The Influence of Human Neutrophils on N-nitrosodimethylamine (NDMA) Synthesis

Abstract

N-nitrozodimethyloamine (NDMA) is a carcinogenic compound that can be formed in vivo. NDMA is synthesized from precursors-amines and nitrosating agents. Nitrosating agents are formed through the reaction of oxide, reactive oxygen species and nitric oxide (NO). Human neutrophils (PMN) are an important source of the most reactive oxygen species as well as of the nitric oxide. The increase in oxygen metabolism of PMN can lead to the increase nitrosating agent and nitroso-forms. Inflammatory process is associated with locally decreased pH that may favor nitrosation reaction.

In the present study, we estimated the NDMA synthesis by LPS-stimulated PMN in the presence of the iNOS inhibitor – N-nitro-L-arginine methyl ester (L-NAME). In the nitrosation reaction dimethylamine (DMA) was used as substrat. The viability of the cells was measured by cytometric method. NDMA concentrations the culture media was measured by GCMS method. NO production was estimated by Griess's method. Expression of iNOS was determined by western blotting.

Results obtained showed that DMA nitrosation is most effective in pH between 3–4.5. Nonstimulated PMN produced lower concentrations of NO than LPS-stimulated cells (1.27 μg/cm³ and 1.57 μg/cm³, respectively). In the culture of nonstimulated PMN supplemented with DMA, there was NDMA (mean – 0.99 ng/cm³). In the culture of LPS-stimulated PMN in the presence of DMA, the concentration of NDMA was higher than in the culture of nonstimulated PMN (median – 1.45 ng/cm³). In the supernatants of cells incubated without DMA and with DMA, LPS and L-NAME, no NDMA was detected. These results indicate that PMN can be one of sources of nitrosating agents and can play a role in endogenous NDMA synthesis. Stimulation of PMN can lead to the increase of NDMA concentration following the increase of NO production. Different pathological conditions associated with PMN activation as well as the decreased pH may favor endogenous NDMA synthesis.

Key Words :

• N-nitrosodimethylamine
• Neutrophils
• Nitric Oxide
• iNOS

Notes

*statistically different between living unstimulated and LPS stimulated cells (p < 0.05),

# statistically different between necrotic unstimulated and LPS stimulated cells (p < 0.001).

*significant difference between cells incubated with DMA and DMA + LPS (p < 0.001).

*significant difference between cultures with DMA (p < 0.001).

*significant differences with A (p < 0.01)

# significant differences with A and B (p < 0.001).