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.

The Sigma-2 receptor (S2R) (a.k.a TMEM97) is an important endoplasmic reticular protein involved in cancer, cholesterol processing, cell migration, and neurodegenerative diseases, including Niemann-Pick Type C. While several S2R pharmacologic agents have been discovered, its recent (2017) cloning has limited biological investigation, and no endogenous ligands of the S2R are known. Histatins are a family of endogenous antimicrobial peptides that have numerous important effects in multiple biological systems, including antifungal, antibacterial, cancer pathogenesis, immunomodulation, and wound healing. Histatin-1 (Hst1) has important roles in epithelial wound healing and cell migration, and is the primary wound healing agent in saliva. Little is understood about the downstream machinery that underpins the effects of histatins, and no mammalian receptor is known to date. In this study, we show, using biophysical methods and functional assays, that Hst1 is an endogenous ligand for S2R and that S2R is a mammalian receptor for Hst1.

The secretome from mesenchymal stem cells (MSCs) have recently gained attention for new therapeutics. However, clinical application requires in vitro cell manufacturing to attain enough cells. Unfortunately, this process often drives MSCs into a senescent state that drastically changes cellular secretion activities. Antioxidants are used to reverse and prevent the propagation of senescence; however, their activity is short‐lived. Polymer‐stabilized crystallization of antioxidants has been shown to improve bioactivity, but the broad crystal size distribution (CSD) significantly increases the efficacy variation. Efforts are made to crystalize drugs in microdroplets to narrow the CSD, but the fraction of drops containing at least one crystal can be as low as 20%. To this end, this study demonstrates that in‐drop thermal cycling of hyaluronic acid‐modified antioxidant crystals, named microcrystal assembly for senescence control (MASC), can drive the fraction of microdrops containing crystals to >86% while achieving significantly narrower CSDs (13 ± 3 µm) than in bulk (35 ± 11 µm). Therefore, this approach considerably improves the practicality of CSD‐control in drops. In addition to exhibiting uniform release, MASC made with antioxidizing N‐acetylcysteine extends the release time by 40%. MASC further improves the restoration of reactive oxygen species homeostasis in MSCs, thus minimizing cellular senescence and preserving desired secretion activities. It is proposed that MASC is broadly useful to controlling senescence of a wide array of therapeutic cells during biomanufacturing.