(W1030-07-40) Screening Primary Parameters Affecting Formulation of Hydrogen Sulfide Donors-Loaded Microparticles using Quality-by-Design (QbD) Approach

Purpose: Hydrogen sulfide (H₂S) is an endogenous gasotransmitter with reported cytoprotective effects such as anti-apoptosis, anti-necrosis, cell proliferation effects, modulation of neurotransmission and neuroprotection.¹ The unique pharmacological effects of H₂S allow several applications in neurodegenerative diseases like glaucoma.² However, its clinical translation is limited by its toxicity, gaseous nature, and low effective therapeutic concentrations. Polymeric microparticles are effective in sustaining the release of H₂S while providing overall efficacy and safety. The performance of microparticles is attributed to several formulation variables and process parameters that need to be carefully optimized to maximize the target product quality. A quality-by-design (QbD) model helps in achieving the desired critical quality attributes (CQAs) systematically by evaluating critical process parameters (CPPs) qualitatively and quantitatively. This study screens and compares the effectiveness of various formulation parameters involved in developing a microparticle based H₂S donors deliver system capable of sustaining the release of H₂S for clinically relevant extended period of time.

Methods: JMP Pro (16.1.0)” was used to generate the QbD design and run the analysis of the model. The CPPs identified for preparation of polymeric microparticles based on literature of preparation of microparticles were polymer to drug ratio, polymer to surfactant ratio, quantity and viscosity of emulsifier, and rate of stirring in emulsification step; with emulsifier viscosity being a nominal variable and others being continuous variables. Three key CQAs for microparticles were size, encapsulation efficiency, and release profile. A “Main Effects” screening QbD model was developed to identify the CPPs significant in determining CQAs. The particle size was evaluated using Malvern Mastersizer 2000 and the encapsulation and release studies were conducted using a H₂S specific electrochemical method (WPI IS0-H₂S electrode). A p-value ≤ 0.05 associated with any parameter was considered significantly effective in providing CQA in the H₂S donor microparticles.

Results: The “Main Effects” screening QbD model recommended 12 formulation designs with variable values of CPPs (Table 1). The microparticles were successfully prepared using a solvent-evaporation coacervation process (Figure 1). From the characterization of 12 formulations and analysis of the model, it was found that the polymer to drug ratio and polymer to surfactant ratio were significant (p = 0.0169 and p = 0.0307, respectively) while emulsifier quantity and rate of stirring were critical but not statistically significant (p = 0.0824 and p = 0.0874, respectively) in determining the CQAs. The effect of viscosity of emulsifier did not affect any of the CQAs (p = 0.14668). Particle sizes (117-349 um) and encapsulation efficiencies (13-79%) were observed to not be affected significantly by any of the CPPs while release-period (1-12 hours) was positively significantly dependent on polymer to drug ratio and negatively on polymer to surfactant ratio. There were no observed secondary and tertiary interactions between CPPs which affected CQAs.

Conclusion: For microparticle preparation, the “Main Effects” screening QbD found polymer-drug and polymer-surfactant ratios as significant in affecting the CPPs identified in the study. Future studies should include the development of a “Response-Surface” model using the two CPPs screened in the “Main Effects” study to further quantify the effects of these CPPs on CQAs.

References: 1. Mhatre, Susmit, Catherine A. Opere, and Somnath Singh. "Unmet needs in glaucoma therapy: The potential role of hydrogen sulfide and its delivery strategies." Journal of Controlled Release 347 (2022): 256-269.
2. Ohia, Sunny E., et al. "Regulation of aqueous humor dynamics by hydrogen sulfide: potential role in glaucoma pharmacotherapy." Journal of Ocular Pharmacology and Therapeutics 34.1-2 (2018): 61-69.

Acknowledgments: Financial support from School of Pharmacy and Health Professions, Creighton University and Summer Research Institute, Health Sciences - Multicultural and Community Affairs Department, School of Medicine, Creighton University.

Funding: This study was funded by Wareham Research Fund Award and NIH NEI 1R15EY032275-01A1.
Conflict of Interest Statements: We confirm that there are no conflicts of interest associated with this work and there has been no significant financial support for this work that could have influenced its outcome.

Figure 1 Microscopic image of the polycaprolactone microparticles at 20x captured on a digital optical microscope.



Table 1 Main effects screening quality-by-design generated using JMP Pro for microparticle preparation CQAs