Retinal pigment epithelial cells: biological property and application in Parkinsonʼs disease

Retinal pigment epithelial changes in Parkinson's disease: A spectral domain optical coherence tomography study

OBJECTIVE

To evaluate retinal pigment epithelium (RPE) changes in Parkinson's Disease (PD) and to compare choroidal thickness (CT) and retinal layers with healthy controls.

METHODS

Parkinson's patients older than 18 and the age-sex match control group were included in this prospective observational study. The neurological and ophthalmological evaluation was performed. All participants were examined by spectral-domain optical coherence tomography. Focal RPE changes were defined as local RPE changes observed in any macula scan.

RESULTS

Forty (24 male, mean age 69.2 years) participants were included in the study group, and 44 (24 male, mean age 68.9 years) participants in the control group. There was no significant difference between groups in terms of age and sex. All patients were using oral dopaminergic and/or non-dopaminergic therapy. The RPE changes in the macular area were observed in 14/40 PD eyes (35%) and were significantly more frequent than in the control group (2/44, 4.5%, P = 0.001). All of the RPE changes were RPE thickening (±additional finding: subretinal deposit, subRPE deposit). The logistic regression model for possible factors that may affect RPE changes revealed statistical significance in prolonging disease duration; however, age, sex, and the presence of hypertension were not significant. Inferior 3-mm RPE layer thickness was found to be thicker in PD. There was no significant difference between groups in terms of CT, retinal layers, and peripapillary retinal nerve fiber layer thickness (RNFLT), except inferonasal RNFLT which was thinner in the study group.

CONCLUSIONS

The RPE changes are more frequent in patients with PD than in the control group in the macular area. The most frequent RPE change is the focal thickening of RPE, and RPE changes were associated with disease duration. We cannot distinguish a potential drug effect from a true potential effect of the disease in question.

Transplantation of human retinal pigment epithelial cells in the nucleus accumbens of cocaine self-administering rats provides protection from seeking

Chronic exposure to drugs and alcohol leads to damage to dopaminergic neurons and their projections in the 'reward pathway' that originate in the ventral tegmental area (VTA) and terminate in the nucleus accumbens (NAc). This damage is thought to contribute to the signature symptom of addiction: chronic relapse. In this study we show that bilateral transplants of human retinal pigment epithelial cells (RPECs), a cell mediated dopaminergic and trophic neuromodulator, into the medial shell of the NAc, rescue rats with a history of high rates of cocaine self-administration from drug-seeking when returned, after 2 weeks of abstinence, to the drug-associated chamber under extinction conditions (i.e., with no drug available). Excellent survival was noted for the transplant of RPECs in the shell and/or the core of the NAc bilaterally in all rats that showed behavioral recovery from cocaine seeking. Design based unbiased stereology of tyrosine hydroxylase (TH) positive cell bodies in the VTA showed better preservation (p<0.035) in transplanted animals compared to control animals. This experiment shows that the RPEC graft provides beneficial effects to prevent drug seeking in drug addiction via its effects directly on the NAc and its neural network with the VTA.

Retinal pigment epithelial cells secrete neurotrophic factors and synthesize dopamine: possible contribution to therapeutic effects of RPE cell transplantation in Parkinson's disease

BACKGROUND

New strategies for the treatment of Parkinson's disease (PD) are shifted from dopamine (DA) replacement to regeneration or restoration of the nigro-striatal system. A cell therapy using human retinal pigment epithelial (RPE) cells as substitution for degenerated dopaminergic (DAergic) neurons has been developed and showed promising prospect in clinical treatment of PD, but the exact mechanism underlying this therapy is not fully elucidated. In the present study, we investigated whether the beneficial effects of this therapy are related to the trophic properties of RPE cells and their ability to synthesize DA.

METHODS

We evaluated the protective effects of conditioned medium (CM) from cultured RPE cells on the DAergic cells against 6-hydroxydopamine (6-OHDA)- and rotenone-induced neurotoxicity and determined the levels of glial cell derived neurotrophic factor (GDNF) and brain derived neurotrophic factor (BDNF) released by RPE cells. We also measured the DA synthesis and release. Finally we transplanted microcarriers-RPE cells into 6-OHDA lesioned rats and observed the improvement in apomorphine-induced rotations (AIR).

RESULTS

We report here: (1) CM from RPE cells can secret trophic factors GDNF and BDNF, and protect DAergic neurons against the 6-OHDA- and rotenone-induced cell injury; (2) cultured RPE cells express L-dopa decarboxylase (DDC) and synthesize DA; (3) RPE cells attached to microcarriers can survive in the host striatum and improve the AIR in 6-OHDA-lesioned animal model of PD; (4) GDNF and BDNF levels are found significantly higher in the RPE cell-grafted tissues.

CONCLUSION

These findings indicate the RPE cells have the ability to secret GDNF and BDNF, and synthesize DA, which probably contribute to the therapeutic effects of RPE cell transplantation in PD.