04/12 - Hardy Hearts - MSMR: What A Year!

Can you imagine going a month without eating anything at all? How about six months? Or a year? Humans can’t go for more than about three weeks without eating before we succumb to starvation.

Pythons, on the other hand, can last more than a year on a single meal. And what a meal! When pythons finally do get around to that annual feast, they can eat well over one quarter of their entire weight in one sitting.

This massive amount of energy required to digest that meal after fasting for so long causes most of the python’s internal organs, particularly the heart, to grow rapidly. In fact, a fed python’s heart can increase in mass by 40% within 48 hours after eating. Imagine if a human heart could grow like that!

Indeed, it is possible for the human heart to expand in size, or hypertrophy, over time. Generally we associate this heart growth with a diseased state where the heart is weak and not able to pump blood efficiently. This may occur as a result of stress, high blood pressure, or damage to the heart tissue.

But it is also possible for the heart to produce new tissue in response to exercise, which is why many professional athletes have enlarged hearts. This enlargement is due to a healthy increase in heart tissue as opposed to an unhealthy increase in size.

In the case of the python, the heart muscle is stimulated to produce new tissue, growing in size much like an athlete’s heart. Dr. Leslie Leinwand, a heart researcher at the University of Colorado – Boulder, was fascinated by the python’s ability to grow new tissue so quickly. She decided to focus her research efforts on understanding this process in the hope that it could lead to novel treatments. Now Dr. Leinwand has identified 3 chemicals in the python’s blood that can induce the same type of rapid tissue growth in mammalian heart cells.

Dr. Leinwand and her team first had to identify the molecule or molecules responsible for this incredible growth spurt of heart tissue. Since the observed tissue growth is not specific to the python heart but occurs in almost all of its organs, the team hypothesized that the molecule was circulating in the bloodstream.

To test this hypothesis, the researchers incubated rat heart cells in culture dishes with the blood plasma, (a fraction of the blood) of recently fed pythons. They found that rat heart cells treated with fed python plasma exhibited the same type of tissue growth observed in a python after it has eaten a meal. Once the team had confirmed that the molecule was circulating in the blood, the next step was to determine which of the thousands of such molecules was causing this extreme tissue growth.

The team began a series of biochemical experiments to better understand the properties of this molecule. Each property would give the scientists an additional clue as to the identity of the growth-stimulating molecule. First, the researchers took samples of fed python blood and treated it with increasing amounts of heat. They then took the heat-treated blood and used it to treat rat heart cells in culture dishes in vitro, It was clear from these experiments that heat did not affect the growth-stimulating molecule, since there was no change in the amount of cell growth despite heating the python blood to very high temperatures. This result ruled out proteins as the molecule the researchers were looking for. Why? Because most proteins become non-functional at high temperatures. And to confirm that the molecule in question was not a protein, the researchers also treated python blood with enzyme:. that eliminated most proteins from the blood before treating the cultured rat heart cells. Even with no proteins present, the python blood had the same stimulating effect on the growth of rat heart cells.

It was clear from these initial experiments that the researchers were not looking for a protein. So what were they looking for? “It seemed likely we were dealing with a fat,” Dr. Leinwand explained. “Python blood is so full of fat it’s almost milky-colored.”

Now in search of one or more fatty acids, the researchers compared the fatty acid concentration of blood samples from fed and fasted pythons at different time points. They identified five candidate fatty acids whose concentrations were significantly increased in the blood of fed pythons when organ growth was highest and tested various combinations of them. Rather than treating cell cultures of rat heart cells with python blood, the researchers treated them with just the combination of fatty acids. In this way, they identified a combination of three fatty acids—myristic acid, palmitic acid and palmitoleic acid—that mimicked the increase in growth of rat heart cells.

To test whether these three fatty acids could increase heart cell growth in a live animal model, the researchers injected fasted pythons with the mixture. As a control group, the researchers also injected a second set of fasted pythons with a combination of fats that were shown to be ineffective.The researchers found that pythons treated with the growth-stimulating mixture experienced heart growth similar to that of fed pythons while the control group experienced no tissue growth.

The next step was to test the mixture of fatty acids in a mammalian model. To do this, the researchers injected a group of mice with the fatty acids. After seven days, the researchers observed the heart tissue for any changes that might be associated with the fatty acid mixture. They also measured markers in the blood that would indicate heart growth, as well as several hormone levels that would indicate whether the animal experienced any negative effects. The researchers found that mice treated with the fatty acid mixture experienced increased heart growth and no elevations in blood markers that would indicate anything harmful. The researchers have now seen this beneficial effect in almost 100 mice.

“These are very exciting results,” Dr. Leinwand commented. “But there is still a long road ahead before we have any type of treatment suitable for humans.”

The next step for the researchers is to determine whether the fatty acids can be beneficial in mouse models of heart disease. These experiments are still in the design phase, and there are many variables involved.

The researchers plan to start with a relatively straightforward experiment: take a mouse model of high blood pressure, treat the animal with fatty acids, and see if the high blood pressure reverses itself or continues to develop. Ultimately, the researchers will likely test several models of heart disease. “Just because it doesn’t work on one model doesn’t mean it won’t work for another,” Dr. Leinwand added. “I am excited about the experiments ahead.”

Dr. Leslie Leinwand is a Professor at the University of Colorado, Boulder. Her research focuses on the healthy and diseased states of the heart. When not in the lab, Dr. Leinwand enjoys spending time with her family, cooking, traveling and going to movies.