Cytotoxicity of Bentonite, Zeolite, and Sepiolite Clay Minerals on Peripheral Blood Mononuclear Cells

Document Type : Original Article


1 Department of Soil Sciences, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran.

2 Department of Internal Medicine, Faculty of Medicine, Shahed University, Tehran, Iran.

3 Immunoregultion Research Center, Shahed University, Tehran, Iran.


Background: Clays and clay minerals have great potential for exerting positive impacts on human health and implementation in medical applications. They are industrial minerals used in various medical applications, like drug delivery. Considering the abundance of clay resources in Iran, we decided to investigate the role of natural clays in peripheral blood mononuclear cells (PBMCs), as effective immune system cells that provide the health of the body in disease and standard times. Investigating the cytotoxicity of these minerals on PBMCs helps to understand their performance in medicine and the treatment of patients.
Materials and Methods: The studied clays, including bentonite, zeolite, and sepiolite, were prepared from Iran mines, and their characterizations were scanned by x-ray fluorescence (XRF), x-ray diffraction, and cation-exchange capacity (CEC) determination. PBMCs were isolated by Ficoll-Hypaque density gradient centrifugation, and 200000 PBMC cells were exposed to different concentrations of clays (1-1000 µg/mL) for 48 h in 96-well cell culture plates. Cell cytotoxicity response was determined using 3-[4, 5-dimethylthiazole-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay.
Results: Bentonite inhibited cell proliferation after 48 h of incubation at a concentration above 0.05 mg/mL, whereas zeolite inhibited cell proliferation at 10 and 5 mg/mL. Sepiolite does not have any cytotoxic effect at all of the concentrations. CEC for bentonite, zeolite, and sepiolite were 86 cmol(+)/kg, 15.5 cmol(+)/kg, and 3.54 cmol(+)/kg, respectively, and showed a direct relationship with cell growth. 
Conclusion: The cytotoxicity of the investigated clays is less than those reported in the literature review. This suggests that the studied clays with beneficial properties have great potential to be used in medicine, taking into account the size, type, and concentration of clays. In vivo and long-term studies on bio-culture and biodistribution are essential to understand better the role of the studied clays. Furthermore, our results could provide a new perspective on the safety of using cheap and naturally available clays in medical and industrial applications.