Human Opiorphin, a natural antinociceptive modulator of opioid-dependent pathways

Abstract

Mammalian zinc ectopeptidases play important roles in turning off neural and hormonal peptide signals at the cell surface, notably those processing sensory information. We report here the discovery of a previously uncharacterized physiological inhibitor of enkephalininactivating zinc ectopeptidases in humans, which we have named Opiorphin. It is a QRFSR peptide that inhibits two enkephalin-catabolizing ectoenzymes, human neutral ecto-endopeptidase, hNEP (EC 3.4.24.11), and human ecto-aminopeptidase, hAP-N (EC 3.4.11.2). Opiorphin displays potent analgesic activity in chemical and mechanical pain models by activating endogenous opioid-dependent transmission. Its function is closely related to the rat sialorphin peptide, which is an inhibitor of pain perception and acts by potentiating endogenous -and ␦-opioid receptor-dependent enkephalinergic pathways. Here we demonstrate the functional specificity in vivo of human Opiorphin. The pain-suppressive potency of Opiorphin is as effective as morphine in the behavioral rat model of acute mechanical pain, the pin-pain test. Thus, our discovery of Opiorphin is extremely exciting from a physiological point of view in the context of endogenous opioidergic pathways, notably in modulating mood-related states and pain sensation. Furthermore, because of its in vivo properties, Opiorphin may have therapeutic implications.dual neutral endopeptidase͞aminopeptidase N inhibitor ͉ human saliva ͉ pain ͉ peptide mediator ͉ enkephalins Z inc metal ectopeptidases control the receptor-dependent activity of neural and hormonal mediators involved in the regulation of important physiological functions in mammals. They are located at the surface of cells in nervous and systemic tissues and catalyze postsecretory processing or metabolism of neuropeptides and regulatory peptides (1, 2). Prominent among these neuronal and͞or hormonal peptide signals are substance P (SP) and enkephalins, which are implicated in the receptor-dependent modulation of behavioral adaptive responses to stressful or threatening environmental stimuli. They notably regulate spinal processing of nociceptive information and analgesic mechanisms, emotional and͞or motivational responses, anxiety, aggression, and neuroimmune inflammatory phenomena (3-6).Because of the physiological importance and the critical role of zinc ectopeptidases in modulating the functional potency of downstream neuronal and hormonal signals, it is essential to focus on what controls their activity and, as a consequence, the overall regulatory cascade. The discovery of upstream regulators of ectopeptidase activity also is exciting from physiopathological and therapeutic points of view because of the potential for developing new candidate drugs. A brain-specific heptapeptide named spinorphin was isolated and characterized from bovine spinal cord based on its inhibitory activity toward enkephalin-degrading ectoenzymes, such as neutral endopeptidase (NEP; EC 3.4.24.11) and aminopeptidase N (AP-N; EC 3.4.11.2) (7,8). In addition, we characterized rat sial...

hSMR3A as a Marker for Patients With Erectile Dysfunction

“…This protein also acts as an NEP inhibitor, suggesting that the physiological effect of this family of proteins is mediated through NEP inhibition. 16 The identification of hSMR3A as a marker for ED has applications as a diagnostic tool for organic ED and in the development of novel therapies. In the era of agents that are noninvasive and successful for treating ED the quest to establish an etiological diagnosis has been downplayed.…”

Noxious mechanical stimulation evokes the segmental release of opioid peptides that induce μ-opioid receptor internalization in the presence of peptidase inhibitors

“…The most likely explanation for this paradox is that there are endogenous peptidase inhibitors that enable the action of opioids. In fact, three endogenous inhibitors of aminopeptidase and neutral endopeptidase have been found: spinorphin -LVVYPWT (Nishimura and Hazato, 1993), sialorphin -QHNPR (Rougeot et al, 2003) and opiorphin -QRFSR (Wisner et al, 2006). The release of these peptidase-inhibiting peptides appears to play a role in pain control, since sialorphin and opiorphin have analgesic properties, while spinorphin increased the antinociception produced by Leu-enkephalin (Honda et al, 2001).…”

Transfer of Opiorphin Through a Blood-Brain Barrier Culture Model

“…A possible explanation for this difference is that in our culture system no serum factors were present during the experiments, which is a limitation of the model. Peptidases are active in blood and rapidly cleave the native opiorphin peptide, which has a metabolic half-life of 6 min in human plasma; therefore, enzyme activity limits the transfer of opiorphin to the CNS in vivo (4,23,24). In vivo data suggest that even in the presence of serum peptidases opiorphin can cross the BBB in sufficient amounts to raise the concentration of endogenous opioid ligands by inhibiting enkephalinases; thus, it can be appropriate for producing central effects.…”

“…Opiorphin as an enkephalinase inhibitor exerts analgesic and antidepressive effects by the protection of endogenous enkephalins released after pain stimuli (6,7). Opiorphin is the only natural enkephalinaseinhibitor characterized in humans and has similar painsuppressive potency to morphine but without adverse effects (4,6). The efficacy of opiorphin has been verified by in vitro methods and its analgesic activity was also shown in different in vivo pain studies (4,6,8).…”

“…Opiorphin is the only natural enkephalinaseinhibitor characterized in humans and has similar painsuppressive potency to morphine but without adverse effects (4,6). The efficacy of opiorphin has been verified by in vitro methods and its analgesic activity was also shown in different in vivo pain studies (4,6,8). According to our previous in vitro maximal binding and affinity measurements, opiorphin is able to increase the binding and affinity of endogenous opiates to opioid receptors (9).…”