Relative sensitivity of undifferentiated and cyclic adenosine 3′,5′-monophosphate-induced differentiated neuroblastoma cells to cyclosporin A:: Potential role of β-amyloid and ubiquitin in neurotoxicity

Cyclosporin A is routinely used in transplant therapy following allogeneic or xenogeneic tissue transplantation to prevent rejection. This immunosuppressive drug is also neurotoxic; however, its mechanisms of action for neurotoxicity are poorly understood. Undifferentiated and cyclic adenosine 3',5'-monophosphate (cAMP)-induced differentiated neuroblastoma (NB) cells were used as an experimental model to study the toxicity of cyclosporin A. Results showed that cyclosporin A promoted the outgrowth of neurites and inhibited the growth of undifferentiated NB cells. When cyclosporin A was added simultaneously with R020-1724, an inhibitor of cyclic nucleotide phosphodiesterase, or with prostaglandin E-1, a stimulator of adenylate cyclase, it markedly enhanced the growth inhibitory and differentiation effects of these cAMP-stimulating agents. In addition, cyclosporin A added to cAMP-induced differentiated NB cells caused dose-dependent degeneration of these cells as evidenced by the vacuolization of cytoplasm and the fragmentation of nuclear and cytoplasmic materials; however, neurites remained intact. Cyclosporin A alone did not alter the intensity of cell immunostaining for ubiquitin or beta-amyloid peptide (amino acids 1-14) (A beta(1-14)); however, it enhanced the intensity of staining for both ubiquitin and A beta in cells that were treated with cAMP-stimulating agents. The intensity of staining of amyloid precursor protein (amino acids 44-63) (APP(44-63)) did not change in any treated group, suggesting that the increase in A beta staining is due to increased processing of APP to A beta. We propose that one of the mechanisms of cyclosporin A-induced neurotoxicity involves increased levels of A beta and ubiquitin.