OBJECTIVETo study the CPS-II mechanism underlying the pathological process of elevated blood ammonia leading to liver injury.

METHODSAn in vitro hyperammonemia hepatocyte cell model was constructed by exposure to various concentrations of NH4Cl. The subsequent changes to cellular morphology were observed by microscopy. to cell apoptosis were determined by flow cytometry, and to mRNA and protein expression of CPS-II were examined by real-time PCR and western blotting, respectively.

RESULTSExposure to NH₄Cl led to dose-dependent morphological damage, apoptosis and necrosis of the hepatocytes. The apoptosis rate was significantly higher for the high-dose group than for the control (no exposure) group (24.7% ± 2.39% vs. 4.1% ± 0.78%, q =8.06, P less than 0.05). Expression of the CPS-II mRNA was significantly elevated in response to NH₄Cl exposure (vs. the control group; F=191.881, P < 0.05).The CPS-II mRNA expression level increased with increasing NH₄Cl concentration (grey values: 1.040 ± 0.045, 1.641 ± 0.123, 2.285 ± 0.167 and 3.347 ± 0.124, respectively). The CPS-II protein expression level was also significantly enhanced in response to the NH₄Cl exposures (CPS-II protein and internal GAPDH grey value ratios: 0.099 ± 0.0130, 0.143 ± 0.025, 0.161 ± 0.036 and 0.223 ± 0.042, respectively; t=3.825, 3.968 and 6.908, P less than 0.05).

CONCLUSIONCPS-II mRNA and protein expression levels become elevated with increase in the NH₄Cl concentrations, suggesting that in addition to the urea cycle, CPS-II may play an important role in the ammonia metabolism under the condition of hyperammonemia.