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    Biomechanics

    (D-154) Preventative and Restorative Effects of Epigallocatechin Gallate (EGCG) on Mechanical Behavior Associated with Elastic Fiber Fragmentation in the Mouse Ascending Aorta

    Friday, October 13, 2023
    3:30 PM – 4:30 PM PDT
    Location: Exhibit Hall - Row D - Poster # 154

      Presenting Author(s)

    • DC

      Dongfang E. Chen

      BME Undergraduate Student
      Washington University in St. Louis
      University City, Missouri, United States

    • AO

      Aidan J. O'Scannlain (he/him/his)

      Biochemistry Undergraduate Student
      Washington University in St./University of Notre Dame
      Portland, Oregon, United States

      • Primary Investigator(s)

    • Jw

      Jessica wagenseil

      PROF
      WASHU, United States

    Introduction::

    Thoracic aortic aneurysm (TAA) is a prominent health concern affecting 5.3 per 100,000 people/year. It is characterized by aortic dilation that can lead to aortic dissection and death in patients. A main contributor to TAAs are defects in the extracellular matrix, specifically, the elastic fibers. Previous research shows that TAA-linked genetic mutations affect pathways involved in elastic fiber formation and cross-linking. A common histopathological finding in TAAs is elastic fiber fragmentation. Elastic fibers are essential to the aorta as they provide the elastic properties that allow the aorta to respond to large pressure and volume changes.2 Despite its prevalence, there are limited effective drug therapy treatments to prevent or restore mechanical changes associated with TAA1.


     


    Epigallocatechin gallate (EGCG) is a plant-based polyphenol that binds to extracellular matrix protein. It has been shown to attenuate abdominal aortic aneurysm (AAA) progression in a rat model.4 Polyphenols including EGCG and pentagalloyl glucose (PGG) are listed as a cross-linking agent for collagen.3 It is potentially useful in treating TAA by stabilizing the extracellular matrix. EGCG has not been tested in TAA models and the mechanical effects of the drug on the vessel wall are unknown. PGG was tested previously and showed potential as a treatment option as it prevented and restored mechanical properties after elastic fiber degradation.2 Based on the PGG results, we hypothesize that EGCG, in a chemical TAA model, can restore and/or prevent mechanical changes caused by elastic fiber fragmentation.



    Materials and Methods:: 3–4 month-old male C57BL6/J mice were euthanized by carbon dioxide inhalation in compliance with the Institutional Animal Care and Use Committee. Ascending thoracic aortas (ATAs) were dissected and mounted on a pressure myograph system (DMT) for biaxial mechanical testing. Each ATA served as its own untreated (UNT) control. ATAs were subject to 3 axial stretch-controlled tests while varying pressure and 3 pressure-controlled tests while varying axial stretch ratio. Data for pressure, outer diameter, axial stretch, and axial force were recorded. Compliance was calculated as the change in diameter for each 15 mmHg pressure step. UNT (N=17) were tested and placed into treatment groups (N=3-5). Elastase was used to simulate the elastic fiber degradation associated with TAAs. A pilot study determined the optimal concentration and timing for ELA and EGCG treatments. For ELA treatment, 7.5 U/ml of ELA was applied for 6 minutes followed by 100 mM of NaCl for 6 minutes to neutralize the ELA. For EGCG treatment, 2.0 mg/ml of EGCG was applied for 30 minutes. Treatments were delivered through the aortic lumen and held at 100 mmHg to mimic clinical treatment methods. The four treatment groups included ELA, EGCG, EGCG+ELA (preventative), and ELA+EGCG (restorative). After treatment, the mechanical properties of the ATAs were tested again. The unloaded dimensions were measured post-testing by imaging cross-sectional cut rings of the ATA.

    Results, Conclusions, and Discussions::

    Single-factor ANOVA tests show significant differences (p< 0.05) between diameter or compliance (ΔD/ΔP) versus pressure for all treatment groups at all pressures (Fig. 1). T-tests were performed between UNT and all treatment groups as well as ELA and all treatment groups as a post-hoc comparison. Statistical analysis was limited due to software availability. After treatment, ATAs were tested at lower stretch ratios to avoid tearing the ATA. The results show that EGCG ATAs are significantly different at low pressures compared to UNT for diameter versus pressure; this can be attributed to the difference in stretch ratios before and after treatment. The ELA treated ATAs have a significant increase in diameter at lower pressures and lower compliance at higher pressures compared to UNT. The preventative (EGCG+ELA) treatment successfully maintained diameter and compliance in the physiological pressure range (90 – 120 mmHg) compared to UNT. The restorative (ELA+EGCG) treatment results are not significantly different from the ELA group for diameter or compliance versus pressure. Comparing the EGCG+ELA and ELA+EGCG, the EGCG+ELA curves are closer to UNT while the ELA+EGCG curves are closer to ELA.


     


    Additionally, circumferential stress and stretch were calculated from the mechanical test data and unloaded dimensions (Fig.2). As the stretch and stress for each ATA depend on the unloaded dimensions, the stretch-stress curves are not quantitatively compared. Each ATA served as its own UNT so there were no ring measurements to calculate UNT stress and stretch. Qualitatively, the EGCG+ELA ATA is closer to EGCG, which resembles previous UNT ATA data, while the ELA+EGCG ATA is closer to ELA. 


     


    EGCG treatment of the ATA before chemically degrading elastic fibers was successful in preventing some mechanical changes. This suggests that EGCG may be an effective pharmaceutical treatment option for TAA. Ongoing research includes constitutive modeling to further characterize the mechanical changes and histological staining of polyphenols to visualize where the EGCG is in the ATA wall. Future work includes the in vivo delivery of EGCG to treat fragmented elastic fibers in genetic models of TAA. 



    Acknowledgements (Optional): : Special thanks to all the members of the Wagenseil Vascular Mechanics Laboratory for all their guidance and assistance with this project.

    References (Optional): :

    1.Aronow WS. Treatment of thoracic aortic aneurysm. Ann Transl Med. 2018 Feb;6(3):66. doi: 10.21037/atm.2018.01.07. PMID: 29610755; PMCID: PMC5879515.




    2.Crandall, C. L., Caballero, B., Viso, M. E., Vyavahare, N. R., & Wagenseil, J. E. (2022). Pentagalloyl glucose (PGG) prevents and restores mechanical changes caused by elastic fiber fragmentation in the mouse ascending aorta. Annals of Biomedical Engineering. https://doi.org/10.1007/s10439-022-03093-x




    3.Sapuła P, Bialik-Wąs K, Malarz K. Are Natural Compounds a Promising Alternative to Synthetic Cross-Linking Agents in the Preparation of Hydrogels? Pharmaceutics. 2023 Jan 11;15(1):253. doi: 10.3390/pharmaceutics15010253. PMID: 36678882; PMCID: PMC9866639.




    4.Setozaki S, Minakata K, Masumoto H, Hirao S, Yamazaki K, Kuwahara K, Ikeda T, Sakata R. Prevention of abdominal aortic aneurysm progression by oral administration of green tea polyphenol in a rat model. J Vasc Surg. 2017 Jun;65(6):1803-1812.e2. doi: 10.1016/j.jvs.2016.06.003. Epub 2016 Jul 26. PMID: 27473778.