The ALIAmide palmitoylethanolamide and cannabinoids, but not anandamide, are protective in a delayed postglutamate paradigm of excitotoxic death in cerebellar granule neurons

The amino acid L-glutamate is a neurotransmitter that mediates fast neuronal excitation in a majority of synapses in the central nervous system. Glutamate stimulates both N-methyl-D-aspartate (NMDA) and non-NMDA receptors. While activation of NMDA receptors has been implicated in a variety of neurophysiologic processes, excessive NMDA receptor stimulation (excitotoxicity) is thought to be primarily responsible for neuronal injury in a wide variety of acute neurological disorders including hypoxia-ischemia, seizures, and trauma. Very little is known about endogenous molecules and mechanisms capable of modulating excitotoxic neuronal death. Saturated N-acylethanolamides like palmitoylethanolamide accumulate in ischemic tissues and are synthesized by neurons upon excitatory amino acid receptor activation. Here we report that palmitoylethanolamide, but not the cognate N-acylamide anandamide (the ethanolamide of arachidonic acid), protects cultured mouse cerebellar granule cells against glutamate toxicity in a delayed postagonist paradigm. Palmitoylethanolamide reduced this injury in a concentration-dependent manner and was maximally effective when added 15-min postglutamate. Cannabinoids, which like palmitoylethanolamide are functionally active at the peripheral cannabinoid receptor CB2 on mast cells, also prevented neuron loss in this delayed postglutamate model. Furthermore, the neuroprotective effects of palmitoylethanolamide, as well as that of the active cannabinoids, were efficiently antagonized by the candidate central cannabinoid receptor (CB1) agonist anandamide. Analogous pharmacological behaviors have been observed for palmitoylethanolamide (ALI-Amides) in downmodulating mast cell activation. Cerebellar granule cells expressed mRNA for CB1 and CB2 by in situ hybridization, while two cannabinoid binding sites were detected in cerebellar membranes. The results suggest that (i) non-CB1 cannabinoid receptors control, upon agonist binding, the downstream consequences of an excitotoxic stimulus; (ii) palmitoylethanolamide, unlike anandamide, behaves as an endogenous agonist for CB2-like receptors on granule cells; and (iii) activation of such receptors may serve to downmodulate deleterious cellular processes following pathological events or noxious stimuli in both the nervous and immune systems.

Mast cell activation causes delayed neurodegeneration in mixed hippocampal cultures via the nitric oxide pathway

Mast cells are pleiotropic bone marrow-derived cells found in mucosal and connective tissues and in close apposition to neurons, where they play important roles in tissue inflammation and in neuroimmune interactions. Connective tissue mast cells, with which intracranial mast cells share many characteristics, contain cytokines that can cause inflammation. Here, we report that myelin basic protein, a major suspected immunogen in multiple sclerosis, as well as an antigenic stimulus, provokes mast cells to trigger a delayed cytotoxicity for neurons in mixed neuron-gila cultures from hippocampus. Neurotoxicity required a prolonged period (12 h) of mast cell incubation, and appeared to depend largely on elaboration of the free radical nitric oxide by astrocytes. Activation of astrocytes was mediated, in part, by mast cell-secreted tumor necrosis factor-alpha. Myelin basic protein and 17 beta-estradiol had a synergistic action on the induction of mast cell-associated neuronal injury. The cognate mast cell line RBL-2H3, when subjected to an antigenic stimulus, released tumor necrosis factor-alpha which, together with exogenous interleukin-1 beta (or interferon-gamma), induced astroglia to produce neurotoxic quantities of nitric oxide. A small but significant proportion of mast cell-derived neurotoxicity under the above conditions occurred independently of glial nitric oxide synthase induction. Further, palmitoylethanolamide, which has been reported to reduce mast cell activation by a local autacoid mechanism, decreased neuron loss resulting from mast cell stimulation in the mixed cultures but not that caused by direct cytokine induction of astrocytic nitric oxide synthase. These results support the notion that brain mast cells could participate in the pathophysiology of chronic neurodegenerative and inflammatory diseases of the nervous system, and suggest that down-modulation of mast cell activation in such conditions could be of therapeutic benefit.

Mast cells express a peripheral cannabinoid receptor with differential sensitivity to anandamide and palmitoylethanolamide

Mast cells are multifunctional bone marrow-derived cells found in mucosal and connective tissues and in the nervous system, where they play important roles in tissue inflammation and in neuroimmune interactions. Very little is known about endogenous molecules and mechanisms capable of modulating mast cell activation. Palmitoylethanolamide, found in peripheral tissues, has been proposed to behave as a local autacoid capable of downregulating mast cell activation and inflammation. A cognate N-acylamide, anandamide, the ethanolamide of arachidonic acid, occurs in brain and is a candidate endogenous agonist for the central cannabinoid receptor (CB1). As a second cannabinoid receptor (CB2) has been found in peripheral tissues, the possible presence of CB2 receptors on mast cells and their interaction with N-acylamides was investigated. Here we report that mast cells express both the gene and a functional CB2 receptor protein with negative regulatory effects on mast cell activation. Although both palmitoylethanolamide and anandamide bind to the CB2 receptor, only the former downmodulates mast cell activation in vitro. Further, the functional effect of palmitoylethanolamide, as well as that of the active cannabinoids, was efficiently antagonized by anandamide. The results suggest that (i) peripheral cannabinoid CB2 receptors control, upon agonist binding, mast cell activation and therefore inflammation; (ii) palmitoylethanolamide, unlike anandamide, behaves as an endogenous agonist for the CB2 receptor on mast cells; (iii) modulatory activities on mast cells exerted by the naturally occurring molecule strengthen a proposed autacoid local inflammation antagonism (ALIA) mechanism; and (iv) palmitoylethanolamide and its derivatives may provide antiinflammatory therapeutic strategies specifically targeted to mast cells ("ALIAmides").

Mast cells synthesize, store, and release nerve growth factor

Mast cells and nerve growth factor (NGF) have both been reported to be involved in neuroimmune interactions and tissue inflammation. In many peripheral tissues, mast cells interact with the innervating fibers. Changes in the behaviors of both of these elements occur after tissue injury/inflammation. As such conditions are typically associated with rapid mast cell activation and NGF accumulation in inflammatory exudates, we hypothesized that mast cells may be capable of producing NGF. Here we report that (i) NGF mRNA is expressed in adult rat peritoneal mast cells; (ii) anti-NGF antibodies clearly stain vesicular compartments of purified mast cells and mast cells in histological sections of adult rodent mesenchymal tissues; and (iii) medium conditioned by peritoneal mast cells contains biologically active NGF. Mast cells thus represent a newly recognized source of NGF. The known actions of NGF on peripheral nerve fibers and immune cells suggest that mast cell-derived NGF may control adaptive/reactive responses of the nervous and immune systems toward noxious tissue perturbations. Conversely, alterations in normal mast cell behaviors may provoke maladaptive neuroimmune tissue responses whose consequences could have profound implications in inflammatory disease states, including those of an autoimmune nature.

Neurotrophin-3 upregulates NGF receptors in a central nervous system glial cell line

The low-affinity nerve growth factor (NGF) receptor (LNGFR) binds the neurotrophins NGF, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) with similar affinities. Here we report on the ability of NT-3 to regulate the expression of the LNGFR in C6 glioma cells. LNGFR-like immunoreactivity (LNGFR-IR) was examined in C6 cells treated for 16 h with NT-3 and exposed to the antibody 192-IgG followed by immunoglobulins conjugated with colloidal gold by means of ultrastructural morphometric analysis. Untreated C6 cells exhibited some positive LNGFR-IR, while C6 cells treated with NT-3 displayed significantly increased (2.3 fold) LNGFR-IR. The increase in LNGFR protein was accompanied by a greater quantity of LNGFR mRNA in NT-3-treated cells. Thus, LNGFR can be upregulated by the structurally related neurotrophin NT-3.

Nerve growth factor (NGF) receptors in a central nervous system glial cell line: upregulation by NGF and brain-derived neurotrophic factor

The neurotrophic proteins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are related in their primary amino acid structures. In this study we investigated the extent to which the low-affinity NGF receptor (LNGFR) in C6 glioma cells can discriminate between the neurotrophins NGF and BDNF. LNGFR-immunoreactivity (IR) was studied in C6 cells treated for 16 hr with NGF (50 ng/ml) or BDNF (10 ng/ml), using immunogold labelling and electron microscopic morphometric analysis. The cells were exposed to the anti-NGFR antibody 192-IgG, followed by immunoglobulin conjugated with colloidal gold. Untreated C6 cells exhibited some surface gold label (positive LNGFR-IR). Cells treated with NGF or BDNF displayed significantly increased LNGFR-IR on all surfaces in terms of gold labeling, which was more pronounced in NGF-treated cells. LNGFR-IR was also localized in coated endocytotic vesicles, in smooth endoplasmic reticulum, and in secondary multivesicular lysosomes in neurotrophin-treated and untreated cells. The increase in LNGFR protein was further substantiated by a correspondingly higher content of LNGFR mRNA detected after 15 hr of either NGF or BDNF treatment. These results suggest that the LNGFR in glial cells can be upregulated by the structurally related neurotrophins NGF and BDNF.