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Articles

Testosterone and Food Restriction Modulate Hepatic Lycopene Isomer Concentrations in Male F344 Rats¹

Thomas W.-M. Boileau^*, Steven K. Clinton, Susan Zaripheh^*, Marcia H. Monaco^*, Sharon M. Donovan^* and John W. Erdman, Jr.^*2

^* Division of Nutritional Sciences, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 and Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, Division of Hematology and Oncology, The Ohio State University, Columbus, Ohio 43210

²To whom correspondence should be addressed at University of Illinois, 449 Bevier Hall, 905 S. Goodwin Avenue, Urbana, IL 61801. E-mail: j-erdman{at}uiuc.edu

	ABSTRACT

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We previously demonstrated that the castration of male rats profoundly increases hepatic lycopene compared with intact controls. Here we further characterized the role of testosterone in modulating hepatic lycopene accumulation and isomer patterns in male rats. Furthermore, because castration significantly decreases ad libitum food consumption, we investigated the influence of food restriction on lycopene metabolism. Forty male F344 rats 8 wk of age were randomly assigned to one of four treatments (n = 10/group): 1) intact, free access to food, 2) castration, free access to food, 3) castration plus testosterone implants, free access to food and 4) intact, 20% food restricted. All rats were fed an AIN-based diet with 0.25 g lycopene (as 10% water-soluble beadlets)/kg diet for 3 wk. Serum testosterone was 5.31 ± 1.46 nmol/L in intact controls allowed free access to food, reduced in castrated animals (0.52 ± 0.10, P < 0.0001 versus controls) and intact, food-restricted rats (1.53 ± 0.49 nmol/L, P < 0.0001 versus controls) and greater (17.23 ± 3.09 nmol/L) in castrated rats administered testosterone (P < 0.0001 versus controls). Castrated rats accumulated approximately twice as much liver lycopene (74.5 ± 8.5 nmol/g; P < 0.01 versus controls) as intact rats allowed free access to food (39.5 ± 5.0) despite 13% lower dietary lycopene intake (P < 0.001; 3.38 ± 0.07 versus 3.95 ± 0.06 mg lycopene/d). Testosterone replacement in castrated rats returned liver lycopene concentrations (32.5 ± 5.5 nmol lycopene/g with 3.76 ± 0.05 mg dietary lycopene/d) to those observed in intact rats. Food restriction resulted in a 20% decrease in lycopene intake but significantly increased liver lycopene by 68% (66.3 ± 7.9 nmol lycopene/g with 3.38 ± 0.00 mg lycopene/d) compared with controls and castrated rats administered testosterone. These results suggest that androgen depletion and 20% food restriction increase hepatic lycopene accumulation. We hypothesize an endocrine and dietary interaction, where higher androgen concentrations and greater energy intake may stimulate lycopene metabolism and degradation.

KEY WORDS: • lycopene • testosterone • prostate cancer • rats • antioxidants

	INTRODUCTION

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Dietary and chemopreventive strategies to prevent or delay prostate cancer progression have focused on many of the nutrients and phytochemicals hypothesized to enhance the host defense against oxidative damage (1) . Lycopene, a C40 open-chain hydrocarbon carotenoid, provides the red pigment in tomatoes and has been demonstrated to be a potent antioxidant in vitro (2 3 4) . Epidemiological studies have associated a greater intake of tomato products with a decreased risk for prostate cancer in U.S. men (5 ,6) . Furthermore, a case-control study (7) evaluating prospectively collected blood carotenoid patterns revealed that men who subsequently develop prostate cancer exhibit lower circulating lycopene concentrations than do men who remain disease free. Our laboratory (8) and others (9 ,10) have reported that lycopene is a predominant carotenoid in the human prostate and that it exists there as a variety of geometrical isomers. Collectively, these and other studies (6) support a hypothesis that lycopene may have a role in protecting men from prostate cancer.

Although dietary hypotheses are beginning to emerge regarding prostate cancer etiology (11) , decades of research have clearly established a critical role for androgens in prostate carcinogenesis (12 ,13) . Androgens are required for the normal development and function of the prostate and are also necessary for the progression of prostate cancer (14 ,15) . The reduction in testosterone bioactivity through orchiectomy and the pharmacological disruption of testosterone production (16) , metabolism (17) or binding to its receptor (18) are critical therapeutic interventions for men with prostate cancer. Human epidemiological studies have also revealed a relationship between elevated serum testosterone concentrations and greater risk of prostate cancer (19 ,20) . Studies in laboratory animals and in vitro systems have gradually elucidated many of the cellular and molecular processes in prostate cancer cells that are regulated by androgens and that influence proliferation, invasion and metastases (14 ,21) . We recently identified alterations in lycopene metabolism in response to androgen ablation in rats, suggesting a possible diet/endocrine interaction (22) . We observed that castrated rats accumulated approximately twice as much hepatic lycopene as did intact controls (22) . The mechanisms by which castration influences lycopene absorption, metabolism or tissue accumulation and potentially interacts with dietary lycopene to influence prostate cancer risk remain speculative.

The major goal of this study was to determine the ability of testosterone to modulate hepatic, adrenal and blood lycopene concentrations and isomer patterns. Androgen status was assessed by comparing intact controls with castrated rats or with castrated rats that had been provided supplemental testosterone. We included a group of rats with modest (20%) food restriction, equivalent to the reduced food intake consistently observed with castration in our earlier studies (22 ,23) , to define the possible role of energy balance in modulating lycopene tissue accumulation in the rat.

	MATERIALS AND METHODS

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Rats, diets and experimental design.

The experimental design is illustrated (Fig. 1 ). Forty male F344 rats (Harlan, Indianapolis, IN) were either castrated (n = 20) or sham operated and left intact (n = 20) at 6 wk of age (after sexual maturity). Beginning at 7 wk of age, rats were allowed free access to a carotenoid-free modified AIN-93G diet (23) . At 8 wk of age, castrated rats were randomly assigned to receive either control (n = 10) or testosterone (n = 10) implants (preparation described later). All intact rats received the control implant. At 9 wk of age, all rats were fed a modified pelleted AIN-93G diet (DYETS, Bethlehem, PA) with a target concentration of 0.25 g lycopene/kg diet and were fed for 3 additional wk. Lycopene was incorporated into the diet as water-dispersible beadlets containing 10 g/100 g lycopene (Hoffmann-La Roche, Basel, Switzerland) (22) . For the duration of the experimental feeding, a group of intact rats (n = 10) were food restricted to 80% of ad libitum consumption, whereas all other rats were allowed free access to unlimited food supplies. Diets were stored at 4°C in the dark. Rats were weighed weekly, and food intake was measured. Fresh diet was provided every 72 h to minimize lycopene degradation. All animal procedures were approved by the University of Illinois Animal Care Advisory Committee.

View larger version (17K): [in this window] [in a new window]   Figure 1. Experimental design. Forty male F344 rats were either castrated (n = 20) or sham operated and left intact (n = 20) at 6 wk of age. Beginning at 7 wk of age, rats were allowed free access to a carotenoid-free modified AIN-93G diet. At 8 wk of age, rats were implanted subcutaneously with Silastic tubes packed with and without testosterone (described in Materials and Methods) and allowed to recover for 1 wk. Beginning at 9 wk of age, all rats were fed a diet containing 0.25 g lycopene/kg diet for 3 wk. Half (n = 10) of the intact rats were also randomly assigned to 20% food restriction at 9 wk of age and restricted until the termination of the study.

At 8 wk of age, rats were administered testosterone as two subcutaneous implants (1.57 mm ID x 0.125 mm OD x 2.54 cm length Silastic laboratory tubing; Dow Corning, Midland, MI), with each containing 30 mg testosterone proprionate (Sigma Chemical, St. Louis, MO), or control implants, which were identical except they did not contain testosterone. Testosterone was drawn into the implants under vacuum pressure, and ends were sealed with silicone adhesive (Dow Corning, Midland, MI). Implants were inserted subcutaneously into the dorsolumbar region of the back using sterile technique, and wounds were sealed with surgical glue. This method of testosterone administration has been previously used and shown to be effective in elevating serum testosterone concentrations (24 25 26) .

Sample collection.

After 3 wk of experimental feeding, all rats were anesthetized with 0.1 mL ketamine/xylazine (95:5)/100 kg body intraperitoneal, and blood samples were taken via cardiac puncture. Rats were killed by CO₂ asphyxiation, and the liver and adrenal glands were collected and weighed. Tissues were rapidly cooled on ice, protected from light and stored at -20°C for lycopene analysis. Blood was allowed to coagulate for 30 min and centrifuged at 250 x g for 10 min to isolate serum. All serum samples were stored at -20^°C for analysis.

Tissue and serum lycopene extraction.

Approximately 0.05 g of tissue was minced thoroughly, dissolved in 6 mL of a KOH/ethanol (1:5) solution containing 1 g butylated hydroxytoluene/L and vortexed. Tissues were saponified at 60°C for 30 min with vortex mixing at 15-min intervals. Lycopene was extracted twice under yellow lights using equal volumes of hexane (6 mL) plus 2 mL distilled water. Extracts were dried in a Speedvac concentrator (model AS160; Savent, Farmingdale, NY) and stored at -20°C for no more than 2 d before HPLC analysis. For serum extraction, ethanol (0.5 mL) containing 1 g butylated hydroxytoluene/L was added to 0.5 mL serum and vortexed. Serum samples were extracted twice under yellow lights using 1.0 mL hexane. Extracts were dried and stored as described earlier.

HPLC analysis of cis-trans lycopene isomers.

HPLC analysis was performed on a Rainin Dynamax gradient pump system model SD-200 (Woburn, MA) using a C30 "carotenoid column" (YMC, Wilmington, NC) and a Rainin Dynamax UV-visible dual-wavelength detector (model UV-DII; Walnut Creek, CA) with monitoring at 472 nm. The gradient and mobile phases were as previously described (22 ,27) . Briefly, mobile phase A (A) consisted of an 83:15:2 mixture of methanol/tert-butyl-methyl-ether/1.5 g ammonia acetate per 100 mL water. Mobile phase B (B) consisted of an 8:90:2 mixture of methanol/tert-butyl-methyl-ether/1.5 g ammonia acetate per 100 mL water. Pumps were programmed to perform the following gradient with a flow rate of 1.0 mL/min: 5 min at 90% A, 10% B; a 12-min linear gradient to 55% A, 45% B; a 12-min linear gradient to 95% B, 5% A; a 5-min hold at 95% B, 5% A; and a 2-min gradient back to 90% A, 10% B.

Lycopene isomer chromatogram peaks were identified by comparison with previously published separations (22 ,27 ,28) . Standard curves were prepared using crystalline lycopene extracted from a tomato oleoresin (Lycored; Natural Industries, Beer Sheva, Israel) and purified on a YMC C30 column. Lycopene was quantified using an external standard curve plotting lycopene peak area versus nanograms of lycopene injected into the HPLC. This laboratory participates quarterly in the National Institutes of Standards in Technology micronutrient measurement proficiency testing program. The coefficient of variance for lycopene analysis is <12%.

Liver crude fat analysis.

Crude liver fat was analyzed by chloroform/methanol (2:1) extraction according to the method of the American Association of Analytical Chemists (29) and expressed on a dry matter basis.

Serum testosterone measurements.

Serum testosterone was measured by enzyme-linked immunosorbent assay (KMI Diagnostics, Minneapolis, MN) (30) .

Statistics.

Differences between treatment groups were analyzed by one-way ANOVA. When significant tests were found (P < 0.05), group differences were further analyzed by the post hoc Fisher’s Protected Least Squares Difference (PLSD) test (StatView; Brain Power, Calabasas, CA) (31) . Data with unequal variances were log transformed and reanalyzed by ANOVA and Fisher’s PLSD but are presented in figures and tables as original nontransformed values for ease of interpretation. Values are means ± SEM.

	RESULTS

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Growth and food intake.

Intact rats (198 ± 2.4 g) weighed (P < 0.0001) more than castrated rats (163 ± 3.5 g) by 7 wk of age (Fig. 2 ). Rats in all treatment groups gained weight, including those restricted in food by 20%, over the duration of the experimental period. As expected, castrated rats had lower (P < 0.001) final body weight (21% reduction) and food intake (14% reduction) than intact rats allowed free access to food (Table 1 ). Castrated rats that were administered testosterone and intact, food-restricted rats did not differ in body weight at the time of killing despite significantly different (P < 0.001) food intakes (Table 1) . Although castrated rats and restricted rats consumed the same amount of total lycopene, lycopene intake–to–body weight ratios were significantly (P < 0.05) different (castration plus control implants: 14.7 ± 0.5 µg lycopene · g body^-1 · d^-1; intact, food-restricted: 13.7 ± 0.3 µg lycopene · g body^-1 · d^-1).

View larger version (17K): [in this window] [in a new window]   Figure 2. The influence of androgen status and 20% food restriction on growth of male F344 rats fed 0.25 g lycopene/kg diet for 3 wk. Castrated (n = 20) and intact (n = 20) male F344 rats were randomly assigned to one of the four groups outlined in Fig. 1 . At 8 wk of age, rats were administered either testosterone or control implants. All rats began lycopene feeding (0.25 g lycopene/kg diet), and intact, food-restricted rats began 20% food restriction at 9 wk of age. By 7 wk of age, castrated rats weighed significantly less (; P < 0.05) than controls; by 9 wk, castrated rats weighed significantly less (; P < 0.05) than castrated rats administered testosterone; and by 10 wk, intact, food-restricted rats weighed significantly less (*P < 0.05) than intact rats allowed free access. Values are means ± SEM, n = 10/group.

Livers from intact rats allowed free access to food and castrated rats administered testosterone did not differ in absolute weight (Table 1) . Castration (20% reduction) and food restriction (36% reduction) both reduced (P < 0.001) absolute liver weight compared with intact controls allowed free access to food (Table 1) . When expressed relative to body weight, the castrated rats did not differ from the controls, and castrated rats administered testosterone had greater liver weights (P < 0.0001) (Table 1) . Livers from food-restricted rats were (P < 0.0001) smaller than those from other groups in both absolute weight and relative units.

Liver crude fat analysis.

We recognize that hepatic lipid content could potentially influence the storage and metabolism of lipophilic compounds such as lycopene, so we determined the crude fat content of the liver. The percent crude fat (dry matter basis) in the liver did not differ between intact rats allowed free access to food, castrated rats and castrated rats administered testosterone (Table 1) . However, the percent fat in the liver of the restricted rats was 35% lower than that of the other three groups when expressed on a dry matter basis (P < 0.01 versus all other groups).

Serum testosterone concentrations.

As expected, castration drastically reduced serum testosterone concentrations compared with intact rats allowed free access (P < 0.0001) (Fig. 3 ). The treatment of castrated rats with testosterone implants increased (P < 0.0001) serum testosterone concentrations above that observed in intact rats allowed free access to food. Food restriction reduced serum testosterone compared with controls (P < 0.0001) to a concentration that did not differ from that of castrated rats.

View larger version (13K): [in this window] [in a new window]   Figure 3. The influence of androgen status and food restriction on serum testosterone of male F344 rats fed 0.25 g lycopene/kg diet for 3 wk. Serum testosterone was measured with a specific ELISA. Data represent means ± SEM, n = 6. Values with different letters are significantly different (P < 0.0001). Data were log-transformed before analysis but are presented as original nontransformed values for ease of interpretation.

Lycopene was incorporated into diets as 10 g/100 g lycopene water-dispersible beadlets with final target lycopene concentrations of 0.25 g lycopene/kg diet. An analysis of the fresh diet revealed a lycopene concentration of 0.16 g lycopene/kg diet. A representative HPLC separation of lycopene isomers from the processed diet is shown (Fig. 4A ). Lycopene was present as an array of isomers with pooled cis-isomers accounting for 57% of total lycopene. The all-trans isomer was the most prominent isomer, accounting for 43% of the total lycopene in the diet.

View larger version (20K): [in this window] [in a new window]   Figure 4. Qualitative C30 column separations of lycopene isomers in diet (A), liver (B) and adrenal glands (C) of male F344 rats fed 0.25 g lycopene/kg diet for 3 wk. Dietary lycopene (as lycopene beadlets incorporated into pelleted diet) contained 57% cis-isomers. Lycopene isomers in tissues did not vary by treatment group. Liver cis-isomers ranged from 53 to 57%. Adrenal tissue (68–72% cis) was enriched in cis-isomers compared with diet, liver or serum (51–57%, chromatogram not shown), suggesting selective uptake and/or isomerization of lycopene by this tissue. Note the relative increase in other cis- and 5-cis-lycopene compared with all-trans in adrenal tissue versus diet and liver. The two major isomers in diet, liver and adrenal glands were all-trans and 5-cis-lycopene. Three to five other cis-isomers that eluted before all-trans were also detected (y-axis is absorbance at 472 nm).

Castration increased (P < 0.01) liver lycopene by 89% compared with the intact controls (Table 2 ). The administration of testosterone to the castrated rats returned liver lycopene concentrations to levels observed in intact rats allowed free access to food. Similar to castration, food restriction increased (P < 0.01) liver lycopene by 68% compared with controls. Treatment group had little effect on the proportion of lycopene present as different isomers or the patterns of isomers, although the total amounts of each isomer varied in proportion to total lycopene content of the livers (Table 2 ). All-trans lycopene accounted for 43–47% of hepatic lycopene among the four dietary groups, whereas the 5-cis isomer also accounted for 43–47%, and other cis-isomers accounted for 10–11% of the total lycopene in livers. A representative separation of liver lycopene is given (Fig. 4B ).

In contrast to the liver, castration did not significantly affect serum lycopene concentrations (Table 3 ). Interestingly, castrated rats administered testosterone had a 42% lower serum lycopene (P < 0.002) than intact controls. Food restriction of 20% resulted in 86% lower serum lycopene concentrations compared with controls (P < 0.0001). Androgen status did not affect the cis-/trans-isomer ratio. However, the proportion of serum lycopene in the cis form was greater (P < 0.05) in the restricted rats than in all other groups (Table 3) .

The adrenal glands are reported to contain higher concentrations of lycopene than many other tissues (22) . Interestingly, adrenal lycopene (nmol/g) and percent lycopene as cis-isomers was not affected by androgen status or food restriction (Table 3) . Adrenal glands were enriched in cis-lycopene isomers (68–77%) compared with diet (57%), liver (53–57%) and serum (51–57%) (Fig. 4C , Table 3 ).

	DISCUSSION

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The potential interactions between hormones and dietary factors that modulate prostate cancer risk have not been thoroughly studied. We previously observed that rats deprived of testicular androgens via castration experienced a dramatic increase in liver lycopene concentration compared with intact controls (22) . The present study was designed to more thoroughly evaluate the role of testosterone in modulating lycopene metabolism and tissue accumulation. In addition, because castration in rats is associated with reduced food intake, which also is a critical modulator of prostate tumorigenesis (23) , we examined the influence of food restriction on blood and tissue lycopene accumulation in the current study.

Several observations concerning the complexities of lycopene metabolism and tissue accumulation were elucidated in this experiment. Rats fed 0.25 g lycopene/kg (quantified at 0.16) diet for 3 wk achieved liver and adrenal serum concentrations of lycopene within the ranges reported for humans (8 ,32 ,33) . Furthermore, lycopene isomer patterns in tissues and blood are similar to those in human biological samples (8) , further supporting the use of rats to evaluate physiologic regulators of in vivo lycopene metabolism. Castrated rats accumulated approximately twice (P < 0.001) the liver lycopene as intact controls, even though they consumed 20% less food and total lycopene due to a spontaneous reduction in food intake. The administration of testosterone to androgen-deprived rats significantly reversed the effects of castration on hepatic lycopene concentrations. Interestingly, a 20% food restriction (20% less lycopene and total food consumed) increased liver lycopene concentration compared with intact controls, suggesting that part of the castration effect could be mediated by effects on energy metabolism. The interrelationships between energy intake and androgens was further supported by the observation that 20% total food restriction also reduced serum testosterone. Although liver lycopene concentrations were altered by androgen status, no major alterations were observed in hepatic cis-isomer profiles.

Both androgen deprivation and modest food restriction increased hepatic lycopene concentrations. The mechanisms responsible for mediating the effects of testosterone or food restriction on liver lycopene accumulation are incompletely understood. The effects of androgens and energy intake on lycopene absorption, hepatic uptake, hepatic catabolism, lycopene incorporation into lipoproteins, clearance from the circulation via lipoprotein receptors and tissue metabolism may all contribute to the results we have observed.

Testosterone and food restriction may indirectly modulate hepatic lycopene accumulation via influences on lipoprotein synthesis and secretion by liver. This mechanism may be particularly relevant in food-restricted rats. Food-restricted rats had lower serum lycopene and greater liver lycopene concentrations than controls allowed free access to food. These data suggest that dietary lycopene accumulation may be secondary to reduced packaging and secretion of liver lycopene into the serum as a component of VLDL. Carotenoids are exclusively transported in plasma in lipoproteins (34) , and energy restriction decreases circulating total lipid and LDL concentrations (35 ,36) .

To determine whether the increased hepatic lycopene concentrations in castrated rats and restricted rats were secondary to increased crude fat content of the liver, we analyzed liver crude fat in each group. The percent liver fat was not altered by castration. However, hepatic crude fat was 35% lower in food-restricted rats (when expressed on a dry matter basis). These observations support the hypothesis that energy restriction alters hepatic lipid metabolism and perhaps contributes to the increased liver lycopene and decreased blood lycopene concentrations observed in the food-restricted rats.

We also hypothesize that androgens may stimulate the activities of hepatic enzymes that metabolize or degrade lycopene in the liver or other androgen-responsive tissues. A reduction in circulating androgens would thereby result in decreased lycopene metabolism and clearance, leading to an increase in tissue lycopene concentrations. However, specific enzymes and/or pathways involved in lycopene metabolism have not been reported. Numerous xenobiotic metabolizing enzymes whose expression is dependent on androgens have been characterized (37) . One such example is the hepatic lauric acid hydroxylase, cytochrome P450 4A. This enzyme is expressed at much higher levels in male rats than in female rats, and expression is greatly decreased by castration (38) . The possibility that cytochrome P450–type enzyme systems contribute to the catabolism of lycopene or other carotenoids warrants additional investigation as catabolic pathways of carotenoids become better characterized in the future.

The nonenzymatic oxidation of lycopene as a result of androgen-induced increases in cellular metabolism could also account for the differences in liver lycopene observed in this study. Testosterone stimulates the expression of enzymes involved in intermediary metabolism (39) and increases the production of reactive oxygen species in prostate cancer cells (40) . Lycopene is a potent in vitro antioxidant and has been proposed to protect tissues from activated oxygen byproducts of metabolism in vivo. Food restriction also decreases overall oxidative stress (41) , and the increase in tissue lycopene in energy-restricted rats may also be a result of decreased lycopene oxidation via nonspecific mechanisms. Lycopene is oxidized via an epoxide to the cyclic oxidation product 2,6-cyclolycopene-1,5 diol, and the presence of this compound in human serum and breast milk suggests that oxidation of lycopene does occur in vivo (42) . However, details of lycopene oxidation remain obscure, and additional efforts will be needed to address the hypothesis that androgens enhance oxidative consumption of carotenoids.

Interestingly, androgens also appear to alter the tissue concentrations of other dietary components thought to modify prostate cancer risk. Feingold and coworkers (43) demonstrated in male rats that liver -tocopherol concentrations are increased in response to castration. Similar to what we observed with lycopene, the effects of castration on liver -tocopherol were reversed by testosterone replacement (44) . In addition, two studies documented that female rats accumulate significantly more liver vitamin E than do age-matched male rats (45 ,46) . A cross-sectional analysis of blood hormones and -tocopherol concentrations of men participating in the -Tocopherol ß-Carotene Cancer Prevention (ATBC) study revealed that both serum testosterone and androstenedione were inversely correlated with serum -tocopherol (47) . These investigators suggested that the androgen/vitamin E relationship may have implications for the 32% reduction in prostate cancer risk observed in the vitamin E–supplemented group in this randomized study (47 ,48) . Chang and coworkers (49) demonstrated differences in tissue accumulation of genistein, the major soy phytoestrogen, between male and female Sprague-Dawley rats. Liver genistein concentrations were 5–11 times greater in female rats than in male rats despite similar liver weights. Pharmacokinetic analysis of serum genistein revealed a significantly greater elimination half-life for genistein in female rats and women compared with male rats (49) and men (50) . These observations with genistein and vitamin E, as well as our studies with lycopene (22) , suggest that androgen status can modulate the metabolism and tissue accumulation of dietary components associated with reduced prostate cancer risk.

Neither androgen status nor food restriction was found to have a major impact on adrenal lycopene concentrations or isomer patterns, which confirms our previous findings (22) . We previously reported that castration influences liver lycopene with little effect in adrenal glands, kidneys, lungs, adipose or serum. It is possible, although speculative, that the liver has a unique androgen-responsive ability to metabolize lycopene that is not present in the adrenal glands or other tissues. Alternatively, the relatively efficient uptake of LDL for steroid biosynthesis by the adrenal gland may provide a continued stable supply of adrenal lycopene even with variations in circulating lycopene. Clearly, the regulation of lycopene metabolism varies among tissues, and it would be inappropriate to extrapolate findings from the liver or adrenal glands to other tissues.

The biological relevance of specific lycopene isomers remains speculative. Different isomers may reflect participation in specific metabolic reactions, or perhaps different isomers possess unique antioxidant properties. In addition, isomeric configuration may influence the incorporation of lycopene into different pools within the host or even within a cell. We previously reported that lycopene is found in the human prostate as 14–18 cis-isomers accounting for 79–88% of the total lycopene (8) , despite the fact that tomatoes and tomato products contain >80% all-trans lycopene (51) . Similarly, our previous work in rats also demonstrated that the lycopene cis-isomers are enriched in tissues compared with the percentage of cis-isomers in the diets (22) . It is possible that compared with foods, some of the cis-isomer enrichment in tissues is due to more efficient absorption of cis-isomers. This hypothesis is supported by studies with the lymph cannulated ferret (28) . In addition, physiochemical studies suggest that cis-isomer geometry allows for more efficient incorporation of lycopene into mixed micelles in the lumen of the intestine and into chylomicrons by the enterocyte (52) . cis-isomers appear to be further concentrated by the liver when lycopene is incorporated into VLDL and secreted into blood. This may in part explain why we observed that the adrenal glands accumulated a higher percentage of cis-isomers than did the liver and serum.

In summary, we report that testosterone and food restriction modulates lycopene metabolism. Twenty percent total food restriction and castration similarly affected liver lycopene accumulation, increasing it 100% compared with intact, freely fed controls. Further studies are needed to more clearly determine the specific pathways involved in lycopene metabolism mediated by androgens and energy balance. We conclude that interactions exist between dietary variables and hormones that may influence prostate cancer etiology and that future epidemiological, clinical and experimental studies should further characterize these interactions.

	FOOTNOTES

 
¹ Supported by U.S. Public Health Service, National Institutes of Health, National Cancer Institute Grant RO172482 (to S.K.C.), Comprehensive Cancer Center, The Ohio State University Grant P30CA16058, National Cancer Institute and the Bremmer Fund at The Ohio State University

Manuscript received November 15, 2000. Initial review completed December 5, 2000. Revision accepted February 21, 2001.

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