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Endothelial cell capture of heparin-binding growth factors under flow.

Zhao B, Zhang C, Forsten-Williams K, Zhang J, Fannon M - PLoS Comput. Biol. (2010)

Bottom Line: The model is based on the flow and reactions within a single hollow fiber and was scaled linearly by the total number of fibers for comparison with experimental results.Our model predicted, and experiments confirmed, that removal of heparan sulfate (HS) from the system would result in a dramatic loss of binding by heparin-binding proteins, but not by proteins that do not bind heparin.Several other key parameters were investigated with the coupling between receptors and proteoglycans shown to have a critical impact on successful capture.

View Article: PubMed Central - PubMed

Affiliation: Department of Ophthalmology and Visual Sciences, University of Kentucky, Lexington, Kentucky, United States of America.

ABSTRACT
Circulation is an important delivery method for both natural and synthetic molecules, but microenvironment interactions, regulated by endothelial cells and critical to the molecule's fate, are difficult to interpret using traditional approaches. In this work, we analyzed and predicted growth factor capture under flow using computer modeling and a three-dimensional experimental approach that includes pertinent circulation characteristics such as pulsatile flow, competing binding interactions, and limited bioavailability. An understanding of the controlling features of this process was desired. The experimental module consisted of a bioreactor with synthetic endothelial-lined hollow fibers under flow. The physical design of the system was incorporated into the model parameters. The heparin-binding growth factor fibroblast growth factor-2 (FGF-2) was used for both the experiments and simulations. Our computational model was composed of three parts: (1) media flow equations, (2) mass transport equations and (3) cell surface reaction equations. The model is based on the flow and reactions within a single hollow fiber and was scaled linearly by the total number of fibers for comparison with experimental results. Our model predicted, and experiments confirmed, that removal of heparan sulfate (HS) from the system would result in a dramatic loss of binding by heparin-binding proteins, but not by proteins that do not bind heparin. The model further predicted a significant loss of bound protein at flow rates only slightly higher than average capillary flow rates, corroborated experimentally, suggesting that the probability of capture in a single pass at high flow rates is extremely low. Several other key parameters were investigated with the coupling between receptors and proteoglycans shown to have a critical impact on successful capture. The combined system offers opportunities to examine circulation capture in a straightforward quantitative manner that should prove advantageous for biologicals or drug delivery investigations.

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Simulation and experimental comparison between pulsatile and steady flow.(A) Simulation results of FGF-2 in the outflow as a function of time for pulsatile (○) or steady (•) flow, (B) Simulation results of FGF-2 bound along the endothelial-lined hollow fiber as a function of distance at 44 sec (pulsatile (○), steady (pink circle) flow) and at 88 seconds (pulsatile (□), steady (green square) flow) as a function of time, C Experimental comparison of FGF-2 in outflow using pulsatile (○) and steady (•) flow. Simulations and experiments used 1 ng of FGF-2 at a flow rate of 0.6 mL/min (1.2 mm/sec) and pulsatile flow was set at ∼36 strokes/min.
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pcbi-1000971-g006: Simulation and experimental comparison between pulsatile and steady flow.(A) Simulation results of FGF-2 in the outflow as a function of time for pulsatile (○) or steady (•) flow, (B) Simulation results of FGF-2 bound along the endothelial-lined hollow fiber as a function of distance at 44 sec (pulsatile (○), steady (pink circle) flow) and at 88 seconds (pulsatile (□), steady (green square) flow) as a function of time, C Experimental comparison of FGF-2 in outflow using pulsatile (○) and steady (•) flow. Simulations and experiments used 1 ng of FGF-2 at a flow rate of 0.6 mL/min (1.2 mm/sec) and pulsatile flow was set at ∼36 strokes/min.

Mentions: Capillary flow is generally steady, and gradually becomes pulsatile at higher flow rates. We conducted simulations and in vitro experiments to compare steady and pulsatile flow at a low flow rate (0.6 mL/min, 1.2 mm/sec) to determine whether our model would predict differences between FGF-2 interactions using steady and pulsatile flow. Simulations predicted no difference in FGF-2 binding at low flow using pulsatile flow conditions versus steady flow in either the FGF binding down the cell-lined hollow fiber (Figure 6A) or in the profile of the outflow (Figure 6B). In vitro experiments were performed using a syringe pump for steady flow and the bioreactor's pulsatile flow pump (Figure 6C). FGF-2 outflow measurements indicated no overall change at 0.6 mL/min (1.2 mm/sec) suggesting that, at low rates typical of capillary flow, no significant change in FGF-2 interactions takes place.


Endothelial cell capture of heparin-binding growth factors under flow.

Zhao B, Zhang C, Forsten-Williams K, Zhang J, Fannon M - PLoS Comput. Biol. (2010)

Simulation and experimental comparison between pulsatile and steady flow.(A) Simulation results of FGF-2 in the outflow as a function of time for pulsatile (○) or steady (•) flow, (B) Simulation results of FGF-2 bound along the endothelial-lined hollow fiber as a function of distance at 44 sec (pulsatile (○), steady (pink circle) flow) and at 88 seconds (pulsatile (□), steady (green square) flow) as a function of time, C Experimental comparison of FGF-2 in outflow using pulsatile (○) and steady (•) flow. Simulations and experiments used 1 ng of FGF-2 at a flow rate of 0.6 mL/min (1.2 mm/sec) and pulsatile flow was set at ∼36 strokes/min.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2965741&req=5

pcbi-1000971-g006: Simulation and experimental comparison between pulsatile and steady flow.(A) Simulation results of FGF-2 in the outflow as a function of time for pulsatile (○) or steady (•) flow, (B) Simulation results of FGF-2 bound along the endothelial-lined hollow fiber as a function of distance at 44 sec (pulsatile (○), steady (pink circle) flow) and at 88 seconds (pulsatile (□), steady (green square) flow) as a function of time, C Experimental comparison of FGF-2 in outflow using pulsatile (○) and steady (•) flow. Simulations and experiments used 1 ng of FGF-2 at a flow rate of 0.6 mL/min (1.2 mm/sec) and pulsatile flow was set at ∼36 strokes/min.
Mentions: Capillary flow is generally steady, and gradually becomes pulsatile at higher flow rates. We conducted simulations and in vitro experiments to compare steady and pulsatile flow at a low flow rate (0.6 mL/min, 1.2 mm/sec) to determine whether our model would predict differences between FGF-2 interactions using steady and pulsatile flow. Simulations predicted no difference in FGF-2 binding at low flow using pulsatile flow conditions versus steady flow in either the FGF binding down the cell-lined hollow fiber (Figure 6A) or in the profile of the outflow (Figure 6B). In vitro experiments were performed using a syringe pump for steady flow and the bioreactor's pulsatile flow pump (Figure 6C). FGF-2 outflow measurements indicated no overall change at 0.6 mL/min (1.2 mm/sec) suggesting that, at low rates typical of capillary flow, no significant change in FGF-2 interactions takes place.

Bottom Line: The model is based on the flow and reactions within a single hollow fiber and was scaled linearly by the total number of fibers for comparison with experimental results.Our model predicted, and experiments confirmed, that removal of heparan sulfate (HS) from the system would result in a dramatic loss of binding by heparin-binding proteins, but not by proteins that do not bind heparin.Several other key parameters were investigated with the coupling between receptors and proteoglycans shown to have a critical impact on successful capture.

View Article: PubMed Central - PubMed

Affiliation: Department of Ophthalmology and Visual Sciences, University of Kentucky, Lexington, Kentucky, United States of America.

ABSTRACT
Circulation is an important delivery method for both natural and synthetic molecules, but microenvironment interactions, regulated by endothelial cells and critical to the molecule's fate, are difficult to interpret using traditional approaches. In this work, we analyzed and predicted growth factor capture under flow using computer modeling and a three-dimensional experimental approach that includes pertinent circulation characteristics such as pulsatile flow, competing binding interactions, and limited bioavailability. An understanding of the controlling features of this process was desired. The experimental module consisted of a bioreactor with synthetic endothelial-lined hollow fibers under flow. The physical design of the system was incorporated into the model parameters. The heparin-binding growth factor fibroblast growth factor-2 (FGF-2) was used for both the experiments and simulations. Our computational model was composed of three parts: (1) media flow equations, (2) mass transport equations and (3) cell surface reaction equations. The model is based on the flow and reactions within a single hollow fiber and was scaled linearly by the total number of fibers for comparison with experimental results. Our model predicted, and experiments confirmed, that removal of heparan sulfate (HS) from the system would result in a dramatic loss of binding by heparin-binding proteins, but not by proteins that do not bind heparin. The model further predicted a significant loss of bound protein at flow rates only slightly higher than average capillary flow rates, corroborated experimentally, suggesting that the probability of capture in a single pass at high flow rates is extremely low. Several other key parameters were investigated with the coupling between receptors and proteoglycans shown to have a critical impact on successful capture. The combined system offers opportunities to examine circulation capture in a straightforward quantitative manner that should prove advantageous for biologicals or drug delivery investigations.

Show MeSH
Related in: MedlinePlus