Production of asymmetric oxidative metabolites of [13C]-β-carotene during digestion in the gastrointestinal lumen of healthy men
Résumé
Background: Asymmetric β-apo-carotenoids (non-vitamin A active metabolites) of provitamin A carotenoids have been observed in humans, but no study has investigated their formation during digestion.
Objective: To follow the formation and absorption of asymmetric β-apo-carotenoids during digestion.
Design: 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 hours, and blood collected over 7 hours. The triglyceride-rich lipoprotein (TRL) fractions of plasma were also isolated. Lipophilic extracts of digesta, plasma, and TRL were analyzed via an LC-MS/MS method developed to identify 13C β-apo-carotenals/carotenone, 13C β-apo-carotenols, and 13C β-apo-carotenoic acids. Results: 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 was 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.
Conclusions: 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.
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