Retinoic acid-induced differentiation in a human neuroblastoma cell line is associated with an increase in nitric oxide synthesis.

The human neuroblastoma cell line SK-N-BE, after incubation with 10 microM retinoic acid (RA) or 20 nM phorbol 12-myristate 13-acetate (PMA), underwent biochemical and morphological signs of differentiation within 10-14 days. In parallel, SK-N-BE cells produced significantly higher amounts of nitric oxide (NO) in comparison with controls, as assessed by the measurement of nitrite and nitrate in the culture supernatant and of NO synthase (NOS) activity in the cell lysates (measured as ability to convert [3H]arginine into [3H]citrulline and as NADPH diaphorase activity). Nitrite/nitrate production was abolished by adding the NO scavenger hemoglobin in the culture medium and was inhibited by aminoguanidine (AG, a selective inhibitor of the inducible NOS isoform) but not by the less selective inhibitor NG-nitro-L-arginine methylester (NAME). Western blotting experiments with monoclonal antibodies against the ncNOS and iNOS isoforms suggest that RA-elicited NOS activation is not attributable to an increased expression of the protein. NAME and AG were not able to revert inhibition of proliferation induced by RA, and the NO donor sodium nitroprusside did not mimic the effect of RA and PMA. These data indicate that increased NO synthesis does not mediate RA- or PMA-induced differentiation but may be an additional marker of differentiation into sympathetic-like neuronal cells.

Correlation between nitric oxide synthase activity and reduced glutathione level in human and murine endothelial cells.

The synthesis of nitric oxide (NO), detected as citrulline production, in human (HUVEC) and murine (tEnd.1) endothelial cells correlated with intracellular GSH. tEnd.1, which exhibited an intracellular GSH level 2.5-fold higher than HUVEC, showed a citrulline production (basally and after ionomycin stimulation) 5-8 times higher than human cells. Ionomycinelicited citrulline synthesis in tEnd.1 cells increased 2.4-fold after loading with GSH, and decreased dose-dependently after GSH depletion. Cell loading with N-(2-mercaptopropionyl)-glycine neither significantly increased citrulline production nor relieved the effect of GSH depletion.

Serum erythropoietin level and marrow erythroid infiltration predict response to recombinant human erythropoietin in myelodysplastic syndromes.

BACKGROUND AND METHODS: In 38 patients with myelodysplastic syndromes (MDS) the values of serum erythropoietin were measured at diagnosis and compared with the haemoglobin level. A highly significant inverse relationship was found between these two parameters, suggesting that the physiologic mechanism of erythroid progenitor cell recruitment is preserved in MDS. Fourteen transfusion-dependent patients were treated with recombinant human erythropoietin at the dose of 150 U/Kg three times weekly for at least 2 months. RESULTS AND CONCLUSIONS: Under recombinant human erythropoietin, three patients became transfusion-independent and 5 had a transient decrease of their transfusion requirement. Two patients under prolonged treatment at the same dose of erythropoietin remain in complete remission after 12 and 15 months respectively. A direct relationship between response to erythropoietin treatment and degree of bone marrow erythroid hyperplasia, coupled to an inverse correlation between response to erythropoietin and baseline serum erythropoietin levels were noted. Based on these findings, recombinant human erythropoietin may represent an effective treatment modality for selected patients with MDS.

Evaluation of bone marrow cellularity by magnetic resonance imaging in patients with myelodysplastic syndrome.

Magnetic resonance imaging (MRI) is a safe modality for examining the bone marrow and it is quite effective in revealing marrow involvement in hematological malignancies. MRI has been compared with needle marrow biopsy in 22 patients with myelodysplastic disorders. A fairly good concordance has been demonstrated in 79% of cases. However, in 5 patients MRI revealed that bone marrow hyperplasia was not generalized. Therefore in elderly patients with MDS, MRI of the spine allows the quantification of bone marrow hyperplasia with a greater accuracy than bone marrow biopsy and this may be useful for monitoring the effect of cytostatic treatment.