Effect of agonist (Nociceptin/Orphanin FQ) and antagonist (UFP-101) of the NOP receptor system in a rat model of experimental colitis

C Petrella1, C Giuli1, H Eutamene2, C Cartier2, M Leveque2, A Bedini3, S Spampinato3, L Bueno2, V Theodorou2, M Broccardo1, G Improta1, S Agostini2. 1Sapienza University of Rome, Physiology and Pharmacology - 00185, Italy, 2INRA, Toulouse, Neuro-Gastroenterology and Nutrition Team - 1331, France, 3University of Bologna, Pharmacology - 40126, Italy

Nociceptin/OrphaninFQ (N/OFQ) and Nociceptin Orphan Peptide (NOP) receptors represent an endogenous system modulating gastrointestinal functions and inflammation. We investigated the effect of the peripheral administration of the agonist N/OFQ (0.02-0.2-2-20 nmol/kg) and the antagonist UFP-101 (1-3-10 nmol/kg) on some inflammatory variables in a rat model of colitis induced by intracolonic (IC) instillation of TNBS (2,4,6 trinitrobenzensulfonic acid) (60 mg/kg, IC). Male Wistar rats (200-250 g) received two intraperitoneal (IP) injections per day of N/OFQ, or UFP-101, or saline for three days after induction of colitis (eight rats for each experimental group). Four days after TNBS, animals were sacrificed and colonic histological damage, myeloperoxidase (MPO) activity, cytokine (IL-1β and IL-10) levels were evaluated. N/OFQ plasmatic concentration was assessed by radioimmunoassay. TNBS instillation (p<0.05) induced inflammatory macroscopic (7.50 ± 0.69 vs. 0.00) and microscopic colonic damage (5.56 ± 0.97 vs. 1.80 ± 0.84) and increased colonic MPO activity (550.40 ± 38.92 vs. 135.00 ± 11.70 U/g protein) in comparison with controls. In colitic rats, N/OFQ (0.02 and 0.2 nmol/kg) improved microscopic damage and MPO activity vs. TNBS group (2.00 ± 1.00 and 196.90 ± 28.21U/g protein, at the dose of 0.2 nmol/kg), whereas at highest doses worsened (p<0.05) colitis. UFP-101 alone (3 and 10 nmol/kg) increased microscopic colonic damage and MPO activity (688.80 ± 35.15 and 828.30 ± 88.14 U/g protein, respectively), whilst at the dose of 1 nmol/kg had no effect and antagonized the protective effect of N/OFQ (0.2 nmol/kg) on colitis. N/OFQ plasmatic levels were not modified in TNBS-treated rats compared with controls (0.36 ± 0.05 vs. 0.41 ± 0.08 ng/ml), whereas they were reduced (p<0.05) in rats treated with UFP-101 at the doses (3 and 10 nmol/kg) that worsen colitis. In conclusion: 1) peripheral low doses of N/OFQ have immunosuppressive and anti-inflammatory effects on TNBS colitis in rats; 2) N/OFQ, at a dose 1000-10000 fold higher than those that protect, worsens colitis. 3) The endogenous peripheral N/OFQergic system plays a protective role in this experimental pathological condition.