Bioavailability of catechins from tea: the effect of milk.

OBJECTIVES: To assess the blood concentration of catechins following green or black tea ingestion and the effect of addition of milk to black tea. DESIGN: Twelve volunteers received a single dose of green tea, black tea and black tea with milk in a randomized cross-over design with one-week intervals. Blood samples were drawn before and up to eight hours after tea consumption. SETTING: The study was performed at the Unilever Research Vlaardingen in The Netherlands. SUBJECTS: Twelve healthy adult volunteers (7 females, 5 males) participated in the study. They were recruited among employees of Unilever Research Vlaardingen. INTERVENTIONS: Green tea, black tea and black tea with semi-skimmed milk (3 g tea solids each). RESULTS: Consumption of green tea (0.9 g total catechins) or black tea (0.3 g total catechins) resulted in a rapid increase of catechin levels in blood with an average maximum change from baseline (CVM) of 0.46 micromol/l (13%) after ingestion of green tea and 0.10 micromol/l (13%) in case of black tea. These maximum changes were reached after (mean (s.e.m.)) t=2.3 h (0.2) and t=2.2 h (0.2) for green and black tea respectively. Blood levels rapidly declined with an elimination rate (mean (CVM)) of t1/2=4.8 h (5%) for green tea and t1/2=6.9 h (8%) for black tea. Addition of milk to black tea (100 ml in 600 ml) did not significantly affect the blood catechin levels (areas under the curves (mean (CVM) of 0.53 h. micromol/l (11%) vs 0.60 h. micromol/l (9%) for black tea and black tea with milk respectively. CONCLUSION: Catechins from green tea and black tea are rapidly absorbed and milk does not impair the bioavailability of tea catechins.

Dietary linoleic acid at high and reduced dietary fat level decreases the faecal excretion of vitamin E in young rats.

Vitamin E is the major lipid-soluble antioxidant in human subjects and is crucial in protecting polyunsaturated fatty acids (PUFA) against lipid peroxidation. Dietary PUFA have been suggested to inhibit the absorption of vitamin E. The present study in young male rats was designed to investigate the effect of increasing concentrations of dietary linoleic acid on the faecal excretion of vitamin E. The rats were fed on semi-synthetic diets containing two concentrations of fat (59 g/kg diet, 15 energy % (en%) or 131 g/kg, 30 en%) for 3 weeks. Triacylglycerol rich in linoleic acid was added at the expense of triacylglycerol rich in saturated fatty acids to obtain dietary concentrations of 13, 39 or 66 g linoleic acid/kg diet for the high-fat diet (131 g fat/kg) and 12, 24 or 36 g linoleic acid/kg diet for the reduced-fat diet (59 g fat/kg). The results from the present study demonstrate that the faecal excretion of vitamin E was significantly lower in rats fed on diets with high levels of linoleic acid compared with rats fed on lower levels of linoleic acid irrespective of the dietary fat content. The concentration of vitamin E in liver and plasma was significantly lower in animals fed on the highest concentration of linoleic acid compared with those fed on the lowest level. Results from the present study also demonstrate that at the same concentration of linoleic acid, the faecal excretion of vitamin E in rats fed on reduced-fat diets was significantly lower than in rats fed on high-fat diets. Our findings indicate that the apparent absorption of vitamin E is not inhibited by dietary PUFA. Results from the present study also demonstrate that a reduction of dietary fat content from 30 en% to 15 en% does not lower the apparent absorption of vitamin E.

Absorption of isomeric, palmitic acid-containing triacylglycerols resembling human milk fat in the adult rat.

The effect of the positional distribution of palmitic acid (16:0) in triacylglycerols (TAG) on 16:0 apparent absorption in adult rats was investigated. The rats were fed two diets which contained 30 energy % as fat with identical total fatty acid compositions, both containing 30% 16:0. The Betapol diet contained TAG with 73% of total 16:0 in the sn-2 position, the control diet contained TAG with 6% of total 16:0 in the sn-2 position. After six weeks on these diets, the rats were killed two or six hours after the last meal, and the small intestine was removed, cut into 10-cm segments, and the fatty acid composition of the segment's contents was determined. At both time points the amount of 16:0 in the intestinal segments starting at 40 cm from the stomach was much lower in the animals fed Betapol than in the animals fed the control diet. Overall absorption of 16:0 and stearic acid was significantly greater in the Betapol group. Absorption of oleic and linoleic acid from the small intestine was similar in both groups, although the overall absorption was significantly greater in the animals fed Betapol. Total fat absorption was significantly higher in the Betapol-fed rats than in the control-fed rats. No effect on calcium and nitrogen absorption, on plasma total cholesterol and TAG levels, and on bodyweights (growth) was seen. The data demonstrate that the positional distribution of the fatty acids in the TAG molecule affects the site of absorption in the small intestine and particularly the net absorption of saturated fatty acids.

The vitamin E nutritional status of rats fed on diets high in fish oil, linseed oil or sunflower seed oil.

Twelve groups of eight rats and two control groups of sixteen rats were given semisynthetic diets with 40% energy as fat for a period of 76 d. All diets contained a minimum of 3% energy as linoleic acid and comparable basal levels of D-alpha- and D-gamma-tocopherol. The diets varied in fat composition and in the content of DL-alpha-tocopheryl acetate. The diets high in polyunsaturated fatty acids (PUFA) were either rich in fish oil (FO; groups 1-4; 10% energy as fish oil PUFA), linseed oil (LN; groups 1-4; 10% energy as alpha-linolenic acid) or sunflower seed oil (SF; groups 1-4; 10 + 3% energy as linoleic acid). The control groups were given a diet high in monounsaturated fatty acids (MUFA; CO 1; 10 + 13% energy as oleic acid) or a diet with an 'average' linoleic acid content (CO 2; 8.5% energy as linoleic acid). Of each high PUFA diet three groups were supplemented with graded levels of DL-alpha-tocopheryl acetate. Steatitis, a sensitive histopathological indicator of vitamin E deficiency in animals fed on diets rich in fatty acids with three or more double bonds, was observed only in the adipose tissue of the FO groups, even in the group with the highest DL-alpha-tocopheryl acetate supplementation. Liver and serum alpha-tocopherol levels were found to be positively correlated and liver and serum gamma-tocopherol levels negatively correlated with dietary DL-alpha-tocopheryl acetate. The groups on the FO diets had significantly reduced liver and serum tocopherol levels in comparison with the groups on the other high-PUFA diets. With the supplementation scheme used for the FO groups the liver alpha-tocopherol levels of both control groups were reached but the serum control levels were not.

Dietary fish and prostanoid formation in man.

Dietary mackerel causes the increase of timnodonic acid (eicosapentaenoic acid) in all platelet phospholipid classes, at the expense of arachidonic acid. Because of these fatty acid changes, the potency of platelets to produce cyclo oxygenase products from the 2-series is greatly reduced. However, upon mild platelet triggering, changes in TxB2 formation are hardly significant, strongly depend on dietary compliance and require a high fish intake. The reduced formation of 2-series prostanoids is only partly compensated for by the increased formation of timnodonic acid-derived products. Urinary PGI metabolites suggest that dietary fish is associated with the enhanced turnover of PGI3 without a concomitant reduction in PGI2 formation. Since the site of PGI formation is not known, and an effect of dietary fish on the prostanoid metabolic routes cannot be excluded, the physiological relevance of these results is uncertain.

Influence of dietary fish on eicosanoid metabolism in man.

Two groups of 40 volunteers were given a dietary supplement consisting of 135 g of mackerel or meat (control) paste per day for 6 weeks. Compliance was about 80% in both groups and the daily intake of 20:5(n-3) and 22:6(n-3) from the mackerel supplement was about 1.3 and 2.3 g, respectively. In collagen-activated platelet rich plasma, the potency of blood platelet to produce HHT from arachidonic acid (AA) clearly reduced in the mackerel group, whereas the formation of HHTE from timnodonic acid (TA) increased slightly. Changes in the formation of HHT and HHTE, measured by HPLC, correlated significantly with those of TxB2 and TxB3, respectively, measured by GC/MS. Changes in the formation of the lipoxygenase products HETE (ex AA) and HEPE (ex TA) were qualitatively similar to that seen for the cyclo-oxygenase products, but quantitatively the responses were smaller. Formation of ir TxB2 in clotting blood significantly reduced in the mackerel group. In collagen-activated, citrated whole blood, TxB2 formation tended to be reduced in the mackerel-supplemented volunteers. Mackerel consumption was associated with the formation of considerable amounts of PGI3, as judged from the appearance of 2,3-dinor-delta 17-6-keto-PGF1 alpha in urine. The amount of the major metabolite of PGI2, 2,3-dinor-6-keto-PGF1 alpha was not reduced, or even increased. The daily amount of tetranor prostaglandin metabolites in the urine did not change significantly, which indicates that mackerel supplementation did not alter the formation of prostaglandins E and F.

Quantitative HPLC analysis of the level of fecapentaenes and their precursors in human feces by a chemical conversion method.

A fast and reliable hplc method for the quantitative analysis of total fecapentaene-12 (FP-12 and its precursors) and total fecapentaene-14 (FP-14 and its precursors) in human feces is described. The analysis is based on the rapid chemical conversion of fecapentaenes and their precursors to more stable methoxytetraenols and the use of synthetic, not naturally occurring, fecapentaene-13 (FP-13) as an internal standard. The synthesis and physical properties of this internal standard are described. The convenience and reproducibility of the method were illustrated by applying the procedure to stool samples obtained from twelve individuals on 3 consecutive days. Levels of total FP's were in the range of 0.1-25.4 micrograms for total FP-12 and 0.1-8.5 micrograms for total FP-14 per g of wet feces. Appreciable fluctuations were observed between levels in samples from the same individual on different days. Reproducibility and recovery were shown to be good.

The urinary excretion of prostaglandins E and their corresponding tetranor metabolites by rats fed a diet rich in eicosapentaenoate.

An HPLC method was developed to determine simultaneously in a single analysis prostaglandin E2, prostaglandin E3, tetranor-prostaglandin E1 and delta 17-tetranor-prostaglandin E1 in rat urine. As internal standard omega-nor-prostaglandin E2 was added to the samples at the beginning of the analysis. The assay was applied in feeding experiments in which rats were fed diets with mixtures of (n-6) and (n-3) fatty acids (linoleate, arachidonate, alpha-linolenate and eicosapentaenoate). The level of urinary prostaglandin E2 was not very much affected by the diet and prostaglandin E3 could never be detected in significant amounts. These primary prostaglandins are assumed to reflect prostaglandin biosynthesis in the kidney medulla. Tetranor-prostaglandin E1 is a characteristic urinary metabolite of prostaglandin E2 in the rat; its level increased after feeding arachidonic acid. delta 17-Tetranor-prostaglandin E1 became a major metabolite when the rats received eicosapentaenoic acid. However, we found that the ratio of urinary tetranor-prostaglandin E1/delta 17-tetranor-prostaglandin E1 is not a very reliable measure of the ratio of prostaglandin E2/prostaglandin E3 formed in the body, because prostaglandin E3 is converted to a much greater extent into delta 17-tetranor-prostaglandin E1 than is prostaglandin E2 into tetranor-prostaglandin E1. As a matter of fact, incubations of tissue homogenates of rats resulted always in predominant formation of prostaglandins of the 2-series, even after high eicosapentaenoate diets. We conclude, in agreement with work carried out earlier, that biosynthetic pathways leading to prostaglandins of the 3-series are of minor importance.

Conversion of linoleic acid and arachidonic acid by skin epidermal lipoxygenases.

Two different lipoxygenases have been identified in human and rat epidermis. One lipoxygenase has a (n-9)-specificity, converts arachidonic acid into 12-hydroxyeicosatetraenoic acid (12-HETE), and has been described by several investigators. Linoleic acid is not a substrate for this enzyme. The other lipoxygenase, with (n-6)-specificity, converts arachidonic acid into 15-HETE and linoleic acid into 13-hydroxyoctadecadienoic acid (13-HOD). Especially the latter lipoxygenase is thought to be involved in the regulation of the differentiation of the skin cells into a proper water-barrier layer. Linoleate is supposed to be the physiological substrate; this fatty acid is especially present in characteristic sphingolipids with unique structures.

Metabolic profile of linoleic acid in porcine leukocytes through the lipoxygenase pathway.

Porcine neutrophilic leukocytes were found to contain a lipoxygenase which converted linoleic acid into 13-hydroxy-9,11-octadecadienoic acid (n-6 specificity), arachidonic acid into 12-hydroxy-5,8,10,14-eicosatetraenoic acid (n - 9 specificity) and 5-hydroxy-6,8,11,14-eicosatetraenoic acid into 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid. This lipoxygenase was partially purified and it appeared that its substrate specificity and other properties were quite different from the 12-lipoxygenase of blood platelets. Incubations of intact or broken porcine leukocytes with added linoleic acid revealed the formation of not only 13-hydroxy-9,11-octadecadienoic acid but also of substantial amounts of epoxyhydroxy and trihydroxy isomers. These products from linoleate, collectively described by the name 'octadecanoids' were characterized in detail by a combination of chemical, chromatographic and mass spectrometric techniques. The phospholipids of porcine leukocytes contain more than twice as much linoleate than arachidonate (22 vs. 8%). In accordance with this fatty acid composition we found that in the stimulated neutrophil the endogenous production of octadecanoids often surpassed that of the eicosanoids. Lipoxygenation of endogenously liberated linoleic acid was especially pronounced when a suspension of leukocytes in citrated plasma was recalcified and allowed to clot.

Influence of a low-selenium diet on erythrocyte glutathione peroxidase and alkane production in exhaled air of rats as a measure of lipid peroxidation in vivo during growth.

Erythrocyte glutathione peroxidase activity and alkane production in exhaled air of growing rats were studied as a measure of lipid peroxidation in vivo. When 4-weeks-old, rats were fed a low-selenium (0.05 mg/kg) refined soy concentrate-based diet but adequate in vitamin E and other nutrients. Rats of control groups were fed the same diet supplemented with varying amounts of selenium as sodium selenite. After 10 weeks, erythrocyte glutathione peroxidase activity in the group fed the low selenium diet had decreased to about 40% of the original level. Feeding this diet for a longer period resulted in a slow increase of the glutathione peroxidase level. After about 37 weeks, this level was equal to the initial level. During the same period of rapid growth, ethane and pentane production in the exhaled air of a group of similar animals on the diet containing 0.05 mg Se per kg was slightly although significantly higher compared with the levels of animals on a supplemented (0.4 mg Se per kg) diet. Differences were highest when glutathione peroxidase activity levels in the erythrocytes were lowest and negligible at the start of the experiment and after the period of rapid growth. These results support the view that the seleno-enzyme glutathione peroxidase is active in the defense mechanism of the cell against lipid peroxidation.

The composition of alkanes in exhaled air of rats as a result of lipid peroxidation in vivo. Effects of dietary fatty acids, vitamin E and selenium.

Alkane production in exhaled air of rats has been studied as an index of lipid peroxidation in vivo in these animals. The effect of feeding essential fatty acid-deficient rats varying levels of n-4, n-6 and n-7 polyunsaturated fatty acids for various periods of time has been studied with regard to the composition of the alkanes produced as well as the fatty acid composition of liver phospholipids and liver and adipose tissue triacylglycerols. It was found that the fatty acid composition of liver lipids depended markedly on the nature and the quantity of polyunsaturated fatty acid in the diet. The composition of the alkanes produced on stimulation of lipid peroxidation in vivo by inhalation of small, non-lethal doses of carbon tetrachloride corresponded closely to the fatty acid composition of the liver phospholipids. The results strongly suggest that the alkanes produced as a result of lipid peroxidation in vivo originate from the methyl end of the fatty acid administered. So ethane is produced from n-3 acid, propane from n-4 acid, pentane from n-6 acid and hexane from n-7 acid. The amounts of a specific alkane produced increase as its corresponding fatty acid, as present in the liver phospholipids, increases. There are indications that relatively more ethane than pentane is produced on stimulation of the in vivo lipid peroxidation although there are considerably more n-6 fatty acids than n-3 fatty acids present in the liver phospholipids.