Silk Proteins May Improve Product Stability and Reduce the Risk of Product Loss in the Cold Chain

Researchers report results of a novel silk protein to help make pharmaceuticals less susceptible to heat-related product loss, highlighting the importance of proper cold chain conditions.

Billions of dollars of pharmaceutical products are lost due to improper storage and shipping, according to researchers Zhang and colleagues at the Tufts University, Department of Chemical & Biological Engineering in Medford, Massachusetts. In addition, the logistical burden of the cold chain, by some estimates, accounts for approximately every $8 out of $10 spent on vaccination, or $200 to $300 million each year.

Some pharmaceutical products that have not been stored at the proper temperature may even make its way to patients, potentially causing them harm. In one case, improper vaccine storage was linked to rising rates of pertussis in certain areas of Houston, Texas.

To combat the problems associated with vaccine storage, Zhang and colleagues developed a technology to make vaccines and antibiotics less susceptible to heat. Using a protein found in silkworms known as silk fibroin, investigators formulated a polymer form of the protein to help control degradation of pharmaceutical products in environments of varying temperatures.

The silk protein under investigation is composed of organized crystalline domains known as beta-sheets that immobilize bioactive molecules, which improves molecular stability and reduces the likelihood that medications will denature.

Researchers tested solutions containing the antibiotics penicillin and tetracycline for stability in solution over 4 weeks at various temperatures, ranging from 4°C to 60°C, with and without the silk protein. Over time, tetracycline stored without the protein lost potency at all temperatures--even under refrigeration at the lowest temperature.

Silk films added to the medication mixture helped retain the tetracycline bioactivity after 6 and 9 months of storage at room temperature. In addition, silk films helped penicillin maintain 50% of its maximum activity after 183 days in storage at room temperature. Use of silk films in formulations of the mumps-measles-rubella vaccine and trivalent influenza vaccine may also help prevent product degradation.

It is important to note that silk films may lead to allergic reactions in some patients. Additionally, it is conceivable that patients could affect the efficacy of the vaccine or medication formulated with silk film proteins.

Although vaccines treated with silk films may be an appropriate future option for some underserved areas that are unable to receive products under proper storage conditions, for now the best hope for improving vaccine and product stability is through improved temperature monitoring, as well as standardization and regulation of storage.

The fact that scientists are considering reformulating vaccines and medications with silkworm proteins to improve product stability in hot environments highlights the importance of vaccine and drug storage within a proper temperature range.

Reference

Zhang J, Pritchard E, Hu X, et al. Stabilization of vaccines and antibiotics in silk and eliminating the cold chain. Proc Natl Acad Sci U S A. 2012;109(30):11981-11986.