Chemistry 150, Fall 2008
Bergamottin and its Role as a The Citrus bergamia also grows in warmer climates and was initially found in Southeast Asia.1 Citrus bergamia is Drug Inhibitor often found in Earl Grey tea.1 This species is the namesake of bergamottin, and it was in the bergamot orange that the Jennifer Murphy, Fall 2008 compound was first isolated.1
Introduction Bergamottin is a member of the furanocoumarin family and is most commonly found in grapefruit juice. Bergamottin is a known drug inhibitor of cytochrome P450 34A. For this reason, it is often recommended that patients avoid consumption of grapefruit juice if currently prescribed medication such as statins, antihistamines, and drugs in several other classes. This drug interaction is often referred to Figure 3. Citrus bergamia. source as “the grapefruit effect” and can cause the compound to (http://cherylinskintherapy.co.uk/images/bergamot.jpg) remain in the body for a prolonged period of time; which may ultimately lead to health risks in some patients. The II. Biological Activity occurrence of bergamottin, the synthesis and biosynthesis of Bergamottin inhibits the cytochrome P450 34A enzyme.3 the compound will be discussed in the following review. Grapefruit juice was first noticed to cause such an inhibition
when it was used as an additive to ease the consumption of the
drug felodipine, which was mixed with ethanol and therefore had a very strong taste.4 It was observed that there was in fact a compound in the grapefruit juice that was causing this cytochrome P450 34A enzyme inhibition to be targeted, and an increase in the oral bioavailability was clearly taking place.4
Figure 1. Bergamottin, a furanocoumarin found in grapefruit To validate this observation, in vitro experimentation was juice. conducted to determine what compounds in grapefruit juice were causing this inhibition.5 It was postulated that three I. Occurrence compounds could be causing this effect; naringin, 6’,7’- dihydroxybergamottin, and bergamottin.5 These same Bergamottin is a furanocoumarin compound found naturally 1 experiments were then conducted in vivo and it turned out that in members of the Citrus Genus. It is most commonly bergamottin did in fact inhibit the cytochrome P450 34A associated with the Citrus x paradisi species, otherwise enzyme in the body, whereas the other two compounds did not known as grapefruit, but this compound was originally 6 1 have any effect on the enzyme. This in vivo inhibition occurs identified in the Citrus bergamia, or Bergamot fruit. The in both the liver and the small intestine; these are the active Citrus x paradisi trees are classified as subtropical trees, and sites for the effected drugs.7, 8, 9 There are many drugs that are are therefore found in warmer climates; such as the southern 1 able to be metabolized by the cytochrome P450 34A enzyme, portion of the United States, Barbados and Southeast Asia. so the inhibition of this enzyme may be a cause for concern; The Citrus x paradisi species originated in Barbados as a although the results from this inhibition are not always hybrid between the Citrus maxima, a pomelo, and a Citrus 10 1 considered to have negative effects. sinensis, an orange. This explains the similarities of the The oral bioavailability of the drugs become much longer grapefruit composition and the pomelo composition; both 2 when bergamottin inhibits the cytochrome P450 34A enzyme, have drug inhibitory effects. and this can be further illustrated with the area under the time versus concentration curve, or the AUG, is taken into account.4 When the cytochrome P450 34A enzyme is not inhibited, this area under the curve is smaller than when bergamottin is present in the human system.4 This increase in oral bioavailability can be considered a positive effect when drugs such as Viagra or the anti-AIDS drug, saquinavir, are being prescribed.4 This is due to the fact that the desirable effects of these drugs will last for a longer period of time.4
The drug saquinavir has an undesirably low oral Figure 2. Citrus x paradisi and Citrus maxima. source bioavailability on its own, but with help from bergamottin, the 4 (http://www.chefdecuisine.com/all_fruit/citrus/grapefruit/ima drug is much more effective. Patients taking drugs related to ges/grapefruit_440x330.jpg) statins, such as Mevacor (lovastatin) and Lipitor (atorvastatin calcium), or antihistamines, such as terfenadine, should be Chemistry 150, Fall 2008
cautious of grapefruit juice consumption.4 There have been alkyl group occurs to form marmesin (4). This process uses reports of serious undesirable side effects when these types of NADPH and oxygen along with a cytochrome P450 mono- 16, 17, 18 drugs are taken with grapefruit juice.4 These adverse effects oxygenase catalyst. This same catalyst and these same are caused by the drug remaining in the biological system for reagents are then used twice more, first to remove the hydroxyisopropyl substituent from marmesin (4) to form a longer period of time than the drug is meant to, leading to a psoralen (5), and then to add a hydroxyl group to form presystemic elimination, which eventually leads to the bergaptol (6).16, 19 Bergaptol (6) can then be methylated with 4 possibility of a patient overdose. SAM, S-Adenosylmethionine, to form bergapten (7).16, 19 There are many different brands of grapefruit products Finally, a GPP, or geranyl pyrophosphate, unit attaches itself containing bergamottin, ranging everywhere from doubly to the newly methylated bergapten (7) to form the target concentrated frozen grapefruit juice to grapefruit flavoured molecule bergamottin (8).19 soda, and each brand contains a different amount of the compound.11 This means that various brands can be less effective than others when inhibiting the cytochrome P450 IV. Synthesis 34A enzyme.11 People can also be effected differently by The synthetic approach to making bergamottin is shown in bergamottin depending on the amount cytochrome P450 34A figure 5.20 The synthesis of this compound was unknown for a produced in their body.4 Measures are being taken to reduce number of years after it was first isolated,21 but this approach the inhibiting properties of bergamottin in grapefruit juice in now used produces the compound with an extremely high hopes that patients advised to avoid grapefruit products may yield of 98%.20 This synthesis is initiated by combining the once again enjoy them.12, 13, 14 The methods that have shown commercially available starting product, bergapten (9), with promise are treating the grapefruit juice with UV irradiation12, magnesium diiodide, MgI .20 This in effect works to heating the juice13, and adding edible fungus to the 2 demethylate the bergapten (9) and forms the bergaptol (10) beverage14; all three methods have shown that the levels of product with a yield of 87%. The bergaptol (10) is then bergamottin are diminished. Other food products, such as red alkylated using the phase transfer conditions that make wine,15 has shown inhibitory properties, but bergamottin selective alkylation possible.20 This reaction forms the remains one of the most effective. bergamottin product with a 98% yield.20
III. Biosynthesis The biosynthesis of bergamottin is shown in figure 4.16 First, the demethylsuberosin (3) product is formed by the alkylation of the umbelliferone (2) compound, which originates from the shikimate pathway.16, 17 This is done with the use of DMAPP (1), dimethylallyl pyrophosphate, which is an isomer of IPP, isopentenyl pyrophosphate, innate in most all living things.16 Next, a cyclization of the newly added
Figure 5. Synthesis of Bergamottin20
Conclusion Bergamottin has proven very effective as a cytochrome P450 34A inhibitor. Inhibition of this enzyme can have both positive and negative effects as it elongates the oral bioavailability for the drugs that act at this site. The consumption of grapefruit products, as well as other bergamottin containing citrus products, especially grapefruit juice should be avoided in patients taking drugs that already have good oral bioavailabilities, as this can lead to a drug overdose. Studies are being conducted to reduce the content of bergamottin in grapefruit juice so that patients concerned with the effect of this compound on their prescribed drug regiments can once again enjoy such food commodities.
Figure 4. Biosynthesis of Bergamottin16 Chemistry 150, Fall 2008
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