Evidence for central opioid receptors in the immunomodulatory effects of morphine: review of potential mechanism(s) of action

This review will discuss studies demonstrating that activation of opioid receptors within the central nervous system alters various immune system parameters. Specifically, natural killer cell cytolytic activity and lymphocyte proliferative responses to mitogen appear to be modulated predominantly, if not exclusively, through central opioid receptors. The potential mechanisms by which central opioid receptors appear to modulate these peripheral immune functions will be examined by evaluating the role of both the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system. The studies discussed below indicate that acute administration of morphine or related compounds appears to primarily alter peripheral immune function through the sympathetic nervous system, while more prolonged exposure to opioids alter the immune system predominantly by activation of the HPA axis. Finally, the potential clinical relevance of these observations are discussed in relationship to both the therapeutic use, as well as the abuse of opioid compounds.

Role of central opioid receptor subtypes in morphine-induced alterations in peripheral lymphocyte activity

Morphine has been shown to decrease proliferative responses of rat T-lymphocytes via central opioid receptors, however, the specific receptor subtype(s) mediating this effect have not been established. To determine the potential role of central mu opioid receptors in morphine-mediated suppression of T-lymphocyte proliferation, 20 nmol/2 microliters of either morphine sulfate or DAMGO (mu-selective agonist) were administered into the lateral ventricle of freely moving Sprague-Dawley rats. Lymphocyte proliferative response to the polyclonal T cell mitogen concanavalin A (ConA), changes in splenic natural killer cell (NK) cytolytic activity, activation of the hypothalamic-pituitary-adrenal (HPA) axis and antinociception (tail-flick latency) were examined. Results indicated that like morphine, DAMGO decreased blood lymphocyte proliferative responses by 80% and elevated both tail-flick latency and plasma corticosterone when compared to saline-treated animals. The proliferation response of lymphocytes from the spleen or thymus and splenic NK cell activity were not significantly altered by either morphine or DAMGO treatment. The effects of DAMGO were determined to be dose-dependent and completely antagonized by naltrexone pretreatment. Central administration of DPDPE (delta-selective agonist) and U-50488 (kappa-selective agonist) produced between 40-50% suppression of blood lymphocyte proliferation responses only at a dose five times greater (100 nmol) than DAMGO treatment, without altering antinociception or activation of the HPA axis. To determine the central opioid receptor subtype(s) involved in the effects of morphine, selective opioid antagonists were microinjected into the lateral ventricle prior to morphine treatment (6 mg/kg, s.c.). CTOP (mu-selective antagonist, 5 micrograms/2 microliters) completely blocked the effects of morphine on all parameters measured, however, naltrindole (delta-selective antagonist, 2 micrograms/2 microliters) or nor-binaltorphimine (kappa-selective antagonist, 73.5 micrograms/2 microliters) failed to block the effects of morphine. Collectively, these results provide evidence that morphine acts primarily through central mu receptors to modulate peripheral blood lymphocyte proliferation responses. Further, the antinociception and blood lymphocyte effects show greater sensitivity to opioids than either natural killer cell cytolytic activity or activation of the HPA axis.

Acute effects of morphine on blood lymphocyte proliferation and plasma IL-6 levels

Administration of morphine (10 mg/kg) to rats was found to decrease the proliferative potential of blood lymphocytes by 60-80% and concurrently elevate circulating levels of the cytokine, interleukin-6 (IL-6), 2- to 4-fold. Both parameters were similarly altered upon the central administration of morphine and were blocked upon pretreatment of animals with the opioid receptor antagonist, naltrexone. These results suggest that the activation of central opioid receptors is involved in morphine-induced inhibition of lymphocyte proliferation as well as increases in circulating levels of IL-6. Studies addressing the potential peripheral mechanisms demonstrated that intact ganglionic transmission was required for both effects of morphine. Although the suppression by morphine of lymphocyte proliferation appeared to be largely independent of stimulation of the hypothalamic-pituitary-adrenal axis, the elevation of IL-6 was completely abolished in adrenalectomized animals. Collectively, these results suggest that central opioid receptor activation results in changes in different immune parameters that can be mediated through distinct peripheral mechanisms.

HESI/FDA workshop on immunomodulators and cancer risk assessment: Building blocks for a weight-of-evidence approach

Profound immunosuppression (e.g., AIDS, transplant therapy) is epidemiologically associated with an increased cancer risk, and often with oncogenic viruses. It is currently unclear how broadly this association translates to therapeutics that modulate immunity. A workshop co-sponsored by the FDA and HESI examined how perturbing the immune system may contribute to carcinogenesis, and highlighted priorities for improving non-clinical risk assessment of targeted immunomodulatory therapies. Conclusions from the workshop were as follows. 1) While profound altered immunity can promote tumorigenesis, not all components of the immune system are equally important in defense against or promotion of cancer and a similar cancer risk for all immunomodulatory molecules should not be assumed. 2) Rodent carcinogenicity studies have limitations and are generally not reliable predictors of cancer risk associated with immunosuppression. 3) Cancer risk needs to be evaluated based on mechanism-based weight-of-evidence, including data from immune function tests most relevant to tumor immunosurveillance or promotion. 4) Information from nonclinical experiments, clinical epidemiology and immunomodulatory therapeutics show that immunosurveillance involves a complex network of cells and mediators. To support a weight-of-evidence approach, an increased focus on understanding the quantitative relationship between changes in relevant immune function tests and cancer risk is needed.

Discovery of radio emission from the brown dwarf LP944-20

Brown dwarfs are not massive enough to sustain thermonuclear fusion of hydrogen at their centres, but are distinguished from gas-giant planets by their ability to burn deuterium. Brown dwarfs older than approximately 10 Myr are expected to possess short-lived magnetic fields and to emit radio and X-rays only very weakly from their coronae. An X-ray flare was recently detected on the brown dwarf LP944-20, whereas previous searches for optical activity (and one X-ray search) yielded negative results. Here we report the discovery of quiescent and flaring radio emission from LP944-20, with luminosities several orders of magnitude larger than predicted by the empirical relation between the X-ray and radio luminosities that has been found for many types of stars. Interpreting the radio data within the context of synchrotron emission, we show that LP944-20 has an unusually weak magnetic field in comparison to active M-dwarf stars, which might explain the previous null optical and X-ray results, as well as the strength of the radio emissions compared to those at X-ray wavelengths.

Relationship between endocervical canal length between 15-24 weeks gestation and obstetric history

The object was to determine whether there is a correlation between the obstetric history and the ultrasonographically determined endocervical canal length between 15 and 24 weeks gestation. A retrospective cohort study was performed in singleton pregnancies of multigravidas with normal and abnormal obstetric histories. They underwent sonographic evaluation for the determination of the endocervical canal length between 15 and 24 weeks gestation. The shortest endocervical canal length measurements between 15 and 20 weeks and also between 21 and 24 weeks of gestation were recorded. An ultrasound diagnosis of cervical incompetence was defined as progressive shortening of the endocervical canal length to <2 cm or a single endocervical canal length measurement <2 cm. A multivariable general linear regression model was used to correlate the relationship between endocervical canal lengths at 15-20 weeks and 21-24 weeks gestation in the current pregnancy with the earliest gestational age at delivery of prior pregnancies. Chi-square test was used to determine the relationship between the development of an ultrasound diagnosis of cervical incompetence and the earliest gestational age at delivery of prior pregnancies. A total of 155 pregnancies were studied. The number of women according to the obstetric history categories were: 57 had delivered <24 weeks, 12 between 24 and 26 weeks, 16 between 27 and 32 weeks, 16 between 33 and 36 weeks, and 54 delivered > or =37 weeks. There was a significant correlation between the endocervical canal length measurements between 15-20 (P < 0.0001) weeks and 21-24 weeks (P < 0.0001) in the studied pregnancy and the earliest gestational age at delivery of prior pregnancies. A significant relationship between the ultrasound diagnosis of cervical incompetence and the obstetric history category (P = 0.0026) was observed. There were 36 cases of ultrasound diagnosed cervical incompetence with 91.7% (33/36) occurring in women who had a prior <27 weeks' gestation delivery. These data provide further evidence that cervical incompetence is a relative condition and not an "all or none" phenomenon. In addition, women with a prior delivery <30 weeks gestation should be followed with second trimester serial cervical sonography to rule out cervical incompetence.

Reversal of acute effects of high dose morphine on lymphocyte activity by chlorisondamine

To explore the mechanisms mediating the effects of acute morphine on the immune system, effects of ganglionic blockade with chlorisondamine on acute high dose morphine-induced alterations in blood lymphocyte proliferation, white blood cell counts, spleen lymphocyte proliferation and splenic natural killer (NK) cell cytolytic activity were examined in male Sprague--Dawley rats. Two hours after morphine (30 mg/kg, s.c.) administration, blood lymphocyte proliferation (ConA) was decreased 85%; this effect was antagonized by chlorisondamine (5 mg/kg, i.p.). Notably, however, such morphine exposure did not significantly decrease splenic lymphocyte proliferation, although depression of NK cell activity was also evident and appeared to be chlorisondamine-sensitive. Immune effects of morphine 1 h after treatment were somewhat different. In this case, blood lymphocyte proliferation decreased and plasma levels of corticosterone increased, with ED(50) values of 2.2 and 7.8 mg/kg, respectively. Splenic lymphocyte proliferation and NK activity were also significantly depressed in the 1-h exposure paradigm, but only after administration of 30 mg/kg morphine. These results indicate that chlorisondamine blocks the effects of relatively high doses of morphine on blood lymphocyte activity and indicate that blood lymphocyte proliferation is more sensitive to effects of acute morphine exposure than splenic lymphocyte proliferation, NK cell cytolytic activity and activation of the HPA axis.

The urge for an AIDS vaccine: perspectives from a developing country

AIDS is inexorably involving all parts of the country and all strata of society, with 10% of the urban and 3% of the rural population infected with HIV. It is increasingly a disease of women and children. The major cofactors for transmission are also sexually transmitted. For most developing countries, in spite of all education efforts, the "silent epidemic" of AIDS continues. AIDS is known but not understood; counselling modifies behavior in only 10-20% of at-risk persons. Under optimal conditions, HIV discordant females have seroconversion rates of 4.7% per year and pregnancy rates of 10.4% per year. The recent political unrest in Zaire and Haiti will further enhance the spread of AIDS in these countries. Despite these difficult periods, the work can and must continue. After all, during our 10th year of collaboration with a Haitian private research group, the Haitian government and Cornell University, Haiti has known seven different political rulers. Finally, I want to make a pledge on behalf of the millions of people who face a certain death from HIV infection and AIDS and who will never make the front page of any newspaper. For these people, you can make a difference. You must give us the tools to carry on this fight. The clinical trials must be done where they are most needed: the developing countries. Vaccines represent the only viable alternative despite the recognized obstacles of viral heterogeneity, immunogenicity, and delivery.

The effects of morphine, nicotine and epibatidine on lymphocyte activity and hypothalamic-pituitary-adrenal axis responses

Acute administration of morphine alters various neuroendocrine and immune parameters via opioid receptors located within the central nervous system. Similar effects have been reported after systemic nicotine treatment. To examine the possible relationship between opioid and nicotinic receptor activation on the immune system, we compared the effects of morphine with both nicotine and the highly selective nicotinic agonist, epibatidine. Male Sprague-Dawley rats were treated with either morphine (10 mg/kg, s.c.), nicotine (2.85 mg/kg, s.c. = 1 mg/kg freebase), or epibatidine (5 microg/kg, s.c.) and sacrificed 2 hours later. Each drug increased plasma corticosterone levels and decreased the magnitude of the peripheral blood lymphocyte proliferation response to the T cell mitogen concanavalin A. None of the treatments had a significant effect on splenic or thymic lymphocyte responses. The effects of nicotine treatment were dose-dependent. Pretreatment with the quaternary ganglionic antagonist chlorisondamine (0.5 mg/kg, i.p.), completely blocked the effect of epibatidine on blood lymphocytes without altering the elevation of corticosterone levels. Although naltrexone (10 mg/kg, s.c.) blocked all effects of morphine, the effects of epibatidine were not blocked by the opioid receptor antagonist. Furthermore, in contrast to morphine (), central injection of neither nicotine (30 or 240 nmol) nor epibatidine (5, 50, or 500 ng) altered blood lymphocyte responses. These results suggest that, like morphine, nicotinic agonists decrease blood lymphocyte proliferation responses, apparently independent of elevated corticosterone. However, unlike morphine, nicotinic agonists appear to act predominantly at peripheral receptors, suggesting that nicotinic receptors are downstream of opioid receptors in a centrally mediated opioid-induced immunomodulatory pathway.