In a proof-of-concept study, NC State University researchers show that genetically engineered green bottle fly (Lucilia sericata) larvae can produce and secrete a human growth factor - a molecule that helps promote cell growth and wound healing.
Sterile, lab-raised green bottle fly larvae are used for maggot debridement therapy (MDT), in which maggots are applied to non-healing wounds, especially diabetic foot ulcers, to promote healing. Maggots clean the wound, remove dead tissue and secrete anti-microbial factors. The treatment is cost-effective and approved by the Food and Drug Administration. However, there is no evidence from randomized clinical trials that MDT shortens wound healing times.
With the goal of making a strain of maggots with enhanced wound-healing activity, NC State researchers genetically engineered maggots to produce and then secrete human platelet derived growth factor-BB (PDGF-BB), which is known to aid the healing process by stimulating cell growth and survival.
Max Scott, an NC State professor of entomology, and colleagues from NC State and Massey University in New Zealand used two different techniques to elicit PDGF-BB from green bottle fly larvae.
One technique utilized heat to trigger the production of PDGF-BB in transgenic green bottle flies. The technique worked - to a point. The human growth factor was detectable in certain structures within the larvae after the larvae were shocked with high heat - a level of 37 degrees Celsius - but PDGF-BB was not detectable in maggot excretions or secretions, making it unworthy of clinical use.
"It is helpful to know that a heat-inducible system can work for certain proteins in the green bottle fly, but the fact that maggots did not secrete the human growth factor makes this technique a non-starter for clinical applications like MDT," Scott said.
The second technique was more successful. Scott and colleagues engineered the flies such that they only made PDGF-BB if raised on a diet that lacked the antibiotic tetracycline. PDGF-BB was made at high levels in the larvae and was found in the excretions and secretions of maggots, making the technique a potential candidate for clinical use.
"A vast majority of people with diabetes live in low- or middle-income countries, with less access to expensive treatment options," Scott said. "We see this as a proof-of-principle study for the future development of engineered L. sericata strains that express a variety of growth factors and anti-microbial peptides with the long-term aim of developing a cost-effective means for wound treatment that could save people from amputation and other harmful effects of diabetes."
The study was published online in the journal BMC Biotechnology.
Note to editors: An abstract of the paper follows.
"Towards next generation maggot debridement therapy: transgenic Lucilia sericata larvae that produce and secrete a human growth factor"
Authors: Rebecca J Linger, Esther J Belikoff, Ying Yan, Fang Li, Holly A Wantuch and Max Scott, North Carolina State University; Helen Fitzsimons, Massey University, New Zealand
Published: Online March 22, 2016, in BMC Biotechnology
Abstract: Diabetes and its concurrent complications impact a significant proportion of the population of the U.S. and create a large financial burden on the American health care system. FDA-approved maggot debridement therapy (MDT), the application of sterile laboratory-reared Lucilia sericata (green bottle fly) larvae to wounds, is a cost effective and successful treatment for diabetic foot ulcers and other medical conditions. Human platelet derived growth factor-BB (PDGF-BB) is a secreted dimeric peptide growth factor that binds the PDGF receptor. PDGF-BB stimulates cell proliferation and survival, promotes wound healing, and has been investigated as a possible topical treatment for non-healing wounds. Genetic engineering has allowed for expression and secretion of human growth factors and other proteins in transgenic insects. Here, we present a novel concept in MDT technology that combines the established benefits of MDT with the power of genetic engineering to promote healing. The focus of this study is to create and characterize strains of transgenic L. sericata that express and secrete PDGF-BB at detectable levels in adult hemolymph, whole larval lysate, and maggot excretions/secretions (ES), with potential for clinical utility in wound healing.