Sulforaphane as an Antagonist to Human PXR-mediated Drug-drug Interactions

Overview

Adverse drug-drug interactions (DDIs) are responsible for approximately 3% of all hospitalizations in the US, perhaps costing more than $1.3 billion per year. One of the most common causes of DDIs is the when one drug alters the metabolism of another. A key enzyme in the liver and intestine, called "cytochrome P450 3A4 (CYP3A4) is generally considered to be the most important drug metabolizing enzyme. The gene for CYP3A4 can be 'turned on' by the presence of certain other drugs, resulting in much higher levels of CYP3A4 in the liver and intestine. Thus, when a drug that induces CYP3A4 is given with or before another drug that is metabolized by 3A4, a 'drug-drug' interaction occurs because the first drug (the inducer) greatly changes the rate at which the second drug (CYP3A4 substrate) is removed from the body. Many drugs increase CYP3A4 activity by binding to a receptor called the Pregnane-X-Receptor (PXR), which is a major switch that controls the expression of the CYP3A4 gene. Using human liver cells we have demonstrated that sulforaphane (SFN), found in broccoli, can block drugs from activating the PXR receptor, thereby inhibiting the switch that causes CYP3A4 induction. The purpose of this project is to determine if SFN can be used to block adverse DDIs that occur when drugs bind to and activate the PXR receptor and subsequently induce CYP3A4 activity. We will recruit 24 human volunteers to participate in the study. This project will determine whether SFN can prevent the drug Rifampin from binding to PXR and increasing CYP3A4 activity in humans following oral administration of SFN (broccoli sprout extract). The rate of removal of a small dose of the drug midazolam will be used to determine the enzymatic activity of CYP3A4 before and following treatment with Rifampin, in the presence or absence of SFN, since midazolam is only eliminated from the bloodstream by CYP3A4. . We predict that SFN will prevent the increase in midazolam clearance (metabolism) that normally follows treatment with the antibiotic, rifampicin. This research is important because it could potentially lead to a simple, cost-effective way of preventing one of the most common causes of adverse drug-drug interactions that occurs today. For example, rifampicin, which is a cheap and effective antibiotic used to treat TB, cannot be used in HIV/AIDS patients because it increases the metabolism of many of the antiretroviral drugs used to treat HIV/AIDS. TB is a major opportunistic infection in AIDS patients, so this is a serious clinical problem, especially in developing countries where more expensive alternative drug therapies are not available. We hypothesize that co-formulation of rifampicin with SFN could block this drug-drug interaction without altering its efficacy, thereby allowing its use in HIV/AIDS patients infected with TB. This is but one example of numerous drug-drug interactions that occur via this mechanism.