Highly specific characterization and discrimination of monosodium urate crystals in gouty arthritis based on aggregation-induced emission luminogens

Existing technologies used to detect monosodium urate (MSU) crystals for gout diagnosis are not ideal due to their low sensitivity and complexity of operation. The purpose of this study was to explore whether aggregation-induced emission luminogens (AIEgens) can be used for highly specific imaging of MSU crystals to assist in the diagnosis of gout. First, we developed a series of luminogens (i.e., tetraphenyl ethylene (TPE)-NH2, TPE-2NH2, TPE-4NH2, TPE-COOH, TPE-2COOH, TPE-4COOH, and TPE-Ketoalkyne), each of which was then evenly mixed with MSU crystals. Next, optimal fluorescence imaging of each of the luminogens was characterized by a confocal laser scanning microscope (CLSM). This approach was used for imaging standard samples of MSU, hydroxyapatite (HAP) crystals, and mixed samples with 1:1 mass ratio of MSU/HAP. We also imaged samples from mouse models of acute gouty arthritis, HAP deposition disease, and comorbidities of interest. Subsequently, CLSM imaging results were compared with those of compensated polarized light microscopy, and we assessed the biosafety of TPE-Ketoalkyne in the RAW264.7 cell line. Finally, CLSM time series and three-dimensional imaging were performed on MSU crystal samples from human gouty synovial fluid and tophi. As a promising candidate for MSU crystal labeling, TPE-Ketoalkyne was found to detect MSU crystals accurately and rapidly in standard samples, animal samples, and human samples, and could precisely distinguish gout from HAP deposition disease. This work demonstrates that TPE-Ketoalkyne is suitable for highly specific and timely imaging of MSU crystals in gouty arthritis and may facilitate future research on MSU crystal-related diseases.