STS News, Winter 2022 — Projects funded through the Society’s charitable arm, The Thoracic Surgery Foundation (TSF), are igniting discoveries that improve the lives of patients and keep cardiothoracic surgeons at the helm of research.
TSF research grant recipient Paul Chun Yung Tang, MD, PhD, is utilizing the lab at the University of Michigan Frankel Cardiovascular Center in Ann Arbor, to explore a better way to ensure that donor hearts serve their recipients well after transplant.
Dr. Tang’s team proposed that infusing valproic acid (VPA), a histone deacetylase inhibitor, into donor hearts during the harvesting process could reduce oxidative stress and inhibit the release of inflammatory molecules during storage, resulting in improved function when the heart resumes beating.
To explore this proposition, Dr. Tang needed a laboratory, he needed hearts, and he needed funding. The Frankel Cardiovascular Center has an excellent environment for the development of clinical and translational science programs, Dr. Tang explained in his TSF grant proposal.
He identified The Gift of Life Michigan organ procurement facility in Ann Arbor, a 15-minute drive from the lab, as a resource that could provide approximately 50 human donor hearts per year for research purposes. And in 2018, Dr. Tang was awarded a TSF Southern Thoracic Surgical Association Resident Research Award, which supplied $25,000 toward the project.
Dr. Tang’s team worked on pig hearts and also collected human donor hearts with a left ventricular ejection fraction between 50% and 65%, but not suitable for clinical transplantation due to issues such as advanced donor age or cardiac hypertrophy. They then preserved the hearts with either traditional histidine-tryptophan-ketoglutarate (HTK) solution alone or with HTK plus VPA.
At various points during cold preservation and mechanical arrest, the investigators collected left ventricular (LV) and right ventricular (RV) tissue samples, and they performed RNA sequencing and differential gene analysis to characterize gene expression and regulation in the two groups. They examined responses related to muscle contraction, cardiac conduction, and gluconeogenesis, as well as cellular apoptosis, innate immune responses, and metabolomic processes.
“We discovered that VPA was able to intervene in some of the metabolic processes and selectively harness the protective metabolites that make the heart more resilient to ischemic injury,” Dr. Tang said. “VPA treatment downregulated the expression of apoptosis-related genes and the expression transcripts related to immune activation during the hypothermic preservation. And it was able to upregulate antioxidant proteins, which would predict improved cardiac function,” continued Dr. Tang. “So VPA appears to have highly beneficial effects in terms of gene expression.”