Metabolism of low concentrations of N-nitrosodimethylamine in isolated liver cells of the guinea pig.

Freshly isolated liver cells of guinea pig were used to study the metabolism of NDMA in the concentration range 0.05 to 100 microM. Analysis was performed using the gas chromatograph-thermal energy analyzer nitrosamine detector method and with radiolabeled NDMA. At concentrations below 10 microM, NDMA was degraded by liver cells (10 mg of protein in 2.5 ml of medium) within 20 min (at 100 microM in 80 min). The majority of metabolized methyl groups were initially associated with volatile compounds and were subsequently integrated into nonvolatile, acid-soluble molecules (57%) or liberated as CO2 (14%). Less than 2% were bound to cellular macromolecules. Ethanol inhibited NDMA degradation competitively, with a Ki of 0.8 mM ethanol. It is concluded that low concentrations of NDMA are metabolized in liver cells, primarily by the high-affinity demethylase and that there are no additional catalytic activities with Km values below 5 microM. Most of the methyl groups, released during metabolism, enter the C1 pool.