide) (NS-398) but not by the COX-1 inhibitor 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC-560). A parallel study with substance P showed similar results. Molecular studies with HK-1-treated explants demonstrated a stimulatory effect on COX-2 expression at both transcription and protein levels. It is noteworthy that this was coupled with HK-1-induced down-regulation of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) mRNA and protein expression. Immunoreactivity for 15-PGDH occurred on inflammatory cells, epithelial cells, platelets, and ganglia. This finding provides an additional mechanism for HK-1-evoked PGE₂ increase, in which HK-1 may interfere with the downstream metabolism of PGE₂ by suppressing 15-PGDH expression. In conclusion, our results uncover a novel inflammatory role for HK-1, which signals via NK₁ and NK₂ receptors to regulate PGE₂ release from human colonic tissue, and may further explain a pathological role for HK-1 in IBD when abnormal levels of PGE₂ occur.

Cytochrome P-450 4F18 is the leukotriene B4 omega-1/omega-2 hydroxylase in mouse polymorphonuclear leukocytes: identification as the functional orthologue of human polymorphonuclear leukocyte CYP4F3A in the down-regulation of responses to LTB4

Leukotriene B(4) (LTB(4)) is a potent chemoattractant for polymorphonuclear leukocytes (PMN) and other cells. Human PMN inactivate LTB(4) by omega-oxidation catalyzed by cytochrome P-450 (CYP) 4F3A. The contribution of the enzymatic inactivation of LTB(4) by CYP4Fs to down-regulating functional responses of cells to LTB(4) is unknown. To elucidate the role of CYP4F-mediated inactivation of LTB(4) in terminating the responses of PMN to LTB(4) and to identify a target for future genetic studies in mice, we have identified the enzyme that catalyzes the omega-1 and omega-2 oxidation of LTB(4) in mouse myeloid cells as CYP4F18. As determined by mass spectrometry, this enzyme catalyzes the conversion of LTB(4) to 19-OH LTB(4) and to a lesser extent 18-OH LTB(4). Inhibition of CYP4F18 resulted in a marked increase in calcium flux and a 220% increase in the chemotactic response of mouse PMN to LTB(4). CYP4F18 expression was induced in bone marrow-derived dendritic cells by bacterial lipopolysaccharide, a ligand for TLR4, and by poly(I.C), a ligand for TLR3. However, when bone marrow-derived myeloid dendritic cells trafficked to popliteal lymph nodes from paw pads, the expression of CYP4F18 was down-regulated. The results identify CYP4F18 as a critical protein in the regulation of LTB(4) metabolism and functional responses in mouse PMN and identify it as the functional orthologue of human PMN CYP4F3A.

Electrical behaviour of interleukin-1 beta (IL-1 beta) and prostaglandin-E2 (PGE2) on colonic myenteric neurones

Abstract Intracellular recordings were used to examine the effects on electrical and synaptic behaviour of interleukin (IL)-1beta and prostaglandin E2(PGE2) on myenteric neurones of the guinea-pig colon. Application of IL-1beta and PGE2resulted in a concentration-dependent slow depolarization with enhanced spike discharge in, respectively, 45% (21/47) and 83% (33/41) of the impaled colonic neurones. Administration of IL-1beta in three neurones (6%) elicited a hyperpolarization. Responses remained during tetrodotoxin application, indicative of a direct effect of both substances on the impaled neurones. The effects of IL-1beta remained in the presence of indomethacine, a prostaglandin synthase inhibitor. Responses were seen in both nitric oxide synthase- and choline acetyl transferase-immunoreactive neurones. IL-1beta evoked a 26% reduction of the fast excitatory postsynaptic potential. These results indicate that the application of IL-1beta and PGE2evoke direct excitatory actions on a subset of myenteric neurones. For IL-1beta, direct inhibition and presynaptic inhibition of the fast excitatory postsynaptic potential has also been found. In the distal colon, responses to IL-1beta are not mediated through PGE2pathways.