AOCS Phospholipid Division
Newsletter April 2007

Bruce Sebree.Greetings From the Chair
Bruce Sebree

Hello once again, for the last time, to the members of the Phospholipids Division of AOCS. Yes, it's hard to believe that two years have flown by so quickly since I accepted the position of chair for this fine division. The gavel will be passed at the Phospholipid luncheon and I can semi-retire (Division-wise at least) to that state where statements at the board of directors meetings can be prefaced with the phrase "well, that's not the way we used to do things, but..."!

In any event, an exceptional group of sessions has once again been put together by the session chairs. Additionally, we have a pre-meeting short course "Lecithin: Properties and Technological Functions" (May 11-12, 2007) that should be of interest to many. If you have not registered yet, please do at your earliest convenience so that we can make a proper estimate on attendance. There is an article in this newsletter with additional information.

Plans have been finalized for the Phospholipids Division luncheon. As this is an election year, nominations and elections for the 2007/2009 board of directors will take place during the luncheon. Highlighting the luncheon will be the presentation of the best paper award to Dr. Anders Vikbjerg et al for "Comparative evaluation of the emulsifying properties of phosphatidylcholine after enzymatic acyl modification." Many thanks to the ILPS for supporting this award. Dr. Vikbjerg will be present to discuss this work as part of the luncheon agenda.

I want to take this time to thank everyone who helped make my time as Chair an enjoyable and (relatively) easy venture. Best of luck to Jonathan Maynes as he takes the reins (should there not be a coup at the luncheon), and to the rest of the new board of directors for the Phospholipids Division. I hope to see all of you in Québec City in a couple of months!

Short Course on Lecithin Properties and Technological Functions

May 11-12, 2007, Quebec City, Quebec, Canada
Venue: Dept of Food Science, Laval Université
Organizers: Willem van Nieuwenhuyzen, Paul Angers, and Joseph Arul.

The AOCS Phospholipid Division, ILPS, and Laval University will present this short course prior to the joint AOCS 98th Annual Meeting and 27th ISF Congress.

Five instructors will teach the properties of plant phospholipids with a focus on their application in food emulsions. Friday afternoon, spent in the Department of Food Science, is devoted to laboratory demonstrations of making emulsions with lecithins and measuring emulsion characteristics. The staff is already busy optimizing the testing protocols.

Instruction with oral presentations and demonstrations will be given by world class experts, including:

Other instructors are Moghis Ahmad of Jina Pharmaceuticals Inc., Bruce Sebree of Archer Daniels Midland, and Willem van Nieuwenhuyzen of Lecipro Consulting.

An extensive Program is available online.

AOCS Phospholipid Division members are invited to contact colleagues and professional friends to encourage them to register. During the coffee breaks, lunches, and dinner (all included in the course fee), you will have excellent opportunities to make friends and to discuss your specific emulsion issues with colleagues and instructors.

GRAS Approval for Enzyme Technology
from inform 18(2) p. 104

Diversa Corporation based in San Diego, California, USA, announced on December 19 that its Purifine(TM) enzyme had obtained GRAS (Generally Recognized As Safe) approval from the U.S. Food and Drug Administration (FDA) for edible oil applications. Earlier approval had been received from the U.S. Environmental Protection Agency (EPA) for nonfood applications, including the use of Purifine enzyme for increasing the efficiency of oilseed processing for biodiesel fuel production.

Use of the enzyme is claimed to facilitate a novel degumming process that increases oil yield and reduces low-value by-products by removal of the phospholipid component.

"The FDA GRAS approval has come earlier than anticipated and will allow us to accelerate the full commercial launch of Purifine enzyme," said Edward T. Shonsey, Diversa's Chief Executive Officer. "We now have the flexibility to initiate full-scale trials in oilseed plants in the U.S. that refine vegetable oil for either food or biofuel applications, or both, greatly increasing the number of plants that can potentially adopt our improved enzymatic degumming process."

Gary List.USB recognizes List

A long-time AOCS member and Contributing Editor to inform, Gary List has been recognized by the United Soybean Board (USB) with its bestowing of the USB Outstanding Achievement Award 2006, the organization's highest award.

The award is given to an individual, organization or group that has made an outstanding positive impact on the soybean industry and the soybean checkoff.

The presentation was made to List at the 2007 Commodity Classic held in Tampa, Florida, USA from February 27 to March 3.

Although officially retired from the Agricultural Research Service (ARS) of the U.S. Department of Agriculture (USDA), List continues to appear for work at the USDA-ARS National Center for Agricultural Utilization Research (NCAUR) at Peoria, Illinois.

Announcement of Research Funds

Improvement of bioavailability and tolerance of actives by phospholipids in oral, topical, pulmonary and parenteral systems

The Phospholipid Research Center located in Heidelberg, Germany was funded as a non-profit organisation and intends to promote and provide a foundation for the use of phospholipids in pharmaceuticals.

The Phospholipid Research Center wants to extend the knowledge of the improvement of bioavailability and tolerance of actives in oral, topical, pulmonary and parenteral systems. It announces research funds for these investigations.

Scientists from home and abroad are encouraged to submit research proposals covering these questions to apply for the funds for non-commercial uses.

Individual researchers and research groups are encouraged to submit research proposals (2-4 pages) written in English in triplicate. The proposals should contain the specifications of costs and list all other funds.

Individual projects will be funded partially or completely. The amount and duration of the financial aid depends on the scale of the problem to be addressed. In addition to the investigation of new aspects, a state-of the-art review should be created as well. The Phospholipid Research Center requests for half-yearly progress reports available to the membership. The results will be published with mention of the Phospholipid Research Center.

The international Scientific Board of the Phospholipid Research Center will decide about the award of research grants.

Please send your application and inquiries by May 1st 2007 to:
Phospholipid Research Center
Dr. Tanja Schaffer
Im Neuenheimer Feld 582
D-69120 Heidelberg
Germany
Tel.: +49 6221 / 588 83 60
info@phospholipids.net

ICBL–ILPS–ELIFE: Three successful lipid conferences in Pécs
Willem van Nieuwenhuyzen and Laszlo Vigh
from inform 18(3) p. 203

A joint meeting of three lipid associations was organized by the staff of the Biological Research Center of the Hungarian Academy of Science (BRC-HAS) and held during September 5–10, 2006, in the city of Pécs,120 miles south of Budapest, Hungary. The former BRC Director and HAS member Laszlo Vigh was conference chair with overall responsibility for the scientific program, with special focus on the International Conference on the Biosciences of Lipids (ICBL) sessions. One of the driving forces behind ICBL and cooperation with the European Lipidomics Initiative (ELIFE) and the International Lecithin & Phospholipid Society (ILPS) was Fritz Spener, former professor at the University of Münster, Germany, who now works from his hometown University of Graz in Austria.

Meeting structure

Under the umbrella of the 47th ICBL Congress, the “science week” started with a six-lecture ELIFE workshop followed by the ICBL Congress and ended with the ILPS Congress.

The ELIFE workshop was held in cooperation with the International Society for the Study of Fatty Acids and Lipids (ISSFAL). The combination of the final two ICBL sessions with two additional sessions constituted the 9th ILPS Congress titled “Phospholipids for Health” focusing on nutrition and biochemistry of phospholipids. These latter sessions were organized by Michael Schneider of Lecithos, Freinsheim, Germany, and ILPS Executive Director Willem van Nieuwenhuyzen. There was overall enthusiasm from registrants for the joint scheduling of the three events.

The scientific program involved 10 sessions with 47 plenary lectures by invited speakers and 17 oral presentations, selected from the submitted abstracts for posters. More than 100 posters were presented. In total over 230 technical registrations were made for all three events, with over 10% coming from Japan and 5% from North America. Abstracts of the lectures and posters were published in the September issue of Chemistry and Physics of Lipids (143:38–114, 2006).

All sessions were held in the art deco styled marble Congress Hall of the Palatinus Hotel in the city center. The social program was excellent, promoting conviviality among all scientists. The opening mixers, a reception in the town hall, a visit to winery caves presenting Transdanubian local color, and a concluding joint congress dinner were all much appreciated.

Sessions

Lipidomics and Health (ELIFE workshop). Jürgen Borlak, Fraunhofer Institute, Hannover, Germany, discussed the role of the lectin-like oxidized (Ox)-LDL receptor LOX-1 in endothelial dysfunction as a possible explanation of aberrant lipid metabolism in human diseases. Balazs Sarkadi, National Medical Center, HAS, Budapest, described the ABC transporters for membrane lipids, while Hee-Young Kim of the National Institute of Health, Bethesda, Maryland, USA, considered the application of mass spectrometry in membrane-related signaling research. Pierre Bougnoux of INSERM, Tours, France, discussed the relationship between diet, breast cancer, and the lipidome (the totality of lipids).

The 10th L.L.M. van Deenen lecture. Ben de Kruijff, University of Utrecht, The Netherlands, addressed “Membranes, Where Lipids and Proteins Meet.” He said that lipids are organized in bilayers and provide the membrane with its barrier function; proteins give rise to the specific functions of membranes such as transport, recognition, and catalysis. A new model considered the key role of membrane phosphatidic acid.

Lipidomics. Markus Wenk, National University of Singapore, discussed lip-idomics of host-pathogen interactions, and Edward Dennis, University of California at San Diego, La Jolla, USA, described the progress being made in lipid maps and eicosanoid lipidomics. Gerd Schmitz, University of Regensburg, Germany, focused on the effect of the differential raft regulation during Ox-LDL and E-LDL (enzymatically modified LDL) loading in human macrophages.

Membrane Microdomains. Janos Szollosi of HAS, Debrecen, Hungary, reported that membrane microdomains are distinct molecular association clusters with function properties, while Gerhard Schütz, Johannes Keppler University, Linz, Austria, examined the nanoscopic organization of the plasma membrane using single molecule microscopy. Toshihide Kobayashi, Riken, Wako-shi (Tokyo), Japan, described the combination of different novel cholesterol probes with the capability of revealing the cholesterol gradient in cell membranes.

Gerrit van Meer of Utrecht University, The Netherlands, discussed dynamic organization and unexpected function of typical raft lipids.

“Tibor Farkas in memorium.” The late Tibor Farkas, who led the Biological Research Center of HAS to excellence, was recognized. During the 1960s he worked in Italy, and later in the United States, at a time when open cooperation between the East and West was still very difficult. He was elected member of the National Academy of Sciences of the United States in 1989 for his work on biochemistry and physiology of lipids with focus on the adaptation of membrane to changes in temperature.

Michael Schlame, New York University, New York City, USA, described the Barth syndrome, a human disorder of cardiolipin metabolism that is caused by mutations of the tafazzin gene leading to reduced content of cardiolipin. Pablo Escriba, University of the Balearic Islands, Palma de Mallorca, Spain, considered the effects of membrane-lipid therapy.

Lipids and Stress. John Zehmer, Arizona State University, Tempe, Arizona, USA, discussed thermal acclimation in raft microdomains of the plasma membrane. John Harwood, Cardiff University, United Kingdom, presented studies on a novel desaturase involved in stress adaptation in the soil protozoon Acanthamoeba castellani. Ibolya Horvath, HAS, Szeged, Hungary, described stress protein responses in mammalian cells under the control of lipid composition and microdomain organization of membranes, while George Carman, Rutgers University, New Brunswick, New Jersey, USA, discussed the regulation of the yeast Mg2+-dependent phosphatidate phosphatase in response to nutrient deprivation.

Gene Regulation by Lipid Signaling. Folkert Kuipers, University of Groningen, The Netherlands, spoke on the regulation of lipid metabolism by the nuclear receptors LXR (liver X receptor) and FXR (farnesoid X recpetor), while Nico Marx, University of Ulm, Germany, considered the cardiovascular effect of PPAR (peroxisome proliferator-activated receptor) activators. Bart Staels, INSERM, Lille, France, demonstrated that nuclear receptors are the therapeutic targets to modulate the metabolic syndrome.

What are Healthy Lipids? Ingeborg Brouwer, VU University, Amsterdam, The Netherlands, reported that n-3 fatty acids are important in preventing cardiac arrhythmia. Bengt Vissby, Uppsala University, Sweden, discussed the health effects of conjugated linoleic acid (CLA), noting there are as yet no proven health benefits of CLA in humans. Scope exists, however, for further clinical trials to document the possible benefits of CLA isomers as antitumorigenic or immunogenic agents. Gwendolyn Barcelo-Coblijn, University of North Dakota, Grand Forks, USA, reported that alpha-linolenic acid-enriched (flaxseed) diets show beneficial effects in cattle and firefighters. These diets significantly increase n-3 fatty acid (FA) content in red blood cells.

Metabolism and Function of Lipids in the Brain. Thomas Brenna, Cornell University, Ithaca, New York, USA, discussed the influence of perinatal long-chain polyunsaturated fatty acid (PUFA) nutrition and prematurity on neural tissue PUFA composition and function in non-human primates. Sylvie Chalon, INSERM, Tours, France, considered the effects of n-3 PUFA on neurotransmission systems, while László Puskás, BRC-HAS, Szeged, described “Protein micro arrays for dietary lipid-induced expression analysis in the brain.”

Andrew Sinclair, Deakin University, Burwood, Australia, asked whether the relationship between long-chain PUFA and brain function will reach the same public status as the “calcium and bone” relationship. Detailed reports on beneficial effects of long-chain n-6 and n-3 PUFA on human brain phospholipids have been available for over 40 years. He said arachidonic acid (AA) and DHA reduce the impact of depression and schizophrenia and that data from animal models of Alzheimer’s show evidence of benefits from DHA application. Benjamin Buaud, ITERG, Bordeaux, France, discussed the effects of n-3 PUFA deficiency on the expression of nuclear receptors and synaptic plasticity markers in rat brain, and Jérémy Skrzypski, University of Bourgogne, Dijon, France, presented studies on the influence of n-3 FA on PUFA metabolism in rat brain in relation to aging.

Sphingolipids. Yoshio Hirabayashi, Riken Brain Science Institute, Wako-shi (Tokyo), discussed the role of glycosphingolipid synthesis in brain development and survival; l-serine is essential for sphingolipid synthesis in neuronal function and activity. Tony Futerman, Weizmann Institute, Rehovot, Israel, described the inclusion of the Longevity Assurance (LASS) gene as a member of the mammalian cer-amide synthase gene family. Gábor Tigyi, University of Tennessee, Memphis, USA, reported on the structural analysis of sphingosine-1-phosphate and LPA (lysophosphatidic acid) receptors from computational models for rational drug design. Howard Riezman, University of Geneva, Switzerland, described the biosynthesis, transport, and functions of sphingolipids in yeast. Yasuyuki Igarashi, Hokkaido University, Sapporo, Japan, discussed topological metabolism and transbilayer dynamics of sphingolipids, and Makoto Ito, Kyushu University Fukuoka, Japan, described the biological significance of ceramide metabolism in development of nervous and vascular systems in zebrafish.

Åke Nilsson, University of Lund, Sweden, considered “Sphingolipids in the Gut. What Are the Key Issues?” Dietary milk sphingolipids have shown positive anti-tumor effects in experimental colon cancer in animals and humans. Peter Slotte, Åbo Akademi, University Turku, Finland, reported that sphingomyelin interacts with cholesterol in cells, reducing desorption rate and oxidation susceptibility. Willem F. Nieuwenhuizen, TNO Quality for Life, Zeist, The Netherlands, described dietary sphingolipids effects on lowering plasma cholesterol and triacylglycerol levels and preventing liver steatosis in APOE*3Leiden mice. He challenged food companies to work on foods with enhanced levels of sphingolipids and phospholipids.

Willem van Nieuwenhuyzen, Lecipro Consulting, Limmen, The Netherlands, reviewed nutritive aspects of soy phospholipids with emphasis on choline supply. Rui-Dong Duan, University of Lund, Sweden, discussed sphingomyelinases and cer-amidases in intestinal mucosa where expression of alkaline sphingomyelinase (alk-SMase) is subject to change by dietary factors and some anticancer drugs. Karel van Erpecum, University Medical Center, Utrecht, The Netherlands, described the influence of bile salts on molecular interactions between sphingomyelin and cholesterol in the biliary and intestinal tracts.

Marine Phospholipids. Erik Lovaas, University of Tromsø/BioSea Management AS, Norway, considered marine phospholipids derived from fish and fish by-products as third-generation n-3 products. He noted that marine phospholipids facilitate n-3 FA transport over the blood-brain barrier, preventing n-3 FA deficiency in the brain. Joseph Hibbeln NIAAA/NIH, Bethesda, Maryland, USA, described the preliminary positive influence of n-3 FA in reducing aggression and violence in alcoholics, possibly by increasing brain serotonin levels. Hee-Yong Kim, also of the NIAAA/NIH, presented her work on the effects of brain phosphatidylserine in neuronal signaling. Dori Pelled, Enzymotec, Migdal-HaEmeq Israel, reported that n-3 phosphatidylserine affects positively both the cognitive performance and Attention Deficit Hyperactivity Disorder (ADHD) in children. Maud Cansell, ISTAB, University of Bordeaux, France, compared the metabolic fate of n-3 PUFA in plasma and liver of rats supplemented with marine lipid-based liposomes or fish oil. Hogne Hallaraker Natural SA, Hovdebygda, Norway, described the functions of long-chain phospholipids focusing on enzymatically transesterified phospholipids based on a number of clinical studies made in cooperation with several institutes.

Awards

The ICBL 2006 Poster Awards were presented to the following authors (name of presenter underlined):

Bellenger, J., F. Guinot, S. Bellenger, and M. Narce, UPRES Lipides et Nutrition, University of Burgundy, Dijon, France; Natter, K., J. Petschnigg, and S.D. Kohlwein, Institute of Molecular Biosciences, University Graz, Austria; Andersson, M.X., M. Goksör, and A.S. Sandelius, Departments of Plant and Environmental Sciences, and of Physics Göteborg University, Sweden.

The presenting authors each received certificates and 500 Euros. The Awards were donated by the Organizing Committee of the ICBL 2006 and presented by the Chair, Laszlo Vigh.

In addition, ICBL decided to offer for the first time a Young Speaker Award to scientists below the age of 40 for short oral presentations. The publication Biochimica et Biophysica Acta (BBA) had agreed to be the sponsor of this award. Fritz Spener, the Executive Manager of BBA Section Molecular and Cell Biology of Lipids, presented the ICBL Young Speaker Award in the form of a certificate and 500 Euros to Harini Sampath, Departments of Nutritional Sciences and of Biochemistry, University of Wisconsin, Madison, USA, for a paper co-authored by M. Miyazaki and J.M. Ntambi.

Sponsorships

All three associations gratefully acknowledged the sponsors. Avanti Polar Lipids Inc., USA, sponsored both ICBL and ILPS conferences. ICBL was sponsored by Hungarian companies and foundations. ILPS was sponsored by ADM—Lecithin Group, USA, and Spectral Service Laboratory GmbH, Germany. The sponsors made it possible for invited speakers to be given travel support.

Near Future Activities

ICBL has scheduled the 48th Conference for Turku, Finland September 4–8, 2007, to be chaired by Peter Slotte, Åbo University, Turku (netlink: www.icbl2007.abo.fi).

ILPS has scheduled its 10th Phospholipid Congress to be held in 2–3 years’ time and is to organize Lecithin Technologies short courses at the 2007 AOCS Annual Meeting & Expo scheduled for Québec City, Canada, and also in Belgium in 2008 (netlink: www.ilps.org).

Willem van Nieuwenhuyzen is Director Lecipro Consulting (willem@lecipro.nl). Laszlo Vigh is Former Director BRC, Member HAS Szeged (vigh@nucleus.szbk.u-szeged.hu).

A number of drivers affect the protein bioadhesives market
Edgar J. Acosta
from inform 18(1) p. 56

Proteins and polysaccharides were the adhesive material of choice before World War II. At that time, Henry Ford, inventor and automobile manufacturer, and George Washington Carver, agricultural researcher and peanut advocate, were among the proponents of “chemurgy,” a concept by which fuels and chemical products (adhesives included) derived from plants and other renewable sources would sustain the growing manufacturing and transport industry. During World War II, inexpensive, moisture-resistant, and high bond strength formaldehyde-based resins were developed to replace “protein glues.”

Sustained by the Haber-Bosch ammonia process (which can introduce nitrogen from air into fertilizers) and developments in biotechnology, the worldwide production of protein-rich grain meal is now close to 100 million tons per year. It is estimated that more than one third of this protein source is underutilized and could be used as raw material for new protein-based industrial products. The current and future developments on protein-based adhesives for industrial and biomedical applications are two topics of major interest.

Proteins as biologically derived adhesive material

In formaldehyde-based resins, the interpenetration and covalent bonding (cross-linking) of polymer chains produce adhesives with high bond strength and moisture resistance. In proteins, however, chain interpenetration is hindered by protein molecular folding, which is the reason why denatured proteins are better adhesives. Hy- drogen bonding, electrostatic, and van der Waals interactions are responsible for cross-linking protein chains. The interaction between proteins is weakened by water molecules, owing to the hydration of ionic groups and hydrogen bonding moieties on the protein chains.

Nature provides evidence that it is possible to produce protein-based high- strength adhesives. The best example of these adhesives is mussel adhesive proteins (MAP) that are capable of adhering marine mussels to various surfaces (including glass and Teflon®). It is believed that MAP owe their strength to a combination of various factors: the shape of the byssus (filamentous secretions) of the mussels, the tight packing of protein bundles in the byssus, and the presence of a water-resistant protein “glue” at the end of the byssus. The cross-linkage of hydrophobic amino acid residues (especially l-3,4 dihydroxy-phenylalanine, l-DOPA) is responsible for the water resistance of MAP.

Although various research groups have tried to synthesize these proteins in genetically modified bacteria, their commercial use is limited owing to high production costs.

The research into protein-based adhesives has been driven by economics and environmental concerns (replacement of formaldehyde-based adhesives). In the United States alone, an estimated 3 million tons of adhesives are sold every year. Wood processing and pulp and paper industries are the largest consumers of adhesives. Among the various protein-based adhesive alternatives, a few representative examples are worthy of discussion.

The Thames-Rawlins group at the University of Southern Mississippi, Hattiesburg, Mississippi, USA, has patented the use of maleinized methyl ester of tung oil (MMETO) as an additive to improve the bond strength and moisture resistance of soy protein-based adhesives. These researchers use glycerol as a plasticizer to unfold the proteins. Protein unfolding improves MMETO penetration and may induce an “entanglement” effect once the MMETO monomer is polymerized, increasing the bond strength of these mixtures. Similarly, a mixture of monomer (phenol formaldehyde), resorcinol, and soy protein is used in a commercial product, the PRF/Soy 2000 wood finger joint adhesive developed at the Battelle Memorial Institute at Columbus, Ohio, USA (Fig. 1).

Xiuzhi Sun’s research group at Kansas State University, Manhattan, Kansas, USA, has mixed various anionic and cationic surfactants that bind to charged groups in the protein molecule, promoting protein unfolding and increasing protein hydrophobicity. Another approach used by Sun’s group is protein esterification with ethanol. This group has noted that there is an optimal level of protein hydrophobicity for maximal bond strength and moisture resistance.

Kaichang Li’s research group at Oregon State University, Corvallis, Oregon, USA, has grafted DOPA-like catechol (pyrocatechol; 1,2-dihydroxybenzene) groups from lignin residues into soy protein isolates in the presence of polyethylenimine. The resulting polymers have superior bond strength and moisture resistance. At optimal formulation conditions the bond strength (measured as shear strength) of these soy protein-modified adhesives is close to 5 MPa (compared with 6 MPa for phenol-formaldehyde).

There are other protein modification approaches not described in this article that produce similar effects to those mentioned before. While all these approaches seem different, they share a number of common principles:

(i) need to unfold the proteins to improve protein-protein interactions;
(ii) reduction of protein-water interaction through hydrophobic additives, while maintaining a certain balance;
(iii) promotion of protein-protein interaction through aromatic and amino groups introduced either as additives or chemically attached to the protein chain.

Proteins as adhesives for biological substrates

Proteins are gifted with different moieties that allow them to adhere to a wide range of substrates through van der Waals, electrostatic, and hydrogen-bonding interactions. The adhesive properties of proteins to biological substrates are evidenced by numerous phenomena such as the adhesion of bacterial films to dental surfaces. One example of the biomedical use of protein bioadhesives as a dental adhesive in wound healing applications is MAP obtained from genetically modified bacteria using recombinant protein adhesive technology developed by Dong Soo Hwang and colleagues at Pohang University of Science and Technology at Pohang, Korea (Kollodis BioScience, Inc.). Another commercial example is Bioglue® (Protein Polymer Technologies, Inc., based at San Diego, California, USA), which, similar to PRF/ Soy 2000, consists of a mixture of proteins (collagen, albumin) with aldehydes, and is used for tissue adhesion.

One area of growing interest is the use of plant-extracted proteins, lectins in particular, as bioadhesives for drug delivery. Lectins (glycoproteins that bind to polysaccharides) adhere to mucous (mucin polysaccharides) membranes such as those found in airways, oral cavities, and in the small intestine. Research in the area of lectin-enhanced drug delivery (including oral and transnasal) began in the mid-1980s and was actively promoted by Barbara Naisbett and John Woodley at the University of Keele in Staffordshire, United Kingdom. This work was driven by the need to improve the bioavailability of hydrophobic drugs and proteins. Currently, oral and transnasal delivery formulations account for 66% of the drug delivery market, which is estimated at $100 billion/year worldwide.

Lectins can be found in numerous legumes, and most of them can go through the digestive system without experiencing significant modification. Lectins have been considered an undesirable family of proteins for nutritional purposes but are associated with numerous immunological processes, including triggering allergic reactions and preventing absorption of nutrients. At low concentrations, however, lectins improve the adsorption of lectin-coated nano- and micro-drug carriers on the small intestine. The increased retention of drug carriers (e.g., liposomes) enhances the uptake of drugs by passive diffusion through the intestinal membrane. In addition, lectins can be covalently bonded to prodrugs and therapeutic proteins to achieve the same effect. The adhesion of lectins to polysaccharides is mediated through a carbohydrate recognition domain (CRD) located in the beta sheet-loops regions of the protein. Figure 2 presents a schematic of the adhesion and drug release mechanism in lectin-mediated drug delivery systems.

The conjugation of the prodrug or the carrier to lectin can be achieved through the carbon diimide method that produces an amide bond (shown in Fig. 2). Lectin can also adhere to the carrier through hydrogen bonding and electrostatic interactions. The latter approach is, however, less efficient and requires higher lectin concentration. Among the different lectins tested, wheat germ agglutinin (WGA) and tomato lectin are the most efficient owing to their high binding capacity and relatively low toxicity. The concept illustrated in Figure 2 has been confirmed in in vitro and in animal studies, but no human tests have been conducted thus far.

We recently posed the question at the 2006 AOCS Annual Meeting & Expo held in St. Louis, Missouri, USA, of whether the bioadhesive properties of lectins could be used to improve the retention of oil-swollen micelles formulated with lecithin (a generic delivery vehicle for hydrophobic drugs).

To answer this question, we mixed lectin and lecithin micelles loaded with isopropyl myristate (IPM, solvent oil), in hopes that lectin would adhere to the surface of lecithin micelles and the surface of the small intestine. The protein-micelle mixture was contacted with a section of pig jejunum using a flow-through dialyzer operated in recirculation (batch) mode.

Figure 3 shows carrier adsorption (retention) as a function of contact time for lecithin micelles (black curve), lecithin micelles with soy-extracted lectin (red curve, 0.007 mg lectin/mg carrier), and lecithin micelles with soluble mustard protein isolate (green curve, 0.7 mg protein/mg carrier).

In the case of lecithin micelles alone (black curve), the carrier absorbed relatively fast within the first two minutes, and then continued to adsorb at a slower rate. Soy lectin increased the instantaneous adsorption of lecithin micelles, but due to the weak bonding between micelles and lectin, this structure dissociated. An interesting finding was that the same adsorption-desorption trend was obtained using high concentrations of water-soluble mustard protein isolate (donated by Levente Diosady at the University of Toronto, Canada). The fact that an inexpensive protein isolate can produce the same effect as purified (and expensive) lectins opens a door to explore new protein-enhanced oral delivery formulations.

It is necessary to investigate the use of covalent bonding between the lectin-enriched protein isolate and the carrier to prevent carrier desorption.

The examples just discussed barely give a taste of recent developments in the area of protein bioadhesives. The conjunction of high oil prices, environmental concerns, new protein modification techniques, and an abundant source of protein-rich grain meals is stimulating the resurgence of the “chemurgy” concept of a bio-based economy.

Edgar J. Acosta, Assistant Professor, Department of Chemical Engineering and Applied Chemistry, University of Toronto, Canada, can be reached via e-mail at acosta@chem-eng.utoronto.ca.

information

• Mittal, K.L., and A. Pizzi (Editors), Handbook of Adhesive Technology, Marcel Dekker, New York, USA, 2003.

• Mathiowitz, E., D. E. Chickering, and C.-M. Lehr, Bioadhesive Drug Delivery Systems: Fundamentals, Novel Approaches, and Development, Marcel Dekker, New York, 1999.