Nitric oxide (NO) effect on chondrocyte apoptosis. (A) Cell death levels in chondrocytes treated with different NO donors was determined by the iodide propidium (PI) method. Control chondrocytes were treated with 1 mM sodium nitroprusside (SNP) and 1 mM N-ethyl-2(1-ethyl-2 hydroxy-2-nitrosohydrazine (NOC-12) for 24 hours. Data are expressed as a percentage of apoptotic (hypodiploid) nuclei. Values are the mean ± SD; n = 5. *P ≤ 0.05 versus untreated chondrocytes (control). (B) Cellular changes induced by NO on normal human chondrocytes were analysed by 49,6-diamino-2-phenylindole dihydrochloride (DAPI staining) and fluorescence microscopy. Shown is a representative example of five experiments.