X-ray microanalysis and phagocytotic activity of cultured retinal pigment epithelial cells in hypoxia

Alterations of Retinal Pigment Epithelium-Photoreceptor Complex in Patients with Type 2 Diabetes Mellitus without Diabetic Retinopathy: A Cross-Sectional Study

AIM

A cross-sectional study was performed to examine the alterations of the retinal pigment epithelium- (RPE-) photoreceptor complex layer in type 2 diabetes mellitus (DM) without diabetic retinopathy (DR), using spectral-domain optical coherence tomography (SD-OCT).

METHODS

Patients with type 2 DM without DR and healthy controls without DM were recruited. All participants underwent examinations including SD-OCT. The thickness measurements of the retinal neural layers were calculated after automatic segmentation. An independent-sample t-test was used to compare the means of the thickness of retinal neural layers in patients with DM and healthy controls.

RESULTS

Sixty-seven eyes from 67 patients with DM and 30 eyes from 30 healthy controls were included in this study. No significant differences were found in age (P = 0.601), gender (P = 0.601), gender (P = 0.601), gender (P = 0.601), gender (P = 0.601), gender (P = 0.601), gender (P = 0.601), gender (P = 0.601), gender (.

CONCLUSION

Lesions in the RPE-photoreceptor complex are present without vascular abnormalities, which may precede the alterations of ganglion cells in patients with type 2 DM.

Effects of gamma irradiation on BCL2 and TPR53BP2 expression in the porcine ciliary body

BACKGROUND

When dissection of porcine eyes from a living body results in the cessation of aqueous humor production and blood flow, programmed cell death regulated by TPR53BP2 and BCL2 genes may occur in the pigmented epithelium (PE) and non-pigmented epithelium (NPE) of the ciliary body. Blood products are subjected to gamma irradiation in order to prevent cellular damage resulting from transfusion-associated graft-versus-host disease. We investigated whether gamma irradiation influenced BCL2 or TPR53BP2 genes as well as the morphology of the porcine ciliary body.

METHODS

We irradiated the anterior segments of porcine eyes by using (60)Co gamma-rays (20 Gy). To study BCL2 and TPR53BP2 expression, the irradiated specimens were fixed in formalin and embedded in paraffin and then incubated with mouse monoclonal anti-human BCL2 or TPR53BP2 antibody.

RESULTS

Following dissection, an imbalance in homeostasis began with positive BCL2 and TPR53BP2 expression in the edematous ciliary processes, and resulted in atrophy of the NPE. Increased BCL2 and TPR53BP2 expression were evident just after gamma irradiation. Decreased TPR53BP2 expression occurred after 8 h of incubation, and thereby suppressed apoptosis in the NPE; hence, the structure of the ciliary body that was incubated for 8 h after gamma irradiation was well preserved.

CONCLUSIONS

Irradiation renders the ciliary body in enucleated porcine eyes less vulnerable to apoptosis, and thereby exerts a profound preservative effect.

Membranes of retinal pigment epithelial cells in vitro are damaged in the phagocytotic process of the photoreceptor outer segment discs peroxidized by ferrous ions

The ferrous ions released from haemoglobin and storage-transferrin ions cause oxidative stress in the eyes. We observed the phagocytotic process of the photoreceptor outer segment discs peroxidized by ferrous ions in the retinal pigment epithelial (RPE) cells in vitro, and investigated how the ferrous ions influenced RPE in vitro and the photoreceptor outer segment discs. We obtained isolated photoreceptor outer segment discs using sucrose gradient of specific gravity after homogenizing porcine retinas. After bovine RPE cells were cultured with isolated photoreceptor outer segment discs containing FeCl2 for 5 and 24 h, we incubated the specimens with rhodamine phalloidin, antimouse alpha-tubulin antibody and antimouse Ig G (FITC and rhodamine labelled). We observed the specimens by a laser scanning microscopy, and made the ultrathin sections with or without 2% uranyl acetate and 2% lead acetate for examination by transmission electron microscopy. Actin filaments and microtubules of specialized cells such as RPE cells were actively involved in phagocytosis of the photoreceptor outer segment discs. Microtubules were damaged during the phagocytotic process of the photoreceptor outer segment discs peroxidized by ferrous ions. The peroxidation increased the granular and aggregated autofluorescence of the photoreceptor outer segment discs. The membranes of the disc and the phagosomes, and lysosomes in RPE cells were damaged by ferrous ions and had fine particles with high electron density staining without uranium acetate and lead citrate. The cytoskeletons such as actin filaments and microtubules, and the membranes of the phagosomes and the lysosomes in RPE cells in vitro were damaged during the phagocytotic process of the photoreceptor outer segment discs peroxidized by ferrous ions.

Effects of fluorescent light on growth of bovine retinal pigment epithelial cells in vitro incubated with linoleic acid or linoleic acid hydroperoxide

Light-induced peroxidation of polyunsaturated fatty acids (PUFA) may generate lipid hydroperoxides, which may have toxic effects on retinal pigment epithelial (RPE) cells in vitro. We investigated the effects of cool-white fluorescent light on the RPE cells incubated with linoleic acids (LA) or linoleic acid hydroperoxides (LHP) and the influence of antioxidative enzymes. We measured the bovine RPE cell number after exposure to fluorescent light (610 and 1,200 lux) in the presence of LA or LHP. Furthermore, the effects of superoxide dismutase (SOD) and catalase on LA- or LHP-treated RPE cells were also examined. Both LA and LHP treatment increased RPE cell number under weak illumination (610 lux), but dose-dependently decreased the number of cells exposed to strong illumination (1,200 lux). With exposure to strong illumination, LA caused a greater reduction in RPE cell number than LHP. Multiple linear regression analysis showed that the number of RPE cells was significantly decreased in a manner dependent on the interactions of the illuminance of light and the concentrations of LA or LHP. The antioxidative enzymes significantly ameliorated the damage to RPE cells from LA or LHP and exposure to light. Therefore, the exposure to fluorescent light augmented the cytotoxic effects of LA and LHP on RPE cells, and this effect is likely to be mediated by reactive oxygen species.

The localization of glutathione peroxidase in the photoreceptor cells and the retinal pigment epithelial cells of Wistar and Royal College of Surgeons dystrophic rats

INTRODUCTION

If degenerating photoreceptor outer segments not phagocytized by RPE cells in the retina of Royal College Surgeons (RCS) rats were to undergo peroxidation, the distribution of glutathione peroxidase (GSH-PO) in the mitochondria or cytoplasm of the retina might be altered. We evaluated the immunocytochemical localization of GSH-PO to identify subcellular organelles in sections of the retinas of RCS rats.

METHODS

Immunoblot analysis confirmed the presence of GSH-PO molecules in the retinas of RCS and Wistar rats aged 3 weeks. Sections were reacted with the F(ab) fragment of anti-rat alphaGSH-PO and then examined by laser scanning microscopy (LSM) and transmission electron microscopy (TEM).

RESULTS

The size of the GSH-PO molecule in the retina was about 21 KD in the mitochondria and 23 KD in the cytosol in both strains of rats. LSM revealed fluorescent granules in the photoreceptor inner segments of the Wistar rats, and immunohistochemical TEM revealed GSH-PO in the mitochondria of their photoreceptor inner segments and retinal pigment epithelial (RPE) cells. In the RCS rats, the degenerating photoreceptor outer segments were clearly seen to be positive for anti-GSH-PO by conventional light microscopy (CLM). However, the photoreceptor inner segments of the RCS rats were negative for staining with anti-GSH-PO by LSM, and no GSH-PO could be detected in the mitochondria of the photoreceptor inner segments or RPE cells by immuno-TEM.

CONCLUSION

Degeneration of the photoreceptor outer segments induced mitochondrial damage in the photoreceptor inner segments, and as a result GSH-PO shifted from the photoreceptor inner segments to the degenerating outer segments.

Changes in lipid peroxide level in retinal pigment epithelial cells in vitro upon addition of linoleic acids or linoleic acid hydroperoxides under varying concentrations of oxygen

We previously observed the presence of autofluorescent lipofuscin or its like in retinal pigment epithelial (RPE) cells, which were incubated with linoleic acid hydroperoxides (LHP). We studied the effect of oxygen on the level of lipid peroxides in RPE cells in the presence of linoleic acids (LA) or LHP. The level of lipid peroxides in these cells was determined by use of the thiobarbituric acid-reactive substance (TBARS), which responded to oxygen concentrations qualitatively, and a linear regression analysis. Multiple linear regression analysis disclosed that treatment with LA for 24 hr resulted in detectable increase in the level of TBARS in the cells, whereas treatment with LA or LHP for 48 hr caused detectable decrease. Stepwise linear regression analysis showed that the level of TBARS decreased in an oxygen-tension dependent manner in the cells incubated with LA for 48 hr. Thus, it was shown that short-term incubation with LA increased the level of TBARS in the cells and that LA decreased its level in an oxygen-tension dependent manner. For these results, the postulation was made that the prolonged auto-oxidation of LA caused production of lipofuscin-like materials, a complex of lipid peroxides and proteins that were insoluble in SDS and acetic acid solution.