The intestinal epithelium: a participant in as well as the target of inflammation?

The role of purinergic pathways in the pathophysiology of gut diseases: pharmacological modulation and potential therapeutic applications

Gut homeostasis results from complex neuro-immune interactions aimed at triggering stereotypical and specific programs of coordinated mucosal secretion and powerful motor propulsion. A prominent role in the regulation of this highly integrated network, comprising a variety of immune/inflammatory cells and the enteric nervous system, is played by purinergic mediators. The cells of the digestive tract are literally plunged into a "biological sea" of functionally active nucleotides and nucleosides, which carry out the critical task of driving regulatory interventions on cellular functions through the activation of P1 and P2 receptors. Intensive research efforts are being made to achieve an integrated view of the purinergic system, since it is emerging that the various components of purinergic pathways (i.e., enzymes, transporters, mediators and receptors) are mutually linked entities, deputed to finely modulating the magnitude and the duration of purinergic signaling, and that alterations occurring in this balanced network could be intimately involved in the pathophysiology of several gut disorders. This review article intends to provide a critical appraisal of current knowledge on the purinergic system role in the regulation of gastrointestinal functions, considering these pathways as a whole integrated network, which is capable of finely controlling the levels of bioactive nucleotides and nucleosides in the biophase of their respective receptors. Special attention is paid to the mechanisms through which alterations in the various compartments of the purinergic system could contribute to the pathophysiology of gut disorders, and to the possibility of counteracting such dysfunctions by means of pharmacological interventions on purinergic molecular targets.

Lipoxins, aspirin-triggered 15-epi-lipoxin stable analogs and their receptors in anti-inflammation: a window for therapeutic opportunity

LXs and 15-epimer LXs are generated during cell-cell interactions that occur during multicellular host response to inflammation, tissue injury or host defense. Results indicate that they are present in vivo during human illness and carry predominantly counter-regulatory biological actions opposing the action of well-characterized mediators of inflammation that appear to lead to resolution of the inflammatory response or promotion of repair and wound healing. The first selective receptor of LXA4 was identified by direct ligand binding and was cloned and characterized. Its signaling involves a novel polyisoprenyl-phosphate pathway that directly regulates PLD (Levy et al. 1999a). LX- and 15-epimer-LX-stable analogs that resist metabolic inactivation were designed, synthesized and shown to be potent LX mimetics and novel topically active anti-inflammatory agents in animal models. These new investigational tools enable structure-function studies of LX signal transduction, further elucidation of the role of LX and 15-epimer LX in host responses and exploitation of their potent bioactions in the design of novel pharmacologic agents.

Inhibition of cytoplasmic phospholipase A2 expression by glucocorticoids in rat intestinal epithelial cells

BACKGROUND & AIMS

Glucocorticoids are the most potent and widely accepted anti-inflammatory agents in the treatment of pathological conditions of the gastrointestinal tract in part by inhibiting the synthesis of proinflammatory prostanoids and leukotrienes. Multiple forms of phospholipase A2 may be associated with the production of these metabolites; this study focused on the molecular mechanism(s) by which glucocorticoids control expression of the arachidonyl-selective, cytosolic phospholipase A2 (cPLA2) in intestinal cells.

METHODS

Northern analysis, a transcriptional assay, and enzymatic evaluation were used to access expression of the cPLA2 gene in rat small intestinal epithelial and mouse fibroblast cell lines treated with dexamethasone.

RESULTS

Basal cPLA2 messenger RNA (mRNA) expression was repressed 75% in the presence of dexamethasone with a concomitant decrease in enzymatic activity. Nuclear runoff assays showed a marked decline in de novo cPLA2 RNA synthesis, implicating a transcriptional mechanism associated with the dexamethasone-mediated suppression of cPLA2. Induced expression of cPLA2 mRNA by several proinflammatory cytokines was blocked by cotreatment with dexamethasone.

CONCLUSIONS

Glucocorticoids are capable of markedly altering basal and cytokine-stimulated cPLA2 gene expression in intestinal epithelial cells, leading to a reduction in arachidonate pools in these cells. Dexamethasone-dependent inhibition occurs through a direct reduction of de novo cPLA2 gene transcription.