Abstract
Calcium-type montmorillonite, a phyllosilicate mineral, has diverse health benefits when introduced into the gastrointestinal tract or applied to the skin. However, the predominant use of this layered material has thus far been in traditional industries, despite its potential application in the pharmaceutical industry. We investigated the effects and mechanism of nano-montmorillonite (NM) on osteoblast and osteoclast differentiation in vivo and in vitro. We examined the osteogenic effects of NM with high calcium content (3.66 wt%) on alkaline phosphatase (ALP) activity, mineralization, bone microarchitecture, and expression level of osteoblast and osteoclast related genes in Ca-deficient ovariectomized (OVX) rats. Micro-computed tomography of OVX rats revealed that NM attenuated the low-Ca-associated changes in trabecular and cortical bone mineral density. It improved ALP activity and mineralization, as well as the expression of osteoblast and osteoclast differentiation associated genes. NM also activated the expression of runt-related transcription factor 2, osteocalcin, bone morphogenetic protein 2, and type 1 collagen via phosphorylated small mothers against decapentaplegic homolog 1/5/8 signaling. Further, NM repressed the expression of receptor activator for cathepsin K, nuclear factor kappa-B ligand and tartrate-resistant acid phosphatase. Therefore, NM inhibits osteoclastogenesis, stimulates osteoblastogenesis, and alleviates osteoporosis.
Highlights
Montmorillonite—a predominantly dioctahedral smectite—is a charged, layered silicate mineral and the main component of “bentonite” [1,2,3]
A previous study on the effects of genistein on osteoblast-associated metabolism proved that genes related to the BMP/SMAD signaling pathway showed the strongest enhancements in human bone marrow stromal cell cultures [53]. This is similar to our results, and these findings prove that BMP/SMAD signaling is an important regulator of hBMSC differentiation into an osteoblast lineage, with BMP2-dependent SMAD5 signaling as a downstream pathway [55]
Recent studies reported that canonical Wnt signaling contributed to bone formation through enhancement of the RUNX2 transcription factor that drives osteoblast differentiation [57]. Consistent with these previous observations, our findings proved that BMP/RUNX2/SMAD signaling was of considerable importance for the enhancement of the osteoblast lineage observed in the presence of NM
Summary
Montmorillonite—a predominantly dioctahedral smectite—is a charged, layered silicate mineral and the main component of “bentonite” [1,2,3]. Nearly pure montmorillonite purified from bentonite has been extensively studied for its use in cosmetics, natural therapies, and pharmaceuticals [9,10,11,12], owing to its specific properties such as high swelling pressure, high cation exchange capacity, and high adsorption ability [13,14,15]. Montmorillonite was found to have an active role in dermatological protection and anti-inflammation, and as an antidiarrheal and antacid [16,17,18,19]. The effect of clay montmorillonite and sodium silicate was studied in human mesenchymal stem cells in osteogenic culture to confirm its role as a biomaterial [22]. The use of montmorillonite for bone therapy has been reported, such as in engineered scaffolds with cytocompatibility, improving thermal stability, and increasing cellular proliferation rates [23,24]
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