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Curcumin (CUR) is a bioactive compound that has been proposed for the treatment of various neurodegenerative diseases. However, its use is limited due to its low solubility in aqueous media and chemical instability under physiological conditions. Herein, we propose a strategy to overcome these limitations by using PAMAM dendrimers of generation 4.5 (DG4.5). Using a combination of biophysical techniques together with in vitro models, we demonstrate that CUR-DG4.5 complexes: (i) increased the solubility and stability of CUR via internalization into dendrimer's pockets and interaction with terminal carboxylic groups; (ii) showed in vitro biocompatibility and increased CUR uptake; (iii) presented DPPH radical scavenging activity and in vitro inhibition of H2O2-induced stress; and (iv) interfere with α-synuclein aggregation. In conclusion, this work lays the foundation to use curcumin-loaded PAMAM dendrimers of generation 4.5 as nanodrugs capable of reducing oxidative stress and inhibiting α-synuclein aggregation to treat synucleinopathies.

The antibiotic tetracycline demeclocycline (DMC) was recently reported to rescue α-synuclein (α-Syn) fibril-induced pathology. However, the antimicrobial activity of DMC precludes its potential use in long-term neuroprotective treatments. Here, we synthesized a doubly reduced DMC (DDMC) derivative with residual antibiotic activity and improved neuroprotective effects. The molecule was obtained by removal the dimethylamino substituent at position 4 and the reduction of the hydroxyl group at position 12a on ring A of DMC. The modifications strongly diminished its antibiotic activity against Gram-positive and Gram-negative bacteria. Moreover, this compound preserved the low toxicity of DMC in dopaminergic cell lines while improving its ability to interfere with α-Syn amyloid-like aggregation, showing the highest effectiveness of all tetracyclines tested. Likewise, DDMC demonstrated the ability to reduce seeding induced by the exogenous addition of α-Syn preformed fibrils (α-SynPFF) in biophysical assays and in a SH-SY5Y-α-Syn-tRFP cell model. In addition, DDMC rendered α-SynPFF less inflammogenic. Our results suggest that DDMC may be a promising drug candidate for hit-to-lead development and preclinical studies in Parkinson’s disease and other synucleinopathies.