jbrehm2, November 3, 2014 | View original publication
Analyzing factors in diabetes meds’ potency
Among the greatest challenges of treating diabetes? Many proteins that agree to taxi pharmaceutical drugs through the bloodstream are already carrying unruly back-seat drivers in the form of glucose.
David Hage, the James Hewett University Professor of Chemistry, is developing approaches to analyze how the bonding of proteins and glucose, or glycation, alters the effectiveness of diabetes medications taken by millions who contend with the disease on a daily basis.
With support from a grant recently renewed by the National Institutes of Health, Hage and his colleagues are exploring applications of a technique known as high-performance affinity chromatography. The researchers have refined a process that involves placing a sample of the blood’s most common protein – human serum albumin, or HSA – in a porous column. By passing a drug-containing liquid solution through this column, the researchers essentially create an intersection where pharmaceuticals can interact with the HSA protein.
The time it takes a specific drug to pass through the column helps the team determine whether and how strongly it binds to HSA, thereby offering insights into how glucose modifies this drug-protein interaction.
“We’re basically mimicking a biological system; we’ve created a synthetic model of the human bloodstream that allows us to focus on this drug-protein interaction,” Hage said. “Our hypothesis was that the modification of this protein (by glucose) affects its ability to bind with these drugs that are used to treat Type 2 diabetes. There were hints that this might be happening, but no one had really done any detailed studies on it until we started this project.”
By comparing normal proteins with those modified by glucose, Hage’s team has found evidence that glycation can significantly impede binding between HSA and drugs used to suppress diabetes-related complications.
Hage said his team has also developed procedures by which to detect and identify differences in the binding process. Their efforts have specifically helped examine HSA’s many potential binding sites, which can exhibit distinct sensitivities to glucose. Accordingly, the researchers are now examining how glucose-driven modifications at different locations on this protein can moderate the behavior of various drugs.
“We have an idea that this binding is having an effect, but now we can also get an idea of why it’s changing,” Hage said. “Sometimes one of the sites will seem to be more affected by these modifications than another, so certain drugs are going to have bigger effects than others, depending on where they’re binding.”
Because diabetes also leads to increased circulation of fatty acids in the bloodstream, Hage’s team is comparing how their effects compare – and potentially combine – with those of glucose.
“We can do studies with the protein that’s just been modified through glycation without the fatty acids present, and we can do it with the fatty acids present,” Hage said. “We’ve seen that there are changes: Sometimes they counterbalance each other, so the net result is not much of a change, and sometimes they enhance each other, so there’s an even bigger change. It depends on the drug, the glycation and the fatty acids. So it’s not simple, which explains why people have been confused about it in the past.”
The researchers’ efforts to analyze the interactions occurring within diabetics further extend to the types and number of pharmaceuticals a person may be taking, Hage said. Those with diabetes often take multiple drugs to address its effects, he said, making this a major focus of future study.
“You have to start thinking about not only how the binding of any particular drug to this protein will be affected, but how the binding of the second drug is being affected by the first, and vice versa,” he said. Hage said the team will also attempt to account for additional factors that influence diabetes treatment, including differences in glucose levels between and within diabetics.
“We already know that there’s often a period of trial and error to get the dosage right,” Hage said. “At least part of that adjustment might be due to the fact that their glucose levels are changing, so we’ll be looking at samples from various patients that have the same level of glucose control to see how the drug binding changes from one patient to the next.”
The group also plans to examine samples obtained from the same person at different points in their treatment to determine how drug-binding changes in accordance with glucose control.
Though the team’s chromatographic approach isn’t yet ready for widespread adoption in conventional clinics, Hage said it could eventually contribute to the personalized treatment of a disease that affects more than 150 million people worldwide.
“At some point, it could be practical to use it in a clinical setting as a screening method for doctors to select drugs for individual patients,” Hage said. “Getting to the point where it’s automated, or at least fairly routine, would allow it to be done.”
The research is funded by the National Institute of Diabetes and Digestive and Kidney Diseases, part of the National Institutes of Health, under grant number R01DK069629.