Delta2 opioid receptor subtype on human vascular endothelium uncouples morphine stimulated nitric oxide release

Distinct neurochemical influences on fMRI response polarity in the striatum

The striatum, known as the input nucleus of the basal ganglia, is extensively studied for its diverse behavioral roles. However, the relationship between its neuronal and vascular activity, vital for interpreting functional magnetic resonance imaging (fMRI) signals, has not received comprehensive examination within the striatum. Here, we demonstrate that optogenetic stimulation of dorsal striatal neurons or their afferents from various cortical and subcortical regions induces negative striatal fMRI responses in rats, manifesting as vasoconstriction. These responses occur even with heightened striatal neuronal activity, confirmed by electrophysiology and fiber-photometry. In parallel, midbrain dopaminergic neuron optogenetic modulation, coupled with electrochemical measurements, establishes a link between striatal vasodilation and dopamine release. Intriguingly, in vivo intra-striatal pharmacological manipulations during optogenetic stimulation highlight a critical role of opioidergic signaling in generating striatal vasoconstriction. This observation is substantiated by detecting striatal vasoconstriction in brain slices after synthetic opioid application. In humans, manipulations aimed at increasing striatal neuronal activity likewise elicit negative striatal fMRI responses. Our results emphasize the necessity of considering vasoactive neurotransmission alongside neuronal activity when interpreting fMRI signal.

Plasma Pro-Enkephalin A and Ischemic Stroke Risk: The Reasons for Geographic and Racial Differences in Stroke Cohort

OBJECTIVES

The opioid neuropeptide pro-enkephalin A (PENK-A) may be a circulating marker of cardiovascular risk, with prior findings relevant to heart failure, kidney disease, and vascular dementia. Despite these findings, the association of PENK-A with ischemic stroke is unknown, so we examined this association in a prospective cohort study and analyzed differences by race and sex.

MATERIALS AND METHODS

The REasons for Geographic and Racial Differences in Stroke study (REGARDS) is a prospective cohort study of 30,239 Black and White adults. Plasma PENK-A was measured in 473 participants that developed first-time ischemic stroke over 5.9 years and 899 randomly selected participants. Cox models adjusted for demographics and stroke risk factors were used to calculate hazard ratios (HRs) of stroke by baseline PENK-A.

RESULTS

PENK-A was higher with increasing age, female sex, White race, lower body mass index, and antihypertensive medication use. Each SD higher increment of PENK-A was associated with an adjusted HR of 1.20 (95% CI 1.01-1.42) for stroke, with minimal confounding by stroke risk factors. Spline plots suggested a U-shaped relationship, particularly in White men, with an adjusted HR 3.88 (95% CI 1.94-7.77) for the 95^th versus 50^th percentile of PENK-A in White men.

CONCLUSIONS

Higher baseline plasma PENK-A was independently associated with future stroke risk in REGARDS. This association was most apparent among White men. There was little confounding by established stroke risk factors, suggesting a possible causal role in stroke etiology. Further research is needed to understand the role of endogenous opioids in stroke pathogenesis.

Hypertensive Effect of Downregulation of the Opioid System in Mouse Model of Different Activity of the Endogenous Opioid System

The opioid system is well-known for its role in modulating nociception and addiction development. However, there are premises that the endogenous opioid system may also affect blood pressure. The main goal of the present study was to determine the impact of different endogenous opioid system activity and its pharmacological blockade on blood pressure. Moreover, we examined the vascular function in hyper- and hypoactive states of the opioid system and its pharmacological modification. In our study, we used two mouse lines which are divergently bred for high (HA) and low (LA) swim stress-induced analgesia. The obtained results indicated that individuals with low endogenous opioid system activity have higher basal blood pressure compared to those with a hyperactive opioid system. Additionally, naloxone administration only resulted in the elevation of blood pressure in HA mice. We also showed that the hypoactive opioid system contributes to impaired vascular relaxation independent of endothelium, which corresponded with decreased guanylyl cyclase levels in the aorta. Together, these data suggest that higher basal blood pressure in LA mice is a result of disturbed mechanisms in vascular relaxation in smooth muscle cells. We believe that a novel mechanism which involves endogenous opioid system activity in the regulation of blood pressure will be a promising target for further studies in hypertension development.

Prospects for Creation of Cardioprotective and Antiarrhythmic Drugs Based on Opioid Receptor Agonists

It has now been demonstrated that the μ, δ1 , δ2 , and κ1 opioid receptor (OR) agonists represent the most promising group of opioids for the creation of drugs enhancing cardiac tolerance to the detrimental effects of ischemia/reperfusion (I/R). Opioids are able to prevent necrosis and apoptosis of cardiomyocytes during I/R and improve cardiac contractility in the reperfusion period. The OR agonists exert an infarct-reducing effect with prophylactic administration and prevent reperfusion-induced cardiomyocyte death when ischemic injury of heart has already occurred; that is, opioids can mimic preconditioning and postconditioning phenomena. Furthermore, opioids are also effective in preventing ischemia-induced arrhythmias.

Morphine induces apoptosis of human endothelial cells through nitric oxide and reactive oxygen species pathways

Morphine has been widely used for pain management. Other than analgesia, it has effects on vascular endothelial cells, including angiogenesis and apoptosis. An in vitro model of human umbilical vein endothelial cells (HUVECs) was made to investigate the effects and comprehensive mechanisms of morphine on vascular endothelial cells. Morphine enhanced apoptosis of HUVECs, increased intracellular reactive oxygen species (ROS), and reduced mitochondrial membrane potentials (MMPs). It also induced the release of NO and activated NF-kappaB in HUVECs. Naloxone, the opioid receptor antagonist, could reverse cell apoptosis and ROS generation, NO production, and MMP loss. Expression levels of Bak and Bax, and the activation of caspases 3 and 7 in HUVECs significantly increased when treated with morphine. Inhibition of NO production by NO synthase inhibitor reduced morphine-induced apoptosis. Morphine could induce apoptosis of HUVECs through both the NO and ROS pathways. Thus, inhibiting NO or ROS may be a potential target in blocking morphine-induced apoptosis of endothelial cells.

Post-treatment with the novel deltorphin E, a delta2-opioid receptor agonist, increases recovery and survival after severe hemorrhagic shock in behaving rats

Deltorphin E was investigated as a pharmaceutical intervention in the ischemic hemorrhagic model. To monitor the hemodynamic biomarkers mean arterial pressure (MAP) and heart rate (HR) and to facilitate i.v. injections, rats were surgically fitted with femoral artery and vein catheters under anesthesia. After removal of 48% of total blood volume (range, 12-15 mL), posthemorrhage i.v. injections of 5.5-mg/kg deltorphin E were found to significantly (P < 0.05) increase maximum MAP, pulse pressure, and survival after hemorrhage, whereas lactic acid concentration was decreased when compared with saline injections. The results for the 5.5-mg/kg deltorphin E-treated animals versus saline controls showed the following values (expressed as mean +/- SEM): maximum MAP, 58 +/- 7 vs. 35 +/- 9 mmHg, respectively; lactic acid, 6.5 +/- 1.25 vs. 8.9 +/- 0.12 mmol/L, respectively; pulse pressure, 47.9 +/- 0.55 vs. 38.3 +/- 0.44 mmHg, respectively; and at least a fourfold increase in survival, 331 +/- 18 vs. 50 +/- 8 min, respectively. Heart rate in deltorphin E-treated groups was not significantly different from that in saline-treated groups (maximum HR, 396 +/- 40 vs. 425 +/- 94 bpm, respectively). Using logistic analysis, deltorphin E did not significantly alter the baroreflex sensitivity. However, a significant deltorphin E dose-dependent correlation was found between survival time and lactic acid production. Increased pulse pressure was also correlated with survival. Glibenclamide, a potassium-sensitive adenosine triphosphate-sensitive channel blocker, did not interfere with the positive effects of deltorphin E. Only the antagonists tested, known to affect delta(2)-opioid receptors, interfered with the deltorphin E survival benefit after hemorrhage. As a conclusion, deltorphin E is an effective pharmaceutical intervention in severe hemorrhagic shock and, perhaps, in other ischemic shock scenarios when administered after the onset of stress. Therefore, deltorphin E may have clinical potential.

Endogenous opioid peptides, endomorphin-1 and -2 and deltorphin I, stimulate angiogenesis in the CAM assay

The opioid peptides modulate extensive bioactivities, including pain, cardiovascular response, development and so on. The effects of endogenous opioid peptides on angiogenesis were evaluated in the chick embryo chorioallantoic membrane (CAM) assay for the first time in the present study. Endomorphin-1, endomorphin-2 and deltorphin I at the dosage of 1, 10, 100 nmol/embryo could stimulate angiogenesis dose-dependently, respectively. Naloxone, the nonselective opioid receptor antagonist, did not influence angiogenesis alone; but it could antagonize the stimulative effects of the opioid peptides on angiogenesis when it was administrated in combination with the opioid peptides. Taken altogether, the results suggested that endogenous opioid peptides (endomorphin-1 and -2 and deltorphin I) stimulated angiogenesis in the CAM assay, and these effects were modulated with the opioid receptors. These data are important for potential future clinical implementation.

24-hour pretreatment with delta opioid enhances survival from hemorrhagic shock

OBJECTIVES

Delta opioids have been shown to confer ischemic preconditioning and pharmacologic ischemic preconditioning to the myocardium. However, their role in providing extended pharmacologic ischemic preconditioning in hemorrhagic shock has not been explored. The authors examined the effects of 24-hour preinfusions of a selective delta opioid receptor agonist, Deltorphin-Dvariant (Delt-Dvar), on hemodynamic stability and duration of survival in a rat model of severe hemorrhagic shock.

METHODS

Conscious Sprague-Dawley rats with indwelling catheters were hemorrhaged at a rate of 3.18 mL/l00 g over 20 minutes. Twenty-four hours before hemorrhage, the control group (n = 14) was infused with 1.0 mL lactated Ringer's solution, and the Delt-Dvar-treated group (n = 22) was infused with 5.0 mg/kg Delt-Dvar in 1.0 mL lactated Ringer's solution. Rats were continuously monitored for heart rate (HR), mean arterial pressure, and four-hour survival rates. Plasma lactate levels were determined at the beginning of hemorrhage and the end of hemorrhage.

RESULTS

At 240 minutes, only one of 14 controls (7.1%) survived, while 16 (72.7%) of the 22 experimental rats survived. No significant differences in heart rate between controls and Delt-Dvar-treated rats were noted. Increases in mean arterial pressure of Delt-Dvar-treated rats at the beginning of hemorrhage and at the end of hemorrhage were found to be significant (p < 0.05). At 240 minutes, heart rate and mean arterial pressure were not different between the single surviving control and the Delt-Dvar group. At the end of hemorrhage, lactate levels in the Delt-Dvar-treated group were 8.5 (+/- 0.5) mmol/L versus 10.8 (+/- 0.6) mmol/L (p < 0.05) in the control group.

CONCLUSIONS

Twenty-four-hour pretreatment with Delt-Dvar decreases plasma lactate levels and improves hemodynamic stability and survival during hemorrhagic shock. The use of delta-specific opioids may improve survival from hemorrhagic shock and have clinical utility in providing ischemic protection in scenarios of planned ischemia.

α2-Adrenoceptor subsensitivity in mesenteric vascular bed of cholestatic rats: The role of nitric oxide and endogenous opioids

Cholestasis is associated with vascular changes and in previous studies decreased response of visceral vessels of cholestatic animals to phenylephrine and acetylcholine has been shown. In the present study, the response of mesenteric vascular bed of cholestatic rats to clonidine (an alpha2-adrenoceptor agonist) was investigated and we also examined the role of endogenous opioids and nitric oxide (NO). Seven-day ligation of bile duct was used as the model to study cholestasis. Six groups of rats, each of which divided into two subgroups (bile duct-ligated and sham-operated), were examined. Three groups of animals were chronically treated with either normal saline, naltrexone (an opioid receptor antagonist, 20 mg/kg/day, s.c.) or aminoguanidine (a selective inducible nitric oxide synthase inhibitor, 150 mg/kg/day, s.c.) for 7 days. After 7 days the response of the mesenteric vascular bed to subsequent doses of clonidine was studied. In other two groups, 7 days after the operation, the response of the mesenteric vascular bed to clonidine in the presence of either yuhimbine, an alpha2-adrenoceptor antagonist, or N(omega)-nitro-L-arginine methyl ester (L-NAME), a non-selective nitric oxide synthase inhibitor, was studied. In the last group, vasodilation response to sodium nitroprusside (an endothelium-independent vasorelaxant) was evaluated. Clonidine caused vasodilation in a dose-dependent manner by acting on endothelial alpha2-adrenoceptors since its effect was antagonized by yohimbine, and this vasodilation was through the L-arginine pathway since there was no response in the presence of L-NAME in the perfusate. Compared to sham-operated rats, there was a significant right shift in the clonidine concentration curves of cholestatic animals. Maximum response in cholestatic rats was significantly lower comparing to the sham group (P<0.01) and the dose of clonidine that causes 50% of maximum response (ED50) was significantly higher in cholestatic rats (P<0.05). Vasodilation response to sodium nitroprusside was the same in cholestatic and sham-operated rats. Seven-day treatment with aminoguanidine recovered the effect of cholestasis. Seven-day treatment with naltrexone caused an increase in maximum response (P<0.01) and a decrease in ED50 (P<0.05) in cholestatic rats, while this treatment in sham-operated rats caused a decrease in the maximum response (P<0.01) and an increase in ED50 (P<0.05). This study showed that cholestasis is associated with decreased responsiveness of mesenteric vascular bed to clonidine and the cholestasis-associated NO overproduction and increased level of endogenous opioids may contribute to this process.

Morphine potentiates dextromethorphan-induced vasodilation in rat superior mesenteric artery

The combined action of morphine and dextromethorphan on the superior mesenteric artery was investigated in this study. The artery was cut into rings, placed in a muscle bath and mounted to a force transducer for recording tension. Rings preconstricted with 1 microM phenylephrine produced a dose-dependent relaxation to graded doses of dextromethorphan but showed no response to morphine. An equimolar combination of morphine and dextromethorphan exhibited a marked synergism quantitated by a factor of 3.7 (1.8-7.7, 95% CI). Naloxone, which had no effect on the dextromethorphan dose-response relation, abolished the synergism. Removal of the endothelium produced a slight attenuation of the morphine-dextromethorphan synergism, but the magnitude of this attenuation was the same when dextromethorphan alone was examined in the denuded preparation. In contrast to the marked synergism seen in the mesenteric artery preparation, similar experiments on the carotid artery and the aorta produced only additive interactions.

Cardiac enkephalins attenuate vagal bradycardia: interactions with NOS-1-cGMP systems in canine sinoatrial node

Endogenous opioids and nitric oxide (NO) are recognized modulators of cardiac function. Enkephalins and inhibitors of NO synthase (NOS) both produce similar interruptions in the vagal control of heart rate. This study was conducted to test the hypothesis that NO systems within the canine sinoatrial (SA) node facilitate local vagal transmission and that the endogenous enkephalin methionine-enkephalin-arginine-phenylalanine (MEAP) attenuates vagal bradycardia by interrupting the NOS-cGMP pathway. Microdialysis probes were inserted into the SA node, and they were perfused with nonselective (Nomega-nitro-l-arginine methyl ester) and neuronal (7-nitroindazole) NOS inhibitors. The right vagus nerve was stimulated and both inhibitors gradually attenuated the resulting vagal bradycardia. The specificity of these inhibitions was verified by an equally gradual reversal of the inhibition with an excess of the NOS substrate l-arginine. Introduction of MEAP into the nodal interstitium produced a quickly developing but quantitatively similar interruption of vagal bradycardia that was also slowly reversed by the addition of l-arginine and not by d-arginine. Additional support for convergence of opioid and NO pathways was provided when the vagolytic effects of MEAP were also reversed by the addition of the NO donor S-nitroso-N-acetyl-penicillamine, the protein kinase G activator 8-bromo-cGMP, or the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. MEAP and 7-nitroindazole were individually combined with the direct acting muscarinic agonist methacholine to evaluate potential interactions with muscarinic receptors within the SA node. MEAP and 7-nitroindazole were unable to overcome the bradycardia produced by methacholine. These data suggest that NO and enkephalins moderate the vagal control of heart rate via interaction with converging systems that involve the regulation of cAMP within nodal parasympathetic nerve terminals.

Alpha-lactorphin and beta-lactorphin improve arterial function in spontaneously hypertensive rats

alpha-lactorphin (Tyr-Gly-Leu-Phe) lowers blood pressure in conscious adult SHR. This tetrapeptide is originally released from milk protein alpha-lactalbumin by enzymatic hydrolysis. In order to evaluate the antihypertensive mechanisms of alpha-lactorphin, the effects of the tetrapeptide on vascular function were investigated in (30-35 weeks old) spontaneously hypertensive rats (SHR) with established hypertension and age-matched normotensive Wistar-Kyoto (WKY) rats in vitro. In addition, we studied the vascular effects of another structurally related tetrapeptide, beta-lactorphin (Tyr-Leu-Leu-Phe), which originates from milk protein beta-lactoglobulin. Endothelium-dependent relaxation to acetylcholine (ACh) was reduced in mesenteric arterial preparations of SHR as compared to those of WKY. In SHR, the ACh-induced relaxation was augmented by alpha-lactorphin or beta-lactorphin. The role of nitric oxide (NO) is suggested, since this improvement was abolished by the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Simultaneous potassium channel inhibitor tetraethylammonium (TEA) elicited no additional effect on the ACh-induced relaxation. The cyclooxygenase inhibitor diclofenac did not attenuate the augmented ACh relaxation induced by alpha-lactorphin or beta-lactorphin, suggesting that endothelial vasodilatory prostanoids were not involved in the effect of the tetrapeptides. Endothelium-independent relaxation to the NO donor sodium nitroprusside (SNP) was augmented in mesenteric arterial preparations of SHR by simultaneous beta-lactorphin. The tetrapeptides did not alter vascular responses in mesenteric arteries from WKY. In conclusion, both alpha-lactorphin and beta-lactorphin improved vascular relaxation in adult SHR in vitro. The beneficial effect of alpha-lactorphin was directed towards endothelial function, whereas beta-lactorphin also enhanced endothelium-independent relaxation.

Morphine sulfate inhibits hypoxia-induced vascular endothelial growth factor expression in endothelial cells and cardiac myocytes

Vascular endothelial growth factor (VEGF) is an angiogenic mitogen, specific for endothelial cells. Hypoxia-induced VEGF in endothelial cells and cardiomyocytes leads to autocrine and paracrine stimulation, respectively. During myocardial ischemia, VEGF is upregulated in the endothelium and myocardium, and may mediate angiogenesis. Morphine sulfate is commonly used in pain relief for patients with acute myocardial infarction. We investigated the effect of morphine sulfate on VEGF expression in cultured endothelial cells and cardiac myocytes subjected to hypoxia. Enzyme-linked immunosorbent assays showed that morphine sulfate significantly inhibited hypoxia-induced VEGF expression in mouse heart microvascular endothelial cells (SMHEC4), primary cultures of human umbilical vein endothelial cells (HUVECs) and in primary cultures of rat cardiac myocytes (P<0.05). Real time reverse transcriptase polymerase chain reaction showed that morphine treatment (100 ng/ml) of hypoxic HUVECs resulted in a significant reduction in mRNA levels of VEGF(121) and VEGF(165) isoforms. Transfection of HUVECs with a human VEGF promoter-luciferase construct showed that hypoxia-induced transcriptional activation of VEGF was markedly inhibited by morphine sulfate (P<0.05). Phosphatidyl inositol-3 kinase and protein kinase C-mediated activation of the VEGF promoter was also inhibited by morphine. The opioid antagonist naloxone significantly reversed the inhibitory effects of morphine in endothelial cells suggesting the involvement of opioid receptors. Our results show that the inhibitory effects of morphine on hypoxia-induced VEGF expression in endothelial cells and cardiac myocytes can lead to a decrease in the autocrine and paracrine stimulation and hence limit neovascularization of the ischemic myocardium.

Mesenteric vascular bed responsiveness in bile duct-ligated rats: roles of opioid and nitric oxide systems

Changes in vascular responsiveness are proposed as the basis for some of the cardiovascular complications in cholestasis. Cholestasis is also associated with accumulation of endogenous opioid peptides and evidence of overproduction of nitric oxide (NO). The possible role of NO or opioid system in cholestasis-induced mesenteric vascular bed responsiveness was investigated. Bile duct-ligated and sham-operated rats were treated for 6 days with either normal saline, naltrexone, an opioid antagonist (20 mg/kg/day) or L-NAME (N(omega)-nitro-L-arginine methyl ester), a nitric oxide synthase inhibitor (3 mg/kg/day). After 7 days, the superior mesenteric artery was cannulated and the mesenteric vascular bed was perfused according to the McGregor method. Baseline perfusion pressure of the mesenteric vascular bed was decreased in bile duct-ligated compared to sham-operated animals. ED(50) of phenylephrine-induced vasoconstriction was increased, but vasoconstriction R(max) was not different in the vascular bed of bile duct-ligated rats and of sham-operated ones. Acetylcholine-induced vasorelaxation was impaired in bile duct-ligated rats (increased ED(50) and decreased vasorelaxation R(max)). Sodium nitroprusside-induced vasorelaxation was not different between bile duct-ligated and sham-operated rats, implying that the smooth muscle components of vasorelaxation were intact. Chronic treatment with L-NAME partially restored both the acetylcholine-induced vasorelaxation and phenylephrine-induced vasoconstriction response in bile duct-ligated rats. Naltrexone treatment also partially restored the acetylcholine-induced vasorelaxation and phenylephrine-induced vasoconstriction in bile duct-ligated rats. There is impaired acetylcholine-induced vasorelaxation in cholestatic rats, probably due to a defect in endothelial function. This study also provided evidence for the involvement of increased opioidergic tone and NO overproduction in cholestasis-induced vascular hyporesponsiveness.

Basal nitric oxide limits immune, nervous and cardiovascular excitation: human endothelia express a mu opiate receptor

Nitric oxide (NO) is a major signaling molecule in the immune, cardiovascular and nervous systems. The synthesizing enzyme, nitric oxide synthase (NOS) occurs in three forms: endothelial (e), neuronal (n) and inducible (i) NOS. The first two are constitutively expressed. We surmise that in many tissues there is a basal level of NO and that the actions of several signaling molecules initiate increases in cNOS-derived NO to enhance momentary basal levels that exerts inhibitory cellular actions, via cellular conformational changes. It is our contention that much of the literature concerning the actions of NO really deal with i-NOS-derived NO. We make the case that cNOS is responsible for a basal or 'tonal' level of NO; that this NO keeps particular types of cells in a state of inhibition and that activation of these cells occurs through disinhibition. Furthermore, naturally occurring signaling molecules such as morphine, anandamide, interleukin-10 and 17-beta-estradiol appear to exert, in part, their beneficial physiological actions, i.e., immune and endothelial down regulation by the stimulation of cNOS. In regard to opiates, we demonstrate the presence of a human endothelial mu opiate receptor by RT-PCR and sequence determination, further substantiating the role of opiates in vascular coupling to NO release. Taken together, cNOS derived NO enhances basal NO actions, i.e., cellular activation state, and these actions are further enhanced by iNOS derived NO.

Endogenous morphine levels increase in molluscan neural and immune tissues after physical trauma

The aim of this study was to demonstrate by biochemical and immunocytochemical methods the presence of endogenous morphine in nervous and immune tissues of the freshwater snail, Planorbarius corneus. High performance liquid chromatography (HPLC) coupled to electrochemical detection performed on tissues from control snails, revealed that the CNS contains 6.20+/-2.0 pmol/g of the alkaloid, the foot tissue contains a much lower level, 0.30+/-0.03 pmol/g, whilst morphine is not detected in the hemolymph and hepatopancreas. In specimens that were traumatized, we detected a significant rise of the CNS morphine level 24 h later (43.7+/-5.2 pmol/g) and an initial decrease after 48 h (19.3+/-4.6 pmol/g). At the same times, we found the appearance of the opiate in the hemolymph (0.38+/-0.04 pmol/ml and 0.12+/-0.03 pmol/ml) but not in the hepatopancreas. Using indirect immunocytochemistry, a morphine-like molecule was localized to a number of neurons and a type of glial cell in the CNS, to some immunocytes in the hemolymph and to amoebocytes in the foot, as well as to fibers in the aorta wall. Simultaneously to the rise of morphine biochemical level following trauma, morphine-like immunoreactivity (MIR) increased in both intensity and the number of structures responding positively, i.e., neurons and fiber terminals. In another mollusc, the mussel Mytilus galloprovincialis, the same pattern of enhanced MIR was found after trauma. Taken together, the data suggest the presence of a morphinergic signaling in invertebrate neural and immune processes resembling those of classical messenger systems and an involvement in trauma response.

Invertebrate opioid precursors: evolutionary conservation and the significance of enzymatic processing

Invertebrate tissues contain mammalian-like proenkephalin, prodynorphin, and proopiomelanocortin. Amino acid sequence determination of these opioid gene products reveals the presence of various opioid peptides exhibiting high sequence identity with their mammalian counterparts. These associated peptides are flanked by dibasic amino acid residues, indicating cleavage sites. Together with the presence of various processing enzymes, i.e., neutral endopeptidase 24.11 and angiotensin-converting enzymes, this suggests that opioid precursor processing is also similar to that described in mammals. It is noted that the levels and/or activity of invertebrate neutral endopeptidase 24.11 can be upregulated by signaling molecules shown to perform the same function in mammals, i.e., morphine. Critical to opioid precursor processing are immunocytes that contain the precursors and transport processing enzymes to sites of inflammation, in part, to cleave these peptide precursors, thus liberating immune-stimulating molecules. Furthermore, in response to lipopolysaccharides, Met-enkephalin levels peak immediately and hours after the exposure, revealing a release and induction process. It appears that the opioid precursors and their processing enzymes first evolved in "simple" animals and the have been maintained and embellished during the course of evolution guided by conformational matching.

What peptides these deltorphins be

The deltorphins are a class of highly selective delta-opioid heptapeptides from the skin of the Amazonian frogs Phyllomedusa sauvagei and P. bicolor. The first of these fascinating peptides came to light in 1987 by cloning of the cDNA of from frog skins, while the other members of this family were identified either by cDNA or isolation of the peptides. The distinctive feature of deltorphins is the presence of a naturally occurring D-enantiomer at the second position in their common N-terminal sequence, Tyr-D-Xaa-Phe, comparable to dermorphin, which is the prototype of a group of mu-selective opioids from the same source. The D-amino acid and the anionic residues, either Glu or Asp, as well as their unique amino acid compositions are responsible for the remarkable biostability, high delta-receptor affinity, bioactivity and peptide conformation. This review summarizes a decade of research from many laboratories that defined which residues and substituents in the deltorphins interact with the delta-receptor and characterized pharmacological and physiological activities in vitro and in vivo. It begins with a historical description of the topic and presents general schema for the synthesis of peptide analogues of deltorphins A, B and C as a means to document the methods employed in producing a myriad of analogues. Structure activity studies of the peptides and their pharmacological activities in vitro are detailed in abundantly tabulated data. A brief compendium of the current level of knowledge of the delta-receptor assists the reader to appreciate the rationale for the design of these analogues. Discussion of the conformation of these peptides addresses how structure leads to further hypotheses regarding ligand receptor interaction. The review ends with a broad discussion of the potential applications of these peptides in clinical and therapeutic settings.