Application of Resonance Raman Spectroscopy to the Detection of Carotenoids
A tissue site that appears to be particularly interesting for the application of the Raman method is the macula lutea. It is located in the human retina and contains the highest concentration of carotenoids in the human body. Of the about ten carotenoid species found in human serum, only two carotenoids, lutein and zeaxanthin, are selectively taken up at this tissue site. Their concentrations can be as high as several 10 ng per gram of tissue, however, in the healthy human retina. Due to their strong absorption in the blue-green spectral range, the macular carotenoids, also termed macular pigment, MP, impart a yellow coloration to the macula, which contains a high density of photoreceptors, enabling high-acuity color vision. When viewed in cross section, MP is located anterior to the photoreceptor outer segments and the retinal pigment epithelium (Snodderly et al. 1984a,b) and therefore is thought to shield these vulnerable tissues from light-induced oxidative damage by blocking phototoxic short-wavelength visible light. Also, MP may directly protect the cells in this area, since lutein and zeaxanthin are ef cient antioxidants and scavengers of reactive oxygen species. There is increasing evidence that MP may help mediate protection against visual loss from age-related macular degeneration, AMD (Seddon et al. 1994, Landrum and Bone 2001, Krinsky et al. 2003, Krinsky and Johnson 2005, AREDS 2007), the leading cause of irreversible blindness affecting a large portion of the elderly population. Since the MP compounds are taken up through the diet, there is a chance that early age screening of MP concentrations to identify individuals with low levels of MP, accompanied with dietary interventions such as nutritional supplementation, will help prevent or delay the onset of the disease.