Development of a dehydrated fortified food base from fermented milk and parboiled wheat, and comparison of its composition and reconstitution behavior with those of commercial dried dairy-cereal blends

Dehydrated blends of milk and cereal are reconstituted and consumed as a nutritious soup or porridge in many regions; the composition and reconstitution behavior of the blends are likely to impact on nutritional quality and consumer acceptability of the soup/porridge. Experimental samples of dried fermented milk-bulgur wheat blend (FMBW) and commercial samples of dried dairy-cereal blends, namely kishk, tarhana, and super cereal plus corn-soy blend (SCpCSB) were compared for composition, color, water sorption, and reconstitution characteristics. FMBW blends had higher contents of protein, Ca, lactose and lactic acid, lower levels of salt (NaCl) and Fe, and a lighter, more-yellow color (higher L* and b*-color co-ordinates) than tarhana or kishk. Compared with SCpCSB, FMBW had numerically higher levels of protein, lactose, and lactic acid, lower levels of Ca, Fe, Zn, and Mg, and lower pH. Tarhana had highest mean levels of starch, and on reconstitution (133 g/kg) had highest water holding capacity, viscosity during pasting and cooling, yield stress (σ 0), consistency coefficient (K), and viscosity on shearing from 20 to 120 s-1 at 60°C. Reconstituted FMBW, kishk, and SCpCSB had similar pasting and flow behavior properties. Overall, the composition (starch, protein, Ca, Mg), pasting and flow behavior characteristics of FMBW were closer to those SCpCSB and kishk than to tarhana. The results suggest that the FMBW powder, on appropriate supplementation with Ca, Fe, Zn and Mg, could be used for the development of customized fortified blended foods for specific groups.

Cereal type significantly affects the composition and reconstitution characteristics of dried fermented milk-cereal composites

BACKGROUND

Dairy and cereal products are frequently combined to create composites with enhanced nutritional benefits. Commercially available dried dairy-cereal composites are typically reconstituted and cooked to produce porridge or soup.

RESULTS

Dried fermented milk-cereal composites (FMCC) with ∼193 g kg^-1 protein were prepared by blending fermented milk with parboiled oats (FMCCo), wheat (FMCCw), or barley (FMCCb), incubating the blend, drying, and milling. Cereal type significantly affected the composition of the FMCC and the properties of the reconstituted, cooked FMCC (R-FMCC). The FMCCo had a higher starch and fat content and lower levels of lactose, lactic acid, and amylose than FMCCb. The R-FMCCo had higher viscosity during cooking at 95 °C and cooling to 35 °C, and higher values of yield stress (σ₀ ), consistency index (K) and viscosity on shearing from 20 to 120 s^-1 at 60 °C than R-FMCCb. The FMCCw had lower levels of fat and β-glucan than FMCCo or FMCCb, but was otherwise closer to FMMCb with respect to composition, cooking properties and flow behavior.

CONCLUSION

Differences in composition and consistency associated with cereal type are likely to affect the nutritional value of the FMCC. © 2018 Society of Chemical Industry.

Antifungal activity of a de novo synthetic peptide and derivatives against fungal food contaminants

The development of novel solutions to fight microbial food contaminants rests upon two pillars, which are the development of resistant strains and consumers' desire for a reduced consumption of synthetic drugs. Natural antimicrobial peptides possess the qualities to overcome these issues. De novo synthesis of novel antifungal compounds is a major progress that has been facilitated by the identification of parameters involved in the antimicrobial activity. A 14-residue peptide named KK14, with the sequence KKFFRAWWAPRFLK-NH₂ , was designed and inhibited conidial germination and fungal growth of food contaminants within the range 6.25 to 50 μg/ml and 6.25 to 100 μg/ml, respectively. The study of three analogues of the peptide highlighted the role of some residues in the structural conformation of the peptide and its antifungal activity. The substitution of a Pro residue with Arg increased the helical content of the peptide not only its antifungal activity but also its cytotoxicity. The insertion of an unnatural bulky residue β-diphenylalanine or a full d-enantiomerization overall increased the antifungal potency. The four peptides showed similar behaviour towards salt increase, heat treatment, and pH decrease. Interestingly, the denantiomer remained the most active at high pH and after proteolytic digestion. The four peptides did not present haemolytic activity up to 200 μg/ml but had different behaviours of cytotoxicity. These differences could be crucial for potential application as pharmaceutical or food preservatives.

Involvement of Calcium in 7β-Hydroxycholesterol and Cholesterol-5β,6β-Epoxide-Induced Apoptosis

Oxidized low-density lipoprotein (oxLDL) is believed to play a central role in the development of atherosclerosis. The induction of apoptosis in cells of the arterial wall is a critical event in the development of atheroma. 7β-Hydroxycholesterol (7 β-OH) and cholesterol-5 β,6 β-epoxide ( β-epoxide) are components of oxLDL and have previously been shown to be potent inducers of apoptosis. The exact mechanism through which these oxysterols induce apoptosis remains to be fully elucidated. A perturbation of intra-cellular calcium homeostasis has been found to trigger apoptosis in many experimental systems. The aim of the present study was to determine the involvement of calcium signaling in 7 β-OH and β-epoxide–induced apoptosis. To this end, the authors employed the calcium channel blockers verapamil and nifedipine and inhibitors of calpain activation, ALLM and ALLN. Verapamil protected against the decrease in viability induced by 7 β-OH whereas nifedipine had a protective effect in both 7 β-OH and β-epoxide–treated cells, though these compounds did not restore viability to control levels. Verapamil, nifedipine, and ALLM prevented apoptosis induced by β-epoxide. None of the compounds employed in the current study protected against 7 β-OH–induced apoptosis. Our results implicate calcium signaling in the apoptotic pathway induced by β-epoxide and also highlight differences between apoptosis induced by 7 β-OH and β-epoxide.

Antioxidant, immunomodulatory and antiproliferative effects of gelatin hydrolysate from unicorn leatherjacket skin

BACKGROUND

The in vitro cellular bioactivities including, antioxidant, immunomodulatory and antiproliferative effects of a gelatin hydrolysate (GH) prepared from unicorn leatherjacket skin, using partially purified glycyl endopeptidase, were investigated in order to optimize the use of fish skin waste products as functional food ingredients.

RESULTS

GH under the tested concentrations (750-1500 µg mL(-1) ) protected against H2 O2 -induced DNA damage in U937 cells. GH also protected against the H2 O2 -induced reduction in cellular antioxidant enzyme activities, superoxide dismutase and catalase, in HepG2 cells. GH demonstrated immunomodulatory potential by reducing pro-inflammatory cytokine (interleukin-6 (IL-6) and IL-1β) production and nitric oxide production in lipopolysaccharide-stimulated RAW 264.7 macrophage cells. Cell proliferation in human colon cancer (Caco-2) cells was significantly reduced in a dose-dependent manner following incubation with GH.

CONCLUSION

These results indicate that GH has several bioactivities which support its potential as a promising functional food ingredient with various health benefits. © 2015 Society of Chemical Industry.

Cellular Transport and Bioactivity of a Major Saffron Apocarotenoid, Picrocrocin (4-(β-D-Glucopyranosyloxy)-2,6,6-trimethyl-1-cyclohexene-1-carboxaldehyde)

The cellular transport and bioactivity of the second major saffron apocarotenoid, picrocrocin, was examined in parallel to that of the major group, crocetin sugar esters, in aqueous extracts. The transport of pure picrocrocin was investigated in comparison to that of other saffron apocarotenoids, trans-crocetin (di-β-D-gentiobiosyl) ester and crocetin using the Caco-2 cell model coupled with an in vitro digestion procedure. RP-HPLC-DAD was employed to quantify the bioaccessible and bioavailable amounts of individual apocarotenoids. Picrocrocin and crocetin sugar esters though highly bioaccessible (75% and 60%, respectively) were transported at minute quantities (0.2% and 0.5%, respectively; 10-fold lower than crocetin). Picrocrocin did not protect against oxidant-induced DNA damage in U937, human monocytic blood cells at the concentration investigated, however, it reduced the proliferation of human adenocarcinoma and hepatocarcinoma cells. Our findings may be useful for the requirements of food legislation regarding saffron preparations, in which both apocarotenoid groups coexist.

Brewers' spent grain (BSG) protein hydrolysates decrease hydrogen peroxide (H2O2)-induced oxidative stress and concanavalin-A (con-A) stimulated IFN-γ production in cell culture

The present study investigated the bioactivity of protein hydrolysates and fractionated hydrolysates prepared from brewers' spent grain (BSG) using proteases, including Alcalase 2.4L, Flavourzyme and Corolase PP. Hydrolysates were designated K-Y, including fractionated hydrolysates with molecular weight (m.w.) < 3, <5 and >5 kDa. Where computable, IC50 values were lower in U937 (1.38-9.78%) than Jurkat T cells (1.15-13.82%). Hydrolysates L, Q and R and fractionated hydrolysates of U and W (<3, <5, >5 kDa) significantly (P < 0.01) protected against hydrogen peroxide (H2O2)-induced reduction of superoxide dismutase (SOD) activity. A fractionated hydrolysate of W (<5 kDa) protected against H2O2-induced DNA damage, P < 0.01. Hydrolysates K, N, P, U, U > 5 kDa, V, V > 5 kDa, W, W > 5 kDa significantly (P < 0.05) reduced a concanavlin-A (con-A) stimulated production of interferon-γ (IFN-γ). In conclusion, BSG protein hydrolysates demonstrate bioactivity in vitro; lower m.w. hydrolysates (<3, <5 kDa) show greatest antioxidant activity and unfractionated or higher m.w. hydrolysates (>5 kDa) possess anti-inflammatory effects.

Phenolic-enriched fractions from brewers' spent grain possess cellular antioxidant and immunomodulatory effects in cell culture model systems

BACKGROUND

Large quantities of brewers' spent grain (BSG), a co-product of the brewing industry, are produced annually. BSG contains hydroxycinnamic acids, and phenolic-rich extracts from BSG have previously demonstrated the ability to protect against oxidant-induced DNA damage. The present study investigated the anti-inflammatory potential of eight phenolic extracts from BSG: four pale (P1-P4) and four black (B1-B4) extracts.

RESULTS

BSG extracts were more cytotoxic in Jurkat T than U937 cells, with lower IC₅₀ values in Jurkat T cells, measured using the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Pale BSG extracts P2 and P3 showed the greatest anti-inflammatory potential, significantly (P < 0.05) reducing interleukin-2 (IL-2), interleukin-4 (IL-4, P2 only), interleukin-10 (IL-10) and interferon-γ (IFN-γ) production. In addition, extracts P1-P3 and B2-B4 showed significant (P < 0.05) antioxidant effects, determined by the cellular antioxidant activity assays superoxide dismutase, catalase and glutathione content (GSH).

CONCLUSION

Phenolic extracts from BSG, particularly the pale BSG extracts, have the ability to reduce a stimulated cytokine production and may also protect against cellular oxidative stress. Results of the present study highlight the potential of BSG phenolic extracts to act as functional food ingredients, providing an alternative use and improving the value of this brewing industry co-product.

Antioxidant and pro-apoptotic effects of marine-derived, multi-mineral aquamin supplemented with a pine bark extract, Enzogenol, and a green tea extract, Sunphenon

A high dietary intake of polyphenols has been associated with a decreased risk of cardiovascular disease and cancer, attributed in part to their antioxidant activity and pro-apoptotic effects. Aquamin is a multi-mineral algal extract that enhances bone mineralization, relieves osteoarthritis, and aids digestion; however, Aquamin has not demonstrated antioxidant activity. In the present study, Aquamin was supplemented with 8% Enzogenol, a pine bark extract with a high phenolic content, and 2% Sunphenon, a green tea extract that also has a high phenolic content to produce a mixed product (A:E:S). The antioxidant activity of A:E:S was compared with that of its constituent compounds and also with catechin and epigallocatechin by measuring total phenol content, ferric-reducing antioxidant potential, and 2,2-diphenyl-2-picrylhydrazyl hydrate. The cytotoxic and apoptotic effects of the compounds were also measured in the U937, human monocytic blood cell line. A:E:S demonstrated an antioxidant activity that was equal to that of the compounds used in its preparation. Aquamin was not cytotoxic in the U937 cell line; however, A:E:S was cytotoxic and the primary mechanism of cell death was apoptosis. The biological effects of Aquamin were enhanced by supplementation with Enzogenol and Sunphenon to include antioxidant effects and the ability to induce apoptosis in U937 cells.

Changes in total and individual crocetin esters upon in vitro gastrointestinal digestion of saffron aqueous extracts

Changes that may be expected in crocetin esters (crocins) upon digestion were examined in saffron aqueous extracts for the first time. Chemical characterization of total and individual crocins and other bioactive compounds was achieved by UV-vis spectrophotometry, RP-HPLC-DAD, and LC-ESI-MS. Antioxidant activity was evaluated using in vitro assays and the comet assay. The observed loss for both total and trans-crocins was higher in saffron (∼50%) than in gardenia extracts (∼30%), which were also examined for comparison. Loss was lower than that reported for hydrophobic carotenoids. cis-Isomers were less affected, leading to the hypothesis that trans/cis isomerization may occur in parallel to degradation reactions. Monitoring changes in the extracts at oral, gastric, or intestinal phases, separately, verified this view pointing out the critical effect of pH, temperature, and duration of process but not of digestive enzymes. No isomerization and less degradation (<20% loss) was evidenced when pure trans-crocetin (di-β-D-gentiobiosyl) ester was subjected to gastric or intestinal conditions.

The hydroxycinnamic acid content of barley and brewers' spent grain (BSG) and the potential to incorporate phenolic extracts of BSG as antioxidants into fruit beverages

The hydroxycinnamic acid (HA) content of starting barley for brewers' spent grains (BSG), whole BSG and phenolic extracts from BSG was measured using high performance liquid chromatography (HPLC) and correlated with antioxidant potential. The effect of BSG phenolic extracts on antioxidant activity of fruit beverages was also assessed (using the total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays). The concentration of HA present in barley extract and BSG was in the order of ferulic acid (FA), p-coumaric acid (p-CA) derivatives, FA derivatives, p-CA, caffeic acid (CA) and CA derivatives. Results suggested that brewing and roasting decreased the HA content. Antioxidant activity was significantly (P<0.05) correlated with caffeic acid (R(2)=0.8309) and total HA (R(2)=0.3942) concentrations. Addition of extracts to fruit beverages resulted in a significant (P<0.05) increase in antioxidant activity of cranberry juice, measured by the FRAP assay. In vitro digestion significantly (P<0.05) reduced TPC, DPPH and FRAP activity of the fruit beverages.

Assessment of the ability of seaweed extracts to protect against hydrogen peroxide and tert-butyl hydroperoxide induced cellular damage in Caco-2 cells

The ability of brown seaweed extracts, Ascophyllum nodosum, Laminaria hyperborea, Pelvetia canaliculata, Fucus vesiculosus and Fucus serratus to protect against tert-butyl hydroperoxide (tert-BOOH) induced stress in Caco-2 cells was investigated. Oxidative stress was determined by measuring alteration in the enzymatic activity of catalase (CAT) and superoxide dismutases (SOD) and cellular levels of glutathione (GSH). L. hyperborea, P. canaliculata and F. serratus significantly protected against tert-BOOH induced SOD reduction but did not protect against the reduction in CAT activity or the increased cellular levels of GSH. The ability of F. serratus and F. vesiculosus to protect against H(2)O(2) and tert-BOOH induced DNA damage was also assessed. The DNA protective effects of the two seaweed extracts was compared to those of three metal chelators; deferoxamine mesylate (DFO), 1,10-phenanthroline (o-phen) and 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (BAPTA-AM). F. serratus and F. vesiculosus significantly protected (P<0.05) against H(2)O(2) (50 μM) induced DNA damage but not tert-BOOH induced damage.

Cytotoxic and apoptotic effects of the oxidized derivatives of stigmasterol in the U937 human monocytic cell line

Dietary exposure to phytosterols has increased in recent years due to the incorporation of these compounds into cholesterol-lowering products. Previous studies have investigated the cytotoxic effects of the oxidized derivatives of β-sitosterol and determined that phytosterol oxidation products (POP) have a similar but less potent toxicity compared to their cholesterol equivalents. In the present study, the cytotoxicity of the oxidized derivatives of stigmasterol were investigated in the U937 cell line. The stigmasta-5,22-diene-3β,7β-diol (7β-OH), 5,6-epoxystigmasta-22,23-diol (epoxydiol), 5,6,22,23-diepoxystigmastane (diepoxide), and (22R,23R)-stigmast-5-ene-3β,22,23-triol (22R,23R-triol) derivatives were identified as the most cytotoxic, and the mode of cell death was identified as apoptosis in cells incubated with 7β-OH, epoxydiol, and diepoxide stigmasterol. The antioxidants α-tocopherol, γ-tocopherol, and β-carotene did not protect against apoptosis induced by 7β-OH and diepoxide stigmasterol; however, α-tocopherol was found to protect against epoxydiol-induced apoptosis. The cellular antioxidant, glutathione, was depleted and the apoptotic protein, Bcl-2, was down-regulated by the stigmasterol oxides identified as apoptotic.

Death-signaling pathways in human myeloid cells by oxLDL and its cytotoxic components 7beta-hydroxycholesterol and cholesterol-5beta,6beta-epoxide

Oxidized low-density lipoprotein contains many potentially proatherogenic molecules, including oxysterols, which have been shown to induce apoptosis in various cell lines. The aim of this study was to investigate the pathway of apoptosis induced by oxidized low-density lipoprotein and the oxysterols, 7beta-hydroxycholesterol and cholesterol-5beta,6beta-epoxide, in two human monocytic cell lines. The HL-60 cells appeared to be more sensitive to oxidized low-density lipoprotein than U937 cells, whereas the isolated oxysterols were more potent inducers of apoptosis in the U937 cells. Caspase-2 inhibition decreased the number of viable cells in oxidized low-density lipoprotein-treated samples; however, it protected against cholesterol-5beta,6beta-epoxide-induced cell death. Western blot analysis was utilized to examine the effect of caspase-2 inhibition on the expression of the antiapoptotic protein Bcl-2. Pretreatment with the inhibitor protected against the decrease in Bcl-2 expression in oxidized low-density lipoprotein- and 7beta-hydroxycholesterol-treated U937 cells. In HL-60 cells, Bcl-2 was overexpressed in oxidized low-density lipoprotein-treated cells, but in the presence of the inhibitor Bcl-2 expression was returned to control levels. Depleted ATP concentrations in the cells suggest that both apoptosis and necrosis may have occurred simultaneously. Our results highlight differences in the signaling pathways induced by oxidized low-density lipoprotein, 7beta-hydroxycholesterol, and cholesterol-5beta,6beta-epoxide in U937 and HL-60 cells.

The role of the mitochondria in apoptosis induced by 7β-hydroxycholesterol and cholesterol-5β,6β-epoxide

Oxysterols are oxygenated derivatives of cholesterol that may be formed endogenously or absorbed from the diet. Significant amounts of oxysterols have frequently been identified in foods of animal origin, in particular highly processed foods. To date, oxysterols have been shown to possess diverse biological activities; however, recent attention has focused on their potential role in the development of atherosclerosis. Oxysterols have been reported to induce apoptosis in cells of the arterial wall, a primary process in the development of atheroma. The aim of the present study was to identify the role of the mitochondria in the apoptotic pathways induced by the oxysterols 7β-hydroxycholesterol (7β-OH) and cholesterol-5β,6β-epoxide (β-epoxide) in U937 cells. To this end, we investigated the effects of these oxysterols on mitochondrial membrane potential, caspase-8 activity, the mitochondrial permeability transition pore and cytochromecrelease. 7β-OH-induced apoptosis was associated with a loss in mitochondrial membrane potential after 2 h, accompanied by cytochromecrelease from the mitochondria into the cytosol after 16 h. Pre-treatment with a range of inhibitors of the mitochondrial permeability transition pore protected against 7β-OH-induced cell death. In contrast, β-epoxide induced a slight increase in caspase-8 activity but had no effect on mitochondrial membrane potential or cytochromecrelease. The present results confirm that 7β-OH-induced apoptosis occurs via the mitochondrial pathway and highlights differences in the apoptotic pathways induced by 7β-OH and β-epoxide in U937 cells.

Evaluation of the antioxidant potential of grape seed and bearberry extracts in raw and cooked pork

The effect of grape seed extract (GSE) and bearberry (BB), on lipid oxidation (TBARS, mg malondialdehyde (MDA)/kg muscle), colour (CIE 'a' redness value), pH, microbial status (log(10)CFU colony forming units/g pork) and sensorial properties of cooked pork patties was investigated. GSE (0-1000μg/g muscle) and BB (0-1000μg/g muscle) were added to raw pork (M. longissimus dorsi) patties which were stored in modified atmosphere packs (MAP) (75% O(2):25% CO(2)) for up to 12 days at 4°C. Cooked pork patties were stored in MAP (70% N(2):30% CO(2)) for up to 4 days at 4°C. Mesophilic plate counts and pork pH were unaffected by GSE and BB. GSE and BB addition decreased (P<0.05) lipid oxidation (TBARS) in raw pork patties on days 9 and 12 of storage, relative to controls. Antioxidant activity of GSE and BB was observed in cooked pork patties demonstrating the thermal stability of GSE and BB. The 'a' redness values of raw and cooked pork patties marginally increased with increasing GSE concentration. The sensory properties of cooked pork patties were unaffected by GSE and BB addition. Results obtained demonstrate the potential for using health promoting nutraceuticals in meat and meat products.

Modulatory Effects of Resveratrol, Citroflavan-3-ol, and Plant-Derived Extracts on Oxidative Stress in U937 Cells

Phytochemicals and plant extracts, present in fruit, vegetables, plants, herbs, and beverages, have been shown to have antioxidant potential that may modulate the etiology of certain chronic diseases. The objective of the present study was to determine the concentration of compound that inhibited cell growth by 50% (IC(50)) of a range of phytochemicals and plant extracts and to investigate their antioxidant and genoprotective effects under conditions of oxidative stress in U937 cells. Two phytochemicals-resveratrol and citroflavan-3-ol-and four plant extracts-grapeseed polyphenols, olive leaf extract, bearberry, and Echinacea purpurea-were examined. Viability was assessed by the fluorescein diacetate/ethidium bromide assay. The IC(50) was calculated. To examine their antioxidant and genoprotective effects, U937 cells were pretreated with the test compounds at levels below the IC(50) and then exposed to oxidants: 0.5 microM etoposide or 100 microM hydrogen peroxide (H(2)O(2)) or 400 microM tert-butylhydroperoxide (tBOOH). Cellular reduced glutathione levels were measured as an indicator of oxidative stress. DNA damage was assessed by the alkaline single-cell gel electrophoresis assay or comet assay. Resveratrol demonstrated the highest IC50 value of 13.7 microg/mL, with Echinacea the lowest at 9,400 microg/mL. Etoposide-induced oxidative stress was strongly reduced by olive leaf extract and bearberry. Grapeseed polyphenols and bearberry strongly protected against H2O2- and tBOOH-induced DNA damage. In conclusion, these results provide evidence that non-nutrient dietary constituents may act as significant bioactive compounds and that plant extracts, such as bearberry, grapeseed polyphenols, and olive leaf extract, strongly protect against oxidative stress.

Comparison of the apoptotic processes induced by the oxysterols 7β-hydroxycholesterol and cholesterol-5β,6β-epoxide

Oxysterols have been shown to induce apoptosis in a variety of cell lines. The mechanism of oxysterol-induced apoptosis is mainly known at the post-mitochondrial level. The aim of the present study was to compare the pathway of apoptosis induced by the oxysterols 7beta-hydroxycholesterol (7beta-OH) and cholesterol-5beta,6beta-epoxide (beta-epoxide) in U937 cells. To this end, we employed a range of inhibitors of apoptosis; a broad-spectrum caspase inhibitor, a specific caspase-3 inhibitor and an inhibitor of cytochrome c release and the antioxidants; trolox, ebselen and resveratrol. The three inhibitors of apoptosis prevented cell death induced by 7beta-OH; however, in beta-epoxide-treated cells, the inhibitor of cytochrome c release did not protect against apoptosis. The cellular antioxidant glutathione was depleted in 7beta-OH-treated cells but not in cells incubated with beta-epoxide. Trolox, a water-soluble synthetic analogue of alpha-tocopherol, prevented 7beta-OH-induced apoptosis but did not protect against cell death induced by beta-epoxide. Ebselen and resveratrol did not protect U937 cells against apoptosis induced by either 7beta-OH or beta-epoxide. Our results suggest that differences occur in the pathways of apoptosis induced by 7beta-OH and beta-epoxide in U937 cells.

Phytosterols: lack of cytotoxicity but interference with beta-carotene uptake in Caco-2 cells in culture

Ingestion of phytosterols has been shown to reduce plasma cholesterol in both animals and humans. The esterified forms of phytosterols are increasingly being incorporated into margarine and fat spreads, which are then marketed as functional foods. The aim was to assess the cytotoxicity and uptake of four phytosterols, beta-sitosterol, campesterol, stigmasterol and stigmastanol, in human intestinal cells in culture. Another aim was to determine if phytosterols would interfere with alpha-tocopherol or beta-carotene uptake by these cells. Human adenocarcinoma Caco-2 cells were supplemented for 24 h with increasing concentrations (0-12.5 microM) of each phytosterol. Cytotoxicity was assessed by neutral red uptake (NRU), lactate dehydrogenase release (LDH) and fluorescein diacetate/ethidium bromide (FDA/EtBr) assays. The phytosterols had no significant effects on Caco-2 cell viability assessed using LDH and FDA/EtBr assays. The highest concentrations of beta-sitosterol and campesterol tested (12.5 microM) resulted in decreased cell viability assessed using the NRU assay. All phytosterols were taken up by Caco-2 cells in culture. The results demonstrate a reduction in the uptake of beta-carotene when Caco-2 cells were supplemented with 20 microM beta-sitosterol. beta-Sitosterol did not interfere with alpha-tocopherol uptake by the cells. In conclusion, Caco-2 cells are a useful model system to study potential interactive effects of phytosterols with fat-soluble dietary components.

Generation of an oxidative stress precedes caspase activation during 7?-hydroxycholesterol-induced apoptosis in U937 cells

The oxysterol 7beta-hydroxycholesterol (7beta-OH) has been shown to induce apoptosis in a number of cell lines. Though not fully elucidated, the mechanism through which this oxysterol induces cell death is thought to involve the generation of an oxidative stress leading to perturbation of the mitochondrion and release of cytochrome c into the cytosol. Cytochrome c together with Apaf-1 causes activation of the initiator caspase, caspase-9, which in turn activates caspase-3 ultimately leading to the degradation of poly(ADP-ribose) polymerase (PARP). The objective of the present study was to investigate the signalling pathway in 7beta-OH-induced apoptosis in U937 cells, a human monocytic blood cell line known to undergo apoptosis upon treatment with 7beta-OH, over a time course of 48 h. Apoptosis was evident after 24 h incubation. Glutathione levels were decreased after 6 h and this was coupled with an increase in SOD activity. Through western blot analysis we examined expression of caspase-3, -8, and -9 and cleavage of the caspase-3 substrate PARP. The sequence proceeded with activation of caspase-9 after 9 h, caspase-3 at the 12 h timepoint, and cleavage of PARP after 24 h treatment with 7beta-OH. Caspase-8 did not appear to play a major role in this particular apoptotic pathway.

Toxicity of cholesterol oxidation products to Caco-2 and HepG2 cells: modulatory effects of alpha- and gamma-tocopherol

Cholesterol can be oxidized to form a variety of cholesterol oxidation products also known as oxysterols. The aims of the present study were to compare the cytotoxic effects of four oxysterols, namely 25-hydroxycholesterol (25-OHC), 7beta-hydroxycholesterol (7beta-OHC), cholesterol-5beta,6beta-epoxide (beta-epox) and cholesterol-5alpha,6alpha-epoxide (alpha-epox), in two human cell culture models. Further, the ability of 10 and 100 micro m alpha- and gamma-tocopherol (alpha-TOC and gamma-TOC, respectively) to protect against oxysterol-induced cytotoxicity was also assessed. Human colonic adenocarcinoma Caco-2 and human hepatoma HepG2 cells were supplemented with increasing concentrations of 25-OHC, 7beta-OHC, beta-epox and alpha-epox (0-25 micro g ml(-1)) for 24, 48 or 96 h. Following 24-h and 48-h exposure, test media were replaced with normal growth media and the cells were maintained for 72 and 48 h, respectively. The 96-h exposure represented a constant challenge to the cells. Cytotoxicity was assessed using the neutral red uptake assay. The concentration of compound that inhibited cell viability by 50% (ic(50) value) was calculated. All four oxysterols investigated induced the greatest cytotoxic effects following 96 h of exposure. 25-Hydroxycholesterol exhibited the greatest cytotoxicity in both cell lines. Both beta-epox and alpha-epox were more toxic to HepG2 cells than to Caco-2 cells after the 48-h exposure. Pretreatment of cells with either alpha- or gamma-TOC did not protect against oxysterol-induced cytotoxicity. The caco-2 cells treated with the high concentration (100 micro m) of gamma-TOC were found to be more susceptible to oxysterol-induced toxicity under the conditions employed in this study.

Characteristics of 7 beta-hydroxycholesterol-induced cell death in a human monocytic blood cell line, U937, and a human hepatoma cell line, HepG2

Oxysterols have been shown in a number of cell lines to induce apoptosis by a mechanism as yet unclear. The induction of apoptosis by certain agents has been associated with the generation of oxidative stress and the depletion of the endogenous antioxidant, glutathione, which may result in cytochrome c release and caspase activation. The aim of the present study was to determine whether 7 beta-hydroxycholesterol (7 beta-OH) alters glutathione levels or the activities of catalase, superoxide dismutase (SOD) or caspase-3 in association with cell death in either the U937 or the HepG2 cell lines. 7 beta-OH, which induced significant apoptosis at 12 h in the U937 cell line, was shown to cause a significant decrease in glutathione levels and an increase in the activity of SOD at this time point. An increase in caspase-3 activity was also observed in the U937 cell line following a 24-h incubation with 7 beta-OH. Glutathione concentration, SOD activity and caspase-3 activity were unchanged in the HepG2 cell line, which underwent necrosis following incubation with 7 beta-OH. The activity of the enzyme catalase remained unchanged in both cell lines. These results provide evidence that the generation of an oxidative stress may be a significant event occurring during 7 beta-OH-induced apoptosis.

Comparative study of the cytotoxicity and apoptosis-inducing potential of commonly occurring oxysterols

The cytotoxicity of the oxysterols 25-hydroxycholesterol, 7beta-hydroxycholesterol, cholesterol-5alpha,6alphaepoxide, cholesterol-5beta,6beta-epoxide, 19-hydroxycholesterol and 7-ketocholesterol was examined in U937 cells, a human monocytic blood cell line. 7beta-Hydroxycholesterol, cholesterol-5beta,6beta-epoxide, and 7-ketocholesterol, at 30 micromol/L concentration, were found to be cytotoxic to this cell line and the mode of cell death was by apoptosis. 25-Hydroxycholesterol, cholesterol-5alpha,6beta-epoxide and 19-hydroxycholesterol (30 micromol/L) did not induce apoptosis in this cell line. Since it has been suggested that the generation of an oxidative stress may occur in the early stages of the apoptotic process, the glutathione concentration and the activity of superoxide dismutase were also measured in the oxysterol-treated cells. 7beta-Hydroxycholesterol was shown to increase the superoxide dismutase activity and decrease the glutathione concentration. However, cholesterol-5beta,6beta-epoxide and 7-ketocholesterol, which were also shown to induce apoptosis, did not affect the glutathione concentration or the superoxide dismutase activity in the U937 cells. Therefore, oxysterol-induced apoptosis may not be dependent on the generation of an oxidative stress.

Limitations of the single-cell gel electrophoresis assay to monitor apoptosis in U937 and HepG2 cells exposed to 7beta-hydroxycholesterol

The single-cell gel electrophoresis (comet) assay is a method which allows the detection of DNA strand breaks in individual cells. It has been suggested that the single cell gel electrophoresis assay, as an index of DNA fragmentation during cell death, may be applied to monitor apoptosis. The aim of the present study was to determine if the pattern of DNA fragmentation determined by the single cell gel electrophoresis assay can be used to discriminate between the mode of cell death in two cell lines (U937, a human monocytic blood cell line and HepG2, a human hepatocarcinoma cell line) which were treated with 30 microM 7beta-hydroxycholesterol (7betaOHC) over a 48 hr period. The single cell gel electrophoresis assay was compared with more established methods for the determination of apoptosis such as morphological examination, flow cytometry and DNA laddering. The percentage of maximally damaged nuclei as measured by the single cell gel electrophoresis assay was found to be similar at 48 hr in both U937 and HepG2 cells when treated with 7betaOHC. However, morphological examination, flow cytometry and DNA laddering techniques showed that 7betaOHC induced apoptosis in U937 cells but not in HepG2 cells. Thus, although the alkaline single cell gel electrophoresis assay detected DNA strand breaks occurring during cell death, these breaks were observed only when the process was fairly well advanced and a major part of the cells had lost membrane permeability. Therefore the present report demonstrates that the single cell gel electrophoresis assay, used in isolation, cannot accurately be used to distinguish between the mode of cell death induced by 7betaOHC in U937 cells (apoptosis), or HepG2 cells (cell lysis).

Cytotoxicity, genotoxicity and oxidative reactions in cell-culture models: modulatory effects of phytochemicals

Much research effort has focused on the identification of phytochemicals in fruit and vegetables which exert beneficial effects. Our research examines modulatory effects of phytochemicals on cytotoxicity, genotoxicity and oxidative reactions in cell systems. Two examples of our studies are discussed. First, the potential beneficial effects of flavonoids are demonstrated. Flavonoids are reported to exhibit a wide variety of biological effects, including antioxidant and free-radical-scavenging activities. The aim of the study was to determine if flavonoids could protect against H2O2-induced DNA damage, as measured by the comet assay, in Caco-2 and HepG2 cells. Both cell lines were supplemented with increasing concentrations of myricetin, quercetin and rutin for 24 h followed by exposure to H2O2 (50 microM) for 30 min. Exposure to H2O2 for 30 min at 37 degrees C resulted in significant DNA damage and pre-incubation with the flavonoids before H2O2 exposure significantly (P <0.05) protected Caco-2 and HepG2 cells against H2O2-induced DNA damage. Secondly, we illustrate the use of cellular models to study oxysterol-induced toxicity. Oxysterols are generated during the cooking and processing of foods and may be produced endogenously by the oxidation of membrane lipids. Recent findings suggest that oxysterols may modulate cytotoxicity by exerting effects on the induction of apoptosis. 7beta-Hydroxycholesterol (7beta-OHC) and 25-hydroxycholesterol, both of which are commonly found in foods, were investigated for their abilities to induce apoptosis in a human monocytic blood cell line, U937, and in the human hepatoma cell line, HepG2 cells. U937 and HepG2 cells were incubated for up to 48 h with 30 microM oxysterol. 7beta-OHC induced apoptosis in U937 cells as measured by non-random DNA fragmentation, condensed and fragmented nuclei, and the generation of hypodiploid cells. In contrast, oxysterols may induce cell death by a different mechanism in the hepatoma cells, possibly by necrosis.

Oxysterol-induced cell death in U937 and HepG2 cells at reduced and normal serum concentrations

BACKGROUND AND AIMS

Cholesterol oxidation products (oxysterols) are commonly found in foods of animal origin and are also produced endogenously in the body. Oxysterols are cytotoxic to certain cell lines and in some cases have been shown to induce apoptosis. The aim of this study was to investigate the effects of 7beta-hydroxy-cholesterol (7beta-OHC) and 25-hydroxycholesterol (25-OHC) on cytotoxicity and induction of apoptosis in U937 and HepG2 cells, treated in media containing either 2.5% foetal calf serum (FCS) or 10% FCS to examine the effect of increasing the cholesterol level.

METHODS

The cells were incubated for 24 and 48 h with 30 microM oxysterol. Viability was assessed by fluorescein diacetate/ethidium bromide staining and cell proliferation was determined by haemocytometer counting. Apoptosis was monitored by detection of DNA fragments (laddering) in 1.5% agarose gels. Cells with condensed or fragmented nuclei were identified by Hoechst 33342 staining. The percentage of cells with sub-G1 levels of DNA was measured by flow cytometry.

RESULTS

Treatment of U937 cells with 7beta-OHC, in contrast to 25-OHC, resulted in a decrease in cell viability and proliferation at 24 and 48 h (P <.01). 25-OHC and 7beta-OHC were both equally cytotoxic to the HepG2 cell line. 7beta-OHC induced DNA laddering and an increase in the percentage of condensed or fragmented nuclei at both time points and at both serum concentrations in the U937 cell line. 25-OHC induced faint laddering in the U937 cells after 48 h in reduced serum media and resulted in a small increase in percentage condensed or fragmented nuclei which was independent of time of oxysterol exposure and serum concentration. The percentage of condensed or fragmented nuclei was low in the HepG2 cell line and no laddering was observed under any of the conditions studied. Flow cytometric analysis showed that only 7beta-OHC treated U937 cells had an increased level of hypodiploid cells.

CONCLUSION

Both oxysterols appear to be equally cytotoxic to the HepG2 cell line. In U937 cells, 25-OHC is much less cytotoxic than 7beta-OHC. In addition, we have shown that 7beta-OHC induces apoptosis in U937 cells. 10% FCS displays a protective effect on cytotoxicity (as well as on 7beta-OHC induced apoptosis in U937 cells), although the data did not reach statistical significance.