Kinetics of the appearance of cereal alkylresorcinols in pig plasma

Simultaneous pharmacokinetic modeling of alkylresorcinols and their main metabolites indicates dual absorption mechanisms and enterohepatic elimination in humans

BACKGROUND

Alkylresorcinols have proven to be useful biomarkers of whole-grain wheat and rye intake in many nutritional studies. To improve their utility, more knowledge regarding the fate of alkylresorcinols and their metabolites after consumption is needed.

OBJECTIVE

The objective of this study was to develop a combined pharmacokinetic model for plasma concentrations of alkylresorcinols and their 2 major metabolites, 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-propanoic acid (DHPPA).

METHODS

The model was established by using plasma samples collected from 3 women and 2 men after a single dose (120 g) of rye bran and validated against fasting plasma concentrations from 8 women and 7 men with controlled rye bran intake (23, 45, or 90 g/d). Alkylresorcinols in the lymph and plasma of a pig fed a single alkylresorcinol dose (1.3 mmol) were quantified to assess absorption. Human ileostomal effluent and pig bile after high and low alkylresorcinol doses were analyzed to evaluate biliary alkylresorcinol metabolite excretion.

RESULTS

The model contained 2 absorption compartments: 1 that transferred alkylresorcinols directly to the systematic circulation and 1 in which a proportion of absorbed alkylresorcinols was metabolized before reaching the systemic circulation. Plasma concentrations of alkylresorcinols and their metabolites depended on absorption and formation, respectively, and the mean ± SEM terminal elimination half-life of alkylresorcinols (1.9 ± 0.59 h), DHPPA (1.5 ± 0.26 h), and DHBA (1.3 ± 0.22 h) did not differ. The model accurately predicted alkylresorcinol and DHBA concentrations after repeated alkylresorcinol intake but DHPPA concentration was overpredicted, possibly because of poorly modeled enterohepatic circulation. During the 8 h following administration, <2% of the alkylresorcinol dose was recovered in the lymph. DHPPA was identified in both human ileostomal effluent and pig bile, indicating availability of DHPPA for absorption and enterohepatic circulation.

CONCLUSION

Intact alkylresorcinols have advantages over DHBA and DHPPA as plasma biomarkers for whole-grain wheat and rye intake because of lower susceptibility to factors other than alkylresorcinol intake.

Chain length of dietary alkylresorcinols affects their in vivo elimination kinetics in rats

Two phenolic acids, 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)- propanoic acid (DHPPA), are the major metabolites of cereal alkylresorcinols (ARs). Like their precursors, AR metabolites have been suggested as biomarkers for intake of whole-grain wheat and rye and as such could aid the understanding of diet-disease associations. This study estimated and compared pharmacokinetic parameters of ARs and their metabolites in rats and investigated differences in metabolite formation after ingestion of different AR homologs. Rats were i.v. infused for 30 min with 2, 12, or 23 μmol/kg DHBA or DHPPA or orally given the same amounts of the AR homologs, C17:0 and C25:0. Repeated plasma samples, obtained from rats for 6 h (i.v.) or 36 h (oral), were simultaneously analyzed for ARs and their metabolites by GC-mass spectrometry. Pharmacokinetic parameters were estimated by population-based compartmental modeling and noncompartmental calculation. A 1-compartment model best described C25:0 pharmacokinetics, whereas C17:0 and AR metabolites best fitted 2-compartment models. Combined models for simultaneous prediction of AR and metabolite concentration were more complex, with less reliable estimates of pharmacokinetic parameters. Although the AUC of C17:0 was lower than that of C25:0 (P < 0.05), the total amount and composition of AR metabolites did not differ between rats given C17:0 or C25:0. The elimination half-life of ARs and their metabolites increased with length of the side chain (P-trend < 0.001) and ranged from 1.2 h (DHBA) to 8.8 h (C25:0). The formation of AR metabolites was slower than their elimination, indicating that the rate of AR metabolism and not excretion of DHBA and DHPPA determines their plasma concentrations in rats.

Present status and perspectives on the use of alkylresorcinols as biomarkers of wholegrain wheat and rye intake

Alkylresorcinols (ARs) were first proposed as potential biomarkers of wholegrain wheat and rye intake a decade ago. Since then there has been a considerable body of research which suggests that ARs do meet most criteria of a biomarker of these foods. Results from human studies on plasma AR and their plasma and urinary metabolites strongly indicate that these compounds are responsive to whole grain wheat and rye intake and are correlated with various measures of AR consumption. This review briefly summarises work on the bioactivities of AR and focuses on aspects related to their use as biomarkers of whole grain wheat and rye intake. Evidence suggests that they thus far broadly fulfil the criteria to act as biomarkers of these cereals. However, there are still gaps in the knowledge on factors relating to the wide interindividual variation, and application to different epidemiological cohorts. Overall, ARs are highly promising biomarkers of whole grain wheat and rye intake and add to our increasing understanding of whole grains and health.

A whole-grain cereal-rich diet increases plasma betaine, and tends to decrease total and LDL-cholesterol compared with a refined-grain diet in healthy subjects

Epidemiological studies have repeatedly found that whole-grain (WG) cereal foods reduce the risk of several lifestyle-related diseases, though consistent clinical outcomes and mechanisms are elusive. To compare the effects of a WG-rich diet with a matched refined-grain (RG) diet on plasma biomarkers and bowel health parameters, seventeen healthy subjects (eleven females and six males) completed an exploratory cross-over study with a 2-week intervention diet based on either WG- or RG-based foods, separated by a washout of at least 5 weeks. Both diets were the same except for the use of WG (150 g/d) or RG foods. Subjects undertook a 4 h postprandial challenge on day 8 of each intervention diet. After 2 weeks, the WG diet tended to decrease plasma total and LDL-cholesterol (both P = 0·09), but did not change plasma HDL-cholesterol, fasting glucose, C-reactive protein or homocysteine compared with the RG diet. Plasma betaine and alkylresorcinol concentrations were elevated after 1 week of the WG diet (P = 0·01 and P < 0·0001, respectively). Clostridium leptum populations in faeces were increased after the WG diet, along with a trend for decreased faecal water pH (P = 0·096) and increased stool frequency (P < 0·0001) compared with the RG diet. A short controlled intervention trial with a variety of commercially available WG-based products tended to improve biomarkers of CVD compared with a RG diet. Changes in faecal microbiota related to increased fibre fermentation and increased plasma betaine concentrations point to both fibre and phytochemical components of WG being important in mediating any potential health effects.

Responsiveness of urinary and plasma alkylresorcinol metabolites to rye intake in finnish women

Alkylresorcinols [ARs] have been proposed for use as biomarkers of whole-grain intake. The aim here was to examine the responsiveness of AR metabolites to rye intake. Sixty women were divided into three groups according to their rye consumption. We observed significant differences between groups in plasma 3-[3,5-dihydroxyphenyl]-1-propanoic acid [DHPPA] and in urinary DHPPA and 3,5-dihydroxybenzoic acid [DHBA]. In addition, these AR metabolites increased proportionally to rye fiber intake. We conclude that these ARs metabolites are accurate and useful biomarkers of rye fiber intake. Further studies are needed to confirm our results in larger and different populations.

Quantification of alkylresorcinols in human plasma by liquid chromatography/tandem mass spectrometry

Alkylresorcinols (AR) are of interest as biomarkers of wholegrain wheat and rye intake in epidemiological studies and are currently mainly measured by gas chromatography/mass spectrometry (GC/MS) after labour-intensive sample preparation including liquid-liquid extraction, solid-phase extraction (SPE) and chemical derivatization. This manuscript describes and validates an alternative approach based on normal-phase liquid chromatography/tandem mass spectrometry for the quantification of alkylresorcinols in human plasma. The method requires neither SPE nor chemical derivatization and has a shortened run time compared to GC/MS. Normal- and reversed-phase columns and various mobile phases were evaluated with and without previous SPE of the samples. Normal-phase chromatography allowed separation of AR from the interfering triacylglycerols, diacylglycerols and sterols and enabled detection of AR even without SPE of the samples. The described method has instrumental lower limits of detection in the 25-75 pg range, and lower limits of quantification in the 75-250 pg range. Pooled human plasma and (2)H(4)-nonadecylresorcinol (internal standard) was applied to calibrate the method in the 20-12 000 nM range. The overall method showed intra-batch precision of 8.6% and an averaged accuracy of 100.2%. Applications for diverse human plasma samples are presented and are compared with the results determined by GC/MS. Based on the presented data; this method requiring less sample preparation is suggested for further evaluation as an alternative to GC/MS for analysis of biomarkers of wholegrain wheat and rye intake in epidemiological studies.

Effect of litreol on the viability of human cancer cells

Members of the family Anacardiaceae are known to contain a number of biologically active substances, such as phenolic lipids, alkyl-catechols and alkyl-resorcinols. In the present study, human cancer cell lines, DU-145 cells (androgen-insensitive prostate cancer cells), KB cells (human epidermoid cells), and human melanoma cell line, M14, were treated for 72 h with 0.59-9.5 microM litreol (3-[pentadecyl-10-enyl-catechol]), a alkyl-catechol isolated from Lithraea caustica (Molina) Hook. & Arn. The results showed, for the first time, that litreol inhibited cancer cell viability in a dose-dependent manner. In addition, the treatment with this compound at 0.59-1.18 microM concentrations induced apoptotic cell death, demonstrated by the fragmentation of genomic DNA and by a significant increase of caspase-3 activity. The significant production of reactive oxygen species (ROS) evidenced in these experimental conditions could trigger the apoptosis cascades. Taken together, these results demonstrate that litreol attenuate the growth of human cancer cells, at least in part, triggering an apoptotic process, and they may offer a further impulse to the development of its analogues with more potent efficacy against human cancer cells.

Urinary 3-(3,5-dihydroxyphenyl)-1-propanoic acid, an alkylresorcinol metabolite, is a potential biomarker of whole-grain intake in a U.S. population

5-n-Alkylresorcinols (AR) are a major group of phenolic compounds in whole-grain wheat, rye, and barley. As such, they may serve as potential biomarkers of whole-grain intake, because they are quantifiable intact in plasma and as metabolites in urine. We examined relationships between 12-h urinary excretion of AR metabolite 3-(3,5-dihydroxyphenyl)-1-propanoic acid (DHPPA) and self-reported habitual intake of whole-grain foods measured by 3-d food record (3DFR) and FFQ. Urine samples from 100 men and women were analyzed for DHPPA using HPLC with coularray detection. DHPPA excretion ranged from 1.3 to 99.4 (mean +/- SE, 14.0 +/- 1.5) mumol/12 h. Whole-grain food intake, as determined by 3DFR and FFQ and adjusted for BMI and energy and fiber intake, was significantly associated with 12-h urinary DHPPA excretion. Based on 3DFR, whole-grain wheat + rye consumers had a 44% higher DHPPA excretion than nonconsumers [ratio of excretion (95% CI) = 1.44 (1.04, 1.97); P = 0.029]. Using whole-grain intake estimated by FFQ, a serving increase in whole-grain wheat + rye intake increased DHPPA excretion by 94% [ratio of excretion (95% CI) = 1.94 (1.35, 2.78); P = 0.001] and a serving increase in whole grains as defined more broadly in epidemiologic studies of whole-grain intake and disease risk (whole-grain wheat, rye, oats, and corn) increased DHPPA by 67% [ratio of excretion (95% CI) = 1.67 (1.28, 2.17); P < 0.0001]. This study supports the potential utility of urinary DHPPA as a biomarker of whole-grain intake in a U.S. population.

Quantification of alkylresorcinol metabolites in plasma by high-performance liquid chromatography with coulometric electrode array detection

This study presents the optimization and validation of a rapid protocol for quantifying alkyresorcinol (AR) metabolites 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-1-propanoic acid (DHPPA) in plasma, using high-performance liquid chromatography (HPLC) coupled with a coulometric electrode array detector. Syringic acid (SyrA) serves as the internal standard. The new method is simple and could be used in large epidemiological studies. The summed AR metabolite concentrations measured in plasma correlate significantly with the summed urinary AR metabolite concentrations (R = 0.613; p < 0.001) and with the summed intact AR (C17:0-C25:0) concentrations in plasma (R = 0.686; p < 0.001). Additional investigation is needed to clarify whether the two plasma AR metabolites are useful as biomarkers of whole-grain intake and helpful in the exploration of the association between whole-grain cereal intake and human diseases.

Alkylresorcinols as biomarkers of whole-grain wheat and rye intake: plasma concentration and intake estimated from dietary records

BACKGROUND

Alkylresorcinols (ARs), phenolic lipids exclusively present in the outer parts of wheat and rye grains, have been proposed as specific dietary biomarkers of whole-grain wheat and rye intake.

OBJECTIVE

The objective was to validate plasma ARs as a biomarker of whole-grain wheat and rye intakes by studying the correlation between their plasma concentration and intake calculated from food records.

DESIGN

In a randomized crossover study, 22 women and 8 men were given a defined amount of either whole-grain or refined-cereal-grain products to be included in their habitual diets for two 6-wk periods. Blood samples were collected and food intakes were recorded before and after each intervention period.

RESULTS

Plasma AR concentrations were significantly higher after the whole-grain diet period than after the refined-grain period (P < 0.0001) and were well correlated with average daily AR intake estimated by self-reported weighed food records (Spearman's r = 0.58, P < 0.001).

CONCLUSION

Plasma AR concentrations are correlated with intake assessed by food records, which suggests that ARs are selective nutritional biomarkers for the intake of whole-grain wheat and rye.

Profiling of Alk(en)ylresorcinols in cereals by HPLC-DAD-APcI-MSn

5-Alk(en)ylresorcinols in rye, wheat, spelt, and barley have been characterized by high-performance liquid chromatography coupled to atmospheric pressure chemical ionization multistage mass spectrometry (HPLC-APcI-MS(n)) for the first time. Among the 29 compounds analysed, several major and minor C(15), C(17), C(19), C(21), C(23), and C(25)-substituted resorcinols with saturated, monoenoic, dienoic, and/or oxygenated side-chains were characterized by their specific fragmentation patterns in collision-induced dissociation experiments. Additionally, a C(27:0) homologue, which has probably been overlooked in previous studies based on HPLC alone, was detected in all cereals analysed. Furthermore, we provide tentative evidence for the occurrence of alkylresorcinols with triolefinic side-chains, which have, to our knowledge, so far not been reported in any cereal species.

Quantification of Alkylresorcinol Metabolites in Urine by HPLC with Coulometric Electrode Array Detection

Background: Whole-grain rye and wheat cereals contain high amounts of alkylresorcinols (ARs), phenolic lipids. ARs can be quantified in plasma. Two recently identified urinary AR metabolites, 3,5-dihydroxyphenylbenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-1-propanoic acid (DHPPA), may be useful as biomarkers of intake of whole-grain rye and wheat.

Methods: We evaluated 4 pretreatment protocols for quantifying urinary DHBA and DHPPA using HPLC coupled with a coulometric electrode array detector. Syringic acid was used as the internal calibrator.

Results: Measured urinary concentrations of DHBA and DHPPA were 0.8–115 μmol/L. The mean recoveries of all added concentrations were 85%–104% for DHBA and 86%–99% for DHPPA, depending on the degree of the purification. The protocol versions with less purification correlated well with the protocol including highest purification. The correlation coefficients (r2) were 0.9699–0.8153 for DHBA and 0.9854–0.8371 for DHPPA.

Conclusion: Although the protocol with the most purification steps was most specific, all protocols were suitable for measuring DHBA and DHPPA in urine. The rapid protocol with simple hydrolysis could be used in large-scale clinical studies. Additional investigation is needed to clarify whether these metabolites are useful biomarkers of whole-grain intake and helpful in the exploration of its association with human diseases.

Alkylresorcinols from whole-grain wheat and rye are transported in human plasma lipoproteins

Alkylresorcinols with alkyl chains C17:0-C25:0 are abundant in whole-grain wheat and rye. Concentrations in human plasma have been suggested to be biomarkers of dietary whole-grain intake. We measured human plasma, erythrocyte, and lipoprotein alkylresorcinol concentrations and alkylresorcinol homolog distribution, and evaluated the use of plasma alkylresorcinol concentration as a dietary biomarker of whole-grain intake compared with serum enterolactone. A total of 15 subjects (8 women) consumed whole-grain wheat or whole-grain rye crisp bread ( approximately 100 g/d) in a crossover design for 1 wk. The test bread periods were preceded by 1-wk periods of consuming refined wheat bread. Plasma, erythrocyte, lipoprotein alkylresorcinol, and serum enterolactone concentrations were measured before and after each period, and plasma alkylresorcinols and serum enterolactone were measured after habitual diet intake before and 1 wk after the trial. Plasma alkylresorcinols are transported in lipoproteins with VLDL and HDL being the main carriers. AR concentrations in plasma, erythrocytes, and lipoproteins were increased (P < 0.05) by whole-grain wheat bread and even more so with rye crisp bread, although interindividual variation was high. The alkylresorcinol homolog C17:0 to C21:0 ratio in plasma was higher after the whole-grain rye diet period compared with the whole-grain wheat diet period (P < 0.05). Serum enterolactone concentrations were increased significantly by whole-grain rye intake only in men. This is the first report to show that alkylresorcinols in human plasma are mainly transported in lipoproteins. The plasma alkylresorcinol C17:0 to C21:0 ratio reflects intake of whole-grain wheat and rye, and the plasma total alkylresorcinol concentration appears to be a useful biomarker of whole-grain cereal intake.

NMR-based metabonomic studies reveal changes in the biochemical profile of plasma and urine from pigs fed high-fibre rye bread

This study presents an NMR-based metabonomic approach to elucidate the overall endogenous biochemical effects of a wholegrain diet. Two diets with similar levels of dietary fibre and macronutrients, but with contrasting levels of wholegrain ingredients, were prepared from wholegrain rye (wholegrain diet (WGD)) and non-wholegrain wheat (non-wholegrain diet (NWD)) and fed to four pigs in a crossover design. Plasma samples were collected after 7 d on each diet, and 1H NMR spectra were acquired on these. Partial least squares regression discriminant analysis (PLSDA) on spectra obtained for plasma samples revealed that the spectral region at 3·25 parts per million dominates the differentiation between the two diets, as the WGD is associated with higher spectral intensity in this region. Spiking experiments and LC–MS analyses of the plasma verified that this spectral difference could be ascribed to a significantly higher content of betaine in WGD plasma samples compared with NWD samples. In an identical study with the same diets, urine samples were collected, and1H NMR spectra were acquired on these. PLS-DA on spectra obtained for urine samples revealed changes in the intensities of spectral regions, which could be ascribed to differences in the content of betaine and creatine/creatinine between the two diets, and LC–MS analyses verified a significantly lower content of creatinine in WGD urine samples compared with NWD urine samples. In conclusion, using an explorative approach, the present studies disclosed biochemical effects of a wholegrain diet on plasma betaine content and excretion of betaine and creatinine.

Human plasma kinetics and relative bioavailability of alkylresorcinols after intake of rye bran

Alkylresorcinols (ARs) are phenolic lipids present in whole grain and bran of wheat and rye. Chemically, they comprise 1,3- dihydroxy-5-alkylbenzene homologs with odd-numbered, mainly saturated hydrocarbon side chains in the range of 17-25 carbon atoms. ARs are evaluated both for physiological effects and for their potential use as biomarkers of whole-grain wheat and rye intake. In this study, plasma kinetics and relative bioavailability of ARs in humans were investigated after a single intake of rye bran 120 g (190 mg ARs). The shapes of plasma concentration time curves were similar in the subjects (n = 6) with 2 peaks at approximately 2.8 and 6.5 h and maximum concentrations (mean +/- SEM) of 1253 +/- 125 and 3365 +/- 309 nmol/L, respectively. The relative bioavailability of different homologs increased with increasing length of the AR side chain (r = 0.97, P < 0.001), indicating differences in metabolism. The apparent half-lives were rather short, approximately 5 h for all homologs, which suggests that the AR concentration in plasma could be used as a short- to medium-term biomarker of regular intake of whole-grain wheat and rye.