Whole-grain rye and wheat alkylresorcinols are incorporated into human erythrocyte membranes

Analysis of the multi-physiological and functional mechanism of wheat alkylresorcinols based on reverse molecular docking and network pharmacology

Alkylresorcinols (ARs) are phenolic lipids present in the bran part of whole grain wheat and rye, which possess antioxidant, anti-inflammatory, anti-cancer and anti-tumor properties. The physiological activities of ARs have been proven to be diverse; however, the specific molecular mechanisms are still unclear. In this study, reverse virtual screening and network pharmacology were used to explore the potential molecular mechanisms of the physiological function of ARs and their endogenous metabolites. The Metascape database was used for GO enrichment and KEGG pathway analysis. Furthermore, molecular docking was used to investigate the interactions between active compounds and potential targets. The results showed that the bioavailability of most ARs and their endogenous metabolites was 0.55 and 0.56, while the bioavailability of certain endogenous metabolites was only 0.11. Multiplex analysis was used to screen 73 important targets and 4 core targets (namely, HSP90AA1, EP300, HSP90AB1 and ERBB2) out of the 163 initial targets. The important targets involved in the key KEGG pathway were pathways in cancer (hsa05200), lipid and atherosclerosis (hsa05417), Th17 cell differentiation (hsa04659), chemical carcinogenesis-receptor activation (hsa05207), and prostate cancer (hsa05215). The compounds involved in the core targets were AR-C21, AR-C19, AR-C17, 3,5-DHPHTA-S, 3,5-DHPHTA-G, 3,5-DHPPTA, 3,5-DHPPTA-S, 3,5-DHPPTA-G, 3,5-DHPPTA-Gly and 3,5-DHPPA-G. The interaction force between them was mainly related to hydrogen bonds and van der Waals. Overall, the physiological activities of ARs are not only related to their multiple targets, but may also be related to the synergistic effect of their endogenous metabolites.

The use of 4-Hexylresorcinol as antibiotic adjuvant

Ever decreasing efficiency of antibiotic treatment due to growing antibiotic resistance of pathogenic bacteria is a critical issue in clinical practice. The two generally accepted major approaches to this problem are the search for new antibiotics and the development of antibiotic adjuvants to enhance the antimicrobial activity of known compounds. It was therefore the aim of the present study to test whether alkylresorcinols, a class of phenolic lipids, can be used as adjuvants to potentiate the effect of various classes of antibiotics. Alkylresorcinols were combined with 12 clinically used antibiotics. Growth-inhibiting activity against a broad range of pro- and eukaryotic microorganisms was determined. Test organisms did comprise 10 bacterial and 2 fungal collection strains, including E. coli and S. aureus, and clinical isolates of K. pneumoniae. The highest adjuvant activity was observed in the case of 4-hexylresorcinol (4-HR), a natural compound found in plants with antimicrobial activity. 50% of the minimal inhibitory concentration (MIC) of 4-HR caused an up to 50-fold decrease in the MIC of antibiotics of various classes. Application of 4-HR as an adjuvant revealed its efficiency against germination of bacterial dormant forms (spores) and prevented formation of antibiotic-tolerant persister cells. Using an in vivo mouse model of K. pneumoniae-induced sepsis, we could demonstrate that the combination of 4-HR and polymyxin was highly effective. 75% of animals were free of infection after treatment as compared to none of the animals receiving the antibiotic alone. We conclude that alkylresorcinols such as 4-HR can be used as an adjuvant to increase the efficiency of several known antibiotics. We suggest that by this approach the risk for development of genetically determined antibiotic resistance can be minimized due to the multimodal mode of action of 4-HR.

Biomarkers of Whole-Grain and Cereal-Fiber Intake in Human Studies: A Systematic Review of the Available Evidence and Perspectives

High whole-grain consumption is related to better health outcomes. The specific physiological effect of these compounds is still unrevealed, partly because the accurate estimation of the intake of whole grains from dietary assessments is difficult and prone to bias, due to the complexity of the estimation of the intake by the consumer. A biomarker of whole-grain intake and type of whole-grain intake would be useful for quantifying the exposure to whole-grain intake. In this review, we aim to review the evidence on the potential biomarkers for whole-grain intake in the literature. We conducted a systematic search in Medline, Embase, Web of Science, and the Cochrane database. In total, 39 papers met the inclusion criteria following the PRISMA guidelines and were included. The relative validity, responsiveness, and reproducibility of these markers were assessed for short-, medium-, and long-term exposure as important criteria for the potential use of these biomarkers from a clinical and research perspective. We found three major groups of biomarkers: (1) alkylresorcinol, as well as its homologs and metabolites, assessed in plasma, adipose tissue biopsies, erythrocyte membranes, and urine; (2) avenacosides, assessed in urine samples; and (3) benzoxazinoid-derived phenylacetamide sulfates, assessed in blood and urine samples. The reviewed biomarkers may be used for improved assessment of associations between whole-grain intake and health outcomes.

Biomarkers of cereal food intake

Background/objectives

Cereal foods are major contributors to the daily energy, protein, and dietary fiber intake all over the world. The role of cereals in human health is dependent on whether they are consumed as refined or whole grain and on cereal species. To unravel the underlying mechanisms of health effects attributed to specific cereal foods and to provide more precise dietary advice, there is a need for improved dietary assessment of whole-grain intake. Dietary biomarkers of specific cereals, different fractions or cereal-containing foods could offer such a possibility. The aim of this review was to summarize the current status on biomarkers of different cereals, fractions, and specific cereal foods.

Subjects and methods

A literature review was conducted and putative biomarkers of different cereals and pseudo-cereals (wheat, oats, rye, barley, rice, and quinoa) as well as for different grain fractions (whole grain, refined grain, bran) and foods were summarized and discussed.

Results

Several putative biomarkers have been suggested for different cereals, due to their unique presence in these grains. Among the biomarkers, odd-numbered alkylresorcinols are the most well-studied and -evaluated biomarkers and reflect whole-grain wheat and rye intake. Even-numbered alkylresorcinols have been suggested to reflect quinoa intake. Recent studies have also highlighted the potential of avenanthramides and avenacosides as specific biomarkers of oat intake, and a set of biomarkers have been suggested to reflect rice bran intake. However, there are yet no specific biomarkers of refined grains. Most biomarker candidates remain to be evaluated in controlled interventions and free-living populations before applied as biomarkers of intake in food and health studies.

Conclusion

Several putative biomarkers of different cereals have been suggested and should be validated in human studies using recently developed food intake biomarker validation criteria.

Serum alkylresorcinols as biomarkers of dietary gluten exposure in coeliac disease

BACKGROUND

Therapy for coeliac disease (CD) mainly relies on following a gluten-free diet (GFD); however, a serum marker for gluten intake has yet to be established.

AIM

To evaluate the utility of alkylresorcinol concentrations for detecting gluten intake in studies of human and mouse.

METHODS

Alkylresorcinol concentrations were compared among treated patients with coeliac disease (n = 34), untreated coeliac disease patients (n = 36) and controls (n = 33). Furthermore, seven additional coeliac disease patients whose serum samples were available at diagnosis and after GFD were evaluated. In mice studies, alkylresorcinol concentrations were compared in the serum of five mice fed a regular chow and 10 mice fed lifelong with a gluten-free chow. In addition, the effect of adding gluten on changes of alkylresorcinol concentrations was also evaluated.

RESULTS

Total alkylresorcinol concentrations were significantly lower in treated with coeliac disease [median (IQR), 3 (2-8) nmol/L], compared to untreated patients [median (IQR), 32 (11-74) nmol/L; P < 0.0001] or healthy controls [median (IQR), 54 (23-112) nmol/L; P < 0.0001]. Moreover, alkylresorcinol concentrations in coeliac disease patients significantly decreased after introduction of a GFD (median, 34 nmol/L at diagnosis vs. 5 nmol/L after GFD, P = 0.02). In the mice, median (IQR) total alkylresorcinol concentrations in serum samples of mice fed lifelong with a gluten-free chow was 1.8 (1.6-2.3) nmol/L, which was further significantly increased to 16 (11-22) nmol/L after 8 days of feeding with the gluten-free chow that had gluten added to it. (P = 0.008).

CONCLUSION

Serum alkylresorcinol concentrations could be a useful marker for dietary gluten in coeliac disease.

Phenolic lipids affect the activity and conformation of acetylcholinesterase from Electrophorus electricus (Electric eel)

Phenolic lipids were isolated from rye grains, cashew nutshell liquid (CNSL) from Anacardium occidentale, and fruit bodies of Merrulius tremellosus, and their effects on the electric eel acetylcholinesterase activity and conformation were studied. The observed effect distinctly depended on the chemical structure of the phenolic lipids that were available for interaction with the enzyme. All of the tested compounds reduced the activity of acetylcholinesterase. The degree of inhibition varied, showing a correlation with changes in the conformation of the enzyme tested by the intrinsic fluorescence of the Trp residues of the protein.

A review of the fundamentals of diet

Dietary recommendations should be individualized for each patient, but certain basic principles apply to most people. A healthful diet should include a wide variety of whole, unprocessed foods that are free of additives and, if possible, grown without the use of pesticides, herbicides, and other potentially toxic agricultural chemicals. For people who do not have specific food intolerances, such a diet generally includes liberal amounts of fresh fruits and vegetables, whole grains, nuts, seeds, and legumes. For most people, animal foods such as eggs, fish, chicken, beef, and dairy products can be healthfully consumed in moderation. It is not necessary to consume animal foods to maintain good health. In fact, compared with omnivores, vegetarians have a lower risk of developing a number of chronic diseases. However, vegetarians must carefully plan their diet so as not to develop nutritional deficiencies.

Alkylresorcinols in Latvian and Finnish breads

The alkylresorcinol (AR) content and relative homologue composition were determined in 9 Latvian and 11 Finnish soft breads. ARs were extracted with hot 1-propanol and quantified, using a gas chromatography-mass spectrometry method. The total AR content (μg/g dry matter) varied from 560 to 840 in rye breads, from 500 to 700 in Finnish mixed rye and wheat flour breads, from 200 to 300 in Latvian mixed rye and wheat flour breads and from 25 to 30 in white wheat breads. Rye and white wheat breads in the two countries varied only slightly in AR content, but there were wide variations in AR content in mixed flour breads. The AR contents in soft breads could be indicators of bran or fibre content, but not of whole-grain flour content.

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.

Antioxidant activity of alkylresorcinols from rye bran and their protective effects on cell viability of PC-12 AC cells

Alkylresorcinols (ARs) are phenolic lipids that are present in high amounts in the bran layer of different cereals. Rye samples, cultivar Hazlet, and a white rye genotype, RT202, were analyzed for their antioxidant properties and AR content and composition, based on six fractions of the bran, where 1 was the outermost fraction and 6 was the bran fraction closest to the endosperm. Gas chromatography-mass spectrometry (GC-MS) analysis demonstrated that the most commonly found AR homologue in Hazlet rye is C19:0 and that the total amount of ARs decreases from the outermost to innermost fractions. The antioxidant activity using oxygen radical absorbance capacity (ORAC) for both white rye genotype RT202 and Hazlet brans was determined to decrease from the outermost fraction (136.05 μmol TE/g for Hazlet fraction 1 and 186.57 μmol TE/g for white rye genotype RT202 fraction 1) to the innermost fraction (9.84 μmol TE/g for Hazlet fraction 6 and 78.75 μmol TE/g for white rye genotype RT202 fraction 2). A positive relationship was seen with GC-MS results. Treatment of PC-12 AC cells with Hazlet fraction 1 increased mitochondrial biogenesis as determined using mitochondrial fluorescent dyes. In the presence of a prooxidant (AAPH), PC-12 AC cells were better protected from free radical attack when treated with Hazlet fraction 1 than with all other bran fractions. The results suggest that higher AR content in bran fractions confers antioxidant protection against free radical damage.

Rye bran alkylresorcinols suppress adipocyte lipolysis and hormone-sensitive lipase activity

The effects of alkylresorcinols (ARs) isolated from rye bran on adipocyte lipolysis, hormone-sensitive lipase activity and phosphorylation and on phosphorylation of protein kinase A substrates were studied. Preincubation with ARs for 18 h suppressed catecholamine-stimulated lipolysis in 3T3-L1 adipocytes. Furthermore, phosphorylation of hormone-sensitive lipase (HSL), a key lipase responsible for stimulated lipolysis, and phosphorylation of protein kinase A substrates, were diminished after preincubation with ARs, whereas HSL protein expression was unaltered. ARs were also shown to inhibit HSL activity in an in vitro assay.

Plasma alkylresorcinol concentrations correlate with whole grain wheat and rye intake and show moderate reproducibility over a 2- to 3-month period in free-living Swedish adults

Plasma alkylresorcinols (AR) are useful as dietary biomarkers of wheat and rye whole grain (WG) during interventions but need to be validated in free-living populations. This study estimated the medium-term reproducibility and relative validity of plasma AR as biomarkers of WG and cereal fiber intake. Seventy-two Swedish adults kept 3-d weighed food records on 2 occasions 2-3 mo apart. Of these men and women, 51 provided a fasting blood sample at the end of each occasion. In addition, 18 participants provided 3 fasting and 3 nonfasting samples for 3 consecutive days on the first and second occasions, respectively. Dietary and blood variables did not differ between the 2 occasions. Nonfasting plasma total AR concentration [210 nmol/L (95% CI: 140, 314)] was higher than fasting [99 nmol/L (95% CI: 72, 137)] (P < 0.0001). Mean WG intake was 70 ± 61 g/d (41% from rye) and the intra-class correlation coefficient was 0.44 (95% CI: 0.26, 0.63) for total WG intake and 0.47 (95% CI: 0.27, 0.67) for the fasting plasma total AR concentration, suggesting moderate reproducibility. Fasting plasma total AR moderately correlated with WG rye + wheat (r(s) = 0.53; P < 0.001) and cereal fiber intake (r(s) = 0.32; P < 0.05) when using mean values from both occasions. This suggests that plasma AR concentration in fasting samples can be used as a biomarker of rye + wheat WG intake in free-living populations with a high and consistent WG intake.

Plasma and urinary alkylresorcinol metabolites as potential biomarkers of breast cancer risk in Finnish women: a pilot study

Alkylresorcinols (ARs) are shown to be good biomarkers of consumption of rye and whole-grain wheat products in man. The aim of this pilot study was to investigate AR metabolites as potential biomarkers of breast cancer (BC) risk in Finnish women since intake of cereal fiber and its components has been proposed to reduce this risk through an effect on the enterohepatic circulation of estrogens. This was a cross-sectional and observational pilot study. A total of 20 omnivores, 20 vegetarians, and 16 BC women (6-12 mo after operation) were investigated on 2 occasions 6 mo apart. Dietary intake (5-days record), plasma/urinary AR metabolites [3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-1-propanoic acid (DHPPA)] and plasma/urinary enterolactone were measured. The groups were compared using nonparametric tests. We observed that plasma DHBA (P = 0.007; P = 0.03), plasma DHPPA (P = 0.02; P = 0.01), urinary DHBA (P = 0.001; P = 0.003), urinary DHPPA (P = 0.001; P = 0.001), and cereal fiber intake (P = 0.007; P = 0.003) were significantly lower in the BC group compared to the vegetarian and omnivore groups, respectively. Based on measurements of AR metabolites in urine and in plasma, whole-grain rye and wheat cereal fiber intake is low in BC subjects. Thus, urinary and plasma AR metabolites may be used as potential biomarkers of BC risk in women. This novel approach will likely also facilitate studies of associations between rye and whole-grain wheat cereal fiber intake and other diseases. Our findings should, however, be confirmed with larger subject populations.

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.

Biological activity of phenolic lipids

Phenolic lipids are a very diversified group of compounds derived from mono and dihydroxyphenols, i.e., phenol, catechol, resorcinol, and hydroquinone. Due to their strong amphiphilic character, these compounds can incorporate into erythrocytes and liposomal membranes. In this review, the antioxidant, antigenotoxic, and cytostatic activities of resorcinolic and other phenolic lipids are described. The ability of these compounds to inhibit bacterial, fungal, protozoan and parasite growth seems to depend on their interaction with proteins and/or on their membrane-disturbing properties.

Plasma alkylresorcinol metabolites as potential biomarkers of whole-grain wheat and rye cereal fibre intakes in women

It has been demonstrated that intact plasma alkylresorcinols (AR) and urinary AR metabolites could be used as biomarkers of whole-grain intake. Thereafter, we developed the method for the plasma AR metabolites, which is more convenient and requires less sample pretreatment than the analysis of intact plasma AR. The aim of the present study is to evaluate whether AR metabolites measured in plasma, in the same population, could also be considered as useful biomarkers of cereal fibre. Fifty-six women were recruited in a cross-sectional and observational study. Dietary intake (5-d record) and plasma AR metabolites (3,5-dihydroxybenzoic acid, DHBA; 3-(3,5-dihydroxyphenyl)-1-propanoic acid, DHPPA) were measured. The relationship between plasma AR metabolites and cereal fibre intake was examined using partial correlation and stepwise regression. Cereal fibre intake correlated significantly with plasma DHBA (r 0·411; P = 0·002) and DHPPA (r 0·463; P = 0·000) even after adjustment for BMI and age. Thus, plasma AR metabolites correlate with cereal fibre intake as noted with plasma intact AR and urinary AR metabolites. We observed that plasma DHPPA was the independent predictor of cereal fibre intake, explaining 18 % of the variance (adjusted r2 0·176; P = 0·002). In epidemiological screening, it might be easier to obtain and to collect plasma than urine samples. In addition, the plasma AR metabolites half-life seems longer than those of intact plasma AR, and their measurements are more convenient, and faster. Thus, sum of plasma AR metabolites and more specifically plasma DHPPA seems to be good and specific biomarkers of cereal fibre intake.

An expedient synthesis of 5-n-alkylresorcinols and novel 5-n-alkylresorcinol haptens

The first synthesis of bioactive long alkyl chain 5-n-alkylresorcinols, present in whole grain products, by a novel modification of the Wittig reaction is described. All the main long chain 5-n-alkylresorcinols present in rye and wheat, including C(23) and C(25) analogues and haptens, which have not been previously prepared, were synthesised. Microwave-promoted reactions of a semi-stabilized ylid and alkanals in water gave good yields in both pressurized and open systems. An alternative microwave-promoted synthesis starting from non-stabilized alkyltriphenylphosphonium salts and 3,5-dimethoxybenzaldehyde worked as well. Aqueous media were suitable for the reactions even if the starting materials were not soluble in water. The 5-n-alkylresorcinols are potential biomarkers of whole grain intake, and the new hapten derivatives of 5-n-alkylresorcinols will open the way for the immunochemical detection techniques of alkylresorcinols.

Dose response of whole-grain biomarkers: alkylresorcinols in human plasma and their metabolites in urine in relation to intake

BACKGROUND

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

OBJECTIVE

The objective was to assess the dose response of plasma ARs and the excretion of 2 recently discovered AR metabolites in 24-h urine samples in relation to AR intake and to establish a pharmacokinetic model for predicting plasma AR concentration.

DESIGN

Sixteen subjects were given rye bran flakes containing 11, 22, or 44 mg total ARs 3 times daily during week-long intervention periods separated by 1-wk washout periods in a nonblinded randomized crossover design. Blood samples were collected at baseline, after the 1-wk run-in period, and after each treatment and washout period. Two 24-h urine samples were collected at baseline and after each treatment period.

RESULTS

Plasma AR concentrations and daily excretion of 2 urinary AR metabolites increased with increasing AR dose (P < 0.001). Recovery of urinary metabolites in 24-h samples decreased with increasing doses from approximately 90% to approximately 45% in the range tested. A one-compartment model with 2 absorption compartments with different lag times and absorption rate constants adequately predicted plasma AR concentrations at the end of each intervention period.

CONCLUSION

Both plasma AR concentrations and urinary metabolites in 24-h samples showed a dose-response relation to increased AR intake, which strongly supports the hypothesis that ARs and their metabolites may be useful as biomarkers of whole-grain wheat and rye intakes.

Gas chromatography/tandem mass spectrometry analysis of alkylresorcinols in red blood cells

Erythrocyte alkylresorcinols (5-alkyl-1,3-dihydroxybenzenes) are potential biomarkers of wholegrain wheat and rye intake. However, their high-throughput quantitative analysis by gas chromatography/mass spectrometry (GC/MS) is hindered by the time-consuming sample preparation and, more importantly, by interfering compounds that still remain after sample cleanup. In the present work we describe a gas chromatography/tandem mass spectrometry (GC/MS/MS) method for the rapid and reliable quantification of alkylresorcinols in erythrocyte samples. The performance of the GC/MS/MS method is compared with that of GC/MS. The main characteristics of the method are: lower limits of detection: 2-10 microg/L standard solution; lower limits of quantification: 6-30 microg/L standard solution; linearity coefficients: 0.9611-0.9888; linear ranges: 2-20 microg/L in erythrocytes; and intra-day precisions (n = 6): 4-13% at endogenous analyte levels in non-spiked erythrocytes. Tandem mass spectrometry showed greatly improved selectivity over single-stage mass spectrometry in the case of erythrocyte samples, eliminating all interferences detectable in single-stage MS and enabling simple peak integration for quantification. Moreover, increased selectivity resulted in GC separation speeded up by a factor of two, allowing the duplicate analysis of over 40 samples per day. This GC/MS/MS method is suggested as an improved alternative to GC/MS for the quantification of alkylresorcinols in erythrocytes for assessing wholegrain wheat and rye intake.

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.

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.

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.

Alkylresorcinol content and homologue composition in durum wheat (Triticum durum) kernels and pasta products

The total alkylresorcinol (AR) content and relative homologue composition of 21 durum wheat (Triticum durum) kernel samples, as well as 5 pasta products and the corresponding flour mixtures, were determined. Durum wheat contained on average 455 microg/g ARs, and the average relative homologue composition was C17:0 (0.4%), C19:0 (14%), C21:0 (58%), C23:0 (21%), and C25:0 (6.5%). The homologue composition was found to be relatively consistent among samples, with durum wheat being different from common wheat by having a higher proportion of the longer homologues. No differences in content or homologue composition were observed in pasta products compared to flour ingredients, showing that alkylresorcinols are stable during pasta processing. The ratio of the homologues C17:0 to C21:0 was < or =0.02 for whole grain durum wheat products, which is different from those of common wheat (0.1) and rye (0.9).

Kinetics of the appearance of cereal alkylresorcinols in pig plasma

Alkylresorcinols (AR) are phenolic lipids found in high amounts in wholegrain wheat and rye. They may be important as bioactive components and/or biomarkers of wholegrain wheat and rye intake. AR absorption was studied with pigs during a habitual diet and after a single meal of AR-rich diet. In study 1, four pigs were fed wholegrain rye (RD) and white wheat bread (WD) for 1 week in a cross-over design. Arterial and venous AR concentrations were determined over 540 min after feeding on days 5 and 7. In study 2, four pigs were fed a synthetic, starch-based diet for 5 d, and arterial and venous AR concentrations were determined over 960 min after feeding a single meal of RD. In study 1, plasma AR concentrations after consuming RD peaked at 120 min, remained elevated between 120 and 420 min, and were re-elevated on refeeding at 480 min. In study 2, AR appeared in the plasma after 60 min, peaked at 180-240 min, and remained elevated after 960 min. The apparent elimination half-life was 3.93 h, and the maximum plasma concentration was 666 (sem 35) nmol/l. Arterial and venous plasma AR concentrations were similar, suggesting that AR are absorbed via the lymphatic system. AR concentrations in pig plasma increase rapidly after a meal containing AR, and persist in plasma for at least 5 d, indicating that AR may be a useful biomarker of wholegrain wheat and rye intake.

Intake of alkylresorcinols from wheat and rye in the United Kingdom and Sweden

Alkylresorcinols, phenolic lipids present in high amounts in whole-grain wheat and rye but not present in appreciable amounts in other foods, are candidates as biomarkers of whole-grain intake from these cereals. We estimated the intake of alkylresorcinols in Sweden and the UK using two different methods: food supply data (FSD); food consumption data (FCD; based on individual and household survey data). The average per capita intake of alkylresorcinols in Sweden was 17.5 mg/d (FSD) and 22.9 (sd 16.6) mg/d (FCD), while in the UK it was 11.9 mg/d (FSD) and 11.8 (sd 18.62) mg/d (FCD). Ninety-six per cent of all Swedes consumed some alkylresorcinols, compared with 50 % of British people surveyed. Both women and men over the age of 40 years had a higher alkylresorcinol intake than younger people. The average results from the two methods were similar, but the FCD data provided more detail about the range of alkylresorcinol intake, and indicate that because the intake of alkylresorcinols varies so widely, they may be good markers of diets rich or poor in whole-grain wheat/rye products.