X-ray crystallography sheds light on why some people suffer liver injuries from supplements
The information came as part of a session at the International Conference on the Science of Botanicals (ICSB) taking place this week in Oxford, MS. The annual conference is put on by the National Center for Natural Products Research that is part of the university’s School of Pharmacy. The session was hosted by Dr Victor Navarro, MD, a hepatologist at the Einstein Healthcare Network in Philadelphia and head of the federally funded Drug Induced Liver Injury Network (DILIN).
Liver injury data acquiring greater power
Dr Navarro has presented on the work and findings of DILIN at the conference in past years. The first iterations of his presentation were a wake up call to industry that liver injury associated with some dietary supplements is a very real risk. Even if industry stakeholders could take comfort in the fact that overall numbers were low, that would come as cold comfort for some of the patients seen through the clinics in the liver network. Some of those cases required liver transplants and in a few instances resulted in deaths.
Navarro said the network is now extensive enough that it has amassed a significant amount of data. He emphasized that the information arose from actual case reports and so is not population based. Nevertheless, he and his fellow clinicians have been at it long enough (well over a decade) that their data set is starting to achieve a certain statistical power.
One of the new twists in that data is a small but emerging signal relating to curcumin supplements. It’s a supplement ingredient that has been in use for decades, so why the case numbers—while still very low (single digits)—are rising, is unknown. However, Dr Navarro observed that the curcumin molecule has some structural similarities to EGCG (epigallocatechin gallate), one of the major bioactive components of green tea extract. This is an ingredient that shows up with more frequency than others in the DILIN case reports.
HLA genetic variation studied
As the DILIN data set has grown, so too has the list of collaborators with the project. One of those collaborators was a fellow presenter during the session, Prof David Ostrov, PhD. His research has helped shed some light as to why EGCG occupies that mournful position, and by extension why certain people may react in idiosyncratic ways to other bioactive molecules.
Ostrov presented the research his team at the University of Florida College of Medicine has done on HLA binding sites. The primary function of HLA (human leucocyte antigen) molecules is to present foreign antigens to elicit T cell immune system responses.
The HLA protein molecule is shaped like a hot dog bun, Ostrov said, with helical structures making up the sides of the bun. The problematical participles bind in the trough and are presented to the T cells in that way at the surface of the infected cells.
Finding the binding site
For people with a certain genetic variation in the gene that encodes the HLA protein, a variation known as HLA-B*57:01, there is a known association with liver injury when they are dosed with abacavir, a drug used to treat HIV.
Using X-ray crystallography, Ostrov was able to show exactly how the abacavir molecule is bound into the HLA molecule for people with this genetic difference.
“We now understand which atoms of the HLA molecule bind to which atoms in abacavir,” he said.
Ostrov said when it was understood just how abacavir and the altered HLA molecules interacted, his team started to look for other molecules that might similarly be bound into the position of the mythical hot dog, and so elicit an immune system reaction where none is called for. The DILIN case reports, many of which included genetic sequence information, gave a clue about other genetic variations.
“The majority of people who have suffered green tea related liver injury carry HLA-B*35:01,” he said.
Using a similar approach as was taken with abacavir, Ostrov’s team showed that the altered HLA molecules scooped up ECGC and flagged it for attack by the T cells. X-ray crystallography, which involves interpreting the diffraction patterns of individual photons, so far has given a good but not perfect picture of where in the hot dog pocket the EGCG molecule is nestled, Ostrov said. But there’s no doubt it’s in there, he said.
Game changing data
By extension, this approach could shed light on the idiosyncratic reactions that account for many adverse event reports related to dietary supplements, said Rick Kingston, PharmD, president of scientific and regulatory affairs for the firm SafetyCall International, which helps drug and supplement companies manage adverse event reporting and recalls. Kingston is also a professor at the University of Minnesota School of Pharmacy. While the term ‘game changer’ is sorely overused, Kingston said this development truly fits that bill.
“These data are impactful. It may hold the key as to why a company can sell millions of servings of a given supplement with minuscule numbers of individuals reporting specific adverse effects. This is always a challenge when evaluating adverse events for a given product. We routinely run into circumstances where a very small number of individuals experience an adverse effect that is unexplained and certainly inconsistent with the expected safety profile,” Kingston said.
“This research may help us understand why such subpopulations may experience a given effect whereas 99.99% of the rest of the population has no difficulties with the substance whatsoever. We may get to a point where people can get a fingerprint of their genomic makeup which can help them identify substances that may pose a specific risk to them personally so they can stay away from it,” he added.