Neuroprotection by melatonin on astrocytoma cell death.

Glial cells play an active role in the homeostatic regulation of the central nervous system (CNS). Astrocytes, the most abundant glial cell types in the brain, provide mechanical and metabolic support for neurons. The regulation of astrocyte apoptosis, therefore, is important for physiological and pathological processes in the CNS. Melatonin is a neurohormone that regulates target cells via binding to specific high-affinity plasma membrane receptors, MT1/MT2. In addition to regulating circadian rhythms, melatonin has recently attracted much interest for its potential regulation of cell apoptosis. We recently showed that melatonin antagonizes apoptosis on U937 cells via intersecting signal transduction events involving binding to MT1/MT2 and activation of lipoxygenase. Here we describe the neuroprotective potential of melatonin, showing that melatonin significantly reduces damage-induced apoptosis in astrocytoma cells. The mechanism of protection is different from that shown in U937 cells, because it does not involve MT1/MT2 or lipoxygenase; likewise, Ca(2+) influx is not involved. Intriguingly, inhibition of phospholipase C (PLC) with neomycin reverses melatonin protection, suggesting that a PLC-dependent signal transduction, different from that triggered by MT1/MT2, is involved in the antiapoptotic pathway of melatonin.

Effects of carbon nanotubes on human monocytes.

Carbon nanotubes are considered to be one of the novel most attractive materials in nanotechnology. Because of their multiple industrial and biomedical applications, thorough studies on their toxicity and biocompatibility become a priority in order to prevent possible health risks. In this study the effects of multiwalled carbon nanotubes (MWCNT) on healthy monocytes from human peripheral blood were investigated. The results indicate that MWCNT exert a cytotoxic effect on monocytes, inducing cell death and increasing the extent of apoptosis induced by a chemotherapic agent. This cytotoxic effect may have important implications, and much attention in terms of evaluation of exposure risks is recommended.

Prevention of TNBS-induced colitis by different Lactobacillus and Bifidobacterium strains is associated with an expansion of gammadeltaT and regulatory T cells of intestinal intraepithelial lymphocytes.

BACKGROUND: Probiotics may protect against inflammatory bowel disease through regulation of lamina propria lymphocytes (LPLs) function. Data are lacking on possible involvement of intraepithelial lymphocytes (IELs). The aim of this study was to investigate whether different probiotic mixtures prevented gut inflammatory disease and the role of both IELs and LPLs. METHODS: BALB/c mice received 2 probiotic mixtures orally for 3 weeks, as Mix1 (Lactobacillus acidophilus and Bifidobacterium longum), or Mix2 (Lactobacillus plantarum, Streptococcus thermophilus, and Bifidobacterium animalis subsp. lactis). Colitis was induced by intrarectal administration of trinitrobenzene sulfonic acid (TNBS). Probiotics in stools were analyzed by real-time polymerase chain reaction (PCR). Colon subpopulations of IELs and LPLs were assayed by flow cytometry. Serum cytokines were measured by cytometric bead array (CBA). RESULTS: All probiotics colonized the intestine. The 2 mixtures prevented the TNBS-induced intestinal damage, and Mix1 was the most effective. The Mix1 protection was associated with a reduction in CD4(+) cells of IELs and LPLs, an increase in gammadeltaT cells of IELs, and a decrease in gammadeltaT cells of LPLs. An expansion of T regulatory (Treg) cells of IELs was induced by Mix1 and Mix2. Both probiotic mixtures inhibited tumor necrosis factor (TNF)-alpha and monocyte chemotactic protein (MCP)-1 production and upregulated interleukin (IL)-10. In addition, Mix1 prevented the TNBS-induced increase of IL-12 and interferon (IFN)-gamma. CONCLUSIONS: The 2 probiotic mixtures were able to prevent the TNBS-induced colitis; the L. acidophilus and B. longum mixture was the most effective. Other than an involvement of LPLs, our results report a novel importance of the IELs population in probiotic protection.

Evidence for a role of glycosphingolipids in CXCR4-dependent cell migration.

Chemotaxis induction is a major effect evoked by stimulation of the chemokine receptor CXCR4 with its sole ligand CXCL12. We now report that treatment of CHP-100 human neuroepithelioma cells with the glucosylceramide synthase (GCS) inhibitor DL-threo-1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol inhibits CXCR4-dependent chemotaxis. We provide evidence that the phenomenon is not due to unspecific effects of the inhibitor employed and that inhibition of GCS neither affects total or plasmamembrane CXCR4 expression, nor CXCL12-induced Ca(2+) mobilization. The effects of the GCS inhibitor on impairment of CXCL12-induced cell migration temporally correlated with a pronounced downregulation of neutral glycosphingolipids, particularly glucosylceramide, and with a delayed and more moderate downregulation of gangliosides; moreover, exogenously administered glycosphingolipids allowed resumption of CXCR4-dependent chemotaxis. Altogether our results provide evidence, for the first time, for a role glycosphingolipids in sustaining CXCL12-induced cell migration.

Melatonin as an apoptosis antagonist.

The pineal hormone melatonin (Mel), in addition to having a well-established role as a regulator of circadian rhythms, modulates nonneural compartments by acting on specific plasma membrane receptors (MT1/MT2) present in many different cell types. Mel plays immunomodulatory roles and is an oncostatic and antiproliferative agent; this led to the widespread belief that Mel may induce or potentiate apoptosis on tumor cells, even though no clear indications have been presented so far. Here we report that Mel is not apoptogenic on U937 human monocytic cells, which are known to possess MT1 receptors at the times (up to 48 h) and doses (up to 1 mM) tested. Mel does not even potentiate apoptosis, but instead, significantly reduces apoptosis induced by both cell-damaging agents (intrinsic pathway) and physiological means (extrinsic pathway). The doses required for the antiapoptotic effect (>or=100 microM) are apparently not compatible with receptor stimulation (receptor affinity<1 nM). However, receptor involvement cannot be ruled out, because we discovered that the actual Mel concentration active on cells was lower than the nominal one because of sequestration by fetal calf serum (FCS). Accordingly, in FCS-free conditions, Mel doses required for a significant antiapoptotic effect are much lower.

Oxidative upregulation of Bcl-2 in healthy lymphocytes.

In many cell systems, pharmacological glutathione (GSH) depletion with the GSH neosynthesis inhibitor buthionine sulfoximine (BSO) leads to cell death and highly sensitizes tumor cells to apoptosis induced by standard chemotherapeutic agents. However, some tumor cells upregulate Bcl-2 in response to BSO, thus surviving the treatment and failing to be chemosensitized. Cell lines of monocytic and lymphocytic origins respond to BSO treatment in an opposite way, lymphocytes being chemosensitized and unable to transactivate Bcl-2. In this article we investigate the response to BSO of lymphocytes freshly isolated from peripheral blood of healthy donors. After ensuring that standard separation procedures do not alter per se lymphocytes redox equilibrium nor Bcl-2 levels in the first 24 h of culture, we show that BSO treatment promotes the upregulation of Bcl-2, with a mechanism involving the increased radical production consequent to GSH depletion. Thus, BSO treatment may increase the differential cytocidal effect of cytotoxic drugs in tumor versus normal lymphocytes.