Diffusion of Epidermal Growth Factor in Rat Brain Extracellular Space Measured by Integrative Optical Imaging

Abstract

Diffusion of epidermal growth factor in rat brain extracellular space measured by integrative optical imaging. J Neurophysiol 92: 3471-3481, 2004. First published July 21, 2004 doi:10.1152/jn. 00352.2004. Epidermal growth factor (EGF) stimulates proliferation, process outgrowth, and survival in the CNS. Understanding the actions of EGF necessitates characterizing its distribution in brain tissue following drug delivery or release from cellular sources. We used the integrative optical imaging (IOI) method to measure diffusion of fluorescently labeled EGF (6,600 M r ; 4 g/ml) in the presence of excess unlabeled EGF (90 g/ml) to compete off specific receptor binding and reveal the "true" EGF diffusion coefficient following injection in rat brain slices (400 m). The effective diffusion coefficient was 5.18 Ϯ 0.16 ϫ 10 Ϫ7 (SE) cm 2 /s (n ϭ 22) in rat somatosensory cortex and the free diffusion coefficient, determined in dilute agarose gel, was 16.6 Ϯ 0.12 ϫ 10 Ϫ7 cm 2 /s (n ϭ 27). Tortuosity ( ), a parameter representing the hindrance imposed on EGF by the convoluted brain extracellular space (ECS), was 1.8, the lowest yet measured by IOI for a protein in brain. Control experiments with fluorescent dextran of similar molecular weight and tetramethylammonium confirmed EGF did not affect local ECS structure. We conclude that transport of smaller growth factors such as EGF through brain ECS is less hindered than that of larger proteins (Ͼ10,000 M r , e.g., nerve growth factor) where typically Ͼ 2.1. Modeling was used to predict that low will allow EGF sources in the brain to be further from target cells and still elicit a biological response. High values for larger growth factors imply more constrained local biological effects than with smaller proteins such as EGF.

Neurovascular Protection by Targeting Early Blood–Brain Barrier Disruption with Neurotrophic Factors after Ischemia–Reperfusion in Rats

“…Epidermal growth factor possesses a low tortuosity (l) value of 1.8 and this low resistance to migration may cause the elevated T 2 value as seen at the early time point of 24 hours. 40 Eight times heavier than EGF, PEDF might have induced a rather persistent elevation in T 2 values as observed with this group. As the core body temperatures of all animals were maintained at 37.5-37.7 1C any influence of temperature on T 2 values may be safely ruled out.…”

Cooperation among cancer cells as public goods games on Voronoi networks

“…The diffusion of EGF in the brain has been estimated to be 5x10 -7 cm 2 /s [Thorne et al 2004] which is equivalent to approximately 0.05 cm/hour; therefore d can be estimated to be approximately 25 to 50 if we assume that the size of a cell is 10-20µm. Thorne et al 2004 actually calculate the diffusion range of EGF; using the curve shown in their Fig.…”

“…The diffusion of EGF in the brain has been estimated to be 5x10 -7 cm 2 /s [Thorne et al 2004] which is equivalent to approximately 0.05 cm/hour; therefore d can be estimated to be approximately 25 to 50 if we assume that the size of a cell is 10-20µm. Thorne et al 2004 actually calculate the diffusion range of EGF; using the curve shown in their Fig. 6, the diffusion range at which the concentration of the growth factor is 50% of the concentration at the source is between 100 and 600 µm, that is (assuming again that cell size is between 10 and 20 µm), d=5-10 to 30-60.…”

A systematic approach to the development of fluorescent contrast agents for optical imaging of mouse cancer models

“…Fluorochrome-labeled epidermal growth factor (EGF) has been a versatile tumor imaging agent because the epidermal growth factor receptor (EGFR) is overexpressed on the surface of many types of tumor cells [20], [21], [22], [23], and [24]. In a study measuring the diffusion of small molecules across the extracellular space in rat brains, Thorne et al [25] showed that EGF labeled with Oregon green 514 could be used as a reporter. Ke et al [26] used Cy5.5-labeled EGF to target human breast tumor cells implanted in mice.…”