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Blockade of OGFr delays the onset and reduces the severity of diabetic ocular surface complications.Experimental Biology and Medicine... Mar 2021The opioid growth factor (OGF)-OGF receptor (OGFr) pathway is present in the ocular surface and functions to maintain homeostasis of the epithelium. The OGF-OGFr pathway...
The opioid growth factor (OGF)-OGF receptor (OGFr) pathway is present in the ocular surface and functions to maintain homeostasis of the epithelium. The OGF-OGFr pathway has been reported to be dysregulated in diabetic individuals and animal models, and is reflected in elevations of the inhibitory growth factor, OGF, chemically termed [Met]-enkephalin. Recently, our laboratory reported elevated levels of OGF and OGFr in the serum and corneal epithelium of type 1 diabetic rats, suggesting that dysregulation of the OGF-OGFr axis may lead to dry eye, abnormal corneal surface sensitivity, and delayed re-epithelialization. Blockade of OGF-OGFr pathway using naltrexone, a potent opioid receptor antagonist, reverses dry eye symptoms and restores corneal surface sensitivity in diabetic rats when used as a therapy. Based on the evidence that both OGF and OGFr are elevated in type 1 diabetic rats, this study examined whether systemic or topical naltrexone treatment initiated at the time of induction of hyperglycemia could protect against the development of diabetic ocular surface complications. Diabetic male Sprague-Dawley rats treated systemically or topically with naltrexone had a delayed onset of dry eye and altered corneal surface sensitivity, and an improved healing rate for corneal wounds, that were comparable to non-diabetic rats. Serum levels of OGF were normal for rats receiving systemic naltrexone, and OGF tissue levels were normal for type 1 diabetic rats receiving twice daily naltrexone drops. OGFr levels remained elevated. These data support the role of the OGF-OGFr axis in regulation of ocular surface complications, and suggest that naltrexone therapy may be beneficial for pre-diabetic and early diabetic individuals.
Topics: Animals; Blood Glucose; Body Weight; Cornea; Diabetes Complications; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Enkephalin, Methionine; Eye; Male; Naltrexone; Rats, Sprague-Dawley; Receptors, Opioid; Severity of Illness Index; Time Factors; Rats
PubMed: 33203224
DOI: 10.1177/1535370220972060 -
The Journal of Physiology Mar 2019Excitatory glutamate neurons are sparse in the rostral hypothalamic arcuate nucleus (ARC), the subregion that has received the most attention in the past. In striking...
KEY POINTS
Excitatory glutamate neurons are sparse in the rostral hypothalamic arcuate nucleus (ARC), the subregion that has received the most attention in the past. In striking contrast, excitatory neurons are far more common (by a factor of 10) in the caudal ARC, an area which has received relatively little attention. These glutamate cells may play a negative role in energy balance and food intake. They can show an increase in phosphorylated Stat-3 in the presence of leptin, are electrically excited by the anorectic neuromodulator cholecystokinin, and inhibited by orexigenic neuromodulators neuropeptide Y, met-enkephalin, dynorphin and the catecholamine dopamine. The neurons project local axonal connections that excite other ARC neurons including proopiomelanocortin neurons that can play an important role in obesity. These data are consistent with models suggesting that the ARC glutamatergic neurons may play both a rapid and a slower role in acting as anorectic neurons in CNS control of food intake and energy homeostasis.
ABSTRACT
Here we interrogate a unique class of excitatory neurons in the hypothalamic arcuate nucleus (ARC) that utilizes glutamate as a fast neurotransmitter using mice expressing GFP under control of the vesicular glutamate transporter 2 (vGluT2) promoter. These neurons show a unique distribution, synaptic characterization, cellular physiology and response to neuropeptides involved in energy homeostasis. Although apparently not previously appreciated, the caudal ARC showed a far greater density of vGluT2 cells than the rostral ARC, as seen in transgenic vGluT2-GFP mice and mRNA analysis. After food deprivation, leptin induced an increase in phosphorylated Stat-3 in vGluT2-positive neurons, indicating a response to hormonal cues of energy state. Based on whole-cell recording electrophysiology in brain slices, vGluT2 neurons were spontaneously active with a spike frequency around 2 Hz. vGluT2 cells were responsive to a number of neuropeptides related to energy homeostasis; they were excited by the anorectic peptide cholecystokinin, but inhibited by orexigenic neuropeptide Y, dynorphin and met-enkephalin, consistent with an anorexic role in energy homeostasis. Dopamine, associated with the hedonic aspect of enhancing food intake, inhibited vGluT2 neurons. Optogenetic excitation of vGluT2 cells evoked EPSCs in neighbouring neurons, indicating local synaptic excitation of other ARC neurons. Microdrop excitation of ARC glutamate cells in brain slices rapidly increased excitatory synaptic activity in anorexigenic proopiomelanocortin neurons. Together these data support the perspective that vGluT2 cells may be more prevalent in the ARC than previously appreciated, and play predominantly an anorectic role in energy metabolism.
Topics: Action Potentials; Animals; Arcuate Nucleus of Hypothalamus; Cholecystokinin; Dopamine; Dynorphins; Eating; Energy Metabolism; Enkephalin, Methionine; Excitatory Postsynaptic Potentials; Glutamic Acid; Homeostasis; Leptin; Mice; Mice, Inbred C57BL; Neurons; Neuropeptide Y; Pro-Opiomelanocortin; STAT3 Transcription Factor; Vesicular Glutamate Transport Protein 2
PubMed: 30618146
DOI: 10.1113/JP277152 -
British Journal of Pharmacology 19801 Methionine (Met)-enkephalin, leucine (Leu)-enkephalin and their synthetic analogues were tested for effects on the spontaneous release of cortical acetylcholine (ACh)...
1 Methionine (Met)-enkephalin, leucine (Leu)-enkephalin and their synthetic analogues were tested for effects on the spontaneous release of cortical acetylcholine (ACh) in vivo. The ability of naloxone to reverse the action of enkephalins on ACh release was compared with its action against morphine. An enkephalin analogue, structurally related to Met-enkephalin, was tested for opiate antagonistic activity in ACh release experiments. 2 Intraventricular administration of Met-enkephalin, Leu-enkephalin, D-Ala2-Met5-enkephalinamide (DALA) and D-Ala2-D-Leu5-enkephalin (DALEU) produced a dose-related inhibition of cortical ACh release. Met- and Leu-enkephalin were very similar both in their potency and the time course of their action on ACh release. Both DALA and DALEU were more potent and had a longer duration of action than Leu-enkephalin. Systemic injections of two pentapeptides, D-Met2-Pro5-enkephalinamide and D-Ala2-MePhe4-Met5(O)-ol-enkephalin (33,824), produced a sustained inhibition of cortical ACh release. 3 Naloxone, administered systemically following the depression of ACh release induced by either intraventricular injections of enkephalins (DALA or DALEU), or systemic injections of enkephalins (D-Met2-Pro5-enkephalinamide or 33,824), reversed this depression and restored the release to baseline levels. The effect of D-Met2-Pro5-enkephalinamide on the release of ACh was reversed by naloxone with difficulty. Naloxone also reversed the inhibitory effect of systemic morphine and this reversal was associated with a large overshoot of ACh release. The latter was never observed in the enkephalin experiments. 4 Intraventricular injection of the pentapeptide, D-Ala2-D-Ala3-Met5-enkephalinamide (TAAPM), at doses that did not influence the basal ACh release, blocked or reversed the inhibitory effect of morphine on this release. This peptide did not block the effect of the non-opiate, chlorpromazine, under similar conditions. In two experiments TAAPM failed to reverse the inhibition of ACh release produced by systemically injected enkephalin, D-Met2-Pro5-enkephalinamide. 5 Effects of morphine and enkephalin on ACh release are discussed in terms of their action on difference opiate receptors.
Topics: Acetylcholine; Animals; Brain; Endorphins; Enkephalin, Methionine; Enkephalins; Injections, Intraventricular; Morphine; Naloxone; Rats
PubMed: 7470736
DOI: 10.1111/j.1476-5381.1980.tb10927.x -
Revista de NeurologiaPrimary peptidergic sensory neurons of the trigeminal ganglion that innervate the cerebral dura have been involved in the pathogenesis of headache, including the...
INTRODUCTION
Primary peptidergic sensory neurons of the trigeminal ganglion that innervate the cerebral dura have been involved in the pathogenesis of headache, including the migraine. In addition, it is known that nociceptive central processes of the trigeminal neurons terminate in the caudal trigeminal nucleus. Moreover, the electrical stimulation of the trigeminal ganglion has been used as an experimental model in order to study the vascular headache, including the migraine.
AIM
To study whether there is or not a decrease of the immunoreactivity for methionine enkephalin, somatostatin and neurotensin in the caudal trigeminal nucleus after electrical stimulation of the trigeminal ganglion.
MATERIAL AND METHODS
The trigeminal ganglia of Wistar albino rats of both sexes were electrically stimulated (frequency, 5 Hz; duration, 5 ms; intensity, 0,8 1.4 mA) and unilaterally for five minutes. Sections of the medulla oblongata containing the caudal trigeminal nucleus were obtained and processed for immunocytochemistry, in which specific antibodies were used against methionine enkephalin, neurotensin and somatostatin 28.
RESULTS
In stimulated animals, we observed a decrease in the immunoreactivity for the three neuropeptides studied in the stimulated (ipsilateral) side, in comparison with the not stimulated side (contralateral). In control animals (not stimulated) the degree of the immunoreactivity was the same on both sides.
CONCLUSIONS
1. The decrease of the immunoreactivity in the ipsilateral side (stimulated) suggests that methionine enkephalin, neurotensin and somatostatin 28 are released in the caudal trigeminal nucleus after electrical stimulation of the trigeminal ganglion; 2. Methionine enkephalin and somatostatin 28 could act in the caudal trigeminal nucleus as inhibitors (with antinociceptive action) of another released exciters neuropeptides (with nociceptive action); and 3. These data will allow in the future to try new therapeutic strategies (e.g., the inhibition of the receptors implicated.), in order to alleviate certain headaches.
Topics: Animals; Electric Stimulation; Enkephalin, Methionine; Female; Immunohistochemistry; Male; Migraine Disorders; Neurons; Neurotensin; Rats; Rats, Wistar; Somatostatin; Trigeminal Caudal Nucleus; Trigeminal Ganglion
PubMed: 12080490
DOI: No ID Found -
British Journal of Pharmacology May 1987The effects of either hypotension induced by sodium nitroprusside or hexamethonium or hypertension produced by angiotensin II or noradrenaline on the circulating levels...
The effects of either hypotension induced by sodium nitroprusside or hexamethonium or hypertension produced by angiotensin II or noradrenaline on the circulating levels of methionine enkephalin ([Met]enkephalin)-like immunoreactivity (MLI), adrenaline and noradrenaline in anaesthetized greyhounds were examined. Nitroprusside infusions (200 and 400 micrograms min-1) induced a fall in blood pressure accompanied by significant rises in plasma MLI and catecholamine concentrations. Concomitant administration of a high dose of naloxone did not alter the fall in blood pressure produced by nitroprusside but was associated with greater rises in circulating MLI and catecholamines when compared to nitroprusside alone, suggesting that [Met]enkephalin is not involved in the hypotensive action of nitroprusside. Intravenous hexamethonium (2.5 mg kg-1) provoked a fall in blood pressure which was not associated with any changes in plasma MLI. However, it produced a fall in plasma noradrenaline and a rise in plasma adrenaline. Thus it appears that neural mechanisms are required, at least in part, for the release of MLI. Angiotensin II (1.25 micrograms kg-1 min-1) and noradrenaline (8 micrograms kg-1 min-1) infusions produced an elevation in blood pressure without altering the circulating MLI levels. Study of the molecular forms of circulating MLI, before and during hypotension, revealed that the large molecular weight enkephalin-containing peptides with approximate molecular sizes of 18kD and 8kD were the predominant forms both in the basal and stimulated states. It is concluded that circulating [Met]enkephalin is not involved in the tonic control of blood pressure but it may modulate catecholamine release following hypotension as part of the stress response.
Topics: Anesthesia; Angiotensin II; Animals; Catecholamines; Chromatography, Gel; Dogs; Enkephalin, Methionine; Epinephrine; Hypertension; Hypotension; Nitroprusside; Norepinephrine; Radioimmunoassay; Time Factors
PubMed: 3594068
DOI: 10.1111/j.1476-5381.1987.tb08988.x -
Zeitschrift Fur Naturforschung. C,... 2001The possible involvement of opioid system in the regulation of hemolymph glucose level in the fresh water crab Oziotelphusa senex senex Fabricius, was investigated....
The possible involvement of opioid system in the regulation of hemolymph glucose level in the fresh water crab Oziotelphusa senex senex Fabricius, was investigated. Opioid agonist and antagonist was also used in addition to methionine-enkephalin itself. Injection of the opioid, methionine-enkephalin and FK 33-824 significantly elevated hemolymph glucose level. In contrast, injection of naloxone in to crab resulted in decrease in hemolymph glucose level. Injection of naloxone prior to injection of methionine-enkephalin blocked the hyperglycemic action of methionine-enkephalin. Injection of methionine-enkephalin, FK 33824 and naloxone produced no significant effect on hemolymph glucose level in eyestalk-less crab. The alterations in the intact crab hemolymph glucose level hypothesised to be due to stimulation of release of hyperglycemic hormone during methionine-enkephalin and FK 33824 treatment and blocking of release of hyperglycemic hormone during naloxone treatment from the eyestalks of crab Oziotelphusa senex senex.
Topics: Animals; Brachyura; D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; Enkephalin, Methionine; Fresh Water; Glucose; Hemolymph; Homeostasis; Naloxone
PubMed: 11531100
DOI: 10.1515/znc-2001-7-824 -
Cancer Biology & Therapy 2015Methionine enkephalin (MENK), an endogenous neuropeptide, plays an crucial role in both neuroendocrine and immune systems. CD4+Foxp3+ regulatory T cells (Tregs) are...
Methionine enkephalin (MENK), an endogenous neuropeptide, plays an crucial role in both neuroendocrine and immune systems. CD4+Foxp3+ regulatory T cells (Tregs) are identified as a major subpopulation of T lymphocytes in suppressing immune system to keep balanced immunity. The aim of this research work was to elucidate the mechanisms via which MENK interacts with Tregs in cancer situation. The influence of MENK on transforming growth factor-β (TGF-β) mediated conversion from naïve CD4+CD25- T cells to CD4+CD25+ Tregs was determined and the data from flow cytometry (FCM) analysis indicated that MENK effectively inhibited the expression of Foxp3 during the process of TGF-βinduction. Furthermore, this inhibiting process was accompanied by diminishing phosphorylation and nuclear translocation of Smad2/3, confirmed by western blot (WB) analysis and immunofluorescence (IF) at molecular level. We established sarcoma mice model with S180 to investigate whether MENK could modulate Tregs in tumor circumstance. Our findings showed that MENK delayed the development of tumor in S180 tumor bearing mice and down-regulated level of Tregs. Together, these novel findings reached a conclusion that MENK could inhibit Tregs activity directly and retard tumor development through down-regulating Tregs in mice. This work advances the deepening understanding of the influence of MENK on Tregs in cancer situation, and relation of MENK with immune system, supporting the implication of MENK as a new strategy for cancer immunotherapy.
Topics: Animals; CD4-Positive T-Lymphocytes; Cell Line, Tumor; Cell Proliferation; Enkephalin, Methionine; Flow Cytometry; Forkhead Transcription Factors; Humans; Immunotherapy; Mice; Sarcoma; T-Lymphocytes, Regulatory; Transforming Growth Factor beta
PubMed: 25701137
DOI: 10.1080/15384047.2014.1003006 -
Human Vaccines & Immunotherapeutics Aug 2012The aim of this study was to investigate the effects of mechanisms of methionine enkephalin (MENK) on lymphocytes in human peripheral blood. We detected CD4+T cells,...
The aim of this study was to investigate the effects of mechanisms of methionine enkephalin (MENK) on lymphocytes in human peripheral blood. We detected CD4+T cells, CD8+T cells, CD4+CD25+ regulatory T cells (Treg), dendritic cells (DCs), natural killer cells (NK), NKT cells and γδT cells before and after treatment with 10 (-12) M MENK, in cell culture by FCM and RT-PCR. Our findings show that MENK stimulating expansion of lymphocyte subpopulationns by inhibiting CD4+CD25+ regulatory T cells (Treg), which is unique discovery of our study. We may use MENK as a drug to treat cancer patients, whose immune systems are damaged by chemotherapy or radiotherapy.
Topics: Adolescent; Adult; Cells, Cultured; Enkephalin, Methionine; Female; Flow Cytometry; Humans; Immunologic Factors; Interferon-gamma; Interleukin-2; Lymphocyte Subsets; Male; Reverse Transcriptase Polymerase Chain Reaction; Young Adult
PubMed: 22854663
DOI: 10.4161/hv.20759 -
Molecules (Basel, Switzerland) Aug 2014Recent histopathological investigations in patients with hepatitis suggested possible involvement of Met-enkephalin and its receptors in the pathophysiology of...
Recent histopathological investigations in patients with hepatitis suggested possible involvement of Met-enkephalin and its receptors in the pathophysiology of hepatitis. Consequently, we evaluated the potential hepatoprotective effects of this endogenous opioid pentapeptide in the experimental model of acetaminophen induced hepatotoxicity in male CBA mice. Met-enkephalin exhibited strong hepatoprotective effects in a dose of 7.5 mg/kg, which corresponds to the protective dose reported for several different animal disease models. In this group plasma alanine aminotransferase and aspartate aminotransferase enzyme activities, as well as liver necrosis score were significantly reduced in comparison to control animals treated with physiological saline (p>0.01). The specificity of the peptide hepatoprotection was investigated from the standpoint of the receptor and peptide blockade. It was concluded that Met-enkephalin effects on the liver were mediated via δ and ζ opioid receptors. Genotoxic testing of Met-enkephalin confirmed the safety of the peptide.
Topics: Acetaminophen; Animals; Chemical and Drug Induced Liver Injury; Enkephalin, Methionine; Humans; Liver; Mice; Protective Agents
PubMed: 25105920
DOI: 10.3390/molecules190811833 -
The Journal of Neuroscience : the... Sep 1983Regulation of cellular content of the endogenous opioid peptides Met5-enkephalin and Leu5-enkephalin was investigated in neuroblastoma X glioma hybrid cells NG108-15...
Regulation of cellular content of the endogenous opioid peptides Met5-enkephalin and Leu5-enkephalin was investigated in neuroblastoma X glioma hybrid cells NG108-15 grown in both serum-supplemented and serum-free defined media. Untreated cells and cells induced to differentiate were stained using anti-Met5-enkephalin and anti-Leu5-enkephalin with the peroxidase-antiperoxidase immunocytochemical technique at the light microscopic level. In untreated NG108-15 cells grown in serum-supplemented medium, intense enkephalin-like immunoreactivity was localized in cell bodies and short processes of a select population of cells. The volume fraction of stained untreated cells remained constant throughout the time period investigated. When cells were induced to differentiate with N6,O2'-dibutyryl adenosine 3':5'-cyclic monophosphate (dBcAMP) or 8-bromo cyclic adenosine monophosphate (1.0 mM) treatment for 5 days, staining was found throughout the cytoplasm of perikarya and the extensive processes which were expressed, and the volume fraction of stained cells increased over 2-fold. Receptor-mediated stimulation of adenylate cyclase by prostaglandin E1 (10 microM) for 5 days produced results similar to those with dBcAMP. Pure cultures of differentiated cells with intense staining were obtained by further treatment of cultures, grown in the presence or absence of dBcAMP, with arabinosylcytosine (araC). Untreated, dBcAMP-treated and araC-treated NG108-15 cells grown in defined medium expressed staining patterns and volume fractions of stained cells similar to those grown in serum-supplemented medium; sodium butyrate (1.0 mM), however, increased the volume fraction of stained cells grown in defined medium over 3-fold, whereas it had little effect on staining of cells grown with serum. The presence of both Met5- and Leu5-enkephalin-like activities in NG108-15 cells was confirmed in acid extracts of cells by radioreceptor assay after separation by reverse phase high pressure liquid chromatography. Induction of differentiation in NG108-15 cells by dBcAMP treatment increased the cellular concentration of both enkephalins to over 2 times the levels found in untreated cells. The biochemical analysis for Met5-enkephalin- and Leu5-enkephalin-like activity compared well with the immunocytochemical data indicating that the enkephalin content is correlated with the state of differentiation of NG108-15 cells.
Topics: 8-Bromo Cyclic Adenosine Monophosphate; Bucladesine; Cell Differentiation; Culture Media; Cyclic AMP; Enkephalin, Leucine; Enkephalin, Methionine; Glioma; Hybrid Cells; Immunochemistry; Neuroblastoma; Staining and Labeling
PubMed: 6193253
DOI: 10.1523/JNEUROSCI.03-09-01713.1983