Peptide opioids and morphine effects on inflammatory process

Primary headache and silent myocardial ischemia in patients with coronary artery disease

OBJECTIVE

The mechanisms by which migraine is linked to ischemic vascular disease remain uncertain and are likely to be complex. The aim of this study was to investigate the correlation between silent myocardial ischemia (SMI) and a history of documented primary headache in a large population of patients with exercise-induced myocardial ischemia.

METHODS

The study involved 1,427 consecutive patients (918 symptomatic and 509 asymptomatic patients) with exercise-induced myocardial ischemia and documented coronary artery disease (CAD).

RESULTS

Patients with anginal symptoms during exercise-induced myocardial ischemia had a significantly higher prevalence of primary headache than those without (41 vs. 30%, p < 0.001). Patients with angina pectoris in daily life also had greater prevalence of primary headache than those without anginal symptoms (37 vs. 20%; p < 0.0001). Symptomatic patients during percutaneous transluminal coronary angiography or myocardial infarction had a greater prevalence of primary headache than asymptomatic patients (p < 0.001 and p = 0.005, respectively).

CONCLUSIONS

Our data suggest that a history of headache in CAD population is correlated to a high probability of anginal symptoms and a decreased probability of SMI. The anamnestic absence of headache requires a close monitoring for patients with risk factors for CAD, because this population seems to have a lower susceptibility to pain and the risk of developing SMI might be increased.

Increased production of inflammatory cytokines in patients with silent myocardial ischemia

OBJECTIVES

The aim of the study was to examine the inflammatory cytokines in patients with myocardial ischemia to evaluate whether silent ischemia patients exhibit any particular cytokine pattern.

BACKGROUND

Silent myocardial ischemia is frequently observed in patients with coronary artery disease. Various endogenous mechanisms control a patient's perceived intensity of pain. Among them, the inflammatory process and the related cytokine production are known to modulate the threshold for activating the primary afferent nociceptors.

METHODS

Seventy-eight patients with reproducible exercise-induced myocardial ischemia were studied: 34 symptomatic patients, with rest and/or stress angina; 44 asymptomatic patients, with no symptoms during daily life activities or during positive exercise stress test. Venous blood samples were taken from all patients to evaluate the expression of CD11b receptors both on neutrophils and monocytes. Frozen plasma samples (at -80 degrees C) were used to quantify the anti-inflammatory (interleukin-4 and -10, transforming growth factor-beta) and the proinflammatory cytokines (tumor necrosis factor-alpha, interferon-gamma, interleukin-1beta and -6).

RESULTS

In asymptomatic patients lower CD11b receptor expression and higher concentration of anti-inflammatory cytokines were observed. Proinflammatory cytokine production was similar in the two groups.

CONCLUSIONS

The data suggest that an "anti-inflammatory pattern" of cytokine production correlates with silent ischemia and that the immune and inflammatory system activation may be crucial for angina symptoms.

Opioid receptors on bone marrow neutrophils modulate chemotaxis and CD11b/CD18 expression

Opiates impair neutrophil-mediated host defense, but the involvement of kappa-opioid receptors in this action has not been defined. The selective kappa-opioid receptor agonist [trans-(+)3,4-dichloro-N-methyl-N[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide methanesulfonate inhibited macrophage inflammatory protein-2-induced chemotaxis of bone marrow neutrophils from C57BL/6 mice. Its effects were concentration-dependent (pIC(50)=10.40+/-0.61) and inhibited by naloxone (K(e)=0.27 nM). The kappa-opioid receptor agonists bremazocine and ICI-204, 488 also inhibited chemotaxis, as did the respective mu- and delta-opioid receptor agonists [D-Ala(2), N-methyl-Phe(4), Gly(5)-ol]enkephalin and [D-Pen(2,5)]enkephalin albeit with lower potencies. U-50,488H also decreased neutrophil expression of the beta(2) integrin CD11b/CD18 (Mac-1) and adhesion to plastic in a naloxone-reversible manner. The results indicate that kappa-opioid receptors expressed by neutrophils rapidly modulate chemotaxis and adhesion in vitro.

Morphine attenuates leukocyte/endothelial interactions

Gram-negative sepsis and subsequent endotoxic shock after surgery remain problematic in the United States and throughout the world. While morphine is widely prescribed for postoperative trauma pain management, there are reports that morphine may compromise the immune system and contribute to postoperative sepsis. The current study tested the hypothesis that morphine attenuates leukocyte rolling and sticking in both arterioles and venules via nitric oxide production. Nude mice implanted with slow-release morphine pellets were used in this study. The dorsal skinfold chamber model for intravital fluorescence microscopy on awake mice was used. Leukocyte/endothelial interactions were evaluated after bolus injection of oxidized low density lipoprotein. Morphine was found to significantly attenuate leukocyte rolling and sticking in both the arterial and venular side of the microcirculation. This attenuation was reversed by simultaneous implantation of naloxone pellets. The mechanisms of this attenuation were further investigated by administration of the nitric oxide synthase inhibitors NG-nitro-l-arginine (NOLA) and aminoguanidine (AG) in drinking water. NOLA was found to significantly reverse this morphine-induced attenuation of leukocyte rolling and sticking in both arterioles and venules. However, AG did not have the same effect. The results indicate that morphine interferes with leukocyte/endothelial cell interactions via stimulation of nitric oxide production.

Scoring the mouse formalin test: validation study

The formalin test is a well-established model for assessing nociceptive processes and analgesic drug effects. Previous studies have provided statistical validation of optimal procedures for conducting and scoring the rat formalin test. In the mouse model, formalin concentration has been subjected to validation studies. The present research extended previous work by subjecting two additional parameters - the behaviors that should be scored and the optimal interval for second-phase formalin response - to empirical validation. Five behavioral (formalin-induced favoring, lifting, and biting/licking, rearing and locomotion) and two physiological measures (paw weight and paw thickness increases reflective of formalin-induced inflammation) were examined under four formalin concentrations (Exp. 1: 0.5, 1.0, 5.0, and 10.0%/25µl formalin) or under four morphine doses (Exp. 2: 0.0, 1.0, 5.0, and 10.0 mg/kg, s.c. with 5% formalin concentration). Multiple regression analyses defined the optimal second-phase formalin response in outbred, Swiss-Webster mice as 15-35 min post formalin injection, and revealed that the second-phase response is best characterized by the cumulative time spent biting/licking the injected paw. Finally, paw physiological measures provided convergent evidence of nociceptive and antinociceptive processes in the mouse formalin test. Copyright 1998European Federation of Chapters of the International Association for the Study of Pain.

Opiate, cannabinoid, and eicosanoid signaling converges on common intracellular pathways nitric oxide coupling

Scientific fields as they emerge initially appear to be unrelated to other projects even if they are in a similar area of interest. This is especially true in the case of opiate, cannabinoid, and eicosanoid signaling processes. In this limited speculative review, we attempt to examine aspects of their intracellular cascading signaling systems for their commonalities. We find intracellular calcium mobilization, nuclear factor kappa B involvement, adenylate cyclase activity, and, finally, constitutive nitric oxide release to be converging points for these signaling processes, occurring by separate and distinct receptor-mediated effector systems. Phosphokinase C, mitogen activated protein kinase, and cytosolic phospholipase A2 also represent points of common impact. In this regard, aspirin also appears to be involved in an aspect of this signaling convergence. We conclude that many of the physiological observations regarding the actions of these signaling molecules, for example, immunosuppression, neurotransmission, vasodilation, cellular adherence, and cytotoxicity, can now be understood by considering their converging biochemical cascades.

Opioid modulation of immune responses: effects on phagocyte and lymphoid cell populations

The literature describing effects of morphine on cells of the immune system points to the clear conclusion that morphine given in vivo suppresses a variety of immune responses that involve the major cell types in the immune system, including natural killer (NK) cells, T cells, B cells, macrophages and polymorphonuclear leukocytes (PMNs). Depression of NK cell activity has been reported in humans, monkeys and rodents. Similarly, responses of T cells are depressed by morphine, as assessed by inhibition of induction of delayed-type hypersensitivity reactions and cytotoxic T-cell activity, modulation of T-cell antigen expression, and depression of responses to T-cell mitogens. Effects on T cells have been reported in humans, monkeys and rodents. Effects of morphine on B-cell activity have mainly been tested in rodents using assays of antibody formation, which also require macrophages and T cells, preventing a conclusion as to the cell type being affected. Consistent effects on phagocytic cell function have been reported in rodents given morphine. In contrast, studies on immunomodulatory effects of morphine added to cells of the immune system in vitro have shown robust effects on some of these cell types, but not others. There is a rich literature demonstrating downregulation of phagocytic cell function by morphine, particularly for human peripheral blood mononuclear cells (PBMCs) and PMNs. Phagocytosis, chemotactic responses, interleukin production, and generation of activated oxygen intermediates and arachidonic acid products have all been reported to be inhibited. On the contrary, the literature does not support direct effects of morphine on NK cell function, is inconclusive concerning effects on B cells, and provides limited evidence for effects on T cells. The divergence between the in vivo and in vitro data suggests that effects on some cells in the immune system observed after in vivo morphine are probably not direct, but mediated. In aggregate, the literature supports the existence of an in vivo neural-immune circuit through which morphine acts to depress the function of all cells of the immune system. Further, there is strong evidence that morphine can directly depress the function of macrophages and PMNs, and modulate expression of one type of T-cell surface marker. There is, however, little evidence for direct effects of morphine on NK cells and B cells. A further complication emerges from reports of immunopotentiation of immune function in in vitro assays using endogenous opioids. The possibility of different receptors for endogenous and exogenous opioids or of interactions among the activated opioid receptors may account for these opposing effects.

Granulocyte defects and opioid receptors in chronic exposure to heroin or methadone in humans

In order to elucidate better the immunological effect of opioid abuse in the absence of HIV infection as a confounding factor, granulocyte function was investigated in three groups of HIV-negative subjects, including 20 active parenteral heroin abusers (H), 20 long-term methadone-maintained former opiate abusers (M) and 20 healthy controls (C). Chemotaxis to N-formyl methionyl-leucyl-phenylalanine (fMLP), casein and activated plasma were markedly and similarly reduced (approx. 50%) in both H and M groups, as was true for superoxide production after fMLP and PMA stimulation, 47% decrease of C values. Polymorphonuclear (PMN) of H and M subjects also exhibited a very marked and similar reduction in the expression of CD11b/CD18 integrin receptors after fMLP treatment, with values that were less than 10% of those in controls, as observed by flow cytometry. In parallel, PMN of H and M individuals presented an approximately four-fold increase in opioid receptors numbers compared to controls, a significant inverse correlation existing between the increase in opiate receptors and defective chemotaxis. The possible mechanism underlying the observed changes in PMN of H and M individuals is discussed.

Immunosuppressive effects of morphine on immune responses in mice

Implantation of a 75-mg morphine sulfate pellet subcutaneously into mice of different strains and sexes caused profound immunosuppression of their spleen cell primary in vitro antibody responses to sheep red blood cells. No sex differences were observed. In mice of the C3H lineage, naltrexone blocked the immunosuppression. In mice in the C57BL/6J lineage, naltrexone was ineffective in blocking the effects of morphine and was itself suppressive. In beige C57BL/6J bgJ/bgJ mice, placebo pellets were also suppressive. The mechanism of the morphine-induced immunosuppression was investigated in C3HeB/FeJ mice. Addition of normal splenic macrophages to in vitro cultures restored immune responses, as did IL-1, IL-6 and IFN-gamma, suggesting that morphine-induced immunosuppression is due to a deficit in macrophage function. Morphine pellet implantation induced splenic atrophy. Whether suppression is attributable to decreased macrophage numbers or to decreased functional capacity of individual macrophages is currently under investigation.

Interaction between (-)naloxone and morphine in modifying superoxide generation from human granulocytes

The effect of the opioid agonist morphine and of the (-) and (+) stereoisomers of the antagonist naloxone were studied on superoxide generation from human granulocytes. Morphine or naloxone had no effect on basal or phorbol 12-myristate 13-acetate (PMA)-stimulated superoxide generation. Combined equimolar (-)naloxone and morphine concentrations (0.1 pM-0.1 microM) inhibited PMA-stimulated superoxide generation, while combined (+)naloxone and morphine had no effect. The stereospecific effect of naloxone suggests the involvement of opioid receptors. Thus, inhibition of superoxide generation by combined (-)naloxone and morphine could result from the unmasking of non opioid effects of morphine. It is suggested that the opioid control of oxidative metabolism in human granulocytes could involve multiple receptors mediating opposite effects.