Yevgeniya Le

Poly(oligo(ethylene glycol)acrylamide) brushes by surface initiated polymerization: effect of macromonomer chain length on brush growth and protein adsorption from blood plasma.

Three hydrolytically stable polyethyleneglycol (PEG)-based N-substituted acrylamide macromonomers, methoxypolyethyleneglycol (350) acrylamide (MPEG350Am) methoxypolyethyleneglycol (750) acrylamide(MPEG750Am) and methoxypolyethyleneglycol (2000)acrylamide (MPEG2000Am) with increasing PEG chain length were synthesized. Surface-initiated aqueous atom transfer radical polymerization (ATRP) using CuCl/1,1,4,7,10,10-hexamethyl triethylene tetramine (HMTETA) catalyst was utilized to generate dense polymer brushes from these monomers via an ester linker group on the surface of model polystyrene (PS) particles. The molecular weight, hydrodynamic thickness, and graft densities of the grafted polymer layers were controlled by changing the reaction parameters of monomer concentration, addition of Cu(II)Cl2, and sodium chloride. The graft densities of surface-grafted brushes decreased with increasing PEG macromonomer chain length, 350 > 750 >> 2000, under similar experimental conditions. The molecular weight of grafts increased with increase in monomer concentration, and only selected conditions produced narrow distributed polymer chains. The molecular weight of grafted polymer chains differs significantly to those formed in solution. The hydrodynamic thicknesses of the grafted polymer layers were fitted to the Daoud and Cotton model (DCM) for brush height on spherical surfaces. The results show that the size of the pendent groups on the polymer chains has a profound effect on the hydrodynamic thickness of the brush for a given degree of polymerization. The new PEG-based surfaces show good protection against nonspecific protein adsorption from blood plasma compared to the bare surface. Protein adsorption decreased with increasing surface density of grafted polymer chains. Poly(MPEG750Am) brushes were more effective in preventing protein adsorption than poly(MPEG350Am) even at low graft densities, presumably due to the increase in PEG content in the grafted layer.

Immunocamouflage: The biophysical basis of immunoprotection by grafted methoxypoly(ethylene glycol) (mPEG)

Development of novel approaches for the immunomodulation of donor cells would have significant utility in transfusion and transplantation medicine. Immunocamouflage of cell surfaces by covalently grafted methoxypoly(ethylene glycol) (mPEG) (PEGylation) has emerged as a promising approach. While previous studies demonstrated the in vitro and in vivo efficacy of immunocamouflaged allogeneic blood cells, the biophysical mechanisms of immunoprotection have not been well-defined due to the fragility of intact cells. To overcome this limitation, polystyrene beads (1.2 and 8.0 microm) were used to elucidate the biophysical effects of polymer size, density and linker chemistry on charge camouflage and protein adsorption. These findings were correlated with biological studies using red blood cells and lymphocytes. Charge camouflage of both beads and cells was best achieved with long polymers. However, protein adsorption studies demonstrated an unexpected effect of target size. For 1.2 microm beads, decreased protein adsorption was best achieved with short (2 kDa) polymers whereas long chain (20 kDa) polymers were optimal for 8.0 microm particles. The biophysical findings correlated well with biological immunocamouflage as measured by particle electrophoresis and the inhibition of antibody-antigen (CD3, CD4 and CD28) recognition. Moreover, it was observed that antigen topography (CD28 vs. CD4) was of significance in selecting the appropriate polymer size. The biophysical interactions of PEGylated surfaces and macromolecules involve complex mechanisms dependent on the molecular weight, grafting concentration, target size and surface complexity. Cellular PEGylation strategies must be customized to account for target cell size, membrane complexity and antigen density and height.

Mesenchymal stromal cells from patients with acute myeloid leukemia have altered capacity to expand differentiated hematopoietic progenitors.

The bone marrow microenvironment may be permissive to the emergence and progression of acute myeloid leukemia (AML). Studying interactions between the microenvironment and leukemia cells should provide new insight for therapeutic advances. Mesenchymal stromal cells (MSCs) are central to the maintenance of the hematopoietic niche. Here we compared the functions and gene expression patterns of MSCs derived from bone marrow aspirates of healthy donors and patients with AML. MSCs expanded from AML patients had heterogeneous morphology and displayed a wide range of proliferation capacity compared to MSCs from healthy controls. The ability of AML-MSCs to support the expansion of committed hematopoietic progenitors from umbilical cord blood-derived CD34+ cells may be impaired while the expression of genes associated with maintaining hematopoietic quiescence appeared to be increased in AML-MSCs compared to healthy donors. These results highlight important potential differences in the biologic profile of MSCs from AML patients compared to healthy donors that may contribute to the emergence or progression of leukemia.

Greater organ involution in highly proliferative tissues associated with the early onset and acceleration of ageing in humans

Domination of cell proliferation over cell death is a driving force for carcinogenesis, whereas reduced cell proliferation and increased cell death are characteristic of ageing. We employed published data to estimate representative mean values of cell turnover times for 31 different organs and tissues in adult humans and animals (when data in humans were lacking) as well as functional mass loss for 5 organs, accounting for actual mass loss and tissue conversion to fat, in humans over the adult period, age 25 to 70. We found that greater actual and functional mass loss was significantly associated (P=0.001 and P<0.0001, respectively) with the log of shorter cell turnover times. We propose that this is characteristic of stem cell exhaustion and replicative senescence. In addition, we provide quantitative evidence that, in many organs, involution is evident even in young adults. On the basis of published mass measurements of major organs, by analysis of covariance, we identified examples of significant (P≤0.05), accelerated actual or functional mass loss and ageing from early to late adulthood. We hypothesise and quantitatively demonstrate that functional mass loss accelerates with ageing by incorporating the contribution of actual mass loss, tissue conversion to fatty or fibrous tissue, and the presence of apoptotic, necrotic and senescent cells. We propose that mass loss, linked to replicative senescence, is an evolutionary adaptation that effectively limits cancer in young adults, as mass loss is first apparent soon after the end of the growth period, accelerating in the more elderly as biological conditions deviate away from those prevailing in youth, when the selective pressure on pleiotropic genes is greatest.

Plasma protein adsorption to surfaces grafted with dense homopolymer and copolymer brushes containing poly(N-isopropylacrylamide).

Growing polymer chains from surface initiators in principle allows much more dense polymer surface layers to be created than can be produced by grafting of whole (self-excluding) chains. We have utilized aqueous atom transfer radical polymerization to graft a series of cleavable hydrophilic poly(N-isopropylacrylamide) (PNIPAM) homopolymers and block copolymers of substituted acrylamides from polystyrene latex to give brushes of controlled MW and surface density. Average chain separations much less than their free solution radii of gyration have been achieved. Exposure to radiolabeled single proteins or to whole plasma and subsequent analysis by SDS-PAGE shows that PNIPAM brushes decrease protein adsorption relative to the latex surface or other substituted polyacrylamides. The PNIPAM brushes exhibit a second-order phase transition around 30°C as reflected by a decrease in the hydrodynamic thickness of the brush at higher temperatures. Total plasma protein adsorption is increased at 40°C compared to 20°C but there is significant differential adsorption behavior among the proteins detected by gel-electrophoresis analysis.

Adipogenic Mesenchymal Stromal Cells from Bone Marrow and Their Hematopoietic Supportive Role: Towards Understanding the Permissive Marrow Microenvironment in Acute Myeloid Leukemia.

PurposeThe role of bone marrow-derived mesenchymal stem/stromal cells (MSCs) in creating a permissive microenvironment that supports the emergence and progression of acute myeloid leukemia (AML) is not well established. We investigated the extent to which adipogenic differentiation in normal MSCs alters hematopoietic supportive capacity and we undertook an in-depth comparative study of human bone marrow MSCs derived from newly diagnosed AML patients and healthy donors, including an assessment of adipogenic differentiation capacity.FindingsMSCs from healthy controls with partial induction of adipogenic differentiation, in comparison to MSCs undergoing partial osteogenic differentiation, expressed increased levels of hematopoietic factors and induced greater proliferation, decreased quiescence and reduced in vitro hematopoietic colony forming capacity of CD34+ hematopoietic stem and progenitor cells (HSPCs). Moreover, we observed that AML-derived MSCs had markedly increased adipogenic potential and delayed osteogenic differentiation, while maintaining normal morphology and viability. AML-derived MSCs, however, possessed reduced proliferative capacity and decreased frequency of subendothelial quiescent MSCs compared to controls.ConclusionOur results support the notion of a bone marrow microenvironment characterized by increased propensity toward adipogenesis in AML, which may negatively impact normal hematopoiesis. Larger confirmatory studies are needed to understand the impact of various clinical factors. Novel leukemia treatments aimed at normalizing bone marrow niches may enhance the competitive advantage of normal hematopoietic progenitors over leukemia cells.

Immunocamouflage of latex surfaces by grafted methoxypoly(ethylene glycol) (mPEG): Proteomic analysis of plasma protein adsorption

Grafting of methoxypoly(ethylene glycol) (mPEG) to cells and biomaterials is a promising non-pharmacological immunomodulation technology. However, due to the labile nature of cells, surface-plasma interactions are poorly understood; hence, a latex bead model was studied. PEGylation of beads resulted in a density and molecular weight dependent decrease in total adsorbed protein with a net reduction from (159.9±6.4) ng cm−2 on bare latex to (18.4±0.8) and (52.3±5.3) ng cm−2 on PEGylated beads (1 mmol L−1 of 2 or 20 kD SCmPEG, respectively). SDS-PAGE and iTRAQ-MS analysis revealed differential compositions of the adsorbed protein layer on the PEGylated latex with a significant reduction in the compositional abundance of proteins involved in immune system activation. Thus, the biological efficacy of immunocamouflaged cells and materials is mediated by both biophysical obfuscation of antigens and reduced surface-macromolecule interactions.

Polymer-Mediated Broad Spectrum Antiviral Prophylaxis: Utility in High Risk Environments

Viral infections are a significant cause of morbidity and mortality in humans throughout the world. However, modern medicine has a very limited ability to prevent viral diseases. While traditional vaccination strategies have been highly successful against a subset of viruses, the antigenic variation of viruses as well as the shear number of viral pathogens has limited the efficacy of this approach. This observation is exemplified by the finding that while most common respiratory infections are caused by Rhinoviruses, Coronaviruses, Adenoviruses and Orthomyxoviruses, a number of other viral families are also frequently implicated. Indeed, over 300 serologically distinct viruses are known to cause the pathology associated with the ‘common cold’ and ‘flu’. [Spector, 1995] Furthermore, vaccinations have yet to prove effective against the single viral family (Rhinoviruses) commonly implicated in >60% of common colds; again due to the extreme antigenic variability found within even this single viral family. As a result, there are currently no broad-spectrum anti-viral prophylactics (either prescription or over-the-counter) capable of preventing or interrupting the progression of viral infections. However, the safe, low cost, low technology, and non-toxic bioengineering of the terminally differentiated nasal pharyngeal epithelial host cells may provide a radically new antiviral prophylactic approach that gives rise to a transient, broad-spectrum, prophylaxis against virally transmitted respiratory infections (Figure 1). [ McCoy & Scott, 2005, Sutton & Scott, 2010] This polymer-based technology is derivative of the polymer-based “immunocamouflage” technology of blood cells being actively developed within the Canadian Blood Services to reduce the risk of transfusion reactions and alloimmunization to donor red blood cells. [Scott et al., 1997, Scott & Murad, 1998, Murad et al., 1999a, Murad et al., 1999b, Bradley et al., 2001, Bradley et al., 2002, Bradley & Scott, 2007, Rossi et al., 2010b] As schematically shown in Figure 1, the non-toxic bioengineering of the nasal cavity attenuates or prevents viral respiratory infections at the primary site of infection the nasopharyngeal cell surface of the upper respiratory tract. Surprisingly to some, the primary mode of viral entry in respiratory diseases is via accidental inoculation of the nasal passage via contaminated hands. As demonstrated in Figure 1A, the initial inoculum (1) is typically

Micro-RNA Profiling of Exosomes from Marrow-Derived Mesenchymal Stromal Cells in Patients with Acute Myeloid Leukemia: Implications in Leukemogenesis

Gene regulatory networks in AML may be influenced by microRNAs (miRs) contained in exosomes derived from bone marrow mesenchymal stromal cells (MSCs). We sequenced miRs from exosomes isolated from marrow-derived MSCs from patients with AML (n = 3) and from healthy controls (n = 3; not age-matched). Known targets of mIRs that were significantly different in AML-derived MSC exosomes compared to controls were identified. Of the five candidate miRs identified by differential packaging in exosomes, only miR-26a-5p and miR-101-3p were significantly increased in AML-derived samples while miR-23b-5p, miR-339-3p and miR-425-5p were significantly decreased. Validation of the predicted change in gene expression of the potential targets was investigated by interrogating gene expression levels from public datasets of marrow-derived CD34-selected cells from patients with AML (n = 69) and healthy donors (n = 40). Two molecules with decreased gene expression in AML (EZH2 and GSK3β) were predicted by the miR profiling and have been previously implicated in AML while three molecules were increased in AML-derived cells and have not been previously associated with leukemogenesis (KRBA2, RRBP1 and HIST2H 2BE). In summary, profiling miRs in exosomes from AML-derived MSCs allowed us to identify candidate miRs with potential relevance in AML that could yield new insights regarding leukemogenesis or new treatment strategies.