Liposomal nanosilver encapsulation for cytotoxic assays

Nanosilver is the most commercialised nanoparticle routinely used for its antibacterial purposes in food preservation, cosmetic and health products such as medical devices and wound treatment products (Vance et al., 2015). Interestingly, research on nanosilver has now progressed beyond antibacterial use to application as anticancer owing to some studies that have demonstrated the anticancer properties of nanosilver (Zhang et al., 2014, Zhang et al., 2016). Unfortunately, the wide antibacterial application of nanosilver coupled with the very high amounts of the nanoparticles in these commercialised and every day consumable products with the new anticancer application portends a serious risk of adverse effects which will be consequent upon repeated human exposures.

There are evidences that high consumption of nanosilver can lead to adverse effects such as inflammation, skin irritation and discolouration, and liver and kidney damage (León-Silva et al., 2016). This can be avoided if the cytotoxicity and method of delivery of nanosilver is improved upon, in such a way that small quantities of nanosilver can achieve therapeutic effects that is currently achieved in high amounts. This rationale has been previously employed in making of DoxilTM, an approved drug by the Food and Drug Administration (FDA)for instance, where doxorubicin, a conventional anticancer drug was enclosed within liposome structure for treatment of ovarian cancer and Kaposi sarcoma (Duggan and Keating, 2011). In addition, there is evidence in the literature that dipalmitoyl phosphatidylcholine (DPPC) which is often used in making liposomes can suppress inflammation induced by nanosilver. As such, we hoped modifying the surface of nanosilver with DPPC may enhance its cytotoxicity and suppress the associated inflammation, making the nanoparticle more effective as antibacterial or anticancer with less or no side effect.

In this study, we modified nanosilver by enclosing it within a DPPC based liposomal case through extrusion in a polycarbonate membrane for the first time, to improve the effectiveness as a drug on a leukemic immune cell line (THP1) and THP1 macrophages as well as prevent any inflammatory responses known to be associated with nanosilver . The cell metabolism and cytotoxic effect of the liposomal nanosilver was were tested by Alamar Blue assay and flow cytometry Live/Dead assay respectively, and it was discovered that very small concentration of liposomal nanosilver resulted in significant cell death both in THP1 and THP1 macrophages when compared to unmodified nanosilver (Yusuf et al., 2018).

Naturally, human cell death occurs for many reasons and in many ways to prevent DNA damage through aging or assault from the environment. We also found by flow cytometric analysis that the modified nanosilver caused DNA damage, raised the Bax/Bcl2 ratio and activated executioner caspases 3 and 7 to induce both THP1 and THP1 macrophage death. However, we found that generation of reactive oxygen species (ROS) which is the main mechanism by which nanosilver induce cell death was suppressed by liposomal nanosilver.

While this may be a great news for cancer treatment considering the emergence of different resistant cancer cells to conventional anticancer drugs, possible inflammatory response to the modified nanosilver is a potential factor that will significantly impact acceptance of the drug for therapy. We analysed secretion of inflammatory molecules, using ELISA kit from ELISAGenie purchased through MSC Dublin, we were able to accurately detect that the liposomal nanosilver suppressed nanosilver induced-inflammation in a fraction of the time required by other ELISA kits. Secretion of interleukins 1β, 6 and 8 as well as tumour necrosis factor alpha were significantly suppressed by liposomal nanosilver in comparison with unmodified nanosilver.

The above result showed that liposomal nanosilver showed superior characteristic to unmodified nanosilver improving the cytotoxicity and suppressing associated inflammation. The reason for this was found to be as a result of the liposome facilitating improved intracellular uptake of the nanosilver when compared with the unmodified nanosilver.

In summary, this research serves as a proof of concept which can be applied not only in cancer treatment but also in antimicrobial applications such as in food preservation, cosmetics disinfection of household items and medical items. As such, improving the cytotoxicity and delivery of nanosilver as well as other nanoparticles with therapeutic potential can be achieved by encapsulating such nanoparticle in liposomes. This research in particular highlights the potential of liposomal nanosilver in treatment of inflammatory diseases such as ulcerative colitis, Crohn’s disease, arthritis and inflammatory breast cancer.

References

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