Comparative Evaluation of the Effects of Taurine and Thiotaurine on Alterations of the Cellular Redox Status and Activities of Antioxidant and Glutathione-Related Enzymes by Acetaminophen in the Rat - Advances in Experimental Medicine and Biology - page 190

20.2.6 Assay of the Plasma and Liver g -Glutamylcysteine

Synthetase (GCS), Glutathione S-Transferase (GST)
and Glutathione Reductase (GR) Activities

The GCS activity was measured according to the method of Zhou and Freed ( 2005 ) ,
the GST activity was measured as described by Habig et al. ( 1974 ) , and the GR
activity was measured by the spectrophotometric method of Wheeler et al. ( 1990 ) .
The results were expressed in U/min/mg of protein.

20.2.7 Statistical Analysis of the Data

The experimental results are reported as mean ± SEM for n = 6. They were analyzed
for statistical significance using unpaired Student's t -test and a commercial com-
puter software (JMP 7, JMP ® Statistical Discovery Software, Cary, NC 27513) fol-
lowed by one-way analysis of variance and Newman-Keuls post hoc test. Intergroup
differences were considered to be statistically significant at p £ 0.05.

20.3 Results and Discussion

The protective effects of TAU and TTAU against APAP-induced hepatotoxicity
were assessed by measuring biochemical parameters consonant with cellular injury
and oxidative stress. To more accurately define their respective potencies, they were
further compared with an equidose (2.4 mmol/kg) of NAC, the current antidote of
choice for APAP overdoses.
The degree of injury to the hepatocytes by a high dose of APAP was investigated
by measuring the plasma ALT, AST, and LDH, three abundant intrahepatic enzymes
whose release into the circulation is taken as evidence of liver injury (Duong and
Loh 2006 ). As shown in Table 20.1 , the plasma activities of all three enzymes were
signi fi cantly elevated ( p < 0.001), with the values decreasing in the order LDH
(+292%) > AST (+135%) > ALT (+64%) probably in direct proportion to their intra-
cellular abundance and location (Moss et al. 1986 ). TAU and TTAU were highly
protective and about equipotent, with the increases amounting to only ~104%
( p < 0.001), ~37% ( p < 0.01), and ~33% ( p < 0.01) of corresponding control values,
respectively. NAC was more potent than either TAU or TTAU since the enzyme
activities of LDH, AST, and ALT were only 60% ( p < 0.001), 28% ( p < 0.01), and
21% ( p < 0.05), respectively, above control values.
Hepatic LPO is a common consequence of acute APAP intoxication which is
typically manifested in rodents by increased ethane inhalation, increased hepatic
MDA, and GSH depletion (Wendel 1983 ). The detection of MDA accumulation is a
rather sensitive indicator of hepatotoxicity since it is increased before the appear-
ance of necrosis (Nakae et al. 1990 ). The results presented in Fig. 20.1 indicate that