Tolerance development to morphine-induced alterations of immune status

GC-MS-based plasma metabolomic investigations of morphine dependent rats at different states of euphoria, tolerance and naloxone-precipitated withdrawal

Long-term or excessive application of morphine leads to tolerance and addiction, which hindered its conventional applications as a drug. Although tremendous progress has been made on the mechanisms of morphine, crucial evidence elaborating the neurobiological basis of tolerance and dependence is still lacking. To further explore the physiological adaptions during morphine's application, a systematic screening of small molecules in blood has been carried out. The plasma of morphine dependent rats was collected at different time points with or without naloxone treatment, and was analyzed by gas chromatography-mass spectrometry (GC-MS). Partial least squares discriminate analysis (PLS-DA) and the Student's t Tests with the false discovery rate (FDR) correction were conducted on the normalized data for the distinction of groups and the identification of the most contributed metabolites. Clear separation is observed between different treatments, and 29 out of 41 metabolites changes significantly compared with the corresponding controls. The concentration of threonine, glycine, serine, beta-d-glucose and oxalic acid are consistently changed in all morphine treated groups compared with controls. Through this experiment we find characteristic metabolites in different dependent states and discuss the possible compensation effects. The interpretation of these metabolites would throw light on the biological effects of morphine and reveal the possibilities to become marker of morphine addiction.

Effects of opioids on immunologic parameters that are relevant to anti-tumour immune potential in patients with cancer: a systematic literature review

Background:

The immune system has a central role in controlling cancer, and factors that influence protective antitumour immunity could therefore have a significant impact on the course of malignant disease. Opioids are essential for the management of cancer pain, and preclinical studies indicate that opioids have the potential to influence these tumour immune surveillance mechanisms. The aim of this systematic literature review is to evaluate the clinical effects of opioids on the immune system of patients with cancer.

Methods:

A systematic search of Ovid MEDLINE (PubMed) and Embase, Cochrane database and Web of Knowledge for clinical studies, which evaluated the effects of opioids on the immune system in patients with cancer, was performed.

Results:

Five human studies, which have assessed the effects of opioids on the immune system in patients with cancer, were identified. Although all of these evaluated the effect of morphine on immunologic end points in patients with cancer, none measured the clinical effects.

Conclusions:

Evidence from preclinical, healthy volunteer and surgical models suggests that different opioids variably influence protective anti-tumour immunity; however, actual data derived from cancer populations are inconclusive and definitive recommendations cannot be made. Appropriately designed and powered studies assessing clinical outcomes of opioid use in people with cancer are therefore required to inform oncologists and others involved in cancer care about the rational use of opioids in this patient group.

Intensive Care Unit-acquired infection as a side effect of sedation

Introduction

Sedative and analgesic medications are routinely used in mechanically ventilated patients. The aim of this review is to discus epidemiologic data that suggest a relationship between infection and sedation, to review available data for the potential causes and pathophysiology of this relationship, and to identify potential preventive measures.

Methods

Data for this review were identified through searches of PubMed, and from bibliographies of relevant articles.

Results

Several epidemiologic studies suggested a link between sedation and ICU-acquired infection. Prolongation of exposure to risk factors for infection, microaspiration, gastrointestinal motility disturbances, microcirculatory effects are main mechanisms by which sedation may favour infection in critically ill patients. Furthermore, experimental evidence coming from studies both in humans and animals suggest that sedatives and analgesics present immunomodulatory properties that might alter the immunologic response to exogenous stimuli. Clinical studies comparing different sedative agents do not provide evidence to recommend the use of a particular agent to reduce ICU-acquired infection rate. However, sedation strategies aiming to reduce the duration of mechanical ventilation, such as daily interruption of sedatives or nursing-implementing sedation protocol, should be promoted. In addition, the use of short acting opioids, propofol, and dexmedetomidine is associated with shorter duration of mechanical ventilation and ICU stay, and might be helpful in reducing ICU-acquired infection rates.

Conclusions

Prolongation of exposure to risk factors for infection, microaspiration, gastrointestinal motility disturbances, microcirculatory effects, and immunomodulatory effects are main mechanisms by which sedation may favour infection in critically ill patients. Future studies should compare the effect of different sedative agents, and the impact of progressive opioid discontinuation compared with abrupt discontinuation on ICU-acquired infection rates.

[Could anaesthesia, analgesia and sympathetic modulation affect neoplasic recurrence after surgery? A systematic review centred over the modulation of natural killer cells activity]

OBJECTIVE

The Natural Killer cells (NK) are an important part of non-specific cellular-mediated and antitumoral immunity. The goal of this review is to recapitulate data published over NK activity during the perioperative period and the influence of anaesthesia, analgesia and modulation of sympathetic system.

DATA SOURCES

Pubmed/Medline database.

STUDY SELECTION AND DATA EXTRACTION

Keywords-based selection, without limit of date: fundamental studies, randomized controlled trials and non-randomized comparative studies.

DATA SYNTHESIS

In human as in animal studies, an important correlation exists between NK activity and prognosis linked to the development of metastasis. The great depression of this cytotoxicity during the perioperative period could be able to compromise host defenses. The influence of anaesthetics and analgesics is important. The effects of the opioids, the agonists and the antagonists of the sympathetic nervous system, the prostaglandins, the NSAIDs, the ketamine, the hypnotics and the locoregional anaesthesia are systematically reviewed. The limits of experimental model presented are covered.

CONCLUSION

The effects of anaesthetic/analgesic drugs and techniques, the consequences of sympathomodulation on NK activity are numerous and sometimes opposite. It is important for the anaesthesiologist to keep in mind that the long term consequences of his techniques on the patients' outcome must be clarified.

Enhanced immune sensitivity to stress following chronic morphine exposure

Chronic administration of escalating doses ofmorphine leads to neuroadaptive changes precipitating development of tolerance to many of the acute effects of morphine, such as analgesia, activation of the hypothalamic-pituitary-adrenal (HPA) axis and suppression of immune cell activities. Interestingly, morphine tolerance has also been shown to be accompanied by heightened immunosuppressive effects of restraint stress using a rodent model. These observations have led to the hypothesis that the altered neuronal state accompanying opioid tolerance may contribute to this enhanced immune sensitivity to stress. To further test this hypothesis using different stressors, Sprague-Dawley rats were treated chronically with morphine for at least 8 days and then challenged with either psychological (water stress) or systemic stressors [morphine withdrawal, lipopolysaccharide (10 mug/kg i.p. challenge)]. It was found that, independent of the type of stress employed, morphine-tolerant animals displayed significantly lower mitogen-stimulated blood lymphocyte responses when compared to the responses of similarly treated saline controls. To determine whether direct activation of central stress pathways may also lead to enhanced immune sensitivity, morphine-tolerant animals were centrally injected with IL-1beta (1 ng/mul i.c.v.), a cytokine that activates the HPA axis by central mechanisms. Similar to the other types of stress, this direct central challenge was also found to be more immunosuppressive in morphine-tolerant animals compared to controls. Collectively, these studies demonstrate that morphine-tolerant animals have an enhanced susceptibility to the debilitating effects of a variety of stressors on immune cell function, an effect that is likely due to the neuroadaptive changes that develop during chronic morphine exposure.

Chronic morphine drinking establishes morphine tolerance, but not addiction in Wistar rats

OBJECTIVE

Some animal models apply morphine in the drinking water to generate addiction, but related reports are not free of conflicting results. Accordingly, this study aimed to figure out if chronic consumption of morphine in the drinking water can induce morphine addiction in Wistar rats.

METHODS

For 3 weeks, the animals received a daily morphine dose of 35 mg/kg by offering a calculated volume of sugar water (5% sucrose) with morphine (0.1 mg/ml) to each rat; animals receiving just sugar water served as controls. Immediately after the treatment phase, the tail immersion test was used to check for morphine tolerance, and all animals were then kept on tap water for one week (withdrawal phase). Afterwards, all rats were allowed to choose their drinking source by offering two bottles, containing sugar water without and with morphine, simultaneously for two days (preference phase).

RESULTS

While the chronic consumption of morphine led to a reduction in body weight and to morphine tolerance, the morphine-treated Wistar rats did not show any preference for the opiate-containing sugar water.

CONCLUSION

Body weight loss and tolerance do not reveal a condition of drug craving, and current animal models should be re-evaluated regarding their potential to establish morphine addicted animals.

Immune response in addicts with chronic hepatitis C treated with interferon and ribavirin

BACKGROUND

The role played by the immune system in the progression of chronic hepatitis C (CHC) is not completely clear. Opioids may facilitate the outbreak of infections through marked immunomodulating effects on the immune response against a virus. To asses if addicts can be treated successfully with interferon (IFN) during detoxification treatment, we evaluated some immune response mediators in addicts affected by CHC.

METHOD

A cohort of heroin users with CHC were enrolled during the detoxification period, divided into two groups and treated with IFN pegilate plus ribavirin (group A treated during methadone administration and group B treated at week 8 after methadone treatment completed). A group of patients with CHC and no history of drug addiction were enrolled as controls. Leukocyte subpopulation NK, CD4+, CD8+ and some cytokines Th1 (IFNgamma, interleukin [IL]2) and Th2 (IL-6, IL-10) were evaluated prior to, during and after methadone treatment. Sustained virological response was evaluated 24 weeks after antiviral treatment was completed.

RESULTS

During methadone treatment, significantly (P < 0.05) higher cytokine Th1 and NK and lower cytokine Th2 levels were observed in groups A and B compared with levels obtained before treatment in the same groups. Relapse occurred at 56 +/- 8 weeks in 34/55 group A patients, at 24 +/- 8 weeks in 33/52 group B patients and at 24 +/- 4 weeks in group C, there being a significant difference (P < 0.05) between group A and B and between group A and C. No significant differences between all groups were detected in CD4+ and CD8+ cell counts.

CONCLUSIONS

Our results revealed that drug addicts with CHC can be treated successfully with IFN pegilate and ribavirin. This therapy can be recommended during the early phase of detoxification treatment to achieve a sustained response.

Oxymorphone Hydrochloride, a Potent Opioid Analgesic, Is Not Carcinogenic in Rats or Mice

Despite their long history of chronic use, little information is available regarding the carcinogenicity of opioid analgesics. Oxymorphone is a potent morphinan-type mu-opioid analgesic used for treatment of moderate-to-severe pain. Oxymorphone was tested for carcinogenicity in Crl:CD IGS BR rats and CD-1 mice. Oxymorphone hydrochloride was administered orally once daily for 2 years to rats at doses of 2.5, 5 and 10 mg/kg/day (males) and 5, 10 and 25 mg/kg/day (females), and mice at 10, 25, 75 and 150 mg/kg/day (65 animals per sex per group; 100 animals per sex in controls). In rats, survival was generally higher than controls in oxymorphone-treated groups, attributable to lower body weight gain. In mice, survival was generally higher than controls in females at all doses and males given < or = 25 mg/kg/day but lower in males given > or = 75 mg/kg/day due to a high incidence of obstructive uropathy. Opioid-related clinical signs and reduced body weight gain occurred in both species throughout the study. Nonneoplastic findings associated with oxymorphone pharmacology included ocular and pulmonary changes in rats considered secondary to inhibition of blinking and mydriasis, and antitussive activity, respectively, and urinary tract and renal findings in mice considered secondary to urinary retention. There was no target organ toxicity, and no increase in any neoplastic lesions attributed to oxymorphone. Plasma oxymorphone levels achieved in these studies exceeded those in patients taking high therapeutic doses of oxymorphone (Area under the curve [AUC(0-24 h)] values up to 5.6-fold and 64-fold in rats and mice, respectively). Oxymorphone is not considered to be carcinogenic in rats or mice under the conditions of these studies.

Morphine withdrawal dramatically reduces lymphocytes in morphine-dependent macaques

The immune effects of chronic opiate exposure and/or opiate withdrawal are not well understood. The results of human studies with opiate abusers are variable and may not be able to control for important factors such as subjects' drug histories, health and nutritional status. Nonhuman primate models are necessary to control these important factors. A model of opiate dependence in macaques was developed to study the effects of opiate dependence and withdrawal on measures of immune function. Four pigtailed macaques drank a mixture of morphine (20 mg/kg/session) and orange-flavored drink every 6 h for several months. During stable morphine dependence, absolute numbers of neutrophils, monocytes and lymphocytes did not change relative to pre-morphine levels. However, there was a significant decrease in the absolute number and percentage of natural killer (NK) cells in morphine dependence. Either precipitated withdrawal or abstinence for 24 h resulted in behavioral withdrawal signs in all animals. Absolute lymphocyte counts decreased and absolute netrophil counts increased significantly in withdrawal, relative to levels during morphine dependence. Lymphocyte subset (CD4+, CD8+, CD20+) cells were also decreased in absolute numbers with little change in their percentage distributions. There was, however, a significant increase in the percentage of NK cells in withdrawal relative to levels during morphine dependence. This study demonstrates the usefulness of voluntary oral self-dosing procedures for maintaining morphine dependence in nonhuman primates and demonstrates that the morphine withdrawal syndrome includes large alterations in blood parameters of immune system function, including nearly 50% reduction in numbers of CD4+, CD8+ and CD20+ cells.

Effects of opioid tolerance and withdrawal on the immune system

Review of the robust literature using acute drug injection paradigms points clearly to the conclusion that morphine is immunosuppressive. In contrast, studies of the effect of subacute or chronic administration of morphine on immune function is limited, with variable results. In some cases tolerance to the immunosuppressive effects of the drug is clearly demonstrated, but in other cases, selected immune parameters do not demonstrate tolerance. Discrepancies in findings may result from differences in species or route and manner of drug administration. Even fewer studies (total of 10) have been published on the effects of withdrawal on immune function. Most immune parameters tested are suppressed following drug withdrawal. Recovery time to baseline response levels varies in the studies. In the single report of withdrawal in humans, immune function was suppressed for up to 3 years. It is clearly established that withdrawal suppresses capacity of murine spleen cells to make an ex vivo antibody response, which contrasts with evidence of polarization of the lymphocytes towards a Th2 phenotype. Several laboratories have shown that subacute and chronic exposure to morphine, as well as drug withdrawal, sensitize to the lethal effects of bacterial lipopolysaccharide. Underlying sepsis, combined with morphine-induced hypofunction of the hypothalamic-pituitary-adrenal (HPA) axis, may be occult variables modulating immune responses during opioid administration and withdrawal. As episodes of withdrawal are common among drug abusers, more intensive investigation is warranted on the effects of withdrawal on immune function, on mechanisms of immune modulation, and on sensitization to infection.

Effects of morphine and its metabolites on immune function in advanced cancer patients

STUDY OBJECTIVE

To determine whether morphine and its active metabolites such as morphine-3-glucuronide (M-3-G) and morphine-6-glucuronide (M-6-G) modulate immune function in patients with advanced cancer who required morphine for pain relief.

DESIGN

Prospective observational clinical study.

SETTING

Pain clinic of a university hospital.

PATIENTS

Fifteen patients who visited our clinic for control of advanced cancer pain.

INTERVENTIONS

During the initiation or changes of morphine therapy, venous blood samples were obtained at the enrollment of this study, 1 and 3 weeks after the change of morphine dose or route.

MEASUREMENTS

Lymphocyte subpopulation CD4+ and CD8+, activity of natural killer cell, phytohemagglutinin (PHA)-induced T-cell proliferation, and plasma immunoglobulin M and G concentrations were measured, as well as plasma concentrations of morphine, M-3-G, and M-6-G.

MAIN RESULTS

At the entry of the study, 6 patients did not receive any type of morphine medication (group 1), whereas 9 patients were treated with morphine for 1 month (group 2). Cancer pain, rated as 4 at the entry period, was reduced to 2 of 10 (visual analogue scale) during the study periods. Although the plasma concentrations of M-3-G and M-6-G in Group 1 were significantly less than those in Group 2, plasma concentrations of immunologic markers were similar between the groups. In Group 1, Spearman linear regression analysis showed negative correlation between morphine-derived metabolites and immunoglobulins or PHA-induced T-cell proliferation, whereas poor correlation was found with all immunologic parameters in Group 2. Stepwise linear regression analyses showed that the metabolites, rather than morphine per se, modulated immune function, reflected by PHA-induced T-cell proliferation and immunoglobulin G concentration in Group 1.

CONCLUSIONS

The present study suggests that some of humoral and cellular immunity are modulated by morphine-derived metabolites at the early phase of morphine therapy in patients with advanced cancer.

Chimeric DNA vaccine reverses morphine-induced immunosuppression and tumorigenesis

Although long-term use of morphine has been shown to promote tumor growth, the question whether tumorigenesis occurs as a result of an immunosuppressive effect remains to be investigated. In mice rendered tolerant to morphine, the efficacy and mechanism of a vaccination to rescue morphine-induced immunosuppression and prevent tumor growth was assessed both in vitro and in vivo. Herein, we found that morphine-injected mice exhibited higher tumor growth rates and lower percentages of CD8+ T lymphocytes. The mechanism of morphine suppression of immunity might be through the suppression of E7-specific CD8+ T lymphocyte proliferation and the promotion of apoptosis of these cells by the Bcl-2 and Bax pathways. The suppressive effect of E7-specific CD8+ T lymphocytes by morphine could be reversed by naloxone. We have previously shown that calreticulin linked with E7 (CRT/E7) could enhance the CD8+ T cell response and the anti-tumor effects (W. F. Cheng et al. (2001) J. Clin. Invest. 108, 669-678). CRT/E7 DNA vaccine could overcome the immunosuppressive effect of morphine and suppress tumor growth. Our findings reveal that long-term morphine treatment dose-dependently promotes tumor growth and a DNA vaccine may serve as a useful approach to treat the profound immunosuppressive function and prevent tumorigenesis after long-term morphine treatment.

The relationship between non-injection drug use behaviors on progression to AIDS and death in a cohort of HIV seropositive women in the era of highly active antiretroviral therapy use

AIMS

To evaluate the effects of longitudinal patterns and types of non-injection drug use (NIDU) on HIV progression in the highly active antiretroviral therapy (HAART) era.

DESIGN

Women's Interagency HIV Study (WIHS), a prospective cohort study conducted at six US sites.

METHODS

Data were collected semi-annually from 1994 to 2002 on 1046 HIV(+) women. Multivariate Cox proportional hazards modeling was used to estimate relative hazards for developing AIDS and for death by pattern and type of NIDU.

FINDINGS

During follow-up, 285 AIDS events and 287 deaths, of which 177 were AIDS-related, were reported. At baseline, consistent and former NIDU was associated with CD4(+) counts of < 200 cells/microl (43% and 46%, respectively) and viral load > 40,000 copies/ml (53% and 55%, respectively). Consistent NIDU reported less HAART use (53%) compared with other NIDU patterns. Stimulant use was associated with CD4(+) cell counts of < 200 cells/microl (53%) and lower HAART initiation (63%) compared with other NIDU types. In multivariate analyses, progression to AIDS was significantly higher among consistent (RH = 2.52), inconsistent (RH = 1.63) and former (RH = 1.56) users compared with never users; and for stimulant (RH = 2.04) and polydrug (RH = 1.65) users compared with non-users. Progression to all-cause death was higher only among former users (RH = 1.48) compared with never users in multivariate analysis. NIDU behaviors were not associated with progression to AIDS-related death.

CONCLUSIONS

In this study, pattern and type of NIDU were associated with HIV progression to AIDS and all-cause mortality. These differences were associated with lower HAART utilization among consistent NIDU and use of stimulants, and poor baseline immunological and virological status among former users.

Randomized clinical trial to compare the effects of methadone and buprenorphine on the immune system in drug abusers

RATIONALE

Buprenorphine may be a useful alternative option to methadone in addicts. Opioids can produce severe changes in the immune system.

OBJECTIVES

The objectives of this study are to compare the effect of sublingual buprenorphine and methadone on the immune system and to compare the two substances on the drying-out program compliance.

METHODS

We studied 62 randomized outpatients for a period of 12 months. Subjects (55 males and 7 females; mean age 25+/-4 years; average history of heroin abuse being 2 years) on maintenance treatment were assigned in two groups (A and B). Methadone chloride (medium dose 100 mg/day) was administered to group A, whereas group B received sublingual buprenorphine (32.40+/-2.8 mg/day). Urine toxicological screening, plasma levels of TNF-alpha interleukin-1, interleukin-beta, lymphocyte CD14 and a self-rating depression questionnaire were measured.

RESULTS

Urine screening was negative for opiates in 17.6% of group A and in 10.7% of group B (p<0.001; r = 0.62). Depression score was 62+/-2 in group A and 55+/-3 in group B (p < 0.01). Cytokine and CD14 revealed higher concentrations both in groups A and B without significant differences (p > 0.05) between the two groups.

CONCLUSIONS

The effects of buprenorphine and methadone tested on the immune system were overlapping in our patients. The elevated cytokine levels observed may suggest that the two drugs stimulate immunologic hyperactivation of an immune system that was formerly inhibited by heroin. Furthermore, our data suggest that buprenorphine can be a valid alternative to methadone in maintenance treatment of chronic heroin abuse and referred a marked decline in depression.

Chronic fentanyl or buprenorphine infusion in the mouse: similar analgesic profile but different effects on immune responses

It is known that morphine has a negative impact on the immune responses. The potent opioids fentanyl and buprenorphine have recently become available as transdermal preparation for the treatment of chronic pain. We analyze the effect of fentanyl and buprenorphine on splenic cellular immune responses in the mouse. The parameters evaluated were lymphoproliferation, natural killer cell activity and interleukin-2 and interferon-gamma production. Drugs were administered acutely at the equianalgesic doses of 0.25 mg/kg for fentanyl and 5 mg/kg for buprenorphine, or delivered continuously with osmotic pumps for 24 h, 3 and 7 days at the rate of 7.5 microg/h per mouse (fentanyl) and 12.5 microg/h per mouse (buprenorphine). After acute administration, a significant decrease of lymphoproliferation is observed in fentanyl-treated animals only. After 24 h of fentanyl administration all the parameters were significantly reduced. After 3 days of fentanyl infusion NK activity had returned to normal values, while all the other parameters were still significantly reduced. In 7 day fentanyl-treated animals immunological tolerance had developed, since no differences with controls were present. In contrast no immune alterations were ever present in buprenorphine-treated animals. No tolerance to the antinociceptive effect of drugs had yet developed. After 1 week of infusion with fentanyl and buprenorphine, new pumps were implanted releasing double amounts of drugs. Neither fentanyl nor buprenorphine-treated animals showed altered immune responses at any time considered. These results indicate that fentanyl and buprenorphine exert different immune effects. Opioid-induced immunosuppression is less relevant in chronic administration than in acute or short-time administration.

Multiple ways that drug abuse might influence AIDS progression: clues from a monkey model

Whether opiates and other drugs of abuse affect AIDS progression has been an unresolved issue for two decades. Credible evidence has suggested that opiates may exacerbate, retard or have 'no effect' on progression of AIDS. Differences may exist in AIDS-progression outcomes after opiate exposures that relate to neural versus, strictly, somatic AIDS; but it is also likely that conditional variables inherent to drug dependency and the nature of the infectious agents involved allow for differing outcomes. Data from epidemiological studies, and from in vitro and basic immunological studies regarding opiate effects on AIDS progression must be interpreted in light of the conditionality of opiate effects. Caution is sounded, also, about interpreting common depressive immunological effects of opiates as indicators of influence over AIDS progression. Current evidence from the monkey model of AIDS indicates that opiates can, under certain defined conditions, retard AIDS progression. The clinical relevance of these data remains to be defined. Importantly, such data imply that opioids and the endogenous opioid system may represent therapeutic tools and targets for altering AIDS progression.

Immune cell activity during the initial stages of withdrawal from chronic exposure to cocaine or morphine

The immunosuppression accompanying illicit drug use has been shown to contribute to a decreased resistance to a variety of pathogens; however, there is relatively little information on how long these effects persist following withdrawal from chronic drug exposure. To begin to address this question, Sprague-Dawley male rats were administered either cocaine (10 mg/kg, i.p., b.i.d.) for 7 days or morphine (escalating doses up to 40 mg/kg, s.c., b.i.d.) for a 10-day period. Control groups of animals received similar saline injections for equivalent time periods. Drug administration was abruptly discontinued and animals were sacrificed at 2, 24, 72 or 96 h following the last dose. At these time points, proliferation responses of peripheral blood T-lymphocytes stimulated by concanavalin A (Con A) and plasma levels of corticosterone were measured. Plasma corticosterone levels of cocaine- or morphine-treated animals were found to be significantly elevated 24 h following drug cessation as compared to saline animals. At this time, proliferation responses were significantly decreased and were further suppressed during cocaine and morphine withdrawal at 96 and 72 h, respectively. These results suggest that abrupt cessation of cocaine or morphine administration leads to activation of stress-related pathways that may contribute to an increased susceptibility of infection during the initial withdrawal phase.

Antagonism of N-methyl-D-aspartate receptors reduces the vulnerability of the immune system to stress after chronic morphine

It has been shown that morphine-tolerant animals have an altered immunological sensitivity to stress. Although the glutamatergic system has been implicated in the neuroadaptive process underlying this tolerant state, its potential role in development of the altered immunological sensitivity consequent to chronic morphine treatment is not known. To determine this, a morphine-tolerant state was induced by 10-day administration of an escalating dose of morphine from 10 to 40 mg/kg (s.c., b.i.d.), and lymphocyte proliferative response to a T-cell mitogen was measured. Morphine challenge (10 mg/kg s.c.) after days of treatment was gradually less immunosuppressive, and this tolerance progression was delayed by concurrent administration of the N-methyl-D-aspartate (NMDA) receptor antagonist (-)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) (0.1 mg/kg s.c.) with chronic morphine. The effect was independent of glucocorticoid level changes and was not a result of an acute interaction of the drugs or the prolonged presence of the antagonist alone. Subsequent to chronic treatment, animals were subjected to opioid withdrawal and water stress. Both stressors induced 50% immunosuppression in morphine-tolerant animals compared with saline-treated controls. Increased immunological sensitivity to these stressors was attenuated when MK-801 was administered with chronic morphine as demonstrated by an accelerated recovery rate and lack of immunosuppression from opioid withdrawal and water stress, respectively. Together, these findings provide the first evidence that the neuroadapted state of the immune response after chronic morphine can be modified by NMDA receptor antagonism, as illustrated by a temporal deceleration of the development of immunological tolerance during chronic treatment that is associated with an attenuation of the immunological vulnerability of morphine-tolerant animals to stress.

Effects of in vitro and in vivo opioids on the production of IL-12 and IL-10 by murine macrophages

We evaluated the ability of the specific micro opioid receptor agonist DAMGO, the kappa-specific agonist U-50488 in vitro, and exogenous opioid morphine administered in vivo both acutely and chronically to modulate IL-12 and IL-10 production by murine peritoneal macrophages. Damgo and U-50488 at the concentrations of 10(-6) and 10(-8) M decreased the production of IL-12 without affecting IL-10. One hour after the acute administration of 5, 10, and 20 mg/kg of morphine a dose-related decrease of both IL-10 and IL-12 levels was present. The pretreatment with naltrexone at doses up to 20 mg/kg did not prevent the decrease of IL-10 and IL-12 induced by morphine. When the drug was administered chronically, a differential development of tolerance to the immune effects was observed. After 3 days of treatment the effect of the acute challenge with 20 mg/kg of morphine on IL-12 was lost. In contrast, morphine-induced inhibition of IL-10 disappeared between 10 and 12 days of treatment, in parallel with tolerance to the antinociceptive effect. These results suggest that opioids modulate macrophage cytokine production. However, the effects exerted by the in vivo administration of morphine are not superimposable onto those induced by the in vitro administration of specific opioid agonists.

Abrupt or precipitated withdrawal from morphine induces immunosuppression

The present studies tested the effect of withdrawal from morphine by two different paradigms, abrupt withdrawal (AW) or precipitated withdrawal (PW), on the capacity of murine spleen cells to mount an in vitro antibody response. Mice were made dependent by chronic treatment using s.c. implanted morphine slow-release pellets. Splenocytes were harvested at various time points after withdrawal and the number of antibody-forming cells determined using a plaque-forming cell (PFC) assay. The results indicate that induction of abstinence from morphine in dependent mice by either paradigm caused marked immunosuppression between 24 and 48 h post-withdrawal. However, the kinetics of onset and recovery from immunosuppression were different in AW and PW.

Effects of tramadol on T lymphocyte proliferation and natural killer cell activity in rats with sciatic constriction injury

We investigated the effects of acute and chronic tramadol treatment on T lymphocyte function and natural killer (NK) cell activity in rats receiving chronic constriction injury (CCI) of the sciatic nerve. T lymphocyte function was evaluated based on concanavalin-A (ConA)- and phytohemagglutinin (PHA)-induced splenocyte proliferation. NK cell activity was measured by lactic acid dehydrogenase release assay. The effects of tramadol on thermal hyperalgesia were also assessed by measuring paw withdrawal latency (PWL) in the rats. PWL was dose-dependently reversed by tramadol after acute treatment (single subcutaneous injection) with 10, 20, and 30 mg/kg, respectively. There was no significant change among acute treatment groups in NK cell activity, whereas splenocyte proliferation induced by ConA and PHA was significantly suppressed starting from a dose of 20 mg/kg. The reversal of the thermal hyperalgesia persisted throughout a period of chronic tramadol treatment of 40 and 80 mg/kg per day, respectively, with continuous subcutaneous infusion for 7 days at a uniform rate via osmotic minipumps. No modulation of NK cell activity was found in either dose group. However, the activity of splenocyte proliferation was decreased in the 80 mg/kg per day group when compared with the saline and 40 mg/kg per day groups. These data suggest that tramadol treatment has an immunological profile different from pure mu-opioid agonists like morphine, which is known to suppress both NK cell activity and T lymphocyte proliferation at a subanalgesic dose in CCI rats. Considering analgesic and immunosuppressive effects, tramadol treatment may be a better choice than morphine for treatment of chronic neuropathic pain, particularly in patients with compromised immunity.

The effects of morphine on cell proliferation

There is increasing evidence that endogenous opioid peptides ("enkephalins") and other neurotransmitters have widespread, receptor-mediated roles as growth regulators in non-neuronal cells and tissues. For example, it is now believed that enkephalins produced in placental trophoblast giant cells have multiple roles in supporting embryo growth, and in maternal adaptation to pregnancy. Since plant and synthetic narcotics (e.g., morphine) bind to the same receptors, the questions immediately arise: Do narcotics also have actions as growth regulators? If so, do these actions have physiological significance in addicts? Recent work on the first of these questions is covered in this review. While the greatest volume of research has been focused on the proliferative effects of narcotics for cells of the immune system, the roles of opioid peptides and narcotics on the growth of a variety of other cells has come under study recently.

Differential tolerance to morphine's immunomodulatory effects following continuous administration

Rats were continuously infused with either morphine or saline via an osmotic minipump for 20 consecutive days. Effects on immune status were assessed on the twentieth day of the chronic administration period following a bolus injection of morphine administered 1 h prior to sacrifice. The morphine injection suppressed measures of splenic natural killer (NK) cell activity, mitogen-stimulated T-cell proliferation, and gamma-interferon (IFN) production in rats that received saline via the minipump. In rats that received chronic morphine via the minipump, the morphine injection also suppressed mitogen-stimulated splenocyte proliferation and gamma-IFN production but did not suppress NK cell activity. These data indicate that chronic morphine administration via osmotic minipumps leads to differential tolerance to the immunomodulatory effects of morphine. These findings support previous results indicating differential tolerance development within the immune system following chronic morphine administration via the drinking water.

Effects of prolonged exposure to morphine and methadone on in vivo parameters of immune function in rats

In rats, two 6-week repeated dose oral toxicity studies were performed with morphine (250 and 500 mg/kg food) and methadone (200 and 400 mg/kg food), respectively. Alterations in immune function were studied by assessing primary and secondary immune responses to sheep red blood cells. In addition, the ability to resist challenge with infectious agents was measured in host resistance models employing the parasite Trichinella spiralis and the bacterium Listeria monocytogenes. The primary and secondary antibody responses to sheep red blood cells were not affected by treatment with either morphine or methadone. The clearance of L. monocytogenes bacteria in the spleen was not affected either. Prolonged treatment with morphine, however, resulted in a decrease in host resistance to T. spiralis infection, as indicated by a 1.5-fold increase in numbers of muscle larvae counted in the carcass, but did not affect the T. spiralis-specific IgM, IgG and IgE antibody responses. In contrast to morphine, the methadone-treated animals did not show a significant change in host resistance to T. spiralis. Total serum IgG levels, however, were increased in high-dose methadone-treated animals. Apparently, prolonged administration of morphine to rats resulted in immune suppression, mediating a slight, though biologically relevant, exacerbation of the T. spiralis infection, whereas methadone did not.

Endogenous opiates: 1997

This paper is the twentieth installment of our annual review of research concerning the opiate system. It summarizes papers published during 1997 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; eating and drinking; alcohol; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunologic responses; and other behaviors.