Reshmi Rajendran

A novel approach to the identification and quantitative elemental analysis of amyloid deposits—Insights into the pathology of Alzheimer's disease

There is considerable interest in the role of metals such as iron, copper, and zinc in amyloid plaque formation in Alzheimers disease. However to convincingly establish their presence in plaques in vivo, a sensitive technique is required that is both quantitatively accurate and avoids isolation of plaques or staining/fixing brain tissue, since these processes introduce contaminants and redistribute elements within the tissue. Combining the three ion beam techniques of scanning transmission ion microscopy, Rutherford back scattering spectrometry and particle induced X-ray emission in conjunction with a high energy (MeV) proton microprobe we have imaged plaques in freeze-dried unstained brain sections from CRND-8 mice, and simultaneously quantified iron, copper, and zinc. Our results show increased metal concentrations within the amyloid plaques compared with the surrounding tissue: iron (85 ppm compared with 42 ppm), copper (16 ppm compared to 6 ppm), and zinc (87 ppm compared to 34 ppm).

Does iron inhibit calcification during atherosclerosis

Oxidative stress has been implicated in the etiology of atherosclerosis and even held responsible for plaque calcification. Transition metals such as iron aggravate oxidative stress. To understand the relation between calcium and iron in atherosclerotic lesions, a sensitive technique is required that is quantitatively accurate and avoids isolation of plaques or staining/fixing tissue, because these processes introduce contaminants and redistribute elements within the tissue. In this study, the three ion-beam techniques of scanning transmission ion microscopy, Rutherford backscattering spectrometry, and particle-induced X-ray emission have been combined in conjunction with a high-energy (MeV) proton microprobe to map the spatial distribution of the elements and quantify them simultaneously in atherosclerotic rabbit arteries. The results show that iron and calcium within the atherosclerotic lesions exhibit a highly significant spatial inverse correlation. It may be that iron accelerates the progression of atherosclerotic lesion development, but suppresses calcification. Alternatively, calcification could be a defense mechanism against atherosclerotic progression by excluding iron.

Consequences of a fat diet in the distribution of minerals within pancreatic tissues of rats and rabbits.

The effects of plasma lipid overload on pancreatic islet function and on mineral imbalance are issues under debate. However, the outcomes may be biased by the different metabolisms of different species. This prospective study evaluated whether a high fat diet intake changed the distribution of physiologically relevant elements within pancreatic endocrine and exocrine tissues of Sprague Dawley rats and New Zealand White rabbits. Nuclear microscopy techniques provided images of the specimen density and structure as well as the elemental distributions and quantification of P, S, Cl, K, Ca, Fe, and Zn using unstained cryosections of pancreas. Our results indicate that pancreatic islets in normal rats and rabbits had lower tissue density and higher Ca, Fe, and Zn content compared to exocrine tissue, and that rabbit islets exhibit the highest Zn content (3,300 μg/g in rabbits versus 510 μg/g in rats). Fat diet intake resulted in large deposits of fat in the pancreas, which modified the density contrast of tissues and also resulted in a twofold decrease of Ca and Zn concentrations in islets of both rats and rabbits. This result indicates that a fat diet leads to a reduction in essential trace element concentrations in pancreas, which in turn may hamper endocrine function.

Zinc mapping and density imaging of rabbit pancreas endocrine tissue sections using nuclear microscopy.

Nuclear microscopy is a suite of techniques based on a focused beam of MeV protons. These techniques have the unique ability to image density and structural variations in relatively thick tissue sections, map trace elements at the cellular level to the microgram per gram (dry weight) level, and extract quantitative information on these elements. The trace elemental studies can be carried out on unstained freeze-dried tissue sections, thereby minimizing any problems of contamination or redistribution of elements during conventional staining and fixing procedures. The pancreas is a gland with different specialized cells and a complex hormonal activity where trace elements play an important role. For example, zinc has an active role in insulin production, and calcium ions participate in the stimulation and secretion process of insulin. Using nuclear microscopy with a spatial resolution of 1 mum, we have located, using zinc mapping, the islets of Langerhans in freeze-dried normal rabbit tissue sections. The islets of Langerhans contain beta-cells responsible for insulin production. Subsequent quantitative analyses have indicated elevations in most elements within the islets of Langerhans, and significantly so for the concentrations of Zn [3,300 compared to 90 microg/g (dry weight)] and Ca [1,100 compared to 390 microg/g (dry weight)].