Protease inhibitors, or PIs, are chemical agents that inhibit the activity of the protease enzyme, which breaks down proteins. Protease is a naturally-occurring chemical inside the cells that invading viruses use to make copies of themselves, which can cause an infection. Several pharmaceutical medications for treating infections such as HIV use this mechanism to prevent the virus from spreading. The AIDS Treatment Data Network notes that protease inhibitor medications are so effective they have helped to reduce death related to AIDS by almost 70 percent. However, several natural protease inhibitors exist that have similar impacts without causing the side effects of pharmaceutical protease inhibitors.
Green tea is a popularly consumed drink that contains several compounds that have health benefits, including natural protease inhibitors. According to research published in 2008 in the medical journal “Inflammopharmacology,” there is evidence that a polyphenol called epigallocatechin, or EGCG, found in green tea is a potent natural protease inhibitor. According to the study, this substance has anti-cancer as well as anti-viral effects in the body. However, the activity of these natural protease inhibitors is not likely potent enough to replace synthetic protease inhibitor medications used to treat HIV and cancers.
Aquatic cyanobacteria is also referred to as blue-green algae that contains natural protease inhibitor compounds. According to a study published in the "Estonian Journal of Ecology" in 2008, this type of algae contains up to 13 bioactive compounds, including trypsin protease inhibitors. However, cyanobacteria also contain several toxins that can cause serious allergic reactions when exposed to the skin. Hence, the specific protease inhibitor compounds must be isolated in a laboratory before they can be used.
Soybean contains a natural protease inhibitor called Bowman-Birk inhibitor, or BBIC, which also exists in other types of legumes. The U.S. National Cancer Institute Drug Dictionary notes that this compound acts against the serine protein enzymes chymotrypsin and trypsin in the body. These enzymes play key roles in blood clotting, immune reactions and inflammation. This function may be beneficial in enhancing the immune system response against malignant or cancer cells in the body.