Chronic morphine up-regulates G alpha12 and cytoskeletal proteins in Chinese hamster ovary cells expressing the cloned mu opioid receptor

The effects of chronic morphine administration on spatial memory and microtubule dynamicity in male mice's brain

The examination of the influence of morphine on behavioral processes, specifically learning and memory, holds significant importance. Additionally, microtubule proteins play a pivotal role in cellular functions, and the dynamics of microtubules contribute to neural network connectivity, information processing, and memory storage. however, the molecular mechanism of morphine on microtubule dynamics, learning, and memory remains uncovered. In the present study, we examined the effects of chronic morphine administration on memory formation impairment and the kinetic alterations in microtubule proteins induced by morphine in mice. Chronic morphine administration at doses of 5 and 10 mg/kg dose-dependently decreased subjects' performance in spatial memory tasks, such as the Morris Water Maze and Y-maze spontaneous alternation behavior. Furthermore, morphine was found to stabilize microtubule structure, and increase polymerization, and total polymer mass. However, it simultaneously impaired microtubule dynamicity, stemming from structural changes in tubulin dimer structure. These findings emphasize the need for careful consideration of different doses when using morphine, urging a more cautious approach in the administration of this opioid medication.

Morphine as a Potential Oxidative Stress-Causing Agent

Morphine exhibits important pharmacological effects for which it has been used in medical practice for quite a long time. However, it has a high addictive potential and can be abused. Long-term use of this drug can be connected with some pathological consequences including neurotoxicity and neuronal dysfunction, hepatotoxicity, kidney dysfunction, oxidative stress and apoptosis. Therefore, most studies examining the impact of morphine have been aimed at determining the effects induced by chronic morphine exposure in the brain, liver, cardiovascular system and macrophages. It appears that different tissues may respond to morphine diversely and are distinctly susceptible to oxidative stress and subsequent oxidative damage of biomolecules. Importantly, production of reactive oxygen/nitrogen species induced by morphine, which have been observed under different experimental conditions, can contribute to some pathological processes, degenerative diseases and organ dysfunctions occurring in morphine abusers or morphine-treated patients. This review attempts to provide insights into the possible relationship between morphine actions and oxidative stress.

Global changes in the rat heart proteome induced by prolonged morphine treatment and withdrawal

Morphine belongs among the most commonly used opioids in medical practice due to its strong analgesic effects. However, sustained administration of morphine leads to the development of tolerance and dependence and may cause long-lasting alterations in nervous tissue. Although proteomic approaches enabled to reveal changes in multiple gene expression in the brain as a consequence of morphine treatment, there is lack of information about the effect of this drug on heart tissue. Here we studied the effect of 10-day morphine exposure and subsequent drug withdrawal (3 or 6 days) on the rat heart proteome. Using the iTRAQ technique, we identified 541 proteins in the cytosol, 595 proteins in the plasma membrane-enriched fraction and 538 proteins in the mitochondria-enriched fraction derived from the left ventricles. Altogether, the expression levels of 237 proteins were altered by morphine treatment or withdrawal. The majority of changes (58 proteins) occurred in the cytosol after a 3-day abstinence period. Significant alterations were found in the expression of heat shock proteins (HSP27, α-B crystallin, HSP70, HSP10 and HSP60), whose levels were markedly up-regulated after morphine treatment or withdrawal. Besides that morphine exposure up-regulated MAPK p38 (isoform CRA_b) which is a well-known up-stream mediator of phosphorylation and activation of HSP27 and α-B crystallin. Whereas there were no alterations in the levels of proteins involved in oxidative stress, several changes were determined in the levels of pro- and anti-apoptotic proteins. These data provide a complex view on quantitative changes in the cardiac proteome induced by morphine treatment or withdrawal and demonstrate great sensitivity of this organ to morphine.

Regulation of mammalian MOR-1 gene expression after chronic treatment with morphine

Morphine is an effective analgesic that acts by binding to the µ-opioid receptor (MOR) coded in the human by the OPRM1 gene. In the present study, we investigated the regulation of µ-opioid receptor (MOR-1) mRNA levels in all-trans-retinoic acid-differentiated SH-SY5Y human neuroblastoma cells under in vitro conditions with 10 µM morphine treatment for 24 h. In addition, we measured the MOR-1 levels in recombinant Chinese hamster ovary (CHO) cells, transfected with human µ-opioid receptor gene (hMOR) with 10 µM morphine treatment for 24 h. The isolated mRNA from these cells was subjected to real-time quantitative RT-PCR analysis to determine the regulation of µ-opioid receptor gene expression. It was observed that morphine treatment did not alter MOR-1 levels in undifferentiated SH-SY5Y cells compared to undifferentiated control cells. However, the MOR-1 levels in all-trans-retinoic acid-differentiated cells were significantly higher compared to the undifferentiated cells. Morphine treatment in differentiated SH-SY5Y cells caused significant downregulation of MOR-1 expression compared to the control cells. In the morphine-treated CHO cells, the hMOR-1 mRNA levels remained the same as the untreated control. Finally, pretreatment of SH-SY5Y cells with 10 µM naloxone, the antagonist of µ-opioid receptor, for 1 h significantly blocked the downregulation of MOR-1 mRNA levels with morphine treatment. These findings suggest that regulation of MOR-1 gene expression is cell-type specific after chronic morphine treatment and provide some evidence in the understanding of morphine tolerance.

Morphine produces immunosuppressive effects in nonhuman primates at the proteomic and cellular levels

Morphine has long been known to have immunosuppressive properties in vivo, but the molecular and immunologic changes induced by it are incompletely understood. To explore how these changes interact with lentiviral infections in vivo, animals from two nonhuman primate species (African green monkeys and pigtailed macaques) were provided morphine and studied using a systems biology approach. Biological specimens were obtained from multiple sources (e.g. lymph node, colon, cerebrospinal fluid, and peripheral blood) before and after the administration of morphine (titrated up to a maximum dose of 5 mg/kg over a period of 20 days). Cellular immune, plasma cytokine, and proteome changes were measured and morphine-induced changes in these parameters were assessed on an interorgan, interindividual, and interspecies basis. In both species, morphine was associated with decreased levels of Ki-67(+) T-cell activation but with only minimal changes in overall T-cell counts, neutrophil counts, and NK cell counts. Although changes in T-cell maturation were observed, these varied across the various tissue/fluid compartments studied. Proteomic analysis revealed a morphine-induced suppressive effect in lymph nodes, with decreased abundance of protein mediators involved in the functional categories of energy metabolism, signaling, and maintenance of cell structure. These findings have direct relevance for understanding the impact of heroin addiction and the opioids used to treat addiction as well as on the potential interplay between opioid abuse and the immunological response to an infective agent.

Neuropharmacology of the naturally occurring kappa-opioid hallucinogen salvinorin A

Salvia divinorum is a perennial sage native to Oaxaca, Mexico, that has been used traditionally in divination rituals and as a treatment for the "semimagical" disease panzón de borrego. Because of the intense "out-of-body" experiences reported after inhalation of the pyrolized smoke, S. divinorum has been gaining popularity as a recreational hallucinogen, and the United States and several other countries have regulated its use. Early studies isolated the neoclerodane diterpene salvinorin A as the principal psychoactive constituent responsible for these hallucinogenic effects. Since the finding that salvinorin A exerts its potent psychotropic actions through the activation of KOP receptors, there has been much interest in elucidating the underlying mechanisms behind its effects. These effects are particularly remarkable, because 1) salvinorin A is the first reported non-nitrogenous opioid receptor agonist, and 2) its effects are not mediated by the 5-HT(2A) receptor, the classic target of hallucinogens such as lysergic acid diethylamide and mescaline. Rigorous investigation into the structural features of salvinorin A responsible for opioid receptor affinity and selectivity has produced numerous receptor probes, affinity labels, and tools for evaluating the biological processes responsible for its observed psychological effects. Salvinorin A has therapeutic potential as a treatment for pain, mood and personality disorders, substance abuse, and gastrointestinal disturbances, and suggests that nonalkaloids are potential scaffolds for drug development for aminergic G-protein coupled receptors.

Differential effects of opioid agonists on G protein expression in CHO cells expressing cloned human opioid receptors

Recent evidence indicates that agonist ligands of G protein coupled receptors (GPCR) can activate different signaling systems. Such "agonist-directed" signaling also occurs with opioid receptors. Previous work from our laboratory showed that chronic morphine, but not DAMGO, up-regulates the expression of Galpha12 and that both morphine and DAMGO decreased Galphai3 expression in CHO cells expressing the cloned human mu opioid receptor. In this study, we tested the hypothesis that chronic opioid regulation of G protein expression is agonist-directed. Following a 20h treatment of CHO cells expressing the cloned human mu (hMOR-CHO), delta (hDOR-CHO) or kappa (hKOR-CHO) opioid receptors with various opioid agonists, we determined the expression level of Galpha12 and Galphai3 by Western blots. Among five mu agonists (morphine, etorphine, DADLE, DAMGO, herkinorin) tested with hMOR-CHO cells, only chronic morphine and etorphine up-regulated Galpha12 expression. All five mu agonists decreased Galphai3 expression. Among six delta agonists (SNC80, DPDPE, deltorphin-1, morphine, DADLE, etorphine) tested with hDOR-CHO cells, all six agonists down-regulated Galphai3 expression or moderately up-regulated Galpha12 expression. Among five kappa agonists, ((-)-ethylketocyclazocine, salvinorin A, U69,593, etorphine, (-)-U50,488) tested with hKOR-CHO cells, only chronic (-)-U50,488 and (-)-EKC up-regulated Galpha12 expression. All kappa agonists decreased Galphai3 expression. These data demonstrate that chronic opioid agonist regulation of G protein expression depends not only on the agonist tested, but also on the type of opioid receptor expressed in a common cellular host, providing additional evidence for agonist-directed signaling.

A comparison of noninternalizing (herkinorin) and internalizing (DAMGO) mu-opioid agonists on cellular markers related to opioid tolerance and dependence

Previous studies established that Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol (DAMGO) and (2S,4aR,6aR,7R,9S,10aS,10bR)-9-(Benzoyloxy)-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho-[2,1-c]pyran-7-carboxylic acid methyl ester (herkinorin) are fully efficacious mu-agonists. Herkinorin (HERK), unlike DAMGO, does not recruit beta-arrestin and promote mu-receptor internalization, even in cells that over express beta-arrestin. We hypothesized that chronic HERK and DAMGO treatment will differentially affect cellular markers of tolerance and dependence. CHO cells expressing the cloned human mu-receptor were treated for 20 h with 10 microM DAMGO, HERK, morphine, or medium. Both DAMGO and HERK acted as full agonists in the [(35)S]GTP-gamma-S binding assay with E(MAX) values of 230% and EC(50) values of 12.8 and 92.5 nM, respectively. In the cAMP assay, DAMGO and HERK had similar E(MAX) values of approximately 80% and EC(50) values of 3.23 and 48.7 nM, respectively. Chronic exposure to both drugs produced moderate tolerance to both drugs ( approximately 2 to 5 fold) in the [(35)S]GTP-gamma-S binding assay. In the cAMP assay, chronic DAMGO produced tolerance to both drugs ( approximately 3 to 4 fold). Chronic HERK eliminated the ability of either drug to inhibit forskolin-stimulated cAMP accumulation. Chronic DAMGO increased, and chronic HERK decreased, forskolin-stimulated cAMP accumulation. Naloxone, after chronic HERK (but not DAMGO) induced a large increase in forskolin-stimulated cAMP accumulation. Viewed collectively with published data, the current data indicate that both internalizing and noninternalizing mu-agonists produce cellular signs of tolerance and dependence.

The antinociceptive effect of morphine is reversed by okadaic acid in morphine-naive but not in morphine-tolerant mice

The activation of specific subtypes of serine/threonine protein phosphatases (PPs) plays a role in the antinociceptive effect of acute morphine, but it is not known whether these enzymes are involved in morphine-induced antinociception in morphine-tolerant animals. We evaluated the effects of both okadaic acid (a selective inhibitor of some serine/threonine PPs) and its inactive analogue L-norokadaone on the antinociception induced by morphine in morphine-naive and -tolerant female mice in the tail-flick test. Okadaic acid (0.01 and 1 pg/mouse, i.c.v.), but not L-norokadaone (1 pg/mouse, i.c.v.), antagonized in a dose-dependent way the antinociception induced by morphine (1-16 mg/kg, s.c.) in morphine-naive animals. However, both okadaic acid (0.01 and 1 pg/mouse, i.c.v.) and L-norokadaone (1 pg/mouse, i.c.v.) were unable to modify the antinociceptive effect of morphine in morphine-tolerant mice. These results suggest that in morphine-induced thermal analgesia, the role of serine/threonine PPs highly sensitive to okadaic acid is different in morphine-tolerant and morphine-naive female mice.

Inhibition of agonist-induced down-regulation of the delta-opioid receptor with a proteasome inhibitor attenuates opioid tolerance in human embryonic kidney 293 cells

This study was designed to test the hypothesis that inhibition of agonist-induced delta-receptor down-regulation would block the development of opioid tolerance in a cell-based model. A human embryonic kidney 293 cell line was established that expressed an epitope-tagged delta-opioid receptor (DOR). Treatment of DOR cells with Tyr-d-Ala-Gly-Phe-d-Leu-enkephalin (DADL) resulted in a time-dependent decrease in the B(max) of delta-opioid receptor binding sites and immunoreactive receptor protein. When cells were coincubated with the proteasome inhibitor N-benzyloxycarbonyl-l-leucyl-l-leucyl-l-leucinal (ZLLL) and DADL, the magnitude of the agonist-induced decrease in B(max) and immunoreactive receptor protein was reduced compared with DADL treatment alone. Acute treatment of DOR cells with DADL caused a 3-fold increase in the level of phosphorylated mitogen-activated protein (MAP) kinase. Prior exposure of DOR cells to DADL completely abrogated the agonist-induced activation of MAP kinase. When DOR cells were coincubated with DADL and ZLLL, the proteasome inhibitor prevented the loss of agonist activation of MAP kinase. Acute treatment of DOR cell membranes with DADL stimulated [(35)S]guanosine 5'-3-O-(thio-)triphosphate (GTPgammaS) binding. When DOR cells were preincubated with DADL, the agonist-induced increase in [(35)S]GTPgammaS binding was attenuated. Coincubation of ZLLL and agonist partially prevented the decreased responsiveness to agonist stimulation. The results of this study demonstrated that inhibition of agonist-induced down regulation with a proteasome inhibitor attenuated opioid tolerance in a cellular model, and suggest that coadministration of a proteasome inhibitor with chronic opioid agonist treatment may be useful for limiting opioid tolerance in vivo.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

Salvinorin A: allosteric interactions at the mu-opioid receptor

Salvinorin A [(2S,4aR,6aR,7R,9S,10aS,10bR)-9-(acetyloxy)-2-(3-furanyl)-dodecahydro-6a,10b-dimethyl-4,10-dioxo-2h-naphtho[2,1-c]pyran-7-carboxylic acid methyl ester] is a hallucinogenic kappa-opioid receptor agonist that lacks the usual basic nitrogen atom present in other known opioid ligands. Our first published studies indicated that Salvinorin A weakly inhibited mu-receptor binding, and subsequent experiments revealed that Salvinorin A partially inhibited mu-receptor binding. Therefore, we hypothesized that Salvinorin A allosterically modulates mu-receptor binding. To test this hypothesis, we used Chinese hamster ovary cells expressing the cloned human opioid receptor. Salvinorin A partially inhibited [(3)H]Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol (DAMGO) (0.5, 2.0, and 8.0 nM) binding with E(MAX) values of 78.6, 72.1, and 45.7%, respectively, and EC(50) values of 955, 1124, and 4527 nM, respectively. Salvinorin A also partially inhibited [(3)H]diprenorphine (0.02, 0.1, and 0.5 nM) binding with E(MAX) values of 86.2, 64, and 33.6%, respectively, and EC(50) values of 1231, 866, and 3078 nM, respectively. Saturation binding studies with [(3)H]DAMGO showed that Salvinorin A (10 and 30 microM) decreased the mu-receptor B(max) and increased the K(d) in a dose-dependent nonlinear manner. Saturation binding studies with [(3)H]diprenorphine showed that Salvinorin A (10 and 40 microM) decreased the mu-receptor B(max) and increased the K(d) in a dose-dependent nonlinear manner. Similar findings were observed in rat brain with [(3)H]DAMGO. Kinetic experiments demonstrated that Salvinorin A altered the dissociation kinetics of both [(3)H]DAMGO and [(3)H]diprenorphine binding to mu receptors. Furthermore, Salvinorin A acted as an uncompetitive inhibitor of DAMGO-stimulated guanosine 5'-O-(3-[(35)S]thio)-triphosphate binding. Viewed collectively, these data support the hypothesis that Salvinorin A allosterically modulates the mu-opioid receptor.