Protective effect of delta opioid agonist [d-Ala2, d-Leu5] enkephalin on spinal cord ischemia reperfusion injury by regional perfusion into abdominal aorta in rabbits

Histological Findings After Aortic Cross-Clamping in Preclinical Animal Models

Spinal cord ischemic injury and paralysis are devastating complications after open surgical repair of thoracoabdominal aortic aneurysms. Preclinical models have been developed to simulate the clinical paradigm to better understand the neuropathophysiology and develop therapeutic treatment. Neuropathological findings in the preclinical models have not been comprehensively examined before. This systematic review studies the past 40 years of the histological findings after open surgical repair in preclinical models. Our main finding is that damage is predominantly in the grey matter of the spinal cord, although white matter damage in the spinal cord is also reported. Future research needs to examine the neuropathological findings in preclinical models after endovascular repair, a newer type of surgical repair used to treat aortic aneurysms.

Effects of D‑Ala2, D‑Leu5‑Enkephalin pre‑ and post‑conditioning in a rabbit model of spinal cord ischemia and reperfusion injury

It has recently been revealed that during the aorta-clamped period, D-Ala², D-Leu⁵-Enkephalin (DADLE) infusion can protect the spinal cord against ischemia and reperfusion (I/R) injury. However, the protective effects of DADLE administration prior to ischemia or at the time of early reperfusion have not yet been investigated. Drug pre- or post-conditioning can serve as a more valuable clinical strategy. Therefore, the present study was designed to investigate the neuroprotective effect of DADLE infusion at different time intervals in order to determine the optimum time point for ischemic spinal cord protection. A total of 40 New Zealand white rabbits were randomly divided into 5 groups: Sham-operated (Sham), normal saline pre-conditioning (NS), DADLE per-conditioning (D_per), DADLE pre-conditioning (D_pre) and DADLE post-conditioning (D_post). All animals were subjected to spinal cord ischemia for 30 min followed by 48 h reperfusion. Hind limb motor functions were assessed according to the Tarlov criterion when the animals regained consciousness, 6, 24 and 48 h after reperfusion. Histological analysis and the number of viable α-motor neurons were also used to assess the extent of spinal cord injury. Compared with the NS group, the Tarlov scores and the number of normal neurons were significantly higher in the D_per group (P<0.05), which were consistent with the results of a previous study. In addition, the paraplegia rate and loss of normal motor neurons were lower in the DADLE per- and post-conditioning groups compared with the DADLE pre-conditioning; however, these were not statistically significant. DADLE 0.05 mg/kg administration at three time points all mitigated normal motor neuron injury in the anterior horn and decreased the paraplegia rates in rabbits. The therapeutic benefits appeared best in the post-conditioning group with DADLE, and worst in the pre-conditioning group.

The influence of experimental inflammation and axotomy on leucine enkephalin (leuENK) distribution in intramural nervous structures of the porcine descending colon

Background

The enteric nervous system (ENS), located in the intestinal wall and characterized by considerable independence from the central nervous system, consists of millions of cells. Enteric neurons control the majority of functions of the gastrointestinal tract using a wide range of substances, which are neuromediators and/or neuromodulators. One of them is leucine–enkephalin (leuENK), which belongs to the endogenous opioid family. It is known that opioids in the gastrointestinal tract have various functions, including visceral pain conduction, intestinal motility and secretion and immune processes, but many aspects of distribution and function of leuENK in the ENS, especially during pathological states, remain unknown.

Results

During this experiment, the distribution of leuENK – like immunoreactive (leuENK-LI) nervous structures using the immunofluorescence technique were studied in the porcine colon in physiological conditions, during chemically-induced inflammation and after axotomy. The study included the circular muscle layer, myenteric (MP), outer submucous (OSP) and inner submucous plexus (ISP) and the mucosal layer. In control animals, the number of leuENK-LI neurons amounted to 4.86 ± 0.17%, 2.86 ± 0.28% and 1.07 ± 0.08% in the MP, OSP and ISP, respectively. Generally, both pathological stimuli caused an increase in the number of detected leuENK-LI cells, but the intensity of the observed changes depended on the factor studied and part of the ENS. The percentage of leuENK-LI perikarya amounted to 11.48 ± 0.96%, 8.71 ± 0.13% and 9.40 ± 0.76% during colitis, and 6.90 ± 0.52% 8.46 ± 12% and 4.48 ± 0.44% after axotomy in MP, OSP and ISP, respectively. Both processes also resulted in an increase in the number of leuENK-LI nerves in the circular muscle layer, whereas changes were less visible in the mucosa during inflammation and axotomy did not change the number of leuENK-LI mucosal fibers.

Conclusions

LeuENK in the ENS takes part in intestinal regulatory processes not only in physiological conditions, but also under pathological factors. The observed changes are probably connected with the participation of leuENK in sensory and motor innervation and the neuroprotective effects of this substance. Differences in the number of leuENK-LI neurons during inflammation and after axotomy may suggest that the exact functions of leuENK probably depend on the type of pathological factor acting on the intestine.

Antioxidative and Antiapoptotic Effects of Delta-Opioid Peptide [D-Ala2, D-Leu5] Enkephalin on Spinal Cord Ischemia-Reperfusion Injury in Rabbits

Background: In our previous study, we found that regional administration of delta-opioid peptide [D-Ala², D-Leu⁵] enkephalin (DADLE) could provide dose-dependent protection on spinal cord ischemia-reperfusion (I/R) injury in rabbits. However, the relative protective molecular mechanisms underlying this neuroprotection remain unclear. The purpose of this study was to investigate whether DADLE provided the protection in spinal cord I/R injury through its antioxidant property by decreasing malondialdehyde (MDA) and nitric oxide (NO) levels and increasing glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) levels and through its antiapoptotic capacity by inhibiting caspase-3 and p53 expression. Methods: The rabbits were divided into three groups. The animals in Group NS and Group DADLE were administered with normal saline (NS) or DADLE via aorta during 30 min of ischemia respectively, while the one in Group Sham received no intervention. During the period of reperfusion, the rabbit's blood samples were collected for enzyme-linked immunoabsorbent assay (ELISA) examinations of MDA, NO, GSH-Px and SOD. At 48 h after reperfusion, the lumbar spinal cords were harvested for immunohistochemical, real-time polymerase chain reaction (PCR) and western blot studies to detect the caspase-3 and p53 expressions. Results: The activities of serum MDA and NO showed significant reductions in the DADLE group as compared with the control group. By contrast, the levels of serum GSH-Px and SOD were significantly higher in the DADLE group than those in the NS group. In addition, caspase-3 and p53 expression were significantly increased in the NS group, while DADLE mitigated these changes. Conclusions: The protective effects of DADLE at the dosage of 0.05 mg/kg may be related to its antioxidant and antiapoptosis properties in the rabbit model of spinal cord I/R injury.

Synthesis of [18 F]Fluoroarenes by Nucleophilic Radiofluorination of N-Arylsydnones

A practical method for radiofluorination of anilines with [18 F]fluoride via N-arylsydnone intermediates is described. These precursors are stable, easy to handle and facilitate direct and regioselective 18 F-labeling to prepare [18 F]fluoroarenes. The value of this methodology is further highlighted by successful application to prepare an 18 F-labeled neuropeptide.

Molecular Pharmacology of δ-Opioid Receptors

Opioids are among the most effective analgesics available and are the first choice in the treatment of acute severe pain. However, partial efficacy, a tendency to produce tolerance, and a host of ill-tolerated side effects make clinically available opioids less effective in the management of chronic pain syndromes. Given that most therapeutic opioids produce their actions via µ-opioid receptors (MOPrs), other targets are constantly being explored, among which δ-opioid receptors (DOPrs) are being increasingly considered as promising alternatives. This review addresses DOPrs from the perspective of cellular and molecular determinants of their pharmacological diversity. Thus, DOPr ligands are examined in terms of structural and functional variety, DOPrs' capacity to engage a multiplicity of canonical and noncanonical G protein-dependent responses is surveyed, and evidence supporting ligand-specific signaling and regulation is analyzed. Pharmacological DOPr subtypes are examined in light of the ability of DOPr to organize into multimeric arrays and to adopt multiple active conformations as well as differences in ligand kinetics. Current knowledge on DOPr targeting to the membrane is examined as a means of understanding how these receptors are especially active in chronic pain management. Insight into cellular and molecular mechanisms of pharmacological diversity should guide the rational design of more effective, longer-lasting, and better-tolerated opioid analgesics for chronic pain management.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 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, drug abuse and alcohol, 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.

Delta Opioid Receptor and Peptide: A Dynamic Therapy for Stroke and Other Neurological Disorders

Research of the opioid system and its composite receptors and ligands has revealed its promise as a potential therapy for neurodegenerative diseases such as stroke and Parkinson's Disease. In particular, delta opioid receptors (DORs) have been elucidated as a therapeutically distinguished subset of opioid receptors and a compelling target for novel intervention techniques. Research is progressively shedding light on the underlying mechanism of DORs and has revealed two mechanisms of DOR neuroprotection; DORs function to maintain ionic homeostasis and also to trigger endogenous neuroprotective pathways. Delta opioid agonists such as (D-Ala2, D-Leu5) enkephalin (DADLE) have been shown to promote neuronal survival and decrease apoptosis, resulting in a substantial amount of research for its application as a neurological therapeutic. Most notably, DADLE has demonstrated significant potential to reduce cell death following ischemic events. Current research is working to reveal the complex mechanisms of DADLE's neuroprotective properties. Ultimately, our knowledge of the DOR receptors and agonists has made the opioid system a promising target for therapeutic intervention in many neurological disorders.