Imaging of Actively Proliferating Bacterial Infections by Targeting the Bacterial Metabolic Footprint with d-[5-11C]-Glutamine.

Since most d-amino acids (DAAs) are utilized by bacterial cells but not by mammalian eukaryotic hosts, recently DAA-based molecular imaging strategies have been extensively explored for noninvasively differentiating bacterial infections from the host's inflammatory responses. Given glutamine's pivotal role in bacterial survival, cell growth, biofilm formation, and even virulence, here we report a new positron emission tomography (PET) imaging approach using d-5-[11C]glutamine (d-[5-11C]-Gln) for potential clinical assessment of bacterial infection through a comparative study with its l-isomer counterpart, l-[5-11C]-Gln. In both control and infected mice, l-[5-11C]-Gln had substantially higher uptake levels than d-[5-11C]-Gln in most organs except the kidneys, showing the expected higher use of l-[5-11C]-Gln by mammalian tissues and more efficient renal excretion of d-[5-11C]-Gln. Importantly, our work demonstrates that PET imaging with d-[5-11C]-Gln is capable of detecting infections induced by both Escherichia coli (E. coli) and methicillin-resistant Staphylococcus aureus (MRSA) in a dual-infection murine myositis model with significantly higher infection-to-background contrast than with l-[5-11C]-Gln (in E. coli, 1.64; in MRSA, 2.62, p = 0.0004). This can be attributed to the fact that d-[5-11C]-Gln is utilized by bacteria while being more efficiently cleared from the host tissues. We confirmed the bacterial infection imaging specificity of d-[5-11C]-Gln by comparing its uptake in active bacterial infections versus sterile inflammation and with 2-deoxy-2-[18F]fluoroglucose ([18F]FDG). These results together demonstrate the translational potential of PET imaging with d-[5-11C]-Gln for the noninvasive detection of bacterial infectious diseases in humans.

Grafting Islets to a Dissected Peritoneal Pouch to Improve Transplant Survival and Function.

BACKGROUND: Although the liver is the primary site for clinical islet transplantation, it poses several restrictions, especially limited tissue volume due to portal vein pressure. We evaluated the preperitoneal space as an extrahepatic islet transplant site to deliver high tissue volumes and sustain long-term graft function. METHODS: A peritoneal pouch was formed by dissecting the parietal peritoneum from the transversalis fascia of mice. Syngeneic C57BL/6 donor islets were transplanted into the peritoneal pouch of diabetic mouse recipients. Blood glucose was monitored for islet function, and miR-375 was analyzed for islet damage. Islet graft morphology and vascularization were evaluated by immunohistochemistry. [F] fluoro-D-glucose positron emission tomography/computed tomography was used to image islet grafts. RESULTS: Transplantation of 300 syngeneic islets into the peritoneal pouch of recipients reversed hyperglycemia for >60 days. Serum miR-375 was significantly lower in the peritoneal pouch group than in the peritoneal cavity group. Peritoneal pouch islet grafts showed high neovascularization and sustained insulin and glucagon expression up to 80 days posttransplantation. A peritoneal pouch graft with high tissue volume (1000 islets) could be visualized by positron emission tomography/computed tomography imaging. Human islets transplanted into the peritoneal pouch of diabetic nude mice also reversed hyperglycemia successfully. CONCLUSIONS: Islets transplanted into a dissected peritoneal pouch show high efficiency to reverse diabetes and sustain islet graft function. The preperitoneal site has the advantages of capacity for high tissue volume, enriched revascularization and minimal inflammatory damage. It can also serve as an extrahepatic site for transplanting large volume of islets necessitated in islet autotransplantation.

Xenosiderophore Utilization Promotes Bacteroides thetaiotaomicron Resilience during Colitis.

During short-lived perturbations, such as inflammation, the gut microbiota exhibits resilience and reverts to its original configuration. Although microbial access to the micronutrient iron is decreased during colitis, pathogens can scavenge iron by using siderophores. How commensal bacteria acquire iron during gut inflammation is incompletely understood. Curiously, the human commensal Bacteroides thetaiotaomicron does not produce siderophores but grows under iron-limiting conditions using enterobacterial siderophores. Using RNA-seq, we identify B. thetaiotaomicron genes that were upregulated during Salmonella-induced gut inflammation and were predicted to be involved in iron uptake. Mutants in the xusABC locus (BT2063-2065) were defective for xenosiderophore-mediated iron uptake in vitro. In the normal mouse gut, the XusABC system was dispensable, while a xusA mutant colonized poorly during colitis. This work identifies xenosiderophore utilization as a critical mechanism for B. thetaiotaomicron to sustain colonization during inflammation and suggests a mechanism of how interphylum iron metabolism contributes to gut microbiota resilience.