To investigate the mechanism of action of
colchicine in blocking
amyloid deposition, two model systems of
amyloidosis in CBA/J mice were studied. In experimental chronic
inflammation, daily injection of
silver nitrate (AgNO3) resulted in the deposition of 667 +/- 68 ng of
amyloid A protein (AA)/mg of spleen after 25 days. Treatment with 10 micrograms of
colchicine daily decreased AgNO3-induced AA deposition to 12 +/- 1 ng of AA/mg of spleen (p less than 0.001).
Colchicine diminished the acute phase
serum amyloid A protein (SAA) response after 24 hours. Over a 25-day period, SAA concentrations declined and approached baseline both in
colchicine-treated and (unexpectedly) in control mice. This suggested that suppression of SAA levels was not the primary event inhibiting
amyloid deposition. In a model of accelerated
amyloid deposition, injection of preformed
amyloid-enhancing factor along with AgNO3 induced the deposition of 974 +/- 46 ng of AA/mg of spleen 48 hours later.
Colchicine only partially decreased
amyloid-enhancing factor-induced
amyloid deposition to 578 +/- 91 ng of AA/mg of spleen, while blunting the acute phase SAA response. These results suggest that
colchicine inhibits
amyloidosis in the predeposition phase, possibly by blocking formation of
amyloid-enhancing factor.