Team:UIUC Illinois/Project/Background Info

Cardiovascular Disease
Many heart illnesses are deemed cardiovascular disease. Cardiovascular disease, also known as heart disease, is the medical term used to describe a slew of heart-related health problems, including myocardial infarctions, heart failure, and stroke. A major source of these problems is the onset of atherosclerosis, a condition characterized by the buildup of plaque in one’s arteries. There are a variety of causes of atherosclerosis, but our project addresses the proatherogenic substance trimethylamine-n-oxide, a metabolite of certain chemicals often found in red meat and energy drinks.


Intestinal Microbiota Promotes Atherosclerosis
Meat consumption correlates to high risk of cardiovascular disease (CVD), mostly because the high level of fats and cholesterol in diet may promote atherosclerosis. Recent research concluded that those two factors may not be sufficient in establishing the link between meat consumption and CVD risk. Researchers in Cleveland Clinic found that intestinal microbiota (gut bacteria) metabolize dietary L-carnitine into trimethylamine (TMA), which is further converted to trimethylamine-N-oxide (TMAO) and accelerates atherosclerosis in mice.

L-carnitine, a quaternary ammonium compound, plays an essential role in the generation of energy in cells due to its function in transporting fatty acids from the cytosol into the mitochondria. For this reason it is sometimes sold in the form of "food supplements" and is marketed as a "natural" health product. However, for normal healthy adults, the cells of the human body produce sufficient amounts of L-carnitine as needed. Recent research in mice with intact intestinal microbiota suggested long-term carnitine consumption "reduced in-vivo reverse cholesterol transport." They also analyzed 2,595 cases of patients who were undergoing cardiac evaluation, and found out a increased rate of cardiac events among those patients with high plasma L-carnitine levels and high TMAO levels.

[[[[[L-carnitine, a quaternary ammonium compound, is essential for generating energy as transporting fatty acids from the cytosol into the mitochondria. Therefore, it is widely available as "food supplements" and being marketed as "natural health products". However, for normal healthy adults, the cells of the human body produce it as needed. So people start to question, is it really good for our body to consume excessive amount of L-carnitine, do we really need it as a supplement? Researchers analyzed 2,595 cases of patients who were undergoing cardiac evaluation, and found out a increased rate of cardiac events among those patients with high plasma L-carnitine levels and high TMAO levels. In order to investigate the mechanism further, recent research in mice with an intact intestinal microbiota, suggested chronic carnitine consumption "altered cecal microbial composition" and "reduced in vivo reverse cholesterol transport". Moreover, when the gut flora was suppressed by antibiotics, the TMAO level turned out to be normal. An interesting discovery also pointed out that vegans and vegetarians produced less TMAO when they were in the chronic L-carnitine consumption trail. With that being said, a well established link between intestinal microbiota and atherosclerosis was confirmed.]]]]


Current Solutions
Current approaches in treating CVD are invasive and come with long recovery times, therefore it would be ideal to start from prevention. The best way to avoid microbiota-dependent atherosclerosis is through diet control and also exercise. However, self-control alone is not the most effective method for promoting public health. Specific to microbiota dependent atherosclerosis, researchers have reported that multiple bacterial strains in gut have different capacity in metabolizing L-carnitine and produce TMA, therefore it is difficult to target and eliminate them. TMA builds up will lead to fish odor syndrome and cause strong body odor, owing to its release via sweat and breath. Therefore it is not wise to cut the process from TMA to TMAO. And so far there are no research to directly target TMAO. So current suggestion is to inhibit the activity of gut flora by ingesting antibiotic cocktail. However, this method is far from satisfying. Because antibiotic pressure might lead to a selection of "super bacteria", which has multiple resistance to antibiotics and might do harm to our body and can't be killed. Also, the activity of gut flora is considered beneficial to host in various aspects, therefore it is crucial to keep a balance of the bacteria composition.


Gut Bacteria Ecology and Intervention
Most current treatments of atherosclerosis are not preventative. Our team looked to provide one such preventative treatment by halting the production of TMAO. Thousands of gut bacteria reside within the human digestive tract, and some L-carnitine loving bacteria found in the flora are responsible for converting L-carnitine into TMA.

Our strategy for combating the production of TMA is to make a probiotic that will out-compete the current gut flora for L-carnitine. This probiotic will then process the L-carnitine into a much less harmful product.


Genetically Modified Nissle 1917
Safety is always a major concern when introducing foreign organisms into the body, so we have chosen to work with escherichia coli strain Nissle 1917 as the platform for creating a safe probiotic. The Nissle strain is deemed safe for human consumption and probiotic use by the United States Food and Drug Administration.

E. coli has a natural L-carnitine uptake system, but to out-compete the preexisting gut bacteria, we decided to genetically modify our strain. The genes CaiX and CbcVW were selected to be implemented into our bacteria from pseudomonas aeruginosa, a bacterium with unique adaptations for L-carnitine uptake and processing.

Additionally, in order to break down the L-carnitine, we introduced the CDH gene from p. aeruginosa into our Nissle cells. This gene encodes for L-carnitine dehydrogenase, a protein that metabolizes L-carnitine along a safer alternative pathway.


Our Solution: Cardiobiotics
The University of Illinois (UIUC) iGEM Team sought a better method for people to be able to eat the food they love while maintaining a healthier heart. With our genetic parts, our Cardiobiotics present a never-before-seen application of synthetic biology to the field of cardiovascular health. Our engineered bacteria can uptake L-carnitine and divert it along pathway toward the end product of glycine-betaine, a much less harmful product than TMAO.