Blueberry juice protects osteocytes and bone precursor cells against oxidative stress partly through SIRT1

Abstract

Oxidative stress and abnormal osteocyte apoptosis are often related to dysregulation of bone turnover and chronic bone loss, and so fruit and vegetables with high antioxidant potential may play an important role in the prevention and/or management of osteoporosis. Osteocytes are the main regulators of bone remodelling. For the first time, we demonstrate here that blueberry juice ( BJ ), obtained from Vaccinium myrtillus , rich in polyphenols, shows antioxidant and antiosteoclastogenic properties in MLO ‐Y4 osteocytes. We report that BJ prevents oxidative stress‐induced apoptosis and reverses the increase in receptor activator of nuclear factor κB ligand and sclerostin expression, crucial factors for osteoclast activation and bone resorption. BJ is also able to prevent oxidative stress‐induced cell cytotoxicity in bone marrow mesenchymal stromal cells ( MSC s), which are considered to be an important tool for cell therapy in bone disorders. No significant difference in preventing these events was observed between BJ and blueberry dry extract containing equal amounts of total soluble polyphenols. We have also shown that blueberry acts as both an antioxidant and an activator of sirtuin type 1, a class III histone deacetylase involved in cell death regulation and considered a molecular target for blocking bone resorption without affecting osteoclast survival. Overall, these novel data obtained in osteocytes and MSC s may help us clarify the mechanisms by which blueberry counteracts oxidative stress‐induced damage in bone remodelling and osteogenesis at the cellular and molecular level. Our findings are consistent with the reported beneficial effects of blueberry on bone tissue reported in animal studies, which suggest that blueberry may be a useful supplement for the prevention and/or management of osteoporosis and osteogenic process.

Blueberry Juice Antioxidants Protect Osteogenic Activity against Oxidative Stress and Improve Long-Term Activation of the Mineralization Process in Human Osteoblast-Like SaOS-2 Cells: Involvement of SIRT1

“…Aliquots of BJ were stored at −20 • C until use. The total soluble polyphenol (TSP) fraction of BJ was quantified with Folin-Ciocalteu reagent using gallic acid as the standard as described in our previous work [33] and via the HPLC method reported below. TSP concentration in BJ obtained from 100 g of BB fresh weight was expressed as mg/100 mL ± SD and the values measured by Folin-Ciocalteu assay or HPLC method were 169.5 ± 19.4 and 158.8 ± 12.3, respectively.…”

“…Western blot analysis was performed in SaOS-2 cells six days after differentiation and treated or not (control) as described above. Whole-cell lysates and nuclear extracts were obtained as previously described in References [13,33], respectively. Equal amounts of nuclear proteins were then incubated with antibody against Runt-related transcription factor 2 (RUNX-2) for 1 h at 4 • C. Subsequently, the immune complexes were precipitated using Protein A/G PLUS-Agarose.…”

“…In particular, BSO treatment was performed at the 40 µM concentration that induces oxidative stress due to significant decrease of GSH/GSSG ratio, an index of the intracellular oxidative status, as previously reported in SaOS-2 cells [13]. BJ containing two different concentrations of TSP (7.5 or 15 µg•mL −1 ), which previously demonstrated antioxidant activity in starved osteocytes [33], was used. Table 2 shows that neither BSO nor the highest concentration of BJ, used alone or together with BSO, significantly altered cell viability as compared to control cells.…”

“…Indeed, SIRT1 is related to the regulation of osteogenic differentiation of tendon and mesenchymal stem cells [46,47], and it is a positive regulator of RUNX-2 [47,48]. Moreover, this enzyme is activated in mammals by dietary blueberry [49,50] and in osteocytes by BJ [33]. Initially, the BJ effect on SIRT1 levels in SaOS-2 cells in the presence or not of BSO-induced oxidative stress was studied.…”

“…Recently, we demonstrated that blueberry juice (BJ), mainly obtained from VM, exhibits osteogenic action, through its antioxidant and antiosteoclastogenic effect, in murine osteocytes, MLO-Y4. Moreover, it shows a protective effect in bone marrow mesenchymal stromal cells (MSCs), fundamental for cell therapy in bone diseases, by preventing oxidative stress-induced toxicity [33].…”