Dose-dependent utilisation of casein-linked lysinoalanine, N(epsilon)-fructoselysine and N(epsilon)-carboxymethyllysine in rats.

During the heat treatment of protein-containing foods, the amino acid lysine is most prone to undergo chemical reactions in the course of amino acid cross-linking or Maillard reactions. Among the reaction products formed, lysinoalanine (LAL), N(epsilon)-fructoselysine (FL) and N(epsilon)-carboxymethyllysine (CML) are those which serve as sensitive markers for the heat treatment applied. From a nutritional perspective, these compounds are ingested with the diet in considerable amounts but information about their metabolic transit and putative in vivo effects is scarce. In the present study, casein-linked LAL, FL and CML were administered to rats in two different doses for 10 days. Quantitation of LAL, FL and CML in plasma, tissue and faeces samples revealed that the kidneys are the predominant sites of accumulation and excretion. The maximum percent of dietary LAL, FL and CML excreted in the urine was 5.6, 5.2 and 29%, whereas the respective recoveries in the kidneys were 0.02, 26 and 1.4%. The plasma and tissue analyses revealed that the endogenous load of either compound is increased by its dietary intake. But the dose-dependent utilisation of dietary protein-linked LAL, FL and CML in rats has been demonstrated for the first time to vary substantially from each other.

Metabolism and bioavailability of trans-resveratrol.

Resveratrol (3,4',5-trihydroxy-trans-stilbene) is a polyphenolic compound accounting to the stilbene class. Most stilbenes in plants act as antifungal phytoalexins, compounds that are usually synthesized only in response to infection or injury. Resveratrol has been detected in trees, in a few flowering plants, in peanuts, and in grapevines. The major dietary sources of resveratrol include grapes, wine, peanuts, and peanut products. Numerous in vitro studies describe different biological effects of resveratrol. The major impacts are the antioxidative, anti-inflammatory, and estrogenic effects as well as anticancer and chemopreventive activities. In order to reveal information on absorption, metabolism, and the consequent bioavailability of resveratrol, different research approaches were performed, including in vitro, ex vivo, and in vivo models, all of which are considered in this review. Summarizing the data, resveratrol is absorbed and metabolized. Around 75% of this polyphenol are excreted via feces and urine. The oral bioavailability of resveratrol is almost zero due to rapid and extensive metabolism and the consequent formation of various metabolites as resveratrol glucuronides and resveratrol sulfates. The potential biologic activity of resveratrol conjugates should be considered in future investigations.

Bioactivity and metabolism of trans-resveratrol orally administered to Wistar rats.

The purpose of this study was to investigate the implications of selected chemopreventive parameters and metabolic conversion of resveratrol in vivo. In two 8-week long feeding experiments with rats, a low-resveratrol diet containing 50 mg resveratrol per kg body weight (bw) and day and a high-resveratrol diet with 300 mg per kg bw and day were administered. For chemopreventive evaluation selected phase I and phase II enzymes of the biotransformation system, the total antioxidant activity, and the vitamin E status of the animals were determined. The level of resveratrol and its metabolites in the feces, urine, plasma, liver, and kidneys was identified and quantitated by high-performance liquid chromatography-diode array detection (HPLC-DAD) using synthesized resveratrol conjugate standards. Feeding of different dosages of resveratrol revealed no effect on the different chemopreventive parameters, except for the total antioxidant activity, which was elevated in plasma by 19% after feeding 50 mg resveratrol per kg bw and day. The formation of trans-resveratrol-3-sulfate, trans-resveratrol-4'-sulfate, trans-resveratrol-3,5-disulfate, trans-resveratrol-3,4'-disulfate, trans-resveratrol-3,4',5-trisulfate, trans-resveratrol-3-O-beta-D-glucuronide, and resveratrol aglycone was detected by HPLC analysis, depending on the biological material. Total resveratrol recovery in urine and feces of rats fed on 50 mg resveratrol per kg bw and day was 15% and 13%, respectively. For rats fed the higher dosage of 300 mg resveratrol per kg bw and day recovery was 54% and 17%, respectively. This is the first study performed with synthesized standards of relevant resveratrol conjugates. The lack of effect on the chemopreventive parameters is probably due to the formation of various resveratrol conjugates reducing its bioavailability in the rat.

Influence of feeding malt, bread crust, and a pronylated protein on the activity of chemopreventive enzymes and antioxidative defense parameters in vivo.

The aim of the present study was to investigate whether feeding of malt, bread crust, and a pronylated albumin modulates chemoprevention enzymes, such as glutathione-S-transferase (GST) and UDP-glucuronyl-transferase (UDP-GT), and antioxidative defense parameters in vivo and whether the intake of these foods rich in Maillard reaction compounds results in an accumulation of compounds formed in in vivo glycation reactions. After quantitation of pronylated lysine in malt and bread crust, male Wistar rats were fed a standard chow supplemented with 28% of protein containing different amounts of casein, bread crust, caraffa malt, or pronyl bovine serum albumin (BSA) for 15 days. GST activity in the kidneys was increased by 18% (p > 0.05) in animals of the bread crust group, while UDP-GT activity was elevated by 27% in the liver of animals administered pronyl-BSA. Contents of tocopherol in plasma were increased by 33, 14, and 14% in the bread crust, malt, and pronyl-BSA group compared to the control group, while the levels of thiobarbituric acid reactive substances were decreased and the total antioxidant capacity was increased. Parameters of endogenous glycation indicated a 32 and 46% higher load of advanced glycation end products in the kidneys after administration of the malt and the pronyl-BSA containing diet. However, the main systemic effects of dietary malt, bread crust, and pronyl-BSA were, for the first time, demonstrated to be the enhanced antioxidant capacity and the particulate increase in chemopreventive enzymes.

Activity-guided identification of a chemopreventive compound in coffee beverage using in vitro and in vivo techniques.

The aim of the present study was to apply an activity-guided screening procedure to coffee brew to identify a key chemopreventive compound by means of in vitro antioxidant tests as well as cell culture experiments and to prove the in vivo activity of that compound by an animal feeding experiment. Solvent fractionation, followed by multiple-step ultrafiltration, revealed that the polar coffee compounds with molecular weights below 1 kDa show the major inhibitory effect on the in vitro peroxidation of linoleic acid as well as the predominant chemopreventive enzyme modulating activity on the NADPH-cytochrome c reductase (CCR) and glutathione S-transferase (GST) in human intestinal Caco-2 cells. To identify the chemical structure of the most active antioxidants and chemopreventive compounds, the polar compounds were further separated by HPLC techniques, followed by the activity-guided screening of the individual HPLC fraction. These experiments demonstrated 5-chlorogenic acid to be the most powerful antioxidant in vitro, whereas, in contrast, chemopreventive effects on the GST activity were found for the N-methylpyridinium ion, the structure of which was elucidated by LC-MS and NMR experiments and confirmed by synthesis. The in vivo activities of coffee beverage and N-methylpyridinium ions were tested in a 15-day feeding experiment on rats. In the liver, feeding of 4.5% coffee beverage resulted in increases of GST and UDP-GT activities by 24 and 40% compared to animals fed the control diet (p > 0.05), respectively. Plasma total antioxidant capacity and plasma tocopherol were elevated in animals fed the coffee beverage and the N-methylpyridinium-containing diet. In summary, the results demonstrating a strong in vitro antioxidant activity for coffee were confirmed by the feeding study. Surprisingly, feeding of N-methylpyridinium also resulted in an increased total antioxidant capacity in the plasma. The data indicate that the mode of action demonstrated for N-methylpyridinium in biological systems is different from that in foods.

Analysis of the tumoricidal and anti-cachectic potential of curcumin.

Curcumin, the extract of the rhizome of Curcuma longa, is known for its health-promoting properties in traditional medicine. It has anti-inflammatory, antitumor and antioxidant properties and stimulates appetite. In the present study, we investigated the stability of curcumin and its effect on cytotoxicity, apoptosis and melanin content in melanoma cells and the effect on atrophic C2C12 muscle cells. Cytotoxicity of curcumin was dose-dependent and the EC50 for 24-h incubation was 69 µM. Saturation was reached at 30 µM for a 48-h incubation. The EC50 for 24-h incubation with degraded curcumin solution was 116 µM and that for 48-h was 94 µM. Curcumin induced a strong increase in caspase-3/7 activity at 30-40 µM. Electrical impedance measurements showed that sub-toxic doses of curcumin counteracted atrophy in an in vitro model system. These findings indicate not only the positive effects of curcumin on melanoma cells in vitro, but also that curcumin was able to considerably trigger anti-cachectic effects in vitro. However, the importance of the stability of curcumin and its tumoricidal and anti-cachectic potential might play a pivotal role in its use in the nutrition and health industrie since it degrades rapidly in aqueous solutions.