to inactivation of superoxide dismutase by singlet oxygen, hydrogen peroxide, and
peroxyl radicals or elimination of highly reactive superoxide (Sun et al. 2007). The
decline in SOD activity of earthworms might also be due to adaptation of the
organisms to its environment (Sandrini et al. 2008).
Catalase (CAT) is a peroxisomal hydroperoxidase found in peroxisomes, cytosol,
and mitochondria that converts H 2 O 2 to water and oxygen. Initially, this antioxidant
may show enhancement, but with the severity of the toxicity, CAT level may show
decrement. Lin et al. (2010) suggested that the earthworm has a capacity to activate
the antioxidant system to tolerate oxidative stress. The increasing CAT activity
might be due to H 2 O 2 produced from SOD mechanisms (Li et al. 2008), and to
maintain the level of H 2 O 2 , the catalase activity gets enhanced (Liu et al. 2011).
El-Shenawy et al. (2012) documented that the increased CAT activity was due to
upregulation of catalase activity, which could be an adaptive mechanism of earthworms to prevent the ROS accumulation. The reduction in CAT activity is due to
inhibition of enzyme by high cellular stress or due to high levels of ROS (Markad
et al. 2012), or it might be due to inactivation by peroxyl radicals, singlet oxygen,
and superoxide radicals (Kono and Fridovich 1982). When the ROS generation
exceeds the ROS scavenging capacity of SOD and CAT, they become CAT inhibitors (Schreck et al. 2008). They further suggested that the decreased CAT activity
may also be caused by damage of the antioxidant defense system, and the defensive
effect of antioxidant enzymes would be suppressed by an increase in stress condition
by toxicant.
Glutathione peroxidase (GPx) removes hydrogen peroxide by using reduced
glutathione as a hydrogen donor (Markad et al. 2012). GSH is used as a hydrogen
donor by GPx to eliminate H 2 O 2 . It also helps to convert the organic hydroperoxides
into alcohols. The product of this reaction is GSSH, which is further reduced by GR
in the presence of NADPH to restore the GSH level in the cell (Halliwell and
Gutteridge 1999). The variation in the GPx activity may be regarded as a sign of
hormesis (Calabrese and Baldwin 1998). The hormetic mechanism was interpreted
as the result of instantaneous balance between the formation and degradation of
specific protein including other processes also such as synthesis, regeneration,
activation vs. inhibition, inactivation, and degradation, and this mechanism may
signify temporary over adaptation. Maity et al. (2008) suggested that the reduction in
concentration of glutathione and antioxidant enzymes may be due to their capability
to remove the metal in biologically inactive form by the induction of metal-binding
proteins (Homa et al. 2005).
The reduction of antioxidant enzymes SOD, CAT, and GPx may be due to the
inactivation of SOD by singlet oxygen, peroxyl radicals, and hydrogen peroxide or
removal of highly reactive superoxide (Sandrini et al. 2008). The biphasic response
of antioxidant enzymes in treated earthworms was also reported by Łaszczyca et al.
(2004). They further suggested that the hormetic-like phenomenon plays a significant role in assessing the degree of environment stress. Overall, the reduction of
CAT and GPx activities in earthworms indicated severe damage to their antioxidant
defense system (Wen et al. 2017). The variations in the activities of antioxidant
enzymes may be due to the phenomenon that initially worms had an ability to
15 Waste Management Practices and Their Impact on Earthworms
257
peroxyl radicals or elimination of highly reactive superoxide (Sun et al. 2007). The
decline in SOD activity of earthworms might also be due to adaptation of the
organisms to its environment (Sandrini et al. 2008).
Catalase (CAT) is a peroxisomal hydroperoxidase found in peroxisomes, cytosol,
and mitochondria that converts H 2 O 2 to water and oxygen. Initially, this antioxidant
may show enhancement, but with the severity of the toxicity, CAT level may show
decrement. Lin et al. (2010) suggested that the earthworm has a capacity to activate
the antioxidant system to tolerate oxidative stress. The increasing CAT activity
might be due to H 2 O 2 produced from SOD mechanisms (Li et al. 2008), and to
maintain the level of H 2 O 2 , the catalase activity gets enhanced (Liu et al. 2011).
El-Shenawy et al. (2012) documented that the increased CAT activity was due to
upregulation of catalase activity, which could be an adaptive mechanism of earthworms to prevent the ROS accumulation. The reduction in CAT activity is due to
inhibition of enzyme by high cellular stress or due to high levels of ROS (Markad
et al. 2012), or it might be due to inactivation by peroxyl radicals, singlet oxygen,
and superoxide radicals (Kono and Fridovich 1982). When the ROS generation
exceeds the ROS scavenging capacity of SOD and CAT, they become CAT inhibitors (Schreck et al. 2008). They further suggested that the decreased CAT activity
may also be caused by damage of the antioxidant defense system, and the defensive
effect of antioxidant enzymes would be suppressed by an increase in stress condition
by toxicant.
Glutathione peroxidase (GPx) removes hydrogen peroxide by using reduced
glutathione as a hydrogen donor (Markad et al. 2012). GSH is used as a hydrogen
donor by GPx to eliminate H 2 O 2 . It also helps to convert the organic hydroperoxides
into alcohols. The product of this reaction is GSSH, which is further reduced by GR
in the presence of NADPH to restore the GSH level in the cell (Halliwell and
Gutteridge 1999). The variation in the GPx activity may be regarded as a sign of
hormesis (Calabrese and Baldwin 1998). The hormetic mechanism was interpreted
as the result of instantaneous balance between the formation and degradation of
specific protein including other processes also such as synthesis, regeneration,
activation vs. inhibition, inactivation, and degradation, and this mechanism may
signify temporary over adaptation. Maity et al. (2008) suggested that the reduction in
concentration of glutathione and antioxidant enzymes may be due to their capability
to remove the metal in biologically inactive form by the induction of metal-binding
proteins (Homa et al. 2005).
The reduction of antioxidant enzymes SOD, CAT, and GPx may be due to the
inactivation of SOD by singlet oxygen, peroxyl radicals, and hydrogen peroxide or
removal of highly reactive superoxide (Sandrini et al. 2008). The biphasic response
of antioxidant enzymes in treated earthworms was also reported by Łaszczyca et al.
(2004). They further suggested that the hormetic-like phenomenon plays a significant role in assessing the degree of environment stress. Overall, the reduction of
CAT and GPx activities in earthworms indicated severe damage to their antioxidant
defense system (Wen et al. 2017). The variations in the activities of antioxidant
enzymes may be due to the phenomenon that initially worms had an ability to
15 Waste Management Practices and Their Impact on Earthworms
257