Researchers at the Indian Institute of Science (IISc), Bangalore have demonstrated a cheap and efficacious way of neutralising bacterial endotoxins in blood that cause sepsis. It involves administering a protein into the body of mice. The protein (bactericidal/permeability-increasing protein or BPI) was produced using a novel process. The results were published on September 20 in the journal Scientific Reports.
Sepsis, a life-threatening condition, is triggered by an infection that very quickly spirals out of control and is a major cause for concern among high-risk patients. Sepsis develops when the body mounts a very strong assault on an infection. This results in a cascading effect that causes inflammation in the entire body. It finally ends up as multi-organ failure and death. There is a high mortality rate of 30-50 per cent associated with sepsis.
All the mice treated with BPI survived, while only two mice in the control group did not die.Though the BPI protein, which neutralises the endotoxin that causes sepsis, is produced in the body, sufficient quantities are not produced to quench the endotoxins when sepsis sets in. Therefore, it is necessary to introduce sufficient quantities of BPI protein externally.
Currently, recombinant human BPI, which is used for treating sepsis induced by lipopolysaccharides (LPS), has a few shortcomings — the half-life is short and it is prohibitively expensive.
To address these shortcomings, a team led by Prof. Dipshikha Chakravortty, from the Department of Microbiology and Cell Biology, IISc and the corresponding author of the paper, turned to gas nanovesicles produced by Halobacteria. The nanovesicles are inert in nature and so do not evoke any immune response in humans. Nanovesicles produced by bacteria are easy to purify and so dramatically reduce the production cost of recombinant BPI.
The Bengaluru team along with Prof. Shiladitya DasSarma from the University of Maryland, U.S., cloned mouse BPI protein in the Halobacterium gene so that when the bacteria produced nanovesicles, the BPI protein was expressed on the surface of the vesicles.
“BPI’s stability gets enhanced when expressed on the surface of the nanovesicles probably because it is anchored to the nanovesicle membrane,” says Prof. Chakravortty. The mouse BPI expressed on the surface of nanovesicles showed antibacterial activity.
To test the efficacy of BPI expressing nanovesicles from preventing sepsis, the 50 mice were first injected with nanovesicles and then challenged with sepsis causing LPS and galactosamine. “All the mice treated with BPI survived, while only two mice in the control group did not die,” says Arjun Balakrishnan, the first author of the paper.
However, when BPI expressing nanovesicles were administered along with or after sepsis causing LPS treatment the mice did not survive. “This suggests that BPI proteins should be administered before sepsis sets in so that it is present in the circulatory system to clear the sepsis-causing endotoxin,” says Prof. Chakravortty. “Cytokine storm will set in within minutes of septic shock. So nothing can be done once sepsis sets in.”
“The therapeutic use of BPI produced in Halobacterium to combat septic shock may be promising from the standpoint of both safety and efficacy,” says Mr. Balakrishnan. The team is now planning to undertake trials in larger animals.