Binding of furanocoumarins in grapefruit juice to Aspergillus niger hyphae

Protein sequestration of lipophilic furanocoumarins in grapefruit juice

The sequestration of grapefruit furanocoumarins by foods was investigated by characterizing the binding between these compounds and foods with contrasting protein, fat, and carbohydrate compositions. Individual grapefruit furanocoumarins exhibited contrasting affinities to foods, where the lipophilic bergamottin and several structurally related dimers bound to foods more tightly than the more polar 6',7'-dihydroxybergamottin. From the investigation of different classes of macromolecules in foods, water-soluble proteins were found to be the major constituents responsible for furanocoumarin sequestration. Studies using bovine serum albumin as a model protein demonstrated the dissociation of grapefruit furanocoumarins from the insoluble juice cloud particles and the subsequent formation of water-soluble bovine serum albumin-furanocoumarin complexes. Fluorescence binding assays further demonstrated the binding of bergamottin and 6',7'-dihydroxybergamottin to bovine serum albumin. These results demonstrate that proteins can be sequestration agents of these important dietary furanocoumarins.

Removal of furanocoumarins in grapefruit juice by edible fungi

Furanocoumarins (FCs) in the human diet irreversibly inhibit human cytochrome P450 3A4 (CYP 3A4) and are responsible for the "grapefruit/drug""interaction phenomenon. Previously, we reported that FCs in grapefruit juice (GFJ) bind to autoclaved Aspergillus niger, and this binding reduced the GFJ inhibition of CYP 3A4. However, A. niger is not an edible fungus, and thus, potentially similar binding by edible fungi was also characterized. In this study, autoclaved Morchella esculenta, an edible ascomycete, removed much of the FC content in GFJ, resulting in decreased inhibition of CYP 3A4 activity by the GFJ. Three other edible fungi, Monascus purpureus, Pleurotus sapidus, and Agaricus bisporus, were evaluated for their binding with two of the major FCs in GFJ, 6',7'-dihydroxybergamottin (DHB) and bergamottin (BM). These autoclaved edible fungi removed these FCs from GFJ, similar to M. esculenta, indicating that binding is a general, passive interaction between FCs and fungal hyphae. The removal of FCs was independent of pH in GFJ. Dried fungal material of M. esculenta was also effective in removing FCs from GFJ and occurred with GFJ samples prepared from both fresh grapefruit and GFJ concentrate.

Aspergillus niger metabolism of citrus furanocoumarin inhibitors of human cytochrome P450 3A4

Fungi metabolize polycyclic aromatic hydrocarbons by a number of detoxification processes, including the formation of sulfated and glycosidated conjugates. A class of aromatic compounds in grapefruit is the furanocoumarins (FCs), and their metabolism in humans is centrally involved in the "grapefruit/drug interactions." Thus far, the metabolism by fungi of the major FCs in grapefruit, including 6', 7'-epoxybergamottin (EB), 6', 7'-dihydroxybergamottin (DHB), and bergamottin (BM), has received little attention. In this study, Aspergillus niger was observed to convert EB into DHB and a novel water-soluble metabolite (WSM). Bergaptol (BT) and BM were also metabolized by A. niger to the WSM, which was identified as BT-5-sulfate using mass spectrometry, UV spectroscopy, chemical hydrolysis, and (1)H and (13)C nuclear magnetic resonance spectroscopy. Similarly, the fungus had a capability of metabolizing xanthotoxol (XT), a structural isomer of BT, to a sulfated analog of BT-5-sulfate, presumably XT-8-sulfate. A possible enzyme-catalyzed pathway for the grapefruit FC metabolism involving the cleavage of the geranyl group and the addition of a sulfate group is proposed.