Levodopa (L-DOPA), a precursor of dopamine, is commonly prescribed for the treatment of the Parkinson’s disease (PD). However, oral administration of levodopa results in a high level of homocysteine in the peripheral circulation, thereby elevating the risk of cardiovascular disease, and limiting its clinical application. Here, we report a non-invasive method to deliver levodopa to the brain by delivering L-DOPA-loaded sub-50 nm nanoparticles via brain-lymphatic vasculature. The hydrophilic L-DOPA was successfully encapsulated into nanoparticles of tannic acid (TA)/polyvinyl alcohol (PVA) via hydrogen bonding using the flash nanocomplexation (FNC) process, resulting in a high L-DOPA-loading capacity and uniform size in a scalable manner. Pharmacodynamics analysis in a PD rat model demonstrated that the levels of dopamine and tyrosine hydroxylase, which indicate the dopaminergic neuron functions, were increased by 2- and 4-fold, respectively. Movement disorders and cerebral oxidative stress of the rats were significantly improved. This formulation exhibited a high degree of biocompatibility as evidenced by lack of induced inflammation or other pathological changes in major organs. This antioxidative and drug-delivery platform administered through the brain-lymphatic vasculature shows promise for clinical treatment of the PD.

Lymph node (LN) targeting through interstitial drainage of nanoparticles (NPs) is an attractive strategy to stimulate a potent immune response, as LNs are the primary site for lymphocyte priming by antigen presenting cells (APCs) and triggering of an adaptive immune response. NP size has been shown to influence the efficiency of LN-targeting and retention after subcutaneous injection. For clinical translation, biodegradable NPs are preferred as carrier for vaccine delivery. However, the selective "size gate" for effective LN-drainage, particularly the kinetics of LN trafficking, is less well defined. This is partly due to the challenge in generating size-controlled NPs from biodegradable polymers in the sub-100-nm range. Here, we report the preparation of three sets of poly(lactic-co-glycolic)-b-poly(ethylene-glycol) (PLGA-b-PEG) NPs with number average diameters of 20-, 40-, and 100-nm and narrow size distributions using flash nanoprecipitation. Using NPs labeled with a near-infrared dye, we showed that 20-nm NPs drain rapidly across proximal and distal LNs following subcutaneous inoculation in mice and are retained in LNs more effectively than NPs with a number average diameter of 40-nm. The drainage of 100-nm NPs was negligible. Furthermore, the 20-nm NPs showed the highest degree of penetration around the paracortex region and had enhanced access to dendritic cells in the LNs. Together, these data confirmed that small, size-controlled PLGA-b-PEG NPs at the lower threshold of about 30-nm are most effective for LN trafficking, retention, and APC uptake after s.c. administration. This report could inform the design of LN-targeted NP carrier for the delivery of therapeutic or prophylactic vaccines.