Role of sodium silicate in induction of scleroderma-related autoantibodies in brown Norway rats through oral and subcutaneous administration

Silica hazard is a growing occupational problem and has been reported to be associated with scleroderma via case reports and occupational studies. The aim of this study is to demonstrate whether oral or subcutaneous silicate exposure can induce an autoimmunity and scleroderma susceptibility in immunosensitive rats. Sodium silicate in a dose of 3 mg in 0.2 ml NS was administered through oral and subcutaneous routes to 20 brown Norway rats. Autoantibodies including ANA, anti-RNP, anti-SCL70 and anti-centromere were measured and compared with pre- and post-challenge serum samples. Serum ANA and anti-RNP were high in significant number of rats (P < 0.05) of only the subcutaneous silicate group. There is an increase in the number of positive readings of autoantibodies at 14th week in comparison with the number of positive readings of autoantibodies at 7th week but P values were not significant. It may be concluded that silicate might induce autoimmunity and scleroderma and it seems to be that the longer the duration of exposure the greater the risk. This is probably the first experimental animal study demonstrating the induction of scleroderma-related autoantibodies after challenge with silicate.