Comparison of sodium urate and calcium pyrophosphate crystal phagocytosis by polymorphonuclear leukocytes

Abstract

Phagocytosis of monosodium urate (MSU) crystals by polymorphonuclear leukocytes (PMN) in vitro results in PMN degranulation, phagolysosome membrane dissolution, and cell death (1). Release of cytoplasmic as well as lysosomal enzymes has been reported to occur after in vitro phagocytosis of urate but not calcium pyrophosphate dihydrate (CPPD) crystals (2,3). Wallingford no distinct phagosome membranes around the urate crystals, although in pseudogout (calcium pyrophosphate crystal synovitis) easily demonstrable phagosomes have been described (5,6). These observations have suggested that the phagolysosome rupture seen with urates may not follow calcium pyrophosphate crystal phagocytosis.This report compares the ultrastructural findings after in vitro CPPD and MSU crystal phagocytosis. As judged by electron microscopy, synthetic CPPD crystals do not produce the rapid sequence of membrane lysis and cell death seen with MSU crystals. CPPD crystals, however, were also phagocytized less avidly than MSU. One possible factor in the decreased phagocytosis is the greater size of the CPPD. Grinding of CPPD or MSU to produce smaller crystals improved phagocytosis and may increase the injurious effect of CPPD on the PMN. MATERIALS AND METHODSSynthetic calcium pyrophosphate dihydrate crystals were prepared as described by Tse and Phelps (7). X-ray diffraction showed predominantly calcium pyrophosphate but also suggested slight contamination by material resembling hydroxyapatite. T h e preparation viewed by polarized light included both monodinic and triclinic crystals that appeared similar to those seen in human pseudogout. Crystals averaged 21 p i n length (95% of crystals were 10 to 26 p) and were wider than MSU crystals. A small amount of nonbirefringent globular material was also seen (Figure 1). The same preparation was used for all experiments.

Superoxide anion production and phagocytosis of crystals by cultured endothelial cells

“…Phagocytosis was a rapid event: Crystals were found intracellularly after as little as 15 minutes ( Figure 7C). CPPD and HA crystals almost always appeared inside phagocytic vacuoles (Figures 7B and C), whereas MSU crystals always appeared free in the cytoplasm, a finding previously reported in neutrophils (29,39). COX crystals were variable in this respect, only sometimes appearing within vacuoles.…”

“…Di Giovine et al (40) found that MSU, but not CPPD, stimulated interleukin-1 release from mononuclear cells, while Poubelle et a1 (41) found marked differences between MSU and CPPD with respect to their ability to activate the excitationresponse coupling sequence of neutrophils. Schumacher et al (39) found that CPPD, but not MSU, crystals were enclosed in cytoplasmic vacuoles after being phagocytized by neutrophils. Similarly, we found that CPPD and HA, but not MSU, were enclosed in cytoplasmic vacuoles in endothelial cells.…”

Pseudogout-Associated Inflammatory Calcium Pyrophosphate Dihydrate Microcrystals Induce Formation of Neutrophil Extracellular Traps

“…CPPD crystals have been detected inside of neutrophils in clinical synovial fluid samples of pseudogout patients (38). To investigate whether crystals are ingested by neutrophils, we exposed adherent neutrophils to 20 mg/ml CPPD crystals on microscope coverslips for 30 min, Sytox Green DNA-binding dye was added to the medium, and live cell imaging was performed using a fluorescent microscope.…”

Crystal-induced neutrophil activation. III. Inflammatory microcrystals induce a distinct pattern of tyrosine phosphorylation in human neutrophils.

“…It is by now well established that the deposition ofmicrocrystalline monosodium urate monohydrate (MSU)' and calcium pyrophosphate dihydrate (CPPD) in joints and their interactions with neutrophils play an important role in the development of gouty arthritis and joint chondrocalcinosis (pseudogout), respectively ( 1,2). However, despite the fact that MSU and CPPD crystals are both involved in these inflammatory processes, they display differential phlogistic properties and metabolic responses, MSU crystals generally being more active than CPPD crystals (3)(4)(5)(6)(7).…”