Figure 2: Effects of nitric oxide radicals on cell viability and nitrite-nitrate formation in cell culture media.
A. SNP was added to MSC in concentrations ranging from 5 µM to 5 mM and respiratory activity was measured by XTT assay. Low doses of SNP (10 µM and 25 µM) activated respiratory activity to some extent. SNP at 100 - 500 µM reduced the respiratory activity of MSC to approximately 80%. Dosages of 1 mM SNP or higher reduced the respiratory activity of MSC to 30% or 20%. Mock-treated MSC served as controls (= 100%).
B. Human MSC was incubated for 24 h in medium without SNP (C1, striated column) or in presence of 1.5 mM SNP (C2, grey column). Addition of SNP reduced the normalized respiratory activity / viability of MSC to 42% compared to the mock-treated controls (= 100%). Addition of 1 mM and 5 mM PNIPAM- 6C60elevated measurably but statistically not significant to 47% and 62%, respectively. Addition of 10 mM, 50 mM, or 100 mM PNIPAM-6C60elevated the respiratory activity / viability of SNP-treated human MSC significantly to 70% (± 13%; p<0.039), 101 (± 29%; p<0.02), and 101 (± 16%, p<0.004; black bars). Addition of PNIPAM-6C60 only did not reduce the respiratory activity / viability of human MSC (white bars).
C. The formation of nitrite / nitrate in MSC cultures was investigated following addition of SNP at concentrations between 5 µM and 1.5 mM and determined after 24 h of incubation. At lower SNP concentrations (up to 500 µM) a steep increase in nitrite / nitrate concentrations (0–35 µM) was measured. Higher SNP concentrations (500 to 1500 µM) resulted in a slight increase of nitrite / nitrate concentration (35 to 40 µM).