Team:Stanford/Description
Project Description
Project Motivation: Combatting Grapefruit-Drug Interaction
The grapefruit-drug interaction is one of the most widely researched food-drug interactions to date. Researchers have found that there are over eighty-five medications that are known or predicted to interact (sometimes fatally) with grapefruit consumption (Bailey et al., 2013). Many of the drugs that experience this interaction are widely prescribed and serve important roles in treating conditions like high cholesterol, cancer, and psychosis (Dahan, 2014). New drugs that experience the grapefruit interaction are hitting the market every year.
Currently, the recommended course of action for patients on these medications is to avoid consumption of grapefruits and similar citrus fruits altogether. However, there are no commercially viable or safe alternatives to mitigate the effect of the grapefruit-drug interaction. Our project aims to create a solution to the grapefruit-drug interaction that will allow patients on these drugs to safely consume grapefruits and take their necessary medication.
Grapefruits contain a chemical compound called furanocoumarins (FCs) which are present in the fruit with the purpose of fighting off fungal attacks (De Castro, 2006). The problem of this molecule, when ingested, arises from their ability to bind with a human metabolic enzyme, cytochrome P450 isoenzyme CYP3A4, which are active and present in the small bowel, and are responsible for digesting drugs that come into the body before they are passed onto the liver (Guo, 2004).
The inhibition of CYP enzymes by furanocoumarins causes drugs to be not metabolised before they get passed into the bloodstream, thus increasing bioavailability of the drug and increasing its potency, leading to illness, and sometimes sudden death.
We aim to create a method of inactivating (blocking) the furanocoumarins from interacting with the CYP enzymes. Our team discovered previous research suggesting that CYP 6YP1B enzymes found in black swallowtail butterflies can degrade furanocoumarins (Dongfack, 2012). We hope to utilise this gene to digest the FCs to the point where they are unable to interact with the cytochromes responsible for drug metabolism. We plan to engineer gut microbes, particularly Saccharomyces cerevisiae (Brewer’s Yeast) as they are eukaryotic organisms, which have more organelles in comparison to prokaryotes such as E. Coli, which would allow for better expression of effective protein structures.
This graphic demonstrates the effect of the furanocoumarins on the CYP enzymes. The furanocoumarins are represented in red.
The above graphic demonstrates how furanocoumarins inhibit proper drug metabolism. The furanocoumarins are represented in red, and the representation of the drugs is in blue.
How Does Citrus Safe Work?
We imagine Citrus Safe functioning as a therapeutic probiotic, and our project this summer acts as proof-of-concept work that acts as the first stepping stone to accomplishing the goal of creating a commercially available therapeutic.
Citrus Safe would come in the form of a pill patients can swallow that would counteract the grapefruit-drug interaction. It’s important to understand the mechanisms of how this therapeutic probiotic would work on a biological level.
When a patient takes their medication at the correct dosage without grapefruit juice involved, there is no overdose. This is because there is a class of enzymes found in the human liver and large intestine called P450s that metabolizes the drug and regulates the level of medication within our bodies (Bibi, 2018). However, grapefruits mess with this natural interaction. The group of compounds in grapefruits that negatively interact with drugs is called furanocoumarins. When a patient consumes their medication after having consumed grapefruit, instead of binding to the medication, the P450s bind to the furanocoumarins (Bailey, Dresser, & Arnold, 2013). Without the binding of the medication to the P450s, there is nothing left in our bodies to metabolize the extra medication, which leads to the negative side effects and potential overdoses.
Citrus Safe hopes to overcome this interaction. One of the main components of our Citrus Safe project was the yeast plasmid we designed (which is covered in greater detail on the Engineering Success page). In this plasmid, we used Saccharomyces cerevisiae (also known as Baker’s yeast) and the CYP6B1 enzyme found in American black swallowtail butterflies (Zhimou, 2006). We used Baker’s yeast because it is naturally occuring in the human gut microbiome, and could safely be used as a probiotic (Ogu & Maxa, 2000). While it can’t be confirmed at this stage of experimentation, our hope is that if a patient were to consume a probiotic containing Baker’s yeast, it would be able to sufficiently populate the gut microbiome to have the desired effect of mitigating the grapefruit-drug interaction.
The black swallowtail butterfly’s digestive system is not naturally equipped to digest furanocoumarins. However, they consume a diet high in furanocoumarins. They have naturally evolved an enzyme called CYP6B1 which metabolizes furanocoumarins (Sevrioukova, 2019). We inserted the CYP6B1 enzyme into a yeast plasmid with the hope that if this yeast plasmid were to become a commercially viable therapeutic probiotic, the Baker’s yeast would populate the gut microbiome. Because the yeast plasmid contains the CYP6B1 enzyme, once the plasmid populates the gut microbiome, the CYP6B1 would also populate the gut microbiome (Mertens-Talcott, 2006). If a patient were to consume this plasmid after consuming grapefruit, the CYP6B1 inside would metabolize the furanocoumarins from the grapefruit. With the furanocoumarins metabolized, the natural relationship between a patient’s medication and the P450 enzymes would be able to resume. The CYP6B1 would metabolize the furanocoumarins and the P450s would metabolize the excess medication, therefore mitigating the grapefruit-drug interaction.
The grapefruit-drug effect can have detrimental effects on human health.
The picture above compares the effect of taking pills with water vs. taking a pills with grapefruit juice. It visually shows the detrimental effect of the interaction, and how it amplifies the potency. This is why Citrus Safe is a really important invention! We could prevent this problem and all of the accidental negative health effects that come with it.
Project Development
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