Near Death Opening of Blood Retinal Barrier Studied with DCE–MRI

Abstract

Abstract: : Purpose: To test the hypothesis that dynamic contrast enhanced magnetic resonance imaging (DCE–MRI) provides a useful in vivo measure of passive blood retinal barrier permeability surface area product (BRB PS) in experimental diabetic retinopathy, and to provide evidence that death or near–death (a necessary component of some other methods to detect permeability) causes an increase in permeability that is not detected when the animals remain alive. Methods: In urethane anesthetized rats dynamic contrast (Gd–DTPA, 590 Da) enhanced MRI (DCE–MRI) was used to detect damage and, when possible, quantify BRB permeability surface product (PS, cm³/min), either before, near, and after death (anesthetic overdose or KCl), or in 8 mo diabetic (and control) rats. BRB integrity was also examined in control and 3 mo diabetic rats using a 93 KDa contrast agent (human serum albumin labeled Gd–DTPA, HSA–Gd). In addition, retina/choroidal thickness was measured using high resolution MRI (23.4 µm² in–plane) in vivo in control, dilutional hyponatremic, and 3 mo diabetic rat groups. Results: No evidence was found (P > 0.05) for BRB damage using HSA–Gd in 3 mo diabetic rats. However, using Gd–DTPA, significant (P < 0.05) BRB damage was found by 8 mo of diabetes. Significant (P < 0.05) increases in retinal thickness, compared with controls, were found following dilutional hyponatremia but not (P > 0.05) in 3 mo diabetic rats. BRB damage was evident (P < 0.05) before loss of respiratory movement (anesthetic overdose) and 2 – 4 minutes after (KCl) death. Conclusions: These results support our early findings of lack of passive leakage through BRB in 2–6 mo diabetic rats, and raise the possibility, for the first time, that experimental methods that involve animal death and / or enucleation during procedures used to assess BRB damage, may cause BRB permeability artifacts. DCE–MRI BRB PS measurement appears to be a reliable procedure for assessing BRB damage, as well as treatment benefits of therapeutic agents.

Keywords: diabetes • ischemia • imaging/image analysis: non–clinical