The development of an oral copolymeric carbon dot drug delivery platform for application in Parkinson’s disease

Abstract

The burden of Parkinson’s disease is global, ranking second to Alzheimer’s disease among neurodegenerative diseases with approximately 10 million new diagnoses made per annum. Parkinson’s is neurodegenerative in nature, which ultimately results in effects ranging from paraesthesias to paralysis and cognitive impairments in middleaged to elderly patients. The golden standard for Parkinson’s disease treatment at the moment is dopamine. These current treatment options are not as effective in treating Parkinson’s as they have less capability of crossing the Blood-Brain Barrier (BBB).

The BBB is a selectively permeable barrier that controls the exchange and transport of substances between the blood and the brain and in comparison, to other vascular endothelial cells found in the body, the BBB has highly expressed tight junction proteins, which function to primarily inhibit the random diffusion of substances between the blood and the brain. This provides an intensely strict regulation of para- and transcellular traversal of molecules (having a reported size of approximately 4 nm) across the BBB. Hence, there is a dire need for the development of nanomedicines for the effective delivery of neurological drugs across the BBB.

To provide a targeted approach for the above limitations, we have proposed the development of a carbon dot technology, loaded with a site-specific therapeutic, dopamine. This research will entail the development of a non-toxic, water soluble, drug-loaded carbon dot system for the delivery of dopamine across the BBB. Carbon dots are zero-dimensional spherical allotropes of carbon and may be the ideal nanocarriers for neurological drugs as they have noteworthy properties, low toxicity, favourable photostability, easily functionalized surfaces, high specific surface area, high quantum yield, high biocompatibility, high thermal stability and being chemically inert; resulting in optimal neuro-availability of drugs. The carbon dots will be synthesized from sodium citrate and urea. This allows for a shorter reaction time, no need for expensive reagents or costly production methods and the resultant carbon dots do not need further surface functionalization. Dopamine is required in the treatment of Parkinson’s disease, hereby providing the platform for the challenging of conventional treatment for Parkinson’s disease. The dopamine-loaded carbon dots would be loaded in a chitosan-alginate nanogel, allowing for the delivery of dopamine across the BBB via the intranasal route. The copolymeric nanogel allows for the complete protection of the dopamine-loaded carbon dots in the gastric environment, enabling delivery and absorption through nasal mucosa only. This results in higher bio- and neuro-availability of dopamine at dopamine receptors in the brain. The physicochemical properties of the loaded and unloaded system were analyzed utilizing Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Zeta size and Zeta Potential analysis. The morphological characteristics of the system was analyzed employing Transmission Electron Microscopy (TEM). The viscoelastic properties of the nanogel was determined by rheological analysis. In vitro drug release studies were undertaken and the toxicity of the system was determined by performing cytotoxicity studies on a PC12 cell line. A Box-Benkhen design was utilized for generation of an optimized formulation. FTIR analysis proved the synthesis of the carbon dots and the surface passivation of dopamine to the carbon dot surface. Zeta potential results also confirmed the surface passivation of dopamine due to the zeta potential becoming more positive. DSC analysis verified the synthesis of the carbon dot and also surface passivation of dopamine to the surface of the carbon dots due to shifts in the transition temperatures. The diffractogram generated from XRD demonstrated the crystalline nature of the carbon dots. TEM images showed the morphology of the carbon dots, which presented distinctive outlines around the circular core. The carbon dots were ~10nm in size, corroborated by zeta size analysis and TEM microscopy. In vitro drug entrapment efficiency was 98.67%. The drug release curves illustrated a controlled and sustained release pattern. In vitro cell studies confirmed that the unloaded carbon dots and the loaded carbon dots were minimally toxic to the neurological cells. Further, cell proliferation was enabled by the unloaded and loaded carbon dots.

This study proved the vast potential for carbon dot usage in drug delivery, specifically for Parkinson’s Disease as highlighted in this specific project. The carbon dots were simplistic cost-effective and not time-consuming to synthesize. The loading of dopamine to the carbon dots was also non-complex and the carbon dots loading capacity was very high. This delivery system could potentially reduce the side effect profiles suffered by the patients drastically as the dosage administered can be reduced and the drug levels could be maintained for an extended period. This would potentially enhance patient outcomes and dramatically increase patient compliance.