Cd Pretreatment Research Articles

Toxic effects of cadmium on LHRH-induced LH release and ovulation in rats

CFY rats were given 5 or 10 mg/kg bw cadmium chloride (CdCl 2) or 0.9% NaCl solution (1 mL/kg) subcutaneously on the day of diestrus II. Six days later (proestrus) at 1200 h they were anesthetized with pentobarbital, 0.5 or 2 μg/kg LHRH was injected intravenously at 1400 h, and blood was collected for LH determination. A second group of animals pretreated with 10 mg/kg bw CdCl 2 and treated with 2 or 4 μg/kg LHRH was allowed to recover from the anesthesia and checked for ovulation the next day (estrus). In rats treated with 10 mg/kg of CdCl 2, the LH content of pituitary gland diminished, but no significant difference was found in the LH response to LHRH. In controls (ovulation blocked by anesthesia) 2 as well as 4 μg/kg of LHRH completely restored ovulation, while after Cd pretreatment, ovulation recovered depending on the dose of LHRH. It is concluded that Cd-induced anovulation is related to altered function of the pituitary gland and ovary, which can be restored by excess LHRH.

Effect of in vivo low-dose cadmium pretreatment on the in vitro interactions of cadmium with isolated interstitial cells of the rat testes

Recent studies have shown that Cd-induced testicular interstitial cell (TIC) tumors can be prevented by low-dose Cd pretreatment. However, the mechanism by which low-dose Cd induces such tolerance is unclear. Thus, in this study we assessed the effects of in vivo Cd pretreatment (3 μmol/kg) on Cd uptake, cytotoxicity, metal content (Zn, K, and Ca), and low molecular weight testicular Cd-binding proteins (low M r TCTBs) of isolated TICs exposed to Cd in vitro. TICs were isolated by collagenase dispersion of Wistar ( WF NCr ) rat testes and incubated with Cd (1.0 m m) for 15 to 60 min. In vivo Cd pretreatment decreased in vitro Cd uptake by 24% after 1 hr of incubation with Cd. In vivo Cd pretreatment also resulted in a marked reduction of in vitro Cd-induced cytotoxicity, as reflected by reduced loss of cellular K, glutamic-oxaloacetic transaminase, as well as reduced lipid peroxidation and decreased Cd-induced Ca influx into TICs in vitro. These cytotoxic effects were not attributed solely to cell death as TIC viability remained high even after 1 hr in vitro Cd exposure. Cd-induced inhibition of intercellular enzymes, as assessed by cellular lactate dehydrogenase activity, was also reduced by low-dose Cd pretreatment. Cd pretreatment did not alter basal levels of Zn, Ca, or K. Neither low-dose in vivo Cd pretreatment nor in vitro Cd exposure appeared to greatly alter levels of the low M r TCBPs as assessed by electrophoresis. In vivo Zn pretreatment, which also effectively inhibits Cd-induced testicular tumors, results in a similar reduction in Cd-induced cytotoxicity in TICs. This indicates that treatments which result in reduced Cd-induced TIC tumors are consistently capable of reducing Cd-induced cytotoxicity in isolated TICs in vitro.

Involvement of sulfhydryl metabolism in tolerance to cadmium in testicular cells

Cadmium (Cd)-induced acute testicular toxicity and testicular interstitial cell (IC) tumors can be prevented by low-dose Cd pretreatment. The mechanism of this self-tolerance is unknown. In this regard glutathione (GSH) may play a role in protecting cells from damage by Cd. Therefore, possible mechanisms of self tolerance to Cd in ICs were investigated with emphasis on sulfhydryl metabolism. Rats were pretreated with low-dose Cd (3.0 μmol/kg, sc). Such low-dose Cd pretreatment prevented the necrotizing effects of normally testopathic doses of Cd (20.0 μmol/kg, sc) given 24 hr later. ICs were isolated by collagenase dispersion 24 hr after pretreatment and incubated with Cd (1.0 m m) for 1 hr. In vivo Cd-pretreatment alone increased GSH levels (as determined by HPLC) of whole cells (17%) and cytosol (17%) compared to nonpretreated control. When ICs from nonpretreated rats were exposed to Cd in vitro, GSH in whole cells declined 8% compared to nonpretreated control and 21% compared to cells from in vivo Cd-pretreated rats. In ICs isolated from pretreated rats and exposed to Cd in vitro, GSH levels were normal in whole cells and slightly increased in cytosol. In whole testes low-dose Cd reduced GSH overall, both in cytosol (34%) and in nuclei (14%). Changes in cysteine levels were also seen, similar to those of GSH in whole ICs and cytosol. Neither low-dose in vivo Cd-pretreatment nor in vitro Cd exposure greatly altered levels of the low M r testicular Cd-binding proteins as assessed by electrophoresis. These results indicate that sulfhydryl metabolism, specifically increased GSH, may be a factor in self tolerance to Cd in ICs.

Cross-tolerance to hyperoxia following cadmium aerosol pretreatment

Preexposure of male Lewis rats to Cd aerosols (1.6 mg Cd/m 3, 3 hr/day, 5 days/week, for 4 weeks) has been found to produce a marked degree of tolerance to hyperoxia (greater than 96% O 2). Cd-pretreated animals were still alive after 8 days of continuous exposure to oxygen. In contrast, hyperoxia was fatal to all air-preexposed animals within 54–62 hr. Lungs of Cd-pretreated animals were characterized by hyperplasia and/or hypertrophy of the type II alveolar cell compartment which may have enabled them to more rapidly repair oxidant damage resulting from hyperoxia. Cd pretreatment augmented enzymatic antioxidant enzyme activities, including total lung Se-dependent glutathione peroxidase, catalase, glutathione reductase, and Mn-superoxide dismutase, and caused elevations in pulmonary nonprotein thiols and metallothionein (MT). MT, a thiol-rich, low-molecular-weight protein, was 400-fold higher in Cd-pretreated animals and bound more than 80% of the total Cd in the lung. We have hypothesized that MT serves as an expendable yet renewable cellular target for free radical damage during oxygen exposure. A systemic acute-phase response, characterized by alterations in plasma Zn and Cu concentrations and increased ceruloplasmin oxidase activity, was initiated in Cd-pretreated animals by the fourth day of hyperoxia. This response was accompanied by improvement in pulmonary status and extensive pulmonary repair.

Metal constitution of metallothionein influences inhibition of δ-aminolaevulinic acid dehydratase (porphobilinogen synthase) by lead

This study was undertaken to evaluate the effect of Zn and Cd pretreatment on the inhibition of delta-aminolaevulinic acid dehydratase (ALAD; porphobilinogen synthase, EC 4.2.1.24) by Pb. Male CD rats were pretreated with 200 mumol of Zn/kg s.c. (subcutaneously) or 18 mumol of Cd/kg s.c., 48 and 24 h before assay of ALAD. Pretreatment with Zn resulted in activation of hepatic and renal ALAD and attenuated the inhibition of this enzyme by Pb in vitro. Pretreatment with Cd increased hepatic ALAD activity, and the inhibitory effect of Pb on the hepatic enzyme was attenuated in this group. In contrast with the situation in liver, pretreatment with Cd did not affect the activity of renal ALAD and did not alter the inhibitory effect of Pb on the renal enzyme. The Pb IC50 (concentration causing half-maximal inhibition) values for hepatic and renal ALAD in Zn-pretreated rats and for hepatic ALAD in Cd-pretreated rats were increased above control, whereas the IC50 for renal ALAD in Cd-pretreated rats was unchanged. Cytosolic binding patterns for the three metals were assessed by gel-filtration chromatography and disclosed that 203Pb was co-eluted with Zn and Cd bound to liver and kidney Zn-thioneins and liver Cd,Zn-thionein, although minimal binding of 203Pb to kidney Cd,Zn-thionein was observed. Estimation of the molar ratio of metals bound revealed Cd/Zn ratios of 2 and 5 for Cd,Zn-thioneins from liver and kidney respectively. The inhibition of purified ALAD by Pb was also attenuated by addition of purified Zn-thioneins and Cd,Zn-thioneins from liver and kidney in the following order: liver Zn-thionein = kidney Zn-thionein greater than liver Cd,Zn-thionein much greater than kidney Cd,Zn-thionein. Thus liver and kidney Zn-thioneins and liver Cd,Zn-thionein with a low Cd/Zn ratio readily decrease the free pool of Pb available to interact with ALAD. These data also demonstrate that the capacity of metallothionein to alter the intracellular distribution of Pb and mediate the inhibition of ALAD by Pb is dependent on the tissue source and relative metal constitution of the metallothionein.

Interaction of benzo(a)pyrene and cadmium on GSH-S-transferase and benzo(a)pyrene hydroxylase in the black sea bass Centropristis striata.

The effect of benzo(a)pyrene (BaP) and cadmium (Cd) upon the hepatic enzymes, BaP hydroxylase and GSH-S-transferase, was investigated in black sea bass. Intraperitoneal (ip) injections of BaP produced a significant increase in BaP hydroxylase activity in the microsomal fraction and GSH-S-transferase activity in the cytosol. Administration of Cd alone had no effect on either enzyme. However, when both Cd and BaP were injected (ip) in the fish, Cd had an inhibitory effect on the activity of these hepatic enzymes. Pretreatment of fish with a low dose of Cd (0.42 mg/kg) prior to injection of BaP and Cd produced a 30% increase in GSH-S-transferase activity and a 50% reduction in BaP hydroxylase activity when compared to fish injected with BaP alone following Cd pretreatment. Thus, a low dose of Cd was effective in producing a tolerance to a subsequent Cd challenge for the enzyme GSH-S-transferase but not for BaP hydroxylase. In contrast, fish pretreated with a high dose of Cd (2.5 mg/kg) prior to BaP treatment alone or with Cd displayed no difference in either enzyme activity. The implications from this study on the exposure of black sea bass to two xenobiotics, Cd and BaP, indicate that BaP hydroxylase may not serve as a good monitor for hydrocarbon pollution in the presence of Cd.

Tolerance to cadmium-induced hepatotoxicity following cadmium pretreatment

Tolerance to several toxic effects of Cd, including lethality, has been shown following pretreatment with Cd. This study was designed to determine if tolerance also develops to Cd-induced hepatotoxicity. Rats were challenged with Cd (2.0, 3.0, 4.0, or 5.0 mg/kg, iv) 24 hr after pretreatment with saline (2 ml/kg, sc) or Cd (2.0 mg/kg, sc). Ten hours following challenge, plasma enzyme activities were dramatically elevated in control rats (sorbitol dehydrogenase 30- to 300-fold and aspartate aminotransferase 3- to 40-fold). In addition, histologic examination revealed moderate to severe hepatic injury, evidenced by cell swelling, cytoplasmic eosinophilia, pyknosis, karyorrhexis, and necrosis. In Cd-pretreated rats, plasma enzyme levels were similar to control values and only slight morphologic changes were evident. This tolerance to Cd-induced hepatotoxicity is probably due to the increase in hepatic metallothionein induced by Cd pretreatment, which has been shown to alter the hepatic subcellular distribution of Cd such that less binds to subcellular organelles and more binds to metallothionein located in the cytosol.

Tolerance to cadmium-induced toxicity depends on presynthesized metallothionein in liver.

Tolerance to Cd-induced toxicity following pretreatment with Cd is well documented, yet the exact mechanism of tolerance and role of metallothionein (MT) remains equivocal. In this study it was determined if the rapid induction of MT following injection of a challenge dose of Cd or the concentration of presynthesized MT induced by Cd pretreatment is more important for development of tolerance by ascertaining (1) whether the rates of synthesis of MT differ following injection of the challenge dose of Cd in control and Cd-pretreated rats and (2) if a relationship exists between presynthesized hepatic or renal MT and tolerance to Cd-induced lethality. Rates of hepatic and renal MT synthesis did not differ following injection of a challenge dose of Cd (2.0 mg Cd/kg, iv) in control and Cd-pretreated (2.0 mg Cd/kg, sc) rats. However, the progressive increase in concentration of MT in liver after Cd pretreatment correlated with the increase in tolerance to a lethal dose of Cd (4.0 mg Cd/kg, iv), as evidenced by a decrease in mortality in pretreated rats. A similar correlation was not observed between kidney MT levels and tolerance. Therefore, it appears that presynthesized MT in liver rather than increased synthesis of MT following injection of a second dose of Cd is responsible for Cd-induced tolerance.

Altered subcellular distribution of cadmium following cadmium pretreatment: Possible mechanism of tolerance to cadmium-induced lethality

Animals pretreated with cadmium (Cd) subsequently develop tolerance to an otherwise lethal dose of Cd. Possible mechanisms for this tolerance include reduced absorption, an altered tissue distribution, and an altered subcellular distribution of Cd. Male rats received a single Cd pretreatment (2.0 mg/kg, sc) 24 hr prior to administration of a typically lethal challenge dose of Cd (3.9 mg/kg, iv). Tolerance was evident because no mortality was observed in Cd-pretreated rats. Since Cd induces synthesis of hepatic metallothionein (MT), a higher percentage of the challenge dose might be sequestered in the liver of Cd-pretreated animals with less distributed to target organs of toxicity. At 2 and 24 hr following Cd challenge, no marked changes in organ distribution of the challenge dose of Cd were observed as a result of Cd pretreatment. However, isolation of hepatic subcellular fractions 2 hr following injection of the challenge dose revealed less Cd in nuclei, mitochondria, and endoplasmic reticulum, and more in cytosol as a result of Cd pretreatment. The increased cytosolic Cd was bound primarily to MT which had been induced markedly by Cd pretreatment. These data indicate that differences in absorption or tissue distribution of Cd are unlikely explanations for development of tolerance to Cd. Rather, tolerance appears to result from an MT-related change in the hepatic subcellular distribution of Cd, evidenced by lower concentrations of Cd in nuclei, mitochondria, endoplasmic reticulum, and cytosolic high-molecular-weight proteins and higher concentrations bound to MT in cytosol.

Potentiation of CCl 4 hepatotoxicity and lethality by chlordecone in female rats

Female Sprague-Dawley rats (175–200 g) were maintained on a commercial powdered rat chow containing 0 or 10 ppm chlordecone (Kepone®; CD). On day 15 of the dietary protocol, a single dose of CCl 4 (5 -100 μl/kg) was administered i.p. in corn oil vehicle. Controls received oil vehicle only. Twenty-four hours after CCl 4 administration, hepatotoxicity was assessed using biochemical, functional, and histopathological parameters. Serum enzymes (GPT, GOT, ICD and OCT) were elevated in a dose related manner in the animals receiving CD-CCl 4 combination. CCl 4 alone at the doses used had no marked effect. Centrilobular necrosis was observed in the animals receiving CD-CCl 4 combination. Biliary excretion of phenolphthalein glucuronide (PG) and the rate of bile flow were decreased in a dose-dependent manner. Forty-eight hour LD 50 of CCl 4 was decreased 26-fold by CD pretreatment. These results indicate that CD potentiates CCl 4 toxicity in female rats as well. Since the hepatic functional status is greatly compromized, the CD potentiated lethality is preceded by hepatic failure. Furthermore, female rats are sensitized to smaller doses of CCl 4 in comparison to male rats.

Effect of acute and chronic Cd exposure on lindane metabolism

This study reports the effects of acute and chronic Cd treatment on the metabolism of lindane by rats 3 days, 1, 2, 3, and 5 weeks after exposure to the heavy metal. Eighty adult male Wistar rats were randomly assigned to one of four exposure groups. One group was injected sc, three times a week throughout the study, with 0.75 mg of Cd/kg body weight. The other three groups received one se injection of either 0, 1.04, or 3.20 mg of Cd/kg body weight. Twenty-four hours prior to sacrifice four rats from each group received a po dose of 1.83 mg of lindane (containing 2.5 μCi of [ 14 C]lindane). Results of this study indicate that Cd pretreatment causes inhibition of lindane metabolism which is of long duration and which is not appreciably relieved by chronic exposure to the metal.