Quantification of longitudinal tissue pO2 gradients in window chamber tumours: impact on tumour hypoxia

Abstract

We previously reported that the arteriolar input in window chamber tumours is limited in number and is constrained to enter the tumour from one surface, and that the p O 2 of tumour arterioles is lower than in comparable arterioles of normal tissues. On average, the vascular p O 2 in vessels of the upper surface of these tumours is lower than the p O 2 of vessels on the fascial side, suggesting that there may be steep vascular longitudinal gradients (defined as the decline in vascular p O 2 along the afferent path of blood flow) that contribute to vascular hypoxia on the upper surface of the tumours. However, we have not previously measured tissue p O 2 on both surfaces of these chambers in the same tumour. In this report, we investigated the hypothesis that the anatomical constraint of arteriolar supply from one side of the tumour results in longitudinal gradients in p O 2 sufficient in magnitude to create vascular hypoxia in tumours grown in dorsal flap window chambers. Fischer-344 rats had dorsal flap window chambers implanted in the skin fold with simultaneous transplantation of the R3230AC tumour. Tumours were studied at 9–11 days after transplantation, at a diameter of 3–4 mm; the tissue thickness was 200 μm. For magnetic resonance microscopic imaging, gadolinium DTPA bovine serum albumin (BSA-DTPA-Gd) complex was injected i.v., followed by fixation in 10% formalin and removal from the animal. The sample was imaged at 9.4 T, yielding voxel sizes of 40 μm. Intravital microscopy was used to visualize the position and number of arterioles entering window chamber tumour preparations. Phosphorescence life time imaging (PLI) was used to measure vascular p O 2 . Blue and green light excitations of the upper and lower surfaces of window chambers were made (penetration depth of light ~50 vs >200 μm respectively). Arteriolar input into window chamber tumours was limited to 1 or 2 vessels, and appeared to be constrained to the fascial surface upon which the tumour grows. PLI of the tumour surface indicated greater hypoxia with blue compared with green light excitation ( P < 0.03 for 10th and 25th percentiles and for per cent pixels < 10 mmHg). In contrast, illumination of the fascial surface with blue light indicated less hypoxia compared with illumination of the tumour surface ( P < 0.05 for 10th and 25th percentiles and for per cent pixels < 10 mmHg). There was no significant difference in p O 2 distributions for blue and green light excitation from the fascial surface nor for green light excitation when viewed from either surface. The PLI data demonstrates that the upper surface of the tumour is more hy...

Cycling hypoxia and free radicals regulate angiogenesis and radiotherapy response

“…There are several excellent reviews on this subject 5,56,57 . The deficiencies of oxygen transport can be summarized as having eight dominant features: first, a relatively sparse arteriolar supply 5,58 ; second, inefficient orientation of microvessels 59,60 ; third, low vascular density; fourth, extreme variations in microvessel red blood cell flux (many tumour vessels do not carry red blood cells, whereas large diameter shunt vessels contain a relative abundance of red blood cells 61 ); fifth, the limited arteriolar supply can lead to pathologically low vascular pO 2 in regions distant from the arteriolar source (longitudinal oxygen gradient) 58,62,63 ; sixth, hypoxic red blood cells stiffen, increasing blood viscosity, which contributes to sluggish flow; and seventh, large diameter shunts can divert blood away from the tumour bed. Consequently, networks of microvessels can exhibit low pO 2 , leading to relatively large regions of tumour that are dominated by microregions of pathologically low pO 2 58,62,64-66 (FIG.…”

Assessment of tumor oxygenation by electron paramagnetic resonance: principles and applications

“…7,8 It is now well established that steep longitudinal gradients of pO 2 along the vascular tree, as opposed to radial diffusion of oxygen, can largely contribute to deficiencies in tumor oxygen supply. 9 Two features of longitudinal gradients lead to intravascular hypoxia. First, the arterioles feeding the tumor are more deoxygenated than comparable arterioles of normal tissues.…”

Acute Hypoxia Enhances Spontaneous Lymph Node Metastasis in an Orthotopic Murine Model of Human Cervical Carcinoma

“…They also lack smooth muscle and enervation and may have an incomplete endothelial lining and basement membrane, which makes them more "leaky" than vessels in normal tissues (8,9). Furthermore, the vessels supplying tumors often develop from post-capillary venules, creating severe longitudinal pO 2 gradients within the vessels themselves (10). All of these factors contribute to a situation in which a significant proportion of tumor cells lie in hypoxic regions beyond the diffusion distance of oxygen (100 -150 m) where they are exposed to chronically low oxygen tensions.…”