Catechin Conjugates Research Articles

Efficient Preparation of Catechin Thio Conjugates by One Step Extraction/Depolymerization of Pine (Pinus pinaster) Bark Procyanidins

The skin penetrating antioxidant cysteamine derivative of (-)-epicatechin as well as other thio conjugates were efficiently obtained with high yields from pine (Pinus pinaster) bark by simultaneous one pot extraction and depolymerization using water and cysteamine hydrochloride. The influence of the concentration of bark, acid, and cysteamine, as well as the reaction time on the total conversion, was studied. The total conversion into the epicatechin and catechin conjugates was as high as 47 g/kg pine bark with 1666 g cysteamine/kg bark and 28 g/kg with 166 g cysteamine/kg bark. A fast cleanup step by absorption/desorption on XAD-16 greatly facilitated further purification of the active major component. At a pilot scale, 4beta-(2-aminoethylthio)epicatechin (1) (conversion 263 g, purity 35% by reversed phase high-performance liquid chromatography/weight) was obtained from 17 kg of pine bark after simultaneous extraction/depolymerization followed by cleanup with the polymeric resin in approximately 10 h. The results show that pine (P. pinaster) bark is a suitable source of flavanols for the preparation of active thio derivatives. Conditions are given for the fast and efficient preparation of the conjugates.

In vitro biological properties of flavonoid conjugates found in vivo

For some flavonoids such as quercetin, isoflavones and catechins, the pathways of absorption and metabolism are now reasonably well characterised and understood. By definition, for biological activity of flavonoids to be manifest, the target tissue, which includes the blood and vascular system, must respond to the form(s) of flavonoid that it encounters. Bioavailability studies have shown that the circulating form of most flavonoids is as conjugates, with a few notable exceptions. There have been several recent papers on the in vitro biological properties of conjugates that have been found in vivo. This paper reviews the properties of these conjugates. Most of the information currently available is on quercetin glucuronides, but also on isoflavone and catechin conjugates. In addition to the biological properties of the conjugates, the partition coefficients and methods of synthesis are also presented.

Amplification of inhibitory activity of catechin against disease-related enzymes by conjugation on poly(epsilon-lysine).

A new inhibitor against disease-related enzymes, collagenase, hyaluronidase, and xanthine oxidase, has been developed by the laccase-catalyzed conjugation of catechin on poly(epsilon-lysine). The resulting poly(epsilon-lysine)-catechin conjugate showed greatly improved inhibition effects on activity of these enzymes, whereas the catechin monomer showed very low inhibition activity. The kinetic analysis on the inhibition of collagenase exhibited that the conjugate was a mixed-type inhibitor. The amplified activities might offer high potential as a therapeutic agent for prevention of various enzyme-related diseases.

Enzymatic synthesis of a catechin conjugate of polyhedral oligomeric silsesquioxane and evaluation of its antioxidant activity.

The antioxidant activity of catechin was amplified by conjugation with amine-terminated polyhedral oligomeric silsesquioxane (POSS) using horseradish peroxidase as catalyst. Compared to intact catechin, the scavenging activity of the POSS-catechin conjugate against superoxide anion was greatly improved. In addition, the conjugate strongly inhibited xanthine oxidase activity.

Enzymatic Synthesis and Antioxidant Property of Poly(allylamine)–Catechin Conjugate

Abstract A polymeric conjugate containing a catechin group has been synthesized by laccase-catalyzed oxidation of catechin in the presence of poly(allylamine). The resulting conjugate showed a good antioxidant property against LDL peroxidation induced by a free radical.

Cation-exchange micropreparative separation of galloylated and non-galloylated sulphur conjugated catechins

Catechin conjugates bearing an amino function can be separated from underivatized monomers by cation-exchange chromatography. Here, chromatographic conditions for the separation of epicatechin gallate-containing conjugates from the non-galloylated conjugates at micropreparative scale are described. The separation was achieved by exploiting either the hydrophobic or hydrophilic interactions of the conjugates with the core polymer. The retention was modulated by changing the amount of organic co-solvents (MeOH, EtOH, CH 3CH, THF) in the elution buffers. The best resolution compatible with small peak widths was obtained at 20–30% EtOH. The experiments were reproducible.

Analysis of urinary metabolites of tea catechins by liquid chromatography/electrospray ionization mass spectrometry.

Tea has been proposed to have beneficial health effects which have been attributed to the polyphenolic compounds known as catechins. The bioavailability and biotransformation of these compounds, however, are not clearly understood. In this study, we used liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS) to determine urinary glucuronidated and sulfated tea catechins and their metabolites (including methylated and ring-fission metabolites) based on the detection of deprotonated molecular ions and aglycone fragment ions. The compound resolution was achieved both chromatographically and mass spectroscopically. After green tea administration, the major conjugates appeared in human, mouse, and rat urine samples were identified as monoglucuronides and monosulfates of (-)-epigallocatechin (EGC) and (-)-epicatechin. We also found O-methyl-EGC-O-glucuronides and -O-sulfates and O-methyl-epicatechin-O-sulfates in human urine. (-)-5-(3',4',5'-Trihydroxyphenyl)-gamma-valerolactone (M4) and (-)-5-(3',4'-dihydroxyphenyl)-gamma-valerolactone (M6), the ring-fission metabolites of EGC and (-)-epicatechin, respectively, were also predominantly in monoglucuronide and monosulfate forms in the urine. In comparison to rats, the urinary metabolite profiles of tea catechins in mice resemble more closely to those in humans. This is the first report describing direct simultaneous analysis of multiple tea catechin conjugates in urine samples. This method will allow more thorough investigations of the biotransformation of tea polyphenols.

(+)-Catechin in human plasma after ingestion of a single serving of reconstituted red wine

Red wine consumption may decrease the risk of coronary heart disease through the actions of its constituent flavonoids. (+)-Catechin is an abundant flavonoid in red wine. The objective was to determine changes in plasma (+)-catechin concentrations after ingestion of a single, moderate serving of dealcoholized red wine reconstituted with either water (DRW) or water and alcohol (ARW). Nine subjects (5 men, 4 women) ingested, in random order, 120 mL DRW on one day and 120 mL ARW on another day. Both the DRW and ARW contained 35 mg (121 micromol) free (+)-catechin. Blood samples were collected at 0, 0.5, 1, 2, 3, 4, and 8 h. Plasma was analyzed by gas chromatography-mass spectrometry for (+)-catechin after enzymatic release of sulfate and glucuronide conjugates. Calcium ions were needed to effectively hydrolyze (+)-catechin conjugates in plasma containing EDTA. Neither the ARW or DRW nor sex affected the area under the curve at 8 h, the maximum concentration (c(max)), or the time it took for plasma total (+)-catechin to reach maximum concentration (t(max)). Pooled mean (+/-SEM) values for the ARW and DRW were as follows: area under the curve, 306.1 +/- 29.5 nmol*h/L; c(max), 76.7 +/- 7.5 nmol/L; and t(max), 1.44 +/- 0.13 h. The half-life of (+)-catechin in plasma was significantly less (P = 0.038) after ingestion of the ARW (3.17 h) than after ingestion of the DRW (4.08 h). Increases in plasma total (+)-catechin concentrations were not significantly different after single moderate servings of either the ARW or DRW. Alcohol in the ARW hastened the elimination of (+)-catechin from the plasma compartment. (+)-Catechin elimination may represent excretion or conversion to methylated derivatives.

Catechin metabolites after intake of green tea infusions.

Green tea contains relatively large amounts of catechins, that have been recognized to be efficient free-radical scavengers. In spite of a largely described antioxidant effect, the metabolic fate of catechins in humans has been scarcely studied. An infusion of green tea (about 400 mg of catechins) was given to healthy volunteers; plasma and urine samples were collected for 5 h and 2 days, respectively. Epigallocatechin gallate and epicatechin gallate were detected in plasma samples, reaching the maximum concentration (2 microM) at 2 h. Urine samples collected at 6-48 h contained detectable amounts of final catechin metabolites, including 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3-methoxy-4-hydroxy-hippuric acid and 3-methoxy-4-hydroxybenzoic acid (vanillic acid). The total content of these metabolites averaged 60 mg. The levels of free plasma catechins account only partly for the increased (approximately +20%) total radical-trapping antioxidant parameter (TRAP) detected after green tea intake. Catechin conjugates (glucuronide and sulphate) and metabolites may add further contribution and explain the measured TRAP increase.

Metabolism and excretion of the liver-protective agent (+)-catechin in experimental hepatitis.

1. Following oral administration of [U-14C](+)-catechin to rats with galactosamine-hepatitis, the biliary and faecal elimination of (+)-catechin metabolites was decreased compared with that in normal animals, Renal excretion of (+)-catechin metabolites was enhanced in galactosamine-hepatitis. 2. Although the biliary metabolites were present in similar proportions in galactosamine-hepatitis animals and controls, the major urinary metabolite, 3'-O-methyl (+)-catechin sulphate, was markedly decreased whereas 3'-O-methyl(+)-catechin glucuronide was increased by over 100%. 3. The total overall excretion of 3'-O-methyl (+)-catechin conjugates in rats with galactosamine-hepatitis was similar to that in normal animals indicating that catechol-O-methyltransferase activity is not significantly depressed in galactosamine-hepatitis. 4. Clearance of radioactivity from the blood following i.v. administration of [U-14C]-(+)-catechin was prolonged in galactosamine-hepatitis. 5. Liver perfusion experiments demonstrated depressed glucuronylation of (+)-catechin metabolites in galactosamine-hepatitis, whereas in liver homogenates synthesis of glucuronide conjugates of (+)-catechin metabolites was enhanced. 6. Lung slices were able to metabolize (+)-catechin and the lung is proposed as an extrahepatic site of (+)-catechin metabolism of increased importance in galactosamine-hepatitis. 7. The effects of galactosamine-hepatitis upon the structure of the hepatocyte plasma membrane are discussed in relation to decreased biliary excretion and glucuronylation.

Studies on flavonoid metabolism. Biliary and urinary excretion of metabolites of (+)-(U- 14 C)catechin.

1. The biliary and urinary excretion of (+)-[U-(14)C]catechin was studied in normal male rats after a single injection of the flavonoid. 2. In rats large amounts of radioactivity (33.6-44.3% of the dose in 24h) were excreted in the bile as two glucuronide conjugates [one of which was a (+)-catechin conjugate] and three other unconjugated metabolites. 3. Excretion of radioactivity in the urine when the bile duct was not cannulated amounted to 44.5% of the dose. 4. In both the urine and bile the new metabolites showed maximum excretion in the (1/2)-1(1/2)h after intravenous injection of [(14)C]catechin. 5. The metabolites m-hydroxyphenylpropionic acid, p-hydroxyphenylpropionic acid, delta-(3-hydroxyphenyl)-gamma-valerolactone and delta-(3,4-dihydroxyphenyl)-gamma-valerolactione originate from the action of the intestinal micro-organisms on the biliary-excreted metabolites of (+)-catechin. These phenolic acid and lactone metabolites are then reabsorped and excreted in the urine. 6. It is proposed that, depending on the route of administration of (+)-catechin, there exists an alternative pathway, involving biliary excretion, for the metabolism of (+)-catechin.