Metabolism of caffeic acid in the isolated perfused rat liver

Metabolism of phenolics in coffee and plant-based foods by canonical pathways: an assessment of the role of fatty acid β-oxidation to generate biologically-active and -inactive intermediates

ω-Phenyl-alkenoic acids are abundant in coffee, fruits, and vegetables. Along with ω-phenyl-alkanoic acids, they are produced from numerous dietary (poly)phenols and aromatic amino acids in vivo. This review addresses how phenyl-ring substitution and flux modulates their gut microbiota and endogenous β-oxidation. 3',5'-Dihydroxy-derivatives (from alkyl-resorcinols, flavanols, proanthocyanidins), and 4'-hydroxy-phenolic acids (from tyrosine, p-coumaric acid, naringenin) are β-oxidation substrates yielding benzoic acids. In contrast, 3',4',5'-tri-substituted-derivatives, 3',4'-dihydroxy-derivatives and 3'-methoxy-4'-hydroxy-derivatives (from coffee, tea, cereals, many fruits and vegetables) are poor β-oxidation substrates with metabolism diverted via gut microbiota dehydroxylation, phenylvalerolactone formation and phase-2 conjugation, possibly a strategy to conserve limited pools of coenzyme A. 4'-Methoxy-derivatives (citrus fruits) or 3',4'-dimethoxy-derivatives (coffee) are susceptible to hepatic "reverse" hydrogenation suggesting incompatibility with enoyl-CoA-hydratase. Gut microbiota-produced 3'-hydroxy-4'-methoxy-derivatives (citrus fruits) and 3'-hydroxy-derivatives (numerous (poly)phenols) are excreted as the phenyl-hydracrylic acid β-oxidation intermediate suggesting incompatibility with hydroxy-acyl-CoA dehydrogenase, albeit with considerable inter-individual variation. Further investigation is required to explain inter-individual variation, factors determining the amino acid to which C6-C3 and C6-C1 metabolites are conjugated, the precise role(s) of l-carnitine, whether glycine might be limiting, and whether phenolic acid-modulation of β-oxidation explains how phenolic acids affect key metabolic conditions, such as fatty liver, carbohydrate metabolism and insulin resistance.

An insight into an intriguing oxidative biotransformation pathway of 5-O-caffeoylquinic acid by a gut bacterium

Microbiota is known to play a pivotal role in generating bioavailable and bioactive low-molecular-weight metabolites from dietary polyphenols. 5-O-caffeoylquinic acid (5-CQA), one of the main polyphenols found in human diet, was submitted to a resting cell biotransformation study using three gut bacteria species Lactobacillus reuteri, Bacteroides fragilis and Bifidobacterium longum. These bacteria were selected according to their belonging to the main phyla found in human gut microbiota. Our study highlighted the ability of only one of the strains studied, L. reuteri, to bioconverse 5-CQA into various metabolites due to the expression of the cinnamoyl esterase enzyme as the first step. Interestingly, one known natural compound, esculetin, was described for the first time as a 5-CQA-derived metabolite after conversion by a gut bacterium, the other metabolites had already been reported. This evidence highlighted an interesting oxidative pathway occurring in vivo by intestinal microbiota leading to esculetin. This molecule was also identified after electrochemical and enzymatic oxidations of caffeic acid. The oxidation capacity of L. reuteri led to less diverse metabolites in comparison to those obtained either electrochemically and enzymatically where dimers and trimers were reported. Thus, esculetin may have interesting and benefical biological effects on gut microbiota, which should be further evaluated. Novel synbiotics could be formulated from the association of L. reuteri with 5-CQA.

Urinary excretion rate and bioavailability of chlorogenic acid, caffeic acid, p-coumaric acid, and ferulic acid in non-fasted rats maintained under physiological conditions

Hydroxycinnamic acids (HAs) are one of the major classes of phenolic compounds and epidemiological studies have suggested that they have beneficial health effects. This study aimed to determine the urinary excretion rate of chlorogenic acid, caffeic acid, p-coumaric acid, and ferulic acid in non-fasted rats and to estimate their bioavailability under physiological conditions. Previous studies have primarily used fasted animals, which exhibit severe changes in various physiological processes. Furthermore, the food matrix can affect HA bioavailability. Thus, our studies using non-fasted rats under physiological conditions may allow for a more accurate determination of both the HA urinary excretion rate and the bioavailability of HAs. HAs were successively gavaged to rats at a dose of 40 mg/kg body weight (BW) with a wash-out period of one week. The rats were fed the AIN-93M diet throughout the experiment. The urine was collected at time intervals of 0–6 h, 6–24 h, and 24–48 h after HA administration. Ingested HAs, except chlorogenic acid, were primarily excreted in the urine within 0–6 h as free forms or conjugated (glucuronidated and/or sulfated) forms. The majority of the ingested chlorogenic acid was detected in the urine at 6–24 h or 24–48 h as caffeic acid, p-coumaric acid, ferulic acid, and their conjugates. The total urinary excretion rate (% of the dose) at 48 h was ferulic acid (73.2%) > caffeic acid (61.6%) > p-coumaric acid (54.1%) >> chlorogenic acid (4.9%). The percentages of the conjugates in the urine differed amongst the rats gavaged with the individual HAs (74% for chlorogenic acid, 83% for caffeic acid, 68% for p-coumaric acid, and 96% for ferulic acid), which may be explained by their distinct bioactivities. These data reveal that caffeic acid, p-coumaric acid, and ferulic acid are much more bioavailable than chlorogenic acid, even though they are excreted more rapidly than chlorogenic acid. Our findings may provide additional insight into the health benefits of HAs and how they function in the body.

Comparative study on the inhibitory effect of caffeic and chlorogenic acids on key enzymes linked to Alzheimer's disease and some pro-oxidant induced oxidative stress in rats' brain-in vitro

This study sought to investigate and compare the interaction of caffeic acid and chlorogenic acid on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and some pro-oxidants (FeSO(4), sodium nitroprusside and quinolinic acid) induced oxidative stress in rat brain in vitro. The result revealed that caffeic acid and chlorogenic acid inhibited AChE and BChE activities in dose-dependent manner; however, caffeic acid had a higher inhibitory effect on AChE and BChE activities than chlorogenic acid. Combination of the phenolic acids inhibited AChE and BChE activities antagonistically. Furthermore, pro-oxidants such as, FeSO(4), sodium nitroprusside and quinolinic acid caused increase in the malondialdehyde (MDA) contents of the brain which was significantly decreased dose-dependently by the phenolic acids. Inhibition of AChE and BChE activities slows down acetylcholine and butyrylcholine breakdown in the brain. Therefore, one possible mechanism through which the phenolic acids exert their neuroprotective properties is by inhibiting AChE and BChE activities as well as preventing oxidative stress-induced neurodegeneration. However, esterification of caffeic acid with quinic acid producing chlorogenic acid affects these neuroprotective properties.

Antiproliferative and apoptotic effects of the oxidative dimerization product of methyl caffeate on human breast cancer cells

Caffeic acid derivatives are increasingly regarded as potential oncoprotective that could inhibit both the initiation and progression of cancer. Here we have synthesized seven 1-arylnaphthalene lignans and related compounds and tested their impact on breast cancer cell growth in tissue culture. The product of the oxidative dimerization of methyl caffeate, 1-phenylnaphthalene lignan, was found to induce a strong decrease in breast cancer cell number (IC(50) ~1 μM) and was selected for further investigation. Flow cytometry analysis revealed a decrease in cell proliferation and an increase in apoptosis in both MCF-7 and MDA-MB-231 breast cancer cell lines that are representative of the two main categories of breast tumors. The 3,4-dihydroxyphenyl group probably induced the biological activity, as the control compounds lacking it had no effect on breast cancer cells. Together, our data indicate that the oxidative dimerization product of methyl caffeate can inhibit breast cancer cell growth at a concentration adequate for pharmacological use.

Biosynthesis, natural sources, dietary intake, pharmacokinetic properties, and biological activities of hydroxycinnamic acids

Hydroxycinnamic acids are the most widely distributed phenolic acids in plants. Broadly speaking, they can be defined as compounds derived from cinnamic acid. They are present at high concentrations in many food products, including fruits, vegetables, tea, cocoa, and wine. A diet rich in hydroxycinnamic acids is thought to be associated with beneficial health effects such as a reduced risk of cardiovascular disease. The impact of hydroxycinnamic acids on health depends on their intake and pharmacokinetic properties. This review discusses their chemistry, biosynthesis, natural sources, dietary intake, and pharmacokinetic properties.

The use of PEGylated liposomes to prolong the circulation lifetime of salvianolic acid B

The clinical application of salvianolic acid B (Sal B), a potential therapeutic agent for cardiovascular diseases isolated from Salvia miltiorrhiza, is greatly restricted by its short half-life and low bioavailability. To improve therapeutic effects and prolong the systemic circulation time of Sal B, liposomes, composed of soybean phosphatidylcholine and cholesterol were prepared by reverse-phase evaporation method. In addition, polyethylene glycol 2000-disteroylphosphoethanolamine (PEG-DSPE 2000) was included to give steric barrier to liposomes. A central composite design was employed to optimize liposomal formulation with high encapsulation efficiency and small particle size. Physicochemical characteristics such as particle size, zeta potential, encapsulation efficiency and in vitro release were investigated. In vivo pharmacokinetic properties of Sal B in beagle dogs and the effect of PEG on the blood circulation time of Sal B-loaded liposomes were also evaluated. An optimized formulation with encapsulation efficiency of 73.68% and mean particle size of 136.6nm were developed. Encapsulation of Sal B into conventional and PEGylated liposomes could prolong the half-life of Sal B by 5.8- and 17.5-fold and enhance the AUC(0-t) of Sal B by 6.7- and 13.3-fold compared with free Sal B, respectively. Therefore, the use of PEGylated liposomes could prolong the circulation time in blood and longevity effect of liposomes on Sal B was increased by PEG.

Synergistic interaction of phenylpropanoids with antibiotics against bacteria

Phenylpropanoids constitute a large part of our daily diet and there is a possibility that they might interact with synthetic drugs. The present work was aimed at studying the interaction of seven phenylpropanoids (cinnamic, p-coumaric, caffeic, chlorogenic, ferulic, 3,4-dimethoxycinnamic and 2,4,5-trimethoxycinnamic acid) with five antibiotics (amikacin, ampicillin, ciprofloxacin, erythromycin and vancomycin) against Gram-negative (Escherichia coli, Enterobacter aerogenes and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria. The interaction studies were performed by chequerboard and time–kill curve assays. Both assays revealed that cinnamic, p-coumaric and ferulic acids were the most active. They combined synergistically with the majority of the antibiotics and exhibited enhanced activity against all the micro-organisms. The time–kill curve parameters were better (P<0.05) for the combinations of amikacin with ferulic, cinnamic or p-coumaric acid than for the individual treatments. Amikacin was the most favourable antibiotic and S. aureus was the most sensitive microbe to most of the combinations. These phenylpropanoids damaged the bacterial membrane as assessed by the LIVE/DEAD BacLight kit, and structure–activity relationship studies indicated that hydrophilic groups enhanced this activity.

Biotransformation of aesculin by human gut bacteria and identification of its metabolites in rat urine

AIM: To observe the biotransformation process of a Chinese compound, aesculin, by human gut bacteria, and to identify its metabolites in rat urine.

METHODS: Representative human gut bacteria were collected from 20 healthy volunteers, and then utilized in vitro to biotransform aesculin under anaerobic conditions. At 0, 2, 4, 8, 12, 16, 24, 48 and 72 h post-incubation, 10 mL of culture medium was collected. Metabolites of aesculin were extracted 3 × from rat urine with methanol and analyzed by HPLC. For in vivo metabolite analysis, aesculetin (100 mg/kg) was administered to rats via stomach gavage, rat urine was collected from 6 to 48 h post-administration, and metabolite analysis was performed by LC/ESI-MS and MS/MS in the positive and negative modes.

RESULTS: Human gut bacteria could completely convert aesculin into aesculetin in vitro. The biotransformation process occurred from 8 to 24 h post-incubation, with its highest activity was seen from 8 to 12 h. The in vitro process was much slower than the in vivo process. In contrast to the in vitro model, six aesculetin metabolites were identified in rat urine, including 6-hydroxy-7-gluco-coumarin (M1), 6-hydroxy-7-sulf-coumarin (M2), 6, 7-di-gluco-coumarin (M3), 6-glc-7-gluco-coumarin (M4), 6-O-methyl-7-gluco-coumarin (M5) and 6-O-methyl-7-sulf-coumarin (M6). Of which, M2 and M6 were novel metabolites.

CONCLUSION: Aesculin can be transferred into aesculetin by human gut bacteria and is further modified by the host in vivo. The diverse metabolites of aesculin may explain its pleiotropic pharmaceutical effects.

Absorption and metabolism of bioactive molecules after oral consumption of cooked edible heads ofCynara scolymusL. (cultivar Violetto di Provenza) in human subjects: a pilot study

The current growing interest for natural antioxidants has led to a renewed scientific attention for artichoke, due not only to its nutritional value, but, overall, to its polyphenolic content, showing strong antioxidant properties. The major constituents of artichoke extracts are hydroxycinnamic acids such as chlorogenic acid, dicaffeoylquinic acids caffeic acid and ferulic acid, and flavonoids such as luteolin and apigenin glycosides.Invitrostudies, using cultured rat hepatocytes, have shown its hepatoprotective functions andin vivostudies have shown the inhibition of cholesterol biosynthesis in human subjects. Several studies have shown the effect on animal models of artichoke extracts, while information on human bioavailability and metabolism of hydroxycinnamates derivatives is still lacking. Results showed a plasma maximum concentration of 6·4 (sd 1.8) ng/ml for chlorogenic acid after 1 h and its disappearance within 2 h (P < 0·05). Peak plasma concentrations of 19·5 (sd6·9) ng/ml for total caffeic acid were reached within 1 h, while ferulic acid plasma concentrations showed a biphasic profile with 6·4 (sd1·5) ng/ml and 8·4 (sd4·6) ng/ml within 1 h and after 8 h respectively. We observed a significant increase of dihydrocaffeic acid and dihydroferulic acid total levels after 8 h (P < 0·05). No circulating plasma levels of luteolin and apigenin were present. Our study confirms the bioavailability of metabolites of hydroxycinnamic acids after ingestion of cooked edibleCynara scolymusL. (cultivar Violetto di Provenza).

MAGNESIUM LITHOSPERMATE B IS EXCRETED RAPIDLY INTO RAT BILE MOSTLY AS METHYLATED METABOLITES, WHICH ARE POTENT ANTIOXIDANTS

To elucidate the in vivo pharmacological activities of magnesium lithospermate B (MLB), an active constituent of Radix Salviae Miltiorrhizae, in the rat, its metabolic fate both in vivo and in vitro was investigated. High-performance liquid chromatography revealed that four major metabolites with lower polarity were excreted into bile after intravenous and oral administration of MLB. The metabolites present in combined samples of bile from rats after intravenous injection were isolated and purified by column chromatography and identified as four meta-O-methylated products, namely 3-monomethyl- (M1), 3,3"'-dimethyl- (M2), 3,3"-dimethyl-, and 3,3",3"'-trimethyl-lithospermic acid B according to their spectroscopic characteristics ((1)H, (13)C NMR, (1)H-(1)H correlation spectroscopy, (1)H-detected multiple quantum coherence, and heteronuclear multiple bond coherence combined with positive ion fast atom bombardment-mass spectroscopy). After administration of MLB at an intravenous dose of 4 mg/kg or an oral dose of 100 mg/kg, the total biliary recovery of the four metabolites after 30 h reached 95.5 +/- 2.4% (with approximately 90% recovered within 2 h) or 5.5 +/- 0.7%, respectively. The metabolic pathway was proposed to involve sequential formation of the four methylated metabolites. Incubation of MLB, M1, M2, or M4 in rat hepatic cytosol in the presence of S-adenosyl-l-methionine demonstrated the formation of all four metabolites, which indicated that the enzyme responsible for the biotransformation is catechol O-methyltransferase. MLB and its main metabolites M1 and M2 showed potent 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activities, the activity of M1 being stronger than those of caffeic acid (the monomer form of MLB) and alpha-tocopherol (a representative antioxidant) but weaker than that of MLB. The rapid and high biliary excretion levels of these metabolites suggested that they could undergo enterohepatic circulation in rats and that they might thereby be largely responsible for the pharmacological effects of MLB.

Chlorogenic acid bioavailability largely depends on its metabolism by the gut microflora in rats

Chlorogenic acid, the ester of caffeic acid with quinic acid, is one of the most abundant polyphenols in the human diet with coffee, fruits and vegetables as its major sources. Its antioxidant and anticarcinogenic properties have been well established in animal studies. However, little is known about its gut absorption and metabolism. In the present work, four groups of rats (n = 8) were fed a diet supplemented with chlorogenic, caffeic or quinic acids (250 micromol/d) or an unsupplemented diet for 8 d. Parent compounds and their metabolites were estimated in urine (24-h collection) and plasma by HPLC-electrospray ionization-tandem mass spectrometry. Significant differences in their levels were observed among the groups. The recovery of chlorogenic acid in urine was low (0.8%, mol/mol), and the total urinary excretion of caffeic acid liberated by hydrolysis of chlorogenic acid and its tissular methylated metabolites (ferulic and isoferulic acids) did not account for >0.5% (mol/mol) of the dose ingested. On the other hand, the metabolites of microbial origin, namely, m-coumaric acid and derivatives of phenylpropionic, benzoic and hippuric acids, represented the major compounds in both urine and plasma. Hippuric acid largely originated from the transformation of the quinic acid moiety, and all other metabolites from the caffeic acid moiety. These microbial metabolites accounted for 57.4% (mol/mol) of the chlorogenic acid intake. Such a high abundance of microbial metabolites shows that the bioavailability of chlorogenic acid depends largely on its metabolism by the gut microflora. Their potential importance in explaining the biological effects of dietary polyphenols is emphasized.

Microbial aromatic acid metabolites formed in the gut account for a major fraction of the polyphenols excreted in urine of rats fed red wine polyphenols

The health effects of dietary polyphenols might be explained by both intact compounds and their metabolites formed either in the tissues or in the colon by the microflora. The quantitative importance and biological activities of the microbial metabolites have seldom been examined in vivo. We measured the microbial metabolites formed in four groups of rats (n = 8) fed for 8 d a diet supplemented with 0.12 g/100 g catechin, 0.25 or 0.50 g/100 g red wine powder containing proanthocyanidins, phenolic acids, flavanols, anthocyanins and flavonols or an unsupplemented diet. Fourteen aromatic acid metabolites were assayed in urine collected for 24 h by an HPLC-electrospray ionization (ESI)-mass spectrometry (MS)-MS method. The three main metabolites formed from the catechin diet were 3-hydroxyphenylpropionic acid, 3-hydroxybenzoic acid and 3-hydroxyhippuric acid. Their total urinary excretion accounted for 4.7 g/100 g of the catechin ingested and that of intact catechins for 45.3 g/100 g. For wine polyphenols, the same microbial metabolites as observed for the catechin diet were identified in urine along with hippuric, p-coumaric, vanillic, 4-hydroxybenzoic and 3-hydroxyphenylacetic acids. All together, these aromatic acids accounted for 9.2 g/100 g of the total wine polyphenols ingested and intact catechins for only 1.2 g/100 g. The higher excretion of aromatic acids by rats fed wine polyphenols is likely due to their poor absorption in the proximal part of the gut. Some of the microbial metabolites still bear a reducing phenolic group and should also prevent oxidative stress in inner tissues. More attention should be given in the future to these microbial metabolites and their biological properties to help explain the health effects of polyphenols that are not easily absorbed through the gut barrier.

Absorption of chlorogenic acid and caffeic acid in rats after oral administration

Absorption of orally administered chlorogenic acid (5-caffeoylquinic acid) and caffeic acid in rats was studied to obtain plasma pharmacokinetic profiles of their metabolites. Rats were administered 700 micromol/kg body weight of chlorogenic or caffeic acid, and blood was collected from the tail for 6 h after administration. Ingested caffeic acid was absorbed from the alimentary tract and was present in the rat blood circulation in the form of various metabolites. On the other hand, only traces of metabolites, supposedly caffeic and ferulic acids conjugates, were detected in rat plasma for 6 h after chlorogenic acid administration. Chlorogenic acid and small amounts of caffeic acid were found in the small intestine for 6 h after chlorogenic acid administration. These results suggest that chlorogenic acid is not well absorbed from the digestive tract, unlike caffeic acid, and subject to almost no structural changes to the easily absorbed forms.

Analysis of the components of Lycopus europaeus L. in body fluids during metabolism studies. Comparison of capillary electrophoresis and high-performance liquid chromatography

During pharmacokinetic studies with extracts obtained from medicinally used plants, analysis in body fluids is mainly performed by HPLC, an established separation method. In this paper high-performance capillary electrophoresis (HPCE) is investigated for its ability to separate such complex extracts. Crude extracts of Lycopus europaeus L. (Lamiaceae) are traditionally used against mild forms of hyperthyroidism. The metabolism of a 70% ethanolic extract with respect to some of its individual main components (rosmarinic and caffeic acid, luteolin-7-glucoside) and a mixture of the pure compounds were investigated using isolated perfused rat liver. After solid-phase extraction metabolites were determined using HPCE and HPLC separation techniques. A buffer solution composed of 0.05 mol l-1 Na2HPO4 at pH 7.0 with 30% acetonitrile was found to be the most suitable electrolyte for HPCE separation. The best mobile phase for isocratic HPLC was 0.03% TFA-acetonitrile (82:18, v/v). Data obtained with HPCE are in good accordance with those from HPLC; HPCE, however, is clearly more rapid and simple to perform.