OR32-05 Carbonyl reductase 1 has a fundamental role in the clearance of exogenous glucocorticoids

Abstract Disclosure: R. Pofi: None. T. Potter: None. S. Coll: None. N. Othonos: None. H. Miller: None. M. Nuria: None. R. Ventura: None. J.W. Tomlinson: None. Background: Prednisolone and prednisone are the most commonly prescribed exogenous glucocorticoid, yet the enzymatic pathways governing their clearance remain largely uncharacterized. We demonstrated that selective 11β-HSD1 inhibition mitigates prednisolone-induced adverse effects1, however this could not be fully explained by the shifting between inactive prednisone and active prednisolone. Other enzymes, including AKR1C1 (20α-hydroxylase), Carbonyl reductase-1 (20β-hydroxylase, CBR1) have been implicated in glucocorticoid metabolism, but their role in regulating prednisone and prednisolone availability and clearance remains unexplored. Methods: HEK293 cells were transfected with either an empty vector (HEK293EV) or overexpressed (OE) with AKR1C1OE or CBR-1OE. Cells were treated with 500nM prednisolone or prednisone. Media predniso(lo)ne metabolites were quantified using LC-MS/MS at multiple time-points over a 48-hour period. Data were analysed using repeated measures and one-way ANOVA. Results: CBR1 was abundantly expressed in HEK293EV and further upregulated in CBR1OE. Following treatment with both prednisolone or prednisone, 20β-metabolites dominated the metabolite profile. After prednisolone treatment, 20β-dihydro-prednisolone levels were detectable, but low in HEK293EV (5.0±1.89ng/mL) and AKR1C1OE (6.3±1.87ng/mL, p=0.56), with the highest levels observed in CBR1OE (19.60±7.15 ng/mL, p<0.05 vs. HEK293EV and AKR1C1OE,) and overall, there was little prednisolone clearance. In contrast, prednisone was cleared effectively, most notably in CBR1OE cells (18%, HEK293EV, 17%, AKR1C1OE, 38% CBR1OE). Reflecting basal levels of CBR1 in HEK293EV cells, 20β-dihydro-prednisone (29.48±9.44ng/mL) accounted for nearly the entire clearance of prednisone (-99.5%). Similarly, in CBR1OE cells, 20β-dihydro-prednisone (40.42±9.89ng/mL) was responsible for 77.8% of prednisone clearance. AKR1C1 expression was low in HEK293EV, but increased in AKR1C1OE. However, 20α-metabolites were almost undetectable in all cell lines suggesting a minimal contribution to prednisone and prednisolone clearance. Conclusions: CBR1 is a major contributor to the metabolism of prednisone and prednisolone, with a preferential affinity for prednisone. These results highlight the underappreciated role of CBR1 in glucocorticoid pharmacokinetics and provide a novel target for modulating glucocorticoid metabolism to improve therapeutic outcomes. References1 11β-HSD1 inhibition in men mitigates prednisolone-induced adverse effects in a proof-of-concept randomised double-blind placebo-controlled trial. Othonos et al, NatComm 2023;doi:10.1038/s41467-023-36541-w. Presentation: Monday, July 14, 2025