The activity of glutathione-S-transferases (GSTs) was
measured by monitoring the increase in the absorbance at
340 nm using 1-chloro-2,4-dinitrobenzene as a substrate according
to the method suggested by Habig et al.14
Catalase (CAT) catalyzes the breakdown of H2O2 to H2O
and O2 and the rate of decomposition of H2O2 was measured
spectrophotometrically at 240 nm following the method suggested
by Beers and Sizer.15
The activity of superoxide dismutase (SOD) was measured
based on the ability of the enzyme to inhibit the autoxidation
of pyrogallol. A modified procedure followed by Soon and
Tan16 was adopted in this study.
The activity of sorbitol dehydrogenase (SDH) was
measured by following the method of Asada and Galambos.17
The SDH catalyzes the reduction of fructose to sorbitol in the
presence of nicotinamide adenine dinucleotide-reduced as the
reducing agent. The activity was measured by monitoring the
decrease in absorbance at 340 nm using fructose as the
substrate.
Aldose reductase (AR) catalyzes the NADPH-linked
reduction of aldose. The activity was measured by monitoring
the decrease in absorbance at 340 nm using glyceraldehyde
as a substrate according to the method suggested by
Hayman and Kinoshita.18
Ascorbic acid is oxidized by copper to form dehydroascorbic
acid and 2,4-dinitrophenyl hydrazone, which then
undergoes rearrangement to form a product with absorption
maximum at 520 nm.19
2.7. Statistical analysis
Duncan’s multiple range test20 was used for testing statistical
significance between groups of data. All results are
expressed as mean standard error of the mean of 10 animals
in each group. A p value < 0.05 was taken to be
significant.