Abstract
Diclofenac is an important analgesic and anti-inflammatory drug that is widely used for the treatment of postoperative pain, rheumatoid arthritis, and chronic pain associated with cancer. Diclofenac is extensively metabolized in the liver, and the main metabolites are hydroxylated and/or glucuronidated conjugates. We show here that loss of multidrug resistance protein 2 (MRP2/ABCC2) and breast cancer resistance protein (BCRP/ABCG2) in mice results in highly increased plasma levels of diclofenac acyl glucuronide, after both oral and intravenous administration. The absence of Mrp2 and Bcrp1, localized at the canalicular membrane of hepatocytes, leads to impaired biliary excretion of acyl glucuronides and consequently to elevated liver and plasma levels. Mrp2 also mediates the biliary excretion of two hydroxylated diclofenac metabolites, 4'-hydroxydiclofenac and 5-hydroxydiclofenac. We further show that the sinusoidal efflux of diclofenac acyl glucuronide, from liver to blood, is largely dependent on multidrug resistance protein 3 (MRP3/ABCC3). Diclofenac acyl glucuronides are chemically instable and reactive, and in patients, these metabolites are associated with rare but serious idiosyncratic liver toxicity. This might explain why Mrp2/Mrp3/Bcrp1(-/-) mice, which have markedly elevated levels of diclofenac acyl glucuronides in their liver, display acute, albeit very mild, hepatotoxicity. We believe that the handling of diclofenac acyl glucuronides by ATP binding cassette transporters may be representative for the handling of acyl glucuronide metabolites of many other clinically relevant drugs.