Identification of hydrogen peroxide as a major cytotoxic component in Maillard reaction mixtures and coffee

Phenolic compounds interfere in the Ampliflu Red/peroxidase assay for hydrogen peroxide

Methods employing horseradish peroxidase (HRP) are popular for quantification of hydrogen peroxide. This communication reports interference of the Ampliflu Red-HRP assay by phenolic compounds, abundant in food and beverages of plant origin. Concentrations of catechin, propyl gallate, quercetin and gallic acid lowering the yield of the product, resorufin, in this system by 50% were lower than 10 μM. The extent of inhibition increased with decreasing hydrogen peroxide concentration. These results point to the necessity of a careful interpretation of results concerning the quantification of hydrogen peroxide in materials containing phenolic compounds with methods employing HRP, especially when low concentrations of hydrogen peroxide are concerned.

Lysine-Derived Maillard Reaction Products Inhibit the Growth of Salmonella enterica Serotype Typhimurium

An emerging consumer trend to purchase minimally heated and ready-to-eat food products may result in processing methods that do not effectively reduce pathogenic populations. Crude Maillard reaction products (MRPs) are naturally generated compounds that have been shown to display antimicrobial effects against pathogens. Crude MRPs were generated from reducing sugars (fructose (Fru), glucose (Glc), ribose (Rib) or xylose (Xyl)) with lysine and the melanoidin equivalence was measured using an absorbance of 420 nm (Ab₄₂₀). The relative antimicrobial activity of each MRP was measured by examining both the length of lag phase and maximum growth rate. MRPs were found to significantly shorten the lag phase and decrease the maximum growth rate of S. Typhimurium (p < 0.05). Glucose-lysine MRP (GL MRP) was determined to have the highest relative melanoidin (1.690 ± 0.048 at Ab₄₂₀) and its efficacy against S. Typhimurium populations was measured at 37 °C and at pH 7.0 and estimated on xylose lysine deoxycholate (XLD) agar. GL MRP significantly reduced S. Typhimurium populations by >1 log CFU/mL at 8 and 24 h after inoculation (p < 0.05). GL MRPs also further decreased S. Typhimurium populations significantly under thermal stress condition (55 °C) compared to optimal (37 °C) by ~1 log CFU/mL (p < 0.05). Overall, GL MRP demonstrated effective antimicrobial activity against S. Typhimurium at 37 °C and 55 °C.

In vitromembrane damage induced by half-fin anchovy hydrolysates/glucose Maillard reaction products and the effects on oxidative statusin vivo

Through induced H₂O₂generationin vitro, HAHp(9.0)-G MRPs increased the antioxidant status in normal mice after short-term intake.

Neutral and acidic products derived from hydroxyl radical-induced oxidation of arabinotriose assessed by electrospray ionisation mass spectrometry

The oxidation of α-(1 → 5)-L-arabinotriose (Ara3), an oligosaccharide structurally related to side chains of coffee arabinogalactans, was studied in reaction with hydroxyl radicals generated under conditions of Fenton reaction (Fe(2+)/H2O2). The acidic and neutral oxidation products were separated by ligand exchange/size-exclusion chromatography, subsequently identified by electrospray ionisation mass spectrometry (ESI-MS) and structurally characterised by tandem MS (ESI-MS/MS). In acidic fraction were identified several oxidation products containing an acidic residue at the corresponding reducing end of Ara3, namely arabinonic acid, and erythronic, glyceric and glycolic acids formed by oxidative scission of the furanose ring. In neutral fractions were identified derivatives containing keto, hydroxy and hydroperoxy moieties, as well as derivatives resulting from the ring scission at the reducing end of Ara3. In both acidic and neutral fractions, beyond the trisaccharide derivatives, the corresponding di- and monosaccharide derivatives were identified indicating the occurrence of oxidative depolymerisation. The structural characterisation of these oxidation products by ESI-MS/MS allowed the differentiation of isobaric and isomeric species of acidic and neutral character. The species identified in this study may help in detection of roasting products associated with the free radical-mediated oxidation of coffee arabinogalactans.

Cell culture condition-dependent impact of AGE-rich food extracts on kinase activation and cell survival on human fibroblasts

Advanced glycation end products (AGEs) are stable end products of the Maillard reaction. Effects of food extracts are often initially analysed in cellular test systems and it is not clear how different cell culture conditions might influence the results. Therefore, we compared the effects of two models for AGE-rich food, bread crust and coffee extract (CE) on WI-38 human lung fibroblasts under different cell culture conditions (sub-confluent versus confluent cells, with and without serum). WI-38 cells responded to coffee and bread crust extract (BCE) with a rapid phosphorylation of PKB (AKT), p42/44 MAPK (ERK 1/2) and p38 MAPK, strongly depending on culture conditions. BCE resulted in increased cell numbers, whereas CE appeared to be cytotoxic. When cell numbers under all culture conditions and treatments were correlated with kinase phosphorylation, the relation between phospho-p38 MAPK and phospho-AKT represented a good, cell culture condition-independent predictor of cell survival.

Cytotoxicity evaluation of electronic cigarette vapor extract on cultured mammalian fibroblasts (ClearStream-LIFE): comparison with tobacco cigarette smoke extract

CONTEXT

Electronic cigarettes (ECs) are used as alternatives to smoking; however, data on their cytotoxic potential are scarce.

OBJECTIVE

To evaluate the cytotoxic potential of 21 EC liquids compared to the effects of cigarette smoke (CS).

METHODS

Cytotoxicity was evaluated according to UNI EN ISO 10993-5 standard. By activating an EC device, 200 mg of liquid was evaporated and was extracted in 20 ml of culture medium. CS extract from one cigarette was also produced. The extracts, undiluted (100%) and in five dilutions (50%, 25%, 12.5%, 6.25% and 3.125%), were applied to cultured murine fibroblasts (3T3), and viability was measured after 24-hour incubation by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. Viability of less than 70% was considered cytotoxic.

RESULTS

CS extract showed cytotoxic effects at extract concentrations above 12.5% (viability: 89.1 ± 3.5% at 3.125%, 77.8 ± 1.8% at 6.25%, 72.8 ± 9.7% at 12.5%, 5.9 ± 0.9% at 25%, 9.4 ± 5.3% at 50% and 5.7 ± 0.7% at 100% extract concentration). Range of fibroblast viability for EC vapor extracts was 88.5-117.8% at 3.125%, 86.4-115.3% at 6.25%, 85.8-111.7% at 12.5%, 78.1-106.2% at 25%, 79.0-103.7% at 50% and 51.0-102.2% at 100% extract concentration. One vapor extract was cytotoxic at 100% extract concentration only (viability: 51.0 ± 2.6%). However, even for that liquid, viability was 795% higher relative to CS extract.

CONCLUSIONS

This study indicates that EC vapor is significantly less cytotoxic compared tobacco CS. These results should be validated by clinical studies.

Escherichia coli K-12 survives anaerobic exposure at pH 2 without RpoS, Gad, or hydrogenases, but shows sensitivity to autoclaved broth products

Escherichia coli and other enteric bacteria survive exposure to extreme acid (pH 2 or lower) in gastric fluid. Aerated cultures survive via regulons expressing glutamate decarboxylase (Gad, activated by RpoS), cyclopropane fatty acid synthase (Cfa) and others. But extreme-acid survival is rarely tested under low oxygen, a condition found in the stomach and the intestinal tract. We observed survival of E. coli K-12 W3110 at pH 1.2–pH 2.0, conducting all manipulations (overnight culture at pH 5.5, extreme-acid exposure, dilution and plating) in a glove box excluding oxygen (10% H₂, 5% CO₂, balance N₂). With dissolved O₂ concentrations maintained below 6 µM, survival at pH 2 required Cfa but did not require GadC, RpoS, or hydrogenases. Extreme-acid survival in broth (containing tryptone and yeast extract) was diminished in media that had been autoclaved compared to media that had been filtered. The effect of autoclaved media on extreme-acid survival was most pronounced when oxygen was excluded. Exposure to H₂O₂ during extreme-acid treatment increased the death rate slightly for W3110 and to a greater extent for the rpoS deletion strain. Survival at pH 2 was increased in strains lacking the anaerobic regulator fnr. During anaerobic growth at pH 5.5, strains deleted for fnr showed enhanced transcription of acid-survival genes gadB, cfa, and hdeA, as well as catalase (katE). We show that E. coli cultured under oxygen exclusion (<6 µM O₂) requires mechanisms different from those of aerated cultures. Extreme acid survival is more sensitive to autoclave products under oxygen exclusion.

Demonstration of antioxidant and anti-inflammatory bioactivities from sugar-amino acid maillard reaction products

Maillard reaction products (MRPs), both crude and fractionated, were assessed for antioxidant potential using cell-free, in vitro 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, Fenton reaction induced deoxyribose degradation and oxygen radical absorbance capacity-fluorescein (ORACFL) chemical assays. All MRPs displayed various affinities to scavenge free radicals generated in different reaction media and using different reactive oxygen species (ROS) substrates. High molecular weight MRPs consistently showed the greatest (P < 0.05) antioxidant potential in chemical assays. Repeating these tests in Caco-2 cells with both reactive oxygen and nitrogen (RNS) intracellular assays revealed that the low molecular weight components (LMW) were most effective at inhibiting oxidation and inflammation. In particular, a glucose-lysine (Glu-Lys) mixture heated for 60 min had marked intracellular antioxidant activity and nitric oxide (NO) and interleukin-8 (IL-8) inhibitory activities compared to other MRPs (P < 0.05). Further studies employing ultrafiltration, ethyl acetate extraction, and semipreparative high-performance liquid chromatography (HPLC) produced a bioactive fraction, termed F3, from heated Glu-Lys MRP. F3 inhibited NO, inducible nitric oxide synthetase (iNOS), and IL-8 in interferon γ (IFN-γ)- and phorbol ester (PMA)-induced Caco-2 cells. F3 modified several gene expressions involved in the NF-κB signaling pathway. Two components, namely, 5-hydroxymethyl-2-furfural (HMF) and 5-hydroxymethyl-2-furoic acid (HMFA), were identified in the F3 fraction, with an unidentified third component comprising a major portion of the bioactivity. The results show that MRP components have bioactive potential, especially in regard to suppressing oxidative stress and inflammation in IFN-γ- and PMA-induced Caco-2 cells.

Activation of antioxidant response element (ARE)-dependent genes by roasted coffee extracts

Coffee beans contain numerous bioactive components that exhibit antioxidant capacity when assessed using both chemical, cell free, and biological, cell-based model systems. However, the mechanisms underlying the antioxidant effects of coffee in biological systems are not totally understood and in some cases vary considerably from results obtained with simpler in vitro chemical assays. In the present study, the physicochemical characteristics and antioxidant activity of roasted and non-roasted coffee extracts were investigated in both cell free (ORAC(FL)) and cell-based systems. A profile of antioxidant gene expression in cultured human colon adenocarcinoma Caco-2 cells treated with both roasted and non-roasted coffee extracts, respectively, was investigated using Real-Time polymerase chain reaction (PCR) array technology. Results demonstrated that the mechanisms of the antioxidant activity associated with coffee constituents assessed by the ORAC(FL) assay were different to those observed using an intracellular oxidation assay with Caco-2 cells. Moreover, roasted coffee (both light and dark roasted) extracts produced both increased- and decreased-expressions of numerous genes that are involved in the management of oxidative stress via the antioxidant defence system. The selective and specific positive induction of antioxidant response element (ARE)-dependent genes, including gastrointestinal glutathione peroxidase (GPX2), sulfiredoxin (SRXN1), thioredoxin reductase 1 (TXNRD1), peroxiredoxin 1 (PRDX1), peroxiredoxin 4 (PDRX4) and peroxiredoxin 6 (PDRX6) were identified with the activation of the endogenous antioxidant defence system in Caco-2 cells.

Advanced glycation endproducts as gerontotoxins and biomarkers for carbonyl-based degenerative processes in Alzheimer's disease

Alzheimer's disease (AD) is the most common dementia disorder of later life. Although there might be various different triggering events in the early stages of the disease, they appear to converge on a few characteristic final pathways in the late stages, characterized by inflammation and neurodegeneration. Here, we review the hypothesis that advanced glycation end products (AGEs), which reflect carbonyl stress, an imbalance between the production of reactive carbonyl compounds and their detoxification, can serve as biomarkers for the progression of disorder. AGE modification may explain many of the neuropathological and biochemical features of AD, such as extensive protein cross-linking shown as amyloid plaques and neurofibrillary tangles, inflammation, oxidative stress and neuronal cell death. Although accumulation of AGEs is a normal feature of aging, it appears to be significantly accelerated in AD. We suggest that higher AGE concentrations in brain tissue and in cerebrospinal fluid might be able to distinguish between normal aging and AD.