Effect of the polyamine analogue N1,N11-diethylnorspermine on cell survival and susceptibility to apoptosis of human chondrocytes

Chondrocyte survival is closely linked to cartilage integrity, and forms of chondrocyte apoptotic death can contribute to cartilage degeneration in articular diseases. Since growing evidence also implicates polyamines in the control of cell death, we have been investigating the role of polyamine metabolism in chondrocyte survival and apoptosis. Treatment of human C-28/I2 chondrocytes with N(1),N(11)-diethylnorspermine (DENSPM), a polyamine analogue with clinical relevance as an experimental anticancer agent, inhibited polyamine biosynthesis and induced polyamine catabolism, thus rapidly depleting all main polyamines. DENSPM did not increase significantly caspase activity, but provoked a late cell death associated to DNA fragmentation. A short treatment with DENSPM did not reduce cell viability when given alone, but enhanced caspase-3 and -9 activation in chondrocytes exposed to tumor necrosis factor-alpha (TNF) and cycloheximide (CHX). A longer treatment with DENSPM however reduced caspase response to TNF plus CHX. Depletion of all polyamines obtained by specific inhibitors of polyamine biosynthesis did not cause cell death and contrasted apoptosis by decreasing caspase activities. In conclusion, following DENSPM treatment, C-28/I2 chondrocytes are initially sensitized to caspase 9-dependent apoptosis in the presence of TNF and CHX and may eventually undergo a late and mainly caspase-independent cell death in the absence of other stimuli. Moreover, these results indicate that a reduction of polyamine levels not only leads to inhibition of cell proliferation, but also of caspase-mediated pathways of chondrocyte apoptosis.