Activity of tryptophan hydroxylase and content of indolamines in discrete brain regions after a long-term hypoxic exposure in the rat

The influence of long-term hypoxia (10% O₂, 14 days) on in vivo activity of tryptophan hydroxylase and on 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentration in discrete brain regions of rats was assessed. The activity of tryptophan hydroxylase was determined through 5-hydroxytryptophan accumulation (5-HTPacc) following the administration of NSD 1015. The 5-HTPacc was significantly decreased in the dorsal and median raphe (56 and 42%, respectively) and in the striatum (62%). Both 5-HTPacc and the ratio of the concentrations of 5-HIAA to 5-HT were decreased in the nucleus raphe magnus (46 and 27%, respectively), the dorsomedian medulla oblongata (52 and 51%), the locus coeruleus (62 and 40%) and the anterior hypothalamic nucleus (30 and 50%). In contrast, 5-HTPacc was increased in the ventrolateral medulla oblongata (55%) and the preoptic area (83%), but the 5-HIAA/5-HT ratio was lower in these two regions. Finally, 5-HIAA/5-HT ratio was also decreased in the periventricular nucleus and in the frontal cortex. Since various patterns of variations in 5-HTPacc and in 5-HIAA/5-HT ratio were observed, the factors affecting serotonin metabolism in hypoxic rats can be different among brain regions. These results show that, in the rat, long-term hypoxia induces changes in in vivo activity of tryptophan hydroxylase and in 5-HT and 5-HIAA content of some brain structures; some of these biochemical changes may be linked to adaptative mechanisms.     

Heparin inhibits the antiparasitic and immune modulatory effects of human recombinant interferon-γ

Interferon-γ (IFN-γ) is a potent immune regulatory cytokine and is, in addition, involved in the induction of antiparasitic effector mechanisms in different cell types. The first step of IFN-γ action is its binding to a specific receptor. Furthermore, it has been shown that IFN-γ binds with a great affinity to the heparin-like structure of heparan sulfate, which is localized in basement membranes and on cell surfaces. In this study, we analyze the effect of heparin and heparan sulfate on three different IFN-γ-mediated activities inducible in human glioblastoma cells (87HG31 and 86HG39). We find firstly that heparin is able to inhibit IFN-γ-mediated induction of major histocompatibility complex (MHC) class II antigen expression on 87HG31 cells, an effect which can be abrogated by protamine. Secondly, we show that heparin inhibits the IFN-γ-induced toxoplasmostasis within 86HG39 cells in a dose-dependent fashion, and thirdly that heparin inhibits the IFN-γ-mediated induction of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase. In contrast to IFN-γ-induced effects, the activity of other cytokines, such as interleukin (IL)-1, IL-2 and IL-6, is not influenced by heparin. The possible mechanism of heparin-induced inhibition of IFN-γ is discussed.     

Lentivirus envelope protein exerts differential neuropathogenic effects depending on the site of expression and target cell

We investigated the neuropathogenic effects of feline immunodeficiency virus (FIV) envelope proteins in the context of both extracellular exposure and intracellular expression in feline neural cells. The envelope from the neurovirulent CSF-derived FIV V1 strain (V1-CSF) conferred infectivity to pseudotyped viruses in peripheral blood mononuclear cells (P < 0.01) in contrast to other cell types. Intracellular V1-CSF envelope expression in macrophages and microglia but not astrocytes resulted in the induction of host inflammatory genes contributing to neurotoxicity including IL-1beta, TNF-alpha, and indolamine 2',3'-dioxygenase (IDO) (P < 0.05) with concurrent neuronal death (P < 0.05). Upregulation of the endoplasmic reticulum stress genes was evident in brains from FIV-infected animals (P < 0.05) and in FIV-infected macrophages (P < 0.05) relative to controls. Intrastriatal implantation of an FIV envelope pseudotyped virus led to marked neuroinflammation and neuronal injury associated with neurobehavioral deficits (P < 0.01). Thus, lentivirus envelope proteins exert differential neuropathogenic effects through mechanisms that depend on the infected or exposed cell type.     

Anti-parasitic effector mechanisms in human brain tumor cells: Role of interferon-γ and tumor necrosis factor-α

Toxoplasma gondii, an obligate intracellular parasite, is able to replicate in human brain cells. We recently showed that interferon (IFN)-γ-activated cells from glioblastoma line 86HG39 were able to restrict Toxoplasma growth. The effector mechanism responsible for this toxoplasmostatic effect was shown by us to be the IFN-γ-mediated activation of indolamine 2,3-dioxygenase (IDO), resulting in the degradation of the essential amino acid tryptophan. In contrast, glioblastoma 87HG31 was unable to restrict Toxoplasma growth after IFN-γ activation, and IFN-γ-mediated IDO activation was weak. We observed that tumor necrosis factor (TNF)-α alone is unable to activate IDO or to induce toxoplasmostasis in any glioblastoma cell line tested. Interestingly, we found that TNF-α and IFN-γ were synergistic in the activation of IDO in glioblastoma cells 87HG31, 86HG39 and U373MG and in native astrocytes. This was shown by the measurement of enzyme activity as well as by the detection of IDO mRNA in TNF-α + IFN-γ activated cells. This IDO activity results in a strong toxoplasmostatic effect mediated by glioblastoma cells activated simultaneously by both cytokines. Antibodies directed against TNF-α or IFN-γ were able to inhibit IDO activity as well as the induction of toxoplasmostasis in glioblastoma cells stimulated with both cytokines. Furthermore, it was found that the addition of L -tryptophan to the culture medium completely blocks the antiparasitic effect. We therefore conclude that both TNF-α and IFN-γ may be involved in the defense against cerebral toxoplasmosis by inducing IDO activity as an antiparasitic effector mechanism in brain cells.     

Cellular immune reactions directed against Toxoplasma gondii with special emphasis on the central nervous system

Toxoplasma gondii is an obligate intracellular parasite which, after primary infection of humans, is maintained in a dormant state by the host cellular immune system. In the event of an acquired immunosuppression, those parasites surviving as dormant cysts in the host may undergo a change in status, proliferate and cause a life-threatening toxoplasmic encephalitis. Over the last decade much knowlege has accumulated concerning the immune response against T. gondii. This review focuses attention particularly on the anti-parasitic effector mechanisms and the cellular immune reactions in the central nervous system during the course of reactivated toxoplasmic encephalitis. Received: 20 August 1996     

Estrogen-signaling pathway: a link between breast cancer and melatonin oncostatic actions

BACKGROUND: Melatonin exerts oncostatic effects on different kinds of tumors, especially on endocrine-responsive breast cancer. The most common conclusion is that melatonin reduces the incidence and growth of chemically induced mammary tumors, in vivo, and inhibits the proliferation and metastatic behavior of human breast cancer cells, in vitro. Both studies support the hypothesis that melatonin oncostatic actions on hormone-dependent mammary tumors are mainly based on its anti-estrogenic actions. METHODS AND RESULTS: Two different mechanisms have been proposed to explain how melatonin reduces the development of breast cancer throughout its interactions with the estrogen-signaling pathways: (a) the indirect neuroendocrine mechanism which includes the melatonin down-regulation of the hypothalamic-pituitary reproductive axis and the consequent reduction of circulating levels of gonadal estrogens and (b) direct melatonin actions at tumor cell level. Melatonin's direct effect on mammary tumor cells is that it interferes with the activation of the estrogen receptor, thus behaving as a selective estrogen receptor modulator. Melatonin also regulates the activity of the aromatases, the enzymes responsible for the local synthesis of estrogens, thus behaving as a selective estrogen enzyme modulator. CONCLUSIONS: The same molecule has both properties to selectively neutralize the effects of estrogens on the breast and the local biosynthesis of estrogens from androgens, one of the main objectives of recent antitumor pharmacological therapeutic strategies. It is these action mechanisms that collectively make melatonin an interesting anticancer drug in the prevention and treatment of estrogen-dependent tumors, since it has the advantage of acting at different levels of the estrogen-signaling pathways.     

Inducible anti-parasitic effector mechanisms in human uroepithelial cells: tryptophan degradation vs. NO production

In murine cells the most important effector mechanism directed against the intracellular pathogen Toxoplasma gondii is the production of toxic nitrogen oxides. In contrast the induction of the tryptophan degrading enzyme indolamine 2,3-dioxygenase (IDO) has been described to be the most effective anti-parasitic mechanism in most human cells. In this report we analysed IDO induction and NO production in the human uroepithelial carcinoma cell line RT4. We found that after stimulation with IFN-γ these cells were able to restrict toxoplasma growth. This was due to an activation of IDO, and the anti-parasitic effect mediated by RT4 cells was abrogated by the addition of l-tryptophan. In addition we found that the costimulation of RT4 cells with IL-1 and IFN-γ results in the production of nitric oxide, and that in RT4 cells stimulated with both these cytokines, IDO activity and toxoplasmostasis was lower than in cells stimulated with IFN-γ alone. This IL-1-mediated inhibition of IFN-γ-induced IDO activity and toxoplasmostasis could be blocked by monomethyl l-arginine, an inhibitor of NO production. We therefore conclude that the induction of indolamine 2,3-dioxygenase activity in human cells is a very important effector mechanism directed against Toxoplasma gondii, and that in human cells the production of NO might be involved in the regulation of IDO activity Received: 26 August 1998     

Behavioral impairments after lesions of the nucleus basalis by ibotenic acid and quisqualic acid

Ibotenic acid (IBO) or quisqualic acid (QUIS) was infused into the region of the nucleus basalis magnocellularis (NBm) in F344 rats in order to behaviorally and biochemically characterize the effects of these two neurotoxins. QUIS infusion resulted in a slightly higher depletion of choline acetyltransferase (ChAT) activity in both anterior and posterior regions of cortex than did lesions caused by infusion of IBO. Both QUIS- and IBO-treated rats demonstrated significantly longer latencies than controls to find a hidden platform in a Morris water maze task. In addition, QUIS-treated rats performed significantly better than IBO-treated rats in the water maze. Analysis of swim speed and open field behavior did not show significant differences in general motor activity. Passive avoidance retention was unaffected by either neurotoxin. Cortical amino acid levels, [3H]neurotensin binding, dopamine, norepinephrine, and serotonin levels were unaffected by either neurotoxin. The levels of HVA and 5-HIAA in the IBO and QUIS groups were significantly reduced compared to controls, but were not significantly different from each other. Histological examination showed greater damage to non-NBm structures with IBO than with QUIS, including the basolateral nucleus of the amygdala and the reticular formation of the thalamus. The greater behavioral deficit seen after IBO lesions may be due to damage to other areas rather than differences in the extent of depletion of corticai ChAT, amino acids, catecholamines or indolamines.