Therapeutic potential of pluripotent stem cell-derived dopaminergic progenitors in Parkinson's disease: a systematic review protocol

Background: Parkinson's disease (PD) is the second most common age-dependent neurodegenerative disease that causes motor and cognitive disabilities. This disease is associated with a loss of dopamine content within the putamen, which stems from the degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). Several approved drugs are available that can effectively treat symptoms of PD. However, long-term medical management is often complicated and does not delay or halt disease progression. Alternatively, cell replacement strategies can address these shortcomings and provide dopamine where it is needed. Although using human pluripotent stem cells (hPSCs) for treatment of PD is a promising alternative, no consensus in the literature pertains to efficacy concerns of hPSC-based therapy for PD. This systematic review aims to investigate the efficacy of primate PSC-derived DA progenitor transplantation to treat PD in preclinical studies. Methods: This is a systematic review of preclinical studies in animal models of PD. We intend to use the following databases as article sources: MEDLINE (via PubMed), Web of Science, and SCOPUS without any restrictions on language or publication status for all related articles published until the end of April 2021. Two independent reviewers will select the titles and abstracts, extract data from qualifying studies, and assess the risk of bias using the SYstematic Review Centre for Laboratory animal Experimentation (SYRCLE) risk of bias tool and the Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies (CAMARADES) checklist. Apomorphine-induced rotation test (APO-IR) and amphetamine-induced rotation test (AMP-IR) are defined as the primary outcomes. The standardized mean difference (SMD) by Hedges' g method (r) and odds ratio (OR) and related 95% confidence interval (CI) will be calculated to determine the size effect of the treatment. The heterogeneity between studies will be calculated by "I-2 inconsistency of values and Cochran's Q statistical test," where I-2 > 50% and/or p < 0.10 suggests high heterogeneity. Meta-analyses of random effects will be run when appropriate. Discussion: This study will present an overview of preclinical research on PSCs and their therapeutic effects in PD animal models. This systematic review will point out the strengths and limitations of studies in the current literature while encouraging the funding of new studies by public health managers and governmental bodies.