Brain Uptake, Retention, and Efflux of Aluminum and Manganese

My colleagues and I investigated the sites and mechanisms of aluminum (Al) and manganese (Mn) distribution through the blood-brain barrier (BBB). Microdialysis was used to sample non-protein-bound Al in the extracellular fluid (ECF) of blood (plasma) and brain. Brain ECF Al appearance after intravenous Al citrate injection was too rapid to attribute to diffusion or to transferrin-receptor-mediated endocytosis, suggesting another carrier-mediated process. The brain:blood ECF Al concentration ratio was 0.15 at constant blood and brain ECF Al concentrations, suggesting carrier-mediated brain Al efflux. Pharmacological manipulations suggested the efflux carrier might be a monocarboxylate transporter (MCT). However, the lack of Al 14C-citrate uptake into rat erythrocytes suggested it is not a good substrate for isoform MCT1 or for the band 3 anion exchanger. Al 14C-citrate uptake into murine-derived brain endothelial cells appeared to be carrier mediated, Na independent, pH independent, and energy dependent. Uptake was inhibited by substrate/inhibitors of the MCT and organic anion transporter families. Determination of 26Al in rat brain at various times after intravenous 26Al suggested a prolonged brain 26Al half-life. It appears that Al transferrin and Al citrate cross the BBB by different mechanisms, that much of the Al entering brain ECF is rapidly effluxed, probably as Al citrate, but that some Al is retained for quite some time. Brain influx of the Mn2+ ion and Mn citrate, determined with the in situ brain perfusion technique, was greater than that attributable to diffusion, suggesting carrier-mediated uptake. Mn citrate uptake was approximately 3-fold greater than the Mn2+ ion, suggesting it is a primary Mn species entering the brain. After Mn2+ ion, Mn citrate, or Mn transferrin injection into the brain, brain Mn efflux was not more rapid than that predicted from diffusion. The BBB permeation of Al and Mn is mediated by carriers that may help regulate their brain concentrations

In Vivo Measurement of Brain GABA Concentrations by Magnetic Resonance Spectroscopy in Smelters Occupationally Exposed to Manganese

Background: Exposure to excessive manganese (Mn) levels is known to induce psychiatric and motor disorders including parkinsonian symptoms. Therefore finding a reliable means for early detection of Mn neurotoxicity is desirable. Objectives: Our goal was to study whether in-vivo brain levels of gamma-aminobutyric acid (GABA), N-acetylaspartate (NAA) and other brain metabolites in smelters were altered as a consequence of Mn exposure. Methods: T1-weighted MRI was used to visualize Mn deposition in the brain. Magnetic resonance spectroscopy (MRS) was used to quantify concentrations of NAA, glutamate and other brain metabolites in globus pallidus, putamen, thalamus, and frontal cortex from a well-established cohort of 10 male Mn-exposed smelters and 10 male age-matched control subjects. The MEGA-PRESS MRS sequence was used to determine GABA levels in a region encompassing the thalamus and adjacent parts of the basal ganglia ("GABA-VOI"). Results: Seven out of ten exposed subjects showed clear T1-hyperintense signals in the globus pallidus indicating Mn accumulation. We found a significant increase (82%; p=0.014) of GABA/tCr in the GABA-VOI of Mn-exposed subjects, as well as a distinct decrease (9%, p=0.04) of NAA/tCr in frontal cortex that strongly correlated (R= - 0.93, p<0.001) with cumulative Mn exposure. Conclusions: We demonstrated elevated GABA levels in the thalamus and adjacent basal ganglia and decreased frontal cortex NAA levels, indicating neuronal dysfunction in a brain area not primarily targeted by Mn. Therefore, the non-invasive in vivo MRS measurement of GABA and NAA may prove to be a powerful tool for detecting presymptomatic effects of Mn neurotoxicity

A novel chalcone derivative which acts as a microtubule depolymerising agent and an inhibitor of P-gp and BCRP in in-vitro and in-vivo glioblastoma models

<p>Abstract</p> <p>Background</p> <p>Over the past decades, in spite of intensive search, no significant increase in the survival of patients with glioblastoma has been obtained. The role of the blood-brain barrier (BBB) and especially the activity of efflux pumps belonging to the ATP Binding Cassette (ABC) family may, in part, explain this defect.</p> <p>Methods</p> <p>The <it>in-vitro </it>activities of JAI-51 on cell proliferation were assessed by various experimental approaches in four human and a murine glioblastoma cell lines. Using drug exclusion assays and flow-cytometry, potential inhibitory effects of JAI-51 on P-gp and BCRP were evaluated in sensitive or resistant cell lines. JAI-51 activity on <it>in-vitro </it>microtubule polymerization was assessed by tubulin polymerization assay and direct binding measurements by analytical ultracentrifugation. Finally, a model of C57BL/6 mice bearing subcutaneous GL26 glioblastoma xenografts was used to assess the activity of the title compound <it>in vivo</it>. An HPLC method was designed to detect JAI-51 in the brain and other target organs of the treated animals, as well as in the tumours.</p> <p>Results</p> <p>In the four human and the murine glioblastoma cell lines tested, 10 μM JAI-51 inhibited proliferation and blocked cells in the M phase of the cell cycle, via its activity as a microtubule depolymerising agent. This ligand binds to tubulin with an association constant of 2 × 10⁵M^-1, overlapping the colchicine binding site. JAI-51 also inhibited the activity of P-gp and BCRP, without being a substrate of these efflux pumps. These <it>in vitro </it>studies were reinforced by our <it>in vivo </it>investigations of C57BL/6 mice bearing GL26 glioblastoma xenografts, in which JAI-51 induced a delay in tumour onset and a tumour growth inhibition, following intraperitoneal administration of 96 mg/kg once a week. In accordance with these results, JAI-51 was detected by HPLC in the tumours of the treated animals. Moreover, JAI-51 was detected in the brain, showing that the molecule is also able to cross the BBB.</p> <p>Conclusion</p> <p>These <it>in vitro </it>and <it>in vivo </it>data suggest that JAI-51 could be a good candidate for a new treatment of tumours of the CNS. Further investigations are in progress to associate the title compound chemotherapy to radiotherapy in a rat model.</p

The IFN-γ-Inducible GTPase, Irga6, Protects Mice against Toxoplasma gondii but Not against Plasmodium berghei and Some Other Intracellular Pathogens

Clearance of infection with intracellular pathogens in mice involves interferon-regulated GTPases of the IRG protein family. Experiments with mice genetically deficient in members of this family such as Irgm1(LRG-47), Irgm3(IGTP), and Irgd(IRG-47) has revealed a critical role in microbial clearance, especially for Toxoplasma gondii. The in vivo role of another member of this family, Irga6 (IIGP, IIGP1) has been studied in less detail. We investigated the susceptibility of two independently generated mouse strains deficient in Irga6 to in vivo infection with T. gondii, Mycobacterium tuberculosis, Leishmania mexicana, L. major, Listeria monocytogenes, Anaplasma phagocytophilum and Plasmodium berghei. Compared with wild-type mice, mice deficient in Irga6 showed increased susceptibility to oral and intraperitoneal infection with T. gondii but not to infection with the other organisms. Surprisingly, infection of Irga6-deficient mice with the related apicomplexan parasite, P. berghei, did not result in increased replication in the liver stage and no Irga6 (or any other IRG protein) was detected at the parasitophorous vacuole membrane in IFN-γ-induced wild-type cells infected with P. berghei in vitro. Susceptibility to infection with T. gondii was associated with increased mortality and reduced time to death, increased numbers of inflammatory foci in the brains and elevated parasite loads in brains of infected Irga6-deficient mice. In vitro, Irga6-deficient macrophages and fibroblasts stimulated with IFN-γ were defective in controlling parasite replication. Taken together, our results implicate Irga6 in the control of infection with T. gondii and further highlight the importance of the IRG system for resistance to this pathogen