| Cadmium (Cd) is now recognized to be one of most important heavy metal contaminants in the environment. Due to its increased industrial uses and environmental pollution with the related waste products, concentrations of cadmium is increasing rapidly in the environment in recent years. Adverse health effects caused by cadmium have provoked a significant public health concern. The kidney is the target organ and the primary accumulation site of chronic cadmium exposure. The nephrotoxicity induced by cadmium has been extensively studied and widely reported in occupationally and environmentally exposed human subjects, as well as in various experimental models. In this study, the toxic effects of cadmium on the kidney of Sprague-Dawley (SD) rats were investigated in vitro, which will offer some theoretic evidences for further exploring the mechanism in nephrotoxicity of cadmium.In studies, the primary cultures of rat proximal tubular cells (rPTCs) were cultured by mechanical grinding, filtering and chemical digestive methods. The first passage was used to perform the experimental design when it was in its highest cell viability.Effects of cadmium (2.5μmol/L, 5μmol/L) on the rPTCs were investigated in the following assays.①Effects of different doses of lead and/or cadmium on the survival rates in rPTCs for a time range of 3, 6, 12 and 24h were detected by using the cck-8 reduction method.②Effects of cadmium on the apoptotic rates, necrotic rates, LDH release, contents of GSH and apoptotic morphological changes in rPTCs over a 12h period were investigated. In addition, the protective effect of N-acetyl-L-cysteine (NAC) against cadmium induced cellular damage was investigated.③Activities of Ca2+-ATPase and Na+/K+-ATPase, intracellular pH, levels of mitochondrial membrane potential (ΔΨ), reactive oxygen species (ROS) and intracellular [Ca2+]i in rPTCs were detected after exposed to lead and/or cadmium for 12h.The results are as follows:①The cell survival rates in the cadmium groups were significantly lower than those of control groups since these cells were exposed to high-dose (5μmol/L) and low-dose (2.5μmol/L) groups for six and twelve hours, respectively (P<0.05 or P<0.01). Furthermore, the degree of decrease in the cell survival rate was positively correlated with the dose and the exposure time.②After exposure to cadmium for 12h, the apoptotic rates, necrotic rates, LDH release in these exposed groups were significantly higher than those in the control group (P<0.01). After a 12h exposure time, it showed typical apoptotic features in the cadmium groups, i.e., nuclear chromatin condensed and fragmented chromatin was characterized by a scattered, drop-like structure. Apoptosis induced by cadmium can be efficiently prevented by NAC, but the necrotic rates and LDH release were not affected by NAC.③Compared with the control group, activities of the GSH level in the exposed groups decreased significantly (P<0.01), and it can be efficiently prevented by NAC.④After exposed to cadmium for 12h, intracellular ROS and [Ca2+] in rPTCs increased significantly (P<0.01), while the mitochondrialΔΨ, intracellular pH, activities of Ca2+-ATPase and Na+/K+-ATPase decreased significantly (P<0.01). Based on these results, the conclusions are as follows:①cadmium exposure induced cellular death in rPTCs, depending on both the concentration and the exposure time.②Cellular death induced by cadmium is medicated by two mechanisms, necrotic and apoptotic. The apoptotic mechanism played a chief role in the cellular death induced by cadmium at these doses. Moreover, oxidative stress could be implicated in the apoptotic mechanism mediated by cadmium. In addition, the cellular damage induced by lead and/or cadmium can be significantly prevented by NAC.③Depletion of mitochondrialΔΨand a disorder of intracellular homeostasis, i.e. intracellular acidification, calcium overload, disturbance in the prooxidant–antioxidant balance, promoted the development of apoptosis in rPTCs. |
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