Cholesterol Medicine Breaks Down Prescription Drugs

Newswise — Researchers at the University of Kansas have discovered that a cholesterol-lowering herbal drug also produces an unwanted side effect: It accelerates the breakdown of prescription drugs that fight the effects of AIDS and cancer.

Experiments showed that guggulsterone, the active ingredient in the herbal drug gugulipid, turns on a cell receptor called PXR. This, in turn, triggers a liver enzyme that breaks down almost 60 percent of the prescription drugs on the market.

Jeff Staudinger, KU assistant professor of pharmacology and toxicology, and research assistant Dan Brobst reported their findings about the receptors that guggulsterone triggers in the Journal of Pharmacology and Experimental Therapeutics.

Drugs affected by guggelsterone include the AIDS drug AZT, anticancer agents and cholesterol-lowering statins.

The liver enzyme also can turn some chemicals that do not cause cancer into carcinogens, Staudinger said.

The PXR cell receptor is one of three that guggulsterone stimulates, Staudinger said.

"This country's diet is atrocious, so there are plenty of people walking around with high cholesterol," Staudinger said. "They'll get on the Web and see that gugulipid herbal therapy lowers cholesterol and is available without a prescription.

"They may then begin self-medicating with gugulipid in addition to other drugs prescribed by their physician. In this study, we've shown that, when they do, they have a high likelihood of causing herb-drug interactions."

Earlier studies had shown that guggulsterones lower cholesterol by turning down the activity of a receptor known as FXR. Brobst, Staudinger and their collaborators decided to experiment with the herbal gugulipid, which they bought at a Lawrence health-food store, and with the pure form, guggulsterone, to see whether other receptors also were implicated in its effect on the body.

PXR and FXR belong to a family of 48 receptors that constitute what Staudinger called a "nuclear receptor superfamily." They are called nuclear receptors because the various molecules caught by these receptors interact with the DNA inside the nucleus of cells, turning genes on and off.

The two other receptors activated by guggulsterone in the study were the estrogen receptor and the progesterone receptor, Staudinger said.