Introduction
Within milk, high-melting-point triglycerides, phospholipids, and glycosphingolipids are encased in the milk fat globule membrane (
MFGM;
Keenan and Patton, 1995The structure of milk: Implication for sampling and storage. The milk lipid globule membrane.
). The glycosphingolipids and phospholipids account for half of the weight percentage of the membrane and function as intracellular signaling molecules in a variety of biological processes, including regulating cell growth, development, adhesion, and cross membrane trafficking (
Astaire et al., 2003- Astaire J.C.
- Ward R.
- German J.B.
- Jiménez-Flores R.
Concentration of polar MFGM lipids from buttermilk by microfiltration and supercritical fluid extraction.
). In addition, a variety of bioactive proteins are embedded in the MFGM, including mucin 1 (
MUC1), xanthine dehydrogenase/oxidase (
XDH/XO), periodic acid Schiff III (
PAS III), cluster of differentiation 36 (
CD36), butyrophilin (
BTN), adipophilin, and periodic acid Schiff 6/7 (
Mather, 2000A review and proposed nomenclature for major proteins of the milk-fat globule membrane.
). There is insufficient information on these proteins to characterize their interaction with the lipids that surround them, making it difficult to ascribe specific functions without the potential interference of lipids.
Over the past 2 decades, evidence has accumulated from both in vivo and in vitro studies to suggest numerous potential health benefits associated with MFGM and its associated proteins and fats, including inhibition of gastrointestinal pathogens (
Sprong et al., 2002- Sprong R.C.
- Hulstein M.F.E.
- Van der Meer R.
Bovine milk fat components inhibit food-borne pathogens.
;
Spitsberg, 2005Bovine milk fat globule membrane as a potential nutraceutical.
), such as
Helicobacter pylori (
Hirmo et al., 1998- Hirmo S.
- Kelm S.
- Iwersen M.
Inhibition of Helicobacter pylori sialic acid-specific haemagglutination by human gastrointestinal mucins and milk glycoproteins.
;
Wang et al., 2001- Wang X.
- Hirmo S.
- Millen R.
- Wadstrom T.
Inhibition of Helicobacter pylori infection by bovine milk glycoconjugates in a BALB/cA mouse model.
) and rotavirus (
RV;
Newburg et al., 1998- Newburg D.S.
- Peterson J.A.
- Ruiz-Palacios G.M.
- Matson D.O.
- Morrow A.L.
- Shults J.
- Guerrero M.L.
- Chaturvedi P.
- Newburg S.O.
- Scallan C.D.
- Taylor M.R.
- Ceriani R.L.
- Pickering L.K.
Role of human-milk lactadherin in protection against symptomatic rotavirus infection.
;
Kvistgaard et al., 2004- Kvistgaard A.S.
- Pallesen L.T.
- Arias C.F.
- Lopez S.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory effects of human and bovine milk constituents on rotavirus infections.
).
Worldwide, RV infection is the most common cause of severe dehydrating gastroenteritis (
Ramig, 2004Pathogenesis of intestinal and systemic rotavirus infection.
;
Widdowson et al., 2005- Widdowson M.-A.
- Bresee J.S.
- Gentsch J.R.
- Glass R.I.
Rotavirus disease and its prevention.
). Rotavirus infections are also a concern for agricultural production because of their high incidence in many species of animals, particularly in weanling calves and piglets (
Kuhlenschmidt et al., 1999- Kuhlenschmidt T.B.
- Hanafin W.P.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Sialic acid dependence and independence of group A rotaviruses.
), resulting in an estimated economic loss of $7 million each year for producers (
House, 1978Economic impact of rotavirus and other neonatal disease agents of animals.
). Most previous studies have focused on the bioactivities of lactadherin and MUC1, 2 glycoproteins that are associated with the MFGM (
Kvistgaard et al., 2004- Kvistgaard A.S.
- Pallesen L.T.
- Arias C.F.
- Lopez S.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory effects of human and bovine milk constituents on rotavirus infections.
). These proteins are thought to bind to pathogens and help remove them from the body via the ciliary action of the gut (
Yolken et al., 1992- Yolken R.H.
- Peterson J.A.
- Vonderfecht S.L.
- Fouts E.T.
- Midthun K.
- Newburg D.S.
Human milk mucin inhibits rotavirus replication and prevents experimental gastroenteritis.
;
Kvistgaard et al., 2004- Kvistgaard A.S.
- Pallesen L.T.
- Arias C.F.
- Lopez S.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory effects of human and bovine milk constituents on rotavirus infections.
). The concentration of lactadherin in human milk varies depending on the stage of lactation; concentrations in colostrum and mature milk average 139 and 66 µg/mL, respectively (
Peterson et al., 1998- Peterson J.A.
- Hamosh M.
- Scallan C.D.
- Ceriani R.L.
- Henderson T.R.
- Mehta N.R.
- Armand M.
- Hamosh P.
Milk fat globule glycoproteins in human milk and in gastric aspirates of mother’s milk-fed preterm infants.
). Lactadherin is resistant to digestion in the stomach because of its high degree of glycosylation (
Cavaletto et al., 2004- Cavaletto M.
- Giuffrida M.G.
- Conti A.
The proteomic approach to analysis of human milk fat globule membrane.
). Therefore, it passes into the intestine intact, where it can serve as a binding site for bacterial and viral pathogens (
Cavaletto et al., 2004- Cavaletto M.
- Giuffrida M.G.
- Conti A.
The proteomic approach to analysis of human milk fat globule membrane.
). An epidemiological study of infants infected with human RV showed that infants consuming human milk with a mean lactadherin concentration of 48.4 µg/mL did not exhibit symptoms of RV infection, whereas infants ingesting human milk with a mean concentration of 29 µg/mL were symptomatic for RV infection (
Newburg et al., 1998- Newburg D.S.
- Peterson J.A.
- Ruiz-Palacios G.M.
- Matson D.O.
- Morrow A.L.
- Shults J.
- Guerrero M.L.
- Chaturvedi P.
- Newburg S.O.
- Scallan C.D.
- Taylor M.R.
- Ceriani R.L.
- Pickering L.K.
Role of human-milk lactadherin in protection against symptomatic rotavirus infection.
).
Using an in vitro focus-forming unit (
FFU) assay,
Kvistgaard et al., 2004- Kvistgaard A.S.
- Pallesen L.T.
- Arias C.F.
- Lopez S.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory effects of human and bovine milk constituents on rotavirus infections.
found that 20 µg of human lactadherin/mL inhibited RV infectivity by 50% in Caco-2 cells infected with the WA strain of human RV. In addition, they quantified and isolated bovine milk lactadherin. Bovine milk lactadherin concentrations were comparable to those in human milk; however, isolated bovine lactadherin did not inhibit infectivity of neuraminidase-sensitive or neuraminidase-insensitive strains of RV (
Kvistgaard et al., 2004- Kvistgaard A.S.
- Pallesen L.T.
- Arias C.F.
- Lopez S.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory effects of human and bovine milk constituents on rotavirus infections.
). This led the authors to propose that other components of the bovine MFGM could be responsible for its anti-RV activity. Indeed, anti-RV components were identified in whole bovine MFGM and macromolecular whey proteins (
MMWP). Bovine mucin, MUC1, is among the major components of MFGM and MMWP. It is a high-molecular-weight, heavily glycosylated protein that exists in a viscous gel in vivo (
Mather, 2000A review and proposed nomenclature for major proteins of the milk-fat globule membrane.
). As a result, MUC1 binds to and sequesters pathogenic microorganisms, such as RV and
Escherichia coli, thus inhibiting their ability to damage the gut epithelium (
Schroten et al., 1992- Schroten H.
- Hanisch F.G.
- Plogmann R.
- Hacker J.
- Uhlernbruch G.
- Nobis-Bosch R.
- Wahn V.
Inhibition of adhesion of S-fimbriated Escherichia coli to buccal epithelial cells by human milk fat globule membrane components: A novel aspect of the protective function of mucins in the nonimmunoglobulin fraction.
;
Yolken et al., 1992- Yolken R.H.
- Peterson J.A.
- Vonderfecht S.L.
- Fouts E.T.
- Midthun K.
- Newburg D.S.
Human milk mucin inhibits rotavirus replication and prevents experimental gastroenteritis.
). When MUC1 isolated from bovine MFGM was tested for anti-RV activity in an FFU assay, a concentration of 6.3 µg of MUC1/mL reduced RV infectivity by 62.5% (
Kvistgaard et al., 2004- Kvistgaard A.S.
- Pallesen L.T.
- Arias C.F.
- Lopez S.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory effects of human and bovine milk constituents on rotavirus infections.
). In human milk, the oligosaccharides contained on MUC-1 include fucose,
N-acetylgalactosamine,
N-acetylglucosamine, galactose, and sialic acid. The
N-linked carbohydrate moieties that contain sialic acid at their nonreducing end appear to be responsible for the virus-inhibitory activity (
Yolken et al., 1992- Yolken R.H.
- Peterson J.A.
- Vonderfecht S.L.
- Fouts E.T.
- Midthun K.
- Newburg D.S.
Human milk mucin inhibits rotavirus replication and prevents experimental gastroenteritis.
;
Newburg et al., 1998- Newburg D.S.
- Peterson J.A.
- Ruiz-Palacios G.M.
- Matson D.O.
- Morrow A.L.
- Shults J.
- Guerrero M.L.
- Chaturvedi P.
- Newburg S.O.
- Scallan C.D.
- Taylor M.R.
- Ceriani R.L.
- Pickering L.K.
Role of human-milk lactadherin in protection against symptomatic rotavirus infection.
). A subsequent study identified immunoglobulin as the primary anti-RV factor in the MMWP (
Bojsen et al., 2007- Bojsen A.
- Buesa J.
- Montava R.
- Kvistgaard A.S.
- Kongsbak M.B.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory activities of bovine macromolecular whey proteins on rotavirus infections in vitro and in vivo.
).
In the current study, the potential for MFGM to inhibit RV infection was investigated, because components of bovine (
Kvistgaard et al., 2004- Kvistgaard A.S.
- Pallesen L.T.
- Arias C.F.
- Lopez S.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory effects of human and bovine milk constituents on rotavirus infections.
) and human (
Newburg et al., 1998- Newburg D.S.
- Peterson J.A.
- Ruiz-Palacios G.M.
- Matson D.O.
- Morrow A.L.
- Shults J.
- Guerrero M.L.
- Chaturvedi P.
- Newburg S.O.
- Scallan C.D.
- Taylor M.R.
- Ceriani R.L.
- Pickering L.K.
Role of human-milk lactadherin in protection against symptomatic rotavirus infection.
) MFGM have been shown to exert anti-RV activity. We compared MFGM isolated from buttermilk or cheese whey buttermilk by microfiltration and supercritical fluid extraction (
SFE). This process selectively extracts triglycerides, which leads to enrichment of polar and more complex lipids in the MFGM (
Astaire et al., 2003- Astaire J.C.
- Ward R.
- German J.B.
- Jiménez-Flores R.
Concentration of polar MFGM lipids from buttermilk by microfiltration and supercritical fluid extraction.
). This extraction method also results in the selective fractionation of various lipids without the use of conventional toxic solvents (
Astaire et al., 2003- Astaire J.C.
- Ward R.
- German J.B.
- Jiménez-Flores R.
Concentration of polar MFGM lipids from buttermilk by microfiltration and supercritical fluid extraction.
). Using buttermilk as a source for these lipids as viral inhibitors is a sound strategy considering its unique properties as a functional food ingredient and its low cost and availability (
;
). We hypothesized that MFGM isolated by SFE would inhibit RV infectivity and that this effect would be due, in part, to the enriched lipid components.
Materials and Methods
Concentration of MFGM in Natural and Whey Cream Buttermilks
Milk (500 L) for each batch of buttermilk was obtained from the Cal Poly Dairy Farm (San Luis Obispo, CA). The skim milk was separated from the cream by a pilot-plant cream separator (DeLaval, Kansas City, MO). Whey cream for this experiment was produced and donated by Hilmar Co. (Hilmar, CA) and 3 batches of cream (120 L) were used. The cream was treated in the pilot plant at Cal Poly and subjected to regular pasteurization: 77.5°C (172°F) for 15 s. Buttermilk was pasteurized before storage at 75°C (169°F) for 15 s. The cream was processed into butter at 12°C using a continuous churn (Egli Co., Gumligen, Switzerland), and buttermilk and whey buttermilk were collected. Buttermilk for each sample was recovered in milk cans, small fat grains or aggregates were removed by filtration through cheese cloth, and the resulting buttermilk was passed through the cream separator again. The buttermilks were stored overnight at 4°C until membrane filtration was performed.
A pilot-plant scale system (R-12 model, GEA-Niro Filtration, Hudson, WI) with 2 spiral-wound polymeric membranes fitted in parallel on the module (10 kDa molecular mass cutoff, 11.33 m2 total surface area) was used to remove most of the mineral salts, lactose, and free oligosaccharides. The process was carried out at 25°C; the trans-membrane pressure was 600 kPa, and the feed pump, attached to a frequency drive, was operated at 35 Hz. Microfiltration was conducted until a 10-fold volumetric concentration factor was reached. Diafiltration was done while continuously adding purified water at 25°C to the feed tank to replace the removed permeate until a 5-fold diafiltration factor was reached. In each step of the filtration, samples of retentates were collected for composition. The final retained fractions from all experiments were spray-dried (NiroFilterlab Spray-Drier, Hudson, WI) using 3,500 kPa of pressure, and inlet and outlet air temperatures of 175°C and 90°C, respectively, to obtain buttermilk powder (BM) and cheese whey buttermilk powder (CW). All runs were performed in triplicate.
Each buttermilk powder was submitted to SFE to remove residual triglycerides from the samples. The SFE system and components were acquired from Thar Designs Inc. (Pittsburgh, PA), including the 500-mL sample vessel, the model P-50 high-pressure pump, the automated back pressure regulator (model BPR-A-200B), and the PolyScience water bath and pump unit (model 9505; PolyScience, Niles, IL). Circulated deionized water at 3°C was used to cool different zones in the SFE apparatus. Carbon dioxide tanks were filled and inspected by A&R Welding Supply (San Luis Obispo, CA). The system conditions were controlled manually by Windows 2000-based software (Hewlett-Packard, Palo Alto, CA). Approximately 200 g of each sample was submitted to 3 extraction cycles using the following conditions: 1,500 g of CO2 at a flow rate of 20 g/min, extraction pressure of 35 MPa, and extraction and collection temperatures of 50°C. The SFE trials were done in triplicate. All the powders were stored in a humidity-controlled chamber at 10°C.
Organic Extraction of Lipids from MFGM
Single-Phase Lipid Extraction and Thin Layer Chromatography
A lipid extraction was performed on each MFGM-enriched powder using the method of
. Briefly, each powder (75 mg) was suspended in water (0.75 mL) and vigorously mixed. While mixing, methanol (2 mL) was slowly added followed by chloroform (1 mL) to make a chloroform:methanol:water mixture of 1:2:0.75. This mixture was centrifuged (1,000 ×
g, 5 min, 4°C), the pellet discarded, and the supernatant collected. Portions of the supernatant were evaporated and suspended in either solvent (thin layer chromatography,
TLC) or minimal essential medium (
MEM; focus-forming unit) assays. Lipids were separated by silica gel TLC using a 55:45:10 ratio of chloroform to methanol to water. Lipids were fluorescently detected with primulin (
White et al. 1998- White T.
- Bursten S.
- Federighi D.
- Lewis R.A.
- Nudelman E.
High-resolution separation and quantification of neutral lipid and phospholipid species in mammalian cells and sera by multi-one-dimensional thin-layer chromatography.
) and carbohydrates were detected with orcinol in sulfuric acid. Lactose, cholesterol, and the ganglioside GM3 were run as standards.
Dual-Phase Lipid Extraction and Iatrobead Chromatography
To better separate the lipid components of the MFGM, a dual-phase lipid extraction was performed on each powder (
Folch et al., 1957- Folch C.J.
- Lees M.
- Sloane Stanley G.H.
A simple method for the isolation and purification of total lipids from animal tissues.
) followed by chromatography. Milk fat globule membrane (1 g) was suspended in 10 mL of water and mixed. While mixing, methanol (16.65 mL) was slowly added followed by chloroform (33.33 mL). The mixture was centrifuged (1,000 ×
g, 10 min, 4°C), producing an aqueous upper layer, a white interface, and a lower chloroform layer. The upper aqueous layer was removed and the lower chloroform layer was collected by carefully inserting a Pasteur pipette through the interface layer. The remaining interface layer was extracted 2 times by adding water (4.5 mL) followed by 22.5 mL of a chloroform:methanol (2:1) solution. After centrifugation, the upper layer was combined with the first aqueous layer and the lower layer was combined with the first chloroform layer. The combined upper layer was concentrated by rotary evaporation to 16 mL, and 80 mL of a chloroform:methanol (2:1) solution was added, the mixture centrifuged as above, and the upper and lower layers collected. Likewise, the combined lower layers from the first extraction were evaporated to dryness, suspended in 6 mL of water, and then 30 mL of a chloroform:methanol (2:1) solution was added. After centrifugation, all of the upper and lower layers were separately combined. Then, the combined aqueous layer was concentrated by rotary evaporation to 10 mL and the lower organic layer was evaporated to dryness.
For initial separation of lipids, the organic phase was applied to an iatrobead column equilibrated in a chloroform:methanol (95:5) solution and eluted using modifications of a previously described procedure (
Rolsma et al., 1998- Rolsma M.D.
- Kuhlenschmidt T.B.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Structure and function of a ganglioside receptor for porcine rotavirus.
). Briefly, the dried organic layer (1 g of MFGM equivalent) was dissolved in 5 mL of a chloroform:methanol (4.5:1) solution and centrifuged to remove any precipitate. The supernatant was applied to the iatrobead column and eluted with a 4.5:1 chloroform:methanol solution; nine 100-mL fractions were collected. The eluant was then changed to a 1:1 chloroform:methanol solution and seven 100-mL fractions were collected. All fractions were dried by rotary evaporation, the 9 samples eluted with chloroform methanol 4.5:1 were suspended with 1 mL of chloroform:methanol 4.5:1, and the 7 fractions eluted with chloroform:methanol 1:1 were suspended with 1 mL of chloroform:methanol 1:1. Portions were analyzed by TLC, SDS-PAGE, and FFU assays.
SDS-PAGE Separation of MFGM
Samples from both single- and dual-phase extractions were dried under nitrogen in microfuge tubes followed by addition of 2.5 µL of 4× NuPage sample buffer (Invitrogen Inc., Carlsbad, CA), 6.5 µL of water, and 1 µL of β-mercaptoethanol. The tubes were heated at 70°C for 10 min and, after cooling, 10 µL of the sample was applied to a NuPage 10% BisTrispolyacrylamide gel (Invitrogen Inc.) and separated by electrophoresis at 200 V for 50 min. SeeBlue molecular weight standards were obtained from Invitrogen Inc., and gels were stained with Coomassie Blue to visualize proteins.
Rotavirus Preparation and FFU Assay
To assess the anti-RV potential of MFGM, in vitro studies were performed using MA-104 cells derived from embryonic African green monkey kidney cells (BioWhittaker, Walkersville, MD), as previously described (
Rolsma et al., 1994- Rolsma M.D.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Assay for evaluation of rotavirus-cell interactions: Identification of an enterocyte ganglioside fraction that mediates group A porcine rotavirus recognition.
;
Andres et al., 2007- Andres A.
- Donovan S.M.
- Kuhlenschmidt T.B.
- Kuhlenschmidt M.S.
Isoflavones at concentrations present in soy infant formula inhibit rotavirus infection in vitro..
). A neuraminidase-sensitive, Group A porcine RV strain (OSU-RV) serotype P9[7]G5 was propagated in MA-104 cells, purified as described
Rolsma et al., 1994- Rolsma M.D.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Assay for evaluation of rotavirus-cell interactions: Identification of an enterocyte ganglioside fraction that mediates group A porcine rotavirus recognition.
, and used for the in vitro experiments.
An FFU assay to measure RV infectivity in the presence or absence of MFGM fractions was performed as described previously (
Rolsma et al., 1998- Rolsma M.D.
- Kuhlenschmidt T.B.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Structure and function of a ganglioside receptor for porcine rotavirus.
). Briefly, 125 µL containing the desired amount of MFGM fraction in MEM or MEM alone was mixed with an equal volume of RV containing approximately 1,000 FFU of infectious activity. This inhibitor-RV mixture was incubated for 30 min at 23°C, before applying 100 µL to duplicate wells in 24-well plates containing confluent MA-104 cell monolayers that had been rinsed free of serum with PBS. After adsorption to the MA-104 cell layer for 30 min at 37°C, the RV-MFGM inoculum was removed. After rinsing the cell layer with PBS, MEM without serum was added to each well and the plate was incubated at 37°C for 16 to 18 h. Immunochemical detection of rotavirus infectivity was performed as described (
Rolsma et al., 1998- Rolsma M.D.
- Kuhlenschmidt T.B.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Structure and function of a ganglioside receptor for porcine rotavirus.
). Results for inhibition by single- or dual-phase extracts are expressed as relative to the total weight of lipids isolated from the MFGM powders.
Statistical Analysis
Statistical analyses were performed using the PROC GLM (generalized linear model) procedure within SAS (version 9.2, SAS Institute Inc., Cary, NC) with a post hoc LSD test using Fisher’s least significant difference test to evaluate the effect of treatment. Statistical significance was defined as P < 0.05. All data are expressed as means ± SEM.
Discussion
Previous studies have identified glycoprotein components of bovine (
Kvistgaard et al., 2004- Kvistgaard A.S.
- Pallesen L.T.
- Arias C.F.
- Lopez S.
- Petersen T.E.
- Heegaard C.W.
- Rasmussen J.T.
Inhibitory effects of human and bovine milk constituents on rotavirus infections.
;
Kuchta et al., 2012- Kuchta A.M.
- Kelly P.M.
- Stanton C.
- Devery R.A.
Milk fat globule membrane—A source of polar lipids for colon health? A review.
;
Le et al., 2012- Le T.T.
- Van de Wiele T.
- Do T.N.H.
- Debyser G.
- Struijs K.
- Devreese B.
- Dewettinck K.
- Van Camp J.
Stability of milk fat globule membrane proteins toward human enzymatic gastrointestinal digestion.
) and human (
Newburg et al., 1998- Newburg D.S.
- Peterson J.A.
- Ruiz-Palacios G.M.
- Matson D.O.
- Morrow A.L.
- Shults J.
- Guerrero M.L.
- Chaturvedi P.
- Newburg S.O.
- Scallan C.D.
- Taylor M.R.
- Ceriani R.L.
- Pickering L.K.
Role of human-milk lactadherin in protection against symptomatic rotavirus infection.
) MFGM with anti-RV activity; however, little attention has been focused on the lipid components of the MFGM. The lipids that make up the MFGM include phosphatidylcholine, phosphatidyl-ethanolamine, sphingomyelin, phosphatidylinositol, phosphatidylserine, and other glycosphingolipid or phospholipid components in trace amounts, such as gangliosides, sphingosine, and ceramides (
Hamosh et al., 1999- Hamosh M.
- Peterson J.A.
- Henderson T.R.
- Scallan C.D.
- Kiwan R.
- Ceriani R.L.
- Armand M.
- Mehta N.R.
- Hamosh P.
Protective functions of human milk: The milk fat globule.
;
Parodi, 1999Conjugated linoleic acid and other anticarcinogenic agents of bovine milk fat.
). We undertook this study of the lipid component of the MFGM based on the results of several clinical and laboratory investigations supporting antiviral and antimicrobial actions of milk fats (
Koopman et al., 1984- Koopman J.S.
- Turkisk V.J.
- Monto A.S.
- Thompson F.E.
- Isaacson R.E.
Milk fat and gastrointestinal illness.
;
Hamosh, 1991Free fatty acids and monoglycerides: Anti-infective agents produced during the digestion of milk fat by the newborn.
;
;
Hamosh et al., 1999- Hamosh M.
- Peterson J.A.
- Henderson T.R.
- Scallan C.D.
- Kiwan R.
- Ceriani R.L.
- Armand M.
- Mehta N.R.
- Hamosh P.
Protective functions of human milk: The milk fat globule.
;
Sprong et al., 2001- Sprong R.C.
- Hulstein M.F.
- Van der Meer R.
Bactericidal activities of milk lipids.
). First, a prospective study of children over the age of 1 yr found that those consuming low fat milk as their only milk source in the 3 wk before illness were at 5 times the risk of requiring a doctor’s visit for acute gastrointestinal illness compared with children drinking only whole milk during the same period (
Koopman et al., 1984- Koopman J.S.
- Turkisk V.J.
- Monto A.S.
- Thompson F.E.
- Isaacson R.E.
Milk fat and gastrointestinal illness.
). This increased risk could not be explained by numerous potentially confounding variables or potential biases, nor did it vary by the children’s age (
Koopman et al., 1984- Koopman J.S.
- Turkisk V.J.
- Monto A.S.
- Thompson F.E.
- Isaacson R.E.
Milk fat and gastrointestinal illness.
). Second, milk fat glycosphingolipids and triglycerides, particularly those containing C10:0 and C12:0 fatty acids, have been shown to protect against foodborne gastroenteritis (
Sprong et al., 2001- Sprong R.C.
- Hulstein M.F.
- Van der Meer R.
Bactericidal activities of milk lipids.
). These fatty acids, which appear to have both antimicrobial and antiviral activities, may be native in milk or may be produced within the gastrointestinal tract as products of digestion (
Hamosh, 1991Free fatty acids and monoglycerides: Anti-infective agents produced during the digestion of milk fat by the newborn.
;
;
Le et al., 2012- Le T.T.
- Van de Wiele T.
- Do T.N.H.
- Debyser G.
- Struijs K.
- Devreese B.
- Dewettinck K.
- Van Camp J.
Stability of milk fat globule membrane proteins toward human enzymatic gastrointestinal digestion.
). Finally, we have shown that gangliosides, which are a minor component of the MFGM, are present in neonatal piglet intestine and serve as specific receptors for sialic acid–dependent group A porcine RV attachment to intestinal epithelial cells (
Rolsma et al., 1994- Rolsma M.D.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Assay for evaluation of rotavirus-cell interactions: Identification of an enterocyte ganglioside fraction that mediates group A porcine rotavirus recognition.
,
Rolsma et al., 1998- Rolsma M.D.
- Kuhlenschmidt T.B.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Structure and function of a ganglioside receptor for porcine rotavirus.
). The 2 major monosialogangliosides both possessed a sialyllactose oligosaccharide moiety characteristic of GM3 gangliosides; however, each ganglioside differed in the type of sialic acid residue it contained (
Rolsma et al., 1998- Rolsma M.D.
- Kuhlenschmidt T.B.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Structure and function of a ganglioside receptor for porcine rotavirus.
). For example, an
N-glycolylneuraminic acid moiety was found in the more polar porcine GM3, whereas the less polar GM3 species contained
N-acetylneuraminic acid. Both the
N-glycolylneuraminic acid GM3 and
N-acetylneuraminic acid GM3 displayed dose-dependent inhibition of virus binding to cells (
Rolsma et al., 1998- Rolsma M.D.
- Kuhlenschmidt T.B.
- Gelberg H.B.
- Kuhlenschmidt M.S.
Structure and function of a ganglioside receptor for porcine rotavirus.
).
The results herein demonstrated that whole bovine MFGM effectively inhibited a neuraminidase-sensitive strain OSU-RV in vitro. The MFGM isolated from either buttermilk or cheese whey was effective at inhibiting RV infectivity. However, when BM and CW MFGM were tested at similar concentrations, the BM was more effective than CW MFGM at inhibiting RV infectivity, which may reflect the greater complexity of the fatty acid composition of BM MFGM. In particular, glycolipids are more abundant and diverse in BM than in CW MFGM (
Gallier et al., 2010- Gallier S.
- Gragson D.
- Cabral C.
- Jiménez-Flores R.
- Everett D.W.
Composition and fatty acid distribution of bovine phospholipids from processed milk products.
).
To determine the potential for lipids associated with the MFGM to inhibit RV infectivity, the MFGM preparations were subjected to single and double organic phase extractions. The extract resulting from a single-phase extraction was enriched in polar lipids, but also contained some proteins. Although the extract retained the ability to inhibit RV in the FFU assay, this activity could not be solely attributed to the lipid components. Thus, a dual-phase extraction procedure was applied that separated the lipid components from the proteins, which were recovered in the aqueous phase and at the interface between the phases. When the lipid and aqueous phases were compared, all anti-RV activity was recovered in the lipid phase, whereas the aqueous phase did not exert any anti-RV activity. This observation was consistent with that of Kvistgaard and colleagues (2004), who found that bovine lactadherin did not inhibit RV after it was purified from the MFGM. The ability of bovine lactadherin to exert its action might be dependent upon its structural conformation when it is present within the MFGM and that conformation is lost upon its isolation. One such example may be the activity of α-lactalbumin in the presence of oleic acid to form HAMLET or BAMLET (
human, or
bovine,
alpha-lactalbumin
made
lethal to
tumor cells), and a further formation of annular oligomers with phospholipids that may explain its function (
Baumann et al., 2012- Baumann A.
- Underhaug Gjerde A.
- Ying M.
- Svanborg C.
- Holmsen H.
- Glomm W.R.
- Martinez A.
- Halskau Ø.
HAMLET forms annular oligomers when deposited with phospholipid monolayers.
).
To further separate the lipids present in the dual-phase extraction, the protein-free lipid extract with anti-RV activity was applied to an iatrobead column, and lipids were eluted in a stepwise fashion moving from relatively nonpolar to more polar solvents. The fraction with the greatest anti-RV activity eluted from the column in the first fraction in a 4.5:1 chloroform:methanol solvent, suggesting that it was relatively nonpolar. The lipids in this fraction inhibited 95% of the RV infectivity in the FFU assay. Further TLC separation of this fraction using a nonpolar solvent, 30:1 chloroform:methanol, resolved at least 5 lipid-containing compounds less polar than simple gangliosides and phospholipids. It is unclear if the SFE treatment would have made a difference because it removed a large part of nonpolar lipids.
The current study demonstrates that it is the lipid component of the MFGM that has anti-RV activity. This is consistent with some reports in the literature that suggest that milk fat sphingolipids and triglycerides, particularly those containing C10:0 and C12:0 fatty acids, protect against foodborne gastroenteritis (
Sprong et al., 2001- Sprong R.C.
- Hulstein M.F.
- Van der Meer R.
Bactericidal activities of milk lipids.
) and have direct antibacterial and antiviral activities (
Hamosh, 1991Free fatty acids and monoglycerides: Anti-infective agents produced during the digestion of milk fat by the newborn.
;
;
Hamosh et al., 1999- Hamosh M.
- Peterson J.A.
- Henderson T.R.
- Scallan C.D.
- Kiwan R.
- Ceriani R.L.
- Armand M.
- Mehta N.R.
- Hamosh P.
Protective functions of human milk: The milk fat globule.
). In addition, our previous work showed a direct inhibitory effect of oleic acid isolated from bovine colostrum on the adhesion of
Cryptosporidium parvum sporozoites to host cells (
Schmidt and Kuhlenschmidt, 2008- Schmidt J.
- Kuhlenschmidt M.S.
Microbial adhesion of Cryptosporidium parvum: Identification of a colostrum-derived inhibitory lipid.
). Taken together, these data and the work presented here suggest that specific lipids derived from milk may serve as natural inhibitors of host cell–microbe interactions. Future studies are needed to determine the potential for MFGM lipids to inhibit RV infectivity in vivo. Isolated lipids could be fed directly to the animals or intact MFGM could be fed in an MFGM-enriched diet and bioactive lipids (
Hamosh, 1991Free fatty acids and monoglycerides: Anti-infective agents produced during the digestion of milk fat by the newborn.
;
) could be released within the small intestine during the process of digestion.
Acknowledgments
This research was funded by US Department of Agriculture-Cooperative State Research, Education, and Extension Service Animal Health funds project #ILLU888-930 at the University of Illinois (to M.S.K.), USDA NRI 2002-35204-12613 at the University of Illinois (to M.S.K.), and CSU Agricultural Research Initiative, California Dairy Research Foundation to California Polytechnic State University at San Luis Obispo (to R.J.F.). K.L.F. was the recipient of Abbott Veterinary Medical Scholars Fellowship from the College of Veterinary Medicine at the University of Illinois. The authors acknowledge William P. Hanafin (Department of Pathobiology, University of Illinois, Urbana) for his assistance with the FFU assays, Pierre Morin and Andrea Laubscher (Dairy Science Department, California Polytechnic State University, San Luis Obispo) for manufacture of MFGM extracts, and Marcia Monaco (Department of Food Science and Human Nutrition, University of Illinois. Urbana) for assistance with statistical analyses.
Article info
Publication history
Published online: April 01, 2013
Accepted:
February 7,
2013
Received:
September 4,
2012
Copyright
© 2013 American Dairy Science Association. Published by Elsevier Inc.