Bioengineering

Chemical engineer produces potential therapy for gluten intolerance
Crowds packed the 7th Annual Stanford Celiac Conference Sept. 16 like a subway platform at rush hour. The sea of people that filled the Fairchild auditorium and churned among tables in the foyer outside displaying gluten-free recipes and foods, illustrated both how pervasive the gluten intolerance disease is, and how eager its sufferers are for help coping with a disease that cannot be treated—yet.

It is much too soon for Celiacs to change their outlook on the disease. The risk that gluten will trigger a self-destructive immune system response gives them no choice but to avoid ingesting the protein found in common grains such as wheat, barley, and rye. But at this year’s conference, Stanford gastroenterology Professor Gary Gray described a set of discoveries that could someday help them to eat with far less fear. Gray, who collaborates closely in work led by chemical engineering and chemistry Professor Chaitan Khosla, told them about a combination of enzymes that in lab testing has completely neutralized substantial amounts of gluten in less than 10 minutes in conditions similar to those in the digestive tract. There is a long way to go before the enzymes could ever be considered a therapy, but through the work of Khosla, Gray and their students, there seems to be emerging hope for hope.

“I think you are going to be pleased with what you hear today,” Gray told the audience. “Things are moving.”

Knowing the enemy
For Khosla the fight against Celiac Sprue disease—as it is formally known— is deeply personal because the condition runs in his family (it affects one in every 133 people worldwide). It is also professionally ideal because as a chemical engineer, Khosla is well trained to grapple with a disease where a single group of proteins is so clearly implicated. Treating Celiac disease is a matter of breaking down gluten quickly. It is essentially a chemical challenge.

“If you follow the trail of this causative chemical through its interactions in the human body, you can hopefully uncover what the problem is with gluten in the context of a patient,” he says. “Having a chemical, albeit a very complex one, to track down is an incredibly valuable tool.”

Sure enough, back in 2001 researchers led by Khosla published an influential study in Science in which they described the structure of gluten and why it takes so long for people to digest it. The study provided not only an explanation of the problem, but also laid the foundation for the more recent development of a candidate treatment.

A gluten molecule is a long chain of amino acids that in Celiacs triggers an “autoimmune response,” meaning that when t-cells and b-cells encounter it, these immune system cells mistakenly start attacking tissues, particularly the small intestine. No one digests gluten quickly, but in Celiacs the persistence of gluten is a huge problem because it allows their flawed immune response to go on for days, resulting in a reduction in the intestine’s ability to absorb nutrients. This, in turn, can cause diarrhea, weight loss, anemia, bone disorders, and other serious problems.

Khosla’s group noted that two amino acids, proline and glutamine, are prevalent in gluten molecules and that the digestive tract lacks enzymes that can break down the bonds they form. Failure to digest the bonds linking these amino acids on the gluten protein essentially prevents the body from breaking down gluten into harmlessly small pieces. When Khosla’s group identified them, they identified gluten’s weakness.

 “That study illuminated the Achilles heel of gluten,” Khosla says. “When you see that, it is relatively straightforward using one’s chemical knowledge to predict how to attack it. Since then it has really been a question of what are the best weapons to attack the Achilles heel.”

Breaking the chain
Those weapons are two enzymes, one that can cut the chain after glutamine and one that can cut the chain after proline. These enzymes are exactly what the body needs to quickly shred gluten to the point where the immune system doesn’t recognize it as a threat.

There are actually several proline-cleaving candidates in a class of enzymes called prolyl endopeptidases (PEPs). Khosla’s group started identifying and testing PEPs in 2001. Other research groups, particularly in Europe, are also working on them now. In a paper published in the journal Chemistry and Biology in June 2006, Khosla, Gray, and several students found that a PEP from the bacterium flavobacterium meningosepticum (FM-PEP) seems especially promising in its ability to reduce the immune system response to gluten.

In that same study, the team also reported on an enzyme that shows great promise in cutting the gluten chain after glutamine. Derived from barley, EP-B2 is able to complement the work of FM-PEP, not only because it cuts gluten in a different place, but also because it can work in the high acidity found in the stomach. FM-PEP works best in the lower acidity of the intestine. Together, EP-B2 and FM-PEP could give Celiacs coverage throughout their digestive tract so that gluten that happens to leave the stomach quickly would still be subject to cleaving in the intestine.

Ultimately what FM-PEP and EP-B2 would do is weaken gluten to the point where the body’s natural digestive enzymes are able to finish it off. Some of those natural enzymes can further break the chain in those few places that aren’t after either a proline or glutamine acid. Other enzymes "nibble" on the ends of the chain to break it down slowly but completely. Every time a cutting enzyme cleaves the chain, it exposes a new end for the nibblers to work on. The more cuts, the more opportunities for nibbling and the faster the gluten disappears.

In lab tests reported in the July study, Khosla’s group exposed gluten to a combination of EP-B2, FM-PEP and the body’s natural enzymes in stomach-like and intestine-like conditions. “Remarkably, gluten treated with pepsin plus EP-B2 followed by pancreatic proteases plus FM-PEP was completely nontoxic within 10 minutes of exposure to the simulated [digestive] environment,” the team found.