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Arizona Cancer Center, The University of Arizona, Tucson, Arizona 85724
| Abstract |
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| Introduction |
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The chemopreventive efficacy of limonene during both the initiation and promotion stages of carcinogenesis has been demonstrated in chemically induced rodent skin (7) , kidney (8) , lung and forestomach (9 , 10) , and mammary (11, 12, 13) tumor model systems. In mammary carcinoma, d-limonene exhibits therapeutic effects against chemically induced mammary tumors in rats, with regression of >80% of carcinomas with little toxicity (11) . Limonene also appears to act in a cytostatic fashion. Its removal from the diet results in significant tumor recurrences (11) . The postinitiation chemopreventive/tumor suppressive activity may be due, in part, to the inhibition of isoprenylation of cell growth-associated small G proteins such as p21ras and induction of apoptosis by limonene and its metabolites (11 , 12) . The initiation-phase chemopreventive effects of d-limonene have been attributed to the modulation of Phase I (14) and Phase II (5) carcinogen-metabolizing enzymes, leading to enhanced detoxification of carcinogens.
Chemotherapeutic activities of pharmaceutical preparations of d-limonene are under evaluation in Phase I/II therapeutic clinical trials (15) . d-Limonene, as a drug, is well tolerated in cancer patients at doses that may have clinical activity. One partial response in a breast cancer patient at a dose of 8 g/m2/day was maintained for 11 months, and three additional patients with colorectal carcinoma showed stabilization of disease for longer than 6 months on d-limonene at 0.5 or 1 g/m2/day (15) . The favorable toxicity profile and the partial response supports additional clinical evaluation.
The principal sources of d-limonene in the diet are the oils of orange, grapefruit, and lemon (16) . It is found naturally in orange juice at an average concentration of 100 mg/liter. d-Limonene (orange oil/essence oil) is also used as a flavoring ingredient for citrus flavor in artificial oils and can be found in nonalcoholic beverages (31 mg/liter), ice cream and ices (68 mg/kg), candy (49 mg/kg), and baked goods (120 mg/kg; Ref. 17 ).
Dietary intake of d-limonene can vary considerably depending on the types of citrus consumed and the preparation and processing procedures (18) . Daily United States per capita consumption of d-limonene, as a result of both its natural occurrence in food and of its presence as a flavor, was estimated to be 0.27 mg/kg body weight/day (16.2 mg/day) for a 60-kg individual (17) . However, d-limonene intake may approach 1 mg/kg body weight (60 mg/day) because of high consumption of citrus juice products (17) . Our previous work has shown that lemonade prepared fresh with whole lemons (Mediterranean-style lemonade) contains d-limonene levels (5001027 mg/liter) >1020 times of those available in commercial citrus juices (18) .
The objective of this study is to determine whether d-limonene or its derived materials would be available systemically after the oral consumption of Mediterranean-style lemonade. Because perillic acid has been identified to be one of the major metabolites of d-limonene in humans (15
, 19)
and has been shown to exert potent biological activities (4
, 6)
, we have chosen to monitor the systemic availability of perillic acid after a single dose administration of Mediterranean-style lemonade (see Fig. 1
for the chemical structures of limonene and perillic acid). This study represents a step toward evaluating the protective activity of dietary limonene intervention and may provide information relating to biomarkers of limonene consumption that could be used in epidemiological and nutrition intervention studies (Fig. 1)
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| Materials and Methods |
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Sample Collection and Analysis.
Once collected, blood samples were kept in the refrigerator and centrifuged at 4°C within 2 h of collection. After centrifugation, plasma was aliquoted into cryotubes and stored at -80°C for the analysis of perillic acid levels. Plasma perillic acid concentrations were determined using a reversed-phase HPLC3
procedure modified from that reported by Ezennia et al. (20)
. One ml of authentic plasma samples or spiked plasma standards were mixed with 1 ml of 0.2 M sodium acetate buffer (pH 3.8) and 25-µl internal standard solution (10 µg perillaldehyde/ml sodium acetate buffer). The mixtures were applied to BakerBond Octadecyl SPE cartridges (100 mg; JT Baker, Philipsburg, NJ) preconditioned with methanol, water, and sodium acetate buffer [0.2 M (pH 3.8)]. After sample application, the cartridges were washed with 1 ml of the sodium acetate buffer. Perillic acid and the internal standard were eluted with 160 µl of methanol twice. The eluent was combined with 100 µl of water, and an aliquot was injected onto the HPLC. Chromatographic separation was achieved using a Supelco LC-ABZ column (150 x 4.6 mm; Supelco, Bellefonte, PA), and a mobile phase consisted of acetonitrile and sodium acetate buffer [25 mM (pH 5.2)] in the ratio of 29:71. The flow rate of the mobile phase was at 1.1 ml/min. The column eluent was monitored with an UV detector at a wavelength of 230 nm. Plasma perillic acid concentrations were quantified using calibration curves prepared with plasma spiked with perillic acid standards. The calibration curve was linear over the concentration range of 0.02 to 2 µg/ml. The inter- and intraday variation for the assay was <10%.
Aliquots of the lemonade preparations were stored at -20°C for the analysis of d-limonene content. The analysis was performed using a reversed-phase HPLC procedure. The lemonade preparation was mixed and diluted with the mobile phase before injecting onto the HPLC. Chromatographic separation was achieved using a Supelco LC-ABZ column (150 x 4.6 mm, Supelco, Bellefonte, PA), and a mobile phase consisted of acetonitrile and sodium acetate buffer [25 mM (pH 5.0)] in the ratio of 70:30. The flow rate of the mobile phase was at 1.1 ml/min. The column eluent was monitored with an UV detector at a wavelength of 230 nm. d-Limonene contents were quantified using calibration curves prepared with d-limonene standards diluted with the mobile phase. The calibration curve was linear over the concentration range of 0.5 to 100 µg/ml.
Data Analysis.
The following pharmacokinetic parameters of perillic acid were estimated using the WINNONLIN program with the model-independent approach (21)
: time to reach maximum plasma concentration (Tmax); maximum plasma concentration (Cmax); area under the plasma concentration-time profile (AUC); terminal elimination half-life (t1/2); and terminal elimination rate constant (
n).
| Results |
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| Discussion |
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Mediterranean-style lemonade is prepared from the whole fruit and is widely consumed by the general population in that region. In our previous study, we found that Mediterranean-style lemonade provides a rich source of d-limonene with d-limonene concentrations >20 times of those found in commercial citrus juice or preparations (18) . The current study aimed to determine whether the consumption of this citrus preparation would deliver active monoterpenes to the systemic blood. We have selected to determine the systemic exposure of perillic acid, a major metabolite of d-limonene, after the consumption of freshly prepared Mediterranean-style lemonade because p.o. administered d-limonene has been shown to rapidly and extensively convert to its metabolites, and plasma d-limonene levels may not be detectable after low dose administration of d-limonene. In addition, because of the preliminary nature of this investigation, we have developed and validated a simple analytical procedure for determination of plasma concentrations of perillic acid instead of a complex analytical procedure for simultaneous determination of plasma levels of d-limonene and its derived metabolites. Consuming 40 oz of freshly prepared Mediterranean-style lemonade provides dlimonene content that is 1020 times higher than intake from regular daily consumption of commercial citrus juice products. Plasma concentrations of the major metabolite of d-limonene, perillic acid, peaked at 1 h after the lemonade consumption, implying that d-limonene consumed was rapidly absorbed and metabolized to perillic acid. Consumption of 40 oz of lemonade (containing 0.596 g d-limonene) resulted in an average peak concentration of 6.2 µM and an average total system exposure (AUC) of 16.87 µM·h. The plasma perillic acid levels declined rapidly as a function of time with an average t1/2 of 1.38 h.
Crowell et al. (19) have determined the plasma concentrations of d-limonene and its metabolites (perillic acid, dihydroperillic acid, and limonene-1,2-diol) at 4 h after ingestion of a 100 mg/kg dose of d-limonene (7 g if assuming an average body weight of 70 kg) in a form of a custard mix that contained 5% orange oil (source of d-limonene). The average concentrations of perillic acid, dihydroperillic acid, and limonene-1,2-diol were found to be 35, 33, and 16 µM, respectively, whereas plasma d-limonene levels were <1 µM or not detected (19) . Vigushin et al. (15) reported the pharmacokinetic data of d-limonene and its metabolites in patients with advanced cancer using a pharmaceutical preparation of d-limonene at doses of 812 g/m2 (13.8420.76 g if assuming an average BSA of 1.73 m2; Ref. 15 ). After high oral dose administration, d-limonene and d-limonene-derived metabolites (perillic acid, dihydroperillic acid, and limonene-1,2-diol, uroterpenol) were present in plasma at concentrations < 100 µM. Perillic acid was present in plasma at levels higher than d-limonene and other d-limonene-derived metabolites. Plasma d-limonene concentrations were between 20 and 50% of perillic acid concentrations. At these high dose levels, the systemic exposure of d-limonene and its metabolites did not increase consistently as the dose increased. A dose of 8 g/m2 or 13.84 g resulted in an average peak perillic acid concentration of 20.7 µM and an AUC of 277 µM·h.
d-Limonene and its derived monoterpenes have been reported to alter p21ras expression either by decreasing overall levels of p21ras or by inhibiting farnesylation of the protein (4 , 6) with the inhibitory effects observed at low mM values. Consumption of citrus or pharmaceutical preparations of d-limonene achieved plasma monoterpene levels at the µM concentration range. Nevertheless, the plasma content of monoterpenes may underpredict the levels at the site of action because d-limonene and its derived metabolites have been shown to accumulate at high levels in the adipose and mammary tissues because of their high lipophilicity (25) . Extensive tissue binding could also significantly increase the tissue-to-plasma partition of these monoterpenes. To determine whether the body mass composition would affect the plasma levels of perillic acid, we have examined the correlation between the systemic perillic acid levels and BMI from subjects who had consumed 40 oz of lemonade. No significant correlation was observed between the two variables, partly because of the limited sample size. It is of interest that those (subjects 2 and 9) with the lowest BMI (lean individuals) had the highest systemic perillic acid exposure.
In summary, Mediterranean-style lemonade provides a rich source of d-limonene. Consumption of such a preparation leads to µM plasma concentration of a major and active metabolite of d-limonene. Studies on the safety and tissue exposure of monoterpenes after chronic high consumption of dietary limonene are necessary to evaluate the feasibility of conducting intervention trial using such a citrus preparation.
| Footnotes |
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1 This work was supported by Public Health Service Grants CA76008 and CA23074 from the National Cancer Institute. ![]()
2 To whom requests for reprints should be addressed, at Arizona Cancer Center, The University of Arizona, Tucson, AZ 85724. Phone: (520) 626-3358; Fax: (520) 626-5348; E-mail: schow{at}azcc.arizona.edu ![]()
3 The abbreviations used are: HPLC, high-performance liquid chromatography; BMI, body mass index. ![]()
Received 3/11/02; revised 7/22/02; accepted 8/ 8/02.
| References |
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24-globulin is necessary for d-limonene promotion of male rat kidney tumors. Cancer Res., 51: 3512-3521, 1991.This article has been cited by other articles:
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H. Mo and C. E. Elson Studies of the Isoprenoid-Mediated Inhibition of Mevalonate Synthesis Applied to Cancer Chemotherapy and Chemoprevention Experimental Biology and Medicine, July 1, 2004; 229(7): 567 - 585. [Abstract] [Full Text] [PDF] |
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