influence of copper on renal and hepatic glutathione content in rats

Proceedings of ECOpole
Vol. 2, No. 2
2008
Andrzej GROSICKI1
INFLUENCE OF COPPER ON RENAL AND HEPATIC
GLUTATHIONE CONTENT IN RATS
INTOXICATED WITH CADMIUM
WPŁYW MIEDZI NA ZAWARTOŚĆ GLUTATIONU W WĄTROBIE I NERKACH
SZCZURÓW ZATRUTYCH KADMEM
Summary: Examinations involved 135 male Wistar rats weighing 200±11 g. After one-week acclimatization the
animals were randomly assigned to three groups of 45 animals each. Rats in groups 1 (controls) fed a standard
laboratory chow (Agros Poland, containing 4.9 mg Cu/kg) and tap water ad libitum. Rats in group 2 were fed the
same diet as in group 1 and additionally treated with CdCl2 given orally by a stomach tube for 28 days (water
solution) at a dose corresponding to 10 mg of cadmium per kg of diet. Rats in group 3 were treated with cadmium
as in group 2 but fed the standard laboratory chow supplemented with copper as CuSO4 up to 49 mg/kg while
manufacturing. The total dose of cadmium was about 7.8 mg. The consumption of feed and water, and body
weight gains were evaluated weekly during the whole experimental period. Animals (5 rats at each time point)
were killed at 7, 14, 21, and 28 days within the dosing period by immersion in gaseous carbon dioxide between
10:00 and 11:00 a.m. to minimize the durnal variation of the parameters examined. At necropsy the liver and
kidneys were removed, weighed, homogenized and centrifuged at 4ºC at 9000 g for 10 min. GSH levels were
estimated by the method of Ellman modified by Griffin. The significance of the results was determined by Student’s test at P < 0.05. Results indicated that all the rats examined showed no alterations in feed and water intake,
and organ to body ratios although a marked increase in body weight gain was found in rats from group 3 as compared with that in rats exposed to cadmium but not fed a copper enriched diet. Rats intoxicated with cadmium
increased temporary hepatic and renal GSH levels as compared with those in group 1. On the other hand, hepatic
GSH levels in rats fed a copper supplemented diet and treated with cadmium increased significantly in comparison
to those in groups 1 and 2 whereas renal GSH levels increases were temporary.
Keywords: cadmium, copper, glutathione, rat
Glutathione is a non-protein compound abundant in the cell. This compound detoxificates hydrogen peroxide and repairs peroxidative damage to lipids, proteins, and nucleic
acids. Moreover, glutathione plays a vital role in incorporation of copper into metalloproteins [1, 2]. Cadmium is a potent inducer of cell oxidative stress [3]. The toxic action of
cadmium includes alterations in GSH (glutathione reduced) content and enzymes of glutathione metabolism [4]. The effect of cadmium on glutathione level is not clear. Tewari
et al [5], Congiu et al [6] provided evidence that cadmium intoxication may increase hepatic GSH content whereas Han et al [7] and El-Maraghy [8] found a decreased content of
GSH in growing pigs intoxicated with various doses of cadmium. On the other hand,
Siegers et al [9] and Wong and Klaassen [9] failed to show any alterations in GSH content
as a result of cadmium exposure.
Copper is reported to interact with cadmium uptake; a diet fortified with copper may
increase cadmium concentrations in tissues of animals and cell lines [10, 11]. Additionally,
copper may generate reactive oxygen species that are involved in lipid peroxidation and
membrane changes [12]. Because copper may modified cadmium toxic action in the body,
the goal of the present studies was to evaluate effects of moderate copper supplements on
1
Laboratory of Radiobiology, National Veterinary Research Institute in Pulawy, al. Partyzantów 57,
24-100 Puławy, tel. 081 889 31 48, email: [email protected]
326
Andrzej Grosicki
GSH levels in the liver and kidneys and selected allometric parameters in rats exposed to
cadmium and copper via the alimentary canal.
Material and methods
Examinations involved 135 male Wistar rats weighing 200 ± 11 g. After one-week acclimatization the animals were randomly assigned to three groups of 45 animals each. Rats
in groups 1 (controls) fed a standard laboratory chow (Agros Poland, containing
4.9 mg Cu/kg) and tap water ad libitum. Rats in group 2 were fed the same diet as in group
1 and additionally treated with CdCl 2 given orally via a stomach tube for 28 days (water
solution) at a dose corresponding to 10 mg of cadmium per kg of diet. Rats in group 3 were
treated with cadmium as in group 2 but fed the standard laboratory chow supplemented
with copper as CuSO4 up to 49 mg/kg while manufacturing. The diets were analysed for
cadmium content (no detectable amounts of the element were found). The total dose of
cadmium per rat was about 7.8 mg. The consumption of feed and water, and body weight
gains were evaluated weekly during the whole experimental period. Animals (5 rats at each
time point) were killed after 7, 14, 21, and 28 days within the dosing period by immersion
in gaseous carbon dioxide between 10:00 and 11:00 a.m. to minimize the durnal variation
of the parameters examined. At necropsy the liver and kidneys were removed, weighed,
homogenized and centrifuged at 4°C at 9000 g for 10 min. GSH levels were estimated by
the method of Ellman modified by Griffin. The protein content was measured according to
Lowry et al. The significance of the results was determined by Student’s t-test at P < 0.05.
Results
Compared with rats in group 1, the intake of diet and water did not change significantly both in the cadmium treated rats (group 2) and the rats supplemented with copper
(group 3). Body weights increased steadily throughout the experimental period. In rats from
group 2 body gains were visibly lower than those found in rats in group 1, whereas rats in
group 3 demonstrated weight gains even higher than those in rats from group 1. However,
the differences were not statistically significant. There were also no significant differences
for hepatic and renal relative weights among the groups tested although the relative weight
of the liver was larger by about 15% in rats from groups 2 and 3 as compared with that in
group 1. Moreover, no visible signs of cadmium exposure on rat behaviour were seen
except some uneasiness found at the beginning of cadmium treatment.
Table 1
Hepatic glutathione concentrations [nmol/mg protein]
Time of measurement
Group 1
Group 2
Group 3
7d
26.39
38.93 *
70.42 **
14 d
59.29
56.54
74.35 **
21 d
59.93
77.17 *
117.88 **
28 d
80.47
74.17
115.66 **
Explanations:
* - indicates statistically significant difference between group 1 and groups 2 and 3 at p < 0.05.
** - indicates statistically significant difference between group 2 and group increased GSH level 3 at p < 0.05
Influence of copper on renal and hepatic glutathione content in rats intoxicated with cadmium
327
The hepatic level of GSH concentration (Table 1) revealed a tendency to increase
within the experimental period in all groups examined. However, in rats from group 2 and
group 3 GSH levels were significantly higher after 7 and 21 days (group 2) and at all time
points (group 3) in comparison with those noticed in group 1.
Renal GSH content (Table 2) in groups 2 and 3 was similar to that in group 1 on days
7, 14, and 21. However, administration of cadmium to rats increased statistically renal GSH
level in groups 2 (at 28 d) and 3 (at 7 d and 28 d). In addition, supplements of copper increased significantly GSH level (group 3) within the whole experimental period as compared with those in groups 1 and 2.
Table 2
Renal glutathione concentrations [nmol/mg protein]
Time of measurement
7d
14 d
21 d
28 d
Group 1
25.43
52.59
41.21
41.79
Group 2
27.06
46.82
39.20
63.19 *
Group 3
37.16 *
58.51
46.22
96.71 **
Explanations:
* - indicates statistically significant difference between group 1 and groups 2 and 3 at p < 0.05
** - indicates statistically significant difference between group 2 and group increased GSH level 3 at p < 0.05
Discussion
Lipid peroxidation is one of the phenomena of cadmium exposure. Cadmium may interact with the mitochondria, microsomes and peroxisomes producing free radicals through
indirect mechanism [15, 16]. GSH is considered the first line of defence against cadmium
toxic action.
Several reports provided reasons that increased lipid peroxidation produced by cadmium may be accompanied by decreases in hepatic and renal GSH levels [8, 18]. This
reducing in GSH levels may lower GSH to GSSG (glutatione oxidized) ratio that results in
an enhanced free radical production.
It is believed that GSH values in normal animals are steady [18]. The presented results
are not in accordance with the report mentioned above. A tendency of GSH content to increase within the experimental period found in the present studies is not frequent in intact
animals. However, it is worth noting that a time dependant increased in glutathione level
was also reported by Berger et al [20] in VACO 5 cell lines. It may be suggest that an increase in GSH levels with time in normal rats observed in the present study corresponds to
the growth of the rats involved.
In cadmium intoxicated rats both hepatic and renal GSH levels revealed temporary increases in comparison with the control values. Similar results were reported by Congiu et
al. [6]. A higher response of hepatic GSH levels to cadmium intoxication than that in the
kidneys may be attributed to a preferential accumulation of cadmium in the liver within
a short time after cadmium exposure.
Supplements of copper in cadmium intoxicated rats caused additional increases in
GSH levels as compared with those in cadmium treated rats. This increase in GSH level is
difficult to elucidate, but the involvement of copper in lipid peroxidation may be a reason
for enhanced GSH levels. However, it is worth noting that the animals that received the
328
Andrzej Grosicki
copper supplementation in addition to cadmium showed higher body gains than those in
non-treated animals. These findings are consistent with other previous studies indicating
a beneficial role of copper in body gains of animals. Therefore under these experimental
conditions used moderate supplements of copper could have resulted in a reduced cadmium
toxic action.
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WPŁYW MIEDZI NA ZAWARTOŚĆ GLUTATIONU W WĄTROBIE I NERKACH
SZCZURÓW ZATRUTYCH KADMEM
Streszczenie: Wykonano badania z uŜyciem 135 szczurów samców szczepu Wista, które po 1-tygodniowej aklimatyzacji podzielono na 3 grupy, liczące 45 szczurów kaŜda. Szczury w grupie 1 spoŜywały standardową paszę
dla gryzoni zawierającą 4,9 mg Cu/kg oraz wodę z kranu. Szczury w grupie 2 otrzymywały tę samą paszę,
a ponadto wodny roztwór chlorku kadmu doŜołądkowo przez okres 28 dni w ilości odpowiadającej około 10 mg
tego metalu w paszy. Szczury w grupie 3 otrzymywały kadm tak jak szczury w grupie 2 oraz spoŜywały paszę
wzbogaconą w miedź do 49 mg/kg. Całkowita ilość kadmu, jaką otrzymywał kaŜdy szczur, wynosiła około
7,8 mg. Podczas doświadczenia określano w odstępach tygodniowych spoŜycie wody, paszy oraz przyrosty masy
ciała. Zwierzęta zabijano po 7, 14, 21 i 28 dniach z uŜyciem gazowego ditlenku węgla zawsze o tej samej porze.
Podczas sekcji pobierano wątrobę i nerki, waŜono, następnie homogenizowano i wirowano w 4°C przy 9000 g
przez 10 min. Poziom glutationu oznaczano metodą Ellmana z modyfikacjami Griffina. RóŜnice statystycznie
istotne określano za pomocą testu t-Studenta dla p < 0,05. Uzyskane wyniki wskazują, Ŝe w warunkach doświadczenia nie stwierdzono istotnych zmian pomiędzy testowanymi zwierzętami w spoŜyciu paszy i wody, w przyrostach masy ciała oraz w masie względnej wątroby i nerek. Warto jednak nadmienić, Ŝe u szczurów spoŜywających
paszę wzbogaconą w miedź notowano największe przyrosty ciała, mimo Ŝe zwierzęta te były naraŜone na kadm.
Poziomy GSH (zredukowanego glutationu) w grupie zatruwanej kadmem wzrosły przejściowo zarówno w wątrobie, jak i w nerkach. Natomiast w grupie karmionej dodatkowo paszą wzbogaconą w miedź poziomy glutationu
w wątrobie wzrosły statystycznie znacząco przez cały okres badań w porównaniu z wartościami notowanymi
w grupach 1 i 2. W przypadku nerek róŜnice były przejściowe i słabiej zarysowane.
Słowa kluczowe: kadm, miedź, glutation, szczur