Browsing by Subject "Vitamin E"

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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.
LC‐Orbitrap‐HRMS determination of two novel plastochromanol homologues
(2023) Hammerschick, Tim; Graf, Jana; Vetter, Walter
Scope: The antioxidant plastochromanol-8 (PC-8) is a tocochromanol which differs from γ-tocotrienol in having an unsaturated side chain of eight instead of three isoprene units. The recent isolation of PC-8 from flaxseed oil indicates the additional presence of lower shares of two previously unknown homologues, plastochromanol-7 (PC-7) and plastochromanol-9 (PC-9), which feature seven and nine isoprenoid units respectively on the γ-chromanol backbone. Here, a fast LC-Orbitrap-HRMS method is applied for the determination of PC-7 and PC-9 in seven plant oils and a plant extract. Methods and results: The presence of PC-7, PC-8, and PC-9 is confirmed in all eight investigated samples by LC-Orbitrap-HRMS analysis after saponification. PC-8 amounts of ≈315–350 mg kg−1 in two flaxseed oils, ≈75 mg kg−1 in rapeseed oil, ≈38 mg kg−1 in camelina oil, ≈80–120 mg kg−1 in two mustard oils, ≈90 mg kg−1 in candle nut oil, and ≈900 mg kg−1 dry weight in Cecropia leaves are determined by quantification. Semi-quantification of PC-7 and PC-9 indicated the presence of ≈0.1–1% of PC-7 and PC-9 in varied relative ratios. Conclusion: The novel plastochromanol homologues are of particular interest to researchers with focus on vitamin E and other tocochromanols because of their unexplored bioactivity.
Tocotrienols, tocopherols and tocomonoenols : characterization in Costa Rican palm oils, and intracellular and tissue distribution as a function of the hepatic alpha-tocopherol transfer protein
(2018) Irías-Mata, Andrea Paola; Frank, Jan
Vitamin E is a generic term for a group of micronutrients exhibiting the biological activity of alpha-tocopherol. Initially, four tocopherols (T) and four tocotrienols (T3) were recognized as the naturally occurring vitamin E compounds. The main difference among T and T3 is the 3-fold unsaturated 16-carbon side chain of the T3 compared to the saturated 16-carbon side chain of the T. Recently, a group of four vitamin E compounds with a single double bond at carbon 11 were discovered, namely tocomonoenols (T1). Edible oils are the major source of T, T3, and of T1. As a fat-soluble vitamin, the vitamin E is absorbed after oral intake and transported in the circulation to the liver, where vitamin E undergoes sorting by the action of the alpha-hepatic-tocopherol transfer protein (TTP) and the cytochrome P450 (CYP) enzymes. alpha-T is preferentially secreted into the bloodstream, while the non-alpha-T congeners are metabolized by CYP to the carboxyethylhydroxychromanols (CEHC), which are excreted via urine and feces. The TTP has been recognized as necessary for the maintenance of normal alpha-T concentrations in plasma and extrahepatic tissues. Interestingly, TTP might also protect the non-alpha-T congeners from side-chain degradation, and therefore prevent their metabolic degradation. The present thesis aimed at increasing our knowledge of the non-αT congeners of vitamin E with respect to their occurrence in food, their intracellular localization upon uptake into liver cells, and their tissue distribution in mammals. A potential role of the TTP in the intracellular and intra-organismic trafficking of the non-alpha-T congeners was a second focus of the current investigations. To this purpose, the vitamin E profiles and contents in oils of three Elaeis Guineensis, two Elaeis Oleifera, and one hybrid OxG palm fruit genotypes from Costa Rica were determined after mechanical extraction with a screw press and chemical extraction with hexane. Vitamin E profiles in the palm oils were similar, irrespective of the genotype and extraction procedure, and alpha- and gamma-T3 were the most abundant congeners. alpha-T1 was found in oils from five of the six varieties. Hexane extraction yielded up to 2.5-fold higher total vitamin E compared to screw press extraction. The two most abundant tocotrienols in the oils were selected for further studies with respect to their cellular uptake and intracellular distribution in cultured liver cells with and without stable expression of TTP and compared to their respective tocopherol counterparts. After uptake, all four congeners were primarily associated with the lysosomes, endoplasmic reticulum and plasma membrane. Overall, the results conclude that neither the structural differences between the four congeners, nor the TTP-expression are important factors behind the intracellular trafficking (uptake and distribution) of the congeners in cultured liver cells. Finally, an animal study was performed to examine the tissue distribution of alpha-T1 in mice in comparison to alpha-T. Besides was investigated the influence of TTP. Wild-type and TTP knockout mice were fed a standard diet with either alpha-T or alpha-T1 for 2 weeks. Concentrations were measured in blood and several tissues. alpha-T1 was only found in blood, not in tissues. Loss of TTP function in knockout mice resulted in almost complete depletion of alpha-T in all tissues. Interestingly, alpha-T1 was still present in blood. In conclusion, alpha-T1 reached the blood in mice with and without TTP function, suggesting that TTP may not, or only to a limited extent, be required for the secretion of alpha-T1 into the systemic circulation. Since more is known about alpha-T than the non-alpha-T congeners, new opportunities for further research on the biological activities and consequent health benefits of the non-alpha-T congeners have arisen based on the contributions of the present thesis.
Walnut oil reduces Aβ levels and increases neurite length in a cellular model of early Alzheimer disease
(2022) Esselun, Carsten; Dieter, Fabian; Sus, Nadine; Frank, Jan; Eckert, Gunter P.
Mitochondria are the cells’ main source of energy. Mitochondrial dysfunction represents a key hallmark of aging and is linked to the development of Alzheimer’s disease (AD). Maintaining mitochondrial function might contribute to healthy aging and the prevention of AD. The Mediterranean diet, including walnuts, seems to prevent age-related neurodegeneration. Walnuts are a rich source of α-linolenic acid (ALA), an essential n3-fatty acid and the precursor for n3-long-chain polyunsaturated fatty acids (n3-PUFA), which might potentially improve mitochondrial function. (2) Methods: We tested whether a lipophilic walnut extract (WE) affects mitochondrial function and other parameters in human SH-SY5Y cells transfected with the neuronal amyloid precursor protein (APP695). Walnut lipids were extracted using a Soxhlet Extraction System and analyzed using GC/MS and HPLC/FD. Adenosine triphosphate (ATP) concentrations were quantified under basal conditions in cell culture, as well as after rotenone-induced stress. Neurite outgrowth was investigated, as well as membrane integrity, cellular reactive oxygen species, cellular peroxidase activity, and citrate synthase activity. Beta-amyloid (Aβ) was quantified using homogenous time-resolved fluorescence. (3) Results: The main constituents of WE are linoleic acid, oleic acid, α-linolenic acid, and γ- and δ-tocopherol. Basal ATP levels following rotenone treatment, as well as citrate synthase activity, were increased after WE treatment. WE significantly increased cellular reactive oxygen species but lowered peroxidase activity. Membrane integrity was not affected. Furthermore, WE treatment reduced Aβ1–40 and stimulated neurite growth. (4) Conclusions: WE might increase ATP production after induction of mitochondrial biogenesis. Decreased Aβ1–40 formation and enhanced ATP levels might enhance neurite growth, making WE a potential agent to enhance neuronal function and to prevent the development of AD. In this sense, WE could be a promising agent for the prevention of AD.