Evaluation of Absorption and Plasma Pharmacokinetics of Tyrosol Acyl Esters in Rats

Hydrolysis and transport characteristics of starch inclusion complexes with long-chain alkyl gallates: Controlled two-step release of gallic acid and retardation of starch digestion

Corn starch inclusion complexes of alkyl gallates (typical phenololipid representatives), including stearyl gallate, dodecyl gallate, octyl gallate, and hexadecyl gallate, were synthesized by using a heat treatment method. Such inclusion complexes exhibited significantly improved two-step release properties for gallic acid. In other words, gallic acid was generated via the breakdown of alkyl gallates that were released from inclusion complexes in an everted rat intestinal sac model, as determined by HPLC-UV analysis. The produced gallic acid could subsequently pass through intestinal membranes. On the other hand, a glucose oxidase-peroxidase analysis revealed that starch inclusion complexes can slow down starch digestion by increasing the proportion of resistant starch (from 12.2 % to 14.5-30.8 %) and decreasing the proportion of rapidly digestible starch (from 51.2 % to 39.4-49.2 %). Importantly, the two-step release characteristics of gallic acid and the retardation behavior of starch digestion can be easily regulated by modifying the acyl carbon chain length.

In vitro hydrolysis of V-type starch inclusion complexes of alkyl gallates: the controlled two-step release behavior of gallic acid and its beneficial effect on glycemic control

The heat treatment method was used to synthesize starch inclusion complexes from starch and short-chain alkyl gallates (a typical representative of phenololipids), such as butyl gallate, propyl gallate, ethyl gallate and methyl gallate. In an everted rat gut sac model, HPLC-UV analysis revealed that the released alkyl gallates from inclusion complexes were degraded to produce gallic acid. Gallic acids (0.009455-0.014160 nmol min-1) and alkyl gallates (0.2695-0.9441 nmol min-1) were both able to pass through intestinal membranes. After transmembrane transfer, alkyl gallates could also be hydrolyzed to produce gallic acid (1.947 × 10-5-2.290 × 10-5 min-1). It was evident that such an inclusion complex demonstrated superior dual sustained-release characteristics for phenolic compounds. Meanwhile, starch inclusion complexes can also slow down starch digestion by raising resistant starch (from 12.2% to 27.2-46.0%) and lowering rapidly digestible starch (from 51.2% to 22.2-51.2%), according to a glucose oxidase-peroxidase analysis. The delayed digestion behavior of starch in inclusion complexes is very beneficial for blood glucose control. Thus, our work effectively established a theoretical foundation for modifying the dual sustained-release behavior of phenolic compounds and the retardation of starch digestion by adjusting the carbon-chain length in starch inclusion complexes.

Design strategies of polysaccharide, protein and lipid-based nano-delivery systems in improving the bioavailability of polyphenols and regulating gut homeostasis

Polyphenols are plant secondary metabolites that have attracted much attention due to their anti-inflammatory, antioxidant, and gut homeostasis promoting effects. However, food matrix interaction, poor solubility, and strong digestion and metabolism of polyphenols cause barriers to their absorption in the gastrointestinal tract, which further reduces bioavailability and limits polyphenols' application in the food industry. Nano-delivery systems composed of biocompatible macromolecules (polysaccharides, proteins and lipids) are an effective way to improve the bioavailability of polyphenols. Therefore, this review introduces the construction of biopolymer-based nano-delivery systems and their application in polyphenols, with emphasis on improving the solubility, stability, sustained release and intestinal targeting of polyphenols. In addition, there are possible positive effects of polyphenol-loaded nano-delivery systems on modulating gut microbiota and gut homeostasis, with particular emphasis on modulating intestinal inflammation, metabolic syndrome, and gut-brain axis. It is worth noting that the safety of bio-based nano-delivery systems still need to be further studied. In summary, the application of the bio-based nano-delivery system to deliver polyphenols provides insights for improving the bioavailability of polyphenols and for the treatment of potential diseases in the future.

Controlled dual release of phenol compounds from phospholipid complexes of short-chain lipophenols

Ethanol evaporation method was applied to synthesize phospholipid complexes from phosphatidylcholine (PC) and short-chain alkyl gallates (A-GAs, a typical representative of lipophenols) including butyl-, propyl- and ethyl gallates. 1H NMR, UV and FTIR showed that A-GAs were interacted with PC through weak physical interaction. Through the analysis of concentrations of A-GAs and gallic acid (GA) by an everted rat gut sac model coupled with HPLC-UV detection, phospholipid complexes were found to gradually release A-GAs. These liberated A-GAs were further hydrolyzed by intestinal lipases to release GA. Both of GA and A-GAs could cross intestinal membrane. Especially, the transmembrane A-GAs could also be hydrolyzed to produce GA. Undoubtedly, the dual release of phenol compounds from phospholipid complexes of short-chain lipophenols will be effective to extend the in vivo residence period of phenol compounds. More importantly, such behavior is easily adjusted by changing the acyl chain lengths of lipophenols in phospholipid complexes.

Metabolic, toxicological, chemical, and commercial perspectives on esterification of dietary polyphenols: a review

Molecular modifications have been practiced for more than a century and nowadays they are widely applied in food, pharmaceutical, or other industries to manipulate the physicochemical, bioactivity, metabolic/catabolic, and pharmacokinetic properties. Among various structural modifications, the esterification/O-acylation has been well-established in altering lipophilicity and bioactivity of parent bioactive compounds, especially natural polyphenolics, while maintaining their high biocompatibility. Meanwhile, various classic chemical and enzymatic protocols and other recently emerged cell factory technology are being employed as viable esterification strategies. In this contribution, the main motivations of phenolic esterification, including the tendency to replace synthetic alkyl phenolics with safer alternatives in the food industry to improve the bioavailability of phenolics as dietary supplements/pharmaceuticals, are discussed. In addition, the toxicity, metabolism, and commercial application of synthetic and natural phenolics are briefly introduced. Under these contexts, the mechanisms and reaction features of several most prevalent chemical and enzymatic esterification pathways are demonstrated. In addition, insights into the studies of esterification modification of natural phenolic compounds and specific pros/cons of various reaction systems with regard to their practical application are provided.

β-cyclodextrin inclusion complexes with short-chain phenolipids: An effective formulation for the dual sustained-release of phenolic compounds

The β-cyclodextrin and short-chain alkyl gallates (A-GAs), which are representative of phenolipids, such as butyl, propyl, ethyl, and methyl gallates, were chosen to form inclusion complexes by the use of the freeze-drying process. In the everted rat gut sac model, HPLC-UV analysis demonstrated that the released A-GAs from inclusion complexes were degraded to yield free gallic acid (GA) (sustained-release function 1). The small intestine membrane may be crossed by both the GA and the A-GAs. A-GAs may also undergo hydrolysis to provide GA (sustained-release function 2) following transmembrane transfer. Clearly, a helpful technique for the dual sustained-release of phenolic compounds is to produce β-cyclodextrin inclusion complexes with short-chain phenolipids. This will increase the bioactivities of phenolic compounds and prolong their in vivo residence length. Moreover, changing the carbon-chain length of these β-cyclodextrin inclusion complexes would readily modify the dual sustained-release behavior of the phenolic compounds. Thus, our work effectively established a theoretical foundation for the use of β-cyclodextrin inclusion complexes containing short-chain phenolipids as new source of functional food components to provide the body with phenolic compounds more efficiently.

Comparative study on the enzymatic degradation of phenolic esters: The HPLC-UV quantification of tyrosol and gallic acid liberated from tyrosol acyl esters and alkyl gallates by hydrolytic enzymes

HPLC-UV analysis was used to evaluate the enzymatic degradation characteristics of tyrosol acyl esters (TYr-Es) and alkyl gallates (A-GAs). Among various hydrolytic enzymes, TYr-Es can be hydrolyzed by pancrelipase, while A-GAs cannot be hydrolyzed by pancrelipase. Interestingly, carboxylesterase-1b (CES-1b), carboxylesterase-1c (CES-1c) and carboxylesterase-2 (CES-2) are able to hydrolyze TYr-Es and A-GAs, and thus to liberate tyrosol (TYr) and gallic acid (GA). By contrast, the degrees of hydrolysis (DHs) of TYr-Es and A-GAs by CES-1b and CES-1c were significantly higher than those by CES-2. Meanwhile, the DHs of TYr-Es were much higher than those of A-GAs. Especially, the DHs firstly increased and then decreased with the increasing alkyl chain length. Besides, DHs positively correlated with the unsaturation degree at the same chain length. Through regulating carbon length, unsaturation degree and the ester bond structure, controlled-release of phenolic compounds and fatty acids (or fatty alcohols) from phenolic esters will be easily achieved.

Synthesis of lipophilic antioxidant tyrosol laurate using imidazolium ionic liquid [Bmim]HSO4 as a catalyst

Tyrosol is a natural phenolic compound with potent antioxidant properties in the field of food manufacturing. However, the low lipophilicity of tyrosol limited its application. Therefore, the construction of tyrosol laurate (Tyr-L) could effectively overcome the limitations of tyrosol. In this work, four ionic liquids (ILs) were applied for TYr-L preparation. Among them, the 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO4) showed the best catalytic performance. The maximum TYr-L yield was achieved (94.24 ± 1.23 %) under the optimal conditions (reaction temperature 119 °C, substrate ratio 1:6.7, IL dosage 9.2 %, and reaction time 12 h). The kinetic and thermodynamic parameters were also evaluated and it was found that Ea, ΔH, ΔS, and ΔG were 80.81 kJ·mol-1, 77.63 kJ·mol-1, -82.08 J·(mol·K)-1, and 109.89 kJ·mol-1, respectively. The acidic [Bmim]HSO4 demonstrated excellent reusability and stability, even after 6 cycles. Furthermore, TYr-L showed superior ABTS radical scavenging ability, which could be further applied in various industrial processes.

In vitro plasma hydrolysis of phenolic esters and their absorption kinetics in rats: Controlled release of phenolic compounds and enhanced health benefits

Phenolic esters are considered as promising functional food ingredients. However, their digestion, absorption and metabolism are still unclear. Tyrosol acyl esters (TYr-Es), hydroxytyrosol acyl esters (HTy-Es) and alkyl gallates (A-GAs) were hydrolyzed by carboxylesterase in plasma and exhibited slow release of polyphenols (phenolic acids). In vitro hydrolysis degrees initially increased and then decreased with the increasing carbon chain length (C2-C16). TYr-Es exhibited higher hydrolysis degrees compared to HTy-Es, and hydrolysis degrees of TYr-Es and HTy-Es were markedly higher than those of A-GAs. Due to the fast hydrolysis rates of TYr-Es and HTy-Es, they were undetectable in all rat plasma samples collected at several times within 24 h after administration. Whereas, A-GAs could be detected in rat plasmas and three absorption peaks were found in the pharmacokinetic profiles. Importantly, the T1/2, MRT, AUC0-∞, AUC0-t in octyl gallate group were longer (or stronger) than those in propyl gallate and dodecyl gallate groups.

The potential of hydroxytyrosol fatty acid esters to enhance oral bioavailabilities of hydroxytyrosol and fatty acids: Continuous and slow-release ability in small intestine and blood

HPLC-UV analysis in rat everted gut sac and in vitro simulated digestion models indicated that hydroxytyrosol fatty acid esters (HTy-Es) could be hydrolyzed by pancreatic lipase to slow-release of free fatty acids (FAs) and HTy. Meanwhile, the HTy-Es, the liberated FAs and the HTy could cross the membrane and were transported into blood circulation. HTy-Es were further hydrolyzed by carboxylesterase in in vitro rat plasma hydrolysis model, which also showed slow-release of FAs (C1-C4) and HTy. Especially, the rates of hydrolysis and transport initially increased and then decreased with the increasing alkyl chain length. Besides, the above rates of the HTy-Es with a straight chain were greater than those of its isomer with a branched chain. Therefore, the above-mentioned continuous and slow-release of FAs and HTy in small intestine and blood clearly demonstrated that HTy-Es would be an effective approach to enhance oral bioavailabilities of free fatty acids and hydroxytyrosol.

Mono- and dioleyl p-coumarate phenolipids and their antioxidant activity in a muscle food model system

Response surface methodology (RSM) was used to optimize the degree of esterification of p-coumaric acid to triolein via lipase-catalyzed acidolysis, and enzyme load, reaction time and mole ratio of substrates were selected as variables in the experimental design. The results showed that the model employed was highly sufficient for determining the effectiveness and interaction of three selected variables, enzyme load, reaction time and the mole ratio of substrates, on the dependent variable, the degree of esterification. Although the optimization point was not found in the selected range of the three variables, the steepest ascent analysis suggested that an increase of these three variables might lead to a stationary point. However, based on the limitations on increasing the range of tested variables, including possible oxidation of synthesized lipids and increased cost, the degree of esterification so yielded in the designed central composite design should be the one closest to the possible ideal optimized degree. The p-coumarates so produced exhibited varying antioxidant performance in the tested muscle food model, which could be explained by their different lipophilicity. Moreover, the potential health benefits of synthesized phenolic lipids have been discussed.

Graphical Abstract

The Effects of Acyl Chain Length on Antioxidant Efficacy of Mono- and Multi-Acylated Resveratrol: A Comparative Assessment

Acylated derivatives of the dietary phenolic, resveratrol, were prepared via enzymatic and chemical transesterification modification with selected vinyl fatty acids to expand the potential application of resveratrol and its acylated derivatives in functional supplement, cosmetic/skincare, and pharmaceutical fields. The acylation was implemented using eight vinyl fatty acids with varying chain lengths (C2:0-C18:0). Eight monoesters enzymatically prepared, eight diesters and four triesters, chemically prepared, were isolated and purified and identified via MS (mass spectra) or/and NMR (nuclear magnetic resonance). The lipophilicity of resveratrol and its acylated derivatives was calculated using ALOGPS 2.1. Compared with related acylated products, resveratrol itself rendered higher antioxidant efficacy in all the antioxidant assays, namely DPPH, ABTS, FRAP, and ferrous chelation tests. Within various ester derivatives of resveratrol, short-chain fatty acid mono- and di-substituted resveratrols, especially the resveratrol monoacetate/diacetate, exhibited higher antioxidant efficacy in DPPH and ABTS assays than the rest of resveratrol derivatives, but the medium-chain monoesters of resveratrol, including caproate, caprylate, caprate, and laurate, showed a higher metal ion chelation ability compared to other acylated resveratrols. These results imply that resveratrol derivatives may be used in lipidic media as health-beneficial antioxidants.

Gastrointestinal Distribution of Tyrosol Acyl Esters in Orally Infected Mice and Their Hydrolysis by Lactobacillus Species Isolated from the Feces of Mice

Phenolipids, which have been widely used as food antioxidants, are also a potential functional ingredient. However, their characteristics of gastrointestinal distribution and microbial hydrolysis remain unexplored. In this study, an in vivo mouse model and an in vitro anaerobic fermentation model were used to evaluate the above characteristics of tyrosol acyl esters (TYr-Es) with fatty acids (FAs) of C12:0, C18:0, and C18:2. HPLC-UV measurements indicated that oral TYr-Es were remarkably stable in the stomach environment of mice. However, TYr-Es were hydrolyzed to free TYr by lipase in the small intestine, which showed a sustained-release behavior. Specially, TYr was rapidly and almost completely absorbed in the small intestine. By contrast, detectable amounts of TYr-Es were found in the cecum and colon and could be further hydrolyzed to free TYr and FAs by Lactobacillus. These TYr and FAs can participate in regulating the composition of the intestinal microorganisms, which may lead to some health benefits.

Distribution of tyrosol fatty acid esters in the gastrointestinal tract of mice and their hydrolysis characteristic by the gut microbiota

Phenolic lipids have been approved as safe and effective antioxidants, are also a potential ingredient for functional foods. However, the characteristics of gastrointestinal distribution and microbial hydrolysis in the gastrointestinal...

Fatty Acid Hydroxytyrosyl Esters of Olive Oils Are Bioaccessible According to Simulated In Vitro Gastrointestinal Digestion: Unraveling the Role of Digestive Enzymes on Their Stability

Recently, new bioactive compounds were identified in olive oil, lipophenols, which are composed of a fatty acid (FA) and a phenolic core, such as HT (HT-FA). However, their bioaccessibility remains unknown. Thus, the present study uncovers the impact of the separate phases of gastrointestinal digestion on the release and stability of HT-FAs from oily matrices under in vitro simulated conditions. Accordingly, it was found that the bioaccessibility of HT derivatives is largely dependent on the type of FA that esterifies HT, as well as the food matrix. Also, the generation of HT-FAs during intestinal digestion was observed, with pancreatin being the enzyme responsible, to a higher extent, for the de novo formation of lipophenolic derivatives. These findings prompt us to identify new applications to oily matrices and their byproducts as potential functional ingredients for the promotion of health, where the possible formation of new lipophenols during digestion should be taken into consideration.

Effect of carbon chain length on the hydrolysis and transport characteristics of alkyl gallates in rat intestine

Phenolipids such as alkyl gallates (A-GAs) have been approved by food industry as non-toxic antioxidant additives. However, their digestion and absorption mechanisms in the intestine have not yet been clarified. In this research, the hydrolysis and transport characteristics of A-GAs with fatty alcohols of various chain lengths (C1:0, C2:0, C3:0, C4:0, C8:0, C12:0 and C16:0) were estimated by the everted-rat-gut-sac model (ERGSM) for the first time. High-performance liquid chromatography measurements proved that measurable peaks corresponding to methyl gallate (G-C1:0), ethyl gallate (G-C2:0), propyl gallate (G-C3:0) and butyl gallate (G-C4:0) were discovered in the serosal fluids, which showed the short-chain alkyl gallates can cross the membrane in the form of esters. Besides, all A-GAs were hydrolyzed to GA in the mucosal solution, which contributed evidently to the transport of GA across the membrane of the small intestine. Meanwhile, the hydrolysis rate of A-GAs and transport rate of GA initially increased and then decreased with the chain length, exhibiting a maximum for octyl gallate (G-C8:0). In general, all A-GAs have the behavior of sustained-release. In consequence, the production of A-GAs should be an effective method to extend action time and further increases biological activities of GA.

Identification of Tyrosyl Oleate as a Novel Olive Oil Lipophenol with Proliferative and Antioxidant Properties in Human Keratinocytes

Lipophenols are an emerging subclass of phenolic compounds characterized by the presence of a lipid moiety. Recently, hydroxytyrosyl oleate (HtyOle), a derivative of hydroxytyrosol, has been identified in olive oil and by-products. Furthermore, HtyOle possesses anti-inflammatory, antioxidant, and tissue regenerating properties. In this work, the potential occurrence of tyrosyl oleate (TyOle) in olive oil was investigated based on the hypothesis that its precursors tyrosol and oleic acid, both present in relatively high amount can be coupled together. Moreover, TyOle effects have been investigated in human keratinocytes to verify its proliferative and antioxidant properties. The quantitative determination of TyOle was carried out by the external standard method in liquid chromatography coupled with mass spectrometry (LC/MS), in negative mode using multiple reaction monitoring (MRM). The proliferative properties of TyOle on immortalized human keratinocytes (HaCat) were evaluated by 3-(4,5-dimethylthiasol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Morphological changes were observed by fluorescent staining with phalloidin (for F-actin) or 4,6-diamidino-2-phenylindole (DAPI, for chromatin) dye. The antioxidant activity was assessed at the level of production of mitochondrial reactive oxygen species (ROS) induced with UV exposure. TyOle was identified in all the oil samples investigated. Interestingly, TyOle concentration was higher in defective or low-quality oils than in extra virgin oils. The formation of TyOle likely occurs during the crushing and kneading processes and its concentration is related to the increase of rancidity and of the concentration of free precursors. Herein we show that TyOle induced an increase in the viability of HaCat cells and cytoskeletal remodeling.

Polyphenols and Fish Oils for Improving Metabolic Health: A Revision of the Recent Evidence for Their Combined Nutraceutical Effects

Polyphenols and omega-3 polyunsaturated fatty acids from fish oils, i.e., eicosapentaenoic and docosahexaenoic acids, are well-recognized nutraceuticals, and their single antioxidant and anti-inflammatory properties have been demonstrated in several studies found in the literature. It has been reported that the combination of these nutraceuticals can lead to three-fold increases in glutathione peroxidase activity, two-fold increases in plasma antioxidant capacity, decreases of 50-100% in lipid peroxidation, protein carbonylation, and urinary 8-isoprotanes, as well as 50-200% attenuation of common inflammation biomarkers, among other effects, as compared to their individual capacities. Therefore, the adequate combination of those bioactive food compounds and their single properties should offer a powerful tool for the design of successfully nutritional interventions for the prevention and palliation of a plethora of human metabolic diseases, frequently diet-induced, whose etiology and progression are characterized by redox homeostasis disturbances and a low-grade of chronic inflammation. However, the certain mechanisms behind their biological activities, in vivo interaction (both between them and other food compounds), and their optimal doses and consumption are not well-known yet. Therefore, we review here the recent evidence accumulated during the last decade about the cooperative action between polyphenols and fish oils against diet-related metabolic alterations, focusing on the mechanisms and pathways described and the effects reported. The final objective is to provide useful information for strategies for personalized nutrition based on these nutraceuticals.

New lipophenols prevent carbonyl and oxidative stresses involved in macular degeneration

Dry age-related macular degeneration and Stargardt disease undergo a known toxic mechanism caused by carbonyl and oxidative stresses (COS). This is responsible for accumulation in the retinal pigment epithelium (RPE) of A2E, a main toxic pyridinium bis-retinoid lipofuscin component. Previous studies have shown that carbonyl stress in retinal cells could be reduced by an alkyl-phloroglucinol-DHA conjugate (lipophenol). Here, we performed a rational design of different families of lipophenols to conserve anti-carbonyl stress activities and improve antioxidant properties. Five synthetic pathways leading to alkyl-(poly)phenol derivatives, with phloroglucinol, resveratrol, catechin and quercetin as the main backbone, linked to poly-unsaturated fatty acid, are presented. These lipophenols were evaluated in ARPE-19 cell line for their anti-COS properties and a structure-activity relationship study is proposed. Protection of ARPE-19 cells against A2E toxicity was assessed for the four best candidates. Finally, interesting anti-COS properties of the most promising quercetin lipophenol were confirmed in primary RPE cells.