Elevated LPS and elevated
cytochrome P-450 2E1 (
CYP2E1) in liver are two major independent risk factors in
alcoholic liver disease. We investigated possible synergistic effects of the two risk factors in causing oxidative stress and liver injury. Sprague-Dawley rats were injected intraperitoneally with
pyrazole (inducer of
CYP2E1) for 2 days, and then LPS was injected via tail vein. Other rats were treated with
pyrazole alone or LPS alone or saline. Eight hours later, blood was collected and livers were excised. Pathological evaluation showed severe inflammatory responses and necroses only in liver sections from rats in the
pyrazole plus LPS
group; blood transaminase levels were significantly elevated only in the combination group. Activities of
caspase-3 and -9 and positive
terminal deoxynucleotidyl transferase-mediated
deoxyuridine triphosphate nick-end labeling staining were highest in the LPS alone and the LPS plus
pyrazole group, with no significant difference between the two groups. Lipid peroxidation and
protein carbonyls in liver homogenate as well as in situ
superoxide production were maximally elevated in the LPS plus
pyrazole group. Levels of
nitrite plus
nitrate and inducible
nitric oxide (
NO) synthase (iNOS) content were comparably elevated in LPS alone and the LPS plus
pyrazole group; however,
3-nitrotyrosine adducts were elevated in the combined group but not the LPS group. It is likely that LPS induction of iNOS, which produces NO, coupled to
pyrazole induction of
CYP2E1 which produces
superoxide, sets up conditions for maximal
peroxynitrite formation and production of
3-nitrotyrosine adducts.
CYP2E1 activity and content were elevated in the
pyrazole and the LPS plus
pyrazole groups. Immunohistochemical staining indicated that distribution of
CYP2E1 was in agreement with that of
necrosis and production of
superoxide. These results show that
pyrazole treatment enhanced LPS-induced
necrosis, not apoptosis. The enhanced liver
necrosis appears to involve an increase in oxidative and nitrosative stress generated by the combination of LPS plus elevated
CYP2E1 levels.