Targeting formyl peptide receptor 1 of activated macrophages to monitor inflammation of experimental osteoarthritis in rat

Abstract

Macrophages play a crucial role in the pathogenesis of osteoarthritis (OA). In this study, the feasibility of a formyl peptide receptor 1 (Fpr1)-targeting peptide probe cFLFLF-PEG- 64Cu via positron emission tomography (PET) imaging was investigated for detection of macrophage activity during development of OA. Monoiodoacetate (MIA) was intraarticularly injected into the knee joint of Sprague-Dawley rats to induce OA. Five days later, cFLFLF-PEG-64 Cu ($7,400 kBq/rat) was injected into the tail vein and microPET/CT imaging was performed to assess the OA inflammation by detecting infiltration of macrophages by Fpr1 expression. In addition, a murine macrophage cell line RAW264.7 and two fluorescent probes cFLFLF-PEG-cyanine 7 (cFLFLF-PEG-Cy7) and cFLFLF-PEG-cyanine 5 (cFLFLF-PEG-Cy5) were used to define the binding specificity of the peptide to macrophages. It was found with the MIA model that the maximal standard uptake values (SUV max ) for right (MIA treated) and left (control) knees were 17.96 AE 5.45 and 3.00 AE 1.40, respectively. Histological evaluation of cryomicrotome sections showed that Fpr1 expression, cFLFLF-PEG-Cy5 binding, and tartrate-resistant acid phosphatase activity were elevated in the injured synovial membranes. The in vitro experiments demonstrated that both fluorescent peptide probes could bind specifically to RAW264.7 cells, which was blocked by cFLFLF but not by the scramble peptide. The findings highlighted the use of cFLFLF-PEG- 64Cu/PET as an effective method potentially applied for detection and treatment evaluation of OA. ß

Deficiency of FAM3D (Family With Sequence Similarity 3, Member D), A Novel Chemokine, Attenuates Neutrophil Recruitment and Ameliorates Abdominal Aortic Aneurysm Development

“…FAM3D deficiency repressed Ly6C high monocyte recruitment and macrophage infiltration in infrarenal abdominal aortas after elastase induction. As Mac-1 also plays a critical role in monocyte recruitment, as well as FPRs are markedly expressed in monocytes/macrophages, 51 , 52 we evaluated the activation of Mac-1 in human monocytes after FAM3D treatment. Indeed, FAM3D could activate Mac-1 in monocytes as well (Figure XII in the online-only Data Supplement ).…”

Role of low-grade inflammation in osteoarthritis

“…Macrophage imaging for detection of active joint inflammation is now being investigated in both animal models [23■■] and humans [24■■]. In a small pilot study of knee osteoarthritis patients [24■■], administration of a labeled folate-receptor agonist to identify activated macrophages using SPECT/CT (single photon emission computed tomography) imaging was reported [24■■].…”

“…76% of knees demonstrated positive signal in capsule, synovium, and subchondral bone, which correlated with radiographic and symptom severity. In a rat model, a labeled formyl peptide receptor-1 (FPRI) agonist was used for similar purposes [23■■]. Computed tomography (CT) and PET imaging 5 days after intra-articular injection of mono-iodoacetate to induce osteoarthritis showed that this agent preferentially localized to the treated knee, and confocal imaging of tissue sections confirmed localization to synovial macrophages.…”

Hyaluronic Acid-Based Optical Probe for the Diagnosis of Human Osteoarthritic Cartilage

“…Increasing evidence supports that synovial macrophages play an important role in the progression of osteoarthritis 11 - 13 . Firstly, the accumulation of macrophages at the synovial lining and cartilage surfaces is the first symptom of osteoarthritis 11 .…”