biomolecules Review Receptor Ligands as Helping Hands to L-DOPA in the Treatment of Parkinson’s Disease Fabio Del Bello , Mario Giannella, Gianfabio Giorgioni * , Alessandro Piergentili and Wilma Quaglia Scuola di Scienze del Farmaco e dei Prodotti della Salute, Università di Camerino, Via S. Agostino 1, 62032 Camerino, Italy;
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[email protected]; Tel.: +39-0737402368 Received: 18 March 2019; Accepted: 6 April 2019; Published: 9 April 2019 Abstract: Levodopa (LD) is the most effective drug in the treatment of Parkinson’s disease (PD). However, although it represents the “gold standard” of PD therapy, LD can cause side effects, including gastrointestinal and cardiovascular symptoms as well as transient elevated liver enzyme levels. Moreover, LD therapy leads to LD-induced dyskinesia (LID), a disabling motor complication that represents a major challenge for the clinical neurologist. Due to the many limitations associated with LD therapeutic use, other dopaminergic and non-dopaminergic drugs are being developed to optimize the treatment response. This review focuses on recent investigations about non-dopaminergic central nervous system (CNS) receptor ligands that have been identified to have therapeutic potential for the treatment of motor and non-motor symptoms of PD. In a different way, such agents may contribute to extending LD response and/or ameliorate LD-induced side effects. Keywords: Parkinson’s disease; levodopa therapy; levodopa-induced side effects; dopaminergic drugs; non-dopaminergic receptor ligands 1. Introduction Parkinson’s disease (PD), also known as idiopathic paralysis agitans, is one of the most frequent chronic neurodegenerative diseases worldwide.