Lycopene attenuates arachidonic acid toxicity in HepG2 cells overexpressing CYP2E1

Biological properties of carotenoids extracted from Halobacterium halobium isolated from a Tunisian solar saltern

Background

Bioactive molecules have received increasing attention due to their nutraceutical attributes and anticancer, antioxidant, antiproliferative and apoptosis-inducing properties. This study aimed to investigate the biological properties of carotenoids extracted from Archaea.

Methods

Halophilic Archaea strains were isolated from the brine of a local crystallizer pond (TS7) of a solar saltern at Sfax, Tunisia. The most carotenoid-producing strain (M8) was investigated on heptoma cell line (HepG2), and its viability was assessed by the MTT-test. The cells were incubated with different sub-lethal extract rates, with carotenoid concentrations ranging from 0.2 to 1.5 μM. Antioxidant activity was evaluated through exposing the cells to sub-lethal extract concentrations for 24 hours and then to oxidative stress induced by 60 μM arachidonic acid and 50 μM H₂O₂.

Results

Compared to non-treated cells, bacterial carotenoid extracts inhibited HepG2 cell viability (50%). A time and dose effect was observed, with cell viability undergoing a significant (P < 0.05) decrease with extract concentration. After exposure to oxidative stress, control cells underwent a significant (P < 0.05) decrease in viability as compared to the non-treated cells.

Conclusions

The bacterial extracts under investigation were noted to exhibit the strongest free radical scavenging activity with high carotenoid concentrations. The carotenoid extract also showed significant antiproliferative activity against HepG2 human cancer cell lines.

Cytochrome P450 2E1: its clinical aspects and a brief perspective on the current research scenario

Research on Cytochrome P450 2E1 (CYP2E1), a key enzyme in alcohol metabolism has been very well documented in literature. Besides the involvement of CYP2E1 in alcohol metabolism as illustrated through the studies discussed in the chapter, recent studies have thrown light on several other aspects of CYP2E1 i.e. its extrahepatic expression, its involvement in several diseases and pathophysiological conditions; and CYP2E1 mediated carcinogenesis and modulation of drug efficacy. Studies involving these interesting facets of CYP2E1 have been discussed in the chapter focusing on the recent observations or ongoing studies illustrating the crucial role of CYP2E1 in disease development and drug metabolism.

Cell-based assay to quantify the antioxidant effect of food-derived carotenoids enriched in postprandial human chylomicrons

We developed a new method to evaluate the antioxidant effect of food products in a biological system. The antioxidant status of HepG2 cells was quantified after incubation with postprandial human chylomicrons after the intake of vegetable products. Three subjects consumed in a meal a vegetable soup containing 8.4 mg of β-carotene and 9 mg of lycopene. After 5 h, the subjects consumed a second meal without carotenoids. Blood samples were collected at basal time and every hour for 9 h. Chylomicrons were isolated from serum samples and used for both carotenoid quantification and HepG2 stimulation. Carotenoid in chylomicrons followed an inter-individual and bimodal carotenoid response. We demonstrated the antioxidant effect of postprandial chylomicrons in HepG2 at the time of maximum carotenoid concentration of chylomicrons with respect to basal time. This cell-based assay seems to be a useful method to evaluate the antioxidant effect of fruit and vegetable products in a biological system.

Synergic effects of α-tocopherol and β-carotene on tert-butylhydroperoxide-induced HepG2 cell injury

Oxidative stress produced by the dietary or chemical substrates is one of the major causes of liver cell injury. In this study, we compared the effects of two dietary antioxidants, α-tocopherol (α-T) and β-carotene (β-C) against tert-butyl hydroperxide (tBHP)-induced oxidative stress in human hepatoma HepG2 cells. Cell proliferation, lipid peroxidation (LPO), cellular lactate dehydrogenase (LDH), [3H]-aflatoxin B1(AFB1)-DNA adduct formation, and cytochrome P450 2E1 (CYP2E1) expression were determined after antioxidants were added to the tBHP-stressed cells. When compared to an ethanol-based control, all biomarkers for the cell damage were significantly increased by treatments. Treatments of β-C or the combination of two antioxidants at 50 ppm for 48 h enhanced cell proliferation ( P < 0.05) compared to tBHP control. The antioxidative and cytoprotective actions of α-T and β-C, alone or in combination, were associated with modulation of microsomal CYP2E1 expression, corresponding to the regulation of LPO production ( P < 0.0001). Our results indicate that α-T and β-C may contribute differently to protection of cellular membrane disruption in CYP2E1-expressing HepG2 cells. Moreover, the combination of α-T and β-C appears to impel the greater protection of pathogenic processes of oxidative stress in liver.

Effects of herbal products and their constituents on human cytochrome P450(2E1) activity

Ethanolic extracts from fresh Echinacea purpurea and Spilanthes acmella and dried Hydrastis canadensis were examined with regard to their ability to inhibit cytochrome P450(2E1) mediated oxidation of p-nitrophenol in vitro. In addition, individual constituents of these extracts, including alkylamides from E. purpurea and S. acmella, caffeic acid derivatives from E. purpurea, and several of the major alkaloids from H. canadensis, were tested for inhibition using the same assay. H. canadensis (goldenseal) was a strong inhibitor of the P450(2E1), and the inhibition appeared to be related to the presence of the alkaloids berberine, hydrastine and canadine in the extract. These compounds inhibited 2E1 with K(I) values ranging from 2.8 microM for hydrastine to 18 microM for berberine. The alkylamides present in E. purpurea and S. acmella also showed significant inhibition at concentrations as low as 25 microM, whereas the caffeic acid derivatives had no effect. Commercial green tea preparations, along with four of the individual tea catechins, were also examined and were found to have no effect on the activity of P450(2E1).

Modulation of aflatoxin toxicity and biomarkers by lycopene in F344 rats

Modulation by lycopene of aflatoxin B(1) (AFB(1))-induced toxic effects, metabolism, and metabolic activations was studied in young F344 rats. Animals were pretreated orally with either corn oil (control group) or lycopene [100 mg/kg body weight (b.w.), intervention group] 5 days/week for 2 weeks. Control animals were then treated daily with AFB(1) (250 microg/kg b.w) alone. Intervention animals were administered lycopene (100 mg/kg b.w.) at 1 h following a daily treatment with AFB(1) (250 mug/kg b.w.). Pretreatment and intervention with lycopene significantly reduced the toxic effect caused by AFB(1) and greatly modulated AFB(1) metabolism and metabolic activation. Urinary excretion of AFB(1) phase 1 metabolites, AFM(1), AFQ(1), and AFP(1), was significantly decreased in lycopene-treated animals. Formation of serum AFB(1)-albumin adducts was also significantly reduced. The rate of reduction was from approximately 30% on day 1 (p<0.05) to 67.7% on day 15 (p<0.001). Lycopene intervention also significantly reduced formation of AFB(1)-DNA adducts in liver compared to control animals, with the highest reduction (52.7%) occurring on day 3 (p<0.05). Levels of AFB(1)-N(7)-guanine excreted in urine were also significantly decreased. Urinary excretion of the phase 2 detoxification metabolite, AFB(1)-mecapturic acid, was significantly increased in lycopene-intervened animals. AFB(1)-induced urinary excretion of 8-hydroxydeoxyguanosine was also reduced to 50% on day 7 after lycopene intervention. Collectively, these results suggest that inhibition of phase 1 metabolism and metabolic activation, as well as induction of phase 2 detoxification enzyme activity are the potential mechanisms for the chemopreventive effects of lycopene.

DLPC ATTENUATES ALCOHOL-INDUCED CYTOTOXICITY IN HEPG2 CELLS EXPRESSING CYP2E1

AIMS

Alcoholic liver injury was shown to result largely from oxidative stress generated by ethanol metabolism via cytochrome P4502E1 (CYP2E1). Our aim was to determine whether this could be overcome by using dilinoleoylphosphatidylcholine (DLPC), an innocuous antioxidant extracted from soybeans.

METHODS

To address this question, we determined whether DLPC protects against alcohol-induced cytotoxicity in HepG2 cells expressing CYP2E1. A HepG2 subclone (2E1) expressing CYP2E1 and a control subclone (Neo) were exposed for 2 h to DLPC (10 microM), and then 100 mM ethanol was added for 5 days.

RESULTS

Ethanol significantly decreased cell viability in the 2E1 cells and increased apoptosis. These alterations were attenuated by DLPC with the most significant effects in the 2E1 cells. This was accompanied by a reduction of the ethanol-induced oxidative stress, including diminished hydrogen peroxide production in the 2E1, but not in the Neo cells. The mitochondrial membrane potential was significantly diminished by ethanol in both cells. It was also improved after adding DLPC, but only in the 2E1 cells. In these cells, mitochondrial glutathione (GSH) was also partially restored by DLPC, which significantly inhibited the CYP2E1 induction by ethanol.

CONCLUSION

DLPC opposes the cytotoxicity induced by alcohol in HepG2 cells expressing CYP2E1, a protective action due, at least in part, to an attenuation of the alcohol-induced oxidative stress and the alteration in the mitochondrial membrane potential. On account of these beneficial effects of DLPC and its innocuity, it is now germane to assess its therapeutic action in alcoholics.

The role of carotenoids in the prevention of human pathologies

Reactive oxygen species (ROS) and oxidative damage to biomolecules have been postulated to be involved in the causation and progression of several chronic diseases, including cancer and cardiovascular diseases, the two major causes of morbidity and mortality in Western world. Consequently dietary antioxidants, which inactivate ROS and provide protection from oxidative damage are being considered as important preventive strategic molecules. Carotenoids have been implicated as important dietary nutrients having antioxidant potential, being involved in the scavenging of two of the ROS, singlet molecular oxygen (1O2) and peroxyl radicals generated in the process of lipid peroxidation. Carotenoids are lipophilic molecules which tend to accumulate in lipophilic compartments like membranes or lipoproteins. Chronic ethanol consumption significantly increases hydrogen peroxide and decreases mitochondrial glutathione (GSH) in cells overexpressing CYP2E1. The depletion of mitochondrial GSH and the rise of hydrogen peroxide are responsible for the ethanol-induced apoptosis. Increased intake of lycopene, a major carotenoid in tomatoes, consumed as the all-trans-isomer attenuates alcohol induced apoptosis in 2E1 cells and reduces risk of prostate, lung and digestive cancers. Cancer-preventive activities of carotenoids have been associated as well as with their antioxidant properties and the induction and stimulation of intercellular communication via gap junctions which play a role in the regulation of cell growth, differentiation and apoptosis. Gap junctional communication between cells which may be a basis for protection against cancer development is independent of the antioxidant property.

Use of a human-derived liver cell line for the detection of cytoprotective, antigenotoxic and cogenotoxic agents

In this paper, we reviewed the data on the use of HepG2 cells to detect cytoprotective, antigenotoxic and cogenotoxic agents. Owing to their intact and inducible phase I and phase II enzymes, HepG2 cells are able to activate and detoxify xenobiotics and therefore reflect the metabolism of xenobiotics in the human body better than other metabolically incompetent cells used in conventional in vitro assays. Several dietary and non-dietary agents were found to be protective against different groups of cytotoxic and DNA-damaging xenobiotics in HepG2 cells and the mechanism of protection includes scavenging of electrophiles, reactive oxygen species and peroxides, inhibition of phase I activating enzymes, induction of phase II detoxifying enzymes and interactions with DNA-repair and/or replication processes. Additionally, certain non-mutagenic substances were found to enhance the effect of genotoxic agents in HepG2 cells by increasing the metabolic activation of the latter. In conclusion, HepG2 cells are of great relevance to detect cytotoxic and genotoxic substances and by extension cytoprotective, antigenotoxic and cogenotoxic agents.

Lycopene attenuates alcoholic apoptosis in HepG2 cells expressing CYP2E1

To test the hypothesis that ethanol-induced hepatic apoptosis is secondary to the oxidative stress generated by cytochrome P4502E1 (CYP2E1), we assessed the effects of the carotenoid lycopene, a potent antioxidant extracted from tomatoes, on oxidative stress and apoptosis in HepG2 cells overexpressing CYP2E1 (2E1 cells). These were exposed for 5 days to 100mM ethanol and 10 microM lycopene or an equal volume of placebo (vehicle). Ethanol significantly increased apoptosis measured by flow cytometry and by TUNEL assay. This was accompanied by an ethanol-induced oxidative stress: hydrogen peroxide production was significantly increased and mitochondrial GSH was strikingly decreased. Both were restored by lycopene, with a significant decrease in apoptosis. The placebo had no protective effect. In conclusion, Lycopene opposes the ethanol-induced oxidative stress and apoptosis in 2E1 cells. The parallelism between these effects suggests a causal link. Furthermore, these beneficial effects and the innocuity of lycopene now justify an in vivo trial.