Extending the Bioavailability of Hydrophilic Antioxidants for Metal Ion Detoxification via Crystallization with...

Although metal ions, such as silver and gold, have been shown to have strong antimicrobial properties, their potential to have toxic effects on human and environmental health has gained interest with an improved understanding of their mechanisms to promote oxidative stress. Redox control is a major focus of many drug delivery systems and often incorporates an antioxidant as the active pharmaceutical ingredient (API) to neutralize overproduced reactive oxygen species (ROS). Nevertheless, there are still limitations with bioavailability and extended redox control with regard to antioxidant drug delivery. Herein, this study develops a colloidal antioxidant crystal system that dissolves sustainably through polymer stabilization using sodium hyaluronate conjugated with dopamine (HA-dopa). We explore the role of dopamine incorporation into crystal-stabilizing polymers and quantify the balance between drug-polymer interactions and competing polymer-polymer interactions. We propose that this type of analysis is useful in the engineering of and provides insight into the release behavior of polymer-crystal complexes. In developing our crystal complex, N-acetylcysteine (NAC) was used as the model antioxidant to protect against silver ion toxicity. We found that our optimized HA-dopa-stabilized NAC crystals prolong the release time of NAC 5-fold compared to a polymer-free NAC crystal. Therefore, following sublethal exposure to AgNO₃, the extended lifetime of NAC was able to maintain normal intracellular ROS levels, modulate metabolic function, mitigate fluctuations in ATP levels and ATP synthase activity, and preserve contraction frequency in engineered cardiac muscle tissue. Furthermore, the protective effects of the HA-dopa-stabilized NAC crystals were extended to a Daphnia magna model where silver-ion-induced change to both cell-level biochemistry and organ function was alleviated. As such, we propose that the packaging of hydrophilic antioxidants as colloidal crystals drastically extends the lifetime of the API, better maintains ROS homeostasis post metal ion exposure, and therefore preserves both intracellular biochemistry and tissue functionality.