Human Practices

6/29 Boston Children’s Hospital MSUD Talk: Kevin Strauss

We reached out to Harvey Levy, a doctor at Boston Children’s Hospital, who treats and researches MSUD and PKU (a similar metabolic disorder). Dr. Levy invited us to the Boston Children’s MSUD Grand Rounds, where we heard from Kevin Strauss, one of the world’s experts on MSUD. He works directly with MSUD patients at the Clinic For Special Children in Pennsylvania. His talk focused on the neurological effects of MSUD and helped us better understand the severity of the disease and the niche our probiotic needs to fill. Dr. Strauss explained that leucine is the most toxic of the BCAAs. When levels are elevated, it binds and prevents transport of other amino acids (including Ile and Val) and neurotransmitters into the brain. This leads to neurological defects, such as low cognitive performance (30-40% lowered IQ) and mental health disorders, such as depression, anxiety, and OCD. As far as treatment goes, Dr. Strauss explained that liver transplants are a good solution because the liver contributes to BCAA metabolism, and a liver transplant removes danger of metabolic crises, allowing patients to eat normal foods. Because this disease affects children, it is hard to enforce the strict diet, so liver transplants are a good option that give the patient more freedom and the parents more peace of mind. This talk really opened our eyes to the impact of MSUD on patients and their families and made us realize the value of a non-invasive therapeutic. It also made us recognize that our therapeutic should eliminate the need for dietary restriction.

7/6 Ginkgo + Synlogic: Vincent Isabella and Ted Moore

In our research we came across a similar probiotic treatment for PKU developed by Synlogic, and found a poster for a discontinued probiotic project for Maple Syrup Urine Disease. We reached out to the team and were able to set up a chat with Vincent Isabella and Theodore Moore. We were able to ask them questions about their research and get clarification on decisions they made. For example, they used E. coli Nissle (EcN) and constitutively converted leucine to isopentanol instead of trying to import the human BCAA breakdown pathway into E. coli, which doesn’t naturally break down BCAAs. We agreed with this approach, as we had already decided that importing the entire BCKDH enzyme coding sequence into E. coli would be complex and decided on using B. subtilis as our chassis. As Synlogic uses EcN as the standard chassis for all of their products, they had not thought about using B. subtilis but told us that our approach was promising

At the time, we were curious why they paused work on the project. We learned that with constitutive expression, engineered auxotrophy, and an inability to divide, their probiotic would be unable to reside in the gut. It is also difficult to get FDA approval for this, as they view it more as a stereotypical drug. In our research, we learned about their probiotic drug for PKU, which is currently in clinical trials. Their approach to breaking down phenylalanine in the gut came from a study that demonstrated that phenylalanine is able to circulate from the bloodstream back into the gut through a process called "enterorecirculation." This means that a buildup of amino acids in the bloodstream from metabolic decompensation can be recycled back into the gut where the probiotic can break them down. After discussing our approach with representatives from Ginkgo and Synlogic, we confirmed that the gut is a promising avenue to approach MSUD.

After our talk with Harvey Levy, we reached out to Vincent Isabella again to learn more about enterorecirculation. He said that the work he did was only on phenylalanine, so it is hard to say if it would apply to BCAAs. However, he referred us to a paper from Chang and Lister (1995), which showed high amounts of leucine in the guts of animals even when they were on a protein-free diet. This suggests that leucine also gets enterorecirculated, but it is something we would like to look into further in the future.

7/8 Harvey Levy

Harvey Levy is a Senior Physician in Medicine and Genetics at Boston Children’s Hospital and a Professor of Pediatrics at Harvard Medical School. He is an expert in metabolic diseases, such as MSUD and PKU, and has done foundational research on these metabolic pathways and newborn screening. Dr. Levy spoke to us about the severity of MSUD and the current treatment options, dietary restriction and liver transplant. He explained that dietary restriction is a lifetime thing and is very annoying. Babies are put on formula very early on and must stay on this formula. Liver transplants are a helpful option, but they are invasive and not readily available. While they allow for dietary freedom, they cannot be given to people less than 1.5-2 years old, as they are too small. This means that liver transplants are only viable after MSUD has caused the neurological effects, and a liver transplant cannot reverse this. Dr. Levy really emphasized that these treatment options leave a need for a treatment that helps patients early (before they are eligible for a liver transplant) in order to prevent neurological defects. We also spoke to him about the specifics of our project, and he thought a probiotic was a very interesting approach. He expressed concern over our B. subtilis’ ability to metabolize dietary BCAAs. Dr. Levy explained that dietary BCAAs are commonly ingested as di and tri-peptides and not “free”, so they are not able to be dehydrogenated. This means our probiotic may not have any BCAAs to actually metabolize from the diet. However, Dr. Levy proposed that enterorecirculation (mentioned above), which is a feature of PKU, may also exist in MSUD. Dr. Levy gave us a few people to reach out to, which led us on a chain that took us all the way back to a paper from Vincent Isabella (of Ginkgo/Synlogic) on PKU and enterorecirculation. See the Ginkgo/Synlogic section above to see what he said!

7/15 MSUD Family Support Group: Karen Dolins

Karen is a parent of an MSUD patient and a board member, research lead and secretary of the MSUD Family Support Group organization. We learned from her that every MSUD patient has to be on the metabolic formula unless they’ve had a liver transplant. To limit branched chain amino acid intake, a patient’s diet consists of a small amount of grains and absolutely no animal or plant proteins, beans, or nuts, which is an extremely difficult diet to manage. She assured us that MSUD patients would be willing to take a probiotic with every meal or daily, but it would have to allow almost entire freedom of diet. An alternative to liver transplantation is essential with numerous hurdles to getting a liver transplant, such as the commonality of rejections, ongoing difficulties, and proximity to a high quality center. Additionally, access to metabolic formula isn’t widespread. These are all factors to consider as we fight to prevent the neurological effects of MSUD, and a new approach is essential since no current treatment plans prevent neurological effects.

7/16 Gerard Vockley

Dr. Vockley is the director of the Center for Rare Disease Therapy at the Children’s hospital in Pittsburgh and chief of Medical Genetics. He specializes in liver transplantation for children with MSUD. After speaking with him, we learned that children with MSUD age 2 and older need to have controlled diets since after they go off formula, to prevent neurological damage. He recommended that this specific age group should be our target audience and also supported the idea of a probiotic because he believed there would be enterorecirculatory reabsorption into the gut as with Phe. Current treatment is the extremely invasive process of liver transplantation at the young age of 2-4, moving to 1-2. Suggested target patients are for patients with milder cases, waiting for a transplant, or unwilling/unable to get a transplant. Transplantation has its own risks, trading one metabolic disease for another such as long-term immunosuppression impacts and secondary malignancies.

Integrated Human Practices

Engaging with experts and people affected by MSUD really helped us better understand the disease and the criteria for a good treatment. We sort of stumbled into this project based on shared interested and an intriguing name, but connecting with the community showed us that MSUD is a disease that has a really unique niche and needs attention. Our main takeaways were that a treatment for MSUD needs to be effective early and must allow for dietary freedom in order to be a helpful improvement. This led us to focus on our chassis and look at the safety of probiotics in babies. While there is not a lot of research on B. subtilis and babies, we were able to find a few articles that suggest that it is safe, and it is definitely something we want to look into further. The consistent feedback that patients really want dietary freedom helped us set goals and think about the level of enzyme activity we want to reach. We want to get as close to non-MSUD levels as possible, which Dr. Levy says would be in the 200-400 umol range for leucine. Testing of our parts is ongoing, but reaching out to the MSUD community and being so welcomed has really inspired us and helped us strive to make a meaningful contribution towards MSUD treatment.