Application of Virtual Twin PBPK Models in Individuals with Obesity via CYP3A4 Phenotyping Using Endogenous Biomarker Data.

Plasma 4β-hydroxycholesterol (4β-OHC) normalized for the levels of its parent cholesterol (4β-OHC/C) is an endogenous biomarker for hepatic CYP3A4. This study evaluated CYP3A4 activity longitudinally in individuals while their obesity status was changing. 4β-OHC/C was measured pre-surgery (n = 54) and 2 years after Roux-en-Y gastric bypass (n = 30) and used as an input for creating virtual twins of each patient within physiologically-based pharmacokinetic (VT-PBPK) models, alongside other available data (e.g., demographics). Additionally, individual CYP3A4 abundance quantified from liver biopsies during surgery was available. Predicted CYP3A4 abundance using 4β-OHC/C was within twofold of the measured abundance in 85% of the individuals (n = 54). Pre-surgery VT-PBPK models informed by biomarker data predicted area under curve after intravenous midazolam (AUCinf,iv) within twofold of observed values in 85% of individuals (geometric mean fold error (GMFE) = 1.58). VT-PBPK models using CYP3A4 protein measurements showed similar performance (83% within twofold, GMFE = 1.66), verifying the biomarker approach. The post-surgery VT-PBPK models were revised to reflect surgery-related alterations and changes in obesity status. Hepatic CYP3A4 activity at 2 years was predicted from 4β-OHC/C measured in the same individuals. Biomarker-informed models predicted midazolam AUCinf,iv within twofold for 87% of individuals (GMFE = 1.48; n = 30). ~60% of observed oral midazolam PK parameters were predicted within twofold, improving to 70% when the surgery model assumed full intestinal CYP3A4/5 recovery. This study highlights the utility of 4β-OHC/C for continuous monitoring of CYP3A4 activity and possibility to use biomarker-informed VT-PBPK models for individual dose requirements of intravenously administered CYP3A substrates in individuals with obesity over the course of weight loss treatment.