C Zoia

Glutamate transporters in platelets: EAAT1 decrease in aging and in Alzheimer's disease

Platelets release glutamate upon activation and are an important clearance system of the amino acid from blood, through high-affinity glutamate uptake, similar to that described in brain synaptosomes. Since platelet glutamate uptake is decreased in neurodegenerative disorders, we performed a morphological and molecular characterization of platelet glutamate transporters. The three major brain glutamate transporters EAAT1, EAAT2 and EAAT3 are expressed in platelets, with similar molecular weight, although at lower density than brain. A Na(+)-dependent-high-affinity glutamate uptake was competitively inhibited by known inhibitors but not by dihydrokainic acid, suggesting platelet EAAT2 does not play a major role in glutamate uptake at physiological conditions. We observed decreased glutamate uptake V(max), without modification of transporter affinity, in aging, which could be linked to the selective decrease of EAAT1 expression and mRNA. Moreover, in AD patients we found a further EAAT1 reduction compared to age-matched controls, which could explain the decrease of platelet uptake previously described. Platelet glutamate transporters may be used as peripheral markers to investigate the role of glutamate in patients with neuropsychiatric disorders.

Fibroblast glutamate transport in aging and in AD: correlations with disease severity

Altered glutamate transport and aberrant EAAT1 expression were shown in Alzheimers disease (AD) brains. It is presently unknown whether these modifications are a consequence of neurodegeneration or play a pathogenetic role. However, recent findings of decreased glutamate uptake, EAAT1 protein and mRNA in AD platelets suggest that glutamate transporter modifications may be systemic and might explain the decreased glutamate uptake. We now used primary fibroblast cultures from 10 AD patients to further investigate the specific involvement of glutamate transporters in this disorder and in normal aging. Decreased glutamate uptake (p<0.001), EAAT1 expression (p<0.05) and mRNA (p<0.01) were observed in aged people, compared to younger controls. In AD fibroblasts, compared to age-matched controls, we observed further reductions of glutamate uptake (p<0.0005) and EAAT1 expression (p<0.005), while EAAT1 mRNA increase (p<0.001) was shown. EAAT1 parameters were mutually correlated (p<0.01) and correlations were shown with dementia severity (p<0.05 MMSE-expression, p<0.005 MMSE-mRNA). We suggest fibroblast cultures as possible ex vivo peripheral model to study the glutamate involvement and possible molecular and therapeutic targets in AD.

Expression and distribution of 'high affinity' glutamate transporters GLT1, GLAST, EAAC1 and of GCPII in the rat peripheral nervous system.

l‐Glutamate is one of the major excitatory neurotransmitters in the mammalian central nervous system, but recently it has been shown to have a role also in the transduction of sensory input at the periphery, and in particular in the nociceptive pathway. An excess of glutamate is implicated in cases of peripheral neuropathies as well. Conventional therapeutic approaches for treating these diseases have focused on blocking glutamate receptors with small molecules or on reducing its synthesis of the receptors through the inhibition of glutamate carboxypeptidase II (GCPII), the enzyme that generates glutamate. In vivo studies have demonstrated that the pharmacological inhibition of GCPII can either prevent or treat the peripheral nerve changes in both BB/Wor and chemically induced diabetes in rats. In this study, we characterized the expression and distribution of glutamate transporters GLT1, GLAST, EAAC1 and of the enzyme GCPII in the peripheral nervous system of female Wistar rats. Immunoblotting results demonstrated that all glutamate transporters and GCPII are present in dorsal root ganglia (DRG) and the sciatic nerve. Immunofluorescence localization studies revealed that both DRG and sciatic nerves were immunopositive for all glutamate transporters and for GCPII. In DRG, satellite cells were positive for GLT1 and GCPII, whereas sensory neurons were positive for EAAC1. GLAST was localized in both neurons and satellite cells. In the sciatic nerve, GLT1 and GCPII were expressed in the cytoplasm of Schwann cells, whereas GLAST and EAAC1 stained the myelin layer. Our results give for the first time a complete characterization of the glutamate transporter system in the peripheral nervous system. Therefore, they are important both for understanding glutamatergic signalling in the PNS and for establishing new strategies to treat peripheral neuropathies.

Enhanced GM1 ganglioside catabolism in cultured fibroblasts from Alzheimer patients

The metabolic processing of GM1 ganglioside, exogenously administered to cultured skin fibroblasts, was investigated on cells obtained from patients affected with Alzheimer disease, in comparison with age-matched control subjects. Cultured fibroblasts were incubated with GM1 ganglioside, [(3)H]-radiolabelled at the sphingosine moiety. It was observed that the extent of tritiated GM2 and GM3 ganglioside formation was higher in AD fibroblasts than in control cells. The activity of acidic beta-D-galactosidase, responsible of GM1 hydrolysis to GM2 within lysosomes, assayed in vitro on cell lysates, was increased in AD fibroblasts in comparison with control cells. These data suggest that up-regulation of lysosomal enzymes could be responsible of the enhanced GM1 catabolism in AD fibroblasts. Finally, it was found that the extent of GM1 hydrolysis in AD fibroblasts was inversely correlated with the mini-mental score index of patients. The increased hydrolysis rate of sphingolipids could be taken as peripheral hallmark of Alzheimers disease patients.

Extracorporeal photochemotherapy: A safety and tolerability pilot study with preliminary efficacy results in refractory relapsing-remitting multiple sclerosis

Extracorporeal photochemotherapy (ECP) is an immunomodulating procedure consisting of autologous reinfusion of peripheral blood mononuclear cells (PBMC) after direct exposure to 8-methoxy-psoralen and UV-A. It has been described as a successful treatment for different T-cell-mediated diseases and preliminary results suggest that ECP might be effective in the treatment of relapsing–remitting multiple sclerosis, but does not significantly alter the course of the progressive form of MS. In this study, we report the safety data and some preliminary efficacy evidence obtained using ECP in the treatment of five patients with refractory relapsing-remitting (RR) MS: in most cases ECP induced a reduction in the relapse rate and an EDSS stabilisation, with an apparent general MRI stabilisation. In conclusion, our results confirm ECP safety and tolerability and suggest that this treatment might be useful as a therapeutic alternative in the subgroup of RRMS patients not responsive to or not eligible for traditional immunomodulating or immunosuppressive treatments.

Impairment of glutamate transport and increased vulnerability to oxidative stress in neuroblastoma SH-SY5Y cells expressing a Cu,Zn superoxide dismutase typical of familial amyotrophic lateral sclerosis

Human neuroblastoma SH-SY5Y cells transfected with either familial amyotrophic lateral sclerosis-typical G93A mutant or wild-type copper/zinc superoxide dismutase were compared to untransfected cells in term of glutamate transport. Vmax of glutamate uptake was reduced in mutant cells, with no change in Km. No difference in EAAT1, EAAT2 and EAAT3 glutamate transporter mRNAs and immunoreactive proteins was found, suggesting that one or more transporters are functionally inactivated, possibly due to increased oxidative stress induced by the G93A mutation. Mutant cells showed a marked sensitivity to oxidants, resulting in a more pronounced reduction of glutamate uptake. Short-term antioxidant treatment did not reverse the impairment of glutamate uptake in G93A cells. Interestlingly, N-acetylcysteine was partially effective in preventing glutamate uptake reduction due to exogenous oxidative insults. Since the inhibition of the EAAT2 transporter subtype had no effect on glutamate re-uptake in this model, our study suggests an impaired function of the EAAT1/3 transporter subtypes, possibly due to oxidative inactivation, in the presence of mutant copper/zinc superoxide dismutase. Therefore, this model might prove to be a valuable tool to study the effects of mutant copper/zinc superoxide dismutase associated with amyotrophic lateral sclerosis on glutamate transport in neuronal cells, without the specific contribution of glial cells. These findings might lead to the identification of new therapeutic strategies aimed at preventing the damage associated with ALS.

Expression, distribution and glutamate uptake activity of high affinity-excitatory aminoacid transporters in in vitro cultures of embryonic rat dorsal root ganglia

Glutamate is the major mediator of excitatory signalling in the mammalian central nervous system, but it has recently been shown to play a role in the transduction of sensory input at the periphery and in peripheral neuropathies. New advances in research have demonstrated that rat peripheral sensory terminals and dorsal root ganglia (DRG) express molecules involved in glutamate signalling, including high-affinity membrane-bound glutamate transporters (GLAST [glutamate aspartate transporter], GLT1 [glutamate transporter 1], EAAC1 [excitatory aminoacid transporter 1]) and that alterations in their expression and/or functionality can be implicated in several models of peripheral neuropathy, neuropathic pain and hyperalgesia. Here we describe, through immunoblotting, immunofluorescence assays and β-counter analysis of [(3)H] l-glutamate uptake, the expression, distribution and activity of the glutamate transporters in in vitro cultures of embryonic dorsal root ganglia sensory neurons, sensory neurons+satellite cells and satellite cells. In this work we demonstrated that glutamate transporters are expressed in all cultures with a peculiar pattern of distribution. Even if GLAST is strongly detected in satellite cells, it is slightly expressed also in sensory neurons. GLT1 immunostaining is very weak in DRG neurons, but it was evident in the satellite cells. Finally, EAAC1 is localized in the soma and in the neuritis of sensory neurons, while it is not detectable in satellite cells. Moreover, all the cell cultures showed a strong sodium-energy-dependent glutamate uptake activity and it is more marked in neurons alone or in co-culture with satellite cells compared to satellite cells alone. Finally, we show that the complete or partial pharmacological inhibition of glutamate transporters virtually completely or partially abolish glutamate uptake in all cell culture. These results, that demonstrate that functionally active glutamate transporters can be studied in dorsal root ganglia cell cultures, provide further evidence for a role of glutamatergic transport in the peripheral nervous system and will be useful for testing whether any changes occur in in vitro models of peripheral nervous system damage.

Multifunctional liposomes interact with Abeta in human biological fluids: Therapeutic implications for Alzheimer's disease

&NA; The accumulation of extracellular amyloid beta (Abeta42) both in brain and in cerebral vessels characterizes Alzheimers disease (AD) pathogenesis. Recently, the possibility to functionalize nanoparticles (NPs) surface with Abeta42 binding molecules, making them suitable tools for reducing Abeta42 burden has been shown effective in models of AD. Aim of this work consisted in proving that NPs might be effective in sequestering Abeta42 in biological fluids, such as CSF and plasma. This demonstration is extremely important considering that these Abeta42 pools are in continuum with the brain parenchyma with drainage of Abeta from interstitial brain tissue to blood vessel and plasma. In this work, liposomes (LIP) were functionalized as previously shown in order to promote high‐affinity Abeta binding, i.e., either with, phosphatidic acid (PA), or a modified Apolipoprotein E‐derived peptide (mApo), or with a curcumin derivative (TREG); Abeta42 levels were determined by ELISA in CSF and plasma samples. mApo‐PA‐LIP (25 and 250 &mgr;M) mildly albeit significantly sequestered Abeta42 proteins in CSF samples obtained from healthy subjects (p < 0.01). Analogously a significant binding (˜20%) of Abeta42 (p < 0.001) was demonstrated following exposure to all functionalized liposomes in plasma samples obtained from selected AD or Downs syndrome patients expressing high levels of Abeta42. The same results were obtained by quantifying Abeta42 content after removal of liposome‐bound Abeta by using gel filtration chromatography or ultracentrifugation on a discontinuous sucrose density gradient. In conclusion, we demonstrate that functionalized liposomes significantly sequester Abeta42 in human biological fluids. These data may be critical for future in vivo administration tests using NPs for promoting sink effect. HighlightsThe use of high affinity Abeta binding liposomes is proposed in human biological fluids.Functionalized liposomes significantly interact with Abeta in plasma and CSF from AD patients.Liposomes may exploit the Abeta “sink effect” as a potential therapeutic strategy.

Novel Therapeutic Targets in Neuropsychiatric Disorders: The Neuroepigenome

The neuroepigenome, i.e., the epigenome of the nervous system, has become interesting for therapeutics in the last years due to widespread availability of dedicated drugs. A pivotal role for neuroepigenetics is certainly implied, both in physiology and pathology, by the highly dynamic structural and functional rearrangements that constantly occur into the nervous system, globally known as plasticity. Moreover, the idea that the pathophysiology of several neuropsychiatric disorders might involve epigenetic mechanisms is increasingly taking place due to accumulating experimental data and by the evidence of a synergistic interaction between genes and environment beneath most sporadic forms of these diseases. In this paper we will review the available evidence on the use of epigenome-modifying drugs in the field of neuropsychiatry, shortly describing for each disease the underlying assumptions of an epigenetic dysregulation.

NMR-driven identification of anti-amyloidogenic compounds in green and roasted coffee extracts

To identify food and beverages that provide the regular intake of natural compounds capable of interfering with toxic amyloidogenic aggregates, we developed an experimental protocol that combines NMR spectroscopy and atomic force microscopy, in vitro biochemical and cell assays to detect anti-Aβ molecules in natural edible matrices. We applied this approach to investigate the potential anti-amyloidogenic properties of coffee and its molecular constituents. Our data showed that green and roasted coffee extracts and their main components, 5-O-caffeoylquinic acid and melanoidins, can hinder Aβ on-pathway aggregation and toxicity in a human neuroblastoma SH-SY5Y cell line. Coffee extracts and melanoidins also counteract hydrogen peroxide- and rotenone-induced cytotoxicity and modulate some autophagic pathways in the same cell line.