Paracetamol hepatotoxicity in metallothionein-null mice.
The role of metallothionein (MT) in protecting the liver against paracetamol (PCT) toxicity was investigated in vivo and in vitro in mice lacking expression of MT-1 and MT-2 genes (MT -/-). In the fed, glycogen replete state, hepatotoxicity (PCT 300 mg/kg i.p.) at 6 h was significantly greater in MT -/- than MT +/+ mice. Plasma lactate dehydrogenase (LD) and alanine aminotransferase (ALT) were 5- and 13-fold greater respectively than in MT +/+ mice. Liver glycogen, glucose and zinc levels were significantly lower in MT -/- mice at this time. In contrast, hepatotoxicity (PCT 135 mg/kg i.p.) at 6 h was similar in both MT +/+ and MT -/- mice fasted 24 h, despite a doubling in liver MT in MT +/+ mice. No differences were found between MT -/- and MT +/+ mice in cytochrome P450 activity. Liver glutathione levels were the same in both groups of mice prior to fasting and were decreased to a similar extent (55-65%) following PCT treatment. Investigation of lower PCT doses (< or = 120 mg/kg) in fasted mice over 24 h demonstrated a greater susceptibility in female MT -/- mice with plasma LD, 2.4-fold and ALT, 7.5-fold greater than in MT +/+ mice at 120 mg/kg PCT. In male MT -/- mice, there was only a trend towards greater susceptibility at 110 mg/kg PCT compared to male MT +/+ mice, and at 120 mg/kg, both male genotypes were equally affected. Investigations with cultured hepatocytes supported the in vivo findings in that there was a trend towards greater toxicity (PCT at 1 and 5 mM for 24 h) in hepatocytes from fed MT -/- mice, with the difference diminished in association with greater hepatotoxicity in hepatocytes from fasted mice. Use of dexamethasone (Dex) to increase MT in the MT +/+ mouse hepatocytes protected from PCT toxicity. Zn alone was not protective. Zn plus Dex offered no protection despite higher MT levels. Generation of apo-MT with Dex may offer more protection than Zn-MT. In conclusion, MT -/- mice were more susceptible than MT +/+ mice to PCT toxicity in the fed state, but the increased susceptibility was much smaller, but still significant, when the effects of glycogen were minimised by fasting.
Rofe
A M
AM
Division of Clinical Biochemistry, Institute of Medical and Veterinary Science, Adelaide, Australia.
Barry
E F
EF
Shelton
T L
TL
Philcox
J C
JC
Coyle
P
P
D000082:Acetaminophen / Q000037:antagonists & inhibitors / Q000633:toxicity*; D000410:Alanine Transaminase / Q000097:blood; D000818:Animals; D002478:Cells, Cultured; D005215:Fasting / Q000378:metabolism; D005260:Female; D007770:L-Lactate Dehydrogenase / Q000097:blood; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008297:Male; D008668:Metallothionein / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains
D000082:Acetaminophen; D008668:Metallothionein; D007770:L-Lactate Dehydrogenase; D000410:Alanine Transaminase