leukotriene-b4 and Abscess

The early events that shape the innate immune response to restrain pathogens during skin infections remain elusive. Methicillin-resistant Staphylococcus aureus (MRSA) infection engages phagocyte chemotaxis, abscess formation, and microbial clearance. Upon infection, neutrophils and monocytes find a gradient of chemoattractants that influence both phagocyte direction and microbial clearance. The bioactive lipid leukotriene B4 (LTB4) is quickly (seconds to minutes) produced by 5-lipoxygenase (5-LO) and signals through the G protein-coupled receptors LTB4R1 (BLT1) or BLT2 in phagocytes and structural cells. Although it is known that LTB4 enhances antimicrobial effector functions in vitro, whether prompt LTB4 production is required for bacterial clearance and development of an inflammatory milieu necessary for abscess formation to restrain pathogen dissemination is unknown. We found that LTB4 is produced in areas near the abscess and BLT1 deficient mice are unable to form an abscess, elicit neutrophil chemotaxis, generation of neutrophil and monocyte chemokines, as well as reactive oxygen species-dependent bacterial clearance. We also found that an ointment containing LTB4 synergizes with antibiotics to eliminate MRSA potently. Here, we uncovered a heretofore unknown role of macrophage-derived LTB4 in orchestrating the chemoattractant gradient required for abscess formation, while amplifying antimicrobial effector functions.

Topics: Abscess; Animals; Arachidonate 5-Lipoxygenase; Bacterial Load; Cells, Cultured; Female; Leukotriene B4; Macrophages; Male; Methicillin-Resistant Staphylococcus aureus; Mice; Mice, Inbred C57BL; Mice, Knockout; Receptors, Leukotriene B4; Staphylococcal Skin Infections

Poorly controlled diabetes leads to comorbidities and enhanced susceptibility to infections. While the immune components involved in wound healing in diabetes have been studied, the components involved in susceptibility to skin infections remain unclear. Here, we examined the effects of the inflammatory lipid mediator leukotriene B4 (LTB4) signaling through its receptor B leukotriene receptor 1 (BLT1) in the progression of methicillin-resistant Staphylococcus aureus (MRSA) skin infection in 2 models of diabetes. Diabetic mice produced higher levels of LTB4 in the skin, which correlated with larger nonhealing lesion areas and increased bacterial loads compared with nondiabetic mice. High LTB4 levels were also associated with dysregulated cytokine and chemokine production, excessive neutrophil migration but impaired abscess formation, and uncontrolled collagen deposition. Both genetic deletion and topical pharmacological BLT1 antagonism restored inflammatory response and abscess formation, followed by a reduction in the bacterial load and lesion area in the diabetic mice. Macrophage depletion in diabetic mice limited LTB4 production and improved abscess architecture and skin host defense. These data demonstrate that exaggerated LTB4/BLT1 responses mediate a derailed inflammatory milieu that underlies poor host defense in diabetes. Prevention of LTB4 production/actions could provide a new therapeutic strategy to restore host defense in diabetes.

Topics: Abscess; Animals; Bacterial Load; Cell Movement; Chemokines; Cytokines; Diabetes Mellitus, Experimental; Female; Inflammation; Leukotriene B4; Macrophages; Male; Methicillin-Resistant Staphylococcus aureus; Mice; Mice, Inbred C57BL; Mice, Knockout; Neutrophils; Receptors, Leukotriene B4; Signal Transduction; Skin; Staphylococcal Skin Infections

Topics: Abscess; Animals; Chemotaxis; Leukotriene B4; Macrophages; Mice; Staphylococcus aureus

It was previously shown that the (99m)Tc-labeled hydrazinonicotinamide (HYNIC)-conjugated LTB4 antagonist MB81 visualized infectious foci in rabbits adequately and within a few hours after injection. Here, the bivalent HYNIC-conjugated LTB4 antagonist MB67 (analog of MB81) was fluorinated with (18)F via hydrazone formation and tested in vivo.. MB67 was [(18)F]-fluorinated via reaction of the [(18)F]-fluorinated intermediate p-[(18)F]-fluorobenzaldehyde ([(18)F]FB) and the HYNIC moiety of MB67 via hydrazone formation. For comparison, MB67 was also labeled with (99m)Tc. The biodistribution of (18)F- and (99m)Tc-labeled MB67 was investigated in rabbits with intramuscular infection.. [(18)F]-MB67 was obtained at a maximum specific activity of 1200 GBq/mmol and proved to be stable in phosphate buffered saline (PBS) at 37 degrees C for at least 4 h. PET images obtained with [(18)F]-MB67 clearly delineated the abscess at 2 and 4 h pi. Counting of dissected tissues at 4 h pi revealed an abscess uptake of 0.073+/-0.005 %ID/g, as compared to 0.160+/-0.010 %ID/g for the (99m)Tc-labeled analog. Abscess-to-muscle ratios were 23+/-4 for [(18)F]-MB67 and 35+/-9 for [(99m)Tc]-MB67.. The present study showed the feasibility of a new [(18)F]-labeling methodology and its application in the production of a new PET tracer for imaging of infection, [(18)F]-MB67.

Topics: Abscess; Animals; Escherichia coli Infections; Fluorine Radioisotopes; Hydrazines; Hydrazones; Indicators and Reagents; Infections; Isotope Labeling; Leukotriene B4; Muscular Diseases; Niacinamide; Positron-Emission Tomography; Rabbits; Radiopharmaceuticals; Technetium; Tissue Distribution

In previous studies we demonstrated that lipophilic (99m)Tc-labeled LTB4 antagonist 1 (RP517) accumulated in infectious foci in rabbits, but hepatobiliary clearance hampered imaging of abdominal lesions. We now report the use of cysteic acid as a pharmacokinetic modifier to improve the water solubility and renal clearance of three hydrophilic analogues of 1. Divalent LTB4 antagonist 17 (DPC11870-11) is a DTPA conjugate for radiolabeling with In-111. Monovalent LTB4 antagonists 15 (BMS57868-88) and divalent LTB4 antagonist 18 (BMS57868-81) are conjugated to bifunctional chelator HYNIC for radiolabeling with (99m)Tc. The three compounds labeled efficiently with 111In or (99m)Tc with high radiochemical purity and specific activities. Scintigraphic images obtained in New Zealand White rabbits having acute intramuscular E. coli infection demonstrated that all agents were able to clearly visualize the abscess, and clearance was exclusively renal. The biodistribution of the (99m)Tc-labeled LTB4 antagonists was affected by the coligands used with the HYNIC chelator and by the monovalent or divalent nature of the receptor binding moiety. The best scintigraphic images were obtained with monovalent HYNIC conjugate 15 using tricine and isonicotinic acid as coligands with HYNIC for coordination with (99m)Tc.

Topics: Abscess; Animals; Binding, Competitive; Chelating Agents; Escherichia coli Infections; Female; Glycine; Granulocytes; Humans; Hydrazines; In Vitro Techniques; Indium Radioisotopes; Isonicotinic Acids; Isotope Labeling; Leukotriene B4; Muscle, Skeletal; Nicotinic Acids; Organotechnetium Compounds; Rabbits; Radioligand Assay; Radiopharmaceuticals; Solubility; Structure-Activity Relationship; Tissue Distribution

The percentage of non-diploid epidermal cells was determined by flow cytometry following application of leukotriene B4 (LTB4) to human skin. Doses in the range 35-500 ng were shown to cause a marked increase in proliferation, the non-diploid cells reaching a maximum between 72 and 96 h after LTB4 application. No difference was observed between the response of healthy controls and the uninvolved skin of psoriatic patients. We suggest, therefore, that the hyperproliferation is a consequence of the physical disruption of the stratum corneum accompanying the rupture of microabscesses.

Topics: Abscess; Cell Division; Epidermis; Humans; Leukotriene B4; Psoriasis; Skin Diseases

Leukotriene B4 is a highly potent leukocyte chemotactic compound. It has been identified in chamber fluid and scale from psoriatic skin lesions, in which epidermal neutrophil infiltration is reported to be one of the earliest pathologic events. The ability of leukotriene B4 to reproduce the inflammatory events of psoriasis, by topical application to the skin of normal human volunteers, was thus studied. Persistent visible inflammatory reactions were elicited by application of amounts of leukotriene B4 as low as 5 ng, and the maximum diameters of the reactions were dose-related up to at least 500 ng. The visible reactions appeared 12-24 h after initial application of leukotriene B4, and persisted for several days, leaving brownish pigmentation and scaling at 7 days. Histologic examination showed intraepidermal neutrophil microabscesses at 24 h, but these had resolved by 48 h. A mixed, perivascular neutrophil and mononuclear cell infiltrate was seen in the dermis at 24 h, becoming predominantly mononuclear after 24 h. Nonspecific chemical irritant contact dermatitis was excluded by the absence of reactions to high doses of two chemically similar metabolites of arachidonic acid which lack significant in vitro chemokinetic activity. These experiments provide further evidence for the role of leukotriene B4 in the pathogenesis of psoriasis, and may lead to the development of an experimental model of the inflammatory events in psoriasis, and of a simple in vivo test of neutrophil function.

Topics: Abscess; Adult; Dose-Response Relationship, Drug; Epidermis; Female; Humans; Leukotriene B4; Male; Middle Aged; Neutrophils; Skin Diseases