Objective: This study aimed to elucidate how iPSC-derived dopaminergic progenitor cells (iPSC-DAPs) acquire the ability to metabolize L‑DOPA in vitro and to evaluate whether the conversion of L‑DOPA to dopamine actually occurs in the brain after transplantation.

Background: In cell therapy for Parkinson’s disease (PD) using pluripotent stem cell–derived dopaminergic progenitor cells (PSC-DAPs), implanted cells are expected not only to autonomously produce and release dopamine but also to metabolize L‑DOPA into dopamine, complementing pharmacological treatment. However, it remains unclear at which stage PSC-DAPs acquire L‑DOPA-metabolizing capacity and whether they indeed metabolize L‑DOPA in the brain following transplantation.

Method: iPSC-DAPs were further matured in culture for 28 days, and the expression of dopaminergic markers was analyzed using qPCR and immunostaining. Dopamine levels in the culture supernatant were measured to assess dopamine production, and dopamine generation in response to L‑DOPA treatment was evaluated. Furthermore, iPSC-DAPs were implanted into a rat PD model, and after administration of L‑DOPA/carbidopa, brains were collected for imaging mass spectrometry (IMS) analysis to visualize the distribution of dopamine and related metabolites.

Results: During maturation culture, expression of TH, KCNJ6, and VMAT2 increased over time, and dopamine release also increased with maturation. DDC, an L-DOPA-metabolizing enzyme, was highly expressed from the early phase of maturation, and dopamine production upon L‑DOPA treatment was clearly observed as early as day 7, suggesting that the cells acquire L-DOPA metabolic capacity relatively early.

In vivo IMS analysis demonstrated increased dopamine levels in the graft region, and in L-DOPA-treated animals, a decrease in L-DOPA and an increase in dopamine were observed in the graft region. These findings directly confirmed that the implanted cells both produce and release dopamine and convert L‑DOPA into dopamine within the brain.

Conclusion: iPSC-DAPs acquire L‑DOPA metabolic capacity early in vitro and convert L‑DOPA to dopamine in the brain after transplantation. This study demonstrates that L‑DOPA metabolism is an important functional property contributing to the therapeutic effects of transplanted cells and suggests that in vitro evaluation of L‑DOPA metabolism may serve as a promising potency assay for quality assessment of cell-based products.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/l-dopa-metabolism-as-a-function-related-to-the-potency-of-ipsc-derived-dopaminergic-progenitor-cells/