Antiapoptotic and cytotoxic properties of delta opioid peptide [D-Ala(2),D-Leu(5)]enkephalin in PC12 cells

Sex differences in the rodent hippocampal opioid system following stress and oxycodone associated learning processes

Over the past two decades, opioid abuse has risen especially among women. In both sexes hippocampal neural circuits involved in associative memory formation and encoding of motivational incentives are critically important in the transition from initial drug use to drug abuse/dependence. Opioid circuits, particularly the mossy fiber pathway, are crucial for associative memory processes important for addiction. Our anatomical studies, especially those utilizing electron microscopic immunocytochemistry, have provided unique insight into sex differences in the distribution of opioid peptides and receptors in specific hippocampal circuits and how these distributions are altered following stress and oxycodone-associative learning processes. Here we review the hippocampal opioid system in rodents with respect to ovarian hormones effects and baseline sex differences then sex differences following acute and chronic stress. Next, we review sex differences in the hippocampal opioid system in unstressed and chronically stressed rats following oxycodone conditioned place preference. We show that opioid peptides and receptors are distributed within hippocampal circuits in females with elevated estrogen states in a manner that would enhance sensitivity to endogenous and exogenous opioids. Moreover, chronic stress primes the opioid system in females in a manner that would promote opioid-associative learning processes. In contrast, chronic stress has limited effects on the opioid system in males and reduces its capacity to support opioid-mediated learning processes. Interestingly, acute stress appears to prime males for opioid associative learning. On a broader scale the findings highlighted in this review have important implications in understanding sex differences in opioid drug use and abuse.

Whether short peptides are good candidates for future neuroprotective therapeutics?

Neurodegenerative diseases are a broad group of largely debilitating, and ultimately terminal conditions resulting in progressive degeneration of different brain regions. The observed damages are associated with cell death, structural and functional deficits of neurons, or demyelination. The concept of neuroprotection concerns the administration of the agent, which should reverse some of the damage or prevent further adverse changes. A growing body of evidence suggested that among many classes of compounds considered as neuroprotective agents, peptides derived from natural materials or their synthetic analogs are good candidates. They presented a broad spectrum of activities and abilities to act through diverse mechanisms of action. Biologically active peptides have many properties, including antioxidant, antimicrobial, antiinflammatory, and immunomodulatory effects. Peptides with pro-survival and neuroprotective activities, associated with inhibition of oxidative stress, apoptosis, inflammation and are able to improve cell viability or mitochondrial functions, are also promising molecules of particular interest to the pharmaceutical industries. Peptide multiple activities open the way for broad application potential as therapeutic agents or ingredients of health-promoting functional foods. Significantly, synthetic peptides can be remodeled in numerous ways to have desired features, such as increased solubility or biological stability, as well as selectivity towards a specific receptor, and finally better membrane penetration. This review summarized the most common features of major neurodegenerative disorders, their causes, consequences, and reported new neuroprotective drug development approaches. The author focused on the unique perspectives in neuroprotection and provided a concise survey of short peptides proposed as novel therapeutic agents against various neurodegenerative diseases.

Sex Differences in the Subcellular Distribution of Corticotropin-Releasing Factor Receptor 1 in the Rat Hippocampus following Chronic Immobilization Stress

Corticotropin-releasing factor receptors (CRFR1) contribute to stress-induced adaptations in hippocampal structure and function that can affect learning and memory processes. Our prior studies showed that female rats with elevated estrogens compared to males have more plasmalemmal CRFR1 in CA1 pyramidal cells, suggesting a greater sensitivity to stress. Here, we examined the distribution of hippocampal CRFR1 following chronic immobilization stress (CIS) in female and male rats using immuno-electron microscopy. Without stress, total CRFR1 dendritic levels were higher in females in CA1 and in males in the hilus; moreover, plasmalemmal CRFR1 was elevated in pyramidal cell dendrites in CA1 in females and in CA3 in males. Following CIS, near-plasmalemmal CRFR1 increased in CA1 pyramidal cell dendrites in males but not to levels of control or CIS females. In CA3 and the hilus, CIS decreased cytoplasmic and total CRFR1 in dendrites in males only. These results suggest that in naive rats, CRF could induce a greater activation of CA1 pyramidal cells in females than males. Moreover, after CIS, which leads to even greater sex differences in CRFR1 by trafficking it to different subcellular compartments, CRF could enhance activation of CA1 pyramidal cells in males but to a lesser extent than either unstressed or CIS females. Additionally, CA3 pyramidal cells and inhibitory interneurons in males have heightened sensitivity to CRF, regardless of stress state. These sex differences in CRFR1 distribution and trafficking in the hippocampus may contribute to reported sex differences in hippocampus-dependent learning processes in baseline conditions and following chronic stress.

Opioids and cancer: friend or foe?

PURPOSE OF REVIEW

Most cancer patients experience pain and many will require opioids. However, the effects of opioids on cancer progression, metastasis, and recurrence is increasingly being questioned. There is evidence that opioids affect immune system function, angiogenesis, apoptosis, and invasion in a potentially deleterious manner. This review will examine the preclinical and clinical evidence.

RECENT FINDINGS

Recent clinical data have struggled to find robust evidence that opioids promote cancer progression. Although most study has involved morphine, differential effects of other opioids on immune function and cancer are revealing a more complex picture.

SUMMARY

Although there is a biologically plausible story, evidence for the action of opioids on cancer is mixed. Indeed, it may even be that in the chronic setting morphine has a beneficial effect on outcome in certain cancer types. This review critically examines and evaluates the evidence for the action of opioids on the processes involved in cancer progression. In the light of the uncertainty of opioid effect on cancer, any decision making should be tempered by knowing that stress and pain undoubtedly contribute to cancer progression.

Morphine as a suspect of aiding the propagation of cancer cells

Controlling pain in cancer patients is important for several reasons including patient quality of life (QOL). In moderate-to-severe cancer-pain management, opioid analgesics are indispensable. Among these, morphine is the most representative. Unfortunately, many studies have shown that morphine is potentially associated with cancer growth, recurrence, and metastasis. Specifically, in animal as well as in vivo and in vitro studies, morphine has been demonstrated to have possibly positive effects on cancer progression. However, those effects have not yet been confirmed as entirely harmful, for several reasons: the results of animal and laboratory research have not been subjected to clinical trials; there are as yet no well-designed clinical studies, and indeed, some studies have shown that morphine can have negative, suppression effects on tumor growth. This review paper will present some of the data on the potentially positive relationships between morphine and cancer. It should not be forgotten, though, that such relationships remain controversial, and that pain itself promotes cancer progression.

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.

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.

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.

Upregulation and activation of δ‑opioid receptors promotes the progression of human breast cancer

δ‑opioid receptor (DOR) belongs to the family of G protein‑coupled receptors (GPCRs). Numerous studies have shown that DOR is widely distributed in human peripheral tissues and is closely related to the development and progression of certain malignant tumours. However, there is controversy in the literature regarding whether DOR has an impact on the development and progression of human breast cancer. The present study comprehensively elaborates on the biological functions of DOR by determining the distribution of DOR expression in breast cancer tissues and cells and by further verifying the effects of DOR on breast cancer progression. DOR was found to be highly expressed in human breast cancer tissues and cells. In addition, the high expression level of DOR positively correlated with tumour grade and clinical stage and negatively correlated with breast cancer metastasis and prognosis. Upregulating and activating DOR promoted the proliferation of human breast cancer cells in a concentration‑dependent manner within a specific concentration range, whereas downregulating or inhibiting DOR activation significantly suppressed cell proliferation. The majority of tumour cells were arrested in G1 phase, and some cells exhibited apoptosis. DOR upregulation and activation induced protein kinase C (PKC) activation, resulting in increased phosphorylation levels of extracellular signal‑regulated kinases (ERKs). After inhibition of the PKC/ERK signalling pathway, the effects of DOR on breast cancer were significantly attenuated in vivo and in vitro. In summary, DOR is highly expressed in breast cancer and is closely related to its progression. These results suggest that DOR may serve as a potential biomarker for the early diagnosis of breast cancer and may be a viable molecular target for therapeutic intervention.

Alpinetin activates the δ receptor instead of the κ and μ receptor pathways to protect against rat myocardial cell apoptosis

Alpinetin is a natural flavonoid that protects cells against fatal injury in ischemia-reperfusion. δ receptor activation protects myocardial cells from trauma; however, the mechanism is unknown. The aim of this study was to explore the function of alpinetin in δ receptor-mediated myocardial apoptosis. The myocardial cells of newly born rats were cultivated and myocardial apoptosis was induced by serum deprivation. The MTT method was used to evaluate cell viability and Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) staining was used to analyze apoptosis. The expression levels of opioid receptor mRNA and protein were tested using reverse transcription-polymerase reaction (RT-PCR) and western blot assays. In addition, an opioid receptor antagonist, as well as protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) inhibitors, were used to determine the inferred signaling pathway. The results showed that that alpinetin reduced the myocardial apoptosis induced by serum deprivation in a concentration-dependent manner. However, the protection conferred to the myocardial cells by alpinetin was blocked by the δ opioid receptor antagonist naltrindole, as well as by PKC and ERK inhibitors (GF109203X and U0126, respectively). In addition, it was shown that alpinetin was able to maintain the stability of the mitochondrial membrane potential, lower the level of intracytoplasmic cytochrome c and reduce Bax displacement from the cytoplasm to the mitochondria. It was concluded that alpinetin was able to activate δ receptors to induce the endogenous protection of myocardial cells via the PKC/ERK signaling pathway.

Crosstalk between delta opioid receptor and nerve growth factor signaling modulates neuroprotection and differentiation in rodent cell models

Both opioid signaling and neurotrophic factor signaling have played an important role in neuroprotection and differentiation in the nervous system. Little is known about whether the crosstalk between these two signaling pathways will affect neuroprotection and differentiation. Previously, we found that nerve growth factor (NGF) could induce expression of the delta opioid receptor gene (Oprd1, dor), mainly through PI3K/Akt/NF-κB signaling in PC12h cells. In this study, using two NGF-responsive rodent cell model systems, PC12h cells and F11 cells, we found the delta opioid neuropeptide [d-Ala², d-Leu⁵] enkephalin (DADLE)-mediated neuroprotective effect could be blocked by pharmacological reagents: the delta opioid antagonist naltrindole, PI3K inhibitor LY294002, MAPK inhibitor PD98059, and Trk inhibitor K252a, respectively. Western blot analysis revealed that DADLE activated both the PI3K/Akt and MAPK pathways in the two cell lines. siRNA Oprd1 gene knockdown experiment showed that the upregulation of NGF mRNA level was inhibited with concomitant inhibition of the survival effects of DADLE in the both cell models. siRNA Oprd1 gene knockdown also attenuated the DADLE-mediated neurite outgrowth in PC12h cells as well as phosphorylation of MAPK and Akt in PC12h and F11 cells, respectively. These data together strongly suggest that delta opioid peptide DADLE acts through the NGF-induced functional G protein-coupled Oprd1 to provide its neuroprotective and differentiating effects at least in part by regulating survival and differentiating MAPK and PI3K/Akt signaling pathways in NGF-responsive rodent neuronal cells.

Delta opioid receptor and its peptide: a receptor-ligand neuroprotection

In pursuit of neurological therapies, the opioid system, specifically delta opioid receptors and delta opioid peptides, demonstrates promising therapeutic potential for stroke, Parkinson’s disease, and other degenerative neurological conditions. Recent studies offer strong evidence in support of the therapeutic use of delta opioid receptors, and provide insights into the underlying mechanisms of action. Delta opioid receptors have been shown to confer protective effects by mediating ionic homeostasis and activating endogenous neuroprotective pathways. Additionally, delta opioid agonists such as (D-Ala 2, D-Leu 5) enkephalin (DADLE) have been shown to decrease apoptosis and promote neuronal survival. In its entirety, the delta opioid system represents a promising target for neural therapies.

Protective effects of the delta opioid peptide [D-Ala2, D-Leu5]enkephalin in an ex vivo model of ischemia/reperfusion in brain slices

INTRODUCTION

The delta opioid peptide [D-Ala2, D-Leu5]enkephalin (DADLE) plays a key role in neuronal protection against both hypoxic and ischemic conditions. However, the cellular mechanisms of action of DADLE under these conditions remain unclear.

METHODS

Ischemia was simulated with perfusing the brain slices with glucose-free artificial cerebrospinal fluid. Apoptosis was examined using an in situ cell death detection kit and expressed as the percentage of positively labeled neurons relative to total number of neurons. PCR was performed by adding cDNA, 5 pm dNTP, 1 μL Taqase, and primers. PCR products were separated with electrophoresis, stained with ethidium bromide, and visualized under ultraviolet light.

AIMS

To investigate the potential effects of DADLE in an ex vivo model of cerebral ischemia/reperfusion.

RESULTS

DADLE attenuated lactic dehydrogenase release and neuronal apoptosis in a concentration-dependent manner. The protective effects of DADLE were attenuated by representative selective delta2, but not delta1 opioid antagonists. Treatment with PD98059, a selective inhibitor of ERK kinase (MEK), also blocked the protective effect of DADLE as well as ERK phosphorylation induced by DADLE.

CONCLUSIONS

Endogenous opioid peptides could promote cell survival via delta2 opioid receptors, possibly through the downstream MEK-ERK pathway.

Mitochondrial ferritin attenuates β-amyloid-induced neurotoxicity: reduction in oxidative damage through the Erk/P38 mitogen-activated protein kinase pathways

AIMS

Mitochondrial ferritin (MtFt), which was recently discovered, plays an important role in preventing neuronal damage in 6-hydroxydopamine-induced Parkinsonism by maintaining mitochondrial iron homeostasis. Disruption of iron regulation also plays a key role in the etiology of Alzheimer's disease (AD). To explore the potential neuroprotective roles of MtFt, rats and cells were treated with Aβ(25-35) to establish an AD model.

RESULTS

We report that knockdown of MtFt expression significantly enhanced Aβ(25-35)-induced neurotoxicity as shown by dysregulation of iron homeostasis, enhanced oxidative stress, and increased cell apoptosis. Opposite results were obtained when MtFt was overexpressed in SH-SY5Y cells prior to treatment with Aβ(25-35). Further, MtFt inhibited Aβ(25-35)-induced P38 mitogen-activated protein kinase and activated extracellular signal-regulated kinase (Erk) signaling.

INNOVATION

MtFt attenuated Aβ(25-35)-induced neurotoxicity and reduced oxidative damage through Erk/P38 kinase signaling.

CONCLUSION

Our results show a protective role of MtFt in AD and suggest that regulation of MtFt expression in neuronal cells may provide a new neuroprotective strategy for AD.

Enkephalin-Degrading Enzymes in Normal and Subfertile Human Semen

Opioid peptides have been reported to have important functions in human reproduction. Indeed, very high concentrations of enkephalins and their degrading enzymes have been reported in human semen. In the present paper, we compare the activity of two enkephalin-degrading enzymes, aminopeptidase N and neutral endopeptidase 24.11, in different fractions of semen from normozoospermic, fertile men and from subfertile patients with different abnormalities revealed by spermiogram analysis (asthenozoospermia, necrozoospermia, and teratozoospermia). High levels of activity of aminopeptidase N were found in the soluble and particulate sperm fractions of semen from patients presenting asthenozoospermia with necrozoospermia. In contrast, lower aminopeptidase N activity was measured in the soluble sperm fraction of asthenozoospermic semen. The percentage of dead spermatozoa was positively correlated with aminopeptidase N activity in both soluble and particulate sperm fractions. In contrast, the percentage of immobile spermatozoa was negatively correlated with aminopeptidase activity in soluble and particulate sperm, and in prostasome fractions. Levels of activity of neutral endopeptidase were found to be unaltered among the different conditions. In summary, the results of the present study indicate that alterations in the activity of aminopeptidase N may be one of the molecular components that contribute to male human subfertility.

Hormesis: its impact on medicine and health

This article offers a broad assessment of the hormetic dose response and its relevance to biomedical researchers, physicians, the pharmaceutical industry, and public health scientists. This article contains a series of 61 questions followed by relatively brief but referenced responses that provides support for the conclusion that hormesis is a reproducible phenomenon, commonly observed, with a frequency far greater than other dose-response models such as the threshold and linear nonthreshold dose-response models. The article provides a detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how hormesis is currently being used within medicine and identifying how this concept could be further applied in the development of new therapeutic advances and in improved public health practices.

Ovarian hormones influence corticotropin releasing factor receptor colocalization with delta opioid receptors in CA1 pyramidal cell dendrites

Stress interacts with addictive processes to increase drug use, drug seeking, and relapse. The hippocampal formation (HF) is an important site at which stress circuits and endogenous opioid systems intersect and likely plays a critical role in the interaction between stress and drug addiction. Our prior studies demonstrate that the stress-related neuropeptide corticotropin-releasing factor (CRF) and the delta-opioid receptor (DOR) colocalize in interneuron populations in the hilus of the dentate gyrus and stratum oriens of CA1 and CA3. While independent ultrastructural studies of DORs and CRF receptors suggest that each receptor is found in CA1 pyramidal cell dendrites and dendritic spines, whether DORs and CRF receptors colocalize in CA1 neuronal profiles has not been investigated. Here, hippocampal sections of adult male and proestrus female Sprague-Dawley rats were processed for dual label pre-embedding immunoelectron microscopy using well-characterized antisera directed against the DOR for immunoperoxidase and against the CRF receptor for immunogold. DOR-immunoreactivity (-ir) was found presynaptically in axons and axon terminals as well as postsynaptically in somata, dendrites and dendritic spines in stratum radiatum of CA1. In contrast, CRF receptor-ir was predominantly found postsynaptically in CA1 somata, dendrites, and dendritic spines. CRF receptor-ir frequently was observed in DOR-labeled dendritic profiles and primarily was found in the cytoplasm rather than at or near the plasma membrane. Quantitative analysis of CRF receptor-ir colocalization with DOR-ir in pyramidal cell dendrites revealed that proestrus females and males show comparable levels of CRF receptor-ir per dendrite and similar cytoplasmic density of CRF receptor-ir. In contrast, proestrus females display an increased number of dual-labeled dendritic profiles and an increased membrane density of CRF receptor-ir in comparison to males. We further examined the functional consequences of CRF receptor-ir colocalization with DOR-ir in the same neuron using the hormone responsive neuronal cell line NG108-15, which endogenously expresses DORs, and assayed intracellular cAMP production in response to CRF receptor and DOR agonists. Results demonstrated that short-term application of DOR agonist SNC80 inhibited CRF-induced cAMP accumulation in NG108-15 cells transfected with the CRF receptor. These studies provide new insights on opioid-stress system interaction in the hippocampus of both males and females and establish potential mechanisms through which DOR activation may influence CRF receptor activity.

Delta opioid peptide DADLE and naltrexone cause cell cycle arrest and differentiation in a CNS neural progenitor cell line

Opioids have been demonstrated to play an important role in CNS development by affecting proliferation and differentiation in various types of neural cells. This study examined the effect of a stable delta opioid peptide [D-Ala(2), D-Leu(5)]-enkephalin (DADLE) on proliferation and differentiation in an AF5 CNS neural progenitor cell line derived from rat mesencephalic cells. DADLE (1 pM, 0.1 nM, or 10 nM) caused a significant growth inhibition on AF5 cells. The opioid antagonist naltrexone at 0.1 nM also caused growth inhibition in the same cells. When DADLE and naltrexone were both added to the AF5 cells, the resultant growth inhibition was apparently additive. DADLE alone or DADLE in combination with naltrexone did not cause apoptosis as evidenced by negative TUNEL staining. The cell-cycle progression analysis indicated that both DADLE (0.1 nM) and naltrexone (0.1 nM) caused an arrest of AF5 cell cycle progression at the G1 checkpoint. Neuronal marker indicated that DADLE- or naltrexone-treated AF5 cells tend to differentiate more when compared to controls. Results demonstrate the nonopioid action of both DADLE and naltrexone on cell cycle arrest and differentiation in a CNS neural progenitor cell line. Results also suggest some potential utilization of DADLE and/or naltrexone in stem cell research.

Effects of intracerebroventricular application of the delta opioid receptor agonist [D-Ala2, D-Leu5] enkephalin on neurological recovery following asphyxial cardiac arrest in rats

The delta opioid receptor (DOR) agonist [D-Ala2, D-Leu5] enkephalin (DADLE) has been implicated as a novel neuroprotective agent in the CNS. The current study was designed to evaluate the effects of intracerebroventricular (ICV) application of DADLE on neurological outcomes following asphyxial cardiac arrest (CA) in rats. Male Sprague-Dawley rats were randomly assigned to four groups: Sham group, CA group, DADLE group (DADLE+CA), and Naltrindole group (Naltrindole and DADLE+CA). All drugs were administered into the left cerebroventricle 30 min before CA. CA was induced by 8-min asphyxiation and the animals were resuscitated with a standardized method. DOR protein expression in the hippocampus was significantly increased in the CA group at 1 h after restoration of spontaneous circulation (ROSC) compared with the Sham group. As time progressed, expression of DOR proteins decreased gradually in the CA group. Treatment with DADLE alone or co-administration with Naltrindole reversed the down-regulation of DOR proteins in the hippocampus induced by CA at 24 h after ROSC. Compared with the CA group, the DADLE group had persistently better neurological functional recovery, as assessed by neurological deficit score (NDS) and Morris water maze trials. The number of surviving hippocampal CA1 neurons in the DADLE group was significantly higher than those in the CA group. However, administration of Naltrindole abolished most of the neuroprotective effects of DADLE. We conclude that ICV administration of DADLE 30 min before asphyxial CA has significant protective effects in attenuating hippocampal CA1 neuronal damage and neurological impairments, and that DADLE executes its effects mainly through DOR.

Mimetics of hormetic agents: stress-resistance triggers

Mimetics of hormetic agents offer a novel approach to adjust dose to minimize the risk of toxic response, and maximize the benefit of induction of at least partial physiological conditioning. Nature selected and preserved those organisms and triggers that promote tolerance to stress. The induced tolerance can serve to resist that challenge and can repair previous age, disease, and trauma damage as well to provide a more youthful response to other stresses. The associated physiological conditioning may include youthful restoration of DNA repair, resistance to oxidizing pollutants, protein structure and function repair, improved immunity, tissue remodeling, adjustments in central and peripheral nervous systems, and altered metabolism. By elucidating common pathways activated by hormetic agent's mimetics, new strategies for intervention in aging, disease, and trauma emerge. Intervention potential in cancer, diabetes, age-related diseases, infectious diseases, cardiovascular diseases, and Alzheimer's disease are possible. Some hormetic mimetics exist in pathways in primitive organisms and are active or latent in humans. Peptides, oligonucleotides, and hormones are among the mimetics that activate latent resistance to radiation, physical endurance, strength, and immunity to physiological condition tolerance to stress. Co-activators may be required for expression of the desired physiological conditioning health and rejuvenation benefits.

Ionic storm in hypoxic/ischemic stress: can opioid receptors subside it?

Neurons in the mammalian central nervous system are extremely vulnerable to oxygen deprivation and blood supply insufficiency. Indeed, hypoxic/ischemic stress triggers multiple pathophysiological changes in the brain, forming the basis of hypoxic/ischemic encephalopathy. One of the initial and crucial events induced by hypoxia/ischemia is the disruption of ionic homeostasis characterized by enhanced K(+) efflux and Na(+)-, Ca(2+)- and Cl(-)-influx, which causes neuronal injury or even death. Recent data from our laboratory and those of others have shown that activation of opioid receptors, particularly delta-opioid receptors (DOR), is neuroprotective against hypoxic/ischemic insult. This protective mechanism may be one of the key factors that determine neuronal survival under hypoxic/ischemic condition. An important aspect of the DOR-mediated neuroprotection is its action against hypoxic/ischemic disruption of ionic homeostasis. Specially, DOR signal inhibits Na(+) influx through the membrane and reduces the increase in intracellular Ca(2+), thus decreasing the excessive leakage of intracellular K(+). Such protection is dependent on a PKC-dependent and PKA-independent signaling pathway. Furthermore, our novel exploration shows that DOR attenuates hypoxic/ischemic disruption of ionic homeostasis through the inhibitory regulation of Na(+) channels. In this review, we will first update current information regarding the process and features of hypoxic/ischemic disruption of ionic homeostasis and then discuss the opioid-mediated regulation of ionic homeostasis, especially in hypoxic/ischemic condition, and the underlying mechanisms.

Defective neuropeptide processing and ischemic brain injury: a study on proprotein convertase 2 and its substrate neuropeptide in ischemic brains

Using a focal cerebral ischemia model in rats, brain ischemia-induced changes in expression levels of mRNA and protein, and activities of proprotein convertase 2 (PC2) in the cortex were examined. In situ hybridization analyses revealed a transient upregulation of the mRNA level for PC2 at an early reperfusion hour, at which the level of PC2 protein was also high as determined by immunocytochemistry and western blotting. When enzymatic activities of PC2 were analyzed using a synthetic substrate, a significant decrease was observed at early reperfusion hours at which levels of PC2 protein were still high. Also decreased at these reperfusion hours were tissue levels of dynorphin-A(1-8) (DYN-A(1-8)), a PC2 substrate, as determined by radioimmunoassay. Further examination of PC2 protein biosynthesis by metabolic labeling in cultured neuronal cells showed that in ischemic cells, the proteolytic processing of PC2 was greatly attenuated. Finally, in mice, an intracerebroventricular administration of synthetic DYN-A(1-8) significantly reduced the extent of ischemic brain injury. In mice those lack an active PC2, exacerbated brain injury was observed after an otherwise non-lethal focal ischemia. We conclude that brain ischemia attenuates PC2 and PC2-mediated neuropeptide processing. This attenuation may play a role in the pathology of ischemic brain injury.

Neuroprotective role of delta-opioid receptors against mitochondrial respiratory chain injury

It is recognized in recent years that activation of delta-opioid receptor (DOR) elicits neuroprotection against hypoxia and ischemia. However, the underlying mechanisms are not well understood yet. Mitochondrial dysfunction plays a key role in hypoxic neuronal injury, but the effect of DOR activation on neurons with a mitochondrial respiratory chain deficiency is poorly elucidated. In this study we tested the effects of DOR activation and inhibition on cultured cortical neurons after inhibiting mitochondrial respiratory chain with sodium azide (NaN(3)) in days 8 cultures. Neuronal injury was assessed by lactate dehydrogenase release. Changes in DOR proteins were investigated using an antibody against the N-terminus of the DOR, which recognizes the 60, 48, and 32 kDa proteins. Our main findings are that 1) delta- but not mu-opioid receptor activation reduces NaN(3)-induced neuronal damage, and this neuroprotective effect is abolished by DOR antagonist (naltrindole, NTI); 2) prolonged DOR inhibition with NTI further increases NaN(3)-induced neuronal damage; 3) NaN(3) treatment down-regulates DOR protein levels in neurons, and the 60 and 32 kDa proteins are particularly sensitive; 4) DADLE, besides activating DOR directly, also reverses the decrease of neuronal DOR protein levels induced by NaN(3), which may contribute greatly to its neuroprotective effect; 5) NTI reverses NaN(3)-induced down-regulation of DOR proteins as well, the effect of NTI amplifying NaN(3)-induced neuronal damage therefore is probably due to its inhibition on DOR activity only. In conclusion, these data suggest that DOR activation plays an important role in neuroprotection against mitochondrial respiratory chain injury.

Effects of delta-opioid agonist SNC80 on white matter injury following spinal cord ischemia in normothermic and mildly hypothermic rats

PURPOSE

Although the delta-opioid agonist SNC80 has been shown to attenuate hind-limb motor function and gray matter injury in normothermic rats subjected to spinal cord ischemia (SCI), its effects on white matter injury remain undetermined. In the present study, we investigated whether SNC80 could attenuate white matter injury in normothermic and mildly hypothermic rats.

METHODS

Forty rats were randomly allocated to one of following five groups: vehicle or SNC80 with 10 min of SCI at 38 degrees C (V-38-10m or SNC-38-10m, respectively), vehicle or SNC80 with 22 min of SCI at 35 degrees C (V-35-22m or SNC-35-22m, respectively), or sham. SNC80 or vehicle was intrathecally administered 15 min before SCI. Forty-eight hours after reperfusion, the white matter injury was evaluated by the extent of vacuolation.

RESULTS

The percent area of vacuolation in the ventral white matter was significantly lower in the SNC-38-10m and SNC-35-22m groups compared with that in the V-38-10m and V-35-22m groups, respectively (P < 0.05).

CONCLUSION

The results indicate that intrathecal treatment with the delta-opioid agonist SNC80 can attenuate the ventral white matter injury following SCI in rats under normothermic and mildly hypothermic conditions.

delta-Opioid receptor stimulation enhances the growth of neonatal rat ventricular myocytes via the extracellular signal-regulated kinase pathway

1. The aims of the present study were to determine whether delta-opioid receptor stimulation enhanced proliferation of and to investigate the role of the extracellular signal-regulated kinase (ERK) pathway in ventricular myocytes from neonatal rats. 2. At concentratins ranging from 10 nmol/L to 10 micromol/L, [D-Ala2,D-Leu5]enkephalin (DADLE) concentration-dependently promoted myocardial growth and DNA synthesis and altered the cytoskeleton. 3. At 1 micromol/L, DADLE also increased the expression and phosphorylation of ERK. 4. These effects of 1 micromol/L DADLE were abolished by 10 micromol/L naltrindole, a selective delta-opioid receptor antagonist, 10 nmol/L U0126, a selective ERK antagonist, 1 micromol/L staurosporine, an inhibitor of protein kinase (PK) C, and 100 micromol/L Rp-adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt hydrate (Rp-cAMPS), an inhibitor of PKA. 5. In conclusion, delta-opioid receptor stimulation enhances the proliferation and development of the ventricular myocytes of neonatal rats. The ERK pathway and related signalling mechanisms, namely PKC and PKA, are involved.

Effects of delta-opioid receptor stimulation and inhibition on hippocampal survival in a rat model of forebrain ischaemia

BACKGROUND

It has been reported that delta-opioid (DOP) receptor agonists may be neuroprotective in the central nervous system. However, the DOP agonist [d-Ala(2), d-Leu(5)]enkephalin (DADLE) does not produce neuroprotection in severe forebrain ischaemia. The aim of this study was to examine the effects of DADLE on hippocampal neurone survival against less severe forebrain ischaemia.

METHODS

Intraperitoneal injection of DADLE (0 or 16 mg kg(-1)) in male Sprague-Dawley rats was performed 30 min before ischaemia. Severe (10 min), moderate (8 min), or mild (6 min) forebrain ischaemia was produced by bilateral carotid occlusion combined with hypotension (35 mm Hg) under isoflurane (1.5%) anaesthesia. Naltrindole (10 mg kg(-1)) (DOP antagonist) was administered 30 min before DADLE in order to confirm DOP receptor activation in the neuroprotective efficacy of DADLE. Naltrindole alone was also administered 30 min before ischaemia to examine endogenous DOP agonism as a self-protecting mechanism against ischaemia. All animals were evaluated neurologically and histologically after a 1 week recovery period.

RESULTS

DADLE improved neurone survival in hippocampal CA3 and dentate gyrus (DG) sectors. CA1 neurones were not protected against moderate and mild ischaemia. Naltrindole abolished DADLE neuroprotection in the CA3 and DG after both moderate and mild ischaemia. Interestingly, regardless of co-administration of DADLE, naltrindole significantly worsened neuronal injury in the CA1 region after mild ischaemia.

CONCLUSIONS

These results suggest that DADLE provides limited neuroprotection to relatively ischaemia-resistant regions but not to selectively vulnerable regions. This was probably mediated by DOP stimulation. Pre-ischaemic treatment with a DOP antagonist, regardless of co-administration of DADLE, worsened neuronal damage at the selectively vulnerable regions only after mild forebrain ischaemia. These data suggest that DOP activation with endogenous DOP ligand may be involved in self-protecting ischaemia-sensitive regions of the brain.

Dose-dependent neuroprotection of delta opioid peptide [d-Ala2, d-Leu5] enkephalin in neuronal death and retarded behavior induced by forebrain ischemia in rats

Cerebral ischemic insult, mainly induced by cardiovascular disease, is one of the most severe neurological diseases in clinical. There's mounting evidence showing that delta opioid agonist [D-Ala2, D-Leu5] enkephalin (DADLE) has a tissue-protective effect. However, whether this property is effective to prevent neuronal death induced by forebrain ischemia is not clear. This study was aimed to investigate whether intracerebroventricular (ICV) administration of DADLE has a neuroprotective effect against forebrain ischemia in rats. We found in our study that administration of DADLE 45 min before forebrain ischemia had significant protective effect against CA1 neuronal lose. Further more, we found that DADLE had a dose-dependent protection for improving behavioral retardation revealed by Morris water maze and motor score test, while naltrindole, the antagonist of delta opioid receptor, partially abolished neuroprotective effect of DADLE, which implicated that both opioid and non-opioid systems are involved in ischemic insults and neuroprotection.

Tuberin: a stimulus-regulated tumor suppressor protein controlled by a diverse array of receptor tyrosine kinases and G protein-coupled receptors

Tuberin, a tumor suppressor protein, is involved in various cellular functions including survival, proliferation, and growth. It has emerged as an important effector regulated by receptor tyrosine kinases (RTKs) and G protein-coupled receptors (GPCRs). Regulation of tuberin by RTKs and GPCRs is highly complex and dependent on the type of receptors and their associated signaling molecules. Apart from Akt, the first kinase recognized to phosphorylate and inactivate tuberin upon growth factor stimulation, an increasing number of kinases upstream of tuberin have been identified. Furthermore, recruitment of different scaffolding adaptor components to the activated receptors appears to play an important role in the regulation of tuberin activity. More recently, the differential regulation of tuberin by various G protein family members have also been intensively studied, it appears that G proteins can both facilitate (e.g., G(i/o)) as well as inhibit (e.g., G(q)) tuberin phosphorylation. In the present review, we attempt to summarize our emerging understandings of the roles of RTKs, GPCRs, and their cross-talk on the regulation of tuberin.

Delta opioid receptors stimulation with [D-Ala2, D-Leu5] enkephalin does not provide neuroprotection in the hippocampus in rats subjected to forebrain ischemia

It has been reported that delta opioid agonists can have neuroprotective efficacy in the central nervous system. This study was conducted to test the hypothesis that a delta opioid receptor (DOR) agonist, [D-Ala2, D-Leu5] enkephalin (DADLE), can improve neuron survival against experimental forebrain ischemia in rats. Using male rats (n=125), intraperitoneal injection of DADLE (0, 0.25, 1, 4, 16 mg kg-1) was performed 30 min before ischemia. Ten minutes interval forebrain ischemia was provided by the bilateral carotid occlusion combined with hypotension (35 mm Hg) under isoflurane (1.5%) anesthesia. All animals were neurologically and histologically evaluated after a recovery period of 1 week. As histological evaluation, percentages of ischemic neurons in the CA1, CA3, dentate gyrus (DG) were measured. During the recovery period, 27 rats died because of apparent upper airway obstruction, seizure, or unidentified causes. There were no differences in the motor activity score among the groups. Ten minutes forebrain ischemia induced approximately 75, 20, and 10% neuronal death in the CA1, CA3, and DG, respectively. Any doses of DADLE did not attenuate neuronal injury in the hippocampus after ischemia. Pre-ischemic treatment of DORs agonism with DADLE did not provide any neuroprotection to the hippocampus in rats subjected to forebrain ischemia.

Activation of delta-, kappa-, and mu-opioid receptors induces phosphorylation of tuberin in transfected HEK 293 cells and native cells

A number of G protein-coupled receptors have been shown to stimulate tuberin phosphorylation, which is critical for the regulation of translation and is apparently involved in neurotrophin-promoted survival of serum-deprived cells. Here, in HEK 293 cells transiently expressing the delta-, kappa-, or mu-opioid receptors, Western blotting analysis using a phosphospecific anti-tuberin antibody revealed a dose- and time-dependent increase in tuberin phosphorylation upon stimulation by specific opioid agonists. In NG108-15, PC12, and SH-SY5Y cells that endogenously express delta-, kappa-, and mu-opioid receptors, respectively, specific opioid agonists also stimulated tuberin phosphorylation in a dose- and time-dependent manner. Pretreatment of cells with pertussis toxin or PI3K inhibitor wortmannin blocked the opioid-stimulated tuberin phosphorylation, implicating the possible involvement of the G(i/o) proteins and the phosphatidylinositol-3 kinase/Akt pathway in opioid-induced tuberin phosphorylation. This is the first study that demonstrates the regulatory role of opioid receptors on tuberin.

Activation of muscarinic M4 receptor augments NGF-induced pro-survival Akt signaling in PC12 cells

Survival or death of neurons during development is mediated by the integration of a diverse array of signal transduction cascades that are controlled by the availability and acquisition of neurotrophic factors and agonists acting at G protein-coupled receptors (GPCRs). Recent studies have demonstrated that GPCRs can modulate signals elicited by receptor tyrosine kinases (RTK) and vice versa. Here, we examined the activity of pro-survival Akt kinase, in response to stimulation by muscarinic acetylcholine receptors (mAChRs) and co-activation with the nerve growth factor (NGF) receptor in PC12 cells endogenously expressing Gi-coupled M4 mAChR and Gq-coupled M1 and M5 mAChRs. Western blotting analysis using a phosphospecific anti-Akt antibody revealed a dose- and time-dependent increase in Akt phosphorylation in cells stimulated with mAChR specific agonist carbachol (CCh). Co-stimulation with CCh and NGF resulted in augmentation of Akt activity in a pertussis toxin (PTX)-sensitive manner, suggesting that M4 mAChR, but not M1 and M5 mAChRs, was associated with this synergistic Akt activation. The use of transducin as a Gbetagamma scavenger indicated that Gbetagamma subunits rather than Galphai/o acted as the signal transducer. Additional experiments showed that CCh treatment augmented NGF-induced phosphorylation and degradation of the Akt-regulated translation regulator tuberin. This augmentation was also inhibited by PTX pre-treatment or overexpression of transducin. Finally, co-stimulation of PC12 cells with CCh and NGF resulted in enhancement of cell survival. This is the first study that demonstrates the augmentation effect between M4 mAChR and NGF receptor, and the regulatory role of mAChR on tuberin.

Opioid-induced regulation of gene expression in PC12 cells stably transfected with mu-opioid receptor

It has been postulated that opiates induce addictive behaviour via changes in gene expression. PC12 cells were stably transfected with the recombinant human mu-opioid receptor (MOR) to study opioid-induced gene expression. Expression was verified by binding assay, immunocytochemistry, and immunblotting experiments. Forskolin-induced cAMP formation was inhibited by [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO 1 microM), a specific MOR agonist. This effect was completely antagonized by naloxone. By using cDNA arrays, including approximately 1,200 well-defined genes normally expressed in neural tissue, we monitored semi-quantitative changes in gene expression after 3 h short-term exposure to DAMGO. Incubation with DAMGO increased mRNA levels for 13 genes and down-regulated 13 other genes. Annexin V, RGS4 and CREB genes showed pronounced increase in expression after stimulation with DAMGO. Quantitative RT-PCR confirmed that DAMGO increased mRNA levels of Annexin V, an apoptosis-induced gene. We suggest that the PC12 cell transfected with the recombinant human MOR is a useful tool for identification of opioid-induced genes that may provide information on opiate effects of relevance for dependence.

Femtomolar concentrations of dextromethorphan protect mesencephalic dopaminergic neurons from inflammatory damage

Inflammation in the brain has increasingly been recognized to play an important role in the pathogenesis of several neurodegenerative disorders, including Parkinson's disease (PD). Progress in the search for effective therapeutic strategies that can halt this degenerative process remains limited. We previously showed that micromolar concentrations of dextromethorphan (DM), a major ingredient of widely used antitussive remedies, reduced the inflammation-mediated degeneration of dopaminergic neurons through the inhibition of microglial activation. In this study, we report that femto- and micromolar concentrations of DM (both pre- and post-treatment) showed equal efficacy in protecting lipopolysaccharide (LPS) -induced dopaminergic neuron death in midbrain neuron-glia cultures. Both concentrations of DM decreased LPS-induced release of nitric oxide, tumor necrosis factor-alpha, prostaglandin E2 and superoxide from microglia in comparable degrees. The important role of superoxide was demonstrated by DM's failure to show a neuroprotective effect in neuron-glia cultures from NADPH oxidase-deficient mice. These results suggest that the neuroprotective effect elicited by femtomolar concentrations of DM is mediated through the inhibition of LPS-induced proinflammatory factors, especially superoxide. These findings suggest a novel therapeutic concept of using "ultra-low" drug concentrations for the intervention of inflammation-related neurodegenerative diseases.

DADLE induces a reversible hibernation-like state in HeLa cells

[D-Ala(2)-D-Leu(5)-Enkephalin] (DADLE) can induce hibernation when injected into ground squirrels in summer and is able to increase the survival time of explanted organs such as liver and lung. Since cell metabolism is a target of this peptide, we have treated HeLa cells with DADLE and investigated its possible effect on transcription and proliferation as well as the resumption of metabolic activity after treatment. The labelling for Pol I, Pol II and for splicing factors such as snRNPs and SC-35 decreased after treatment as did the nucleolar labelling for UBF. In treated cells, several spherical nuclear bodies were found to be labelled for hnRNPs. In parallel, the number of proliferating cells decreased after treatment with DADLE. After recovery, there was a gradual resumption of cell function: transcription and splicing factors had a distribution similar to that of controls; proliferation resumed; nuclear bodies, representing storage sites for RNPs, disappeared.

Pertussis toxin-sensitive Gi/o proteins are involved in nerve growth factor-induced pro-survival Akt signaling cascade in PC12 cells

In Galpha(z)-deficient mice, survival of sympathetic neurons is significantly attenuated in the presence of pertussis toxin (PTX). This suggests that G(i/o) proteins may have distinct roles in neuronal survival. Here, we investigated the possible involvement of G(i/o) proteins in nerve growth factor (NGF)-induced pro-survival phosphatidylinositol-3-kinase (PI3K)/Akt signaling in rat pheochromocytoma PC12 cells. Treatment of PC12 cells with NGF increased the Akt phosphorylation level in a time- and dose-dependent manner. The NGF-dependent Akt activation was partially attenuated by PTX or overexpression of regulators of G protein signaling Z1 (RGSZ1) and Galpha-interacting protein (GAIP)), indicating the participation of G(i/o) proteins. In contrast, epidermal growth factor (EGF)-mediated Akt phosphorylation was unaffected by PTX or RGSZ1 and GAIP. Expression of PTX-resistant mutants of Galpha(i1), Galpha(i3), Galpha(oA), and Galpha(oB), but not Galpha(i2), abolished the inhibitory effect of PTX on NGF-induced Akt activation. The use of transducin as a Gbetagamma scavenger further revealed that Gbetagamma subunits rather than Galpha(i/o) acted as the signal transducer. The activation profiles of Akt-regulated downstream effectors such as Bad, IKK, and nuclear factor-kappaB (NFkappaB) were also examined. NGF-stimulated phosphorylation of Bad and IKK and transcriptional activity of NFkappaB were indeed sensitive to treatments with PTX. This is the first study that demonstrates the involvement of G(i/o) proteins in NGF-induced Akt signaling.

Oxygen-sensitive {delta}-opioid receptor-regulated survival and death signals: novel insights into neuronal preconditioning and protection

The detrimental effect of severe hypoxia (SH) on neurons can be mitigated by hypoxic preconditioning (HPC), but the molecular mechanisms involved remain unclear, and an understanding of these may provide novel solutions for hypoxic/ischemic disorders (e.g. stroke). Here, we show that the delta-opioid receptor (DOR), an oxygen-sensitive membrane protein, mediates the HPC protection through specific signaling pathways. Although SH caused a decrease in DOR expression and neuronal injury, HPC induced an increase in DOR mRNA and protein levels and reversed the reduction in levels of the endogenous DOR peptide, leucine enkephalin, normally seen during SH, thus protecting the neurons from SH insult. The HPC-induced protection could be blocked by DOR antagonists. The DOR-mediated HPC protection depended on an increase in ERK and Bcl 2 activity, which counteracted the SH-induced increase in p38 MAPK activities and cytochrome c release. The cross-talk between ERK and p38 MAPKs displays a "yinyang" antagonism under the control of the DOR-G protein-protein kinase C pathway. Our findings demonstrate a novel mechanism of HPC neuroprotection (i.e. the intracellular up-regulation of DOR-regulated survival signals).

Picomolar concentrations of hibernation induction delta opioid peptide [D-Ala2,D-Leu5]enkephalin increase the nerve growth factor in NG-108 cells

The delta opioid peptide [D-Ala2,D-Leu5]enkephalin (DADLE) has been shown to be a neuroprotective agent via mechanisms that are not totally understood. We previously demonstrated that the i.p. injection of DADLE in mice causes an increase of nerve growth factor (NGF) in the brain. To further clarify the NGF-increasing action of DADLE, we examined here the NGF-increasing effect of DADLE in vitro, using cultured NG-108 cells. DADLE dose-dependently increases the immunoreactive level of NGF in NG-108 cells in a bell-shape manner, with the effective DADLE concentrations in the picomolar range (0.01-100 pM). Also, DADLE at 1 pM selectively increases c-Jun and c-Fos, but not c-Rel. These results indicate that DADLE is one of the most potent agents in increasing the NGF in the biological system and that this action of DADLE involves selective increases of c-Jun and c-Fos, transcription factors that promote the NGF expression.

Control of programmed cell death by neurotransmitters and neuropeptides in the developing mammalian retina

It has long been known that a barrage of signals from neighboring and connecting cells, as well as components of the extracellular matrix, control cell survival. Given the extensive repertoire of retinal neurotransmitters, neuromodulators and neurotrophic factors, and the exhuberant interconnectivity of retinal interneurons, it is likely that various classes of released neuroactive substances may be involved in the control of sensitivity to retinal cell death. The aim of this article is to review evidence that neurotransmitters and neuropeptides control the sensitivity to programmed cell death in the developing retina. Whereas the best understood mechanism of execution of cell death is that of caspase-mediated apoptosis, current evidence shows that not only there are many parallel pathways to apoptotic cell death, but non-apoptotic programs of execution of cell death are also available, and may be triggered either in isolation or combined with apoptosis. The experimental data show that many upstream signaling pathways can modulate cell death, including those dependent on the second messengers cAMP-PKA, calcium and nitric oxide. Evidence for anterograde neurotrophic control is provided by a variety of models of the central nervous system, and the data reviewed here indicate that an early function of certain neurotransmitters, such as glutamate and dopamine, as well as neuropeptides such as pituitary adenylyl cyclase-activating polypeptide and vasoactive intestinal peptide is the trophic support of cell populations in the developing retina. This may have implications both regarding the mechanisms of retinal organogenesis, as well as pathological conditions leading to retinal dystrophies and to dysfunctional cellular behavior.

Met5-enkephalin-induced cardioprotection occurs via transactivation of EGFR and activation of PI3K

Our previous studies indicated that opioid-induced cardioprotection occurs via activation of mitochondrial ATP-sensitive K(+) (K(ATP)) channels. However, other elements of the Met(5)-enkephalin (ME) cardioprotection pathway are not fully characterized. In the present study, we investigated the role of tyrosine kinase, MAPK, and phosphatidylinositol 3-kinase (PI3K) signaling in ME-induced protection. Ca(2+)-tolerant, adult rabbit cardiomyocytes were isolated by collagenase digestion and subjected to simulated ischemia for 180 min. ME was administered 15 min before the 180 min of simulated ischemia; blockers were administered 15 min before ME. Cell death was assessed by trypan blue as a function of time. The epidermal growth factor receptor (EGFR) kinase inhibitor AG-1478 (250 nM) blocked ME-induced protection, but the inactive analog AG-9 (100 microM) did not. Treatment with herbimycin (1 microM) completely eliminated ME-induced protection. To verify that ME activates EGFR and to determine the involvement of Src, Western blotting of EGFR was performed after ME administration with and without herbimycin A. ME resulted in herbimycin-sensitive robust phosphorylation of EGFR at Tyr(992) and Tyr(1068). Administration of the selective MAPK inhibitor PD-98059 (10 nM) and the specific MEK1/2 inhibitor U-0126 (10 microM) also inhibited ME-induced cardioprotection. ME-induced ERK1/2 phosphorylation was significantly reduced by PD-98059, the EGFR kinase inhibitor PD-153035 (10 microM), and chelerythrine (2 microM). The PI3K inhibitor LY-294002 (20 microM) abrogated ME-induced protection, and ME-induced Akt phosphorylation at Ser(473) was suppressed by LY-294002, PD-153035, and chelerythrine. We conclude that ME-induced cardioprotection is mediated via Src-dependent EGFR transactivation and activation of the PI3K and MAPK pathways.