Pain inhibition by blocking leukocytic and neuronal opioid peptidases in peripheral inflamed tissue

Abstract

Inflammatory pain can be controlled by endogenous opioid peptides. Here we blocked the degradation of opioids in peripheral injured tissue to locally augment this physiological system. In rats with hindpaw inflammation, inhibitors of aminopeptidase N (APN; bestatin) or neutral endopeptidase (NEP; thiorphan), and a dual inhibitor, NH(2)-CH-Ph-P(O)(OH)CH(2)-CH-CH(2)Ph(p-Ph)-CONH-CH-CH(3)-COOH (P8B), were applied to injured paws. Combined bestatin (1.25-5 mg)/thiorphan (0.2-0.8 mg) or P8B (0.0625-1 mg) alone elevated mechanical nociceptive thresholds to 307 and 227% of vehicle-treated controls, respectively. This analgesia was abolished by antibodies to methionine-enkephalin, leucine-enkephalin, and dynorphin A 1-17, by peripherally restricted and by selective μ-, δ-, and κ-opioid receptor antagonists. Flow cytometry and photospectrometry revealed expression and metabolic activity of APN and NEP on macrophages, granulocytes, and sciatic nerves from inflamed tissue. Radioimmunoassays showed that inhibition of leukocytic APN and NEP by bestatin (5-500 μM)/thiorphan (1-100 μM) combinations or by P8B (1-100 μM) prevented the degradation of enkephalins. Blockade of neuronal peptidases by bestatin (0.5-10 mM)/thiorphan (0.1-5 mM) or by P8B (0.1-10 mM) additionally hindered dynorphin A 1-17 catabolism. Thus, leukocytes and peripheral nerves are important sources of APN and NEP in inflamed tissue, and their blockade promotes peripheral opioid analgesia.

Preventive and alleviative effects of the dual enkephalinase inhibitor (Denki) PL265 in a murine model of neuropathic pain

“…The physiological ligands of MOP and DOP are beta-endorphin, endomorphin-1 and -2 as well as the most abundant pentapeptides Met and Leuenkephalins (Giraud et al, 1983). We decided to test in models of neuropathic pain the efficacy of these latter pentapeptides which are locally released under nocifensive stimuli (Yaksh et al, 1981;Bourgoin et al, 1986;Schreiter et al, 2012).…”

The efficacy of Dynorphin fragments at the κ, μ and δ opioid receptor in transfected HEK cells and in an animal model of unilateral peripheral inflammation

“…It has previously been demonstrated that inhibition of leukocytic and neuronal peptidases in the inflamed paws of rats results in analgesia [17]. However, when the peptidase inhibitors were applied in combination with antibodies against met-enkephalin, leucine-enkephalin and dynorphin 1-17 to the rats paws peripherally, the analgesia was abolished [17].…”

Modulation of disulfide dual ENKephalinase inhibitors (DENKIs) activity by a transient N-protection for pain alleviation by oral route

“…In contrast, the concomitant inhibition of both peptidases produces analgesic responses [11,13]. All together, this indicates that increasing enkephalin concentrations at the nociceptor level promotes "physiological analgesia" [6,12], as demonstrated by microdialysis experiments [12e14] and use of antibodies for measurement of enkephalins in injured tissues [15].…”