Cell Damage in Light Chain Amyloidosis: FIBRIL INTERNALIZATION, TOXICITY AND CELL-MEDIATED SEEDING

Differences in Protein Concentration Dependence for Nucleation and Elongation in Light Chain Amyloid Formation

Light chain (AL) amyloidosis is a lethal disease characterized by the deposition of the immunoglobulin light chain into amyloid fibrils, resulting in organ dysfunction and failure. Amyloid fibrils have the ability to self-propagate, recruiting soluble protein into the fibril by a nucleation-polymerization mechanism, characteristic of autocatalytic reactions. Experimental data suggest the existence of a critical concentration for initiation of fibril formation. As such, the initial concentration of soluble amyloidogenic protein is expected to have a profound effect on the rate of fibril formation. In this work, we present in vitro evidence that fibril formation rates for AL light chains are affected by the protein concentration in a differential manner. De novo reactions of the proteins with the fastest amyloid kinetics (AL-09, AL-T05, and AL-103) do not present protein concentration dependence. Seeded reactions, however, exhibited weak protein concentration dependence. For AL-12, seeded and protein concentration dependence data suggest a synergistic effect for recruitment and elongation at low protein concentrations, while reactions of κI exhibited poor efficiency in nucleating and elongating preformed fibrils. Additionally, co-aggregation and cross seeding of κI variable domain (V_L) and the κI full length (FL) light chain indicate that the presence of the constant domain in κI FL modulates fibril formation, facilitating the recruitment of κI V_L. Together, these results indicate that the dominant process in fibril formation varies among the AL proteins tested with a differential dependence of the protein concentration.

Phase 2 trial of daily, oral epigallocatechin gallate in patients with light-chain amyloidosis

Previous studies have suggested that an increase in mitochondrial reactive oxygen species may cause organ damage in patients with light-chain (AL) amyloidosis; however, this damage can be decreased by antioxidant-agent treatment. Epigallocatechin gallate (EGCG), the major natural catechin in green tea, has potent antioxidant activity. Because EGCG has recently been reported to have a favorable toxicity profile for treating amyloidosis, we sought to examine the clinical efficacy and toxicity of EGCG in patients with AL amyloidosis. Fifty-seven patients were randomly assigned to the EGCG and observation groups and observed for six months. There were no increases in grade 3-5 adverse events and EGCG therapy was well tolerated. Although a decrease in the urinary albumin level was found in the EGCG group in patients with obvious albuminuria after treatment initiation, its antioxidant activity may not be sufficient to clarify the potential effect of EGCG in patients with AL amyloidosis. Because some of the biological markers responsible for organ damage were well correlated to the level of antioxidant potential in patients' plasma, the status of oxidative stress in the blood may indicate the extent of organ damage in clinical situations.