[Catalyst 2018]

PHOTOSYNTHETIC BACTERIA:
Shining Light on Heart Disease
Swathi Rayasam
F
lashing lights. Chest compressions.
A cry of “clear!” We commonly
associate heart attacks with this
frantic mental picture. However, a heart
attack will only develop into fatal heart
rhythms through a cascade of cardiac
events. Before we explore the evolution of
a basic heart attack into cardiac death, we
need a broad overview of heart disease.
The leading cause of death worldwide,
cardiovascular disease is costly – both in
terms of money and in terms of years of
life. 1 Although several recent advances
have explored repair and regeneration
after significant cardiac trauma, 2-3
tackling cardiac injury closer to its onset
would minimize serious damage due to
treatment delay.
A heart attack is characterized by an
obstruction that prevents proper blood
Scientists at Stanford
University have explored
the possibility of
introducing other
photosynthetic agents
into the body to provide a
source of oxygen for
cardiac cells.
flow to the heart. 4 While this is certainly
serious on its own, the cascade of
events that are triggered more largely
contributes to patient death. First, the
blockage of circulation can cause a lack of
oxygen in the heart, known as ischemia. 5
This condition can lead to cardiac cell
death if present for an extended period
of time, as in the case of delayed CPR and
transport to the hospital. If the human
body had an alternate route to bypass the
roadblock and deliver oxygen to the heart,
then there would likely be less heart
tissue injury and improved survival.
The fact that trees generate oxygen
may imply that introducing plant cells
internally might prevent and resolve
ischemia. Photosynthetic processes in
such a situation would merely rely on a
light source and chemical compounds
abundant in the human body to engineer
oxygen production in ischemic areas. 6
This new oxygen source would also
lessen the immediate need for proper
blood flow. However, while maintaining
internal plant cells is not exactly feasible,
scientists at Stanford University have
explored the possibility of introducing
other photosynthetic agents into the body
to provide a source of oxygen for cardiac
cells.
Stanford cardiovascular surgeon Dr.
Joseph Woo recently began a research
study to bring this fantasy to fruition.
He initially limited his efforts to plants,
by grinding kale and spinach to obtain
chloroplasts, plant organelles that
perform photosynthesis. 6 When these
structures did not survive outside of the
plant cell itself, Dr. Woo and his colleagues
found an alternate option. They identified
Synechococcus elongatus, originally
used to study circadian rhythms, 7-8 as
a viable photosynthetic cyanobacteria
for introduction into the body. The
team considered S. elongatus an ideal
candidate because they could easily
engineer it to produce more metabolites,
such as oxygen or glucose. 9-10
To test whether this cyanobacterium
could immediately deliver oxygen to a
tissue, the researchers induced ischemia
in several rodents. They then randomly
grouped these rodents and injected
their hearts with S. elongatus in the
light, S. elongatus in the dark, or saline.
The researchers prevented any light
exposure in the dark group but exposed
the other two groups directly to light to
examine any differences in oxygenation
levels due to photosynthesis. Originally,
baseline oxygen levels were comparable
between the groups and dropped close
to zero when ischemia was induced. At
reassessment 10 and 20 minutes after
injection, S. elongatus caused a 25-fold
increase in oxygen from the onset of
ischemia in the light group. This was
astounding when compared to the merely
3-fold increase in oxygen levels in the
other two treatment groups. This finding
supports the idea that injection with
S. elongatus in light leads to enhanced
oxygenation in ischemic conditions,
suggesting improved metabolism and
cardiac function. 11
Dr. Woo and his team next aimed to
evaluate the metabolic state of the
heart in the living rodent body, using
temperature as an indicator of activity.
Using a form of videography, they found
10 | CATALYST