Relevance of Electrostatics for the Interaction of Tyrosine Hydroxylase with Porous Silicon Nanoparticles

Abstract

Tyrosine hydroxylase (TH) is the enzyme catalyzing the rate-limiting step in the synthesis of dopamine in the brain. Developing enzyme replacement therapies using TH could therefore be beneficial to patient groups with dopamine deficiency, and the use of nanocarriers that cross the blood–brain barrier seems advantageous for this purpose. Nanocarriers may also help to maintain the structure and function of TH, which is complex and unstable. Understanding how TH may interact with a nanocarrier is therefore crucial for the investigation of such therapeutic applications. This work describes the interaction of TH with porous silicon nanoparticles (pSiNPs), chosen since they have been shown to deliver other macromolecular therapeutics successfully to the brain. Size distributions obtained by dynamic light scattering show a size increase of pSiNPs upon addition of TH and the changes observed at the surface of pSiNPs by transmission electron microscopy also indicated TH binding at pH 7. As pSiNPs are negatively charged, we also investigated the binding at pH 6, which makes TH less negatively charged than at pH 7. However, as seen by thioflavin-T fluorescence, TH aggregated at this more acidic pH. TH activity was unaffected by the binding to pSiNPs most probably because the active site stays available for catalysis, in agreement with calculations of the surface electrostatic potential pointing to the most positively charged regulatory domains in the tetramer as the interacting regions. These results reveal pSiNPs as a promising delivery device of enzymatically active TH to increase local dopamine synthesis.

Personalized Medicine to Improve Treatment of Dopa-Responsive Dystonia—A Focus on Tyrosine Hydroxylase Deficiency

“…Crucially, the stability of TH was maintained through loading and preserved during storage, and there was an increase in intracellular L-DOPA synthesis following NP uptake [145]. The same group also investigated the interactions between TH and a more modifiable and biodegradable NP, namely, porous silicon nanoparticles (pSiNPs) [146]. This study showed that the enzymatic activity of TH remained intact upon binding to the pSiNP surface, and pSiNPs could represent another promising device for therapeutic delivery of TH [146].…”

“…The same group also investigated the interactions between TH and a more modifiable and biodegradable NP, namely, porous silicon nanoparticles (pSiNPs) [146]. This study showed that the enzymatic activity of TH remained intact upon binding to the pSiNP surface, and pSiNPs could represent another promising device for therapeutic delivery of TH [146]. This could potentially be achieved through intravenous injection, which would require pSiNP-bound TH to be stabilized during circulation followed by uptake into the brain by crossing the BBB.…”

“…This could potentially be achieved through intravenous injection, which would require pSiNP-bound TH to be stabilized during circulation followed by uptake into the brain by crossing the BBB. Another possible approach is by direct delivery to the brain using hydrogel implants containing TH-loaded pSiNPs [146]. However, it is important to note that the use of ERT for THD has not yet been tested in live animals, and this approach must be further investigated and optimized in future work.…”

Measurement of enzyme activity of insoluble substrates based on ordered porous layer interferometry and the application in evaluation of thrombolytic drugs

“…20 The Sailor group has spearheaded innovative research in using porous silicon ( pSi) as a matrix for substrate immobilization to assay enzyme activity. [21][22][23][24] The surface of pSi has been chemically modified to specifically adsorb a variety of substrates or enzymes, thereby enabling the construction of sensors tailored for particular enzymatic activities. Enzymatic activity is continuously monitored by observing the alterations in the optical properties of pSi throughout the enzyme-catalyzed reactions.…”