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Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111
* To whom correspondence should be addressed. E-mail: xiang-dong.wang{at}tufts.edu.
| ABSTRACT |
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(TNF
) and the incidence of hepatic inflammatory foci. Both plasma and hepatic lycopene concentrations were greater in alcohol-fed rats than in control rats supplemented with identical doses of lycopene. In contrast, alcohol-fed rats had a lower percentage of lycopene cis isomers in the plasma and the liver compared with control rats fed the same dose of lycopene. Notably, lycopene supplementation at the higher dose significantly induced hepatic CYP2E1 protein, TNF
mRNA, and the incidence of inflammatory foci in the alcohol-fed rats but not in the control rats. These data indicate an interaction between chronic alcohol ingestion and lycopene supplementation and suggest a need for caution among individuals consuming high amounts of both alcohol and lycopene.
| Introduction |
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B inflammatory pathway, leading to the activation of several proinflammatory cytokines, including tumor necrosis factor-
(TNF
), and increased hepatic infiltration by inflammatory cells. Whereas some antioxidants such as tea polyphenols are protective against alcohol-induced changes in the liver (7,8), others such as vitamin E have no beneficial effect (9).
Whereas the antioxidant properties of lycopene have been demonstrated both in vivo and in vitro (10), recent evidence suggests that it also functions as an antiinflammatory agent (11,12). It has been demonstrated that lycopene can inhibit the expression of inflammatory cytokines and reverse the loss of antioxidant enzymes induced by inflammation caused by either injecting with lipopolysaccharide or by exposure to iron (11,13,14). Although the data for lycopene's role both as an antioxidant and an antiinflammatory agent in various models are compelling, such effects have not been demonstrated in an in vivo model of alcohol-induced oxidative stress and inflammation. One human study has shown that lycopene was inversely associated with concentrations of alcohol-induced
-glutamyl-transferase, an indicator of liver damage, in moderate and heavy drinkers (15). An in vitro study demonstrated that in addition to decreasing alcohol-induced oxidative stress, lycopene could also ameliorate alcohol-modified hepatic biomarkers (16). In that study, incubating hepatic HepG2 cells that overexpressed CYP2E1 with lycopene resulted in decreased alcohol-induced apoptosis and hydrogen peroxide formation and restoration of mitochondrial glutathione levels (16). However, no in vivo studies have examined the effect of lycopene on alcohol-induced oxidative stress and inflammation, particularly with regard to dose responsiveness.
The goal of this study was to investigate potential interactions between alcohol feeding and lycopene supplementation in vivo and to determine the effects of escalating doses of lycopene on alcohol-induced hepatic biomarkers.
| Materials and Methods |
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70 mL/d of the diet. The diets were prepared twice per week and were stored at 4°C in opaque bottles to prevent degradation of the lycopene. BW were recorded once per week for the period of the study. After 11 wk of treatment, the rats were killed by terminal exsanguination under deep anesthesia. Blood and livers were collected for future analyses. This study protocol was reviewed and approved of by the Animal Care and Use Committee at the Human Nutrition Research Center on Aging at Tufts University. HPLC analyses. Liver and plasma concentrations of all-trans and cis isomers (5-cis, 13-cis, and 9-cis) of lycopene were determined by HPLC. A Water's separation system fitted with a C30 column was used to separate lycopene and its isomers. The HPLC system, the mobile phase, and the gradient procedures used have been previously described (22). Liver tissue (100 mg) or plasma (1 mL) was homogenized in 3 mL of saline and ethanol (1:2 ratio). Lycopene was then extracted from the samples using 5 mL of hexane and ether (1:1 ratio) by vortexing for 3 min, centrifuging at 2000 x g for 10 min at 4°C, and collecting the upper layer. Samples were extracted 3 times and were evaporated under nitrogen gas, after which they were reconstituted with 100 µL of ethanol and ether (2:1). A 50-µL sample of the final extract was injected into the system to measure lycopene isomer concentrations. In this HPLC system, 13-cis lycopene, 9-cis lycopene, all-trans lycopene, and 5-cis lycopene were eluted at 28.4, 32.0, 35.0, and 35.3 min, respectively. Retinyl acetate and echinenone were used as internal controls to determine the efficiency of extraction. Extraction efficiency > 80% was considered adequate to calculate concentrations of all-trans, 13-cis, 9-cis, and 5-cis lycopene. All procedures were conducted under red light.
Western blotting. Tissue homogenates were prepared from frozen liver tissue by homogenizing with ice-cold, whole-cell lysate buffer containing inhibitors. Protein concentrations were determined by spectrophotometry using Coomassie Blue and proteins in the tissue homogenates were resolved on a 10% SDS polyacrylamide gel, after which they were transferred onto nitrocellulose membranes. The membranes were blocked using 5% milk and were incubated with the CYP2E1 primary antibody (Chemicon) for 2 h at room temperature followed by the secondary antibody for 1 h at room temperature. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (Chemicon) was used as a loading control. Results were quantified using a densitometer and are expressed as fold of the control group.
Histopathology. Liver sections were fixed in buffered formalin, embedded in paraffin, sectioned, and stained with hematoxylin and eosin for examination. The number of clusters of infiltrating mononuclear cells (foci of inflammation) on each slide (2 liver sections) was examined at both 10x and 40x magnification and counted by 2 independent investigators who were unaware of the treatment. The mean number of clusters in each group was compared.
Real-time PCR.
mRNA levels of TNF
were determined by real-time quantitative PCR. Liver RNA was extracted using TriPure reagent (Roche Applied Science) according to the manufacturer's instructions and cDNA was synthesized using random primer Moloney murine leukemia virus reverse transcriptase (Invitrogen). Primers for rat TNF
and GAPDH were designed using the Primer Express version 2.0 (Applied Biosystems) software. The sequences for TNF
(accession no. NM-012675.2) were as follows: sense, 5'-CCAGACCCTCACACTCAGATCA-3' and antisense, 5'-TCCGCTTGGTGGTTTGCTA-3'. The sequences for GAPDH (accession no. NM-017008.2) were as follows: sense, 5'-AGTGCCAGCCTCGTCTCATAG-3' and antisense, 5'-CCTTGACTGTGCCGTTGAACT-3'. Real-time PCR was performed using the SYBR Green qPCR kit (Invitrogen) according to the manufacturer's instructions on an Applied Biosystems 7000 sequence detection system. Gene expression was quantified relative to the values of the control group after adjusting for GAPDH by the 2–
CT method as described previously (23). Results were expressed as fold of the control group.
Statistical analyses. SPSS (version 14.0) and Graph Pad PRISM (version 3.0) software were used for statistical analyses. Samples identified as outliers by the SPSS statistical software were excluded from the analyses. Two-way ANOVA and trend analyses were used to analyze the data. After determining the presence of significant interactions between alcohol feeding and lycopene supplementation for hepatic lycopene concentrations and all the biomarkers assessed, we used 1-way ANOVA followed by Tukey's honestly significant difference test to test for differences between means of multiple groups for results discussed in this study. Differences between means were considered significant at P < 0.05. Results are expressed as means ± SEM.
| Results |
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Hepatic CYP2E1 protein. We assessed the effect of alcohol and lycopene supplementation on hepatic protein levels of CYP2E1. Alcohol feeding significantly increased expression of CYP2E1 compared with control rats (Fig. 2) as previously documented (26). Lycopene supplementation alone did not affect CYP2E1 expression. However, in the presence of alcohol, we observed a trend of increasing CYP2E1 protein expression with an increasing dose of lycopene (P-trend = 0.003). High dose lycopene with alcohol feeding increased hepatic CYP2E1 expression compared with rats fed alcohol alone without lycopene (P of interaction between alcohol feeding and lycopene supplementation = 0.005).
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expression and inflammation (27), we assessed hepatic levels of TNF
mRNA (Fig. 3). We did not detect any significant increase of hepatic TNF
mRNA in alcohol-fed rats supplemented with placebo or low dose lycopene vs. control rats treated similarly. However, lycopene supplementation at the high dose induced the expression of TNF
in the liver of alcohol-fed rats compared with the other groups (P of interaction between alcohol feeding and lycopene supplementation = 0.032). Lycopene supplementation alone, in the absence of alcohol, at either dose did not affect TNF
expression. We further investigated the effects of lycopene supplementation on hepatic infiltration by mononuclear inflammatory cells (Fig. 4). Alcohol feeding or lycopene supplementation alone did not affect the incidence of hepatic inflammatory foci. However, in the presence of alcohol, high dose lycopene supplementation was associated with an increased incidence of inflammatory foci in the liver (P of interaction between alcohol feeding and lycopene supplementation = 0.036).
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| Discussion |
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9.4 mg/d of lycopene (21); therefore, both the experimental doses were higher than the usual intake. However, these doses are currently present in dietary supplements and are being tested in prostate cancer clinical trials (28–30), emphasizing the importance of our observations from the current animal study. Furthermore, the hepatic lycopene concentrations that we detected (1.07–7.30 nmol/g) in the rats are within the range normally seen in humans (0.1–20.7 nmol/g) (31,32), indicating that the interaction between chronic alcohol intake and supplementary lycopene and their combined effect on hepatic biomarkers takes place at physiologically relevant tissue concentrations of lycopene. Plasma concentrations in the rats (3.82–12.22 nmol/L), however, were much lower than those observed in humans (260–900 nmol/L) (33). Alcohol-fed rats accumulated more lycopene than control animals supplemented with the same dose of lycopene. Interestingly, chronic alcohol intake is also associated with increased plasma (34) and hepatic concentrations (35) of another carotenoid, β-carotene. The accumulation of β-carotene in the liver has been attributed to the inhibition of its catabolism to retinoids by chronic alcohol intake (36). In the case of lycopene, however, the mechanism(s) involved is unknown at present. Multiple mechanisms could be involved; e.g. alcohol intake could increase the solubility and/or bioavailability of lycopene for absorption, or it could decrease lycopene catabolism. Recently, we have shown that the carotene 9',10'-oxygenase can cleave cis isomers of lycopene into apo-10'-lycopenoid metabolites (37) and other investigators have reported apo-8'- and 12'-lycopenals in rat livers after lycopene supplementation (25). However, we did not detect any apo-lycopenoids in the livers of rats with lycopene supplementation and observed no changes in hepatic carotene 9',10'-oxygenase protein levels or in the formation of the unidentified polar metabolites in alcohol-fed rats vs. the control rats (S. Veeramachaneni and X-D. Wang, unpublished data). It is, therefore, unlikely that alcohol altered lycopene degradation, suggesting that the increased concentrations of lycopene in vivo might result from enhanced absorption in the gut due to alcohol ingestion. However, this hypothesis needs to be addressed in future studies using intestinal perfusion models as previously described (38).
Though the lycopene beadlet predominantly contained all-trans lycopene, the rat livers had a higher accumulation of cis lycopene compared with that in the diet. This observation is similar to what is normally seen in humans, where higher concentrations of lycopene cis isomers are detected in the body although dietary lycopene is predominantly in the all-trans form (39). In the current study, the percentage of cis isomers of lycopene decreased in the livers, but not in the plasma, with increasing lycopene dose (Table 1) in both the control and the alcohol-fed groups. This suggests that the ratio of cis/trans lycopene isomers in the circulation may not be reflective of isomerization of the all-trans isomer to cis isomers in the liver. Interestingly, the alcohol-fed rats had a lower percentage of cis lycopene accumulation than the control rats fed the same dose of lycopene. It is unknown whether this decrease in cis lycopene accumulation is a result of either decreased absorption of cis isomers in the gut or decreased isomerization of the all-trans isomer to cis isomers by chronic alcohol ingestion.
Chronic alcohol ingestion can induce the levels of CYP2E1 (26), which plays an important role in metabolizing excess amounts of alcohol in the liver via the microsomal ethanol oxidizing system (26). During this process, CYP2E1 generates several reactive oxygen species, including hydrogen peroxide and superoxide, leading to increased oxidative stress (1,3,40). Reactive oxygen species generated by CYP2E1 induce mitochondrial damage and induce cell membrane damage by increasing lipid peroxidation and lipid aldehyde formation. Alcohol regulates CYP2E1 levels both by inducing its transcription (41) and by stabilizing the protein against degradation (42,43). In the present study, in addition to the expected induction of CYP2E1 in response to alcohol treatment, we observed a trend of increased CYP2E1 protein with increasing lycopene dose in the alcohol-fed rats. This increase was significantly greater when lycopene was supplemented at the high dose in rats compared with the rats that were supplemented with the placebo. Although the mechanisms for these results are currently unknown, our observation suggests that lycopene supplementation at a high dose may potentiate the harmful effects of excessive alcohol intake. This notion is further supported by the following observations. First, it has been previously documented that chronic alcohol intake was associated with increased incidence of inflammatory foci in the livers of alcohol-fed rats compared with control rats (44,45). Although we observed no significant increase in inflammatory foci with alcohol feeding, we found that rats fed both alcohol and high dose lycopene had a significantly higher incidence of hepatic inflammatory foci compared with the other groups. Second, previous evidence has shown that alcohol induces the expression of TNF
in rats (27), and patients with alcoholic liver disease have increased levels of several proinflammatory cytokines, including TNF
(46). In our model, hepatic TNF
mRNA did not differ between the control and alcohol-fed groups supplemented with placebo. This is in agreement with earlier in vivo data showing no significant differences in TNF
expression in the livers of mice fed control or alcohol Lieber-DeCarli liquid diets (47). However, our observations in Fischer rats are contradictory to findings from another study using alcohol-fed Sprague-Dawley rats (27). Although the exact reasons for the differences in response to alcohol feeding are not known, it is possible that different strains of rats react differently to chronic alcohol feeding. Rats fed both alcohol and high dose lycopene had significantly higher expression of TNF
compared with all other groups. Interestingly, rats fed alcohol and low dose lycopene (equal to one-third of the dose supplemented to the high dose groups) had no significant induction of TNF
expression. Lycopene has been shown to act as a prooxidant or an antioxidant depending on the dose at which it is administered (48,49). In this study, although neither dose was protective, lycopene supplementation at the higher dose had a more pronounced effect on alcohol-related changes compared with the lower dose. Further studies are needed to understand both the interaction between alcohol and lycopene and the mechanisms by which high doses of lycopene, in the presence of alcohol, modulate hepatic inflammation and CYP2E1 expression.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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2 Author disclosures: S. Veeramachaneni, L. M. Ausman, R. M. Russell, S. W. Choi, and X.-D. Wang, no conflicts of interest. ![]()
3 Abbreviations used: BW, body weight; CYP2E1, cytochrome P4502E1; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; TNF
, tumor necrosis factor
. ![]()
Manuscript received 24 January 2008. Initial review completed 3 March 2008. Revision accepted 12 April 2008.
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