Silicon Treatment Preserves Antibiotics and Vaccines for Years

A novel method for encasing molecules of biomedical interest such as antibodies and vaccines in silica "cages" stabilizes them against denaturing thermal treatment and long-term ambient-temperature storage, and subsequently enables them to be released into solution with their structure and function intact.

Biological substances based on proteins, including vaccines, antibodies, and enzymes, typically degrade at room temperature over time due to denaturation, as proteins unfold with loss of secondary and tertiary structure. Their storage and distribution therefore relies on a "cold chain" of continuous refrigeration, which is costly and not always effective, as any break in the chain leads to rapid loss of effectiveness and potency. Efforts have been made to make vaccines thermally stable using treatments including freeze-drying (lyophilization), biomineralization, and encapsulation in sugar glass and organic polymers.

In a new approach, investigators at the University of Bath and colleagues at the University of Newcastle used a silica-based process to stabilize protein structure. In this process, a protein in solution was mixed with silicon dioxide, which bound closely around the protein to match its shape, and quickly built up many layers, encasing the protein. This method did not require freeze-drying, a treatment that potential destroys half of all vaccines.

The investigators reported in the April 24, 2017, online edition of the journal Scientific Reports that they had used this "ensilication" process to treat hen egg white lysozyme (HEWL), a robust and well-characterized protein with enzymatic activity; horse hemoglobin, a heterotetrameric protein with a complex tertiary and quaternary structure; and tetanus toxin C-fragment (TTCF)22, a vaccinogenic tetanus fragment, which is a part of the commonly used DTP vaccine. Results revealed that the proteins could be heated to 100 degrees Celsius or stored at 22 degrees Celsius for at least six months with no loss of function.

Senior author Dr. Asel Sartbaeva, a research fellow in chemistry at the University of Bath, said, "We have demonstrated with ensilication that we can simply and reliably keep proteins from breaking down even at up to 100°C, or store them as a powder for up to three years at room temperature without loss of function. We are very excited by the potential applications of ensilication and our next steps will be to test our findings on more vaccines, antibodies, antiviral and anti-venom drugs, and other biopharmaceuticals."