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R Rapoport

Publications and source records attributed to R Rapoport.

At least 19 recordsLinked to original sources
PubMed2000

Age-related brain volume reductions in amphetamine and cocaine addicts and normal controls: implications for addiction research.

The study evaluated the relationship between age and frontal and temporal lobe volumes in young cohorts of cocaine-dependent (CD), amphetamine-dependent (Am), and normal control subjects. Ten CD, nine Am, and 16 age- and gender-matched control subjects underwent magnetic resonance imaging (MRI). The volume of the frontal and temporal lobes was measured from an identically positioned slab of seven contiguous 3-mm-thick coronal images. Follow-up measures of the gray and white matter subcomponents of these volumes were also obtained. Both CD and Am groups had a significantly smaller temporal lobe volumes, but only the CD group demonstrated a significantly greater decline in temporal lobe volume with age (intracranial volume, education, and race were controlled for in all statistical analyses). Segmenting the brain regions into gray and white matter revealed that the negative correlation between age and temporal lobe volume of CD patients was mostly due to a significant age-related decline in the gray matter subcomponent. Negative trends between age and gray matter volumes were also observed in the Am and normal groups. In the frontal lobes, age was negatively correlated with gray matter volume in the control, CD, and Am groups. Unlike the consistent decreases in gray matter volumes, white matter showed non-significant increases in volume with age. The data suggest that CD patients may have an accelerated age-related decline in temporal lobe gray matter volume and a smaller temporal lobe volume compared to normal controls. In the frontal lobe, age-related gray matter volume reductions occur in all three groups. These age-related cortical gray matter volume reductions may be a biological marker for the risk of addictive behavior, which also decreases with age.

Adult↗
PubMed2000

Characterization of the vasculogenic block in the absence of vascular endothelial growth factor-A.

Vascular endothelial growth factor (VEGF) signaling is required for both differentiation and proliferation of vascular endothelium. Analysis of differentiated embryonic stem cells with one or both VEGF-A alleles deleted showed that both the differentiation and the expansion of endothelial cells are blocked during vasculogenesis. Blood island formation was reduced by half in hemizygous mutant VEGF cultures and by 10-fold in homozygous mutant VEGF cultures. Homozygous mutant cultures could be partially rescued by the addition of exogenous VEGF. RNA levels for the endothelial adhesion receptors ICAM-2 and PECAM were reduced in homozygous mutant cultures, but ICAM-2 RNA levels decreased substantially, whereas PECAM RNA levels remained at hemizygous levels. The quantitative data correlated with the antibody staining patterns because cells that were not organized into vessels expressed PECAM but not ICAM-2. These PECAM+ cell clumps accumulated in mutant cultures as vessel density decreased, suggesting that they were endothelial cell precursors blocked from maturation. A subset of PECAM+ cells in clumps expressed stage-specific embryonic antigen-1 (SSEA-1), and all were ICAM-2(-) and CD34(-), whereas vascular endothelial cells incorporated into vessels were PECAM(+), ICAM-2(+), CD34(+), and SSEA-1(-). Analysis of flk-1 expression indicated that a subset of vascular precursor cells coexpressed PECAM and flk-1. These data suggest that VEGF signaling acts in a dose-dependent manner to affect both a specific differentiation step and the subsequent expansion of endothelial cells. (Blood. 2000;95:1979-1987)

Animals↗
PubMed2000

Increased CSF volumes are associated with diminished subjective responses to cocaine infusion.

We evaluated the hypothesis that ventricular and cortical CSF volume increases are associated with reductions in the magnitude of euphoric effects produced by intravenous IV cocaine infusion in cocaine dependent (CD) individuals. Eleven CD patients participating in a cocaine-infusion study and eleven control subjects underwent magnetic resonance imaging (MRI). Two CSF regions of interest (lateral ventricles and frontal cortex CSF) and two comparison regions (third ventricle and posterior cortex CSF) were measured. Self-reported ratings of the intensity of euphoric response ("high") were obtained from the CD subjects at 3, 10, and 30 minutes after IV administration of cocaine. A significant negative correlation was observed between the volume of the lateral ventricles and subjective ratings of the "high" experienced at 3 minutes, but not at 10 and 30 minutes after cocaine infusion. In contrast, a significant negative correlation between frontal cortex CSF volume and the intensity of euphoric response was observed at 30 minutes after IV cocaine. No significant associations were observed between the volumes of the two comparison regions and any subjective ratings of "high." No significant volume differences were observed between the CD and control groups in any region. The results suggest larger lateral ventricular volumes are associated with a decrease in immediate euphoria while larger frontal cortex CSF volumes are associated with a decrease in the duration of the euphoria induced by cocaine infusion. The age-related brain volume reductions underlying the volume increase in these two CSF spaces may be the neurobiological basis of the age-related reduction in the rates of addiction.

Adult↗
PubMed1998

Antioxidant capacity is correlated with steroidogenic status of the corpus luteum during the bovine estrous cycle.

The reactions of steroid hormone biosynthesis are accompanied by formation of oxygen radicals. We determined the levels of some antioxidants and antioxidative enzymes at different developmental stages of bovine corpora lutea to examine their correlation with steroidogenic status. Plasma progesterone concentrations of estrous cycle synchronized cows increased until day 16, and then decreased rapidly during luteal regression. The levels of steroidogenic cytochrome P450scc and adrenodoxin paralleled the changes in plasma progesterone. Among the antioxidative enzymes examined, the SOD and catalase activities showed patterns most similar to plasma progesterone. Catalase and SOD activities increased 6-8 fold from day 6 to 16 of the estrous cycle and then decreased during the luteal regression. Ascorbate and beta-carotene showed low but significant correlation with P450scc and plasma progesterone levels. The profiles of two lipophilic antioxidants in corpora lutea were very different. beta-carotene concentration increased by approximately 6 fold from day 6 to 16, and decreased in regressive tissue. alpha-tocopherol showed a 3 fold increase between days 6 and 9 followed by a rapid decrease. Thus, at the peak of steroidogenesis at mid-luteal phase alpha-tocopherol levels decreased, but beta-carotene levels increased. The correlation between the levels of some antioxidant enzymes and compounds with progesterone levels indicates that antioxidative mechanisms are activated to cope with steroidogenesis dependent oxyradical formation in the bovine corpus luteum.

Adrenodoxin↗
PubMed1997

Yolk sac-derived murine macrophage cell line has a counterpart during ES cell differentiation.

Macrophages are phagocytic hematopoietic cells involved in several immune processes, but they are also present early in mammalian development and may participate in embryonic tissue remodeling. We have isolated and characterized a cell line, Py-YSA, from the mouse yolk sac. Py-YSA cells have several functional properties of macrophages, including uptake of acetylated low density lipoprotein and phagocytic capability. They express the murine macrophage markers F4/80 and Mac-1, and they express RNA for the c-fms receptor. Their expansion in culture requires fibroblast conditioned medium or exogenous monocyte-colony stimulating factor. Murine ES (embryonic stem) cell cultures that undergo in vitro differentiation recapitulate yolk sac development, and during this process cells arise that express both Mac-1 and F4/80 and morphologically resemble the Py-YSA cells. The kinetics and distribution pattern of the Mac-1+ cells during a time course of ES cell differentiation suggest that they originate in the blood islands, and that they subsequently leave the blood islands and disperse to tissue sites. Both F4/80 and Mac-1 are first expressed in primary cultures from day 9.5 yolk sacs. The Py-YSA cultured cells thus resemble embryonic tissue macrophages by several criteria, and they share a marker profile with a cell type found in yolk sacs and differentiating ES cells. Py-YSA cells will be a useful reagent for further understanding the role of embryonic tissue macrophages in development.

3T3 Cells↗
PubMed1996

Blood island formation in attached cultures of murine embryonic stem cells.

Differentiation of murine embryonic stem cells in suspension culture results in the formation of cystic embryoid bodies that develop blood islands. In this study pre-cystic embryoid bodies were attached to a substratum, and the program of differentiation was monitored. The attached ES cell cultures formed blood islands on a cell layer that migrated out from the center of attachment and beneath a mesothelial-like cell layer. Morphological and in situ marker analysis showed benzidine-positive hematopoietic cells surrounded by vascular endothelial cells that expressed PECAM and took up DiI-Ac-LDL. Waves of morphological differentiation were evident, suggesting a graded response to differentiation signals. Electron microscopy of the blood islands showed that they were similar to blood islands of cystic embryoid bodies and mouse yolk sacs, and cell-cell junctions were evident among the blood island cells. RNA expression analysis was consistent with the presence of hematopoietic precursor cells of several lineages and a primitive vascular endothelium in the cultures. Thus a program of vascular and hematopoietic development can be elaborated in attached ES cell cultures, and these blood islands are accessible to experimental manipulation.

Animals↗
PubMed1995

Electron leakage from the adrenal cortex mitochondrial P450scc and P450c11 systems: NADPH and steroid dependence.

In the present study we examined the coupling of NADPH oxidation to substrate hydroxylation and the effects of steroids on this process in reconstituted P450scc and P450c11 systems. To determine the relative rates of substrate hydroxylation vs electron leakage we assayed both the steroid product and H2O2 in the same sample. For both P450 systems the rates of steroid product and superoxide formation increased as NADPH concentration was increased. However, P450c11 was found to be more leaky. The leakage from the P450scc system was not affected by pregnenolone, the product of cholesterol side chain cleavage. In contrast, corticosterone, the product of P450c11, increased the rate of futile NADPH oxidation by the P450c11 system. We also tested a series of steroids to analyze the stereospecificity of their effects. Relative to the control without steroid, both C-19 and C-21 steroids with 11 alpha-hydroxy groups (11 alpha-OH-testosterone and 11 alpha-OH-cortisol) decreased leakage, and those with 11 beta-OH groups (11 beta-OH-testosterone and cortisol) stimulated both NADPH oxidation and electron leakage as measured by H2O2 formation. The results revealed a correlation between the effects previously observed in living cells and in our reconstituted systems. These findings provide further evidence that mitochondrial P450 systems indeed function as a significant source of oxygen radicals in steroidogenic cells.

Adrenal Cortex↗
PubMed1995

Expression and inducibility of vascular adhesion receptors in development.

ICAM-1 and VCAM are cell adhesion receptors expressed on vascular endothelial cells, and their expression is up-regulated as part of the inflammatory response. Tumor-derived Py-4-1 cells were a source of murine endothelial cells, and they showed increased lymphocyte binding when incubated with TNF alpha. Py-4-1 cells stimulated with TNF alpha or LPS also had elevated levels of ICAM-1 and VCAM RNAs, with maximum levels at 2 h. Developmental expression of adhesion receptors was assayed in murine yolk sacs and in cystic embryoid bodies (CEBs) that differentiate in vitro from murine embryonic stem cells. ICAM-1 and VCAM RNAs were expressed in unstimulated yolk sacs and CEBs. Expression was inducible in CEBs by exposure to LPS at all developmental stages, beginning at day 6. The time course of RNA induction in CEBs was similar to that of the Py-4-1 endothelial cell line. ICAM-1 protein expression was localized to vascular and hematopoietic blood islands in the CEBs. These results show that embryonic cells respond to inflammatory mediators by up-regulating expression of vascular adhesion receptors, and they imply an early ontogeny for the endothelial cell signal transduction pathway necessary for leukocyte recruitment.

Animals↗
PubMed1994

A fluorimetric assay for hydrogen peroxide, suitable for NAD(P)H-dependent superoxide generating redox systems.

We report a simple and sensitive fluorimetric method for quantitative assay of the production rate of hydrogen peroxide, and indirectly of superoxide, during electron transfer reactions. The assay requires the inclusion of superoxide dismutase, catalase, and 6% methanol in the tested reaction system, to stochiometrically produce formaldehyde per molecule of H2O2 generated. The reaction is terminated by adding 2 vol of Nash reagent and heating at 60 degrees C for 10 min, to convert accumulated formaldehyde to diacetyldihydrolutidine (DDL). The standard curve for formaldehyde, based on the fluorescence of DDL, is highly reproducible and allows measurement of 1 microM amounts in the reaction sample (coefficient of variation < 15%). The excitation and emission wavelengths of DDL at 412 and 505 nm are distant from those of NAD(P)H. Thus, the method can be used in NAD(P)H-dependent enzymatic systems to measure both NAD(P)H oxidation and superoxide production in the same sample. We validated the assay in a mitochondrial P450 system determining the fraction of total electron flow that is channeled to oxy-radical formation. The assay should be useful in the study of this and other superoxide/H2O2 generating systems.

Catalase↗
PubMed1993

Electron leakage from the mitochondrial NADPH-adrenodoxin reductase-adrenodoxin-P450scc (cholesterol side chain cleavage) system.

In electron (e-) transfer systems some e- may "leak," reducing O2 to a superoxide radical. This study examined the sites and kinetics of e-leakage from the mitochondrial P450scc system. Adrenodoxin reductase alone oxidized NADPH, reducing O2 to a superoxide radical at a very low rate. However, the reductase-adrenodoxin system reduced O2 at a rapid steady-state rate with Michaelis-Menten dependence on [adrenodoxin](Vmax = 3.5 micro M e-/min). After depletion of NADPH, reduced adrenodoxin was oxidized (autooxidation) with pseudo first order kinetics and the rate of e- transfer decreased 10-fold. Ca2+ (< 1 mM) stimulated e- leakage in both phases. The reductase-adrenodoxin-P450scc system exhibited the highest rate of leakage (Vmax = 7.8 microM e-/min). At low [adrenodoxin] the majority of e-leaked through P450scc and not through adrenodoxin. In the presence of the substrate, cholesterol, leakage drastically decreased to <0.5 microM e-/min. These results indicate that the mitochondrial P450 systems can leak e-, producing O2 derived free radicals. Reduction of leakage during P450scc conversion of cholesterol to pregnenolone provides a clue to understanding physiological mechanisms that control e-leakage. These may include coregulation of NADPH and cholesterol availability to the P450scc system and a system of antioxidants for quenching the oxygen radicals.

Adrenal Cortex↗
PubMed1988

Hydrogen peroxide-mediated inhibition of T-cell response to mitogens is a result of direct action on T cells.

Hydrogen peroxide, a reactive oxygen intermediate produced by activated neutrophils, has been shown to inhibit the response of human T lymphocytes to mitogens and alloantigens. Since hydrogen peroxide is known to react with iron and to induce lipid peroxidation, we compared the effects of hydrogen peroxide and a lipid peroxidation product, malondialdehyde, on the response of human peripheral blood mononuclear cells to T-cell mitogens. Peripheral blood mononuclear cells pretreated with 1 mmol/L of malondialdehyde, washed, and resuspended in fresh medium exhibited no inhibition of phytohemagglutinin responsiveness. Peripheral blood mononuclear cells treated in the same manner but with 200 mumol/L of hydrogen peroxide were inhibited by more than 95%. The addition of ferric edetate did not alter the inhibitory effects of 50 to 100 mumol/L of hydrogen peroxide, nor did the addition of deferoxamine, an iron chelator. These studies suggest that exogenous lipid peroxidation does not affect lymphocyte activation but that hydrogen peroxide has a direct inhibitory effect. Although monocytes are necessary for T-cell mitogenic responses, the effect of hydrogen peroxide was found to be directed at T lymphocytes. Exposure of T cells to a single dose of 200 mumol/L of hydrogen peroxide resulted in more than 71% suppression of the proliferative response measured 48 hours later, but the effect was spontaneously reversed by 72 to 96 hours. Repeated exposure of the cells to hydrogen peroxide resulted in continued inhibition of the proliferative response. These findings suggest that hydrogen peroxide produced by inflammatory phagocytic cells might be capable of suppressing the immune response of nearby T lymphocytes.

Deferoxamine↗
PubMed1987

Inhibition of early events in the human T-lymphocyte response to mitogens and alloantigens by hydrogen peroxide.

Hydrogen peroxide (100 to 200 microM) inhibited the response of human peripheral-blood mononuclear cells (PBMCs) in phytohemagglutinin, concanavalin A, and mixed lymphocyte culture assays by more than 90% without affecting cell viability. The response of PBMCs to pokeweed mitogen was stimulated twofold by 50 microM H2O2, but 200 microM H2O2 inhibited the pokeweed mitogen response by more than 95%. A 50 microM concentration of H2O2 completely blocked the generation of cytotoxic T cells in the mixed lymphocyte culture but did not inhibit the production of interleukin 2. Concentrations of 100 microM to 200 microM H2O2 inhibited interleukin 2 production by 45% to 57%. The H2O2 appeared to block early events in T-cell activation, since 200 microM H2O2 was not inhibitory when added one hour after stimulating the cells with phytohemagglutinin. Treatment of PBMCs with 200 microM H2O2 did not decrease the total cellular thiol pool, suggesting that H2O2-mediated inhibition of the proliferative response was not due to thiol oxidation. However, pretreatment of PBMCs with the lipid antioxidants butylated hydroxyanisole, butylated hydroxytoluene, and n-propyl gallate blocked more than 75% of the inhibitory effect of H2O2, suggesting that H2O2 inhibits T-cell activation by inducing lipid peroxidation.

B-Lymphocytes↗
PubMed1986

Characterization of functional T-cell lines derived from MRL mice.

In an effort to characterize further the role of T cells in the autoimmune disease of MRL/Mp-lpr/lpr (lpr) mice, continuous cell lines were established from spleen and lymph nodes using EL-4 lymphoma supernatants as a source of T-cell growth factor(s). Five lines were derived from lpr spleen and lymph nodes, and an equal number from MRL/Mp- +/+ (+/+). All of the lines lost their alloreactivity after a short time in culture. Surprisingly, every line manifested marked proliferation in response to autologous irradiated spleen cells. This response was restricted to I-Ak, as it was blocked with monoclonal anti-I-Ak antibodies, and as B10.A(4R) accessory cells were stimulatory while B10.A(3R) were not. There was no difference in the degree of stimulation from lpr accessory cells compared to that in those from +/+ or other H-2k mice. The T-cell lines bore Thy-1, Ly-1, L3T4, and 7D4 (interleukin 2 (IL-2) receptor), but lacked Ly-2 and surface Ig. They proliferated in response to both conventional and recombinant DNA-derived IL-2. When cocultured with Ia-identical B cells, the T-cell lines provoked B-cell division and antibody production. The cells also caused intense proliferation when cultured with freshly isolated lpr (but not +/+) lymph node cells. The results indicate that lpr lymphoid tissue contains functional T cells reactive to autologous Ia molecules and capable of inducing both B-cell activation and the proliferation of lpr lymphocytes. Such cells may be of importance in inducing hypergammaglobulinemia, autoantibody production, and lymphoproliferation in these SLE mice.

Animals↗
PubMed1985

Anti-Sm autoantibodies in MRL mice: analysis of precursor frequency.

Individual MRL-lpr mice vary in their capacity to generate anti-Sm autoantibodies spontaneously. We have compared the frequency of B-cell precursors for this autoantibody in serologically negative and serologically positive MRL-lpr mice, and in normals. Anti-Sm precursors were present in a frequency of approximately 1 per 10-30,000 in spleen cell cultures from anti-Sm positive mice, but were undetectable when spleen cells from serologically negative MRL-lpr mice or from normal mice were examined. Despite LPS stimulation, neither IgM nor IgG precursors could be detected. In parallel cultures, in contrast, anti-DNA autoantibody precursors were readily detected. The results thus indicate that, for the lupus-specific autoantibodies, the absence of antibody in autoimmune mice reflects a deficit in precursor B lymphocytes rather than an active regulatory mechanism. It is suggested that the generation of anti-Sm may reflect a low-probability random event in the generation of B-cell diversity.

Animals↗
PubMed1979

Acute stress reduces the sensitivity of the vasculature to sympathetic control.

Vascular smooth muscle from rabbits subjected to acute severe stress exhibits decreased sensitivity to sympathetic regulation. Stimulation of the sympathetic innervation of isolated vascular segments resulted in a similar subsensitivity as did exposure to norepinephrine (NE) but not histamine. Periodic contraction of these segments caused an increase in their maximum ability to contract independent of the constrictor procedure used. These results suggest that the increase in sympathetically mediated NE release that occurs in stress and some other pathological conditions may result in a blunting of neural control and possibly resistance to certain therapeutic agents.

Animals↗
PubMed1979

Release of endogenous norepinephrine from a rabbit cerebral artery.

Cerebral arteries are relatively unresponsive to sympathetic nerve stimulation, in spite of extensive adrenergic innervation. To determine whether these nerves are functional, release of endogenous norepinephrine (NE) was measured using a radioenzymatic assay. Fractional release of NE per stimulation pulse was more than 5 times greater from the rabbit basilar artery than from the ear artery. Thus, while the NE content of the two vessels is quite similar, transmitter release is considerably greater in the basilar artery. Since NE accumulation is also much greater in the basilar artery, it seems possible that an active parameter such as NE release or accumulation may be a better index of functional nerve capacity than NE content. Previous studies have shown that alpha adrenergic blocking agents do not block the contractile response to nerve stimulation of the basilar artery, but actually increase it. Thus, the possibility that blockade of presynaptic adrenergic receptors leads to increased transmitter release was tested. Indeed, both phenoxybenzamine and phentolamine significantly increased stimulation-evoked NE release. It appears that postsynaptic events in cerebral arteries are atypical, while release of transmitter, including modulation by presynaptic alpha adrenergic receptors is similar to other blood vessels.

Animals↗