Anti-betanodavirus activity of isoprinosine and improved efficacy using carbon nanotubes based drug delivery system

Viral nervous necrosis (VNN) disease has caused mass mortality in cultured marine and freshwater fish worldwide, resulting in enormous economic losses in the aquaculture industry. The causative agent of VNN is betanodavirus [also known as nervous necrosis virus (NNV)], which classified as a member of the Nodaviridae family. NNV mainly infects the central nervous system (CNS) of hosts, which is protected by an elaborate barrier system, limiting the number of drugs reaching the infected sites to tackle the infections. Therefore, it is important to develop alternative drugs and smart delivery technologies for treatment the NNV infection. In the study, the anti-NNV activity of an immunomodulatory antiviral drug, isoprinosine, was checked both in vitro and in vivo. Besides, single-walled carbon nanotubes (SWCNTs) were used as a carrier to improve the anti-NNV activity. Results showed that isoprinosine could effective protect SSN-1 cell from NNV infection, and the percentage of apoptosis was significantly decreased following isoprinosine treatment. Similarly, isoprinosine also showed a strong anti-NNV activity in zebrafish, and the IC50 (inhibitory concentration at half-maximal activity) values were 86.44 and 52.47 mg/L after exposure to isoprinosine for 3 and 5 days, respectively. The expression levels of IL-1 beta, IFN-gamma and TNF-alpha were up-regulated following isoprinosine treatment, indicating that isoprinosine can improve the immune responses to against NNV infection. A smart delivery system (named as SWCNTs-I) based on SWCNTs, bovine serum albumin (BSA) and isoprinosine was constructed and characterized by transmission electron microscope, FTIR spectroscopy and UV-vis spectroscopy. SWCNTs-I was internalized inside the SSN-1 cells, and showed a systemic distribution in the zebrafish larvae. SWCNTs-I has a stronger anti-NNV activity than naked isoprinosine, and the mortality of larvae treated with SWCNTs-I was 39.3% during 7 days post infection, while that were 96.7% and 58% for the control and naked isoprinosine treatment groups, respectively. Results so far indicated that isoprinosine is a powerful anti-NNV drug, and drug delivery with SWCNTs has a potential application value to control fish viral diseases in aquaculture.