Treatment with delta opioid peptide enhances in vitro and in vivo survival of rat dopaminergic neurons

[D-Ala2, D-Leu5] enkephalin (DADLE) protects liver against ischemia-reperfusion injury in the rat

BACKGROUND

[D-Ala(2), D-Leu(5)] enkephalin (DADLE) is a synthetic delta class of opioid and is reported to induce hibernation as well as hibernation induction trigger (HIT) in the serum of hibernating mammals. DADLE and HIT have been demonstrated to protect the heart, lung, and jejunum against ischemia-reperfusion (I-R) injury. In the present study, we examined the effect of DADLE on I-R injury of the liver in rats.

METHODS

After administration of DADLE (DADLE group) or normal saline as a vehicle (Control group), partial hepatic ischemia was induced by occluding the vessels supplying 92% of the liver for 45 min, followed by declamping the vessels and resection of the non-ischemic lobe. After 120 min of reperfusion, serum glutamic-pyruvic transaminase (GPT), hyaluronic acid (HA) levels, and concentrations of malondialdehyde (MDA) of the liver tissue were measured. Additionally, bile output from the ischemic lobes was measured after reperfusion.

RESULTS

GPT levels were significantly lower in the DADLE group as compared to those of the Control group (P < 0.05), but the serum levels of HA were not different between the two groups. The concentrations of MDA of the liver tissue were significantly lower in the DADLE group than in the Control group (P < 0.01). The bile output after reperfusion was not significantly different between the two groups.

CONCLUSIONS

DADLE protects against I-R injury in hepatocytes, but not in the sinusoidal endothelial cells of the liver in rats. An anti-oxidative effect is suggested to be responsible for this effect.

Effect of a delta receptor agonist on duration of survival during hemorrhagic shock

OBJECTIVES

Selective delta receptor agonists have been shown to stabilize membrane physiologic processes, reduce metabolic rates, and provide protection against ischemic insults through K(ATP) channel opening in a variety of organ beds. However, their potential for affecting outcomes in states of generalized ischemia has not been explored. The authors examined the effect of the nonselective delta receptor agonist, DADLE (D-Ala2-Leu5-enkephalin), on hemodynamic stability and duration of survival in an animal model of severe hemorrhagic shock.

METHODS

Conscious Sprague Dawley rats with indwelling catheters were hemorrhaged at a rate of 3.25 mL/100 grams over 20 minutes after half of the group received 1% DADLE (1 mg/kg IV). Following the hemorrhage, all rats were continuously monitored for heart rate (HR), mean arterial pressure (MAP), and life signs for up to three hours (death defined as apnea, systolic blood pressure < 30 mm Hg without pulsations, and electroencephalographic silence). Survival rates and hemodynamic trends were compared between the control and DADLE-treated groups.

RESULTS

In the 14 rats studied (8 DADLE; 6 controls), initial hemorrhage resulted in similar hemodynamic shock (average MAP fall: 118 to 59 vs 119 to 55 mm Hg). Analysis of survival at 3.5 hours revealed statistically significant differences between the control and DADLE groups. While 50% of the DADLE group survived past the three hours, no control animals were still alive at the end of the experimental period. The MAP trended downward and the HR increased for the control group, but all hemodynamic parameters stabilized in the rats treated with DADLE.

CONCLUSIONS

Most current strategies for treating shock focus on the supply side of resuscitation. The coordinated various actions of DADLE have the potential to work in concert in the intact organism to improve overall survival during severe hemorrhagic shock. In an animal model of severe hemorrhagic shock, there was improvement in hemodynamic stability and a prolonged survival with DADLE treatment. Physiologic manipulation with DADLE appears to be a way to improve survival during shock with possible clinical implications.

Chronic [D-Ala2, D-Leu5]enkephalin treatment increases the nerve growth factor in adult mouse brain

The delta opioid peptide [D-Ala(2), D-Leu(5)]enkephalin (DADLE) has been shown to enhance the survival of dopaminergic neurons. Here, we found that chronic treatment with DADLE caused a significant increase in nerve growth factor (NGF) in the hippocampus and the midbrain of adult albino Swiss (CD-1) mice, but not in the striatum or frontal cortex. Glia-derived neurotrophic factor (GDNF) was not significantly affected. Thus, the neuroprotective action of DADLE may be mediated in part by NGF.

Squirreling away at Parkinson's

A compound that triggers hibernation in ground squirrels can also protect brain cells from the lack of oxygen following a stroke.

Immunoreactive neurons in the brain of two mouse strains after incubation with an antiserum recognizing Asp-Val-Val-Gly.NH2 (DVVG), the C-terminal fragment of (D-Ala2)-deltorphin I

D-Ala(2)-deltorphin I (DADTI) is a heptapeptide amide first extracted from frog skin that displays a high selectivity and affinity for delta opioid receptors. Previous studies using a polyclonal antiserum specific for its C-terminal tetrapeptide-amide (DVVG) have already described in rat and mouse brain the presence of immunoreactive neurons, most of them belonging to the mesencephalic dopaminergic neurons. C57BL/6J (C57) and DBA/2J (DBA) are two inbred strains of mice well known for showing marked genotype-dependent differences for phenotypes related to differential brain dopamine functioning. Brain specimens of both inbred mouse strains were frozen, cut and immunostained using the same antiserum. Some sections were also double immunostained with monoclonal anti-tyrosine hydroxylase (TH). DVVG-immunoreactive neurons were observed among both dopaminergic and non-dopaminergic neurons. DVVG- and TH-immunoreactive neurons were observed among the dopaminergic A8, A9 and A10 mesencephalic nuclei. They were on average 21.9% more numerous in DBA than in C57 mice. DVVG-immunoreactive nerve fibres could be seen in limbic, striatal, cortical and thalamic areas. The distribution patterns of DVVG-IR and TH-IR nerve fibres differed most conspicuously within the infralimbic, prelimbic and cingulate cortices, forming a dense network in DBA but rare in C57 mice. Non-dopaminergic DVVG-immunoreactive neurons did not differ significantly in the two strains. Our finding that the number and distribution pattern of this dopaminergic neuronal subpopulation differed in the two mouse strains could provide morphological support for the known behavioural differences between the DBA and C57 strains under normal and experimental conditions.

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

The delta opioid peptide [D-Ala(2),D-Leu(5)]enkephalin (DADLE) has been shown to promote organ survival and to protect against methamphetamine-induced neurodegeneration. However, the cellular mechanisms of these actions of DADLE are not totally clear. We examined the action of DADLE in serum-deprived pheochromocytoma cells (PC12) and found that DADLE protected against cell death in those cells. However, the dose-response curves of the protective effects of DADLE are U-shaped as judged by three biochemical or morphological assays: the LDH release, the DNA laddering, and the apoptotic nuclei. It was found that femtomolar to picomolar concentrations of DADLE are antiapoptotic, whereas micormolar concentrations of DADLE are cytotoxic in PC12 cells. The protective effect of DADLE could be attenuated by a selective delta2 opioid antagonist and the cytotoxic action of DADLE was reduced by a selective mu opioid receptor antagonist. The treatment of cells with PD98059, a selective inhibitor of ERK kinase (MEK), or the transfection of cells with a dominant interfering form of MEK (MEK-KA97) blocked both the protective effect of DADLE and the ERK phosphorylation induced by DADLE. Cytotoxic concentrations of DADLE, on the other hand, caused an increase of Fas-ligand (FasL) in PC12 cells that was attenuated by a selective mu antagonist. Our results suggest, therefore, that endogenous opioid peptides may, at low concentrations, promote cell survival via the MEK-ERK pathway perhaps through delta2 opioid receptors, whereas they may kill cells at high concentrations via the activation of FasL through an as-yet unknown mechanism involving mu opioid receptors.

Endogenous opiates: 2000

This paper is the twenty-third installment of the annual review of research concerning the opiate system. It summarizes papers published during 2000 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Blockade of dopamine transporter and tyrosine hydroxylase activity loss by [D-Ala(2), D-Leu(5)]enkephalin in methamphetamine-treated CD-1 mice

[D-Ala(2), D-Leu(5)]enkephalin (DADLE) has been previously reported to prolong the survival of tissues both in the periphery and in the central nervous system. Here, we show that DADLE was able to block the protein as well as the functional loss of dopamine transporter (DAT) and tyrosine hydroxylase (TH) induced by methamphetamine. Male CD-1 mice received four injections of methamphetamine (10 mg/kg, i.p. ) at 2-h intervals. DADLE (4 mg/kg, i.p.) was given 30 min before each injection of methamphetamine. Western blotting and enzymatic assays showed that DADLE blocked the protein loss and functional impairment of DAT and TH induced by methamphetamine.