|Fig. 1: Synechoccus under the microscope (Source: Wikimedia Commons)|
Approximately 16.7 millions deaths globally are associated with cardiovascular disease (CVD), which includes heart attacks, stroke, and hypertension. Every 36 seconds, one person in the United States dies of CVD-related complications.  Heart attack patients, in particular, are at risk of developing acute and chronic heart failure due to oxygen deprivation and weakened heart muscles from the initial heart attack. To treat cardiac deoxygenation and tissue damage, physicians and heart surgeons have utilized a variety of methods such as drugs, stents, and catheters; however, these methods are not able to directly provide oxygen to the damaged heart.  To address this challenge, Dr. Joseph Woo, professor of cardiothoracic surgery at Stanford Medical School, developed a renewable energy source that can provide oxygen directly to the heart. That renewable energy source is a photosynthetic bacteria called Synechococcus elongatus, as shown in Fig. 1 as a Differential Interference Contrast (DIC) microscopy image. S. elongatus is essentially a pond scum, which can change energy from the sun into oxygen, similar to any other plant. 
Members of the Woo Lab first tested to see how these naturally occurring photosynthetic bacteria would interact with cardiomyocytes (heart cells). To test this hypothesis, 500,000 cardiomyocytes were added to 3 wells of a 24-well plate. An additional 3 wells on the same plate were coated with 500,000 cardiomyocytes as well as 107 S. elongatus. A duplicate 24-well plate was also prepared to compare the activities of the cardiomyocytes in light and dark conditions. The 24 well plates were incubated at 37oC for 16 hours. Plate 1 was placed in dark conditions while Plate 2 was exposed to light. Results showed a significant increase in oxygen tension and cell viability for cardiomyocytes with S. elongatus that received light. To further confirm the results of the in-vitro experiments, the Woo Lab tested whether S. elongatus could transfer photosynthetic energy to increase cardiac viability in in-vivo mouse models. To mimic a heart attack, the left coronary artery was clamped, then the mice received either a PBS (saline solution) or 106 S. elongatus injection and exposed to strong light or placed in dark conditions.  Compared to the mice that did not receive S. elongatus, the treated mice showed significantly higher levels of oxygenation, an approximate 25 fold increase, and significantly healthier hearts, especially in mice exposed to light. 
This research, if approved to enter clinical trials, could save the lives of millions of cardiovascular patients around the world. The technique utilizes renewable, organic energy that does not involve any batteries or fossil fuels, just simply light. The cost of cardiovascular disease in the US was $457.4 billion in 2006; therefore, this technique can help reduce healthcare costs of cardiovascular illnesses that result from heart attacks.  These bacteria are also found in the natural environment in large quantities in ponds and natural bodies of water. 
One challenge to using this technique is finding a light source that can be directed on the heart without involving invasive surgeries. Another challenge is harnessing renewable light energy. If sunlight from solar cells or alternative energy can be harnessed to generate the light energy, this technique would not require energy from fossil fuels; however, if synthetic light is needed, this technique may no longer be considered renewable.  Another barrier is the extremely lengthy timeline for approving any clinical technique. Just obtaining FDA approval for a drug requires 10-15 years and hundreds of millions of dollars. Therefore, this research may not be used in patients, who need better treatments options now. 
Despite these disadvantages, this research provides hope for patients who have suffered from heart attacks, and the Woo Lab has shown the incredible applications of renewable energy in medicine.  This has opened the door for more research on renewable energy sources in healthcare and medicine as well as bioengineering in cardiology.
© Michelle Bach. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 J. E. Cohen et al., "An Innovative Biologic System for Photon-Powered Myocardium in the Ischemic Heart," Sci. Adv. 3, e1603078 (2017).
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