The occurrence and receptor specificity of endogenous opioid peptides within the pancreas and liver of the rat. Comparison with brain

Insulinoma mimic: methadone-induced hypoglycaemia

Methadone use for opioid use disorder and chronic pain has increased since the start of the century with about 4.4 million dispensed prescriptions in 2009. With increased use of methadone, there has been increasing reporting of less commonly reported side effects (ie, hypoglycaemia). Here, we describe a woman in her 70s with history of opioid use disorder on methadone, stage 4 chronic kidney disease and prior hypoglycaemic episodes who initially presented with perforated gastric ulcer requiring surgical repair. Her perioperative course was complicated by profound hyperinsulinaemic hypoglycaemia. Given concern for methadone-induced hypoglycaemia, methadone was discontinued with monitoring of subsequent blood glucose, insulin, C peptide, proinsulin, β-hydroxybutyrate and blood methadone levels. As the serum methadone levels decreased, insulin levels substantially decreased in parallel. After 21 days off methadone, dextrose infusion was discontinued with restoration of euglycaemia. In a patient with hyperinsulinaemic hypoglycaemia and methadone use, it is important to consider discontinuing methadone and re-evaluate fasting glucose levels prior to an extensive and invasive insulinoma workup.

Fentanyl but Not Morphine or Buprenorphine Improves the Severity of Necrotizing Acute Pancreatitis in Rats

Opioids are widely used for the pain management of acute pancreatitis (AP), but their impact on disease progression is unclear. Therefore, our aim was to study the effects of clinically relevant opioids on the severity of experimental AP. Various doses of fentanyl, morphine, or buprenorphine were administered as pre- and/or post-treatments in rats. Necrotizing AP was induced by the intraperitoneal injection of L-ornithine-HCl or intra-ductal injection of Na-taurocholate, while intraperitoneal caerulein administration caused edematous AP. Disease severity was determined by laboratory and histological measurements. Mu opioid receptor (MOR) expression and function was assessed in control and AP animals. MOR was expressed in both the pancreas and brain. The pancreatic expression and function of MOR were reduced in AP. Fentanyl post-treatment reduced necrotizing AP severity, whereas pre-treatment exacerbated it. Fentanyl did not affect the outcome of edematous AP. Morphine decreased vacuolization in edematous AP, while buprenorphine pre-treatment increased pancreatic edema during AP. The overall effects of morphine on disease severity were negligible. In conclusion, the type, dosing, administration route, and timing of opioid treatment can influence the effects of opioids on AP severity. Fentanyl post-treatment proved to be beneficial in AP. Clinical studies are needed to determine which opioids are best in AP.

Casomorphins and Gliadorphins Have Diverse Systemic Effects Spanning Gut, Brain and Internal Organs

Food-derived opioid peptides include digestive products derived from cereal and dairy diets. If these opioid peptides breach the intestinal barrier, typically linked to permeability and constrained biosynthesis of dipeptidyl peptidase-4 (DPP4), they can attach to opioid receptors. The widespread presence of opioid receptors spanning gut, brain, and internal organs is fundamental to the diverse and systemic effects of food-derived opioids, with effects being evidential across many health conditions. However, manifestation delays following low-intensity long-term exposure create major challenges for clinical trials. Accordingly, it has been easiest to demonstrate causal relationships in digestion-based research where some impacts occur rapidly. Within this environment, the role of the microbiome is evidential but challenging to further elucidate, with microbiome effects ranging across gut-condition indicators and modulators, and potentially as systemic causal factors. Elucidation requires a systemic framework that acknowledges that public-health effects of food-derived opioids are complex with varying genetic susceptibility and confounding factors, together with system-wide interactions and feedbacks. The specific role of the microbiome within this puzzle remains a medical frontier. The easiest albeit challenging nutritional strategy to modify risk is reduced intake of foods containing embedded opioids. In future, constituent modification within specific foods to reduce embedded opioids may become feasible.

The effect of tramadol on blood glucose concentrations: a systematic review

INTRODUCTION

Studies comprehensively summarizing the impact of tramadol use on glucose homeostasis are very sparse. Thus, the present study was performed to collect and summarize the latest information about this issue in a systematic way.

AREAS COVERED

An exhaustive literature search was carried out using relevant keywords. Web of Sciences, PubMed, Scopus, and Google scholar were interrogated until 30 June 2019. Case-control, cohort, cross-sectional, clinical trial, case report, and animal studies that focused on the objective of the study were retrieved. This review summarizes the results of 761 papers on glycemic changes due to tramadol exposure. Thirty-six publications reported hypoglycemia and 17 hyperglycemia during tramadol use. Twenty-two studies either reported normal blood glucose concentrations, or did not observe any difference in the blood glucose levels following tramadol use. Finally, hypoglycemia was reported in diabetic individuals exposed to tramadol in 12 studies.

EXPERT OPINION

The data suggest that primarily hypoglycemia but some degree of hyperglycemia has been reported with tramadol use. Importantly, all studies on tramadol use in diabetes reported hypoglycemia. Tramadol-induced hypoglycemia may be severe in some cases. The risk of alterations in glucose homeostasis accompanying tramadol exposure indicates time importance of careful blood glucose monitoring during tramadol use.

A Case of Unintentional Methadone Overdose Followed by Hypoglycaemia

Methadone overdose is expected to result in intoxication simulating the other opioids. We report a case of hypoglycaemia following accidental methadone ingestion. A 21-year-old woman presented to a local accident and emergency department 10 hours after ingestion of 800 mg of methadone. She was found to have coma, respiratory suppression, hypotension, prolonged QTc and hypoglycaemia. The hypoglycaemia was reversed by dextrose replacement. The patient required intubation and inotropic support because of cardio-respiratory instability. She eventually recovered without consequence. To date, this is the first reported case of methadone overdose induced hypoglycaemia.

A Mouse Model of Chronic Pancreatitis Induced by an Alcohol and High Fat Diet

Background/Aims:

Study of acute pancreatitis in chemically-induced rodent models has provided useful data; models of alcoholic chronic pancreatitis have not been available in mice. The aim of the present study was to characterize a mouse model of chronic pancreatitis induced solely with an alcohol and high fat (AHF) diet.

Methods:

Mice were fed a liquid high fat diet containing 6% alcohol as well as a high fat supplement (57% total dietary fat) over a period of five months or as control, normal chow ad libitum. Pain related measures utilized as an index of pain included mechanical sensitivity of the hind paws determined using von Frey filaments and a smooth/rough textured plate. A modified hotplate test contributed information about higher order behavioral responses to visceral hypersensitivity. Mice underwent mechanical and thermal testing both with and without pharmacological treatment with a peripherally restricted μ-opioid receptor agonist, loperamide.

Results:

Mice on the AHF diet exhibited mechanical and heat hypersensitivity as well as fibrotic histology indicative of chronic pancreatitis. Low dose, peripherally restricted opiate loperamide attenuated both mechanical and heat hypersensitivity.

Conclusion:

Mice fed an alcohol and high fat diet develop histology consistent with chronic pancreatitis as well as opioid sensitive mechanical and heat hypersensitivity.

Increase in plasma glucose lowering action of rosiglitazone by electroacupuncture at bilateral Zusanli acupoints (ST.36) in rats

OBJECTIVES

Hypoglycemia induced by electroacupuncture (EA) is due to an increase of insulin secretion and/or mediation of beta-endorphin. We applied EA at the Zusanli (ST.36) acupuncture point (acupoint) in combination with rosiglitazone (TZD) administration to evaluate their effect on plasma glucose and to explore possible mechanisms of action.

METHODS

Thirty six normal adult Wistar rats were randomly divided into four groups: the 0.1 mg/kg TZD group (0.1TZD), 0.1 mg/kg TZD and EA group (0.1TZD + EA), EA group, and control group. In other experiments, streptozotocin was used to induce type 2 diabetes mellitus in neonatal rats; these were then randomly divided into a 0.1TZD group, 0.1TZD + EA group, and EA group and changes in plasma glucose and insulin concentrations evaluated.

RESULTS

A marked hypoglycemic response was observed in the normal rat 0.1TZD, 0.1TZD + EA and EA groups, with the response more significant in the 0.1TZD + EA group than in the 0.1TZD group. Among the diabetic animals, the hypoglycemic responses in the 0.1TZD + EA and EA groups were greater than in the 0.1TZD group. In both the normal and diabetic rats, insulin secretion was increased by EA or 0.1TZD + EA treatment, but not by 0.1TZD.

CONCLUSIONS

The plasma glucose lowering action of rosiglitazone was increased by EA in both normal and diabetic rats, indicating that the application of EA may enhance the hypoglycemic action of this insulin sensitizer.

Fentanyl inhibits glucose-stimulated insulin release from β-cells in rat pancreatic islets

AIM: To explore the effects of fentanyl on insulin release from freshly isolated rat pancreatic islets in static culture.

METHODS: Islets were isolated from the pancreas of mature Sprague Dawley rats by common bile duct intraductal collagenase V digestion and were purified by discontinuous Ficoll density gradient centrifugation. The islets were divided into four groups according to the fentanyl concentration: control group (0 ng/mL), group I (0.3 ng/mL), group II (3.0 ng/mL), and group III (30 ng/mL). In each group, the islets were co-cultured for 48 h with drugs under static conditions with fentanyl alone, fentanyl + 0.1 μg/mL naloxone or fentanyl + 1.0 μg/mL naloxone. Cell viability was assessed by the MTT assay. Insulin release in response to low and high concentrations (2.8 mmol/L and 16.7 mmol/L, respectively) of glucose was investigated and electron microscopy morphological assessment was performed.

RESULTS: Low- and high-glucose-stimulated insulin release in the control group was significantly higher than in groups II and III (62.33 ± 9.67 μIU vs 47.75 ± 8.47 μIU, 39.67 ± 6.18 μIU and 125.5 ± 22.04 μIU vs 96.17 ± 14.17 μIU, 75.17 ± 13.57 μIU, respectively, P < 0.01) and was lowest in group III (P < 0.01). After adding 1 μg/mL naloxone, insulin release in groups II and III was not different from the control group. Electron microscopy studies showed that the islets were damaged by 30 ng/mL fentanyl.

CONCLUSION: Fentanyl inhibited glucose-stimulated insulin release from rat islets, which could be prevented by naloxone. Higher concentrations of fentanyl significantly damaged β-cells of rat islets.

Acute effect of electroacupuncture at the Zusanli acupoints on decreasing insulin resistance as shown by lowering plasma free fatty acid levels in steroid-background male rats

Background

Insulin sensitivity has been enhanced by electroacupuncture (EA) in rats, but the EA phenomenon in an insulin resistant state is still unclear. This study reports the use of a large dose of prednisolone to evaluate the effects of EA in a state of insulin resistance.

Methods

The plasma levels of free fatty acids (FFAs) were estimated in steroid-background rats (SBRs) and compared with those in healthy rats treated with normal saline. In addition, plasma glucose and endogenous insulin levels were assayed to calculate the homeostasis model assessment (HOMA) index. Intravenous glucose tolerance test (IVGTT) was carried out to compare glucose tolerance. The SBRs were randomly divided into EA-treatment and non-EA treatment groups and 15-Hz EA was applied to the bilateral Zusanli acupoints to investigate its effects on insulin resistance. In addition to an insulin challenge test (ICT) and IVGTT, the plasma levels of FFAs were measured and western blot was performed to help determine the effects of EA on the insulin resistant state.

Results

The plasma levels of FFAs increased markedly in SBRs, the HOMA index was markedly higher, and glucose tolerance was impaired. EA improved glucose tolerance and insulin sensitivity by decreasing the plasma levels of FFAs. Further, the insulin signaling proteins (IRS1) and glucose transporter isoform protein (GLUT4) in skeletal muscle inhibited by prednisolone recovered after EA.

Conclusion

Insulin resistance was successfully induced by a large dose of prednisolone in male rats. This insulin resistance can be improved by 15 Hz EA at the bilateral Zusanli acupoints, as shown by decreased plasma levels of FFAs.

The MOR-1 opioid receptor regulates glucose homeostasis by modulating insulin secretion

In addition to producing analgesia, opioids have also been proposed to regulate glucose homeostasis by altering insulin secretion. A considerable controversy exists, however, regarding the contribution of the mu-opioid receptor (MOR-1) to insulin secretion dynamics. We employed congenic C57BL/6J MOR-1 knockout (KO) mice to clarify the role of MOR in glucose homeostasis. We first found that both sexes of MOR-1 KO mice weigh more than wild-type mice throughout postnatal life and that this increase includes preferentially increased fat deposition. We also found that MOR-1 KO mice exhibit enhanced glucose tolerance that results from insulin hypersecretion that reflects increased beta-cell mass and increased secretory dynamics in the MOR-1 mutant mice compared with wild type. Analysis of the isolated islets indicated that islet insulin hypersecretion is mediated directly by MOR expressed on islet cells via a mechanism downstream of ATP-sensitive K(+) channel activation by glucose. These findings indicate that MOR-1 regulates body weight by a mechanism that involves insulin secretion and thus may represent a novel target for new diabetes therapies.

Enkephalin-encoding herpes simplex virus-1 decreases inflammation and hotplate sensitivity in a chronic pancreatitis model

Background

A chronic pancreatitis model was developed in young male Lewis rats fed a high-fat and alcohol liquid diet beginning at three weeks. The model was used to assess time course and efficacy of a replication defective herpes simplex virus type 1 vector construct delivering human cDNA encoding preproenkephalin (HSV-ENK).

Results

Most surprising was the relative lack of inflammation and tissue disruption after HSV-ENK treatment compared to the histopathology consistent with pancreatitis (inflammatory cell infiltration, edema, acinar cell hypertrophy, fibrosis) present as a result of the high-fat and alcohol diet in controls. The HSV-ENK vector delivered to the pancreatic surface at week 3 reversed pancreatitis-associated hotplate hypersensitive responses for 4–6 weeks, while control virus encoding β-galactosidase cDNA (HSV-β-gal) had no effect. Increased Fos expression seen bilaterally in pain processing regions in control animals with pancreatitis was absent in HSV-ENK-treated animals. Increased met-enkephalin staining was evident in pancreas and lower thoracic spinal cord laminae I–II in the HSV-ENK-treated rats.

Conclusion

Thus, clear evidence is provided that site specific HSV-mediated transgene delivery of human cDNA encoding preproenkephalin ameliorates pancreatic inflammation and significantly reduces hypersensitive hotplate responses for an extended time consistent with HSV mediated overexpression, without tolerance or evidence of other opiate related side effects.

micro-Opioid receptor activation prevents acute hepatic inflammation and cell death

BACKGROUND AND AIMS

The detrimental impact of opioid agonist on the clinical management of inflammatory diseases remains elusive. Given the anti-inflammatory properties of the mu-opioid receptor (MOR) agonists at the intestinal barrier, we hypothesised that MOR activation might also dampen acute hepatic inflammation and cell death-major determinants in the pathogenesis of liver diseases.

PATIENTS AND METHODS

The expression of MOR in liver biopsy specimens and peripheral blood mononuclear cells of untreated patients with chronic hepatitis C virus infection and controls, primary hepatocytes and cell lines was determined by quantitative PCR, immunoblotting and/or immunohistochemistry. The effects of peripheral MOR agonist (d-Ala2,NMe-Phe4,Gly5-ol (DAMGO)) and/or antagonist (naloxone methiodide) were explored in two models of acute hepatitis in mice. MOR-deficient mice were used to evaluate the essential regulatory role of MOR during carbon tetrachloride (CCl(4))-induced hepatitis. The role of DAMGO in cell death was investigated using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) analysis and quantification of lactate dehydrogenase release.

RESULTS

The key role of MOR in the prevention of acute hepatic inflammation and cell death in vivo and in vitro is reported. Whereas MOR gene expression increased transiently in the model of acute liver injury and TNFalpha-treated HepG2 cells, an impaired expression of MOR mRNA in human chronic hepatitis C samples was found. Furthermore, preventive administration of the selective MOR agonist DAMGO enhanced hepatoprotective-signalling pathways in vivo that were blocked by using naloxone methiodide. Consistently, genetic and pharmacological inhibition of MOR enhanced the severity associated with experimental hepatotoxin-induced hepatitis. Finally, treatment with DAMGO was shown to prevent cell death in vitro in HepG2 cells in a MOR-dependent manner and to prevent concanavalin A- and CCl(4)-induced cell death in vivo, providing a possible explanation for the anti-inflammatory role of MOR activation in the liver.

CONCLUSIONS

The results indicate that MOR agonists may prevent acute hepatitis and hold promising therapeutic use to maintain remission in both chronic inflammatory bowel and liver diseases.

Indium-Labeled Macrocyclic Conjugates of Naltrindole: High-Affinity Radioligands for In Vivo Studies of Peripheral δ Opioid Receptors

We have identified a series of hydrophilic indium-labeled DOTA and DO3A conjugates of naltrindole (NTI) that are suited to in vivo studies of peripheral delta opioid receptors. Indium(III) complexes, linked to the indole nitrogen of NTI by six- to nine-atom spacers, display high affinities (0.1-0.2 nM) and excellent selectivities for binding to delta sites in vitro. The [111In]-labeled complexes can be prepared in good isolated yields ( approximately 65%) with high specific radioactivities (>3300 mCi/mumol). The spacers serve as pharmacokinetic modifiers, and log D7.4 values range from -2.74 to -1.79. These radioligands exhibit a high level of specific binding (75-94%) to delta opioid receptors in mouse gut, heart, spleen, and pancreas in vivo. Uptakes of radioactivity are saturable by the non-radioactive complexes, inhibited by naltrexone, and blocked by NTI. Thus, these radiometal-labeled NTI analogues warrant further study by single-photon emission computed tomography.

Dynorphin knockout reduces fat mass and increases weight loss during fasting in mice

Endogenous opioids, particularly dynorphins, have been implicated in regulation of energy balance, but it is not known how they mediate this in vivo. We investigated energy homeostasis in dynorphin knockout mice (Dyn(-/-) mice) and probed the interactions between dynorphins and the neuropeptide Y (NPY) system. Dyn(-/-) mice were no different from wild types with regards to body weight and basal and fasting-induced food intake, but fecal output was increased, suggesting decreased nutrient absorption, and they had significantly less white fat and lost more weight during a 24-h fast. The neuroendocrine and thermal responses to fasting were at least as pronounced in Dyn(-/-) as in wild types, and there was no stimulatory effect of dynorphin knockout on 24-h energy expenditure (kilocalories of heat produced) or physical activity. However, Dyn(-/-) mice showed increased circulating concentrations of 3,4-dihydroxyphenlacetic acid and 3,4-dihydroxyphenylglycol, suggesting increased activity of the sympathetic nervous system. The respiratory exchange ratio of male but not female Dyn(-/-) mice was reduced, demonstrating increased fat oxidation. Interestingly, expression of the orexigenic acting NPY in the hypothalamic arcuate nucleus was reduced in Dyn(-/-) mice. However, fasting-induced increases in pre-prodynorphin expression in the arcuate nucleus, the paraventricular nucleus, and the ventromedial hypothalamus but not the lateral hypothalamus were abolished by deletion of Y(1) but not Y(2) receptors. Therefore, ablation of dynorphins results in increases in fatty acid oxidation in male mice, reductions in adiposity, and increased weight loss during fasting, possibly via increases in sympathetic activity, decreases in intestinal nutrient absorption, and interactions with the NPYergic system.

Changes in levels of serum insulin, C-Peptide and glucose after electroacupuncture and diet therapy in obese women

Our purpose was to investigate the effects of electroacupuncture (EA) therapy on body weight and on levels of serum insulin, c-peptide and glucose in obese women. 52 healthy women were included in this study and were allocated into three groups: 1) Placebo EA group (n = 15; mean age = 41.8 +/- 4.6 and mean body mass index {BMI} = 33.2 +/- 3.5); 2) EA group (n = 20; mean age = 42.1 +/- 4.4 and BMI = 35.9 +/- 3.6) and 3) Diet restriction group (n = 20; mean age = 42.9 +/- 4.3 and BMI = 34.7 +/- 2.7). EA was applied to the ear points Hunger and Shen Men on alternating days and to the body points LI 4, LI 11, St 36 and St 44 once a day for 30 minutes over 20 days. Diet restriction that entailed a 1450 kilocalorie (kcal) diet program was applied to the three groups for 20 days. An increase in weight loss was observed when weight loss in the EA group (p < 0.000) was compared to that in the diet restricted and placebo EA groups using the Tukey HSD test. There were increases in the serum insulin (p < 0.001) and c-peptide levels (p < 0.000) in the women treated with EA compared to those in the women treated with the placebo EA and diet restriction groups. A decrease was observed in the glucose levels (p < 0.01) in both the EA and diet restriction groups compared to those in the placebo EA group. Our results suggest that EA therapy is an effective method in treating obesity. EA therapy also helps serum glucose levels to decrease through the increase of serum insulin and c-peptide levels.

Downstream regulatory element antagonistic modulator regulates islet prodynorphin expression

Calcium-binding proteins regulate transcription and secretion of pancreatic islet hormones. Here, we demonstrate neuroendocrine expression of the calcium-binding downstream regulatory element antagonistic modulator (DREAM) and its role in glucose-dependent regulation of prodynorphin (PDN) expression. DREAM is distributed throughout beta- and alpha-cells in both the nucleus and cytoplasm. As DREAM regulates neuronal dynorphin expression, we determined whether this pathway is affected in DREAM(-/-) islets. Under low glucose conditions, with intracellular calcium concentrations of <100 nM, DREAM(-/-) islets had an 80% increase in PDN message compared with controls. Accordingly, DREAM interacts with the PDN promoter downstream regulatory element (DRE) under low calcium (<100 nM) conditions, inhibiting PDN transcription in beta-cells. Furthermore, beta-cells treated with high glucose (20 mM) show increased cytoplasmic calcium (approximately 200 nM), which eliminates DREAM's interaction with the DRE, causing increased PDN promoter activity. As PDN is cleaved into dynorphin peptides, which stimulate kappa-opioid receptors expressed predominantly in alpha-cells of the islet, we determined the role of dynorphin A-(1-17) in glucagon secretion from the alpha-cell. Stimulation with dynorphin A-(1-17) caused alpha-cell calcium fluctuations and a significant increase in glucagon release. DREAM(-/-) islets also show elevated glucagon secretion in low glucose compared with controls. These results demonstrate that PDN transcription is regulated by DREAM in a calcium-dependent manner and suggest a role for dynorphin regulation of alpha-cell glucagon secretion. The data provide a molecular basis for opiate stimulation of glucagon secretion first observed over 25 years ago.

Association of the mu-opioid receptor gene with type 2 diabetes mellitus in an African American population

African Americans (AA) are at increased risk for developing type 2 diabetes mellitus (T2DM) relative to European Americans. We previously detected linkage of T2DM to 6q24-q27 (LOD 2.26) at 163.5 cM, closest to marker D6S1035, in a genome-wide scan of AA families. The mu-opioid receptor gene (OPRM1) is located within the LOD-1 support interval of this linkage peak. OPRM1 is an attractive positional candidate gene for T2DM susceptibility since agonists of OPRM1 affect glucose-induced insulin release and OPRM1 knockout mice have a more rapid induction of insulin resistance than wild-type. Twenty-two SNPs in this gene, at an average spacing of 3.9 kb, were genotyped in 380 AA T2DM cases and 276 AA controls. In single SNP association analyses, rs648007 demonstrated significant evidence of association with T2DM (P=0.013). Four blocks of high linkage disequilibrium were detected across the OPRM1 gene. Association analyses of haplotypes in each of these blocks revealed two haplotype blocks with significant overall P values (P=0.007 and 0.046). Significant, but rare, risk and protective haplotypes were identified as driving these associations with T2DM (P=0.034-0.047). These associations suggest that the OPRM1 gene plays a role in T2DM susceptibility in African Americans.

Loperamide increases glucose ultilization in streptozotocin-induced diabetic rats

1. Loperamide has an ability to lower the plasma glucose concentration in streptozotocin (STZ)-induced diabetic rats. In the present study, we investigated the molecular mechanisms by which loperamide regulates plasma glucose concentrations in the absence of insulin. 2. Loperamide, at a dose sufficient (17.6 microg/kg) to activate mu-opioid receptors, significantly decreased plasma glucose levels in STZ-diabetic rats. The mRNA and protein levels of glucose transporter 4 (GLUT-4) in soleus muscle, detected by northern and western blotting, respectively, were increased after repeated intravenous administration of loperamide (17.6 micro g/kg) to STZ-diabetic rats over 3 days. Moreover, similar treatment with loperamide (17.6 microg/kg) for 3 days reversed the elevated mRNA and protein levels of phosphoenolpyruvate carboxykinase (PEPCK) in the liver of STZ-diabetic rats to near the levels seen in normal rats. 3. These results suggest that activation of mu-opioid receptors by loperamide can increase glucose utilization in peripheral tissues and/or reverse the higher gene expression of PEPCK to inhibit hepatic gluconeogenesis, thereby lower plasma glucose in diabetic rats lacking insulin.

Morphine induces desensitization of insulin receptor signaling

Morphine analgesia is mediated principally by the micro -opioid receptor (MOR). Since morphine and other opiates have been shown to influence glucose homeostasis, we investigated the hypothesis of direct cross talk between the MOR and the insulin receptor (IR) signaling cascades. We show that prolonged morphine exposure of cell lines expressing endogenous or transfected MOR, IR, and the insulin substrate 1 (IRS-1) protein specifically desensitizes IR signaling to Akt and ERK cascades. Morphine caused serine phosphorylation of the IR and impaired the formation of the signaling complex among the IR, Shc, and Grb2. Morphine also resulted in IRS-1 phosphorylation at serine 612 and reduced tyrosine phosphorylation at the YMXM p85-binding motifs, weakening the association of the IRS-1/p85 phosphatidylinositol 3-kinase complex. However, the IRS-1/Grb2 complex was unaffected by chronic morphine treatment. These results suggest that morphine attenuates IR signaling to Akt by disrupting the IRS-1-p85 interaction but inhibits signaling to ERK by disruption of the complex among the IR, Shc, and Grb2. Finally, we show that systemic morphine induced IRS-1 phosphorylation at Ser612 in the hypothalamus and hippocampus of wild type, but not MOR knockout, mice. Our results demonstrate that opiates can inhibit insulin signaling through direct cross talk between the downstream signaling pathways of the MOR and the IR.

Close apposition of dynorphin-positive nerve fibres to lymphocytes in the liver suggests opioidergic neuroimmunomodulation

The liver is innervated by sympathetic efferent, spinal afferent, vagal afferent and probably also vagal efferent fibres. To assess potential functional roles of the various neuronal subsets, data on transmitter systems are of crucial importance. This study was aimed at elucidating a possible opioidergic system in the mouse and rat liver. In particular relationships of opioidergic neurons to immune cells were emphasised. Material from perfusion-fixed mice ( n=29) of different strains (BALB/c, NMRI, C57Bl6, SV 129 inbred) and Wistar rats ( n=7) was cryosectioned at 12-14 microm and incubated for single or double immunofluorescence. Antibodies directed against dynorphin A, met-enkephalin, endomorphin 1 and 2, mu, kappa- and delta-opioid receptors (MOR, KOR, DOR), tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), CD4, CD8 and macrophages were used. Binding sites were detected using Cy3-, FITC-, DTAF-, Cy2-, Alexa 555- and Texas red-tagged secondary antibodies. Specimens were analysed using confocal laser scanning microscopy (CLSM). Numerous nerve fibres staining for dynorphin were found in periportal areas of both mouse and rat livers. Neither met-enkephalin nor endomorphin could be detected in axons. No immunopositive neuronal cell bodies or other cellular elements were seen. All dynorphin positive fibres costained for TH while not every TH-positive fibre costained for dynorphin. Thus, most if not all dynorphin-positive nerve fibres may be of sympathetic origin. KOR immunostaining could be localised to round mononuclear cells which often costained for CD4, less frequently for CD8 and rarely for the pan-macrophage marker BM8. Altogether, about 45% of KOR-positive cells were identified as T-lymphocytes. In some instances, close appositions of dynorphin-positive axons to KOR-positive cells were revealed by CLSM. No KOR immunoreactivity was detected in nerve fibres. Hence, sympathetic neurons innervating the liver may interfere with inflammatory processes, in addition to their well-established beta(2)-adrenergic effect, via an opioidergic action on immune cells.

Morphine enhances hepatitis C virus (HCV) replicon expression

Little information is available regarding whether substance abuse enhances hepatitis C virus (HCV) replication and promotes HCV disease progression. We investigated whether morphine alters HCV mRNA expression in HCV replicon-containing liver cells. Morphine significantly increased HCV mRNA expression, an effect which could be abolished by either of the opioid receptor antagonists, naltrexone or beta-funaltrexamine. Investigation of the mechanism responsible for this enhancement of HCV replicon expression demonstrated that morphine activated NF-kappaB promoter and that caffeic acid phenethyl ester, a specific inhibitor of the activation of NF-kappaB, blocked morphine-activated HCV RNA expression. In addition, morphine compromised the anti-HCV effect of interferon alpha (IFN-alpha). Our in vitro data indicate that morphine may play an important role as a positive regulator of HCV replication in human hepatic cells and may compromise IFN-alpha therapy.

Role of mu-opioid receptors in insulin release in the presence of inhibitory and excitatory secretagogues

In mouse pancreatic islets incubated under static conditions, the inhibitory effects on glucose-evoked insulin release induced by adrenaline (1 microM), clonidine (2 microM) and UK 14,304 (brimonidine, 0.001-1 microM) were abolished by naloxone (30 nM). Only CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH(2), 0.1 microM), a very selective mu-opioid receptor antagonist, blocked the response to UK 14,304. Glucose-induced insulin secretion was attenuated by both beta-endorphin (0.01 microM) and endomorphin-1 (0.1 microM). Naloxone and CTOP prevented these inhibitory responses. The stimulatory effect of glibenclamide (1 microM) was also reduced by endomorphin-1. However, when islets were incubated in the presence of K(+) (30 mM), carbachol (100 microM) or forskolin (0.1 microM), neither the inhibitory effect induced by UK 14,304 was reversed by naloxone, nor endomorphin-1 altered the responses promoted by the excitatory agents. Thus, alpha(2)-adrenoceptor stimulation might inhibit glucose-induced insulin secretion by releasing endogenous opioids. Mu-Opioid receptor activation and opening of K(ATP) channels could be involved in the response.

Hepatic Met-enkephalin immunoreactivity is enhanced in primary biliary cirrhosis

BACKGROUND/AIMS

In contrast to the normal adult liver, the fetal human and rat livers, and the liver of rats with cholestasis secondary to bile duct resection (BDR) express the preproenkephalin (ppENK) mRNA, which codes for the endogenous opioid peptide Met-enkephalin. In addition, Met-enkephalin immunoreactivity (MEIR) is detected in hepatocytes and in proliferating bile ductules in the cholestatic rat liver. These data suggest that cholestasis is associated with the resurgence of cells that produce Met-enkephalin. To explore further the status of opioids in cholestasis, we studied the expression of MEIR in liver tissue.

METHODS

The MEIR was sought in paraffin-preserved liver tissues from patients with primary biliary cirrhosis (PBC) (n = 10).

RESULTS

The MEIR was detected in all the PBC livers. Its intensity varied from weak to strong on hepatocytes and bile ducts and the strongest expression appeared as coarse granules. The MEIR was either absent or only faintly expressed by some hepatocytes from disease and nondisease control biopsies, but absent from bile ducts.

CONCLUSION

These results suggest that the human liver in cholestasis may be a source of endogenous opioids.

Plasma glucose-lowering effect of tramadol in streptozotocin-induced diabetic rats

The effect of tramadol on the plasma glucose level of streptozotocin (STZ)-induced diabetic rats was investigated. A dose-dependent lowering of plasma glucose was seen in the fasting STZ-induced diabetic rats 30 min after intravenous injection of tramadol. This effect of tramadol was abolished by pretreatment with naloxone or naloxonazine at doses sufficient to block opioid mu-receptors. However, response to tramadol was not changed in STZ-induced diabetic rats receiving p-chlorophenylalanine at a dose sufficient to deplete endogenous 5-hydroxytrptamine (5-HT). Therefore, mediation of 5-HT in this action of tramadol is ruled out. In isolated soleus muscle, tramadol enhanced the uptake of radioactive glucose in a concentration-dependent manner. The stimulatory effects of tramadol on glycogen synthesis were also seen in hepatocytes isolated from STZ-induced diabetic rats. The blockade of these actions by naloxone and naloxonazine indicated the mediation of opioid mu-receptors. The mRNA and protein levels of the subtype 4 form of glucose transporter in soleus muscle were increased after repeated treatments for 4 days with tramadol in STZ-induced diabetic rats. Moreover, similar repeated treatments with tramadol reversed the elevated mRNA and protein levels of phosphoenolpyruvate carboxykinase in the liver of STZ-induced diabetic rats. These results suggest that activation of opioid mu-receptors by tramadol can increase the utilization of glucose and/or decrease hepatic gluconeogenesis to lower plasma glucose in diabetic rats lacking insulin.

Loss of plasma glucose lowering response to cold stress in opioid mu-receptor knock-out diabetic mice

Opioid mu-receptor plays an important role in the regulation of glucose homeostasis in diabetic rats lacking insulin. Opioid mu-receptor knockout mice were employed to identify the essential role of this receptor in the present study. Western blotting analysis characterized the deletion of opioid mu-receptor in liver of knockout mice as compared to that of normal (wild-type) mice. We found that the plasma glucose concentration of diabetic mice induced by intraperitoneal injection of streptozotocin was markedly decreased after exposure to cold-stress in a cold room for 1 h. However, this plasma glucose lowering response to cold-stress was disappeared in diabetic mice lacking opioid mu-receptor. The important role of opioid mu-receptor in the plasma glucose lowering response to cold stress can thus be considered. Moreover, bilateral adrenalectomy abolished this plasma glucose lowering response to cold stress in diabetic mice with opioid mu-receptor, as compared to the shamed-operated animals. Therefore, activation of opioid mu-receptor by opioid from adrenal gland appears to be responsible for the plasma glucose lowering response to cold-stress in diabetic mice with insulin deficiency.

Expression of melanin-concentrating hormone receptors in insulin-producing cells: MCH stimulates insulin release in RINm5F and CRI-G1 cell-lines

Melanin-concentrating hormone (MCH) is a hypothalamic orexigenic peptide. Recently, an orphan G-protein-coupled receptor (SLC-1) was identified that binds MCH with high affinity. Here, we demonstrate the mRNA expression of this receptor in insulin-producing cells including CRI-G1 and RINm5F cells, and in rat islets of Langerhans. Immunofluorescence studies in CRI-G1 and RINm5F cell-lines demonstrated cell-surface expression of the receptor. Rat MCH significantly stimulated insulin secretion in both cell-lines. The potency and the efficacy of MCH were significantly increased in the simultaneous presence of forskolin, suggesting that MCH may amplify the insulinotropic effect of cyclic AMP elevating stimuli. Salmon MCH, which differs from rat/human MCH by six amino acids, was less efficacious than rat/human MCH in stimulating insulin release. The data provide evidence for the expression of MCH receptors in insulin producing cells. The insulinotropic effect of MCH may contribute to the regulation of metabolism and energy balance by this peptide.

Investigations of the mechanism of the reduction of plasma glucose by cold-stress in streptozotocin-induced diabetic rats

Exposure to a cold environment may increase the activity of the sympathetic nervous system inducing an elevation of plasma norepinephrine and may result in hyperglycemia. In the present study, we found that a hypoglycemic effect was produced in streptozotocin-induced diabetic rats after cold-exposure at 4 degrees C for 1 h. In addition to the blockade of this hypoglycemic effect by guanethidine (a ganglion-blocking agent) and prazosin (an alpha1-adrenoceptor antagonist), an increase of plasma norepinephrine was also observed in streptozotocin-induced diabetic rats receiving this cold-stress. Participation of sympathetic hyperactivity can thus be considered. Furthermore, naloxone, in a dose (0.5 mg/kg, i.p.) sufficient to block opioid receptors, reversed this hypoglycemia. Also, an increase of plasma beta-endorphin-like immunoreactivity was observed in streptozotocin-induced diabetic rats receiving this cold-stress. Intravenous injection of beta-endorphin into streptozotocin-induced diabetic rats produced a lowering of plasma glucose. Administration of methoxamine at a dose sufficient to activate the alpha1-adrenoceptors produced hypoglycemia and a similar increase of plasma beta-endorphin-like immunoreactivity in streptozotocin-induced diabetic rats. However, plasma beta-endorphin-like immunoreactivity level was not modified by similar treatment with methoxamine or cold-stress in normoglycemic rats. Therefore, beta-endorphin appears to be responsible for the induction of hypoglycemic effects in streptozotocin-induced diabetic rats after cold exposure which is different to the response in normal rats.

Opioid growth factor (OGF) inhibits human pancreatic cancer transplanted into nude mice

Nude mice inoculated with human pancreatic cancer (BxPC-3) cells and receiving 5 mg/kg of opioid growth factor ([Met5]enkephalin; OGF) three times daily exhibited a marked retardation in tumorigenicity compared to animals injected with sterile water (controls). OGF-treated animals had a delay of 43% in initial tumor appearance compared to control subjects (10.6 days). At the time when all of the control mice had tumors, 62% of the mice in the OGF group had no signs of neoplasia. Tumor tissue excised from mice after 30 days was assayed for levels of [Met5]enkephalin and zeta opioid receptors. Tumor tissue levels of [Met5]enkephalin were 24-fold greater in OGF-treated mice than controls, but plasma levels of OGF were 8.6-fold lower in animals receiving OGF. Specific and saturable binding of radiolabeled [Met5]enkephalin to nuclear homogenates of pancreatic tumor tissue was recorded, with a binding affinity (Kd) of 10 nM and a binding capacity (Bmax) of 46.8 fmol/mg protein. Binding capacity, but not affinity, of [3H-Met5]enkephalin was reduced by 58% of control levels in tumor tissue from mice of the OGF group. OGF and the zeta (zeta) opioid receptor were detected in human pancreatic tumor cells by immuno-cytochemistry. These results demonstrate that an endogenous opioid and its receptor are present in human pancreatic cancer, and act as a negative regulator of tumorigenesis in vivo.

Hepatic concentrations of proenkephalin-derived opioids are increased in a rat model of cholestasis

The liver of adult rats with cholestasis secondary to bile duct resection has been shown to express the proenkephalin gene and, by immunohistochemical stains, to contain met-enkephalin. To further study hepatic opioids in cholestasis, concentrations of proenkephalin-derived endogenous opioids were measured in a rat model of cholestasis by the use of radioimmunoassays. The specificity of the immunoreactivity detected by the assays was confirmed by high performance liquid chromatography (HPLC). In adult male rats with cholestasis due to BDR, the concentrations of three proenkephalin-derived opioid peptides were increased. Specifically, the mean hepatic concentrations of met-enkephalin, Met-Enk-Arg6-Phe7 and leu-enkephalin were 2.5 (p < 0.005), 2.1 (p < 0.005) and 2.5 (p < 0.01) fold higher than the corresponding mean for controls. These findings provide further independent evidence that opioid peptides accumulate in the liver in a model of cholestasis and are consistent with de novo synthesis of opioid peptides occurring in the cholestatic liver. This phenomenon may have relevance to the altered function of the opioid system in cholestasis and to the role of the liver as a neuroendocrine organ.

Evidence for reversible sequestration of morphine in rat liver

The residence of morphine in the systemic circulation is prolonged despite a high systemic clearance, suggestive of significant extravascular sequestration. The present study was conducted to test the hypothesis that morphine binds significantly in tissues, and that the liver plays an important role in morphine binding. [14C]Morphine was administered to male Sprague-Dawley rats 55 min before unlabeled morphine or saline. Blood 14C increased immediately after injection of unlabeled morphine; the area under the blood concentration-time curve (AUC) for 14C increased approximately 2-fold after morphine compared with saline injection. Residual radioactivity in the liver was lower in morphine-treated rats than in controls, suggesting that unlabeled drug displaced [14C]morphine (or a metabolite) from binding sites. To examine this phenomenon more directly, a recirculating isolated perfused liver system was employed. [14C]Morphine was added to the perfusate reservoir 15 min before unlabeled morphine or saline; perfusate and bile samples were collected for 120 min. Upon termination of perfusion, the liver was fractionated to identify the hepatic subcellular fraction(s) in which morphine was sequestered. The perfusate AUC for [14C]morphine was increased approximately 2-fold in response to unlabeled drug, consistent with the in vivo experiment. Morphine was associated preferentially with the cytosolic fraction, and [14C]morphine in all relevant fractions was reduced after administration of unlabeled morphine. In contrast, unlabeled drug had no influence on derived [14C]morphine-3-beta,D-glucuronide. These data are consistent with significant, reversible binding of morphine in hepatic tissue.

The hypothalamic-pituitary-adrenal axis in obesity

The hypothalamic-pituitary-adrenal (HPA) axis normally maintains the concentration of cortisol within a narrow range with a diurnal variation characterized by higher cortisol concentrations in the morning and reduced levels in the evening. Excessive or deficient secretion of cortisol is associated with pathologic changes. Obesity has been linked with age, sex and racial alterations in the functioning of the HPA axis which are reviewed. The possible relationship of altered HPA axis activity with the long-term complications of obesity are considered.

Expression of two proopiomelanocortin mRNAs in the islets of Langerhans of neonatal rats

Proopiomelanocortin-(POMC) derived peptides have been found in pituitary and in nonpituitary tissues including the endocrine pancreas. However, only a truncated 800-base POMC-like mRNA is demonstrable in most nonpituitary tissues. The functional relevance of this RNA is doubtful, because it lacks the sequences of translation initiation and signal peptide (exon 1 and 2). Recently we have demonstrated the truncated POMC-like mRNA in pancreatic islets. Using PCR techniques in this paper we prove the existence of a full-length POMC mRNA in this tissue. This RNA contains the sequences of exon 1 and 2, as shown by Southern blot technique and by sequencing parts of the PCR products. We suppose that this RNA is the source of the POMC peptides in islets despite of its small amount.

Plasma met-enkephalin in type I diabetes

Physiological and pathological evidence suggests that opioid peptides may play a role in glucose homeostasis. We measured plasma levels of beta-endorphin (beta-END) and met-enkephalin (met-ENK) in 22 type I diabetic patients and 15 healthy women (control group). No differences were observed in plasma beta-END levels, whereas plasma met-ENK levels were significantly higher (Student's t test, P less than .005) in diabetics than in controls before (68 +/- 3 pg/mL v 32 +/- 7 pg/mL) and 1 hour after, a standard meal and administration of insulin therapy (81 +/- 9 pg/mL v 32 +/- 7 pg/mL). This is the first report of met-ENK levels in insulin-dependent diabetes mellitus (IDDM), and an impaired feedback of insulin/met-ENK is suggested.

An opioid pancreatic peptide produces ileal muscle inhibition and naloxone-reversible analgesia

The opioid activity of immunoreactive beta-endorphin-like peptide extracted from pork pancreas duplicates the effects of morphine and synthetic beta-endorphin when measured by inhibition of isolated guinea pig ileal muscle response to electro-stimulation in vitro and by morphine-like analgesia following intravenous injection in the mouse. These responses are reversed by the opiate antagonist naloxone, indicating that a potent opioid mu receptor binding ligand is present in pancreatic extract. These findings imply a pancreatic source of plasma immunoreactive beta-endorphin that may explain a number of physiological and behavioral effects generally attributed to hypophyseal beta-endorphin alone.

Dual action of beta-endorphin on insulin release in genetically obese and lean mice

Intraperitoneal administration of beta-endorphin (1 mg/kg) to ob/ob mice doubled fasting plasma insulin concentrations within 30 min, while plasma glucose concentrations were unaltered. In lean mice, beta-endorphin failed to alter plasma insulin or glucose responses. In glucose-loaded ob/ob mice, beta-endorphin (1 mg/kg) reduced insulin levels at 40 min, and delayed glucose disposal. A lower dose of beta-endorphin (0.1 mg/kg) decreased plasma insulin at 90 min, with no effect on plasma glucose disposal. In lean mice, only the higher dose of beta-endorphin suppressed the glucose-stimulated rise in plasma insulin concentrations, without affecting plasma glucose. Beta-endorphin's actions were blocked by naltrexone and could not be mimicked by N-acetyl-beta-endorphin. Beta-endorphin (10(-8)M) enhanced insulin release from isolated ob/ob and lean mouse islets incubated in medium containing 6 mM glucose, but inhibited release when 20 mM glucose was present. These effects were naloxone reversible. The results indicate that 1) ob/ob mice display a greater magnitude of response in vivo to beta-endorphin's actions on insulin release compared with lean mice, 2) high concentrations of beta-endorphin exacerbate glucose disposal in ob/ob mice. 3) the prevailing glucose concentration is an important determinant of whether beta-endorphin's effects on insulin release will be stimulatory or inhibitory and 4) these actions are mediated via opiate receptors.