Capillary morphogenesis gene 2 (CMG2) mediates growth factor-induced angiogenesis by regulating endothelial cell chemotaxis

Anthrax protective antigen (PA) is a potent inhibitor of pathological angiogenesis with an unknown mechanism. In anthrax intoxication, PA interacts with capillary morphogenesis gene 2 (CMG2) and tumor endothelial marker 8 (TEM8). Here, we show that CMG2 mediates the antiangiogenic effects of PA and is required for growth-factor-induced chemotaxis. Using specific inhibitors of CMG2 and TEM8 interaction with natural ligand, as well as mice with the CMG2 or TEM8 transmembrane and intracellular domains disrupted, we demonstrate that inhibiting CMG2, but not TEM8 reduces growth-factor-induced angiogenesis in the cornea. Furthermore, the antiangiogenic effect of PA was abolished when the CMG2, but not the TEM8, gene was disrupted. Binding experiments demonstrated a broad ligand specificity for CMG2 among extracellular matrix (ECM) proteins. Ex vivo experiments demonstrated that CMG2 (but not TEM8) is required for PA activity in human dermal microvascular endothelial cell (HMVEC-d) network formation assays. Remarkably, blocking CMG2-ligand binding with PA or CRISPR knockout abolishes endothelial cell chemotaxis but not chemokinesis in microfluidic migration assays. These effects are phenocopied by Rho inhibition. Because CMG2 mediates the chemotactic response of endothelial cells to peptide growth factors in an ECM-dependent fashion, CMG2 is well-placed to integrate growth factor and ECM signals. Thus, CMG2 targeting is a novel way to inhibit angiogenesis.

Identification of Basp1 as a novel angiogenesis-regulating gene by multi-model system studies

We have previously used the genetic diversity available in common inbred mouse strains to identify quantitative trait loci (QTLs) responsible for the differences in angiogenic response using the corneal micropocket neovascularization (CoNV) assay. Employing a mouse genome-wide association study (GWAS) approach, the region on chromosome 15 containing Basp1 was identified as being significantly associated with angiogenesis in inbred strains. Here, we developed a unique strategy to determine and verify the role of BASP1 in angiogenic pathways. Basp1 expression in cornea had a strong correlation with a haplotype shared by mouse strains with varied angiogenic phenotypes. In addition, inhibition of BASP1 demonstrated a dosage-dependent effect in both primary mouse brain endothelial and human microvascular endothelial cell (HMVEC) migration. To investigate its role in vivo, we knocked out basp1 in transgenic kdrl:zsGreen zebrafish embryos using a widely adopted CRISPR-Cas9 system. These embryos had severely disrupted vessel formation compared to control siblings. We further show that basp1 promotes angiogenesis by upregulating β-catenin gene and the Dll4/Notch1 signaling pathway. These results, to the best of our knowledge, provide the first in vivo evidence to indicate the role of Basp1 as an angiogenesis-regulating gene and opens the potential therapeutic avenues for a wide variety of systemic angiogenesis-dependent diseases.

Angiogenic responses in a 3D micro-engineered environment of primary endothelial cells and pericytes

Angiogenesis plays a key role in the pathology of diseases such as cancer, diabetic retinopathy, and age-related macular degeneration. Understanding the driving forces of endothelial cell migration and organization, as well as the time frame of these processes, can elucidate mechanisms of action of important pathological pathways. Herein, we have developed an organ-specific microfluidic platform recapitulating the in vivo angiogenic microenvironment by co-culturing mouse primary brain endothelial cells with brain pericytes in a three-dimensional (3D) collagen scaffold. As a proof of concept, we show that this model can be used for studying the angiogenic process and further comparing the angiogenic properties between two different common inbred mouse strains, C57BL/6J and 129S1/SvlmJ. We further show that the newly discovered angiogenesis-regulating gene Padi2 promotes angiogenesis through Dll4/Notch1 signaling by an on-chip mechanistic study. Analysis of the interplay between primary endothelial cells and pericytes in a 3D microfluidic environment assists in the elucidation of the angiogenic response.

A Method for Developing Novel 3D Cornea-on-a-Chip Using Primary Murine Corneal Epithelial and Endothelial Cells

Microfluidic-based organ-on-a-chip assays with simultaneous coculture of multi-cell types have been widely utilized for basic research and drug development. Here we describe a novel method for a primary cell-based corneal microphysiological system which aims to recapitulate the basic functions of the in vivo cornea and to study topically applied ocular drug permeation. In this study, the protocols for isolating and cultivating primary corneal epithelial cells and endothelial cells from mouse inbred strain C57BL/6J were optimized, to allow for the development of a primary-cell based microfluidic 3D micro-engineered cornea. This tissue unit, by overcoming the limitations of 2D conventional cell culture, supports new investigations on cornea function and facilitates drug delivery testing.

PR1P ameliorates neurodegeneration through activation of VEGF signaling pathway and remodeling of the extracellular environment

Neurodegenerative diseases affect millions of people worldwide. Optic neuropathies are the most commonly occurring neurodegenerative diseases, characterized by progressive retinal ganglion cell (RGC) degeneration. We recently reported that Prominin-1, a protein found on the surface of stem cells, interacts with VEGF and enhances its activity. VEGF is known to have various protective roles in the nervous system. Subsequently, we have developed a 12-mer peptide derived from Prominin-1, named PR1P, and investigated its effects on neuronal survival of damaged RGCs in a rat model of optic nerve crush (ONC). PR1P prevented RGC apoptosis resulting in improvement of retinal function in the rat ONC model. PR1P treatment significantly increased phosphorylation of ERK and AKT and expression its downstream proteins c-fos and Egr-1 in the retina. Additionally, PR1P beneficially increased the MMP-9/TIMP-1 ratio and promoted glial activation in the retina of ONC rats. Thus, PR1P displayed neuroprotective effects through enhanced VEGF-driven neuronal survival and reconstruction of the extracellular environment in ONC model. Our data indicate that PR1P may be a promising new clinical candidate for the treatment of neurodegenerative diseases.

Epsin deficiency promotes lymphangiogenesis through regulation of VEGFR3 degradation in diabetes

Impaired lymphangiogenesis is a complication of chronic complex diseases, including diabetes. VEGF-C/VEGFR3 signaling promotes lymphangiogenesis, but how this pathway is affected in diabetes remains poorly understood. We previously demonstrated that loss of epsins 1 and 2 in lymphatic endothelial cells (LECs) prevented VEGF-C-induced VEGFR3 from endocytosis and degradation. Here, we report that diabetes attenuated VEGF-C-induced lymphangiogenesis in corneal micropocket and Matrigel plug assays in WT mice but not in mice with inducible lymphatic-specific deficiency of epsins 1 and 2 (LEC-iDKO). Consistently, LECs isolated from diabetic LEC-iDKO mice elevated in vitro proliferation, migration, and tube formation in response to VEGF-C over diabetic WT mice. Mechanistically, ROS produced in diabetes induced c-Src-dependent but VEGF-C-independent VEGFR3 phosphorylation, and upregulated epsins through the activation of transcription factor AP-1. Augmented epsins bound to and promoted degradation of newly synthesized VEGFR3 in the Golgi, resulting in reduced availability of VEGFR3 at the cell surface. Preclinically, the loss of lymphatic-specific epsins alleviated insufficient lymphangiogenesis and accelerated the resolution of tail edema in diabetic mice. Collectively, our studies indicate that inhibiting expression of epsins in diabetes protects VEGFR3 against degradation and ameliorates diabetes-triggered inhibition of lymphangiogenesis, thereby providing a novel potential therapeutic strategy to treat diabetic complications.

Identification of Padi2 as a novel angiogenesis-regulating gene by genome association studies in mice

Recent findings indicate that growth factor-driven angiogenesis is markedly influenced by genetic variation. This variation in angiogenic responsiveness may alter the susceptibility to a number of angiogenesis-dependent diseases. Here, we utilized the genetic diversity available in common inbred mouse strains to identify the loci and candidate genes responsible for differences in angiogenic response. The corneal micropocket neovascularization assay was performed on 42 different inbred mouse strains using basic fibroblast growth factor (bFGF) pellets. We performed a genome-wide association study utilizing efficient mixed-model association (EMMA) mapping using the induced vessel area from all strains. Our analysis yielded five loci with genome-wide significance on chromosomes 4, 8, 11, 15 and 16. We further refined the mapping on chromosome 4 within a haplotype block containing multiple candidate genes. These genes were evaluated by expression analysis in corneas of various inbred strains and in vitro functional assays in human microvascular endothelial cells (HMVECs). Of these, we found the expression of peptidyl arginine deiminase type II (Padi2), known to be involved in metabolic pathways, to have a strong correlation with a haplotype shared by multiple high angiogenic strains. In addition, inhibition of Padi2 demonstrated a dosage-dependent effect in HMVECs. To investigate its role in vivo, we knocked down Padi2 in transgenic kdrl:zsGreen zebrafish embryos using morpholinos. These embryos had disrupted vessel formation compared to control siblings. The impaired vascular pattern was partially rescued by human PADI2 mRNA, providing evidence for the specificity of the morphant phenotype. Taken together, our study is the first to indicate the potential role of Padi2 as an angiogenesis-regulating gene. The characterization of Padi2 and other genes in associated pathways may provide new understanding of angiogenesis regulation and novel targets for diagnosis and treatment of a wide variety of angiogenesis-dependent diseases.

Effect of transmembrane pressure control on energy efficiency during skim milk concentration by ultrafiltration at 10 and 50°C

The efficiency of the ultrafiltration process during skim milk concentration was studied using both dynamic and constant (465 or 672kPa) transmembrane pressure experiments at refrigerated temperature (10°C) and high temperature (50°C). The pilot-scale module was equipped with a 10-kDa polyethersulfone spiral-wound membrane element with a surface area of 2.04m². Permeation flux, resistance-in-series model, mineral and protein rejection, and energy consumption were studied as a function of temperature and transmembrane pressure applied. Higher permeation flux values were systematically obtained at 50°C. Also, a significant temperature effect was found for calcium rejection, which was lower at 10°C compared with 50°C. Total hydraulic resistance and reversible fouling resistance were higher at 50°C than at 10°C. No change in protein rejection was observed, depending on the operating mode studied. Permeation flux, which was higher at 50°C, had lower pumping energy consumption compared with ultrafiltration at the colder temperature. Also, the low ultrafiltration temperature required a higher total energy consumption to reach the 3.6× retentate compared with ultrafiltration at 50°C. Overall, our study shows that the operating parameters and temperature can be optimized using an energy efficiency ratio.

Melanocyte pigmentation inversely correlates with MCP-1 production and angiogenesis-inducing potential

The incidence of certain angiogenesis-dependent diseases is higher in Caucasians than in African Americans. Angiogenesis is amplified in wound healing and cornea models in albino C57 mice compared with black C57 mice. Moreover, mouse and human melanocytes with low pigmentation stimulate endothelial cell (EC) proliferation and migration in vitro more than melanocytes with high pigmentation. This effect is due, in part, to the secretion of an angiogenic protein called fibromodulin (FMOD) from lowly pigmented melanocytes. Herein, we expand upon the mechanism contributing to increased angiogenesis in lighter skin and report that monocyte chemotactic protein-1 (MCP-1) is secreted by nonpigmented mouse melanocytes by 5- to 10-fold more than pigmented melanocytes. MCP-1 protein stimulates EC proliferation and migration in vitro and angiogenesis in vivo. Mechanistic studies determine that FMOD is upstream of MCP-1 and promotes its secretion from both melanocytes and activated ECs via stimulation of NF-κB activity. Mice injected with FMOD-neutralizing antibodies show 2.3-fold decreased levels of circulating MCP-1. Human studies confirmed that, on average, Caucasians have 2-fold higher serum levels of MCP-1 than African Americans. Taken together, this study implicates the FMOD/MCP-1 pathway in the regulation of angiogenesis by local melanocytes and suggests that melanogenic activity may protect against aberrant angiogenic diseases.

Melanocyte-secreted fibromodulin promotes an angiogenic microenvironment

Studies have established that pigmentation can provide strong, protective effects against certain human diseases. For example, angiogenesis-dependent diseases such as wet age-related macular degeneration and infantile hemangioma are more common in light-skinned individuals of mixed European descent than in African-Americans. Here we found that melanocytes from light-skinned humans and albino mice secrete high levels of fibromodulin (FMOD), which we determined to be a potent angiogenic factor. FMOD treatment stimulated angiogenesis in numerous in vivo systems, including laser-induced choroidal neovascularization, growth factor-induced corneal neovascularization, wound healing, and Matrigel plug assays. Additionally, FMOD enhanced vascular sprouting during normal retinal development. Deletion of Fmod in albino mice resulted in a marked reduction in the amount of neovascularization induced by retinal vein occlusion, corneal growth factor pellets, and Matrigel plugs. Our data implicate the melanocyte-secreted factor FMOD as a key regulator of angiogenesis and suggest an underlying mechanism for epidemiological differences between light-skinned individuals of mixed European descent and African-Americans. Furthermore, inhibition of FMOD in humans has potential as a therapeutic strategy for treating angiogenesis-dependent diseases.

Abstract 2140: Oral antiangiogenic therapy suppresses xenograft growth and is well tolerated in rats

Lodamin, the oral formulation of TNP-470, a methionine aminopeptidase 2 (MetAp2) inhibitor, was previously shown to significantly inhibit angiogenesis and suppress the progression of fast growing murine tumors. Lodamins’ unique structure as a polymer micelle composed of poly(ethylene-glycol)-poly(lactic)acid (PEG-PLA) conjugate of TNP-470 is pharmacologically advantageous over the non-conjugated form. It shows better stability, oral availability, solubility in water and importantly, has an improved safety profile (Benny O. Folkman J et al, Nat Biotech, 2008). We now report the successful large scale synthesis of Lodamin, yielding pure and active product composed of mPEG-PLA-TNP-470 conjugate without residual free drug as confirmed by NMR and LC-MS/MS. The safety profile of Lodamin was studied in an acute high dose rat study (4 fold higher than therapeutic dose). Lodamin was administered at 10mg/kg or 60mg/kg via oral gavage while control rats were given vehicle only. After 7 days of daily treatment, no changes in body weight or behavior were observed compared to the control group. On day 8 post treatment, gross pathology of all rats was examined. This data showed Lodamin treatment had no adverse effect on tissue morphology. Lodamin is a potent antiangiogenic drug in numerous in vivo murine models including the corneal micropocket assay, matrigel assay, Delayed-Type Hypersensitivity (DTH) reaction and the choroidal neovascularization (CNV) model (Benny O. Folkman J et al, Nat Biotech, 2008, Benny O. D'Amato R et al, Plos One 2010). We now show that in addition to its dramatic anti-cancer effects on Lewis lung carcinoma and B16F10 melanoma murine tumors, Lodamin suppresses human tumors induced in nude mice. The volume of subcutaneous (s.c) human glioblastoma (U87MG) xenografts were reduced by 70% after 30 days, and 71% after 45 days when administered by gavage or in drinking water, respectively. Human breast tumor (MDA-MB231, s.c) growth was inhibited by 62% after 47 days of administration, and Human hepatocarcinoma (HepG2, s.c) tumor growth was inhibited by 60% after only 12 days. Taken together we have established Lodamin as a potent antiangiogenic drug which retains TNP-470 activity without TNP-470-associated side effects. Lodamin is a safe and efficacious drug in our animal models and hopefully will be reintroduced for the treatment of cancer in patients.

Citation Format: Ofra Benny, Lauren Bazinet, Robert D'Amato. Oral antiangiogenic therapy suppresses xenograft growth and is well tolerated in rats. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2140. doi:10.1158/1538-7445.AM2013-2140

1,2,3,4,6-Penta-O-galloyl-β-D-glucopyranose inhibits angiogenesis via inhibition of capillary morphogenesis gene 2

Capillary morphogenesis gene 2 (CMG2) is a transmembrane extracellular matrix binding protein that is also an anthrax toxin receptor. We have shown that high-affinity CMG2 binders can inhibit angiogenesis and tumor growth. We recently described a high-throughput FRET assay to identify CMG2 inhibitors. We now report the serendipitous discovery that PGG (1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose) is a CMG2 inhibitor with antiangiogenic activity. PGG is a gallotannin produced by a variety of medicinal plants that exhibits a wide variety of antitumor and other activities. We find that PGG inhibits CMG2 with a submicromolar IC50 and it also inhibits the migration of human dermal microvascular endothelial cells at similar concentrations in vitro. Finally, oral or intraperitoneal administration of PGG inhibits angiogenesis in the mouse corneal micropocket assay in vivo. Together, these results suggest that a portion of the in vivo antitumor activity of PGG may be the result of antiangiogenic activity mediated by inhibition of CMG2.

A FRET-based high throughput screening assay to identify inhibitors of anthrax protective antigen binding to capillary morphogenesis gene 2 protein

Anti-angiogenic therapies are effective for the treatment of cancer, a variety of ocular diseases, and have potential benefits in cardiovascular disease, arthritis, and psoriasis. We have previously shown that anthrax protective antigen (PA), a non-pathogenic component of anthrax toxin, is an inhibitor of angiogenesis, apparently as a result of interaction with the cell surface receptors capillary morphogenesis gene 2 (CMG2) protein and tumor endothelial marker 8 (TEM8). Hence, molecules that bind the anthrax toxin receptors may be effective to slow or halt pathological vascular growth. Here we describe development and testing of an effective homogeneous steady-state fluorescence resonance energy transfer (FRET) high throughput screening assay designed to identify molecules that inhibit binding of PA to CMG2. Molecules identified in the screen can serve as potential lead compounds for the development of anti-angiogenic and anti-anthrax therapies. The assay to screen for inhibitors of this protein–protein interaction is sensitive and robust, with observed Z' values as high as 0.92. Preliminary screens conducted with a library of known bioactive compounds identified tannic acid and cisplatin as inhibitors of the PA-CMG2 interaction. We have confirmed that tannic acid both binds CMG2 and has anti-endothelial properties. In contrast, cisplatin appears to inhibit PA-CMG2 interaction by binding both PA and CMG2, and observed cisplatin anti-angiogenic effects are not mediated by interaction with CMG2. This work represents the first reported high throughput screening assay targeting CMG2 to identify possible inhibitors of both angiogenesis and anthrax intoxication.

Broad spectrum antiangiogenic treatment for ocular neovascular diseases

Pathological neovascularization is a hallmark of late stage neovascular (wet) age-related macular degeneration (AMD) and the leading cause of blindness in people over the age of 50 in the western world. The treatments focus on suppression of choroidal neovascularization (CNV), while current approved therapies are limited to inhibiting vascular endothelial growth factor (VEGF) exclusively. However, this treatment does not address the underlying cause of AMD, and the loss of VEGF's neuroprotective can be a potential side effect. Therapy which targets the key processes in AMD, the pathological neovascularization, vessel leakage and inflammation could bring a major shift in the approach to disease treatment and prevention. In this study we have demonstrated the efficacy of such broad spectrum antiangiogenic therapy on mouse model of AMD.

Doxycycline induces membrane expression of VE-cadherin on endothelial cells and prevents vascular hyperpermeability

The endothelium lining blood vessels serves as a barrier against vascular hyperpermeability, and its maintenance is critical to organ health. Inflammatory mediators evoke tissue edema by disrupting the expression of membrane junctional proteins, which mediate binding between endothelial cell membranes. Endothelial cell-cell junctions form a diffusion barrier between the intravascular and interstitial space. To prevent the morbidity and mortality caused by exaggerated vascular permeability associated with pathological states (e.g., inflammatory and hypersensitivity disorders, pulmonary edema, traumatic lung injury, cerebral edema resulting from stroke, and others), it is important to develop therapeutic approaches to stabilize these interendothelial junctions. Vascular endothelial growth factor (VEGF), a potent proangiogenic cytokine, was first described as vascular permeability factor (VPF). Doxycycline, a tetracycline derivative, has been shown to inhibit angiogenesis in both humans and animal models. We now report that oral doxycycline prevents VPF/VEGF-induced vascular permeability, interleukin-2-induced pulmonary edema, and delayed-type hypersensitivity (DTH) in mice. Remarkably, doxycycline also inhibits tumor growth and tumor-associated vascular hyperpermeability. Finally, we show that doxycycline targets the adherens junction in vascular endothelial cells by inducing the total amount of VE-cadherin expression while decreasing the degree of its phosphorylation. The potential of doxycyline as a therapeutic inhibitor of vascular hyperpermeability in human clinical conditions is promising and warrants further studies.

An orally delivered small-molecule formulation with antiangiogenic and anticancer activity

Targeting angiogenesis, the formation of blood vessels, is an important modality for cancer therapy. TNP-470, a fumagillin analog, is among the most potent and broad-spectrum angiogenesis inhibitors. However, a major clinical limitation is its poor oral availability and short half-life, necessitating frequent, continuous parenteral administration. We have addressed these issues and report an oral formulation of TNP-470, named Lodamin. TNP-470 was conjugated to monomethoxy-polyethylene glycol-polylactic acid to form nanopolymeric micelles. This conjugate can be absorbed by the intestine and selectively accumulates in tumors. Lodamin significantly inhibits tumor growth, without causing neurological impairment in tumor-bearing mice. Using the oral route of administration, it first reaches the liver, making it especially efficient in preventing the development of liver metastasis in mice. We show that Lodamin is an oral nontoxic antiangiogenic drug that can be chronically administered for cancer therapy or metastasis prevention.

Dendritic cells augment choroidal neovascularization

PURPOSE

Dendritic cells (DCs) are innate immune cells that have recently been shown to support angiogenesis in tumors, endometriosis, and lymph nodes. A major cause of legal blindness is wet age-related macular degeneration (wet ARMD), wherein abnormal blood vessels grow under the retina, an abnormality also referred to as choroidal neovascularization (CNV). The purpose of the present study was to investigate the role of DCs in the development of CNV.

METHODS

Laser photocoagulation was used to induce CNV in C57BL/6J mice. The authors analyzed CNV lesions for the presence of DCs using flow cytometry and immunostaining at designated times. They also analyzed the effects of intravenous DC transplantation on CNV development by measuring the lesion area using confocal microscopy 1 week after laser injury.

RESULTS

The authors analyzed CNV lesions for the presence of DCs by flow cytometry and observed that CD11c(+) major histocompatibility complex (MHC) class II(+) DCs transiently infiltrated the CNV lesions, reaching a peak at 2 to 4 days after laser injury. These DCs were mostly immature (CD11c(+) MHCII(low)) and expressed vascular endothelial growth factor receptor 2. Immunostaining of laser-induced CNV lesions confirmed that DCs are located at the sites of newly formed blood vessels. Intravenously injected DCs incorporated into the CNV lesions. However, only immature DCs enhanced CNV size.

CONCLUSIONS

These results suggest a role for DCs in promoting angiogenesis and lesion growth in laser-induced CNV. The present data suggest that DCs may represent potential cellular targets for therapeutic intervention in wet ARMD.

Dendritic cells support angiogenesis and promote lesion growth in a murine model of endometriosis

Endometriosis affects 10-15% of women and is associated with pelvic pain and infertility. Angiogenesis plays an essential role in its pathogenesis. Dendritic cells (DCs) were recently implicated in supporting tumor angiogenesis. As both tumors and endometriosis lesions depend on angiogenesis, we investigated the possibility that DCs may also play a role in endometriosis. We induced endometriosis in 8-wk-old female C57BL/6 mice by implantation of autologous endometrium into the peritoneal cavity. We observed an abundance of CD11c(+) DCs infiltrating sites of angiogenesis in endometriosis lesions. We noticed a similar pattern of infiltrating DCs at sites of angiogenesis in the peritoneal Lewis lung carcinoma tumor model. These DCs were immature (major histocompatability complex class II(low)) and expressed vascular endothelial growth factor receptor 2. Peritoneal implanted bone marrow-derived DCs (BMDCs) incorporated into both endometriosis lesions and into B16 melanoma tumors and enhanced their growth at 8 days compared with controls (5.1+/-2.5 vs. 1.5+/-0.5 mm(2), n=4 and 4, P<0.0001 for endometriosis; 67.6+/-15.1 vs. 22.7+/-14.6 mm(2), n=5 and 7, P=0.0004 for mouse melanoma). Finally, immature BMDCs but not mature BMDCs enhanced microvascular endothelial cell migration in vitro (219+/-51 vs. 93+/-32 cells, P=0.02). Based on these findings, we suggest a novel role for DCs in supporting angiogenesis and promoting lesion growth both in endometriosis and in tumors.

Bipolar membrane electroacidification of demineralized skim milk

The aim of this study was to evaluate the effect of decreasing the mineral content of skim milk by electrodialysis (ED) prior to electroacidification with bipolar membrane (BMEA) on the performance of the process, the chemical composition, and the physicochemical and functional properties of the isolates produced. ED used to demineralize the skim milk solution was very efficient. However, the electroacidification parameters were influenced by the demineralization level of the skim milk solution: the energy efficiency was decreased with an increase in demineralization, but it was still possible to perform BMEA at a very low conductivity level. Moreover, the isolates produced by BMEA after electrodialysis demineralization at different rates showed similar chemical composition, except on potassium and lactose contents for 75% demineralized isolate. These isolates, except on protein load for 75% demineralization rate, showed similar physicochemical and functional properties, whatever the demineralization rate.

Effect of added salt and increase in ionic strength on skim milk electroacidification performances

Bipolar-memibrane electroacidification (BMEA) technology which uses the property of bipolar membranes to split water and the demineralization action of cation-exchange membranes (CEM), was tested for the production of acid casein. BMEA has numerous advantages in comparison with conventional isoelectric precipitation processes of proteins used in the dairy industry. BMEA uses electricity to generate the desired ionic species to acidify the treated solutions. The process can be precisely controlled, as electro-acidification rate is regulated by the effective current density in the cell. Water dissociation at the bipolar membrane interface is continuous and avoids local excess of acid. In-situ generation of dangerous chemicals (acids and bases) reduces the risks associated with the handling, transportation, use and elimination of these products. The aim of this study was to evaluate the performance of BMEA in different conditions of added ionic strength (p(added) = 0, 0.25, 0.5 and 1.0 M) and added salt (CaCl2, NaCl and KCl). The combination of KCl and p(added) = 0.5 M gave the best results with a 45% decrease in energy consumption. The increased energy efficiency was the result of a decrease in the anode/cathode voltage difference. This was due to an increase of conductivity, produced by addition of salt, necessary to compensate for the lack of sufficiently mobile ions in the skim milk. However, the addition of salts, irrespective of type or ionic strength, increased the required operation time. The protein profile of isolates were similar under all experimental conditions, except at 1.0 M-CaCl2.

Effect of cationic membrane permselectivity on the efficiency of skim milk electroacidification

Bipolar membrane electroacidification (BMEA) uses the property of bipolar membranes to split water and the demineralization action of cation-exchange membranes (CEM). As milk mineral salt content is very sensitive to ionic strength and pH changes, the aim of this study was to better understand the effect of changes in mineral content during pH decrease and demineralization of skim milk. The objectives were to investigate the effect of different cationic permselective membranes (CSV and CMX membranes) on skim milk cation migration and protein precipitation during BMEA. The permselectivity of both membranes tested does not influence the final efficiency of BMEA. The purity of the bovine milk casein isolates produced was similar to or higher (97-98% versus 93.4-96.7) than those of commercial isolates, due to a reduced ash content (1.2 versus 2.0-3. 8%) resulting from the CEM demineralizing phenomenon. For both membranes, the main ionic species to migrate was the potassium ions.

Effect of temperature on the separation of soybean 11 S and 7 S protein fractions during bipolar membrane electroacidification

The purpose of this study was to evaluate the effect of temperature (10 and 27 degrees C) on the efficiency of bipolar membrane electroacidification (BMEA) to fractionate soybean proteins. BMEA is a technology derived from electrodialysis, based on the isoelectric precipitation of proteins. It appears that temperature has a significant effect on the selective precipitation of the soybean protein fractions, mainly 11 S and 7 S, during BMEA. At 27 degrees C, the precipitation profile of the four protein fractions is situated in a pH range from 6.6 to 4.4, with no possibility of separating any of theses fractions. However, at 10 degrees C, the 11 S globulin precipitates at a higher pH than at 27 degrees C, pH 6.7 vs 5.9, allowing the fractionation of 11 S from the other fractions. Using electroacidification it is possible to obtain a precipitate solution enriched in the 11 S fraction (71.8% of 11 S and 10.8% of 7 S) and a supernatant solution enriched in the 7 S fraction (46.6% of 7 S and 4.6% of 11S).

Bipolar membrane electroacidification to produce bovine milk casein isolate

Bipolar membrane electroacidification (BMEA) has been developed previously (Bazinet et al., Report for the Canadian Electricity Association 9326 U 987, 1996; Bazinet et al., J. Agric. Food Chem. 1997, 45, 2419-2425, 3788-3794) and has been used for isoelectric precipitation of soybean proteins. The purpose of this study was to validate the feasibility of BMEA for the precipitation of milk casein and to investigate the effect of flow rate. High-purity isolates containing 1.23 and 2.00% ash and 85.4 and 91.6% total protein were obtained with flow rates of 0.2 and 1.2 gal/min. The molecular composition profiles of the isolates obtained by HPLC showed that only caseins were precipitated. However, except for protein precipitation curves, the flow rate did not influence the final composition and purity of the isolates. These results showed that BMEA is a new alternative process for the production of high-purity bovine milk casein isolate.