Long-term kinetics of AA amyloidosis and effects of inflammatory restimulation after disappearance of amyloid depositions in mice

Abstract

SummaryAmyloid A (AA) amyloidosis is characterized by extracellular pathogenic deposition of insoluble fibril protein in various body organs. Deposited amyloid generally remains in a variety of organs for long periods, but its disappearance has been reported after the precursor protein is diminished. The kinetics of AA deposition are not completely understood and, in particular, the roles of cells and cytokines in the deposition and clearance of amyloid remain unclear. In this study, we investigated the disappearance of amyloid depositions in mice over a 1-year period. AA amyloidosis was induced experimentally in mice by injecting amyloidenhancing factor (AEF) and silver nitrate. Mice were killed at different time-points to examine the occurrence and disappearance of amyloid depositions. Maximum levels of amyloid depositions were observed at 20 days after inoculation. Clearance of amyloid depositions was observed from the 40th day onwards, with only minute traces of amyloid present by 240 days. A second inflammatory stimulus consisting of AEF and silver nitrate was given at 330 or 430 days, after amyloid depositions had disappeared almost completely. After that, serum amyloid A was overproduced and redeposition of amyloid was observed, indicating that all mice were primed for aggressive amyloid depositions. After administration of the inflammatory stimuli, the proinflammatory environment was found to have increased levels of interleukin (IL)-6, while anti-inflammatory conditions were established by IL-10 as regression of amyloid deposition occurred. These results suggest that the proinflammatory and anti-inflammatory status have key roles in both amyloid deposition and clearance.

Longitudinal study of experimental induction of AA amyloidosis in mice seeded with homologous and heterologous AA fibrils

“…In this study, peak AA deposition was observed 20 days after AA fibril administration. After reaching peak levels of AA deposition, clearance of amyloid deposits was observed [7,18]. Clearance of AA deposits was faster in mice inoculated with bovine AA fibrils, which may be due to the lesser accumulation of bovine AA deposits.…”

“…Based on such findings, it was suggested that amyloid seeding potential is not solely based on primary structure, and that further study of the 3-D conformation of the protein is required [19]. More aggressive and severe forms of AA deposition were observed after the second inoculation, because the mice were primed after the first inoculation [7,22]. The maximal AA deposition was observed in mice receiving a second inoculation of murine AA fibrils, followed by bovine AA fibrils and lastly administration of silver nitrate alone.…”

“…AA deposition was only observed in mice administered with both silver nitrate and AA fibrils. The pro-inflammatory cytokine IL-6 causes a significant increase in the level of amyloid precursor protein SAA and hence AA amyloid deposition [7,29]. Serum levels of IL-6 were observed to increase and decline thereafter.…”

“…Evaluation for AA amyloid deposition was performed using conventional and polarized light microscopy with a BX 43 (Olympus, Tokyo, Japan), as described previously [7]. For immunohistochemistry (IHC), retrieval of antigen epitopes was performed using steam/heat treatment.…”

“…After the apparent disappearance of AA deposits, a second inoculation caused more severe AA deposition in mice. The pro-and anti-inflammatory cytokine environments were observed during AA deposition and clearance, respectively [7].…”