Propolis and its extracts reduced Pb bioavailability and procyanidins declined Cd bioavailability in rice

Toxic metals in the environment enter the food chain through various ways and may cause a variety of hazards to human body, such as excessive intake of cadmium causing bone fragility or kidney damage, and lead causing kidney and brain poisoning (glioma). Some specific dietary supplements (vitamins, antioxidants, mineral elements) can alleviate the stress and toxicity of heavy metals, but the mechanism of reducing the bioavailability of heavy metals in the intestinal process is still unclear. Therefore, it is of great practical significance to explore the influencing factors and regulatory mechanisms of dietary intervention on the absorption, transport and accumulation of heavy metals for mitigating or preventing the toxicity and harm of cadmium and lead to human body.

Inhibitory effects of a variety of antioxidants and mineral elements on the bioavailability and toxicity of heavy metals in simulated gastrointestinal tract and mice was studied. The results showed that the addition of propolis and its extract significantly reduced the bioavailability of lead in brown rice (P<0.05) (Figure 1); The bioaccessibility and bioavailability of cadmium in brown and polished rice were significantly reduced by medium dose procyanidins (up to 76%). It was also found that the decrease of bioavailability and bioavailability of lead in brown rice was significantly negatively correlated with rice iron content. Propolis extract and procyanidins can effectively reduce the content of H2O2 and MDA in the liver of mice, and restore the level of reduced glutathione (GSH) (p<0.05), indicating that they have a certain effect on reducing the oxidative damage of Pb and Cd in vivo. This study confirmed that antioxidants can better inhibit the bioavailability of heavy metals. Propolis and its extract and procyanidins may be alternative dietary supplements to interfere with human lead or cadmium exposure.

Moreover, procyanidins, metallothionein and zinc gluconate significantly reduced the bioavailability of Cd in simulated gastrointestinal digestion and Caco-2 cells by 60.5%, 82.5% and 73%, respectively. They effectively reduced the transmembrane transport of cadmium and enhanced the transmembrane resistance (Teer), indicating that these supplements have a protective effect on cadmium induced barrier dysfunction. Transcriptomic results showed that dietary supplements down regulated the expression of related genes, revealing that these components can regulate the expression of genes in specific pathways related to dietary cadmium toxicity and absorption, such as apoptosis pathway (Jun, DDIT3), antioxidant pathway (cat, HMOX1) and mineral absorption pathway (MT, slc39a4) (Figure 2). Eating fruits and vegetables rich in procyanidins and zinc can control the negative effects of oral cadmium intake to a certain extent.

The study entitled “Bioaccessibility and bioavailability of Pb and Cd in rice is affected by propolis and its extracts and Fe intervention” and “Transmembrane and transcriptome analysis reveals the mechanism of dietary supplements in reducing cadmium absorption and toxicity” were (online) published in Science of the Total Environment and Environment Technology and Innovation, respectively. Dr. Sun Shuo is the first author of the paper, and researcher Zhuang Ping is the corresponding authors. This research was jointly funded by the National Natural Science Foundation and the Science and Technology Planning Project of Guangdong Province and other projects. The articles link to: https://doi.org/10.1016/j.scitotenv.2024.175697 and https://doi.org/10.1016/j.eti.2024.103771

Figure 1. The effects of propolis and its extract on in vitro and in vivo bioavailability of Pb.

Figure 2. Proposed model for response mechanisms of procyanidins, metallothionein and zinc gluconate to Cd stress.