CYP3A4-Catalyzed Simvastatin Metabolism as a Non-Invasive Marker of Small Intestinal Health in Celiac Disease

OBJECTIVES: Histological examination of duodenal biopsies is the gold standard for assessing intestinal damage in celiac disease (CD). A noninvasive marker of disease status is necessary, because obtaining duodenal biopsies is invasive and not suitable for routine monitoring of CD patients. As the small intestine is a major site of cytochrome P450 3A4 (CYP3A4) activity and also the location of the celiac lesion, we investigated whether patients with active CD display abnormal pharmacokinetics of an orally administered CYP3A4 substrate, simvastatin (SV), which could potentially be used for noninvasive assessment of their small intestinal health. METHODS: Preclinical experiments were performed in CYP3A4-humanized mice to examine the feasibility of the test. Subsequently, a clinical trial was undertaken with 11 healthy volunteers, 18 newly diagnosed patients with CD, and 25 celiac patients who had followed a gluten-free diet (GFD) for more than 1 year. The maximum concentration (C-max) of orally administered SV plus its major non-CYP3A4-derived metabolite SV acid (SV equivalent (SVeq)) was measured, and compared with clinical, histological, and serological parameters. RESULTS: In CYP3A4-humanized mice, a marked decrease in SV metabolism was observed in response to enteropathy. In the clinical setting, untreated celiac patients displayed a significantly higher SVeq C-max (46 +/- 24 nM) compared with treated patients (21 +/- 16 nM, P < 0.001) or healthy subjects (19 +/- 11 nM, P < 0.005). SVeq C-max correctly predicted the diagnosis in 16/18 untreated celiac patients, and also the recovery status of all follow-up patients that exhibited normal or near-normal biopsies (Marsh 0-2). All patients with abnormal SVeq C-max showed a reduction in the value after 1 year of following a GFD. CONCLUSIONS: SVeq C-max is a promising noninvasive marker for assessment of small intestinal health. Further studies are warranted to establish its clinical utility for assessing gut status of patients with CD.