Paul Milbury, PhD is an Assistant Professor at the Friedman School of Nutrition Science and Policy at Tufts University and a Scientist II in the Antioxidants Research Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University. His research is focused on determining dietary bioavailability and the effectiveness of flavonoids and anthocyanins in modifying redox status and oxidative stress in aging related disorders. Anthocyanins are the phytochemicals that make fruit, wine, and berries red and blue.
Prior to joining Tufts, Dr. Milbury spent a year as a Harvard Research Fellow at Massachusetts General Hospital studying oxidative stress in neurodegenerative disorders.
As a senior research scientist in Long Range Research Lab at ESA, Inc., Dr. Milbury helped develop methodology for HPLC separation and electrochemical array detection linked to generation of large metabolic databases. Funded in part by NIH National Institute on Aging grants and utilizing prototypic instrumentation to separate, Dr. Milbury quantified, and databased literally hundreds of oxidizable compounds from plasma demonstrating the utility of large metabolic databases in the study of degenerative disorders.
Using immobility osteopenia as a test model, Dr. Milbury organized and managed a unique collaboration of NASA scientists and wildlife biologists to collect plasma and to compare metabolic patterns from human bedrest subjects with those of denning bears in the wild. The objective was to identify unique metabolites with high probability of involvement in immobility induced osteopenia. The project highlighted six compounds that may reveal mechanisms explaining the bear’s exceptional ability to avoid the debilitating effects of immobility induced bone loss.
Before joining ESA, Inc., Dr. Milbury conducted research for 18 years at Massachusetts General Hospital investigating the synergistic effects of endogenous and exogenous metabolites on mircrovascular second messenger signal mechanisms in stroke and thyroid function.
Dr. Milbury received degrees in Chemistry, Animal Sciences/Cellular Biology, and a Ph.D. in Animal and Nutritional Science from the University of New Hampshire. He also holds an Aviation Science degree and is an FAA Certified Instrument and Commercial Flight Instructor. Dr. Milbury flies seaplanes and had the unique experience of flying the NASA VMS space shuttle simulator at Ames NASA Research Facility. In his spare time, Dr. Milbury is a fly fisherman and raises working champion Nova Scotia Duck Tolling Retrievers.
Dr. Milbury ardently believes that major advancements in the sciences seldom emanate from the centers of scientific dogma but occur where the fringes of scientific fields overlap. Throughout his career, he has sought to be a bridge scientist, facilitating communication of ideas across scientific boundaries.
Xenobiotic Metabolism and Berry Flavonoid Transport Across the Blood Brain Barrier
Paul E. Milbury*1 and Wilhelmina Kalt 2
*1 Jean Mayer USDA Human Nutrition Center on Aging at Tufts University
711 Washington Street, Boston, MA 02111-1524.
2 Agriculture and Agri-Food Canada. Atlantic Food and Horticulture Research Centre 32 Main St. Kentville, Nova Scotia B4N 1J5.
The International Society for the Study of Xenobiotics defines the term xenobiotic as compounds that are foreign to an organism or are not part of its normal nutrition. Xenobiotic metabolism involves ancient and well conserved pathways that cause biotransformation and removal of foreign compounds taken in by an organism. Whether flavonoids in berries are to be considered xenobiotics to animals consuming them may depend upon whether they are perceived as nutrients or not. In either case, mammals quickly remove these polyphenolic compounds from the body via xenobiotic metabolism. (1) Nevertheless, evidence suggests that flavonoids may protect neurological tissues by possibly reducing neuroinflammation, decreasing age-related neurodegenerative disorders and cognitive decline. (2)
The health beneficial effects of flavonoids have been attributed to their antioxidant properties and their potential to quench damaging free radicals. Yet low bioavailability and status as xenobiotics assures that the direct contribution of flavonoids as radical quenchers in vivo is negligible.(3) However, research of the past decades has clearly demonstrated that flavonoids are potent modulators of cell signal transduction and capable of altering hundreds of metabolic pathways once present in tissues.(4) Many studies of flavonoid bioavailability to circulating blood exist; however, despite numerous studies of flavonoid/drug transporter interactions,(5) less is known about flavonoid bioavailability to brain tissue. To understand whether flavonoids and/or flavonoid metabolites are plausibly bioactive in the brain, it is critical that their bioavailability to the brain be ascertained.
In most cases, when plant flavonoids are consumed, they are quickly metabolized to aglycones which are then subject to extensive biotransformation and conjugation during absorption and during hepatic metabolism.
Many unanswered questions remain regarding what forms of flavonoids can be found in tissues after flavonoid feeding and what, if any, in vivo bioactivity these forms may have. A clear understanding of the relative bioavailability of individual flavonoids to the brain is further hampered by the fact that only a few compounds from each flavonoid class have been examined to date. Frequently these studies are conducted using high (pharmacological) doses; however, a few studies present findings using doses that are achievable in the diet or have investigated the presence of flavonoids after consumption of high flavonoid content foods or food extract. (6, 7, 8) Given the number and diversity of dietary flavonoids available in diets rich in, fruits, vegetables, grains and nuts, there is considerable work yet to be done. Fortunately, analytical instruments and techniques are improving yearly and are now providing the sensitivity necessary to quantify levels of flavonoids found in tissues.
All interstitial tissues in the body are protected from exogenous compounds by barriers formed by the vascular endothelium, a class of epithelial cells lining the intima of blood vessels that plays a critical role in maintaining interstitial tissue fluid homeostasis and determining which macromolecules gain passage into interstitial tissues. (9) The brain and neurological tissues are protected by an endothelial barrier structurally unique from other vascular barriers in physical characteristics and in the nature and number of transporters encompassed within it. (10) Direct measurements reveals differences between flavonoid classes regarding their ability to cross the blood brain barrier, (11, 12) and these differences appear to be dependent in part on compound lipophilicity and polarity. As a consequence O-methylation and glucuronidation may have a significant impact on flavonoid bioavailability to the brain.
Little research has been conducted on this aspect of flavonoid bioavailability; however, research on morphine-glucuronide access to the brain (13) suggests there might be uptake mechanisms capable of transporting glucuronides into the brain. Evidence exists from in situ research demonstrating that P-glycoprotein transporters play a role in the flux of flavonoids into the brain. (14 It is becoming increasingly clear that berry anthocyanins can penetrate the blood brain barrier in rodents (15, 16) and can also be found in the brain and ocular tissues of pigs after blueberry feeding. (17)
This paper reviews data on flavonoid bioavailability to the brain, cites some of the pitfalls and difficulties in determining bioavailability to the brain, and presents data regarding blueberry anthocyanin bioavailability and metabolism in the brain.
Keywords: LC/MS/MS; flavonoid; bioavailability; metabolism; transport; brain
(1) Croft, K. D. The chemistry and biological effects of flavonoids and phenolic acids. Ann. N. Y. Acad. Sci. 1998, 854, 435-442.
(2) Vauzour, D.; Vafeiadou, K.; Rodriguez-Mateos, A.; Rendeiro, C.; Spencer, J.P. The neuroprotective potential of flavonoids: a multiplicity of effects Genes Nutr. 2008, 3, 115-126.
(3) Williams, R.J.; Cadenas, E.; Rice-Evans, C. Flavonoids: antioxidants or signalling molecules? Free Radical Biology and Medicine. 2004, 36, 838-849.
(4) Tsuda, T.; Ueno, Y.; Yoshikawa, T.; Kojo, H.; Osawa, T. Microarray profiling of gene expression in human adipocytes in response to anthocyanins. Biochem. Pharmacol. 2006, 71, 1184197.
(5) Custodio, J.M.; Wu, C.Y.; Benet, L.Z. Predicting drug disposition, absorption/elimination/transporter interplay and the role of food on drug absorption. Adv. Drug Deliv. Rev. 2008, 60, 717-733.
(6) Andres-Lacueva, C.; Shukitt-Hale, B.; Galli, R.L.; Jauregui, O.; Lamuela-Raventos, R.M.; Joseph, J.A. Anthocyanins in aged blueberry-fed rats are found centrally and may enhance memory. Nutr Neurosci. 2005, 8,111-120.
(7) Borges, G.; Roowi, S.; Rouanet, J.M.; Duthie, G.G.; Lean, M.E.; Crozier, A. The bioavailability of raspberry anthocyanins and ellagitannins in rats. Mol. Nutr. Food Res. 2007, 51, 714-725.
(8) Papandreou, M.A.; Dimakopoulou, A.; Linardaki, Z.I.; Cordopatis, P.; Klimis-Zacas, D.; Margarity, M.; Lamari, F.N. Effect of a polyphenol-rich wild blueberry extract on cognitive performance of mice, brain antioxidant markers and acetylcholinesterase activity. Behavioural. Brain Research, 2009, 198, 352 358.
(9) Aird, W.C. Phenotypic heterogeneity of the endothelium: I. Structure, function, and mechanisms, Circ. Res. 2007, 100,158-173.
(10) Pardridge, W.M., Drug and gene targeting to the brain with molecular Trojan horses. Nat. Rev. Drug Disc. 2002, 1, 131-139.
(11) Milbury, P.E. Transport of flavonoids into the brain. In Micronutrients and Brain Health, edition no. 1; Packer, L; Helmut Sies, H; Eggersdorfer, M; Cadenas, E., Eds; CRC Press; London, UK, 2009. pp. 432
(12) Youdim, K.A.; Shukitt-Hale, B.; Joseph, J.A. Flavonoids and the brain: interactions at the blood-brain barrier and their physiological effects on the central nervous system. Free Radic. Biol. Med. 2004, 37, 1683693.
(13) Bourasset, F.; Cisternino, S.; Temsamani, J.; Scherrmann, J.M. Evidence for an active transport of morphine-6-beta-d-glucuronide but not P-glycoprotein-mediated at the blood-brain barrier. Journal of Neurochemistry. 2003, 86, 1564567.
(14) Youdim, K.A.; Qaiser, M.Z.; Begley, D.J.; Rice-Evans, C.A.; Abbott, N.J. Flavonoid permeability across an in situ model of the blood-brain barrier. Free Radic. Biol. Med. 2004, 36,59204.
(15) Talavera, S.; Felgines, C.; Texier, O.; Besson, C.; Gil-Izquierdo, A.; Lamaison, J.L.; Remesy, C. Anthocyanin metabolism in rats and their distribution to digestive area, kidney, and brain. J. Agric. Food Chem. 2005, 53, 3902908.
(16) Abd, E.; Mohsen, M.M.; Marks, J.; Kuhnle, G.; Moore, K.; Debnam, E.; Kaila, S.S.; Rice-Evans, C.; Spencer, J.P.E.; Absorption, tissue distribution and excretion of pelargonidin and its metabolites following oral administration to rats. Br. J. Nutr. 2006, 95, 518.
(17) Kalt, W.; Blumberg, J.B.; McDonald, J.E.; Vinqvist-Tymchuk, M.R.; Fillmore, S.A.; Graf, B.A.; O’Leary, J.M.; Milbury, P.E. Identification of anthocyanins in the liver, eye, and brain of blueberry-fed pigs. J. Agric. Food Chem. 2008, 56, 705-712.