Onion (Allium cepa) extract prevents cadmium induced renal dysfunction

Introduction

Our environment and diet expose us to cadmium (CD).[1] Although Cd exposure may contribute to essential hypertension,[2] affect respiratory system, cause bone diseases, and affect reproductive system, the kidney remains the critical target organ for cadmium toxicity.[34] Most studies on cadmium toxicity, therefore, centres on the detection of early signs of kidney dysfunction which results from oxidation.[5] In other words, Cd causes its injurious effects by generation of reactive oxygen species (ROS).[5]

On the contrary, Allium cepa (containing sulphur compounds and flavonoids) has anti-oxidant properties.[6] This research work was, therefore, targeted at knowing whether or not oral administration of the AcE will prevent cadmium's adverse effects of on renal clearance as a representative of renal functions.

Materials and Methods

A total of 72 adult male Wista rats (180-220 g) were used for this study. They were inbreed at the Animal House section of the Department of Physiology, Ladoke Akintola University of Technology, Ogbomoso, Nigeria. The animals were acclimatized over a period of two weeks.

Results

The following results were obtained and are presented as mean ± SEM. Level of significance is taken at P < 0.05.

Discussion

The results of this study show that neither chronic administration of 1.0 ml AcE nor acute exposure to cadmium significantly affects weight increase [Table 1]; this supports the findings of Campos et al.[14] that acute exposure to cadmium mainly affects the respiratory system and gastrointestinal system but has no immediate effect on body weight. This can be linked to the low caloric and low protein (approximately 1% by weight) content of Allium cepa.[15] On the other hand cadmium did not cause any significant difference in weight gain probably because it was administered for only three days (acute exposure). Chronic administration of cadmium (for twelve weeks) in a previous study[16] showed that Cd significantly (P < 0.05) affects weight gain. These same reasons could be responsible for the non significant difference in the kidney weight across the three groups [Table 2].

Table 3 shows that there was no significant difference in 24 hour urine volume of animals pretreated with onion before cadmium administration and the control, while there was significant (P > 0.05) reduction in animals treated with cadmium only. This goes along with the findings of Asagba and Obi[17] that cadmium toxicity brings about a reduction in 24 hour Urine Volume. This is because cadmium (as well as most other heavy metals) interferes with glomerular filtration rate (GFR) and tubular processes (tubular re-absorption and tubular secretion)[18] which are the major determinants of Urine Volume. The pre-administered onion would therefore be responsible for the prevention of these lowering effects of cadmium on 24 hour Urine volume (ml) by preventing the lowering of GFR.

In a similar way renal creatinine clearance (RCC) and renal urea clearance (RUC) of animals pretreated with onion before cadmium administration are not significantly different (P > 0.05) from those of the Control. Meanwhile, animals treated with cadmium showed a highly significant (P < 0.01) decrease in RCC [Table 4] and a significant decrease (P < 0.05) in RUC [Table 5] compared to the control. This supports the findings of Machiko et al. (1978)[19] which says that cadmium toxicity brings about reduction in renal clearance among other renal functions. Therefore, Allium cepa (onion) was able to prevent cadmium's adverse effects on RC which could serve as a representative of renal functions. In other words, onion is able to prevent Cd's adverse effect on renal functions.

There was no significant difference in SOD activity of both the plasma and tissue of the control and that of the animals pretreated with onion before cadmium exposure. On the contrary, there was a highly significant (P < 0.01) decrease in plasma [Table 6] and tissue [Table 7] SOD Activity in animals treated with cadmium only compared to the control. This finding is in agreement with Jamall and Crispin (1985),[20] and is at the same time in support of Allium cepa as an antioxidant,[6] since increase in SOD activity is linked to reduction in the activities of reactive oxygen species.

Both plasma [Table 8] and tissue [Table 9] cAT activity of animals treated with cadmium only were significantly (P < 0.01 and P < 0.05, respectively) low relative to Control. There was, however no significant (P > 0.05) difference between the control and the animals pretreated with onion before cadmium administration in this respect. Since increase in CAT activity is, as well, linked to reduction in the activities of reactive oxygen species and vice versa, it is therefore further established that Allium cepa must have reduced the oxidative stress that cadmium could cause.

Finally, there was no significant (P > 0.05) difference in both plasma and tissue MDA concentration of control and those of the animals pretreated with onion before cadmium administration. While animals treated with cadmium only shows a significant (P < 0.05) increase in both plasma and tissue MDA concentration [Tables 10 and 11, respectively]. Normally, decrease in MDA concentration is a sign of reduction in the activities of reactive oxygen species. It seems likely therefore that it was Allium cepa that reduced the oxidative stress that cadmium exposure could have caused in the onion pretreated animals.

It can be concluded that exposure to cadmium adversely affects renal functions (using renal clearance as a marker) due to cadmium's ability to cause oxidative stress by interfering with the activities of SOD and that of CAT, and thereby given freedom to free radicals [for example reactive oxygen species, (ROS)] to cause oxidation which manifests as increase in the concentration of MDA (in the case of lipid peroxidation). Allium cepa, however, prevents cadmium from adversely affecting renal functions. This would be a result of the anti-oxidant properties of Allium cepa which ensures reduced activity of ROS.