Long-term cryopreservation of potassium bromate positive assay controls for measurement of oxidatively damaged DNA by the Fpg-modified comet assay: results from the hCOMET ring trial

The formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay is widely used for the measurement of oxidatively generated damage to DNA. However, there has not been a recommended long-term positive control for this version of the comet assay. We have investigated potassium bromate as a positive control for the Fpg-modified comet assay because it generates many Fpg-sensitive sites with a little concurrent generation of DNA strand breaks. Eight laboratories used the same procedure for the treatment of monocytic THP-1 cells with potassium bromate (0, 0.5, 1.5, and 4.5 mM) and subsequent cryopreservation in a freezing medium consisting of 50% foetal bovine serum, 40% RPMI-1640 medium, and 10% dimethyl sulphoxide. The samples were analysed by the Fpg-modified comet assay three times over a 3-year period. All laboratories obtained a positive concentration-response relationship in cryopreserved samples (linear regression coefficients ranging from 0.79 to 0.99). However, there was a wide difference in the levels of Fpg-sensitive sites between the laboratory with the lowest (4.2% Tail DNA) and highest (74% Tail DNA) values in THP-1 cells after exposure to 4.5 mM KBrO3. In an attempt to assess sources of inter-laboratory variation in Fpg-sensitive sites, comet images from one experiment in each laboratory were forwarded to a central laboratory for visual scoring. There was high consistency between measurements of %Tail DNA values in each laboratory and the visual score of the same comets done in the central laboratory (r = 0.98, P < 0.001, linear regression). In conclusion, the results show that potassium bromate is a suitable positive comet assay control.

DNA strand break levels in cryopreserved mononuclear blood cell lines measured by the alkaline comet assay: results from the hCOMET ring trial

The comet assay is widely used in biomonitoring studies for the analysis of DNA damage in leukocytes and peripheral blood mononuclear cells. Rather than processing blood samples directly, it can be desirable to cryopreserve whole blood or isolated cells for later analysis by the comet assay. However, this creates concern about artificial accumulation of DNA damage during cryopreservation. In this study, 10 laboratories used standardized cryopreservation and thawing procedures of monocytic (THP-1) or lymphocytic (TK6) cells. Samples were cryopreserved in small aliquots in 50% foetal bovine serum, 40% cell culture medium, and 10% dimethyl sulphoxide. Subsequently, cryopreserved samples were analysed by the standard comet assay on three occasions over a 3-year period. Levels of DNA strand breaks in THP-1 cells were increased (four laboratories), unaltered (four laboratories), or decreased (two laboratories) by long-term storage. Pooled analysis indicates only a modest positive association between storage time and levels of DNA strand breaks in THP-1 cells (0.37% Tail DNA per year, 95% confidence interval: -0.05, 0.78). In contrast, DNA strand break levels were not increased by cryopreservation in TK6 cells. There was inter-laboratory variation in levels of DNA strand breaks in THP-1 cells (SD = 3.7% Tail DNA) and TK6 reference sample cells (SD = 9.4% Tail DNA), whereas the intra-laboratory residual variation was substantially smaller (i.e. SD = 0.4%-2.2% Tail DNA in laboratories with the smallest and largest variation). In conclusion, the study shows that accumulation of DNA strand breaks in cryopreserved mononuclear blood cell lines is not a matter of concern.

Inter-laboratory variation in measurement of DNA damage by the alkaline comet assay in the hCOMET ring trial

The comet assay is a simple and versatile method for measurement of DNA damage in eukaryotic cells. More specifically, the assay detects DNA migration from agarose gel-embedded nucleoids, which depends on assay conditions and the level of DNA damage. Certain steps in the comet assay procedure have substantial impact on the magnitude of DNA migration (e.g. electric potential and time of electrophoresis). Inter-laboratory variation in DNA migration levels occurs because there is no agreement on optimal assay conditions or suitable assay controls. The purpose of the hCOMET ring trial was to test potassium bromate (KBrO3) as a positive control for the formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay. To this end, participating laboratories used semi-standardized protocols for cell culture (i.e. cell culture, KBrO3 exposure, and cryopreservation of cells) and comet assay procedures, whereas the data acquisition was not standardized (i.e. staining of comets and image analysis). Segregation of the total variation into partial standard deviation (SD) in % Tail DNA units indicates the importance of cell culture procedures (SD = 10.9), comet assay procedures (SD = 12.3), staining (SD = 7.9) and image analysis (SD = 0.5) on the overall inter-laboratory variation of DNA migration (SD = 18.2). Future studies should assess sources of variation in each of these steps. On the positive side, the hCOMET ring trial demonstrates that KBrO3 is a robust positive control for the Fpg-modified comet assay. In conclusion, the hCOMET ring trial has demonstrated a high reproducibility of detecting genotoxic effects by the comet assay, but inter-laboratory variation of DNA migration levels is a concern.

Visual comet scoring revisited: a guide to scoring comet assay slides and obtaining reliable results

Measurement of DNA migration in the comet assay can be done by image analysis or visual scoring. The latter accounts for 20%-25% of the published comet assay results. Here we assess the intra- and inter-investigator variability in visual scoring of comets. We include three training sets of comet images, which can be used as reference for researchers who wish to use visual scoring of comets. Investigators in 11 different laboratories scored the comet images using a five-class scoring system. There is inter-investigator variation in the three training sets of comets (i.e. coefficient of variation (CV) = 9.7%, 19.8%, and 15.2% in training sets I-III, respectively). However, there is also a positive correlation of inter-investigator scoring in the three training sets (r = 0.60). Overall, 36% of the variation is attributed to inter-investigator variation and 64% stems from intra-investigator variation in scoring between comets (i.e. the comets in training sets I-III look slightly different and this gives rise to heterogeneity in scoring). Intra-investigator variation in scoring was also assessed by repeated analysis of the training sets by the same investigator. There was larger variation when the training sets were scored over a period of six months (CV = 5.9%-9.6%) as compared to 1 week (CV = 1.3%-6.1%). A subsequent study revealed a high inter-investigator variation when premade slides, prepared in a central laboratory, were stained and scored by investigators in different laboratories (CV = 105% and 18%-20% in premade slides with comets from unexposed and hydrogen peroxide-exposed cells, respectively). The results indicate that further standardization of visual scoring is desirable. Nevertheless, the analysis demonstrates that visual scoring is a reliable way of analysing DNA migration in comets.

Stable Isotope Dilution Analysis (SIDA) to Determine Metabolites of Furan and 2-Methylfuran in Human Urine Samples: A Pilot Study

Furan and 2-methylfuran (2-MF) are food contaminants that are classified as potentially carcinogenic to humans. The main source of exposure for adults via food is coffee consumption. Furan and 2-MF are volatile, which complicates exposure assessment because their content measured in food prior to consumption does not afford a reliable dosimetry. Therefore, other ways of exposure assessment need to be developed, preferably by monitoring exposure biomarkers, e.g., selected metabolites excreted in urine. In this study, cis-2-buten-1,4-dial (BDA)-derived urinary furan metabolites Lys-BDA (l-2-amino-6-(2,5-dihydro-2-oxo-1H-pyrrol-1-yl)hexanoic acid), AcLys-BDA (l-2-(acetylamino)-6-(2,5-dihydro-2-oxo-1H-pyrrol-1-yl)hexanoic acid) and GSH-BDA (N-[4-carboxy-4-(3-mercapto-1H-pyrrol-1-yl)-1-oxobutyl]-l-cysteinyl-glycine cyclic sulfide), as well as acetyl acrolein (AcA, 2-oxo-pent-2-enal)-derived metabolites Lys-AcA (l-2-(acetylamino)-6-(2,5-dihydro-5-methyl-2-oxo-1H-pyrrol-1-yl)-hexanoic acid) and AcLys-AcA (l-2-amino-6-(2,5-dihydro-5-methyl-2-oxo-1H-pyrrol-1-yl)-hexanoic acid) and their stable isotopically labeled analogs, were synthesized and characterized through NMR and MS, and a stable isotope dilution analysis (SIDA) with UPLC-ESI-MS/MS was established. As a proof of concept, urinary samples of a four-day human intervention study were used. In the frame of this study, ten subjects ingested 500 mL of coffee containing 0.648 µmol furan and 1.059 µmol 2-MF. Among the furan metabolites, AcLys-BDA was the most abundant, followed by Lys-BDA and GSH-BDA. Exposure to 2-MF via the coffee brew led to the formation of Lys-AcA and AcLys-AcA. Within 24 h, 89.1% of the ingested amount of furan and 15.4% of the ingested amount of 2-MF were detected in the urine in the form of the investigated metabolites. Therefore, GSH-BDA, Lys-BDA, AcLys-BDA, Lys-AcA and AcLys-AcA may be suitable as short-term-exposure biomarkers of furan and 2-MF exposure.

Polyphenol-Rich Beverage Consumption Affecting Parameters of the Lipid Metabolism in Healthy Subjects

Polyphenols are a diverse and widely distributed class of secondary metabolites, which possess numerous beneficial properties including a modulation of glucose and lipid metabolism. This placebo-controlled human intervention study was performed to explore effects of polyphenol-rich beverage (PRB) uptake on lipid metabolism, as well as DNA integrity. In this case, 36 healthy men were randomly divided to consume either 750 mL of a PRB (containing 51% chokeberry, cranberry, and pomegranate) or a placebo drink daily for eight weeks. Only PRB consumption was found to decrease fat and protein intakes significantly compared to the preceding one-week washout period. During the intervention with PRB an increased fat-free mass was shown after four weeks, whereas a significant elevation in body weight and leptin was observed in placebo group. Blood lipids were not significantly altered after PRB consumption, while triglyceride levels increased after placebo drink intake. In platelets, a significant inhibition of phosphodiesterase (PDE) activity was observed, more pronounced in test group. Consuming the PRB decreased total DNA strand breaks in whole blood as well as H₂O₂-induced breaks in isolated lymphocytes. Overall, our study suggested beneficial effects on lipid metabolism by reduced energy intake, modulation of biomarkers such as PDE activity and improved DNA integrity associated with PRB consumption.

Fractionation of Extracts from Black Chokeberry, Cranberry, and Pomegranate to Identify Compounds That Influence Lipid Metabolism

Polyphenols show a spectrum of bioactive effects, including an influence on lipid metabolism. In this study, we performed activity-guided fractionations of black chokeberry (aronia), cranberry, and pomegranate extracts to identify the biologically active compounds. The extracts were prepared from fruit juice concentrates with the adsorbent resin Amberlite XAD-7 and were separated into a copigment and an anthocyanin fraction, followed by fractionation into a polymer and monomeric fraction by means of hexane precipitation. For further fractionation of the cranberry and pomegranate copigment fractions, high-performance countercurrent chromatography (HPCCC) was used. The compounds in each fraction were identified by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS), and the quantification was performed by ultra high-performance liquid chromatography-diode array detector (UHPLC-DAD) analyses. Each of the (sub-)fractions was tested in three in vitro assays: phosphodiesterase 3B (PDE) activity, lipid accumulation, and lipolysis in 3T3-L1 cells. The results showed that various fractions and subfractions can inhibit lipid accumulation and PDE activity as well as increase lipolysis, particularly copigments. Overall, our results indicate an influence of polyphenol-rich (sub-)fractions on the lipid metabolism.

Clinical outcomes among patients with tuberculous meningitis receiving intensified treatment regimens

SETTING: National Center for Tuberculosis and Lung Diseases (NCTLD), Tbilisi, Georgia.OBJECTIVE: To determine clinical outcomes of patients with tuberculous meningitis (TBM) treated with an intensified regimen including a fluoroquinolone (FQ) and an injectable agent.DESIGN: Prospective cohort of patients aged ≥16 years initiating treatment for TBM at the NCTLD from January 2018 to December 2019. Treatment outcomes and neurologic disability at 1, 6 and 12 months after treatment initiation were assessed.RESULTS: Among 77 patients with median follow-up time of 363 days (IQR 269-374), 97% received a FQ, 62% an injectable agent, 44% linezolid and 39% a carbapenem. Fifty-seven patients (74%) successfully completed treatment, 2 (2.6%) had treatment failure, 6 (7.8%) died, and the remainder (12%) were lost to follow up. Among 11 patients treated for multidrug-resistant TBM, the median follow-up time was 467 days and one patient (8%) died. Regarding neurologic outcomes, 14/76 (18%) patients had Modified Rankin Scores of 0 at baseline, improving to 85% (56/66) and 94% (47/50) at 6 and 12 months, respectively.CONCLUSION: Intensified multidrug treatment regimens including a FQ and an injectable agent in all patients and newly implemented drugs in patients with multidrug-resistant TBM resulted in low mortality and favorable neurologic outcomes.

Potassium bromate as positive assay control for the Fpg-modified comet assay

The comet assay is a popular assay in biomonitoring studies. DNA strand breaks (or unspecific DNA lesions) are measured using the standard comet assay. Oxidative stress-generated DNA lesions can be measured by employing DNA repair enzymes to recognise oxidatively damaged DNA. Unfortunately, there has been a tendency to fail to report results from assay controls (or maybe even not to employ assay controls). We believe this might have been due to uncertainty as to what really constitutes a positive control. It should go without saying that a biomonitoring study cannot have a positive control group as it is unethical to expose healthy humans to DNA damaging (and thus potentially carcinogenic) agents. However, it is possible to include assay controls in the analysis (here meant as a cryopreserved sample of cells i.e. included in each experiment as a reference sample). In the present report we tested potassium bromate (KBrO3) as a positive comet assay control for the formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay. Ten laboratories used the same procedure for treatment of monocytic THP-1 cells with KBrO3 (0.5, 1.5 and 4.5 mM for 1 h at 37°C) and subsequent cryopreservation. Results from one laboratory were excluded in the statistical analysis because of technical issues in the Fpg-modified comet assay. All other laboratories found a concentration-response relationship in cryopreserved samples (regression coefficients from 0.80 to 0.98), although with different slopes ranging from 1.25 to 11.9 Fpg-sensitive sites (%DNA in tail) per 1 mM KBrO3. Our results demonstrate that KBrO3 is a suitable positive comet assay control.

Long-Term Consumption of Anthocyanin-Rich Fruit Juice: Impact on Gut Microbiota and Antioxidant Markers in Lymphocytes of Healthy Males

Polyphenols are considered protective against diseases associated with oxidative stress. Short-term intake of an anthocyanin-rich fruit juice resulted in significantly reduced deoxyribonucleic acid (DNA) strand-breaks in peripheral blood lymphocytes (PBLs) and affected antioxidant markers in healthy volunteers. Consequently, effects of long-term consumption of fruit juice are of particular interest. In focus was the impact on nuclear factor erythroid 2 (NFE2)-related factor 2 (Nrf2), the Nrf2-regulated genes NAD(P)H quinone oxidoreductase 1 (NQO-1) and heme oxygenase 1 (HO-1) as well as effects on the gut microbiota. In a nine-week placebo-controlled intervention trial with 57 healthy male volunteers, consumption of anthocyanin-rich juice significantly increased NQO-1 and HO-1 transcript levels in PBLs compared to a placebo beverage as measured by real-time polymerase chain reaction (PCR). Three Nrf2-promotor single nucleotide polymorphisms (SNPs), analyzed by pyrosequencing, indicated an association between individual Nrf2 transcript levels and genotype. Moreover, the Nrf2 genotype appeared to correlate with the presence of specific microbial organisms identified by 16S-PCR and classified as Spirochaetaceae. Furthermore, the microbial community was significantly affected by the duration of juice consumption and intake of juice itself. Taken together, long-term consumption of anthocyanin-rich fruit juice affected Nrf2-dependent transcription in PBLs, indicating systemic effects. Individual Nrf2 genotypes may influence the antioxidant response, thus requiring consideration in future intervention studies focusing on the Nrf2 pathway. Anthocyanin-rich fruit juice had an extensive impact on the gut microbiota.

Consumption of anthocyanin-rich beverages affects Nrf2 and Nrf2-dependent gene transcription in peripheral lymphocytes and DNA integrity of healthy volunteers

Recently, we demonstrated that the consumption of a bolus of bilberry extract modulates the transcription of Nrf2-regulated genes in peripheral blood lymphocytes (PBL) of healthy volunteers, accompanied by decreased DNA-damage. In the present study, we addressed the question whether consumption of consumer-relevant amounts of anthocyanin-rich beverages can achieve similar effects. The impact of three different anthocyanin-rich beverages on Nrf2-dependent gene transcription as well as and the status of DNA-damage in whole blood was investigated. After a polyphenol-reduced diet, five healthy male subjects consumed a bolus (700 mL) of respective test beverages with blood sampling up to 8 h after intake. All beverages affected the transcription of Nrf2, HO-1 and NQO-1, but showed different potencies and persistence of effects. Consumption of red fruit juice significantly reduced total DNA strand breaks (with formamidopyrimidine-DNA-glycosylase-(fpg) treatment) after 8 h in blood samples of the volunteers, suggesting antioxidant and DNA protective effects, albeit transcript levels of Nrf2-dependent genes had reached the basal state. The amount of basic DNA strand breaks (damage without oxidative DNA strand breaks) remained unchanged during the monitoring period. In contrast, a beverage prepared from grape skin extract significantly increased basic and total DNA strand breaks 2 h after intake, underlining the necessity of further investigations regarding composition, safety and consumer´s acceptance of respective products to exclude undesired adverse effects. Consumption of a bolus of anthocyanin-rich beverages affected Nrf2 and Nrf2-dependent gene transcription in human PBL and DNA integrity, which is indicative for systemic effects.

Carbohydrate Hydrolase-Inhibitory Activity of Juice-Based Phenolic Extracts in Correlation to Their Anthocyanin/Copigment Profile

Red fruits and their juices are rich sources of polyphenols, especially anthocyanins. Some studies have shown that such polyphenols can inhibit enzymes of the carbohydrate metabolism, such as α-amylase and α-glucosidase, that indirectly regulate blood sugar levels. The presented study examined the in vitro inhibitory activity against α-amylase and α-glucosidase of various phenolic extracts prepared from direct juices, concentrates, and purees of nine different berries which differ in their anthocyanin and copigment profile. Generally, the extracts with the highest phenolic content-aronia (67.7 ± 3.2 g GAE/100 g; cyanidin 3-galactoside; chlorogenic acid), pomegranate (65.7 ± 7.9 g GAE/100 g; cyanidin 3,5-diglucoside; punicalin), and red grape (59.6 ± 2.5 g GAE/100 g; malvidin 3-glucoside; quercetin 3-glucuronide)-showed also one of the highest inhibitory activities against α-amylase (326.9 ± 75.8 μg/mL; 789.7 ± 220.9 μg/mL; 646.1 ± 81.8 μg/mL) and α-glucosidase (115.6 ± 32.5 μg/mL; 127.8 ± 20.1 μg/mL; 160.6 ± 68.4 μg/mL) and, partially, were even more potent inhibitors than acarbose (441 ± 30 μg/mL; 1439 ± 85 μg/mL). Additionally, the investigation of single anthocyanins and glycosylated flavonoids demonstrated a structure- and size-dependent inhibitory activity. In the future in vivo studies are envisaged.

Toxicological testing of syringaresinol and enterolignans

Lignans are secondary plant constituents with dibenzylbutane skeletons found in cereals, oilseeds, and nuts. Two members of this class, syringaresinol (Syr) and secoisolariciresinol (Seco), occur at relatively high levels in cereals and processed food products as well as in coniferous trees. In vitro studies have shown that Seco and its metabolites enterodiol (END) and enterolactone (ENL), which are formed by intestinal microbes, exhibit strong antioxidant activity because of their phenolic character. The biological activity and discussion of dietary supplementation with these substances led to questions about the potential adverse health effects of these compounds, which are explored here. Syr and the metabolites END and ENL were investigated by combining structural information generated in silico with practical testing in vitro. An in silico structure-activity analysis was performed using ToxTree and NexusPrediction to suggest plausible mechanisms of toxicity and estimate toxicological endpoints of these compounds. Structural alerts were generated based on the presence of phenolic units with coordinating substituents that could potentially form quinoid structures, promote reactive oxygen species (ROS) formation, bind to cellular structures, or damage chromosomes. To assess the in silico results, the cytotoxicity and genotoxic potential of the studied compounds were tested in vitro using the resazurin reduction and comet assays, respectively. Incubating HepG2 and HT29 cells for 1 h or 24 h with 0–100 μM Syr, END, or ENL induced no cytotoxic effects. Additionally, even the highest tested concentrations of END and ENL showed no modulation of background and total DNA damage. The initial in silico screen thus generated structural alerts linked to toxicological endpoints, but experimental assessments of the studied compounds revealed no detectable toxicity, demonstrating the need for individual mechanistic experimental verification of in silico predictions. This approach makes it possible to connect known biological activity, such as reported antioxidative effects, to underlying mechanisms such as proton abstraction or donation. This in turn can yield insights – for example, that a compound's tendency to act as a pro- or anti-oxidant (and hence to exert adverse or beneficial health effects) may depend on its concentration and the cellular state.

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Potential of toxicologic mechanisms: cellular stress and chromosomal damage were identified in silico for syringaresinol, enterdiol and enterlactone.

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However, in confirmatory in vitro assays (cytotoxicity, DNA damage and DNA strand breaks) in HepG2 and HT29 cells no such toxicities were induced by physiological and higher concentrations of syringaresinol and enterolignans.

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This study serves as a cautionary tale of using in silico prediction of toxicity mechanisms. Experimental verification of in silico predictions is needed as these methodologies are still under development.

Alkylpyrazines from Coffee are Extensively Metabolized to Pyrazine Carboxylic Acids in the Human Body

SCOPE

Coffee is a complex mixture of over 1000 compounds, including diverse heteroaromatic compounds such as alkylpyrazines. Little is known about the intake, metabolism, and bodily distribution of these compounds. Therefore, a human intervention study is conducted to investigate the excretion of alkylpyrazine metabolites in urine after the ingestion of brewed coffee containing alkylpyrazines.

METHODS AND RESULTS

After consuming a diet without heat-processed food, ten volunteers consumed 500 mL of freshly brewed coffee prepared from coffee pads, providing intakes of 2-methylpyrazine (2-MeP), 2,5-dimethylpyrazine (2,5-DMeP), and 2,6-dimethylpyrazine (2,6-DMeP) amounting to 17.2, 4.4, and 4.9 µmol, respectively. These alkylpyrazines are metabolized into the corresponding pyrazine carboxylic acids, namely pyrazine-2-carboxylic acid (PA), 5-hydroxypyrazine-2-carboxylic acid (5-OHPA), 5-methylpyrazine-2-carboxylic acid (5-MePA), and 6-methylpyrazine-2-carboxylic acid (6-MePA). In total, 64% of the ingested 2-MeP is excreted as PA, as well as 26% as 5-OHPA, while 91% and 97% of the ingested 2,5-DMeP and 2,6-DMeP are recovered as 5-MePA and 6-MePA, respectively, in urine samples collected after coffee consumption.

CONCLUSION

This study provides evidence that alkylpyrazines are rapidly metabolized into the corresponding carboxylic acids and excreted via urine by humans, which is consistent with earlier rodent studies.

Urinary Excretion of Niacin Metabolites in Humans After Coffee Consumption

SCOPE

Coffee is a major natural source of niacin in the human diet, as it is formed during coffee roasting from the alkaloid trigonelline. The intention of our study was to monitor the urinary excretion of niacin metabolites after coffee consumption under controlled diet.

METHODS AND RESULTS

We performed a 4-day human intervention study on the excretion of major niacin metabolites in the urine of volunteers after ingestion of 500 mL regular coffee containing 34.8 μmol nicotinic acid (NA) and 0.58 μmol nicotinamide (NAM). In addition to NA and NAM, the metabolites N1 -methylnicotinamide (NMNAM), N1 -methyl-2-pyridone-5-carboxamide (2-Py), and nicotinuric acid (NUA) were identified and quantified in the collected urine samples by stable isotope dilution analysis (SIVA) using HPLC-ESI-MS/MS. Rapid urinary excretion was observed for the main metabolites (NA, NAM, NMNAM, and 2-Py), with tmax values within the first hour after ingestion. NUA appeared in traces even more rapidly. In sum, 972 nmol h-1 of NA, NAM, NMNAM, and 2-Py were excreted within 12 h after coffee consumption, corresponding to 6% of the ingested NA and NAM.

CONCLUSION

The results indicate regular coffee consumption to be a source of niacin in human diet.

Biomarker monitoring of controlled dietary acrylamide exposure indicates consistent human endogenous background

The aim of the present study was to explore the relation of controlled dietary acrylamide (AA) intake with the excretion of AA-related urinary mercapturic acids (MA), N-acetyl-S-(carbamoylethyl)-l-cysteine (AAMA) and N-acetyl-S-(1-carbamoyl-2-hydroxyethyl)-l-cysteine (GAMA). Excretion kinetics of these short-term exposure biomarkers were monitored under strictly controlled conditions within a duplicate diet human intervention study. One study arm (group A, n = 6) ingested AA via coffee (0.15–0.17 µg/kg bw) on day 6 and in a meal containing an upper exposure level of AA (14.1–15.9 μg/kg bw) on day 10. The other arm (group B) was on AA minimized diet (washout, 0.05–0.06 µg/kg bw) throughout the whole 13-day study period. On day 6, these volunteers ingested ¹³C₃D₃-AA (1 μg/kg bw). In both arms, urinary MA excretion was continuously monitored and blood samples were taken to determine hemoglobin adducts. Ingestion of four cups of coffee resulted in a slightly enhanced short-term biomarker response within the background range of group B. At the end of the 13-day washout period, group B excreted an AAMA baseline level of 0.14 ± 0.10 µmol/d although AA intake was only about 0.06 µmol/d. This sustained over-proportional AAMA background suggested an endogenous AA baseline exposure level of 0.3–0.4 µg/kg bw/d. The excretion of ¹³C₃D₃-AA was practically complete within 72–96 h which rules out delayed release of AA (or any other MA precursor) from deep body compartments. The results provide compelling support for the hypothesis of a sustained endogenous AA formation in the human body.

Monitoring urinary mercapturic acids as biomarkers of human dietary exposure to acrylamide in combination with acrylamide uptake assessment based on duplicate diets

The present human intervention study investigated the relation between the intake of acrylamide (AA) in diets with minimized, low, and high AA contents and the levels of urinary exposure biomarkers. As biomarkers, the mercapturic acids, N-acetyl-S-(carbamoylethyl)-L-cysteine (AAMA), and N-acetyl-S-(1-carbamoyl-2-hydroxyethyl)-L-cysteine (GAMA) were monitored. The study was performed with 14 healthy male volunteers over a period of 9 days, under controlled conditions excluding any inadvertent AA exposure. Dietary exposure to AA was measured by determining AA contents in duplicates of all meals consumed by the volunteers. The study design included an initial washout period of 3 days on AA-minimized diet, resulting in dietary AA exposure not exceeding 41 ng/kg bw/d. Identical washout periods of 2 days each followed the AA exposure days (day 4, low exposure, and day 7, high exposure). At the respective AA intake days, volunteers ingested 0.6-0.8 (low exposure) or 1.3-1.8 (high exposure) μg AA/kg bw/d with their food. Both low and high AA intakes resulted in an AAMA output within 72 h corresponding to 58 % of the respective AA intake. At the end of the initial 3-day washout period, an AAMA baseline level of 93 ± 31 nmol/d was recorded, suggestive for an assumed net AA baseline exposure level of 0.2-0.3 μg AA/kg bw/d.

Abstract LB-249: Coffee drinking decreases background DNA strand breaks in humans: A randomized controlled trial

Effects of coffee consumption on the level of spontaneous DNA strand breaks in peripheral white blood cells have not been reported yet. In this human intervention study the impact of consuming a dark roast coffee blend on the level of spontaneous DNA strand breaks was investigated.

Healthy men (n=84) were randomized to consume daily for 4 weeks either 750 ml of fresh coffee brew or 750 ml of water, subsequent to a run in washout phase of 4 weeks. The study coffee was a blend providing substantial amounts of both, caffeoylquinic acids and the roast product N-methylpyridinium. Before and after the coffee/water phases, spontaneous strand breaks were determined by Comet assay.

Both groups exhibited a similar level of spontaneous DNA strand breaks at baseline.In the intervention phase spontaneous ( background) DNA strand breaks slightly increased in the water only group, whereas they significantly decreased in the coffee group,leading to a 27 percent difference between both arms (p=0.0002).

Food frequency questionnaires indicated no differences in the overall diet between groups, mean body weight during the intervention phases remaining stable. Consumption of the study coffee was found associated with a markedly lower level of pontaneous DNA strand breaks in white blood cells.

Conclusion: Regular coffee consumption contributes to DNA integrity.

Citation Format: Gerhard Eisenbrand, Tamara Bakuradze, Roman Lang, Thomas Hofmann, Dorothea Schipp, Jens Galan, Elke Richling. Coffee drinking decreases background DNA strand breaks in humans: A randomized controlled trial. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-249. doi:10.1158/1538-7445.AM2014-LB-249

Effect of coffee combining green coffee bean constituents with typical roasting products on the Nrf2/ARE pathway in vitro and in vivo

This study investigated Nrf2-activating properties of a coffee blend combining raw coffee bean constituents with 5-O-caffeoylquinic acid (CGA) as a lead component with typical roasting products such as N-methylpyridinium (NMP). In cell culture (HT29) the respective coffee extract (CN-CE) increased nuclear Nrf2 translocation and enhanced the transcription of ARE-dependent genes as exemplified for NAD(P)H:quinone oxidoreductase and glutathione-S-transferase (GST)A1, reflected in the protein level by an increase in GST enzyme activity. In a pilot human intervention study (29 healthy volunteers), daily consumption of 750 mL of CN-coffee for 4 weeks increased Nrf2 transcription in peripheral blood lymphocytes on average. However, the transcriptional response pattern of Nrf2/ARE-dependent genes showed substantial interindividual variations. The presence of SNPs in the Nrf2-promoter, reported recently, as well as the detection of GSTT1*0 (null) genotypes in the study collective strengthens the hypothesis that coffee acts as a modulator of Nrf2-dependent gene response in humans, but genetic polymorphisms play an important role in the individual response pattern.