Optical Cryoimaging of Tissue Metabolism in Renal Injuries: Rodent Model

Abstract

Injured tissues are often accompanied by morphological or biochemical changes that can be detected optically. Therefore, it would be valuable to visualize the changes in both structure and biochemistry responses of organs for early detection of disease and monitoring of its progression. Oxidative stress is a biochemical byproduct of these diseases. Thus, obtaining sensitive and specific measurements of oxidative stress at the cellular level would provide vital information for understanding the pathogenesis of a disease. The objective of this research was to use a fluorescence optical imaging technique in order to evaluate the cellular redox state in kidney tissues, and develop an instrument to acquire high resolution 3D images of tissue. I have improved upon a custom-designed device called a cryoimager to acquire autofluorescent mitochondrial metabolic coenzyme (NADH, FAD) signals. The ratio of these fluorophores, referred to as the mitochondrial redox ratio (RR = NADH/ FAD), can be used as a quantitative metabolic marker of tissue. The improvement to the instrument includes addition of higher resolution imaging capabilities to the system. This improvement in the resolution of image acquisition enables microscopy imaging in cryo temperatures to obtain high resolution 3D images. The imaging is performed in cryogenic temperatures to increase the quantum yield of the fluorophores for a higher signal to noise ratio. I also implemented an automated tissue boundary detection algorithm. The algorithm will help provide more accurate results by removing the background of low contrast images. I examined the redox states of kidneys from genetically modified salt sensitive rats (SSBN13, SSp67phx -/-, and SSNox4-/-), in order to study the contribution of chromosome 13, the p67phox gene and the Nox4 gene in the development of salt sensitive hypertension. The result showed that the genetically manipulated rats are more resistant to hypertension caused by excess dietary salt ,, in comparison with salt sensitive (SS) rats. I also studied how endoglin genes affected the redox state and vascular networks of mice kidneys using high resolution images. The results showed that the next generation of the cryoimager can simultaneously monitor the structural changes and physiological state of tissue to quantify the effect of injuries. In conclusion, the combination of high resolution optical instrumentation and image processing tools provides quantitative physiological and structural information of diseased tissue due to oxidative stress.