Comparison of the Absorption and Distribution of Cadmium via Cadmium Chloride and Cadmium-contaminated Rice in Rats.

Cadmium (Cd) is considered a toxic element of which food is the major source of acquisition, which can lead to diseases such as renal dysfunction, cancer and osteoporosis. Cd is classified as a group I carcinogen by the International Agency for Research on Cancer. The results of dietary exposure to cadmium in Europe in 2012 showed that the contribution rate from the broad food categories of grain and grain products accounted for 26.9%, which was the food with the highest contribution rate to cadmium exposure. Similarly, the contribution of cadmium from rice and noodles to the total cadmium intake of Chinese residents is higher than that of any other food. A recent study of 484 rice samples from five contaminated areas in China found that more than 18% of rice contained Cd above the maximum levels of cadmium in China’s standard. Rice is a staple food for more than half the world’s population, and this crop is more susceptible to Cd contamination than other crops. Cadmium pollution in rice poses a serious threat to food safety and human health. The various forms of Cd in food could greatly affect its absorption, distribution and bioavailability of Cd in the human or animal organism, which may result in the different biological effects of Cd. Cd in rice binds to rice protein. Cd-binding protein in rice was isolated and expressed by Escherichia coli, and its molecular weight was found to be 26.34 kD. The toxicity of Cd in rice may be overestimated if only the total amount of Cd in rice is used as the evaluation standard. In this study, rice-contaminated Cd was used as the research object to compare the utilization of Cd in rice with inorganic Cd in rats. In vivo, the content of Cd in various tissues of the Cd rice and CdCl2 groups and the distribution of Cd in blood at different time points were determined, and the differences between the bioavailability of Cd in rice and CdCl2 were comprehensively compared. Cadmium-contaminated rice (Natural contamination) was collected from Jiujiang city, Jiangxi province. Cadmium-contaminated rice and the animal tissue or plasma analysis for inductively coupled plasma mass spectrometry (ICP-MS, NexIon 350X; PerkinElmer, USA). Male SPF (Specific Pathogen Free, SPF) grade Sprague Dawley rats (Quality Certificate Number: 42000600026041) were purchased from Hubei Provincial Experimental Animal Research Center (Wuhan, China). This study was approved by the Animal Research Ethical Committee of Huazhong University of Science and Technology (Wuhan, China. IACUC Number: 654). Fifty-four rats were randomly divided into three different groups for the blood metabolism experiment. Ninety rats were divided to exposure to low doses of cadmium for 28 d. The three groups were as follows: (1) negative control, (2) CdCl2 group (10 μg/kg bw by intragastric administration), and (3) Cd rice group (10 μg/kg bw by intragastric administration). Cd rice and ultra-pure water was added to the electric rice cooker at a ratio of 1:1.5 (g/mL), the steamed Cd rice was placed in a 40 °C oven at drying moisture, and the rice was shattered. An appropriate amount of Cd rice powder was mixed with ultra-pure water to make a mixture solution with a cadmium concentration of 0.5 μg/mL. Eighteen rats in each group were randomly divided into three groups for alternate blood collection. One millilitre of orbital blood was collected from all of the rats at 0.5, 1, 2, 4, 8, 16, 32,