Submitted to: Analytical Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/8/2010
Publication Date: 5/15/2010
Citation: Adhikary, R., Mukherjee, P., Krishnamoorthy, G., Kunkle, R.A., Casey, T.A., Rasmussen, M.A., Petrich, J.W. 2010. Fluorescence Spectroscopy of the Retina for Diagnosis of Transmissible Spongiform Encephalopathies. Analytical Chemistry. 82(10):4097-4101. Interpretive Summary: Scrapie is a fatal neurologic disease of sheep and goats, a type of transmissible spongiform encephalopathy (TSE), which is typically diagnosed in affected animals by examination of brain tissue after death. A diagnosis of scrapie results in condemnation of the sheep carcass at slaughter. The diagnostic platforms call for antibodies specific to prion proteins which appear to be the causative agents of TSE. These post-mortem tests are labor-intensive and require hours to days for completion which delays releasing or condemning suspect carcasses. This study utilizes fluorescence technology to examine retinal tissue of the sheep eye to diagnose scrapie. The retina is an extension of the central nervous system (CNS) and as such reflects certain pathologic changes present in brain tissue which produce characteristic optical signals when examined by fluorescence spectroscopy. The characteristic fluorescent signal is apparently a result of aggregated prions and other proteins in the CNS, including the retina. Retinal tissue from scrapie-affected sheep had distinctly different fluorescence patterns from those retina of healthy sheep. The procedure described could be adapted to real-time examination of sheep eyes at the time of slaughter, greatly reducing the time required for testing carcasses post-slaughter.
Technical Abstract: Central nervous system (CNS) tissue provides optical signatures that can be detected with great sensitivity. The fundamental hypothesis proposed in this study was that diseased or damaged central nervous system (CNS) tissue produces optical signals that can be detected and made useful for diagnostic or other purposes. Given that the eye is the most direct and noninvasive entry point to the CNS, the eyes of sheep were collected from animals that were diagnosed with respect to scrapie status using conventional histopathology and immunohistochemistry examinations. The retinas were subsequently analyzed using fluorescent spectroscopy. The results of this study indicate that distinct differences in retinal fluorescence can be observed in animals naturally infected with scrapie. Using an excitation wavelength of 470 nm, two peaks of fluorescent intensity at 550 and 600 nm were observed. The differences in total fluorescence due to disease status greatly exceeded any other differences observed. The characteristic fluorescent signature is thought to be the result of an accumulation of lipofuscin in the retina. It appears that the eye, in particular the retina, is a useful tissue for noninvasive examination of neurological pathologies such as scrapie. The development of procedures based on examinations of the eye that permit the detection of neurological disorders in animals holds great promise.