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Tolerance development to cadmium-induced decrease in hepatic oxidative xenobiotic metabolism and cytochrome P-450
Abstract:
Cadmium, in dose of 0.84 mg/kg (ip), produces a marked inhibition in hepatic oxidative xenobiotic metabolism which results from a decreased cytochrome P-450 content in the male rat. The inhibitions in microsomal metabolism of aniline, ethylmorphine, or p-nitroanisole were not elicited by the 0.84 mg/kg cadmium dose in rats which had been pretreated (72 hours prior) with a lower dose of cadmium (0.21 mg Cd/kg, ip). Likewise, the decreases in both microsomal cytochrome P-450 content and in microsomal spectral binding of hexobarbital or aniline produced by the 0.84 mg/kg cadmium dose were not elicited in the rats pretreated with the low cadmium dose. The 0.21 mg/kg cadmium dose produced an increase (370%) in the cadmium-binding capacity as well as an increase (395%) in total hepatic metallothionein. These data are consistent with the hypothesis that the pretreatment of animals with relatively low cadmium doses produces an increase in the cellular levels of metallothionein which can then bind and ameliorate the toxicological effects of a subsequently administered toxic dose of cadmium.
Insights
Pretreating male rats with a low dose of cadmium (0.21 mg/kg) prevents liver damage from a higher dose (0.84 mg/kg). This is because the low dose increases metallothionein, a protein that binds and neutralizes cadmium.
Area of Science:
- Toxicology
- Biochemistry
- Environmental Health
Background:
- Cadmium exposure can inhibit hepatic oxidative xenobiotic metabolism.
- Cytochrome P-450 is crucial for metabolizing foreign compounds in the liver.
- Metallothionein is a protein involved in heavy metal detoxification.
Purpose of the Study:
- To investigate the protective effect of low-dose cadmium pretreatment against high-dose cadmium-induced liver toxicity.
- To determine the role of metallothionein in cadmium detoxification.
Main Methods:
- Male rats were administered varying doses of cadmium intraperitoneally.
- Hepatic oxidative xenobiotic metabolism and cytochrome P-450 content were measured.
- Cadmium-binding capacity and metallothionein levels were quantified.
Main Results:
- A high dose of cadmium (0.84 mg/kg) significantly inhibited hepatic metabolism and decreased cytochrome P-450.
- Pretreatment with a low dose of cadmium (0.21 mg/kg) prevented these inhibitory effects.
- The low cadmium dose significantly increased hepatic metallothionein levels and cadmium-binding capacity.
Conclusions:
- Pretreatment with low-dose cadmium induces metallothionein, which confers protection against subsequent high-dose cadmium toxicity.
- Metallothionein plays a key role in ameliorating the toxic effects of cadmium exposure.
- This finding has implications for understanding and mitigating cadmium poisoning.