Impact of Silica Nanoparticles on Rat Immune Responses

RATIONALE: Nanoparticles (NPs) of silica (SiO2) used as a food additives may impact the immune system and anaphylaxis in rats.

METHODS: Silica NPs (“Orisil 300®”) a nanopowder of SiO2 5-30 nm were administered at 0.1 to 100 mg/kg for 30 days intragastrically to 95 male Wistar rats weighing 150-180 g divided into 6 groups. Aqueous SiO2 after sonication was given to Groups 2 , 4 and 6 for 28 days by intragastrically at 100 mg / kg. On days 1,3,5 and 21 Groups 1,2,3 and 4 were sensitized intraperitoneally with ovalbumin (OVA ) plus aluminum hydroxide. IV challenge with OVA occurred on day 29. IgE antibodies to OVA were assessed by passive cutaneous anaphylaxis and IgG by ELISA. Lymphocytes (CD45RA+), CD3+, CD4+ , CD8+, CD161a+) was assessed by flow cytometry. Sera IL6, TNF- alpha and IL10 were assessed by ELISA.

RESULTS: Silica NPs at all doses decreased body weight 10-15%; at 100 mg/kg did not impact anaphylactic shock and OVA specific IgG; decreased leukocytes by 33% ; decreased CD4+ cells 13%; decreased CD4+/CD8+ ratio 27% due to increase CD8+ cells; increased serum TNF-alpha 5- fold.

CONCLUSIONS: Silica NPs in low doses did not induce any adverse effects on rat immune systems, with immunotoxic effects only at high doses of 100 mg / kg body weight. The use of silica NPs as a food additive should be the subject of food hygiene regulations.