expertise: Toxicology

Education

• PhD in Pharmaceutical Sciences, University of Newcastle-upon-Tyne, England
• BSc, Heriot-Watt University, Scotland
• Postdoctoral Fellow, UW

Research Areas

• Biochemistry of the human CYP2 and CYP4 families of P450s
• Pharmacogenomics of cardiovascular drugs
• P450-dependent bioactivation and associated adverse reactions

Taking Students: No

Biography

Dr. Rettie obtained a PhD in Pharmaceutical Sciences in 1983 from the University of Newcastle-upon-Tyne, England, before moving to Seattle to post-doc with Drs. Mont Juchau and Dr. Bill Trager at the UW in the areas of extra-hepatic drug metabolism and mechanisms of drug-drug interactions. He joined the faculty of the UW School of Pharmacy in 1987 and was Department Chair from 2000-2014.

Dr. Rettie’s research interests have focused mainly on the human P450 enzymes and attempts to understand mechanisms of catalysis, substrate specificity, pharmacogenetic variability and adverse drug reactions related to these monooxygenases. He has published over 190 peer-reviewed papers and held research grants from the National Institutes of Health (NIH) in these topic areas for the last 25 years.

Dr. Rettie has served on the editorial boards of Drug Metabolism and Disposition, Drug Metabolism Reviews, Journal of Pharmacology and Therapeutics, Current Drug Metabolism, Chemico-Biological Interactions and Chemical Research in Toxicology, as well as numerous NIH grant review panels. He has chaired the Scientific Affairs Committee of the International Society for Study of Xenobiotics (ISSX) and is Past Chair of the International Union of Basic and Applied Pharmacology’s Section of Drug Metabolism and Transport. In 2005, Dr. Rettie received the North American Scientific Achievement Award from ISSX for his work on elucidating metabolic and pharmacogenetic mechanisms of adverse reactions to the anticoagulant drug, warfarin, and in 2016 was appointed a Fellow of the Japanese Society for the Study of Xenobiotics.

Research Overview

Metabolism by the cytochrome P450s is the principal means whereby lipid-soluble drugs and compounds foreign to the body are converted to water-soluble derivatives that can be readily excreted. This is a beneficial effect of the enzyme system. However, it is well recognized that P450-mediated bioactivation of drugs and other xenobiotics is an important mechanism of chemical toxicity (Baillie and Rettie, 2011). Moreover, unexpected interruptions in P450 activity, due to genetic variation (Danese et al., 2012) or administration of agents that inhibit P450 activity (McDonald et al., 2015), can cause serious adverse drug reactions and contribute to disease states.

Much of the research in the Rettie laboratory focuses on the biochemistry and pharmacogenetics of the vitamin K cycle with an emphasis on how P450 enzymes interact with components of the cycle to maintain homeostasis. Human CYP2C9, for example, is the primary catalyst of (S)-warfarin metabolism (Daly et al., 2018). This vitamin K antagonist is an anticoagulant drug that is very difficult to dose correctly, and there are many drug-drug and drug-gene interactions associated with its use (Rettie and Tai, 2006).

An important goal for the laboratory is to define sources of inter-individual variability in warfarin dosing that can span a 100-fold range (Cooper et al., 2008). We have shown that common genetic polymorphisms in CYP2C9 decrease warfarin dose requirements by reducing the metabolic clearance of (S)-warfarin, while common polymorphisms in the warfarin target enzyme, VKORC1, affect warfarin dose by changing hepatic concentrations of this critical recycling enzyme (Rieder et al., 2005). We found that CYP4F2 and CYP4F11 are key vitamin K catabolizing enzymes (Edson et al., 2013) and common variation in CYP4F2 at least, affects warfarin dose, likely by modulating hepatic vitamin K concentrations (McDonald et al., 2009). We are currently examining the role of novel genetic variation in determining warfarin response in underserved populations (Henderson et al., 2019).

Other research in the laboratory is concerned with CYP4 enzymes that are potential drug targets because of their critical roles in health and disease (Edson et al., 2013; Johnson et al., 2015). Efforts are ongoing to synthesize chemical inhibitors of specific CYP4-family members to better dissect their physiological roles. CYP4B1 metabolizes a host of pro-toxins, including furans, aromatic amines, and certain fatty acids to reactive intermediates that can damage the cell. In this regard, CYP4B1 is a curious member of the CYP4 family because these enzymes typically have
a restricted substrate specificity that does not extend much beyond endogenous fatty acids. To evaluate the role of CYP4B1 in chemical toxicity, we have also developed a knockout mouse model (Parkinson et al, 2013). Most recently, we identified structural determinants of human CYP4B1 that confer high activity towards 4-ipomeanol (Wiek et al., 2015), and evaluated the substrate specificity of the ‘optimized’ human enzyme (Roellecke et al., 2017).

Our CYP4 research extends to the study of ‘orphan P450s’, like CYP4V2 and CYP4Z1, whose substrate specificity is unknown. We have reported on the fatty acid substrate specificity of CYP4V2 (Nakano et al., 2009) and the enzyme’s distribution in the eye (Nakano et al., 2012). Intriguingly, polymorphisms in CYP4V2 are found in patients suffering from the eye disease Bietti’s Crystalline Dystrophy (BCD). A knockout mouse model for CYP4V2 that recapitulates BCD has been developed in collaboration with the Kelly laboratory that should be of help in ‘deorphanizing’ the enzyme (Lockhart et al., 2014). Finally, the newest project in the Rettie lab concerns CYP4Z1, an unusual CYP that is localized to mammary tissue in humans and is up-regulated in breast cancer. We have expressed the enzyme in yeast and HepG2 cells and reported on the fatty acid metabolite profile of the enzyme (McDonald et al., 2017) and the development of novel, selective chemical inhibitors of CYP4Z1 (Kowalski et al., 2020).

In general, we use genetic re-engineering coupled with conventional protein biochemistry methods for the expression and isolation of CYP2 and CYP4 proteins and mutants of interest from heterologous hosts such as E.coli, insect cells and yeast (Mosher et al., 2008; Roberts et al., 2010). We also make extensive use of mass spectrometry for analyte quantification, including evaluation of structural changes in mutant proteins and lipidomic analysis to probe changes in endogenous metabolism due to CYP4V and CYP2C enzyme polymorphisms. Gene sequencing to discover novel polymorphisms in important pharmacogenes and disease-associated P450s is a continuing focus of the laboratory. Synthetic chemistry comes into play in the preparation of new substrates, inhibitors and metabolites for P450s of interest. Our long-term goals are to understand how structure and function are related for these important P450 enzyme families, and how their dysregulation affects drug response and disease.

Recent Publications