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Biomedical subjects

R Linden

Publications and source records attributed to R Linden.

At least 19 recordsLinked to original sources
PubMed2006

Apoptotic effect of fludarabine is independent of expression of IAPs in B-cell chronic lymphocytic leukemia.

Despite the efficiency of fludarabine in the induction of clinical responses in B-cell chronic lymphocytic leukemia (B-CLL) patients, resistance to this drug has been documented. The present study tested whether resistance to fludarabine is related to the expression of inhibitor of apoptosis proteins (IAPs) family members. We analyzed the expression of c-IAP1, c-IAP2 and XIAP, by immunocytochemistry, in 30 blood samples from B-CLL patients and correlated protein expression to fludarabine-induced apoptosis estimated by an annexin-V assay. Expression of c-IAP1, c-IAP2 and XIAP were found predominantly in the cytoplasm, and a wide range of staining intensities was observed among distinct samples. No correlation was found between the levels of IAPs expression and prognostic factors such as age, gender, lymphocyte doubling time, white blood cell count or previous treatment. The expression of IAPs also failed to predict the sensitivity to fludarabine-induced apoptosis. Alternative pathways of cell death may explain the independence of fludarabine-induced apoptosis from the high expression of IAPs.

Adult↗
PubMed2005

Rapid and long-term plasticity in the neonatal and adult retinotectal pathways following a retinal lesion.

The uncrossed retinotectal projection restricts its terminal fields to the ventral boundary of the visual layers at the rostral tectum during early post natal development. During this critical period, temporal retinal lesions in one eye induce laminar rearrangements in the uncrossed pathway of the intact eye toward the collicular surface previously occupied, almost exclusively, by the crossed retinal axon population. We have compared, using anterograde tracing techniques, the time course and magnitude of the axonal sprouting resulting from retinal lesions in neonates and adults. Early retinal lesions (within the first two post natal weeks) induced extensive and rapid plasticity of the ipsilateral projection 48 h after the lesions. On the third post natal week, similar retinal lesions induced a small reorganization of the intact eye's uncrossed projection within a 3-week survival time. Nevertheless, giving the animals a long-term survival, resulted in an increased plastic capability, suggesting that even after the critical period, intact retinal axons can respond efficiently to injury. The results suggest two phases of axonal reorganization within this subcortical pathway: a rapid plasticity within the critical period and a slow, but continuous plasticity in adulthood.

Age Factors↗
PubMed2005

Modulation of the expression of the transcription factor Max in rat retinal ganglion cells by a recombinant adeno-associated viral vector.

Exclusion of the transcription factor Max from the nucleus of retinal ganglion cells is an early, caspase-independent event of programmed cell death following damage to the optic axons. To test whether the loss of nuclear Max leads to a reduction in neuroprotection, we developed a procedure to overexpress Max protein in rat retinal tissue in vivo. A recombinant adeno-associated viral vector (rAAV) containing the max gene was constructed, and its efficiency was confirmed by transduction of HEK-293 cells. Retinal ganglion cells were accessed in vivo through intravitreal injections of the vector in rats. Overexpression of Max in ganglion cells was detected by immunohistochemistry at 2 weeks following rAAV injection. In retinal explants, the preparation of which causes damage to the optic axons, Max immunoreactivity was increased after 30 h in vitro, and correlated with the preservation of a healthy morphology in ganglion cells. The data show that the rAAV vector efficiently expresses Max in mammalian retinal ganglion cells, and support the hypothesis that the Max protein plays a protective role for retinal neurons.

Animals↗
PubMed2005

Phagocytosis of apoptotic cells: a matter of balance.

Efficient clearance of apoptotic cells is required to control homeostasis in normal and pathological circumstances, and inappropriate clearance of cell corpses may lead to autoimmune diseases and inflammation. The multiplicity of phagocytotic mechanisms points to the relevance of removing apoptotic cells. A variety of surface molecules present in either the apoptotic bodies or phagocytes help in attachment and initiation of engulfment. Nonetheless, uncontrolled phagocytosis of apoptotic cells and other particles may lead to tissue injury; therefore, negative signals are important in balancing phagocytotic activity. This review aims at a systematic examination of positive and negative signals that modulate the uptake of apoptotic bodies and the signaling mechanisms involved in the clearance of apoptotic cells.

Animals↗
PubMed2004

Radiation-induced apoptosis in developing mouse retina exhibits dose-dependent requirement for ATM phosphorylation of p53.

Ionizing radiation (IR) induces DNA breakage to activate cell cycle checkpoints, DNA repair, premature senescence or cell death. A master regulator of cellular responses to IR is the ATM kinase, which phosphorylates a number of downstream effectors, including p53, to inhibit cell cycle progression or to induce apoptosis. ATM phosphorylates p53 directly at Ser15 (Ser18 of mouse p53) and indirectly through other kinases. In this study, we examined the role of ATM and p53 Ser18 phosphorylation in IR-induced retinal apoptosis of neonatal mice. Whole-body irradiation with 2 Gy IR induces apoptosis of postmitotic and proliferating cells in the neonatal retinas. This apoptotic response requires ATM, exhibits p53-haploid insufficiency and is defective in mice with the p53S18A allele. At a higher dose of 14 Gy, retinal apoptosis still requires ATM and p53 but can proceed without Ser18 phosphorylation. These results suggest that ATM activates the apoptotic function of p53 in vivo through alternative pathways depending on IR dose.

Animals↗
PubMed2003

Herbimycin A induces sympathetic neuron survival and protects against hypoxia.

We have examined how herbimycin affects the survival and neuritogenesis of avian sympathetic neurons. Herbimycin promoted sympathetic neuron survival and neuritogenesis. At higher concentrations (> or = 100 ng/ml), herbimycin still enhanced neuron survival but blocked neuritogenesis. Addition of herbimycin (10-30 ng/ml) to neurons cultured in the presence of NGF or retinal conditioned medium altered neuronal morphology, with an increase in the number of neurites. Addition of NGF during hypoxia rescued 52% of the neurons compared to 14% survival in control conditions. Herbimycin alone rescued about 50% of the neurons. In the presence of NGF and 100 ng/ml herbimycin, 81% of the neurons survived hypoxia. Our results show that herbimycin promotes survival of chick sympathetic neurons and potentiates the effects of NGF.

Adrenergic Fibers↗
PubMed2002

Activation of p38 mitogen-activated protein kinase during normal mitosis in the developing retina.

The p38 member of the mitogen-activated protein kinase superfamily is engaged by phosphorylation in response to environmental stress signals, and may have either permissive or inhibitor roles upon cell proliferation. The cell cycle in the proliferative zone of the retina is tightly controlled and proceeds in synchrony with interkinetic migration of the neuroblast nuclei. We examined the association of p38 kinase activity with the cell cycle in the normal, non-stressed retina of the developing rat, maintained either in vivo or in vitro. Using immunohistochemistry, we show that mitotic profiles in the developing retina are highly enriched for phosphorylated p38. Blockade of p38 activity with the chemical inhibitor SB203580 for 4 h transiently arrested cells at the metaphase-anaphase transition and induced cell death after 20 h. p38 inhibition induced an aberrant mitotic profile, with chromosomes arranged in one side of the cell. The data show that p38 is active during normal mitosis and we suggest that p38 is required for the proper cell cycle progression during metaphase-anaphase transition in retinal neuroblasts.

Aging↗
PubMed2001

Fas ligand triggers pulmonary silicosis.

We investigated the role of Fas ligand in murine silicosis. Wild-type mice instilled with silica developed severe pulmonary inflammation, with local production of tumor necrosis factor (TNF)-alpha, and interstitial neutrophil and macrophage infiltration in the lungs. Strikingly, Fas ligand-deficient generalized lymphoproliferative disease mutant (gld) mice did not develop silicosis. The gld mice had markedly reduced neutrophil extravasation into bronchoalveolar space, and did not show increased TNF-alpha production, nor pulmonary inflammation. Bone marrow chimeras and local adoptive transfer demonstrated that wild-type, but not Fas ligand-deficient lung macrophages recruit neutrophils and initiate silicosis. Silica induced Fas ligand expression in lung macrophages in vitro and in vivo, and promoted Fas ligand-dependent macrophage apoptosis. Administration of neutralizing anti-Fas ligand antibody in vivo blocked induction of silicosis. Thus, Fas ligand plays a central role in induction of pulmonary silicosis.

Adoptive Transfer↗
PubMed2001

Depletion of cortical target induced by prenatal ionizing irradiation: effects on the lateral geniculate nucleus and on the retinofugal pathways.

Studies using neonatal surgical lesions to reduce the target area of the retina have supported the idea that developing axons show only a limited specificity in their targeting. This investigation tested whether retinogeniculate axons adjust for partial target depletion by repositioning of axons. We used adult Swiss mice exposed to gamma rays at the time when layer IV cells are generated in the ventricular zone (16 days of gestation). Nissl-stained brain sections were used for histological analyses in thalamus and cortex. Retinal ganglion cells were backfilled from the optic tract with horseradish peroxidase. Intraocular injections of horseradish peroxidase were used to study the retinal projections. In the posterior cortex there was a nearly complete absence of layer IV. The irradiated animals showed a 75% reduction of the dorsal lateral geniculate nucleus. The ventral division, superior colliculus, and other visually related nuclei were not affected. The loss in the ganglion cells (15.7%) was significant but clearly smaller than that observed in the dorsal lateral geniculate nucleus (75%). Therefore, the shrinkage of the dorsal lateral geniculate nucleus led to a reduction in the area available for retinal projections. Despite partial target loss, pattern of retinal projections did not differ from that of the controls. The effect on the dorsal lateral geniculate nucleus is discussed in the light of differences between prenatal and neonatal damage of the presumptive visual cortex. The absence of aberrant retinal projections suggests that repositioning of axons is not the first mechanism employed by retinal axons to match connections in numerically disparate populations.

Animals↗
PubMed2001

Effects of prenatal ionizing irradiation on the development of the ganglion cell layer of the mouse retina.

Prenatal exposure to ionizing irradiation has been shown to be an effective method to eliminate selectively certain neuronal population. This investigation studied the effects on the ganglion cell layer of the retinae of adult mice exposed to a gamma source (total dose=3 Gy) at 16 days gestation. There was a significant reduction in the total number of neurons (displaced amacrine+ganglion cells) in the ganglion cell layer (33%) that was mainly caused by a pronounced loss (59%) of displaced amacrine cells. The diameters of the surviving retinal ganglion cells were consistently larger than those of the controls. Prenatal irradiation is the first experimental approach that partially eliminates displaced amacrine cells. It is suggested that the morphogenesis of retinal ganglion cells may be affected by displaced amacrine cells.

Animals↗
PubMed2001

Differentiation-dependent sensitivity to cell death induced in the developing retina by inhibitors of the ubiquitin-proteasome proteolytic pathway.

The effects of inhibitors of proteasome function were studied in the retina of developing rats. Explants from the retina of neonatal rats at postnatal day (P) 3 or P6 were incubated with various combinations of the proteasome inhibitor carbobenzoxyl-leucinyl-leucinyl-leucinal (MG132), the protein synthesis inhibitor anisomycin, or the adenylyl cyclase activator forskolin. MG132 induced cell death in a subset of cells within the neuroblastic (proliferative) layer of the retinal tissue. The cells sensitive to degeneration induced by either MG132 or anisomycin, were birthdated by bromodeoxyuridine injections. This showed that the MG132-sensitive population includes both proliferating cells most likely in their last round of cell division, and postmitotic undifferentiated cells, at a slightly earlier stage than the population, sensitive to anisomycin-induced cell death. The results show that sensitivity to cell death induced by proteasome inhibitors defines a window of development in the transition from the cell cycle to the differentiated state in retinal cells.

Animals↗
PubMed2001

Paracrine neuroprotective effect of nitric oxide in the developing retina.

The retina of newborn rats consists of the ganglion cell layer (GCL), the inner plexiform layer (IPL), the inner nuclear layer (INL) containing amacrine cells and the neuroblastic layer (NBL). In retinal explants, the GCL enters cell death after sectioning of the optic nerve, whereas there is almost no cell death in the NBL. When protein synthesis is inhibited with anisomycin, cell death is blocked in the GCL and induced in the NBL. We tested the roles of nitric oxide (NO) on cell death in the retina in vitro. Either L-arginine, the substrate for NO synthase or the NO donor S:-nitroso-acetylpenicillamine (SNAP) blocked cell death induced by anisomycin in the NBL, but had no effect in the GCL. Sepiapterin, a precursor of the nitric oxide synthase (NOS)-cofactor tetrahydrobiopterin also had a protective effect against anisomycin. The use of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble form of guanylyl cyclase, showed that anti-apoptotic effect of SNAP is partially mediated by cGMP generated by activation of guanylyl cyclase. NADPH-diaphorase histochemistry stained cells only in the GCL and INL. Thus, the degenerative effect of anisomycin is observed within the NBL, whereas the localization of NOS is restricted to the GCL and INL. The protective effect of both the NO substrate and cofactor upon cell death induced by anisomycin in the NBL, indicates that NO produced by amacrine and ganglion cells is a paracrine modulator of cell death within the retinal tissue.

Animals↗
PubMed2000

Chloramphenicol induces apoptosis in the developing brain.

Programmed cell death was studied in the superior colliculus of the developing rat brain following injections of chloramphenicol. Neonatal rats were either subject to unilateral eye removal or left untouched. Following a 3-h post-operative survival, the animals were perfused with fixatives and frozen sections of their brains were examined for apoptosis after either neutral-red staining, in situ nick-end labeling of fragmented DNA, or immunocytochemistry to activated caspase-3. Chloramphenicol induced apoptosis in control brains and potentiated cell death in deafferented superior colliculi. The results show that CMP has a general pro-apoptotic effect in the developing brain.

Afferent Pathways↗
PubMed2000

Laminin modulates neuritogenesis of developing rat retinal ganglion cells through a protein kinase C-dependent pathway.

Dissociated cells from rat retinae (P2-P21) were cultured to investigate interactions between brain-derived neurotrophic factor (BDNF), various substrates (poly-L-lysine, collagen, and laminin), and protein kinases upon the neuritogenesis of retinal ganglion cells (RGCs). We found that BDNF-promoted neuritogenesis was enhanced by forskolin in RGCs from rats at P2-P21 plated on either poly-L-lysine or collagen. In contrast, in cultures with a laminin substrate, the enhancer effect of forskolin was observed only in RGCs taken from the retina of rats at P2-P6. Laminin blocked the enhancement of BDNF-induced RGCs neuritogenesis by forskolin, in RGCs from either P14 or P21, and induced a tenfold increase of protein kinase C (PKC) activity compared to poly-L-lysine. This blockade was reverted with a selective PKC inhibitor and was reproduced in poly-L-lysine cultures of P14-P21 RGCs with a PKC activator. Because axotomized RGCs need both BDNF and forskolin to regenerate, we suggest that laminin can hinder this effect by simultaneous PKC activation according to a developmentally regulated pattern. We further propose a model of interaction in the optic pathways triggered by BDNF, forskolin, and laminin that may be useful in elucidating some of the biological effects seen with regenerating axons.

Animals↗
PubMed2000

The anti-death league: associative control of apoptosis in developing retinal tissue.

Apoptosis, the major form of programmed cell death (PCD), is executed through a proteolytic cascade that can be differentially engaged by various extracellular signals. Modulation of both the sensitivity to PCD and of the actual sequence of apoptotic events is, therefore, strongly dependent on cell interactions. This paper reviews the use of a retinal explant preparation as a model of the organized nervous tissue, to study the effects of neural messengers in the control of sensitivity to apoptosis. Studies of retinal explants showed that dopamine, glutamate and nitric oxide may have anti-apoptotic effects upon developing retinal cells. At least the effects of nitric oxide are clearly paracrine. In addition, preliminary evidence has been gathered of a role for gap junctional communication in the control of sensitivity of retinal cells to the induction of apoptosis. These findings underscore the importance of selective cell interactions in the control of PCD in the developing nervous system.

Animals↗
PubMed2000

Evidence that the bifunctional redox factor / AP endonuclease Ref-1 is an anti-apoptotic protein associated with differentiation in the developing retina.

Retinal cell differentiation leads to resistance to apoptosis induced by inhibition of protein synthesis, suggesting the accumulation of anti-apoptotic proteins. The redox factor/AP endonuclease Ref-1 (APE, APEX, HAP1) affects both DNA repair and the activity of various transcription factors, and controls sensitivity to genotoxic insults. We studied the expression of Ref-1 in the retina and brain of developing rats. Ref-1 immunoreactivity increased progressively within the nucleus of differentiating retinal cells, whereas it decreased in the developing hippocampal formation. During both natural and experimentally-induced cell death, Ref-1 disappeared from the nucleus of apoptotic cells. Degradation of Ref-1 in axotomized ganglion cells preceded the morphological characteristics of apoptosis. The sensitivity to apoptosis triggered by either thapsigargin or okadaic acid was the highest in photoreceptors, that contain the least Ref-1 among differentiated retinal cells. In both these differentiated cell types, inhibition of protein synthesis prevented the loss of Ref-1 and rescued the neurons. The data suggest that Ref-1 is an anti-apoptotic protein associated with cell differentiation in the retina.

Animals↗
PubMed2000

Response surface analysis applied to the preparation of tablets containing a high concentration of vegetable spray-dried extract.

This work relates to the formulation of tablets containing a high proportion of spray-dried extracts (SDEs) from Passiflora edulis leaves. The tablets were prepared by direct compression. Colloidal silicon dioxide was selected as a glidant and moisture adsorbent, cross-linked carboxymethycellulose was used as the disintegrant, microcrystalline cellulose was the filler/binder, and tricalcium phosphate as a spray-drying adjuvant. The colloidal silicon dioxide and cross-linked carboxymethycellulose quantities and their influences on the tablet hardness and disintegration time were studied by a central composite design. The model equations were fitted to the experimental data and then validated. It could be concluded that the colloidal silicon dioxide proportion increased the hardness, and the cross-linked carboxymethycellulose proportion determined a linear decrease of the disintegration time. The optimal values chosen were 2.0% Aerosil 200 and 2.5% Ac-Di-Sol. The tablets showed a hardness of 85.02 N and a disintegration time of 7.35 min.

Chemistry, Pharmaceutical↗