Transferrin, One of the Major Vitreous Proteins, is Produced Within the Eye

Laicine, Eduardo Miguel; Haddad, Antônio

doi:10.1006/exer.1994.1129

Cited by 30 publications

(22 citation statements)

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“…Smaller molecules present in the liquid phase include inorganic salts, glucose, ascorbic acid, and multiple polypeptides and proteins, including albumin, transferrin, IgG, cartilage matrix-like glycoprotein, and others (Laicine and Haddad, 1994). These components serve to provide a transparent light path and contribute to the maintenance of normal ocular structure and function.…”

Section: Discussionmentioning

confidence: 99%

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Vitreous humor and albumin augment the proliferation of cultured retinal precursor cells

Yang

Klassen

Pries

et al. 2008

J of Neuroscience Research

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Intravitreal injection is an important delivery route for studies involving the transplantation of various types of precursor cells to the retina; however, the effect on these cells of exposure to the vitreous microenvironment has not been specifically investigated. Here vitreous humor was evaluated for the potential to influence the proliferation of rat retinal precursor cells in vitro. Cells were isolated at embryonic day 19 and plated in standard proliferation medium in the presence or absence of fluid expressed from porcine vitreous humor. Cellular proliferation at different concentrations of vitreous fluid supplementation was quantified by using a (3)H-thymidine incorporation assay. Active components of vitreous fluid were partially characterized by gel filtration chromatography (GFC) and UV spectral analysis. The effect of each vitreous fraction on proliferation was determined as well. Results showed that addition of 20% vitreous fluid to primary rat retinal cultures significantly increased (3)H-thymidine incorporation compared with growth medium without vitreous supplementation. A vitreous fraction showing growth-promoting activity was localized to a molecular mass range <1000 Da, consistent with ascorbic acid. Ascorbic acid was confirmed in vitreous fluid by UV spectral analysis. Growth-augmenting activity was present in higher molecular mass vitreous fractions, consistent with protein components. Albumin, the major protein in vitreous fluid, was found to augment proliferation. Because vitreous-associated augmentation of retinal precursor proliferation remains an epidermal growth factor-dependent phenomenon, the proliferative status of transplanted cells in the vitreous cavity is likely determined by a combination of factors.

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Section: Discussionmentioning

confidence: 99%

“…A small molecule known to be concentrated in vitreous humor is ascorbic acid (Laicine and Haddad, 1994). The presence of ascorbic acid in a solution is characterized spectrophotometrically by a distinct absorption band with a maximum at 265 nm.…”

Section: The Low-molecular-mass Vitreous Fraction With Proliferation-mentioning

confidence: 99%

Vitreous humor and albumin augment the proliferation of cultured retinal precursor cells

Yang

Klassen

Pries

et al. 2008

J of Neuroscience Research

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“…Because of the restriction of trans-RPE transport of circulatory proteins such as apo-Tf or apo-HPX, the retina is likely to provide its own protective mechanisms and, indeed, it has been shown that this tissue (Davis and Hunt, 1993) as well as other parts of the eye (Laicine and Haddad, 1994) synthesize apo-Tf. This ocular apo-Tf probably functions not only as a protective agent sequestering any free ferric iron that may be present in retinal extracellular fluids but also participates in the normal transport of iron between the apical surface of RPE cells and the cells of the neural retina (Davis and Hunt, 1993).…”

mentioning

confidence: 98%

Hemopexin in the human retina: Protection of the retina against heme-mediated toxicity

Hunt

Gaur

et al. 1996

J. Cell. Physiol.

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The existence of the blood-retinal barrier means that proteins that protect the retina from damage by reactive oxygen species must either be made locally or specifically transported across the barrier cells; however, such transepithelial transport does not seem to occur. Among the circulatory proteins that protect against iron-catalyzed production of free radicals are apo-transferrin, which binds ferric iron and has previously been shown to be made by cells of the neural retina (Davis and Hunt, 1993, J. Cell Physiol., 156:280-285), and the extracellular antioxidant, apo-hemopexin, which binds free heme (iron-protoporphyrin IX). Since hemorrhage and heme release can be important contributing factors in retinal disease, evidence of a hemopexin-based retinal protection system was sought. The human retina has been shown to contain apo-hemopexin which is probably synthesized locally since its mRNA can be detected in retinal tissue dissected from human donor eyes. It is likely that the retina contains a mechanism for the degradation of hemopexin-bound heme since the blood-retinal barrier also precludes the exit of heme-hemopexin from the retina. Retinal pigment epithelial cells have been found to bind and internalize heme-hemopexin in a temperature-dependent, saturable, and specific manner, analogous to the receptor-mediated endocytic system of hepatoma cells. Moreover, the binding of heme-hemopexin to the cells stimulates the expression of heme oxygenase-1, metallothionein-1, and ferritin.

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“…Heme is similarly complexed to apo-hemopexin (Smith, 1990). Neither of these proteins can cross the bloodretinal barrier, and iron in the retina is bound by apoTf made locally in photoreceptor (Davis and Hunt, 1993) and other (Laicine and Haddad, 1994) cells. Recently, we have shown that retinal cells also produce apo-HPX while RPE cells express the HF' X receptor and heme-HPX stimulates these cells to induce the expression of heme oxygenase-1, ferritin, and metallothionein-1 (see accompanying paper), and here it has been shown that both apo-Tf and apo-HPX can protect RPE cells against oxidative damage.…”

Section: Discussionmentioning

confidence: 99%

Heme-mediated reactive oxygen species toxicity to retinal pigment epithelial cells is reduced by hemopexin

1996

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Catalysis of the formation of reactive oxygen species (RO2S) by low molecular weight complexes of iron has been implicated in several pathological conditions in the retina since photoreceptors and retinal pigment epithelial cells are likely to be especially sensitive to RO2S. Since protective proteins cannot cross the blood-retinal barrier, it is likely that the retina performs its own protective functions by synthesizing proteins that bind iron and nonprotein iron complexes, the major catalysts of RO2S generation. Investigations were carried out to determine whether pigment epithelial cells are themselves sensitive to iron-generated RO2S and whether apo-transferrin and apo-hemopexin, known to be made locally in the retina, can perform a protective function. In 51Cr release assays, the toxicity of exogenous RO2S including hydrogen peroxide or superoxide (generated by xanthine oxidase/hypoxanthine) to human retinal pigment epithelial cells was inhibited by the iron chelators, desferrioxamine and apo-transferrin. Free but not protein-bound ferric iron and heme exacerbated the toxic effect. The toxic effect of heme was abolished by the heme-scavenging, extracellular antioxidant, apo-hemopexin, and also by exogenous bovine serum albumin. In addition, heme toxicity was inhibited by a 3 h preincubation of cells with either heme, apo-hemopexin, or heme-hemopexin 24 h prior to the toxicity assay. It is concluded, first, that toxic effects of iron and heme can be prevented by apo-transferrin or apo-hemopexin and, second, that exposure of RPE cells to free heme or hemopexin sets in motion a series of biochemical events resulting in protection against oxidative stress. It is probable that these include heme oxygenase induction.

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Transferrin, One of the Major Vitreous Proteins, is Produced Within the Eye

Cited by 30 publications

References 0 publications

Vitreous humor and albumin augment the proliferation of cultured retinal precursor cells

Vitreous humor and albumin augment the proliferation of cultured retinal precursor cells

Hemopexin in the human retina: Protection of the retina against heme-mediated toxicity

Heme-mediated reactive oxygen species toxicity to retinal pigment epithelial cells is reduced by hemopexin

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