The cardiovascular and renal effects of a highly potent mu-opioid receptor agonist, cyclo[N epsilon,N beta-carbonyl-D-Lys2,Dap5]enkephalinamide

Opioids and the kidney: two sides of the same coin

Renal dysfunction, including acute renal failure (ARF) and chronic kidney disease (CKD), continues to present significant health challenges, with renal ischemia-reperfusion injury (IRI) being a pivotal factor in their development and progression. This condition, notably impacting kidney transplantation outcomes, underscores the urgent need for innovative therapeutic interventions. The role of opioid agonists in this context, however, remains a subject of considerable debate. Current reviews tend to offer limited perspectives, focusing predominantly on either the protective or detrimental effects of opioids in isolation. Our review addresses this gap through a thorough and comprehensive evaluation of the existing literature, providing a balanced examination of the dualistic nature of opioids' influence on renal health. We delve into both the nephroprotective and nephrotoxic aspects of opioids, dissecting the complex interactions and paradoxical effects that embody the "two sides of the same coin" phenomenon. This comprehensive analysis is vital for understanding the intricate roles of opioids in renal pathophysiology, potentially informing the development of novel therapeutic strategies for preventing or treating hypoxic kidney injury.

Potential functional and pathological side effects related to off-target pharmacological activity

Most pharmaceutical companies test their discovery-stage proprietary molecules in a battery of in vitro pharmacology assays to try to determine off-target interactions. During all phases of drug discovery and development, various questions arise regarding potential side effects associated with such off-target pharmacological activity. Here we present a scientific literature curation effort undertaken to determine and summarize the most likely functional and pathological outcomes associated with interactions at 70 receptors, enzymes, ion channels and transporters with established links to adverse effects. To that end, the scientific literature was reviewed using an on-line database, and the most commonly reported effects were summarized in tabular format. The resultant table should serve as a practical guide for research scientists and clinical investigators for the prediction and interpretation of adverse side effects associated with molecules interacting with components of this screening battery.

N-terminal guanidinylation of the cyclic 1,4-ureido-deltorphin analogues: the synthesis, receptor binding studies, and resistance to proteolytic digestion

The synthesis of a series of N-guanidinylated cyclic ureidopeptides, analogues of 1,4-ureido-deltorphin/dermorphine tetrapeptide is described. The δ- and μ-opioid receptor affinity of new guanidinylated analogues and their non-guanidinylated precursors was determined by the displacement radioligand binding experiments. Our results indicate that the guanidinylation of cyclic 1,4-ureidodeltorphin peptide analogues does not exhibit a uniform influence on the opioid receptor binding properties, similarly as reported earlier for some linear peptides. All analogues were also tested for their in vitro resistance to proteolysis during incubation with large excess of chymotrypsin, pepsin, and papain by means of mass spectroscopy. Guanidinylated ureidopeptides 1G-4G showed mixed μ agonist/δ agonist properties and high enzymatic stability indicating their potential as therapeutic agents for treatment of pain.

Unique transcriptional profile of sustained ligand-activated preconditioning in pre- and post-ischemic myocardium

Background

Opioidergic SLP (sustained ligand-activated preconditioning) induced by 3–5 days of opioid receptor (OR) agonism induces persistent protection against ischemia-reperfusion (I-R) injury in young and aged hearts, and is mechanistically distinct from conventional preconditioning responses. We thus applied unbiased gene-array interrogation to identify molecular effects of SLP in pre- and post-ischemic myocardium.

Methodology/Principal Findings

Male C57Bl/6 mice were implanted with 75 mg morphine or placebo pellets for 5 days. Resultant SLP did not modify cardiac function, and markedly reduced dysfunction and injury in perfused hearts subjected to 25 min ischemia/45 min reperfusion. Microarray analysis identified 14 up- and 86 down-regulated genes in normoxic hearts from SLP mice (≥1.3-fold change, FDR≤5%). Induced genes encoded sarcomeric/contractile proteins (Myh7, Mybpc3,Myom2,Des), natriuretic peptides (Nppa,Nppb) and stress-signaling elements (Csda,Ptgds). Highly repressed genes primarily encoded chemokines (Ccl2,Ccl4,Ccl7,Ccl9,Ccl13,Ccl3l3,Cxcl3), cytokines (Il1b,Il6,Tnf) and other proteins involved in inflammation/immunity (C3,Cd74,Cd83, Cd86,Hla-dbq1,Hla-drb1,Saa1,Selp,Serpina3), together with endoplasmic stress proteins (known: Dnajb1,Herpud1,Socs3; putative: Il6, Gadd45g,Rcan1) and transcriptional controllers (Egr2,Egr3, Fos,Hmox1,Nfkbid). Biological themes modified thus related to inflammation/immunity, together with cellular/cardiovascular movement and development. SLP also modified the transcriptional response to I-R (46 genes uniquely altered post-ischemia), which may influence later infarction/remodeling. This included up-regulated determinants of cellular resistance to oxidant (Mgst3,Gstm1,Gstm2) and other forms of stress (Xirp1,Ankrd1,Clu), and repression of stress-response genes (Hspa1a,Hspd1,Hsp90aa,Hsph1,Serpinh1) and Txnip.

Conclusions

Protection via SLP is associated with transcriptional repression of inflammation/immunity, up-regulation of sarcomeric elements and natriuretic peptides, and modulation of cell stress, growth and development, while conventional protective molecules are unaltered.

Current research on opioid receptor function

The use of opioid analgesics has a long history in clinical settings, although the comprehensive action of opioid receptors is still less understood. Nonetheless, recent studies have generated fresh insights into opioid receptor-mediated functions and their underlying mechanisms. Three major opioid receptors (μ-opioid receptor, MOR; δ-opioid receptor, DOR; and κ-opioid receptor, KOR) have been cloned in many species. Each opioid receptor is functionally sub-classified into several pharmacological subtypes, although, specific gene corresponding each of these receptor subtypes is still unidentified as only a single gene has been isolated for each opioid receptor. In addition to pain modulation and addiction, opioid receptors are widely involved in various physiological and pathophysiological activities, including the regulation of membrane ionic homeostasis, cell proliferation, emotional response, epileptic seizures, immune function, feeding, obesity, respiratory and cardiovascular control as well as some neurodegenerative disorders. In some species, they play an essential role in hibernation. One of the most exciting findings of the past decade is the opioid-receptor, especially DOR, mediated neuroprotection and cardioprotection. The upregulation of DOR expression and DOR activation increase the neuronal tolerance to hypoxic/ischemic stress. The DOR signal triggers (depending on stress duration and severity) different mechanisms at multiple levels to preserve neuronal survival, including the stabilization of homeostasis and increased pro-survival signaling (e.g., PKC-ERK-Bcl 2) and antioxidative capacity. In the heart, PKC and KATP channels are involved in the opioid receptor-mediated cardioprotection. The DOR-mediated neuroprotection and cardioprotection have the potential to significantly alter the clinical pharmacology in terms of prevention and treatment of life-threatening conditions like stroke and myocardial infarction. The main purpose of this article is to review the recent work done on opioids and their receptor functions. It shall provide an informative reference for better understanding the opioid system and further elucidation of the opioid receptor function from a physiological and pharmacological point of view.

Enkephalin derivative, cyclo[Nepsilon,Nbeta-carbonyl-D-Lys2, Dap5] enkephalinamide (cUENK6), induces a highly potent antinociception in rats

The aim of the study was to evaluate whether the newly synthesized analog of enkephalin, cyclo[N(epsilon),N(beta)-carbonyl-D-Lys(2), Dap(5)] enkephalinamide (cUENK6), a highly potent mu- (guinea pig ileum assay) and delta-receptors (mouse vas deferens assay) ligand, induces an antinociceptive effect in the hot-plate test and tail-immersion test after intracerebroventricular administration. Our study indicated that this peptide at the dose of 0.25 nmol produced comparable but at the dose of 0.5 nmol stronger than morphine (13 nmol), antinociceptive effect in both tests. Furthermore, rats with developed tolerance to morphine indicated cross-tolerance to antinociceptive effects of cUENK6. The antinociceptive effects of cUENK6 and morphine were inhibited by non-selective opioid receptor antagonist--naloxone. More detailed study indicated that the delta-opioid receptor antagonist - naltrindole very strongly and, to the lower extent, mu-opioid antagonist - beta-funaltrexamine (beta-FNA), inhibited antinociceptive effect of cUENK6 in the tail-immersion test. Nor-binaltorphimine (nor-BNI), a kappa-opioid receptor antagonist, did not influence this effect. These data suggest the dominant role of delta-opioid receptors as compared with mu-receptors in mediation antinociceptive effect of cUENK6. Furthermore, we found that cUENK6 is much more effective in inhibiting pain in the hot-plate (ED(50)=0.0792 nmol) than in the tail-immersion (ED(50)=0.3526 nmol) test. However, cUENK6 at the antinociceptive doses induced hypolocomotion, and although this effect is observed after administration of opioid agonists in rats as a one phase of their biphasic action (inhibition followed by activation), in our study it was not naloxone-reversible. Therefore, our study suggests that not only opioid receptors may be involved in behavioral effects of cUENK6.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Cyclic enkephalin and dermorphin analogues containing a carbonyl bridge

Four cyclic enkephalin analogues and four cyclic dermorphin analogues have been synthesized. Cyclization of linear peptides containing basic amino acid residues of various side chain length in position 2 and 5 (enkephalin analogues) or 2 and 4 (dermorphin analogues) was achieved by treatment with bis-(4-nitrophenyl) carbonate to form a urea unit. The peptides were tested in the guinea-pig ileum (GPI) and mouse vas deferens (MVD) assays. Diverse activity was observed, depending on the size of the ring and the location of the urea unit. The conformation of two dermorphin analogues has been studied: one of high activity (IC(50) = 4.15 nM in the GPI assay) and a second of low activity (IC(50) = 6700 nM in the GPI assay). The conformational space of these peptides was examined using the EDMC method. Using data from the NMR spectra, each peptide was described as an ensemble of conformers. Biological activity was discussed in light of the structural data.