Suppression of cytokine synthesis in spleen and brain and small changes in c-fos expression in rat brain after intranasal administration of single-walled carbon nanotubes

The purpose of this work is to study cytokine synthesis in the brain, blood, spleen, and liver and cfos expression in a rat brain 24 h after the intranasal administration of single-walled carbon nanotubes (SWCNTs) at a low dose (1 μg per rat, or 4 μg/kg). A RT-PCR analysis of cytokine mRNA synthesis has demonstrated that the cytokine profile in the brain does not change significantly under the influence of SWCNTs, but a reduction of the total content of all cytokine mRNA is observed. At the same time, the mRNA content of colony-stimulating factor IL-5 and proinflammatory cytokine IL-18 increases in the liver; only IL-18 mRNA increases in the blood, which indicates a possible activation of Th-2 lymphocytes and macrophages in the liver and only macrophages in the blood. In the spleen, mRNA levels of all cytokines that were detected in the norm were decreased. This indicates a suppression of the transcription of cytokines in the spleen, the main organ of immune system, and hence an immunosuppressive effect of SWCNTs. Administration of SWCNTs does not alter c-fos expression in 35 of 43 brain structures studied compared to the control. The c-fos expression increased only in the olfactory bulb and in the piriform cortex and in six brain structures this index was reduced; i.e., SWCNTs have little effect on the activity of brain structures. It is assumed that the low-dose intranasal administration of SWCNTs can be used in medicine for drug delivery to the brain. In addition, it is not excluded that the immunosuppressive properties of SWCNTs can be applied for the prevention of transplant rejection and treatment of autoimmune disorders. When using SWCNTs for medical and biological purposes it is necessary to take into account the probability of their immunosuppressive effects.