Jean More

Peroxisome proliferator-activated receptor alpha-isoform deficiency leads to progressive dyslipidemia with sexually dimorphic obesity and steatosis.

The α-isoform of the peroxisome proliferator-activated receptor (PPARα) is a nuclear transcription factor activated by structurally diverse chemicals referred to as peroxisome proliferators. Activators can be endogenous molecules (fatty acids/steroids) or xenobiotics (fibrate lipid-lowering drugs). Upon pharmacological activation, PPARα modulates target genes encoding lipid metabolism enzymes, lipid transporters, or apolipoproteins, suggesting a role in lipid homeostasis. Transgenic mice deficient in PPARα were shown to lack hepatic peroxisomal proliferation and have an impaired expression and induction of several hepatic target genes. Young adult males show hypercholesterolemia but normal triglycerides. Using a long term experimental set up, we identified these mice as a model of monogenic, spontaneous, late onset obesity with stable caloric intake and a marked sexual dimorphism. Serum triglycerides, elevated in aged animals, are higher in females that develop a more pronounced obesity than males. The latter show a marked and original centrilobular-restricted steatosis and a delayed occurrence of obesity. Fat cells from their liver express substantial levels of PPARγ2 transcripts when compared with lean cells. These studies demonstrate, in rodents, the involvement of PPARα nuclear receptor in lipid homeostasis, with a sexually dimorphic control of circulating lipids, fat storage, and obesity. Characterization of this pathological link may help to delineate new molecular targets for therapeutic intervention and could lead to new insights into the etiology and heritability of mammalian obesity.

Effects of nematode infection on sensitivity to intestinal distension: Role of tachykinin NK2 receptors

Distension of the rat intestine causes a depressor response which is predictive of nociception. This study investigated the effects of previous infection with Nippostrongylus (N.) brasiliensis on the sensitivity to intestinal distension and the role of tachykinin NK2 receptors. The tachykinin NK2 receptor antagonist, SR48968 (S)-N-methyl-N[4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichloropheny l)butyl]benzamide) inhibited the nociceptive response (ED50 = 0.7 mg/kg) in control rats. In post-N. brasiliensis-infected rats sensitivity to intestinal distension was increased which was accompanied by an increase in the apparent potency value of SR48968 (ED50 = 0.1 mg/kg). The hypersensitivity was limited to areas of hypermastocytosis. It is concluded that the post-inflammatory changes that occur in post-infected rats increase visceral sensitivity and the apparent potency of tachykinin NK2 receptor antagonists.

Protective role of vagal afferents in experimentally-induced colitis in rats

The aim of this study was to evaluate the regulatory role of vagal afferents in the development of colonic inflammation induced by trinitrobenzenesulfonic acid (TNBS) in rats. Groups of Wistar rats were treated with capsaicin or its vehicle applied perivagally (sham treatment). Colonic transit time was evaluated, and, two days later, one half of the animals received an intracolonic instillation of TNBS/ethanol (40 mg/kg), and the other received saline. Inflammation was evaluated functionally (gut permeability), biochemically (myeloperoxydase activity) and histologically. Vagal capsaicin deafferentation did not modify colonic transit time. In TNBS treated groups, inflammation was enhanced by capsaicin pretreatment, as determined by an increased gut permeability, MPO activity, and histological damage score. These results suggest that vagal afferents have a protective role in TNBS-induced colitis in rats, unrelated to changes in colonic transit time.

Comparative effects of nonpeptide tachykinin receptor antagonists on experimental gut inflammation in rats and guinea-pigs

Previous studies have shown tachykinins implicated in gut inflammation. The aim of this work was to evaluate the effect of treatments with tachykinin NK1, NK2, and NK3 selective receptor antagonists on the development of gut inflammation induced by trinitrobenzenesulfonic acid (TNBS) in rats and guinea-pigs. On day 0, rats and guinea-pigs received an intraluminal instillation of TNBS/ethanol (40 mg/kg). Each group was daily treated with intraperitoneally injected NK1 (SR 140333; 0.3 mg/kg/day), NK2 (SR 48968; 5 mg/kg/day), or NK3 (SR 142801; 1, 5, or 10 mg/kg/day) receptor antagonists or their vehicle. On day 4, inflammatory levels were evaluated by measuring gut permeability, myeloperoxidase activity, macro- and microscopic damage scores. In TNBS treated rats, daily administration of SR 140333 (0.3 mg/kg/day) and SR 48968 (5 mg/kg/day) reduced colonic inflammation. In TNBS treated guinea-pigs, daily administration of SR 48968 (5 mg/kg/day) and SR 142801 (at 5 and 10 mg/kg/day) attenuated significantly ileal injury. These results suggest that non-peptide tachykinin receptor antagonists are potent anti-inflammatory agents on gut inflammation in rats and guinea-pigs. However, their activity depends upon the animal species and type of receptor considered.

Platelet-activating factor and interleukin 1 are involved in colonic dysmotility in experimental colitis in rats.

BACKGROUND Intracolonic administration of trinitrobenzene sulfonic acid (TNBS) to rats produces chronic colitis associated with an increased release of eicosanoids, platelet-activating factor (PAF), and interleukins. METHODS Motor effects of TNBS on proximal colon were evaluated electromyographically in rats. Mediator involvement was investigated using eicosanoids and PAF antagonists. RESULTS The colonic myoelectrical activity was 59 +/- 17 spike bursts per hour lasting 6.9 +/- 1.3 seconds. Two to eight days after TNBS treatment, spike-burst duration was significantly (P < 0.05) higher, with a maximal 1.5-4-fold enhancement at day 3. These alterations were significantly (P < 0.05) reduced by daily treatment with MK-886, a 5-lipoxygenase inhibitor (10 mg/kg, orally), whereas indomethacin (1 mg/kg per day, intramuscularly) was ineffective. At day 3, RP55778, a PAF antagonist (45, 60 mg/kg, intraperitoneally), and rIRAP, an interleukin 1 antagonist (0.3 mg/kg, intraperitoneally) but not KT1-32, a thromboxane A2 antagonist (30, 60 mg/kg orally), nor SKF104,353, a leukotriene D4 antagonist (2, 4 mg/kg, orally), significantly (P < 0.05) reduced the TNB-induced motor effects. CONCLUSION TNBS-induced colitis in rats involves a delayed long-lasting dysmotility involving PAF, interleukin 1, and some leukotrienes but not leukotriene D4, thromboxane A2, or other cyclo-oxygenase products.

Role of 5-HT3 receptors and afferent fibers in the effects of mast cell degranulation on colonic motility in rats

BACKGROUND/AIMS Mediators released by mast cell degranulation contribute to digestive motility disturbances. According to the role of serotonin and the close proximity of mast cells to nerves, the aim of this study was to assess the role of 5-hydroxytryptamine 3 (5-HT3) receptors, capsaicin-sensitive afferent fibers, and some of their neuropeptides (substance P and calcitonin gene-related peptide) in colonic motor alterations induced by degranulation of mast cells by the compound BrX-537A. METHODS The effects of BrX-537A (2 mg/kg intraperitoneally) were determined by electromyography in conscious rats implanted with electrodes in the cecocolonic wall. RESULTS BrX-537A inhibited cecocolonic myoelectric activity for 7-8 hours. A primary and dramatic reduction of spike burst frequency, lasting 30 minutes, was affected by none of the pretreatments tested. The following inhibition was fully antagonized by ketotifen (mast cell stabilizer), granisetron and ondansetron (5-HT3 antagonists), RP-67,580 (NK1 antagonist), and perivagal capsaicin pretreatment. A temporary blockade was observed after administration of CP-96,345 (NK1 antagonist) and in rats systemically treated by capsaicin. The calcitonin gene-related peptide antagonist hCGRP(8-37) did not modify the BrX-537A-induced inhibition. CONCLUSIONS 5-HT3 receptors, sensory afferent fibers reaching the vagus nerves, and substance P are major components of the colonic motor inhibition induced by mast cell degranulation.

Boosted systemic immune and local responsiveness after intestinal inflammation in orally sensitized guinea pigs

BACKGROUND & AIMS Intestinal inflammation resulting in disruption of the mucosal barrier function has been proposed as a cause of increased incidence of allergic diseases. This study was designed to evaluate whether intestinal inflammation is able to change the immune responsiveness to sensitization and antigen challenge responses. METHODS Guinea pigs orally sensitized to cows milk proteins were either treated or not treated with trinitrobenzenesulfonic acid (TNBS) to induce intestinal inflammation and compared with control animals (not sensitized). Systemic immune and local responsiveness to antigen challenge were assessed by measuring antibody serum titers, colonic fluid secretion, mucosal histamine level, and mucus depletion. Intestinal permeability was evaluated from 51Cr-ethylenediaminetetraacetic acid (EDTA) recovery and beta-lactoglobulin serum level. RESULTS Immunoglobulin E titers were higher in TNBS-treated animals than in non-TNBS-treated sensitized animals. Antigen challenge in TNBS-treated animals induced a fourfold increase of colonic secretion and greater histamine and mucus depletion than in non-TNBS-treated animals. Permeability to 51Cr-EDTA increased 5 days after TNBS treatment but was unchanged after antigen challenge. In contrast to controls, beta-lactoglobulin was not detected in the sera of challenged sensitized and TNBS-treated animals. CONCLUSIONS Intestinal inflammation increasing gut permeability enhances the sensitization process. Therefore, local anaphylactic reactions are exacerbated after antigen challenge.

Brain Fos expression and intestinal motor alterations during nematode-induced inflammation in the rat

Brain-gut interactions and intestinal motility were studied during pulmonary and jejunal inflammation induced by Nippostrongylus brasiliensis. Jejunal electromyographic activity was continuously recorded from day 1 before to day 28 after infection. Expression of c- fos was assessed in the brain by immunohistochemistry, and myeloperoxidase (MPO) activity was determined in lung and intestine on days 1, 7, 14, 21, and 28 postinfection. The cyclic intestinal motor pattern was replaced by an irregular activity from day 4, corresponding to larvae migration to the intestine, to day 14. c- fos was expressed in the caudal nucleus of the solitary tract (NTS) and lateral parabrachial nucleus (LPB) on day 1 (lung stage of N. brasiliensis) and in the medial part of the NTS, the LPB, and locus ceruleus on day 7. Pulmonary and intestinal MPO activity was increased from days 1 to 21 postinfection. During N. brasiliensis infection, c- fos expression indicates that specific and different brain nuclei are activated at the onset of pulmonary and intestinal inflammation, which is associated with motor disorders.

Inverse regulation of α- and β-adrenoceptors during trinitrobenzenesulfonic acid (TNB)-induced inflammation in guinea-pig small intestine

The hypothesis has been raised that intestinal motor disturbances induced by inflammation of the digestive tract may reflect alterations in intestinal cell-membrane receptors. This question has been addressed herein for adrenoceptors by performing [3H]prazosin, [3H]rauwolscine and [3H]DHA binding studies on guinea-pig jejunal smooth-muscle membrane preparations from both healthy controls and 3, 6, and 10 days after TNB-induced intestinal inflammation. Each of the adrenoceptor subtype-selective radioligands used bound selectively to a single saturable class of sites, with no significant (p<0.05) variation of dissociation constant (KD) values along the inflammatory process. In contrast maximal binding capacities (Bmax) for the different radioligands varied moderately but significantly (p<0.05 and p<0.01) according to the time after TNB injection. The α-adrenoceptors were significantly upregulated, respectively from (mean ± SE in fmoles/mg of roteins) 27 ± 3.8 (controls) to 91 ± 3.1 (day 10) fortheα1-subtype, and from 26 ± 2.7 (controls) to 102 ± 5.9 (day 10) for the α2-subtype. In contrast β-adrenoceptors were down-regulated from 384 ± 34.6 (rmcontrols) to 158 ± 17.2 (day 10). These findings highlighted an apparently inverse pathological regulation of intestinal α- and β- adrenoceptor densities. They suggest that changes in intestinal adrenoceptors, probably resulting from functional denervation of the inflamed bowel tissue, may contribute to the altered intestinal motility observed in inflammatory bowel diseases.

Inflammatory neutrophils secrete annexin 1 during experimentally induced colitis in rats

Immunoblotting and immunohistochemical analysiswere performed to identify the cells expressing andsecreting annexin 1 during experimental rat colitisinduced by trinitrobenzene sulfonic acid. Annexin 1 expression was increased during theinflammation. Likewise, annexin 1 secretion was inducedin inflamed colons at one, three, six, and nine daysafter trinitrobenzene sulfonic acid treatment but wasnot detected in colons from controls and rats at 12days. Immunohistochemistry showed that the rise inannexin 1 expression resulted from the infiltration oftwo types of leukocytes highly positive for annexin 1: neutrophils (the most abundant) andmacrophages. At day 1 after treatment, neutrophils ofthe inflammatory site, in mucosa and submucosa, are theonly cells expressing annexin 1. Immunoblotting showed that they secreted annexin 1 whereasneutrophils from blood or tunica muscularis did not.This indicates that, during this colitis, annexin 1 canbe secreted by neutrophils located in the inflammatorysite.