Browsing by Person "Montoya Arroyo, Alexander"

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Identification and quantification of tocomonoenol isomers in plants and microalgae and investigation of their metabolism in liver cells
(2022) Montoya Arroyo, Alexander; Frank, Jan
Tocopherols (T), tocomonoenols (T1), and tocotrienols (T3) are tocochromanols, a group of bioactive compounds composed of a chromanol ring and a 16-carbon sidechain with biological functions, such as the protection of lipid membranes from oxidation and the modulation of cellular signaling. T have saturated sidechains, while T1 and T3 have a single or three double bonds in theirs, respectively. The prefixes alpha-, beta-, gamma-, and delta- are assigned based on the number and positions of methyl groups on the chromanol ring. alpha-, beta-, gamma-, and delta-congeners of T1 have been reported, with alpha-T1 being the predominantly identified congener. Two different alpha-T1 isomers are known, 11-alpha-T1, which has been mainly found in land plants, and 12-alpha-T1, which has been mostly detected in marine organisms. However, little is known regarding the occurrence of T1 in photosynthetic organisms and their metabolism in the liver, a strong determinant of bioavailability and bioactivity. The aim of this thesis was to evaluate underutilized plant-based food sources, cyanobacteria, and microalgae as potential sources of T1 and to characterize the uptake and conversion into metabolites of T1 in cultured liver cells in comparison to T and T3. Acrocomia aculeata fruits were analyzed for alpha-T1 due to its phylogenetic relationship with Elaeis spp, the most common source of this congener. No alpha-T1 was detected in oils from endosperm and mesocarp of wild fruits of Acrocomia aculeata from Costa Rica. Aerial parts of the local underutilized leafy vegetable Urtica leptophylla were evaluated as source of T1 due to its agronomical potential and previous reports of T1 in leaves of plants. LC-MS analyses indicated that leaves and flowers of Costa Rican Urtica leptophylla contain minor amounts of alpha-T1 and gamma-T1. Cyanobacteria and microalgae from different species and origins were analyzed as source of alpha-T1 due to their role as primary producers in aquatic ecosystems and the reported presence of 12-alpha-T1 in marine phytoplankton. alpha-T1 in cyanobacteria and microalgae ranged from traces up to 17% of the total tocochromanol content. alpha-T1 concentrations alone were higher than the sum of all four T3. 11-alpha-T1 was the major alpha-T1 isomer in cyanobacteria and microalgae, as determined by GC-MS. Hence, 11-alpha-T1 is a product of biosynthetic pathways even in aquatic organisms. The effect of nitrogen depletion during the cultivation of microalgae on their alpha-T1 content was investigated. Nitrogen depletion did neither significantly affect the relative or absolute content of alpha-T1, despite an increase in tocochromanol content, nor the proportion of 11-alpha-T1/12-alpha-T1 in microalgae. The uptake and conversion into metabolites of 11-alpha-T1 in HepG2 liver cells was compared to those of alpha-T3 and alpha-T. Cellular uptake of alpha-T1 in liver cells was higher than that of alpha-T. 11-alpha-T1, similar to alpha-T, was converted mostly to alpha-carboxymethylhydroxychroman in a time dependent manner, but to lower extend than alpha-T3. The effect of both ring methylation and sidechain saturation on the uptake and metabolism of the alpha- and gamma-congeners of T1, T and T3 was studied in HepG2 cells. gamma-Congeners were metabolized at higher extent than alpha-congeners and metabolite production increased with increasing number of double bonds in the sidechain independently of chromanol ring methylation. In conclusion, alpha-T1 is present with up to 17% of total tocochromanols in cultured microalgae, which thus are an important new source of this congener. gamma-T1 is only a minor tocochromanol in U. leptophylla flowers. 11-alpha-T1, and not 12-alpha-T1, is the major alpha-T1 isomer in cyanobacteria and microalgae and nitrogen depletion of microalgae does not significantly affect alpha-T1 concentration. The metabolic conversion of alpha-T1 into alpha-carboxymethylhydroxychroman in HepG2 cells is similar to that of alpha-T and significantly lower than that of alpha-T3, suggesting that it may be handled by the organism similar to alpha-T. In conclusion, novel potential food sources of alpha-T1 have been identified and, because of similarities with alpha-T, its pharmacokinetics and biological activities warrant further investigation.