Biomedical subjects

Loren A Matheson

Publications and source records attributed to Loren A Matheson.

10 recordsLinked to original sources

PubMed2006

Traffic between the plant endoplasmic reticulum and Golgi apparatus: to the Golgi and beyond.

Significant advances have been made in recent years that have increased our understanding of the trafficking to and from membranes that are functionally linked to the Golgi apparatus in plants. New routes from the Golgi to organelles outside the secretory pathway are now being identified, revealing the importance of the Golgi apparatus as a major sorting station in the plant cell. This review discusses our current perception of Golgi structure and organization as well as the molecular mechanisms that direct traffic in and out of the Golgi.

Endoplasmic Reticulum↗

PubMed2006

Seeking a way out: export of proteins from the plant endoplasmic reticulum.

The functionality of the secretory pathway relies on the efficient transfer of cargo molecules from their site of synthesis in the endoplasmic reticulum (ER) to successive compartments within the pathway. Although transport mechanisms of secretory proteins have been studied in detail in various non-plant systems, it is only recently that our knowledge of secretory routes in plants has expanded dramatically. This review focuses on exciting new findings concerning the exit mechanisms of cargo proteins from the plant ER and the role of ER export sites in this process.

Animals↗

PubMed2006

Cyclic biaxial strain affects U937 macrophage-like morphology and enzymatic activities.

As monocytes migrate to the site of a foreign body and differentiate into mature monocyte-derived macrophages (MDMs), the cells undergo a morphological transformation that involves mechanical stimulation via membrane stretch. Because the site of many cardiovascular implant devices includes substrates that are also undergoing mechanical change, it is of interest to assess the effect of such dynamic conditions on cellular-biomaterial responses. This study investigated the influence of cyclic (0.25 Hz) biaxial strain (maximum 10% amplitude) on human U937 macrophage-like cells cultured on a flexible siloxane membrane. Cell attachment was unaffected by the strain but total protein levels were significantly higher in stimulated cells. Intracellular esterase and released acid phosphatase activities were elevated by dynamic loading in addition to a strain-induced increase of monocyte-specific esterase protein as demonstrated by immunoblotting analysis. The morphology of static cells changed with cyclic strain from a round cell shape to an irregular, spread phenotype with a progressive reorganization of filamentous actin. The focal adhesion protein vinculin showed distinct reorganization in structure going from a well-defined arrangement in static cells to a diffuse staining pattern in mechano-stimulated cells. This study has demonstrated that U937 cells respond to cyclic deformation with an augmentation of select enzymatic activities that have been identified as being important in polymer biodegradation processes, as well as morphological changes, which may be characteristic of mechanical stress-induced cell activation.

Alkaline Phosphatase↗

PubMed2006

Characterization of the Flexcell Uniflex cyclic strain culture system with U937 macrophage-like cells.

Mechanical forces alter many cell functions in a variety of cell types. It has been recognized that stimulation of cells in culture may be more representative of some physiologic conditions. Although there are commercially available systems for the study of cells cultured in a mechanical environment, very little has been documented on the validation techniques for these devices. In this study, Flexcell's recently introduced Uniflex cyclic strain system was programmed to apply 10% longitudinal sinusoidal strain (0.25 Hz) for 48 h to U937 cells cultured on Uniflex plates. Image analysis was employed to characterize the actual strain field. For a chosen amplitude of 10% the applied strain was highly reproducible and relatively uniform (10.6+/-0.2%) in a central rectangular region of the membrane (dimensions of 9.2+/-2 x 13.6+/-0.8 mm2). The strain increased the release of IL-6, esterase and acid phosphatase activity (p<0.05) from adherent U937 cells. Cells also displayed altered morphology, aligning and lengthening with the direction of strain, whereas static cells maintained a round appearance showing no preferred orientation. These data indicate that cyclic mechanical strain applied by the Uniflex strain system modulates U937 cell function leading to selective increases in enzymatic activities as well as orientation in a favored direction.

Acid Phosphatase↗

PubMed2006

The functional response of U937 macrophage-like cells is modulated by extracellular matrix proteins and mechanical strain.

Extracellular matrix proteins (ECMs) play a significant role in the transfer of mechanical strain to monocyte-derived macrophages (MDMs) affecting morphological changes in a foreign body reaction. This study investigated how the functional responses of U937 macrophage-like cells differed when subjected to 2 dynamic strain types (nonuniform biaxial or uniform uniaxial strain) while cultured on siloxane membranes coated with either collagen type I or RGD peptide repeats (ProNectin). Biaxial strain caused an increase in intracellular esterase and acid phosphatase (AP) activities, as well as monocyte-specific esterase (MSE) protein levels in cells that were seeded on either uncoated surfaces (shown previously) or collagen, but not ProNectin. Released AP activity, but not released esterase activity, was increased on all surfaces. Biaxial strain increased IL-6, but not IL-8 on all surfaces. When cells were subjected to uniaxial strain, intracellular esterase increased on coated surfaces only, whereas intracellular AP activity was unaffected. Both esterase and AP released activities increased on all surfaces. Uniaxial strain increased the release of IL-6 on all surfaces, but IL-8 on coated surfaces only. This study demonstrated for the first time that ECM proteins could specifically modulate cellular responses to different types of strain. Using this approach with an in vitro cell system may help to unravel the complex function of MDMs in the foreign-body reaction.

Cell Culture Techniques↗

PubMed2005

The human macrophage response during differentiation and biodegradation on polycarbonate-based polyurethanes: dependence on hard segment chemistry.

Human monocytes, isolated from whole blood, were seeded onto tissue culture grade polystyrene (PS) and three polycarbonate-based polyurethanes (PCNUs) (synthesized with either 1,6-hexane diisocyanate (HDI) or 4,4'-methylene bis-phenyl diisocyanate (MDI), poly(1,6-hexyl 1,2-ethyl carbonate) diol (PCN) and 1,4-butanediol (BD) in different stoichiometric ratios (HDI:PCN:BD 4:3:1 or 3:2:1 and MDI:PCN:BD 3:2:1) (referred to as HDI431, HDI321 and MDI321, respectively). Following their differentiation to monocyte-derived macrophages (MDMs) the cells were trypsinized and reseeded onto each of the PCNUs synthesized with either 14C-HDI or 14C-BD and degradation was measured by radiolabel release (RR). When the differentiation surface was MDI321, there was more RR from 14C-HDI431 than from any other surface (p < 0.0001) whereas the amount of esterase (identified by immunoblotting) as well as the esterase activity was the greatest in MDM differentiated on PS, reseeded on 14C-HDI431 (p < 0.0001). The effect of potential degradation products (methylene dianiline (MDA) and BD) from the PCNUs was carried out to determine possible links between products and substrate-induced activation of MDM. MDA was found to inhibit RR 60% from MDM seeded on 14C-MDI321B (p < 0.0001), approximately 20% from 14C-HDI431 (p = 0.002) and no effect from 14C-HDI321B. MDA inhibited esterase activity 30% from MDM only on 14C-MDI321B (p = 0.003), but no effect on esterase activity was observed for the other two polymers. BD had no inhibitory effect on RR from any PCNU, but did inhibit esterase activity in MDM on 14C-HDI431 (p = 0.025). This study indicates that the degradation of a specific material is a multi-factorial process, dictated by its susceptibility to hydrolysis, the effect of specific products generated during this course of action, and perhaps not as well appreciated, the material's inherent ability to influence enzyme synthesis and release.

Absorbable Implants↗

PubMed2005

Polycarbonate-urethane hard segment type influences esterase substrate specificity for human-macrophage-mediated biodegradation.

Previous studies have shown that esterase activity can degrade a variety of polyurethanes (PUs), including polycarbonate-based PUs (PCNUs). When cultured on PCNUs, differing in their chemistries, monocyte-derived macrophages (MDM) synthesized and secreted different amounts of both cholesterol esterase (CE) and monocyte-specific esterase (MSE). MDM were seeded on PCNUs synthesized with hexane diisocyanate (HDI) or 4,4'-methylene-bis-phenyl diisocyanate (MDI), PCN and [14C]butanediol (BD) in the ratio 3:2:1 (referred to as HDI321 or MDI321). The effect of phenylmethylsulfonyl fluoride (PMSF, a serine esterase and proteinase inhibitor), sodium fluoride (NaF, a MSE inhibitor) and sodium taurocholate (NaT, a CE stimulator) was assessed on degradation (measured by radiolabel release (RR)) and esterase activity in MDM lysate. The results were compared to the effect that these reagents had on commercially available CE and carboxyl esterase (CXE), which has a specificity similar to MSE. NaF inhibited CXE- and MDM-mediated RR to the same extent as for both PCNUs. However, the MDM-mediated RR from MDI321 was 1.8-times higher than HDI321 in the presence of NaT (P = 0.005). This study suggests that the difference in diisocyanate chemistry may dictate the relative contribution of each esterase to a specific material's degradation. This may be related to both the substrate specificity of each esterase, as well as by the relative amount of each esterase that the specific biomaterial substrates induce the cells to synthesize and secrete.

Biocompatible Materials↗

PubMed2004

Changes in macrophage function and morphology due to biomedical polyurethane surfaces undergoing biodegradation.

Monocytes are recruited to the material surface of an implanted biomedical device recognizing it as a foreign body. Differentiation into macrophages subsequently occurs followed by fusion to form foreign body giant cells (FBGCs). Consequently, implants can become degraded, cause chronic inflammation or become isolated by fibrous encapsulation. In this study, a relationship between material surface chemistry and the FBGC response was demonstrated by seeding mature monocyte-derived macrophages (MDMs) on polycarbonate-based polyurethanes that differed in their chemical structures (synthesized with poly(1,6-hexyl 1,2-ethyl carbonate) diol, and either (14)C-hexane diisocyanate and butanediol (BD) (referred to as HDI) or 4,4'-methylene bisphenyl diisocyanate and (14)C-BD (referred to as MDI)) and material degradation assessed. At 48 h of cell-material interaction, the FBGC attached to HDI were more multinucleated (73%) compared to MDI or the polystyrene (PS) control (21 and 36%, respectively). There was a fivefold increase in the synthesis and secretion of a protein with an approximate molecular weight of 48 kDa and a pI of 6.1 (determined by two-dimensional gel electrophoresis) only from cells seeded on HDI. Immunoprecipitation confirmed that MSE and CE were synthesized and secreted de novo. Immunoblotting also showed an increase in secreted monocyte-specific esterase (MSE) and cholesterol esterase (CE) from cells seeded on HDI relative to PS and MDI. Significantly more radiolabel ((14)C) release and esterase activity were elicited by MDMs on HDI than MDI (P < 0.05). The material that was more degradable (HDI), elicited greater protein synthesis and esterase secretion as well as more multinucleated MDMs than MDI, suggesting that the material surface chemistry modulates the function of MDM at the site of an inflammatory response to an implanted device.

Absorbable Implants↗

PubMed2002

Biodegradation of polycarbonate-based polyurethanes by the human monocytes-derived macrophage and U937 cell systems.

The prominent cell type found on implanted medical devices during the chronic inflammatory response is the monocyte-derived macrophage (MDM). Using an activated in vitro cell system, it was possible to show that MDMs possess esterolytic activities that may contribute to the degradation of polyurethanes. In the present study, the U937 cell line was paralleled to the MDM cell system in order to validate the use of a cell line that could expedite studies on biomaterial biocompatibility and biostability. Using 12-o-tetradecanoylphorbol 13-acetate (PMA), the optimum differentiation time for the U937 cells was 72 h based on biodegradation, degradative potential, and (35)S-methionine uptake. After activation of the cells by resuspending from tissue culture polystyrene plates and reseeding onto a (14)C-labeled polycarbonate-based polyurethane(PCNU), both U937 cells and the MDMs elicited comparable radiolabel release (measure of polymer breakdown) and esterase activity (measure of degradative potential) at 48 h. There was no difference in the effect on radiolabel release and esterase activity elicited by both cell types with inhibitors of protein synthesis, esterase activity, and phospholipase A(2). This established that both cell types likely used similar hydrolytic activities and signaling pathways to cause degradation of the PCNU. Immunoblotting demonstrated that both cell systems secreted monocyte-specific esterase and cholesterol esterase enzymes previously shown to degrade PCNUs. The U937 cell system is more convenient and reproducible than MDMs for pursuing possible biological pathways elucidating the mechanism of polyurethane biodegradation. Once established with U937s, the pathways can then be validated with the more physiologically relevant human MDM cell system.

Aristolochic Acids↗

PubMed2002

Human macrophage-mediated biodegradation of polyurethanes: assessment of candidate enzyme activities.

A predominant cell type associated with explanted failed devices is the monocyte-derived macrophage (MDM). However, there is still very little known about the specific cellular enzyme activities involved in interactions with these devices. The current study investigates the nature of candidate enzymes that may be involved in the degradation of polymeric biomaterials through the use of specific enzyme inhibitor agents. When MDM were incubated with a polycarbonate-based polyurethane (PCNU) synthesized with 14C-labeled hexane diisocyanate (HDI), polycarbonate diol and butanediol (BD) (referred to as 14C-HDI431), the radiolabel release (RR) measured was inhibited by phenylmethylsulfonyl fluoride, diethyl-p-nitrophenyl phosphate (serine protease/esterase inhibitors), and sodium fluoride (NaF) (a carboxyl esterase (CXE) inhibitor). Sodium taurocholate (NaT) (a cholesterol esterase (CE) stimulator) had little effect on RR. The two candidate enzymes proposed were CE and CXE, based on the fact that both were identified by immunoblotting in the releasate of MDM following 48 h incubation with 14C-HDI431. The effect of the above reagents on the RR caused by purified CE and CXE, was measured and compared to changes in their activity with p-nitrophenylbutyrate (PNB). The effect of NaF on MDM was similar to that of purified CXE (inhibitory on both RR and lysate esterase activity), suggesting the involvement of CXE. However, NaT inhibited the PNB activity of purified CXE, but had no effect on MDM-mediated RR or PNB activity, implicating another esterase in the biomaterial degradation. Since NaT stimulated CE-mediated RR and PNB activity, it may also be involved in MDM-mediated biodegradation of PCNUs. The results of these studies point to both esterases as being candidates. However, the current methods were unable to determine the relative contribution of each one to the observed biodegradation.

Biocompatible Materials↗