Afaf Kamal-Eldin

The supramolecular chemistry of lipid oxidation and antioxidation in bulk oils

The microenvironment formed by surface active compounds is being recognized as the active site of lipid oxidation. Trace amounts of water occupy the core of micro micelles and several amphiphilic minor components (e.g., phospholipids, monoacylglycerols, free fatty acids, etc.) act as surfactants and affect lipid oxidation in a complex fashion dependent on the structure and stability of the microemulsions in a continuous lipid phase such as bulk oil. The structures of the triacylglycerols and other lipid-soluble molecules affect their organization and play important roles during the course of the oxidation reactions. Antioxidant head groups, variably located near the water-oil colloidal interfaces, trap and scavenge radicals according to their location and concentration. According to this scenario, antioxidants inhibit lipid oxidation not only by scavenging radicals via hydrogen donation but also by physically stabilizing the micelles at the microenvironments of the reaction sites. There is a cut-off effect (optimum value) governing the inhibitory effects of antioxidants depending inter alias on their hydrophilic/lipophilic balance and their concentrations. These complex effects, previously considered as paradoxes in antioxidants research, are now better explained by the supramolecular chemistry of lipid oxidation and antioxidants, which is discussed in this review.

Determination of alkylresorcinols and their metabolites in biological samples by gas chromatography-mass spectrometry.

High throughput GC-MS methods for quantification of alkylresorcinols (AR), biomarkers of whole grain wheat and rye intake, in plasma and adipose tissue and their metabolites in urine were developed and optimised. Alkylresorcinols in plasma (200μL) and adipose tissues (10-50mg) were extracted with diethyl ether, whereas main AR metabolites such as DHBA and DHPPA and newly identified metabolites in urine (50μL) were extracted with ethyl acetate after enzymatic deconjugation. All extracts were purified on OASIS-MAX solid phase extraction cartridges. Plasma and adipose tissue sample extracts were then derivatised with trifluoroacetic anhydride and reconstituted in undecane, whereas AR metabolites in urine samples were derivatised with BSTFA+TMCS (99:1, v/v, 100μL). Prepared samples were quantified by GC-MS (EI-SIM). Analysis of all compounds in the different matrices showed good selectivity, sensitivity, linearity, precision (<15% within and between batches), adequate recovery (75-108%), and short total run time (10-12min). The methods developed are applicable to large-scale sample sets such as epidemiological studies.

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.

Tocopherols and tocotrienols as antioxidants for food preservation

Abstract The number and position of methyl groups of tocopherols and tocotrienols influence their ease to donate hydrogens and hence their antioxidant effectiveness. Tocopherols have been found to increase the induction period of bulk oils and emulsions, but their relative activity was found to differ under different conditions. There are several peculiarities regarding the antioxidant efficacy of tocopherols, e.g. the immediate changes from induction to propagation period, their loss of efficacy at higher concentrations and the unknown mechanisms behind their synergistic interactions with secondary antioxidants (e.g. phospholipids and amino acids). The recent understanding of the role of the physical factors, e.g. the log P value and size and orientation of antioxidant molecules help to understand these peculiarities.

Animal source food intake and association with blood cholesterol, glycerophospholipids and sphingolipids in a northern Swedish population

Background The high intake of game meat in populations with a subsistence-based diet may affect their blood lipids and health status. Objective To examine the association between diet and circulating levels of blood lipid levels in a northern Swedish population. Study design We compared a group with traditional lifestyle (TLS) based on reindeer herding (TLS group) with those from the same area with a non-traditional lifestyle (NTLS) typical of more industrialized regions of Sweden (NTLS group). The analysis was based on self-reported intake of animal source food (i.e. non-game meat, game meat, fish, dairy products and eggs) and the serum blood level of a number of lipids [total cholesterol (TC), low-density lipoprotein cholesterol (LDL), high-density lipoprotein cholesterol (HDL), triglycerides (TG), glycerophospholipids and sphingolipids]. Results The TLS group had higher cholesterol, LDL and HDL levels than the reference group. Of the TLS group, 65% had cholesterol levels above the threshold for increased risk of coronary heart disease (≥240 mg/dl), as compared to 38% of the NTLS group. Self-reported consumption of game meat was positively associated with TC and LDL. Conclusions The high game meat consumption of the TLS group is associated with increased cholesterol levels. High intake of animal protein and fat and low fibre is known to increase the risk of cardiovascular disease, but other studies of the TLS in northern Sweden have shown comparable incidences of cardiovascular disease to the reference (NTLS) group from the same geographical area. This indicates that factors other than TC influence disease risk. One such possible factor is dietary phospholipids, which are also found in high amounts specifically in game meat and have been shown to inhibit cholesterol absorption.

Alkylresorcinol Metabolism in Swedish Adults Is Affected by Factors Other Than Intake of Whole-Grain Wheat and Rye

The urinary alkylresorcinol (AR) metabolites, 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-propanoic acid (DHPPA), could potentially serve as biomarkers for intake of whole-grain (WG) wheat and rye. Excretion of AR metabolites is largely dependent on the intake of AR but may also be influenced by other factors. This study aimed to investigate the validity of free and conjugated AR metabolites as biomarkers for WG intake of wheat and rye and to identify potential determinants of AR metabolites in urine. We quantified free aglycones and conjugates of AR metabolites in 24-h urine collections from 52 free-living Swedish adults and calculated correlation coefficients between urinary AR metabolite excretion and self-reported WG intake. We used partial least-squares regression to identify possible determinants of urinary AR metabolites. Approximately 50% of urinary AR metabolites were found as conjugates. Excretions of individually quantified free and conjugated AR metabolites and their sums were correlated to self-reported intake of WG rye and wheat (r = 0.50-0.68; P < 0.001). Excretion of urinary AR metabolites was mainly dependent on intake of 2 major dietary AR homologs, C19:0 and C21:0. Sex, BMI, and vitamin C intake were identified as determinants of the proportion of free and glucuronidated DHPPA in the present study. Urinary AR metabolites may be useful in reflecting short-term to medium-term intake of WG, but urine samples should be deconjugated prior to quantification. Anthropometric and dietary factors affecting the proportion of conjugated AR metabolites in urine may to some extent influence AR elimination and thereby the performance of urinary AR metabolites as biomarkers.

The New Paradigm for Lipid Oxidation and Insights to Microencapsulation of Omega-3 Fatty Acids

The consumption of omega-3 fatty acids provides a wide range of health benefits. However, the incorporation of these fatty acids in foods is limited because of their high oxidative instability. A new paradigm has emerged to better explain the oxidation mechanism of polyunsaturated fatty acids, which will be discussed here with reference to bulk lipids considered a special case of water in oil microemulsion. This paradigm suggests that lipid oxidation reactions are initiated by heterogeneous catalysis by metal oxides followed by the formation of micelles containing initial hydroperoxides, water, and other amphiphilic compounds. The induction period comes to the end when the formed micelles reach a critical micelle concentration and start to decompose opening the way to intense free radical reactions. Antioxidants and synergists extend the induction period not only by scavenging free radicals but also by stabilizing the micelles. With better understanding of the lipid oxidation mechanism, a tailored choice of antioxidants and synergistic combinations, and efficient encapsulation methods may be optimized to provide stable encapsulates containing highly n-3 polyunsaturated fatty acids. Smart processing and encapsulation technologies utilizing properly stabilized oils as well as optimized packaging parameters aiming to enhance n-3 fatty acid stability by smart selection/design of antioxidants, control of the interfacial physics and chemistry, and elimination of surface oil are needed for this purpose.

Pharmacological Properties of Melanin and its Function in Health

The biological pigment melanin is present in most of the biological systems. It manifests a host of biological and pharmacological properties. Its role as a molecule with special properties and functions affecting general health, including photoprotective and immunological action, are well recognized. Its antioxidant, anti-inflammatory, immunomodulatory, radioprotective, hepatic, gastrointestinal and hypoglycaemic benefits have only recently been recognized and studied. It is also associated with certain disorders of the nervous system. In this MiniReview, we consider the steadily increasing literature on the bioavailability and functional activity of melanin. Published literature shows that melanin may play a number of possible pharmacological effects such as protective, stimulatory, diagnostic and curative roles in human health. In this MiniReview, possible health roles and pharmacological effects are considered.

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.

Development of antibodies for determination of alkylresorcinol metabolites in human urine and elucidation of ELISA cross-reactivity

Alkylresorcinols (ARs) are amphiphilic phenolic lipids and their two main metabolites, 3-(3,5-dihydroxyphenyl)-propanoic acid (DHPPA) and 3,5-dihydroxybenzoic acid (DHBA), can be used as biomarkers of whole grain wheat and rye intake. The aim of this study was to develop antibodies against DHBA and DHPPA for use in ELISA analysis. Good calibration curves were obtained for ELISA using alkaline phosphatase (AP) conjugates. The highest sensitivity for DHPPA was found using a reagent combination of anti-DHPPA-BSA and DHPAA-AP in a direct ELISA (IC50=1.5μmol/L), and for DHBA using a reagent combination of anti-DHBA-OV and DHBA-AP (IC50=1.3μmol/L). Calibration was conducted in the linear range (0.3-27.4μmol/L), with limit of detection (LOD) 0.1μmol/L. Intra and inter CVs was in the range of 0.7-7.2% and 5.1-11.5%, respectively, for DHPPA and 1.3-9.4% and 3.5-20%, respectively, for DHBA. Mean recovery was 104% for DHPPA and 102% for DHBA. The ELISA method developed was then used for analysis of 120 urine samples from free-living men and women that had previously been analysed by gas chromatography-mass spectrometry (GC-MS). ELISA produced several-fold higher values than GC-MS. Application of high-resolution Orbitrap mass spectrometry (HR Orbitrap MS) allowed several compounds, including novel putative AR metabolites, to be identified, synthesised and confirmed as compounds with high ELISA cross-reactivity.