Rocío López-Posadas

Effect of flavonoids on rat splenocytes, a structure–activity relationship study

Flavonoids are polyphenols frequently consumed in the diet which have been suggested to exert a number of beneficial actions on human health, including intestinal anti-inflammatory activity. Their properties have been studied in numerous cell types, but little is known about their effect on leukocyte biology. We have selected 9 flavonoids (extended to 14 flavonoids plus the related polyphenol resveratrol in some cases) with different structural features to characterize their effects on leukocyte viability, proliferation, and expression of cyclooxygenase 2 (EC 1.14.99.1), inducible nitric oxide synthase (iNOS, EC 1.14.13.39) and proinflammatory cytokines (TNF-alpha, IFN-gamma, IL-2), as well as to elucidate the structural requirements in each case. Quiescent and concanavalin A-stimulated rat splenocytes were used as a model. Flavonoids (50 microM) had a dramatic inhibitory effect on cytokine secretion. Inducible nitric oxide synthase expression was also blocked largely by some flavonoids, especially quercetin, luteolin and apigenin, while cyclooxygenase 2 was downregulated only by apigenin, diosmetin and quercetin. Apigenin, luteolin, genistein and quercetin had substantial cytotoxic/proapoptotic effects, while chrysin, daidzein, hesperetin and kaempferol did not reduce cell viability. In contrast, all flavonoids had powerful antiproliferative effects. However, none of the compounds activated caspase 3 (EC 3.4.22.56), but actually lowered caspase 3 activation and expression in concanavalin A-stimulated cells. The activity of the quercetin metabolite isorhamnetin was generally lower than that of the parent compound. We conclude that flavonoids have powerful effects on lymphocytes with distinct structural requirements that may contribute to their intestinal anti-inflammatory activity. The bioactivity of orally administered flavonoids may be dampened by biotransformation in vivo, particularly in extraintestinal sites.

Bovine Glycomacropeptide Has Intestinal Antiinflammatory Effects in Rats with Dextran Sulfate-Induced Colitis

Milk κ-casein-derived bovine glycomacropeptide (GMP) has immunomodulatory and bacterial toxin-binding effects, and it has been shown to exert intestinal antiinflammatory activity in the trinitrobenzenesulfonic acid-induced model of colitis. However, its mechanism of action is not well characterized, and it is not known whether GMP is effective in other experimental models. The intestinal antiinflammatory activity of GMP was assessed in the dextran sulfate sodium (DSS)-induced model of rat colitis. DSS was applied at a starting concentration of 5% (wt:v) in drinking water and adjusted when the disease activity index (DAI) increased substantially for 10 d. There were 3 experimental groups: control (no inflammation), DSS, and GMP (GMP-treated rats with DSS-induced colitis). GMP pretreatment (500 mg · kg(-1) · d(-1), starting 2 d before DSS treatment) reduced the DAI by 60% and lowered the colonic damage score by 44% (P < 0.05). GMP fully normalized the colonic expression of interleukin (IL) 1β, IL17, IL23, IL6, transforming growth factor β, IL10, and Foxp3 as assessed by quantitative RT-PCR. The production of interferon-γ by mesenteric lymph node cells ex vivo was also normalized by GMP treatment. In contrast, GMP did not change colonic thickening, myeloperoxidase, cyclooxygenase 2, or alkaline phosphatase. Histology analysis showed better preservation of the epithelium and attenuated infiltration and submucosal thickening in rats treated with GMP. We conclude that GMP exerts intestinal antiinflammatory activity in this model, which may be primarily related to actions on Th1 and Th17 lymphocytes and perhaps macrophages.

Exogenous alkaline phosphatase treatment complements endogenous enzyme protection in colonic inflammation and reduces bacterial translocation in rats.

Alkaline phosphatase (AP) inactivates bacterial lipopolysaccharide and may therefore be protective. The small intestine and colon express intestinal (IAP) and tissue nonspecific enzyme (TNAP), respectively. The aim of this study was to assess the therapeutic potential of exogenous AP and its complementarity with endogenous enzyme protection in the intestine, as evidenced recently. IAP was given to rats by the oral or intrarectal route (700U/kgday). Oral budesonide (1mg/kgday) was used as a reference treatment. Treatment with intrarectal AP resulted in a 54.5% and 38.0% lower colonic weight and damage score, respectively, and an almost complete normalization of the expression of S100A8, LCN2 and IL-1β (p<0.05). Oral AP was less efficacious, while budesonide had a more pronounced effect on most parameters. Both oral and intrarectal AP counteracted bacterial translocation effectively (78 and 100%, respectively, p<0.05 for the latter), while budesonide failed to exert a positive effect. AP activity was increased in the feces of TNBS colitic animals, associated with augmented sensitivity to the inhibitor levamisole, suggesting enhanced luminal release of this enzyme. This was also observed in the mouse lymphocyte transfer model of chronic colitis. In a separate time course study, TNAP was shown to increase 2-3 days after colitis induction, while dextran sulfate sodium was a much weaker inducer of this isoform. We conclude that exogenous AP exerts beneficial effects on experimental colitis, which includes protection against bacterial translocation. AP of the tissue-nonspecific isoform is shed in higher amounts to the intestinal lumen in experimental colitis, possibly aiding in intestinal protection.

Tissue-nonspecific alkaline phosphatase is activated in enterocytes by oxidative stress via changes in glycosylation.

Background: Intestinal inflammation produces an induction of alkaline phosphatase (AP) activity that is attributable in part to augmented expression, accompanied by a change in isoform, in epithelial cells. Methods: This study focuses on induction of AP in intestinal epithelial cells in vitro. Results: Treatment with the oxidants H2O2, monochloramine, or tButOOH increases AP activity in vitro in Caco‐2, HT29, and IEC18 cells. We selected IEC18 cells for further testing. Basal AP activity in IEC18 cells is of the tissue‐nonspecific (bone‐liver‐kidney) type, as indicated by Northern and Western blot analysis. Oxidative stress augments AP activity and the sensitivity of the enzyme to levamisole, homoarginine, and heat in IEC18 cells. Increased immunoreactivity to tissue‐nonspecific AP antibodies suggests an isoform shift from liver to either kidney or bone type. This effect occurs without changes at the mRNA level and is sensitive to tunicamycin, an inhibitor of N‐glycosylation, and neuraminidase digestion. Saponin and deoxycholate produce similar effects to oxidants. Butyrate but not proinflammatory cytokines or LPS can induce a similar effect but without toxicity. The AP increase is not prevented by modulators of the MAPK, NF‐&kgr;B, calcium, and cyclic adenosine monophosphate (cAMP) pathways, and is actually enhanced by actinomycin D via higher cell stress. Conclusions: Oxidative stress causes a distinct increase in enterocyte AP activity together with cell toxicity via changes in the glycosylation of the enzyme that correspond to a shift in isotype within the tissue‐nonspecific paradigm. We speculate that this may have physiological implication for gut defense. (Inflamm Bowel Dis 2011)

The intestinal antiinflammatory agent glycomacropeptide has immunomodulatory actions on rat splenocytes

Bovine glycomacropeptide (GMP) is an immunologically active milk peptide that is a part of the normal human diet. GMP has therapeutic value in preclinical models of intestinal inflammation, and its mechanism may be related to effects on lymphocytes. This study focuses on the actions of GMP on rat splenocytes in vitro and in vivo. Bovine serum albumin and lactoferrin were used for comparative purposes. GMP (0.01-0.1mgmL(-1)) enhanced Concanavalin A (ConA) evoked but not basal splenocyte proliferation. At 1mgmL(-1) GMP lost this effect but augmented basal TNF-alpha secretion and also iNOS and COX2 expression. IFN-gamma, IL-2 and IL-17 were not affected by GMP in quiescent splenocytes, but IL-10 was augmented at all concentrations tested. On the other hand, GMP produced a marked inhibitory effect (70%) on IFN-gamma secretion and to a lower extent (50%) also on TNF-alpha. GMP was shown to block STAT4 but not IkappaB-alpha phosphorylation. The Treg marker Foxp3 was markedly upregulated by GMP. Bovine serum albumin had some effects on splenocyte function which were of lower magnitude and not entirely coincidental, while lactoferrin had a strong antiproliferative effect, as expected, indicating a specific effect of GMP. When administered for 3 days to normal Wistar rats, GMP reproduced the Foxp3 induction effect observed previously in vitro. This was observed in splenocytes but not in thymocytes, and only when administered by the oral rather than the intraperitoneal route. Thus our results support the hypothesis that GMP may limit intestinal inflammation acting at least in part on lymphocytes.

A Porphyra columbina hydrolysate upregulates IL-10 production in rat macrophages and lymphocytes through an NF-κB, and p38 and JNK dependent mechanism.

The marine environment represents a relatively untapped source of functional ingredients. Here we characterise a hydrolysate obtained from Phorphyra columbina (PcRH) and its effects on primary splenocytes, macrophages and T lymphocytes in vitro. Our product had a high degree of hydrolysis, due to the use of a mixture of endo-peptidase and exo-peptidase, and was enriched in Asp, Ala and Glu. PcRH had mitogenic effects on rat splenic lymphocytes. IL-10 secretion was enhanced by PcRH in splenocytes (235%), macrophages (150%) and in lymphocytes (472%), while the production of TNFα and other proinflammatory cytokines by macrophages was inhibited (15-75%), especially under lipopolysaccharide stimulation. The effect of the hydrolysate on IL-10 was evoked by JNK, p38 MAPK and NF-κB dependent pathways in T lymphocytes. We conclude that PcRH has immunomodulatory effects on macrophages and lymphocytes, activating NF-κB and MAPK dependent pathways, and predominantly inducing IL-10 production.

The bisphosphonate alendronate improves the damage associated with trinitrobenzenesulfonic acid-induced colitis in rats

The nitrogen‐containing bisphosphonates are drugs used successfully in the treatment of osteoporosis. They act inhibiting farnesyl diphosphate synthase. This mechanism may also produce anti‐inflammatory effects. The therapeutic activity of alendronate was tested in vivo using a model of inflammatory bowel disease.

Fructooligosacharides reduce Pseudomonas aeruginosa PAO1 pathogenicity through distinct mechanisms.

Pseudomonas aeruginosa is ubiquitously present in the environment and acts as an opportunistic pathogen on humans, animals and plants. We report here the effects of the prebiotic polysaccharide inulin and its hydrolysed form FOS on this bacterium. FOS was found to inhibit bacterial growth of strain PAO1, while inulin did not affect growth rate or yield in a significant manner. Inulin stimulated biofilm formation, whereas a dramatic reduction of the biofilm formation was observed in the presence of FOS. Similar opposing effects were observed for bacterial motility, where FOS inhibited the swarming and twitching behaviour whereas inulin caused its stimulation. In co-cultures with eukaryotic cells (macrophages) FOS and, to a lesser extent, inulin reduced the secretion of the inflammatory cytokines IL-6, IL-10 and TNF-α. Western blot experiments indicated that the effects mediated by FOS in macrophages are associated with a decreased activation of the NF-κB pathway. Since FOS and inulin stimulate pathway activation in the absence of bacteria, the FOS mediated effect is likely to be of indirect nature, such as via a reduction of bacterial virulence. Further, this modulatory effect is observed also with the highly virulent ptxS mutated strain. Co-culture experiments of P. aeruginosa with IEC18 eukaryotic cells showed that FOS reduces the concentration of the major virulence factor, exotoxin A, suggesting that this is a possible mechanism for the reduction of pathogenicity. The potential of these compounds as components of antibacterial and anti-inflammatory cocktails is discussed.

It may not be intestinal, but tissue non-specific alkaline phosphatase

The interesting study by Tuin et al 1 in a recent issue of Gut uncovers a hitherto unrecognised protective role of alkaline phosphatase (AP) in intestinal inflammation. These authors measured AP activity (including lipopolysaccharide (LPS) as a substrate) and mRNA level of the intestinal isoform (IAP) in inflamed and non-inflamed mucosa of patients with inflammatory bowel disease. IAP expression and AP activity were virtually non-existent in the colon when compared to the ileum.nnThese researchers follow up on a recent paper by Richard Hodins group2 which describes …