Diprotin A

The involvement of bradykinin and some other inflammatory mediators in formalin-induced oedema and plasma extravasation was examined. Formalin was injected in rat paws at two doses, 1.75% or 5%. The lower dose induced the development of an immediate oedema associated with a progressive accumulation of 125I-labelled albumin in the paws. These changes were suppressed by pretreatment with capsaicin or xylocaine. They were abolished by RP67580, a NK1 receptor antagonist, and increased by phosphoramidon or diprotin A. They were not affected by HOE140, a bradykinin B2 antagonist, captopril, methysergide, mepyramine, indomethacin, ketoprofen or L-N(G)-nitroarginine. The higher dose of formalin induced a swelling of the paws which took place in two phases associated with two periods of increase in vascular permeability. This oedema was reduced by pretreatment with capsaicin but not with xylocaine. It was reduced by RP67580 injected before or 30 min after formalin. It was inhibited by mepyramine, methysergide, indomethacin and NS-398, a cyclooxygenase-2 inhibitor. It was not modified by HOE140. Its development was similar in normal and kininogen-deficient rats. We concluded that formalin administered at a low dose induces an oedema which mainly results from a neurogenic inflammation mediated by neuropeptides such as substance P.

Proline-specific dipeptidyl peptidase (DPP IV) is an established enzyme known to degrade neuropeptides and peptide hormones in vertebrate tissues. DPP IV cleaves peptides at the Pro2 residue. Because several neuropeptides of the cockroach Leucophaea maderae, such as LemTRP-1 (APSGFLGVRamide), are potential substrates for this peptidase, we investigated the occurrence of proline-specific DPP activity in cockroach tissues. Partly purified DPP activity was characterized from the brain and midgut of L. maderae by using Gly-Pro-4-nitroanilide as a substrate. The highest activity was obtained from the membrane fraction of intestine; about 10 times less activity (per milligram protein) was obtained from brain membranes. A smaller amount of soluble DPP activity could also be identified in both tissues. Gel chromatography of the solubilized intestinal DPP activity revealed a molecular mass of about 75 kDa. The enzyme had a pH optimum of 8.5. Diprotin A (Ile-Pro-Ile) was an efficient competitive inhibitor of the cockroach DPP, whereas other known DPP inhibitors were found to be less potent. When incubated with human and cockroach DPP IV, the cleavage products of LemTRP-1 were AP and SGFLGVRamide (des-AP-LemTRP-1) as determined by mass spectrometry of high-performance liquid chromatography (HPLC)-purified peptide fragments.

The endogenous opioid system is involved in the control of gastrointestinal (GI) motility. The potential use of endogenous MOR ligands, endomorphins (EMs), as therapeutics is limited because of their rapid enzymatic degradation and short duration of action. Targeting enzymatic degradation is an approach to prolong EM activity. In the present study, we characterized the effects of novel blockers of EM degradation in GI tissue preparation in vitro. The effects of actinonin, diprotin A (DIP) and the novel peptide EM degradation blockers Tyr-Pro-DClPhe-Phe-NH(2) (EMDB-1), Tyr-Pro-Ala-NH(2) (EMDB-2) and Tyr-Pro-Ala-OH (EMDB-3) on EM-2-mediated inhibition of electrically induced cholinergic twitch contractions were compared in rat ileum in vitro using an organ bath. EMDB-1 and EMDB-2 significantly prolonged the inhibitory effect of EM-2 on smooth muscle contractility in rat ileum. EMDB-2 extended the EM-2 action for up to 60 min compared to 10 min in controls and was more potent than the conventional peptidase inhibitor DIP. EMDB-1 and EMDB-2 are potent EM degradation blockers, which prolong the inhibitory effects of EM-2 on smooth muscle contractility in rat ileum. These novel compounds may be of future use when targeting the endogenous opioid system in the treatment of GI motility disorders such as diarrhea.