The protection of selenium on ROS mediated-apoptosis by mitochondria dysfunction in cadmium-induced LLC-PK1 cells

Selenium, an essential trace element, showed the significant protective effects against liver and kidney damage induced by some heavy metals. However, the mechanism how selenium suppresses cadmium (Cd)-induced cytotoxicity remains unclear. In this study, we investigated the protective mechanism of selenium on Cd-induced apoptosis in LLC-PK₁ cells via reactive oxygen species (ROS) and mitochondria linked signal pathway. Studies of PI and Annexin V dual staining analysis demonstrated that 20 μM Cd-induced apoptosis as early as 18 h. A concomitant by the generation of ROS, the loss of mitochondrial membrane potential, cytochrome c (cyt c) release, activation of caspase-9, -3 and regulation of Bcl-2 and Bax were observed. N-acetylcysteine (NAC, 500 μM), a free radical scavenger, was used to determine the involvement of ROS in Cd-induced apoptosis. During the process, selenium played the same role as NAC. The anti-apoptosis exerted by selenium involved the blocking of Cd-induced ROS generation, the inhibition of Cd-induced mitochondrial membrane potential collapse, the prevention of cyt c release, subsequent inhibition of caspase activation and the changed level of Bcl-2 and Bax. Taken together, we concluded that Cd-induced apoptosis was mediated by oxidative stress and selenium produced a significant protection against Cd–induced apoptosis in LLC-PK₁ via ameliorating the mitochondrial dysfunction.     

Cadmium induces apoptosis partly via caspase-9 activation in HL-60 cells.

Cadmium (Cd), a potent immunotoxic metal, induces apoptosis both in vitro and in vivo. However, the mode of action remains unclear. We previously reported that Cd-induced apoptosis was partly dependent on mitochondria. In the present study, we investigated the involvement of caspase-9, which is the apex caspase in the mitochondoria-dependent apoptosis pathway, in Cd-induced apoptosis in human promyelocytic leukemia HL-60 cells. A specific inhibitor of caspase-9, Z-LEHD-FMK, partly inhibited DNA fragmentation induced by Cd treatment in HL-60 cells. Moreover, treatment of HL-60 cells with Cd resulted in the appearance of Cytochrome c (Cyt c), a potent activator of caspase-9, in the cytosol at 3 h, which closely paralleled the activation of caspase-9. Caspase-9 is an initiator caspase that is a potent activator of downstream effector caspases such as caspase-3. Caspase-3 activation was subsequent to the Cyt c release at 6 h. DNA fragmentation, an index of induction of apoptosis, also appeared 6 h after Cd treatment. The effects were more pronounced at 9 h after Cd addition. A broad-specificity inhibitor of caspases, Z-Asp-CH(2)-DCB, inhibited caspase-3 activation and DNA fragmentation induced by Cd in a dose-dependent fashion. The results suggest that Cd-induced apoptosis is partly caused by caspase-9 activation triggered by Cyt c.     

Imexon activates an intrinsic apoptosis pathway in RPMI8226 myeloma cells

Imexon is a new antitumor agent with high activity in multiple myeloma. This drug induces apoptosis, oxidative stress and mitochondrial alterations. However, it was unknown whether imexon activates an intrinsic apoptotic pathway that is associated with activation of caspase-9 or an extrinsic pathway that is induced by receptor-mediated signals such as Fas ligand characterized by caspase-8 activation. In addition, we wanted to investigate the effect of imexon on Bcl-2 family proteins. In RPMI8226 myeloma cells, imexon activated caspase-9 and -3 in a time- and concentration-dependent manner. In contrast, cleavage of procaspase-8 was observed late and only after exposure to very high concentrations of imexon. Confocal microscopy confirmed that caspase-3 is also activated after treatment with imexon. High imexon concentrations activated caspase-3 and -9 at 12 h, while caspase-8 activation occurred only at 48 h. Imexon cytotoxicity was unchanged in three RPMI8226 cell lines with different levels (low, medium and high) of FAS expression. Similarly, the levels of Bcl-2, Bax and Bcl-xL were unchanged in imexon-treated cells. However, Bcl-xL was translocated to the mitochondria. These data suggest that imexon-induced oxidation activates the intrinsic or mitochondrial pathway of apoptosis, involving cytochrome release and activation of caspase-9 and -3.     

Calcium–calmodulin signaling elicits mitochondrial dysfunction and the release of cytochrome c during cadmium-induced apoptosis in primary osteoblasts

Cadmium (Cd) is a toxic heavy metal used in industry and is associated with adverse effects on human health following long- or short-term environmental exposure. Although Cd is known to induce apoptosis in many human organ systems, the mechanism that underlies its toxicity in primary osteoblasts (OBs) is not yet established. In the present study, we confirmed that Cd induced apoptosis in OBs isolated from the craniums of fetal Sprague-Dawley rats. We then showed that exposure to Cd transiently increased intracellular calcium ([Ca²⁺]i) levels for up to 1.5 h, after which the levels returned to normal. Pretreatment with the calcium chelator BAPTA-AM was able to prevent Cd-induced apoptosis by reversing Cd-induced changes in the mitochondrial transmembrane potential (ΔΨm). In addition, we found that the antagonist of calcium-dependent calmodulin (CaM), W-7, inhibited the conformational change of calmodulin induced by Cd. Furthermore, Cd-induced apoptosis could be inhibited by W-7 through the suppression of the mitochondrial release of cytochrome c to the cytosol and the reversal of Cd-activation of caspase-3. These data indicate that activated Ca²⁺/CaM might transmit apoptotic signals to the mitochondria during Cd-induced apoptosis. Our findings provide new insights into the mechanisms underlying apoptosis in OBs following exposure to Cd.     

Cadmium-induced non-apoptotic cell death mediated by oxidative stress under the condition of sulfhydryl deficiency

Cadmium (Cd), which accumulates primarily in the liver and the kidney, induces apoptosis and also causes necrotic cell death in certain pathophysiologic situations. Previously, we have shown that Cd activated mitogen-activated protein kinases and that sulfur amino acid deficiency potentiated Cd-induced cytotoxicity via activation of mitogen-activated protein kinases. In the present study, we established the mechanistic basis of apoptotic and non-apoptotic cell death induced by Cd in H4IIE cells a rat-derived hepatocyte cell line. Cd at 0.3-10 microM decreased viability of cells in a concentration-dependent manner. Cd-induced cytotoxicity was enhanced by pretreatment with buthionine sulfoximine (BSO). Cd at 0.3 microM induced translocation of Bad to mitochondria, decreased the level of mitochondrial BcL(XL) with the release of cytochrome c, and induced procaspase-9 activation and poly(ADP-ribose) polymerase (PARP) cleavage. Sulfhydryl deficiency by BSO, however, blocked PARP cleavage in spite of the decrease in procaspase-9. Cytochrome c release, procaspase-9 activation and PARP cleavage were all increased by 1 microM Cd irrespective of BSO pretreatment. We also used H(2)O(2) (10-100 microM) as a source of oxidative stress. Cd (0.3-1 microM) + H(2)O(2) (70 microM) resulted in greater extents of cytochrome c release, procaspase-9 activation and PARP cleavage in H4IIE cells than Cd alone. Flow cytometric analysis confirmed apoptotic and non-apoptotic cell death by Cd depending on cellular glutathione (GSH) content. These results provide evidence that Cd at the physiologically obtainable concentration causes non-apoptotic cell death under the condition of sufhydryl deficiency, whereas Cd at the micromolar level induces apoptosis. The cell death mechanism involves cytochrome c release from mitochondria and decrease in the level of procaspase-9, but not PARP cleavage, implying that alterations in cellular sulfhydryls may be the major determining factor for the path of cell death in response to low level of Cd.     

Cadmium-induced apoptosis in murine macrophages is antagonized by antioxidants and caspase inhibitors

Cadmium is a toxic heavy metal that accumulates in the environment and is commonly found in cigarette smoke and industrial effluents. This study was designed to determine the role of reactive oxygen species (ROS) generation, and its antagonism by antioxidants, in cadmium-mediated cell signaling and apoptosis in murine macrophage cultures. Cadmium-generated ROS production was observed in J774A.1 cells at 6 h, reverting to control levels at 16 and 24 h. The ROS production was concentration related between 20 and 500 microM cadmium. Activation of caspase-3 was observed at 8 h and DNA fragmentation at 16 h in the presence of 20 microM cadmium, suggesting that caspase-3 activation is a prior step to DNA fragmentation in cadmium-induced apoptosis. Inhibitors of caspase-3, -8, -9, and a general caspase inhibitor suppressed cadmium-induced caspase-3 activation and apoptosis indicating the importance of caspase-3 in cadmium-induced toxicity in these cells. Protection against the oxidative stress with N-acetylcysteine (NAC) and silymarin (an antioxidant flavonoid) blocked cadmium-induced apoptosis. Pretreatment of cells with NAC and silymarin prevented cadmium-induced cell injury, including growth arrest, mitochondrial impairment, and necrosis, and reduced the cadmium-elevated intracellular calcium ([Ca2+]i), suggesting that the oxidative stress is a source of increased [Ca2+]i. NAC inhibited cadmium-induced activation of mitogen-activated protein kinases, the c-Jun NH2-terminal protein kinase (JNK) and extracellular signal-regulated kinase (ERK). However, silymarin provided only a partial protection for JNK activation, and only at the low concentration did it inhibit cadmium-induced ERK activation. Inhibition of caspase-3 protected oxidative stress produced by cadmium, suggesting that the activation of caspase-3 also contributes to generation of reactive oxygen species (ROS). Results emphasized the role of ROS, Ca2+ and mitogen-activated protein kinases in cadmium-induced cytotoxicity in murine macrophages.     

The protective effects of selenium on cadmium-induced oxidative stress and apoptosis via mitochondria pathway in mice kidney

Selenium, an essential trace element, showed the significant protective effects against kidney damage induced by some heavy metals. Our previous research have found that the protection effects of selenium on ROS mediated-apoptosis by mitochondria dysfunction in cadmium (Cd)-induced LLC-PK1 cells. The present study as a continuation of our earlier one to investigate the protective effects and mechanism of selenium on Cd-induced apoptosis of kidney in vivo. Cadmium exposure increased the production of reactive oxygen species (ROS) and altered the levels of oxidative stress related biomarkers in kidney tissue. A concomitant by the loss of mitochondrial membrane potential, cytochrome c release and regulation of VDAC, Bcl-2 and Bax were observed. Apoptotic nature of cell death is confirmed by activation of caspase-3, which is also supported by histological examination. During the process, selenium played a beneficial role against Cd-induced renal damage. Pretreatment with selenium partially blocked Cd-induced ROS generation, inhibited Cd induced mitochondrial membrane potential collapse, prevented cytochrome c release, inhibited caspase activation and changed the level of VDAC, Bcl-2 and Bax. Combining all, results suggest that selenium has an ability to inhibit mitochondrial apoptotic pathway in oxidative stress mediated kidney dysfunction caused by cadmium.     

Cadmium induces Ca2+-dependent necrotic cell death through calpain-triggered mitochondrial depolarization and reactive oxygen species-mediated inhibition of nuclear factor-kappaB activity

This study investigates the mechanism of cell death induced by cadmium (Cd) in Chinese hamster ovary (CHO) cells. Cells exposed to 4 microM Cd for 24 h did not show signs of apoptosis, such as DNA fragmentation and caspase-3 activation. The pro-apoptotic (Bax) or anti-apoptotic (Bcl-2 and Bcl-xL) protein levels in the Bcl-2 family were not altered. However, an increase in propidium iodide uptake and depletion of ATP, characteristics of necrotic cell death, were observed. Cd treatment increased the intracellular calcium (Ca2+) level. Removal of the Ca2+ by a chelator, BAPTA-AM, efficiently inhibited Cd-induced necrosis. The increased Ca2+ subsequently mediated calpain activation and intracellular ROS production. Calpains then triggered mitochondrial depolarization resulting in cell necrosis. Cyclosporin A, an inhibitor of mitochondrial permeability transition, recovered the membrane potential and reduced the necrotic effect. The generated ROS reduced basal NF-kappaB activity and led cells to necrosis. An increase of NF-kappaB activity by its activator, PMA, attenuated Cd-induced necrosis. Calpains and ROS act cooperatively in this process. The calpain inhibitor and the ROS scavenger synergistically inhibited Cd-induced necrosis. Results in this study suggest that Cd stimulates Ca2+-dependent necrosis in CHO cells through two separate pathways. It reduces mitochondrial membrane potential by activating calpain and inhibits NF-kappaB activity by increasing the ROS level.     

Methylmercury induces pancreatic beta-cell apoptosis and dysfunction

Mercury is a well-known toxic metal, which induces oxidative stress. Pancreatic beta-cells are vulnerable to oxidative stress. The pathophysiological effect of mercury on the function of pancreatic beta-cells remains unclear. The present study was designed to investigate the effects of methylmercury (MeHg)-induced oxidative stress on the cell viability and function of pancreatic beta-cells. The number of viable cells was reduced 24 h after MeHg treatment in a dose-dependent manner with a range from 1 to 20 microM. 2',7'-Dichlorofluorescein fluorescence as an indicator of reactive oxygen species (ROS) formation after exposure of HIT-T15 cells or isolated mouse pancreatic islets to MeHg significantly increased ROS levels. MeHg could also suppress insulin secretion in HIT-T15 cells and isolated mouse pancreatic islets. After 24 h of exposure to MeHg, HIT-T15 cells had a significant increase in mercury levels with a dose-dependent manner. Moreover, MeHg displayed several features of cell apoptosis including an increase of the sub-G1 population and annexin-V binding. Treatment of HIT-T15 cells with MeHg resulted in disruption of the mitochondrial membrane potential and release of cytochrome c from the mitochondria to the cytosol and activation of caspase-3. Antioxidant N-acetylcysteine effectively reversed the MeHg-induced cellular responses. Altogether, our data clearly indicate that MeHg-induced oxidative stress causes pancreatic beta-cell apoptosis and dysfunction.     

Cadmium-induced apoptosis in rat hepatocytes does not necessarily involve caspase-dependent pathways

Cadmium (Cd) is a well-known hepatotoxic environmental pollutant. Depending on the exposure conditions, Cd may cause necrosis or apoptosis. Oxidative stress is believed to participate in Cd toxicity but the molecular signaling responsible for Cd-induced apoptosis in non-malignant liver cells still needs to be clarified. Therefore we have studied apoptosis in primary cultures of rat hepatocytes incubated with low levels of Cd for short exposure times. Studies of nuclear morphology, chromatin condensation, and oligonucleosomal DNA fragmentation demonstrate that 1–5 μM Cd induces apoptosis as early as 6–12 h with minor effects on MTT activity. A concomitant time- and concentration-dependent increase in caspase-9 and -3 activities was observed, whereas Cd did not affect caspase-8 activity as much, suggesting a minor role of the death-receptor pathway. Significant release of cytochrome c into the cytosol demonstrated the involvement of a mitochondrial-dependent apoptotic pathway. However, cell pre-treatment with caspase inhibitors (Z-VAD-fmk or Ac-DEVD-CHO) did not prevent apoptosis. Increases in the cytosolic levels of the mitochondrial apoptosis-inducing factor (AIF) were also observed: kinetics of cytochrome c and AIF release were similar. These results show that Cd-induced apoptosis in rat hepatocytes is time- and concentration-dependent. The early apoptotic events involved mitochondrial-dependent pathways but not necessarily caspase-dependent signaling.     

Cadmium-induced apoptosis of hepatocytes is not associated with death receptor-related caspase-dependent pathways in the rat

Cadmium (Cd) is a heavy metal of considerable environmental and occupational concern. The liver is the major target organ of Cd toxicity that follows from repeated exposure to Cd. The aim of this study was to investigate the mechanism of cell death of Cd-induced hepatotoxicity in a rat model. Eighteen adult male Sprague–Dawley (SD) rats were injected daily with a dose of Cd acetate (30 μM/kg body weight, subcutaneously). After 1, 2 and 7 days rats were euthanized and blood and liver tissues were sampled for analysis. Biochemical analyses of the level of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were undertaken. Histopathological and Western blot analyses for liver cellular damage and cell death were also performed. The results for the Cd-treated group of animals were compared to those from 12 control rats. The serum AST/ALT levels increased significantly 24 h after CD exposure. From the Western blot analyses, activation of Bid, independent of caspase-8 was seen and Bax induced the release of cytochrome c into the cytosol from mitochondria in a dose-dependent manner. The level of Bcl-2 was decreased. Eventually, caspase-9 and caspase-3 were activated, and poly(ADP-ribose) polymerase (PARP) was cleaved in a dose-dependent manner. A histopathological analysis and DNA fragmentation test showed apoptotic cell death of the hepatocytes increased over time. These results suggest that Cd-induced liver cell apoptosis in the rat, over a period of 7 days, may not be related to the death-receptor pathway. Moreover, apoptosis is dose-dependent and associated with the decrement of Bcl-2.     

A rapid and transient ROS generation by cadmium triggers apoptosis via caspase-dependent pathway in HepG2 cells and this is inhibited through N-acetylcysteine-mediated catalase upregulation

Although reactive oxygen species (ROS) have been implicated in cadmium (Cd)-induced hepatotoxicity, the role of ROS in this pathway remains unclear. Therefore, we attempted to determine the molecular mechanisms relevant to Cd-induced cell death in HepG2 cells. Cd was found to induce apoptosis in the HepG2 cells in a time- and dose-dependent fashion, as confirmed by DNA fragmentation analysis and TUNEL staining. In the early stages, both rapid and transient ROS generation triggered apoptosis via Fas activation and subsequent caspase-8-dependent Bid cleavage, as well as by calpain-mediated mitochondrial Bax cleavage. The timing of Bid activation was coincided with the timing at which the mitochondrial transmembrane potential (MMP) collapsed as well as the cytochrome c (Cyt c) released into the cytosol. Furthermore, mitochondrial permeability transition (MPT) pore inhibitors, such as cyclosporin A (CsA) and bongkrekic acid (BA), did not block Cd-induced ROS generation, MMP collapse and Cyt c release. N-acetylcysteine (NAC) pretreatment resulted in the complete inhibition of the Cd-induced apoptosis via catalase upregulation and subsequent Fas downregulation. NAC treatment also completely blocked the Cd-induced intracellular ROS generation, MMP collapse and Cyt c release, indicating that Cd-induced mitochondrial dysfunction may be regulated indirectly by ROS-mediated signaling pathway. Taken together, a rapid and transient ROS generation by Cd triggers apoptosis via caspase-dependent pathway and subsequent mitochondrial pathway. NAC inhibits Cd-induced apoptosis through the blocking of ROS generation as well as the catalase upregulation.     

Critical role of calcium overloading in cadmium-induced apoptosis in mouse thymocytes

Cadmium (Cd) is a well-known environmental carcinogen and immunotoxin. Currently the direct cytotoxic effects of Cd on thymocytes are largely unexplored. The main objective of the present study was to investigate the apoptogenic property of Cd and the mechanisms involved, using primary cultured mouse thymocytes as a model. Cd-induced apoptosis in thymocytes was studied by TdT-mediated dUTP nick end-labeling assay and DNA gel electrophoresis. The results showed that Cd was able to cause apoptosis in mouse thymocytes in a time- and dose-dependent manner. Moreover, Cd exposure led to a rapid and sustained intracellular calcium (Ca2+) elevation, followed by caspase-3 activation and PARP cleavage, all of which preceded the characteristic DNA fragmentation. BAPTA-AM, a specific intracellular Ca2+ chelator, abolished Cd-induced Ca2+ overloading and subsequently inhibited caspase-3 activation, PARP cleavage, and apoptosis.It is believed that intracellular Ca2+ elevation may trigger caspase-3 activation either through mitochondria or through activation of Ca2+-dependent protease in Cd-treated thymocytes. Results from this study thus provide new information for a better understanding of the immunotoxic and immunomodulatory effects of Cd.     

Mitochondrial pathway of apoptosis in the hepatopancreas of the freshwater crab Sinopotamon yangtsekiense exposed to cadmium

Cadmium (Cd) is one of the most common toxic metals in water. To investigate the mechanism of Cd-induced apoptosis in the hepatopancreas, freshwater crabs Sinopotamon yangtsekiense were exposed to 0, 3.56, 7.12, 14.25, 28.49 and 56.98 mg/L Cd for 48 h. After a 48 h exposure, apoptosis and necroptosis were apparent in the group exposed to 28.49 mg/L Cd and only one case of necrosis was observed in the highest concentration of Cd. Electronic microscopy revealed chromatin condensation under nuclear membrane and mitochondrial membrane rupture in 14.25 and 28.49 mg/L Cd treatment groups. Brown colored apoptotic cells were detected with the TUNEL test in all Cd-treatment groups. The AI in 56.98 mg/L group was 1.4-fold greater than that in crabs exposed to 14.25mg/L Cd. Caspase-9, caspase-3, SDH and Ca(2+)-ATPase activities increased with increasing Cd concentration. However, the activities of caspase-8 and LDH did not change significantly compared with control group. These results implied that Cd induced apoptosis in the hepatopancreas occurs through a mitochondrial pathway.     

Induction of apoptosis in cells by cadmium: quantitative negative correlation between basal or induced metallothionein concentration and apoptotic rate.

Metallothionein (MT) often reduces the adverse effects of cadmium (Cd), but how it may alter Cd-induced apoptosis is unclear. The goal of this study was to define the role of MT in Cd-induced apoptosis using cell lines with widely varying sensitivity to Cd. Effects of Cd on growth of human hepatocellular carcinoma cell lines (HepG2 and PLC/PRF/5) were investigated and compared with Chang cells. These cells were cultured with 0, 5, 10, 20, 40, 80, and 120 microM of Cd for 3, 6, 12, and 24 h. Significant cytolethality was observed in HepG2 and PLC/PRF/5 cells in a time- and concentration-dependent manner, with LC(50) values of 24 microM and 13 microM, respectively. However, Chang cells were much less sensitive to Cd-induced cytotoxicity (LC(50), 64 microM). Apoptotic cell death occurring at cytolethal concentrations was demonstrated in all cell lines by DNA fragmentation on agarose gel electrophoresis or by ELISA. When MT was measured, there was a highly significant negative linear correlation between the basal cellular MT concentration or Cd-induced MT and the rate of apoptosis induced by Cd in these cell lines. Treating HepG2 cells with zinc (Zn) made the relatively sensitive HepG2 cell line resistant to Cd-induced apoptosis, likely due to Zn-induced MT. In fact, there was also a significant negative linear correlation between the amount of Zn-induced MT in HepG2 cells and the rate of Cd-induced apoptosis. These findings revealed that basal or induced MT perturbs Cd-induced apoptotic cell death in various cell lines, and a strong negative correlation exists between cellular MT content and the rate of apoptosis induced by Cd.     

Induction of CDK inhibitors (p21(WAF1) and p27(Kip1)) and Bak in the beta-lapachone-induced apoptosis of human prostate cancer cells

beta-Lapachone, a novel anti-neoplastic drug, induces various cancer cells to undergo apoptosis. In a previous report, we showed that beta-lapachone-induced apoptosis of HL-60 cells is mediated by oxidative stress. However, in the present study, we found that beta-lapachone-induced apoptosis of human prostate cancer (HPC) cells may be independent of oxidative stress. In contrast to the 10-fold beta-lapachone-induced increase in H(2)O(2) production seen in HL-60 cells, only a 2- to 4-fold increase was observed in HPC cells. N-acetyl-L-cysteine (NAC), a thiol antioxidant, inhibited the apoptosis in DU145 cells after 12 h exposure to beta-lapachone. Nonetheless, NAC, along with other antioxidants, failed to exert similar effect in HPC cells subjected to beta-lapachone treatment for 24 h. Under this premise, we suggest that the oxidative stress may not play a crucial role in beta-lapachone-mediated HPC cell apoptosis. Here we demonstrate that damage to genomic DNA is the trigger for the apoptosis of HPC cells induced by beta-lapachone. According to our results, beta-lapachone stimulates DNA dependent kinase expression and poly(ADP-ribose) polymerase cleavage in advance of significant morphological changes. beta-Lapachone promotes the expression of cyclin-dependent kinase (cdk) inhibitors (p21(WAF1) and p27(Kip1)), induces bak expression, and subsequently stimulates the activation of caspase-7 but not of caspase-3 or caspase-8 during the apoptosis of HPC cells. Taken together, these results suggest that the signaling pathway involving the beta-lapachone-induced apoptosis of HPC cell may be by DNA damage, induction of cdk inhibitors (p21 and p27), and then subsequent stimulation of caspase-7 activation.     

Cadmium-induced apoptosis of hepatocytes is not associated with death receptor-related caspase-dependent pathways in the rat

Cadmium (Cd) is a heavy metal of considerable environmental and occupational concern. The liver is the major target organ of Cd toxicity that follows from repeated exposure to Cd. The aim of this study was to investigate the mechanism of cell death of Cd-induced hepatotoxicity in a rat model. Eighteen adult male Sprague–Dawley (SD) rats were injected daily with a dose of Cd acetate (30 μM/kg body weight, subcutaneously). After 1, 2 and 7 days rats were euthanized and blood and liver tissues were sampled for analysis. Biochemical analyses of the level of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were undertaken. Histopathological and Western blot analyses for liver cellular damage and cell death were also performed. The results for the Cd-treated group of animals were compared to those from 12 control rats. The serum AST/ALT levels increased significantly 24 h after CD exposure. From the Western blot analyses, activation of Bid, independent of caspase-8 was seen and Bax induced the release of cytochrome c into the cytosol from mitochondria in a dose-dependent manner. The level of Bcl-2 was decreased. Eventually, caspase-9 and caspase-3 were activated, and poly(ADP-ribose) polymerase (PARP) was cleaved in a dose-dependent manner. A histopathological analysis and DNA fragmentation test showed apoptotic cell death of the hepatocytes increased over time. These results suggest that Cd-induced liver cell apoptosis in the rat, over a period of 7 days, may not be related to the death-receptor pathway. Moreover, apoptosis is dose-dependent and associated with the decrement of Bcl-2.