(T1430-02-08) Bioadhesive and Sustained Release Epinephrine-Loaded Sodium Alginate Hydrogel Accelerates Hemostasis to Manage Gastrointestinal Bleeding

Purpose: Gastrointestinal bleeding is a serious and common clinical problem with an incidence of approximately 3-10% in the general population, with even higher incidences in at-risk populations such as those on systemic anticoagulants or those with ventricular assist devices [1]–[3]. Currently, common techniques and products used to treat spontaneous and post-polypectomy bleeding include mucosal injection of epinephrine, and the use of topical hemostatic agents has been explored. Despite the increasing availability and complexity of advanced endoscopic procedures for the management of gastrointestinal disorders, tools to manage spontaneous and iatrogenic gastrointestinal bleeding remain limited [4]. In this context, we herein present the development of an injectable epinephrine-loaded sodium alginate hydrogel via in situ gelation upon reaction with CaCl₂ that can be used as an aid in endoscopic procedures which need to have bioadhesive properties

Methods: Sodium alginate of different concentrations, namely, 2% w/v, 1.5% w/v, 1% w/v, 0.75% w/v and 0.5% w/v were dissolved in distilled water until a clear solution was formed. Afterwards, CaCl₂ (1 M) was added to polymers solution in order to develop bioadhesive polymeric hydrogel via ionotropic gelation (Figure 1). Hydrogels viscosity as a function of shear rate and shear stress was assessed in order to evaluate Newtonian or non-Newtonian behavior of hydrogels. Furthermore, on one hand, epinephrine in a concentration ratio of 1:10,000 was loaded into sodium alginate and in vitro release study was conducted over time under physiological relevant conditions. While on other hand, epinephrine microparticles were developed and mixed with the hydrogels precursors to fabricate epinephrine loaded alginate hydrogel to compare and achieve sustained release epinephrine-loaded sodium alginate hydrogel. In this context, the in vitro release study of epinephrine was assayed using Hanson diffusion cell with the purpose of proving the sustained release of epinephrine from the hydrogel matrix.

Results: The gelation reaction between sodium alginate and CaCl₂ as well as the resulting gels were rheologically characterized as a function of shear rate and shear stress (Figure 2). For these graphs, the curvature indicates non-Newtonian behavior. These gels show shear thinning. Thus, when being injected and going through the tubing of the injection needle the viscosity decreases, and when at rest it increases again, giving the submucosal lift a better chance of staying in place while reducing the amount of force or difficulty in injecting the gel that is to form in the tissue. Besides that, in vitro epinephrine release study demonstrates that epinephrine could release for at least 72 hours from gel loaded with epinephrine microparticles (Figure 3). Altogether, this study shows the feasibility of sustained epinephrine release in injectable and mucoadhesive gels using a combination of degradable gel polymers and epinephrine microparticles.

Conclusion: Sodium alginate hydrogel was successfully developed upon reaction with CaCl₂ via ionotropic gelation. The detailed in vitro, ex vivo and in vivo experiments of epinephrine-loaded sodium alginate hydrogel cross-linked with CaCl₂ exhibited excellent rheological and release properties.

References: [1] P. Vora, A. Pietila, M. Peltonen, G. Brobert, and V. Salomaa, “Thirty-Year Incidence and Mortality Trends in Upper and Lower Gastrointestinal Bleeding in Finland,” JAMA Netw. Open, vol. 3, no. 10, pp. 1–11, 2020, doi: 10.1001/jamanetworkopen.2020.20172.
[2] D. K. Mullady, A. Y. Wang, and K. A. Waschke, “AGA Clinical Practice Update on Endoscopic Therapies for Non-Variceal Upper Gastrointestinal Bleeding: Expert Review,” Gastroenterology, vol. 159, no. 3, pp. 1120–1128, 2020, doi: 10.1053/j.gastro.2020.05.095.
[3] K. A. Ghassemi and D. M. Jensen, “Lower GI bleeding: Epidemiology and management topical collection on large intestine,” Curr. Gastroenterol. Rep., vol. 15, no. 7, 2013, doi: 10.1007/s11894-013-0333-5.
[4] N. G. Burgess et al., “Risk Factors for Intraprocedural and Clinically Significant Delayed Bleeding After Wide-field Endoscopic Mucosal Resection of Large Colonic Lesions,” Clin. Gastroenterol. Hepatol., vol. 12, no. 4, pp. 651–661, 2014, doi: 10.1016/j.cgh.2013.09.049.

Acknowledgements: We acknowledge Maryland Innovation Initiative (MII) for funding this project.

Figure 1: Cross-linking reaction between sodium alginate (Alg) and calcium chloride (CaCl2)

Figure 2: Graphs showing the viscosity as a function of shear rate vs shear stress as evaluated using rheometer. [A] and [B] graphs represent the rheological properties of the representative polymer as a function of shear rate and shear stress. Gel polymer can be screened for those displaying Newtonian behavior and hysteresis.

Figure 3: [A] Vertical diffusion cell system (MIXdrive 6, Hanson Research Corporation) [B] Graph showing the cumulative release of epinephrine from representative formulations containing epinephrine and epinephrine microparticles; compared to simple epinephrine, the epinephrine microparticles greatly extended the duration of release of epinephrine.