Pulmonary toxicity comparison of raw and super-purified single-wall carbon nanotubes after intra-tracheal instillation in rats

Abstract

Single-wall carbon nanotubes (SWCNTs) possess many properties and have various potential applications. Nanotubes are very light and could become airborne and potentially reach lungs. In order to evaluate the relation between the respiratory toxicological effects of carbon nanotubes and their physicochemical characteristics, we compared raw and super-purified SWCNTs toxicity. Oxidative stress and inflammation involvements as possible mechanisms of the toxicological effects of these nanotubes were examined. Rats were intratracheally instilled with 200 micro g of raw or super-purified SWCNTs, and euthanized 1, 7, 30, 90 or 180 days after the single treatment for histo-pathological study of the lungs, broncho-alveolar fluids and mRNA expression measurements. SWCNTs were suspended at 1.4 mg/ml in 3% ethanol and 1.4 mg/ml of BSA. The suspension was sonicated for 10 min in an ultrasonic bath. These two types of SWCNTs can induce granulomas. The quantity and size of granulomas appear to be greater after treatment with raw SWCNTs than super-purified SWCNTs. Regarding inflammation, interleukin-1s and interleukin-6 expression increased 24 h after instillation, more with super-purified than with raw SWCNTs. Oxidative stress enzymes expression (Heme oxygenase 1 and iNOS) were induced with a maximum reached at 7 days with raw SWCNTs and 1 month with super purified SWCNTs. Overall, the biological response after treatment with raw SWCNTs containing a high amount of iron (20%) occurred earlier than after treatment with super-purified SWCNTs containing a small amount of iron (2%). Raw SWCNTs seem eliminated more rapidly than super-purified SWCNTs. Purity of SWCNT is an important factor in pulmonary toxicity.