Track 19. Biotransport

7785 Tu, 17:15-17:30 (P25) Transmural water and macromolecular transport in atherosclerosis prone and resistant vessels

Y. Shou 1 , Z. Zeng 1 , K.-M. Jan 2, D.S. Rumschitzki 1,2. 1Department ef Chemical Engineering, City College & GSUC of CUNY, New York, NY, USA, 2Department of Medicine, Columbia University College of Physicians & Surgeons, New York, NY, USA

In this talk we compare the aorta, a large, atherosclerosis-prone artery, with the smaller, rarely atherosclerotic pulmonary artery and the inferior vena cava, a vein that is normally immune to disease. We review the basic features of water and macromolecular transport and macromolecular accumulation in large arteries and go through a number of new sets of experiments - both structure studies as well as water and tracer transport experiments - from our lab that shed light on the differences in transport processes between vessels. We address the role of convective transport into the walls of each vessel, involving localized hot spots for macromolecular transport that correlate with regions of low wall shear stress, in view of each vessel's very different trans- mural pressure that drives such transport. Finally, we use these experimental measurements to construct a transport theory that explains the similarities and differences between the aorta and the pulmonary artery. Combination of this theory with our earlier lipid accumulation kinetics seems to shed some light on why certain chronic conditions, such as pulmonary hypertension, can shift the balance in certain vessels from disease-resistant to susceptible.

19.4. Transport in Native and Engineered Cells and Tissues 4083 We, 11:00-11:15 (P32) Electric field-mediated enhancement of in vivo transport of plasmid DNA in tumor interstitium J.W. Henshaw 1, D.A. Zaharoff 2, B.J. Mossop 1 , F. Yuan 1. 1Department of Biomedical Engineering, Duke University, Durham, NC, USA, 2Laboratory of Tumor Immunology and Biology, National Cancer Institute (NIH), Bethesda, MD, USA

The interstitial space is a physiological barrier to non-viral gene delivery. Exter- nal pulsed electric fields have been proposed as a driving force for increasing gene transport in the interstitium. However, no direct in vivo quantification of this phenomenon has been reported. In this study, an in vivo technique was developed to quantify the electrophoretic transport of plasmid DNA (pDNA) in tumor interstitium during the local application of electric fields typical of those used during electric field mediated gene delivery. 4T1 and B16.F10 tumors implanted in dorsal skin-fold chambers of Balb/C and C57BL/6 mice, respectively, were used as tumor models. The implanted tumor cell suspension also included 1.0~tm yellow-green latex microspheres (MS) used as tissue markers during image analysis. Rhodamine labeled pDNA was administered into the tumor via microinjection prior to pulse application. Four pulse se- quences, each consisting of 10 pulses, 100 or 400V/cm in magnitude, 20 or 50 ms in duration, with 1 s pulse intervals, were examined. Cross correlation analysis of confocal images of fluorescently labeled pDNA and MS, taken immediately before and after pulse application, were used to determine total pDNA and MS displacement. Net pDNA movement was then determined by subtraction of the total pDNA displacement vector from the MS displacement vector. The net pDNA movement increased with both increasing pulse duration and increasing pulse magnitude. The effect of increasing pulse duration was significantly greater with the 400 V/cm field compared to the 100V/cm field. There was no significant difference in net pDNA movement between 4T1 and B16.F10 tumors under any of the pulsing conditions investigated. The net pDNA movement obtained under the highest energy pulse sequence was relatively small with respect to the size of the tumor, indicating that pulsed, high intensity electric fields alone may not be suitable for macroscopic transport within 4T1 or B16.F10 tumor interstitium. However, the effect of micron scale movement on improved gene delivery, and therefore increased therapeutic efficacy, may still be significant.

4384 We, 11:15-11:30 (P32) A time-dependent electrodiffusion-convection model for charged macromolecular transport in the interstitial space

B. Chen 1 , B.M. Fu 1,2. 1Department of Mechanical Engineering, University of Nevada, Las Vegas, Las Vegas, NV, USA, 2Department of Biomedical Engineering, The City University of New York, New York, NY, USA

The extravascular matrix carries negative charge due to its composition of glycosaminoglycans (GAGs). Numerous experiments have shown that the negative charge affects transvascular passage and interstitial accumulation of charged molecules in both normal and pathological tissues. On the basis of the previous models [1-3], we developed a new electrodiffusion-convection model to investigate the mechanisms by which the negatively charged tissue matrix

19.4. Transport in Native and Engineered Cells and Tissues $377

modifies the interstitial transport of charged macromolecules, e.g., albumin. Our model demonstrated that the apparent tissue diffusion coefficient of nega- tively charged albumin (net charge =-19) in rat mesentery was comparable to that of neutral dextran with equivalent hydrodynamic radius. The discrepancy in their distribution profiles of the interstitial concentration observed by Fox and Wayland [4] can be explained by the charge effect, especially by the partition between the vascular and extravascular compartments, instead of by the different apparent diffusion coefficients that Fox and Wayland suggested. This charge effect induces equivalent to about two-fold difference in apparent tissue diffusion coefficients of charged albumin and neutral dextran with same free diffusion coefficients. Furthermore, our results indicated that the positively charged macromolecules accumulated faster in the interstitial space as compared with the similar-sized ones bearing zero or negative charges.

References [1] Fu B.M., Adamson R., Curry F.E., Weinbaum S. Ann. Biomed. Eng. 1997; 25:

375-397. [2] Hu X., Weinbaum S. Microvasc. Res. 1999; 58: 281-304. [3] Chen B., Fu B.M.J. Biomech. Eng. 2004; 126: 614~24. [4] Fox J.R., Wayland H. Microvasc Res. 1979; 18: 255-276.

4895 We, 11:30-11:45 (P32) The importance of pressure in describing the forces on a cell in an extracellular matrix W. McCarty, M. Johnson. Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA

Purpose: Forces on cells in an extracellular matrix (ECM) created by interstitial flows are known to be important regulators of cell motility, gene expression, and signaling. While recent focus has been on the shear stresses this flow produces, we investigated the relative magnitude of pressure forces acting on a cell as compared to the shear forces. Methods: Specific hydraulic conductivity (SHC) data were collected by mixing latex microspheres (5% by weight; 30 or 90nm) into solutions of Matrigel basement membrane (10.5mg/ml) at 4°C. This mixture was injected into a modified Ussing chamber supported by 50 nm pore-size filters, allowed to gel at 25°C for 30 min, and connected to a perfusion system. The experimentally measured SHC values of the gels alone (Kg) and with latex (Knet) were compared to predictions using Brinkman's equation, which accounts for the additional drag forces due to particles of radius a and volume fraction ¢.

(1) Kne t + 2 ~ 2 + ~ ~Tk:~n e t

In equation (1), the contribution of shear to the total force acting on the microspheres is represented by the term a/K~net, while that due to pressure gradient acting on the microspheres is a2/(3Knet). Results: The experimental results matched well with predictions from equa- tion (1) at low pressures (5-30mmHg) and were slightly less permeable than predicted for higher pressures (30-100mmHg). The pressure term was typically two orders of magnitude greater than the shear term for physiological values of a and Kg. Conclusions: Our experiments confirmed the predictions of Brinkman theory for microspheres embedded in Matrigel. Stokes solution for flow around a sphere in an unconfined fluid shows pressure and shear forces to be com- parable. However, Brinkman's equation, applicable for flow around a cell in an extracellular matrix, predicts the net pressure forces to be much larger than the shear forces. Thus, the response of a cell to pressure, in addition to the shear forces, should be further investigated in order to better understand this aspect of cell-environment interaction.

6177 We, 11:45-12:00 (P32) Albumin transport across human endothelium co-cultured with vascular smooth muscle cells O. Ogunrinade, C.S. Wallace, G.A. Truskey. Department of Biomedical Engineering, Duke University, Durham, NC, USA

In vivo, the close apposition of endothelial cells (ECs) and smooth muscle cells (SMCs) in blood vessels facilitates interactions between the two cell types. Indeed, ECs release nitric oxide and activate transforming growth factor beta which alter SMC function. We used a direct co-culture model to examine the effect of SMCs on albumin transport across ECs (Lavender et al. Biomaterials (2005) 26: 4642). The endothelium formed a continuous monolayer as shown by PECAM staining. The overall albumin permeability of co-cultures was less than that of ECs alone and declined with time in culture. To determine the relative contributions of the endothelium and smooth muscle cells, the permeability of each was measured separately and used to predict to permeability of co-cultures assuming resistances in series. We found that we could accurately predict the overall permeability of cultures from the permeability of each cell type alone suggesting that the untreated cell types behaved independently. However, when co-cultured cells were exposed to forskolin, which elevates cAMP levels, the overall permeability rose. This is in