Microbial Targeting of ^99mTc-Labeled Recombinant Human β-Defensin-3 in an Animal Model of Infection: A Feasibility Pilot Study

Abstract

Human b-defensin-3 (HBD-3) is an antimicrobial peptide with bactericidal effects on many gram-positive and gram-negative bacteria and some yeast species and, if radiolabeled, might be used to distinguish bacterial infection from sterile inflammation. The goals of the present study were to develop methods for radiolabeling HBD-3 with 99m Tc and to perform preliminary investigations on 99m Tc-labeled HBD-3 as a means to evaluate induced infection in an animal model. To this purpose, Staphylococcus aureus-induced infection was used to evaluate the capability of 99m Tc-HBD-3 to distinguish infection from aseptic inflammation in rats. Methods: Twenty to 40 mg of recombinant HBD-3 were labeled with 99m Tc 1 hexa-coordinated with 3 molecules of CO and H 2 O and separated by a column from free 99m Tc. 99m Tc-HBD-3 was added to cultures of a bacterial suspension of S. aureus and Escherichia coli to evaluate in vitro antibacterial activity. A bacterial suspension of S. aureus and a carrageenan solution were used to induce infection and sterile inflammation, respectively, in opposite thighs of 9 adult rats. Three separate experiments were performed on groups of 3 rats each. The animals received different doses of 99m Tc-HBD-3 injected through a cannula into the jugular vein. After sacrifice of the animals, tissue samples were obtained from sites of infection, inflammation, and control muscle (left foreleg) at 1, 3, and 5 h after 99m Tc-HBD-3 administration. Tissue samples were weighed and then counted in a well-counter. Simultaneously, 1 mL of a standard solution of 99m Tc-HBD-3 corresponding to each administered dose was counted. Results: 99m Tc-HBD-3 retained antibacterial activity. Radioactivity in tissue samples from the infected sites was significantly higher than that in samples of either induced inflammation or normal control muscle (ratio, ;3:1) at 3 and 5 h after injection, whereas similar radioactivity counts were observed for tissue samples from aseptic inflammation sites and normal control muscle. Conclusion: In this investigation, 99m Tc-HBD-3 retained antibacterial activity and successfully distinguished infection from aseptic inflammation in adult rats.

The Potential Role of Increasing the Release of Mouse β- Defensin-14 in the Treatment of Osteomyelitis in Mice: A Primary Study

“…Accurate and early detection of infectious and non-infectious is of great importance for elucidation of the cause of the disease, early prevention of the onset of complications, and rapid implementation of a tailored therapeutic regimen [55], [56]. In the study, the significant difference of the expression of HBD-3 which has been connected with antibacterial tasks has also been found between inflamed interfacial membranes and not inflamed interfacial membranes.…”

“…In the future, a feasible application of HBD-3 may even help doctors make a distinction between periprosthetic joint infection and aseptic loosening by intraoperative histological biopsy of the interfacial membranes. Another more practical approach, in further clinical studies, maybe to radiolabel HBD-3 with the goal of assessing the potential of HBD-3 radiolabeled as a radiopharmaceutical for imaging periprosthetic joint infection because the anti- microbial peptide HBD-3 selectively bind to the bacterial cell membrane [55], [56].…”

Synthesis, in vitro evaluation, and 68Ga‐radiolabeling of CDP1 toward PET/CT imaging of bacterial infection

“…Moreover, 68 Ga‐NOTA‐UBI fragments were also reported to show bacterial selectivity and specificity in vitro . Furthermore, human neutrophil peptide, neutrophil elastase inhibitor peptide human β‐defensin, and human lactoferrin‐derived peptide have also been successfully evaluated for imaging bacterial infection …”

Radionuclide Imaging of Infection: In Search of the Grail

“…These investigators speculated that decreased sensitivity over time may have been related to the effects of the protective biofilm or glycocalix secreted by the bacteria. Would the results of Liberatore et al (24) have been different had they injected greater or lesser quantities of bacteria into the animals or had they increased or decreased the interval between inoculation and tracer injection?…”

“…In this issue of The Journal of Nuclear Medicine, Liberatore et al (24) report on microbial targeting with a 99m Tc-labeled antimicrobial peptide, recombinant human b-defensin-3, that exerts bactericidal effects on grampositive and gram-negative bacteria, as well as on some yeasts. The investigators demonstrated that by 3 h after injection, tracer uptake in a Staphylococcus aureus infection model was significantly higher than uptake in sterile inflammation, lending credence to the concept of a ''specific'' infection imaging agent.…”