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Moshe Gavish - One of the best experts on this subject based on the ideXlab platform.

  • In vitro catabolic effect of protoporphyrin IX in human osteoblast-like cells: possible role of the 18 kDa mitochondrial translocator protein
    Journal of Bioenergetics and Biomembranes, 2013
    Co-Authors: Nahum Rosenberg, Leo Veenman, Abraham Weizman, Orit Rosenberg, Moshe Gavish
    Abstract:

    In several pathological conditions, when conversion of Protoporphyrin (PP)IX into heme is impaired, a toxic accumulation of PPIX might occur. PPIX has been found to have affinity to the mitochondrial Translocator Protein 18 kDa. Since it is known that TSPO is abundant in human osteoblast cells, thus we assumed that PPIX can affect cellular functions via interactions with TSPO in these cells. Therefore we aimed to study the metabolic responses of human osteoblast to a high (10^−5M) concentration of PPIX in vitro. We found that in primary culture of human osteoblast-like cells cell numbers decreased following exposure to PPIX(10^−5M). Cellular [^18F]-FDG incorporation, mitochondrial mass, ATP content were suppressed, and ΔΨm collapsed. Lactate dehydrogenase activity was enhanced in culture media, indicating overall cell death, while no increase in apoptotic levels was observed. Cellular proliferation was not affected. Protein expression of TSPO, VDAC 1, and hexokinase 2 decreased, although the synthesis of mRNA for hexokinase 2 increased. Thus, PPIX(10^−5M) has a cytotoxic effect on human osteoblast-like cell in vitro. Since these cells remain viable following exposure to another TSPO ligand, PK 11195 (10^−5M), as observed previously by us, the mode of action of PPIX on osteoblast-like cells is not identical to that of PK 11195. Accordingly pathological accumulation of PPIX may cause necrosis of osteoblasts leading to bone mass loss. We show that this phenomenon is unrelated to iron overload.

  • The nitric oxide donor sodium nitroprusside requires the 18 kDa Translocator Protein to induce cell death
    Apoptosis, 2012
    Co-Authors: Luba Shargorodsky, Leo Veenman, Svetlana Leschiner, Beatriz Caballero, Yelena Pe’er, Julia Bode, Moshe Gavish
    Abstract:

    Various studies have shown that several lethal agents induce cell death via the mitochondrial 18 kDa Translocator Protein (TSPO). In this study we tested the possibility that nitric oxide (NO) is the signaling component inducing the TSPO to initiate cell death process. Cell viability assays included Trypan blue uptake, propidium iodide uptake, lactate dehydrogenase release, and DNA fragmentation. These assays showed that application of the specific TSPO ligand PK 11195 reduced these parameters for the lethal effects of the NO donor sodium nitroprusside (SNP) by 41, 27, 40, and 42 %, respectively. TSPO silencing by siRNA also reduced the measured lethal effects of SNP by 50 % for all of these four assays. With 2,3-bis[2-methoxy-4-nitro-5-sulphophenyl]-2 H -tetrazolium-5-carboxyanilide (XTT) changes in metabolic activity were detected. PK 11195 and TSPO knockdown fully prevented the reductions in XTT signal otherwise induced by SNP. Collapse of the mitochondrial membrane potential was studied with the aid of JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-benzimidazolylcarbocyanine chloride). PK 11195 and TSPO knockdown reduced, respectively by 36 and 100 %, the incidence of collapse of the mitochondrial membrane potential otherwise induced by SNP. 10- N -Nonyl-Acridine Orange (NAO) was used to detect mitochondrial reactive oxygen species generation due to SNP. PK 11195 and TSPO knockdown reduced this effect of SNP by 65 and 100 %, respectively. SNP did not affect TSPO protein expression and binding characteristics, and also did not cause TSPO S-nitrosylation. However, β-actin and various other proteins (not further defined) were S-nitrosylated. In conclusion, TSPO is required for the lethal and metabolic effects of the NO donor SNP, but TSPO itself is not S-nitrosylated.

  • In vitro mitochondrial effects of PK 11195, a synthetic translocator protein 18 kDa (TSPO) ligand, in human osteoblast-like cells
    Journal of Bioenergetics and Biomembranes, 2011
    Co-Authors: Nahum Rosenberg, Leo Veenman, Fuad Fares, Abraham Weizman, Orit Rosenberg, Svetlana Leschiner, Yaakov Sakoury, Michael Soudry, Gary Weisinger, Moshe Gavish
    Abstract:

    The role of the TSPO in metabolism of human osteoblasts is unknown. We hypothesized that human osteoblast metabolism may be modulated by the TSPO. Therefore we evaluated the presence of TSPO in human osteoblast-like cells and the effect of its synthetic ligand PK 11195 on these cells. The presence of TSPO was determined by [3H]PK 11195 binding using Scatchard analysis: Bmax 7682 fmol/mg, Kd 9.24 nM. PK 11195 did not affect significantly cell proliferation, cell death, cellular viability, maturation, [18F]-FDG incorporation and hexokinase 2 gene expression or protein levels. PK 11195 exerted a suppressive effect on VDAC1 and caused an increase in TSPO gene expression or protein levels. In parallel there was an increase in mitochondrial mass, mitochondrial ATP content and a reduction in ΔΨm collapse. Thus, it appears that PK11195 (10−5 M) stimulates mitochondrial activity in human osteoblast-like cells without affecting glycolytic activity and cell death.

  • channel like functions of the 18 kda translocator protein tspo regulation of apoptosis and steroidogenesis as part of the host defense response
    Current Pharmaceutical Design, 2007
    Co-Authors: Leo Veenman, Vassilios Papadopoulos, Moshe Gavish
    Abstract:

    Due to its channel-like properties, the peripheral-type benzodiazepine receptor (PBR) has been renamed the translocator protein (TSPO). In eukaryotes, the TSPO is primarily located in the outer mitochondrial membrane. In prokaryotes, it is found in the cell membrane. A broad spectrum of functions has been attributed to the TSPO, including various host defense responses, developmental processes, and mitochondrial functions. In the present review, we focus on the role of TSPO in immunological responses, apoptosis, and steroidogenesis, to determine whether these functions may be governed by a common denominator including TSPO. At physiological concentrations (nM range), the TSPO specific ligands, PK 11195 and Ro5-4864, appear to be anti-apoptotic. Knockdown of TSPO by genetic manipulation, resulting a reduction by more than 50% in [3H]PK 11195 binding, was reported to show anti-apoptotic effects, suggesting a potential pro-apoptotic function of TSPO. However, a reduction of more than 70% of TSPO abundance was found to cause cell death, possibly due to impairment of other essential cell functions. The pro-apoptotic function of TSPO may involve the modulation of the channel formed by the mitochondrial voltage-dependent anion channel (VDAC) and the adenine nucleotide transporter (ANT) [i.e., the mitochondrial permeability transition pore (MPTP)]. The frequently reported pro-apoptotic effects of PK 11195 and Ro5-4864 may be due to sites with low-affinity binding for these specific TSPO ligands, and not directly related to VDAC and ANT. Also at concentrations in the nM range, PK 11195 and Ro5-4864 appear to stimulate steroidogenesis. For this function TSPO by itself appears to suffice i.e. no involvement of VDAC and ANT. TSPO appears to operate as a translocator/channel to transfer cholesterol into mitochondria where it is converted to pregnenolone, a precursor of further steroidogenesis. Apoptosis and steroids play important roles in various aspects of the host defense response. Thus, our review suggests that the involvement of TSPO and its ligands in such seemingly disparate biological functions as immunological responses, apoptosis, and steroidogenesis may have a common denominator in the multidimensional role of TSPO in the host-defense response to disease and injury.

  • PK 11195 aggravates 3,5-diethoxycarbonyl-1,4-dihydrocollidine-induced hepatic porphyria in rats
    Hepatology, 1996
    Co-Authors: Ora Fonia, Ronit Weizman, R Coleman, E Kaganovskaya, Moshe Gavish
    Abstract:

    There is evidence to suggest that peripheral-type benzodiazepine receptors (PBR) are involved in porphyrin transport during erythroid differentiation, and it is possible that these receptors have an important role in heme biosynthesis. We examined the biochemical and ultrastructural alterations in rat liver following experimentally induced acute hepatic porphyria, as well as the effects of the administration of a selective PBR ligand, PK 11195. The most severe pathological conditions were found in rats that received a combined treatment of the porphyrinogenic agent 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) and PK 11195. Transmission electron microscopy showed a correlation between the ultrastructural pathology of the liver, the total porphyrin levels in urine and liver, and the porphobilinogen levels in urine. Hepatocytes in this acute porphyria showed the development of large secondary lysosomes containing crystalline aggregates of protoporphyrin. Bile canaliculi were grossly enlarged, contained aggregates of protoporphyrin crystals, and showed the presence of bile thrombi. In addition, prominent bundles of collagen fibers (fibrosis) were commonly found in livers of rats that had been treated with DDC or DDC and PK 11195. We conclude that the administration of PK 11195 to porphyric rats aggravates porphyrin accumulation and cellular damage in the liver. Perhaps this evidence suggests that PK 11195 blocks the binding of protoporphyrin IX to PBR, thus elevating the content of protoporphyrin IX in liver.

Vassilios Papadopoulos - One of the best experts on this subject based on the ideXlab platform.

  • Translocator protein (18 kDa) ligand PK 11195 induces transient mitochondrial Ca2+ release leading to transepithelial Cl- secretion in HT-29 human colon cancer cells
    Biology of the Cell, 2020
    Co-Authors: Mariano A. Ostuni, Vassilios Papadopoulos, R. Ducroc, Gabriel Péranzi, Marie-christine Tonon, Jean-jacques Lacapère
    Abstract:

    Background information. TSPO (translocator protein), known previously as PBR (peripheral-type benzodiazepine receptor), is a 18 kDa protein expressed in the mitochondrial membrane of a variety of tissues. TSPO has been reported to be over-expressed in human colorectal tumours and cancer cell lines, but Its function is not well characterized. Results. We investigated the expression and function of TSPO in the human colon cancer cells HT-29. Immunohis-tochemical studies revealed that TSPO is localized in mitochondria, and its endogenous ligand, the polypeptide diazepam-binding inhibitor, in the cytosol. Radioligand binding studies using the specific high-affinity drug ligand [ 3 H]PK 11195 and membrane fraction demonstrated saturable binding, with K d and Bmax values of 13.5 ± 1.5 nM and 10.1±1.0 pmol/mg respectively. PK 11195 induced a rapid and transient dose-dependent rise in intracellular [Ca 2+ ], which was unaffected by extracellular Ca 2+ , but was blocked by the PTP (permeability transition pore) inhibitor, cyclosporin A, and by the TSPO partial agonist, flunitrazepam. Using HT-29 clone 19A cell line, which forms cell monolayers, we demonstrated that TSPO ligand stimulated a Ca 2+ -dependent transepithelial Cl - secretion. This secretion was inhibited: (i) after removal of extracellular Cl - ; (ii) by apical addition of the Cl - channel blocker NPPB [5-nitro-2-(3-phenylpropylamino)-benzoate]; and (iii) by basolateral addition of the Na + -K + -2Cl - co-transporter inhibitor bumetanide. Furthermore, the intracellular Ca 2+ chelator BAPTA/AM [bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetrakis(acetoxymethyl ester)] and cyclosporin A abolished the rise in PK 11195-induced Cl- secretion. Conclusions. These findings indicate that TSPO is located in mitochondrial membranes of HT-29 and reveal that its activation induces a rise in cytosolic Ca 2+ , leading to the stimulation of Cl - secretion.

  • distribution pharmacological characterization and function of the 18 kda translocator protein in rat small intestine
    Biology of the Cell, 2009
    Co-Authors: Mariano A. Ostuni, Vassilios Papadopoulos, R. Ducroc, Gabriel Péranzi, Magali Fasseu, Branislav Vidic, Janice Dumont, Jean-jacques Lacapère
    Abstract:

    Background information. The TSPO (18 kDa translocator protein) is a mitochondrial transmembrane protein involved in cholesterol transport in organs that synthesize steroids and bile salts. Different natural and synthetic high-affinity TSPO ligands have been characterized through their ability to stimulate cholesterol transport, but also to stimulate other physiological functions including cell proliferation, apoptosis and calcium-dependent transepithelial ion secretion. Here, we investigate the localization and functions of TSPO in the small intestine. Results. TSPO was present in enterocyte mitochondria but not in rat intestinal goblet cells. Enterocyte cytoplasm also contained the endogenous TSPO ligand, polypeptide DBI (diazepam-binding inhibitor). Whereas intestinal TSPO had high affinity for the synthetic ligand PK 11195, the pharmacological profile of TSPO in the duodenum was distinct from the jejunum and ileum. Specifically, benzodiazepine Ro5-4864 and protoporphyrin IX showed 5–13-fold lower affinity for duodenal TSPO. The mRNA and protein ratios of TSPO to other mitochondrial membrane proteins VDAC (voltage-dependent anion channel) and ANT (adenine nucleotide transporter) were significantly different. PK 11195 stimulated calcium-dependent chloride secretion in the duodenum and calcium-dependent chloride absorption in the ileum, but did not affect jejunum ion transport. Conclusions. The functional differences in subpopulations of TSPO in different regions of the intestine could be related to structural organization of mitochondrial protein complexes that mediate the ability of TSPO to modulate either chloride secretion or absorption in the duodenum and ileum respectively.

  • channel like functions of the 18 kda translocator protein tspo regulation of apoptosis and steroidogenesis as part of the host defense response
    Current Pharmaceutical Design, 2007
    Co-Authors: Leo Veenman, Vassilios Papadopoulos, Moshe Gavish
    Abstract:

    Due to its channel-like properties, the peripheral-type benzodiazepine receptor (PBR) has been renamed the translocator protein (TSPO). In eukaryotes, the TSPO is primarily located in the outer mitochondrial membrane. In prokaryotes, it is found in the cell membrane. A broad spectrum of functions has been attributed to the TSPO, including various host defense responses, developmental processes, and mitochondrial functions. In the present review, we focus on the role of TSPO in immunological responses, apoptosis, and steroidogenesis, to determine whether these functions may be governed by a common denominator including TSPO. At physiological concentrations (nM range), the TSPO specific ligands, PK 11195 and Ro5-4864, appear to be anti-apoptotic. Knockdown of TSPO by genetic manipulation, resulting a reduction by more than 50% in [3H]PK 11195 binding, was reported to show anti-apoptotic effects, suggesting a potential pro-apoptotic function of TSPO. However, a reduction of more than 70% of TSPO abundance was found to cause cell death, possibly due to impairment of other essential cell functions. The pro-apoptotic function of TSPO may involve the modulation of the channel formed by the mitochondrial voltage-dependent anion channel (VDAC) and the adenine nucleotide transporter (ANT) [i.e., the mitochondrial permeability transition pore (MPTP)]. The frequently reported pro-apoptotic effects of PK 11195 and Ro5-4864 may be due to sites with low-affinity binding for these specific TSPO ligands, and not directly related to VDAC and ANT. Also at concentrations in the nM range, PK 11195 and Ro5-4864 appear to stimulate steroidogenesis. For this function TSPO by itself appears to suffice i.e. no involvement of VDAC and ANT. TSPO appears to operate as a translocator/channel to transfer cholesterol into mitochondria where it is converted to pregnenolone, a precursor of further steroidogenesis. Apoptosis and steroids play important roles in various aspects of the host defense response. Thus, our review suggests that the involvement of TSPO and its ligands in such seemingly disparate biological functions as immunological responses, apoptosis, and steroidogenesis may have a common denominator in the multidimensional role of TSPO in the host-defense response to disease and injury.

  • in vivo and in vitro peripheral type benzodiazepine receptor polymerization functional significance in drug ligand and cholesterol binding
    Biochemistry, 2003
    Co-Authors: Franck Delavoie, Gabriel Péranzi, Jean-jacques Lacapère, Hua Li, Matthew Hardwick, Jeanclaude Robert, Christoforos Giatzakis, Jean Maccario, Vassilios Papadopoulos
    Abstract:

    Peripheral-type benzodiazepine receptor (PBR) is an 18 kDa high-affinity drug ligand and cholesterol binding protein involved in various cell functions. Antisera for distinct PBR areas identified immunoreactive proteins of 18, 40, and 56 kDa and occasionally 72, 90, and 110 kDa in testicular Leydig and breast cancer cells. These sizes may correspond to PBR polymers and correlated to the levels of reactive oxygen species. Treatment of Leydig cells with human chorionic gonadotropin rapidly induced free radical, PBR polymer, and steroid formation. UV photoirradiation generates ROS species, which increased the size of intramembraneous particles of recombinant PBR reconstituted into proteoliposomes consistent with polymer formation, determined both by SDS-PAGE and by freeze-fracture electron microscopy. Spectroscopic analysis revealed the formation of dityrosines as the covalent cross-linker between PBR monomers. Moreover, photoirradiation increased PK 11195 drug ligand binding and reduced cholesterol binding capacity of proteoliposomes. Further addition of PK 11195 drug ligand to polymers increased the rate of cholesterol binding. These data indicate that reactive oxygen species induce in vivo and in vitro the formation of covalent PBR polymers. We propose that the PBR polymer might be the functional unit responsible for ligand-activated cholesterol binding and that PBR polymerization is a dynamic process modulating the function of this receptor in cholesterol transport and other cell-specific PBR-mediated functions.

Leo Veenman - One of the best experts on this subject based on the ideXlab platform.

  • In vitro catabolic effect of protoporphyrin IX in human osteoblast-like cells: possible role of the 18 kDa mitochondrial translocator protein
    Journal of Bioenergetics and Biomembranes, 2013
    Co-Authors: Nahum Rosenberg, Leo Veenman, Abraham Weizman, Orit Rosenberg, Moshe Gavish
    Abstract:

    In several pathological conditions, when conversion of Protoporphyrin (PP)IX into heme is impaired, a toxic accumulation of PPIX might occur. PPIX has been found to have affinity to the mitochondrial Translocator Protein 18 kDa. Since it is known that TSPO is abundant in human osteoblast cells, thus we assumed that PPIX can affect cellular functions via interactions with TSPO in these cells. Therefore we aimed to study the metabolic responses of human osteoblast to a high (10^−5M) concentration of PPIX in vitro. We found that in primary culture of human osteoblast-like cells cell numbers decreased following exposure to PPIX(10^−5M). Cellular [^18F]-FDG incorporation, mitochondrial mass, ATP content were suppressed, and ΔΨm collapsed. Lactate dehydrogenase activity was enhanced in culture media, indicating overall cell death, while no increase in apoptotic levels was observed. Cellular proliferation was not affected. Protein expression of TSPO, VDAC 1, and hexokinase 2 decreased, although the synthesis of mRNA for hexokinase 2 increased. Thus, PPIX(10^−5M) has a cytotoxic effect on human osteoblast-like cell in vitro. Since these cells remain viable following exposure to another TSPO ligand, PK 11195 (10^−5M), as observed previously by us, the mode of action of PPIX on osteoblast-like cells is not identical to that of PK 11195. Accordingly pathological accumulation of PPIX may cause necrosis of osteoblasts leading to bone mass loss. We show that this phenomenon is unrelated to iron overload.

  • The nitric oxide donor sodium nitroprusside requires the 18 kDa Translocator Protein to induce cell death
    Apoptosis, 2012
    Co-Authors: Luba Shargorodsky, Leo Veenman, Svetlana Leschiner, Beatriz Caballero, Yelena Pe’er, Julia Bode, Moshe Gavish
    Abstract:

    Various studies have shown that several lethal agents induce cell death via the mitochondrial 18 kDa Translocator Protein (TSPO). In this study we tested the possibility that nitric oxide (NO) is the signaling component inducing the TSPO to initiate cell death process. Cell viability assays included Trypan blue uptake, propidium iodide uptake, lactate dehydrogenase release, and DNA fragmentation. These assays showed that application of the specific TSPO ligand PK 11195 reduced these parameters for the lethal effects of the NO donor sodium nitroprusside (SNP) by 41, 27, 40, and 42 %, respectively. TSPO silencing by siRNA also reduced the measured lethal effects of SNP by 50 % for all of these four assays. With 2,3-bis[2-methoxy-4-nitro-5-sulphophenyl]-2 H -tetrazolium-5-carboxyanilide (XTT) changes in metabolic activity were detected. PK 11195 and TSPO knockdown fully prevented the reductions in XTT signal otherwise induced by SNP. Collapse of the mitochondrial membrane potential was studied with the aid of JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-benzimidazolylcarbocyanine chloride). PK 11195 and TSPO knockdown reduced, respectively by 36 and 100 %, the incidence of collapse of the mitochondrial membrane potential otherwise induced by SNP. 10- N -Nonyl-Acridine Orange (NAO) was used to detect mitochondrial reactive oxygen species generation due to SNP. PK 11195 and TSPO knockdown reduced this effect of SNP by 65 and 100 %, respectively. SNP did not affect TSPO protein expression and binding characteristics, and also did not cause TSPO S-nitrosylation. However, β-actin and various other proteins (not further defined) were S-nitrosylated. In conclusion, TSPO is required for the lethal and metabolic effects of the NO donor SNP, but TSPO itself is not S-nitrosylated.

  • In vitro mitochondrial effects of PK 11195, a synthetic translocator protein 18 kDa (TSPO) ligand, in human osteoblast-like cells
    Journal of Bioenergetics and Biomembranes, 2011
    Co-Authors: Nahum Rosenberg, Leo Veenman, Fuad Fares, Abraham Weizman, Orit Rosenberg, Svetlana Leschiner, Yaakov Sakoury, Michael Soudry, Gary Weisinger, Moshe Gavish
    Abstract:

    The role of the TSPO in metabolism of human osteoblasts is unknown. We hypothesized that human osteoblast metabolism may be modulated by the TSPO. Therefore we evaluated the presence of TSPO in human osteoblast-like cells and the effect of its synthetic ligand PK 11195 on these cells. The presence of TSPO was determined by [3H]PK 11195 binding using Scatchard analysis: Bmax 7682 fmol/mg, Kd 9.24 nM. PK 11195 did not affect significantly cell proliferation, cell death, cellular viability, maturation, [18F]-FDG incorporation and hexokinase 2 gene expression or protein levels. PK 11195 exerted a suppressive effect on VDAC1 and caused an increase in TSPO gene expression or protein levels. In parallel there was an increase in mitochondrial mass, mitochondrial ATP content and a reduction in ΔΨm collapse. Thus, it appears that PK11195 (10−5 M) stimulates mitochondrial activity in human osteoblast-like cells without affecting glycolytic activity and cell death.

  • channel like functions of the 18 kda translocator protein tspo regulation of apoptosis and steroidogenesis as part of the host defense response
    Current Pharmaceutical Design, 2007
    Co-Authors: Leo Veenman, Vassilios Papadopoulos, Moshe Gavish
    Abstract:

    Due to its channel-like properties, the peripheral-type benzodiazepine receptor (PBR) has been renamed the translocator protein (TSPO). In eukaryotes, the TSPO is primarily located in the outer mitochondrial membrane. In prokaryotes, it is found in the cell membrane. A broad spectrum of functions has been attributed to the TSPO, including various host defense responses, developmental processes, and mitochondrial functions. In the present review, we focus on the role of TSPO in immunological responses, apoptosis, and steroidogenesis, to determine whether these functions may be governed by a common denominator including TSPO. At physiological concentrations (nM range), the TSPO specific ligands, PK 11195 and Ro5-4864, appear to be anti-apoptotic. Knockdown of TSPO by genetic manipulation, resulting a reduction by more than 50% in [3H]PK 11195 binding, was reported to show anti-apoptotic effects, suggesting a potential pro-apoptotic function of TSPO. However, a reduction of more than 70% of TSPO abundance was found to cause cell death, possibly due to impairment of other essential cell functions. The pro-apoptotic function of TSPO may involve the modulation of the channel formed by the mitochondrial voltage-dependent anion channel (VDAC) and the adenine nucleotide transporter (ANT) [i.e., the mitochondrial permeability transition pore (MPTP)]. The frequently reported pro-apoptotic effects of PK 11195 and Ro5-4864 may be due to sites with low-affinity binding for these specific TSPO ligands, and not directly related to VDAC and ANT. Also at concentrations in the nM range, PK 11195 and Ro5-4864 appear to stimulate steroidogenesis. For this function TSPO by itself appears to suffice i.e. no involvement of VDAC and ANT. TSPO appears to operate as a translocator/channel to transfer cholesterol into mitochondria where it is converted to pregnenolone, a precursor of further steroidogenesis. Apoptosis and steroids play important roles in various aspects of the host defense response. Thus, our review suggests that the involvement of TSPO and its ligands in such seemingly disparate biological functions as immunological responses, apoptosis, and steroidogenesis may have a common denominator in the multidimensional role of TSPO in the host-defense response to disease and injury.

William R. Mancini - One of the best experts on this subject based on the ideXlab platform.

  • Localization of the peripheral-type benzodiazepine binding site to mitochondria of human glioma cells
    Journal of Neuro-Oncology, 1992
    Co-Authors: James M. Olson, Anne B. Young, Wakelin Mcneel, William R. Mancini
    Abstract:

    Subcellular fractionation was performed on human U251 glioblastoma cultures. In all subcellular fractions, the binding of the peripheral benzodiazepine ligand, [^3H]PK 11195, correlated with the specific activity of monoamine oxidase (r = 0.95, p < 0.001) and succinate dehydrogenase (r = 0.93, p < 0.001), two mitochondrial enzymes. The specific activity of plasma membrane and nuclear markers correlated poorly with the presence of PK 11195 binding sites. These data support the mitochondrion as the primary location of peripheral-type benzodiazepine binding sites (PBBS) in human glioma cells. Mitochondria-rich preparations were then assayed for [^3H]Ro5-4964 binding. Six nM [^3H]Ro5-4964 failed to specifically bind to human U251 mitochondria, but bound vigorously to mitochondria from rat C6 glioma. These data indicate that the low affinity of Ro5-4864 for PBBS in human glioma cells compared to those in rat is due to interspecies receptor variation rather than impaired drug transport into human cells.

Roger F. Butterworth - One of the best experts on this subject based on the ideXlab platform.

  • Chronic exposure of rat primary astrocyte cultures to manganese results in increased binding sites for the 'peripheral-type' benzodiazepine receptor ligand 3H-PK 11195.
    Neuroscience Letters, 1999
    Co-Authors: Alan S. Hazell, Paul Desjardins, Roger F. Butterworth
    Abstract:

    Abstract Alterations of ‘peripheral-type’ benzodiazepine receptors (PTBRs) in brain are a feature of hepatic encephalopathy (HE). Although ammonia toxicity has been implicated in the disorder, recent findings suggest an accumulation of manganese in the brains of cirrhotic patients dying in hepatic coma. In this study, we examined the expression of PTBRs as well as the binding of the selective PTBR ligand 3 H-PK 11195 in cultured astrocytes following chronic exposure to manganese. When astrocytes were exposed to 100 μM manganese for 1 week, a 57% increase in B max for 3 H-PK 11195 binding was detected ( P K d value. However, an examination by RT-PCR of the expression of the isoquinoline-binding moiety of the PTBR complex in these cells revealed no change in PTBR mRNA levels following manganese treatment. These findings suggest that manganese up-regulates 3 H-PK 11195 binding sites by a process which does not involve a change in transcription. In view of the proposed role of astrocytic PTBRs in ‘neurosteroid’ synthesis, manganese-induced increases of PTBRs could contribute to the pathogenesis of HE.

  • Increased Densities of Binding Sites for the Peripheral-Type Benzodiazepine Receptor Ligand [3H]PK 11195 in Congenital Ornithine Transcarbamylase-Deficient Sparse Fur Mouse
    Pediatric Research, 1993
    Co-Authors: I A Qureshi, Roger F. Butterworth
    Abstract:

    ABSTRACT: Peripheral-type (mitochondrial) benzodiazepine receptors (PTBR) were studied in the brain and peripheral organs (kidney, liver, and testis) of normal male mice (CD-1/Y) and the congenially hyperammonemic sparse fur (spf/Y) mouse. Radioligand binding assays were performed with [3H]PK 11195, a ligand with high selectivity and affinity for PTBR. Densities (maximal number of binding sites) of [3H]PK 11195 binding sites were greatest in kidney, followed by liver, testis, and brain. Densities of [3H]PK 11195 binding sites were significantly increased in all tissues of spf mice compared with control animals. In view of the localization of PTBR on the outer mitochondrial membrane, changes in PTBR in spf mouse tissues may modulate the altered mitochondrial function and oxidative metabolism, in brain and peripheral tissues, in congenital OTC deficiency. The positron emission tomography ligand 11C-PK 11195 could find an application in the assessment of end organ dysfunction in this disorder.

  • Increased densities of binding sites for the ‘peripheral-type’ benzodiazepine receptor ligand [3H]PK 11195 in rat brain following portacaval anastomosis
    Brain Research, 1992
    Co-Authors: J F Giguère, E Hamel, Roger F. Butterworth
    Abstract:

    Abstract Using quantitative receptor radioautography, binding sites for the ‘peripheral-type’ benzodiazepine receptor ligand [3H]PK 11195 were studied in rats 4 week after end-to-side portacaval anastomosis and in sham-operated controls. Portacaval anastomosis resulted in region-selective increases in density of [3H]PK 11195 binding sites in cerebellum, pons > thalamus, cerebral cortex > hippocampus > striatum. Possible mechanisms implicated in these changes include (i) the action of endogenous ligands for the mitochondrial benzodiazepine receptor such as octadecaneuropeptide and (ii) neurotoxic actions of ammonia. In view of the proposed role of these receptors as modulators of intermediary metabolism and neurosteroid biosynthesis, such changes could contribute to the neurochemical mechanisms responsible for portal-systemic encephalopathy.

  • Increased densities of peripheral‐type benzodiazepine receptors in brain autopsy samples from cirrhotic patients with hepatic encephalopathy
    Hepatology, 1990
    Co-Authors: Joël Lavoie, Gilles Pomier Layrargues, Roger F. Butterworth
    Abstract:

    Peripheral-type benzodiazepine receptors were evaluated using the specific ligand [3H]-PK 11195 in brain homogenates from nine cirrhotic patients who died in hepatic coma and from an equal number of age-matched control subjects. Histopathological studies showed evidence of severe Alzheimer type II astrocytosis in the brains of all cirrhotic patients. Saturation-binding assays revealed a single saturable binding site for [3H]-PK 11195 in brain, with affinities in the 2- to 3-nmol/L range. Diazepam was found to be a relatively potent inhibitor of 3H-PK 11195 binding (IC50 = 253 nmol/L), whereas the central benzodiazepine antagonist Ro 15-1788 displaced 3H-PK 11195 binding with low affinity (IC50 >40 μmol/L). Densities of [3H]-PK 11195 binding sites were found to be increased by 48% (p < 0.01) and 25% (p < 0.05) in frontal cortex and caudate nuclei, respectively, from cirrhotic patients. Densities of [3H]-PK 11195 binding sites in frontal cortex from two nonencephalopathic cirrhotic patients were not significantly different from control values. No concomitant changes of affinities of these binding sites were observed. Because it has been suggested that peripheral-type benzodiazepine receptors may be localized on mitochondrial membranes and may therefore be involved in cerebral oxidative metabolism, the alterations observed in this study could be of pathophysiological significance in hepatic encephalopathy.(HEPATOLOGY 1990; 11:874-878.)