Can In vitro extraction tests predict Cd relative bioavailability in rice?

With the development of economy and the acceleration of urbanization, human activities have led to the pollution of harmful heavy metals in large areas of farmland, especially paddy soil. Cadmium (Cd) is a common toxic metal in soil pollution. The nationwide survey of soil pollution in China indicated that the pollution of Cd is very severe, and the over standard rate of Cd is 7.0%. According to a national survey, nearly 65% of the rice produced near the mining area contains more Cd than the national food standard (0.2 mg/kg). The rice polluted by heavy metals will go through the digestion process in the stomach and intestines after being ingested into the human body by mouth, and then accumulate into the different tissues and organs of the human body with the blood circulation, resulting in the changes of the tissue morphology and metabolism of the organs, thus producing toxic effects on the human body. There is widespread concern that health risk caused by the accumulation of heavy metals in the body via rice consumption.

In order to evaluate the heavy metals in contaminated food, the bioavailability of metals must be measured. Bioavailability was used to characterize the proportion of the total amount of heavy metals that could pass through the gastrointestinal tract and finally enter the circulation of the human system. Usually, in vivo experiment was used. Bioavailability is the indicator of the greatest oral route bioavailability of pollutants, so many studies on the bioavailability of pollutants take bioavailability as the starting point and object of research, usually by means of in vitro simulation test (in Vitro) has the advantages of overcoming the high cost, long cycle and moral defects of animal models. However, bioavailability is not the same as bioavailability. Whether in vitro simulation can effectively predict bioavailability and regulatory factors is unclear.

Researchers from South China Botanical Garden under Chinese Academy of Sciences conducted both in vitro bioaccessibility (using four methods) and in vivo bioavailability (using a mouse model) of Cd from six rices. The relative bioavailability (RBA) for Cd ranged from 15 to 56%, 18 to 56% and 3.71 to 54% based on kidney, liver and femur, respectively, which was negatively correlated with total Cd concentration in contaminated rice. Results of cadmium bioaccessibility in rice varied among different assays. When the relationship between the in vitro and in vivo data was assessed, all the correlations between the four in vitro methods and the mouse assay based on the liver or kidney were generally weak. Results of in vitro digestion models varied drastically among the different methods, suggesting that there were limitations for the in vitro methods to predict Cd relative bioavailability in contaminated rice. Together with the observation of poor correlations between the in vivo and in vitro results, it is strongly suggested that further exploration and more optimization of in vitro methods are required for use in human health risk assessment.

The research results entitle by “Bioavailability and bioaccessibility of cadmium in contaminated rice by in vivo and in vitro bioassays” was published in Science of The Total Environment. For details, please refer to: https://www.sciencedirect.com/science/article/pii/S0048969720309633?via%3Dihub