Leishmania donovani amastigote component-induced colony-stimulating factor production by macrophages: modulation by morphine.

The neuroimmunomodulatory effects of opiates during microbial infections are now well known; however, not much is known during leishmaniasis. Here, we report the effects of morphine on purified approximately 12-kDa component of Leishmania donovani amastigote antigen (LDAA-12)-induced colony-stimulating factor (CSF) production by mouse peritoneal macrophages (PMs) in vitro. Low concentrations (1 x 10(-9) and 1 x 10(-11) M) of morphine significantly (P < 0.05) augmented the production of CSFs, whereas high concentrations (1 x 10(-3) and 1 x 10(-5) M) inhibited CSF production. Morphine exerted a similar concentration-dependent biphasic effect on the LDAA-12-induced elaboration of granulocyte (G)-macrophage (M)-CSF (GM-CSF) and M-CSF by PMs in their conditioned medium, as quantified by using enzyme-linked immunosorbent assay. Furthermore, selective agonists of mu-(DAGO) and delta-(DPDPE) opioid receptors also, respectively, augmented and inhibited the production of CSFs. Pretreatment of PMs with naloxone (1 x 10(-5) M) significantly (P < 0.05) blocked the augmenting effect of morphine. In contrast, at 1 x 10(-5) M, naloxone lacked any effect on the inhibitory effect of morphine; however, its 100-fold higher concentration partially blocked it. This study, apparently for the first time, demonstrates that morphine, via surface opioid receptors, biphasically modulates the LDAA-12-induced CSF production by PMs, in vitro. These results thus show the implications of opiate abuse on the outcome of therapeutic interventions in areas where both visceral leishmaniasis and drug abuse are rampant.

Morphine-induced neuroimmunomodulation in murine visceral leishmaniasis: the role(s) of cytokines and nitric oxide.

Opioid modulation of host resistance to infectious diseases is well documented; however, not much is known during visceral leishmaniasis (VL). Low doses of morphine, administered subcutaneously in Leishmania donovani-infected BALB/c mice, on days 0 and +15, significantly (p < 0.05) suppressed (1 mg/kg/day) or even sterile-cleared (2 mg/kg/day) the infection; paradoxically, high doses (10 and 30 mg/kg/day) exacerbated the infection. In vitro, low concentration (1 x 10(-9) and 1 x 10(-11) M) morphine treatment of L. donovani-infected mouse peritoneal macrophages (PM), endowed them with significant (p < 0.05) leishmanicidal activity, whereas a high-concentration (1 x 10(-5) M) treatment augmented intramacrophage parasite growth. Naloxone pre-treatment of infected-mice (4 mg/kg x 2) and of infected-PM (1 x 10(-5) M), blocked only the morphine low dose/concentration-induced protective effect. The splenocytes from protected mice and morphine low concentration-treated infected-PM, elaborated significantly (p < 0.05) enhanced levels of interleukin-12, interferon-gamma, tumor necrosis factor-alpha, granulocyte-macrophage colony-stimulating factor and nitrite in the culture medium; a high dose/concentration suppressed their elaboration. Curiously, only morphine high dose/concentration-treated infected mice splenocytes and infected PM, produced significantly (p < 0.05) increased quantity of transforming growth factor-beta1. Aminoguanidine, significantly (p < 0.05) blocked the morphine low dose/concentration-induced protective effect, in vivo and in vitro. This first study demonstrates dose-dependent biphasic modulatory effects of morphine in L. donovani-infected mice and PM, in vitro, apparently via nitric oxide-dependent mechanisms. These results thus demonstrate the implications of opiate abuse on the efficacy assessment of antileishmanial drugs and vaccines, and on the reactivation of latent VL in areas where both drug abuse and VL are rampant.

Neuroimmunomodulatory effects of morphine in Leishmania donovani-infected hamsters.

OBJECTIVE: The effect of morphine on host defense during Leishmania donovani infection in golden hamsters was studied. METHODS: Hamsters were intracardially infected with L. donovani amastigotes and then monitored by spleen touch print microscopic examination. Morphine and naloxone were administered subcutaneously and intraperitoneally, respectively. Leukocytes were counted by a hemocytometer, and ex vivo phagocytosis was determined by the examination of stained adherent macrophages. RESULTS: Low doses of morphine, 1.75 and 2.5 mg/kg x 2, administered subcutaneously on day 0 and day 15 significantly (p < 0.05) suppressed the infection, whereas high doses (20.0 and 50.0 mg/kg x 2) exacerbated the infection. On day 30, hamsters treated with low doses of morphine showed a significant (p < 0.05) increase in the number of circulating leukocytes and the pool size and phagocytic activity of peritoneal macrophages ex vivo; in hamsters treated with high doses, all these parameters appeared to be diminished. The bone marrow of morphine-treated hamsters showed a fall in total cellularity and no change in the number of monocytes; however, in those treated with low doses, the infection was completely eliminated by day 30, and paradoxically, a significant (p < 0.05) potentiation of infection was observed in hamsters treated with high doses. The spleens of hamsters treated with both low and high doses of morphine showed a significant (p < 0.05) decrease and increase in weight, respectively; treatment with low doses also caused an almost 2-fold increase in the percentage of monocytes. Morphine apparently exerted its protective effects via naloxone-sensitive opioid receptors; naloxone pretreatment did not affect the potentiation of infection. CONCLUSION: Conditional doses of morphine apparently biphasically modulated the course of L. donovani infection in hamsters, at least in part through macrophage-mediated mechanisms.