Production of asymmetric oxidative metabolites of [13C]-β-carotene during digestion in the gastrointestinal lumen of healthy men

Abstract

Asymmetric β-apo-carotenoids (nonvitamin A-active metabolites) of provitamin A carotenoids have been observed in humans, but no study has investigated their formation during digestion. The aim of this study was to follow the formation and absorption of asymmetric β-apo-carotenoids during digestion. Healthy men were intragastrically and intraduodenally intubated, and randomly assigned to consume a lipid-rich control meal (n=3) or a lipid-rich test meal containing 20 mg [13C-10]-β-carotene (n=7). Digesta samples were collected over 5 h, and blood collected over 7 h. The triglyceride-rich lipoprotein (TRL) fractions of plasma were also isolated. Lipophilic extracts of digesta, plasma, and TRL were analyzed via a high-performance liquid chromatography-tandem mass spectrometry method developed to identify [13C]-labeled β-apo-carotenals/carotenone, [13C]-β-apo-carotenols, and [13C]-β-apo-carotenoic acids. Relative to [13C]-β-carotene, [13C]-β-apo-carotenal levels remained ∼3 orders of magnitude lower throughout digestion (no [13C]-β-apo-carotenols, or [13C]-β-apo-carotenoic acids were observed). A mixed model determined relative influence of digesta type and time on digesta metabolite level. Increasing time significantly increased the model levels of digesta [13C]-β-apo-10',12',14',15-carotenal and [13C]-β-apo-13-carotenone (P<0.05) and trended toward decreased [13C]-β-apo-8'-carotenal (P=0.0876). Gastric digesta were associated with a significantly higher level of [13C]-β-apo-8'-carotenal (P=0.0289), and lower levels of [13C]-β-apo-12',14',15-carotenal (P<0.05), relative to duodenal digesta. Anticipated retinoids, but no asymmetric [13C]-β-apo-carotenals, [13C]-β-apo-carotenols, or [13C]-β-apo-carotenoic acids, were observed in the blood or TRL samples. β-Carotene appears to be robust to digestion, with minor amounts of β-apo-carotenals/carotenone formed. Absence of asymmetric [13C]-β-apo-carotenals in plasma and TRL suggests lack of absorption, levels below the limit of detection, lack of stability, or further conversion during the digestive process to as-yet unidentified products. Lack of asymmetric [13C]-β-apo-carotenals in plasma also suggests a lack of postprandial intestinal BCO2 activity in healthy humans. This trial was registered at clinicaltrials.gov as NCT03492593.