Effect on biochemical parameters
Significantly (P<0.05) higher in aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) mean values (IU/L) were observed in rats of group 2, 3 and group 4 on 15
th and 29
th day respectively when compared with group 1. However, there was a significant (P<0.05) difference in mean values in the rats of combined toxic dose (
i.e. group 4) than the rats of individual treated groups 2 and 3 (Table 1).
Effect on antioxidative parameters
The mean values of reduced glutathione concentration (GSH) and superoxide dismutase activity (SOD) were significantly (P<0.05) lower in group 2, 3 and group 4 compared with group 1 on 15
th and 29
th day of the experiment. Again, these values were significantly (P<0.05) lower in rats of group 4 compared to groups 2 and 3 (Table 1).
Histopathological findings in liver
At the end of the experiment animals were sacrificed and thoroughly examined for gross changes if any. Hepatomegaly with round edges was noticed on 15
th and 29
th day of experiment. The liver showed mild to moderate congestion in rats of groups 2 and 3 and moderate to severe in group 4 on 15
th and 29
th day of the experiment. Liver sections of control group showed normal architecture of hepatic parenchyma with central vein and portal triad (Fig 1a). The sections of liver in group 2 rats on 15
th day showed increased sinusoidal spaces and mild degenerative changes (Fig 1b). On 29
th day, vacuolar degeneration and areas of necrosis were observed (Fig 1c). The sections of liver on 15
th day in rats of group 3 showed perivascular lymphocytic infiltration and disrupted cords with swollen hepatocytes (Fig 1d). On 29
th day, the changes were more pronounced as well as focal areas of necrosis was evident (Fig 1e). In the rats of group 4, the liver sections showed similar type of lesion as noticed in groups 2 and 3 on 15
th and 29
th day but the intensity was moderate to severe (Fig 1f to 1i). In addition, moderate perivascular fibrosis of portal triad and shrunken, irregular hepatic cords were observed (Fig 1j).
Biochemical parameters revealed a significant (P<0.05) increase in the activity of AST, ALT and ALP in groups 2, 3 and 4 on 15
th and 29
th day of the experiment. An increased activity of AST, ALT and ALP in cadmium and CPF treated rats separately indicated liver dysfunction, which was accompanied by elevated levels of these hepatic marker enzymes in the blood stream. Elevated levels of ALP suggested biliary damage, which disrupts flow of blood to the liver. Similar findings were reported by
Tomaszewska et al., (2015) and
Nasim Babaknejad et al., (2015) in Cd treated rats. In the present study, these results are in accordance with the findings of
Ambali et al., (2010) and
Barski and Spodniewska (2018). Co-administration of both the toxicants produced further increase in these enzyme levels as compared to individual administration of either toxicant. The increased levels could be due to severe degeneration and necrosis of hepatocytes that result in release of transaminases in the blood. These findings can be correlated with the histological changes in the present study and are in agreement with the reports of
Prabu et al., (2012) and
Singh et al., (2016).
Significant (P<0.05) reduction in GSH and SOD levels in rats liver of combined group than those in the individual toxicity groups is suggestive of oxidative stress in the present study.
El-Sharaky et al., (2007) observed that the increase in lipid peroxidation might be attributed to alterations in the antioxidant defence system. This defence system includes the glutathione peroxidase, thioredoxin reductase as well as the reduced glutathione (GSH), which normally protect the biological system against free radical toxicity.
Sarkar et al., (1998) demonstrated that Cd modulates toxic effects through oxidative stress mechanisms. The changes in CdCl
2 treated rats are in agreement with those of
Renugadevi and Prabu (2010),
Messaoudia et al., (2010), Pari and Shagirtha (2012) and
Christian et al., (2016). The results in Group 3 indicated that CPF exposure inhibited GSH and SOD. These depletion might be due to the decreased synthesis of enzymes or oxidative inactivation of enzyme protein. The changes in CPF group were similar to the reports of
Aly et al., (2010), Hassani et al., (2014) and
Deng et al., (2016). In rats of group 4, a marked reduction in GSH levels compared to groups 2 and 3 indicated synergistic action of CdCl
2 and CPF leading to higher oxidative damage.
The Cd induced hepatotoxicity was thought to be mediated through the cadmium metallothionein (Cd-Mt) complex, which is synthesized in the liver, released into circulation and taken up by renal proximal tubule cells
(Dudley et al., 1985). In fact, when the synthesis of Mt becomes insufficient for binding all Cd ions in the liver, Cd not bound to Mt produce hepatocytes injury and caused different histopathological lesions. Similar lesions were also noticed by
Jihen et al., (2008), Renugadevi and Prabu (2010) and
Prabu et al., (2012). The histopathological changes are further corroborated by the decreased levels of GSH and SOD in rats exposed to CPF that might have caused membrane damage of cells resulting into degenerative to necrotic changes in liver. Similar changes were also reported by
Savithri et al., (2010) and
Singh et al., (2016). Irregular hepatic cords were observed. Similar observations were also noticed by
Singh et al., (2016) and might be due to synergistic action of CdCl
2 and CPF.