Molecular Mechanisms in Amyloid Disorders. Novel Treatment Options in Hereditary Cystatin C Amyloid Angiopathy.

The pathophysiological process in Alzheimer’s disease and other amyloid disorders usually involves the transformation of a soluble monomeric protein via potentially toxic oligomers into amyloid fibrils. The structure and properties of the intermediary oligomers have been difficult to study due to their instability and dynamic equilibrium with smaller and larger species. This has hampered the development of a deeper understanding of the molecular pathophysiology of the disorders and strategies for their treatment. In hereditary cystatin C amyloid angiopathy (HCCAA), a cystatin C variant is deposited in arterial walls and causes brain hemorrhage in young adults. Although carriers of the cystatin C variant may be easily identified by genetic testing, no treatments are available. In the present investigation, redox experiments involving a recombinant double-cysteine mutant of cystatin C were used to generate stable oligomers (dimers, trimers, tetramers, decamers and high-molecular-weight oligomers) and these were characterised concerning size, shape and function. The results showed the oligomers to be highly ordered, domain-swapped assemblies of cystatin C and that the oligomers could not build larger oligomers, or fibrils, without domain swapping. The stabilised oligomers were used to induce antibody formation in rabbits. Oligomer-specific antibodies were obtained and these could be used to selectively remove cystatin C dimers from biological fluids containing both dimers and monomers. A miniaturised high-throughput system was developed and used to test 12 monoclonal antibodies and 1040 drugs in a clinical drug library for their capacity to reduce cystatin C dimer formation in vitro. Several candidates for treatment of HCCAA could be identified. In a different set of patients, scheduled for elective surgery, the plasma levels of cystatin C, creatinine and four inflammatory markers were studied in order to investigate the influence of inflammation on cystatin C, to evaluate its usefulness as a marker of glomerular filtration rate (GFR, ‘kidney function’). The cystatin C level did not change significantly during the observation period (seven days) and did not correlate with the level of any of the four inflammatory markers, and thus, the inflammatory status of a patient does not influence the role of cystatin C as a marker of GFR