Monosodium urate crystals, leukocytes

The term gout describes a disease spectrum including hyperuricemia, recurrent attacks of acute arthritis associated with monosodium urate crystals in leukocytes found in synovial fluid, deposits of monosodium urate crystals in tissues (tophi), interstitial renal disease, and uric acid nephrolithiasis. 

Gout can be diagnosed by the presence of negatively birefringent monosodium urate crystals in aspirated synovial fluid examined by polarized-light microscopy. Here, crystals are within polymorphonuclear leukocytes. 

Naked monosodium urate crystals stimulate oxygen radical release by human polymorphonuclear leukocytes. Very recently, two papers dealing with superoxide anion generation by human neutrophils exposed to monosodium urate have been published. From the comparison of the data derived from nitroblue tetrazolium and cytochrome c reduction, it has been suggested that radical production in response to urate crystals is compartmentalized and occurs predominantly in the intracellular space. Microcrystalline sodium urate-induced oxygen consumption and nitroblue tetrazolium reduction were present for at least 15 min after stimulation of the cells. To enhance extracellular radicals neutrophils were converted to secretory non phagocitic cells by use of cytochalasin... 

The definitive diagnosis is accomplished by aspiration of synovial fluid from the affected joint and identification of intracellular crystals of monosodium urate monohydrate in synovial fluid leukocytes. 

Fig, 1 shows that the addition of microcrystalline monosodium urate (4 mg/ml) to a suspension of leukocytes in phosphate buffered saline saturated with urate gives rise to a chemiluminescence response after a latency period of about 20 sec. The height of the chemiluminescence peak is at least 18 times lower than that obtained by adding latex particles (1 pm diameter, 5 mg/ml) to a suspension of leukocytes in phosphate buffered saline or in phosphate buffered saline saturated with urate. The chemiluminescence peak obtained with urate crystals is sharper than that obtained using latex particles. After 4 min, the chemiluminescence response of urate activated cells disappears while light emission for more than 10 min is observed using latex particles. 

---